Stability of AgIII towards Halides in Organosilver(III) Complexes

Article abstract of DOI:10.1002/chem.202101859

The involvement of silver in two-electron Ag^I/Ag^III processes is currently emerging. However, the range of stability of the required and uncommon Ag^III species is virtually unknown. Here, the stability of Ag^III towards the whole set of halide ligands in the organosilver(III) complex frame [(CF₃)₃AgX]^? (X=F, Cl, Br, I, At) is theoretically analyzed. The results obtained depend on a single factor: the nature of X. Even the softest and least electronegative halides (I and At) are found to form reasonably stable Ag^III?X bonds. Our estimates were confirmed by experiment. The whole series of nonradiative halide complexes [PPh₄][(CF₃)₃AgX] (X=F, Cl, Br, I) has been experimentally prepared and all its constituents have been isolated in pure form. The pseudohalides [PPh₄][(CF₃)₃AgCN] and [PPh₄][(CF₃)₃Ag(N₃)] have also been isolated, the latter being the first silver(III) azido complex. Except for the iodo compound, all the crystal and molecular structures have been established by single-crystal X-ray diffraction methods. The decomposition paths of the [(CF₃)₃AgX]^? entities at the unimolecular level have been examined in the gas phase by multistage mass spectrometry (MSⁿ). The experimental detection of the two series of mixed complexes [CF₃AgX]^? and [FAgX]^? arising from the corresponding parent species [(CF₃)₃AgX]^? demonstrate that the Ag?X bond is particularly robust. Our experimental observations are rationalized with the aid of theoretical methods. Smooth variation with the electronegativity of X is also observed in the thermolyses of bulk samples. The thermal stability in the solid state gradually decreases from X=F (145 °C, dec.) to X=I (78 °C, dec.) The experimentally established compatibility of Ag^III with the heaviest halides is of particular relevance to silver-mediated or silver-catalyzed processes.

Full text of DOI:10.1002/chem.202101859

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Stability of AgIII towards Halides in Organosilver(III)
Complexes
Daniel Joven-Sancho,[a] Miguel Baya,[a] Larry R. Falvello,[b] Antonio Martín,[a] Jesús Orduna,[b]
and Babil Menjón*[a]
Dedicated to the Memory of Prof. Dr. Víctor Riera
Abstract: The involvement of silver in two-electron AgI/AgIII
processes is currently emerging. However, the range of
stability of the required and uncommon AgIII species is
virtually unknown. Here, the stability of AgIII towards the
whole set of halide ligands in the organosilver(III) complex
frame [(CF3)3AgX]À (X=F, Cl, Br, I, At) is theoretically analyzed.
The results obtained depend on a single factor: the nature of
X. Even the softest and least electronegative halides (I and At)
are found to form reasonably stable AgIIIÀ X bonds. Our
estimates were confirmed by experiment. The whole series of
nonradiative halide complexes [PPh4][(CF3)3AgX] (X=F, Cl, Br, I)
has been experimentally prepared and all its constituents
have been isolated in pure form. The pseudohalides
[PPh4][(CF3)3AgCN] and [PPh4][(CF3)3Ag(N3)] have also been
isolated, the latter being the first silver(III) azido complex.
Except for the iodo compound, all the crystal and molecular
structures have been established by single-crystal X-ray
diffraction methods. The decomposition paths of the
[(CF3)3AgX]À entities at the unimolecular level have been
examined in the gas phase by multistage mass spectrometry
(MSn). The experimental detection of the two series of mixed
complexes [CF3AgX]À and [FAgX]À arising from the corre-
sponding parent species [(CF3)3AgX]À demonstrate that the
AgÀ X bond is particularly robust. Our experimental observa-
tions are rationalized with the aid of theoretical methods.
Smooth variation with the electronegativity of X is also
observed in the thermolyses of bulk samples. The thermal
stability in the solid state gradually decreases from X=F
°
°
(145 C, dec.) to X=I (78 C, dec.) The experimentally estab-
lished compatibility of AgIII with the heaviest halides is of
particular relevance to silver-mediated or silver-catalyzed
processes.
Introduction
RÀ [AgIII]À X entity. The success of this crucial step depends on
the ease with which the RÀ X bond is cleaved and on the
stability of the final product. In general, the RÀ X bond is more
easily broken on going down the halogen Group: F<Cl<Br<I.
For this reason, the heavier RÀ Br and RÀ I molecules are
preferentially used over the lighter RÀ F and RÀ Cl ones in this
kind of process.[1a] However, the reducing ability of the halide
ions follows exactly the same trend, an unfortunate coincidence
that might compromise the stability and even the credibility of
any tentative RÀ [AgIII]À I intermediate. In this context, it is worth
noting that the transient species [Me2RAgI]À presumably formed
upon oxidative addition of RÀ I to the homoleptic [Me2Ag]À
derivative could not be detected either even using the most
advanced spectroscopic techniques.[4] In actual fact, there is a
lack of experimental evidence confirming the existence of these
critical and elusive intermediates.
The involvement of silver in two-electron redox processes was
only recently demonstrated.[1,2] This new paradigm opens a
wealth of possibilities for a metal, which has been traditionally
confined to a limited role as a one-electron reagent. As a result
of these new findings, novel AgIII species belonging to the
select class of high-valent organometallic derivatives[3] are now
considered as feasible reaction intermediates. A key step in this
new reactivity pattern for silver is the oxidative addition of a
halocarbon, RX, to the AgI centre to afford the oxidized
[a] D. Joven-Sancho, Dr. M. Baya, Dr. A. Martín, Dr. B. Menjón
Instituto de Síntesis Química y Catálisis Homogénea (iSQCH)
CSIC-Universidad de Zaragoza
C/ Pedro Cerbuna 12, 50009 Zaragoza (Spain)
E-mail: menjon@ctq.csic.es
Oxidation state III is still rare for silver and the highest
currently available for this metal.[5,6] The only known binary
silver(III) halide is the fluoride AgF3,[7] which is unstable and
extremely reactive.[8] Complex fluorides include the paramag-
netic material Cs2K[AgF6][9] and a number of salts of the square-
planar diamagnetic anion [AgF4]À (Scheme 1).[10] In contrast,
none of the heavier AgX3 halides (X=Cl, Br, I) has ever been
prepared. In fact, they were calculated to be unstable in the gas
phase and better viewed as XAg·X2 adducts (Scheme 1).[11] In a
recent study, Grochala et al. showed that the silver(II) chloride,
[b] Prof. Dr. L. R. Falvello, Dr. J. Orduna
Instituto de Nanociencia y Materiales de Aragón (INMA)
CSIC-Universidad de Zaragoza
C/ Pedro Cerbuna 12, 50009 Zaragoza (Spain)
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/chem.202101859
© 2021 The Authors. Chemistry - A European Journal published by Wiley-
VCH GmbH. This is an open access article under the terms of the Creative
Commons Attribution Non-Commercial NoDerivs License, which permits use
and distribution in any medium, provided the original work is properly cited,
the use is non-commercial and no modifications or adaptations are made.
