Reaction of bistrifluoromethylaminosulphenyl chloride with fluoro-olefins and hexafluorobut-2-yne under free-radical conditions

Reaction of bistrifluoromethylaminosulphenyl chloride with unsymmetrical fluoro-olefins in daylight or under photochemical conditions gives both possible 1:1 adducts ($\text{ca}$. 1:1 ratio) arising from homolytic fission of the SCl bond. Addition to octafluorobut-2-ene and hexafluorobut-2-yne gives mixtures of the $\text{syn}$- and $\text{anti}$- adducts.     

ESCA investigation of the electronic structure of polyhexafluorobut-2-yne

Polyperfluorobut-2-yne is prepared by a fluoride ion-induced polymerization of hexafluorobut-2-yne. The mass spectrum indicates a regular fragmentation pattern but the ESCA spectrum establishes the structure as a polyene, rather than a crosslinked system, and the occurrence of a shake-up peak assists in this assignment.     

Preparation and thermal degradation of polyperfluorobut-2-yne

Polyperfluorobut-2-yne has been prepared by the fluoride ion-catalyzed polymerization of hexafluorobut-2-yne. The thermal stability of the polymer was monitored by TGA and DTA in air, argon, and vacuum environments. The major breakdown route appears to be depolymerization into fragments of lower molecular weight. Copolymerization of the acetylene with fluoroolefins was attempted; however, homopolymerization of the acetylene occurred at a far greater rate than the copolymerization reaction.     

Preparation of large ring acetylenic lactones by iodo lactonisation

Reaction of ω-ene-7-yne carboxylic acids with (biscollidine)iodine(I) hexafluorophosphate led to large ring acetylenic lactones. In the case of 5- or 6-yne carboxylic acids, iodo enol lactones were preferentially obtained.     

Increased activity of in situ catalysts for alkyne metathesis

[reaction: see text] Reaction of an enyne (1,1-diphenyl-pent-1-ene-3-yne) with a preheated mixture of Mo(CO)6/4-chlorophenol/3-hexyne at 130 degrees C furnished 1,1,6,6-tetraphenylhex-1,5-diene-3-yne in an 80% yield. If the starting material was heated with a mixture of Mo(CO)6 and 4-chlorophenol under identical conditions, no reaction was observed.     

Synthesis of substituted quinolines by iron-catalyzed coupling reactions between chloroenynes and Grignard reagents

This letter reports the preparation of quinolines, substituted at the 2- or 3-position by a 4-substituted but-3-en-1-yne group, by the environmentally friendly iron(III)-catalyzed coupling reaction of Grignard reagents with 1-chloro-4-(2-quinolyl)but-1-en-3-yne. The extension and the scope of this non-toxic and chemoselective procedure to various functionalized unsaturated vinyl chlorides are described.     

Synthesis, structure, and thermochemistry of adduct formation between N-heterocyclic carbenes and isocyanates or mesitylnitrile oxide

Reaction of N-heterocyclic carbenes (NHCs) with isocyanates yields stable zwitterionic imidates/amidates in toluene solution. These compounds were fully characterized and the crystal structures of several species were determined by X-ray crystallography. The thermochemistry of binding of these and related species was studied by solution calorimetry. Comparison is made of the enthalpies of binding of NHC to isocyanates (RNCO) and isomeric nitrile oxides (RCNO) as well as CO₂. DFT calculations were performed to additionally assess the nature of bonding in these compounds.     

Unusual reactivity of a disilyne with 4-dimethylaminopyridine: formation of an intramolecularly N-coordinated silylene and its isomerization to a zwitterionic silyl anion

Reaction of isolable 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasila-2-yne (1) with an equiv amount of 4-dimethylaminopyridine unexpectedly produced the intramolecularly N-coordinated silylene 2 as the primary product. However, 2 was not thermally stable at room temperature in solution and slowly isomerized to silyl anion 3 with a zwitterionic structure via 1,2-hydrogen migration followed by Si-N bond formation.     

