Kinetics of the mediatory reduction ofgem-dichlorocyclopropanes

The effect of the nature of organic electron transfer agents and of Pt^II, Pd^II, Rh^II, Co^II, Ni^II, Cu^II, Cr^III, Mn^II, Ti^III, V^III, Zn^II, and Ag^I metal ions on the kinetics of the homogeneous reduction ofgem-dichlorocyclopropanes has been studied. Pt^II, Pd^II, Rh^III, Co^II, and Ni^II ions accelerate this process, V^III and Ag^I ions exert practically no effect on the reduction rate, and the rest of the metal ions exhibit inhibitor properties.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1407–1410, August, 1993.     

1, 3, 4-Thiadiazole-2, 5-dithiol as a Complexing Agent II. Complexes of NiII,RhI, PdII,PtII, AuIII,and CuII

1, 3, 4-Thiadiazol-2, 5-Dithiol als Komplexierungsreagenz. II. Komplexe des Ni^II, Rh^I, Pd^II, Pt^II, Au^III und Cu^II Complexes of Ni^II, Rh^I, Pd^II, Pt^II, Au^III, and Cu^II with 1, 3, 4-thiadiazole-2, 5- dithiol have been prepared. Probable structures have been proposed for the complexes on the basis of chemical analysis, magnetic susceptibility and spectral data. Crystal field parameters have been calculated which are in keeping with the structures proposed.     

Coordination Chemistry of N‐Heterocyclic Nitrenium‐Based Ligands

Comprehensive studies on the coordination properties of tridentate nitrenium‐based ligands are presented. N‐heterocyclic nitrenium ions demonstrate general and versatile binding abilities to various transition metals, as exemplified by the synthesis and characterization of Rh^I, Rh^III, Mo⁰, Ru⁰, Ru^II, Pd^II, Pt^II, Pt^IV, and Ag^I complexes based on these unusual ligands. Formation of nitrenium–metal bonds is unambiguously confirmed both in solution by selective ¹⁵N‐labeling experiments and in the solid state by X‐ray crystallography. The generality of N‐heterocyclic nitrenium as a ligand is also validated by a systematic DFT study of its affinity towards all second‐row transition and post‐transition metals (Y–Cd) in terms of the corresponding bond‐dissociation energies.     

Electrochemical and quantum chemical investigation of the CuI and CuII complexes with biquinolyl monomer and polymer ligands

Structural reorganization of polyamide (PA) and low-molecular-weight Cu^I and Cu^II complexes with biquinolyl (biQ) ligands during their mutual redox transformations in solution was studied using the electrochemical methods (cyclic voltammetry and preparative electrolysis) and quantum chemical DFT calculations. The influence of electronic factors and geometry distortions in the complexes on the ionization energy on going from Cu^I to Cu^II was evaluated in comparison. The catalytically active form of the [Cu^I(PA)L₂]BF₄ complex can be synthesized in situ from the stable tetrahedral complex [Cu^I(PA)₂]BF₄ by the series of successive redox transitions Cu^I → Cu^II → Cu^I accompanied by the loss of one biQ-containing macroligand. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1331–1340, July, 2007.     

Synthesis, characterization, catalytic, electrochemical and thermal properties of tetradentate Schiff base complexes

In this study, the Schiff base ligands H₂L¹–H₂L³ and their Cu^II, Co^II, Ni^II, Fe^III Ru^III and VO^IV complexes have been prepared and characterized by spectroscopic and analytical techniques. All the complexes are mononuclear. Keto-enol tautomeric forms of the ligands have been investigated in polar and apolar solvents. The ligands favor the keto-form in the C₇H₈ and C₆H₁₄. The C–C coupling reaction of the 2,6-di-t-butylphenol has been investigated by the Co^II and Cu^II complexes. Thermal properties of the complexes have been assessed using thermal techniques and similar properties were found. In the Fe^III and Ru^III complexes, firstly, the coordinated water molecule is lost from the complex; in the second step, the chloride ion leaves the molecule in the 300–350 °C temperature range. Finally, the complexes decompose to the appropriate metal oxide at the higher temperature ranges. The electrochemical properties of the complexes have been studied in the two different solvents (DMF and CH₃CN).     

