Preparation of Dimeric Monopentamethylcyclopentadienyltitanium(III) Dihalides and Related Derivatives.

The synthesis, crystal structure, and reactivity of a series of half-sandwich titanium(III) dihalide complexes [Ti(η-CMe)X] (X = Cl, Br, I) and several of its Lewis base derivatives were investigated. The reaction of the trihalides [Ti(η-CMe)X] (X = Cl (), Br (), I ()) with LiAlH (≥1 equiv) in toluene at room temperature results in the formation of the halide-bridged dimers [{Ti(η-CMe)X(μ-X)}] (X = Cl (), Br (), I ()). The treatment of with [Li{N(SiMe)}] (≥2 equiv) at room temperature affords the precipitation of the amido titanium(III) complex [{Ti(η-CMe)(μ-Cl){N(SiMe)}}] (), but analogous reactions of with other lithium reagents [LiR] (R = Me, CHSiMe, NMe) lead to disproportionation into titanium(IV) [Ti(η-CMe)R] and presumably titanium(II) derivatives. Similarly, complex in solution at temperatures higher than 100 °C undergoes disproportionation as demonstrated by its reactions with cobaltocene and -(4-methylbenzylidene)aniline yielding the ionic paramagnetic compound [Co(η-CH)][Ti(η-CMe)Cl] () and the diamagnetic diazatitanacyclopentane [Ti(η-CMe)Cl{N(Ph)CH(-tolyl)}], respectively. Treatment of complex with 2 equiv of 2,6-dimethylphenylisocyanide or -butylisocyanide in toluene at room temperature affords the paramagnetic titanium(III) dinuclear adducts [{Ti(η-CMe)Cl(μ-Cl)(CNR)}] (R = 2,6-MeCH (), Bu ()). Magnetic studies for polycrystalline show that it displays a weak intramolecular antiferromagnetic coupling between the Ti ions, which is consistent with the long Ti-Ti distance of 3.857(1) Å determined by X-ray diffraction. The isocyanide ligands in complex undergo a reductive coupling reaction in toluene to give the titanium(IV) iminoacyl derivative [{Ti(η-CMe)Cl}(μ-η:η-BuN═C-C═NBu)] (). Whereas an analogous dinuclear structure was found in the aqua titanium(III) complex [{Ti(η-CMe)Cl(μ-Cl)(OH)}] (), resulting from the reaction of with adventitious amounts of water, compound reacts with excess ammonia to give a mononuclear adduct [Ti(η-CMe)Cl(NH)] () with a robust layered pattern in the solid state.