Stereoselektive Synthesen von substituierten Tricarbonyl[tris(methylen)methan]eisen(0)-Komplexen

Stereoselective Syntheses of Substituted Tricarbonyl[tris(methylen)methan]iron(0) Complexes The complexes 3 , 9 , 10 , 22 , and 23 with one, two, and three Me substituents at the tris(methylen)methane moiety have been synthesized from the (acyloxy-1,3-diene)(tricarbonyl)iron(0) complexes 1 , 4 , 5 , 20 , and 21 , respectively, by ionic hydrogenation with BF₃ and Et₃SiH at ?78° in CH₂C1₂. These reductions are completely stereoselective, and their course can be predicted by assuming a dominant stereoelectronic control of the reaction. Formation of the carbocationic intermediates 11 from 4 and 12 from 5 , e.g., takes place only if the dissociating O? C bond is antiperiplanar to the donor C(β)? Fe bond. Fast H-transfer then converts the intermediate 11 to 9 and 12 to 10 . The configurations of 17 and 20 can be deduced from the structure of 22 and those of 18 and 21 from that of 23 . An X-ray structure determination of (1R,4S)camphanoate (?)- 13 derived from alcohol (?)- 7 confirms the configuration of 5 deduced above, The structures of the complexes 9 and 10 , 22 and 23 were determined by their unique NMR spectra. The diastereoisomeric complexes 6 and 7 have been synthesized from aldehyde 8 with MeMgI, the diastereoisomers 17 and 18 analogously from 16 or from methyl ketone 19 by reduction with LiAlH₄. Optically active starting materials (+)- 1 , (?)- 13 , (+)- 20 , and (+)- 21 gave, by ionic hydrogenation, the complexes (?)-(3R)- 3 , (+)-(2S,4S)- 10 , (?)-(R,R, S)- 22 , and (?)-(R,R,R)- 23 respectively, with known absolute configurations.     

Solution extraction of transition and post-transition heavy and precious metals by chelate and macrocyclic ligands

This review focuses on compounds and methods that can be used for the extraction and separation from solution of two classes of elements that we define as heavy metals and precious metals. These elements are often targeted because they are toxic, costly, and their coordination chemistry has already been well studied, and because there is a need to develop methods of economically extracting, separating and recovering them from waste sites. This review outlines possible strategies that can be used, and reviews the present literature regarding the available methods for their extraction.     

C5H4-BR2 bending in ferrocenylboranes: a delocalized through-space interaction between iron and boron

A comparison of the molecular structures of mono-, di- and tetraborylated ferrocenes [Fc{B(R(1))(R(2))}] (R(1)/R(2)=Br/Br, Br/Fc, Br/Me, Me/Me, Me/OH, OMe/OMe), 1,1'-[fc{B(R(1))(R(2))}(2)] (R(1)/R(2)=Br/Br, Br/Me, OMe/OMe), and 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)] revealed the boryl substituent(s) to be bent out of the Cp ring plane towards the iron center. The corresponding dip angle alpha* decreases with decreasing Lewis acidity of the boron atom and with increasing degree of borylation at the ferrocene core. This trend is well reproduced by DFT calculations (including [FcBH(2)], not yet accessible experimentally). A Bader analysis of the electron density topology of [FcBH(2)] (alpha*=26.5 degrees ; BP86/TZVP) clearly showed that there is no direct iron-boron bonding in this compound. Instead, strongly delocalized orbital interactions have been identified that involve the boron p orbital, C(ipso) of the adjacent Cp ring, d orbitals at iron, and a through-space interaction with the second Cp ring. A second important factor is attractive electrostatic interactions, which are enhanced upon ligand bending. Cyclic voltammetric measurements on the series [FcBMe(2)], 1,1'-[fc(BMe(2))(2)], and 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)] indicate a substantial anodic shift in the oxidation potential of the central iron atom upon introduction of BMe(2) substituents. Addition of 4-dimethylaminopyridine (DMAP) does not just counterbalance this effect, but leads to a cathodic shift of the Fe(II)/Fe(III) redox transition far beyond the half-wave potential of parent ferrocene. In the Mossbauer spectra, a continuous decrease in the quadrupole splitting (QS) is observed upon going from parent ferrocene to [FcBMe(2)], to 1,1'-[fc(BMe(2))(2)], and to 1,1',3,3'-[Fe{C(5)H(3)(BMe(2))(2)}(2)]. In contrast, no significant differences are found between the QS values of ferrocene, [Fc(BMe(2)-DMAP)], and 1,1'-[fc(BMe(2)-DMAP)(2)].     

