(40g) Viral-Templated Palladium Nanocatalysts for Suzuki Coupling Reaction

Viruses have gained substantial attention recently as nanoscale templates for functional nanomaterial synthesis.  Suzuki reaction plays an important role in synthesis of value-added compounds. We demonstrate and thoroughly examine tobacco mosaic virus (TMV)-templated palladium (Pd) nanocatalysts for the ligand-free Suzuki coupling reaction under mild conditions. The surface-assembled TMV templates allow for facile catalyst synthesis under mild aqueous conditions that leads to high Pd surface loading and stability. Further, the chip-based format enables simple catalyst separation and reuse as well as facile product recovery. We found that the solvent ratio played an important role in the Suzuki reaction selectivity; a higher water/acetonitrile ratio significantly facilitated the desired cross-coupling pathway.  AFM, GISXAS and XPS results showed minimal particle size change and stability along with the overall stability of Pd-TMV complexes in the catalytic reaction conditions employed. The majority of reaction products were formed within the first 5 h at 50ºC, with “apparent” reaction rate of 0.0165 mol/(min·g) based on the amount of Pd employed for each batch reaction.  Preliminary reaction mechanism studies suggest that the Suzuki reactions may be catalyzed largely by trace amounts of Pd species (1–90 ppb) in the reaction solution enlisted in our study.  The TMV-templated Pd nanoparticles are thus considered as “pre-catalysts” of the catalytically active Pd species in the reaction solution. We envision that our viral template-based bottom-up assembly approach can be readily extended to other biotemplates, metal catalysts and organic reaction systems.