Synthesis, characterization and reactivity of N-heterocyclic carbene gold(III) complexes

A series of (NHC)Au^ICl (1, NHC = N,N′-bis(2,6- diisopropylphenyl)imidazol-2-ylidene (IPr); 2, NHC = N,N′-bis(2,4,6- trimethylphenyl)imidazol-2-ylidene (IMes); 3, NHC = N,N′-bis(2,6- diisopropylphenyl)-imidazolin-2-ylidene (SIPr); 4, NHC = N,N′-bis(2,4,6- trimethylphenyl)imidazolin-2-ylidene (SIMes); 5, NHC = N,N′- dicyclohexylimidazol-2-ylidene (ICy); 6, NHC = N,N′-diadamantylimidazol-2- ylidene (IAd); 7, NHC = N,N′-di-terf-butylimidazol-2-ylidene (I'Bu)) complexes were reacted with LiBr to generate [(IPr)AuBr] (8), [(IMes)AuBr] (9), [(SIPr)AuBr] (10), [(SIMes)AuBr] (11), [(ICy)AuBr] (12), [(IAd)-AuBr] (13), and [(I^tBu)AuBr] (14). These (NHC)Au^IBr complexes undergo oxidative addition of elemental bromine, leading to the new Au(III) complexes [(IPr)AuBr₃] (15), [(IMes)AuBr₃] (16), [(SIPr)AuBr ₃] (17), [(SIMes)AuBr₃] (18), [(ICy)AuBr₃] (19), [(IAd)AuBr₃] (20), and [(I^tBu)AuBr₃] (21). Complete characterization by NMR spectroscopy and single-crystal X-ray diffraction were performed in order to discern structural differences between organogold(I/III) congeners. A preliminary study examining the activity of (NHC)Au^III species on the addition of water to alkynes is also presented.