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Electrocatalysis The Ru complex is set on its path, along which it must cross either a high mountain (EEC pathway) or a smaller hill (ECE pathway) to reach the glittering green palace where it can fulfill its goal of converting CO2 to CO. The sun shines brighter on the ECE path, which is alluring and less energy‐demanding. The complex can tread that path provided that its Ru heart has electrons (e−) pumped in (tBu on terpyridine), and that the CH3CN is easily removed. This is achieved by a CH3 group at the bipyridine, which pushes the bipyridine into the CH3CN with the force of a bull, thereby facilitating CH3CN dissociation from the complex. More information can be found in the Full Paper by S. Ott, S. Maji et al. on page 14870 ff. [ABSTRACT FROM AUTHOR]

Azocarboxamides occupy a special place among azo ligands owing to their versatility for metal coordination. Herein ruthenium complexes with two different azocarboxamide ligands that differ in the presence (or not) of a coordinating pyridyl heterocycle are presented. By making full use of the O,N(amide), N(azo), and N(pyridyl) coordinating sites, the first diruthenium complex that is bridged by an azo ligand containing two different binding pockets was obtained. Moreover, it was conclusively proven that, in the mononuclear complexes, oxidation at the ruthenium center leads to a complete change of coordination at the chelating binding pocket. The complexes were characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. Additionally, the mechanism of the aforementioned redox‐triggered change in the chelating binding pocket and the electronic structures of all the complexes were investigated by a combination of electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations. This is first instance in which a redox‐driven change in the complete chelating binding pocket has been observed in a ruthenium complex as well as with azo‐based ligands. These results thus show the potential of these versatile azocarboxamide ligands to act as redox‐driven switches with possible relevance to electrocatalysis. Join at the tip: Ruthenium complexes of azocarboxamide ligands with and without a coordinating pyridyl heterocycle were synthesized. By making full use of the O,N(amide), N(azo), and N(pyridyl) coordinating sites, the first diruthenium complex bridged by an azo ligand containing two different binding pockets was obtained. Moreover, in the mononuclear complexes, oxidation at the Ru center leads to a change in the coordination mode at the chelating binding pocket (see scheme). [ABSTRACT FROM AUTHOR]

Abstract: Invited for the cover of this issue is the group of Bas de Bruin at the University of Amsterdam, Monica Trincado and Hansjörg Grützmacher at ETH Zürich. The image is inspired by Sergio Leone's spaghetti western “The Good, the Bad and the Ugly”, and matches the theme of the paper. Non‐innocent ligands not only give rise to intriguing electronic structures, but can also trigger unexpected ligand‐centered reactivity. The trop2dad molecule is a “pure‐blood” example. Read the full text of the article at 10.1002/chem.201705957. [ABSTRACT FROM AUTHOR]

Ruthenium polypyridyl complexes have received widespread attention as potential chemotherapeutics in photodynamic therapy (PDT) and in photochemotherapy (PACT). Here, we investigate a series of sixteen ruthenium polypyridyl complexes with general formula [Ru(tpy)(N−N)(L)]+/2+ (tpy=2,2′:6′,2′′-terpyridine, N−N=bpy (2,2′-bipyridine), phen (1,10-phenanthroline), dpq (pyrazino[2,3-f][1,10]phenanthroline), dppz (dipyrido[3,2-a:2′,3′-c]phenazine, dppn (benzo[i]dipyrido[3,2-a:2′,3′-c]phenazine), pmip (2-(4-methylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline), pymi ((E)-N-phenyl-1-(pyridin-2-yl)methanimine), or azpy (2-(phenylazo)pyridine), L=Cl− or 2-(2-(2-(methylthio)ethoxy)ethoxy)ethyl-β-d-glucopyranoside) and their potential for either PDT or PACT. We demonstrate that although increased lipophilicity is generally related to increased uptake of these complexes, it does not necessarily lead to increased (photo)cytotoxicity. However, the non-toxic complexes are excellent candidates as PACT carriers. [ABSTRACT FROM AUTHOR]

The potential use of organoruthenium complexes as anticancer drugs is well known. Herein, a family of activatable tethered ruthenium(II) arene complexes of general formula [Ru{η6:κ1-C6H5(C6H4)NH2}(XY)] n+ (closed tether ring) bearing different chelating XY ligands (XY=aliphatic diamine, phenylenediamine, oxalato, bis(phosphino)ethane) is reported. The activation of these complexes (closed- to open-tether conversion) occurs in methanol and DMSO at different rates and to different reaction extents at equilibrium. Most importantly, RuII-complex activation (cleavage of the Ru−Ntether bond) occurs in aqueous solution at high proton concentration (upon Ntether protonation). The activation dynamics can be modulated by rational variation of the XY chelating ligand. The electron-donating capability and steric hindrance of XY have a direct impact on the reactivity of the Ru−N bond, and XY= N, N′-dimethyl-, N, N′-diethyl-, and N, N, N′, N′-tetramethylethylenediamine afford complexes that are more prone to activation. Such activation in acidic media is fully reversible, and proton concentration also governs the deactivation rate, that is, tether-ring closure slows down with decreasing pH. Interaction of a closed-tether complex and its open-tether counterpart with 5′-guanosine monophosphate revealed selectivity of the active (open) complex towards interaction with nucleobases. This work presents ruthenium tether complexes as exceptional pH-dependent switches with potential applications in cancer research. [ABSTRACT FROM AUTHOR]

In recent years terpyridines (tpy) and mesoionic carbenes (MIC) have been widely used in metal complexes. With the right combination with a metal center, both of these ligands are individually known to generate excellent catalysts for CO2 reduction. In this study, we combine the potentials of PFC (PFC=polyfluorocarbon) substituted tpy and MIC ligands within the same platform to obtain a new class of complexes, which we investigated with respect to their structural, electrochemical and UV/Vis/NIR spectroelectrochemical properties. We further show that the resulting metal complexes are potent electrocatalysts for CO2 reduction in which CO is exclusively formed with a faradaic efficiency of 92 %. A preliminary mechanistic study, including the isolation and characterization of a key intermediate is also reported. [ABSTRACT FROM AUTHOR]

