Zirconium compounds, synthesis

Flores, J. C. Chien, J. C. W. Rausch, M. D. [N,N -Bis(trimethylsilyl)benzamidinato]titanium and -zirconium compounds. Synthesis and application as precursors for the syndiospecific polymerization of styrene. Organometallics 1995,14, 1827-1833. 

Hydroalumination of terminal alkenes using EtjAl as the hydride source must be carried out with titanium catalysts [24], since zirconium compounds lead to the formation of alumacyclopentanes [60, 61] (Scheme 2-11) and carbometallated products [62]. Suitable substrates for hydroalumination include styrene, allylnaphthalene and vinylsilanes. Only one of the ethyl groups in EtjAl takes part in these reactions, allowing the synthesis of diethylalkylalanes, which are difficult to obtain by other methods. 

Many of the most important achievements in organic chemistry in the last 20—25 years have been associated in some way with the use of transition metal complexes. Among these complexes, an increasingly important place is occupied by zirconium compounds, which have a number of unique properties enabling them to be used as highly reactive reagents in organic synthesis [1—9]. 

Mono(cyclooctatetraenyl) lanthanide(III) compounds, synthesis and characteristics, 4, 124 Mono(cyclooctatetraenyl) zirconium(III) compounds, preparation and reactions, 4, 743 Mono(cyclopentadienyl) amido complexes alkane elimination, 4, 446 amine elimination, 4, 442 HCL elimination, 4, 446 metathesis reactions, 4, 438 miscellaneous reactions, 4, 448 properties, 4, 437... 

Synthesis of l-chloro-2,8,9-carbagermatrane (221) by trans-metallation reaction of trial-lylamine and GeCLt in the presence of zirconium compounds (equation 59) was reported recently632. Subsequent reactions with organomagnesium or organolithium derivatives lead to l-organyl-2,8,9-carbagermatranes (222) (e.g. R = Bu, Ph, Vin, All). 

Syndiotactic polystyrene was first obtained only recently by Ishihara et al. [5] in polymerisation with a homogeneous catalyst derived from a transition metal compound such as monocyclopentadienyltitanium trichloride and methylalu-minoxane in toluene. Since then, several authors have reported on the synthesis of syndiotactic polystyrene promoted by different catalysts based on metal hydrocarbyls such as benzyl compounds, half-sandwich metallocenes (e.g. monocyclopentadienyl, monopentamethylcyclopentadienyl and monoindenyl metal derivatives), metal alkoxides, metallocenes and some other compounds. These catalysts are commonly derived from titanium or zirconium compounds, either activated with methylaluminoxane or aluminium-free, such as those activated with tris(pentafluorophenyl)boron, and promote the syndiospecific polymerisation of styrene and substituted styrenes [5-10,21,48-70], Representative examples of the syndiospecific polymerisation of styrene using catalysts based on various titanium compounds and methylaluminoxane are shown in Table 4.2 [6,52,53,56,58],... 

Zirconium acetylacetonate was first prepared by Biltz and Clinch by the reaction of zirconyl nitrate and sodium acetylacetonate in water solution. The compound was crystallized as the 10-hydrate from a slightly acid solution and dehydrated by several crystallizations from alcohol. Von Hevesy and Logstrup later developed a method for the preparation of hafnium acetylacetonate that has been found applicable to the synthesis of the zirconium compound and this forms the basis of the present procedure. 

Following the discovery of the a-olefin synthesis, a systematic investigation of metal compounds was undertaken. In 1953, zirconium acetylacetonate was used as a cocatalyst. Instead of liquid a-olefins, a voluminous white precipitate was produced. This new substance was a polymer of ethylene. Ten years later, millions of pounds of this Ziegler-type polyethylene were made in the United States alone. In addition to the zirconium compound, other transition metal compounds were found to be effective cocatalysts. Today titanium tetrachloride or trichloride is used as the cocatalyst with an organoaluminum compound. 

Dobrzynski, P., Kasperczyk, J., 2006a. Synthesis of biodegradable copolymers with low-toxicity zirconium compounds. IV. Copolymerization of glycolide with trimethylene carbonate and 2,2-dimethyltrimethylene carbonate microstructure analysis of copolymer chains by high-resolution nuclear magnetic resonance spectroscopy. Journal of Polymer Science Part A Polymer Chemistry 44, 98—114. 

Contrary to earlier observations, Saxena et al have reported the successful synthesis of even the tetrakis derivatives in the step-wise reactions of zirconium isopropoxide with acetylacetone, benzoylacetone, dibenzoylmethane and ethylaceto-acetate. Ebulliometric molecular weight determinations in benzene revealed the monomeric behaviour of all zirconium /6-diketonate derivatives except the triisopropoxide mono-j6-diketonate derivatives, which show dimeric behaviour. The bidentate character of the /6-diketonate ring in zirconium compounds has been adduced from infrared spectra which show the carbonyl bands in the lower region (1580-1601 cm ), and the hexacoordinated dimeric structure (/S-dik)(01V)2Zr(/z-0Pr )2Zr(0lV)2()8-dik), with isopropoxide bridging has been suggested for [ Zr(OIV)3()S-dik) 2] derivatives. 

L.-P. Mo, Z.-H. Zhang, Recent apphcations of zirconium compounds as catalysts or reagents in organic synthesis, Curr. Org. Chem. 15 (2011) 3800—3823. 

Many of the palladium- and nickel-catalysed reactions of alkenyl-aluminium or -zirconium compounds which fail or give low yields of cross-coupled products can be promoted to give the desired product in high yield by the addition of catalytic amounts of zinc chloride. " Trisubstituted olefins (40), for example, can be synthesized in good yield (ca. 70%) from the metal complex (38) in the presence of a palladium or nickel phosphine complex and zinc chloride. This reaction is particularly attactive for the one-pot synthesis of natural products containing... 

In recent years, catalytic carboalumination of acetylenes has found use in the synthesis of cycloalkenes [98-101], trisubstituted olefins, homoallyl alcohols, a,p-unsaturated esters, 1,3-enyne-l,4-disilanes [102-105], a,p-unsaturated organoboron or zirconium compounds, and also natural and biologically active compounds. For example, key synthons for the preparation of prostaglandins [86,... 

The wide applicability of the PK reaction is apparent in the synthesis of pyrroles, for example, 45, en route to novel chiral guanidine bases, levuglandin-derived pyrrole 46, lipoxygenase inhibitor precursors such as 47, pyrrole-containing zirconium complexesand iV-aminopyrroles 48 from 1,4-dicarbonyl compounds and hydrazine derivatives. The latter study also utilized Yb(OTf)3 and acetic acid as pyrrole-forming catalysts, in addition to pyridinium p-toluenesulfonate (PPTS). 

Related results in this area have been reported studying the synthesis and the reactivity of zirconium-butadiene functionality bonded to the j9-Bu -calix[4]-(0)2 (OMe)2 dianion.30 The synthesis of the parent compound used in this study, 43, is displayed, along with the analogous diphenyl derivative, in Scheme 7, and its structure in Fig. 5. 

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