Synthesis and reactivity of cationic lanthanide metallocene complexes. Hexabromocarborane and tetraphenylborate as counter ions

Article abstract of DOI:10.1039/a804311f

Treatment of unsolvated Cp″₂Ln(II) [Cp″ = 1,3-(Me₃Si)₂C₅H₃] with 1 equivalent of Ag(1)Y, or reaction of [Cp″₂LnI]₂ with 2 molar equivalents of Ag(CB₁₁Br₆H₆) in pure toluene at room temperature gave Lewis base-free cationic lanthanide metallocene complexes [Cp″₂Ln]Y (Y = BPh₄^-, Ln = Sm 1, Yb 2; Y = CB₁₁Br₆H₆^-, Ln = Sm 3, Er 4) in good yield. They slowly undergo decomposition reaction at room temperature. The reactivity of these Lewis base-free cationic complexes is highly dependent upon the coordinating nature of the counter ions. Complexes 3 and 4 are much more reactive than 1 and 2. Recrystallization of 1 and 2 from 1,2-dimethoxyethane (DME) and THF yielded [Cp″₂Sm(DME)][BPh₄] 5 and [Cp″₂Yb(THF)₂][BPh₄] 6, respectively. However, recrystallization of 3 and 4 from THF resulted in the ring-opening polymerization of THF. The THF coordinated complexes [Cp″₂Ln(THF)₂][CB₁₁Br₆H ₆] (Ln = Sm 7, Er 8) were isolated via recrystallization of 3 and 4 from toluene containing a small amount of THF. The Lewis base-free cation Cp″₂Er⁺ can abstract one bromine atom from the counter ion CB₁₁Br₆H₆^- or one chlorine atom from CH₂Cl₂ to form [Cp″₂ErBr]₂ or [Cp″₂ErCl]₂, respectively. Unfortunately, these cations do not exhibit reactivity towards 1-hexene at room temperature. Molecular structures of 5, 7, 8 and [Cp″₂ErBr]₂ have been confirmed by single-crystal X-ray analyses.

Full text of DOI:10.1039/a804311f

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Synthesis and reactivity of cationic lanthanide metallocene
complexes. Hexabromocarborane and tetraphenylborate as counter
ions
Zuowei Xie,* Zhixian Liu, Zhong-Yuan Zhou and Thomas C. W. Mak
Department of Chemistry, The Chinese University of Hong Kong, Shatin NT, Hong Kong, China.
E-mail: zxie@cuhk.edu.hk
Received 8th June 1998, Accepted 3rd August 1998
Treatment of unsolvated CpЉ2Ln() [CpЉ = 1,3-(Me3Si)2C5H3] with 1 equivalent of Ag()Y, or reaction of [CpЉ2LnI]2
with 2 molar equivalents of Ag(CB11Br6H6) in pure toluene at room temperature gave “Lewis base-free” cationic
lanthanide metallocene complexes [CpЉ2Ln]Y (Y = BPh4Ϫ, Ln = Sm 1, Yb 2; Y = CB11Br6H6Ϫ, Ln = Sm 3, Er 4) in
good yield. They slowly undergo decomposition reaction at room temperature. The reactivity of these “Lewis
base-free” cationic complexes is highly dependent upon the coordinating nature of the counter ions. Complexes
3 and 4 are much more reactive than 1 and 2. Recrystallization of 1 and 2 from 1,2-dimethoxyethane (DME)
and THF yielded [CpЉ2Sm(DME)][BPh4] 5 and [CpЉ2Yb(THF)2][BPh4] 6, respectively. However, recrystallization
of 3 and 4 from THF resulted in the ring-opening polymerization of THF. The THF coordinated complexes
[CpЉ2Ln(THF)2][CB11Br6H6] (Ln = Sm 7, Er 8) were isolated via recrystallization of 3 and 4 from toluene containing
a small amount of THF. The “Lewis base-free” cation “CpЉ2Erϩ” can abstract one bromine atom from the counter
ion CB11Br6H6Ϫ or one chlorine atom from CH2Cl2 to form [CpЉ2ErBr]2 or [CpЉ2ErCl]2, respectively. Unfortunately,
these cations do not exhibit reactivity towards 1-hexene at room temperature. Molecular structures of 5, 7, 8 and
[CpЉ2ErBr]2 have been confirmed by single-crystal X-ray analyses.
