cis–trans Geometrical isomerization of bis(2-pyridinecarboxylato)nitrosylruthenium complex accompanying electrochemical one-electron reduction

cis-[Ru(NO)(CH₃CN)(pyca)₂] and trans-[Ru(NO)(OH)(pyca)₂] (pyca = 2-pyridinecarboxylato) were synthesized and characterized by X-ray crystallography. Electrochemical behaviors of cis-[Ru(NO)(CH₃CN)(pyca)₂] and cis-[Ru(NO)(CH₃O)(pyca)₂] in acetonitrile were studied. These complexes showed two reduction processes in CH₃CN. The controlled potential electrolyses of cis-[Ru(NO)(CH₃O)(pyca)₂] in a methanol–acetonitrile mixed solution were performed at the potential of the first reduction process. trans-[Ru(NO)(CH₃O)(pyca)₂] was isolated from the electrolyzed solution and characterized by IR and CV. The cis–trans geometrical change reaction occurred in the electrochemical one-electron reduction of cis-[Ru(NO)(CH₃O)(pyca)₂].     

Polymeric (NO)3(N2O) n , (NO)3(N2O) n + , and (NO)3(N2O) n − : an interpretation of experimental observations

Semi-empirical and ab initio calculations are reported which provide a possible explanation for reported experimental results on 2-photon ionization of NO containing a few percent of N₂O, which found (NO)₃(N₂O) _n ^+or? clusters to be significantly more abundant than other (NO) _m (N₂O) _n products. It is found that the observed abundances of (NO)₃(N₂O) _n ionic clusters may be accounted for by the existence of covalent cyclic trimers of nitric oxide attached to oligomers of nitrous oxide. The extra stability of NO trimers in the observed clusters appears to arise from (NO) ₃ ⁺ rather than (NO)₃. Attachment of an (N₂O) _n side chain to (NO) ₃ ⁺ occurs exothermically. It is suggested that the addition of N₂O to cyclic-(NO) ₃ ⁺ might provide a means of making a polymer of nitrous oxide, which could have useful properties.     

Formation of paramagnetic mononuclear iron nitrosyl complexes from diamagnetic di- and tetranuclear iron-sulphur nitrosyls: characterisation by EPR spectroscopy and study of thiolate and nitrosyl ligand exchange reactions

The diamagnetic Roussin esters Fe₂(SR)₂(NO)₄ readily underwent exchange with thiols R′SH to yield Fe₂(SR′)₂(NO)₄: the exchange was faster in polar, coordinating solvents where paramagnetic, mononuclear complexes of types [Fe(NO)₂(solvent)₂]⁺ and Fe(NO) ₂(SR)(solvent) were formed. With the corresponding thiolate anions RS^-, the esters Fe₂(SR)₂(NO)₄ formed the mononuclear complexes [Fe(SR)₂(NO)₂]^-, which were fully characterised by EPR spectroscopy for R = H, Me, Et, i-Pr, t-Bu and PhCH₂: assignments of hyperfine couplings were confirmed by use of ¹⁵N. With Fe₂(SR)₂(NO)₄ and a different set of thiolate anion, R′S ^-, in excess, thiol exchange occurred to give [Fe(SR′)₂(NO)₂]^-. A mechanism for formation of Fe₂(SR′)₂(NO)₄ from Fe₂(SR)₂(NO)₄ has been proposed. The paramagnetic mononuclear complexes [Fe(SR)₂(NO)₂] were also readily formed from the diamagnetic clusters [Fe₄S₃(NO)₇]^- and Fe₄S₄(NO)₄, together with [Fe(SR)₃(NO)]^-, and additionally from [Fe(CO)₃NO]^-. [Fe(SMe)₂(NO)₂]^-. was found to be a precursor of isolable Fe₂(SMe)₂(NO)₄, and [Fe(SH)₂ (NO)₂]^- to be the common precursor of both Roussin′s red anion [Fe₂S₂(NO)₄]^- and Roussin's black anion [Fe₄S₃ (NO)₇]^- interconvertible by appropriate adjustment of pH. The nitrosyl groups in these complexes were freely labile, and mononitrosyliron and dinitrosyliron fragments were readily interconvertible: FE(NO) fragments were favoured by the dimethyldithiocarbamate ligand (Me₂NCS ₂) and Fe(NO)₂ fragments by thiolate ligands, RS^-, regardless of the origin of the Fe(NO)_x(x = 1,2) fragment: both mono- and dinitrosyliron complexes persisted with [(i-PrO)₂S₂]^- as ligand. Isotopic labelling showed the occurrence of rapid exchange of nitrogen between nitrosyl ligands and added nitrite in Fe(NO)(S₂CNMe₂)₂ and [Fe(SR)₂(NO)₂]^-     

