CsPbBr₃ in the Activation of the C–Br Bond of CBrX₃ (X = Cl, Br) under Sunlight

Abstract

A newly synthesized green-fluorescent, orthorhombic, bromide-rich, perovskite nanocrystal (Φ ∼ 0.93, τ ∼ 12.5 ns, E ox = +1.6 V) obtained from an unprecedented bromide precursor dibromoisocyanuric acid was found to be an excellent visible-light (sunlight or blue-light-emitting diode (LED)) photocatalyst toward the synthesis of gem-dihaloenones for the first time. The photoactivated CsPbBr3 catalyzed the homolytic cleavage of CBrX3 (X = Cl, Br) to generate the •CX3 radical, which underwent cascaded C–C cross-coupling with terminal alkynes into the corresponding gem-dihaloenones. Radical-trapping experiments and luminescence-quenching studies helped establish a single-electron-transfer (SET) mechanism. Interestingly, other highly stable CsPbBr3 NCs, obtained from N-bromosuccinimide (NBS) and dibromohydantoin (DBHT) precursors, are unable to carry out these transformations. These results not only enrich the CsPbBr3 synthetic methodology but also encourage the research community to develop efficient and cost-effective photocatalytic materials.

CsPbBr3 Perovskite Photocatalyst in Chemodivergent Functionalization of N-Methylalkanamides Using CBr4

“…The use of CBr 4 as a brominating agent is also noteworthy, , as it is a highly reactive species that can undergo radical reactions with organic substrates . In addition, CBr 4 has also been used in organic synthesis as a halogen bond donor catalyst. , Mal and co-workers have shown a regioselective bromination of phenyl acetylene using CsPbBr 3 perovskite nanocrystals (NCs) as the photocatalyst for the synthesis of gem -dibromoenones (Figure a) . However, in this work, we demonstrate a photocatalytic bromination reaction of N -methyl- N ,3-diphenylpropiolamide using an orthorhombic CsPbBr 3 perovskite NC as the photocatalyst and CBr 4 as the brominating agent, under visible light (blue LED, 450–470 nm) irradiation in acetonitrile (Figure b).…”

“…The CsPbBr 3 perovskites used in this work were synthesized by hot injection methods. , The photocatalytic activity was also examined by the perovskites NBS-CsPbBr 3 (cubic), DBHT-CsPbBr 3 (cubic), and DBIA-CsPbBr 3 (orthorhombic) which were obtained using bromide precursors N -bromosuccinimide (NBS), 1,3-dibromo-5,5-dimethyl hydantoin (DBHT), and dibromoisocyanuric acid (DBIA), respectively (Table b). Their characterization data are given in detail in the Supporting Information.…”

“…22 The redox potentials of CBr 4 and CsPbBr 3 NCs were also helpful in understanding the reaction. 22 According to the energy diagram (Figure 4a), the hole transfer (HT) is not expected from CsPbBr 3 to CBr 4 after the photoexcitation because of the greater oxidation potential of CBr 4 (E ox = 1.21 eV) than the excited state of CsPbBr 3 NCs (E* red = 1.17 eV). Therefore, the electron transfer (ET) might have taken place from the conduction band (CB) of CsPbBr 3 to CBr 4 to generate the radical anion of carbon tetrabromide, which led to the formation of a bromide radical.…”

“…The CsPbBr 3 perovskite nanocrystals (NCs) have been explored as photocatalysts in organic synthesis in recent years. − CsPbBr 3 perovskite NCs are a type of metal halide perovskite material that has been extensively studied in the field of optoelectronics, particularly in the development of solar cells and light-emitting diodes (LEDs). , The CsPbBr 3 perovskite NCs are a promising new class of photocatalysts that have the potential to significantly improve the efficiency and selectivity of organic reactions . However, their low stability and limited efficiency have been a major challenge to their practical use. , …”

“…(a) Photocatalytic activation of the C–Br bond of CBr 4 . (b) Our work using the CsPbBr 3 photocatalyst for a chemodivergent synthesis of 3,8-dibromo-1-methyl-4-phenyl-1-azaspiro[4.5]­deca-3,6,9-trien-2-on or 3-bromo-1-methyl-4-phenyl-1-azaspiro[4.5]­deca-3,6,9-triene-2,8-dione or 3-bromo-6-( tert -butyl)-1-methyl-4-phenylquinolin-2­(1 H )-one.…”