posted on 2023-11-16, 16:48authored byCarrie Salmon, Yuan Xue, Valentin Gogonea
Although the synthesis of chlorophosphazene
polymers
has been explored
for more than 100 years, the shortest yet most illusive monomer, Cl3PNH, has never been isolated and fully characterized.
Here we investigate the formation of Cl3PNH from
PCl5 and NH3 in chlorobenzene through quantum
mechanical calculations. The potential energy surface was mapped using
the MP2 Hamiltonian in conjunction with Dunning’s correlation-consistent
basis sets (aug-cc-pVXZ, where X = D and T). Along with HOMO/LUMO
frontier molecular orbitals and natural bond orbital analyses, we
found that instead of following the SN1 path proposed in
the literature, the reaction proceeds via an addition–elimination
mechanism. Our results also indicate that due to the low-lying stable
intermediates (IM), most steps are exothermic such that the production
of Cl3PNH·2HCl can be completed once the energy
barrier for the formation of [PCl4-NH3]+Cl– is overcome. Therefore, our theoretical
work might explain the challenges in isolating any of the IMs in a
typical chlorophosphazene reaction in chlorobenzene.