Monocyclooctatetraenyl(dithiolene)uranium compounds

Article abstract of DOI:10.1002/ejic.200400403

The neutral mononuclear dithiolene compounds [U(cot)-(dithiolene)(tppo) ₂] [cot = η-C₈H₈; dithiolene = dddt (9), dmio (10), mdt (11)], [U(cot)(dithiolene)(hmpa)₂] [dithiolene = dddt (12), dmio (13), mdt (14)], [U(cot)(mdt)(bipy)] (15) and [U(cot)(mdt)(terpy)] (16) were obtained by treating the dimeric complexes [{U(cot)(dithiolene)} ₂] [dithiolene = dddt (3), dmio (4), mdt (5)] (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate; dmio = 1,3-dithiole-2-one-4,5- dithiolate; mdt = 1,3-dithiole-4,5-dithiolate) with the corresponding Lewis base [triphenylphosphine oxide (tppo), hexamethylphosphoramide (hmpa), 2,2′-bipyridine (bipy), or 2,2′:6′,2″-terpyridine (terpy)]. Complexes 9.2THF, 11.2THF, 12, 13, 14, 15 and 16.1.5py have been crystallographically characterized. The crystal structures show a significant interaction between the C=C double bond of the dithiolene ligand and the metal centre. The ¹H NMR spectra reveal the fluxional behaviour of the compounds in solution in relation to the facile inversion of the dithiolene ring. The variation of the activation energies of the inversion process reflects the steric congestion of the complexes. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200400403

FULL PAPER
Monocyclooctatetraenyl(dithiolene)uranium Compounds
[a]
[a]
[b]
[a]
´ `
´
´
Therese Arliguie,* Pierre Thuery, Marc Fourmigue, and Michel Ephritikhine
Keywords: Cyclooctatetraenyl ligands / Lewis bases / S ligands / Uranium
The neutral mononuclear dithiolene compounds [U(cot)-
(dithiolene)(tppo)2] [cot = η-C8H8; dithiolene = dddt (9), dmio
(terpy)]. Complexes 9·2THF, 11·2THF, 12, 13, 14, 15 and
16·1.5py have been crystallographically characterized. The
crystal structures show a significant interaction between the
C=C double bond of the dithiolene ligand and the metal
centre. The 1H NMR spectra reveal the fluxional behaviour
of the compounds in solution in relation to the facile inver-
sion of the dithiolene ring. The variation of the activation en-
(10), mdt (11)], [U(cot)(dithiolene)(hmpa)2] [dithiolene
=
dddt (12), dmio (13), mdt (14)], [U(cot)(mdt)(bipy)] (15) and
[U(cot)(mdt)(terpy)] (16) were obtained by treating the di-
meric complexes [{U(cot)(dithiolene)}2] [dithiolene = dddt (3),
dmio (4), mdt (5)] (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithi-
olate; dmio = 1,3-dithiole-2-one-4,5-dithiolate; mdt = 1,3-di- ergies of the inversion process reflects the steric congestion
thiole-4,5-dithiolate) with the corresponding Lewis base [tri- of the complexes.
phenylphosphine oxide (tppo), hexamethylphosphoramide ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
(hmpa), 2,2Ј-bipyridine (bipy), or 2,2Ј:6Ј,2ЈЈ-terpyridine
Germany, 2004)
Introduction
Dithiolene complexes of the d-block transition metals
have received much attention for their remarkable structural
features and physicochemical properties, finding appli-
cations in the elaboration of novel conducting and magnetic
materials.[1] In contrast, such compounds of the f-block ele-
ments have been practically neglected,[2] mainly due to the
presumption that this type of complex should be unstable.
In fact, lanthanides and actinides have proved to have a
strong affinity for sulfur,[3Ϫ12] and the synthesis of their di-
thiolene complexes is worth considering since their coordi-
nation flexibility, paramagnetism and redox behaviour
could favour the emergence of interesting structures and
electronic interactions. For these reasons we have started
studies on organouraniumϪdithiolene compounds, in par-
ticular bis(pentamethylcyclopentadienyl) and monocyclooc-
Scheme 1. The dithiolene ligands and dithiocarbonates (dddt ϭ
5,6-dihydro-1,4-dithiine-2,3-dithiolate; dmio ϭ 1,3-dithiole-2-one-
4,5-dithiolate; mdt ϭ 1,3-dithiole-4,5-dithiolate)
We recently reported that anionic bis(dithiolene) deriva-
tatetraenyl derivatives, for comparison with the heteroleptic tives could be obtained from the metathesis reaction of the
cyclopentadienyl/dithiolene complexes of the metals of uranium bis(borohydride) complex [U(cot)(BH4)2] with 2
groups 4Ϫ6[13,14] and with the uranium bis(thiolate) com- mol-equiv. of Na2dddt in THF, affording, in the presence
plexes [U(cp*)2(SR)2][11] and [{U(cot)(SR)2}2][7] (cp* ϭ η- of 18-crown-6, red crystals of a THF solvate of [Na(18-
C5Me5; cot ϭ η-C8H8). The dithiolene ligands selected for crown-6)(THF)2]2[U(cot)(dddt)2] (1). Complex 1 was a un-
this work are represented in Scheme 1.
