The roles of oxidation state, Lewis acid cocatalyst and solvent polarity in activating titanium compounds for olefin polymerization

Abstract

The polymerization activity of the following three catalyst systems towards ethylene has been investigated and compared: 1) methyltitanocene chloride-M+lC1, 2) q3-allyltitanocene-M%AlCl and 3) titanium dichloride tetrahydrofuranate-Me&Cl.The f i s t two catalysts formed homogeneous phases and produced linear polymer; the last catalyst functioned in a heterogeneous medium and formed crosslinked polymer. The titanium (Iv) catalyst was about 30 times more active than the t i t a n i u m 0 system and the titanium(II) catalyst on MgC1, could be made 8 times more active than the t i t a n i u m 0 system. A novel mechanism is proposed to explain the behavior and activity of the titanium@) system.

The Synthesis and Reactivity of Group 4 Zwitterionic Complexes of the Type Mt+CH2AlCl3−: One‐Component Stereoselective Polymerization and Oligomerization Catalysts for Olefins and Acetylenes

“…Melting points were determined on a Thomas-Hoover Unimelt capillary melting point apparatus and are uncorrected. TiCl 4 , ZrCl 4 , HfCl 4 , and trimethylaluminum and dimethylaluminum chloride were obtained from commercial sources in at least 97% purity, and were stored or transferred for use under pure argon. Appropriate transfer techniques employing siphon, cannula or syringe have been described elsewhere.…”

“…The major product is 1,1-diphenylethylene (12), which can readily be viewed as resulting from the methylenation via 11, just as the methylenetitanium() compounds or Tebbe reagents achieve such a transformation with a carbonyl substrate [Equation (4)]. (4) The necessity for an electrophilic Ti atom in 9b is shown by the lack of formation of 12 when the reaction is attempted in ether. Solvation of 9b by the Lewis base ether would obviously inhibit electrophilic attack of 9b on the ketone.…”

“…Accordingly, as a precis of the evidence in support of the empirical formula of AlCCl 3 H 2 Ti for 9a or 9b, we offer the following: 1) the yield of black solid 9 isolated was 94% of that expected from such a formula; 2) the yield of the Me 2 AlCl by-product was essentially 100% of that expected according to reactions 1 and 2 of Scheme 2, and all starting Me 3 Al had been consumed; 3) the type of gas and the amounts evolved in the protolysis of 9, 1.45 mol-equiv. of a 2:1 molar ratio of CH 4 and H 2 , was 97% of that expected from the protolysis according to Equation (2); 4) the 1 H and 13 C NMR spectra of 9 show signals for a CH x group, which then in a 13 C PENDANT experiment was shown to undergo signal inversion and thus was unmistakably identified as a CH 2 group; 5) the sole 27 Al NMR signal in the spectrum of a solution of 9 was found at δ ϭ 101 ppm, a signal region that is typically associated with tetracoordinate aluminate anions (for example, that of AlCl 4 Ϫ at δ ϭ 103 ppm); and 6) reagent 9 displayed its methylenating, titanium()-reducing and Lewis-acidic characteristics in discrete reactions with benzophenone [Equations (3) and (4) of the expected by-product 6, NMR spectroscopic data on 25 or 26 could not be recorded because of the insolubility of these complexes in CDCl 3 or other inert solvents. (6) Although the available physical data for 25 and 26 therefore do not compellingly support the suggested methylene structure or zwitterionic counterpart M t ϩ ϪCH 2 ϪAlCl 3 Ϫ (27), the chemical reactions of 25 and 26 are exactly parallel to those of the titanium analog 9.…”

“…of a 4:1 mixture of methane and dihydrogen (the latter from Ti 2ϩ Ǟ Ti 3ϩ ) expected from 8, 1.45 Ϯ 0.05 equiv. of a 2:1 mixture of CH 4 and H 2 evolved from the black solid 9 [Equation (2)].…”

“…of Me 3 Al (5) to give TiCl 2 (7) (Scheme 2), and the reaction was conducted in toluene so as to avoid Lewis complexation of either the reactants or the products with any THF present. [3,4,10] Scheme 2…”