Thiolate-Bridged Dinuclear Ruthenium and Iron Complexes as Robust and Efficient Catalysts toward Oxidation of Molecular Dihydrogen in Protic Solvents

Remarkable Stability of a Molecular Ruthenium Complex in PEM Water Electrolysis

The dinuclear Ru diazadiene olefin complex, [Ru₂(OTf)(μ-H)(Me₂dad)(dbcot)₂], is an active catalyst for hydrogen evolution in a Polymer Exchange Membrane (PEM) water electrolyser. When supported on high surface area carbon black and at 80 °C, [Ru₂(OTf)(μ-H)(Me₂dad)(dbcot)₂]@C evolves hydrogen at the cathode of a PEM electrolysis cell (400 mA cm⁻², 1.9 V). A remarkable turn over frequency (TOF) of 7800 mol_H2 mol_catalyst⁻¹ h⁻¹ is maintained over 7 days of operation. A series of model reactions in homogeneous media and in electrochemical half cells, combined with DFT calculations, are used to rationalize the hydrogen evolution mechanism promoted by [Ru₂(OTf)(μ-H)(Me₂dad)(dbcot)₂].

Molecular dinuclear ruthenium complexes deposited on conducting carbon serve as active sites for the evolution of hydrogen from neutral water in a Polymer Exchange Membrane (PEM) water electrolyser.

4-Coordinated, 14-electron ruthenium(ii) chalcogenolate complexes: synthesis, electronic structure and reactions with PhICl2 and organic azides

The 4-coordinated Ru^II chalcogenolate complexes [Ru(STipp)₂(PPh₃)₂] (Tipp = 2,4,6-triisopropylphenyl, 1) and [Ru(SeMes)₂(PPh₃)₂] (Mes = 2,4,6-trimethylphenyl, 2) have been synthesized, and their reactions with PhICl₂ and organic azides have been studied. Complex 2 synthesized from [Ru^II(PPh₃)₃Cl₂] and NaSeMes displays a seesaw structure with P-Ru-P and Se-Ru-Se bond angles of 103.43(13) and 145.26(6)°, respectively. Natural bond order analyses revealed that in each of 1 and 2, there are two n →σ* (donor-acceptor) π interactions between the chalcogen lone pairs and the Ru-P antibonding molecular orbitals. The calculated second-order perturbation interaction energies of the two interactions for 1 (20.5 and 18.3 kcal mol^-1) are stronger than those of 2 (13.6 and 11.0 kcal mol^-1), suggesting the thiolate ligand (TippS^-) is a stronger π-donor than the selenolate ligand (MesSe^-) with respect to Ru^II. Chlorination of 1 with PhICl₂ afforded the dichloride complex [Ru(STipp)₂Cl₂(PPh₃)] (3), which was hydrolyzed to the hydroxo complex [Ru(STipp)₂(OH)Cl(PPh₃)] (4) after column chromatography on silica in air. Treatment of 4 with HCl and methyl triflate gave 3 and [Ru(STipp)₂(OH)(OTf)(PPh₃)] (OTf = triflate, 5), respectively. Reactions of 1 and 2 with p-tolyl azide (p-tolN₃) afforded the tetrazene complexes [Ru{N₄(p-tol)₂}(ER)₂(PPh₃)] (ER = STipp (6), SeMes (7)), whereas that with tosyl azide (TsN₃) gave the imido complexes [Ru(κ²-NTs)(STipp)₂(PPh₃)] (ER = STipp (8), SeMes (10)). The short Ru-N_imido distances in 8 [1.883(3) Å] and 10 [1.892(2) Å] are indicative of multiple bond character. Treatment of 8 with TsN₃ afforded the tetrazene complex [Ru(N₄Ts₂)(STipp)₂(PPh₃)] (9), but no cycloaddition was found between 10 and TsN₃. Nucleophilic attack of the imido ligand in 10 with methyl triflate yielded the amido complex [Ru(κ²-NMeTs)(SeMes)₂(PPh₃)](OTf) (11). The crystal structures of 2, 4, 6, and 8-11 have been determined.

A low-valent dinuclear ruthenium diazadiene complex catalyzes the oxidation of dihydrogen and reversible hydrogenation of quinones

The dinuclear ruthenium complex [Ru2H(μ-H)(Me2dad)(dbcot)2] contains a 1,4-dimethyl-diazabuta-1,3-diene (Me2dad) as a non-innocent bridging ligand between the metal centers to give a [Ru2(Me2dad)] core. In addition, each ruthenium is bound to one dibenzo[a,e]cyclooctatetraene (dbcot) ligand. This Ru dimer converts H2 to protons and electrons. It also catalyzes reversibly under mild conditions the selective hydrogenation of vitamins K2 and K3 to their corresponding hydroquinone equivalents without affecting the C[double bond, length as m-dash]C double bonds. Mechanistic studies suggest that the [Ru2(Me2dad)] moiety, like hydrogenases, reacts with H2 and releases electrons and protons stepwise.

Biomimetic catalytic oxidative coupling of thiols using thiolate-bridged dinuclear metal complexes containing iron in water under mild conditions

A green approach to disulfides via aerobic oxidative coupling of thiols was developed with a thiolate-bridged heteronuclear complex in water.

Syntheses and crystal structures of ruthenium complexes with bidentate salicylaldiminato and dithiophosphato ligands

Treatment of the bidentate Schiff base 2-[(2,6-diisopropyl-phenylimino)-methyl]-phenol (HL1) with one equivalent of (Et4N)[RuCl4(MeCN)2] in the presence of triethylamine afforded (Et4N)[RuCl3(κ 2-N,O-L1)(MeCN)] (1), which reacted with two equivalents of K[S2P(O i Pr)2] to produce a neutral ruthenium(III) complex [Ru(κ 2-N,O-L1){η 2-S2P(O i Pr)2}2] (2) bearing both salicylaldiminato and dithiophosphato ligands. Reactions of the bidentate Schiff bases 2-[(3-chloro-phenylimino)-methyl]-phenol (HL2) and 2-[(2,4,6-trimethyl-phenylimino)-methyl]-phenol (HL3) with one equivalent of [Ru(CO)2Cl2] in the presence of triethylamine led to formation of the corresponding anionic ruthenium(II) carbonyl complexes (Et3NH)[RuCl2(κ 2-N,O-L2)(CO)2] (3) and (Et3NH)[RuCl2(κ 2-N,O-L3)(CO)2] (4). The molecular structures of complexes 2–4 have been determined by single-crystal X-ray diffraction.

Reactant or reagent? Oxidation of H2 at electronically distinct nickel-thiolate sites [Ni2(μ-SR)2]+ and [Ni–SR]+

The chemical bond between a Lewis-acidic metal and a Brønsted/Lewis-basic sulphur donor provides M–S structures with functional properties that are relevant for a variety of processes such as the heterolytic cleavage of H₂.

Catalytic Activity of Thiolate-Bridged Diruthenium Complexes Bearing Pendent Ether Moieties in the Oxidation of Molecular Dihydrogen

Thiolate-bridged diruthenium complexes bearing pendent ethers have been found to work as effective catalysts toward the oxidation of molecular dihydrogen into protons and electrons in water. The pendent ether moiety in the complex plays an important role to facilitate the proton transfer between the metal center and the external proton acceptor.