Protonation of the heterocyclic Cp-anion equivalent [pyrrolyl-B(C6F5)(3)]Li - Formation of a useful neutral Bronsted acid for the generation of homogeneous metallocene Ziegler catalysts

N-pyrrolyllithium (1) adds to B(C6F5)(3) to yield [(C4H4N)B(C6F5)(3)]Li (3) The corresponding monoetherate (3 . OEt2) was characterized by X-ray diffr action and shows an eta (5) coordination of the pyrrolyl moiety to the Lith ium cation. Treatment of 3 with HCl in ether leads to H+ addition at a pyrr olyl a-position to yield the neutral dipolar Bronsted acid system [(C4H5N)B (C6F5)(3)] (4) The reagent 4 can be used to protonate Cp2Zr(CH3)(3) to yiel d [Cp2Zr(CH3)(+)(C4H4N)B(C6F5)(3)(-)] (6) and methane. H+ transfer from 4 t o (butadiene)-zirconocene results in the formation of the (pi -allyl)metall ocene salt [(C4H7)ZrCp2+(C4H4N)B(C6F5)(3)(-)] (8). In analogous reactions. the neutral Bronsted acid was employed as a protonating activator component for the generation of homogeneous Ziegler catalysts derived from a variety of (butadiene)or (dimethyl)ansa-metallocenes. The systems generated by tre atment with 4 show comparable activities in ethene or propene polymerizatio n reactions as conventionally generated Group 4 metallocene Ziegler catalys ts.