Chemie polyfunktioneller moleküle: LXXVI. Metallcarbonyl-, metallnitrosylcarbonyl-und metallnitrosyl-komplexe des bis(diphenylphosphino)amins

The compound Ph₂PN(H)PPh₂ (I) reacts under special conditions with M(CO)₆ (M  Cr, Mo), Fe(NO)₂(CO)₂ and Co(NO)(CO)₃ to give the new complexes cis-M(CO)₂[Ph₂PN(H)PPh₂]₂ (III, IV), [Fe(NO)₂(CO)Ph₂P]₂NH (V), [Fe(NO)₂Ph₂-PN(H)PPh₂]₂ (VI) and Co(NO)(CO)₂Ph₂PN(H)PPh₂ (VII). Compound VI can also be prepared reacting V with I. For III and IV proton NMR spectra indicate some interaction between o-protons of the phenyl rings and cis-M(CO)₂ groups. VI exists an eight-membered ring complex without a metal-metal bond. On the basis of spectroscopic data VII seems to exist in two conformers.     

Ratiometric two-photon excited photoluminescence of quantum dots triggered by near-infrared-light for real-time detection of nitric oxide release in situ

Probe-donor integrated nanocomposites were developed from conjugating silica-coated Mn²⁺:ZnS quantum dots (QDs) with MoS₂ QDs and photosensitive nitric oxide (NO) donors (Fe₄S₃(NO)₇⁻, RBS). Under excitation with near-infrared (NIR) light at 808 nm, the Mn²⁺:ZnS@SiO₂/MoS₂-RBS nanocomposites showed the dual-emissive two-photon excited photoluminescence (TPEPL) that induced RBS photolysis to release NO in situ. NO caused TPEPL quenching of Mn²⁺:ZnS QDs, but it produced almost no impact on the TPEPL of MoS₂ QDs. Hence, the nanocomposites were developed as a novel QDs-based ratiometric TPEPL probe for real-time detection of NO release in situ. The ratiometric TPEPL intensity is nearly linear (R² = 0.9901) with NO concentration in the range of 0.01∼0.8 μM, which corresponds to the range of NO release time (0∼15 min). The detection limit was calculated to be approximately 4 nM of NO. Experimental results confirmed that this novel ratiometric TPEPL probe possessed high selectivity and sensitivity for the detection of NO against potential competitors, and especially showed high detection performance for NIR-light triggered NO release in tumor intracellular microenvironments. These results would promote the development of versatile probe-donor integrated systems, also providing a facile and efficient strategy to real-time detect the highly controllable drug release in situ, especially in physiological microenvironments.     

Ruthenium and rhodium nitrosyl complexes containing dichalcogenoimidodiphosphinate ligands

