Nucleophilic Activation of Red Phosphorus for Controlled Synthesis of Polyphosphides

Abstract

Reactions between red phosphorus (P red ) and potassium ethoxide in various organic solvents under reflux convert this rather inert form of the element to soluble polyphosphides. The activation is hypothesized to proceed via a nucleophilic attack by ethoxide on the polymeric structure of P red , leading to disproportionation of the latter, as judged from observation of P(OEt) 3 in the reaction products. A range of solvents has been probed, revealing that different polyphosphide anions (P 7 3− , P 16 2− , P 213− , and P 5 − ) can be stabilized depending on the combination of the boiling point and dielectric constant (polarity) of the solvent. The effectiveness of activation also depends on the nature of nucleophile, with the rate of reaction between P red and KOR increasing in the order t-Bu < n-Hex < Et < Me, which is in agreement with the increasing order of nucleophilic strength. Thiolates and amides were also examined as potential activators, but the reaction with these nucleophiles were substantially slower; nonetheless, all reactions between P red and NaSR yielded exclusively P 16 2− as a soluble polyphosphide product.

Solution phase synthesis of the less-known Form II crystalline red phosphorus

“…It is clearly shown from the XRD results that the pro- sphide anions. The existence of those polyphosphide clusters, especially P 16 2− , one of the most commonly reported polyphosphide anions 29,30 after RP activation, could also be affirmed via resonance signals detected in the 31 P NMR spectrum (Fig. 4f).…”

“…28 Thus, in order to accomplish a facile solvothermal reaction towards crystalline red phosphorus and to better understand the phase transition pathway, the selection of a mild nucleophilic solvent and appropriate reaction conditions to activate a-RP is of great significance. [29][30][31][32] Herein, we developed a solution-phase solvothermal pathway to prepare Form II red phosphorus by employing 1,2diaminopropane as a nucleophilic agent and systematically characterized the crystalline products. Crystals with high quality were obtained via optimizing the synthesis procedure, in which the reaction mechanism was demonstrated.…”

Frontiers in the solution-phase chemistry of homoatomic group 15 Zintl clusters

“…59 It was found that the distribution of polyphosphides was highly solvent dependant, and could be expanded to affect the preparation of [P 7 ] 3− and [P 11 ] 3− polyphosphides. 60 These reactions are thought to proceed via nucleophilic attack that initiates a cascade of disproportionation reactions and rearrangements. This work was expanded to implement a topdown approach for the activation of shelf-stable P(red) using organic solvents and convenient nucleophiles in a flow-reactor to attain soluble polyphosphides on continuous multi-gram scale.…”

“…The nucleophiles that activated P(red) were expanded to include other alkoxides (KOR; where R = methyl, n-hexyl and t-butyl), thiolates (NaSR; where R = Me, Et, n-hex, i-Pr, t-Bu), and amides (KHMDS, LiHMDS, and LDA), with varying degrees of efficiency. 59,60 Hänisch and Sundermeyer found that when methylcarbonate salts were allowed to react with P(SiMe 3 ) 3 the organic salts of PCO − could be attained. However, in a similar fashion when they reacted methylcarbonate salts with Sb (SiMe 3 ) 3 , rather than SbCO − salts, XRD analysis revealed the formation of [P(nBu) 3 Me] + 3 [Sb 11 ] 3− .…”

Substituted aromatic pentaphosphole ligands – a journey across the p-block

“… 4 The isolobal relationship between the CH fragment and the P atom 5 and the diagonal relationship between carbon and phosphorus suggest a comparable reactivity for the pentaphospholide anion cyclo -P 5 − . 6 However, investigations on the reactivity of the salts of cyclo -P 5 − towards alkylhalogenides showed further aggregation to polyphosphides, 7 leaving the chemistry of pentaphospholes cyclo -P 5 R to theoretical studies for decades. 8 Similar to Cp − , cyclo -P 5 − can be stabilized within the coordination sphere of different TMs 9 and is thus closely associated with the TM-mediated conversion of P 4 .…”