103191-28-2Relevant academic research and scientific papers
Secondary to normal alkyl group rearrangements in octahedral iridium(III) complexes. 1. Monoalkyl derivatives
Bennett, Martin A.,Crisp, Geoffrey T.
, p. 1792 - 1800 (2008/10/08)
sec-Alkyliridium(III) complexes IrYI-sec-R(CO)L2 (Y = Cl, I; L = PMe3, PMe2Ph) formed by oxidative addition of sec-alkyl iodides to IrY(CO)L2 rearrange cleanly by a first-order process to the n-alkyl isomers on dissolution in dichloromethane containing protic solvents. The order of efficacy of these solvents in promoting alkyl group rearrangement is CF3CO2H ? CH3OH ? C2H5OH > CH3CO2H ≈ CH3CH2CH2OH > (CH3)2CHOH, while in the more strongly coordinating medium THF the order is H2O ? CH3OH. These orders correlate with the anion-solvating ability of the solvents and, together with the observed retardation by added iodide ion, suggest that the rate-determining step in the rearrangement is dissociation of iodide ion trans to the sec-alkyl group. Rapid, reversible β-hydride elimination in the resulting cation and stereospecific return of iodide ion trans to the resulting n-alkyl group complete the process. The rearrangement is promoted by increasing bulk, both of the alkyl group, up to a certain limit, and of the tertiary phosphine (PMe2Ph > PMe3). Treatment of IrClI{CH(CH3)2}(CO)(PMe2Ph)2 (2c) with AgBF4 in acetonitrile induces immediate alkyl group rearrangement to give the n-propyliridium(III) salt [IrCl(CH2CH2CH3)(CO)(NCMe)(PMe 2Ph)2]BF4 (6). Studies of analogous CD2CH3 compounds suggest that they, and presumably other n-alkyliridium(III) complexes, undergo reversible β-hydride elimination more slowly than the sec-alkyl complexes. The deuterium labels in the isobutyl-d2 complex IrClI{CD2CH(CH3)2}(CO)(PMe3) 2 (1e′) scramble over all the alkyl carbon atoms when the compound is heated in CD2Cl2/CD3OD, indicating that a tert-butyliridium(III) species is accessible. Surprisingly, the complexes IrClI{CH2CH(CH3)CH2CH3}(CO)(PMe 3)2 (1h) and IrClI{CH2CH2CH(CH3)2}(CO)(PMe 3)2 (1i) do not interconvert under the same conditions, implying that a tert-pentyliridium(III) species cannot be formed. The results are compared with alkyl group rearrangements that occur in other transition-metal systems, especially those promoted by dissocation of triphenylphosphine in (η-C5H5)FeR(CO)(PPh3).
