Expanding the Library of Uranyl Amide Derivatives: New Complexes Featuring the tert -Butyldimethylsilylamide Ligand

Article abstract of DOI:10.1021/acs.inorgchem.8b00298

New uranyl derivatives featuring the amide ligand, -N(SiHMe₂)^tBu, were synthesized and characterized by X-ray crystallography, multinuclear NMR spectroscopy, and absorption spectroscopies. Steric properties of these complexes were also quantified using the computational program Solid-G. The increased basicity of the free ligand -N(SiHMe₂)^tBu was demonstrated by direct comparison to -N(SiMe₃)₂, a popular supporting ligand for uranyl. Substitutional lability on a uranyl center was also demonstrated by exchange with the -N(SiMe₃)₂ ligand. The increased basicity of this ligand and diverse characterization handles discussed here will make these compounds useful synthons for future reactivity.

Full text of DOI:10.1021/acs.inorgchem.8b00298

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Expanding the Library of Uranyl Amide Derivatives: New Complexes
Featuring the tert-Butyldimethylsilylamide Ligand
Scott A. Pattenaude, Ezra J. Coughlin, Tyler S. Collins, Matthias Zeller, and Suzanne C. Bart*
H.C. Brown Laboratory, Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
S
* Supporting Information
ABSTRACT: New uranyl derivatives featuring the amide ligand,
−N(SiHMe2)tBu, were synthesized and characterized by X-ray
crystallography, multinuclear NMR spectroscopy, and absorption
spectroscopies. Steric properties of these complexes were also
quantified using the computational program Solid-G. The
increased basicity of the free ligand −N(SiHMe2)tBu was
demonstrated by direct comparison to −N(SiMe3)2, a popular
supporting ligand for uranyl. Substitutional lability on a uranyl
center was also demonstrated by exchange with the −N(SiMe3)2
ligand. The increased basicity of this ligand and diverse
characterization handles discussed here will make these
compounds useful synthons for future reactivity.
constant of the Si−H moiety in −N(SiHMe2)tBu can probe
INTRODUCTION
The uranyl moiety, UO22+, which features strongly bonded
■
protonation of the ligand (3JHH coupling with NH) or the
presence of a secondary Si−H interaction (1JSiH), both of which
trans-oxo ligands, dominates the coordination chemistry of high
can also be confirmed using IR spectroscopy.
valent uranium.1 In the environment, such compounds are
Despite being well-studied on the d-block,9−17 less is known
found as inorganic salts that are highly soluble in water.1 The
about the use of the −N(SiHMe2)tBu ligand to frame f-block
low solubility of this form in common organic solvents makes
metals.18−21 Recent work from the Sadow group highlights that
its nonaqueous coordination chemistry difficult to study, which
is necessary for future design of organic ligand extractants.2 To
this ligand effectively supports several rare earth elements,
forming RE(N(SiHMe2)tBu)3 (RE = Y, Sc, and Lu).19 In these
circumvent this issue, neutral organometallic derivatives have
been developed, with amide congeners being particularly
cases, three Si−H functionalities participate in secondary
interactions with the rare earth center, and their exchange
advantageous due to their steric and electronic modularity.
rate is determined spectroscopically. Similarly, the erbium
One example, UO2(N(SiMe3)2)2(THF)2, originally reported by
analogue, Er(N(SiHMe2)tBu)3, is proposed to contain
Andersen,3 has risen to popularity because of its ease of
synthesis, stability, and solubility. Furthermore, the crystallinity
secondary Si−H interactions based on the fact that the tert-
butyl groups all point away from the erbium in the molecular
imparted by the bis(trimethylsilyl)amide ligands facilitates the
structure.20 Livinghouse showed that complexes [Li][RE(N-
structural characterization, typically as Lewis base deriva-
(SiMe2H)tBu)4] (RE = Y and La) were useful synthons to
generate amide precatalysts for enantioselective hydroamina-
tion/cyclization,21 and recently, Andersen also demonstrated
the synthesis of the organocerium compound, Cp*2CeN-
(SiHMe2)tBu.18 Surprisingly, there are no reports of this amide
ligand supporting actinide elements.
tives.4−7 More recently, Arnold and co-workers reported a
variation of this compound where one methyl is replaced by a
phenyl on each silyl substituent, UO2(N(SiMe2Ph)2)2.8 Despite
these positive attributes of amide ligands, there have been few
developments in the realm of neutral amide derivatives of
uranyl in recent years.
This −N(SiHMe2)tBu ligand is thus an attractive choice for
uranyl chemistry, as it would facilitate ligand substitution
chemistry due to its increased lability. It also has the potential
to form an Si−H secondary interaction with uranium not
typically noted for actinide elements. Uranyl compounds
featuring this ligand would be a rare example of those
containing a nonchelating alkylated amide, which are often
challenging to isolate due to unwanted uranyl reduction.22
Although UO2(N(SiMe3)2)2(THF)2 is a useful high-valent
uranyl starting material for nonaqueous chemistry, less bulky,
more basic alternatives are desirable due to the increased
lability. The tert-butyl dimethyl silyl amide (−N(SiHMe2)tBu)
is attractive in this regard, as it is more substitutionally labile as
well as being sterically less demanding and has the potential to
facilitate new chemistry. Furthermore, the −N(SiHMe2)tBu
ligand has more spectroscopic handles than its predecessor.
While derivatives of the −N(SiMe3)2 ligand only display a
1
singlet in the H NMR spectrum and lack diagnostic infrared
Received: February 2, 2018
(IR) absorptions, the chemical shift, multiplicity and coupling
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b00298
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
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1H NMR (CDCl3, 300 MHz, 25 °C): δ 0.05 (d, 3JHH = 3.1 Hz, 6 H,
SiH(CH3)2), 0.48 (br s, 1 H, NH), 1.11 (s, 9 H, C(CH3)3), 4.49 (d
Herein, we present our initial findings on the coordination
chemistry of the −N(SiHMe2)tBu ligand with uranyl
derivatives, including the synthesis and spectroscopic and
structural characterization of three new derivatives. Reactivity
studies are also included that highlight the relative basicity and
lability of this amide ligand.
