Lanthanide bis(trifluoromethanesulfonyl)amides, synthesis, characterization and catalytic activity

Article abstract of DOI:10.1016/S0022-1139(03)00038-1

The synthesis of lanthanum, neodymium and ytterbium bis(trifluoromethanesulfonyl)amides, named triflimidates, from acetates, carbonates and oxides is investigated. When the synthesis is performed in water, all the salts contain one molecule of water and the lanthanum and neodymium salts synthesized from the acetates also contain one molecule of acetic acid. After removal of the water and acetic acid in refluxing ethanol, the salts are obtained anhydrous but associated for lanthanum and neodymium, whereas the ytterbium salt is monomeric and volatile. When the synthesis is performed directly in ethanol, the neodymium salt contains two molecules of coordinated ethanol. In non-hazardous solvents, these triflimidates are better catalysts than the analogous triflates toward either Friedel-Crafts acylations, or Fries transpositions or Baeyer-Villiger oxidations. Unexpectedly, the cerium(IV) triflimidate catalyzes the oxidation of aromatic ketones to give the corresponding acids.

Full text of DOI:10.1016/S0022-1139(03)00038-1

Journal of Fluorine Chemistry 121 (2003) 233–238
Lanthanide bis(trifluoromethanesulfonyl)amides, synthesis,
characterization and catalytic activity
a
Denise Barbier Baudry , Alain Dormond , Fanny Duris ,
a,*
a
b
Jean Marie Bernard , Jean Roger Desmurs
Laboratoire de Synth e` se et d’Electrosynth e` se Organom e´ talliques (LSEO, UMR 5632),
Facult e´ des Sciences Mirande, Avenue Alain Savary, BP 47870, 21078 Dijon Cedex, France
c
a
b
Rhodia PPMC, CRIT Carri e` res, 85 Avenue des Fr e` res Perret, BP 62, 69192 Saint Fons Cedex, France
c
Rhodia Organique, Immeuble Etoile, 190 Avenue Thiers, 69457 Lyon Cedex 08, France
Received 16 October 2002; received in revised form 24 January 2003; accepted 28 January 2003
Abstract
The synthesis of lanthanum, neodymium and ytterbium bis(trifluoromethanesulfonyl)amides, named triflimidates, from acetates,
carbonates and oxides is investigated. When the synthesis is performed in water, all the salts contain one molecule of water and the
lanthanum and neodymium salts synthesized from the acetates also contain one molecule of acetic acid. After removal of the water and acetic
acid in refluxing ethanol, the salts are obtained anhydrous but associated for lanthanum and neodymium, whereas the ytterbium salt is
monomeric and volatile. When the synthesis is performed directly in ethanol, the neodymium salt contains two molecules of coordinated
ethanol.
In non-hazardous solvents, these triflimidates are better catalysts than the analogous triflates toward either Friedel–Crafts acylations, or
Fries transpositions or Baeyer–Villiger oxidations. Unexpectedly, the cerium(IV) triflimidate catalyzes the oxidation of aromatic ketones to
give the corresponding acids.
#
2003 Elsevier Science B.V. All rights reserved.
Keywords: Lanthanide; Bis(trifluoromethanesulfonyl)amide; Catalysis; Friedel–Crafts acylation; Fries transposition; Baeyer–Villiger oxidation
1
. Introduction
ca. 1.5 equivalent of acetic acid: Sc[N(SO CF ) ] , 1.5AcOH
2 3 2 3
and nothing was reported concerning thepresence of ancillary
ligands for the ytterbium and yttrium complexes.
Bis(trifluoromethanesulfonyl)amides of lanthanum [1],
ytterbium, yttrium [2] and scandium [3]: Ln[N(SO CF ) ]
have been described as strong Lewis acids, more powerful
catalysts for Diels–Alder [1,2], or acylation reactions [3,4]
than the analogous triflates.
To obtain more information about the exact structure
of these salts and the eventual influence of the additional
ligands on their catalytic activity, the synthesis and the
characterization of bis(trifluoromethanesulfonyl)amides of
three representative lanthanides: lanthanum, neodymium
and ytterbium, was investigated. The catalytic activity of
these salts was tested and compared to the activity of the
analogous triflates in three reactions catalyzed by Lewis
acids: the Friedel–Crafts acylation, the Fries transposition
and the Baeyer–Villiger oxidation.
