Methyl(N-pyrrolyl)zirconocene (8a) reacts with tris(pentafluorophenyl)borane selectively by transfer of the heterocyclic ligand to give the methylzirconocene cation, which is an active ethylene polymerization catalyst when generated in situ in toluene. In contrast, (diethylamido)methylzirconocene (8b) undergoes only transfer of the methyl group when treated with the B(C6F5)3Lewis acid, to five the (diethylamido)zirconocene cation (10b). The [(Et2N)ZrCp2+MeB(C6F5)3-] salt is not stable and rapidly reacts at room temperature with methane elimination and formation of a cationic (η2-iminoacyl)metallocene system. The resulting [Cp2Zr(η2-MeC=NEt)+HB(C6F5)3-] species (11b) is isolated with an 84% yield. Methyl(N-piperidyl)zirconocene (8c) reacts similarly when treated with B(C6F5)3to give the (η2-iminoacylium)zirconocene (11c) via the intermediate 10a. © 1995.
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