Two- and Three-Connected Phosphazenes

Following the first preparation of stable iminophosphines by Niecke and Flick [6] in 1973, over 60 compounds of the type R-P-N-R have now been studied. The most powerful and widely applicable route to these iminophosphines is indicated in 

The reaction of bis(trimethylsilyl)amino difluorophosphine with trimethyl-silylamino lithium leads to the formation of a compound of the type R2N-P=N-R (7.517). Bis(trimethylsilyl)amino phosphine is a pale yellow-green liquid which is very sensitive to hydrolysis, but is stable in the dark below 0°C. Under nitrogen the compound slowly polymerises at 25°C to form a cyclophospha-zane (7.518) [6]. 

Bulky isopropyl and tertiary butyl stabilising groups may take the place of trimethylsilyl groups to give other iminophosphoranes as in Equation 7.519. Other reactions of this type of compound include (7.520) and cycloadditions such as (7.521) 

The product from (7.519) reacts according to scheme (7.522) to give a compound of type RjN-P=0, which rapidly polymerises to a ring derivative with mp = 109 C. The monomer can, however, be obtained in stabilised form by metal complex formation [10] (8.364). 

The compound Bu-P=N- Bu is an air and water-sensitive yellow liquid which is stable at -40 C for a few days after preparation. It is obtained by reaction scheme (7.523), but the monomer quickly dimerises at 0°C [11,12]. 

---