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Tin coordination derivatives are notable for the availability of obtaining, safety in use and high stability. Together with their useful properties, this determines the prospects for their use in medicine...

The concept of using redox-active ligands, which has become extremely widespread in organometallic chemistry, is often considered from ‘their effect on the metal center properties’ point of view and ‘how to modify the ligands’. In this paper, we present the reverse side of this effective approach – a dramatic change of redox properties of ligands under the influence of a redox-inert metal. Germanium derivatives based on 2,3-dihydroxynaphthalene (1) and N,N′-bidentate ligands, namely 2,2′-bipyridine (2) and 1,10-phenanthroline (3), were obtained and characterized by CV, UV-vis spectroscopy, DFT calculations and in the case of 3 X-ray diffraction. It was shown that the HOMO of the complexes is almost completely located on the naphthalene fragment while the LUMO is on the N,N-ligands. At the same time, there are no boundary molecular orbitals on the germanium atom, but it forms the axial part of the molecule holding two opposite motifs together. Moreover, it sharply affects the level of HOMO and LUMO. Derivatives 2 and 3 are more easily oxidized compared to 2,3-dihydroxynaphthalene by 0.31–0.34 V (7–8 kcal mol−1) and are more easily reduced compared to N,N-donors by 1.08–1.15 V (25–26.5 kcal mol−1). All this together makes it possible to form a system with a narrow HOMO/LUMO gap (∼2 eV). The crystal structure of 3 consists of alternating monomolecular easily oxidizing and easily reducing layers formed due to intermolecular interactions, in particular π-stacking. In addition, in contrast to 1 that starts to decompose noticeably at the temperatures from 200 °C, 2 and 3 have an extremely high thermal stability. They remain stable with no signs of decomposition and melting up to 400 °С. We believe that this approach to the formation of the supramolecular structure may present prospects for obtaining new functional materials.

New Schiff base germanate derivative containing the chain Ar–C=N→Ge←N=C–Ar was synthesized and characterized by physical methods including X-ray diffraction. The stability of the corresponding radical anion obtained electrochemically was confirmed by cyclic voltammetry, the results were compared with UV-VIS data and quantum chemical calculations.

Purpose: The aim of the present article is to identify new dangers and threats posed by the state of peaceful war, which is inherent in the information network society, as well as corresponding to these threats’ new aspects of Russia's national security. Methodology: As research methodology we use an interdisciplinary research strategy, a topological approach, a synergy paradigm, the concept of the Internet of things, the theory of cultural-historical psychology, the concept of positive construction of social reality, propositions of quantum sociology, the concept of “peaceful war” (“hybrid war”, “multidimensional war”), strategies and methods for implementing the systemic nature of Russia's national security. Result: The result is that new aspects of Russia's national security, connected with the “peaceful war”, peculiarities of the impact of new information and communication technologies (ICT) and the Internet of Things as a global computing system (network of networks) on human consciousness, giving specific features to the system of security, and, first of all, its information, psychological, military, cultural and educational components, are shown for the first time. Applications: The application of interdisciplinary, topological and synergistic approaches makes it possible to find out the peculiarities of the impact of ICT and Internet of Things on human consciousness, which functions in accordance with the Mobius band metaphor. Novelty/Originality: The scientific novelty consists in an attempt to apply the concept of “peaceful war”, encompassing all spheres of public life, in order to develop an adequate system for ensuring Russia's national security.

The concept of using redox-active ligands, which has become extremely widespread in organometallic chemistry, is often considered from 'their effect on the metal center properties' point of view and 'how to modify the ligands'. In this paper, we present the reverse side of this effective approach - a dramatic change of redox properties of ligands under the influence of a redox-inert metal. Germanium derivatives based on 2,3-dihydroxynaphthalene (1) and

International audience; Bis-phenyl derivative of a novel family of bis-metallatranes, 1,1'-diphenyl-bis-germatrane, was synthesized and characterized. One-electron oxidation of this compound is electrochemically and chemically reversible providing a persistent radical cation.

