Benzyl complexes of lanthanide(II) and lanthanide(III) metals: Trends and comparisons

Article abstract of DOI:10.1515/znb-2008-0307

A variety of benzyllanthanide complexes have been prepared by the metathesis reaction of benzylpotassium precursors with lanthanide halides. Syntheses and crystal structures for the following complexes are described: [2-Me₂N-α-Me₃Si-benzyl]₂Eu(II) ·(THF)₂ (1-Eu), (2-Me₂N-benzyl)₃Ln(III) (2-Ln with Ln = Nd, Sm, Dy, Ho, Yb), (4-R-C₆H₄CH ₂)₃Ln·(THF)₃ (3-Y: Ln = Y, R = H; 3-La: Ln = La, R = tBu). Complexes of types 1 and 2 are thermally robust on account of a stabilization by a benzylic Me₃Si substituent and/or intramolecular coordination of the Me₂N substituent. Comparison of the crystal structures of these new series of lanthanide complexes shows several similarities and trends. In addition, comparisons with alkali metal and alkaline earth metal benzyl complexes are made.

Full text of DOI:10.1515/znb-2008-0307

Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals:
Trends and Comparisons
Sjoerd Hardera, Christian Ruspica, Nollaig N´ı Bhriainb, Frederic Berkermanna, and
Markus Schu¨rmannc
a Universita¨t Duisburg-Essen, Universita¨tsstraße 5, 45117 Essen, Germany
b Dow Benelux, Terneuzen, Netherlands
c Technische Universita¨t Dortmund, Otto-Hahn-Straße 6, 44221 Dortmund, Germany
Reprint requests to Prof. Dr. S. Harder. E-mail: sjoerd.harder@uni-due.de
Z. Naturforsch. 2008, 63b, 267 – 274; received December 1, 2007
A variety of benzyllanthanide complexes have been prepared by the metathesis reaction of
benzylpotassium precursors with lanthanide halides. Syntheses and crystal structures for the
following complexes are described: [2-Me2N-α-Me3Si-benzyl]2Eu(II)·(THF)2 (1-Eu), (2-Me2N-
benzyl)3Ln(III) (2-Ln with Ln = Nd, Sm, Dy, Ho, Yb), (4-R-C6H4CH2)3Ln·(THF)3 (3-Y: Ln = Y,
R = H; 3-La: Ln = La, R = tBu). Complexes of types 1 and 2 are thermally robust on account of a
stabilization by a benzylic Me3Si substituent and/or intramolecular coordination of the Me2N sub-
stituent. Comparison of the crystal structures of these new series of lanthanide complexes shows
several similarities and trends. In addition, comparisons with alkali metal and alkaline earth metal
benzyl complexes are made.
Key words: Benzyl Complexes, Lanthanide(II) Metal Complexes, Lanthanide(III) Metal
Complexes, Crystal Structures
Introduction
Some years ago, we reported syntheses and struc-
tures of the first homoleptic benzyl complexes of lan-
thanide metals in their less stable 2+ oxidation state
(1-Yb and 1-Sm, Eq. 1, Ln = lanthanide) [1]. The
rather large coordination spheres of the Ln(II) cen-
ters are shielded by intramolecularly chelating Me2N
substituents and the bulky Me3Si substituents in α-
position. As organometallic Ln(II) complexes display
a high degree of ionicity in the Ln–C bond, the silyl
substituent adds significantly to the stability of such
compounds.
(2)
Me2N substituent in ortho-position, could not only be
obtained for the small Y3+ ion (ionic radius, 6-co-
ordinate: 0.900 A [4]) but also for the largest Ln3+ ion
˚
La3+ (1.032 A). As 2-Y and 2-La crystallize isomor-
˚
phously, it was anticipated that the new synthetic route
and crystallization procedure are valid for the whole
lanthanide series [3]. It was also shown that even the
less reactive yttrium complex is a potent deprotonating
reagent and a convenient starting material in lanthanide
chemistry.
(1)
Subsequent work of the Hessen group [5] showed
that simpletris-benzyl lanthanum complexes without
intramolecular chelating amino substituents (3-La in
Eq. 3) are available via the same synthetic route. The
lanthanum complexes crystallize as tris-THF adducts
and display similar octahedral metal coordination geo-
metries as observed for 2-Y and 2-La.
The first homoleptic Sc(III) benzyl complex had
been introduced at an early stage by Manzer et al. [2]
(2-Sc in Eq. 2). We reported a simple procedure
for the syntheses of analogous homoleptic benzyllan-
thanide(III) complexes (Eq. 2) [3]. These complexes,
which are stabilized by an intramolecular chelating
c
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268
S. Harder et al. · Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals
(3)
Here we report new benzyl complexes of types 1 – 3
and discuss trends in their crystal structures and physi-
cal data. In addition, comparisons with alkali metal and
alkaline earth metal benzyl complexes are made.
