Karl B. Ulmschneider

Paramagnetische organothallium(III)-verbindungen in lösung : II. Esr-untersuchungen paramagnetischer diphenylthallium(III)-komplexemit o-aminophenolen und o-phenylendiaminen

Abstract Diphenylthalliumhydroxide reacts in organic solvents with o-aminophenols and o-phenylenediamines to form paramagnetic species, the ESR spectra of which have been investigated. The reaction has been run using 32 ligands in numerous solvents, therefore the general application of the reaction is proved. The ESR spectra of the solutions show typical hydrogen nitrogen hyperfine structures indicating a NH-analogue semiquinone structure for the ligands. Furthermore a very large splitting due to magnetic coupling of the free electron with 203Tl- and 205Tl-nuclei is observed. In contrast to the paramagnetic diphenylthallium—semiquinone complexes [1a], the different coupling of 203Tl- and 205Tl-nuclei could be resolved in several cases. The thallium splitting observed increases from the semiquinone complexes (~10 G) to the aminophenol radicals (~40 G) and reaches a maximum value for the o-phenylenediamine derivatives (~90 G). The corresponding g-values decrease strongly in this direction. Thus a clear distinction of these classes of ligands becomes possible. The experimental thallium coupling constants and the g-factors depend largely on the substituent of the ligand, the solvent and the temperature. These effects are interpreted in terms of solvation phenomena. Based on the sum of the observed effects we assume that in all cases the radicals investigated are ion pairs in which the diphenylthallium cation interacts with a new type of ligand, namely NH-analogue semiquinones.

Paramagnetische zwischenprodukte bei der synthese von mono- BZW. Diarylthallium(III)-komplexen. Isotrope thallium-hyperfeinstruktur (Tl-HFS)

Abstract Monoaryl- and diaryl-thallium(III) compounds react with 2-amino-4,6-di-t-butylphenol in polar solvents to yield diamagnetic stable monoaryl- and diaryl-thallium(III) complexes. The structures of these new compounds are investigated by several spectroscopic methods. ESR measurements show these reactions of monoorganothallium(III) compounds to proceed via several thallium-containing paramagnetic intermediates, which are formed successively by temperature and solvation dependent equilibria. The observed thallium coupling constants are very large and depend strongly on temperature and solvent.

ESR- und ENDOR-Untersuchungen von p-Benzosemichinon-Diarylthallium-Ionenpaaren / ESR- and ENDO R-Investigations of p-Benzosemiquinone-Diarylthallium Ion Pairs

Diarylthallium hydroxides react very smoothly in organic solvents with hydroquinones to stable paramagnetic complexes. This reaction has been investigated with two ligands and several organometallic compounds in 8 different solvents. In basic solutions clearly two paramagnetic species can be detected by ESR spectroscopy. One component exhibits a large doublet splitting assigned to the thallium counterion and the second radical does not show any metal coupling. The relative concentrations of both radicals depend strongly on the solvent and the temperature. Therefore, a slow equilibrium betw een a contact ion pair and a solvent separated ion pair is assumed. The thermodynamic parameters are determined to ⊿H = 0.8 kcal/mol, ⊿G293 = -0.1 kcal/mol, ⊿S = 3.04 cl/mol. The proton and thallium coupling constants as well as the g-value of the contact ion pair show a rem arkable temperature dependence. The signs of proton splitting constants are determined by ENDOR-TRIPLE investigations. The change of the electronic structure of the radical anion by formation of a contact ion pair is discussed. For interpretation of these results we assumed a fast equilibrium between different conformations of the contact ion pair according to behaviour of comparable aroxyl radicals. Therefore, the systems investigated allow a simultaneous observation of solvent separated and different contact ion pairs.

Ionenpaare von o-Semichinonen mit Diorganothallium(III)- Kationen / Ion Pairs of Semiquinones with Diorgano Thallium (III) Cations

Diorgano thallium hydroxide reacts very smoothly in organic solvents with catechols to stable paramagnetic ion pairs. This reaction has been investigated with two semiquinone anions and 13 different diorgano thallium cations. The data obtained indicate a strong dependence of the thallium coupling constant on the nature of the metal substituents. The effects observed are discussed in terms of electronic and steric interactions. All ion pairs indicate remarkable temperature dependence of the thallium splitting and the g-factor. These results are compared with the results obtained in alkali metal ion pairs using a model described in the literature