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Thus, we turned to the homoleptic AgI complex [CF3AgCF3]À as
a potential precursor. The most straightforward method would
be the oxidative addition of CF3I to the AgI homoleptic
precursor [CF3AgCF3]À . This method with optimal atom econo-
my was successfully applied in gold chemistry. Thus, the
photoinduced oxidative addition of CF3I to the linear complex
[CF3AuCF3]À cleanly afforded the square-planar gold(III) deriva-
tive [(CF3)3AuI]À and provided an efficient entry to the (CF3)3Au
moiety.[18] This procedure, however, failed when applied to the
AgI precursor (Scheme 2). On the other hand, it has been
recently reported that the non-fluorinated homologous species
[Me2Ag]À underwent oxidative addition of MeI at low
temperature.[4] Although the primary product, [Me3AgI]À , could
not be directly detected, its intermediacy was inferred from the
nature of the final derivatives formed.
Scheme 1. Currently known silver(III) fluorides and other related halides (see
text for details). Compounds 1–7 are studied in this work. Aside from the
astato complex 5, all other compounds were isolated and characterized.
Access to the (CF3)3Ag moiety was in general not easy
because the formation of the homoleptic species [(CF3)4Ag]À is
largely favored. It can be said that this symmetric, fully
substituted compound acts as a thermodynamic sink in many
of these processes. In fact, it was the main compound obtained
by treatment of [CF3AgCF3]À with PhI(OAcF)2 and Me3SiCF3 in
the presence of CsF (Scheme 2).[19] In this context, it is worth
noting that the chloro complex [(CF3)3AgCl]À was first detected
(19F NMR) as an intermediate species in the synthesis of the
mixed-valence salt Ag[(CF3)4Ag] by Dukat and Naumann.[20]
Isolation of the chloro complex proved difficult though. The
material obtained by reacting DME solutions of
[PPh4][(CF3)3AgCN] with AcCl was later reported to consist of
[PPh4][(CF3)3AgCl] with around 90% purity content as estimated
by spectroscopic methods.[15] In a subsequent work, the [N-
(PPh3)2][(CF3)3AgCl] salt was purportedly isolated as a white solid
in 33.7% yield by treating MeCN solutions of the aforemen-
tioned solvento complex (CF3)3Ag(NCMe) with [N(PPh3)2]Cl
followed by column-chromatography purification. Unfortu-
nately, no analytic data were provided and therefore, the purity
of the obtained material is unknown.[16]
AgCl2, was metastable in the solid state with respect to AgCl+
1
= Cl2.[12] The heavier halides AgBr2 and AgI2 are known to be
2
even less stable.[13] In the realm of organometallic chemistry, we
recently
[PPh4][(CF3)3AgF] shows an ideal combination of thermal
stability and chemical reactivity, as was briefly
found
that
the
organosilver(III)
fluoride
communicated.[14] The heavier organosilver(III) halides
[(CF3)3AgX]À (X=Cl, Br, I) had been detected in solution by Eujen,
Hoge and Brauer, but could not be isolated.[15] Although the
isolation of the [N(PPh3)2][(CF3)3AgX] (X=Cl, Br) salts was later
claimed,[16] only fragmentary information and insufficient data
were reported. Thus, little is known about the compatibility of
AgIII with the heavier halides.
Here, we provide a theoretical evaluation of the compat-
ibility of AgIII with every halogen, including the heaviest
naturally occurring one: At. Furthermore, we first isolate
compounds with AgIIIÀ Br and AgIIIÀ I bonds, thereby lending
experimental support for the existence of related transient and
intermediate species. An unprecedented silver(III) azido com-
plex, [PPh4][(CF3)3Ag(N3)], has also been obtained, isolated and
characterized.
We have devised a more convenient method to obtain
analytically pure samples of the salt [PPh4][(CF3)3AgCl] (2), which
consisted of treating [PPh4][CF3AgCF3] with PhICl2 in CH2Cl2
°
solution at À 55 C (Scheme 2). The procedure involved both
Results and Discussion
metal oxidation and ligand exchange. Only 2= of the total metal
3
amount suffered oxidation from AgI to AgIII, whereas the
1
Synthetic procedures
remaining = portion acted as CF3-transfer reagent. As a result,
3
Considering the existing precedents,[15,16] the solvento complex
(CF3)3Ag(NCMe) might be viewed as the most suitable synthon
of the (CF3)3Ag moiety. This widely sought complex is known to
arise in different processes and under various conditions, yet in
nonselective means. The most successful synthesis among them
all involves treatment of Li[(CF3)4Ag] with ICl in MeCN to
eventually afford the desired product in only about 8%
estimated yield.[16] Its isolation as a colorless oil is, however,
intriguing, since the gold homologue (CF3)3Au(NCMe) is known
to be a white solid.[17] In the search for an alternative synthesis,
it becomes apparent that, aside from the extremely reactive
AgF3 and [AgF4]À species, there is a lack of suitable AgIII
precursors. A different synthetic strategy was therefore needed.
Scheme 2. AgI is successfully oxidized to AgIII with the organoiodine(III)
reagents PhI(OAcF)2 (see ref. [19]) and PhICl2, but not with CF3I.
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the silver(I) halide complex [PPh4][AgCl2] was formed along with
the desired product. Fortunately, this inorganic byproduct was
efficiently removed by taking advantage of its virtual insolubility
in DME.[21] In this way, compound 2 was finally isolated as a
pale-yellow solid in 75% yield with respect to the theoretical
amount expected in the indicated process (Scheme 2).
The pseudohalide complexes [PPh4][(CF3)3AgCN] (6) and
[PPh4][(CF3)3Ag(N3)] (7) were similarly obtained by reacting the
fluoro complex 1 with the appropriate Me3SiX’ reagent (X’=CN,
N3). Following this procedure, the cyano complex 6 is obtained
virtually free of contaminants, whereas it contained about 5%
of the homoleptic compound [PPh4][(CF3)4Ag] when obtained
by treatment of [PPh4][trans-(CF3)2Ag(CN)2] with AcCl.[15] The
azido complex 7 is particularly interesting given the relevance
of the azide group in silver chemistry.[25] The binary silver(I)
azide, Ag(N3), has been known for more than a century:[26] its
explosive behavior has attracted much attention and has been
thoroughly studied.[27] Considering the potential explosive
nature of the new compound 7, only small amounts were
prepared in each synthetic batch and the solid samples were
handled with great caution. Nevertheless, in our experience,
compound 7 proved to be not particularly sensitive to heat and
shocks. It can be described as a moderately stable compound
With complex 2 in hand, we wanted to check whether the
AgIII ion belongs to class a or class b metals according to the
AhrlandÀ ChattÀ Davis classification,[22] which directly relates to
the more general hard and soft classification.[23] To this aim, we
treated complex 2 with alkali metal salts of the heavier halides
(KBr, NaI) in CH2Cl2 solution at room temperature. Under these
experimental conditions, substitution did actually occur and the
heavier homologues [(CF3)3AgBr]À and [(CF3)3AgI]À were formed.
