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

Novel fluorous alkenyl-fluorosilanes (CnF2n+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 (CnF2n+1CHCHC6H5, 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-(C4F9CHCH)C6H4X], independently of the electronic effect of their substituent (X = Br, CF3, CH3, OCH3). These volatile products can easily be isolated by steam-distilltaion and purified further by distillation. chanism 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).