Orthophosphate and Sulfate Utilization for C–E (E = P, S) Bond Formation via Trichlorosilyl Phosphide and Sulfide Anions

Abstract

Reduction of phosphoric acid (H3PO4) or tetra-n-butylammonium bisulfate ([TBA]­[HSO4]) with trichlorosilane leads to the formation of the bis­(trichlorosilyl)­phosphide ([P­(SiCl3)2]−, 1) and trichlorosilylsulfide ([Cl3SiS]−, 2) anions, respectively. Balanced equations for the formation of the TBA salts of anions 1 and 2 were formulated based on the identification of hexachlorodisiloxane and hydrogen gas as byproducts arising from these reductive processes: i) [H2PO4]− + 10HSiCl3 → 1 + 4O­(SiCl3)2 + 6H2 for P and ii) [HSO4]− + 9HSiCl3 → 2 + 4O­(SiCl3)2 + 5H2 for S. Hydrogen gas was identified by its subsequent use to hydrogenate an alkene ((−)-terpinen-4-ol) using Crabtree’s catalyst ([(COD)­Ir­(py)­(PCy3)]­[PF6], COD = 1,5-cyclooctadiene, py = pyridine, Cy = cyclohexyl). Phosphide 1 was generated in situ by the reaction of phosphoric acid and trichlorosilane and used to convert an alkyl chloride (1-chlorooctane) to the corresponding primary phosphine, which was isolated in 41% yield. Anion 1 was also prepared from [TBA]­[H2PO4] and isolated in 62% yield on a gram scale. Treatment of [TBA]1 with an excess of benzyl chloride leads to the formation of tetrabenzylphosphonium chloride, which was isolated in 61% yield. Sulfide 2 was used as a thionation reagent, converting benzophenone to thiobenzophenone in 62% yield. It also converted benzyl bromide to benzyl mercaptan in 55% yield. The TBA salt of trimetaphosphate ([TBA]3[P3O9]·2H2O), also a precursor to anion 1, was found to react with either trichlorosilane or silicon­(IV) chloride to provide bis­(trimetaphosphate)­silicate, [TBA]2[Si­(P3O9)2], characterized by NMR spectroscopy, X-ray crystallography, and elemental analysis. Trichlorosilane reduction of [TBA]2[Si­(P3O9)2] also provided anion 1. The electronic structures of 1 and 2 were investigated using a suite of theoretical methods; the computational studies suggest that the trichlorosilyl ligand is a good π-acceptor and forms σ-bonds with a high degree of s character.

Phosphorus recovery and recycling – closing the loop

“…In a subsequent report, the dehydration step was eliminated, and the same [P(SiCl 3 ) 2 ] À anion could be accessed directly from phosphoric acid and trichlorosilane. 31 In this case, isolation of the pure [P(SiCl 3 ) 2 ] À anion was not possible, but it could be generated in situ and reacted further to an organophosphorus derivative. These studies show that it really is possible to completely bypass the use of white phosphorus in the synthesis of useful organophosphorus compounds, 32 and it will be interesting to see if these can be developed into useful industrial processes.…”

Unexpected Formation of the Highly Symmetric Borate Ion [B(SiCl3)4]−

“…Trichlorosilyl substituted anions of main group elements have been recently shifted into the focus of research. The following anions have been characterized since 2015: [C(SiCl 3 ) 3 ] À , [13,14,15] [Si(SiCl 3 ) 3 ] À , [16,17] [Ge(SiCl 3 ) 3 ] À , [16] [P(SiCl 3 ) 2 ] À , [18,19] and [S(SiCl 3 )] À . [19] Especially [P(SiCl 3 ) 2 ] À received considerable attention as synthon for the generation of phosphorus chemicals, that had previously only been available from white phosphorus (P 4 ).…”

“…The following anions have been characterized since 2015: [C(SiCl 3 ) 3 ] À , [13,14,15] [Si(SiCl 3 ) 3 ] À , [16,17] [Ge(SiCl 3 ) 3 ] À , [16] [P(SiCl 3 ) 2 ] À , [18,19] and [S(SiCl 3 )] À . [19] Especially [P(SiCl 3 ) 2 ] À received considerable attention as synthon for the generation of phosphorus chemicals, that had previously only been available from white phosphorus (P 4 ). [20] Neutral molecules like [C(SiCl 3 ) 4 ], [21,22,23,24,25,26] [E(SiCl 3 ) 4 ] (E=Si, Ge), [27,28,29,30] and [N(SiCl 3 ) 3 ] [31,32,33] have been prepared earlier.…”

The power of trichlorosilylation: isolable trisilylated allyl anions, allyl radicals, and allenyl anions

“…Analogous to the above-mentioned release of [SiCl3]from Si2Cl6/Cl -, also other main-group anions [RnE]can readily be generated under mild conditions from precursor fragme nts RnE-SiCl3 upon addition of Lewis basic anions, such as For Cl -(E = e.g., C, Si, Ge, P, S). 13,14,[20][21][22][23] Herein, we fill the gap in the series of perchlorinated substrate s and report on the reaction of the C3 substrate hexachloroprope ne (C3Cl6) with the Si2Cl6/Clsystem. In striking contrast to the previous cases (Scheme 1), there is now no quantitative Cl/SiCl3 exchange, but we rather obtain selective ly the trisilylated, dichlorinated allyl anion [1] -(Scheme 2).…”