Titanium compounds 14-membered ring structures

Planar six-membered rings from triple-decker complexes (179) for P and As (Table XXXVIII) with metals including V, Nb, Cr, Mo, and W. These complexes have been examined by extended Hiickel calculations, as have the E5 analogues.476 Unlike the E5 system, no compounds with only one metal moiety attached to a planar E6 group have been described. The compound [CpTi]2P6 has titanium atoms on opposite sides of a P6 ring, but each Ti atom is only bonded to three of the P atoms and the result is a cubane-like structure (180). Various isomeric forms of P6 have been examined by SCF MO calculations.216... 

The mixed cyclopentadienyl-cycloheptatrienyl ( 5-7 ) titanium complex Cp( -C7H7)Ti has been prepared in 33 -40% yield by the reduction of CpTiCb with isopropylmag-nesium bromide or Mg in the presence of cycloheptatriene. Reduction of Cp TiCb in THF with Mg in the presence of cycloheptatriene gives Cp ( -C7H7)Ti in 68% yield. Titanium 5-7 complexes exhibit sandwich structures see Sandwich Compound) with the five-membered and seven-membered rings nearly parallel to each other. 

Initially, a series of soluble, highly isospecific catalysts were developed for propylene polymerization [168]. These materials are zirconium, titanium, or hafiiium based metallocenes, such as racemic 1,1-ethylene-di-ri -indenylzirconium dichloride. The term metallocene applies to complexes of transition metals sandwiched between two aromatic rings, usually two cyclopentadienyl. They are rigid structures, due to ethylene bridges between the two five-membered rings. Syntheses of these compounds yield racemic mixtures of two enantiomers. Both produce isotactic polypropylene ... 

Common with Tbf titanium compounds are intermolecular face-to-face n-stacking interactions [43] in solid state between the Tbf ligands, resulting in the abovementioned low solubility of these compounds. This phenomenon is to be found in all solid-state structures discussed so far and is most intense in the solid-state structure of compound IX (see Fig. 6.8), in which the distance between the centroids of the five-membered ring and one of the six-membered rings amounts to 3.470 A, being indicative of strong face-to-face k interactions. This correlates with the compound s solubility, which is lowest by comparison. 

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