The combination of 2,2′:6′,2′′-terpyridines (tpy) and RuII is known to deliver molecular and supramolecular assemblies with remarkable properties. Here new RuII complexes, with modified tpy ligands substituted with varying numbers of dimethlyamino groups, are presented. Electrochemistry shows that the incorporation of the strongly electron-donating groups on the tpy ligands leads to a negative shift of the RuII oxidation potential by close to 1 V. The reductive electrochemical responses are strongly dependent on the nature of the working electrode, with glassy carbon and gold working electrodes showing the best results. These observations led to the development of a modified Optically Transparent Thin Layer Electrochemical (OTTLE) cell, based on a gold working electrode. The use of UV/Vis/NIR spectroelectrochemical methods with that OTTLE cell, together with simulations of the cyclic voltammograms, allowed the characterization of four reduction steps in these complexes, the final two of which lead to bond activations at the ruthenium center. This observation is to the best of our knowledge unprecedented in coordinatively saturated complexes of type [Ru(tpy)2]2+. The various redox states of the complexes were characterized by EPR spectroelectrochemistry and through DFT calculations. The results presented here establish these substituted tpy ligands as highly attractive ligands in coordination chemistry, and display the utility of a gold-based OTTLE cell for spectroelectrochemical measurements. [ABSTRACT FROM AUTHOR]

An alternative approach to replacing the isothiocyantate ligands of the N3 photosensitizer with light-harvesting bidentate ligands is investigated for application in dye-sensitized solar cells (DSSCs). An in-depth theoretical analysis has been applied to investigate the optical and redox properties of four non-innocent ligand platforms, which is then corroborated with experiment. Taking advantage of the 5- and 7-positions of 8-oxyquinolate, or the carboxyaryl ring system of the N-arylcarboxy-8-amidoquinolate ligand, fluorinated aryl substituents are demonstrated as an effective means of tuning complex redox potentials and light-harvesting properties. The non-innocent character, resulting from mixing of both the central metal-dπ and ligand-π manifolds, generates hybrid metal-ligand frontier orbitals. These play a major role by contributing to the redox properties and visible electronic transitions, and promoting an improved power conversion efficiency in a Ru DSSC device featuring non-innocent ligands. [ABSTRACT FROM AUTHOR]

The reaction of the Ru(PPh3)3Cl2 with HL1−3−OH (−OH stands for the oxime hydroxyl group; HL1−OH=diacetylmonoxime‐S‐benzyldithiocarbazonate; HL2−OH=diacetylmonoxime‐S‐(4‐methyl)benzyldithiocarbazonate; and HL3−OH=diacetylmonoxime‐S‐(4‐chloro)benzyl‐dithiocarbazonate) gives three new ruthenium complexes [RuII(L1−3−H)(PPh3)2Cl] (1–3) (−H stands for imine hydrogen) coordinated with dithiocarbazate imine as the final products. All ruthenium(II) complexes (1–3) have been characterized by elemental (CHNS) analyses, IR, UV‐vis, NMR (1H, 13C, and 31P) spectroscopy, HR‐ESI‐MS spectrometry and also, the structure of 1–2 was further confirmed by single crystal X‐ray crystallography. The solution/aqueous stability, hydrophobicity, DNA interactions, and cell viability studies of 1–3 against HeLa, HT‐29, and NIH‐3T3 cell lines were performed. Cell viability results suggested 3 being the most cytotoxic of the series with IC50 6.9±0.2 μM against HeLa cells. Further, an apoptotic mechanism of cell death was confirmed by cell cycle analysis and Annexin V‐FITC/PI double staining techniques. In this regard, the live cell confocal microscopy results revealed that compounds primarily target the mitochondria against HeLa, and HT‐29 cell lines. Moreover, these ruthenium complexes elevate the ROS level by inducing mitochondria targeting apoptotic cell death. [ABSTRACT FROM AUTHOR]

A new family of ruthenium complexes based on the N-pentadentate ligand Py2Metacn (N-methyl-N',N''-bis(2-picolyl)-1,4,7-triazacyclononane) has been synthesised and its catalytic activity has been studied in the water-oxidation (WO) reaction. We have used chemical oxidants (ceric ammonium nitrate and NaIO4) to generate the WO intermediates [RuII(OH2)(Py2Metacn)]2+, [RuIII(OH2)(Py2Metacn)]3+, [RuIII(OH)(Py2Metacn)]2+ and [RuIV(O)(Py2Metacn)]2+, which have been characterised spectroscopically. Their relative redox and pH stability in water has been studied by using UV/Vis and NMR spectroscopies, HRMS and spectroelectrochemistry. [RuIV(O)(Py2Metacn)]2+ has a long half-life (>48 h) in water. The catalytic cycle of WO has been elucidated by using kinetic, spectroscopic, 18O-labelling and theoretical studies, and the conclusion is that the rate-determining step is a single-site water nucleophilic attack on a metal-oxo species. Moreover, [RuIV(O)(Py2Metacn)]2+ is proposed to be the resting state under catalytic conditions. By monitoring CeIV consumption, we found that the O2 evolution rate is redoxcontrolled and independent of the initial concentration of CeIV. Based on these facts, we propose herein that [RuIV(O)(Py2Metacn)]2+ is oxidised to [RuV(O)(Py2Metacn)]2+ prior to attack by a water molecule to give [RuIII(OOH)(Py2Metacn)]2+. Finally, it is shown that the difference in WO reactivity between the homologous iron and ruthenium [M(OH2)(Py2Metacn)]2+ (M=Ru, Fe) complexes is due to the difference in the redox stability of the key MV(O) intermediate. These results contribute to a better understanding of the WO mechanism and the differences between iron and ruthenium complexes in WO reactions. [ABSTRACT FROM AUTHOR]

Three distinct functionalisation strategies have been applied to the in, in-[{RuII(trpy)}2(μ-bpp)(H2O)2]3+ (trpy=2,2′:6′,2′′-terpyridine, bpp=bis(pyridine)pyrazolate) water-oxidation catalyst framework to form new derivatives that can adsorb onto titania substrates. Modifications included the addition of sulfonate, carboxylate, and phosphonate anchoring groups to the terpyridine and bis(pyridyl)pyrazolate ligands. The complexes were characterised in solution by using 1D NMR, 2D NMR, and UV/Vis spectroscopic analysis and electrochemical techniques. The complexes were then anchored on TiO2-coated fluorinated tin oxide (FTO) films, and the reactivity of these new materials as water-oxidation catalysts was tested electrochemically through controlled-potential electrolysis (CPE) with oxygen evolution detected by headspace analysis with a Clark electrode. The results obtained highlight the importance of the catalyst orientation with respect to the titania surface in regard to its capacity to catalytically oxidize water to dioxygen. [ABSTRACT FROM AUTHOR]

