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 Li [RP⋅BH ], with R=Ph or Cy, are reported in THF solution. These were obtained by double deprotonation of the corresponding primary phosphine-borane precursors RPH ⋅BH . Their in-depth structural study, based on multinuclear ( H, Li, Li, B, C, 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 phosphandiides), likely to be the most flexible precursors of a variety of phosphorus targets.

Easy Access to Phosphine‐Borane Building Blocks

“…During our investigations, [19] Oulyadi, Gaumont, Harrison‐Marchanda et al. reported on the characterization of the gem‐ dilithium phosphido‐borane Li 2 [PhP⋅BH 3 ] intermediate 3 a in THF solution, which matches with our findings, but they did not provide structural characterization in the solid state [20] . We anticipated that the BH 3 moiety might assist the crystallization of this unique dianion and indeed found it to be possible to obtain the highly reactive phosphanediide 3 a as a colorless solid (91 %), which can be recrystallized from a mixture of THF, DME and hexanes at −78 °C to provide colorless crystals suitable for X‐ray analysis.…”

“…During our investigations, [19] Oulyadi,G aumont, Harrison-Marchanda et al reported on the characterization of the gemdilithiump hosphido-borane Li 2 [PhP•BH 3 ]i ntermediate 3a in THF solution, which matches with our findings, but they did not provides tructural characterization in the solid state. [20] We anticipated that the BH 3 moiety might assist the crystallization of this unique dianion and indeedf ound it to be possible to obtain the highly reactive phosphanediide 3a as ac olorless solid (91 %), which can be recrystallizedf rom am ixture of THF, DME and hexanes at À78 8Ct op rovide colorless crystals suitable for X-ray analysis. The molecular structure of 3a features the dianionic [PhP•BH 3 ]f ragment, of which the phosphorus atom connects to four lithium ions in the polymeric chain in the direction of the crystallographic b-axis (P1ÀLi1 2.550(3), P1ÀLi2 2.524(4), P1ÀLi1 ii 2.540(4), P1ÀLi2 ii 2.561(4) ;F igure 4).…”

The interpretation of small molecule diffusion coefficients: Quantitative use of diffusion-ordered NMR spectroscopy

“…Other organolithium complexes characterised using an internal calibration method include chiral enolate aggregates [173], THF-solvated 1,4-dienolates [174], 2,2,6,6tetramethylpiperidides [175,176], pinacolone enolate [177], aryl and alkyl gem-dilithium phosphido-boranes [178], chiral lithium amides derived from valinol derivatives [179,180], N-isopropyl alaninol [181] and S-valine [182], as well as the identification of hexameric and octameric sec-butyllithium/sec-butoxide mixed aggregates [183]. Such studies are not limited to single metal complexes.…”

Substituent Effects on the Structures of Alkali Metal Phosphido‐Borane Complexes

“…Since then, a limited number of alkali and alkaline earth metal complexes, [7,8] a very limited number of p‐block complexes, [6,7b,10] and a small number of transition metal complexes of these ligands have been reported [4,5] . A small number of diaminophosphido‐borane complexes [(R 2 N) 2 P(BH 3 )]M have also been isolated, [11] while, very recently, the synthesis of a series of gem ‐dilithium phosphido‐boranes [RP(BH 3 )]Li 2 has been described [12] . In view of the limited previous studies of the coordination chemistry of phosphido‐borane ligands, a systematic study of the impact of the substituents and metal centers on the structures of these compounds appears warranted.…”

“…[4,5] A small number of diaminophosphido-borane complexes [(R 2 N) 2 P(BH 3 )]M have also been isolated, [11] while, very recently, the synthesis of a series of gem-dilithium phosphido-boranes [RP(BH 3 )]Li 2 has been described. [12] In view of the limited previous studies of the coordination chemistry of phosphido-borane ligands, a systematic study of the impact of the substituents and metal centers on the structures of these compounds appears warranted. In this contribution, we report the synthesis of a series of differently-substituted phosphidoborane complexes of lithium and sodium and show how the structures of these compounds are affected by the nature of the substituents and the alkali metal.…”