The process, however, was not clean and the corresponding
complexes could not be isolated in pure form, at least under
the assayed conditions. Although of little synthetic use, the
process sufficed to classify the AgIII ion within the class b (soft)
metals in analogy to the well-established behavior of AuIII.[24]
The isolation of compounds [PPh4][(CF3)3AgBr] (3) and
[PPh4][(CF3)3AgI] (4) required a different synthetic approach (see
below).
°
decomposing without exploding at 92 C (TGA: Figure S36 in
the Supporting Information). This behavior can be associated to
the large size of the cation, as found in several homoleptic
azides of various transition metals.[28] To the best of our
knowledge, no silver(III) azide had been isolated thus far. In
contrast, several azides of AuIII are currently known, including
the neutral compounds (NHC)Au(N3)3,[29] (terpy-kN)Au(N3)3,[30]
and (N&C)Au(N3)2,[31] as well as the cationic complex [(BPI)
Au(N3)][PF6][32] and different salts of the homoleptic complex
[Au(N3)4]À .[28,33] The isolation of compound 7 lends support to
the existence of the formally related species [Ag(OH)3(N3)]À ,
which, according to kinetic and mechanistic studies, was
suggested to operate as a key intermediate in the reduction of
AgIII by azide in aqueous alkaline media.[34]
According to the class b behavior of AgIII, all previous
attempts to prepare the lighter fluoro complex [(CF3)3AgF]À by
halide exchange with fluoride were unsuccessful.[15] The reac-
tion of the solvento complex (CF3)3Ag(NCMe) with [N(PPh3)2]F,
KF and HF also failed.[16] We have found, however, that the
reaction of complex 2 with AgF in MeCN (Scheme 3) affords the
fluoro-derivative [PPh4][(CF3)3AgF] (1), which is isolated as a
white solid in 75% yield.[14] This is the first organosilver(III)
fluoride compound to have been prepared or even detected.
Our preliminary assays demonstrated that the terminal F-ligand
in compound 1 is reactive, as it readily undergoes solvolysis
with H2O and with thiols RSH.[14] We took further advantage of
the reactivity of this unique compound.
Spectroscopic characterization
The fluoro complex 1 provides an efficient entry to the
heavier halide homologues [(CF3)3AgBr]À and [(CF3)3AgI]À , which
had eluded isolation to date. It is worth noting that although
Naumann et al. claimed the isolation of the bromo complex
[N(PPh3)2][(CF3)3AgBr], in their report the authors provided
neither experimental nor spectroscopic details to support their
claim.[16] Compounds [PPh4][(CF3)3AgBr] (3) and [PPh4][(CF3)3AgI]
(4) were cleanly obtained by reaction of the fluoro complex 1
with the corresponding silyl halide Me3SiX (Scheme 3). The
isolated halide complexes [PPh4][(CF3)3AgX] (1À 4) were increas-
ingly colored solids along the series: F (white)<Cl (pale
yellow)<Br (yellow)<I (orange).
All the compounds described here have been characterized by
analytical and spectroscopic methods. The results are given in
the Experimental Section and the original spectra are shown in
the Supporting Information. In the following discussion,
especial emphasis will be put on the comparison of the data
presented here with those already known for the homologous
gold(III) derivatives, [(CF3)3AuX]À , wherever such comparison
can be established.[18] This will enable to evaluate from an
experimental viewpoint to which extent these twofold AgIII
/
AuIII series show similar properties as should be expected for
isoleptic and isoelectronic species. This experimental relation-
ship is of particular importance considering that the oxidation
Scheme 3. Synthesis of the organosilver(III) halide and pseudohalide complexes [(CF3)3AgX]À .
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state of related CuIII species has been questioned and is still
much debated.[35–37]
bromo complex 3 (Δδ�0.6 ppm) and turns inverted in the iodo
complex 4 (Δδ � À 8 ppm). The chemical shift of each kind of
CF3 group shows almost linear dependence of the electro-
negativity of the involved halogen, χ(X), measured in the
Sanderson scale (Figure 1).[43] The dependence is more pro-
nounced in the mutually trans CF3 groups than in the one trans
to the varying substituent X. This surprising dependence was
already observed in the homologous gold(III) system,[18] as well
as in the related set of isoleptic and isoelectronic platinum(II)
derivatives [(CF3)3PtX]2À (X=Cl, Br, I).[44] In the cyano complex 6,
the positions of the nominal septet versus quartet signals
appear also inverted (Δδ�À 5 ppm), as is usually found in
square-planar [(CF3)3MX]nÀ complexes with anionic and neutral
π-acceptor ligands (e.g., CN, CO, CNR, PR3), and also with
X=I.[17,18, 44]
The IR spectra are shown in Figures S1À S6. Here, only the
most relevant features will be commented on. The absorption
assigned to the M–Cl stretching mode in compound 2,
ν(AgÀ Cl)=348 cmÀ 1 (Figure S2), appears at slightly higher
frequency than observed in the corresponding gold homo-
logue: ν(AuÀ Cl)=341 cmÀ 1.[18] This is the standard trend in ν(M–
X) vibrations of 4d versus 5d metals, as exemplified in the case
of the PdII / PtII couple,[38] which is isoelectronic (d8) with the AgIII
/ AuIII one. The standard trend is reversed in the fluoro
complexes, since the ν(MÀ F) vibration in compound 1 (Fig-
ure S1) appears at lower frequency (492 cmÀ 1) than that
observed for gold (511 cmÀ 1).[18] Given that the metal coordina-
tion environment and even the cation are exactly the same in
both cases, [PPh4][(CF3)3MF] (M=Ag, Au), the reverse trend
observed here would suggest that in these compounds, the
AgÀ F bond is weaker than the AuÀ F one. It is worth noting that
the IR-active νa(MF4) stretching mode (Eu) in the simple Cs[MF4]
salts appears again at higher frequency for Ag (595 cmÀ 1)[39]
than for Au (585 cmÀ 1).[40] In the cyano complex 6, no
absorption is observed that might be assigned to the ν(CN)
vibration (Figure S5). As this vibration mode should be IR active
in a local Cs symmetry (see structural data below), the failure to
observe the corresponding absorptions in the [PPh4][(CF3)3MCN]
compounds can be due to just poor intensity in both cases
(M=Ag, Au). The absorption appearing at 407 cmÀ 1 in com-
pound 6 can be ascribed to the ν(AgÀ CN) vibration. In the
homologous gold compound, the corresponding ν(AuÀ CN)
absorption appears at 425 cmÀ 1.[18] The azido complex 7 shows
a sharp absorption at 2042 cmÀ 1 (Figure S6), which can be
assigned to the νa(NNN) mode. An additional absorption at
396 cmÀ 1 can be ascribed to the ν(AgÀ N) vibration mode, as
typically found in terminal MÀ N3 complexes.[41]
In the 19F NMR spectrum of the azido complex 7, all fine
features are clearly resolved (Figure 2). The positions of the
nominal septet (δF =À 25.76) and quartet (δF =À 35.02) are near
the positions observed in the fluoro complex 1 (δF =À 24.43
and À 37.60 ppm, respectively). The remarkable spread of CF3
signals observed for the [(CF3)3Ag(N3)]À anion (Δδ�9 ppm) and
the fluoro complex 1 (Δδ�13 ppm) denotes largely different
chemical environments for the two inequivalent CF3 groups in
both anionic species.
