Conformations of (aryloxy)-lambda(3)-cyclotriphosphazanes. Single crystal X-ray structures of [EtNP(OR)](3) [R = C6H4Br-2 (CIS), C6H3Me2-2,6 (Trans)]

The reaction of the lambda(3)-cyclotriphosphazane, (EtNPCl)(3) with 2-bromo or 2-nitro phenol in the presence of diazabicyclooctane yields a cis-trans isomeric mixture of [EtNP(OC6H4X-2)](3) (X = Br or NO2) from which the cis-[EtNP(OC6H4Br-2)](3) or trans-[EtNP(OC6H4NO2-2)](3) is isolated in a pure state by fractional crystallisation. The two compounds have been characterised by elemental analysis and NMR (P-31, C-13, and H-1) spectroscopic data. Variable temperature (303-363 K) P-31 NMR studies on cis-[EtNP(OC6H4Br-2)](3) indicate its slow conversion to the trans-analogue with increasing temperature. The structure of cis-[EtNP(OC6H4Br-2)](3) and the previously known trans-[EtNP(OC6H3Me2-2,6)](3) have been determined by single crystal X-ray analysis. The six-membered P3N3 ring adopts a chair and a twist conformation in cis-[EtNP(OC6H3Br-2)](3) and trans-[EtNP(OC6H3Me2-2,6)](3) respectively. The structural features are compared with those observed for other lambda(3)-cyclotriphosphazanes