Bis-cyclopentadienyl titanium compounds

Olefines can be polymerised not only with ethers of orthotitanum acid, but also with halogenised cyclopentadienyl titanium compounds, bis(cyclopentadienyl)titaniumdichloride, as well as diphenyl-bis(cyclopentadienyl) titanium compounds combined with aluminumtrial-kyls, or tetrakys(trimethylsiloxy)titanium combined with aluminumtrialkyl and aluminum alkylhalogenides. 

The polymerization activities of bis-cyclopentadienyl titanium compounds are lower than those of bridged bis-cyclopentadienyl titanium compounds. Miya-shita et al. reported the polymerization activities of several bridged bis-cyclopentadienyl titanium compounds [15]. They found that the catalytic activity of CH2(Cp)2TiCl2 is the highest among bis-cyclopentadienyl titanocene compounds. The data indicate that the polymerization activities and also syndiospecificity increase with a decreasing angle between the Cp centroid-Ti-Cp centroid in bis-cyclopentadienyl titanocene compounds. 

While it is not the purpose here to review all Cp-Ti compounds, there is obviously a very close relationship between CpTi moieties and their rearrangement product (CsH TiH via ring-to-titanium a-hydrogen shift, as has been alluded to above. The nature of the Ti-H species involved in reactions between low-valent titanium compounds and dinitrogen is not always clear. There seems little doubt that some form of bis(cyclopentadienyl) titanium is an active intermediate in dinitrogen coordination reactions (31, 37-39), but there is as yet no conclusive evidence that a Ti-H species is involved in the initial reaction (11), despite some claims to the contrary (40). The existence of different forms of Cp2Ti is referred to again below. 

Breslow (139) discovered a homogeneous system well suited for kinetic analysis. He realized that bis(cyclopentadienyl)titanium(IV) compounds, which are very soluble in aromatic hydrocarbons, could be used instead of titanium tetrachloride as the transition-metal compound together with aluminum alkyls to give Ziegler catalysts. Subsequent research on this and other systems with various alkyl groups has been conducted by Natta et al. (140, 141), Belov el at. (142-144), Patat (145), Patat and Sinn (146) Sinn et al. (119, 147), Shilov and co-workers (148-150), Chien and Hsieh (20), Adema (151), Clauss and Bestian (152), Henrici-Olive and Olive (153), and Reichert and Schoetter (154) and Fink (155). 

The polymerization of a-olefins, promoted by homogeneous Ziegler-Natta catalysts based on bis(cyclopentadienyl)titanium(IV) or analogous zirconium compounds and aluminum alkyls, occurs simultaneously with a series of other reactions that greatly complicate the kinetic interpretation of the polymerization process (see Scheme 3). 

Among the titanium complexes producing SPS, monocyclopentadienyltita-nium compounds show the highest polymerization activities and highest syn-dio-directing stereospecificity as compared with non-cyclopentadienyl, bis-cyclopentadienyl and bridged bis-cyclopentadienyl titanium complexes. 

For the preparation of cyclopropanes from transition-metal complexes see Section 5.2.6., p 1849. Various transition-metal complexes are able to undergo addition to the exocyclic double bond of methylenecyclopropanes with formation of a (7 bond between the carbon and metal atoms. A variety of methylenecyclopropanes with one or two methyl groups in positions 1 and 2 were reacted with bis(cyclopentadienyl)titanium dichloride and isopropylmagnesium bromide to give the corresponding neutral bis(cyclopentadienyl)cyclopropylmethyltitanium(III) compounds 1 in yields ranging from 23 to The carbon-metal [Pg.1512]

Most of the homogeneous Ziegler-type catalysts have been preferentially investigated in order to understand the elementary steps of the polymerization, which is simplified in soluble systems. Bis(cyclopentadienyl)titanium(IV) compounds, which are soluble in aromatic hydrocarbons could be used together with aluminum alkyls to give Ziegler-catalysts. As to the kinetics of polymerization and to side reactions of the catalyst components, this system is probably the best understood. It has not been used in a technical process because of the low activity and short life of systems that contain chloride (see Table 1). 

I] could also be prepared by reaction of [II] with two to three equivalents of allyl magnesium chloride in tetrahydrofuran at room temperature pure [I] could be isolated from the violet reaction mixture in the same way as described above. If only one equivalent of allyl magnesium chloride was used, however, the solution turned brown after evaporation a brown oil separated. This product may contain allyl-bis(cyclopentadienyl)-titanium monochloride, but so far all attempts to isolate this compound have failed, even when the solvent was varied and the temperature of the solution kept as low as -80°,... 

