Tuning the electronic states of Pd(II) defect-engineered metal-organic framework catalysts for efficient conversion of isocyanides

Recently, defective sites in MOFs have become an important tool for tuning the catalytic performance of MOFs. Herein, we report a heterogeneous catalyst "Pd-UiO-67(N)_x" by utilizing the active site of defective MOF to modulate the electronic state of Pd, which demonstrates excellent catalytic performances in the oxidative cyclization reaction of isocyanides with o-aminophenols benefiting from the electron-deficient nature of the Pd species. When the Pd loading in defective Pd-UiO-67(N)_x system was decreased to 0.37 mol %, the catalytic efficiency was significantly enhanced and the Pd turnover number (TON) increased to 232, which was 27 and 2.6 times higher than that of homogeneous Pd catalysts and defect-free Pd-UiO-67(N)₀, respectively. The open pore structure of d-MOFs supports the adsorption of o-aminophenols. Additionally, the domain-limiting effect of the framework restricts the aggregation of Pd, resulting in good stability of the Pd species, which without significant loss of its activity in five consecutive reaction cycles. This work provides an insight into the improvement of stereoelectronic properties of organometallic catalysts through defect-engineered MOFs.