Self-assembly and chemical reactivity of alkenes on platinum nanoparticles.

Stable platinum nanoparticles were synthesized by the self-assembly of alkene derivatives onto the platinum surface, possibly forming platinum-vinylidene (Pt═C═CH-) or -acetylide (Pt-C≡) interfacial bonds as a result of dehydrogenation and transformation of the olefin moieties catalyzed by platinum. Transmission electron microscopic measurements showed that the nanoparticles were well-dispersed without apparent agglomeration, indicating effective passivation of the nanoparticles by the ligands, and the average core was estimated to be 1.34 ± 0.39 nm. FTIR measurements showed the emergence of a new vibrational band at 2023 cm(-1), which was ascribed to the formation of Pt-H and C≡C from the dehydrogenation of alkene ligands on platinum surfaces. Consistent behaviors were observed in photoluminescence measurements, where the emission profiles were similar to those of alkyne-functionalized Pt nanoparticles that arose from intraparticle charge delocalization between the particle-bound acetylene moieties. Selective reactivity with imine derivatives further confirmed the formation of Pt═C═CH- or Pt-C≡ interfacial linkages, as manifested in NMR and electrochemical measurements. Further structural insights were obtained by X-ray absorption near-edge spectroscopy and extended X-ray absorption fine structure analysis, where the coordinate numbers and bond lengths of the Pt-Pt and Pt-C linkages suggested that the metal-ligand interfacial bonds were in the intermediate between those of Pt-C≡ and Pt-Csp(2).