53195-18-9

Upstream product

• 7732-18-5 water 
• 72098-82-9 pentamminehydroxoruthenium(III) dithionate 
• 1493-13-6 trifluorormethanesulfonic acid 
• 84278-98-8 pentaamminetrifluoromethanesulfonato ruthenium(III) trifluoromethanesulfonate 

Downstream Products

• 82917-81-5 (dibenzylmalononitrile)pentaammineruthenium(II) hexafluorophosphate 

Relevant academic research and scientific papers

Binuclear ruthenium complexes bridged by the dicyanamide anion

As shown by the value of the extinction coefficient for the intervalence band for μ-dicyanamido-bis(pentaammineruthenium)(4+), ε 2.8 × 103 M-1 cm-1, dicyanamide ion as a bridging group produces quite strong electronic coupling in the mixed-valence molecule. A number of properties, among them the bandwidth at half-height, the dependence of the band energy on solvent properties, and the rather small value of the comproportionation constant, 3.4 × 102, show the species to be valence trapped. Replacing trans ammonias by pyridine or by isonicotinamide decreases the electronic coupling, suggesting that the dominant coupling mechanism, in spite of the negative charge on the ligand, is πd-π* delocalization rather than πd-π.

The unusually fast reactions between ruthenium(III)-ammine complexes and NO revisited

The kinetics of the unusually fast reactions between [RuIII(NH3)5X](3-n)+ (Xn- = Cl-, NH3, H2O) and NO were reinvestigated in acidic aqueous solution in order to clarify the underlying reaction mechanism. The measured second-order rate constants (kNH3 = 0.30 ± 0.01 M-1 s-1, kH2O = 55.6 ± 3.2 M-1 s-1 at 26°C) are in good agreement with literature data for X = ammonia and halide. The activation parameters determined for the reactions are: ΔH≠ = 41 ± 2 kJ mol-1, ΔS≠ = -114 ± 7 J K-1 mol-1 and ΔV≠ = -13.6 ± 0.3 cm3 mol-1 for [Ru(NH3)6]3+; ΔH≠ = 34.4 ± 1.0 kJ mol-1, ΔS≠ = -132 ± 3 J K-1 and ΔV≠ = -18.0 ± 0.5 cm3 mol-1 for [Ru(NH3)5Cl]2+; and ΔH≠ = 31.0 ± 0.7 kJ mol-1 and ΔS≠ = -108 ± 2 J K-1 mol-1 for [Ru(NH3)5(H2O)]3+. Bond formation with the entering nucleophile appears to be substantial in the transition state for the reaction. An associative substitution mechanism coupled to a concerted electron transfer process to produce [RuII(NH3)5- (NO+)]3+ is proposed for all three reactions. Possible reasons for the significantly faster reaction observed in case of the aqua complex are discussed.

Donor-acceptor electronic coupling as a function of bridging group: Mixed-valence diruthenium(II,III) complexes bridged by isonicotinato and isonicotinamido ligands

Binuclear, mixed-valence μ-isonicotinato and μ-isonicotinamido complexes capped by pentaammineruthenium(II) at the pyridine site and pentaammineruthenium(III) at the carboxylato or amido site have been synthesized and characterized. On the basis of their electronic absorption spectra and redox properties, the amido complexes are assigned as the N-bonded (RuIII-NHC(O)R) isomers. The mixed-valence complexes exhibit intervalence charge-transfer bands at 720 nm (ε = 2.6 × 102 M-1 cm-1) and 761 nm (0.9 × 103 M-1 cm-1), respectively, in aqueous acetate buffer at pH 4.8. The redox potentials of the two sites differ by 0.44 V in the isonicotinato and by 0.54 V in the isonicotinamido complexes in the above medium, and the donor-acceptor coupling elements, evaluated from the intensities of the intervalence bands, are 300 and 510 cm-1, respectively. Solvent dependences of the electronic spectra and electrochemical parameters are also reported. Both bridges provide significant coupling between the Ru(II) and Ru(III) metal centers in the mixed-valence complexes. These coupling energies serve as a point of departure for a consideration of coupling mechanisms in related polyproline-bridged systems for which thermal electron-transfer rates have been determined. It is concluded that hole transfer pathways predominate when osmium(II) pentaammine is the donor and cobalt(III) or ruthenium(III) pentaammine is the electron acceptor.

