Issue 18, 2020

Half-sandwich (η5-Cp*)Rh(iii) complexes of pyrazolated organo-sulfur/selenium/tellurium ligands: efficient catalysts for base/solvent free C–N coupling of chloroarenes under aerobic conditions

Abstract

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 ligands (L1–L3) and [(η5-C5Me5)RhCl]2 in methanol. The complexes were fully characterised by various spectroscopic techniques, and the molecular structures of complexes 1 and2 were also established through single crystal X-ray crystallographic analysis, which indicates a pseudo-octahedral half-sandwich piano-stool geometry around the rhodium metal. All three complexes were found to be thermally stable and insensitive towards 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. 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 the telluro-ether functionalised complex (3). In contrast to the previously reported C–N coupling reactions the present reaction works under solvent- and base-free conditions, and the coupling reaction is accomplished in just 6 h with a high yield of the coupling product. The present methodology was also found to be efficient for a 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.

Graphical abstract: Half-sandwich (η5-Cp*)Rh(iii) complexes of pyrazolated organo-sulfur/selenium/tellurium ligands: efficient catalysts for base/solvent free C–N coupling of chloroarenes under aerobic conditions

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Supplementary files

Article information

Article type
Paper
Submitted
13 Mar 2020
Accepted
21 Apr 2020
First published
21 Apr 2020

Org. Biomol. Chem., 2020,18, 3599-3606

Half-sandwich (η5-Cp*)Rh(III) complexes of pyrazolated organo-sulfur/selenium/tellurium ligands: efficient catalysts for base/solvent free C–N coupling of chloroarenes under aerobic conditions

C. Sharma, A. K. Srivastava, K. N. Sharma and R. K. Joshi, Org. Biomol. Chem., 2020, 18, 3599 DOI: 10.1039/D0OB00538J

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