Insertion of activated acetylenes into the metal-hydride bond of [(η5-C5H5)2M(CO)H] (M = Nb,Ta)

Reactions of [Cp₂M(CO)H] (M = Nb, Ta; Cp = η⁵-C₅H₅) with various acetylenes RCCR having electron-withdrawing groups were investigated. They give the σ-al- kenyl complexes [Cp₂M(CO)(CRCHR)] via insertion of the alkyne into the MH bond. On the basis of ¹H and ¹⁹F NMR data the reactions were shown to be: (i) regioselective, monosubstituted alkynes giving only the α-R metallated complex; (ii) stereoselective, exclusive formation of the Z-isomer being observed with hexafluorobut-2-yne. The Z isomer has been shown to exist as two conformers, the steric requirements of the ligands creating a barrier to rotation of the alkenyl group around the MC σ bond.     

Unusual regioselectivity of Pd(0)-catalyzed coupling reaction of electron-deficient alkenyl halides with allenic/propargylic zinc reagents. Highly selective synthesis of 6-phenylhex-5-yn-2(or 3)-enoates/enitrile and 4-phenyl-6-substituted-hexa-2,4,5-trienoates

The Pd(0)-catalyzed coupling reaction of electron-deficient alkenyl halides with the organozinc formed by the subsequent treatment of 1-phenylalk-1-yne with n-BuLi and ZnBr2 with or without a catalytic amount of HgCl2 was studied. Both the allene-formation- and the alkyne-formation-type coupling reactions were observed with high regio- and stereoselectivity: the reaction of 1-phenylprop-1-yne afforded 6-phenylhex-5-yn-2(or 3)-enoates and -enitriles, while the reaction of 1-phenylhex-1-yne formed 4-phenyl-6-substituted-hexa-2,4,5-trienoates. A plausible explanation for the regioselectivity was discussed. The double bonds in 6-phenylhex-5-yn- 2-enoates were prone to migrate to the position conjugated with the carbon-carbon triple bonds to form 6-phenylhex-5-yn-3-enoates at higher temperature. The migration did not occur in absence of an excess amount of allenic/propargylic zinc reagent or at low temperature.     

Enantioselective cyclization/hydrosilylation of 1,6-enynes catalyzed by a cationic rhodium bis(phosphine) complex

[reaction: see text] Reaction of 4,4-dicarbomethoxy-1-octene-6-yne (1) with triethylsilane and a catalytic 1:1 mixture of [Rh(COD)(2)](+) SbF(6)(-) and (R)-BIPHEMP (5 mol %) at 70 degrees C for 90 min gave (Z)-1,1-dicarbomethoxy-3-(1-triethylsilyl)ethylidene-4-methylcyclopentane (2) in 81% isolated yield with 98% de and 92% ee.     

Replacement of N-heterocyclic carbenes by N-heterocyclic silylenes at a Pd(0) center: Experiment and theory

Via NMR-spectroscopy the relative reactivity of N-heterocyclic silylenes (NHSi) and carbenes (NHC) was studied. Reaction of sterically crowded bis-N-heterocyclic Pd(0) carbene complexes with free N-heterocyclic silylenes led to complete displacement of the N-heterocyclic carbene, which is unexpected knowing that usually a silylene is a weaker bound ligand compared to a carbene. High-level DFT calculations on a small model system and the experimentally used complexes confirm the experimental findings and indicate that steric interactions play an important role in the substitution reaction.     