Photoresponsive molecular memory films were fabricated by a layer-by-layer (LbL) assembling of two dinuclear Ru complexes with tetrapodal phosphonate anchors, containing either 2,3,5,6-tetra(2-pyridyl)pyrazine or 1,2,4,5-tetra(2-pyridyl)benzene as a bridging ligand (Ru-NP and Ru-CP, respectively), using zirconium phosphonate to link the layers. Various types of multilayer homo- and heterostructures were constructed. In the multilayer heterofilms such as ITO||(Ru-NP) m|(Ru-CP) n, the difference in redox potentials between Ru-NP and Ru-CP layers was approximately 0.7 V, which induced a potential gradient determined by the sequence of the layers. In the ITO||(Ru-NP) m|(Ru-CP) n multilayer heterofilms, the direct electron transfer (ET) from the outer Ru-CP layers to the ITO were observed to be blocked for m>2, and charge trapping in the outer Ru-CP layers became evident from the appearance of an intervalence charge transfer (IVCT) band at 1140 nm from the formation of the mixed-valent state of Ru-CP units, resulting from the reductive ET mediation of the inner Ru-NP layers. Therefore, the charging/discharging ('1'and '0') states in the outer Ru-CP layers could be addressed and interconverted by applying potential pulses between −0.5 and +0.7 V. The two states could be read out by the direction of the photocurrent (anodic or cathodic). The molecular heterolayer films thus represent a typical example of a photoresponsive memory device; that is, the writing process may be achieved by the applied potential (−0.5 or +0.7 V), while the readout process is achieved by measuring the direction of the photocurrent (anodic or cathodic). Sequence-sensitive multilayer heterofilms, using redox-active complexes as building blocks, thus demonstrate great potential for the design of molecular functional devices. [ABSTRACT FROM AUTHOR]

The electronic structures within a series of square‐planar ruthenium(II) pincer complexes with dialkyl‐, vinyl alkyl‐, and divinyl amido pincer backbones is compared in an experimental and computational study. Although [RuCl{N(CH2CH2PtBu2)2}] exhibits a low‐spin (S=0) ground state and low‐lying triplet (S=1) excited state, [RuCl{N(CH2CH2PtBu2)(CHCHPtBu2)}] and [RuCl{N(CHCHPtBu2)2}] adopt intermediate‐spin (S=1) ground states with strong magnetic anisotropy due to large zero‐field splitting (D>+200cm–1). The change in ground‐state electronic configuration is attributed to tailored pincer ligand‐to‐metal π‐donation within the PNP ligand series. For more details, see the Full Paper by S. Schneider et al. on page 579 ff. [ABSTRACT FROM AUTHOR]

Functionalization of the PNP pincer ligand backbone allows for a comparison of the dialkyl amido, vinyl alkyl amido, and divinyl amido ruthenium(II) pincer complex series [RuCl{N(CH2CH2P tBu2)2}], [RuCl{N(CHCHP tBu2)(CH2CH2P tBu2)}], and [RuCl{N(CHCHP tBu2)2}], in which the ruthenium(II) ions are in the extremely rare square-planar coordination geometry. Whereas the dialkylamido complex adopts an electronic singlet ( S=0) ground state and energetically low-lying triplet ( S=1) state, the vinyl alkyl amido and the divinyl amido complexes exhibit unusual triplet ( S=1) ground states as confirmed by experimental and computational examination. However, essentially non-magnetic ground states arise for the two intermediate-spin complexes owing to unusually large zero-field splitting ( D>+200 cm−1). The change in ground state electronic configuration is attributed to tailored pincer ligand-to-metal π-donation within the PNP ligand series. [ABSTRACT FROM AUTHOR]

The synthesis of dinuclear ruthenium alkenyl complexes with {Ru(CO)(PiPr3)2(L)} entities (L=Cl− in complexes Ru2‐3 and Ru2‐7; L=acetylacetonate (acac−) in complexes Ru2‐4 and Ru2‐8) and with π‐conjugated 2,7‐divinylphenanthrenediyl (Ru2‐3, Ru2‐4) or 5,8‐divinylquinoxalinediyl (Ru2‐7, Ru2‐8) as bridging ligands are reported. The bridging ligands are laterally π‐extended by anellating a pyrene (Ru2‐7, Ru2‐8) or a 6,7‐benzoquinoxaline (Ru2‐3, Ru2‐4) π‐perimeter. This was done with the hope that the open π‐faces of the electron‐rich complexes will foster association with planar electron acceptors via π‐stacking. The dinuclear complexes were subjected to cyclic and square‐wave voltammetry and were characterized in all accessible redox states by IR, UV/Vis/NIR and, where applicable, by EPR spectroscopy. These studies signified the one‐electron oxidized forms of divinylphenylene‐bridged complexes Ru2‐7, Ru2‐8 as intrinsically delocalized mixed‐valent species, and those of complexes Ru2‐3 and Ru2‐4 with the longer divinylphenanthrenediyl linker as partially localized on the IR, yet delocalized on the EPR timescale. The more electron‐rich acac− congeners formed non‐conductive 1 : 1 charge‐transfer (CT) salts on treatment with the F4TCNQ electron acceptor. All spectroscopic techniques confirmed the presence of pairs of complex radical cations and F4TCNQ.− radical anions in these CT salts, but produced no firm evidence for the relevance of π‐stacking to their formation and properties. [ABSTRACT FROM AUTHOR]

[RuCl(arene)(μ-Cl)]2 dimers were treated in a 1:2 molar ratio with sodium or thallium salts of bis- and tris(pyrazolyl)borate ligands [Na(Bp [ABSTRACT FROM AUTHOR]

Treatment of [Cp*RuCl2]2, 1, [(COD)IrCl]2, 2 or [(p‐cymene)RuCl2]2,3 (Cp*=η5‐C5Me5, COD= 1,5‐cyclooctadiene and p‐cymene=η6‐iPrC6H4Me) with heterocyclic borate ligands [Na[(H3B)L], L1 and L2 (L1: L=amt, L2: L=mp; amt=2‐amino‐5‐mercapto‐1,3,4‐thiadiazole, mp=2‐mercaptopyridine) led to the formation of borate complexes having uncommon coordination. For example, complexes 1 and 2 on reaction with L1 and L2 afforded dihydridoborate species [LAM(μ‐H)2BHL] 4–6 (4: LA=Cp*, M=Ru, L=amt; 5: LA=Cp*, M=Ru, L=mp; 6: LA=COD, M=Ir, L=mp). On the other hand, treatment of 3 with L2 yielded cis‐ and trans‐bis(dihydridoborate) species, [Ru{(μ‐H)2BH(mp)}2], cis‐7 and trans‐7. The isolation and structural characterization of fac‐ and mer‐[Ru{(μ‐H)2BH(mp)}{(μ‐H)BH(mp)2}], 8 from the same reaction offered an insight into the behaviour of these dihydridoborate species in solution. Fascinatingly, despite having reduced natural charges on Ru centres both at cis‐and trans‐7, they underwent hydroboration reaction with alkynes that yielded both Markovnikov and anti‐Markovnikov addition products, 10 a–d. [ABSTRACT FROM AUTHOR]

