Heterogenized molecular Pd(ii) catalyst on ultrathin 2D metal–organic frameworks with nanoflower-like morphology for isonitrile-involved cyclization reaction

Abstract

Heterogeneous Pd(II) catalysts with high efficiency, high Pd atom utilization, high stability and easy recyclability are always a pursuit in the field of green organic synthesis chemistry. Herein, a two-dimensional (2D) metal–organic framework (MOF) based Pd(II) catalyst Zr-BTB-Bpy-Pd is synthesized through continuous three-step coordination assembly strategy. A variety of structural characterization techniques establish Zr-BTB-Bpy-Pd as a nanoflower structure with ultrathin 2D nanoplate petals (3.9 nm), which provides fully exposed single-site Pd(II) active sites and a similar homogeneous reaction space. Consequently, Zr-BTB-Bpy-Pd exhibits excellent activity for the cyclization reactions of isonitriles with N-acyl-o-alkynylanilines, far exceeding the three-dimensional (3D) MOF based Pd(II) catalyst Pd-UiO-67-Bpy and homogeneous Pd(OAc)₂, with turnover frequency (TOF) values being 2.3 and 864 times higher, respectively. The Zr-BTB-Bpy-Pd catalyst could be used for the gram-scale synthesis of 2-aminoquinoline derivatives in up to 90% yield with a TOF of 1900 and in five consecutive reaction cycles without significant loss of activity.