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Enhanced catalytic four-electron dioxygen (O2) and two-electron hydrogen peroxide (H2O2) reduction with a copper(II) complex possessing a pendant ligand pivalamido group

Title
Enhanced catalytic four-electron dioxygen (O2) and two-electron hydrogen peroxide (H2O2) reduction with a copper(II) complex possessing a pendant ligand pivalamido group
Authors
Kakuda S.Peterson R.L.Ohkubo K.Karlin K.D.Fukuzumi S.
Ewha Authors
Shunichi FukuzumiKenneth D. Karlin
SCOPUS Author ID
Shunichi Fukuzumiscopus
Issue Date
2013
Journal Title
Journal of the American Chemical Society
ISSN
0002-7863JCR Link
Citation
vol. 135, no. 17, pp. 6513 - 6522
Indexed
SCI; SCIE; SCOPUS WOS scopus
Abstract
A copper complex, [(PV-tmpa)CuII](ClO4)2 (1) [PV-tmpa = bis(pyrid-2-ylmethyl){[6-(pivalamido)pyrid-2-yl]methyl}amine], acts as a more efficient catalyst for the four-electron reduction of O 2 by decamethylferrocene (Fc*) in the presence of trifluoroacetic acid (CF3COOH) in acetone as compared with the corresponding copper complex without a pivalamido group, [(tmpa)Cu II](ClO4)2 (2) (tmpa = tris(2-pyridylmethyl) amine). The rate constant (kobs) of formation of decamethylferrocenium ion (Fc*+) in the catalytic four-electron reduction of O2 by Fc* in the presence of a large excess CF3COOH and O2 obeyed first-order kinetics. The k obs value was proportional to the concentration of catalyst 1 or 2, whereas the kobs value remained constant irrespective of the concentration of CF3COOH or O2. This indicates that electron transfer from Fc* to 1 or 2 is the rate-determining step in the catalytic cycle of the four-electron reduction of O2 by Fc* in the presence of CF3COOH. The second-order catalytic rate constant (kcat) for 1 is 4 times larger than the corresponding value determined for 2. With the pivalamido group in 1 compared to 2, the Cu II/CuI potentials are -0.23 and -0.05 V vs SCE, respectively. However, during catalytic turnover, the CF3COO - anion present readily binds to 2 shifting the resulting complex's redox potential to -0.35 V. The pivalamido group in 1 is found to inhibit anion binding. The overall effect is to make 1 easier to reduce (relative to 2) during catalysis, accounting for the relative kcat values observed. 1 is also an excellent catalyst for the two-electron two-proton reduction of H 2O2 to water and is also more efficient than is 2. For both complexes, reaction rates are greater than for the overall four-electron O2-reduction to water, an important asset in the design of catalysts for the latter. © 2013 American Chemical Society.
DOI
10.1021/ja3125977
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자연과학대학 > 화학·나노과학전공 > Journal papers
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