SYNTHESIS AND PROPERTIES OF MOLYBDENUM COMPLEXES WITH PYRIDOXAL DERIVATIVES

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1 FACULTY F SCIECE Jana Pisk SYTHESIS AD PRPERTIES F MLYBDEUM CMPLEXES WITH PYRIDXAL DERIVATIVES DCTRAL THESIS Zagreb, 2012 i

2 PRIRDSLV-MATEMATIČKI FAKULTET Jana Pisk SITEZA I SVJSTVA KMPLEKSIH SPJEVA MLIBDEA S DERIVATIMA PIRIDKSALA DKTRSKI RAD Zagreb, ii

3 FACULTY F SCIECE Jana Pisk SYTHESIS AD PRPERTIES F MLYBDEUM CMPLEXES WITH PYRIDXAL DERIVATIVES DCTRAL THESIS Supervisor: Dr. Višnja Vrdoljak, Associate Professor Zagreb, 2012 iii

4 PRIRDSLV-MATEMATIČKI FAKULTET Jana Pisk SITEZA I SVJSTVA KMPLEKSIH SPJEVA MLIBDEA S DERIVATIMA PIRIDKSALA DKTRSKI RAD Mentor: Dr. sc. Višnja Vrdoljak, izvanredni profesor Zagreb, iv

5 This Doctoral Thesis was mainly done in the Laboratory of General and Inorganic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb, Croatia under the supervision of Dr. Višnja Vrdoljak, Associate Professor. Catalytic activity of prepared and previously fully characterised complexes was performed at LCC Toulouse and the Department of Chemistry in Castres, Paul Sabatier University- Toulouse III, Castres, France under the supervision of Dr. Dominique Agustin, Assistant Professor, member of the LCC-CRS research team of Dr. Rinaldo Poli, Professor (Croatian Science Foundation project 03.01/ and French Embassy scholarship) during nine months stay (academic year 2010/11). v

6 Acknowledgments one of the work in natural sciences is done only by one person. For that reason, I own special thanks to the team of experts who have unconditionally helped me during this research: Dr. Višnja Vrdoljak, Associate Professor, who guided and supervised the research through my whole PhD life Dr. Dominique Agustin, Assistant Professor, who guided and supervised the research done in France Dr. Dubravka Matković-Čalogović, Full Professor, and Dr. Biserka Prugovečki, Assistant Professor, for the help in solving crystal structures Dr. Predrag ovak, Full Professor and Tomislav Jednačak, PhD Student, for the help with recording and analysing nuclear magnetic resonance spectra Dr. Damir Pajić, Assistant Professor, for the help with recording and analysing magnetochemical measurements Dr. Saša Kazazić, Senior Research Associate, for the help with recording and analysing mass spectra and all the members of the evaluation committee vi

7 hvala svim ljudima iz sjene kaj su tolerili sve te moje lucidne trenutke... jana vii

8 Preface The fundamental chemistry of which transition element has been most rapidly and extensively advanced in the last decade? Such a question can provoke a number of answers, perhaps limited only by the number of transition elements and subjectivity of the respondent! Richard R. Holm (Coordination Chemistry Review 1990) ver the last couple of decades, scientist have been bombarded with a questions like Why is it useful?, What is the possible application? etc. If there is no practical use, research is often not profitable and proposed projects have not been acepted. Some areas of scientific research seem to remote from everyday life and unlikely to bring instantaneous applications. Research presented herein, might distract the reader from the terms of everyday use, but it could/should also broaden horizons and move the boundaries of thinking. It also might become springboard for new ideas which might be implied in common life. It is something (I would dare to define) as fundamental science with very likely appliance in future and it has been a journey I have been on for the last five years. viii

9 ABSTRACT University of Zagreb Faculty of Science Department of Chemistry Doctoral Thesis SYTHESIS AD PRPERTIES F MLYBDEUM CMPLEXES WITH PYRIDXAL DERIVATIVES JAA PISK Division of General and Inorganic Chemistry, Department of Chemistry, Faculty of Science, University of Zagreb Horvatovac 102a, Zagreb, Croatia The work presented herein relates the coordination chemistry of molybdenum(vi) and (V) complexes with pyridoxal based ligands. Coordination abilities of pyridoxalthiosemicarbazones, hydrazones and Schiff bases obtained from diamines were investigated. Forty novel molybdenum complexes had been prepared and fully characterised. The reactions of [Mo 2(acac) 2] and tridentate pyridoxal derivates, in methanol, afforded mononuclear molybdenum(vi) complexes [Mo 2(L)(Me)] or [Mo 2(HL)(Me)]Cl, while the same reaction in acetonitrile resulted with polynuclear molybdenum(vi) complexes [Mo 2(L)] n or [{Mo 2(HL)}Cl] n. Varying ratio of the ligand towards [Mo 2(acac) 2] created new salts of the formula [{Mo 2(HL)} 2]Mo 6 19 or [Mo 2(HL)(MeC)] 2Mo 6 19 composed of hexamolybdate oxo-clusters and cationic molybdenum(vi) complex. In addition, molybdenum(vi) complexes with ligands were obtained offering different type of coordination to the molybdenum atom tetradentate [Mo 2(L)] or didentate [{Mo 2(Me) 2} 2L]. The reactions of molybdenum(v) starting compounds and pyridoxal derivates resulted in the formation of mononuclear [MoCl 2(HL)] (in ethanol) and [MoCl 2(H 2L)]Cl (in acetonitrile) or dinuclear oxomolybdenum(v) complexes [Mo 2 3(L) 2] or [Mo 2 3(HL) 2]Cl 2. Dinuclear molybdenum(v) complexes were also prepared by the reduction of the mononuclear [Mo 2(L)(Me], [Mo 2(HL)(Me)]Cl or polynuclear complexes [Mo 2(L)] n, [{Mo 2(HL)}Cl] n with PPh 3. Molybdenum(VI) complexes with tridentate ligands, as well as, hybrid organic-inorganic polyoxomolybdates were used as (pre)catalysts for olefin epoxidation under solvent-free conditions. All products were identified by means of elemental analysis and characterized by IR, UV-Vis spectroscopy, MR, TGA, DSC, magnetochemical measurements (VSM, EPR) and X-ray diffraction on polycrystalline and monocrystal samples. Thesis is deposited at the ational and University Library (Zagreb, Croatia) and the Central Chemical Library, Faculty of Science, University of Zagreb (Zagreb, Croatia). The thesis includes: 194 pages, 98 figures, 5 tables, 12 schemes, 177 references. The original is written in English. Key words: molybdenum(vi) and (V) complexes / pyridoxal / thiosemicarbazones / hydrazones / diamines / AT / solvent free epoxidation / cyclooctene Supervisor: Dr. Višnja Vrdoljak, Associate Professor Reviewers: Dr. Davor Kovačević, Associate Professor Dr. Višnja Vrdoljak, Associate Professor Dr. Dominique Agustin, Assistant Professor Substitute: Dr. Marina Cindrić, Full Professor Thesis accepted: 4 th July 2012 ix

10 SAŽETAK Sveučilište u Zagrebu Prirodoslovno-matematički fakultet Kemijski odsjek Doktorski rad SITEZA I SVJSTVA KMPLEKSIH SPJEVA MLIBDEA S DERIVATIMA PIRIDKSALA JAA PISK Zavod za opću i anorgansku kemiju, Kemijski odsjek, Prirodoslovno-matematički fakultet, Sveučilište u Zagrebu Horvatovac 102a, Zagreb, Hrvatska vaj rad pripada području koordinacijske kemije molibdena(vi) i (V) s piridoksalnim ligandima. Istraženi su kompleksni spojevi molibdena s derivatima piridoksala tiosemikarbazona i njihovih hidroklorida, hidrazona i Schiffovih baza nastalih iz diamina. Pripravljeno je četrdeset novih molibdenskih spojeva koji su u potpunosti identificirani. Reakcije [Mo 2(acac) 2] s tridentatnim ligandima derivatima piridoksala, u metanolu, su rezultirale stvaranjem mononuklearnih kompleksnih spojeva molibdena(vi) [Mo 2(L)(Me)] ili [Mo 2(HL)(Me)]Cl, dok su reakcijama u acetonitrilu dobiveni polinuklearni kompleksi molibdena(vi) [Mo 2(L)] n ili [{Mo 2(HL)}Cl] n. Variranjem omjera liganda i [Mo 2(acac) 2] priređeni su hibridni organsko-anorganski spojevi opće formule [{Mo 2(HL)} 2]Mo 6 19 ili [Mo 2(HL)(MeC)] 2Mo sim kompleksnih spojeva s tridentatnim ligandima, pripravljeni su i molibdenski(vi) kompleksi s ligandima koji su koordinirani na atom molibdena kao tetradentatni [Mo 2(L)] ili kao premošćujući didentatni ligandi [{Mo 2(Me) 2} 2L]. Reakcije (H 4) 2[MoCl 5] i [Mo 2 3(acac) 4] s piridoksalnim ligandima rezultirale su nastankom mononuklearnih kompleksnih spojeva molibdena(v) [MoCl 2(HL)] (u etanolu) i [MoCl 2(H 2L)]Cl (u acetonitrilu) ili dinuklearnih kompleksa [Mo 2 3(L) 2] i [Mo 2 3(HL) 2]Cl 2. Dinuklearni kompleksi molibdena(v) priređeni su i reakcijama redukcije mononuklearnih [Mo 2(L)(Me)] i [Mo 2(HL)(Me)]Cl ili polinuklearnih kompleksnih spojeva [Mo 2(L)] n i [{Mo 2(HL)}Cl] n s PPh 3. Tridentatni kompleksi molibdena(vi) te hibridni polioksomolibdati su ispitani kao (pred)katalizatori za epoksidaciju olefina bez korištenja dodatnih organskih otapala, s vrlo malim udjelom molibdenskog kompleksa. Svi produkti su identificirani na osnovi elementne analize, IR, UV-Vis spektroskopije, MR, TGA, DSC, magnetokemijskih mjerenja, rentgenskom difrakcijom na polikristalnom i monokristalnom uzorku. Rad je pohranjen u acionalnoj i sveučilišnoj knjižnici (Zagreb, Hrvatska) i u Središnjoj kemijskoj knjižnici Prirodoslovno-matematičkog fakulteta u Zagrebu (Zagreb, Hrvatska). Rad sadrži: 194 stranica, 98 slika, 5 tablica, 12 shema, 177 referenci. riginal je napisan na engleskom jeziku. Ključne riječi: molibden(vi) and (V) kompleksi / piridoksal / tiosemikarbazoni / hidrazoni / diamini / AT / epoksidacija bez dodatnih otapala / ciklookten Mentor: Dr. sc. Višnja Vrdoljak, izvanredni profesor cjenjivači: Dr. sc. Davor Kovačević, izvanredni profesor Dr. sc. Višnja Vrdoljak, izvanredni profesor Dr. sc. Dominique Agustin, docent Zamjena: Dr. sc. Marina Cindić, redovni profesor Rad prihvaćen: 04. srpnja x

11 PRŠIREI SAŽETAK Kemija molibdena je raznolika zbog mogućnosti nastajanja kompleksnih spojeva u kojima atom molibdena može imati različita oksidacijska stanja, kao i zbog mogućnosti stvaranja kompleksa s ligandima koji sadrže različite donorne atome. Posebna pažnja je posvećena kompleksima s ligandima za koje je poznato da posjeduju biološka svojstva, primjerice antitumorna, antivirusna te protuupalna svojstva. Veliki broj važnih kemijskih reakcija kataliziran je molibdenovim spojevima. Među njima, najvažnija katalitička uloga molibdena je ta što sudjeluje u biološki važnim procesima kod različitih enzima. Tu su uočeni, među ostalima, enzimi poput oksidaze, reduktaze i dehidrogenaze. Svojstva i struktura molibdoenzima ispituju se posredno preko modela jer se smatra da oponašaju aktivne centre. U tu svrhu najčešće se koriste dioksomolibdenski(vi) kompleksi koji kao donorne atome sadrže kisik, dušik i/ili sumpor oponašajući koordinacijsku sferu molibdena u biološkim sustavima. Reakcije prijenosa kisika se najčešće opisuju kao reakcije koje uključuju interakciju molibdenskog kompleksa i jedne molekule PPh3 pri čemu nastaje Ph3P= i oksokompleks molibdena(iv). Dioksomolibdenski(VI) spojevi s pentakoordiniranim oksomolibdenskim(iv) spojevima mogu stvarati kisikom premoštene dinuklearne molibdenske(v) spojeve: LMo VI 2 + LMo IV Mo V 23L2 sim dinuklearnih spojeva molibdena(v), ispitivani su i mononuklearni spojevi koji su vrlo rijetko opisani u literaturi. Molibdenski kompleksi imaju veliku primjenu kao katalizatori za epoksidaciju olefina. Većina epoksidacijih reakcija se provodi u organskim otapalima ili u ionskim xi

12 tekućinama. S ciljem očuvanja prirode i u skladu s ekonomijom održivog razvoja, naročito su važne katalitičke reakcije koje se provode bez dodatka bilo kakvog organskog otapala. Također, uporaba tert-butilhidroperoksida, kao oksidansa, je ekološki prihvatljiva jer se tert-butanol (sporedni produkt) može izdvojiti, reciklirati te ponovno upotrijebiti u industrijskim procesima. Kompleksni spojevi molibdena s polidentatnim Schiffovim bazama zanimljivi su za istraživanje jer sadrže donorne atome slične onima pronađenim kod enzima. Imajući na umu činjenice da kemija koordinacijskih spojeva molibdena s bilo kojim derivatom piridoksala nije do sada opisana u literaturi, te da ne postoje podatci o katalitičkim svojstvima dioksomolibdenskih(vi) kompleksa s tridentatnim Schiffovim bazama u reakcijama epoksidacije olefina, bez dodatka organskih otapala, razlozi za provedbu navedenog znanstvenog istraživanja su višestruki. Za pripravu kompleksnih spojeva su odabrane tri skupine derivata piridoksala: - tiosemikarbazoni i njihovi hidrokloridi (S() ligandi) Shema 1, H H H H R R S H + Cl - S R 1 = H R 2 = CH 3 R 3 = C 6 H 5 Shema 1. Piridoksal tiosemikarbazoni (lijevo) i njihovi hidrokloridi (desno). xii

13 - hidrazoni (() ligandi) Shema 2, H R R 4 = R 5 = R 6 = Shema 2. Piridoksal hidrazoni. - te Schiffove baze priređene iz diamina ( ligandi) Shema 3 i odgovarajući diamini priređeni njihovom redukcijom Shema 4. H R R 7 = C 2 H 4 R 9 = C 3 H 6 H R 10 = C 6 H 4 Shema 3. Schiffove baze priređene iz piridoksala i diamina. H R H H R 8 = C 2 H 4 H Shema 4. Diamini priređeni redukcijom Schiffovih baza. xiii

14 avedeni derivati su zanimljivi zbog različitih stupnjeva protonacije, te mogu biti prisutni kao neutralni H2L, monodeprotonirani HL ili dvostruko deprotonirani ligandi L 2. Svi ligandi su priređeni reakcijama kondenzacije piridoksala ili piridoksal hidroklorida s odgovarajućim tiosemikarbazidom, hidrazidom ili diaminom u etanolu. astale Schiffove baze su stabilne, blijedožute do narančaste boje. Schiffove baze, pripravljene reakcijom piridoksala i diamina su reducirane pomoću natrijeva tetrahidroborata. Reakcija je vrlo osjetljiva te je nastali bijeli produkt vrlo teško izolirati. Ispitani su uvjeti nastajanja, izolacije i identifikacije kompleksnih spojeva molibdena(vi) i (V) s navedenim ligandima. Svi produkti su identificirani na osnovi elementne analize, IR, UV-Vis i MR spektroskopije, termogravimetrijske analize (TG), razlikovne pretražne kalorimetrije (DSC), magnetokemijskih mjerenja (EPR, VSM) te rentgenskom difrakcijom na polikristalnom uzorku. Pojedinim kompleksima je određena kristalna i molekulska struktura metodom rentgenske strukturne analize u Zavodu za opću i anorgansku kemiju. Kao polazni molibdenski spojevi korišteni su dioksobis(2,4-pentandionato)molibden(vi) [Mo2(acac)2], μ-okso-dioksotetrakis(2,4-pentandionato)molibden(v) [Mo23(acac)4] te amonijev pentaklorooksomolibdat(v) (H4)2[MoCl5]. Doktorska disertacija je podijeljena u četiri cjeline: - molibdenski kompleksi s S() ligandima, - molibdenski kompleksi s () ligandima, - molibdenski kompleksi s ligandima, - te katalitička svojstva pripravljenih kompleksnih spojeva molibdena(vi). U prvom dijelu opisana su svojstva i priprava molibdenskih kompleksa s S() ligandima. Reakcijom [Mo2(acac)2] s odgovarajućim piridoksal tiosemikarbazonom H2L 1, u metanolu, priređen je mononuklearni kompleks molibdena(vi) xiv

15 [Mo2(L 1 )(Me)] (Shema 5.). Mononuklearne komplekse [Mo2(L 2,3 )(Me)] nije bilo moguće izolirati iz otopine, već su svaki puta izolirani polinuklearni kompleksi, bez obzira na izbor otapala, omjer korištenog metanola i acetonitrila ili omjer liganda i [Mo2(acac)2]. vakvo ponašanje moguće je objasniti tendencijom stvaranja Mo=... Mo interakcija u polinuklearnim kompleksima [Mo2(L 2,3 )]n. Reakcijom sa svim ligandima H2L 1-3 u acetonitrilu su dobiveni polinuklearni spojevi [Mo2(L 1-3 )]n. Mononuklearni kompleksi mogu biti međusobno povezani ili preko terminalnog kisikovog atoma ili preko kisikovog atoma hidroksilmetilne skupine (što je rjeđi primjer) dajući pri tome dinuklearne ili polinuklearne spojeve. U pripravljenim kompleksima, uočena su oba načina polimerizacije. jih je najjednostavnije odrediti usporedbom karakterističnih apsorpcijskih maksimuma infracrvenih spektara. Ukoliko je riječ o polimerizaciji ostvarenoj preko terminalnog kisikovog atoma tada u infracrvenom spektru postoji karakteristična široka vrpca oko 800 cm 1, a ukoliko kompleksi polimeriziraju preko kisikovog atoma iz hidroksilmetilne skupine, karakteristične su dvije intenzivne vrpce oko 950 i 900 cm 1. Također su ispitivani mogući prijelazi mononuklearnih u polinuklearne spojeve i obrnuto, odgovarajućim reakcijama u otopini. xv

16 [Mo 2 (L 2,3 )] n [Mo 2 (L 1 )] n R H S Mo R= CH 3 (2) H (3) CH 3 [{Mo 2 (HL 1,2 )} 2 ]Mo 6 19 R= C 6 H 5 (10) CH 3 (11) R H S Mo R= C 6 H 5 (1) CH 3 MeC H 2 L 2,3 1/7 H 2 L 1,2 MeC H 2 L 1 MeC PPh 3 MeC, Ar [Mo 2 (acac) 2 ] H 2 L 1 Me MeC Me [Mo 2 3 (L 1,2 ) 2 ] R= C 6 H 5 (7) CH 3 (8) PPh 3 MeC, Ar R H [Mo 2 (L 1 )(Me)] H 3 C S Mo R= C 6 H 5 (1a) CH 3 Shema 5. Priprava molibdenskih(vi) i (V) kompleksa s piridoksal tiosemikarbazonima. Reakcijom [Mo2(acac)2] s odgovarajućim piridoksal tiosemikarbazonskim hidrokloridom H2L 1 HCl, u metanolu, nastaje mononuklearni kompleks [Mo2(HL 1 )(Me)]Cl, a reakcijom sa svim ligandima H2L 1-3 HCl, u acetonitrilu, polinuklearni spojevi [{Mo2(HL 1-3 )}Cl]n (Shema 6). Jednako kao i u reakcijama s piridoksal tiosemikarbazonima, mononuklearne komplekse [Mo2(HL 2,3 )(Me)]Cl nije bilo moguće izolirati, iz već spomenutih razloga. xvi

17 [{Mo 2 (HL 2,3 )}Cl] n [{Mo 2 (HL 1 )Cl}] n R H S Mo R= CH 3 (2*) H (3*) CH 3 H Cl [{Mo 2 (HL 1,2 )} 2 ]Mo 6 19 R= C 6 H 5 (10) CH 3 (11) R H CH 3 S Mo H Cl R= C 6 H 5 (1*) H 2 L 2,3. HCl MeC 1/7 H 2 L 1,2. HCl MeC H 2 L 1. HCl MeC PPh 3 MeC, Ar [Mo 2 (acac) 2 ] Me MeC H 2 L 1. HCl Me [Mo 2 3 (HL 1-3 ) 2 ]Cl 2 R= C 6 H 5 (7*) CH 3 (8*) H (9*) PPh 3 MeC, Ar R [Mo 2 (HL 1 )(Me)]Cl H H 3 C S Mo R= C 6 H 5 (1*a) CH 3 H Cl Shema 6. Priprava molibdenskih(vi) i (V) kompleksa s piridoksal tiosemikarbazonskim hidrokloridima. U svim navedenim kompleksima ligand H2L je prisutan u različitim stupnjevima protonacije (kao neutralni H2L, monoprotonirani HL ili deprotonirani L 2 tridentatni ligand). Svojstva spojeva različitog stupnja protonacije ispitivana su, između ostalog, i u otopini UV-Vis spektroskopijom. Reakcijom (H4)2[MoCl5] s piridoksal tiosemikarbazonskim hidrokloridima H2L 1-3 HCl, u acetonitrilu, nastaju mononuklearni spojevi [MoCl2(H2L 1-3 )]Cl s neutralnim ligandom koordiniranim na molibdenski ion. Ako se reakcija provodi u etanolu nastaju mononuklearni spojevi [MoCl2(HL 1-3 )] u kojima je ligand monodeprotoniran. Može se pretpostaviti da etanol potiče eliminaciju HCl, a time i nastajanje [MoCl2(HL 1-3 )] kompleksa. Priređeni spojevi su strukturno jednaki spojevima pripravljenim iz piridoksal tiosemikarbazona H2L 1-3 u istom otapalu. xvii

18 Dinuklearni spojevi molibdena(v) [Mo23(L 1-3 )2] i [Mo23(HL 1-3 )2]Cl2 ne mogu se prirediti reakcijom [Mo23(acac)4] s piridoksal tiosemikarbazonima H2L 1-3 u acetonitrilu, odnosno reakcijom s piridoksal tiosemikarbazonskim hidrokloridima H2L 1-3 HCl. jih je moguće pripraviti reakcijama redukcije odgovarajućih mononuklearnih ili polinuklearnih kompleksa molibdena(vi), pomoću trifenilfosfina u acetonitrilu. astajanje dinuklearnih spojeva molibdena(v) tom reakcijom potvrđeno je i magnetokemijskim mjerenjima s obzirom da je dijamagnetizam karakteristika spojeva molibdena(v) premoštenih kisikom. o, duljim izvođenjem reakcije osim dinuklearnih dijamagnetičnih spojeva, nastaju i tragovi mononuklearnih molibdenskih(v) spojeva, što je i potvrđeno EPR spektroskopijom. Hibridni spojevi, koji u svom sastavu sadrže Lindqvistov anion i molibdenski(vi) kompleks kao kation [{Mo2(HL 1,2 )}2]Mo619, pripravljeni su reakcijom [Mo2(acac)2] s piridoksal tiosemikarbazonima H2L 1,2 ili njihovim hidrokloridima H2L 1,2 HCl u omjeru 7:1, u acetonitrilu. U navedenim spojevima, kompleksni kation je dimer, a dimerizacija je ostvarena preko hidroksilmetilne skupine. iti jedan od dobivenih produkata ne sadrži klor u svojoj strukturi. U drugom dijelu opisana su svojstva i priprava molibdenskih kompleksa s () ligandima. Sa sintetskog stajališta, druga cjelina je analogna prvoj. Reakcijom [Mo2(acac)2] s piridoksal hidrazonima H2L 4-6, u metanolu, priređeni su mononuklearni [Mo2(L 4-6 )(Me)] kompleksi molibdena(vi). Istom reakcijom u acetonitrilu dobiveni su polinuklearni spojevi [Mo2(L 4-6 )]n (Shema 7). xviii

