A study of the polarities, anisotropic polarisabilities and carbonyl infrared vibrational frequencies of the complexes [M(CO)5{P(OCH2)3CMe}](M = Cr, Mo or W) and the crystal structure of [Mo(CO)5{P(OCH2)3CMe}]: evidence for π-acceptor behaviour in co-ordinated phosphorus

Abstract

Studies of electric dipole moments, electric birefringences, carbonyl infrared frequencies and interatomic bond distances provide mutually reinforcing evidence for π-acid behaviour of the bicyclic phosphite ligand in [M(CO)₅{P(OCH₂)₃CMe}] complexes (M = Cr, Mo or W). Molecular optical anisotropies and directional polarisabilities from experiment are analysed to show strong polarisability enhancement along the molecular symmetry axis and concomitant diminution of polarisability perpendicular to that axis, relative to a hypothetical σ-bonded P–M model. The results provide evidence for a highly deformable π-component in the phosphorus–metal bonding and for a π-delocalised P–M–CO(trans) system. Comparisons are made with other [M(CO)₅L] compounds where L = quinuclidine, PMe₃ or PCl₃. The crystal structure of [Mo(CO)₅{P(OCH₂)₃CMe}] is reported and bond dimensions are compared with those of related molybdenum complexes.