Slow inversion of coordinated thioether groups in SNS-type ruthenium pincer complexes

Abstract

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.