Basicity, cyclophosphazenes

Structure 1 Generic representation of the structures of basic types of binary phosphorus-nitrogen heterocycles cyclophosphazanes (I), cyclophosphazenes (II), cyclic phosphoranes (III)... 

The Lewis basicity of cyclophosphazenes is enhanced by replacement of the chlorine substituents by electron-donating groups, e.g. Me or Me2N, as illustrated by the formation of complexes of (NPMe2) ( = 6, 8) with transition metal... 

Structure, Conformation, and Basicity in Cyclophosphazenes and Related Compounds... 

The results so far achieved by means of basicity studies on cyclophosphazenes can be summarised as follows (1) (i) establishment of a basicity series in homogeneously substituted compounds, e.g., for the six-imembered ring system, N3P3X , X =... 

A considerable amount of basicity data has been published on cyclophosphazenes, i.e., systems containing only P-N-P segments. 

As a result of the extensive compilation of basicity data for cyclo-triphosphazenes, it has been possible to evaluate substituent constants for different groups (2 78-180). These constants, can be used to calculate the pKa value of a cyclophosphazene derivative containing one or more substituents (179, 180). Hence, a comparison of calculated and observed pKa values can often provide information for the complete characterization of a derivative (180). Basicity data for cyclotetrapho-sphazenes and higher homologs are limited (175, 321), and substituent constants have not been evaluated. 

We called humorously this chemical game BASIC challenge, BASIC initials being for RINO/TNSA/SPIRO 7N CYCLOPHOSPHAZENES. 

One of the keys of the BASIC system lies in the fact that reaction of 1,3-diaminopro-pane (DAP) on a PCl2-containing cyclophosphazene leads quantitatively to a purely SPIRO derivative. 

As a conclusion, we must emphasize once more the high stereospecificity and stereoselectivity of the two reactions described here. It seems from now that any merged chemical containing several SPIRO and/or ANSA and/or BINO moieties may be commonly synthesized in a quantitative manner. This is at least a nice game for the chemist and we propose to label this game as BASIC , i.e. MNO/4NSA-SPIRO IH CYCLOPHOSPHAZENES. 

More unusual alkoxy-derivatives of N3P3CI6 are formed in the reactions with sodium salts of cellulose, which obey second-order kinetics, and in copolymers derived from arabinose, the latter being hydrolysed by alkaline phosphatase. By contrast, (95) is not hydrolysed by this phosphatase. Relative basicity measurements,obtained from the i.r. spectra of cyclophosphazenes mixed with phenol, show that fluoroalkoxy-derivatives N3P3(ORp)6 are more basic than NaPaClg. 

Polyphosphazenes, [N=PR2]n, are the largest family of inorganic polymers. Over 800 different types of polyphosphazenes are known [16, 21-23]. The common feature of all of these polymers is the backbone which is made up of alternate nitrogen and phosphorus atoms. While the nitrogen is trivalent and dicoordinate, phosphorus is pentavalent and tetracoordinate. Thus, nitrogen does not contain any substituents. Phosphorus, on the other hand, is attached to two substituents. Thus, the basic sfructural feature of the repeat unit of polyphosphazenes is exactly similar to what is found in cyclophosphazenes. 

Similarly, cationic initiators such as protic or Lewis acids jne also not very effective as polymerization catalysts for these systems. The basicity of the skeletal nitrogen atoms of the cyclophosphazene rings overwhelms the reactivity of the cationic initiators towards olefin polymerization. Thus, the cyclophosphazene rings are readily protonated or metalated and thus prevent both protic and Lewis acids from initiation of polymerization. 

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