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SynopsisBis(arene) complexes of zerovalent titanium, zirconium, and hafnium supported on partially dehydroxylated, fumed alumina are effective catalysts for the polymerization of olefins. The zerovalent complexes react with surface hydroxyls with loss of one equivalent of arene to yield the active species. The polyethylenes derived from these catalysts are very high molecular weight. Polymerization of propylene yields elastomeric stereoblock polymers which are composed of isotactic and stereoirregular sequences. The polymers are stiffer than polypropylenes obtained with similar catalysts derived from tetra(neophy1)zirconium. The chain microstructures of the various components of the whole polymers have been characterized by %NMR and solvent extraction studies. The ether soluble component of these polymers is of a relatively high molecular weight and the microstructure of the backbone is largely stereoirregular. It is the cocrystallization of this fraction of the polymer with the crystalline, isotactic fractions which is critical to the observed elastomeric properties.

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Although sulfur tetrafluoride is a remarkably versatile agent for selectively introducing fluorine atoms into organic compounds, its existence was doubted as late as 1950. A colorless gas boiling at ‐38o C, sulfur tetrafluoride was probably first made by treatment of sulfur with uranium hexafluoride and subsequently by the reaction of sulfur with cobalt(III) fluoride. Both products were of questionable purity. In 1950 sulfur tetrafluoride was unequivocally synthesized by electrical decomposition of trifluormethylsulfur pentafluoride. It was not until 1955 that gram amounts were prepared and thus making sulfur tetrafluoride a viable compound. This led the way for the discovery of its remarkable fluorinating ability. The ability of sulfur tetrafluoride to replace carbonyl oxygen selectively is probably the most useful synthetic application.

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