Framework Conversion of Oxido-Bridged Dinuclear Ruthenium Complexes

Pyrazine-Coordinated Dinuclear and Mononuclear Ruthenium Complexes Formed via the Conversion of the Triply Chlorido-Bridged Diruthenium(II) Complex

The pyrazine-coordinated dinuclear and mononuclear ruthenium complexes were synthesized through the framework conversion reactions of the triply chlorido-bridged diruthenium(II) complex [{RuII,II(bbpma)}2(μ-Cl)3]+ (bbpma; benzylbis(2-pyridylmethyl)amine, [1]+) in the presence of pyrazine, which could function as the simple molecular multinucleation ligand of metal compounds. A reduction reaction of fac-[RuIIICl3(bbpma)] with zinc in the presence of hydrochloric acid afforded [1]+ in solution, and the following addition of pyrazine (1 equiv) in the solution led to the formation of a singly pyrazine (pz)-bridged diruthenium complex, [{RuII,II(μ-Cl2ZnCl2)(bbpma)}2(μ-pz)] ([2(II,II)(ZnCl2)2]). The stoichiometric two-electron oxidation of [2(II,II)(ZnCl2)2] was successfully proceeded, and a Ru(III)-Ru(III) species, [{RuIII,IIICl2(bbpma)}2(μ-pz)](PF6)2 ([III,III](PF6)2), was isolated. The reaction of [1]+ with excess amounts of pyrazine without hydrochloric acid afforded mononuclear Ru(III) and Ru(II) complexes containing one or two pyrazine, fac-[RuClm(pz)3-m(bbpma)]+ (m = 2; [3]+; m = 1; [4]+). The details of the electrochemical and spectroscopic properties of [1]+-[4]+ in organic and aqueous solutions were discussed.

Edge-sharing bi-octahedral diruthenium(IV,IV) compounds containing Ru-Ru bonds chelated and bridged by two carbonate and two oxo groups

From paddle-wheel starting material Na3Ru2(CO3)4·6H2O, a family of edge-sharing bi-octahedral (ESBO) diruthenium(IV,IV) compounds formulated as Ru2O2(CO3)2(H2O)2L2·nH2O [L = piperazine (1) or 2-methylpiperazine (2), n = 4, and L = 2,2-dimethylpiperazine (3), n = 12] and Ru2O2(CO3)2(OH)4{M(H2O)4}2·nH2O [M = Mg (4), n = 4, and Ni (5), n = 2] were prepared and structurally characterized. The Ru28+ dimer is chelated and bridged by two CO32- and two μ-O in a trans manner, and the Ru-Ru distances fall in the range 2.3808(6)-2.4001(4) Å. Compound 2 shows the shortest Ru-Ru distance for all known ESBO Ru2 compounds reported thus far. Increasing -CH3 groups of terminal piperazine ligands coordinated to the Ru(μ-O)2(μ-O3C)2Ru core, and according to Raman spectra experiments combined with theoretical calculations, the intense bands of compounds 1-3 appearing at ∼360 cm-1 can be assigned to the stretching of Ru-Ru bonds.

Ru(IV)-Ru(IV) complexes having the doubly oxido-bridged core with a bridging carbonato or hydrogencarbonato ligand

Ru(IV)-Ru(IV) complexes having the doubly oxido-bridged diamond core with a bridging carbonato or hydrogencarbonato ligand, [{Ru^IV(ebpma)}₂(μ-O)₂(μ-O₂CO(H)_m)]X_n (ebpma; ethylbis(2-pyridylmethyl)amine, m = 0; [IV,IV]X₂ (X = PF₆, ClO₄), m = 1; [IV,IV_1H](ClO₄)₃), were isolated via the oxidation of the corresponding carbonato-bridged Ru(III)-Ru(IV) complex ([III,IV]⁺), and "[IV,IV](ClO₄)₂ and [IV,IV_1H](ClO₄)₃" were structurally characterized. The electrochemical and spectroscopic properties of [IV,IV]²⁺ and [IV,IV_1H]³⁺ were investigated both in organic solvents and aqueous solutions. The reactivity toward organic solvents having (a) methyl group(s) and reactions with organic substrates were studied as well. This should be the first time when systematic comparisons of the Ru(IV)-Ru(IV) species and corresponding Ru(III)-Ru(IV) complexes in the same tridentate ligand system were made.