19 (H 4 L 4 )[Mo 6 19 ] H 2 L 4 (Me) 2 C [Mo 2 (HL 4-6 )(MeC)] 2 Mo 6 19 R= C 5 H 4 (IX) C 6 H 5 (X) C 6 H 6 (XI) MeC 1/7 H 2 L 4-6 [Mo 2 (acac) 2 ] H 2 L 4-6 H 2 L 4-6 Me MeC [Mo 2 (L 4-6 )] n Mo R R= C 5 H 4 (I) C 6 H 5 (II) C 6 H 6 (III) Me H 3 C Mo R CH 3 MeC [Mo 2 (L 4-6 )(Me)] R= C 5 H 4 (Ia) C 6 H 5 (IIa) C 6 H 6 (IIIa) CH 3 PPh * 3 * Me MeC air [Mo 2 3 (L 4,5 ) 2 (Et) 2 ] R= C 5 H 4 (VIa) C 6 H 5 (VII) H 2 L 4,5 Et H 2 L 4 [Mo 2 3 (acac) 4 ] [Mo 2 3 (L 4 ) 2 (Me) 2 ] Me R= C 5 H 4 (VIb) Shema 7. Priprava molibdenskih(vi) i (V) kompleksa s piridoksal hidrazonima. Reakcija se može provesti samo u slučaju kompleksa koji sadrži ligand (L 5 ) 2, * reakcija se može provesti samo u slučaju kompleksa koji sadrži ligand (L 4 ) 2. U svim navedenim kompleksima H2L je derivat piridoksala koji se pojavljuje kao deprotonirani L 2 tridentatni ligand. U otopini su ispitani mogući prijelazi mononuklearnih u polinuklearne spojeve i obrnuto. S obzirom da sve polinuklearne komplekse nije bilo moguće prevesti u mononuklearne, reakcijama u otopini, cilj ih je bio prirediti reakcijama u čvrstom stanju i to zagrijavanjem mononuklarnih kompleksa pri 100 i 200 C (Shema 8). Ustanovljeno je da zagrijavanjem pojedini kompleksi gube otapalo i prelaze u pentakoordinirane komplekse [Mo2(L 4,5 )], koje je moguće izlaganjem parama metanola vratiti u početne mononuklearne komplekse [Mo2(L 4,5 )(Me)]. Daljnjim zagrijavanjem kompleksi [Mo2(L 4,5 )] polimeriziraju i daju [Mo2(L 5 )]n ili smjese nedefiniranog sastava. Polinuklearne komplekse nije xix

20 moguće ponovno prevesti u mononuklearne izlaganjem parama metanola. Kompleks molibdena(vi) s piridoksal benzhidrazonom (H2L 5 ) nastaje zagrijavanjem mononuklearnog kompleksa na 200 C, dok kompleks molibdena(vi) s piridoksal 4-hidroksibenzhidrazonom (H2L 6 ) već na sobnoj temperaturi gubi metanol iz kristalne strukture, a na 100 C prelazi u [Mo2(L 6 )]. Shema 8. Termički inducirane transformacije u čvrstom stanju molibdenskih(vi) kompleksa s piridoksal hidrazonima. predstavlja odgovarajući mononuklearni kompleks, predstavlja pentakoordinirani spoj [Mo 2(L)], predstavlja odgovarajući polinuklearni kompleks, predstavlja amorfnu tvar. Reakcijom (H4)2[MoCl5] s piridoksal hidrazonima H2L 4,5, u etanolu, nastaju mononuklearni spojevi [MoCl2(HL 4,5 )], a reakcijom s [Mo23(acac)4] nastaju dinuklearni spojevi molibdena(v) [Mo23(L 4,5 )2(R)2] (gdje je R metanol ili etanol, ovisno u kojem je otapalu reakcija provedena). Za razliku od reakcija s piridoksal tiosemikarbazonima i njihovim hidrokloridima, reakcije nije bilo moguće izvesti u acetonitrilu zbog slabe topljivosti hidrazonskih liganada, te su stoga provođene u alkoholima. Mononuklearni molibdenski(vi) kompleks, [Mo2(L 4 )(Me)], bilo je moguće reducirati, pomoću PPh3, u dinuklearni xx

21 molibdenski(v) kompleks [Mo23(L 4 )2(R)2]. Dinuklearni molibdenski(v) kompleksi, kao i analozi s tiosemikarbazonima, pokazali su dijamagnetska svojstva. Hibridni spojevi koji u svom sastavu sadrže Lindqvistov anion i molibdenski(vi) kompleks kao kation [Mo2(HL 4-6 )(MeC)]2Mo619 pripravljeni su u acetonitrilu reakcijom [Mo2(acac)2] s piridoksal hidrazonima H2L 4-6 u omjeru 7:1. Za razliku od analognih spojeva s tiosemikarbazonskim ligandima, strukturu ovih spojeva čine dva kationska kompleksa molibdena(vi), u kojima šesto koordinacijsko mjesto zauzima molekula acetonitrila. avedeni spojevi su izrazito nestabilni, i ako se [Mo2(HL 4 )(MeC)]2Mo619 prekristalizira iz acetona može se dobiti polioksometalat u kojem je kation dvostruko protonirani piridoksal hidrazon (H4L 4 )Mo619. Postojanost acetonitrilnih otopina hibridnih poliokso vrsta potvrđena je i UV-Vis spektroskopijom gdje su uspoređivani apsorpcijski maksimumi poliokso vrsta (Bu4)2Mo619, (Bu4)Mo826 te [Mo2(HL 4-6 )(MeC)]2Mo619 s mononuklearnim kompleksima [Mo2(L 1-3 )(Me)]. Treća cjelina, Molibdenski kompleksi s ligandima, se temelji na pripravi i karakterizaciji kompleksa sa Schiffovim bazama pripravljenim kondenzacijom piridoksala i diamina (Shema 9). Kompleksi molibdena(vi) s ligandima sintetizirani su reakcijom [Mo2(acac)2] i odgovarajućeg liganda, u alkoholima, te imaju opću formulu [Mo2(L 8,9 )], gdje je ligand tetradentatno koordiniran na molibden ili pak [{(Mo2(Me)2}2(L 7,10 )] u kojem je ligand didentatno koordiniran na svaki atom molibdena. Reakcijom [Mo23(acac)4] s ligandima, u etanolu, nastaju dinuklearni kompleksi molibdena(v) opće formule [Mo23(L 9,10 )2]. Pojedine komplekse moguće je pripraviti reakcijama prijenosa kisika molibdenskih(vi) kompleksa [Mo2(L 9 )], pomoću trifenilfosfina. Dinuklearni kompleksi molibdena(v) s ligandima, kao i kompleksi s S() i () ligandima, pokazuju dijamagnetska svojstva. Primjenom masene spektrometrije dokazano je da je riječ o dinuklearnim molibdenskim(v) spojevima. xxi

22 H Mo H H 3 C H H 3 C H Mo Mo CH 3 CH 3 H H [Mo 2 (L 8 )] (A*) [{Mo 2 (Me) 2 }(L 7 )] (A) Me H 2 L 8 H 2 L 10 Me [Mo 2 (acac) 2 ] H 2 L 7 Et Me H 2 L 9 H 3 C H H 3 C H Mo CH 3 CH 3 Mo Mo H [{Mo 2 (Me) 2 }(L 10 )] (C) [Mo 2 (L 9 )] (B) H PPh 3 Et Ar [Mo 2 3 (L 7 ) 2 ] (D) [Mo 2 3 (L 10 ) 2 ] (F) H 2 L 7,10 Et [Mo 2 3 (acac) 4 ] H 2 L 9 Et [Mo 2 3 (L 9 ) 2 ] (E) Slika 8. Priprava molibdenskih(vi) i (V) kompleksa s piridoksal diaminskim ligandima. Pripravljeni kompleksi molibdena s ligandima pokazuju slična svojstva. U svim mononuklearnim i polinuklearnim kompleksima molibdena(vi) s S() i () ligandima, ligand je koordiniran na molibden kao tridentatni deprotonirani ligand L 2. Mononuklearni spojevi su općenito stabilni u otopini, a nakon izolacije, duljim stajanjem na zraku gube otapalo. Svi polinuklearni kompleksi su izrazito stabilni čak i nakon duljeg stajanja. Mononuklearni kompleksi su žute ili narančaste boje, a polinuklearni tamnocrvene ili smeđe boje. Priprava polinuklearnih kompleksa xxii

23 zahtjeva vrlo dugo vrijeme reakcije (10-16 sati najčešće), dok je sinteza mononuklearnih kompleksa relativno kraća (oko 3 sata). topine dinuklearnih molibdenskih(v) spojeva su vrlo nestabilne. Promjena boje iz tamnosmeđe u žutu ukazuje na potencijalnu oksidaciju kompleksa molibdena(v) u odgovarajući kompleks molibdena(vi) te je dobivene produkte potrebno izolirati odmah po završetku reakcije. Izolirani kompleksi su stabilni daljnjim stajanjem na zraku. Svi kompleksi molibdena(v) su tamnosmeđe do crne boje. Hibridni kompleksi [{Mo2(HL 1,2 )}2]Mo619 te [Mo2(HL 4-6 )(MeC)]2Mo619 su nakon izolacije relativno osjetljivi na zraku, ali su stabilni u otopini. Većinom su žute do narančaste boje. Molibdenski(VI) kompleksi sa Schiffovim bazama pripravljenim iz diamina su puno osjetljiviji, čak i u otopini. Zahtjevaju brzu manipulaciju jer se u protivnom raspadaju (u početku gube otapalo te postaju tamniji, a u nekim slučajevima mijenjaju boju u plavo-zelenu). To se posebice odnosi na komplekse u kojima je premošćujući ligand didentatno koordiniran na svaki atom molibdena. Svjetložute su boje. Dinuklearni kompleksi molibdena(v) su stabilni i smeđe su boje. Svi priređeni kompleksi su većinom topljivi u koordinirajućim otapalima i netopljivi u nekoordinirajućim. Posljednja cjelina, Katalitička svojstva pripravljenih molibden(vi) kompleksa, temelji se na ispitivanju primjene molibdenskih kompleksa u katalitičkim reakcijama. Monuklearni i polinuklearni kompleksi molibdena(vi) s tridentatnim ligandima te hibridni polioksomolibdati testirani su kao (pred)katalizatori u reakcijama epoksidacije ciklooktena. Za istraživanje su korištene vodene otopine tert-butilhidroperoksida, kao oksidacijsko sredstvo, bez dodatnih organskih otapala te uz vrlo malu količinu (pred)katalizatora. mjeri množina (pred)katalizatora i olefina su: n(mo u kompleksu) : n(olefin) = 0,01 mmol : 20 mmol (gdje su kompleksi: [Mo2(L 1-6 )]n, [{Mo2(HL 1-3 )}Cl]n ili [Mo2(L 1,4-6 )(Me)], [Mo2(HL 1 )(Me)]Cl) xxiii

24 ili n([{mo2(hl 1,2 )}2]Mo619 ili [Mo2(HL 4-6 )(MeC)]2Mo619) : n(olefin) = 0,005 mmol : 20 mmol, što je prvo istraživanje u ovakvim uvjetima. S ciljem provođenja epoksidacijskih reakcija u vodenim uvjetima, prethodno je ispitana stabilnost molibdenskih(vi) kompleksa u prisustvu vlage. Utvrđeno je da poliokso vrste, opće formule [{Mo2(HL 1,2 )}2]Mo619, tj. [Mo2(HL 4-6 )(MeC)]2Mo619, L= S(), tj. () ligand, ne mogu nastati iz polinuklearnih kompleksa [Mo2(L 1-6 )]n. Pokazano je da se molibdenski(vi) kompleksi s S() i () derivatima piridoksala mogu koristiti kao katalizatori u reakcijama epoksidacije ciklooktena. Kao najbolji (pred)katalizator, govoreći u okvirima konverzije ciklooktena 97 %, selektivnosti 97 %, TF h 1 i T 1940, pokazao se mononuklearni kompleks priređen iz piridoksal tiosemikarbazona [Mo2(L 1 )(Me)] (Tablica 1), čime su postignuti do sada najbolji rezultati (u navedenim reakcijskim uvjetima). Istražen je utjecaj metanola tako što su polinuklearnim kompleksima [Mo2(L 1-3 )]n dodavani različiti molarni ekvivalenti metanola (0, 1, 12,5, 25 i 50). Dodatak ekvivalentne množine metanola polinuklearnom kompleksu [Mo2(L 1 )]n, tj. prevođenje polinuklearnog u mononuklearni kompleks [Mo2(L 1 )(Me)] imalo je kao posljedicu najbrže i najefikasnije nastajanje odgovarajućeg epoksida. S druge pak strane, povećanje dodane količine metanola polinuklearnim kompleksima [Mo2(L 2,3 )]n, imalo je kao posljedicu povećanje katalitičke aktivnosti testiranih (pred)katalizatora. Potencijalno objašnjenje se krije u načinu polimerizacije testiranih polinuklearnih (pred)katalizatora. xxiv

25 Tablica 1. Rezultati katalitičkih ispitivanja uporabom molibdenskih(vi) (pred)katalizatora s piridoksal tiosemikarbazonima. pća formula znaka kompleksa n (Me) / mol u odnosu na 1 mol kompleksa Konverzija a / % Selektivnost b / % TF 20min c / h -1 T d [Mo 2(L 1 )(Me] 1a , [Mo 2(L 1-3 )] n [Mo 2(acac) 2] [a] Pretvorba ciklooktena u odgovarajući epoksid računata nakon provođenja reakcije u trajanju od 6 h. [b] Selektivnost - nastajanje epoksida po jednoj molekuli ciklooktena nakon 6 h. [c] Broj oksidiranih molekula ciklooktena po jednom aktivnom centru n(transformiran ciklookten) / n((pred)katalizator) / u prvih 20 minuta reakcije [d] Broj ciklusa koje (pred)katalizator može učiniti prije nego li se deaktivira n(transformiran ciklookten) / n(katalizator) nakon 6 h. xxv

26 Ispitivan je i utjecaj protonacije tiosemikarbazonskih liganada na katalitička svojstva. U usporedbi s molibdenskim (pred)katalizatorima s piridoksal tiosemikarbazonima, (pred)katalizatori s piridoksal tiosemikarbazonskim hidrokloridima pokazuju nešto drugačije ponašanje (Tablica 2). Za razliku od mononuklearnog kompleksa s piridoksal 4-feniltisemikarbazonom (gdje su postignuti najbolji rezultati), analogni kompleks s protoniranim ligandom pokazuje najmanju konverziju, te najmanju TF vrijednost u usporedbi s ostalim testiranim molibdenskim(vi) (pred)katalizatorima. Kao najbolji (pred)katalizator, u smislu proučavanih parametara, pokazao se molibdenski kompleks s piridoksal tiosemikarbazonskim hidrokloridom. Utjecaj protonacije liganda je najveći kod piridoksal 4-feniltiosemikarbazonskog hidroklorida, a najmanji kod piridoksal tiosemikarbazonskog hidroklorida. Tablica 2. Rezultati katalitičkih ispitivanja uporabom molibdenskih(vi) (pred)katalizatora s piridoksal tiosemikarbazonskim hidrokloridima. pća formula znaka kompleksa Konverzija a / % Selektivnost b / % TF 20min c / h -1 T d [Mo 2(HL 1 )(Me)]Cl 1a* * [{Mo 2(HL 1-3 )}Cl] n 2* * [a] Pretvorba ciklooktena u odgovarajući epoksid računata nakon provođenja reakcije u trajanju od 6 h. [b] Selektivnost - nastajanje epoksida po jednoj molekuli ciklooktena nakon 6 h. [c] Broj oksidiranih molekula ciklooktena po jednom aktivnom centru n(transformiran ciklookten) / n((pred)katalizator) / u prvih 20 minuta reakcije [d] Broj ciklusa koje (pred)katalizator može učiniti prije nego li se deaktivira n(transformiran ciklookten) / n(katalizator) nakon 6 h. Uspoređujući rezultate molibdenskih (pred)katalizatora s S() i () ligandima, općenito govoreći, rezultati katalitičkih ispitivanja bolji su korištenjem (pred)katalizatora s S() ligandima. U usporedbi s ostalim molibdenskim(vi) (pred)katalizatorima s () ligandima, mononuklearni kompleks s piridoksal xxvi

27 izoniazidom ima najmanju vrijednost konverzije, za razliku od istog polinuklearnog analoga koji ima najveću vrijednost (Tablica 3). Tablica 3. Rezultati katalitičkih ispitivanja uporabom molibdenskih(vi) (pred)katalizatora s piridoksal hidrazonima. pća formula znaka kompleksa Konverzija a / % Selektivnost b / % TF 20min c / h -1 T d I [Mo 2(L 4-6 )] n II III Ia [Mo 2(L 4-6 )(Me)] IIa IIIa [a] Pretvorba ciklooktena u odgovarajući epoksid računata nakon provođenja reakcije u trajanju od 6 h. [b] Selektivnost - nastajanje epoksida po jednoj molekuli ciklooktena nakon 6 h. [c] Broj oksidiranih molekula ciklooktena po jednom aktivnom centru n(transformiran ciklookten) / n((pred)katalizator) / u prvih 20 minuta reakcije [d] Broj ciklusa koje (pred)katalizator može učiniti prije nego li se deaktivira n(transformiran ciklookten) / n(katalizator) nakon 6 h. Rezultati dobiveni testiranjem hibridnih polioksomolibdata, kao pred(katalizatora), su posebno zanimljivi jer je to prvo istraživanje katalitičke aktivnosti ovakvih vrsta uopće (Tablica 4). S obzirom da u literaturi ne postoje podatci za ovakvo istraživanje, (Bu4)2Mo619 je odabran kao referentni kompleks s kojim su uspoređivani ostali polioksomolibdati. Uočeno je da hibridni spojevi [{Mo2(HL 1,2 )}2]Mo619 te [Mo2(HL 4-6 )(MeC)]2Mo619 imaju dva aktivna mjesta; jedno koje potječe od polianiona {Mo619} 2 te drugo iz dioksomolibdenskog(vi) kompleksa. Također, [{Mo2(HL 1,2 )}2]Mo619 su se pokazali kao bolji (pred)katalizatori. xxvii

28 Tablica 4. Rezultati katalitičkih ispitivanja dobivenih uporabom hibridnih organsko-anorganskih vrsta Lindqvist tipa s molibdenskim(vi) kompleksom kao (pred)katalizatorom. pća formula znaka kompleksa Konverzija a / % Selektivnost b / % TF 20min c / h -1 T d [{Mo 2(HL 1,2 )} 2]Mo IX [Mo 2(HL 4-6 )(MeC)] 2Mo 6 19 X XI (Bu 4) 2Mo [a] Pretvorba ciklooktena u odgovarajući epoksid računata nakon provođenja reakcije u trajanju od 6 h. [b] Selektivnost - nastajanje epoksida po jednoj molekuli ciklooktena nakon 6 h. [c] Broj oksidiranih molekula ciklooktena po jednom aktivnom centru n(transformiran ciklookten) / n((pred)katalizator) / u prvih 20 minuta reakcije [d] Broj ciklusa koje (pred)katalizator može učiniti prije nego li se deaktivira n(transformiran ciklookten) / n(katalizator) nakon 6 h. Zaključno, predložena disertacija daje rezultate ispitivanja priprave i svojstava kompleksnih spojeva molibdena(vi) i (V) s derivatima piridoksala te ispitivanja njihove primjene kao (pred)katalizatora za katalitičku epoksidaciju ciklooktena. xxviii

29 Table of contents Preface viii ABSTRACT ix SAŽETAK x PRŠIREI SAŽETAK xi I ITRDUCTI HW DID IT START? AIMS AD SCPE 2 II LITERATURE REVIEW 3 III 2.1. MLYBDEUM Biological role of molybdenum Selected types of oxo-molybdenum complexes xo-atom transfer Polyoxomolybdates VITAMI B THISEMICARBAZES AD HYDRAZES Thiosemicarbazones and hydrazones in general Thiosemicarbazone and hydrazone coordination SCHIFF BASES DERIVED FRM DIAMIES Schiff bases derived from diamines in general Coordination of Schiff bases derived from diamines WHY T CHSE PYRIDXAL DERIVATES WITH THISEMICARBAZES, HYDRAZES AD SCHIFF BASES DERIVED FRM DIAMIES AS LIGADS? ITRDUCTI T CATALYSIS Homogeneous vs. heterogeneous catalysis General terms used in catalysis CATALYTIC EPXIDATI Epoxides Molybdenum epoxidation catalyst 27 EXPERIMETAL PART MATERIALS AD METHDS Starting materials Identification methods Elemental analysis (EA) Infrared spectroscopy (IR) Thermogravimetric analysis (TG) Differential scanning calorimetry (DSC) Ultraviolet visible spectroscopy (UV-Vis) Magnetic measurements Electron paramagnetic spectroscopy (EPR) Superconducting Quantum Interferometer Device (SQUID) and Vibration Sample Magnetometer (VSM) Gouy balance uclear magnetic resonance spectroscopy (MR) Gas chromatography (GC) Mass spectrometry (MS) X-ray Crystallography Single crystal diffraction Powder diffraction 34 xxix

30 3.2. PREPARATI F THE LIGADS H 2L 1-3 HCl H 2L H 2L 7,9, H 2L PREPARATI F THE STARTIG MLYBDEUM CMPUDS Dioxobis(2,4-pentanedionato)molybdenum(VI) [Mo 2(acac) 2] μ-xodioxotetrakis(2,4-pentanedionato)dimolybdenum(v) [Mo 2 3(acac) 4] Diammonium pentachlorooxomolybdate(v) (H 4) 2[MoCl 5] REACTIS WITH S() LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes The mononuclear complex [Mo 2(L 1 )(Me)] Me (1a Me) Polynuclear complexes [Mo 2(L 1-3 )] n Synthesis and properties of molybdenum(v) complexes xomolybdenum(v) complexes [MoCl 2(HL 1-3 )] Reaction of complexes 1 and 2 with PPh REACTIS WITH S() HCl LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes The mononuclear complex [Mo 2(HL 1 )(Me)]Cl 1.5Me (1*a 1.5Me) Polynuclear complexes [{Mo 2(HL 1-3 )}Cl] n Synthesis and properties of molybdenum(v) complexes xomolybdenum(v) complexes [MoCl 2(H 2L 1 )]Cl Reaction of complexes 1*-3* with PPh Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() ligands [{Mo 2(HL 1,2 )} 2]Mo REACTIS WITH () LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes Mononuclear complexes [Mo 2(L 4-6 )(Me)] Polynuclear complexes [Mo 2(L 4-6 )] n Synthesis and properties of molybdenum(v) complexes xomolybdenum(v) complexes [MoCl 2(HL 4,5 )] Et μ-xodioxodimolybdenum(v) complexes [Mo 2 3(HL 4,5 ) 2(R) 2] Reactions with [Mo 2 3(acac) 4] Reaction of complex Ia with PPh Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with () ligands [(Mo 2(HL 4-6 )(MeC)] 2Mo REACTIS WITH LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes Synthesis and properties of μ-oxodioxodimolybdenum(v) complexes GEERAL PRCEDURE FR THE EPXIDATI F CYCLCTEE BY AQUEUS tert-butyl HYDRPERXIDE SLUTI (TBHP) Epoxidation of cyclooctene by aqueous TBHP molybdenum(vi) mononuclear and polynuclear (pre)catalysts with S() and () ligands Epoxidation of cyclooctene by aqueous TBHP Hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() and () ligands Exp. A m, C m and D m Epoxidation of cyclooctene by the use of the complexes 1 3 with addition of Me before t=0 min Exp. B 50 Epoxidation of cyclooctene by the use of the complex 1 with addition of Me at t=90 min 57 xxx

