Rhodium(I) complexes containing 9,10-phenanthrenequinone-N-substituted thiosemicarbazone ligands: Synthesis, structure, DFT study and catalytic diastereoselective nitroaldol reaction studies

Abstract

New rhodium(I) complexes [Rh(CO)(L)] (1–3) were prepared by the reaction of [RhCl(CO)(PPh3)2] with 9,10-phenanthrenequinone-N-substituted thiosemicarbazones (HL1-3) and characterized by elemental and spectral analyses (IR, UV–Vis, 1H and 13C NMR, ESI-Mass). The structure of the complex, [Rh(CO)(L1)] (1) has been established by single-crystal X-ray diffraction analysis. The structure has also been optimized by DFT method using LANL2DZ basis set. The synthesized complexes used as catalysts for the diastereoselective nitroaldol reaction of benzaldehyde with nitroethane in presence of ionic liquid at room temperature. The optimized catalyst 2 was found efficient in the asymmetric Henry reaction between various aromatic aldehydes and nitroalkane. The reusability of the catalyst was checked up to five catalytic runs. The result shows marginal loss in yield and the product retains the diastereoselectivity. It is believed that this procedure provides an opportunity for facilely synthesize of large amounts of diastereomerically enriched β-nitroalcohol.