Carbon-Fluorine Bond Activation Coupled with Carbon-Hydrogen Bond Formation to Iridium: Kinetics, Mechanism, and Diastereoselectivi
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- 作者：Shaun A. Garratt ; Russell P. Hughes ; Ivan Kovacik ; Antony J. Ward ; Stefan Willemsen ; and Donghui Zhang
- 刊名：Journal of the American Chemical Society
- 出版年：2005
- 出版时间：November 9, 2005
- 年：2005
- 卷：127
- 期：44
- 页码：15585 - 15594
- 全文大小：243K
- 年卷期：v.127,no.44(November 9, 2005)
- ISSN：1520-5126
文摘
Reactions of iridium(fluoroalkyl)hydride complexes Cp*Ir(PMe3)(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 migrationto give Cp*Ir(PMe3)(CYFRF)X as variable mixtures of diastereomers. Solution conformations and relativediastereomer 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. Isotopelabeling 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 
-CF bond, giving anidentical 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 bondactivation. Detailed kinetic studies are reported, which demonstrate that lack of complete diastereoselectivityis not a function of the C-F bond activation/H migration steps but that a cationic intermediate plays adouble role in loss of diastereoselectivity; the intermediate can undergo epimerization at iridium beforebeing trapped by halide and can also catalyze the epimerization of kinetic diastereomer product tothermodynamic product. A detailed mechanism is proposed and simulations performed to fit the kineticdata.
-CF bond, giving anidentical 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 bondactivation. Detailed kinetic studies are reported, which demonstrate that lack of complete diastereoselectivityis not a function of the C-F bond activation/H migration steps but that a cationic intermediate plays adouble role in loss of diastereoselectivity; the intermediate can undergo epimerization at iridium beforebeing trapped by halide and can also catalyze the epimerization of kinetic diastereomer product tothermodynamic product. A detailed mechanism is proposed and simulations performed to fit the kineticdata.