Polymer-supported reactions phosphazenes

Computational studies concerning theoretical approaches to the intrinsic basicity of neutral nitrogen bases have been reported, including those of phos-phoranimines. The non-ionic phosphazene bases BEMP (112), BTPP (113) and (114, R = Ph) appear to be excellent catalysts for the Michael addition reactions. Thus the yield of the coupling reaction of ethyl isocyanoacetate with l,2-bis(4-bromomethylphenyl)ethane is increased by the addition of the phosphazene base BEMP. Polymer-supported BEMP (P-BEMP) has been applied for the allylation of 2H-benzo[d]l,3-dioxolan-5-ol by allyl bromide. " Cyclodehydration of 1,2 diacylhydrazines by tosyl chloride in the presence of P-BEMP leads to excellent yields of 1,3,4,-oxadiazoles. Addition of P-BEMP also improves the yield of the Hofmann elimination step in the synthesis of tertiary mines using REM resin (polymer-bound acrylate ester). ... 

In more recent work a different polystyrene supported dehydrating agent (Fig. 16.4a) was used for synthesis of 1,3,4-oxadiazoles under thermal and microwave conditions [107]. Addition of a homogeneous base, for example guanidine, improved the cyclodehydration reaction and led to completion under thermal and, even more significantly, microwave conditions. This required subsequent purification steps to remove the base for clean and quantitative isolation of the desired products, however. On the other hand, use of a polymer supported phosphazene base (Fig. 16.4b) as a base additive circumvents the need for additional purification of the reaction mixture for product isolation. 

In conclusion, the light-induced grafting reactions of organic macromolecules onto pho hazene polymer films is a process that depends on several factors, i.e. the type of POP used as grafting support, the characteristics and the concentration of the exploited monomers, the type of photoinitiator, the swelling of the phosphazene substrate, etc. The accurate control of these parameters is mandatary in order to prepare phosphazene grafted copolymers of predictable characteristics. 

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