Linkage isomerization reactions of (acetone)pentaammineruthenium(III) and -ruthenium(II) complexes

A complete kinetic and thermodynamic analysis of the linkage isomerizations of [Ru(NH3)5(acetone)]3+/2+ is presented. Each oxidation state exists as two linkage isomers in which acetone is bound via O in an η1 fashion (favored by Ru(III)) and via C and O of the carbonyl group in an η2 fashion (favored by Ru(II)). The [Ru(NH3)5(η2-OC(CH3) 2)]2+ and [Ru(NH3)5(η1-OC(CH3) 2)]3+ complexes were characterized by spectroscopic methods (IR, UV/vis, and NMR), and the kinetic and thermodynamic data for these isomerizations were obtained by electrochemical methods. In acetone, the [Ru(NH3)5(η2-OC(CH3) 2)]3+/2+ couple is observed at E1/2 = -337 mV as ferrocenium/ferrocene (Fc+/Fc) at 25°C, while the [Ru(NH3)5(η1-OC(CH3) 2)]3+/2+ couple is observed at E1/2 = -478 mV (vs Fc+/Fc at 25°C). For the η1 → η2 linkage isomerization of [Ru(NH3)5(acetone)]2+, the rate and equilibrium constants at 25°C in acetone and the enthalpy and entropy of activation are 18 ± 1 s-1, 16 ± 1, 63 ± 1 kJ mol-1, and -10 ± 2 J K-1 mol-1, respectively. Similarly, for the η2 → η1 linkage isomerization of [Ru(NH3)5(acetone)]3+, they are 0.46 ± 0.03 s-1, 14 ± 1, 48 ± 2 kJ mol-1, and -91 ± 7 J K-1 mol-1, respectively. The rate constant for the exchange of coordinated acetone with free acetone in the Ru(III) complex is (6.9 ± 0.5) × 10-6 s-1, at 0°C. This is much slower than the Ru(III) η1 → η2 isomerization rate, (4.3 ± 0.4) × 10-3 s-1, at the same temperature, indicating an intramolecular isomerization. In a 50% v/v acetone/acetonitrile mixture, at 3°C, the Ru(II) η1 → η2 isomerization rate is 0.3 s-1, while the rate constant for the substitution of the coordinated acetone is 0.4 s-1. Therefore, it was not possible to distinguish between an intra- and an intermolecular process. IR spectroscopy and other evidence indicate that the η2 complex is stabilized by both π-back-bonding and σ-bonding via the ketone double bond, with the latter being more important. At -23°C, a second ECE process is observed involving the [Ru(NH3)5(OSO2CF3)]2+/+ couple (E1/2 = -494 mV vs Fc+/Fc) and the η2-acetone complex; the rate constant for the substitution of the triflate ligand, in the Ru(II) complex, by acetone was found to be 1.2 ± 0.2 s-1, compared to 0.109 s-1 for the Ru(II) linkage isomerization under the same conditions. The analogous hexafluoroacetone complexes exist entirely in the η2 form and have redox characteristics similar to those of the η2-acetone complexes.

Aromatic sulfonation by SO32- and the reduction potential of the sulfite radical: Oxidation of sulfite by the tetraammine(phenanthroline)ruthenium(III) cation

The reaction of [Ru(NH3)4(phen)]3+ (phen = 1,10-phenanthroline) with SO32- has been studied in aqueous solution at 25°C and μ = 0.1 M (NaCF3SO3). Above pH 8 the reaction is 2[Ru(NH3)4(phen)]3+ + SO32- + H2O → 2[Ru(NH3)4(phen)]2+ + SO42- + 2H+. Under more acidic conditions an additional reaction occurs: 2[Ru(NH3)4(phen)]3+ + SO32- → [Ru(NH3)4(phen)]2+ + [Ru(NH3)4(phen-SO3)]+ + H+, where phen-SO3 is 1,10-phenanthroline-4-sulfonate. The rate law is -d[Ru(III)]/dt = [Ru(NH3)4(phen)3+]{2k1[S(IV)]/(1 + [H+]/Ka) + 2kdQd(S(IV)]2/(1 + Ka/[H+])2} with k1 = (3.7 ± 0.2) × 104 M-1 s-1, kdQd = (3.2 ± 0.5) × 10-2 M-2 s-1, and Ka = (8.0 ± 0.9) × 10-8 M, where Ka is the acid dissociation constant of HSO3-. The product distribution follows a pH function quite different from the rate law, indicating that the rate-limiting step is the same for both sets of products. No sulfonation occurs in the presence of allyl alcohol, demonstrating that SO3- is an intermediate. In the proposed mechanism, the k1 pathway represents electron transfer from SO32- to Ru(III) to form SO3-, which can be further oxidized to SO42-. The mechanism of sulfonation is unclear, possibly occurring by attack of HSO3 or SO3. The reaction [Ru(NH3)4(phen)]2+ + SO3- → [Ru(NH3)4(phen)]3+ + SO32- was studied by pulse radiolysis, and its rate constant was found to be 1.0 × 108 M-1 s-1. Combining this rate constant with k1 and Ef for the [Ru(NH3)4(phen)]3+/2+ couple leads to a value of Ef = 0.72 V for the SO3-/SO32- redox couple. An effective self-exchange rate constant of 4 M-1 s-1 is derived for the SO3-/SO32- redox couple by use of the Marcus cross-relationship, and this is shown to be consistent with a major portion of the barrier arising from the "umbrella" distortional mode.

