The salts [(eta-C(5)Me(5))Ru(NO)(bipy)][OTf](2) (1[OTf](2)) and [(eta-C(5)Me(5))Ru(NO)(dppz)][OTf](2) (2[OTf](2)) are obtained from the treatment of (eta-C(5)Me(5))Ru(NO)(OTf)(2) with 2,2'-bipyridine (bipy) or dipyrido[3,2-a:2',3'-c]phenazine (dppz) (OTf = OSO(2)CF(3)). X-ray data for 1[OTf](2): monoclinic space group P2(1)/c, a = 11.553 (4) Å, b = 16.517 (5) Å, c = 14.719 (4) Å, beta = 94.01 (2) degrees, V = 2802 (2) Å(3), Z = 4, R1 = 0.0698. X-ray data for 2[OTf](2): monoclinic space group P2(1)/c, a = 8.911 (2) Å, b = 30.516 (5) Å, c = 24.622 (4) Å, beta = 99.02 (1) degrees, V = 6613 (2) Å(3), Z = 8, R1 = 0.0789. Both 1[OTf](2) and 2[OTf](2) are soluble in water where they exhibit irreversible electrochemical oxidation and reduction. A fluorescence-monitored titration of a DNA solution containing 2[OTf](2) with ethidium bromide provides evidence that 2(2+) intercalates into DNA with a binding constant greater than 10(6) M(-)(1). DNA cleavage occurs when the DNA solutions containing 2[OTf](2) are photolyzed or treated with H(2)O(2) or K(2)S(2)O(8).

Treatment of Cp‘Ru(NO)(CH3)2 with 2 equiv of HOSO2CF3 (HOTf) leads to the formation of the ditriflate complexes Cp‘Ru(NO)(OTf)2 (1a,b) (Cp‘ = η-C5(CH3)5, Cp* (1a), η-C5(CH3)4(CH2CH3), Cp† (1b)). The complex salts [Cp†Ru(NO)(OTf)(OH2)][OTf] (2b) and [Cp†Ru(NO)(OH2)2][OTf]2 (3b) can be isolated from the hydration of 1b. The structures of 1b, 2b, and 3b are determined by single-crystal X-ray diffraction methods. In 0.1 M H2O/CH2Cl2 the equilibria 1a   2a + + OTf-   3a 2+ + 2OTf- exist, with 1a being the predominant complex and ΔH 1 = −15(3) kcal/mol and ΔS 1 = −60(30) eu (for K 1) and ΔH 2 = −9(1) kcal/mol and ΔS 2 = −40(25) eu (for K 2). For comparison, the equilibria 1a [Cp*Ru(NO)(OTf)(THF)]+ + OTf- [Cp*Ru(NO)(THF)2]2+ + 2OTf- exist in neat THF with ΔH 1 = −4.5(3) kcal/mol and ΔS 1 = −30(10) eu (for K 1) and ΔH 2 = −4.1(1) kcal/mol and ΔS 2 = −20(10) eu (for K 2). The anion exchange equilibria in CH2Cl2 1a + 2Cl- [Cp*Ru(NO)(OTf)(Cl) + OTf- + Cl- [Cp*Ru(NO)Cl2] + 2OTf- has ΔH 1 = −9(1) kcal/mol and ΔS 1 = −30(10) eu (for K 1) and ΔH 2 = −11(1) kcal/mol and ΔS 2 = −30(10) eu (for K 2). While loss of the OTf- ligands is exothermic, the displacement of OTf- from the coordination sphere carries a significant entropy cost due to the formation of ions in a more-ordered solvent cage. Complex salts 1a,b dissolve in water to give acidic red-orange solutions containing an equilibrium mixture of the diaqua complex cations [Cp‘Ru(NO)(OH2)2]2+ (3a 2+, pK a = 2.7; 3b 2+) and the dinuclear cations [Cp‘Ru(NO)(μ-OH)]2 2+ (4a 2+, pK a = 5.5; 4b 2+). The cations 4a 2+ and 4b 2+ exist as a mixture of cis (major) and trans (minor) isomers; X-ray results show 4b 2+ to be cis in the solid state. Crossover between 4a 2+ and 4b 2+ to give the mixed Cp*/Cp† dimer 4c 2+ occurs readily under acidic conditions but not under basic conditions. The pH dependence together with kinetic and van't Hoff analyses support the process 2 3a 2+ ⇄ 4a 2+ + 2H3O+. The ∠Ru−N−O values of ca. 160°, correspondingly low νNO values in the Nujol mull IR spectra, and relatively short Ru−O bonds show the H2O and OH- ligands to be significant π-donors to the electrophilic Ru center. Dissolution of 4a,b in basic D2O causes complete deuteration of the ring CH3 groups but no deuteration of the Cp†-CH2CH3 group; the CD3 groups are easily exchanged to CH3 by exposure to basic H2O conditions. Chloride substitution by H2O occurs when Cp‘Ru(NO)Cl2 is dissolved in water, giving an equilibrium mixture of undissociated [Cp‘Ru(NO)Cl2]aq together with the [Cp‘Ru(NO)(Cl)(OH2)]+ and [Cp‘Ru(NO)(μ-OH)]2 2+ ions. H/D exchange on the Cp‘ ring CH3 groups also occurs slowly when Cp‘Ru(NO)Cl2 is dissolved in D2O but not when dissolved in a D2O/DCl mixture. The present work suggests that Cp‘-ring slippage and the reversible release of H+/D+ is facilitated by the π-donor ability of the H2O and OH- ligands.

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CpCr(N0)2(N02) exists as a mixture of the nitro and nitrito linkage isomers, with the nitrito isomer predominating in both solution and the solid state (Cp = rj5-C5H5). The Cr-N02 ** Cr-ONO equilibrium is markedly solvent and temperature dependent: in CDC13, AH^= 1.8(3) kcal/mol and £«, = 9.3(9) eu. The treatment of CpCr(N0)2(N02) with Na15N02 in MeOH leads to the exchange of free and bound N02~, eventually giving a statistical distribution of the 15N label in the NO and N02 ligands and free N02" at equilibrium. The linkage isomers of the labeled CpCr(N0)2(15N02) complex convert to a statistical mixture of the CpCr(15NO)(NO)(N02) and CpCr(15NO)(NO)(ONO) isotopomers in solution and in the solid state. The initial disappearance rate of the CpCr(NO)2(15N02) isotopomer is first-order, leading to AH* = 11.3(6) kcál/mol and AS* = 10(2) eu in MeOH and AH* = 14(1) kcal/mol and AS* = 20(1) eu in toluene. This behavior, together with the fact that CpCr-(N0)2(i5N02) equilibrates to CpCr(l5N0)(N0)(N02) in the solid state, supports an intramolecular O atom transfer process between «'¿-coordinated NO and N02 ligands.

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