Preparation and NMR Spectra of the (Trifluoromethyl)argentates(III) [Ag(CF3)nX4-n]-, with X = CN (n = 1−3), CH3, C⋮CC6H11, Cl, Br (n = 2, 3), and I (n = 3), and of Related Silver(III) Compounds. Structures of [PPh4][trans-Ag(CF3)2(CN)2] and [PPh4][Ag(CF3)3(CH3)]†
dataset
posted on 1997-03-26, 00:00 authored by Reint Eujen, Berthold Hoge, David J. BrauerTrifluoromethylation of
[Ag(CN)2]- with
(CF3)2Cd·diglyme yields
[Ag(CF3)(CN)]-. The anion is
readily oxidized
by bromine to the argentates(III),
[Ag(CF3)n(CN)4-n]-,
n = 1−4. The stability of these species decreases
with
an increasing number of CN groups. Halogenation of these complexes
with acetyl chloride or with bromine
affords the moderately stable (n = 3) or unstable
(n = 2) haloargentates of the type
[Ag(CF3)nX4-n]-,
X = Cl or
Br. Their dehalogenation with AgNO3 in a donor solvent
D gives the adducts [Ag(CF3)3D] and
[Ag(CF3)2D2]+,
respectively. Decomposition of most argentates(III) proceeds
by reductive elimination of CF3X (X = Cl, Br,
or
CN), but ligand exchange with participation of the CF3
groups is also observed. The latter is used to
prepare
Ag(CF3)3 derivatives from the readily
accessible
[trans-Ag(CF3)2(CN)2]-
anion. The syntheses of methyl(trifluoromethyl)argentates(III) and of
(cyclohexylethynyl)(trifluoromethyl)argentates(III) are
accomplished by
reaction of the cyanoargentates (n = 2, 3) with
CH3MgCl or LiC⋮CC6H11,
respectively. Often multinuclear
(109Ag, 19F, 13C,
1H) NMR data of transient and stable Ag(III) species
establish unambiguously not only their
constitution but also the square-planar coordination of the metal.
Couplings to the spin-1/2 silver nuclei
are
interpreted on the basis of 5s(Ag) orbital participation in
competition with 4d orbital contributions to
Ag−CF3
bonding. Crystals of
[PPh4][Ag(CF3)2(CN)2]
belong to the monoclinic space group C2/c, with
a = 18.174(2) Å,
b = 7.8881(8) Å, c = 18.881(2) Å,
β = 93.036(8)°, and Z = 4, whereas
[PPh4][Ag(CF3)3(CH3)]
crystallizes in
the orthorhombic space group Pca21, with
a = 24.941(3) Å, b = 7.2629(6) Å,
c = 14.9985(14) Å, and Z =
4.
The coordination environments of these two argentates are
approximately square planar. The Ag-CF3 bonds
in
the dicyano complex (2.105(4) Å) are distinctly longer than the
Ag−CN linkages (2.013(3) Å). In the
[Ag(CF3)3(CH3)]-
anion, the Ag−CH3 distance (2.097(5) Å) is slightly
shorter than the average Ag−CF3 bond
lengths (2.119(10) Å).
