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Zerovalent palladium and nickel complexes of heterocyclic carbenes: Oxidative addition of organic halides, carbon-carbon coupling processes, and the Heck reaction

Citation

McGuinness, DS and Cavell, KJ and Skelton, BW and White, AH, Zerovalent palladium and nickel complexes of heterocyclic carbenes: Oxidative addition of organic halides, carbon-carbon coupling processes, and the Heck reaction, Organometallics, 18, (9) pp. 1596-1605. ISSN 0276-7333 (1999) [Refereed Article]

DOI: doi:10.1021/om9809771

Abstract

Zerovalent carbene complexes of Pd containing the 1,3,4,5-tetramethylimidazol-2-ylidene ligand (tmiy) have been synthesized. Pd(COD)(alkene) (COD = cyclooctadiene) reacts with the nucleophilic carbene tmiy to produce the complexes Pd(tmiy)2(alkene) (alkene = maleic anhydride (MAH) (2), tetracyanoethylene (TCNE) (3)). Spectroscopic studies on the complexes provide strong evidence of the almost purely donor nature of the carbene ligand. Oxidative addition of hydrocarbyl halide and dihalide substrates to 2 and 3 yield the PdII derivatives Pd(tmiy)2(Ph)I (4), Pd(tmiy)2I2 (5), Pd(tmiy)2(4-nitrophenyl)I (6), and Pd(tmiy)2Br2 (7). The zerovalent Ni complex Ni(tmiy)2 was produced in situ from the reaction of Ni(COD)2 with tmiy, and the oxidative addition of organic halides yields Ni(tmiy)2(o-tolyl)Br (8), Ni(tmiy)2-(Me)I (9), and Ni(tmiy)2I2 (10). X-ray crystal structures of complexes 8 and 10 are reported which reveal square-planar coordination with the carbene ligands inclined at significant angles to the coordination planes of the complexes. Metal to ligand bond distances are all indicative of the electron density induced on the metal center by the donor carbene ligands. Halide abstraction from 6 in the presence of n-butyl acrylate leads to migratory insertion of the olefin and elimination of the Heck coupling product. Under stoichiometric reaction conditions hydrocarbyl-imidazolium ions are also produced as byproducts. Selected complexes were tested as catalysts for the Heck reaction (Pd) and Suzuki coupling (Pd, Ni) and were found to be highly active. The observed reaction behavior is interpreted, and a mechanism for the Heck coupling is provided.

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:McGuinness, DS (Dr David McGuinness)
Author:Cavell, KJ (Professor Kingsley Cavell)
ID Code:16469
Year Published:1999
Web of Science® Times Cited:358
Deposited By:Chemistry
Deposited On:1999-08-01
Last Modified:2011-08-04
Downloads:0

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