Redox system for perfluoroalkylation of arenes and α-methylstyrene derivatives using titanium oxide as photocatalyst

Photoirradiation of titanium oxide (TiO₂) excites the electrons from the valence band to the conduction band, leaving holes in the valence band. Using these holes and electrons, it is possible to perform one-electron oxidations and reductions. We developed a method for the photocatalytic perfluoroalkylation of aromatic rings such as benzene and its derivatives, naphthalene and benzofuran with perfluoroalkyl iodide by the combination of reduction and oxidation reactions with TiO₂. Perfluoroalkyl iodide was reduced to a perfluoroalkyl radical by the excited electrons in the conduction band of TiO₂, and the resulting radical reacted with an aromatic ring to form an arenium radical that was successively oxidized to a cation by the holes in the valence band of TiO₂. Similarly, the photocatalytic reaction of α-methylstyrene with perfluoroalkyl iodide afforded perfluoroalkylated α-methylstyrene, in which the perfluoroalkyl group is on a methyl carbon.     

Perylene-Grafted Silicas: Mechanistic Study and Applications in Heterogeneous Photoredox Catalysis

A mechanistic study is herein presented for the use of heterogeneous photocatalysts based on perylene moieties. First, the successful immobilization of perylene diimides (PDI) on silica matrices is demonstrated, including their full characterization by means of electronic microscopy, surface area measurements, powder XRD, thermogravimetric analysis, and FTIR, ²⁹Si and ¹³C solid-state NMR, fluorescence, and diffuse reflectance spectroscopies. Then, the photoredox activity of the material was tested by using two model reactions, alkene oxidation and 4-nitrobenzylbromide reduction, and mechanistic studies were performed. The mechanistic insights into their photoredox activity show they have promising dual photocatalytic activity for both organic oxidations and reductions.     

Electrochemical studies on three polar diruthenium(II,III) complexes

Electrochemical studies on a new class of diruthenium(II,III) compounds were done. The complexes having a polar arrangement of ligands across the diruthenium unit in Ru₂Cl(hp)₄(Hhp), Ru₂Cl(chp)₄ and Ru₂Cl(PhNpy)₄ where Hhp, Hchp and PhNHpy are 2-hydroxypyridine, 6-chloro-2-hydroxypyridine, and 2-anilinopyridine, respectively, undergo two or more oxidations and reductions. The metal centered reductions in the range of +0.1 to ?0.75 V and oxidations in the range +0.5 to +1.2 V are discussed and compared with diruthenium carboxylato and amidato complexes.     

Growth of p- and n-dopable films from electrochemically generated C60 cations

The formidable electron-acceptor properties of C60 contrast with its difficult oxidations. Only recently it has become possible to achieve reversibility of more than one electrochemical anodic process versus the six reversible cathodic reductions. Here we exploit the reactivity of electrochemical oxidations of pure C60 to grow a film of high thermal and mechanical stability on the anode. The new material differs remarkably from its precursor since it conducts both electrons and holes. Its growth and properties are consistently characterized by a host of techniques that include atomic force microscopy (AFM), Raman and infrared spectroscopies, X-ray-photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), scanning electron microscopy and energy-dispersive X-ray analysis (SEM-EDX), matrix-assisted laser desorption/ionization (MALDI), and a variety of electrochemical measurements.     

Access to optically pure 4- and 5-substituted lactones: a case of chemical-biocatalytical cooperation

Optically pure or highly enantiomerically enriched 4- and 5-substituted lactones are rather difficult to obtain. Chemical or enzymatic syntheses alone are not particularly successful. A combination of chemical catalysis and biocatalysis, however, provides a convenient route to a variety of these useful chiral compounds. In this paper we describe the synthesis of several optically pure 4- and 5-substituted lactones obtained via whole cell-catalyzed Baeyer-Villiger oxidations of highly enantiomerically enriched 3-alkyl cyclic ketones. Such chiral ketones are readily accessed by recently developed copper-catalyzed asymmetric conjugate reductions of the corresponding enones. A very high proximal regioselectivity and complete chirality transfer was obtained by employing biological Baeyer-Villiger oxidations, using recombinant E. coli strains that overexpress cyclopentanone monooxygenase (CPMO). A comparative study showed that CPMO gives superior results to those obtained with cyclohexanone monooxygenase (CHMO) catalyzed oxidations.     

A new class of organic donor-acceptor molecules with large third-order optical nonlinearities

Donor-acceptor molecules with 4-(dimethylamino)phenyl donor and 1,1,4,4-tetracyanobuta-1,3-diene acceptor moieties are readily prepared by short, high-yielding routes. The quite small chromophores are characterised by X-ray crystallography and feature intense intramolecular charge-transfer bands, substantial quinoid character in the donor rings, reversible electrochemical reductions and oxidations and powerful third-order optical nonlinearities.     

