Tris-pyrazolylborate complexes of redox inactive lanthanides - The structures of [(TpMe2)2NdX] (X=Cl, NPh2, dpm, H2BEt2)

Article abstract of DOI:10.1016/j.poly.2003.11.014

A range of complexes of Ce and Nd have been prepared to compare the chemistry of the non-reducible [(Tp^Me2)₂LnX] (Ln=Ce, Nd) with that reported previously for the redox-active samarium ion. The chloride [(Tp^Me2)₂NdCl] is a useful starting material for the preparation of the seven coordinate [Nd(Tp^Me2)₂OAr] (Ar=C₆H₄-4-X; X=H, Bu^t, Br, Ph, OMe, F, Me) and [Nd(Tp^Me2)₂NPh₂]. Crystal structures of [Nd(Tp^Me2)₂Cl] and [Nd(Tp^Me2) ₂NPh₂] are isostructural with those of the analogous samarium species. The eight coordinate species [Nd(Tp^Me2) ₂(β-dike)] (β-dike=(RC=O)₂CH, R=Me, Ph; Bu ^t) and their cerium analogues (R=Ph, Bu^t) have also been prepared. The complexes are fluxional, the extent of this behaviour depending on the steric bulk of the substituents. The structure of [Nd(Tp ^Me2)₂(Bu^tCO)₂CH] has been determined. Finally, in efforts to prepare a neodymium hydride, the unexpected borohydride [Nd(Tp^Me2)₂(H₂BEt₂)] has been isolated serendipitously and structurally characterized.

Full text of DOI:10.1016/j.poly.2003.11.014

Polyhedron 23 (2004) 253–262
www.elsevier.com/locate/poly
Tris-pyrazolylborate complexes of redox inactive lanthanides –
the structures of [(TpMe2)2NdX] (X ¼ Cl, NPh2, dpm, H2BEt2) q
Jennifer L. Galler , Sam Goodchild , James Gould , Robert McDonald ,
a
a
a
b
a,
*
Andrea Sella
a
Christopher Ingold Laboratories, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
b
Department of Chemistry, University of Alberta, Edmonton, Alta. T6G 2G2, Canada
Received 15 May 2003; accepted 22 August 2003
Abstract
A range of complexes of Ce and Nd have been prepared to compare the chemistry of the non-reducible [(TpMe2)2LnX] (Ln ¼ Ce,
Nd) with that reported previously for the redox-active samarium ion. The chloride [(TpMe2)2NdCl] is a useful starting material for
the preparation of the seven coordinate [Nd(TpMe2)2OAr] (Ar ¼ C6H4-4-X; X ¼ H, But, Br, Ph, OMe, F, Me) and
[Nd(TpMe2)2NPh2]. Crystal structures of [Nd(TpMe2)2Cl] and [Nd(TpMe2)2NPh2] are isostructural with those of the analogous sa-
marium species. The eight coordinate species [Nd(TpMe2)2(b-dike)] (b-dike ¼ (RC@O)2CH, R ¼ Me, Ph; But) and their cerium
analogues (R ¼ Ph, But) have also been prepared. The complexes are fluxional, the extent of this behaviour depending on the steric
bulk of the substituents. The structure of [Nd(TpMe2)2(ButCO)2CH] has been determined. Finally, in efforts to prepare a neodymium
hydride, the unexpected borohydride [Nd(TpMe2)2(H2BEt2)] has been isolated serendipitously and structurally characterized.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Lanthanides; Neodymium; X-ray structures; Alkoxides; Pyrazolylborates; Borohydrides
1. Introduction
been developed [1] and nitrogen donor alternatives have
been used by a growing number of workers [2]. The
pyrazolylborates (Tp) [3] have proved extremely effective
in providing a well-defined coordination sphere for the
lanthanides. Both first and second-generation Tp ligands
[3b,3c] have been explored to generate both sandwich
and half-sandwich systems which are resistant to ligand
redistribution and which afford mononuclear products.
In the case of sandwich complexes, use of the easily ac-
cessible TpMe2 ligand has led to a rich divalent reactivity
being uncovered for divalent samarium. [Sm(TpMe2)2]
has been shown to react by electron transfer with oxi-
dizers including O2 [4], azobenzene [5], dichalcogenides
[6,7], metal-metal bonds [8,9] etc. to give trivalent spe-
cies. Hydrides [10] and hydrocarbyls [15] are attractive
synthetic targets for catalyst studies. Unfortunately,
with TpMe2 ligands no hydrides have been observed and
only two complexes containing Sm–C bonds have been
prepared: the acetylide, [Sm(TpMe2)2CCPh], and the cy-
clopentadienyl, [Sm(TpMe2)2(g5-C5H5)] by redox trans-
metallation with mercury phenylacetylide [11] and
The past few years have witnessed the rapid growth of
interest in the lanthanides. This is part driven by a per-
ception of the rare earths as representing a ‘‘last frontier’’
in the periodic table. At the same time the potential ap-
plications of the lanthanides in catalysis, diagnostics, and
materials chemistry have provided a powerful impetus to
this work. A key theme which has underpinned these
developments is the observation that kinetic stabilization
of the metal centre through the use of bulky ancillaries is
critical to the isolation of well-defined species. Although
cyclopentadienyls and their derivatives still dominate the
field, chemistry using other carbocyclic systems have
q Dedicated with admiration and affection to the Great Crawdad of
pyrazolylborate chemistry, Jerry Trofimenko – you have been a
pioneer, an inspiration, and a friend.
* Corresponding author. Fax: +44-0-20-7679-7463/+44-071-380-
7463.
E-mail address: a.sella@ucl.ac.uk (A. Sella).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.11.014

254
J.L. Galler et al. / Polyhedron 23 (2004) 253–262
thallium cyclopentadienide [12], respectively. The weak
basicity of these ligands, however, precludes many pro-
tonolysis reactions. Attempts to use other mercury re-
agents in analogous reaction have failed and metathesis
methods have been equally unsuccessful usually as a re-
sult of reduction of the metal to the highly insoluble
complex [Sm(TpMe2)2] [13,14]. Here we present analo-
gous chemistry to that of samarium using the non-
reducible lanthanides Ce and Nd together with attempts
to prepare hydrides and hydrocarbyls.
