Gas Phase Formation of Methylgermylene (HGeCH3)

The methylgermylene species (HGeCH₃; X¹A′) has been synthesized via the bimolecular gas phase reaction of ground state methylidyne radicals (CH) with germane (GeH₄) under single collision conditions in crossed molecular beams experiments. Augmented by electronic structure calculations, this elementary reaction was found to proceed through barrierless insertion of the methylidyne radical in one of the four germanium-hydrogen bonds on the doublet potential energy surface yielding the germylmethyl (CH₂GeH₃; X²A′) collision complex. This insertion is followed by a hydrogen shift from germanium to carbon and unimolecular decomposition of the methylgermyl (GeH₂CH₃; X²A′) intermediate by atomic hydrogen elimination leading to singlet methylgermylene (HGeCH₃; X¹A′). Our investigation provides a glimpse at the largely unknown reaction dynamics and isomerization processes of the carbon-germanium system, which are quite distinct from those of the isovalent carbon system thus providing insights into the intriguing chemical bonding of organo germanium species on the most fundamental, microscopic level.     

Gas Phase Formation of the Interstellar Molecule Methyltriacetylene

Methyltriacetylene – the largest methylated polyacetylene detected in deep space – has been synthesized in the gas phase via the bimolecular reaction of the 1-propynyl radical with diacetylene under single-collision conditions. The barrier-less route to methyltriacetylene represents a prototype of a polyyne chain extension through a radical substitution mechanism and provides a novel low temperature route, in which the propynyl radical piggybacks a methyl group to be incorporated into methylated polyynes. This mechanism overcomes a key obstacle in previously postulated reactions of methyl radicals with unsaturated hydrocarbon, which fail the inclusion of methyl groups into hydrocarbons due to insurmountable entrance barriers thus providing a fundamental understanding on the electronic structure, chemical bonding, and formation of methyl-capped polyacetylenes. These species are key reactive intermediates leading to carbonaceous nanostructures in molecular clouds like TMC-1.     

Darstellung und Kristallstruktur von [(Me3SiCH2)2InP(H)Ad]2

Preparation and Crystal Structure of [(Me₃SiCH₂)₂InP(H)Ad]₂ Reaction of (Me₃SiCH₂)₃ In with AdPH₂ (Ad = adamantyl) in the presence of AgNO₃ leads to [(Me₃SiCH₂)₂InP(H)Ad]₂ 1 in 30% yield. The crystal structure of 1 is discussed.     

Directed Gas Phase Formation of the Elusive Silylgermylidyne Radical (H3SiGe,X2A′′)

The previously unknown silylgermylidyne radical (H₃SiGe; X²A′′) was prepared via the bimolecular gas phase reaction of ground state silylidyne radicals (SiH; X²Π) with germane (GeH₄; X¹A₁) under single collision conditions in crossed molecular beams experiments. This reaction begins with the formation of a van der Waals complex followed by insertion of silylidyne into a germanium-hydrogen bond forming the germylsilyl radical (H₃GeSiH₂). A hydrogen migration isomerizes this intermediate to the silylgermyl radical (H₂GeSiH₃), which undergoes a hydrogen shift to an exotic, hydrogen-bridged germylidynesilane intermediate (H₃Si(μ-H)GeH); this species emits molecular hydrogen forming the silylgermylidyne radical (H₃SiGe). Our study offers a remarkable glance at the complex reaction dynamics and inherent isomerization processes of the silicon-germanium system, which are quite distinct from those of the isovalent hydrocarbon system (ethyl radical; C₂H₅) eventually affording detailed insights into an exotic chemistry and intriguing chemical bonding of silicon-germanium species at the microscopic level exploiting crossed molecular beams.     

