Exploring the potential energy surface of the association of Cu+ to oxaziridine, nitrosomethane, and formaldoxime

The catalytic role of Cu+ on the isomerization processes among oxaziridine and its isomers methylenimine N-oxide, nitrosomethane, and formaldoxime has been investigated by studying the corresponding potential energy surfaces through the use of high-level DFT calculations. The geometries of the different stationary points were optimized at the B3LYP/6-311G(d,p) level while the final energies were obtained using a 6-311+G(2df,2p) basis set expansion. Our results show that oxaziridine, contrary to what has been found for formamide, behaves as a nitrogen base when the reference acid is Cu+, since the oxygen-attached species is predicted to be 9.2 kcal/mol less stable than the nitrogen-attached structure. Both nitrosomethane and formaldoxime are also predicted to be nitrogen bases in gas-phase reactions with Cu+, while for methylenimine N-oxide only the oxygen and the carbon-attached complexes were found to be minima of the potential energy surface, the former being almost 21 kcal/mol more stable than the latter. Among the cationized species the most stable corresponds to the attachment of the metal cation to the nitrogen atom of formaldoxime, which is also the most stable neutral. However, the energy gaps found for the neutral species differ significantly from those found for the corresponding Cu+ complexes. Cu+ association to oxaziridine catalyzes the C-O bond fission, favoring the formation of an open H2C-NH-OCu+ complex. The isomerization processes leading from nitrosomethane to formaldoxime and to methylenimine N-oxide as well as that connecting the latter two compounds are also catalyzed by Cu+ association in the gas phase.