Syntheses and molecular structures of ruthenium(II) complexes of the atropisomeric ligands 1,1′-biphenyl-2,2′-diamino and 3,3′-diamino-2,2′-bipyridine

The unique ligands of [Ru(bipy)(2)(bpda)](PF6)(2) (1, bpda = 1,1'-biphenyl-2,2'-diamine) and [Ru(bipy)(2)(dabipy)](PF6)(2) (2, dabipy = 3,3'-diamino-2,2'-bipyridine) are atropisomeric (exhibit hindered rotation about the sigma bonds that connect the two aromatic groups), so the complexes are diasteromeric with conformation isomers possible for the atropisomeric ligands and configurational isomers possible at the metal centers. Only one diastereomer is observed in the solid-state in both cases. The seven- (1) and five-membered (2) chelate ring of dabipy and bpda (the ligand is bound through its pyridyl groups) ligands are delta when the configuration at the metal is Delta. No evidence for atropisomerization is found in solution. For 1, we conclude bpda binds stereospecifically; however, the atropisomerization barrier of dabipy may be sufficiently low for 2 to preclude the observation of diastereomers by low-temperature NMR spectroscopy. (C) 2000 Elsevier Science B.V. All rights reserved.