We synthesized two 4Me−PNP ligands which block metal‐ligand cooperation (MLC) with the Ru center and compared their Ru complex chemistry to their two traditional analogues used in acceptorless alcohol dehydrogenation catalysis. The corresponding 4Me−PNP complexes, which do not undergo dearomatization upon addition of base, allowed us to obtain rare, albeit unstable, 16 electron mono‐CO Ru(0) complexes. Reactivity with CO and H2 allows for stabilization and extensive characterization of bis‐CO Ru(0) 18 electron and Ru(II) cis and trans dihydride species that were also shown to be capable of C(sp2) −H activation. Reactivity and catalysis are contrasted to non‐methylated Ru(II) species, showing that an MLC pathway is not necessary, with dramatic differences in outcomes during catalysis between iPr and tBu PNP complexes within each of the 4Me and non‐methylated backbone PNP series being observed. Unusual intermediates are characterized in one of the new and one of the traditional complexes, and a common catalysis deactivation pathway was identified. [ABSTRACT FROM AUTHOR]

Novel arene RuII complexes containing 2,2'‐azobispyridine ligands were synthesized and characterized by using 1H and 13C NMR spectroscopy, UV/vis spectroscopy, electrochemistry, DFT calculations and single‐crystal X‐ray diffraction. Z‐configured complexes featuring unprecedented seven‐membered chelate rings involving the nitrogen atom of both pyridines were isolated and were shown to undergo irreversible isomerization to the corresponding E‐configured five‐membered chelate complexes in response to light or electrochemical stimulus. [ABSTRACT FROM AUTHOR]

A new class of C2‐symmetric, chiral cyclopentadienyl ligand based on planar chiral ferrocene backbone was developed. A series of its corresponding rhodium(I), iridium(I), and ruthenium(II) complexes were prepared as well. In addition, the rhodium(I) complexes were evaluated in the asymmetric catalytic intramolecular amidoarylation of olefin‐tethered benzamides via C−H activation. [ABSTRACT FROM AUTHOR]

The transition metal catalysed formation and cleavage of C−C bonds is of utmost importance in synthetic chemistry. While most of the existing homogeneous catalysts are mononuclear, knowledge of the behaviour of polynuclear species is much more limited. By using computational methods, here we shed light into the mechanistic details of the thermally‐induced isomerization of Cp*3Ru3(μ‐H)2(μ3‐η2‐pentyne)(μ3‐pentylidyne) (2) into Cp*3Ru3(μ‐H)2(μ3‐η2‐octyne)(μ3‐ethylidyne) (3), a process that involves the migration of a C3 fragment between the hydrocarbyl ligands and across the plane formed by the three Ru centres. Our results show this to be a complex transformation that comprises of five individual rearrangements in an A→B→A→B→A order. Each so‐called rearrangement A consists of the CH migration from the μ3‐η2‐alkyne into the μ3‐alkylidine ligand in the other side of the Ru3 plane. This process is facilitated by the cluster's ability to adopt open‐core structures in which one Ru−Ru bond is broken and a new C−C bond is formed. In contrast, rearrangements B do not involve the formation or cleavage of C−C bonds, nor do they require the opening of the cluster core. Instead, they consist of the isomerization of the μ3‐η2‐alkyne and μ3‐alkylidyne ligands on each side of the triruthenium plane into μ3‐alkylidyne and μ3‐η2‐alkyne, respectively. Such transformation implies the migration of three H atoms within the hydrocarbyl ligands, and in this case, it is aided by the cluster's ability to behave as a H reservoir. All in all, this study highlights the plasticity of these Ru3 clusters, whereby Ru−Ru, Ru−C, Ru−H, C−C, and C−H bonds are formed and broken with surprising ease. [ABSTRACT FROM AUTHOR]

Although the chemistry of transition‐metal complexes with carbonyl (CO) and thiocarbonyl (CS) ligands has been well developed, their heavier analogues, namely selenocarbonyl (CSe) and tellurocarbonyl (CTe) complexes remain scarce. The limited availability of such CSe and CTe complexes has so far hampered our understanding of the differences between such chalcogenocarbonyl (CE: E=O, S, Se, Te) ligands. Herein, we report the synthesis and properties of a series of cationic half‐sandwich ruthenium CE complexes of the type [CpRu(CE)(H2IMes)(CNCH2Ts)][BArF4] (Cp=η5‐C5H5−; H2IMes=1,3‐dimesitylimidazolin‐2‐ylidene; ArF=3,5‐(CF3)2C6H3). A combination of X‐ray diffraction analyses, NMR spectroscopic analyses, and DFT calculations revealed an increasing π‐accepting ability of the CE ligands in the order O

Ruthenium–arene complexes are a unique class of organometallic compounds that have been shown to have prominent therapeutic potencies. Here, we have investigated the interactions of Ru‐cymene complexes with a zinc‐finger protein NCp7, aiming to understand the effects of various ligands on the reaction. Five different binding modes were observed on selected Ru‐complexes. Ru‐cymene complex can bind to proteins through either noncovalent binding alone or through a combination of covalent and noncovalent binding modes. Moreover, the noncovalent interaction can promote the coordination of RuII to NCp7, resulting synergistic effects of the different ligands. The binding of Ru(Cym) complexes leads to dysfunction of NCp7 through zinc‐ejection and structural perturbation. These results indicate that the reactivity of Ru‐complexes can be modulated by ligands through different approaches, which could be closely correlated to their different therapeutic effects. [ABSTRACT FROM AUTHOR]

Optical sensing offers a low‐cost and effective means to sense carbon monoxide in air and in solution. This contribution reports the synthesis of a new series of vinyl complexes [Ru(CH=CHR)Cl(CO)(TBTD)(PPh3)2] (R=aryl, TBTD=5‐(3‐thienyl)‐2,1,3‐benzothiadiazole) and shows them to be highly sensitive and selective probes for carbon monoxide in both solution and air. Depending on the vinyl substituent, chromogenic and fluorogenic responses signalled the presence of this invisible, odourless, tasteless and toxic gas. Adsorbing the complexes on silica produced colorimetric probes for the ′naked eye′ detection of CO in the gas phase with a limit of detection as low as 8 ppm in some cases, while the release of the TBTD fluorophore allowed detection at much lower concentrations through the fluorescence response. Structural data were obtained by single‐crystal X‐ray diffraction techniques, while the photophysical behaviour was explored computationally using TD‐DFT experiments. The systems were also shown to be selective for CO over all other gases tested, including water vapour and common organic solvents. By introducing a poly(ethylene)glycol chain to the vinyl functionality, water compatibility was achieved and these non‐cytotoxic complexes were employed in the sensing of CO in HeLa cells, offering a simple and rapid system for sensing this gasotransmitter in this challenging medium. Chromo‐fluorogenic ruthenium and osmium compounds: TBTD (5‐(3‐thienyl)‐2,1,3‐benzothiadiazole) complexes can be used to detect carbon monoxide in solution, in air and in cells (see figure). [ABSTRACT FROM AUTHOR]

