Between Oxirane and Phosphirane: The Spring‐loaded Oxaphosphirane Ring
Arturo Espinosa Ferao, Alicia Rey Planells, Rainer Streubel
Abstract
Abstract Due to the potential interest of oxaphosphiranes in ring‐opening polymerizations, accurate ring strain energies (RSEs) of a wide variety of oxaphosphirane derivatives was computed, after validation of the optimization method by comparison with reported X‐ray structures. The parent oxaphosphirane exhibits a moderate RSE (22.44 kcal/mol) that is significantly enhanced by κ ‐P‐complexation (especially with boranes), the introduction of P=O or P + ‐Me groups as well as exocyclic double bonds at the ring carbon, such as 3‐methylene, 3‐imino and 3‐oxo functionalities. However, C3 alkyl substitution or pentacoordination at P in σ 5 λ 5 ‐oxaphosphirane does not lead to significant variation of RSE. Bicyclic spiro‐oxaphosphirane derivatives show an RSE decrease when the size of the spiro ring increases. A moderate linear correlation between RSE and G(r)/ρ(r) values calculated at the ring critical points and also with the relaxed force constant ( k 0 ) for the P−C bond is observed for most oxaphosphiranes. The possibility of ring‐opening polymerization by using better (anionic) nucleophiles in the initiation step can be foreseen from the exergonicity and relatively low barrier of the endocyclic C−O cleavage by nucleophilic attack of methanol, thus underlining the effect of the RSE as driving force compared to acyclic analogs.