Bildung siliciumorganischer Verbindungen. XXXXVI. Si-fluorierte Carbosilane

Formation of organosilicon compounds. XXXXVI. Si-fluorinated carbosilanes Compounds (1)–(7) (see “Inhaltsübersicht”) are obtained by reaction of carbosilanes containing Si? Cl groups with ZnF₂. The linear compounds (8) and (9) are prepared from ZnF₂ and (Cl₃Si)₂CCl₂, and (Cl₃Si? CCl₂)SiCl₂, respectively, whereas the cyclic compounds are formed by photochemical chlorination. Photochemical chlorination of (3) goes via compounds (13) and (14) (isolation is possible); both of them can be prepared too by reaction of Si? Cl derivatives with ZnF₂. Compounds (16) and (17) are obtained from the corresponding Si? Cl derivatives.     

Cationic iridium complex is a new and efficient Lewis acid catalyst for aldol and Mannich reactions

A cationic iridium complex [Ir(cod)₂]SbF₆ was found to be a new and efficient Lewis acid catalyst for Mukaiyama aldol and Mannich reactions. Aldehydes react smoothly with silyl enol ethers to give β-siloxy ketones in the presence of 0.5 mol % of [Ir(cod)₂]SbF₆. The reaction of N-alkyl arylaldimines with ketene silyl acetals in the presence of 5 mol % [Ir(cod)₂]SbF₆/P(OPh)₃ gave β-amino esters. After Mannich reaction was complete, stirring of the reaction mixture for 24 h led to cyclization to give β-lactam. The reaction of N-aryl benzaldimine with silyl enol ether derived from acetophenone gave a tetrahydroquinoline derivative as a single diastereomer.     

The electron-impact-induced fragmentation of some alkyl isocyanides and α-branched alkyl cyanides

The HRP mass spectra of some alkyl isocyanides (R? NC in which R equals CH₃, C₂H₅, n-C₃H₇, n-C₄H₉ and t-C₄H₉) and two methyl branched alkyl cyanides (R? CN in which R equals i-C₃H₇ and t-C₄H₉) have been studied. Using metastable ion transitions and appearance potentials, the fragmentation patterns and spectral characteristics of the isocyanides can be given. A comparison has been made with the mass spectral data of the corresponding cyanides. Although the mass spectra of alkyl cyanides and isocyanides show close relationship, evidence could be obtained that this resemblance is not caused by rearrangement of the isocyanide into cyanide molecules. The main difference between the spectra of both compounds is caused by the strength of the α-bond, being weaker in the case of the isocyanides. The abundance of ions formed by α-bond cleavage decreases with increasing size of the alkyl group.     

Composes d'addition entre les pentafluorures d'uranium et d'antimoine,preparation des composes UF5. n SbF5 (n = 1 ou2)

The adduct UF₅.2SbF₅ has been obtained from the reaction of UF₅ with SbF₅ and the reaction of UF₆ with SbF₅ in the presence of freon 114. From this preparation and also from studies on UF₆, SbF₅ solutions, the fluorinating properties of UF₆ were found to be enhanced by the presence of SBF₅. An x-ray diffraction study has shown that crystals of UF₅.2SbF₅ are monoclinic, space group P2₁/c, with unit cell dimensions a = 8.036(3) Å ; b = 14.112(13) Å ; c = 10.028(17) Å ; β = 96.91(7)°.The adduct UF₅.SbF₅ is obtained by thermal decomposition of UF₅.2SbF₅.     

Reactions of perfluorinated 1-ethyltetrahydronaphthalene, 1-ethylindan, and 1,1-diethylindan with pentafluorobenzene in antimony pentafluoride

The reaction of perfluoro(1-ethyltetrahydronaphthalene) with pentafluorobenzene in SbF₅, followed by treatment of the reaction mixture with water, afforded a mixture of 1-hydroxyperfluoro(1-phenyl-4-ethyletetrahydronaphthalene) and perfluoro(5-phenyl-8-ethyl-2,6,7,8-tetrahydronaphthalen-2-one). From perfluoro(1,1-diethylindan), 1-hydroxyperfluoro(1,1-diethyl-3-phenylindan) was obtained. Perfluoro(1-ethylindan) reacted with an equimolar amount of pentafluorobenzene in SbF₅ to give (after hydrolysis) 1-hydroxyperfluoro-(3-ethyl-1-phenylindan), 1-hydroxyperfluoro(3-ethyl-1,3-diphenylindan), and perfluoro(1-ethyl-1-phenylindan), while in the reaction with excess pentafluorobenzene, followed by treatment with anhydrous hydrogen fluoride, perfluoro(1-ethyl-3-phenylindan) and perfluoro(1-ethyl-1,3-diphenylindan) were formed.     