Experimental ground-state structures
The isolation of the [(CF3)3AgX]À complexes 1–4 provides an
unprecedented opportunity to obtain structural information on
the Ag(III)À X bonds (X=Cl, Br, I). Single crystals were obtained
for all the compounds described here and were studied by X-
ray diffraction (XRD) methods. Unfortunately, the anion of the
iodo complex 4 suffered from heavy disorder of the substitu-
ents around the metal, thus precluding to obtain the desired
structural parameters in this case. In the previously reported kL-
(BEDT-TTF)2[(CF3)3AgCl]·CHCl2CH2Cl salt (monoclinic, Pnma),[45]
the anion was also heavily disordered and thus no detailed
The 19F NMR spectra of the [(CF3)3AgX]À compounds are
particularly rich and informative (Figures S7À S18). They all
consist of basically a quartet and a septet in 2:1 integrated
ratio, corresponding to the two chemically inequivalent CF3
groups in each molecule, namely the mutually perpendicular
CF3À AgÀ CF3 (trans) and CF3À AgÀ X (trans) units. This basic
pattern undergoes further splitting by coupling to the
107Ag/109Ag nuclei with 51.84:48.16 natural abundance[42]
—
both of them with nuclear spin I=1= . The resulting pattern can
2
appear therefore complex in aspect. Nevertheless, the spectral
parameters can be directly obtained from the experimental
spectra. The accuracy of the analysis was further checked by
simulation (see Supporting Information). The spectroscopic data
of the cyano complex (6) and the heavier halides (2À 4) had
been masterfully assigned by Eujen and his coworkers relying
on solutions samples.[15] Our data generally agree with their
assignments and will not be described in detail here. In the
spectrum of the fluoro-derivative 1 (Figure S7), the complex
signal at high field (δF =À 236.22 ppm) is assigned to the
terminal F-ligand. The resonances of the chemically inequiva-
lent CF3 groups show the largest separation within the halide
series (Δδ �13 ppm). The separation decreases markedly in the
chloro complex 2 (Δδ=5 ppm), becomes very small in the
Figure 1. Correlation between the δF values of the [PPh4][(CF3)3AgX]
compounds 1–4 (19F NMR in CD2Cl2 solution at room temperature) and the
electronegativity of the halogen involved, χ(X), on the Sanderson scale.[43]
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Figure 2. 19F NMR spectrum of the azido complex 7 in CD2Cl2 solution at room temperature with relevant parameters indicated (δF in ppm; J in Hz). The ratio
of the couplings to the 109Ag and 107Ag isotopes in each case is the ratio of their respective gyromagnetic constants: γ(109Ag)/γ(107Ag)�1.15.
structural information could be gained, either. In turn, the
diffraction experiments of compounds 1–3 were satisfactory as
detailed in the Supporting Information.[46] In the obtained
structures, cations and anions appear separated in the crystal
lattices except for the fluoro complex 1. In the latter case, the
terminal F ligand forms loose [Ag]À F···HC(sp2) hydrogen bonds
with the cation, as already pointed out in our previous
communication.[14] The experimentally obtained structures of
the [(CF3)3AgX]À anions (X=F, Cl, Br) are invariably square-planar
(Figure 3), as is usually found in d8 metal complexes. The most
relevant geometric parameters are given in Table 1, where they
are compared with those corresponding to the all-organo-
metallic [PPh4][(CF3)3AgR] compounds (R=CH3,[15] CF3).[19] The
geometry of the CF3À AgÀ CF3 axis shows little variation along
the series, being almost linear and with AgÀ C bond distances of
approximately 210 pm. The AgÀ C bond in the perpendicular
CF3À AgÀ X axis is shorter, which is consistent with the lower
trans influence of the halide ligands.[47] The AgÀ C bond in the
CF3À AgÀ F unit (1) is particularly short (203.6(2) pm), while the
associated AgÀ F bond (198.4(1) pm) is longer than that found
in the purely inorganic salt K[AgF4]: 188.9(3) pm.[48] The
observed elongation of the AgÀ F bond in compound 1 can be
ascribed to the comparatively larger trans influence of the CF3
group.[49] The AgÀ F bond distance in compound 1 is identical to
that found in the naked diatomic silver(I) fluoride molecule AgF
in the gas phase: 198.32 pm.[50] This coincidence is surprising
considering the different oxidation state and coordination
number of the metal in each case. The observed AgÀ X bond
distances in compounds 2 and 3 (AgÀ Cl 232.03(4) pm; AgÀ Br
246.25(2) pm) are, in turn, slightly longer than those found in
gaseous AgX: AgÀ Cl 228.08 pm and AgÀ Br 239.22 pm.[51]
Figure 3. Displacement-ellipsoid diagram (50% probability) of the organo-
silver(III) anionic complexes: a) [(CF3)3AgF]À in 1 (see ref. [14]), b) [(CF3)3AgCl]À
in 2, and c) [(CF3)3AgBr]À in 3.
Table 1. Relevant structural parameters of the [PPh4][(CF3)3AgX] salts, as
determined by single-crystal XRD methods.[a]
[b]
[c]
[e]
X
AgÀ X
XAgÀ CF3
AgÀ C2
CÀ AgÀ X[d]
�ff [ ]
°
°
[pm]
[pm]
[pm]
[ ]
[f]
CH3
CF3
209.7(5)
209.8(2)
198.4(1)
232.03(4) 206.7(2)
246.25(2) 207.7(2)
212.7(5)
209.8(2)
203.6(2)
211.5(5)
209.8(2)
209.8(2)
212.3(2)
211.2(2)
210.4(2)
[211.2(3)]
173.8(2)
176.8(1)
179.46(7)
177.87(5)
175.03(9)
178.47(7)
360.4(2)
[g]
360.07(9)
359.98(8)
359.97(7)
359.8(1)
F (1)[h]
Cl (2)
Br (3)
CN (6)
[Au]–
CN[i]
204.0(2)
207.1(2)
360.08(8)
[205.9(3)] [206.8(3)]
[178.50(9)] [360.0(1)]
It would be useful to compare the structural parameters
obtained for the silver(III) halide complexes 1–3 with their gold
(III) homologues. These compounds are indeed known,[18] but
their structures have not yet been determined by XRD methods.
