Reduced State of Iridium PCP Pincer Complexes in Electrochemical CO₂ Hydrogenation

Abstract

We present a computational study on the mechanism for electrochemical reduction of CO2 using a PCP pincer iridium­(III) dihydride complex. Our results point toward a mechanism that involves an in situ-generated iridium­(I) hydride as the active species for the CO2 to formate reduction. The iridium­(III) path can operate in parallel but is associated with higher activation free energies in the reaction between the metal hydride and CO2, compared to the reaction at the in situ-generated iridium­(I) species.

Proton Independent Electrocatalytic Transfer Hydrogenation of Styrene with [(tBuPCP)Ir(H)(Cl)] and Water

“…In fact, based on quantum chemical calculations by Ahlquist et al an anionic hydride species related to 2, but in a ( tBu POCOP) pincer ligand environment, was previously proposed as the active species for electrochemical CO 2 reduction to formate with the POCOP analogue of complex 1. 40,41 Further experimental evidence for the existence of such previously only theoretically proposed anionic Ir(I) hydrides like 2, is now provided by negative mode LIFDI-MS data (liquid injection field desorption/ionization mass spectrometry) obtained from in situ reduced solutions of 1 that were treated with electride solutions of [K(2.2.…”

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

“…The electrochemical observations suggest that the catalyst resides largely as 59a in the electrocatalytic steady state, whereas 59 is the reactive specie (Scheme 41). In 2016, Ahlquist performed computational studies on the electrochemical CO 2 hydrogenation catalyzed by the iridium complex 59, identifying the in situ reduced cationic iridium(I)-H complex as the active specie for the transformation [581].…”

“…Catalysts 2020, 10, 773 32 of 115 catalyzed by the iridium complex 59, identifying the in situ reduced cationic iridium(I)-H complex as the active specie for the transformation [581]. Müller investigated the insertion of CO2 into metal-phenoxide bonds using homogeneous cobalt and zinc catalysts typically used in the copolymerization of epoxides and CO2 and shown in Figure 4 [582].…”

DataSheet1.PDF

“…A large number of pincer catalysts have been developed for various catalytic applications. (Bernskoetter and Hazari, 2017;Irina et al, 2016;Garbe et al, 2019;Kumar et al, 2019;Kar et al, 2020;Wen et al, 2021). However, PNP and PCP pincer complexes have been studied mostly than NNN pincer complexes (Bernskoetter and Hazari, 2017;Bertini et al, 2016;Kar et al, 2019;Tang et al, 2019).…”

“…In this context, Mn pincer complexes in catalytic carbon dioxide hydrogenation have seen much progress over a much shorter time (Bertini et al, 2017;Garbe et al, 2017;Kar et al, 2017). The PNP, PCP PNN pincer complexes have been commonly used to develop transition metal pincer complexes (Kumar et al, 2019;Bernskoetter and Hazari, 2017;Irina et al, 2016;Bertini et al, 2016;Jan et al, 2020). It is necessary to understand the donor-acceptor strength of the ligand during the rational ligand designing for new catalyst development.…”