Coordination modes of multidentate azodye ligand derived from 4,4′‐methylenedianiline towards some transition metal ions: Synthesis,spectral characterization,thermal investigation and biological activity

Nine new azodye metal complexes of Mn(II), Co(II), Ni(II), Cu(II), Cr(III), Fe(III), Ru(III), Hf(IV) and Zr(IV) ions have been prepared via the reaction of 5,5′‐((1E,1′E)‐(methylenebis(1,4‐phenylene))bis(diazene‐2,1‐diyl))bis(6‐hydroxy‐2‐thioxo‐2,3‐dihydropyrimidin‐4(5H)‐one) (H₄L) with the corresponding metal salts affording sandwich (1 L:1 M), mononuclear (2 L:1 M), binuclear (1 L,2 M) and tetranuclear (1 L,4 M) complexes. Elemental analyses, spectral methods, magnetic moment measurements and thermal studies were utilized to confirm the mode of bonding and geometrical structure for the ligand and its metal complexes. Infrared spectral data show that the H₄L ligand chelates with some metal ions in keto–enol–thione or keto–thione manner. It behaves in a neutral/dibasic tetradentate fashion in sandwich and binuclear complexes. Also, it acts as a neutral bidentate moiety in the Cr(III) complex. The spectra reveal that azo group participates in chelation in all complexes. Octahedral geometry was suggested for all chelates but the Cu(II) complex with square planar geometry. The thermal stability and decomposition of the compounds were studied, the data showing that the thermal decomposition ended with metal or metal oxide mixed with carbon as final product. The electron spin resonance spectrum of the Cu(II) complex demonstrates that the free electron is located in the ( ) orbital. Measurements of biological activity against human cell lines Hep‐G₂ and MCF‐7 reveal that the Cu(II) complex has a higher cytotoxicity in comparison to the free ligand and other metal complexes, with IC₅₀ values of 6.10 and 5.2 μg ml^?1, respectively, while the ligand has anti‐tumour activity relative to some of the investigated metal complexes.     

Pyrimidoquinazolinophenanthroline Opens Next Chapter in Design of Bridging Ligands for Artificial Photosynthesis**

The synthesis and detailed characterization of a new Ru polypyridine complex containing a heteroditopic bridging ligand with previously unexplored metal-metal distances is presented. Due to the twisted geometry of the novel ligand, the resultant division of the ligand in two distinct subunits leads to steady state as well as excited state properties of the corresponding mononuclear Ru(II) polypyridine complex resembling those of prototype [Ru(bpy)₃]²⁺ (bpy=2,2'-bipyridine). The localization of the initially optically excited and the nature of the long-lived excited states on the Ru-facing ligand spheres is evaluated by resonance Raman and fs-TA spectroscopy, respectively, and supported by DFT and TDDFT calculations. Coordination of a second metal (Zn or Rh) to the available bis-pyrimidyl-like coordination sphere strongly influences the frontier orbitals, apparent by, for example, luminescence quenching. Thus, the new bridging ligand motif offers electronic properties, which can be adjusted by the nature of the second metal center. Using the heterodinuclear Ru−Rh complex, visible light-driven reduction of NAD⁺ to NADH was achieved, highlighting the potential of this system for photocatalytic applications.     

Redox,spectroscopic, photo-induced ligand exchange,and DNA interaction studies of a new Ru(II)Pt(II) bimetallic complex

A new bimetallic complex, [Ru(biq)₂(dpp)PtCl₂](PF₆)₂ (where biq = 2,2′-biquinoline and dpp = 2,3-bis(2-pyridyl)pyrazine), containing a cis-PtCl₂ moiety coupled to a sterically strained Ru(II)-based chromophore was designed, synthesized, and investigated with respect to its spectroscopic, redox, photo-induced ligand exchange, and DNA-interaction properties. The electrochemistry of the designed complex was found to be consistent with the bridging coordination of the dpp ligand and formation of the bimetallic complex. The complex displays intense ligand-based π → π* transitions in the UV region and metal-to-ligand charge-transfer transitions (MLCT) in the visible region. The loss of bridging coordination of the dpp ligand and formation of complexes, [Ru(biq)₂(CH₃CN)₂]²⁺ and [Pt(dpp)(CH₃CN)₂]²⁺ was observed when an acetonitrile solution of the metal complex was irradiated with visible light (λ_irr ≥ 550 nm). The designed complex displays covalent binding with DNA in dark through the cis-PtCl₂ moiety, as confirmed by agarose gel electrophoresis. Upon photoirradiation, the complex dissociates into two DNA-binding moieties and displays covalent binding through: (i) a cis-PtL₂ subunit of [Ptdpp(L)₂]²⁺ and (ii) open coordination sites of the ruthenium of [Ru(biq)₂(L)₂]²⁺ (L = solvent). The designed complex represents the first Ru(II)Pt(II) complex that undergoes photo-induced ligand exchange and displays multifunctional interactions with DNA upon photoirradiation.     

