We report hydroboration of carbodiimide and isocyanate substrates catalyzed by a cyclic carbodiphosphorane catalyst. The cyclic carbodiphosphorane outperformed the other Lewis basic carbon species tested, including other zerovalent carbon compounds, phosphorus ylides, an N‐heterocyclic carbene, and an N‐heterocyclic olefin. Hydroborations of seven carbodiimides and nine isocyanates were performed at room temperature to form N‐boryl formamidine and N‐boryl formamide products. Intermolecular competition experiments demonstrated the selective hydroboration of alkyl isocyanates over carbodiimide and ketone substrates. DFT calculations support a proposed mechanism involving activation of pinacolborane by the carbodiphosphorane catalyst, followed by hydride transfer and B−N bond formation. A cyclic carbodiphosphorane catalyzes the hydroboration of carbodiimide and isocyanate substrates. DFT calculations support a mechanism involving activation of pinacolborane by the carbodiphosphorane catalyst, followed by hydride transfer and B−N bond formation.