| This thesis describes research on paramagnetic chromium complexes coordinated by β-diketiminato ligands. Chapter 1 discusses a novel class of homogeneous β-diketiminato chromium complexes that have been prepared and characterized. (Ph)2nacnacCrCl 2THF2 ((Ph)2nacnac = 2,4-pentane-N,N′ bis(phenyl)ketiminimato) was synthesized and found to polymerize ethylene in the presence of excess methylaluminoxane (MAO). Attempted alkylation of the dichloride resulted in a disproportionation to a chromium(II) species, [(Ph)2nacnac]2Cr.; Chapter 2 details the synthesis, characterization and reactivity of β-diketiminato organochromium complexes in various oxidation states. Alkylation of the dinuclear chloride [(2,6-iPr2Ph)2nacnacCrCl(μ-Cl)] 2 resulted in reduction to the chromium (II) species [(2,6-i Pr2Ph)2nacnacCr(μ-Cl)] 2. A series of chromium (II) alkyls of the type [(2,6-iPr 2Ph)2nacnacCrR]n, (R = methyl, ethyl, n = 2; R = trimethylsilylmethyl, benzyl, n = 1) could be isolated by alkylation of the chloride. In the presence of MAO, the chromium (II) alkyls catalyzed the polymerization of ethylene, however, without cocatalyst only oligomers of ethylene were obtained. Oxidation of the methyl derivative resulted in formation of the chromium (III) alkyl cation [(2,6-iPr2Ph) 2nacnacCrCH3(Et2O)]+BAr4 −. The chromium (III) alkyl cation catalyzed the polymerization of ethylene and the copolymerization of ethylene with 1hexene. Chromium complexes in the +IV and +V oxidation states have also been isolated and their reactivity is described.; Chapter 3 reports on the synthesis, characterization and reactivity of (2,6-McPh)2nacnac chromium (III) complexes. The chloride species, (2,6-Me2Ph)2nacnacCrCl2(THF)2 could be readily alkylated with either LiCH2SiMe3 or McMgCl to yield (2,6-Me2Ph)2nacnacCr(CH2Si(CH 3)3)2 or (2,6-Me2Ph)2nacnacCrMe 2(THF), respectively. Although they are coordinatively unsaturated, the dialkyls did not polymerize ethylene without cocatalyst. The addition of cocatalysts (MAO or B(C6F5)3 imparted catalytic activity to the dialkyls and allowed for the isolation of polyethylene. Reaction of the trimethylsilylmethyl derivative with H+(Et 2O)2+BARF− resulted in the isolation of a chromium (III) alkyl cation [(2,6-Me2Ph) 2nacnacCrCH2Si(CH3)3]+BARF −, which catalyzed the polymerization of ethylene in the absence of cocatalyst. |
