Re2 O 7 +17CO. WCl 6 +CO+Et 3 Al

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1 Chapter 2: Dative igands 2.1 Introduction Chapters 2-4: presents illustrative summary of the types of complexes Chapter 2: steric and electronic properties of neutral ligands (Chapters 3&4: formally anionic ligands) 2.2 Carbon onoxide and elated igands Properties of Free Carbon onoxide small dipole moment with negative end located on carbon strongvibrationiniat2143cm -1 neutral ligand, commonly binds to metal C's lone pair elecrtrons normally binds to one metal, but bridging coordination is possible (-C-angleismuchlessthan120 ) Types of etal Carbonyl Complexes Preparation of metal-carbonyl complexes from bulk metal from reduction of complexes in higher oxidation state 1atm Ni Ni() 4 e2 O e 2 () WCl 6 ++Et 3 Al W() 6 polynuclear carbonyl complexes Fe() 5 Os() 5 Os 3 () 12 stable much less stable more stable homoleptic carbonyl complexes in2ndand3rdrow polynuclear structure is more favorable Classification of metal carbonyl complexes: Figure odels for Binding: Introduction of Backbonding binds strongly to electron-rich, low valent metals(backbonding, soft metal and soft ligand) Evidnce for Backbonding in Terminal Carbonyl Infrared and X-ray Diffraction Data for Complexes with Bridiging Carbonyls I, C-O length

2 Thermodynamics of the - Bonds dissociation of ligands: key step in many reactions Table 2.3 Cr() 6 <o() 6 <W() 6 Ni() 4 <Cr() 6 Ir(P i Pr 3 ) 2 Cl()(particularystrong) higher enegy of orbitals, backdonation third row, electron-rich alkylphosphine Isoelectronic Analogs of : Isocyanides and Thiocarbonyls C N isocyanide stronger -donor, weaker -acceptor than weakerc-x -bondthan 2.3 Dative Phosphorous igands and eavier Congeners Tertiary Phosphines and elated igands Chelating Phosphines bidentate, asymmetric bisphosphine, P--P angle trans coordination Ph 2 P Fe e Fe P P Ph 2 Ph 2 Transphos e PPh 2 Ph-Trap Properties of Free Phosphines P 3 vs N 3 binding: to transition metals more strongly(soft-soft) steric effect: less pronounced(larger atom, longer -P) high inversion barrier => P-chiral phosphine Ar 3 P,(O) 3 Plesssensitivetoair(lesselectronrich) Properties of Phosphine Complexes Bonding and Electronic Properties Electron-donatingability: 3 P>Ar 3 P>(O) 3 P greaters-characterofsp 2 -hybridizedorbitalofaryl =>weaker electron donor than alkyl electron-donation: alkyl > alkoxy -acceptor orbital: hybrid of P-X *-orbital and phosphorus d-orbital(figure 2.9) -acceptor ability: NF 3 Py P 3 P(Oe) 3 PF 3 PCl Ne 3 N PPh 3 Pe theoretical scale

3 electrondonatingability( in[ni() 3 ]) (cm -1 ) (cm -1 ) PtBu 3 PCy 3 Pe 3 P(C Oe) PPh 3 P(Oe) 3 P(OPh) 3 PF Steric Properties cone angle, solid angle(figure 2.11) Effect of Phosphine Steric and Electronic Properties on Structure and eactivity liganddissociationinni 4 (and related Pd complexes) Pe 3 <Pe 2 Ph<PePh 2 <PEt 3 <PPh 3 <PiPr 3 <PCy 3 <PPhtBu 2 bulky phosphines bind trans to one another deviation from the ideal coordination geomety because of bulky phosphines e.g.)wilkinsoncomplexhcl(pph 3 ) 3 =>nonplanar(normally,squareplanarford 8 h(i)) Pathways for the Decomposition of Phosphorus igands oxidation: more electron rich phosphine P-C bond cleavage Ar 3 P X Pd PAr 3 Ar' Ar 3 P Ar 3 P Pd X Ar'PAr Pd 3 X PAr 2 Ar' Ar P-Xclevage(X=O,N 2 )bywateroralcohol N Spectroscopic Properties of Phosphines 31 P:1/2spin,100%abundant relative receptivity: ( = 1, C = ) Cl Pe e 3 P Pe 3 3 u e 3 P Cl u e 3 P Pe 3 Cl e 3 P Cl Pe 3 trans cis :-6.63(s) :9.0(t)-12.7(t) J=35z eavier Congeners of Phosphorus igands - bond strength Steric effect of substituents P-C/As-C cleavage P>As>Sb>Bi P>As>Sb(-bondlength) P>As

