Thorocene adducts of the neutral 2,2′-bipyridine and its radical anion. Synthesis and crystal structures of [Th(η8-C 8H8)2(κ2-bipy)] and [Th(μ-η8:η5-C8H8) 2(κ2-bipy)K(py)2]∞

Article abstract of DOI:10.1016/j.crci.2013.09.006

Thorocene [Th(Cot)₂] (Cot = η⁸-C ₈H₈) readily reacts with 2,2′-bipyridine to give [Th(Cot)₂(κ²-bipy)], which has an unusual bent geometry. This compound is rapidly reduced by KC₈ into the anionic derivative [(Th(Cot)₂(κ²-bipy)]^-. X-ray diffraction studies suggest the latter to be a Th(IV) compound with the bipyridyl radical anion. These complexes are rare examples of bent actinocene [An(Cot)₂(L)]^q- (q = 0, 1; An = actinide) and bipyridine-containing thorium species.

Full text of DOI:10.1016/j.crci.2013.09.006

C. R. Chimie 17 (2014) 526–533
Contents lists available at ScienceDirect
Comptes Rendus Chimie
www.sciencedirect.com
´
Full paper/Memoire
Thorocene adducts of the neutral 2,20-bipyridine and its
radical anion. Synthesis and crystal structures of
[Th(h8-C8H8)2(k2-bipy)] and
[Th(m- :
h8 h5-C8H8)2(k2-bipy)K(py)2]1
*
´
Jean-Claude Berthet , Pierre Thuery, Michel Ephritikhine
CEA, IRAMIS, SIS2M, CNRS UMR 3299, CEA/Saclay, 91191 Gif-sur-Yvette, France
A R T I C L E I N F O
A B S T R A C T
Thorocene [Th(Cot)2] (Cot = h8-C8H8) readily reacts with 2,20-bipyridine to give
[Th(Cot)2(k2-bipy)], which has an unusual bent geometry. This compound is rapidly
reduced by KC8 into the anionic derivative [(Th(Cot)2(k2-bipy)]ꢀ. X-ray diffraction studies
suggest the latter to be a Th(IV) compound with the bipyridyl radical anion. These
complexes are rare examples of bent actinocene [An(Cot)2(L)]qꢀ (q = 0, 1; An = actinide)
and bipyridine-containing thorium species.
Article history:
Received 19 August 2013
Accepted after revision 12 September 2013
Available online 15 December 2013
Keywords:
Thorocene
´
ß 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Uranocene
Bipyridine
Crystal structure
Reduction
Bent geometry
´
´
R E S U M E
Le thoroce`ne [Th(Cot)2] (Cot = h8-C8H8) re´agit imme´diatement avec la 2,20-bipyridine pour
´
Mots cles :
donner le complexe [Th(Cot)2(k2-bipy)], qui presente une geometrie coudee peu courante.
`
Thorocene
´
´
´
´
Ce complexe est rapidement reduit par KC8 en son derive anionique [Th(Cot)2(k2-bipy)]ꢀ.
Uranoce`ne
´
´
´
Bipyridine
La comparaison des structures cristallines des deux compose´s sugge`re que le complexe
Structure cristalline
Re´duction
´
´
reduit est un compose de Th(IV) comportant le radical anion de la bipyridine. Les adduits
´
Th-bipy sont peu nombreux et ces deux complexes sont de rares exemples de composes de
Ge´ome´trie coude´e
formule [An(Cot)2(L)]qꢀ (q = 0, 1 ; An = actinide) avec un fragment actinoce`ne coude´.
ß 2013 Acade´mie des sciences. Publie´ par Elsevier Masson SAS. Tous droits re´serve´s.
1. Introduction
compound, rapidly followed by the synthesis of the
lanthanide (Ln) and actinide (An) derivatives [Mf(Cot)2]qꢀ
Organometallic complexes involving the dianionic Cot
ligand (Cot = h8-C8H8) are predominant species in the f-
element chemistry since Streitwieser et al. reported the
uranium compound [U(Cot)2], the first analogue of
ferrocene with a C8 aromatic ligand, in 1968 [1,2]. The
discovery of this linear and highly symmetric sandwich
(Mf = Th, Pa, Np, Pu, Ce and q = 0 [3–5]; Mf = Ln, U, Th, Pu
and q = 1 [2,6,7]), was an experimental and theoretical
entry for a better understanding of the Mfꢀ ligand bonding.
The weak reactivity of the uranium compound, in
particular, induced considerable debates and interest
[3,8]. For 40 years, the reluctance of the [Mf(Cot)2]qꢀ
(q = 0, 1) species to ligand coordination, attributed to the
steric protection of the two parallel Cot ligands, clearly
evidenced the poor reactivity of these compounds and
their inability to form bent derivatives [9].
*
Corresponding author.
E-mail address: jean-claude.berthet@cea.fr (J.-C. Berthet).
1631-0748/$ – see front matter ß 2013 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2013.09.006

J.-C. Berthet et al. / C. R. Chimie 17 (2014) 526–533
527
However, the first bent [Mf(Cot)2] complexes, obtained
through two different strategies, were recently character-
ized. In 2008, uranocene was found to capture the cyanide
ion, a strongly coordinating ligand with appropriate small
only one but two coordination sites are available on the
bent thorocene fragment (Scheme 1).
