Silver(I) fluoride and related compounds in chemical synthesis

Article abstract of DOI:10.1002/hc.10102

Silver(I) fluoride is a versatile tool in desulfuration-fluorination reactions with thiuram disulfides and thioureas. Reactions of AgF and trimethyl(perfluoroorgano)- and trimethyl(alkynyl)-silanes offer a convenient approach to the corresponding organosilver derivatives, which are excellent reagents for oxidative organylations of group 12-16 elements. Reactions of AgF and elements of groups 13-16 open a convenient access to the corresponding fluorides.

Full text of DOI:10.1002/hc.10102

Heteroatom Chemistry
Volume 13, Number 6, 2002
Silver(I) Fluoride and Related Compounds
in Chemical Synthesis
Wieland Tyrra
Institut fu¨ r Anorganische Chemie, Universita¨t zu Ko¨ln, Greinstr. 6, D-50939 Ko¨ln, Germany
Received 24 May 2002
purity from several commercial sources and can be
ABSTRACT: Silver(I) fluoride is a versatile tool
used as received.
in desulfuration-fluorination reactions with thiu-
For the reactions described in this paper,
ram disulfides and thioureas. Reactions of AgF and
the choice of the solvent was essential. Solvents
trimethyl(perfluoroorgano)- and trimethyl(alkynyl)-
without “acidic” protons were suitable. Because
silanes offer a convenient approach to the corre-
of the extremely low solubility of AgF in nonpolar
sponding organosilver derivatives, which are excellent
solvents such as alkanes, halogenated alkanes,
reagents for oxidative organylations of group 12–16
aromatics (benzene, toluene), and ethers ((C2H5)2O,
elements. Reactions of AgF and elements of groups 13–
THF, 1,2-dimethoxyethane (DME)), the palette of
16 open a convenient access to the corresponding flu-
solvents was restricted to nitriles (CH3CN, C2H5CN,
C
orides. 2002 Wiley Periodicals, Inc. Heteroatom Chem
13:561–566, 2002; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.10102
C3H7CN), DMF, pyridine, N-methylimidazol, and N-
methylmorpholine. Of these solvents, propionitrile
was the solvent of choice because of its minimum
side reactions, good availability, and convenient
handling.
INTRODUCTION
RESULTS
Among silver(I) halides two characteristic features of
Desulfuration-Fluorinations
with Silver(I) Fluoride
AgF are striking—its extremely good solubility in wa-
ter (1800 g/l at 25 C) and the fact that it is the only sil-
ver halide that forms hydrates. In contrast, the heav-
ier halides are almost insoluble in water. This is at-
tributed to the ionic character of the silver–fluorine
bond, which has been calculated to be 70% ionic
while those of the heavier halides exhibit values of
only 30% for AgCl, 23% for AgBr, and 11% for AgI [1].
Some general remarks have to be made on the
quality of AgF for synthetic purposes. Silver(I) flu-
oride should be yellow or orange. Impurities by
bronze Ag2F and brown AgF2 sometimes give AgF a
darker color. However, AgF is obtained in sufficient
Several methods are known to convert a C S moi-
ety into a C F unit [2]. In all these, either toxic
materials or a combination of reagents are in-
volved. Reactions of AgF and thiuramdisulfides dis-
play the advantage of a selective approach to ei-
ther thiocarbamoyl fluorides (R2NC(S)F) or triflu-
oromethylamines (R2NCF3). Thiuramdisulfides can
easily be converted into the corresponding thio-
carbamoyl fluoride and the silver dithiocarbamate
(AgSC(S)NR2) in 1:1 reactions. Stoichiometries of
AgF and [R2NC(S)S]2 of 3:1 and 6:1 offer direct ap-
proaches to diorgano(trifluoromethyl)amines, as in-
dicated in Scheme 1 [3]. Trifluoromethylamines are
also formed in separate reactions of R2NC(S)F or
AgSC(S)NR2 with AgF.
Correspondence to: Wieland Tyrra; e-mail: tyrra@uni-koeln.de
c
2002 Wiley Periodicals, Inc.
561

