Titanium and Zirconium Catalysts

Early attempts by Asinger to enlarge the scope of hydroalumination by the use of transition metal catalysts included the conversion of mixtures of isomeric linear alkenes into linear alcohols by hydroalumination with BU3AI or BU2AIH at temperatures as high as 110°C and subsequent oxidation of the formed organoaluminum compounds [12]. Simple transition metal salts were used as catalysts, including tita-nium(IV) and zirconium(IV) chlorides and oxochlorides. The role of the transition metal in these reactions is likely limited to the isomerization of internal alkenes to terminal ones since no catalyst is required for the hydroalumination of a terminal alkene under these reaction conditions. 

In 1976, Sato reported the hydroalumination of terminal alkenes with LiAlH4 in the presence of ZrCh [13]. For example, 1-hexene was quantitatively converted into n-hexane at room temperature after hydrolytic workup, whereas no reaction occurred in the absence of a catalyst Halogenation of the reaction mixtures indicated that these reactions in fact proceed through organoaluminum intermediates. Later, TiCh was found to be an even more active catalyst [14, 15]. 

The hydroalumination of terminal alkenes by LiAlH4 catalyzed by titanocene and zirconocene dichloride, CpjTiCh and CpjZrCh, respectively, has been reported by Isagawa [16] and Sato [14]. Again, the titartium compound proved to be more active 

TiCh and ZrCh were found to be less effective catalysts than Cp2ZrCl2, and Cp2TiCl2 shows no catalytic activity under similar conditions [23]. However, the hy- 

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Alkene Hydrogenation with Titanium and Zirconium Catalysts... 

Octene trimers are the main products of the 1-octene oligomerization in the presence of the system TiCl4-Et3Al2Cl3, and ZrCU modified with AICI3 oligomerizes 1-decene to trimers and tetramers with a yield of 93% [944]. All of these titanium and zirconium catalysts have one deficiency they promote alkylation of olefins with aromatic solvents [944]. 

Scheme 5.61 Titanium and zirconium catalysts used for the asymmetric Mukaiyama aldol reaction.

It should be noted that cationic titanium and zirconium catalysts, which are isoelectronic to neutral group 3 metal complexes, cyclize only aminoalkenes with a secondary amino group, whereas primary amines are urueactive [61, 62]. It has been proposed that the lanthanide-like insertion mechanism is operating in these systems, which is in agreement with DFT calculations [63]. 

Section 14 15 Coordination polymerization of ethylene and propene has the biggest eco nomic impact of any organic chemical process Ziegler-Natta polymer ization IS carried out using catalysts derived from transition metals such as titanium and zirconium tt Bonded and ct bonded organometallic com pounds are intermediates m coordination polymerization... 

Dialkylaminoethyl acryhc esters are readily prepared by transesterification of the corresponding dialkylaminoethanol (102,103). Catalysts include strong acids and tetraalkyl titanates for higher alkyl esters and titanates, sodium phenoxides, magnesium alkoxides, and dialkyitin oxides, as well as titanium and zirconium chelates, for the preparation of functional esters. Because of loss of catalyst activity during the reaction, incremental or continuous additions may be required to maintain an adequate reaction rate. 

Recently some information became available on a new type of highly active one-component ethylene polymerization catalyst. This catalyst is prepared by supporting organometallic compounds of transition metals containing different types of organic ligands [e.g. benzyl compounds of titanium and zirconium 9a, 132), 7r-allyl compounds of various transition metals 8, 9a, 133), 7r-arene 134, 185) and 71-cyclopentadienyl 9, 136) complexes of chromium]. 

Mn(II) > Mg(II).270 It should be underlined that titanium and zirconium alkoxides are efficient catalysts for both stages of reaction. Lanthanide compounds such as 2,2/-bipyridyl, acetylacetonate, and o-formyl phenolate complexes of Eu(III), La(III), Sm(III), Er(III), and Tb(III) appear to be even more efficient than titanium alkoxides, Ca or Mn acetates, Sb203, and their mixtures.273 Moreover, PET produced with lanthanides has been reported to exhibit better thermal and hydrolytic stability as compared to PET synthesized with the conventional Ca acetate -Sb203 catalytic system.273... 

Transition metal catalysis plays a key role in the polyolefin industry. The discovery by Ziegler and Natta of the coordination polymerization of ethylene, propylene, and other non-polar a-olefins using titanium-based catalysts, revolutionized the industry. These catalysts, along with titanium- and zirconium-based metallocene systems and aluminum cocatalysts, are still the workhorse in the manufacture of commodity polyolefin materials such as polyethylene and polypropylene [3-6],... 

Given the importance of chiral amines to synthetic chemistry as well as other fields asymmetric hydrogenation of imines has attracted wide interest but limited success compared to C=C and C=0 bond reduction. The first asymmetric hydrogenation of imines was carried out in the seventies with mthenium- and rhodium-based catalysts, followed later by titanium and zirconium systems [82]. Buchwald found that... 

Production of HMF from glucose was also evaluated using titanium and zirconium oxides as solid acid catalysts in hot compressed water (473 K) [78-80], Interestingly, it was found that the Zr02 catalyst acts as an acido-basic catalyst. Therefore, Zr02 was able to promote a tandem reaction involving (1) the isomerization of glucose to fructose and (2) the dehydratation to fructose to HMF (yield of HMF = 20% Scheme 8). 

The use of supporting amido ligands for transition metal based catalysts was intensified by reports of the use of bidentate amide donors of type V, with titanium and zirconium " (the related ligand W is also known). ... 

BERZELIUS, J. J. (1779-1848). A native of Sweden, Berzelius was one of the foremost chemists of the 19th century. He made many contributions to both fundamental and applied chemistry coined the words isomer and catalyst classified minerals by chemical compound. He recognized organic radicals which maintain their identity in a series of reactions discovered selenium and thorium, and isolated silicon, titanium, and zirconium did pioneer work with solutions of proteinaceous materials which he recognized as being different from true solutions. 

Lewis acids accelerate the addition of zinc organometallics to carbonyl derivatives. Titanium and zirconium(iv) salts are especially efficient catalysts. Oguni and co-workers have shown in pioneering work that various... 

A. H. Hoveyda, Chiral Zirconium Catalysts for Enantioselective Synthesis, in Titanium and Zirconium in Organic Synthesis (Ed. I. Marek, Wiley-VCH, Weinheim, 2002, pp. 180-229). 

An earlier review of the promoter literature revealed that cerium, cobalt, chromium, copper, iron, hafnium, lanthanum, molybdenum, niobium, nickel, titanium, and zirconium are elements that are commonly reported to enhance the activity (170). Cations of these elements are suggested to form solid solutions with the catalyst, KVO)yMi (where M is a... 

For less activated aromatic systems (those without a nitro substituent), the halogcn-ex-changc reaction has been investigated with potassium fluoride in a variety of polar aprotic solvents in the presence or absence of a catalyst (see Table 13). Many different types of catalysts have been investigated these include crown ethers, quaternary ammonium salts, 3,164 pjjos-phonium salts, aminophosphonium salts, compounds containing a phosphorus and an amino function, and inorganic fluorides of boron, aluminum, tin, phosphorus, titanium and zirconium. Different forms of potassium fluoride have been used these include spray-dried potassium fluoride, freeze-dried potassium fluoride, potassium fluoride recryslal-lized from methanol, and potassium fluoride dispersed on caleium fluoride. ... 

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