Overview on oxidation mechanisms of organic compounds by TiO2 in heterogeneous photocatalysis

This review provides the reader with a general overview on heterogeneous photocatalytic oxidation mechanisms in the presence of TiO₂, with a special address to conversion of aliphatic and aromatic organic species. The aim was to clarify the steps of the photo-oxidation of the various classes of compounds and to relate them with the properties of the catalysts and the experimental conditions used. Reactions carried out to perform complete degradation and photocatalytic partial oxidations have been deeply discussed. Recent isotopic studies highlighted new reaction pathways concerning partial oxidation of alcohols to aldehyde and oxidation of benzene while EPR investigations confirmed that not only the photogenerated hole but also the OH radicals are involved in the oxidation of the substrates.     

Synthesis and characterization of tricyanovinyl-capped oligothiophenes as low-band-gap organic materials

Tricyanovinyl-capped oligothiophenes of up to six rings have been synthesized and characterized. The substituted oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison to unsubstituted oligomers. The solvatochromic behavior of the terthiophene-substituted molecule was investigated in a variety of solvents. Stable oxidations and reductions were exhibited by the sexithiophene-substituted molecule on the CV time scale. [structure: see text]     

A study of the synthesis and some reactions of perimidines

A study of the preparation of perimidines from 1,8-diaminonaphthalene and carbonyl compounds is presented. The optimum conditions for the reaction of the above diamine with carboxylic acids and esters, acid chlorides, anhydrides and aldehydes are defined. The chemical behavior and a number of previously unreported reactions of perimidines are presented. The latter include N-alkylations, reductions, oxidations and acylations.     

Synthesis and Properties of a BenzoquinoneDihydrotetrathiafulvalene Diad

Abstract

A new donor–acceptor diad compound 6 with the donor dihydro-TTF and acceptor quinone functions in very close proximity has been prepared and characterized. The X-ray structure shows an interesting stacking pattern and electrochemically it undergoes two reversible oxidations and two reversible reductions. An ESR signal has been observed due to thermal population of the radical anion/radical cation state.     

Pteridines,LXXXIV. Synthesis,reactivity and properties of 1,3-dimethyllumazine-6- and 7-carboxaldehyde derivatives

Convenient syntheses of 1,3-dimethyllumazine-6- (7) and -7-carboxaldehyde ( 19 ) are described. The reactivity of the carboxaldehyde group has been investigated by oxidations, reductions and various carbonyl reactions forming a series of new derivatives. The newly synthesized compounds were characterized by elemental analysis, uv and ¹H-nmr spectra.     

Electrocatalysis at polycrystalline silver in base: an example of the complexity of surface active state behaviour

Four low-level redox responses, attributed to the involvement of four different types of active surface state (or site) transitions, were observed within the double layer region in the case of polycrystalline silver electrodes in base; there is now independent evidence for such premonolayer behaviour in data reported by other authors. The potentials for each of these transitions were correlated with the onset/termination potentials of different electrocatalytic processes, usually for oxidations or reductions but in some cases for both types. The data obtained are in good agreement with the IHOAM model of electrocatalysis which was outlined earlier for the other Group 11 metals, gold and copper. Electronic Publication     

Proton Relays in Molecular Catalysis of Electrochemical Reactions: Origin and Limitations of the Boosting Effect

Homogeneous catalysis of electrochemical reactions, related to contemporary energy challenges, often involves proton‐coupled electron transfer sequences. The idea rapidly emerged that installing the proton donor (for reductions, or acceptor for oxidations) inside the catalyst molecule should be beneficial in terms of efficiency, as it would then be closer to the nerve center of the process (usually the metal in the case of transition metal complex catalysts). If this proton relay has indeed done the job, it has lost its proton at the end of each catalytic loop, and must therefore be reprotonated (for reductions, or deprotonated for oxidations) from acid (or base) from the solution before a new catalytic loop can start. The impression may thus be that there is a zero‐sum game. The conditions under which this is not the case may entail, in contrast, a considerable boosting of catalysis. This will also allow explain why the proton is such a specifically appropriate agent for this task.     

Ultrathin functional films of titanium(IV) oxide

Chemistry and physics of thin semiconducting layers of various types are subjects of intense research. Especially when nanotechnology methods such as self-assembly are involved, amazing structural and/or functional properties may appear. Also modern physical methods using variously organized plasma arrangements are able to produce uniform structures with distinctive functionality. In this review, based virtually on our own work, discussions on the preparation, structure, morphology, and function of titanium(IV) oxide nanoscopic thin films are presented. It was shown that structurally and functionally similar titanium(IV) oxide films can be prepared via completely different preparation techniques. Function tests were arranged as “primary”, covering the assessment of the light induced charge separation efficiency, and “secondary”, based on photocatalytic surface oxidations.     

Chemical reactions in fast atom bombardment mass spectrometry

Examples of various chemical reactions occurring in the matrix or in the selvedge region in fast atom bombardment (FAB) mass spectrometry are discussed. These are categorized as oxidations and reductions; substitutions; clusterings and additions; and sample decomposition or transformation. Some reactions observed showed significant time behaviour and in one case it was possible to determine rate constants. These data suggest that chemical reactions can be accelerated significantly by fast atom bombardment.     