Transition-state volumes in solvent exchange. Water exchange on the aqueous aquapentaammineruthenium(III) ion

The rate of water exchange on Ru(NH3)5OH23+ in aqueous CF3SO3H (0.01 mol L-1) is characterized by k298.2 = 2.30 × 10-4 s-1, ΔH* = 91.5 kJ mol-1, ΔS* = -7.7 J K-1 mol-1, and ΔV* = -4.0 cm3 mol-1. The order of lability of M(NH3)5OH23+ in water exchange is (M=) Ru > Cr > Rh > Co ? Ir and is governed by ΔH*. For substitution reactions of metal complexes involving hard leaving groups, the lability sequence first third transition series may be general. For a series of related aqua complexes such as M(NH3)5OH23+, variations in ΔV* for water exchange and the molar volume of the complex as M is changed are largely compensatory, so that the molar volume of the transition state varies relatively little. This reflects reduced accessibility of the complex to associative attack as the central ion becomes smaller.

Interactions of the ruthenium(III)-ruthenium(II) couple with malononitrile and related ligands

When dicyanamide and tricyanomethane act as bridging groups in binuclear pentaammineruthenium species, the bridging groups remain anionic over wide pH ranges. When malononitrile, fert-butylmalononitrile, and ethylmalononitrile are the bridging groups, the behavior is complicated by proton dissociation from the bridging ligand and instability of the mixed-valence form after proton dissociation. Electrochemical studies have led to estimates of the pKa values for [3,L,3] and [3,L,2] for the first two ligands. These are -4.8 and -0.7 for L = malononitrile and -3.0 and 1.6 for L = butylmalononitrile. In the [2,L,2] states only lower limits on pKa, were set, and these are 13 and 15 for malononitrile and tert-butylmalononitrile, respectively. The pKa values of the free ligand are 11.2 and 13.1. The enormous enhancement of acidity when the nitrile is coordinated to (NH3)5RuIII is shown also in the mononuclear tert-butylmalononitrile complex, where pKa was observed to be 3.85, here with use of a spectrophotometric method. The most striking feature of the UV-visible spectra is the strong absorption at high wavelengths shown by the anion-Ru(III) unit. For the [3,L-,3] species the values of λmax(ε) are (units of nm and M-1 cm-1, respectively) 784 (2.8 × 104), 695 (1.7 × 104), 562 (4.5 × 103), and 400 (2 × 103) for the tert-butylmalononitrile, malononitrile, tricyanomethanide, and dicyanamide anions, respectively. For the same bridging ligands, the characteristics of the near-IR absorption of the mixed-valence species are 1170(1.6 × 104), 1280 (>104), 1550 (6.2 × 103), and 1100 (2.8 × 103). The quotients governing the comproportionation equilibrium [3,L-,3] + [2,L-,2] = 2[3,L-,2] for the same four bridging ligands are >1010°, >1011, 2.3 × 103, and 2 × 102, respectively. These data and other properties such as the width of the near-IR band at half-height suggest that the mixed-valence species based on the anions of tert-butylmalononitrile and malononitrile are strongly delocalized but that with the dicyanamide anion as bridging group the systems are valence trapped. When the lone electron pair of the central atom in the bridging group, which mainly appears to account for the coupling in the malononitrile anions, is engaged, as for example when dibenzylmalononitrile is the bridging group, coupling is very weak. This is evidenced by the small value (1.6 × 102* M-1cm-1) of ε for the near-IR band in the corresponding mixed-valence species as well as the small value (-10) for the comproportionation constant.