Redox-Induced Structural Switching through Sporadic Pyridine-Bridged Co^IICo^II Dimer and Electrocatalytic Proton Reduction

Abstract

The homodinuclear CoII helicate complex [CoII(DQPD)]2 (1) was prepared by treating [Co­(H2O)6]­(ClO4)2 with the deprotonated form of the ligand N 2,N 6-bis­(quinolin-8-yl)­pyridine-2,6-dicarboxamide (DQPDH2). Complex 1 represents a discrete homodinuclear helicate complex with two CoII centers having a distorted-octahedral geometry through an unprecedented pyridine bridge. Complex 1, upon treatment with H2O2, undergoes oxidation at one of the CoII centers followed by a structural deformation to generate the mixed-valence complex [CoIIICoII(DQPD)2]­(ClO4) (2·ClO 4 ). In complex 2, the bridging through the central pyridine collapses along with the formation of Co­(III) octahedral and Co­(II) tetrahedral environments. Complexes 1 and 2 interconvert to one another. The effective magnetic moments for complexes 1 and 2 are respectively 5.88 and 4.30 μB. Complexes 1 and 2 have been employed for electrocatalytic proton reduction using AcOH as the proton source in 95/5 (v/v) DMF/H2O. A TOF of 30000 mmol of H2 h–1 (mol of 1)−1 at a potential of −1.7 V vs SCE was achieved. A resting-state analysis has been carried out to support the mechanism for the catalytic proton reduction.

Electrocatalytic proton reduction by dinuclear cobalt complexes in a nonaqueous electrolyte

“…The cyclic-voltammogram of similar types of dinuclear complexes have been reported in the literature. 19,22 a ,23 Furthermore, the catalyst exhibited four reductions at E 1/2 = −1.39 V, −1.61 V, −1.70 V, and E 1/2 = −1.90 V vs. SCE. The peak E 1/2 = −1.39 V and E 1/2 = −1.90 V vs. SCE were assigned to ligand-centered reductions, whereas the reductions at −1.61 V and −1.70 V vs. SCE are due to the Co II Co II /Co II Co I and Co II Co I /Co I Co I peaks, respectively.…”

“…This preference of active participation of the reductively formed Co III –H intermediate in the generation of H 2 agrees with the reports suggested by some research groups. 22 a ,23…”

“…The formation of the [Co( ii )Co( ii )–H] species as an active intermediate drives the reduction process. 23 Therefore, as a part of this ongoing research on dinuclear analogs, our group successfully incorporated two metal cores into the benzimidazole-derived ligand scaffold that catalyzed the system to generate hydrogen in an organic medium. Benzimidazole-derived ligands serve as a potential scaffold for designing electrocatalysts due to their high metal-binding affinity, high stability under catalytic conditions, and ease of synthesis.…”

Electrocatalytic hydrogen production by dinuclear cobalt(ii) compounds containing redox-active diamidate ligands: a combined experimental and theoretical study

“…The cationic compounds 3 and 4 constitute rare examples of mixedvalent species with topologically adjacent octahedral (N 6 ) and tetrahedral (N 4 ) coordination environments for the Co(III) and Co(II) ions. 52 Both neutral complexes were then investigated for electrocatalytic proton reduction activity in DMF with AcOH as a proton source. Compound 2, in which the electron donating tert-butyl group has been incorporated into the 4-position of the pyridine moiety, exhibited higher activity than its unsubstituted analogue 1 and thus, the electron donating substituent has a positive impact on the turnover frequency.…”

Distinct Bimetallic Cooperativity Among Water Reduction Catalysts Containing [CoIIICoIII], [NiIINiII], and [ZnIIZnII] Cores

“…Structural cooperativity seems prevalent in the work by Padhi et al [10] . based on a di(quinolino)pyridine ligand that gave a bridged [Co II (μ‐pyridine)Co II ] core with Co⋅⋅⋅Co=3.13 Å.…”