Configurationally stable tris(tetrathioaryl)methyl molecular propellers

Tris(tetrathioaryl)methanols and tris(tetrathioaryl)methanes are direct precursors and metabolites, respectively, of tris(tetrathioaryl)methyl radicals, which are very attractive paramagnetic spin probes for many magnetic resonance applications. Due to steric hindrance, these propeller-shaped molecules display slow interconversion between their two enantiomeric conformations (right-handed and left-handed propeller conformations). Syntheses and HPLC resolutions carried out on a chiral stationary phase have been achieved. The influence of the hybridization of the central carbon atom as well as the para substitutient on the conformational stability were experimentally and theoretically studied. Depending on their particular structure, the free activation energy for the isomerization process determined by kinetics of racemization varies from 24.4 to 26.4 kcal mol -1 and corresponds to racemization half-lives of 12 and 343 h, respectively. Computational and NOESY/exchange spectroscopy (EXSY) studies are consistent with a two-ring flip mechanism for the isomerization process of tris(tetrathioaryl)methanols, radicals and tris(tetrathioaryl) methanes. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.