Formation of donor-acceptor complexes between dichlorosilylene, SiCl2, and allyl halides, AllHal(Hal= Cl, Br) was detected in Ar matrixes using matrix IR spectroscopy. In agreement with the predictions of the performed quantum chemical calculations, only broad unstructured absorption bands contributed by different conformers of the 1 : 1 complexes between SiCl2 and AllHal were observed in IR spectra of matrixes after deposition in the regions of characteristic vibrations of starting reactants. Annealing of matrixes resulted in strong narrowing the bands due to conversions of different conformers into the most stable structures. The predominantly formed conformers in both the reaction systems were those of complexes with SiCl2 coordinated to the Hal atoms of AllHal in the gauche conformations. At the same time, according to the calculations, the complexes with SiCl2 coordination to the double bonds of AllHal can be only slightly less stable than the complexes with coordination to the Hal atoms, and all these basic centers can be considered as comparable in their activity in the complexation. The only products revealed upon photolysis of complexes were the products of silylene insertion into the C–Hal bonds, viz., AllSiCl3 and AllSiCl2Br. Theoretical study of thermal transformations in the SiCl2 + AllHal systems showed that formal insertion of SiCl2 in the C–Hal bonds and its addition to the double bonds of AllHal have low activation barriers of 3–8 kcal mol–1. However, these barriers are too high for these reactions to occur under the matrix isolation conditions.

A reaction of activated silicon with alcohols in an autoclave at 240—270 °C was studied. It was found that primary alcohols form tetraalkoxysilanes Si(OR)4 with high selectivity (up to 97%), while the secondary PriOH gave a mixture of compounds HSi(OPri)3, Si(OPri)4, HSi(OPri)2OSi(OPri)2H, HSi(OPri)2OSi(OPri)3, and Si(OPri)3OSi(OPri)3 with the predominance of trialkoxysilane (up to 67%). Carrying out the reaction under the indicated conditions has the advantage of experimental simplicity, reagent availability, high conversion of silicon, good isolated yields of products.

A matrix FTIR study of interaction between SiCl2 and 1,3-butadiene revealed that at low temperatures, it stops at the step of complexation between the reactants. This allowed us to investigate a photochemical version of this interaction resulting in the formation of both 1,1-dichloro-1-silacyclopent-3-ene and 1,1-dichloro-2-vinylsilirane in contrast to the thermal reaction giving only the first of these products.

International audience; Complexes of tetra‐ and hexa‐coordinated germanium AdrCat2Ge (1, AdrCat = adrenaline catecholate), AldCat2Ge (2, AldCat = 4‐formylcatecholate), AldCat3Ge(Et3NH)2 (3) were synthesized by the reaction of germanium dioxide with adrenaline and 3,4‐dihydroxybenzaldehyde in aqueous solution. The structures of the complexes were confirmed by 1H and 13C NMR and IR spectroscopy, HRMS, and elemental analysis. Cyclic voltammetry in phosphate buffer solutions (pH = 6.86) has shown the oxidation potentials Ep of these complexes to be shifted by ca. 330–360 mV to more positive potentials compared to the parent aromatic diols, which means that their electron‐releasing properties were diminished by about 7.6–8.3 kcal mol–1. A study of the kinetics of the reaction of these complexes with 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) free radical in the presence of 5 % acetonitrile reveals a decrease of approximately one order of magnitude in the radical scavenging activity of adrenaline and model 3,4‐dihydroxybenzaldehyde upon their complexation with Ge. The corresponding rate constants drop from (3.23 ± 0.07) × 103 L mol–1 s–1 (adrenaline) to (3.80 ± 0.20) × 102 L mol–1 s–1 for 1, and from (4.40 ± 0.20) × 103 L mol–1 s–1 (3,4‐dihydroxybenzaldehyde) to (4.45 ± 0.25) × 102 L mol–1 s–1 for 2 and 3 (germanium is equally capable to bind two or three molecules of the diol). Keeping in mind that 1,2‐diols are widespread in the living nature and often have important biological functions, these results will contribute to the understanding of role of germanium dioxide in metabolic mechanisms and to alert against unreasonable use of Ge preparations.

