A two-step catalytic cycle for the acceptorless dehydrogenation of ethane by group 10 metal complexes: role of the metal in reactivity and selectivity

Acceptorless dehydrogenation of ethane was achieved in the gas phase via a two-step catalytic cycle involving ternary cationic metal hydrides, [(phen)M(H)]⁺, 1, and metal ethides, [(phen)M(CH₂CH₃)]⁺, 2, (where M = Ni, Pd, or Pt, and phen = 1,10-phenanthroline). Species 1 and 2 were generated and their reactivity studied in a quadrupole ion trap mass spectrometer. It was found that 1 readily reacted with ethane releasing H₂ and forming 2, with the relative reactivity being Pt > Ni ≫ Pd. Density functional theory (DFT) calculations for this metathesis reaction agree with the experimental reactivity order. Species 2 can in turn be converted into 1 and release ethylene when sufficient energy is supplied via collision-induced dissociation. DFT calculations also provided insight into competing side reactions (e.g., dehydrogenation of 2 and formation of protonated phen ligand) that become competitive during this endothermic step. The catalytic cycle can be repeated in the mass spectrometer several times. Multiple entry points into the cycle have been identified and discussed.