Ditopic complexes of silene H2SiCH2 with bidentate ligands Me2NCH2SiHnF3-n. Structures, formation energies, AIM and ELF analyses.

Ditopic complex formation of silene H₂SiCH₂ with bidentate ligands Me₂NCH₂SiH_nF_3-n (n = 0-3) was studied at the MP4(SDQ(T)6-311G(d,p))//MP2/6-31G(d,p) levels of theory. The AIM and ELF analyses have shown that π-bonding in the silenic Si¹C moiety in the relatively weak (H₂Si¹CH₂)·(Me₂NCH₂Si²H_nF_3-n) (n = 2, 3) ditopic complexes is partially preserved.     

The structure and energy of SiH+5. comparisons with CH+5 and BH5

Differences between SiH⁺₅ and CH⁺₅ are more significant than the similarities. The proton affinity of SiH₄ exceeds than of CH₄ by ≈25 kcal/mol. but the heat of hydrogenation of SiH⁺₃ is smaller than that of CH⁺₃ by nearly the same amount. Like CH⁺₅ the C₅ structures of SiH⁺₅ are preferred, but SiH⁺₅ is best regarded as a weaker SiH⁺₃—H₂ complex. D_3h, C_2v, and C_4v forms are much higher in energy and SiH⁺₅ should not undergo hydrogen scrambling (pseudorotation) readily, as does CH⁺₅ The neutral BH₅ is only weakly bound toward loss H₂, and the D_3h. C_2v, and C_4v forms are also high in energy. The contral-atom electronegativities, C⁺ > B > Si⁺, control this behavior. The electronegativities also determine the ability to bear positive charges. Thermodynamically. SiH⁺₅ and SiH⁺₃ are more stable than CH⁺₅ and CH⁺₃, respectively; hydride transfer occurs from SiH₄ to CH⁺₃ and proton transfer from CH⁺₅ to SiH₄.     

Facile hydrosilylation of norbornadiene by silanes R3SiH and R2SiH2 with molybdenum catalysts

Photochemically activated [Mo(CO)₆] and [Mo(CO)₄(η⁴-nbd)] have been demonstrated to be very effective catalysts for hydrosilylation of norbornadiene (nbd) by tertiary (Et₃SiH, Cl₃SiH) and secondary (Et₂SiH₂ and Ph₂SiH₂) silanes to give 5-silyl-2-norbornene, which under the same reaction conditions transform in ring-opening metathesis polymerization (ROMP) to unsaturated polymers and to a double hydrosilylation product, 2,6-bis(silyl)norbornane. The yield of a particular reaction depends very strongly on the kind of silane involved. The reaction products were identified by means of chromatography (GC–MS) and ¹H and ¹³C NMR spectroscopy. In photochemical reaction of [Mo(CO)₄(η⁴-nbd)] and Ph₂SiH₂ in cyclohexane-d₁₂, η²-coordination of the SiH bond to the molybdenum atom is supported by ¹H NMR spectroscopy due to the detection of two equal-intensity doublets with ²J_HH = 5.4 Hz at δ 6.12 and −5.86 ppm.     

Triosmium compounds containing the oxametallacycle [Os(CO)3{C(R)CHC(O)CHC(H)C5H4FeC5H5}] moiety. Synthesis and electrochemical studies

The compounds [Os₃(CO)₁₀{μ,η³-(SCH₂CH₂SCCHC(O)CHCH(C₅H₄)Fe (C₅H₅)}] (2), [Os₃(CO)₉{μ,η³-(SCH₂CH₂SCCHC(O)CHCH(C₅H₄)Fe(C₅H₅)}] (3) and [Os₃(CO)₈{μ₃,η²-{CCHC(O)CHCH(C₅H₄)Fe(C₅H₅)}(SCH₂CH₂S)}] (4) have been obtained by rupture of S-C bonds in the ketene dithioacetal [C₅H₅FeC₅H₄CHCHC(O)CHC(SCH₂CH₂S)], in their reaction with the activated cluster [Os₃(CO)₁₀(NCMe)₂]. The presence of an oxametallacycle in these derivatives has been confirmed by an X-ray diffraction analysis. The electrochemical study has indicated the ability of these compounds to modify the electrode surfaces.     

