Heterocyclen aus Bis(alkoxycarbonyl)keten-ethylen-acetalen ( = Dialkyl-2-(1,3-dioxolan-2-yliden)propan-1,3-dioate). Synthese und Eigenschaften einer neuen Klasse von Pyrazolium-Betainen

Heterocycles Starting from Bis(alkoxycarbonyl)ketene Ethylene Acetals ( = Dialkyl 2-(1,3-Dioxolan-2-ylidene)propane-1,3-dioate). Synthesis and Properties of a New Class of Pyrazolium Betaines The readily available bis(alkoxycarbonyl)ketene ethylene acetals 1 react with bifunctional nucleophiles to give heterocycles 2–5 (Scheme 1). Their reactions with N,N-dialkylhydrazines lead to the pyrazolium betaines 7a–f (Scheme 4). Cyclic N,N-dialkylhydrazines give spiro compounds 7d–f . The reaction of thioketene acetal 12 and of the derivative 15 of methanetricarboxylic acid with N,N-dimethylhydrazine results in the formation of 3-(methylthio)- and 3-methoxypyrazolium betaine 7g and 7h , respectively (Scheme 4). The chemical reactivity of the synthesized pyrazolium betaines 7 was tested. The structure of the 3-(methylthio) derivative 7g was determined by X-ray analysis.     

Übergangsmetall-thioketen-komplexe: VII. Erzeugung eines vinyliden-liganden aus einem thioketen durch schwefelabspaltung

The thioketene iron cluster (CH₃)₄C₆H₆CS(PPh₃)₂(CO)₄Fe₂S (I) reacts with thioketene in excess quantitatively to a vinylidene complex, as confirmed by X-ray analysis.     

Übergangsmetall-heteroallen-komplexe: XIII. Reaktionen der cobalt-thioketen-komplexe [Co(R2CCS)(C5H5)] mit elektrophilen

Reaction of the η²(C,S)-coordinated thioketene cobalt complex [Co(C₁₁H₁₈S)-(PMe₃(C₅H₅)] (2a) with the electrophils [Mn(CO)₂(THF)(C₅H₅] and [Cr(CO)₅(THF)] gives the dinuclear thioketene complexes (4) with two different metal atoms in the molecule. The structure of the cobalt manganese compound was determined by X-ray diffraction. Protonation of the mononuclear thioketene complexes 2 give novel cationic η²-bonded thioacyl compounds [Co(η²-RCS)-(PMe₃(C₅H₅)]⁺ (9), as confirmed by X-ray analysis.     

Übergangsmetall-heteroallen-komplexe: XXVI. Synthese und Struktur von zweikernigen molybdän-thioketen-komplexen

The thioketene C₁₁H₁₈S (3) reacts with [Mo₂(CO)₄(C₅H₅)₂] to give the complex [Mo₂(CO)₄(C₅H₅)₂(C₁₁H₁₈S)] (1b). A mixed thioketene-ketenimine-Mo-complex (2c) was synthesized by reaction of the ketenimine complex 1a with the thioketene C₁₁H₁₈S (3). The structures of 1b and 2c were determined by X-ray diffraction studies.     

Reaction paths of the [2+2] cycloaddition of X=C=Y molecules (X, Y=S or O or CH2). Ab initio study

The reaction paths of [2+2] cycloaddition of the X=C=Y cumulenes were modeled at the MP2/aug-cc-pVDZ level. Cycloadditions of allene and CO2, CS2, or OCS lead in part to the same four-membered products as dimerizations of either ketene or thioketene or addition of ketene and thioketene, respectively. All the reactions studied are concerted and mostly asynchronous. The majority of the allene cycloadditions studied are endoergic and proceed with much higher activation barriers than do the alternative (thio)ketene additions. In comparison with the energy of the substrates, the four-membered cycles incorporating S-atoms are stabilized more than the analogous structures with O-atoms built into the rings. There are also some products that are thermodynamically disfavored, yet seem to be obtainable thanks to a relatively low barrier of the reaction. The AIM analysis of the electron density distribution in the transition state structures allowed distinguishing pericyclic from pseudopericyclic and nonplanar-pseudopericyclic types of reaction.     

