N-Heterocyclic Carbene-Phosphinidene Complexes of the Coinage Metals

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 [(Me2 S)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(BAr(F) ) or AgSbF6 afforded the tetranuclear complexes [(IPr⋅PPh)2 M4 Cl2 ]X2 (X=BAr(F) or SbF6 ), which contain unusual eight-membered M4 Cl2 P2 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.