Metal Coordination Effects on the Photophysics of Dipyrrinato Photosensitizers

Within this work, we review the metal coordination effect on the photophysics of metal dipyrrinato complexes. Dipyrrinato complexes are promising candidates in the search for alternative transition metal photosensitizers for application in photodynamic therapy (PDT). These complexes can be activated by irradiation with light of a specific wavelength, after which, cytotoxic reactive oxygen species (ROS) are generated. The metal coordination allows for the use of the heavy atom effect, which can enhance the triplet generation necessary for generation of ROS. Additionally, the flexibility of these complexes for metal ions, substitutions and ligands allows the possibility to tune their photophysical properties. A general overview of the mechanism of photodynamic therapy and the properties of the triplet photosensitizers is given, followed by further details of dipyrrinato complexes described in the literature that show relevance as photosensitizers for PDT. In particular, the photophysical properties of Re(I), Ru(II), Rh(III), Ir(III), Zn(II), Pd(II), Pt(II), Ni(II), Cu(II), Ga(III), In(III) and Al(III) dipyrrinato complexes are discussed. The potential for future development in the field of (dipyrrinato)metal complexes is addressed, and several new research topics are suggested throughout this work. We propose that significant advances could be made for heteroleptic bis(dipyrrinato)zinc(II) and homoleptic bis(dipyrrinato)palladium(II) complexes and their application as photosensitizers for PDT.     

Ruthenium(II) complexes with new large-surface ligands based on electron-accepting expanded pyridiniums: insights from density functional theory

With the aim of designing new inorganic photosensitizers for photovoltaic applications, the structural and electronic properties of two Ru(II) complexes containing terpyridine-based ligands derived from expanded pyridiniums both branched—polyphenyl—and fused—polycyclic—were investigated by the means of density functional theory (DFT) and time-dependent DFT (TD-DFT). In particular, the structure and electronic absorption of the fused architectures—including the isolated ligand and its complex—were compared with those of their respective branched precursors with the aim to account for the their enhanced electronic features in the visible spectral region. The theoretical insights gained into the “large-surface” ligand and its associated complex open the route for a joint experimental and theoretical design of new inorganic photosensitizers based on fused expanded pyridiniums.     

A strategy for improving the room-temperature luminescence properties of Ru(II) complexes with tridentate ligands

Several ruthenium(II) complexes with new tridentate polypyridine ligands have been prepared, and their photophysical properties have been studied. The new tridentate ligands are tpy-modified systems (tpy = 2,2':6',2' '-terpyridine) in which aromatic substituents designed to be coplanar with the tpy moiety are introduced, with the aim of enhancing delocalization in the acceptor ligand of the potentially luminescent metal-to-ligand charge-transfer (MLCT) state and increasing the MLCT-MC energy gap (MC = metal-centered excited state). Indeed, the Ru(II) complexes obtained with this new family of tridentate ligands exhibit long-lived luminescence at room temperature (up to 200 ns). The enhanced luminescence properties of these complexes support this design strategy and are superior to those of the model Ru(tpy)22+ compound and compare favorably with those of the best Ru(II) complexes with tridentate ligands reported so far.     

Organometallic chemistry, biology and medicine: ruthenium arene anticancer complexes

Our work has shown that certain ruthenium(II) arene complexes exhibit promising anticancer activity in vitro and in vivo. The complexes are stable and water-soluble, and their frameworks provide considerable scope for optimising the design, both in terms of their biological activity and for minimising side-effects by variations in the arene and the other coordinated ligands. Initial studies on amino acids and nucleotides suggest that kinetic and thermodynamic control over a wide spectrum of reactions of Ru(II) arene complexes with biomolecules can be achieved. These Ru(II) arene complexes appear to have an altered profile of biological activity in comparison with metal-based anticancer complexes currently in clinical use or on clinical trial.     

