Oxygenation by Ruthenium Monosubstituted Polyoxotungstates in Aqueous Solution: Experimental and Computational Dissection of a Ru(III)–Ru(V) Catalytic Cycle

Abstract

Molecular polyoxometalates with one embedded ruthenium center, with general formula [Ru(II/III)(DMSO)XW11O39](n-) (X = P, Si; n = 4-6), are readily synthesized in gram scale under microwave irradiation by a flash hydrothermal protocol. These nanodimensional and polyanionic complexes enable aerobic oxygenation in water. Catalytic oxygen transfer to dimethylsulfoxide (DMSO) yielding the corresponding sulfone (DMSO2 ) has been investigated with a combined kinetic, spectroscopic and computational approach addressing: (i ) the Ru(III) catalyst resting state; (ii ) the bimolecular event dictating its transformation in the rate-determining step; (iii ) its aerobic evolution to a high-valent ruthenium oxene species; (iv ) the terminal fate to diamagnetic dimers. This pathway is reminiscent of natural heme systems and of bioinspired artificial porphyrins. The in silico characterization of a key bis-Ru(IV)-μ-peroxo-POM dimeric intermediate has been accessed by density functional theory. This observation indicates a new landmark for tracing POM-based manifolds for multiredox oxygen reduction/activation, where metal-centered oxygenated species play a pivotal role.

Cage Effect on Oxidation of Dimethyl Sulfoxide via Pd2L4 Prolate Spheroids

“…The [Pd 2 L 4 ] 4+ cage's skeleton safely exists in H 2 O 2 /Me 2 SO solution without any significant dissociation (Supporting Information Figure S5), and thus the behavior of the cage in H 2 O 2 /Me 2 SO for Me 2 SO oxidation was scrutinized. The reaction was monitored by gas chromatography, mass spectrometry, and 1 H NMR spectra (Figure ).…”

Preparation and Structural Characterization of Mono‐Ru‐Substituted α2‐Dawson‐Type Phosphotungstate with a Carbonyl Ligand and Other Ru(CO)‐Substituted Heteropolytungstates

“…[1] Recently, considerable attention has been directed towards mono-ruthenium (Ru)-substituted heteropolytungstates because of their unique redox and catalytic properties. [2] Catalytic activities of monoRu-substituted Keggin-type heteropolytungstates [ Figure 1 (a)] for the oxidation of cyclooctene, [3] water, [4] dimethyl sulfoxide (DMSO), [5] alkanes, [6] para-xylene, [7] and alcohols [8] and for electrochemical reduction of DMSO, 8-, was produced together with the α 2 -derivative, as confirmed by CV, IR, mass spectroscopy, and 31 P NMR spectroscopy.…”

“…The two two-electron redox pairs assigned to the reduction of tungsten are dependent on pH with a slope of ca. 60 mV per unit of pH, indicating that two protons were involved in each two-electron redox step [Equation (5) and Equation (6) , and Ru(acac) 3 were reacted in water at 170°C for 4 days, and then a black solid was isolated by the addition of acetone. The IR spectrum of the black solid showed a typical Dawson-type phosphotungstate and a strong peak at 1950 cm -1 [ Figure 3 (c)] that was assigned to a CO stretching vibration peak for the coordinated carbonyl ligand.…”

A Novel Ruthenium-Decorating Polyoxomolybdate Cs3Na6H[MoVI14RuIV2O50(OH)2]·24H2O: An Active Heterogeneous Oxidation Catalyst for Alcohols

“…Noble metals containing polyoxometalates (POMs), in particular ruthenium (Ru)-incorporating structures [1], have been widely implemented in homo-/heterogeneous oxidation catalysis of both organic [2,3,4,5,6,7,8,9,10,11,12,13] and water-splitting reactions [14,15,16,17,18], and have therefore been attracting ever-increasing attention in recent decades. Since the discovery of the first Ru-containing POM [SiW 11 O 39 RuL] n− in 1989 [2], this domain has been further explored by the research groups of Neumann, Sadakane, Bonchio, Pope, Nomiya, Proust, Hill, Bond, Kortz, Bi and others [19].…”

“…Among them, the wholly inorganic Ru-containing POMs represent an important subclass, which had been studied previously but with only a few structures reported as compared to those with inorganic-organic hybrid Ru-containing POMs. Up until now, the majority of investigations in this area of research have been dominated by the preparations and characterizations of Ru-substituted or -sandwiched lacunary Keggin/Dawson-type heteropolytungstates [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43], such as mono-Ru substituted polyanions [XW 11 O 39 Ru III (H 2 O)] n− (X = Si, Ge, P) [2,3,4,5,20,21,22,23,24,25] and [P 2 W 17 O 61 Ru III (H 2 O)] 5− [26,27,28], di-Ru-sandwiched/substituted polyanions {O[Ru IV (X)P 2 W 17 O 61 ] 2 } 16− (X = OH, Cl) [27], {[(XZnRu 2 III (OH)(H 2 O)](ZnW 9 O 34 ) 2 } n− (X = W, Zn) [29,30,…”