Complex titanium

Alkyltitanium halides are prepared using a variety of alkylating agents. Methyltitanium trichloride may be prepared from methyl aluminium compounds. 

MesAl + T1CI4 Hexene MeTiC(3 + A(Me2C( NoCl 

In the above reactions volatile aluminiumcompounds are made involatile by complex formation, as shown, enabling the MeTiCh to be separated by distillation. Also shown are some reactions of MeTiCU including complex formation with donor ligands. 

Pyrazolylborate complexes of titanium [12] have been studied for SPS polymerization. Similarities between the cyclopentadienyl ligand and the hydridotris(pyrazolyl)borate ligand have been noted for transition metal complexes. But the catalytic activities of pyrazolylborate complexes are much lower than those of the analogous pentamethylcyclopentadienyl complexes. This ligand may donate too much electron density to the titanium. 

TABLE 2.3 Catalytic Activities of Titanium Compounds with Cyclopentadienyl Ligands 

Mw=weight average molecular weight Mn=number average molecular weight. 

Catalytic Activities of Titanium Compounds with Cyclopentadienyl 

In this correlation, the catalytic activities of titanium compounds with bulky substituents at the cyclopentadienyl ligand show lower activities than expected from the chemical shifts of Ti-NMR. The electron densities of titanium compounds can also be observed when the titanium complexes possess the same 

The development of other efficient methods for the enantioselective oxidation of sulfides to sulfoxides has been pursued for many years. Various chiral additives and metal complexes have been investigated. However, most of these systems have disadvantages such as formation of sulfone, long reaction times, unsatisfactory yields and poor enantiomeric excesses. Diethyl tartrate remains the additive (combined with titanium alcoholates) which gives the best results in terms of enantioselectivity. Since 1989, it has been found that other chiral ligands can be efficient in asymmetric induction. 

A similar methodology was applied by Colonna et al. [101] to the oxidation of aryl alkyl sulfides with Bu OOH as oxidizing agent and a catalytic amount of a titanium A-salicylidene-L-amino acid complex (47) (0.1 mol equiv) in benzene at room temperature. This catalyst is not very enantioselective, and often yields mixtures of sulfoxides and sulfones. The highest enantioselectivity was achieved in the oxidation of f-butyl (p-nitrophenylthio)acetate, which gave sulfoxide in 21% ee and 25% yield. Like the Kagan reagent, but to a lesser measure, the use of a stoichiometric amount of titanium complex substantially influences the enantioselectivity, which increases from 12% (catalytic) to 21% (stoichiometric) for the oxidation of methyl p-tolyl sulfide. 

Another asymmetric sulfoxidation reported by Fujita et al. [102] used a chiral binuclear titanium(IV) complex (4 mol% equiv) in methanol with trityl hydroperoxide at 0°C, which gave methyl phenyl sulfoxide with an ee of 53% and a good yield (87%). The complex was prepared by treating TiC in pyridine with -disalicylidene-(f ,/ )-l,2-cyclohexanediamine. The structure of the catalyst was determined by x-ray analysis. A binuclear titanium (IV) complex was present with an oxygen bridge between the two titanium atoms (Ti—O— Ti unit). This oxygen apparently comes from atmospheric or solvent moisture. Each titanium atom is octahedrally coordinated, and the planes of each titanium atom with its associated Schiff bases are almost parallel to each other. 

In this procedure, the complex is formed in toluene and can be used over a range of temperatures (0 to -25°C), without any effect upon the enantioselectivity. The originality of this procedure is the amount of water utilized, more than 1 unusual feature of water per sulfide being essential to produce an effective catalyst, both for high enantioselectivity and to retain the catalytic activity of the titanium-binaphthol complex for an extended time. 

