Integration of N-Aryl Phenoxazine Photosensitizers and Nickel Catalysts in Polymer Supports Enhances Photocatalytic Organic Transformations

Abstract

Enhancing the catalytic activity of photosensitizers is critical for photocatalysis, especially in dual catalytic systems. We present the integration of N-aryl phenoxazine photosensitizers and nickel-bipyridine catalysts into linear and crosslinked polyacrylate matrices, creating robust polymer-supported dual photocatalysts. The linear flexible polymer confers good solubility in organic solvents to ensure efficient interactions between catalytic sites and substrates. The proximity of phenoxazine units and nickel complexes in the linear copolymer P1-Ni boosts electron, energy, and radical transfers, significantly enhancing the catalytic activity of phenoxazine photosensitizers. P1-Ni exhibits high activity in catalyzing visible-lightdriven sulfonylation, esterification, and etherification reactions across a broad substrate scope at extraordinarily low catalyst loadings (0.1 to 0.2 mol %) and with exceptionally high turnover numbers approaching 1000. P1-Ni outperforms its homogeneous control by 27-to 38-fold. Additionally, an insoluble cross-linked polymer catalyst (P2-Ni) was synthesized by incorporating a divinyl cross-linking agent. P2-Ni swells in organic solvents, displays activity comparable to that of P1-Ni, and is readily recovered via centrifugal separation and used in six catalytic cycles with minimal loss of activity. This work demonstrates the ability of polymer supports to enhance the activities of organic photosensitizers in photocatalytic organic transformations by facilitating electron, energy, and/or radical transfers.