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 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.