Semiconductor–nanometal interfacing enables a dual-mode NiZn–CdS alloy catalyst for light-driven Suzuki–Miyaura cross-coupling and regioselective reactions under palladium- and copper-free conditions

The synthesis of cost-effective, noble metal and copper-free NiZn alloy, CdS quantum dots (QDs), and their hybrid NiZn–CdS nanocomposite is reported and their efficiency as heterogeneous catalysts for visible light-mediated Suzuki–Miyaura cross-coupling (SMCC) and regioselective azide–alkyne cycloaddition (AAC) reactions is compared. A key breakthrough of this study is the catalytic inefficiency of hierarchically arranged NiZn alloy alone for SMCC reaction, under visible light illumination. However, upon integrating CdS QDs onto NiZn alloy nanoparticles via nanoscale interfacial engineering, a remarkable catalytic enhancement is observed. The newly developed NiZn–CdS composite exhibits unprecedented photocatalytic efficiency for SMCC reaction. In contrast, for AAC reaction, the composite demonstrates no catalytic activity under visible light. Interestingly, when CdS QDs are decoupled, the NiZn alloy alone shows outstanding catalytic performance for the regioselective formation of 1,4-disubstituted 1,2,3-triazoles at room temperature. This represents the first report of a room temperature, copper-free catalytic system without the use of any noble metal, that outperforms many previously reported copper-free catalysts for AAC, both in terms of activity and selectivity. Further, the sustainability matrices of the developed catalytic protocols are determined through comprehensive green chemistry assessments which demonstrate the protocol's environmental friendliness and adherence to green chemistry principles.