Reaction of carbon oxides with an ethylene-bridged PH/B Lewis pair

Abstract

The reaction of 2,4,6-tri(tert-butyl)phenyl vinyl phosphane with Piers’ borane [HB(C₆F₅)₂] gave the ethylene-bridged PH/B frustrated Lewis pair (FLP) system. It is a monomer at high temperature (>323 K), but exists as an associated 12-membered macrocyclic trimer below 273 K. The PH/B FLP splits dihydrogen and serves as a metal-free hydrogenation catalyst. It adds carbon dioxide. It serves as a PH/B template for the reduction of carbon monoxide by the HB(C₆F₅)₂ borane to the formyl stage. The resulting six membered P/B/O containing heterocycle is opened upon treatment with pyridine and it reacts with benzaldehyde in a boron mediated Claisen-Tishchenko reaction.