Crystal structure of the uranium oxo borohydride complex U 2(μ-O)(BH4)6(dme)2 (dme = 1,2-dimethoxyethane) and reformulation of U2(μ-H) 2(BH4)6(dme)2

Article abstract of DOI:10.1016/j.poly.2011.11.003

The reaction of uranium tetrachloride, UCl₄, with sodium N,N-dimethylaminodiboranate, Na(H₃BNMe₂BH₃), in refluxing 1,2-dimethoxyethane (dme) yields small amounts of a new complex, which we formulate as (μ-oxo)hexakis(tetrahydroborato)bis(1,2- dimethoxyethane)diuranium(IV), toluene solvate, U₂(μ-O)(BH ₄)₆(dme)₂·C₇H₈, 1. Most likely, the formation of BH₄^- groups from H ₃BNMe₂BH₃^- occurs with the elimination of [Me₂NBH₂]₂, and the formation of the oxo group involves adventitious hydrolysis. Each uranium center in 1 adopts a fac octahedral geometry (counting the BH₄^- groups as occupying one coordination site); the bridging oxygen atom and the two coordinated oxygen atoms of the dme ligand occupy positions trans to the three BH₄^- groups. The hydrogen atom positions were located in the electron density difference maps and reveal that all three BH ₄^- groups are bound in a κ³H fashion. The U...B distances to the two BH₄^- groups that are cis to the bridging oxygen atom are 2.574(6) and 2.584(6) , whereas the U...B distance of 2.635(7) to the BH₄^- group that is trans to the bridging oxygen is distinctly longer. Thus, the bridging oxygen atom exerts a noticeable trans influence. The crystallographic and ¹H NMR data strongly suggest that the previously reported uranium hydride complex U ₂(μ-H)₂(BH₄)₆(dme)₂ should be reformulated as this oxo complex U₂(μ-O)(BH ₄)₆(dme)₂.

Full text of DOI:10.1016/j.poly.2011.11.003

Polyhedron 33 (2012) 41–44
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Crystal structure of the uranium oxo borohydride complex
U2(
l-O)(BH4)6(dme)2 (dme = 1,2-dimethoxyethane) and reformulation
of U2(
l-H)2(BH4)6(dme)2
a,
Scott R. Daly a, Michel Ephritikhine b, , Gregory S. Girolami
⇑
⇑
a The School of Chemical Sciences, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, IL 61801, USA
b CEA, IRAMIS, SIS2M, CNRS UMR 3299, 91191 Gif-Sur-Yvette, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of uranium tetrachloride, UCl4, with sodium N,N-dimethylaminodiboranate, Na(H3BN-
Received 5 August 2011
Accepted 2 November 2011
Available online 9 November 2011
Me2BH3), in refluxing 1,2-dimethoxyethane (dme) yields small amounts of a new complex, which we for-
mulate as (l-oxo)hexakis(tetrahydroborato)bis(1,2-dimethoxyethane)diuranium(IV), toluene solvate,
U2(
l
-O)(BH4)6(dme)2ꢀC7H8, 1. Most likely, the formation of BH4ꢁ groups from H3BNMe2BH3ꢁ occurs with
the elimination of [Me2NBH2]2, and the formation of the oxo group involves adventitious hydrolysis. Each
uranium center in 1 adopts a fac octahedral geometry (counting the BH4ꢁ groups as occupying one coor-
dination site); the bridging oxygen atom and the two coordinated oxygen atoms of the dme ligand occupy
positions trans to the three BH4ꢁ groups. The hydrogen atom positions were located in the electron den-
Keywords:
Uranium
Borohydride
Hydride
Oxo
sity difference maps and reveal that all three BH4ꢁ groups are bound in a
j
3H fashion. The Uꢀ ꢀ ꢀB distances
to the two BH4ꢁ groups that are cis to thꢁe bridging oxygen atom are 2.574(6) and 2.584(6) Å, whereas the
Uꢀ ꢀ ꢀB distance of 2.635(7) Å to the BH4 group that is trans to the bridging oxygen is distinctly longer.
