Abstract
Nitrile is frequently high-available as commodity chemicals; however, nitrile (CΞN 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 lignin-derived rhodium phosphide (Rh2P) catalyst with H2 (or hydrazine hydrate) as hydrogen sources. The high catalytic performance of Rh2P/LC is attributable to enhanced charge transfer on Rh site as well as strong interactions between P and Rh. Our isotope trace experiment confirms the presence of H/D exchange between H2 and the inert –CD3 group of CD3CN via an intramolecular D-shift. Reusability of Rh2P/LC is demonstrated by seven-time recycling without evident loss of activity. This research thus highlights a vast potential in organic transformation with nitrile as a synthetic building block.
Highlights
Benzimidazole and its derivatives are pharmaceutically important heterocyclic compounds with a broad range of biological activities and pharmacological properties such as anti-viral, anti-fungal, anti-bacterial, anti-ulcer, anti-inflammatory, anti-hypertensive, anti-histaminic, anti-cancer, anti-tumor, and anti-HIV features (Chakrabarti et al, 2019; Keri et al, 2015)
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 (Rh2P) catalyst supported on ligninderived carbon (LC) using H2 as a hydrogen source
The high catalytic performance of Rh2P/LC is attributed to enhanced charge transfer to Rh and strong PÀRh interactions
Summary
Benzimidazole and its derivatives are pharmaceutically important heterocyclic compounds with a broad range of biological activities and pharmacological properties such as anti-viral, anti-fungal, anti-bacterial, anti-ulcer, anti-inflammatory, anti-hypertensive, anti-histaminic, anti-cancer, anti-tumor, and anti-HIV features (Chakrabarti et al, 2019; Keri et al, 2015). 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 (Rh2P) catalyst supported on ligninderived carbon (LC) using H2 (or hydrazine hydrate) as a hydrogen source. The developed Rh2P/LC demonstrates high efficiency by coupling serial tandem reactions of nitrile hydrogenation, cyclization and dehydration in one-pot (Scheme 2B).
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