The use of iron carbonyls in the C—C bond formation reactions

Russian Chemical Bulletin - The review systematizes material by key types of reactions promoted by iron carbonyls. The reaction types are subdivided into several principal directions, focusing...     

The role of μ-hydroxo-ligands in the catalytic properties of binuclear copper—tertiary amine complexes

The influence of the structure of copper/tert. amine-complexes on their catalytic activity in oxidative coupling reactions has been investigated. Only binuclear complexes with bridging hydroxo ligands proved to be catalytically active compounds. This has been revealed using a model complex of copper chloride and N,N,N′,N′-tetramethylethane-1,2-diamine, for which spectroscopic and structural data are presented.We studied the same phenomenon by using soluble copper complexes with two non-crosslinked linear copolymers of styrene, acting as polymeric amine ligands: at-Poly-styrene-co-4-vinylpyridine and at-Poly-styrene-co-N- vinylimidazole. A similar effect of the OH⁻ ions on the catalytic activity has been observed using these polymeric homogeneous catalysts.     

Fourier transform far-infrared study of the νσ vibration in hydrogen-bonded complexes involving a CH group

The far-infrared spectra (200-20 cm⁻¹) of hydrogen-bonded complexes involving chloroform, 3-chloropropine, phenylacetylene and a number of dihalonitromethanes with dimethylsulphoxide and N,N-dimethylformamide have been investigated in carbon tetrachloride solution. In all cases, broad, low intensity bands near 100 cm⁻¹ have been observed and are assigned to the intermolecular stretching vibration ν_σ. The force constants K_σ have been calculated in diatomic approximation.     

Urinary calculi — atypical source of information on mercury in human biomonitoring

Chemical analysis of various biological matrices is routinely used for assessment of human exposure to various toxic metals. In this work, 489 samples of urinary calculi originating from almost the whole of The Czech Republic, were collected and subjected to mineralogical and elemental analysis. This study was aimed at mercury, the content of which was determined using thermo-oxidation — cold vapor — atomic absorption spectrometry. The effects of mineralogical composition, sex, age and region were recorded in order to verify the applicability of urinary calculi for biomonitoring. Relationships with other minor and trace elements were also investigated. Association of mercury with whewellite mineral was observed as well as a remarkable relationship with selenium, confirming the role of selenium in mercury excretion. No statistically significant effect was observed on the mercury content in stones with regard to the sex or region. Median values in age groups follow a trend with the maximum median value 0.365 mg kg^?1 in the group of 41–50 year old donors, decreasing to 0.060 mg kg^?1 for the oldest group (81–92 years). Our results confirm that urinary calculi can be helpful in providing complementary information on human exposure to mercury and its excretion.

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Dioxetanones’ peroxide bond as a charge-shifted bond: implications in the chemiluminescence process

Six dioxetanone molecules, ranging in complexity from simple dioxetanone to firefly dioxetanone, were studied by performing M06/6-311G(d,p) calculations. The quantum theory of atoms in molecules and the electron localization function was applied to analyze the peroxide and carbon–carbon bonds of the dioxetanone ring. Both approaches demonstrated that the peroxide bond is not covalent, but charge-shifted. This means that for this bond the covalent “electron sharing” is relatively unimportant, and it is the stabilizing resonance energy that causes the bonding. For the contrary, the carbon–carbon bond is covalent. These discoveries indicate that no biradical species should be formed in the dioxetanone decomposition, and that the most probable rate-determining step should be the carbon–carbon cleavage.     

Belousov-Zhabotinskii oscillatory chemical reactions involving complexes of transition metals with 1,10-phenanthroline and 2,2′-bipyridyl

An analysis is given of features of the catalytic effect of complexes of manganese, iron and ruthenium with 1,10-phenanthroline and with 2,2-bipyridyl on the oscillatory Belousov-Zhabotinskii chemical reaction. On the basis of the experimental results, the redox properties of the various complexes and the composition of their coordination spheres consideration is given to the possibility (not previously taken into account) of the conversion of the catalyst during the formation and consumption of key substances [bromide ion, bromous acid HBrO₂, the bromyl and malonyl radicalsBrO₂ andCO(COOH)₂], the concentrations of which govern the oscillatory regime of the reaction. A scheme is proposed for the action of the complexes of transition metals with 1,10-phenanthroline and 2,2-bipyridyl which removes the discrepancies between the usually accepted mechanism for the Belousov-Zhabotinskii reaction and the experimental results.Sonar Scientific Research Center for the Automation of Biotechnical Systems, Cybernetics Institute of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 3, pp. 346–353, June, 1991. Original article submitted March 14, 1991.     

