An interchangeable homogeneous ⇔ heterogeneous catalyst system for furfural upgrading

Abstract

Intercalation of benzimidazolium cations [BI]⁺ into the nanogalleries of Na⁺/montmorillonite (MMT) clay leads to generation of recyclable supported precatalysts [BI]⁺/MMT, which, upon treatment with a base, catalyze furfural self-condensation coupling reaction into furoin in almost constant yields of >96% over the three cycles investigated. This catalyst system combines the best features of both homogeneous and heterogeneous catalyst systems, as it performs the homogeneous molecular catalysis by the discharged N-heterocyclic carbene catalyst in solution and then recovers the catalyst through in situ heterogenization after the reaction via re-intercalation of the charged precatalyst. The [^12,12BI]⁺/MMT catalyst system carrying two long-chain C₁₂ dodecyl substituents on the [BI] nitrogen atoms is particularly effective for achieving both high product yield and catalyst recyclability.