Mass spectrometric study of high-temperature dehydroxylation of disperse silicas and the interpretation of their IR spectra in the region of Si-O stretching vibrations

Field-desorption mass spectrometry has been used to determine the lower boundary of the temperature interval for the removal of surface hydroxyl groups ofaerosil. Both in the regime of cation desorption and in the regime of anion desorption, at temperatures above 900°K, OH ions of the corresponding sign are registered. It is concluded that the thermal decomposition of the surface bonds Si-OH is homolytic in character. A mechanism is proposed for the dehydroxylation of SiO₂, according to which the initially formed radical centers Si and SiO^. change into ions: Si⁺ (I) and SiO^– (II). The bands at 888 and 908 cm^–1 in the IR spectra of silicas obtained at high temperatures are assigned to vibrations of Si-O bonds in I and II, respectively.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 1, pp. 61–66, January–February, 1985.     

DFT study of the mechanism of alkane hydrogenolysis by transition metal hydrides. 1. Interaction of silica-supported zirconium hydrides with methane

Model reactions of silica-supported zirconium hydrides (Si—O—)₃ZrH and (Si—O—)₂ZrH₂ with methane, resulting in cleavage of a C—H bond in the methane molecule and the formation of (Si—O—)₃ZrCH₃ and (Si—O—)₂Zr(H)CH₃ as products were studied using the DFT approach with the PBE density functional. The processes proceed as bimolecular reactions without preliminary formation of agostic complexes. According to calculations, zirconium dihydrides (Si—O—)₂ZrH₂ are more reactive toward the methane C—H bonds than zirconium monohydrides (Si—O—)₃ZrH. The calculated activation energies of the reactions with participation of zirconium dihydrides (Si—O—)₂ZrH₂ are in better agreement with the known experimental data for the Yermakov—Basset catalytic system.     

Free Radical Reactions of N2O Molecules

Experimental data are presented on the spectral (ESR, IR, and optical) and thermochemical characteristics of a complex between the (Si–O)₃Si^.radical and an N₂O molecule. The rate constants of separate reactions in the systems (Si–O)₃Si^.+ N₂O and (Ge–O)₃Ge^.+ N₂O are found. The results of quantum chemical calculations of potential energy surfaces and spectral characteristics are presented for the following systems: H^.+ N₂O, H₃C^.+ N₂O, H₃Si^.+ N₂O, F₂HSi^.+ N₂O, F₃Si^.+ N₂O, and F₃Ge^.+ N₂O. The latter three systems served as molecular models for experimentally found systems. Based on experimental and theoretical data, the product of N₂O addition to (Si–O)₃Si^.has the structure Si–N=N–O^.. The reactions of free radicals H^., H₃C^., H₃Si^., F₂HSi^., F₃Si^., (Si–O)₃Si^., and (Ge–O)₃Ge^.with N₂O are compared. The spectrum of optical absorbance of the (Si–O)₃Si–O^.radical is recorded and qualitatively characterized.     

Mechanisms of Reactions of H2O and NH3 Molecules with (≡Si–O)3Si⋅and (≡ Si–O)3Si–⋅ Radicals on the Silica Surface

Spin traps, which are diamagnetic centers (SiO)₂Si, are used to register low-molecular radicals OH, NH₂, and H formed by the reactions of H₂O and NH₃ molecules with the radicals (Si–O)₃Si and (Si–O)₃Si–O stabilized on the silica surface. The experimental data and the results of quantum-chemical calculations for model systems are used to determine the mechanism and thermochemical characteristics of these reactions. A new paramagnetic center (Si–O)₂SiNH₂ was identified on the silica surface, and its radiospectroscopic characteristics are determined.     

Mechanisms of Heterogeneous Processes in the System SiO2 + CH4: I. Methane Chemisorption on a Reactive Silica Surface

Experimental and quantum chemical study of reactive silica surface methylation is carried out. The main product of the reaction is the (Si–O)₂Si(H)(CH₃) groups, which are formed via a radical-chain process with the participation of methane molecules and paramagnetic and diamagnetic defects on the oxide surface. Spectral (optical and IR) characteristics of the groups participating in the process (Si–O)₂Si^·–CH₃, (Si–O)₂Si(H)(CH₃), and (Si–O)₂Si(CH₃)(CH₃) are determined. Information on the kinetics of separate steps of the process is obtained including rate constants and the activation energies of steps.     