)90 °C, apart from the typical Curie dependence of the
chemical shifts Scheme 1.
Metathesis of 1 with NaNPh2 in THF results in the
isolation of [Nd(TpMe2)2NPh2] (3).
½NdðTpMe2Þ ClꢀþNaNPh2 ! ½NdðTpMe2Þ NPh2ꢀþNaCl:
2
2
In striking contrast to its samarium analogue [13], which
is a fairly intense red colour, 3 displays the pale blue/lilac
typical of Nd(III) species. This suggests that the red
colour in [Sm(TpMe2)2NPh2] arises from a LMCT tran-
sition from the amide to the more reducible metal cen-
tre. Like its samarium analogue, 3 gives a more complex
spectrum than 2, indicating a non-fluxional C2 sym-
metric coordination sphere – the phenyl groups of the
amide ligand presumably prevent the methyl groups of
the TpMe2 ligands from rotating around the Sm-B axis
and thereby effectively lock the coordination sphere. The
spectra were assigned on the basis of the integrals and
the line widths of the methyl groups in the 3-positions
which are expected to be significantly broader than
those in the 5-position. Curiously, the ortho hydrogens
of the NPh2 were quite sharp, showing a normal 6 Hz
coupling to their neighbours. The meta and para pro-
tons, on the other hand, were strongly broadened by the
neodymium centre.
By contrast to the synthesis of the NPh2 derivative,
attempts to prepare the corresponding N(SiMe3)2 com-
plex by metathesis of 1 in THF using KN(SiMe3)2 were
not successful and gave greenish mixtures of products
indicative of TpMe2 decomposition. Attempts to prepare
the corresponding diethylamide complex by metathesis
with LiNEt2 resulted in recovery of starting material
and significant amounts of LiTpMe2. Such transfers of
Tp ligands from rare earths to lithium or magnesium
have been reported sporadically and presumably reflect
the size mismatch between the large lanthanide centre,
the rather tight Tp ligand [3,15] and the stronger, more
covalent bonding in the latter metals.
2. Results and discussion
Reaction of NdCl3 with either Na or KTpMe2 in THF
leads to the formation of the pale blue complex
[Nd(TpMe2)2Cl] (1) in variable yields although the use of
NdCl3(THF)2 proved to be a rather more reliable.
NdCl3 þ 2KTpMe2 ! ½NdðTpMe2Þ Clꢀ þ 2KCl
2
Like its samarium analogue 1 dissolves in THF and ar-
omatic solvents, but not in petroleum ether, and give
simple, though paramagnetically shifted 1H spectra
consistent with a fluxional coordination sphere. The Eu
analogue 1-Eu may be prepared analogously, has simi-
lar solubility, and is obtained in similar yield. 1-Eu can be
reduced readily to the known insoluble orange divalent
complex [Eu(TpMe2)2] by stirring with sodium chips [14].
Attempts to prepare the analogous complex with yt-
trium, [Y(TpMe2)2Cl], was not successful – no significant
soluble products were isolated apart from dimethylpy-
razole, indicating extensive decomposition.
Compound 1 is a useful starting material for a range
of derivatives. Reaction of 1 with NaOAr (Ar ¼ C6H4-4-
R) gives seven coordinate phenoxides, [Nd(TpMe2)2OAr]
(Ar ¼ C6H5 (2a); C6H4-4-But (2b); C6H4-4-Br (2c);
C6H4-4-Ph (2d); C6H4-4-OMe (2e); C6H4-4-F (2f);
C6H4-4-Me (2g)) analogous to the samarium complexes
some of which have been crystallographically charac-
terized and have been or will be reported elsewhere
[13,17].
Metathesis of 1 with sodium b-diketonates in THF
results in the isolation of eight-coordinate complexes
[Nd(TpMe2)2(b-dike)] (b-dike ¼ (RC@O)2CH, R ¼ Me,
4-Nd; R ¼ Ph, 5-Nd; R ¼ But, 6-Nd)
NdðTpMe2Þ Cl þ NaOAr ! NdðTpMe2Þ OAr þ NaCl
½NdðTpMe2Þ Clꢀ þ Naðb-dikeÞ
2
2
2
! ½NdðTpMe2Þ ðb-dikeÞꢀ þ NaCl:
Complexes 2a–2g were isolated by pumping down the
filtered reaction mixture and were only characterized by
their 1H NMR spectrum. The aryloxides are fluxional in
solution giving simple spectra with a 9:9:3 pattern of
singlets for the TpMe2 resonances and two broadened
and very strongly shifted resonances for the ortho and
meta hydrogens of the phenyl groups, respectively. The
ortho protons were particularly striking as they gener-
ally appear around +45 ppm as a very broad hump in
the baseline only visible after long accumulation times.
The spectrum of 2a (Ar ¼ C6H5) was invariant down to
2
As with the previous compounds, the diketonates are
soluble in THF and aromatic solvents and moderately
air stable.
The acac complex, 4-Nd (R ¼ Me) gave an unread-
able 1H NMR spectrum at room temperature with a
mixture of sharp and broad peaks. On cooling to 203 K
the spectrum separated into 11 broad peaks, indicating
that the eight-coordinate molecule has C2 symmetry but
it is fluxional at room temperature on the NMR time-

J.L. Galler et al. / Polyhedron 23 (2004) 253–262
255
H
B
H
B
N
N
N
N
N
N
N
N
N
N
N
N
Ph
Ph
HOAr
Nd
N
OAr
Nd
N
N
N
N
N
N
N
N
N
N
N
N
B
H
B
H
2a-2g
3
NaNPh2/THF
NaOAr/THF
H
B
H
B
N
N
N
N
O
N
N
N
N
N
N
N
N
N
N
R
Na(β-dike)/THF
THF
K+
+ NdCl3(THF)2
HBÐ
N
N
Nd Cl
Nd
N
2
O
N
N
N
N
N
N
N
R
N
N
N
N
N
N
B
H
B
H
H
B
4-6
1
N
N
N
N
N
N
"KHBEt3"/Toluene
KR
N
N
H
B
Nd
N
H
B
N
N
N
N
N
N
N
N
N
N
N
H
H
N
N
N
N
N
N
B
H
B
Nd
N
Nd
N
R
N
N
N
N
N
N
N
N
B
H
N
N
B
H
7
Scheme 1.
scale. The corresponding greenish dbm complex
(R ¼ Ph), 5-Nd, on the other hand, is close to the slow
exchange limit at room temperature and gives 13 fairly
sharp lines, again consistent with C2 symmetry. Cooling
the sample results in sharper lines. The dpm (R ¼ But)
complex, 6-Nd, is static at room temperature.
