Synthesis of the Cation Complex [TaCp*Me₃]⁺ and a Comparison of Its Reactivity with That of [TaCp*Me₄]^†

The new ionic compound [TaCp*Me3][MeB(C6F5)3] (1; Cp* = η5-C5Me5) was obtained by reaction of [TaCp*Me4] with B(C6F5)3. Addition of pyridine to the strongly acidic cation of 1 gave the new pyridine-coordinated cation [TaCp*Me3(py)]+ (2). Hydrolysis of 1 in wet dichloromethane yielded the ionic compound [(TaCp*Me2)2(μ-O)][MeB(C6F5)3]2 (3), containing a dinuclear dication identified by X-ray diffraction. Similar hydrolysis of cation 1 as well as its pyridine adduct 2 with H2O·B(C6F5)3 afforded the neutral oxoborane compound [TaCp*Me2{O·B(C6F5)3}] with elimination of B(C6F5)3 and py·B(C6F5)3, respectively. Cation 1 inserted 1 equiv of PhC(O)H at room temperature to give the cationic alkoxo complex [TaCp*Me2(OCHMePh)]+ (4), which reacted further with an additional 1 equiv of PhC(O)H to give a mixture of the rac and meso diastereoisomers of [TaCp*Me(OCHMePh)2]+ (5), whereas only the neutral alkoxo compound [TaCp*Me3(OCHMePh)] (6) was formed from the reaction of [TaCp*Me4] with PhC(O)H upon heating. Cation 1 also reacted with 1 and 2 equiv of PhNCO to give [TaCp*Me2{OC(Me)NPh}]+ (7) and [TaCp*Me{OC(Me)NPh}2]+ (8) by insertion of isocyanate into one or two Ta−C bonds, respectively. However, heating [TaCp*Me4] with PhNCO gave the dinuclear μ-oxo compound [(TaCp*Me3)2(μ-O)] (9). Compound 1 showed rather low activity when tested as an ethylene polymerization catalyst.