Reversible Metalation and Catalysis with a Scorpionate-like Metallo-ligand in a Metal-Organic Framework

The installation of metallo-ligands in metal-organic frameworks (MOFs) is an effective means to create site-isolated metal centers toward single-site heterogeneous catalysis. Although trispyrazolyborate (Tp) and tripyrazolylmethane (Tpm) form one of the most iconic classes of homogeneous catalysts, neither has been used as a metallo-ligand for the generation of MOFs thus far. Here, we show that upon in situ metalation with Cu^I, a tricarboxylated Tpm ligand reacts with ZrOCl₂ to generate a new MOF exhibiting neutral scorpionate-like chelating sites. These sites undergo for facile demetalation and remetalation with retention of crystallinity and porosity. When remetalated with Cu^I, the MOF exhibits spectroscopic features and catalytic activity for olefin cyclopropanation reactions that are similar to the molecular [Cu(CH₃CN)Tpm*]PF₆ complex (Tpm* = tris(3,5-dimethylpyrazolyl)methane). These results demonstrate the inclusion of Tp or Tpm metallo-ligands in a MOF for the first time and provide a blueprint for immobilizing Tpm* catalysts in a spatially isolated and well-defined environment.