Titanium carboxylates

Balthis, J. "Polymeric Hydroxyl-Containing Titanium Carboxylates and Methods for Preparing Same," US Patent 2,621,194(1950). 

Ti(0 Bu)4 (100 mM) and carbobenzyloxy-L-alanine (Cbz-L-Ala, 25 mM) were mixed in toluene/ethanol and stirred at room temperature for more than 12 h. After addition of water and aging for several hours, the stock solution was diluted with toluene, and subjected to the surface sol-gel process. Uniform adsorption was observed up to 15 cycles with frequency shifts of 140-160 Hz per cycle. The template molecule, Cbz-L-Ala, was removed from the gel film by dipping in 1 wt % aqueous ammonia, as confirmed from the disappearance of characteristic peaks of the titanium-carboxylate complex and carbamate in reflection FT-IR spectra. 

The titanium carboxylates [CpTi(OCOR)2]2 (R= H, Ph) are obtained when titanocene (CpTiH)2(G10H8) reacts with carboxylic acids the three bridge groups are replaced by four carboxylato bridges (Scheme 415). The structure of the resulting formiato complex has been determined by X-ray crystallography.995... 

The coordination chemistry of Cp titanium carboxylates and related complexes has been reviewed. The synthetic methods, structural characteristics, coordination modes, and reactivities are covered.1570... 

The coordination and organometallic chemistry of zirconium and hafnium are surveyed for the year 1991.107,108 There is useful material in a review of homogeneous Group 4 metallocene Ziegler-Natta catalysts, a review of the coordination chemistry of cyclopentadienyl titanium carboxylate and related complexes O and a review of bis(cycIopentadienyl)zirconium(IV) or hafnium(IV) complexes with Si-, Ge-, Sn-, N-, P-, As-, Sb-, 0-, S-, Se-, Te- or transition metal-centred anionic ligands. Cationic zirconocene or hafiiocene complexes serve as Lewis acids with unique reactivities, they are active for C-F bond activation, coordinative activation of ether linkages, carbonyl activation and C-O bond cleavage. New synthetic methods based on the... 

The synthesis of [Cp2Ti(T 3-aUyl)] complexes having a variety of substituents on the allyl moieties has been reportedi and the compounds shown to react with carbon dioxide to give single P,y-unsaturated carboxylic acids of a few possible regioisomeric products aftra- hydrolytic work-up of the titanium carboxylates. 

Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

The structure of these products is uncertain and probably depends on pH and concentrations in solution. The hydroxyl or carboxyl or both are bonded to the titanium. It is likely that most, if not all, of these products are oligomeric in nature, containing Ti—O—Ti titanoxane bonds (81). Thek aqueous solutions are stable at acidic or neutral pH. However, at pH ranges above 9.0, the solutions readily hydroly2e to form insoluble hydrated oxides of titanium. The alkaline stabiUty of these complexes can be improved by the addition of a polyol such as glycerol or sorbitol (83). These solutions are useful in the textile, leather (qv), and cosmetics (qv) industries (see Textiles). 

A group of violet titanium(III) acylates has been prepared from TiCl and alkafl carboxylates. AH of the acylates are strong reducing agents similar to TiCl (189). Studies of Ti(III) compounds include the reaction (190)... 

In titanium acylates, the carboxylate ligands are unidentate, not bidentate, as shown by ir studies (333,334). The ligands are generally prepared from the hahde and silver acylate (335). The ben2oate is available also from a curious oxidative addition with ben2oyl peroxide (335—338) ... 

A confusing picture emerges from the stereochemical outcome of the Mukaiyama variation of the aldol addition. The titanium(IV) chloride mediated addition of silylketene acetals to isobutyraldehyde confirms this statement while there is a reasonable correlation between the predominance of the (/t)-silylkctenc acetal 2 over the (Z)-acetal, and the favored formation of the an/t -carboxylic ester over the. svn-product, the pure (Z)-diastereomer displays no syn selectivity26. 

In another approach, a glucose-derived titanium enolate is used in order to accomplish stereoselective aldol additions. Again the chiral information lies in the metallic portion of the enolate. Thus, the lithiated /m-butyl acetate is transmetalated with chloro(cyclopentadienyl)bis(l,2 5,6-di-0-isopropylidene- -D-glucofuranos-3-0-yl)titanium (see Section I.3.4.2.2.I. and 1.3.4.2.2.2.). The titanium enolate 5 is reacted in situ with aldehydes to provide, after hydrolysis, /i-hydroxy-carboxylic acids with 90 95% ee and the chiral auxiliary reagent can be recovered76. 

Acetylsultam 15 is also used for stereoselective syntheses of a-unsubstituted /1-hydroxy-carboxylic acids. Thus, conversion of 15 into the silyl-A/O-ketene acetal 16 and subsequent titanium(IV) chloride mediated addition to aldehydes lead to the predominant formation of the diastereomers 17. After separation of the minor diastereomer by flash chromatography, alkaline hydrolysis delivers /f-hydroxycarboxylic acids 18, with liberation of the chiral auxiliary reagent 1919. 

