Confined Metal Centers in a Symmetric Cage: Mono- and Heterodinuclear Complexes for Photocatalytic Hydrogen Evolution

Abstract

We report a selective metallation strategy that enables the controlled incorporation of one or two distinct metal ions within a chiral and symmetric tris(2-pyridylmethyl)amine (TPMA)-based molecular cage. Unlike typical homoditopic ligands, which often lead to scrambling and statistical mixtures, our approach affords well-defined mononuclear (CoH₄) and heterodinuclear (CoZn, CoCu) complexes in a straightforward and reproducible manner. This represents a rare example of heterometallic cage complexes from a symmetric scaffold, where the stepwise addition of metal ions affords well-defined mono- and dinuclear species. To illustrate the functional relevance of this strategy, we evaluated the photocatalytic hydrogen evolution activity of the different mono- and dinuclear complexes. The results reveal that the mononuclear CoH₄ cage displays the highest performance, which we propose to arise from second-sphere proton transfer facilitated by the non-coordinated TPMA unit. Complementary DFT calculations support this mechanistic hypothesis. Overall, this study demonstrates a reliable strategy to access mono- and heterodinuclear cage complexes and illustrates its utility through a photocatalytic proof-of-concept study.