The overarching goal of Wu group's research is to apply advanced engineered micro-tubing reactors to serve as better platforms to provide new chemical transformations and sustainable manufacturing with relevance to contemporary problems. Our lab is focusing on exploring new fundamental reactions that directly transform abundant feedstocks (natural gases, unfunctionalized alkanes and silanes) into value-added products in an atom- and step-economic fashion, and harvest visible-light by chemical means and using light-energy as energy input for chemical transformations.
Researches of our group have been highlighted and summarized by:
Our group invented the first time a “stop-flow” micro-tubing (SFMT) reactor platform, which combines elements from both continuous-flow and conventional batch reactors. Continuous-flow micro-tubing reactor is not efficient for parallel reaction screening and long-term reactions. The SFMT reactor effectively addresses these limitations. It is proven to be quite efficient during screening for gas/liquid and light-mediated reactions. Owing to its ease of access and operation, high efficiency, enhanced safety, and green nature, the SFMT platform promises to become an important method complementary to the current reaction apparatus used in organic laboratories.
(i) Chem. Sci. 2017, 8, 3623-3627.
(ii) Video see: J. Vis. Exp. 2018, 131, e56897
Development of Advanced Reactors
C-H, Si-H, B-H Activation under Visible-light-irradiation
Direct C-H, Si-H transformation has attracted continuous interest since the early 1970s because it meets not only the atom- and step-economy for green and sustainable synthesis, but also the understanding of the intrinsic features of the broadly existing C-H bonds in organic molecules, such as their accessibility, activity, and selectivity. The emerging photocatalysis provides mild and convenient strategies to access open-shell reactive radicals, offering enormous opportunities for C-H, Si-H bond functionalization. In line with our continuous interests in developing green and sustainable synthetic methodology using visible-light as the energy source, our research group has contributed to C-H and Si-H activations via three different strategies:
(i) C(sp3)-H activations via only photoredox: Chem. Sci. 2017, 8, 4654; ACS Catal. 2018, 8, 6224.
(ii) C(sp3)-H activations via direct HAT photocatalysis: Angew. Chem. Int. Ed. 2018, 57, 8514.
(iii) C(sp3)-H activations via synergistic merging of photoredox and HAT catalysis: J. Am. Chem. Soc. 2017, 139, 13579. Angew. Chem. Int. Ed. 2017, 56, 16621. Angew. Chem. Int. Ed. 2018, 57, 12661.
Development of novel photo-catalysts
Two major categories of photocatalysts have been identified effectively. Transition-metal chromophores such as Ru and Ir polypyridyl complexes have garnered particular recognition due to their rich redox chemistry at the MLCT (metal-to-ligand charge-transfer) excited states. On the other hand, organic photocatalysts enable unique chemistries far more than just “metal-free” alternatives to transition-metal photocatalysts. There remains a critical need for the development of new photocatalysts, especially heterogeneous catalysts, to enable novel and valuable synthetic processes.
(i) Catal. Sci. Technol. 2018, 8, 4257.
Visible-light-mediated fine chemical synthesis using natural gas feedstocks
Natural gas feedstocks such as acetylene, CO2, methane and ethane are inexpensive, non-toxic and available in virtually unlimited amounts, which can be used as substitutes for limited fossil fuel resources. However, its research and application for fine chemical synthesis is significantly restricted by the requirement of complicate apparatus, especially for high-pressure and photo-transformations. The development of SFMT reactor provides an ideal platform to evaluate gas-involved transformation under light promoted conditions due to the increased light penetration and enhanced gas/liquid surface to volume ratio associated tieh micro-tubing reactors. Our group has developed several new fundamental reactions that directly convert inexpensive gaseous feedstocks to value added-chemicals using visible-light as the energy source.
Acetylene gas: Chem. Sci. 2017, 8, 3623-3627.
CO2 gas: (i) J. Am. Chem. Soc. 2018, 140, 5257−5263; (ii) Angew. Chem. Int. Ed. 2018, 57, 17220-17224.
Ethane gas: Angew. Chem. Int. Ed. 2018, 57, 12661.
Ethylene gas: Chem. 2019, 5, 192-203.
Development of flow-based end-to-end API synthesis
Compared to stepwise batch synthesis, multistep continuous flow synthesis enables the combination of multiple synthetic steps into a single and uninterrupted reactor network, thereby circumventing the need to isolate intermediates, and enabling automated synthesis. However, despite many advantages and much progress in end-to-end API continuous-flow synthesis, several hurdles still need to be overcome. For instance, solvent and reagent incompatibility between individual steps, build-up pressure of reactors, substrate dispersion, and requirement of regeneration of reagent and scavenger columns, limit the maximum number of sequential steps in flow. We are trying to develop new prototypes of multistep flow synthesis that can avoid those problems.