More recently, Uemura et al. [104] have actively developed this sulfoxidation 

As illustrated in Fig. 7-2, in dichloromethane solution the complex undergoes a rather complicated redox pathway [18]. The first, irreversible anodic step has been tentatively attributed to the oxidation of one ferrocene ligand, at an electrode potential p of 0.25 V, according to the following reaction  

The subsequent anodic processes, which possess features of chemical reversibility, have been assigned to the oxidation of biferrocene and ferrocene, respectively both molecules should derive from the fast degradation of the instantaneously electrogenerated monocation [Cp2Ti(Fc)2]. Finally, the reversible cathodic step is attributed to the reduction of the central titanium ion, according to the following reaction. 

The redox behavior exhibited by the triferrocenyl complex (jy -C5H,)Ti([f/ -C5H4)Fe( 7 - C5H5)]3 is less complicated [19]. As illustrated in Fig. 7-4, in dich-loromethane solution it exhibits a single oxidation process, reversible in character ( ° = 4-0.41 V). Controlled potential coulometry showed that this process involves three electrons/molecule. 

Also in this case, the occurrence of a single-step three-electron process indicated that the three ferrocenyl ligands, from which the electrons are concomitantly removed, are non-communicating. In addition, if one considers that, under the same experimental conditions, ferrocene undergoes oxidation at E° = 4-0.45 V, it is evident that the ferrocenyl ligands are only slightly electronically perturbed by complex formation with the CpTi fragment. 

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Aqueous solutions containing titanium(IV) give an orange-yellow colour on addition of hydrogen peroxide the colour is due to the formation of peroxo-titanium complexes, but the exact nature of these is not known. 

Several structures of the transition state have been proposed (I. D. Williams, 1984 K. A. Jorgensen, 1987 E.J. Corey, 1990 C S. Takano, 1991). They are compatible with most data, such as the observed stereoselectivity, NMR measuiements (M.O. Finn, 1983), and X-ray structures of titanium complexes with tartaric acid derivatives (I.D. Williams, 1984). The models, e. g., Jorgensen s and Corey s, are, however, not compatible with each other. One may predict that there is no single dominant Sharpless transition state (as has been found in the similar case of the Wittig reaction see p. 29f.). 

Flame-Retardant Treatments For Wool. Although wool is regarded as a naturally flame-resistant fiber, for certain appHcations, such as use in aircraft, it is necessary to meet more stringent requirements. The Zirpro process, developed for this purpose (122,123), is based on the exhaustion of negatively charged zirconium and titanium complexes on wool fiber under acidic conditions. Specific agents used for this purpose are potassium hexafluoro zirconate [16923-95-8] [16923-95-8] K ZrF, and potassium hexafluoro titanate [16919-27-0], K TiF. Various modifications of this process have been... 

Similar to IFP s Dimersol process, the Alphabutol process uses a Ziegler-Natta type soluble catalyst based on a titanium complex, with triethyl aluminum as a co-catalyst. This soluble catalyst system avoids the isomerization of 1-butene to 2-butene and thus eliminates the need for removing the isomers from the 1-butene. The process is composed of four sections reaction, co-catalyst injection, catalyst removal, and distillation. Reaction takes place at 50—55°C and 2.4—2.8 MPa (350—400 psig) for 5—6 h. The catalyst is continuously fed to the reactor ethylene conversion is about 80—85% per pass with a selectivity to 1-butene of 93%. The catalyst is removed by vaporizing Hquid withdrawn from the reactor in two steps classical exchanger and thin-film evaporator. The purity of the butene produced with this technology is 99.90%. IFP has Hcensed this technology in areas where there is no local supply of 1-butene from other sources, such as Saudi Arabia and the Far East. 

In galvanic coupling, titanium is usually the cathode metal and consequently not attacked. The galvanic potential in flowing seawater in relation to other metals is shown in Table 10. Because titanium is a cathode metal, hydrogen absorption may be of concern, as it occurs with titanium complexed to iron (38). 

