Polymeric Micelles with Chiral Diamine-Ru(II) Catalysts for Asymmetric Transfer Hydrogenation of Ketones in Water

Chiral aromatic alcohols with unique structures have attracted wide attention in asymmetric catalysis for decades. In this study, polymeric micelles with chiral diamine-Ru(II) catalysts in the hydrophobic core for asymmetric transfer hydrogenation of ketones affording chiral aromatic alcohols were presented. Firstly, block copolymers with (1R,2R)-(+)-1,2-diphenyl ethylenediamine (DPEN) in the pendant chain were successfully synthesized by Ring-Opening Metathesis Polymerization (ROMP) using 1,1-dimethyl ethyl N-(2-amino-1,2-diphenylethyl) carbamate (NB-DPEN-Boc) and polyethylene glycol (NB-PEG2000) with norbornene groups as raw materials. The structures of block copolymers P(DPEN)-co-P(PEG2000) were characterized by FT-IR and 1H NMR. Next, Block copolymers with chiral DPEN ligand in the pendant chain coordinate with [RuCl2(p-cymene)]2 to provide amphiphilic polymers with chiral diamine-Ru(II) catalyst. Then, the self-assembly of the amphiphilic polymers in water produced the polymeric micelles with chiral diamine-Ru(II) catalysts in the hydrophobic core. The particle sizes were found to be 65 nm by DLS analysis. The polymeric micelles as catalytic nanoreactors were successfully applied in the asymmetric transfer hydrogenation (ATH) of various ketones in water. The heterogenization of homogeneous catalysts and construction of catalysts for aqueous catalysis demonstrate potential application prospects in the preparation of chiral aromatic alcohols.