Titanium dimethyl

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. 

Monocyclopentadienyl and (monoindenyl)titanium trichlorides are generating interest as catalyst precursors for syndiospecific polymerization of styrene (112-127). A class of highly active olefin pol5unerization catalysts based on a (monocyclopentadienyl)titanium dimethyl cation [CpTi(CH3)2l+, generated hy... 

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] ... 

There are many colorimetric methods used for trace analysis of peroxides using reagents such as ferrous ion, leuco base of methylene blue, yy -diphenylcarbohydrazide, titanium(IV), iodide ion, and Ai,A7-dimethyl- -phenylenediamine. The latter two are the most commonly used reagents... 

Solvent for Electrolytic Reactions. Dimethyl sulfoxide has been widely used as a solvent for polarographic studies and a more negative cathode potential can be used in it than in water. In DMSO, cations can be successfully reduced to metals that react with water. Thus, the following metals have been electrodeposited from their salts in DMSO cerium, actinides, iron, nickel, cobalt, and manganese as amorphous deposits zinc, cadmium, tin, and bismuth as crystalline deposits and chromium, silver, lead, copper, and titanium (96—103). Generally, no metal less noble than zinc can be deposited from DMSO. 

Oiganometallic usage is shown in the piepaiation of titanium- oi vanadium-containing catalysts foi the polymerisation of styrene or butadiene by the reaction of dimethyl sulfate with the metal chloride (145). Free-radical activity is proposed for the quaternary product from dimethylaruline and dimethyl sulfate and for the product from l,l,4,4-tetramethyl-2-tetra2ene and dimethyl sulfate (146,147). 

Organic titanates can be used to cross-link sUicones on leather (49). Tetrabutyltitanate and tetrakis( P-aminoethoxy)titanium cross-link sUicones, eg, poly(dimethyl sUoxane), to iacrease both water repeUency and durabUity. For example, good repeUency results from the impregnation of leather with a solution of 10 wt % tetrabutyltitanate ia butyl acetate, foUowed by impregnation with a 9 1 mixture of sUicones and tetrabutyltitanate (50). 

Other Rea.ctlons, The anhydride of neopentanoic acid, neopentanoyl anhydride [1538-75-6] can be made by the reaction of neopentanoic acid with acetic anhydride (25). The reaction of neopentanoic acid with acetone using various catalysts, such as titanium dioxide (26) or 2irconium oxide (27), gives 3,3-dimethyl-2-butanone [75-97-8] commonly referred to as pinacolone. Other routes to pinacolone include the reaction of pivaloyl chloride [3282-30-2] with Grignard reagents (28) and the condensation of neopentanoic acid with acetic acid using a rare-earth oxide catalyst (29). Amides of neopentanoic acid can be prepared direcdy from the acid, from the acid chloride, or from esters, using primary or secondary amines. 

A reagent more reactive than tris(dimethylamino)arsine employed by Weingarten and White 39) was tetrakis(dimethylamino)titanium (145). With this compound it was possible to prepare N,N-dimethyl(l-isopropyl-2-methylpropcnyl)amine (147) from diisopropyl ketone. Weingarten and White 39) have suggested a possible mechanism for this reaction (see p. 88). If benzaldehyde 39,111), formaldehyde 111), or acetaldehyde 39) is used, the corresponding gem diamine or aminal (143) is formed. 

Polybibenzoates are a kind of thermotropic polyesters obtained by polycondensation of 4,4 -biphenyldicar-boxylic acid (p,p -bibenzoic acid) with a diol. These polyesters contain the biphenyl group, which is one of the simplest mesogens. They are synthesized by melt transesterification of the dimethyl or diethyl ester of p,p -bibenzoic acid and the corresponding diol, using a titanium compound as catalyst, according to the following scheme ... 

Diphenol carbonate is produced by the reaction of phosgene and phenol. A new approach to diphenol carbonate and non-phosgene route is by the reaction of CO and methyl nitrite using Pd/alumina. Dimethyl carbonate is formed which is further reacted with phenol in presence of tetraphenox titanium catalyst. Decarbonylation in the liquid phase yields diphenyl carbonate. 

On the other hand, the predominant formation of the diastereomeric aldols 3 b results from the titanium enolate 1 b of (S )-5,5-dimethyl-4-tert-butyldimethylsilyloxy-3-hexanone. For this purpose, the ketone is first deprotonated with A-(bromomagnesio)-2,2,6,6-tetramethylpiperidine and the magnesium enolate, presumably (E) configurated, formed is thereby treated with hexamethylphosphoric triamide and triisopropyloxytitanium chloride. After sonification, the aldehyde is added to give predominantly aldol adducts 3b the diastereomeric ratio of 3b/2b surpasses 95 5 and the chemical yields range from 85 to 88%53b. 