Introduction
Results and discussion
Synthesis
Cationic Group 4 metallocene complexes have been the subject
of intensive research activity over the past decade because of
their extraordinary characteristics as olefin polymerization
catalysts.1 These studies have helped chemists to better
understand the fundamental aspects of olefin oligomerization
and polymerization reactions. In contrast to this Group 4
system, cationic lanthanide metallocene chemistry is much less
developed.2 Only a few reports on this type of complex have
appeared in the literature.3–9 All of the known cationic lanthan-
ide metallocene complexes are those in which a lanthanide
metal is strongly bound to the Lewis bases (donor solvents),
[Cp2LnL2][X] [L = OC4H8, SC4H8, N2H4, DME; Ln = La,4 Ce,5
Treatment of unsolvated CpЉ2Ln() [CpЉ = 1,3-(SiMe3)2C5H3]
with 1 equivalent of AgY in toluene at room temperature and
removal of the Ag precipitate gave a complex which has been
formulated as [CpЉ2Ln]Y on the basis of elemental analyses
and chemical analyses [eqn. (1), Y = BPh4Ϫ, Ln = Sm 1, Yb 2;
CpЉ2Ln ϩ AgY toluene [CpЉ2Ln]Y ϩ Ag
(1)
Y = CB11Br6H6Ϫ, Ln = Sm 3]. Complex [CpЉ2Yb][CB11Br6H6]
was not isolated in the pure form because of its decomposition
at room temperature. For those metals, for which a divalent
precursor is not available, an unsolvated trivalent complex
[CpЉ2LnI]2 can be used instead. Reaction of [CpЉ2LnI]2 with two
molar equivalents of Ag(CB11Br6H6) in toluene at room tem-
perature, and removal of the AgI precipitate yielded a complex
[CpЉ2Ln][CB11Br6H6] as shown in eqn. (2) (Ln = Sm 3, Er 4).
9
Sm,3,6 Yb;7–9 X = BPh4,3–8 Co(CO)4 ]. The coordinated Lewis
bases cannot be removed from the metal centre under very
high vacuum on heating,3 which results in very unreactive
cationic species. In fact, [Cp*2Sm(THF)2]ϩ (Cp* = C5Me5) has
shown no reactivity towards CO, azobenzene, ethylene, phenyl-
acetylene, epoxybutane or pyridine.3 In view of recent develop-
ments in cationic Group 4 metallocene chemistry,10 the syn-
thesis, structure and reactivity studies of “base-free” cationic
lanthanide metallocene compounds becomes a very interesting
subject. The first example of such a “base-free” cationic Group
3 metallocene compound, CpЈ2YMeؒB(C6F5)3 (CpЈ = C5H5,
C5H4SiMe3), has been reported very recently.11 It is much more
reactive than the Lewis base coordinated cationic Group 3
species, [Cp2LnL2][X].3–9 We are interested in the effect of
counter ions on the stability and reactivity of cationic lanthan-
ide metallocene compounds. We report here the synthesis
and reactivity of several new cationic lanthanide metallocene
compounds in which the counter ions are the hexabromo-
carborane anion [7,8,9,10,11,12-Br6-1-closo-CB11H6]Ϫ and tetra-
phenylborate BPh4Ϫ, respectively.
¹[CpЉ2LnI]2 ϩ Ag(CB11Br6H6) toluene
¯
²
[CpЉ2Ln][CB11Br6H6] ϩ AgI (2)
These new complexes (1–4) are extremely air and moisture
sensitive, and relatively thermally unstable. They do not re-
dissolve in arene solvents once isolated, so that recrystallization
from toluene, benzene or fluorobenzene is extremely difficult.
Numerous attempts were made during the course of this study
to grow single crystals of complexes 1–4 from their mother-
liquor suitable for X-ray analysis. However, all efforts were
hampered by the slow decomposition of these complexes at
room temperature, resulting in difficulty in the characterization
J. Chem. Soc., Dalton Trans., 1998, 3367–3372
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of these complexes. The reaction of [CpЉ2SmI]2 with AgSbF6
gave the fluoride abstraction product [CpЉ2SmF]2.12a The
reaction of [CpЉ2SmCl]2 with Ag(CB11Br6H6) was slow and
did not proceed to completion.
Reactivity
Complexes 1–4 are not thermally stable, and 3 and 4 are even
less stable than 1 and 2. They slowly undergo decomposition at
room temperature. Not surprisingly, heat can dramatically
increase the thermolysis rate. Thus complex 1 decomposed
into the more stable CpЉ3Sm in 50% isolated yield at 80 ЊC.
The decomposition of complex 2 may be complicated. Unlike
complex 1, no CpЉ3Yb was isolated presumably due to the
smaller size of the ytterbium ion which makes the formation of
CpЉ3Yb extremely difficult.13 On the other hand, a small
amount of benzene was detected by GC/MS from its hydrolysis
Fig. 1 Perspective ORTEP16 drawing of the molecular structure of
[CpЉ2Sm(DME)]ϩ in 5ؒ0.25C7H8. All hydrogen atoms are omitted for
products, suggesting that CpЉ2Ybϩ may abstract one phenyl
clarity (thermal ellipsoids drawn at the 35% probability).
Ϫ 14
group from the counter ion BPh4
.
