Silicon and Phosphinomethanides: A Novel Entry to Hypervalent and Low Valent Organosilicon Chemistry

Phosphinomethanides [R₂P-C(X)(Y)]- react with R' ₂SiC1 via Si-C bond formation tc give (a) R₂P-C(X)(Y)(SiR'₃), or, depending on the substituents X and Y, via Si-P bond formation, to give the ylides (b) Rt₃Si-PR₂=C(X)(Y). The latter rearrange to (a), provided that X and Y are not PR₂ substituents. With di- or triphosphinomethanides (X,Y=PR₂), the ylides are stable and fluctional, which may be rationalized by a pentacoordinate transition state. With R'₂SiC1₂, diphosphinomethanides form hexacoordinate complexes. In certain cases, these complexes may release silylenes RI₂Si via a redox reaction with low valency transition metals. Stable Si(I1) compounds with diphosphinomethanides are obtained under reducing conditions. Various skeleton rearrangements are observed starting from R'SiC1₃, including novel heterocycles and stable silylene-phosphine donor complexes.