Interaction of a C-F bond with the π-system of a C═C bond or "head on" with a proximate C-H bond

We describe the synthesis and preliminary study of two molecules, in which a fluorine atom is positioned proximately above the π-orbitals of a C═C bond or else wherein a C-F bond interacts in a "head on" fashion with a proximate C-H bond. The spectroscopic characteristics of these unusual interactions are documented, X-ray crystallographic analyses are reported, and theoretical calculations are employed to support the observed spectroscopy.     

The π-acceptor effect in the substitution reactions of tridentate N-donor ligand complexes of platinum(ii): a detailed kinetic and mechanistic study

The nucleophilic substitution reactions of complexes [Pt{4'-(2'-CH(3)-phenyl)-2,2':6',2'-terpyridine}Cl]CF(3)SO(3), [CH(3)PhPtCl], [Pt{4'-(2'-CH(3)-phenyl)-6-(3'-isoquinoyl)-2,2'bipyridine}Cl]SbF(6), [CH(3)PhisoqPtCl], [Pt{2-(2'-pyridyl)-1,10-phenanthroline}Cl]Cl, [pyPhenPtCl], and [Pt(terpyridine)Cl](+), [PtCl] with a series of nucleophiles: thiourea (TU), N,N-dimethylthiourea (DMTU), N,N,N,N-tetramethylthiourea (TMTU), I(-), Br(-), and SCN(-) were studied in 0.1 M LiCF(3)SO(3) in methanol (in the presence of 10 mM LiCl). The reactivity of the investigated complexes follows the order pyPhenPtCl > PtCl > CH(3)PhPtCl > CH(3)PhisoqPtCl. The lability of the chloride ligand is dependent on the strength of π-backbonding properties of the spectator ligands around the platinum centre. The experimental data is strongly supported by DFT calculations. The dependence of the second-order rate constants on concentration of the nucleophiles as well as the large negative values reported for the activation entropy (ΔS(?)) confirmed an associative mechanism of substitution.     

The CF bond as a tool in the conformational control of amides

The conformation of 2-fluoro-N-(2-fluoroethyl)-propionamide 4 in the solid state indicates the influence of both a β-fluorine-amide gauche effect and an α-fluoroamide effect. The structure reveals the influence of two recently observed stereoelectronic effects associated with the CF bond, which has resulted in the successful prediction of the solid state conformation of amide 4. A gauche relationship (−69.9°) was observed for atoms N(1)C(4)C(5)F and a syn planar (2.0°) relationship was observed for N(1)C(3)C(2)F. The paper demonstrates the predictive power of using the CF bond as a tool in influencing the conformation of amides and peptides.     

Gas phase ion–molecule reactions in a modified ion trap: H/D exchange of non-covalent complexes and coordinatively unsaturated platinum complexes

A commercially available electrospray ionization ion trap mass spectrometer has been modified to carry out gas phase ion–molecule reactions. The ability to study gas phase ion–molecule reactions in conjunction with collision induced dissociation (CID) based methods and the multistage trapping capabilities of the ion trap have been exploited in two ways: (i) gas phase H/D exchange reactions inside the ion trap, coupled with CID tandem mass spectrometry have been used to provide insights into the reactivity of non covalent complexes of amino acids and simple peptides, and (ii) CID prior to performing ion–molecule reactions has been used to synthesize and examine the reactivity of coordinatively unsaturated platinum complexes. © 1998 John Wiley & Sons, Ltd.     

Evolution of bond orders in the reversible reactions of alkylene oxides with R-β-hydroxyalkyl sulfides and the role of the intermolecular hydrogen bond in initiation and at intermediate reaction stages

Semiempirical (PM3) calculations of the changes in the structures and energies of the reactants, intermediates, transition states, and final products have been carried out for the reversible reaction of β-hydroxyethyl methyl sulfide with propylene oxide. The evolution of the electron density distribution during the reaction is analyzed. It is demonstrated that the transformation proceeds via two intermediate products and the O⋯H⋯O bridge persists throughout the reaction pathway.     

The cuticle of the cactusCereus peruvianus as a source of a homo-α-d-galacturonan

The waxy pecto-cellulosic cuticle of cladodes of the columnar cactusCereus peruvianus (19% of the whole phytobiomass; dry wt) is a source of an α-d-polygalacturonic or pectic acid (35–40% yield, on a dry wt based on the wax-free pectocellulose layer). Warm EDTA/oxalate or room temperature strong acid/alkali cycles are efficient for pectic acid extraction, since divalent cation (mainly Ca²⁺) is a barrier to be removed within the native and compact architecture of the cuticle. Despite some molecular dispersion arising from the application of strong mineral acid in the first extraction step, the pectic material appears to be quite homogeneous and, on acid or enzymatic analyses, was shown to contain onlyd-galacturonic acid as its monomer.Cereus cuticle pectate (sodium salt) tends to gel above a concentration of 1%, a useful property that can be more easily obtained by the inclusion of sucrose, light addition of calcium salt, and/or mild acidification.     