562 Tyrra
temperature selectively gave bis(dimethylamino)-
difluoromethane, [(CH3)2N]2CF2, and Ag2S in app-
roximately quantitative yield.
Bis(dimethylamino)difluormethane can be re-
garded as a “liquid fluoride source” [5], as has been
demonstrated in its reaction with (CH3)3SiOSO2CF3
to give tetramethylfluoroformamidinium trifluo-
romethanesulfonate, {[(CH3)2N]2CF}OSO2CF3.
The situation becomes more complicated in
reactions with trialkylthioureas. In principle,
sulfur is substituted by two fluorine atoms
but the corresponding dialkylamino(monoalkyl-
amino)difluoromethane, (R2N)(R0NH)CF2, forms
an equilibrium with the HF-adduct of the fluo-
roformamidine. HF is intercepted by addition of
the pyridine-borontrifluoride adduct to give the
fluoroformamidine in pure form.
Reactions with N,N0-dialkylthioureas pro-
ceed via different (not yet analyzed) fluorine-
containing intermediates to yield finally dialkyl-
carbodiimides, RN C NR, while reactions with
N,N-dialkylthioureas exclusively yield dialkyl-
cyanamides, R2NC N. Reactions with monoalkylth-
ioureas give cyclic trialkyl-[1,3,5]-triazinetrione
triimine whereas thiourea is selectively converted
into cyanamide, H2NC N. Further investigations in
this field are in progress.
SCHEME 1 Desulfuration-fluorination reactions of AgF and
thiuramdisulfides.
Investigations on desulfuration-fluorination re-
actions have been extended to differently substituted
thioureas (Scheme 2) [4].
The reaction of tetramethylthiourea, (CH3)2-
NC(S)N(CH3)2, and AgF in propionitrile at room
Reactions with Trimethylsilyl Derivatives
The interactions of trimethyl(perfluoroorgano)-
silanes and silver(I) fluoride offer a new, convenient
access to perfluoroorganosilver(I) compounds. In
these reactions, the fluoride source itself, AgF, be-
comes the center to which the perfluoroorgano group
is transferred. These reactions have been most in-
tensively studied with the trifluoromethyl [6] and
the pentafluorophenyl group [6,7]. Propionitrile has
been the solvent of choice although other N-donor
solvents are also suitable.
CH3CH2CN
(CH3)3SiCF3 + AgF
→ AgCF3 + (CH3)3SiF
r.t., 5 min
Trifluoromethylsilver equilibrates with silver-
[bis(trifluoromethyl)argentate(I)] and a second not
yet characterized species [8]. These reactions
offer the advantage that the formation of
tetrakis(trifluoromethyl)argentate(III), [Ag(CF3)4] ,
which is formed in ligand exchange reactions of
SCHEME 2 Desulfuration-fluorination reactions of AgF and
thioureas.

Silver(I) Fluoride and Related Compounds in Chemical Synthesis 563
different silver salts and Cd(CF3)2 complexes [8,9]
or Bi(CF3)3, is nearly completely suppressed.
Addition of [PNP]Cl to solutions of AgCF3 se-
lectively yielded the argentates [PNP][Ag(CF3)2] and
[PNP][Ag(CF3)Cl], ([PNP]+ = Ph3P N PPh3+).
Both compounds were obtained as colorless, light-
sensitive crystalline solids. While the composition of
the anion [Ag(CF3)2] could only be proved by NMR
spectroscopy (Fig. 1), single crystal structure analy-
sis of [PNP][Ag(CF3)Cl] exhibited the expected com-
position and anion geometry (Fig. 2).
Besides having excellent properties as a trifluo-
romethylating reagent in nucleophilic halide substi-
tutions, AgCF3 opened the possibility of synthesizing
trifluoromethyl element compounds of groups 12–
16 elements directly from the elements via oxidative
2AgCF3 + [PNP]Cl
CH3CH2CN
→ [PNP][Ag(CF3)2] + AgCl
r.t.
CH3CH2CN
AgCF3 + [PNP]Cl
→ [PNP][Ag(CF3)Cl]
r.t.
FIGURE 1 109Ag, 19F HMQC spectrum of [PNP][Ag(CF3)2] (horizontal trace: 19F NMR spectrum; vertical trace: 109Ag NMR
spectrum; (19F) = 25.6; (109Ag) = +556; 1JF, C = 371 Hz; 1JAg,C = 280 Hz; 2JAg,F = 100 Hz).

