Synthesis, Characterization and Reactivity of N-Heterocyclic Carbene Gold(III) Complexes

A series of (NHC)Au I Cl ( 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- tert -butylimidazol-2-ylidene (I t 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 t Bu)AuBr] ( 14 ). These (NHC)Au I Br complexes undergo oxidative addition of elemental bromine, leading to the new Au(III) complexes [(IPr)AuBr 3 ] ( 15 ), [(IMes)AuBr 3 ] ( 16 ), [(SIPr)AuBr 3 ] ( 17 ), [(SIMes)AuBr 3 ] ( 18 ), [(ICy)AuBr 3 ] ( 19 ), [(IAd)AuBr 3 ] ( 20 ), and [(I t Bu)AuBr 3 ] ( 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.