Binuclear metallocenes

For more examples of this type of complexes, see Section 4.05.6. The synthesis of homobinuclear and heterobi-nuclear bis-Cp titanium complexes is reviewed. The research about their activity on polymerization of cr-olefins is summarized. The mechanism about binuclear metallocene catalyst is also discussed in this chapter.1079... 

Binuclear metallocenes—with two atoms, rather than one in the center of a sandwich structure—are also known. Perhaps the best known of these metallocenes is decamethyldiz-incocene, (T7 -C5Me5)2Zn2 (Figure 13.33), which was prepared from decamethylzincocene. 

Complexation of 1,3-butadiynes In the reactions of complex 1 with various butadiynes, binuclear complexes with intact C4 units between the two metal centers are found. The former diynes are transformed to zig-zag butadiene ligands or g-r (l-3),r (2-4)-trans,-trans-tetradehydrobutadiene moieties between two metallocene cores. The bond type in 19 is unknown for the corresponding zirconocene complexes. 

Haselwander, T., Beck, S. and Brintzinger H. H., Binuclear Titanocene and Zirconocene Cations with //-Cl and fi — CH3 Bridges in Metallocene-based Zieg-ler-Natta Catalyst Systems - solution-NMR studies , in Ziegler Catalysts, Springer-Verlag, Berlin, 1995, pp. 181-197. 

Fujita, Tohi, Mitani, Matsui, Saito, Nitabaru, Sugi, Makio, and Tsutsui, from Mitsui Chemicals, Inc. Post-metallocene catalysts are more varied than metallocene. These are using a wide variety of M from Ti to Cu. Also ligands have diverse structures. Thus, close to M radicals R and R control the reaction. They are struaurally and electronically flexible showing dependent on M electron-receptive or electron-donating properties. Ivanchev et al. discussed another group of binuclear phenoxyimine Ti catalysts... 

In a few cases, however, a more quantitative analysis can be undertaken whereby the desired solvent-dependent AG int values are obtained experimentally from optical ET reorganization energies for related binuclear systems. An example of this approach, involving self exchanges of metallocenium-metallocene (Cp2M ") redox couples in various polar Debye solvents is worth highlighting here since ET rate-solvent dependencies are observed that span the limits of nonadiabatic and adiabatic behavior [12]. For ferrocenium-ferrocene couples, the rate constants k gx (corrected for AG -solvent variations) are almost independent of the solvent dynamics, as... 

The reactions of the branched tetraalkynylsilanes (RC = C)4Si (R = Ph, Bu, SiMes) with the metallocene source Cp2Ti(ri -Me3SiC = CSiMe3) and Cp2Zr(THF)(ri -Me3SiC = CSiMe3) led to complexes 44. These gave a novel type of binuclear carbon-rich spiro complexes and the conversions proved to be independent of the metals, the substituents R and the stoichiometries em-ployed. ... 

Yamazaki reported meso-selective formation of binuclear fx-oxo-ansa-metallocenes [75]. This can be a convenient method for separating meso and racemo-isomers of ansa-bis(substituted cyclopentadienyl)metallocenes, although it might be less effective for non-substituted ansa-bisindenyl complexes [76]. 

Soga and Shiono used some C -symmetric ansa-metallocenes for their ZnEtj-assisted system. Typical catalyst precursors for isospecific propylene polymerization, such as 44,45 and 46, produced highly isotactic poly(MMA) with catalyst control [141, 142]. Marks showed that the binuclear cationic species [(rac-MejSillndljZrljlp-Me)] with PBB anion gave highly isotactic poly(MMA) ([mnj]=0.93) [135]. 

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