Rudolf Herrmann

Redox potential and substituent effects at ferrocene derivatives. Estimates of Hammett σp and Taft polar σ substituent constants

Abstract The anodic behaviour of 34 ferrocene derivatives (8 of which have been prepared for the first time) of the general type Fc-CHYZ [Y = R (hydrogen, alkyl or aryl), Fc or Fc+; Z = amino or related functionalized groups, various unsaturated N-moieties (such as cyano, isocyano, imidazoyl, azide or triazene derivative), alkylammonium, hydroxy, alkoxy, thiolate, acyloxy, phosphinyl or thiocarbonyl groups] has been studied by cyclic voltammetry (and, in some cases, also by conrolled-potential electrolysis and differential pulse polarography) at a Pt electrode in an aprotic solvent. The compounds undergo a one-electron reversible or quasi-reversible oxidation centred at each iron centre and the effect of the substituents on the half-wave oxidation potential is discussed in terms of their electronic properties. Linear correlations have been recognized between this potential and the Hammett σp constant or the Taft polar σ* constant for the substituent, and have been used, in the cases they were not known, to estimate the values of these constants for the above-mentioned substituents and of the latter constant for a total of 73 of these substituents or their Z groups. The anomalous behaviours of complexes with an hydroxy, a carbonyl, an acylamido, a thiocarbonyl, or a phosphinyl group are discussed.

Redox potential and substituent effects in ferrocene derivatives: II

Abstract The anodic behavior of 31 ferrocene derivatives (FcX) (four of which have been prepared for the first time) of the types shown below has been investigated by cyclic voltammetry (and, in some cases, also by controlled-potential electrolysis and differential pulse polarography) at a Pt electrode, in an aprotic solvent: FcC(Y)Z (class A; Y  R (hydrogen, alkyl or unsaturated-carbon moiety) or Cl; Z  CRR′, derived functionalized groups or {W(CO) 5 }); FcC(Y)O (class B; Y  R or OH); other types (class C, including azide, other unsaturated N moieties, acyloxy or phosphino); disubstituted ferrocenes (class D, with alkyl, aminoalkyl, phosphino, B(OH) 2 or −HGCl substituents, or the SSS bridge). All these substituted ferrocenes exhibit a one-electron reversible oxidation centered at iron and the effect of the substituents on the half-wave oxidation potential is discussed in terms of electronic properties. Using the accepted linear correlations between the half-wave oxidation potential and the Hammett constant σ p of the substituent, σ p was estimated for the first time for 29 of the substituents in the ferrocenes listed above. The anomalous behavior of complexes with a hydroxy or a carbonyl group is discussed. No correlation was observed between the oxidation potential and either the energy of the electronic absorption bands or the 1 H NMR chemical shift of the unsubstituted cyclopentadienyl ring, although there are rough correlations for class A compounds. This behaviour is compared with those of [Fc-CHYZ]. kw]Iron; Redox potentials; Ferrocenes; Electrochemistry; Substituent effects

A simple and efficient preparation of sulfinyl chlorides from disulfides and sulfuryl chloride

Abstract Disulfides react with sulfuryl chloride in the presence of acetic acid to form. the corresponding sulfinyl chlorides in nearly quantitative yield.

MOLECULES WITH POTENTIAL APPLICATIONS FOR NON-LINEAR OPTICS: THE COMBINATION OF FERROCENE AND AZULENE

Abstract The synthesis of ferrocene derivatives connected by an imino bridge to the azulene moiety is described, and the properties of the compounds were studied (NMR, UV–vis, redox potentials). The first hyperpolarizability of one of the compounds was determined by hyper-Rayleigh scattering (HRS).

