At present I’m working on ‘Visible-Light-Mediated C–C Bond Formation Reaction via Transition Metal/Photoredox Dual Catalysis’. Here also the formation of the C–C bond is one of the central goal and photoredox/transition metal catalysis is an alternative to the traditional methods. We wish to use visible light as the sole energy source to drive these reactions. Abundant and less toxic organic reductants will be utilized as the sacrificial reductant. The method will be applied for making Csp3-Csp2, Csp2-Csp2, and Csp3-Csp3 bonds and other reductive functionalization reactions. We envisioned that the mildness of the developed protocol would accommodate larger functional groups. It will also enable the synthesis and late-stage functionalization of targeted bioactive molecules. Transition-metal-catalyzed cross-coupling reaction between C–X electrophiles (X = Cl, Br, OTf, etc.) and C–M nucleophiles (M = Mg, Zn, B, Si, Sn) is one of the most powerful tools in organic synthesis. It played a vital role in the preparation of complex medicinal drugs, designing functional ligands, molecular materials, including industrial applications. However, unavailability of the organometallic C–M nucleophiles, their cost, handling issues under ambient conditions, and generation of copious waste demanded an alternative of traditional cross-coupling reaction. In recent years, a conceptually different approach that is the reductive cross-coupling reaction between two electrophiles has emerged. The method utilizes bench-stable high-valent late-transition metal salts (such as Pd, Ni, Co, Fe, Cr) as a catalyst and excess amount metallic terminal reductants (such as Zn, Mn, In, Sm, Mg). Importantly, these protocols avoid the individual preparation of hazardous organometallics reagents and offered wide availability of diverse electrophiles for coupling. However, the use of an excessive amount of metallic powder as a reductant generates an over-stoichiometric amount of metal salts as waste that not only complicates the work-up and purification procedure but also creates environmental concern over waste disposal. Not only that, reductant-derived metal salts often reduce the catalytic performance of the low-valent catalysts by coordination to the active sites. Additionally, functional group tolerance is not too much due to the presence of an external metal reductant. To overcome these concerns, an alternative catalytic method of activation is in high demand.
Visible light photoredox catalysis has emerged as a powerful arsenal in organic synthesis. It leverages abundant visible light for the bond activation process in a controlled manner without the need for toxic and hazardous reagents. Upon excitation with visible light, a photoredox catalyst can simultaneously act as a powerful oxidant and reductant. We envision that merging photoredox catalysis with transition metal catalysis in a dual-catalysis fashion might address the challenges of the classical cross-coupling reaction and might pave the way for the development of the novel bond formation reactions.