Difference in Reactivity of Cyclopentadienyltitanium Fluorides and Chlorides Using AlR3 (R ) Me, Et): Syntheses and Structures of Ti(III)-F(Cl)-Al Compounds (η-C5Me5)2Ti2(μ-Cl)6Al2Me4, (η-C5Me5)2Ti2(μ-F)8Al4Me8, and [(η-C5H4Me)2Ti(μ-F)2AlEt2]2

The reaction of Cp*TiX3 [X ) Cl (1a), F (1b), Cp* ) η-C5Me5] with an excess of AlMe3 afforded the methylated products Cp*TiCl2Me (2a) and (Cp*TiF2Me)(AlMe2F) (2b), respectively, whereas under thermal conditions the reduced titanium species Cp*2Ti2(μ-Cl)6Al2Me4 (3) and Cp*2Ti2(μ-F)8Al4Me8 (4) were obtained in moderate yields. The reduction of Ti(IV) to Ti(III) is observed when Cp′2TiF2 (Cp′ ) η-C5H5, η-C5H4Me, Cp*) and Cp*TiF3 are treated with AlEt3, leading to [Cp′2Ti(μ-F)2AlEt2]2 [Cp′ ) η-C5H5 (5), η-C5H4Me (6), Cp* (7)] and Cp*2Ti2(μ-F)8Al4Et8 (8), respectively. The crystal structures of complexes 3, 4, and 6 have been determined by X-ray single-crystal structure analyses. The core of structure 3 is described as a chair conformation. The environments of the Al and Ti atoms in 3 are distorted tetrahedral and pseudo square pyramidal, respectively. The single-crystal structure analysis of 4 shows an octahedral metal core for Al4Ti2 with the Ti atoms occupying trans positions. The core of complex 6 is a nonplanar eight-membered ring consisting of two titanium atoms, two aluminum atoms, and four bridging fluorine atoms.