CpTiX

Synthesis. The discovery of stable cyclopentadienyltitanium compounds, in particular Cp2TiCl2, stimulated the synthesis and study of a host of related compounds. These include both CpTiX and Cp2TiX2. 

Mixed cyclopentadienyl-diene titanium complexes, Cp TiX(diene)(X = Cl, Br, I), have been prepared in 30-60% yield by the stoichiometric reaction of CpTiXs with (2-butene-l,4-diyl)magnesium derivatives or by the reduction of CpTiXs with RMgX (R = i-Pr, f-Bu, Et X = Cl, Br, I) in the presence of conjugated dienes, as shown in Scheme 4. The butadiene, 1,3-pentadiene, and 1,4-diphenylbutadiene complexes of Cp TiX exhibit a unique prone (endo) conformation (13), while the isoprene, 2,3-dimethylbutadiene, and 2,3-diphenylbutadiene complexes prefer the supine (exo) conformation (14). Reduction of Cp TiX(diene) with RMgX or Mg gives a low-valent species, which catalyzes a highly selective (>99%) tail-to-head linear dimerization of isoprene and 2,3-dunethylbutadiene. " ... 

No suggestions have yet been made as to either the precise structures of these active forms or how they differ from the more stable green fulvalene form. Several attempts have been made to prepare similar species by electrochemical reduction of CpzTiX2 and CpTiXs compounds (e.g., Ref. 30, and references therein). Blue solutions have been obtained, but the identity of the species at present remains uncertain, although recent studies have indicated that anionic species are the probable products in THF solution according to Refs. 34-36 ... 

Alkoxo complexes CpTiX(OR)2 (Scheme 754) have been used as catalysts for organic aldol condensation reactions in the synthesis of stereogenic centers.1909... 

Monocyclopentadienyl complexes of titanium (CpTiXs) perform poorly as catalysts for ethylene or propylene polymerization, but in the presence of MAO, they polymerize styrene to stereo- and regioregular syndiotactic polystyrene, a crystalline material with very high melting point (273 °C) and glass transition temperature (100°C). In this case, the active polymerizing species is a complex (Figure 8). Each styrene monomer inserts in a secondary manner and the stereoregularity is maintained by the conformation of the last inserted unit (chain-end control). 

Ru(II) complexes is mostly d character, while the lowest unoccupied empty orbital is ligand-based ti orbital. A number of Pt(II) diimine complexes also display MLCT emission. Cp2TiX2, Cp 2TiX2, CpTiXs, and Cp"TiX3, where Cp = cyclopentadienyl anion, Cp = substituted cyclopentadienyl anion and X = halide known to display charge-transfer transitions from the filled Cp or Cp n orbital to the empty d orbital of the Ti(IV) center. ... 

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