Formation of σ- and π-Type Dimer Radical Cations by the Photochemical One-Electron Oxidation of Aromatic Sulfides

Abstract

The formation of dimer radical cations from aromatic sulfides has been studied by photochemical one-electron oxidation in acetonitrile. When dicyanonaphthalene and thioanisole in acetonitrile were irradiated with nanosecond laser flash (308 nm), two types of dimer radical cations were detected at 470 and 800 nm at the expense of the monomer radical cation (520 nm). The intramolecular formation of similar radical ion complexes was observed for the cases of 1,n-bis(phenylthio)alkanes with n ) 3 and 4, while bissulfides with n ) 2, 6, and 8 showed radical cation spectra quite different from the above cases of n ) 3 and 4. These facts indicate that dimer radical cations absorbing at around 460-500 nm are assigned as the σ-type complex of the sulfur-sulfur three-electron bond and that radical cations absorbing at around 800 nm are of the π-type complex associated with two phenylthio groups. For the case of p-methylthioanisole the formation of π-type dimer was shown to be reduced owing to the steric hindrance of two methyl groups. No formation of dimer radical cations was observed for cases of p-methoxythioanisole and diphenyl sulfide where the corresponding monomer radical cations are stabilized by the delocalization of positive charge on the sulfur atom. The density functional BLYP/6-31G* calculations on thioanisole predicted the existence of σand π-type dimer radical cations, in accordance with the experimental observation of approximately equal stability.

Electron transfer reactions of organic sulfoxides with photochemically generated ruthenium(III)–polypyridyl complexes

“…The spectra shown in Figure 4 show two strong absorptions at 300-350 and 500-550 nm. Comparing these data with the spectral data obtained for the sulfide radical cation by Baciocchi et al, 25, 26 Yokoi et al, 27 and others 28 and from our recent study 20 we feel it reasonable that the peaks at 300-350 and 500-550 nm may be attributed to the sulfoxide radical cation. The absorption spectrum and the lifetime of this transient are not affected by the presence of oxygen.…”

What can we learn from two‐center three‐electron bonding with the topological analysis of ELF?

“…It is worth noting that competition can occur between two-center three-electron bonds and hydrogen bonding, as suggested by theoretical studies [39], further supported, for example, by ion/molecule association reactions in mixtures of methyl halide and dimethyl sulfide studied by mass spectrometry [14]. The competitive formation of σ (i.e., 2c-3e)-type or π-type bonding has also been evidenced in the photochemical oneelectron oxidation of aromatic sulfides [40] and has been shown to be sensitive to the steric and electronic influence of substituents. Finally, although it is formally out of the scope of heteroatom chemistry, 3e bonds involving metal atoms exist: the ferryl group Fe O in di-iron enzymes core models [41], the Al І N or the Al І C bonds that are formed spontaneously after insertion of the Al atom into alkyl ethers [42] or into the NH 3 molecule [43], and the Rh І Rh bond [44] or Rh І Ir bond [45] in bridged complexes, which have been evidenced by X-ray structural studies.…”

One‐Electron Oxidation Pathways during β‐Cyclodextrin‐Modified TiO2 Photocatalytic Reactions

“…Similar spectral changes were observed in the absence of CM‐β‐CD. The newly observed absorption bands at around 520 and 800 nm are assigned to the σ‐type complex of the sulfur–sulfur three‐electron bond and the π‐type complex associated with two 4‐(methylthio)phenyl groups, respectively 18. 52 The spectrum of (MTPM) 2 .+ , which is obtained by the pulse radiolysis technique, is also indicated for comparison (solid line).…”