Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study

Alkane metathesis transforms small alkanes into their higher and lower homologues. The reaction is catalyzed by either supported d0 metal hydrides (M = Ta, W) or d0 alkyl alkylidene complexes (M = Ta, Mo, W, Re). For the silica-supported tantalum hydrides, several reaction mechanisms have been propo...

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Fecha de publicación:: 2017

Institución:: Universidad de Medellín

Repositorio:: Repositorio UDEM

Idioma:: eng

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repository_id_str
dc.title.spa.fl_str_mv	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
title	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
spellingShingle	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
title_short	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
title_full	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
title_fullStr	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
title_full_unstemmed	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
title_sort	Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study
dc.contributor.affiliation.spa.fl_str_mv	Núñez-Zarur, F., Instituto de Química, Universidad de Antioquia, Calle 70 No. 52-21, Medellín, Colombia, Facultad de Facultad de Ciencias Básicas, Universidad de Medellín, Carrera 87 No. 30-65, Medellín, Colombia Solans-Monfort, X., Departament de Química, Universitat Autònoma de Barcelona, Bellaterra, Spain Restrepo, A., Instituto de Química, Universidad de Antioquia, Calle 70 No. 52-21, Medellín, Colombia
description	Alkane metathesis transforms small alkanes into their higher and lower homologues. The reaction is catalyzed by either supported d0 metal hydrides (M = Ta, W) or d0 alkyl alkylidene complexes (M = Ta, Mo, W, Re). For the silica-supported tantalum hydrides, several reaction mechanisms have been proposed. We performed DFT-D3 calculations to analyze the viability of the proposed pathways and compare them with alkane hydrogenolysis, which is a competitive process observed at the early stages of the reaction. The results show that the reaction mechanisms for alkane metathesis and for alkane hydrogenolysis present similar energetics, and this is consistent with the fact that the process taking place depends on the concentrations of the initial reactants. Overall, a modified version of the so-called one-site mechanism that involves alkyl alkylidene intermediates appears to be more likely and consistent with experiments. According to this proposal, tantalum hydrides are precursors of the alkyl alkylidene active species. During precursor activation, H2 is released and this allows alkane hydrogenolysis to occur. In contrast, the catalytic cycle implies only the reaction with alkane molecules in excess and does not form H2. Thus, the activity for alkane hydrogenolysis decreases. The catalytic cycle proposed here implies three stages: (i) β-H elimination from the alkyl ligand, liberating ethene, (ii) alkene cross-metathesis, allowing olefin substituent exchange, and (iii) formation of the final products and alkyl alkylidene regeneration by olefin insertion and three successive 1,2-CH insertions to the alkylidene followed by α abstraction. These results relate the reactivity of silica-supported hydrides with that of the alkyl alkylidene complexes, the other common catalyst for alkane metathesis. © 2017 American Chemical Society.
