Mechanism of methane activation by electrophiles generated in the AlBr5 system:: an MNDO/PM3 study of the potential energy surface of the [AlBr5 + CH4] system

Fragments of the potential energy surfaces (PES) of the AlBr5 (I) and [AlBr5 + CH4] (II) systems were studied by the MNDO/PM3 method. Five local minima corresponding to Br-2 . AlBr3 donor-acceptor complexes were found on the PES of system I. Two of these complexes have a pronounced ionic character. In system II, among the products of barrierless addition of Br-2 . AlBr3 complexes to CH4, the methane molecule is activated only in two complexes. These are products of the attack of the most electrophilic AlBr5 complexes on a H atom of the methane molecule. The potential barriers to conversion of these products into complexes with structures formally corresponding to the products of the attack of electrophiles on a C-H bond (the Olah scheme) or the C atom of methane molecule (the Schreiner scheme) were calculated.