Abstract
The syntheses and crystal structures of three cyclo-triphosphazenes, all with fluorinated ar-yloxy side groups that generate different steric characteristics, viz. hexa-kis-(penta-fluoro-phen-oxy)cyclo-triphosphazene, N3P3(OC6F5)6, 1, hexa-kis-[4-(tri-fluoro-methyl)-phen-oxy]cyclo-triphosphazene, N3P3[OC6H4(CF3)]6, 2 and hexa-kis-[3,5-bis(-tri-fluoro-methyl)-phen-oxy]cyclo-triphosphazene, N3P3[OC6H3(CF3)2]6 3, are reported. Specifically, each phospho-rus atom bears either two penta-fluoro-phen-oxy, 4-tri-fluoro-methyl-phen-oxy, or 3,5-tri-fluoro-methyl-phen-oxy groups. The central six-membered phosphazene rings display envelope pucker conformations in each case, albeit to varying degrees. The maximum displacement of the 'flap atom' from the plane through the other ring atoms [0.308 (5) Å] is seen in 1, in a mol-ecule that is devoid of hydrogen atoms and which exhibits a 'wind-swept' look with all the aromatic rings displaced in the same direction. In 3 an intra-molecular C-H(aromatic)⋯F inter-action is observed. All the -CF3 groups in 2 and 3 exhibit positional disorder over two rotated orientations in close to statistical ratios. The extended structures of 2 and 3 are consolidated by C-H⋯F inter-actions of two kinds: (a) linear chains, and (b) cyclic between mol-ecules related by inversion centers. In both 1 and 3, one of the six substituted phenyl rings has a parallel-displaced aromatic π-π stacking inter-action with its respective symmetry mate with slippage values of 2.2 Å in 1 and 1.0 Å in 3. None of the structures reported here have solvent voids that could lead to clathrate formation.
Highlights
The syntheses and crystal structures of three cyclotriphosphazenes, all with fluorinated aryloxy side groups that generate different steric characteristics, viz. hexakis(pentafluorophenoxy)cyclotriphosphazene, N3P3(OC6F5)6, 1, hexakis[4(trifluoromethyl)phenoxy]cyclotriphosphazene, N3P3[OC6H4(CF3)]6, 2 and hexakis[3,5-bis(trifluoromethyl)phenoxy]cyclotriphosphazene, N3P3[OC6H3(CF3)2]6 3, are reported
The extended structures of 2 and 3 are consolidated by C—HÁ Á ÁF interactions of two kinds: (a) linear chains, and (b) cyclic between molecules related by inversion centers
The structures of 1, 2 and 3 (Figs. 1, 2 and 3) presented in this report have the hexaphenoxy-cyclotriphosphazene moiety as the common core of the molecule, and differ only in the substitutions on the phenyl rings
Summary
Cyclic organophosphazenes have a long history as representatives of inorganic heterocyclic rings, and are the focus of arguments about reactivity and pseudoaromaticity in inorganic systems (Allcock, 1972; Steudel, 1992). In our research program these compounds serve another purpose – as synthesis and structural models for linear high polymeric organophosphazenes. These cyclic small molecules provide preliminary information related to intra- and intermolecular side-group interactions, which affect many polymer properties. As part of our ongoing work in this area, the three cyclotriphosphazenes hexakis(pentafluorophenoxy)cyclotriphosphazene N3P3(OC6F5) (1), hexakis[4-(trifluoromethyl)phenoxy]cyclotriphosphazene N3P3[OC6H4(CF3)]6 (2) and hexakis[3,5-bis(trifluoromethylphenoxy]cyclotriphosphazene; N3P3[OC6H3(CF3)2]6 (3) were synthesized by the reactions of hexachlorocyclotriphosphazene with the appropriate sodium fluoro-aryloxides in THF or dioxane solvent. Forcing reaction conditions (boiling dioxane) were required for complete chlorine replacement in the case of the pentafluorophenoxy derivative (1) presumably due to steric hindrance. The non-fluorinated hexa(phenoxy)cyclotriphosphazene tetrahydrofuran solvate x-ray structure was described earlier (Dietrich et al, 2000)
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