ISSN:1042-7147    

DOI:10.1002/pat.1995.220060301

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractMulti‐electron transfer plays an important role in many chemical reactions. A collection of examples, both of metal complexes that exhibit one‐step, multi‐electron transfer process, and of chemical reactions based on a multi‐electron transfer system, is presented. Emphasis is placed on the role of multi‐electron transfer process in a sense that some molecular conversion systems such as reduction of O2and oxidation of H2O become feasible through multi‐electron transfer. As an important example of molecular conversion, oxidative polymerization of sulfur‐containing compounds through two‐electron transfer, i

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060302

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractVarious electroactive reactants that undergo multipleelectron transfer reactions at electrodes are divided into two broad classes. The first class exhibits a series of single electron steps at different electrode potentials. The second class exhibits multiple‐electron transfer in a single voltammetric step. Examples from each class are offered and the reasons for their electrochemical behavior are describe

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060303

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSimultaneous bidirectional forward and backward electron transfers take place on a light‐exited semiconductor particle, even at the same geometric site. The potentials of the electron pathways are different, giving rise to two independent molecular conversion reactions. This type of multi‐electron transfer reactions is overviewed and the stepwise unidirectional multi‐electron transfer on the excited semiconductor particle is also desc

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060304

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAt different phthalocyanines and related macrocycles it is shown that one‐step, multi‐electron transfer and one‐step, multi‐change of oxidation states occur. At first, the catalytic oxidations of thiols and sulfide in the presence of different Co(II)phthalocyanines are discussed. Thiolates are oxidized to disulfides via a two‐electron transfer whereas the reduction of O2occurs via a two‐ or four‐electron transfer to H2O2or H2O. Zn(II) and Al(III)phthalocyanines are efficient sensitizers for the conversion of triplet to singlet dioxygen under illumination with visible light. In the presence of thiolates or sulfides an efficient photo‐oxidation to sulfonic acids or sulfate is observed. The oxidation state of sulfur changes from −2 to +4 or +6, respectively. This process of singlet oxygen reactions finds application in the photodynamic therapy of cancer. The unsubstituted zinc(II)‐phthalocyanine as p‐type molecular semiconductor can efficienfly reduce O2in photoelectrochemical experiments whereas zinc(II)phthalocyanines with electronwithdrawing groups as n‐type conductors are active in the photoelectrochemical oxidation of thiols. All processes include multi‐electron transfer. The electrocatalytic reduction of CO2is investigated at electrodes modified with Co(II)phthalocyanine. In particular, the phthalocyanine in a polyvinylpyridine membrane is active, so the CO2is reduced to CO by multi‐electron transfer. In addition, two photon excitations of a Mg(II)phthalocyanine are presented and

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060305

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe in situ spectrocyclic voltammetric investigations of the dimeric ruthenium complex used for water oxidation, [(bpy)2(H2O)Ru–O–Ru(H2O)(bpy)2]4+(H2O–RuIII–RuIII–OH2), were carried out in a homogeneous aqueous solution and in a Nafion membrane under different pH conditions. The in situ absorption spectra recorded for the dimer show that the dimer H2O–RuIII–RuIII–OH2complex underwent reactions initially to give the detectable H2O–RuIII–RuIV–OH and H2O–RuIII–RuIV–OH2complexes, and at higher positive potentials, this oxidized dimer underwent further oxidation to produce a presumably higher oxidation state RuV–RuVcomplex. Since this RuV–RuVcomplex is reduced rapidly by water molecules to H2O–RuIII–RuIV–OH2, it could not be detected by absorption spectrum. Independent of the pH conditions and homogeneous solution/Nafion membrane systems, the dimer RuIII–RuIVwas detected at higher potentials, suggesting that the dimer complex acts as a three‐electron oxidation catalyst. However, in the Nafion membrane system it was suggested that the dimer complex may act as a four‐electron oxidation catalyst. While the dimer complex was stable under oxidation conditions, the reduction of the dimer RuIII–RuIIIto RuII–RuIIled to decomposition

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060306

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe time evolution of a self‐sustained potential oscillation under constant current oxidation of formaldehyde was observed on the rotating ring disk electrode assemble. Under the condition when the potential was controlled, the laser deflection voltammogram as well as the conventional cyclic voltammogram were measured. The mechanism of the multi‐electron oxidationof formaldhyde on a platinum electode is discus

