Radical and Thermal Reactions of N‑Heterocyclic Carbene Boranes with Diazo Compounds

Reactions
of NHC-boranes with several diazo compounds and one diazonium
salt give new classes of N-substituted
NHC-boranes. Reactions with diazo compounds and azo initiators such
as AIBN provide N-(cyanoalkyl)-N-borylhydrazones. However, the reactant diazo 2,2-dimethyl-1,3-dioxane-4,6-dione
adds directly to the NHC-borane to give an N-boryl
hydrazone product arising formally from 1,1-hydroboration. A similar
thermal reaction of an NHC-borane with a diazonium salt gives an intermediate
that upon neutralization undergoes air oxidation to provide the first
NHC-boryl azoxy compound.