Chlorosulfonylated polystyrene, a commodity resin, reacts with enantiopure 1,2-diamines to afford, in a single step, high loading catalytic resins involving monosulfonylated 1,2-diamino moieties. These functional polymers form stable (p-cymene)ruthenium chloride [RuCl(p-cymene)] complexes that efficiently catalyze (down to S/C=150) the asymmetric transfer hydrogenation (ATH) of alkyl aryl ketones with formic acid-triethylamine under essentially solvent-free (down to 0.25 mL mmol-1) reaction conditions. Among these resins, the immobilized version of TsDPEN stands out as a most practical catalyst for ATH: Uniformly high enantioselectivities are achieved with its use at low catalyst loading, and the resin can be recycled with virtually no limits.
R. Marcos, C. Jimeno, M. A. Pericàs
Adv. Synth. Catal. 2011, 353, 1345-1352
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