Two Copper-Carbenes from One Diazo Compound.

Many transition-metal complexes ML decompose diazo compounds N═CRR generating metal-carbenes LM═CRR which transfer the carbene group to other substrates, constituting an important tool in organic synthesis. All previous reports have shown that the CRR 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 CRR ligand has undergone a modification from the initial diazo reagent. When TpCu(THF) (Tp = hydrotris(3-mesityl)pyrazolylborate ligand) was reacted with -diethyl diazoacetamide [N═C(H)(CONEt)], the stable copper carbene TpCu═C(H)(NEt) was isolated, resulting from a decarbonylation process, with carbon monoxide being trapped as TpCu(CO). The simultaneous observation of products derived from the intramolecular carbene insertion reaction into C-H bonds demonstrates that the expected TpCu═C(H)(CONEt) 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.