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
(−(CH2)n {n = 0,
3} and −CH2(bpy)CH2−).
X-ray structural data
were obtained for the ligand Chiragen[3]. (Crystal data: 
orthorhombic, space group
P212121, a
= 12.229(1) Å,
b = 12.790(1) Å, c = 20.215(1) Å,
V = 3161.8(4) Å3, Z = 4.)
Combination of the ligands with
Ru(bpy)2Cl2
(where bpy is 2,2‘-bipyridine) led to a mixture of diastereomers, while
the use of enantiomerically pure Δ- or
Λ-[Ru(bpy)2(py)2](dibenzoyltartrate)
or Δ-Ru(CG[m-xyl])Cl2 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, 1H-NMR
spectroscopy indicates C2 point group symmetry
for the structures in solution, confirming the absence of
ΔΛ
diastereomers.