It is experimentally found that allyltrichlorosilane dissociates under vacuum pyrolysis (~10–2 Torr) at temperatures above 1100 K to form three labile intermediates: allyl radical, dichlorosilylene, and monoatomic chlorine. On the basis of experimental and theoretical data obtained, it is shown that the decomposition reaction proceeds in two steps. The first step is a typical reaction of homolytic decomposition to two radicals (C3H5 and SiCl3) at the weakest Si—C bond. Due to weakness of the Si—Cl bond in the SiCl3 radical, the energy of which is even somewhat lower than the dissociation energy of the Si—C bond in starting AllSiCl3, this radical undergoes further dissociation to SiCl2 and Cl, thus resulting in three intermediates of different classes of highly reactive species formed from AllSiCl3.

International audience; The antioxidant activity of Ge-132 (2-carboxyethylgermanium sesquioxide, [(O0.5)3GeCH2CH2COOH]n), a widely used organic germanium dietary supplement, was assessed by cyclic voltammetry and through its interaction with a stable radical 2,2,-diphenyl-1-picrylhydrazyl (DPPH) monitored by UV-Vis and EPR spectroscopy in water, CH3CN, DMF, MeOH, and their mixtures with water. The results obtained by these methods are coherent in that Ge-132 can manifest its antioxidant activity only in the absence of water because the latter hydrolyses its Ge-O-Ge fragment responsible for quenching free radicals. Thus, contrary to a common use of Ge-132 as a water-soluble agent, it can act as an antioxidant solely in a lipid environment, which is important for understanding the mechanism of its biological activity.

The aim of the current study was to compare different approaches to the direct synthesis of alkoxysilanes, which were previously discussed in the literature, to obtain high selectivity for trimethoxysilane and satisfying silicon conversion. The possibility of obtaining alkoxysilanes by the reaction of elemental silicon with several organic precursors (first of all, alcohols) was investigated. Trialkoxysilanes and tetraalkoxysilanes were the main products of the reaction. They were identified by means of elemental analysis, NMR- and IR spectroscopies, and chemical analysis. Primary kinetic regularities were investigated as well. The direct process was carried out in 4 different reactor types: flask-like liquid-phase; tube-like gas/solid-phase; flask-like gas/solid-phase with strong UV irradiation, and an autoclave. As a result of optimization there were obtained both HSi(OAlk)3 and Si(OAlk)4 with very high selectivity (> 90 %). The data are very promising in terms of development of new chlorine-free alkoxysilanes production techniques.

Time-resolved studies of chlorosilylene, ClSiH, generated by the 193 nm laser flash photolysis of 1-chloro-1-silacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reaction with trimethylsilane-1-d, Me(3)SiD, in the gas phase. The reaction was studied at total pressures up to 100 Torr (with and without added SF(6)) over the temperature range of 295-407 K. The rate constants were found to be pressure independent and gave the following Arrhenius equation: log[(k/(cm(3) molecule(-1) s(-1))] = (-13.22 ± 0.15) + [(13.20 ± 1.00) kJ mol(-1)]/(RT ln 10). When compared with previously published kinetic data for the reaction of ClSiH with Me(3)SiH, kinetic isotope effects, k(D)/k(H), in the range from 7.4 (297 K) to 6.4 (407 K) were obtained. These far exceed values of 0.4-0.5 estimated for a single-step insertion process. Quantum chemical calculations (G3MP2B3 level) confirm not only the involvement of an intermediate complex, but also the existence of a low-energy internal isomerization pathway which can scramble the D and H atom labels. By means of Rice-Ramsperger-Kassel-Marcus modeling and a necessary (but small) refinement of the energy surface, we have shown that this mechanism can reproduce closely the experimental isotope effects. These findings provide the first experimental evidence for the isomerization pathway and thereby offer the most concrete evidence to date for the existence of intermediate complexes in the insertion reactions of silylenes.

