Search

Oxidative degradation and transformation of catalysts are commonly observed in water oxidation by molecular catalysts, especially when a highly oxidizing reagent such as (NH4)2[Ce(NO3)6] [Ce(IV)] is used. We report herein the synthesis of a ruthenium(III) complex bearing an oxidative resistant bipyridine-bis(alkoxide) ligand, [Ru(bdalk)(pic)2]+ (1, H2bdalk = 2,2′-([2,2′-bipyridine]-6,6′-diyl)bis(propan-2-ol), pic = 4-picoline) as a water oxidation catalyst (WOC). A ruthenium(II) nitrosyl complex [Ru(Hbdalk)(NO)(pic)2]2+ (3) was also formed during the water oxidation process by 1/Ce(IV), and was isolated and structurally characterized. Complex 3 was found to be an active WOC, with the nitrosyl group remaining intact during water oxidation.

The development of efficient and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is of intense interest because H2 is one of the most promising renewable energy sources. Herein, we report a highly efficient and stable HER electrocatalyst composed of ruthenium nanoparticles embedded in nitrogen-doped carbon (NC), which is synthesized via a simple thermolysis process using a ruthenium complex as metal precusor and using ethylenediaminetetraacetic acid tetrasodium (Na4EDTA) salt as ligand and carbon source. It is found that the amount of Na4EDTA employed plays an important role in achieving sutiable and uniform Ru nanoparticles. The resulting Ru@NC(1 : 5) was found to exhibit excellent HER activity and robust stability in alkaline media (1.0 M KOH) with a low overpotential at 10 mA cm−2 (29 mV), small Tafel slope (27 mV per decade) and a high turnover frequency (TOF) of 0.96 s−1 at an overpotential of 50 mV, which are comparable to the state-of-the-art commercial Pt/C catalyst. Based on the characterization of the samples and the electrochemical measurements, this high performance of Ru@NC(1 : 5) is ascribed to its smallest particle size (ca. 2.1 nm diameter), large active site density and the high electrochemical conductivity by the N-doped carbon support. In addition, Ru@NC(1 : 5) also works well in acidic media (0.5 M H2SO4) indicating it is a pH-universal catalyst.

The reduction of metal nitride to ammonia is a key step in biological and chemical nitrogen fixation. We report herein the facile reduction of a ruthenium(VI) nitrido complex [(L)RuVI(N)(OH2)]+ (1, L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) to [(L)RuIII(NH3)(OH2)]+ by l-cysteine (Cys), an ubiquitous biological reductant, in aqueous solution. At pH 1.0–5.3, the reaction has the following stoichiometry: [(L)RuVI(N)(OH2)]+ + 3HSCH2CH(NH3)CO2 → [(L)RuIII(NH3)(OH2)]+ + 1.5(SCH2CH(NH3)CO2)2. Kinetic studies show that at pH 1 the reaction consists of two phases, while at pH 5 there are three distinct phases. For all phases the rate law is rate = k2[1][Cys]. Studies on the effects of acidity indicate that both HSCH2CH(NH3+)CO2– and –SCH2CH(NH3+)CO2– are kinetically active species. At pH 1, the reaction is proposed to go through [(L)RuIV(NHSCH2CHNH3CO2H)(OH2)]2+ (2a), [(L)RuIII(NH2SCH2CHNH3CO2H)(OH2)]2+ (3), and [(L)RuIV(NH2)(OH2)]+ (4) intermediates. On the other hand, at pH around 5, the proposed in...

Water oxidation catalysts (WOCs) based on transition metal complexes often undergo oxidative degradation of the ligands, leading to unidentifiable products. We report here the use of a ruthenium(III) complex bearing a bpy-bis(phenoxy) ligand, [Ru(L)(pic)2]+ (1, H2L = 6,6'-bis(2-hydroxyphenyl)-2,2'-bipyridine, pic = 4-picoline) as WOC. This phenoxy-type ligand in 1 is readily oxidized by Ce(IV) in aqueous acidic medium to give a ruthenium bpy-dicarboxylate complex ([Ru(bda)(pic)2]+) via ruthenium bpy-phenoxybenzoquinone (1') and ruthenium bpy-bis(benzoquinone) (1'') intermediates. All four ruthenium species can oxidize water, however 1 and 1' are rapidly oxidized to 1" by Ce(IV). On the other hand, 1" is robust enough that it is responsible for the majority of O2 evolution before finally oxidized to CO2 and [Ru(bda)(pic)2], the latter species is a highly active WOC.

A series of luminescent carbonyl hydrido ruthenium(II) complexes with various diimine ligands with diverse electronic properties, including Me2bpy (bpy = bipyridine), Me2phen (phen = phenanthroline), PhenCOOH, PhenCN, Me2Ph2phen, Ph2phen, and π-conjugating dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq), dipyrido[3,2-a:2′,3′-c](6,7,8,9-tetrahydro)phenazine (dpqc), and dipyridophenazine (dppz) have been synthesized and characterized. Four of these complexes have been structurally characterized by X-ray crystallography. The photophysical and electrochemical properties of these complexes have been studied. The effects of the electronic features and π-conjugation of the diimine ligand on the electronic and photophysical properties of these complexes have also been discussed. Our study revealed that the luminescence performance of these complexes could be significantly enhanced by increasing the rigidity and π-conjugation of the diimine ligand.

