Preparation of Mono and Bis-Hydrazino-Substituted N-Heterocyclic Carbene Boranes

We report the formation of NHC complexes of mono- and bis-hydrazino boranes with N-N-B and N-N-B-N-N chains via the reaction of NHC-boranes with electrophilic azo reagents. The influence of steric hindrance on the carbene and on the azo reagent has been shown to be crucial for the reactivity. The hydroboration of dissymmetric azo reagents is regioselective only when the latter is sufficiently electronically twisted. Bis-hydrazino borane complexes with two different hydrazine arms could be obtained via sequential addition. Hydroboration of electrophilic azo reagents with NHC-boranes leads to the formation of NHC complexes of mono- and bis-hydrazino boranes with N-N-B and N-N-B-N-N chains. Steric hindrance on the carbene (primarily) and on the azo reagent (somewhat less) is crucial for the reactivity. Bis-hydrazino borane complexes with two different hydrazine arms could be obtained via sequential additions.image