Abstract: The Ru complex [RuII(bda‐κ‐N2O2)(N‐NH2)2] (1; bda2−=2,2′‐bipyridine‐6,6′‐dicarboxylate, N‐NH2=4‐(pyridin‐4‐yl)aniline) was used as a synthetic intermediate to prepare new RuII and RuIII bda complexes that contain NO+, MeCN, or H2O ligands. In acidic solution complex 1 reacts with an excess of NO+ (generated in situ from sodium nitrite) to form a new Ru complex in which the aryl amine ligand N−NH2 is transformed into a diazonium salt [N‐N2+=4‐(pyridin‐4‐yl)benzenediazonium)] together with the formation of a new Ru(NO) moiety in the equatorial zone, to generate [RuII(bda‐κ‐N2O)(NO)(N‐N2)2]3+ (23+). Here the bda2− ligand binds in a κ‐N2O tridentate manner with a dangling carboxylate group. Similarly, complex 1 can also react with a coordinating solvent, such as MeCN, at room temperature to give [RuII(bda‐κ‐N2O)(MeCN)(N‐NH2)2] (3). In acidic aqueous solutions, a related reaction occurs in which solvent water coordinates to the Ru center to form {[RuII{bda‐κ‐(NO)3}(H2O)(N‐NH3)2](H2O)n}2+ (42+) and is strongly hydrogen‐bonded with additional water molecules in the second coordination sphere. Furthermore, under acidic conditions the aniline ligands are also protonated to form the corresponding anilinium cationic ligands N‐NH3+. Additionally, the one‐electron oxidized complex {[RuIII{bda‐κ‐(NO)3.5}(H2O)(N‐NH3)2](H2O)n}3+ (53+) was characterized, in which the fractional value in the κ notation indicates the presence of an additional contact to the pseudo‐octahedral geometry of the Ru center. The coordination modes of the complexes were studied in the solid state and in solution through single‐crystal XRD, X‐ray absorption spectroscopy, variable‐temperature NMR spectroscopy, and DFT calculations. While κ‐N2O is the main coordination mode for 23+ and 3, an equilibrium that involves isomers with κ‐N2O and κ‐NO2 coordination modes and neighboring hydrogen‐bonded water molecules is observed for 42+ and 53+. [ABSTRACT FROM AUTHOR]

Abstract: Four new RuII complexes, [Ru(tpy)(L)(CH3CN]+, where tpy=2,2′:6′,2“‐terpyridine and L represents a series of acetylacetonate‐based ligands, were synthesized for enhanced photoinduced ligand release with red light, λirr=655 nm. The metal‐to‐ligand charge transfer, 1MLCT, transitions of these complexes are red‐shifted and exhibit quantum yields of ligand dissociation that are five‐ to seven‐fold greater than that of [Ru(tpy)(bpy)(CH3CN)]2+ (bpy=2,2′‐bipyridine), despite the absence of additional steric distortion. This series of complexes represents a new scaffold for drug photocaging and one of the first examples of RuII photocages that can release nitriles with light in the photodynamic therapy (PDT) window required for optimal tissue penetration. [ABSTRACT FROM AUTHOR]

We report the use of phosphorus-doped carbon (P-C) as support to grow ultrasmall (1–3 nm) and ligand-free precious metal nanocrystals (PMNCs) via chemical reduction. We show that the valence states of surface phosphorus species are critical in tuning the affinity between the carbon support and metal precursors, which rationally controls the loading size and uniformity of resultant PMNCs. Five kinds of PMNCs, including Ru, Ag, Au, Rh, and Pd, were grown in situ to demonstrate the key role of surface phosphorus sites on the P-C support. As a proof-of-concept application, Ru nanocatalysts with an average diameter of 1.0±0.2 nm supported on P-C were examined for the electrocatalytic hydrogen evolution reaction (HER). Ultrasmall and ligand-free Ru nanocatalysts exhibited superior HER activity and stability compared to its counterparts with surface agents or larger sizes. An overpotential of 27.6 mV (vs. reversible hydrogen electrode) for Ru nanocatalysts was achieved at a current density of 10 mA cm−2. This novel method opens a new avenue to immobilize ligand-free and well-dispersed PMNCs on carbon; and, more importantly, it provides a new library of supported PMNCs with high catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: In this work, it was found that DNA can undergo B‐Z transformational changes and compaction in the presence of DNA intercalators such as ruthenium(II) polypyridyl complexes. The link between B‐Z transition and condensation is weak but can be strengthened under certain circumstances with slight alterations to the structures of the ruthenium(II) complexes. Here, following on from previous research, this work reports a series of ruthenium(II) complexes with imidazophenanthroline ligands, which vary in size and planarity. The complexes exhibit distinct effects on DNA structures, ranging from little impact to the transformation of DNA secondary structures to the formation of higher‐order DNA structures. Further studies on DNA morphological changes induced by chiral ruthenium(II) complexes are observed by atomic force microscopy and transmission electron microscopy. [ABSTRACT FROM AUTHOR]

[2.2]Paracyclophane, with its unique structure, allows the design of unusual 3D structures by functionalization of this rigid and stable hydrocarbon scaffold. Therefore different mono- and homodisubstituted [2.2]paracyclophanes with pyridyl, pyrimidyl and oxazolinyl substituents were developed in order to evaluate their ability as bridging ligands for two ruthenium centres. With the successfully synthesized [2.2]paracyclophane-based N-donor functions, the cycloruthenation reaction using [RuCl2( p-cymene)]2 as precursor was explored. Compared to 2-phenylpyridine, the [2.2]paracyclophane derivative is clearly inferior in the cycloruthenation reaction, resulting in poor yields for the neutral complexes. By addition of KPF6, the cationic complexes can be obtained in good yields and are formed diastereoselectively in case of a pyridyl substituent, resulting in only one diastereomer for dinuclear ruthenium complexes of bispyridyl-substituted [2.2]paracyclophanes as bridging ligands. [ABSTRACT FROM AUTHOR]

