Similarly to halides, molecular compounds EXn, where X= OR, NR2, etc., are Lewis acids through E atom and Lewis bases through oxygen atoms nitrogen of the terminal groups, so they can exchange these groups by four centers mechanisms.
In this reation H- and MeO- are exchanged between silicon and aluminum. The reaction proceeds via an intermediate with alcohóxido and hydride double bridge.
The reaction intermediate, with a coordination number one unit higher than the starting compound, has the structure of trigonal bipyramid. Both groups, incoming Y and outgoing X groups, are bonded to the central atom. The subsequent dissociation of the leaving group X restores the tetrahedral geometry of the compound.
The reaction intermediate, with a coordination number one unit higher than the starting compound, has square planar structure.
The reaction intermediate has a coordination number 7, one unit higher than the starting compound. These heptacoordinadas species are fluxional; here we present one of the suggested intermediate geometries for the intermediate reaction.