Preparation of tetrabutylammonium salt of a mono-Ru(iii)-substituted α-Keggin-type silicotungstate with a 4,4′-bipyridine ligand and its electrochemical behaviour in organic solvents

Abstract

The tetrabutylammonium (TBA) salt of a mono-ruthenium(III)-substituted α-Keggin-type silicotungstate with a 4,4'-bipyridine (bipy) ligand, TBA5[α-SiW11O39Ru(III)(bipy)] (1), which is soluble in various organic solvents, was prepared by a cation exchange reaction of Cs5[α-SiW11O39Ru(III)(bipy)] with tetrabutylammonium bromide. Compound 1 was characterised using IR, (1)H-NMR, elemental analysis, single crystal X-ray analysis, X-ray absorption near-edge structure (XANES) analysis (Ru L3-edge), electron spin resonance (ESR), cyclic voltammetry (CV) and UV-Vis. Single crystal X-ray analysis of 1 revealed that the Ru(III) unit was incorporated into the α-Keggin-type silicotungstate framework and coordinated by a bipy molecule through a Ru-N bond. CV indicated that the incorporated Ru(III)-bipy was reversibly oxidised to the Ru(IV)-bipy derivative and reduced to the Ru(II)-bipy derivative in organic solvents. The redox potential of Ru(IV/III)-bipy was found to be affected by organic solvents. Moreover, the Ru(V)-bipy derivative was observed in acetonitrile.

Preparation and Redox Studies of α1- and α2-Isomers of Mono-Ru-Substituted Dawson-type Phosphotungstates with a DMSO Ligand: [α1/α2-P2W17O61RuII(DMSO)]8–

“…As shown in Figure 5a, the IR spectrum of the isolated black solid A shows a typical Dawson-type phosphotungstate structure together with a weak peak around 1161 cm −1 that is assigned to an S−O stretching vibration peak for the coordinated DMSO ligand. 9,15,16 These data together with results of elemental analysis and high resolution mass 6a), typical for the α 2 -isomer of a monometal-substituted Dawson-type structure with C s symmetry. 30 The 1 H NMR spectrum shows one peak appearing at 3.15 ppm that corresponded to the proton of the methyl group of DMSO coordinated to diamagnetic Ru II (Figure 3c).…”

“…In order to reduce any Ru III species into Ru II species, ascorbic acid as a reducing reagent is added before NMR measurements. 16 Two large peaks at −8.66 and −13.45 ppm (integration ratio ca. 1: 1) are observed with four small peaks.…”

“…In the course of our research on mono-Ru-substituted polyoxometalates, we have reported preparation and structural characterization of various mono-ruthenium-substituted α-Keggin-type heteropolytungstates with a terminal aqua ligand, [α-XW 11 O 39 Ru III (H 2 O)] n− , (X = Si (n = 5), Ge (n = 5), and P (n = 4)), 8,14,15 and with a DMSO ligand, [α-XW 11 O 39 Ru-(DMSO)] n− (X = Si, Ge, and P). 9,15,16 The complexes with a terminal aqua ligand, [α-XW 11 O 39 Ru III (H 2 O)] n− (X = Si (n = 5), Ge (n = 5), and P (n = 4)), were prepared by reactions of monolacunary heteropolytungstates, [XW 11 O 39 ] n− (X = Si (n = 8), Ge (n = 8), and P (n = 7)), with Ru(acac) 3 (acac: acetylacetonate) or Ru 2 (benzene) 2 Cl 4 under hydrothermal conditions (eq 1). 8,14 Two DMSO-coordinated complexes, [α-XW 11 O 39 Ru III (DMSO)] 5− (X = Si or Ge), were produced by r e a c t i o n o f w a t e r -c o o r d i n a t e d c o m p l e x e s [ α -XW 11 O 39 Ru III (H 2 O)] 5− (X = Si or Ge), with DMSO (eq 2 ) , 1 5 , 1 6 a n d t h e p h o s p h o r u s d e r i v a t i v e [ α -PW 11 O 39 Ru II (DMSO)] 5− was produced by a reaction of monolacunary heteropolytungstates, [PW 11 O 39 ] 7− , with Ru-(DMSO) 4 Cl 2 under hydrothermal conditions (eq 3).…”

Recent Advances in the Development of Molecular Catalyst‐Based Anodes for Water Oxidation toward Artificial Photosynthesis

“…To address this limitation, polyoxometalates (POMs), which are capable of hosting several metal centers, have been reported as robust inorganic ligands for molecular catalysts . Numerous Ru POM‐based molecular catalysts have been developed to promote efficient water oxidation in homogeneous solutions, including, for example, [{Ru 4 O 4 (OH) 2 (H 2 O) 4 }(γ‐SiW 10 O 36 ) 2 ] 10− (complex 9 ; Figure ) . Complex 9 promotes homogeneous water oxidation using both [Ru(bpy)] 3+ (TON=18 and TOF max =0.25 s −1 at pH 7) and Ce IV oxidants (TOF=0.13 s −1 at pH 0.6) .…”

Easy Ligand Activation in the Coordination Sphere of Ru inside the [PW11O39]7– Backbone

“…Catalytic activities of [PW11O39Ru III (H2O)] 4− , [PW11O39Ru II (DMSO)] 5− (DMSO: dimethyl sulfoxide), [SiW11O39Ru III (H2O)] 5− , [SiW11O39Ru III (DMSO)] 5− , and [GeW11O39Ru III (H2O)] 5− in oxidation of olefins [3][4][5], water [6][7][8], DMSO [9,10], and alcohols [11,12]; reduction of DMSO [10] and carbon dioxide [13]; and oxidative C-C bond formation [14] have been reported. The H2O ligand attached to Ru is exchangeable with other organic and inorganic donor molecules to form Ru-pyridine [10,15,16], Ru-pyrazine [12], Ru-DMSO [10,17,18], Ru-NO [19][20][21], Ru-Cl [22], Ru-CO [23][24][25], Ru-olefin [10], and Ru-O-Ru derivatives [26,27].…”