Restricted Phenyl Rotation in Pyridyl Thioether Ligands N,S‐Chelated to Congested Diiminoruthenium Cores

Abstract

The thioethers 2-pyridylmethyl p-tolyl sulfide (a) and p-chlorophenyl 2-pyridylmethyl sulfide (b) react with the precursors cis-[RuCl 2 (N,N-diimine) 2 ] [diimine = di-2-pyridyl sulfide (dps), 1; 2,2Ј-bis(4-methylpyridyl) sulfide (4mdps), 2; 2,2Ј-bis(5-methylpyridyl) sulfide (5mdps), 3; di-2-pyrimidyl sulfide (dprs), 4; and 2,2Ј-bis(5-ethylpyrimidyl) sulfide (5edprs), 5] in the presence of NH 4 PF 6 to give the complexes [Ru(N,Ndiimine) respectively. As a consequence of the N,S chelation all the complexes contain a five-membered RuSCCN(Ru−N) ring, the sulfur and ruthenium atoms of which are stereogenic centres, with (R) and (S) and ∆ and Λ configurations, respectively. Furthermore, the coordinated thioethers contain anisochronous methylene protons and phenyl protons which are sensor nuclei for pyramidal sulfur inversion and rotation of the pendant phenyl ring, respectively. In the low-temperature 1 H NMR spectra of the complexes a single AB system for the methylene protons, in agreement with a fast sulfur inversion, is observed. Well-separated signals of the two ortho-as well as the meta-phenyl protons, indicating restricted phenyl rotation, are also observed. At higher temperatures

Hemilabile Thioether Ligands Based on Pyrimidine and/or Pyridine Derivatives that Interconvert between N,S‐ and N‐Coordination in Congested Ruthenium(II) Complexes

“…Thus, a fast sulfur inversion occurs, even at low temperatures, which is in accordance with the presence of a flexible five-membered chelate ring. [37,38] On the other hand, the splitting patterns of the methylene protons at higher temperatures (single AB system) rule out the possibility of racemization (Δ h Λ), which should average the environments of the methylene protons.…”

“…[37,38] In fact, the methylene protons of 6a give only one AB system. On the contrary, if slow inversion occurs at low temperatures, the presence of two diasteroisomers ΔR (ΛS) and ΔS (ΛR) should produce two AB systems in the methylene region of the spectrum.…”

“…[35] In such species some dynamic processes occur, as shown by the temperature dependence of the NMR spectra, but only the restricted uncoordinated ring rotation could be studied and the total dynamic stereochemistry remained unclear. [35] We have been able to obtain activation-energy data for the pyramidal inversion at the coordinated sulfur atom [36] as well as for the restricted rotation of the pendant ring [37] when the ruthenium(ii) center is N,S-chelated by thioether ligands based on pyridine or pyrimidine, and benzyl or phenyl derivatives.…”

“…Since the potentially polydentate ligands L [L = 2-methylpyridyl pyridyl sulfide (L 1 ), 2-methylpyridyl pyrimidyl sulfide (L 2 ) and 2-methylpyridyl 2-(4-methylpyrimidyl) sulfide (L 3 )] may bind to the ruthenium center through nitrogen atoms [27,28,32,[35][36][37] or nitrogen and sulfur atoms, [35][36][37] an NMR spectroscopic study has been carried out to identify the different coordination species obtained when L reacts with Ru(bipy) 2 Cl 2 , Ru(dprs) 2 Cl 2 , and Ru(5edprs) 2 Cl 2 and to examine any dynamic process which might lead to their interconversion.…”

Crystal structure of di(pyrazin-2-yl)sulfane, C8H6N4S

“…Chalcogenobispyridines and derivates display a wide range of biological and industrial applications, as well as of building blocks for supramolecular assembly [2][3][4][5][6]. However, nitrogen rich diheterocyclic sulfides have been rarely reported [7].…”