Nitrogen molecules are ubiquitous ligands in coordina-
tion chemistry. They can modulate the electronic richness of
size,
to
give
the
mono
cyanide
derivative
the metal centre through their donor and p-accepting
[U(Cot)2(CN)][NR4] [10]. In 2011, the free adducts
[Mf(1,4-{Ph3Si}2C8H6)2]qꢀ (Mf = Ce and q = 1, Mf = U and
q = 0), were also found to adopt a bent geometry as the
result of steric constraints imposed by the very bulky Ph3Si
substituents in 1,4 positions of the Cot ring [11]. These
results incited us to re-examine the coordination chem-
istry of tetravalent actinocenes (U, Th) towards neutral and
anionic ligands.
properties and provide interesting redox activity. They are
also of importance in various fields from extraction
processes to the elaboration of materials with specific
luminescent and/or magnetic properties. However, it is
noteworthy that in contrast to that observed with d-
transition metals, 2,20-bipyridine complexesof the actinides
are not common [18–20], particularly, those involving the
reduced (bipy)ꢀ or (bipy)2ꢀ ligand [21].
Because [U(Cot)2] proved too stable and unreactive
with ligands less coordinating than cyanide, we replaced
Here, we report that, in striking difference with
uranocene, bending of the [Th(Cot)2] fragment is readily
U4+ by the larger Th4+ ion (r(Th4+) ꢁ r(U4+) + 0.05 A) [12],
achieved with 2,20-bipyridine (bipy) to give [Th(Cot)2(k2
bipy)], which can be easily reduced into [Th(Cot)2(k2
-
-
˚
and focused our interest on [Th(Cot)2] (1) which has been
far less studied than its uranium counterpart. Some
chemical features however emerged, which differentiate
thorocene from its uranium congener [13–15], such as the
more facile hydrolysis, the ready formation of the mono-
Cot compound and the lower thermodynamic stability as
observed through competition reactions of the substituted
thorocene and [UCl4]. These differences, attributed to the
less covalent Th ꢀ Cot bonding [15,16], led us to suppose
that further distinct chemical behavior could be revealed.
By considering the more ionic character in thorocene, a
greater mobility of the Cot ligand around the metal centre
was expected, that should be more favorable to ligand
coordination.
In that perspective, a series of coordinating mole-
cules have recently been reacted with thorocene, such
as isonitrile and aromatic nitrogen molecules [17] and
proved to be efficient wedges to open this molecular
sandwich, leading to unique neutral [Th(Cot)2(L)]
complexes with bent geometry (Scheme 1). In the
presence of phenanthroline (phen) or its tetramethyl
derivative, the much more stable compounds
[Th(Cot)2(R4phen)] (R = H, Me), were isolated and the
crystal structure clearly revealed the bidentate coordi-
nation mode of the ligand, thus, demonstrating that not
bipy)]ꢀ, a thorium(IV) complex involving the bipyꢀ radical
anion.
2. Experimental
2.1. Materials and reagents
The complexes described below are moisture sensitive.
Syntheses and manipulations of the compounds were
conducted under ultra-high purity argon atmosphere with
rigorous exclusion of air and water, using Schlenk-vessel
and vacuum-line techniques or in a glove box. The solvents,
toluene, pentane and tetrahydrofuran, were dried over a
mixture of sodium-benzophenone and pyridine over
potassium, and were distilled immediately before use.
Deuterated pyridine (Eurisotop) was distilled over K and
˚
stored over 3 A molecular sieves in the glove box. K2Cot
[2,22], [ThCl4(dme)2] [23] and [U(Cot)2] [1,2] were prepared
as previously described and [Th(Cot)2] (1) [13] was obtained
from a modified method starting from [ThCl4(dme)2][17].
2,20-Bipyridine (bipy), was purchased from Aldrich, dried
undervacuumandstored underargon. The1H NMR signal of
K2C8H8 is at
that of C8H8 is at
signals of pyridine were referenced at
d
6.67 in [D5]pyridine and
5.64 in [D5]pyridine [24]. The 1H NMR
8.57, 7.41 and 7.0. IR
d 5.67 in [D8]THF and
d
d
samples were prepared as Nujol mulls between KBr round
cell windows and the spectra recorded on a PerkinElmer FT-
IR 1725X spectrometer. The 1H and 13C{1H} NMR spectra
were recorded at 23 8C on a Bruker DPX 200 instrument and
referenced internally using the residual protio solvent
resonances relative to tetramethylsilane (d 0). Elemental
analyses were performed by Analytische Laboratorien at
Lindlar (Germany) or by Medac Ltd at Chobham (Surrey,
UK). The systematic low carbon content in the analytical
results for compounds 2 and 3 is presumably due to thorium
carbide formation [15,17,25].
Caution! Depleted uranium (primary isotope 238U) is a
weak
a
-emitter (4.197 MeV) with
a
half-life of
4.47 ꢂ 109 years; natural thorium (primary isotope
232Th) is a weak
a-emitter (4.012 MeV) with a half-life
of 1.41 ꢂ 1010 years; all the manipulations and reactions
should be carried out in monitored fume hoods or in a
glove-box in
a laboratory equipped with a- and
Scheme 1. Reactions of 1 with neutral Lewis bases.
b
-counting equipment.

528
J.-C. Berthet et al. / C. R. Chimie 17 (2014) 526–533
2.2. Syntheses
(3.4 mg), the solution turned purple (Kbipy) and then
became darker. After 1 h at 90 8C, the 1H NMR spectrum
only showed the presence of K2Cot ( = 5.68), free bipy,
[U(Cot)2] and other unidentified paramagnetic Cot signals.
2.2.1. Synthesis of [Th(Cot)2(bipy)] (2)
d
A 25-mL round-bottom flask was charged with 1
(150 mg, 0.34 mmol), bipy (54 mg, 0.34 mmol) and acet-
onitrile (5 mL). A brown solid was immediately formed.