Thus, the bridging oxygen atom exerts a noticeable trans influence. The crystallographic and 1H NMR data
Crystal structure
Aminodiboranate
strongly suggest that the previously reported uranium hydride complex U2(l-H)2(BH4)6(dme)2 should be
reformulated as this oxo complex U2( -O)(BH4)6(dme)2.
l
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
[7] were prepared by following the literature routes. The 1H NMR
data were obtained on a Varian Unity Inova 600 instrument at
600 MHz. Chemical shifts are reported in d units (positive shifts
to high frequency) relative to TMS.
The isolation of uranium(IV) hydride U2(l-H)2(BH4)6(dme)2,
where dme = 1,2-dimethoxyethane, in 1987 provided crystallo-
graphic evidence that uranium(IV) hydrides are intermediates in
the reduction of UIV borohydrides to UIII [1]. This complex is also
notable as one of the few crystallographically characterized
actinide hydrides [2–5]. We now present evidence that this
2.1. (l-Oxo)hexakis(tetrahydroborato)bis(1,2-dimethoxyethane)-
diuranium(IV), 1
U2(
l
-H)2(BH4)6(dme)2 complex is actually the bridged oxo species
-O)(BH4)6(dme)2.
To a suspension of UCl4 (0.27 g, 0.71 mmol) in 1,2-dimethoxy-
ethane (15 mL) was added a solution of sodium N,N-dimethyl-
aminodiboranate (0.27 g, 2.8 mmol) in 1,2-dimethoxyethane
(15 mL). The reaction mixture was heated to reflux for 12 h, over
which time the solution color changed from green to light brown,
and a dark precipitate formed. The solvent was removed under
vacuum to afford a sticky, dark brown solid. The residue was
extracted with toluene (20 mL), and the filtered extract was
concentrated to ca. 10 mL and layered with pentane (10 mL). The
mixture was kept at room temperature for several hours, and
small green prisms formed. The crystals were collected, and the
mother liquor was decanted and cooled to ꢁ20 °C overnight to
yield a second crop of green prisms. Yield: 20 mg (7%). 1H NMR
U2(l
2. Experimental
All operations were carried out in vacuum or under argon using
standard Schlenk techniques. The solvents 1,2-dimethoxyethane
and pentane were distilled under nitrogen from sodium/benzophe-
none and purged with argon immediately before use. Toluene was
dried similarly over molten sodium. UCl4 [6] and Na(H3BNMe2BH3)
⇑
Corresponding authors. Tel.: +1 217 333 2729; fax: +1 217 333 2685 (G.S.
Girolami).
(C7D8, ꢁ60 °C):
d
ꢁ115 (s, fwhm = 290 Hz, BH4, 4H), ꢁ62.0
E-mail addresses: michel.ephritikhine@cea.fr (M. Ephritikhine), girolami@
scs.illinois.edu (G.S. Girolami).
(s, fwhm = 110 Hz, OMe, 6H), ꢁ52.9 (s, fwhm = 110 Hz, OCH2,
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.11.003

42
S.R. Daly et al. / Polyhedron 33 (2012) 41–44
2H), ꢁ32.4 (s, OCH2, fwhm = 80 Hz, 2H), 727 (br s, fwhm = 2700 Hz,
disordered toluene molecule were constrained to be equal within
an esd of 0.01 Å, and the aromatic cores were constrained to
hexagonal geometries. The boranyl hydrogen atoms were located
in the difference maps, and their positions were refined with
independent isotropic displacement parameters. Tꢁhe chemically
equivalent B–H and Hꢀ ꢀ ꢀH distances within the BH4 groups were
constrained to be equal within an esd of 0.01 Å. Hydrogen atoms
on methyl, methylene, and aromatic carbons were placed in
idealized positions with C–H = 0.98, 0.99, and 0.95 Å, respectively;
the methyl groups were allowed to rotate about the C–C or C–O
axis to find the best least-squares positions. The displacement
parameters for methylene and aromatic hydrogens were set equal
to 1.2 times Ueq for the attached carbon; those for methyl
hydrogens were set to 1.5 times Ueq for the attached carbon. No
correction for isotropic extinction was necessary. Successful
convergence was indicated by the maximum shift/error of 0.000
for the last cycle. Final refinement parameters are given in Table 1.
BH4).
