2-Diphenylphosphinobenzaldehyde as Chelating Ligand in Trimethylphosphine Complexes of Cobalt and Nickel

Methylnickel complexes activate the C(O)−H function of 2-diphenylphosphinobenzaldehyde to form five-membered chelate rings Ni(Ph₂P⌒CO) which occupy OC-axial and P-equatorial positions in the trigonal bipyramidal configuration of nickel(d⁸) compounds Ni(Ph₂P⌒CO)X(PMe₃)₂ (X = Cl (1), Br (2), I (3), Me (4)). Methylcobalt complexes react with 2-diphenylphosphinobenzaldehyde to afford an isoelectronic species Co(Ph₂P⌒CO)(PMe₃)₃ (5) of similar configuration, while cobalt halides CoX(PMe₃)₃ oxidatively add the aldehyde function to produce octahedral compounds mer-CoH(X)(Ph₂P⌒CO)(PMe₃)₂ (X = Cl (6), Br (7), I (8)). Carbon monoxide replaces an axial trimethylphosphine in 5, while iodomethane gives rise to an oxidative substitution producing CoI(Ph₂P⌒CO)(PMe₃)₂ (10) (17 valence electrons). The molecular structures of compounds 3, 5, 6, and 10 have been solved by X-ray crystallography.