Understanding Reactive Sulfur Species through P/S Synergy

Abstract

We investigated the differential oxidative and nucleophilic chemistry of reactive sulfur and oxygen anions (SSNO^-, SNO^-, NO₂^-, S₄^2-, and HS^-) using the simple reducing electrophile PPh₂Cl. In the case of SSNO^- reacting with PPh₂Cl, a complex mixture of mono and diphosphorus products is formed exclusively in the P(V) oxidation state. We found that the phosphine stoichiometry dictates selectivity for oxidation to P=S/P=O products or transformation to P₂ species. Interestingly, only chalcogen atoms are incorporated into the phosphorus products and, instead, nitrogen is released in the form of NO gas. Finally, we demonstrate that more reducing anions (S₄^2- and HS^-) also react with PPh₂Cl with P=S bond formation as a key reaction driving force.

Figure 1

(a) Selected examples of biological P-S motifs. Prior work including (b) nucleophilic attack/oxidation of P(III)-Cl with HS⁻, (c) photoinduced rearrangement of P=S diphosphorus species, (d) electrochemical reduction of S=PPh₂SH, and (e) this work: controlled oxidation of P(III)-Cl with small reactive anions.

Figure 2.

Product profile of [PNP][SSNO] and PPh₂Cl and ³¹P NMR spectrum. Approximate conversions were calculated by integration against inert [PNP]⁺ peak.

Figure 3.

Effect of PPh₂Cl stoichiometry on sulfur and oxygen incorporation into P(V) products.

Figure 4

Reactions with PPh₂Cl and various small anions (a) [PNP][NO₂], (b) K₂S₄(18-crown-6)₂, and (c) NaSH(15-crown-5).