Cationic group 4 metallocene complexes with pendant imine and pyridine donor groups were prepared as stable crystalline [B­(C6F5)4]− salts either by protonation of the intramolecularly bound ketimide moiety in neutral complexes [(η5-C5Me5)­{η5-C5H4CMe2CMe2C­(R)N-κN}­MCl] (M = Ti, Zr, Hf; R = t-Bu, Ph) by PhNMe2H+[B­(C6F5)4]− to give [(η5-C5Me5)­{η5-C5H4CMe2CMe2C­(R)NH-κN}­MCl]+[B­(C6F5)4]− or by chloride ligand abstraction from the complexes [(η5-C5Me5)­(η5-C5H4CMe2CH2C5H4N)­MCl2] (M = Ti, Zr) by Li­[B­(C6F5)4]·2.5Et2O to give [(η5-C5Me5)­(η5-C5H4CMe2CH2C5H4N-κN)­MCl]+[B­(C6F5)4]−. Solid state structures of the new compounds were established by X-ray diffraction analysis, and their electrochemical behavior was studied by cyclic voltammetry. The cationic complexes of Zr and Hf, compared to the corresponding neutral species, exhibited significantly enhanced luminescence predominantly from triplet ligand-to-metal (3LMCT) excited states with lifetimes up to 62 μs and quantum yields up to 58% in the solid state. DFT calculations were performed to explain the structural features and optical and electrochemical properties of the complexes.

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.

The role of the ketimide ligand geometry in Ti half‐sandwich complexes and the consequent effects in olefin polymerization catalysis (ethylene, styrene, 1‐hexene polymerization, and ethylene/1‐hexene copolymerization) were investigated under various conditions. [CpTiCl2(N=CtBu2)] (1; Cp=η5‐cyclopentadienyl) was used as a reference compound for comparison with the recently described complex [{η5‐C5H4CMe2CMe2C(tBu)=N‐κN}TiCl2] (2 a) and a new derivative that has a longer linker between Cp and the ketimide, [{η5‐C5H4CH2CH2CMe2C(tBu)=N‐κN}TiCl2] (9). The presence of a distorted intramolecularly tethered ketimide moiety reduces the polymerization activity significantly in systems that contain Al‐based cocatalysts (methylaluminoxane, triisobutylaluminum). However, in Al‐free systems both types of compounds provided active polymerization catalysts. Notably, the recently reported activation system Et3SiH/B(C6F5)3 was for the first time demonstrated to activate Ti complexes for ethylene and 1‐hexene (co)polymerization catalysis by hydride transfer.

The asymmetric unit of the title crystal structure is shown in the figure. Tables 1 and 2 contain details of the measurement method and a list of the atoms including atomic coordinates and displacement parameters. Source of materialThe 68, 5.96, 6.04, 6.90(4x m, 1 H, C5H4), 5 H, Ph) ppm. Experimental detailsThe structure was solved by direct methods