Surprising Differences of Alkane C‐H Activation Catalyzed by Ruthenium Nanoparticles: Complex Surface‐Substrate Recognition?

Abstract

The activation of CÀH bonds of alkanes remains a major challenge for chemistry. In a series of deuteration experiments with D 2 in contact with bis-(diphenylphosphino) butane (dppb) stabilized ruthenium nanoparticles (liquid substrates, 60 8C, 6 bar D 2 ) we have observed a surprisingly large reactivity of cyclopentane as compared to cyclohexane and other alkanes. DFT calculations using a ligand-free Ru 13 H 17 model cluster as catalyst indicate oxidative CÀH cleavage of the bound substrates as rate limiting reaction step. They also indicate similar binding and activation enthalpies of reactions of cyclopentane and cyclohexane.

Reactions of D2 with 1,4‐Bis(diphenylphosphino) butane‐Stabilized Metal Nanoparticles‐A Combined Gas‐phase NMR, GC‐MS and Solid‐state NMR Study

“…Similar results are also observed for the fraction of butane (Figure ). This observation is in excellent agreement with the deuteration of alkanes on Ru/dppb MNPs as demonstrated in our previous work …”

“…Together with the results from our former paper on alkane deuteration a variety of side reactions can be identified as illustrated in Figure . The reaction steps A1 and A2 describe the C−P bond cleavage catalyzed by the particle that leads to the formation of benzene and butane.…”

“…While the isotopomers from d 0 ‐d 6 can be formed by hydrogenation/deuteration of the aromatic ring, for the isotopomers from d 7 ‐d 12 in case of cyclohexane and d 7 ‐d 14 in case of methylcyclohexane, a C−H bond activation on the surface of the Ru/dppb NPs is required. Note: The reactions were performed according to our previous work with 6 bar D 2 gas at 60 °C. 3 batch cycles, each taking 24 h were carried out.…”

Chemoselective H/D exchange catalyzed by nickel nanoparticles stabilized by N-heterocyclic carbene ligands

“…24,25 The combination of these reactivities may render the NPs active catalysts for H/D exchange, which in turn can serve as a good model reaction to understand the surface reactivity and selectivity of the MNPs. 26 For instance, our research groups have already shown that Ru NPs can efficiently catalyze C-H activation reactions leading to selective deuterium incorporation into several nitrogen-containing compounds such as pyridines, indoles, alkylamines, etc. 27,28 Later on, it was shown that Ru and RuPt NPs are good catalysts for the enantiospecific deuteration of peptides at the α position of nitrogen atoms.…”

“…27,28 Later on, it was shown that Ru and RuPt NPs are good catalysts for the enantiospecific deuteration of peptides at the α position of nitrogen atoms. [24][25][26][27][28][29] However, a typical limitation of Ru-based NPs in H/D exchange reactions is their high reactivity towards aromatic rings, leading, in some cases, to the formation of considerable amounts of undesired reduced side-products. 30,31 In this respect, Ni NPs, less prone to hydrogenate aromatic rings, can appear as a more earth-abundant and less-costly alternative to Ru NPs for H/D exchange reactions.…”