Tunnel effects in oxidative addition reaction of methane to bare Pd atom

Adding a New Dimension to the Investigation of Platinum-Mediated Arene C−H Activation Reactions Using 2D NMR Exchange Spectroscopy. Dynamics of Pt(II) Phenyl/Benzene Site Exchange

“…The kinetic data in Table lead to A D / A H = 12.8 and E a D − E a H = 9.4 kJ/mol, which fulfill both criteria to suggest tunneling. The possibility that tunneling may be involved in C−H activation and related reactions at transition metals has been proposed on the basis of experiments − and calculations, − including additions of methane at coordinatively unsaturated Pd 0 centers.…”

Hydrido Complexes of Palladium

“…A number of theoretical calculations on Pd hydrides and their reactions have been carried out over the last 20 years. ,− In one of the earliest ab initio MO studies 245 it was shown that the neutral NiH and PdH have different ground states, namely 2 Δ and 2 Σ, respectively, because in NiH the bonding is largely a 4s−1s interaction, whereas in PdH it is 4d−1s. Molecules such as PdH, ,,,, PdH 2 , − , PdH + , and PdH 2 + 243 have been theoretically studied by various research groups.…”

“…Molecules such as PdH, ,,,, PdH 2 , − , PdH + , and PdH 2 + 243 have been theoretically studied by various research groups. Among the reactions investigated, there have been the addition of hydrogen to palladium atoms, ions, naked 3-atomic clusters, and complexes, ,,,,− , activation of C−H and C−C bonds, ,, reductive elimination of H 2 and CH 4 , , and various migratory insertion processes involving olefins and CO. − ,, It is worth noting that the existence of transition metal dihydrogen complexes was first predicted on the basis of the theoretical studies of [(R 3 P) 2 Pd 2 (H 2 )] 247 and [Pd(H 2 )] . These calculations were performed and published a few years before the first dihydrogen complexes were isolated and unambiguously characterized. − Ironically, no stable molecular hydrogen complexes of palladium have been prepared thus far, although [Pd(H 2 )] has been successfully isolated and characterized in frozen inert gas matrices …”

Hydrogen Tunneling in Protonolysis of Platinum(II) and Palladium(II) Methyl Complexes: Mechanistic Implications

“…While the possibility of the oxidative addition route cannot be firmly excluded for the cases studied here, we suggest that they proceed instead by direct protonation at the M−C bond and that there is a connection between that mechanism and the observed tunneling. We would also expect to see evidence for proton tunneling (high KIEs at room temperature or higher) in electrophilic C−H activation by Pd II and Pt II when the microscopic reverse of this process (direct proton loss from the sigma complex) is operating . Given the importance of C−H activation in Pd II and Pt II systems, more studies (both experimental and theoretical) are underway to investigate the correlation between proton tunneling and the mechanisms involved.…”