For comparison purposes the corresponding cerium
complexes, [(TpMe2)2Ce(b-dike)] (b-dike ¼ (RC@O)2CH;
dbm, R ¼ Ph, 5-Ce; dpm, R ¼ But, 6-Ce). were also
prepared by metathesis starting, however, from the tri-
flate, [Ce(TpMe2)2OTf] [16], which in our hands is more
easily prepared than the chloride.
symmetric molecule. Assignment of these spectra was
made with the aid of EXSY spectra which, by corre-
lating the exchange pathways, allowed unambiguous
assignment of the methyl peaks to the 3- or 5-positions,
respectively. Contrary to what has been observed for
the less sterically crowded analogous Tp systems, there
is no indication that and of the species 4, 5, and 6 ex-
change by anything other than an intramolecular mech-
anism [18].
We attempted to convert 1 to the corresponding
fluoride, the samarium analogue of which has been
prepared previously by redox chemistry [14], and which
we hoped might prove an even more useful starting
material. Unfortunately, metathesis with both KF and
AgF led only to the recovery of the starting material.
A number of attempts were made to introduce a hy-
dride or a hydrocarbyl group into the metal coordina-
tion sphere, all of which were unsuccessful. The reaction
of 1 with an aged sample of potassium superhydride,
‘‘KHBEt3’’ in toluene, a reagent which has been used
½CeðTpMe2Þ OTfꢀ þ Naðb-dikeÞ
2
! ½CeðTpMe2Þ ðb-dikeÞꢀ þ NaOTf:
2
While the 1H NMR spectrum of 6-Ce is fairly sharp and
readable at room temperature, that of the dbm complex,
5-Ce, is rather broad and sharpens up on cooling to )40
°C. In both cases the static spectrum indicates a C2

256
J.L. Galler et al. / Polyhedron 23 (2004) 253–262
previously by Takats to prepare hydride complexes
[15], resulted instead in the isolation of crystals of the
unexpected complex [Nd(TpMe2)2(H2BEt2)] which was
crystallographically, but not spectroscopically, charac-
terized (vide infra). Examination of the 11B NMR
spectrum of the potassium superhydride stock solution
used in the reaction showed this to consist of a mixture
of KH2BEt2and KBEt4 as has been observed previously
by Fryzuk [19] and Morris [20]. We do not believe that
the fact that this behaviour has only ever been observed
in Canada is of any great chemical significance. Thus the
reaction may be seen as follows:
counterparts reported elsewhere, 1 [13,14]. A view of the
molecular structures of 1 and 3 are shown in Figs. 1 and
2. Both compounds are seven coordinate adopting a
distorted pentagonal bipyramidal metal coordination
sphere and show virtually identical metrical parameters
as their analogues, allowing for the difference in ionic
radius of the metal. We feel it is unnecessary to discuss
them further.
The dpm complex, 6-Nd, is also largely unremark-
able, crystallizing with two independent molecules in the
asymmetric unit. The differences between the two are
insignificant. The eight-coordinate molecule shows the
expected tridentate TpMe2 and the bidentate dpm li-
gands. A view of the molecular structure of 6-Nd is
shown in Fig. 3. Although the complex does not have
any crystallographically imposed symmetry, the mole-
½NdðTpMe2Þ Clꢀ þ KH2BEt2
2
! ½NdðTpMe2Þ ðH2BEt2Þꢀ þ KCl:
2
The reaction was repeated several times with an au-
thentic sample of KHBEt3 in THF (the toluene solution
being no longer commercially available). Unfortunately
such reactions resulted in extensive decomposition and
ligand redistribution and only the fluxional pyrazolide
complex [Nd(TpMe2)2(3,5-dmpz)] could be isolated in
low yields. While frustrating, this decomposition reac-
tion is intriguing since it may point to the formation of a
transient hydride which then attacks one of the TpMe2
ligands, in a manner similar to what we have proposed
recently for the hydrolytic decomposition of these li-
gands at lanthanide centres [21]. Other attempts to
prepare this elusive terminal hydride from 1 using KH,
by analogy with BaudryÕs work [22], or by reaction with
Ph2SiH2 and Ph3SnH, resulted only in the recovery of
the starting material.
1
cule is effectively C2 symmetric consistent with the H
NMR spectra. The geometry around the metal is do-
decahedral, as has been observed previous for other
eight-coordinate TpMe2 complexes of the lanthanides
[24]. This is in contrast to the Tp complexes which tend
to favour square antiprismatic coordination sphere [3a].
Such differences can be attributed to minimization of
contacts between the methyl groups of the TpMe2 and
dpm ligands. As has become typical in rare earth
structures with TpMe2 [3c], twisting of some of the pyr-
azolyl groups around the B–N bond is observed. For 6-
Nd two pyrazolyl groups on the same ligand and one on
the other twist by between 23° and 26° in opposite di-
rections to accommodate the dpm ligand in the wedge
between them.
The final molecule, 7, is rather more interesting as a
result of the coordination of the unusual H2BEt2 ligand.
A view of the molecular structure of 7 is shown in Fig. 4.
The compound crystallized in the space group C2/c with
a somewhat disordered molecule of pentane in the lattice
and showed no intermolecular contacts. The molecule
lies on a crystallographic C2 axis. The two tridentate
TpMe2 ligands are partnered by a bidentate H2BEt2 li-
gand, a species which has only been characterized once
before [20]. Formally, therefore the molecule is eight-
coordinate. However, the average Nd–N distance,
Attempts to introduce hydrocarbyl groups into the
coordination sphere using potassium reagents (e.g.
