124 / 2023-10-11 06:02:58

Triplet Arylphosphinidenes

phosphinidene; phosphirane; phospholene

Phosphorus in Origin of Life and Space Science > 2) Phosphorus compounds in space

This work is aimed at EPR spectroscopic registration of new triplet phosphinidenes, which are a unique class of radicals postulated as intermediates in numerous organophosphorus reactions. In 2017 we have published the first recorded EPR spectrum of triplet phosphinidene – mesitylphosphinidene [1]. In the present study we considered a series of triplet arylphosphinidenes which have been stabilised and detected for the first time using EPR spectroscopy by photolysis of 1-arylphosphiranes [2] or 1-aryl-3-pospholenes. We focused on the effect of varying aryl substituents on magnetic parameters, and showed the DFT and CASSCF/NEVPT2 calculations of spin–spin and spin–orbit components of magnetic parameters. Surprisingly, photolysis of bulky arylphosphirane Mes*PС₂Н₄ (Mes* = 2,4,6-Bu^tC₆H₂) results in no formation of the stabilized triplet phosphinidene under similar experimental conditions. The performed quantum chemical calculations showed that the highly unstable singlet phosphinidene Mes*P undergoes an almost barrier-free rearrangement affording stable insertion product, thereby hindering the conversion of the singlet intermediate to a more stable triplet phosphinidene. The obtained data explained many unsuccessful efforts to detect the related intermediates in previous studies of various authors.