Preparation and NMR Spectra of the (Trifluoromethyl)argentates(III) [Ag(CF<sub>3</sub>)<i><sub>n</sub></i>X<sub>4-<i>n</i></sub><i></i>]<sup>-</sup>, with X = CN (<i>n</i> = 1−3), CH<sub>3</sub>, C⋮CC<sub>6</sub>H<sub>11</sub>, Cl, Br (<i>n</i> = 2, 3), and I (<i>n</i> = 3), and of Related Silver(III) Compounds. Structures of [PPh<sub>4</sub>][<i>trans</i>-Ag(CF<sub>3</sub>)<sub>2</sub>(CN)<sub>2</sub>] and [PPh<sub>4</sub>][Ag(CF<sub>3</sub>)<sub>3</sub>(CH<sub>3</sub>)]<sup>†</sup>
dataset
posted on 1997-03-26, 00:00 authored by Reint Eujen, Berthold Hoge, David J. BrauerTrifluoromethylation of
[Ag(CN)<sub>2</sub>]<sup>-</sup> with
(CF<sub>3</sub>)<sub>2</sub>Cd·diglyme yields
[Ag(CF<sub>3</sub>)(CN)]<sup>-</sup>. The anion is
readily oxidized
by bromine to the argentates(III),
[Ag(CF<sub>3</sub>)<sub>n</sub>(CN)<sub>4-<i>n</i></sub><i></i>]<sup>-</sup>,
<i>n</i> = 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 (<i>n</i> = 3) or unstable
(<i>n</i> = 2) haloargentates of the type
[Ag(CF<sub>3</sub>)<i><sub>n</sub></i>X<sub>4-<i>n</i></sub><i></i>]<sup>-</sup>,
X = Cl or
Br. Their dehalogenation with AgNO<sub>3</sub> in a donor solvent
D gives the adducts [Ag(CF<sub>3</sub>)<sub>3</sub>D] and
[Ag(CF<sub>3</sub>)<sub>2</sub>D<sub>2</sub>]<sup>+</sup>,
respectively. Decomposition of most argentates(III) proceeds
by reductive elimination of CF<sub>3</sub>X (X = Cl, Br,
or
CN), but ligand exchange with participation of the CF<sub>3</sub>
groups is also observed. The latter is used to
prepare
Ag(CF<sub>3</sub>)<sub>3</sub> derivatives from the readily
accessible
[<i>trans</i>-Ag(CF<sub>3</sub>)<sub>2</sub>(CN)<sub>2</sub>]<sup>-</sup>
anion. The syntheses of methyl(trifluoromethyl)argentates(III) and of
(cyclohexylethynyl)(trifluoromethyl)argentates(III) are
accomplished by
reaction of the cyanoargentates (<i>n</i> = 2, 3) with
CH<sub>3</sub>MgCl or LiC⋮CC<sub>6</sub>H<sub>11</sub>,
respectively. Often multinuclear
(<sup>109</sup>Ag, <sup>19</sup>F, <sup>13</sup>C,
<sup>1</sup>H) 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-<sup>1</sup>/<sub>2</sub> silver nuclei
are
interpreted on the basis of 5s(Ag) orbital participation in
competition with 4d orbital contributions to
Ag−CF<sub>3</sub>
bonding. Crystals of
[PPh<sub>4</sub>][Ag(CF<sub>3</sub>)<sub>2</sub>(CN)<sub>2</sub>]
belong to the monoclinic space group <i>C</i>2/<i>c</i>, with
<i>a</i> = 18.174(2) Å,
<i>b</i> = 7.8881(8) Å, <i>c</i> = 18.881(2) Å,
β = 93.036(8)°, and <i>Z</i> = 4, whereas
[PPh<sub>4</sub>][Ag(CF<sub>3</sub>)<sub>3</sub>(CH<sub>3</sub>)]
crystallizes in
the orthorhombic space group <i>Pca</i>2<sub>1</sub>, with
<i>a</i> = 24.941(3) Å, <i>b</i> = 7.2629(6) Å,
<i>c</i> = 14.9985(14) Å, and <i>Z</i> =
4.
The coordination environments of these two argentates are
approximately square planar. The Ag-CF<sub>3</sub> bonds
in
the dicyano complex (2.105(4) Å) are distinctly longer than the
Ag−CN linkages (2.013(3) Å). In the
[Ag(CF<sub>3</sub>)<sub>3</sub>(CH<sub>3</sub>)]<sup>-</sup>
anion, the Ag−CH<sub>3</sub> distance (2.097(5) Å) is slightly
shorter than the average Ag−CF<sub>3</sub> bond
lengths (2.119(10) Å).
