Molecular Architecture of Polynuclear Ruthenium Bipyridyl Complexes with Controlled Metal Helicity

The synthesis of di- and trinuclear ruthenium(II) complexes is reported, where each metal center has a tris(bidentate) octahedral coordination sphere with predetermined stereochemistry. New members of the "Chiragen" ligand series, consisting of two linked chiral 4,5-pineno-2,2'-bipyridine groups, have been prepared, with small spacer units between the coordination centers (-(CH(2))(n)() {n = 0, 3} and -CH(2)(bpy)CH(2)-). X-ray structural data were obtained for the ligand Chiragen[3]. (Crystal data: orthorhombic, space group P2(1)2(1)2(1), a = 12.229(1) Å, b = 12.790(1) Å, c = 20.215(1) Å, V = 3161.8(4) Å(3), Z = 4.) Combination of the ligands with Ru(bpy)(2)Cl(2) (where bpy is 2,2'-bipyridine) led to a mixture of diastereomers, while the use of enantiomerically pure Delta- or Lambda-[Ru(bpy)(2)(py)(2)](dibenzoyltartrate) or Delta-Ru(CG[m-xyl])Cl(2) led to almost complete stereoselectivity in the products. Circular dichroism spectra show that the complexes are composed of one helical diastereomer, with the expected absolute configuration predetermined by the chiral building block used. Additionally, (1)H-NMR spectroscopy indicates C(2) point group symmetry for the structures in solution, confirming the absence of DeltaLambda diastereomers.