Diboron Reagents in N-N Bond Cleavage of Hydrazines, N-Nitrosamines, and Azides: Reactivity and Mechanistic Insights.

Abstract

Diboron reagents are known for their ability to promote the deoxygenation of amine or pyridine oxides, nitroarenes, and nitrones through the formation of B-O-B bonds. In this study, we have investigated the potential of diboron reagents to induce N-N bond cleavage in hydrazines, N-nitrosamines and azides. Our findings show that the combination of B2nep2 as diboron source and KOMe as a Lewis base can effectively promote the N-N cleavage of a wide variety of substrates. For hydrazines and nitrosamines, the presence of an aryl group is essential for the reaction to proceed, probably due to a better stabilization of the negative charge developed during N-N bond cleavage. Both types of azides, aromatic and aliphatic, are easily reduced, and the resulting amines can be in situ converted into the corresponding amides by simple treatment with a carboxylic acid. Experimental and theoretical calculations suggest a non-radical mechanism, with concerted B-B and N-N bond cleavage in the case of hydrazines and azides, and a stepwise mechanism in the case of N-nitrosamines, where deoxygenation occurs as the first step, involving the formation of an N-nitrene intermediate.