Palladium macrocomplexes for the aerobic oxidation of alcohols

The homogeneous aerobic alcohol oxidation to ketones or aldehydes catalyzed by palladium(II) complexes bearing nitrogen ligands is of considerable interest since water or hydrogen peroxide are formed as the only side products.[1] Among palladium-based complexes, used for the latter catalytic reactions, Uemura's catalyst (i.e. trans-[Pd(OAc)2(pyridine)2] (OAc = acetate)) has found wide application.[2] Recently we anchored the latter catalyst on P(L)LA (poly(L-lactide)) and used the so obtained macrocomplex in the aerobic alcohol oxidation carried out in toluene. The catalytic system was recyclable provided that n-pentane was used to precipitate the anchored catalyst.[3] In this presentation we show: (i) an improved recyclability of Uemura's catalyst from toluene solution, by exploiting the stereo-complex formation between the iso-tactic segments (i.e. P(L)LA and P(D)LA)) of PLA-based macroligands as shown in Scheme 1; (ii) the application of Uemura's catalyst in water using pyridine-end-capped PEG (poly(ethylene glycol)) as water-soluble macroligand. Scheme 1. Aerobic oxidation catalyzed by PLA- and PEG-based Pd(II) macrocomplexes. References [1] S. S. Stahl Angew. Chem. Int. Ed. 2004, 43, 3400. [2] T. Nishimura, T. Onoue, K. Ohe, S. Uemura J. Org. Chem. 1999, 64, 6750. [3] G. Giachi, M. Frediani, W. Oberhauser, E. Passaglia J. Polym. Sci. Part. A: Polym. Chem. 2012, in press (DOI:10.1002/pola.26039).