Cationic and macroporous amberlite resins with formate (HCOO−) as the counter anion (ARF) have been used to prepare a new class of heterogeneous Pd/Cu bimetallic composite nanoparticles (NPs) (Pd/Cu–ARF). The physicochemical characteristics of Pd/Cu–ARF were examined with the help of FTIR spectroscopy, X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and atomic absorption spectroscopy (AAS). XRD and TEM showed the existence of composite NPs made of metallic Pd, PdO and CuO. The TEM analysis revealed fairly uniform distributions of composite NPs of average size ∼4.9 nm. The as-synthesized nanocomposite material (Pd/Cu–ARF) exhibited high catalytic activity in the Sonogashira cross-coupling reaction between aryl iodide and terminal alkynes. Heterogeneity of the catalytic activity was evidenced from different tests (hot-filtration and catalyst-poisoning experiments) and the recycling ability of the catalyst was examined for five consecutive runs without any significant loss of activity.
Emission from Regioisomeric Bis(phenylethynyl)benzenes during Pulse Radiolysis
作者:Shingo Samori、Sachiko Tojo、Mamoru Fujitsuka、Torben Ryhding、Aaron G. Fix、Brittany M. Armstrong、Michael M. Haley、Tetsuro Majima
DOI:10.1021/jo900494j
日期:2009.5.15
Emission from charge recombination between radical cations and anions of a series of regioisomeric 1,4-, 1,3-, and 1,2-bis(phenylethynyl)benzenes (bPEBs) substituted by various electron donor and/or acceptor groups was measured during pulse radiolysis in benzene (Bz). The formation of bPEB in the excited singlet state ((1)bPEB*) can be attributed to the charge recombination between bPEB(center dot+) and bPEB(center dot-), which are initially generated from the radiolytic reaction. This mechanism is reasonably explained by the relationship between the annihilation enthalpy change (-Delta H degrees) for the charge recombination of bPEB(center dot+) and bPEB(center dot-) and excitation energy of (1)bPEB*. Since the degree of the pi-conjugation in the S-1 state and HOMO-LUMO levels of bPEB change with the substitution pattern of phenylacetylene groups on the central benzene ring and the various kinds of donor and/or acceptor group, the fine-tuning of the emission color and intensity of bPEB can be easily carried out during pulse radiolysis in Bz. For donor-acceptor-substituted bPEB, it was found that the difference in the charge transfer conjugated pathways between donor and acceptor substituents (linear-, cross-, and "bent"-conjugated pathways) strongly influenced the HOMO-LUMO energy gap.