Synthesis, Structure, and Reactivity of Gold(I) α-Oxo Carbenoid Complexes

The trifluoromethanesulfonate α-oxo carbenoid complexes (IPr)AuCH(OTf)COR [R = OEt (1a), p-tolyl (1b)] were isolated from reactions of (IPr)Au(OTf) with the corresponding α-diazo carbonyl compounds. The pyridinium α-oxo carbenoid complexes [(IPr)AuCH(4-MeC5H4N)COR]+OTf- (2), the sulfonium α-oxo carbenoid complexes [(IPr)AuCH(SR′2)COR]+OTf- [3 (R′ = Me), 4 (R′ = Ph)], and the α,α-dioxo carbenoid complexes [(IPr)AuC(R)(CO2Me)2]+OTf- [R = 4-MeC5H4N (5), R = SPh2 (6)] were synthesized either via reaction of complexes 1 with 4-picoline or dimethyl sulfide or via reaction of (IPr)Au(OTf) with stabilized ylides. Complexes 1-6 were thermally stable and were characterized in solution and, in the cases of complexes 2 and 3, by single-crystal X-ray diffraction. Complex 1b underwent carbene transfer to cyclohexene in modest yield at 75 °C. The pyridinium and sulfonium α-oxo carbenoid complexes 2 and 3 displayed no reactivity toward dimethyl sulfide, 4-picoline, 1-octyne, or p-methoxystyrene. Complex 5 underwent rapid displacement of the ylide ligand in the presence of dimethyl sulfide or 4-picoline. Taken together, we obtained no evidence suggesting that these sulfonium or pyridinium α-oxo carbenoid complexes might behave as α-oxo carbene surrogates.