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

The solvento species obtained by the treatment of cis-RuCl 2 (N,N-L) 2 [L = di-2-pyridyl sulfide (dps), di-2-pyrimidyl sulfide (dprs)] with AgPF 6 , reacted with dithioethers L 0 [L 0 = 2,6-bis(2-pyridylthiomethyl)pyridine (pytmp), 2,6-bis (2-pyrimidylthiomethyl)pyridine (prtmp) and 2,6-bis{2-(4-methyl) pyrimidylthiomethyl} pyridine (mprtmp)] to afford the compounds [Ru(N,N-L) 2 (N,S-L 0 )][PF 6 ] 2 . The 1 H NMR spectra indicate that L 0 is chelated through S and N atoms with the formation of a four-membered ring. As a consequence, the ruthenium and sulfur atoms are stereogenic centers with D and K and (R) and (S) configurations, respectively. NMR spectra, at low temperatures, show that two invertomers, of similar abundance, as enantiomeric couples DS, KR and DR, KS are present. In the methylene region, four AB systems are observed that in both the species contain two non-equivalent methylene groups. Variable-temperature NMR spectra and EXSY experiments show that the sulfur inversion produces an exchange between the invertomers. The one-dimensional band-shape analysis of the exchanging methylene signals showed that the energy barriers for the process are in the 43-52 kJ mol -1 range. The possible mechanisms of the sulfur inversion are discussed.

The structure of 2,6-bis(2-pyridyltsulfanylmethyl)pyridine (pytmp), (I), C(17)H(15)N(3)S(2), presents a twisted conformation, with the three planar moieties almost perpendicular to each other. The structures of two related derivatives, namely 2,6-bis(6-methyl-2-pyridylsulfanylmethyl)pyridine (mpytmp), (II), C(19)H(19)N(3)S(2), and 2,6-bis(4-methyl-2-pyrimidylsulfanylmethyl)pyridine (mprtmp) n-pentane hemisolvate, (III), C(17)H(17)N(5)S(2).0.5C(5)H(12), present extended planar fragments with just one quasi-perpendicular arylsulfanylmethyl side arm, such that the molecules are folded in an L-shaped conformation. All three conformations appear different from those adopted by similar compounds, demonstrating the great flexibility of such species, although such differences in conformational behaviour might drive specific coordination modes.