Synthesis and structural studies of heteroleptic complexes of ytterbium(III) involving aryloxy- or alkoxy- and cyclopentadienyl ligands

Article abstract of DOI:10.1016/j.ica.2003.11.009

Treatment of tris-cyclopentadienyl-ytterbium in thf with one equivalent of 2,6-di(tert-butyl)phenol, N,N-dimethyl-2-aminoethanol or N,N-diethyl-2- aminoethanol resulted in substitution of one cyclopentadienyl ligand and formation of [YbCp₂(O-C₆H₃^tBu-2,6) (thf)] (1), [{YbCp₂(μ-OCH₂CH₂NMe ₂)}₂] (2) or [{YbCp₂(μ-OCH ₂CH₂NEt₂)}₂]·(thf) ₂ (3), respectively. All compounds were characterised by spectroscopic and X-ray crystallographic techniques, the latter two also being studied by variable temperature ¹H NMR spectroscopy. Compound (1) is mononuclear with the Yb centre bound by two η⁵-cyclopentadienyl ligands one O-bound thf and an O-bound phenoxy ligand. Compounds (2) and (3) are centrosymmetric dimers with the Yb centre bound by two η⁵- cyclopentadienyl ligands, while the bidentate ligands chelate the metal centre and also bridge to the adjacent Yb through the alkoxy oxygen atom. Variable temperature ¹H NMR studies on compounds (2) and (3) show a solution-state equilibrium between the dimeric solid-state structure and one with the nitrogen atoms non-bound to Yb.

Full text of DOI:10.1016/j.ica.2003.11.009

Inorganica Chimica Acta 357 (2004) 2125–2133
www.elsevier.com/locate/ica
Synthesis and structural studies of heteroleptic complexes
of ytterbium(III) involving aryloxy- or alkoxy- and
cyclopentadienyl ligands q
a
a,
b
b,
*
Thilo Hahn , Evamarie Hey-Hawkins *, Matthias Hilder , Peter C. Junk
b,1
Matthew K. Smith
,
a
Institut f€ur Anorganische Chemie der Universit€at Leipzig, D-04103 Leipzig, Germany
School of Chemistry, Monash University, P.O. Box 23, Clayton, Vic. 3800, Australia
b
Received 31 October 2003; accepted 8 November 2003
Abstract
Treatment of tris-cyclopentadienyl-ytterbium in thf with one equivalent of 2,6-di(tert-butyl)phenol, N,N-dimethyl-2-aminoeth-
t
anol or N,N-diethyl-2-aminoethanol resulted in substitution of one cyclopentadienyl ligand and formation of [YbCp2(O-C6H3 Bu-
2,6)(thf)] (1), [{YbCp2(l-OCH2CH2NMe2)}2] (2) or [{YbCp2(l-OCH2CH2NEt2)}2] ꢀ (thf)2 (3), respectively. All compounds were
1
characterised by spectroscopic and X-ray crystallographic techniques, the latter two also being studied by variable temperature H
NMR spectroscopy. Compound (1) is mononuclear with the Yb centre bound by two g5-cyclopentadienyl ligands one O-bound thf
and an O-bound phenoxy ligand. Compounds (2) and (3) are centrosymmetric dimers with the Yb centre bound by two g5-cy-
clopentadienyl ligands, while the bidentate ligands chelate the metal centre and also bridge to the adjacent Yb through the alkoxy
oxygen atom. Variable temperature 1H NMR studies on compounds (2) and (3) show a solution-state equilibrium between the
dimeric solid-state structure and one with the nitrogen atoms non-bound to Yb.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Ytterbium; Aryloxides; Cyclopentadienyl; Alkoxides; X-ray structures
1. Introduction
dicious choice of ligand and stoichiometry, the synthesis
of heteroleptic complexes can be achieved. Heteroleptic
lanthanoid compounds have extensive applications as
catalysts in a wide range of reactions [13–22]. In ho-
mogenous catalysis, the co-ligand can have a large in-
fluence on the catalytic activity and selectivity, and the
catalytic properties of these complexes can be fine-tuned
by modifying the co-ligands [23]. Additionally, the het-
eroleptic complexes can be more stable towards hydro-
lysis. Some of them can even be used in protic organic
reaction media or even in water. Co-ligands that have an
intramolecular heteroatom (O, N, P) that can form a
coordinative bond through chelation are attractive in
the quest for heteroleptic lanthanoid catalysts. These
heteroatoms can form intramolecularly solvated com-
plexes which can be involved in equilibria with their
unsolvated counterparts in solution [24–27]. Thus,
formally coordinatively unsaturated metal centres that
The cyclopentadienyl ligand is ubiquitous in or-
ganolanthanoid chemistry [1]. Tris-cyclopentadienyl
lanthanoid complexes have found uses in chemical va-
pour deposition of rare earths into group 13–15 (III–V)
semiconductors [2] but also as useful starting materials
for the synthesis of heteroleptic lanthanoid complexes
[3–12]. Treatment of LnCp3 complexes with compounds
of greater thermodynamic acidity than CpH, can result
in substitution of the Cp ligand, and therefore, by ju-
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2003.11.009.
