Pentadentate ligands containing polypyridyl systems can provide metal complexes with hexa coordination having a labile sixth site which is usually occupied by a solvent molecule. The polypyridyl group stabilizes the metal complex and several reports have been published with tetra and pentadendate polypyridyl complexes. Recently we have reported the synthesis and characterization of mononuclear Co complexes, [Co(DPA-Bpy)Cl]Cl (1a) and [Co(DPA-Bpy)(H2O)](PF6)3 (1b), with a pentadentate ligand (DPA-Bpy = N,N-bis(2-pyridinylmethyl)-2,2'-bipyridine-6-methanamine). The complex 1b was found to be a good catalyst for electro- and photocatalytic H2 evolution in aqueous solution (Figure 1). The overpotential for complex 1b for electrocatalytic H2 evolution was found to be 600 mV in pH 7 buffer.3 Tuning the DPA-Bpy ligand scaffolds to get more efficient catalysts with lower overpotentials, high activity is an interesting protocol. Introducing electron withdrawing groups into the ligand scaffold may reduce overpotential while maintaining the activity. In this context, we have designed a new catalyst by introducing pyridine groups with more electron-withdrawing carboxyester moiety which may result in more positive potentials and lower overpotentials in electrocatalytic hydrogen evolution from aqueous media. Hydrolysis of ester can provide carboxylic acid groups which can produce a hydrophilic environment around the cobalt center.

Synthesis of Co-complexes with pentadentate ligands for catalytic hydrogen evolution

249th National Meeting (2015)

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