Homogeneous catalytic reduction of dioxygen using transfer hydrogenation catalysts

Zachariah M Heiden; Thomas B Rauchfuss

doi:10.1021/ja073774p

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Journal article

Homogeneous catalytic reduction of dioxygen using transfer hydrogenation catalysts

Zachariah M Heiden and Thomas B Rauchfuss

Journal of the American Chemical Society, Vol.129(46), pp.14303-14310

11/21/2007

DOI: https://doi.org/10.1021/ja073774p

Handle:

https://hdl.handle.net/2376/104230

PMID: 17958423

Abstract

Amines - chemistry

Magnetic Resonance Spectroscopy

Models, Chemical

Oxidation-Reduction

Ethylenediamines - chemistry

Deuterium - chemistry

Benzoquinones - chemistry

Hydrogen - chemistry

Hydrogenation

Ruthenium - chemistry

Spectrophotometry, Ultraviolet

Toluene - chemistry

Toluene - analogs & derivatives

Thermodynamics

Oxygen - chemistry

Water - chemistry

Organometallic Compounds - chemistry

Catalysis

Kinetics

Iridium - chemistry

Solutions of Cp*IrH(rac-TsDPEN) (TsDPEN = H2NCHPhCHPhN(SO2C6H4CH3)-) (1H(H)) with O2 generate Cp*Ir(TsDPEN-H) (1) and 1 equiv of H2O. Kinetic analysis indicates a third-order rate law (second order in [1H(H)] and first order in [O2]), resulting in an overall rate constant of 0.024 +/- 0.013 M(-2) s(-1). Isotopic labeling revealed that the rate of the reaction of 1H(H) + O2 was strongly affected by deuteration at the hydride position (k(HH2)/k(DH2) = 6.0 +/- 1.3) but insensitive to deuteration of the amine (k(HH2)/k(HD2) = 1.2 +/- 0.2); these values are more disparate than for conventional transfer hydrogenation (Casey, C. P.; Johnson, J. B. J. Org. Chem. 2003, 68, 1998-2001). The temperature dependence of the reaction rate indicated DeltaH = 82.2 kJ/mol, DeltaS = 13.2 J/mol K, and a reaction barrier of 85.0 kJ/mol. A CH2Cl2 solution under 0.30 atm of H2 and 0.13 atm of O2 converted to H2O in the presence of 1 and 10 mol % of H(OEt2)2BAr(F)4 (BAr(F)4- = B(C6H3-3,5-(CF3)2)4-). The formation of water from H2 was verified by 2H NMR for the reaction of D2 + O2. Solutions of 1 slowly catalyze the oxidation of amyl alcohol to pentanal; using 1,4-benzoquinone as a cocatalyst, the conversion was faster. Complex 1 also catalyzes the reaction of O2 with RNH2BH3 (R = H, t-Bu), resulting in the formation of water and H2. The deactivation of the catalyst 1 in its reactions with O2 was traced to degradation of the Cp* ligand to a fulvene derivative. This pathway is not observed in the presence of amine-boranes, which were shown to reduce fulvenes back to Cp*. This work suggests the potential of transfer hydrogenation catalysts in reactions involving O2.

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Title: Homogeneous catalytic reduction of dioxygen using transfer hydrogenation catalysts
Creators: Zachariah M Heiden - School of Chemical Sciences, University of Illinois, Urbana, Illinois 61801, USA
Thomas B Rauchfuss
Publication Details: Journal of the American Chemical Society, Vol.129(46), pp.14303-14310
Academic Unit: Chemistry, Department of
Publisher: United States
Identifiers: 99900546756801842
Language: English
Resource Type: Journal article

Homogeneous catalytic reduction of dioxygen using transfer hydrogenation catalysts

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