Chiral perrocenylalkylamines from (-)-menthone

Abstract Three enantiomerically pure ∝-ferrocenylalkylamines are directly obtained from (-)-menthone. The isomerizations of the ∝-ferrocenylalkyl carbocation intermediates are studied and exploited in stereoselective syntheses. These carbocations are the basis of the configurational assignment of the amines. Their usefulness as chiral templates of stereoselective four component condensations is demonstrated by the synthesis of a model compound for peptides.

lsocyanide derivatives of ferrocene. Preparation, complexation and redox properties

Abstract Syntheses and properties of 11 isocyanides containing the ferrocene moiety, including 7 chiral compounds, are described. The redox properties and spectroscopic data of some of these isocyanides are discussed together with those of their chromium carbonyl complexes.

Perylene-Labeled Silica Nanoparticles: Synthesis and Characterization of Three Novel Silica Nanoparticle Species for Live-Cell Imaging

The increasing exposure of humans to nanoscaled particles requires well-defined systems that enable the investigation of the toxicity of nanoparticles on the cellular level. To facilitate this, surface-labeled silica nanoparticles, nanoparticles with a labeled core and a silica shell, and a labeled nanoparticle network-all designed for live-cell imaging-are synthesized. The nanoparticles are functionalized with perylene derivatives. For this purpose, two different perylene species containing one or two reactive silica functionalities are prepared. The nanoparticles are studied by transmission electron microscopy, widefield and confocal fluorescence microscopy, as well as by fluorescence spectroscopy in combination with fluorescence anisotropy, in order to characterize the size and morphology of the nanoparticles and to prove the success and homogeneity of the labeling. Using spinning-disc confocal measurements, silica nanoparticles are demonstrated to be taken up by HeLa cells, and they are clearly detectable inside the cytoplasm of the cells.

Ferrocene derivatives containing anthracene linked by spacers

Abstract Several ferrocene derivatives linked by a non-conjugated spacer to a 9,10-diphenylanthracene unit have been prepared, among them an amphiphilic isoquinolinium salt. By X-ray structure analysis of the intermediate 9,10-bis(4-hydroxyphenyl)anthracene, an almost perpendicular arrangement of the phenyl groups with respect to the anthracene was found. The properties of the compounds were studied by NMR and cyclovoltammetry, which suggest that the isoquinolinium salt forms inverse micelles in organic solvents. No indication for intramolecular aggregation of ferrocene and isoquinolinium moieties by folding of the flexible alkyl spacers could be detected. The compound forms a monolayer when spread on water which can be transferred to a quartz surface. Repeated transfer leads to a non-centrosymmetric Z-type array of layers in the Langmuir-Blodgett film.

Chiral sulfoxides from (R)-α-dimethylaminoethylferrocene

Abstract Chiral sulfoxides and sulfones of potential interest in organic synthesis are prepared by the reaction of 2-lithio-1-(dimethylaminoethyl)-ferrocene with disulfides, followed by oxidation of the sulfides thus obtained with sodium metaperiodate on alumina or with 3-chloropcrbenzoic acid. Most of the reactions, in particular oxidations of the sulfides to form the sulfoxides, proceed with high diastereoselectivity. The sulfoxides and sulfones can be isolated as pure enantiomers. Assignment of absolute configurations is based on independent synthesis together with 1 H- and 13 C-NMR data and ORD measurements.

Rapid degradation of zinc oxide nanoparticles by phosphate ions

Summary Zinc oxide nanoparticles are highly sensitive towards phosphate ions even at pH 7. Buffer solutions and cell culture media containing phosphate ions are able to destroy ZnO nanoparticles within a time span from less than one hour to one day. The driving force of the reaction is the formation of zinc phosphate of very low solubility. The morphology of the zinc oxide particles has only a minor influence on the kinetics of this reaction. Surface properties related to different production methods and the presence and absence of labelling with a perylene fluorescent dye are more important. Particles prepared under acidic conditions are more resistant than those obtained in basic or neutral reaction medium. Surprisingly, the presence of a SiO2 coating does not impede the degradation of the ZnO core. In contrast to phosphate ions, β-glycerophosphate does not damage the ZnO nanoparticles. These findings should be taken into account when assessing the biological effects or the toxicology of zinc oxide nanoparticles.