Hetero‐ and homo‐leptic Ru(II) catalyzed synthesis of cyclic carbonates from CO2; Synthesis,spectroscopic characterization and electrochemical properties

Based on the a ligand BDPPZ [(9a,13a‐dihydro‐4,5,9,14‐tetraaza‐benzo[b]triphenylene‐11‐yl)‐phenyl‐methanone] (1) and its polypyridyl hetero‐ and homoleptic Ru(II) metal complexes, [Ru(bpy)₂L](PF₆)₂ (2), [Ru(phen)₂L](PF₆)₂ (3), [Ru(dafo)₂L](PF₆)₂ (4), [Ru(dcbpy)₂L](PF₆)₂ (5) and [RuL₃](PF₆)₂ (6) (where, L = ligand, bpy = 2,2′‐bipyridine, phen = 1,10‐phenantroline, dafo = 4,5‐diazafluoren‐9‐one and dcbpy = 3,3′‐dicarboxy‐2,2′‐bipyridine), have been synthesized and characterized by elemental analysis, UV–vis, FT‐IR, ¹H and ¹³C‐NMR spectra (for ligand), molar conductivity measurements and X‐ray powder techniques. The electrochemical parameters of the substituted ligand and its polypyridyl hetero‐ and homoleptic Ru(II) metal complexes are reported by cyclic voltammetry. UV–vis spectroscopy is used to compare the differences between the conjugated π systems in this ligand and its Ru(II) metal complexes. The polypyridyl hetero‐ and homoleptic Ru(II) metal complexes also tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. The results showed that the [Ru(L)₃](PF₆)₂ (6) complex is more efficient than the other Ru(II) complexes for the formation of cyclic organic carbonates from carbon dioxide. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel oxime-imine ligands and their heteronuclear ruthenium(III) complexes

Vicinal carbonyl oxime (HL¹) and oxime-imine (H₂L²) ligands and their mononuclear Ru(III) and Cu(II), heterodinuclear Ru(III)-Mn(II), Ru(III)-Ni(II), Ru(III)-Cu(II), and heterotrinuclear Ru(III)-Cu(II)-Ru(III) chelates were synthesized and characterized by elemental analysis, molar conductivity, IR, ESR, ICP-OES, magnetic moment measurements, and thermal analyses studies. The free ligands were also characterized by ¹H NMR spectra. The carbonyl-oxime ligand coordinates through the oxygen of =N-OH to form a six-membered chelate ring. The quadridentate tetraaza ligand (H₂L²) obtained by condensing of the bidentate ligand 1-p-diphenylmethane-2-hydroxyimino-2-(1-naphthylamino)-1-ethanone (HL¹) with 1,2-phenylenediamine coordinates with Ru(III) through its nitrogen donors in the equatorial position with the loss of one of the oxime protons and concomitant formation of an intramolecular hydrogen bond. Stoichiometric and spectral results of the metal complexes indicated that the metal: ligand ratios in the mononuclear complexes of the ligand (HL¹) were found to be 1: 2, while these ratios were 1: 1 in the mononuclear complexes of the ligand (H₂L²). The metal: ligand ratios of the dinuclear complexes were found to be 2: 1, and this ratio was 3: 2 in the trinuclear complex. The article is published in the original.     