ique example of a dianionic monocyclooctatetraenyluran-
ium compound, although the [U(cot)X3]Ϫ anions were
found to be stable in the presence of an excess of XϪ (X ϭ
SR,[7] NR2,[15] BH4 [16]). Its oxidation with AgBPh4 in THF
afforded the corresponding monoanionic compound
[Na(18-crown-6)(THF)][U(cot)(dddt)2] (2), which was
structurally characterized.[17] Complex 2 was the first urani-
um() compound with metalϪsulfur bonds and, after the
cycloheptatrienyl sandwich compound [K(18-crown-
[a]
´
Service de Chimie Moleculaire, DSM, DRECAM, CNRS URA
331, CEA/Saclay,
91191 Gif-sur-Yvette, France
E-mail: arliguie@drecam.cea.fr
[b]
´
Laboratoire de Chimie Inorganique, Materiaux et Interfaces
´
(CIMI), FRE 2447 CNRS-Universite d’Angers,
2 Bd. Lavoisier, 49045 Angers, France
4502
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200400403
Eur. J. Inorg. Chem. 2004, 4502Ϫ4509

Monocyclooctatetraenyl(dithiolene)uranium Compounds
FULL PAPER
6)][U(η-C7H7)2],[18] a new example of an anionic organour- 1,3-dithiolo[4,5-b][1,4]dithiine-2-one; dmioCO ϭ 1,3,4,6-
anium() derivative. tetrathiapentalene-2,5-dione). In the presence of 2,2Ј-bipyri-
We also disclosed that the same borohydride, [U(cot)- dine (bipy) or 2,2Ј:6Ј,2ЈЈ-terpyridine (terpy) in THF, 5 was
(BH4)2], could act as a hydride reagent in the reductive transformed into [U(cot)(mdt)(bipy)] (15) and [U(cot)(mdt)-
fission of dithiocarbonates, affording a series of neutral di- (terpy)] (16), respectively. Complexes 6Ϫ16 were isolated
metallic dithiolene complexes [{U(cot)(dithiolene)}2] [dithi- as red to dark-brown crystals or powders with yields from
olene ϭ dddt (3), dmio (4), mdt (5)].[19] Upon dissolution 65 to 95%.
in pyridine, those dimeric compounds could be transformed
At least one example of each type of the Lewis-base ad-
into the mononuclear complexes [U(cot)(dithiolene)(py)2] ducts of 3Ϫ5 with tppo or hmpa (11, 12 and 13) was
[dithiolene ϭ dddt (6), dmio (7), mdt (8)]. The crystal struc- characterized by elemental analysis, as were 15 and 16 , and
ture of 8 revealed a significant interaction between the di- the X-ray crystal structures of 9·2THF, 11·2THF, 12, 13,
thiolene ligand and the metal centre.[19] With the aim of 14, 15 and 16·1.5py were also determined.
understanding and controlling this interaction, we have
studied the complexation of 3Ϫ5 with various Lewis bases,
such as triphenylphosphine oxide (tppo) or hexameth-
ylphosphoramide (hmpa), and chelating pyridines such as
Crystal Structures of the Complexes
bipyridine or terpyridine.
The crystal structure of the dinuclear compound 5 (Fig-
ure 1) has already been described in a preliminary report;[19]
only the main geometrical features will be recalled for com-
parison with its congeners.
Here we report the synthesis of a series of adducts of
general formula [U(cot)(dithiolene)(L)n] (n ϭ 1 and L ϭ
bipy or terpy; n ϭ 2 and L ϭ tppo or hmpa). We describe
the X-ray crystal structures of the complexes, paying special
attention to the interaction between the dithiolene ligand
and the metal centre, and we present the 1H NMR spectra,
which reveal the dynamic behaviour of the complexes in
solution, related to the facile ring-inversion process of the
dithiolene ligand.[17,19]
Results and Discussion
The bis adducts [U(cot)(dithiolene)(tppo)2] [dithiolene ϭ
dddt (9), dmio (10), mdt (11)] and [U(cot)(dithi-
olene)(hmpa)2] [dithiolene ϭ dddt (12), dmio (13), mdt (14)]
were obtained by treatment of 3Ϫ5 with 2 mol-equiv. of
tppo or hmpa in THF (Scheme 2). With the exception of
10, these complexes could also be prepared in a one-pot
reaction from [U(cot)(BH4)2], L and the dithiocarbonates
dddtCO or dmioCO, which are the protected forms of the
corresponding dithiolene ligands (dddtCO ϭ 5,6-dihydro-
Figure 1. View of the complex [{U(cot)(mdt)}2] (5); the hydrogen
atoms have been omitted for clarity; the displacement ellipsoids are
drawn at the 30% probability level; symmetry code: Ј ϭ Ϫ x,
1 Ϫy, Ϫz
The Lewis-base adducts of general formula [U(cot)(dithio-
lene)(L)2] adopt a four-legged piano-stool configuration,
the base of which is defined by the S(1) and S(2) atoms of
the dithiolene ligand and the two oxygen [O(1) and O(2)]
or the two nitrogen [N(1) and N(2)] atoms of the Lewis
base. The structures of 9 (Figure 2), 14 (Figure 3) and 15
(Figure 4), which are representatives of the series, are shown
below; selected bond lengths and angles in the complexes
[U(cot)(dithiolene)(L)2] are listed in Table 1. Complex 15
has crystallographic mirror symmetry.
Scheme 2. Synthesis of the mononuclear compounds 6Ϫ14
Eur. J. Inorg. Chem. 2004, 4502Ϫ4509
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´
T. Arliguie, P. Thuery, M. Fourmigue, M. Ephritikhine
FULL PAPER
Figure 2. View of the complex [U(cot)(dddt)(tppo)2] (9); the hydro-
gen atoms have been omitted for clarity; the displacement ellipsoids
are drawn at the 30% probability level
Figure 4. View of the complex [U(cot)(mdt)(bipy)] (15); the hydro-
gen atoms have been omitted for clarity; the displacement ellipsoids
are drawn at the 30% probability level; symmetry code: Ј ϭ x, 0.5
Ϫ y, z
[24]
˚
distance of 2.63(2) A in [NEt4][U(NCS)5(bipy)2],
which
is the other uranium()Ϫbipy complex to have been crys-
tallographically characterized. The O(1)ϪUϪO(2) or
N(1)ϪUϪN(2) angles are quite similar, with an average
value of 75(1)°, except for the NϪUϪN angle of the biden-
tate bipy ligand, which is equal to 63.12(19)°.
The UϪS distances in the series of [U(cot)(dithi-
˚
olene)(L)2] complexes vary from 2.720(3) A in 8 to 2.859(3)
˚
A in 13 and are larger than the UϪS bond lengths in the
monomeric uranium() thiolate compounds, which range
between 2.61(5)
in [U(SiPr)2(hmpa)4][BPh4][9] and
˚
A
2.744(2) A in [Na(18-crown-6)][U(Cp*)2(S)(StBu)].[10] How-
ever, as expected for terminal SR ligands, these distances
are shorter than the mean bridging SR bond length of
˚
˚
2.88(8) A in the dimeric compound 5. The S(1)ϪUϪS(2)
angles in the mononuclear compounds are close to 75°,
Figure 3. View of one of the two independent molecules of
while they are slightly smaller in 5, with values of 68.29(6)
[U(cot)(mdt)(hmpa)2] (14); the hydrogen atoms have been omitted
for clarity; the displacement ellipsoids are drawn at the 30% prob- and 71.98(6)°.
ability level
In all the complexes, the characteristics of the dithiolene
ligands, such as the average C(sp2)ϪS distances, which vary
˚
˚
˚
from 1.720(13) A in 14 to 1.796(17) A in 9, and the CϭC
The cot ligand in all the complexes is planar within distances, which lie between 1.343(10) A in 12 and 1.394(17)
Ϯ0.09 A. The average UϪC(cot) distances in the Lewis- A in 14, are consistent with those found in [Mo(cp)2(dddt)]
base adducts [U(cot)(dithiolene)(L)2], with a typical value [1.76(1) and 1.33(1) A],
˚
˚
[25]
˚
[NEt4]2[Ni(dmio)2] [1.75(1) and
[26]
˚
˚
˚
of 2.71 A, are longer than that of 2.640(2) A in 5, and are 1.34(1) A]
at the upper limit of the range of UϪC(cot) bond lengths A].
and [NBu4][Ni(mdt)2] [1.74(2) and 1.36(2)
[27]
˚
in monocyclooctatetraenyluranium() compounds, which
Special attention should be paid to the folding of the me-
˚
vary from 2.62(2)
A
in the bis(thiolate) complex tallacycle as this reflects the interaction of the dithiolene
[{U(cot)(SiPr)2}2][7] to 2.71(4)
A
in [U(cot)(NEt2)- ligand with the metal centre. The S4C2 fragment of the di-
˚
(THF)3][BPh4].[20]
thiolene ligands is planar within Ϯ0.06 A and forms a di-
˚
In the tppo and hmpa adducts, the UϪO distances vary hedral angle, θ, with the corresponding SϪUϪS plane.
˚
˚
from 2.302(8) A in 13 to 2.444(8) A in 14 and are unexcep- Scheme 3 shows the variation of this folding angle and the
˚
tional; they are similar to those of 2.27(1) A in [U(cot)- distinct conformations of the dithiolene ligands in the com-
(BH4)2(tppo)][21] and 2.461(8) A in [U(cot)(Cp*)(hmpa)].
plexes. Previous studies on dithiolene compounds of the d-
[22]
˚
˚
The UϪN distance in 15 [2.555(4) A] can be compared with block transition metals have shown that θ increases upon
˚
those in 8 [2.636(9) and 2.691(10) A], [U(cot)Cl2(py)2] lowering the electron density at the metal atom, reflecting
[2.639(5) and 2.644(6) A],[23] and to the average UϪN(bipy) the strength of the interaction of an empty metal orbital
˚
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Monocyclooctatetraenyl(dithiolene)uranium Compounds
FULL PAPER
˚
Table 1. Selected bond lengths [A] and angles [°] in the neutral mononuclear complexes 8, 9 and 11Ϫ15
8[19]
9[a]
11[a]
12
13
14[b]
15
UϪC(cot)
UϪS(1)
UϪS(2)
UϪC(1)
UϪC(2)
UϪO(1) or
UϪN(1)
2.70(3)
2.70(2)
2.703(17)
2.773(2)
2.781(2)
3.086(9)
3.081(8)
2.354(5)
2.716(17)
2.736(2)
2.793(2)
3.181(8)
3.179(8)
2.363(5)
2.71(3)
2.71(2); 2.72(3)
2.686(7)
2.7511(14)
2.720(3)
2.751(3)
2.889(11)
2.965(11)
2.745(5)
2.782(5)
3.089(15)
3.11(2)
2.801(3)
2.859(3)
3.679(15)
3.674(14)
2.327(8)
2.791(3); 2.739(3)
2.751(3); 2.821(3)
3.146(10); 2.969(11)
3.154(13); 3.020(11)
2.354(8); 2.444(8)
2.879(5)
2.555(4)
2.398(10)
2.691(10)
UϪO(2) or
UϪN(2)
2.376(12)
2.424(5)
2.353(5)
2.302(8)
2.367(8); 2.312(8)
2.636(9)
1.389(16)
1.732(12)
1.781(12)
1.749(11)
1.749(13)
77.08(10)
C(1)ϪC(2)[c]
C(1)ϪS(1)
C(1)ϪS(4)[c]
C(2)ϪS(2)
C(2)ϪS(3)
S(1)ϪUϪS(2)
O(1)ϪUϪO(2) or
N(1)ϪUϪN(2)
θ[d]
1.35(2)
1.796(17)
1.772(19)
1.72(2)
1.79(2)
73.67(15)
74.1(4)
1.363(12)
1.740(8)
1.765(9)
1.742(9)
1.772(8)
75.74(7)
74.2(2)
1.343(10)
1.757(7)
1.774(8)
1.757(8)
1.774(8)
73.74(6)
74.78(19)
1.378(16)
1.742(15)
1.754(14)
1.722(14)
1.762(13)
73.89(9)
1.348(16); 1.394(17)
1.732(12); 1.720(13)
1.795(11); 1.762(12)
1.733(12); 1.742(12)
1.795(13); 1.772(12)
75.26(9); 75.48(9)
76.1(3); 74.8(3)
1.374(10)
1.748(5)
1.768(6)
77.13(6)
77.1(3)
74.3(3)
75.6(3)
63.12(19)
80.60(5)
71.89(12)
71.32(6)
65.97(6)
20.93(19)
66.98(9); 75.97(9)
[a]
[b]
[c]
Complexes 9 and 11 crystallize with two THF molecules.
Values are given for the two independent molecules. C(1)ϪC(2) and
[d]
C(1)ϪS(4) are C(1)ϪC(1Ј) and C(1)ϪS(2) in complex 15. θ is the folding angle as defined in the text.
˚
centre at less than 3 A. With the exception of 14, the folding
angles in the tppo and hmpa adducts are smaller than 75°,
and are probably limited by the steric interaction between
the dithiolene and cot ligands. One of the two independent
molecules of 14 presents a θ angle of 75.97(9)° despite the
exo conformation of the dithiolene ligand. The low value
of θ in the dmio complex 13 [20.93(19)°] seems peculiar
since the complexes [Ti(Cp)2(dithiolene)] (dithiolene ϭ
dddt, dmio or dmit) exhibit quite similar θ angles of
47Ϫ50°.[13,14] However, this distinct feature of 13 might be
ascribed to the presence in the crystal structure of weak
intermolecular O(3)···HϪC interactions[30Ϫ32] with four H
atoms of the hmpa or cot groups of two neighbouring mol-
˚
ecules, with O(3)···H distances in the range 2.621Ϫ2.893 A.
The structures of the other neutral dithiolene complexes ex-
hibit weak intermolecular CϪH···S contacts, shorter than 3
Scheme 3. Conformation of the dithiolene ligands
˚
˚
A and as low as 2.70 A; such interactions have been ob-
served in a large number of tetrathiafulvalene derivatives.[33]
The crystal structure of the terpy adduct 16 is shown in
with the HOMO of the dithiolene ligand.[13,28] For example,
in the series of [M(Cp*)(dmit)2]Ϫ1,0 compounds, the d2 Figure 5; selected bond angles and distances are given in
complexes [M(Cp*)(dmit)2]Ϫ1 (M ϭ Mo, W) adopt an exo- Table 2. Complex 16 is a unique example of a distorted oc-
exo conformation, and the d0 derivative [Ti(Cp*)(dmit)2]Ϫ1 tahedral monocyclooctatetraenyluranium compound; the
is found in an exo-endo conformation, while the geometry apical positions are occupied by the centroid of the cot ring
of the d1 complex [M(Cp*)(dmit)2]· (M ϭ Mo, W) com- and the S(2) atom, while S(1) and the three nitrogen atoms
pounds is intermediate between those of the MoIV or WIV of the terpy ligand define the equatorial plane, with a mean
and TiIV analogues.[29]
deviation of Ϯ0.002 A. This plane is almost parallel to the
˚
In the series of Lewis-base adducts [U(cot)(dithi- planar cot ligand, with a dihedral angle of 4.38(13)°, and
olene)(L)2], the dithiolene ligand is found in the exo confor- the U atom is located between the two planes at a distance
˚
mation, except in the pyridine and bipyridine derivatives 8 of 0.8687(13) and 2.0148(15) A, respectively. The planar di-
and 15. The lower steric hindrance of these nitrogen li- thiolene ligand is practically perpendicular to both the cot
gands, in comparison with tppo and hmpa, permits the ring and equatorial plane, with dihedral angles of 88.93(7)
folding of the US2C2 fragment towards the endo position, and 84.72(5)°, respectively. The long UϪS distances of
˚
with θ being equal to 75.6(3) and 80.60(5)° in 8 and 15, 2.8203(10) and 2.8304(10) A and the small folding angle, θ,
respectively; the C(1) and C(2) atoms approach the metal of 20.40(4)° reflect the electronic and steric saturation of
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T. Arliguie, P. Thuery, M. Fourmigue, M. Ephritikhine
FULL PAPER
Dynamic Behaviour of the Complexes in Solution
1
The H NMR spectroscopic data of the complexes are
reported in Table 3. Complex 9 is not soluble in THF, while
15 and 16 are not soluble in THF or pyridine; their NMR
spectra could therefore not be recorded. The spectra of the
tppo and hmpa adducts in pyridine are more complicated,
showing partial substitution of the L ligands by solvent
molecules. At 20 °C, the cot ligand in all the complexes
gives rise to a signal at δ ഠ Ϫ30 ppm, characteristic of mon-
ocyclooctatetraenyluranium compounds.[7,15,21,35] Two sig-
nals of equal intensities corresponding to the magnetically
non-equivalent methylene protons of the dddt and mdt li-
gands in the Lewis-base adducts [U(cot)(dithiolene)(L)2]
are visible at 20 °C, or at lower temperature in the case of
12, as already observed for 6 and 8.[19] Coalescence of these
resonances occurred upon increasing the temperature, and
the fast limit spectrum was obtained for complex 12.
Figure 5. View of the complex [U(cot)(mdt)(terpy)] (16); the hydro-
gen atoms and solvent molecules have been omitted for clarity; the
displacement ellipsoids are drawn at the 30% probability level
The dynamic behaviour of the complexes can be ascribed
to the dithiolene ring inversion represented in Scheme 4; a
similar fluxionality has been observed in a variety of
the complex. The average UϪN distance of 2.589(9) A can [M(Cp)2(dithiolene)] compounds.[13,14] The ring inversion
˚
III
˚
be compared with that of 2.63(3) A in the U cation should proceed via the trigonal bipyramidal intermediate
[U(terpy)3]3ϩ, the other terpyridine uranium complex to (A in Scheme 4) which renders the methylene protons equiv-
have been crystallographically characterized.[34]
alent. It is conceivable that, for the sterically less saturated
complexes 6 and 8, the octahedral intermediate [U(cot)(di-
˚
Table 2. Selected bond lengths [A] and angles [°] in [U(cot)(mdt)(terpy)]·1.5py (16·1.5py)
ϽUϪC(cot)Ͼ
UϪN(1)
C(1)ϪS(1)
2.72(2)
2.582(3)
1.743(4)
1.783(4)
71.06(3)
61.94(10)
81.48(7)
81.96(7)
114.0
UϪS(1)
UϪN(2)
C(1)ϪS(4)
C(1)ϪC(2)
N(1)ϪUϪN(2)
S(1)ϪUϪN(1)
S(2)ϪUϪN(1)
cotϪUϪN(1)[a]
cotϪUϪS(1)
2.8203(10)
2.585(3)
1.771(4)
1.336(5)
62.57(10)
125.45(7)
64.23(7)
107.9
UϪS(2)
UϪN(3)
C(2)ϪS(2)
2.8304(10)
2.599(3)
1.746(4)
C(2)ϪS(3)
S(1)ϪUϪS(2)
N(2)ϪUϪN(3)
S(1)ϪUϪN(3)
S(2)ϪUϪN(3)
cotϪUϪN(3)
N(1)ϪUϪN(3)
S(1)ϪUϪN(2)
S(2)ϪUϪN(2)
cotϪUϪN(2)
cotϪUϪS(2)
119.58(10)
134.27(7)
77.15(7)
113.0
106.3
163.6
[a]
cot is the centroid of the C8H8 ring.
1
Table 3. H NMR spectroscopic data of the complexes[a]
Compound
T [°C]
cot ligand[b]
Dithiolene ligand
L ligands or 18-crown-6[c]
[U(cot)(dddt)(py)2] (6)[19]
[U(cot)(dddt)(hmpa)2] (12)
ϩ20
Ϫ40
ϩ60
Ϫ80
ϩ20
ϩ20
Ϫ30.98 (12 Hz)
Ϫ38.75 (12 Hz)
Ϫ26.13 (6 Hz)
Ϫ45.2 (130 Hz)
Ϫ32.07 (12 Hz)
Ϫ31.46 (15 Hz)
10.87 (33 Hz, 4 H)
20.2 and 15.1 (500 Hz, 2 ϫ 2 H)
Ϫ3.6 (140 Hz, ca 3 H)
1.30 (36 H)
Ϫ1.60 (36 H)
1.33 and Ϫ5.10 (35 Hz, 2 ϫ 2 H)
[U(cot)(dmio)(py)2] (7)[19]
[U(cot)(dmio)(tppo)2] (10)
7.11 (6 H), 6.73 (12 H)
5.30 (45 Hz, 12 H)
1.93 (36 H)
[U(cot)(dmio)(hmpa)2] (13)
[U(cot)(mdt)(py)2] (8)[19]
ϩ20
ϩ90
Ϫ30
ϩ20
Ϫ30.44 (12 Hz)
Ϫ24.82 (8 Hz)
Ϫ37.51 (3 Hz)
Ϫ29.52 (4 Hz)
11.21 (35 Hz, 2 H)
17.08 (45 Hz, 1 H)[d]
[U(cot)(mdt)(tppo)2] (11)
5.22 and Ϫ2.74 (20 Hz, 2 ϫ 1 H)
7.07 (6 H), 6.68 (12 H)
3.78 (45 Hz, 12 H)
0.07 (36 H)
[U(cot)(mdt)(hmpa)2] (14)
ϩ20
Ϫ28.78 (4 Hz)
3.29 and Ϫ4.79 (35 Hz, 2 ϫ 1 H)
[a]
In [D8]THF; 6, 7 and 8 in [D5]pyridine. The half-height width and the relative integral of the singlet signal are given in parentheses.
[b]
[c]
[d]
The cot signal integrates for 8 H. When not specified, the half-height width is between 10 and 30 Hz.
mdt ligand is masked by the solvent resonances.
The other signal of the
4506
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 4502Ϫ4509

Monocyclooctatetraenyl(dithiolene)uranium Compounds
FULL PAPER
gand and the metal centre observed in the solid state is
favoured with the sterically less demanding Lewis bases
which allow an endo conformation of the ligand. Still, the
characteristics of the dithiolene ligands, such as the average
C(sp2)ϪS and CϭC distances, are not greatly influenced by
the nature of the Lewis base. In the whole series, the vari-
able temperature 1H NMR spectra show the fluxionality of
the complexes due to the facile dithiolene ring inversion.
Scheme 4. Ring inversion process of the dithiolene ligand
thiolene)(py)3], with a structure similar to that of the terpy
adduct 16, should be involved in the reaction. However,
such an associative mechanism is not likely for the other
Lewis-base adducts, since addition of tppo or hmpa has no
influence on the fluxional process. The coalescence tem-
peratures, Tc, and the activation energies, ∆G‡, for the dithi-
olene ring inversion process are given in Table 4. The values
of ∆G‡ are in the range of those calculated for the
[Ti(Cp)2(dithiolene)] compounds, which vary from 40.5 to
69 kJ·molϪ1 when the dithiolene is S2C2(CN)2 and mdt,
Experimental Section
General Remarks: All reactions were carried out under argon
(Ͻ5 ppm oxygen or water) using standard Schlenk and vacuum-
line techniques or in a glove box. Solvents were dried by standard
1
methods and distilled immediately before use. The H NMR spec-
tra were recorded with a Bruker DPX 200 instrument and refer-
enced internally using the residual protio solvent resonances rela-
tive to tetramethylsilane (δ ϭ 0 ppm). Elemental analyses were per-
respectively;[14] they can also be compared with those meas- formed by Analytische Laboratorien at Lindlar (Germany).
[U(cot)(BH4)2],[21] [U(cot)I2(THF)2],[37] dddtCO,[38] dmioCO[39]
ured for the metallacyclopentene ring inversion in bis(cyclo-
and Na2dddt[13] were prepared by published methods. The synth-
pentadienyl)diene complexes of group 4 metals and actin-
eses of 3, 4, 5 and 8 were described in our previous paper.[19]
ides.[36] In the (dithiolene)titanium compounds, a corre-
lation was found between the activation energy ∆G‡ and the
Synthesis of [U(cot)(dddt)(py)2] (6) and [U(cot)(dmio)(py)2] (7):
These complexes were obtained by dissolving 3 and 4, respectively,
in pyridine. After concentration to dryness, a dark-red powder of
6 and a brown powder of 7 were obtained in almost quantitative
folding angle θ.[14] However, in the [U(cot)(dithiolene)(L)2]
derivatives, the variation of ∆G‡ seems better related to the
steric congestion of the complex and the difficulty of the
ligands to rearrange around the metal centre. The lower
barrier in the dddt compounds 6 and 12, by comparison
yield.
with the mdt analogues 8 and 14, respectively, would corre-
spond to a greater steric interaction between the dithiolene
and L ligands in the ground state of the complex.
Synthesis of [U(cot)(dddt)(tppo)2] (9): An NMR tube was charged
with 3 (5.0 mg, 4.6 µmol) and tppo (2.6 mg, 9.2 µmol) in [D8]THF
(0.4 mL). Upon standing at 50 °C for 2Ϫ3 d, red crystals of 9
suitable for X-ray analysis were deposited.
Table 4. Coalescence temperatures and activation energies for the
ring-inversion process
Synthesis of [U(cot)(dmio)(tppo)2] (10): An NMR tube was charged
with 4 (5.0 mg, 4.8 µmol) and tppo (5.3 mg, 19.1 µmol) in [D8]THF
(0.4 mL). After 1 h at 20 °C, the spectrum of the brown solution
showed the quantitative formation of 10.
Compound
Tc [°C]
∆G‡ [kJ·molϪ1
]
[U(cot)(dddt)(py)2] (6)[19]
[U(cot)(dddt)(hmpa)2] (12)
[U(cot)(mdt)(py)2] (8)[19]
[U(cot)(mdt)(tppo)2] (11)
[U(cot)(mdt)(hmpa)2] (14)
Ϫ30
ϩ20
ϩ30
ϩ80
ϩ80
43(1)
53(1)
50(1)
63(1)
63(1)
Synthesis of [U(cot)(mdt)(tppo)2] (11). (a): An NMR tube was
charged with 5 (5.0 mg, 4.9 µmol) and tppo (5.5 mg, 19.6 µmol) in
[D8]THF (0.4 mL). After standing at 65 °C for 3 h, brown crystals
of 11 suitable for X-ray analysis were deposited. (b): A flask was
charged with [U(cot)(BH4)2(THF)] (113 mg, 0.254 mmol) and tppo
(142 mg, 0.51 mmol) in THF (25 mL). The reaction mixture was
stirred at 20 °C for 15 min and a solution of dmioCO (53 mg,
0.254 mmol) in THF (10 mL) was added to the flask. After re-
fluxing for 3 h, the solution was filtered and the solvents were eva-
porated to dryness, leaving a brown powder of 11 (276 mg, 90%).
11·2THF, C55H56O4P2S4U (1209.3): calcd. C 54.63, H 4.67, S 10.61;
found C 54.45, H 4.50, S 10.78.
Conclusion
We have prepared a series of Lewis-base adducts of gen-
eral formula [U(cot)(dithiolene)(L)n] (n ϭ 1, L ϭ bipy or
terpy and dithiolene ϭ mdt; n ϭ 2, L ϭ tppo or hmpa and
dithiolene ϭ dddt, dmio, mdt). Crystallographic and NMR
studies revealed that the solid-state structure and dynamic
behaviour of these dithiolene complexes of an f-block ele-
ment are similar to those of the d-block transition metal
analogues, in particular the mixed cyclopentadienyl/dithi-
Synthesis of [U(cot)(dddt)(hmpa)2] (12): An NMR tube was charged
with 3 (5.0 mg, 4.8 µmol) in [D8]THF (0.4 mL) and hmpa (3.3 µL,
19.1 µmol) was introduced with a microsyringe. After 1 h at 20 °C,
the spectrum of the red solution showed the quantitative formation
of 12. After standing at 20 °C overnight, red crystals of 12 suitable
for X-ray analysis were deposited. C24H48N6O2P2S4U (880.93):
olene derivatives. The interaction between the dithiolene li- calcd. C 32.72, H 5.49, S 14.56; found C 32.59, H 5.51, S 14.41.
Eur. J. Inorg. Chem. 2004, 4502Ϫ4509
www.eurjic.org  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 4507

´
´
T. Arliguie, P. Thuery, M. Fourmigue, M. Ephritikhine
FULL PAPER
˚
Synthesis of [U(cot)(dmio)(hmpa)2] (13): A flask was charged with
ite-monochromated Mo-Kα radiation (λ ϭ 0.71073 A). The crystals
[U(cot)(BH4)2(THF)] (208 mg, 0.56 mmol) and hmpa (201 mg, were placed inside glass capillaries with a protecting ‘‘Paratone-
1.12 mmol) in THF (30 mL) and dmioCO (233 mg, 1.12 mmol) was N’’ oil (Hampton Research) coating. The unit-cell parameters were
added to the solution. After stirring at 20 °C for 24 h, the solution
was filtered and the solvents were evaporated to dryness. The dark-
red powder of 13 was washed with diethyl ether (50 mL), THF
determined from ten frames, then refined on all data. A 180° ϕ-
range was scanned with 2° steps during data collection, with a crys-
tal-to-detector distance fixed at 28 mm, giving complete data sets
(20 mL)
and
dried
under
vacuum
(460 mg,
93%). up to an angle, θmax, of 25.7°. The data were processed with
C23H44N6O3P2S4U (880.88): calcd. C 31.36, H 5.03, S 14.56; found
C 31.13, H 5.03, S 14.39.
DENZO-SMN.[41] The structures were solved by direct methods
with SHELXS-97 and subsequent Fourier-difference synthesis and
refined by full-matrix least squares on F2 with SHELXL-97.[42] Ab-
sorption effects were corrected empirically with the program DE-
LABS from PLATON.[43] The correct enantiomorph in compound
13 was determined from the Flack parameter [Ϫ0.020(10)].[44]
Three compounds crystallize as solvates: 9 and 11 with two tetra-
hydrofuran molecules and 16 with 1.5 pyridine molecules. A second
form of compound 11, with only one tetrahydrofuran solvent mol-
ecule, has been isolated and characterized [crystal data:
Synthesis of [U(cot)(mdt)(hmpa)2] (14): An NMR tube was charged
with 5 (5.0 mg, 4.9 µmol) in [D8]THF (0.4 mL) and hmpa (3.4 µL,
19.6 µmol) was introduced with a microsyringe. After 1 h at 65
°C, the spectrum of the brown solution showed the quantitative
formation of 14. After standing at 65 °C overnight, the tube was
allowed to cool to room temperature and red crystals of 14 suitable
for X-ray analysis were deposited.