publishDate	2017
dc.date.accessioned.none.fl_str_mv	2017-12-19T19:36:42Z
dc.date.available.none.fl_str_mv	2017-12-19T19:36:42Z
dc.date.created.none.fl_str_mv	2017
dc.type.eng.fl_str_mv	Article
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dc.type.driver.none.fl_str_mv	info:eu-repo/semantics/article
dc.identifier.issn.none.fl_str_mv	201669
dc.identifier.uri.none.fl_str_mv	http://hdl.handle.net/11407/4260
dc.identifier.doi.none.fl_str_mv	10.1021/acs.inorgchem.7b01464
dc.identifier.reponame.spa.fl_str_mv	reponame:Repositorio Institucional Universidad de Medellín
dc.identifier.instname.spa.fl_str_mv	instname:Universidad de Medellín
identifier_str_mv	201669 10.1021/acs.inorgchem.7b01464 reponame:Repositorio Institucional Universidad de Medellín instname:Universidad de Medellín
url	http://hdl.handle.net/11407/4260
dc.language.iso.none.fl_str_mv	eng
language	eng
dc.relation.isversionof.spa.fl_str_mv	https://www.scopus.com/inward/record.uri?eid=2-s2.0-85028926911&doi=10.1021%2facs.inorgchem.7b01464&partnerID=40&md5=3ee308857653f4bcc9e01659e1ad5acb
dc.relation.ispartofes.spa.fl_str_mv	Inorganic Chemistry Inorganic Chemistry Volume 56, Issue 17, 5 September 2017, Pages 10458-10473
dc.relation.references.spa.fl_str_mv	Adamo, C., & Barone, V. (1999). Toward reliable density functional methods without adjustable parameters: The PBE0 model. Journal of Chemical Physics, 110(13), 6158-6170. Amakawa, K., Sun, L., Guo, C., Hävecker, M., Kube, P., Wachs, I. E., . . . Trunschke, A. (2013). How strain affects the reactivity of surface metal oxide catalysts. Angewandte Chemie - International Edition, 52(51), 13553-13557. doi:10.1002/anie.201306620 Avenier, P., Solans-Monfort, X., Veyre, L., Renili, F., Basset, J. -., Eisenstein, O., . . . Quadrelli, E. A. (2009). H/D exchange on silica-grafted tantalum(V) imido amido [(≡SiO) 2Ta(V)(NH)(NH2)] synthesized from either ammonia or dinitrogen: IR and DFT evidence for heterolytic splitting of D 2. Topics in Catalysis, 52(11), 1482-1491. doi:10.1007/s11244-009-9295-0 Avenier, P., Taoufik, M., Lesage, A., Solans-Monfort, X., Baudouin, A., De Mallmann, A., . . . Quadrelli, E. A. (2007). Dinitrogen dissociation on an isolated surface tantalum atom. Science, 317(5841), 1056-1060. doi:10.1126/science.1143078 Bailey, B. C., Schrock, R. R., Kundu, S., Goldman, A. S., Huang, Z., & Brookhart, M. (2009). Evaluation of molybdenum and tungsten metathesis catalysts for homogeneous tandem alkane metathesis.Organometallics, 28(1), 355-360. doi:10.1021/om800877q Balcells, D., Clot, E., & Eisenstein, O. (2010). C-H bond activation in transition metal species from a computational perspective. Chemical Reviews, 110(2), 749-823. doi:10.1021/cr900315k Basset, J. M., Copéret, C., Lefort, L., Maunders, B. M., Maury, O., Le Roux, E., . . . Thivolle-Cazat, J. (2005). Primary products and mechanistic considerations in alkane metathesis. Journal of the American Chemical Society, 127(24), 8604-8605. doi:10.1021/ja051679f Basset, J. -., Copéret, C., Soulivong, D., Taoufik, M., & Thivolle Cazat, J. (2010). Metathesis of alkanes and related reactions. Accounts of Chemical Research, 43(2), 323-334. doi:10.1021/ar900203a Becke, A. D. (1993). Density-functional thermochemistry. III. the role of exact exchange. The Journal of Chemical Physics, 98(7), 5648-5652. Bernardi, F., Bottoni, A., & Miscione, G. P. (2003). DFT study of the olefin metathesis catalyzed by ruthenium complexes. Organometallics, 22(5), 940-947. doi:10.1021/om020536o Blanc, F., Copéret, C., Thivolle-Cazat, J., & Basset, J. -. (2006). Alkane metathesis catalyzed by a well-defined silica-supported mo imido alkylidene complex: [(≡SiO)mo(=NAr)(=CHtBu)(CH2tBu)].Angewandte Chemie - International Edition, 45(37), 6201-6203. doi:10.1002/anie.200602171 Blanc, F., Copéret, C., Thivolle-Cazat, J., Basset, J. -., Lesage, A., Emsley, L., . . . Schrock, R. R. (2006). Surface versus molecular siloxy ligands in well-defined olefin metathesis catalysts: [{(RO)3SiO}mo(=NAr)(=CHtBu)(CH2tBu)]. Angewandte Chemie - International Edition, 45(8), 1216-1220. doi:10.1002/anie.200503205 Blanc, F., Thivolle-Cazat, J., Basset, J. -., & Copéret, C. (2008). Structure-reactivity relationship in alkane metathesis using well-defined silica-supported alkene metathesis catalyst precursors. Chemistry - A European Journal, 14(29), 9030-9037. doi:10.1002/chem.200800864 Burnett, R. L., & Hughes, T. R. (1973). Mechanism and poisoning of the molecular redistribution reaction of alkanes with a dual-functional catalyst system. Journal of Catalysis, 31(1), 55-64. doi:10.1016/0021-9517(73)90270-4 Cavallo, L. (2002). Mechanism of ruthenium-catalyzed olefin metathesis reactions from a theoretical perspective. Journal of the American Chemical Society, 124(30), 8965-8973. doi:10.1021/ja016772s Chabanas, M., Baudouin, A., Copéret, C., & Basset, J. -. (2001). A highly active well-defined rhenium heterogeneous catalyst for olefin metathesis prepared via surface organometallic chemistry [3]. Journal of the American Chemical Society, 123(9), 2062-2063. doi:10.1021/ja000900f Chabanas, M., Copéret, C., & Basset, J. -. (2003). Re-based heterogeneous catalysts for olefin metathesis prepared by surface organometallic chemistry: Reactivity and selectivity. Chemistry - A European Journal, 9(4), 971-975. doi:10.1002/chem.200390119 Chabanas, M., Vidal, V., Copéret, C., Thivolle-Cazat, J., & Basset, J. -. (2000). Low-temperature hydrogenolysis of alkanes catalyzed by a silica- supported tantalum hydride complex, and evidence for a mechanistic switch from group IV to group V metal surface hydride complexes. Angewandte Chemie - International Edition, 39(11), 1962-1965. doi:10.1002/1521-3773(20000602)39:11<1962 Chen, Y., Abou-Hamad, E., Hamieh, A., Hamzaoui, B., Emsley, L., & Basset, J. -. (2015). Alkane metathesis with the tantalum methylidene [(≡SiO)ta(=CH2)Me2]/[(≡SiO)2Ta(=CH2)me] generated from well-defined surface organometallic complex [(≡SiO)TaVMe4]. Journal of the American Chemical Society, 137(2), 588-591. doi:10.1021/ja5113468 Copéret, C. (2010). C-H bond activation and organometallic intermediates on isolated metal centers on oxide surfaces. Chemical Reviews, 110(2), 656-680. doi:10.1021/cr900122p Copéret, C., Maury, O., Thivolle-Cazat, J., & Basset, J. -. (2001). σ-Bond metathesis of alkanes on a silica-supported tantalum(v) alkyl alkylidene complex: First evidence for alkane cross-metathesis.Angewandte Chemie - International Edition, 40(12), 2331-2334. doi:10.1002/1521-3773(20010618)40 Ehlers, A. W., Böhme, M., Dapprich, S., Gobbi, A., Höllwarth, A., Jonas, V., . . . Frenking, G. (1993). A set of f-polarization functions for pseudo-potential basis sets of the transition metals ScCu, YAg and LaAu.Chemical Physics Letters, 208(1-2), 111-114. doi:10.1016/0009-2614(93)80086-5 Floryan, L., Borosy, A. P., Núñez-Zarur, F., Comas-Vives, A., & Copéret, C. (2017). Strain effect and dual initiation pathway in CrIII/SiO2polymerization catalysts from amorphous periodic models. Journal of Catalysis, 346, 50-56. doi:10.1016/j.jcat.2016.11.037 Frisch, M. J. (2009). Gaussian 09. Frisch, M. J., Pople, J. A., & Binkley, J. S. (1984). Self-consistent molecular orbital methods 25. supplementary functions for gaussian basis sets. The Journal of Chemical Physics, 80(7), 