Hiyama coupling reaction of fluorous alkenyl-fluorosilanes: Scope and mechanistic considerations

Article abstract of DOI:10.1016/j.jfluchem.2012.03.007

Novel fluorous alkenyl-fluorosilanes (C_nF _2n+1CHCHSiMe₂F; n = 4, 6, 8; 5a-c) were synthetized in a three step procedure from perfluoroalkyliodides and dimethylvinylchlorosilane. They were first reacted with iodobenzene at room temperature in Hiyama coupling reaction (DMF, Pd(OAc)₂, TBAF, 72 h) to afford the appropriate ω-perfluoroalkyl-styrenes (C_nF_2n+1CHCHC ₆H₅, n = 4, 6, 8); then the reactivity of 5a with monosubstituted iodobenzenes was studied. The coupling reaction of 5a with o-substituted iodobenzenes usually failed, while that of with the m- and p-substituted ones gave fluorous styrenes [m- or p-(C₄F ₉CHCH)C₆H₄X], independently of the electronic effect of their substituent (X = Br, CF₃, CH₃, OCH ₃). These volatile products can easily be isolated by steam-distilltaion and purified further by distillation. The mechanism of the above coupling reactions was a pure Hiyama type involving fluoride-ion induced transmetallation without any Heck type contribution, since no coupling product of C₆F₁₃CHCH₂ and C₆H₅I was observed in blank control experiments using similar conditions (DMF, TBAF, Pd(OAc)₂, 72 h, 25°C).