After 1 h at 60 8C, this solid was filtered off, washed with
toluene (2 ꢂ 5 mL) and dried under vacuum for 5 h at 23 8C
(198 mg, 97%). C26H24N2Th requires: C 52.35, H 4.06, N
4.70; found C 51.23, H 4.18, N 5.05. 1H NMR ([D5]pyridine,
The presence of
observed.
a green powder of uranocene was
2.3. Crystallography
The data were collected at 150(2) K on a Nonius Kappa-
23 8C):
J =7 Hz, 2 H); 7.33 (signal partially masked by py, 2 H), 6.14
(s, 16 H, Cot);13C{1H} NMR:
= 148.43, 138.98, 125.72,
d
= 8.61 (broad, 2 H), 8.28 (d, J = 4 Hz, 2 H), 7.78 (t,
CCD area detector diffractometer [26] using graphite-
˚
a radiation (l = 0.71073 A). The
crystals were introduced into glass capillaries with a
protecting ‘‘Paratone-N’’ oil (Hampton Research) coating.
The unit cell parameters were determined from ten
frames, then refined on all data. The data (combinations of
monochromated Mo K
d
122.51, 102.8(Cot). IR (cmꢀ1): 1863 m, 1747 m, 1602 s,
1561 w,1315 s, 1178 m, 1157 s, 1100 w, 1011 s, 922 s,
784 m, 790 s, 777 s, 725 s, 695 s, 642 w. The IR spectrum
of [Th(Cot)2] is: 1865s, 1750s,1631 m, 1602 m, 1316s,
1178w, 1082w, 897s, 791 m, 778 m, 743s, 697s, 507w.
Black crystals of 2 were obtained the by slow diffusion of
Et2O into a pyridine solution, or by heating a MeCN or THF
suspension of 2 at 90 8C for 15 h.
w
- and v-scans giving complete data sets up to u = 308C
and a minimum redundancy of 4 for 90% of the reflections)
were processed with HKL2000 [27]. Absorption effects
were corrected with SCALEPACK [27]. The structures were
solved by direct methods with SHELXS-97, expanded by
subsequent Fourier-difference synthesis and refined by
full-matrix least-squares on F2 with SHELXL-97 [28]. All
non-hydrogen atoms were refined with anisotropic
displacement parameters. The hydrogen atoms were
introduced at calculated positions and were treated as
riding atoms with an isotropic displacement parameter
equal to 1.2 times that of the parent atom. The drawings
were done with ORTEP-3 [29]. Crystal data and structure
refinement parameters are given in Table 1 and the
selected bond lengths and angles are listed in Table 2.
CCDC-920364 and 920365 contain the supplementary
crystallographic data for compounds 2 and 3(py)2. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
2.2.2. Synthesis of [Th(Cot)2(bipy)][K] (3)
A 25-mL round-bottom flask was charged with 2
(80 mg, 0.13 mmol), KC8 (25 mg, 0.18 mmol) and THF
(5 mL) immediately affording a dark-red solution with a
black C8 deposit. After 1 h at 23 8C, the solution was filtered
and the solvent evaporated off, giving 3 as a dark-brown
solid (81 mg, 95%). C26H24N2ThK requires: C 49.13, H 3.81,
N 4.41; found: C 47.97, H 4.21, N 4.37. The 1H NMR spectra
at 23 8C in [D8]THF or [D5]pyridine do not show any signal
for Cot and bipy ligands. 13C{1H} NMR ([D8]THF, 23 8C):
91.45, 66.13, 16.04. IR (cmꢀ1): 1865 m, 1815w, 1743 m,
1677 m, 1582s, 1542s, 1491s, 1279s, 1260s, 1212s, 1143s,
1106s, 1082s, 1046 m, 1014s, 1003s, 949s, 900s, 836s,
784 m, 749s, 706s, 677s, 641s, 603 m, 551 m, 446 m, 424 m.
Black crystals of 3(py)2 were obtained by slow diffusion of
Et2O into a brown pyridine solution of 3.
An NMR tube was charged with bipy (4.0 mg,
0.025 mmol), KC8 (3.5 mg, 0.025 mmol) and [D8]THF
(0.5 mL). The solution immediately turned purple and
the 1H NMR spectrum did not show the signals for reduced
bipy. Addition of yellow 1 (11.2 mg, 0.025 mmol) induced
instantaneous formation of a dark brown precipitate. No
Table 1
Crystal data and structure refinement details.
2
3(py)2
Chemical formula
M (g molꢀ1
C26H24N2Th
596.51
Monoclinic
P21/c
C36H34KN4Th
793.81
Monoclinic
P21/m
)
Crystal system
Space group
1H NMR signal, except for a weak signal related to free
˚
2ꢀ
a(A)
8.6148(2)
31.8694(4)
14.8246(3)
93.7902(5)
4061.17(14)
8
10.4981(5)
9.3769(2)
15.0666(7)
98.436(2)
1467.10(10)
2
C8H8 at
d 5.68.
˚
b(A)
˚
c(A)
(8)
2.2.3. Reaction of 3 with TlBPh4
b
V(A )
3
˚
An NMR tube was charged with
3
(11.5 mg,
Z
0.018 mmol), TlBPh4 (9.5 mg, 0.018 mmol) in [D5]pyridine
Dcalcd (g cmꢀ3
)
1.951
1.797
(0.5 mL). Immediately,
a grey powder of Tl(0) was
m(Mo K
a
) (mmꢀ1
)
7.358
5.257
observed. The 1H NMR spectrum showed the signals
F(000)
2272
774
relative to 2.
