Methane C-H Bond Activation by "Naked" Alkali Metal Imidyl and Alkaline Earth Metal Imide Complexes. The Role of Ligand Spin and Nucleophilicity

High accuracy correlation consistent Composite Approach (ccCA) calculations have been used to investigate methane C-H bond activation with alkali metal imidyl and alkaline earth metal imide complexes. Alkali metals (Li, Na) and alkaline earth metals (Be, Mg) are used in this research given their redox innocence, namely, M+ and M2+, respectively. The ccCA calculations for methane activation by imidyl radical NH center dot- and triplet nitrene NH center dot center dot show a thermodynamic (Delta Delta H = 132 kcal/mol) and kinetic (Delta Delta H-double dagger = 15.9 kcal/mol) preference for the former. Methane activation by LiNH center dot and MgNH proceeds via hydrogen atom abstraction (HAA) and [2 + 2] transition states; only HAA pathways are isolated for NaNH and BeNH. The ccCA computed enthalpies lead to the hypothesis that the nucleophilicity of the nitrogen of the activating ligand (NR) is the key ingredient in activating the strongest sp(3) C-H bonds like that of methane.