Time-resolved studies of chlorosilylene, ClSiH, generated by the 193 nm laser flash photolysis of 1-chloro-1-silacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reaction with trimethylsilane, Me(3)SiH, in the gas phase. The reaction was studied at total pressures up to 100 torr (with and without added SF(6)) over the temperature range 297-407 K. The rate constants were found to be pressure independent and gave the following Arrhenius equation: log(k/cm(3) molecule(-1) s(-1)) = (-13.97 +/- 0.25) + (12.57 +/- 1.64) kJ mol(-1)/RT ln 10. The Arrhenius parameters are consistent with a mechanism involving an intermediate complex, whose rearrangement is the rate-determining step. Quantum chemical calculations of the potential energy surface for this reaction and also the reactions of ClSiH with SiH(4) and the other methylsilanes support this conclusion. Comparisons of both experiment and theory with the analogous Si-H insertion processes of SiH(2) and SiMe(2) show that the main factor causing the lower reactivity of ClSiH is the secondary energy barrier. The calculations also show the existence of a novel intramolecular H-atom exchange process in the complex of ClSiH with MeSiH(3).

Radical cations of Me 3 СSiMe 3 and Me 3 СGeMe 3 were detected in hexane solution using the method of time-resolved magnetic field effect. The structures and electronic distributions of neutral molecules Me 3 CEMe 3 and their radical cations: Me 3 СEMe 3 + (E = C, Si, Ge, Sn) were investigated by DFT PBE/TZ2P calculations. The calculated and the experimental hyperfine coupling constants a(H) are in good agreement. The structures of Me 3 СSi Me 3 + , Me 3 СGe Me 3 + , and Me 3 СSn Me 3 + are in essence a tight radical cation pairs of the type CMe 3 / EMe 3 + .

Time-resolved studies of germylene, GeH2, generated by the 193 nm laser flash photolysis of 3,4-dimethyl-1-germacyclopent-3-ene, have been carried out to obtain rate constants for its bimolecular reactions with ethyl- and diethylgermanes in the gas phase. The reactions were studied over the pressure range 1-100 Torr with SF6 as bath gas and at five temperatures in the range 297-564 K. Only slight pressure dependences were found for GeH2 + EtGeH3 (399, 486, and 564 K). The high pressure rate constants gave the following Arrhenius parameters: for GeH2 + EtGeH3, log A = -10.75 +/- 0.08 and Ea = -6.7 +/- 0.6 kJ mol-1; for GeH2 + Et2GeH2, log A = -10.68 +/- 0.11 and Ea = -6.95 +/- 0.80 kJ mol-1. These are consistent with fast, near collision-controlled, association processes at 298 K. RRKM modeling calculations are, for the most part, consistent with the observed pressure dependence of GeH2 + EtGeH3. The ethyl substituent effects have been extracted from these results and are much larger than the analogous methyl substituent effects in the SiH2 + methylsilane reaction series. This is consistent with a mechanistic model for Ge-H insertion in which the intermediate complex has a sizable secondary barrier to rearrangement.

Chlorosilylene, ClSiH, was prepared by 193 nm laser flash photolysis of 1-chloro-1-silacyclopent-3-ene in the gas phase. ClSiH was monitored in real time at 457.9 nm using a CW argon ion laser. The kinetics of reactions of ClSiH with C 2 H 4 , CH 2 CHCMe 3 , C 2 H 2 , Me 2 O, SO 2 , HCl, MeSiH 3 , Me 2 SiH 2 , Me 3 SiH, MeGeH 3 , Me 2 GeH 2 and precursor have been studied at ambient temperatures for the first time. Addition reactions of ClSiH and reactions with lone pair donors are faster than insertion reactions. Surprisingly ClSiH inserts faster into Si–H than Ge–H bonds. ClSiH is intermediate in reactivity between SiH 2 and SiCl 2 . Relative reactivities of ClSiH and SiH 2 vary considerably.

