Poly(2-oxazoline)s functionalized with palladium carbene complexes:: Soluble, amphiphilic polymer supports for C-C coupling reactions in water

This paper describes the synthesis and characterization of a new class of amphiphilic, water-soluble diblock copolymers based on 2-oxazoline derivatives with pendent N-heterocyclic carbene/palladium. catalysts in the hydrophobic block. The synthetic strategy involves a four-step synthesis of three functionalized monomers, each composed of a bis(imidazoline-2-ylidene)palladium(II) diiodide derivative that is covalently linked to a 2-oxazoline monomer via a flexible alkyl spacer (alkyl = butyl, hexyl, octyl). The structure of the monomers was analyzed by H-1 and C-13 NMR spectroscopy, MALDI-TOF, and elemental analysis. Three diblock copolymers P1-P3 with the monomers being part of the hydrophobic block were prepared by living cationic ring-opening polymerization. The structure and composition of the polymers was characterized by H-1 and C-13 NMR spectroscopy as well as GPC measurements and indicated rather low PDI of 1.3 and about 65% incorporation of the N-heterocyclic carbene/palladium-functionalized monomer into the polymer. Dynamic light scattering measurements of the polymers P1-P3 in water revealed aggregate formation with a hydrodynamic radius of 10-30 nm with high polydispersity as visualized by TEM micrographs. Subsequently, polymers P1-P3 were successfully utilized as a polymeric support for the Heck coupling of iodobenzene with styrene as a model reaction in water, showing high activities with turnover frequencies (TOF) up to 570 h(-1) at 90 degreesC.