4 Organometallics Study eeting#6 2011/5/12 Kimura 2.4 Carbenes Classes of Free and Coordinated Carbenes Properties of Free Carbenes carbenes with electron negative substituents with only hydrogen or alkyl groups more stable in singlet state triplet state N N NC nitrogen acts as strong -donor to unoccupied p-orbital Properties of Carbene Complexes Fischer Carbene Schrock Carbene e.g.) () 5 Cr Oe e.g.) t-bu t-bu Ta t-bu e t-bu electrophilic at carbene carbon carbene with electronegative substituents groups6-8(late)metalinalowoxdationstate bearing -accepting ligands such as -C bond: not strongly polarized considered as neutral ligands ( -donation and -backdonation like ) nucleophilic at carbene carbon carbene with hydrogen or alkyl groups groups 4-6(early) metal, high oxidation state more polar -C bond considered as dianionic ligands ybrid of Fischer and Schrock Carbene e.g.) Vinylidene complex e.g.) 3 P 3 P u C 2 Ph 2 P u e e PPh 2 C C Ph late metal, low oxidation state carbane ligand lacking heteroatom substituent with strongly donating ligand inatead of unsaturated hydrocarbyl group suchasphenylorvinyl considered as neutral ligand one methylene substituent at carbene carbon free vinyldene: electrophilic(like dihalocarbene) :pronetorearrangetoalkyne tautomers of alkyne and vinylidene(eq. 2.10a,b) (relative stability depends on the number and identity of ligand) electrophilic at carbene carbon(c ) nucleophilic at metal and C

5 Bonding of Carbenes siglet carbene triplet carbene closely related with donate two electrons to metal through a dative bond accept d-electrons in -backbonding oftenhaveweakp-bonds(large Ebet.d andp ) low rotation barrier(8~10 kcal/mol) considered as dianionic donationoftwoelectronpairstometal( ) NC Spectroscopic Characteristics of Carbene Complexes N N 13 C Fischer X=O X=N 290~365ppm 185~280ppm strong -donor, weak -acceptor : carbon is soft and less electronegative than most heteroatom ewis base : p-orbital of carbene carbon participates in strong -bonding with amino subsituents like phosphine, but stronger -donor two fold symmetry("fences rather than cones") Schrock 240 ~ 330 ppm 1 10~20ppm

6 2.5 Transition etal Carbyne Complexes C General Preparation ethod (1)viametathesisof-or-triplebondwithalkyne (2) transformation of existing ligand(carbene) into carbyne (3) modification of existing carbyne to exchange substituents at carbyne C carbyne eactivity [2+2] cycloaddition(chapters 13 and 20) attack by nucleophiles(chpter 11) by electrophiles(chapter 12) Bonding and Structure of Carbyne Comlexes C carbyne mostly, group 5~7 metal complexes carbene is typically considered trianionic (cf. monocationic like linear nitrosyl) bonding interaction: carbene + additional -bond in the case of heteroatom-substituted carbyne OO: metal UO:oneofthe *-orbitalsof-cbond => nuclephiles attack carbyne carbon C C C =N 2 ( -donorgroup):decrease -acidity = 3 Si(electropositivegroup):increase -acidity =alkyl( -donorgroup):increasethe enegiesofalltheorbitals => more polarized -C bond, C becmes more nucleophlic C Spectroscopic Characteristics of Carbyne Comlexes 13 C:200~350ppm,triplebondvibration:1250~1400cm Organic igands Bound Through ore than One Atom Olefin Comlexes * C-C Chatt-Dewar-Duncanson model C-C Stability of etal-olefin Comlexes electron-rich metal => olefin bering EWG (e.g. Ni(0)) inhigeroxdationstate(withchargesgreaterthan+1andd 0 ): olefin complexes are less common(cf. olefin polymerization) also sensitive to steric effects(binding: ethylene > -olefins)

7 Structures of etal-olefin Comlexes StructuralChangesUponBinding *backbonding:sp 2 =>sp 3 Cr( 5 ) + + Cr() 5 trans-cycloctene cis-cycloctene Structural Changes Upon Binding -donor + -acceptor electronic preference for orientaion about -olefin axis orientation of olefin: controlled by metal OO d 10 trigonal planar d 8 trigonal bipyramidal d 6 trigonal bipyramidal Spectral Properties of etal-olefin Comlexes N electron-poor metal complex: close to free olefin electron-rich metal complex: upfield shift Alkyne Comlexes -Bonding -Donation -Backbonding Structural Characteristics of Alkyne Complexes distorted to the geometry of cis-olefin if -backdonation is strong enough "metallacyclopropene" strained alkynes stabilized upon coordinationto the metal

8 Physical and Chemical Properties of Alkyne Complexes Complexes of Organic Carbonyl Compounds electron-rich metal fragments (low-valent late metal) e.g.) bind to aldehyde/ketone in 2 -fassion Cp 2 o O C 2 Ph 3 P Ph 3 P Ni O C CF 3 CF AreneandelatedComplexes n arene is stronger electron donor than three ligands electron-releasingsubstituentsonaromaticringinvariablystabilize 6 -areneligand steric interactions counteract this electronic effect coordination with T deplets arene of much of its -electron density N 2 2 Cr Cr less basic than aniline more acidic than benzoic acid u 4 -arenecomplexes distortion from planarity, large loss of aromaticity preparedbyreductionof( 6 -arene)dication 2.7ComplexesofigandsBoundThroughN,OandS Neutral Nitrogen Donor igands Amine Complexes ammonia, amines: classic ligand in coordination chemistry these ewis bases are less commonly used N proton of coordinated amine tend to be reactive tertiary amines bind weakly(hard-soft mismatch) tertiary amins are morer sterically congested than tertially phosphine (shorter C-N bond, larger C-N-C angle) N u 2 1 N O

