Tris zirconium

Polymer-supported BINOLs thus prepared were treated with Zr(Ot-Bu)4 to form polymer-supported zirconium 20. In the presence of 20 mol% of various zirconium 20, the model aza Diels-Alder reactions of imine Id with Danishefsky s diene (7a) were performed results from selected examples are shown in Table 5.8. Whereas the 4-t-butylphenyl group resulted in lower enantiomeric excess (ee), higher ee were obtained when 3,5-xylyl, 4-biphenyl, 4-fluorophenyl, and 3-tri-... 

Zirconium, tetrakis(acetylacetonate)-stereochemistry, 1, 32, 94 Zi rconium, tris(phenylenedithio)-structure, 1, 63 Zirconium alkoxides oligomeric structure, 2,346 Zirconium chloride... 

In general, Group 4 benzamidinates show poor activities as olefin polymerization catalysts.158-162 However, bis(benzamidinate) complex (52) affords isotactic PP (>95% mmmm) at >7 atm propylene pressure 163 at ambient pressure atactic PP is produced.164 An unsymmetrical tris (benzamidinate) zirconium complex has also been shown to afford highly isotactic PP.165... 

Tetraneopentyl zirconium reacts in the same way as tetraneopentyl titanium to give, on a silica (soo), a tris(neopentyl) monografted species [32]. Treatment under H2 of this surface species yields silica-supported zirconium hydrides [33], which have been characterized as a mixture of mono- (65-70%) and bis- (35-30%) hydrides based on double quanta NMR experiments (Scheme 2.11) [34]. Interestingly, the double quantum experiment allows us to prove not only the presence of the two hydrides and the monohydride of zirconium by the presence or the absence of the double quanta correlation but also to detect the through space magnetic interaction between the zirconium monohydride and the silicon di-hydride, proving thus the spatial arrangement on the surface. This confirms the mechanism by which these hydrides have been formed on the surface. 

Reaction of tris(neopentyl) complexes of titanium, zirconium and hafnium with molecular oxygen furnishes the corresponding tris(neopentoxy) complexes [42, 43, 51]. A peroxo complex is an intermediate in this reaction, being relatively stable in the case of titanium [42]. The alkoxide species can also be formed upon reaction with alcohols under mild conditions [42, 52]. The alcoholysis reaction is fast, with a low dependence on the steric hindrance of the alkyl chain [42]. Hydrolysis leads to ](=SiO)M(OH)3] or ](=SiO)2M(OH)2], depending on the precursor species. Deu-... 

Mono(siloxy) metalhydrocarbyl species can be converted into bis- or tris(siloxy) metal hydrides by reaction with hydrogen, as shown for zirconium and tantalum. Such species are less susceptible to leaching and this route can be extended to titanium and hafnium surface species that are potential precatalysts for hydrogenolysis of C-C bonds, alkane metathesis and epoxidation reactions. 

In 1808 Sir Humphry Davy tried in vain to decompose zirconia with the electric current, but Berzelius (36) finally obtained the metal in 1824 by heating a dry mixture of potassium and potassium zirconium fluoride in a very small closed iron tube placed inside a platinum crucible. After the quiet reaction had taken place, he cooled the tube and placed it in distilled water, whereupon, to use his own words, There fell from the tube a black powder as fast as the salt dissolved, and at the same time there was evolved a small quantity of hydrogen.. . . The zirconium obtained in this manner is easily deposited. It can be washed with water without oxidizing. Washed and dried, it forms a black powder resembling charcoal, which cannot be compressed nor polished like a metal (15). 

Hydroalumination (cj8, 506-507). This zirconium compound can catalyze hydroalumination of alkenes with trialkylalanes containing /5-hydrogens, such as tri-isobutylalane and lri-/-butylalane.5... 

ALDOL CONDENSATION Cesium fluoride. Dialkylboron trifluoromethane-sulfonates. Dichlorobis(cyclopentadi-enyl)zirconium. Diisobutylaluminum phenoxide. 2,5-Dimethylphenylpropi-onate. DimetIiyl(phenyllhio)aIuminum. Lithium iodide. Triethylborane. Tri-methylsilyl trifluoromethanesulfonate. Triphenyltin chloride. TrisCdiethyI-amino)sulfonium difluorotrimethyl-siliconate. 

More recently, a novel metal-substituted methylenecyclopropene (triafulvene) derivative was obtained when bis(propyne)zirconocene was treated with one equivalent of tris(pentafluorophenyl)borane, followed by excess of benzonitrile (equation 367)430. The first step involves alkynyl ligand coupling to give the isolable Cp2Zr(//-2,4-hexadiyne)B(C6F5)3 betaine. This undergoes a formal intramolecular nitrile insertion into the Zr—C(sp2) c-bond of the adjacent alkenyl zirconocene unit, leading to the zirconium-boron triafulvene-betaine. X-ray analysis of the triafulvene confirmed the planar... 

Butylmagnesium bromide-Vanadi-um(III) chloride, 219 Chlorobis(cyclopentadienyl)hydrido-zirconium(IV)-Magnesium, 351 Ethylmagnesium bromide, 203, 221 Ethylmagnesium bromide-Methyl-aluminum bis(2,4,6-tri-f-butyl-phenoxide), 203... 

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