Übergangsmetall-heteroallen-komplexe XVII .Reaktionen des aza-allyl-komplexes (ketenimin)Fe2(CO)6 mit phosphanen

The aza-allyl complex (ketene imine)Fe₂(CO)₆ (3a) reacts with phosphanes PR₃ to give substitution products of the type (ketene imine)Fe₂(CO)₅PR₃ (4a,b). In addition, the phosphane PMe₃ yields a ferrole complex (5). Phosphites react with complex 3a to form mono- and di-substitution products (ketene imine)- Fe₂(CO)₅P(OR)₃ (4c,d) and (ketene imine)Fe₂(CO)₄(P(OR)₃)₂ (6). Diphosphanes yield substituted complexes of type (ketene imine)Fe₂(CO)₄(μ-Ph₂P ^⌢ PPh₂) (7). The structures of (ketene imine)Fe₂(CO)₅PMe₃ (4a), the ferrole complex 5, and (ketene imine)Fe₂(CO)₄(ν-Ph₂PCH₂CH₂PPh₂) (7b) were determined by X-ray analysis.     

THEORETICAL INVESTIGATION OF KETENE BONDING MODES IN BIS(PHOSPHINE) PALLADIUM KETENE COMPLEXES

Abstract

Theoretical studies were carried out on a series of bis(phosphine) palladium ketene complexes (PR₃)₂Pd(CH₂=C=O), and on the related CH₂=C=O and Pd(PR₃)₂ molecular fragments in order to investigate the electronic structure and the bonding of the ketene ligand to the metal fragment in these complexes. An analysis of the frontier MOs has been performed in order to understand the interactions between the ketene and the metal fragments. The calculated results have shown that the η²-(C,C) mode is preferred over the η²-(C,O) mode by 10–15 kcal/mol in bis(phosphine) palladium ketene complexes. The basicity and bulkiness of the phosphine ligands PR₃ have little effect on the bonding mode in (PR₃)₂Pd(CH₂=C=O) complexes. The most stable structure was calculated to be the η²-(C,C) square planar geometry with the CH₂ group of ketene out of the molecular plane. Comparison and discussion between the two bonding modes were also presented in this paper.     

Oxidative Polymerization of Silylthioketene Dimer

Summary: The first π‐conjugated poly(thioketene dimer) was synthesized via the homopolymerization of a silylthioketene dimer by a chemical oxidation‐reduction process. The polymerization of trimethylsilylthioketene dimer in the presence of FeCl₃ (in CHCl₃ at 70 °C for 24 h) gave the corresponding doped poly(thioketene dimer). After treatment of the doped polymer with an aqueous solution of ammonia, the neutral poly(thioketene dimer) was obtained with an incidental desilylation. The polymer obtained was soluble in DMF and DMSO. From gel permeation chromatographic analysis (DMF, polystyrene standards), the number‐average molecular weight of the polymer was found to be 7 460. The polymer showed low oxidation potentials derived from the thioketene dimer unit. An effective extension of the π‐conjugation was observed in the polymer.

Synthesis of π‐conjugated poly(thioketene dimer).     

Methoxycarbonyltrifluoromethylthioketene

A new method was developed for the synthesis of methoxycarbonyltrifluoromethylthioketene by thermal cleavage of tert-butyl 1,3,3,3-tetrafluoro-2-methoxycarbonylpropenyl sulfide in the presence of P₂O₅. This thioketene was demonstrated to exhibit high reactivity in reactions with nucleophiles as well as in ene and diene syntheses.     

Theoretical and experimental studies of the diketene system: Product branching decomposition rate constants and energetics of isomers

The kinetics and mechanism for the thermal decomposition of diketene have been studied in the temperature range 510–603 K using highly diluted mixtures with Ar as a diluent. The concentrations of diketene, ketene, and CO₂ were measured by FTIR spectrometry using calibrated standard mixtures. Two reaction channels were identified. The rate constants for the formation of ketene (k₁) and CO₂ (k₂) have been determined and compared with the values predicted by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory for the branching reaction. The first-order rate constants, k₁ (s⁻¹) = 10^{15.74 ± 0.72} exp(−49.29 (kcal mol⁻¹) (±1.84)/RT) and k₂ (s⁻¹) = 10^{14.65 ± 0.87} exp(−49.01 (kcal mol⁻¹) (±2.22)/RT); the bulk of experimental data agree well with predicted results. The heats of formation of ketene, diketene, cyclobuta-1,3-dione, and cyclobuta-1,2-dione at 298 K computed from the G2M scheme are −11.1, −45.3, −43.6, and −40.3 kcal mol⁻¹, respectively. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 580–590, 2007     

Mechanism and rate constants of the CH2 + CH2CO reactions in triplet and singlet states: A theoretical study

