Crystal structures of [W(CO)5(PPh3)], [M(CO)5(AsPh3)] and [M(CO)5(SbPh3)](M = Mo or W): a comparative study of structure and bonding in [M(CO)5(EPh3)] complexes (E = P, as or Sb; M = Cr, Mo or W)

Abstract

Crystal structures have been determined for [W(CO)₅(PPh₃)], [M(CO)₅(AsPh₃)] and [M(CO)₅-(SbPh₃)](M = Mo or W) as part of a systematic study of a series of nine [M(CO)₅(EPh₃)] complexes (M = Cr, Mo or W; E = P, As or Sb). Trends in bond lengths and angles are rationalised in terms of steric and electronic interactions between the bonded M(CO)₅ and EPh₃ fragments. Comparison is made between the solid-state geometry of the free and co-ordinated EPh₃. Torsion angles defining the disposition of the EPh₃ groups in relation to M(CO)₅ show little variation within the [M(CO)₅(EPh₃)] series. For all nine complexes the EPh₃ groups have propeller geometry with small deviations from symmetric C₃ structures. The studies were extended to include other related [M(CO)₅L] complexes. Trends in the structural parameters of 29 such compounds are related to the steric behaviour and π-acceptor capacity of the ligands L. It is shown that M–P bond dimensions are not adequately explained by hybridisation changes of the phosphorus atom in the ligand L.