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The mechanism of catalytic hydrocarbon oxidation by molecular oxygen and halogenated ruthenium and iron porphyrins

Citation

Birnbaum, Eva Rachel (1995) The mechanism of catalytic hydrocarbon oxidation by molecular oxygen and halogenated ruthenium and iron porphyrins. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-09112007-142146

Abstract

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Highly halogenated ruthenium and iron porphyrins are shown to be active catalysts for alkene oxidation with dioxygen or iodosobenzene. The synthesis and characterization of [...]-octachloro-tetrakis(pentafluorophenyl)porphyrinato-ruthenium(II) carbonyl [RuTFPPCl[...](CO)] and [...]-octabromo-tetrakis(pentafluorophenyl)porphyrinato-iron(III) chloride [Fe(TIPPBr[...])Cl] are reported. Crystal structures of RuTFPPC1[...](CO) and the zinc and free ligand precursor complexes show extensive distortion of the halogenated porphyrin macrocycles due to steric interactions between the b-chlorine atoms and the pentafluorophenyl rings. [...]FNMR is developed as a method to characterize both paramagnetic and diamagnetic fluorinated porphyrins in solution. The anodically shifted reduction potentials and red shifted absorptions in the UV-Vis spectroscopy of the halogenated porphyrins are discussed in terms of steric and electronic effects on porphyrin frontier orbitals.

Both Fe(TFPPBr[...])Cl and RuTFPPCl[...](CO) catalyze the oxidation of cyclohexene with dioxygen and without added coreductant, with 73 and 296 turnovers, respectively, in 24 hours. Although both porphyrins will catalyze reactions with iodosobenzene, showing selectivity consistent with high-valent metal-oxo formation, overall activity with dioxygen is much higher. In accord with earlier work, cyclohexene oxidation by Fe(TFPPBr[...])Cl is consistent with a mechanism involving porphyrin-mediated decomposition of alkyl peroxides, which generates free radicals in solution. Catalysis with RuTFPPCl[...](CO) is shown to be of a photochemical nature, as irradiation with low energy light results in a dramatic increase in the reaction rate. A reaction mechanism involving olefin binding to the excited ruthenium porphyrin is suggested by laser photolysis experiments. This catalyst represents the first stable, effective metalloporphyrin catalyst for olefin oxidation with dioxygen and light.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Bercaw, John E. (advisor)
  • Gray, Harry B. (advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:8 May 1995
Record Number:CaltechETD:etd-09112007-142146
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-09112007-142146
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:3473
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:25 Sep 2007
Last Modified:26 Dec 2012 03:00

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