Sulphur substituted organotin compounds : VII. Charge transfer interactions of arylthiomethyl(triphenyl)tin compounds with tetracyanoethylene

Thermolysis of η²-benzoyl(phenyl)zirconocene yields the η²-benzophenonzirconocene complex 2, isolated as a dimer. 2 exhibits an ambivalent reactivity pattern. The formation of five-membered metallacycles from 2 and olefinic hydrocarbons possibly proceeds analogous to reactions of “normal” metalolefin π-complexes. However, both reactions with the electron-deficient olefins dimethylfumarate and -maleate and the behavior towards electrophilic and protic reagents as well as aromatic hydrocarbons might be interpreted in terms of a metallaoxirane-character of 2.     

A hammett correlation for the addition of organotin hydride to benzaldehydes

The relative rates for tri-n-butyltin hydride additions to substituted benzaldehydes under free radical and polar conditions have been determined from competitive reactions. The relative rates have been correlated by the Hammett σ or σ⁺ constants. The polar addition is correlated best by σ and the free radical addition by σ⁺. Interpretations of the results are presented.     

Electrochemical preparation of some organotin compounds

Organotin dihalides R₂SnX₂ (X  Cl, Br, I) and their adducts with bidentate donor ligands have been prepared in high yield by the direct electrochemical reaction of metallic tin with alkyl or aryl halides in organic media at room temperature. Dimethyltin diiodide can be converted to tetramethyltin by reaction with methyl iodide at a cadmium anode. Electrochemical halide abstraction has been used to prepare R₆Sn₂ (R  Me, Ph) from the corresponding R₃Sn halide. The mechanism of these reactions is discussed.     

Rate coefficients for the gas-phase reaction of hydroxyl radicals with 2-methoxyphenol (guaiacol) and related compounds

2-Methoxyphenol (guaiacol) and its derivatives are potential marker compounds for wood smoke emissions in the atmosphere. To investigate the atmospheric reactivity of this type of compounds, rate coefficients for their reactions with hydroxyl (OH) radicals have been determined at 294 ± 2 K and 1 atm using the relative rate method with gas chromatography for chemical analysis. The rate coefficients (in units of cm3 molecule?1 s?1) are: 2-methoxyphenol, (7.53 ± 0.41) × 10?11; 3-methoxyphenol, (9.80 ± 0.46) × 10?11; 4-methoxyphenol, (9.50 ± 0.55) × 10?11; 2-methoxy-4-methylphenol, (9.45 ± 0.59) × 10?11; and methoxybenzene, (2.20 ± 0.15) × 10?11. The estimated atmospheric lifetime for 2-methoxyphenol is ~2 h, indicating that it is too reactive to be used as a tracer for wood smoke emissions. The reactivity of the methoxyphenols is compared with other substituted aromatics and interpreted in relation to the type, number, and positions of the different substituents on the aromatic ring. The atmospheric implications of the reactions are also discussed.     

Studies on organotin compounds using the Del Re method : VIII. Mössbauer spectra or organotin compounds

A method for calculating the electron density at the nucleus of the tin atom in a tetravalent compound has been developed using the quantities available from the Del Re calculations. The calculated electron densities show a fair correlation with the experimental Mössbauer isomer shifts, and a value of +3.2 × 10^?4 is obtained for (ΔR/R), in excellent agreement with the value +3.30 × 10^?4 obtained from an independent method using internal electron conversion measurements. By defining an assymmetry parameter, A, which is a measure of the deviation of the calculated p-electron distribution from the hypothetical spherically-symmetric distribution, in which the p-electron would be distributed equally between the three p-orbitals, the experimental quadrupole splittings have been correlated and interpreted. Factors governing the magnitude of quadrupole splitting are also discussed.     

