A Palladium Tetraiodide Supported Catalyst for the Oxidative Carbonylation of β-Amino Alcohols to 2-Oxazolidinones

A novel PdI42--supported catalyst, based on imidazolium-functionalized polyhedral oligomeric silsesquioxanes (POSS) functionalized with imidazolium arms grafted on amorphous silica, is prepared through a straightforward synthetic procedure allowing to accede to high local concentration spots of palladium sites surrounding the POSS core. The hybrid material was fully characterized by thermogravimetric analysis coupled with differential scanning calorimetry (TGA-DSC), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), and X-ray photoelectron spectroscopy (XPS). This material was successfully used as heterogeneous catalyst for the oxidative carbonylation of beta-amino alcohols to 2-oxazolidinones as well as 2-aminopyridin-3-ol to oxazolo[4,5-b]pyridin-2(3H)-one under relatively mild conditions (100 degrees C for 3 h under 40 atm of a 4:1 mixture CO-air) in DME as the solvent and with aerobic oxygen as the simplest external oxidant, with the formation of water as benign coproduct. The catalyst could be successfully recycled up to four times, before beginning to undergo partial deactivation due to palladium reduction, as evidenced by XPS and TEM. ICP-OES analysis of some representative products evidenced a low metal contamination (palladium content <1 ppm), making our approach interesting for applications in the life science field, where a high degree of purity is required.