Evaluation of protonation sites in two MacMillan catalysts in solution by gas phase predissociation spectroscopy and electronic structure calculations

The protonation sites of first and second generation MacMillan catalyst were evaluated using cryogenic ion vibrational predissociation spectroscopy. The comparison with calculated spectra showed that when isolated in the gas phase, the species are protonated at the secondary amine, as would be expected by the difference in free energy of the calculated protomers. The relative energies of the conformers were also calculated for the species in solution using the SMD model, in water, methanol and in a 1:1 (v/v) water:methanol mixture. This comparison indicates that the trends observed in the gas phase are retained in solution, and that the secondary amine is the protonation site regardless the solvent used. [GRAPHICS] .