Computational Study of the Curtius-like Rearrangements of Phosphoryl,Phosphinyl,and Phosphinoyl Azides and Their Corresponding Nitrenes

摘要

The free energies of reaction(AG)and activation(DELTA G~≠)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 DELTA G~≠ 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 DELTA G~≠ 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 phospho-rylnitrenes 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.