Tuning of redox potentials by introducing a cyclometalated bond to bis-tridentate ruthenium(II) complexes bearing bis(N-methylbenzimidazolyl)benzene or -pyridine ligands

A series of asymmetrical bis-tridentate cyclometalated complexes including [Ru(Mebib)(Mebip)](+), [Ru(Mebip)(dpb)](+), [Ru(Mebip)(Medpb)](+), and [Ru(Mebib)(tpy)](+) and two bis-tridentate noncyclometalated complexes [Ru(Mebip)(2)](2+) and [Ru(Mebip)(tpy)](2+) were prepared and characterized, where Mebib is bis(N-methylbenzimidazolyl)benzene, Mebip is bis(N-methylbenzimidazolyl)pyridine, dpb is 1,3-di-2-pyridylbenzene, Medpb is 4,6-dimethyl-1,3-di-2-pyridylbenzene, and tpy is 2,2':6',2″-terpyridine. The solid-state structure of [Ru(Mebip)(Medpb)](+) is studied by X-ray crystallographic analysis. The electrochemical and spectroscopic properties of these ruthenium complexes were studied and compared with those of known complexes [Ru(tpy)(dpb)](+) and [Ru(tpy)(2)](2+). The change of the supporting ligands and coordination environment allows progressive modulation of the metal-associated redox potentials (Ru(II/III)) from +0.26 to +1.32 V vs Ag/AgCl. The introduction of a ruthenium cyclometalated bond in these complexes results in a significant negative potential shift. The Ru(II/III) potentials of these complexes were analyzed on the basis of Lever's electrochemical parameters (E(L)). Density functional theory (DFT) and time-dependent DFT calculations were carried out to elucidate the electronic structures and spectroscopic spectra of complexes with Mebib or Mebip ligands.     

Electrochemical properties of dinuclear [Ru([n]aneS4)] complexes of 2,3-bis(2-pyridyl)pyrazine

The syntheses of three new dinuclear [Ru([n]aneS(4))] complexes, where n = 12, 14, 16, bridged by the ligand 2,3-bis(2-pyridyl)pyrazine, (dpp) are reported. The absorption spectra of the complexes show changes in the energy of the MLCT bands within the series, indicating that the thiacrown ligands stabilise the Ru(II) oxidation state to different degrees. Electrochemical studies are also consistent with these observations, and reveal that the pi-acceptor properties of [n]aneS(4) ligands lead to metal based oxidation couples occurring at potentials that are more anodic than those observed in the analogous dinuclear [Ru(bpy)(2)](2+) complex. Despite the back-bonding properties of the thiacrown ligands leading to a reduction in ligand-bridge mediated metal-metal coupling, electrochemical interactions between the metals are still considerable.     

Electrostatic bubbles and supramolecular assistance of photosensitization by carboxylated Ru(II) complexes

The paper examines the supramolecular effects at play during photosensitization by carboxylated Ru(II) sensitizers, both by experiment and by modeling. Experimentally, twelve Ru(II) complexes of pyrazolylpyridine and polypyridine ligands, including two benchmark complexes and two new species, were assessed as photosensitizers by measurement of the kinetics of methyl viologen cation radical (MV(*)(+)) generation through an oxidative, photoinduced electron transfer (PET) to methyl viologen (MV(2+)) under continuous irradiation in the presence of a sacrificial reductant. All complexes, luminescent or not, produced measurable amounts of MV(*)(+) in CH(3)CN. The assessment protocol was found to be useful with sensitizers of widely varying excited-state lifetimes (tau) as well as being easier and faster than conventional approaches. The seven sensitizers bearing peripheral COOH groups were found to be significantly more active than their non-carboxylated analogues, which is consistent with ionization of the COOH groups and electrostatic promotion of PET. Only the luminescent complexes were active in aqueous solvents, where tau appears to be the dominant effector. The benefits are exemplified by the singly carboxylated [Ru(H1)(bpy)(2)](2+) (H1 is 1-(4-carboxyphenyl)-3-(2-pyridyl)-4,5,6,7-tetrahydroindazole), a weakly luminescent sensitizer that was less active in aqueous solvents than [Ru(bpy)(3)](2+) (bpy is 2,2'-bipyridine), but which became the better sensitizer in CH(3)CN. Computationally, electrostatic field and dissociation energy calculations demonstrated that even a single peripheral COO(-) substituent suffices to provide supramolecular assistance: it defines a spheric "bubble" of electrostatically attractive space that is sufficiently large to allow the supramolecular preassociation of MV(2+), which provides an entropic advantage to PET that reduces the importance of tau in organic solvent. Calculations also show that the PET is electrostatically favored over its reverse (BET) even with cationic sensitizers because the "bubble" contracts after PET while the bulk medium becomes more repulsive, and favorable cation exchanges can occur to effect post-PET dissociation. Two peripheral COO(-) groups can define a two-point binding site for MV(2+) in an attractive sector of space that contracts to a kidney-shaped "bubble" after PET. This enables unimolecular PET while the reverse reaction remains bimolecular. The resultant benefits are illustrated with [Ru(Na1)(2)(bpy)](2+), a very weakly luminescent sensitizer that was totally inactive in H(2)O but appreciably active in CH(3)CN, despite the need to displace Na(+) in order to derive any electrostatic benefit. The Marcus free energies of activation for PET and BET corroborate the benefits of carboxylation, solvent, and other factors and correlated with the experimental rate constants.     

