Ulrich Klabunde

Methylene exchange reactions catalyzed by alkylidene derivatives of titanium and phosphorus

Abstract Although olefin metathesis is generally catalyzed by compounds of Mo, W, or Re, alkylidene derivatives of titanium and of phosphorus also catalyze methylene exchange between olefins, the so-called degenerate metathesis reaction. In contrast to the metal-based catalysts, the phosphorus-based catalysts are effective with olefins in which the CC bond is conjugated with a functional group such as CN or COOR. These new families of catalysts may operate by an alkylidene/metallacycle mechanism like that now generally accepted for conventional olefin metatheses. The titanium system can be used to study some of the individual steps in metatheses and to help elucidate the role of the commonly used alkylaluminum cocatalyst. Titanacyclobutenes have been isolated from the reactions of acetylenes with methylenetitanium complexes. The structures have been determined crystallographically.

Reaction of nitrogen oxides with π-allyl complexes: A model for propylene oxidation☆

η3-Allylnickel bromide dimer reacts with nitric oxide to form a 3-oxi-minopropene complex, Ni(CH2CHCHNOH)Br(NO). μ-Dichlorobis-(η3-allylpalladium) does not react with NO under the conditions used for the analogous nickel compound but reacts with NO2 to give [PdCl(NO)]n and allyl nitrate. η3-Allyldicarbonyl(hydrotris(pyrazolyl)borato)molybdenum(II) reacts similarly with NO2 to give allyl nitrate and nitrosyldicarbonyl(hydrotris(pyrazolyl)borato)molybdenum, along with some 3-nitro-propene and a new nitrosylmolybdenum complex. The relevance of these results to surface processes in the heterogeneous catalysis of acrylonitrile synthesis from propylene and nitric oxide is discussed.

Synthesis of highly active alkene polymerization catalysts using MgCl2 vapour

The condensation of MgCl2 vapours in a frozen matrix produces highly activated, high surface area materials which, when treated with TiCl4, yield MgCl2-supported, highly active Ziegler–Natta calaysts with controlled catalyst and polymer properties.