2
3 2 3
These salts were obtained after reaction of the correspond-
ing oxides, acetates, or carbonates with bis(trifluorometha-
nesulfonyl)amine in water [5,6] and after removal of the
remaining water under reduced pressure. Nevertheless,
as it was impossible to isolate suitable crystalline species
for an X-ray structural analysis, the characterization of the
isolated products remained uncertain, the structure of the salt
seemed to be different according to the element and to the
nature of the starting material. The lanthanum salt was
described as monohydrated La[N(SO CF ) ] ꢀH O, whereas
2. Results and discussion
2
3 2 3
2
the scandium salt obtained from scandium acetate, contained
2.1. Syntheses and qualitative analyses
*
The synthesis of lanthanide bis(trifluoromethanesul-
fonyl)amides (abbreviated as triflimidates: Ln(NTf ) )
Corresponding author. Tel.: þ33-3-8039-6084; fax: þ33-3-8039-6084.
E-mail address: adormond@u-bourgogne.fr (A. Dormond).
2 3
0022-1139/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-1139(03)00038-1

234
D.B. Baudry et al. / Journal of Fluorine Chemistry 121 (2003) 233–238
Scheme 1.
was performed from the corresponding acetates, carbonates,
or oxides.
From the acetates, 3 equivalent of the very strong acid
absolute ethanol and the solution was evaporated under
reduced pressure. The operation was repeated three times,
and the white powders, [Ln]Ac/W/Et, [Ln]Car/W/Et, [Ln]Ox/W/Et
(Ln ¼ La, Nd), were finally dried under vacuum for 24 h at
110 8C. All attempts to obtain the ytterbium salts failed,
affording viscous brown oils.
bis(trifluoromethanesulfonyl)amine: H(NTf ) were added
2
and the solution was stirred for 30 min at room temperature.
From the carbonates, only 2.75 equivalent of H(NTf ) were
2
used and the excess of carbonate was eliminated by filtration
after 30 min stirring at room temperature. The reaction with
The IR spectra of the salts did not show the peaks of water
and their 1H NMR spectra established the absence of
coordinated ethanol. The pH of the aqueous solutions was
near neutral.
the oxides needed 5.5 equivalent of H(NTf ) and 1 h reflux-
2
ing in water; the excess of acid was removed under vacuum
(
Scheme 1).
After removal of the water, the salts were dried for 24 h at
An interesting fact was the absence of the peak at
ꢁ1
1320 cm (S¼O stretching) in the spectra of these anhy-
1
10 8C under reduced pressure. The extremely hygroscopic
drous compounds, whereas a strong peak appeared at ca.
ꢁ1
white powders thus obtained were stored in a glove box.
For clarity, the following notation will be used to desig-
nate the salts: the symbol of the element is followed by Ac
for acetate, Car for carbonate, Ox for oxide. The solvents
used for treatment will be designated as follow: water, W;
water then ethanol, W/Et; ethanol alone: Et. For example,
the lanthanum salt obtained from the acetate in water
1270 cm (instead of a weak peak in the coordinated
compounds). This lowering of the S¼O frequency could
be attributed to an Ln–O¼S coordination in an associated
structure.
An attempt to obtain the anhydrous neodymium salt
directly by the addition of H(NTf ) to a solution of neody-
2
mium acetate in ethanol (Scheme 2) afforded a white powder
containing coordinated ethanol after work-up.
solution, then treating it with ethanol is called [La]Ac/W/Et
.
The pH of these salts dissolved in distilled water was
measured. It is worthy noting that the lanthanum and neody-
The 19F NMR spectra of the isolated salts were recorded
in deuteriated acetone. For the CF groups, they all show a
3
mium salts obtained from the acetates, [La]Ac/Wand [Nd]Ac/W
remained strongly acidic (pH 3.7). The ytterbium salt,
Yb]Ac/W, was much less acidic (pH 4.5), whereas the salts
,
unique signal at ca. ꢁ78.8 ppm. These values are very close
to this reported for the magnesium salt: ꢁ78.6 ppm [6] and
ca. 1.8 ppm downfield compared to the free bis(trifluoro-
methanesulfonyl)amine [9]. It is very interesting that the
diamagnetic lanthanum and the paramagnetic neodymium
and ytterbium salts show the same chemical shift, in accor-
dance with the fact that these complexes were dissociated in
solution.