Interaction of [Ru(NO)Cl₃(PPh₃)₂] with K[N(R₂PS)₂] in refluxing N,N-dimethylformamide afforded trans-[Ru(NO)Cl{N(R₂PS)₂}₂] (R = Ph (1), Prⁱ (2)). Reaction of [Ru(NO)Cl₃(PPh₃)₂] with K[N(Ph₂PSe)₂] led to formation of a mixture of trans-[Ru(NO)Cl{N(Ph₂PSe)₂}₂] (3) and trans-[Ru(NO)Cl{N(Ph₂PSe)₂}{Ph₂P(Se)NPPh₂}] (4). Reaction of Ru(NO)Cl₃ · xH₂O with K[N(Ph₂PO)₂] afforded cis-[Ru(NO)(Cl){N(Ph₂PO)₂}₂] (5). Treatment of [Rh(NO)Cl₂(PPh₃)₂] with K[N(R₂PQ)₂] gave Rh(NO){N(R₂PQ)₂}₂] (R = Ph, Q = S (6) or Se (7); R = Prⁱ, Q = S (8) or Se (9)). Protonation of 8 with HBF₄ led to formation of trans-[Rh(NO)Cl{HN(Prⁱ₂PS)₂}₂][BF₄]₂ (10). X-ray diffraction studies revealed that the nitrosyl ligands in 2 and 4 are linear, whereas that in 9 is bent with the Rh–N–O bond angle of 125.7(3)°.     

Photoactive ruthenium nitrosyls derived from quinoline- and pyridine-based ligands: Accelerated photorelease of NO due to quinoline ligation

The ruthenium nitrosyl [(PaPy₂Q)Ru(NO)](BF₄)₂, derived from the quinoline-based ligand PaPy₂QH (PaPy₂QH = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-quinaldine-2-carboxamide; H = dissociable proton) has been synthesized and characterized by X-ray crystallography and spectroscopic techniques. This {Ru–NO}⁶ nitrosyl is soluble in aqueous media and stable under physiological conditions at pH 7. [(PaPy₂Q)Ru(NO)]²⁺ releases NO rapidly upon exposure to low-intensity UV light (5 mW/cm²). The NO donor capacity of this nitrosyl (quantum yield = 0.20, λ_irr = 365 nm) is considerably higher than that of analogous nitrosyl derived from a polypyridyl ligand without the quinoline moiety.     

Quantum chemical study of the bond orders in the ruthenium,diruthenium and dirhodium nitrosyl complexes

Density functional calculations with the B3LYP functional were carried out for the [Ru(NO)Cl₅]²⁻, [Ru(NO)(NH₃)₅]³⁺, [Ru(NO)(CN)₅]²⁻, [Ru(NO)(CN)₅]³⁻, [Ru(NO)(hedta)]^q (hedta = N-(hydroxyethyl)ethylenediaminetriacetate triple-charged anion; q = 0, −1, −2), Rh₂(O₂CR)₄, Rh₂(O₂CR)₄(NO)₂, Ru₂(O₂CR)₄, Ru₂(O₂CR)₄(NO)₂, Ru₂(dpf)₄, and Ru₂(dpf)₄(NO)₂ (dpf = N,N′-diphenylformamidinate ion; R = H, CH₃, CF₃) complexes. The electronic structure was analyzed in terms of Mayer and Wiberg bond order indices. The technique of bond order indices decomposition into σ-, π-, and δ-contributions was proposed.     

Crystal structure,electrochemical and photochemical studies of the trans-[Fe(cyclam)(NO)Cl]Cl2 complex (cyclam = 1,4,8,11-tetraazacyclotetradecane)

The trans-[Fe(cyclam)(NO)Cl]Cl₂ complex was synthesized by the reaction of cis-[Fe(cyclam)Cl₂]Cl with NO gas. The X-ray structure of the complex showed that the [Fe–NO] moiety is linear, consistent with the NO⁺ character of the nitric oxide ligand. This suggestion was reinforced by the IR data, which showed the νNO at 1888 cm⁻¹. The cyclic voltammogram of the trans-[Fe(cyclam)(NO)Cl]²⁺ complex presented three electrochemical processes at −0.70, 0.08 and 0.40 V versus Ag/AgCl. The first and last redox processes are centered at the NO ligand, whereas the second is characteristic of the generated aqua species, trans-[Fe(cyclam)Cl(H₂O)]²⁺. Upon irradiation at 330 nm, pH 3.4, the title complex releases the NO moiety with the concomitant generation of the trans-[Fe(cyclam)(H₂O)Cl]⁺ complex as suggested by electronic and IR spectroscopy as well as by cyclic voltammetry technique.     

