Successive heterolytic cleavages of H2 achieve N2 splitting on silica-supported tantalum hydrides: A DFT proposed mechanism

Handle URI:
http://hdl.handle.net/10754/562239
Title:
Successive heterolytic cleavages of H2 achieve N2 splitting on silica-supported tantalum hydrides: A DFT proposed mechanism
Authors:
Soláns, Xavier Luis; Chow, Catherine; Gouré, Eric; Kaya, Yasemin; Basset, Jean-Marie ( 0000-0003-3166-8882 ) ; Taoufik, Mostafa; Quadrelli, Elsje Alessandra; Eisenstein, Odile
Abstract:
DFT(B3PW91) calculations have been carried out to propose a pathway for the N2 cleavage by H2 in the presence of silica-supported tantalum hydride complexes [(≡ SiO)2TaHx] that forms [(≡SiO)2Ta(NH)(NH2)] (Science2007, 317, 1056). The calculations, performed on the cluster models {μ-O[(HO)2SiO] 2}TaH1 and {μ-O[(HO)2SiO] 2}TaH3, labelled as (≡SiO)2TaH x (x = 1, 3), show that the direct hydride transfers to coordinated N-based ligands in (≡SiO)2TaH(η2-N2) and (≡SiO)2TaH(η2-HNNH) have high energy barrier barriers. These high energy barriers are due in part to a lack of energetically accessible empty orbitals in the negatively charged N-based ligands. It is shown that a succession of proton transfers and reduction steps (hydride transfer or 2 electron reduction by way of dihydride reductive coupling) to the nitrogen-based ligands leads to more energetically accessible pathways. These proton transfers, which occur by way of heterolytic activation of H2, increase the electrophilicity of the resulting ligand (diazenido, N 2H-, and hydrazido, NHNH2-, respectively) that can thus accept a hydride with a moderate energy barrier. In the case of (≡SiO)2TaH(η2-HNNH), the H 2 molecule that is adding across the Ta-N bond is released after the hydride transfer step by heterolytic elimination from (≡SiO) 2TaH(NH2)2, suggesting that dihydrogen has a key role in assisting the final steps of the reaction without itself being consumed in the process. This partly accounts for the experimental observation that the addition of H2 is needed to convert an intermediate, identified as a diazenido complex [(≡SiO)2TaH(η 2-HNNH)] from its ν(N-H) stretching frequency of 3400 cm -1, to the final product. Throughout the proposed mechanism, the tantalum remains in its preferred high oxidation state and avoids redox-type reactions, which are more energetically demanding. © 2012 American Chemical Society.
KAUST Department:
KAUST Catalysis Center (KCC); Physical Sciences and Engineering (PSE) Division; Chemical Science Program
Publisher:
American Chemical Society
Journal:
Inorganic Chemistry
Issue Date:
2-Jul-2012
DOI:
10.1021/ic300498b
PubMed ID:
22712747
Type:
Article
ISSN:
00201669
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Chemical Science Program; KAUST Catalysis Center (KCC)

Full metadata record

DC FieldValue Language
dc.contributor.authorSoláns, Xavier Luisen
dc.contributor.authorChow, Catherineen
dc.contributor.authorGouré, Ericen
dc.contributor.authorKaya, Yaseminen
dc.contributor.authorBasset, Jean-Marieen
dc.contributor.authorTaoufik, Mostafaen
dc.contributor.authorQuadrelli, Elsje Alessandraen
dc.contributor.authorEisenstein, Odileen
dc.date.accessioned2015-08-03T09:57:37Zen
dc.date.available2015-08-03T09:57:37Zen
dc.date.issued2012-07-02en
dc.identifier.issn00201669en
dc.identifier.pmid22712747en
dc.identifier.doi10.1021/ic300498ben
dc.identifier.urihttp://hdl.handle.net/10754/562239en
dc.description.abstractDFT(B3PW91) calculations have been carried out to propose a pathway for the N2 cleavage by H2 in the presence of silica-supported tantalum hydride complexes [(≡ SiO)2TaHx] that forms [(≡SiO)2Ta(NH)(NH2)] (Science2007, 317, 1056). The calculations, performed on the cluster models {μ-O[(HO)2SiO] 2}TaH1 and {μ-O[(HO)2SiO] 2}TaH3, labelled as (≡SiO)2TaH x (x = 1, 3), show that the direct hydride transfers to coordinated N-based ligands in (≡SiO)2TaH(η2-N2) and (≡SiO)2TaH(η2-HNNH) have high energy barrier barriers. These high energy barriers are due in part to a lack of energetically accessible empty orbitals in the negatively charged N-based ligands. It is shown that a succession of proton transfers and reduction steps (hydride transfer or 2 electron reduction by way of dihydride reductive coupling) to the nitrogen-based ligands leads to more energetically accessible pathways. These proton transfers, which occur by way of heterolytic activation of H2, increase the electrophilicity of the resulting ligand (diazenido, N 2H-, and hydrazido, NHNH2-, respectively) that can thus accept a hydride with a moderate energy barrier. In the case of (≡SiO)2TaH(η2-HNNH), the H 2 molecule that is adding across the Ta-N bond is released after the hydride transfer step by heterolytic elimination from (≡SiO) 2TaH(NH2)2, suggesting that dihydrogen has a key role in assisting the final steps of the reaction without itself being consumed in the process. This partly accounts for the experimental observation that the addition of H2 is needed to convert an intermediate, identified as a diazenido complex [(≡SiO)2TaH(η 2-HNNH)] from its ν(N-H) stretching frequency of 3400 cm -1, to the final product. Throughout the proposed mechanism, the tantalum remains in its preferred high oxidation state and avoids redox-type reactions, which are more energetically demanding. © 2012 American Chemical Society.en
dc.publisherAmerican Chemical Societyen
dc.titleSuccessive heterolytic cleavages of H2 achieve N2 splitting on silica-supported tantalum hydrides: A DFT proposed mechanismen
dc.typeArticleen
dc.contributor.departmentKAUST Catalysis Center (KCC)en
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical Science Programen
dc.identifier.journalInorganic Chemistryen
dc.contributor.institutionDepartament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spainen
dc.contributor.institutionUniversité de Lyon, Institut de Chimie de Lyon, C2P2 (CNRS, CPE Lyon, Université Lyon 1), Ecole Supérieure de Chimie Physique Electronique de Lyon, 43 Boulevard du 11 Novembre 1918, F-69616 Villeurbanne Cedex, Franceen
dc.contributor.institutionInstitut Charles Gerhardt, UMR 5253 CNRS, Université Montpellier 2, cc 1501, Place E. Bataillon, F-34095 Montpellier, Franceen
dc.contributor.institutionDepartment of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, V6T 1Z1, Canadaen
dc.contributor.institutionLeiden Institute of Chemistry, Universiteit Leiden, P.O. Box 9502, 2300 RA Leiden, Netherlandsen
kaust.authorBasset, Jean-Marieen

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