Carbodiimide and Isocyanate Hydroboration by a Cyclic Carbodiphosphorane Catalyst**

Abstract

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.

Mixed Lithium–Aluminum Hydrides Bearing Ar-Bian Ligands: Reactivity Toward Heteroallenes

“…So, the first examples of catalytic hydroboration of isocyanate by pinacolborane (HBpin) to form N , O -bis­(boryl)­hemaminals or N -borylmethyl amines were achieved by using β-diketiminato and hydridotriphenylborate magnesium complexes. Pioneer studies of the catalytic hydroboration of carbodiimides were carried out by Hill and Okuda, utilizing the same magnesium compounds. , Further studies have discovered a wide range of catalytic systems, including derivatives of transition metals, − main group elements, ,− or actinides, , that are able to catalyze these reactions. However, the hydroboration of isocyanates and carbodiimides typically results in the formation of mixtures of products.…”