The thioethers L [L = 4-methylbenzyl 2-pyridyl sulfide (L1), 4-chlorobenzyl 2-pyridyl sulfide (L2), 3-chlorobenzyl 2-pyridyl sulfide (L3), 1,4-bis(2-pyridylthiomethyl)benzene (L4), 4-methylbenzyl 2-pyrimidinyl sulfide (L5), and 4-chlorobenzyl 2-pyrimidinyl sulfide (L6)], containing a CH2R group bonded to the sulfur atom, were prepared and characterized. Compounds L1, L2, L3, and L4 reacted with cis-Ru(N,N-dprs)2Cl2 or cis-Ru(N,N-dps)2Cl2 (dprs = di-2-pyrimidinyl sulfide, dps = di-2-pyridyl sulfide) leading to the complexes [Ru(N,N-dprs)2(N,S-L)][PF6]2 and [Ru(N,N-dps)2(N,S-L)][PF6]2. Similar products were obtained from [Ru(N,N-dps)2(NO2)(NO)][PF6]2 and L5 or L6. As a consequence of the L ligand N,S-chelation, all the complexes contain the four-membered ring RuSCN(Ru−N). Since the ruthenium and sulfur atoms are stereogenic centres, with Δ and Λ, and R and S configurations, respectively, they led to four isomers, including the enantiomers. NMR investigations show that the sulfur inversion produces an exchange between the diastereoisomers ΔR and ΔS, as well as ΛS and ΛR. The one-dimensional band-shape analysis of the exchanging methylene proton signals showed that the inversion barriers (ΔG‡298 K) for the dprs complexes are in the 54.9−53.8 kJ mol−1 range, with the two invertomers exhibiting similar abundance. Substitution of dprs with dps affects the relative invertomer population leaving the magnitude of ΔG‡298 K (52.0−50.6 kJ mol−1) practically unchanged. Conversely, the substitution of the pyridine thioethers (L1, L2) with pyrimidine thioethers (L5, L6) influences the inversion barriers, and ΔG‡298 K values of 47.5 and 47.0 kJ mol−1 were found for [Ru(N,N-dps)2(N,S-L5)][PF6]2 and [Ru(N,N-dps)2(N,S-L6)][PF6]2, respectively. An intramolecular mechanism without any bond rupture is suggested on the basis of the ΔS‡ values (negative or close to zero) and the NMR spectra, temperature-reversible and concentration-independent. The contemporary presence of the congested Ru(N,N-dps)2 or Ru(N,N-dprs)2 core and sterically demanding N,S-coordinated thioether ligands is invoked to explain the low energy barrier of the process. This hypothesis is also corroborated by the different behaviour observed for the complex [Ru(bipy)2(N,S-L1)][PF6]2.
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