Stereodynamics and conformational equilibria in some chiral pseudo-octahedral tungsten crotyl complexes

The complexes W(CO)₂(η³-crotyl)(diphos)X, where X = Cl and I, and [W(CO)₃(η³-crotyl)(diphos)]SbF₆ were prepared and characterized. The solution dynamics were examined with low temperature NMR experiments, with focus on the effect of the crotyl ligand on controlling the chirality at the metal. A steric influence of halide was also observed which results in different conformational and configurational preferences for the crotyl group. The spontaneous resolution of the neutral complex W(CO)₂(η³-crotyl)(diphos)Cl provides a route for obtaining optically active samples of these compounds. It was found that the conversion to the cationic tricarbonyl complex greatly increases the racemization barrier of the chiral center in the crotyl and also renders the η³-ligand more susceptible to nucleophilic attack.