A readily available chiral Ag-based N-heterocyclic carbene complex for use in efficient and highly enantioselective Ru-catalyzed olefin metathesis and Cu-catalyzed allylic alkylation reactions

A new chiral bidentate N-heterocyclic carbene (NHC) ligand has been designed and synthesized. The NHC ligand bears a chiral diamine backbone and an achiral biphenol group; upon metal complexation (derived from Ag(I), Ru(II), or Cu(II)), the diamine moiety induces >98% diastereoselectivity such that the biaryl unit coordinates to the metal center to afford the desired complex as a single atropisomer. Because the ligand does not require optically pure biaryl amino alcohols, its synthesis is significantly shorter and simpler than the related first generation ligands bearing a chiral binaphthyl-based amino alcohol. The chiral NHC ligand can be used in the preparation of highly effective Ru- and Cu-based complexes (prepared and used in situ from the Ag(I) carbene) that promote enantioselective olefin metathesis and allylic alkylations with scope that is improved from previously reported protocols. In many cases, transformations promoted by the chiral NHC-based complexes proceed with higher enantioselectivity and reactivity than was observed with previously reported complexes.     

Ru-Pt and Ru-Pd heterobimetallic complexes based on a new ligand with two distinct chelate sites

A new ligand p-[N-2-(2'-pyridyl)benzimidazolyl]-[N-2-(2'-pyridyl)indolyl]-benzene (L1) has been synthesized and fully characterized. L1 has two distinct chelating sites: one N,N-chelate site and one N,C-chelate site. This ligand has been found to be very effective in selective binding to two different metal ions. Two new heterobimetallic complexes Ru-Pt and Ru-Pd using L1 as the bridging ligand have been successfully synthesized and fully characterized. To understand the mutual influence of the two metal centers on electronic and photophysical properties, the corresponding monometallic Ru(II), Pt(II) and Pd(II) compounds have also been synthesized and investigated. All Ru(II)-containing complexes have been found to be luminescent. Electronic communication between the two different metal centers in the heterobimetallic compounds was found to be weak. The Pt(II) moiety appears to enhance the phosphorescent efficiency of the Ru(II) unit while the Pd(II) analogue has little influence.     

Ruthenium(III) chloride complex with a tridentate bis(arylimino)pyridine ligand: synthesis, spectra, X-ray structure, 9-ethylguanine binding pattern, and in vitro cytotoxicity

The synthetic, spectroscopic, structural, and biological studies of a bis(arylimino)pyridine Ru(III) chloride compound containing the ligand, 2,6-bis(2,4,6-trimethylphenyliminomethyl)pyridine are reported. The bis(arylimino)pyridine ligand, with three donor nitrogen atoms, was synthesized by condensation of 2,6-pyridinedicarboxaldehyde with 2,4,6-trimethylaniline. The Ru(III) complex, with formula [RuCl 3(L1)](H 2O) (RuL1), where L1 = 2,6-bis(2,4,6-trimethylphenyliminomethyl)pyridine, was structurally determined on the basis of analytical and spectroscopic (IR, UV-vis, ESI-MS) studies. A straightforward strategy to fully characterize the paramagnetic compound using advanced (1)H NMR is reported. This new complex is a prototype for a series of new anticancer Ru(III) and Ru(II) compounds with improved cytostatic properties; likely to be modified in a desirable manner due to the relatively facile ligand modification of the bis(imino)pyridines and their molecular architecture. The present Ru(III) complex is the first example of this family of Ru(III)/Ru(II) anticancer compounds with the aimed physicochemical characteristics. Although the ligand itself is moderately active in selected cell lines (EVSA-T and MCF-7), the activity of the [Ru(L1)Cl 3] complex has increased significantly for a broad range of cancer cell lines tested in vitro (IC 50 values = 11 approximately 17 microM). Reaction of the RuL1 species with the DNA model base 9-ethylguanine (9EtGua) was found to produce in a redox reaction the species trans-[Ru(II)(L1)(9EtGua) 2(H 2O)](ClO 4) 2 (abbreviated as RuL1-9EtGua), which was studied in solution and also in the solid state, by X-ray crystallography. The structure comprises the as yet unknown trans-bis(purine)Ru(II) unit.     

