Polymerisation and Rearrangement in Compounds with Multiple Bonds

3 Polymerisation and Rearrangement in Compounds with Multiple Bonds [4] 

Compounds in which the P atom forms a multiple bond are frequently unstable and are liable to polymerise, usually to a dimer, but sometimes a trimer and occasionally a higher form. Equilibria may be set up, but the relative stabilities of the different forms are heavily dependent upon the substituent groups which are present. Only a few examples are known for some of the reactions listed below (see also Chapters 6, 7 and 8). 

Replacement of P=C in an unstable monomer by P-C in the dimeric form is fairly common (13.280). Similarly, P C monomers will dimerise as in Equation 13.281. The dimer may in some cases be capable of undergoing further reaction (called 2-1-2 cycloaddition or cyclotetramerisation) to form a cubane molecule (13.282). Further examples of dimerisations are provided by phosphake-tenes (13.283), phosphathioketenes (13.284) and phosphaallyl derivatives (13.285) and (13.286). 

Compounds of type ArP=C=SiRR are of interest because of the possibility of alternative ways of dimerisation [20]. 

In some polymerisations P-C linkages are not directly involved, for example, [21] 

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