Hydrido(acylenolato)cobalt(III) compounds containing trimethylphosphane ligands:: Insertion reactions with alkynes and the first carbonylcobalt(III) complexes

Formal insertion of phenylethyne into Co-H functions of mer-octahedral acyl(enolato)cobalt(III) hydrides 1 - 3 proceeds under ambient conditions affording eta(1)-vinylcobalt(III) compounds where the dianionic acyl(enolato) ligands are derived from 2-formyl-4-phenylcyclohexanone (4), 1-formyl-cyclohexan-2-one (5), and 3-hydroxo-2,3-diphenyl-propenal (6). Dissociation and association of trimethylphosphane results in a reversible transformation of penta-coordinate complexes 4 - 6 into hexa-coordinate ones 7 - 9, respectively, involving different tautomeric vinyl species. In toluene solution 9 rearranges by reductive C,C coupling into a 5,6-eta(2)-olefin(enolato)cobalt(I) complex 10. Trimethylsilylethyne undergoes a hydrolytic desilylation reaction which is followed by reductive C,C-coupling reactions of acyl and vinyl functions selectively producing chelating eta(1)-enolato-5,6-eta(2)-olefin ligands in cobalt(I) compounds 13 - 16 where the (ax,eq)chelating ligands are derived from 1-formyl-cyclohexan-2-one (13), 3-hydroxo-2,3-diphenyl-propenal (14), 2-formyl-alpha-tetralone (15), and 3-formyl-4-tertbutyl-cyclohexanone (16). An axial position of the enolato-O donor in the trigonal bipyramidal configuration of complex 15 has been confirmed by X-ray diffraction analysis. With 1,4-bis(trimethylsilyl)buta-diyne 1,2-addition in cobalt(III) hydrides 2, 3, 11 (as deriverd from 2-formyl-alpha-tetralone), and 12 (as derived from 2-formyl-4-tert-butyl-cyclohexanone) produces 2-metalated vinyl groups in compounds 17 - 20. Dissociation of trimethylphosphane from 17 and 19 does not activate C,C coupling at the cobalt(III) centre of penta-coordinate 21 and 22. Steric congestion in compounds 17, 18, and 20 favours exchange of trimethylphosphine for carbon monoxide affording the first octahedral carbonyl complexes of cobalt (d(6)) (23 - 25). In the crystal and in solution a meridional configuration is adopted by complex 23 with the CO group in a position opposite to the acyl function.