Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H]⁺: Experimental and Computational Studies of their Hydricities, Interaction with CO₂, and Photochemistry

Abstract

We prepared two geometric isomers of [Ir(tpy)(ppy)H](+), previously proposed as a key intermediate in the photochemical reduction of CO2 to CO, and characterized their notably different ground- and excited-state interactions with CO2 and their hydricities using experimental and computational methods. Only one isomer, C-trans-[Ir(tpy)(ppy)H](+), reacts with CO2 to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH3CN/TEOA, a common reactive C-trans-[Ir(tpy)(ppy)](0) species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO2 and produces CO with the same catalytic efficiency.

A hexanuclear cobalt metal–organic framework for efficient CO2 reduction under visible light

“…[14][15][16][17] Utilizing clean and renewable solar energy as the power source to accomplish this conversion could be the most economical and environmentally friendly choice. 18 Therefore, the exploration of high-performance photocatalytic systems for CO 2 reduction has been the fundamental goal of experts. In photocatalytic systems, there are three essential steps to achieve the transition from solar energy to chemical energy, [19][20][21][22] including light harvesting, generation of electron-hole pairs, and transferring redox equivalents to reactive centers for redox reactions.…”

[Ir(tpy)(bpy)Cl] as a Photocatalyst for CO2 Reduction under Visible‐Light Irradiation

“…The proposed reaction mechanism of [Ir(tpy)(ppy)Cl] + includes the formation of a one‐electron‐reduced (OER) species, followed by the loss of the coordinated Cl − and formation of the hydride species([Ir(tpy)(ppy)H] + ) with further reduction. However, when CO 2 reduction reaction was conducted over isolated [Ir(tpy)(ppy)H] + , the [Ir(tpy)(ppy)H] + was not the active catalyst, instead the hydride complex acted as a photo acid to produce a penta‐coordinated Ir complex acting as the true active catalyst for CO 2 reduction to CO . Recently, several research groups have reported new mononuclear Ir complex photocatalysts for CO 2 reduction .…”

Metal‐Terpyridine Complexes in Catalytic Application – A Spotlight on the Last Decade

“…Mechanistic studies were performed and suggested the formation of an [Ir(tpy)(ppy)H] + intermediate, as the virtual photocatalytically active species; moreover, the formation of dinuclear complexes was discussed as one potential deactivation pathway (Figure ). The catalytic cycle, with a focus on the reaction of the [Ir(tpy)(ppy)H] + intermediate with CO 2 , was investigated in more detail by using spectroscopic and computational methods . The two possible geometrical isomers, i. e ., the C ‐ trans and the C ‐ cis hydride isomer, yielded the same penta‐coordinate two‐electron reduced [Ir(tpy)(ppy)] 0 complex within the photocatalytic cycle to which CO 2 was subsequently bound in a C ‐ trans ‐fashion.…”