The use of transition-metal-based catalysts for the transfer of carbene units from diazo compounds constitutes a powerful tool in organic synthesis.[1] Several metals have been reported to mediate this transformation effectively, and the appropriate selection of ligands has permitted excellent selectivities. Highly chemo-, diastereo-, and/or enantioselective systems have been reported with rhodium-, copper-, or cobaltcontaining catalysts. In fact, nearly all 12 elements of Groups 8-11 have been found to decompose diazo compounds and transfer a carbene unit to saturated or unsaturated organic substrates, [2] leading to the insertion or addition product, respectively (Scheme 1). Only one of these 12 elements remains unexplored in this chemistry: gold. [3] Although the other members of Group 11-copper and, to a lesser extent, silver-have been described to induce such transformations, conducting this type of catalytic reaction with gold remains a challenge. We therefore focused our attention on the development of a gold-based catalyst, as a result of our experience in the area of metal-catalyzed carbene transfer from ethyl diazoacetate (EDA). [4] We recently reported the catalytic behavior of [(IPr)CuCl] (1, IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene) for the transfer of carbene from ethyl diazoacetate to olefins, amines, and alcohols to form cyclopropanes, amino acid derivatives, and ethers, respectively.[5]

The complex TpBr3Cu(NCMe) catalyzes, at room temperature, the insertion of a nitrene group from PhINTs into the carbon-hydrogen bond of cyclohexane and benzene, as well as into the primary C-H bonds of the methyl groups of toluene and mesitylene, in moderate to high yield.

A series of catalysts of general formula TpXCu (TpX = homoscorpionate ligand) promote the insertion of :CHCO2Et (ethyl diazoacetate as the carbene source) into the C-H bonds of cycloalkanes and cyclic ethers in moderate to high yield. A correlation between the steric hindrance of these catalysts and the yield of the transformation has been observed.