Mechanisms of Heterogeneous Processes in the System SiO2 + CH4: III. Products of >Si

Permenov  D. G.  Radzig  V. A. 《Kinetics and Catalysis》2004,45(2):273-278

A new procedure for the synthesis of arylor hetaryl-substituted conjugated diynes

On treatment with two equivalents of NaNH₂ in liquid ammonia the enyne sulfides RCC–CH=CHSEt (cis-isomers, where R is an aryl or a hetaryl) afford sodium salts of 1,3-diynes. The latter react with ethyl bromide to produce disubstituted diynes RCC–CCEt in high yields.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 348–350, February, 1993.     

Cyclosilethynes containing exocyclic cyclopentyl and cyclohexyl groups

The reaction of BrMgCCSiMe₂CCSiMe₂CCSiMe₂CCSiMe₂CCMgBr with chloro(cyclopentyl)(methyl)silane in a large excess of THF gave 1-cyclopentyl-1,4,4,7,7,10,10,13,13-nonamethyl-1,4,7,10, 13-pentasilacyclopentadeca-2,5,8,11,14-pentayne. Similarly, 1,10-di(cyclopentyl)- or 1,6-di(cyclopentylmethyl)-1,4,4,7,7,10,13,13,16,16-decamethyl-1,4,7,10,13,16-hexasilacyclooctadeca-2,5,8,11,14,17-hexaynes were synthesized from BrMgCCSiMe₂CCSiMe₂CCMgBr and dichloro(cyclopentyl)methylsilane or dichloro(cyclopentylmethyl)(methyl)silane. Condensation of Me₂Si(CCMgBr)₂ with dichloro(cyclohexyl)-methylsilane afforded 1,7-di(cyclohexyl)-1,4,4,7,10,10-hexamethyl-1,4,7,10-tetrasilacyclododeca-2,5,8,11-tetrayne.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 8, 2004, pp. 1282–1284.Original Russian Text Copyright © 2004 by O. Yarosh, Zhilitskaya, N. Yarosh, Albanov, Klyba, Voronkov.This revised version was published online in April 2005 with a corrected cover date.     

Overton-Region IR Registration of (≡Si–O)2Si=O and (≡Si–O)2Si〈O2〉C=O Groups on the Silica Surface

IR spectroscopy in a range of 2050–4000 cm^–1 (the range of overtones and composite frequencies) is used to study the groups (Si–O)₂Si=O and (Si–O)₂SiO₂C=O with different isotopic compositions (¹⁶O, ¹⁸O, ¹²C, and ¹³C). Analysis of the experimental data and quantum-chemical calculations of vibrational spectra for the model compounds are used to identify the IR bands. New data are obtained on the vibrational spectra of these groups. Their identification is shown to be possible in the spectral range that is convenient for the study of silica samples.     

Investigation of electronic structure of impurity and defect centers on the surface of silica by the MNDO method

The electronic structure of cluster models of fragments of a. silica surface with defect centers [stressed disiloxane bridges, radical (Si, SiO) and ionic (Si⁺, SiO^–) groups] and impurity centers (boron and aluminum atoms) has been investigated by the MO-LCAO-SCF method in the MNDO approximation. It has been shown on the basis of an analysis of the energetics of the defect structures (with complete optimization of the geometry of the clusters) that the dehydroxylation of silica with the formation of radical and ionic centers is energetically significantly more favorable than is the formation of disiloxane bridges. The influence of impurity boron and aluminum atoms on the properties of the surface fragments of SiO₂ has been considered. It has been shown that the migration of impurity boron atoms, which isomorphously replace silicon atoms in the lattice, from the bulk to the surface of silica is energetically unfavorable.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 407–418, July–August, 1988.     

Kinetics and mechanisms of halide ion catalysis of CO substitution reactions in Os3(CO)12 and Ru3(CO)12 metal carbonyl clusters