Recent Investigations on Thiocyanate-Free Ruthenium(II) 2,2′-Bipyridyl Complexes for Dye-Sensitized Solar Cells

Three decades ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the energy of the sun and for converting it into electricity. Since then, a lot of work has been devoted to create better global photovoltaic efficiencies and long term stability. Among photosensitizers for DSSCs, thiocyanate-free ruthenium(II) complexes have gained increasing interest due to their better stability compared to conventional thiocyanate-based complexes, such as benchmark dyes N719 and Z907. In this mini-review, two classes of thiocyanate-free Ru(II) complexes are presented: (a) bis-bipyridyl compounds bearing an ancillary cyclometalating bidentate ligand; (b) bipyridyl compounds bearing non-cyclometalating ancillary ligands. The coverage, mainly from 2014 up to now, is not exhaustive, but illustrates the most recent design strategies and photovoltaic properties of these two families of ruthenium(II) dyes.     

Wire-type ruthenium(II) complexes with terpyridine-containing [2]rotaxanes as ligands: Synthesis, characterization, and photophysical properties

[2]Rotaxanes based on the 1,2-bis(pyridinium)ethane subset[24]crown-8 ether motif were prepared that contain a terminal terpyridine group for coordination to a transition-metal ion. These rotaxane ligands were utilized in the preparation of a series of heteroleptic [Ru(terpy)(terpy-rotaxane)]2+ complexes. The compounds were characterized by 1D and 2D 1H NMR spectroscopy, X-ray crystallography, and high-resolution electrospray ionization mass spectrometry. The effect of using a rotaxane as a ligand was probed by UV/Vis/NIR absorption and emission spectroscopy of the Ru(II) complexes. In contrast with the parent [Ru(terpy)(2)]2+ complex, at room temperature the examined complexes exhibit a luminescence band in the near infrared region and a relatively long lived triplet metal-to-ligand charge-transfer (3MLCT) excited state, owing to the presence of strong-electron-acceptor pyridinium substituents on one of the two terpy ligands. Visible-light excitation of the Ru-based chromophore in acetonitrile at room temperature causes an electron transfer to the covalently linked 4,4'-bipyridinium unit and the quenching of the MLCT luminescence. The 3MLCT excited state, however, is not quenched at all in rigid matrix at 77 K. The rotaxane structure was found to affect the absorption and luminescence properties of the complexes. In particular, when a crown ether surrounds the cationic axle, the photoinduced electron-transfer process is slowed down by a factor from 2 to 3. Such features, together with the synthetic and structural advantages offered by [Ru(terpy)2]2+-type complexes compared to, for example, [Ru(bpy)3]2+-type compounds, render these rotaxane-metal complexes promising candidates for the construction of photochemical molecular devices with a wire-type structure.     

Molecular conductance switch-on of single ruthenium complex molecules

Thiol-tethered Ru(II) terpyridine complexes were synthesized for a voltage-driven molecular switch and used to understand the switch-on mechanism of the molecular switches of single metal complexes in the solid-state molecular junction in a vacuum. Molecularly resolved scanning tunneling microscopy (STM) images revealed well-defined single Ru(II) complexes isolated in the highly ordered dielectric monolayer. When a negative sample-bias was applied, the threshold voltage to the high conductance state in the molecular junctions of the Ru(II) complex was consistent with the electronic energy gap between the Fermi level of the gold substrate and the lowest ligand-centered redox state of the metal complex molecule. As an active redox center leading to conductance switching in the molecule, the lowest ligand-centered redox state of Ru(II) complexes was suggested to trap an electron injected from the gold substrate. Our suggestions for a single-molecule switch-on mechanism in the solid state can provide guidance in a design that improves the charge-trapping efficiency of the ligands with different metal substrates.     

