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.