Zwitterionic phosphasilenes

Vsip couplings of 186.4, 131.8 and 116.4 Hz have been observed by Hansen et al ° for the labile, zwitterionic halfparent phosphasilene L Si=PH (L =CH[(C=CH2)CMe(N-2,6-i-Pr2C6H3)2] and its two stable 4-dimethylaminopyridine and l,3,4,5-tetramethylimidazol-2-ylidene adducts, respectively. Interestingly, the Vhp couplings determined for these compounds are almost identical, 143.0,144.1 and 144.1 Hz, respectively. 

The phosphinosilylene has the ability to undergo a 1,2-TMS shift affording the zwitterionic N-heterocyclic zwitterionic phosphasi-lene [LSi(SiMe3)=PSiMe3] at elevated temperature (7). The phosphinosilylene has sufficient 8-donation ability at the silicon to form a bissilylene nickel complex [ (LSi)2P(TMS) Ni(COD)] (8). The phosphinosilylene can also generate an acyl-functionalized phosphasilene by the addition of acid halide and subsequent elimination of MeaSiCl (9). 

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