Non‐innocent ligand transition metal complexes are appealing due to their remarkable redox properties imparted by the presence of extensive metal(dπ)–ligand(π) bonding. The non‐innocent character derived from the mixing of ruthenium dπ and oxyquinolate or N‐carboxyamidoquinolate π orbitals generates hybrid metal–ligand frontier orbitals that play a major role in contributing to an improved power conversion efficiency in a Ru non‐innocent ligand sensitized DSSC device. More information can be found in the Full Paper by J. Rochford and co‐workers on page 7497. [ABSTRACT FROM AUTHOR]

The tripodal, tetradentate tris(1-(diphenylphosphanyl)-3-methyl-1 H-indol-2-yl)phosphane PP3-ligand 1 stabilizes Ru in the RuII, RuI, and Ru0 oxidation states. The octahedral [(PP3)RuII(Cl)2] ( 2), distorted trigonal bipyramidal [(PP3)RuI(Cl)] ( 3), and trigonal bipyramidal [(PP3)Ru0(N2)] ( 4) complexes were isolated and characterized by single-crystal X-ray diffraction, NMR, EPR, IR, and ESI-MS. Both open-shell metalloradical RuI complex 3 and the closed-shell Ru0 complex 4 undergo facile (net) abstraction of a Cl atom from dichloromethane, resulting in formation of the corresponding RuII and RuI complexes 2 and 3, respectively. [ABSTRACT FROM AUTHOR]

A library of new bis-picolinamide ruthenium(III) dihalide complexes of the type [RuX2L2] (X=Cl or I, L=picolinamide) have been synthesised and characterised. The complexes exhibit different picolinamide ligand binding modes, whereby one ligand is bound (N,N) and the other bound (N,O). Structural studies revealed a mixture of cis and trans isomers for the [RuCl2L2] complexes but upon a halide exchange reaction to yield [RuI2L2], only single trans isomers were detected. High cytotoxic activity against human cancer cell lines was observed, with the potencies of some complexes similar to or better than cisplatin. The conversion to [RuI2L2] substantially increased the activity towards cancer cell lines by more than twelvefold. The [RuI2L2] complexes displayed potent activity against the A2780cis (cisplatin-resistant human ovarian cancer) cell line, with a more than fourfold higher potency than cisplatin. Equitoxic activity was observed against normoxic and hypoxic cancer cells, which indicates the potential to eradicate both the hypoxic and aerobic fractions of solid tumours with similar efficiency. The activity of selected complexes against non-cancer ARPE-19 cells was also tested. The [RuI2L2] complexes were found to be more potent than the [RuCl2L2] analogues and also more selective towards cancer cells with a selectivity factor in excess of sevenfold. [ABSTRACT FROM AUTHOR]

The nitrogen- and sulfur-containing 1,2-benzothiazines meloxicam and piroxicam are widely used as nonsteroidal anti-inflammatory drugs. Intrigued by the presence of multiple donor atoms and therefore potentially rich coordination chemistry, we prepared a series of organometallic Ru and Os compounds with meloxicam and piroxicam featuring either as mono- or bidentate ligand systems. The choice of the solvent and the pH value was identified as the critical parameter to achieve selectively mono- or bidentate coordination. The coordination modes were confirmed experimentally by NMR spectroscopy and single crystal X-ray diffraction analysis. Using DFT calculations, it was established that complexes in which meloxicam acts as a bidentate N, O donor are energetically more favorable than coordination as O, O and S, O donor systems. Since meloxicam and piroxicam derivatives have shown anticancer activity in the past, we aimed to compare the complexes with mono- and bidentate ligands on their in vitro anticancer activity. However, stability studies revealed that only the latter complexes were stable in [D6]DMSO/D2O (5:95) and therefore no direct comparisons could be made. The meloxicam complexes 1 and 2 showed moderate cytotoxicity, whereas the piroxicam derivatives 5 and 6 were hardly active against the utilized cell lines. [ABSTRACT FROM AUTHOR]

Recognition and regulation of G-quadruplex nucleic acid structures is an important goal for the development of chemical tools and medicinal agents. The addition of a bromo-substituent to the dipyridylphenazine (dppz) ligands in the photophysical 'light switch', [Ru(bpy)2dppz]2+, and the photochemical 'light switch', [Ru(bpy)2dmdppz]2+, creates compounds with increased selectivity for an intermolecular parallel G-quadruplex and the mixed-hybrid G-quadruplex, respectively. When [Ru(bpy)2dppz-Br]2+ and [Ru(bpy)2dmdppz-Br]2+ are incubated with the G-quadruplexes, they have a stabilizing effect on the DNA structures. Activation of [Ru(bpy)2dmdppz-Br]2+ with light results in covalent adduct formation with the DNA. These complexes demonstrate that subtle chemical modifications of RuII complexes can alter G-quadruplex selectivity, and could be useful for the rational design of in vivo G-quadruplex probes. [ABSTRACT FROM AUTHOR]

The transfer hydrogenation (TH) reaction of ketones with catalytic systems based on a methandiide-derived ruthenium carbene complex was investigated and optimised. The complex itself makes use of the noninnocent behaviour of the carbene ligand (MCR2→MHC(H)R2), but showed only moderate activity, thus requiring long reaction times to achieve sufficient conversion. DFT studies on the reaction mechanism revealed high reaction barriers for both the dehydrogenation of iPrOH and the hydrogen transfer. A considerable improvement of the catalytic activity could be achieved by employing triphenylphosphine as additive. Mechanistic studies on the role of PPh3 in the catalytic cycle revealed the formation of a cyclometalated complex upon phosphine coordination. This ruthenacycle was revealed to be the active species under the reaction conditions. The use of the isolated complex resulted in high catalytic activities in the TH of aromatic as well as aliphatic ketones. The complex was also found to be active under base-free conditions, suggesting that the cyclometalation is crucial for the enhanced activity. [ABSTRACT FROM AUTHOR]

Ring opening of thiophenes containing an azo function in 2-position and subsequent dimerization through CC coupling were observed on reaction with [Ru(acac)2(CH3CN)2] (acac=acetylacetonate) to produce two 1,3,5-hexatriene-linked redox-active azothiocarbonyl chelate systems. Interaction of the non-innocent chelate ligands and of the metals at a nanoscale distance of 1.45 nm via the conjugated hexatriene bridge was studied by magnetic and electron spectroscopic measurements in conjunction with DFT calculations, revealing four-center magnetic interactions of this unique setting and weak intervalence coupling after reduction. [ABSTRACT FROM AUTHOR]