* Corresponding authors. Tel.: +61399054570; fax: +61399054597.
E-mail addresses: hey@rz.uni-leipzig.de (E. Hey-Hawkins),
peter.junk@sci.monash.edu.au (P.C. Junk).
1
Visiting student from the Department of Chemistry, James Cook
University, Townsville, Qld. 4811, Australia.
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.11.009

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T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
can be involved in small molecule catalysis are gener-
ated. Such heteroatoms would preferably be atoms that
would form only moderate interactions with the metal
centre, and for the lanthanoid elements, the softer donor
atoms N and P are preferential.
This present paper describes the substitution of one
cyclopentadienyl ligand by a phenolato (2,6-di(tert-
butyl)phenol) or aminoalcoholato (N,N-dimethyl-2-
aminoethanol, N,N-diethylaminoethanol, respectively)
co-ligand by treating tris-cyclopentadienyl ytterbium
with the respective alcohol. Thus, we report herein, the
t
synthesis and characterisation of [YbCp2(O-C6H3 Bu-
2,6)(thf)] (1), [{YbCp2(l-OCH2CH2NMe2)}2] (2) and
[{YbCp2(l-OCH2CH2NEt2)}2] ꢀ (thf)2 (3).
Fig. 1. X-ray crystal structure of mononuclear [YbCp2(O-C6H3tBu2-
2,6)(thf)] (1). Hydrogen atoms have been removed for clarity.
2. Results and discussion
Compounds (1) to (3) were conveniently synthesised
by treating [YbCp3(thf)] with an equimolar amount of
the alcohols 2,6-di(tert-butyl)phenol, N,N-dimethyl-2-
aminoethanol or N,N-diethyl-2-aminoethanol, respec-
tively, as shown in Eq. (1) [28,29]. The Brønstedt acidity
of the co-ligand dictates whether substitution takes
place. To substitute the Cp ligand its acidity must be
greater than that of HCp and in this case, the pKa of
each of the alcohols is approx. 9–10 compared with a
pKa of approx. 15 for cyclopentadiene.
ꢀ
The Yb–Cp(centroid) distances of 2.345 and 2.353 A
are similar to those in another related eight-coordinate
,
cyclopentadienyl complex involving YbIII
[YbCp2(OC10H7)(thf)] (where the average Yb–Cp(cen-
e.g.
ꢀ
troid) distance is 2.310 A) [7]. The Yb–OðthfÞ distance is
significantly longer (2.385(4) A) as expected than for the
ꢀ
ꢀ
phenolato ligand (2.127(4) A). The Cpcentroid–Yb–
Cpcentroid angle is 124.9(4)°.
In general the structure is primarily governed by the
bulkiness of the phenolato ligand, thus preventing oligo-
or polymerisation and having a stabilising influence for
formation of a monomeric species. The Yb–O–CðarylÞ
angle (149.6(4)°) is significantly more obtuse than for an
sp3 hybridised oxygen atom, but also departs substan-
tially from linearity. The CpðcentroidÞ–Yb–O angles are
99.6° and 104.8° (for thf), whereas they are 108.4° and
115.5° for the phenolato ligand. The deviation from
tetrahedral geometry is due to the steric bulk of the
phenolato ligand. Interestingly, the solvent-free com-
plexes of the composition [SmCp*2(O-C6H2-tBu3-2,4,6)]
[30] and [SmCp*2(O-C6HMe4-2,3,5,6)] [31] (Cp* ¼ pen-
tamethylcyclopentadienyl) have been previously studied.
Even though the phenolato ligands have similar steric
bulk about the lanthanoid centre, the Cp* ligands are
sterically much more demanding than non-substituted
Cp, and thus, a solvent-free species was obtained. In
accordance with this is the observation that the neo-
dymium phenolato complex [NdCp2(O-C6H3-Ph2-
2,6)(thf)] is obtained with coordinating thf [32]. In
compound (1), the sp2 hybridised a-carbon atom of the
phenyl ring lies within the ring plane whereas the
C(CH3)3 atoms of the two tert-butyl groups reside out
thf
½YbCp3ðthfÞꢁ þ R-OH!½YbCp2ðO-RÞꢁ ðthfÞ þ HCp
m
n
ð1Þ
(1), R ¼ 2,6-di(tert-btuyl) phenyl; m ¼ 1, n ¼ 1,
(2), R ¼ N,N-dimethylaminoethyl; m ¼ 2, n ¼ 0,
(3), R ¼ N,N-diethylaminoethyl; m ¼ 2, n ¼ 2.
