N-Heterocyclic Carbene-Phosphinidene Complexes of the Coinage Metals

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