Titanium biscyclopentadienyl

Miscellaneous.—Hydridofluorophosphates have been prepared for the first time, and the anion (129) has been found to have an octahedral structure, with hydrogens trans.116 Phosphorus pentafluoride forms an adduct with biscyclopentadienyl titanium difluoride.116 The phosphorane (130) has been prepared as shown.117... 

The expected intermediate for the metathesis reaction of a metal alkylidene complex and an alkene is a metallacyclobutane complex. Grubbs studied titanium complexes and he found that biscyclopentadienyl-titanium complexes are active as metathesis catalysts, the stable resting state of the catalyst is a titanacyclobutane, rather than a titanium alkylidene complex [15], A variety of metathesis reactions are catalysed by the complex shown in Figure 16.8, although the activity is moderate. Kinetic and labelling studies were used to demonstrate that this reaction proceeds through the carbene intermediate. 

A rather special case of bimolecular termination was described recently in the literature by Chien (7). It concerns the polymerization of ethylene initiated by a soluble biscyclopentadienyl titanium dichloride-dimethyl aluminium chloride complex. Such a polymerization should be classified as a coordination polymerization and not as an ionic polymerization. Nevertheless, some similarity to anionic polymerization justifies its discussion at this place. It was shown that the termination is kineti-cally bimolecular, and it is postulated that it involves the reduction of two TiIV+ to TiIII+ complexes, proceeding simultaneously with the disproportion of 2 polymeric chains,... 

An excellent review on soluble systems, including also the more recent progresses in ethylene polymerization, is that of Sinn and Kaminsky who even developed soluble catalytic systems with extremely high activities by using alumoxane and biscyclopentadienyl-titanium or-zirconium compounds. Interesting results have also been obtained in ethylene oligomerization and in propylene dimerization... 

The first metallocene catalysts were biscyclopentadienyl titanium complexes and dialkylaluminum chloride. These catalysts were not stable and produced very low yields. However, they were the first catalyst systems to produce copolymers of polypropylene and 1-butene with very high comonomer uniformity, due to the fact that they had only one type of active site. 

Most of the assignments for the and E-, modes are consistent with those made previously for biscyclopentadienyl titanium (IV) derivatives (31) in similar matrices, but differs somewhat from the assignments of Balducci et al (30) for the matrix isolated spectra of the biscyclopentadienyl dihalides. Although the E2 modes of the Cp2Tix2 derivatives (where X=F, Cl, Br, I), were previously assigned by Balducci, correlations can not be made with the solid state spectra. Tentative assignments for the E2 mode have therefore been made and are given in Table 3. 

Chemical composition distribution Biscyclopentadienyl titanium dichloiide Biscydopentadienyl zirconium dichloride Ethylenebis(indenyl)zirconium dichloride Ethylenebis(tetrahydroindenyl)zirconium dichloride Ethylidene(l-tetramethylcyclopentadienylKindenyl) titanium dichloride... 

In 1975 Kaminsky found that a slight amoimt of water added to a mixture of biscyclopentadienyl titanium dimethyl and trimethyl aluminum rapidly polymerized ethylene. Eventually it was determined that the addition of water produced methylaluminoxane (MAO), which was responsible for the boost in activity (261). Although these CP2MX2/MAO catalyst systems rapidly polymerized ethylene and copolymerized other monomers with ethylene, they were less effective for the polymerization of propylene. There were several critical shortcomings with these early metallocene catalysts toward the polymerization of propylene low activity, poor stereospecificity, and low molecular weight polypropylene production. 

To decrease the reduction rate of the titanium system, we investigated (instead of the ethyl-containing system) the reaction of biscyclopentadienyl-titanium dimethyl and trimethylaluminum (TMA), mainly by NMR analysis at low temperatures. The formation of new CH2-bridged titanium aluminum complexes were observed by a slow a-hydrogen transfer (5) [20] ... 

The biscyclopentadienyl derivatives of titanium(III) Ti( j -C5H5)2(R) undergo carbon monoxide insertion ... 

The classical route to many l,3-dichalcogenole-2-thiones starts from a vicinal dihalogenoethene followed by lithiation and reaction with selenium the intermediate diselenate may be isolated as a titanium-biscyclopentadienyl complex (137) as shown in the example in Scheme 31 <93CL1851>. 

Different polystyrene-bound biscyclopentadienyl complexes have been prepared. One example is shown as 69 in Eq. 5-9 [180]. Treatment of soluble copolymers of styrene and methacrylic acid with dichlorotitanocene resulted in soluble titanium-containing copolymers 70 (Eq. 5-10] [181]. Finally polymeric organometallic mesogens 71 with [l,3-(diethynyl)cyclobutadiene]cyclopentadi-enyl Co(II) moieties were prepared by Heck coupling of a corresponding cyclobutadiene monomer with 2,5-diiodothiophene [182],... 

Biscylcopentadienyl alkyls, titanium(III), thermal stability Blscylcopentadlenyl alkyls, titanium(III), chemical reactivity1 Biscylcopentadienyl titanium chloride Biscyclopentadienyl aryls, tltanium(II)... 

Disproportionation reactions, titanium complexes Biscyclopentadienyl allyls, titanium Dlhaptoacyl complexes, titanium Allyl elimination reactions, titanium complexes Biscyclopentadienyl alkyls, titanium, pyridine metalatlon reactions... 

Biscyclopentadienyl complexes and bridged metallocene complexes of titanium show lower polymerization activities than the monocyclopentadienyl complexes (39). The catalytic activity and S5nidiospecificity for bridged metallocenes does increase by decreasing the bite-angle (51). Although ansa-monocyclopentadienyl-amido titanium complexes are essentially inactive for homopolymerization of styrene, efficient sPS formation with nonbridged amido cylcopentadienyl complexes of titanium has been reported (52). 

Biscyclopentadienyl (bis-Cp) metal complexes were not the only single-site catalysts for olefin polymerization. Monocyclopentadienyl complexes often showed activity, but generally were not competitive catalysts except when linked to a bulky amido group. Thus, Bercaw s CpSiNR ligand was placed on titanium by workers at Dow and Exxon and found to produce very active catalysts with attractive features (Figure 15). Both companies filed patents in the US and... 

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