Synthesis and Identification of Aryl and Alkyl Gem-Dilithium Phosphido-Boranes: A Boost to the Chemistry of Phosphandiides

Abstract

The synthesis and identification of unprecedented gem-dianionic phosphorus compounds, that is, gem-dilithium phosphido-boranes Li₂ [RP⋅BH₃ ], with R=Ph or Cy, are reported in THF solution. These were obtained by double deprotonation of the corresponding primary phosphine-borane precursors RPH₂ ⋅BH₃ . Their in-depth structural study, based on multinuclear (¹ H, ⁶ Li, ⁷ Li, ¹¹ B, ¹³ C, ³¹ P) mono- and bi-dimensional NMR analyses, indicates a strong influence of the phosphorus substituent on the structure of the gem-dianionic phosphorus structure; a monomeric arrangement was obtained when R=phenyl, whereas a cyclic oligomer was observed for R=cyclohexyl. These compounds represent a new type of useful reagent, and their access paves the way for the concept of "RP synthons" (i.e., RP^2- phosphandiides), likely to be the most flexible precursors of a variety of phosphorus targets.

Keywords: NMR structure; RP-synthon; phosphandiides; phosphido-boranes; primary phosphine.