Thermal decomposition
of 3 in toluene or fluorobenzene produced CpЉ3Sm, and
12
some unidentified species. No [CpЉ2SmF]2 was detected by
MS spectroscopy. Complex 4 in toluene or fluorobenzene
decomposed to generate [CpЉ2ErBr]2, and some unidentified
species at room temperature. No fluoride abstraction product
was observed either. Reaction of CpЉ2Yb with 1 equivalent of
Ag(CB11Br6H6) in toluene at room temperature resulted in the
isolation of [CpЉ2YbBr]2 in 11% yield which could be increased
to 41% at 40 ЊC. It is rational to propose that compounds
[CpЉ2LnBr]2 resulted from the bromide abstract reaction
between “CpЉ2Lnϩ” and the counter ion CB11Br6H6Ϫ. The
above results indicate that “CpЉ2Lnϩ” is an extremely strong
electrophile and its electrophilicity is even higher than that of
the silylium ion (R3Siϩ) at least with respect to the bromide
abstraction reactions.15 These cationic lanthanide metallocene
species can also abstract the chloride from CH2Cl2. For
example, treatment of 4 with CH2Cl2 at room temperature
afforded [CpЉ2ErCl]2 in 65% yield; reaction of CpЉ2Yb with
Ag(CB11Br6H6) in CH2Cl2 gave [CpЉ2YbCl]2 in 70% yield.
“Base-free” cationic lanthanide metallocene complexes
are strong Lewis acids. Recrystallization of complex 1 from
DME/toluene produced a DME coordinated cationic complex
[CpЉ2Sm(DME)][BPh4] 5. Complex 2 dissolved in THF to yield
a THF coordinated ionic complex [CpЉ2Yb(THF)2][BPh4] 6.
No obvious THF ring-opening polymerization products were
observed. On the other hand, recrystallization of complex 3
or 4 from THF resulted in the formation of a gum identified
as poly(tetrahydrofuran). The THF coordinated complex
[CpЉ2Ln(THF)2][CB11Br6H6] (Ln = Sm 7, Er 8) can be isolated
by recrystallization of the corresponding “Lewis base-free”
complex [CpЉ2Ln][CB11Br6H6] from toluene containing a small
amount of THF. Like other Lewis base coordinated cationic
lanthanide metallocene complexes,3–9 7 and 8 cannot initiate the
ring-opening polymerization of THF. Attempts to prepare
complexes 7 and 8 by the reaction of CpЉ2Ln with Ag(CB11-
Br6H6) in THF, a well-established method for the preparation
of [Cp2Ln(THF)2][BPh4],3–9 failed due to the formation of
poly(tetrahydrofuran). These results imply that [CpЉ2Ln]-
[CB11Br6H6] is much more electrophilic than [CpЉ2Ln][BPh4],
suggesting that the less coordinating carborane anion can
largely enhance the electrophilicity (Lewis acidity) of CpЉ2Lnϩ
cation, which is consistent with cationic Group 4 and silylium
ion chemistry.1,10,15 However, neither 3 nor 4 exhibits any re-
activity towards 1-hexene at room temperature.
Fig. 2 Perspective ORTEP drawing of the molecular structure of
[CpЉ2Sm(THF)2]ϩ in 7ؒOC4H8. All hydrogen atoms are omitted for
clarity (thermal ellipsoids drawn at the 35% probability).
Fig. 3 Perspective ORTEP drawing of the molecular structure of
[CpЉ2Er(THF)2]ϩ in 8ؒ1.25C7H8. All hydrogen atoms are omitted for
clarity (thermal ellipsoids drawn at the 35% probability).
Ϫ
Ϫ
(L2 = DME, 2THF) cations and CB11Br6H6 or BPh4 anions.
The apparent voids in the structures are filled by several dis-
ordered solvent molecules. Complexes 7 and 8 are isomorphous.
In each cation, the lanthanide ion is η5 bound to each of
two cyclopentadienyl rings and two oxygen atoms from
the coordinated THF or DME molecules in a distorted tetra-
hedral geometry (Figs. 1–3), which is similar in structure to
Structure
Crystal structures of cationic lanthanide metallocene com-
plexes 5, 7 and 8. The solid state structures of 5, 7 and 8
as derived from single-crystal X-ray diffraction studies all
consist of well separated, alternating layers of [CpЉ2LnL2]ϩ
the reported lanthanide metallocene cations of the type
ϩ 3–9
Cp2LnL2
.
Selected bond distances and angles for each
3368
J. Chem. Soc., Dalton Trans., 1998, 3367–3372

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complex are summarized in Tables 1–3, respectively. Table 4
lists some structural parameters for lanthanide metallocene
average Sm–C distance of 2.71(2) Å in 7. The average Er–O
distance of 2.336(4) Å is 0.075 Å shorter than that of Sm–O in
7. These differences can be compared to the 0.075 Å difference
between Shannon’s ionic radii17 of eight-coordinate Sm3ϩ
(1.079 Å) and Er3ϩ (1.004 Å). The 131.4(1)Њ Cent–Er–Cent
angle is quite similar to the 130.2(3)Њ in 7 and the 129.4(4)Њ in 5.
Ϫ
Ϫ
cations of the type Cp2LnL2ϩ. Both BPh4 and CB11Br6H6
anions have normal distances and angles.
The two cations, [CpЉ2Sm(DME)]ϩ and [CpЉ2Sm(THF)2]ϩ,
have a very similar geometry in terms of average Sm–C,
Sm–Cent (centroid of the cyclopentadienyl ring), Sm–O
bond distances and Cent–Sm–Cent angles. These structural
parameters can be compared to those found in [(C5Me5)2-
Sm(THF)2]ϩ (Table 4).3 The Er–C distances in [CpЉ2Er-
(THF)2]ϩ range from 2.563(6) to 2.694(7) Å with an average
value of 2.627(6) Å. This measured value is identical to the
2.629(2) Å in [CpЉ2ErBr]2. It is about 0.083 Å shorter than the
Crystal structure of [CpЉ2ErBr]2. [CpЉ2ErBr]2 is a centro-
symmetric bromide-bridging dimer with pseudo-tetrahedral
geometry around each Er atom, typical of the structures
of [CpЉ2LnX]2 dimeric organolanthanide fluoride12 and
chloride18a–c complexes (Fig. 4). Selected bond distances and
angles are listed in Table 5. The average Er–C distance of
2.629(2) Å compared to the 2.640(9) Å in CpЉ2ErI(THF)19
and the 2.59(1) Å in [(C5H5)2ErBr]2.18d The 2.875(1) Å average
Er–Br distance is longer than the value of 2.820(1) Å in
[(C5H5)2ErBr]2 probably due to steric reasons. The 83.2(1)Њ
Br(1)–Er(1)–Br(1A) angle is smaller than the 84.2(1)Њ in
[(C5H5)2ErBr]2.
Table 1 Selected bond distances (Å) and angles (Њ) for compound 5
Sm(1)–C(1)
Sm(1)–C(2)
Sm(1)–C(3)
Sm(1)–C(4)
Sm(1)–C(5)
Sm(1)–C(6)
Sm(1)–Cent(1)
2.732(16) Sm(1)–C(7)
2.720(17) Sm(1)–C(8)
2.680(18) Sm(1)–C(9)
2.719(21) Sm(1)–C(10)
2.753(17) Sm(1)–O(1)
2.695(15) Sm(1)–O(2)
2.710(16)
2.693(17)
2.695(16)
2.739(18)
2.432(17)
2.386(14)
2.427
2.436
Sm(1)–Cent(2)
O(1)–Sm(1)–O(2)
Cent(1)–Sm(1)–Cent(2) 129.4
Cent(1)–Sm(1)–O(1) 106.4
65.1(5)
Cent(1)–Sm(1)–O(2) 115.0
Cent(2)–Sm(1)–O(1) 110.4
Cent(2)–Sm(1)–O(2) 111.5
Table 2 Selected bond distances (Å) and angles (Њ) for compound 7
Sm(1)–C(2)
Sm(1)–C(3)
Sm(1)–C(4)
Sm(1)–C(5)
Sm(1)–C(6)
Sm(1)–C(7)
Sm(1)–Cent(1)
2.70(2)
2.70(2)
2.77(2)
2.68(2)
2.67(2)
2.70(2)
2.420
Sm(1)–C(8)
Sm(1)–C(9)
Sm(1)–C(10)
Sm(1)–C(11)
Sm(1)–O(1)
Sm(1)–O(2)
Sm(1)–Cent(2)
2.74(2)
2.74(2)
2.69(2)
2.69(2)
2.424(12)
2.401(11)
2.432
Fig. 4 Perspective ORTEP drawing of the molecular structure of
[CpЉ2ErBr]2. All hydrogen atoms are omitted for clarity (thermal
ellipsoids drawn at the 35% probability).
O(1)–Sm(1)–O(2)
Cent(1)–Sm(1)–Cent(2) 130.2
Cent(1)–Sm(1)–O(1) 104.1
94.1(4)
Cent(1)–Sm(1)–O(2) 108.2
Cent(2)–Sm(1)–O(1) 109.0
Cent(2)–Sm(1)–O(2) 105.4
Table 5 Selected bond distances (Å) and angles (Њ) for compound
[CpЉ2ErBr]2
Table 3 Selected bond distances (Å) and angles (Њ) for compound 8
Er(1)–C(1)
Er(1)–C(2)
Er(1)–C(3)
Er(1)–C(4)
Er(1)–C(5)
Er(1)–C(6)
Er(1)–C(7)
Er(1)–C(8)
2.631(2)
2.644(2)
2.617(2)
2.616(2)
2.627(2)
2.659(2)
2.655(2)
2.600(2)
Er(1)–C(9)
2.586(2)
2.659(2)
2.878(1)
2.872(1)
2.872(1)
2.334
Er(1)–C(2)
Er(1)–C(3)
Er(1)–C(4)
Er(1)–C(5)
Er(1)–C(6)
Er(1)–C(7)
Er(1)–Cent(1)
2.590(8)
2.666(8)
2.641(7)
2.608(6)
2.608(7)
2.630(8)
2.324
Er(1)–C(8)
Er(1)–C(9)
Er(1)–C(10)
Er(1)–C(11)
Er(1)–O(1)
Er(1)–O(2)
Er(1)–Cent(2)
2.655(8)
2.694(7)
2.613(6)
2.563(6)
2.335(4)
2.336(4)
2.342
Er(1)–C(10)
Er(1)–Br(1)
Er(1)–Br(1A)
Br(1)–Er(1A)
Er(1)–Cent(1)
Er(1)–Cent(2)
2.338
O(1)–Er(1)–O(2)
Cent(1)–Er(1)–Cent(2) 131.4
Cent(1)–Er(1)–O(1) 106.4
91.2(2)
Cent(1)–Er(1)–O(2) 107.7
Cent(2)–Er(1)–O(1) 108.2
Cent(2)–Er(1)–O(2) 104.5
Br(1)–Er(1)–Br(1A)
Cent(1)–Er(1)–Cent(2) 130.3
Cent(1)–Er(1)–Br(1)
83.2(1)
Cent(1)–Er(1)–Br(1A) 107.0
Cent(2)–Er(1)–Br(1) 109.2
Cent(2)–Er(1)–Br(1A) 109.7
107.2
Table 4 Selected structural parameters for some lanthanide metallocene cations
ave. Ln–C/Å
ave. Ln–O/Å
Cent(1)–Ln–Cent(2)/Њ
O(1)–Ln–O(2)/Њ
Ref.
[CpЉ2Sm(DME)]ϩ
2.714(14)
2.71(2)
2.627(7)
2.69(2)
2.73(2)
2.83(1)
2.74(3)
2.57(2)
2.619(4)
2.586(1)
2.409(17)
2.413(12)
2.335(4)
2.46(1)
2.470(2)
2.627(8)
129.4
130.2
131.4
134.2
138.9
65.1(5)
94.1(4)
91.2(2)
92.9(4)
This work
This work
This work
3
6
4
5
9
8
7
[CpЉ2Sm(THF)2]ϩ
[CpЉ2Er(THF)2]ϩ
[Cp*2Sm(THF)2]ϩ
[Cp*2Sm(N2H4)(THF)]ϩ
[CpЉ2La(DME)(MeCN)]ϩ
[Cp*2Ce(SC4H8)2]ϩ
61.5(3)
134.6(1)
126.0
137.2
[(MeOCH2CH2C5H4)2Yb(THF)]ϩ
[Cp*2Yb(THF)2]ϩ
2.32(1)
2.341(3)
2.290(5)
92.2(1)
86.0(3)
[(ButC5H4)2Yb(THF)2]ϩ
126.4
J. Chem. Soc., Dalton Trans., 1998, 3367–3372
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[CpЉ2Yb][BPh4] 2. To a mixture of CpЉ2Yb (0.157 g, 0.26
mmol) and Ag(BPh4) (0.131 g, 0.30 mmol) was added toluene
(30 cm3) at 0 ЊC under stirring. The reaction mixture was
allowed to warm to room temperature and stirred for 24 h.
A black precipitate formed during this period, and then was
filtered off. Removal of most of the solvent under vacuum
gave a red solid which was washed with toluene and then
hexane to afford 2 as a red solid (0.18 g, 74%) (Found: C, 60.12;
H, 6.75; Yb, 19.25. C46H62BSi4Yb requires C, 60.60; H, 6.86;
Yb, 18.99%); IR (KBr, ν/cmϪ1): 3089w, 2954s, 2899m, 1579m,
1479m, 1251s, 912s, 831vs.
Conclusions
The preparation and reactivity of “Lewis base-free” cationic
lanthanide metallocene complexes of the type [CpЉ2Ln][CB11-
Br6H6] and [CpЉ2Ln][BPh4] have been described for the first
time. They can be synthesized by the reaction of unsolvated
CpЉ2Ln() or [CpЉ2LnI]2 with silver() salts of the weakly
coordinating anions in pure toluene. Their chemical reactivities
are highly dependent upon the coordinating nature of the
counter ions. The more weakly coordinating carborane anion
CB11Br6H6Ϫ can greatly enhance the reactivity (electrophilicity)
of the cation CpЉ2Lnϩ. For example, [CpЉ2Ln][CB11Br6H6] can
initiate the ring-opening polymerization of THF, abstract one
bromine atom from the counter ion CB11Br6H6Ϫ or one chlorine
atom from the solvent CH2Cl2.
[CpЉ2Yb(THF)2][BPh4]ؒ2THF 6ؒ2THF. Recrystallization of
2 (0.15 g, 0.16 mmol) from THF/toluene (10:1, 20 cm3) at room
temperature gave complex 6ؒ2THF (0.16 g, 83%) as red crystals
over a period of 2 d (Found: C, 62.33; H, 7.76. C62H94BO4Si4Yb
requires C, 62.08; H, 7.90%); δH (C5D5N): 0.45 (s, Me3Si), 1.27
(m, THF), 3.34 (m, THF), 6.96 (m, C6H5), 7.23 (m, C6H5), 8.44
(br, C5H3), 8.64 (br, C5H3); δC (C5D5N): 2.49 (Me3Si), 27.25,
69.30 (THF); 124.6, 128.4, 139.5 (C5H3), 165.5, 165.0, 164.2,
163.9 (BPh4Ϫ); δB (C5D5N): Ϫ6.90; IR (KBr, ν/cmϪ1): 3050m,
3032m, 2955s, 2898m, 1578m, 1478m, 1448m, 1250s, 1080s,
921s, 831vs, 731s.
Experimental
General procedures
All experiments were performed under an atmosphere of dry
dinitrogen with the rigid exclusion of air and moisture using
standard Schlenk or cannula techniques, or in a glovebox.
All organic solvents were freshly distilled from sodium
benzophenone or CaH2 immediately prior to use. CpЉ2Sm,20
CpЉ2Yb,21 Ag(BPh4),22 and Ag(CB11Br6H6)23 were prepared
according to the literature methods. [CpЉ2LnI]2 (Ln = Sm, Er)
can be conveniently prepared from CpЉ2LnI(THF)19 by sub-
limation at 200–230 ЊC at 10Ϫ2 Torr. All other chemicals were
purchased from Aldrich Chemical Company and used as
received unless otherwise noted. Infrared spectra were obtained
from a KBr pellet, prepared in the glovebox, on a Nicolet
Magna 550 Fourier-transform spectrometer. MS spectra were
[CpЉ2Sm][CB Br H ] 3. To a suspension of Ag(CB Br H )
(0.193 g, 0.27 mmol) in 15 cm3
solution (15 cm
3) of CpЉ Sm (0.146 g, 0.26 mmol) with stirring
11
6
6
11
6
6
of toluene was added a toluene
2
at 0 ЊC. The reaction mixture was then allowed to warm to
room temperature and stirred for 2 d, followed by the procedure
similar to that used in the synthesis of 1, yielding 3 as a yellow
solid (0.155 g, 51%) (Found: C, 22.87; H, 3.95; Sm, 12.55.
C23H48B11Br6Si4Sm requires C, 23.30; H, 4.08; Sm, 12.68%);
IR (KBr, ν/cmϪ1): 3057w, 2957m, 2603s (br), 1251m, 835s.
Compound 3 can also be prepared by the reaction of
[CpЉ2SmI]2 with 2 equivalents of Ag(CB11Br6H6) in toluene
in 40% yield.
Compound 3 does not redissolve in pure toluene or fluoro-
benzene once isolated, so that NMR data are not available.
If this suspension is heated for 2 h at 45 ЊC, a small amount
of orange crystals can be isolated and identified as CpЉ3Sm by
MS and 1H NMR spectroscopy.12,20
recorded on a Bruker APEX FTMS spectrometer. H and 13C
1
NMR spectra were recorded on a Bruker 300 MHz DPX
spectrometer at 300.13 and 75.47 MHz, respectively. 11B NMR
spectra were recorded on a Bruker ARX-500 spectrometer at
160.46 MHz. All chemical shifts are reported in δ units with
reference to the residual protons of deuteriated solvent or
external SiMe4 (0.00 ppm) for proton and carbon chemical
shifts, to external BF3ؒOEt2 (0.00 ppm) for boron chemical
shifts. Complexometric metal analyses were conducted by titra-
tion with EDTA.
Complex 3 (23 mg) was dissolved in 5 cm3 of THF with
stirring at room temperature. The clear yellow solution slowly
became sticky and finally became a gum after 12 h. An
additional 5 cm3 of THF was added to the gum giving a very
viscous solution which became a gum again after 10 h. This
gum was identified as poly(tetrahydrofuran) by 1H and 13C
NMR spectroscopy.24
Preparations
[CpЉ2Sm][BPh4] 1. To a mixture of CpЉ2Sm (0.207 g, 0.36
mmol) and Ag(BPh4) (0.202 g, 0.47 mmol) was added toluene
(30 cm3) with stirring at 0 ЊC. The reaction mixture was allowed
to warm to room temperature and stirred for 24 h. A black
precipitate formed during this period, and then was filtered off.
Removal of most of the solvent under vacuum gave a yellow
solid which was washed with toluene and then hexane to afford
1 as a yellow powder (0.207 g, 64%) (Found: C, 61.81; H, 7.18;
Sm, 16.86. C46H62BSi4Sm requires C, 62.18; H, 7.03; Sm,
16.92%); IR (KBr, ν/cmϪ1): 3086w, 3052w, 2954s, 1252s, 833vs.
Complex 1 does not redissolve in toluene once isolated,
so the NMR data are not available. Recrystallization of 1 from
hot toluene (80 ЊC) afforded orange crystals identified as
CpЉ3Sm (50% based on 1) by MS and 1H NMR spectroscopy as
well as the unit cell measurements.12,20
[CpЉ2Sm(THF)2][CB11Br6H6] 7. Recrystallization of 3 (0.15 g)
from toluene containing 5% THF (35 cm3) at room temperature
gave complex 7 as yellow crystals (0.10 g, 60%) (Found: C,
28.61; H, 4.67. C31H64B11Br6O2Si4Sm requires C, 28.00; H,
4.85%); δH (C5D5N): Ϫ0.08 (s, Me3Si), 1.52 (m, THF), 3.56
(m, THF), 3.40 (s, CH of carborane), 8.20 (br, C5H3), 10.12
(br, C5H3); δC (C5D5N): Ϫ1.24 (Me3Si), 25.29, 67.31 (THF),
118.6, 128.1, 135.9 (C5H3); δB (C5D5N): 4.8 (s, 1 B), Ϫ3.6 (s,
5 B), Ϫ15.2 (d, 5 B); IR (KBr, ν/cmϪ1): 3057w, 2958m, 2896m,
2603s (br), 1450m, 1385vs, 1250m, 1077s, 953m, 834s.
[CpЉ2Sm(DME)][BPh4] 5. Recrystallization of 1 (0.20 g, 0.22
mmol) from DME/toluene (10:1, 20 cm3) at room temperature
gave complex 5 (0.18 g, 84%) as yellow crystals over a period of
2 d (Found: C, 61.12; H, 7.35. C50H72BO2Si4Sm requires C,
61.36; H, 7.42%); δH (C5D5N): Ϫ0.42 (s, Me3Si), 2.84 (br,
DME), 3.06 (br, DME), 6.72 (m, C6H5), 6.90 (m, C6H5), 7.70
(br, C5H3), 9.61 (br, C5H3); δC (C5D5N): Ϫ0.87 (Me3Si), 58.14,
71.58 (DME), 121.9, 125.8, 136.8 (C5H3), 164.9, 164.2, 163.6,
162.9 (BPh4Ϫ); δB (C5D5N): Ϫ14.6; IR (KBr, ν/cmϪ1): 3088w,
2965s, 1437m, 1255s, 1079s, 922m, 833vs.
Reaction of CpЉ2Yb with Ag(CB11Br6H6). A suspension of
CpЉ2Yb (0.320 g, 0.54 mmol) and Ag(CB11Br6H6) (0.392 g, 0.54
mmol) was mixed in toluene (40 cm3) under stirring at 0 ЊC.
The reaction mixture was then allowed to warm to room tem-
perature and stirred for 2 d. The black precipitate was filtered
off. Slow evaporation of the solvent gave red crystals (0.04 g,
11% based on CpЉ2Yb) identified as [CpЉ2YbBr]2. No pure
[CpЉ2Yb][CB11Br6H6] was isolated. Repeating the above experi-
ment at 40 ЊC resulted in the isolation of red crystals identified
as [CpЉ2YbBr]2 (0.15 g, 41% based on CpЉ2Yb) (Found: C,
3370
J. Chem. Soc., Dalton Trans., 1998, 3367–3372

View Article Online
39.33; H, 6.76. C44H84Br2Si8Yb2 requires C, 39.33; H, 6.30%);
IR (KBr, ν/cmϪ1): 3067w, 2954s, 2898m, 1438w, 1249s, 1085s,
835vs, 753s; MS (EI, m/z): 672 (¹Mϩ, 4%), 592 ([CpЉ2Yb]ϩ,
loss of the solvent molecules in the crystal lattices of com-
pounds 5ؒ0.25C7H8, 7ؒOC4H8 and 8ؒ1.25C7H8, these crystals
were sealed with a drop of mother-liquor under N2 in a thin-
walled glass capillary. Data were collected at 294 K on a MSC/
Rigaku RAXIS-IIC imaging plate using Mo-Kα radiation
(0.71073 Å) from a Rigaku rotating-anode X-ray generator
operating at 50 kV and 90 mA. An absorption correction was
applied by correlation of symmetry-equivalent reflections using
the ABSCOR program.25 All structures were solved by direct
methods and subsequent Fourier-difference techniques, and
refined anisotropically for all non-hydrogen atoms by full-
matrix least squares, on F2 for 7ؒOC4H8 and 8ؒ1.25C7H8 using
the Siemens SHELXTL V 5.03 program package (PC ver-
sion),26a and on F for 5ؒ0.25C7H8 and [CpЉ2ErBr]2 using the
Siemens SHELXTL V 4.1 program package (PC version).26b
The hydrogen atoms were geometrically fixed using the riding
model. One of the Me3Si groups (Si1) in 5ؒ0.25C7H8 is dis-
ordered over two sets of positions with 0.60:0.40 occupancies.
The toluene molecule in the lattice of 5ؒ0.25C7H8 is also dis-
ordered over two sets of positions with 0.50:0.50 occupancies.
One toluene molecule in the lattice of 8ؒ1.25C7H8 is disordered
over two sets of positions with 0.50:0.50 occupancies. The
other toluene molecule in the lattice of 8ؒ1.25C7H8 is highly
disordered, so that only the hexagonal ring could be found.
CCDC reference number 186/1116.
¯
²
30%), 383 ([CpЉYb]ϩ, 5%).
If the above reaction was conducted in CH2Cl2, [CpЉ2YbCl]2
was isolated as red crystals in 70% yield (Found: C, 41.95; H,
6.65%. Calc. for C44H84Cl2Si8Yb2: C, 42.11; H, 6.75%) which
was also identified by MS.13 If the reaction was carried out in
THF, poly(tetrahydrofuran) was obtained.
[CpЉ2Er][CB11Br6H6] 4. Ag(CB11Br6H6) (0.147 g, 0.20 mmol)
and [CpЉ2ErI]2 (0.148 g, 0.10 mmol) were mixed in toluene
(30 cm3) under stirring at 0 ЊC. The reaction mixture was then
allowed to warm to room temperature and stirred for 2 d, the
yellow precipitate was filtered off. Concentration of the clear
filtrate gave a pink solid which was washed with toluene and
then hexane to yield 4 as a pink solid (0.145 g, 60%) (Found: C,
22.65; H, 4.00; Er, 13.78. C23H48B11Br6ErSi4 requires C, 22.97;
H, 4.02; Er, 13.91%); IR (KBr, ν/cmϪ1): 2955s, 2900m, 2603s
(br), 1251s, 835vs.