564 Tyrra
sensitive compound which loses propionitrile at 87–
93 C to give donor-free AgC6F5, which is at ca. 270 C
selectively decomposed into (C6F5)2 and elemental
silver.
Although all arylsilver derivatives structurally
characterized till date form tetrameric units in the
solid state [11], AgC6F5 CH3CH2CN crystallizes in in-
finite chains (Fig. 3) [7].
In the crystal structure of AgC6F5 CH3CH2CN,
two crystallographically different Ag atoms are
found. Both are located on special sites of the space
group C2/c. One silver atom is in ideal linear coor-
dination of two carbon atoms with a silver–carbon
bond length of 213 pm. The carbon atoms belong
to two C6F5 groups, which act as bridging ligands
to the second silver atoms. Here, silver–carbon
bonds are significantly longer (239 pm) compared
to those of the linear unit because of additional
bonds to two CH3CH2CN molecules, building up
a strongly distorted tetrahedral geometry at this
silver atom. The bridging functionality of the
FIGURE 2 Structure of the anion [Ag(CF3)Cl] ([PNP]
[Ag(CF3)Cl]): triclinic, P-1, a = 972.4 pm; b = 1098.3 pm;
c = 1710.8 pm; = 105.7 ; = 93.9 ; = 102.2 ).
trifluoromethylations.
CH3CH2CN
nAgCF3 + E
→ E(CF3)n + nAg
Yields and conditions of these reactions are summa-
rized in Table 1.
Several pathways for the synthesis of AgC6F5 are
mentioned in the literature [10]. All reactions give
AgC6F5 in moderate yields after long reaction times
and extensive working-up procedures. The synthesis
according to
C6F5 groups leads to infinite chains according
1
to
∞[Ag(2)(CH3CH2CN)2/1(C6F5)2/2Ag(1)(C6F5)2/2],
which are oriented along the [001] direction of the
unit cell.
CH3CH2CN
(CH3)3SiC6F5 + AgF
→ AgC6F5 + (CH3)3SiF
r.t., 30 min
In a manner similar to that described for the
trifluoromethyl derivatives, AgC6F5 could be trans-
ferred into the corresponding argentate in reactions
with [PNP]Br from which [PNP][Ag(C6F5)2] was iso-
lated as a colorless solid in 74% yield decomposing
at 123–126 C.
has the advantage that AgC6F5 is selectively formed
within 30 min at room temperature, with concomi-
tant formation of volatile (CH3)3SiF in nearly quan-
titative yield. After distilling off all volatile com-
pounds in vacuo, AgC6F5 is obtained as the 1:1
adduct with propionitrile. It is a colorless, light-
2AgC6F5 + [PNP]Br
CH3CH2CN
TABLE 1 Transmetalations of Group 12–16 Elements and
Trifluoromethylsilver
→ [PNP][Ag(C6F5)2] + AgBr
r.t.
As expected, AgC6F5 showed excellent properties
in oxidative transmetalations with a great number
of group 12–16 elements, giving the corresponding
pentafluorophenyl element compounds in moderate
to excellent yields (Table 2).
It was also found that trimethyl(alkynyl)silanes
react in a manner that is similar to the way
trimethyl(perfluoroorgano)silanes react with AgF.
These reactions were most intensively studied only
with the phenylethynyl group.
T
( C)
Reaction
Time
Yield
(%)
E
Product
Zn
Cd
0
0
21
4 h
1 h
1 h
Zn(CF3)2 2CH3CH2CN
Cd(CF3)2 2CH3CH2CN
Cd(C2F5)2, AgC2F5,
C2F4, CF3H, F-polymers
C2F4, CF3H, F-polymers
Hg(CF3)2
66
75
50
21
21
21
30 min
<5 min
72 h
48 h
96 h
Hg
Ga
In
85
Ga[Ag(CF3)4]3
In(CF3)3 2CH3CH2CN
Tl
21
TlI[AgI(CF3)2] (85%),
TlI[AgIII(CF3)4] (10%),
AgF + (CH3)3SiC CC6H5
Ag[TlIII(CF3)4] (5%)
Sn(CF3)4
CH3CH2CN
Sn
Pb
As
Sb
Bi
50
50
55
65
50
50
12 h
24 h
16 h
24 h
24 h
16 h
→ AgC CC6H5 + (CH3)3SiF
r.t., 12 h or 50 C, 1 h
Pb(CF3)4
AsF3 (total decomposition)
Sb(CF3)3
However, because of the polymeric nature of
[AgC CC6H5]∞ [12] transmetalations with selected
elements required extended reaction times or higher
temperatures compared with AgCF3 and AgC6F5
(Table 3).
Bi(CF3)3
39
75
Se
Se(CF3)2, Se2(CF3)2,
AgSeCF3
Te(CF3)2 CH3CH2CN
Te
50
12 h