Ruthenocene‐Type Complexes of N‐Fused Porphyrins

Ruthenocene‐type hybrid complexes with N‐fused porphyrinato ligands, [Ru(NFp)Cp] (NFp=N‐fused porphyrin, Cp=cyclopentadienyl), have been prepared and characterized by NMR and UV/Vis/NIR spectroscopy, cyclovoltammetry, and X‐ray crystallography. [Ru(NFp)Cp] is a common low‐spin ruthenium(II) complex and shows strong aromaticity. The Ru–Cp distance (1.833 Å) in [Ru(NFp)Cp] is comparable to that in [RuCp₂] (1.840 Å). DFT calculations on [Ru(NFp)Cp] showed the unequivocal contribution of the RuCp moiety as well as the NFp moiety to both the HOMO and LUMO, constructing a three‐dimensional d–π conjugated system. The HOMO–LUMO gaps of [Ru(NFp)Cp] are insensitive to the substituents on the NFp ligand, which is illustrated spectroscopically as well as theoretically. This is in sharp contrast to the ligand precursor, the N‐fused porphyrin, in which the HOMO–LUMO gap is affected by substituents in a similar manner to standard porphyrins and related macrocycles.     

Synthesis and properties of 6,6′-dithienyl-4,4′-bipyrimidine and its hetero- and homo-leptic Ru(II) complexes

Hetero- and homo-leptic Ru(II) complexes of a new 4,4′-bipyrimidine ligand, th₂bpm (6,6′-di(2″-thienyl)-4,4′-bipyrimidine), have been synthesized and characterized. The parent ligand th₂bpm has electron rich thiophene units on the periphery of a bidentate ligand which is capable of binding to metal ions. The heteroleptic complex of th₂bpm [Ru(bpy)₂th₂bpm]²⁺ (bpy = 2,2′-bipyridine) exhibits a Ru-to-bpm metal-to-ligand charge transfer (MLCT) absorption centered at 547 nm and a Ru-to-bpy MLCT absorption centered at 438 nm. The assignment of the low energy absorption is supported by the relative ease of electrochemical reduction of the new complex as compared to [Ru(bpy)₃]²⁺. The homoleptic complex, [Ru(th₂bpm)₃]²⁺, exhibits a Ru-to-bpm MLCT absorption at slightly higher energy (544 nm). Both complexes are emissive at room temperature in fluid solution and 5 is one of the lowest energy emitters based on tris-bidentate Ru(II) complexes known (λ_max = 770 nm). The luminescence spectra is red-shifted compared to [Ru(bpy)₃]²⁺ and this effect is ascribed to the delocalization in the acceptor ligand.     

Synthesis,structural, spectroscopic,and thermal studies of some transition-metal complexes of a ligand containing the amino mercapto triazole moiety

A new series of transition-metal complexes of Schiff base ligand containing the amino mercapto triazole moiety ( HL ) was prepared. The Schiff base and its metal complexes were elucidated by different spectroscopic techniques (infrared [IR], ¹H nuclear magnetic resonance, UV–Visible, mass, and electron spin resonance [ESR]), and magnetic moment and thermal studies. Quantum chemical calculations have been carried out to study the structure of the ligand and some of its complexes. The IR spectra showed that the ligand is chelated with the metal ion in a neutral, tridentate, and bidentate manner using NOS and NO donors in complexes 1 – 6 , 10–12 , and 7 and 8 , respectively, whereas it behaves in a monobasic tridentate fashion using NOS donor sites in copper(II) nitrate complex ( 9 ). The magnetic moment and electronic spectra data revealed octahedral and square pyramidal geometries for complexes 2 , 11 , 12 , and 5 – 8 and 10 , respectively. However, the other complexes were found to have tetrahedral ( 4 ), trigonal bipyramidal ( 1 and 3 ), and square planar ( 9 ) structures. Thermal studies revealed that the chelates with different crystallized solvents undergo different types of interactions and the decomposition pathway ended with the formation of metal oxygen (MO) and metal sulfur (MS) as final products. The ESR spectrum of copper(II) complex 10 is axial in nature with hyperfine splitting with ²B_1g as a ground state. By contrast, complexes 7 and 8 undergo distortion around the Cu(II) center, affording rhombic ESR spectra. The HL ligand and some of its complexes were screened against two bacterial species. Data showed that complex 12 demonstrated a better antibacterial activity than HL ligand and other chelates.     

