Complexes of new chiral terpyridyl ligands. Synthesis and characterization of their ruthenium(II) and rhodium(III) complexes

Enantiomerically pure, chiral terpyridyl-type ligands L-1 ('dipineno'-[5,6:5 ",6 "]-fused 2,2':6',2 "-terpyridine) and L-2 ('dipineno'-[4,5: 4'',5"]-fused 2,2':6',2 "-terpyridine) have been synthesized in high yields starting from 2,6-diacetylpyridine and enantiopure a-pinene. Complexes of L' and L-2 with Rh-III and Ru-II have been prepared and studied spectroscopically. The complexes [Ru(L),(2)][PF6](2) (L = L-1 or L-2) were obtained in high yields using microwave heating in ethylene glycol as solvent. The rhodium(III) and ruthenium(II) complexes of L-1 and L-2 have a helically distorted terpyridyl moiety, as shown by the considerable optical activity in the ligand centered and metal to ligand charge transfer transitions. Crystal structures of [Rh(L-1)Cl-3] and [Ru(L-1)Cl-3] show a considerable out of plane distortion of the terpyridyl moiety, whereas free L-2 and [Ru(trpy)(L-2)][PF6](2) have a more planar arrangement of the pyridyl units.