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    Competition between Intramolecular and Intermolecular C-H Activation in Iridium Ethene Complexes

    Bell, Tanachat W. and Brough, Sally-Ann and Partridge, Martin G. and Perutz, Robin N. and Rooney, A. Denise (1993) Competition between Intramolecular and Intermolecular C-H Activation in Iridium Ethene Complexes. Organometallics, 12 (8). pp. 2933-2941. ISSN 0276-7333

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    The ethene complexes CpIr(L)(C2H4) (Cp = 7)1 2345-C5H5, L = PPh3, CO) undergo two competing photochemical reactions in solution: (i) isomerization to the vinyl hydride CpIr(L) (C2H3)H and (ii) dissociation of ethene and insertion into solvent C-H bonds to form CpIr(L)(R)H. The vinyl hydride is favored over the intermolecular product by longer wavelength photolysis, lower temperature, and a more rigid surrounding medium and by L = PPh3 compared to L = CO. The vinyl hydride isomer is the exclusive product of UV irradiation of CpIr(CO)(C2H4) in solid toluene (77 K) or solid argon (12 K) but competes with formation of CpIr(CO)2 in CO-doped Ar matrices and CpIr(CO)(CH3)H in methane matrices. The latter is also formed by secondary photolysis of the vinyl hydride. The barrier for the thermal conversion of CpIr(L)(C2H3)H to the parent ethene complex CpIr(L)(C2H4) increases in the following order: L = C2H4, AH* = 67 ± 5 kJ moH; L = CO, AH* = 95 ± 4 kJ mol·1; L = PPh3, AG* = 135 ± 3 kJ mol·1 at 318 K. These findings are consistent with our proposal that C-H bond activation occurs via a “cagecomplex” intermediate. However, the marked influence of temperature on the reaction indicates that intermolecular C-H bond activation involves a thermally activated step. The photochemical reaction of CpIr(C2H4)2 with PPh3 in CD3CN generates the vinyl hydride Cplr(PPh3)(03 3) via Cplr (PPh3) (C3H4). The corresponding reaction occurs in benzene with the additional formation of the solvent activation product CpIr(PPh3)(Ph)H.

    Item Type: Article
    Additional Information: Cite as: Organometallics 1993, 12, 8, 2933–2941 Publication Date:August 1, 1993
    Keywords: Competition; Intramolecular; Intermolecular; C-H; Activation; Iridium; Ethene; Complexes;
    Academic Unit: Faculty of Science and Engineering > Chemistry
    Item ID: 14525
    Identification Number:
    Depositing User: Dr. Denise Rooney
    Date Deposited: 09 Jun 2021 15:15
    Journal or Publication Title: Organometallics
    Publisher: American Chemical Society
    Refereed: Yes
    Use Licence: This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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