Electronic Control of Stereochemistry in Carbon-Carbon Bond Formation at Metal Centers

Abstract

Product distribution in catalytic reactions can often be rationalized in terms of steric effects of the ligands. The relative thermodynamic stabilities of intermediates can be associated with steric factors and subsequently correlated with the stereochemistry of products. For example, the effect of phosphine bulk has traditionally been important in explanations of the isomer ratio in modified oxo processes.1 The steric bulk of substituents in optically active phosphines is also often attributed a role in determining optical yield in catalytic asymmetric syntheses.2 It is inevitably difficult to completely dissect the interactions into effects arising from steric interactions and those arising from electronic interactions. Nevertheless, a situation will be illustrated in which the direction of attack of an incoming nucleophile upon a coordinated olefinic moiety is controlled primarily by electronic factors. In this system the asymmetry arises from differences between a carbonyl and nitrosyl ligand; yet the difference is sufficient to produce stereospecific reactions.