Synthesis of 1,2-Disubstituted Benzimidazoles via Acceptorless Dehydrogenative Coupling Using Ru(II)-Arene Catalysts Containing Ferrocene Thiosemicarbazone

The catalytic activity of Ru(II)-arene complexes containing ferrocene thiosemicarbazone (Fc-TSC) ligands was investigated towards the selective synthesis of 1,2-disubstituted benzimidazoles via acceptorless dehydrogenative coupling of diamines with primary alcohols. A series of Ru(II)-p-cymene complexes (1-4) containing Fc-TSC ligands (L-1-L-4) were synthesized and characterized. From single crystal X-ray crystallographic studies, the molecular structures of L-3 and 4 were confirmed. The influence of electronic effect of ligands on the catalytic activity of their complexes was studied. The activity of good performer i. e. 4 was compared with that of its benzene counterpart (5). The catalysis was extended to aromatic, aliphatic and heterocyclic substituted primary alcohols, and phenylenediamines with electron-donating or -withdrawing substituents. Overall, synthesis of 1,2-disubstituted benzimidazoles was accomplished with good to moderate yields, with hydrogen and water as only by-products.

Automated summary

The catalytic activity of Ru(II)-arene complexes containing ferrocene thiosemicarbazone (Fc-TSC) ligands towards the selective synthesis of 1,2-disubstituted benzimidazoles via acceptorless dehydrogenative coupling of diamines with primary alcohols was investigated. The electronic effect of ligands on the catalytic activity of their complexes was studied, leading to the conclusion of achieving good to moderate yields in the synthesis of 1,2-disubstituted benzimidazoles.