The results of kinetic studies on ligand substitution in [M₃(CO)₁₁X]^– complexes (M = Ru, Os; X = Cl, Br, I) are summarized. The [Os₃(CO)₁₁X]^– complexes react with PPh₃ under mild conditions to initially yield monosubstituted products [Os₃(CO)₁₀(PPh₃)X]^–. The rate of CO substitution obeys a first-order equation with respect to the concentration of the complex and does not depend on the ligand concentration. The rates of the reactions decrease in the order Cl > Br > I withH values increasing from 15 to 18 kcal mol^–1 and S values varying from –19 to –13 cal mol^–1 K^–1. The enhanced reactivities of these complexes as well as the low activation energies and negative activation entropies are discussed in terms of the effects of -X bridge formation on the transition state of the reaction. Reactions of PPN[Ru₃(CO)_11–x (Cl)] (PPN is the bis(triphenylphosphine)iminium cation;x=0, 1) and PPN[Ru₃(CO)₉(₃-I)] with alkynes are also reported. The reactivities of alkynes follow the order BuCCH PhCCH EtCCEt PhCCPh. The higher rates of the reactions of monosubstituted acetylenes compared with those of their disubstituted analogs are explained by agostic interaction between the metal atom and the C-H bond in the reaction transition state and by steric effects. The results obtained attest that the reaction with alkynes occursvia intermediates containing halide bridges and that ₃-halide complexes are more reactive than ₂-halide complexes.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1540–1545, September, 1994.This work was supported by a Presidential Grant from Northwestern University. One of the authors (F. Basolo) wishes to thank Academician M. E. Vol'pin for the invitation to participate in the Workshop The Modern Problems of Organometallic Chemistry (INEOS-94) and Academician O. M. Nefedov for the invitation to publish a review in theRussian Chemical Bulletin.     

A study of the interaction of diethylzinc with the Aerosil surface

The interaction of diethylzinc with Aerosil has been examined by IR spectroscopy and mass spectrometry. The reaction involves both free hydroxyl groups and siloxane groups of the surface resulting in the formation of Si-O-Zn-Et and Si-Et fragments. At temperatures above 300 °C, these structures undergo decomposition with the recovery of Si-OH groups on the Aerosil surface and liberation of metallic zinc.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1666–1668, September, 1994.The authors are grateful to M. B. Molotovshchikova for continuous help in performing the experiment.     

Synthesis of novel symmetrical and nonsymmetrical 6-membered heterocycles with pendant electron-rich organoiron substituents

The functionalized complexes [(dppe)Cp^*Fe(CC)]₂-(Py) (Py=2,6-C₅H₃N and 3,5-C₅H₃N (dppe=1,2-bis(diphenylphosphino)ethane) were isolated in good yields from reaction of the chloro complex (dppe)Cp^*FeCl with the protected bis-acetylenic heterocyclic precursor. These electron-rich pyridyl ligands constitute interesting examples of organometallic heterocycles bearing redox-active substituents. Attempts to find an alternative route starting from the alkynyl complex [(dppe)Cp^*Fe(CCH)] and the corresponding dibromopyridines using a Sonogashira cross-coupling reaction are also described. By this route, the monofunctionalized products [(dppe)Cp^*Fe(CC)]-2,6-Py-Br and [(dppe)Cp^*Fe(CC)]-3,5-Py-Br could be cleanly isolated. These compounds open the way to the generation of heteroaromatics featuring nonequivalent alkyne substituents such as [(dppe)Cp^*Fe(CC)]-2,6-Py-[(CC)SiMe₃] or [(dppe)Cp^*Fe(CC)]-3,5-Py-[(CC)SiMe₃] by further coupling.In commemoriation of the centenary of Academician A. N. Nesmeyanov.UMR CNRS 6509 Organométalliques et catalyse: Chimie et Electrochimie Moléculaires, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1207–1218, September, 1999.     

Synthesis, Characterization and Luminescence Studies of Trinuclear Rhenium–Cobalt Mixed-Metal Alkynyl Complexes Containing a Tetrahedral Co2C2 Cluster Unit

The reaction of rhenium(I) diynyl complexes [Re(CO)₃(N–N)(CC--CCH)] [N–N = ^tBu₂bpy (1), bpy (2)] with Co₂(CO)₈ in THF yielded a new class of luminescent trinuclear rhenium–cobalt mixed-metal alkynyl complexes, [Co₂{-HC₂CC[Re(CO)₃(N–N)]}(CO)₆] [N–N = ^tBu₂bpy (3), bpy (4)]. Their luminescence and electrochemical properties have also been studied.     