Two bis(2,2′-bipyridyl)ruthenium(II) complexes bearing hydroxy-substituted diimine ligands [RuII(bpy)2(N-N)](BF4)2 (N-N = phenOH or bpyOH) have been synthesized and characterized. These complexes can be readily deprotonated under basic conditions to yield the deprotonated forms [RuII(bpy)2(N-N)](BF4) (N-N = phenO– or bpyO–). The structures of one of the complexes and its deprotonated form have been determined by X-ray crystallography. The photophysical and electrochemical properties of these complexes have been examined. Detailed photophysical studies showed that the luminescent properties of these complexes are sensitive to the nature of the solvent media. In addition, the emission properties of these complexes exhibit a strong dependence on the pH of the aqueous medium, and hence these complexes are potentially useful as phosphorescent pH probes.

The kinetics and mechanism of the reaction of S(IV) (SO3 (2-) +HSO3 (-) ) with a ruthenium(VI) nitrido complex, [(L)Ru(VI) (N)(OH2 )](+) (Ru(VI) N, L=N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion), in aqueous acidic solutions are reported. The kinetic results are consistent with parallel pathways involving oxidation of HSO3 (-) and SO3 (2-) by Ru(VI) N. A deuterium isotope effect of 4.7 is observed in the HSO3 (-) pathway. Based on experimental results and DFT calculations the proposed mechanism involves concerted N-S bond formation (partial N-atom transfer) between Ru(VI) N and HSO3 (-) and H(+) transfer from HSO3 (-) to a H2 O molecule.

Seven-coordinate ruthenium oxo species have been proposed as active intermediates in catalytic water oxidation by a number of highly active ruthenium catalysts, however such species have yet to be isolated. Reported herein is the first example of a seven-coordinate group 8 metal-oxo species, [Os(V)(O)(qpy)(pic)Cl](2+) (qpy = 2,2':6',2'':6'',2'''-quaterpyridine, pic = 4-picoline). The X-ray crystal structure of this complex shows that it has a distorted pentagonal bipyramidal geometry with an Os=O distance of 1.7375 Å. This oxo species undergoes facile O-atom and H-atom-transfer reactions with various organic substrates. Notably it can abstract H atoms from alkylaromatics with C-H bond dissociation energy as high as 90 kcal mol(-1). This work suggests that highly active oxidants may be designed based on group 8 seven-coordinate metal oxo species.

A cancer-cell selective bis(guanidine)-ruthenium(iii) complex induces apoptosis, whereas its amidine analogue effectively kills cancer cells through paraptosis pathways., Two novel series of (salen)ruthenium(iii) complexes bearing guanidine and amidine axial ligands were synthesized, characterized, and evaluated for anticancer activity. In vitro cytotoxicity tests demonstrate that these complexes are cytotoxic against various cancer cell lines and the leading complexes have remarkable cancer-cell selectivity. A detailed study of the guanidine complex 7 and the amidine complex 13 reveals two distinguished modes of action. Complex 7 weakly binds to DNA and induces DNA damage, cell cycle arrest, and typical apoptosis pathways in MCF-7 cells. In contrast, complex 13 induces paraptosis-like cell death hallmarked by massive vacuole formation, mitochondrial swelling, and ER stress, resulting in significant cytotoxicity against human breast cancer cells. Our results provide an extraordinary example of tuning the mechanism of action of (salen)ruthenium(iii) anticancer complexes by modifying the structure of the axial ligands.

Polypyridyl and related ligands have been widely used for the development of water oxidation catalysts. Supposedly these ligands are oxidation-resistant and can stabilize high-oxidation-state intermediates. In this work a series of ruthenium(II) complexes [Ru(qpy)(L)2 ](2+) (qpy=2,2':6',2'':6'',2'''-quaterpyridine; L=substituted pyridine) have been synthesized and found to catalyze Ce(IV) -driven water oxidation, with turnover numbers of up to 2100. However, these ruthenium complexes are found to function only as precatalysts; first, they have to be oxidized to the qpy-N,N'''-dioxide (ONNO) complexes [Ru(ONNO)(L)2 ](3+) which are the real catalysts for water oxidation.

In the presence of pyridine, [RuVI(N)(L)(MeOH)]+ (L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) readily oxidizes hydroquinone to p-benzoquinone under ambient conditions. Experimental and computational studies suggest a mechanism that involves an initial electrophilic attack at the aromatic ring of hydroquinone by the nitrido ligand.

Proton-coupled electron-transfer reactions of phenols have received considerable attention because of their fundamental interest and their relevance to many biological processes. Here we describe a remarkable four-electron oxidation of phenols by a (salen)ruthenium(VI) complex in the presence of pyridine in CH3OH to afford (salen)ruthenium(II) p-benzoquinone imine complexes. Mechanistic studies indicate that this reaction occurs in two phases. The first phase is proposed to be a two-electron transfer process that involves electrophilic attack by Ru≡N at the phenol aromatic ring, followed by proton shift to generate a Ru(IV) p-hydroxyanilido intermediate. In the second phase the intermediate undergoes intramolecular two-electron transfer, followed by rapid deprotonation to give the Ru(II) p-benzoquinone imine product.

Reaction of [RuII(PR3)3Cl2] with 2-methyl-8-quinolinolate (MeQ) in the presence of Et3N in MeOH produced the neutral carbonyl hydrido complexes [RuII(MeQ)(PR3)2(CO)(H)] (R = Ph (1), MeC6H4 (2), MeO...

Kinetic and mechanistic studies on the intermolecular activation of strong C-H bonds of alkanes by a (salen)ruthenium(VI) nitride were performed. The initial, rate-limiting step, the hydrogen atom transfer (HAT) from the alkane to Ru(VI)≡N, generates Ru(V)=NH and RC·HCH(2)R. The following steps involve N-rebound and desaturation.