Coupling Reaction of Enol Derivatives with Silyl Ketene Acetals Catalyzed by Gallium Trihalides

A cross‐coupling reaction between enol derivatives and silyl ketene acetals catalyzed by GaBr₃ took place to give the corresponding α‐alkenyl esters. GaBr₃ showed the most effective catalytic ability, whereas other metal salts such as BF₃?OEt₂, AlCl₃, PdCl₂, and lanthanide triflates were not effective. Various types of enol ethers and vinyl carboxylates as enol derivatives are amenable to this coupling. The scope of the reaction with silyl ketene acetals was also broad. We successfully observed an alkylgallium intermediate by using NMR spectroscopy, suggesting a mechanism involving anti‐carbogallation among GaBr₃, an enol derivative, and a silyl ketene acetal, followed by syn‐β‐alkoxy elimination from the alkylgallium. Based on kinetic studies, the turnover‐limiting step of the reaction using a vinyl ether and a vinyl carboxylate involved syn‐β‐alkoxy elimination and anti‐carbogallation, respectively. Therefore, the leaving group had a significant effect on the progress of the reaction. Theoretical calculations analysis suggest that the moderate Lewis acidity of gallium would contribute to a flexible conformational change of the alkylgallium intermediate and to the cleavage of the carbon?oxygen bond in the β‐alkoxy elimination process, which is the turnover‐limiting step in the reaction between a vinyl ether and a silyl ketene acetal.     

Indium-catalyzed coupling reaction between silyl enolates and alkyl chlorides or alkyl ethers

The coupling reactions of alkyl chlorides with silyl enolates catalyzed by InBr₃, and the coupling reactions of alkyl ethers with silyl enolates catalyzed by the combined Lewis acid of InBr₃/Me₃SiBr are described. In both reaction systems, various types of silyl enolates were used to give corresponding α-alkylated esters, ketones, carboxylic acids, amides, thioesters, and aldehydes.     

Stereochemistry of reactions in the 1,2-dimethylsilacyclopentane ring system. II. Stereoselective transformation

A number of stereoselective reactions of 1-substituted-1,2-dimethylsilacyclopentanes are described. Reactions of the silyl chloride (II) with ZnF₂ and with alcohols catalyzed by amines are stereoselective as a result of rapid isomerization of II. Alcoholysis of silicon hydride (I) catalyzed by transition metals is apparently an inversion reaction regardless of the nature of the catalyst, but can appear to be stereoselective because of isomerization of alkoxysilane product. Reduction of silyl fluoride (IV) by lithium aluminum hydride is nonstereoselective, a result which is proposed to arise through rapid isomerization of intermediates with expanded coordination.     

Alkynylcyanation of alkynes and dienes catalyzed by nickel

Alkynyl cyanides are found to add across alkynes and 1,2-dienes in the presence of a catalyst prepared in situ from Ni(cod)₂, xantphos, and BPh₃. A range of functionalized conjugated cis-enynes are obtained with high regioselectivity. The addition reaction across norbornadiene proceeds in the absence of BPh₃ to give exo-cis adduct exclusively. A stoichiometric reaction of an alkynyl cyanide, Ni(cod)₂, xantphos, and BPh₃ gives trans-(xantphos)Ni(CNBPh₃)(CCSiMe₂t-Bu), which is suggested to be a plausible reaction intermediate of the alkynylcyanation reaction.     

Synthesis and properties of sulfur cyanide trifluoride,SF3CN,sulfur dicyanide difluoride,SF2(CN)2, and sulfinyl cyanide fluoride,FS(O)CN

Sulfur cyanide trifluoride, SF₃CN, and sulfur dicyanide difluoride, SF₂(CN)₂, have been prepared by metathesis between sulfur tetrafluoride, SF₄, and trimethyl silyl cyanide, (CH₃)₃SiCN, at – 30°C. Treatment of SF₃CN with freshly sublimed selenium dioxide, SeO₂, lead to sulfinyl cyanide fluoride, FS(O)CN. IR, Raman, ¹⁹F-NMR, uv and mass spectra of the novel compounds are presented as well as some physical and chemical properties.     

