Preparation and reactivity of the versatile uranium(IV) imido complexes U(NAr)Cl2(R2bpy)2 (R = Me, tBu) and U(NAr)Cl2 (tppo)3

Article abstract of DOI:10.1021/ic5014208

Uranium tetrachloride undergoes facile reactions with 4,4'-dialkyl-2,2'-bipyridine, resulting in the generation of UCl₄(R₂bpy)₂, R = Me, ^tBu. These precursors, as well as the known UCl₄ (tppo)₂ (tppo = triphenylphosphine oxide), react with 2 equiv of lithium 2,6-di-isopropylphenylamide to provide the versatile uranium(IV) imido complexes, U(NDipp)Cl₂ (L)_n (L = R₂bpy, n = 2; L = tppo, n = 3). Interestingly, U(NDipp)Cl₂ (R₂bpy)₂ can be used to generate the uranium(V) and uranium(VI) bisimido compounds, U(NDipp)₂X(R₂bpy)₂, X = Cl, Br, I, and U(NDipp)₂I₂ (^tBu₂bpy), which establishes these uranium(IV) precursors as potential intermediates in the syntheses of high-valent bis(imido) complexes from UCl₄. The monoimido species also react with 4-methylmorpholine-N-oxide to yield uranium(VI) oxo-imido products, U(NDipp)(O)Cl₂ (L)_n (L = ^tBu₂bpy, n = 1; L = tppo, n = 2). The aforementioned molecules have been characterized by a combination of NMR spectroscopy, X-ray crystallography, and elemental analysis. The chemical reactivity studies presented herein demonstrate that Lewis base adducts of uranium tetrachloride function as excellent sources of U(IV), U(V), and U(VI) imido species.

Full text of DOI:10.1021/ic5014208

Article
pubs.acs.org/IC
Preparation and Reactivity of the Versatile Uranium(IV) Imido
t
Complexes U(NAr)Cl2(R2bpy)2 (R = Me, Bu) and U(NAr)Cl2(tppo)3
Robert E. Jilek, Neil C. Tomson, Ryan L. Shook, Brian L. Scott, and James M. Boncella*
MPA Division, Los Alamos National Laboratory, MS J514, Los Alamos, New Mexico 87545, United States
S
* Supporting Information
ABSTRACT: Uranium tetrachloride undergoes facile reactions
with 4,4′-dialkyl-2,2′-bipyridine, resulting in the generation of
t
UCl4(R2bpy)2, R = Me, Bu. These precursors, as well as the
known UCl4(tppo)2 (tppo = triphenylphosphine oxide), react
with 2 equiv of lithium 2,6-di-isopropylphenylamide to provide
the versatile uranium(IV) imido complexes, U(NDipp)Cl2(L)n
(L = R2bpy, n = 2; L = tppo, n = 3). Interestingly,
U(NDipp)Cl2(R2bpy)2 can be used to generate the uranium(V) and uranium(VI) bisimido compounds, U(NDipp)2X(R2bpy)2,
X = Cl, Br, I, and U(NDipp)2I2(tBu2bpy), which establishes these uranium(IV) precursors as potential intermediates in the
syntheses of high-valent bis(imido) complexes from UCl4. The monoimido species also react with 4-methylmorpholine-N-oxide
t
to yield uranium(VI) oxo-imido products, U(NDipp)(O)Cl2(L)n (L = Bu2bpy, n = 1; L = tppo, n = 2). The aforementioned
molecules have been characterized by a combination of NMR spectroscopy, X-ray crystallography, and elemental analysis. The
chemical reactivity studies presented herein demonstrate that Lewis base adducts of uranium tetrachloride function as excellent
sources of U(IV), U(V), and U(VI) imido species.
Herein, we report the syntheses of monoimido uranium(IV)
complexes, U(NDipp)Cl2(L)n (L = R2bpy, n = 2, R = Me, tBu;
L = tppo, n = 3). These compounds are readily prepared from
UCl4(L)2, (L = tppo, R2bpy; R = Me, tBu). The
aforementioned imido complexes are extremely versatile
starting materials for a range of U(IV), U(V), and U(VI)
complexes; their reactivity is described in detail.
INTRODUCTION
■
Understanding the role of f-orbitals in uranium-element
multiple bonding continues to be a focus for many actinide
chemists. In particular, uranium imido complexes have received
much attention over the past several years. Imido ligands offer
both steric and electronic flexibility where their oxo analogues
do not, making them attractive to researchers. A number of
U(IV),1−4 U(V),5−13 and U(VI)8,14−19 imido species have been
prepared in recent years, most of which contain cyclo-
pentadienide ligands or bulky amides. One such species,
U(NtBu)2I2(THF)2, is prepared readily from uranium metal,
iodine, and tert-butylamine and is isoelectronic with the uranyl
ion.18 This synthesis allowed, for the first time, a direct
RESULTS AND DISCUSSION
■
Synthesis of UCl4(R2bpy)2. The reaction of uranium
tetrachloride with 2 equiv of R2bpy in THF rapidly generates a
t
pale green solution (R = Bu) or a white precipitate (R = Me;
Scheme 1). The former is crystallized from THF/hexane to
provide UCl4(tBu2bpy)2 (1) in a nearly quantitative yield. The
latter is isolated from THF and dried under vacuum to provide
UCl4(Me2bpy)2 (2), also in high yield.
comparison of U(NR)2 to UO22+. Unfortunately, arylimido
2+
analogues could only be obtained from UI3(THF)4, often
requiring a more arduous workup to remove unwanted
byproducts. For this reason, a facile route to U(NR)22+, R =
aryl, would be advantageous.
Complex 1 is a pale green, crystalline solid, which is soluble
1
in THF and CH2Cl2. The paramagnetic H NMR spectrum
contains three sharp resonances at −7.61, 3.38, and 15.03 ppm
We recently reported the facile synthesis of uranium(IV)
imido dihalides via metathesis reactions of UCl4 and lithium
anilides. This previously unknown class of compounds offers
tremendous potential for chemical exploration. Still, numerous
Lewis base adducts of UCl4 remain which may serve as useful
precursors to uranium(IV) imido species. For example, the
bipyridine (bpy), phenanthroline, and triphenylphosphine
oxide (tppo) adducts, UCl4(L)2, have been known for nearly
50 years,20−22 with the Me2bpy adduct being reported much
later.23 Surprisingly, the 4,4′-dialkylbipyridine (R2bpy, R = Me,
tBu) adducts have yet to be characterized by NMR spectros-
copy or single crystal X-ray crystallography, and very little is
known about their chemical reactivity.
Scheme 1
Received: June 16, 2014
Published: August 29, 2014
© 2014 American Chemical Society
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corresponding to the bpy aryl hydrogens. A fourth resonance at
−2.52 ppm is attributed to the tert-butyl groups. In contrast,
complex 2 is a white powder, which is insoluble in THF and
Scheme 2
1
CH2Cl2. It is soluble in pyridine, however, and a H NMR
spectrum acquired in pyridine-d5 suggests that solvent
molecules coordinate to the metal center, perhaps by replacing
one of the Me2bpy ligands. As such, pyridine has been avoided
when conducting experiments with 1 and 2.
