PINCER COMPLEXES OF PRECIOUS METALS

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  • March 22, 2019
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  • Grajeda, Javier
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • The synthesis and characterization of several new iridium(I) and iridium(III) carbonyl complexes supported by aminophosphinite pincer ligands is reported. A surprising diversity of reaction pathways were accessible upon treatment of Ir carbonyl complexes with salts of redox-inactive alkali, alkaline earth, and lanthanide metal cations. Iridium(III) hydridocarbonyl chloride complexes underwent either halide abstraction or halide substitution reactions, whereas iridium(I) carbonyl complexes underwent protonative oxidative addition reactions. When the nitrogen donor of the pincer ligand is an aza-crown ether macrocycle, cation–macrocycle interactions can be supported, leading to divergent reactivity in some cases. New iridium and rhodium complexes supported by aminophosphinite pincer-crown ether ligands were synthesized. Iridium-catalyzed hydroformylation of allylbenzene was explored. Catalytic amounts of LiOTf (OTf = trifluoromethanesulfonate) doubled the rate of hydrofunctionalization. The iridium pincer complexes were found to undergo remetallation pathways under the conditions of catalysis. This guided the design of a new, more active iridium catalyst supported by a pincer ligand with a methoxy substituent incorporated to prevent remetallation. Rhodium-catalyzed hydroformylation of 1-octene was explored as well. A systematic decrease in the n (linear) to iso (branched) aldehyde ratio was observed in the presence of increasingly bulky ammonium additives. However, catalyst stability studies showed that rhodium pincer complexes undergo decomposition under hydroformylation conditions and presumably simply act as pre-catalysts. The first mononuclear gold(III) PNP pincer complexes (PNP = bis(2- diisopropylphosphinophenyl)amide) are reported. The chloro complex [(PNP)Au(Cl)][OAcF] (OAcF = OCOCF3) was synthesized by microwave irradiation of a tetrachloroaurate salt and the neutral PNHP ligand. Dehalogenation with AgOAcF afforded the trifluoroacetate-bound complex [(PNP)Au(OAcF)][OAcF]. Electronic absorption spectroscopy and time-dependent density functional theory studies assigned the electronic transition that imbues the complexes with a deep royal blue color. The Au(III) trifluoroacetate complex is surprisingly stable, and no reactivity towards ethylene was observed, even under high pressures and at high temperatures. Density functional theory calculations suggest that the lack of reactivity is due to the high energy of the putative dicationic ethylene-bound intermediate invoked in a formal insertion reaction.
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Advisor
  • Johnson, Jeffrey
  • Miller, Alexander
  • Leibfarth, Frank
  • Meyer, Gerald
  • Meyer, Thomas
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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