Structural Studies of Asymmetric Hydrogenation. III. The Crystal Structure of (<i>R</i>)-1-(Methoxycarbonyl)ethyl(<i>R</i>)(+)-α-methylbenzylaminebis(dimethylglyoximato)cobalt(III)

Abstract

Abstract The structure of (R)-1-(methoxycarbonyl)ethyl(R)(+)-α-methylbenzylaminebis(dimethylglyoximato)cobalt(III) has been determined by X-ray analysis. The crystal is monoclinic, the space group P21 Z=2 with a=7.899(5), b=16.397(2), c=9.054(7) Å, and β=90.98(7)°. The structure was deduced by the heavy atom method and refined by the block-diagonal least-squares method to a final R value of 0.048 for 2146 observed reflections. The bis(dimethylglyoximato) cobalt moiety is twisted around its long axis, owing to the steric repulsion from the (R)-1-(methoxycarbonyl)ethyl group and the optically active amine. It is proposed that this twist is one of the factors inducing the asymmetry in the hydrogenation catalyzed by the complex of bis(dimethylglyoximato)cobalt and the active amine. At the step of Co–C bond cleavage the reaction proceeds mainly through inversion of the configuration.