Organometallic Chemistry. A structured introduc5on to a complex but fascina5ng field!

Transcription

1 Organometallic Chemistry A structured introduc5on to a complex but fascina5ng field!

2 Late discovery 1956 A zillion concepts at once Why study it?

3 Checking the importance of a topic.. 1. List of Nobel Prizes in recent years. 2. Check with important journals. 3. See what research is funded. 4. How much of the economy is driven by this topic?

4 Nobel Prizes Heck, Negishi and Suzuki, 2010 Schrock, R. H. Grubbs, and Chauvin, 2005 Sharpless, Knowles and Noyori, 2001 Fukui and R. Hoffman 1981 Herbert Brown, G. WiZg 1979 W. Lipscomb 1976 Wilkinson and E. O. Fischer 1973 Zeigler and Na^a 1963

5 Nobel Prizes Heck, Negishi and Suzuki, 2010 Schrock, R. H. Grubbs, and Chauvin, 2005 Sharpless, Knowles and Noyori, 2001 Fukui and R. Hoffman 1981 Herbert Brown, G. WiZg 1979 W. Lipscomb 1976 Wilkinson and E. O. Fischer 1973 Zeigler and Na^a 1963

6 Nobel Prizes Heck, Negishi and Suzuki, 2010 Schrock, R. H. Grubbs, and Chauvin, 2005 Sharpless, Knowles and Noyori, 2001 Fukui and R. Hoffman 1981 Herbert Brown, G. WiZg 1979 W. Lipscomb 1976 Wilkinson and E. O. Fischer 1973 Zeigler and Na^a 1963

7 Nobel Prizes Heck, Negishi and Suzuki, 2010 Schrock, R. H. Grubbs, and Chauvin, 2005 Sharpless, Knowles and Noyori, 2001 Fukui and R. Hoffman 1981 Herbert Brown, G. WiZg 1979 W. Lipscomb 1976 Wilkinson and E. O. Fischer 1973 Zeigler and Na^a 1963

8 Nobel Prizes Heck, Negishi and Suzuki, 2010 Schrock, R. H. Grubbs, and Chauvin, 2005 Sharpless, Knowles and Noyori, 2001 Fukui and R. Hoffman 1981 Herbert Brown, G. WiZg 1979 W. Lipscomb 1976 Wilkinson and E. O. Fischer 1973 Zeigler and Na^a 1963

9 Nobel Prizes Heck, Negishi and Suzuki, 2010 Schrock, R. H. Grubbs, and Chauvin, 2005 Sharpless, Knowles and Noyori, 2001 Fukui and R. Hoffman 1981 Herbert Brown, G. WiZg 1979 W. Lipscomb 1976 Wilkinson and E. O. Fischer 1973 Zeigler and Na^a 1963

10 Nobel Prizes Heck, Negishi and Suzuki, 2010 Schrock, R. H. Grubbs, and Chauvin, 2005 Sharpless, Knowles and Noyori, 2001 Fukui and R. Hoffman 1981 Herbert Brown, G. WiZg 1979 W. Lipscomb 1976 Wilkinson and E. O. Fischer 1973 Zeigler and Na^a 1963

11 Assessing Importance of a subject? 1. List of Nobel Prizes in recent years? OK! 2. Check with important journals? 3. See what research is funded? 4. How much of the economy is driven by it?

12 TOP 20 ar5cles accessed from JACS As of 20 th Sept Review Ac)va)on of C H Bonds by Metal Complexes Abstract. Full Text HTML Hi- Res PDF[1214 KB] Ci5ng Ar5cles Alexander E. Shilov and Georgiy B. Shul'pin* N. N. Semenov Ins5tute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia Chem. Rev., 1997, 97 (8), pp DOI: /cr Publica5on Date (Web): December 18, 1997 Copyright 1997 American Chemical Society

13 Palladium- Catalyzed Ligand- Directed C H Func)onaliza)on Reac)ons Thomas W. Lyons and Melanie S. Sanford Chem. Rev., 2010, 110(2), pp DOI: / cr900184e

14 Total Synthesis of (+)- Complanadine A Using an Iridium- Catalyzed Pyridine C H Func)onaliza)on Daniel F. Fischer and Richmond Sarpong J. Am. Chem. Soc., 2010, 132(17), pp DOI: /ja101893b

15 NATURE Vol 463, 28 January doi: /nature08730 Cleaving carbon carbon bonds by inser5ng tungsten into unstrained aroma5c rings Aaron Sa^ler & Gerard Parkin

16 PNAS 2005, vol. 102 p Characteriza)on of an organometallic xenon complex using NMR and IR spectroscopy Graham E. Ball,Tamim A. Darwish, Spili Gerakis Michael W. George, Douglas J. Lawes Peter Por5us, Jonathan P. Rourke,

17 19 F NMR spectra of Re( i PrCp)(CO) 2 (PF 3 ) (1) in liquid Xe at 163 K obtained during prolonged photolysis and expansions of the highlighted region that corresponds to one of the resonances from 3. (1) NMR Using 129 Xe as solvent. (2) Using unlabeled Xe. A small splizng caused by 3 J XeF can be seen. (a) No splihng in the spectrum with unlabeled Xe. Ball G E et al. PNAS 2005;102: by National Academy of Sciences

18 Assessing Importance of a subject? 1. List of Nobel Prizes in recent years? 2. Check with important journals? 3. See what research is funded? 4. How much it is driving the industry..