Reflections collected
93454
54986
4721
Independent reflections
12383
Observed reflections [I > 2
s(I)]
10609
4199
2.2.4. Treatment of [U(Cot)2] with bipy
Rint
0.039
0.068
An NMR tube containing [U(Cot)2] (10 mg,
0.022 mmol), bipy (3.5 mg, 0.022 mmol) and [D8]THF
(0.5 mL) was heated at 90 8C. After 1 h, the pale green
solution contained a large quantity of poorly soluble
[U(Cot)2] and the 1H NMR spectrum revealed the presence
of free bipy and [U(Cot)2]. After addition of 1 equiv KC8
Parameters refined
523
218
R1
0.025
0.024
wR2 (all data)
0.055
0.044
S
0.988
0.973
ꢀ3
˚
Drmin (e Aꢀ3
)
ꢀ2.14
ꢀ1.47
˚
Drmax (e A
)
1.10
0.76

J.-C. Berthet et al. / C. R. Chimie 17 (2014) 526–533
529
Table 2
´
˚
Selected bond lengths (A) and angles (8) in 2 and 3(py)2.
2
3(py)2
Th–C
Th1–C11 2.787(3); Th1–C12 2.784(3); Th1–C13 2.774(3)
Th–C11 2.828(3)
Th–C12 2.816(3)
Th–C13 2.889(2)
Th–C14 2.945(2)
Th–C15 2.913(3)
Th–C16 2.847(3)
Th–C17 2.840(3)
Th–C18 2.833(3)
Th1–C14 2.822(3); Th1–C15 2.865(3); Th1–C16 2.866(3)
Th1–C17 2.813(2); Th1–C18 2.788(2); Th1–C19 2.794(3)
Th1–C20 2.788(2); Th1–C21 2.784(2); Th1–C22 2.833(3)
Th1–C23 2.892(3); Th1–C24 2.860(3); Th1–C25 2.805(3)
Th1–C26 2.796(3)
Th2–C37 2.789(3); Th2–C38 2.804(3); Th2–C39 2.795(3)
Th2–C40 2.816(3); Th2–C41 2.866(3); Th2–C42 2.856(3)
Th2–C43 2.806(3); Th2–C44 2.784(3); Th2–C45 2.799(3)
Th2–C46 2.773(2); Th2–C47 2.767(3); Th2–C48 2.828(2)
Th2–C49 2.898(2); Th2–C50 2.892(3); Th2–C51 2.814(2)
2.82(4)
<Th–C(Cot)>
ThꢄꢄꢄCga
2.86(4)
2.20
2.14/2.15
ThꢀN
Th1ꢀN1 2.732(2); Th1ꢀN2 2.700(2)
Th2ꢀN3 2.693(2); Th2ꢀN4 2.687(2)
2.703(17)
2.549(2)
<Th–N>
N1–Th–N2
Cg1ꢄꢄꢄThꢄꢄꢄCg2
CgꢄꢄꢄKꢄꢄꢄCg
KꢀN, KꢀC
59.11(6)/59.95(6)
62.75(7)
143.7/142.9
140.0
131.6
K–N3 3.009(3)
K–N4 3.184(3)
K–C11 3.414(3)
K–C12 3.338(3)
K–C13 3.212(3)
K–C14 3.176(3)
K–C15 3.368(3)
a
Cg is the centroid of the cyclooctatetraenyl ring.
3. Results and discussion
‘‘actinocene’’ [An(Cot)2] fragment [17,30]. After [Th(Cot)2(-
Me4Phen)] [17], 2 is the second example of an [An(Cot)2(L)2]
species. Under similar conditions, [Th(Cot)2] only retains a
single pyridine molecule whereas there is space enough for
two [17], which shows the importance of chelation so as to
get a larger coordination number in complex 2. After
3.1. Synthesis and characterization
In contrast to uranocene, which we found inert in the
presence of bipyridine, [Th(Cot)2], (1) [13] reacted
immediately with 1 equiv bipy in THF or acetonitrile to
give immediately a brown powder which was filtered off
and washed with toluene. The 1H NMR spectrum in
[(Cp00)2Th(F)(
m
-F)2Th(Cp00)(F)(bipy)]
(Cp00 = h5-1,3-
(Me3C)2C5H3), 2 is the second structurally characterized
Th-bipy compound [21b].
pyridine, which shows a diamagnetic Th–Cot signal at
d
A special attention has been recently paid to the
synthesis and physicochemical properties of unusual low-
valent lanthanide and actinide compounds or their
synthetic equivalents containing reduced ligands [31],
such as aromatic polydentate nitrogen ligands
[18a,18g,32]. Anionic bipyꢃꢀ or bipy2ꢀ are such redox
active ligands favouring reduction chemistry [21]. It was
then of interest to consider the reduction of 2 into the
formally Th(III) derivative [Th(Cot)2(bipy)]ꢀ, that would
6.14, shifted upfield in comparison to that of 1 ( 6.28) and
d
new signals corresponding to bipy, suggests the formation
of [Th(Cot)2(k2-bipy)] (2). Black crystals suitable for X-ray
diffraction were obtained by heating a suspension of the
product in THF or acetonitrile or by slow diffusion of Et2O
into a pyridine solution of 2 (Scheme 2).
The crystal structure of 2 clearly evidences the coordina-
tion of one bipy in a bidentate fashion onto an unusual bent
Scheme 2. Synthesis of 2 and 3.

