Photocontrol of catalysis in CuAAC reactions by air stable Cu(i) complexes of phenylazopyrazole-incorporated ligands

Abstract

Metal complexes containing organic photoswitches are capable of modulating the steric and electronic environment around the metal center through photoisomerization, enabling their use in photoswitchable catalysis. Herein, we design a new class of photoswitchable tripodal tetradentate ligands L1–L3 that can readily form air-stable Cu(I) complexes (C1-PF₆, C1-BF₄, C2, C3). The design strategy integrates flexible spacers and phenylazopyrazole units in the same ligand framework that ensures efficient photoisomerization and sustained stability of the photoswitched state. The complexes were screened for catalyzing the CuAAC reaction between alkynes and azides and C1-PF₆ was identified as a catalyst capable of exerting temporal control over the reaction through photoisomerization. Based on the optimized conditions and the substrate scope, the ZZZ (photoswitched) form of complex C1-PF₆ exhibits substantially improved catalytic performance compared to its EEE (native) form. In this article, we describe detailed experimental and computational investigations aimed at understanding how photoisomerization regulates the catalytic activity of Cu(I) complexes of arylazopyrazole-based tripodal tetradentate ligands.