Ligand exchange between metals: synthesis and characterisation of binuclear and trinuclear iron-alkyne complexes. Crystal structures of [(η5-C5H5)2Fe3(CO)3(μ3-CO)(μ-CO)(CF3C2CF3] and [{μ-CF3CC(CF3)S} {Fe(CO)3}2]

Reaction of[(η⁵-C₅H₅)(CO)Fe{μ-C(CF₃)C(CF₃)SMe}₂Fe(CO)(η⁵-C₅H₅)] with Fe₃(CO)₁₂ leads to an exchange of ligands (hexafluorobut-2-yne, cyclopentadienyl or sulphur) between the metal centres and the formation of several new complexes.Two of These, [(η⁵-C₅H₅)₂Fe₃(CO)₃(μ₃-CO)(μ-CO)(CF₃C₂CF₃)] and [{μ-CF₃CC (CF₃)S Fe(CO)₃}₂], have been shown by X-ray diffraction to contain μ₃-η²-| CF₃C₂CF₃ units bridging Fe₃ and Fe₂S triangles, respectively.     

Syntheses and pyrolyses of furan analogues of α-oxo-o-quinodimethanes. Formation of methylenecyclobutenone and 1-buten-3-yne via a vinylcarbene-cyclopropene rearrangement

Flash vacuum pyrolyses (FVP) of benzoic 2-methyl-3-furoic anhydride (12) and benzoic 3-methyl-2-furoic anhydride (13) at 550 °C and ca. 10(-2) Torr both give methylenecyclobutenone (16) and 1-buten-3-yne (17) as the main products. A mechanism involving generation of furan analogues of α-oxo-o-quinodimethane, 10 and 11, from FVP of 12 and 13, respectively, followed by elimination of a CO molecule to give the respective carbenes 34 and 36 is proposed. Carbenes 34 and 36 are interconvertible via a cyclopropene intermediate 35. A ring contraction from 36 will give 16, whereas a ring-opening of 34 followed by elimination of a CO molecule then leads to 17. The proposed mechanism is supported by substituent- and deuterium-labeling study on FVP of the derivatives of 12.     

Chloromethylthio-Substituted Chromium(III), Cobalt(III), and Aluminum(III) Acetylacetonates

SCl-Substituted chromium(III), cobalt(III), and aluminum(III) acetylacetonates react with carbenes similarly to organylsulfenyl chlorides, with insertion of the carbenes into the S-Cl bond. Reaction with diazomethane gave chloromethylthio-substituted complexes whose structure was proved by IR, ¹H NMR, and mass spectroscopy. The thermal oxidative degradation of the complexes was studied. Chlorination of SCH₃-substituted acetylacetonates does not yield such complexes.     

A highly stable N-heterocyclic carbene complex of trichloro-oxo-vanadium(V) displaying novel Cl-Ccarbene bonding interactions

Reaction of 1,3-dimesitylimidazol-2-ylidene and trichloro-oxo-vanadium(V) yields an air stable 1:1 adduct, which demonstrates the utility of N-heterocyclic carbenes to stabilize metal complexes in high oxidation states. The molecular structure of this compound reveals that the chloride ligands cis to the carbene are oriented toward the Ccarbene atom. Density functional theory calculations show that a bonding interaction occurs between lone pairs of these chlorides and the formally unoccupied p-orbital of the carbene. Previous studies indicated that this orbital was not involved in the bonding of N-heterocyclic carbenes to transition metals. The observed interaction therefore represents a new bonding mode for these widely used ligands.     

The crystal and molecular structure of μ-μ-dichlorobis(hexafluorobut-2-enyl)-bis(cycloocta-1,5-dienyl)diiridium(III).

The title compound is isolated from reaction of hexafluorobut-2-yne with μ-μ-Dichlorobis(cycloocta-1,5-diene)diiridium(I) at 90°C. Crystals of the complex, solvated with deuterobenzene, are monoclinic, space group $\text{P}$2₁/$\text{n}$ with $\text{a}$ = 10.97 $\text{+}$ 0.02, $\text{b}$ = 17.96 $\text{+}$ 0.03, $\text{c}$ = 11.63 $\text{+}$ 0.02 », β = 127.4 $\text{+}$ 0.60°. The acetylene has abstracted a hydrogen atom forming a σ-bonded $\text{cis}$-vinylic group and the original cyclooctadiene, having lost a proton, is coordinated as the cycloocta-1,5-dienyl ligand. Mean bond lengths are IrCl 2.467, IrC (allylic) 2.17, IC (olefinic) 2.36 and IrC (vinylic) 2.09 ».     