Preparation and Characterization of Antimony and Arsenic Tricyanide and Their 2,2′‐Bipyridine Adducts

The arsenic(III) and antimony(III) cyanides M(CN)₃ (M=As, Sb) have been prepared in quantitative yields from the corresponding trifluorides through fluoride–cyanide exchange with Me₃SiCN in acetonitrile. When the reaction was carried out in the presence of one equivalent of 2,2′‐bipyridine, the adducts [M(CN)₃ ? (2,2′‐bipy)] were obtained. The crystal structures of As(CN)₃, [As(CN)₃ ? (2,2′‐bipy)] and [Sb(CN)₃ ? (2,2′‐bipy)] were determined and are surprisingly different. As(CN)₃ possesses a polymeric three‐dimensional structure, [As(CN)₃ ? (2,2′‐bipy)] exhibits a two‐dimensional sheet structure, and [Sb(CN)₃ ? (2,2′‐bipy)] has a chain structure, and none of the structures resembles those found for the corresponding arsenic and antimony triazides.     

Reaction of perfluorobenzocycloalkenes with SiO<Subscript>2</Subscript>-SbF<Subscript>5</Subscript> and skeleton transformations of their carbonyl derivatives in SbF<Subscript>5</Subscript> medium

The reaction of perfluorinated benzocyclobutene and tetraline with SiO₂-SbF₅ led to the formation in a high yield of their mono- and further dicarbonyl derivatives. The monocarbonyl derivatives on heating with SbF₅ underwent disproportionation into the corresponding perfluorobenzocycloalkenes and diketones. Both mono- and diketones in the SbF₅ medium are liable to suffer skeleton rearrangements yielding five- and six-membered oxygen-containing heterocycles and/or products of the opening of the alicyclic fragment of the substrate, and from the perfluorobenzocyclobutenone compounds were also obtained with a number of carbon atoms greater than that of the initial ketone.     

Studies of the Reaction Behavior of Nitryl Compounds Towards Azides: Evidence for Tetranitrogen Dioxide,N4O2

The reaction behavior of NaN₃, AgN₃, and Me₃SiN₃ towards FNO₂, CINO₂, NO₂SbF₆, and NO₂BF₄ was investigated. At -30°C or below in a solvent-free system sodium azide did not react with CINO₂, NO₂BF₄, or NO₂SbF₆. Below -30°C silver azide did not react either with neat C1NO₂. Treatment of Me₃SiN₃ with pure C1NO₂ led to the formation of C1N₃, N₂O, and Me₃SiOSiMe₃. A mechanism for this reaction has been proposed. Pure chlorine azide was isolated by fractional condensation and identified by its low-temperature Raman spectrum (liquid state). The reaction of Cp₂Ti(N₃)₂ with C1NO₂ also yielded C1N₃ as the only azide-containing reaction product. Treatment of FNO₂ with NaN₃ at temperatures as low as -78°C always ended in an explosion which was probably due to the formation of FN₃ as one of the reaction products. The reaction of NO₂SbF₆ with NaN₃ in liquid CO₂ (-55°C· T· -35°C) as the solvent afforded a new azide species which was stable at low temperature in solution only and was investigated by means of low-temperature Raman spectroscopy. The obtained vibrational data give strong evidence for the presence of tetranitrogen dioxide, N₄O₂, which can be regarded as nitryl azide (NO₂N₃). The structure and vibrational frequencies of N₄O₂ were computed ab initio at correlated level (MP2/6-31 + G^*). In liquid xenon (-100°C· T· -60°C) NaN₃ did not react with NO₂SbF₆. A previous literature report on the preparation of N₄O₂ could not be established.     

