Trivalent uranium phenylchalcogenide complexes: Exploring the bonding and reactivity with CS2 in the Tp2UEPh series (E = O, S, Se, Te)

Article abstract of DOI:10.1021/ic5020658

The trivalent uranium phenylchalcogenide series, Tp×₂UEPh (Tp = hydrotris(3,5-dimethylpyrazolyl)borate, E = O (1), S (2), Se (3), Te (4)), has been synthesized to investigate the nature of the U-E bond. All compounds have been characterized by ¹H NMR, infrared and electronic absorption spectroscopies, and in the case of 4, X-ray crystallography. Compound 4 was also studied by SQUID magnetometry. Computational studies establish Mulliken spin densities for the uranium centers ranging from 3.005 to 3.027 (B3LYP), consistent for uranium-chalcogenide bonds that are primarily ionic in nature, with a small covalent contribution. The reactivity of 2-4 toward carbon disulfide was also investigated and showed reversible CS₂ insertion into the U(III)-E bond, forming Tp×₂U(κ²-S₂CEPh) (E = S (5), Se (6), Te (7)). Compound 5 was characterized crystallographically.

Full text of DOI:10.1021/ic5020658

Article
pubs.acs.org/IC
Trivalent Uranium Phenylchalcogenide Complexes: Exploring the
Bonding and Reactivity with CS2 in the Tp*2UEPh Series (E = O, S, Se,
Te)
Ellen M. Matson,† Andrew T. Breshears,‡ John J. Kiernicki,† Brian S. Newell,§ Phillip E. Fanwick,†
Matthew P. Shores,§ Justin R. Walensky,*,‡ and Suzanne C. Bart*,†
†H.C. Brown Laboratory, Department of Chemistry, Purdue University, West Lafayette 47907, Indiana, United States
‡Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
§Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, United States
S
* Supporting Information
ABSTRACT: The trivalent uranium phenylchalcogenide series,
Tp*2UEPh (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate, E = O
(1), S (2), Se (3), Te (4)), has been synthesized to investigate the
nature of the U−E bond. All compounds have been characterized by
1H NMR, infrared and electronic absorption spectroscopies, and in
the case of 4, X-ray crystallography. Compound 4 was also studied by
SQUID magnetometry. Computational studies establish Mulliken
spin densities for the uranium centers ranging from 3.005 to 3.027
(B3LYP), consistent for uranium−chalcogenide bonds that are
primarily ionic in nature, with a small covalent contribution. The
reactivity of 2−4 toward carbon disulfide was also investigated and
showed reversible CS2 insertion into the U(III)−E bond, forming
Tp*2U(κ2-S2CEPh) (E = S (5), Se (6), Te (7)). Compound 5 was
characterized crystallographically.
late),21 and Tp*2USPh.22 Across the actinide series, [Pu-
INTRODUCTION
■
(Se2PPh2)4]− has recently been reported,10 along with
For nuclear energy to be viable as an efficient energy source,
americium and curium complexes of bis(2,4,4-trimethylpentyl)-
the nuclear fuel cycle must be completed by recycling of the
dithiophosphinic acid.23 While these represent important
complicated mixture of heavy elements in the spent fuel.1
preliminary findings, further study on actinide−ligand bonding,
Understanding uranium−ligand bonding to find distinguishing
especially in the +3 oxidation state, with soft donor atoms is
characteristics from the other lanthanides and actinides,
justified.
especially in the trivalent oxidation state, is central to
Recently, we reported the synthesis, spectroscopic, and
developing new separations strategies.2−4 Soft donor ligands
structural characterization of Tp*2USPh, a rare example of a
have recently come to the forefront of improving separation
uranium(III) phenylchalcogenide complex.22 Given the grow-
techniques5,6 in part due to actinides showing enhanced
ing interest in understanding trivalent uranium−chalcogen
extraction with sulfur-based agents as compared to lantha-
nides.5,7 While the origin of this dichotomy is currently under
interactions and the lack of a self-contained chalcogenide series
in this oxidation state, we targeted the synthesis and
investigation, current findings suggest that the higher degree of
characterization of the rest of the U(III) phenylchalcogenide
covalency in actinide−ligand bonding may play a role in this
selectivity.8−10
series, Tp*2UEPh (E = O, Se, Te). This family was prepared in
high yields, and the identities of the compounds were verified
Despite the redox chemistry and small molecule activation of
U3+ leading to unprecedented reactivity,11−14 relatively few
trivalent uranium complexes have been isolated with a ligand
capable of undergoing further functionalization. Additionally,
few An3+ (An = actinide) complexes with soft donor chalcogen-
based ligands comprised of sulfur, selenium, and/or tellurium
have been reported. Rare examples of trivalent derivatives
include the homoleptic complexes, [U(N(κ2-E,E′-(EPR)2)3] (R
1
by H NMR spectroscopy, infrared spectroscopy, and in the
case of Tp*2UTePh, X-ray crystallography. The bonding and
electronic properties of this series were also explored using
electronic absorption spectroscopy and computational methods
to help evaluate the degree of covalency, if any, in the U(III)−E
bond. Subsequent reactivity of the Tp*2UEPh series toward
CS2 insertion is also discussed.
8,15−17
= Ph, Pr; E = S,
Se,15 Te18) and U(SMes*)3 (Mes* =
i
2,4,6-tBu3C6H2),19 as well as heteroleptic [Cp*2U(SiPr)2]1−,20
[Cp*2U(dddt)]− (dddt = 5,6-dihydro-1,4-dithine-2,3-dithio-
Received: August 28, 2014
Published: November 21, 2014
© 2014 American Chemical Society
12977
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
the data are reproducible. Data were corrected for the magnetization of
the sample holder by subtracting the susceptibility of an empty
container and for diamagnetic contributions of the sample by using
Pascal’s constants.
EXPERIMENTAL SECTION
■
General Considerations. All air- and moisture-sensitive manip-
ulations were performed using standard Schlenk techniques or an
MBraun inert atmosphere drybox with an atmosphere of purified
nitrogen. The MBraun drybox was equipped with a coldwell designed
for freezing samples in liquid nitrogen as well as two −35 °C freezers
for cooling samples and crystallizations. Solvents for sensitive
manipulations were dried and deoxygenated using literature
procedures with a Seca solvent purification system.24 Benzene-d6 was
purchased from Cambridge Isotope Laboratories, dried with molecular
sieves and sodium, and degassed by three freeze−pump−thaw cycles.
Depleted uranium was purchased from Manufacturing Science in Oak
Ridge, TN. NOTE: Depleted uranium (primarily isotope 238U) is a
weak α-emitter with a half-life of 4.47 × 109 years. All handling should
be performed in fume hoods, using Schlenk lines, or in an inert-
atmosphere drybox with proper PPE and monitoring devices.