1
1
sept, JSiH = 192.4 Hz, 1 H, SiH(CH3)2). H NMR (C6D6, 300 MHz,
3
25 °C): δ 0.13 (d, JHH = 3.0 Hz, 6 H, SiH(CH3)2), 1.11 (s, 9 H,
C(CH3)3), 4.83 (d sept, 1JSiH = 192.1 Hz, 1 H, SiH(CH3)2). IR (KBr,
cm−1): 3391 m (νNH), 2964 s, 2905 s, 2870 m, 2106 s br (νSiH), 1465
m, 1376 s, 1362 s, 1250 s, 1229 s, 1015 s, 913 s, 888 s, 839 s, 774 s, 752
m, 698 m, 686 m, 625 m.
Synthesis of LiN(SiHMe2)tBu. Modified from a literature
procedure.25 In a glovebox, a 250 mL round-bottomed flask was
charged with HN(SiHMe2)tBu (4.500 g, 34.28 mmol) and pentane
(100 mL). This clear, colorless solution was frozen in the coldwell.
EXPERIMENTAL SECTION
■
General Considerations. All air- and moisture-sensitive manip-
ulations were performed using standard Schlenk techniques or in an
MBraun inert atmosphere drybox with an atmosphere of purified
nitrogen. The MBraun drybox was equipped with 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.23 Benzene-d6 was
purchased from Cambridge Isotope Laboratories, dried with molecular
sieves and sodium, and degassed by three freeze−pump−thaw cycles.
THF-d8 was purchased from Cambridge Isotope Laboratories in a
sealed ampule and dried over an alumina plug before it was dried
additionally with sodium. Chloroform-d was purchased from Cam-
bridge Isotope Laboratories and used without further purification.
tBuNH2, SiHMe2Cl, nBuLi, and tBu2bipy (tBu2bipy = 4,4′-di-tert-butyl-
2,2′-dipyridine) were purchased from Sigma-Aldrich and used without
further purification. [UO2Cl2(THF)2]2 was prepared according to
literature procedures24 using UO3 obtained from IBI Inc. Caution: U-
238 is a weak α-emitter with a half-life of t1/2 = 4 × 109 years. All
manipulations were performed in an inert atmosphere glovebox in a
laboratory equipped with proper detection equipment.
n
Upon thawing, BuLi (2.5 M in hexanes, 13.5 mL, 33.8 mmol) was
added dropwise over 5 min. This solution was stirred as it warmed to
ambient temperature over the course of 3 h. After concentration of the
solution in vacuo, a white solid was collected and assigned as
LiN(SiHMe2)tBu (4.607 g, 33.57 mmol, 98%).
3
1H NMR (C6D6, 400 MHz, 25 °C): δ 0.35 (d, JHH = 2.8 Hz, 6 H,
SiH(CH3)2), 1.26 (s, 9 H, C(CH3)3), 4.86 (br m, 1JSiH = 169 Hz, 1 H,
SiH(CH3)2). 7Li NMR (C6D6, 155 MHz, 25 °C): δ 2.14 (Li). 13C(1H)
NMR (C6D6, 100 MHz, 25 °C): δ 5.40 (SiH(CH3)2), 37.44
(C(CH3)3), 52.61 (C(CH3)3. 29Si(1H) NMR (C6D6, 80 MHz, 25
°C): −23.27 (SiH(CH3)2). IR (KBr, cm−1): 2953 s, 2852 m, 2043 s br
(νSiH), 1465 m, 1354 m, 1244 m, 1188 m, 1037 m, 1015 m, 914 m, 884
m, 830 m, 767 m, 748 m, 692 m.
Synthesis of [Li(THF)3][UO2(N(SiHMe2)tBu)3] (1). A 20 mL
scintillation vial was charged with [UO2Cl2(THF)2]2 (0.100 g, 0.103
mmol) and THF (4 mL), creating a bright yellow suspension. After
stirring for 10 min, the solid fully dissolved, forming a light yellow
solution, which was then frozen in the coldwell. In a separate 20 mL
vial, LiN(SiHMe2)tBu (0.085 g, 0.62 mmol) was dissolved in THF (2
mL), forming a clear, colorless solution that was also frozen in the
coldwell. While thawing, the LiN(SiHMe2)tBu solution was added
dropwise to the thawing uranyl chloride solution. After complete
addition, the resulting solution gradually darkened to red-orange over
the course of 1 min. The reaction mixture was stirred for 1 h as it
warmed to ambient temperature. This red-orange solution was then
concentrated to a dark residue in vacuo. This residue was dissolved in
Et2O (6 mL), filtered to remove LiCl, and concentrated to a red-
orange powder assigned as [Li(THF)3][UO2(N(SiHMe2)tBu)3] (1)
(0.155 g, 0.175 mmol, 85%). Red crystalline needles suitable for X-ray
analysis were grown from a dilute pentane solution overnight at −35
°C. Elemental analysis was attempted twice for compound 1. Results
regularly showed low C and H values, consistent with some degree of
THF desolvation from the lithium cation.
1H NMR spectra were recorded at 25 °C on a Varian Inova 300,
Bruker AV-III-400-HD, or Bruker AV-III-500-HD spectrometer
operating at 299.96, 400.13, and 500.23 MHz, respectively. All
1
chemical shifts are reported relative to the peak for SiMe4, using H
7
(residual) chemical shifts of the solvent as a secondary standard. Li
NMR spectra were recorded on a Bruker AV-III-400-HD spectrometer
operating at 155.51 MHz. 13C(1H) NMR spectra were recorded on a
Bruker AV-III-400-HD or Bruker AV-III-500-HD spectrometer
operating at 100.62 and 125.80 MHz, respectively. 29Si NMR spectra
were recorded on a Bruker AV-III-400-HD or Bruker AV-III-500-HD
spectrometer operating at 79.49 and 99.37 MHz, respectively. 29Si(1H)
NMR spectra were recorded on a Bruker AV-III-500-HD spectrometer
operating at 99.37 MHz. For all molecules, the NMR data are reported
with the chemical shift, followed by the multiplicity, any relevant
coupling constants, the integration value, and the peak assignment.