Rate constants for the reactions of CCl(X2II) with a series of silanes

Rate constants for the gas phase reactions of CCl generated by the flash photolysis of CHBr₂Cl with a series of silanes have been obtained by kinetic absorption spectroscopy. In general, the rate constants are very high, and range from (4.8 ± 0.5) × 10⁸ (SiH₄) to (6.4 ± 0.34) × 10⁹ for Si₂H₆. CCl does not insert into the SiC or primary CH bonds of silanes and its rate of reaction with tertiary SiH bonds is 600 times greater than with tertiary CH bonds. CCl reacts slowly with the SiSi bond. k_H/k_D varies from 1.9 to 1.0 on going from primary to tertiary SiH bonds. The electrophilic character of CCl is manifested, on a per SiH bond basis, by excellent correlations between the rate constants and the hydrilic character of the SiH bond, and between log k and the ionization potential.     

Kinetic calculation for the reaction of H with Si2H6 using the variational transition state theory

The reaction of disilane with atomic hydrogen has been studied. This reaction involves both substitution and abstraction. Calculations show that the hydrogen abstraction is the strongest competing channel. The canonical variational transition state theory with a small curvature tunneling correction (SCT) has been used for the kinetic calculation. The theoretical results are in good agreement with the available experimental data. Comparing the reactions of atomic hydrogen with disilane and silane, it can be seen that the reactivity of the Si-H bond is higher in Si₂H₆ than that in SiH₄.     

A reactive Si4 cage: K(SitBu3)3Si4

KR∗₃Si₄, 2, (R∗ = SitBu₃), formed by the reaction of R∗₄Si₄ with 2 KC₈, is an orange red solid stable at r.t. but decomposes in solution into R∗₄Si₄ and a compound that reacts with excess Me₃SiCl to form (Me₃Si)₄R∗₃ClSi₈. Compound 2 is very sensitive to air and moisture. Its alcoholysis does not stabilize the protonated species HR∗₃Si₄ and ends up in R∗₃Si₃H₃. Compound 2 reacts with 1/2 equivalent ICl to form a violet solid R∗₆Si₈. A 1:1 reaction of 2 with SiBr₄ runs differently to form ditetrahedranyl, R∗₃Si₄-Si₄R∗₃ which is stable at r.t. but transforms into its violet isomer R∗₆Si₈ at higher temperatures. Compound 2 crystallizes as R∗₃Si₄K(18-crown-6) and its crystal structure shows a Si₄-cage with a short Si-K linkage. It opens up at higher temperatures to acquire a unique structure in which a -CH₂-CH₂- group detaches itself from an ether to insert into Si-Si linkage of Si₄-unit to form a bicyclic ring. The residual chain (CH₂)₁₀O₆ closes itself on to a Si atom to form R∗₃Si₃(CH₂-CH₂)Si(C₁₀H₂₀O₆)K(18-C-6).     

Reaction of multifunctional molecule (Ph2P(o-C6H4)CHNCH2CH2)3N with triosmium carbonyl clusters

Reaction of (Ph₂P(o-C₆H₄)CHNCH₂CH₂)₃N with 3 equiv. of Os₃(CO)₁₀(NCMe)₂ at ambient temperature affords the triple cluster [Os₃(CO)₁₀Ph₂P(o-C₆H₄)CHNCH₂CH₂]₃N (1) through coordination of the phosphine and imine groups. Thermolysis of 1 in benzene leads to decarbonylation and C-H/C-N bond activation of the ligand to generate (μ-H)Os₃(CO)₈(μ₃-Ph₂P(o-C₆H₄)CHNCCH₂) (2). The molecular structure of 2 has been determined by an X-ray diffraction study.     

