The synthesis and structural characterization of new paramagnetic amine bis(phenolate) [ONNO]-vanadium(III) and -vanadium (II) complexes, V III (acac) [ONNO], V III (Cl) (THF) [ONNO], and V II (TMEDA)[ONNO], is described. These compounds complete the family of [ONNO]-vanadium(IV/V) complexes previously reported. The members of the [ONNO]-vanadium family at various oxidation states that range from vanadium(II) to vanadium(V), in association with
IntroductionIn the past decade, a tremendous amount of effort has been devoted to the design of new "non-metallocene" group 4 transition metal complexes because of their importance as α-olefin polymerization catalysts.[1] Particularly, chelating diamide, [1a,2-4] dialkoxide, [1a,5-6] or phenoxyimine [7,8] ligands have been extensively studied as rigid supporting environments for titanium and zirconium complexes, which has resulted in the emergence of a great deal of novel and useful chemistry, including the discovery of highly active olefin polymerization precatalysts. Among these new ligands, chelating, dianionic [ONNO]-type amine bis(phenolate) ligands associated with group 4 metal complexes [5] have proven to be highly active 1-hexene polymerization catalysts, and in some cases, even isospecific living polymerization was possible.[5a] Recently yttrium-[ONNO] complexes have been reported for their catalytic activity in the ring-opening polymerization of ε-caprolactone. [9] Vanadium-based catalysts in homogeneous ZieglerNatta polymerization have been known for about half a century.[10] Although generally less active, their use presents a number of interesting advantages over group 4 metal catalysts: [11] (i) the synthesis of high molecular weight polymers with narrow polydispersity, (ii) the preparation of ethylene/ α-olefin copolymers with high α-olefin incorporation, and (iii) the preparation of syndiotactic polypropylene. The major reason for the low activity of these systems is their deactivation during the polymerization process, probably due to reduction of the catalytically active vanadium species [a]
2850EtAlCl 2 cocatalyst, were studied in the polymerization of ethylene and in the copolymerizations of ethylene-1-hexene and ethylene-norbornene. Poly(ethylene-co-1-hexene) and poly(-ethylene-co-norbornene) were produced with co-monomer content of up to 11 mol-% and 29 mol-% for 1-hexene and norbornene, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) to low-valent, less active or inactive species. Nevertheless, V(acac) 3 is currently employed in the synthesis of EP (ethylene-propylene) and EPDM (ethylene-propylene-diene monomer) elastomers.As part of an ongoing study of vanadium chemistry with various supporting ligands, [12] and in particular of vanadium complexes for olefin polymerization, we have recently used ancillary diamido ligands with sterically demanding protecting groups [13] or imido ligands [14] on vanadium(iv) complexes as a way to overcome the problem of catalyst deactivation by stabilization of the formal ...