Time resolved studies of germylene, GeH2, generated by laser flash photolysis of 3,4-dimethylgermacyclopentene-3, have been carried out to obtain rate constants for its bimolecular reaction with ethylene, C2H4. The reaction was studied in the gas-phase over the pressure range 1–100 Torr, with SF6 as bath gas, at 5 temperatures in the range 293–555 K. The reaction shows the characteristic pressure dependence of a third-body assisted association reaction. The high pressure rate constants, obtained by extrapolation, gave the Arrhenius equation: log(k∞/cm3 molecule−1 s−1) = (−10.61 ± 0.08) + (5.37 ± 0.56 kJ mol−1)/RT ln10. These Arrhenius parameters are consistent with a fast reaction occurring at approximately half the collision rate at 298 K. RRKM modelling based on a variational transition state, used in combination with a weak collisional deactivation model, gave good fits to the pressure dependent curves for a choice of the critical energy, E0 = 130 kJ mol−1. Quantum chemical calculations (both DFT and ab initio G2//QCISD) of the GeC2H6 potential energy surface (PES), show that GeH2 + C2H4 initially form a π-complex, which can either collapse to germirane or isomerise by a 1,2 H-shift to ethylgermylene with a relatively low barrier. This indicates that the observed pressure dependence must correspond the formation of two products, of which ethylgermylene is the more stable. It also shows that germiranes with 1-H substituents will thermally rearrange to ethylgermylenes with very low barriers. A detailed examination of the PES shows that other potential reaction products are unlikely to be formed. Thermochemical considerations show that germirane is less strained than silirane, and that divalent state stabilisation energies (DSSE) for germylenes are hardly greater than those for silylenes.

Temperature study of Raman spectra of alkylgermanes (Alk = Bun, n-C6H13) in liquid, polycrystalline, and glassy states was carried out. The spectra of liquid samples are complicated, because compounds exist as equilibrium mixtures of rotational isomers due to hindered rotation about C—C and Ge—C bonds. In crystals, only the most stable conformer persists, which results in simplification of the spectrum. Unlike n-hexylgermanes, n-butylgermanes crystallize on cooling with difficulties. Quantum-chemical calculations of the geometry and normal coordinate analysis of the possible conformers of the BunGeH3, BunGeCl3, and Bun 2GeCl2 molecules were performed. The unusually large (∼65 cm–1) difference between the experimental ν(Ge—C) stretching frequencies of the trans and gauche conformers about the C—C bond nearest to the Ge atom is attributed to the difference in the electronic structure of these conformers, which is manifested in the differences in the Ge—C bond lengths, molecular geometry, and their force fields and, consequently, affects the mode frequencies and eigenvectors.

Gas-phase rate constants for the title reactions have been obtained by laser flash photolysis at 297 K, by use of photoprecursors, 3,4-dimethyl-1-germacyclopent-3-ene for GeH 2 and pentamethyldigermane for GeMe 2 . The values obtained were ( k ( cm 3 molecule −1 s −1 ) ): (2.38±0.11)×10 −10 for GeH 2 , (2.26±0.10)×10 −13 for GeMe 2 . These results show that the insertion reaction of GeMe 2 is 1050 times slower than that of GeH 2 into the GeH bonds of Me 2 GeH 2 . This is explained in terms of a general mechanism involving an intermediate H-bridged complex, applicable to both silylene and germylene insertions. For the GeMe 2 insertion, reactants are in equilibrium with the complex, which rearranges to the product in the rate controlling step.

3 pags, 1 figs, 2 tabs, 2 schs, A kinetic isotope effect (kD/kH) of 7.4 has been found for the reaction of chlorosilylene with trimethylsilane (Me3SiD vs Me3SiH). Such a value can be accounted for by theoretical modeling, but only if an internal rearrangement of the initially formed complex is included in the mechanism. This provides the first concrete evidence for such complexes. © 2011 American Chemical Society., This work was supported by the award of an RSC Journals grant to R.B. R.B. also thanks the Ministerio de Educacion y Ciencia (Spain) for support under Project CTQ2006-10512.

The thermochromic phase transition of poly(di- n -hexylgermane) ( 1 ) was reinvestgated using low-molecular-weight ( lmw ) and high-molecular-weight ( hmw ) polymer samples. The equilibrium phase transition temperature T c of 1 , determined by variable temperature Raman and UV spectroscopy as well as by DSC, was found to lie not in the interval from +15 to −10°C, as was reported previously, but in the region 45–55 °C, that is, very close to T c of the Si and Sn analogues. Thus, the phase behaviour of the polymetallanes [ n Hex 2 M] n , M=Si, Ge, Sn is governed not by the nature of the main chain but by intermolecular interactions of the substituent groups. The nature of the order–disorder phase transition of 1 depends on the polymer molecular weight and the sample thermal history. Above T c , hmw polymer 1 exists as hexagonal columnar mesophase while lmw 1 is in amorphous state, both with disordered backbone. On cooling to room temperature, hmw polymer transforms to a crystalline modification with an all- anti conformation of the backbone and ordered hexyl groups, whereas the process of ordering of the main chain for lmw sample is more complicated.

First, previously unknown, cyclic organogermanium peroxides, 1,2,4,5,7,8-hexaoxa-3-germonanes, were synthesized by the reaction of 1,1′-dihydroperoxydi(cyclododecyl)peroxide with (di)alkyl(aryl)dihalogengermanes. The new compounds have a higher tendency to undergo hydrolysis compared to silicon-containing analogs.

3-Nitro-ω-benzylideneacetophenone (1) reacts with carbanions containing leaving groups to give addition products to the electrophilic side chain. As a result of conjugated addition and subsequent intramolecular vicarious nucleophilic substitution of hydrogen (VNS) in the nitroaromatic ring of 1 in the position para to the nitro group, 4-cyano-7-nitro-3-phenyl-1,2,3,4-tetrahydronaphthalen-1-one and 4-cyano-7-nitro-3-phenylnaphth-1-ol are obtained. Smooth intramolecular VNS in the position para to the nitro group was observed for 4-chloro-1-(3-nitrophenyl)-3-phenyl-4-(p-tosyl)butanol.

The chloromethyl trans-β-styryl sulfone carbanion reacts with benzaldehyde and acrylonitrile under phase-transfer catalysis conditions to give 2-phenyl-3-(trans-β-styrylsulfonyl)oxirane and bis(2-cyanoethyl)chloromethyl trans-β-styryl sulfone, respectively, and with nitroarenes to form the products of vicarious nucleophilic substitution of hydrogen.

A series of 1,1-dihaloalk-2-ynes 1–3 has been prepared by halogenation of the formylacetylenes 8 with PCl5 or an equimolar mixture of PCl5 and Br2. A simple, general means of access to the alkynylhalocarbenes 5 has been developed via base-initiated α-elimination of 1,1-dihaloalk-2-ynes (1–3). The carbenes 5a–i have been trapped by alkenes, to form 1-alkynyl-1-halocyclopropanes (11) in up to 90% yield. Under the same conditions compound 1g was converted into the buta-diene 12. Experimental evidence for the electrophilicity and the singlet nature of carbenes 5 has been obtained.

The chloromethyl trans-β-styryl sulfone carbanion reacts with benzaldehyde and acrylonitrile under phase-transfer catalysis conditions to give 2-phenyl-3-(trans-β-styrylsulfonyl)oxirane and bis(2-cyanoethyl)chloromethyl trans-β-styryl sulfone, respectively, and with nitroarenes to form the products of vicarious nucleophilic substitution of hydrogen.