A polypyridyl ruthenium(II) complex, cis-[RuII(2,9-Me2phen)2(H2O)2]2+, has been adsorbed onto the cation-exchange resins Dowex-50W and Chelex-100. The potential use of the supported ruthenium(II) complex as catalyst for the oxidative degradation of organic pollutants in water has been investigated using bisphenol A, an emerging endocrine disruptor, as substrate; and the environmentally friendly H2O2 as oxidant. These solid-supported catalysts are found to be efficient for the degradation of bisphenol A in aqueous solution by H2O2 under ambient conditions. The intermediates and products formed during the oxidative degradation of bisphenol A by these catalytic systems have been identified and a mechanism is proposed. The supported catalysts are easily recovered by simple filtration and display no loss of activity when recycled.

Four cyano-bridged 1D bimetallic polymers have been prepared by using the paramagnetic building block trans-[Ru(acac)(2)(CN)(2)](-) (Hacac=acetylacetone): {[{Ni(tren)}{Ru(acac)(2)(CN)(2)}][ClO(4)].CH(3)OH}(n) (1) (tren=tris(2-aminoethyl)amine), {[{Ni(cyclen)}{Ru(acac)(2)(CN)(2)}][ClO(4)].CH(3)OH}(n) (2) (cyclen=1,4,7,10-tetraazacyclododecane), {[{Fe(salen)}{Ru(acac)(2)(CN)(2)}]}(n) (3) (salen(2-)=N,N'-bis(salicylidene)-o-ethyldiamine dianion) and [{Mn(5,5'-Me(2)salen)}(2){Ru(acac)(2)(CN)(2)}][Ru(acac)(2)(CN)(2)].2CH(3)OH (4) (5,5'-Me(2)salen=N,N'-bis(5,5'-dimethylsalicylidene)-o-ethylenediimine). Compounds 1 and 2 are 1D, zigzagged NiRu chains that exhibit ferromagnetic coupling between Ni(II) and Ru(III) ions through cyano bridges with J=+1.92 cm(-1), zJ'=-1.37 cm(-1), g=2.20 for 1 and J=+0.85 cm(-1), zJ'=-0.16 cm(-1), g=2.24 for 2. Compound 3 has a 1D linear chain structure that exhibits intrachain ferromagnetic coupling (J=+0.62 cm(-1), zJ'=-0.09 cm(-1), g=2.08), but antiferromagnetic coupling occurs between FeRu chains, leading to metamagnetic behavior with T(N)=2.6 K. In compound 4, two Mn(III) ions are coordinated to trans-[Ru(acac)(2)(CN)(2)](-) to form trinuclear Mn(2)Ru units, which are linked together by pi-pi stacking and weak Mn...O* interactions to form a 1D chain. Compound 4 shows slow magnetic relaxation below 3.0 K with phi=0.25, characteristic of superparamagnetic behavior. The Mn(III)...Ru(III) coupling constant (through cyano bridges) and the Mn(III)...Mn(III) coupling constant (between the trimers) are +0.87 and +0.24 cm(-1), respectively. Compound 4 is a novel single-chain magnet built from Mn(2)Ru trimers through noncovalent interactions. Density functional theory (DFT) combined with the broken symmetry state method was used to calculate the molecular magnetic orbitals and the magnetic exchange interactions between Ru(III) and M (M=Ni(II), Fe(III), and Mn(III)) ions. To explain the somewhat unexpected ferromagnetic coupling between low-spin Ru(III) and high-spin Fe(III) and Mn(III) ions in compounds 3 and 4, respectively, it is proposed that apart from the relative symmetries, the relative energies of the magnetic orbitals may also be important in determining the overall magnetic coupling in these bimetallic assemblies.

The reaction of [Ru(VI)(N)(L)(MeOH)](PF(6)) [1; L = N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion] with a stoichiometric amount of RSH in CH(3)CN gives the corresponding (salen)ruthenium(IV) sulfilamido species [Ru(IV){N(H)SR}(L)(NCCH(3))](PF(6)) (2a, R = (t)Bu; 2b, R = Ph). Metathesis of 2a with NaN(3) in methanol affords [Ru(IV){N(H)S(t)Bu}(L)(N(3))] (2c). 2a undergoes further reaction with 1 equiv of RSH to afford a (salen)ruthenium(III) sulfilamine species, [Ru(III){N(H)(2)S(t)Bu}(L)(NCCH(3))](PF(6)) (3). On the other hand, 2b reacts with 2 equiv of PhSH to give a (salen)ruthenium(III) ammine species [Ru(III)(NH(3))(L)(NCCH(3))](PF(6)) (4); this species can also be prepared by treatment of 1 with 3 equiv of PhSH. The X-ray structures of 2c and 4 have been determined. Kinetic studies of the reaction of 1 with excess RSH indicate the following schemes: 1 --2a --3 (R = (t)Bu), 1 --2b --4 (R = Ph). The conversion of 1 to 2 probably involves nucleophilic attack of RSH at the nitrido ligand, followed by a proton shift. The conversions of 2a to 3 and 2b to 4 are proposed to involve rate-limiting H-atom abstraction from RSH by 2a or 2b. 2a and 2b are also able to abstract H atoms from hydrocarbons with weak C-H bonds. These reactions occur with large deuterium isotope effects; the kinetic isotope effect values for the oxidation of 9,10-dihydroanthracene, 1,4-cyclohexadiene, and fluorene by 2a are 51, 56, and 11, respectively.