KCH2SiMe3) simply gave greenish solutions from
which, again, only small amounts of [Nd(TpMe2)2(3,5-
dmpz)] could be recovered. Reaction of the silver acet-
ylide cluster ‘‘(AgBut)14’’ [23] with 1, with a view to
preparing [Nd(TpMe2)2(CBCBut)] by metathesis gave no
detectable reaction apart from the formation of some
silver metal. We presume that the stability of the silver
acetylide cluster is such as to overcome the driving force
provided by the precipitation of AgCl.
ꢀ
ꢀ
2.602(6) A, is closer to those in 1, 2.59(1) A and 3,
Thus the problem of preparing the, presumably
highly reactive, hydride and hydrocarbyl species with
these ancillaries remains intractable.
ꢀ
2.582(6) than that seen for 6, 2.634 A, and is consistent
with the fact that the bite angle of the small bidentate
borohydride is fairly tight and the complex may be
thought of has having an intermediate coordination
number. Nevertheless one pyrazolyl groups of the TpMe2
ligands shows a 35° twist, once more away from the
3. X-ray crystallography
ꢀ
third ligand. The Nd–B distance, 2.883(8) A is signifi-
Single crystals of compounds 1, 3, 6-Nd, and 7 were
obtained and their structures have been determined.
Selected crystallographic and experimental details for all
four structures are given in Table 1. Selected bond
lengths and angles are reported in the Figure captions.
Compounds 1 and 3 are very similar to their samarium
cantly longer than that in [Nd(C5H4CH2CH2OMe)2
ꢀ
ꢀ
2.68, 2.74 A. [26] and in [K(18-crown-6){Nd(C13H8)
(BH4)], 2.66(3) A [25], [Nd2(l-C7H7)(THF)4(BH4)3],
ꢀ
ꢀ
CPh2(C5H4)(BH4)2}]2, 2.641(8) A, 2.623(7) A [27] all
of which contain tridentate BH4 ligands. The longer
distance is consistent with the bidentate binding mode

J.L. Galler et al. / Polyhedron 23 (2004) 253–262
257
Table 1
Compound
1
3
6-Nd
7
A. Crystal data
Formula
C30H44B2ClN12Nd
774.08
C42H54B2N13Nd
906.84
C41H63B2N12NdO2
921.89
C36:5H62B3N12Nd
845.65
Formula weight
Crystal dimensions (mm)
Crystal color, habit
Crystal system
0.30 ꢁ 0.30 ꢁ 0.29
pale blue, prism
orthorhombic
Pna21 (No. 33)
0.23 ꢁ 0.18 ꢁ 0.16
pale blue, prism
trigonal
0.38 ꢁ 0.37 ꢁ 0.32
pale blue, prism
triclinic
0.50 ꢁ 0.38 ꢁ 0.31
pale blue, prism
monoclinic
Space group
Unit cell parametersa
R3c (No. 167)
P1 (No. 2)
C2=c (No. 15)
ꢀ
a (A)
18.6429 (13)
10.2665 (7)
18.4475 (13)
25.4664 (6)
12.6560 (8)
17.7835 (11)
21.1954 (13)
81.5820 (12)
84.1022 (12)
80.3489 (11)
4637.2 (5)
4
15.7054 (11)
15.9634 (11)
19.5882 (13)
ꢀ
b (A)
ꢀ
c (A)
38.2875 (18)
a (°)
b (°)
c (°)
112.9030 (11)
3
ꢀ
V (A )
3530.8 (4)
4
21504.2 (12)
18
1.260
4523.8 (5)
4
Z
qcalc: (g cmꢂ3
l (mmꢂ1
)
1.456
1.586
1.320
1.167
1.242
1.186
)
1.129
B. Data collection and refinement conditions
Diffractometer
Bruker PLATFORM/SMART 1000 CCDb
graphite-monochromated
ꢀ
Radiation (k [A])
Mo Ka (0.71073)
Temperature (°C)
Scan type
)80
)80
)80
)80
x scans (0.2°)
(25 s exposures)
52.78; 100%
18922
x scans (0.2°)
(25 s exposures)
52.76; 99.9%
34583
x scans (0.2°)
(25 s exposures)
52.74; 97.9%
26269
x scans (0.2°)
(20 s exposures)
52.84; 99.4%
11019
Data collected 2h limit (°); completeness
Total data collected
Independent reflections ðRint
Þ
6426 (0.0367)
5454
direct methods
4899 (0.0543)
4185
Patterson search
18578 (0.0186)
15956
direct methods
4621 (0.0264)
4099
Patterson search/
Observed reflections (NO[Fo2 P rFo2Þ])
Structure solution method
c
c
(SHELXS-86
)
structure expansion
d
(
SHELXS-86
)
structure expansion
d
(
DIRDIF-96
)
(
DIRDIF-96
)
e
Refinement method
Absorption correction method
full-matrix least-squares on F 2
multi-scan
(
multi-scan
SHELXL-93 )
Gaussian integration
(face-indexed)
0.7065–0.6655
multi-scan
(SADABS)
(SADABS)
0.6563–0.6476
6426/0/428
(SADABS)
0.8400–0.7813
4899/0/269
Range of transmission factors
Data [Fo2 P ꢂ 3rðFo2Þ]/restraints/
params
0.7100–0.5885
4621/4f /241
18578/0/1063
Flack absolute structure parameterg
0.493 (14)
1.038
Goodness-of-fit ðS½Fo2 P ꢂ 3rðFo2ÞꢀÞ
1.166
1.021
1.160
h
Final R indicesi
R1ðF Þ½Fo2 P rðFo2Þꢀ
0.0304
0.0702
0.0388
0.1430
0.0294
0.0776
0.0420
0.1295
wR2ðF 2Þ½Fo2 P ꢂ 3rðFo2Þꢀ
ꢂ3
ꢀ
Largest difference peak and hole (e A
)
0.992; )0.334
1.789; )0.321
0.857; )0.430
1.589; )0.576
a 1: obtained from least-squares refinement of 4361 reflections from the data collection with 4.37°<2h<52.63°; 3: 5814 reflections with
4.52°<2h<52.49°; 6-Nd: 6399 reflections with 4.69°<2h<52.72°; 7: 7908 reflections with 4.51°<2h<52.74°.
b Programs for diffractometer operation, data collection, data reduction and absorption correction were those supplied by Bruker.
c Sheldrick, G.M. Acta Crystallogr. 1990, A46, 467–473.
d Beurskens, P.T., Beurskens, G., Bosman, W.P., de Gelder, R., Garcia Granda, S., Gould, R.O., Israel, R., Smits, J.M.M. (1996). The DIRDIF-96
program system. Crystallography Laboratory, University of Nijmegen, The Netherlands.
e Sheldrick, G.M. SHELXL-93. Program for crystal structure determination. University of Gottingen, Germany, 1993.
