Selective Intramolecular [N]CH Activation in Bis(1-ethenylamino-Cp)zirconium−Butadiene Complexes and Related Systems

Treatment of 6-(dimethylamino)-6-methylpentafulvene ( 2a ) with methyllithium in ether at −40 °C leads to CH 3 addition to the C6-fulvene carbon atom to yield the [C 5 H 4 −CMe 2 −NMe 2 ]Li reagent 3a, whereas treatment of 2a with MeLi in THF at −78 °C results in deprotonation with formation of [C 5 H 4 −C( CH 2 )−NMe 2 ]Li ( 4a ). In contrast, treatment of 6-diethylamino-6-methylfulvene ( 2b ) with methyllithium under any of these conditions leads only to H + -abstraction to give [C 5 H 4 −C( CH 2 )−NEt 2 ]Li ( 4b ). Treatment of the reagents 4 with CpZrCl 3 yields the enamino-Cp-substituted bent metallocenes [η 5 -C 5 H 4 −C( CH 2 )−NR 2 ]CpZrCl 2 5a (R = CH 3 ) and 5b (R = C 2 H 5 ), respectively. Analogous treatment of 4b with zirconium tetrachloride gave the doubly functionalized zirconocene complex [η 5 -C 5 H 4 −C( CH 2 )−NEt 2 ] 2 ZrCl 2 ( 6b ). The complexes 5a, 5b, and 6b were characterized by X-ray diffraction. Treatment of 3a with CpZrCl 3 gave [η 5 -C 5 H 4 −CMe 2 −NMe 2 ]CpZrCl 2 ( 8a ); the analogous reaction with ZrCl 4 gave [η 5 -C 5 H 4 −CMe 2 −NMe 2 ] 2 ZrCl 2 ( 8b ). Both complexes 8 reacted with (butadiene)magnesium with replacement of both chloride ligands at zirconium. The probably generated (η 4 -butadiene)zirconocene complexes were, however, not stable under the applied reaction conditions, but reacted further by C−H activation at the N−CH 3 group with intramolecular hydrogen transfer to the butadiene ligand to yield the cyclometalated products [η 5 -C 5 H 4 −CMe 2 − N(CH 3 )−CH 2 −]Zr(L)(CH 2 CHCHCH 3 ) 13a (L = Cp) and 13b (L = [η 5 -C 5 H 4 −CMe 2 −NMe 2 ]), respectively. Complex 5a reacts analogously with (butadiene)magnesium to yield the C−H activation product [η 5 -C 5 H 4 −C( CH 2 )−N(CH 3 )−CH 2 −]ZrCp(CH 2 CHCHCH 3 ) 14 . The 1-diethylaminoethenyl-Cp-substituted systems 5b and 6b react differently with (butadiene)magnesium. They form the stable η 4 -butadiene complexes s - trans - 15 and s - cis - 15A/B (from 5b ) and s - trans - 17 and s - cis - 17 (from 6b ), respectively. [N]CH activation was not observed in these cases. Treatment of the cyclometalated products 13a, 14, and 15 with B(C 6 F 5 ) 3 gave active homogeneous Ziegler − Natta catalysts for ethene polymerization, whereas the systems 13b/ B(C 6 F 5 ) 3 and 17/ B(C 6 F 5 ) 3 were close to inactive under comparable conditions.