Stereochemical control in the choice of donor atoms in metal complexes of a ‘bifunctional’ bidentate ligand

Abstract

Metal complexes of two phosphorus–nitrogen ligands, 2-bis(diphenylphosphino)methyl-6-methylpyridine (ppn) and 2-[2-diphenylphosphino-1-(diphenylphosphinomethyl)ethyl]-6-methylpyridine (ppn′), are described. Although each ligand contains one pyridine and two tertiary phosphine groups, not more than two of the three potential donor atoms co-ordinate to the same metal atom. Both modes of bidentate behaviour (‘PN’ and ‘PP’) are found for complexes of ppn but only ‘PP co-ordination’ for those of ppn′. The choice of donor atoms is interpreted in terms of chelate ring size and the stereochemical preferences of the various metal ions. The latter include Fe^II, Co^II, Ni^II, Pd^II, Zn, Cd, and Hg^II. The structures of the complexes are deduced from their vibrational and electronic spectra and other physical properties.