A Quantitative Structure–Reactivity Assessment of Phenols by Investigation of Rapid Iodination Kinetics Using Hydrodynamic Voltammetry: Applicability of the Hammett Equation in Aqueous Medium

Halogenations of aromatic substrates in aqueous medium are essentially electrophilic substitutions proceeding at rates concomitant with the nature of the substrates and substituent motifs. Kinetics as an investigatory tool for the quantitative assessment of the structure–reactivity correlation in these reactions for a diverse range of substrates has rarely been reported, presumably due to the rapidity of these reactions in aqueous medium. We have used hydrodynamic voltammetry to investigate the rapid kinetics of uncatalyzed iodination of phenol and eight substituted phenols by iodine monochloride at constant pH in aqueous medium. The Arrhenius plots for these reactions yield comprehensive kinetic and thermodynamic data. The quantitative structure–reactivity correlation stemming from the regio‐ and stereospecificity of the substituent motifs on the substrates has been examined through the Hammett plot, which shows a negative slope of 1.87. The magnitudes of the rate constants, energies of activation, frequency factors, and entropy change obtained for the nine fast reactions reported, reflect the relative ease of the reaction dynamics in quantitative terms thereby ascertaining the relative reactivities of the phenols studied herein.     

Modification of singlet carbene reactivities by solvent

The solvent effect on the reactivity of singlet carbenes has been investigated. Competition reactions between pairs of alcohols for arylcarbenes in various solvents indicates that the O—H insertion selectivity is influenced only by 1,4-dioxane. Thus, phenylcarbene is some 33 times more reactive toward methanol relative to t-butyl alcohol in 90 mol% dioxane than without solvent. Similar competition reactions between alcohol and olefin indicate that the O—H insertion-addition selectivities of arylcarbenes are considerably altered by dioxane. These results are interpreted as indicating that dioxane stabilizes singlet carbenes by complexing with its lone pairs of electrons.     

Rapid determination of organotin compounds by headspace solid-phase microextraction

Headspace solid-phase microextraction (SPME) followed by gas chromatography (GC) coupled to pulsed flame photometric detection have been investigated for the simultaneous speciation analysis of 14 organotin compounds, including methyl-, butyl-, phenyl-, and octyltins compounds. The analytical process (sorption on SPME fibre and thermal desorption in GC injection port) has been optimised using experimental designs. Six operating factors were considered in order to evaluate their influence on the performances of a SPME-based procedure. The evaluation of accuracy, precision and limits of detection (LODs) according to ISO standards and IUPAC recommendations has allowed the method to be validated. The LODs obtained for the 14 studied organotins compounds are widely sub-ng(Sn) l(-1). The precision evaluated using relative standard deviation ranges between 9 and 25% from five determinations of the analytes at 0.25-125 ng(Sn) l(-1) concentrations. The accuracy was studied throughout the analysis of spiked environmental samples. These first results show that headspace SPME appears really as attractive for organotins determination in the environment and the monitoring of their biogeochemical cycle.     

Reactivity of the cadmium ion in concentrated phosphoric acid solutions

The solvation transfer coefficients which characterize the changes of ion reactivity with phosphoric acid concentration have been calculated for cadmium from the constants of the successive chloride complexes, and for silver and diethyldithiophosphate from potentiometric measurements. They evidence the strong desolvation of the cadmium species in concentrated phosphoric acid media, causing a remarkable increase of its reactivity. They allow the results of liquid-liquid extraction, precipitation and flotation reactions to be correctly interpreted and their changes to be foreseen when the reagents are modified.     

Synthesis of cyclohepta-1,3,5-trienes by the reaction of aromatic hydrocarbons with diazo compounds in the presence of transition metal complexes

A preparative method has been developed for the synthesis of cyclohepta-1,3,5-trienes, using the reaction of aromatic hydrocarbons with diazomethane, methyldiazoacetate, adamantanoyldiazomethane, and 1-diazo-3-phenylpropan-2-one, with rhodium trifluoroacetate as catalyst. The order of activity and the relative reactivity coefficients of substituted benzenes have been determined, and the link between these characteristics and the energy of the highest occupied molecular orbital of the aromatic ring has been established. In catalyzed reactions of benzenes with diazomethane or methyldiazoacetate, leading to cycloheptatrienes, effects of chemical polarization of the ring have not been observed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1063–1069, May, 1991.     

