Jason Williams

This review summarizes recent advances made with photoactive Cr^III, Fe^II, Cu^I, Zn^II, Zr^IV, Mo⁰ and U^VI complexes in the context of synthetic organic photoredox chemistry using visible light as an energy input. Mechanistic considerations are combined with discussions of reaction types and scopes. Perspectives for the future of the field are discussed against the background of recent significant developments of new photoactive metal complexes made from earth-abundant elements. More information can be found in the Review article on page 2039 ff.

Designing strategies to access stereodefined olefinic organoboron species is an important synthetic challenge. Despite significant advances, there is a striking paucity of routes to Z-α-substituted styrenyl organoborons. Herein, this strategic imbalance is redressed by exploiting the polarity of the C(sp²)−B bond to activate the neighboring π system, thus enabling a mild, traceless photocatalytic isomerization of readily accessible E-α-substituted styrenyl BPins to generate the corresponding Z-isomers with high fidelity. Preliminary validation of this contra-thermodynamic EZ isomerization is demonstrated in a series of stereoretentive transformations to generate Z-configured trisubstituted alkenes, as well as in a concise synthesis of the anti-tumor agent Combretastatin A4.

It's EZ: Exploitation of the polarity of the C(sp²)−B bond to activate the neighboring π system enables a mild, traceless photocatalytic isomerization of readily accessible E-α-substituted styrenyl BPins to generate the corresponding Z-isomers with high fidelity. The method is used for a series of stereoretentive transformations to generate Z-configured trisubstituted alkenes, as well as in a concise synthesis of the anti-tumor agent combretastatin A4.

Solid reagents, leaching catalysts, and heterogeneous photocatalysts are commonly employed in batch processes but are ill-suited for continuous-flow chemistry. Heterogeneous catalysts for thermal reactions are typically used in packed-bed reactors, which cannot be penetrated by light and thus are not suitable for photocatalytic reactions involving solids. We demonstrate that serial micro-batch reactors (SMBRs) allow for the continuous utilization of solid materials together with liquids and gases in flow. This technology was utilized to develop selective and efficient fluorination reactions using a modified graphitic carbon nitride heterogeneous catalyst instead of costly homogeneous metal polypyridyl complexes. The merger of this inexpensive, recyclable catalyst and the SMBR approach enables sustainable and scalable photocatalysis.

A flow system for processing solids enables the efficient and scalable utilization of heterogeneous photocatalysis for selective fluorinations.