Molecular Co-Catalyst Confined within a Metallacage for Enhanced Photocatalytic CO₂ Reduction

The construction of structurally well-defined supramolecular hosts to accommodate catalytically active species within a cavity is a promising way to address catalyst deactivation. The resulting supramolecular catalysts can significantly improve the utilization of catalytic sites, thereby achieving a highly efficient chemical conversion. In this study, the Co-metalated phthalocyanine (Pc-Co) was successfully confined within a tetragonal prismatic metallacage, leading to the formation of a distinctive type of supramolecular photocatalyst (Pc-Co@Cage). The host-guest architecture of Pc-Co@Cage was unambiguously elucidated by single-crystal X-ray diffraction (SCXRD), NMR, and ESI-TOF-MS, revealing that the single cobalt active site can be thoroughly isolated within the space-restricted microenvironment. In addition, we found that Pc-Co@Cage can serve as a homogeneous supramolecular photocatalyst that displays high CO₂ to CO conversion in aqueous media under visible light irradiation. This supramolecular photocatalyst exhibits an obvious improvement in activity (TON_CO = 4175) and selectivity (Sel_CO = 92%) relative to the nonconfined Pc-Co catalyst (TON_CO = 500, Sel_CO = 54%). The present strategy provided a rare example for the construction of a highly active, selective, and stable photocatalyst for CO₂ reduction through a cavity-confined molecular catalyst within a discrete metallacage.