posted on 2021-03-18, 12:04authored byMaría Álvarez, Maria Besora, Francisco Molina, Feliu Maseras, Tomás R. Belderrain, Pedro J. Pérez
Many transition-metal complexes MLn decompose diazo
compounds N2CR1R2 generating
metal-carbenes LnMCR1R2 which
transfer the carbene group to other substrates, constituting an important
tool in organic synthesis. All previous reports have shown that the
CR1R2 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 CR1R2 ligand has undergone a modification from the
initial diazo reagent. When TpMsCu(THF) (TpMs = hydrotris(3-mesityl)pyrazolylborate ligand) was reacted
with N,N-diethyl diazoacetamide [N2C(H)(CONEt2)], the stable copper carbene TpMsCuC(H)(NEt2) was isolated, resulting from a decarbonylation process,
with carbon monoxide being trapped as TpMsCu(CO). The simultaneous
observation of products derived from the intramolecular carbene insertion
reaction into C–H bonds demonstrates that the expected TpMsCuC(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.