Activation of Methane by Oligomeric (AlO3)_x~+ (x = 3,4,5): The Role of Oxygen-Centered Radicals in Thermal Hydrogen-Atom Abstraction

摘要

Selective activation of C—H bonds constitutes a major challenge in the syntheses of added-value products. For methane in particular, a number of factors make the activation difficult: CH4 is thermodynamically the most stable of all alkanes (Δ_fG~0 = -50.8 kJ mol~(-1)) and the C-H bond strength is the largest of all sp~3-hybridized hydrocarbons (439 kJ mol~(-1)). Furthermore, the negative electron affinity, a large ionization energy, the wide HOMO/LUMO gap, an extremely high pK_a value, and its relatively modest proton affinity are very unfavorable intrinsic factors for its activa-tion.