Synthesis of platinum complexes containing (+)-bornyl- and (−)-menthylammonium in the outer coordination sphere and their catalytic activity in hydrosilylation reactions

Optically active (+)-bornyl- and (−)-menthylammonium platinates were synthesized starting from H₂[PtCl₆] · 4H₂O and hydrochlorides of the corresponding amines. Catalytic activity of the complexes in the hydrosilylation reactions of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 1,1,3,3-tetramethyldisiloxane and acetophenone with diphenylsilane was studied. The addition of the siloxanes leads to a predominant formation of β-adduct. Activity of the catalysts, evaluated on the 50% conversion of the substrate, decreases in the following sequence: (−)-(menthylNH₃)₂[PtCl₆] > (Et₃NH)₂[PtCl₆] > (+)-(bornylNH₃)₂[PtCl₄] > (+)-(bornylNH₃)₂[PtCl₆]. Asymmetric induction is observed in the hydrosilylation of aceto-phenone in the presence of (+)-(bornylNH₃)₂[PtCl _n ] (n = 4, 6); (+)-(bornylNH₃)₂[PtCl₆] showed the highest catalytic activity and selectivity. The hydrosilylation of acetophenone gave 1-phenylethoxy(diphenyl)silane, 1-phenylvinyloxy(diphenyl)silane, and 2-phenylethyl-2-diphenylsiloxy(diphenyl)silane as the products. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 341–349, February, 2008.     

An ab initio investigation of chalcogen–hydride interactions involving HXeH as a chalcogen bond acceptor

This work presents an ab initio study on chalcogen–hydride interactions in several binary complexes of chalcogen-containing molecules with HXeH. The geometries, H–Xe stretching frequencies and interaction energies of XCY···HXeH binary complexes are investigated at MP2/aug-cc-pVTZ and CCSD(T)/aug-cc-pVTZ levels of theory, where X = O, S, Se, Te and Y = S, Se, Te. For each XCY···HXeH complex, a chalcogen–hydride bond is formed between the negatively charged hydrogen atom of the HXeH molecule and the most positive electrostatic potential region (σ-hole) on the surface of the interacting atom Y. Upon complex formation, a notable blue shift is found for the H–Xe stretch vibration. This result reveals that there is a stronger H^?(XeH)⁺ ion-pair character in XCY···HXeH complexes than in free HXeH molecule. In order to shed light on the origin of the chalcogen–hydride interactions, molecular electrostatic potential, quantum theory of atoms in molecules and interaction energy decomposition analyses are performed. Cooperative effects between a conventional chalcogen bond and the chalcogen–hydride interaction in OCY···OCY···HXeH complexes are also investigated.     

Understanding the electronic and π-conjugation roles of quinoline on ligand substitution reactions of platinum(II) complexes

A kinetic and mechanistic study of chloride substitution by thiourea nucleophiles, namely thiourea, N-methylthiourea, N,N-dimethylthiourea and N,N,N′,N′-tetramethylthiourea in the complexes chlorobis-(2-pyridylmethyl)amineplatinum(II) (Pt1), chloro N-(2-pyridinylmethyl)-8-quinolinamineplatinum(II) (Pt2), chloro N-(2-pyridinylmethylene)-8-quinolinamineplatinum(II) (Pt3) and chlorobis(8-quinolinyl)amineplatinum(II) (Pt4) was undertaken under pseudo-first-order conditions using UV–visible spectrophotometry. The study showed that lability of the chloro leaving group is dependent on the strength of π-interactions between the filled dπ-orbitals of the metal and the empty π*-orbitals of the chelating ligand in the following manner: Pt1 > Pt3 > Pt2 > Pt4. Introduction of the quinoline moiety within the non-labile chelated framework of the Pt(II) complexes results in a more electron-rich metal centre which retards the approach of the nucleophile through repulsion. Moreover, the net σ-effect of the ligand moiety plays a significant role in controlling the reactivity of the complexes. The experimental results are interpreted with the aid of computational data obtained by density functional theory (B3LYP(CPCM)/LANL2DZp//B3LYP/-LANL2DZp) calculations. The mode of substitution remains associative as supported by negative entropies and the dependence of the second-order rate constants on the concentration of entering nucleophiles.     

