Synthesis and Characterization of Chiral Iridium Complexes Bearing Carbohydrate Functionalized Pyridincarboxamide Ligands and Their Application as Catalysts in the Asymmetric Transfer Hydrogenation of α-Ketoacids in Water

[Cp*IrLnCl] complexes [L1 = (methyl-β-d-glucopyranosid-2-yl)picolinamide, 1; L2 (methyl-3,4,6-tri-O-acetyl-β-d-glucopyranosid-2-yl)picolinamide, 2; L3 (2,3,4,6-tetra-O-acetyl-β-d-glucopyranosid-1-yl)picolinamide, 3] have been synthesized and completely characterized in solution, by 1D- 2D-NMR spectroscopy, the solid state, X-ray single crystal diffractometry. Despite chirality of Ln-moiety metal, a diastereoisomer is observed for L1 (1) (2) having (R)-iridium configuration: pyranose moiety oriented way to minimize interactions axial protons, vicinal amide moiety, Cp*, with OMe-group pointing toward Cp*-ligand away from Ir–Cl. Such also favored establishment an O–H···Cl–Ir hydrogen bond (2.356 Å) minimization steric repulsion between one acetyl Cp* picolinamide ligands 1 2, respectively. DFT calculations computed stabilization more than 5.9 3.1 kcal/mol this respect other possible ones. Two interconverting diastereoisomers different at iridium are instead solution complex 3 which −CH2OAc [3a, 63%, (R)] −OAc [3b, 37%, (S)] moieties, respectively, N-arm ligands. Consistently, indicate that 3a 3b comparable stability (ΔE 1.2 kcal/mol). Complexes 1–3 catalyze asymmetric transfer hydrogenation RC(O)C(O)OH RCH(OH)C(O)OH [R Ph (PGA), CH2Ph (PPA), CH2(4-OH)C6H4 (HPPA)], using both HCOOH H3PO3 as donor, water pH 7 (by phosphate buffer), excellent chemoselectivity efficiency (conversion >99%) moderate good enantioselectivity (30–70% ee). Utilizing catalyst bearing pseudoenantiomeric ligand, causes reduction percentage major enantiomer (R) PGA inversion stereoselectivity (S) PPA HPPA substrates.