Substrate‐Selective Olefin Hydrogenation with a Cavitand‐Based Bis(N‐anisyl iminophosphorane)

Abstract

A distally‐substituted resorcin[4]arene cavitand equipped with two remote N‐anisyl‐imino‐phosphoranyl (AIP) units has been synthesised and assessed in the competitive hydrogenation of α‐olefins (rhodium catalyst). A substrate‐selectivity factor of 39.2 in favour of the linear olefin was observed after 1 h in the reduction of stoichiometric amounts of hex‐1‐ene and 3‐ethyl‐pent‐1‐ene. The catalyst was also shown to be suitable for the regioselective reduction of a compound that has two double bonds in different steric environments. The remarkable olefin discrimination probably arises from the ability of the ligand to generate a cavity‐capping N,O‐chelator involving both AIP groups. Chelate formation positions the reactive metal sites inside the receptor moiety, the restricted size of which may retard the coordination of larger α‐olefins. The results of this study encourage the further development of cavitands as shape‐selective catalysts.