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 -40degreesC leads to CH3 addition to the C6-fulvene carbon atom to yield the [C5H4-CMe2NMe2]Li reagent 3a, whereas treatment of 2a with MeLi in THF at -78 degreesC results in deprotonation with formation of [C5H4-C(=CH2)-NMe2]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 [C5H4-C(=CH2)-NEt2]Li (4b). Treatment of the reagents 4 with CpZrCl3 yields the enamino-Cp-substituted bent metallocenes [eta(5)-C5H4-C(=CH2)-NR2]CpZrCl2 5a (R = CH3) and 5b (R = C2H5), respectively. Analogous treatment of 4b with zirconium tetrachloride gave the doubly functionalized zirconocene complex eta(5)-C5H4-C(= CH2)-NEt2]2ZrC12 (6b). The complexes 5a, 5b, and 6b were characterized by X-ray diffraction. Treatment of 3a with CpZrCl3 gave [eta(5)-C5H4-CMe2-NMe2]CpZrCl2 (8a); the analogous reaction with ZrCl4 gave [eta(5)-C5H4-CMe2-NMe2](2)ZrCl2 (8b). Both complexes 8 reacted with (butadiene)magnesium with replacement of both chloride ligands at zirconium. The probably generated (eta(4)-butadiene)zirconocene complexes were, however, not stable under the applied reaction conditions, but reacted further by C-H activation at the N-CH3 group with intramolecular hydrogen transfer to the butadiene ligand to yield the cyclometalated products [eta(5)-C5H4-CMe2- N(CH3)-CH2-]Zr(L)(CH2CHCHCH3) 13a (L = Cp) and 13b (L = [eta(5)-C5H4CMe2-NMe2]), respectively. Complex 5a reacts analogously with (butadiene)magnesium to yield the C-H activation product [eta(5)-C5H4-C(=CH2)-N(CH3)-CH2-]ZrCp(CH2CHCHCH3) 14. The 1-diethylaminoethenyl-Cp-substituted systems 5b and 6b react differently with (butadiene)magnesium. They form the stable eta(4)-butadiene complexes s-trans-15 and s-cas15A/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(C6F5)(3) gave active homogeneous Ziegler-Natta catalysts for ethene polymerization, whereas the systems 13b/B(C6F5)(3) and 17/B(C6F5)(3) were close to inactive under comparable conditions.