Unraveling the mechanism of water oxidation catalyzed by nonheme iron complexes
dc.contributor.author
dc.date.accessioned
2015-03-25T12:00:04Z
dc.date.available
2015-03-25T12:00:04Z
dc.date.issued
2014
dc.identifier.issn
0947-6539
dc.identifier.uri
dc.description.abstract
Density functional theory (DFT) is employed to: 1)propose a viable catalytic cycle consistent with our experimental results for the mechanism of chemically driven (CeIV) O2 generation from water, mediated by nonheme iron complexes; and 2)to unravel the role of the ligand on the nonheme iron catalyst in the water oxidation reaction activity. To this end, the key features of the water oxidation catalytic cycle for the highly active complexes [Fe(OTf)2(Pytacn)] (Pytacn: 1-(2′-pyridylmethyl)-4,7- dimethyl-1,4,7-triazacyclononane; OTf: CF3SO3 -) (1) and [Fe(OTf)2(mep)] (mep: N,N′-bis(2-pyridylmethyl)-N, N′-dimethyl ethane-1,2-diamine) (2) as well as for the catalytically inactive [Fe(OTf)2(tmc)] (tmc: N,N′,N″,N″′- tetramethylcyclam) (3) and [Fe(NCCH3)(MePy 2CH-tacn)](OTf)2 (MePy2CH-tacn: N-(dipyridin-2-yl)methyl)-N′,N″-dimethyl-1,4,7-triazacyclononane) (4) were analyzed. The DFT computed catalytic cycle establishes that the resting state under catalytic conditions is a [FeIV(O)(OH 2)(LN4)]2+ species (in which LN 4=Pytacn or mep) and the rate-determining step is the O-O bond-formation event. This is nicely supported by the remarkable agreement between the experimental (ΔG≠=17.6±1.6kcalmol -1) and theoretical (ΔG≠=18.9kcalmol -1) activation parameters obtained for complex 1. The O-O bond formation is performed by an iron(V) intermediate [FeV(O)(OH)(LN 4)]2+ containing a cis-FeV(O)(OH) unit. Under catalytic conditions (CeIV, pH0.8) the high oxidation state Fe V is only thermodynamically accessible through a proton-coupled electron-transfer (PCET) process from the cis-[FeIV(O)(OH 2)(LN4)]2+ resting state. Formation of the [FeV(O)(LN4)]3+ species is thermodynamically inaccessible for complexes 3 and 4. Our results also show that the cis-labile coordinative sites in iron complexes have a beneficial key role in the O-O bond-formation process. This is due to the cis-OH ligand in the cis-Fe V(O)(OH) intermediate that can act as internal base, accepting a proton concomitant to the O-O bond-formation reaction. Interplay between redox potentials to achieve the high oxidation state (FeVO) and the activation energy barrier for the following O-O bond formation appears to be feasible through manipulation of the coordination environment of the iron site. This control may have a crucial role in the future development of water oxidation catalysts based on iron. Give me a high 5! The full DFT catalytic cycle for the water oxidation mediated by nonheme iron complexes has allowed the identification of the key steps in this reaction as: 1)FeIV/Fe V, and 2)the energy barrier for the O-O bond formation (see figure). This may have a crucial role in the future development of water oxidation catalysts based on iron
dc.description.sponsorship
We thank European Research Foundation for project FP7-PEOPLE-2010-ERG-268445 (J.L.-F.) and ERC-2009-StG-239910 (M. C.), MICINN for projects CTQ2009-08464 (M. C.) and CTQ2011-23156/BQU (J.M.L.), for a Ramon y Cajal con-tract (J.L.-F.) and Generalitat de Catalunya for an ICREA Academia Award and project 2009SGR637, and the RahuCat is acknowledged by a generous gift of tritosylTACN
dc.format.mimetype
application/pdf
dc.language.iso
eng
dc.publisher
Wiley-VCH Verlag
dc.relation
MICINN/PN 2010-2012/CTQ2009-08464
info:eu-repo/grantAgreement/MICINN//CTQ2011-23156/ES/AVANCES EN CATALISIS Y AROMATICIDAD/
AGAUR/2009-2014/2009 SGR-637
dc.relation.isformatof
Reproducció digital del document publicat a: http://dx.doi.org/10.1002/chem.201304367
dc.relation.ispartof
© Chemistry - A European Journal, 2014, vol. 20, p. 5696-5707
dc.relation.ispartofseries
Articles publicats (D-Q)
dc.rights
Tots els drets reservats
dc.subject
dc.title
Unraveling the mechanism of water oxidation catalyzed by nonheme iron complexes
dc.type
info:eu-repo/semantics/article
dc.rights.accessRights
info:eu-repo/semantics/embargoedAccess
dc.embargo.terms
Cap
dc.date.embargoEndDate
info:eu-repo/date/embargoEnd/2026-01-01
dc.relation.projectID
info:eu-repo/grantAgreement/EC/FP7/268445/EU/Modular Ligands for Water Splitting/WATERSPLIT
info:eu-repo/grantAgreement/EC/FP7/239910/EU/Bio-inspired Design of Catalysts for Selective Oxidations of C-H and C=C Bonds/BIDECASEOX
dc.type.version
info:eu-repo/semantics/publishedVersion
dc.identifier.doi
dc.identifier.idgrec
019139
dc.contributor.funder
dc.relation.ProjectAcronym
dc.identifier.eissn
1521-3765