Ab initio and density functional CCSD(T)-F12/cc-pVQZ-f12//B2PLYPD3/6-311G** calculations have been performed to unravel the reaction mechanism of triplet and singlet methylene CH₂ with ketene CH₂CO. The computed potential energy diagrams and molecular properties have been then utilized in Rice–Ramsperger–Kassel–Marcus-Master Equation (RRKM-ME) calculations of the reaction rate constants and product branching ratios combined with the use of nonadiabatic transition state theory for spin-forbidden triplet-singlet isomerization. The results indicate that the most important channels of the reaction of ketene with triplet methylene lead to the formation of the HCCO + CH₃ and C₂H₄ + CO products, where the former channel is preferable at higher temperatures from 1000 K and above. In the C₂H₄ + CO product pair, the ethylene molecule can be formed either adiabatically in the triplet electronic state or via triplet-singlet intersystem crossing in the singlet electronic state occurring in the vicinity of the CH₂COCH₂ intermediate or along the pathway of CO elimination from the initial CH₂CH₂CO complex. The predominant products of the reaction of ketene with singlet methylene have been shown to be C₂H₄ + CO. The formation of these products mostly proceeds via a well-skipping mechanism but at high pressures may to some extent involve collisional stabilization of the CH₃CHCO and cyclic CH₂COCH₂ intermediates followed by their thermal unimolecular decomposition. The calculated rate constants at different pressures from 0.01 to 100 atm have been fitted by the modified Arrhenius expressions in the temperature range of 300–3000 K, which are proposed for kinetic modeling of ketene reactions in combustion. © 2018 Wiley Periodicals, Inc.     

New vibronic bands of CH2 observed in a pulsed supersonic jet

Spectroscopic studies of the methylene radical in a supersonic expansion have resulted in the observation of previously unreported CH₂ B?¹ B₁ ← ã¹A₁, hot band transitions. These ã state levels are populated by radiative cascade following multiphoton dissociation of ketene. Multiphoton excitation of ketene is also found to produce a diffuse luminescence with a lifetime longer than 50 μs. The conclusion of Lengel and Zare are singlet methylene is not produced one-photon nitrogen laser photolysis of cold ketene is confirmed.     

A Metal-Metal Bonded Dinuclear Ruthenium Ketene Complex

We report the synthesis of metal-metal bonded dinuclear ruthenium ketene complex [CpRu(CO)]₂(μ-CH₂CO)(μ-CO), 3 , (Cp=η⁵-C₅H₅) which contains the unique structural feature, of a μ-η²(C,C) ketene group bridging two metal centers. Complex 3 is prepared by a rare intramolecular CO insertion to the methylene group of a Ru complex [CpRu(CO)₂]₂(μ-CH₂), 1 , in the absence of CO or any donor ligand. The cis and trans isomers of 3 originating from the arrangement of the Cp groups and the unsymmetrically bridging ketene group, are observed in the NMR spectra. Unlike a ketene complex without a metal-metal bond [CpRu(CO)₂]₂(μ-CH₂CO), 2 , complex 3 exhibits the chemistry of a ketene molecule and might be used as a stoichiometric ketene precusor in organic reactions.     

Effects of vibrational energy of the reactivity of ketene molecular ions by photoionization mass spectrometry

The major ion-molecule reaction pathways in ketene-d₂ have been studied by photoionization mass spectrometry and ion cyclotron resonance spectroscopy. For process involving the molecular ion the variation of reaction cross section with ion vibrational state are pronounced. The threshold determined for the endothermic process CH₂CO⁺ + CH₂CO → C₂H⁺₄ + 2CO provides a novel confirmation of the recent redetermination of the heat of formation of ketene.     

CH2(1A1) from CH2N2 photolyses at 4358 and 3660 Å vibrational energy distributions upon reaction with cyclobutane

Approximate vibrational energy distribution for CH^*₂(¹A₁) from diazomethane photolyses at 4358 and 3660 Å have been determined to be reasonably broad. These distributions apply to CH^*₂(¹A₁) at the time of reaction with cyclobutane and were deduced from the internal energy distribution of the formed chemically activated methylcyclobutane. An apparent anomaly in the pressure dependence of the decompositions of CH₂(¹A₁) generated chemically molecules is explained. The anomaly pertains to the relative behavior of systems utilizing ketene and diazomethane photolyses as CH₂(¹A₁) sources. The explanation offered is that the vibrational energy distributions for CH^*₂(¹A₁) are narrow for ketene photolyses at 3340 or 3130 Å and broad for diazomethane photolyses at 4358 or 3660 Å.     