The effect of cations on nucleophilic additions to carbonyl compounds: carbonyl complexation control versus ionic association control. application to t

The fundamental influence of cations in nucleophilic additions to carbonyl compounds is discussed in terms of either carbonyl complexation or ionic association with the nucleophile. Since loose ion pairs react essentially under complexation control while tight ion pairs react under association control, an experimental criterion is proposed to determine which factor controls the reactivity (complexation or association) based on the kinetic effects of cryptand or crown-ether addition.An application of this duality is then examined for the regioselectivity of nucleophilic additions to α-enones and correlated with perturbational arguments based on abinitio calculations. Under complexation control, attack at carbon 2 is favoured, especially when a soft nucleophile is involved and the counter-ion is Li⁺ rather than Na⁺. Under association control two cases are considered according to whether the cation is directly bound or not to the nucleophilic center; in addition, the influence of hard or soft metals and the possibility of a cationic bridge in the transition state have been discussed. Several kinetic controlled reactions have been examined and interpreted in this way. An extension of this concept to other reactions will be considered.     

Exchange reactions between organotin compounds and thallium trichloride

Summary A study was made of the exchange reactions between thallium trichloride and tetraethyl-, tetrabutyl-, tetraphenyl-, tetra-o-tolyl-, tetra-p-tolyl-, tetrakis-o-methoxyphenyl-, tetra-cis-propenyl-, tetra-trans-propenyl-, tetraisopropenyl-, and tetravinyl-tins, and the reaction products were characterized.     

Reactions of hexafluorobenzene and pentafluorophenylamino compounds with amides and anilides (steric effects)

Contrary to N-lithium-N-methylanilide and N-lithium-diphenylamide, trimethyl-N-lithium-N-phenyl-silylamide gave with hexafluorobenzene in molar ratio 2:1, only the monosubstituted compound. Competitive reactions gave the following order of reactivity toward N-lithiumanilide: 2,3,4,5,6-pentafluorotriphenylamine > 2,3,4,5,6-pentafluoro-N-methyl-diphenylamine > hexafluorobenzene ? trimethyl-2,3,4,5,6-pentafluoro-N,N-diphenyl-silylamine. A reason for the low reactivity of trimethyl-2,3,4,5,6-pentafluoro-N,N-diphenyl-silylamine against aromatic amides has been proposed.Some new aromatic amines have been synthesized, among them hexamethyl-N-pentafluorophenyl-disilylamine.     

Synthesis and characterization of coordination compounds of organotin(IV) with nitrogen and sulfur donor ligands

The reactions of dimethyltin dichloride with nitrogen and sulfur donor ligands derived by condensation of S‐benzyldithiocarbazate with indol‐3‐carboxylaldehyde, thiophene‐2‐aldehyde and furfuraldehyde have been investigated in 1:1 and 1:2 molar ratios in anhydrous alcohol. These ligands act as mononegatively charged bidentate species and coordinate to the central tin(IV) atom through the thiosulfur by proton exchange with the azomethine nitrogen. The newly synthesized complexes have been characterized by elemental analysis, conductance measurements and molecular weight determinations. The mode of bonding and the geometry of the complexes have been suggested on the basis of infrared, electronic and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, and probable structures have been assigned to these complexes. A few representative ligands and their tin(IV) complexes have also been screened for their antifungal and antibacterial activities and found to be quite active in this respect. Copyright © 2001 John Wiley & Sons, Ltd.     

Combination and disproportionation reactions of allylic radicals with ethyl,propyl, and t-Butyl Radicals

1-Methylallyl, 1,1-dimethylallyl, 1,2-dimethylallyl, 1,3-dimethylallyl, 1,1,2-trimethylallyl, and 1-ethylallyl radicals have been generated in the gas phase at 20 ± 1°C by addition of H atoms, formed by Hg(6³P₁) photosensitization of H₂, to appropriate dienes. Their combination reactions with ethyl radicals have been studied and the relative reactivities of the reaction centers in each allylic radical determined. Similar measurements have been made for some combination reactions of n-propyl, i-propyl, and t-butyl with 1-methylallyl and 1,1,2-trimethylallyl radicals. The more substituted reaction centers are found to be the less reactive. In addition the self-combination and disproportionation of 1-methylallyl radicals has been investigated, as has cross disproportionation of each allylic radical with ethyl. The results establish a general pattern of reactivity for these radicals, which is interpreted primarily in terms of the effects of steric interaction during reaction.     