It appears that the structure of the bis(trifluoromethane-
sulfonyl)amide of the lanthanides depends on the ionic
radius of the element and also on the experimental proce-
dure, so quantitative analyses were performed to establish
their structure accurately.
[
obtained from carbonates, [La]Car/W, [Nd]Car/W, [Yb]Car/W, or
oxides, [Yb]Ox/W, were near neutral (pH 5.5–6.5).
Thus, [La]Ac/W and [Nd]Ac/W contained a significant
1
quantity of acetic acid. This fact was confirmed by H
NMR (singlet at 2 ppm in D O) and also by IR spectroscopy
2
1
(
sence of coordinated water in these complexes was also esta-
C¼O stretching peaks at 1682 and 1672 cmꢁ ). The pre-
ꢁ1
blished by IR spectroscopy (peaks at 3450 and 1630 cm
7]).
The coordination of acetic acid to lanthanum and neody-
[
mium was unexpected and precluded the use of the classical
method using methylorthoformate [8] to obtain anhydrous
salts, formic acid being able to coordinate lanthanides in the
same manner as acetic acid.
To obtain anhydrous salts, removal of the water by ethanol
was performed; after drying, the salts were dissolved in
Scheme 2.

D.B. Baudry et al. / Journal of Fluorine Chemistry 121 (2003) 233–238
235
Table 1
Thermal decomposition of the lanthanum and neodymium salts
Compound
Loss (%, 20–150 8C)
Loss (%, 150–330 8C)
Loss (%, 330–450 8C)
Residue (%)
[
[
[
[
[
[
[
[
[
La]Ac/W
0.7
5.57 (200)
0.5
1.2
76.6 (385; 400)
78.7 (394)
17.1
20.4
19.2
19.0
16.5
21.1
18.4
17.3
17.9
La]Ac/W/Et
La]Car/W/Et
La]Ox/W/Et
Nd]Ac/W
0.4
0.8
78.0 (374; 404)
79.2 (391; 411)
75.2 (369; 392)
77.6 (372; 386)
72.6 (368 388)
81.2 (374; 386)
81.3 (379)
0.9 (120)
0.8
0.8 (260)
7.5 (210)
0.1
Nd]Ac/W/Et
Nd]Ac/Et
1.2 (116)
9 (154)
0.6
9 (154)
0.8
Nd]Car/W/Et
Nd]Ox/W/Et
0.4
0.4
200 8C: Temperature corresponding to the maximum of weight loss.
2
.2. Quantitative analyses
Atmospheric water, which is absorbed during the hand-
ling of hygroscopic species, is eliminated between 70 and
120 8C, whereas the coordinated molecules of solvent were
successively eliminated between 150 and 300 8C. The fol-
lowing step was the decomposition of the salt and finally a
stable residue was obtained. The behavior of the lanthanum
and neodymium salts is summarized in Table 1. It is clear
that the weight loss corresponding to the loss of the coordi-
nated molecules, which occurs in the 150–330 8C range, is
The amount of coordinated water was measured by Karl
Fischer titration; the results are in very good accordance
with the expected formulae. The [Ln]Ac/W salts contained
ca. 1.8% of water, corresponding to one molecule of coor-
dinated H O, whereas the [Ln]
2
salts were anhydrous
Ac/W/Et
(
ca. 0.2% of water).
Thermogravimetric analysis was used to characterize the
lanthanide triflates [10,11], more particularly to estimate the
number of molecules of coordinated water in the adducts and
also to study the decomposition process.
in good accordance with the previous results: 1H O and
1CH CO H for [La] and [Nd]Ac/W, and 2EtOH for
Ac/W
2
3
2
[Nd]Ac/Et (Fig. 1). For the ‘‘anhydrous’’ salts, the plateau
2 3 2 3 3 2 2
Fig. 1. Thermogram of the Nd[N(SO CF ) ] (CH CH OH) : [Nd]Ac/Et adduct.

