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

A series of mono-cationic half-sandwich rhodium(III) complexes have been synthesized in methanol using phenylhydrazone-derived ligands (L-1-L-6) and the starting precursor [(eta(5)-C5Me5)(2)Rh-2(mu-Cl)(2)Cl-2] 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, UVevisible, NMR spectroscopy and mass spectrometry. The molecular structure of complex [(eta(5)-C5Me5)Rh(L-1)Cl](BPh4) (1) was confirmed by single-crystal X-ray structure analysis. Complex [(eta(5)-C5Me5)Rh(L-3)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 degrees C in the presence of hydroxyl amine hydrochloride and sodium bicarbonate. (c) 2019 Elsevier B.V. All rights reserved.