Recent aspects of transition metal carbonyl carbene complexes

Abstract

The general preparative route and the bonding properties of transition metal complexes with acyclic carbene ligands are discussed. Phenylmethoxycarbene pentacarbonylchromium(0) forms 1,2-dimethoxy-1,1,2,2-tetraphenylethane with phenyllithium. This reaction is in accord with the δ+ charged Ccarbeneatom in the complex. Thiolysis and selenolysis of methoxyorganylcarbene pentacarbonylchromium(0) or tungsten(0) yield thio- and selenocarbene complexes, respectively, l.r. and dipole measurements of the complexes (CO)5W C(XCH3)CH3(X = O, S, Se, NH) show that the negative charge transfer from the carbene ligand to the W(CO)5residue increases in the sequence O < Se < S < NH. The x-ray structure on the novel ethoxydimethyl aminocarbene pentacarbonylchromium(0) confirms for the first time a trans effect of the carbene ligand. The bond distances exhibit a stronger π-charaeter for the Ccarbene—N bond than for the Ccarbene—O bond. The reaction of Cr(CO)6with (CH3)2PLi in ether at — 80°C and the subsequent alkylation with [(C2H5)30] [BF4] yielded a complex with the formula CrC14H2206P2. Instead of the expected dimethylphosphinoethoxycarbene pentacarbonyl-chromium(0). a complex which we suggest to be cis-(bisdimethylphosphino-ethoxycarbene) tetracarbonylchromium(0) is formed. According to x-ray results methoxyphenylcarbene enneacarbonyldimanganese has the carbene ligand in the equatorial position like its technetium and rhenium homologues and the methoxymethylcarbene analogues. Several preparative routes are given for mononuclear carbene tetracarbonyliron complexes. The addition of 2,6-dimethoxyphenyllithium to Fe(CO)5and the subsequent ethylation yields binuclear Fe2(CO)7C(OC2H5)C6H3(OCH3)2, whose structure was proved by x-ray analysis. Details of the preparation and properties of tetra coordinated mixed transition metal carbene complexes of Ni. Co and Fe follow. Cleaved methoxyphenylcarbene ligands form with organic substrates such as methyl trans-crotonate, ethyl vinyl ether and diethyl fumarate cyclopropane derivatives. The isomer ratio of the cyclopropane derivatives is shown to be dependent on the metal of the parent carbene complex. Insertion of methoxyphenylcarbene ligands occurs with diphenylsilane and methanol. © 1972, Walter de Gruyter. All rights reserved.