Experimental and computational evidence for the participation of nonclassical dihydrogen species in proton transfer processes on Ru-Arene complexes with uncoordinated N centers. Efficient catalytic deuterium labeling of H2 with CD3OD

Article abstract of DOI:10.1021/om300015j

The protonation with Bronsted acids HB (HBF₄ and CF ₃CO₂H) of [RuH₂(arene)(PPh₂Het)] derivatives (PPh₂Het = dpim, Het = 2-N-methylimidazolyl; PPh ₂Het = PPh₂py, Het = 2-pyridyl) that contain uncoordinated N atoms has been analyzed experimentally by NMR spectroscopy and through computational studies. Initially, at low temperature, the uncoordinated N atoms of the phosphine are protonated and a proton-hydride exchange is observed by ¹H NMR spectroscopy. The proton transfer leads to the corresponding cationic trihydride intermediates, which exhibit a dual character of classical and nonclassical hydrides, with the nonclassical species being more stable, especially when Het = 2-pyridyl. In fact, the release of H₂ and the formation of the respective monohydride complexes [RuH(arene) (κ²-N,P-PPh₂Het)]B was observed at room temperature. The participation of the uncoordinated N center in the proton transfer process in the stabilization of RuH(H₂)⁺ with respect to RuH ₃⁺ species and in the hydride-dihydrogen exchange (cis effect) are discussed. Calculations on the complex [RuH₃(p-cymene) (PPh₃)]⁺ have also been carried out for the sake of comparison. A dual character was also found, but in this case the classical species is more stable. H/D exchange of the hydride ligands of the dihydride complexes, using CD₃OD as the deuterium source, has been studied. The very rapid deuterium labeling of H₂, catalyzed by the aforementioned dihydrides, has been observed. The known compound [RuH₂(p-cymene) (PPh₃)] is also active in this labeling process, and the possible mechanism for both the H/D exchange and the deuterium labeling of H₂ is discussed in light of theoretical studies.