31 IV V VI RESULTS AD DISCUSSI REACTIS WITH S() AD S() HCl LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes UV-Vis spectroscopy of molybdenum(vi) complexes Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() ligands Synthesis and properties of oxomolybdenum(v) complexes Mononuclear molybdenum(v) complexes Dinuclear molybdenum(v) complexes REACTIS WITH () LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with () ligands UV-Vis spectroscopy Synthesis and properties of oxomolybdenum(v) complexes Mononuclear molybdenum(v) compounds Dinuclear molybdenum(v) compounds REACTIS WITH LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes Synthesis and properties of dinuclear μ-oxodioxodimolybdenum(v) complexes CATALYTIC ACTIVITY F MLYBDEUM(VI) CMPLEXES WITH PYRIDXAL DERIVATES Molybdenum(VI) (pre)catalysts with S() and S() HCl ligands Molybdenum(VI) (pre)catalysts with S() ligands Molybdenum(VI) (pre)catalysts with S() HCl ligands Molybdenum(VI) (pre)catalyst with () ligands Hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() and () ligands 108 CCLUSIS SYTHESIS F MLYBDEUM CMPLEXES WITH PYRIDXAL DERIVATES PRPERTIES F MLYBDEUM CMPLEXES WITH PYRIDXAL DERIVATES AD SLVET-FREE EPXIDATI F CYCLCTEE 114 REFERECES 117 VII ABBREVIATIS ADCMPLEX LABELS cxxv VIII APPEDIX cxxxi Appendix A - MR data of molybdenum(vi) complexes cxxxii Appendix B IR spectra of prepared molybdenum complexes cxxxviii Appendix C Mass spectra of the complex E in Me clvii IX CURRICULUM VITAE clviii xxxi

32 I ITRDUCTI 1

33 1.1. HW DID IT START? AIMS AD SCPE Interest for this research arises from the several facts: the chemistry of molybdenum is versatile because molybdenum can exist in different oxidation states and it has ability to create complexes with various donor atoms. Also, molybdenum complexes could serve as models for metalloenzymes. Regardless many researched molybdenum complexes (considering the ligand nature, molybdenum oxidation number etc.), molybdenum complexes with pyridoxal derivates have not been reported so far. In addition to the above, dinuclear complexes of molybdenum(v) have been poorly represented. Those intriguing features were encouraging and challenging for implementation and application for further research. For that reason, the presented work provides an overview of oxomolybdenum(vi) and (V) complexes with Schiff bases derived from pyridoxal (the preparation, isolation, characterisation and catalytic testing). General ideas and goals, presented in the thesis, were: - to research different synthetic approaches (in the solution and in the solid state) - to characterise molybdenum(vi) and (V) complexes with pyridoxal derivates - to contribute to the understanding of ligand chelation depending on the reaction conditions, starting material which were used etc. - to study oxo-atom transfer reactions from various molybdenum(vi) species - to test obtained molybdenum(vi) species as possible (pre)catalysts for olefin epoxidation of cyclooctene under solvent-free conditions with low molybdenum loading At the end, forty unique compounds had been prepared by conventional synthetic procedure and fully characterised by elemental analysis, infrared-, ultraviolet-, nuclear magnetic resonance spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Fifteen novel structures were determined by X-ray diffraction on monocrystal. Selected molybdenum(vi) compounds (twenty-one) had been used for catalytic research. 2

34 II LITERATURE REVIEW 3

35 2.1. MLYBDEUM The chemistry of molybdenum is quite interesting because of the possibility to form different complexes with large number of available oxidation states and its ability to form stable complexes with oxygen, nitrogen and sulphur containing ligand atoms. 1 Complexes formed in that way mimic active sites in molybdenum enzymes Biological role of molybdenum Above all present elements in the periodic table, molybdenum is the most prominent one for use as a bio-catalyst. 2 Interest in molybdenum, as found in biological systems, is due to importance of its metal ion as an essential trace element participating in many enzymatic reactions. 3-6 Enzymes that contain molybdenum are e.g. oxidases 7 9 reductases and dehydrogenases Molybdenoenzymes consist of two molybdenum atoms per molecule, usually bridged by one or two oxido- or sulphidoatoms The molybdenum atom, in molybdenoenzymes, changes from +VI to +IV oxidation state, although it also involves oxidation state +V Active site of enzymes that include Mo in oxidation state +VI and +IV had been determined by X-ray diffraction, but determination of molybdenum(v) transition state is still relied on spectroscopy Selected types of oxo-molybdenum complexes xo-atom transfer umerous dioxo molybdenum(vi) complexes are usually prepared by ligand addition, exchange and/or metathesis in reaction with with cis-{mo2} 2+ starting compounds (e.g. [Mo2(acac)2], [Mo2X2], [Mo2X2(L)2] (X=halide, L=H2, DMS, PPh3). In general, they are diamagnetic, usually dark yellow to orange compounds. Since the key point of the research, presented in the experimental part of the thesis, is molybdenum complexes with Schiff bases, an introductory overview had been 4

36 restricted to this specific kind of complexes. Schiff bases usually bind to molybdenum atom as tridentate ligands through X donor set (X = S, or in most of the cases). Generally speaking, dioxomolybdenum(vi) complexes are present as mononuclear complexes [Mo2(L)(D)], where D is donor molecule and L is tridentate Schiff base, dinuclear [Mo2(L)]2, or polynuclear ones [Mo2(L)]n. Mononuclear complexes can be easily converted into dinuclear or polynuclear ones in solution depending upon used solvent, in solid state (thermally induced transitions or mechanochemically) if the donor molecule (coordinately bonded completing octahedral coordination around molybdenum) can be simply removed. In dinuclear and polynuclear complex, dimerization and polymerisation is mostly achieved through terminal oxygen atom... Mo=... Mo=... (Fig. 1). 27,28 Mo Mo Fig. 1. Polymerization achieved through terminal oxygen atom. The easiest way to distinguish mononuclear from dinuclear or polynuclear complexes is by comparison of IR spectra. The IR spectra of mononuclear complex showed two characteristic vibration bands in the region cm 1. n the other hand, dinuclear complexes had strong absorption round 850 cm 1 and polynuclear ones around 800 cm 1, which was absent in mononuclear compounds. In most cases, polynuclear compounds had single absorption band around 930 cm 1 instead of cis-{mo2} 2+ doublet. Dioxomolybdenum(VI) species can serve as oxo-atom transfer agents. The acceptor X may be a thiol, a phosphine or any organic molecule, capable to abstract one oxygen atom form the molybdenum complex: 29 Mo VI 2L + X Mo IV L + X 5

37 xo-transfer may be visualised as simple reaction that includes interaction between [Mo2(L)] and one PPh3 molecule, leading to the formation of Ph3P= compound and oxomolybdenum(iv) complex. The reaction may be considered as two electrons redox/oxygen atom transfer process. Fairly stable oxomolybdenum(iv) complexes are scarce to their dioxomolybdenum(vi) counterparts and structurally characterized oxomolybdenum(iv) complexes are extremely rare. xomolybdenum(iv) complexes are conventionally synthesised by refluxing solution of an appropriate dioxomolybdenum(vi) complex with PPh3 in an inert atmosphere. Usually, those complexes are almost insoluble in non-coordinating solvents, but fairly soluble in polar aprotic coordinating solvents, as DMF or DMS, forming brown solutions. The brown colour of DMS solution usually gradually changes into the orange one implying oxidation process (oxygen transfer from DMS) to molybdenum(vi) species. It was assumed that the presence of sulphur atom, coordinated to molybdenum centre, is required for AT reaction. 30 However, molybdenum(vi) complexes with ligands had been found to oxidize tertiary triphenylphosphines. 31,32 The mechanism involves formation of molybdenum(iv) species as an intermediate (Scheme 1). 33 S Me Mo PPh 3 PPh 3 Me Mo S Me Mo S Scheme 1. Proposed mechanism of oxo transfer reaction from DMS to PPh Unreacted dioxomolybdenum(vi) complex with pentacoordinated oxomolybdenum(iv) complex can result in the formation of an oxo-bridged dimolybdenum(v) complex: 6

38 LMo VI 2 + LMo IV Mo V 23L2 μ-xodimer occurs unless its formation is sterically hindred. therwise it is pervasive. If there is no monocrystalline sample, formation of the [Mo23(L)2] species can be proven from reaction stoichiometries, mass spectrometry, MR and absorption spectra. 34 Schiff base complexes containing {Mo23} 4+ core with S ligands tend to reveal distinctive absorption spectra. Usually, an intense visible band appears between nm and another band shoulder at nm. By combination of the mentioned chemical and spectroscopic methods, it should be possible to detect formation of species with {Mo23} 4+ core. However, some molybdenum(v) complexes were also determined by X-ray diffraction Complexes with the {Mo23} 4+ core are usually not biologically relevant. 38 Some molybdenum(v) compounds are also used as catalysts for oxygen transfer from DMS or pyridine--oxide to triphenyphosphine. 39 Besides dinuclear, molybdenum(v) complex exist as mononuclear ones as well. A range of molybdenum(v) complexes can be obtained by reduction of molybdate {Mo4} 2 or molybdenum(vi) oxide Mo3 in acidic solution either chemically either electrolytically. ne of the species often used as starting material for preparation other molybdenum(v) complexes is [MoCl5] 2 ion or [MoCl4]. Mononuclear complexes [MoCl2(HL)], where L present tridentate thiosemicarbazone Schiff base, were obtained by the reaction of (H4)2[MoCl5] and ligand (1:1) in dry acetonitrile, under argon atmosphere: 40 (H4)2[MoCl5] + H2L [MoCl2(HL)] + 2 H4Cl + HCl Mononuclear molybdenum(v) complexes are relatively rare because of propensity of molybdenum(v) to form di- or polynuclear species. Generally, dinuclear oxo complexes of molybdenum(v) are of two main types: i) singly bridged ones that exist in cis- and trans- rotamers, ii) doubly bridged ones which are in cis (Fig. 2). 7

39 Mo Mo Mo Mo Mo Mo a. b. c. Fig. 2. Dinuclear oxo complexes of molybdenum(v): a. singly-bridged cis-rotamer, b. singly-bridged trans-rotamer as in (μ 2-oxo)-dioxo-bis(salicyladehyde-4-phenylthiosemicarbazonato-S)-dimolybdenum(V) acetonitrile solvate, c. doubly bridged as in bis(-methylpyridinium) bis(μ 2-oxo)-dioxo-bis(oxalate)-di-molybdate(V). In all mono- and dinuclear oxo complexes of molybdenum(v), ligands trans to Mo= bonds are weakly bonded and are often entirely absent. A trans effect had been defined as the effect of coordinated groups on the rate of substitution reactions of ligands trans to itself Polyoxomolybdates Polyoxometalates (PMs) represents a large class of metal-oxygen cluster anion. 41 They usually incorporate atoms of V, b, Ta, Cr, Mo or W as the primary constituents ( addenda atoms ). 42 The minimum number of addenda atoms is set to be between two and six. The largest numbers of PMs are containing Mo, V or W atoms. Lately, development of the new class of functionalised polyoxometalates, where terminal oxo-atom is replaced by organic ligand, has attracted considerable interest Hexamolybdate anion (Lindqvist type), {Mo619} 2, is well represented in the chemistry of polyoxomolybdates (Fig. 3). Formation of the {Mo619} 2 anion is usually dependant on the ph, solvent, temperature or countercations. 8

40 Fig. 3. Lindqvist s type polyoxometalates. Structurally characterised example of Lindqvist anion is bis(tetramethylammonium) hexamolybdate hydrate 48,49 where each molybdenum atom is coordinated by six oxygen atoms in a distorted octahedral arrangement. Wide number of hybrid PMs can be obtained by benchtop methods or by hydrothermal synthesis. ver recent years, modification and functionalization of {Mo619} 2 with organic ligands has been exploited to achieve more desirable attributes. By incorporating inorganic and organic counterparts in single structure, the functionality of organic-inorganic hybrid materials can be multiplied both from organic linker molecule and inorganic species. 50 Hybrids based on Lindqvist {Mo619} 2 anion are still relatively rare. To our knowledge, there have been only few examples so far ([Mo2(HL)(MeC)2]Mo619, H2L = aroylhydrazone ligand). The majority of literature and patent data considering application of polyoxometalates is in the area of catalysis (around 85 %). They are also used in analytical chemistry, electrochemistry, clinical analysis and sensor chemistry. 9

41 2.2. VITAMI B6 Vitamin B6 (Fig. 4) is the generic term for pyridoxal (PL), pyridoxine (P) and pyridoxamine (PM). 51 These three species differ in a variable group present at their 4 th position PL has aldehyde, P hydroxyl and PM amino group. All species can be phosphorylated. Pyridoxal 5`-phosphate (PLP) is, biologically speaking, the most active form and is used as a co-factor in more than 140 enzymatic reactions. H 2 a. b. c. P P P H H H H 2 d. e. f. Fig. 4. B6 vitamers: a. pyridoxal, b. pyridoxine, c. pyridoxamine, d. pyridoxal 5-phosphate, e. pyidoxamine 5-phosphate, f. pyridoxine 5-phosphate. The vitamin B6 has been brought into the context with abiotic stress. Researchers have shown that it has antioxidative capacities that rival from tocopherols or ascorbic acid. The new feature of vitamin B6 is as a reactive oxygen species scavenger and its potential ability to increase resistance to biotic and abiotic stresses has brought new directions of B6 plant research in photosynthesis. 10

42 2.3. THISEMICARBAZES AD HYDRAZES Thiosemicarbazones and hydrazones in general Thiosemicarbazones and hydrazones are Schiff bases of general formula R 1 R 2 C 2 = 1 2 (H) C 1 (=S) 3 R 3 R 4 and R 1 R 2 C 2 = 1 2 (H) C 1 (=)R 3, respectively (Fig. 5). R 1 C 2 1 C 1 R 3 R 2 2 H 3 S R 4 R 1 R 2 C H C 1 R 3 a. b. Fig. 5. General scheme of a. thiosemicarbazone and b. hydrazone. Synthesis of thiosemicarbazones and hydrazones involves condensation of aldehyde or ketone with proper thiosemicarbazide and hydrazide, respectively Thiosemicarbazones are broadly classified as: 55 Monothiosemicarbazones Bisthiosemicarbazones Monothiosemicarbazones (Fig. 6) have different substituents (R 1, R 2, R 3, R 4 ). Thiosemicarbazones obtained from aldehyde have hydrogen atom as a R 2 substituent, while R 1 substituent is an alkyl, an aryl or a heterocyclic group. Substituents R 3 and R 4 are hydrogen atoms, one hydrogen atom and an alkyl or an aryl or 1 atom can be a part of ring. In case of thiosemicarbazones obtained from ketones, substituents on C 2 atom can be two hydrogen atoms or one hydrogen atom and alkyl or aryl group. 11

43 R 1 R 2 C H S C 1 3 R 3 R 4 Fig. 6. Monothiosemicarbazone ligand. Bisthiosemicarbazones have two arms connected via ring or C C bond (Fig. 7). S S H 2 H R 2 H H 2 R 1 R 3 Fig. 7. Bisthiosemicarbazone ligand. Thiosemicarbazone and hydrazone ligands exist in two tautomeric forms (Fig. 8). In solid state dominates thione form of thiosemicarbazones and keto form of hydrazones, while in solution coexists equilibrium between two forms (thioketo/thioenol for thiosemicarbazones and keto/enol for hydrazones). S R 1 R 1 C 2 1 C 1 R 3 C 2 1 R 2 2 H 3 R 2 R 4 SH 2 C 1 3 R 3 R 4 R 1 R 1 C 2 1 C 1 C 2 1 R 2 2 R 3 R 2 H 2 C 1 R 3 a. b. Fig. 8. Tautomeric forms of thiosemicarbazones (up) and hydrazones (down): a. thioketo (up) and keto (down), b. thioenol (up) and enol (down) form. 12

44 Thiosemicarbazone and hydrazone coordination Thiosemicarbazones and hydrazones can bind to a metal centre in the neutral or in anion form (after deprotonation of 2 H and SH in thiosemicarbazones and deprotonation of 2 H and in hydrazones). In neutral form, thiosemicarbazones can bind through S atom as monodentate ligands 56 (Fig. 9a), or S atom can bridge two metal atoms 57,58 (Fig 9b). S R S R M M M M 3 S S M a. b. c. d. M 3 Fig. 9. a. and b. Monodentate coordination of thiosemicarbazones, c. and d. didentate coordination of thiosemicarbazones. Thiosemicarbazones can also coordinate as didentate 3 S chelating ligands (Fig. 9c) or 3 S chelating / S - bridging ligands (Fig. 9d). If there is an additional donor atom, it can also be engaged in the coordination to metal centre (Fig. 10). X 3 S 3 X 3 M M M M M S X S a. b. c. Fig. 10. Tridentate X 3 S chelation of thiosemicarbazones: a. non-bridging, b. S bridging, c. X bridging (X = or atom). 13

45 Hydrazones can also bind as X 3 chelating ligands, X bridging or atom. (Fig. 11). 3 X M M X 3 Fig. 11. Tridentate X 3 chelation of hydrazones, X bridging atom (X = or ). As anions 62,63, thiosemicarbazones can coordinate to a metal centre as shown in Fig. 12 and hydrazones as shown in Fig S 2 M M M M S a. b. Fig. 12. Coordination of thiosemicarbazones as anions: a. 2 S chelation, b. 2 S bridging ligand. X M 3 X M X 3 M X Fig. 13. Tridentate X 3 chelation of hydrazones, X bridging (X =, 3 atom). A very rare example of pentadentate coordination 64 is shown in Fig

46 X M 3 1 S 2 M M Fig. 14. Coordination of thiosemicarbazone as pentadentate coordinated ligand. Bisthiosemicarbazones can bind as neutral molecules or as anions (Fig. 15) M M S S S S Fig. 15. Coordination of bisthiosemicarbazones. 15

47 2.4. SCHIFF BASES DERIVED FRM DIAMIES Schiff bases derived from diamines in general Diamine is a type of a polyamine with two amino groups. Diamines with linear carbon chains and aromatic ring are: 1,2-ethanediamine (2 carbons) propane-1,3-diamine (3 carbons) butane-1,4- diamine (4 carbons) benzene-1,2-diamine (2 carbons chain, but aromatic linker) etc. Diamines are used to obtain bridged Schiff bases (Fig. 16). Two molecules of aldehydes or ketones and one of diamine are required to prepare bridged Schiff base. R 1 R 2 R R 1 R 2 Fig. 16. Bridged Schiff base. In the reaction with abh4, bridged Schiff bases can be reduced to diamines, as shown in Fig. 17. R 1 H R H R 1 R 2 R 2 Fig. 17. Diamine upon the reduction of Schiff base. 16

48 Coordination of Schiff bases derived from diamines Bridged Schiff bases usually coordinate to a metal centre as tetradentate ligand via atoms (Fig. 18). M Fig. 18. Coordination of tetradentate ligand. They can also chelate as ligands,, bridging (Fig. 19a) or, bridging ones (Fig. 19b). M M M M M a. b. Fig. 19. chelation of tetradentate ligands a., bridging, b., bridging. 17

49 2.5. WHY T CHSE PYRIDXAL DERIVATES WITH THISEMICARBAZES, HYDRAZES AD SCHIFF BASES DERIVED FRM DIAMIES AS LIGADS? Pyridoxal derivated with thiosemicarbazones, hydrazones and Schiff bases derived from diamines can be found in different protonation states from neutral zwitterionic form H2L to dianion one L 2 which is demonstrated on the pyridoxal thiosemicarbazone example. 68 It has been found that in ferric complexes H2L thiosemicarbazone ligand can exist in all protonation forms ([Fe(H2L)2](3)3, [Fe(HL)2]Cl and a[fe(l)2]). The monoanionic form is the most usual one. The protonation state of the ligand could be the key parameter for controlling; for instance, redox properties and spin state of the metal ion (e.g. iron in this case). H H H H H 2 H 2 H + S H + S a. b. H H H 2 S c. Fig. 20. Pyridoxal thiosemicarbazone protonation states: a. H 2L, b. HL, c. L 2. The protonation state is influenced by the nature of the used solvent, the resulting ph of the solution, reaction temperature etc. It is worth to note that H2L usually acts as mono- or deprotonated ligand when it reacts with metal acetates, and as neutral or monodeprotonated when metal nitrates are used. Complexes possessing ligand in neutral form H2L have been isolated from ethanol, and the ones possessing ligand in 18

50 monoanion form HL from water. The thio-amide group is very easily and spontaneously deprotonated in water, which is much less likely in alcohol. The zinc complexes obtained from H2L thiosemicarbazone Schiff base, contain the ligand in monodeprotonated or neutral form of the ligand, when water or ethanol has been used respectively. Pyridoxal thiosemicarbazone ligands usually coordinate to the metal centre through S donor atoms. Fig. 21. presents dimeric copper complex [CuCl(H2L)]2 in which copper atom is pentacoordinated through S atoms and chlorine atom in basal plane and hydroxymethyl oxygen from the neighbouring complex molecule. 72 The ligand is in its neutral form. Fig. 21. Mercury PV-Ray rendered view of the dimeric copper complex with pyridoxal thiosemicarbazone ligand. 72 Pyridoxal hydrazone ligands usually coordinate to the metal centre through donor atoms. Fig. 22. presents copper complex [CuCl(HL)] where the ligand is in monoprotonated form

51 Fig. 22. Mercury PV-Ray rendered view of the copper complex with pyridoxal hydrazone ligand. 83 It has also been shown that pyridoxal isonicotinoyl hydrazone is biocompatible iron chelating agent. 69 The ligand is sensitive to the hydrolysis in aqueous solution and it degrades into pyridoxal and isoniazid. ne quite interesting research, with simple hydrazone type ligands derived from salicylaldehyde, had been noted. 70 An ethanolic solution of the ligand (4,6-dimethyl 2-hydrazino pyrimidine and salicylaldehyde), when added to an hydrochloride ethanolic solution of [Mo2(acac)2], either at room temperature or under reflux, yielded by [Mo2(L 1 )Cl] complex (L refers to deprotonated ligand). n the other hand, an ethanolic solution of the ligand (4,6-dimethyl 2-hydrazino pyrimidine and o-hydroxy acetophenone), when added to an acidified ethanolic solution of [Mo2(acac)2], at room temperature, resulted in the formation of the mononuclear [Mo2(L)Cl2] species. Under reflux, oxo-bridged [Mo25(L)2Cl2] species (L refers to newly formed bidentate pyrimidyl pyrazole ligand) was formed. It has been known, from the literature data, that tetradentate ligands are formed when aldehyde:diamine ratio is 2:1. If the ratio is 1:1, tridentate ligand is formed which should be taken into consideration when preparing these ligands. Tetradentate pyridoxal Schiff bases with diamines have large tendency to hydrolyze. The chemical insertion of longer hydrocarbon chains between amino groups of 20

52 species that end up with pyridoxal moieties should create Schiff base with remarkable better chelate ability. In thorium complex with bis-pyridoxal Schiff base [Th(L)2] (Fig. 23), all four hydroxyl groups are deprotonated and two ligands are linked to one metal centre. Fig. 23. Mercury PV-Ray rendered view of the thorium complex with bis-pyridoxal Schiff base. 94 Complexes with reduced derivates seem to be more stable. The difference in the stability could be explained by lacking C= bonds resulting in significantly less strain in the formed complex. 71 In zinc complex with reduced form of bis-pyridoxal Schiff base [ZnCl(HL)] (Fig. 24), one hydroxyl group is deprotonated and pyridinum rings are protonated. 97 Fig. 24. Mercury PV-Ray rendered view of the zinc complex with bis-pyridoxal Schiff base in reduced form

