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

Abstract

The C(2)-symmetric chiral pinene[5,6]bipyridine V (Chart 1) 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 1) 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.

[6,6′-Bis(chloromethyl)-2,2′-bipyridyl]dichlorocobalt(II)

“…74 (14) . This structure is consistent with the structures of three variously substituted bipyridyl Co II -dichloride complexes previously reported (Baker et al, 1988;Bolm et al, 1990;Lotscher et al, 2001).…”

Chiral 2,2′-bipyridines: ligands for asymmetric induction

“…32,34- 38 The latter readily undergoes a stereospecific lithiation at the pinenyl methylene carbon adjacent to the pyridine ring, allowing a large range of substituents to be appended. 34,[36][37][38] While pinene derivatives remain the most studied chiral appendage, the enantiomeric pair of the menthone derived species 17 have also recently been reported by Kocovsky and co-workers. 34…”

Crystal structure of di-μ-chlorido-bis{chlorido[(−)-5,6-pinenebipyridine]cobalt(II)} aquadichlorido[(−)-5,6-pinenebipyridine]cobalt(II)

“…However, a few mononuclear complexes with ligands containing the 5,6pinenebipyridine moiety in their skeleton have been reported. A tetrahedral Co II complex, UCUFAZ, containing a bidentate bipyridine ligand analogue to the ligand L but containing two pinene groups, has been characterized (Lo ¨tscher et al, 2001). Two tridentate ligands, UKITOX and UKIVAL (Suhr et al, 2002), composed of 2,2 0 :6 0 ,2 00 terpyridine containing two pinene groups annelated to the terminal pyridine rings, coordinated by a Co II cation together with two chloride anions to form a complex whose geometry is pseudo-trigonal-bipyramidal.…”