Side-Group Construction in High Polymeric Phosphazenes via Lithiophenoxy Intermediates

The new (lithiophenoxy)phosphazene high polymers [NP(OC6H4Li-p)I(OC6H4Br)y]n and [NP(OC6H4Li-p),(OPh)y]n have been prepared by a metal-halogen exchange reaction between n-butyllithium and [NP(OC6H4Br-p)2]n or [NP(OC6H4Br-p),(OPh)y]n at -40 to -60 °C. The lithio derivatives were used as reactive intermediates for the synthesis of polymers of formula [NP(OC6H4X-p),(OC6H4Br-p)y]n, where X = PPh2 or PPh2C4H9+Br- or [NP(OC6H4X-p)1(OPh)y]rt, where X = PPh2, PPh2C4H9+Br-, SnPh3, AuPPhs, or COOH. Evidence was obtained that the replacement of bromine by lithium is rapid up to the point at which half of the phenoxy groups bear a lithium substituent. Beyond that stage lithiation is extremely slow. The replacement of lithium by the electrophiles ClPPh2, ClSnPh3, ClAuPPh3, or C02 was rapid and complete. Quaternization of pendent PPh2 groups by n-butyl bromide was also a facile reaction. The differences between these high polymeric reactions and those of analogous small-molecule cyclic phosphazene model systems are discussed. Comparisons are also made with the lithiation reactions of poly (p-bromostyrene).