Polyphosphazenes with transition metals

Polyphosphazenes with Transition Metals in the Side Groups... 

The synthesis of polyorganophosphazenes with transition metals linked to the side groups has been accomplished with the use of aryloxy-substituted polyphosphazenes. The over-all synthetic pathways are summarized in Scheme III... 

The design of functionalized polymers with a specific utilization is seen in new polysiloxanes used by Zeldin (p. 199) as phase transfer catalysts. Novel functional polyphosphazenes have been reported as well by Allcock (p. 250). The introduction of transition metal cyclopentadienyl, metal carbonyl and carborane moieties into polyphosphazene macromolecules is representative of truly novel chemistry achieved after careful model studies with corresponding molecular systems. 

In this paper we consider two specific challenges. First, how might transition metals be linked to phosphazene high polymers Such systems are of interest as immobilized catalysts or materials with unusual electrical properties. Second, how can bioactive agents be attached to polyphosphazenes to prepare, for example, targeted, slow release chemotherapeutic agents ... 

Lithiation Reactions. One of the earliest reactions of this type made use of metal-halogen exchange reactions carried out on poly[bis(p-bromophenoxy)phosphazene]. Polyphosphazenes that bear p-bromophenoxy side oups are normally unreactive. However, they can be lithiated, as shown in Scheme III, and the lithio derivatives react with a wide variety of electrophiles that range from chlorophosphines (19) to organometallic halides (42-45), This provides an access route to polymer-bound transition metal catalysts and other metallated or silylated polymers. 

We have devoted a major effort in recent years to the synthesis of polyphosphazenes that bear transition metals in the side group structure [60]. One purpose of these studies has been to examine the possibility that metal-containing side groups might superimpose electroactive, catalytic, or magnetic propeties onto the solid state or surface properties normally associated with polyphosphazenes. Only one example will be given here. 

Scheme 7.4 Polyphosphazenes with borazine, organosilicon, or transition metal organometallic side groups.

From a fundamental scientific point of view, opportunities and challenges exist in the expansion of the polyphosphazene platform to incorporate elements other than phosphorus and nitrogen. As discussed, this has already been accomplished for skeletal systems that contain phosphorus, nitrogen, and carbon or sulfur, but numerous alternatives exist using other elements from both the main group and transition series. Especially intriguing is the possibility that transition metals can be incorporated into the skeleton with the possible development of electronic conductivity along... 

The uses of polyphosphazenes in the formation of stabilized nano-particles with controlled size is another subject that has deserved some attention. In a comparative study on the efficacy of various polymeric stabilizers of modem transition-metal nano-clusters, poly(bis(ethoxy)phosphazene) was found to influence lr(0) nanocluster nucleation. ... 

Polyphosphazenes, substituted with steroids or transitional metal complexes, reagents, catalysts Poly(L-lysine)... 

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