53 In addition, pyridoxal Schiff bases chosen for this research, show biological activity such as antiviral, antitumor, anti-fungicidal properties. The research on CCDC Database (ctober 2011) showed that there are not many, structurally characterised, metal complexes with the above mentioned ligands: 17 metal complexes with thiosemicarbazone ligands (where metal centre is Cu 72,73, Fe 74-77, Mn 73, Co 78,79, i 80, Au 81, Ti 82 ), 8 metal complexes with hydrazone ligands (where metal centre is Cu 83,84, Fe 85-87, V 88, U 89 ), 10 metal complexes with bis-pyridoxal Schiff bases (where metal centre is i 90,Cu 91,92, U 93, Th 94, Pr 95, Ce 95, d 92, Eu 92 ), 3 metal complexes with bis-pyridoxal Schiff bases in reduced form (where metal centre is V 71, Mn 96 and Zn 97 ). Although there are much more examples of Schiff bases obtained from salicylaldehyde, they are not comparable to the ones derived from pyridoxal and for that reason they will not be mentioned in this thesis. o matter pyridoxal is often (wrongly) stressed as the compound similar to the salicylaldehyde, it is different system with distinct behavioural pattern. Even though they are likely to have similar coordination chemistry, pyridoxal Schiff bases are expected to prove superior as supramolecular synthons - additional site for hydrogen bond acceptance (ring, from CH2) and donation (H from CH2). 22

54 2.6. ITRDUCTI T CATALYSIS Catalysis implies chemical reaction which is easier and faster to be achieved (by the use of a catalyst). Catalytic processes are performed in two main types of reactors: batch reactor for small and medium scaled processes (e.g. chemicals, pharmaceuticals), continuous flow reactors for large scale processes (e.g. producing and treating bulk chemicals). Chemical concentrations on batch processes change during the time, while in continuous flow reactors they remain the same Homogeneous vs. heterogeneous catalysis In homogeneous catalysis, catalyst, reactants and products are in the same phase. Many homogeneous catalysts are based on transition metal complexes in which the ligand can have different functions. For instance, the ligand can stabilize active metal atom within the active phase, it can also have the role of chiral agent. The ligand is usually an organic molecule. Different types of ligands change catalyst s properties. n the other hand, heterogeneous catalysis implies the cases where substrate and catalyst are in different phases. Usually, it is a system in which the catalyst is solid and reactants are in gas or liquid phase General terms used in catalysis When speaking about catalysis, specific terms are generally used. Considering the reaction, depicted in the following inscription: A cat B where A is reactant, B is product, and cat is catalyst. CVERSI of A refers to the ratio between the number of molecules of A that have reacted up to time t and theoretical number of molecules A that should react, if the reaction was complete, 23

55 SELECTIVITY is the ratio between the number of molecules B produced up to time t and theoretical number of molecules B that should be produced, if the reaction was complete. Conversion and selectivity are often expressed in percentage. When comparing catalyst efficiency, following terms are used: TURVER UMBER (T) is the number of cycles that a catalyst can run before it deactivates; number of A molecules that one molecule of catalyst can convert, TURVER FREQUECY (TF) is turnover number divided by time interval which indicates formation velocity of the activated form (highest slope in the kinetic profile); number of A molecules that convert into B molecules per unit time (second, minute or hour). Those definitions are valid when performing homogenous catalysis. When performing heterogeneous catalysis, T and TF are often defined per active site or per gram of catalyst (because of the heterogeneous distribution of the active species within the solid). Usual way to express amount of catalyst used in the certain reaction is AMUT RATI F CATALYST or CATALYST LADIG, which is defined as the amount of catalyst per amount of substrate. 24

56 2.7. CATALYTIC EPXIDATI Epoxides Epoxide functional group consists of a three-membered ring with two carbon atoms and one oxygen atom. These moieties can be found in some natural organic molecules (e.g. in disparlure (cis-7,8-epoxy-2-methyloctadene), pheromone or in squalene 2,3-epoxide, biological precursor for cholesterol and steroidal hormones), and are very useful compounds in industry (e.g. propylene oxide or epoxy). In classical organic chemistry, epoxides are obtained through a variety of methods, using oxidants in excess in presence of organic solvents most of the time. ne traditional method is the reaction between alkenes and inorganic or organic peracid (as chloric acid, peroxyformic-, peroxybenzoic-, trifluoroperoxyacetic- or metachloroperoxybenzoic acid) (Fig. 25) Although meta-chloroperoxybenzoic acid is the most popular oxidizing agent in those reactions, deficit of hydrogen peroxide contributes to very complicated preparative way of high purity mcpba. A major advantage of using peroxyacids is the rapid epoxidation of unfunctionalised alkenes. R 1 R 3 RC 3 H R 1 R 3 R 2 R 4 R 2 Fig. 25. Preparation of epoxide. R 4 Epoxidation processes usually lead to low selectivity due to variety of secondary nucleophilic ring opening reactions and they generate large amount of waste. Byproducts are defined as all what are not desired products. Besides the non desired organic products, wastes are usually inorganic salts like sodium chloride, potassium hydrogensulphate, sodium or ammonium sulphate, depending on the nature of the oxidizing agent (sodium chlorate, potassium peroxymonosulphate, sodium or ammonium peroxosulphate, respectively). The central topic for future development for epoxidation systems, both in industry and in academic society, needs to be focused on environmentally friendly oxidant 25

57 and highly economic processes. The key is to minimize waste tending to follow 12 principles of green chemistry. 101 Environmental considerations have pushed chemists to replace stronger oxidants by smoother ones Tertiary hydroperoxides are used more often since primary or secondary alkyl hydroperoxides can easily decompose. Alkyl hydroperoxides are more soluble and stable in organic solvents than hydrogen peroxide. 105 Tert-butyl hydroperoxide, (CH3)3(C), and cumyl hydroperoxide, (CH3)2(C)C6H5, are widely used and they usually require transition metal catalyst in order to form epoxide. Among all metals, molybdenum is the most researched one In some extent, one challenge in the chemistry of epoxides stays in the control of the stereochemistry of the reaction. The Sharpless reaction is an enantioselective chemical reaction to prepare 2, 3 epoxyalcohols from primary and secondary allylic alcohols (Fig. 26). 116 When titanium isopropoxide-diethyl tartrate is used as catalyst and tert-butylhydroperoxide as an oxygen donor, trans-disubstituted allylic alcohol can be epoxidized at 15 C to 20 C in at least 94 % enantiomeric excess with w = 5 % Ti(-i-Pr)4 and % tartrate. The reaction is generally complete in 1-4 hours. Cis-disubstituted allylic alcohols require longer reaction time (1-2 days), more catalyst (n(catalyst) : n(substrate) = 1 mol : 10 mol) and slightly higher reaction temperatures. R 2 R 1 R 3 Ti( i Pr) 4 t Bu, CH 2 Cl 2, molecular sieves R 2 R 1 R 3 Fig. 26. Sharpless epoxidation. Another relevant example concerns the Jacobsen catalyst (Fig. 27) (C2 symmetric manganese(iii) complex with salen-like ligand). It allows enantioselective epoxidation of unfunctionalized alkyl- ar aryl- substituted olefins. 117 An oxidizing 26

58 agent in Jacobsen reaction was iodosylmesitylene or acl. With the use of 1-8 mol of catalyst, obtained selectivities were % (usually better with aromatic olefins) and yields were %. R R 1 Mn III -salen complex R R 1 acl(aq), CH 2 Cl 2 Fig. 27. Jacobsen epoxidation Molybdenum epoxidation catalyst Molybdenum oxo-complexes have been investigated as epoxidation catalysts of alkenes in the presence of an oxidant since They have a number of important applications in the petroleum 119 and plastics industries. 120,121 Another major use is in the hydrodesulfurisation (HDS) of petroleum, petrochemicals and coal-derived liquids. The choice of oxidant depends on the stability of molybdenum complex (e.g. H22 degrades to water which might destroy the complex). Although hydrogen peroxide is more environmentally friendly, TBHP is widely used in industry because of its stability and solubility in organic solvents. Its by-product in the reaction, tert-butanol, can be separated, recycled and used in other industries. 122,123 It can be also converted into methyl tert-butyl ether (MTBE), a high-octane component for gasoline. 124 Usual, molybdenum complexes used for catalytic epoxidation are dioxomolybdenum(vi) complexes 125, , since it has been observed that higher epoxidation yields could be achieved. 126 Most of the epoxidation reactions have been performed in organic solvents 127,128 or ionic liquids. 129 There was only one example of the epoxidation reaction processed without any addition of organic solvent with the use of aqueous TBHP, following principles of green chemistry. 104 As it can be seen from the Table 1, the most common amount ratio n((pre)catalyst) : n(substrate) = 1 % and TBHP is usually in decane. High values of conversion and selectivity are obtained under specified reaction conditions. 27

59 Table 1. Some examples of epoxidation data of cis-cyclooctene using TBHP catalyzed by the complexes with {Mo 2} 2+ core. Reaction temperature is 80 C. {Mo 2} 2+ complex [Mo 2Cl 2(L) 2] L= 4,4-bis- methoxycarbonyl-2,2- bipyridine [Mo 2(phox) 2] phox = 2-(2- hydroxyphenyl)oxazoline ligand [Mo 2(L)(Me)] L= donor [Mo 2(L)] L=H 2salen type of ligand [Mo 2Cl 2(L)] L= donor [Mo 2(CH 3) 2(L) 2] L= diimino ligand Solvent (n(complex) in : Conversion Selectivity Solvent which n(substrate)) / % / % is x 100 / % TBHP no decane TF Ref / h dichloroethane not defined not 1 dichloroethane defined no decane no decane no decane Besides the complexes bearing "Mo2" unit, polyoxometalates could be interesting compounds in terms of epoxidation. 135 Indeed, they show the following advantages in oxidation catalysis: i. redox and acid base properties can be controlled by changing chemical composition, ii. they are not sensitive towards oxidative and thermal degradation compared to organometallic complexes, iii. catalytically active sites can be designed by insertion metals and ligands. Various catalytic systems for H22 bases epoxidation catalyzed by PMs have been developed and can be divided into two groups (based on the structural and mechanistic properties of PM): 136 i. catalytic precursors of peroxotungstate and peroxomolybdate species, ii. transition metal substituted polyoxometalates. 28

60 Although Fe-, Mn-, Co-, Zn-, i-substituted polyoxometalates show high turnover numbers, the efficiency to H22 utilisation, selectivity to epoxide and activity towards epoxidation of non-reactive terminal olefins should be improved. For the synthesis of the heterogeneous catalysts based on PMs, following items should be taken into an account: i. development of supporting catalysts without loss of intrinsic activity and selectivity, ii. complexation of PMs with appropriate cations in order to form micro- / meso- structures which would increase selectivity. To our knowledge, there are no literature examples for epoxidation reactions with the use of Lindqvist type of polyoxometales and no epoxidation reaction with the use of PM in the solvent-free conditions. 29

61 III EXPERIMETAL PART 30

62 3.1. MATERIALS AD METHDS Starting materials Pyridoxal hydrochloride, thiosemicarbazide, 4-methyl-3-thiosemicarbazide, 4-phenyl-3-thiosemicarbazide, isonicotinic acid hydrazide, benzhydrazide, 4-hydroxybenzhydrazide, 1,2-diaminoethane, propane-1,3-diamine, benzene-1,2-diamine, ammonium heptamolybdate tetrahydrate, acetylacetone, triphenylphosphine, sodium borohydride and zinc were commercially available. Acetonitrile was dried over phosphorus pentoxide. Methanol and ethanol were dried using magnesium turnings and iodine, and then distilled Identification methods Elemental analysis (EA) C, H, and S analyses were provided by the Analytical Services Laboratory of Ruđer Bošković Institute, Zagreb. Chloride was determined by the gravimetric method as silver chloride Infrared spectroscopy (IR) Infrared spectra were recorded in KBr pellets with a Perkin Elmer 502 spectrophotometer in the cm 1 region. All data were processed in Spekwin 32 Programme and IR spectra are presented in the Chapter VIII APPEDIX Appendix B Thermogravimetric analysis (TG) Thermogravimetric analyses were performed using a Mettler TG 50 thermo balance with aluminium crucibles. All experiments were recorded with a heating rate of 31

63 5 C min 1 in a dynamic oxygen atmosphere with a flow rate of 200 cm 3 min 1 and analyzed by the Mettler STAR e Software Differential scanning calorimetry (DSC) Differential Scanning Calorimetry measurements were carried out with a Mettler Toledo DSC823e calorimeter and analyzed by the Mettler STAR e Software Ultraviolet visible spectroscopy (UV-Vis) Electronic absorption spectra were recorded at ambient temperature on a Cary 100 UV-Vis Spectrophotometer Magnetic measurements Electron paramagnetic spectroscopy (EPR) EPR spectra in X band frequencies were measured at 293 K using a Varian E-109 spectrometer operating at 100 khz modulation, equipped with a dual sample cavity. As a g-factor standard 2,2-diphenyl-1-picrylhydrazyl (DPPH, g = ) was used Superconducting Quantum Interferometer Device (SQUID) and Vibration Sample Magnetometer (VSM) The powder samples for magnetic measurements were dispersed and fixed in paraffin within measuring ampoule to avoid rotation of particles/grains in changing magnetic field. Magnetization measurements were performed using commercial Quantum Design MPMS5 magnetometer equipped with SQUID. Magnetic hysteresis loops M(H) were measured in the field range ±5 T at temperatures 5 and 290 K. Besides the SQUID magnetometer, we used vibrating sample magnetometer PAR EG&G VSM 4500 for measurements of magnetic hysteresis loops at room temperature with applied fields up to ± 0.95 T. 32

64 Gouy balance The solid sample is hung from the pan of a balance and is placed such that one end of the sample is between the pole-pieces of the magnet and the other one is outside the field. The force exerted on the sample by the inhomogeneous magnetic field is obtained by measuring the apparent change in the mass of the sample uclear magnetic resonance spectroscopy (MR) For ligands and complexes identification, MR spectra were obtained using a Bruker Advance DRX500 spectrometer. The spectra were recorded in DMS-d6 with TMS as internal standard. MR data for ligands and mononuclear or polynuclear molybdenum(vi) and molybdenum(vi) complexes with tetradentate ligands are presented in the Chapter VIII APPEDIX Appendix A. For catalytic studies, 1 H MR spectra were obtained using Bruker Advance DPX-200 spectrometer at MHz Gas chromatography (GC) Chromatograms were obtained using Agilent 6890A chromatograph equipped with FID detector, a DB5-MS capillary column (30 m x 0.32 mm x 0.25 µm). The GC parameters were quantified with authentic samples of the reactants and products. The conversion of cis-cyclooctene and the formation of cyclooctene oxide were calculated from calibration curves relatively to acetophenone Mass spectrometry (MS) Mass spectra were recorded using ion trap mass spectrometer Amazon ETD (Bruker Daltonics, Bremen, Germany) with electrospray ionization. While recording mass spectra, the entering capillary was grounded and the voltage at the input metallisized glass capillaries was 4500 V. Dispersal gas (nitrogen) is introduced the ion source under pressure of 8.0 psi. Desolvatation gas (nitrogen) had a flow rate of 33

65 5.0 L / min and a temperature of 200 C. Mass spectra are recorded in the range m / z = , the sample solution was directly introduced into the instrument using infusion pumps with constant flow rate of 1uL / min. Sample solution was 0.5 pmol / μl. When recording tandem or multistage fragmentation spectra, ion signal (fragmented with the width of 4 Da) was isolated. The relative collision energy ranged from ne complex example is presented in the Chapter VIII APPEDIX, Appendix C X-ray crystallography Single crystal diffraction The single-crystal X-ray diffraction data were collected by -scans on an xford Diffraction Xcalibur 3 CCD diffractometer with graphite-monochromated Mo-Kα radiation ( = Å) Powder diffraction The powder X-ray diffraction data were collected by the Panalytical X Change powder diffractometer in the Bragg Brentano geometry using Cu-Kα radiation. The sample was contained on a Si sample holder. Patterns were collected in the range of 2θ = 5 50 with the step size of 0.03 and at 1.5 s per step. The data were collected and visualized using the X Pert programs Suite

66 3.2. PREPARATI F THE LIGADS H2L 1-3 HCl Ligands were prepared according to the procedure described in the literature. 74,75 Pyridoxal hydrochloride (0.05 mmol) and appropriate thiosemicarbazide (0.05 mmol) were dissolved in 20 ml Et and refluxed for three hours. After cooling, deep yellow precipitate was obtained, filtered off, rinsed with Et and dried under vacuum H2L 1-6 Ligands were prepared according to the procedure described in the literature. 89, Pyridoxal (in its neutral form) 142 (0.05 mmol) and appropriate thiosemicarbazide or hydrazide (0.05 mmol) were dissolved in 20 ml Et and refluxed for three hours. After cooling, deep yellow precipitate was obtained, filtered off, rinsed with Et and dried under vacuum H2L 7,9,10 Ligands were prepared according to the procedure described in the literature. 94,96 Pyridoxal hydrochloride (2.24 g, 11 mmol) was dissolved in water (50 ml) and ph was adjusted to 6.5 by addition of concentrated K. 1,2-Ethanediamine, propane- 1,3-diamine, benzene-1,2-diamine (5 mmol) was added drop wise. Yellow solution was refluxed for one hour. Yellow precipitate was formed, filtered off, rinsed with Et, Et2 and dried under vacuum H2L 8 The ligand was prepared according to the procedure described in the literature. 71 abh4 (0.11 g, 3 mmol) dissolved in 25 ml of Me containing K was added to 35

67 the suspension of H2L 7 (1 g, 2.8 mmol) in methanol/chloroform (3:2, 50 ml). The mixture was stirred overnight and yellow solution turned colourless. The ph was adjusted to 4-5 by addition of aqueous HCl (2 mol dm 3 ) and solution was stirred for two hours. The ph was increased to 10 by addition of aqueous K (3 mol dm 3 ). The white precipitate that was formed during the reaction, was filtered off, rinsed with Et, Et2 and dried under vacuum. *** Elemental analysis, melting points, IR, 1 H and 13 C MR spectra of all pyridoxal derivates are according to literature references. 36

68 3.3. PREPARATI F THE STARTIG MLYBDEUM CMPUDS Dioxobis(2,4-pentanedionato)molybdenum(VI) [Mo2(acac)2] 143 Ammonium heptamolybdate (H4)6Mo724 4H2 (5 g, 4 mmol) is dissolved in water (15 ml) and acetylacetone (7 ml) is added and the ph of solution is adjusted to 3.5 by addition of H3 (w = 10 %). Reaction mixture is stirred for one hour in dark. After yellow precipitate is formed, reaction mixture is left in dark for two hours, filtered off and rinsed with Et and Et2 and dried in a desiccator up to constant weight μ-xodioxotetrakis(2,4-pentanedionato)dimolybdenum(v) [Mo23(acac)4] 144 Dioxobis(2,4-pentanedionato)molybdenum(VI) [Mo2(acac)2] (2.5 g, 7.7 mmol) is dissolved in acetylacetone (10 ml) by gentle heating and stirring for half an hour. Zinc is carefully added in small portions (0.3 g, 4.6 mmol) and stirring is continued for three more hours. After the brown precipitate is formed, it is filtered off, rinsed with Et and dried in a desiccator up to constant weight Diammonium pentachlorooxomolybdate(v) (H4)2[MoCl5] 145 Molybdenum pentachloride MoCl5 (5.42 g, mol) is dissolved, by gentle heating, in concetrated hydrochloric acid (20 ml) which contains dissolved ammonium chloride (5.54 g, 0.1 mmol). Solution was cooled down to 0 C in gas stream of dried hydrogen chloride until intensive green precipitate is formed. Precipitate is filtered off, rinsed with Et2 and dried in a desiccator up to constant weight. *** Elemental analysis, melting points, IR, 1 H and 13 C MR spectra of all prepared molybdenum starting material are according to literature references. 37

69 3.4. REACTIS WITH S() LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes The mononuclear complex [Mo2(L 1 )(Me)] Me (1a Me) A mixture of [Mo2(acac)2] (0.16 g, 0.5 mmol) and pyridoxal 4-phenylthiosemicarbazone ligand H2L 1 (0.16 g, 0.5 mmol) in dry acetonitrile (10 ml) and dry methanol (10 ml) was refluxed for five hours. The solution was left at the room temperature for one day and the obtained orange crystalline precipitate of [Mo2(L 1 )(Me)] Me (1a Me) was filtered off, rinsed with acetonitrile and dried in a desiccator up to constant weight. Crystals of 1a Me lose solvated molecules at room temperature and were analyzed as unsolvated species 1a. Yield: 0.11 g (48 %). Anal. Calcd. mass fractions of elements, w / %, for C16H18Mo45S (Mr=474.34) are: C 40.51, H 3.82, 11.81, S 6.70; found: C 40.73, H 3.19, 12.36, S TG: Me, 7.16 % (Calcd %); Mo3, % (Calcd %). IR (KBr) (ṽmax /cm 1 ): 1596, 1533 (C=), 1318 (C ), 930 (Mo2) asym, 890 (Mo2) sym, 631 (C S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxxxviii, Fig. 61) Polynuclear complexes [Mo2(L 1-3 )]n [Mo2(acac)2] (0.16 g, 0.5 mmol) was dissolved in dry acetonitrile (20 ml) and appropriate pyridoxal thiosemicarbazone ligand H2L 1-3 was added (0.4 mmol). The suspension was refluxed. The precipitate, formed during refluxing of the acetonitrile solution, was filtered off, rinsed with acetonitrile and dried in a desiccator up to constant weight. R= Ph Complex [Mo2(L 1 )]n (1): Dark red product. Reaction time: 5 h. Yield: 0.14 g (63 %). Anal. Calcd. mass fractions of elements, w / %, for C15H14Mo44S (Mr=442.30): C 40.73, H 3.19, 12.67, S 7.25; found: C 41.02, H 3.41, 13.03, S TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1589, 1541 (C=),

70 (C ), 947 (Mo2)asym, 901 (Mo2)sym, 636 (C S). UV-Vis(Me): max / nm: 350 and 418 (log / dm 3 mol -1 cm -1 : 3.21 and 3.85) (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxii and Appendix B IR spectra of prepared molybdenum complexes, page cxxxvii, Fig. 62) R=Me Complex [Mo2(L 2 )]n (2): Brown product. Reaction time: 5 h. Yield: 0.13 g (71 %). Anal. Calcd. mass fractions of elements, w / %, for C10H12Mo44S (Mr=380.23): C 31.59, H 3.18, 14.73, S 8.43; found: C 31.40, H 3.43, 14.70, S TG: Mo3, % (Calcd %). IR(KBr) (ṽmax/ cm 1 ): 1580, 1533 (C=), 1304 (C ), 937 (Mo=), 811 (Mo= Mo), 630 (C S). UV-Vis(Me): /nm: 326 and 403 (log /dm 3 mol -1 cm -1 : 4.23 and 3.56) (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxii and Appendix B IR spectra of prepared molybdenum complexes, page cxxxix, Fig. 63). R=H Complex [Mo2(L 3 )]n (3): Dark brown product. Reaction time: 12 h. Yield: 0.08 g (46 %). Anal. Calcd. mass fractions of elements, w / %, for C9H10Mo44S (Mr=366.20): C 29.52, H 2.75, 15.30, S 8.76; found: C 29.71, H 3.10, 15.51, S TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1589, 1538, (C=), 1299 (C ), 934 (Mo=), 820 (Mo= Mo), 625 (C S). UV-Vis(Me)): /nm: 293 and 385 (log /dm 3 mol -1 cm -1 ): 4.25 and 3.22 (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxii and Appendix B IR spectra of prepared molybdenum complexes, page cxxxix, Fig. 64) Synthesis and properties of molybdenum(v) complexes xomolybdenum(v) complexes [MoCl2(HL 1-3 )] A mixture of (H4)2[MoCl5] (0.12 g, 0.5 mmol) and an appropriate pyridoxal thiosemicarbazone ligand H2L 1-3 (0.5 mmol) in dry ethanol (20 ml) was refluxed for six hours. The dark red, almost black precipitate that deposited during warming of 39

