Theoretical Studies on N–O or N–N Bond Formation from Aryl Azide Catalyzed by Iron(II) Bromide Complex

Abstract

DFT calculations have been carried out to study the reaction mechanism on N-O or N-N bond formation from aryl azide catalyzed by iron(II) bromide complex. A favorable reaction pathway is proposed to account for the construction of the core structure of 2H-indazoles or 2,1-benzisoxazoles.

Iron Catalysis in Organic Synthesis

“…In this case catalytic amounts of iron(II) bromide were sufficient to form benzo[ c ]isoxazoles, indazoles, and pyrazoles. Li and co-workers studied this transformation by computational methods and were able to determine a favorable pathway …”

A DFT study of the mechanism of copper-catalyzed synthesis of 2H-indazoles from aryl azide

“…The energy profiles clearly show that the CuI-terminal coordination pathway is more favorable than the CuI-internal coordination pathway. This is in contrast to the iron(II)-catalyzed systems, 8 for which the Fe-internal coordination pathway is more favorable than the Fe-terminal coordination pathway. This difference between the copper(I) and iron(II) systems can possibly be traced to the following reasons.…”

“…The transition state TS12T CuI shows the concerted loss of N 2 and ring closure, which is consistent with the iron(II)-catalyzed synthesis of the 2H-indazoles in our previous report. 8 Moreover, seen from the structure of TS12T CuI (Fig. 2), formation of 2H-indazole 2T should occur in a concerted manner, albeit with nitrogen expulsion more prominent than ring closure (N 1 -N 4 = 2.049 Å and N 1 -N 2 = 1.605 Å for TS12T CuI ).…”

“…7f,g We recently theoretically investigated N-O or N-N bond formation from aryl azide catalyzed by the iron(II) bromide complex. 8 The report demonstrated that the N-O or N-N bond was formed through two possible pathways: (i) Fe coordinated to the internal N atom of the azide group to give an iron nitrene intermediate; (ii) Fe coordinated to the terminal N atom of the azide group, and intramolecular cyclization then took place followed by N 2 loss (Scheme 1). The results indicated that the iron-catalyzed N-N or N-O bond formation reaction was mainly initiated by Fe coordinating to the internal N atom of the azide group, which gives an iron nitrene intermediate.…”

Recent Advances in Nitrogen–Nitrogen Bond Formation

“…From computational studies, the complex M7, mainly initiated by iron coordinating to the internal nitrogen atom of the azide, was proposed by Li and co-workers to be a more appropriate intermediate. 27…”