Complex 1 has been characterized crystallographically. Pale
green, nearly colorless plates were grown from a hexane layered
THF solution at −40 °C. The compound exhibits approximate
square antiprismatic geometry about uranium; the molecular
structure is shown in Figure 1. The average U−Cl bond length
(THF)2 (5) (Scheme 2). The isolation of this compound is
not unprecedented, as evidenced by the previously reported
complex, U(NtBu)I2(tBu2bpy)(THF)2.4
The terminal imido complex 5 has been characterized by
single crystal X-ray crystallography. Dark red blocks were
grown from a hexane layered THF solution at room
temperature. The complex adopts approximate monocapped
trigonal prismatic geometry about its uranium center (Figure
2). This is in contrast to the tert-butyl imido analogue,
Figure 1. Solid state molecular structure of 1 with thermal ellipsoids
set at the 50% probability level. Selected bond lengths (Å) and angles
(deg): U1−Cl1 2.622(2), U1−Cl2 2.635(1), U1−Cl3 2.639(1), U1−
Cl4 2.641(1), U1−N1 2.617(3), U1−N2 2.646(3), U1−N3 2.674(3),
U1−N4 2.654(3); N1−U1−N2 62.11(10), N3−U1−N4 61.59(10).
of 2.634(2) Å compares favorably with other eight-coordinate
adducts of UCl4.24−27 The average U−N bond length of
2.648(4) Å is much shorter than the corresponding U−N bond
in UCl4(tmeda)2.27 This is likely a result of bpy having a more
rigid structure than tmeda.
Synthesis of U(NDipp)Cl2(R2bpy)2. The reaction of
UCl4(Me2bpy)2 with 2 equiv of LiNHDipp, Dipp = 2,6-di-
isopropylphenyl, in THF immediately generates a dark red
solution. Recrystallization of the product from CH2Cl2/hexane
provides U(NDipp)Cl2(Me2bpy)2 (3) in a reasonable yield
(Scheme 2). This species is a dark red, polycrystalline solid with
limited solubility in THF and reasonable solubility in CH2Cl2.
The 1H NMR spectrum of 3 is paramagnetic but readily
interpretable. Imido resonances at 11.36, 28.35, 53.19, and
64.27 ppm are narrow singlets that compare favorably with
previously reported 2,6-di-isopropylphenyl imido uranium(IV)
dichlorides.4 Resonances at −66.25, −19.45, and −10.51 ppm
are slightly more broad and have been assigned to the bpy aryl
hydrogens. A peak at −9.92 ppm is attributed to the bpy methyl
groups. Most importantly, the peak integrations are consistent
with a Me2bpy:imido ratio of 2:1. These data, in combination
with bulk sample elemental analysis, are consistent with the
formulation of 3 as the bis(bpy) species U(NDipp)-
Cl2(Me2bpy)2.28
Figure 2. Solid state molecular structure of 5 with thermal ellipsoids
set at the 50% probability level. Selected bond lengths (Å) and angles
(deg): U1−N1 1.981(2), U1−Cl1 2.7320(6), U1−Cl2 2.7231(5),
U1−N2 2.626(2), U1−N3 2.607(2), U1−O1 2.590(2), U1−O2
2.544(2); N1−U1−N2 89.59(7), N2−U1−N3 62.36(6), Cl2−U1−
O1 77.87(4), Cl1−U1−O2 73.11(4).
U(NtBu)I2(tBu2bpy)(THF)2, which adopts a pentagonal
bipyramidal geometry about uranium.4 The geometric differ-
ence between these isoelectronic molecules is likely due to
differences in the steric properties of the imido substituents.
The UN bond length of 1.981(2) Å compares favorably with
previously reported terminal arylimido uranium(IV) spe-
cies1,2,29 but is ca. 0.05 Å longer than that in the tert-butyl
analogue.
While we have not been able to crystallize the bis(tBu2bpy)
complex 4, a comparison of the properties of 4 with those of 5
supports the notion that 4 is generated in situ. For example, 4 is
extraordinarily soluble in CH2Cl2, while 5 is only sparingly
soluble. This is consistent with the presence of additional tert-
t
Under similar reaction conditions, the Bu2bpy analogue
U(NDipp)Cl2(tBu2bpy)2 (4) is not isolated. Instead, crystal-
lization from THF/hexane yields U(NDipp)Cl2(tBu2bpy)-
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butyl groups on 4, which would serve to increase the molecule’s
solubility. Compound 4 is also a greasy semisolid, while 5 can
be isolated as a crystalline material, again consistent with the
presence of additional tert-butyl groups on 4. Given both the
limited chelation effect of R2bpy on uranium30 and the facile
ligand displacement during functionalization (see below), it is
t
conceivable that 4 and [5 + Bu2bpy] exist in a non-negligible
equilibrium in THF solutions. A crystal packing preference for
5 could then favor its isolation from solution, even though an
t
equivalent of Bu2bpy is present during crystallization.
Synthesis of U(NAr)Cl2(tppo)x. Exchanging R2bpy for
triphenylphosphine oxide (tppo) as an auxiliary Lewis base
provides similar reactivity. Treatment of UCl4(tppo)2 (6) with
2 equiv of either LiNHDipp or KNHMes* (Mes* =
2,4,6-tBu3C6H2) in the presence of excess tppo generates
U(NAr)Cl2(tppo)3 (7, Ar = Dipp; 8, Ar = Mes*) in 62−72%
yield (Scheme 3).
Figure 3. Solid state molecular structure of 7 with thermal ellipsoids
set at the 50% probability level. Selected bond lengths (Å) and angles
(deg): U1−N1 1.995(5), U1−Cl1 2.722(2), U1−Cl2 2.703(2), U1−
O1 2.352(4), U1−O2 2.373(4), U1−O3 2.375(4); N1−U1−O2
177.62(16), Cl1−U1−Cl2 165.01(5), O1−U1−O3 171.57(14).
Scheme 3
in the Cl1−U−Cl2 angles, which are 165.01(5) and 148.53(3)
degrees, respectively.
Complexes 9 and 10 are dimeric, adopting distorted
octahedral geometries about their respective uranium centers
(molecular structures of 9 and 10 are shown in the Supporting
Information). Compound 9 is symmetric about its U2N2 core
with cis-tppo and cis-chloride ligands. The UN bond lengths
are 2.182(5) and 2.252(5) Å (one-half molecule per
asymmetric unit), which compare favorably to similar bridging
imido species.4 Surprisingly, the bonding in 10 is quite
different, with one uranium center containing cis-tppo ligands
and the other bound to trans-tppo ligands. Such a configuration
is likely necessary to relieve strain caused by the bulkier mesityl
imido bridges. The differences between 9 and 10 can also be
seen in the UN bond lengths. In complex 10, these distances
are shorter at one uranium center (2.196(9), 2.202(9) Å) than
the other (2.252(10), 2.251(9) Å), while each uranium center
in 9 contains one short and one long UN bond.
