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Title: Hydricity, electrochemistry, and excited-state chemistry of Ir complexes for CO 2 reduction

Here, we prepared electron-rich derivatives of [Ir(tpy)(ppy)Cl] + with modification of the bidentate (ppy) or tridentate (tpy) ligands in attempt to increase the reactivity for CO 2 reduction and the ability to transfer hydrides (hydricity). Density functional theory (DFT) calculations reveal that complexes with dimethyl-substituted ppy have similar hydricities to the non-substituted parent complex, and photocatalytic CO 2 reduction studies show selective CO formation. Substitution of tpy for bis(benzimidazole)-phenyl or -pyridine (L3 and L4, respectively) induces changes in the physical properties much more pronounced than addition of methyl groups to ppy. Theoretical data predict [Ir(L3)(ppy)(H)] is the strongest hydride donor among complexes studied in this work, but [Ir(L3)(ppy)(NCCH 3)] + cannot be reduced photochemically because the excited state reduction potential is only 0.52 V due to the negative ground state potential of –1.91 V. The excited state [Ir(L4)(ppy)(NCCH 3)] 2+ is the strongest oxidant among complexes studied in this work and the singly reduced species is formed readily upon photolysis in the presence of tertiary amines. Both [Ir(L3)(ppy)(NCCH 3)] + and [Ir(L4)(ppy)(NCCH 3)] 2+ exhibit electrocatalytic current for CO 2 reduction. While a significantly greater overpotential is needed for the L3 complex, a small amount of formate (5-10 %) generationmore » in addition to CO was observed as predicted by the DFT calculations.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [1] ;  [1] ;  [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Baruch College, CUNY, New York, NY (United States)
Publication Date:
Report Number(s):
BNL-113279-2016-JA
Journal ID: ISSN 1359-6640; FDISE6; R&D Project: CO026; KC0304030
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Faraday Discussions
Additional Journal Information:
Journal Name: Faraday Discussions; Journal ID: ISSN 1359-6640
Publisher:
Royal Society of Chemistry
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1337642

Manbeck, Gerald F., Garg, Komal, Shimoda, Tomoe, Szalda, David J., Ertem, Mehmed Z., Muckerman, James T., and Fujita, Etsuko. Hydricity, electrochemistry, and excited-state chemistry of Ir complexes for CO2 reduction. United States: N. p., Web. doi:10.1039/C6FD00223D.
Manbeck, Gerald F., Garg, Komal, Shimoda, Tomoe, Szalda, David J., Ertem, Mehmed Z., Muckerman, James T., & Fujita, Etsuko. Hydricity, electrochemistry, and excited-state chemistry of Ir complexes for CO2 reduction. United States. doi:10.1039/C6FD00223D.
Manbeck, Gerald F., Garg, Komal, Shimoda, Tomoe, Szalda, David J., Ertem, Mehmed Z., Muckerman, James T., and Fujita, Etsuko. 2016. "Hydricity, electrochemistry, and excited-state chemistry of Ir complexes for CO2 reduction". United States. doi:10.1039/C6FD00223D. https://www.osti.gov/servlets/purl/1337642.
@article{osti_1337642,
title = {Hydricity, electrochemistry, and excited-state chemistry of Ir complexes for CO2 reduction},
author = {Manbeck, Gerald F. and Garg, Komal and Shimoda, Tomoe and Szalda, David J. and Ertem, Mehmed Z. and Muckerman, James T. and Fujita, Etsuko},
abstractNote = {Here, we prepared electron-rich derivatives of [Ir(tpy)(ppy)Cl]+ with modification of the bidentate (ppy) or tridentate (tpy) ligands in attempt to increase the reactivity for CO2 reduction and the ability to transfer hydrides (hydricity). Density functional theory (DFT) calculations reveal that complexes with dimethyl-substituted ppy have similar hydricities to the non-substituted parent complex, and photocatalytic CO2 reduction studies show selective CO formation. Substitution of tpy for bis(benzimidazole)-phenyl or -pyridine (L3 and L4, respectively) induces changes in the physical properties much more pronounced than addition of methyl groups to ppy. Theoretical data predict [Ir(L3)(ppy)(H)] is the strongest hydride donor among complexes studied in this work, but [Ir(L3)(ppy)(NCCH3)]+ cannot be reduced photochemically because the excited state reduction potential is only 0.52 V due to the negative ground state potential of –1.91 V. The excited state [Ir(L4)(ppy)(NCCH3)]2+ is the strongest oxidant among complexes studied in this work and the singly reduced species is formed readily upon photolysis in the presence of tertiary amines. Both [Ir(L3)(ppy)(NCCH3)]+ and [Ir(L4)(ppy)(NCCH3)]2+ exhibit electrocatalytic current for CO2 reduction. While a significantly greater overpotential is needed for the L3 complex, a small amount of formate (5-10 %) generation in addition to CO was observed as predicted by the DFT calculations.},
doi = {10.1039/C6FD00223D},
journal = {Faraday Discussions},
number = ,
volume = ,
place = {United States},
year = {2016},
month = {12}
}

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