71 the reaction mixture was filtered off, rinsed with Et and dried in a desiccator up to constant weight. The same products can be obtained by the same preparation procedure using an appropriate pyridoxal thiosemicarbazone hydrochloride ligand H2L 1-3 HCl. R=Ph Complex [MoCl2(HL 1 )] Et (4 Et): (Crystals of [MoCl2(HL 1 )] Et (4 Et) lose solvated molecules at room temperature. They were left in a desiccator up to constant weight and analyzed as unsolvated species 4: Yield: 0.22 g (88.3 %). Anal. Calcd. mass fractions of elements, w / %, for C15H15Cl2Mo43S (Mr=498.22): C 36.16, H 3.03, Cl 14.23, 11.25, S 6.43; found: C 35.81, H 2.81, Cl 13.93, 10.89, S TG: Mo3, % (Calcd %). IR(KBr) (ṽmax /cm 1 ): 1578, 1543 (C=), 1320 (C ), 944 (Mo=), 618 (C S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxl, Fig. 65). R=Me Complex [MoCl2(HL 2 )] (5): Yield: 0.1 g (45.5 %). Anal. Calcd. mass fractions of elements, w / %, for C10H13Cl2Mo43S (Mr=436.13): C 27.54, H 3.00, Cl 16.26, 12.85, S 7.35; found: C 27.47, H 2.75, Cl 16.12, 12.57, S TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1567, 1529 (C=), 1331 (C ), 955 (Mo=), (C S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxl, Fig. 66). R=H Complex [MoCl2(HL 3 )] (6): Yield: 0.95 g (45.2 %). Anal. Calcd. mass fractions of elements, w / %, for C9H11Cl2Mo43S (Mr=422.12): C 25.61, H 2.63, Cl 16.80, 13.27, S 7.60; found: C 25.40, H 2.41, Cl 16.53, 13.04, S TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1583, 1559, (C=), 1363 (C ), 959 (Mo=), 615 (C S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxli, Fig. 67) Reaction of complexes 1 and 2 with PPh3 All reactions were performed under a dry argon atmosphere. PPh3 (0.02 g, 0.08 mmol) and -picoline (8 L) were dissolved in dry acetonitrile (15 ml) and then 40

72 complex 1 or 2 (0.08 mmol) was added. The suspension was heated for 10 h. A dark red-brown microcrystalline product, formed during the reaction, was collected by filtration, rinsed with acetonitrile and dried. R = Ph: Complex [Mo23(L 1 )2] (7): Yield: g (62 %) (obtained from 1). Anal. Calcd. mass fractions of elements, w / %, for C30H28Mo287S2 (Mr = ): C 41.48, H 3.25, 12.90, S 7.38; found: C 42.57, H 4.90, 10.60, S TG: % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1600, 1549 (C=), 1393 (C-), 965 (Mo=), 789 (Mo Mo), 625 (C-S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxli, Fig. 68). R = Me: Complex [Mo23(L 2 )2] (8): Yield: 0.01 g (35 %) (obtained from 2). Anal. Calcd. mass fractions of elements, w / %, for C20H24Mo287S2 (Mr = ): C 32.27, H 3.25, 15.05, S 8.61; found: C 32.21, H 3.08, 14.99, S TG: % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1589, 1501 (C=), 1389 (C-), 961 (Mo=), 787 (Mo Mo), 624 (C-S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxlii, Fig. 69). 41

73 3.5. REACTIS WITH S() HCl LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes The mononuclear complex [Mo2(HL 1 )(Me)]Cl 1.5Me (1*a 1.5Me) A mixture of [Mo2(acac)2] (0.16 g, 0.5 mmol) and pyridoxal 4-phenylthiosemicarbazone hydrochloride H2L 1 HCl (0.14 g, 0.4 mmol) in dry acetonitrile (10 ml) and dry methanol (10 ml) was refluxed for 5 hours. The solution was left at room temperature for one day and the obtained red orange crystalline precipitate was filtered off, rinsed with acetonitrile and dried in a desiccator up to constant weight. Yield: 0.14 g (55 %). Anal. Calcd. mass fractions of elements, w / %, for C17.5H25ClMo46.5S (Mr = ): C 37.61, H 4.50, Cl 6.34, 10.03, S 5.74; found: C 37.73, H 3.95, Cl 6.55, 10.56, S TG: Me, 13.9 % (Calcd %); Mo3, 26.5 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1602, 1553 (C=), 1367 (C ), 939 (Mo2)asym, 904 (Mo2)sym, 639 (C S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxliii, Fig. 72) Polynuclear complexes [{Mo2(HL 1-3 )}Cl]n [Mo2(acac)2] (0.16 g, 0.5 mmol) was dissolved in dry acetonitrile (20 ml) and appropriate pyridoxal thiosemicarbazone ligand H2L 1-3 HCl was added (0.4 mmol). The suspension was refluxed. The precipitate, formed during refluxing of the acetonitrile solution, was filtered off, rinsed with acetonitrile and dried in a desiccator up to constant weight. R = Ph: Complex [{Mo2(HL 1 )}Cl]n (1*): Dark red product. Reaction time: 5 hours. Yield: 0.22 g (94 %). Anal. Calcd. mass fractions of elements, w / %, for C15H15ClMo44S (Mr = ): C 37.63, H 3.16, Cl 7.41, 11.70, S 6.70; found: C 37.41, H 3.11, Cl 7.14, 11.80, S TG: Mo3, 29.8 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1604, 1557 (C=), 1362 (C-), 954 (Mo2)asym, 935 (Mo2)sym, 641 (C-S). UV-Vis(Me): /nm: 354 and 434 (log /dm 3 mol -1 cm -1 ): 4.17 and 3.92 (see 42

74 Appendix A - MR data of molybdenum(vi) complexes, page cxxxii and Appendix B IR spectra of prepared molybdenum complexes, page cxliv, Fig. 73). R = Me: Complex [{Mo2(HL 2 )}Cl]n (2*): Brown product. Reaction time: 12 hours. Yield: g (43 %). Anal. Calcd. mass fractions of elements, w / %, for C10H13ClMo44S (Mr = ): C 28.82, H 3.14, Cl 8.51, 13.45, S 7.70; found: C 28.66, H 3.25, Cl 8.21, 13.50, S TG: Mo3, 34.3 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1591, 1540 (C=), 1358 (C-), 930 (Mo=), 801 (Mo= Mo), 621 (C-S). UV-Vis(Me): /nm: 325 and 405 (log /dm 3 mol -1 cm -1 ): 4.25 and 3.37 (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxii and Appendix B IR spectra of prepared molybdenum complexes, page cxliv, Fig. 74). R = H: Complex [{Mo2(HL 3 )}Cl]n (3*): Dark brown product. Reaction time: 12 hours. Yield: 0.08 g (46 %). Anal. Calcd. mass fractions of elements, w / %, for C9H11ClMo44S (Mr = ): C 26.85, H 2.75, Cl 8.80, 13.91, S 7.96; found: C 26.53, H 2.92, Cl 8.54, 13.65, S TG: Mo3, 35.5 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1617, 1559 (C=), 1357 (C-), 930 (Mo=), 815 (Mo= Mo), 621 (C-S). UV-Vis(Me): /nm: 342 and 427 (log /dm 3 mol -1 cm -1 ): 4.25 and 3.28 (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxii and Appendix B IR spectra of prepared molybdenum complexes, page cxlv, Fig. 75) Synthesis and properties of molybdenum(v) complexes xomolybdenum(v) complexes [MoCl2(H2L 1 )]Cl A mixture of (H4)2[MoCl5] (0.12 g, 0.5 mmol) and pyridoxal 4-phenylthiosemicarbazone hydrochloride H2L 1 HCl (0.5 mmol) in dry acetonitrile was refluxed for 6 h. The dark red precipitate that deposited during warming of the reaction mixture was filtered off, rinsed with acetonitrile and dried in a desiccator up to constant weight. 43

75 R=Ph: Complex [MoCl2(H2L 1 )]Cl (4*): Yield: 0.22 g, 88.3 %. Anal. Calcd. mass fractions of elements, w / %, for C15H17Cl3Mo43S (Mr = ): C 33.63, H 3.20, Cl 19.85, 10.46, S 5.99; found: C 33.11, H 2.91, Cl 19.31, 9.99, S TG: Mo3, % (Calc %). IR(KBr) (ṽmax / cm 1 ): 1583, 1545 (C=), 1318 (C ), 980 (Mo=), 637 (C S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxlv, Fig. 76). Recrystallisation of the compound 4* in Et, in the air, leads to the formation of dioxomolybdenum(vi) compound [Mo2(H2)(HL 1 )]Cl Et. Crystals of compound were obtained in very small amount, sufficient only for X-ray diffraction analysis Reaction of complexes 1*-3* with PPh3 All reactions were performed under a dry argon atmosphere. PPh3 (0.02 g, 0.08 mmol) and -picoline (8 L) were dissolved in dry acetonitrile (15 ml) and then complex 1*, 2* or 3* (0.08 mmol) was added. The suspension was heated for 10 h. A dark red-brown microcrystalline product was collected by filtration, rinsed with acetonitrile and dried. R = Ph: Complex [Mo23(HL 1 )2]Cl2 (7*): Yield: 0.02 g (52 %) (obtained from 1*). Anal. Calcd. mass fractions of elements, w / %, for C30H30Cl2Mo289S2 (Mr = ): C 38.27, H 3.21, Cl 7.53, 11.90, S 6.81; found: C 38.11, H 3.42, Cl 7.21, 11.85, S TG: 30.8 % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1601, 1552 (C=), 1363 (C-), 948 (Mo=), 788 (Mo Mo), 625 (C-S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxlvi, Fig. 77). R = Me: Complex [Mo23(HL 2 )2]Cl2 (8*): Yield: g (46 %) (obtained from 2*). Anal. Calcd. mass fractions of elements, w / %, for C20H26Cl2Mo287S2 (Mr = ): C 29.39, H 3.21, Cl 8.67, 13.71, S 7.85; found: C 29.24, H 3.68, Cl 8.23, 13.64, S TG: 35.0% Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1606,

76 (C=), 1366 (C-), 953 (Mo=), 783 (Mo Mo), 611 (C-S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxlvi, Fig. 78). R = H: Complex [Mo23(HL 3 )2]Cl2 (9*): Yield: g (41 %) (obtained from 3*). Anal. Calcd. mass fractions of elements, w / %, for C18H22Cl2Mo287S2 (Mr = ): C 27.39, H 2.81, Cl, 8.98, 14.20, S 8.12; found: C 27.25, H 3.10, Cl 8.65, 14.12, S TG: 36.5 % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1617, 1560 (C=), 1343 (C ), 948 (Mo=), 779 (Mo Mo), 621 (C-S) (see Appendix B IR spectra of prepared molybdenum complexes, page cxlvii, Fig. 79) Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() ligands [{Mo2(HL 1,2 )}2]Mo619 Thiosemicarbazone ligand H2L 1,2 HCl (0.07 mmol) was dissolved in dry acetonitrile by heating and [Mo2(acac)2] (0.16 g, 0.5 mmol) was added. Red-brown solution was heated for 4 hours. A small amount of precipitate, formed during refluxing of the acetonitrile solution, was filtered off and the resulting filtrate was concentrated under vacuum to one fifth of its volume and left in refrigerator. After two days, crystals suitable for X-ray diffraction were obtained. The same products can be obtained by the same preparation procedure using an appropriate pyridoxal thiosemicarbazone ligand H2L 1,2. R= Ph: Complex [{(Mo2(HL 1 )}2]Mo619 (10): Yield: 0.02 g (30 %). Anal. Calcd. mass fractions of elements, w / %, for C30H34Mo8827S2 (Mr = ): C 20.35, H 1.94, 6.33, S 3.62; found: C 19.24, H 1.56, 5.78, S TG: 64.8 % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1578, 1534 (C=), 1365 (C ), 960 (Mot_as), 948 (Mo2)asym, 910 (Mo2)sym, 796 (Mob_as), 756 (bmot) (see Appendix B IR spectra of prepared molybdenum complexes, page cxli, Fig. 70). R = Me: Complex [{(Mo2(HL 2 )}2]Mo619 2CH3C (11 2CH3C): Yield: 0.02 g (30 %). Anal. Calcd. mass fractions of elements, w / %, for C24H32Mo81027S2 45

77 (Mr = ): C 16.70, H 1.99, 8.11, S 3.72; found: C 16.30, H 1.56, 7.89, S TG: 65.8 % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1581, 1539 (C=), 1365 (C ), 960 (Mot)as, 947 (Mo2)asym, 913 (Mo2) sym, 796 (Mob_as), 605 (bmot) (see Appendix B IR spectra of prepared molybdenum complexes, page cxliii, Fig. 71). 46

78 3.6. REACTIS WITH () LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes Mononuclear complexes [Mo2(L 4-6 )(Me)] A mixture of [Mo2(acac)2] (0.065 g, 0.2 mmol) and appropriate ligand H2L 4-6 (0.2 mmol) in dry methanol (20 ml) was refluxed for 5 hours. The solution was left at room temperature for three days and the obtained crystalline precipitate was filtered off, rinsed with methanol and dried in desiccator up to constant weight. R = C5H4: Complex [Mo2(L 4 )(Me)] (Ia): range yellow product. Yield: 0.09 g (9 %). Anal. Calcd. mass fractions of elements, w / %, for C15H16Mo46 (Mr = ): C 40.55, H 3.63, 12.61; found: C 39.3, H 3.12, TG: 6.73 % Me, (Calcd %), Mo3, 31.1 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1603, 1548 (C=), 1290 (C-), 946, 924 (Mo=). UV-Vis(MeC): /nm: 271 and 408 (log /dm 3 mol -1 cm -1 ): 4.21 and 3.50 (see Appendix B IR spectra of prepared molybdenum complexes, page cxlvii, Fig. 80). R = C6H5: Complex [Mo2(L 5 )(Me)] (IIa): Yellow product. Yield: g (16 %). Anal. Calcd. mass fractions of elements, w / %, for C16H17Mo36 (Mr = ): C 43.35, H 3.87, 9.48; found: C 42.1, H 2.67, TG: 7.61 %Me, (Calcd %), Mo3, 32.3 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1611, 1539 (C=), 1256 (C-), 950, 926 (Mo=). UV-Vis(MeC): /nm: 265 and 405 (log /dm 3 mol -1 cm -1 ): 4.01 and 3.38 (see Appendix B IR spectra of prepared molybdenum complexes, page cxlvii, Fig. 81). R = C6H5: Complex [Mo2(L 6 )(Me)] Me (IIIa Me): range red product. Yield: g (15 %). Anal. Calcd. mass fractions of elements, w / %, for C17H21Mo38 (Mr = ): C 41.56, H 4.31, 8.55; found: C 40.7, H 4.12, TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1613, 1559 (C=),

79 (C-), 939, 912 (Mo=). UV-Vis(MeC): /nm: 296 and 413 (log /dm 3 mol -1 cm -1 ): 4.48 and 4.03 (see Appendix B IR spectra of prepared molybdenum complexes, page cxlviii, Fig. 82) Polynuclear complexes [Mo2(L 4-6 )]n A mixture of [Mo2(acac)2] (0.065 g, 0.2 mmol) and appropriate ligand H2L 4-6 (0.2 mmol) in dry acetonitrile (20 ml) was refluxed. A precipitate that was formed was filtered off, rinsed with acetonitrile and dried in desiccator up to constant weight. R = C5H4: Complex [Mo2(L 4 )] (I): Dark yellow product. Reaction time: 16 hours. Yield: 0.07 g (83 %). Anal. Calcd. mass fractions of elements, w / %, for C14H12Mo45 (Mr = ): C 40.79, H 2.93, 13.59; found: C 41.76, H 2.71, TG: Mo3, 34.5 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1610, 1559 (C=), 1260 (C-), 930, 908 (Mo=) (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxix and Appendix B IR spectra of prepared molybdenum complexes, page cxlix, Fig. 83). R = C6H5: Complex [Mo2(L 5 )] (II): Yellow product. Reaction time: 12 hours. Yield: g (16 %). Anal. Calcd. mass fractions of elements, w / %, for C16H17Mo35 (Mr = ): C 43.81, H 3.19, 10.22; found: C 43.84, H 2.99, TG: Mo3, 32.3 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1608, 1537 (C=), 1252 (C-), 953, 932 (Mo=) (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxix and Appendix B IR spectra of prepared molybdenum complexes, page cxlix, Fig. 84). R = C6H5: Complex [Mo2(L 6 )] MeC (III MeC): range red product. Reaction time: 12 hours. Yield: g (6 %). Anal. Calcd. mass fractions of elements, w / %, for C17H16Mo46 (Mr = ): C 43.6, H 3.44, 11.96; found: C 42.7, H 3.11, TG: CH3C, 9.87 % (Calcd %), Mo3, % (Calcd %). IR(KBr) 48

80 (ṽmax / cm 1 ): 1661, 1590 (C=), 1259 (C-), 935, 889 (Mo=) (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxix and Appendix B IR spectra of prepared molybdenum complexes, page cl, Fig. 85) Synthesis and properties of molybdenum(v) complexes xomolybdenum(v) complexes [MoCl2(HL 4,5 )] Et A mixture of (H4)2[MoCl5] (0.12 g, 0.5 mmol) and an appropriate pyridoxal thiosemicarbazone ligand H2L 4,5 (0.5 mmol) in dry ethanol (20 ml) was refluxed for 8 h under argon atmosphere. The dark brown black precipitate that deposited during warming of the reaction mixture was filtered off, rinsed with Et and dried in a desiccator up to constant weight. R = C5H4: Complex [MoCl2(HL 4 )] Et (IV Et): Yield: 0.04 g (16 %). Anal. Calcd. mass fractions of elements, w / %, for C16H19Cl2Mo45 (Mr = ): C 37.37, H 3.72, Cl 13.79, 10.90; found: C 36.91, H 3.69, Cl 14.1, TG: Mo3, 26.4 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1632, 1569 (C=), 1246 (C-), 953 (Mo=) (see Appendix B IR spectra of prepared molybdenum complexes, page cl, Fig. 86). R = C6H5: Complex [MoCl2(HL 5 )] Et (V Et): Yield: 0.05 g (19 %). Anal. Calcd. mass fractions of elements, w / %, for C17H20Cl2Mo35 (Mr = ): C 39.79, H 3.93, Cl 13.82, 8.19; found: C 40.15, H 3.95, Cl 13.21, TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1614, 1580 (C=), 1256 (C-), 937 (Mo=) (see Appendix B IR spectra of prepared molybdenum complexes, page cli, Fig. 87). 49

81 μ-xodioxodimolybdenum(v) complexes [Mo23(HL 4,5 )2(R)2] Reactions with [Mo23(acac)4] [Mo23(acac)4] (0.11 g, 0.15 mmol) is dissolved in dry alcohol (Me or Et) (40 ml) by heating in argon atmosphere and ligand H2L 4,5 (0.3 mmol) is added. Dark brown solution is refluxed for 8 hours and is left in refrigerator. After few days black precipitate is obtained, filtered off and rinsed with alcohol. R = C5H4: Complex [Mo23(HL 4 )2(Me)2] (VIa): Yield: 0.05 g (38 %). Anal. Calcd. mass fractions of elements, w / %, for C30H38Mo2811 (Mr = ): C 41.01, H 4.36, 12.75; found: C 43.1, H 2.71, TG: 30.1 % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1610, 1575 (C=), 1258 (C ), 946,915 (Mo=), 754 (Mo Mo) (see Appendix B IR spectra of prepared molybdenum complexes, page cli, Fig. 87). The same compound can be obtained by the procedure R = C5H4: Complex [Mo23(HL 4 )2(Et)2] (VIb): Yield: 0.05 g (39 %). Anal. Calcd. mass fractions of elements, w / %, for C30H32Mo2811 (Mr = 872.5): C 41.30, H 3.07, 12.84; found: C 43.1, H 3.36, TG: % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1610, 1575 (C=), 1368 (C ), 951,916 (Mo=), 740 (Mo Mo) (see Appendix B IR spectra of prepared molybdenum complexes, page cli, Fig. 88). R = C6H5: Complex [Mo23(HL 5 )2(Et)2] (VII): Yield: 0.05 g (31 %). Anal. Calcd. mass fractions of elements, w / %, for C34H38Mo2611 (Mr = 898.6): C 45.14, H 4.26, 9.35; found: C 44.1, H 4.1, TG: % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1617, 1589 (C=), 1379 (C ), 949, 936 (Mo=), 789 (Mo Mo) (see Appendix B IR spectra of prepared molybdenum complexes, page clii, Fig. 89). 50

82 Reaction of complex Ia with PPh3 PPh3 (0.01 g, 0.04 mmol) was dissolved in dry methanol (30 ml) and then Ia (0.04 mmol) was added. The suspension was heated for 8 h in argon atmosphere. A dark red-brown microcrystalline product was collected by filtration, rinsed with methanol and dried. btained product was identified as [Mo23(HL 4 )2(Me)2] (VIa) Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with () ligands [(Mo2(HL 4-6 )(MeC)]2Mo619 Appropriate ligand H2L 4-6 (0.07 mmol) and [Mo2(acac)2] (0.16 g, 0.5 mmol) were heated for 4 hours in acetonitrile. A small amount of precipitate, formed during refluxing of the acetonitrile solution, was filtered off and the resulting filtrate was concentrated under vacuum to one fifth of its volume and left in refrigerator. After few days obtained precipitate was filtered off and rinsed with acetonitrile. R = C5H4: Complex [Mo2(HL 4 )(MeC)]2Mo619 (IX): Yellow product, crystals suitable for X-ray diffraction. Yield: 0.06 g (50 %). Anal. Calcd. mass fractions of elements, w / %, for C32H30Mo81029 (Mr = ): C 21.52, H 1.69, 7.84; found: C 20.01, H 1.77, TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1637, 1569 (C=), 1366 (C ), 960 (Mot)asym, 912(Mo2)sym, 793 (Mob)ayms, 739 (bmot). UV-Vis(MeC): / nm: 263 and 329 (log /dm 3 mol -1 cm -1 ): 3.98 and 3.77 (see Appendix B IR spectra of prepared molybdenum complexes, page clii, Fig. 90). R = C6H5: Complex [Mo2(HL 5 )(MeC)]2Mo619 (X): Yellow product. Yield: g (33 %). Anal. Calcd. mass fractions of elements, w / %, for C34H34Mo8829 (Mr = ): C 22.86, H 1.92, 6.27; found: C 21.53, H 1.8, TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1605, 1582 (C=), 1360 (C ), 51

83 961 (Mot)asym, (Mo2)asym, 912, 886 (Mo2)sym, 795 (Mob)asym, 603 (bmot). UV-Vis(MeC): /nm: 257, 322 and 414 (log /dm 3 mol -1 cm -1 ): 4.12, 4.19 and 3.96 (see Appendix B IR spectra of prepared molybdenum complexes, page cliii, Fig 91). R = C6H5: Complex [Mo2(HL 6 )(MeC)]2Mo619 (XI): range product. Yield: g (26 %). Anal. Calcd. mass fractions of elements, w / %, for C34H34Mo8831 (Mr = ): C 22.46, H 1.88, 6.16; found: C 21.62, H 1.59, TG: Mo3, % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1612, 1505 (C=), 1355 (C ), 932 (Mot)asym, 914 (Mo2)asym, 889, 853 (Mo2)sym, 750 (Mob)asym, 605 (bmot). UV-Vis(MeC): /nm: 259, 344 and 438 (log /dm 3 mol -1 cm -1 ): 4.69, 4.51 and 4.52 (see Appendix B IR spectra of prepared molybdenum complexes, page cliii, Fig. 92). 52

