A theoretical density functional study of association of Zn~(2+) with oxazolidine and its thio derivatives in the gas phase

摘要

We have performed density functional theory (DFT) calculations in order to study the gas-phase interaction of oxoand thio-oxazolidine derivatives with Zn~(2+). The calculations were performed at B3LYP/6-311R(2df,2p) level of theory. It has been found, in all cases, that the direct association of Zn~(2+) with the carbonyl and thiocarbonyl groups takes place at the heteroatom attached to position 2 irrespective of its nature. This preference has been attributed to the resonance effects caused by the nearest heteroatoms (oxygen and nitrogen). The most stable complexes correspond to structures with Zn~(2+) bridging between the heteroatom at position 2 or 4 of the 4- or 2-enol (or the 4- or 2-enethiol) tautomer and the dehydrogenated ring nitrogen atom, N3. Zn~(2+) association has a clear catalytic effect on the tautomerization processes which connect the oxo-thione forms with the enol-enethiol tautomers. Hence, although the enol-enethiol tautomers of oxazolidine and its thio derivatives should not be observed in the gas phase, the corresponding Zn~(2+) complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Zn~(2+) binding energies.