Bimetallic compounds containing aluminium and a transition metal are of interest because of their potential as catalysts, and several novel systems have been investigated. The reaction of trimethylaluminium with a number of bis(cyclopentadienyl)titanium... 

Regarding the compounds XLI-XLIII as representatives of di-, tetra- and polynuclear cyclopentadienyl titanium complexes, the optimum cure rates ranged between 38 and 70%, whereby as long as bis(cyclopentadienyl) titanium moieties were present, the antitumor activity was still more pronounced than in the case of XLII containing four mono-(cyclopentadienyl) titanium units. The oxobridged complexes XLI and XLII are typical examples of products formed by hydrolytic reactions after dissolution of I and XXXVIII, respectively, in water. The clearly reduced strength of their antitumor potency in comparison to the parent compoimds underlines that hydrolysis does not seem to be a step producing the intrinsically active species. 

Treatment of animals bearing subcutaneously growing B16 melanoma with diverse bis-(cyclopentadienyl) titanium or bis(cyclopentadienyl) iron compounds significantly influenced tumor development and reduced the growth of the tumors by 50-80% (Tables 8, 9). For T/C ratios between 50 and 20%, there was a clear dependence on the doses applied. This was observed after application of sublethal doses of the neutral... 

The fact that both kinds of antitumor titanium compounds, i.e. bis(cyclopentadienyl)-titanium and bis(benzoylacetonato)titanium complexes, cause liver toxicity as main side effect may be a hint to titanium or titanium-containing moieties to be responsible for die induction of functional and structural liver damage. This feature is further confirmed by the enrichment of titanium in the liver after injection of I (cf. Chap. IX.A.). On the... 

In case of borate as cocatalyst, the catalytic activity of the titanium complex with a pentamethylcyclopentadienyl hgand is high, but a titanium complex with a cyclopentadienyl ligand without any substituents is not active for the syndiospecific styrene polymerization. The reason is that the reaction product of the borate and the cycopentadienyltitanium compound is unstable. The stability of the active site with the borate compound is lower in comparison to that with MAO. The reaction of CH2(Cp)2Ti(Me)2 with dimethylanilinium tetrakis(pentafiuorophenyl)borate or tris(pentafluorophenyl)borane in an equimolar mixture has been examined by Miyashita, Nabika, and Suzuki [11]. Two types of methylene bis(cyclopentadienyl)titanium ion complexes were isolated (see Fig. 3.6). These complexes were active in the polymerization of styrene, but only atactic polystyrene was formed. 

Covalently bonded chiral auxiliaries readily induce high stereoselectivity for propionate enolates, while the case of acetate enolates has proved to be difficult. Alkylation of carbonyl compound with a novel cyclopentadienyl titanium carbohydrate complex has been found to give high stereoselectivity,44 and a variety of ft-hydroxyl carboxylic acids are accessible with 90-95% optical yields. This compound was also tested in enantioselective aldol reactions. Transmetalation of the relatively stable lithium enolate of t-butyl acetate with chloro(cyclopentadienyl)-bis(l,2 5,6-di-<9-isopropylidene-a-D-glucofuranose-3-0-yl)titanate provided the titanium enolate 66. Reaction of 66 with aldehydes gave -hydroxy esters in high ee (Scheme 3-23). 

Binding energy, pentacarbonyliron, 6, 3 Binuclear complexes bis-Cp titanium halides, 4, 522 with Ni-M and Ni-C cr-bonds heterometallic clusters, 8, 115 homometallic clusters, 8, 111 Binuclear dicarbonyl(cyclopentadienyl)hydridoiron complexes, with rand C5 ligands, 6, 178 Binuclear iridium hydrides, characteristics, 7, 410 Binuclear monoindenyl complexes, with Ti(IV), 4, 397 Binuclear nickel(I) carbonyl complexes, characteristics, 8, 13 Binuclear osmium compounds, with hydrocarbon bridges without M-M bonds, 6, 619... 

The moisture- and air-sensitive dark-green titanium derivative (dec. > 180°) was also obtained in 54% yield when bis[cyclopentadienyl]diphenyltitanium in heptane and elemental tellurium were refluxed for 12 days. The compound was purified by recrystallization from dry toluene3. The activation energy of the ring inversion of the metallocycle was determined by H-NMR spectroscopy to be 51kJ mol-1. 

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