2.2. Crystallographic studies [8]
Single crystals of U2(
l
-O)(BH4)6(dme)2ꢀC7H8, grown from a 1:1
mixture of toluene and pentane, were mounted on glass fibers with
Paratone–N oil (Exxon) and immediately cooled to ꢁ75 °C in a cold
nitrogen gas stream on the diffractometer. Standard peak search
and indexing procedures gave rough cell dimensions, and least
squares refinement using 975 reflections yielded the cell
dimensions given in Table 1.
Data were collected with an area detector by using the
measurement parameters listed in Table 1. The triclinic lattice
and the average values of the normalized structure factors
ꢀ
suggested the space group P1, which was confirmed by the success
of the subsequent refinement. The measured intensities were
reduced to structure factor amplitudes and their estimated
standard deviations (esd’s) by correction for background, scan
speed, and Lorentz and polarization effects. No corrections for
crystal decay were necessary, but a face-indexed absorption
correction was applied, the minimum and maximum transmission
factors being 0.251 and 0.610. Systematically absent reflections
were deleted and symmetry equivalent reflections were averaged
The largest peak in the final Fourier difference map (1.63 e Åꢁ3
)
was located 1.07 Å from U2. A final analysis of variance between
observed and calculated structure factors showed no apparent
errors.
3. Results and discussion
ꢀ
Recently, several papers have described the synthesis of actꢁi-
to yield a set of unique data. The reflections 001 and 011 were
nide complexes of the chelating borohydride ligand H3BNMe2BH3
,
obscured by the beam stop and were deleted; the remaining
5603 unique data were used in the least squares refinement.
The structure was solved using direct methods (SHELXTL). Correct
positions for the uranium atoms were deduced from an E-map.
Subsequent least-squares refinement and difference Fourier
calculations revealed the positions of the remaining non-hydrogen
atoms. The toluene molecule that co-crystallized with the
compound was disordered over two positions. The quantity
the N,N-dimethylaminodiboranate anion [9–11]. For example, at
room temperature, UCl4 reacts with 4 equiv of Na(H3BNMe2BH3)
[7,12,13] in diethyl ether to yield U(H3BNMe2BH3)3, whereas
reactions carried out in the presence of tetrahydrofuran afford
the adduct U(H3BNMe2BH3)3(thf) [9,10]. In both cases, the reaction
is accompanied by reduction to uranium(III) and no uranium(IV)
products could be isolated.
In further studying this system, we carried out the reaction of
UCl4 and 4 equiv of Na(H3BNMe2BH3) in refluxing 1,2-dimethoxy-
ethane (dme). This reaction yields small amounts of a new
P
2
minimized by the least-squares program was wðF2o ꢁ Fc2Þ , where
w = {[r
(Fo)]2 + (0.0106P)2}ꢁ1 and P ¼ ðFo2 þ 2F2c Þ=3. The analytical
approximations to the scattering factors were used, and all
structure factors were corrected for both real and imaginary
components of anomalous dispersion. In the final cycle of least
squares, independent anisotropic displacement factors were
refined for the non-hydrogen atoms. The C–Me distances in the
complex, which we formulate as U2(
l
-O)(BH4)6(dme)2ꢀC7H8, 1, as
emerald green prisms by crystallizaꢁtion from a 1:1 toluene/penꢁ-
tane mixture. The formation of BH4 groups from H3BNMe2BH3
at elevated temperatures has
a precedent: we have shown
elsewhere that an identical conversion takes place in the coordina-
tion sphere of thorium at elevated temperatures, and that this
reaction occurs with the elimination of 1 equiv of the aminoborane
[Me2NBH2]2 [11]. The bridging oxo ligand in 1 almost certainly
arises from adventitious water [14,15].
Table 1
Crystallographic data for U2(
l-O)(BH4)6(dme)2ꢀC7H8, 1.