Synthesis and crystal structure of an iron triazole complex resulting from the unexpected ligand cleavage of a triazolium carbene precursor

Typically reactions of N-heterocyclic carbenes with transition metals are straightforward and require a carbene salt, a base strong enough to deprotonate such a salt and a metal. Yet when carbene precursors are in the form of triazolium salts, reaction may not proceed as easily as expected. In our work, we intended to obtain a triazolylidene complex of iron(II) chloride, but due to the presence of small amounts of water in the tetrahydrofuran solvent used, bis(acetonitrile)tetrakis(1-benzyl-1H-1,2,4-triazole-κN⁴)iron(II) μ-oxido-bis[trichloridoferrate(III)] acetonitrile disolvate, [Fe(C₉H₉N₃)₄(CH₃CN)₂][Fe₂Cl₆O]·2CH₃CN – an interesting anion with a linear geometry of the O atom – was formed instead of the iron carbene complex. Reaction proceeded via cleavage of the alkyl N-substituent of the triazolium salt. The formation of the product was confirmed by X-ray crystallography. The crystal structure and possible reaction pathways are discussed.     

Synthesis and molecular structure of new acyclic analogues of nucleotides with a 1,2-alkadienic skeleton

Reaction of 1-chloro-4-(diethoxyphosphonyl)alka-2,3-dienes 14,15 with purine and pyrimidine heterocyclic bases in the presence of cesium carbonate afforded new acyclic analogues of nucleotides containing a 1,2-alkadienic skeleton 18-23. Dealkylation of 18-23 furnished phosphonic acids 2a-f. In contrast, alkylation reaction with 1-chloro-4-(diethoxyphosphonyl)octa-2,3-diene 16 led to Z- and E-1,3-alkadienic phosphonates 25a,b and 26a,b. A similar reaction with 1-chloro-4-(diethoxyphosphonyl)-2-methylbuta-2,3-diene 17 led to the elimination of hydrochloride and formation of 4-(diethylphosphonyl)-2-methylbut-1-en-3-yne 24. Molecular structures of new acyclic nucleotides 18 and 2f are determined by X-ray crystallographic analysis.     

Bimolecular rate constant and product branching ratio measurements for the reaction of C2H with ethene and propene at 79 K

The reactions of the ethynyl radical (C(2)H) with ethene (C(2)H(4)) and propene (C(3)H(6)) are studied under low temperature conditions (79 K) in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by 193 nm photolysis of acetylene (C(2)H(2)) and the reactions are studied in nitrogen as a carrier gas. Reaction products are sampled and subsequently photoionized by the tunable vacuum ultraviolet radiation of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The product ions are detected mass selectively and time-resolved by a quadrupole mass spectrometer. Bimolecular rate coefficients are determined under pseudo-first-order conditions, yielding values in good agreement with previous measurements. Photoionization spectra are measured by scanning the ALS photon energy while detecting the ionized reaction products. Analysis of the photoionization spectra yields-for the first time-low temperature isomer resolved product branching ratios. The reaction between C(2)H and ethene is found to proceed by H-loss and yields 100% vinylacetylene. The reaction between C(2)H and propene results in (85 ± 10)% C(4)H(4) (m/z = 52) via CH(3)-loss and (15 ± 10)% C(5)H(6) (m/z = 66) by H-loss. The C(4)H(4) channel is found to consist of 100% vinylacetylene. For the C(5)H(6) channel, analysis of the photoionization spectrum reveals that (62 ± 16)% is in the form of 4-penten-1-yne, (27 ± 8)% is in the form of cis- and trans-3-penten-1-yne and (11 ± 10)% is in the form of 2-methyl-1-buten-3-yne.