Beiträge zur Chemie des Phosphors, 139 [1] Triethyl-cyclotriphosphan, Trimethyl-cyclotriphosphan; Gleichgewichte zwischen Cyclophosphanen (PR)n bei erhöhten Temperaturen/Contributions to the Chemistry of Phosphorus, 139 [1] Triethylcyclotriphosphane, Trimethylcyclotriphosphane; Equilibria between Cyclophosphanes (PR)n at Elevated Temperatures

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Abstract
Triethylcyclotriphosphane, (PEt)3 (1), has been generated by thermolysis of tetraethylcyclotetraphosphane, (PEt)4. 1 can be obtained as a 43% solution in 1,2,3-triethyl-1,2,3-triphosphole, (PEt)3C2H2 (3), by fractional distillation of the product mixture formed in the reaction of K2(PEt)4 with ClHC=CHCl. 3 has been isolated and fully characterized. Furthermore 1 as well as (PMe)3 (2) and (PPh)3 exist besides (PR)4 (R = Et, Me, Ph) in thermodynamic equilibrium with (PR)5 at elevated temperatures; for R = Ph(PPh)6 is also formed. The thermodynamic data of the reactions 3/5 (PMe)5 ⇌ (PMe)3 and 4/5 (PMe)5 ⇌ (PMe)4 have been calculated from the equilibrium constants between 60 and 160 °C. The ring strain of 2 is much smaller than that of cyclopropane but increases with increasing size and bulk of the substituents R at the phosphorus threemembered ring.