3265-3269. Goldman, A. S., Roy, A. H., Huang, Z., Ahuja, R., Schinski, W., & Brookhart, M. (2006). Catalytic alkane metathesis by tandem alkane dehydrogenation-olefin metathesis. Science, 312(5771), 257-261. doi:10.1126/science.1123787 Gouré, E., Avenier, P., Solans-Monfort, X., Veyre, L., Baudouin, A., Kaya, Y., . . . Quadrelli, E. A. (2011). Heterolytic cleavage of ammonia N-H bond by bifunctional activation in silica-grafted single site ta(V) imido amido surface complex. importance of the outer sphere NH3 assistance. New Journal of Chemistry, 35(5), 1011-1019. doi:10.1039/c1nj20032a Grimme, S., Antony, J., Ehrlich, S., & Krieg, H. (2010). A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-pu. Journal of Chemical Physics, 132(15) doi:10.1063/1.3382344 Grimme, S., Ehrlich, S., & Goerigk, L. (2011). Effect of the damping function in dispersion corrected density functional theory. Journal of Computational Chemistry, 32(7), 1456-1465. doi:10.1002/jcc.21759 Hamieh, A., Chen, Y., Abdel-Azeim, S., Abou-hamad, E., Goh, S., Samantaray, M., . . . Basset, J. M. (2015). Well-defined surface species [(≡Si - O -)W(=O)Me3] prepared by direct methylation of [(≡Si - O -)W(=O)Cl3], a catalyst for cycloalkane metathesis and transformation of ethylene to propylene. ACS Catalysis, 5(4), 2164-2171. doi:10.1021/cs5020749
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dc.publisher.spa.fl_str_mv	American Chemical Society
dc.publisher.faculty.spa.fl_str_mv	Facultad de Ciencias Básicas
dc.source.spa.fl_str_mv	Scopus
institution	Universidad de Medellín
repository.name.fl_str_mv	Repositorio Institucional Universidad de Medellin
repository.mail.fl_str_mv	repositorio@udem.edu.co
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spelling	2017-12-19T19:36:42Z2017-12-19T19:36:42Z2017201669http://hdl.handle.net/11407/426010.1021/acs.inorgchem.7b01464reponame:Repositorio Institucional Universidad de Medellíninstname:Universidad de MedellínAlkane metathesis transforms small alkanes into their higher and lower homologues. The reaction is catalyzed by either supported d0 metal hydrides (M = Ta, W) or d0 alkyl alkylidene complexes (M = Ta, Mo, W, Re). For the silica-supported tantalum hydrides, several reaction mechanisms have been proposed. We performed DFT-D3 calculations to analyze the viability of the proposed pathways and compare them with alkane hydrogenolysis, which is a competitive process observed at the early stages of the reaction. The results show that the reaction mechanisms for alkane metathesis and for alkane hydrogenolysis present similar energetics, and this is consistent with the fact that the process taking place depends on the concentrations of the initial reactants. Overall, a modified version of the so-called one-site mechanism that involves alkyl alkylidene intermediates appears to be more likely and consistent with experiments. According to this proposal, tantalum hydrides are precursors of the alkyl alkylidene active species. During precursor activation, H2 is released and this allows alkane hydrogenolysis to occur. In contrast, the catalytic cycle implies only the reaction with alkane molecules in excess and does not form H2. Thus, the activity for alkane hydrogenolysis decreases. The catalytic cycle proposed here implies three stages: (i) β-H elimination from the alkyl ligand, liberating ethene, (ii) alkene cross-metathesis, allowing olefin substituent exchange, and (iii) formation of the final products and alkyl alkylidene regeneration by olefin insertion and three successive 1,2-CH insertions to the alkylidene followed by α abstraction. These results relate the reactivity of silica-supported