Two Copper-Carbenes from One Diazo Compound

[Image: see text] Many transition-metal complexes ML(n) decompose diazo compounds N(2)=CR(1)R(2) generating metal-carbenes L(n)M=CR(1)R(2) which transfer the carbene group to other substrates, constituting an important tool in organic synthesis. All previous reports have shown that the CR(1)R(2) fragment at the metal-carbene remains intact from the parent diazo compound. Herein we report the detection and isolation of a monosubstituted copper carbene where the CR(1)R(2) ligand has undergone a modification from the initial diazo reagent. When Tp(Ms)Cu(THF) (Tp(Ms) = hydrotris(3-mesityl)pyrazolylborate ligand) was reacted with N,N-diethyl diazoacetamide [N(2)=C(H)(CONEt(2))], the stable copper carbene Tp(Ms)Cu=C(H)(NEt(2)) was isolated, resulting from a decarbonylation process, with carbon monoxide being trapped as Tp(Ms)Cu(CO). The simultaneous observation of products derived from the intramolecular carbene insertion reaction into C–H bonds demonstrates that the expected Tp(Ms)Cu=C(H)(CONEt(2)) complex is also formed. Experimental data, DFT calculations, and microkinetic models allow us to propose that the latter undergoes CO loss en route to the former.