84 3.7. REACTIS WITH LIGADS Synthesis and properties of dioxomolybdenum(vi) complexes A mixture of [Mo2(acac)2] (0.045 g, 0.14 mmol) and appropriate ligand H4L 7-9 (0.14 mmol) in dry methanol (20 ml) was refluxed for 5 hours. The solution was left in the refrigerator for three days after which air-unstable yellow crystalline precipitate suitable for X-ray diffraction was obtained. R = C2H4: Complex [{Mo2(Me)2}2(L 7 )] 3Me (A 3Me): Yield: 0.01 g (11 %). Anal. Calcd. mass fractions of elements, w / %, for C22H36Mo2412 (Mr = ): C 35.69, H 4.9, 7.57; found: C 35.03, H 4.12, 7.17 %. TG: Mo3, 38.9 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1632, 1537 (C=), 1387, 1306 (C-), 935, 896 (Mo=) (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxvi and Appendix B IR spectra of prepared molybdenum complexes, page xxxiv). R = C2H6: Complex [Mo2(L 8 )] (A*): Yield: g (7 %). Anal. Calcd. mass fractions of elements, w / %, for C18H24Mo46 (Mr = ): C 44.27, H 4.95,, 11.47; found: C 43.78, H 4.06, 11.07, %. TG: Mo3, 27.3 % (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1591, 1549 (C-), 1361 (C-), 919, 903 (Mo=) (see Appendix A - MR data of molybdenum(vi) complexes, page cxxxvi and Appendix B IR spectra of prepared molybdenum complexes, page cliv, Fig. 93). R = C3H6: Complex [Mo2(L 9 )] (B): Complex was prepared according to the literature procedure 146, with the exception of the use of ethanol instead of methanol as a solvent. R = C6H4: Complex [{Mo2(Me)2}2(L 7 )] (C): Yield: g (36.4 %). Anal. Calcd. mass fractions of elements, w / %, for C30H44Mo2412 (Mr = ): C 42.66, H 5.25,, 6.63; found: C 42.93, H 4.96, 7.61, %. TG: Mo3, 32.3 % (Calcd %). IR(KBr) 53

85 (ṽmax / cm 1 ): 1620, 1554 (C=), 1383(C-), 923, 896 (Mo=) (see Appendix B IR spectra of prepared molybdenum complexes, page cliv, Fig 94) Synthesis and properties of μ-oxodioxodimolybdenum(v) complexes [Mo23(acac)4] (0.04 g, 0.06 mmol) was dissolved in dry Et (25 ml) by heating in argon atmosphere and ligand H4L 7,9,10 (0.12 mmol) was added. Dark brown solution was refluxed for 2 hours and brown precipitate was obtained. Precipitate was filtered off and rinsed with alcohol. R = C2H4: Complex [Mo23(L 7 )] 2Et (D 2Et): Yield: 0.01 g (23 %). Anal. Calcd. mass fractions of elements, w / %, for C40H52Mo2813 (Mr = ): C 45.98, H 5.02, 10.73; found: C 44.27, H 4.37, TG: 27.3 % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1636, 1617 (C=), 1293, 1258 (C ), 941 (Mo=), 758 (Mo Mo) (see Appendix B IR spectra of prepared molybdenum complexes, page clv, Fig. 95). R = C3H6: Complex [Mo23(L 9 )] (E): Yield: 0.01 g (21 %). Anal. Calcd. mass fractions of elements, w / %, for C38H44Mo2811 (Mr = ): C 46.54, H 4.53, 11.43; found: C 44.57, H 4.90, TG: 27.9 % Mo3 (Calcd %). IR(KBr) (ṽmax / cm 1 ): 1617, 1560 (C=), 1385(C ), 938 (Mo=), 766 (Mo Mo) (see Appendix B IR spectra of prepared molybdenum complexes, page clv, Fig. 96 and Appendix C Mass spectra of the complex E in Me, page clvii). The same compound can be obtained by the following reaction: Complex B (0.05 g, 0.01 mmol) was dissolved in dry Et (20 ml) and PPh3 was added (0.026 g, 0.1 mmol). The solution was refluxed in argon atmosphere for 7 hours. Brown precipitate was obtained, filtered off and rinsed with Et. R = C6H4: Complex [Mo23(L 10 )] (F): Yield: g (26 %). Anal. Calcd. mass fractions of elements, w / %, for C44H40Mo2811 (Mr = ): C 50.39, H 3.84, 10.68; found: C 49.57, H 4.01, TG: 28.1 % Mo3 (Calcd %). IR(KBr) 54

86 (ṽmax / cm 1 ): 1616, 1554 (C=), 1385(C ), 943 (Mo=), 744 (Mo Mo) (see Appendix B IR spectra of prepared molybdenum complexes, page clvi, Fig. 97). 55

87 3.8. GEERAL PRCEDURE FR THE EPXIDATI F CYCLCTEE BY AQUEUS tert-butyl HYDRPERXIDE SLUTI (TBHP) Epoxidation of cyclooctene by aqueous TBHP molybdenum(vi) mononuclear and polynuclear (pre)catalysts with S() and () ligands A mixture of cyclooctene (2.76 ml, 20 mmol), acetophenone (0.1 ml, internal reference) and molybdenum (pre)catalyst 1, 1*, 1a, 1a*, 2, 2*, 3, 3*, I, Ia, II, IIa, III, IIIa (see Chapter VII) (0.01 mmol) was stirred and heated up to 80 C before addition of aqueous TBHP (w = 70 %, 5.48 ml, 40 mmol). The reaction was followed for 6 h. Aliquots (0.1 ml) of the organic phase were taken at required times from the reaction media, mixed with 2 ml of Et2 and a small quantity of Mn2 was added. The mixture was then filtered off through silica and analyzed by 1 H MR in CDCl3 or GC Epoxidation of cyclooctene by aqueous TBHP Hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() and () ligands The procedure was the same as the previous general procedure except that amount of molybdenum (pre)catalyst 10, 11, IX, X, XI (see Chapter VII) was (0.005 mmol). The mixture was analyzed by GC Exp. Am, Cm and Dm Epoxidation of cyclooctene by the use of the complexes 1 3 with addition of Me before t=0 min The procedure was the same as the previous general procedure except that m equivalents of methanol per Mo atom were added to reaction mixture together with the complex 1, 2 or 3. The reaction was followed by GC. 56

88 Exp. B50 Epoxidation of cyclooctene by the use of the complex 1 with addition of Me at t=90 min The procedure was the same as for Exp. A one, but 50 molar equivalents of Me were added to the reaction mixture at t=90 min. The reaction was followed by GC. 57

89 IV RESULTS AD DISCUSSI 58

90 4.1. REACTIS WITH S() AD S() HCl LIGADS The goal of the research based on molybdenum complexes with thiosemicarbazones and their hydrochlorides was to undeceive and discuss forms of the proposed S() or S() HCl ligands, ways of coordination to the molybdenum atom and complexation modes. For that reason, along with the usual methods of characterization (e.g. X-ray diffraction on monocrystal, IR or MR spectroscopy), titrations with base and acid followed by UV-Vis spectroscopy had been implemented Synthesis and properties of dioxomolybdenum(vi) complexes Dioxomolybdenum(VI) complexes have been prepared by the reactions of the corresponding pyridoxal thiosemicarbazone ligand H2L 1-3 (Scheme 2) or hydrochloride analogues H2L 1-3 HCl with [Mo2(acac)2] in dry acetonitrile, dry methanol or by combination of both solvents (Scheme 3 and Scheme 4). Dry solvents (methanol and acetonitrile) were used to prevent hydrolysis of the ligands. H H H H R R S H + Cl - S R 1 = H R 2 = CH 3 R 3 = C 6 H 5 a. b. Scheme 2. Pyridoxal based a. thiosemicarbazones (H 2L 1-3 ) and b. thiosemicarbazone hydrochlorides (H 2L 1-3 HCl). 59

91 [Mo 2 (L 2,3 )] n [Mo 2 (L 1 )] n R H S Mo CH 3 [Mo 2 (HL 1,2 )] 2 Mo 6 19 R= C 6 H 5 (10) CH 3 (11) R H S Mo CH 3 R= CH 3 (2) H (3) R= C 6 H 5 (1) MeC H 2 L 2,3 1/7 H 2 L 1-3 MeC H 2 L 1 MeC PPh 3 MeC, Ar [Mo 2 (acac) 2 ] H 2 L 1 Me MeC Me [Mo 2 3 (L 1,2 ) 2 ] R= C 6 H 5 (7) CH 3 (8) PPh 3 MeC, Ar R H [Mo 2 (L 1 )(Me)] H 3 C S Mo CH 3 R= C 6 H 5 (1a) Scheme 3. Preparation of molybdenum(vi) and dinuclear molybdenum(v) complexes with pyridoxal thiosemicarbazones. [{Mo 2 (HL 2,3 )}Cl] n [{Mo 2 (HL 1 )Cl}] n R H S Mo R= CH 3 (2*) H (3*) CH 3 H Cl [Mo 2 (HL 1,2 )] 2 Mo 6 19 R= C 6 H 5 (10) CH 3 (11) R H S Mo R= C 6 H 5 (1*) CH 3 H Cl H 2 L 2,3. HCl MeC 1/7 H 2 L 1,2. HCl MeC H 2 L 1. HCl MeC PPh 3 MeC, Ar [Mo 2 (acac) 2 ] Me MeC H 2 L 1. HCl Me [Mo 2 3 (HL 1-3 ) 2 ]Cl 2 R= C 6 H 5 (7*) CH 3 (8*) H (9*) PPh 3 MeC, Ar R [Mo 2 (HL 1 )(Me)]Cl H H 3 C S Mo R= C 6 H 5 (1*a) CH 3 H Cl Scheme 4. Preparation of molybdenum(vi) and dinuclear molybdenum(v) complexes with pyridoxal thiosemicarbazone hydrochlorides. 60

92 Complexes synthesised from pyridoxal 4-phenylthiosemicarbazone ligand were characterised as mononuclear 1a Me (Fig. 28) or polynuclear 1, depending on the solvent used for the reaction (mononuclear complexes are favoured from methanol and polynuclear ones from acetonitrile). 147 Fig. 28. Mercury PV-Ray rendered view of the complex 1a. Similary, complexes synthesised from pyridoxal 4-phenylthiosemicarbazone hydrochloride ligand resulted in the formation of mononuclear 1*a 1.5Me (Fig. 29) or polynuclear analogues 1*. 148 Fig. 29. Mercury PV-Ray rendered view of the complex 1*a. 61

93 In the case of 1a Me and 1 doubly deprotonated ligand (L 1 ) 2 is bonded to cis-{mo2} 2+ core whereas in the case of 1*a 1.5Me and 1* the ligand is in monodeprotonated form HL. Degree of ligand protonation depends on the nature of the used ligand (H2L vs. H2L HCl ) and is not affected by the choice of the solvent. Crystals of mononuclear complexes (1a Me and 1*a 1.5Me) are stable for few hours after which they lose solvated methanol molecule and become unsolvated species 1a and 1*a. In both mononuclear complexes, the sixth coordination site around molybdenum is coordinated by methanol molecule. The existence of cis-{mo2 2+ } core, in neutral complexes, was confirmed by appearance of two strong absorption bands in IR spectra; 930 and 890 cm 1 for complex 1a and 949 and 901 cm 1 for complex In charged analogues, absorption bands appeared at 939 and 904 cm 1 for complex 1*a and at 954 and 935 cm 1 for complex 1*. Complexes 2, 2*, 3 and 3* were synthesised from pyridoxal 4-methylthiosemicarbazone ligand, (H2L 2 and H2L 2 HCl) as well as, from pyridoxal thiosemicarbazone, (H2L 3 and H2L 3 HCl) by the reaction with [Mo2(acac)2] in acetonitrile. They were characterised as polynuclear ones. The single strong band, in IR spectra, appearing at 937 cm 1 in 2 and 934 cm 1 in 3 is assigned to Mo= and is accompanied by strong broad band at 811 cm 1 in 2 and 820 cm 1 in 3 which is attributed to an intramolecular Mo=... Mo. Intense broad bands characteristic for molybdenum oxygen interaction are also observed at 801 cm 1 and 815 cm -1 in the IR spectra of 2* and 3*, respectively. This bands are accompanied by a single strong absorption band at 930 cm 1 assigned to Mo= groups Attempts and efforts were made to obtain corresponding mononuclear complexes (with ligands H2L 2,3 and H2L 2,3 HCl) by performing reaction in methanol. Unfortunately, polynuclear complexes were isolated each time no matter ligand ratio, complex concentration, solvent choice or ratio variations of methanol and acetonitrile. This can be explained due to high tendency to form Mo=... Mo interactions. 62

94 The mononuclear complex (1a and 1*a) can be converted to the coordination polymer (1 and 1*) upon its dissolution in acetonitrile. The reverse transformation can be achieved by dissolution of the coordination polymer 1 and 1* in methanol (Fig. 30). Fig. 30. Transformation of the 1a/ 1*a into 1/1*. Circle represents pyridoxal thiosemicarbazone ligand. Polynuclear complexes show different modes of polymerisation. Complexes 2, 2* and 3, 3* accomplish it by the intramolecular Mo=... Mo interaction, while in the complexes 1 and 1* is achieved by coordination of hydroxymethyl oxygen from the neighbouring complex molecule to cis-{mo2} 2+ core. This conclusion is based on comparison of all three IR spectra of polymers. IR spectra of polymer 1 or 1* shows absence of strong absorption band in the region cm 1 associated with the presence of double oxygen bridge Mo2(μ-)2 group or Mo=... Mo interaction In all dioxomolybdenum(vi) complexes, tridentate ligand is coordinated to molybdenum centre through phenyl oxygen, imine nitrogen and thiol sulphur. 161 For all complexes the stretching frequencies attributed to coordinated groups are found at about 1600 and 1580 cm 1 (for C=), 1320 cm 1 (for C-) and 630 cm 1 (for C-S) which are in agreement with the literature. When the mononuclear dioxomolybdenum(vi) complex 1a is heated in an oxygen atmosphere, the first weight loss (in the range C) is attributed to the loss of 63

95 the coordinated methanol molecule and conversion into [Mo2(L 1 )]. Upon further heating, the weight loss is indicative for complex decomposition (in the range C). When the charged analogue 1*a is heated in an oxygen atmosphere, loss of the coordinated methanol molecule occurs in the range C, followed by the complex decomposition in the range C. The weight losses in the range C (1), C (1*), C (2), C (2*), C (3) and C (3*) correspond to the decomposition of the polynuclear complexes. All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All mononuclear and polynuclear complexes are soluble in coordinating solvents and slightly soluble in non-coordinating ones UV-Vis spectroscopy of molybdenum(vi) complexes UV-Vis absorption spectra of molybdenum(vi) complexes with pyridoxal thiosemicarbazones and hydrochloride analogues had been recorded in order to investigate different protonation forms of the ligands in solution. The electronic spectra of thiosemicarbazone complexes 1 3 recorded in methanol exhibited S(pπ) Mo(dπ) LMCT in the region nm as well as (pπ) Mo(dπ) and (pπ) Mo(dπ) LMCT bands at nm. 158 Spectral characteristics are influenced by the nature of the ligand and by its degree of protonation. Addition of HCl or Et3 aliquots (2 μl into cuvettes) to the methanol solution of 1-3 was monitored by UV-Vis spectroscopy. Results were compared with those of the corresponding H2L 1-3 HCl ligands. A titration experiment was also carried out by adding HCl to 1*. The spectral changes associated with the complex 1 and the ligand H2L 1 HCl are presented in Fig. 31. Addition of HCl to the solution obtained from 1 resulted in a bathochromic and hyperchromic shift of bands at 354 and 438 nm to the ones at 363 and 461 nm, respectively. These changes are due to the protonation of the ligand and formation of the [Mo2(H2L 1 )(Me)] 2+ complex cation. The corresponding bands of 1a, 64

96 containing the ligand in the most deprotonated form [Mo2(L 1 )(Me)] are at lower wavelengths than for 1, exhibiting two bands at 416 and 349 nm. Addition of Et3 to the methanolic solution of 1 has shown bands at 390 and 312 nm. The spectrum of the obtained solution is different from the spectrum of the [Mo2(L 1 )(Me)] complex and similar to the one of deprotonated ligand (L 1 ) 2 obtained upon addition of Et3 to the solution of H2L 1 HCl. It seems that an addition of Et3 to the solution destabilizes the association between the ligand and the molybdenum atom. The corresponding behaviour is identical with compounds 2 and 3. In the case of 2, addition of HCl results with bathochromic shift of bands at 325 and 405 nm to 360 and 442 nm, respectively. Similarly, the spectrum of 3 has absorption maximum at 342 and 427 nm, whereas addition of HCl shifts the bands to 361 and 438 nm, respectively. A A λ / nm λ / nm Fig. 31. a) UV-Vis spectra of thiosemicarbazone complexes: 1*a (red), 1*a+HCl (blue), 1a (black) and 1a+Et 3 (green) in methanol at ambient temperature. b) UV-Vis spectrum of H 2L 1 HCl in methanol at ambient temperature. All spectra were recorded in methanol, c = mol dm 3. 65

97 Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() ligands Hybrid organic inorganic compounds 10 and , based on the Lindqvist PM and dioxomolybdenum(vi) complexes, were obtained by the reaction of [Mo2(acac)2] with the corresponding ligand (H2L 1,2, H2L 1,2 HCl) in acetonitrile, when molar ratio of [Mo2(acac)2] to H2L was 7 : 1. Compounds of the general formula [{Mo2(HL 1,2 )}2]Mo619 consist of Lindqvist oxomolybdate polyanion and dinuclear cationic complex. one of the products has chlorine in its structure. The existence of the same species prepared either from ligands H2L 1,2, H2L 1,2 HCl had been confirmed by PXRD. Crystal and molecular structure of the compound 11 had been determined (Fig. 32). 161 The cyclic dinuclear complex cation represents rare example of assembly containing two {Mo2} 2+ cores and corresponding pyridoxal ligands. Two cationic complexes are dimerised through hydroxyl methyl group. This kind of dimerization had been previously reported, but never in presence of PM anions. 72 At the same time, preparation of the hybrid organic inorganic compound using ligands H2L 3 or H2L 3 HCl, was not successful. It is proven that traces of moisture in solvent were key factor in obtaining {Mo619} 2- anion. In such conditions acetylacetonato complex [Mo2(acac)2] hydrolyses and molybdate anions joint together form hexamolybdate anion. If suitable arylated cation, e.g. PPh4 +, is added to the acetonitrile solution of [Mo2(acac)2], separation of polyoxometalate anion can be achieved. 159 Counter cations derived from pyridoxal thiosemicarbazones provide good basis for synthesis of hybrid organic inorganic Lindqvist based PMs since they can take different protonation degrees, as already mentioned before (see Chapter 2.6). Since catalytic activity (see Chapter 5) of all molybdenum(vi) complexes was determined in the presence of water, it was also researched if hexamolybdenum species could be obtained directly by the recrystallization of polynuclear complexes (1, 1*, 2, 2*, 3, 3*) in wet acetonitrile. It was found that hexanuclear species cannot be formed in such a way, nor by the reaction of tetrabutylammonium hexamolybdate with appropriate mono- (1a, 1*a) or polynuclear species (1, 1*, 2, 2*, 3, 3*). 66

98 Fig. 32. Mercury PV-Ray rendered view of the complex 11. In the IR spectra, the absorption band at 960 cm 1 was attributed to Mo=t of the hexamolybdate anion. 159 Asymmetric absorption band characteristic for cis-{mo2} 2+ core was found around 910 cm 1 in complexes 10 and 11. Symmetric absorption band characteristic for cis-{mo2} 2+ core was found at 942 cm 1 in the complex 11, while, in the complex 10, it was overlapped by strong band at 960 cm 1. Complexes also have strong broad band at 795 cm 1 significant for νasym(mo b). Absorption bands characteristic for C=imine and C phenolic are present at frequencies of ca and 1540 cm 1. They point out coordination of the monodeprotonated ligand to molybdenum through the phenolic oxygen and the azomethine nitrogen. The band around 1360 cm 1 is evidence of ligand enolization. The thermal analysis data of PM complexes [{Mo2(HL 1,2 )}2]Mo619 showed that they decompose in the range C (10) and C (11). All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. 67

99 Synthesis and properties of oxomolybdenum(v) complexes Prepared oxomolybdenum(v) species can be divided in two groups: i) mononuclear and ii) dinuclear ones. (H4)2[MoCl5], had been used as a starting compound for preparation of mononuclear molybdenum(v) compounds, while dinuclear ones had been prepared by the reduction of previously obtained molybdenum(vi) compounds (1, 1*, 2, 2* and 3*). Attempts were made to prepare dinuclear compounds from [Mo23(acac)4], as a starting compound, but the purity of the resulting product was not satisfactory enough Mononuclear molybdenum(v) complexes Mononuclear molybdenum(v) complexes 4, 5 and 6 were prepared by the reaction of (H4)2[MoCl5] and appropriate pyridoxal thiosemicarbazone ligand H2L 1-3 or hydrochloride analogues H2L 1-3 HCl in ethanol (Scheme 5). The existence of the same compounds, regardless of the used ligand H2L or its hydrochloride, was confirmed by PXRD. Formation of gaseous HCl during the reaction had been qualitatively verified. It seems that, in this case of molybdenum(v) complexes with H2L 1-3 HCl ligands, ethanol promotes the elimination of hydrochloride from the ligand. The ligand is coordinated to the central molybdenum atom in monodeprotonated form HL (Fig. 33). The presence of the monoprotonated HL, and not bideprotonated ligand L 2, can be clarified by presence of acidic media due to HCl generation during the reaction. 68,72,160 Presence of Mo= is confirmed by strong IR bands at 944 (in 4), 955 (in 5) and 960 cm 1 (in 6). 68

100 Et HCl R [MoCl 2 (H 2 L 1 )]Cl Cl S Mo H Cl H CH 3 H Cl R= C 6 H 5 (4*) H 2 L 1. HCl MeC, Ar (H 4 ) 2 [MoCl 5 ] H 2 L 1-3 or H 2 L 1-3. HCl Et R [MoCl 2 (HL 1-3 )] Cl S Mo H Cl R= C 6 H 5 (4) CH 3 (5) H (6) CH 3 H Et, air [Mo 2 (H 2 L 1 )(H 2 )]Cl R H S H2 Mo R= C 6 H 5 CH 3 H Cl Scheme 5. Preparation of the monunclear molybdenum(v) complexes with pyridoxal thiosemicarbazones and its hydrochlorides. Fig. 33. Mercury PV-Ray rendered view of the complex 4. In order to obtain different types of compounds with greater protonation degree of thiosemicarbazone ligand, different solvents were used. Since ligands (in)solubility is a drawback, and molybdenum(v) starting compound is air sensitive, limitations were also in that field. Using acetonitrile instead of ethanol, mononuclear molybdenum(v) compound 4* obtained from pyridoxal 4-phenylthiosemicarbazone 69

101 hydrochloride, containing the ligand in its neutral form H2L (Fig. 34) 161 was prepared. Presence of Mo= is confirmed by strong IR band at 980 cm 1. The formation of pure compounds [MoCl2(H2L 2,3 )]Cl (5*, 6*) was not successful due to very low solubility of corresponding molybdenum complexes [MoCl2(H2L 2,3 )]Cl and H4Cl in acetonitrile. Fig. 34. Mercury PV-Ray rendered view of the complex 4*. Recrystallisation of impure compounds [MoCl2(H2L 1-3 )]Cl (4*-6*) in ethanol led to the formation of the complexes [MoCl2(HL 1-3 )] (4-6) containing ligand in its monodeprotonated form. It seems that ethanol used for recrystallisation promotes elimination of HCl and formation of the neutral complexes. It should be noted that all solutions of the complexes in their most protonated form are quite instable and air sensitive, which results in colour change, from dark brown red to yellowish one, indicating oxidation process and the presence of molybdenum(vi) complexes in solution. Exposure of the red filtrate solution of 4 to the air results in formation of the yellow molybdenum(vi) complex needles, suitable for X-ray diffraction on monocrystal (Fig. 35)