530
J.-C. Berthet et al. / C. R. Chimie 17 (2014) 526–533
observed by 1H NMR. The infrared spectrum of 3 suggests
the formation of a Th(IV)-(bipyꢀ) species rather than a true
Th(III) complex with neutral bipyridine since it contains a
strong band at 949 cmꢀ1 and vibrations at 1542 and
1582 cmꢀ1 consistent with a reduced bipyridyl radical
anion [21d]. Neutral bipyridine is known to display a
strong absorption at ꢁ1600 cmꢀ1 without strong bands in
the 900–1000 cmꢀ1 range, whereas the bipyridyl radical
anion shows an absorption near 900–1000 cmꢀ1 due to the
ring deformation of the ligand, and several C5C and C5N
stretching frequencies in the 1475–1625 cmꢀ1 region
[21d]. At last, the formation of 3 was definitively evidenced
by growing black crystals of {[Th(Cot)2(bipy)K(py)2]}
1
(3(py)2) by the slow diffusion of Et2O into a pyridine
Fig. 1. View of one of the two independent molecules in [Th(Cot)2(k2
-
solution of 3.
bipy)] (2) with displacement ellipsoids drawn at the 40% probability level
and hydrogen atoms omitted.
3.2. Crystal structures of [Th(Cot)2(bipy)] (2) and
{[Th(Cot)2(bipy)K(py)2]} (3(py)2)
1
open attractive chemical perspectives and further com-
parisons with the corresponding bent metallocene species
[(Th(C5H5-nRn)2(bipy)] involving the bipy2ꢀ ligand [21a–c].
In contrast to [Th(C8H6{SitBuMe2}2)2][K(DME)2], which
is a stable green Cot-substituted derivative of the trivalent
thorocene [6], we could not get [Th(Cot)2]ꢀ, the treatment
of 1 with K(18-crown-6)C8 in THF leading only to the
reproducible formation of pale green platelets of the
Views of the structures of 2 and 3 are shown in Figs. 1
and 2, respectively. Both 2 and 3 contain a bent thorocene
fragment coordinated with a bidentate and almost
planar (bipy)qꢀ ligand. The two pyridyl moieties of the
bipy ligand in 2 form a small dihedral angle of 3.9(2)8 but
they are perfectly co-planar in 3. If the neutral compound
2 is monomeric, the anionic derivative 3(py)2 is a
+
polymer due to the bridging role of the K(py)2 group.
bimetallic hydride [{Th(Cot)2}2(
m
-H)]–[30]. This latter
As represented in Fig. 2b, 3 forms an infinite chain where
could result from the transient formation of [Th(Cot)2]ꢀ,
which would be much less stable than [Th(C8H6{SitBu-
Me2}2)2][K(DME)2] [6], which is stabilized by the steric and
electron attracting effects of the SitBuMe2 substituents. In
contrast, 2 was found to react rapidly with KC8 in THF to
give immediately a dark-red solution of the expected
[Th(Cot)2(bipy)][K] (3), with the precipitation of graphite.
Usual work-up afforded a dark-brown solid, which is 1H
NMR silent but whose analysis is in agreement with the
formula of 3. The reaction is reversible and the oxidation of
3 with TlBPh4 gave back 2 almost quantitatively as
the [Th(Cot)2(bipy)]ꢀ anions are linked by cationic
K(py)2 groups sandwiched in h5-fashion by two Cot
+
ligands from two adjacent [Th(Cot)2(bipy)] anions.
Mixed sandwich complexes involving M(Cot)Ln(Cot)
linkages are uncommon (M = Li, K, Na) [33] and 3(py)2
is the unique f-element species containing
(C8H8)2K moiety whereas this latter is linear in
the tetrametallic complex [(Cot)Er(Cot)K(Cot)
Er(Cot)K(THF)4] [33a]. Five K–C distances are in the
a bent
˚
range 3.212(2)–3.414(3) A while the other three dis-
˚
tances are somewhat larger at 3.525(3)–3.596(3) A;
Fig. 2. (a) View of [Th(
omitted. (b) View of the 1D polymer (green: K+, blue: Th4+).
m- :
h8 h5-C8H8)2(k2-bipy)K(py)2] (3(py)2) with displacement ellipsoids drawn at the 40% probability level and hydrogen atoms
1

J.-C. Berthet et al. / C. R. Chimie 17 (2014) 526–533
531
these values are larger than those of 2.985(10)–
˚
h8 h8-Cot)] [34].
2.936(6)–3.029(7) A in [K2(THF)3(m- :
Along the chain, the pyridine and the bipy ligands are
in opposite positions and the (Th, N1, N2) and (K, N3, N4)
groups of atoms form parallel planes (Figs. 1 and 2).
