ACID-BASE CHEMISTRY OF [PCl2N]3

A cooperative role for the counteranion in the PCl5-initiated living, cationic chain growth polycondensation of the phosphoranimine Cl3P═NSiMe3

The counteranion associated with the cationic initiator [Cl(3)P═N═PCl(3)](+) ([4](+)) generated during the PCl(5)-initiated living, cationic chain growth polycondensation of the N-silylphosphoranimine Cl(3)P═NSiMe(3) (3) to give poly(dichlorophosphazene), [N═PCl(2)](n) (2), has been found to have a dramatic effect on the polymerization. When the counteranion of [4](+) was changed from PCl(6)(-) or Cl(-) to the weakly coordinating anions [BAr*(F)(4)](-) and [BAr(F)(4)](-) (Ar*(F) = 3,5-{CF(3)}(2)C(6)H(3), Ar(F) = C(6)F(5)) instead of the polymerization of 3 being complete in 4-6 h, no reaction was observed after 24 h. Remarkably, the polymerization of 3 may be initiated by Cl(-) anions even in the absence of an active cation such as [4](+). However, in the presence of [4](+), the reaction proceeded significantly faster and allowed for molecular weight control. These results reveal that the currently accepted mechanism for the PCl(5)-initiated living polymerization of 3 needs to be revised to reflect the key role of the counteranion present.

Polymeric materials based on main group elements: the recent development of ambient temperature and controlled routes to polyphosphazenes

This Perspective discusses the development of new routes to polyphosphazenes, [R(2)P[double bond, length as m-dash]N](n), that occur at ambient temperature and, in some cases, allow molecular weight control and access to narrow molecular weight distributions and block copolymers. For example, the room temperature silyl-carborane initiated ring-opening polymerisation of (NPCl(2))(3) is described together with chain growth condensation polymerisations of phosphoranimines Cl(3)P[double bond, length as m-dash]NSiMe(3) and BrMePhP[double bond, length as m-dash]NSiMe(3). Recent works on donor-stabilised cationic phosphoranimines are also discussed.

Phosphazene Cations

Cations derived from (NPCl2)3, hexachloro-cyclo-triphosphazene, the weakly basic precursor of phosphazene polymers, have been prepared using strongly electrophilic reagents based on carborane anions. N-protonated, N-methylated, and N-silylated adducts of (NPCl2)3 have been isolated and characterized by X-ray crystallographic and spectroscopic methods. The normally potent chloride-abstracting silyl reagents of the type R3Si(carborane) are unable to abstract chloride from (NPCl2)3, even though the coordinatively unsaturated N2P2Cl5+ cation is widely accepted as a reactive intermediate in the ring-opening polymerization of (NPCl2)3.