Hydrogenative coupling of nitriles with diamines to benzimidazoles using lignin-derived Rh(2)P catalyst

Nitrile (C≡N bond) activation for direct organic synthesis has been less explored so far due to a high redox potential of nitrile and its low dissociation energy of C−CN bond. Herein, we demonstrate a direct reductive coupling of nitriles and 1,2-phenylenediamines to yield various benzimidazoles in excellent yields (95%–99%) by using rhodium phosphide (Rh(2)P) catalyst supported on lignin-derived carbon (LC) using H(2) (or hydrazine hydrate) as a hydrogen source. The high catalytic performance of Rh(2)P/LC is attributed to enhanced charge transfer to Rh and strong P−Rh interactions. Our isotope trace experiment confirms the presence of H/D exchange between H(2) and the inert –CD(3) group of CD(3)CN via an intramolecular D-shift. Reusability of Rh(2)P/LC is further demonstrated by a seven-time recycling without evident loss of activity. This research thus highlights a great potential in organic transformation with nitrile as a synthetic building block.