Computational Study of Methane C–H Activation by Diiminopyridine Nitride/Nitridyl Complexes of 3d Transition Metals and Main-Group Elements

The C–H bond activation of
methane using Ph,MePDI–M≡N [Ph,MePDI = 2,6-(PhNCMe)2C5H3N]
(M = V, Mn, Fe, Co, Ni, Al, or P) has been studied via three reaction
pathways: [2σ + 2π] addition, hydrogen
atom abstraction (HAA), and direct insertion. The activating ligand
is a nitride/nitridyl (N), with diiminopyridine (PDI) as the supporting
ligand. Calculations show reasonable C–H activation barriers
for Co, Ni, Al, and P Ph,MePDI nitrides, complexes that
favor an HAA pathway. Electrophilic Ph,MePDI nitride complexes
of the earlier metals with a nucleophilic actor ligandV, Mn,
Fefollow a [2σ + 2π] addition
pathway for methane activation. Free energy barriers for methyl migration, Ph,MePDI–M­(CH3)NH → Ph,MePDI–M–N­(H)­CH3, are also interesting in the
context of alkane functionalization; discriminating factors in this
mechanistic step include the strengths of the σ-bond and metal-actor
ligand π-bond that are broken and the electrophilicity of the
actor ligand to which methyl migrates.