1 research outputs found
Iridium(III) Bis-Pyridine-2-Sulfonamide Complexes as Efficient and Durable Catalysts for Homogeneous Water Oxidation
A family of tetradentate bisÂ(pyridine-2-sulfonamide)
(bpsa) compounds was synthesized as a ligand platform for designing
resilient and electronically tunable catalysts capable of performing
water oxidation catalysis and other processes in highly oxidizing
environments. These wrap-around ligands were coordinated to IrÂ(III)
octahedrally, forming an anionic complex with chloride ions bound
to the two remaining coordination sites. NMR spectroscopy documented
that the more rigid ligand frameworksî—¸[IrÂ(bpsa-Cy)ÂCl<sub>2</sub>]<sup>−</sup> and [IrÂ(bpsa-Ph)ÂCl<sub>2</sub>]<sup>−</sup>î—¸produced <i>C</i><sub>1</sub>-symmetric complexes,
while the complex with the more flexible ethylene linker in [IrÂ(bpsa-en)ÂCl<sub>2</sub>]<sup>−</sup> displays <i>C</i><sub>2</sub> symmetry. Their electronic structure was explored with DFT calculations
and cyclic voltammetry in nonaqueous environments, which unveiled
highly reversible IrÂ(III)/IrÂ(IV) redox processes and more complex,
irreversible reduction chemistry. Addition of water to the electrolyte
revealed the ability of these complexes to catalyze the water oxidation
reaction efficiently. Electrochemical quartz crystal microbalance
studies confirmed that a molecular species is responsible for the
observed electrocatalytic behavior and ruled out the formation of
active IrO<sub><i>x</i></sub>. The electrochemical studies
were complemented by work on chemically driven water oxidation, where
the catalytic activity of the iridium complexes was studied upon exposure
to ceric ammonium nitrate, a strong, one-electron oxidant. Variation
of the catalyst concentrations helped to illuminate the kinetics of
these water oxidation processes and highlighted the robustness of
these systems. Stable performance for over 10 days with thousands
of catalyst turnovers was observed with the <i>C</i><sub>1</sub>-symmetric catalysts. Dynamic light scattering experiments
ascertained that a molecular species is responsible for the catalytic
activity and excluded the formation of IrO<sub><i>x</i></sub> particles