Slow Inversion of Coordinated Thioether Groups in SNS-Type Ruthenium Pincer Complexes

The thioether-group-containing SNS-type pincer complex [({EtSCH₂CH₂}₂NH)RuCl(H)(PPh₃)] ( 2 ) exists in three different diastereomers ( 2 a – c ). The molecular structures obtained from single crystal X-Ray diffraction studies of all three isomers reveal a difference in the relative orientation of the respective EtS-groups, while other commonly observed diastereomers as the result of cis-/trans- or fac-/mer-isomerism are not observed. Chemical exchange between the three diastereomers 2 a – c was discovered by phase-sensitive ¹H and ³¹P NOESY NMR spectroscopy, and further quantified by line shape analysis of ¹H NMR spectra. The experimentally derived averaged Gibbs energies of activation for the interconversion of the isomers (65–70 kJ/mol) are in good agreement with the results obtained from DFT calculations, which suggest an inversion of the ligating sulfur atoms, although a dissociative pathway for the configurational inversion can be competitive.