ortho‐Metalation of Triarylphosphane at Cobalt and Template Synthesis of Chelating 2‐(Diarylphosphanyl)aroyl Ligands

Elimination of methane from thermally labile CoMe(PPh3)(PMe3)3 generates ortho-metalated Co(2-Ph2PC6H4)(PMe3)3 (1). Addition of dihydrogen causes ring-opening which is followed by a ligand dismutation reaction giving CoH(PMe3)4 and CoH(PMe3)2(PPh3)2. The system does not catalytically hydrogenate olefins. CO insertion into the Co−C bond of 1 results in ring expansion and constitutes a template synthesis of the anionic 2-phosphanylbenzoyl chelate ligand as shown in the molecular structure of Co(2-Ph2PC6H4CO)(CO)(PMe3)2 (3). Oxidative addition of iodomethane transforms 1 into diamagnetic CoMeI(2-Ph2PC6H4)(PMe3)2 (7), while benzoyl chloride oxidizes 1 to paramagnetic CoCl(2-Ph2PC6H4)(PMe3)2 (8). The preservation of the four-membered metallacycle in three successive oxidation states is supported by single-crystal X-ray analyses of 1, 7, and 8.