Enantioselective Immobilization of Nonprecious Metal Complexes on Chiral Covalent Organic Frameworks for Improved Single‐Site Photocatalytic Hydrogen Evolution

The noncovalent assembly of molecular catalysts into photocatalytic systems represents a pivotal strategy for exploring single-site heterogenous catalysts, excluding the need for elaborate functionalization design. However, the reliance on weak noncovalent interactions (e.g., van der Waals forces) often leads to inefficient outer-sphere electron transfer and inferior structural stability. Herein, we report the enantioselective immobilization of cobalt-based molecular catalysts with chiral tetradentate ligands onto the surface of a β-ketoenamine-linked chiral covalent organic framework (COF) synthesized through chirality induction. The enantiomeric assembly enables axial coordination between the molecular catalysts and the chiral COF, accompanied by enamine-to-imine tautomerization. Leveraging efficient inner-sphere electron transfer, the resulting composite exhibits a significantly enhanced H₂ evolution rate (5.70 mmol g^-1 h^-1) and sustained performance without the use of precious metals. The enantiomeric assembly strategy on a COF platform demonstrates a viable approach to improve both the stability and activity of molecular catalysts, thereby expanding the design paradigm of single-site photocatalysts.