The carbon atoms of the C8 rings of 2 and 3(py)2 are co-
angles) coupled with the M–N bond lengths are generally
good indicators to differentiate neutral or reduced
bipyridine. The X-ray data on 3(py)2 support the infrared
data in showing that a reduced bipyridyl radical anion is
present. Indeed, alternating distinct C–C bonds in the
pyridyl groups and a short C–C distance (g) connecting the
two pyridine rings, together with the planarity of the
whole molecule, are characteristic of a reduced bipy
[18a,21d]. The C–C(bipy) distances are quite similar in 2
3.018(25) A in [{K(THF)3(
˚
m- :
h8 h8-Cot)}2Eu] [33d] and
˚
planar with a maximum rms deviation of 0.037 A and the
CgꢄꢄꢄThꢄꢄꢄCg angle (Cg = ring centroid) deviates notably from
linearity, with values of 143.7 [142.9] and 140.08, respec-
tively. These angles are quitesmaller than thosefound inthe
complexes [Th(Cot)2(L)]qꢀ with monodentate L ligands
(L = tBuNC, py, 4,4’-bipy, CNꢀ, N3ꢀ) which are in the range
˚
but alternately differ by ꢁ 0.04 A in 3(py)2, suggesting the
presence of more localized double bonds, as represented in
˚
Fig. 3. At last, the g bond length of 1.482(3) A in 2 is close to
˚
that in free bipy [1.490(3) A] and in f-metal complexes of
[1488–154.38] or in the bimetallic [{Th(Cot)2}2(
m
-
neutral
bipyridine,
such
as
[Ce(C5Me5)2I(bipy)]
˚ ˚
[1.490(3) A] [18a] or [UI3(bipy)2(py)] [1.49(2) A] [18d],
H)][Na(18-crown-6)(THF)2] (1488) [17,30]. The angle in 2
is comparable to that measured in [Th(Cot)2(Me4phen)]
(144.28), whereas the smaller value in 3(py)2 can be related
to an excess of charge within the bipy ligand, leading to a
greater electronic repulsion with the Cot groups. These
angles are notably larger than those found in the metallo-
˚
for example. This distance decreases by 0.06 A in 3(py)2,
and the value of 1.424(4) A is similar to the corresponding
C–C distance in [K(bipy)(ethylenediamine)] or in com-
plexes of the bipyꢃꢀ anion, such as [U(C5Me5)(Cot)(bipyꢃꢀ)]
˚
1
ꢃꢀ
˚
˚
[1.427(3) A] [21d] or [Sm(C5Me5)2(bipy )] [1.429(4) A]
cenes
[Th(C5H2tBu3)2(bipy)]
[134.5(5)8]
and
[35]. This trend is reflected in the Th–N(bipy) distances
[Th(C5H3tBu2)2(bipy)] [124.1(8)8] containing the bipy2ꢀ
dianion [21a–c]. In comparison and as a result of the larger
ionic radius of the potassium ion, the CgꢄꢄꢄKꢄꢄꢄCg angle in
3(py)2 is smaller, with a value of 131.68 (Fig. 3).
which are in the range 2.687(2)–2.732(2) A for 2, with a
˚
˚
˚
mean value of 2.703(17) A longer by 0.15 A than the
corresponding mean Th–N distance in 3(py)2. A shortening
˚
of the U–N bond length by ca 0.2 A was observed in U(IV)
˚
The average Th–C(Cot) distance of 2.82(4) A in 2 (the
compounds of neutral and reduced bipyridine, such as
˚
same in the two independent molecules) is close to that in
in [U(OSiMe3)2I2(bipy)2] [2.646(5) and 2.670(5) A]
˚
˚
3(py)2 [2.86(4) A] and larger than that in 1 [2.701(10) A]
[18k] and [U(C5Me5)(Cot)(bipyꢀ)] [2.429(2) and
˚
[14]. However, the range spanned in the ten-coordinate
2.468(2) A] [21d]. All these structural features clearly
˚
linear parent 1 [2.679(14)–2.714(12) A] is narrower than in
demonstrate that 3(py)2 is a Th(IV) complex of the
˚
˚
2 [2.767(3)–2.898(2) A] and 3(py)2 [2.816(3)–2.945(2) A].
The larger Th–C(Cot) distances in 3(py)2 by comparison
with those in 1 and 2 reflect the bridging vs the terminal
position of the Cot ligands. The mean Th–C(Cot) distance in
bipyridine radical anion rather than a true Th(III)
species. At last, it is interesting to note that in the
structure of 3(py)2, the potassium cation is not
interacting with the bipyꢀ ligand but with the Cot
dianions. Because the bonding in f-element complexes
is essentially ionic, the K+ ion is likely more prone to
interact with the more accessible and charged Cot
ligand than with the monoanionic bipyꢀ in which the
charge is delocalized over two aromatic cycles. More-
over, that the Cot dianion can bridge two different
metals is now well established [33].
˚
3(py)2 can also be compared with that of 2.789(6) A (for
the capped Cot ligand) in the ten-coordinate trivalent
complex [(C8H6{tBuMe2Si}2)2Th)[K(DME)2] [6]. These dif-
ferences also reflect the variation in the coordination
numbers and the charge of the complexes.
The geometrical parameters of the bidentate bipy
ligand (C–C/N distances listed in Fig. 3 and dihedral
ꢃꢀ
˚
Fig. 3. Bond lengths (A) within the bipy and (bipy) ligands in 2 and 3(py)2.

532
J.-C. Berthet et al. / C. R. Chimie 17 (2014) 526–533
[15] (a) C. Levanda, A. Streitwieser, Inorg. Chem. 20 (1981) 656;
4. Conclusion
(b) C. Levanda, J.P. Solar, A. Streitwieser, J. Am. Chem. Soc. 102 (1980)
2128.
The greater reactivity of [Th(Cot)2] versus [U(Cot)2]
was evidenced in its reaction with 2,20-bipyridine, which
gives [Th(Cot)2(bipy)] and provides a novel example of
an unusual bent thorocene fragment. This bipy complex
easily trapped one electron to give the anionic derivative
[Th(Cot)2(bipy)][K(py)2], which forms a 1D polymer in
the solid state. The comparison of the crystal structures
of these two geometrically similar compounds reveals
that the metal ion in [Th(Cot)2(bipy)]ꢀ is not Th3+ but
Th4+ coordinated to the bidentate radical anion (bipy)ꢀ.
[16] F. Ferraro, C.A. Barboza, R. Arratia-Perez, J. Phys. Chem. A 116 (2012)
4170.
[17] J.C. Berthet, P. Thue´ry, N. Garin, J.P. Dognon, T. Cantat, M. Ephritikhine, J.
Am. Chem. Soc. 135 (2013) 10003.