Silver(I) Fluoride and Related Compounds in Chemical Synthesis 565
1
FIGURE 3 Section of the infinite chain [Ag(CH3CH2CN)2/1(C6F5)2/2Ag(C6F5)2/2] (AgC6F5 CH3CH2CN): monoclinic, C2/c
∞
(no. 15), Z = 8, a = 2301.4 pm; b = 1078.8 pm; c = 948.0 pm; = 113.2 ).
that has been mentioned only once in literature
[13].
Reactions of Silver(I) Fluoride
and Selected Elements
Reactions of excess AgF with the elements Al, Ga,
Ge, Sn, and Te proceed selectively with formation
of the corresponding fluoroelementates, whereas re-
actions with Sb and Bi gave only the correspond-
ing trifluorides SbF3 and BiF3, respectively. The re-
action with elemental selenium gave spectroscopic
evidence for SeF4 but several not yet identified by-
products were also formed (Scheme 3).
Silver fluoride itself exhibits the properties of a good
oxidative fluorinating reagent for group 13–16 ele-
ments under mild to moderate conditions, a property
TABLE 2 Transmetalations of Group 12–16 Elements and
Pentafluorophenylsilver
Reaction
Time
Yield
(%)
E
T ( C)
Product
CONCLUSIONS
Zn
Cd
Hg
Ga
In
Sn
Pb
As
Sb
Bi
21
21
21
65
21
65
65
21/65
65
50
4 h
Zn(C6F5)2 2CH3CH2CN
77
62
85
69
35
92
65a
79
88
73
73
60
<5 min Cd(C6F5)2 2CH3CH2CN
<5 min Hg(C6F5)2
Silver(I) fluoride is
desulfuration-fluorinations of thioureas and re-
lated compounds.
a versatile reagent in
72 h
48 h
16 h
24 h
48/8 h
24 h
24 h
16 h
12 h
Ga(C6F5)3 CH3CH2CN
In(C6F5)3 CH3CH2CN
Sn(C6F5)4
Pb(C6F5)4
As(C6F5)3
Sb(C6F5)3
Bi(C6F5)3
Se(C6F5)2
Te(C6F5)2
TABLE 3 Transmetalations of Group 12–16 Elements and
Phenylethynylsilver
E
T ( C) Reaction Time
Product
Yield (%)
Se
Te
50
50
Hg
As
Sb
Bi
Se
Te
21
50
50
50
50
50
75 min
7 d
7 d
21 d
4 d
7 d
Hg(C CC6H5)2
As(C CC6H5)3
Sb(C CC6H5)3
Bi(C CC6H5)3
Se(C CC6H5)2
Te(C CC6H5)2
88
74
72
0
54
65
CH3CH2CN
aAgC6F5 + Pb
Pb[Ag(C6F5)2]2 + 2Ag
→
20–90 C
1 Torr
→
Pb(C6F5)4 + 2Ag
160 C

566 Tyrra
Dr. Dieter Naumann for supporting this work in all
fields.
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Organosilver
compounds
with
electron-
withdrawing groups could easily be prepared
from AgF and the corresponding trimethylsilyl
derivatives.
Beside the expected and known properties of
organosilver compounds as reactive species in nu-
cleophilic halide substitutions, these compounds
also exhibited excellent properties in oxidations of
a variety of group 12–16 elements.
Silver(I) fluoride itself could be used as a fluori-
nating reagent for group 13–16 elements.
ACKNOWLEDGMENTS
I thank Dr. Mathias S. Wickleder for doing the crys-
tal structure analyses, Harald Scherer for record-
ing and interpreting the HMQC spectra, my techni-
cians and laboratory assistants Sigrid Buslei, Silke
Quadt, and Sascha Go¨b for their help in doing a great
part of the preparative work, and my friend Prof.
[13] Seel, F.; Budenz, R.; Gombler, W.; Seiter, H. Z Anorg
Allg Chem 1970, 377, 353.