Chloro(η6‐p‐cymene)(2‐methyl‐5‐oxo‐7‐phenyl‐5,6‐di­hydro‐2H‐1,2,4‐triaz­epine‐3‐thiol­ato‐κ2N4,S)­ruthenium(II)

The novel title ruthenium(II) complex, [RuCl(C₁₀H₁₄)(C₁₀H₁₀N₃OS)], was synthesized from the reaction of 1,2,4‐triazepine, a new class of bidentate ligands, with [Ru(p‐cymene)Cl₂]₂. The 1,2,4‐triazepine ligand is coordinated to the metal centre through the N‐4 and S atoms, forming a four‐membered chelate ring. This is the first structural example of a transition metal complex containing a 1,2,4‐triazepine ligand.     

Mono-, di-, and tetranuclear ruthenium(II) complexes containing 3-(pyridin-2-yl)-as-triazino[5,6-f]1,10-phenanthroline: synthesis, characterization, and electrochemical and photophysical properties

Mono-, di-, and tetranuclear Ru(II) polypyridine complexes based on the bridging ligand pdtp, where pdtp is 3-(pyridin-2-yl)-as-triazino[5,6-f]1,10-phenanthroline, have been synthesized and characterizated. This asymmetric bridging ligand is composed of two nonequivalent coordinating sites: one involves the phenanthroline moiety, and the other one involves the pyridyltriazine moiety. Electrochemical data show that the first redox process in these complexes is pdtp based and the metal-metal interaction in di- and tetranuclear complexes is very weak. The two oxidations (+1.41 and +1.56 V vs SCE) observed in dinuclear complex 2 are mainly ascribed to the different coordination environments of two metal centers. Absorption spectra are essentially the sum of the spectra of the component monometallic species. The emission spectra are measured both at room temperature and at 80 K in a 4:1 (v/v) EtOH/MeOH matrix. The complexes all display luminescence properties which are close to that featured by the parent [Ru(phen)(3)](2+) species. It is also noted that center-to-periphery energy transfer occurs in the dendritic tetranuclear complex 3.     

Structural characterization,thermal investigation and biological activity of metal complexes containing Schiff Base ligand (Z)‐3‐(1‐((4,6‐dimethyl‐1H‐pyrazolo[3,4‐b] pyridin‐3‐yl)imino)ethyl)‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one

A new series of metal complexes containing Co(II), Pd(II), Fe(III) chloride and Cu(II) salts (chloride, bromide, sulphate and perchlorate) have been prepared with Schiff base ligand ( HL ). The synthesized compounds were elucidated using elemental analyses, spectral techniques, molar conductance, magnetic measurements and thermogravimetric studies. The analytical data established (1 M:1 L) stoichiometry for complexes ( 1 ), ( 2 ), ( 4 ), ( 6 ) and ( 7 ) as well as (1 M:2 L) and (2 M:3 L) stoichiometry for complexes ( 5 ) and ( 3 ), respectively. As a result, the ligand HL coordinates in complexes ( 1 ), ( 2 ), ( 4 ), ( 6 ) as a monobasic tridentate ONN moiety via the oxygen atom of the deprotonated phenolic OH, the nitrogen atoms of the azomethine and the imine group in pyrazolopyridine ring. While, it behaves as a neutral bidentate in complexes ( 3 , 7 ), chelates via oxygen and nitrogen atoms of enolic OH and azomethine groups. Also, in complex ( 5 ) Cu²⁺ ion binds via NO sits of two ligand molecules in its monobasic and neutral forms. The magnetic moment and electronic spectral data proposed octahedral structure for complexes ( 2 , 3 and 7 ) as well as triagonal bipyramidal and square pyramidal geometry for complexes ( 1 and 4 ), while, chelates ( 5 ) and ( 6 ) possess square planar geometry. TG/DTG studies confirmed the chemical formula for these complexes and established the thermal decomposition processes ended with the formation of metal or metal oxides contaminated with carbon residue. An axial electron spin resonance spectra were suggested for Cu(II) complexes pointing to ²B_1g as a ground state with hyperfine structure for complex ( 4 ). In vitro antibacterial and antioxidant activities were performed for HL ligand and its metal complexes. The biological studies indicate that complex ( 3 ) has better antibacterial activity compared to the ligand and the other complexes.     