The first co-ligand investigated was 2,6-di(tert-bu-
tyl)phenol. Due to resonance stabilisation effects of the
phenolate anion it shows a remarkable acidity. Fur-
thermore, since it contains the two bulky substituents in
the 2,6-positions, it was envisaged that based on steric
effects, the nuclearity could be restricted to a monomeric
species. Indeed, by letting [YbCp3(thf)] react with one
molar equivalent of 2,6-di(tert-butyl)phenol red single
crystals suitable for X-ray diffraction analysis were iso-
lated from thf.
t
[YbCp2(O-C6H3 Bu-2,6)(thf)] (1) crystallises in the
monoclinic space group P21=c with one monomeric en-
tity constituting the asymmetric unit (Fig. 1). Selected
bond lengths and angles are given in Table 1. The eight-
coordinate Yb centre is bound by two g5-cyclopenta-
dienyl, one phenolato ligand as well as one thf molecule.
Evidently, the phenolato ligand is not sufficiently bulky
to prevent the coordination of solvent molecules. The
four ligands form a distorted tetrahedral (if the cent-
roids of the Cp rings are considered the point of binding
to the Yb centre) environment around Yb.
ꢀ
of this plane by )0.343(6) and )0.323(7) A, respectively,
while the phenolato oxygen atom lies out of this plane
ꢀ
by 0.246(4) A giving the phenolato group a curved
conformation away from the metal centre. There is a
reasonably close contact between the Yb centre and two

T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
2127
Table 1
Selected bond (i) distances (A) and (ii) angles (°) for [YbCp2(O-C6H3tBu2-2,6)(thf)] (1)
ꢀ
Atoms
Distance
Atoms
Distance
(i)
Yb(1)–O(1)
Yb(1)–O(2)
2.127(4)
2.385(4)
Yb(1)–Cen(1)
Yb(1)–Cen(2)
2.345
2.353
Atoms
Angle
Atoms
Angle
(ii)
O(1)–Yb(1)–O(2)
Cen(1)–Yb(1)–O(1)
Cen(2)–Yb(1)–O(1)
99.0(2)
108.4
115.5
Cen(1)–Yb(1)–Cen(2)
Cen(1)–Yb(1)–O(2)
Cen(2)–Yb(1)–O(2)
124.9
104.8
99.7
protons of the tert-butyl groups with distances of 3.015
ꢀ
and 2.810 A and may be considered as agostic interac-
Following the same route as described above (see Eq.
(1)) [YbCp3(thf)] was treated with one equivalent of the
aliphatic aminoalcohol in thf. From the reaction mix-
tures yellow-orange single crystals could be obtained
which were suitable for X-ray diffraction analysis.
The X-ray crystal structures of [{YbCp2(l-
OCH2CH2NMe2)}2] (2) and [{YbCp2(l-OCH2CH2
NEt2)}2] ꢀ (thf)2 (3) in the solid state are shown in Figs. 2
and 3 and selected bond lengths and angles are compiled
in Table 2.
Compounds (2) and (3) represent the second struc-
tural reports of heteroleptic lanthanoid cyclopentadienyl
complexes containing aminoalcoholates as ligands. Re-
lated lanthanoid complexes (R; R)-[{LnCp2(l-OCH2CH-
(Et)NMe2)}2] (Ln ¼ Nd, Sm, Tb, Y) [34], were reported
recently. Both compounds (1) and (2) have similar di-
meric structures which reside on a centre of inversion.
The Yb centre is bound by two g5-cyclopentadienyl li-
gands and an aminoalcoholato ligand which chelates via
the N and O atoms and also bridges to the other Yb cen-
tre (via the oxygen atom) resulting in nine-coordination
about Yb. The environment around the ytterbium centre
can be described as a distorted trigonal bipyramid (if the
tions. Such interactions with similar distances have been
reported before for [Sm(l; g5-Cp*)2(O-C6H2-tBu2-2,6-
Me-4)(thf)2K] [30]. Wu and coworkers [7] reported a
related compound involving a naphtholato ligand, viz
[YbCp2(OC10H7)(thf)]. Bond distances, angles and
structural parameters are comparable to the present
compound. Some angles however reflect the fact that the
naphtholato ligand is sterically less demanding than the
phenolato ligand. The Cpcentroid–Yb–Cpcentroid angle for
example is about 6° smaller for the phenolato ligand
than it is for the naphtholato ligand. Other angles in-
volving Yb obey the same trend implying that the phe-
nolato ligand repels the other ligands to a greater extent.