Infrared spectra were recorded using a Thermo Nicolet 6700
spectrometer; samples were prepared by evaporating C6D6 solutions of
the desired compound onto KBr salt plates. Electronic absorption
measurements were recorded at 25 °C in sealed 1 cm quartz cuvettes
with Cary 6000i UV-vis-NIR spectrophotometer. Elemental analyses
were performed by Midwest Microlab (Indianapolis, IN).
1H NMR (C6D6, 400 MHz, 25 °C): δ 0.66 (d, 3JHH = 3.3 Hz, 18 H,
SiH(CH3)2), 1.28 (br s, 12 H, THF−CH2), 1.89 (s, 27 H, C(CH3)3),
3.40 (br s, 12 H, THF−CH2), 6.84 (sept, 3JHH = 3.3 Hz, 1JSiH = 164.5
7
Hz, 3 H, SiH(CH3)2). Li NMR (C6D6, 155 MHz, 25 °C): δ 0.77
(Li(THF)3). 13C(1H) NMR (C6D6, 100 MHz, 25 °C): δ 4.86
(SiH(CH3)2), 25.54 (THF-CH2), 38.07 (C(CH3)3), 56.96 (C(CH3)3),
68.13 (THF−CH2). 29Si(1H) NMR (C6D6, 100 MHz, 25 °C): δ
−21.86 (SiH(CH3)2). 29Si NMR (C6D6, 100 MHz, 25 °C): δ −21.89
(d sept, 1JSiH = 165.1 Hz, 2JSiH = 5.9 Hz, SiH(CH3)2). IR (KBr, cm−1):
2959 s, 2901 m, 2091 s br (νSiH), 1464 w, 1356 w, 1246 m, 1187 m,
1033 m, 902 s br, 836 s, 781 m.
Single crystals of 1, 1-crown, 2, and 3 suitable for X-ray diffraction,
were coated with poly(isobutylene) oil in a glovebox and quickly
transferred to the goniometer head of a Bruker Quest diffractometer
with a fixed chi angle, a sealed fine-focus X-ray tube, single-crystal
curved graphite incident beam monochromator and a Photon100
CMOS area detector. Examination and data collection were performed
with Mo Kα radiation (λ = 0.71073 Å). See the Supporting
Information for details on single-crystal structure determination.
Synthesis of HN(SiHMe2)tBu. Following a modified literature
Synthesis of [Li(12-crown-4)2][UO2(N(SiHMe2)tBu)3] (1-
crown). A 20 mL scintillation vial was charged with [Li(THF)3]-
[UO2(N(SiHMe2)tBu)3] (0.150 g, 0.170 mmol) and THF (10 mL).
Then, 12-crown-4 (0.060 g, 0.34 mmol) was added neat, causing no
change to the solution color. The resulting red-orange reaction
mixture was stirred for 1 h before it was concentrated in vacuo to an
orange residue. This residue was triturated with pentane and
concentrated in vacuo to ensure complete removal of residual THF.
An orange powder assigned as [Li(12-crown-4)2][UO2(N-
(SiHMe2)tBu)3] (1-crown) was isolated in quantitative yield. Red
crystalline blocks suitable for X-ray analysis were grown from a dilute
benzene solution overnight at 25 °C.
procedure,25 in a fume hood, BuNH2 (75 mL, 0.71 mol) and Et2O
t
(75 mL) were added to a round-bottomed flask and cooled to −78 °C
in a dry ice and acetone bath. SiHMe2Cl (25 mL, 0.23 mol) and Et2O
(25 mL) were added to an addition funnel and slowly added to the
tBuNH2 solution over the course of 1 h. The resulting reaction mixture
was then allowed to warm to room temperature in the acetone bath for
4 h. Once warmed, the reaction mixture was vacuum filtered on a
Buchner funnel and washed with Et O (2 × 10 mL). The filtrate was
̈
2
carefully concentrated with the aid of a fractional distillation column
until all of the Et2O was removed, leaving a clear liquid assigned as
HN(SiHMe2)tBu (20.2 g, 0.154 mol, 68%).
1H NMR (C6D6, 300 MHz, 25 °C): δ 0.80 (d, 3JHH = 3.3 Hz, 18 H,
SiH(CH3)2), 2.07 (s, 27 H, C(CH3)3), 3.42 (br s, 32 H, 12-crown-4),
B
DOI: 10.1021/acs.inorgchem.8b00298
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3
1
6.45 (sept, JHH = 3.2 Hz, 3 H, SiH(CH3)2). H NMR (THF-d8, 500
MHz, 25 °C): δ 0.25 (br s, 18 H, SiH(CH3)2), 1.58 (br s, 27 H,
C(CH3)3), 3.66 (br s, 32 H, 12-crown-4), 5.77 (br m, 1JSiH = 175.8 Hz,
3 H, SiH(CH3)2). 7Li NMR (C6D6, 155 MHz, 25 °C): δ −3.12
(Li(12-crown-4)2). 13C(1H) NMR (THF-d8, 125 MHz, 25 °C): δ 4.55
(SiH(CH3)2), 37.10 (C(CH3)3), 56.52 (C(CH3)3), 68.66 (12-crown-
4). 29Si(1H) NMR (THF-d8, 100 MHz, 25 °C): δ −28.07
(SiH(CH3)2).29Si NMR (THF-d8, 100 MHz, 25 °C): δ −28.08 (d
Scheme 1. Synthesis of Uranyl Silylamide Complexes 1, 1-
crown, and 2
sept, JSiH = 176.0 Hz, JSiH = 6.5 Hz, SiH(CH3)2). IR (KBr, cm−1):
2942 m, 2899 m, 2865 m, 2034 m br (νSiH), 1445 m, 1364 m, 1347 m,
1303 w, 1288 m, 1243 m, 1229 m, 1188 m, 1134 s, 1095 s, 1024 s, 976
m, 917 s, 893 s, 824 s, 773 s, 751 s, 687 m, 637 m. Analysis for
C34H80N3O10Si3LiU: Calcd C, 40.03; H, 7.90; N, 4.12. Found C,
39.74; H, 7.69; N, 3.91.
