Synergistic Photoredox and High-Spin Cobalt Cluster Dual Heterogeneous Catalysis: Visible-Light-Driven C(sp²)–H Bond Functionalization

We report visible-light-driven C(sp²)-H functionalization of indoles with naphthoquinone using a dual photocatalytic system of Eosin Y and a high-spin cobalt cluster. This one-pot transformation provides efficient access to a variety of pharmaceutically relevant heterocycles from readily available indoles under chemical oxidant-free and environmentally benign conditions. The reaction scope is further extended to the cyclization of aromatic amines, yielding amination products in moderate to good yields. Mechanistic investigations reveal that the formation of 3-indolylquinone proceeds via a single-electron transfer (SET) mechanism, followed by hydrogen atom transfer (HAT), with radical intermediates clearly detected by EPR spectroscopy. Moreover, the cooperative interactions between the cobalt centers enhance the catalytic efficiency, offering advantages over the mononuclear cobalt catalyst. This work introduces a novel approach for selective C-H functionalization through metallaphotoredox catalysis and expands its potential applications in organic synthesis.