The development of efficient, mild, economical, and low‐waste processes is a cornerstone of sustainable chemistry. One such synthetic strategy that exemplifies these characteristics is the use of catalytic dehydrogenation in small‐molecule functionalization. This has been achieved in recent history through the use of photoredox catalysis in conjunction with cobaloximes, a class of catalysts that are capable of proton reduction. This has allowed for a variety of bond formations to be achieved with few to no stoichiometric additives while often producing hydrogen gas as the sole stoichiometric by‐product. Herein, select advancements made in this area of sustainable chemistry and catalysis are detailed and the mechanistic insights this body of work has provided thus far are evaluated. As such, this review aims to aid in the further development and study of synthetic strategies involving photoredox‐promoted hydrogen evolution.

The synergy between two catalysts and blue light is depicted giving rise to enones. The acridinium photocatalyst provides electrons to a cobaloxime catalyst, pictured receiving electrons within the lightbulb. This interaction liberates the small molecules hydrogen and carbon dioxide, shown as evolving from the lightbulb. More information can be found in the Research Article by J. A. Tunge and co‐workers (DOI: 10.1002/chem.202202781).

A photoredox/cobalt dual catalytic procedure has been developed that allows benzoylation of olefins. Here the photoredox catalyst effects the decarboxylation of α-ketoacids to form benzoyl radicals. After addition of this radical to styrenes, the cobalt catalyst abstracts a H-atom. Hydrogen evolution from the putative cobalt hydride intermediate allows a Heck-like aroylation without the need for a stoichiometric oxidant. Mechanistic studies reveal that electronically different styrenes lead to a curved Hammett plot, thus suggesting a change in product-determining step in the catalytic mechanism.

Benzylic alkylation of enolates and acetylides has been achieved through the use of a decarboxylative benzylation strategy. Previous research in this area is often limited by the need for extended conjugation in the electrophiles that are coupled. Herein, we report that the use of 1,1'-bis(diphenylphosphino)ferrocene (dppf) ligand allows the coupling of simple benzyl electrophiles with enolates, while the use of XPhos ligand promotes the decarboxylative couplings of propiolates.

Invited for the cover of this issue is the group of Jon Tunge at the University of Kansas. The image depicts the direct cross‐coupling of α‐oxo acids and styrenes through the release of CO2 and H2 gas in a metallaphotoredox process. Read the full text of the article at 10.1002/chem.202202781.