1
2
Synthesis of (tBu2bipy)UO2(N(SiHMe2)tBu)2 (2). A 20 mL
scintillation vial was charged with [UO2Cl2(THF)2]2 (0.300 g, 0.309
mmol) and THF (5 mL), creating a bright yellow suspension. After
stirring for 10 min, the solid fully dissolved, forming a light yellow
solution. A solution of tBu2bipy (0.166 g, 0.618 mmol) in THF (2 mL)
was added dropwise to the uranyl chloride solution, causing a color
change from yellow to orange. After stirring for 10 min, this solution
was frozen in the coldwell. In a separate 20 mL vial, LiN(SiHMe2)tBu
(0.170 g, 1.236 mmol) was dissolved in THF (2 mL), forming a clear,
colorless solution that was also frozen in the coldwell. While thawing,
the LiN(SiHMe2)tBu solution was added dropwise to the thawing
uranyl chloride solution. After complete addition, the resulting
solution gradually darkened to red-orange over the course of 1 min.
The reaction mixture was stirred for 30 min as it warmed to ambient
temperature. This red-orange solution was then concentrated to a dark
residue in vacuo. This residue was dissolved in Et2O (10 mL), filtered
to remove LiCl, and concentrated to a red powder assigned as
(tBu2bipy)UO2(N(SiHMe2)tBu)2 (2) (0.476 g, 0.596 mmol, 96%).
Red crystalline blocks suitable for X-ray analysis were grown from a
dilute pentane solution overnight at −35 °C.
1H NMR (C6D6, 400 MHz, 25 °C): δ 0.85 (d, 3JHH = 3.4 Hz, 12 H,
SiH(CH3)2), 0.96 (s, 18 H, CC(CH3)3), 2.26 (s, 18 H, NC(CH3)3),
3
3
6.80 (sept, JHH = 3.4 Hz, 3 H, SiH(CH3)2), 7.14 (dd, JHH = 5.8 Hz,
4JHH = 1.8 Hz, 2 H, bipy−CH), 7.73 (d, JHH = 1.7 Hz, 2 H, bipy−
4
CH), 9.83 (d, JHH = 5.7 Hz, 2 H, bipy−CH). 13C(1H) NMR (C6D6,
3
100 MHz, 25 °C): δ 5.61 (SiH(CH3)2), 30.06 (bipy−C(CH3)3), 35.03
(bipy−C(CH3)3), 38.18 (NC(CH3)3), 58.38 (NC(CH3)3), 119.49
(bipy−C), 122.14 (bipy−C), 151.90 (bipy−C), 156.80 (bipy−C),
163.69 (bipy−C). 29Si(1H) NMR (C6D6, 100 MHz, 25 °C): δ −21.35
(SiH(CH3)2). 29Si NMR (C6D6, 100 MHz, 25 °C): δ −21.36 (d sept,
1JSiH = 182.0 Hz, 2JSiH = 6.7 Hz, SiH(CH3)2). IR (KBr, cm−1): 2964 s,
2902 m, 2081 s br (νSiH), 1611 s, 1545 m, 1478 m, 1463 m, 1403 m,
1377 w, 1366 m, 1354 w, 1246 m, 1187 m, 1016 w, 993 w, 954 m, 899
s, 846 m, 773 m, 714 w, 692 m, 607 m. Analysis for C30H56N4O2Si2U:
Calcd C, 45.10; H, 7.06; N, 7.01. Found C, 44.67; H, 6.75; N, 6.81.
1
Figure 1. Comparison of H NMR spectroscopic data (C6D6, 25 °C)
for the Si−H resonance and IR data for the Si−H stretch in
H(NSiHMe2)tBu and 1, highlighting the utility of the Si−H group as a
characterization handle.
RESULTS AND DISCUSSION
As an entry into this work, the parent amine, HN(SiHMe2)tBu,
was generated using a modified literature procedure, in which
■
(SiHMe2)tBu were used, based on the stoichiometric ratio,
[Li(THF)3][UO2(N(SiHMe2)tBu)3] (1) was obtained in high
yield as an orange-red powder.
t
Me2SiHCl is slowly added to a cold solution of excess NH2 Bu
(Scheme 1).25 Following workup, analysis by 1H NMR
spectroscopy (C6D6, 25 °C) shows a diagnostic resonance at
4.83 ppm as a doublet of septets with an Si−H coupling of 192
Hz (Figure 1).
Single crystals of 1, formed as red needles, were obtained
from a dilute pentane solution cooled to −35 °C. From
refinement of the data, the resulting molecular structure shows
a C3v symmetric molecule with a trigonal bipyramidal uranium
center featuring the characteristic trans-oxo ligands in the axial
positions (Figure 2, structural parameters in Table 1). The
structure was modeled with exact 1:1 disorder about a
crystallographic mirror plane (Table S1, Figure S29). The
three amide ligands are situated in the equatorial plane with
115.6(4)−123.8(4)° angles with respect to each other. The U−
N distances of 2.304(6), 2.274(10), and 2.348(11) Å and the
U−O distance of 1.785(4) Å are all on the order of those
In order to generate uranyl derivatives using salt metathesis,
the lithium amide derivative, LiN(SiHMe2)tBu, was synthesized
according to a modified literature procedure, furnishing the
desired product in high yield.25 Subjecting 0.5 equiv of
[UO2Cl2(THF)2]2 to 2 equiv of LiN(SiHMe2)tBu, in
anticipation of generating “UO2(N(SiHMe2)tBu)2”, instead
produced in poor yield [Li(THF)3][UO2(N(SiHMe2)tBu)3]
(1), as determined by X-ray crystallography (vide infra).
