Selectivity in propene polymerization with metallocene catalysts.

More than half of the 170 million metric tons of polymers produced each year are polyolefins. Current technology uses highly active cationic catalysts, which suffer from an inability to tolerate heteroatoms such as oxygen, nitrogen, and sulfur. These systems require scrupulously clean starting materials and activating cocatalysts. A family of catalysts has been developed whose members are tolerant of both heteroatoms and less pure starting materials. These heteroatom-tolerant neutral late transition metal complexes are in fact highly active systems that produce high-molecular-weight polyethylene, polymerize functionalized olefins, and require no cocatalyst.

https://science.sciencemag.org/content/sci/287/5452/460.full.pdf

Neutral, single-component nickel (II) polyolefin catalysts that tolerate heteroatoms

Alkyl and aryl derivatives of π-cyclopentadienyl compounds of chromium, molybdenum, tungsten, and iron

Vanadium compounds exert preventive effects against chemical carcinogenesis on animals, by modifying, mainly, various xenobiotic enzymes, inhibiting, thus, carcinogen-derived active metabolites. Studies on various cell lines reveal that vanadium exerts its antitumor effects through inhibition of cellular tyrosine phosphatases and/or activation of tyrosine phosphorylases. Both effects activate signal transduction pathways leading either to apoptosis and/or to activation of tumor suppressor genes. Furthermore, vanadium compounds may induce cell-cycle arrest and/or cytotoxic effects through DNA cleavage and fragmentation and plasma membrane lipoperoxidation. Reactive oxygen species generated by Fenton-like reactions and/or during the intracellular reduction of V(V) to V(IV) by, mainly, NADPH, participate to the majority of the vanadium-induced intracellular events. Vanadium may also exert inhibitory effects on cancer cell metastatic potential through modulation of cellular adhesive molecules, and reverse antineoplastic drug resistance. It also possesses low toxicity that, in combination with the synthesis of new, more potent and better tolerated complexes, may establish vanadium as an effective non-platinum, metal antitumor agent.

/pdf/vanadium-in-cancer-treatment-2tbgtbwiwz.pdf

Vanadium in cancer treatment.

The fascinating story of the discovery of the metallocene–methylaluminoxane catalysts for olefin polymerization is reviewed from its conception up until the first commercial production of polymers. A great number of different titanocenes and zirconocenes have been synthesized that give tailored polymers of totally different structures, and allows control of polymer tacticity, molecular weight and molecular weight distribution to be more efficient. New kinds of copolymers and elastomers can be synthesized.

J. M. Birmingham

Papers

Bis-cyclopentadienyl Compounds of Ti, Zr, V, Nb and Ta