236
D.B. Baudry et al. / Journal of Fluorine Chemistry 121 (2003) 233–238
Scheme 3.
appears as near horizontal, suggesting the presence of a very
small amount of coordinated water or of a slow decomposi-
tion process.
anhydride mixture, rather than the very hazardous nitro-
methane [3] with 1% or less of catalyst [14]. Only a weak
loss of reactivity is observed when monohydrated salts or
crude salts containing acetic acid are used instead of the
anhydrous salt. In the same conditions, phenetole afforded
ethoxyacetophenone in similar yield.
The Fries transposition of a-naphthyl acetate was also
investigated (Scheme 3). It had previously been reported that
scandium triflate (5 mol.%) was an efficient catalyst for this
reaction, whereas lower yields were obtained with ytterbium
triflate [15]. The catalytic activity of ytterbium triflimidate,
[Yb]Ac/W, neodymium triflimidate, [Nd]Ac/W/Et, and ytter-
Rapid decomposition of the salts, resulting in a sharp
weight loss, occurred between 360 and 450 8C and pro-
ceeded in two steps and a horizontal plateau was obtained
after the complete thermal decomposition. X-Ray electron
microprobe analysis (EDX analysis) established that the
residues were the trifluorides, LaF and NdF . Neither LaOF
3
3
nor NdOF were detected. These results are very similar to
those reported for the ytterbium and lanthanum triflates
[
10,11]; the fluorides were finally obtained and a two step
process was also observed in the thermal decomposition of
the ytterbium triflate.
bium triflate, Yb(OTf) , were compared (Table 2); Ytter-
3
bium triflimidate is a better catalyst than ytterbium triflate
affording 70% versus 45% of 2-hydroxyacetonaphthone and
also than neodymium triflimidate (15% yield).
Lanthanide triflates are known to catalyze the Baeyer–
Villiger oxidation [16]. Ytterbium triflimidate is also a good
catalyst, giving similar yields (98 versus 95%) in the oxida-
tion of cyclohexanone or 4-methylacetophenone.
Cerium(IV) triflate was widely used to oxidize toluene,
alkyl benzenes or benzylic alcohols to give the correspond-
ing aldehydes [17–19]. These reactions need at least 2
The behavior of the ytterbium salts is different, a decom-
position process began at a lower temperature with a max-
imum at ca. 300 8C and a small amount (2.8%) of residue
was finally obtained. Thus, the ytterbium triflimidate is a
volatile salt and a sublimation experiment was performed.
ꢁ
2
At 240 8C, 10 Torr, a microcrystalline product, ([Yb]Ac/W/
Sub), was obtained. The H and 19F NMR spectra of this
product were identical to those of [Yb]Ac/W and the analysis
corresponded to the anhydrous salt. The easy sublimation of
this salt establishes the existence (at least at the sublimation
temperature) of a monomeric form. This is a new class of
volatile fluorinated lanthanide complexes; generally volatile
lanthanides containing fluorine are b-diketonates [12] or
alkoxides [13].
1
Table 2
Yields in Fries transposition with ytterbium and neodymium triflimidates
a
and ytterbium triflate as catalysts
Catalyst
2-Hydroxyacetonaphthnone
yield (%)
a-Naphthol
yield (%)
All these results allow the attribution of the following
formulae for these salts.
NdAcW/Et
YbAcW
Yb(Otf)3
15
70
45
8
18
5
1
2
3
4
5
. For the salts obtained from the acetates: Ln[N(SO2-
CF ) ] (H O)(CH CO H) (Ln ¼ La, Nd).
3
2 3
2
3
2
. For the neodymium salt obtained in ethanol:
Ln[N(SO CF ) ] (CH CH OH) .
a
5
refluxing.
mol.% catalyst, 1 M solution of a-naphthyl acetate in toluene, 24 h
2
3 2 3
3
2
2
. For the anhydrous salts: {Ln[N(SO CF ) ] } (Ln ¼ La,
2
3 2 3 x
Nd).
. For the ytterbium salt obtained in water: Yb[N(SO2-
CF ) ] ꢀH O.
3
2 3
2
. For the sublimated ytterbium salt: Yb[N(SO CF ) ] .
2 3 2 3
2
.3. Reactivity
The catalytic activity of the lanthanide triflimidates
has been tested in Friedel–Crafts acetylation of anisole.
This reaction has been performed in a acetic acid–acetic
Scheme 4.

