Stereoselective Synthesis of Chiral Pinene[5,6]bipyridine Ligands and Their Coordination Chemistry

The C2-symmetric chiral pinene[5,6]bipyridine V (Chart ) was synthesized according to a procedure published
by our group recently (Kolp, B.; Abeln, D.; Stoeckli-Evans, H.; Zelewsky, A. v. Eur. J. Inorg. Chem. 2001,
1207). A series of stereoselectively alkylated derivatives (Va−Vo) (Table ) was prepared. The solid-state structures
of the compounds Vc and Vk were determined by single-crystal X-ray diffraction, where both compounds show
a transoid conformation of the bipyridine unit and proved to be alkylated stereoselectively from the sterically less
hindered side of the pinene moiety. The X-ray structure of the cobalt complex 4 shows the metal ion to be
tetrahedrally coordinated by one chiral bipyridine V and two chloride ligands. If 2 equiv of ligand V was used,
2:1 complexes were obtained with Cu(I), Ag(I), and Co(II) ions.