METAL-ASSISTED REACTIONS .24. THE IMPORTANCE OF SOLVENTS IN LIQUID-PHASE HETEROGENEOUS CATALYTIC TRANSFER REDUCTION

In liquid-phase catalytic transfer reduction in which a hydrogen donor is used to effect hydrogenation of a substrate, reaction often proceeds sluggishly in single phase solvents but goes rapidly in biphasic solvent systems in which the catalyst usually resides in one or other of the phases. Depending on the nature of the substrate and donor, an excess of either can lead to the catalyst surface becoming saturated with one component, thereby preventing reaction. It is shown that the biphasic solvent system is, in practice, a simple means of controlling access to the catalyst by either the substrate or donor such that both are present on the surface in comparable amounts, leading to optimum or near optimum reaction rates.