Gas‐Phase Synthesis of the Benzyl Radical (C6H5CH2)

Dicarbon (C₂), the simplest bare carbon molecule, is ubiquitous in the interstellar medium and in combustion flames. A gas‐phase synthesis is presented of the benzyl radical (C₆H₅CH₂) by the crossed molecular beam reaction of dicarbon, C₂(X¹Σ_g⁺, a³Π_u), with 2‐methyl‐1,3‐butadiene (isoprene; C₅H₈; X¹A′) accessing the triplet and singlet C₇H₈ potential energy surfaces (PESs) under single collision conditions. The experimental data combined with ab initio and statistical calculations reveal the underlying reaction mechanism and chemical dynamics. On the singlet and triplet surfaces, the reactions involve indirect scattering dynamics and are initiated by the barrierless addition of dicarbon to the carbon–carbon double bond of the 2‐methyl‐1,3‐butadiene molecule. These initial addition complexes rearrange via multiple isomerization steps, leading eventually to the formation of C₇H₇ radical species through atomic hydrogen elimination. The benzyl radical (C₆H₅CH₂), the thermodynamically most stable C₇H₇ isomer, is determined as the major product.     

Gas‐Phase Synthesis of 1‐Silacyclopenta‐2,4‐diene

Silole (1‐silacyclopenta‐2,4‐diene) was synthesized for the first time by the bimolecular reaction of the simplest silicon‐bearing radical, silylidyne (SiH), with 1,3‐butadiene (C₄H₆) in the gas phase under single‐collision conditions. The absence of consecutive collisions of the primary reaction product prevents successive reactions of the silole by Diels–Alder dimerization, thus enabling the clean gas‐phase synthesis of this hitherto elusive cyclic species from acyclic precursors in a single‐collision event. Our method opens up a versatile and unconventional path to access a previously rather obscure class of organosilicon molecules (substituted siloles), which have been difficult to access through classical synthetic methods.     

Thermal Methane Activation by [Si2O5].+ and [Si2O5H2].+: Reactivity Enhancement by Hydrogenation

The thermal reactions of methane with the oxygen‐rich cluster cations [Si₂O₅]^?+ and [Si₂O₅H₂]^?+ have been examined using Fourier transform–ion cyclotron resonance (FT‐ICR) mass spectrometry in conjunction with state‐of‐the‐art quantum chemical calculations. In contrast to the inertness of [Si₂O₅]^.+ towards methane, the hydrogenated cluster [Si₂O₅H₂]^.+ brings about hydrogen‐atom transfer (HAT) from methane with an efficiency of 28 % relative to the collision rate. The mechanisms of this process have been investigated in detail and the reasons for the striking reactivity difference of the two cluster ions have been revealed.     

CuAAC Click Reactions in the Gas Phase: Unveiling the Reactivity of Bis‐Copper Intermediates

Copper‐catalysed azide alkyne cycloaddition (CuAAC) has been considered a breakthrough transformation over the last 15 years. Its debated mechanism arouses continuously growing interest. By means of a mass spectrometer modified ad hoc, the entire catalytic cycle of CuAAC reaction has been investigated in the gas phase. Ion‐molecule reactions were performed inside the mass spectrometer to reproduce step‐by‐step, at a molecular level, the complete catalytic cycle of the click reaction. We successfully challenged the reactivity of elusive mono‐ and bis‐copper intermediates by ion‐molecule reactions leading to the production of mass‐characterized triazole products, paving the way for detailed energetic studies to be performed in the gas phase. The structures of the relevant species, calculated at a DFT level, helped rationalise our experimental results.     

Differences and Commonalities in the Gas‐Phase Reactions of Closed‐Shell Metal Dioxide Clusters [MO2]+ (M=V,Nb, and Ta) with Methane

High‐level electronic structure calculations, in combination with Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometric studies, permit the mechanism by which closed‐shell, “naked” [TaO₂]⁺ brings about C?H bond activation of methane to be revealed. These studies also help to understand why the lighter congeners of [MO₂]⁺ (M=V, Nb) are unreactive under ambient conditions.     