Treatment of N-benzoyl-L-alanine with oxalyl chloride, followed by methanolic triethylamine, yields methyl 4-methyl-2-phenyloxazole-5-carboxylate 32 <95CC2335>. a-Keto imidoyl chlorides, obtained from acyl chlorides and ethyl isocyanoacetate, cyclise to 5-ethoxyoxazoles by the action of triethylamine (e.g.. Scheme 8) <96SC1149>. The azetidinone 33 is converted into the oxazole 34 when heated with sodium azide and titanium chloride in acetonitrile <95JHC1409>. Another unusual reaction is the cyclisation of compound 35 to the oxazole 36 on sequential treatment with trifluoroacetic anhydride and methanol <95JFC(75)221>. 

The DPE reduction is used as a test reaction to characterize the materials and optimize the preparation conditions of the catalyst. Since hydroaluminations can also be used for the synthesis of carboxylic acids, deuterated products, or vinyl halides via quenching with CO2, D2O or Br2 [44], the method is also a valuable organic synthesis tool. However, as compared with molecular catalysts like Cp2TiCl2 that are known to catalyze hydroaluminations [44], the titanium nitride materials described here are solid catalysts and can be separated by centrifugation. Moreover, they can be reused several times, which is an advantage as compared to molecular catalysts. 

Esterification and transesterification using TiIV compounds are useful methods for functionalization of ester moieties under mild conditions. In the transformation of carboxylic acids to esters, a catalytic amount of TiCl(OTf)3 is effective (Scheme 30).110 Titanium alkoxides, such as Ti(OEt)4 or Ti(0 Pr)4, easily promote transesterification of alkoxy groups to other ones—even to more hindered groups.111 Anomerization of glycosides to Q-isomers using a Tilv-bascd Lewis acid is an important method for controlling the product structure.112... 

The third general classification of solution synthesis approaches used for inorganic electronic thin film fabrication is referred to as metallo-organic decomposition, or MOD for short.23-29,37,38,85 Historically long-chain carboxylate compounds, such as lead 2-ethylhexanoate, zirconium neodecanoate, and titanium di-methoxy di-neodecanoate have been used.23-29,85 Both commercially available precursors and in-house synthesized starting reagents have been used. 

Gagliardi, C. D. Dunuwila, D. Van Vlierberge-Torgerson, B. A. Berglund, K. A. 1992. Reaction kinetics for the hydrolysis of titanium isopropoxide carboxylate complexes. In Better Ceramics Through Chemistry V, edited by Hampden-Smith, M. J. Klemperer, W. G. Brinker, C. J. Mat. Res. Soc. Symp. Proc. 271 257-262. 

The chemistry of titanium has been reviewed in COMC (1982) and COMC (1995)40 41 as well as in Comprehensive Coordination Chemistry II. 2 Since then, several contributions have covered the coordination chemistry of cyclopenta-dienyltitanium carboxylates and related complexes,43 new titanium imido chemistry,44 the use of titanium(iv) chloride45 and isopropoxide46 in stereoselective synthesis, the preparation and synthetic applications of l, -dicarba-nionic titanium intermediates47 and organotitanium complexes,48 49 and titanium-catalyzed enantioselective... 

Additionally, it has been shown that novel benzylidene titanium complexes of type 74 react with polymer-bound carboxylic esters to form the corresponding enol ethers (Scheme 28).79... 

The bisfunctionalization of alkynes by both C02 and another electrophile can also be achieved, as shown in Scheme 9.17,17a The titanium-carbon bond in the titanacycle complex 31, which was formed by reaction of C02 with the titanacyclopropene 30, can be substituted with various electrophiles. For example, its reaction with NBS or I2 afforded the synthetically useful vinyl bromide or iodide 32, respectively, while the reaction with D20 yielded the /3-deuterated a,/ -unsaturated carboxylic acid. When an aldehyde such as PhCHO was used as an electrophile, butenolide 33 was produced after acidic workup. 

Covalently bonded chiral auxiliaries readily induce high stereoselectivity for propionate enolates, while the case of acetate enolates has proved to be difficult. Alkylation of carbonyl compound with a novel cyclopentadienyl titanium carbohydrate complex has been found to give high stereoselectivity,44 and a variety of ft-hydroxyl carboxylic acids are accessible with 90-95% optical yields. This compound was also tested in enantioselective aldol reactions. Transmetalation of the relatively stable lithium enolate of t-butyl acetate with chloro(cyclopentadienyl)-bis(l,2 5,6-di-<9-isopropylidene-a-D-glucofuranose-3-0-yl)titanate provided the titanium enolate 66. Reaction of 66 with aldehydes gave -hydroxy esters in high ee (Scheme 3-23). 

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