9 Pyridine and Imine Complexes nitrogens in pyridine, imine, oxazoline are softer heteroarenes can act as -acceptors * examples: figure 2.39 they lack reactive N- bond monoimines tend to be reactive species Dinitrogen Complexes N 2 isisoelctronicwith,bindsmostoftenasan 1 -ligand lessbasicthan,less -acidicthan N 2 acceptingabilityofn 2 isstrongerthan -donatingpropety N 2 isgenerallymoreelectron-acceptingthanitiselectron-donating most dinitrogen complexes contain electron-rich metal center mostly, mononuclear complex, weak interaction Cp* Zr N 2 N 2 N N ZrCp* Cp* Zr N 2 N 2 N N ZrCp* dinuclearcomplex N-Nbondismuchlonger muchmoreactivatedn 2 insideoncomplex Complexes of Neutral Oxygen Donors 2 O,eO,TF,DE,acetoneDSO,Ar 3 POetc. Cp 2 Zr NtBu O even dessociate readily from more-oxophilic high-valent transition metals 3 POtendtobindmorestronglythan 2 O despite of weak bindings, these can influence reaction chemistry (without forming stable complexes) TF, DE, phosphine oxides are common(figure 2.44) dissociate readily => temporaly masking of reactive intermediate bindentate ligand with mixture of P and O(figure 2.45) Complexes of Neutral Sulfur Donors Se Pd X Se neutral sulfur donors: softer and more polarizable than neutral oxygen donors thioethers and sulfoxides are most common trans influence of neutral sulfur donor is greater than neutral oxygen donor compatible with amine -S 2 isstrongerthan-n 3 bond,butweakerthan-p 3 bond spectrochemicalseries:p 3 >S 2 >Cl - O 3 P O S u P 3 DSO to low-valent late metals: through electron pair on sulfur to harder high-valent metals: through electron pairs on oxygen DSO can induce isomerization of square-planar complexes to nonrigid five-coordinate intermediate

10 2.8 Sigma Complexes Overview of Sigma Complexes n n * dihydrogen, alkanes, silane, boranes(x- bond) electron donation from X- -bonding orbital backdonation from metal to X- *-orbital like olefin's Chatt-Dewar-Duncanson model ( donation from -bonding and backbonding to *-orbital) bonding intercation is much weaker than olefin -bonding enegy is in lower(less basic) -bonding is higher in enegy(less -acidic) E between and is too large? ->complexation=>longerx-bond=>less E n Dihydrogen Complexes PropertiesthateadtoStable 2 Complexes Ph 3 P PPh 3 u PPh 3 2 -complexes:arrestedoxidativeadditionofdihidrogen metalbackbondsto 2 *,butcleaves-onlypartially most metal: in low oxidation state(backbonding) many of these low-valent complexes are cationic (neutral, low-valent metal is too much electron-rich) neutral 2 complexeshave -acceptingcarbonylgroup [o( 2 )()(dppe) 2 ]:dihydrogencomplex [W 2 ()(dppe) 2 ]:dihydridecomplex second-row metals: dihydrogen complex third-row metals: dihydride complex SpectroscopicSignaturesof 2 Complexes eactivityof 2 Complexes * reactivity dissociation of dihydrogen addition of dihydrogen to form dihydride deprotonation of hydrogen by external base Dissociationof 2 PCy 3 W PCy 3 +P(Oe) 3-2 PCy 3 P(Oe) 3 W PCy 3 2 isreplacedby,p 3,nitriles notreplacedby 2 Onorethers binding entropic term is surprizingly large rate of substitution reaction => 0 order in incoming ligand rateofdisplacement=rateofdissociationof 2

11 P 3 W P 3 P 3 W P 3 Additionof 2 toformdihydride oxidative addition to cleave - bond inmanycases.equibriumbetween 2 anddyhydride barrier: structural change to accomodate two hydrides in some cases: dihydrogen as kinetic product at low temp Alkane and Silane Comlexes Si property and reactivity: closely related to those of dihydrogen complexes silane complexes: similar stability to dihydrogen-comlex(or slightly unstable) alkane complexes: not so much study (too unstable in solution) Stabilityelativeto 2 Complexes Si silane complexes: similar stabiliy to dihydrogen complexes(despite greater steric effect) Si-bondismorebasicthan-or-bond Si- bond is much longer weaker, has lower energy *-orbital alkanecomplexses:lessstablethan 2 orsi-complexes steric effect is not compensated by smaller E between and *-orbitals Evidence for Alkane Complexes Intramolecular Coordination of Aliphatic C- Bonds(Agostic Interactions) -agostic -agostic -agostic agostic interaction with a dative ligand intermediate to -hydrogen elimination (Chapte 10) electrophilic metal carbene in high oxidation state unsaturated metal (dpme)cl 3 Ti 86 severe distortion from agostic interaction agostic interaction: dynamic C-inmethyl:singlepeakinN