Hydrogen evolution catalyzed by a cobalt complex containing an asymmetric Schiff-base ligand

Abstract

A cobalt(iii) complex containing an asymmetric Schiff-base ligand has been found to be active for proton reduction. Catalysis occurs at -1.2 V vs. Fc(+)/Fc (0.56 V vs. NHE), resulting in an overpotential of 350 mV. Additionally, the complex is active with a turnover frequency of 420 s(-1). An enhancement in activity is observed upon addition of water.

A Bis(µ‐chlorido)‐Bridged Cobalt(II) Complex with Silyl‐Containing Schiff Base as a Catalyst Precursor in the Solvent‐Free Oxidation of Cyclohexane

“…The absence of the reoxidation peak in the reverse scan indicates irreversible chemical changes of the dimeric dication upon reduction of the dicobalt core. The peak potential falls into the range reported for Co II /Co I reductions of related dinuclear Co complexes with amine–bis(phenolate) ligands,, complexes with similar Schiff bases as well as cobaltoximes, supporting the assignment performed. Further reduction at more negative potentials revealed additional irreversible reduction features with E p red = –1.85, –2.1 and –2.5 V, respectively (Figure a; II, III, IV).…”

When the Metal Makes the Difference: Template Syntheses of Tridentate and Tetradentate Salen-Type Schiff Base Ligands and Related Complexes

“…Further interactions with anions or co-crystallized solvent molecules are also present (Figure 7b). [Co( G L) 2 ](X) complexes have been deeply studied for their catalytic performances in C-C coupling reactions [44,122], asymmetric epoxidation of chalcones [131], and electrocatalytic hydrogen generation [125,132] with relevant results, but they have been also investigated as DNA binding and cleavage agents [133]. The possibility to either liberate the tridentate Schiff base or react the [M( G L) 2 ] + complexes with a second carbonyl derivative to obtain unsymmetrically substituted tetradentate Schiff base ligands coordinated to M is not reported for M = iron(III), chromium(III), and cobalt(III).…”

Role of Anation on the Mechanism of Proton Reduction Involving a Pentapyridine Cobalt Complex: A Theoretical Study

“…In recent years, finding an efficient way of producing synthetic hydrogen is the major concern for most of the researchers since it is an alternative potential molecular fuel. In this context, electrochemical oxidation of hydrogen using earth abundant metals plays an alternative route for proton reduction. , Molecular electrocatalyst is the one which involves mainly in the conversion of chemical energy into electrical energy occurred by the electrochemical oxidation of hydrogen using a metal. − In particular, the use of the most-abundant metal-based water-stable molecular electrocatalysts is a proper chemical design for the efficient hydrogen production at low overpotential. ,− In this connection, diverse ligand skeletons with iron-, cobalt-, and molybdenum-based complexes were found to generate molecular hydrogen in organic and aqueous media. ,− But they are found to produce hydrogen relatively at high overpotentials and often require the organic additives. , In order to overcome these issues, recent reports reveal that cobalt­(II) complexes containing polypyridine ligand framework is found to produce robust hydrogen in both aqueous and acetonitrile mixtures. ,− Bigi and co-workers show that tetradentate polypyridyl (Co II PY4) complexes are observed to perform catalytic hydrogen production in 1:1 water and NCMe mixtures where the proton reduction occurs at an overpotential 400 mV. The onset of electrocatalysis occurs near the Co II /Co I redox couple reveals the involvement of reduced Co­(I) species in the catalytic cycle.…”

“…2,12−15 But they are found to produce hydrogen relatively at high overpotentials and often require the organic additives. 16,17 In order to overcome these issues, recent reports reveal that cobalt(II) complexes containing polypyridine ligand framework is found to produce robust hydrogen in both aqueous and acetonitrile mixtures. 13,18−22 Bigi and coworkers 23 show that tetradentate polypyridyl (Co II PY4) complexes are observed to perform catalytic hydrogen production in 1:1 water and NCMe mixtures where the proton reduction occurs at an overpotential 400 mV.…”