Synthesis of dimetallic μ-alkylideneamido zirconocene dications by a thermodynamically favorable lithium chloride elimination pathway

The reagent [butyl-B(C6F5)3]−Li+ reacts with the complexes Cp2ZrCl(NCHR) (6) (RCH3 or p-tolyl) at ambient temperature by chloride abstraction. The resulting in situ formed [Cp2Zr(NCHR)]+ cations (8) dimerize under the reaction conditions. After removal of a stoichiometric amount of lithium chloride the corresponding μ-alkylideneamido-bridged dimeric [Cp2Zr(NCHR)]2 2+ dications 9a (R=CH3) and 9b (R=p-tolyl) are isolated in yields of ca. 80% (with [butyl-B(C6F5)3]− counteranion). The complexes 9a and 9b are each obtained as mixtures of cis- and trans-isomers. Crystallization from dichloromethane gave pure trans-9a and trans-9b samples. Both were characterized by X-ray crystal structure analyses. Treatment of the dications 9 with acetonitrile gave the respective mononuclear monocationic adduct complexes [Cp2Zr(NCHR1)NCCH3]+[butyl-B(C6F5)3]− (16).