Summary: The highly electrophilic borane B(C6F5)3 reacts with octadecanoic acid (n‐C17H35CO2H, stearic acid) to form 1:1 and 2:1 adducts [n‐C17H35CO2H][B(C6F5)3] and [n‐C17H35CO2H][B(C6F5)3]2. These adducts exhibit enhanced acidities, and react with Cp*TiMe3 in methylene chloride and toluene to give methane and the complexes [Cp*TiMe2][n‐C17H35CO2{B(C6F5)3}1,2]; the 2:1 complex in particular is a very good initiator for the carbocationic polymerization of isobutene (IB) and copolymerization of IB with isoprene at temperatures as high as −30 °C. High conversions to high molecular weight homo‐ and copolymers are obtained, consistent with the anion [n‐C17H35CO2{B(C6F5)3}2]− being very weakly coordinating.Novel class of Brønsted acidic initiators behave as very good initiators, e.g. in homopolymerisation of isobutene.magnified imageNovel class of Brønsted acidic initiators behave as very good initiators, e.g. in homopolymerisation of isobutene.

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