Synthesis,characterization, DNA-binding and DNA-photocleavage studies of [Ru(bpy)2(pmip)] and [Ru(phen)2(pmip)] (pmip = 2-(2′-pyrimidyl)imidazo[4,5-f][1,10]phenanthroline

Two new Ru(II) complexes, [Ru(bpy)₂(pmip)]²⁺ (1) and [Ru(phen)₂(pmip)]²⁺ (2), have been synthesized and characterized by elemental analysis, ESI-MS and ¹H NMR spectra. Their DNA-binding properties were studied by means of UV–VIS, emission and CD spectra, thermal denaturation and viscosity measurements as well as their DNA-photocleavage properties. The experimental results show that both 1 and 2 can bind to DNA in an intercalative mode; the DNA-binding affinity of 2 is greater than that of 1, which suggests that the ancillary ligands have a significant effect on the spectroscopic properties and DNA-binding behavior of the Ru(II) complexes. Under irradiation with UV light, the Ru(II) complexes show excellent efficiency of cleaving DNA. This research may provide valuable insight into the interactions of metal complexes with DNA, knowledge that is an excellent backdrop for the rational design of promising drugs.     

Reactivity and spectroscopy of the {Ru(DMAP)5} fragment: an {Ru(NH3)5} analogue

Reaction of trans-Ru(DMSO)4Cl2 with DMAP (DMAP = 4-dimethylaminopyridine) yields the yellow [Ru(DMAP)6](2+) cation in good yield. The crystal and molecular structure of [Ru(DMAP)6]Cl2.6CH3CH2OH was determined by X-ray diffraction methods. The complex crystallizes in the trigonal R3 space group with a = b = 16.373(1), c = 20.311(1) A, gamma = 120 degrees , and Z = 3 molecules per unit cell. The reaction of [Ru(DMAP)6](2+) in aerobic water gives the red [Ru(III)(DMAP)5(OH)](2+) cation. This complex shows a chemical behavior similar to [Ru(III)(NH3)5Cl](2+) and allows the preparation of a family of [Ru(DMAP)5L](n+) complexes. Their electronic properties indicate that the {Ru(II)(DMAP)5} fragment is a weaker pi-donor than {Ru(II)(NH 3)5}. Our density functional theory (DFT) calculations show that in {Ru(II)(DMAP)5} the DMAP ligands can compete for the pi electron density of the ruthenium making the fragment a weaker pi-donor.     

Electroreduction of Ru(III) Oxalate Complexes on DME at Variable Supporting-Electrolyte Concentration

The recharging of Ru(III) oxalate complexes is studied on DME in mixed sulfate–oxalate electrolytes of variable concentration. The discovered deceleration of the process with decreasing supporting-electrolyte concentration qualitatively agrees with the expected effect of the EDL structure on the recharging kinetics, but the obtained quantitative data are at severe variance with theory. At low supporting-electrolyte concentrations the process rate in freshly-prepared solutions depends on the concentration of oxalate ions. The dependence has nothing to do with trioxalate complexes of Ru(III) coexisting in the bulk solution with Ru(III) complexes, which have a reduced number of coordinated ligands, as such complexes emerge only after 2–3 days of storing the solutions. The most probable factor responsible for such a dependence seems to be a volume reaction of charge transfer from the formed Ru(II) complexes onto trioxalate complexes of Ru(III). The reaction has a catalytic effect on the hydration of the latter and seems to be responsible for the discrepancy between experiment and theory.     

Areneruthenium(II) 4-acyl-5-pyrazolonate derivatives: coordination chemistry, redox properties, and reactivity

Areneruthenium(II) molecular complexes of the formula [Ru(arene)(Q)Cl], containing diverse 4-acyl-5-pyrazolonate ligands Q with arene = cymene or benzene, have been synthesized by the interaction of HQ and [Ru(arene)Cl(micro-Cl)]2 dimers in methanol in the presence of sodium methoxide. The dinuclear compound [{Ru(cymene)Cl}2Q4Q] (H2Q4Q = bis(4-(1-phenyl-3-methyl-5-pyrazolone)dioxohexane), existing in the RRuSRu (meso form), has been prepared similarly. [Ru(cymene)(Q)Cl] reacts with sodium azide in acetone, affording [Ru(cymene)(Q)N3] derivatives, where Cl- has been replaced by N3-. The reactivity of [Ru(cymene)(Q)Cl] has also been explored toward monodentate donor ligands L (L = triphenylphosphine, 1-methylimidazole, or 1-methyl-2-mercaptoimidazole) and exo-bidentate ditopic donor ligands L-L (L-L = 4,4'-bipyridine or bis(diphenylphosphino)propane) in the presence of silver salts AgX (X = SO3CF3 or ClO4), new ionic mononuclear complexes of the formula [Ru(cymene)(Q)L]X, and ionic dinuclear complexes of the formula [{Ru(cymene)(Q)}2L-L]X2 being obtained. The solid-state structures of a number of complexes were confirmed by X-ray crystallographic studies. Their redox properties have been investigated by cyclic voltammetry and controlled potential electrolysis, which, on the basis of their measured RuII/III reversible oxidation potentials, have allowed the ordering of the bidentate acylpyrazolonate ligands according to their electron-donor character and are indicative of a small dependence of the HOMO energy upon the change of the monodentate ligand. This is accounted for by DFT calculations, which show a relevant contribution of acylpyrazolonate ligand orbitals to the HOMOs, whereas that from the monodentate ligand is minor.     