Highly stereoselective formation of. syn-adducts (syn/anti. >95 < 5) results from the titanium(IV) chloride induced addition ofa-unsubsliluled enolsilanes, as well as of the a-dimethyl silylketene acetal, to 2-benzyloxypropanal3. 

The titanium(IV) chloride catalyzed addition of allylic silanes to (E)-(2-nitroethenyl)benzene affords y,<5-unsaturated nitronates which, on treatment with low valent titanium species [generated in situ from titanium(IV) and zinc], give y,<5-unsaturated nitriles. For example, [(Zs)-2-butenyl]-(dimethyl)phenylsilane underwent reaction with ( )-(2-nitroethenyl)benzene to give 3-methyl-2-phenyl-4-pentenenitrile in 65 % yield as a 3 1 mixture of diastereomers of unassigned configuration22. 

The guanidinate-supported titanium imido complex [Me2NC(NPr02l2Ti = NAr (Ar = 2,6-Me2C6H3) (cf. Section IILB.2) was reported to be an effective catalyst for the hydroamination of alkynes. The catalytic activity of bulky amidinato bis(alkyl) complexes of scandium and yttrium (cf. Section III.B.l) in the intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine has been investigated and compared to the activity of the corresponding cationic mono(alkyl) derivatives. 

The titanium reagent also dimethylates aromatic aldehydes." Triethylaluminum reacts with aldehydes, however, to give the mono-ethyl alcohol, and in the presence of a chiral additive the reaction proceeds with good asymmetric induction." A complex of Me3Ti-MeLi has been shown to be selective for 1,2 addition with conjugated ketones, in the presence of nonconjugated ketones." ... 

Scheme 17 Synthesis of a titanium pentasulfide from the dimethyl titanium complex...

The 4-thiazolidinyl phosphonates 143 (Scheme 44) are known for their therapeutical properties, in particular as anti-inflammatory agents [5,89]. Their asymmetric synthesis by hydrophosphonylation of 3-thiazolines has been described using various chiral auxiliaries chiral phosphites such as (2S,4i )-2H-2-oxo-5,5-dimethyl-4-phenyl-l,3,2-dioxaphosphorinane (de = 2-8%) [90] or BINOL-phos-phite (de = 65-90%) [91] and also chiral catalyst such as titanium or lanthanide chiral complexes (ee = 29-98%) [92]. Hydrophosphonylation of C2-chiral3-thi-azolines has also been performed (de = 32-38%) [93]. 

Organic hydroperoxides have also been used for the oxidation of sulphoxides to sulphones. The reaction in neutral solution occurs at a reasonable rate in the presence of transition metal ion catalysts such as vanadium, molybdenum and titanium - , but does not occur in aqueous media . The usual reaction conditions involve dissolution of the sulphoxide in alcohols, ethers or benzene followed by dropwise addition of the hydroperoxide at temperatures of 50-80 °C. By this method dimethyl sulphoxide and methyl phenyl sulphoxide have been oxidized to the corresponding sulphone in greater than 90% yields . A similar method for the oxidation of sulphoxides has been patented . Unsaturated sulphoxides are oxidized to the sulphone without affecting the carbon-carbon double bonds. A further patent has also been obtained for the reaction of dimethyl sulphoxide with an organic hydroperoxide as shown in equation (19). 

Demeestere, K., Dewulf, J., Ohno, T., Salgado, P.H., and Van Langenhove, H. (2005) Visible light mediated photocatalytic degradation of gaseous trichloroethylene and dimethyl sulfideonmodified titanium dioxide. Applied Catalysis B Environmental,... 

Dimethyl terephthalate, Titanium butoxide See Dimethyl terephthalate Ethylene glycol, Titanium butoxide... 

The key step in the synthesis of A-ring fragment 50 [56] is the chelation-controlled addition of allylstannane 53 to aldehyde 52, which sets the C7 stereocenter and introduces the C8 gem-dimethyl moiety. Aldehyde 52 is itself prepared from 1,3-propanediol using the author s protocol for titanium-catalyzed enantioselective allylstannation [57], which sets the C5 stereocenter, followed by chelation-controlled Mukaiyama aldol addition [58] to establish the C3 stereocenter (Scheme 5.6). 

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