One-pot dual catalysis for the hydrogenation of heteroarenes and arenes

A simple dinuclear monohydrido bridged ruthenium complex [{(eta(6)-p-cymene)RuCl}(2)(mu-H-mu-Cl)] acts as an efficient and selective catalyst for the hydrogenation of various heteroarenes and arenes. The nature of the catalytically active species was investigated using a combination of techniques includingin situreaction monitoring, kinetic studies, quantitative poisoning experiments and electron microscopy, evidencing a dual reactivity. The results suggest that the hydrogenation of heteroarenes proceedsviamolecular catalysis. In particular, monitoring the reaction progress by NMR spectroscopy indicates that [{(eta(6)-p-cymene)RuCl}(2)(mu-H-mu-Cl)] is transformed into monomeric ruthenium intermediates, which upon subsequent activation of dihydrogen and hydride transfer accomplish the hydrogenation of heteroarenes under homogeneous conditions. In contrast, carbocyclic aryl motifs are hydrogenatedviaa heterogeneous pathway, byin situgenerated ruthenium nanoparticles. Remarkably, these hydrogenation reactions can be performed using molecular hydrogen under solvent-free conditions or with 1,4-dioxane, and thus give access to a broad range of saturated heterocycles and carbocycles while generating no waste