A series of ruthenium(II) bis(8-quinolinolato) complexes bearing isocyanide ligands (RNC) have been synthesized by the reaction of [RuQ3] (Q = 8-quinolinolate) with RNC in the presence of Zn/Hg. These complexes have the general formula [RuQ2(RNC)2] (1, R = tert-butyl; 2, R = 4-MeOPh; 3, R = 4-ClPh; 4, R = 2,4,6-Br3Ph). Both the yellow cis,cis,trans (a) and orange-red trans,trans,trans (b) isomers have been isolated for complexes 1−4. trans,trans,trans-[Ru(Tol-Q)2(tBuNC)2] (6, HTol-Q = 8-hydroxyl-5-tolylquinoline) has also been prepared from [Ru(PPh3)2Cl2]. The structures of 2a, 3a, and 4b have been determined by X-ray crystallography. These complexes exhibit an intense absorption band in the UV region (λmax = 320−390 nm) with molar extinction coefficients (e) on the order of 104 dm3 mol−1 cm−1 and a moderately intense absorption with e on the order of 103 dm3 mol−1 cm−1 at 400−492 nm. The intense absorption at 320−390 nm is assigned to the ligand-centered π→π* transitions of the quinolinolate ligands, pro...

Reduction of RuQ3 (1a, Q = 8-quinolinolato) with Zn/Hg in the presence of various π-acceptor ligands in ethanol affords RuQ2L2 (L2 = (dimethylsulfoxide)2 (2); (4-picoline)2 (3); N,N′-dimethyl-1,4-diazabuta-1,3-diene, dab (4); cyclooctadiene, COD (5); norborna-2,5-diene, nbd (6)). Compound 6 is isolated as an equimolar mixture of cis,trans (6a) and trans,cis (6b) isomers, which can be separated by column chromatography. DFT calculations have been performed on 6a and 6b. Oxidation of 3 and 6b affords the corresponding ruthenium(III) species 7 and 8, respectively. The structures of 2, 3, 4 and 6 have been determined by X-ray crystallography.

Reaction of [Ru (VI)(N)(L (1))(MeOH)] (+) (L (1) = N, N'-bis(salicylidene)- o-cyclohexylenediamine dianion) with excess pyridine in CH 3CN produces [Ru (III)(L (1))(py) 2] (+) and N 2. The proposed mechanism involves initial equilibrium formation of [Ru (VI)(N)(L (1))(py)] (+), which undergoes rapid N...N coupling to produce [(py)(L (1))Ru (III) N N-Ru (III)(L (1))(py)] (2+); this is followed by pyridine substituion to give the final product. This ligand-induced N...N coupling of Ru (VI)N is utilized in the preparation of a series of new ruthenium(III) salen complexes, [Ru (III)(L)(X) 2] (+/-) (L = salen ligand; X = H 2O, 1-MeIm, py, Me 2SO, PhNH 2, ( t )BuNH 2, Cl (-) or CN (-)). The structures of [Ru (III)(L (1))(NH 2Ph) 2](PF 6) ( 6), K[Ru (III)(L (1))(CN) 2] ( 9), [Ru (III)(L (2))(NCCH 3) 2][Au (I)(CN) 2] ( 11) (L (2) = N, N'-bis(salicylidene)- o-phenylenediamine dianion) and [N ( n )Bu 4][Ru (III)(L (3))Cl 2] ( 12) (L (3) = N, N'-bis(salicylidene)ethylenediamine dianion) have been determined by X-ray crystallography.

This review summarizes the kinetics and mechanisms of the oxidation of various inorganic and organic substrates by trans -dioxoruthenium(VI) complexes containing macrocyclic tertiary amine ligands during the period 1993–2006.

The oxidation of ascorbic acid (H2A) by [Ru(VI)(N)(L)(MeOH)](+) in aqueous acidic solutions has the following stoichiometry: 2[Ru(VI)(N)] + 3H2A → 2[Ru(III)(NH2-HA)](+) + A. Mechanisms involving HAT/N-rebound at low pH (≤2) and nucleophilic attack at the nitride at high pH (≥5) are proposed.

The dimetallic compounds [Ni(2,3,2-tet)]2[Ru(CN)6]·8H2O (1), [Ni(pn)2]2[Ru(CN)6]·5H2O (2) [Ni(tacd)(H2O)]2[Ru(CN)6]·8H2O (3) and {[Cu(dipn)]3[Ru(CN)6]}(ClO4)2·4H2O (4) [2,3,2-tet = N,N′-bis(2-aminoethyl)-1,3-propanediamine, pn = 1,3-diaminopropane, tacd = 1,5,9-triazacyclododecane, dipn = dipropylenetriamine] have been prepared from the reaction of [Ru(CN)6]4− with [Ni(2,3,2-tet)]2+, [Ni(pn)2]2+, [Ni(tacd)(H2O)]2+ and [Cu(dipn)]2+, respectively. Compounds 1 and 2 contain a two-dimensional square network, compound 3 has a one-dimensional, crossed-double chain structure, while compound 4 has an unusual, two-dimensional, double-edged, honeycomb network. A very weak antiferromagnetic interaction is observed in 2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride.