Titanium Complexes of Unsaturated Alcohols. TetraaHyl titanate can be prepared by reaction of TYZOR TPT with aHyl alcohol, followed by removal of the by-product isopropyl alcohol. EbuUioscopic molecular weight determinations support its being the dimeric product, octaaHoxydititanium. A vinyloxy titanate derivative can be formed by reaction of TYZOR TPT with vinyl alcohol formed by enolization of acetaldehyde (11) ... 

Sohd, water-soluble a-hydroxycarboxyhc acid and oxaUc acid titanium complexes can be formed by reaction of the acid and a tetraaLkyl titanate in an inert solvent, such as acetone or heptane. The precipitated complex is filtered, rinsed with solvent, and dried to give an amorphous white soHd, which is water- and alcohol—water-soluble (81,82). 

These mixed phosphate ester titanium complexes or their amine salts are useful as fuel additives to help maintain cleanliness of carburetors and inhibit surface corrosion. Chloride-free mixed alcohol phosphate esters can be obtained if a tetraalkyl titanate is used (101). 

Chiral Titanium Complexes. Chiral titanium complexes are useful for the enantioselective addition of nucleophiles to carbonyl groups ... 

The advantages of titanium complexes over other metallic complexes is high selectivity, which can be readily adjusted by proper selection of ligands. Moreover, they are relative iaert to redox processes. The most common synthesis of chiral titanium complexes iavolves displacement of chloride or alkoxide groups on titanium with a chiral ligand, L ... 

The chemistry of complexes having achiral ligands is based solely on the geometrical arrangement on titanium. Optically active alcohols are the most favored monodentate ligands. Cyclopentadienyl is also well suited for chiral modification of titanium complexes. 

One of the most famous chiral titanium complexes is the Sharpless catalyst (16), based on a diisopropyl tartarate complex. Nmr studies suggest that the complex is dimeric ia nature (146). An excellent summary of chiral titanium complexes is available (147). 

The intense reddish-brown color of the acetylacetone titanium complexes impart a yellow discoloration to white inks. This discoloration is accentuated when the inks are used to print substrates that contain phenol-based antioxidants. The phenoHc compounds react with the organic titanate to form a highly colored titanium phenolate. Replacement of 0.25 to 0.75 moles of acetylacetone with a malonic acid dialkyl ester, such as diethyl malonate, gives a titanium complex that maintains the performance advantages of the acetyl acetone titanium complexes, but which is only slightly yellow in color (505). These complexes still form highly colored titanium phenolates. 

Mixtures of a titanium complex of saturated diols, such as TYZOR OGT, and a titanium acylate, such as bis- -butyl-bis-caproic acid titanate, do not have a yellowing or discoloring effect on white inks used to print polyolefin surfaces (506). The complexes formed by the reaction of one or two moles of diethyl citrate with TYZOR TPT have an insignificant color on their own and do not generate color with phenol-based antioxidants (507). The complexes formed by the addition of a mixture of mono- and dialkyl phosphate esters to TYZOR TBT are also low color-generating, adhesion-promoting additives for use in printing polyolefin films (508). 

Sulfur imides with a single NR functionality, S5NR (6.12), SeNR (6.13) (R = Oct), " SgNH (6.14), ° and S9NH (6.15) ° are obtained by a methodology similar to that which has been used for the preparation of unstable sulfur allotropes, e.g., S9 and Sio. Eor example, the metathesis reaction between the bis(cyclopentadienyl)titanium complexes 6.8-6.10 and the appropriate dichlorosulfane yields 6.14 and 6.15 (Eq. 6.4). °... 