However, when the appropriate equivalents of LiN-
C
DOI: 10.1021/acs.inorgchem.8b00298
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Figure 2. Molecular structures of [Li(THF)3][UO2(N(SiHMe2)tBu)3] (1), [Li(12-crown-4)2][UO2(N(SiHMe2)tBu)3] (1-crown), and (tBu2bipy)-
t
UO2(N(SiHMe2)tBu)2 (2) shown at 30% probability ellipsoids. Disorder, cocrystallized solvent molecules, selected hydrogen atoms, selected Bu
methyl groups on the amide ligands, and the Li(12-crown-4)2 countercation in 1-crown have been omitted for clarity.
ligand around a 2-fold rotation axis (Table S2, Figure S30). The
molecular structure was very similar to that of 1, but showed
that the lithium was indeed encapsulated and removed from the
primary coordination sphere (Figure 2, Table 1). Again, the
uranium appears to be in a trigonal bipyramidal geometry, with
two of the amides and both oxygen atoms related by a mirror
plane. The U−N bond distances (2.315(7) and 2.352(11) Å) in
the equatorial plane are within error of those in parent
compound 1. Significantly, the U−O distances of 1.787(6) Å
are now equivalent. The structural parameters for 1-crown are
similar to those noted for [Cp*2Co][UO2(N(SiMe3)2)3],
which features an outer sphere pentamethylcobaltocenium
cation.29 In this case, the U−N distances average 2.32 Å, while
the U−O distances of 1.811(5) and 1.788(5) Å are signature
for uranyls. The inequivalence in these distances is surprising,
given that the cobaltocenium is not associated with a uranyl
oxygen. In solution, the behavior of 1-crown is also very similar
to that of 1, with little shift (∼0.2 ppm or less) in the
Table 1. Bond Distances (Å) for Compounds 1, 1-crown, 2,
and 3
1
1-crown
2
3
U−Ouranyl
U−Ouranyl
U−Namide
U−Namide
U−Namide
U−Nbipy
1.785(4)
1.853(5)
2.304(6)
2.274(10)
2.348(11)
1.787(6)
1.787(6)
2.315(7)
2.315(7)
2.352(11)
1.748(5)
1.803(5)
2.297(5)
2.332(6)
1.786(4)
1.841(4)
2.292(4)
2.298(4)
2.308(4)
2.636(4)
2.559(5)
U−Nbipy
6
observed for UO2(N(SiMe3)2)2(THF)2 and UO2(N-
(SiMe2Ph)2)2.8 The other U−O bond shows elongation to
1.853(5) Å, which is likely due to capping by the lithium
countercation. A more appropriate comparison is to the uranyl
tris(amide), [Na(THF)2][UO2(N(SiMe3)2)3].26 In this case,
the U−N distances range from 2.305(4) to 2.318(4) Å, while
the U−O distances are 1.781(5) and 1.810(5) Å. Again,
elongation of the latter U−O distance is due to the association
with the sodium cation to a uranyl oxygen, similar to
compound 1.
1
resonances of the H NMR spectrum (C6D6, 25 °C). Again,
there is no indication of the presence of any secondary Si−H
interactions to the uranium ion.
Further characterization of 1 by 1H NMR spectroscopy
(C6D6, 25 °C) showed a C3v symmetric spectrum in solution,
with the largest resonances at 0.66 (SiH(CH3)2) and 1.89 ppm
(C(CH3)3). The other notable resonance is that for the Si−H,
appearing as a septet at 6.84 ppm with 1JSiH = 165 Hz, which is
substantially shifted downfield compared to the value of the
parent amine (4.83 ppm, 192 Hz) (Figure 1). The 29Si NMR
(C6D6, 25 °C) spectrum shows a doublet of septets at −21.89
Formation of uranyl tris(amide) derivative 1 likely results
from addition of 1 equiv of LiN(SiHMe2)tBu to transient
“[UO2(N(SiHMe2)tBu)2]”. We hypothesized that this inter-
mediate could be stabilized by the use of a bulky Lewis base,
furnishing the neutral uranyl bis(amide) species, rather than an
additional equivalent of the lithium amide salt, which produced
the “-ate” complex. Pretreating half an equiv of
[UO2Cl2(THF)2]2 with 1 equiv of 4,4′-di-tert-butyl-2,2′-
bipyridine followed by addition of LiN(SiHMe2)tBu at low
temperature resulted in a red-orange solution that was dried to
a red powder after workup.
X-ray quality crystals of this product were obtained by
cooling a concentrated pentane solution to −35 °C. The
structure was modeled with disorder around a crystallographic
mirror plane (Table S3, Figure S31). Analysis confirmed the
identity of the product as (tBu2bipy)UO2(N(SiHMe2)tBu)2 (2),
featuring a pseudo-octahedral uranium center with trans-oxo
ligands and cis-amides (Figure 2, Table 1). Notable features of
this molecule include the O−U−O angle, which is slightly bent
at 175.8(2)°, likely due to the steric pressure imparted by the
cis-amides. Interestingly, the U−O distances are significantly
different from each other at 1.748(5) and 1.803(5) Å, despite
the lack of any countercations.
7
ppm (1JSiH = 165.1 Hz) for the silyl group, whereas the Li
NMR (C6D6, 25 °C) shows a singlet at δ 0.77 (Li(THF)3). The
strong Si−H coupling constant indicates that despite the
proximity of the Si−H bonds to the uranium center, no
secondary Si−H interactions are noted in this case. This is
surprising, given the observation of Si−H secondary
interactions on lanthanide derivatives of this ligand,19,20 as
well as of C−H agostic bonds of −N(SiMe3)2 on low-valent
uranium,27 both of which give insight into unique f-orbital
participation in bonding.28
To remove the lithium countercation from the coordination
sphere, 1 was treated with 12-crown-4, which produced [Li(12-
crown-4)2][UO2(N(SiHMe2)tBu)3] (1-crown) as an orange
solid in quantitative yield. Red block crystals that deposited
from a concentrated benzene solution at room temperature
were analyzed by X-ray diffraction, showing a disordered amide
D
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As expected, the U−N distances of 2.297(5) and 2.332(6) Å
are within error of those in 1 and 1-crown, and the dative U−N
bond lengths for the bipyridine are much longer at 2.636(4)
and 2.559(5) Å. Compound 2 is reminiscent of
UO2(Ar2nacnac)(bipy) (Ar2nacnac = ((2,6-iPr2C6H3)NC-
(Me))2CH), reported by Hayton and co-workers, which
features both a 2,2′-bipyridine and a Ar2nacnac ligand in the
equatorial plane.30 In this case, the U−Nbipy distances of
(2.643(6) and 2.636(6) Å) point toward dative bonds,
confirming the coordination mode in 2. By comparison, the
U−O bonds of 1.833(5) and 1.821(5) Å in UO2(Ar2nacnac)-
(bipy) are both longer and more similar to each other than
those in compound 2.
Analysis of compound 2 by 1H NMR spectroscopy (C6D6, 25
°C) shows very similar parameters to the tris(amide)
derivatives, with not more than a difference in chemical shift
of ∼0.3 ppm for the amide ligand resonances. Additional
resonances for the 4,4′-di-tert-butyl-2,2′-bipyridine ligand are
found at 0.96 ppm for the symmetric tert-butyl groups and in
the range of 7.14−9.83 ppm for the aromatic protons.
As demonstrated here, use of the bulky 2,2′-bipyridine ligand
blocks two coordination sites in the equatorial plane of the
uranyl ion, preventing ligand rearrangement and formation of
the “-ate” complex. The result is isolation of a neutral, six-
coordinate uranyl bis(amide) complex similar to UO2(N-
(SiMe3)2)2(THF)2 and UO2(N(SiMe2Ph)2)2. Unavoidable
formation of uranyl “-ate” complexes with the −N(SiMe3)2
ligand is highly dependent on the alkali metal used in the
synthesis.26 For compound 2, addition of a chelating Lewis base
allows for a smaller, harder ion (Li) to be used, while avoiding
the apparent driving force for “-ate” complex formation, evident
in the preferable formation for 1 (vide supra).
Figure 3. UV−vis plot (as THF solutions at ambient temperature) for
compounds 1, 1-crown, and 2.
Scheme 2. Direct Basicity Comparison of −N(SiHMe2)tBu
and −N(SiMe3)2
equimolar amounts of LiN(SiHMe2)tBu and HN(SiMe3)2 in
C6D6 resulted in complete conversion to HN(SiHMe2)tBu and
LiN(SiMe3)2 as determined by multinuclear NMR spectrosco-
py (Figures S23 and S24). Analysis of this reaction by 1H NMR
spectroscopy validates the uility of the Si−H moiety as a
characterization handle. Although it is not possible to
definitively distinguish HN(SiMe3)2 (0.10 ppm) from LiN-
(SiMe3)2 (broad 0.13 ppm), the presence of HN(SiHMe2)tBu
is clearly evident based on the observation of a doublet of
The infrared spectra for compounds 1, 1-crown, and 2 each
display a single band for the Si−H stretch in a narrow range.
Compound 1 has the highest energy stretch (νSiH) at 2091
cm−1, while compound 1-crown has the lowest energy stretch
at 2034 cm−1. The absorption for 2 is between the others with a
band at 2081 cm−1. The Si−H stretching modes in the
−N(SiHMe2)tBu ligands have been shown to trend to much
lower energies (<2000 cm−1) upon formation of an interaction
with a metal.19 The νSiH energies for the uranyl complexes are
shifted only slightly from HN(SiHMe2)tBu (2106 cm−1) or
LiN(SiHMe2)tBu (2043 cm−1), supporting our conclusions
from Si−H NMR coupling constants that there are no
secondary interactions with uranium in these complexes.
Electronic absorption spectroscopy was used to evaluate the
−N(SiHMe2)tBu series in the ultraviolet (UV), visible, and
near-infrared (NIR) regions (Figure 3). No absorbances are
observed in the NIR region for 1, 1-crown, or 2, consistent
with an f 0 configuration of the assigned U(VI) centers. Broad
absorbances at the edge of the UV region are observed for 1
(λmax = 360 nm, 4640 M−1 cm−1), 1-crown (λmax = 362 nm,
3721 M−1 cm−1), and 2 (λmax = 339 nm, 2576 M−1 cm−1).
These absorbances extend into the visible region and are
consistent with the orange or red colors observed for each
complex. Additional absorbances are observed in the UV region
for 2 (λmax = 283 nm, 17030 M−1 cm−1; λmax = 240 nm, 16319
M−1 cm−1), which are likely due to electronic transitions
1
septets at 4.79 ppm with a JSiH coupling constant of 192 Hz.
Resonances for LiN(SiHMe2)tBu are not observed, which
1
would appear as a broad resonance at 4.86 ppm with a JSiH
7
coupling constant of 169 Hz. Li NMR spectroscopy confirms
the presence of LiN(SiMe3)2 with only one resonance at 1.04
ppm, whereas LiN(SiHMe2)tBu would be observed at 2.14
ppm. The same product distribution is obtained when
equimolar amounts of HN(SiHMe2)tBu and LiN(SiMe3)2 are
mixed (Figures S25−S26).
With the understanding that −N(SiHMe2)tBu has increased
basicity over that of −N(SiMe3)2, we sought to demonstrate
the subsequent increase in reactivity with the new uranyl
complexes. Addition of 3 equiv of HN(SiMe3)2 to compound 1
in THF slowly results in conversion to [Li(THF)2][UO2(N-
(SiMe3)2)3] (3) over the course of 48 h (Scheme 3; Figure
1
S27). Compound 3 was characterized by H NMR spectros-
copy, which showed a singlet at 0.65 ppm, along with
resonances for lithium-bound THF observed at 1.18 and 3.24
ppm.
Orange needle crystals of 3 suitable for X-ray crystallography
were grown directly from a benzene solution at room
temperature in a sealed tube. Analysis of one of these crystals
revealed the expected trigonal bipyramidal uranium center with
the expected axial oxo ligands and three equatorial amide
ligands (Figure 4, select bond distances in Table 1). Similar to
compound 1, one oxo ligand is capped by a lithium cation.
Again, this is evident in the uranyl bond distances as the
uncapped oxo ligand has a U−O distance of 1.786(4) Å, and
the lithium capped oxo ligand has a longer distance of 1.841(4)
t
associated with the Bu2bipy ligand.
To put the electronic properties of the −N(SiHMe2)tBu
ligand into perspective with those of known uranyl ligands, a
direct comparison of the basicity of [−N(SiHMe2)tBu]1− and
[−N(SiMe3)2]1− was probed (Scheme 2). Dissolution of
E
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Inorganic Chemistry
Article
3% less of the uranium coordination sphere compared to
Scheme 3. Synthesis of Compound 3
−N(SiMe3)2.
CONCLUSION
■
In summary, we report the synthesis and characterization of
three new uranyl complexes featuring the −N(SiHMe2)tBu
ligand, which are the first actinide derivatives of this amide.
