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    Controlling Structure and Reactivity in Cationic Solid-State Molecular Organometallic Systems Using Anion Templating


    McKay, Alasdair I. and Martinez-Martinez, Antonio J. and Griffiths, Hannah and Rees, Nichollas H. and Waters, Jordan B and Weller, Andrew S. and Krämer, Tobias and Macgregor, Stuart A. (2018) Controlling Structure and Reactivity in Cationic Solid-State Molecular Organometallic Systems Using Anion Templating. Organometallics, 37. pp. 3524-3532. ISSN 0276-7333

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    Abstract

    The role that the supporting anion has on the stability, structure, and catalytic performance, in solid-state molecular organometallic systems (SMOM) based upon [Rh- (Cy2PCH2CH2PCy2)(η2 η2 -NBD)][BArX 4], [1-NBD][BArX 4], is reported (X = Cl, F, H; NBD = norbornadiene). The tetra-aryl borate anion is systematically varied at the 3,5-position, ArX= 3,5- X2C6H3, and the stability and structure in the solid-state compared with the previously reported [1-NBD][BArCF34] complex. Single-crystal X-ray crystallography shows that the three complexes have different packing motifs, in which the cation sits on the shared face of two parallelepipeds for [1- NBD][BArCl4], is surrounded by eight anions in a gyrobifastigium arrangement for [1-NBD][BArF 4], or the six anions show an octahedral cage arrangement in [1-NBD][BArH 4], similar to that of [1-NBD][BArCF34]. C−X···X−C contacts, commonly encountered in crystal-engineering, are suggested to be important in determining structure. Addition of H2 in a solid/gas reaction affords the resulting σ-alkane complexes, [Rh(Cy2PCH2CH2PCy2)(η2 η2 -NBA)][BArX 4] [1-NBA][BArX 4] (NBA = norbornane), which can then proceed to lose the alkane and form the zwitterionic, anion-coordinated, complexes. The relative rates at which hydrogenation and then decomposition of σ-alkane complexes proceed are shown to be anion dependent. [BArCF34] − promotes fast hydrogenation and an indefinitely stable σ-alkane complex. With [BArH 4] − hydrogenation is slow and the σ-alkane complex so unstable it is not observed. [BArCl4] − and [BArF 4] − promote intermediate reactivity profiles, and for [BArCl4] −, a single-crystal to single-crystal hydrogenation results in [1-NBA][BArCl4]. The molecular structure derived from X-ray diffraction reveals a σalkane complex in which the NBA fragment is bound through two exo Rh···H−C interactions-different from the endo selective binding observed with [1-NBA][BArCF34]. Periodic DFT calculations demonstrate that this selectivity is driven by the microenvironment dictated by the surrounding anions. [1-NBA][BArX 4] are catalysts for gas/solid 1-butene isomerization (298 K, 1 atm), and their activity can be directly correlated to the stability of the σ-alkane complex compared to the anion-coordinated decomposition products.

    Item Type: Article
    Keywords: Controlling Structure; Reactivity; Cationic Solid-State Molecular; Organometallic Systems; Anion; Templating;
    Academic Unit: Faculty of Science and Engineering > Chemistry
    Item ID: 13248
    Identification Number: https://doi.org/10.1021/acs.organomet.8b00215
    Depositing User: Tobias Kraemer
    Date Deposited: 17 Sep 2020 13:07
    Journal or Publication Title: Organometallics
    Publisher: American Chemical Society
    Refereed: Yes
    URI:

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