Cyanide Adducts on the Diruthenium Core of [Ru2(L)4]+ (L = ap, CH3ap, Fap, or F3ap). Electronic Properties and Binding Modes of the Bridging Ligand

The products of the reaction between CN- and four different diruthenium complexes of the type Ru2(L)4Cl where L = 2-CH3ap (2-(2-methylanilino) pyridinate anion), ap (2-anilinopyridinate anion), 2-Fap (2-(2-fluoroanilino)pyridinate anion), or 2,4,6-F3ap (2-(2,4,6-trifluoroanilino)pyridinate anion) are reported. Mono- and/or dicyano adducts of the type Ru2(L)4(CN) and Ru2(L)4(CN)2 are found exclusively as reaction products when either the 2-CH3ap or the ap derivative is reacted with CN-, but diruthenium complexes with formulations of the type Ru2(Fxap)3[(mu)-(o-NC)Fx-1ap]((mu)-CN) or Ru2 (Fxap)4((mu)-CN)2 (x = 1 or 3) are also generated when Ru2(Fap)4Cl or Ru2(F3ap)4Cl is reacted with CN-. More specifically, four products formulated as Ru2(Fap)4(CN), Ru2(Fap)4(CN)2, Ru2(Fap)3[(mu)-(o-NC)ap]((mu)-CN), and Ru2(Fap)4((mu)-CN)2 can be isolated from a reaction of CN- with the Fap derivative, but the exact type and yield of these compounds depend on the temperature at which the experiment is carried out. In the case of the F3ap derivative, the only diruthenium complex isolated from the reaction mixture has the formulation Ru2(F3ap)3[(mu)-(o-NC)F2ap]((mu)-CN) and this compound has structural, electrochemical, and spectroscopic properties quite similar to that of previously characterized Ru2(F5ap)[(mu)-(o-NC)F4ap] ((mu)-CN). Both the mono- and dicyano derivatives synthesized in this study possess the isomer type of their parent chloro complexes. The Ru-Ru bond lengths of Ru2(ap)4(CN) and Ru2(2-CH3ap)4(CN) are longer than those of Ru2(ap)4Cl and Ru2(CH3ap)4Cl, respectively, and this is accounted for by the strong (sigma)-donor properties of the CN- ligand as compared to Cl-. The Ru-C bonds in Ru2(ap)4(CN)2 are significantly shorter than those in Ru2(ap)4(CN), thus revealing a greatly enhanced Ru-CN interaction in the dicyano adduct, a result which is also indicated by the fact that (nu)CN in Ru2 (ap)4(CN)2 is 50 cm^-1 higher than (nu)CN in Ru2(ap)4(CN). Although both (4,0) Ru2(ap)4(CN)2 and (3,1) Ru2(Fap)4(CN)2 possess the same formulation, there are clear structural differences between the two complexes and this can be explained by the fact that the two cyano derivatives possess a different binding symmetry of the bridging ligands. Each mono- and dicyano adduct was electrochemically investigated in CH2Cl2 containing TBAP as supporting electrolyte. Ru2(ap)4(CN), Ru2(CH3ap)4(CN), and Ru2(Fap)4(CN) undergo one reduction and two oxidations. The two dicyano adducts of the ap and Fap derivatives are characterized by two reductions and one oxidation. The potentials of these processes are all negatively shifted in potential by 400-720 mV with respect to half-wave potentials for the same redox couples of the monocyano derivatives, with the exact value depending upon the specific redox reaction.