Dimensioning the term carbenoid

Abstract

The current use of the term carbenoid is discussed, particularly in the context of carbene transfer reactions from diazo compounds, where intermediates of type LnM=CR1R2, or one of its resonance forms, are tagged which such name. We herein discuss this issue, on the basis of the data evidencing the metal-carbene nature of those intermediates, as well as the existence of carbenoids of type (N2)(M)C R1R2 en route to the formation to LnM=C R1R2’ from diazo reagents. We propose the exclusive use of the carbenoid term to species of type (X)(M)C R1R2 with a tetrasubstituted carbon center that upon loss of X afford an effective carbene transfer process.