Synthesis of dimethylcobalt(III) complexes containing trimethylphosphine and 2-formyl-phenolato- or 2-formyl-enolato(O:O) ligands

Substituted salicylaldehydes [C6HR1R2R3(CHO)(OH)] react with CoMe3(PMe3)3 to afford 6-coordinate (cis-dimethyl)(2-formyl-phenolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[C6HR1R2R3(CHO)(O)Me2](PMe3)2 (1: R1 = H; R2 = Me; R3 = tert-Bu; 2: R1, R2 = C6H4; R3 = H). Accordingly, substituted enolated malonic dialdehydes (CHO–CR4double bond; length as m-dashCR5–OH) react with CoMe3(PMe3)3 to afford 6-coordinate (cis-dimethyl)(2-formyl-enolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[(CHO–CR4double bond; length as m-dashCR5–O)(Me)2](PMe3)2 (3: R4, R5 = (CH2)2C6H4; 4: R4 = R5 = C6H5). In the molecular structure of 4, the cobalt atom is centred in an octahedral coordination geometry brought about by a six-membered chelate ring (O:O-ligand), cis-dimethyl and trans-trimethylphosphine groups. A reaction mechanism is suggested.