The desired comparison can, however, be established between
the corresponding cyano complexes [PPh4][(CF3)3MCN] (M=Ag
(6) and Au). This comparison is particularly reliable, since the
N3 (7)
205.6(5)
202.9(7)
210.6(13)
176.2(3) 360.0(3)
[a] Average values indicated where not unique. [b] The AgÀ C distance
trans to X is here indicated. [c] Average of the two independent AgÀ C
bond lengths in trans arrangement. [d] Nearly linear trans-standing
CÀ AgÀ X unit. [e] Summation of all adjacent EÀ AgÀ E’ angles as a measure
of planarity. [f] Ref. [15]. [g] Ref. [19]. [h] Ref. [14]. [i] The gold compound
[PPh4][(CF3)3AuCN] is included here for comparison: see Ref. [18].
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diffraction data of these isomorphous single crystals (mono-
clinic, P21/c, Z=4) with very similar lattice constants and
virtually the same cell volume, were also taken at the same
temperature (100 K) and were solved to similar final accuracy
levels producing comparable standard deviations. The obtained
structural parameters around the metal are virtually identical
within the experimental error in both compounds (Figure 4 and
Table 1) and confirm our former conclusion that AgIII and AuIII
have similar covalent radii, at least in square-planar coordina-
tion environments.[52]
The structure of the anion [(CF3)3Ag(N3)]À as found in
crystals of 7 is depicted in Figure 5.[46] The azide unit is almost
α
β
γ
°
linear: N À N À N 175.0(5) . It acts as a terminal ligand with a
α
β
°
distinct bent arrangement, AgÀ N À N 120.9(5) , and a twist out
α
β
°
of the metal coordination plane by 51.9(4) . The N À N bond is
slightly elongated: NαÀ Nβ 119.8(7) pm versus NβÀ Nγ 115.4(6) pm;
Δr=4.4 pm.[53] The latter feature is characteristic of a significant
degree of covalency in the MÀ N3 interaction and is in keeping
with the νa(NNN) vibration observed in the IR spectrum of 7
(see above).[53] The AgÀ N distance (205.6(5) pm) is significantly
shorter than found in the linear silver(I) complex (SIDipp)Ag(N3)
(209.5(2) pm)[54] and in the terminal moiety of the homoleptic
silver(I) complex [PPh4][Ag(N3)2]: 213.9(4) pm.[25]
Figure 4. Displacement-ellipsoid diagram (50% probability) of the anion
[(CF3)3AgCN]À as found in crystals of 6.[46] The MÀ C bond lengths (in gray) are
compared with those found in the isomorphous homologous gold
compound [PPh4][(CF3)3AuCN] (in yellow).[18]
Calculated ground-state structures
The geometries of the individual [(CF3)3AgX]À anions have been
optimized (DFT/M06) and the results are shown in Figure S43.
The obtained square-planar geometries are energy minima for
every halogen, including the heaviest naturally occurring one
X=At (5). The calculated structures of the lighter halogens (X=F,
Cl, Br) show reasonable agreement with those established by
XRD for compounds 1–3 (Figure 3). The observed differences in
the corresponding AuÀ X bond lengths are <5 pm in every
case. The electronic structures have also been systematically
calculated and analyzed in order to determine some periodic
trends along the halogen Group with special focus on the
AgIIIÀ X bonding. The energy levels are compared in Figure 6a
Figure 5. Displacement-ellipsoid diagram (50% probability) of the anion
[(CF3)3Ag(N3)]À as found in crystals of 7.[46]
Figure 6. a) Energy levels and b) contour isosurfaces (isovalue: 0.02) of the frontier orbitals and near lower MO’s of the [(CF3)3AgX]À complexes 1–5 obtained at
the DFT/M06 level of theory. More complete sets including the MOs with main M(d) contribution are shown in Figures S47 and S48.
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and the frontier MO contours of all these Cs complexes are
shown in Figure 6b.
(QTAIM)[55] gives a rather homogeneous picture, as shown in
Figure S45 and Table 2. The critical point along the AgÀ X
bonding path (BCP) shows just a marginal shift towards the
halogen ligand (in % of the corresponding bond length) with
decreasing X electronegativity. Most importantly, the electron
density 1(r) on that critical point substantially decreases down
the Group indicating a decrease in the AgÀ X bond strength.
The positive values of the Laplacian denote strongly polar AgÀ X
bonds with substantial ionic character, especially for the fluoro
The HOMOÀ LUMO gap (Figure 6a) is largest for the fluoro
complex 1 (4.71 eV) and decreases monotonically up to the
iodo complex 4 (3.60 eV). The slight increase calculated for the
astato complex 5 (3.70 eV) is due to destabilization of the
LUMO. The LUMO and HOMO sets in the full series of
complexes 1–5 are consistently ligand-based orbitals in all cases
(Figure 6b). The a’ LUMO set is mainly antibonding with regard
to the AgÀ X and all the AgÀ C interactions. The a’’ HOMO is, in
turn, mainly bonding with regard to the trans CÀ AgÀ C σ-bond
system with anti-phase minor contribution of the in-plane X(px)
orbital. This MO acquires increasing X(p) character down the
Group and is particularly destabilized for the heaviest halogens
I and At. The immediately lower orbitals are roughly similar for
complexes 2–5 but show significant reordering in the lightest
complex 1. For this reason, we will focus on the chloro-
derivative 2 as the model compound and will derive all the
other therefrom.
The HOMO-1 level in complex 2 mainly involves the X(pz)
orbital with just a marginal antiphase contribution of the M(dyz)
orbital. This virtually nonbonding a’ MO is the HOMO-1 in
complexes 2–5 and appears as the HOMO-3 level in complex 1.
It occurs perpendicular to the coordination plane (xy) and
shows the largest energy variation along the series, in line with
the increasing destabilization of the X(p) atomic orbitals down
the halogen Group.
