MOLECULAR ARCHITECTURE OF POLYNUCLEAR RUTHENIUM BIPYRIDYL COMPLEXES WITH CONTROLLED METAL HELICITY

The synthesis of di- and trinuclear ruthenium(II) complexes is reporte d, where each metal center has a tris(bidentate) octahedral coordinati on sphere with predetermined stereochemistry. New members of the ''Chi ragen'' ligand series, consisting of two linked chiral 4,5-pineno-2,2' -bipyridine groups, have been prepared, with small spacer units betwee n the coordination centers (-(CH2)(n) {n = 0, 3} and -CH2(bpy)CH2-). X -ray structural data were obtained for the ligand Chiragen[3]. (Crysta l data: orthorhombic, space group P2(1)2(1)2(1), a = 12.229(1) Angstro m, b = 12.790(1) Angstrom, c = 20.215(1) Angstrom, V = 3161.8(4) Angst rom(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 u se of enantiomerically pure Delta- or Lambda-[Ru(bpy)(2)(py)(2)](diben zoyltartrate) or Delta-Ru(CG[m-xyl])Cl-2 led to almost complete stereo selectivity 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, H-1-NMR spectroscopy indicates C-2 point group symmetr y for the structures in solution, confirming the absence of Delta Lamb da diastereomers.