Zirconocene dimethyls

The reaction of tris(pentafluorophenyl)borane, B(C6F5)3, with a variety of zirconocene dimethyl complexes proceeds rapidly and quantitatively at room temperature in noncoordinating solvents to yield cationic alkylzirconocene methyltriarylborate complexes (34 eq 26). Reaction with excess of... 

The Lewis acidity of aluminoxanes can arise from functionality other than three-coordinate Al centers. Barron et al. found that, in the case of aluminoxane clusters such as 5, three-coordinate aluminum is not a prerequiste for ethylene polymerization activity when combined with zirconocene dimethyl. Coordi-natively saturated aluminoxane 5 reacts exothermically with Cp2ZrMe2 at room temperature to produce, according to the H NMR spectrum, an ethylene polymerization-active tightly ion paired species, Cp2-ZrMe ( Bu)6Al6( 3-0)6Me (74). The driving force for... 

Another group of compounds that were recently reported as capable of initiating cationic polymerizations are metallocene/borate complexes. Such material can, for instance, be generated from zirconocene dimethyl compounds (Cp2ZrMe2) and anUinium borate. Thus, [HNMe2Ph] -1- [B ( 5115)4] will polymerize amine-functionalized a-olefins [51] as well as isobutylene homo and copolymerizations [52]. Also, when compounds, like Cp MMe3 (M = Ti, Zr, and Hf where... 

With discoveries of boron-based cocatalysts such as triphenyl-boron, ammonium tetraphenylborate salts, and finally pentafiuorophenyl derivatives of borate [B(C6H5)4] , olefin polymerization catalysis was developed without a reliance on alkylaluminum species. Although the activity with nonfiuori-nated boron-based cocatalysts was invariably low, the fiuorinated analogs exhibited olefin polymerization behavior similar to that of metallocene/MAO catalyst systems. The boron and borate compoimds are typically used in a 1 1 molar ratio with transition metal (stoichiometric or near stoichiometric). Because these activators do not alkylate the transition metal, the metallocene precatalyst employed must already bear alkyl groups. Thus, zirconocene dimethyl species combine with boron or borate activators to nerate active cationic polymerization catalysts. Figure 8 shows typical activation reactions with borate (a, b) and boron (c) activators. 

The compounds 2 and 3, have all been isolated from reactions of phenylsilane with either dimethyltitanocene (1 2) or dimethyl-zirconocene (r ). All of the evidence points to the fact that these compounds are probably resting species and are not involved in the catalytic cycle. They do nevertheless give some indication of the complex series of reactions that transform the dimethyl-metallocene to active catalyst. 

Some of the bicyclo[3.1.0]hexene zirconocene derivatives, especially those containing a phenyl group, rearrange quantitatively to the corresponding 4-vinyl-l-metalla-2-cyclobutene derivatives when heated in toluene to 60-80 °C for several hours (equation 131). The 6,6-dimethyl-2,3-diphenyl-2-zirconabicyclo[3.1.0]hex-3-ene derivative prefers ring-opening to the isomeric j/. -allylic complex upon thermolysis. 

Dimethylselenides, bacterial degradation, 12, 610 Dimethylsilyl bridges, in -titanocenes, 4, 619 Dimethylsilylene-bridged -zirconocenes, synthesis, 4, 949 Dimethyl sulfoxide, for water-solubilization, 1, 827 Dinitrogens... 

As one partial solution, the selective cross-cyclization is possible by stepwise reaction of Cp2Zr (113), generated from zirconocene dichloride and BuLi, with three different symmetric internal alkynes in one pot. The method is based on the conversion of zirconacyclopentadiene 114 to the benzene derivative 115 by the treatment with dimethyl acetylenedicarboxylate and CuCl [52],... 

A novel Si-macrocycle was prepared by the demetalation of the zirconocene-containing dimeric cyclophane intermediate, which was formed by the coupling of dimethyl-fc(4-trimethylsilylethynylphenyl)silane with [Zr(Cp)2Cl2] <02CEJ74>. Synthesis, X-ray analysis, and characterization of a dibenzo macrocyclic acetylenic diphenylsilane have been reported <02TL2079>. 

The metathesis reaction of zirconocene dichloride 51 at low temperatures with Z equiv of -butyllithium followed by Z molar equiv of trimethylsilylpropyne yields l,l-bis(cyclopentadienyl)-3,4-dimethyl-2,5-bis(trimethylsilyl)-Tzirco-nacyclopenta-2,4-diene 52 (Equation 8). 

Photolysis of the 5e/36 mixture at sufficiently low temperature, or a thermally induced reaction of 3,3-dimethyl-3-butanone with the pure (j-frflrts-7j -isoprene)zirconocene isomer (3e) eventually effects the reversal of the regioselectivity. The regioisomer 18A resulting from C—C coupling at C4 of the isoprene unit dominates over 18B by a ratio of 78 22. 

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