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.