Optically active amphiphilic hyperbranched polyglycerols as templates for palladium nanoparticles

We report a systematic study on the encapsulation of palladium nanoparticles in optically active amphiphilic hyperbranched polyglycerols with different optical signs and different degrees of polymerization, namely (-)-P(G(40)C16(0.5)) I and (+)-P(G(73)C16(0.5)) 2. Several issues have been addressed here: (a) relatively wide size distributions (1-5 nm) of palladium nanoparticles have been achieved, (b) a remarkable template effect (1, DPn = 40, 1.2 +/- 0.1 nm; 2, DPn, = 73, 2.3 +/- 0.1 nm average particle size) has been observed using TEM technique, as shown by the particle size dependent on the degree of polymerization of the polymers, (c) NaBH4 is found to be a convenient reducing agent to produce small particle size compared with gaseous hydrogen, (d) catalytic Heck reaction of 2,3-dihydrofuran and aryl triflate has been tested successfully without enantiocontrol. (c) 2005 Elsevier B.V. All rights reserved.