hydrides with that of the alkyl alkylidene complexes, the other common catalyst for alkane metathesis. © 2017 American Chemical Society.engAmerican Chemical SocietyFacultad de Ciencias Básicashttps://www.scopus.com/inward/record.uri?eid=2-s2.0-85028926911&doi=10.1021%2facs.inorgchem.7b01464&partnerID=40&md5=3ee308857653f4bcc9e01659e1ad5acbInorganic ChemistryInorganic Chemistry Volume 56, Issue 17, 5 September 2017, Pages 10458-10473Adamo, C., & Barone, V. (1999). Toward reliable density functional methods without adjustable parameters: The PBE0 model. Journal of Chemical Physics, 110(13), 6158-6170.Amakawa, K., Sun, L., Guo, C., Hävecker, M., Kube, P., Wachs, I. E., . . . Trunschke, A. (2013). How strain affects the reactivity of surface metal oxide catalysts. Angewandte Chemie - International Edition, 52(51), 13553-13557. doi:10.1002/anie.201306620Avenier, P., Solans-Monfort, X., Veyre, L., Renili, F., Basset, J. -., Eisenstein, O., . . . Quadrelli, E. A. (2009). H/D exchange on silica-grafted tantalum(V) imido amido [(≡SiO) 2Ta(V)(NH)(NH2)] synthesized from either ammonia or dinitrogen: IR and DFT evidence for heterolytic splitting of D 2. Topics in Catalysis, 52(11), 1482-1491. doi:10.1007/s11244-009-9295-0Avenier, P., Taoufik, M., Lesage, A., Solans-Monfort, X., Baudouin, A., De Mallmann, A., . . . Quadrelli, E. A. (2007). Dinitrogen dissociation on an isolated surface tantalum atom. Science, 317(5841), 1056-1060. doi:10.1126/science.1143078Bailey, B. C., Schrock, R. R., Kundu, S., Goldman, A. S., Huang, Z., & Brookhart, M. (2009). Evaluation of molybdenum and tungsten metathesis catalysts for homogeneous tandem alkane metathesis.Organometallics, 28(1), 355-360. doi:10.1021/om800877qBalcells, D., Clot, E., & Eisenstein, O. (2010). C-H bond activation in transition metal species from a computational perspective. Chemical Reviews, 110(2), 749-823. doi:10.1021/cr900315kBasset, J. M., Copéret, C., Lefort, L., Maunders, B. M., Maury, O., Le Roux, E., . . . Thivolle-Cazat, J. (2005). Primary products and mechanistic considerations in alkane metathesis. Journal of the American Chemical Society, 127(24), 8604-8605. doi:10.1021/ja051679fBasset, J. -., Copéret, C., Soulivong, D., Taoufik, M., & Thivolle Cazat, J. (2010). Metathesis of alkanes and related reactions. Accounts of Chemical Research, 43(2), 323-334. doi:10.1021/ar900203aBecke, A. D. (1993). Density-functional thermochemistry. III. the role of exact exchange. The Journal of Chemical Physics, 98(7), 5648-5652.Bernardi, F., Bottoni, A., & Miscione, G. P. (2003). DFT study of the olefin metathesis catalyzed by ruthenium complexes. Organometallics, 22(5), 940-947. doi:10.1021/om020536oBlanc, F., Copéret, C., Thivolle-Cazat, J., & Basset, J. -. (2006). Alkane metathesis catalyzed by a well-defined silica-supported mo imido alkylidene complex: [(≡SiO)mo(=NAr)(=CHtBu)(CH2tBu)].Angewandte Chemie - International Edition, 45(37), 6201-6203. doi:10.1002/anie.200602171Blanc, F., Copéret, C., Thivolle-Cazat, J., Basset, J. -., Lesage, A., Emsley, L., . . . Schrock, R. R. (2006). Surface versus molecular siloxy ligands in well-defined olefin metathesis catalysts: [{(RO)3SiO}mo(=NAr)(=CHtBu)(CH2tBu)]. Angewandte Chemie - International Edition, 45(8), 1216-1220. doi:10.1002/anie.200503205Blanc, F., Thivolle-Cazat, J., Basset, J. -., & Copéret, C. (2008). Structure-reactivity relationship in alkane metathesis using well-defined silica-supported alkene metathesis catalyst precursors. Chemistry - A European Journal, 14(29), 9030-9037. doi:10.1002/chem.200800864Burnett, R. L., & Hughes, T. R. (1973). Mechanism and poisoning of the molecular