Dynamic nuclear magnetic resonance study of Group 6 metal pentacarbonyl complexes. Pyramidal inversion and 1,2-metal shifts in the complexes [M(CO)5(Me2CCH2EECH2)](M = Cr, Mo, or W; E = S or Se)

Abstract

Mononuclear complexes of the type [M(CO)₅(Me₂[graphic omitted]H₂)], where M = Cr, Mo, or W and E = S or Se, have been prepared. Detailed variable-temperature n.m.r. studies have established the existence of pyramidal inversion about the co-ordinated sulphur or selenium ligand atom and an intramolecular 1,2-metal shift between adjacent chalcogen ligand atoms. The energy barriers associated with both rate processes have been evaluated by dynamic n.m.r. methods. The metal pentacarbonyl complexes of naphtho[l,8-cd]-dithiole and -thiaselenole, [M (CO)₅(C₁₀H₆EE′)](M = W, E = E′= S; M = Cr, E = S, E′= Se) have also been prepared but no fluxionality was evident.