Cyanation of Aryl Bromides with K4[Fe(CN)6] Catalyzed by Dichloro[bis{1‐(dicyclohexylphosphanyl)piperidine}]palladium,a Molecular Source of Nanoparticles,and the Reactions Involved in the Catalyst‐Deactivation Processes

Dichloro[bis{1‐(dicyclohexylphosphanyl)piperidine}]palladium [(P{(NC₅H₁₀)(C₆H₁₁)₂})₂PdCl₂] ( 1 ) is a highly active and generally applicable C? C cross‐coupling catalyst. Apart from its high catalytic activity in Suzuki, Heck, and Negishi reactions, compound 1 also efficiently converted various electronically activated, nonactivated, and deactivated aryl bromides, which may contain fluoride atoms, trifluoromethane groups, nitriles, acetals, ketones, aldehydes, ethers, esters, amides, as well as heterocyclic aryl bromides, such as pyridines and their derivatives, or thiophenes into their respective aromatic nitriles with K₄[Fe(CN)₆] as a cyanating agent within 24 h in NMP at 140 °C in the presence of only 0.05 mol % catalyst. Catalyst‐deactivation processes showed that excess cyanide efficiently affected the molecular mechanisms as well as inhibited the catalysis when nanoparticles were involved, owing to the formation of inactive cyanide complexes, such as [Pd(CN)₄]^2?, [(CN)₃Pd(H)]^2?, and [(CN)₃Pd(Ar)]^2?. Thus, the choice of cyanating agent is crucial for the success of the reaction because there is a sharp balance between the rate of cyanide production, efficient product formation, and catalyst poisoning. For example, whereas no product formation was obtained when cyanation reactions were examined with Zn(CN)₂ as the cyanating agent, aromatic nitriles were smoothly formed when hexacyanoferrate(II) was used instead. The reason for this striking difference in reactivity was due to the higher stability of hexacyanoferrate(II), which led to a lower rate of cyanide production, and hence, prevented catalyst‐deactivation processes. This pathway was confirmed by the colorimetric detection of cyanides: whereas the conversion of β‐solvato‐α‐cyanocobyrinic acid heptamethyl ester into dicyanocobyrinic acid heptamethyl ester indicated that the cyanide production of Zn(CN)₂ proceeded at 25 °C in NMP, reaction temperatures of >100 °C were required for cyanide production with K₄[Fe(CN)₆]. Mechanistic investigations demonstrate that palladium nanoparticles were the catalytically active form of compound 1 .     

Silicium-verbindungen mit starken intramolekularen sterischen wechselwirkungen : VI. Darstellung und eigenschaften des tri-t-butylsilans und der tri-t-butylhalogensilane

Tri-t-butylsilane has been prepared by treatment of t-butyllithium with HSiCl₃ or HSiF₃. Reactions of this compound with the halogens Cl₂, Br₂, I₂, and the pentafluorides PF₅ or SbF₅ gave the expected tri-t-butylhalosilanes. With SO₃ bis(tri-t-butylsilyl) sulfate is obtained via tri-t-butylsilanole. Reaction with dihalocarbenes obtained from phenyl(trihalomethyl)mercury compounds or the system haloform/base leads to the corresponding tri-t-butyl(dihalomethyl)silanes. The reactions with nucleophiles proceed much less readily. Until now only the reaction of tri-t-butylhalosilanes with LiAlD₄ and with KOH giving tri-t-butylsilane-d₁ and tri-t-butylsilanole could be carried out.The attempted preparation of long-living tri-butylsilyl-radicals as well as the direct observation of tri-t-butylsilicenium ions was unsuccessful. In the first case intermolecular hydrogen abstraction by the radical leads to the hydrosilane, and in the second case the experimental results are better explained by Lewis-acid—base interactions than by silicenium ion formation.     

Synthesis and Study of Cationic,Two‐Coordinate Triphenylphosphine– Gold–π Complexes

Cationic, two‐coordinate triphenylphosphine–gold(I)–π complexes of the form [(PPh₃)Au(π ligand)]⁺ SbF₆^? (π ligand=4‐methylstyrene, 1? SbF₆), 2‐methyl‐2‐butene ( 3? SbF₆), 3‐hexyne ( 6? SbF₆), 1,3‐cyclohexadiene ( 7? SbF₆), 3‐methyl‐1,2‐butadiene ( 8? SbF₆), and 1,7‐diphenyl‐3,4‐heptadiene ( 10? SbF₆) were generated in situ from reaction of [(PPh₃)AuCl], AgSbF₆, and π ligand at ?78 °C and were characterized by low‐temperature, multinuclear NMR spectroscopy without isolation. The π ligands of these complexes were both weakly bound and kinetically labile and underwent facile intermolecular exchange with free ligand (ΔG^≠≈9 kcal mol^?1 in the case of 6? SbF₆) and competitive displacement by weak σ donors, such as trifluoromethane sulfonate. Triphenylphosphine–gold(I)–π complexes were thermally unstable and decomposed above ?20 °C to form the bis(triphenylphosphine) gold cation [(PPh₃)₂Au]⁺SbF₆^? ( 2? SbF₆).     

