White phosphorus (P4) is prone to undergo degradation by nucleophiles and is reluctant to do so with electrophiles. Silylenes possess a strong singlet character but at the same time bear a largely inert lone pair orbital at the silicon atom. Thus they predominantly react in a similar way to electrophilic carbenes. Due to the poor π-character of the P-P bonds in white phosphorus, the overlap with the empty orbital for the electrophilic silylene is less facile and results in a relatively large barrier for the addition reaction. The electrophilic approach of the silylene to white phosphorus is catalyzed by addition of a second P4, forming a trigonal bipyramidal transition state geometry. Its stability towards fragmentation is essentially lower than that of the silyl cation. The entropy contributions for bimolecular versus termolecular reactions are discussed.
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