To determine the scope of this synthetic methodology, we
attempted analogous reactions with the sterically less-
encumbering LiNHPh and LiNHMes. While these reactions
failed to yield the desired terminal imido products, they
provided the dimeric compounds [U(μ-NAr)Cl2(tppo)2]2 (9,
Ar = Ph; 10, Ar = Mes) in 50−65% yield (Scheme 3).
1H NMR spectra of the mononuclear complexes 7 and 8 are
paramagnetic and complicated by the presence of two unique
tppo environments. Fortunately, the imido resonances are
much sharper than those of tppo, and for 8, the imido group
tert-butyl resonances appear at 4.0 and 8.9 ppm, while the aryl
Reactivity Studies − U(IV). The ability to substitute the
chloride ligands on the monoimido U(IV) compounds would
extend the utility of these materials. As an example, the reaction
of 7 with NaSPh generates the monothiolate species,
U(NDipp)Cl(SPh)(tppo)3 (11, Scheme 4). The treatment of
resonance appears at 26.8 ppm.31 The H NMR spectra of
1
compounds 9 and 10 are more straightforward, with 9
exhibiting phenyl resonances at 2.21 and 13.9 ppm (with the
third resonance obscured by tppo), while the mesityl
resonances of 10 appear at −18.4, 15.5, and 18.4 ppm. The
31P NMR spectra of compounds 7−10 should all contain two
unique tppo environments. This is observed for 7, which
exhibits chemical shifts at −188.7 and 206.9 ppm, but the 31P
NMR spectrum of 8 contains only one observable resonance,
and no resonances were observed for 9 and 10.32
Scheme 4
Compounds 7−10 have also been characterized crystallo-
graphically. Complexes 7 and 8 are mononuclear and adopt
octahedral geometries about their respective uranium centers
(Figure 3 and Supporting Information). The UN bond
lengths are 1.995(5) and 2.009(3) Å, which are longer than the
UN bonds in previously reported terminal imido dihalides of
uranium(IV).4 This is likely due to the combined steric bulk of
the tppo ligands and aryl substituents. The steric difference
between the Dipp and Mes* groups accounts for the difference
7 with 2 equiv of NaSPh in THF resulted in an orange solution,
from which 11 was isolated by crystallization from hexane/
THF. A H NMR spectrum of 11 reveals the presence of two
isomers in solution, which display similar, paramagnetically
shifted resonances for the Dipp group. The molecular structure
of 11 was determined crystallographically and found to be
pseudo-octahedral, with mer-disposed tppo ligands and a new
S−U bond at 2.823(3) Å (see Supporting Information). The
1
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two isomers observed by NMR could result from fac/mer
isomerization of the tppo ligands or from disorder within the
mer arrangement of the PhS, Cl, and imido substituents.
In addition to salt metathesis chemistry, reactivity of the
imido group is also of interest. While a more thorough study of
the nucleophilic character of the U(IV) imido groups in these
compounds will be communicated elsewhere, initial studies
have shown that protonolysis of the NDipp group in 7 can be
effected by treatment with 2 equiv of HO(2,6-tBu2-C6H3)
(HOAr′) in THF, to provide the bis(aryloxide) complex
U(OAr′)2Cl2(tppo)2 (12, Scheme 4) as a green crystalline
solid. Loss of one tppo ligand results in an overall pseudo-
octahedral coordination environment, with two, cis-disposed
phenoxide ligands replacing the imido group. The U−O/Cl
distances are unremarkable, but distortion of the Ar′ rings is
evident (see Supporting Information), likely resulting from the
steric congestion about the metal center.
Only small amounts of 12 have been isolated, as reaction
mixtures indicate the presence of multiple products, which
appear to result from both incomplete protonolysis of the
imido group and ligand redistribution reactivity. In particular,
NMR spectroscopic data on a pale green powder that has been
isolated in moderate yields suggest the presence of a C2v-
symmetric molecule containing one OAr′ ligand for every two
tppo groups. This formulation would be consistent with
U(OAr′)Cl3(tppo)2, as would result from disproportionation
of 12.
(ii) generate easily removable byproducts, and (iii) avoid the
use of UI3(THF)4, the synthesis of which can be problematic.34
The addition of 2.0 LiNHDipp to stirred solutions of 4 in
THF resulted in a modest color change from red-brown to dark
red. The subsequent addition of I2 caused the solution to
immediately turn dark green. The U(VI) product U-
(NDipp)2I2(tBu2bpy) (14) was isolated from this mixture in
reasonable yields following crystallization from hexane/toluene.
As was observed for the synthesis of U(NDipp)2Cl(Me2bpy)2
from UCl4, reactions of 1 with 4 equiv of LiNHDipp, followed
by oxidation with I2 also provided reasonable yields of 14,
consistent with 4 serving as a functional intermediate during
the synthesis of U(VI) bis(imido) complexes.
In order to test the versatility of this preparative method, we
explored reactions of 1 with 4 equiv of LiNHMes (Mes = 2,4,6-
trimethylphenyl) followed by oxidation with I2. Indeed, this
reaction produced U(NMes)2I2(tBu2bpy) (15) in good yield
(Scheme 6). Attempts to isolate a U(IV) mono(mesitylimido)
Scheme 6
Reactivity Studies − Substitution and Oxidation to
U(V) and U(VI). The reaction chemistry of 3 and 4 has been
explored with respect to the formation of additional UE
multiple bonds.
Previous work had shown that a bis(imido) uranium(V)
complex, U(NDipp)2Cl(Me2bpy)2, could be formed directly
from UCl4 in high yield, by treating the uranium starting
material with 2 equivs of Me2bpy and 4 equiv of LiNHDipp,
followed by in situ oxidation with CH2Cl2.10 The treatment of
compound 3 with 2 equiv of LiNHDipp and CH2Cl2 (Scheme
5) also led to the isolation of U(NDipp)2Cl(Me2bpy)2 (13) in
species analogous to 4 were unsuccessful, but the isolation of
14 and 15 from 1 demonstrates the versatility of this reagent as
a synthon for bis(arylimido) uranium(VI) species. It was
further found that the use of 2 equiv of R2bpy were not
necessary for forming high valent derivatives of the U(IV)
monoimido species. More convenient preparations of 14 and
15 were carried out by initially forming UCl4(tBu2bpy) adducts
instead of UCl4(tBu2bpy)2. So doing minimized resources with
no loss in either yield or purity.
Complexes 14 and 15 are both dark red-green, crystalline
1
solids, which are soluble in most organic solvents. Their H
NMR spectra exhibit, respectively, Dipp imido resonances at
Scheme 5
0.89, 3.83, 5.43, and 6.83 ppm for 14 and mesityl imido
t
resonances at 2.65, 2.77, and 6.52 ppm for 15. The Bu2bpy
chemical shifts for 14 and 15 are nearly identical.