A series of heteropentanuclear oxalate-bridged Ru(NO)-Ln (4d-4f) metal complexes of the general formula ( nBu4N)5[Ln{RuCl3(μ-ox)(NO)}4], where Ln=Y ( 2), Gd ( 3), Tb ( 4), Dy ( 5) and ox=oxalate anion, were obtained by treatment of ( nBu4N)2[RuCl3(ox)(NO)] ( 1) with the respective lanthanide salt in 4:1 molar ratio. The compounds were characterized by elemental analysis, IR spectroscopy, electrospray ionization (ESI) mass spectrometry, while 1, 2, and 5 were in addition analyzed by X-ray crystallography, 1 by Ru K-edge XAS and 1 and 2 by 13C NMR spectroscopy. X-ray diffraction showed that in 2 and 5 four complex anions [RuCl3(ox)(NO)]2− are coordinated to YIII and DyIII, respectively, with formation of [Ln{RuCl3(μ-ox)(NO)}4]5− (Ln=Y, Dy). While YIII is eight-coordinate in 2, DyIII is nine-coordinate in 5, with an additional coordination of an EtOH molecule. The negative charge is counterbalanced by five nBu4N+ ions present in the crystal structure. The stability of complexes 2 and 5 in aqueous medium was monitored by UV/Vis spectroscopy. The antiproliferative activity of ruthenium-lanthanide complexes 2- 5 were assayed in two human cancer cell lines (HeLa and A549) and in a noncancerous cell line (MRC-5) and compared with those obtained for the previously reported Os(NO)-Ln (5d-4f) analogues ( nBu4N)5[Ln{OsCl3(ox)(NO)}4] (Ln=Y ( 6), Gd ( 7), Tb ( 8), Dy ( 9)). Complexes 2- 5 were found to be slightly more active than 1 in inhibiting the proliferation of HeLa and A549 cells, and significantly more cytotoxic than 5d-4f metal complexes 6- 9 in terms of IC50 values. The highest antiproliferative activity with IC50 values of 20.0 and 22.4 μ M was found for 4 in HeLa and A549 cell lines, respectively. These cytotoxicity results are in accord with the presented ICP-MS data, indicating five- to eightfold greater accumulation of ruthenium versus osmium in human A549 cancer cells. [ABSTRACT FROM AUTHOR]

In an effort to explore the effect of ancillary ligands on the spectral properties and overall G-quadruplex DNA binding behavior, two new ruthenium(II) complexes [Ru(phen)2(dppzi)]2+ ( 1) and [Ru(dmp)2(dppzi)]2+ ( 2) (phen=1,10-phenanthroline, dmp=2,9-dimethyl-1,10-phenanthroline, dppzi=dipyrido[3,2-a:2′,3′-c]phenazine-10,11-imidazole) were prepared. Complex 1 can emit luminescence in the absence and presence of G-quadruplexes DNA. However, with CH3 substituent on the 2- and 9-positions of the phen ancillary ligand, no detectable luminescence is observed for complex 2 in any organic solvent or in the absence and/or presence of G-quadruplex DNA. Experimental and molecular docking studies indicated that both complexes interacted with the human telomeric repeat AG3(T2AG3)3 (22AG) G-quadruplex with the stoichiometric ratio of 1:1, but the two complexes showed different G-quadruplex DNA binding affinity. Complex 1 binds to the G-quadruplexes DNA more tightly than complex 2 does. Our results demonstrate that methyl groups on the phen ancillary ligand significantly affect the spectral properties and the overall DNA binding behavior of the complexes. Such difference in spectral properties and DNA binding affinities of these two complexes can be reasonably explained by DFT/TD-DFT calculations. This work provides guidance not only on exploring the G-quadruplexes DNA binding behavior of complexes, but also understanding the unique luminescence mechanism. [ABSTRACT FROM AUTHOR]

A new non-innocent ligand redox system, N, N′-bis(4-dimethylaminophenyl) substituted acetamidinato/acetamidinyl, has been designed and described by example of structurally and spectroscopically characterized ruthenium complexes. The hitherto unreported ligand is responsible for rather intense and narrow absorptions in the near-infrared region of the one- and two-electron oxidized forms. The spectroscopic, computational, and first structural characterization of an amidinyl radical complex adds to the list of established N-based radical ligands. [ABSTRACT FROM AUTHOR]

A series of trans-(Cl)-[Ru(L)(CO)2Cl2]-type complexes, in which the ligands L are 2,2′-bipyridyl derivatives with amide groups at the 5,5′-positions, are synthesized. The C-connected amide group bound to the bipyridyl ligand through the carbonyl carbon atom is twisted with respect to the bipyridyl plane, whereas the N-connected amide group is in the plane. DFT calculations reveal that the twisted structure of the C-connected amide group raises the level of the LUMO, which results in a negative shift of the first reduction potential ( Ep) of the ruthenium complex. The catalytic abilities for CO2 reduction are evaluated in photoreactions ( λ>400 nm) with the ruthenium complexes (the catalyst), [Ru(bpy)3]2+ (bpy=2,2′-bipyridine; the photosensitizer), and 1-benzyl-1,4-dihydronicotinamide (the electron donor) in CO2-saturated N,N-dimethylacetamide/water. The logarithm of the turnover frequency increases by shifting Ep a negative value until it reaches the reduction potential of the photosensitizer. [ABSTRACT FROM AUTHOR]

Tuning of ligand properties is at the heart of influencing chemical reactivity and generating tailor-made catalysts. Herein, three series of complexes [Ru(L)(Cl)(X)]PF6 (X=DMSO, PPh3, or CD3CN) with tripodal ligands (L1-L5) containing pyridine and triazole arms are presented. Triazole-for-pyridine substitution and the substituent at the triazole systematically influence the redox behavior and photoreactivity of the complexes. The mechanism of the light-driven ligand exchange of the DMSO complexes in CD3CN could be elucidated, and two seven-coordinate intermediates were identified. Finally, tuning of the ligand framework was applied to the catalytic oxygenation of alkanes, for which the DMSO complexes were the best catalysts and the yield improved with increasing number of triazole arms. These results thus show how click-derived ligands can be tuned on demand for catalytic processes. [ABSTRACT FROM AUTHOR]

A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5 e(BF4) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the CN bond assisted either by the pincer ligand or a second coordinated H2 molecule. [ABSTRACT FROM AUTHOR]

