Dimensioning the Term Carbenoid

The current use of the term carbenoid is discussed, particularly in the context of carbene transfer reactions from diazo compounds, in which intermediates of type LnM=CR1R2, or one of its resonance forms, are tagged which such a name. We 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)CR1R2 en route to the formation to LnM=CR1R2′ from diazo reagents. We propose the exclusive use of the carbenoid term to species of type (X)(M)CR1R2 with a tetrasubstituted carbon center that upon loss of X afford an effective carbene transfer process.