The solid-state molecular structures of 14 and 15 have been
determined by X-ray crystallography. Dark red-green blocks
were grown from a hexane-layered solution in toluene or
CH2Cl2 solution, respectively, at room temperature. Both
species exhibit octahedral geometry about their uranium centers
(Figure 4). The short UN bond lengths of 14 (1.869(3) Å)
2+
and 15 (1.867(3) Å) are typical of UO2 and its analogues,
where an inverse trans-influence results in very short uranium-
element multiple bonds.35,36 As expected, the UN bond
lengths are similar to those of previously reported U(VI)
arylimido compounds, U(NPh)2I2(THF)3 (1.863(3) Å) and
U(NDipp)2I2(THF)3 (1.887(3) Å).17
In addition to metathesis chemistry, we attempted the direct
oxidation of compounds 3, 4, and 7. In particular, we were
interested in developing a facile, economical route to oxo-imido
uranium(VI) species. The established route to this motif
involves using the expensive water reagent H2O·B(C6F5)3.16 As
such, very little is known about the chemical reactivity of U(VI)
oxo-imido compounds. We initially explored reactions of 3 with
the oxygen-atom transfer reagent 4-methylmorpholine-N-oxide.
The product was identified by NMR spectroscopy as being
high yield, suggesting that 3 is either an intermediate in the
previously reported reaction sequence or at least a viable
starting material for the introduction of an additional imido
group.
It is unknown at this point if the reaction of 3 with 2.0
LiNHDipp generates [U(NAr)(NHAr)2] or [U(NAr)2], but
we were intrigued to test whether this species could also
function as a precursor for U(VI) bis(imido) complexes.
Previous routes to bis(arylimido) uranium(VI) involve
complicated procedures for removing triethylammonium
iodidea byproduct of the reaction of UI3(THF)4 with aniline
and triethylamine.17,33 A preferred synthetic route would (i)
allow for a large degree of variability in the imido substituent,
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a factor that would account for the aforementioned broadening
1
in the H NMR spectrum of 16.
The 1H NMR spectrum of 17 is diamagnetic with
characteristic 2,6-di-isopropylphenyl resonances at 0.82, 4.26,
5.72, and 6.81 ppm.17 A single resonance is observed in the 31
P
NMR spectrum at 46.34 ppm. Crystallographic data were
obtained more readily in this case, revealing a pseudo-
octahedral complex with extremely short UN and UO
bonds of 1.847(3) and 1.778(2) Å, respectively (solid state
molecular structure shown in the Supporting Information).
These bond lengths compare favorably with those of previously
reported U(NtBu)(O)I2(tppo)2 (1.821(7) and 1.764(5) Å).16
SUMMARY
■
In this paper, we have described the syntheses of the versatile
uranium(IV) complexes, U(NDipp)Cl2(L)n (L = R2bpy, n = 1;
L = tppo, n = 3). These species are made via salt metathesis on
Lewis base adducts of UCl4, leaving only easily separable salts
and anilines as byproducts. Compounds 3, 4, and 7 are useful
chemical synthons which can be used to prepare bis(imido)
uranium(V), bis(imido) uranium(VI), and oxo-imido uranium-
(VI) products. The wide variety of chemistry reported herein
demonstrates the synthetic utility of the mono(imido) U(IV)
motif and further suggests that these compounds have may be
useful as synthons for currently unknown uranium complexes.
We anticipate that the development of this chemistry will
provide a template for the preparation of analogous transuranic
compounds, of which there are currently no known imido
species. Synthetic efforts in this area are currently underway in
our laboratories.
Figure 4. Solid state molecular structures of 14 (left) and 15 (right)
with thermal ellipsoids set at the 50% probability level. Selected bond
lengths (Å) and angles (deg) for 14: U1−N1 1.869(3), U1−N2
1.868(3), U1−N3 2.532(3), U1−N4 2.486(3), U1−I1 3.0243(4),
U1−I2 2.9931(3); N1−U1−N2 168.40(14), N3−U1−N4 63.16(11),
I1−U1−I2 95.36(1). Selected bond lengths (Å) and angles (deg) for
15: U1−N1 1.867(3), U1−N2 2.505(3), U1−I1 3.0126(6); N1−U1−
N1A 173.74(19), N2−U1−N2A 63.01(14), I1−U1−I1A 108.46(2).
diamagnetic, but we were unable to structurally characterize the
compound. However, when analogous reactions were carried
out with 4 and 7, U(NDipp)(O)Cl2(L)n (16, L = tBu2bpy, n =
1; 17, L = tppo, n = 2) were generated in good yields (Scheme
7), and the products were readily separated from the neutral
ligand (tBu2bpy and tppo) byproducts via crystallization.
Scheme 7
EXPERIMENTAL SECTION
■
General. All reactions and subsequent manipulations were
performed under anaerobic and anhydrous conditions either under
high vacuum or an atmosphere of argon. Hexane, THF, diethyl ether,
CH2Cl2, toluene, and benzonitrile were purchased anhydrous and
stored over activated 4 Å molecular sieves for 24 h before use. NMR
solvents C7D8, CD2Cl2, CDCl3, and C4D8O were also dried over
activated 4 Å molecular sieves prior to use. UCl4 was synthesized by
the published procedure.37 LiNHAr (Ar = Ph, Mes, Dipp) were
prepared from the appropriate aniline and nBuLi in hexane. KNHMes*
was prepared from H2NMes* and potassium bis(trimethylsilyl)amide
in diethyl ether. 4,4′-dimethyl-2,2′-dipyridyl, 4,4′-di-tert-butyl-2,2′-
dipyridyl, 4-methylmorpholine-N-oxide, and 2,6-di-tert-butylphenol
were purchased from commercial suppliers and used as received.
NMR experiments were performed on either a Bruker AVA300 or a
Bruker Ascend 400 NMR spectrometer. 1H NMR spectra are
referenced to external SiMe4 using the residual protio solvent peaks
as internal standards. Elemental analyses were performed at Midwest
Microlab, LLC.
UCl4(tBu2bpy)2 (1). UCl4 (250 mg, 0.658 mmol) was suspended in
THF (3 mL) and solid Bu2bpy (353 mg, 1.316 mmol) was added.
t
Complex 16 is a green-black, crystalline solid with good
solubility in most organic solvents. The H NMR spectrum is
1
The resulting light green solution was stirred for 16 h, filtered through
Celite, and layered with hexane (10 mL). After 2 days at −40 °C,
solvent was decanted to reveal nearly colorless, light green crystals,
which were dried in vacuo for 2h (597 mg, 99%). Anal. Calcd for
C36H48Cl4N4U: C, 47.17; H, 5.28; N, 6.11. Found: C, 47.13; H, 5.29;
N, 6.33. 1H NMR (CD2Cl2, 25 °C, 300 MHz): δ −7.61 (s, 2H,
tBu2bpy), −2.52 (s, 18H, tBu2bpy), 3.38 (s, 2H, tBu2bpy), 15.03 (s, 2H,
tBu2bpy) ppm.
