One-electron reduction of di-imidosulphur compounds, S(NR)2, and some complexes of Group 6A metal carbonyl derivatives containing S(NR)2 ligands: studies of the radical products by electron spin resonance spectroscopy

Abstract

Reduction of the di-imidosulphur compounds, S(NR)2(R = But, Ph, 4-MeC6H4, or 4-O2NC6H4), in 1,2-dimethoxyethane solution with a potassium mirror in vacuo gives fairly stable solutions of the corresponding anion radicals [S(NR)2]– which have been studied by e.s.r. spectroscopy. The frozen-solution e.s.r spectrum of K[S(NBut)2] has also been recorded. Isotropic coupling constants A(14N), A(1H) and, for R = But, A(33S) have been deduced and analysed in terms of the electronic structures of the radicals using empirical electron-density relationships. Some CNDO/2 and INDO calculations have been made and the experimental and calculated electron-spin densities compared. Variable-temperature e.s.r. measurements have given no indication of the presence of distinct geometric isomers of the anions in solution. The model calculations suggest that the E/E conformation is most stable and that interconversion to give the E/Z or Z/Z forms is unlikely. The experimental evidence in all cases indicates the two nitrogen atoms to the magnetically equivalent. Alkali-metal isotropic coupling constants A(MI) for the species MI[S(NBut)2](MI=7Li, 23Na, or 39K) have been estimated and indicate that the metal–anion interaction increases in the order K < Na < Li.Potassium-metal reduction of [M(Co)4{S(NBut)2}](M = Cr, Mo, or W) produces the corresponding anions with well defined isotropic e.s.r spectra. Values for A(14N) and A(M)(M =95/97Mo or 183W) have been deduced and the spectra analysed. The results suggest that the unpaired electron is located mainly in the S(NBut)2 ligand. CNDO/2 calculations for the chromium anion are consistent with this observation. Attempts to produce [M(CO)4{S(NPh)2}]– have been unsuccessful except for M = Cr, when an unstable species is formed. A tentative analysis of the e.s.r spectrum of this radical anion is presented.