The electrophilic substitution reaction of the dithionitronium cation [SNS](+) with benzene

The compound [SNS](+) ([SNS][AsF6]) reacts with benzene in liquid sulfur di oxide to give orange-, blue-, and then purple-colored solutions. The assign ment of the orange color to a molecule-ion charge-transfer complex [C6H6. S NS](+) is supported by the linear dependence of the ionization potential of the arenes (C6H6, C6H5Me, C6H5But, C6HMe5) and the energy of the charge-tr ansfer absorption of freshly prepared arene-[SNS][AsF6]mixtures in liquid S O2 solution. Variable-temperature multinuclear NMR studies of the reactions of [SNS][AsF6] and [SNS][Sb2F11] with benzene are consistent with the blue color being due to a sulfur protonated substitution product [C6H5(S2N)H](), providing the first example of a CII. electrophilic substitution reactio n of SNS+. The geometries calculated at the RHF/6-31G* level for [C6H5(SNS) H](+), the isomeric [C6H5NSSH](+), and [C6H5N(S)SH](+), together with NMR d ata, support [C6H5(SNS)H]+ (i.e., suggest S, not N, is attached to the ring ) as the structure of the cation. The electrophilic aromatic substitution r eaction of [SNS](+) and benzene is also supported by NMR studies of [SNS][A sF6] and other arenes (e.g., C6HMe5) in SO2 solution. The UV-visible spectr um of [SNS](+) ([SNS][AsF6]) in liquid SO2 is reported, and the absorption (lambda = 406 nm, epsilon = 80) responsible for the yellow color is assigne d to the [SNS]+ HOMO-LUMO transition. Evidence is also presented for the fo rmation of a molecule-ion charge-transfer complex between 5-methyl-1,3,2,4- dithiadiazolium and hexamethylbenzene in liquid SO2, the first dithiadiazol ium charge-transfer complex.