852814-39-2Relevant academic research and scientific papers
Carbon-fluorine bond activation coupled with carbon-carbon bond formation at iridium. Confirmation of complete kinetic diastereoselectivity at the new carbon stereocenter by intramolecular trapping using vinyl as the migrating group
Hughes, Russell P.,Laritchev, Roman B.,Zakharov, Lev N.,Rheingold, Arnold L.
, p. 6325 - 6334 (2007/10/03)
The iridium(perfluoropropyl)(vinyl) complex Cp*Ir(PMe 3)(n-C3F7)(CH=CH2) (5) has been prepared. It has been characterized by X-ray crystallography, and its ground state conformation in solution has been determined by 19F{ 1H} HOESY NMR studies. It reacts with the weak acid lutidinium iodide to afford the η1-allylic complex Cp*Ir(PMe 3)((Z)-CH2CH=CFC2F5)I (6), which has also been characterized crystallographically. The mechanism of C-F bond activation and C-C bond formation leading to 6 has been elucidated in detail by studying the reaction of 5 with lutidinium tetrakis[3,5-bis(trifluoromethyl) phenyl]borate [LUtH+B(ArF)4-], containing a weakly coordinating counteranion. The main kinetic product of this reaction, determined by 19F{1H} HOESY studies at -50 °C, is the endo-Cp*Ir(PMe3)(anti-η3-CH 2CHCFCF2CF3)-[B(ArF)4] diastereomer 9, along with a small amount of the exo-syn-isomer 8. Isomer 9 rearranges at -20 °C to its exo-anti isomer 7, and subsequently to the thermodynamically favored exo-syn-isomer 8, which has been isolated and crystallographically characterized. Complex 8 reacts with iodide to afford complex 6. On the basis of the unambiguously defined kinetically controlled stereochemistry of 9 and 8, a detailed mechanism for the C-F activation/C-C coupling reaction is proposed, the principal conclusion of which is that C-F activation is completely diastereoselective.