Biological chemistry of organotin compounds: Interactions and dealkylation by dithiols

In this paper, we review our past and current efforts toward the elucidation of the biological chemistry of organotin compounds. In particular, we cover two prominent aspects of organotin compounds: their reactivity toward biological dithiols, and their degradation (or metabolization) mechanism using a combination of experimental and computational techniques.     

Investigation of substituted-benzene dopants for charge exchange ionization of nonpolar compounds by atmospheric pressure photoionization

Atmospheric pressure photoionization (APPI) using a dopant enables both polar and nonpolar compounds to be analyzed by LC/MS. To date, the charge exchange ionization pathway utilized for nonpolar compounds has only been efficient under restrictive conditions, mainly because the usual charge exchange reagent ions--the dopant photoions themselves--tend to be consumed in proton transfer reactions with solvent and/or dopant neutrals. This research aims to elucidate the factors affecting the reactivities of substituted-benzene dopant ions; another, overriding, objective is to discover new dopants for better implementing charge exchange ionization in reversed-phase LC/MS applications. The desirable properties for a charge exchange dopant include low reactivity of its photoions with solvent and dopant neutrals and high ionization energy (IE). Reactivity tests were performed for diverse substituted-benzene compounds, with substituents ranging from strongly electron withdrawing (EW) to strongly electron donating (ED). The results indicate that both the tendency of a dopant's photoions to be lost through proton transfer reactions and its IE depend on the electron donating/withdrawing properties of its substituent(s): ED groups decrease reactivity and IE, while EW groups increase reactivity and IE. Exceptions to the reactivity trend for dopants with ED groups occur when the substituent is itself acidic. All told, the desirable properties for a charge exchange dopant tend towards mutual exclusivity. Of the singly-substituted benzenes tested, chloro- and bromobenzene provide the best compromise between low reactivity and high IE. Several fluoroanisoles, with counteracting EW and ED groups, may also provide improved performance relative to the established dopants.     

Solid state reactivity of organic compounds with inorganic compounds II.

Cobalt acetate reacts with aniline, 2-, 3- and 4-chloroanilinehydrobromides in the solid state to give the products CoBr₂. 2 amine in which the acetate is replaced by bromide and the amine gets attached to the metal in a concerted step. The products have been identified by elemental, spectral and thermoanalytical methods. The kinetics of these reactions have been studied by the mass loss method. The values of energy of activation are 142.0, 41.0, 77.0 and 71.4 kJ mol^?1. The greater reactivity of 2-chloro is due to ortho effect. An intermediate adduct (RNH₃)₂(Co(CH₃COO)₂Br₂) has also been characterized.     

Dramatic size effects and evidence of structural isomers in the reactions of rhodium clusters, Rhn+/-, with nitrous oxide

The reactions of gas phase rhodium clusters, Rhn+/- (n<30), with nitrous oxide, N2O, have been investigated under single collision conditions by Fourier transform ion cyclotron resonance mass spectrometry. The only significant reaction observed is the sequential generation of oxides. Absolute rate constants for the reactions of all clusters have been determined and, in the case of the cationic clusters especially, they exhibit large fluctuations as a function of cluster size with local minima observed for n=5, 19, 28. Striking similarities are observed with the variation in rate constants for these clusters in reactions with small hydrocarbons (C. Adlhart and E. Uggerud, J. Chem. Phys., 2005, 123, 214709). Corresponding size effects are also observed but are less marked in the reactions of the anionic clusters. The reactions of several clusters exhibit marked deviations from simple pseudo-first-order kinetics suggesting the presence of multiple isomeric forms: Rh11+, Rh12+ and Rh8- exhibit characteristic biexponential decays which are interpreted in terms of the existence of different structural forms of the cluster which have markedly different reactivity. By contrast, Rh6+, Rh7+ and Rh8+ show rates which apparently increase with time, probably due to collisional activation. Thermalisation of the clusters prior to reaction by exposure to pulses of argon results in changes to the kinetics of these anomalous systems which can be explained in terms of collision induced isomerisation.