The preparation and characterisation of some new binary fluorides of antimony

Antimony pentafluoride acts as a useful oxidising agent towards many non-metals, giving interesting cations, and in the process is itself reduced. It would be helpful to know what the reduced products are, and under what conditions they are formed. Therefore, SbF₅ and the known SbF₅·SbF₃⁽¹⁾ in AsF₃ solution were reduced by iodine and/or PF₃ giving crystals of the new adduct, (SbF₃)₆(SbF₅)₅ [Monoclinic, a = 11.638(1), b = 8.995(1), c = 16.723(3) ā, β = 106.81(1)°, P2₁/c]; (SbF₃)₅(SbF₅)₃ [Orthorhombic, a = 19.187(9), b = 15.890(2), c = 15.713(3) ā, Pnma] and (SbF₃)₃SbF₅ [Monoclinic, a = 10.895(3), b = 10.941(3), c = 4.772(1) ā, β = 96.66(3)°, P2₁/m]. (SbF₃)₃SbF₅ seemed to be the most reduced adduct, no evidence was obtained for (SbF₃)_n(SbF₅) n > 3, under these conditions. The (SbF₃)₆(SbF₅)₅ adduct has a Raman spectrum identical to that reported by Gillespie⁽²⁾ and coworkers for an adduct of approximate composition SbF₃·SbF₅ and has a very different structure to that of (SbF₃)₆(SbF₆)₅ reported by Edwards.⁽³⁾ The crystal structures of the new adducts will be discussed and the cations they contain compared with those found in SbF₃·SbF₅⁽¹⁾ and (SbF₅)₆(SbF₅)₅⁽³⁾ (Edward's form).     

Chalice-Type Tridentate Silicon Lewis Acids of C3 Symmetry in a Single Step Starting from Hexadehydrotribenzo[12]annulene

Tridentate Lewis acids with aligned functions were synthesized based on the rigid framework hexadehydrotribenzo[12]annulene. The backbone and its fluorinated analogue were synthesised in one-pot syntheses, with alkyne deprotection and Sonogashira cross coupling reaction being carried out in one step. Hydrosilylation of the annulene with chlorohydrosilanes proceeded highly selectively and afforded rigid poly-Lewis acids with three SiCl₃ or SiCl₂Me substituents perfectly oriented to one side of the molecule in a single step. The progress of hydrosilylation was investigated by time-correlated NMR spectroscopic studies. The crystal structures show that the framework is symmetrically functionalised and the silyl substituents are aligned in one direction. To increase the acidity of the Lewis acids the chlorosilyl substituents were fluorinated with SbF₃. Further investigation of hydrometallation reactions (M=B, Al, Ga, Sn) did not lead to corresponding structures.     

The bromine catalysed oxidation of arsenic trifluoride by antimony pentafluoride

Antimony pentafluoride dissolves in excess arsenic trifluoride presumably with the formation of AsF₃·SbF₅ [1,2] and possibly (AsF₃)_nSbF₅ n = 2, [3], 3, [4], in equilibrium with one another and the solvent. However, O. Ruff [5] found in 1906 that in the presence of bromine, antimony pentafluoride oxidises arsenic trifluoride to arsenic pentafluoride with formation of a solid he suggested was SbBrF₄. In the course of our work we investigated this reaction and found that trace quantities of bromine (<0.1 mole per cent) catalyse the formation of arsenic pentafluoride and SbF₃·SbF₅ [6], according to equation (1).AsF₃ + 2SbF₅ = AsF₅ + SbF₃·SbF₅ (1)Reaction (2) is endothermic to the extent of ca. 33 Kcals mole^?1 [7–9], but reaction (1) occurs spontaneously in presence of bromine, being more favourable than reaction (2) by the heat of reaction (3).AsF₃ + SbF₅ = AsF₅ + SbF₃ (2)SbF₃ + SbF₅ = SbF₃·SbF₅ (3)