Diphenyl disulfide, diphenyl diselenide, diphenyl ditelluride, and
phenol were purchased from Sigma-Aldrich and dried under a vacuum
prior to use. Anhydrous carbon disulfide was purchased from Sigma-
Aldrich, dried over CaH2, and distilled prior to use. Elemental analyses
were performed by Midwest Microlabs LLC in Indianapolis, IN, and
Atlantic Microlabs Inc. in Norcross, GA. Tp*2UCH2Ph25 was
synthesized according to a literature procedure.
Computational Details. The electronic structures of complexes
1−4 were examined using the Gaussian09 suite of software28 at the
B3LYP29 (Becke-330 exchange and Lee−Yang−Parr31 correlation
functional) level. 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
set32 and the corresponding effective core potential (ECP). For
uranium, the most diffuse s, p, d, and f functions were removed, leaving
a basis set of 7s/6p/5d/3f. For sulfur, selenium, and tellurium the
LANL-DZ2P basis set was employed.33 The Pople double-ζ quality
basis set, 6-31G(d,p),34,35 was used for all remaining atoms. Complex
1 was found to be difficult to converge at the global minimum so we
report the geometry with one imaginary frequency.
Preparation of Tp*2U(OPh) (1). A 20 mL scintillation vial was
charged with Tp*2UCH2Ph (0.100 g, 0.108 mmol) and approximately
3 mL of THF. This dark green solution was cooled to −35 °C. In a
separate vial, an equivalent of phenol (0.011 g, 0.117 mmol) was
dissolved in approximately 3 mL of diethyl ether. The clear phenol
solution was added to the uranium solution, resulting in an
instantaneous color change to purple. After 5 min of stirring, solvents
were removed under reduced pressure. The remaining dark residue
was washed with cold ether/pentane (1:20), allowing isolation of
Tp*2U(OPh) as a purple solid. Yield = 0.085 g (0.092 mmol, 85%).
Analysis for C36H49N12B2UO1: Calcd C, 46.72; H, 5.34; N, 18.16.
1H NMR spectra were recorded on a Varian Inova 300
spectrometer operating at a frequency of 299.992 MHz. All chemical
shifts were reported relative to the peak for SiMe4 using 1H (residual)
chemical shifts of the solvent as a secondary standard. The spectra for
paramagnetic molecules were obtained using an acquisition time of 0.5
s; thus the peak widths reported have an error of 2 Hz. For
paramagnetic molecules, the 1H NMR data are reported with the
chemical shift, followed by the peak width at half height in Hertz, the
integration value, and where possible, the peak assignment. 11B NMR
spectra were recorded on a Varian Mercury-300 spectrometer
operating at a frequency of 96.24 MHz. All chemical shifts were
reported relative to the peak for BF3·Et2O (0 ppm). Solid state
infrared spectra were recorded using a PerkinElmer FT-IR Spectrum
RX I spectrometer. Samples were made by crushing the solids, mixing
with dry KBr, and pressing into a pellet. Electronic absorption
measurements were recorded at 294 K in THF in a sealed 1 cm quartz
cuvette with a Jasco V-670 spectrophotometer.
1
Found C, 46.66; H, 5.42; N, 17.98. H NMR (C6D6, 25 °C): δ =
−12.84 (33.4, 18H, Tp*-CH3), −0.83 (5.13, 18H, Tp*-CH3), 4.85
(141.2, 2H, B-H) 7.14 (7.1, 6H, Tp*-CH), 18.35 (32.9, 1H, p-CH),
21.26 (43.0, 2H, m-CH), 42.57 (79.3, 2H, o-CH). IR: 2538, 2551 cm−1
(B−H). 11B NMR (C6D6, 25 °C): δ = −1.2 (H-B, Tp*).
General Preparation of Tp*2UEPh (E = S, Se, Te). A 20 mL
scintillation vial was charged with Tp*2UCH2Ph (0.100 g, 0.108
mmol) and approximately 5 mL of THF. In a separate vial, one-half
equivalent of PhEEPh [E = S (0.011 g, 0.054 mmol); Se (0.017 g,
0.054 mmol); Te (0.022 g, 0.054 mmol)] was dissolved in diethyl
ether and added dropwise to the prepared solution of Tp*2UCH2Ph,
causing immediate darkening. After 5 min, solvents were removed in
vacuo.
Single crystals of Tp*2UTePh (4) for X-ray diffraction were coated
with polybutenes oil in a glovebox and quickly transferred to the
goniometer head of a Nonius KappaCCD image plate diffractometer
equipped with a graphite crystal, incident beam monochromator.
Preliminary examination and data collection were performed with Mo
Kα radiation (λ = 0.71073 Å). Single crystals of Tp*2U(κ2-S2CSPh)
(5) for X-ray diffraction were coated with polybutenes oil in a
glovebox and quickly transferred to the goniometer head of a Rigaku
Rapid II image plate diffractometer equipped with a MicroMax002+
high intensity copper X-ray source with confocal optics. Preliminary
examination and data collection were performed with Cu Kα radiation
(λ = 1.54184 Å). Cell constants for data collection were obtained from
least-squares refinement. The space groups were identified using the
program XPREP.26 The structures were solved using the structure
solution program PATTY in DIRDIFF99.27 Refinement was
performed on a LINUX PC using SHELX-97.26 The data were
collected at a temperature of 150(1) K.
Magnetic susceptibility (dc) data for 4 were collected with a
Quantum Design MPMS-XL SQUID magnetometer in the temper-
ature range 4−300 K at an applied field of 1000 Oe. Powdered
microcrystalline samples were loaded into gelatin capsules in the
glovebox, inserted into a straw and transported to the SQUID
magnetometer under dinitrogen. The absence of significant
ferromagnetic impurities was confirmed for each sample by observing
a linear relationship between magnetization and applied field (0.1−5
T) at 125 K. Susceptibility data reproducibility were probed via spot
checks performed on multiple samples, including separate batches: the
air-sensitivity of the samples results in some variation of the room
temperature μeff values but the qualitative temperature dependence of
Tp*2USPh (2). The product was washed with pentane to remove
bibenzyl, leaving dark blue powder (0.094 g, 0.100 mmol, 96%).
1
Compound 2 was characterized by H NMR and IR spectroscopies
against previously published data.22 11B NMR (C6D6, 25 °C): δ = 0.1
(H-B, Tp*).