A new, general route to 1-chloro-1-ethynylcyclopropanes 6 has been developed via cycloaddition of previously unknown chloro(trimethylsilylethynyl)carbene 4b to olefins with formation of the corresponding cyclopropanes 5a-f in 35-65% yield and subsequent removal of the trimethylsilyl group under the action of KF2H 2 O in aqueous DMF to give cyclopropanes 6 in up to 80% yield.

1,1-Dichloro-2-alkynes R1C≡CCHCl2 (4a–g; R1=Me, n-Pr, c-Pr, t-Bu, Ad, Nor, Ph) were synthesized with yields of 50–75% by chlorination with PCl5 of formylacetylenes (3a–g), prepared by oxidation of propargyl alcohols (1a–d) with CrO3·Py·HCl complex or acidolysis of propargyl acetals (2a–c) in the presence of catalytic quantities of pyridine; the corresponding alkynylchlorocarbenes, R1C≡CCCl (5a–g) were generated from them with powdered KOH in a two-phase system or t-BuOK. The latter were trapped by olefins with formation of 1-chloro-1-alkynylcyclopropanes (6a–t) with yields of up to 90%.

Time-resolved studies of silylene, SiH2, and dimethylsilylene, SiMe2, generated by the 193 nm laser flash photolysis of appropriate precursor molecules have been carried out to obtain rate constants for their bimolecular reactions with dimethylgermane, Me2GeH2, in the gas phase. SiMe2 + Me2GeH2 was studied at five temperatures in the range 299-555 K. Problems of substrate UV absorption at 193 nm at temperatures above 400 K meant that only three temperatures could be used reliably for rate constant measurement. These rate constants gave the Arrhenius parameters log(A/cm3 molecule(-1) s(-1)) = -13.25 +/- 0.16 and E(a) = -(5.01 +/- 1.01) kJ mol(-1). Only room temperature studies of SiH2 were carried out. These gave values of (4.05 +/- 0.06) x 10(-10) cm3 molecule(-1) s(-1) (SiH2 + Me2GeH2 at 295 K) and also (4.41 +/- 0.07) x 10(-10) cm3 molecule(-1) s(-1) (SiH2 + MeGeH3 at 296 K). Rate constant comparisons show the surprising result that SiMe2 reacts 12.5 times slower with Me2GeH2 than with Me2SiH2. Quantum chemical calculations (G2(MP2,SVP)//B3LYP level) of the model Si-H and Ge-H insertion processes of SiMe2 with SiH4/MeSiH3 and GeH4/MeGeH3 support these findings and show that the lower reactivity of SiMe2 with Ge-H bonds is caused by a higher secondary barrier for rearrangement of the initially formed complexes. Full details of the structures of intermediate complexes and the discussion of their stabilities are given in the paper. Other, related, comparisons of silylene reactivity are also presented.

Time-resolved studies of germylene, GeH(2), and dimethygermylene, GeMe(2), generated by the 193 nm laser flash photolysis of appropriate precursor molecules have been carried out to try to obtain rate coefficients for their bimolecular reactions with dimethylgermane, Me(2)GeH(2), in the gas-phase. GeH(2) + Me(2)GeH(2) was studied over the pressure range 1-100 Torr with SF(6) as bath gas and at five temperatures in the range 296-553 K. Only slight pressure dependences were found (at 386, 447 and 553 K). RRKM modelling was carried out to fit these pressure dependences. The high pressure rate coefficients gave the Arrhenius parameters: log(A/cm(3) molecule(-1) s(-1)) = -10.99 +/- 0.07 and E(a) =-(7.35 +/- 0.48) kJ mol(-1). No reaction could be found between GeMe(2) + Me(2)GeH(2) at any temperature up to 549 K, and upper limits of ca. 10(-14) cm(3) molecule(-1) s(-1) were set for the rate coefficients. A rate coefficient of (1.33 +/- 0.04) x 10(-10) cm(3) molecule(-1) s(-1) was also obtained for GeH(2) + MeGeH(3) at 296 K. No reaction was found between GeMe(2) and MeGeH(3). Rate coefficient comparisons showed, inter alia, that in the substrate germane Me-for-H substitution increased the magnitudes of rate coefficients significantly, while in the germylene Me-for-H substitution decreased the magnitudes of rate coefficients by at least four orders of magnitude. Quantum chemical calculations (G2(MP2,SVP)//B3LYP level) supported these findings and showed that the lack of reactivity of GeMe(2) is caused by a positive energy barrier for rearrangement of the initially formed complexes. Full details of the structures of intermediate complexes and the discussion of their stabilities are given in the paper.

