PNNL

Abstract

We report the hydrogenation of aromatic groups at room temperature and low hydrogen pressure by [(CAAC)Rh(COD)Cl] (CAAC = cyclic alkyl amino carbene), which was generated from the reaction of free CAAC and [Rh(COD)Cl]2. Facile access to the molecular catalyst precursor, mild reaction conditions, and operational simplicity are notable advantages that allow for kinetic, mechanistic, and spectroscopic studies to elucidate the nature of the catalyst. The cumulative results of these studies, which support the formation of a heterogeneous catalyst from a molecular CAAC-Rh precursor for arene hydrogenation, contrast with that of a previously reported homogeneous CAAC-rhodium catalyst for arene hydrogenation. We determined the site selectivity of this arene hydrogenation system through detailed competition experiments in small molecules bearing aromatic rings of varying electronic and steric influence. With the growing popularity of CAAC ligands in synthetic inorganic chemistry and homogeneous catalysis, this work illustrates the remarkable potential of CAAC ligands in the modification and stabilization of heterogeneous catalysts, in light of the burgeoning interest in organometallic approaches using structurally well-defined precursors for the controlled generation of nanocatalysts.