1,10]-Phenanthrolin-2-yl ketones and their coordination chemistry

A synthetic protocol involving the Friedl?nder reaction of 8-amino-7-quinolinecarbaldehyde followed by potassium dichromate oxidation was applied to 2,3,4-pentanetrione-3-oxime and 1-(pyrid-2'-yl)propane-1,2-dione-1-oxime to provide the ligands di-(phenathrolin-2-yl)-methanone (1) and phenanthrolin-2-yl-pyrid-2-yl-methanone (8), respectively. Ligand 1 complexed as a planar tetradentate with Pd(II) to form [Pd(1)](BF4)2 and with Ru(II) and two 4-substituted pyridines (4-R-py) to form [Ru(1)(4-R-py)2](PF6)2 where R = CF3, CH3, and Me2N. With [Ru(bpy)2Cl2], the dinuclear complex [(bpy)2Ru(1)Ru(bpy)2](PF6)4 was formed (bpy = 2,2'-bipyridine). Ligand 8 afforded the homoleptic Ru(II) complex [Ru(8)2](PF6)2, as well as the heteroleptic complex [Ru(8)(tpy)](PF6)2 (tpy = 2,2';6,2'-terpyridine). The ligands and complexes were characterized by their NMR and IR spectra, as well as an X-ray structure determination of [Ru(1)(4-CH3-py)2](PF6)2. Electrochemical analysis indicated metal-based oxidation and ligand-based reduction that was consistent with results from electronic absorption spectra. The complexes [Ru(1)(4-R-py)2](PF6)2 were sensitive to the 4-substituent on the axial pyridine: electron donor groups facilitated the oxidation while electron-withdrawing groups impeded it.     

Ruthenium(II) complexes of NSO donor ligands in the form of ring-substituted 4-phenyl-thiosemicarbazones of salicylaldehyde and o-hydroxyacetophenone

This work describes the preparation and characterisation of ruthenium(II) complexes of several ONS donor ligands in the form of ring-substituted 4-phenylthiosemicarbazones of salicylaldehyde and o-hydroxyacetophenone. Reactions of these thiosemicarbazone ligands with [Ru(PPh₃)₃]Cl₂ in refluxing MeOH furnished ruthenium(II) complexes of general formula [Ru(PPh₃)₂(LH)Cl] where the ligands acted as monoanionic tridentate ONS donors attached to the ruthenium(II) acceptor centre through the deprotonated phenolic oxygen, thione sulphur and azomethine nitrogen.     

Preparation and study of a family of dinuclear Ru(II) complexes that catalyze the decomposition of water

An approach is developed for the four-electron oxidation of water to provide dioxygen that involves the juxtaposition of two Ru(II) centers such that a metal-bound water molecule might interact with one or both of the metals. The key element in this approach is an appropriate bridging ligand that will hold the metal assembly intact through the full redox cycle. Various synthetic approaches to such ligands are described with the ultimate preparation of four closely related bis-tridentate polypyridine-type systems in which the bridging and distal portions of the ligand are varied. All of these ligands self-assemble with two Ru(II) centers bridged by a Cl ion in the equatorial plane and four axial monodentate substituted pyridines or N-methylimidazoles to form the well-organized catalyst complexes. These complexes are characterized by their distinctive (1)H NMR spectra as well as an X-ray structure of one representative species. The photophysical and electrochemical features of these complexes are consistent with electronegativity and delocalization effects in the equatorial and axial ligands. Of the 14 complexes studied, all but 2, which each contain four axial N-methylimidazole ligands, catalyze the decomposition of water in the presence of excess Ce(IV) as a sacrificial oxidant at pH = 1. Both the rates of oxygen evolution and the catalyst turnover numbers (TNs) are measured. For the active catalysts, the relative rates vary from 1 to 51 and the TNs measure from 80 to 689. Various analytical methods for making these measurements are discussed, and it is found that there is an approximately linear relationship between the rate and TN. Future work will involve optimization of these systems and studies aimed at a better understanding of the mechanism.     

