N-Heterocyclic Carbene-Phosphinidene Complexes of the Coinage Metals

Abstract

Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPr·PPh (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me2S)AuCl], which afforded the monometallic complexes [(IPr·PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr·PPh)(MCl)2] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr·PPh)(CuOTf)2] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr·PPh)(MCl)2] (M=Cu, Au) with Na(BArF) or AgSbF6 afforded the tetranuclear complexes [(IPr·PPh)2M4Cl2]X2 (X=BArF or SbF6), which contain unusual eight-membered M4Cl2P2 rings with short cuprophilic or aurophilic contacts along the chlorine-bridged M⋯M axes. Complete chloride abstraction from [(IPr·PPh)(AuCl)2] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPr·PPh){Au(THT)}2][SbF6]2. The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions.