A review with 12 refs. Two Ru/pyridine complexes, [Ru(tpy)(bpy)(py)]2+ (tpy = 2,2':6',2"-terpyridine; bpy = 2,2'-bipyridine) and [Ru(bpy)2(py)2]2+, were found to photocatalyze the regioselective redn. of 1-benzyl-3-carbamoyl-pyridinium cation to the corresponding dihydro deriv. (BNAH) with no formation of half-reduced dimers, while BNAH was not consumed even after log-term irradn. The regioselectivity of BNAH formed can be controlled by selection of ligands of the photocatalysts. A novel type of photocatalysis proceeds via the photosubstitution of a pyridine ligand of the Ru complexes followed by the photoformation of [Ru(tpy)(bpy)H+] or [Ru(bpy)2(py)H]+. [on SciFinder(R)]