Sequential Gas-Phase Activation of Carbon Dioxide and Methane by [Re(CO)]: The Sequence of Events Matters!

The potential of carbonyl rhenium complexes in activating and coupling carbon dioxide and methane has been explored by using a combination of gas-phase experiments (FT-ICR mass spectrometry) and high-level quantum chemical calculations. While the complexes [Re(CO)] (x = 0, 1, 3) are thermally unreactive toward CO, [Re(CO)] abstracts one oxygen atom from this substrate spontaneously at ambient conditions. Based on C and O labeling experiments, the newly generated CO ligand is preferentially eliminated, and two mechanistic scenarios are considered to account for this unexpected finding. The oxo complex [ORe(CO)] reacts further with CH to produce the dihydridomethylene complex [ORe(CO)(CH)(H)]. However, coupling of the CO and CH ligands to form CH═C═O does not take place. Further, the complexes [Re(CO)(CH)] (x = 1, 2), generated in the thermal reaction of [Re(CO)] (x = 1, 2) with CH, are inert toward CO. Mechanistic insight on the origin of this remarkable reactivity pattern has been derived from detailed quantum chemical calculations.