Recently, Professor Liangnian He published a paper on Angew. Chem. Int. Ed, reporting a breakthrough on Carbon Dioxide Fixation. He’s group reported Betaine as an excellent and sustainable organocatalyst for reductive functionalization of CO2 with various amines and diphenylsilane. This is the first report of selective two-, four-, and six-electron reduction of CO2 coupled with C-N bond formation. Betaine catalysis afforded products with diversified energy content i.e. formamide, aminal and methylamine.
Professor He was appointed as the professor of Nankai University in 2003. His research involves CO2 chemistry and green synthetic chemistry, particularly chemical transformation of CO2 and CO2 capture. He is the author of Carbon Dioxide Chemistry, which introduced CO2 activation through molecular catalysis.
In recent years, CO2 has been employed as a sustainable C1 building block in organic synthesis. In this context, metal-based catalytic systems and a number of organocatalysts have shown high activity. However, until He’s Betaine catalysis, the hierarchical reduction of CO2 with amine and hydrosilane to access formamides, aminals, and methylamines remains unknown.
To resolve hierarchical reduction of CO2, the selection of a well-balanced catalyst to subtly control the kinetics of CO2 reduction is crucial. Betaine is known as an inner salt with an onium cation and a negatively charged moiety, for example, a carboxylate anion, which could interact with the silicon atom of hydrosilane and thereby generate either the penta- or hexacoordinated silicon species with enhanced hydride-donating abilities. With reasonable interaction towards hydrosilane, betaine catalysis may balance the reactivity of CO2 reduction and allow the C+II, C0, and C-II species to be stabilized selectively, thus achieving hierarchical reduction of CO2.
He’s group first investigated the reductive functionalization of CO2 with N-methylaniline in the presence of diphenylsilane as a reductant and then found out the optimal reaction conditions. Under the optimal conditions, they evaluated the scope of this newly developed catalyst and excellent functional-group tolerance was observed. To gain insight into the mechanism of the reaction, the dependence of the catalytic performance on the reaction time was further studied by the group.
In summary, He’s group have developed an efficient organocatalytic process for reductive functionalization of CO2 with amines and diphenylsilane promoted by glycine betaine. Through tuning the amount of CO2 and the reaction temperature, this protocol enables three levels of reductive products with various energy contents, that is, formamide, methylamine, and aminal, and represents hierarchical reduction of CO2 to formic acid, formaldehyde, and methanol oxidation levels. This method can be used to produce versatile chemicals and energy-storage materials, and can provide materials which are found in petroleum feedstocks. It is appealing and promising in CO2 industry.
For more information about the research, please see the Link: