A Cobalt(III)−Hydroxo Complex Bearing a Pentadentate Amidate Ligand as an Electrocatalyst for Water Oxidation

Abstract

A Co(III)−hydroxo complex, [CoIII(dpaq)OH]ClO4 (1‐OH) bearing a pentadentate ligand, H‐dpaq, (H‐dpaq=(2‐[bis(pyridin‐2‐ylmethyl)]amino‐N‐quinolin‐8‐yl‐acetamidate]) catalyses water oxidation in mildly alkaline medium (pH 8.0) at a potential of 1.4 VNHE with an average Turn‐Over‐Frequency (TOFmax) of 2.8×104 s−1 and faradaic efficiency of 88 %. Post‐electrolysis characterization of the electrode rules out the formation of any heterogeneous electroactive species. Electrochemical results and theoretical calculations confirm the occurrence of both metal and ligand centered PCET processes during anodic scanning. The resulting formally Co(V)−oxo/oxyl intermediate undergoes water nucleophilic attack to install the O−O bond. The role of axial ligand in water oxidation by Co(III)−dpaq system has been examined by comparing the reactivity of the Co‐hydroxide complex (1‐OH) with that of its chloride‐ligated counterpart, [CoIII(dpaq)Cl]Cl (1‐Cl). The results confirm the ability of the Co‐dpaq complexes to bind water/or water derived ligands over chloride or non‐aqueous solvents. The interplay of ligand redox non‐innocence and σ‐donating ability of the N5‐carboxamido ligand helps to store oxidizing equivalents and triggers O−O bond formation.

C–H bond activation by high-valent iron/cobalt–oxo complexes: a quantum chemical modeling approach

“…Here, our calculated spin state energies also match with previously studied Co III -OH complexes. 47 Additionally, we have also computed the qualitative molecular orbital diagram of this intermediate, which demonstrated the occupancy of all six electrons in the d-orbitals (see Fig. S7 of the ESI †).…”

“…Here, our calculated spin state energies also match with previously studied Co III –OH complexes. 47…”

Deciphering the active species and reaction mechanism in water oxidation catalyzed by a copper complex with redox-active ligands

“…Consequently, there is a pressing need to explore cost-effective and efficient alternatives in the form of base metal catalysts for water oxidation. Over the past decade, considerable attention has been directed towards firstrow transition metals, specifically Mn-, [12][13][14] Fe-, 15,16 Co-, 17,18 Ni-, 19 and Cu-based [20][21][22][23][24][25] water oxidation catalysts (WOCs), leading to notable advancements.…”