€
f
ꢀ
Distances0 within the solvent n-pentane molecule were given fixed idealized values: d(C1S–C2S) ¼ d(C2S–C3S) ¼ 1.54 A; d(C1Sꢃ ꢃ ꢃC3S) ¼
0
ꢀ
d(C2Sꢃ ꢃ ꢃC2S ) ¼ 2.51 A (C2S is related to C2S via rotation about the crystallographic twofold axis (0, y, 1/4)).
g Flack, H.D. Acta Crystallogr. 1983, A39, 876–881. The Flack parameter will refine to a value near zero if the structure is in the correct con-
figuration and will refine to a value near one for the inverted configuration. The value observed for 1 is indicative of racemic twinning, and was
accomodated during the refinement (using the SHELXL-93 TWIN instruction [see Ref. d]).
P
h S ¼ ½ wðFo2 ꢂ Fc2Þ =ðn ꢂ pÞꢀ (n, number of data; p, number of parameters varied; w ¼ ½r2ðFo2Þ þ ðA0PÞ þ A1Pꢀꢂ1, where P ¼ ½Max:ðFo2; 0Þ þ
2Fc2ꢀ=3 and A0 and A1 are coefficients adjusted as suggested by the refinement program; for 1, A0 ¼ 0:0391 and A1 ¼ 0; for 3, A0 ¼ 0:0894 and
A1 ¼ 49:1609; for 6-Nd, A0 ¼ 0:0406 and A1 ¼ 2:4216; for 7, A0 ¼ 0:0747 and A1 ¼ 7:8740).
2
1=2
2
P
P
P
P
2
1=2
i R1 ¼ jjFoj ꢂ jFcjj= jFoj; wR2 ¼ ½ wðFo2 ꢂ Fc2Þ = wðFo4Þꢀ
.

258
J.L. Galler et al. / Polyhedron 23 (2004) 253–262
Fig. 3. ORTEP view of the molecular structure of [Nd(TpMe2)2(dpm)]
ꢀ
(6-Nd), hydrogens omitted for clarity. Selected bond lengths (A) and
angles (°) for molecule A. Nd–O1 2.257(2), Nd–O2 2.393(2), Nd–N(12)
2.668(2), Nd–N(22) 2.595(2), Nd–N(32) 2.706(2), Nd–N(42) 2.706(2),
Nd–N(52) 2.536(2), Nd–N(62) 2.636(2), Nd–B(1) 3.679(2), Nd–B(2)
3.599(2), B1–Nd–B2 141.3(2).
Fig. 1. ORTEP view of the molecular structure of [Nd(TpMe2)2Cl] (1),
ꢀ
hydrogens omitted for clarity. Selected bond lengths (A) and angles (°):
Nd–Cl 2.676(1), Nd–N(12) 2.488(3), Nd–N(22) 2.570(4),Nd–N(32)
2.713(4), Nd–N(42) 2.487(4), Nd–N(52) 2.672(4), Nd–N(62) 2.596(4),
Nd–B(1) 3.555(1), Nd–B(1) 3.605(1), B1–Nd–B2 144.2(1).
Fig. 4. ORTEP view of the molecular structure of [Nd(TpMe2
)
2
Fig. 2. ORTEP view of the molecular structure of [Nd(TpMe2)2NPh2],
3, hydrogens omitted for clarity. Primed atoms are related to unprimed
via the crystallographic twofold axis (0, y, 1/4). Selected bond lengths
(H2BEt2)] (7), non-borohydride hydrogens omitted for clarity. Primed
atoms are related to unprimed via the crystallographic twofold axis (0,
ꢀ
y, 1/4). Selected bond lengths (A) and angles (°): Nd–B(2) 2.883(8),
Nd–N(12) 2.660(4), Nd–N(22) 2.523(4), Nd–N(32) 2.624(3), Nd–B(1)
ꢀ
(A) and angles (°): Nd–N(1) 2.480(5), Nd–N(12) 2.498(3), Nd–N(22)
2.612(3),Nd–N(32) 2.635(4), Nd–B 3.555(5), B–Nd–B0 151.6(2).
3.590(5), B(1)–Nd–B(1)0 144.8(2).

J.L. Galler et al. / Polyhedron 23 (2004) 253–262
259
of the BH2Et2 ligand and the rather crowded metal
centre.
Infrared (IR) spectra were recorded as KBr pellets on
a Nicolet 205 or BOMEM MB100 FTIR spectrometer.
NMR samples were prepared in the dry box and sealed
under vacuum. 1H NMR spectra in solution were
recorded on Bruker AM400 FT spectrometers at 400
MHz, respectively. 11B NMR spectra were recorded on
the Bruker AM400 instrument at 128 MHz. Spectra
were calibrated using residual proton resonances and
are reported relative to tetramethylsilane (TMS). 11B
chemical shifts are reported relative to external
F3BOEt2. Elemental analyses were determined by
Mr. Alan Stones of the UCL Analytical Services or the
Microanalytical Laboratory, Department of Chemistry,
University of Alberta.
4. Conclusions
A range of simple seven- and eight-coordinate com-
plexes of cerium and neodymium have been prepared by
metathesis and the structures of [Nd(TpMe2)2Cl] (1),
[Nd(TpMe2)2(NPh2)] (3), and [Nd(TpMe2)2(dpm)], 6-Nd,
have been determined. The behaviour of these com-
plexes is broadly similar to that of the analogous sa-
marium complexes. Thus all the complexes are fluxional,
and the extent to which the dynamics can be slowed at
low temperature depends largely on the steric demand of
the substituents on the non-Tp ligand. Attempts to
prepare thermally stable hydrides and hydrocarbyls
have foundered on the twin rocks of pyrazolyborate
fragmentation or of inappropriate solubilities for the
products. From one of these attempts, the unusual bis-
borohydride complex [Nd(TpMe2)2(H2BEt2)] (7) was
isolated and its structure determined.