The ruthenium(II) complex cis-[Ru(6, 6'-Cl(2)bpy)(2)(OH(2))(2)](CF(3)SO(3))(2) (1) is a robust catalyst for C-H bond oxidations of hydrocarbons, including linear alkanes, using tert-butyl hydroperoxide (TBHP) as terminal oxidant. Alcohols can be oxidized by the "1 + TBHP" protocol to the corresponding aldehydes/ketones with high product yields at ambient temperature. Oxidation of 1 with Ce(IV) in aqueous solution affords cis-[Ru(VI)(6, 6'-Cl(2)bpy)(2)O(2)](2+), which is isolated as a green/yellow perchlorate salt (2). Complex 2 is a powerful stoichiometric oxidant for cycloalkane oxidations under mild conditions. Oxidation of cis-decalin is highly stereoretentive; cis-decalinol is obtained in high yield, and formation of trans-decalinol is not observed. Mechanistic studies showing a large primary kinetic isotope effect suggest a hydrogen-atom abstraction pathway. The relative reactivities of cycloalkanes toward oxidation by 2 have been examined through competitive experiments, and comparisons with Gif-type processes are presented.

Hydrogen-bridged dinuclear ruthenium carbene complexes supported by salen have been prepared and found to be active catalysts for the cyclopropanation of alkenes; electrochemical and theoretical studies suggest the existence of electronic communication between the Ru centers.

An efficient catalyst is applied to the oxidation of secondary- and primary alcohols to the corresponding ketones (II) or mixtures of aldehydes (IV) and carboxylic acids (V) with excellent conversions at room temperature.

Nitrido complexes (M≡N) may be key intermediates in chemical and biological nitrogen fixation and serve as useful reagents for nitrogenation of organic compounds. Osmium(VI) nitrido complexes bearing 2,2':6',2″-terpyridine (terpy), 2,2'-bipyridine (bpy), or hydrotris(1-pyrazolyl)borate anion (Tp) ligands are highly electrophilic: they can react with a variety of nucleophiles to generate novel osmium(IV)/(V) complexes. This Account describes our recent results studying the reactivity of nitridocomplexes of ruthenium(VI), osmium(VI), and manganese(V) that bear Schiff bases and other simple anionic ligands. We demonstrate that these nitrido complexes exhibit rich chemical reactivity. They react with various nucleophiles, activate C-H bonds, undergo N···N coupling, catalyze the oxidation of organic compounds, and show anticancer activities. Ruthenium(VI) nitrido complexes bearing Schiff base ligands, such as [Ru(VI)(N)(salchda)(CH3OH)](+) (salchda = N,N'-bis(salicylidene)o-cyclohexyldiamine dianion), are highly electrophilic. This complex reacts readily at ambient conditions with a variety of nucleophiles at rates that are much faster than similar reactions using Os(VI)≡N. This complex also carries out unique reactions, including the direct aziridination of alkenes, C-H bond activation of alkanes and C-N bond cleavage of anilines. The addition of ligands such as pyridine can enhance the reactivity of [Ru(VI)(N)(salchda)(CH3OH)](+). Therefore researchers can tune the reactivity of Ru≡N by adding a ligand L trans to nitride: L-Ru≡N. Moreover, the addition of various nucleophiles (Nu) to Ru(VI)≡N initially generate the ruthenium(IV) imido species Ru(IV)-N(Nu), a new class of hydrogen-atom transfer (HAT) reagents. Nucleophiles also readily add to coordinated Schiff base ligands in Os(VI)≡N and Ru(VI)≡N complexes. These additions are often stereospecific, suggesting that the nitrido ligand has a directing effect on the incoming nucleophile. M≡N is also a potential platform for the design of new oxidation catalysts. For example, [Os(VI)(N)Cl4](-) catalyzes the oxidation of alkanes by a variety of oxidants, and the addition of Lewis acids greatly accelerates these reactions. [Mn(V)(N)(CN)4]2(-) is another highly efficient oxidation catalyst, which facilitates the epoxidation of alkenes and the oxidation of alcohols to carbonyl compounds using H2O2. Finally, M≡N can potentially bind to and exert various effects on biomolecules. For example, a number of Os(VI)≡N complexes exhibit novel anticancer properties, which may be related to their ability to bind to DNA or other biomolecules.

Chemical and visible-light-driven water oxidation catalyzed by a number of Ni complexes and salts have been investigated at pH 7-9 in borate buffer. For chemical oxidation, [Ru(bpy)3](3+) (bpy = 2,2'-bipyridine) was used as the oxidant, with turnover numbers (TONs) >65 and a maximum turnover frequency (TOFmax) >0.9 s(-1). Notably, simple Ni salts such as Ni(NO3 )2 are more active than Ni complexes that bear multidentate N-donor ligands. The Ni complexes and salts are also active catalysts for visible-light-driven water oxidation that uses [Ru(bpy)3](2+) as the photosensitizer and S2 O8 (2-) as the sacrificial oxidant; a TON>1200 was obtained at pH 8.5 by using Ni(NO3)2 as the catalyst. Dynamic light scattering measurements revealed the formation of nanoparticles in chemical and visible-light-driven water oxidation by the Ni catalysts. These nanoparticles aggregated during water oxidation to form submicron particles that were isolated and shown to be partially reduced β-NiOOH by various techniques, which include SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, XRD, and IR spectroscopy. These results suggest that the Ni complexes and salts act as precatalysts that decompose under oxidative conditions to form an active nickel oxide catalyst. The nature of this active oxide catalyst is discussed.

We report experimental and computational studies of the facile oxidative C-N bond cleavage of anilines by a (salen)ruthenium(VI) nitrido complex. We provide evidence that the initial step involves nucleophilic attack of aniline at the nitrido ligand of the ruthenium complex, which is followed by proton and electron transfer to afford a (salen)ruthenium(II) diazonium intermediate. This intermediate then undergoes unimolecular decomposition to generate benzene and N2.

cis-[Ru(2,9-Me(2)phen)(2)(OH(2))(2)](2+) reacts readily with chlorite at room temperature at pH 4.9 and 6.8. The ruthenium(II) complex can catalyze the disproportionation of chlorite to chlorate and chloride, the oxidation of chlorite to chlorine dioxide, as well as the oxidation of alcohols by chlorite.

