Titanium halide compounds

Attempts to synthesize transition metal alkyl compounds have been continuous since 1952 when Herman and Nelson (1) reported the preparation of the compound C H6>Ti(OPri)3 in which the phenyl group was sigma bonded to the metal. This led to the synthesis by Piper and Wilkinson (2) of (jr-Cpd)2 Ti (CH3)2 in 1956 and a large number of compounds of titanium with a wide variety of ligands such as ir-Cpd, CO, pyridine, halogen, etc., all of which were inactive for polymerization. An important development was the synthesis of methyl titanium halides by Beerman and Bestian (3) and Ti(CH3)4 by Berthold and Groh (4). These compounds show weak activity for ethylene polymerization but are unstable at temperatures above — 70°C. At these temperatures polymerizations are difficult and irreproduceable and consequently the polymerization behavior of these compounds has been studied very little. In 1963 Wilke (5) described a new class of transition metal alkyl compounds—x-allyl complexes,... 

The low-pressure polymerization of olefins using Ziegler-Natta catalysts, i.e., mixtures of compounds of transition groups IV to VI of the periodic table of the elements together with organometallic compounds of groups I to III is widely applied. Such catalysts, consist of titanium alkyl compounds and aluminum alkyl compounds or alkylaluminum halides. 

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... 

For instance, in the field of elastomers, alkyllithium catalyst systems are used commercially for producing butadiene homopolymers and copolymers and, to a somewhat lesser extent, polyisoprene. Another class of important, industrial polymerization systems consists of those catalyzed by alkylaluminum compounds and various compounds of transition metals used as cocatalysts. The symposium papers reported several variations of these polymerization systems in which cocatalysts are titanium halides for isoprene or propylene and cobalt salts for butadiene. The stereospecificity and mechanism of polymerization with these monomers were compared using the above cocatalysts as well as vanadium trichloride. Also included is the application of Ziegler-Natta catalysts to the rather novel polymerization of 1,3-pentadiene to polymeric cis-1,4 stereoisomers which have potential interest as elastomers. 

Other mixed gm-dimetalhc compounds containing zinc and either zirconium, aluminum, or titanium have been successfully prepared from alkynylzinc halide compounds via hydrozirconation by H(Cl)ZrCp2 (the Schwartz s reagent) or carbometalation by a combination of Me3AECp2TiCl2 (Scheme 15). 

The Diels-Alder reaction is one of the most fundamental means of preparing cyclic compounds. Since discovery of the accelerating effect of Lewis acids on the Diels-Alder reaction of a,)3-unsaturated carbonyl compounds [341-344], its broad and fine application under mild reaction conditions has been amplified. Equations (140) [341] and (141) [345], respectively, illustrate typical dramatic effects from an early reaction and from one reported more recently. Lewis acid-promoted Diels-Alder reactions have been reviewed [7,8,346-353]. In addition to the acceleration of the reaction, other important feature is its alteration of chemo-, regio-, and diastereoselectivity this will be discussed below. The titanium compounds used in Diels-Alder reaction are titanium halides (TiX4), alkoxides (Ti(OR)4), or their mixed salts (TiX (OR)4 n = 1-3). A cyclopentadienyl complex such as Cp2Ti(OTf)2 is also documented as a very effective promoter of a Diels-Alder reaction [354], In addition to these titanium salts, a few compounds such as those in Eq. (142) [355] have recently been reported to effect the Diels-Alder reaction. The third, [(/-PrO)2Ti(bpy)(OTf)(i-PrOH)] (OTf), was estimated to be a more active catalyst than Cp2Ti(OTf)2. 

Reactions of simple silanediols and disilanols with titanium orthoesters, titanium halides and titanium amides proceed to give cyclic titanasiloxanes [30]. On the other hand, the silanetriols with three functional OH groups would prove appropriate synthons for constructing three-dimensional titanasiloxanes which would in turn serve as model compounds for catalytically useful Ti-doped zeolites [32]. The synthesis of cubic titanasiloxanes has been achieved in two ways. 

The only work on the catalysis of diene polymerization by structurally defined organotitanium compounds that can be mentioned is that of Dolgoplosk and coworkers [50]. As these authors have found, tetrabenzyltitanium and the tribenzyl-titanium halides can catalyze the stereospecific diene polymerization without any co-catalyst. 

The alkoxytitanium propene compound Ti(T] -propene)(OTr)2 (46) [153], which is believed to be generated from Ti(0 Pr)4 and two equivalents of /-PrMgCl, reacts with internal alkynes to give titanium-alkyne compounds Ti(ri-alkyne) (0 Pr)2 (47) in quantitative yield (Scheme 6.9) [154,155]. 46 reacts with carboxylic esters to produce cyclo-propan- 1 -ols in modest yields [ 156,157]. Oxidative addition of allyllic halides or allyllic alcohols to 46 proceeds readily to form allyl titanium compounds 48, whose reaction with aldehyde provides a stereoselective synthesis of homoallylic alcohols [153]. 

Nitrogen compounds. Nitrogen compounds with N—H bonds appear to react with titanium halides to give initially an adduct, from which hydrogen halide is eliminated by base catalysis. Thus the action of diluted gaseous... 

Step 1 A titanium halide and an ethylaluminum compound combine to place an ethyl group on titanium, giving the active catalyst. Titanium has one or more vacant coordination sites, shown here as an empty orbital. 

A more speeialized reaetion involves the use of a Ziegler eatalyst, formed from vanadium and titanium halides eomplexed with alkyl aluminum compounds, to synthesize alternating copolymers from propylene and dienes, but the meehanism is now different. 

It should be noted that the monomer coordination step shown in Eq. (2.82) may not be a distinct step as discussed previously. An important feature of this mechanism which affects the stereospecificity of olefin polymerizations using these types of soluble catalysts is the fact that the insertion of the monomer into the transition metal-carbon bond involves a secondary insertion reaction, i.e., the more substituted carbon of the double bond in the monomer becomes bonded to the transition metal (Corradini et al., 1985). In contrast, a primary insertion mechanism to form a transition metal bond to the less substituted carbon on the double bond of the monomer Ti-CH2CHR-P is involved in polymerizations using typical heterogeneous catalysts, e.g., from titanium halides and alkylaluminum compounds (Boor, 1979). 

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