Metal–Organic\nFramework Stabilizes a Low-Coordinate\nIridium Complex for Catalytic Methane Borylation

Abstract

Catalytic\nborylation has recently been suggested as a potential\nstrategy to convert abundant methane to fine chemicals. However, synthetic\nutility of methane borylation necessitates significant improvement\nof catalytic activities over original phenanthroline- and diphosphine-Ir\ncomplexes. Herein, we report the use of metal–organic frameworks\n(MOFs) to stabilize low-coordinate Ir complexes for highly active\nmethane borylation to afford the monoborylated product. The mono­(phosphine)-Ir\nbased MOF, <b>Zr-P1-Ir</b>, significantly outperformed other\nIr catalysts in methane borylation to afford CH₃Bpin with\na turnover number of 127 at 110 °C. Density functional theory\ncalculations indicated a significant reduction of activation barrier\nfor the rate limiting oxidative addition of methane to the four-coordinate\n(<b>P1</b>)­Ir^III(Bpin)₃ catalyst to form\nthe six-coordinate (<b>P1</b>)­Ir^V(Bpin)₃(CH₃)­(H) intermediate, thus avoiding the formation of\nsterically encumbered seven-coordinate Ir^V intermediates\nas found in other Ir catalysts based on chelating phenanthroline,\nbipyridine, and diphosphine ligands. MOF thus stabilizes the homogeneously\ninaccessible, low-coordinate (<b>P1</b>)­Ir­(boryl)₃ catalyst to provide a unique strategy to significantly lower the\nactivation barrier for methane borylation. This MOF-based catalyst\ndesign holds promise in addressing challenging catalytic reactions\ninvolving highly inert substrates.