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Catalytic dioxygen reduction mediated by a tetranuclear cobalt complex supported on a stannoxane core
Citation key Chandra2020
Author Chandra, Anirban and Mebs, Stefan and Kundu, Subrata and Kuhlmann, Uwe and Hildebrandt, Peter and Dau, Holger and Ray, Kallol
Pages 6065-6073
Year 2020
DOI 10.1039/D0DT00475H
Journal Dalton Trans.
Volume 49
Publisher The Royal Society of Chemistry
Abstract The synthesis, spectroscopic characterization (infrared, electron paramagnetic resonance and X-ray absorption spectroscopies) and density functional theoretical calculations of a tetranuclear cobalt complex Co4L1 involving a nonheme ligand system, L1, supported on a stannoxane core are reported. Co4L1, similar to the previously reported hexanuclear cobalt complex Co6L2, shows a unique ability to catalyze dioxygen (O2) reduction, where product selectivity can be changed from a preferential 4e−/4H+ dioxygen-reduction (to water) to a 2e−/2H+ process (to hydrogen peroxide) only by increasing the temperature from −50 to 30 °C. Detailed mechanistic insights were obtained on the basis of kinetic studies on the overall catalytic reaction as well as by low-temperature spectroscopic (UV-Vis, resonance Raman and X-ray absorption spectroscopies) trapping of the end-on μ-1,2-peroxodicobalt(iii) intermediate 1. The Co4L1- and Co6L2-mediated O2-reduction reactions exhibit different reaction kinetics, and yield different ratios of the 2e−/2H+ and 4e−/4H+ products at −50 °C, which can be attributed to the different stabilities of the μ-1,2-peroxodicobalt(iii) intermediates formed upon dioxygen activation in the two cases. The deep mechanistic insights into the transition-metal mediated dioxygen reduction process that are obtained from the present study should serve as useful and broadly applicable principles for future design of more efficient catalysts in fuel cells.
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