Behavior of nitrite forms of nitrosylruthenium on extraction and back extraction of heterometalic Ru/Zn complexes with trioctylphosphine oxide

The state of ruthenium in conjugated phases upon extraction of trans-[Ru(¹⁵NO)(¹⁵NO₂)₄(OH)]^2? complex with tri-n-octylphosphine oxide (TOPO) in the presence of Zn²⁺ and subsequent back extraction with H¹⁵NO₃ and NH₃(concd.) solutions was studied by ¹⁵N NMR. Binuclear complexes [Ru(NO)(NO₂)_5?n (μ-NO₂) _n?1(μ-OH)Zn(TOPO) _n ] and [Ru(NO)(NO₂)_4?n (ONO)(μ-NO₂) _n?1(μ-OH)Zn(TOPO) _n ], where n = 2, 3, are predominant forms in extract. Kinetic restrictions for ruthenium extraction with TOPO solution in hexane and its back extraction with aqueous solutions of nitric acid and ammonia are eliminated in the absence of direct coordination of extractant to ruthenium. fac-Dinitronitrosyl forms [Ru(NO)(H₂O)₃(NO₂)₂]⁺, [Ru(NO)(H₂O)₂(NO₂)₂(NO₃)]⁰ (3 and 6 M HNO₃) and [Ru(NO)(H₂O)(NO₂)₂(NO₃)₂]^? (6 M HNO₃) prevail in nitric acid back extracts. Equilibrium constant at ambient temperature (0.05 ± 0.01) was assessed for the coordination of second nitrate ion to nitrosylruthenium dinitronitrato complex. Complex species [Ru(NO)(NO₂)₄(OH)]^2? and [Ru(NO)(NO₂)₃(ONO)(OH)]^2? prevail in ammonia back extract.     

Intramolekulare Redoxreaktionen bei der thermischen Zersetzung von Additionskomplexen des Typs Mo(NO)2Cl2L2 und Mo(NO)Cl3L2

The intermediates formed from Mo(NO)₂Cl₂ L ₂ and Mo(NO)Cl₃ L ₂ by splitting-off of weakly-coordinated ligandsL (alcohols, glycols, nitriles) decompose in exothermic reactions: the decomposition products are N₂, MoOCl₄ and MoO₃. If the ligandL is strongly coordinated and is reducing (DMFA, DMSO, Pph₃, Asph₃), the NO groups oxidize the ligandL by formation of N₂ in an exothermic intramolecular redox process under 300?. The central atom is oxidized by NO, and N₂O is formed above 300? in the case of non-reducing ligandsL (OPph₃, OAsph₃). An endothermic redox reaction with chlorine formation is observed during decomposition of the trichloro complex. The solid residue is metallic molybdenum.     

NO binds to unsaturated Os(IV) polyhydrides as a redox reagent

Reaction of Os(H)₃ClL₂(LPⁱPr₃) with equimolar NO occurs via a detectable paramagnetic species, to form OsCl(NO)L₂ + H₂, then Os(H)₂Cl(NO)L₂, together with the product of halogen transfer, OsHCl₂(NO)L₂. For comparison, equimolar NO and the dichloride Os(H)₂Cl₂L₂ react to give OsHCl₂(NO)L₂. DFT(PBE) calculations on potential radical intermediates reveal cases where spin density is on NO (vs. on Os), and show how coordinated H₂ can lead to the observed halogen transfer.     

[M(CO)2(NO)], a new core in bioorganometallic chemistry: model complexes of [Re(CO)2(NO)] and [Tc(CO)2(NO)]