Time-dependent quantum study of the kinetics of the H(2S) + FO(2II) OH(2II) + F(2P) reaction

Quantum mechanical wave packet calculations are carried out for the H((2)S) + FO((2)II) --> OH((2)II) + F((2)P) reaction on the adiabatic potential energy surface of the ground (3)A' triplet state. The state-to-state and state-to-all reaction probabilities for total angular momentum J = 0 have been calculated. The probabilities for J > 0 have been estimated from the J = 0 results by using J-shifting approximation based on a capture model. Then, the integral cross sections and initial state-selected rate constants have been calculated. The calculations show that the initial state-selected reaction probabilities are dominated by many sharp peaks. The reaction cross section does not manifest any sharp oscillations and the initial state-selected rate constants are sensitive to the temperature.     

基于2(5H)-呋喃酮的碳-杂成键反应研究进展

2(5H)-呋喃酮结构单元广泛存在于天然产物中,同时许多2(5H)-呋喃酮类化合物也是重要的有机合成中间体.因此,基于常见2(5H)-呋喃酮(1)的有机合成研究近年来引起了人们的关注.根据在有机合成反应中成键方式的不同,综述了在2(5H)-呋喃酮(1)环上形成C-O,C-N,C-S,C-P,C-Se,C-Si等碳-杂键的反应研究进展.     

Stereoretentive Copper‐Catalyzed Directed Thioglycosylation of C(sp2)−H Bonds of Benzamides

An efficient thioglycosylation of C(sp²)?H bonds with thiosugars has been established for the first time. Using only Cu(OAc)₂?H₂O as a catalyst and Ag₂CO₃ as an additive in DMSO, the protocol proved to have broad scope, and a variety of complex thioglycosides have been prepared in good yields with exclusive β‐selectivity.     

Metal‐Free,Room‐Temperature Oxygen‐Atom Transfer in the N2O/CO Redox Couple as Catalyzed by [Si2Ox].+ (x=2–5)

The thermal reduction of N₂O by CO mediated by the metal‐free cluster cations [Si₂O_x]^.+ (x =2–5) has been examined in the gas phase using Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry in conjunction with quantum chemical calculations. Three successive oxidation/reduction steps occur starting from [Si₂O₂]^.+ and N₂O to form eventually [Si₂O₅]^.+; the latter as well as the intermediate oxide cluster ions react sequentially with CO molecules to regenerate [Si₂O₂]^.+. Thus, full catalytic cycles occur at ambient conditions in the gas phase. Mechanistic aspects of these sequential redox processes have been addressed to reveal the electronic origins of these unparalleled reactions.     

基于 H2/O2 等离子体和钛硅沸石的丙烯气相环氧化方法

 将 H₂/O₂ 非平衡等离子体现场产生的气态 H₂O₂和丙烯与耦合反应器中钛硅沸石 TS-1 直接接触, 实现了丙烯气相环氧化反应. 结果表明, 非平衡等离子体生成气态 H₂O₂ 的速率由介质阻挡放电的输入功率决定, 环氧丙烷的生成速率和选择性取决于钛硅沸石催化剂和反应条件. 在 H₂ 和 O₂ 进料流量分别为 170 和 8 ml/min, 介质阻挡放电输入功率为 3.5 W, 环氧化反应温度为 110 ^oC, 丙烯进料量为 18 ml/min, 催化剂用量为 0.8 g 的条件下, 生成环氧丙烷产率达 246.9 g/(kg•h)、环氧丙烷选择性和 H₂O₂ 有效利用率分别为 95.4% 和 36.1%, 反应 36 h 内未见催化剂失活.     

Iron‐Promoted CC Bond Formation in the Gas Phase

An unusual iron transfer and carbon–carbon coupling take place in gas‐phase ionized mixtures containing ferrocene and dichloromethane. Ferrous chloride and the protonated benzenium ion are eventually formed by a thermal and efficient reaction, through stable intermediates that undergo a remarkable reorganization. The mechanism of the concerted iron extrusion, carbon–chlorine bond activation and carbon–carbon bond formation is elucidated by electronic structure calculations that show the crucial role of iron.