UCl4(Me2bpy)2 (2). UCl4 (250 mg, 0.658 mmol) was suspended in
THF (5 mL) and solid Me2bpy (243 mg, 1.319 mmol) was added. The
resulting suspension was stirred for 16 h, and the product was isolated
on a fritted glass filter and washed with THF (2 × 3 mL). The off-
white powder was dried in vacuo for 2h (470 mg, 95%). Anal. Calcd for
C24H24Cl4N4U: C, 38.52; H, 3.23; N, 7.49. Found: C, 38.46; H, 3.44;
diamagnetic with Dipp imido resonances appearing at 0.84,
4.10, 5.58, and 6.73 ppm. These chemical shifts resemble those
of the closely related compound, U(NDipp)2I2(tBu2bpy) (14),
with coordinated bipyridine resonances appearing at 1.54, 7.86,
8.49, and 11.00 ppm. These values compare favorably with
compounds 14 and 15, but the bipyridine resonances of 16 are
significantly broadened. Attempts to obtain crystallographic
data on 16 resulted only in badly twinned structures, but the
data were suitable for establishing connectivity, which clearly
demonstrates that this species is a chloride-bridged dimer in the
solid state. It is likely that the solution-state behavior involves
rapid exchange between terminal and bridging chloride ligands,
9822
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N, 7.48. A procedure for the preparation of this compound in ethyl
acetate has been previously reported.23
KNHMes* (78.8 mg, 0.263 mmol) was added. The resulting red slurry
was stirred for 5 h. The reaction mixture was filtered through Celite,
and the red filtrate was layered with hexane (5 mL). After 3−4 days at
−40 °C, several red-orange crystals were isolated and dried in vacuo
U(NDipp)Cl2(Me2bpy)2 (3). UCl4(Me2bpy)2 (121.5 mg, 0.161
mmol) and LiNHDipp (59 mg, 0.322 mmol) were combined in a
20 mL scintillation vial and THF was added (3 mL). The resulting red
solution was stirred for 4 h and THF was removed in vacuo.
Dichloromethane (3 mL) was added, and the contents were filtered,
layered with hexane (3 mL), and left at −40 °C. After 2−3 days,
solvent was decanted to reveal dark red needles, which were dried in
vacuo for 1 h (70 mg, 51%). Anal. Calcd for C36H41Cl2N5U: C, 50.71;
H, 4.85; N, 8.21. Found: C, 50.60; H, 4.78; N, 8.29. 1H NMR
(CD2Cl2, 25 °C, 300 MHz): δ −66.25 (v br, 4H, -bpyH), −19.45 (br,
4H, -bpyH), −10.51 (br, 4H, -bpyH), −9.92 (br, 12H, -Me2bpy), 11.36
(s, 12H, −CH(CH3)2), 28.35 (s, 1H, -DippHpara), 53.19 (s, 2H,
-DippHmeta), 64.27 (br, 2H, −CH(CH3)2) ppm.
1
(115 mg, 62%). H NMR (300 MHz, CD2Cl2, 25 °C) δ −2.8 (v br,
t
t
tppo), 4.0 (s, 18H, Bu), 8.9 (s, 9H, Bu), 12.9 (br, tppo), 14.0 (v br,
tppo), 26.8 (s, 2H, -mes*H) ppm. 31P NMR (121.5 MHz, CD2Cl2, 25
°C) δ 175.0 ppm. The second 31P signal is not observed within our
spectral window. Anal. Calcd for C72H74Cl2NO3P3U: C, 61.63; H,
5.32; N, 1.00. Found: C, 61.82; H, 5.26; N, 1.05.
[U(NAr)Cl2(tppo)2]2, Ar = Ph (9), Mes (10). UCl4 (50 mg, 0.132
mmol) and tppo (73.3 mg, 0.263 mmol) were combined in THF (3
mL) and stirred in a 20 mL scintillation vial. After 10 min,
UCl4(tppo)2 had formed and solid LiNHAr (0.263 mmol) was
added. The resulting dark red solution was stirred for 4 h and THF
was removed in vacuo. Dichloromethane (2 mL) was added and the
slurry was filtered through Celite to remove LiCl. The red filtrate was
layered with hexane and after 2−3 days at −40 °C, orange-brown
U(NDipp)Cl2(tBu2bpy)2 (4). This compound is synthesized as for 5
(see below). Removal of volatile materials from the CH2Cl2 solution
provides a tacky brown semisolid that contains a mixture of the
product and H2NDipp. Because of the difficulty in handling this
material, it is best generated and used in solution. Attempts to
crystallize this complex resulted only in the isolation of compound 5.
U(NDipp)Cl2(tBu2bpy)(thf)2 (5). UCl4 (150 mg, 0.395 mmol) and
tBu2bpy (212 mg, 0.790 mmol) were combined in a vial, and ca. 3 mL
of THF was added. The mixture was stirred at room temperature,
quickly becoming a homogeneous green solution. Solid LiNHDipp
(144.7 mg, 0.790 mmol) was added as a solid causing the color of the
solution to immediately turn dark red. After stirring the mixture
overnight, the volatile materials were removed under vacuum, and the
residue was extracted with 2 mL of CH2Cl2. Filtering through Celite
removed a white solid and provided a clear, dark red filtrate. The
volatile materials were again removed under vacuum. The residue was
dissolved in minimal THF and layered with hexane (1:5 THF:hexane),
and then stored at −35 °C for several days. The product was collected
by decanting the solvent and removing traces of volatile material under
1
crystals were isolated and dried in vacuo. 9 (66 mg, 50%): H NMR
(300 MHz, CD2Cl2, 25 °C) δ 2.21 (br, 4H, Ph), 13.87 (br, 4H, Ph)
ppm. The para proton is obscured by triphenylphosphine resonances;
no 3 1 P NMR signal was observed. Anal. Calcd for
C85H72Cl6N2O4P4U2: C, 51.09; H, 3.63; N, 1.40. Found: C, 51.47;
1
H, 3.78; N, 1.50. 10 (85 mg, 65%): H NMR (300 MHz, CD2Cl2, 25
°C) δ −18.36 (br, 6H, Me), 15.47 (br, 3H, Me), 18.42 (br, 2H, arylH)
ppm. 31P signal not observed. Anal. Calcd for C90H82Cl4N2O4P4U2: C,
54.12; H, 4.14; N, 1.40. Found: C, 53.80; H, 4.15; N, 1.30.
U(NDipp)(SPh)Cl(tppo)3 (11). U(NDipp)Cl2(tppo)3 (100.0 mg,
0.076 mmol) was combined as a solid with NaSPh (20.0 mg, 0.152
mmol). The addition of THF (5 mL) resulted in an orange solution,
which was stirred overnight at room temperature. Filtration, followed
by concentrating to ca. 2 mL and slowly adding 10 mL of hexane,
resulted in an orange powder, which was collected by filtration and
dried under a vacuum. Yield: 0.83 g (78%). Material suitable for
crystallographic analysis was obtained by layering a THF solution with
1
vacuum. Yield: 246 mg, 69%. H NMR (pyr-d5, 25 °C, 300 MHz): δ
1
hexane and storing at room temperature. H NMR (CD2Cl2, 25 °C,
−18.39 (s, 2H, -bpyH), −14.03 (s, 2H, -bpyH), −6.77 (s, 18H,
-tBu2bpy), 13.18 (s, 12H, −CH(CH3)2), 29.60 (s, 1H, -DippHpara),
54.24 (s, 2H, -DippHmeta), 67.33 (br s, 2H, −CH(CH3)2) ppm.
Coordinated tBu2bpy and THF are readily displaced in pyr-d5
300 MHz): Isomer 1: δ 66.05 (br, 2H, −CH(CH3)2), 52.75 (d, 2H,
-DippHmeta), 29.45 (t, 1H, -DippHpara), 11.73 (s, 12H, −CH(CH3)2)
ppm; Isomer 2: δ 66.40 (br, 2H, −CH(CH3)2), 53.31 (d, 2H,
-DippHmeta), 29.70 (t, 1H, -DippHpara), 11.36 (s, 12H, −CH(CH3)2)
ppm. Anal. Calcd for C72H67ClNO3P3SU: C, 62.09; H, 4.85; N, 1.01.
Found: C, 62.38; H, 5.02; N, 1.00.
1
solutions to give what is presumably U(NDipp)Cl2(pyr-d5)41. The H
NMR spectral data for this latter compound are as follows: H NMR
(pyr-d5, 25 °C, 300 MHz): δ 13.60 (s, 12H, −CH(CH3)2), 29.73 (s,
1H, -DippHpara), 54.04 (s, 2H, -DippHmeta), 66.41 (br s, 2H,
−CH(CH3)2) ppm. Resonances at δ 1.65 and 3.63 ppm are assigned
to free THF, and they integrate to values corresponding to two
molecules of THF per Dipp group.
U(OAr′)2Cl2(tppo)2 (12). U(NDipp)Cl2(tppo)3 (100.0 mg, 0.076
mmol) was suspended in THF (4 mL). HOAr′ (31.3 mg, 0.152
mmol) was added as a solid, and the mixture was stirred for 48 h. The
mixture formed a yellow, homogeneous solution over ca. 30 min, and
then the color turned progressively more yellow-green over the course
of the reaction. The volatile materials were removed under a vacuum,
and then the residue was extracted with toluene, layered under an
equal volume of hexane, and stored at ambient temperature. The dark
green spikes that formed were found by crystallographic analysis to be
12. Yield: 7 mg (7%). When the THF solution of the reaction mixture
was filtered and layered with hexane, a pale green powder formed,
which was tentatively identified by NMR spectroscopic analysis as
U(OAr′)Cl3(tppo)2: 1H NMR (CDCl3, 25 °C, 400 MHz): δ 30.06 (d,
2H, -Ar′Hmeta), 22.44 (t, 1H, -Ar′Hpara), 12.23 (br s, 12H, tppo), 8.00
U(NDipp)Cl2(tppo)3 (7). UCl4 (200 mg, 0.527 mmol) and tppo
(439.6 mg, 1.58 mmol) were combined in THF (3 mL) and stirred in
a 20 mL scintillation vial. After 10 min, UCl4(tppo)2 had formed and
solid LiNHDipp (192.9 mg, 1.05 mmol) was added. The resulting red
reaction mixture was stirred for 16 h. At this time, an orange
precipitate had formed, which was isolated on a frit and recrystallized
from CH2Cl2/hexane to provide orange crystals. The product was
dried open to the box atmosphere for 1 h (486 mg, 70%). As a finely
divided orange powder, the product decomposes over 10−12 days (in
the box atmosphere) to form U(NDipp)2Cl2(tppo)2 and other,
currently unidentified products. The isolated orange crystals are stable
t
(s, 18H, tppo), 5.09 (s, 18H, Bu) ppm.
1
U(NDipp)2Cl(Me2bpy)2 (13). Solid LiNHDipp (30.1 mg, 0.164
mmol) was added to a slurry of 3 (70 mg, 0.082 mmol) in THF (2
mL). The resulting red solution was stirred for 4 h, and solvent was
removed in vacuo. Toluene (2 mL) was added and the contents were
filtered, layered with hexane, and left at RT. After 2 days, dark red
blocks precipitated, which were isolated by decanting solvent and dried
in vacuo (58 mg, 72%). Analytical data for this compound were
identical to those reported previously.10
for months in the drybox atmosphere. H NMR (300 MHz, CD2Cl2,
25 °C) δ −35.0 (br, tppo), −10.0 (v br, tppo), −9.0 (br, tppo), 11.5
(s, 12H, −CH(CH3)2), 16.9 (br, tppo), 24.5 (br, tppo), 29.9 (t, 1H,
-DippHpara), 31.2 (br, tppo), 53.5 (d, 2H, -DippHmeta), 66.5 (br, 2H,
−CH(CH3)2) ppm. 31P NMR (121.5 MHz, CD2Cl2, 25 °C) δ −188.7
(v br, 2 cis-tppo), 206.9 (br, trans-tppo) ppm. The 1H NMR is
extremely difficult to interpret outside of the Dipp resonances due to a
combination of paramagnetism and two distinct tppo environments.
Anal. Calcd for C66H62Cl2NO3P3U: C, 60.10; H, 4.74; N, 1.06. Found:
C, 59.06; H, 4.69; N, 1.28.
