Stereochemical rigidity of the square-pyramidal W(CO)5 moiety during 1,2- and 1,3-metallotropic shifts in sulphur ligand complexes
Abstract
N.m.r. studies of tungsten pentacarbonyl complexes of type [W(CO)5L] where L refers to open-chain ligands (PhCH2SSCH2Ph or MeSCH2SMe) and cyclic ligands (β-[graphic omitted]HMe, or [graphic omitted]H2) have revealed no evidence of carbonyl scrambling accompanying the tungsten–sulphur 1,2- or 1,3-metallotropic shifts. This implies stereochemical rigidity of the square-pyramidal W(CO)5 moiety, on the two-dimensional 13C n.m.r. time-scale, during these intersulphur–metal commutations, energy barriers (ΔGDagger;) for any carbonyl rearrangement being in excess of ca. 90 kJ mol–1. The results further indicate that the metallotropic shifts involve lateral movements of the rigid W(CO)5 moieties with no tendency to distort to seven-co-ordinate tungsten(0) species in the transition states.