Funktionelle Trimethylphosphanderivate, XXVI [1]. Silylsubstituierte Phosphinomethane und Lithiumphosphinomethanide / Functional Trimethylphosphine Derivatives, XXVI [1] Silyl-substituted Phosphinomethanes and Lithiumphosphinomethanides

Abstract

The lithium phosphinomethanides LiCH(X)(PMe₂) (X = H, PMe₂ SiMe₃) react with Me₃SiCl to give silylsubstituted phosphinomethanes CH(X)(PMe₂)(SiMe₃). The latter are metalated by LiR (R = ^tBu, ⁿBu). This metalation is facilated by the presence of Me₂NCH₂CH₂NMe₂ (TMEDA). X-ray structure determinations of {(TMEDA)Li[CH(PMe₂)(SiMe₃)]}₂ (3b) and (TMEDA){Li[C(PMe₂)(SiMe₃)₂]}₂ (5b) show the marked influence of increasing silyl substitution on the structures of lithium phosphinomethanides: the Li-C contacts are weakened, whereas phosphorus forms additional (bridging) Li···P contacts to the second Li atom in the dimeric arrangements. In 3b, a six-membered ring in twist conformation is formed by head-to-tail dimerization. Likewise, 5b forms a six-membered ring, in this case by head-to-head dimerization. however, which may be regarded as a complex of a chelating phosphinomethyl lithiate ligand to [(TMEDA)Li]⁺ .