Structural investigations of phosphorus-nitrogen compounds. 7. Relationships between physical properties, electron densities, reaction mechanisms and hydrogen-bonding motifs of N3P3Cl(6-n)(NHBut)(n) derivatives

A series of compounds of the N3P3Cl(6-n)(NHBut)n family (where n = 0, 1, 2, 4 and 6) are presented and their molecular parameters are related to trends in physical properties, which provides insight into a potential reaction mechanism for nucleophilic substitution. The crystal structures of N3P3Cl5(NHBut) and N3P3Cl2(NHBut)4 have been determined at 120K and those of N3P3Cl6 and N3P3Cl4(NHBut)2 have been re-determined at 120K. These are compared with the known structure of N3P3(NHBut)6 studied at 150K. Trends in molecular parameters (phosphazene ring, P-Cl & P-N(HBut) distances, PCl2 angles and endo- and exo-cyclic phosphazene ring parameters) across the series are observed. Hydrogen-bonding motifs are identified, characterised and compared. Both the molecular and hydrogen bonding parameters are related to the electron distribution in bonds and the derived basicities of the cyclophosphazene series of compounds. These findings provide evidence for a proposed mechanism for nucleophilic substitution at a phosphorus site bearing a PCl(NHBut) moiety

Ansa isomer selectivity in the reactions of cyclotetraphosphazene with octafluorohexane-1,6-diol

The reaction of octachlorocyclotetraphosphazene, N4P4Cl8 (1), in three stoichiometries (1:1, 1:2 and 1:3) with the sodium derivative of the fluorinated diol, 2,2,3,3,4,4,5,5-octafluorohexane-1,6-diol (2), in THF solution at room temperature produced five products: the open chain compound N4P4Cl7[OCH2(CF2)4CH2OH] (3), the spiro compound N4P4Cl6[OCH2(CF2)4CH2O] (4b), the 1,5-ansa compound N4P4Cl6[OCH2(CF2)4CH2O] (4c), the cis-1,3;5,7-bis-ansa derivative N4P4Cl4[OCH2(CF2)4CH2O]2 (5a) and the 1,3;1,3;5,7;5.7-tetrakis-ansa compound, N4P4(OCH2(CF2)4CH2O)4 (6a). The structures were determined by elemental analysis, mass spectrometry, 1H, 19F and 31P NMR spectroscopies and for compounds 4c and 5a, where suitable single crystals were obtained, the structures were characterised by X-ray crystallography. It was found that the (PN)4 ring in compound 4c is in a slightly-twisted tub conformation but in compound 5a the first symmetrical crown conformation of the (PN)4 ring is observed. The results of all the reactions were compared with previous work on the reaction of hexachlorocyclotriphosphazene, N3P3Cl6, with the sodium derivative of the diol (2), in a 1:1.2 mole ratio in the same solvent, where intermolecular bridging reactions were preferred. The regio-selective formation of mainly ansa derivatives of the fluorohexanediol with cyclotetraphosphazene was rationalised in terms of non-bonded 1,3 and 1,5 P…P distances of the tetramer ring