A STUDY OF THE POLARITIES, ANISOTROPIC POLARIZABILITIES 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 PI-ACCEPTOR BEHAVIOR IN COORDINATED PHOSPHORUS

Studies of electric dipole moments, electric birefringences, carbonyl infrared frequencies and interatomic bond distances provide mutually reinforcing evidence for pi-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 sigma-bonded P-M model. The results provide evidence for a highly deformable pi-component in the phosphorus-metal bonding and for a pi-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.