An insertion reaction of nitrosonium ion (NO+) into the metal−carbon bond of cyclometalated ruthenium(II) complexes is prepared with experimental evidence supporting a bimolecular direct NO+ insertion into the metal−carbon bond (i.e., M−R + NO+ → [M−N(═O)−R]+) but not an intramolecular migratory insertion (i.e., R−M−(NO) + L → L−M−N(═O)R) as the reaction mechanism. Theoretical calculations suggest that the direct NO+ insertion into the M−C bond may be rationalized as a frontier orbital interaction between the [Ru−aryl]-dominated HOMO of the Ru(II) complexes and the LUMO of the NO+. Accepted version

Cyano-mediated interaction of the alternating high-spin Mn(II) centers and low-spin Ru(III) centers in {Mn[Ru(acac)2 (CN)2 ]2 }n (Hacac=acetylacetone) results in long-range ferromagnetic ordering below 3.6 K. This novel Mn(II) Ru(III) coordination polymer, which has a diamond-like structure, was constructed from [Ru(acac)2 (CN)2 ](-) and Mn(2+) ions.

The synthesis and characterization of [RuII(terpy)(dcbipy)(H2O)]2+(terpy = 2,2′:6′,2″-terpyridine; dcbipy = 6,6′-dichloro-2,2′-bipyridine) are described. Oxidation of this complex with CeIV gave [RuIV(terpy)(dcbipy)O]2+, isolated as a greenish yellow perchlorate salt. The RuIVO complex is paramagnetic (µeff= 2.83) and exhibits a RuO stretch at 780 cm–1. It is a powerful oxidant with E°(RuIV–RuIII)= 1.13 V vs. saturated calomel electrode at pH 1.0 and can selectively oxidize the tertiary C–H bond of adamantane. The mechanism of alkene oxidation by RuIVO has been investigated and discussed. The complex [RuII(terpy)(dcbipy)(H2O)]2+ is a robust catalyst for the oxidation of saturated alkanes by tert-butyl hydroperoxide.

Reaction of excess cyanide with a ruthenium(VI) nitrido complex bearing a tridentate Schiff base ligand produces a novel tricyanoruthenium(III) complex in which nucleophilic substitution of an imine hydrogen of the Schiff base by cyanide has occurred, this complex is a useful building block for the construction of 3d-Ru(III) magnetic materials.

The treatment of [Ru(VI)(N)(L)(MeOH)]PF(6) (1) (L = N,N'-bis(salicylidene)-o-cyclohexyldiamine dianion) with 2 equiv of RNC (R = (a) (t)Bu, (b) Cy) in CH(2)Cl(2) affords a mixture of blue cis-beta-[Ru(III)(NCNR)(L)(CNR)] (2) and green trans-[Ru(III)(L)(CNR)(2)]PF(6) (3) products. The reduction of 3 with a stoichiometric amount of Cp(2)Co in CH(3)CN gives red trans-[Ru(II)(L)(CNR)(2)] (4). Refluxing 4 with 3 equiv of RNC in methanol in the presence of 5 equiv of NH(4)PF(6) affords a yellow complex, mer-[Ru(II)(eta(3)-HL)(CNR)(3)](PF(6)) (5), in which the ligand is in an eta(3)-coordination mode. These complexes are characterized by IR, UV-vis, ESI-MS, CV, magnetic measurements, and CHN elemental analysis. The structures of 2a, 3a, 4a, 4b, and 5a have been determined by X-ray crystallography.

The synthesis and characterization of [RuII(terpy)(dcbipy)(H2O)]2+(terpy = 2,2′:6′,2″-terpyridine; dcbipy = 6,6′-dichloro-2,2′-bipyridine) are described. Oxidation of this complex with CeIV gave [RuIV(terpy)(dcbipy)O]2+, isolated as a greenish yellow perchlorate salt. The RuIVO complex is paramagnetic (µeff= 2.83) and exhibits a RuO stretch at 780 cm–1. It is a powerful oxidant with E°(RuIV–RuIII)= 1.13 V vs. saturated calomel electrode at pH 1.0 and can selectively oxidize the tertiary C–H bond of adamantane. The mechanism of alkene oxidation by RuIVO has been investigated and discussed. The complex [RuII(terpy)(dcbipy)(H2O)]2+ is a robust catalyst for the oxidation of saturated alkanes by tert-butyl hydroperoxide.

The oxidation of ascorbic acid (H(2)A) by a trans-dioxoruthenium(VI) species, trans-[Ru(VI)(tmc)(O)(2)](2+) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), has been studied in aqueous solutions under argon. The reaction occurs in two phases: trans-[Ru(VI)(tmc)(O)(2)](2+) + H(2)A --trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + A, trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + H(2)A --trans-[Ru(II)(tmc)(OH(2))(2)](2+) + A. Further reaction involving anation by H(2)A occurs, and the species [Ru(III)(tmc)(A(2-))(MeOH)](+) can be isolated upon aerial oxidation of the solution at the end of phase two. The rate laws for both phases are first-order in both Ru(VI) and H(2)A, with the second-order rate constants k(2) = (2.58 +/- 0.04) x 10(3) M(-1) s(-1) at pH = 1.19 and k(2)' = (1.90 +/- 0.03) M(-1) s(-1) at pH = 1.24, T = 298 K and I = 0.1 M for the first and second phase, respectively. Studies on the effects of acidity on k(2) and k(2)(') suggest that HA(-) is the kinetically active species. Kinetic studies have also been carried out in D(2)O, and the deuterium isotope effects for oxidation of HA(-) by Ru(VI) and Ru(IV) are 5.0 +/- 0.3 and 19.3 +/- 2.9, respectively, consistent with a hydrogen atom transfer (HAT) mechanism for both phases. A linear correlation between log(rate constants) for oxidation by Ru(VI) and the O-H bond dissociation energies of HA(-) and hydroquinones is obtained, which also supports a HAT mechanism.