Generation and reactions of anionic σ-adducts of 1,3-dinitrobenzene and 1,3,5-trinitrobenzene with carbanions in a gas phase,using an electrospray ion source as the chemical reactor

Di- and trinitrophenide anions generated by decarboxylation of the anions of 2,4-, 3,5-, and 2,6-dinitrobenzoic acids and 1,3,5-trinitrobenzoic acid in the medium-pressure region of an electrospray ion source react locally with various C-H acids delivered in the form of vapors mixed with the curtain gas, yielding anionic sigma-adducts. Positive results were obtained for aliphatic aldehydes, ketones, esters and nitriles. All three dinitrobenzoic acids bearing NO(2) groups in the meta position to each other gave the same sigma-adducts which can be rationalized by a reaction sequence including proton transfer from the C-H acid to the nitrophenide anion and subsequent formation of the sigma-adduct by the reaction of 1,3-dinitrobenzene with the carbanion within the ion-molecule complex. It was found that such a reaction is possible only for C-H acids with a gas-phase acidity lying within a narrow, strictly defined range whose location on the acidity scale depends on the acidity of the nitroarene. The sigma-adduct formed in the reaction of the 2,4-dinitrophenide anion with CH(2)Cl(2) undergoes rapid HCl elimination yielding an anion with the same composition as that produced by the Vicarious Nucleophilic Substitution of hydrogen reaction but with a different structure.     

Metal complexes as ligands—VII: The chemistry of the monothiooxalate complexes

A synthesis of potassium monothiooxalate, K₂C₂SO₃, and its reactions with metal ions are reported. The spectroscopic properties of the complexes, M(C₂SO₃)_nⁿ⁻, for M  Ni(II), Cu(II), Zn(II) (n = 2); and M  Cr(III), Co(III), Fe(III) (n = 3) are indicative of (SO) chelated ligands while the Al(III) (n = 3) complex is an (OO) bonded chelate. The copper(II) complex undergoes an irreversible oxidation at 0.43 V. This oxidation is accompanied by reduction of the copper(II) and evolution of CO₂ and SCO.The inert cations which accompany the anionic monothiooxalate complexes are readily replaced by the coordinatively unsaturated (Ph₃P)₂M⁺, M  Ag(I), Cu(I) complex cations. The bridging of the monothiooxalate ligand in the resulting polynuclear complexes is of the type MOOC₂SOM′, M  Al(III), Fe(III), M′  Ag(I), Cu(I); M  Cr(III), M′  Cu(I) and MSOC₂O₂M′, M  Cr(III), Co(III), M′  Cu(I).     

Surface electrochemistry of the oxidation reactions of α- and β-alanine at a platinum electrode

The electrochemical oxidation reactions of α- and β-alanine at a Pt electrode were investigated in aqueous solutions at pH 1, 7, and 13 using steady-state current-potential measurements, cyclic voltammetry, and open circuit potential decay. The capacitance behaviour and the high Tafel slopes suggest the production of free radicals at the surface of the electrode accompanied by a second reaction involving loss of CO₂ which is the rate determining step. In the surface electro-oxidation of α-alanine, it appears that the adsorbed intermediate species is either hydrolyzed anodically to acetaldehyde and ammonia, or is oxidized to a carbonium ion which is subsequently hydrolyzed to acetaldehyde and ammonia in solution, analogous to the behaviour observed for glycine [D.G. Marangoni, R.S. Smith and S.G. Roscoe, Can. J. Chem., 67 (1989) 921]. The mechanisms for β-alanine would be similar except carbonium ion formation would probably be accompanied by a hydride transfer to form acetaldehyde. No dimerized products were detected by gas chromatography. These mechanisms differ from the dimerization process typical of the radical reactions associated with the Kolbe mechanism.     

Speciation studies of mono- and binuclear Pd(II) complexes involving mixed nitrogen–sulfur donor ligand and 4,4′-bipiperidine as a linker

Pd(MME)Cl₂ complex, where MME = methionine methyl ester, was synthesized and characterized by elemental analysis and spectroscopic techniques. [Pd(MME)(H₂O)₂]²⁺ interacts with some DNA constituents giving 1 : 1 and 1 : 2 complexes. The binuclear complexes having 4,4′-bipiperidine as a linker and involving [Pd(MME)(H₂O)₂]²⁺ and DNA constituents were investigated. The results show formation of [(H₂O)(MME)Pd(Bip)Pd(MME)(H₂O)]⁴⁺. Inosine, uracil, and thymine interact with the previously mentioned complex by substitution of the two coordinated water molecules. Formation constants of all possible mono- and binuclear complexes were determined and their speciation diagrams were evaluated.     

β-Hydroxylation of anthraquinone derivatives with benzaldehyde oxime as a source of hydroxyl group

Hydroxyanthraquinones are of significant interest due to their broad spectrum of biological activity, coloring properties and synthetic applications. Here, we describe a mild and convenient method for β-hydroxylation of anthraquinone derivatives that can be used during late stages of modifications. The scheme is based on the Miller-Loudon-Snyder reaction, which uses benzaldoxime as a source of a hydroxyl group. The influence of different leaving groups and neighboring substituents at the anthraquinone core on reaction rate and yield has been evaluated. A series of β-hydroxyanthraquinone derivatives was synthesized using the developed approach.