Tp*2USePh (3). The blue-green residue left in the vial was washed
with cold pentane producing a green solid (0.098 g, 0.100 mmol,
96%). Analysis for C36H49N12B2Se1U1. Calcd C, 43.74; H, 5.00; N,
1
17.00. Found C, 43.77; H, 5.05, N, 17.01. H NMR (C6D6, 25 °C): δ
= −11.34 (38, 18H, Tp*-CH3), −0.68 (20, 18H, Tp*-CH3), 5.43
(802, 2H, B-H), 7.36 (20, 6H, Tp*-CH), 11.00 (7, 1H, p-CH), 12.97
(24, 2H, m-CH), 19.38 (33, 2H, o-CH). IR: 2523, 2549 cm−1 (B-H).
11B NMR (C6D6, 25 °C): δ = −0.6 (H-B, Tp*).
Tp*2UTePh (4). The remaining blue solid was recrystallized from a
pentane and THF mixture (2:1) resulting in the isolation of a blue
solid (0.076 g, 0.074 mmol, 69%). Analysis for C36H49N12B2Te1U1.
Calcd C, 41.69; H, 4.76; N, 16.21. Found C, 41.48; H, 4.87; N, 15.96.
1H NMR (C6D6, 25 °C): δ = −10.89 (22, 18H, Tp*-CH3), −0.50 (8,
18H, Tp*-CH3), 6.41 (447, 2H, B-H), 7.08 (8, 6H, Tp*-CH), 10.44
(34, 1H, p-CH), 12.37 (54, 2H, m-CH), 18.48 (85, 2H, o-CH). IR:
2521, 2552 cm−1 (B-H). 11B NMR (C6D6, 25 °C): δ = −0.7 (H-B,
Tp*).
Equilibrium Experiments for the Generation of Tp*2U(κ2-
S2CEPh) (5−7). A J. Young NMR tube was charged with Tp*2UEPh
(E = S: 0.020 g (0.021 mmol); Se: 0.020 g (0.020 mmol); E = Te:
0.020 g (0.019 mmol)) and 1.0 mL of benzene-d6, producing a dark
blue solution. The appropriate amount (S, Se = 0.5, 1.0, 1.5, 2.0 equiv;
Te: 2.5, 5.0, 10.0 equiv) of a CS2 standard solution (1.65 M in
benzene-d6) was added to the tube via microsyringe, resulting in an
12978
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
instantaneous color change to green. After being stirred for 10 min, the
equilibrium mixture was monitored by H NMR spectroscopy, and
the synthesis of 2 in the presence of 1,4-cyclohexadiene showed
formation of toluene rather than bibenzyl, supporting the
presence of benzyl radicals in solution during the preparation of
2−4.
1
conversions were determined by integration versus starting material.
Because of the reversibility of the insertion reaction, the products,
Tp*2US2CEPh, could not be isolated in the solid state, precluding
yield determination or elemental analysis.
Analysis of complexes 1−4 by 1H NMR spectroscopy
showed analogous symmetric spectra with seven paramagneti-
cally broadened and shifted resonances (Figure 1). The
1
Tp*2U(κ2-S2CSPh) (5). H NMR (C6D6, 25 °C): −21.76 (56, 6H,
Tp*-CH3), −11.72 (30, 6H, Tp*-CH3), −0.83 (21, 6H, Tp*-CH3),
1.17 (21, 6H, Tp*- CH3), 2.18 (20, 6H, Tp*-CH3), 3.16 (42, 6H,
Tp*-CH3), 4.02 (22, 2H, Tp*-CH), 6.32 (187, 2H, B-H), 6.92 (18,
2H, Tp*-CH), 7.82 (t, J = 7 Hz, 2H, m-CH), 8.31 (t, J = 7 Hz, 1H, p-
CH), 10.30 (d, J = 7 Hz, 2H, o-CH), 11.69 (35, 2H, Tp*-CH). IR: 688
(C−S−Casym), 645 (C−S−Csymm), 2522, 2548 cm−1 (B-H).
1
Tp*2U(κ2-S2CSePh) (6). H NMR (C6D6, 25 °C): δ = −21.37 (46,
6H, Tp*-CH3), −11.69 (28, 6H, Tp*-CH3), −0.84 (23, 6H, Tp*-
CH3), 1.24 (18, 6H, Tp*-CH3), 1.79 (29, 6H, Tp*-CH3), 3.17 (44,
6H, Tp*-CH3), 4.18 (23, 2H, Tp*-CH), 6.27 (407, 2H, B-H), 6.83
(22, 2H, Tp*-CH), 7.84 (t, J = 6 Hz, 2H, m-CH), 8.32 (t, J = 8 Hz,
1H, p-CH), 9.49 (d, J = 8 Hz, 2H, o-CH), 11.75 (45, 2H, Tp*-CH).
IR: 692 (C−S−Casym), 645 (C−S−Csymm), 2520, 2552 cm−1 (B-H).
1
Tp*2U(κ2-S2CTePh) (7). H NMR (C6D6, 25 °C): δ = −20.74 (78,
6H, Tp*-CH3), −11.37 (35, 6H, Tp*-CH3), −0.83 (36, 6H, Tp*-
CH3), 1.25 (35, 6H, Tp*-CH3), 1.44 (40, 6H, Tp*-CH3), 3.07 (68,
6H, Tp*-CH3), 4.23 (38, 2H, Tp*-CH), 6.22 (202, 2H, B-H), 6.78
(32, 2H, Tp*-CH), 7.79 (t, J = 8 Hz, 2H, m-CH), 8.24 (t, J = 6, 1H, p-
CH), 9.59 (d, J = 6 Hz, 2H, o-CH), 11.63 (59, 2H, Tp*-CH). IR: 692
(C−S−Casym), 646 (C−S−Csymm), 2523, 2548 cm−1 (B-H).
Crystallization of Tp*2U(κ2-S2CSPh) (5). A 20 mL scintillation vial
was charged with 2 (100 mg, 0.110 mmol) and approximately 1 mL of
a THF/toluene mixture (1:1) and cooled to −35 °C. In a separate vial,
CS2 (6.7 μL, 0.110 mmol) was dissolved in approximately 2 mL of
pentane and cooled to −35 °C. The solution of CS2 was slowly layered
on top of the THF solution of complex 2 and stored at −35 °C
overnight. After 12 hours, bright green crystals collected on the
bottom of the vial.
