Preparation and structural elucidation of novel cis ruthenium(II) bis(bipyridine) sulfoxide complexes

Four novel cis-ruthenium bis(bipyridine) sulfoxide complexes with the general formula cis-[Ru(A)(2)(B)(Cl)]X (2, A=2,2'-bipyridine (bpy), B=dimethyl sulfoxide (DMSO); 3, A=4,4'-dimethyl-2,2'-bipyridine (dmbpy), B=DMSO; 4, A=bpy, B=tetramethylene sulfoxide (TMSO); and 5, A=dmbpy, B=TMSO; X=Cl-, I-, PF6- or ClO4-) were synthesized from cis-[Ru(bpy)(2)Cl-2] 1 or trans-[Ru(dmbpy)(2)Cl-2] 6 in the substrate sulfoxide solutions at 60-120 degrees C, i.e. by a thermal process. This cis selectivity is in contrast to previously reported results. However, photoirradiation of 1 in the presence of DMSO selectively produced trans-ruthenium bis(bipyridine) sulfoxide; when 6 was photoirradiated in the presence of DMSO cis-[Ru(dmbpy)(2)(DMSO)Cl]Cl was the sole product. These complexes were fully characterized by elemental analysis, IR, UV/vis, H-1, C-13 and 2-D NMR spectroscopy. The sulfoxide ligands co-ordinate through a Ru-S bond in all cases. The NMR studies of 2 imply that no rotation around the Ru-S bond occurs, in accord with quantum mechanics calculations. Crystallographic structural determinations of 2 . PF6- (from acetone-diethyl ether) and 2 . I- (from water) showed that both complexes share similar octahedral geometries, but different conformations were found for the sulfoxide ligands with Cl-Ru-S-O dihedral angles of 121.6 and 56.3 degrees, respectively, thus demonstrating that a different energetically favored conformation may exist in low or high dielectric environment. The stability of complexes 2-5 allowed separation into their Delta and Lambda enantiomers, and the circular dichroism spectra were obtained. Thermal substitution reactions were also carried out using 2 . Cl- which was converted into cis-[Ru(bpy)(2)Cl-2] 1 or cis-[Ru(bpy)(2)I-2] 7. Several examples in which the resolved complex Delta-2 . PF6- reacts with bipyridine nucleophiles with nearly complete retention of chirality are also given.