A noble-metal-free metal-organic framework for alkane borylation

Abstract

Catalytic borylation of unactivated C(sp3)‒H bond is of great interest but quite challenging. Reported catalysts mostly contain noble metals such as iridium and ruthenium. Here, we report an earth-abundant zirconium-based metal-organic framework (MOF) catalyst with zirconium hydride (Zr‒H) active sites for methane borylation. Isotope exchange experiment and spectroscopic evidence confirm methane activation by Zr‒H active sites to generate Zr‒CH3 and H2, possibly via σ-bond metathesis. Theoretical calculations suggest another σ-bond metathesis step for C‒B bond formation. The MOF catalyst selectively borylates end methyl group in alkanes and other compounds. For example, the MOF catalyst mono-borylated the end methyl group of n-pentane in 87% yield with > 98% selectivity. The selectivity of primary C‒H bond over secondary C‒H bond is attributed to the steric effect around the Zr‒H site in the MOF, as Zr‒H sites on supports with less stringent steric control have poorer selectivity. This work provides new insights into developing catalysts for alkane functionalization.