Synthesis,Characterization and Antifungal Activity of Metal Complexes of 2-(5-((2-Chlorophenyl)Diazenyl)-2-Hydroxybenzylidene) Hydrazinecarbothioamide

Abstract

New metal complexes of Co(II), Cu(II), Ni(II), Zn(II), Mn(II), Fe(III), Ru(III), UO₂(II), and VO(II) with the Schiff base, 2-(5-((2-chlorophenyl)diazenyl)-2-hydroxy- benzylidene) hydrazine-carbothioamide (H₂L) have been prepared and characterized by elemental and thermal analyses, FT-IR, UV–Vis, mass spectra, ¹H-NMR, and ESR as well as conductivity and magnetic moments measurements. The IR spectra showed that the ligand acts as neutral tridentate, neutral bidentate or monobasic tridentate ligand. The geometries of metal complexes were either octahedral or square pyramidal. The ESR spectra of the solid copper(II) complexes indicated an axial symmetry type of a d_(x2-y2) ground state with considerably ionic or covalent environment. The effect of the presence of an azo group on the biological activity of the ligand was investigated. The ligand and its complexes are biologically inactive due to the presence of azo group.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the related elements to view the free supplemental file.     

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.     

Ruthenium (II) complexes bearing thioether-appended α-iminopyridine ligands: Arene precursors permit access to κ2-N,N and κ3-N,N,S complexes

Herein we report the preparation of a series of Ru(II) complexes featuring α-iminopyridine ligands bearing thioether functionality (NNS^R, where R = Me, CH₂Ph, Ph). Metallation using [(p-cymene)RuCl]₂ permits access to Ru complexes with a κ²-N,N donor set in which the thioether moiety remains uncoordinated. In the presence of a strong field ligand such as acetonitrile or triphenylphosphine, the p-cymene moiety is displaced, and the ligand adopts a κ³-N,N,S binding mode. These complexes are characterized using a combination of solution and solid state methods, including the crystal structure of [(NNS^Me)Ru (NCMe)₂Cl]Cl. The κ²-N,N-Ru(II) complexes are shown to serve as efficient precatalysts for the oxidation of sec-phenethyl alcohol at modest loadings (alcohol: Ru = 20:1), using a variety of external oxidants and solvents. The complex bearing an S-Ph donor was found to be the most active oxidation catalyst of those surveyed, suggesting that the thioether donor plays an active role in the catalytic cycle.     

Synthesis and Application of Ruthenium(II) Alkenyl Complexes with Perylene Fluorophores for the Detection of Toxic Vapours and Gases

A series of new ruthenium(II) vinyl complexes has been prepared incorporating perylenemonoimide (PMI) units. This fluorogenic moiety was functionalised with terminal alkyne or pyridyl groups, allowing attachment to the metal either as a vinyl ligand or through the pyridyl nitrogen. The inherent low solubility of the perylene compounds was improved through the design of poly-PEGylated (PEG=polyethylene glycol) units bearing a terminal alkyne or a pyridyl group. By absorbing the compounds on silica, vapours and gases could be detected in the solid state. The reaction of the complexes [Ru(CH=CH-Per^Im)Cl(CO)(py-3PEG)(PPh₃)₂] and [Ru(CH=CH-3PEG)Cl(CO)(py-Per^Im)(PPh₃)₂] with carbon monoxide, isonitrile or cyanide was found to result in modulation of the fluorescence behaviour. The complexes were observed to display solvatochromic effects and the interaction of the complexes with a wide range of other species was also studied. The study suggests that such complexes have potential for the detection of gases or vapours that are toxic to humans.     

"Long-range" metal-ligand cooperation in H2 activation and ammonia-promoted hydride transfer with a ruthenium-acridine pincer complex

The acridine-based pincer complex 1 exhibits an unprecedented mode of metal-ligand cooperation involving a "long-range" interaction between the distal acridine C9 position and the metal center. Reaction of 1 with H(2)/KOH results in H(2) splitting between the Ru center and C9 with concomitant dearomatization of the acridine moiety. DFT calculations show that this process involves the formation of a Ru dihydride intermediate bearing a bent acridine ligand in which C9 is in close proximity to a hydride ligand followed by through-space hydride transfer. Ammonia induces transfer of a hydride from the Ru center of 1 to C9 of the flexible acridine pincer ligand, forming an unusual dearomatized fac-acridine PNP complex.