Structural and electronic forms of doubly oxido/Pz and triply oxido/(Pz)2 bridged mixed valent and isovalent diruthenium complexes (Pz = pyrazolate)

The article reported on the diastereomeric dinuclear mixed-valent complexes [(acac)₂Ru(III)(μ-O)(μ-Pz^R)Ru(IV)(acac)₂] (R = H, Me, meso: ΔΛ, 1a-1c; rac: ΔΔ/ΛΛ, 2a-2c) and rac-[(acac)₂Ru(III)(μ-O)(μ-Iz)Ru(IV)(acac)₂], (2d) (HPz = pyrazole, HIz = indazole, acac = acetylacetonate). Moreover, the diruthenium(II,II) complexes [(HPz)₃Ru(II)(μ-O)(μ-Pz)₂ Ru(II)(HPz)₃] (3a) and [(HIz)₃Ru(II)(μ-O)(μ-Iz)₂Ru(II)(HIz)₃] (3d) were presented. The analogous form of 3a, i.e., [(HPz)₂(Pz)Ru(III)(μ-O)(μ-Pz)₂Ru(III)(Pz)(HPz)₂], was previously reported. Single crystal X-ray structures of 1a-1c/2a-2d and representative 3a showed their molecular forms, including the diastereomeric nature of the former. The Ru-O-Ru angle decreased appreciably on switching from doubly bridged 1 and 2 (128-135°) to triply bridged 3a (114°). Both series of complexes displayed rhombic symmetry in their EPR spectra, with g₁ and g₂ being very similar for 1a-1c with an almost axial look. The mixed-valence complex with a Ru(III)Ru(IV) (S = 1/2) state of 1 and 2 would lead to iso-valence complexes of Ru(III)Ru(III) and Ru(IV)Ru(IV) with an EPR inactive state by one electron redox reaction. On the other hand, metal based {Ru(II)Ru(II)/Ru(II)Ru(III), 3a/3a⁺} and terminal ligand (HPz/HPz^-, 3a/3a^-) based redox processes displayed anisotropic and free radical EPR, respectively. An IVCT (intervalence charge transfer) band was found for the delocalised mixed valent 1 and 2 {Ru(III)Ru(IV)} or 3a⁺ {Ru(II)Ru(III)} in the NIR region. The intense metal-to-ligand charge transfer (MLCT) transitions of 1-3 in the visible region varied systematically as a function of the metal oxidation state.

Synthesis of Carbonato- and Doubly Oxido-Bridged Diruthenium(III,IV) Complex and Reactions with Cations

Doubly oxido-bridged transition metal moieties, {M₂(μ-O)₂}, play important roles as oxidation reaction centers in nature. This work features a diruthenium(III,IV) complex with a doubly oxido-bridged core {Ru₂^III,IV(μ-O)₂}³⁺ with a carbonato bridged between the two ruthenium centers, M[{Ru^III,IV(ebpma)}₂(μ-O)₂(μ-O₂CO)]₂(PF₆)₃ (M[1_CO3]₂(PF₆)₃; Carbonato complex, ebpma; ethylbis(2-pyridymethyl)amine), and explores the interactions of this complex with cations (H⁺ and M⁺). M[1_CO3]₂(PF₆)₃ was formed via reactions of a singly oxido-bridged complex, [{Ru^III,IVCl₂(ebpma)}₂(μ-O)]PF₆·(CH₃)₂CO, with M₂CO₃ (M = K, Na) or with CO₂(g), adjusted to around pH 12 with NaOH(aq.), in a water-acetone mixed solvent. The Carbonato complex was isolated as a powder in the form of M[1_CO3]₂(PF₆)₃ (M = K, Na), because of the interactions between the carbonato moiety and K⁺ or Na⁺ in the solid structure. In acidic aqueous solutions, unexpectedly, the carbonato ligand remained bound to the doubly bridged core, {Ru₂^III,IV(μ-O)₂}³⁺ or {Ru₂^III,IV(μ-O)(μ-OH)}⁴⁺, without decarboxylation even under pH 1.0. Two-step one-protonation/deprotonation occurred reversibly between pH 1.0 and 13.2 to the bridging oxido and carbonato ligands. The structures of the corresponding one- and two-protonated complexes ([1_CO3H]²⁺ and [1_CO32H]³⁺) were successfully characterized.