102 Fig. 35. Mercury PV-Ray rendered view obtained after exposure of the filtrate 4 to the air. The solvent ethanol molecule is omitted. As shown, ligand is coordinated to the central metal atom through S atoms and is present in monodeprotonated form HL. In molybdenum coordination sphere there are terminal oxygen atoms and sixth coordination site is occupied by water molecule. The presence of water can be explained by the traces of moisture in the filtrate. In all molybdenum(v) complexes, vibrations which appear at about and cm 1 (for C=), cm 1 (for C ) and 620 cm 1 (for C S) are characteristic for coordinated groups of the ligand. In the structure where the ligand is coordinated through the thione sulfur a medium or weak intensity C=S band is at 940 cm 1. The thermal analysis data of the complexes [MoCl2(HL 1-3 )] showed that they decompose in the range C (4), C (5) C (6). All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All complexes are soluble in coordinating solvent and insoluble in non-coordinating ones. 71

103 Dinuclear molybdenum(v) complexes Reactions of the dioxomolybdenum(vi) complexes 1, 1*, 2, 2* or 3* with triphenylphosphine (PPh3) were performed in dry acetonitrile under an inert atmosphere, in the presence of -picoline to improve the solubility of the corresponding molybdenum complex (Scheme 3 and 4). The AT reactions resulted in the formation of dinuclear oxo-bridged molybdenum(v) complexes of the general formula [Mo V 23(L 1-3 )2] (7, 7*, 8, 8*, 9). The IR spectra of all dinuclear molybdenum(v) compounds exhibit bands around 950 cm 1 and 780 cm 1, assigned to terminal Mo= and Mo Mo bridging groups, respectively. Vibrations which appear around 1600 and 1540 cm 1 (for C=), 1360 cm 1 (for C _ ) and 620 cm 1 (for C _ S) are characteristic for coordinated groups of the ligand. The existence of molybdenum(v) instead of molybdenum(iv) complexes was confirmed by magnetic measurements since diamagnetism is characteristic of an oxo-bridged molybdenum(v) dimer. Longer reaction time (15 h) affords not only complexes 7, 7*, 8, 8* and 9, but also traces of EPR active compounds which confirms existence of molybdenum(v) species (Fig. 36) Fig. 36. EPR spectra of traces of the mononuclear molybdenum(v) complex present in the sample of the complex 7. The observed spectra have the characteristic pattern and parameters of molybdenum(v) species. btained dinuclear molybdenum(v) complexes show similar behaviour pattern as previously published and structurally determined 72

104 dimeric molybdenum(v) complexes with thiosemicarbazone ligands derived from salicylaldehyde. 36 All dimeric molybdenum(v) complexes are insoluble in weak donor solvent and for that reason MR spectra were not recorded. They are soluble in coordinating solvents and their solutions result in colour change from dark red to orange-yellow implying oxidation process to molybdenum(vi) complexes. The thermal analysis data of the complexes [Mo23(L 1,2 )2] and [Mo23(HL 1-3 )2]Cl2 showed that they decompose in the range C (7), C (7*), C (8), C (8*) and C (9*). All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. 73

105 4.2. REACTIS WITH () LIGADS The aim of this research part was to prepare molybdenum(vi) and (V) complexes with pyridoxal hydrazones, as well as to investigate their properties. Having in mind that some of the species, described in literature 167,168, showed the possibility of reversible crystal solvent exchange in solid state (at room temperature); the leading idea was to investigate possible mechanically and thermally induced solid state transitions Synthesis and properties of dioxomolybdenum(vi) complexes Dioxomolybdenum(VI) complexes with () ligands have been prepared by the reactions of the corresponding pyridoxal hydrazone ligand H2L 4-6 (Scheme 6) with [Mo2(acac)2] in dry methanol or dry acetonitrile (Scheme 7). Dry solvents were used to prevent hydrolysis of the ligands. H R R 4 = R 5 = R 6 = Scheme 6. Pyridoxal hydrazones. In all dioxomolybdenum(vi) complexes ligands are coordinated to the central metal atom in dianionic form L When the reaction is performed in methanol, the cis-{mo2} 2+ core is additionally coordinated by the solvent molecule resulting in formation of mononuclear complexes Ia, IIa and IIIa Me (Scheme 7). Reaction carried out in acetonitrile resulted in obtaining the polynuclear complexes I, II and III. In these compounds, octahedral coordination around molybdenum(vi) centre is completed by an oxygen atom from hydroxyl group of the pyridoxal moiety. 74

106 (H 4 L 4 )[Mo 6 19 ] H 2 L 4 (Me) 2 C [Mo 2 (HL 4-6 )(MeC)] 2 Mo 6 19 R= C 5 H 4 (IX) C 6 H 5 (X) C 6 H 6 (XI) MeC 1/7 H 2 L 4-6 [Mo 2 (acac) 2 ] H 2 L 4-6 H 2 L 4-6 Me MeC [Mo 2 (L 4-6 )] n Mo R R= C 5 H 4 (I) C 6 H 5 (II) C 6 H 6 (III) Me H 3 C Mo R CH 3 MeC [Mo 2 (L 4-6 )(Me)] R= C 5 H 4 (Ia) C 6 H 5 (IIa) C 6 H 6 (IIIa) CH 3 PPh * 3 * Me MeC air [Mo 2 3 (L 4,5 ) 2 (Et) 2 ] R= C 5 H 4 (VIa) C 6 H 5 (VII) H 2 L 4,5 Et H 2 L 4 [Mo 2 3 (acac) 4 ] [Mo 2 3 (L 4 ) 2 (Me) 2 ] Me R= C 5 H 4 (VIb) Scheme 7. Synthesis of molybdenum(vi) and dinuclear molybdenum(v) complexes with pyridoxal based hydrazones. The reaction can be performed only in the case of complex containing the ligand (L 5 ) 2, * the reaction can be performed only in the case of the complex containing the ligand (L 4 ) 2. Mononuclear complexes Ia, IIa and IIIa Me (Fig. 37) were easily obtained from methanol solution in higher yield in comparison with polynuclear analogues I, II and III. Yellow to orange red crystals of Ia, IIa and IIIa Me were obtained after slow evaporation of the solvent. 161 Preparation of polynuclear complexes required longer reaction time (12 16 hours) due to low solubility of the ligands in acetonitrile. At the same time, longer reaction time caused ligand decomposition due to its instability. 169 For those reasons, reaction yields for complexes obtained from the reaction of [Mo2(acac)2] and benzhydrazone ligands H2L 5,6 case of III and 16 % in the case of II). were extremely low (6 % in the 75

107 nly themononuclear complex IIa could be transformed to the polynuclear one by performing the reaction in acetonitrile and all polynuclear complexes I, II and III could be transformed to mononuclear ones by dissolution in methanol. a. b. c. Fig. 37. Mercury PV-Ray rendered view of the complexes a. Ia, b. IIa, c. IIIa. Since Ia and IIIa could not be transformed into polynuclear complexes, by previously described procedures, the idea was to investigate possible thermally 76

108 induced transformations of corresponding crystalline mononuclear to polynuclear compounds in solid state. Samples of all three compounds were heated at 100 and 200 C. This was followed by comparison of PXRD diffractograms of the mononuclear complexes with the transformed ones. All observations with thermally induced solid state transformations are summarised in Fig. 38. Fig. 38. Thermally induced solid state transformations of molybdenum(vi) complexes with pyridoxal hydrazones. indicates corresponding hexacoordinated mononuclear complex, indicates pentacoordinated species, indicates polynuclear complex, indicates amorphous solid. When the complex Ia is heated at 100 C for three hours, in oxygen atmosphere, it remains the same as the starting one (Fig. 39). The first structural changes could be observed if the starting complex is heated at 200 C for 3 hours. Exposure of the resulting sample, after the complex was heated on 200 C, to methanol vapours did not result in complete return to the starting mononuclear compound. Possible explanation could be hidden in the premise that the new sample is mixture of pentacoordinated mononuclear and polynuclear complex. However, completion of polymerisation process was not achieved by further heating at the same temperature (2 more hours). The obtained species were carbonificated and amorphous. 77

109 Fig. 39. Powder X-ray diffraction patterns of: the mononuclear complex Ia (blue), after heating the mononuclear complex Ia at 100 C for 3 hours (green), after heating the mononuclear complex Ia at 200 C for 3 hours (black), the polynuclear complex I (pink). Complex IIa also undergoes solid state transformations upon heating the mononuclear complex (Fig. 40). These transformations occur through steps: gradual loss of coordinated methanol molecule and transition into polynuclear species. At 100 C complex IIa starts to lose coordinated solvent molecule and pentacoordinated complex can be easily transformed back to starting mononuclear complex IIa after exposure to methanol vapours. Product formed upon heating at 200 C has not shown that ability. The obtained product is completely transformed into polynuclear one. Possible explanation could be lightened by considering polymerization mode. Based on previous observations with thiosemicarbazonato complexes, it can be assumed that polymerization in the case of complex II, takes place through the hydroxyl group of the pyridoxal moiety. 78

110 Fig. 40. Powder X-ray diffraction patterns of: the mononuclear complex IIa (blue), after heating the mononuclear complex IIa at 100 C for 3 hour (green), after heating the mononuclear complex IIa at 200 C for 3 hours (black), the polynuclear complex II (pink). An interesting feature has been noticed by the isolation of the species IIIa Me. Crystal colour change from yellow-orange into dark red (after a short period) implies escape of crystallised methanol. Despite colour change, X-ray diffraction on monocrystal specimen showed the same structure. It can be concluded that part of the lattice methanol molecules left only from the crystal surface and crystal structure had not been seriously disrupted. Exposure of the dark red product IIIa to methanol vapours results in returning the colour into orange one and formation of IIIa Me. Formation of the same species IIIa Me had been proven by powder diffraction and TG measurements. After the prolonged standing of the monocrystals at room temperature (few weeks), samples completely lose coordinated and crystallised methanol molecule and turn into polycrystalline material. If the complex IIIa is heated at 100 C, for 3 hours, it turns into pentacoordinated species which can be partially restored into the starting compound IIIa after exposure to methanol vapours (Fig. 41). Heating of the complex IIIa at 200 C causes sample carbonification. 79

111 Fig. 41. Powder X-ray diffraction patterns of: the mononuclear complex IIIa 2 hours after isolation (blue), after heating the mononuclear complex IIIa at 100 C for 3 hour (green), the mononuclear complex IIIa which was heated at 100 C and after exposed to methanol vapours (black), mononuclear complex IIIa 5 min after isolation (pink). Thermally induced solid state transformations imposed study of possible transformations achieved by mechanochemical procedures. When complexes Ia, IIa, IIIa Me are grinded for half an hour they turn into amorphous ones, but with methanol vapours can be transformed in starting ones. This suggests that the products are pentacoordinated as those obtained by heating of mononuclear complexes Ia, IIa and IIIa Me at corresponding temperature (200 C for Ia, 100 C for IIa and 25 C for IIIa). IR spectra of the pentacoordinated complexes obtained either by grinding or by heating, are different than corresponding mononuclear compounds, as well as polynuclear compounds. For all the mononuclear complexes, vibrations corresponding to the cis-{mo2} 2+ core are observed in the region cm 1 and cm 1 and are in accordance with the similar stretching frequencies for polynuclear complexes ( cm 1 and cm 1 ). Appearance of the new band around 1050 cm 1 in all mononuclear compounds is characteristic for the stretching of C- band from coordinated methanol molecule. The IR spectra of all prepared compounds shows absence of the bands characteristic for the H and C= (~3245 and 1680 cm 1 in H2L 4-6 ). In all dioxomolybdenum(vi) complexes ligands are coordinated to the central metal atom 80

112 through () atoms. Absorption bands significant for C=imine and C phenolic are present at frequencies of ca and 1550 cm 1 in all mono- and polynuclear complexes. Those bands are indicative for enol form of ligands and coordination to the molybdenum atom through the deprotonated enolic-oxygen atom. When the mononuclear dioxomolybdenum(vi) complexes Ia and IIa are heated in an oxygen atmosphere the first weight loss in the range C (Ia) and C (IIa) is attributed to the loss of the coordinated methanol molecule. Upon further heating the weight loss is indicative for complex decomposition (in the range C for Ia and C for IIa). When the mononuclear dioxomolybdenum(vi) complex IIIa is heated in an oxygen atmosphere the first weight loss which starts around 25 C is attributed to the loss of crystallised methanol molecule, which is simultaneously followed by the loss of the coordinated methanol molecule and the complex decomposition. The weight losses in the range C (I), C (II), C (III) correspond to the decomposition of polynuclear complexes. It should be mentioned that decomposition of the polynuclear complex III starts with the loss of crystallised acetonitrile molecule in the range C. All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All complexes are soluble in coordinating solvent and slightly soluble in non-coordinating ones Synthesis and properties of hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with () ligands Following the same synthetic procedure for the preparation of hexamolybdenum species with S() ligands, similar compounds using () ligands had been tried to obtain. When performing reaction of [Mo2(acac)2] and H2L 4-6 (7:1 molar ratio) in wet acetonitrile, the products IX-XI, 161 of general formula 81

113 [Mo2(HL 4-6 )(MeC)]2Mo619 (Scheme 7, Fig. 42) were isolated. In comparison with thiosemicarbazone hybrid organic-inorganic compounds, hybrids IX-XI did not consist of dimerised cation but from two mononuclear complex cations. The ligand was found to be in the monodeprotonated form and coordinated to the cis-{mo2} 2+ core. Additionally, octahedral coordination around molybdenum in complex cation is completed by the solvent molecule (acetonitrile). As found in the case of compounds with pyridoxal thiosemicarbazones, mono- and polynuclear complexes did not hydrolyze in corresponding PMs. Fig. 42. Mercury PV-Ray rendered view of the complex IX. Recrystallization of the complex IX in acetone resulted in complex cation decomposition and formation of the hybrid compound VIII in which protonated pyridoxal hydrazone had served as a cation (Fig. 43). 161 Association between cis-{mo2} 2+ core and ligand is destabilised in acetone yielding the free doubly protonated hydrazone. 82

114 Fig. 43. Mercury PV-Ray rendered view of the complex VIII obtained after recrystallization of the hexanuclear hybrid compound IX in acetone. By recrystallization of hybrid organic crystals X and XI from acetone, compounds having similar structure (as with complex IX) were not obtained. This indicates that such complex instability is characteristic for only for the complex IX. In the IR spectra, the absorption band at 960 cm 1 was attributed to Mo=t of the hexamolybdate anion. 159 For all the complexes (IX, X, XI) asymmetric absorption band characteristic for cis-{mo2} 2+ core was found around 910 cm 1, while symmetric one was overlapped by strong band at 960 cm 1. Complexes also have strong broad band at 795 cm 1 significant for νasym(mo b). Absorption bands characteristic for C=imine and C phenolic are present at frequencies of ca and 1550 cm 1. They point out coordination of monodeprotonated ligand to the cis-{mo2} 2+ core through phenolic oxygen and azomethine nitrogen. The thermal analysis data of the complexes IX, X and XI showed that they decompose in the range around C (IX), C (X), C (XI). All 83

115 residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All the complexes are slightly soluble in both coordinating and non-coordinating solvents UV-Vis spectroscopy UV-Vis absorption spectra of (Bu4)2Mo619, (Bu4)4Mo826, hexamolybdate complex IX and mononuclear complex Ia in acetonitrile had been recorded in order to prove presence of hexamolybdate species in solution (Fig. 44). The lowest energy electronic transition at 325 nm in the electronic spectra of the (Bu4)2Mo619 was assigned to (pπ) Mo(dπ) LMCT. This transition is, in the spectra of IX, bathochromically shifted by 5 nm and intensity remains almost the same showing there is no strong interaction between the metal oxygen cluster and the cationic molybdenum(vi) complex In the spectra of [Mo2(L 4 )] and (Bu4)4Mo826 the characteristic band for {Mo619} 2 is not observed. This is additional evidence that hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with pyridoxal based hydrazones, cannot be formed by dissolving the mononuclear pyridoxal based hydrazonato complexes in acetonitrile. 84

116 A λ / nm Fig. 44. UV-Vis absorption spectra of: (Bu 4) 4Mo 8 26 (green), (Bu 4) 2Mo 6 19 (blue), the complex IX (black), the complex Ia (red). All spectra were recorded in acetonitrile, c = mol dm 3. Spectral data for the mononuclear and hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with H2L 5,6 ligands are consistent with those described above Synthesis and properties of oxomolybdenum(v) complexes Prepared oxomolybdenum(v) species can be divided in two groups: i) mononuclear and ii) dinuclear ones. (H4)2[MoCl5], had been used as a starting compound for mononuclear molybdenum(v) compounds, while dinuclear ones had been prepared or from [Mo23(acac)4] or by the reduction of previously obtained molybdenum(vi) compound (Ia). Reactions with ligand H2L 6 were not possible, because reaction solution immediately turned from dark brown to pale yellow which signifies oxidation process and possible hydrolysis. Attempts had been made with the use of different solvent, but none of them resulted with the formation of molybdenum(v) compound. 85

117 Mononuclear molybdenum(v) compounds Mononuclear molybdenum(v) complexes had been prepared by the reaction of (H4)2[MoCl5] and ligands H2L 4,5 in dry ethanol (Scheme 8). Dry ethanol, instead of dry acetonitrile (as in the case of the reactions performed with S() donors) was chosen since better solubility of () ligands and to prevent ligand hydrolysis. The synthesis of molybdenum(v) complex by the reaction of (H4)2[MoCl5] and H2L 6 ligand was not possible due to oxidation process (regardless of the inert atmosphere in which the reaction had been tried. The colour of the reaction mixture immediately turned to yellow one. [MoCl 2 (HL 4,5 )] (H 4 ) 2 [MoCl 5 ] H 2 L 4,5 Et R Cl Mo Cl CH 3 H R= C 6 H 4 (IV) C 6 H 5 (V) Scheme 8. Preparation of mononuclear molybdenum(v) complexes with pyridoxal hydrazones. In complex IV Et and V Et, ligand is coordinated to the central molybdenum atom in monoanionic form, as HL. Presence of Mo= is confirmed by strong absorption bands at 953 cm 1 in IV Et and 937 cm 1 in V Et. Vibrations that appear around 1600 and 1540 cm 1 (for C=), 1260 cm 1 (for C _ ) are characteristic for coordinated groups of the ligand. The thermal analysis data of complexes [MoCl2(HL 4,5 )] Et showed that they decompose in the range C (IV Et), C (V Et). All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All the complexes are soluble in coordinating solvents and insoluble in noncoordinating ones. 86

118 Dinuclear molybdenum(v) compounds Dinuclear complexes [Mo23(L 4,5 )2(Et)2] had been prepared by the reaction of [Mo23(acac)4] and appropriate ligand H2L 4,5 in ethanol (Scheme 7). Efforts had been made to obtain the same products by the reduction of corresponding mononuclear molybdenum(vi) complexes [Mo2(L 4,5 )(Me)]. The reduction reaction (with PPh3) could not be performed in ethanol due to immediate oxidation process (solution turned into pale yellow one). Solvent change was natural choice. The reduction with PPh3, in methanol, was successfully done with the complex Ia, but not with the complex IIa. In order to prove formation of the same dinuclear molybdenum(v) species, the reaction of [Mo23(acac)4] and ligand H2L 4 in methanol was performed. Resulting complex VIa showed characteristic Mo= vibration pattern at 946 cm 1 and Mo Mo bridging groups at 754 cm 1. Unfortunately, existence of the exactly same species VIa obtained by different synthetic procedure could not be proved by PXRD since species are amorphous, but was done by comparison of IR spectra (Fig. 45) and elemental analysis. 80 T / % ṽ max / cm Fig. 45. Comparison of IR spectra of the complex VIa obtained from [Mo 2 3(acac) 4] (black) and by the reduction reaction from Ia (red). 87

119 Resulting molybdenum(v) complexes showed characteristic Mo= vibration pattern at 949 cm 1 (VIb) and 952 cm 1 (VII) and Mo Mo bridging groups at 740 cm 1 (VIb) and 789 cm 1 (VII), respectively. It was possible to isolate mononuclear molybdenum(vi) complex Ia from filtrate solution of complex VIa, after exposure to air, as it was confirmed by XRD on monocrystal. The thermal analysis data of the complexes VIa, VIb and VII showed that they decompose in the range C. All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All complexes are partially soluble in coordinating solvents and insoluble in non-coordinating ones. 88

120 4.3. REACTIS WITH LIGADS ligands had shown to be the most instable and the most difficult to prepare, especially in reduced form. First idea was to prepare set of Schiff base ligands varying used diamine (from 1,2-diaminoethane, over propane-1,3-diamine to benzene-1,2-diamine or 1,2-cyclohexanediamine). Preparation of ligands containing 1,2-cyclohexanediamine did not result in the formation of pure compounds and it was excluded from the investigation point. Emphasis was on reduction reaction of previously prepared molybdenum(vi) complexes with the above mentioned ligands. evertheless, interesting examples of different ligand binding modes to central molybdenum atom were found, that have not been known in literature. We have also entered a new discussion point on molybdenum(iv) and (V) complexes with tetradentate ligands Synthesis and properties of dioxomolybdenum(vi) complexes Dioxomolybdenum(VI) complexes with ligands were prepared by the reaction of [Mo2(acac)2] and the appropriate ligand H2L 7-10 (Scheme 9 and Scheme 10) in an appropriate alcohol (Scheme 11). Solvent choice depends on better reaction yield. Dry solvents were used in order to prevent hydrolysis of the ligands. nly the ligand H2L 8 was successfully reduced from the ligand H2L 7 by abh4. The reduced forms of the two other ligands H2L 9,10 were not possible to isolate from the solution no matter solvent choice or by the use of precipitant. H R R 7 = C 2 H 4 R 9 = C 3 H 6 H R 10 = C 6 H 4 Scheme 9. Schiff bases obtained from pyridoxal and diamines. 89

121 H R H H R 8 = C 2 H 4 H Scheme 10. Ligands prepared upon reduction of Schiff bases. H Mo H H 3 C H H 3 C H Mo Mo CH 3 CH 3 H H [Mo 2 (L 8 )] (A*) [{Mo 2 (Me) 2 }(L 7 )] (A) Me H 2 L 8 H 2 L 10 Me [Mo 2 (acac) 2 ] H 2 L 7 Et Me H 2 L 9 H 3 C H H 3 C H Mo CH 3 CH 3 Mo Mo H [{Mo 2 (Me) 2 }(L 10 )] (C) [Mo 2 (L 9 )] (B) H PPh 3 Et Ar [Mo 2 3 (L 7 ) 2 ] (D) [Mo 2 3 (L 10 ) 2 ] (F) H 2 L 7,10 Et [Mo 2 3 (acac) 4 ] H 2 L 9 Et [Mo 2 3 (L 9 ) 2 ] (E) Scheme 11. Synthesis of molybdenum(vi) and (V) complexes with ligands. 90

122 Molecular structures of the obtained products are presented in Fig. 46 and Fig Interesting feature was perceived in the complex A and C, where the ligand has the role of bridge between two molybdenum centres. Regardless ligand to [Mo2(acac)2] ratio the same complex was isolated each time. It seems that the Schiff base derived from H2L 7 is not flexible enough to adopt cis-bent configuration as in the complex [Mo2(salen)]. 173 Based on elemental analysis data, it was concluded that the ligand H2L 10 coordinates to the molybdenum centre in the same way as H2L 7 ligand. This can be explained by the presence of the phenyl ring in the ligand structure. Unlike the Schiff base H2L 7, reduced form H2L 8, as well as the ligand H2L 9, show more flexibility. The coordination of the tetradentate ligands through two phenolate and two amine/imine has been usual way of binding to the central molybdenum atom. In all of the complexes ligand is present in doubly deprotonated form. Infrared bands around cm 1 and cm 1 are attributed to the symmetrical and antisymmetrical stretching of cis-{mo2} 2+ moiety and are in agreement with literature data. a. 91

123 b. Fig. 46. Mercury PV-Ray rendered view of the complex (a) A and (b) B. Fig. 47. Mercury PV-Ray rendered view of the complex A*. The weight losses of molybdenum(vi) complexes occur in the range C (A), C (A*) and C (C) and correspond to the complex decomposition. All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All complexes are soluble in coordinating solvents and insoluble in non-coordinating ones. 92

