Photoinduced hydrogen evolution with new tetradentate cobalt(ii) complexes based on the TPMA ligand

Abstract

Hydrogen production from water splitting is nowadays recognized as a target, fundamental reaction for the production of clean fuels. Indeed, tremendous efforts have been devoted towards the research of suitable catalysts capable of performing this reaction. With respect to heterogeneous systems, molecular catalysts such as metal complexes are amenable to chemical functionalization in order to fine tune the catalytic properties. In this paper a new class of tris(2-pyridylmethyl)-amine (TPMA) cobalt(ii) complexes (CoL0-4) has been synthesized and employed as hydrogen evolving catalysts under photochemical conditions taking advantage of Ru(bpy)3(2+) (where bpy is 2,2'-bipyridine) as a light-harvesting sensitizer and ascorbic acid as a sacrificial electron donor. Tuning of the photocatalytic activity has been attempted through the introduction of different substituents at the catalyst periphery rather than through a direct chemical modification of the chelating TPMA ligand. The results show that CoL0-4 behave as competent hydrogen evolving catalysts (HECs), although the effects played by the different substituents on the catalysis are relatively modest. Possible reasons supporting the observed behavior as well as possible improvements of the aforementioned tuning approach are discussed.

Electro‐ and Photocatalytic Generation of H2 Using a Distinctive CoII “PN3P” Pincer Supported Complex with Water or Saturated Saline as a Hydrogen Source

“…Examples include N‐macrocyclic complexes, cobalt thiolates, glyoxime‐based compounds, complexes with heterocyclic carbene ligands, and cobalt complexes bearing polyphosphine ligands . Polypyridyl ligation afforded complexes that in some cases use water as a substrate and are among the most efficient homogeneous catalyst for H 2 generation . These include Co complexes of 2,6‐bis(1,1‐bis(2‐pyridyl)ethyl)pyridine (“PY5Me2”) and a Co III complex of the pentadentate bis(2‐pyridylmethyl)‐2,2′‐bipyridine‐6‐methanamine (DPA‐Bpy) ligand .…”

“…This strategy has been exploited to prepareH 2 -evolvingc atalysts for av ariety of cobalt complexes. [28][29][30][31][32][33][34][35][36][37][38][39] These include Co complexes of 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine ("PY5Me2") and aC o III complex of the pentadentate bis(2-pyridylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy) ligand. [25][26][27] Polypyridyl ligation afforded complexes that in somec ases use water as as ubstrate and are among the mostefficienthomogeneous catalystfor H 2 genera-tion.…”

“…[25][26][27] Polypyridyl ligation afforded complexes that in somec ases use water as as ubstrate and are among the mostefficienthomogeneous catalystfor H 2 genera-tion. [28][29][30][31][32][33][34][35][36][37][38][39] These include Co complexes of 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine ("PY5Me2") and aC o III complex of the pentadentate bis(2-pyridylmethyl)-2,2'-bipyridine-6-methanamine (DPA-Bpy) ligand. [40] Importantly,amajority of these complexes requiret he presenceo fa cids as the sourceo fh ydrogen in order to electrocatalytically produce H 2 in polar organic solvents.…”

Hydrogen Evolution by FeIII Molecular Electrocatalysts Interconverting between Mono and Di‐Nuclear Structures in Aqueous Phase

“…Hydrogen evolution is confirmed by controlled‐potential electrolysis at −1.79 V versus SCE (∼0.25 cm 2 carbon paper as working electrode), with a faradaic yield (FY) of 50 % (Figure S9) . The intensity of i cat (i.e., the catalytic peak current) shows a linear dependence with [TFA] up to about 10 m m (inset in Figure ), corresponding to a global second‐order reaction in acid . This observation is consistent with the formation of a metal hydride as the reactive intermediate, then collapsing to H 2 by a proton–hydride reaction.…”

Effects of Position and Electronic Nature of Substituents on Cobalt‐Porphyrin‐Catalyzed Hydrogen Evolution Reaction

“…Fc + /Fc . Hydrogen evolution activity of metallo‐porphyrins, phthalocyanines and corroles can be tuned by modifying electronic nature of the substituents of the supporting ligand . Apart from that, designing catalysts with amines as functional groups for efficient H 2 evolution has attracted significant attention because nature has used this strategy in the iron–only hydrogenase to deliver protons to the active site so that a high turnover number of hydrogen evolution can be achieved .…”