Efficient and Selective Methane Borylation Through Pore Size Tuning of Hybrid Porous Organic-Polymer-Based Iridium Catalysts.

Abstract

As a new energy source that could replace petroleum, the global reserves of methane hydrate (combustible ice) are estimated to be approximately 20 000 trillion cubic meters. A large amount of methane hydrate has been found under the seabed, but the transportation and storage of methane gas far from coastlines are technically unfeasible and expensive. The direct conversion of methane into value-added chemicals and liquid fuels is highly desirable but remains challenging. Herein, we prepare a series of iridium complexes based on porous polycarbazoles with high specific areas and good thermochemical stabilities. Through structure tuning we optimized their catalytic activities for the selective monoborylation of methane. One of these catalysts (CAL-3-Ir) can produce methyl boronic acid pinacol ester (CH3 Bpin) in 29 % yield in 9 h with a turnover frequency (TOF) of approximately 14 h-1 . Because its pore sizes favor monoborylated products, it has a high chemoselectivity for monoborylation (CH3 Bpin:CH2 (Bpin)2 =16:1).