Titanium complexes with dialkyls

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). 

Asymmetric epoxidation is another important area of activity, initially pioneered by Sharpless, using catalysts based on titanium tetraisoprop-oxide and either (+) or (—) dialkyl tartrate. The enantiomer formed depends on the tartrate used. Whilst this process has been widely used for the synthesis of complex carbohydrates it is limited to allylic alcohols, the hydroxyl group bonding the substrate to the catalyst. Jacobson catalysts (Formula 4.3) based on manganese complexes with chiral Shiff bases have been shown to be efficient in epoxidation of a wide range of alkenes. 

In fact it can be assumed that, in the catalytic system TiCl4-bis[(S)-2-methyl-butyl]-zinc, dialkyl zinc alkylates the titanium atom (19) and that the titanium alkyl thus formed gives more stable complexes with the (S) olefin than with the (R) olefin, thus favouring the adsorption and polymerization of the (S) antipode (104). The influence exerted by the asymmetric groups bound to transition metals on the type of complexes formed by olefins with the same metal atom, has been recently investigated by Pajaro, Corradini, Palumbo and Panunzi (90). 

To date, the hydrofunctionalization route has mainly been used to prepare PBs. Both conceivable strategies, namely the hydroboration of unsaturated phosphines and the hydrophosphination of unsaturated boranes have been reported (Scheme 25). With dialkyl and diarylboranes, the reactions proceed spontaneously under mild conditions, while the addition of boronates HB(OR)2 is catalyzed by a titanium complex, and the... 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

The alkyl transfer properties of dialkyl zinc reagents have been studied in the reaction of Zn[CH(SiMe3>2]2 with TiCU- The monoalkyl trichloro titanium complex TiCl3[CH(SiMe3)2] was obtained in 83% yield.10... 

Dialkyltitanium complexes supported by aminotroponiminato ligands have been described. The treatment of TiCl2(LL)2 (LL = N,N -dimethylaminotroponiminato) with Grignard reagents under different conditions and molar ratios leads to the synthesis of dialkyl or chloro alkyl titanium complexes (Scheme 55). The solid-state structure of some of these complexes have been established by X-ray diffraction. Their reactivity has been widely studied (Section 4.05.2.3).-123-125... 

The reactivity of the dialkyl complexes TiR2(LL)2 (LL = N,N -dimethylaminotroponiminato) has been widely studied. Reactions with CO and aldehydes or ketones afford unsymmetrical diolato complexes that convert to the corresponding vicinal diols after hydrolysis. CO and acetylene react to form the oxametallacyclopentene complex. Treatment with RNC yields the free imine and low-valent titanium species (Scheme 131). In the reaction with BucNC, free ButN=CMe2 is formed and the addition of benzaldehyde or benzyl reagents affords titanium diolato or enediolato complexes. Thiolato-alkoxo or amido-alkoxo titanium complexes can also be similarly prepared (Scheme 132).123-125... 

The bis-Cp dichloro complexes with (diisopropylamino)ethyl-functionalized Cp rings have been synthesized by metathesis reaction between the lithium salt of the Cp ring and TiCl4. Dialkyl and diphenoxo titanium complexes are also prepared (Scheme 466). The chloro complexes are pre-catalysts in the polymerization of ethylene.1094... 

Gp alkylidene titanium complexes have been generally generated by decomposing dialkyl and related titanium derivatives or from treatment of thioacetals with Ti(n) compounds. Thermolyzing diazoalkane complexes permits the synthesis of non-Gp alkylidene titanium derivatives (see Section 4.05.2). 

An IR study of the complexes fonned from TiCl4 and dialkyl H-phosphonates indicates that at low temperatures, a a-donor complex through the phosphoryl oxygen atom is formed [415], Similar to the analogous complexes of tin halides, these titanium complexes are thermally unstable and easily undergo dealkylation with cleavage of alkyl halides even at low temperatures. 

The first practical method for asymmetric epoxidation of primary and secondary allylic alcohols was developed by K.B. Sharpless in 1980 (T. Katsuki, 1980 K.B. Sharpless, 1983 A, B, 1986 see also D. Hoppe, 1982). Tartaric esters, e.g., DET and DIPT" ( = diethyl and diisopropyl ( + )- or (— )-tartrates), are applied as chiral auxiliaries, titanium tetrakis(2-pro-panolate) as a catalyst and tert-butyl hydroperoxide (= TBHP, Bu OOH) as the oxidant. If the reaction mixture is kept absolutely dry, catalytic amounts of the dialkyl tartrate-titanium(IV) complex are suflicient, which largely facilitates work-up procedures (Y. Gao, 1987). Depending on the tartrate enantiomer used, either one of the 2,3-epoxy alcohols may be obtained with high enantioselectivity. The titanium probably binds to the diol grouping of one tartrate molecule and to the hydroxy groups of the bulky hydroperoxide and of the allylic alcohol... 

Complexes of titanium, such as 2,6-(RNCH2)2NC H2TiCl2, prepared by reaction of TiCl with 2,6((CH2)3Si)RNCH2)2NC H2, can react with various Grignard reagents to prepare conformationady rigid diamide mono- and dialkyl titanate complexes (218,219). 

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