Formula
C15H52B6O5U2
853.49
0.71073
Single-crystal X-ray diffraction studies of 1 support the assigned
stoichiometry (Fig. 1). Each uꢁranium center adopts a fac octahedral
geometry (counting the BH4 groups as occupying one coordina-
tion site); the bridging oxygen atom and the two coordinated
oxygen atoms of the dme ligand occupy positions trans to the three
Formula weight (g molꢁ1
)
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
triclinic
ꢀ
P1
9.595(3)
11.500(4)
14.135(4)
85.383(4)
83.555(4)
85.021(4)
1540.0(8)
2
1.841
10.520
face-indexed
0.610, 0.251
5603/475/395
0.845
ꢁ
BH4 groups. The hydride positions were located in the difference
ꢁ
maps and reveal that all three BH4 groups are bꢁound in a
j
3H
a
(°)
(tridentate) fashion. The Uꢀ ꢀ ꢀB distance to the BH4 group that is
trans to the bridging oxygen, 2.635(7) Å, is about 0.06 Å longer that
the Uꢀ ꢀ ꢀB distances to the two groups that are cis to the bridging
oxygen atom, 2.574(6) and 2.584(6) Å. Thus, the bridging oxygen
atom exerts a noticeable trans influence, as is usually seen for
b (°)
c
(°)
V (Å3)
Z
qcalc (g cmꢁ3
)
l
(mmꢁ1
)
oxo groups. In general, the Uꢀ ꢀ ꢀB distances are similar to those
observed in other UIV complexes with
j
3-BH4 groups [3,16].
Absorption correction
ꢁ
Maximum, minimum transmission factors
Data/restraints/parameters
The U–O bond distances to the dme molecule are 2.498(3)–
2.544(4) Å. The distances are slightly longer than those observed
for the adducts of U(BH4)4 with dimethyl ether (2.44 Å) [17],
diethyl ether (2.49 Å) [17], di-n-propyl ether (2.48 Å) [18], and
tetrahydrofuran (2.47 Å) [19]. The bridging oxygen atom in 1 rests
between the uranium atoms, and the U–O–U angle is nearly linear
at 172.9(2)°. The U–O distances of 2.074(3) and 2.080(3) Å are
Goodness-of-fit (GOF) on F2
R1 [I > 2
r
(I)]a
0.0236
0.0505
1.632, ꢁ1.219
wR2 (all data)b
Largest difference peak and hole (e Åꢁ3
)
P
P
R1
=
|Fo| ꢁ |Fc|/| |Fo| for reflections with F2o > 2
r
ðF2oÞ.
a
P
P
2
2
wR2 = [ w(F2o ꢁ F2c Þ / ðF2oÞ ]1/2 for all reflections.
b

S.R. Daly et al. / Polyhedron 33 (2012) 41–44
43
noted that there was a spurious peak of electron density midway
between the two uranium atoms that could not be explained. We
believe that this peak was due to an oxygen atom and that the
hydride complex should be reformulated as U2(l-O)(BH4)6(dme)2.
In the study of U2( -H)2(BH4)6(dme)2, direct evidence in
l
support of the presence of two bridging hydrides was unavailable:
no hydride resonance could be located in the 1H NMR spectrum,
and no electron density corresponding to a pair of bridging
hydrogen atoms could be found in the electron density difference
map. It is well known that it is difficult to obtain direct evidence
of bridging hydrogen atoms in uranium complexes owing to the
paramagnetism and the low X-ray scattering power of hydrogen
atoms relative to uranium, but a re-evaluation of the evidence
suggests that the two uranium atoms are bridged by an oxygen
atom and not by two hydrogen atoms. The paper describing the
uranium hydride reported that the microanalytical data were
satisfactory, and this finding is consistent with the proposed
reformulation: the calculated C, H, B, and U weight percentages
of 12.6%, 5.83%, 8.52%, and 62.5% for the oxo formula and 12.9%,
6.20%, 8.68%, and 63.7% for the hydride formula are almost
identical.
Interestingly, the unit cell for 1 is different from that reported
for the uranium hydride, the current cell having approximately
twice the volume and different cell parameters. But we believe that
both crystal structures are of the same crystalline substance. If the
cell parameters for the hydride crystal structure are designated
with primes, then the two unit cells are related by the following
Fig. 1. Molecular structure of U2(l-O)(BH4)6(dme)2, 1. Ellipsoids are drawn at the
35% probability level. Hydrogen atoms and the disordered toluene solvate molecule
have been omitted. The primed and unprimed atoms are not related by symmetry,
but are related by the inversion center in the smaller cell chosen for U2(
l-
0
~
0
0
~
~
~
~
~
~
~
transformation: a = ½ (ꢁa + c), b = ½ (a + c), and c = b. If we apply
this transformation to the cell parameters measured for 1, the
result is as follows (with the cell parameters reported for the
hydride given in parentheses): a0 = 8.084 (8.126), b0 = 8.976
(8.950), c0 = 11.500 (11.638) Å, a0 = 83.70 (83.50)°, b0 = 88.92
(89.44)°, and c0 = 68.21 (69.76)°. The exact values are slightly
different, probably because the crystal temperature was different
for the two data sets.
