In pursuit of homoleptic actinide alkyl complexes

Article abstract of DOI:10.1021/ic300867m

This Forum Article describes the pursuit of isolable homoleptic actinide alkyl complexes, starting with the pioneering work of Gilman during the Manhattan project. The initial reports in this area suggested that homoleptic uranium alkyls were too unstable

Full text of DOI:10.1021/ic300867m

Forum Article
pubs.acs.org/IC
In Pursuit of Homoleptic Actinide Alkyl Complexes
Lani A. Seaman,† Justin R. Walensky,*,‡ Guang Wu,† and Trevor W. Hayton*,†
†Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
‡Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
S
* Supporting Information
ABSTRACT: This Forum Article describes the pursuit of isolable
homoleptic actinide alkyl complexes, starting with the pioneering work of
Gilman during the Manhattan project. The initial reports in this area
suggested that homoleptic uranium alkyls were too unstable to be isolated,
but Wilkinson demonstrated that tractable uranium alkyls could be
generated by purposeful “ate” complex formation, which serves to saturate
the uranium coordination sphere and provide the complexes with greater
kinetic stability. More recently, we reported the solid-state molecular
structures of several homoleptic uranium alkyl complexes, including [Li(THF)4][U(CH2 Bu)5], [Li(TMEDA)]2[UMe6],
t
[K(THF)]3[K(THF)2][U(CH2Ph)6]2, and [Li(THF)4][U(CH2SiMe3)6], by employing Wilkinson’s strategy. Herein, we
t
describe our attempts to extend this chemistry to thorium. The treatment of ThCl4(DME)2 with 5 equiv of LiCH2 Bu or
t
LiCH2SiMe3 at −25 °C in THF affords [Th(CH2 Bu)5] (1) and [Li(DME)2][Th(CH2SiMe3)5 (2), respectively, in moderate
yields. Similarly, the treatment of ThCl4(DME)2 with 6 equiv of K(CH2Ph) produces [K(THF)]2[Th(CH2Ph)6] (3), in good
yield. Complexes 1−3 have been fully characterized, while the structures of 1 and 3 were confirmed by X-ray crystallography.
Additionally, the electronic properties of 1 and 3 were explored by density functional theory.
reactions was not uranium metal but a uranium(III) hydride,
namely, UCl2H.6
INTRODUCTION
History. The pursuit of isolable homoleptic uranium alkyl
■
complexes has been ongoing since the 1940s.1−8 This research
was first motivated by the need for volatile uranium compounds
for centrifugal isotope separation during the Manhattan project.
Inspired by the volatility of main-group organometallics, such as
PbMe4,2 Gilman and co-workers attempted the preparation of
homoleptic uranium alkyls, including tetramethyluranium. Few
experimental details were given in the original paper describing
this work, but it was mentioned that the compounds were too
unstable to be isolated.1,2 Four decades later, the synthesis of
homoleptic alkyls was revisited by Marks and Seyam.3 They
Recognizing that the coordinative unsaturation of the metal
center in these complexes is a likely cause of their thermal
instability,4,12 Wilkinson and Sigurdson purposefully reacted
UCl4 with an excess of alkyllithium reagents to produce ‘ate’
complexes. These reactions afforded isolable, homoleptic alkyl
‘ate’ species with the formulation [Li(solvent)4]2[UR6] (solvent
= THF, Et2O; R = Me, C6H5, CH2SiMe3).4 These molecules
were characterized by 1H NMR spectroscopy, magnetic
susceptibility, and, where possible, elemental analysis. In
t
addition, the reaction of excess LiR (R = Me, CH2 Bu,
CH2SiMe3) with U2(OEt)10 in dioxane was reported to provide
the uranium(V) octa(alkyl) complexes [Li(dioxane)]3[UR8].
However, the formulation of both the uranium(IV) and -(V)
complexes, in the absence of solid-state structural data, was
later called into question.12
In parallel with the efforts of Wilkinson, Thiele and co-
workers reported the synthesis of U(CH2Ph)4·MgCl2. Separa-
tion of MgCl2 from the uranium component could not be
achieved. Additionally, the compound reportedly decomposed
above 130 °C.13 Other than elemental analysis, little character-
ization of this material was provided, but it is likely that the
ability of the benzyl ligand to adopt multidentate coordination
modes provides enhanced kinetic stability. Similarly, Andersen
and co-workers discovered that “UR4”-type complexes could be
t
n
t
treated UCl4 with 4 equiv of LiR (R = Me, CH2 Bu, Bu, Bu,
iPr) at low temperatures to generate “UR4”, which rapidly
decomposed on warming.3,7 The organic decomposition
products were found to be mostly alkanes, and small amounts
of alkenes, the latter likely formed by β-hydrogen elimination.
For example, the reaction of UCl4 with 4 equiv of n-BuLi in
hexane reportedly yields 23.6% n-butane, 5.6% 1-butene, and
0.4% octane after 1 h at room temperature. They also
concluded that U−C bond homolysis was not a major reaction
pathway, based on the observation that the stereochemistry of
the 2-cis-2-butenyl and 2-trans-2-butenyl fragments is retained
upon thermolysis of the corresponding tetrakis(2-cis-2-
butenyl)- and 2-trans-2-butenyluranium complexes.9 Other
groups have also explored the reactivity of UCl4 with
alkyllithium reagents and reported the formation of finely
divided uranium metal.3,5,9−11 However, Evans and co-workers
thoroughly reinvestigated the reaction of UCl4 with both tert-
BuLi and n-BuLi and concluded that the likely product in these
Special Issue: Inorganic Chemistry Related to Nuclear Energy
Received: April 27, 2012
Published: June 20, 2012
© 2012 American Chemical Society
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stabilized by the addition of phosphines,14 which allowed them
to isolate the well-characterized complexes AnR4(dmpe)n (An =
U, Th; R = Me, CH2Ph; n = 1, 2).14,15 Finally, in 1989
Sattelberger and co-workers synthesized the first well-
characterized homoleptic actinide alkyl, namely, U[CH-
(SiMe3)2]3, by the reaction of U(O-2,6-tBu2C6H3)3 with 3
equiv of LiCH(SiMe3)2.8 While not coordinatively saturated,
kinetic stabilization of this complex is afforded by the extremely
bulky −CH(SiMe3)2 ligand. In the solid state, U[CH(SiMe3)2]3
exhibits a trigonal-pyramidal geometry, similar to that of
U(N(SiMe3)2)3,16 which has piqued the interest of theoret-
icians.17,18
with 6 equiv of MeLi, in the presence of excess TMEDA
(Scheme 1). In the solid state, this complex exhibits an
octahedral geometry about the uranium center, unlike its
transition-metal counterparts (vide infra), which display
trigonal-prismatic geometries, suggesting that there is little
involvement of the 6d orbitals in the U−C σ bond.19 This
complex is quite temperature-sensitive and decomposes rapidly
above −25 °C, both in solution and in the solid state.
Additionally, the reaction of UCl4 with 6 equiv of K(CH2Ph) in
THF results in the formation of [K(THF)]3[K(THF)2][U-
(CH2Ph)6]2 as a deep-red solid in good yield (Scheme 1). In
the solid state, this complex exists as an extended 3D solid, in
which [U(CH2Ph)6]2− monomers are linked via arene···K+
bridging interactions. Notably, all of the benzyl groups exhibit
an η1-coordination mode.
[Li(DME)3][U(CH2SiMe3)5] has proven to be amenable to
further synthetic elaboration. For example, the reaction of
[Li(DME)3][U(CH2SiMe3)5] with 0.5 equiv of I2, followed by
1 equiv of Li(CH2SiMe3), in Et2O at −25 °C, leads to the
formation of a novel homoleptic uranium(V) alkyl, [Li-
(THF)4][U(CH2SiMe3)6].20 In the solid state, [Li(THF)4][U-
(CH2SiMe3)6] exhibits an octahedral geometry. Further
oxidation of this complex to uranium(VI) is also possible.
