A set of new class benzimidazole-derived dinuclear cobalt complexes, [CoII2(L1)2] (1) and [CoII2(L2)2] (2) as molecular electrocatalysts are employed in a homogeneous system for electrocatalytic proton reduction (where L1= 2-{[2-(8-hydroxyquinolin-2-yl)-1H-benzimidazol-1-yl]methyl}quinolin-8-ol...

Quinoline‐based benzimidazole compounds have been successfully synthesized and characterized by various spectroscopic techniques like FT‐IR, 1H NMR, 13C NMR, and mass spectral analysis, and the structures have been authenticated by single crystal X‐ray diffraction method. Here, we report an economical, mild, and efficient procedure that involves condensation of 8‐hydroxyquinoline‐2‐carbaldehyde with various diamines as substrates to give bis‐imines. A systematic study towards both aliphatic and aromatic bis‐imines has been conducted to investigate the ring‐closure reaction that generates the benzimidazole moiety in the heterocyclic compounds discussed in this study. Aliphatic bis‐imines does not undergo cyclization; however, the bis‐imines derived from o‐phenylenediamine and derivatives generates heterocyclic compounds with benzimidazole moiety. In contrast to synthetic procedures reported earlier for benzimidazoles, the reaction conditions herein reported are simpler. Path for reactions holds initial condensation with one equivalent of 8‐hydroxyquinoline‐2‐carbaldehyde to form mono‐imine followed by immediate intramolecular ring closure. The subsequent nupleophilic attack to another equivalent of 8‐hydroxyquinoline‐2‐carbaldehyde and migration of hydride generates the benzimidazole moiety and the active methylene group. The ─CH2 group was confirmed from 1H and 13C NMR, wherein the two hydrogens appeared at around 6.40–6.52 ppm and the carbon center appeared at 51.54–51.77 ppm. The single crystal X‐ray diffraction also confirmed the formation of benzimidazole moiety and the active methylene group in the heterocyclic compounds discussed in this study.

The new ligand pyridin-4-yl) quinoline) and the corresponding aqua complex [Ru(Qltpy)(bpy)(OH 2 )](PF 6 ) 2 (1) have been synthesized and characterized by the different spectroscopic methods. This complex shows two pK a values, pK a 1 due to the deprotonation from the protonated N atom located on the quinoline moiety at 3.0 and another pK a 2 at 10.5 due to the deprotonation from aqua ligand. The catalytic activity of the complex 1 towards water oxidation was studied in CF 3 SO 3 H solution (pH % 1) using Ce IV as an oxidant. The free N atom of the substituted quinoline moiety of the complex gets protonated at pH % 1 and acts as an electron withdrawing group instead of electron donating group. Due to the electron withdrawing effect it shows a lower catalytic activity towards chemical water oxidation having turnover number (TON) of 18 (out of 25) and initial turnover frequency (TOF) 0.003 s À1 as compared to the previously reported [Ru II (QCl-tpy)(bpy)(H 2 O)] 2 + complex.[a] J.

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