Synthesis, Spectroscopic Investigation and X-ray Structural Characterization of Some Primary Ammonium Phosphine Oxide, (R-C6H6NH3+)(-O)P(:O)2H

Abstract

The synthesis and identification of the first primary ammonium phosphonate
RC₆H₄NH₃(^-O)P(:O)₂H,  where R = H,  o-CH₃,  m-CH₃,  and
p-CH₃,  are reported. These compounds were prepared from reaction of
phosphorus trichloride and corresponding amines. Evidence for formation
of these molecules,  either in solution or in the solid, based on ¹H,  ³¹P NMR,
IR, MS and X-ray crystallography has been obtained. (o-CH₃C₆H₄NH₃⁺)
(^-O)P(:O)₂H crystallizes from ethanol/chloroform and is triclinic (m.p.
158-160°C) in space group P-1, with unit cell parameters a = 4.6782(13)
Å, b = 9.574(3) Å. c = 11.253(4) Å., α = 107.18(4^o), β = 101.37(4)°, γ=
96.99(3)° and Z = 2. The crystal structure, solved by direct methods. and
refined to R₁ = 0.0474 and wR₂ = 0.0699 for 2010 observed reflections.
The P—O distances are 1.499(3) Å. 1.499(3) Å and 1.565(3) Å. The
O—P—O angles are 116.5(2)°, 107.53(18)° and 111.97(18)°.
(p-CH₃C₆H₄NH₃⁺)(^-O)P(:O)₂H  crystallizes from DMF/ethanol or ethanol
and is orthorhombic (m.p. 174-176°C) in space group pca21, with unit
cell parameters a = 14.003 Å, b = 8.908 Å. c = 7.451 Å;  α = β = γ = 90°
and Z = 4.  The crystal structure is solved by direct methods, and refined
to Rl = 0.0427 and wR2 = 0.0871 for 5580 observed reflections. The P—O
distances are 1.481(2) Å, 1.493(3) Å and 1.540(3) Å, TheO—P—O angles
are 114.79(14) Å, 112.86(15) Å and 108.07(18)°. The P—O distances and
O—P—O angles show that these compounds have two identical P==O and
one P—O bonds.