[18] (a) T. Mehdoui, J.C. Berthet, P. Thue´ry, L. Salmon, E. Rivie`re, M. Ephri-
tikhine, Chem. Eur. J. 11 (2005) 6994;
(b) J.C. Berthet, M. Nierlich, M. Ephritikhine, Dalton Trans. (2004)
2814;
(c) J.C. Berthet, M. Nierlich, M. Ephritikhine, Chem. Commun. (2003)
1660;
(d) C. Rivie`re, M. Nierlich, M. Ephritikhine, C. Madic, Inorg. Chem. 40
(2001) 4428;
(e) L. Arnaudet, R. Bougon, B. Buu, M. Lance, M. Nierlich, J. Vigner, Inorg.
Chem. 33 (1994) 4510;
(f) T. Arliguie, P. Thue´ry, M. Fourmigue´, M. Ephritikhine, Eur. J. Inorg.
Chem. (2004) 450;
(g) M.A. Antunes, L.C.J. Pereira, I.C. Santos, M. Mazzanti, J. Marc¸alo, M.
Almeida, Inorg. Chem. 50 (2011) 9915;
(h) R.O. Wiley, R.B. Von Dreele, T.M. Brown, Inorg. Chem. 19 (1980)
3351;
(i) L. Maria, A. Domingos, A. Galvao, J. Ascenso, I. Santos, Inorg. Chem.
43 (2004) 6426;
(j) P.B. Duval, C.J. Burns, D.L. Clark, D.E. Morris, B.L. Scott, J.D. Thomp-
son, E.L. Werkema, L. Jia, R.A. Andersen, Angew. Chem., Int. Ed. 40
(2001) 3358;
(k) J.L. Brown, C.C. Mokhtarzadeh, J.M. Lever, G. Wu, T.W. Hayton,
Inorg. Chem. 50 (2011) 5105;
(l) S. Panchanan, R. Hamalainen, P.S. Roy, J. Chem. Soc., Dalton Trans.
(1994) 2381;
(m) G.B. Deacon, P.I. Mackinnon, J.C. Taylor, Polyhedron 4 (1985) 103;
(n) N.W. Alcock, D.J. Flanders, D. Brown, J. Chem. Soc., Dalton Trans.
(1985) 1001;
(o) N.W. Alcock, D.J. Flanders, D. Brown, Inorg. Chim. Acta 94 (1984)
279;
(p) M.F. Schettini, G. Wu, T.W. Hayton, Inorg. Chem. 48 (2009) 11799;
(q) L. Spencer, P. Yang, B.L. Scott, E.R. Batista, J.M. Boncella, Inorg.
Chem. 48 (2009) 11615;
Compounds
2 and 3(py)2 are rare examples of
[An(Cot)2(L)2] complexes, and they are among the first
molecular thorium species involving neutral or mono-
anionic bipyridine ligands. These results also clearly
demonstrate that the An4+ ion in [An(Cot)2] complexes is
normally accessible to ligand coordination and can
support one or even two ligands in its coordination
sphere as it is the case within the analogous bis(C5Me5)2
series. Further work is in progress to explore the unique
reactivity of thorocene and to explain theoretically the
differences between uranium and thorium, which are
likely attributable to the distinct covalent character of
the AnꢀCot bond [17].
Acknowledgements
This work was financially supported by CEA and CNRS.
Appendix. Supplementary data
(r) L. Spencer, E.J. Schelter, P. Yang, L. Gdula, B.L. Scott, J.L. Kiplinger,
E.R. Batista, J.M. Boncella, Angew. Chem., Int. Ed. 48 (2009) 3795;
(s) L. Spencer, P. Yang, B.L. Scott, E.R. Batista, J.M. Boncella, C.R. Chim.
13 (2010) 758;
(t) A.R. Schake, L.R. Avens, C.J. Burns, D.L. Clark, A.P. Sattelberger, W.H.
Smith, Organometallics 12 (1993) 1497.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.crci.2013.09.006.
[19] (a) G.B. Andreev, A.M. Fedosseev, N.A. Budantseva, M.Y. Antipin, Men-
deleev Commun. (2001) 58;
(b) G.B. Andreev, M.Y. Antipin, A.M. Fedoseev, N.A. Budantseva, Russ. J.
Coord. Chem. 27 (2001) 211;
References
(c) G.B. Andreev, N.A. Budantseva, I.G. Tananaev, B.F. Myasoedov,
Inorg. Chem. Commun. 12 (2009) 109;
(d) I.A. Charushnikova, C. Den Auwer, Russ. J. Coord. Chem. 30 (2004)
511;
(e) I.A. Charushnikova, N.N. Krot, Z.A. Starikova, Radiochim. Acta 95
(2007) 495;
(f) M.S. Grigoriev, N.N. Krot, A.A. Bessonov, K.Y. Suponitsky, Acta
Crystallogr. E 63 (2007) m561.
[1] A. Streitwieser, U. Mu¨ ller-Westerhoff, J. Am. Chem. Soc. 90 (1968) 7364.
[2] A. Streitwieser, U. Mu¨ller-Westerhoff, G. Sonnichsen, F. Mares, D.G.
Morrell, K.O. Hodgson, C.A. Harmon, J. Am. Chem. Soc. 95 (1973) 8644.
[3] (a) D. Seyferth, Organometallics 23 (2004) 3562;
(b) T.J. Marks, A. Streitwieser, in: J.J. Katz, G.T. Seaborg, L.R. Morss
(Eds.), 2nd ed, The Chemistry of the Actinide and Transactinide
Elements, Vol. 2, Chapman and Hall, London, 1986, , p. 1547Chp. 2;
[20] N. Kumar, D.G. Tuck, Inorg. Chem. 22 (1983) 1951.