H)2(BH4)6(dme)2.
comparable to those observed in other UIV
as U2( -O)2[C5H3(SiMe3)2]4 (2.10 and 2.13 Å) [20], U2(
(C5H4SiMe3)6 (2.11 Å) [21], and U3( -O)3(C5H4SiMe3)6 (2.05–
l-oxo compounds, such
l
l
-O)
l
2.12 Å) [22]. Only one other uranium oxo/borohydride complex
has been isolated and crystallographically characterized, the
uranyl complex UO2(
phosphoramide [23].
Aside from the identity of the bridging ligands, the structure of
U2( -O)(BH4)6(dme)2 is remarkably similar to that of a previously
reported complex, the hydride U2( -H)2(BH4)6(dme)2 (Table 2).
j
2-BH4)2(hmpa)2, where hmpa = hexamethyl-
In the larger (correct) unit cell, the bridging oxygen atom lies at
a general position, but its coordinates are very near (1 4,0,3 4). As a
result, this atom lies almost exactly halfway between inversion
ꢀ
l
centers in the ac plane of the larger P1 unit cell (Fig. 2). Because
l
the individual molecules of 1 have very nearly ideal (but noncrys-
tallographic) inversion symmetry, there is a large degree of
pseudosymmetry: the crystal coordinates almost (but not exactly)
Both compounds crystallize from 1:1 pentane:toluene in the
ꢀ
triclinic space group P1, with one molecule of toluene per dinucle-
ꢀ
ar unit. The Uꢀ ꢀ ꢀU distance is 4.146(3) Å in 1 versus 4.12 Å in the
correspond to a smaller unit cell, also of P1 symmetry, in which an
hydride, and all the ligands are disposed in exactly the same
additional inversion center is present on the bridging oxygen atom.
Several lines of evidence speak in support of the larger unit cell
being the correct one: (1) additional (albeit weak) reflections
appear in the diffraction record that correspond only to this larger
cell, (2) the two ends of each molecule in the larger unit cell are not
related by symmetry (as assessed by Platon) [24], (3) there are no
large correlation coefficients between any of the parameters for the
non-hydrogen atoms in the least squares matrix, and (4) hydrogen
atoms could be located and refined (which was not possible for the
crystal of the supposed uranium hydride, although this result could
also have been a consequence of larger errors in the intensity
measurements). In the previous refinement, in contrast, the
incorrect choice of unit cell and consequent averaging of the
atomic coordinates related by the pseudosymmetry caused some
significant errors. For example, the boron atom trans to the
bridging oxo group had unusually large displacement parameters,
and, in contrast to the expected trans influence, its Uꢀ ꢀ ꢀB distance
was 0.09 Å shorter (instead of 0.06 Å longer) than the two Uꢀ ꢀ ꢀB
fashion. Significantly, the structure report for U2(l-H)2(BH4)6(dme)2
Table 2
Selected bond lengths and angles for U2(
l-O)(BH4)6(dme)2ꢀC7H8, 1, with those
reported for U2(
l-H)2(BH4)6(dme)2ꢀC7H8 in square brackets.
Bond lengths (Å)
U(1)–O(1)
U(1)–O(2)
U(1)–B(1)
U(1)–B(2)
U(1)–B(3)
U(1)–O(3)
U(1)–U(2)
2.544(4)
2.498(3)
2.574(6)
2.584(8)
2.635(7)
2.080(3)
4.146(3)
[2.53]
[2.47]
[2.64]
[2.64]
[2.53]
[N.A.]
