Synthesis and characterization of nitrosyl diruthenium complexes. Interaction between NO and CO across the metal-metal bond

Two neutral diruthenium complexes and one anionic diruthenium complex, Ru-2(dPf)(4)(NO), Ru-2(dPf)(4)(NO)(2), and [RU2(dPf)(4)(NO)](-), where dpf is diphenylformamidinate anion, were synthesized and characterized as to their electrochemical and spectroscopic properties. Two of the compounds, RU2(dPf)4(NO) and RU2(dPf)4(NO)2, were also structurally characterized. RU2(dPf)(4)(NO) undergoes reversible one-electron reductions under N-2 at E-1/2 = 0.06 and -1.24 V in CH2Cl2, 0.1 M TBABr. These processes are shifted to E-1/2 = 0.18 and -0.78 V under CO due to the trans-coordination of a CO molecule which stabilizes the singly and doubly reduced forms of the metalmetal bonded complexes, thus leading to easier reductions. CO does not coordinate to RU2(dPf)(4)(NO)(2) but it does bind to the singly reduced species to generate [Ru-2(dPf)(4)(NO)(CO)](-) under a CO atmosphere in solution; characteristic NO and CO bands are seen for this compound at v(NO) = 1674 cm(-1) and v(CO) = 1954 cm(-1). RU2(dPf)(4)(NO)(2) displays a reversible one-electron reduction at E-1/2 = -1.24 V versus SCE and an irreversible reduction at E-pc = -1.96 V in CH2O2, 0.1 M TBAP under N-2. There are also two reversible one-electron oxidations at E-1/2 = 0.24 and 1.15 V. Spectroelectrochemical monitoring of the RU2(dPf)(4)(NO)(2) oxidation processes in a thin-layer cell shows only a single NO vibration for each electrogenerated product and v(NO) is located at 1726 (neutral), 1788 (singly oxidized), or 1834 (doubly oxidized) cm(-1). Finally, a labile CO complex, [RU2(dPf)(4)(NO)(CO)](-), could be generated by passing CO into a solution of [RU2(dPf)(4)(NO)](-). Formation of the mixed CO/NO adduct was confirmed by electrochemistry and infrared spectroscopy. Analysis of the NO and CO stretching vibration frequencies for [RU2(dPf)(4)(NO)(CO)](-) by in-situ FTIR spectroelectrochernistry and comparisons with data for RU2(dPf)(4)(NO) and RU2(dPf)(4)(CO) reveal the presence of a strong interaction between NO and CO across the Ru-Ru bond.