In this study selected bidentate (L²) and tridentate (L³) ligands were coordinated to the Re(I) or Tc(I) core [M(CO)₂(NO)]²⁺ resulting in complexes of the general formula fac-[MX(L²)(CO)₂(NO)] and fac-[M(L³)(CO)₂(NO)] (M = Re or Tc; X = Br or Cl). The complexes were obtained directly from the reaction of [M(CO)₂(NO)]²⁺ with the ligand or indirectly by first reacting the ligand with [M(CO)₃]⁺ and subsequent nitrosylation with [NO][BF₄] or [NO][HSO₄]. Most of the reactions were performed with cold rhenium on a macroscopic level before the conditions were adapted to the n.c.a. level with technetium (^99mTc). Chloride, bromide and nitrate were used as monodentate ligands, picolinic acid (PIC) as a bidentate ligand and histidine (HIS), iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) as tridentate ligands. We synthesised and describe the dinuclear complex [ReCl(μ-Cl)(CO)₂(NO)]₂ and the mononuclear complexes [NEt₄][ReCl₃(CO)₂(NO)], [NEt₄][ReBr₃(CO)₂(NO)], [ReBr(PIC)(CO)₂(NO)], [NMe₄][Re(NO₃)₃(CO)₂(NO)], [Re(HIS)(CO)₂(NO)][BF₄], [⁹⁹Tc(HIS)(CO)₂(NO)][BF₄], [^99mTc(IDA)(CO)₂ (NO)] and [^99mTc(NTA)(CO)₂(NO)]. The chemical and physical characteristics of the Re and Tc-dicarbonyl-nitrosyl complexes differ significantly from those of the corresponding tricarbonyl compounds.     

New method for the synthesis of trans-hydroxotetraamminenitrosoruthenium(II) dichloride and its characterization

A procedure for the synthesis of mpa h c-[Ru(NO)(NH₃)₄(OH)]Cl₂ in a nearly quantitative yield (～95%) comprising treatment of a solution of (NH₄)₂[Ru(NO)Cl₅] with ammonium carbonate at t ～80°C was developed. It was found that [Ru(NO)(NH₃)₄(H₂O)]Cl₃·H₂O and trans-[Ru(NO)(NH₃)₄Cl]Cl₂ formed in the reaction of [Ru(NO)(NH₃)₄(OH)]Cl₂ with hydrochloric acid at various temperatures most often contain some initial hydroxy complex. The former compound is unstable, even at room temperature, it slowly eliminates water and HCl. A procedure for preparing the latter compound in a pure state in 85–90% yield was proposed. The acidity constant of the complex trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺ at room temperature (K _a = (4 ± 1) × 10^?2) was estimated by ¹⁴N NMR spectroscopy.     

NO donors cis-[Ru(bpy)2(L)NO] and [Fe(CN)4(L)NO] complexes immobilized on modified mesoporous silica spheres

The reaction of [Ru(bpy)₂Cl₂] and Na₂[Fe(CN)₄(dmso)₂] complexes with isonicotinic acid immobilized on silica spheres (Si-ATPS-ISN) followed by a NO bubbling produced Si-ATPS-ISN-[Ru(bpy)₂(NO)] (system I) and Si-ATPS-ISN-[Fe(CN)₄(NO)] (system II). The characterization of these systems was carried out by UV–Vis, FTIR spectroscopy and electrochemical techniques. As judged by the FTIR data, the nitric oxide ligand has an NO⁺ character in both systems (ν(NO⁺): 1938 cm⁻¹). The NO release, which was monitored by means of FTIR, electrochemistry, and NO sensor electrode, was observed for both systems upon white light irradiation and chemical reduction by cysteine. These results indicated that the system (II) presents a higher potential for controlled NO release. The characterization (FTIR and UV–Vis) of the systems after the NO release suggested the formation of the aqua systems ATPS-ISN-[Ru(bpy)₂(OH₂)] and ATPS-ISN-[Ru(bpy)₂(OH₂)].     

ESR and electronic absorption spectra of chromium acetylacetonato nitrosyl complexes

The cis- and trans-chromium nitrosyl complexes with formulae [Cr(NO)(acac)₂L] (L = H₂O, NH₃, pyridine and imidazole) and [Cr(NO)(ac     

Electrochemical reduction of dialkylamide and bis-trimethylsilylamido complexes of chromium(III) and ytterbium in non-aqueous solvents

The electrochemical reductions of (a) Cr[N(SiMe₃)₂]₃, Cr(NPrⁱ₂)₃, Cr(NO)[N(SiMe₃)₂]₃, Cr(NO)(NPrⁱ₂)₃ and Cr(NO)(OBu^t)₂(NPrⁱ₂) in acetonitrile, and (b) Yb[N(siMe₃)₂]₃ in dimethylsulphoxide, have been studied using cyclic voltammetry (platinum bead electrode) and controlled potential coulometry (mercury pool electrode). The results are interpreted in terms of quasi-reversible or irreversible one-electron reduction and possible side-reactions. A number of similar complexes of titanium, vanadium, manganese, iron and cobalt were investigated but electrochemical studies were precluded due to reactions with solvent and/or supporting electrolyte.     