5.1.1. [Nd(TpMe2)2Cl] (1)
NdCl3 (1.50 g, 3.80 mmol) was suspended in THF (25
cm3) in a round bottom flask. KTpMe2 (2.55 g, 7.58
mmol) was dissolved separately in THF (25 cm3). The
solution of KTpMe2 was added to the NdCl3(THF)2 over
5 minutes. The pale blue solid was seen to dissolve
giving a milky pale blue solution. The suspension was
stirred for 2 h and then the solvent was removed under
reduced pressure. The pale blue residue was extracted
with several portions of warm toluene (total volume 50
cm3), centrifuging each time to remove undissolved salt.
Concentrating the solution to 25 cm3 and cooling to )20
°C) yielded an analytically pure pale blue powder. Yield:
1.66 g (56%). A second crop was obtained. Total yield:
1.94 g (66%). IR (KBr, cmꢂ1): 2563 (BH). 1H NMR
(C6D6, 298 K): )6.75 (s, 18H, 3-Me); 2.83 (s, 18H, 5-
Me); 7.62 (s, 6H, CH). 13C NMR (CDCl3, 298 K): 11.2
(q, 3 or 5Me); 14.2 (q, 5 or 3Me); 105.4 (d, 4-C); 145.5
(s, 3- or 5-C); 149.4 (s, 5- or 3-C). Anal. Calc. for
C30H44N12B2ClNd: C, 46.55; H, 5.73; N, 21.79. Found:
C, 46.60; H, 5.71; N, 21.40%.
5. Experimental
5.1. General procedures
All preparations and subsequent manipulations were
carried out using standard Schlenk line and dry box
techniques in an atmosphere of dinitrogen. Oxygen-free
nitrogen was further purified by passage over columns
containing BASF Cu based catalyst (RE-11) at 100 °C
and Aquasorb (Mallinkrodt, P2O5 on an inert support) or
ꢀ
3 A molecular sieves and MnO. Glassware was routinely
dried at 250 °C and cooled by a nitrogen atmosphere
prior to use. All solvents were pre-dried over 5 A mo-
ꢀ
lecular sieves or sodium wire (UCL). Hexane and pentane
were washed with sulfuric acid, dried over MgSO4 prior
to distillation (U of A). The solvents were distilled from
appropriate drying agents before use; Na (toluene, hex-
ane, HMPA), K (benzene), K/benzophenone ketyl
(THF), Na/K alloy (petroleum ether b.p. 4060 °C, pen-
tane, diethyl ether), CaH2 (CH2Cl2). The deuterated
solvents for NMR (THF-d8, benzene-d6 and toluene-d8)
were vacuum distilled from Na/K alloy (1:3), CDCl3 from
P2O5. All solvents were degassed prior to use.
NdCl3 was prepared from Nd2O3 by the HCl/NH4Cl
method. NdCl3(THF)2 was prepared by Soxhlet extraction
of anhydrous NdCl3 with THF. The THF content was
confirmed by elemental analysis. The ligands, potassium
and sodium hydrotris(3,5-dimethylpyrazolyl) borate (Na/
KTpMe2), were prepared by standard methods [28].
NaNPh2 wasprepared by heating HNPh2 withexcessNaH
in THF, followed by removal of solvent. [Ce(TpMe2)2OTf]
was prepared by literature procedures [16].
5.1.2. [Eu(TpMe2)2Cl] (1-Eu)
1-Eu was prepared from EuCl3 analogously to 1. Yield:
1
69%. IR (KBr, cmꢂ1): 2564 (BH). H NMR (C6D6, 298
K): 10.74 (s, 18H, 3-Me); 1.96 (s, 6H, CH); 1.86 (s, 18H, 5-
Me). Anal. Calc. for C30H44N12B2ClNd: C, 46.55; H, 5.73;
N, 21.79. Found: C, 46.60; H, 5.71; N, 21.40%.
5.1.3. [Nd(TpMe2)2OPh] (2a)
1 (200 mg, 0.26 mmol) and NaOPh were each dissolved
in THF (10 cm3) in separate Schlenk flasks. Addition of
the NaOPh to the solution of 1 resulted in a pale blue/lilac
solution from which a fine white precipitate formed
overnight. Removal of solvent was followed by extraction
into toluene. Removal of the solvent under reduced
pressure gave a pale blue solid. Yield: 110 mg (51%).
IR (KBr) 2553 cmꢂ1. 1H NMR (C6D6, 298 K): )5.66
(s, 18H, 3-Me); 1.24 (s, 18H, 5-Me); 7.41 (s, 6H, 4-CH);
17.48 (br s, 1H, p-Ph); 21.88 (br s, 2H, m-Ph); 44.89 (v br
s, 2H, o-Ph). IR (KBr): 2554 (BH) cmꢂ1. Anal. Calc. for

260
J.L. Galler et al. / Polyhedron 23 (2004) 253–262
C36H49N12B2ONd: C, 51.98; H, 5.94; N, 20.21. Found:
C, 50.34; H, 5.86; N 18.95%.
5.1.10. [Nd(TpMe2)2NPh2] (3)
1 (200 mg, 0.260 mmol) was suspended in THF (6
cm3) in a round bottom flask. NaNPh2 (54 mg, 0.280
mmol) was dissolved separately in THF (4 cm3). The
solution of NaNPh2 was added to the solution of 1 in
four portions. The suspension was stirred for 2 h and
then the solvent was removed under reduced pressure.
The pale blue residue was extracted with warm toluene
(2 cm3), centrifuging to remove undissolved salt. Con-
centrating the solution to 2 cm3 and cooling to )40 °C)
yielded an analytically pure pale blue microcrystals of 3.
Yield: 1.66 g (56%). A second crop was obtained. Total
5.1.4. [Nd(TpMe2)2OPh-4-But] (2b)
t-Butyl phenol (39 mg, 0.26 mmol) was dissolved in
THF and added dropwise to an excess of NaH suspended
in THF and stirred until hydrogen evolution stopped.