[21] (a) W. Ren, G. Zi, M.D. Walter, Organometallics 31 (2012) 672;
(b) W. Ren, H. Song, G. Zi, M.D. Walter, Dalton Trans. 41 (2012) 5965;
(c) W. Ren, W.W. Lukens, G. Zi, L. Maron, M.D. Walter, Chem. Sci. 4
(2013) 1168;
`
(c) A. Streitwieser, S.A. Kinsley, in: T.J. Marks, I. Fragala (Eds.), Funda-
mental and Technological Aspects of Organo-f-Element Chemistry,
Reidel, Dordrecht, Holland, 1985, p. 77.
[4] C.J. Burns, B.E. Bursten, Comments Inorg. Chem. 9 (1989) 61.
[5] M.D. Walter, C.H. Booth, W.W. Lukens, R.A. Andersen, Organometallics
28 (2009) 698.
[6] J.S. Parry, F.G.N. Cloke, S.J. Coles, M.B. Hursthouse, J. Am. Chem. Soc. 121
(1999) 6867.
[7] (a) T.R. Boussie´, D.C. Eisenberg, J. Rigsbee, A. Streitwieser, A. Zalkin,
Organometallics 10 (1991) 1922;
(d) M.K. Takase, M. Fang, J.W. Ziller, F. Furche, W.J. Evans, Inorg. Chim.
Acta 364 (2010) 167;
(e) G. Del Piero, G. Perego, A. Zazetta, G. Brandi, Cryst. Struct. Commun.
4 (1975) 521.
[22] T.J. Katz, J. Am. Chem. Soc. 82 (1960) 3784.
[23] T. Cantat, B.L. Scott, J.L. Kiplinger, Chem. Commun. 46 (2010) 919.
[24] L.H. Simons, J.J. Lagowski, Tetrahedron Lett. 43 (2002) 1771.
[25] M. Nishiura, Z. Hou, Y. Wakatsuki, Organometallics 23 (2004) 1359.
[26] R.W.W. Hooft, COLLECT; Nonius BV, Delft, The Netherlands, 1998.
[27] Z. Otwinowski, W. Minor, Methods Enzymol. 276 (1997) 307.
[28] G.M. Sheldrick, Acta Crystallogr., Sect. A, 64 (2008) 112.
[29] L.J. Farrugia, J. Appl. Crystallogr 30 (1997) 565.
[30] A. Herve´, N. Garin, P. Thue´ry, M. Ephritikhine, J.C. Berthet, Chem.
Commun. 49 (2013) 6304.
(b) D.G. Karraker, J.A. Stone, J. Am. Chem. Soc. 96 (1974) 6885.
[8] J.C. Berthet, P. Thue´ry, M. Ephritikhine, Inorg. Chem. 49 (2010) 8173.
[9] T.R. Boussie, R.M. Moore, A. Streitwieser, A. Zalkin, J. Brennan, K.A.
´
Smith, Organometallics 9 (1990) 2010.
[10] J.C. Berthet, P. Thue´ry, M. Ephritikhine, Organometallics 27 (2008)
1664.
[11] V. Lorenz, B.M. Schmiege, C.G. Hrib, J.W. Ziller, A. Edelmann, S. Blaurock,
W.J. Evans, F.T. Edelmann, J. Am. Chem. Soc. 133 (2011) 1257.
[12] R.D. Shannon, Acta Crystallogr. 32 (1976) 751.
[13] A. Streitwieser, N. Yoshida, J. Am. Chem. Soc. 91 (1969) 7528.
[14] A. Avdeef, K.N. Raymond, K.O. Hodgson, A. Zalkin, Inorg. Chem. 11
(1972) 1083.
[31] (a) F. Nief, Dalton Trans. 39 (2010) 6589;
(b) W.J. Evans, Inorg. Chem. 46 (2007) 3435;
(c) M. Ephritikhine, Dalton Trans. (2006) 2501.

J.-C. Berthet et al. / C. R. Chimie 17 (2014) 526–533
[32] (a) C.J. Kuehl, R.E. Da Re, B.L. Scott, D.E. Morris, K.D. John, Chem. met.Chem. C15 (1994) 469;
533
Commun. (2003) 1336;
(d) W.J. Evans, J.L. Shreeve, J.W. Ziller, Polyhedron 14 (1995) 2945;
(e) J. Xia, X. Zhuang, Z. Jin, W. Chen, Polyhedron 15 (1996) 3399;
(f) G.W. Rabe, M. Zhang-Presse, J.A. Golen, A.L. Rheingold, Acta Crystal-
logr. E 59 (2003) m255;
(g) V. Lorenz, A. Edelmann, S. Blaurock, F. Freise, F.T. Edelmann, Orga-
nometallics 26 (2007) 6681;
(b) C.H. Booth, D. Kazhdan, E.L. Werkema, M.D. Walter, W.W. Lukens,
E.D. Bauer, Y.J. Hu, L. Maron, O. Eisenstein, M. Head-Gordon, R.A.
Andersen, J. Am. Chem. Soc. 132 (2010) 17537;
(c) M.D. Walter, D.J. Berg, R.A. Andersen, Organometallics 26 (2007)
2296.
[33] (a) J. Xia, Z. Jin, W. Chen, Chem. Commun. (1991) 1214;
(b) J. Jizhu, J. Zhongsheng, W. Gecheng, C. Wenqi, Z. Yin, Chin. J. Inorg.
Chem. 9 (1993) 326;
(h) C. Meermann, K. Ohno, K.W. Tornroos, K. Mashima, R. Anwander,
Eur. J. Inorg. Chem. (2009) 76.
[34] N. Hu, L. Gong, Z. Jin, W. Chen, J. Organomet. Chem. 352 (1988) 61.
[35] W.J. Evans, D.K. Drummond, J. Am. Chem. Soc. 111 (1989) 3329.
(c) U. Kilimann, M. Schafer, R. Herbst-Irmer, F.T. Edelmann, J. Organo-