Cu₂O Nanocrystals‐Catalyzed Photoredox Sonogashira Coupling of Terminal Alkynes and Arylhalides Enhanced by CO₂

Abstract

Herein the first visible-light-activated Sonogashira CÀCc oupling reaction at room temperature catalyzed by single-metal heterogeneous Cu 2 Ot runcated nanocubes (Cu 2 OT NCs) was developed. Aw ide varietyo fa ryl halidesa nd terminal alkynes workedw ell in this recyclable heterogeneous photochemical process to form the corresponding Sonogashira CÀCc oupling products in good yields. Mechanistic control studies indicated that CO 2 enhances the formation of light-absorbing heterogeneous surface-bound Cu I -phenylacetylide (l max = 472 nm), which further undergoes single-electron transfer with aryl iodides/bromides to enable Sonogashira C sp 2ÀC sp bond formation. In contrastt ol iterature-reported bimetallic TiO 2 -containing nanoparticles as photocatalyst, this work avoided the need of cocatalysis by TiO 2 .S ingle-metalC u I in Cu 2 OT NCs wass olely responsible for the observed C sp 2ÀC sp couplingr eactions under CO 2 atmosphere.The Sonogashira coupling reactioniso ne of the most powerful and straightforwardm ethods forc onstruction of aryl alkynes/conjugated alkynes through C sp 2À C sp cross-coupling of aryl/alkenyl halidesa nd terminal alkynes, which are the most substantial intermediates in the synthesis of natural products as well as pharmaceutical, polymeric, and organic materials. [1] In such transformations, conventional methodologies involvet he use of palladiump hosphine complexes along with copper as ac ocatalyst in the presence of excess organic amine bases (Scheme 1a). [2] However, these methodso ften requiree xpensive Pd catalysts and Cu salts as cocatalyst with excessive ligands/ amines or harsh thermal conditions. Recently,a number of reports have demonstrated different modifications in ac atalytic fashion, [3] such as a) Cufree Pd-catalytic systems, [3a-d] b) Pd-free Fe-, Ni-, or Cu-complexes, [3e,f] and c) Cu-catalystsw ith ligandsu nder harsh conditions. [3g] Among them,P d-free copper-catalyzed Sonoga-shira cross-couplings are the predominant inexpensive protocols for constructing conjugated alkynes, [3d, 4, 5] However,t he usage of excessl igands and the harsh thermalr eaction conditions diminish their merits.To addresst he above challenges, we previously reported visible-light-triggered CuCl-catalyzed Sonogashira crosscoupling between aryl halides and terminal alkynes at room temperature. [6] We envisioned that the CÀCc oupling reactions can be initiated by photoexcited copper(I)-phenylacetylide that undergoes as ingle-electron transfer (SET) process with ground-state aryl halidesv ia inner-coordination sphere to initiate the CÀCc oupling reactionu pon visible-light irradiation. We questioned whether it is possible to replace the molecular CuCl catalystw ith recyclable solid copper-containing nanoparticles (NPs) for the Sonogashira C sp 2ÀC sp cross-coupling reactions between aryl halides and terminal alkynes under visiblelight irradiation at room temperature. Such recyclableh eterogeneous photocatalysts are highly desirable for Sonogashira coupling reactions and remainunexplored in th...

Multifunctional CuO/Cu2O Truncated Nanocubes as Trimodal Image-Guided Near-Infrared-III Photothermal Agents to Combat Multi-Drug-Resistant Lung Carcinoma

“…The size distribution analysis using the dynamic light scattering (DLS) technique reveals an average particle size of ∼293.6 nm. The polydispersibility index (PDI) value is 0.118, which clearly indicates that plasmonic CuO/Cu 2 O TNCs are moderately monodispersed (please refer to our previous publication) . The UV–vis–NIR absorption spectrum of plasmonic CuO/Cu 2 O TNCs displayed broad absorption up to 1800 nm, covering the NIR-I (650–950 nm), -II (980–1350 nm), and -III (1550–1800 nm) biological windows, respectively (Figure (D)).…”

“…It was reported that the bandgap of a p-type semiconductor CuO is 1.3–1.6 eV, which is lower than the corresponding bandgap of Cu 2 O (2.0 eV) . Very recently, we have reported the visible-light-activated Sonogashira C–C coupling reaction at room temperature catalyzed by single-metal heterogeneous Cu 2 O truncated nanocubes (Cu 2 O TNCs) . It is possible that CuO/Cu 2 O will form a type II band structure and eventually improve the photocatalytic activities by enhancing the charge separation.…”

“…24 Very recently, we have reported the visible-light-activated Sonogashira C−C coupling reaction at room temperature catalyzed by singlemetal heterogeneous Cu 2 O truncated nanocubes (Cu 2 O TNCs). 25 It is possible that CuO/Cu 2 O will form a type II band structure and eventually improve the photocatalytic activities by enhancing the charge separation. However, so far the biomedical applications of CuO/Cu 2 O nanostructures have not yet been explored.…”

Temperature Controlled Evolution of Pure Phase Cu9S5 Nanoparticles by Solvothermal Process

“…These properties are strongly influenced by their morphology, phase and surface characteristics. Their potential application in various fields such as catalysis (Shanmugam et al, 2020), non-linear optics (Chen et al, 2014), photoelectrochemistry (Hao et al, 2020), light emitting diodes (Chen et al, 2020) and biosensing (Yue et al, 2020) is dependent on the ability to manipulate these properties by controlling their size, shape and phase.…”

Well-defined Cu2O photocatalysts for solar fuels and chemicals

“…[156][157][158][159][160][161] A recent study showed that when Cu 2 O nanocrystals with truncated nanocube morphology were used for the photocatalytic Sonogashira reaction in the presence of the K 2 CO 3 and CO 2 atmosphere, a CuO layer was formed in the exposed crystal surface. 161 Another fascinating hybrid photocatalyst where the Cu 2 O nanocube was decorated with SnO 2 nanoparticles showed a unique post-illumination photocatalytic "memory" effect, which means it can still be catalytically active in the dark aer the illumination was switched off for a certain period of time. 154 This "memory effect" was possible due to the presence of reversible chemical states (Sn 2+ vs. Sn 4+ ) in SnO 2 .…”