The
behavior of the tetracoordinate boron of N-methyliminodiacetic
acid (MIDA) boronates as a nucleophile and an
electrophile during the 1,2-boryl migration promoted by a Lewis acid
and the 1,4-boryl migration promoted by a neighboring atom, respectively,
have been investigated using density functional theory and the quantum
theory of atoms in molecules. We found that when boron acts as a nucleophile,
the electron density of the B–N interaction of the BMIDA moiety
maintains the charge concentration over the boron atom, facilitating
its transport toward the electron-deficient center. In this process,
the BMIDA remains as a tetracoordinate. On the other hand, the B–N
weakening generates a charge depletion region over the boron, allowing
it to interact with the electron-rich center of O1, developing
the boron atom, a pentacoordinate form. Then, the B–N bond
breaking triggers a series of changes in the electronic structure
of the boron atom. Our results explain the role of the MIDA ligand
upon the remarkable susceptibility of the boron atom for switching
its structural and electronic characteristics in the migration processes.
In addition, the dichotomous behavior was evaluated with a different
scenario, considering tricoordinate pinacol boronate as a boryl migrating
group.
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