These two structures are the only Yb complexes in-
volving Cp as well as aryloxo co-ligands. Besides the
above mentioned Sm [30,31] and Nd [32] complexes, a
closely related TiIII compound, viz [TiCp2(O-C6H2-2,6-
tBu-4-Me)], was reported by Lappert and coworkers
[33], which has, while unsolvated, similar bonding pa-
rameters to the present complex. The Ti–O–C(aromatic)
angle of 142.3(2)° is slightly more acute than that in
compound (1). The tertiary carbon atoms C (CH3)3 of
ꢀ
the tert-butyl group also resides out of the plane (0.36 A)
defined by the aromatic ring in a similar manner as
described for compound (1).
Our question now was, how would the structure
change if another class of co-ligand was introduced to
the system? In place of phenolato ligands it was our
intention to study alcoholato ligands. The electronic
properties of these saturated aliphatic compounds are
very different to their aromatic relatives. This results in
much less acidic OH groups compared to phenolic OH
groups. Additionally, they are sterically less demanding
than the phenyl ring with two tert-butyl groups adjacent
to the alcohol residue. Oligo- or polymerisation or the
coordination of solvent molecules could therefore be
expected. To prevent these phenomena it was decided to
use bifunctional co-ligands (N,N-dimethyl-2-aminoeth-
anol and N,N-diethyl-2-aminoethanol) whose additional
electron-donor atoms could bind to the metal centre and
coordinatively saturate YbIII.
Fig. 2. X-ray crystal structure of dimeric [{YbCp2(l-
OCH2CH2NMe2)}2] (2). Hydrogen atoms have been removed for
clarity.

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T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
the phenolato co-coordinated compound (1) above. The
Yb–OðchelateÞ and Yb–OðbridgingÞ distances for [{YbCp2(l-
OCH2CH2NMe2)}2] are 2.224(4) and 2.273(3) A,
ꢀ
ꢀ
whereas they are 2.193(5) and 2.273(5) A for [{YbCp2(l-
OCH2CH2NEt2)}2] ꢀ (thf)2. It is worthy to mention that
these Yb–O distances are significantly longer than Yb–
Ophenolato in compound (1), but this could be expected
based on an increase in coordination number. The
Yb2O2 core is necessarily planar by symmetry. Such
subunits have been reported before for ytterbium alco-
holato complexes [6,35–41] as well as with phenolato
ligands [42].
The most distinguishable feature between the two
structures is the bond length difference of the Yb–N
ꢀ
bond. In compound (2) this distance is 2.691(4) A,
ꢀ
whereas it is significantly longer (2.895(7) A) in com-
pound (3). The reason for this bond lengthening in
compound (3) is mysterious and the only explanation is
that the ethyl group is more sterically demanding than
the methyl groups in (2). The distances are still longer
than those involving other tertiary amines in ytter-
bium(III) complexes (e.g. [YbNa(L)Cl2] ꢀ MeOH (with
L ¼ N3,O5 macrocyle)) where the Yb–N distance is
Fig. 3. X-ray crystal structure of dimeric [{YbCp2(l-
OCH2CH2NEt2)}2] ꢀ (thf)2 (3). Hydrogen atoms and lattice thf mole-
cules have been removed for clarity.
ꢀ
2.593(4) A [43].
centroids of the Cp rings are considered the points of
attachment to Yb) where the nitrogen and the bridging
oxygen atoms occupy the apical positions of the poly-
hedron. The distances between the two Yb centres are
In the case of the aminoalcoholato complexes there is
no doubt that in the solid state Yb is coordinated by
oxygen as well as by nitrogen. It was also of interest to
understand the nature of compounds (2) and (3) in so-
lution. Of special interest is the coordinative nature of
the Yb–N bond. If the Yb–N bond is cleaved in solution
the metal can become coordinatively unsaturated,
opening the possibility of catalytic activity. Some pos-
sible conformations of these dinuclear species in solu-
tion in equilibrium are shown in Fig. 4.
ꢀ
ꢀ
3.7072(6) A for [{YbCp2(l-OCH2CH2NMe2)}2] and
3.6910(8) A for [{YbCp2(l-OCH2CH2NEt2)}2] ꢀ (thf)2,
which rule out direct metal-metal interactions.
