THE NMR-SPECTROSCOPY AND X-RAY CRYSTAL-STRUCTURE DETERMINATION OF 2 ISOMERIC FORMS OF THE DIOXODIPHOSPHORUS MACROCYCLE 5,13-DIPHENYL-1,9-DIOXA-5,13-DIPHOSPHACYCLOHEXADECANE-5,13-DIOXIDE

Single crystal X-ray structure analysis confirms the existence of two geometrical isomers of 5,13-diphenyl-1,9-dioxa-5,13-diphosphacyclohexadecane. In the solid state, the trans isomer has exact C-i symmetry while the cis isomer shows virtual C-2 symmetry. Pairs of oxygen donor atoms are directed to opposite sides of the macrocycle in each ligand; in the cis-isomer, the phosphine oxide oxygens lie on the same side of the macrocycle, opposite to the ring ether oxygens while in the trans-isomer one phosphine oxide and one ether oxygen lie opposite to their symmetry-related counterparts. In solution, each isomer is identifiable by C-13 and P-31 NMR but analysis of mixtures in the latter case is complicated by concentration-dependent chemical shifts.