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060307

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe oxidative coupling reaction of 2,6‐dimethylphenol may result in either a desired polymeric substance (i.e. the polyphenylene ether, PPE) or the undesired “dimeric” species diphenoquinone, DPQ. The relative amounts of each product depend on the experimental conditions and the used catalytic system.Usually copper amine compounds are used as a catalyst for the oxidative coupling reactions. They have the advantage of easy access and produce high yields of high molecular PPE; however, other metal coordination compounds, like those of Mn, may also be used as catalysts.The present paper focuses on mechanistic studies with various copper (aliphatic and aromatic) amine compounds as catalysts. Owing to the steric constraints of the amine ligands, dinuclear Cu(II) compounds, with small bridging anionic ligands, are easily formed. Such species are believed to be the catalyst precursors. Upon addition of a base (1:1 on copper) and excess phenol, phenolate ligands coordinate as bridging ligands to copper. After a two‐electron transfer reaction, the resulting phenoxonium ligand, which is a rather poor ligand, remains attached to the Cu(I), probably coordinating via its aromatic ring. Nucleophilic attack by a phenol to the phenoxonium ion at the 4‐position is likey to be most important to the coupling reaction. In the beginning of the reaction the undesired side product DPQ is also formed via a C–C coupling reaction. With copper(II) compounds containing imidazole‐type chelating ligands, good activity was obtained; in the case of pyrazole‐based and bridging S‐donor chelating ligands, that no or very weak activity was found.In a study of the mechanism of the propagation reaction the rate‐determining reaction was thought to be probably a one‐step, two‐electron transfer, during which the two Cu(II) ions in the dinuclear complex oxidize the phenolate to phenoxonium. After the phenoxium ion is formed the bonding with the (then) Cu(I) species is weakened and the reactions with phenolic end groups can take place. The effect of the amine ligands appears to be both steric and electronic. With certain ligands the reoxidationof the reduced c

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060308

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractOligo(p‐phenylene sulfide) is synthesized by oxidative polymerization of diphenyl disulfide with oxygen catalyzed by vanadyl acetylacetonate under strongly acidic conditions. The mechanistic studies reveal that the redox cycles of the vanadyl complexes give rise to catalysis through a two‐electron transfer between diphenyl disulfide and molecular oxygen. The VO catalysts act as an excellent electron mediator to bridge a 1.0 V potential gap between the oxidation potential of disulfides and the reduction potential of oxygen. The VO‐catalyzed oxygen‐oxidative polymerization provides pure oligo(pphenylene sulfide)s containing an S–S bond. The polymeric product is of low molecular weight due to the insolubility under these conditions.(N,N′‐ethylenebis(salicylideneaminato))oxovanadium‐(IV), VO(salen), was used as an inert model compound to elucidate the redox chemistry of the vanadium complex. VO(salen) reacts with trifluoromethanesulfonic acid (CF3SO3H) or triphenylmethyl tetrafluoroborate (ϕ3C(BF4)) to form a deoxygenated complex, VIV(salen)2+, and a μ‐oxodinuclear complex, [(salen)VOV(salen)]X2, (X = CF3SO3−or BF4−). The dimerization of VO(salen) is initiated by deoxygenation to produce V(salen)2+which enters into an equilibrium with a second VO(salen) complex to produce the μ‐oxo dimer. The two‐electron transfer of the μ‐oxo dinuclear

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060309

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractPolymerization of olefins mediated by transition metal derivatives (Ziegler–Natta polymerization) is one of the most scientifically and industrially important processes of molecular conversion. Electron transfer mechanism could play a significant role in both heterogeneous and homogeneous catalysts. The catalytic activity strongly depends on the presence of two metallocene ligands attached to the transition metal (more commonly zirconium) which grants the valence form of zirconium in complexes of the type Cp2ZrX2(X=Cl or CH3) followed by the formation of the (Cp2ZrX)+cation under the effect of a Lewis acid. On the other hand, Ti complexes with only one metallocene ligand give the syndiospecific polymerization of styrene, where the phenyl group appears to act as electron donor for the transition metal. The remarkable electronic effect of the metallocene groups in determining catalytic activity is demonstrated by the study of substituted metallocene ligands as well as other ligands around the metal. These effects cannot be, however, completely separated from steric effects which seem to be responsible for the impressive and versatile stereochemical control determined by symmetry properties of the transition metal comple

ISSN:1042-7147    

DOI:10.1002/pat.1995.220060310

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY