Iodo bis bistrimethylsilylamido lanthanides

Article abstract of DOI:10.1016/S0022-328X(01)00793-8

Reactions of lanthanide triiodides with potassium bistrimethylsilyl amide have been investigated. For lanthanum, recrystallisation from THF-toluene led to monocrystals of the dimeric bisamide [La(μ-I){N(TMS)₂}₂(THF)]₂. We have shown that samarium diiodide and lanthanide triiodides are efficient for lanthanum and samarium reactions, a mixture of tris amides and iodo bisamides is obtained, while only the latter compound is obtained for ytterbium.

Full text of DOI:10.1016/S0022-328X(01)00793-8

Journal of Organometallic Chemistry 628 (2001) 271–274
www.elsevier.nl/locate/jorganchem
Iodo bis bistrimethylsilylamido lanthanides
Jacqueline Collin a,*, Nicolas Giuseppone a, Nada Jaber a, Angela Domingos b,
Leonor Maria b, Isabel Santos b
a Laboratoire de Catalyse Mole´culaire, UPRESA 8075, ICMO, Uni6ersite´ Paris-sud, 91405 Orsay, France
b Departamento de Quimica, ITN, 2688 Saca6e´m Codex, Portugal
Received 5 February 2001; accepted 29 March 2001
Abstract
Reactions of lanthanide triiodides with potassium bistrimethylsilyl amide have been investigated. For lanthanum, recrystallisa-
tion from THF–toluene led to monocrystals of the dimeric bisamide [La(m-I){N(TMS)2}2(THF)]2. We have shown that samarium
diiodide and lanthanide triiodides are efficient for lanthanum and samarium reactions, a mixture of tris amides and iodo bisamides
is obtained, while only the latter compound is obtained for ytterbium. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Lanthanides; Amides
avoiding the preparation of the instable binaphthoxide
potassium salts. Some heteroleptic amido lanthanide
derivatives have been isolated [10], but lanthanide
amido halide complexes are scarce. Bistrimethylsily-
lamido lanthanide chlorides have been prepared with
several lanthanides but the corresponding bromide only
with samarium [13,14]. The biscyclohexyl amido chloro
samarium has also been characterised [15]. To the best
of our knowledge, the only iodo heteroleptic amido
lanthanide described is the divalent iodo bistrimethylsi-
lyl amido samarium [16].
1. Introduction
In the course of our previous investigations we had
shown samarium diiodide and lanthanide triiodides as
efficient Lewis acid catalysts for a wide range of reac-
tions [1–3]. These findings led us to synthesise new iodo
lanthanide complexes coordinated with asymmetric cy-
clopentadienyl [4–6] or binaphthol [7] ligands, for their
evaluation as enantioselective catalysts. Iodobinaph-
thoxide lanthanide compounds are active and enan-
tioselective catalysts for Diels–Alder reactions.
Replacing the binaphthol ligand by bis-3,3%-o-anisyl-bi-
naphthol led to an improvement of enantiomeric ex-
cesses and to variations of the sense of induction with
temperature [8,9]. For the preparation of the catalysts
we used mainly metathesis reactions starting with lan-
thanide triiodides and the potassium salts of the lig-
ands. However, in lanthanide chemistry, the reaction of
alcohols with trivalent homoleptic trisamides [R2N]3Ln,
specially bistrimethylsilylamides [10–13], is a well-
known clean and practical method for the preparation
of alkoxides. Thus, we thought that lanthanide iodo
amides could be convenient starting materials allowing
a ready access to lanthanide iodo binaphthoxides,
In this paper, we report the characterisation of iodo
bis bistrimethylsilyl amides of lanthanum, samarium
and ytterbium.
2. Results
With the aim of preparing heteroleptic lanthanides,
we studied the reaction of LaI3(DME)2 (1a) with two
equivalents of potassium bistrimethylsilylamide,
KN(TMS)2 (2), in THF. We observed a change of
colour of the reaction mixture from beige to off-white
and precipitation of a white powder of potassium io-
dide. After filtration and evaporation of THF, we
obtained a powder that has been analysed. The 1H-
NMR spectrum of this powder in CDCl3 showed two
resonances at 0.16 and 0.13 ppm. The resonance at 0.13
* Corresponding author. Tel.: +33-1-69154740; fax: +33-1-
69154680.
E-mail address: jacollin@icmo.u-psud.fr (J. Collin).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00793-8

272
J. Collin et al. / Journal of Organometallic Chemistry 628 (2001) 271–274
far from 180° for the regular geometry. The equatorial
plane is defined by the two amide nitrogen atoms and
by the other bridging iodide (N(1)ꢀLaꢀN(2), 120.8(3);
IꢀLaꢀN(1), 119.4(2); IꢀLaꢀN(2), 119.7(2)°). The LaꢀN
bond lengths are identical within experimental error
,
(LaꢀN(1), 2.352(9); LaꢀN(2), 2.331(8) A), with an aver-
,
age of 2.342(9) A. The LaꢀO(THF) bond distance is
,
2.561(8) A. A comparison of LaꢀI and the LaꢀO(THF)
bond distances (average 3.3074(11) and 2.561(8) A,
,
respectively) can also be made with the corresponding
distances in the seven-coordinate pentagonal bipyrami-
dal LaI3(THF)4 structure (average 3.154(4) and 2.554(8)
Fig. 1. Structure of iodo bis bistrimethylsilyl lanthanum amide 3a.
,
A) [2]. The LaꢀI distance in 3a is longer as expected for
a bridging LaꢀmI distance even though it is in a lower
coordinate complex. The LaꢀO(THF) distance in 3a is
ppm was identified as La[N(TMS)2]3 (4a) by compari-
son with
a
real sample prepared by reacting
,
in the range 2.535(8)–2.576(8)
A
observed in
LaI3(DME)2 with KN(TMS)2 in THF in the molar
ratio 1:3. The identification of the other species was
made by X-ray crystallographic analysis together with
NMR spectroscopy. In fact recrystallisation from tolu-
ene–THF of the crude product obtained in the reaction
of 1 with 2 in the molar ratio 1:2 allowed us to obtain
two different types of single crystals. Some of them,
yellow needle shaped crystals, were analysed as being
La[N(TMS)2]3 (4a), by comparison of their cell parame-
ters with the cell parameters of Nd[N(TMS)2]3 [17], they
were found to be isomorphous. The second type of
crystals were light yellow and by X-ray diffraction
analysis were identified as iodo bis(bistrimethylsilyl)
amide 3a with the dimeric structure [La(m-I)-
{N(TMS)2}2(THF)]2. The structure of 3a is a cen-
trosymmetric dimer with asymmetrically bridging io-
LaI3(THF)4. No unusually short intra- and intermolec-
ular contacts are observed. The structure of 3a is very
similar to the reported structures of [Sm(m-
X){N(TMS)2}2(THF)]2 (X=Cl, Br) [14].
We then studied reactions of SmI3(THF)3 (1b) or
YbI3(THF)3 (1c) with two equivalents of potassium
bistrimethylsilylamide 2 in THF and also observed by
NMR the formation of two species in the case of Sm.
1
The H-NMR spectra of the crude product obtained in
the reaction with samarium presented one resonance at
−1.58 and another at −1.68 ppm. The presence of tris
bistrimethylsilyl amide 4b (samarium) was established
by comparison with the reported shifts [11] and with
the NMR of a real sample prepared by reacting the
corresponding triiodide with three equivalents of 2. By
extraction of the crude product obtained in the reaction
with hexane, the insoluble samarium triiodide was sepa-
rated from the samarium bis and tris bistrimethylsilyl
amides. Then the trisamide 4b (white powder) was
sublimed and separated from the pure bisamide 3b
isolated as a yellow powder. Only one peak (C6D6,
,
dide ligands (3.3096(11) and 3.3051(11) A), as shown in
Fig. 1. Selected bond distances and angles are given in
Table 1. The planar La2I2 ring presents angles at the La
atom noticeably smaller than at the I atom (IꢀLaꢀI%
76.05(3)°, LaꢀIꢀLa% 103.95(3)°), with a La···La% separa-
1
,
tion of 5.210 A. The coordination at the La atom is
l= −1.68 ppm) was observed in the H-NMR spec-
five-coordinate with a geometry described as distorted
trigonal bipyramidal, with the THF oxygen and one
bridging iodide in axial positions, OꢀLaꢀI% 153.6(2)°,
trum of the non-sublimed product, and elemental anal-
ysis of the yellow powder was consistent with
[SmI[N(TMS)2]2]2 (3b). The ratios of bis and tris amides
3 and 4 were measured by integration of 1H-NMR
spectra of crude products: for lanthanum 3a/4a, 86:14;
for samarium 3b/4b, 70:30. By NMR spectroscopy and,
in the case of 3a, by X-ray analysis we concluded that
both iodoamides 3a (La) and 3b (Sm) have one
molecule of THF coordinated. Heteroleptic chloro bis
trimethylsilylamido europium [18] and divalent iodo
bistrimethylsilyl amido samarium [16] have been pre-
pared by disproportionation reactions. Similarly, we
observed that a mixture of lanthanum triiodide 1a and
lanthanum tris bistrimethylsilyl amide 4a in THF, at
room temperature, yielded lanthanum iodo bisamide
Table 1
,
Selected bond lengths (A) and angles (°) for 3a
LaꢀN(1)
LaꢀN(2)
LaꢀO
Si(1)ꢀN(1)
Si(2)ꢀN(1)
2.352(9)
2.331(8)
2.561(8)
1.716(9)
1.715(9)
LaꢀI
LaꢀI
Si(3)ꢀN(2)
Si(4)ꢀN(2)
3.3096(11)
3.3051(11)
1.718(9)
a
1.711(10)
N(1)ꢀLaꢀN(2)
N(1)ꢀLaꢀO
N(2)ꢀLaꢀO
IꢀLaꢀI a
120.8(3)
85.4(3)
106.2(3)
76.05(3)
119.4(2)
103.6(2)
N(2)ꢀLaꢀI
N(2)ꢀLaꢀI a
O(1)ꢀLaꢀI
O(1)ꢀLaꢀI a
LaꢀIꢀLa a
119.7(2)
90.6(2)
77.9(2)
153.6(2)
103.95(3)
N(1)ꢀLaꢀI
1
3a, as indicated by H-NMR spectroscopy.
N(1)ꢀLaꢀI a
For ytterbium after the metathesis reaction we tried
to separate ytterbium tris bistrimethylsilyl amide 4c
a Atoms related by the symmetry operation: −x,−y+1,−z+1.

J. Collin et al. / Journal of Organometallic Chemistry 628 (2001) 271–274
273
from the crude product by sublimation under vacuum.
A prolonged heating at 125°C under 1×10−4 Torr [11]
did not allow the sublimation of 4c. Elemental analysis
of the off-white powder was consistent with the struc-
ture [YbI[N(TMS)2]2]2 (3c). The bis bistrimethylsilyl
amido ytterbium is obtained readily as a pure com-
pound without contamination by ytterbium tris
bistrimethylsilylamide. This behaviour, in comparison
with the results observed for lanthanum and samarium,
can be explained by the smaller size of the metal. The
heteroleptic chloro bistrimethylsilyl amido lanthanides
are stable only for the smaller metals due to steric
insaturation for the other [13].
The X-ray diffraction study of the iodo bis amide
lanthanum 3a indicates a dimeric structure. We have no
information concerning the monomeric or dimeric
structures of the samarium and ytterbium derivatives 3b
and 3c. The structure of the trivalent bis bistrimethylsi-
lylamido bromo samarium and chloro samarium [14],
or chloro ytterbium [13] are reported to be dimeric.
Thus, in spite of the differences of size of iodine with
respect with bromine and chlorine, we believe that
samarium and ytterbium amides 3b and 3c are dimers.
molar ratio 1:0.5 at room temperature (r.t.).
LaI3(DME)2 was prepared from La powder and iodine
[20]. Bruker AM 200 and Varian Unity 300 spectrome-
ters, operating at 200 and 300 MHz, were used for the
NMR spectra. Chemical shifts are reported in parts per
million (ppm) downfield from Me4Si for spectra in
CDCl3. Infrared spectra were recorded as Nujol mulls
using NaCl plates on a Perkin–Elmer 1000 FTIR spec-
trometer and are reported in cm−1. Carbon, hydrogen
and nitrogen elemental analyses were performed on a
Perkin–Elmer automatic analyser.
4.1. Reactions of lanthanum triiodide 1a and samarium
triiodide 1b with potassium amide
To a suspension of LaI3(DME)2 (1a) (0.350 g, 0.50
mmol) or SmI3(THF)3 (1b) (0.373 g, 0.50 mmol) in 10
ml THF was added under magnetic stirring a solution
of potassium bistrimethylsilyl amide 2 (0.199 g, 1.0
mmol) in 10 ml THF within 15 min. A change of colour
of the reaction mixture from beige (lanthanum) or
yellow (samarium) to off-white was observed, together
with formation of a white precipitate. After 18 h the KI
was filtrated and the supernatant solution was evapo-
rated under vacuum yielding an off-white powder of
1
3. Conclusions
3+4. Two peaks are observed in the H-NMR spectra
of the crude product.
We have characterised heteroleptic iodo bis amido
complexes of lanthanum, samarium and ytterbium sta-
bilised with bistrimethylsilylamide ligands. For lan-
thanum and samarium the complexes are contaminated
with small quantities of the corresponding tris amides.
X-ray crystallographic analysis for La bisamide has
shown a dimeric structure for the complex, with one
molecule of THF coordinated to each lanthanum atom.
The ytterbium complex is isolated as a pure compound
and the first exchange reactions with binaphthol or bis
3,3%-o-anisylbinapthol have been realised. The com-
plexes obtained give similar results in Diels–Alder reac-
tions as the previously prepared ytterbium iodo
binaphthoxide [9]. This seems to indicate that ytterbium
bis amide is a good precursor for the preparation of a
variety of ytterbium based catalysts.
3a+4a: [CDCl3, 200 MHz, l ppm: 0.13 (14%) 4a,
0.16 (86%) 3a].
3b+4b: [C6D6, 300 MHz, l ppm: −1.58 (30%) 4b,
−1.68 (70%) 3b].
For 3b+4b the crude product was extracted with
hexane to separate the insoluble samarium triiodide.
After evaporation the residue was heated at 120°C
under 10−4 Torr, 4b was sublimed. The non-sublimed
1
product is a yellow powder of 3b. H-NMR (C6D6, 300
MHz, l ppm): −1.68 (s). IR (w, cm−1): 1250, 1160,
1090, 1010, 950, 860, 835, 800, 650. Anal. Found: C
22.97; H 7.27; N 4.16. Calc. for C12H36IN2Si4Sm: C
24.10; H 6.03; N 4.69%.
4.2. Preparation of tris bistrimethylsilyl amido
lanthanum 4a and samarium 4b
To a suspension of LaI3(DME)2 (1a) (0.350 g, 0.5
mmol) in 10 ml THF or SmI3(THF)3 (1b) (0.373 g, 1
mmol) was added under magnetic stirring a solution of
potassium bistrimethylsilyl amide 2 (0.300 g, 1.5 mmol)
in 10 ml THF. After 18 h the KI was filtered and the
supernatant solution was evaporated under vacuum
yielding an off-white powder. Heating the residue under
10−4 Torr at 140°C for lanthanum, and 120°C for
samarium, allowed to sublime, respectively, 4a and 4b
4. Experimental
All manipulations were carried out under an argon
atmosphere using standard Schlenk or glove-box tech-
niques. THF and hexane were distilled from sodium
benzophenone ketyl and degassed immediately prior to
use. CDCl3 and C6D6 were distilled from CaH2 and
degassed immediately prior to use. SmI2 and YbI2 were
prepared according to published methods [19].
SmI3(THF)3 and YbI3(THF)3 were, respectively, ob-
tained by reacting SmI2 and YbI2 with I2 in THF in the
1
as white powders. 4a: H-NMR (CDCl3, 200 MHz, l
ppm) 0.13. 4b: 1H-NMR (C6D6, 300 MHz, l ppm)
−1.58.

