Tetra-heteroelementsubstituierte Methane und isomere Phosphorylide: C- versus P-Nucleophilie ambidenter Phosphinomethanide / Tetra-Heteroelement Substituted Methanes and Isomeric Phosphorus Ylides: C- versus P-Nucleophilicity of Ambidentate Phosphinomethanides

Abstract

Fully heteroelement substituted carbanions, i.e. phosphinomethanides of the type [(Me 2 P)C(X)(Y)]- (X, Y = PMe 2 , SiMe 3 ) react with organoelement chlorides (X—Cl, Y—Cl) to give tetra-heteroelement substituted methanes and/or isomeric phosphorus ylides with an element-phosphorus bond. The latter in some cases are rigid, in others fluctional and in certain cases may rearrange to the isomeric methane derivatives. The results are explained by the involvement of pentacoordinated silicon derivatives, which only occur as transient species, however. A compound with pentacoordinated silicon in the ground state is obtained from Li[(Me 2 P) 2 C(SiMe 3 )] and RSiCl 3 (R = Ph), but it slowly rearranges to the isomeric methane derivate (Me 2 P) 2 (Me 3 Si)(Cl 2 PhSi)C within four weeks at + 20°C. Within six weeks, further rearrangement occurs to give the ylide Me 2 P —PMe 2 =C(SiMe 3 )(SiPhCl 2 ). For R = t Bu, only the analogous rearranged ylide is found. Its molecular structure was confirmed by an X-ray structure determination.