Temperature-programmed desorption/pulse surface reaction (tpd/tpsr) studies of CH4, C2H6, C2H4, and CO over a cobalt/MWNTs catalyst

Summary Temperature-programmed desorption (TPD) of CH₄, C₂H₆, C₂H₄, and CO and temperature-programmed pulse surface reactions (TPSR) of CH₄, C₂H₆, C₂H₄, CO, and CO/H₂ over a Co/MWNTs catalyst have been investigated. The TPD results indicated that CH₄ and C₂H₆ mainly exist as physisorbed species on the Co/MWNTs catalyst surface, whilst C₂H₄ and CO exist as both physisorbed and chemisorbed species. The TPSR results indicated that CH₄ and C₂H₆ do not undergo reaction between room temperature and 450^oC. Pulsed C₂H₄ can be transformed into CH₄ at 400 ^oC whilst pulsed CO can be transformed into CO₂ at 100 or 150^oC. In gaseous mixtures of CO and H₂ containing excess CO, the products of pulsed reaction were CH₃CHO and CH₃OH. When the ratio of CO and H₂ was 1:2, pulsed CO and H₂ were transformed into CH₃CHO, CH₃OH and CH₄. In H₂ gas flow, pulsed CO was transformed into a mixture of CH₃CHO and CH₄ between 200 and 250^oC and was transformed into CH₄ only above 250^oC.     

Theoretical Study of Interaction Between S2 and SiHx (x=1, 2, 3) in Porous Silicon

The interaction between S₂ molecule and SiH_x (x=1, 2, 3) in porous silicon is investigated using the B3LYP method of density functional theory with the lanl2dz basis set. The model of porous silicon doped with CH₃,Si-O-Si and OH species is built. By analyzing the binding energy and electronic transfer, we conclude that the interaction of S₂ molecule with SiH_x (x=1, 2, 3) is much stronger than the interaction of S₂ molecule with CH₃ and OH, as S₂ molecule is located in different sites of the model. Using the transition state theory, we study the Si₂H₆+S2→H₃SiH₂SiS+HS reaction, and the reaction energy barrier is 50.2 kJ/mol, which indicates that the reaction is easy to occur.     

Silicon version of enamines: Amino-substituted disilenes by the reactions of the disilyne RSiSiR (R = SiPr[CH(SiMe3)2]2) with amines

The reaction of 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne 1 with secondary or primary amines produced amino-substituted disilenes R(R₂′N)SiSiHR 2a-d (R = SiⁱPr[CH(SiMe₃)₂]₂, R₂′NEt₂N (2a), (CH₂CH₂)₂N (2b), ^tBu(H)N (2c), and Ph₂N (2d)). Spectroscopic and X-ray crystallographic analyses of 2 showed that 2a-c have a nearly coplanar arrangement of the SiSi double bond and the amino group, giving π-conjugation between the SiSi double bond and the lone pair on the nitrogen atom, whereas 2d has a nearly perpendicular arrangement precluding such conjugation. Theoretical calculations indicate that π-conjugation between the π-orbital of the SiSi double bond and the lone pair on the nitrogen atom is markedly influenced by the torsional angle between the SiSi double-bond plane and the amino-group plane.     

Ab initio chemical kinetics for the unimolecular decomposition of Si2H5 radical and related reverse bimolecular reactions