Using a laser flash photolysis/laser probe technique, we report the observation of strong absorption signals in the wavelength region 450-520 nm (highest intensity at 514.5 nm) from four potential precursors of dimethylstannylene, SnMe(2), subjected to 193 nm UV pulses. From GC analyses of the gaseous products, combined with quantum chemical excited state CIS and TD calculations, we can attribute these absorptions largely to SnMe(2), with SnMe(4) as the cleanest source of the species. Kinetic studies have been carried out by time-resolved monitoring of SnMe(2). Rate constants have been measured for its reactions with 1,3-C(4)H(6), MeC[triple bond]CMe, MeOH, 1-C(4)H(9)Br, HCl, and SO(2). No evidence could be found for reaction of SnMe(2) with C(2)H(4), C(3)H(8), Me(3)SiH, GeH(4), Me(2)GeH(2), or N(2)O. Limits of less than 10(-13) cm(3) molecule(-1) s(-1) were set for the rate constants for these latter reactions. These measurements showed that SnMe(2) does not insert readily into C-H, Si-H, Ge-H, C-C, Si-C, or Ge-C bonds. It is also unreactive with alkenes although not with dienes or alkynes. It is selectively reactive with lone pair donor molecules. The possible mechanisms of these reactions are discussed. These results represent the first visible absorption spectrum and rate constants for any organo-stannylene in the gas phase.

A series of 1,1-dihaloalk-2-ynes 1–3 has been prepared by halogenation of the formylacetylenes 8 with PCl5 or an equimolar mixture of PCl5 and Br2. A simple, general means of access to the alkynylhalocarbenes 5 has been developed via base-initiated α-elimination of 1,1-dihaloalk-2-ynes (1–3). The carbenes 5a–i have been trapped by alkenes, to form 1-alkynyl-1-halocyclopropanes (11) in up to 90% yield. Under the same conditions compound 1g was converted into the buta-diene 12. Experimental evidence for the electrophilicity and the singlet nature of carbenes 5 has been obtained.

The results of studies on exoemission employing various excitation procedures are examined from the single standpoint of physicochemical reactions on the surfaces of solids. The prospects for the application of exoemission in scientific research and in engineering are discussed. The bibliography includes 164 references.

1. The action of t-BuOK or KOH in the presence of phase transfer catalysts on 2-dichlorofuran and 2-dichloromethylthiophene generated (2-furyl)chlorocarbene and (2-thienyl)-chlorocarbene, respectively. The singlet ground state and electrophilic nature of these carbenes were established. 2. The carbenes thus generated, in contrast to the reported (2-furyl) carbenes and (2-thienyl) carbenes, display a great tendency to undergo intermolecular cycloaddition to olefins, apparently as a consequence of the stabilizing effect of the clorine atom.

Both gem-(2-furyl)chlorocyclopropanes in yields up to 44% and 2-(chloromethylene)-5-tert-butoxy-2, 5-2,5-dihydrofuran in yields up to 12% are formed upon the action of potassium tert-butylate on 2-dichloromethylfuran in excess olefin acceptor. This result is attributed to the reaction of the intermediate (2-furyl)chlorocarbene in ambident form.