Results and Discussion
Syntheses and crystal structures
The dibenzyl Eu(II) complex 1-Eu could be ob-
tained in pure crystalline form (93 %) according to
the metathesis route in Eq. 1. 1-Eu represents the
first benzyleuropium(II) complex and complements
the series of other known homoleptic aryl, allyl, and
alkyl-europium(II) compounds: (C6F5)2Eu [6], [2,6-
(Ph)2C6H4]2Eu [7], [1,3-(Me3Si)2-allyl]2Eu [8] and
[(Me3Si)3C]2Eu [9]. On account of the high deproto-
nating power of the benzyl anion it is anticipated that
this complex is a convenient precursor for the synthe-
ses of a large variety of Eu(II) compounds.
Fig. 1. (a) Crystal structure of 1-Eu. Hydrogen atoms are not
shown for clarity except the benzylic hydrogen atoms, which
were located and refined. Geometrical parameters are given
in Table 1. (b) Comparison of the crystal structures of 1-Eu
(thick grey lines) with that of 1-Sm (striped black lines, left)
and that of 1-Sr (striped black lines, right).
sition (ca. 3 % o-Me2N-toluene is observed). Solutions
◦
can also be heated to 75 C with only minor decom-
Complex 1-Eu crystallizes as an asymmetric R/S
diastereomer (Fig. 1). The 2-Me2N-α-Me3Si-benzyl
ligand coordinates to Eu as a bidentate C, N ligand with
position (ca. 5 % o-Me2N-toluene was observed after
heating overnight). The advantageous stability of 2-Ln
complexes is likely due to the intramolecular coordi-
nation of the Me2N substituents.
As expected, all complexes crystallize isomorphous
to 2-Y and 2-La: the crystal structures show the typ-
ical paddle-wheel geometry (Fig. 2) with prismatic
metal coordination. The threefold symmetry is broken
by “up-side down” coordination of one of the biden-
tate benzyl ligands. The Ln–C and Ln–N bond lengths
nicely correlate with the ionic radii for the Ln3+ ions
(vide infra: trends and comparisons).
˚
average C–Eu and N–Eu bond lengths of 2.772(3) A
˚
and 2.779(3) A, respectively. In contrast to the struc-
ture of 1-Yb, the somewhat larger Eu2+ in 1-Eu also
shows short contacts to the aryl ring with Eu–C bond
˚
lengths varying from 2.833(2) to 2.939(3) A. The
crystal structure of 1-Eu is isomorphous to those of
1-Sm [1] and 1-Sr [10]. The remarkably good agree-
ment of the crystal structures (Fig. 1b) is due to very
similar ionic radii for Eu2+ (8-coordinate: 1.17 A),
˚
2+
Sm2+ (1.22 A) and Sr (1.18 A) [4].
˚
˚
In order to prove the generality of our previously
The series of unstabilized tris-benzyllanthanide
reported synthetic route to (2-Me2N-benzyl)3Ln(III) complexes has been extended with the synthesis and
complexes (2-Ln), we prepared the following com- crystal structure of the yttrium(III) complex 3-Y (R =
plexes in crystalline purity: 2-Nd, 2-Sm, 2-Ho, 2-Dy H). In addition, the new lanthanum(III) complex 3-La
and 2-Yb (Eq. 2). All compounds show excellent sol- (R = tBu) has been prepared. The tBu substituents in
ubility in aromatic solvents and are remarkably stable the latter complex were introduced for higher solubility
towards thermal decomposition. Toluene solutions of in apolar solvents. The solubilities in aromatic solvents
these homoleptic compounds can be stored at r. t. for and the thermal stabilities of 3-Y and 3-La are much
more than four months with only negligible decompo- lower than those of the Me2N-stabilized series 2-Ln.
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S. Harder et al. · Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals
269
˚
Table 1. Selected bond lengths (A), angles (deg) and NMR parameters for benzyllanthanide(II) and alkaline earth metal
complexes of type 1-M. A comparison is also made with the structures of the analogous Li and K compounds.
1-M
Ca
Yb
Eu
Sr
Sm
Lia
Kb
Ionic radiusc
Average M–Cα
Average M–N
Average M–O
Average M···Cring
Cα –Ln–N
1.12
1.14
1.25
1.26
1.27
0.92
1.51
2.628(3)
2.600(2)
2.407(2)
3.095(3)
67.1(1)
1.449(3)
113.9(2)
344(1)
116
2.651(3)
2.614(3)
2.454(3)
3.089(3)
67.1(1)
1.443(5)
113.9(3)
346(1)
117
2.772(3)
2.757(2)
2.554(2)
2.902(3)
62.7(1)
1.435(4)
114.3(2)
349(1)
–
2.781(2)
2.771(2)
2.546(2)
2.927(2)
62.6(1)
1.430(3)
114.2(2)
350(1)
120
2.779(3)
2.764(2)
2.564(2)
2.904(2)
62.7(1)
1.434(4)
114.4(3)
349(1)
–
2.219(6)
2.143(7)
–
2.435(6)
82.8(2)
1.426(4)
114.2(3)
358(1)
123
2.966(4)
2.906(3)
2.633(4)
3.163(3)
59.5(1)
1.403(4)
113.4(3)
360(1)
132
d
Average Cα –Cipso
C
ortho–Cα –Cꢀortho
ΣꢁCα
1JC−H (Hz)
δ1Hpara (ppm)
6.33
112.4
6.36
112.4
–
–
6.29
110.8
b
–
–
6.29
107.0
5.78
102.7
13
δ
a
C
(ppm)
para
Data for the Li analog 2-Me2N-α-Me3Si-benzyllithium·(TMEDA) [10];
data for the K analog 2-Me2N-α-Me3Si-benzyl-
potassium·(THF) [10]; c ionic radii for 8-coordinate metal ions (A) [4]; average contacts to the two ring atoms: Cipso and Cortho
.
d
˚
Fig. 2. General structural motif for the series 2-Ln (shown
here for 2-Nd). Hydrogen atoms are not shown for clarity.
Geometrical parameters are given in Table 2.
THF solutions gradually darken within hours already at
r. t. After standing overnight, considerable quantities of
toluene (or 4-tBu-toluene) can be detected. Although
the exact nature of the decomposition reaction could
not be established, it has been proposed that carbene
type intermediates like PhCH2Ln=CHPh are formed
by α-elimination [11].
Fig. 3. Crystal structures of 3-Y (R = H) and 3-La (R = tBu).
Hydrogen atoms are not shown for clarity except the benzylic
hydrogen atoms, which were located and refined. Geometri-
cal parameters are given in Table 3.
The crystal structures of 3-Y (R = H) and 3-La (R =
tBu) could be determined (Fig. 3). Both, the Y and the
La complex, crystallize similar to the earlier reported
3-La (R = H) [5]. The distorted octahedral coordina-
tion environment with three benzyl groups in a facial
arrangement is completed by three THF ligands. It is
not clear why the negatively charged benzyl ligands
are arranged in close proximity. It might be speculated
that this preferred facial orientation can be explained
unusual bent decametallocene structures of heavier al-
kaline earth and lanthanide metals [12]. Whereas the
benzyl anions in 3-La (R = tBu) are partially bound
in η2 fashion, those in 3-Y (R = H) merely show η1
metal coordination.
Trends and comparisons
Three series of benzyllanthanide complexes are de-
by arguments similar to those used to rationalize the scribed. For each of these series, structural parameters
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270
S. Harder et al. · Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals
as a function of the metal are now available. This al-
lows an evaluation of the metal effects on structure and
bonding in benzylmetal chemistry.
For complexes of type 1, comparisons can be made
within the lanthanide series or with analogous heavier
alkaline earth metal complexes which are known to be
structurally similar [1]. Table 1 summarizes structural
as well as NMR spectroscopic features in the series
1-Ca, 1-Sr, 1-Yb, 1-Eu and 1-Sm. For sake of compar-
ison, also data of alkali metal complexes based on the
2-Me2N-α-Me3Si-benzyl ligand have been included.
The M–C, M–N and M–O bond lengths increase
with increasing ion size. Structural parameters for
1-Ca show close similarities to those for 1-Yb whereas
the structure of 1-Sr is very similar to the lan-
thanide complexes 1-Sm and 1-Eu. Increase of bond
lengths with ion size is not proportional: the difference
Scheme 1.
These delocalization effects are also associated with
˚
of 0.553 A between the Eu–C bond and the shortest
carbon metal bond, C–Li, is significantly larger than the hybridization at the benzylic carbon atom. Al-
˚
the difference of 0.32 A in the ionic radii for Li and Eu. though the determination of hydrogen positions in
heavy atom X-ray diffraction structures should be
taken with precaution, all benzylic hydrogen atoms
have been located in the difference-Fourier maps and
could be refined isotropically. This allows an evalu-
ation of the hybridization of the benzylic carbon as
a function of metal size and metal charge. The sum
of the valence angles at the benzylic carbon atom
(excluding angles involving the metal) is a measure
for hybridization: ΣꢁCα ≈ 328◦ for sp3 hybridiza-
tion and 360◦ for sp2 hybridization. The sp2 char-
acter at the benzylic carbon atom increases with in-
creasing metal size and decreasing metal charge (Ta-
ble 1). The potassium complex 2-Me2N-α-Me3Si-
benzylpotassium·(THF) [10] displays a perfectly pla-
nar benzylic carbon atom. As 1J(C–H) NMR coupling
constants are highly sensitive to hybridization effects,
we also measured coupled 13C NMR spectra for the
diamagnetic complexes. The 1J(Cα –H) coupling con-
stants increase with the extent of s character in the
C–H bond, i. e. with increasing planarization of the
benzylic carbon (Table 1). Thus, solution structures
are in agreement with the geometrical parameters ob-
served in the solid state structures. The chemical shifts
of the para-carbon and para-hydrogen atoms are addi-
tional NMR probes for the evaluation of charge delo-
calization. An increased negative charge on the para-
carbon atom generally results in a high-field shift of
its NMR signals [13]. Decrease of chemical shift val-
ues with increasing extent of charge delocalization is
indeed observed. Especially the potassium complex
The larger metals Eu, Sr, Sm and K display short
interactions with two carbon atoms in the ring (Cipso
and Cortho). The M···Cring bond lengths, defined as the
average values of the M–Cipso and M–Cortho contacts,
are between 4.5 – 6.6 % longer than the M···Cα bonds.
For Ca and Yb much larger contacts are observed: the
M···Cring distances are 16.5 – 17.8 % longer than the
Cα ··· metal contacts. Another obvious trend is the in-
crease of the bite angle Cα –M–N with increasing ion
size. Also the effect of metal size on the delocaliza-
tion of the negative charge from the benzylic carbon
into the aryl ring can be observed. Two geometrical
parameters are very sensitive to the extent of charge
delocalization [3, 13]. First, the Cα –Cipso bond length
shortens on account of charge delocalization. All reso-
nance structures, including the predominant resonance
structure with a formal negative charge on the para-
carbon atom (Scheme 1), display double bond charac-
ter for the Ca–Cipso bond. A second parameter sensitive
towards charge delocalization is the endocyclic angle
at Cipso. This angle is significantly squeezed with re-
spect to an idealized sp2 valence angle on account of
charge delocalization. Analysis of these two parame-
ters in Table 1 shows that: a) 2+ metal cations (Ca2+
,
Yb2+, Sr2+, Sm2+, Eu2+) localize the negative charge
on the benzylic carbon whereas the weaker Lewis acids
(Li+ and K+) allow for significant charge delocaliza-
tion and b) with respect to the larger congeners within
a group, smaller cations (Ca2+, Yb2+ and Li+) give
rise to extensive charge localization.
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S. Harder et al. · Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals
271
˚
Table 2. Selected bond lengths (A) and angles (deg) for benzyllanthanide(III) complexes of type 2-Ln.
2-Ln
La
1.032
Nd
0.983
Sm
0.958
Dy
0.912
Ho
0.901
Y
0.900
Yb
0.868
˚
Ionic radius 6-coordinate (A)
Average Ln–Cα
Average Ln–N
2.645(3)
2.699(2)
2.894(2)
64.7(1)
1.432(4)
115.0(2)
2.567(3)
2.647(2)
2.855(3)
66.2(1)
1.442(3)
115.4(3)
2.531(4)
2.626(3)
2.841(4)
66.9(1)
1.438(5)
114.9(3)
2.470(3)
2.577(2)
2.828(2)
68.5(1)
1.447(4)
115.7(2)
2.476(3)
2.563(3)
2.824(3)
68.4(1)
1.432(4)
115.4(3)
2.472(3)
2.566(3)
2.822(3)
68.8(1)
1.445(4)
115.1(3)
2.419(3)
2.549(3)
2.833(3)
69.4(1)
1.454(5)
115.5(3)
a
Average M···Cring
Cα –Ln–N
Average Cα –Cipso
Cortho–Cα –Cꢀortho
a
Average contact to the two ring atoms Cipso and Cortho
.
˚
Table 3. Selected bond lengths (A) and angles (deg) for ben-
zyllanthanide(III) complexes of type 3-Ln.
3-Ln
3-Y
3-La
3-La
3-La
(R = H) (R = tBu) (R = H) [5] (R = Me) [5]
Average Ln–Cα
Average Ln–O
2.460(2) 2.633(2) 2.645(2)
2.408(2) 2.672(2) 2.664(2)
2.626(2)
2.692(2)
2.970(2)
1.446(3)
—
Average Ln···Cipso 3.387(3) 3.033(2) 2.978(2)
Average Cα –Cipso 1.466(2) 1.443(2) 1.436(3)
ΣꢁCα
336(1)
345(2)
—
carbon Cα into the ring (the bond length Cα –Cipso
and the endocyclic angle at Cipso) do not vary sig-
nificantly along the series. However, comparison of
these values for the largest metal ion (La3+) with those
for the smallest metal ion (Yb3+) indeed confirms a
slight decrease in charge delocalization with decreas-
ing ion size. The benzylic hydrogen atoms could only
be located in some of the crystal structures. There-
fore, trends in the hybridization of the benzylic car-
bon atoms are not evaluated. As most Ln3+ ions are
paramagnetic, only NMR data for 2-La and 2-Y have
Fig. 4. Linear correlation between ionic radii and metal-
ligand bond lengths in the series 2-Ln.
shows very small chemical shifts for the para-H and
C atoms.
