4′,4′,6′,6′-Tetrachloro-2-(6-methylpyridin-2-yl)-1H,2H-spiro[naphtho[1,2-e][1,3,2]oxazaphosphinine-3,2′-[1,3,5,2,4,6]triazatriphosphinine]

The title compound, C17H14Cl4N5OP3, is a spiro-phosphazene derivative with bulky naphthalene and pyridine rings. The phosphazene and the six-membered N/O rings are in flattened-boat and twisted-boat conformations, respectively. The naphthalene ring system and the pyridine ring are oriented at a dihedral angle of 18.06 (8)°. In the crystal, weak π–π stacking between the pyridine rings and between the pyridine rings and the naphthalene ring system [centroid–centroid distances = 3.594 (2) and 3.961 (2) Å, respectively] occur. Weak C—H⋯π interactions are also observed. These interactions link the molecules into a three-dimensional supramolecular network.

The title compound, C 17 H 14 Cl 4 N 5 OP 3 , is a spiro-phosphazene derivative with bulky naphthalene and pyridine rings. The phosphazene and the six-membered N/O rings are in flattened-boat and twisted-boat conformations, respectively. The naphthalene ring system and the pyridine ring are oriented at a dihedral angle of 18.06 (8) . In the crystal, weak stacking between the pyridine rings and between the pyridine rings and the naphthalene ring system [centroidcentroid distances = 3.594 (2) and 3.961 (2) Å , respectively] occur. Weak C-HÁ Á Á interactions are also observed. These interactions link the molecules into a three-dimensional supramolecular network.
In the phosphazene ring, the P-N bond lengths are in the range of 1.571 (3)-1.598 (3) Å [average value is 1.583 (3) Å] (Table 1), exhibiting a regular variation with distances from P1: -N3, and showing double-bond character. However, the exocyclic P1-N4 bond [1.665 (3) Å] is at the lower limit of the single bond length. In the phosphazene compounds, the P-N and P═N bonds are generally in the ranges of 1.628-1.691 and 1.571-1.604 Å, respectively (Allen et al., 1987). The shortening in the P1-N4 bond is probably due to electron transfer from N4 to the phosphazene ring.

Experimental
Hexachlorocyclotriphosphazene (1.00 g, 2.88 mmol) in dry THF (100 ml) was introduced into a 250 ml three-necked round-bottomed flask. One equivalent of 1-[(6-methylpyridin-2-ylamino)methyl]naphthalene-2-ol (0.76 g, 2.88 mmol) and triethylamine (5 ml, 36.00 mmol) were dissolved in dry THF (50 ml) and placed in an addition funnel. The 1-[(6methylpyridin-2-ylamino)methyl]-naphthalene-2-ol and triethylamine solution was added dropwise to the hexachlorocyclotriphosphazene solution and allowed to react for 24 h. The progress of the reaction was monitored by TLC. The precipitated triethylamine hydrochloride was filtered off. The solvent was evaporated and the product was purified through a silica gel column with a mobile phase of CHCl 3 . The oily product was recrystallized in n-hexane [m.p. 495.5 K, yield: 0.70 g, 45%].

Refinement
H atoms were positioned geometrically with C-H = 0.95, 0.99 and 0.98 Å for aromatic, methylene and methyl H atoms, and constrained to ride on their parent atoms, with U iso (H) = k × U eq (C), where k = 1.5 for methyl H-atoms and k = 1.2 for all other H-atoms.

Computing details
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012) and PLATON (Spek, 2009    Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.