Structure, bonding and reactivity of (stable) transition metal carbonyl carbene complexes

Abstract

The generally applicable method for the preparation of stable metal carbonyl carbene complexes by nucleophilic addition of a carbanion from an organolithium reagent to a carbonyl group with subsequent methylation of the resulting acylcarbonyl metallate by diazomethane or trimethyloxonium-tetrafluoroborate is described. The i.r. and 1H-n.m.r. spectra of new cyclopentadienyl carbonyl nitrosyl carbene complexes of chromium, molybdenum and tungsten confirm the idea of the bonding of methoxyorganylcarbene ligands as being predominantly a donation of electron density from the ligand to the rest of the molecule, with only a very much weaker π-acceptance of electrons. Five types of reaction of carbonyl carbene complexes, CO substitution, carbene substitution, ester cleavage, addition and rearrangement, and H substitution are described with representative examples. The kinetic results on the aminolysis of phenylmethoxycarbene pentacarbonyl chromium, and the conclusions which can be drawn from the i.r. and 1H-n.m.r. spectra of some o-, m- and p-substituted derivatives and arene chromium dicarbonyl carbene complexes are discussed. Results obtained from the analogous iron carbonyl system are briefly given. Some of the general features of bonding of this type of compound are summarized by the x-ray results obtained for six carbene complexes. Finally, an account of the secondary reactions of cleaved carbene ligands with themselves and olefins close this survey of this new field of organometallic chemistry. © 1970, Walter de Gruyter. All rights reserved.