The Cpcen–Yb–Cpcen angles for [{YbCp2(l-OCH2
CH2NMe2)}2] and [{YbCp2(l-OCH2CH2NEt2)}2] ꢀ
(thf)2 are 121.8 and 123.2°, respectively, being similar to
Table 2
Selected bond parameters for [{YbCp2(l-OCH2CH2NMe2)}2] (2) and [{YbCp2(l-OCH2CH2NEt2)}2] ꢀ (thf)2 (3)
Compound (1)
Compound (2)
ꢀ
ꢀ
Distances in A, angles in °
Distances in A, angles in °
Yb(1)–O(1)
Yb(1)–O(10)
Yb(1)...Yb(10)
Cen(1)–Yb(1)
2.224(4)
2.273(3)
3.7072(6)
2.414
2.193(5)
2.273(5)
3.6910(8)
2.392
Cen(2)–Yb(2)
2.406
2.397
O(1)–Yb(1)–O(10)
Yb(1)–O(1)–Yb(10)
Cen(1)–Yb(1)–Cen(2)
69.0(2)
111.1(2)
121.8
68.6(2)
111.4(2)
123.2
Fig. 4. Stepwise mechanism of ring opening with some possible conformations.

T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
2129
This ring opening mechanism would provide two
major advantages. Firstly, after the ring opening, the
coordination sphere around the Yb cation would be less
saturated due to the lack of coordination by the nitro-
gen. These coordinatively unsaturated centres avail co-
ordination sites for substrate binding, thus resulting in a
higher potential catalytic activity. Secondly, the ring
opening will lead to a free electron pair on the nitrogen
atom to which another metallic complex could be
bound. Heterobimetallic catalysts with two different
catalytic active centres could therefore be obtained [44].
In other words if we could demonstrate opening of the
chelate ring in solution, the potential for catalytic ac-
tivity could be increased dramatically.
Yb3þ is strongly paramagnetic. The presence of
paramagnetic compounds changes the chemical shift of
organic fragments significantly. In the presence of Yb3þ
complexes the scale of an 1H NMR spectrum can
therefore expand up to 290 ppm. It was decided to de-
termine if ring opening occurs by NMR spectroscopy.
The solvent of choice was dried, deuterated chloroform,
which is sufficiently polar to dissolve appreciable
quantities of the lanthanoid complexes for NMR stud-
ies, without coordinating to the metal centre.
(metathetical exchange) [34]. From this result it can be
assumed that even in solution the dimeric core is
maintained. This will presumably be also the case in the
present complexes (2) and (3).
1H NMR spectra of [{YbCp2(l-OCH2CH2NMe2)}2]
were recorded in the range of )100 to 300 ppm at var-
ious temperatures. Fig. 5 shows the change of the
chemical shift with temperature, whereas Fig. 6 shows
the dependence of the signal width with the temperature.
The spectrum at room temperature shows four sig-
nals in the range of )23.3 to 75.7 ppm. At room tem-
perature the Cp ligand shows a signal at )23.3 ppm (20
H). The methyl group protons are at 64.6 ppm in reso-
nance (12 H). There are two signals at 58.7 ppm (4 H)
and 75.7 ppm (4 H) which belong to either the N–CH2
or the O–CH2 protons. Since the intensities are the same
a proper assignment of the peaks is difficult. The signal
at 75.7 ppm is attributed to the O–CH2 group due to the
greater electronegativity of O compared with N, whereas
the signal at 58.7 ppm is assigned to the N–CH2 group.
None of the signals show any fine structure, which leads
to the assumption that the complex exists in its open
structure (N non-bound to Yb) at room temperature. At
lower temperatures, the Cp signals are shifted to lower
frequencies (upfield), whereas the other signals are
shifted towards higher frequencies (downfield). A plot of
the temperature dependence of the chemical shift shows
a nearly linear relationship between d and T, indicating
a continuous change of the magnetic moments probably
due to slight structural changes (Fig. 5). These changes
of the chemical shift with varying temperature are hard
to analyse. The main reason is an anisotropic effect of
the magnetic moment of the paramagnetic Yb3þ, which
is hard to predict.
It is possible that an equilibrium between dimeric and
monomeric species exists:
½fYbCp2ðOCH2CH2NR2Þg2ꢁ
ꢀ2 ½YbCp2ðOCH2CH2NR2Þꢁ
ð2Þ
Fischer and coworkers [34,40] have performed NMR
experiments (VT NMR experiments in solution and, for
some complexes, NMR studies in the solid state) on
comparable bis-cyclopentadienyl complexes (R; R)-
[{LnCp2(l-OCH2CH(Et)NMe2)}2] (Ln ¼ La, Pr, Nd,
Sm, Tb, Y, Tm, Yb, Lu). A mixture of two different
homodinuclear complexes did not show signals of
heterodinuclear complexes in the 1H NMR spectrum
As expected the line width increases with decreasing
temperature (Fig. 6). The line width for the Cp ligands
for example is 110 Hz at 25 °C, whereas it is 4000 Hz at
90
70
50
30
10
-10
-30
-40
-30
-20
-10
0
10
20
30
Temperature in ˚C
C5H5 NCH2 NCH3 OCH2
Fig. 5. Temperature dependence of the chemical shifts in the 1H NMR spectrum of [{YbCp2(l-OCH2CH2NMe2)}2] (2).

2130
T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
4000
3000
2000
1000
0
-40
-30
-20
-10
0
10
20
30
Temperature in ˚C
C5H5 NCH2 NCH3 OCH2
Fig. 6. Temperature dependence of the 1H NMR signal widths in [{YbCp2(l-OCH2CH2NMe2)}2] (2).
)38 °C. At high temperatures it seems that the complex
exists in its open structure. The Cp ligands can rotate
freely and therefore all protons on the ligand are
equivalent which results in one sharp signal. At lower
temperatures the interaction between Yb and N in-
creases which leads to a limited mobility of the Cp
ligands. The protons of the two Cp ligands become non-
equivalent and line widening occurs. This line broad-
ening can also be observed for the two sets of methylene
protons. The line broadening for the methyl protons is
less significant. It appears that the N–Cmethyl bond is
insignificantly affected by the increased interaction be-
tween Yb and N.
From these results it can be assumed that at high
temperatures the open structure is formed. With de-
creasing temperature the interaction between Yb and N
increases. The broad lines however indicate that there
are different structural species in equilibrium.
VT-1H NMR studies of the compounds [{YbCp2(l-
OCH2CH2NEt2)}2] ꢀ (thf)2 as well as of the solvent free
analogue [{YbCp2(l-OCH2CH2NEt2)}2] were recorded.
The results are shown in Figs. 7 and 8.
In the temperature range of 30 to )40 °C the spectra
do not differ significantly. The presence of thf in the
lattice does not initiate any significant structural chan-
ges. The coordinated Cp protons are at a chemical shift
of )56.2 ppm (20 H). The CH2 protons of the N–
CH2CH3 group show a signal at 77.0 ppm (8 H) and the
signal for the CH3 protons of the same group occurs at
48.5 ppm (12 H). There are two signals for the methylene
protons of the O–CH2CH2–N group at 176.2 and 232.4
ppm, respectively (both 4 H). In respect to the higher
electronegativity of oxygen relative to nitrogen the signal
at 232.4 ppm is attributable to the O–CH2 group,
whereas the signal at 176.2 ppm has its origin in the N–
CH2 protons. The line width of these signals is much
larger than those of the other signals of this spectrum.
Again line broadening for all signals can be observed
with decreasing temperature (Fig. 8). This is most
significant for all methylene protons, namely for the
300
200
100
0
-100
-40
-30
-20
-10
0
10
20
30
Temperature in ˚C
C5H5 NCH2CH3 NCH2CH3 NCH2 OCH2
Fig. 7. Temperature dependence of the chemical shifts in the 1H NMR spectrum of [{YbCp2(l-OCH2CH2NEt2)}2] (3).

T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
2131
3000
2500
2000
1500
1000
500
0
-40
-30
-20
-10
0
10
20
30
Temperature in ˚C
C5H5 NCH2CH3 NCH2CH3 NCH2 OCH2
Fig. 8. Temperature dependence of the 1H NMR signal widths in [{YbCp2(l-OCH2CH2NEt2)}2] (3).
N–CH2-CH3 group and for the two sets of protons of
the O–CH2–CH2–N group. These are therefore the
protons which are most affected by increased Yb–N
interaction. It is interesting to note that with decreasing
temperature the signals of the O–CH2–CH2–N protons
are shifted to lower frequencies (upfield), whereas the
signal for the methylene protons of the N–CH2–CH3
groups is shifted to higher frequencies (downfield)
(Fig. 7). Again the line broadening for the methyl pro-
tons of the ethyl group is relatively small compared to
the methylene protons. Also the chemical shift is fairly
constant. The signal of the methyl protons shifts to
slightly higher frequencies (downfield) at low tempera-
ture. This indicates that the methyl group is not signif-
icantly influenced by the increased interaction between
Yb and N. The chemical shift for the Cp protons is also
very constant, it is shifted to slightly lower frequencies
(upfield) at lower temperatures. Seemingly, the Cp
ligands are less affected by the increased interaction
between Yb and N. This reflects also the line widen-
ing, which is much smaller than it is for the
dimethylaminoalcoholato complex.
found in the solid state and those where the N donor was
not bound to Yb. This should allow the potential for ca-
talysis in these formally coordinatively unsaturated
compounds.
4. Experimental
All reactions were carried out under inert atmosphere
such as argon or purified dinitrogen gas using Schlenk,
vacuum line and glovebox techniques. All solvents were
refluxed for several days over a sodium benzophenone
mixture and were freshly distilled when required. All
glassware was flamed out and purged with inert gas for
several times before use. Dicyclopentadiene and alcohols
were purchased from Aldrich Chemical Co. NaCp was
synthesised from the reaction of sodium metal with an
excess of freshly cracked CpH in thf. [YbCp3(thf)] or
[YbCp3] [45] was prepared according to literature pro-
cedures. NMR experiments were performed using a
Bruker AVANCE DRX 400 Spectrometer: 1H NMR
(400.13 MHz) in CDCl3, standard TMS. FT-IR-Spectra
were recorded between 400 and 4000 cmꢂ1 using a
Perkin–Elmer (System 2000) spectrometer.
3. Conclusions
Treatment of [YbCp3(thf)] with 2,6-di-tert-butylphe-
nol, dimethylaminoethanol or diethylaminoethanol re-
sulted in clean substitution of a Cp ligand with the
4.1. Syntheses
t
4.1.1. Preparationof[YbCp2(O-C6H3 Bu2-2,6)(thf)](1)
t
t
alcoholato ligand yielding [YbCp2(O-C6H3 Bu2-
[YbCp2(O-C6H3 Bu2-2,6)(thf)] was prepared by the
2,6)(thf)], [{YbCp2(l-OCH2CH2NMe2)}2] and [{YbCp2
(l-OCH2CH2NEt2)}2] ꢀ (thf)2, respectively. The sterically
demanding phenolato ligand stabilises a monomeric
structure while for the bifunctional ligands, centrosym-
metric dimers were isolated. Variable-temperature 1H
NMR studies showed that for the latter two compounds,
there exists an equilibrium in solution between complexes
addition of 2,6-di(tert-butyl)phenol (0.056 g, 0.27 mmol)
in 5 mL thf to [YbCp3(thf)] (0.12 g, 0.27 mmol) in thf
(15 mL). After stirring at rt for 6 h, the red solution was
filtered, concentrated and cooled to )15 °C giving (1) as
a red powder. Recrystallisation from thf gave large red
crystals of the title compound. Yield: 0.11 g (73%). IR
(KBr; in cmꢂ1): ~m ¼ 3083 w, 3021 w, 2962 s, 2909 m,

2132
T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
2874 w, 1426 m, 1403 m, 1261 s, 1097 s, 1018 s, 860 m,
802 s, 747 m, 402 m, 394 m, 386 m.
Centre as supplementary publication numbers CCDC
223178–223180. Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: (+44) 1223 336-033;
email: deposit@ccdc.cam.ac.uk).
4.1.2. Preparation of [{YbCp2(l-OCH2CH2NMe2)}2]
(2)
[YbCp3(thf)] (0.17 g, 0.39 mmol) was dissolved in
dried thf (15 mL). To this green solution was slowly
added N,N-dimethyl-2-aminoethanol (0.039 ml, 0.39
mmol) in thf (5 mL). The resulting orange-yellow solu-
tion was stirred at room temperature for 2 h. The so-
lution was concentrated to half its volume and cooled to
)15 °C. Orange-yellow single crystals suitable for X-ray
analysis deposited after several days. Yield: 0.10 g (68
5. Crystal refinement data
5.1. Crystal data for C28H39O2Yb, (1)
M ¼ 580:63, 0.26 ꢃ 0.24 ꢃ 0.12 mm3, monoclinic,
space group P21=c (No. 14), a ¼ 19:3429ð13Þ,
ꢀ
b ¼ 8:4363ð6Þ, c ¼ 17:0342ð12Þ A, b ¼ 114:9220ð10Þ°,
1
%). Mp.: 185 °C (dec.). H NMR (RT): d )23.3 (10 H,
C5H5), 58.7 (2 H, NCH2), 64.6 (6 H, NCH3), 75.7 (2 H,
OCH2) ppm. For VT 1H NMR spectra see Figs. 5 and 6.
3
3
ꢀ
V ¼ 2520:8ð3Þ A , Z ¼ 4, Dc ¼ 1:530 g/cm , F000 ¼ 1172,
T ¼ 296ð2Þ K, 11,145 reflections collected, 3628 unique
(Rint ¼ 0:0872). Final GooF ¼ 1:007, R1 ¼ 0:0411,
wR2 ¼ 0:0991, R indices based on 3130 reflections with
I > 2rðIÞ (refinement on F 2), 286 parameters, 0 restraints.