Ligational behaviour of two biologically active N−S donors towards cobalt(III), iron(III), iron(II) and rhodium(III)

Summary The chelating behaviour of two biologically active ligands, pyridine-2-carboxaldehyde(4-phenyl) thiosemicarbazone(L₁H) and pyridine-2-carboxaldehyde thiosemicarbazone(LH), towards Fe^III, Co^III, Fe^II and Rh^III has been investigated. The ligands act as tridentate N–N–S donors, resulting in the formation of bis-chelate complexes of the type M^III(A)₂X·nH₂O (A=L₁ or L; X=Cl, ClO₄; M=Co^III, Rh^III, Fe^III), Fe^II(L₁H)₂SO₄·2H₂O and Fe^II(L₁)₂·H₂O. Biological activity of the ligands and the metal complexes in the form ofin vitro antibacterial activities towardsE. coli has been evaluated and the possible reasons for enhancement of the activity of ligands on coordination to metal ion is discussed.     

Chelatbildung mit N-unsubstituierten 1.2-Diiminliganden

Fe^II, Co^III, Ni^II, Pd^II, and Rh^III chelates with the N-unsubstituted 1-2-diimine ligands benzildiimine and 9.10-phenanthrenequinonediimine have been prepared. The compounds are characterised chemically, spectroscopically (uv, vis, ir) and polarographically. The results indicate remarkable π-back bonding in the chelates. The unusual magnetic moments of the Fe^II, Co^III and Rh^III chelates are caused by temperature-independent paramagnetism. Fe^II, Co^III, Ni^II and Cu^II chelates of the partially deprotonated phenanthrenequinone diimine are obtained.     

Electrochemical Properties of a Rhodium(III) Mono-Terpyridyl Complex and Use as a Catalyst for Light-Driven Hydrogen Evolution in Water

Molecular hydrogen (H₂) is considered one of the most promising fuels to decarbonize the industrial and transportation sectors, and its photocatalytic production from molecular catalysts is a research field that is still abounding. The search for new molecular catalysts for H₂ production with simple and easily synthesized ligands is still ongoing, and the terpyridine ligand with its particular electronic and coordination properties, is a good candidate to design new catalysts meeting these requirements. Herein, we have isolated the new mono-terpyridyl rhodium complex, [Rh^III(tpy)(CH₃CN)Cl₂](CF₃SO₃) (Rh-tpy), and shown that it can act as a catalyst for the light-induced proton reduction into H₂ in water in the presence of the [Ru(bpy)₃]Cl₂ (Ru) photosensitizer and ascorbate as sacrificial electron donor. Under photocatalytic conditions, in acetate buffer at pH 4.5 with 0.1 M of ascorbate and 530 μM of Ru, the Rh-tpy catalyst produces H₂ with turnover number versus catalyst (TON_Cat*) of 300 at a Rh concentration of 10 μM, and up to 1000 at a concentration of 1 μM. The photocatalytic performance of Ru/Rh-tpy/HA^–/H₂A has been also compared with that obtained with the bis-dimethyl-bipyridyl complex [Rh^III(dmbpy)₂Cl₂]⁺ (Rh2) as a catalyst in the same experimental conditions. The investigation of the electrochemical properties of Rh-tpy in DMF solvent reveals that the two-electrons reduced state of the complex, the square-planar [Rh^I(tpy)Cl] (Rh^I-tpy), is quantitatively electrogenerated by bulk electrolysis. This complex is stable for hours under an inert atmosphere owing to the π-acceptor property of the terpyridine ligand that stabilizes the low oxidation states of the rhodium, making this catalyst less prone to degrade during photocatalysis. The π-acceptor property of terpyridine also confers to the Rh-tpy catalyst a moderately negative reduction potential (Ep_c(Rh^III/Rh^I) = −0.83 V vs. SCE in DMF), making possible its reduction by the reduced state of Ru, [Ru^II(bpy)(bpy^•−)]⁺ (Ru⁻) (E_1/2(Ru^II/Ru⁻) = −1.50 V vs. SCE) generated by a reductive quenching of the Ru excited state (*Ru) by ascorbate during photocatalysis. A Stern–Volmer plot and transient absorption spectroscopy confirmed that the first step of the photocatalytic process is the reductive quenching of *Ru by ascorbate. The resulting reduced Ru species (Ru⁻) were then able to activate the Rh^III-tpy H₂-evolving catalyst by reduction generating Rh^I-tpy, which can react with a proton on a sub-nanosecond time scale to form a Rh^III(H)-tpy hydride, the key intermediate for H₂ evolution.     