1
Figure 1. Comparison of H NMR spectroscopic data for Tp*2UEPh
[E = O (1), S (2), Se (3), Te (4)] measured in benzene-d6 at 25 °C.
resonances for the Tp* endo methyl groups range from −10
to −13 ppm, while those for the equivalent exo Tp* protons
appear from 0 to −1 ppm. The equivalent pyrazole protons of
the Tp* ligand all appear around 7 ppm, while the broad
resonance of the B−H is evident from 4 to 7 ppm for 1−4. For
1, signals at 18.35, 21.26, and 42.57 ppm are assigned as the
protons of the phenyl group, reflective of free rotation in
solution and similar to C2 symmetric Tp*2UOMes (Mes =
2,4,6-trimethylphenyl).36 For compounds 2−4, these equivalent
phenyl resonances are noted by an upfield shift relative to 1,
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Tp*2UEPh Com-
plexes. In order to explore the bonding and reactivity in the
series of trivalent uranium phenylchalcogenide complexes,
Tp*2UEPh (E = O, S, Se, Ph), synthesis of each compound
was initially targeted. The oxygen congener, Tp*2UOPh (1),
was generated by treating a green solution of Tp*2UCH2Ph
with an equivalent of phenol, which resulted in a purple powder
after workup (eq 1). Examination of the organics from a sealed
1
ranging from 10 to 21 ppm. The H NMR spectrum for 2
matches that previously reported, which was originally
synthesized by the addition of thiophenol to Tp*2UCH2Ph.22
The 1H NMR spectral data for 1−4 show that the resonances
shift toward the diamagnetic region as the radius of the
chalcogenide bonded to uranium increases. For example, in
Tp*2UOPh (1), the endo-Tp* methyl appears at −12.97 ppm,
and shifts downfield (S = −11.55; Se = −11.34, Te = −10.89
ppm) as Group 16 is descended. Likewise, the corresponding
trend is noted for the -EPh protons for 1−4, which shift upfield
as the distance between the paramagnetic uranium center and
phenyl protons increases on account of the larger chalcogen. It
should be noted that this shifting is not as extreme between
sulfide, selenide and telluride species as it is in the case of the
oxygen analogue, 1. This has also been noted in the series of
complexes, Cp*2U(EPh)2 (E = S,37 Se,38 Te39), where the Cp*
and -EPh resonances shift according to the same trend as for
Tp*2UEPh.
Compound 4 was also characterized by X-ray crystallography,
as little structural data exists for uranium(III)-telluride
interactions. Blue, block-shaped crystals grown from a
concentrated solution of toluene and diethyl ether (1:2) over
48 h at −35 °C were analyzed, and refinement of the data
revealed a seven-coordinate uranium center in a capped
octahedral geometry (Figure 2, structural parameters in Table
1). One triangular face of the octahedron is formed by N21,
tube experiment by 1H NMR spectroscopy showed the
formation of toluene, indicating successful protonation of the
U−C bond. The rest of the family of phenylchalcogenides was
accessible by adding one-half equivalent of PhEEPh (E = S, Se,
or Te) to THF solutions of Tp*2UCH2Ph, causing immediate
color changes to blue (eq 1). In each case, rapid formation of
the phenylchalcogenide product, Tp*2UEPh (E = S (2), Se (3),
Te (4)) was observed along with one-half equivalent of
1
bibenzyl as identified by H NMR spectroscopy. Performing
12979
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
Figure 2. Molecular structure of 4 (left) and 5 (right) shown with 30% probability ellipsoids. Selected hydrogen atoms and cocrystallized solvent
molecules have been omitted for clarity.
Table 1. Structural Parameters of 4 and 5
bond
U1−N11
U1−N12
U1−N21
U1−N31
U1−N61
U1−N71
U1−N81
U1−Te40
U1−Te40−C41
4
5
bond
U1−S41
U1−S42
S41−C40
S42−C40
4
5
2.844(7) Å
2.829(6) Å
2.547(7) Å
2.577(6) Å
2.483(7) Å
2.660(6) Å
2.541(6) Å
3.2392(6) Å
106.0(2)°
2.555(4) Å
2.9643(13) Å
2.9756(13) Å
1.698(5) Å
1.678(5) Å
123.9(3)°
2.598(4) Å
2.716(4) Å
2.579(4) Å
2.678(5) Å
2.707(4) Å
S41−C40−S42
S41−U1−S42
60.19(3)°
N31, and N71, while the other is composed of N61, N81, and
the midpoint of N11−N12, and is capped by the tellurium
atom. The U−N distances for the Tp* ligands, ranging from
2.483(7) to 2.844(7) Å, are consistent with those observed for
bis-Tp* complexes and Tp*2USPh (2).22,25 The unusual
coordination for 4, where a single Tp* ligand is coordinated
in a κ4 fashion, has been observed previously for Tp*2UI.40 The
U−N distances of the η2-pyrazole ring of Tp*2UI (2.807(5)
and 2.833(5) Å) compare favorably with that of complex 4,
which has corresponding distances of 2.844(7) and 2.829(6) Å.
The unusual κ4-coordination of the Tp* ligand is not observed
and has been observed in lanthanide44 and uranium38,39,43
phenylchalcogenide families.
Previous analysis by Arnold et al. has shown that structural
parameters may be used as an indicator to determine the extent
of covalency in actinide-chalcogen bonding.45 For instance, in
the series Cp*2UOPh, CpMe42USPh, Cp*2USePh, and
Cp*2UTePh, the short U−O distance relative to the other
compounds was determined to be a result of steric crowding
and an increased ionic contribution to bonding from a U+O−
resonance form rather than of a O→ U π donation. While the
crystallographic data for the Tp* series is not complete,
comparison of Tp*2UOMes,36 Tp*2USPh, and Tp*2UTePh is
possible. As in the uranium(IV) series, the data for these
trivalent derivatives show the same trends, with an unusually
short U−O distance as compared to the sum of the U and O
covalent radii as well as the largest U−E−C angle of the series
(Table 2). This short U−O bond distance indicates a large
degree of ionic character in this trivalent series.
1
in the solution H NMR spectrum, as all endo-protons of the
Tp* are equivalent and chemically distinct from the exo-Tp*
methyl groups, which are equivalent to each other.
The U−Te distance in 4 of 3.2392(6) Å is similar to that in
the homoleptic uranium(III) telluride complex, [U(N(κ2-
Te,Te′-(TePPh)2)3], which has distances ranging from
3.1270(7) to 3.1990(7) Å,18 but is slightly longer than those
in tetravalent Cp*2U(TePh)2 (3.0383(6) Å),39 Cp*2U(η2-
TeC6H4) (2.9648(4) Å),39 and bis-μ-telluride [Na(DME)3]2-
[{((AdArO)3N)U}2(μ-Te)2] (3.031(1), 3.112(1) Å).41 As
expected, this U−Te distance in 4 is also longer than that in
pentavalent Cp*2U(N-2,6-iPr2-C6H3)(TePh) (3.0845(9)
Å)42 and hexavalent [U(NtBu)2(TePh)2(tBu2bpy)]
(3.0405(8) and 3.0335(8) Å)43 due to the larger ionic radius
of U3+ as compared to U5+ and U6+. The smaller U−Te−C
angle in 4 of 106.0(2)° as compared to that of the sulfur
analogue, 2 (113.8(2)°), is consistent with the decreasing
degree of s-hybridization moving down the chalcogen series
Table 2. Structural Parameters for Tp*2UOMes,36
a
Tp*2USPh, and Tp*2UTePh
E ionic
radius
effective
U radius
compound
avg U−E avg U−E−C
Tp*2UOMes
Tp*2USPh
Tp*2UTePh
2.159(10)
2.857(15)
3.2392(6)
168.2(10)
113.8(2)
106.0(2)
1.35
1.84
2.21
0.81
1.02
1.03
a
The ionic radius of the chalcogenide as reported in ref 45 and the
calculated effective U radius are also shown.
12980
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
Electronic Absorption Spectroscopy. The optical
properties of complexes 1−4 were examined by electronic
absorption spectroscopy. Data for the series were recorded in
Tp*2UOPh but is not visible within the range of the
experiment for the rest of the series. Changes in features in
the f−f spectral region for a chalcogen series of uranium
complexes has been observed for the pentavalent family,
Cp*2U(N-2,6-iPr2-C6H3)(EPh) (E = O, S, Se, Te), reported
by Kiplinger and co-workers.48,49 Similar to 1−4, this family
shows a significant change in optical properties between the
aryloxide and thiophenoxide species (E = O → S), while the
heavier, “softer” organochalcogenide species (E = S, Se, Te)
have largely the same transitions. The authors attribute the
difference in spectra within the Cp*2U(N-2,6-iPr2-C6H3)-
(EPh) family to variation in f-orbital involvement of the
aryloxide versus the arylsulfide, selenide, or telluride ligands,
prompting further exploration of 1−4 through computational
experiments.
Magnetism. The lack of magnetic data for trivalent uranium
compounds containing U−Te bonds prompted exploration of 4
by SQUID magnetometry (Figure 4). The room temperature
moment of 3.58 μB (295 K) for 4 is just slightly below what
would be expected for a free U(III) ion (4I9/2, 3.62 μB).11 This
moment decreases gradually to 2.86 μB at 7 K. Only below this
temperature does a more significant drop occur, to 2.77 μB at 4
K. The decrease in the effective magnetic moment as
temperature decreases is less drastic than what is observed
for uranium(IV) compounds with similar ligand sets but is
more like trivalent Tp*2UI.50 While Tp*2UI has μeff = 3.01 μB
at 300 K, 4 shows higher room and low temperature moments.
Interestingly, both Tp*2UI and the recently reported [Tp*2U-
(bpy)][I]51 behave as single-molecule magnets. Given the
structural similarity of 4 to these species, combined with the
slow relaxation of magnetization typically observed in other
U(III) complexes,52,53 4 may also be a candidate to show
single-molecule magnetic properties.
Computation. The electronic structures of complexes 1−4
were examined by density functional theory (DFT) at the
B3LYP29 level of theory. Complexes 2 and 4 were optimized
from their coordinates generated from X-ray crystallographic
analyses. Upon successful optimization of 2, the sulfur atom
was replaced with oxygen or selenium and reoptimized to afford
1 and 3, respectively. The calculated uranium−sulfur and
uranium−tellurium bond distances of 2.832 (2) and 3.233 Å
(4), respectively, are nearly identical to the experimentally
determined lengths of 2.8573(15) and 3.2392(6) Å. Addition-
ally, the calculated U−Te−C angle of 106.88° is close to the
Figure 3. Electronic absorption spectra of Tp*2UOPh (1, orange),
Tp*2USPh (2, green), Tp*2USePh (3, blue), and Tp*2UTePh (4,
red) in THF at ambient temperature. Inset shows the near-infrared
region of the spectra. Solvent overtones between 1670 and 1760 nm
have been removed for clarity.
THF over the range of 400−2100 nm, (Figure 3) and showed
analogous low-to-mid intensity absorption bands distributed
throughout the UV and visible regions. Complexes 1 and 2
have sharp, color producing d-f charge-transfer bands at 578 nm
(1: ε = 767 M−1cm−1; 2: ε = 788 M−1cm−1), whereas these
appear at 575 nm for 3 (ε = 771 M−1cm−1) and 4 (ε = 836
M−1cm−1).46 These bands in the visible region, as well as those
present throughout the near-infrared region of the spectra,
show weak, ill-defined parity forbidden f−f transitions for 1−4,
confirming the +3 oxidation state of uranium.46,47 Prominent
features in the near-infrared regions include the sharp bands
between 1150 and 1350 nm for 1−4; however, the bands for 1
differ from those for 2−4. For 1, this band is visible at 1189 nm
(ε = 246 M−1 cm−1) and appears to red shift as group 16 is
descended. For 2, this band is evident at 1244 nm (ε = 169 M−1
cm−1) and shifts farther to 1251 nm for 3 (ε = 156 M−1 cm−1)
and 4 (ε = 170 M−1 cm−1). An additional feature located at
2017 nm (ε = 116 M−1 cm−1) is observed in the spectrum of
Figure 4. Susceptibility (left) and effective magnetic moment (right) versus temperature for Tp*2UTePh (4). Susceptibility data were collected at a
1000 Oe measuring field.
12981
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
Figure 5. Visualization of orbitals for Tp*2UTePh (4). HOMO (left), HOMO-1 (left middle), and HOMO-2 (right middle) depict the uranium
based f-orbitals that each house one of the three unpaired electrons for the U(III), 5f 3 ion. HOMO-3 (right) shows the U−Te σ-bond in complex 4.
experimental bond angle of 106.0(2)° for 4. The uranium−
oxygen bond distance for 1 was calculated to be 2.199 Å and is
similar to those observed for the terminal aryloxide ligands in
[U(O-2,6-iPr2C6H3)3]2 (2.214(7) Å)54 and on the order of that
in Tp*2UOMes (2.159(10) Å).36 No terminal organoselenide
complexes of U(III) exist for comparison with 3, but the
theoretical uranium−selenium bond distance calculated for 3 of
2.997 Å is slightly shorter than that of 3.0869(4) Å, which was
observed for trivalent [U(N(κ2-Se,Se′-(SePPh)2)3]. The
calculated distance for 3 is also longer than that for
uranium−phenylselenide bonds in tetravalent Cp*2U(SePh)2
(2.8011(7), 2.7997(7) Å), which is expected as the uranium-
(III) ionic radius is ∼0.1 Å longer than the radius for
uranium(IV).55
The electronic structures of complexes 1−4 were established
by examining the Mulliken spin densities for uranium. This
parameter is a useful metric for paramagnetic molecules as it
shows the amount of electron density being gained or donated
from bonded atoms and is, in general, more independent from
functional and basis set than Mulliken population analysis.56,57
Analysis shows the family of complexes 1−4 consist of U(III),
5f3 centers, with respective Mulliken spin densities of 3.005,
3.019, 3.022, and 3.027 (B3LYP). To reiterate the functional
independence, the Mulliken spin densities for complexes 2 and
4 were calculated at the B3PW91 level of theory to be 3.037
and 3.046 and using PBE to be 3.006 and 3.011. The three
unpaired electrons are contained in the HOMO, HOMO-1,
and HOMO-2, which are mainly uranium f orbital in character
(Figure 5). The spin density numbers do not deviate
significantly from their expected value of 3.000 for three
unpaired electrons, suggesting the U−E bond in this family is
primarily ionic, with only small covalent character (Table 3).