Successful synthesis was achieved by salt metathesis with
LiN(SiHMe2)tBu, forming compounds that were readily soluble
in nonaqueous conditions. Spectroscopic and structural
characterization did not reveal any Si−H secondary interactions
with the uranium center, contrary to previous examples for rare
earth elements. Reactivity studies established that −N-
(SiHMe2)tBu is more basic and labile than the established
−N(SiMe3)2 derivative. These compounds represent versatile,
soluble starting materials for nonaqueous uranyl coordination
chemistry. Future work will be aimed at examining the lability
of these amides in ligand substitution chemistry and exploring
the benefits of the increased basicity associated with this amide
ligand.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00298.
■
S
Figure 4. Molecular structure of [Li(THF)2][UO2(N(SiMe3)2)3] (3)
shown at 30% probability ellipsoids. Disorder, hydrogen atoms, and
tBu methyl groups have been omitted for clarity.
NMR spectroscopic and general crystallographic details
(PDF)
Accession Codes
Å. The U−N distances for the −N(SiMe3)2 ligands range from
2.292(4) to 2.308(4) Å, similar to the U−N distances observed
in 1. Interestingly, the lithium cation in 3 has only two solvate
THF molecules coordinated, similar to the known pyridine
solvate [Li(py)2][UO2(N(SiMe3)2)3].5 This is in contrast to
the three lithium-coordinated THF molecules in 1, a difference
that could potentially be an artifact of the differing steric
environments of −N(SiMe3)2 and −N(SiHMe2)tBu.
CCDC 1818694−1818696 and 1830212 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Author
*E-mail: sbart@purdue.edu.
■
To analyze the steric profile of the −N(SiHMe2)tBu ligand,
computational analysis via Solid-G was conducted.31,32 This
model quantifies the steric environment imparted by ligands
based on the percentage of the metal sphere that is blocked by
each ligand. Compound 1 was chosen for analysis based on the
structural similarity to both [Li(py)2][UO2(N(SiMe3)2)3] (py
= pyridine) and [Li(THF)2][UO2(N(SiMe3)2)3] (3).5 Table 2
shows the results for each of these three complexes. While the
uranium−amide bond distances do not change significantly
between the three complexes, a clear trend emerges in the
G(amide) values. Compound 1 has consistently smaller
G(amide) values that range from 21.30 to 22.51%, while the
−N(SiMe3)2)3 compounds range between 24.85 and 25.55%.
This difference indicates that −N(SiHMe2)tBu occupies about
ORCID
Tyler S. Collins: 0000-0003-1026-4379
Suzanne C. Bart: 0000-0002-8918-9051
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge a grant from the Center for Actinide Science
and Technology (CAST), an Energy Frontier Research Center
(EFRC) funded by the U.S. Department of Energy (DOE),
Office of Science, Basic Energy Sciences (BES), under Award
Table 2. Solid G31,32 Analysis Comparing Solid Angle Parameters for Compounds 1, 3, and [Li(py)2][UO2(N(SiMe3)2)3]5
[Li(THF)3][UO2(N(SiHMe2)tBu)3] (1)
[Li(THF)2][UO2(N(SiMe3)2)3] (3)
[Li(py)2][UO2(N(SiMe3)2)3]
U−N distances (Å)
G(amide), %
2.304(6)
2.274(10)
2.348(11)
21.30
2.292(4)
2.298(4)
2.308(4)
25.15
2.295(11)
2.279(12)
2.280(13)
24.95
21.86
25.03
25.55
22.51
24.85
25.17
G(complex), %
92.33
94.18
94.05
F
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Inorganic Chemistry
Article
(19) Eedugurala, N.; Wang, Z.; Yan, K.; Boteju, K. C.; Chaudhary,
U.; Kobayashi, T.; Ellern, A.; Slowing, I. I.; Pruski, M.; Sadow, A. D. B-
SiH-Containing Tris(Silazido) Rare-Earth Complexes as Homoge-
neous and Grafted Single-Site Catalyst Precursors for Hydroamination.
Organometallics 2017, 36, 1142−1153.
(20) Rees, W. S., Jr.; Just, O.; Schumann, H.; Weimann, R. Structural
Characterization of a Tris-Agostic Lanthanoid-H-Si Interaction. Angew.
Chem., Int. Ed. Engl. 1996, 35, 419−22.
Number DE-SC0016568. X-ray diffraction data were collected
on instruments funded by the National Science Foundation
through the Major Research Instrumentation Program under
grant number CHE-1625543. We also acknowledge Dr. John S.
7
Harwood of Purdue University for assistance with Li and 29Si
NMR experiments.
(21) Huynh, K.; Anderson, B. K.; Livinghouse, T. Enantioselective
Hydroamination/Cyclization of Aminoalkenes by (Bis)-C2 Symmetric
and (Mono)-C2 Symmetric Anionic Tetraamide Complexes of
La(III). Tetrahedron Lett. 2015, 56, 3658−3661.
REFERENCES
■
(1) Arnold, P. L.; Love, J. B.; Patel, D. Pentavalent Uranyl
Complexes. Coord. Chem. Rev. 2009, 253, 1973−1978.
(2) Liddle, S. T. The Renaissance of Non-Aqueous Uranium
Chemistry. Angew. Chem., Int. Ed. 2015, 54, 8604−8641.
(3) Andersen, R. A. Uranyl Complexes with (Hexamethyldisilyl)-
Amido and Nonafluoro-Tert-Butoxo Ligands. Inorg. Chem. 1979, 18,
209−209.
(4) Arnold, P. L.; Patel, D.; Blake, A. J.; Wilson, C.; Love, J. B.
Selective Oxo Functionalization of the Uranyl Ion with 3d Metal
Cations. J. Am. Chem. Soc. 2006, 128, 9610−9611.
(5) Jones, G. M.; Arnold, P. L.; Love, J. B. Oxo−Group-14-Element
Bond Formation in Binuclear Uranium(V) Pacman Complexes. Chem.
- Eur. J. 2013, 19, 10287−10294.
(6) Vaughn, A. E.; Barnes, C. L.; Duval, P. B. X-Ray Crystal Structure
of Trans-UO2(N(SiMe3)2)2(THF)2: One in a Series of Uranyl(VI)
Complexes Supported by Bis(Trimethylsilyl)Amido Ligands. J. Chem.
Crystallogr. 2007, 37, 779−782.
