A Computational Study into the Mechanism of B-B Bond Cleavage in a Magnesium(II) Diboranate Complex

The breaking of the asymmetric B-B bond within a MgII diboranate complex, [Mg](pinBB(nBu)pin) when [(MeBDIDipp)Mg]equivalent to[Mg], in the presence of DMAP (4-dimethylaminopyridine), is analyzed with DFT (Density Functional Theory) and NBO (Natural Bond Orbital) methods. The formation of a magnesium-boryl species, [Mg](Bpin)(DMAP)], which exhibits boron "umpolung" nucleophilic behaviour, is explored through "inner" and "outer" sphere mechanisms, alongside a spontaneous base capture pathway. Charges, bond occupancies, Frontier Orbitals and a steric parameter are used to rationalise the mechanistic features of the system, as well as various reactivity observations. Functional testing results and attempts to model unusual 11B NMR data are also reported. The reactivity of a magnesium(II) diboranate complex has been explored using DFT calculations, to rationalize outer sphere (at boron) and inner sphere (at magnesium) mechanistic behaviour. The study investigates specifically how the base DMAP facilitates cleaving the B-B bond, alongside functional testing of the methodology and computed NMR spectra.image