A chiral titanium complex with 3-cinnamoyl-l,3-oxazolidin-2-one was isolated by Jagensen et al. from a mixture of TiCl 2(0-i-Pr)2 with (2R,31 )-2,3-0-isopropyli-dene-l,l,4,4-tetraphenyl-l,2,3,4-butanetetrol, which is an isopropylidene acetal analog of Narasaka s TADDOL [48]. The structure of this complex was determined by X-ray structure analysis. It has the isopropylidene diol and the cinnamoyloxazolidi-none in the equatorial plane, with the two chloride ligands in apical (trans) position as depicted in the structure A, It seems from this structure that a pseudo-axial phenyl group of the chiral ligand seems to block one face of the coordinated cinnamoyloxazolidinone. On the other hand, after an NMR study of the complex in solution, Di Mare et al, and Seebach et al, reported that the above trans di-chloro complex A is a major component in the solution but went on to propose another minor complex B, with the two chlorides cis to each other, as the most reactive intermediate in this chiral titanium-catalyzed reaction [41b, 49], It has not yet been clearly confirmed whether or not the trans and/or the cis complex are real reactive intermediates (Scheme 1.60). 

We employed malononitrile and l-crotonoyl-3,5-dimethylpyrazole as donor and acceptor molecules, respectively. We have found that this reaction at room temperature in chloroform can be effectively catalyzed by the J ,J -DBFOX/Ph-nick-el(II) and -zinc(II) complexes in the absence of Lewis bases leading to l-(4,4-dicya-no-3-methylbutanoyl)-3,5-dimethylpyrazole in a good chemical yield and enantio-selectivity (Scheme 7.47). However, copper(II), iron(II), and titanium complexes were not effective at all, either the catalytic activity or the enantioselectivity being not sufficient. With the J ,J -DBFOX/Ph-nickel(II) aqua complex in hand as the most reactive catalyst, we then investigated the double activation method by using this catalyst. 

The titanium complexes of calixarene were obtained by Olmstead et al. [44] and Bott et al. [45], who examined their x-ray characteristics. Recent research in that field has been conducted by Rudkevich et al, [46]. They prepared calix[4]arene-triacids as receptors for lan-tanides. 

A new process developed by Institut Francais du Petrole produces butene-1 (1-butene) by dimerizing ethylene.A homogeneous catalyst system based on a titanium complex is used. The reaction is a concerted coupling of two molecules on a titanium atom, affording a titanium (IV) cyclic compound, which then decomposes to butene-1 by an intramolecular (3-hydrogen transfer reaction. ... 

A derivative 5 of the 1,3-dithiolopentathiepin system was obtained by the action of disulfur dichloride on the titanium complex 4 under conditions of high dilution.397... 

Figure 6.2 Enantiofacial differentiation in AE, depending on the configuration of the diethyl tartrate ligand in the titanium complex 2.

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. 

The titanium complex 4, prepared from (A./ )-2,3-0-isopropylidenc-1,1.4,4-tetraphenyl-1,2,3,4-butanetetrol7,113 and chlorotriisopropoxytitanium or tetraisopropoxytitanium, is treated with 2-propenylmagnesium bromide. The resulting titanate affords, with benzaldehyde, ( —)-(5)-l-phenyl-3-butenol. Several further attempts, which do not include allylation, have also been reported113, as have examples using the dichloride114. 

Table 8. 1-Substituted 3-Butenols from Enantiosclcctive Allylation of Aldehydes by Chiral Titanium Complexes...

Titanium complex of (S)-l-phenyl-3-butenol 13 (Kyl-tridecen-4-ol yield 97% 95% ec... 

If the following glycine derived ester is deprotonated and transmetalated with the (/ ,/ )-lartaric acid derived titanium complex, and then added to butanal, the sy -a-amino-/Thydroxy ester, which is enantiomeric to the products obtained above, is formed. 

A combination of diethylzinc with sulfonamides 18 or 19 offers another possibility for the enantioselective acetate aldol reaction39,41. The addition of silyl enol ethers to glyoxylates can be directed in a highly enantioselective manner when mediated by the binaphthol derived titanium complex 2040. 

On the other hand, if the allylsilane anion is first complexed with certain metals, a-regioselectivity then predominates, and a high degree of complementary diastereoselectjvity (19) can be attained with aldehydes as electrophiles. For example, boron, aluminium and titanium complexation all induce threo selectivity whereas the use of tin results in an erytbro... 

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