(22) Seaman, L. A.; Schnaars, D. D.; Wu, G.; Hayton, T. W. Isolation
of a Uranyl Amide by ″Ate″ Complex Formation. Dalton Trans. 2010,
39, 6635−6637.
(23) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Safe and Convenient Procedure for Solvent
Purification. Organometallics 1996, 15, 1518−1520.
(24) Wilkerson, M. P.; Burns, C. J.; Paine, R. T.; Blosch, L. L.;
Andersen, R. A. Di(μ-Chloro)bis{chlorodioxobis(tetrahydrofuran)-
uranium(VI)}, {UO2Cl2(THF)2}2. Inorg. Synth. 2004, 34, 93−95.
(25) Kim, J.; Bott, S. G.; Hoffman, D. M. Synthesis of Indium Amide
Compounds. Inorg. Chem. 1998, 37, 3835−3841.
(26) Burns, C. J.; Clark, D. L.; Donohoe, R. J.; Duval, P. B.; Scott, B.
L.; Tait, C. D. A Trigonal Bipyramidal Uranyl Amido Complex:
Synthesis and Structural Characterization of [Na(THF)2][UO2(N-
(SiMe3)2)3]. Inorg. Chem. 2000, 39, 5464−5468.
(27) Arnold, P. L.; Prescimone, A.; Farnaby, J. H.; Mansell, S. M.;
Parsons, S.; Kaltsoyannis, N. Characterizing Pressure-Induced
Uranium C−H Agostic Bonds. Angew. Chem., Int. Ed. 2015, 54,
6735−6739.
(28) Katz, J.; Morss, L. R.; Seaborg, G. T. The Chemistry of the
Actinide Elements; Chapman Hall: New York, 1980.
(29) Brown, J. L.; Fortier, S.; Wu, G.; Kaltsoyannis, N.; Hayton, T.
W. Synthesis and Spectroscopic and Computational Characterization
of the Chalcogenido-Substituted Analogues of the Uranyl Ion,
[OUE]2+ (E = S, Se). J. Am. Chem. Soc. 2013, 135, 5352−5355.
(30) Schettini, M. F.; Wu, G.; Hayton, T. W. Coordination of N-
Donor Ligands to a Uranyl(V) β-Diketiminate Complex. Inorg. Chem.
2009, 48, 11799−11808.
(7) Lewis, A. J.; Carroll, P. J.; Schelter, E. J. Reductive Cleavage of
Nitrite to Form Terminal Uranium Mono-Oxo Complexes. J. Am.
Chem. Soc. 2013, 135, 511−518.
(8) Arnold, P. L.; Jones, G. M.; Odoh, S. O.; Schreckenbach, G.;
Magnani, N.; Love, J. B. Strongly Coupled Binuclear Uranium-Oxo
Complexes from Uranyl Oxo Rearrangement and Reductive Silylation.
Nat. Chem. 2012, 4, 221−227.
(9) Procopio, L. J.; Carroll, P. J.; Berry, D. H. η2-Silanimine
Complexes of Zirconocene: Synthesis, Structure, and Reactivity of
Cp2Zr(η2-SiMe2NtBu)(PMe3). J. Am. Chem. Soc. 1991, 113, 1870−
2.
(10) Procopio, L. J.; Carroll, P. J.; Berry, D. H. Agostic β-Silicon-
Hydrogen Interactions in Silylamido Complexes of Zirconocene. J.
Am. Chem. Soc. 1994, 116, 177−85.
(11) Procopio, L. J.; Carroll, P. J.; Berry, D. H. Structure and
Reactivity of Cp2Zr(η2-Me2SiNtBu)(CO): An Unusual Silanimine
Carbonyl Complex with Extensive Σ-Π* Back-Bonding. Polyhedron
1995, 14, 45−55.
(12) Bi, S.; Zhu, S.; Zhang, Z. Mechanisms of H2, H2CCH2, and
OCH2 Insertion into Cp2Zr(η2-SiMe2NtBu)(PMe3). Eur. J. Inorg.
Chem. 2007, 2007, 2046−2054.
(31) Guzei, I. A.; Wendt, M. An Improved Method for the
Computation of Ligand Steric Effects Based on Solid Angles. Dalton
Trans. 2006, 3991−3999.
(32) Guzei, I. A.; Wendt, M. Program Solid-G; University of
Wisconsin: Madison, WI, 2004.
(13) Ignatov, S. K.; Khalimon, A. Y.; Rees, N. H.; Razuvaev, A. G.;
Mountford, P.; Nikonov, G. I. B-Agostic Silylamido and Silyl-Hydrido
Compounds of Molybdenum and Tungsten. Inorg. Chem. 2009, 48,
9605−9622.
(14) Yan, K. K.; Ellern, A.; Sadow, A. D. Nonclassical β-Hydrogen
Elimination of Hydrosilazido Zirconium Compounds Via Direct
Hydrogen Transfer. J. Am. Chem. Soc. 2012, 134, 9154−9156.
(15) Okazaki, M.; Ebina, S. Synthesis and Structure of an η2-
Silanimine-Coordinated Half-Sandwich-Type Titanium Complex.
Chem. Lett. 2014, 43, 1089−1091.
(16) Yan, K. K.; Pindwal, A.; Ellern, A.; Sadow, A. D. Direct
Hydrosilylation by a Zirconacycle with β-Hydrogen. Dalton Trans.
2014, 43, 8644−8653.
(17) McLeod, N. A.; Kuzmina, L. G.; Korobkov, I.; Howard, J. A. K.;
Nikonov, G. I. Hydridosilylamido Complexes of Ta and Mo Isolobal
with Berry’s Zirconocenes: Syntheses, β-Si-H Agostic Interactions,
Catalytic Hydrosilylation, and Insight into Mechanism. Dalton Trans.
2016, 45, 2554−2561.
(18) Rozenel, S. S.; Perrin, L.; Eisenstein, O.; Andersen, R. A.
Experimental and DFT Computational Study of β-Me and β-H
Elimination Coupled with Proton Transfer: From Amides to Enamides
in Cp*2MX (M = La, Ce). Organometallics 2017, 36, 97−108.
G
DOI: 10.1021/acs.inorgchem.8b00298
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