Nature-Inspired Homogeneous Catalytic Perchlorate Reduction Using Molybdenum Complexes
Madeleine A. Ehweiner, Fabian Wiedemaier, Bassam Lajin, Jörg A. Schachner, Ferdinand Belaj, Walter Goessler, Nadia C. Mösch‐Zanetti
Abstract
Inspired by the reactivity of (per)chlorate reducing molybdoenzymes and encouraged by the lack of molybdenum-containing functional models thereof, two molybdenum(VI) complexes of the type [MoO2L2] (L = pyrimidine-2-thiolate or 6-methylpyridine-2-thiolate) were found to be active homogeneous catalysts for the reduction of ClO4– to ClO3– in CH2Cl2 using PPh3 as sacrificial oxygen acceptor. The subsequent stepwise reduction of ClO3– to Cl– is facilitated by our catalysts, but it can also proceed with only PPh3 without the aid of a catalyst. We followed the decrease in perchlorate concentration in the catalytic solutions not only indirectly by oxidation of PPh3 to OPPh3 via 1H NMR spectroscopy but also directly by determining the perchlorate concentration at certain time points over 24 h with high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS/MS). These experiments revealed the pyrimidine-2-thiolate system to be more efficient. The reduction of ClO4– to ClO3– with [MoOL2], which is generated after the reaction of [MoO2L2] with PPh3, was computed to be highly exergonic with low kinetic barriers for both catalysts. Thus, the rate-determining step of the overall catalytic reaction is the initial oxygen atom transfer from [MoO2L2] to PPh3.