The filtered supernatant was added dropwise to a stirred
solution of 1 (200 mg, 0.26 mmol) in THF (10 cm3). The
mixture was stirred overnight and a fine white precipitate
formed. After removal of THF under reduced pressure
the residue was extracted with toluene. The resulting
solution was filtered and pumped down to give an oily
solid. Washing with petroleum ether (b.p. 40/60) gave a
pale blue powder. Yield: 100 mg (43%).
1H NMR (C6D6, 298 K): )5.31 (s, 18H, 3-Me); 1.40 (s,
18H, 5-Me); 7.35 (s, 9H, But); 7.50 (s, 6H, 4-CH); 21.93
(br s, 2H, m-Ph); 44.33 (v br s, 2H, o-Ph). IR (KBr): 2557
(BH) cmꢂ1. Anal. Calc. for C40H57N12B2ONd: C, 54.11;
H, 6.47; N, 18.93. Found: C, 53.02; H, 6.43; N, 18.19%.
1
yield: 1.94 g (66%). H NMR (C6D6, 298 K: )26.72 (s,
6H, 3-Me); )6.34 (s, 2H, CH); )5.74 (s, 6H, 5-Me); )5.1
(br s, 2H, p-Ph); )1.84 (s, 6H, 5-Me); 2.11 (s, 2H, CH);
3.514 (s, 6H, 5-Me); 5.26 (br s, 6H, 3-Me); 6.05 (br s,
4H, m-Ph); 9.55 (d JHH ¼ 6 Hz, 4H, o-Ph); 19.05 (s, 2H,
CH); 23.10 (br s, 6H, 3-Me). Anal. Calc. for C42H54-
N13B2Nd: C, 55.63; H, 6.00; N, 20.08. Found: C, 55.27;
H, 5.72; N, 20.35%.
5.1.5. [Nd(TpMe2)2OPh-4-Br] (2c)
The procedure was analogous to that of 2a. Yield:
5.1.11. [Nd(TpMe2)2(acac)] (4-Nd)
2,4-Pentanedione (26 mg, 0.26 mmol) was added
dropwise to excess NaH suspended in THF. After ef-
fervescence had subsided, the solution was filtered di-
rectly into a solution of 1 (200 mg, 0.26 mmol) in THF
(10 cm3). The resulting yellowish solution was stirred
overnight. Workup as for 2a yielded an oily greenish
solid which was pure by NMR but failed to give reliable
analyses.
IR (KBr, cmꢂ1): 2515. 1H NMR (C7D8, 233 K):
)35.0 (br s, 6H, 3-Me); )8.60 (s, 2H, 4-CH); )9.6 (s, 6H,
3-CH3); )5.5 (s, 6H, 5-Me); 2.32 (s, 6H, 5-Me); 2.38 (s,
6H, 5-Me); 6.02 (s, 2H, 4-CH); 17.0 (s, 2H, 4-CH); 19.0
(s, 6H, acac-Me); 33.0 (s, 6H, 3-Me); 34.5 (s, 1H,
dike-CH). Anal. Calc. for C35H51N12B2O2Nd: C,
50.18; H, 6.13; N, 20.06. Found: C, 47.23; H, 6.00; N,
18.19%.
120 mg (44%) IR (KBr): 2550 cmꢂ1
.
1H NMR (400 MHz, C6D6, 298 K, d ppm): )5.44 (s,
18H 3-Me), 1.31 (s, 18H 5-Me), 7.42 (s, 6H 4-CH), 21.86
(2H Hm), 44.15 (2H Ho).
5.1.6. [Nd(TpMe2)2OPh-4-Ph] (2d)
The procedure was analogous to that of 2a. Yield: 92
mg (38%) IR (KBr): 2550, 2524.
1H NMR (400 MHz, C6D6, 298K, d ppm): )5.66 (s,
18H 3-Me), 0.32 (s, 18H 5-Me), 5.88 (s, 6H 4-CH), 9.75
(1H [Ph2]Hp), 11.39 (2H [Ph2]Hm), 14.64 (2H [Ph2]Ho),
24.67 (2H Hm), 45.05 (2H Ho).
5.1.7. [Nd(TpMe2)2OPh-4-OMe] (2e)
The procedure was analogous to that of 2a. Yield:
124 mg (38%) IR (KBr, cmꢂ1): 2554.
1H NMR (400 MHz, C6D6, 298K, d ppm): )5.00 (s,
18H 3-Me), 0.95 (s, 18H 5-Me), 3.65 (s, 3H, CH3) 10.0
(s, 6H 4-CH), 22.0 (2H Hm), 46.0 (2H Ho).
5.1.12. [Nd(TpMe2)2(dbm)] (5-Nd)
1 (200 mg, 2.60 mmol) and Na(dbm) (64 mg, 2.6
mmol) were dissolved separately in THF (10 cm3) in
Schlenk flasks under nitrogen. The yellow solution
Na(dbm) solution was added dropwise to the solution of
1 with stirring to give a greenish solution. After stirring
overnight the solvent was removed under reduced
pressure and the residue extracted with warm toluene
(2 ꢁ 10 cm3). Crystallisation at )20 °C afforded a
greenish solid. Yield: 0.80 g (33%).
IR (KBr, cmꢂ1): 2500. 1H NMR (C6D6, 298 K:
)21.30 (s, 6H, 3-Me); )3.09 (s, 6H, 3-CH3); )2.03 (s,
6H, 5-Me); 0.57 (s, 6H, 5-Me); 1.00 (s, 6H, 5-Me); 3.80
(s, 2H, 4-CH); 5.20 (br s, 2H, 4-CH); 9.17 (s, 2H, p-Ph);
9.59 (s, 2H, m-Ph); 13.16 (s, 2H, 4-CH); 15.76 (s, 4H, o-
Ph); 22.35 (br s, 6H, 3-Me); 26.56 (s, 1H, dike-CH).
5.1.8. [Nd(TpMe2)2OPh-4-F] (2f)
The procedure was analogous to that of 2a. Yield:
144 mg (50%). IR (KBr, cmꢂ1): 2553.
