jo0711687_si_002.pdf (370.2 kB)
Computational Study of the Curtius-like Rearrangements of Phosphoryl, Phosphinyl, and Phosphinoyl Azides and Their Corresponding Nitrenes
journal contribution
posted on 2007-12-07, 00:00 authored by Ryan D. McCulla, Gamal A. Gohar, Christopher M. Hadad, Matthew S. PlatzThe free energies of reaction (ΔG) and activation (ΔG⧧) were determined for the Curtius-like rearrangement
of dimethylphosphinoyl, dimethylphosphinyl, and dimethylphosphoryl azides as well as the corresponding
singlet and triplet nitrenes by CBS-QB3 and B3LYP computational methods. From CASSCF calculations,
it was established that the closed-shell configuration was the lower energy singlet state for each of these
nitrenes. The triplet states of dimethylphosphinyl- and dimethylphosphorylnitrene are the preferred ground
states. However, the closed-shell singlet state is the ground state for dimethylphosphinoylnitrene. The
CBS-QB3 ΔG⧧ values for the Curtius-like rearrangements of dimethylphosphinyl and dimethylphosphoryl
azides were 45.4 and 47.0 kcal mol-1, respectively. For the closed-shell singlet dimethylphosphinyl- and
dimethylphosphorylnitrene, the CBS-QB3 ΔG⧧ values for the rate-limiting step of the Curtius-like
rearrangement were 22.9 and 18.0 kcal mol-1, respectively. It is unlikely that the nitrenes will undergo
a Curtius-like rearrangement because of competing bimolecular reactions that have lower activation barriers.
The pharmacology of weaponized organophosphorus compounds can be investigated using phosphorylnitrenes as photoaffinity labels. Dominant bimolecular reactivity is a desirable quality for a photoaffinity
label to possess, and thus, the resistance of phosphorylnitrenes to intramolecular Curtius-like rearrangements
increases their usefulness as photoaffinity labels.