C-H activation on platinum, a mechanistic study

C-H activation on heterogeneous Pt catalysts is found to be most facile at low Pt dispersion and surface structure insensitive at dispersions above 10%. Two distinct processes have been identified which lead to the formation of mono- and polydeuterated products, respectively. The ratio of mono-/polydeuteration processes increases with increasing disper ion. Evidence is provided for the formation of π-intermediates as the initiator of polydeuteration. The most facile mechanism of exchange propagation in a single molecule is through a π-allyl-type interconversion. The deuterium in monodeuterated n-hexane is located at the terminal position by high-resolution deuterium NMR. NMR spectroscopy also provides evidence for steric effects which prevent significant H/D exchange at positions close to quaternary centers. C-H activation appears to be sensitive to steric hindrance, the C-H bond energy, and the partial pressure of the substrate.