Solvent Dependent Selectivity in the Synthesis of 1,2-Disubstituted and 2-Substituted Benzimidazoles by Dehydrogenative Coupling Reactions with Ruthenium-Polyoxoniobate Catalysts

Ruthenium-polyoxoniobate complexes were found to be efficient catalysts for the selective synthesis of 2-substituted benzimidazoles and 1,2-disubstituted benzimidazoles by solvent switching. The current strategy enables the synthesis of 2-substituted benzimidazoles in water as a green solvent. Switching to aprotic solvents resulted in the formation of 1,2-disubstituted benzimidazoles as the major product. Control experiments showed the involvement of both acceptorless dehydrogenative and oxidative coupling pathways. The method was extended to synthesize various 2-substituted and 1,2-disubstituted benzimidazole derivatives, and the desired products were obtained in moderate to good yields.