Shanghai Advanced Research Institute and others made new progress in the research of low-carbon alkane activation
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[ Instrument R&D of Instrumentation Network ] On July 3, Shanghai University of Science and Technology and the Sun Yuhan Research Group of the Chinese Academy of Sciences Shanghai Institute of Advanced Education jointly trained graduate student Deng Yuchao as a co-first author, and published a new online article in Science Scientific research achievements have made new progress in the research of visible light catalysis of low-carbon paraffin C(sp3)-H bond activation. The first author is Gabriele Laudadio of Eindhoven University of Technology in the Netherlands, and Timothy Noel is the corresponding author.
Direct activation of gaseous hydrocarbons remains a major challenge in the chemical community. Due to the inherent inertness of these compounds, harsh reaction conditions are usually required to cleave the C(sp3)–H bond. Methane is the main component of natural gas and is rich in reserves. It has a high hydrogen-to-carbon ratio in all gaseous alkanes. Due to the inherent inertness of these C–H bonds, the industrial process of value-added processing of these compounds is limited to high temperature and high pressure conversion, such as Fischer -Tropsch process or oxidative coupling of methane. The general synthesis strategy of selectively activating a variety of light hydrocarbons under mild reaction conditions is an ongoing goal of scientists.
The study reported a general and relatively mild method that uses inexpensive tungsten salts as photocatalysts at room temperature to activate C(sp3) in methane, ethane, propane and isobutane by hydrogen atom transfer (HAT) – H key. W10O324- is a multifunctional and inexpensive polyoxometalate-based hydrogen atom transfer photocatalyst, which can effectively break the strong bonds of light paraffins and unactivated C-H bonds. Due to the gaseous nature and the low solubility of light paraffins in organic solvents, the use of flow techniques can promote the gas-liquid decomposition of tungstate-mediated processes. The short scale (usually less than 1 mm optical path) in the microfluidic reactor can illuminate the entire reaction medium uniformly, which can efficiently produce alkyl radicals. The direct participation of gaseous hydrocarbons in the carbon-carbon coupling reaction eliminates the requirement for pre-functionalization and improves the atomic efficiency of this important type of conversion.
One of the challenging reactions in organic synthesis is the selective functionalization of the C(sp3)–H bond. In synthetic organic chemistry, haloalkanes are widely used as electrophiles in nucleophilic substitution reactions, or as substrates for elimination reactions with high regioselectivity to generate double bonds. The pre-functionalization of alkanes may lead to low yields and non-selective conversions, which requires a large amount of energy consumption and carefully designed purification and recycling processes, resulting in a large amount of toxic waste. The (Bu4N)4[W10O32] salt of tungsten metal (TBADT) captures hydrogen atoms of inert carbon-hydrogen bonds to produce alkyl radicals. The corresponding carbon-centered radicals can be effectively captured by various Michael acceptors The corresponding hydroalkylated adduct is isolated in high yield and high selectivity. In view of the wide availability and cheap nature of these raw materials, as well as simplifying the reaction and reducing waste generation, the development of this conversion has important theoretical value and application significance.