¯
C51H48O3P2S4U, M ϭ 1137.10, triclinic, space group P1, a ϭ
Synthesis of [U(cot)(mdt)(bipy)] (15): An NMR tube was charged
with 5 (21.0 mg, 20.6 µmol) and bipy (6.4 mg, 41.2 µmol) in
[D8]THF (0.4 mL). After standing at 5 °C overnight, dark brown
crystals of 15 suitable for X-ray analysis were deposited.
C21H18N2S4U (664.68): calcd. C 37.95, H 2.73, S 19.30; found C
38.10, H 2.85, S 19.05.
˚
12.5818(13), b ϭ 12.7381(13), c ϭ 16.4223(14) A, α ϭ 71.253(6)°,
3
˚
β ϭ 72.669(6)°, γ ϭ 72.573(4)°, V ϭ 2318.0(4) A , Z ϭ 2, Dc ϭ
1.629 g·cmϪ3, µ ϭ 3.793 mmϪ1, F(000) ϭ 1128]. As it is essentially
similar to the first form, it is not further described here. Some dis-
order is present in several complexes. In 9·2THF, the atoms C(3)
and C(4) of the dithiolene ligand may be disordered, but the differ-
ent positions are not resolved and these atoms have been refined
with restraints on bond lengths and displacement parameters. In
16·1.5py, one pyridine solvent molecule is disordered around a
symmetry centre and the nitrogen atom has not been located. All
non-hydrogen atoms were refined with anisotropic displacement
parameters, with some restraints on bond lengths and/or displace-
ment parameters for some disordered or badly behaving atoms,
particularly in the solvent molecules. Hydrogen atoms were intro-
duced at calculated positions and were treated as riding atoms with
Synthesis of [U(cot)(mdt)(terpy)] (16): An NMR tube was charged
with 5 (10.0 mg, 9.8 µmol) and terpy (4.6 mg, 19.6 µmol) in
[D8]THF (0.4 mL). After standing at 5 °C overnight, dark-brown
crystals of 16 suitable for X-ray analysis were deposited.
C26H21N3S4U (741.76): calcd. C 42.10, H 2.85, S 17.29; found C
41.92, H 2.96, S 17.06.
X-ray Crystallography: The data were collected at 100(2) K with a
Nonius Kappa-CCD area-detector diffractometer[40] using graph-
Table 5. Crystal data and structure refinement details
9·2THF
11·2THF
12
13
14
15
16·1.5py
Empirical formula C56H58O4P2S4U C55H56O4P2S4U C24H48N6O2P2S4U C23H44N6O3P2S4U C23H46N6O2P2S4U C21H18N2S4U C33.5H28.5N4.5S4U
M [g molϪ1
]
1223.23
monoclinic
P21/c
17.4062(10)
11.2254(5)
26.2282(17)
90
91.459(5)
90
5123.1(5)
4
1209.21
monoclinic
P21/c
17.8541(9)
10.8390(5)
25.8930(12)
90
91.377(3)
90
5009.4(4)
4
880.89
monoclinic
P21/n
11.2254(8)
16.2142(17)
18.7509(18)
90
92.248(6)
90
3410.2(5)
4
880.85
orthorhombic
P212121
10.3673(6)
15.8278(15)
20.0597(18)
90
90
90
3291.6(5)
4
1.777
866.87
triclinic
¯
P1
664.64
monoclinic
P21/m
7.4304(5)
14.4901(9)
10.0511(7)
90
109.787(4)
90
1018.28(12)
2
860.38
monoclinic
P21/n
14.1685(4)
14.9404(4)
15.3685(5)
90
105.399(2)
90
3136.46(16)
4
Crystal system
Space group
˚
a [A]
10.7430(6)
16.2499(10)
20.5468(10)
67.938(3)
86.563(3)
87.829(3)
3317.8(3)
4
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
3
˚
V [A ]
Z
Dcalcd. [g cmϪ3
µ(Mo-Kα) [mmϪ1
F(000)
]
1.586
3.440
2448
1.603
3.517
2416
1.716
5.130
1744
1.735
5.271
1712
2.168
8.391
628
1.822
5.474
1668
]
5.317
1736
Reflections collected 28649
33582
21645
19862
22784
7023
20975
Ind. reflections
Obsd. reflections
[I Ͼ 2σ(I)]
Rint
9533
3607
9466
6356
6432
4471
6128
4979
11554
8411
2006
1757
5908
4911
0.093
0.094
595
0.088
364
0.129
364
0.074
704
0.068
130
0.054
388
Parameters refined 604
R1
wR2
S
∆ρmin [e·A
∆ρmax [e·A
0.087
0.053
0.106
1.019
Ϫ1.02
1.24
0.050
0.094
1.019
Ϫ1.03
0.89
0.056
0.129
1.013
Ϫ1.23
1.15
0.070
0.154
1.104
Ϫ2.02
4.41
0.030
0.059
1.023
Ϫ0.91
0.62
0.027
0.055
1.017
Ϫ0.78
0.74
0.135
0.933
Ϫ1.00
0.90
Ϫ3
˚
˚
]
]
Ϫ3
4508
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 4502Ϫ4509

Monocyclooctatetraenyl(dithiolene)uranium Compounds
FULL PAPER
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[19]
[20]
[21]
[22]
[23]
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www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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