Oxidation-reduction exchange of 2-acylenolato and trimethylphosphane ligands between d8 complexes of nickel and cobalt

A series of seven (C:O)-dianionic 1-acyl-2-enolato ligands C(O)-C=C-O in a redistribution reaction between is-electron metal-d(8) complexes Ni[C(O)-C=C-O](PMe3)(3) [C=C = 3-CMe3-5-Me-C6H2 (1), 3,5-CMe3CbH2 (2), 3,4-benzo-cyclohexene (3), 5-phenyl-cyclohexene (4), 5-tert-butyl-cyclohexene (5), cyclohexene (6), 1,2-diphenylethene (7)] and Co(CCPh)(PMe3)(4) (1:1) have been transferred to cobalt to afford the novel compounds mer-trans-Co[C(O)-C=C-O](CCPh)(PMe3)(3) (8-14) in stoichiometric reactions and transforming the nickel into Ni(PMe3)(4). In the X-ray crystal structure of the parent nickel compound 7, the 2-acylenolato ligand is seen to span C-axial and O-equatorial positions in a distorted trigonal bipyramid. The molecular structure of compound 14 shows an octahedral coordination of cobalt: a chelate ring accurately retaining angles and bond distances, and an alkynyl ligand occupying the position opposite to the O-donor function. (C) 2000 Elsevier Science S.A. AII rights reserved.