Thus, the treatment of [Li(THF)4][U(CH2SiMe3)6] with
U(OtBu)6 in THF (Scheme 2) cleanly generates U-
(CH2SiMe3)6, according to 1H NMR spectroscopy. The
solid-state molecular structure of U(CH2SiMe3)6 would be of
significant interest; however, this material is quite thermally
sensitive and rapidly decomposes above −25 °C, making its
isolation an experimental challenge.
In 2009, our research group reinvestigated the syntheses
reported by Wilkinson and Sigurdson. We found that the
t
reaction of UCl4 with 5 equiv of LiR (R = CH2 Bu, CH2SiMe3)
produced [Li(solvent)x][UR5] (solvent = DME, THF) in good
yields (Scheme 1).19 Both complexes were fully characterized,
Scheme 1
More recently, Bart and co-workers reported the synthesis of
base-free U(CH2Ph)4, by alkylation of UCl4 with K(CH2Ph) in
THF.21 In the solid state, this complex features a pseudote-
trahedral arrangement of four η4-benzyl ligands. This complex
is thermally sensitive, generating toluene and bibenzyl upon
standing. Also of note, the addition of the redox-active
MesDABMe ligand [MesDABMe = ArNC(Me)C(Me)NAr;
Ar = 2,4,6-Me3C6H2] to U(CH2Ph)4 results in the formation of
(
MesDABMe)U(CH2Ph)2 and 1 equiv of bibenzyl, via a reductive
elimination pathway.21 In related work, Diaconescu and co-
workers reported the in situ formation of “U-
(CH2Ph)3(THF)n”, which they subsequently used to prepare
a pyridinyldi(amido) complex.22
including analysis by X-ray crystallography in the case of R =
t
CH2 Bu. This complex exhibits a trigonal-bipyramidal structure
about uranium. The (trimethylsilyl)methyl analogue was
presumed to be isostructural, based on the structural character-
ization of trigonal-bipyramidal [Li14(OtBu)12Cl][U-
(CH2SiMe3)5].19 Interestingly, no evidence for the formation
of octahedral [UR6]2−-type complexes was observed, even
when 6 equiv of LiR were used in the reaction. Thus, it seems
likely that Wilkinson and Sigurdson originally isolated [Li-
(solvent)x][UR5]-type complexes, instead of the proposed
hexa(alkyl) species.
In contrast to the rich chemistry reported for uranium, there
has been limited progress toward the synthesis and character-
ization of homoleptic thorium alkyl complexes. To date, only
one homoleptic thorium alkyl complex has been structurally
characterized, namely, the heptamethyl complex [Li-
(TMEDA)]3[ThMe7].23 The complex exhibits a distorted
monocapped trigonal-prismatic geometry, which differs from
the six-coordinate geometry found for [Li-
(TMEDA)]2[UMe6].19 This difference is likely due to the
larger ionic radius of ThIV versus UIV (for CN = 6: U4+ = 89
We also prepared a homoleptic uranium(IV) methyl
complex, [Li(TMEDA)]2[UMe6], by the reaction of UCl4
Scheme 2
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Scheme 3
pm, Th4+ = 94 pm).24 The homoleptic benzyl complexes
octahedral geometry is also expected if M−L bonding is
predominantly ionic,70 a fact that likely explains the octahedral
geometries observed for [Li(TMEDA)]3[LnMe6] (Ln = Ho,
Er, Lu).71−73 The synthesis and characterization of new
homoleptic actinide alkyl complexes could help untangle
these effects, and in this context, thorium is especially
interesting because its f orbitals are thought to be too high in
energy to interact with the ligands, leaving the d orbitals as the
primary orbitals for forming M−L bonds.57,74 These observa-
tions prompted us to explore the synthesis of new homoleptic
thorium alkyl complexes.
25
26
Th(CH2-3,5-Me2C6H3)4 and Th(CH2Ph)4 have also been
reported, but their structures have not been confirmed by X-ray
crystallography, although a phosphine adduct of Th(CH2Ph)4,
namely, Th(CH2Ph)4(dmpe), has been structurally character-
ized.14 Finally, Th(CH2SiMe3)4(DME)n was prepared by the
reaction of ThCl4(DME)2 and 4 equiv of LiCH2SiMe3, but its
isolation was hampered by its thermal instability.27
Structure and Bonding. Interest in high-valent, homo-
leptic organometallic complexes has not been restricted to the
actinides. In fact, transition metal complexes of the type [MR6]n
(R = alkyl, aryl, H; n = 0, −1, −2) have been the focus of
intense theoretical and experimental scrutiny.28−42 Interest in
this area was spurred by the observation that [Li-
(TMEDA)]2[ZrMe6] exhibits a trigonal-prismatic D3h geome-
try in the solid state.38 Similarly, an X-ray crystallographic
determination of WMe6 by Seppelt and Pfennig revealed a
distorted trigonal-prismatic C3v geometry,35,43,44 confirming the
results of an earlier gas-phase electron diffraction study.45 Since
these pioneering studies, many homoleptic complexes exhibit-
ing trigonal-prismatic structures have been structurally
characterized, including ReMe6, [Ta(CCSitBu3)6]−, [M-
(C6H5)6]− (M = Nb, Ta), and [Zr(SC6H4-p-Me)6]2−.35,36,46−49
Many theoretical studies have been performed to uncover the
electronic structures responsible for this geometry preference.
Interestingly, both molecular orbital and valence-bond analyses
predict an energetic preference for trigonal-prismatic geo-
metries in systems where dn ≤ 1 and the metal is ligated by σ-
only ligands.28−30,32−34,39−41,50 In these systems, the distortion
away from Oh is favored because it allows for greater metal d-
o r b i t a l i n v o l v e m e n t i n t h e m e t a l − l i g a n d
bond,28−30,32,34,35,37,51,52 resulting in a strengthening of the σ
interaction.29,30 Electronic configurations with dn > 1 force the
p orbitals to participate in M−R bonding, thereby favoring an
octahedral geometry.29,30,35,37 Thus, the observation of a
nonoctahedral geometry is evidence for d-orbital involvement
in metal−ligand bonding. This final point is of particular
importance to actinide chemists, who are currently engaged in
an intense effort to quantify the participation of the 6d and 5f
orbitals in An−L bonding.53−67 However, all three structurally
characterized [UR6]n-type complexes (n = −1, −2; R = Me,
CH2Ph, CH2SiMe3) isolated thus far exhibit octahedral
geometries.19,20 This difference in the geometry preference
can be explained by the ability of uranium to engage its f
orbitals in bonding. The ungerade character of the 5f orbitals,
like the ungerade character of the p orbitals, should enforce an
octahedral geometry for six-coordinate complexes.37,65,68,69 In
fact, f-orbital participation in [U(CH2SiMe3)6]− is predicted to
be significant. For example, the HOMO−1, HOMO−2, and
HOMO−3 orbitals (HOMO = highest occupied molecular
orbital) in [U(CH2SiMe3)6]−, which comprise the t1u set,
exhibit ca. 29% 5f-orbital participation.20 Alternately, an
RESULTS AND DISCUSSION
■
Synthesis. We initially attempted to prepare a homoleptic
six-coordinate [ThMe6]2− complex, for comparison with the
uranium analogue, [UMe6]2−. However, the reaction of
ThCl4(DME)2 with 6 equiv of MeLi in Et2O at −25 °C, in
the presence of TMEDA, results in the formation of the
previously characterized [Li(TMEDA)]3[ThMe7], as the only
identifiable species by 1H NMR spectroscopy (see the
Supporting Information).23 Its presence is marked by a singlet
at 0.18 ppm in C6D6, assignable to the Th−CH3 groups. This is
identical with the chemical shift reported by Marks et al.23 We
also attempted to access [ThMe6]2− by demethylation of
[Li(TMEDA)]3[ThMe7].23 Thus, the addition of 1 equiv of
Me3SiCl to [Li(TMEDA)]3[ThMe7] in C6D6 results in the
formation of a yellow solution and generation of a white
1
precipitate (see the Supporting Information). The H NMR
spectrum reveals a sharp singlet at 0 ppm, assignable to SiMe4.
Also present is a broad resonance at 0.20 ppm, which we have
assigned to the methyl protons of the starting material,
[Li(TMEDA)]3[ThMe7] (eq 1). No other methyl environ-
ments are observed. Performing the reaction on a preparatory
scale leads only to isolation of the starting material in 45% yield.
Attempts to abstract a methyl group with 1 equiv of NEt3HCl
produce similar results (see the Supporting Information). Thus,
it appears that demethylation simply results in the re-formation
of [Li(TMEDA)]3[ThMe7] via methyl scrambling, with
concomitant formation of an unobserved decomposition
product.
[Li(TMEDA)]3[ThMe7]
⎯M⎯⎯e⎯3⎯S⎯⎯i→Cl [Li(TMEDA)]3[ThMe7] + Me4Si
−LiCl
C
D
6
6
+ decomposition
(1)
Because of the presumed instability of [ThMe6]2‑, we turned
our attention to alkylating reagents with bulkier R substituents,
t
namely, LiCH2 Bu, LiCH2SiMe3, and KCH2Ph. The addition of
t
5 equiv of LiCH2 Bu to a THF solution of ThCl4(DME)2 at
−25 °C gives a pale-yellow solution. After recrystallization from
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Et2O, the five-coordinate neopentylthorium complex, [Li-
t
(THF)4][Th(CH2 Bu)5] (1), can be isolated in 50% yield as
colorless crystals (Scheme 3). Similarly, the addition of 5 equiv
of LiCH2SiMe3 to a THF solution of ThCl4(DME)2 at −25 °C
produces a colorless solution. Crystallization from Et2O/DME,
provides [Li(DME)2][Th(CH2SiMe3)5] (2) as a white solid in
t
54% yield. Notably, the addition of 6 equiv of either LiCH2 Bu
or LiCH2SiMe3 to ThCl4(DME)2 also results in the formation
of the five-coordinate complexes.
Complexes 1 and 2 are thermally unstable solid that can be
stored indefinitely at −25 °C under an inert atmosphere. Both
1 and 2 are insoluble in hexane but are very soluble in Et2O and
THF. The 1H NMR spectrum of 1 in THF-d8 reveals
resonances at +1.02 and −0.07 ppm, corresponding to the
methyl and methylene protons, respectively. The 13C{1H}
NMR spectrum in THF-d8 features resonances at 117.96 and
37.58 ppm, assignable to the methylene and methyl carbons,
respectively. A resonance at 39.14 ppm is assignable to the
quaternary carbon. Finally, there is a single resonance at 0.50
ppm in the 7Li NMR spectrum. The 1H NMR spectrum of 2 in
THF-d8 exhibits resonances at −0.01 and −0.63 ppm,
corresponding to the methyl and methylene protons of the
(trimethylsilyl)methyl ligand, respectively. Likewise, the
13C{1H} NMR spectrum in THF-d8 exhibits resonances at
82.97 and 5.08 ppm, assignable to the methylene and methyl
carbons of the (trimethylsilyl)methyl ligand, respectively.
Figure 1. Solid-state molecular structure of 1 with 30% probability
ellipsoids. [Li(THF)4]+ cation and hydrogen atoms excluded for
clarity. Selected bond lengths (Å) and angles (deg): Th1−C1 =
2.52(3), Th1−C2 = 2.50(2), Th1−C3 = 2.56(2), Th1−C4 = 2.46(2),
Th1−C5 = 2.53(2); Th1−C1−C6 = 131(2), Th1−C2−C10 = 145(2),
Th1−C3−C14 = 129(2), Th1−C4−C18 = 125(2), Th1−C5−C22 =
148(2), C1−Th1−C3 = 132(1), C1−Th1−C4 = 116.4(9), C3−Th1−
C4 = 111.4(8), C2−Th1−C5 = 173.0(9).
7
Finally, the Li NMR spectrum in THF-d8 exhibits a single
resonance at −0.53 ppm.
Both 1 and 2 are stable in THF at room temperature for
several hours, according to 1H NMR spectroscopy, but after 24
h, evidence of decomposition is present in both samples. Both 1
and 2 are unstable in aromatic solvents. Dissolution of 1 in
C6D6 results in immediate decomposition, affording a colorless
solution in which neopentane is the only identifiable product,
according to 1H NMR spectroscopy. Complex 2 also
decomposes immediately in the presence of C6D6, affording
insoluble in hexane and toluene but very soluble in THF. Its 1H
NMR spectrum in THF-d8 exhibits resonances at 6.69, 6.27,
6.11, and 1.34 ppm, corresponding to the three aryl CH
environments and the methylene protons, respectively. The
13C{1H} NMR spectrum in THF-d8 at 0 °C exhibits very broad
resonances at 153.0, 124.1, and 115.9 ppm, assignable to the
carbon environments of the aryl ring. Additionally, a broad
resonance at 89.6 ppm is assignable to the methylene
resonance. We suggest that the broadness of the 13C resonances
is due to the fluxional behavior of the benzyl ligand (vide infra).
Attempts to probe this behavior with variable-temperature
13C{1H} NMR spectroscopy were thwarted by the insolubility
of 3 in cold THF, which prevents low-temperature spectra from
being recorded, and its thermal sensitivity, which prevents high-
temperature spectra from being recorded. For example, toluene
is observed in a THF-d8 solution of 3 after only 5 min at room
temperature. Upon further standing, the solution turns orange-
red and the resonances associated with 3 disappear, while those
of toluene increase in intensity.
Complex 3 crystallizes in the monoclinic space group Pn and
consists of two crystallographically independent thorium
centers (Figure 2). Each thorium is coordinated by six benzyl
ligands in a severely distorted octahedral geometry [e.g., C1−
Th1−C5 = 73.4(6)°, C1−Th1−C4 = 114.6(5)°, C8−Th2−C9
= 115.5(6)°, and C7−Th2−C10 = 80.2(6)°]. This distortion is
due to the presence of a multidentate benzyl ligand in each
thorium coordination sphere.14,78,79 For Th1, the multidentate
benzyl ligand exhibits a Th−C(ipso) distance of Th1−C16 =
3.04(2) Å, while the corresponding Th−Cbenzyl distance is
Th1−C4 = 2.63(2) Å. Additionally, the Th−C−C angle is
Th1−C4−C16 = 93(1)°, while the Th−C(ortho) distances are
3.28(2) and 3.91(2) Å. Overall, these metrical parameters are
1
several unidentifiable resonances in the H NMR spectrum.
Similar results are observed in pyridine-d5.
Complex 1 crystallizes in the monoclinic space group P212121
with two crystallographically independent molecules in the
asymmetric unit. They exhibit similar metrical parameters, and
only one will be discussed in detail. In the solid state, 1 exhibits
a trigonal-bipyramidal geometry about the thorium center
(Figure 1) and is isostructural with its uranium(IV) analogue,
19
t
[Li(THF)4][U(CH2 Bu)5]. The Th−C bond lengths range
from 2.46(2) to 2.56(2) Å and are similar to those reported for
[Li(TMEDA)]3[ThMe7] [2.571(9)−2.723(8) Å] and other
neosilyl and neopentyl thorium complexes [2.438(16)−2.54(2)
Å].23,27,75−77 Additionally, the Th−C−C bond angles range
from 125(2)° to 148(2)°. These comparatively large angles
may be evidence for α-agostic C−H−Th interactions. Emslie
and co-workers observed similar angles in [LTh(CH2SiMe3)2]
[L = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dime-
thylxanthene], which they determined were due to the presence
of α-agostic C−H−Th interactions.27
We have also explored the reactivity of ThCl4(DME)2 with
K(CH2Ph). The addition of 6 equiv of K(CH2Ph) to a THF
solution of ThCl4(DME)2 at −25 °C results in the formation of
a red-orange solution. Crystallization of this material from
THF/hexane provides [K(THF)]2[Th(CH2Ph)6] (3) as a
yellow-orange solid, in 80% yield (Scheme 3).
Complex 3 is a thermally unstable solid; however, it can be
stored indefinitely at −25 °C under an inert atmosphere. It is
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consistent with the presence of an η3-benzyl ligand within the
coordination sphere of Th1.14 For Th2, the multidentate benzyl
ligand exhibits a Th−C(ipso) distance of Th2−C21 = 3.20(1)
Å, while the corresponding Th−Cbenzyl distance is Th2−C9 =
2.61(1) Å. The Th−C−C angle is Th2−C9−C21 = 100(1)°,
while both Th−C(ortho) distances are >3.5 Å. These metrical
parameters are consistent with the presence of an η2-benzyl
ligand within the coordination sphere of Th2.14 The remaining
benzyl ligands for both Th1 and Th2 exhibit metrical
parameters consistent with η1 coordination.14 The Th−Cbenzyl
bond lengths for these ligands range from 2.59(2) to 2.69(2) Å
and are comparable to the Th−Cbenzyl bond lengths observed in
the multidentate ligands and those seen in other actinide benzyl
complexes.14,80−83 For example, The U−Cbenzyl distances in
[K(THF)]3[K(THF)2][U(CH2Ph)6]2 range from 2.50(2) to
2.57(2) Å.19 In addition, there are four potassium cations in the
asymmetric unit of 3. Each potassium participates in three η6-
coordinated π interactions with three aryl rings,84 resulting in
the formation of an extended 3D solid. Similar π interactions
have been observed in other systems,84−86 including the
uranium(IV) benzyl analogue [K(THF)]3[K(THF)2][U-
(CH2Ph)6]2.19 Unlike complex 3, however, the uranium
analogue exhibits no η2-benzyl interactions, an observation
that can be rationalized by the smaller ionic radius of U4+ versus
Th4+.
Theoretical Studies. Despite our inability to isolate
[ThMe6]2−, we were interested in exploring its electronic
structure by density functional theory (DFT), specifically to
address its ground-state geometry. Calculations were performed
at the B3LYP level on [ThMe6]2− and allowed to optimize to
the lowest-energy geometry. A single-point calculation was also
performed using an idealized octahedral geometry. Interest-
ingly, the fully optimized structure for [ThMe6]2− exhibits D3h
symmetry and is estimated to be 78.6 kcal/mol lower in energy
than the octahedral case.28,65 The C−Th−C bond angles are
76.9, 86.4, and 121.4°, while the Th−C bond distances are ca.
2.66 Å. In D3h symmetry (Figure 3), the HOMO, which has A2″
symmetry, exhibits 3% f character. HOMO−1 and HOMO−2
(E′) are doubly degenerate and contain 8% 6d character.
Figure 2. Solid-state molecular structure of 3 with 50% probability
ellipsoids. Hydrogen atoms omitted for clarity. Selected bond lengths
(Å) and angles (deg): Th1−C1 = 2.69(2), Th1−C2 = 2.62(2), Th1−
C3 = 2.59(2), Th1−C4 = 2.62(2), Th1−C5 = 2.64(2), Th1−C6 =
2.66(1), Th2−C7 = 2.61(2), Th2−C8 = 2.67(2), Th2−C9 = 2.60(2),
Th2−C10 = 2.63(2), Th2−C11 = 2.61(2), Th2−C12 = 2.69(2);
Th1−C1−C13 = 124(1), Th1−C2−C14 = 121(1), Th1−C3−C15 =
113(1), Th−C4−C16 = 93(1), Th1−C5−C17 = 108(1), Th1−C6−
C18 = 117(1), Th2−C7−C19 = 132(1), Th2−C8−C20 = 104(1),
Th2−C9−C21 = 100(1), Th2−C10−C22 = 119(1), Th2−C11−C23
= 110(1), Th2−C12−C80 = 119(1).
Figure 3. Bonding molecular orbitals of [ThMe6]2− in Oh symmetry (left). Bonding molecular orbitals of [ThMe6]2− in D3h symmetry (right).
Isolevel shown at 0.0250.
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HOMO−3 and HOMO−4 (E″) are also doubly degenerate and
contain 16% 6d character, while HOMO−5 (A′1) contains 17%
7s character.
crystal structure, namely, 132(1), 116.4(4), and 111.4(8)°. As
was observed for [ThMe6]2−, the Th−C interactions are highly
polarized and contain significant carbon 2p character with
varying contributions of hybrid metal-based orbitals (Table 3).
Clearly, the Th−C bonding interactions in D3h [ThMe6]2−
are predicted to be quite ionic. For example, the largest thorium
character is only 17% (HOMO−5), while three bonding
molecular orbitals have less than 10% thorium character
(HOMO, HOMO−1, and HOMO−2). This is also true in
octahedral symmetry (Figure 3), where HOMO, HOMO−1,
and HOMO−2 are triply degenerate and contain only 6%
thorium (5f) character. HOMO−3 exhibits 9% 7s character,
while doubly generate HOMO−4 and HOMO−5 have 15% 6d
character.
Table 3. Mulliken Populations and Orbital Energies for
t
[Th(CH2 Bu)5]− (1)
energy
(eV)
orbital
s
p
d
f
total
type
HOMO
−1.333
0.02
0.00
0.07
0.07
0.16 dσ + fσ +
sσ
HOMO−1 −1.769
HOMO−2 −2.150
HOMO−3 −2.503
HOMO−4 −2.803
0.00
0.00
0.06
0.11
0.00
0.00
0.00
0.00
0.14
0.17
0.12
0.08
0.02
0.00
0.00
0.03
0.16 dσ + fσ
0.17 dσ
As expected, the major difference between the Oh and D3h
geometries is participation of the 6d orbitals (Tables 1 and 2),
0.18 dσ + sσ
0.22 sσ + dσ +
fσ
Table 1. Mulliken Populations and Orbital Energies for
[ThMe6]2− in D3h Symmetry
For example, HOMO contains both 7% 5f and 7% 6d character,
while HOMO−1 (14% 6d), HOMO−2 (17% 6d), and
HOMO−3 (12% 6d) show predominately 6d orbital
participation. Additionally, HOMO−3 and HOMO−4 exhibit
6% and 11% 7s character, respectively. We have previously
reported calculations on [U(CH2SiMe3)5]− that reveal similar
trends in the M−C bonding interactions.20 However, the f-
orbital participation is much greater in the uranium complex.
For example, in [U(CH2SiMe3)5]−, HOMO−3 has 19% f
character, whereas the maximum 5f character seen in any
molecular orbital of 1 is 7%. This is consistent with the
anticipated decrease in the f orbital energy on moving from
thorium to uranium.57
energy
(eV)
orbital
s
p
d
f
total
type
HOMO
3.537
2.912
2.912
2.122
2.122
1.442
0.00
0.00
0.00
0.00
0.00
0.17
0.02
0.00
0.00
0.00
0.00
0.00
0.00
0.08
0.08
0.16
0.16
0.00
0.03
0.02
0.02
0.00
0.00
0.00
0.05 fσ + pσ
0.10 dσ + fσ
0.10 dσ + fσ
0.16 dσ
HOMO−1
HOMO−2
HOMO−3
HOMO−4
HOMO−5
0.16 dσ
0.17 sσ
Table 2. Mulliken Populations and Orbital Energies for
[ThMe6]2− in Oh Symmetry
A distorted octahedral geometry is predicted for complex 3,
which matches the observed geometry about the thorium
center in the experimental structure. In particular, the
equatorial benzyl groups display C−Th−C bond angles of
98.8, 78.6, 83.3, and 105.4°. The DFT calculations did not
predict the presence of a multidentate benzyl ligand in 3.
Additionally, the potassium counterions were not used in the
optimization. Complex 3 shows a similar pattern of small 5f and
moderate 6d and 7s contributions, in which HOMO through
HOMO−5 contain the Th−C bonding orbitals (Table 4).
orbital
energy (eV)
s
p
d
f
total type
HOMO
4.626
4.626
4.626
2.367
2.177
2.177
0.00
0.00
0.00
0.09
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.15
0.15
0.06
0.06
0.06
0.00
0.00
0.00
0.06
0.06
0.06
0.09
0.15
0.15
fσ
HOMO−1
HOMO−2
HOMO−3
HOMO−4
HOMO−5
fσ
fσ
sσ
dσ
dσ
which are much more prominent in D3h symmetry than in Oh
symmetry. In D3h symmetry, the 6d orbitals participate in
HOMO−1, HOMO−2, HOMO−3, and HOMO−4, whereas
they only participate in two Th−C molecular orbitals in Oh
symmetry. This suggests a similar role for the 6d orbitals in the
deviation of [ThMe6]2− from octahedral, as is found for
comparable transition-metal [MR6]n complexes.29,30 These
results also complement the findings of Straka and Kaupp for
[AnH6]2− (An = Th, U),65,66 who predicted that [ThH6]2−
should adopt a D3h geometry with only a small amount f-orbital
participation and much larger d-orbital participation.65,66
Additionally, in [ThMe6]2−, the 7s contribution increases
noticeably in going from Oh to D3h symmetry. This occurs with
a concomitant 0.925 eV lowering of the energy of this
molecular orbital. This latter effect is somewhat unanticipated
because a change in 7s orbital participation was not seen in
previous calculations on [ThH6]2− or [ThF6]2−.65,66
Calculations on complexes 1 and 3 were also conducted at
the B3LYP level of theory. For 1, HOMO through HOMO−4
correspond to the molecular orbitals involved in the Th−C
bonds. The optimized geometry of 1 reveals a distorted
trigonal-bipyramidal structure with approximate D3h symmetry.
The three C−Th−C bond angles for the equatorial
(CH2CMe3)− groups were found to be 129.0, 118.5, and
112.5°. These values compare well with those observed in the
Table 4. Mulliken Populations and Orbital Energies for
[Th(CH2Ph)6]2− (3)
energy
(eV)
orbital
s
p
d
f
total
type
HOMO
1.089
0.952
0.843
0.163
0.136
0.054
0.00
0.00
0.00
0.00
0.00
0.10
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.02
0.06
0.14
0.13
0.00
0.05
0.05
0.04
0.00
0.00
0.00
0.05 fσ
HOMO−1
HOMO−2
HOMO−3
HOMO−4
HOMO−5
0.07 fσ + dσ
0.10 dσ + fσ
0.14 dσ
0.13 dσ
0.10 sσ
Most importantly, the calculations reveal that the Th−C
interactions in 3 are even more ionic than those in 1. For
example, HOMO, HOMO−1, and HOMO−2 (which
comprise the t1u set) only exhibit 5%, 7%, and 10% thorium
character, respectively. Furthermore, as observed in 1, complex
3 exhibits very little 5f character, and because of the Oh
symmetry, only two orbitals have notable 6d character (i.e.,
HOMO−3 and HOMO−4, which exhibit 13% and 14% d
character, respectively). In principle, complex 3 could increase
d-orbtial participation by adopting a lower-symmetry geometry;
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t
cold solution of LiCH2 Bu (95 mg, 1.21 mmol) in Et2O (3 mL). This
resulted in the immediate generation of a pale-yellow solution
concomitant with the formation of a white precipitate. The solution
was allowed to stir for 10 min, whereupon the volatiles were removed
in vacuo and the resulting oil was extracted into Et2O (4 mL). The
solution was filtered through a Celite column (2 cm × 0.5 cm)
supported on glass wool, and the volume of the filtrate was reduced in
vacuo. The solution was layered with hexanes (2 mL), and subsequent
storage at −25 °C for 24 h resulted in the deposition of colorless
crystals (108 mg, 50% yield). 1H NMR (500 MHz, 25 °C, THF-d8): δ
3.54 (s, 16H, α-THF), 1.70 (s, 16H, β-THF), 1.02 (s, 45H, CH3),
however, we suspect that 3 remains octahedral as a result of
steric considerations because the benzyl groups may not be able
to accommodate the smaller C−Th−C angles required for D3h
symmetry.
CONCLUDING REMARKS
The reaction of ThCl4(DME)2 with several common alkylating
reagents provides a series of homoleptic thorium alkyl
■
t
complexes, namely, [Li(THF)4][Th(CH2 Bu)5], [Li(DME)2]-
[Th(CH2SiMe3)5], and [K(THF)]2[Th(CH2Ph)6]. These
complexes were pursued in an effort to determine their
geometries and thereby gain insight into d-orbital participation
in actinide−ligand bonding. As with their closely related
uranium analogues, these complexes are thermally sensitive in
solution, decomposing rapidly in a variety of solvents.
7
−0.07 (s, 10H, CH2). Li{1H} NMR (194 MHz, 25 °C, THF-d8): δ
0.50 (s). 13C{1H} NMR (125 MHz, 25 °C, THF-d8): δ 117.96 (s, CH2
methylene), 39.14 (s, C tert-butyl), 37.58 (s, CH3 tert-butyl). Anal.
Calcd for C41H87LiO4Th: C, 55.76; H, 9.93. Found: C, 55.60; H,
10.18.
[Li(DME)2][Th(CH2SiMe3)5] (2). A cold (−25 °C) solution of
ThCl4(DME)2 (153 mg, 0.28 mmol) in THF (2 mL) was added to a
cold (−25 °C) stirring solution of LiCH2SiMe3 (130 mg, 1.38 mmol)
in Et2O (3 mL). This resulted in the immediate generation of a pale-
yellow solution concomitant with the formation of a white precipitate.
The solution was allowed to stir for 15 min, whereupon the white
precipitate was removed by filtration through a Celite column (2 cm ×
0.5 cm) supported on glass wool. The volatiles were removed in vacuo,
and the resulting oil was extracted into Et2O (4 mL). The solution was
again filtered through a Celite column (2 cm × 0.5 cm) supported on
glass wool. DME (0.5 mL) was subsequently added to the filtrate. The
solution was layered with hexanes (3 mL), and subsequent storage at
−25 °C for 24 h resulted in the deposition of colorless oil. The oil was
rinsed with hexanes (3 × 1 mL) and subsequently dried in vacuo to
[Th(CH2 Bu)5]− exhibits a trigonal-bipyramidal geometry in
t
the solid state, while the benzyl complex [Th(CH2Ph)6]2−
exhibits an octahedral geometry in the solid state. DFT
calculations on these materials reveal highly ionic Th−C
interactions with very little 5f character in the Th−C bonds but
somewhat more 6d character. Several attempts to prepare
[ThMe6]2− were unsuccessful. Interestingly, however, this
material is predicted by DFT to exhibit D3h symmetry, similar
to the previously studied transition-metal hexa(methyl)
complexes. Ultimately, the challenge of demonstrating d-orbital
participation in An−L bonding by observation of a non-
octahedral (D3h or C3v) geometry has yet to be achieved. Future
success in this area will likely require the use of alkyl ligands
with different steric and electronic properties than those used in
this study.
1
give a white microcrystalline powder (127 mg, 54% yield). H NMR
(400 MHz, 25 °C, THF-d8): δ 3.43 (s, 8H, CH2 DME), 3.27 (s, 12H,
CH3 DME), −0.01 (s, 45H, CH3), −0.63 (s, 10H, CH2). Li{1H}
7
NMR (155 MHz, 25 °C, THF-d8): δ −0.53 (s). 13C{1H} NMR (151
MHz, 25 °C, THF-d8): δ 82.97 (s, CH2), 72.93 (s, CH2 DME), 59.07
(s, CH3 DME), 5.08 (s, CH3). Anal. Calcd for C28H75LiO4Si5Th: C,
39.32; H, 8.84. Found: C, 39.26; H, 8.67.
EXPERIMENTAL SECTION
■
General Procedures. All reactions and subsequent manipulations
were performed under anaerobic and anhydrous conditions under an
atmosphere of argon or nitrogen. Diethyl ether, hexanes, and
tetrahydrofuran (THF) were dried using a Vacuum Atmospheres
DRI-SOLV solvent purification system. Dimethoxyethane (DME) was
distilled from sodium benzophenone ketyl. All deuterated solvents
were purchased from Cambridge Isotope Laboratories Inc. and were
dried over activated 4 Å sieves for 24 h prior to use. ThCl4(DME)2,
[K(THF)]2[Th(CH2Ph)6] (3). To a cold (−25 °C), stirring solution
of ThCl4(DME)2 (217 mg, 0.391 mmol) in THF (2 mL) was added a
cold solution of K(CH2Ph) (305 mg, 2.34 mmol) in THF (3 mL).
This resulted in the formation of a red-orange solution and a gray
precipitate. The solution was allowed to stir for 10 min, whereupon
the solution was filtered through a Celite column (2 cm × 0.5 cm)
supported on glass wool and the volume of the filtrate was reduced in
vacuo. The solution was layered with hexanes (2 mL), and storage of
this solution at −25 °C for 24 h resulted in the deposition of a yellow-
orange powder (312 mg, 80% yield). X-ray-quality crystals were grown
t
[Li(TMEDA)]3[ThMe7], LiCH2 Bu, and K(CH2Ph) were prepared
according to published procedures.23,87−89 All other reagents were
obtained from commercial sources and used as received.
1
NMR spectra were recorded on a Varian UNITY INOVA 400 MHz
spectrometer, a Varian UNITY INOVA 500 MHz spectrometer, or a
Varian UNITY INOVA AS600 600 MHz spectrometer. 1H and
13C{1H} NMR spectra are referenced to external SiMe4 using the
residual protio solvent peaks as internal standards (1H NMR
experiments) or the characteristic resonances of the solvent nuclei
from a dilute THF solution layered with Et2O. H NMR (500 MHz,
25 °C, THF-d8): δ 6.69 (s, 12H, o-CH), 6.27 (s, 12H, m-CH), 6.11 (s,
6H, p-CH), 3.54 (s, 8H, α-THF), 1.69 (s, 8H, β-THF), 1.34 (s, 12H,
CH2). 13C{1H} NMR (125 MHz, 0 °C, THF-d8): δ 153.0 (br s, ipso-
C), 124.1 (br s, m-CH, o-CH), 115.9 (br s, p-CH), 89.6 (br s, CH2).
Anal. Calcd for C50H58K2O2Th: C, 59.98; H, 5.84. Found: C, 57.61; H,
5.31. The carbon percentage was found to be low over several
measurements, likely because of the thermal instability of the material.
X-ray Crystallography. Data for 3 were collected on a Bruker 3-
axis platform diffractometer equipped with a SMART-1000 CCD
detector using a graphite monochromator with a Mo Kα X-ray source
(α = 0.71073 Å). A hemisphere of data was collected at 150(2) K
using ω scans with 0.3° frame widths, using 25 s frame exposures. Data
for 1 were collected on a Bruker Proteum2 diffractometer equipped
with a PLATINUM CCD detector using multilayer optics with a Cu
Kα X-ray source (α = 1.4178 Å). The crystals of 1 were mounted on a
cryoloop under Paratone-N oil, and all data were collected at 100(2) K
using an Oxford nitrogen gas cryostream system. Frame exposures of 7
s were used for 1. Data collection and cell parameter determination
were conducted using the SMART program.95 Integration of the data
frames and final cell parameter refinement were performed using
SAINT software.96 Absorption correction of the data for 1 was carried
out using the multiscan method SADABS,97 while the absorption
7
(13C NMR experiments). Li{1H} NMR spectra are referenced to an
external saturated solution of LiCl in deuterium oxide. Elemental
analyses were performed by the Micro-Mass Facility at the University
of California, Berkeley.
Computational Details. The electronic structures of [Th-
t
(CH2Ph)6]2−, [Th(CH2 Bu)5]−, and [ThMe6]2− were examined
using the Gaussian09 software program90 at the B3LYP level.91,92
Full geometry optimizations were performed and stationary points
were determined to be global minima using analytical frequency
calculations with the Stuttgart/Dresden triple-ζ quality basis set93 and
the corresponding effective core potential for thorium. The most
diffuse s, p, d, and f functions were removed, leaving 7s/6p/5d/3f. The
Pople double-ζ quality basis set, 6-31G(d′),94 was used for the carbon
and hydrogen atoms. Mulliken population analyses on all compounds
were performed to determine orbital involvement.
t
[Li(THF)4][Th(CH2 Bu)5] (1). To a cold (−25 °C), stirring solution
of ThCl4(DME)2 (135 mg, 0.24 mmol) in THF (2 mL) was added a
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correction of the data for 3 was carried out empirically based on
reflection ψ scans. Subsequent calculations were carried out using
SHELXTL.98 Structure determination was done using direct or
Patterson methods and difference Fourier techniques. All hydrogen-
atom positions were idealized and rode on the atom of attachment,
with exceptions noted in the subsequent paragraph. Structure solution,
refinement, graphics, and creation of publication materials were
performed using SHELXTL.98 A summary of relevant crystallographic
data is presented in Table 5.
Security’s National Technical Nuclear Forensics Center and
U.S. Nuclear Regulatory Commission for support.
REFERENCES
■
(1) Gilman, H.; Jones, R. G.; Bindschadler, E.; Blume, D.; Karmas,
G.; Martin, G. A.; Nobis, J. F.; Thirtle, J. R.; Yale, H. L.; Yoeman, F. A.
J. Am. Chem. Soc. 1956, 78, 2790−2792.
(2) Gilman, H. Adv. Organomet. Chem. 1968, 7, 33.
(3) Marks, T. J.; Seyam, A. M. J. Organomet. Chem. 1974, 67, 61−66.
(4) Sigurdson, E. R.; Wilkinson, G. Dalton Trans. 1977, 812−818.
(5) Cernia, E.; Mazzei, A. Inorg. Chim. Acta 1974, 10, 239−252.
(6) Evans, W. J.; Wink, D. J.; Stanley, D. R. Inorg. Chem. 1982, 21,
2565−2573.
(7) Seyam, A. M. Inorg. Chim. Acta 1983, 77, L123−125.
(8) Van der Sluys, W. G.; Burns, C. J.; Sattelberger, A. P.
Organometallics 1989, 8, 855−857.
Table 5. X-ray Crystallographic Data for Complexes 1 and 3
1
3
empirical formula
cryst habit, color
cryst size (mm)
cryst syst
C41H87LiO4U
rod, colorless
0.30 × 0.20 × 0.05
orthorhombic
P212121
9459.9(6)
10.3960(4)
16.7648(7)
54.2778(18)
90
C50H58K2O2U
block, orange
0.70 × 0.50 × 0.15
monoclinic
Pn
(9) Marks, T. J. J. Organomet. Chem. 1975, 95, 301−315.
(10) Streitweiser, A. Preparation and Chemistry of Uranocences. In
Organometallics of the f-Elements; Marks, T. J., Fischer, R. D., Eds.; D.
Reidel Publishing: Dordrecht, Holland, 1978; p 154.
(11) Miller, M. J.; Streitwieser, A. J. Organomet. Chem. 1981, 209,
C52−C54.
space group
volume (Å3)
a (Å)
4607(2)
9.341(3)
29.955(7)
16.497(4)
90
b (Å)
c (Å)
α (deg)
(12) Marks, T. J. Prog. Inorg. Chem. 1979, 25, 223−333.
β (deg)
90
93.604(10)
90
(13) Thiele, K. H.; Opitz, R.; Kohler, E. Z. Anorg. Allg. Chem. 1977,
̈
435, 45−48.
γ (deg)
90
(14) Edwards, P. G.; Andersen, R. A.; Zalkin, A. Organometallics
1984, 3, 293−398.
Z
8
4
fw (g/mol)
density (calcd) (Mg/m3)
883.09
1001.20
1.444
(15) Edwards, P. G.; Andersen, R. A.; Zalkin, A. J. Am. Chem. Soc.
1981, 103, 7792−7794.
1.240
abs coeff (mm−1
)
10.399
3.454
(16) Stewart, J. L.; Andersen, R. A. Polyhedron 1998, 17, 953−958.
(17) Ortiz, J. V.; Hay, P. J.; Martin, R. L. J. Am. Chem. Soc. 1992, 114,
2736−2737.
F000
3664
2008
total no. of reflns
unique reflns
31125
37828
13407
17026
(18) Hay, P. J.; Martin, R. L. J. Alloys Compd. 1994, 213, 196−198.
(19) Fortier, S.; Melot, B. C.; Wu, G.; Hayton, T. W. J. Am. Chem.
Soc. 2009, 131, 15512−15521.
final R indices [I > 2σ(I)] R1 = 0.0830, wR2 =
R1 = 0.0536, wR2 =
0.1075
0.2306
largest diff peak and hole 2.467 and −1.937
3.475 and −1.656
(20) Fortier, S.; Walensky, J. R.; Wu, G.; Hayton, T. W. J. Am. Chem.
Soc. 2011, 133, 11732−11743.
(e/Å3)
GOF
1.162
0.992
(21) Kraft, S. J.; Fanwick, P. E.; Bart, S. C. J. Am. Chem. Soc. 2012,
134, 6160−6168.
(22) Duhovic, S.; Khan, S.; Diaconescu, P. L. Chem. Commun. 2010,
46, 3390−3392.
For complex 1, several carbon atoms were refined isotropically due
to disorder. For complex 3, a THF molecule was disordered over two
positions in a 50:50 ratio. Hydrogen atoms were not assigned to
disordered carbon atoms.
(23) Lauke, H.; Swepston, P. J.; Marks, T. J. J. Am. Chem. Soc. 1984,
106, 6841−6843.
(24) Shannon, R. D. Acta Crystallogr. 1976, A32, 751−767.
(25) Eisen, M. S.; Marks, T. J. J. Am. Chem. Soc. 1992, 114, 10358−
10368.
ASSOCIATED CONTENT
* Supporting Information
■
S
(26) Kohler, E.; Bruser, W.; Thiele, K.-H. J. Organomet. Chem. 1974,
76, 235−240.
(27) Cruz, C. A.; Emslie, D. J. H.; Harrington, L. E.; Britten, J. F.;
Robertson, C. M. Organometallics 2007, 26, 692−701.
(28) Demolliens, A.; Jean, Y.; Eisenstein, O. Organometallics 1986, 5,
1457−1464.
(29) Kang, S. K.; Albright, T. A.; Eisenstein, O. Inorg. Chem. 1989,
28, 1611−1613.
(30) Kang, S. K.; Tang, H.; Albright, T. A. J. Am. Chem. Soc. 1993,
115, 1971−1981.
(31) Tanpipat, N.; Baker, J. J. Phys. Chem. 1996, 100, 19818−19823.
(32) Kaupp, M. J. Am. Chem. Soc. 1996, 118, 3018−3024.
(33) Kaupp, M. Chem.Eur. J. 1998, 4, 1678−1686.
(34) Kaupp, M. Angew. Chem., Int. Ed. 2001, 40, 3534−3575.
(35) Pfennig, V.; Seppelt, K. Science 1996, 271, 626−628.
(36) Kleinhenz, S.; Pfennig, V.; Seppelt, K. Chem.Eur. J. 1998, 4,
1687−1691.
Experimental procedures, crystallographic details (as CIF files),
and spectral data for 1−3, optimized Cartesian coordinates for
[ThMe6]2−, 1, and 3, and the complete version of ref 90. This
material is available free of charge via the Internet at http://
pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: hayton@chem.ucsb.edu (T.W.H.), walenskyj@
missouri.edu (J.R.W.).
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Research at the University of California, Santa Barbara, was
supported by the U.S. Department of Energy, Office of Basic
Energy Sciences, Chemical Sciences, Biosciences, and Geo-
sciences Division under Contract DE-FG02-09ER16067. J.R.W.
gratefully acknowledges the U.S. Department of Homeland
(37) Seppelt, K. Acc. Chem. Res. 2003, 36, 147−153.
(38) Morse, P. M.; Girolami, G. S. J. Am. Chem. Soc. 1989, 111,
4114−4116.
(39) Landis, C. R.; Cleveland, T.; Firman, T. K. J. Am. Chem. Soc.
1995, 117, 1859−1860.
3563
dx.doi.org/10.1021/ic300867m | Inorg. Chem. 2013, 52, 3556−3564

Inorganic Chemistry
Forum Article
(40) Landis, C. R.; Firman, T. K.; Root, D. M.; Cleveland, T. J. Am.
Chem. Soc. 1998, 120, 1842−1852.
(74) Bursten, B. E.; Strittmatter, R. J. Angew. Chem., Int. Ed. 1991, 30,
1069−1085.
(75) Bruno, J. W.; Smith, G. M.; Marks, T. J.; Fair, C. K.; Schultz, A.
J.; Williams, J. M. J. Am. Chem. Soc. 1986, 108, 40−56.
(76) Butcher, R. J.; Clark, D. L.; Grumbine, S. K.; Scott, B. L.;
Watkin, J. G. Organometallics 1996, 15, 1488−1496.
(77) Fredrick, C. M.; Mintz, E. A.; Schertz, L. D.; Marks, T. J.; Day,
V. W. Organometallics 1984, 3, 819−821.
(41) Landis, C. R.; Cleveland, T.; Firman, T. K. J. Am. Chem. Soc.
1998, 120, 2641−2649.
(42) Jonas, V.; Frenking, G.; Gauss, J. Chem. Phys. Lett. 1992, 194,
109−117.
(43) Shortland, A. J.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1973,
872−876.
(78) Scholz, J.; Rehbaum, F.; Thiele, K.-H.; Goddard, R.; Betz, P.;
Kruger, C. J. Organomet. Chem. 1993, 443, 93−99.
(79) Bassi, I. W.; Allegra, G.; Scordamaglia, R.; Chioccola, G. J. Am.
Chem. Soc. 1971, 93, 3787−3788.
(80) Monreal, M. J.; Diaconescu, P. L. Organometallics 2008, 27,
1702−1706.
(81) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J.
Organometallics 2002, 21, 5978−5982.
(82) Jantunen, K. C.; Burns, C. J.; Castro-Rodriguez, I.; Da Re, R. E.;
Golden, J. T.; Morris, D. E.; Scott, B. L.; Taw, F. L.; Kiplinger, J. L.
Organometallics 2004, 23, 4682−4692.
(83) Perego, G.; Cesari, M.; Farina, F.; Lugli, G. Acta Crystallogr.,
Sect. B 1976, 32, 3034.
(84) Meyer, N.; Roesky, P. W.; Bambirra, S.; Meetsma, A.; Hessen,
B.; Saliu, K.; Takats, J. Organometallics 2008, 27, 1501−1505.
(85) Chitsaz, S.; Neumuller, B. Organometallics 2001, 20, 2338−
2343.
(86) Andrews, P.; Kennedy, A. R.; Mulvey, R. E.; Raston, C. L.;
Roberts, B. A.; Rowlings, R. B. Angew. Chem., Int. Ed. 2000, 39, 1960−
1962.
(44) Galyer, A. L.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1976,
2235−2238.
(45) Haaland, A.; Hammel, A.; Rypdal, K.; Volden, H. V. J. Am.
Chem. Soc. 1990, 112, 4547−4549.
(46) Vaid, T. P.; Veige, A. S.; Lobkovsky, E. B.; Glassey, W. V.;
Wolczanski, P. T.; Liable-Sands, L. M.; Rheingold, A. L.; Cundari, T.
R. J. Am. Chem. Soc. 1998, 120, 10067−10079.
(47) El-Kurdi, S.; Seppelt, K. Chem.Eur. J. 2011, 17, 3956−3962.
(48) Kleinhenz, S.; Schubert, M.; Seppelt, K. Chem. Ber. 1997, 130,
903−906.
(49) Friese, J. C.; Krol, A.; Puke, C.; Kirschbaum, K.; Giolando, D.
M. Inorg. Chem. 2000, 39, 1496−1500.
(50) Hoffmann, R.; Howell, J. M.; Rossi, A. R. J. Am. Chem. Soc.
1976, 98, 2484−2492.
(51) McGrady, G. S.; Downs, A. J. Coord. Chem. Rev. 2000, 197, 95−
124.
(52) Cremades, E.; Echeverría, J.; Alvarez, S. Chem.Eur. J. 2010, 16,
10380−10396.
(53) Denning, R. Struct. Bonding (Berlin) 1992, 79, 215−276.
(54) Denning, R. G. J. Phys. Chem. A 2007, 111, 4125−4143.
(55) Denning, R. G.; Green, J. C.; Hutchings, T. E.; Dallera, C.;
Tagliaferri, A.; Giarda, K.; Brookes, N. B.; Braicovich, L. J. Chem. Phys.
2002, 117, 8008−8020.
(87) Cantat, T.; Scott, B. L.; Kiplinger, J. L. Chem. Commun. 2010,
46, 919−921.
(88) Schlosser, M.; Hartmann, J. Angew. Chem., Int. Ed. 1973, 12,
508−509.
(56) Prodan, I. D.; Scuseria, G. E.; Martin, R. L. Phys. Rev. B 2007,
76, 033101.
(57) Walensky, J. R.; Martin, R. L.; Ziller, J. W.; Evans, W. J. Inorg.
(89) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100,
3359−3370.
(90) Frisch, M. J.; et al. Gaussian 09, revision A.02; Gaussian, Inc.:
Wallington, CT, 2009.
Chem. 2010, 49, 10007−10012.
(58) Kozimor, S. A.; Yang, P.; Batista, E. R.; Boland, K. S.; Burns, C.
J.; Clark, D. L.; Conradson, S. D.; Martin, R. L.; Wilkerson, M. P.;
Wolfsberg, L. E. J. Am. Chem. Soc. 2009, 131, 12125−12136.
(59) Arnold, P.; Turner, Z.; Kaltsoyannis, N.; Pelekanaki, P.;
Bellabarba, R.; Tooze, R. Chem.Eur. J. 2010, 16, 9623−9629.
(60) Raymond, K. N.; Eigenbrot, C. W. Acc. Chem. Res. 1980, 13,
276−283.
(91) Becke, A. D. J. Chem. Phys. 1993, 98, 5648−5652.
(92) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J.
Phys. Chem. 1994, 98, 11623−11627.
(93) Kuechle, W.; Dolg, M.; Stoll, H.; Preuss, H. J. Chem. Phys. 1994,
100, 7535−7542.
(94) Petersson, G. A.; Bennett, A.; Tensfeldt, T. G.; Al-Laham, M. A.;
Shirley, W. A.; Mantzaris, J. J. Chem. Phys. 1988, 89, 2193−2218.
(95) SMART Software Users Guide, version 5.1; Bruker Analytical X-
ray Systems, Inc.: Madison, WI, 1999.
(96) SAINT Software User’s Guide, version 5.1; Bruker Analytical X-
ray Systems, Inc.: Madison, WI, 1999.
(97) Sheldrick, G. M. SADABS; University of Gottingen: Gottingen,
Germany, 2005.
(98) Sheldrick, G. M. SHELXTL, version 6.12; Bruker Analytical X-
ray Systems, Inc.: Madison, WI, 2001.
(61) Cantat, T.; Graves, C. R.; Jantunen, K. C.; Burns, C. J.; Scott, B.
L.; Schelter, E. J.; Morris, D. E.; Hay, P. J.; Kiplinger, J. L. J. Am. Chem.
Soc. 2008, 130, 17537−17551.
(62) Li, J.; Bursten, B. E. J. Am. Chem. Soc. 1997, 119, 9021−9032.
(63) Tassell, M. J.; Kaltsoyannis, N. Dalton Trans. 2010, 39, 6719−
6725.
(64) Ingram, K. I. M.; Kaltsoyannis, N.; Gaunt, A. J.; Neu, M. P. J.
Alloys Compd. 2007, 444−445, 369−375.
(65) Straka, M.; Hrobarik, P.; Kaupp, M. J. Am. Chem. Soc. 2005, 127,
2591−2599.
(66) Straka, M.; Patzschke, M.; Pyykko, P. Theor. Chem. Acc. 2003,
109, 332−340.
(67) Minasian, S. G.; Keith, J. M.; Batista, E. R.; Boland, K. S.; Clark,
D. L.; Conradson, S. D.; Kozimor, S. A.; Martin, R. L.; Schwarz, D. E.;
Shuh, D. K.; Wagner, G. L.; Wilkerson, M. P.; Wolfsberg, L. E.; Yang,
P. J. Am. Chem. Soc. 2012, 134, 5586−5597.
(68) King, R. B. Inorg. Chem. 1992, 31, 1978−1980.
(69) King, R. B. Inorg. Chem. 1998, 37, 3057−3059.
(70) Cameron, A. D.; Fitzgerald, G.; Zerner, M. C. Inorg. Chem.
1988, 27, 3437−3439.
(71) Schumann, H.; Mueller, J.; Bruncks, N.; Lauke, H.; Pickardt, J.;
Schwarz, H.; Eckart, K. Organometallics 1984, 3, 69−74.
(72) Schumann, H.; Pickardt, J.; Bruncks, N. Angew. Chem., Int. Ed.
1981, 20, 120−121.
(73) Schumann, H.; Lauke, H.; Hahn, E.; Pickardt, J. J. Organomet.
Chem. 1984, 263, 29−35.
3564
dx.doi.org/10.1021/ic300867m | Inorg. Chem. 2013, 52, 3556−3564