Amidation of aldehydes using mono-cationic half-sandwich rhodium(III) complexes with functionalized phenylhydrazone ligands

Article abstract of DOI:10.1016/j.jorganchem.2019.02.018

A series of mono-cationic half-sandwich rhodium(III) complexes have been synthesized in methanol using phenylhydrazone-derived ligands (L₁–L₆) and the starting precursor [(η⁵-C₅Me₅)₂Rh₂(μ-Cl)₂Cl₂] in a 2:1 molar ratio. The N,N′-phenylhydrazone complexes have been isolated as tetraphenylborate salts. All complexes were characterized by elemental analysis, FT-IR, UV–visible, NMR spectroscopy and mass spectrometry. The molecular structure of complex [(η⁵-C₅Me₅)Rh(L₁)Cl](BPh₄) (1) was confirmed by single-crystal X-ray structure analysis. Complex [(η⁵-C₅Me₅)Rh(L₃)Cl](BPh₄) (3) was used as an efficient catalyst for the amide formation reaction, with up to 99% conversion after 2 h in toluene at 110 °C in the presence of hydroxyl amine hydrochloride and sodium bicarbonate.