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.