Inorganic Chemistry, Vol.59, No.8, 5483-5489, 2020
Nucleophilic Activation of Red Phosphorus for Controlled Synthesis of Polyphosphides
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-21(3)-, 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 P16(2-)as a soluble polyphosphide product.