19 Papers with the concept organometallics ~ 2300 in papers in papers in papers in key papers every year on the topic organometallics

20 Is the subject important? 1. List of Nobel Prizes in recent years OK 2. Check with important journals OK 3. See what research is funded OK 4. See what research is prackced in the industry

21 Industrial uses of organometallics Metal complexes used as addi5ves in polymers and fuels. (Sn and Mn compounds) Many million tons of silicones, and organolithium compounds are made. Metal complexes used as catalysts for making polymers Ace5c acid, acetaldehyde, and fine chemicals,

22 Is the subject important? 1. List of Nobel Prizes in recent years OK 2. Check with important journals OK 3. See what research is funded OK 4. See what research is prackced OK

23 Why is the subject important? Are we dealing with a special element?

24 C What is special about carbon? Forms bonds with other carbons (C- C) readily and they are strong (catena5on) Forms strong mul5ple bonds (C=C) Forms very strong bonds with another special element H!! Cyclic C=C- C fragments would be extra stable AROMATIC..

25 C and its Electronic configura5on! 1s 2 2s 2 2p 2 `Why is this special? To form a full shell, it would require 4 covalent bonds Gap between the 2s and 2p is 1s 2 2s 1 2p x 1 2p y 1 2p z 1 just right! When 4 equivalent covalent bonds are formed, no extra electrons / no vacant orbitals

26 Tm Transi5on metals are exactly the opposite!! Vacant orbitals Or extra electrons. Rarely do they keep a noble gas configura5on Consider [Co(H 2 O) 6 ] e 7 electrons + 12 electrons Ni 2+ aquo complex has 20 e. V 2+ complex has 15 e. Very few complexes would have exactly 18 electrons! Full shell / no extra electrons is rare.

27 What happens to Tm in Tm- organometallics The 18 electron rule prevails.. Most complexes with Tm- C bonds have a full shell. C seems to have forced its preferences on the metal! When C combines with a transi5on metal Both metal and carbon loose their iden5ty!

28 So what about carbon?

29

30

31 Why is the subject important? 1. List of Nobel Prizes in recent years 2. Check with important journals 3. See what research is funded 4. See what research is prackced We are dealing with a special combina5on of elements!!

32 Challenges for today Synthesis and understanding of new compounds and their reac5vity Ac5va5on of inert molecules like CH 4, CO 2, R 3 C- F Cataly5c efficiencies far exceeding approaching that of enzymes! Asymmetric induc5on in catalysis

33 Organiza5on of the course.. Modular, based on ligand systems How does one classify the ligand? Hap5city of the ligand is the key: η with superscript: η 3 number of carbons bonded to the metal is 3

34

35

36

37

38

39 Current approach Simple to complex: Avoid complex ligands un5l we discuss them towards the la^er part of the course. Integrate discussion on reac5ons with study of new structure types Deal with inser5on reac5ons (purely C1 chemistry) Only oxida5on state change at the metal! Oxida5on state change and C- C coupling!

40 Text books? Title Authors Publisher ISBN no. Organometallics: A Concise Introduc5on Organometallic Chemistry, Fundamentals of Organometallic Catalysis Christoph Elschenbroich Wiley- VCH 3rd Edi5on B. D. Gupta and Anil J. Elias Universi5es Press Dirk Steinborn Wiley- VCH ISBN:

41 Electron coun5ng the organometallic way.. Metal has all d electrons whatever be the oxdn. state Ligands can be ionic or neutral / adjust metals d- electron count Net charge is added (electrons are nega5ve and so the no. of electrons in the complex are reduced if the charge is +ve. If the charge is ve then one has to add to the electron count)

42 Electron coun5ng in two ways Let us try a few.. Cp 2 TiCl 2 complex is neutral Handout with homework

43 Stoichiometric reac5ons and Catalysis Reac5ons with increasing complexity.. Without oxida5on state change.. Subs5tu5on and inser5on reac5ons.. With oxida5on state change Reac5ons with oxida5on state change at metal.. Ox- ad and Red- el Catalysis and cataly5c cycles A series of stoichiometric reac5ons regenera5ng the catalyst when the product is formed.

44 Ligands Ionic Method A Method B H Cl, Br, I OH, OR CN CH 3, CR 3 NO (bent M- N- O) CO, PR 3 NH 3, H 2 O =CRR H 2 C=CH 2 (ethylene) CNR =O, =S 2 (H - ) 2 (X - ) 2 (OH -,OR - ) 2 (CN - ) 2 (CH 3-,CR 3- ) 2 (NO - ) (O 2-,S 2- )

45 Ligands Ionic Method A Method B NO (Linear M- N- O) η 3 - C 3 H 5 (π- allyl) CR (Carbyne) N Ethylenediamine (en) Bipyridine (Bipy) Butadiene η 5 - C 5 H 5 (cyclopentadienyl) η 6 - C 6 H 6 (benezene) η 7 - C 7 H 7 (cycloheptatrienyl) 2 (NO + ) 2 (C 3 H 5+ ) 3 6 (N 3- ) 4 (2 per nitrogen) 4 (2 per nitrogen) 4 6 (C 5 H 5- ) 6 6 (C 7 H 7+ )

46 Counting electrons Method A Determine formal oxidation state of metal Deduce number of d electrons Add d electrons + ligand electrons (A) Method B Ignore formal oxidation state of metal Count number of d electrons for M(0) Add d electrons + ligand electrons (B) The end result will be the same

47

48 Nitrosyls are very complicated few +ve charged donors exist NO M M & NO M NO & NO M NO ( ) Now NO + is like CO Alternatively if it is : M ( & NO ) N = O M N O Angle will be less than 180 Due to sp 2 hybridization Remember the odd electron is on a π