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Cationic methylpalladium(II) complexes containing bidentate N-O ligands as catalysts for the copolymerisation of CO and ethylene. Identification and isolation of intermediates from the stepwise insertion reactions, and subsequent detailed mechanistic interpretation

Citation

Green, MJ and Britovsek, GJP and Cavell, KJ and Gerhards, F and Yates, BF and Frankcombe, KE and Skelton, BW and White, AH, Cationic methylpalladium(II) complexes containing bidentate N-O ligands as catalysts for the copolymerisation of CO and ethylene. Identification and isolation of intermediates from the stepwise insertion reactions, and subsequent detailed mechanistic interpretation, Journal of the Chemical Society, Dalton Transactions , (7) pp. 1137-1144. ISSN 0300-9246 (1998) [Refereed Article]

DOI: doi:10.1039/a707199j

Abstract

A series of cationic methylpalladium(II) complexes containing bidentate N-O ligands, of the general formula [PdMe(N-O)L]BF 4 (N-O = methyl picolinate, methyl 6-methylpicolinate, N,N-diisopropylpicolinamide, 6-methyl-N,N-diisopropylpicolinamide; L = PPh 3 or PCy 3 ) have been prepared and characterised. The solid-state structure of [PdMe(N-O)(PPh 3 )]BF 4 (N-O = N,N-diisopropylpicolinamide), in comparison with that for the complex with N-O = methyl picolinate, indicates a significant lengthening of the Pd-P bond ["(Pd-P) = 0.018(3) Å] possibly due to the presence of the more strongly co-ordinating N-O ligand. Complexes with L = PPh 3 were found to be active for the copolymerisation of CO and ethylene to give polyketone. The complexes [PdMe(N-O)(PPh 3 )]BF 4 (N-O = methyl 6-methylpicolinate or diisopropylpicolinamide) have the highest catalytic activities (80 g polymer per g Pd per hour and 58 g polymer per g Pd per hour respectively, at 20°C). Examples of the complexes form simple acyl complexes when treated with CO at room temperature and pressure and the spectroscopic data of the resulting acetyl complexes are reported. The stepwise migratory insertion of CO and ethylene into the complex [PdMe(N-O)(PPh 3 )]BF 4 (N-O = methyl picolinate) has been carefully monitored and the individual insertion products have been characterised. Insertion of ethylene into the Pd-acyl bond of [Pd(COMe)(N-O)(PPh 3 )]BF 4 (N-O = methyl picolinate) affords one of the first examples of an isolable product from insertion of an unstrained alkene into a Pd-acyl bond. A detailed mechanism for the co-reaction of CO and ethylene catalysed by complexes containing chelate ligands with distinct donor groups is discussed and an explanation of the observed reaction behaviour provided. The proposed mechanism represents one of the most comprehensive interpretations of this important reaction.

Item Details

Item Type:Refereed Article
Research Division:Chemical Sciences
Research Group:Other Chemical Sciences
Research Field:Organometallic Chemistry
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Chemical Sciences
Author:Green, MJ (Ms Melinda Jane Green)
Author:Britovsek, GJP (Dr George Britovsek)
Author:Cavell, KJ (Professor Kingsley Cavell)
Author:Gerhards, F ( Gerhards)
Author:Yates, BF (Professor Brian Yates)
Author:Frankcombe, KE (Ms Katrina Ellen Frankcombe)
ID Code:14112
Year Published:1998
Web of Science® Times Cited:47
Deposited By:Chemistry
Deposited On:1998-08-01
Last Modified:2011-08-09
Downloads:0

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