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.

A series of ferrocene‐hydrazone based Ru(II)‐p‐cymene complexes were investigated for their catalytic activity towards acceptorless dehydrogenative coupling (ADC) reactions. Ru(II)‐p‐cymene isonicotinic Fc‐hyrazone complex performed better in the solvent‐free synthesis of 1,2‐disubstituted benzimidazoles (up to 88%) and quinazolinones (up to 95%). The catalysis was extended to a wide range of benzylic alcohols. The synthesis of 1,2‐disubstituted benzimidazoles was accomplished with electron‐donating/‐withdrawing o‐phenylenediamines as well. A catalytic structure‐activity relationship was established by varying the steric and electronic parameters on the substrates. All the catalytic experiments exhibited good to moderate yields, with hydrogen and water as the only by‐products. The prepared complexes were well characterized using analytical and spectroscopic techniques. The molecular structures of the ligands and complex were resolved using single crystal X‐ray crystallographic studies.