Titanium complexes with magnesium compounds

A synthetically useful diastereoselectivity (90% dc) was observed with the addition of methyl-magnesium bromide to a-epoxy aldehyde 25 in the presence of titanium(IV) chloride60. After treatment of the crude product with sodium hydride, the yy -epoxy alcohol 26 was obtained in 40% yield. The yyn-product corresponds to a chelation-controlled attack of 25 by the nucleophile. Isolation of compound 28, however, reveals that the addition reaction proceeds via a regioselective ring-opening of the epoxide, which affords the titanium-complexed chloro-hydrin 27. Chelation-controlled attack of 27 by the nucleophile leads to the -syn-diastereomer 28, which is converted to the epoxy alcohol 26 by treatment with sodium hydride. 

Two groups of elements appear in significant concentrations in the original crude oil, associated with well-defined types of compounds. Zinc, titanium, calcium, and magnesium appear in the form of organometallic soaps with surface-active properties, adsorbed in the water-oil interfaces, and act as emulsion stabilizers. However, vanadium, copper, nickel, and part of the iron found in crude oils seem to be in a different class and are present as oil-soluble compounds (Reynolds, 1997). These metals are capable of complexing with pyrrole pigment... 

In Example 7 of the 429 patent a complex with the composition of MgjTi2Clj2( thyl acetate) exhibited an ethylene polymerization activity of 167,000 gPE/gTi at 10 atm ethylene, 3 atm hydrogen at 85°C and a 4 hr polymerization time, which was 50 times more active than the titanium-only complex TiCljiethyl acetate, demonstrating the importance of the magnesium compound in improving polymerization activity. Results for complexes based on ethanol and benzonitrile are shown in Table 2.11. 

As described in the previous section, a-elimination of dialkyltitanocenes is of limited use for the preparation of titanocene-alkylidenes. Since thioacetals are readily available from carbonyl compounds or through alkylation of bis(phenylthio)methane and related organosulfur compounds, a thioacetal-titanocene(II) system enables the use of different types of carbene complexes. Use of appropriate thioacetals is of crucial importance in this system for the preparation of alkylidene complexes 48, the corresponding diphenyl thioacetals are the starting materials of choice. No carbene complexes are formed from dialkylthio-acetals. To generate vinylcarbene complexes 49, trimethylene thioacetals of aji-unsaturated aldehydes or l,3-bis(phenylthio)propene derivatives are employed (Scheme 4.41). The low-valent titanium species 44 is also easily prepared by the reduction of titanocene dichloride with magnesium in the presence of triethyl phosphite at room temperature. The presence of molecular sieves 4A is essential for the reproducibility of this preparation. In relatively large-scale preparations, care should be taken to control the reaction temperature [92, 93g]. 

It may be interesting, in connection with the ethylene/propylene copolymers mentioned above, to present here some homogeneous Ziegler-Natta catalysts formed by soluble complexes of titanium and magnesium chlorides with alkyl phosphates as catalyst precursors and alkylaluminium compounds as activators (TiCl4)x.(MgCl2)r [0=P(0Bu)3]3-A1(/-Bu)3 and Cl3TiOMgCl-[0 = P(0Bu)3]3- A1(z -Bu)3 (Al/Ti molar ratio of ca 10 1). These catalysts have been used for random ethylene/propylene copolymerisation [73],... 

Active polymerization catalysts have been derived from organomagnesium compounds, for example by reaction with titanium (tv) chloride [7] the polymerization of various vinyl monomers has been initiated by organomagnesium compounds [8] and recently polymerization initiated by magnesium ate complexes has been described [9, 10]. 

Allyltitanium complexes (22) readily add to carbonyl compounds with high regio- and stereo-selection. They are prepared by reaction of a chlorotitanium complex (21) with an allyl-magnesium or -lithium derivative (equation 13). Some of these unsaturated Ti complexes, like (23)-(25) in Scheme 2, obtained from allylmagnesium halides or allyllithium by reaction with titanium tetraisopropoxide or titanium tetramides, are known as titanium ate complexes . The structure of these ate complexes, at least from a formal point of view, can be written with a pentacoordinate Ti atom. Some ate complexes have synthetic interest, as is the case of (allyl)Ti(OPr )4MgBr which shows sharply enhanced selectivity towards aldehydes in comparison with the simple (allyl)Ti(OPr )3. ... 

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