Computational study of the Curtius-like rearrangements of phosphoryl, phosphinyl, and phosphinoyl azides and their corresponding nitrenes.
The free energies of reaction (DeltaG) and activation (DeltaG) 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 DeltaG 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 DeltaG 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.
McCulla
Ryan D
RD
Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210, USA.
Gohar
Gamal A
GA
Hadad
Christopher M
CM
Platz
Matthew S
MS
D001386:Azides / Q000737:chemistry*; D003198:Computer Simulation; D007097:Imines / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D009943:Organophosphorus Compounds / Q000138:chemical synthesis / Q000737:chemistry*
D001386:Azides; D007097:Imines; D009943:Organophosphorus Compounds; C017621:phenylnitrene