Unsymmetrical (1-λ3)-1,2,4,6-thiatriazinyls with aryl and trifluoromethyl substituents: synthesis, crystal structures, EPR spectroscopy and voltammetry
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Date
2011
Authors
Boeré, René T.
Roemmele, Tracey L.
Yu, Xin
Journal Title
Journal ISSN
Volume Title
Publisher
ACS Publications
Abstract
A general synthetic route to 3-trifluoromethyl-5-aryl-1λ3-1,2,4,6-thiatriazinyl radicals
was developed. X-ray structures were obtained for all five neutral radicals and show that they
exist in the solid state as co-facial dimers linked by S···S contacts. X-ray structures were also
obtained for two of the precursor chlorothiatriazines along with several aryl N-imidoylamidines,
p-methoxybenzamidine and N-chlorosulfonyl-N,N'-benzamidine. Cyclic voltammetric studies
were performed on the [R2C2N3S]• radicals in CH3CN and CH2Cl2 with [nBu4N][PF6] as the
supporting electrolyte under vacuum in an all-glass electrochemical cell. The results provide
quasi-reversible formal potentials for the [R2C2N3S]−/0 process in the range of −0.61 to −0.47 V,
irreversible peak potentials for the [R2C2N3S]0/+ process from 0.59 to 0.91 V at lower
concentrations, and the appearance of a second, reversible oxidation process from 0.69 to 0.94 V
at higher concentrations (versus the Fc0/+ couple; Fc = Ferrocene). This behavior was indicative
of monomer-dimer equilibrium in solution as ascertained from digital models of the
voltammograms. There is a small but measurable trend in both the oxidation and reduction
potentials with varying remote aryl substituents. EPR spectra were obtained for all five neutral
radicals in CH2Cl2 solutions, which confirm concentration of the unpaired electron density on the
heterocyclic core. Trends were also seen in the hyperfine splitting constants aN with varying
remote aryl substituents. Calculations were performed for all three oxidation states of the
[R2C2N3S]-/•/+ monomeric rings; the resulting theoretical redox energies correlate well with
solution phase voltammetric data.
Description
Sherpa Romeo white journal. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Inorganic Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher.
Keywords
Free radical , Thiatriazinyl , Electron paramagnetic resonance , Cyclic voltammetry , Ionization potential , Electrochemistry , DFT calculations
Citation
Boeré, R. T., Roemmele, T. L., & Yu, X. (2011). Unsymmetrical (1λ3)-1,2,4,6-thiatriazinyls with aryl and trifluoromethyl substituents: Synthesis, crystal structures, EPR spectroscopy and voltammetry. Inorganic Chemistry, 50(11), 5123-5135. doi: 10.1021/ic2003996