Di- and trivalent lanthanide complexes stabilized by sterically demanding aminopyridinato ligands

Article abstract of DOI:10.1002/ejic.200400823

Deprotonation of Ap*H (Ap*H = (2,6-diisopropylphenyl)-[6-(2,4, 6-triisopropylphenyl)pyridin-2-yl]amine} and Ap′H (Ap′H = (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyridin-2-yl]amine} using KH leads to polymeric [Ap*K]_n and [Ap′K]_n

Full text of DOI:10.1002/ejic.200400823

FULL PAPER
Di- and Trivalent Lanthanide Complexes Stabilized by Sterically Demanding
Aminopyridinato Ligands
Natalie M. Scott[a] and Rhett Kempe*[a,b]
Keywords: Aminopyridinato ligands / Lanthanides / Neodymium / N ligands / Olefin polymerization / Samarium /
Ytterbium
Deprotonation of Ap*H {Ap*H = (2,6-diisopropylphenyl)-[6-
(2,4,6-triisopropylphenyl)pyridin-2-yl]amine} and ApЈH
the “THF-free” silylamide [Nd(ApЈ)2{N(SiMe3)2}]. Further-
more rare examples of heteroleptic amido-iodo complexes of
selected divalent lanthanides can be stabilized by deproton-
ated Ap*H. Reaction of [Ap*K]n with [LnI2(THF)3] (Ln = Yb,
Sm) in THF leads, after workup in hexane, to [Yb(Ap*)I-
(THF)2]2 and [Sm(Ap*)I(THF)2]2. All lanthanide complexes,
four of them are paramagnetic, were characterized by X-ray
crystal structure analysis. These compounds exhibit an excel-
lent solubility in nonpolar solvents like hexane.
{ApЈH = (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)pyr-
idin-2-yl]amine} using KH leads to polymeric [Ap*K]n and
[ApЈK]n which undergo clean salt metathesis reactions with
NdCl3 in THF forming [Nd(Ap*)Cl2(THF)2]2 and [Nd(ApЈ)2-
Cl(THF)], respectively. Ethylene polymerization activities of
the two chloro complexes (after activation with MAO) were
studied. Derivatization of the chloro compounds proceeds
without ate complex formation, for instance the reaction of
[Nd(ApЈ)2Cl(THF)] with one equiv. of [K{N(SiMe3)2}] leads to
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
reactivity of lanthanide complexes stabilized by deproton-
ated 1 and 2.
Introduction
During the renaissance[1] of amido[2] metal chemistry,
aminopyridinato ligands (Ap)[3] have been used extensively
to stabilize lanthanide (Ln) complexes. These compounds
(Scheme 1) have been shown to exhibit unusual stoichio-
metric and catalytic reactivity.[4]
Scheme 2. Proligands Ap*H (1) and ApЈH (2).
The maximum atom-to-atom distance in deprotonated 1
(determined from its Li salt[5] is 15 Å (vector a in Scheme 3,
top). Approximately perpendicular to it is vector b = 8 Å.
Comparing these measurements with those of the bulky, η5-
coordinated Cp*-ligand[6] (Cp* = pentamethylcyclopen-
tadienyl) (Scheme 3, bottom), which has a distance of a =
b = 6.2 Å, indicates that deprotonated 1 would be effective
for the protection of large metal ions such as lanthanides.
Furthermore, the stabilization of mono-amide [mono-
(aminopyridinato)] complexes, in which ligand redistri-
bution is blocked, should become possible.
Scheme 1. An aminopyridinato ligand in its strained η2 binding
mode, typical for early transition metals and lanthanides ([Ln] =
lanthanide moiety; R = aryl, silyl or alkyl substituent).
The size of the aminopyridinato ligands used thus far
has been relatively small, resulting in a low steric demand
of the metal, especially in the plane perpendicular to the
pyridine moiety. This, in turn, gives rise to highly nitrogen-
coordinated lanthanide complexes. Recently, we described
the preparation of bulky aminopyridinato ligands by the
introduction of 2,6-alkylphenyl substituents at the amido-
N atom and also in the 6-position of the pyridine ring
(Scheme 2).[5] Here, we report on synthesis, structure and
The size of deprotonated 2 is somewhat smaller than de-
protonated 1 with a = 13 Å and b = 8 Å.
Results and Discussion
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Synthesis and Structure of Neodymium Complexes
E-mail: kempe@uni-bayreuth.de
The reactions of the lithium salts of 1 or 2 (prepared by
deprotonation in situ with BuLi) with NdCl3 did not result
[b] Leibniz-Institut für Organische Katalyse,
Buchbinderstrasse 5–6, 18055 Rostock, Germany
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DOI: 10.1002/ejic.200400823
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N. M. Scott, R. Kempe
FULL PAPER
mental details are summarized in Table 1. The molecular
structure of 5 is shown in Figure 1.
Scheme 5. Synthesis of 5 and 6 (Dip = 2,6-diisopropylphenyl, Tip
= 2,4,6-triisopropylphenyl, Dmp = 2,6-dimethylphenyl).
Scheme 3. Description of the steric demand of deprotonated 1 in
comparison to Cp*.
These investigations revealed 5 to be a dinuclear
mono(aminopyridinato) complex. Reacting K to Nd ratios
of 1:1 or 2:1 gave rise to the same product. The steric bulk
of deprotonated 1 seems to favor the formation of a one to
one Ap to Ln ratio. The N–Nd–N angle (53°) underlines
the strained nature of the aminopyridinato coordination
and the different Nd–N distances indicate a localization of
the anionic function of the ligand at the amido-N atom – a
classic amidoϪmetal bond and a standard pyridine–neo-
dymium bond. The amido-N···neodymium distance
(2.380 Å) is in accordance with the reported values from
the literature (standard value 2.356 Å[7]), as is the pyridine-
N···neodymium distance at 2.659 Å (standard value
2.670 Å[8]). This is in contrast to the coordination of silyl-
in the isolation of a neodymium complex (only starting ma-
terial was recovered). Deprotonation of 1 or 2 using KH
gives rise to polymeric products 3 and 4, as shown in
Scheme 4.[5]
Scheme 4. Synthesis of 3 (R, RЈ, iPr = isopropyl) and 4 (R =
methyl, RЈ = H).
Compounds 3 and 4 react with [NdCl3] in a salt metathe- aminopyridinato lanthanide complexes, where a delocalized
sis reaction affording 5 and 6, see Scheme 5. No ate com- binding mode, including equivalent metal···nitrogen dis-
plex formation was observed. Compounds 5 and 6 were tances, has been observered in all compounds described so
characterized by X-ray crystal structure analysis. Experi- far.[4] The molecular structure of 6 is shown in Figure 2.
Table 1. Details of the X-ray crystal structure analyses of 5, 6, 7, 8, and 9.
Compound
5
6
7
8
9
Crystal system
Space group
triclinic
P1
triclinic
P1
monoclinic
P21/c
triclinic
P1
monoclinic
P21/c
¯
¯
¯
a [Å]
b [Å]
c [Å]
α [°]
10.266(2)
12.340(3)
18.481(4)
84.31(3)
76.41(3)
71.98(3)
2163
12.985(3)
14.336(3)
14.377(3)
104.45(3)
91.17(3)
99.73(3)
2549
12.4893(4)
26.6564(7)
18.9051(6)
10.972(5)
13.144(5)
18.497(5)
84.183(5)
78.661(5)
82.795(5)
2587
12.059(5)
17.584(5)
19.978(5)
β [°]
97.121(3)
97.907(5)
γ [°]
V [Å3]
6245
4196
Z
1
2
4
1
2
Crystal size [mm3]
ρcalcd. [g cm–3]
μ [mm–1]
0.36×0.31×0.15
1.251
1.355
0.21×0.18×0.16
1.260
1.110
0.29×0.22×0.20
1.176
0.909
0.45×0.31×0.28
1.340
2.443
0.11×0.06×0.05
1.389
2.167
T [K]
θmax. [°]
293
26.06
173
25.99
193
26.05
193
25.95
193
26.34
No. of reflections unique
No. of reflections obsd. [I 6238
Ͼ 2σ (I)]
7737
9350
3982
12305
8494
10074
8504
8264
2636
No. of parameters
wR2 (all data)
R value [I Ͼ2σ (I)]
426
0.142
0.057
562
0.127
0.056
631
0.073
0.030
455
0.131
0.042
195
0.366
0.131
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Di- and Trivalent Lanthanide Complexes Stabilized by Aminopyridinato Ligands
FULL PAPER
plain the parity of two N–Ln bonds in silylaminopyridinato
ligands. Compound 5 and 6 are soluble in nonpolar sol-
vents such as hexane and salt metathesis reactions proceed
in this solvent without ate complex formation. The reaction
of 6 with one equiv. of [K{N(SiMe3)2}] leads to the silyl-
amide 7, uncoordinated by THF (Scheme 6).
Scheme 6. Synthesis of 7.
Figure 1. Molecular structure of 5 (ellipsoids correspond to the
50% probability level); selected bond lengths [Å] and angles [°]:
NdϪN1 2.380(4), NdϪO2Ј 2.510(4), NdϪO1Ј 2.510(4), NdϪCl1
2.6443(19), NdϪN2 2.659(4), NdϪCl2 2.7919(17), NdϪCl2A
2.8511(17); NdϪCl2ϪNdA 108.37(5), Cl1ϪNdϪCl2 99.81(6),
N1ϪNdϪN2 53.25(14).
Compound 7 was characterized by X-ray crystal struc-
ture analysis. Experimental details are summarized in
Table 1. The molecular structure of 7 is shown in Figure 3.
Figure 3. Molecular structure of 7 (ellipsoids correspond to the
50% probability level); selected bond lengths [Å] and angles [°]:
Nd1ϪN5 2.280(2), Nd1ϪN3 2.407(2), Nd1ϪN1 2.414(2),
Nd1ϪN2 2.544(2), Nd1ϪN4 2.552(2); N5ϪNd1ϪN3 123.78(8),
N5ϪNd1ϪN1 125.18(8), N5ϪNd1ϪN2 108.02(8), N1ϪNd1ϪN2
54.56(7), N5ϪNd1ϪN4 110.50(8), N3ϪNd1ϪN4 54.57(7).
Figure 2. Molecular structure of 6 (ellipsoids correspond to the
50% probability level); selected bond lengths [Å] and angles [°]:
Nd1ϪN1 2.361(6), Nd1ϪN3 2.386(7), Nd1ϪO1 2.442(7),
Nd1ϪN4 2.569(6), Nd1ϪCl1 2.599(3), Nd1ϪN2 2.622(6),
Nd1ϪC1 2.936(8); N3ϪNd1ϪN4 54.9(2), N1ϪNd1ϪCl1
90.50(17), N3ϪNd1ϪCl1 103.37(16), N4ϪNd1ϪCl1 107.91(15),
N1ϪNd1ϪN2 54.1(2), Cl1ϪNd1ϪN2 142.91(14).
The coordination can be described as rectangular pyram-
idal with the four aminopyridinato-N atoms forming the
In contrast to 5 a bis(aminopyridinato) complex is rectangle. As far as we are aware the silylamido–Nd bond
formed which is monomeric in the solid state. Despite the length represents the shortest observed so far and should
fact that the differences of the steric bulk of deprotonated indicate a highly Lewis-acidic metal center. Compounds 5
1 and 2 are rather small in comparison to the size of the and 6 were tested as catalysts for ethylene polymerization
ligands, selective formation of mono- or bis(aminopyridin- after activation with MAO. The complexes were dissolved
ato) complexes are observed. The neodymium···N distances in toluene and treated with MAO (aluminium to catalyst
of 6 are indicative of a localization of the anionic function. ratio = 250:1). A 1-L laboratory autoclave was charged with
This appears to be a general phenomenon and is illustrated the catalyst solution and an ethylene overpressure of 10 bar
by the 90° dihedral angle between the pyridine plane and was applied at 60 °C for 30 minutes. Compounds 5 and 6
–1
arylamido plane. It is probable that the two alkyl substitu- showed activities of 51.4 and 42.4 kgpolyethylene molcat
ents prevent an interaction between the two π-systems. In h–1 bar–1, respectively. These moderate activities[9] indicate
silylaminopyridinato lanthanide complexes the pyridine π- the potential of these compounds in olefin polymerization.
system may interact with the silicon atom to cause further Detailed studies of olefin insertion into neutral or cationic
delocalization. This delocalization may go some way to ex- lanthanide complexes are underway.
Eur. J. Inorg. Chem. 2005, 1319–1324
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N. M. Scott, R. Kempe
FULL PAPER
Synthesis and Structure of the Heteroleptic Ytterbium and
Samarium Complexes
Pioneering work by Evans and coworkers[10,11] has
shown that divalent lanthanide complexes exhibit a particu-
larly rich reaction chemistry owing to the accessibility of
different oxidation states;[12] for example, although
[Cp*2Sm] and [Cp*2Sm(THF)2] do not possess a metal–car-
bon bond they both show polymerization activity towards
ethylene[13,14] The majority of this chemistry has been car-
ried out utilizing homoleptic Cp* complexes. However,
complexes incorporating a single Cp* ligand and a second
anionic ligand (heteroleptic compounds), which may allow
for further tuning of the reactivity, have received inadequate
attention. This is partially due to the low stability of the
mono-ligated starting materials. For example, the com-
Figure 4. Molecular structure of 8 (ellipsoids correspond to the
50% probability level); selected bond lengths [Å] and angles [°]:
Yb1ϪN1 2.423(4), Yb1ϪO2 2.432(4), Yb1ϪO1 2.445(4), Yb1ϪN2
2.508(4), Yb1ϪC1 2.922(5), Yb1ϪI1 3.1225(10), Yb1ϪI1
3.1241(8), I1ϪYb1 3.1225(10); N1ϪYb1ϪO2 156.82(14),
N1ϪYb1ϪO1 97.23(15), O2ϪYb1ϪO1 81.22(15), N1ϪYb1ϪN2
55.30(13), O2ϪYb1ϪN2 101.54(13), O1ϪYb1ϪN2 87.55(14),
[15]
pounds [(Cp*)Sm(μ-I)(THF)2]2
and [(Me3Si)2NSm(μ-I)-
[16]
(DME)(THF)]2
(DME = dimethoxyethane) have been
described and are reported to undergo facile ligand redistri-
bution to give [SmI2(THF)x] and [SmL2] [L = Cp*,
(Me3Si)2N]. Divalent “heteroleptics” have been well docu-
mented in the case of donor-functionalized Cp-ligands but
rarely described for alkoxy and amido ligands.[16,17] We ex-
N1ϪYb1ϪI1A
104.44(10),
O2ϪYb1ϪI1A
98.42(10),
O1ϪYb1ϪI1A 83.99(11), N2ϪYb1ϪI1A 156.84(9), N1ϪYb1ϪI1
pected deprotonated 1 to be an excellent candidate for the 97.46(10), O2ϪYb1ϪI1 87.29(10), O1ϪYb1ϪI1 164.43(10),
N2ϪYb1ϪI1 105.12(9), C1ϪYb1ϪI1 102.77(9), I1ϪYb1ϪI1A
87.36(3).
stabilization of such divalent complexes. The reaction of 3
with [LnI2(THF)3] (Ln = Yb, Sm) in THF leads, after
workup in hexane, to mono-iodido complexes, which prove
to be binuclear in the solid state (Scheme 7). Experimental
details of the X-ray crystal structure analyses are summa-
rized in Table 1.
Scheme 7. Synthesis of 8 and 9.
The molecular structures of 8 and 9 are shown in Fig-
ure 4 and Figure 5, respectively. The coordination of the
two Yb centers of 8 is best described as octahedral with a
dihedral angle of 95.1° between the Yb1–Yb1A–I1–I1A
plane and the pyridine planes. Proton NMR spectra of 8
([D8]THF, [D8]toluene) show a single signal set with well-
Figure 5. Molecular structure of 9 (ellipsoids correspond to the
50% probability level).
resolved signals for the isopropyl groups in C6D5CD3.
Since the paramagnetic nature of 9 prevents structural
characterization by NMR spectroscopy, X-ray analysis was
lanthanides. The steric demands of this ligand result in a
performed. Only very weak diffracting crystals of 9 could
reduction of ligand redistribution during synthesis. Struc-
be obtained. However, the connectivity could be estab-
turally, its lanthanide complexes can be compared to that
lished. Owing to the low quality of structural data, a de-
of other bulky amide-containing compounds, such as tro-
tailed discussion of bond length and angles is waived. The
poniminate or amidate complexes but the chemistry should
molecular structure of 9 is similar to that of 8 but the struc-
be somewhat different owing to higher ligand asymmetry.
tures are not isomorphous.
Surprisingly, deprotonated 2 gives selectively a bis(amino-
pyridinato) complex for neodymium, despite the relatively
small difference in the structural size when compared with
Conclusions
Deprotonated 1 is an excellent ligand for the stabilization 1. This study underlines the importance of fine-tuning, even
of mono(aminopyridinato) complexes of di- and trivalent surely in the “nano range”.
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Di- and Trivalent Lanthanide Complexes Stabilized by Aminopyridinato Ligands
FULL PAPER
of the title complex were afforded (0.06 g, 42%). C68H104N5NdSi2
(1192): calcd. C 68.52, H 8.79, N 5.88; found C 68.85, H 7.98, N
6.31. Highly resolved NMR spectroscopic data could not be ob-
tained.
Experimental Section
General Procedures: All reactions and manipulations with air-sensi-
tive compounds were performed under dry argon, using standard
Schlenk and drybox techniques. Solvents were distilled from so-
dium benzophenone ketyl. Deuterated solvents were obtained from
Cambridge Isotope Laboratories and were degassed, dried (CaH2)
and distilled prior to use. NMR spectra were obtained using either
a Bruker ARX 250, Bruker DRX 500, Varian Unity Inova 400 or
300 spectrometer. Chemical shifts are reported in ppm relative to
the deuterated solvent. Elemental analyses were carried out with
an Elementar Vario EL III. 1, 2, 3, and 4[5] as well as [LnI2(THF)3]
(Ln = Yb, Sm)[18] were synthesized following literature procedures.
Other starting materials were purchased from commercial suppli-
ers. X-ray crystal structure analyses were performed with a
[Yb(Ap*)I(THF)2]2 (8): [YbI2(THF)3] (0.70 g, 1.09 mmol),
3
(0.54 g, 1.09 mmol) and THF (40 cm3) were added to a flask, and
the mixture was stirred for 15 h. The solvent was removed under
vacuum and a mixture of toluene (20 cm3)/hexane (10 cm3) was
added. The red suspension was filtered and upon standing at –
20 °C for 48 h, dark red crystals (suitable for X-ray analysis) of
the title complex formed (0.80 g, 82%). C80H118I2N4O4Yb2 (1798):
1
calcd. C 53.39, H 6.61, N, 3.11; found C 52.85, H 6.38, N 2.96. H
3
NMR (400 MHz, C7D8, 298 K): δ = 1.22 (d, J = 7.0 Hz, 12 H,
H28,29,32,33), 1.27 (d, 3J = 7.0 Hz, 6 H, H24,25,26,27), 1.34 (d, 3J = 7.0
Hz, 6 H, H30,31), 1.35 (br, 8 H, β-CH2, THF), 1.48 (d, 3J = 7.0 Hz,
STOE-IPDS
I or II equipped with an Oxford Cryostream
3
3
6 H, H24,25,26,27), 2.78 (sept, J = 7.0 Hz, 1 H, H15), 3.28 (sept, J
low-temperature unit. Structure solution and refinement was ac-
complished using SIR97,[19] SHELXL97,[20] and WinGX.[21]
CCDC-251807 (for 5), -251808 (for 6), -251809 (for 7), -251810 (for
8), and CCDC-251811 (for 9) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
= 7.0 Hz, 2 H, H13,14), 3.41 (br, 8 H, α-CH2, THF), 3.85 (sept, J
3
= 7.0 Hz, 2 H, H22,23), 5.65 (d, J = 8.4 Hz, 1 H, H3), 5.85 (d, J
3
3
= 6.8 Hz, 1 H, H5), 6.76 (dd, J = 8.4 Hz, J = 6.8 Hz, 1 H, H4),
3
3
3
3
7.04 (s, 2 H, H9,11), 7.11 (vt, J = 8.0 Hz, 1 H, H19), 7.23 (d, J =
8.0 Hz, 2 H, H18,20) ppm. 13C NMR (100.5 MHz, C7D8, 298 K): δ
= 25.3 (s, C30,31), 25.7 (s, C24,25,26,27), 26.3 (s, β-CH2, THF), 26.5
(s, C28,29,32,33), 26.6 (s, C24,25,26,27), 26.7 (s, C28,29,32,33), 28.9 (s,
C22,23), 31.3 (s, C13,14), 35.7 (s, C15), 70.1 (s, α-CH2, THF), 108.5
(s, C3), 109.0 (s, C5), 121.7 (s, C9,11), 123.5 (s, C19), 124.7 (s, C18,20),
138.3 (s, C4), 139.3 (s, C7), 144.8 (s, C17,21), 147.9 (s, C10), 149.26
(s, C8,12), 149.32 (s, C16), 156.9 (s, C6), 171.0 (s, C2) ppm.
Preparation of the Lanthanide Complexes
[Sm(Ap*)I(THF)2]2 (9): THF (40 cm3) was added to the solids
[SmI2(THF)3] (0.62 g, 1.00 mmol) and 3 (0.99 g, 1.00 mmol) and
the mixture was stirred for 15 h. The solvent was removed in vacuo
and hexane (10 cm3) was added. The dark blue suspension was fil-
tered and on standing at –20 °C for 72 h small dark blue crystals
(suitable for X-ray analysis) of the title complex formed (0.23 g,
26%). C80H118I2N4O4Sm2 (1754): calcd. C 54.77, H 6.78, N 3.19;
found C 53.72, H 6.67, N 3.30. Highly resolved NMR spectro-
scopic data could not be obtained.
Polymerization of Ethylene: The complex (Ϸ 20 mg) was dissolved
in 15 cm3 of toluene and treated with MAO solution (30% in tolu-
ene; aluminium to catalyst ratio = 250:1). The catalyst mixture was
transferred to a larger flask and n-pentane (250 cm3) was added. A
BÜCHI laboratory autoclave (1 L) was charged with the catalyst
solution and an ethylene overpressure of 10 bar was applied at
60 °C for 30 minutes. The reaction was stopped by relieving the
pressure in the reactor. The polymers were washed with hydrochlo-
ric acid and acetone and then air-dried.
[Nd(Ap*)Cl2(THF)2]2 (5): [NdCl3] (0.38 g, 1.50 mmol), 3 (0.75 g,
1.50 mmol) and THF (40 cm3) were added to a flask, and the mix-
ture was stirred for 15 h. The solvent was removed under vacuum
and hexane was added (30 cm3). The light blue reaction mixture
was filtered and on standing at room temperature for 2 h pale blue
crystals of the title complex formed (0.80 g, 48%).
C80H118Cl4N4Nd2O4 (1630): calcd. C 58.94, H 7.30, N 3.44; found
C 58.95, H 7.14, N 3.05. Highly resolved NMR spectroscopic data
could not be obtained. (2:1 Ligand/Nd reaction resulted in the for-
mation of 5.)
Acknowledgments
[Nd(ApЈ)2Cl(THF)] (6): [NdCl3] (0.34 g, 0.93 mmol), 4 (0.74 g,
1.87 mmol) and THF (40 cm3) were added to a flask, and the mix-
ture was stirred for 24 h. The solvent was removed under vacuum
and hexane was added (30 cm3). The light blue reaction mixture
was filtered and the filtrate allowed to stand at room temperature
for 2 h whereupon small green-blue crystals of the title complex
formed (0.37 g, 64%). C54H66ClN4NdO (967): calcd. C 67.08, H
6.88, N 5.79; found C 66.85 H 7.17, N 5.61. Highly resolved NMR
spectroscopic data could not be obtained.
We thank Wolfgang Milius for his support in the X-ray lab and
Christine Denner for her help during the polymerization studies.
Financial support from the Alexander von Humboldt Stiftung (N.
M. S.), the Deutsche Forschungsgemeinschaft (Schwerpunktpro-
gramm 1166 “Lanthanoidspezifische Funktionalitäten in Molekül
und Material”) and the Fonds der Chemischen Industrie is grate-
fully acknowledged.
[Nd(ApЈ)2{N(SiMe3)2}]•(hexane) (7): Hexane (30 cm3) was added to
6 (0.11 g, 0.11 mmol) and [K{N(SiMe3)2}] (0.02 g, 0.11 mmol) and
the mixture was stirred for 15 h. The reaction mixture was filtered
and the filtrate concentrated to ca. 15 cm3. The reaction mixture
was cooled to –20 °C and on standing for 12 h pale blue crystals
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[2] M. F. Lappert, P. P. Power, A. R. Sanger, R. C. Srivastava, Me-
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Received: October 01, 2004
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Eur. J. Inorg. Chem. 2005, 1319–1324