Diborylcarbenes as Reactive Intermediates in Double 1,2‐Rearrangements with Low Activation Enthalpies

Despite three neighboring electron‐deficient centers, dicarborylcarbenes are not too high in energy to be accessible thermally. This was shown by the low activation enthalpies (≈22–23 kcal mol⁻¹) of double 1,2‐rearrangements of borylmethyleneboranes, in which alkyl groups migrate from carbon to boron and aryl groups from boron to carbon. Ab initio calculations reveal that tetramethyldiborylcarbene 2 is only 23.1 kcal mol⁻¹ higher in energy than tetramethylborylmethyleneborane 1. (Figure Presented.)