η2-Alkene complexes of [Rh(PONOP-iPr)(L)]+ cations (L = COD, NBD, Ethene). Intramolecular alkene-assisted hydrogenation and dihydrogen complex [Rh(PONOP-iPr)(η-H2)].

JOHNSON, Alice, ROYLE, Cameron G., BRODIE, Claire N., MARTÍNEZ-MARTÍNEZ, Antonio J., DUCKETT, Simon B. and WELLER, Andrew S. (2021). η2-Alkene complexes of [Rh(PONOP-iPr)(L)]+ cations (L = COD, NBD, Ethene). Intramolecular alkene-assisted hydrogenation and dihydrogen complex [Rh(PONOP-iPr)(η-H2)]. Inorg Chem, 60 (18), 13903-13912.

[img]
Preview
PDF
Johnson-η2-AlkeneComplexes(VoR).pdf - Published Version
Creative Commons Attribution.

Download (2MB) | Preview
Official URL: https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c0...
Open Access URL: https://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem... (Published version)
Link to published version:: https://doi.org/10.1021/acs.inorgchem.0c03687
Related URLs:

    Abstract

    Rhodium-alkene complexes of the pincer ligand κ3-C5H3N-2,6-(OPiPr2)2 (PONOP-iPr) have been prepared and structurally characterized: [Rh(PONOP-iPr)(η2-alkene)][BArF4] [alkene = cyclooctadiene (COD), norbornadiene (NBD), ethene; ArF = 3,5-(CF3)2C6H3]. Only one of these, alkene = COD, undergoes a reaction with H2 (1 bar), to form [Rh(PONOP-iPr)(η2-COE)][BArF4] (COE = cyclooctene), while the others show no significant reactivity. This COE complex does not undergo further hydrogenation. This difference in reactivity between COD and the other alkenes is proposed to be due to intramolecular alkene-assisted reductive elimination in the COD complex, in which the η2-bound diene can engage in bonding with its additional alkene unit. H/D exchange experiments on the ethene complex show that reductive elimination from a reversibly formed alkyl hydride intermediate is likely rate-limiting and with a high barrier. The proposed final product of alkene hydrogenation would be the dihydrogen complex [Rh(PONOP-iPr)(η2-H2)][BArF4], which has been independently synthesized and undergoes exchange with free H2 on the NMR time scale, as well as with D2 to form free HD. When the H2 addition to [Rh(PONOP-iPr)(η2-ethene)][BArF4] is interrogated using pH2 at higher pressure (3 bar), this produces the dihydrogen complex as a transient product, for which enhancements in the 1H NMR signal for the bound H2 ligand, as well as that for free H2, are observed. This is a unique example of the partially negative line-shape effect, with the enhanced signals that are observed for the dihydrogen complex being explained by the exchange processes already noted.

    Item Type: Article
    Uncontrolled Keywords: 0302 Inorganic Chemistry; 0306 Physical Chemistry (incl. Structural); 0399 Other Chemical Sciences; Inorganic & Nuclear Chemistry
    Identification Number: https://doi.org/10.1021/acs.inorgchem.0c03687
    Page Range: 13903-13912
    SWORD Depositor: Symplectic Elements
    Depositing User: Symplectic Elements
    Date Deposited: 17 Mar 2022 15:12
    Last Modified: 17 Mar 2022 15:15
    URI: http://shura.shu.ac.uk/id/eprint/29952

    Actions (login required)

    View Item View Item

    Downloads

    Downloads per month over past year

    View more statistics