Alkylidyne complexes

presentation

1. By fariha un nisa Bs chemistry uog 1

2. Alkylidyne complexes 2

3. History In early 1970’s Richard R. Schrock , former student of John Osborn at Harvard made important discovery of first nucleophillic alkylidyne complex In 1973, E.O Fischer synthesized first metal carbyne complex 3

4. Introduction : Definition: Transition metal carbyne complexes are organometallic compounds with a triple bond  between carbon and the transition metal T riple bond consists of a  σ-bond and two π-bonds .   4

5. Cont. A lso called metal alkylidynes length of the M-C bond varies between 1.65 and 1.90 Ǻ depending on the metal . Monomeric metal carbyne complexes exhibit linear M–C–R linkages according to X-ray crystallography . M–C distances are typically shorter than the M–C bonds found in metal carbenes. bond angle : 170 ° to 180 ° . 5

6. Classification of Alkylidyne complexes : Fischer alkylidynes stabilized by heteroatoms and bonded with low oxidation state transition metals (usually later transition metals ). H ave π–acceptor ligands on the metal making the carbyne essentially electrophilic. 6

7. Cont .   Tungsten is a very common metal used to make Fischer carbynes . Fischer is very famous in the organometallic field, winning the Nobel Prize  in 1973.   7

8. Cont. Schrock alkylidynes : H ave no heteroatoms, and are found with high oxidation state metals (early transition metals ). The other ligands on the metal are usually strong σ-donors, which makes the carbon essentially  nucleophilic . They usually form complexes with less than 18 electrons and the metals tend to be d . 8

9. cont.  The Schrock carbyne is an example of a quartet carbyne. It forms 3 covalent bonds to the metal because it has 3 unpaired electron. 9

10. Synthesis of alkylidyne complexes: From low valent metal complexes: Metal like W and molebdenum undergo synthesis of alkylidynes by this method X= cl-,Br- and R= Alkyl group 10

11. synthesis cont. From alkylidene 11

12. Cont. Other routes: 12

13. Cont. From dichlorocarbene : Highly reactive compound. Treatment with aryl lithium leads to double halide abstraction 13

14. References: Manfred bochmann , organometallics 1, alkylidene and alkylidyne complexes , pg (84-87) Inorganic chemistry by Miessler and Tarr , 3 rd edition, chapter 13,pg(510-512) 14