Turning Teflon-coated magnetic stirring bars to catalyst systems with metal nanoparticle trace deposits – A caveat and a chance

[Display omitted] ► Metal nanoparticles can be deposited on a polytetrafluorethylene (PTFE) surface. ► Such a PTFE surface can be a Teflon-coated magnetic stirring bar. ► Trace metal nanoparticle deposits turn a stirring bar into a re-usable catalyst system. ► Traces of Rh-nanoparticles on a stirring bar are active hydrogenation catalysts. ► Stirring bars can turn into re-usable and easily handable catalyst systems. It could be an unintentional effect to deposit metal nanoparticles on a simple Teflon-coated magnetic stirring bar. Rhodium nanoparticles, as an example, were reproducibly deposited onto a standard, commercial Teflon-coated magnetic stirring bar by easy and rapid microwave-assisted decomposition of the metal carbonyl precursor Rh6(CO)16 in the ionic liquid 1-n-butyl-3-methyl-imidazolium tetrafluoroborate. Such metal nanoparticle deposits are not easy to remove from the Teflon surface by simple washing procedures and present active catalysts which one is not necessarily aware of. Barely visible metal-nanoparticle deposits on a stirring bar can act as trace metal impurities in catalytic reactions. As a proof-of-principle the rhodium-nanoparticle deposits of 32μg or less Rh metal on a 20mm×6mm magnetic stirring bar were shown to catalyze the hydrogenation reaction of neat cyclohexene or benzene to cyclohexane with quantitative conversion. Rhodium-nanoparticle-coated stirring bars were easily handable, separable and re-usable catalyst system for the heterogeneous hydrogenation with quantitative conversion and very high turnover frequencies of up to 32,800mol cyclohexene×(molRh)−1×h−1 under organic-solvent-free conditions.