STERIC LIGAND EFFECTS OF 6 BIDENTATE BIPYRIDYL LIGANDS

The synthesis and characterization of a series of [Ru(H2O)(N-N)(trpy)]2+ complexes (where N-N = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (4,7-Me(2)phen),; 2,9-dimethyl-1,10-phenanthroline (2,9-Me(2)phen), 2,2'-biquinoline (biq), and 6,6'-dichloro-2,2'-bipyridine (6,6'-Cl(2)bpy), and trpy = 2,2': 6'2/''-terpyridine) are described. The rate constants for ligand substitution of the aqua ligand for acetonitrile were determined for the [Ru(H2O)(N-N)(trpy)](2+) complexes as well as for a series of [Ru(H2O)(bpy)(2)(PR(3))](2+) complexes in pH = 2.2 HNO3/NaNO3 (mu=0.1) solution at 25 degrees C. The electronic (E) and steric (S) properties of the phopshine ligands in the [Ru(H2O)(bpy)(2)(PR(3))](2+) complexes correlated well with the rate constants for ligand substitution (k(ls)) using the relationship In k(ls) = aE + bS + c (where a-c are constants which were determined by linear regression analyses). The equation for the [Ru(H2O)(bpy)2(PR(3))](2+) complexes was used to calculate the cone angles of the six bidentate bipyridyl ligands (N-N). These cone angles represent the first quantitative estimates of steric ligand effects for bidentate bipyridyl ligands.