SYNTHESIS, PROPERTIES AND CRYSTAL-STRUCTURES OF DIASTEREOMERIC ARENERUTHENIUM(II) CHIRAL SCHIFF-BASE COMPLEXES

Diastereomers (S(Ru),S(C))-1a and (R(Ru),S(C))-1b, in a ratio of 85:15 and formulated as {Ru(eta-MeC6H4Pri-p)Cl(L*)], have been prepared by treating [{Ru(eta-MeC6H4Pri-p)Cl2}2] with the sodium salt of (S)-alpha-methylbenzylsalicylaldimine (HL*) in tetrahydrofuran at - 70-degrees-C. The reaction of 1 (1a + 1b) with AgClO4 in acetone followed by an addition of PPh3 or 4-methylpyridine (4Me-py) leads to the formation of adducts [Ru(eta-MeC6H4Pri-p)(PPh3)(L*)]ClO4 2 [(S(Ru),S(C)) 2a, (R(Ru),S(C)) 2b] and [Ru(eta-MeC6H4Pri-p)(4Me-py)(L*)]ClO4 3 [(S(Ru),S(C)) 3a, (R(Ru),S(C)) 3b] in the diastereomeric ratios (S(Ru),S(C)):(R(Ru),S(C)) of 2:98 and 76:24, respectively. Complex 1 crystallises with equal numbers of 1a and 1b molecules in an asymmetric unit of monoclinic space group P2(1) with a = 10.854(1), b = 17.090(1), c = 12.808(4) angstrom, beta = 110.51(1)-degrees, and Z = 4. The structure was refined to R = 0.0552 and R' = 0.0530 with 2893 reflections having I greater-than-or-equal-to 1.5-sigma(I). The absolute configurations of the chiral centres in the optically pure single crystal of the PPh3 adduct have been obtained from an X-ray study. Crystals of formulation [Ru(eta-MeC6H4Pri-p)-(PPh3)(L*)]2[ClO4][PF6].1.5 CHCl3, obtained in presence of both ClO4 and PF6 anions, belong to the non-centric triclinic space group P1 with a = 10.852(2), b = 14.028(l), c = 15.950(2) angstrom, alpha = 91.51(1), beta = 105.97(1), gamma = 106.11(1)-degrees, and Z = 2. The final residuals were R = 0.0713, R' = 0.0752 with 7283 reflections having I greater-than-or-equal-to 2.5-sigma(I). The crystal structures of 1a,1b, and the PPh3 adduct (2b,2b') consist of a ruthenium(II) centre bonded to a eta-p-cymene, a bidentate chelating Schiff base, and a unidentate ligand (Cl or PPh3). The chirooptical properties of the complexes have been studied using H-1 NMR and CD spectral data. The presence of a low-energy barrier for the intermediate involved in these reactions, showing both retention as well as inversion of the metal configuration, is discussed.