MOF-Supported Diphosphine Ligands for Iridium-Catalyzed C–H Borylation of Arenes

Abstract

Postsynthetic methods have been used to immobilize a carboxylate-functionalized diphosphine ligand, N,N-bis[(diphenylphosphino)methyl]glycinate (dppmg), in different metal–organic framework (MOF) supports. H(dppmg) reacts quantitatively with Zn–OH groups in MFU-4l-OH (1) to provide solid-state ligands (1-H-x) with controllable diphosphine loadings. Postsynthetic metalation with [Ir(OMe)(cod)]₂ (cod = 1,5-cyclooctadiene) generates heterogeneous precatalysts (1-Ir-x) that show excellent activity toward C–H borylation of arenes. This activity is dependent on both the catalyst site density and initial concentration of the borylating reagent. Homogeneous catalysts supported by analogous diphosphine ligands exhibit low catalytic activity, demonstrating the beneficial role of catalyst site isolation. Immobilization of dppmg-Ir catalysts at the Zr-based nodes of MOF-808 (2-P-Ir) and NU-1000 (3-P-Ir) results in materials with relatively poor catalytic activity toward C–H borylation of toluene, revealing the importance of the MOF support in catalyst design.