Group 9 Metal Complexes of meso‐Aryl‐Substituted Rubyrin

The metalation of meso‐tetrakis(pentafluorophenyl)‐substituted [26]rubyrin has been explored with Group 9 metal salts (Rh^I, Co^II, Ir^III), affording a Hückel aromatic [26]rubyrin–bis‐Rh^I complex with a highly curved gable‐like structure, a Hückel antiaromatic [24]rubyrin–bis‐Co^II complex that displays intramolecular antiferromagnetic coupling between the two Co^II ions (J=?4.5 cm^?1), and two Cp*‐capped Ir^III complexes; in one, the iridium metal sits on the [26]rubyrin frame with two Ir?N bonds, whereas the other has an additional Ir?C bond, although both Ir^III complexes display moderate aromatic character. This work demonstrates characteristic metalation abilities of this [26]rubyrin toward Group 9 metals.     

Synthesis, in situ spectroelectrochemical, in situ electrocolorimetric and electrocatalytic investigation of brown-manganese phthalocyanines

α- and β-substituted tetrakis(6-hydroxyhexylthiol) phthalocyaninato manganese (III) chloride complexes have been prepared via cyclotetramerization. Both complexes have been characterized by elemental analysis, FTIR, MS and UV–Vis spectral data. The voltammetric and in situ spectroelectrochemical studies reveal that both complexes exhibit an oxidation and three reduction processes having reversible, one-electron, and diffusion controlled mass transfer characteristics, which are assigned to Mn^IIIPc²⁻/Mn^IVPc²⁻, Mn^IIIPc²⁻/Mn^IIPc²⁻, Mn^IIPc²⁻/Mn^IPc²⁻, and Mn^IPc²⁻/Mn^IPc³⁻ couples respectively. The existence of oxygen in solution significantly affects the in situ spectroelectrochemical behavior of the complexes due to the formation of μ-oxo MnPc species. An in situ electrocolorimetric method has been applied to investigate the colors of the electro-generated anionic and cationic forms of the complexes for the first time in this study. The complexes, coated on a glassy carbon electrode potentiostatically, show considerable high electrocatalytic activity to hydrogen evolution reactions in aqueous solution.     

Kinetic studies on promazine oxidation by FeIII/CuII in acidic aqueous bromide solutions. Spectroscopic and kinetic non-additivity as evidence for the CuII–Br–FeIII-type heterobimetallic complex formation

The formation of Cu^II–Br–Fe^III-type heterobimetallic complexes was observed spectrophotometrically, given the non-additivity of the spectra from the copper(II) and iron(III) complexes. The kinetics of the oxidation of promazine radical (ptz^+•) to promazine 5-oxide, by iron(III) bromides, copper(II) bromides, and a mixture of these complexes in acidic aqueous solutions, have been studied using UV–Vis spectroscopy at I = 1.0 M (H⁺, Cu²⁺, Fe³⁺, Br⁻) and T = 318 K. Copper(II) inhibits the oxidation of the promazine radical to promazine sulfoxide using iron(III) complexes. A rate retardation effect, characterized by the dependence of the pseudo second-order rate constant (k ^II) on the copper(II) concentration k ^II = a/(1 + b[Cu^II]), can be rationalized as a result of Cu^II–Br–Fe^III-type heterobimetallic complex formation.     

