Homogeneous vanadium-based catalysts for the Ziegler-Natta polymerization of alpha-olefins.

Although their activity is often inferior to that of other systems, the use of vanadium-based catalysts in homogeneous Ziegler-Natta polymerizations allows the preparation of high-molecular-weight polymers with narrow molecular-weight distributions, ethene/alpha-olefin copolymers with high alpha-olefin incorporation, and syndiotactic polypropene. The main reason for the low activity of these catalysts is their deactivation during catalysis by reduction of active vanadium species to low-valent, less active or inactive species. We here present an up-to-date review of this area with particular emphasis on the attempts to improve catalyst performance and stability by the use of additives or ancillary ligands.

The first homologous series of self-assembled aryl bromo- and aryl cyanocuprates, -argentates, and -aurates; MLi(2)XAr(2) (M = Cu(I), Ag(I), Au(I); X = Br, C(triple bond)N; Ar = [C(6)H(4)CH(2)N(Et)CH(2)CH(2)NEt(2)-2]-).

Reaction of 2 molar equiv of the diamine chelated aryllithium dimers Li(2)(C(6)H(4)[CH(2)N(Et)CH(2)CH(2)NEt(2)]-2)(2) (Li(2)Ar(2)) with the appropriate metal bromide allows the synthesis of the first homologous series of monomeric group 11 bromoate complexes of type MLi(2)BrAr(2) (M = Cu (7), Ag (8), Au (9)). Both in the solid state and in solution, the bromocuprate 7 is isostructural with the bromoargentate 8. The crystal structures of 7 and 8 consist of a MLi(2) core, and each of the two aryl ligands bridges via electron-deficient bonding between the group 11 metal and one Li atom (d(C(ipso)-M) = 1.

A Homologous Series of Homoleptic Zinc Bis(1,4-di-tert-butyl-1,4-diaza-1,3-butadiene) Complexes: K(x)[Zn(t-BuNCHCHN-t-Bu)(2)], Zn(t-BuNCHCHN-t-Bu)(2), and [Zn(t-BuNCHCHN-t-Bu)(2)](OTf)(x) (x = 1, 2).

A homologous series of mono- and dicationic, neutral, and mono- and dianionic zinc diazabutadiene complexes, K(x)[Zn(t-BuNCHCHN-t-Bu)(2)], Zn(t-BuNCHCHN-t-Bu)(2), and [Zn(t-BuNCHCHN-t-Bu)(2)](OTf)(x) (x = 1, 2), have been prepared and isolated in pure form. The crystal structures of the mono- and dicationic as well as of the monoanionic complexes are reported. In this series, the formal charge on the t-BuNCHCHN-t-Bu ligands ranges from -2 to +2, and the way in which the molecular geometry of the ligands varies with the charge is discussed.

Influence of Intramolecular Coordination on the Aggregation of Sodium Phenolate Complexes. X-ray Structures of [NaOC(6)H(4)(CH(2)NMe(2))-2](6) and [Na(OC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4)(HOC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4)](2).

The structural characterization of two new sodium phenolate complexes, containing ortho-amino substituents, enables the influence of intramolecular coordination on the aggregation of sodium phenolate complexes to be determined. Crystals of hexameric [NaOC(6)H(4)(CH(2)NMe(2))-2](6) (1a) are monoclinic, space group P2(1)/c, with a = 11.668(4) Å, b = 18.

A Proposal for Positive Cooperativity in Anion-Cation Binding in Yttrium and Lutetium Complexes Based on o-Amino-Substituted Phenolate Ligands. On the Way to Coordination Polymers by Self-Assembly. Molecular Structures of [ClLu(OAr)(3)Na] (X-ray) and [ClY(OAr')(3)Y(OAr')(3)Na] (X-ray and (89)Y-NMR).

Unique hetero(poly)metallic complexes [ClM(OAr)(3)Na] (M = Lu (3a), Y (3b)) and [ClY(OAr')(3)Y(OAr')(3)Na] (4) containing the bis (OAr = OC(6)H(2)(CH(2)NMe(2))(2)-2,6-Me-4) and mono (OAr' = OC(6)H(4)(CH(2)NMe(2))-2) o-amino-substituted phenolate ligands have been synthesized and characterized by NMR ((1)H, (13)C, and (89)Y) and X-ray structure determinations (3a and 4). Crystals of 3a are triclinic, space group P&onemacr;, with unit cell dimensions a = 10.706(1) Å, b = 14.