1H NMR (400 MHz, C6D6, 298K, d ppm): )5.19 (s,
18H 3-Me), 1.16 (s, 18H 5-Me), 7.42 (s, 6H 4-CH), 21.68
(2H Hm), 47.50 (2H Ho).
5.1.9. [Nd(TpMe2)2OPh-4-Me] (2g)
The procedure was analogous to that of 2a. Yield:
165 mg (51%). IR (KBr, cmꢂ1): 2553.
1H NMR (400 MHz, C6D6, 298K, d ppm): )5.11 (s,
18H 3-Me), 1.00 (s, 18H 5-Me), 7.42 (s, 6H 4-CH), 10.63
(s, 3H 4-CH3Ph), 22.63 (2H Hm), 46.13 (2H Ho).

J.L. Galler et al. / Polyhedron 23 (2004) 253–262
261
Anal. Calc. for C45H55N12B2O2Nd: C, 55.84; H, 5.73; N,
17.36. Found: C, 55.60; H, 5.69; N, 17.06%.
(TpMe2)2(NPh2)] (3), [Nd(TpMe2)2(dpm)], (6-Nd), and
[Nd(TpMe2)2(H2BEt2)] (7) have been deposited with the
CCDC, 12, Union Road. Cambridge. CB2 1EZ, UK
(fax: +44-1223-336033; E-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk) with reference
numbers CCDC 210687 1, CCDC 210689 3, CCDC
210688 6-Nd, CCDC 210686 7, respectively.
5.1.13. [Ce(TpMe2)2(dbm)] (5-Ce)
[Ce(TpMe2)2OTf] (500 mg, 5.66 mmol) and Na(dbm)
(141 mg, 5.66 mmol) were mixed in a Schlenk flask
under nitrogen, and dissolved in 20 ml of THF. The
yellow solution was stirred overnight, during which time
a fine white precipitate formed. The solution was filtered
and the solvent removed under reduced pressure, leaving
a bright orange solid. The product was then extracted
with toluene. Recrystallisation afforded a bright orange
crystalline solid. Yield: 0.35 g (64%).
Acknowledgements
This work has been supported by EPSRC and
NSERC Canada. A.S. is grateful to University of Al-
berta for a Visiting Professorship and to UCL for leave
of absence. We are grateful to Dr. Abil Aliev for assis-
tance with the EXSY spectra. A.S. in particular wishes
to acknowledge the contributions of Prof. J. Takats to
this work and for his comments during the preparation
of this manuscript.
1H NMR (CD2Cl2, 213 K: )33.97 (s, 6H, 3-Me);
)4.56 (s, 2H, 4-CH); )2.21 (s, 6H, 5-CH3); )1.70 (s, 6H,
5-Me); )1.00 (s, 6H, 3-Me); 3.78 (s, 6H, 5-Me); 5.42 (s,
2H, 4-CH); 8.89 (s, 4H, m-Ph); 8.96 (s, 2H, p-Ph); 12.70
(s, 4H, o-Ph); 16.75 (s, 2H, 4-CH); 27.5 (br s, 6H, 3-Me);
35.4 (br s, 1H, dike-CH). Anal. Calc. for C45H55N12-
B2O2Ce1: C, 56.43; H, 5.79; N, 17.55. Found: C, 55.88;
H, 6.12; N, 17.92%.
References
5.1.14. [Nd(TpMe2)2(dpm)] (6-Nd)
The compound was prepared analogously with 4.
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(b) F.T. Edelmann, D.M.M. Freckmann, H. Schumann, Chem.
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1
Yield: 120 mg (50%). IR (KBr, cmꢂ1): 2527. H NMR
(C6D6, 298 K): )27.94 (s, 6H, 3-Me); )5.58 (s, 6H, 3-
CH3); )1.94 (s, 6H, 5-Me); 1.23 (s, 18H, But); 2.79 (s,
6H, 5-Me); 5.76 (s, 2H, 4-CH); 7.00 (s, 6H, 5-Me); 14.05
(s, 2H, 4-CH); 16.14 (s, 2H, 4-CH); 20.56 (s, 6H, 3-Me);
25.35 (s, 1H, dike-CH). Anal. Calc. for C41H63N12-
B2O2Nd1: C, 53.41; H, 6.88; N, 18.23. Found: C, 53.87;
H, 6.23; N, 17.99%.
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^
[7] I. Lopes, A.C. Hillier, S.Y. Liu, A. Domingos, J. Ascenso, A.
[Ce(TpMe2)OTf] (0.500 g, 5.66 mmol) and Na(dpm)
(0.117 g, 5.66 mmol) were mixed in a Schlenk flask un-
der nitrogen, and dissolved in 20 cm3 of THF. The
yellow solution was stirred overnight, during which time
a fine white precipitate formed. The solution was filtered
and the solvent removed under reduced pressure, leaving
a bright yellow solid. The product was then extracted
with toluene. Recrystallisation afforded bright yellow
needle crystals. Yield: 0.075 g (15%).
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^
[12] I. Lopes, G. Lin, A. Domingos, R. McDonald, N. Marques,
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1H NMR (CDCl3, 298 K): )26.42 (s, 6H, 3-Me); 0.80
(br s, 6H, 3-CH3); 1.46 (s, 2H, 4-CH); 2.90 (s, 6H, 5-
Me); 3.30 (s, 6H, 5-Me); 4.50 (s, 2H, 4-CH); 6.54 (s, 6H,
5-Me); 7.26 (s, 18H, But); 14.80 (s, 2H, 4-CH); 17.49 (br
s, 6H, 3-Me); 25.90 (s, 1H, dike-CH). Anal. Calc. for
C41H63N12B2O2Ce1: C, 53.65; H, 6.92; N, 18.31. Found:
C, 53.44; H, 6.77; N, 18.50%.
[14] A.C. Hillier, X.W. Zhang, G.H. Maunder, S.Y. Liu, T.A. Ebersp-
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Day, A. Sella, J. Takats, Inorg. Chem. 40 (2001) 5106.
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[17] J.L. Galler, A. Sella, D.A. Tocher, unpublished results.
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6. Supporting information available
X-ray crystallographic files in CIF format for the
structure determinations of [Nd(TpMe2)2Cl] (1), [Nd
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262
J.L. Galler et al. / Polyhedron 23 (2004) 253–262
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