Browsing by Author "Liu, Jie"

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    Cooperative catalytic methoxycarbonylation of alkenes: Uncovering the role of palladium complexes with hemilabile ligands
    (Cambridge : RSC, 2018) Dong, Kaiwu; Sang, Rui; Wei, Zhihong; Liu, Jie; Dühren, Ricarda; Spannenberg, Anke; Jiao, Haijun; Neumann, Helfried; Jackstell, Ralf; Franke, Robert; Beller, Matthias
    Mechanistic studies of the catalyst [Pd2(dba)3/1,1′-bis(tert-butyl(pyridin-2-yl)phosphanyl)ferrocene, L2] for olefin alkoxycarbonylation reactions are described. X-ray crystallography reveals the coordination of the pyridyl nitrogen atom in L2 to the palladium center of the catalytic intermediates. DFT calculations on the elementary steps of the industrially relevant carbonylation of ethylene (the Lucite α-process) indicate that the protonated pyridyl moiety is formed immediately, which facilitates the formation of the active palladium hydride complex. The insertion of ethylene and CO into this intermediate leads to the corresponding palladium acyl species, which is kinetically reversible. Notably, this key species is stabilized by the hemilabile coordination of the pyridyl nitrogen atom in L2. The rate-determining alcoholysis of the acyl palladium complex is substantially facilitated by metal-ligand cooperation. Specifically, the deprotonation of the alcohol by the built-in base of the ligand allows a facile intramolecular nucleophilic attack on the acyl palladium species concertedly. Kinetic measurements support this mechanistic proposal and show that the rate of the carbonylation step is zero-order dependent on ethylene and CO. Comparing CH3OD and CH3OH as nucleophiles suggests the involvement of (de)protonation in the rate-determining step.
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    Numerical simulation of breakdown properties and streamer development processes in SF6/CO2mixed gas
    (New York, NY : American Inst. of Physics, 2022) Zhang, Runming; Wang, Lijun; Liu, Jie; Lian, Zhuoxi
    In this paper, the dielectric breakdown properties in SF6/CO2 mixed gas, the development of the streamer in SF6/CO2 mixed gas, and the distribution of each component with time were studied. First, the electron transport parameters (mean energy, longitudinal diffusion coefficients, Townsend coefficient, critical reduced electric field coefficients, and electron energy distribution function) in SF6/CO2 mixtures with different ratios in the E/N range of over 50-1000 Td were obtained by two-term Boltzmann equation analysis. Then, coupled with the Boltzmann drift-diffusion equation and Poisson equation, the hydrodynamic model of discharge of SF6/CO2 mixtures in a strongly non-uniform electric field was established. Many different influence factors are considered, such as the gas mixture ratio, applied voltage, space temperature, space pressure, and electrode structures. The results indicate that the increase in SF6 content in the mixed gas will reduce the ionization rate of the total mixed gas, and therefore, it takes a longer time for breakdown. The higher the pressure, the more concentrated the form of the streamer. As the temperature increases, the shape of the streamer head becomes more scattered, and it loses its contoured shape at about 3000 K; in addition, the existence of the maximum electron number density value appears at the tip of the rod electrode rather than at the streamer head. The simulation also revealed that the dielectric strength of SF6/CO2 mixtures is stronger than that of SF6/N2 mixtures and reached a turning point at an SF6 ratio of 60% under extremely non-uniform electric fields, which agreed well with experiments.
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    Toward Green Acylation of (Hetero)arenes: Palladium-Catalyzed Carbonylation of Olefins to Ketones
    (Washington, DC : ACS Publ., 2017) Liu, Jie; Wei, Zhihong; Jiao, Haijun; Jackstell, Ralf; Beller, Matthias
    Green Friedel-Crafts acylation reactions belong to the most desired transformations in organic chemistry. The resulting ketones constitute important intermediates, building blocks, and functional molecules in organic synthesis as well as for the chemical industry. Over the past 60 years, advances in this topic have focused on how to make this reaction more economically and environmentally friendly by using green acylating conditions, such as stoichiometric acylations and catalytic homogeneous and heterogeneous acylations. However, currently well-established methodologies for their synthesis either produce significant amounts of waste or proceed under harsh conditions, limiting applications. Here, we present a new protocol for the straightforward and selective introduction of acyl groups into (hetero)arenes without directing groups by using available olefins with inexpensive CO. In the presence of commercial palladium catalysts, inter- and intramolecular carbonylative C-H functionalizations take place with good regio- and chemoselectivity. Compared to classical Friedel-Crafts chemistry, this novel methodology proceeds under mild reaction conditions. The general applicability of this methodology is demonstrated by the direct carbonylation of industrial feedstocks (ethylene and diisobutene) as well as of natural products (eugenol and safrole). Furthermore, synthetic applications to drug molecules are showcased.