Isobutene polymerization and copolymerization with isoprene initiated by [Cp*TiMe2]+ in the presence of a novel type of weakly coordinating counteranion

The highly electrophile borane B(C(6)F(5))(3) reacts with octadecanoic acid (n-C(17)H(35)CO(2)H, stearic acid) to form 1:1 and 2:1 adducts [n-C(17)H(35)CO(2)H][B(C(6)F(5))(3)] and [n-C(17)H(35)CO(2)H][B((6)F(5))(3)](2.) These adducts exhibit enhanced acidities, and react with Cp*TiMe(3) in methylene chloride and toluene to give methane and the complexes [Cp*TiMe(2)]-[n-C(17)H(35)CO(2){B(C(6)F(5))(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 -30degrees. High conversions to high molecular weight homo- and copolymers are obtained, consistent with the anion [n-C(17)H(35)CO(2){B(C(6)F(5))(3)}(2)](-) being very weakly coordinating.