Table 2 summarizes selected geometrical param-
eters for tris-(2-Me2N-benzyl)lanthanide complexes
(2-Ln). The Ln–Cα and Ln–N bonds increase lin-
early with increasing ion size (Fig. 4). The difference
1
been obtained [3]. The JC−H value for Cα in 2-La
(142.8 Hz) is significantly larger than that in 3-Y
(133.2 Hz). This confirms the less extensive charge de-
localization (and concomitant pyramidalization of the
benzylic carbon) in the latter complex.
˚
of 0.226(3) A between the longest (Ln = La) and short-
est (Ln = Yb) Ln–Cα bond is somewhat larger than
˚
the difference of 0.164 A in ionic radii of La and Yb.
Table 3 summarizes selected geometrical data for
benzyllanthanide complexes of type 3-Ln. The Ln–C
and Ln–O bond lengths for the three La complexes
compare well and are hardly influenced by alkyl sub-
stitution in para-position. Comparison of these bond
lengths with those in 3-Y (R = H) show that bonds to
La are in general excessively long. Whereas the differ-
˚
On the other hand, the difference of 0.150(3) A be-
tween longest and shortest Ln–N bonds agrees well
˚
with the difference of 0.164 A in ionic radii. The
more distinct increase of Ln–C bond lengths with ion
size is due to a more pronounced multihapto bonding
for the larger lanthanide metals. Table 2 shows that
the La···Cring distance in 2-La, defined as the aver-
age value of La···Cipso and La···Cortho, is only 9.4 %
longer than the La–Cα bond, whereas this difference
increases to a value of 17.1 % for 2-Yb.
ence in ionic radii between La3+ and Y3+ is 0.132 A,
˚
˚
La–C and La–O bonds are on average 0.174(2) A
˚
and 0.268 A longer, respectively. This we attribute to
more extensive Ln···Cipso interaction for the larger La
Another trend in the series is the observed increase atom. As can be deduced from a comparison of the
in the C,N bite angle in going from the larger to the Cα –Cipso bond lengths, substituents in para-position
smaller metals. The two parameters associated with hardly influence the extent of charge delocalization in
delocalization of negative charge from the benzylic the aryl ring. According to expectation, less extensive
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S. Harder et al. · Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals
charge delocalization is observed in 3-Y. This corre- THF in the crystal lattice. After isolation of the crystals the
mother liquor was concentrated and cooled again. The com-
bined fractions gave a yield of 1.45 g (93 %) – M. p. 168 ◦C
(decomp.) – C36H64N2O3Si2Eu (781.06): calcd. C 55.36,
H 8.26; found C 54.98, H 7.94.
sponds to the more pyramidalized Cα atom in 3-Y.
Conclusion
Benzyl complexes of the lanthanide metals have
been routinely prepared by a simple protocol: the
metathesis reaction of benzylpotassium precursors
with the appropriate lanthanide halide. All benzyllan-
thanide complexes are powerful deprotonating agents
and are therefore useful and easily accessible key pre-
cursors in Ln(II) as well as Ln(III) chemistry. Espe-
cially the robust, well-soluble complexes of type 2-Ln
are expected to become standard reagents in lanthanide
2-Yb
◦
A cooled solution (−50 C) of 2.08 g (12.0 mmol) 2-
Me2N-α-Me3Si-benzylpotassium in 20 mL of THF was
◦
added to a cooled slurry (−50 C) of 1.12 g (4.01 mmol)
YbCl3 in 30 mL of THF. An immediate color change
to dark blue was observed. The reaction mixture was al-
lowed to warm up to r. t. and stirred for 1 h at 25 ◦C.
After centrifugation the volatiles were evaporated under
chemistry. They are available for the whole lanthanide vacuum (25 ◦C, 1 Torr, 30 min), and the residue re-
crystallized from toluene/hexane in the form of dark blue
series (from the small Sc to the much larger La). Ex-
cept for the Sc complex, for which hitherto no crys-
tal structure is available, they all crystallize isomor-
phously and can be easily obtained in pure crystalline
form.
◦
blocks. Yield: 596 mg (26 %) – M. p. 157 C (decomp.) –
C27H36N3Yb (575.63): calcd. C 56.34, H 6.30; found
C 56.01, H 6.42.
2-Sm
The crystal structure of the benzylytterbium(II)
complex 1-Yb shows a striking similarity to that of the
analogous calcium compound 1-Ca. The Ln(II) com-
plexes 1-Eu and 1-Sm are very similar to 1-Sr. The
structures show that charge delocalization into the aryl
ring and Ln···Cring interactions increase with increas-
ing metal size. Concomitant hybridization effects are
observed at the benzylic carbon atoms. Similar trends
are noticeable for the Ln(III) complexes of type 2-Ln
and 3-Ln.
Same procedure as described for 2-Yb, but with SmBr3
instead of YbCl3. The product crystallized◦in the form of
dark red blocks. Yield: 21 % – M. p. 150 C (decomp.) –
Despite its paramagnetic behavior reasonably well-resolved
NMR spectra could be obtained (the assignments are ten-
tative); 1H NMR (300 MHz, C6D6): δ = −1.77 (b, 18H,
NMe2), 4.58 (b, 3H, aryl), 7.12 (b, 3H, aryl), 7.25 (b, 3H,
aryl), 9.80 (b, 3H, aryl), 14.25 (b, 6H, CH2). – 13C NMR
(75 MHz, C6D6): δ = 39.4 (NMe2), 44.7 (CH2), aromat-
ics: 111.9, 122.7, 124.3, 128.7, 131.5, 154.7. – C27H36N3Sm
(552.95): calcd. C 58.65, H 6.56; found C 58.23, H 6.62.
Experimental Section
2-Nd
All manipulations were performed under a dry and
oxygen-free atmosphere (argon or nitrogen) by using
freshly dried solvents and Schlenk line and glove
box techniques. The reactants 2-Me2N-α-Me3Si-benzyl-
potassium [10], 2-Me2N-benzylpotassium [14], 4-tBu-benz-
ylpotassium [15], EuI2·(THF)2 [16], YCl3·(THF)3.5 [17] and
LaBr3·(THF)3.1 [18] were prepared according to literature
procedures.
Same procedure as described for 2-Yb, but with NdCl3
instead of YbCl3. The product crystallized in the form
of green-brown blocks. Yield: 32 % – M. p. 146 ◦C (de-
comp.) – C27H36N3Nd (546.83): calcd. C 59.30, H 6.64;
found C 59.13, H 6.81.
2-Dy
Same procedure as described for 2-Yb but with DyCl3
instead of YbCl3. The product crystallized in the form of
yellow blocks. Yield: 38 % – M. p. 154 ◦C (decomp.) –
C27H36N3Dy (565.09): calcd. C 57.39, H 6.42; found
C 57.05, H 6.59.
1-Eu
A mixture of 2-Me2N-α-Me3Si-benzylpotassium (1.00 g,
4.07 mmol) and EuI2·(THF)2 (1.10 g, 2.00 mmol) in 20 mL
of THF was stirred in a glovebox for 40 h. After removing
the solvent under high vacuum, the product was extracted
with two 20 mL portions of benzene. Removing all solvents
under vacuum gave an orange-red foam which was dissolved
2-Ho
Same procedure as described for 2-Yb but with HoI3
in a mixture of 15 mL of hexane and 8 mL of THF by heat- instead of YbCl3. The product crystallized in the form of
ing to reflux temperature. Slow cooling of the orange solu- orange blocks. Yield: 38 % – M. p. 156 ◦C (decomp.) –
tion to +4 ◦C gave well-formed orange needles of the para- C27H36N3Ho (567.53): calcd. C 57.14, H 6.39; found
magnetic product 1-Eu with one equivalent of uncoordinated C 56.79, H 6.29.
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S. Harder et al. · Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals
273
Table 4. Crystal structure data for 1-Eu, 2-Nd, 2-Sm, 2-Dy, 2-Ho, 2-Yb, 3-Y (R = H) and 3-La (R = tBu).
1-Eu
2-Nd
2-Sm
2-Dy
2-Ho
2-Yb
3-Y (R = H) 3-La (R = tBu)
Formula
C32H56O2N2Si2Eu C27H36N3Nd C27H36N3Sm C27H36N3Dy C27H36N3Ho C27H36N3Yb C33H45O3Y C45H69O3La
· (C4H8O)
· (C4H8O)2
56578.60 941.12
monoclinic monoclinic monoclinic monoclinic monoclinic monoclinic triclinic
Mr
781.03
546.83
552.95
P21/c
565.09
P21/c
567.52
P21/c
575.63
P21/c
Crystal system triclinic
¯
¯
P1
Space group
a, A
b, A
c, A
P1
P21/c
16.9666(8) 16.8989(8) 16.8456(6) 16.8083(6) 16.8969(5) 17.3879(9) 14.2601(4)
9.4546(5) 9.4648(7) 9.4500(3) 9.4614(3) 9.4642(3) 20.9547(10) 914.7473(4)
16.6784(10) 16.6603(10) 16.6181(5) 16.6151(4) 16.6694(5) 8.4526(4) 15.3114(5)
90 90 90 90 90 90 110.177(1)
110.685(3) 110.911(3) 111.123(2) 111.217(2) 111.297(2) 93.286(3) 96.731(2)
Cc
˚
˚
˚
9.9253(7)
10.3021(8)
20.1525(12)
85.728(6)
89.639(5)
75.215(6)
1986.7(2)
2
α, deg
β, deg
γ, deg
90
90
90
90
90
90
115.043(1)
3
˚
V, A
2503.0(2)
4
2489.2(3)
4
2467.7(1)
4
2563.2(1)
4
2483.7(1)
4
2467.7(1) 2603.8(1)
Z
4
2
Dcalcd, g cm−3 1.306
1.451
2.092
1116
173
1.475
2.377
1124
173
1.521
3.046
1140
173
1.530
3.230
1144
173
1.539
3.783
1156
203
1.250
1.926
1124
203
1.200
0.862
1000
203
µ(MoKα ), cm−1 1.672
F(000), e
T, K
818
203
27.1
θ
max, deg
27.5
27.5
27.5
27.5
27.6
35.5
30.0
Refl. measured 9216
Refl. unique 8720
Refl. I ≥ 2σ(I) 8204
Rint 0.014
Param. refined 592
27182
5713
3559
0.035
286
0.029
0.046
0.80
25069
5690
2922
0.042
286
0.030
0.047
0.66
24890
5645
4613
0.041
305
0.021
0.044
0.99
24756
5637
4489
0.035
280
0.024
0.052
1.00
48573
5761
5092
0.052
402
0.022
0.056
1.11
80223
11636
9166
0.065
358
0.036
0.088
1.00
135472
15059
13317
0.034
584
0.031
0.088
1.07
R(F)
0.028
wR(F2) all
0.078
1.08
GoF (F2)
∆ρfin (max/min), −1.15 / 1.16
−1.68 / 0.87 −1.92 / 0.95 −0.87 / 1.76 −0.98 / 1.63 −1.17 / 0.50 −0.84 / 0.51 −0.61 / 0.89
−3
˚
e A
3-Y (R = H)
THF was added to LaBr3·(THF)3.1 (1.07 g, 1.82 mmol).
The resulting yellow suspension was stirred for 2 h at 0 ◦C.
◦
A cold dark-red solution (−50 C) of benzylpotassium
(0.90 g, 6.91 mmol) in 20 mL of THF was added to
YCl3·(THF)3.5 (1.12 g, 4.01 mmol). An immediate color
change to yellow-orange was observed, and a grey precipitate
formed. After stirring for 30 min the mixture was concen-
trated to 50 % of its original volume, and 10 mL of hexane
was added. The yellow-white precipitate was isolated, and
the product was extracted from this solid with two 20 mL
portions of a THF/hexane mixture (1/1). The combined ex-
tracts were concentrated under high vacuum to 25 % of
their ori◦ginal volume, and the solution was slowly cooled
to −30 C. The product was isolated in the form of light-
The mother liquor was separated from the precipitate by
centrifugation and concentrated to 10 mL. The THF solution
was layered ca◦refully with 10 mL of pentane and slowly
cooled to −30 C. The product was isolated in the form of
◦
orange crystals (0.36 g, 25 %) – M. p. 118 C (decomp.) –
1H NMR (300 MHz, [D8]-THF): δ = 1.18 (s, 27H, tBu),
1.31 (s, 6H, CH2), 1.72 (m, 12H, THF), 3.57 (m, 12H,
THF), 6.07 (d, J = 8.0 Hz, 6H, aryl), 6.89 (d, J = 8.0 Hz,
6H, aryl). – 13C NMR (75 MHz, [D8]-THF): δ = 25.3
(THF), 32.3 (Me3C), 34.2 (Me3C), 64.3 (CH2), 68.5 (THF),
aromatics: 121.4, 127.4, 137.6, 149.0. – C45H69O3La
(796.95): calcd. C 67.82, H 8.73; found C 67.41, H 8.62.
◦
yellow crystals (0.32 g, 24 %) – M. p. 136 C (decomp.) –
1H NMR (300 MHz, C6D6): δ = 1.17 (m, 12H, THF),
1.75 (d, 2J(1H–89Y) = 2.1 Hz, 6H, CH2), 3.40 (m, 12H,
THF), 6.73 (m, 9H, aryl), 7.12 (m, 6H, aryl). – 13C NMR
Crystal structure determinations
The structures were solved by Direct Methods (SHELXS-
97) [19] and refined with SHELXL-97 [20]. All geometry cal-
culations and graphics were performed with PLATON [21].
Crystal data are summarized in Table 4.
CCDC 665306 (2-Yb), 665307 (2-Sm), 671057 (3-La),
671058 (3-Y), 671059 (2-Dy), 671060 (2-Ho), 671061
(2-Nd), 671062 (1-Eu) contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free
(75 MHz, C6D6): δ = 25.3 (THF), 52.7 (d, J(13C–89Y) =
1
31.3, CH2), 68.5 (THF), aromatics: 117.4, 123.2, 129.3,
151.8. – C33H45O3Y (578.63): calcd. C 68.50, H 7.84; found
C 68.06, H 7.81.
3-La (R = tBu)
A
cold dark-red solution (−50 ◦C) of 4-tBu- of charge from The Cambridge Crystallographic Data Centre
benzylpotassium (1.00 g, 5.37 mmol) in 40 mL of via http://www.ccdc.cam.ac.uk/data request/cif.
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274
S. Harder et al. · Benzyl Complexes of Lanthanide(II) and Lanthanide(III) Metals
Acknowledgements
The Deutsche Forschungsgemeinschaft is acknowledged
for support of this work within the SPP 1166 program. Prof.
Dr. R. Boese and D. Bla¨ser (Universita¨t Duisburg-Essen) are
thanked for the collection of part of the X-ray diffraction
data.
[1] S. Harder, Angew. Chem. 2004, 116, 2768; Angew.
Chem. Int. Ed. 2004, 43, 2714.
3385; e) T. P. Hanusa, Organometallics 2002, 21, 2559;
f) M. Schultz, C. J. Burns, D. J. Schwartz, R. A. Ander-
sen, Organometallics 2002, 21, 2559; g) W. J. Evans,
L. A. Hughes, T. P. Hanusa, J. Am. Chem. Soc. 1984,
106, 4270.
[2] L. E. Manzer, J. Am. Chem. Soc. 1978, 100, 8068.
[3] S. Harder, Organometallics 2005, 24, 373.
[4] R. D. Shannon, Acta Cryst. 1976, A32, 751.
[5] S. Bambirra, A. Meetsma, B. Hessen, Organometallics
2006, 25, 3454.
[13] D. Hoffmann, W. Bauer, F. Hampel, N. J. R. van
Eikema Hommes, P. von R. Schleyer, P. Otto,
U. Pieper, D. Stalke, D. S. Wright, R. Snaith, J. Am.
Chem. Soc. 1994, 116, 528.
[14] S. Harder, F. Feil, Organometallics 2002, 21, 2268.
[15] S. Harder, S. Mu¨ller, E. Hu¨bner, Organometallics
2004, 23, 178.
[16] P. Watson, T. H. Tulip, I. Williams, Organometallics
1990, 9, 1999.
[17] P. Bruin, J. H. Booij, J. H. Teuben, A. Oskam, J. Or-
ganomet. Chem. 1988, 350, 17.
[18] G. B. Deacon, T. Feng, P. C. Junk, G. Meyer, N. M.
Scott, B. W. Skelton, A. White, Austr. J. Chem. 2000,
53, 853.
[19] G. M. Sheldrick, SHELXS-97, Program for the Solution
of Crystal Structures, University of Go¨ttingen, Go¨ttin-
gen (Germany) 1997.
[20] G. M. Sheldrick, SHELXL-97, Program for the Refine-
ment of Crystal Structures, University of Go¨ttingen,
Go¨ttingen (Germany) 1997.
[21] A. L. Spek, PLATON, A Multipurpose Crystallographic
Tool, Utrecht University, Utrecht (The Netherlands)
2000. See also: A. L. Spek, J. Appl. Cryst. 2003, 36,
7 – 13.
[6] G. B. Deacon, C. M. Forsyth, Chem. Eur. J. 2004, 10,
1798.
[7] G. Heckmann, M. Niemeyer, J. Am. Chem. Soc. 2000,
122, 4227.
[8] C. K. Simpson, R. E. White, C. N. Carlson, D. A.
Wrobleski, C. J. Ku¨hl, T. A. Croce, I. M. Steele, B. L.
Scott, V. G. Young, T. P. Hanusa, Organometallics
2005, 24, 3685.
[9] C. Eaborn, P. B. Hitchcock, K. Izod, Z.-R. Lu, J. D.
Smith, Organometallics 1996, 15, 4783.
[10] F. Feil, S. Harder, Organometallics 2001, 20, 4616.
[11] a) I. S. Guzman, N. N. Chigir, O. K. Sharaev, G. N.
Bondarenko, E. I. Tinyakova, B. A. Dolgoplosk, Dokl.
Akad. Nauk SSSR 1979, 249, 860; b) N. N. Chigir, I. S.
Guzman, O. K. Sharaev, E. I. Tinyakova, B. A. Dolgo-
plosk, Dokl. Akad. Nauk SSSR 1982, 263, 375.
[12] a) R. A. Andersen, J. M. Boncella, C. J. Burns,
R. Blom, A. Haaland, H. V. Volden, J. Organomet.
Chem. 1986, 312, C49; b) R. A. Williams, T. P.
Hanusa, J. C. Huffman, Organometallics 1990, 9,
1128; c) M. Kaupp, P. v. Schleyer, M. Dolg, H. Stoll,
J. Am. Chem. Soc. 1992, 114, 8202; d) T. K. Hollis,
J. K. Burdett, B. Bosnich, Organometallics 1993, 12,
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