X-RAY CRYSTALLOGRAPHIC STUDY OF A 1,3,2-DIOXAPHOSPHORINANE DIMER CONTAINING 5-COORDINATED PHOSPHORUS IN THE 12-MEMBERED RING

Attempted preparation of phosphorane 9 with a 1,3,2-dioxaphosphorinane ring attached diequatorially to phosphorus led to a mixture of produc ts from which was isolated 12-membered ring phosphorane 10, formally t he dimer of 9, in low yield (22%). An X-ray crystal structure of 10 re vealed a highly symmetrical molecule with trigonal bipyramidal geometr y at both phosphorus atoms. The 12-membered ring is attached to phosph orus diequatorially. The ring is strongly puckered about phosphorus wi th an equatorial O-P-0 angle of 110-degrees. The chemical shift equiva lence of the CH2O resonances in the H-1 NMR spectrum of 10 shows the 1 2-membered ring to be highly mobile at ambient probe temperature. At - 89-degrees-C, these resonances are fully decoalesced. The value of DEL TAG(double dagger) for the process that averages these peaks was found to be 10.1 kcal/mol at coalescence (-42.O-degrees-C).