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    Solid-state molecular organometallic chemistry. Single-crystal to single-crystal reactivity and catalysis with light hydrocarbon substrates


    Chadwick, Mark and McKay, Alasdair I. and Martinez-Martinez, Antonio J. and Rees, Nichollas H. and Krämer, Tobias and Mcgregor, Stuart A. and Weller, Andrew S. (2017) Solid-state molecular organometallic chemistry. Single-crystal to single-crystal reactivity and catalysis with light hydrocarbon substrates. Chemical Science, 8. pp. 6014-6029. ISSN 2041-6539

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    Abstract

    Single-crystal to single-crystal solid/gas reactivity and catalysis starting from the precursor sigma-alkane complex [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] (NBA = norbornane; ArF = 3,5-(CF3)2C6H3) is reported. By adding ethene, propene and 1-butene to this precursor in solid/gas reactions the resulting alkene complexes [Rh(Cy2PCH2CH2PCy2)(alkene)x][BArF4] are formed. The ethene (x = 2) complex, [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4]-Oct, has been characterized in the solid-state (single-crystal X-ray diffraction) and by solution and solid-state NMR spectroscopy. Rapid, low temperature recrystallization using solution methods results in a different crystalline modification, [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4]-Hex, that has a hexagonal microporous structure (P6322). The propene complex (x = 1) [Rh(Cy2PCH2CH2PCy2)(propene)][BArF4] is characterized as having a π-bound alkene with a supporting γ-agostic Rh⋯H3C interaction at low temperature by single-crystal X-ray diffraction, variable temperature solution and solid-state NMR spectroscopy, as well as periodic density functional theory (DFT) calculations. A fluxional process occurs in both the solid-state and solution that is proposed to proceed via a tautomeric allyl-hydride. Gas/solid catalytic isomerization of d3-propene, H2C[double bond, length as m-dash]CHCD3, using [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] scrambles the D-label into all possible positions of the propene, as shown by isotopic perturbation of equilibrium measurements for the agostic interaction. Periodic DFT calculations show a low barrier to H/D exchange (10.9 kcal mol−1, PBE-D3 level), and GIPAW chemical shift calculations guide the assignment of the experimental data. When synthesized using solution routes a bis-propene complex, [Rh(Cy2PCH2CH2PCy2)(propene)2][BArF4], is formed. [Rh(Cy2PCH2CH2PCy2)(butene)][BArF4] (x = 1) is characterized as having 2-butene bound as the cis-isomer and a single Rh⋯H3C agostic interaction. In the solid-state two low-energy fluxional processes are proposed. The first is a simple libration of the 2-butene that exchanges the agostic interaction, and the second is a butene isomerization process that proceeds via an allyl-hydride intermediate with a low computed barrier of 14.5 kcal mol−1. [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] and the polymorphs of [Rh(Cy2PCH2CH2PCy2)(ethene)2][BArF4] are shown to be effective in solid-state molecular organometallic catalysis (SMOM-Cat) for the isomerization of 1-butene to a mixture of cis- and trans-2-butene at 298 K and 1 atm, and studies suggest that catalysis is likely dominated by surface-active species. [Rh(Cy2PCH2CH2PCy2)(η2η2-NBA)][BArF4] is also shown to catalyze the transfer dehydrogenation of butane to 2-butene at 298 K using ethene as the sacrificial acceptor.

    Item Type: Article
    Additional Information: This article is licensed under a Creative Commons Attribution 3.0 Unported Licence https://creativecommons.org/licenses/by/3.0/. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material. Cite as: Solid-state molecular organometallic chemistry. Single-crystal to single-crystal reactivity and catalysis with light hydrocarbon substrates F. M. Chadwick, A. I. McKay, A. J. Martinez-Martinez, N. H. Rees, T. Krämer, S. A. Macgregor and A. S. Weller, Chem. Sci., 2017, 8, 6014 DOI: 10.1039/C7SC01491K
    Keywords: Solid-state molecular organometallic chemistry; Single-crystal to single-crystal reactivity; light hydrocarbon substrates;
    Academic Unit: Faculty of Science and Engineering > Chemistry
    Item ID: 10766
    Identification Number: https://doi.org/10.1039/C7SC01491K
    Depositing User: Tobias Krämer
    Date Deposited: 01 May 2019 16:03
    Journal or Publication Title: Chemical Science
    Publisher: Royal Society of Chemistry
    Refereed: Yes
    URI:

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