Developing a fulvene route to C1-bridged “constrained geometry” Ziegler catalyst systems

6-dimethylamino-6-methylfulvene (7) was converted to the [(C₅H₄)–CMe₂–NMe₂]⁻ ligand system (8) by treatment with methyllithium. Its reaction with MCl₄ (M = Zr, Ti) followed by treatment with CH₃Li gave the respective [(C₅H₄)–CMe₂–NMe₂]₂M(CH₃)₂ complexes (12). Their reaction with B(C₆F₅)₃ led to reactive metallocene cation complexes that instantaneously underwent CH activation at a N–CH₃ group to yield the metallacyclic cation complexes 15. (tert-butylaminomethyl)fluorene was prepared by the addition of tert-butylisocyanate to fluorenyllithium followed by hydride reduction. Deprotonation by a variety of bases gave rise to a series of competing and consecutive reactions to yield several unusually structured products, among them a fluorenyl-anellated η⁵-1-azapentadienyl anion equivalent (25) and [(flu)-CH₂–NCMe₃]Li₂ (23). An improved way of generating synthetically useful C₁-linked [Cp–C₁(R) _n –NR¹]^2- dianion equivalents was developed starting from 6-amino-6-methylfulvene (26). N-silylation followed by double deprotonation with, e.g., lithium diisopropylamide cleanly furnished the respective [(C₅H₄)–C(=CH₂)–NSiMe₃]^2- dianion 33 (isolated as the dilithio derivative). Its reaction with Cl₂Zr(NEt₂)₂ in THF gave [η⁵:κ-N-(C₅H₄)–C(=CH₂)–NSiMe₃]Zr(NEt₂)₂ 36. Activation of 36 with methylalumoxane in toluene led to the formation of a C₁-linked “constrained geometry” Ziegler catalyst that polymerized ethylene similarly as the [(C₅Me₄)SiMe₂NCMe₃]ZrCl₂ derived literature system. This revised version was published online in June 2006 with corrections to the Cover Date.