An interchangeable homogeneous double left right arrow heterogeneous catalyst system for furfural upgrading

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 [(BI)-B-12,12](+)/MMT catalyst system carrying two long-chain C-12 dodecyl substituents on the [BI] nitrogen atoms is particularly effective for achieving both high product yield and catalyst recyclability.