Ruthenium(II) complexes with improved photophysical properties based on planar 4'-(2-pyrimidinyl)-2,2':6',2' '-terpyridine ligands

A series of new tridentate polypyridine ligands, made of terpyridine chelating subunits connected to various substituted 2-pyrimidinyl groups, and their homoleptic and heteroleptic Ru(II) complexes have been prepared and characterized. The new metal complexes have general formulas [(R-pm-tpy)Ru(tpy)]2+ and [Ru(tpy-pm-R)2]2+ (tpy = 2,2':6',2' '-terpyridine; R-pm-tpy = 4'-(2-pyrimidinyl)-2,2':6',2' '-terpyridine with R = H, methyl, phenyl, perfluorophenyl, chloride, and cyanide). Two of the new metal complexes have also been characterized by X-ray analysis. In all the R-pm-tpy ligands, the pyrimidinyl and terpyridyl groups are coplanar, allowing an extended delocalization of acceptor orbital of the metal-to-ligand charge-transfer (MLCT) excited state. The absorption spectra, redox behavior, and luminescence properties of the new Ru(II) complexes have been investigated. In particular, the photophysical properties of these species are significantly better compared to those of [Ru(tpy)2]2+ and well comparable with those of the best emitters of Ru(II) polypyridine family containing tridentate ligands. Reasons for the improved photophysical properties lie at the same time in an enhanced MLCT-MC (MC = metal centered) energy gap and in a reduced difference between the minima of the excited and ground states potential energy surfaces. The enhanced MLCT-MC energy gap leads to diminished efficiency of the thermally activated pathway for the radiationless process, whereas the similarity in ground and excited-state geometries causes reduced Franck Condon factors for the direct radiationless decay from the MLCT state to the ground state of the new complexes in comparison with [Ru(tpy)2]2+ and similar species.     

Water oxidation catalysis: influence of anionic ligands upon the redox properties and catalytic performance of mononuclear ruthenium complexes

Aiming at highly efficient molecular catalysts for water oxidation, a mononuclear ruthenium complex Ru(II)(hqc)(pic)(3) (1; H(2)hqc = 8-hydroxyquinoline-2-carboxylic acid and pic = 4-picoline) containing negatively charged carboxylate and phenolate donor groups has been designed and synthesized. As a comparison, two reference complexes, Ru(II)(pdc)(pic)(3) (2; H(2)pdc = 2,6-pyridine-dicarboxylic acid) and Ru(II)(tpy)(pic)(3) (3; tpy = 2,2':6',2"-terpyridine), have also been prepared. All three complexes are fully characterized by NMR, mass spectrometry (MS), and X-ray crystallography. Complex 1 showed a high efficiency toward catalytic water oxidation either driven by chemical oxidant (Ce(IV) in a pH 1 solution) with a initial turnover number of 0.32 s(-1), which is several orders of magnitude higher than that of related mononuclear ruthenium catalysts reported in the literature, or driven by visible light in a three-component system with [Ru(bpy)(3)](2+) types of photosensitizers. Electrospray ionization MS results revealed that at the Ru(III) state complex 1 undergoes ligand exchange of 4-picoline with water, forming the authentic water oxidation catalyst in situ. Density functional theory (DFT) was employed to explain how anionic ligands (hqc and pdc) facilitate the 4-picoline dissociation compared with a neutral ligand (tpy). Electrochemical measurements show that complex 1 has a much lower E(Ru(III)/Ru(II)) than that of reference complex 2 because of the introduction of a phenolate ligand. DFT was further used to study the influence of anionic ligands upon the redox properties of mononuclear aquaruthenium species, which are postulated to be involved in the catalysis cycle of water oxidation.     

钌(II)-吡啶基NNN配合物催化酮的室温(不对称)氢转移反应

合成了一种基于吡啶骨架含有苯并咪唑和手性咪唑啉基团的三齿NNN配体及其二价钌(II)配合物,通过核磁共振波谱学和X射线单晶晶体结构测定确认了钌(II)配合物的分子结构.这些配合物在室温下催化酮的氢转移反应,表现出了优异的催化活性,收率和ee值最高分别可达99%和97%.