X‐Ray crystallographic study of a 1,3,2‐dioxaphosphorinane dimer containing five‐coordinated phosphorus in the 12‐membered ring

Abstract

AbstractAttempted preparation of phosphorane 9 with a 1,3,2‐dioxaphosphorinane ring attached diequatorially to phosphorus led to a mixture of products from which was isolated 12‐membered ring phosphorane 10, formally the dimer of 9, in low yield (22%). An X‐ray crystal structure of 10 revealed a highly symmetrical molecule with trigonal bipyramidal geometry at both phosphorus atoms. The 12‐membered ring is attached to phosphorus diequatorially. The ring is strongly puckered about phosphorus with an equatorial O‐P‐O angle of 110°. The chemical shift equivalence of the CH2O resonances in the 1H NMR spectrum of 10 shows the 12‐membered ring to be highly mobile at ambient probe temperature. At −89°C, these resonances are fully decoalesced. The value of ΔG‡ for the process that averages these peaks was found to be 10.1 kcal/mol at coalescence (−42.0°C).