Polymer/carrier composites as materials and reactors for organic synthesis

In this work new polymer/carrier composites are described which serve as novel materials in flow-through reactors for polymer-supported organic solution-phase synthesis. Monolithic polymer/carrier columns are prepared by a new precipitation polymerization process inside the void pore volume of megaporous glass carrier materials. Chemical functionalization of the internal polymer phase with chlorosulfonic acid or trimethylamine generates small, interconnected ion-exchange resin beads with a diameter of 1-3 microm which can be used for a large variety of organic syntheses. These monolithic rods are incorporated into an appropriate casing and can conveniently be operated in the flow-through mode. Important successful applications are polymer-assisted solution-phase reductions, oxidations and Horner-Emmons olefinations. Additionally, the use of these monolithic columns as catalytic microreactors and their performance in selected reactions are described.     

Reaction of 2-(arylazo)pyridine complexes of type [OsX2L2] (X = Cl or Br) with heterocyclic bases (B): spectra and electrochemistry of [OsX(B)L2]ClO4·H2O

Summary The synthesis and characterization of a series of complexes of the type [OsX(B)L₂] ⁺ (X = Cl or Br, B = pyridine (py) and pyrazine (pyz), L = 2-(phenylazo)pyridine (L¹) or 2-(m-tolylazo)pyridine (L²)) is described. The cations have been isolated as crystalline perchlorate monohydrates after purification by column chromatography. The diamagnetic compounds display several spin-allowed and spin-forbidden m.l.c.t. transitions in the visible region. The metal-centred oxidations and ligand-based reductions of the complexes are studied electrochemically in MeCN. Two consecutive one-electron oxidations corresponding to Os^III/Os^II and Os^IV/Os^III couples occur at ca. 1.3 and ca. 2.3 V versus s.c.e. respectively. Four successive azo-reductions are observable in the potential range -0.4 to -2.4V.     

Use of medium effects to tune the Delta E(1/2) values of bimetallic and oligometallic compounds

The redox potentials of bis(fulvalene)dinickel, 1, and the tetrakis(ferrocenyl)nickel dithiolene complex 2 have been measured in a variety of nonaqueous electrolytes. The difference in E1/2 values of the two successive one-electron oxidations of 1 (i.e., DeltaE1/2 values) increased from a low of 212 mV in anisole/[NBu4]Cl to a high of 850 mV in CH2Cl2-Na[B(C6H3(CF3)2)4], reflecting an increase of over 1010 in the comproportionation constant (Kcomp = [1+]2/[1][12+]). Six reversible one-electron processes are possible for compound 2, the four oxidations arising from the ferrocenyl substituents, and the two reductions arising from the Ni dithiolene moiety. The E1/2 spreads of the four oxidation waves and the two reduction waves are both highly sensitive to medium effects. For both 1 and 2, the largest DeltaE1/2 values for cationic products are found in solvents of low polarity and donor strength containing electrolyte salts having large anions and small cations. Conversely, the smallest DeltaE1/2 values for anionic products are found under these conditions, culminating in the observation of a single two-electron reduction wave for 2/22- in CH2Cl2-Na[B(C6H3(CF3)2)4]. A combination of solvation and ion-pairing effects must be considered, and may be used to advantage, when using DeltaE1/2 values as a measure of electronic interactions between redox centers in compounds containing two or more electron-transfer sites.     

Electrochemical studies of tetraphenylporphyrin and vanadyl porphyrin

The electrochemical reductions and oxidations of tetraphenylporphyrin (TPP) and vanadyl por-phyrin (TPP-VO) were investigated in dimethylformamide at platinum,glass carbon and microdisk electrodes.A new eleetrode reaction mechanism of TPP and TPP-VO is proposed.The kinetic parameters have also been determined.In addition,the theory of molecular hybrid orbitals is used to explain the reduction and oxidation regularity of the transition metal porphyrms     

Fiber-optic infrared spectroelectrochemical studies of six-coordinate manganese nitrosyl porphyrins in nonaqueous media

The redox behavior of the six-coordinate (por)Mn(NO)(1-MeIm) (por = tetraphenylporphyrin dianion (TPP), tetratolylporphyrin dianion (TTP), or tetra-p-methoxyphenylporphyrin dianion (T(p-OMe)PP)) complexes were examined by cyclic voltammetry at room temperature and at -78 degrees C in two nonaqueous solvents (CH2Cl2 and THF) at a Pt disk electrode. In CH2Cl2 at room temperature, the compounds undergo four oxidations and two reductions within the solvent limit; in THF, the compounds undergo one oxidation and three reductions. In both solvents, the first oxidation represents a chemically irreversible one-electron process involving the rapid loss of nitric oxide. The oxidation occurs at the MnNO site as judged from bulk electrolysis, UV-vis spectroscopy at room temperature, and IR spectroelectrochemistry at room temperature and at -78 degrees C. The second oxidation, accessible in CH2Cl2, is also chemically irreversible and occurs at the porphyrin ring; the third and the fourth oxidations are, on the other hand, chemically reversible but also occur at the porphyrin ring. The first reduction is chemically irreversible in CH2Cl2, occurs at the porphyrin ring, and is followed by loss of NO. In THF, the first reduction is chemically reversible and is followed by reversible loss of NO.