This is highlighted for compound 4 in Figure 5, which shows
the uranium−tellurium bonding (HOMO-3) orbital. Here, the
U−Te has a significant σ-bond with no π interaction present.
Analysis of the composition of the U−Te bond shows less than
5% of 5f orbital contribution, with a 71% contribution from the
Te 5p orbital. The spin density values calculated for 1−4
deviate from that of the U(III) center in Cp*2[iPrNC(Me)-
NiPr]U (3.079), as well as its transuranic analogues,
Cp*2[iPrNC(Me)NiPr]An (An = Np - Am), implying the
amidinate series better supports covalent bonding character
with uranium.58 The corresponding spin densities of the
chalcogenides in 1−4 are also small; thus minimal E → U
donation is observed. Therefore, the uranium−chalcogenide
bond in complexes 1−4 can best be described as primarily ionic
with a small covalent contribution.
The computational results for 1−4 are consistent with those
reported for the model compound, USR′(SR)2 (R = 2-tBuC6H4
; R′ = C6H5), previously calculated for trivalent U(SMes*)3.
This study shows the U(III)-S bonds are ionic and strongly
polarized at the sulfur.19 However, several examples for trivalent
uranium have been demonstrated to contain a small covalent
component in the uranium-chalcogen bond. The trivalent
anion, [Cp*2U(dddt)]−, was established by structural and
computational analyses to possess some covalent character in
the U−S bonds.21 Similarly, results from studying the
i
uranium(III) series, [U(N(κ2-E,E′-(EPR)2)3] (R = Ph, Pr; E
= S,8,15−17 Se,15 Te18), found a covalent contribution for the
U−E bonds but also noted a slight increase in the degree of
covalency as the chalcogen donor group is descended.17 This
trend can also be observed in 1−4 with increasing deviation
from the expected spin density with concomitant increase in
spin density on E and constant spin density on all nitrogen
atoms. This indicates the change in spin density on the uranium
is due primarily to the chalcogenide and parallels those results
of previous studies in which covalent bonding increases going
down the chalcogen series.16,17 The bis(Tp*) system seems to
have less covalency, which may be attributed to the fact that
previous homoleptic complexes only have bonds that are
uranium-chalcogenide in nature.
Reactivity of Tp*2UEPh with CS2. The reactivity of 2−4
toward carbon disulfide was explored. Layering a cold, dark
blue THF solution (−35 °C) of Tp*2USPh with a pentane
solution of CS2 of the same temperature and cooling for 12 h
resulted in the deposition of large, green needles of the
trithiocarbonate product, Tp*2U(κ2-S2CSPh) (5), arising from
CS2 insertion into the U−S bond (eq 2). Likewise exposure of
either 3 or 4 to CS2 also produced the requisite color change
from blue to green as seen for 2, indicating formation of
Tp*2U(κ2-S2CEPh) (E = Se (6), Te (7)), respectively (eq 2).
However, workup under reduced pressure for 5−7 returned the
deep blue color of the starting material, indicating a reversible
CS2 insertion process for each. Thus, complexes 5−7 were
Table 3. Mulliken Spin Densities for Complexes 1−4
Calculated at the B3LYP Level of Theory
Mulliken spin densities
complex
uranium(III)
E
Σ N (coordinated to U)
1, E = O
2, E = S
3, E = Se
4, E = Te
3.005
3.019
3.022
3.027
−0.016
−0.018
−0.020
−0.024
−0.059
−0.057
−0.057
−0.058
1
generated in J. Young NMR tubes and characterized by H
12982
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
formation of the trithiocarbonate, Tp*2U(κ2-S2CSPh). Com-
pound 5 has an eight coordinate uranium center similar in
coordination geometry to that of Tp*2U(κ2-E2CCH2Ph) (E =
O, S).25 The U−N distances for the bis-Tp* framework are as
expected, ranging from 2.555(4) to 2.716(4) Å.22,25,61 The U−
S distances for the trithiocarbonate ligands in 5 of 2.9643(13)
and 2.9756(13) Å support the uranium(III) assignment, as
these are similar to those in trivalent Tp*2U(κ2-S2CCH2Ph)
(2.943(4), 3.016(4) Å).25 These distances are roughly 0.1 Å
longer than those in tetravalent Cp*2U(StBu)(κ2-S2CStBu)
(2.885(4), 2.821(5) Å)37 and [{((AdArO)3N)U}2(μ-κ2:κ2-
S2CS)] (2.868(2), 2.872(2) Å).60 The C−S distances in 5 of
1.698(5) and 1.678(5) Å are within error of each other, and
close to those observed for Tp*2U(κ2-S2CCH2Ph) (1.656(17),
1.712(16) Å)25 and [{((AdArO)3N)U}2(μ-κ2:κ2-S2CS)]
(1.707(4), 1.710(4) Å), supporting delocalization of the
monoanionic charge across the bidentate trithiocarbonate
ligand.
To more thoroughly explore the role of insertion equilibria in
the generation of 5−7, titration experiments were performed
and the data is tabulated in Table S2, Supporting Information.
From these experiments, equilibrium constants for compounds
5, 6, and 7 of 2550 80, 24 3, and 70 2 M−1, respectively,
were measured. The significantly higher value for 5 as
compared to 6 and 7 is consistent with higher conversions of
starting material to product in the presence of excess carbon
disulfide, which facilitated the isolation of X-ray quality crystals
of 5, but not for 6 or 7. The large driving force for the
formation of 5 relative to 6 and 7 can most likely be attributed
to the strong C−S bond (167(2) kcal/mol)62 that is formed by
CS2 insertion in comparison to the weaker C−Se (139(23)
kcal/mol)62 and C−Te (66 kcal/mol)63 bonds.
NMR spectroscopy in benzene-d6 (Table 4) in the presence of
CS2. No reaction with carbon disulfide was noted for
Tp*2UOPh (1).