124 Synthesis and properties of dinuclear μ-oxodioxodimolybdenum(v) complexes Considering previously results with thiosemicarbazones and hydrazones, molybdenum(v) complexes obtained from [Mo23(acac)4] and ligands H2L 7,9,10 as a starting material, had been tried to prepare (Scheme 11). Since the literature does not provide many data in that field, 174,175 there were doubts considering ligand coordination to the central metal atom. Schiff base ligands H2L 7,9,10 can bind to the central molybdenum atoms in two ways: i) the ligand has a role of the bridge between two molybdenum atoms 175 or ii) the one ligand is tetradentate chelating agent to one molybdenum atom. 174 The analysed complexes D-F showed to be diamagnetic ones. Since they were insoluble in donor solvents, MR measurements were excluded as identification method. Based on the MS measurements (see Chapter VIII APPEDIX C) and the fact that the complexes D-F are dark brown and air stable, obtained products were characterised as μ-oxo bridged hexacoordinated molybdenum(v) dinuclear complexes. They showed characteristic IR bands in the area around 940 cm 1 and cm 1, assigned to terminal Mo= and Mo--Mo bridging groups, respectively. Complex E was also possible to prepare by the reduction of the complex B with PPh3. The existence of the same species, B and E, was confirmed by powder diffraction. In this case, it tetradentate ligand coordination to one Mo atom could be assumed. Complexes A and C did not participate in the reduction reaction with PPh3 since the ligands have specific binding mode. Besides, complexes A and A* are air unstable and not possible to manipulate with. The weight loss of molybdenum(v) complexes D 2Et occurs in two steps. First step corresponds to the loss of crystal ethanol the range C and second step occurs in the range C resulting in the formation of Mo3. The complex E decomposes in the range C, while the complex F decomposes in the range C. 93

125 All residues of thermal analysis are identified as Mo3. The agreement between the theoretical and experimental weight loss is within the experimental error. All complexes are slightly soluble in coordinating solvents (with the exception of the complex D which is totally insoluble) and insoluble in non-coordinating ones. 94

126 4.4. CATALYTIC ACTIVITY F MLYBDEUM(VI) CMPLEXES WITH PYRIDXAL DERIVATES The obtained molybdenum(vi) complexes (1, 1*, 1a, 1a*, 2, 2*, 3, 3*, 10, 11, I, Ia, II, IIa, III, IIIa, IX, X, XI see Chapter VII) were tested as (pre)catalysts for cyclooctene epoxidation by aqueous solution of TBHP and without addition of organic solvent. Emphasis and importance has been given to the extremely low Mo loading (n(mo in complex) : n(olefin) = 0.01 mmol : 20 mmol (where complex is [Mo2(L 1-6 )]n, [{Mo2(HL 1-3 )}Cl]n or [Mo2(L 1,4-6 )(Me)], [Mo2(HL 1 )(Me)]Cl), n([{mo2(hl 1,2 )}2]Mo619 or [Mo2(HL 4-6 )(MeC)]2Mo619) : n(olefin) = mmol : 20 mmol ) and solvent-free conditions (Scheme 12). It has to be noticed that conditions presented herein are challenging since there are very few epoxidation experiments performed without solvent. 104 Mo catalyst TBHP(aq) Scheme 12. General scheme of Mo-catalyzed epoxidation of cyclooctene. All tested complexes are sparingly soluble in cyclooctene and insoluble in water at room temperature, but dissolve in the organic phase (i.e. the substrate) after addition of aqueous TBHP at 80 C. The aqueous phase was colourless and the organic one yellow, indicating that the catalyst is mainly confined in the organic phase. The relevance of the ligand S() and () coordination to molybdenum in catalytic reaction was confirmed by the fact that complex [Mo2(acac)2] gave poorer results while all of the investigated H2L 1-6, H2L 1-3 HCl ligands alone were not active at all. otation and calculation of all physical parameters researched in this chaper had been previously clarified in the Chapters

127 Molybdenum(VI) (pre)catalysts with S() and S() HCl ligands Molybdenum(VI) (pre)catalysts with S() ligands The selectivity is very high (84 99 %) for all tested molybdenum complexes, following the order 3 ~ 1a > 2 > 1 (see Chapter VII, page xi, Fig. 48). 1 cyclooctene conversion t / min Fig. 48. Converted cyclooctene vs. time with molybdenum(vi) (pre)catalysts: complex 1a, complex 1, complex 2, complex 3. Conditions: n(mo) : n(substrate) : n(tbhp) = 1 : 2000 : 4000, T = 353 K. The epoxide yield is moderate to very good after 6 h (43 94 %), with the activity and yield following the order 1a >> 3 ~ 2 >> 1 (Fig. 49). Initial turnover frequencies (TF20min) for the tested compounds are very good with only 0.01 mol of molybdenum complex, the lowest being 645 h 1 for the 1 and the highest one 3360 h 1 for the 1a. Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 96

128 % a Fig. 49. Results of catalyzed cyclooctene epoxidation in the presence of aqueous TBHP after 6 h at 80 C. Epoxide selectivity (light parallelepipeds); epoxide yield (dark cylinders). Catalytic reaction with the mononuclear compound 1a provides a TF value 5 times higher than its corresponding polynuclear compound 1. Since the monuclear complex 1a contains coordinated methanol molecule, it certainly has an influence. With the purpose of explaining the role of methanol, additional experiments had been made using the polynuclear compound 1 with different quantities of methanol. Methanol (m molar equivalents of Me vs. Mo) was added at the beginning of the reaction before the TBHP addition, Exp. Am (m = 0, 1, 12.5, 25, 50). The kinetic profiles of these experiments are shown in Fig. 50. As specified in the literature, the presence of methanol, as a solvent, in catalytic oxidations (in general) with molybdenum(vi) complexes coordinated by two bidentate ligands [Mo2(L)2] should increase the catalytic activity. 176 This observation was explained by higher polarity of the reaction medium. Experiments Am 25 showed greater activity than experiment A0, but the activity decreases by addition of more than one molar equivalent of Me until it falls below the curve of A0 representing cyclooctene conversion without addition of Me. The fastest and most efficient reaction occurs in case of A1, corresponding to 1:1 stoichiometry of the mononuclear molybdenum complex. 97

129 cyclooctene conversion t /min Fig. 50. Converted cyclooctene vs. time with the complex 1 with different Me:Mo ratio: A 1 ( ) (n(me) : n(mo) = 1 : 1), A 12.5 ( ) (n(me) : n(mo) = 12.5 : 1), A 25 ( ) (n(me) : n(mo) = 25 : 1), A 0 ( ) (n(me) : n(mo) = 0 : 1), A 50 ( ) (n(me) : n(mo) = 50 : 1). For better understanding of the methanol implication within the process, experiment B50 was carried out by running experiment A0 as above, with an exception of the addition of 50 molar equivalents of Me after 90 min. The kinetic profile of this experiment is shown in Fig. 51, and compared with experiments A0 and A50. As expected, catalytic reaction in the experiment B50 initially follows the same profile as the one with the polymeric catalyst without addition of methanol (A0). Methanol addition, in the experiment B50, had initiated sudden change in (pre)catalyst behaviour, continuing along the same kinetic profile as experiment A50 after 120 minutes. Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 98

130 cyclooctene conversion t /min Fig. 51. Converted cyclooctene vs. time with the complex 1 without methanol addition (A 0, ) (n(me) : n(mo) = 0 : 1), with methanol addition at t = 0 min (exp. A 50, ) (n(me) : n(mo) = 50 : 1), with methanol addition at t = 90 min (exp. B 50, ) (n(me) : n(mo) = 50 : 1). These results seem to indicate that methanol addition does not increase the reaction rate, but decreases it. Possible interpretation of this effect is to take in consideration loss of coordinated Me from the coordinated sphere in the mononuclear complex [Mo2(L 1 )(Me)]. Vacant sixth coordination site enables formation of the catalytically active pentacoordinated species [Mo2(L 1 )]. n the other hand, both (pre)catalysts, 1 and 1a, dissolve completely in the reaction medium at the beginning of the experiment which suggests that the complex 1 might not retain a polymeric structure in the catalytic medium in all experiments. It is possible that it is present as oligomeric soluble form in which molybdenum atoms at the end of the oligomeric chain are pentacoordinated, while the neighbouring ones are bridged through oxygen atom of hydroxymethyl group (from the neighbouring complex). Presumably, access to the catalytically active pentacoordinate intermediate obtained from the 1 may be slower for this oligomeric species compared to the mononuclear complex. Since no induction time was observed (in all experiments), it can be assumed that the (pre)catalyst maintains its equilibrium with the catalytic Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 99

131 intermediates throughout the process. The fact that two (pre)catalysts (mononuclear and polynuclear one) with the same thiosemicarbazone ligand display such different catalytic activity suggests that the (pre)catalyst also corresponds to the catalyst resting state. n the other hand, influence of methanol on reactivity with polynuclear compounds 2 and 3 has been studied in the experiments Cm and Dm (m = 0, 1, 25, 50), respectively. As expected, considering the different ways of polymerization (through terminal and not through hydroxyl oxygen atom), increasement of catalytic activity by the use of the methanol had not been observed (in the case of the complex 2 and 3 (Fig. 52 and Fig. 53). cyclooctene conversion t / min Fig. 52. Converted cyclooctene vs. time with the complex 2 with different Me:Mo ratio: C 25 ( ) (n(me) : n(mo) = 25 : 1), C 50 ( ) (n(me) : n(mo) = 50 : 1), C 1 ( ) (n(me) : n(mo) = 1 : 1), C 0 ( ) (n(me) : n(mo) = 0 : 1). Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 100

132 cylooctene conversion t / min Fig. 53. Converted cyclooctene vs. time with the complex 3 with different Me:Mo ratio: D 50 ( ) (n(me) : n(mo) = 50 : 1), D 25 ( ) (n(me) : n(mo) = 25 : 1), D 1 ( ) (n(me) : n(mo) = 1 : 1), D 0 ( ) (n(me) : n(mo) = 0 : 1). Generally, addition of methanol increases the catalytic activity of species 2 and 3, while conversion of cyclooctene retains almost the same. Possible explanation could be found in higher polarity of the reaction media, as previously reported. Since it has not been possible to isolate mononuclear molybdenum complexes with the ligands H2L 2,3, it cannot be claimed that addition of 1 molar eqivalents of methanol into solution (Exp. C1 and D1) leads to the formation of corresponding mononuclear compounds [Mo2(L 2,3 )(Me)]. Selectivity patterns for 2 and 3 follow the same behaviour as in the case of 1. It decreases by the methanol addition. All relevant catalytic data are presented in Table 2. Possible mechanistic studies had been discussed in reference. 177 Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 101

133 Table 2. Relevant data of epoxidation catalyses with molybdenum(vi) (pre)catalyst with pyridoxal thiosemicarbazones. General formula Complex label n(me) / mol with regard to 1 mol of the complex Experiment Label Conversion a / % Selectivity b / % TF 20min c / h -1 T d [Mo 2(L 1 )(Me] 1a 1a A A A 12.5 e A 25 e A 50 e B 50 f C [Mo 2(L 1-3 )] n 2 1 C 1 e C 25 e C 50 e D D 1 e D 25 e D 50 e [Mo 2(acac) 2] [a] Conversion of cyclooctene calculated after the reaction was performed for 6 h. [b] Selectivity formation of epoxide per molecule of cyclooctene after 6 h. [c] umber of oxidised cyclooctene per one active centre n(cyclooctene transformed) / n((pre)catalyst) / calculated for the initial 20 minutes of the reaction [d] umber of cycles that pre(catalyst) can run before it is deactivated n(cyclooctene transformed) / n((pre)catalyst) after 6 h. 102

134 Molybdenum(VI) (pre)catalysts with S() HCl ligands The aim of the research presented herein is to clearify how the protonation degree of the ligands effect on the catalytic activity of the molybdenum (pre)catalyst. Pyridoxal thiosemicarbazone hydrochlorides are used as ligands. All tested molybdenum(vi) compounds show relatively high selectivity (74 89 %) with moderate to very good conversions after 6 h (48 79 %) in the order 1a* < 1* < 2* ~ 3* (see Chapter VII, page xii, Fig. 54). cyclooctene conversion t /min Fig. 54. Converted cyclooctene vs. time with charged dioxomolybdenum(vi) (pre)catalysts: complex 1, complex 1*, complex 2, complex 3. Conditions: n(mo) : n(substrate) : n(tbhp) = 1 : 2000 : 4000, T = 353 K. The selectivity and conversion with the mononuclear compound 1* are the lowest (even lower than [Mo2(acac)2]), which is contrary to the results obtained with the corresponding molybdenum(vi) compounds with pyridoxal thiosemicarbazones. In comparison with polynuclear [Mo2(L 1-3 )]n complexes, catalytic activity of [{Mo2(HL 1-3 )}Cl]n complexes has a different activity since the T with 1*, 2* and 3* are 1960, 1253 and 1580 and those with the corresponding [Mo2(L)]n 1, 2 and 3 are 1040, 1420 and 1380, respectively. The ligand protonation has a strongly positive influence for H2L 1 HCl, a moderately positive one in case of H2L 2 HCl and a weakly Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 103

135 negative one for H2L 3 HCl. Ligand protonation has a lower effect on the activity than methanol coordination. Comparison of conversion and selectivity, in the cyclooctene epoxidation by the four complexes (mononuclear 1a and 1a* or polynuclear 1 and 1*) containing ligand L 1 is presented in Fig. 55. All these results might be linked to the protonation state of the ligands and presumably due to the energy needed to remove methanol from the coordination sphere of molybdenum atom in case of mononuclear compounds. 1* 100% 1a 0 1a* 1 conversion selectivity Fig. 55. Comparison of conversion ( ) and selectivity ( ) in the cyclooctene epoxidation by aqueous TBHP catalyzed by 1, 1*, 1a, 1a* molybdenum(vi) complexes synthesized from the H 2L 1 ligand. Table 3. hydrochlorides. Epoxidation data for molybdenum(vi) (pre)catalyst with pyridoxal thiosemicarbazone General formula Complex label Conversion a / % Selectivity b / % TF 20min c / h -1 T d [Mo 2(HL 1 )(Me)]Cl 1a* * [{Mo 2(HL 1-3 )Cl}] n 2* * [Mo 2(acac) 2] [a] Conversion of cyclooctene calculated after the reaction was performed for 6 h. [b] Selectivity formation of epoxide per molecule of cyclooctene after 6 h. [c] umber of oxidised cyclooctene per one active centre n(cyclooctene transformed) / n((pre)catalyst) / calculated for the initial 20 minutes of the reaction [d] umber of cycles that pre(catalyst) can run before it is deactivated n(cyclooctene transformed) / n((pre)catalyst) after 6 h. 104

136 cyclooctene conversion Molybdenum(VI) (pre)catalyst with () ligands The tested compounds were mono, [Mo2(L 4-6 )(Me)], (Ia, IIa, IIIa) and polynuclear ones, [Mo2(L 4-6 )]n, (I, II, III) (see Chapter VII). The influence of the ligand will be discussed. The cyclooctene conversion, for all tested molybdenum compounds, is moderate after 6 h (41-72 %), with the activity and yield following the order I > IIa > IIIa ~ II > Ia (Fig. 56 and Fig. 57). Initial turnover frequencies (TF20min) for tested compounds are good with low molybdenum loading, n(mo from [Mo 2(L 4-6 )] n or [Mo 2(L 4-6 )(Me)] : n(olefin) = 0.01 mmol : 20 mmol, the lowest being 480 h 1 for I and the highest one 1200 h 1 for IIa. The selectivity is moderate to high (67 87 %) for all tested molybdenum compounds with pyridoxal hydrazones, following the order I = II > IIa > III > Ia > IIIa (Table 4) t / min Fig. 56. Converted cyclooctene vs. time with mononuclear dioxomolybdenum(vi) (pre)catalysts with pyridoxal hydrazones: complex IIIa, complex IIa, complex Ia. Conditions: n(mo) : n(substrate) : n(tbhp) = 1 : 2000 : 4000, T = 353 K. Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 105

137 When comparing epoxide yield of mononuclear dioxomolybdenum(vi) pre(catalysts) with pyridoxal hydrazine ligands, it has been shown that the best epoxide yield is obtained by the complex IIIa, and the lowest one by Ia. It seems that the nature of ligand has crucial influence. Complex obtained from ligand (L 6 ) 2 with hydroxyl substituted phenyl ring (IIIa) seems to be more easily transformed to the catalytically active pentacoordinated species [Mo2(L 6 )] than the one containing ligand (L 4 ) 2 with pyridinium ring (Ia). Those results are in accordance with the ones obtained for solid state transformations and methanol release, which were discussed in the Chapter cyclooctene conversion t / min Fig. 57. Converted cyclooctene vs. time with polynuclear dioxomolybdenum(vi) (pre)catalysts with pyridoxal hydrazones: complex I, complex II, complex III. Conditions: n(mo) : n(substrate) : n(tbhp) = 1 : 2000 : 4000, T = 353 K. n the other hand, opposite behaviour pattern can be seen in the case of catalytic experiments with polynuclear compounds. Pre(catalyst), in which hydrazone pyridine ring (L 4 ) 2 (complex I) has better conversion rate after 6 hours than the one obtained from the ligand with phenyl ring (L 5 ) 2 (complex II) or from 4-hydroxy substituted phenyl ring (L 6 ) 2 (complex III), which leads to conclusion that Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 106

138 depolymerisation step seems to be faster in the complex I than in the complexes II and III. By comparing activity of polynuclear vs. mononuclear molybdenum(vi) (pre)catalysts in the first 20 min of catalytic reaction, TF20min ratio Ia/I is 1.9 (~2), IIa/II is 1.5 and IIIa/III is (~1) which seems to indicate slightly faster formation of catalytic activated species from mononuclear compounds in the case of system Ia/I. Table 4. Epoxidation data for molybdenum(vi) (pre)catalyst with pyridoxal hydrazones. General formula Complex label Conversion a / % Selectivity b / % TF 20min c / h -1 T d I [Mo 2(L 4-6 )] n II III Ia [Mo 2(L 4-6 )(Me)] IIa IIIa [Mo 2(acac) 2] [a] Conversion of cyclooctene calculated after the reaction was performed for 6 h. [b] Selectivity formation of epoxide per molecule of cyclooctene after 6 h. [c] umber of oxidised cyclooctene per one active centre n(cyclooctene transformed) / n((pre)catalyst) / calculated for the initial 20 minutes of the reaction [d] umber of cycles that pre(catalyst) can run before it is deactivated n(cyclooctene transformed) / n((pre)catalyst) after 6 h. 107

139 Hybrid organic-inorganic compounds based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with S() and () ligands After testing dioxomolybdenum complexes as (pre)catalysts in epoxidation processes, the catalytic investigation was expanded on the prepared compounds containing PM, in order to see the influence of {Mo619} 2- on the capacities of [Mo2(HL)] + complexes. Since there is no literature data based on this type of compounds, (Bu4)2Mo619 was chosen as an appropriate compound to compare results with. Comparison of tested molybdenum complexes [{Mo2(HL 1,2 )}2]Mo619 (10, 11) and [Mo2(HL 4-6 )(MeC)]2Mo619 (IX-XI) showed that in all types of hybrid compounds cation composition (ligand species) contributes to better cyclooctene conversion, following the trend 11 > 10 (S() ligands, Fig. 58) and XI > X ~IX (() ligands, Fig. 59). However, selectivity values remain almost the same in all tested compounds (55-58 %). cyclooctene conversion t time / min / s Fig. 58. Converted cyclooctene vs. time with hybrid organic-inorganic (pre)catalysts based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with pyridoxal thiosemicarbazones: complex 11, complex 10, (Bu 4) 2Mo Conditions: n(mo) : n(substrate) : n(tbhp) = 1 : 2000 : 4000, T = 353 K. Lines connecting points do not correspond to any mathematical function that describes the curve. They are only in the purpose of eye-guidance for easier following. 108

140 cyclooctene conversion t / min time / s Fig. 59. Converted cyclooctene vs. time with hybrid organic-inorganic (pre)catalysts based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with pyridoxal hydrazones: complex XI, complex X, Δ complex IX, (Bu 4) 2Mo Conditions: n(mo) : n(substrate) : n(tbhp) = 1 : 2000 : 4000, T = 353 K. When discussing TF values, it should be taken into an account that in all investigated [{Mo2(HL 1,2 )}2]Mo619 and [Mo2(HL 4-6 )]2Mo619 compounds there are two types of active sites per molecule; one type coming from cationic part and the other one from {Mo619} 2 anion. For that reason, TF values are not calculated in the same way for (Bu4)2Mo619 and [{Mo2(HL 1,2 )}2]Mo619 or [Mo2(HL)]2Mo619 compounds. evertheless, complex 11 has higher TF value than 10, as well as XI has higher TF value than X=IX, certainly implying a faster activation time of the mentioned compounds (Table 5). n the other hand, PMs 10, 11 and IX show similar kinetic profile as polynuclear complexes 1*, 2* and I. 109

141 Table 5. Epoxidation data for hybrid organic-inorganic (pre)catalysts based on the Lindqvist PMs and dioxomolybdenum(vi) complexes with pyridoxal thiosemicarbazones and pyridoxal hydrazones. General formula Complex label Conversion a / % Selectivity b / % TF 20min c / h -1 T d [{Mo 2(HL 1,2 )} 2]Mo IX [Mo 2(HL 4-6 )(MeC)] 2Mo 6 19 X XI (Bu 4) 2Mo [a] Conversion of cyclooctene calculated after the reaction was performed for 6 h. [b] Selectivity formation of epoxide per molecule of cyclooctene after 6 h. [c] umber of oxidised cyclooctene per one active centre n(cyclooctene transformed) / n((pre)catalyst) / calculated for the initial 20 minutes of the reaction [d] umber of cycles that pre(catalyst) can run before it is deactivated n(cyclooctene transformed) / n((pre)catalyst) after 6 h. When comparing these results with previously described mono- or polynuclear (pre)catalysts (Fig. 60) it has been shown that conversion in the case of PMs IX and 10 is the same as with the corresponding polynuclear species I and 1*, respectively (72 %). n the other hand, corresponding mononuclear complexes Ia and 1*a have lower conversions (41 and 48 % respectively). It seems that the cation composition has an positive influence on the increase of conversion, in comparison with (Bu4)2Mo619, but at the same time hybrids based on Lindqvist type of PM and dioxomolybdenum(vi) complex seem to deactivate anion part and the only contribution to the conversion comes from the cationic part which behaves as polynuclear complex. In all other examples of tested (pre)catalysts, conversion in the case of all PMs X, XI and 11 has higher values than in the corresponding poly- (II, III, 2*, respectively) or mononuclear analogues (IIa, IIIa) which should imply positive anion effect on the increase of conversion. 110

142 However, in all of the tested (pre)catalysts mono- and polynuclear complexes have higher selectivity towards cyclooctene epoxide than the corresponding PMs. () donors donors % S() donors IX I Ia X II IIa XI III IIIa 10 1* 1a* 11 2* Fig. 60. Comparison of the conversion of cyclooctene (dark cylinders) and selectivity towards cyclooctene oxide (light parallelepipeds). Symbol represents polyoxometalate of the general formula [Mo 2(HL 4-6 )] 2Mo 6 19 for the complexes IX, X, XI and polyoxometalate of the general formula [{Mo 2(HL 1,2 )} 2]Mo 6 19 for the complexes 10 and 11, represents polynuclear complex of the general formula [Mo 2(L 4-6 )] n for the complexes I, II and III and polynuclear complex of the general formula [{Mo 2(HL 1-2 )}Cl] n for the complexes 1* and 2*, while represents mononuclear complex of the general formula [Mo 2(L 4-6 )(Me)] for the complexes Ia, IIa and IIIa and the mononuclear complex of the general formula [Mo 2(HL 1 )(Me)]Cl for the complex 1a*. Since this is the first catalytic research of this kind on hybrid PMs, further results and conclusions could be discussed in greater detail only after obtaining more experimental data. 111