U(NDipp)2I2(tBu2bpy) (14). UCl4 (209.1 mg, 0.5505 mmol) and
tBu2bpy (147.6 mg, 0.5499 mmol) were combined in THF (6 mL),
and the resulting light green solution was stirred for 15 min. Solid
LiNHDipp (403.4 mg, 2.202 mmol) was added, resulting in a dark red
solution, and the reaction mixture was stirred for 4 h. Solid I2 was
U(NMes*)Cl2(tppo)3 (8). UCl4 (50 mg, 0.132 mmol) and tppo (91.6
mg, 0.329 mmol) were combined in THF (3 mL) and stirred in a 20
mL scintillation vial. After 10 min, UCl4(tppo)2 had formed and solid
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Table 1. X-ray Crystallographic Data for Complexes 1·THF·hexane, 5, 7·3CH2Cl2, 8, and 9·8CH2Cl2
1·THF·hexane
5
7·3CH2Cl2
8
9·8CH2Cl2
empirical formula
crystal habit, color
crystal size (mm)
crystal system
space group
volume (Å3)
a (Å)
C46H70Cl4N4OU
block, colorless
0.20 × 0.12 × 0.10
monoclinic
P21/n
C38H57Cl2N3O2U
block, dark red
0.24 × 0.14 × 0.10
triclinic
C69H68Cl8NO3P3U
block, red-orange
0.20 × 0.12 × 0.04
triclinic
C72H74Cl2NO3P3U
block, red-orange
0.38 × 0.26 × 0.10
triclinic
C92H86Cl20N2O4P4U2
block, dark red
0.18 × 0.12 × 0.08
monoclinic
P21/n
P1
̅
P1
̅
P1
̅
4863.0(6)
16.542(1)
11.554(1)
25.530(2)
90
1966.31(17)
10.8616(5)
11.6484(6)
15.7897(8)
99.832(1)
91.493(1)
91.875(1)
2, 1
3326.1(9)
13.297(2)
13.955(2)
19.417(3)
69.718(2)
83.685(2)
80.296(2)
2, 1
3263.3(4)
13.511(1)
13.697(1)
18.199(2)
102.956(1)
90.359(1)
95.898(1)
2, 1
4542.4(8)
14.437(2)
14.781(2)
21.803(2)
90
b (Å)
c (Å)
α (deg)
β (deg)
94.701(1)
90
102.499(1)
90
γ (deg)
Z, Z′
4, 1
4, 0.5
formula weight (g/mol)
density (calc) (Mg/m3)
absorption coefficient
1074.92
896.8
1573.86
1.317
1403.16
1.428
2592.69
1.350
1.515
1.399
3.588
4.298
2.634
2.689
3.792
(mm−1
F000
)
1968
896
1320
1416
1864
8262
total reflections (Io > 2σIo) 9233
8008
12237
13248
a
final R indices (Io > 2σIo) R1 = 0.0319,
R1 = 0.0172,
wR2 = 0.0432
R1 = 0.0476,
wR2 = 0.0988
R1 = 0.0368,
wR2 = 0.0824
R1 = 0.0456,
wR2 = 0.1056
wR2 = 0.0696
a
final R indices (all data)
largest diff peak/hole (e·
R1 = 0.047, wR2 = 0.075 R1 = 0.019, wR2 = 0.044 R1 = 0.0719,
wR2 = 0.1078
R1 = 0.0466,
wR2 = 0.0869
R1 = 0.0731,
wR2 = 0.1140
1.028/−1.088
0.905/−0.376
1.488/−1.028
1.347/−1.174
1.864/−0.856
Å−3
)
a
4
2
R1 = Σ |(|Fo| − |Fc|)|/Σ |Fo|, wR2 = [Σw(|Fo|2 − |Fc|2)2/ΣwFo ]1/2, p = [Fo2 + 2Fc2]/3. 1·THF·hexane, w = [σ2Fo2 + (0.0319p)2]−1. 5, w = [σ2Fo
+
2
2
2
(0.0172p)2]−1. 7·3CH2Cl2, w = [σ2Fo + (0.0476p)2]−1. 8, w = [σ2Fo + (0.0368p)2]−1. 9·3CH2Cl2, w = [σ2Fo + (0.0456p)2]−1.
added, which caused the solution to turn dark green immediately. The
reaction mixture was stirred for 1 h, and THF was removed in vacuo.
Toluene (15 mL) was added, the contents were filtered through
Celite, separated into three vials and layered with hexane (10 mL
each). After 2−3 days at RT, solvent was decanted to reveal dark green
blocks, which were dried in vacuo (331.5 mg, 54%). Anal. Calcd for
C42H58N4I2U: C, 45.41; H, 5.26; N, 5.04. Found: C, 46.51; H, 5.07; N,
4.30. 1H NMR (CDCl3, 25 °C, 300 MHz) δ 0.89 (d, 24H,
reaction mixture was filtered, layered with hexane (3 mL), and left at
−40 °C. After 2−3 days, the solvent mixture was left at RT and within
minutes, black blades began forming. Solvent was decanted and the
1
crystals were dried in vacuo (60 mg, 59%). H NMR (CDCl3, 25 °C,
300 MHz): δ 0.84 (d, 24H, −CH(CH3)2), 1.54 (s, 36H, tBu), 4.10 (m,
4H, −CH(CH3)2), 5.58 (t, 2H, -DippHpara), 6.73 (d, 4H, -DippHmeta),
7.86 (br, 4H, -bpyH), 8.49 (br, 4H, -bpyH), 11.00 (br, 4H, -bpyH)
ppm. 13C NMR (CD2Cl2, 25 °C, 100 MHz) δ 25.41, 26.92, 30.54,
36.05, 118.81, 120.74, 123.73, 128.58, 149.08, 149.47, 154.36, 157.79,
165.52 ppm.
t
−CH(CH3)2), 1.61 (s, 18H, Bu), 3.83 (sp, 4H, −CH(CH3)2), 5.43
(t, 2H, -DippHpara), 6.83 (d, 4H, -DippHmeta), 8.14 (d, 2H, -bpyH),
8.77 (s, 2H, -bpyH), 11.27 (d, 2H, -bpyH) ppm. 13C NMR (CD2Cl2,
25 °C, 100 MHz MHz) δ 25.82, 26.55, 30.47, 36.35, 118.63, 121.42,
124.10, 128.74, 149.10, 150.45, 151.89, 157.17, 166.43 ppm.
U(NDipp)(O)Cl2(tppo)2 (17). U(NDipp)Cl2(tppo)3 (75 mg, 0.057
mmol) was dissolved in CH2Cl2 (3 mL) and solid 4-methylmorpho-
line-N-oxide (6.7 mg, 0.057 mmol) was added. After being stirred for
16 h, the dark reaction mixture was filtered and solvent was removed
until ∼1 mL remained. Toluene (6−8 mL) was added and the
contents were stirred for 16 h. The reaction mixture was filtered (to
remove tppo), and the solvent was removed in vacuo. The product was
dissolved in CH2Cl2 (2 mL), layered with hexane (2 mL), and left at
−40 °C. After 2−3 days, black crystals formed which were isolated by
U(NMes)2I2(tBu2bpy) (15). UCl4 (219.7 mg, 0.5784 mmol) and
tBu2bpy (155.2 mg, 0.5783 mmol) were combined in THF (6 mL),
and the resulting light green solution was stirred for 15 min. Solid
LiNHMes (425.5 mg, 2.306 mmol) was added, resulting in a dark
brown solution, and the reaction mixture was stirred for 4 h. Solid I2
was added, which caused the solution to turn dark green immediately.
The reaction mixture was stirred for 1 h and THF was removed in
vacuo. Dichloromethane (5 mL) was added, the contents were filtered
through Celite and layered with hexane (10 mL). After 2−3 days at
RT, solvent was decanted to reveal dark green blocks, which were
dried in vacuo (348.3 mg, 59%). Anal. Calcd for C36H46N4I2U: C,
1
decanting solvent and drying in vacuo (42 mg, 70%). H NMR (300
MHz, CDCl3, 25 °C) δ 0.82 (d, 12H, −CH(CH3)2), 4.26 (m, 2H,
−CH(CH3)2), 5.72 (t, 1H, -DippHpara), 6.81 (d, 2H, -DippHmeta), 7.47
(br, 12H, tppo), 7.60 (m, 6H, tppo), 8.10 (m, 12H, tppo) ppm. 31P
NMR (121.5 MHz, CDCl3, 25 °C) δ 46.34 ppm. Anal. Calcd for
C48H47Cl2NO3P2U: C, 54.55; H, 4.48; N, 1.33. Found: C, 54.19; H,
4.81; N, 1.48.
1
42.12; H, 4.52; N, 5.46. Found: C, 41.89; H, 4.41; N, 5.49. H NMR
t
(CDCl3, 25 °C, 300 MHz) δ 1.62 (s, 18H, Bu), 2.65 (s, 12H,
-Mes(CH3)ortho), 2.77 (s, 6H, -Mes(CH3)para), 6.52 (s, 4H, -MesH),
8.13 (d, 2H, -bpyH), 8.71 (s, 2H, -bpyH), 11.26 (d, 2H, -bpyH) ppm.
