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

Abstract

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 CuI, 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 CuI, 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.