For plasma enhanced and catalytic chemical vapor deposition (PECVD and Cat‐CVD) processes using small silanes as precursors, disilanyl radical (Si₂H₅) is a potential reactive intermediate involved in various chemical reactions. For modeling and optimization of homogeneous a‐Si:H film growth on large‐area substrates, we have investigated the kinetics and mechanisms for the thermal decomposition of Si₂H₅ producing smaller silicon hydrides including SiH, SiH₂, SiH_3, and Si₂H₄, and the related reverse reactions involving these species by using ab initio molecular‐orbital calculations. The results show that the lowest energy path is the production of SiH + SiH₄ that proceeds via a transition state with a barrier of 33.4 kcal/mol relative to Si₂H₅. Additionally, the dissociation energies for breaking the Si? Si and H? SiH₂ bonds were predicted to be 53.4 and 61.4 kcal/mol, respectively. To validate the predicted enthalpies of reaction, we have evaluated the enthalpies of formation for SiH, SiH₂, HSiSiH₂, and Si₂H₄(C_2h) at 0 K by using the isodesmic reactions, such as ²HSiSiH₂ + ¹C₂H₆→¹Si₂H₆ + ²HCCH₂ and ¹Si₂H₄(C_2h) + ¹C₂H₆ → ¹Si₂H₆ + ¹C₂H₄. The results of SiH (87.2 kcal/mol), SiH₂ (64.9 kcal/mol), HSiSiH₂ (98.0 kcal/mol), and Si₂H₄ (68.9 kcal/mol) agree reasonably well previous published data. Furthermore, the rate constants for the decomposition of Si₂H₅ and the related bimolecular reverse reactions have been predicted and tabulated for different T, P‐conditions with variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory by solving the master equation. The result indicates that the formation of SiH + SiH₄ product pair is most favored in the decomposition as well as in the bimolecular reactions of SiH₂ + SiH₃, HSiSiH₂ + H₂, and Si₂H₄(C_2h) + H under T, P‐conditions typically used in PECVD and Cat‐CVD. © 2013 Wiley Periodicals, Inc.     

Reaction mechanisms of Cp-containing silene complexes toward H2: A DFT study

The 18e Cp-containing silene tungsten complex, Cp₂W(η²-Me₂SiCH₂), can break H-H bond to afford the product, Cp₂WH(SiMe₃). The mechanisms on reaction of Cp₂W(η²-Me₂SiCH₂) with H₂ are investigated in this paper by using density functional theory (DFT). On the basis of the features of the reaction and experimental proposal for the reaction mechanisms, three possible pathways are proposed, which are related to the migration of silicon group, Cp ring slippage, and σ-bond metathesis, respectively. Our results of calculations indicate that the pathway involving migration of silicon group is the most favored, supporting the experimental observations. The other two paths are quite unfavorable kinetically.     

Bildung siliciumorganischer Verbindungen. 111. Die Hydrierung Si-chlorierter,C-spiroverbrückter 2,4-Disilacyclobutane mit LiAlH4 und iBu2AlH. Der Zugang zum Si8C3H20

Formation of Organosilicon Compounds. 111. The Hydrogenation of Si-chlorinated, C-spiro-linked 2,4-Disilacyclobutanes with LiAlH₄ or iBu₂AlH. The Access to Si₈C₃H₂₀ The hydrogenation of Si-chlorinated, C-spiro-linked 2,4-disilacyclobutanes containing C(SiCl₃)₂ terminal groups with LiAlH₄ in Et₂O proceeds under complete cleavage of the fourmembered rings and under elimination of one SiH₃ group. Such, Si₈C₃Cl₂₀ 4 forms (H₃Si)₂CH? SiH₂? CH(SiH₃)? SiH₂? CH(SiH₃)₂ 4 α, and even Si₈C₃H₂₀ 4a with LiAlH₄ forms 4 α. The hydrogenation of related compounds containing however CH(SiCl₃) terminal groups similarly proceeds under ring cleavage but no SiH₃ groups are eliminated. Such, (Cl₃Si)CH(SiCl₂)₂CH(SiCl₃) 41 forms (H₃Si)₂CH? SiH₂? CH₂(SiH₃) 41 α. However, in reactions with iBu₂AlH in pentane neither the disilacyclobutane rings are cleaved nor are SiH₃ groups eliminated. Only by this method Si₈C₃H₂₀ is accessible from 4 , Si₆C₂H₁₆ 3a from Si₆C₂Cl₁₆ 3 and Si₄C₂H₁₂ 41a from 41 . C(SiCl₃)₄ cleanly produces C(SiH₃)₄. Based on the knowledge about the different properties of LiAlH₄ and iBu₂AlH in hydrogenation reactions of disilacyclo-butanes it was possible to elucidate the composition and the structures of the hydrogenated derivatives of the product mixture from the reaction of MeCl₂Si? CCl₂? SiCl₃ with Si(Cu) [1] and to trace them back to the initially formed Si chlorinated disilacyclobutanes Si₆C₂Cl₁₅Me 34 , Si₆C₂Cl₁₄Me₂ 35 , Si₈C₃Cl₁₉Me 36 and Si₈C₃Cl₁₈Me₂ 37 . Compound 4a forms colourless crystals of space group P1 with a = 799.7(6), b = 1263.6(12), c = 1758.7(14) pm, α = 103.33(7)°, β = 95.28(6)°, γ = 105.57(7)° and Z = 4.     

