Title
Carbon-fluorine bond activation coupled with carbon-hydrogen bond formation α to iridium: Kinetics, mechanism, and diastereoselectivity
Document Type
Article
Publication Date
11-9-2005
Abstract
Reactions of iridium(fluoroalkyl)hydride complexes Cp*Ir(PMe 3)(CF2RF)Y (RF = F, CF3; Y = H, D) with LutHX (Lut = 2,6-dimethylpyridine; X = Cl, I) results in C-F activation coupled with hydride migration to give Cp*Ir(PMe 3)(CYFRF)X as variable mixtures of diastereomers. Solution conformations and relative diastereomer configurations of the products have been determined by 19F{1H}HOESY NMR to be (SC, SIr)(RC, RIr) for the kinetic diastereomer and (RC, SIr)(SC, RIr) for its thermodynamic counterpart. Isotope labeling experiments using LutDCl/Cp*Ir(PMe3)(CF2RF)H and Cp*Ir(PMe3)(CF2RF)D/LutHCl) showed that, unlike a previously studied system, H/D exchange is faster than protonation of the α-CF bond, giving an identical mixture of product isotopologues from both reaction mixtures. The kinetic rate law shows a first-order dependence on the concentration of iridium substrate, but a half-order dependence on that of LutHCl; this is interpreted to mean that LutHCl dissociates to give HCl as the active protic source for C-F bond activation. Detailed kinetic studies are reported, which demonstrate that lack of complete diastereoselectivity is not a function of the C-F bond activation/H migration steps but that a cationic intermediate plays a double role in loss of diastereoselectivity; the intermediate can undergo epimerization at iridium before being trapped by halide and can also catalyze the epimerization of kinetic diastereomer product to thermodynamic product. A detailed mechanism is proposed and simulations performed to fit the kinetic data. © 2005 American Chemical Society.
Publication Source (Journal or Book title)
Journal of the American Chemical Society
First Page
15585
Last Page
15594
Recommended Citation
Garratt, S., Hughes, R., Kovacik, I., Ward, A., Willemsen, S., & Zhang, D. (2005). Carbon-fluorine bond activation coupled with carbon-hydrogen bond formation α to iridium: Kinetics, mechanism, and diastereoselectivity. Journal of the American Chemical Society, 127 (44), 15585-15594. https://doi.org/10.1021/ja0545012