Substrate-Selective Olefin Hydrogenation with a Cavitand-Based Bis(N-anisyl iminophosphorane): Substrate-Selective Olefin Hydrogenation with a Cavitand-Based Bis(N-anisyl iminophosphorane)
Résumé
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.