Two Copper-Carbenes from One Diazo Compound

High Resolution Image Download MS PowerPoint Slide 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.