A new mechanism for the addition of alcohols to disilenes revealed by DFT and ONIOM calculations

Density functional and ONIOM calculations of alcohol and phenol additions to two (tetramethyl and tetramesityl) disilenes were carried out. The dimer of MeOH adds to Me2SiSiMe2 more readily than the monomer. The trimer does not afford the adduct, but a zwitter-ionic intermediate. In the (CF3OH)2 addition to Me2SiSiMe2, H⋯Si bond formation is more advanced than O⋯Si bond formation in the transition state (TS). Addition of seven phenol derivatives to Me2SiSiMe2 was examined, and the dimer reactions were found to be superior to the monomer reaction regardless of the substituents on the benzene rings. (MeOH)2 reacts also with Mes2SiSiMes2 favorably, and an isomer of the reactant-like complex (precursor) may afford an adduct of different stereochemistry via internal rotations. Generally, the dimer of the alcohol or phenol is the reactant toward the disilenes. Exceptionally, a monomer of p-(dimethylamino)phenol reacts with Mes2SiSiMes2 owing to steric congestion by the four mesityl groups.

Dimers of aliphatic alcohols and phenols were found to react with disilenes via ready proton relays. Monomers may also react but give large activation energies. The effect of four mesityl groups on the addition reactivity was discussed in detail.Figure optionsDownload as PowerPoint slide