In the HOMO-2 level of complex 2 there is some π-bonding
overlap of the anti-phase CÀ AgÀ C (trans) unit with the in-plane
X(px) orbital. There is also just a marginal contribution of the
M(dxy) orbital. This a’’ MO lying in the coordination plane (xy)
appears as the HOMO-2 level in complexes 1–3 and as the
HOMO-3 level in complexes 4 and 5. It shows little energy
variation along the series except for the fluoro complex 1,
where it appears substantially stabilized. The corresponding MO
with the dual AgÀ X π-antibonding interaction (a’’) is the HOMO
in all cases.
The HOMO-4 level is a bonding MO (a’) encompassing the
whole C3AgX unit and involving a hybrid sdz2 metal orbital as
well as the in-phase X(py) AO. This MO is common to all
compounds 1–5 and shows small energy variation along the
series. The energy dependence is more pronounced in the
corresponding a’ MO, which involves an antiphase X(py)
contribution and is therefore antibonding with respect to the
AgÀ X unit. This level appears scattered through the series, as
HOMO-1 (F), HOMO-3 (Cl, Br) and HOMO-2 (I, At).
2
complex 1, where r 1(r)=0.544 au. The ionic component also
decreases down the Group reaching its minimum for the
heaviest halides I and At.
We conclude that compounds 1–5 are stable chemical
species exhibiting inverted ligand field. The intrinsically stable
AgÀ X bonds show no anomalous variation with respect to the X
ligand as follows from the QTAIM analyses. Now, a critical
evaluation of the most plausible decomposition paths will
enable us to identify the weakest flanks in the [(CF3)3AgX]À
complexes and thereby to test the strength of the AgÀ X bonds,
as will be discussed next.
Stability assessment
Only the isolation of a chemical substance enables a reliable
determination of its stability. The presence of solvents or any
accompanying byproduct can largely alter the intrinsic decom-
position routes and further open new ones. The most efficient
way to avoid the involvement of any spurious mechanism is to
study the evolution of a given chemical substance in the gas
phase by multistage mass spectrometry (MSn) under collision-
induced dissociation (CID) conditions.[56] We have performed
these measurements for all the compounds isolated in this
work. The singly charged [(CF3)3AgX]À anions are efficiently
transferred to the gas phase under mild ionization conditions
(see the Experimental Section). The MS2 results are shown in
Figures S19–S24. The energy profiles of the experimentally
observed decomposition paths together with other potentially
reasonable mechanisms were mapped by theoretical methods
(Schemes S1–S7). A selection of the most relevant processes is
Table 2. Critical-point (CP) topology of the AgÀ X bond path (BP) in the
[(CF3)3AgX]À anions.[a]
X
F
Cl
Br
I
At
1(r) [au]
0.099
0.544
0.032
198.4(1)
198.9
104.5
94.4
0.151
À 0.165
À 0.015
1.518
0.076
0.221
0.025
232.03(4)
236.2
114.1
122.1
0.071
0.068
0.155
0.015
246.25(2)
250.2
118.5
131.7
0.053
0.058
0.086
0.006
–
269.8
125.0
144.8
0.035
À 0.048
À 0.013
0.599
0.065
0.088
0.008
–
267.1
123.7
143.4
0.040
À 0.058
À 0.018
0.611
2
It is worth noting that the metal d orbitals are just
marginally involved in the frontier orbitals or the four lower
levels. The (dxy, dxz, dyz) threefold appears as HOMO-5, HOMO-6
and HOMO-7 (Figure S48). Finally, one has to dive into the
HOMO-10 to find the MO with major dz2 metal contribution
r 1(r) [au]
ellipticity, ɛ
AgÀ X[b] [pm]
BP length [pm]
rb(Ag)[c] [pm]
rb(X)[c] [pm]
G(r) [au]
(Figure S48) and even below to find the dx2 metal orbital. This
À y2
V(r) [au]
H(r) [au]
G(r)/1(r)
À 0.087
À 0.016
0.933
À 0.067
À 0.014
0.778
non-standard arrangement of the metal d orbitals is character-
istic of inverted ligand field[36] and was also identified in the
related homoleptic complex [(CF3)4Ag]À .[19]
The topological analysis of the electron density in com-
pounds 1–5 using the quantum-theory of atoms in molecules
[a] Contour diagrams are shown in Figure S45. [b] Experimental values
from XRD analysis (Table 1). [c] The bonded radii rb(Ag) and rb(X) along the
AgÀ X axis are defined as the distance of the BCP from the given nucleus.
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shown in Scheme 4 and the calculated energy values are
gathered in Table 3. Since both calculation and experiment
were carried out in the gas phase, the results obtained from
each method are directly comparable[57] and will be discussed
jointly.
unstable and would readily evolve into the known linear anion
[CF3AgCF3]À by spontaneous (À 1.2 kcalmolÀ 1) radical dissocia-
tion of the elongated stem CF3 group (trans to the void), which
bears 60% spin density of the unpaired electron.[35,61] Except in
the case of the fluoro-derivative 1 (Figure S19), the homoleptic
organosilver(I) ion [CF3AgCF3]À was actually observed as a minor
species in every other MS2 spectra (Figures S20–S22). This anion,
however, might also arise if the stepwise radical splitting took
place in reverse order, that is, CF3 followed by X dissociation
(Scheme 4, paths 6 and 7). A concerted reductive elimination of
X–CF3 from the parent ion might also occur (Scheme 4, path 8).
Although energetically favored, this process would entail a
transition state located at ΔG� =41.8À 31.8 kcalmolÀ 1 (Table 3,
entry 8). These values suggest that the concerted reductive
elimination of X–CF3 can be discarded for the fluoro complex 1,
but may become feasible for the heavier halides. In any case,
the higher energy required for the process would justify the
presence of the [CF3AgCF3]À ion as a minor product.
