Biscyclopentadienyl zirconium

Reaction of achiral biscyclopentadienyl zirconium-( /2-acyl-C,0) complexes, such as la and lb, with sodium hexamethyldisilazide generates the di-hapto enolates 2a and 2b91. Enolate 2b is believed to adopt a Z geomeLry, only one isomer was observable by H-NMR spectroscopy (d.r. >98 2). 

Both enolate species 2a and 2b are readily alkylated by iodomethane to provide the corresponding acyl complexes 3a and 3b, respectively (yield of 3b is not reported)91. No examples of the generation of zirconium-acyl enolates from chiral biscyclopentadienyl zirconium complexes has yet been reported. The reported preparation of the enantiomerically pure complex 4 indicates that chiral zirconium-acyl enolate species may be accessible92. 

Fig. 6. Side reactions in the zirconocene system biscyclopentadienyl zirconium dichloride, and triethyl aluminum at 20°C in toluene solvent (65).

Figure 3.18 Theoretical study of ethylene insertion into the Zr-C bond in the silylene-biscyclopentadienyl(methyl)zirconium cation [H2Si(Cp)2Zr—Me]+. E — energy...

An excellent review on soluble systems, including also the more recent progresses in ethylene polymerization, is that of Sinn and Kaminsky who even developed soluble catalytic systems with extremely high activities by using alumoxane and biscyclopentadienyl-titanium or-zirconium compounds. Interesting results have also been obtained in ethylene oligomerization and in propylene dimerization... 

Chemical composition distribution Biscyclopentadienyl titanium dichloiide Biscydopentadienyl zirconium dichloride Ethylenebis(indenyl)zirconium dichloride Ethylenebis(tetrahydroindenyl)zirconium dichloride Ethylidene(l-tetramethylcyclopentadienylKindenyl) titanium dichloride... 

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