Propylene-bridged bis

Compounds 43-45 were synthesized in an analogous manner by cyclization of the bis-mesylate. The propylene-bridged oxa-thiacrown ethers 46 and 47 were prepared from dibromide having trimethylene units. 

Formanovskii and Murakhovskaya, 1985 Formanovskii et al., 1988, 1989 Markovich et al., 1983). Biernat and coworkers have prepared a series of dibenzodiaza-crowns by methods V-12 (above) and V-13 (below), except that some of their macrocycles contained propylene bridges and they used dichlorides as well as activated diacid derivatives as starting materials (Biernat and Luboch, 1984 Biernat et al., 1979). The bis-imidazolides shown in method... 

The most simple artificial system consists of cofacial bis-quinone cyclo-phanes in which the two quinones have different redox potentials. Extreme differences in relative orientations have been realized with the ortho and geminal isomers in which a tetracyanoquinomethane oxidant and dimethoxy hydroquinone reduc-tants are connected by two propylene bridges (Fig. 7.2.4). A strong broad charge transfer band (600-1000 nm) was observed for the geminal isomer (e = 35(X)) and a weaker one for the ortho isomer (e = 120), indicating the importance of the relative orientation of electron donors and acceptors (Staab and BCnaus, 1979). 

FIGURE 1.12 Methylene-, isopropyhdene-, and ethylene-bridged bis(indenyl) an a-metaUocenes 11-13 for isoselective propylene polymerization. Only one enantiomer of the racemic pair is shown. 

In comparison to bis(indenyl) anM-metallocenes, there are considerably fewer examples of C2-symmetric isoselective metallocene catalysts on the basis of bridged bis(cyclopentadienyl) ligand framework. Representative complexes 14-17 are illustrated in Figure 1.13. Many of the reported chiral bis(cyclopentadienyl) flni fl-zirconocenes produce highly stereoregular iPP, but with polymerization activies much lower than those of the structurally optimized bis(indenyl)-based catalysts. For example, in liquid propylene at 70 °C, 16 produces iPP with mmmm > 94%,... 

C-2-Bridged Bis(indenyl) Zirconocene Precatalysts Activated with MAO in Propylene Polymerization... 

The partial oxidation of propylene occurs via a similar mechanism, although the surface structure of the bismuth-molybdenum oxide is much more complicated than in Fig. 9.17. As Fig. 9.18 shows, crystallographically different oxygen atoms play different roles. Bridging O atoms between Bi and Mo are believed to be responsible for C-H activation and H abstraction from the methyl group, after which the propylene adsorbs in the form of an allyl group (H2C=CH-CH2). This is most likely the rate-determining step of the mechanism. Terminal O atoms bound to Mo are considered to be those that insert in the hydrocarbon. Sites located on bismuth activate and dissociate the O2 which fills the vacancies left in the coordination of molybdenum after acrolein desorption. 

---