Enhancement of Solar Fuel Production Schemes by Using a Ru,Rh,Ru Supramolecular Photocatalyst Containing Hydroxide Labile Ligands

Polyazine‐bridged Ru^IIRh^IIIRu^II complexes with two halide ligands, Cl^? or Br^?, bound to the catalytically active Rh center are efficient single‐component photocatalysts for H₂O reduction to H₂ fuel, with the coordination environment on Rh impacting photocatalysis. Herein reported is a new, halide‐free Ru^IIRh^IIIRu^II photocatalyst with OH^? ligands bound to Rh, further enhancing the photocatalytic reactivity of the structural motif. H₂ production experiments using the photocatalyst bearing OH^? ligands at Rh relative to the analogues bearing halides at Rh in solvents of varying polarity (DMF, CH₃CN, and H₂O) suggest that ion pairing with halides deactivates photocatalyst function, representing an exciting phenomenon to exploit in the development of catalysts for solar H₂ production schemes.     

Structural and Electronic Influences on Rates of Tertpyridine−Amine CoIII−H Formation During Catalytic H2 Evolution in an Aqueous Environment

In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co^II−Cl]⁺ species results in the formation of [Co^II(κ⁴-L)(OH₂)]²⁺. Further reduction produces [Co^I(κ⁴-L)(OH₂)]⁺, which undergoes a rate-limiting structural rearrangement to [Co^I(κ⁵-L)]⁺ before being protonated to form [Co^III−H]²⁺. The rate of [Co^III−H]²⁺ formation is similar for all complexes in the series. Using E_1/2 values of various Co species and pK_a values of [Co^III−H]²⁺ estimated from PR experiments, we found that while the protonation of [Co^III−H]²⁺ is unfavorable, [Co^II−H]⁺ reacts with protons to produce H₂. The catalytic activity for H₂ evolution tracks the hydricity of the [Co^II−H]⁺ intermediate.     

On the Ligand‐to‐Metal Charge‐Transfer Photochemistry of the Copper(II) Complexes of Quercetin and Rutin

In contrast to the UV‐photoinduced ligand photoionization of the flavonoid complexes of Fe^III, redox reactions initiated in ligand‐to‐metal charge‐transfer excited states were observed on irradiation of the quercetin ( 1 ) and rutin ( 2 ) complexes of Cu^II. Solutions of complexes with stoichiometries [Cu^IIL₂] (L=quercetin, rutin) and [Cu^II₂L_n] (n=1, L=quercetin; n=3, L=rutin) were flash‐irradiated at 351 nm. Transient spectra observed in these experiments showed the formation of radical ligands corresponding to the one‐electron oxidation of L and the reduction of Cu^II to Cu^I. The radical ligands remained coordinated to the Cu^I centers, and the substitution reactions replacing them by solvent occurred with lifetimes τ<350 ns. These are lifetimes shorter than the known lifetimes (τ>1 ms) of the quercetin and rutin radical's decay.     

Intercomponent and interfacial electron transfer processes in polynuclear metal complexes anchored on transparent TiO2 films

A series of polynuclear complexes based on Ru^II, Os^II, Re^I and Rh^III polypyridine moieties have been prepared in the context of intramolecular energy and electron transfer studies and of interfacial electron transfer with nanocrystalline TiO₂. The polynuclear complexes allow for the occurrence of vectorial intramolecular energy and electron transfer and have been proven to be efficient sensitizers of the wide band-gap semiconductor. The performance of photoregenerative cells based on these systems and the dynamics of the excited state intramolecular processes and of the interfacial electron transfer processes are discussed.     

Darstellung und Charakterisierung einige Thiocyanat- und Selenocyanat-Komplexe von Übergangsmetallen

Some 6:1 thiocyanate complexes of Fe^III, Mo^III, Ru^III, Os^III, Ir^III and some 6:1 or 4:1 selenocyanate complexes of Fe^II, Fe^III, Mo^III, Rh^III, Pd^II, Pt^II, and Au^III have been prepared as salts of large organic cations. The compounds are characterized by their infra-red spectra and by conductance measurements. In particular the linkage property of the thiocyanate and selenocyanate ligand is discussed together with the consequences it has on the AHRLAND -CHATT -DAVIES -PEARSON classification of the central ions.     