D.B. Baudry et al. / Journal of Fluorine Chemistry 121 (2003) 233–238
237
equivalents of cerium salt. Unexpectedly, a small amount
of cerium(IV) triflimidate catalyzes the oxidation of
-methylacetophenone to give 4-methylbenzoic acid
Scheme 4). The best results (85% yields) are obtained with
0% of salt and 3 equivalents of H O . Other aromatic
4.1.2. Materials
The bis(trifluoromethanesulfonyl)amine was supplied
by Rhodia Chemical and purified by sublimation (50 8C,
0.1 Torr) before use. The lanthanide acetates, carbonates,
oxides and triflates were supplied by Rhodia Chemical and
used without any further purification. Anisole, a-naphthyl
acetate, cyclohexanone, 4-methylacetophenone were pur-
chased from Aldrich and used without purification.
4
(
1
2
2
ketones: 4-nitroacetophenone, 1,4-diacetylbenzene, propio-
phenone, give also the corresponding acids.
3
. Conclusion
4.2. Syntheses of bis(trifluoromethanesulfonyl)amides
The synthetic results are in good accordance with the
4.2.1. From the acetates: La[N(SO CF ) ]
3 2 3
2
decreasing ability, connected to the decreasing ionic radius
of the lanthanides, of coordinating ancillary ligands: large
lanthanum or neodymium are able to coordinate two mole-
cules of a solvent and, after removal of this solvent, the
anhydrous salts only exist in an associated non-sublimable
form. On the contrary, the small ytterbium coordinates
only one molecule of water. By heating, this adduct gives
a monomeric anhydrous salt.
(H O)(CH CO H) [La]
2 3 2 Ac/W
An amount of 2.44 g (6.96 mmol) of lanthanum acetate
hydrate were dissolved in 5 ml water, 5. 87 g (20.88 mmol)
of bis(trifluoromethanesulfonyl)amine were added and the
solution was stirred for 30 min. After removal of the water,
the viscous oil was dried for 24 h at 110 8C under vacuum
ꢁ
2
(10 Torr). The white powder (7.20 g, 98% yield) was
stored in the glove box.
As expected, these salts are efficient catalysts for reac-
tions usually catalyzed by Lewis acids, the presence of a
small amount of coordinated water having only a small
effect on their catalytic activity. The lanthanum salt, less
soluble than its neodymium or ytterbium analogues, is also
less efficient. But the most interesting reaction is the selec-
tive oxidation of aromatic ketones catalyzed by the cerium
salt. This reaction is currently being investigated and com-
plete results will soon be published.
Nd[N(SO CF ) ] ꢀH O(CH CO H) and Yb[N(SO2-
2
3 2 3
2
3
2
CF ) ] ꢀH O were obtained in the same manner.
3
2 3
2
4.2.2. {La[N(SO CF ) ] } : [La]
Ac/W/Et
2
3 2 3 x
The crude product obtained after the removal of water, as
above, was dissolved in 20 ml ethanol, after 10 min stirring,
the solvent was evaporated and the residue was dried for 2 h
at room temperature under vacuum. The operation was
repeated two times and the salt was finally dried under
vacuum for 24 h at 110 8C to give 6.45 g and 95% yield of
white powder.
4
4
4
. Experimental
Analytically calculated for C O N S F La: C, 7.35; N,
6
12 3 6 18
4.29; S, 19.61; Found: C, 6.95; N, 4.53; S, 19.48.
{Nd[N(SO CF ) ] } was obtained in the same manner.
.1. General experimental procedures
2
3 2 3 x
.1.1. Analytical techniques
The handling and storage of the hygroscopic materials
4.2.3. Nd[N(SO CF ) ] (CH CH OH) : [Nd]
2 3 2 3 3 2 2 Ac/Et
To a stirred suspension of 1.70 g (5 mmol) of neodymium
acetate hydrate in 20 ml ethanol, 4.22 g (15 mmol) of bis-
(trifluoromethanesulfonyl)amine were added at room tem-
perature. After 30 min stirring, the solution was evaporated
and the residue was dried under vacuum for 2 h at room
temperature, then for 24 h at 110 8C. The 5.22 g, 97% yield
of white powder were obtained.
were performed in a Jacomex glove box under purified argon
atmosphere.