Our main concern throughout the present study was to
check the stability of the AgIIIÀ X bond. To our surprise, this unit
proved to be remarkably stable even for the heavier halides Br
and I. According to our calculations, simple halide XÀ dissocia-
tion (Scheme 4, path 1) should be a highly endergonic process
requiring energies in the range 74.5–50.3 kcalmolÀ 1 (Table 3,
entry 1). This heterolytic dissociation would render the neutral
(CF3)3Ag moiety, which would not be observable by MSn
techniques. Hence, we specifically looked for the presence of
any released XÀ anion as a fingerprint of this dissociation path,
but none was experimentally observed.[58,59] It can therefore be
concluded that heterolytic halide dissociation does not take
place under the measuring conditions, in agreement with the
high energy estimated for the process. Homolytic dissociation
of the AgÀ X bond would invariably render the homoleptic
organosilver(II) ion [(CF3)3AgII]À (Scheme 4, path 2), which was
not observed in any of our experiments. Homolytic AgÀ X
dissociation would require energies in the 68.4–37.3 kcalmolÀ 1
range (Table 3, entry 2).[60] It must be noted, however, that the
T-shaped, open-shell species [(CF3)3AgII]À , if formed, should be
*
*
The major species invariably observed upon fragmentation
of the corresponding parent ions (Figures S19–S22) were the
mixed organosilver(I) halide complexes [CF3AgX]À , where the
AgÀ X unit is still preserved. This entity results from the loss of a
C2F6 mass, which may occur following a concerted or a stepwise
mechanism. The former (Scheme 4, path 5) is hampered by a
high-energy transition state (ΔG� 37.9–31.7 kcalmolÀ 1). The
latter (Scheme 4, paths 3 and 4) is actually the least energeti-
cally demanding of all the primary dissociation paths under
study (Table 3): Homolytic splitting of the first AgÀ C bond in
the CF3À AgÀ CF3 axis requires <25 kcalmolÀ 1, whereas the
second will take place at virtually no energy cost (�
1.1 kcalmolÀ 1).[61] Consequently, this is the suggested mecha-
nism to account for the major signals observed in every MS2
experiment. This fragmentation pattern is also in line with the
elongated AgÀ C bonds (210À 212 pm) in the CF3À AgÀ CF3 axis
*
(Table 1). Stepwise radical dissociation of two CF3 units was
also observed and demonstrated in the homoleptic organo-
silver(III) complex [(CF3)4Ag]À .[35]
The geometries of the major fragmentation products
[CF3AgX]À were optimized at the DFT/M06 level of calculation.
The results are shown in Figure 7. The AgÀ X bond lengths in
these linear molecules (d10) are all very similar to those obtained
for their square-planar [(CF3)3AgX]À counterparts (d8). We note
that the calculated AgÀ Cl bond distance (235.5 pm) compares
well with that experimentally established by Tyrra and
Naumann in the [N(PPh3)2][CF3AgCl] salt: 233.88(15) pm.[62] This
AgÀ Cl interatomic distance is slightly longer than the AuÀ Cl
bond length found in the homologous gold compound
[PPh4][CF3AuCl] (229.1(1) pm),[63] which is consistent with AuI
being smaller than AgI.[64] This difference, which has been
ascribed to the particularly strong relativistic effects operating
in AuI, vanishes with the metals in the oxidation state III, as
commented above.
Scheme 4. Most relevant unimolecular fragmentation processes potentially
operating in the [(CF3)3AgX]À anions. Calculated ΔG values are given in
°
Table 3. Unabridged mappings are given in Schemes S1–S7.
Table 3. Standard free-energy values, ΔG [kcalmolÀ 1], calculated for the
°
indicated dissociation processes in the [(CF3)3AgX]À anions.[a]
Process[b]
X=F
X=Cl
X=Br
X=I
X=At
1
2
74.5
68.4
57.2
58.3
54.0
46.0
50.3
37.3
49.6
34.1
3
24.8
19.8
19.5
18.6
19.3
4
1.1
0.1
0.3
À 0.5
[31.7]�
À 63.1
22.1
À 0.2
[31.8]�
À 62.0
19.8
5[c]
[37.9]�
À 55.3
35.3
[33.5]�
À 61.3
30.4
[32.3]�
À 62.0
26.7
6
7
32.0
26.7
18.1
14.0
13.1
8[c]
[41.8]�
À 52.4
[40.3]�
À 20.8
[37.8]�
À 16.2
[31.8]�
À 13.2
[29.1]�
À 12.7
The mixed organosilver(I) halide complexes [CF3AgX]À were
further subjected to MS3 experiments under CID conditions
(Figures S25–S28). They all undergo CF2 extrusion eventually
affording the triatomic fluoride complexes [FAgX]À [Eq. (1)],
which, aside from the symmetric fluoride [FAgF]À ,[65] had not
[a] More complete sets of possible fragmentation paths are given in
Schemes S1–S5. [b] Numbering as in Scheme 4. [c] The value in square
brackets indicates the energy of the corresponding transition state, ΔG�
[kcal molÀ 1].
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versus AuIII is a general feature in the chemistry of these
coinage metals.
Once the decomposition temperatures were known, the
thermolyses of solid samples of compounds 1–4 were carried
out in sealed tubes (see the Experimental Section) and the
soluble products formed were analyzed by 19F NMR spectro-
scopy (Figures S37–S40). Metal deposition occurred in most
cases. The homoleptic species [(CF3)4Ag]À invariably appears as
a major decomposition product. This clearly evidences that
ligand exchange takes place during the process, which marks a
fundamental difference with the data obtained from our
unimolecular MSn measurements in the gas phase. Nevertheless,
*
there is convincing evidence of CF3 radical dissociation
operating also in the condensed phase. Thus, multiple, non-
selective trifluoromethylation of the phenyl rings of the [PPh4]+
cation is observed together with formation of substantial
amounts of CF3H. In addition to the radical dissociation process,
there is also evidence for the participation of concerted XÀ CF3
elimination (Scheme 4, path 8). As already pointed out, our
calculations predict an associated transition state for the latter
process, the energy of which considerably decreases down the
halogen Group (Table 3, entry 8). Our experimental observa-
tions nicely confirm our calculations. Thus, in the fluoro
complex 1 with an associated ΔG� =41.8 kcalmolÀ 1 value, none
of the required elimination products, [CF3AgCF3]À or CF4, was
experimentally observed in the gas phase (Figure S19) or in the
condensed phase (Figure S37). By contrast, the decomposition
of the iodo complex 4 produced considerable amounts of both
[CF3AgCF3]À (Figures S22 and S40) and ICF3 (Figure S40). This
accessible decomposition path would justify the failure in the
reverse reaction commented above, that is, the oxidative
addition of ICF3 onto the linear organosilver(I) derivative
[CF3AgCF3]À (Scheme 2). Moreover, the detection of increasing
amounts of XÀ CF3 (Figures S37À S40) and [CF3AgCF3]À
(Figures S19À S22) down the Group are in excellent agreement
with our calculations. We conclude that the sizable energy of
the transition states required to reductively eliminate CF3À CF3
or XÀ CF3 (ΔG� >30 kcalmolÀ 1) is a key factor determining the
stability of compounds 1–4.
Figure 7. Optimized geometries of the anionic complexes [CF3AgX]À (left)
and the [FAgX]À (right) in the gas phase (X=F, Cl, Br, I) calculated at the DFT/
M06 level. All these species were experimentally observed by multistage
mass spectrometry (MSn). Calculated AgÀ C and AgÀ X bond distances [pm]
are indicated.
been detected thus far.[66] Given the ease with which AgI
undergoes ligand exchange and/or associative processes in the
condensed phase, these interesting silver(I) fluorohalide com-
plexes are not likely to be isolated in pure form.
