Gas-Phase Reaction Studies of Dipositive Hafnium and Hafnium Oxide Ions: Generation of the Peroxide HfO22+

Coupling of Methane and Carbon Dioxide Mediated by Diatomic Copper Boride Cations

The use of CH₄ and CO₂ to produce value-added chemicals via direct C-C coupling is a challenging chemistry problem because of the inertness of these two molecules. Herein, mass spectrometric experiments and high-level quantum-chemical calculations have identified the first diatomic species (CuB⁺ ) that can couple CH₄ with CO₂ under thermal collision conditions to produce ketene (H₂ C=C=O), an important intermediate in synthetic chemistry. The order to feed the reactants (CH₄ and CO₂ ) is important and CH₄ should be firstly fed to produce the C₂ product. Molecular-level mechanisms including control of product selectivity have been revealed for coupling of CH₄ with CO₂ under mild conditions.

Sequential Gas-Phase Activation of Carbon Dioxide and Methane by [Re(CO)2]+: 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]⁺ (x = 0, 1, 3) are thermally unreactive toward CO₂, [Re(CO)₂]⁺ abstracts one oxygen atom from this substrate spontaneously at ambient conditions. Based on ¹³C and ¹⁸O 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)₂]⁺ reacts further with CH₄ to produce the dihydridomethylene complex [ORe(CO)(CH₂)(H)₂]⁺. However, coupling of the CO and CH₂ ligands to form CH₂═C═O does not take place. Further, the complexes [Re(CO)_x(CH₂)]⁺ (x = 1, 2), generated in the thermal reaction of [Re(CO)_x]⁺ (x = 1, 2) with CH₄, are inert toward CO₂. Mechanistic insight on the origin of this remarkable reactivity pattern has been derived from detailed quantum chemical calculations.