Luminescent Cationic Group 4 Metallocene Complexes Stabilized by Pendant N-Donor Groups

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 [(eta(5)-C5Me5){eta(5)-C5H4CMe2CMe2C(R)=N-kappa N}MCl] (M = Ti, Zr, Hf; R = t-Bu, Ph) by PhNMe2H+[B(C6F5)(4)](-) to give [(eta(C5Me5)-C-5){eta(5)-C5H4CMe2CMe2C(R)=NH-kappa N}MCl](+)[B(C6F5)(4)]or by chloride ligand abstraction from the complexes [(eta(C5Me5)-C-5) (eta(5)-C5H4CMe2CH2C5H4N-kappa N)MCl2] (M = Ti, Zr) by Li [ B(C6F5)(4)]center dot 2. 5 Et2O to give [(eta(5)-C5Me5)(eta(5)center dot C5H4Me2CH2C5H4N-kappa N)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 ((LMCT)-L-3) excited states with lifetimes up to 62 mu s 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.