Effect of alkaline modification of products of thermal vacuum and hydrothermal treatment of NH4Na-Y zeolite according to the IR spectral data

The effect of alkaline modification on the structure of the products of heat treatment of NH₄Na-Y zeolite (53% NH ₄ ⁺ , Si/Al - 2.37) in a vacuum at 573 K and in water vapors at 873 K was investigated with the IR spectrum of vibrations of the zeolite framework in the 400–1200 cm^–1 region. It was shown that the high-frequency shift of the bands in the spectra of the products obtained, the stretching vibration of v_as(TO₄) tetrahedrons in particular (T=Si, Al) at 1023 cm^–1 by 6 and 19 cm^–1, is determined by a decrease in the excess negative charge of the framework due to weakening and hydrolytic splitting of Al-O bonds of the deammoniated units with the formation of bridging Si-O(H)...Al and terminal Si-OHHO-Al hydroxyl groups. Treatment of these samples with an aqueous solution of KOH (pH 13.4) at 293 and 353 K restores the normal framework Si-O-Al bonds at the sites of formation of bridging and terminal hydroxyl groups. In the second case, restoration is hindered by substitution of H⁺ by K⁺ with some silanol groups.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. I. V. Grebenshchikov Institute of Silicate Chemistry, Russian Academy of Sciences, 199164 St. Petersburg. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1733–1739, August, 1992.     

Photochemistry of Aliphatic Nitroxide Radicals Grafted onto Activated Aerosil Surface

The mechanism of photoinduced transformations of nitroxide radicals SiON(O^·)CH₃ (I) and SiOCH₂N(O^·)CH₃ (II) obtained on the activated aerosil surface was studied. The nitroxides were photolyzed with 436-nm light at 77 K. It was shown that the action of light in the long-wavelength absorption band corresponding to the n–* transition resulted in the dissociation of the O–N or C–N bond in radicals I or II, respectively. The quantum yields of these reactions were found to be 0.6 and 0.002, respectively.     

Synthesis and protonation of an OS3(μ-H)(CO)10(μ-σ,η2-C≡CCMe2OMe) cluster

Triosmium cluster Os₃(-H)(CO)₁₀(--²-CCC Me₂OMe) (1) was obtained by treating OS₃(-H)(-Cl)(CO)₁₀ with LiCCCMe₂OMe. The reaction of cluster1 with HBF₄ · Et₂O at –60 °C leads to the cationic complex [Os₃(-H)(CO)₁₀(-,,²-C=C=C Me₂)]⁺BF₄ ^– (2) with an allenylidene ligand. The^s1H and¹³C NMR spectra of complex2 reveal the temperature dependence caused by migration of hydrocarbon and carbonyl ligands. Thermodynamic parameters were obtained for be exchange process of the allenylidene ligand.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp, 2990–2992, December, 1996.     

Disproportionation of the alkynyl derivatives of alkali metal aluminum hydrides in electron-donor solvents

Conclusions The reaction of disproportionation of mixed hydride alkynyl complexes of aluminum in ether, THF, and hexametapol was studied by²⁷Al NMR, and it was shown that the stability of MAlH(3–n)) (CCR)_n, where M=Li, Na, K, and R=Ph, n-Bu decreases in the order: MAlH(CCR)₃ < MAlH₂(CCR)₂ < MAlH₃(CCR). The tendency of these complexes to disproportionate increases with an increase in the solvation of the cation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 343–349, February, 1984.We would like to thank A. V. Kisin for recording the²⁷Al NMR spectra.     

Synthesis and structures of silicon-, germanium-, and tin-containing tungsten carbyne complexes (ButO)3W≡C—EPh3 and [(ButO)3W≡C]2EPh2 (E = Si,Ge, Sn)

New tungsten carbyne complexes (Bu^tO)₃WC—SiPh₃, [(Bu^tO)₃WC]₂SiPh₂, [(Bu^tO)₃WC]₂GePh₂, and [(Bu^tO)₃WC]₂SnPh₂ were prepared by the reactions of (Bu^t)₆W₂ with Ph₃SiCC—Pr or Ph₂E(CC—Pr)₂ (E = Si, Ge, Sn) in individual crystalline form in 48—80% yields. The structures of both the (Bu^tO)₃WC—GePh₃ and (Bu^tO)₃WC—SnPh₃ compounds synthesized earlier and the new complexes were established by X-ray diffraction analysis.     

Structure and charge distribution of some alkynoyl cations

We have performedab initio calculations to determine the structure and charge distribution of some alkynoyl cations and their parent alkynoyl fluorides. We have used Mulliken population analysis and a new technique developed by Yáñez, Stewart and Pople. Our results indicate that the mesomeric form O⁺C–CC–R is one of the most important contributors to the structure of these cations, in agreement with experimental conclusions. We have also found that the participation of mesomeric form O=C=C=C⁺ -R is not negligible and increases with -substitution. In the 3-phenylpropynoyl cation substantial delocalization of charge into the phenyl group occurs. Calculations from YSP population analysis are in good agreement with experimental evidence.