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Redox Metal-Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes

Garrido-Barros, Pablo and Moonshiram, Dooshaye and Gil-Sepulcre, Marcos and Pelosin, Primavera and Gimbert-Suriñach, Carolina and Benet-Buchholz, Jordi and Llobet, Antoni (2020) Redox Metal-Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes. Journal of the American Chemical Society, 142 (41). pp. 17434-17446. ISSN 0002-7863. https://resolver.caltech.edu/CaltechAUTHORS:20200924-144350658

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Abstract

Water oxidation catalysis stands out as one of the most important reactions to design practical devices for artificial photosynthesis. Use of late first-row transition metal (TM) complexes provides an excellent platform for the development of inexpensive catalysts with exquisite control on their electronic and structural features via ligand design. However, the difficult access to their high oxidation states and the general labile character of their metal–ligand bonds pose important challenges. Herein, we explore a copper complex (1²⁻) featuring an extended, π-delocalized, tetra-amidate macrocyclic ligand (TAML) as water oxidation catalyst and compare its activity to analogous systems with lower π-delocalization (2²⁻ and 3²⁻). Their characterization evidences a special metal–ligand cooperativity in accommodating the required oxidative equivalents using 1²⁻ that is absent in 2²⁻ and 3²⁻. This consists of charge delocalization promoted by easy access to different electronic states at a narrow energy range, corresponding to either metal-centered or ligand-centered oxidations, which we identify as an essential factor to stabilize the accumulated oxidative charges. This translates into a significant improvement in the catalytic performance of 1²⁻ compared to 2²⁻ and 3²⁻ and leads to one of the most active and robust molecular complexes for water oxidation at neutral pH with a k_(obs) of 140 s⁻¹ at an overpotential of only 200 mV. In contrast, 2²⁻ degrades under oxidative conditions, which we associate to the impossibility of efficiently stabilizing several oxidative equivalents via charge delocalization, resulting in a highly reactive oxidized ligand. Finally, the acyclic structure of 3²⁻ prevents its use at neutral pH due to acidic demetalation, highlighting the importance of the macrocyclic stabilization.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1021/jacs.0c06515DOIArticle
ORCID:
AuthorORCID
Garrido-Barros, Pablo0000-0002-1489-3386
Moonshiram, Dooshaye0000-0002-9075-3035
Gil-Sepulcre, Marcos0000-0002-2839-8108
Pelosin, Primavera0000-0003-4646-7223
Gimbert-Suriñach, Carolina0000-0002-4412-7607
Benet-Buchholz, Jordi0000-0003-3984-3550
Llobet, Antoni0000-0002-6176-5272
Additional Information:© 2020 American Chemical Society. Received: June 20, 2020; Published: September 16, 2020. Support from MINECO, FEDER, and AGAUR is gratefully acknowledged (CTQ2016-80058-R, SEV-2013-0319, ENE2016-82025-REDT, CTQ2016-81923-REDC, and 2017-SGR-1631). P.G.-B acknowledges the “La Caixa” Foundation for the Ph.D. grant. D.M. acknowledges support from the Severo Ochoa Excellence program (SEV-2016-0686) from the Instituto IMDEA Nanociencia Acciones de Dinamization Europa Investigacion grant (EIN2019-103399), and the “Ministerio de Ciencia, Innovacion y Universidades Grant” (PID2019-111086RA-I00). XAS experiments were performed at the CLAESS beamline at ALBA Synchrotron with the beamline support of the ALBA staff under proposal no. 2016091818 and additionally used resources of sector 20 beamline at the Advanced Photon Source (APS) at Argonne National Laboratory. Sector 20 beamline at APS is operated by the U.S DOE, under contract no. DE-AC02-06CH11357 and the Canadian Light Source. Author Contributions: All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest. Notes: CIF files for complexes 12–, 1–, 22–, and 2– with CCDC numbers 1959709–1959712 are available at https://www.ccdc.cam.ac.uk/.
Funders:
Funding AgencyGrant Number
Ministerio de Economía, Industria y Competitividad (MINECO)CTQ2016-80058-R
Ministerio de Economía, Industria y Competitividad (MINECO)SEV-2013-0319
Ministerio de Economía, Industria y Competitividad (MINECO)ENE2016-82025-REDT
Ministerio de Economía, Industria y Competitividad (MINECO)CTQ2016-81923-REDC
Agencia de Gestión de Ayudas Universitarias y de Investigación2017-SGR-1631
Fondo Europeo de Desarrollo Regional (FEDER)UNSPECIFIED
La Caixa FoundationUNSPECIFIED
Severo OchoaSEV-2016-0686
Acciones de Dinamización Europa InvestigacionEIN2019-103399
Ministerio de Ciencia e Innovación (MCINN)PID2019-111086RA-I00
ALBA Synchrotron2016091818
Department of Energy (DOE)DE-AC02-06CH11357
Canadian Light SourceUNSPECIFIED
Issue or Number:41
Record Number:CaltechAUTHORS:20200924-144350658
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200924-144350658
Official Citation:Redox Metal–Ligand Cooperativity Enables Robust and Efficient Water Oxidation Catalysis at Neutral pH with Macrocyclic Copper Complexes Pablo Garrido-Barros, Dooshaye Moonshiram, Marcos Gil-Sepulcre, Primavera Pelosin, Carolina Gimbert-Suriñach, Jordi Benet-Buchholz, and Antoni Llobet Journal of the American Chemical Society 2020 142 (41), 17434-17446 DOI: 10.1021/jacs.0c06515
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105520
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:24 Sep 2020 22:56
Last Modified:14 Oct 2020 21:31

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