Non-Classical Molecular Activation by Phosphines and N-Heterocyclic Carbenes and Its Application to Catalytic Reactions

Abstract

Abstract This Award Account reports our recent studies concerning the catalytic transformations that involve a non-classical mode of molecular activation by tertiary phosphines and N-heterocyclic carbenes (NHCs). Regarding organophosphine catalysis, we successfully designed reactions based on a P(III)/P(V) redox couple. A catalytic protocol for generating pentacoordinate P(V) species was devised by the reaction of tertiary phosphines, acyl fluorides and alkynoates. The ability of the thus generated fluorophosphoranes to participate in ligand coupling and ligand metathesis with organosilicon nucleophiles enables synthetic transformations that are otherwise unattainable, including the intermolecular carbofluorination of alkynes and the hydroalkenylation of enol ethers. Regarding nucleophilic NHC catalysis, the use of imidazolium-based NHCs can generate deoxy-Breslow intermediates that are sufficiently nucleophilic to promote the aromatic substitution of aryl halides, aryl ethers and anilides. The protocol can also be used for the nucleophilic activation of styrene derivatives, allowing for the generation of a series of ylide intermediates that can serve as non-stabilized vinyl anion equivalents. These results demonstrate that synthetic transformations involving non-stabilized carbanions can be conducted under catalytic conditions without the use of strong organometallic nucleophiles.