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The palladium diphosphine complex 4converts ethylene to hyperbranched unsaturated oligomers (Mn≈ 330 g/mol) at 22 °C. In addition to the high stability of this catalyst observed at temperatures up to 75 °C, an increase of the reaction temperature leads to a decrease in branching densities of the oligomers, in sharp contrast to the palladium and nickel diimine catalyst systems. One-pot oligomerizations/hydrogenations were carried out to form hyperbranched saturated oligomers.

Nickel(II) α-diimine dibromide complexes incorporating 8-p-tolylnaphthylimino groups have been prepared and used for ethylene polymerization by activation with modified methylalumoxane (MMAO). These catalysts possess increased axial bulk relative to standard diimine-nickel complexes, resulting in lower rates of chain transfer relative to chain propagation rates and thus higher polymer molecular weights and narrower PDIs. They yield the most highly branched PE produced by Ni catalysts seen to date. The easy synthesis of 8-aryl-1-naphthylamines provides ready access to a new class of α-diimine-based nickel catalysts in which the 8-substituent is ideally positioned to provide steric bulk at the axial sites.

A series of 8-halonapthalen-1-amines (6a–d, X = F, Cl, Br, I) were prepared and converted to the α-diimines of 2,3-butanedione (7a–d). The nickel dibromide and zinc dibromide complexes of these diimines (3a–dand 8a–d, respectively) were obtained in good yields from standard precursors. NMR spectroscopic analysis of the zinc diimine complexes show the existence of synand antidiastereomers with syn/antiratios of ca. 2:1 (F), 2:1 (Cl), 1:1.5 (Br), and ca. 1:22 (I). Variable temperature NMR spectroscopy was used to calculate barriers to interconversion of these diastereomers which fall in the range 17–18.5 kcal/mol. Activation of nickel dibromide complexes 3a–dwith modified methyl alumoxane (MMAO) yields cationic diimine complexes in which the 8-halo substituents lie over the axial coordination sites. Ethylene polymerization using these activated complexes is reported. The antidiastereomer of the diiodo catalyst (10d) in which both axial sites are blocked yields high molecular weight PE (ca. 106g/mol) as the major fraction with a high turnover frequency at 40 °C. The minor syndiastereomer of 10din which only one axial site is blocked produces low molecular weight PE as a minor fraction. PE formed from the dichloro catalyst 10balso exhibits a bimodal polymer distribution, but the high molecular weight fraction from the antidiastereomer is minor, while the syndiastereomer produces low molecular weight PE. The dibromo complex (10c) is unique in that interchange of diastereomers is on a time scale such that the PE produced shows a very broad molecular weight distribution (MWD ca. 14), spanning the range from the low to high molecular weight regimes. Catalyst 10a, bearing the small fluoro substituents, yields very low molecular weight PE (ca. 600 g/mol).

New silver(I) -diketiminate complexes have been prepared and characterized. Monomeric complexes with ethylene (4), triphenylphosphine (5), and IMes (IMes 1,3-dimesitylimidazol-2-ylidene) (8) as well as a dinuclear acetonitrile complex (3) were characterized by 1H NMR, 13C NMR, elemental analysis, and X-ray crystallography. These complexes are stable in the solid state at ambient temperature and inert atmosphere.