Rhodium and iridium NHC complexes from chiral NHC precursors: Synthesis, structure, transfer hydrogenation catalysis and method validation

Abstract

Heteroleptic [RhIIICp*(NHC)] and [IrIIICp*(NHC)] complexes bearing a N-amino acid functionality derived from imidazolium salts were synthesized and characterized by NMR, IR, HR-MS, and single-crystal X-ray diffraction. A discussion of the structure of the [RhCp*{κ2(C,O)–NHC}Cl] complex 3f as a pair of diastereomers is presented. Catalysts were assessed for the transfer hydrogenation (TH) of ketones in basic propan-2-ol, obtaining good yields for the reduction products. A chromatographic method applied for measurements of compounds in TH as analytes was validated. The Rh and Ir complexes described here offer an original approach in the development of catalysts based in classic NHC precursors.