Inorganic Chemistry
DOI: 10.1021/ic4016405
The new complexes [Ir(Cp*)(phpy)3,5-bis(trifluoromethyl)benzonitrile]+ (1-NCAr+) and [Ir(Cp*)(phpy)(styrene)]+ (1-Sty+, Cp* = η5-pentamethylcyclopentadienyl, phpy = 2-phenylene-κC1′-pyridine-κN) were prepared as analogues of reported iridium water oxidation catalysts, to study their reactions with oxygen atom transfer (OAT) reagents at low temperatures. In no case was the desired product, an Ir(V)oxo complex, observed by spectroscopy. Instead, ligand oxidation was implicated. Oxidation of 1-NCAr+ with the OAT reagent dimethyldioxirane (DMDO) yielded dioxygen when analyzed by GC, but formation of a heterogeneous or paramagnetic species was simultaneously observed. This amplifies uncertainty over the actual identity of iridium catalysts in the harsh oxidizing conditions required for water oxidation. Catalyst stability was then assessed for a reported styrene epoxidation mediated by [Ir(Cp*)(phpy)(OH2)]+ (1-OH2+). It was found that the OAT reagent iodosobenzene (PhIO) extensively oxidized the organic ligands of 1-OH2+. Acetic acid was detected as a decomposition product. In addition, both the molecular structure and the aqueous electrochemistry of 1-OH2+ are described for the first time. Oxidative scans revealed rapid decomposition of the complex. All of the above experiments indicate that degradation of the organic ligands in catalysts built with the Ir(Cp*)(phpy) framework are facile under oxidizing conditions. In separate experiments designed to promote ligand substitution, an unexpected silver-bridged, dinuclear Ir(III) species with terminal hydrides, [{Ir(Cp*)(phpy)H}2Ag]+ (2), was discovered. The source of Ag+ for complex 2 was identified as AgCl.
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Electrochemical evidence that pyranopterin redox chemistry controls the catalysis of YedY, a mononuclear Mo enzyme
Hope Adamson a, Alexandr N. Simonov b, Michelina Kierzek c, Richard A. Rothery c, Joel H. Weiner c, Alan M. Bond b, and Alison Parkin a,1 a Department of Chemistry, University of York, Heslington, York YO10 5DD, United Kingdom; b School of Chemistry, Monash University, Clayton, VIC 3800, Australia; and c Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada Edited by Harry B. Gray, California Institute of Technology, Pasadena, CA, and approved October 13, 2015 (received for review August 25, 2015) http://www.pnas.org/content/112/47/14506.short A long-standing contradiction in the field of mononuclear Mo enzyme research is that small-molecule chemistry on active-site mimic compounds predicts ligand participation in the electron transfer reactions, but biochemical measurements only suggest metal-centered catalytic electron transfer.With the simultaneous measurement of substrate turnover and reversible electron transfer that is provided by Fourier-...
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