Pd-nanoparticles stabilized by bipyridine-functionlized poly(lactic acid) as catalyst for alkyne hydrogenation

The selective carbon-carbon triple bond hydrogenation has been primarily carried out over powdered catalysts based on monometallic Pd. In this context, Pd-nanoparticles (NPs) showed the highest alkene selectivity, which was related to the distinct alkyne/alkene adsorption energies [1]. Since polymer ligands are of great use in the preparation and stabilization of Pd-NPs, we synthesized well-defined Pd-NPs anchored on the stereocomplex of functionalized poly(lactic acid) (PLA) by a synthesis protocol which comprised: (a) the synthesis of 4,4'-(dihydroxymethyl)-2,2'-bipyridine-functionalized L- and D-PLA (i.e. LL and LD); (b) the stereocomplex formation between LL and LD [2]; (c) the successive reaction of the resulting stereocomplex with Pd(OAc)2 (OAc = acetate) and Pd reduction in dichloromethane by means of dihydrogen. The obtained supported Pd-NPs (i.e. Pd@[LL/LD] were used as heterogeneous catalyst for the hydrogenation of selected alkynes. [1] D. Mei, P.A. Sheth, M. Neurock, C.M. Smith, J. Catal. 2006, 242, 1. [2] D. Sawai, Y. Tsugane, M. Tamada, T. Kanamoto, M. Sungil, S. Hyon, J. Polym. Sci. Part B: Polym. Phys. 2007, 45, 2632.