Catalysis of the Nitroso-Diels-Alder cycloaddition reaction between CHN=O and cis-1,3-butadiene by pnictogen bonding, a theoretical study.

Density functional theory calculations at the M06-2X/aug-cc-pVTZ level of theory have been used to examine the Nitroso-Diels-Alder (N-D-A) cycloaddition reaction between the CHN=O and cis-1,3-butadiene in the presence of POX (X=F, Cl, OH) as a catalyst. The effect of the above POX compounds on the activation energy of the N-D-A reaction, has been studied here. In the first stage, the energies of two different bonding interactions, via P⋯N versus P⋯O binding, between the POX and CHN=O molecules were calculated. The results showed that the largest values of the interaction energy between the above molecules belong to the POF, when connects to the nitrogen atom of the CHN=O. Also, calculations showed that all the above POX compounds, decrease the activation energies of N-D-A reaction studied here via both P⋯N and P⋯O interactions. However, the largest effect on activation energies of the reaction belongs to the POF catalyst when acts via P⋯N bonding. The activation strain model (ASM) was used to analyze the influence of the POX catalyst on the studied reaction. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analysis were performed to understand the nature of forming interactions at the TS structures. The results of this study showed that the POX (X=F, Cl, OH) compounds may be suggested as efficient catalysts for N-D-A reactions.