1
Table 4. H NMR Data for Tp*2U(κ2-S2CEPh) (5−7)
Measured in Ppm in Benzene-d6 at 25° C
5 (E = S)
6 (E = Se)
7 (E = Te)
Tp*-CH3 −21.76, −11.72,
−0.83, 1.17, 2.18,
3.16
−21.37, −11.69,
−0.84, 1.24, 1.79,
3.17
−20.74, −11.34,
−0.83, 1.25, 1.44,
3.07
Tp*-CH
B−H
m-CH
4.02, 6.95, 11.69
4.11, 6.86, 11.75
4.23, 6.82, 11.63
6.32
7.82
8.31
9.48
6.27
7.84
8.32
9.49
6.22
7.79
8.24
9.59
p-CH
o-CH
Analysis of 5−7 by 1H NMR spectroscopy revealed
asymmetric spectra composed of 13 paramagnetically shifted
and broadened resonances analogous to Tp*2U(κ2-S2CCH2Ph)
(Table 4).25 The endo- and exo-methyls of the Tp* ligand are
chemically inequivalent, with six resonances appearing from 3
to −22 ppm integrating to six protons each, due to the sterically
bulky dithiocarboxylate ligand. The three corresponding
singlets for the pyrazole protons are located in the range of
4−12 ppm, integrating to 2H. Those for phenyl protons are
located from 7 to 10 ppm and are identifiable due to the
presence of splitting, as these signals are now farther from the
paramagnetic uranium center following CS2 insertion.
CONCLUSIONS
■
In summary, we have synthesized and characterized a series of
trivalent uranium phenylchalcogenide species, Tp*2UEPh (E =
O (1), S (2), Se (3), Te (4)). The optical properties of these
compounds have been probed using electronic absorption
spectroscopy, supporting the uranium(III) oxidation states in
1−4. DFT calculations show the uranium−chalcogenide bonds
in compounds 1−4 are primarily ionic but do show the trend of
increasing covalent bonding with heavier chalcogens as has
been previously noted. Additionally, the U−S, U−Se, and U−
Te bonds were found to undergo reversible insertion of CS2,
forming the monoanionic dithiocarboxylate ligand derivatives
5−7.
While insertion of CS2 into uranium−chalcogenide bonds
has rarely been observed for uranium(III) species, this has been
studied in tetravalent systems. For instance, Ephritikhine and
co-workers showed CS2 insertion with Cp3USiPr, which further
reacts to form Cp2U(S2CSiPr)2.59 For their related system,
The uranium(III)-chalcogen derivatives presented here are
rare members of an analogous series in which the steric and
electronic properties of all the other components in the system
are held constant; thus a true comparison of the role of the
chalcogen can be made. In analogy to the [U(N(κ2-E,E′-
(EPR)2)3] series, hydrotris(3,5-dimethylpyrazolyl)borate deriv-
atives 1−4 show a slight increase in covalency is noted as
Group 16 is descended, with the primary contribution to
bonding being ionic in character.
i
t
Cp*2U(SR)2 (R = Me, Pr, Bu), CS2 insertion generates
Cp*2U(SR)(S2CSR),37 from which the double insertion
products, Cp*2U(S2CSMe)2 and Cp*2U(S2CStBu)2, can be
generated with an additional equivalent of CS2. In a similar
fashion, Meyer and co-workers demonstrated reactivity of CS2
with the sterically crowded uranium(IV) chalcogenide-bridged
family [{((AdArO)3N)U}2(μ-E)] (E = S, Se), facilitating
isolation of the uranium chalcogenide mixed carbonate species
[{((AdArO)3N)U}2(μ-κ2:κ2-S2C-E)].60 In this family of mole-
cules, no CS2 insertion is noted at the strong U−O bonds of
the supporting aryloxide ligand, which is in line with the
observed lack of reactivity of 1.
ASSOCIATED CONTENT
* Supporting Information
■
S
1H NMR spectra of 1−7; electronic absorption spectra for 5−
7; data for equilibrium experiments; crystallographic exper-
imental information; crystallographic information files. This
material is available free of charge via the Internet at http://
pubs.acs.org.
The stability of compound 5 allowed for characterization by
X-ray diffraction of suitable crystals grown from layering a CS2/
pentane solution over a concentrated THF/toluene solution of
2 at −35 °C (Figure 2, Table 1). Analysis confirmed the
12983
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
(28) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery Jr., J. A.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J.; Brothers, E. N.;
Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.;
Tomasi, J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.;
Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: sbart@purdue.edu.
*E-mail: walenskyj@missouri.edu.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge the National Science Foundation (CAREER
grant to S.C.B., CHE-1149875; also grant to M.P.S., CHE-
1058889) and the U.S. Nuclear Regulatory Commission
Faculty Development Award (J.R.W.) for funding this work.
We also thank Stacey Opperwall for her assistance with
electronic absorption spectroscopic measurements.
̈
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09; Gaussian, Inc.: Wallingford, CT, USA, 2009.
(29) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. J.
Chem. Phys. 1994, 98.
REFERENCES
(30) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(31) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
■
(1) Gras, J.-M.; Quang, R. D.; Masson, H.; Lieven, T.; Ferry, C.;
Poinssot, C.; Debes, M.; Delbecq, J.-M. J. Nucl. Mater. 2007, 362, 383.
(2) Panak, P. J.; Geist, A. Chem. Rev. 2013, 113, 1199.
(3) Wang, C.-Z.; Lan, J.-H.; Wu, Q.-Y.; Zhao, Y.-L.; Wang, X.-K.;
Chai, Z.-F.; Shi, W.-Q. Dalton Trans. 2014, 43, 8713.
(4) Abraham, F.; Arab-Chapelet, B.; Rivenet, M.; Tamain, C.;
Grandjean, S. Coord. Chem. Rev. 2014, 266−267, 28.
(5) Hudson, M. J.; Harwood, L. M.; Laventine, D. M.; Lewis, F. W.
Inorg. Chem. 2013, 52, 3414.
(32) Kuchle, W.; Dolg, M.; Stoll, H.; Preuss, H. J. Chem. Phys. 1994,
̈
100, 7535.
(33) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(34) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213.
(35) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.; Gordon,
M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77, 3654.
(36) Antunes, M. A.; Domingos, A.; Cordeiro dos Santos, I.;
Marques, N.; Takats, J. Polyhedron 2005, 24, 3038.
(37) Lescop, C.; Arliguie, T.; Lance, M.; Nierlich, M.; Ephritikhine,
M. J. Organomet. Chem. 1999, 580, 137.
(6) Kolarik, Z. Chem. Rev. 2008, 108, 4208.
(7) Lewis, F. W.; Hudson, M. J.; Harwood, L. M. Synlett 2011, 2011,
(38) Evans, W. J.; Miller, K. A.; Kozimor, S. A.; Ziller, J. W.;
DiPasquale, A. G.; Rheingold, A. L. Organometallics 2007, 26, 3568.
