Computational Study of Methane C-H Activation by Main Group and Mixed Main Group-Transition Metal Complexes.

In the present density functional theory (DFT) research, nine different molecules, each with different combinations of A (triel) and E (divalent metal) elements, were reacted to effect methane C-H activation. The compounds modeled herein incorporated the triels A = B, Al, or Ga and the divalent metals E = Be, Mg, or Zn. The results show that changes in the divalent metal have a much bigger impact on the thermodynamics and methane activation barriers than changes in the triels. The activating molecules that contained beryllium were most likely to have the potential for activating methane, as their free energies of reaction and free energy barriers were close to reasonable experimental values (i.e., ΔG close to thermoneutral, ΔG‡ ~30 kcal/mol). In contrast, the molecules that contained larger elements such as Zn and Ga had much higher ΔG‡. The addition of various substituents to the A-E complexes did not seem to affect thermodynamics but had some effect on the kinetics when substituted closer to the active site.