Asymmetric catalysis; 140: Tris(2-pyridyl)methane derivatives with a chiral bridging atom

Two different series of C-1-symmetric tris(2-pyridyl)methane tripod ligands were synthesized with pyridin-2-yl, 6-phenylpyridin-2-yl and 6-methoxy- or 6-menthyloxypyridin-2-yl substitutents. The menthoxy devivatives were resolved with respect to the bridging carbon atom by chromatography. In reactions with CuCl2 and RhCl3 complexes were obtained which could be analyzed by X-ray crystallography. In the formation of the Rh complex an ortho-metallation of the 6-phenyl substituent occurred giving rise to a Delta/Lambda -element of chirality. Whereas the chiral tripod ligand conferred a stable configuration to the Rh atom, a fast equilibration of the Delta- and Lambda -isomers was observed.