Extraktiv-photometrische Eisenbestimmung als Tris-(Dibenzylsulfoxid) Eisen(III)-rhodanid

Zusammenfassung Die Extraktion des Eisens aus 0,5-n salzsaurer Lösung, die 3% Kaliumrhodanid enthält, in 8%ige Lösung von Dibenzylsulfoxid in Methylenchlorid ermöglicht bei 500 nm die extraktiv-photometrische Bestimmung von 5 bis 100g Fe³⁺ als [Fe(CNS)₃(OS{CH₂C₆H₅}₂)₃]. Es werden neben Bi³⁺, Cr³⁺, Mg²⁺, Zn²⁺ Spezifitäten Fe³⁺: Fremdion = 110⁴, neben Al³⁺, Ca²⁺, Cd²⁺, Co²⁺, Hg²⁺, Mn²⁺, Ni²⁺, VO²⁺, Zr⁴⁺ solche von 110⁵ und darüber erreicht. An verschiedenartigen Beispielen wird die Anwendbarkeit des Verfahrens ausgewiesen.

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Extractive-photometric iron determination as tris(dibenzylsulfoxide) iron(III)-thiocyanate

Summary The extraction of iron from 0.5N hydrochloric acid solution, that contains 3% potassium thiocyanate, into 8% solution of dibenzylsulfoxide in methylene chloride makes possible the extractive-photometric determination at 500 nm of 5–100g of Fe³⁺ as [Fe(CNS)₃(OS{CH₂C₆H₅}₂)₃]. Specifities for Fe³⁺: foreign ion = 110⁴ are attained in the presence of Bi³⁺, Mg²⁺, Zn²⁺, and specificities of 110⁵ and above have been reached in the presence of Al³⁺, Ca²⁺, Cd²⁺, Co²⁺, Hg²⁺, Mn²⁺, Ni²⁺, VO²⁺, Zr⁴⁺. The applicability of the procedure has been demonstrated on various specimens.

     

Ab initio investigation of the stability of Si3C3 clusters and their structural and bonding features

Various structural possibilities for Si₃C₃ clusters are investigated by ab initio calculations employing basis sets of double- and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Plesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A “pyramidlike” structure with various multicenter bonds, followed by a C_s symmetric isomer closely related to the ground state Si₆ structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si-C-C-C-Si-Si structure, which is calculated to lie about 38 kcal/mole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities.     

A PbSe diode laser spectrometer to be used in air pollution monitoring and mineral prospecting

A high resolution infra-red PbSe diode laser spectrometer has been developed for application in air pollution monitoring and mineral prospecting. This instrument possesses three cells for measurement and calibration. Correlation techniques have been applied to increase the sensitivity. SO₂ concentrations of around 5 ppm have been monitored at 7.3m with the diode operating at 77 K.     

Electrochemical response of nitrogen-doped multi-walled carbon nanotubes decorated with gold and iridium nanoparticles toward ferrocyanide/ferricyanide redox system

Novel composite films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold (AuNP) and iridium (IrNP) nanoparticles possessing diameters of 12.5 and 2.7 nm, respectively. The electrochemical responses of fabricated composite films, further denoted as N-MWCNTs/MNPs (M: Au and Ir), toward ferrocyanide/ferricyanide, [Fe(CN)₆]^3−/4− redox couple was probed by means of cyclic voltammetry and electrochemical impedance spectroscopy techniques. The findings demonstrate that both N-MWCNT/MNP composite films exhibit greater electrochemical response and sensitivity toward [Fe(CN)₆]^3−/4− compared to unmodified N-MWCNTs. The results verify that the N-MWCNT/MNP composite films are extremely promising for application in electrochemical sensing.