Studies on the stereochemistry of diphenyl diketone monothio-semicarbazone and its transition metal complexes

Summary The stereochemistry and complexation behaviour of diphenyl diketone monothiosemicarbazone (DKTS) with Cu^II, Co^II, Ni^II, Cd^II, Zn^II, Pd^II, Pt^II, Ru^III, Rh^III and Ir^III have been investigated by means of chemical, magnetic and spectral (i.r., Raman, ¹H- and ¹³C-n.m.r. and electronic) studies. The ligand forms complexes of the M(DKTS)₂ type with Ni^II, Cu^II and Co^II having a distorted octahedral geometry. The absence of a v(M—X) band in the i.r. spectra, coupled with their 1:1 electrolytic conductances, suggests that Ru^III, Rh^III and Ir^III form octahedral complexes of the [M(DKTS)₂]Cl type. A four-coordinate structure involving bridging halides is proposed for the Zn^II, Cd^II, Pd^II and Pt^II complexes, which have relatively low v(M—X) vibration modes.     

Azo‐MICs: Redox‐Active Mesoionic Carbene Ligands Derived from Azoimidazolium Dyes

Azoimidazolium dyes were used as precursors for mesoionic carbene ligands (Azo‐MICs). The properties of these ligands were examined by synthesizing Rh^I, Au^I, and Pd^II complexes. Experimental (NMR, IR) and theoretical investigations show that Azo‐MICs are potent σ‐donor ligands. Yet, they feature a small singlet–triplet gap and very low‐lying LUMO levels. The unique electronic properties of Azo‐MICs allow for reversible one‐electron reductions of the metal complexes, as evidenced by cyclic voltammetry.     

Nickel complexes with cyclic ligands containing P and N atoms as coordination sites: novel biomimetic catalysts for hydrogen oxidation

Nickel complexes with new cyclic ligands containing phosphorus and nitrogen atoms as coordination sites are novel efficient catalysts for hydrogen oxidation. A systematic study of their electrochemical properties made it possible to classify the nickel systems in question into four groups according to the sequence of electron transfer processes in the reduction (M^II-M^I-M⁰) and to the nature of solvents and counterions. Regularities of catalytic transformations involving nickel complexes with P,N-cyclic ligands in the H₂ oxidation reaction in the coordination sphere of the catalyst and a correlation between the structure of the complex and its redox properties were established. The most efficient catalysts contain phenyl and 2-pyridyl substituents at the phosphorus atom and benzyl or 2-pyridyl substituents at the nitrogen atom.     

Synthesis,structure, and electrochemistry of <Emphasis Type="Italic">trans</Emphasis>-[Co<Superscript>III</Superscript>{(BA)<Subscript>2</Subscript>pn}(L)<Subscript>2</Subscript>]ClO<Subscript>4</Subscript> complexes

The structure, spectroscopic, and electrochemical properties of [Co{(BA)₂pn}(L)₂]ClO₄ complexes, where (BA)₂pn = N,N′-bis(benzoylacetone)-1,3-propylenediimine dianion and the two ancillary ligands (L) are pyridine, py (1), and 4-methylpyridine, 4-Mepy (2), have been investigated. These complexes have been characterized by elemental analyses, IR, UV–Vis and ¹H-NMR spectroscopy. The crystal structure of [Co{(BA)₂pn}(py)₂]ClO₄ (1) has been determined by X-ray diffraction. The coordination geometry around cobalt(III) is best described as a distorted octahedron. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Co^III–Co^II is electrochemically irreversible, which is accompanied by the dissociation of the axial N(py)–cobalt bonds. This process becomes quasi-reversible upon the addition of excess py ligands. The second reduction step of Co^II/I shows reversible behavior and is not influenced by the nature of the axial ligands. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.