Two Copper-Carbenes from One Diazo Compound

Many transition-metal complexes MLn decompose diazo compounds N-2=(CRR2)-R-1 generating metal-carbenes LnM=(CRR2)-R-1 which transfer the carbene group to other substrates, constituting an important tool in organic synthesis. All previous reports have shown that the (CRR2)-R-1 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 (CRR2)-R-1 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)(CONEt2)], the stable copper carbene Tp(Ms)Cu=C(H)(NEt2) 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)(CONEt2) 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.

Automated summary

This study reports the detection and isolation of a monosubstituted copper carbene where the ligand has undergone a modification from the initial diazo reagent. Additionally, carbon monoxide was trapped as a product of the decarbonylation process. Experimental data, DFT calculations, and microkinetic models support the proposal that a copper carbene complex undergoes CO loss en route to the formation of another complex.