Aqueous Chemistry of Chlorocyclophosphazenes: Phosphates {PO₂}, Phosphamides {P(O)NHR}, and the first Phosphites {PHO} and Pyrophosphates {(PO)₂O} of These Heterocycles

Abstract

Cyclotriphosphazenes have been functionalized with various oxo-groups at one of the ring phosphorus atoms. Starting from geminal dichlorides (A) which are equipped with amino groups at the other two phosphorus atoms {(Z'(2)P)(2)N(3)PCl(2) (Z' = NHCy) and (Z''P)(2)N(3)PCl(2) (Z'' = {EtN(C(3)H(6))NEt}), respectively}, phosphate (B), pyrophosphate (C), phosphamide (D), and phosphite (E) derivatives have been prepared. The zwitterionic phosphate (Z'(2)P)(2)N(3)H(2)PO(2) B is obtained via the 4-dimethylamino pyridine (dmap)-catalyzed hydrolysis of A in a biphasic mixture of aqueous KOH and tetrahydrofuran (thf). B contains a PO(2) moiety neighboring two protonated ring nitrogen sites. It crystallizes as the tetrahydrate (Z'(2)P)(2)N(3)H(2)PO(2).4H(2)O, which consists of a double helix: A helical chain of hydrogen bonded zwitterions is intertwined with a helical chain of water molecules. The reaction of A with only dmap in CHCl(3) produces the dication [(Z'(2)P)(2)N(3)P(dmap)(2)](2+), which binds two dmap ligands at one phosphorus atom. The tetrahydrate dehydrates at 160 degrees C in vacuo under formation of the pyrophosphate {(Z'(2)P)(2)N(3)HPO}(2)O C, which contains a O=P-O-P=O residue linking the two phosphazene rings. When heated in a mixture of aqueous KOH, primary amine, and thf, A undergoes a concurrent aminolysis-hydrolysis reaction, which gives the phosphamide (Z(2)P)(2)N(3)HP(O)NHR D featuring a P(=O)NHR residue. The corresponding reaction of A with alpha,alpha'-diamino-p-xylene in a 2:1 ratio leads to the formation of {(Z'(2)P)(2)N(3)HP(O)NHCH(2)}(2)C(6)H(4), in which two phosphamide moieties are linked by a xylylene bridge. Phosphites E containing PHO moieties are obtained via reduction of the dichloride with potassium and subsequent treatment with KOH. The product consists of a hexameric potassium complex, which features a central K(6)O(6) double cube arrangement and contains the anionic ligand [(Z''P)(2)N(3)PHO](-) that offers two bidentate N-P-O coordination sites. Addition of NH(4)Cl yields the neutral phosphite (Z''P)(2)N(3)HPHO. The title compounds are amphiphilic featuring hydrophilic NH and PO(x) moieties and hydrophobic alkyl groups. In addition, they show amphiprotic behavior via protonation/deprotonation at ring N atoms.