Unsymmetrical (1-λ3)-1,2,4,6-thiatriazinyls with aryl and trifluoromethyl substituents: synthesis, crystal structures, EPR spectroscopy and voltammetry

Thumbnail Image
Boeré, René T.
Roemmele, Tracey L.
Yu, Xin
Journal Title
Journal ISSN
Volume Title
ACS Publications
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.
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.
Free radical , Thiatriazinyl , Electron paramagnetic resonance , Cyclic voltammetry , Ionization potential , Electrochemistry , DFT calculations
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