The infrared spectra were recorded in nujol mulls on a
Bruker IFS 66V spectrometer. The H and 19F NMR spectra
were recorded on a Bruker AC 300 apparatus in D O or
1
2
CDCl . The elemental analyses were carried out on a Fisons
3
Instruments EA 1108 CHNS-O. The Karl Fischer analyses
were performed by using a Metrohm KF 684 coulometer.
The thermogravimetric analyses were performed by using
a TA Instruments 2960 apparatus at a heating rate of
4.2.4. From the carbonates (general procedure)
To a stirred suspension of 1 g (2.2 mmol) of lanthanum
carbonate, La (CO ) , in 5 ml water, 3.42 g (12.2 mmol) of
2
3 6
2
0 8C/min under nitrogen atmosphere or under atmospheric
bis(trifluoromethanesulfonyl)amine were added at room
temperature. After 30 min stirring, the excess of carbonate
was filtered out and the solution was evaporated, then treated
conditions. The EDX analyses were performed by using an
Oxford EDX microprobe coupled to a Jeol JSM 6400F
scanning electron microscope. The composition and yields
of the reaction products were determined with a Fisons
Instruments GC 9000 gas chromatograph equipped with a
flame ionization detector a data jet integrator and a
asabovetoobtain[La]Car/W,[Nd]Car/W,[Yb]Car/W,[La]Car/W/Et
and [Nd] Car/W/Et.
,
4.2.5. From the oxides (general procedure)
To a stirred suspension of 1 g (3.06 mmol) of lantha-
num oxide, La O , in 10 ml water, 4.78 g (17 mmol) of
3
capillary column.
0 m ꢂ 0:53 mm OV 624 or a 50 m ꢂ 0:32 mm HP-FFAP
2
3

238
D.B. Baudry et al. / Journal of Fluorine Chemistry 121 (2003) 233–238
bis(trifluoromethanesulfonyl)amine were added and the
mixture was refluxed for 1 h. The clear solution was evapo-
solvent was evaporated under reduced pressure, the residue
was subsequently dissolved in 25 ml of diethyl ether.
A sample was taken and analyzed by GC after esterification
of the 4-methylbenzoic acid with trimethylchlorosilane,
rated, then treated as above to obtain [Yb]Ox/W, [La]Ox/W/Et
and [Nd]Ox/W/Et.
,
85% yield.
4
4
.3. Reactivity
Acknowledgements
.3.1. Acetylation of anisole (general procedure)
In the glove box, 50.6 mg (0.05 mmol) of Nd(NTf2)3
[Nd]Ac/W/Et) were weighed in a 50 ml vessel. The vessel
We thank Dr Laurent Buisson from the Institut de Car-
act e´ risation des Mat e´ riaux (ICM), University of Burgundy,
for the EDX analyses and helpful comments.
(
was connected to a nitrogen inlet; anisole: 0.54 g (5 mmol),
acetic anhydride: 2.83 g (30 mmol) and acetic acid: 2.77 g
(
46.2 mmol) were added with a syringe and the mixture was
magnetically stirred at 120 8C for 3 h. After cooling, 20 ml
of diethyl ether were added and the solution was washed
with a saturated solution of sodium hydrogen carbonate
until neutral. The organic layer was dried over magnesium
sulfate and the solvent was removed. A sample was taken
and analyzed by GC. Yield ca. 95%.
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.3.2. Fries transposition of a-naphthyl acetate
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(
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[
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4.3.4. Oxidation of 4-methylacetophenone by
cerium triflimidate
[
In the glove box, 203 mg (0.16 mmol) of Ce(NTf ) were
x
[16] H. Kotsuki, K. Arimura, T. Araki, T. Shinohara, Synth. Lett. (1999)
62–464.
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2
4
weighed in a 50 ml vessel; 210 mg (1.57 mmol) of 4-methy-
lacetophenone and 16 ml of acetic acid were added and the
mixture was stirred and refluxed under atmospheric pressure
of oxygen. After 30, 60 and 90 min, 20 ml of H O (30 wt.%)
[
[
1
2
2
[19] K.K. Laali, M. Herbert, B. Cushnyr, A. Bhatt, D. Terrano, J. Chem.
are added for a total amount of 0.5 mmol. After 6 h, the
Soc., Perkin Trans. I (2001) 578–583.