| Abstract: Alkenyl (cyclopentadienyl) metal derivatives, which are new kind of organometallic monomers, has attracted increasing attention during recent years. However, only a few examples of alkenyl (cyclopentadienyl) tita nium derivatives have been reported. We have reported that the system consisting of Cp2TiCl2 and i-C3H7 MgBr or other organometallic reducing agent are active catalysts for isomerization of a series of unconjugated diene. But in the case of 1,5-hexadiene such catalysts result in a mixture of 1,4-hexadiene, 1,3-hexadiene, 2,4-hexadiene, methylcyclopentene and methylenecyclopen-tane. Recently we have studied, the effect of substituent on cyclopentadienyl group on isomerization and found that the catalytic results, especially selectivity, depends strongly,on the nature of substituent on cyclopentadienyl ring.In order to study the substitution effect systematically, we designed and synthesized a series of new alkenyl cyclopentadiene and their titanium derivatives 1-16, which were characterized by elemental analysis, IR, 1H-NMR and MS. Their physical constants and yields are summarized in Table 1. Among them, the compounds 12 and 13 are first examples of diene-substituted cyclopentadienyl titanium derivatives. In the case of isomerization of 1,5-hexadiene, the alkenyl substituted cyclopentadienyl titanium derivatives are very active and more selective catalysts to the formation of linear product. Some of results are listed in Table 2. It seems that competitive coordination of alkenyl group in Cp ring to the Ti(Ⅲ) hinders intramolecular coordination and insertion of C=C bond of alkenyl attached to Ti and leads linear isomerizatioii. We have isolated and characterized compound 16 after protolysis of the reaction mixture with hydrochloric acid. This provides strong support to the mechanism shown as scheme 2. |
