Dynamic Stereochemical Behaviour of Congested Ruthenium(II) Complexes Containing Asymmetric Thioether Ligands Based on Pyridine and Pyrimidine

Abstract

The asymmetric thioethers L [L = 2-pyridylmethyl 2Ј-pyrimidyl sulfide (pps) and 2-(4-methylpyrimidyl) 2Ј-pyridylmethyl sulfide (mps)] reacted with cis-[RuCl 2 (N,N-LЈ) 2 ] [LЈ = di-2-pyridyl sulfide (dps); 2,2Ј-bis(4-methylpyridyl) sulfide (4mdps); 2,2Ј-bis(5-methylpyridyl) sulfide (5mdps)] to give the five-membered-ring chelate complexes [Ru(N,N-LЈ)++ as the major products (92-95 %). Because the sulfur and ruthenium atoms are stereogenic centres, with (R) and (S) and ∆ and Λ configurations, respectively, four isomers, including the enantiomers were obtained. At low temperature and in the methylene region of the 1 H NMR spectra, two AB systems due to the enantiomer couples ∆S ΛR (a) and ∆R ΛS (b) were observed with abundances of 77-89 and 6-18 %, respectively. Furthermore, NMR spectroscopic investigations showed that the hybrid polydentate ligands L change their coordination mode. Thus, although a and b largely predominate, a mixture of species containing L and the Ru(N,N-LЈ) 2 unit in the ratio 1:1 are present. The four-memberedring chelate complexes [Ru(N,N-LЈ) ++ (c), as minor species (abundance 1-8 %), are always observed, whereas the dinuclear species [{Ru(N,N-LЈ) 2 } 2 (µ-L) 2 ] +4 (d, e) are observed when LЈ = dps or 5mdps. In these cases, four

Fluxional rearrangement in congested ruthenium(II) complexes containing pyrimidine- and/or pyridine-based dithioether ligands

“…Recently, the reactions of cis-Ru(N,N-diimmine) 2 Cl 2 [diimmine = di-2-pyridyl sulfide, 2,2 0 -bis(4-methylpyridyl) sulfide, 2,2 0 -bis(5-methylpyridyl) sulfide] with L 1 [L 1 = 2-pyridylmethyl 2 0 -pyrimidyl sulfide (pps) and 2-(4-methylpyrimidyl) 2 0 -pyridylmethyl sulfide (mps)] were reported [11]. The compounds obtained [Ru(N,N-diimmine) 2 L 1 ][PF 6 ] 2 are a mixture of species, in which the invertomers (a and b) containing the five-membered ring N,S-chelate largely predominate, while the species (c) containing the four-membered ring N,S-chelate is present in low abundance (1-8%).…”

“…Our recent NMR studies concerned the solution stereodynamics of ruthenium(II) complexes of a range of hybrid sulfur nitrogen ligands based on pyridine or pyrimidine [7][8][9][10][11]. The ligands in question are asymmetric and/or symmetric and potentially polydentate but act, generally, as bidentate.…”

“…This bonding mode can promote the stereochemical non-rigidity of the complexes. Significant changes in geometry such as the inversion of the metalcoordinated sulfur [8,11] and the restricted rotation of the pendant ring can be observed [9].Furthermore, other dynamic processes such as bond breaking and reforming [10] and, if at least a donor atom remains uncoordinated, the exchange between different coordination modes can be observed [11]. This type of process was previously studied in the terpyridine complexes, in which the exchange occurs between pendant and coordinated pyridyl rings, and then in metal complexes containing polydentate sulfur nitrogen ligands if restricted to the bidentate bonding mode [16][17][18].…”

“…The ligands in question are asymmetric and/or symmetric and potentially polydentate but act, generally, as bidentate. The symmetric ligands L (L = di-2-pyridyl sulfide, di-2-pyrimidyl sulfide and derivatives) are normally N,N-chelate forming six-membered rings [7][8][9][10][11][12][13][14][15]. As a consequence of this coordination, a robust cis-Ru(L) 2 -core was formed in which the two sterically hindering L ligands favor the N,S-coordination of a further ligand with formation of four-or five-membered chelate ring and the presence of a pendant ring [7][8][9][10][11]15].…”

“…The sulfur inversion and the restricted rotation were studied when potentially bidentate ligands were used [7][8][9], whereas exchange between different coordination mode was examined when thioethers, generally asymmetrical, potentially terdentate were used [10,11].…”