redistribution reaction of alkanes with a dual-functional catalyst system. Journal of Catalysis, 31(1), 55-64. doi:10.1016/0021-9517(73)90270-4Cavallo, L. (2002). Mechanism of ruthenium-catalyzed olefin metathesis reactions from a theoretical perspective. Journal of the American Chemical Society, 124(30), 8965-8973. doi:10.1021/ja016772sChabanas, M., Baudouin, A., Copéret, C., & Basset, J. -. (2001). A highly active well-defined rhenium heterogeneous catalyst for olefin metathesis prepared via surface organometallic chemistry [3]. Journal of the American Chemical Society, 123(9), 2062-2063. doi:10.1021/ja000900fChabanas, M., Copéret, C., & Basset, J. -. (2003). Re-based heterogeneous catalysts for olefin metathesis prepared by surface organometallic chemistry: Reactivity and selectivity. Chemistry - A European Journal, 9(4), 971-975. doi:10.1002/chem.200390119Chabanas, M., Vidal, V., Copéret, C., Thivolle-Cazat, J., & Basset, J. -. (2000). Low-temperature hydrogenolysis of alkanes catalyzed by a silica- supported tantalum hydride complex, and evidence for a mechanistic switch from group IV to group V metal surface hydride complexes. Angewandte Chemie - International Edition, 39(11), 1962-1965. doi:10.1002/1521-3773(20000602)39:11<1962Chen, Y., Abou-Hamad, E., Hamieh, A., Hamzaoui, B., Emsley, L., & Basset, J. -. (2015). Alkane metathesis with the tantalum methylidene [(≡SiO)ta(=CH2)Me2]/[(≡SiO)2Ta(=CH2)me] generated from well-defined surface organometallic complex [(≡SiO)TaVMe4]. Journal of the American Chemical Society, 137(2), 588-591. doi:10.1021/ja5113468Copéret, C. (2010). C-H bond activation and organometallic intermediates on isolated metal centers on oxide surfaces. Chemical Reviews, 110(2), 656-680. doi:10.1021/cr900122pCopéret, C., Maury, O., Thivolle-Cazat, J., & Basset, J. -. (2001). σ-Bond metathesis of alkanes on a silica-supported tantalum(v) alkyl alkylidene complex: First evidence for alkane cross-metathesis.Angewandte Chemie - International Edition, 40(12), 2331-2334. doi:10.1002/1521-3773(20010618)40Ehlers, A. W., Böhme, M., Dapprich, S., Gobbi, A., Höllwarth, A., Jonas, V., . . . Frenking, G. (1993). A set of f-polarization functions for pseudo-potential basis sets of the transition metals ScCu, YAg and LaAu.Chemical Physics Letters, 208(1-2), 111-114. doi:10.1016/0009-2614(93)80086-5Floryan, L., Borosy, A. P., Núñez-Zarur, F., Comas-Vives, A., & Copéret, C. (2017). Strain effect and dual initiation pathway in CrIII/SiO2polymerization catalysts from amorphous periodic models. Journal of Catalysis, 346, 50-56. doi:10.1016/j.jcat.2016.11.037Frisch, M. J. (2009). Gaussian 09.Frisch, M. J., Pople, J. A., & Binkley, J. S. (1984). Self-consistent molecular orbital methods 25. supplementary functions for gaussian basis sets. The Journal of Chemical Physics, 80(7), 3265-3269.Goldman, A. S., Roy, A. H., Huang, Z., Ahuja, R., Schinski, W., & Brookhart, M. (2006). Catalytic alkane metathesis by tandem alkane dehydrogenation-olefin metathesis. Science, 312(5771), 257-261. doi:10.1126/science.1123787Gouré, E., Avenier, P., Solans-Monfort, X., Veyre, L., Baudouin, A., Kaya, Y., . . . Quadrelli, E. A. (2011). Heterolytic cleavage of ammonia N-H bond by bifunctional activation in silica-grafted single site ta(V) imido amido surface complex. importance of the outer sphere NH3 assistance. New Journal of Chemistry, 35(5), 1011-1019. doi:10.1039/c1nj20032aGrimme, S., Antony, J., Ehrlich, S., & Krieg, H. (2010). A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-pu. Journal of Chemical Physics, 132(15) doi:10.1063/1.3382344Grimme, S., Ehrlich, S., & Goerigk, L. (2011). Effect of