Modular Synthesis of Templated Bimetallic Sites in Metal–Organic Framework Pores

Abstract

Binuclear metal active sites are found throughout all subfields of catalysis, from homogeneous and heterogeneous systems to enzymes. Here, we report a synthetic route to install well-defined bimetallic sites in metal–organic frameworks that offer independent control over the ligand environment, metal identity, metal–metal distance, and pore environment. Our approach uses thermolabile tertiary carbamate cross-linkers to template pairs of amine functional groups within framework pores. The templated amine pairs can be quantitatively converted into diverse chelating sites, such as iminopyridine and bis(2-pyridylmethyl)amine ligands, and metalated with a variety of metal cations [M = Mn(II), Fe(II), Co(II), Ni(II), Cu(I), and Cu(II)]. A combination of density functional theory, extended X-ray absorption fine structure spectroscopy, and electron paramagnetic resonance spectroscopy is used to confirm the local coordination environment and support the proximal nature of the templated bimetallic sites. The templating strategy described here will enable the exploration of new bimetallic motifs in heterogeneous catalysis.