OXIDATIVE ETA(2)-IMINOACYL FORMATION BY REACTION OF AMIDOZIRCONOCENE COMPLEXES WITH TRIS(PENTAFLUOROPHENYL)BORANE

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 c atalyst when generated in situ in toluene. In contrast, (diethylamido) methylzirconocene (8b) undergoes only transfer of the methyl group whe n treated with the B(C6F5)(3) Lewis acid, to give the (diethylamido)zi rconocene cation (10b). The [(Et(2)N)ZrCp(2)(+) MeB(C6F5)(3)(-)] salt is not stable and rapidly reacts at room temperature with methane elim ination and formation of a cationic (eta(2)-iminoacyl)metallocene syst em. The resulting [Cp(2)Zr(eta(2)-MeC=NEt)(+) HB(C6F5)(3)(-)] species (11b) is isolated with an 84% yield. Methyl(N-piperidyl)zirconocene (8 c) reacts similarly when treated with B(C6F5)(3) to give the (eta(2)-i minoacylium)zirconocene (11c) via the intermediate 10a.