CO and H2 gas-free efficient reductive carbonylation of aryl iodides. Use of smart recyclable metal-based catalysts

In this paper, we studied an efficient protocol of reductive carbonylation of two aryl iodides, namely 2-iodo-5-ethylthiofene and 5-iodobenzo[d][1,3] dioxole, employing formic acid, propylphosphonic anhydride (T3P) and a base, to afford aldehydes used as such as industrial flavors/fragrances or as key intermediates for some APIs and other fragrances. Our approach, comparing to the previously described protocol [1], not only avoids the use of unsafe reagents and/or solvents but, noteworthy, uses easily prepared heterogeneous catalysts with a low content of metal(s), such as 0.3 % Pd/Al2O3, (0.18 % Pd, 0.44 % Cu)/Al2O3 and 1 % Cu/Al2O3. These catalysts, as well as commercial Pd/C species tested here for a comparison, are also recyclable and have been characterized before and after use by FE-SEM, EDS and TEM spectroscopy. Noteworthy, both the bimetallic system Pd-Cu/Al2O3, containing a very low amount of expensive palladium (0.18 %) and Cu/Al2O3, containing no palladium at all, showed very high activities.