Synthesis and structural characterization of [H(OEt2)2]+ [(C3H3N2){B(C6F5)3}2]- -: a Bronsted acid with an imidazole-derived 'non-coordinating' anion

Lithium imidazolide, generated by N-H deprotonation of imidazole with n-butyllithium, reacts with two molar equivalents of tris(pentafluorophenyl)borane with N-B bond formation to yield the product Li+[(C3H3N2){B(C6F5)(3)}(2)](-) (6a, isolated in > 70% yield). The analogous reaction sequence starting from 4,5-dimethylimidazole gives the corresponding salt 6b. Its THF coordination product [Li(THF)(4)](+)[(C3HMe2N2){B(C6F5)(3)}(2)](-) (6b(.)THF) was characterized by X-ray diffraction. Deprotonation of benzimidazole followed by the addition of two B(C6F5)(3) equivalents gave the corresponding benzimidazolide-based anion, isolated as the lithium compound 6c. The lithium salts 6 of the large 'non-nucleophilic' anion system [(C3HR2N2){B(C6F5)(3)}(2)](-) were employed in the generation of Group 4 metallocene cations by salt metathesis. Treatment of 6a with HCl in diethyl ether afforded the product [H(OEt2)(2)](+)[(C3H3N2){B(C6F5)(3)}(2)](-) (9), that was also characterized by X-ray crystal structure analysis. The Bronsted acid 9 was used to generate the Group 4 metallocene cation system [Cp2Zr(CH3)(OEt2)](+) (11) (with [(C3H3N2){B(C6F5)(3)}(2)](-) anion) starting from dimethylzirconocene. (C) 2002 Published by Elsevier Science B.V.