274
J. Collin et al. / Journal of Organometallic Chemistry 628 (2001) 271–274
Table 2
Crystallographic data for 3a
1010, 970, 835, 770, 650, 610. Anal. Found: C 22.92; H
6.00; N 3.56. Calc. for C12H36IN2Si4Yb: C 23.2; H 5.81;
N 4.50%.
Formula
C16H44ILaN2OSi4
Formula weight
Crystal system
Space group
658.70
Triclinic
P
Acknowledgements
Unit cell dimensions
,
a (A)
10.6124(10)
11.9212(7)
14.127(2)
71.933(8)
74.201(9)
63.482(7)
1501.4(3)
2
1.457
2.618
0.0640
0.0953
We thank CNRS for financial support and
MENRES for a fellowship for N. Giuseppone. The
work at ITN and at Orsay was partially supported by
ICCTI/MENRES through a French–Portuguese re-
search network.
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
v (mm−1
)
References
a
R1
b
wR2
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(1998) 7845.
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;
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.
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mmol) in 10 ml THF was added under magnetic stir-
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(0.231 g, 1.16 mmol) in 10 ml THF within 15 min. A
change of colour of the reaction mixture from orange
to off-white was observed, together with formation of a
white precipitate. After 18 h the KI was filtered (0.172
g, 89%) and the supernatant solution was evaporated
under vacuum yielding an off-white powder of 3c (0.350
g, 97% yield). IR (w, cm−1): 1255, 1245, 1175, 1090,
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