Conformational composition, molecular structure and decomposition of difluorophosphoryl azide in the gas phase

Abstract

The conformational composition, molecular structure and decomposition of difluorophosphoryl azide F2P(O)N3 in the gas phase were studied using gas electron diffraction (GED), matrix isolation IR spectroscopy, and quantum-chemical calculations, respectively. While computational methods predict only minor differences in the total energy between the two possible conformers (syn and anti), the analysis of electron diffraction data reveals the dominating abundance of the syn conformer in the gas phase at room temperature. Ab initio frequency analyses suggest that a low-frequency large-amplitude motion of the N3 group with respect to the P-N-N-N torsion is to be expected for the syn conformer. The large amplitude motion was included explicitly into the GED structure refinement procedure. It presumably contributes to a thermodynamic stabilization of the syn-conformer with respect to the anti-conformer in the gas phase at ambient temperature. Upon flash vacuum pyrolysis, this syn conformer undergoes a stepwise decomposition via the difluorophosphoryl nitrene, F2P(O)N, which features as the first experimentally observed phosphoryl nitrene that can be thermally produced in the gas phase. To reveal the reaction mechanism, quantum-chemical calculations on the potential energy surface (PES) of F2P(O)N3 were performed. Both B3LYP/6-311+G(3df) and CBS-QB3 calculation results strongly support a stepwise decomposition into the singlet F2P(O)N, which prefers intersystem crossing to the thermally persistent triplet ground state instead of a Curtius rearrangement into FP(O)NF.

Phosphorus Analogues of Methyl Nitrite and Nitromethane: CH3OPO and CH3PO2

“…In contrast, the symmetric N 3 stretching mode is located at 1251.8 cm −1 due to distinct 15 N‐isotope shifts of 9.9 and 26.0 cm −1 (Figure S6) for the two pairs of 15 N‐labeled nitrene isotopomers. Unlike the thermal persistency of the perfluorinated phosphoryl nitrene F 2 P(O)N in the gas phase, the absence of CH 3 OP(O)(N 3 )N among the HVFP products of CH 3 OP(O)(N 3 ) 2 indicates its fragmentation (→ CH 3 OPO + 2 N 2 ) under the pyrolysis conditions. Upon 365 nm UV‐light irradiation in N 2 matrix, CH 3 OP(O)(N 3 )N undergoes additional homolytic P−N bond cleavage, forming .…”

Spectroscopic Properties, Conformation and Structure of Difluorothiophosphoryl Isocyanate in the Gaseous and Solid Phase

“…[13] The isocyanate group in all cases is almost linear, i. e. ∡(NCO) is always larger than 170°, and the bond lengths in this unit do not vary much in the examples listed in Table 2. [38] Comparing the PÀ S bond length to the analogous distances in PF 2 H(S), PClF 2 (S) and PBrF 2 (S) the reported r a values (1.876(3), 1.864(8) and 1.881(4) Å, respectively) [39] the one determined for F 2 P(S)NCO (1.874(1) Å) is most similar to the length found for the hydrogen compound PF 2 H(S). The PÀ N bond length of F 2 P(S)NCO is also the shortest among the examples listed in Table 2.…”

Chemical Dynamics Simulations of Curtius Reaction of Acetyl- and Fluorocarbonyl Azides

“…Curtius rearrangement is the production of N 2 + RNCO (isocyanate) from carbonyl azides RC­(O)­N 3 upon thermal or photochemical excitation. This reaction is useful in many areas of synthetic chemistry including medicinal chemistry. − Several experimental and theoretical studies investigating the mechanism of the Curtius reaction have been reported in the literature. − Two mechanisms, viz., a stepwise and a concerted pathway have been proposed. The stepwise mechanism involves the formation of a nitrene RC­(O)N by N 2 elimination, followed by an intramolecular rearrangement of the nitrene, yielding the isocyanate.…”