Bildung siliciumorganischer Verbindungen. 102. Zur Umsetzung von Chlormethanen mit elementarem Silicium (Bildung und Aufklärung linearer Carbosilane)

Formation of Organosilicon Compounds. 102. Reaction of Chlormethanes with Elemental Silicon. (Formation and Investigation of Linear Carbosilanes) Reactions of CH₂Cl₂, HCCl₃ and CCl₄ with silicon (Cu catalyst) in a fluid bed at about 320°C were carried out to investigate especially the Si-rich compounds. In the reactions of CH₂Cl₂ and CHCl₃, but not of CCl₄, in addition to already published compounds Si-rich viscous products are formed. The SiCl-containing mixtures were reacted with LiAlH₄, and the SiH-containing derivatives were separated by means of HPLC. CH₂Cl₂/Si forms unbranched chains of carbosilanes as Si_nC_n–1H_4n (n = 4—12,2 terminal SiH₃ groups) and Si_nC_nH_4n+2 (n = 4—9, 1 terminal SiH₃ and 1 CH₃ group) as well as 1,3,5-trisilacyclohexanes with carbosilane chains of various length attached either to a Si atom or to a C atom. CHCl₃/Si yields in addition to unbranched chains with terminal silyl group chains with one or two C-branches and 1,3,5-trisilacyclohexanes with 1, 2, or 3 silyl substituents attached to C atoms. The structure of the isolated compounds was investigated by nmr and mass spectrometry.     

Electronic interactions in 1-ethynyl-2-phenyltetramethyldisilanes HCCSiMe2SiMe2C6H4X

1-Ethynyl-2-phenyltetramethyldisilanes HCCSiMe₂SiMe₂C₆H₄X [X = NMe₂ (1), H (2), CH₃ (3), Br (4), CF₃ (5)] are accessible from ClSiMe₂SiMe₂Cl, BrMgC₆H₄X and HCCMgBr in a two step Grignard reaction. The crystal structure of 1 as determined by single crystal X-ray crystallography exhibits a nearly planar PhNMe₂ moiety and an unusual gauche array of the phenyl and the acetylene group with respect to rotation around the Si-Si bond. Full geometry optimization (B3LYP/6-31+G^∗∗) of the gas phase structures of 1-5 affords minima for the gauche and the anti rotational isomers, both being very close in energy with a rotational barrier of only 3-5 kJ/mol. Experimental and calculated (time-dependent DFT B3LYP/TZVP) UV absorption data of 1-5 show pronounced electronic interactions of the HCC- and the C₆H₄X π-systems with the central Si-Si bond.     

