Pentamethylcyclopentadienyl-zirconium dichloride

Bis(pentamethylcyclopentadienyl)zirconium dichloride is prepared readily in 50-60% yield following Reactions 4 and 5. Although (ry5-CsMes Zrb (7) can be obtained by treating ( -CsMes ZrC with Li+fBH Hs ]- or with Na+[AlH2(0CH2CH20CH3)2] in THF or benzene, respectively, its isolation from these reaction mixtures is extremely difficult. We therefore used an indirect synthesis (Reactions 6 and 7). Compound K -CsMes Zr fe (8) is obtained as a pure crystalline material in 60% yield its structure is reported elsewhere (13). Structure 8 reacts quantitatively (NMR) with H2 at 0°C according to Reaction 7. 

FIG. 13 (a) Oscillating metallocene catalysts. (From Ref. 6.) (b) Ethylene bis(pentamethylcyclopentadienyl) zirconium dichloride. 

In his first article on soluble metallocene/methylalumoxane catalyst systems producing isotactic polypropylene,112 Ewen reported the 13C NMR analysis of the end-groups of the atactic polypropylene formed with bis(cyclopentadienyl)zirconium dichloride or bis(pentamethylcyclopentadienyl) zirconium and methylalumoxane. The polymer formed at 50°C contained M-propyl and vinylidene end-groups in 1 1 ratio, consistent with /3-hydrogen elimination from the metal-primary carbon bond and subsequent reinitiation via primary insertion ... 

The reaction of bis-(pentamethylcyclopentadienyl) zirconium(IV) dichloride, 110, with dilithio-acetylene or dilithiodiacetylene, 111, formed zirconocene acetylene polymers (Scheme 2.32).197 Polymers 112 showed limited solubility in organic solvents other than n-hexane and possessed weight-average molecular weights between 55,000 and 68,000. 

Scheme 35 shows the formation of zirconocene acetylene polymers from the reaction of bis(pentamethylcyclopentadienyl)zirconium (I VO dichloride 118 with dilithiodiacetylene 119. Polymer 120 displayed a weight-average molecular weight of 68,000. 

Similarly conjugated zirconocene acetylene polymers (51) were prepared by reaction of Z)w-pentamethylcyclopentadienyl zirconium(IV) dichloride (49) with dilithioacetylene or dilithiodiacetylene (50) (Scheme 13). These relatively high MW polymers (M =55,000-68,000) displayed limited solubility in organic solvents other than n-hexane. 

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