Fulvenes titanium complexes

In the foregoing sections on thermal decomposition of Cp TiR compounds (R = alkyl), we mentioned the formation of a titanium compounds where one of the Cp groups has lost a hydrogen atom producing Cp (C (CH ) CH2)Ti, formally a fulvene titanium complex. Generation of such a fulvene ligand, C,.(CH )seems to be rather common in Cp Ti [41,45,49] and Cp Zr chemistry [50]. 

A mechanistically obscure transformation occurs upon treatment of the tetramethylfulvene titanium complex 161 with methallyl Grignard, producing bridged titanacyclobutane complex 162. This reaction is proposed to proceed by intramolecular alkylation at the central carbon of an 7]4-fulvene, 7]3-methallyl intermediate, but with due consideration... 

Cp/amido titanium complexes with /)3-C1-bridges, (CsH2Me2-CHR-NBut)TiX2 (X = NMe2, Cl) (Scheme 318), are synthesized using fulvenes with substituents in 1-, 4-, and 6-positions. The compounds G5H3Me2-GHR-NHBut... 

The isomerization process of the fulvene titanium allyl complex Cp (Fv)Ti(773-C3Fl5)1293 (Fv = CsMe4CH2) (Scheme 506 Section 4.05.4.2.1) to the 1-propenyl Cp FvTi( 71-CH=CHMe) has been investigated. Mechanistic, kinetic, and thermodynamic aspects suggest that the reaction proceeds via reversible first-order steps with the participation of four intermediates.1323... 

The reductive coupling of fulvenes is a convenient method and a novel and versatile route for the preparation of ansa-bis-Cp titanium complexes with ethylene bridges. The ansa-bis-Cp complexes shown in Scheme 640 have been prepared by reduction of the appropriate fulvene reagent with TiCl2. The complexes in combination with MAO are highly active in ethylene polymerization and give linear, high density polymers.1654... 

The fulvene route was also successfully employed in the preparation of a compound, which can be regarded as one of the most advanced molecular models for a catalytically active titanium center on a silica surface. When Cp Ti(C5Me4CH2) was reacted with the monosilylated silsesquioxane precursor 12 in refluxing toluene a color change from deep purple to amber was observed. Crystallization afforded a bright-yellow material, which was subsequently shown to be the novel mo o(pentamethyleyclopentadienyl) titanium(IV) silsesquioxane complex 126 (69% yield). Its formation is illustrated schematically in Scheme 42. 

Interestingly, a similar process is observed for the thermal decomposition of dimethylbis(pentamethylcyclopentadienyl)titanium(IV) (65). The decomposition takes place at elevated temperatures around about 110 °C and results in the formation of fulvene complex 68 and methane. Extensive labeling experiments and kinetic measurements resulted in two reaction pathways compatible with the experimental observations. Either one involves a titanium methylene species 66 as the key intermediate. The next step is an intramolecular C,H-activation leading to fulvene complex 67, similar to the formation of 63. Einally, a hydrogen shift accounts for the final product, fulvene complex 68 (Scheme 10.23) [71]. 

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