The kinetics and mechanisms of the oxidation of I (-) and Br (-) by trans-[Ru (VI)(N 2O 2)(O) 2] (2+) have been investigated in aqueous solutions. The reactions have the following stoichiometry: trans-[Ru (VI)(N 2O 2)(O) 2] (2+) + 3X (-) + 2H (+) --> trans-[Ru (IV)(N 2O 2)(O)(OH 2)] (2+) + X 3 (-) (X = Br, I). In the oxidation of I (-) the I 3 (-)is produced in two distinct phases. The first phase produces 45% of I 3 (-) with the rate law d[I 3 (-)]/dt = ( k a + k b[H (+)])[Ru (VI)][I (-)]. The remaining I 3 (-) is produced in the second phase which is much slower, and it follows first-order kinetics but the rate constant is independent of [I (-)], [H (+)], and ionic strength. In the proposed mechanism the first phase involves formation of a charge-transfer complex between Ru (VI) and I (-), which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [Ru (IV)(N 2O 2)(O)(OHI)] (2+), and a one electron transfer to give [Ru (V)(N 2O 2)(O)(OH)] (2+) and I (*). [Ru (V)(N 2O 2)(O)(OH)] (2+) is a stronger oxidant than [Ru (VI)(N 2O 2)(O) 2] (2+) and will rapidly oxidize another I (-) to I (*). In the second phase the [Ru (IV)(N 2O 2)(O)(OHI)] (2+) undergoes rate-limiting aquation to produce HOI which reacts rapidly with I (-) to produce I 2. In the oxidation of Br (-) the rate law is -d[Ru (VI)]/d t = {( k a2 + k b2[H (+)]) + ( k a3 + k b3[H (+)]) [Br (-)]}[Ru (VI)][Br (-)]. At 298.0 K and I = 0.1 M, k a2 = (2.03 +/- 0.03) x 10 (-2) M (-1) s (-1), k b2 = (1.50 +/- 0.07) x 10 (-1) M (-2) s (-1), k a3 = (7.22 +/- 2.19) x 10 (-1) M (-2) s (-1) and k b3 = (4.85 +/- 0.04) x 10 (2) M (-3) s (-1). The proposed mechanism involves initial oxygen atom transfer from trans-[Ru (VI)(N 2O 2)(O) 2] (2+) to Br (-) to give trans-[Ru (IV)(N 2O 2)(O)(OBr)] (+), which then undergoes parallel aquation and oxidation of Br (-), and both reactions are acid-catalyzed.

Reaction of trans-[Ru(VI)(L)(O)(2)](2+) (1, L = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, a tetradentate macrocyclic ligand with N(2)O(2) donor atoms) with nitrite in aqueous solution or in H(2)O/CH(3)CN produces the corresponding (nitrato)oxoruthenium(IV) species, trans-[Ru(IV)(L)(O)(ONO(2))](+) (2), which then undergoes relatively slow aquation to give trans-[Ru(IV)(L)(O)(OH(2))](2+). These processes have been monitored by both ESI/MS and UV/vis spectrophotometry. The structure of trans-[Ru(IV)(L)(O)(ONO(2))](+) (2) has been determined by X-ray crystallography. The ruthenium center adopts a distorted octahedral geometry with the oxo and the nitrato ligands trans to each other. The Ru=O distance is 1.735(3) A, the Ru-ONO(2) distance is 2.163(4) A, and the Ru-O-NO(2) angle is 138.46(35) degrees . Reaction of trans-[Ru(VI)(L)((18)O)(2)](2+) (1-(18)O(2)) with N(16)O(2)(-) in H(2)O/CH(3)CN produces the (18)O-enriched (nitrato)oxoruthenium(IV) species 2-(18)O(2). Analysis of the ESI/MS spectrum of 2-(18)O(2) suggests that scrambling of the (18)O atoms has occurred. A mechanism that involves linkage isomerization of the nitrato ligand and reversible oxygen atom transfer is proposed.

The kinetics of the oxidation of hydroquinone (H(2)Q) and its derivatives (H(2)Q-X) by trans-[Ru(VI)(tmc)(O)(2)](2+) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) have been studied in aqueous acidic solutions and in acetonitrile. In H(2)O, the oxidation of H(2)Q has the following stoichiometry: trans-[Ru(VI)(tmc)(O)(2)](2+) + H(2)Q --trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + Q. The reaction is first order in both Ru(VI) and H(2)Q, and parallel pathways involving the oxidation of H(2)Q and HQ(-) are involved. The kinetic isotope effects are k(H(2)O)/k(D(2)O) = 4.9 and 1.2 at pH = 1.79 and 4.60, respectively. In CH(3)CN, the reaction occurs in two steps, the reduction of trans-[Ru(VI)(tmc)(O)(2)](2+) by 1 equiv of H(2)Q to trans-[Ru(IV)(tmc)(O)(CH(3)CN)](2+), followed by further reduction by another 1 equiv of H(2)Q to trans-[Ru(II)(tmc)(CH(3)CN)(2)](2+). Linear correlations between log(rate constant) at 298.0 K and the O-H bond dissociation energy of H(2)Q-X were obtained for reactions in both H(2)O and CH(3)CN, consistent with a H-atom transfer (HAT) mechanism. Plots of log(rate constant) against log(equilibrium constant) were also linear for these HAT reactions.