the damping function in dispersion corrected density functional theory. Journal of Computational Chemistry, 32(7), 1456-1465. doi:10.1002/jcc.21759Hamieh, A., Chen, Y., Abdel-Azeim, S., Abou-hamad, E., Goh, S., Samantaray, M., . . . Basset, J. M. (2015). Well-defined surface species [(≡Si - O -)W(=O)Me3] prepared by direct methylation of [(≡Si - O -)W(=O)Cl3], a catalyst for cycloalkane metathesis and transformation of ethylene to propylene. ACS Catalysis, 5(4), 2164-2171. doi:10.1021/cs5020749ScopusMechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT StudyArticleinfo:eu-repo/semantics/articlehttp://purl.org/coar/version/c_970fb48d4fbd8a85http://purl.org/coar/resource_type/c_6501http://purl.org/coar/resource_type/c_2df8fbb1Núñez-Zarur, F., Instituto de Química, Universidad de Antioquia, Calle 70 No. 52-21, Medellín, Colombia, Facultad de Facultad de Ciencias Básicas, Universidad de Medellín, Carrera 87 No. 30-65, Medellín, ColombiaSolans-Monfort, X., Departament de Química, Universitat Autònoma de Barcelona, Bellaterra, SpainRestrepo, A., Instituto de Química, Universidad de Antioquia, Calle 70 No. 52-21, Medellín, ColombiaNúñez-Zarur F.Solans-Monfort X.Restrepo A.Instituto de Química, Universidad de Antioquia, Calle 70 No. 52-21, Medellín, ColombiaDepartament de Química, Universitat Autònoma de Barcelona, Bellaterra, SpainFacultad de Facultad de Ciencias Básicas, Universidad de Medellín, Carrera 87 No. 30-65, Medellín, ColombiaAlkane metathesis transforms small alkanes into their higher and lower homologues. The reaction is catalyzed by either supported d0 metal hydrides (M = Ta, W) or d0 alkyl alkylidene complexes (M = Ta, Mo, W, Re). For the silica-supported tantalum hydrides, several reaction mechanisms have been proposed. We performed DFT-D3 calculations to analyze the viability of the proposed pathways and compare them with alkane hydrogenolysis, which is a competitive process observed at the early stages of the reaction. The results show that the reaction mechanisms for alkane metathesis and for alkane hydrogenolysis present similar energetics, and this is consistent with the fact that the process taking place depends on the concentrations of the initial reactants. Overall, a modified version of the so-called one-site mechanism that involves alkyl alkylidene intermediates appears to be more likely and consistent with experiments. According to this proposal, tantalum hydrides are precursors of the alkyl alkylidene active species. During precursor activation, H2 is released and this allows alkane hydrogenolysis to occur. In contrast, the catalytic cycle implies only the reaction with alkane molecules in excess and does not form H2. Thus, the activity for alkane hydrogenolysis decreases. The catalytic cycle proposed here implies three stages: (i) β-H elimination from the alkyl ligand, liberating ethene, (ii) alkene cross-metathesis, allowing olefin substituent exchange, and (iii) formation of the final products and alkyl alkylidene regeneration by olefin insertion and three successive 1,2-CH insertions to the alkylidene followed by α abstraction. These results relate the reactivity of silica-supported hydrides with that of the alkyl alkylidene complexes, the other common catalyst for alkane metathesis. © 2017 American Chemical Society.http://purl.org/coar/access_right/c_16ec11407/4260oai:repository.udem.edu.co:11407/42602020-05-27 18:24:43.336Repositorio Institucional Universidad de Medellinrepositorio@udem.edu.co

Mechanistic Insights into Alkane Metathesis Catalyzed by Silica-Supported Tantalum Hydrides: A DFT Study

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