of isolation from reactants and product mixtures. Despite these advantages, developing heterogeneous catalysts de novo is challenging as mechanistic features of a catalytic process are much more difficult to study in the solid state. By contrast, homogeneous catalytic process are easier to study and optimize based on mechanistic insights but are inherently less amenable to facile catalyst recovery and reuse. Ideally, one could transfer well-defined homogeneous catalytic systems directly to solid supports in a modular and robust way without diminishing catalyst activity and/or selectivity. Fig. . a, Previous methods to immobilize traditionally homogeneous catalysts have involved the use of polymer networks, or metal-organic frameworks (MOFs). However, these approaches typical result in a trade-off between catalytic activity, and desirable materials properties. b, The polyMOC catalyst-containing network (polyCAT) uses the templated assembly of metal organic cages (MOCs) to allow tunable and predictable catalyst environments regardless of catalyst identity. The polymer strands linking the MOCs dictate the physical and mechanical properties of the material, and can be changed without altering the catalyst environment.