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UBC Theses and Dissertations
Aerobic alcohol and amine oxidations catalyzed by Trans-dioxo(porphyrinato)ruthenium(VI) complexes Dodson, Heather K.
Abstract
The stoichiometric and aerobic catalytic oxidations of amines and benzhydrols by Trans-Ru(porp)(O)2 complexes (porp = TMP, OCP, OCP-Cl8, see Figure) in benzene under mild conditions are described. [Figure with caption: Trans-dioxo(porphyrinato)ruthenium(VI) complexes. TMP, OCP and OCP-Cl8 are the dianions of meso-tetramesitylporphyrin, meso-tetra(2,6- dichlorophenyl)porphyrin and meso-tetra(2,6-dichlorophenyl)-β- octachloroporphyrin, respectively.] Kinetic data, determined by UV-VIS and ¹H-NMR spectroscopic analyses, for the stoichiometric oxidation of p-substituted benzhydrols indicate that the oxidation mechanism proceeds through the formation of a {Ru-alcohol} adduct (governed by an equilibrium constant K) which subsequently decomposes in a slower step (with rate constant k1) leading to ketone formation. Isotope effects of KH/KD ~ 0.6 and k1H/k1D ~ 15 for α-deuteration of the alcohol indicate that the adduct is formed through hydrogen-bonding interactions probably between the Ru=0 and the α-CH with cleavage of this C-H bond occurring in the rate-determining step. Electron-donating substituents favour alcohol oxidation, as illustrated by a limited linear Hammett relationship of k1 with 2σp for di-p-substituted benzhydrols. The {Ru-alcohol} adduct formation is essentially isenthalpic, while the k1 activation parameters are ΔH1‡ = 58 ± 10 kJ/mol and ΔS1‡ = -120 ± 30 J/(mol K). Trans-RuIV(TMP)(alkoxo)2 complexes have been isolated from the stoichiometric oxidation reactions and characterized by ¹H-NMR, UV-VIS and IR spectroscopies. Aerobic oxidation of benzhydrols is catalyzed by trans-Ru(porp)(O)2 at 50°C in benzene; ketones are the only organic products of the reaction. Water is essential for higher catalytic activity and turnovers of up to 24 (98% conversion) are seen at 50°C after 19 h. Under these conditions, the catalyst activities follow the trend: trans-Ru(OCP-C18)(O)2 > trans-Ru(TMP)(O)2 > trans-Ru(OCP)(O)2. Limited linear Hammett relationships, based on % conversion after 45 h at 50°C, indicate that catalytic oxidation is also favoured by the p-substitution of electron-donating substituents on the benzhydrols. Catalytic activity is limited by the rate of Ru(VI)-dioxo regeneration. Stoichiometric amine oxidation by trans-Ru(OCP)(O)2 and trans-Ru(TMP)(O)2 studied by UV-VIS spectroscopy gives irreproducible results. The source of the irreproducibility is not determined, though it is not from trace oxygen, the amine, the catalyst, trace acid or water in the system. The reactions, however, are light-sensitive. Aerobic oxidation of amines is catalyzed by trans-Ru(porp)(O)2 at 50°C under 1 atm of air; however, turnovers greater than 3 are only seen after 90 h in biphasic benzene/water systems, a result that contradicts a previous report. [Certain scientific formulae used in this abstract could not be reproduced.]
Item Metadata
Title |
Aerobic alcohol and amine oxidations catalyzed by Trans-dioxo(porphyrinato)ruthenium(VI) complexes
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1998
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Description |
The stoichiometric and aerobic catalytic oxidations of amines and benzhydrols by
Trans-Ru(porp)(O)2 complexes (porp = TMP, OCP, OCP-Cl8, see Figure) in benzene
under mild conditions are described. [Figure with caption: Trans-dioxo(porphyrinato)ruthenium(VI) complexes. TMP, OCP and
OCP-Cl8 are the dianions of meso-tetramesitylporphyrin, meso-tetra(2,6-
dichlorophenyl)porphyrin and meso-tetra(2,6-dichlorophenyl)-β-
octachloroporphyrin, respectively.] Kinetic data, determined by UV-VIS and ¹H-NMR spectroscopic analyses, for the
stoichiometric oxidation of p-substituted benzhydrols indicate that the oxidation
mechanism proceeds through the formation of a {Ru-alcohol} adduct (governed by an
equilibrium constant K) which subsequently decomposes in a slower step (with rate
constant k1) leading to ketone formation. Isotope effects of KH/KD ~ 0.6 and k1H/k1D ~ 15
for α-deuteration of the alcohol indicate that the adduct is formed through hydrogen-bonding
interactions probably between the Ru=0 and the α-CH with cleavage of this C-H
bond occurring in the rate-determining step. Electron-donating substituents favour
alcohol oxidation, as illustrated by a limited linear Hammett relationship of k1 with 2σp
for di-p-substituted benzhydrols. The {Ru-alcohol} adduct formation is essentially
isenthalpic, while the k1 activation parameters are ΔH1‡ = 58 ± 10 kJ/mol and ΔS1‡ = -120
± 30 J/(mol K). Trans-RuIV(TMP)(alkoxo)2 complexes have been isolated from the
stoichiometric oxidation reactions and characterized by ¹H-NMR, UV-VIS and IR
spectroscopies.
Aerobic oxidation of benzhydrols is catalyzed by trans-Ru(porp)(O)2 at 50°C in
benzene; ketones are the only organic products of the reaction. Water is essential for
higher catalytic activity and turnovers of up to 24 (98% conversion) are seen at 50°C after
19 h. Under these conditions, the catalyst activities follow the trend: trans-Ru(OCP-C18)(O)2 > trans-Ru(TMP)(O)2 > trans-Ru(OCP)(O)2. Limited linear Hammett
relationships, based on % conversion after 45 h at 50°C, indicate that catalytic oxidation
is also favoured by the p-substitution of electron-donating substituents on the
benzhydrols. Catalytic activity is limited by the rate of Ru(VI)-dioxo regeneration.
Stoichiometric amine oxidation by trans-Ru(OCP)(O)2 and trans-Ru(TMP)(O)2
studied by UV-VIS spectroscopy gives irreproducible results. The source of the
irreproducibility is not determined, though it is not from trace oxygen, the amine, the
catalyst, trace acid or water in the system. The reactions, however, are light-sensitive.
Aerobic oxidation of amines is catalyzed by trans-Ru(porp)(O)2 at 50°C under 1 atm of
air; however, turnovers greater than 3 are only seen after 90 h in biphasic benzene/water
systems, a result that contradicts a previous report. [Certain scientific formulae used in this abstract could not be reproduced.]
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Extent |
6642332 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-05-23
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0061592
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1998-11
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.