4.1.3. Preparation of [{YbCp2(l-OCH2CH2NEt2)}2] ꢀ
3 (thf)2 (3)
Lp and absorption corrections applied, l ¼ 3:731 mmꢂ1
5.2. Crystal data for C28H40N2O2Yb2, (2)
.
In a similar manner to that described above
[YbCp3(thf)] (0.12 g, 0.27 mmol) was treated with N,N-
diethyl-2-aminoethanol (0.036 ml, 0.27 mmol), yielding
after similar work up orange-yellow crystals of the title
M ¼ 782:70, 0.30 ꢃ 0.20 ꢃ 0.20 mm3, monoclinic,
1
compound. Yield 86%. H NMR (RT) d )56.3 (10 H,
space group C2=c (No. 15), a ¼ 13:9757ð12Þ, b ¼
C5H5), 48.6 (6 H, NCH2CH3), 77.3 (4 H, NCH2CH3),
176.0 (2 H, NCH2), 232.1 (2 H, OCH2) ppm. For VT 1H
NMR spectra see Fig. 5 and 6. IR (KBr; in cmꢂ1):
ꢀ
A,
9:3595ð8Þ,
c ¼ 21:0611ð19Þ
b ¼ 103:008ð2Þ°,
3
3
ꢀ
V ¼ 2684:2ð4Þ A , Z ¼ 4, Dc ¼ 1:937 g/cm , F000 ¼ 1512,
T ¼ 296ð2Þ K, 6000 reflections collected, 1935 unique
(Rint ¼ 0:0552). Final GooF ¼ 1:058, R1 ¼ 0:0361,
wR2 ¼ 0:0957, R indices based on 1535 reflections with
I > 2rðIÞ (refinement on F 2), 154 parameters, 10 re-
straints. Lp and absorption corrections applied,
~
m ¼ 3092 w, 2968 s, 2936 m, 2871 m, 2851 m, 2817 m,
1631 w, 1530 w, 1475 m, 1460 m, 1441 m, 1372 m, 1261
s, 1097 s, 1078 s, 1038 s, 1013 s, 916 m, 896 m, 780 s, 733
w, 590 w.
l ¼ 6:952 mmꢂ1
.
The thf-free complex [{YbCp2(l-OCH2CH2NEt2)}2]
was obtained from [YbCp3] and N,N-diethyl-2-amino-
ethanol in toluene.
5.3. Crystal data for C20H24NO3Yb, (3)
4.2. X-ray crystallography
M ¼ 499:44, 0.30 ꢃ 0.24 ꢃ 0.22 mm, orthorhombic,
space group Pnma (No. 62), a ¼ 9:5581ð9Þ,
3
ꢀ
ꢀ
All X-ray quality crystals were sealed and mounted in
thin walled capillaries, with hemispheres of data col-
lected at room temperature on a Bruker SMART 1000
CCD diffractometer, MoKa radiation (k ¼ 0:71073 A),
b ¼ 30:572ð3Þ, c ¼ 13:6722ð13Þ A, V ¼ 3995:1ð6Þ A ,
Z ¼ 8, Dc ¼ 1:661 g/cm3, F000 ¼ 1960, Bruker SMART
1000 CCD diffractometer, MoKa radiation, k ¼ 0:71073
ꢀ
ꢀ
A, T ¼ 296ð2ÞK, 2hmax ¼ 46:6°, 17,483 reflections col-
using the omega scan mode with total reflections and
unique data listed below. Data sets were corrected for
absorption using the program SADABS [46]. Structures
were solved using the Patterson method and refined on
F 2 using SHELXL-97-2 [47] with X-SEED as the graphic
interface [48]. All non-hydrogen atoms were located and
were refined with anisotropic thermal parameters. Hy-
drogen atoms were placed in calculated positions (riding
model) and were not refined. Details of the X-ray data
collection and refinements appear below and selected
bond lengths and angles are compiled in tables.
lected, 2942 unique (Rint ¼ 0:0553). Final GooF ¼ 1:155,
R1 ¼ 0:0414, wR2 ¼ 0:1083, R indices based on 2362
reflections with I > 2rðIÞ (refinement on F 2), 244 pa-
rameters, 36 restraints. Lp and absorption corrections
applied, l ¼ 4:698 mmꢂ1
.
Acknowledgements
We thank the DFG (Graduate College ‘‘Mechanistical
and Applicational Aspects of Non-conventional Oxidation
Reactions’’) for generous support (T.H., E.H.-H.). We
are grateful to the Australian Research Council for
continued support (P.J.).
Crystallographic data (excluding structure factors)
for the structure reported in this paper have been de-
posited with the Cambridge Crystallographic Data

T. Hahn et al. / Inorganica Chimica Acta 357 (2004) 2125–2133
2133
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