Theoretical Studies on the Reaction Mechanism of Platinum-Catalyzed Diboration of Allenes

The reaction mechanism of Pt(0)-catalyzed diboration reaction of allenes is investigated by the density functional method B3LYP. The overall reaction mechanism is examined. The electronic mechanisms of the allene insertion into the Pt-B bond are discussed in terms of the electron donation, back-donation, and d-pi interaction. During allene insertion into the Pt-B bond, the internal carbon atom of allene is preferred over the terminal one due to the stronger electron back-donation and stronger charge transfer in the former case than that in the latter one. By using the monosubstituted allenes (CN, Ph, Me, and NH2) the influence of the substituents on the allene insertion into the Pt-B bond is analyzed. For CN, B-B bond addition to the terminal C=C bond of allene is favored over the internal one, while for Ph, Me, and NH2, the internal one is preferred over the terminal one. This result can be explained by the influence of substituents on the charge transfer in the d-pi interaction.