Synthesis and characterization of new heterocyclic Schiff base palladacycles: Ring activation through N-oxide formation

Reaction of the Schiff base ligand derived from 4-pyridinecarboxaldehyde NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂], (1), with palladium(II) acetate in toluene at 60 °C for 24 h gave [Pd{NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂]}₂(OCOCH₃)₂], (2), with two ligands coordinated through the pyridine nitrogen. Treatment of the Schiff base ligand derived from 4-pyridinecarboxaldehyde N-oxide, 4-(O)NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂], (4), with palladium(II) acetate in toluene at 75 °C gave the dinuclear acetato-bridged complex [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(OCOCH₃)]₂, (5) with metallation of an aromatic phenyl carbon. Reaction of complex 5 with sodium chloride or lithium bromide gave the dinuclear halogen-bridged complexes [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)]₂, (6) and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Br)]₂, (7), after the metathesis reaction. Reaction of 6 and 7 with triphenylphosphine gave the mononuclear species [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)(PPh₃)], (8) and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}-(Br)(PPh₃)], (9), as air stable solids. Treatment of 6 and 7 with Ph₂P(CH₂)₂PPh₂ (dppe) in a complex/diphosphine 1:2 molar ratio gave the mononuclear complexes [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][Cl], (10), and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][PF₆], (11), with a chelating diphosphine. The molecular structure of complex 9 was determined by X-ray single crystal diffraction analysis.     

Heterobimetallic aluminium and zinc complex with N-arylanilido-imine ligand: Synthesis, structure and catalytic property for ring-opening polymerization of ε-caprolactone

Treatment of a N-arylanilido-imine ligand [ortho-C₆H₄(NHAr)CHN]₂CH₂CH₂ (Ar = 2,6-Me₂C₆H₃) (LH₂) with one equiv. of AlMe₃ affords a monometallic complex [C₆H₄(NHAr)–CHN)]CH₂CH₂(C₆H₄(NAr)CHNAlMe₂) (1). The monometallic complex 1 reacts with one equiv. of ZnEt₂ to give a heterobimetallic complex [C₆H₄(NAr)–CHNZnEt]CH₂CH₂[C₆H₄(NAr)–CHNAlMe₂] (2). Both complexes were characterized by ¹H and ¹³C NMR spectroscopy and elemental analyses, and the molecular structures of 1 and 2 were determined by X-ray diffraction analysis. The complexes 1 and 2 both are efficient catalysts for ring-opening polymerization of ε-caprolactone in the presence of benzyl alcohol yielding polymers with narrow polydispersity values and complex 2 initiates the polymerization in a controllable manner.     

Spektroskopische und physikalische Daten von Jodsilanen

Zusammenfassung Von den Jodderivaten der Silane SiH₄, Si₂H₆ und Si₃H₈ werden Dichte, Dampfdruck und Molrefraktion sowie die entsprechenden Atom- und Bindungsinkremente mitgeteilt. Die Ramanspektren von SiH₃J, Si₂H₅J und Si₃H₇J werden aufgenommen und zugeordnet.

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Spectroscopic and other physical investigations of silanyl iodides

Density, vapour pressure and molecular refraction as well as the corresponding atom increments and bond increments of the iodine derivatives of the silanes SiH₄, Si₂H₆ and Si₃H₈ are communicated. The Raman spectra of SiH₃J, Si₂H₅J and Si₃H₇J are recorded and assigned.

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XX. Mitt.:F. Fehér, B. Mostert, A. G. Wronka undG. Betzen, Mh. Chem.103, 959 (1972).

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A. G. Wronka, Dissertation Univ. Köln 1961.

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B. Mostert, Dissertation Univ. Köln 1961.     

Reactions of (η5-C5H5)2Tir compounds with organic cyanides

The syntheses and properties of the titanium(III) complexes Cp₂Tir · R′CN (R = C₆H₅, o-, m-, p-CH₃C₆H₄, CH₂C₆H₅, C₆F₅, Cl; R′ = CH₃, t-C₄H₉, C₆H₅, o-CH₃C₆H₄, 2,6-(CH₃)₂C₆H₃) are described. In the complexes the nitrogen atom of the cyanide ligands is coordinated to the metal. The thermal stabilities of the complexes depend markedly on R and R′; on heating they undergo a novel reaction in which two cyanide ligands are coupled by formation of a CC bond, while the metal is oxidized to titanium(IV).