Coupling photocatalytic water oxidation with reductive transformations of organic molecules

Abstract

The utilization of readily available and non-toxic water by photocatalytic water splitting is highly attractive in green chemistry. Herein we report that light-induced oxidative half-reaction of water splitting is effectively coupled with reduction of organic compounds, which provides a light-induced avenue to use water as an electron donor to enable reductive transformations of organic substances. The present strategy allows various aryl bromides to undergo smoothly the reductive coupling with Pd/g-C3N4* as the photocatalyst, giving a pollutive reductant-free method for synthesizing biaryl skeletons. Moreover, the use of green visible-light energy endows this process with more advantages including mild conditions and good functional group tolerance. Although this method has some disadvantages such as a use of environmentally unfriendly 1,2-dioxane, an addition of Na2CO3 and so on, it can guide chemists to use water as a reducing agent to develop clean procedures for various organic reactions.

Coupling photocatalytic overall water splitting with hydrogenation of organic molecules: a strategy for using water as a hydrogen source and an electron donor to enable hydrogenation

“…In theory, such an electronic effect agrees with the SeT mechanism because an increase in the electron density of the aromatic ring would accelerate the SeT from the catalyst to the substrate by improving the electron-accepting capacity of the substrate. 67–69 Moreover, such an electronic effect has been authenticated in previous literature as SeT-mediated cleavage of aryl C–Br bonds. 67–69 In contrast, oxidative metal addition-mediated reactions have a different electronic effect: electron-deficient aryl halides have lower reactivity.…”

“…67–69 Moreover, such an electronic effect has been authenticated in previous literature as SeT-mediated cleavage of aryl C–Br bonds. 67–69 In contrast, oxidative metal addition-mediated reactions have a different electronic effect: electron-deficient aryl halides have lower reactivity. 71,72 In summary, the observed electronic effect under our conditions is consistent with SeT rather than the oxidative metal addition mechanism, which confirms the reliability of our conclusion that the present reactions proceed via the SeT mechanism.…”

“…62 One is characterized by oxidative metal addition (Scheme 5a), 62,66 while the other undergoes the for-mation of an aryl radical anion (ArX •− ) via single electron transfer (SeT) from catalysts to aryl halides (Scheme 5b). 52,53,62,[67][68][69] Thus we performed several control experiments where the well-known radical inhibitor 2,6-di-tertbutyl-4-methylphenol (BHT) or 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) 70 was added into the reaction system. As shown in Scheme 6, the presence of BHT or TEMPO led to a dramatic decrease in the yields, which reveals that the present reaction possibly proceeds through the SeT pathway.…”

Photocatalytic Transfer Hydrogenation Reactions Using Water as the Proton Source

“…As the most common and nonpolluting solvent, water also has enormous potential for use in other types of reactions. It has been demonstrated that water can participate in reactions as an oxidizing or reducing agent, such as hydrogenolysis and couplings. , This provides directions for the development of water involvement in reactions.…”

“…It has been demonstrated that water can participate in reactions as an oxidizing or reducing agent, such as hydrogenolysis 60 and couplings. 61,62 This provides directions for the development of water involvement in reactions. In conclusion, although the field is still in its nascent stage and has many challenges, discoveries will propel the field by solving these issues with an increasing understanding of their organocatalytic and photochemical reactivity, which will have a significant impact on the energy transition to a zero-carbon economy.…”