Group 4 Metal Complexes of Chelating Cyclopentadienyl-ketimide Ligands

A pendant nitrile group attached to the lithium cyclopentadienide moiety in (C5H4CMe2CMe2CN)Li was alkylated using organyl lithium reagents (RLi, R = Ph, t-Bu, Me), giving rise to dianionic cyclopentadienyl-ketimides [C5H4CMe2­CMe2C­(R)N]­Li2, which were subsequently utilized as chelating ligands for the synthesis of group 4 bent metallocene or half-sandwich complexes (12 examples of the types [(η5-C5R′5)­{η5-C5H4CMe2­CMe2C­(R)N-κN}­MCl], R′ = H or Me, M = Ti, Zr, or Hf, and [{η5-C5H4CMe2­CMe2C­(R)N-κN}­TiX2], X = Cl or NMe2, respectively, were prepared and characterized). Consecutive protolysis of the intramolecularly bound ketimide moiety in bent metallocenes afforded pendant imine or cationic iminium moieties, respectively, attached to group 4 organometallic fragments. Selected compounds were used as precatalysts in a preliminary screening for ethylene polymerization activity.