[RuVI(N)(salchda)(CH3OH)]PF6 (1) (salchda = N,N'-bis(salicylidene)o-cyclohexyldiamine dianion) reacts readily with 2,3-dimethyl-2-butene at room temperature in the presence of pyridine or 1-methylimidazole to give initially [RuIV(Az1(-H))(salchda)(py)]PF6 (2, Az1 = 2,2,3,3-tetramethylaziridine), which is then slowly reduced to [RuIII(Az1)(salchda)(py)]PF6 (3). 1 also reacts with a variety of aryl-substituted alkenes such as styrene and trans-beta-methylstyrene in the presence of py or 1-MeIm to give the corresponding ruthenium(III) aziridine complexes. The structures of 3 and [RuIII(Az2)(salchda)(1-MeIm)]PF6 (4, Az2 = trans-2-methyl-3-phenylaziridine) have been determined by X-ray crystallography. The Ru-N(aziridine) distances (2.1049, 2.097 A) are consistent with a neutral aziridine ligand. The C-C and C-N distances in the aziridine ligands are all indicative of single bonds.

The ruthenium(II) complex cis-[Ru(6, 6'-Cl(2)bpy)(2)(OH(2))(2)](CF(3)SO(3))(2) (1) is a robust catalyst for C-H bond oxidations of hydrocarbons, including linear alkanes, using tert-butyl hydroperoxide (TBHP) as terminal oxidant. Alcohols can be oxidized by the "1 + TBHP" protocol to the corresponding aldehydes/ketones with high product yields at ambient temperature. Oxidation of 1 with Ce(IV) in aqueous solution affords cis-[Ru(VI)(6, 6'-Cl(2)bpy)(2)O(2)](2+), which is isolated as a green/yellow perchlorate salt (2). Complex 2 is a powerful stoichiometric oxidant for cycloalkane oxidations under mild conditions. Oxidation of cis-decalin is highly stereoretentive; cis-decalinol is obtained in high yield, and formation of trans-decalinol is not observed. Mechanistic studies showing a large primary kinetic isotope effect suggest a hydrogen-atom abstraction pathway. The relative reactivities of cycloalkanes toward oxidation by 2 have been examined through competitive experiments, and comparisons with Gif-type processes are presented.

The polypyridylruthenium(II) complex, cis-[Ru(2,9-Me2phen)2(OH2)2]2+, is a highly efficient catalyst for the oxidation of alcohols to carbonyl products in water using sodium bromate (NaBrO3) as the terminal oxidant. Excellent conversions and yields are readily achieved at room temperature.

A series of cationic ruthenium(VI) nitrido species containing the cyclohexyl-bridged salen ligand (L) and its derivatives, [RuVI(N)(L)]+, have been prepared by treatment of [NBun4][RuVI(N)Cl4] with H2L in methanol. The structure of [RuVI(N)(L)](ClO4) (1a) has been determined by X-ray crystallography, d(RuN) = 1.592 A. In solvents such as DMF or DMSO, [RuVI(N)(L)]+ undergoes a facile N...N coupling reaction at room temperature to produce N2 and [RuIII(L)(S)2]+ (S = solvent). 1a reacts rapidly with secondary amines to produce diamagnetic RuIV-hydrazido(1-) species, [RuIV(N(H)NR2)(L)(HNR2)]+. The reaction with morpholine is first order in RuVI and second order in morpholine with k(CH3CN, 25 degrees C) = 2.08 x 106 M-2 s-1. This rate constant is over 4 orders of magnitude larger than that of the corresponding reaction of the electrophilic osmium nitride, trans-[OsVI(N)(tpy)(Cl)2]+, with morpholine. The structure of [Ru(NHNC4H8)(L)(NHC4H8)](PF6)2 has been determined by X-ray crystallography, the Ru-N(hydrazido) distance is 1.940 A, and the Ru-N-N angle is 129.4 degrees .

Reaction of [Ru(VI)(N)(sap)Cl] with excess NaN(3) affords a novel paramagnetic triazidoruthenium(III) complex [Ru(III)(sap)(N(3))(3)](2-), which is isolated as a PPh(4)(+) salt (1). Reaction of 1 with Ni(2+) and Co(2+) ions produce two isostructural hexanuclear [Ru(4)M(2)] compounds, [Ru(IV)(4)M(II)(2)(μ(3)-OMe)(2)(μ-OMe)(2)(μ-N)(2)(μ-N(3))(2)(μ-O(phenoxy))(2)(sap)(4) (MeOH)(4)] (M = Ni 2 or Co 3). The molecular structures of 1-3 have been determined by X-ray crystallography. 1 is a mononuclear ruthenium(III) compound where three azide ligands are bonded to ruthenium in a meridional fashion, while compounds 2 and 3 are isostructural hexanuclear compounds containing a defective face-sharing dicubane-like core with two missing vertexes. Variable-temperature dc magnetic susceptibility studies have been carried out for 2 and 3. These data indicate that there are four diamagnetic Ru(IV) ions in 2 and 3 and there is ferromagnetic interaction between the two Ni(2+) in 2 and Co(2+) in 3 via the methoxy bridges.