Ab Initio and DFT studies, NBO and NICS analysis of the structures and thermodynamic properties of the decomposition ([2+2] elimination) of 3-halo-2,3-dihydrophosphinine

Decomposition of 3-fluoro2,3-dihydrophosphinine(1),3-chloro2,3-dihydrophosphinine(3), 3-bromo2,3-dihydrophosphinine(5) to phosphininewas investigated using ab initio Molecular Orbital (MO)and Density Functional Theory (DFT).For all HX(X=F, CL, Br)elimination reactions examined here,transition states have a four-centeredtransition structure. Study on the B3LYP 6-311+G** level of theoryrevealed that the required energy for the decompositionof compounds1, 3 and 5 to phosphinineis 31.23,28.91and 25.13(kcal mol−1), respectively. HF 6-311+G** B3LYP 6-311+G** calculated barrier height for the decomposition of compounds1, 3 and 5 to phosphinineare 58.62, 38.30, and 31.27(kcal mol−1), respectively. Also, MP2 6-311+G** B3LYP 6-311+G** results indicate that the barrier height for the decompositionof compounds1, 3 and 5 to phosphinineare47.86, 48.41, and 43.92 (kcal mol−1), respectively.NaturalBond Orbital (NBO) population analysis and Nuclear Independent Chemical Shift (NICS) results showed that, reactants are non-aromatic but products of elimination reaction are aromatic, C-H and C-X bonds are broken and H-X bond is appear.