13C NMR (CD2Cl2, 25 °C, 100 MHz) δ 18.42, 18.49, 30.51, 36.37,
121.73, 123.16, 123.98, 138.36, 139.53, 149.34, 153.28, 157.40, 166.72
ppm.
X-ray Crystallography. The crystal structures of compounds 1·
THF·hexane, 5, 7·3CH2Cl2, 8, 9·8CH2Cl2, 10·4CH2Cl2, 11, 12, 14,
15, and 17·C7H8 were determined as follows. The crystal was
mounted in a nylon cryoloop from Paratone-N oil under argon gas
flow. Data were collected on a Bruker X-ray diffractometer, with a D8
goniometer and an APEXII charge-coupled device (CCD) detector.
The crystal was cooled with a KRYO-FLEX liguid nitrogen vapor
cooling device to 141 K. The instrument was equipped with a graphite
monochromatized Mo Kα X-ray source (λ = 0.71073 Å), with
MonoCap X-ray source optics. A hemisphere of data was collected
using ω scans, with 5-s frame exposures and 0.3° frame widths. Data
[U(NDipp)(O)(μ-Cl)Cl(tBu2bpy)]2 (16). UCl4(tBu2bpy)2 (120 mg,
0.131 mmol) was dissolved in THF (3 mL), and solid LiNHDipp (48
mg, 0.262 mmol) was added. The resulting red solution was stirred for
4 h and THF was removed in vacuo. Dichloromethane (2 mL) was
added, the contents were filtered, and solid 4-methylmorpholine-N-
oxide (15.3 mg, 0.131 mmol) was added. Upon stirring for 16 h, the
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Article
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collection and initial indexing and cell refinement were handled using
APEXII software.38 Frame integration, including Lorentz-polarization
corrections, and final cell parameter calculations were carried out using
SAINT+ software.39 The data were S5 corrected for absorption using
the SADABS program.40 Decay of reflection intensity was monitored
via analysis of redundant frames. The structures were solved using
either Direct methods or a Patterson solution and difference Fourier
techniques. All hydrogen atom positions were idealized and refined as
riding on the atoms they were attached to. The final refinement
included anisotropic temperature factors on all non-hydrogen atoms.
Structure solution, refinement, graphics, and creation of publication
materials were performed using SHELXTL.41 Structures 1, 7, 9, and
10 contained solvents of crystallization, which were removed with the
function Squeeze in the program Platon. A summary of relevant
crystallographic data is found in Tables 1 and 2, and full details are
provided in the CIFs (see Supporting Information).
(12) Stewart, J. L.; Andersen, R. A. New J. Chem. 1995, 19, 587.
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Am. Chem. Soc. 1990, 112, 3237.
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(17) Hayton, T. W.; Boncella, J. M.; Scott, B. L.; Batista, E. R.; Hay,
P. J. J. Am. Chem. Soc. 2006, 128, 10549.
(18) Hayton, T. W.; Boncella, J. M.; Scott, B. L.; Palmer, P. D.;
Batista, E. R.; Hay, P. J. Science 2005, 310, 1941.
(19) Warner, B. P.; Scott, B. L.; Burns, C. J. Angew. Chem., Int. Ed.
1998, 37, 959.
(20) Gans, P.; Smith, B. C. J. Chem. Soc. 1964, 4177.
(21) Gans, P.; Marriage, J. J. Chem. Soc., Dalton Trans. 1972, 1738.
(22) Bombieri, G.; Brown, D.; Graziani, R. J. Chem. Soc., Dalton
Trans. 1975, 1873.
(23) Wassef, M. A.; Atya, L. Egypt. J. Chem. 1982, 25, 281.
(24) Cotton, F. A.; Marler, D. O.; Schwotzer, W. Acta Crystallogr.
Sect. C 1984, 40, 1186.
(25) Schnaars, D. D.; Wu, G.; Hayton, T. W. Dalton Trans. 2008,
6121.
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray crystallographic details of 1·THF·hexane, 5, 7·3CH2Cl2,
8, 9·8CH2Cl2, 10·4CH2Cl2, 11, 12, 14, 15, and 17·C7H8 are
included in CIF format, as well as images and important bond
lengths/angles for compounds 8, 9, 10, 11, 12, and 17. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(26) Van Den Bossche, G.; Rebizant, J.; Spirlet, M. R.; Goffart, J. Acta
Crystallogr. Sect. C 1986, 42, 1478.
(27) Zalkin, A.; Edwards, P. G.; Zhang, D.; Andersen, R. A. Acta
Crystallogr. Sect. C 1986, 42, 1480.
(28) Despite attempts to crystallize this compound from a variety of
solvent systems, only polycrystalline materials have been obtained.
(29) Zi, G.; Jia, L.; Werkema, E. L.; Walter, M. D.; Gottfriedsen, J. P.;
Andersen, R. A. Organometallics 2005, 24, 4251.
AUTHOR INFORMATION
Corresponding Author
*E-mail: boncella@lanl.gov.
Notes
■
The authors declare no competing financial interest.
̀
(30) Riviere, C.; Nierlich, M.; Ephritikhine, M.; Madic, C. Inorg.
Chem. 2001, 40, 4428.
ACKNOWLEDGMENTS
(31) The NDipp resonances of 1 compare favorably with those of the
■
previously reported species, U(NDipp)I2(THF)4.4
R.E.J. and N.C.T. thank the G. T. Seaborg Institute at Los
Alamos National Laboratory for fellowships in partial support
of this research. This work was supported by the U.S.
Department of Energy, Office of Science, under the Heavy
Element Chemistry program. Los Alamos National Laboratory
is managed and operated by Los Alamos National Security,
LLC (LANS), under Contract Number DE-AC52-06NA25396
for the Department of Energy’s National Nuclear Security
Administration (NNSA).
(32) It is not uncommon for paramagnetic uranium complexes to
exhibit no 31P NMR resonances.
(33) The difficulty removing [Et3N]I is not explicitly stated in ref 17,
but our experience in this area has illustrated the need for repeated
recrystallizations to remove reaction byproducts.
(34) Monreal, M. J.; Thomson, R. K.; Cantat, R.; Travia, N. E.; Scott,
B. L.; Kiplinger, J. L. Organometallics 2011, 30, 2031.
(35) Denning, R. G. Struct. Bonding (Berlin) 1995, 79, 215.
(36) O’Grady, E.; Kaltsoyannis, N. Dalton Trans. 2002, 1233.
(37) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J.
Organometallics 2002, 21, 5978.
(38) APEXII 1.08; Bruker AXS, Inc.: Madison, WI, 2004.S15.
(39) SAINT+ 7.06; Bruker AXS, Inc.: Madison, WI, 2003.
(40) Sheldrick, G. M. SADABS 2.03; University of Gottingen,
Gottingen, Germany, 2001.
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