Dicyclopentadienyl zirconium

R)- and (,S )-1.1,2-Triphenyl-l,2-ethancdiol which are reliable and useful chiral auxiliary groups (see Section 1.3.4.2.2.3.) also perform ami-sclcctive aldol additions with remarkable induced stereoselectivity72. The (/7)-diastercomer, readily available from (7 )-methyl mandelate (2-hy-droxy-2-phcnylaeetate) and phenylmagnesium bromide in a 71 % yield, is esterified to give the chiral propanoate which is converted into the O-silyl protected ester by deprotonation, silylation, and subsequent hydrolysis. When the protected ester is deprotonated with lithium cyclohexyliso-propylamide, transmetalated by the addition of dichloro(dicyclopentadienyl)zirconium, and finally reacted with aldehydes, predominantly twm -diastereomers 15 result. For different aldehydes, the ratio of 15 to the total amount of the syn-diastereomers is between 88 12 and 98 2 while the chemical yields are 71 -90%. Furthermore, high induced stereoselectivity is obtained the diastereomeric ratios of ami-15/anti-16 arc between 95 5 and >98 2. 

Preparation. This hydride is prepared by reduction of dicyclopentadienyl-zirconium dichloride (zirconocene dichloride) with either LiAlH(0-r-Bu)3 or NaAlHj (OC2 H4 OCH3 >2... 

Metallocene catalysts, for example dicyclopentadienyl zirconium dichloride, in combination with the cocatalyst methylalumoxane, helped establish a regulated set of properties, making it possible to customize molar mass, molar mass distribution, tacticity, heat resistance, rigidity, hardness, cold impact strength, and transparency. Added to these advantageous physical properties is the reactivity of this catalyst... 

The addition of trialkylalanes to alkenes is also catalysed by dicyclopentadienyl-zirconium dichloride to afford hydroalumination products that undergo protonolysis to yield alkanes. Thus, reaction of oct-l-ene with Bu gAl with a catalytic quantity of cpaZrCl2 at 0 °C gives n-octane in 97 % yield. Reduction of alkenes containing hydroxyl, phenylthiolato, and bromo functions can also be reduced in the same way. ... 

The auxiliaries R) and (S)-triphenylglycol 172 were also applied to achieve anti-selective propionate aldol additions, as shown by Braun and coworkers. It turned out that, for this purpose, the tertiary hydroxyl group of the propionate (R)-204 had to be protected by silylation. This was easily accomplished by a one-pot procedure that delivered the ester (R)-205. After deprotonation with LICA, the lithium enolate was transmetallated with dichloro(dicyclopentadienyl)zirconium and reacted with aliphatic aldehydes to give predominantly anti-diastereomers 206, the diastereomeric ratio surpassing 95 5. Reduction with lithium aluminum hydride finally led to diols 207 under the release of the chiral auxiliary R)-172. After its removal by chromatography, diastereomerically pure diols 207 were isolated with >95% ee (Scheme 4.45) [107]. For the benzaldehyde adduct 206 (R = Ph), alkaline hydrolysis was also performed and found to lead to epimerization to only a small degree. 

Dicyclopentadienyl(isoprene)zirconium, (CsH5)2Zr(CH2 CHC CH2) orange, air-sensitive. Preparation.1 CH3... 

Figure 3.8 Zirconium and hafnium dicyclopentadienyl-1,3-dienyl complexes. See text for explanation of the structures.

Zirconium Neodecanoate Cobalt Pentanedione Ferric Pentanedione Ferrous Dicyclopentadienyl Ferrous Pentanedione Titanium Pentanedione Cobalt Dicyclopentadienyl Vanadium Neodecanoate Ferrous Stearate Ferric Naphthenate Control... 

Cano, A. Cuenca, T. Gomez-Sal, R Manzanero, A. Royo, P. Dicyclopentadienyl titanium and zirconium complexes with the double bridged bis(dimethylsilanodiyl)dicyclopentadienyl [(Me2Si)2(ti -... 

Titanium bis-enolate 19, readily available by transmetallation of the lithium enolate of acetaldehyde with dicyclopentadienyl titanium dichloride (Cp2TiCl2), was characterized by a crystal structure analysis [53, 54]. Mono-enolates of titanium and zirconium 20 were obtained analogously from Cp2Ti(Me)Cl and... 

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