The [Ru(CO)H(PNN)] pincer complex based on a dearomatised PNN ligand (PNN: 2-di- tert-butylphosphinomethyl-6-diethylaminomethylpyridine) was examined for its ability to isomerise alkenes. The isomerisation reaction proceeded under mild conditions after activation of the complex with alcohols. Variable-temperature (VT) NMR experiments to investigate the role of the alcohol in the mechanism lend credence to the hypothesis that the first step involves the formation of a rearomatised alkoxide complex. In this complex, the hemilabile diethylamino side-arm can dissociate, allowing alkene binding cis to the hydride, enabling insertion of the alkene into the metal-hydride bond, whereas in the parent complex only trans binding is possible. During this study, a new uncommon Ru0 coordination complex was also characterised. The scope of the alkene isomerisation reaction was examined. [ABSTRACT FROM AUTHOR]

A series of tunable G0-G3 dendritic 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β-ketoesters, α-ketoesters, and α-ketoamides to reveal the effects of dendron size on the catalytic properties. The second- and third-generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first-generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second-generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity. [ABSTRACT FROM AUTHOR]

A reaction of a 2-(imidazol-1-yl)methyl-6-(pyrazol-3-yl)pyridine with [RuCl2(PPh3)3] resulted in tautomerization of the imidazole unit to afford the unsymmetrical pincer-type ruthenium complex 2 containing a protic pyrazole and N-heterocyclic carbene (NHC) arms. Deprotonation of 2 with one equivalent of a base led to the formation of the NHC-pyrazolato complex 3, indicating that the protic NHC arm is less acidic. When 2 was treated with two equivalents of a base under H2 or in 2-propanol, the hydrido complex 4 containing protic NHC and pyrazolato groups was obtained through metal-ligand cooperation. [ABSTRACT FROM AUTHOR]

A common bridging ligand, 3,3′,5,5′-tetrakis( N-methylbenzimidazol-2-yl)biphenyl, and four terpyridine terminal ligands with various substituents (amine, tolyl, nitro, and ester groups) have been used to synthesize ten cyclometalated diruthenium complexes 12+- 102+. Among them, compounds 12+- 62+ are redox nonsymmetric, and others are symmetric. These complexes show two RuIII/II processes and an intervalence charge transfer (IVCT) transition in the one-electron oxidized state. The potential separation (Δ E) of 12+- 102+ has been correlated to the energy difference Δ G0, the energy of the IVCT band Eop, and the ground-state delocalization coefficient α2. Time-dependent (TD)DFT calculations suggest that the absorptions in the visible region of 12+- 62+ are mainly associated with the metal-to-ligand charge-transfer transitions from both ruthenium ions and to both terminal ligands and the bridging ligand. However, the energies of these transitions vary significantly. DFT calculations have been performed on 12+- 62+ and 13+- 63+ to give information on the electronic structures and spin populations of the mixed-valent compounds. The TDDFT-predicted IVCT excitations reproduce well the experimental trends in transition energies. In addition, three monoruthenium complexes have been synthesized for a comparison study. [ABSTRACT FROM AUTHOR]

Metalmetal singly-bonded diruthenium complexes, bridged by naphthyridine-functionalized N-heterocyclic carbene (NHC) ligands featuring a hydroxy appendage on the naphthyridine unit, are obtained in a single-pot reaction of [Ru2(CH3COO)2(CO)4] with 1-benzyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (BIN ⋅HBr) or 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazolium bromide (PIN ⋅HBr), TlBF4, and substituted benzaldehyde containing an electron-withdrawing group. The modified NHC-naphthyridine-hydroxy ligand spans the diruthenium unit in which the NHC carbon and hydroxy oxygen occupy the axial sites. All the synthesized compounds catalyze acceptorless dehydrogenation of alcohols to the corresponding aldehydes in the presence of a catalytic amount of weak base 1,4-diazabicyclo[2.2.2]octane (DABCO). Further, acceptorless dehydrogenative coupling (ADHC) of the alcohol with amines affords the corresponding imine as the sole product. The substrate scope is examined with 1 (BIN, p-nitrobenzaldehyde). A similar complex [Ru2(CO)4(CH3COO)(3-PhBIN)][Br], that is devoid of a hydroxy arm, is significantly less effective for the same reaction. Neutral complex 1 a, obtained by deprotonation of the hydroxy arm in 1, is found to be active for the ADHC of alcohols and amines under base-free conditions. A combination of control experiments, deuterium labeling, kinetic Hammett studies, and DFT calculations support metal-hydroxyl/hydroxide and metal-metal cooperation for alcohol activation and dehydrogenation. The bridging acetate plays a crucial role in allowing β-hydride elimination to occur. The ligand architecture on the diruthenium core causes rapid aldehyde extrusion from the metal coordination sphere, which is responsible for exclusive imine formation. [ABSTRACT FROM AUTHOR]

A rare example of a mononuclear complex [(bpy)2Ru(L1−H)](ClO4), 1(ClO4) and dinuclear complexes [(bpy)2Ru( μ-L1−2H)Ru(bpy)2](ClO4)2, 2(ClO4)2, [(bpy)2Ru( μ-L2−2H)Ru(bpy)2](ClO4)2, 3(ClO4)2, and [(bpy)2Ru( μ-L3−2H)Ru(bpy)2](ClO4)2, 4(ClO4)2 (bpy=2,2′-bipyridine, L1=2,5-di-(isopropyl-amino)-1,4-benzoquinone, L2=2,5-di-(benzyl-amino)-1,4-benzoquinone, and L3=2,5-di-[2,4,6-(trimethyl)-anilino]-1,4-benzoquinone) with the symmetrically substituted p-quinone ligands, L, are reported. Bond-length analysis within the potentially bridging ligands in both the mono- and dinuclear complexes shows a localization of bonds, and binding to the metal centers through a phenolate-type 'O−' and an immine/imminium-type neutral 'N' donor. For the mononuclear complex 1(ClO4), this facilitates strong intermolecular hydrogen bonding and leads to the imminium-type character of the noncoordinated nitrogen atom. The dinuclear complexes display two oxidation and several reduction steps in acetonitrile solutions. In contrast, the mononuclear complex 1+ exhibits just one oxidation and several reduction steps. The redox processes of 11+ are strongly dependent on the solvent. The one-electron oxidized forms 23+, 33+, and 43+ of the dinuclear complexes exhibit strong absorptions in the NIR region. Weak NIR absorption bands are observed for the one-electron reduced forms of all complexes. A combination of structural data, electrochemistry, UV/Vis/NIR/EPR spectroelectrochemistry, and DFT calculations is used to elucidate the electronic structures of the complexes. Our DFT results indicate that the electronic natures of the various redox states of the complexes in vacuum differ greatly from those in a solvent continuum. We show here the tuning possibilities that arise upon substituting [O] for the isoelectronic [NR] groups in such quinone ligands. [ABSTRACT FROM AUTHOR]