(1)
The geometries of all these triatomic [FAgX]À complexes
were also calculated by theoretical methods and are shown in
Figure 7. The obtained interatomic distances do not substan-
tially depart from those obtained for the parent organosilver(I)
species [CF3AgX]À . The AgÀ X bond distances obtained in both
series of anionic complexes [CF3AgX]À and [FAgX]À appear
elongated with respect to the neutral diatomic AgX molecules
(see above); this can be ascribed to the increase in both the
metal coordination number and the global charge.
It is worth noting that the AgÀ X bonds are preserved along
the major dissociation paths in the explored MSn experiments,
thus giving proof of their intrinsic stability. In contrast, none of
the initial AgÀ C bonds are present in the final fragmentation
products. They are broken first as the result of homolytic
cleavage and then following CF2 extrusion.
In the solid state, the cyano complex 6 decomposes at
°
144 C (Figure S35) showing therefore similar stability to the
fluoro complex 1. The azido complex 7 is, in turn, in the lower
°
We have also studied the stability of the isolated com-
pounds [PPh4][(CF3)3AgX] (1–4) in the bulk by TGA/DTA
measurements (Figures S31–S34). According to the observed
range of stability, as it decomposes at 92 C (Figure S36). No
sign of explosive or violent behavior was observed for the latter
compound in the TGA/DTA experiments, in its thermolysis or in
the customary laboratory handling. Even so, solid samples of 7
were always handled with caution. The bulk thermolyses of the
pseudohalide complexes 6 and 7 (Figures S41 and S42) proceed
in a similar way as in the halides 1–4. Also the unimolecular
decompositions in the gas phase are qualitatively similar,
whereby the mixed species [CF3AgX’]À (Figures S23 and S24)
and [FAgX’]À (Figures S29 and S30) are equally observed
(X’=CN, N3). As far as we know, these species had not been
previously detected with the only exception of the cyano
complex [CF3AgCN]À .[15] The observed fragmentation sequence
denotes that the AgÀ X’ unit in compounds 6 and 7 is also
surprisingly robust.
°
decomposition temperatures [ C], the stability decreases in the
following order: F (145)>Cl (140)>Br (134)>I (78). We can
conclude that these organosilver(III) halide complexes show
remarkable stability even for the heavier halides Br and I.
Nevertheless, they are less stable than the homoleptic, all-
organometallic compound [PPh4][(CF3)4Ag], which melts at
[19]
°
°
135 C and decomposes at 188 C. They are also considerably
less stable than their corresponding gold(III) homologues
[PPh4][(CF3)3AuX], for which the following decomposition tem-
°
peratures [ C] were experimentally determined: Cl (315)>Br
(295)>F (267)>I (245).[18] The large stability difference of AgIII
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J. Serra, J. M. Luis, J. Lloret-Fillol, M. Costas, X. Ribas, Nat. Commun.
2014, 5, 4373.
Conclusion
[2] T. Elkoush, C. L. Mak, D. W. Paley, M. G. Campbell, ACS Catal. 2020, 10,
4820.
[3] M. Malischewski, in Comprehensive Organometallic Chemistry IV, Vol. 1
(Ed.: P. L. Holland), Elsevier, 2021; DOI: 10.1016/B978-0-12-820206-
7.00004-4.
The isolation of the whole series of halide complexes
[(CF3)3AgX]À (X=F, Cl, Br, I) has enabled us to establish an
experimental correlation between their individual stability and
the nature of the heteroligand, X. Thus, a delicate balance
[4] a) M. Deuker, Y. Yang, R. A. J. O’Hair, K. Koszinowski, Organometallics
2021, 40, 2354; b) S. Weske, R. A. Hardin, T. Auth, R. A. J. O’Hair, K.
Koszinowski, C. A. Ogle, Chem. Commun. 2018, 54, 5086.
[5] a) A. Higelin, S. Riedel in Modern Synthesis Processes and Reactivity of
Fluorinated Compounds, Vol. 3 (Eds.: H. Groult, F. Leroux, A. Tressaud),
Elsevier, Amsterdam, 2017, Ch. 19, pp. 561–586; b) S. Riedel in
Comprehensive Inorganic Chemistry II (Eds.: E. V. Antipov, A. M. Abaku-
mov, A. V. Shevelkov), Elsevier, Amsterdam, 2013, Ch. 2.08, pp. 187–221;
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*
between radical CF3 dissociation and the reductive elimination
of CF3X is observed upon thermolysis in the gas phase that
absolutely depends on the nature of X. The energy profiles for
both processes have been calculated by theoretical methods.
The calculated profiles for these unimolecular processes show
remarkable agreement with the experimental data in the gas
phase. In the solid state, however, additional intermolecular
rearrangements that involve CF3 transfer between silver centers
operate. We further demonstrate that the AgIIIÀ Br and AgIIIÀ I
bonds are not intrinsically unstable. The remarkable stability of
our system is further effected by the sizable energy barriers
associated with reductive elimination processes. In contrast, the
instability of the simple AgX3 and [AgX4]À species with X¼F can
be attributed to the ease with which X2 is reductively
eliminated. This holds true even for the binary fluoride AgF3,
which readily and spontaneously undergoes reduction in the
condensed phase.[7] It should be emphasized that, in our
system, inner-sphere full electron transfer from the heavier
halide ligands X to the AgIII center does not take place as readily
as might be anticipated.
Our results prove that organosilver(III) halides are indeed
feasible for every halogen, including the more polarizable and
less electronegative Br and I. The implications of the stability of
AgIII towards halogens are substantial, particularly in the
plethora of silver-mediated chemical processes as well as in
fundamental chemistry. Needless to say, however, that the
precise stability of any particular entity will heavily depend on
the nature of the accompanying ligands at the AgIII center.
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This work was supported by the Spanish MICIU/FEDER (projects
PGC2018-094749-BÀ I00 and PGC2018-093451-BÀ I00) and the
Gobierno de Aragón (Grupo E17 20R). BIFI (Instituto de
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Manuscript received: May 26, 2021
Accepted manuscript online: June 30, 2021
Version of record online: ■■■, ■■■■
Chem. Eur. J. 2021, 27, 1–12
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11
© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
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These are not the final page numbers!

FULL PAPER
Unexpectedly robust: We provide
theoretical evidence and experimental
proof of the unexpected stability of
the AgIIIÀ X bond with every halogen
(X=F, Cl, Br and I) in the series of
square-planar organosilver(III) deriva-
tives [PPh4][(CF3)3AgX]. Unimolecular
decomposition paths were analyzed
by combined theoretical and experi-
mental methods, whereby the two
series of linear complexes [CF3AgX]À
and [FAgX]À were detected. The first
silver(III) azide was also prepared,
isolated and structurally characterized.
D. Joven-Sancho, Dr. M. Baya,
Prof. Dr. L. R. Falvello, Dr. A. Martín,
Dr. J. Orduna, Dr. B. Menjón*
1 – 12
Stability of AgIII towards Halides in
Organosilver(III) Complexes