Chemically activated methylcyclobutane exothermicity of singlet methylene reactions and the heat of formation of singlet methylene

The specific decomposition rates of chemically activated methylcyclobutane produced from CH₂(¹A₁) reaction with cyclobutane have been determined. CH₂(¹A₁)was produced from ketene photolyses at 3340 and 3130 Å and from diazomethane photolyses at 4358 and 3660 Å. Comparisons of the excitation energies of the methylcyclobutane, determined by RRKM theory calculations, and the experimental results for the ketene systems, with thermochemically predicted maximum excitation energies, favor an Arrhenius A factor in the range of 5 × 10¹⁵ to 1 × 10¹⁶ sec^?1 for methylcyclobutane. This result is consistent with (1) the comparison of RRKM theory calculations and the experimental unimolecular falloff for methylcyclobutane, (2) the comparison of experimental A factors for cyclobutane and other alkylcyclobutane decompositions, and (3) two out of three reported experimental A factors for methylcyclobutane. An analysis of these and previous results leads to a value of the CH₂(¹A₁) ? CH₂(³B₁) energy splitting of 9±3 kcal/mole.     

Cationic copolymerization of 2-methylene-5,5-dimethyl-1,3-dioxane with 2-methylene-1,3-dioxolane and 2-methylene-1,3-dioxane

Copolymers of the cyclic ketene acetals, 2-methylene-5,5-dimethyl-1,3-dioxane, 3 , (M₁) with 2-methylene-1,3-dioxolane, 4 , (M₂) or 2-methylene-1,3-dioxane, 5 , (M₂), were synthesized by cationic copolymerization. An experimental method was designed to study the reactivity of these very reactive and extremely acid sensitive cyclic ketene acetal monomers. The reactivity ratios, calculated using a computer program based on a nonlinear minimization algorithm, were r₁ = 6.36 and r₂ = 1.25 for the copolymerization of 3 with 4 , and r₁ = 1.56 and r₂ = 1.42 for the copolymerization of 3 with 5. FTIR and ¹H-NMR spectra when combined with the values of r₁ and r₂ showed that these copolymers were formed by a cationic 1,2-polymerization (ring-retained) route. Furthermore the tendency existed to form very short blocks of M₁ or M₂ within the copolymers. Cationic copolymerization of cyclic ketene acetals have the potential to be used for synthesis of novel polymers. © 1996 John Wiley & Sons, Inc.     

[Cp2Ln(m-h1:h2-OC(SR)=CPh2 )]2 的合成和表征

[Cp2Ln（μ-SR）]2 was reacted with Ph2C=C=O to yield ketene mono-insertion products [Cp2Ln（μ-η1：η2-OC（SR）=CPh2）]2 [R=Bn, Ln=Yb （1）, Er （2）, Y （3） and R--Ph, Ln=Yb （4）], indicating that the reactions of organolanthanide thiolates with ketenes are independent of the nature of the thiolate ligand and the ketene as well as the reaction condition. These reactions could provide an efficient method for the synthesis of organolanthanide complexes with the a-thiolate-substituted enolate ligand. All these complexes were characterized by elemental analysis and spectroscopic properties and the structure of complex 1 was determined through X-ray single crystal diffraction analysis.     

Transition-state structures for the reaction between styrene and tbutyl cyanoketene: Theoretical evidence for antarafacial characteristics in a π2 + π2 thermal cycloaddition

Semiempirical AM 1 SCF ? MO models for the cycloaddition between monosubstituted alkenes (RCH = CH₂, R = Me, Ph, CF₃) and ^tbutyl cyanoketene predict the lowest-energy transition state to be relatively polar and asynchronous in character and to have a cis relationship between the R and the ^tbutyl groups, in agreement with the experimentally determined product for R = Ph. We interpret this stereochemistry as resulting from the presence of a significant antarafacial component in the transition state, which enables these two bulky groups to adopt pseudoequatorial positions in which steric interactions are minimized. The alternative higher energy trans geometry forces the R and the cyano groups to adopt more sterically hindered pseudoaxial positions. Alternative biradical-like transition states inferred by others from ab initio MCSCF calculations on the reaction between ketene and ethene do not retain any significant antarafacial component on the ketene and, therefore, form less satisfactory models for this specific reaction. © 1992 John Wiley & Sons, Inc.     

New Route for the Synthesis of Four‐Membered Cyclic Ketene Dithioacetals

Novel ketene dithioacetals have been synthesized by a one‐pot condensation reaction of active methylene compounds with CS₂ in the presence of alkyl acetylenecarboxylates. This reaction proceeds in a regioselective manner and provides products in good yields. The structures of the ketene dithioacetals were characterized by IR, ¹H‐ and ¹³C‐NMR, and MS data, and elemental analyses.