Half-sandwich (η5-Cp*)Rh(III) complexes of pyrazolated organo-sulfur/selenium/tellurium ligands: Eff

Org. Biomol. Chem. 2020, 18, 3599.

Three new pyrazolated chalcogenoether ligated Rh(III) half-sandwich complexes (1-3) were synthesised by the thermal reaction of chalcogenoether (S, Se and Te) substituted 1H-pyrazole ligand (L1-L3) and [(η5-C5Me5)RhCl]2 in methanol. The complexes were fully characterised by various spectroscopic techniques, and the molecular structures of the complex (1-2) were also established through the single crystal X-ray crystallographic analysis, which indicates a pseudo-octahedral half sandwich piano-stool geometry around rhodium metal. All three complexes were found thermally stable and insensitive towards the air and moisture. One mol% of Rh(III) complexes (1-3) along with 10 mol% of Cu(OAc)2 were explored for the Buchwald-Hartwig type C−N coupling reactions of amine and aryl chloride. The good to excellent yields (89-92%) of the coupling products were obtained with seleno- and thio-ether functionalised pyrazolated Rh(III) complexes (1 and 2), while an average yield (39%) was obtained with telluro-ether functionalised complex (3). In contrast to the previously reported C−N coupling reactions the presented reaction works under a solvent and base free conditions, and the coupling reaction accomplished in just 6 h with high yield of coupling product. The present methodology was also found to be efficient for the wide variety of functionalised aryl halides, and aliphatic or aromatic amines (1° and 2°). Moreover, the reaction also enables the C−N coupling of electron-withdrawing substrates and base sensitive functionalities.