STATIC AND DYNAMIC STRUCTURES OF PENTACARBONYL-CHROMIUM(0) AND -TUNGSTEN(0) COMPLEXES OF DITHIOETHER LIGANDS .2. UNSYMMETRICAL DITHIOETHER LIGAND COMPLEXES OF GENERAL TYPE [M(CO)5(MESCH2SR)]

All six transition metal complexes of type [M(CO)5MeSCH2SR)] (M = Cr, W; R =(i)Pr, (t)Bu, Ph) have been synthesized. In CDCl3 or CD2Cl2 solvents, the complexes exist as an equilibrium mixture of MeS-bonded and RS-bonded isomers, with the MeS-bonded species predominating. Variable temperature H-1 NMR studies have identified pyramidal inversion of the coordinated sulphur atoms and activation energy data have been obtained. DELTAG(double dagger) (298.15 K) values for the process are in the range 38-44 kJ mol-1, and vary with the attached alkyl group (Me > (i)Pr almost-equal-to (t)Bu).