Asymmetric hydrogenation using a covalently immobilized Ru-BINOL-AP@MSNs catalyst

Abstract

The present work describes an unprecedented blueprint for the chiral (S)-1,1′-Bi-2-naphthol ligand (BINOL) immobilized on amine functionalized mesoporous silica nanoparticles (MSNs) via a linker, which is then converted into a ruthenium complex, i.e., Ru-BINOL-AP@MSNs (where AP = (3-aminopropyl)trimethoxysilane), without the use of deprotecting or protecting groups. Using a variety of techniques, such as FTIR, N₂ adsorption–desorption isotherms, solid-state ¹³C CP MAS NMR, powder XRD, FESEM, HRTEM, XPS, and thermogravimetric analysis, the as-synthesized catalyst was persuasively verified. Asymmetric transformations of enantiomerically enriched chiral alcohols can be achieved with the aforesaid active catalytic precursors, making the proposed method even more appealing. During the asymmetric hydrogenation reaction, the Ru-BINOL-AP@MSNs catalyst proved to be catalytically competent, leading to an 84% conversion with an enantioselectivity >90% of the R-isomer. Furthermore, the synthesized catalyst was capable of being recycled five consecutive times with only a minute loss of its effectiveness, thereby reducing solvent waste and precious metal or ligand losses.