Complex 4 does not redissolve in toluene. Recrystallization
of 4 (0.10 g) from hot toluene (50 cm3, 60 ЊC) gave pink crystals
identified as [CpЉ2ErBr]2 (Found: C, 40.01; H, 6.65. C44H84-
Br2Er2Si8 requires C, 39.67; H, 6.36%); IR (KBr, ν/cmϪ1):
3054w, 2955s, 2897m, 1439w, 1249s, 1078s, 834vs, 753s.
Recrystallization of 4 from CH2Cl2 at room temperature
13,18a,b
resulted in the isolation of [CpЉ2ErCl]2
in 65% yield
Acknowledgements
We thank the Hong Kong Research Grants Council (Ear-
marked Grant CUHK 306/96P) for financial support.
(Found: C, 42.08; H, 6.75. Calc. for C44H84Cl2Er2Si8: C, 42.50;
H, 6.82%).
[CpЉ2Er(THF)2][CB11Br6H6] 8. Recrystallization of 4 (0.13 g)
from toluene containing 5% THF (35 cm3) at room tempera-
ture gave compound 8 as pink crystals (0.06 g) (Found: C,
27.35; H, 4.80. C31H64B11Br6ErO2Si4 requires C, 27.65; H,
4.79%); δB (C5D5N): 10.6 (s, 1 B), 2.85 (s, 5 B), Ϫ8.23 (d, 5 B);
IR (KBr, ν/cmϪ1): 3066w, 2955s, 2900m, 2603s (br), 1436m,
1251s, 1078s, 1001s, 835vs, 799s. The 1H and 13C NMR spectra
consisted of many broad, unresolved resonances.
References
1 For recent reviews, see: M. Bochmann, J. Chem. Soc., Dalton
Trans., 1996, 225; W. Kaminsky, Macromol. Chem. Phys., 1996, 197,
3907; H. H. Brintzinger, D. Fisher, R. Mülhaupt, B. Rieger and
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Crystallography
2 For recent reviews, see: H. Schumann, J. A. Meese-Marktscheffel
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A summary of crystal data and details of data collection and
structure refinement for compounds 5ؒ0.25C7H8, 7ؒOC4H8,
8ؒ1.25C7H8 and [CpЉ2ErBr]2 is given in Table 6. Due to the facile
Table 6 Crystal data and summary of data collection and refinement for 5ؒ0.25C7H8, 7ؒOC4H8, 8ؒ1.25C7H8 and [CpЉ2ErBr]2
5ؒ0.25C7H8
7ؒOC4H8
8ؒ1.25C7H8
[CpЉ2ErBr]2
Formula
Crystal size/mm
M
Crystal class
Space group
C51.75H74BO2Si4Sm
0.12 × 0.15 × 0.40
1001.63
Monoclinic
P21/n
C35H72B11Br6O3Si4Sm
0.30 × 0.10 × 0.30
1402.01
Monoclinic
P21/n
C39.5H69.5B11Br6O2Si4Er
0.14 × 0.12 × 0.14
1454.44
Monoclinic
P21/n
C44H84Br2Si8Er2
0.12 × 0.25 × 0.40
1332.20
Triclinic
¯
P1
a/Å
b/Å
c/Å
α/Њ
13.281(1)
22.413(1)
19.449(1)
90.00
95.14(1)
90.00
5766(3)
4
1.154
13.487(3)
33.769(7)
14.365(3)
90.00
99.34(3)
90.00
6456(2)
4
1.443
13.444(3)
33.625(7)
14.327(3)
90.00
99.17(3)
90.00
6394(2)
4
1.511
10.686(2)
11.663(2)
13.233(2)
73.24(2)
83.89(2)
76.62(2)
1534.9(8)
1
β/Њ
γ/Њ
U/Å3
Z
Dc/Mg mϪ3
1.411
Radiation (λ/Å)
Mo-Kα (0.71073)
3.0–55.0
1.134
Mo-Kα (0.71073)
3.0–55.0
4.725
Mo-Kα (0.71073)
3.0–55.0
5.166
Mo-Kα (0.71073)
3.0–55.0
4.198
2θ Range/Њ
µ/mmϪ1
F(000)
T/K
2094
294
2756
294
2864
294
666
294
No. observed reflections [I > Xσ(I)]
No. parameters refined
3540 (X = 3)
537
8494 (X = 2)
573
5665 (X = 2)
564
5509 (X = 3)
256
Goodness of fit
R1
1.53
0.067
0.89
0.061
0.98
0.069
2.65
0.037
wR2
0.190
0.168
0.171
0.152
J. Chem. Soc., Dalton Trans., 1998, 3367–3372
3371

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3372
J. Chem. Soc., Dalton Trans., 1998, 3367–3372