Regiospecific Cyclometalation of Diphenyl(2‐substituted phenyl)phosphane with Methyltetrakis(trimethylphosphane)cobalt(<scp>I</scp>)

Abstract

Abstract The pre‐chelate molecules 2‐(diphenylphosphanyl)‐ N , N ‐dimethylaniline, [2‐(diphenylphosphanyl)benzyl]dimethylamine, 1‐(diphenylphosphanyl)‐2‐ethylbenzene, 1‐(diphenylphosphanyl)‐2‐isopropylbenzene, and 2‐(diphenylphosphanyl)benzonitrile, in a reaction with [CoMe(PMe 3 ) 4 ], eliminate methane to afford the selectively 6‐ ortho ‐metalated complexes 1 − 5 that contain four‐membered metallacycles. The molecular structure of 3 shows a tbp‐coordinated cobalt atom, with axial C and PMe 3 donor groups. Metalation in the aliphatic side‐chain occurs with 2‐(diphenylphosphanyl)toluene, giving complex 6 that contains a five‐membered metallacycle. Benzyldiphenylphosphane is selectively ortho ‐metalated in the benzyl group, affording 7 . As shown by the molecular structures, complex 7 is a true ligand isomer of 6 . Substitution of a trimethylphosphane group in compounds 4 and 6 by ethene gives the pentacoordinate complexes 8 and 9 , respectively. The ethene ligand is π‐coordinated in the equatorial plane of a trigonal bipyramid. Under 1 bar of CO, complex 6 forms monocarbonyl complex 10 . Carbonylation of complexes 3 and 4 proceeds by insertion of CO into the Co−C bond under ring expansion, affording the aroylcobalt complexes 11 and 12 , respectively. Complex 6 reacts with iodomethane in an oxidative substitution reaction yielding a structurally characterized octahedral complex mer ‐ 13 , which eliminates a methyl group in THF at 20 °C to form a pentacoordinate cobalt( II ) complex 14 . Complex 3 oxidatively adds iodomethane in a stereoselective cis addition to give the cobalt( III ) complex mer ‐ 15 , which retains its four‐membered metallacycle and the CoCH 3 group. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2003)