The evolution of new generaton 'single-site' Ziegler-Natta polymerization catalysts

Since the discovery of stereospecific polymerization of olefins by K. Ziegler and G. Natta in 1955, tremendous developments have occurred in the area of designing polymerization catalysts. Rapid advances in organometallic chemistry research practised both at academic and industrial laboratories throughout the world have led to the emergence of new generation olefin polymerization catalysts and polyolefin products. The purpose of this article is to highlight some of the major events that have occurred in the area of Ziegler- Natta catalysis and to illustrate the contributions of organometallic chemistry in the exciting story of the evolution of well-defined, 'single-site' metallocene catalysts. The developments in the mechanistic understanding of key steps of polymerization processes such as generation of active species, chain propagation and chain termination emerging from organometallic modeling studies are also highlighted. Also, the recent discovery of late transition metal olefin polymerization catalyst systems and its implications for further research in Ziegler- Natta catalysis is described

Polypyrazolylborate mixed-ligand complexes of Zr(IV), VO(IV) and MoO₂(VI)

446-449Mixed-ligand complexes of Zr(IV), VO(IV) and MoO2(VI) containing tris(3,5-dimethylpyrazolyl)borate(L) and acetylacetonate(acac) have been prepared by the ligand exchange reactions of the appropriate acetylacetonate complct'xes with sodium hydrotris(3,5-dimethylpyrazolyl)borate ligand. The isolated 1:1 complexes Zr(acac)3L, VO(acac)L and MoO2(acac)L have been characterized by IR, NMR and EPR methods. The susceptibility of the mixed-ligand complexes Zr(acac)3L and VO(acac)L to undergo oxidation and reduction reactions have been examined by electrochemical methods. Thermoanalytical studies on VO (acac)L and VO(acac)2 have been performed by TG and DTG methods to study the influence of the chelating ligand L on the thermal stability of these metal acetylacetonate complexes

Synthesis, structure and reactivity of zirconium(IV), vanadium(IV), cobalt(II), nickel(II) and copper(II) complexes derived from carbohydrazide schiff base ligands

415-420A series of polydentate schiff base ligands have been prepared by the condensation of carbohydrazide, H2N-NH-CONH-NH2, with various aldehydes and the isolated ligands characterized by elemental analysis and spectral methods. In order to investigate the coordination behaviour of these ligands, metal complexes of the type M(acac)x L[M = Zr(IV), VO(IV), Co(II), Ni(II) and Cu(II); L = Schiff base ligands; x = 0 or 2] have been prepared from the reaction of these ligands with their corresponding metal acetylacetonates. On the basis of analytical and spectral data, square antiprism, square pyramid and square planar structures have been proposed. The biological activities of all isolated ligands and their metal complexes have been studied by screening the compounds against organisms such as E. coli, S. aureus, A. niger and C. albicans and the results have been compared