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 (ΔG^Dagger;) 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.