Nitrosoruthenium hydroxo and aqua complexes of the trans-dipyridine series: Synthesis,structures, and characterization

A procedure for the synthesis of trans-Ru(NO)(Py)₂Cl₂(OH) (I) from K₂[Ru(NO)Cl₅] was proposed. Treatment of hydroxo complex I with HCl or H₂SO₄ at room temperature gave the corresponding salts trans-[Ru(NO)(Py)₂Cl₂(H₂O)]Cl · 2H₂O (II) and trans-[Ru(NO)(Py)₂Cl₂(H₂O)]HSO₄ (III). All the complexes obtained were characterized by ¹H and ¹³C NMR and IR spectroscopy and elemental analysis; their structures were determined by X-ray diffraction. The structures are stabilized by π-stacking between the pyridine ligands of adjacent complex species.     

Bridge cleavage reactions of cyclopalladated nitrosamines with thioamides and related compounds

The palladacycle [Pd(μ-O₂CMe){κ²C,N-4-MeC₆H₃N(Me)NO}]₂ readily undergoes bridge cleavage reactions with a variety of compounds containing donor functionalities including thioamides, 8-hydroxyquinoline, thioureas, selenoureas, acetylacetone derivatives, dithiocarbamates, xanthates, as well as bidentate N-donors to afford either the monomeric, neutral Pd(II) complexes [Pd{κ²C,N-4-MeC₆H₃N(Me)NO}{L-L}] or the monocationic complexes [Pd{κ²C,N-4-MeC₆H₃N(Me)NO}(N-N)]PF₆ in high yields. A series of 15 different complexes was prepared and fully characterised spectroscopically and, in some cases, by X-ray diffraction. It was also found that the dithiocarbamato complex undergoes a disproportionation reaction in solution to give the bis(cyclometallated) complex [Pd{κ²C,N-4-MeC₆H₃N(Me)NO}₂] as well as the bis(dithiocarbamato) complex [Pd{κ²S-S₂CNEt₂}₂].     

Chirality changes in reactions of asymmetric molybdenum complexes

Optical rotatory dispersion and circular dichroism studies have allowed the determination of the changes in configuration at the molybdenum center upon displacement of carbonyl and iodide in neomenthylcyclopentadienyl—Mo(allyl)(NO)X systems. Displacement of carbonyl by iodide occurs with retention of configuration. Replacement of iodide with benzenesulfonate followed by replacement of the sulfonate with iodide occurs stereospecifically with net retention of configuration. In the case of cyclopentadienylMo(cyclooctenyl)(NO)I, the enantiomers were separated via a spontaneous resolution through crystallization of the complex in the space group P2₁2₁2₁. These studies have allowed the correlation not only of the absolute configuration at the metal center with CD studies, but also have established that a long wavelength optically active transition at approximately 400 nm can be correlated with endo-exo isomerism. Comparison of the rates of interconversion suggest that endo to exo isomerization occurs via a clockwise rotation of the allyl in the (R)-isomer. Crystallographic details: (—)-(S)-(NMCp)Mo(allyl)(NO)I crystallizes in the space group P2₁2₁2₁ with a 7.221(1), b 12.686(7), c 21.603(7) Å, Z = 4, V = 1979(2) ų; R₁ = 0.039, R₂ = 0.046; (—)-(S)-(Cp)Mo(cyclooctenyl)(NO)I crystallizes in the space group P2₁2₁2₁ with a 8.466(1), b 10.449(2), c 16.372(2) Å, Z = 4, V = 1448.3(6), R₁ = 0.038, and R₂ = 0.046.