Isotopic H/D exchange via C–H activation is an attractive methodology for the synthesis of deuterium-labeled compounds. Labeled compounds are of great interest for several areas, ca. they are employed in the pharmaceutical industry to enhance the pharmacokinetic properties of some drugs, as metabolic tracers or as mass spectrometry standards. In addition, they can be used as markers for mechanistic studies in organic and organometallic chemistry. Ligand stabilized ruthenium nanoparticles have shown to be highly selective catalysts in the deuteration of aza coumpounds in organic and aqueous phases under mild conditions. Thus, we wanted to explore their reactivity toward deuteration of alkanes that bind very weakly to the Ru surface. To this end we used ruthenium nanoparticles stabilized by bis(diphenylphosphino)butane (dppb). In the present work, we have observed a surprisingly larger reactivity of cyclopentane as compared to cyclohexane and other alkanes. DFT calculations using a ligand-free Ru13H17 model cluster as catalyst indicate an oxidative C-H cleavage of the bound substrates as the rate-limiting reaction step. They also indicate similar binding and activation enthalpies for the reactions with cyclopentane and cyclohexane. This means that the liganded Ru-surface exhibits a specific recognition for cyclopentane whose origin is not yet understood, but must arise from a complex interplay of various intra- and intermolecular surface-substrate interactions.

Surprising differences of alkane C-H activation catalyzed by ruthenium nanoparticles

2019 Spring National Meeting

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