(39) Evans, W. J.; Miller, K. A.; Ziller, J. W.; DiPasquale, A. G.;
Heroux, K. J.; Rheingold, A. L. Organometallics 2007, 26, 4287.
(40) Sun, Y.; McDonald, R.; Takats, J.; Day, V. W.; Eberspacher, T.
A. Inorg. Chem. 1994, 33, 4433.
(41) Lam, O. P.; Heinemann, F. W.; Meyer, K. Chem. Sci. 2011, 2,
1538.
(42) Graves, C. R.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L. Chem.
Commun. 2009, 776.
(43) Spencer, L. P.; Yang, P.; Scott, B. L.; Batista, E. R.; Boncella, J.
2609.
(8) Ingram, K. I. M.; Tassell, M. J.; Gaunt, A. J.; Kaltsoyannis, N.
Inorg. Chem. 2008, 47, 7824.
(9) Arnold, P. L.; Turner, Z. R.; Kaltsoyannis, N.; Pelekanaki, P.;
Bellabarba, R. M.; Tooze, R. P. Chem.Eur. J. 2010, 16, 9623.
(10) Jones, M. B.; Gaunt, A. J.; Gordon, J. C.; Kaltsoyannis, N.; Neu,
M. P.; Scott, B. L. Chem. Sci. 2013, 4, 1189.
(11) Castro-Rodriguez, I.; Meyer, K. Chem. Commun. 2006, 1353.
(12) Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C. Nature 2008,
455, 341.
(13) Korobkov, I.; Gambarotta, S. Prog. Inorg. Chem. 2005, 54, 321.
(14) Evans, W. J.; Kozimor, S. A. Coord. Chem. Rev. 2006, 250, 911.
(15) Gaunt, A. J.; Scott, B. L.; Neu, M. P. Chem. Commun. 2005,
3215.
M. Inorg. Chem. 2009, 48, 2693.
(44) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L.
Organometallics 1985, 4, 112.
(45) Minasian, S. G.; Krinsky, J. L.; Arnold, J. Chem.Eur. J. 2011,
(16) Ingram, K. I. M.; Kaltsoyannis, N.; Gaunt, A. J.; Neu, M. P. J.
17, 12234.
Alloys Compd. 2007, 444−445, 369.
(46) Katz, J.; Morss, L. R.; Seaborg, G. T. The Chemistry of the
Actinide Elements; Chapman Hall: New York, 1980.
(47) Nakai, H.; Hu, X.; Zakharov, L. N.; Rheingold, A. L.; Meyer, K.
Inorg. Chem. 2004, 43, 855.
(17) Gaunt, A. J.; Reilly, S. D.; Enriquez, A. E.; Scott, B. L.; Ibers, J.
A.; Sekar, P.; Ingram, K. I. M.; Kaltsoyannis, N.; Neu, M. P. Inorg.
Chem. 2008, 47, 29.
(18) Gaunt, A. J.; Scott, B. L.; Neu, M. P. Angew. Chem., Int. Ed.
(48) Graves, C. R.; Kiplinger, J. L. Chem. Commun. 2009, 3831.
(49) Graves, C. R.; Scott, B. L.; Morris, D. E.; Kiplinger, J. L. J. Am.
Chem. Soc. 2007, 129, 11914.
(50) Coutinho, J. T.; Antunes, M. A.; Pereira, L. C. J.; Bolvin, H.;
Marcalo, J.; Mazzanti, M.; Almeida, M. Dalton Trans. 2012, 41, 13568.
(51) Antunes, M. A.; Pereira, L. C. J.; Santos, I. C.; Mazzanti, M.;
Marcalo, J.; Almeida, M. Inorg. Chem. 2011, 50, 9915.
(52) Rinehart, J. D.; Long, J. R. J. Am. Chem. Soc. 2009, 131, 12558.
(53) Rinehart, J. D.; Meihaus, K. R.; Long, J. R. J. Am. Chem. Soc.
2010, 132, 7572.
2006, 45, 1638.
(19) Roger, M.; Barros, N.; Arliguie, T.; Thuery, P.; Maron, L.;
Ephritikhine, M. J. Am. Chem. Soc. 2006, 128, 8790.
(20) Arliguie, T.; Lescop, C.; Ventelon, L.; Leverd, P. C.; Thuery, P.;
Nierlich, M.; Ephritikhine, M. Organometallics 2001, 20, 3698.
(21) Roger, M.; Belkhiri, L.; Thuery, P.; Arliguie, T.; Fourmigue, M.;
Boucekkine, A.; Ephritikhine, M. Organometallics 2005, 24, 4940.
(22) Matson, E. M.; Fanwick, P. E.; Bart, S. C. Organometallics 2011,
30, 5753.
(23) Jensen, M. P.; Bond, A. H. J. Am. Chem. Soc. 2002, 124, 9870.
(24) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(54) Van der Sluys, W. G.; Burns, C. J.; Huffman, J. C.; Sattelberger,
A. P. J. Am. Chem. Soc. 1988, 110, 5924.
(55) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(56) Fortier, S.; Walensky, J. R.; Wu, G.; Hayton, T. W. J. Am. Chem.
Soc. 2011, 133, 11732.
(57) Prodan, I. D.; Scuseria, G. E.; Martin, R. L. Phys. Rev. B 2007,
76, 033101.
(58) Walensky, J. R.; Martin, R. L.; Ziller, J. W.; Evans, W. J. Inorg.
Chem. 2010, 49, 10007.
(25) Matson, E. M.; Forrest, W. P.; Fanwick, P. E.; Bart, S. C. J. Am.
Chem. Soc. 2011, 133, 4948.
(26) Sheldrick, G. M. Acta Crystallogr. 2008, 112, A64.
(27) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Garcia-Granda,
S.; Gould, R. O.; Smits, J. M. M. DIRDIF2008 Program System;
Crystallography Laboratory, University of Nijmegen: The Nether-
lands, 2008.
12984
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985

Inorganic Chemistry
Article
(59) Leverd, P. C.; Ephritikhine, M.; Lance, M.; Vigner, J.; Nierlich,
M. J. Organomet. Chem. 1996, 507, 229.
(60) Lam, O. P.; Franke, S. M.; Heinemann, F. W.; Meyer, K. J. Am.
Chem. Soc. 2012, 134, 16877.
(61) Matson, E. M.; Forrest, W. P.; Fanwick, P. E.; Bart, S. C.
Organometallics 2012, 31, 4467.
(62) Dean, J. A. Lange’s Handbook of Chemistry, 15th ed.; McGraw
Hill: New York, 1999.
(63) McAllister, T. J. Cryst. Growth 1989, 96, 552.
12985
dx.doi.org/10.1021/ic5020658 | Inorg. Chem. 2014, 53, 12977−12985