[4.12]
U(2)–O(10)
U(2)–O(20)
U(2)–B(10)
U(2)–B(20)
U(2)–B(30)
U(2)–O(3)
2.503(4)
2.518(4)
2.595(7)
2.577(7)
2.631(7)
2.074(3)
Bond angles (°)
O(1)–U(1)–O(2)
B(1)–U(1)–B(2)
B(1)–U(1)–B(3)
B(2)–U(1)–B(3)
O(1)–U(1)–B(1)
O(1)–U(1)–B(3)
O(2)–U(1)–B(2)–
O(2)–U(1)–B(3)
U(1)–O(3)–U(2)
65.12(12)
104.2(2)
96.8(2)
[65.1]
[105]
[103]
[97]
[93.4]
[84]
[96]
[78]
[180]
O(10)–U(2)–O(20)
B(10)–U(2)–B(20)
B(10)–U(2)–B(30)
B(20)–U(2)–B(30)
O(10)–U(2)–B(10)
O(10)–U(2)–B(30)
O(20)–U(2)–B(20)
O(20)–U(2)–B(30)
65.39(13)
104.8(2)
95.6(2)
95.6(2)
98.8(2)
84.63(18)
90.79(19)
89.14(18)
96.0(2)
ꢁ
distances to the other two BH4 ligands.
88.68(19)
88.82(18)
101.83(18)
83.00(17)
172.94(18)
The 1H NMR spectrum of U2(
C7D8 closely resembles that reported for U2( -H)2(BH4)6(dme)2
l
-O)(BH4)6(dme)2 at ꢁ60 °C in
l
under similar conditions (Table 3). The most striking similarity is
the chemical shift of one of the BH4 resonances, which is shifted

44
S.R. Daly et al. / Polyhedron 33 (2012) 41–44
In summary, the crystallographic and 1H NMR data presented
here strongly suggest that the uranium hydride complex
U2(
l
-H)2(BH4)6(dme)2 should be reformulated as the oxo complex
-O)(BH4)6(dme)2.
U2(l
Acknowledgments
S.R.D. and G.S.G. thank the National Science Foundation
(CHE07-50422 and DMR-0420768) and the PG Research Foundation
for support of this research, and Scott Wilson and Teresa
Wieckowska-Prussak at the George L. Clark X-ray facility at the
University of Illinois for collecting the X-ray diffraction data. M.E.
gratefully acknowledges support from the Centre National de la
Recherche Scientifique (CNRS) and the Commissariat à l’Energie
Atomique (CEA).
Appendix A. Supplementary data
CCDC 838088 contains the supplementary crystallographic data
for compound 1. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk.
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Fig. 2. Unit cell of U2(
are drawn at the 50% probability level. Both disordered components of the toluene
l
-O)(BH4)6(dme)2ꢀC7H8, viewed down the a-axis. Ellipsoids
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Table 3
1H NMR shifts for U2(
l
-O)(BH4)6(dme)2, 1, at ꢁ60 °C in toluene (600 MHz) and
comparison to those reported for U2( -H)2(BH4)6(dme)2 (60 MHz) [1].
l
U2(l-O)(BH4)6(dme)2 U2( -H)2(BH4)6(dme)2
l
[12] P.C. Keller, J. Chem. Soc. D (1969) 1465.
[13] P.C. Keller, Inorg. Chem. 10 (1971) 2256.
BH4
BH4
OCH2
OCH2
OMe
727 (br s, fwhm = 2700 Hz)
ꢁ115 (s, fwhm = 290 Hz, 4H)
ꢁ32.4 (s, fwhm = 80 Hz, 2H)
ꢁ52.9 (s, fwhm = 110 Hz, 2H)
ꢁ62.0 (s, fwhm = 110 Hz, 6H)
752.6 (br s, fwhm = 530 Hz, 4H)
ꢁ121.3 (br s, fwhm = 140 Hz, 8H)
ꢁ31.6 (s, 2H)
[14] W.E. Hunter, D.C. Hrncir, R.V. Bynum, R.A. Penttila, J.L. Atwood,
Organometallics 2 (1983) 750.
[15] N.A. Yakelis, R.G. Bergman, Organometallics 24 (2005) 3579.
[16] A. Haaland, D.J. Shorokhov, A.V. Tutukin, H.V. Volden, O. Swang, G.S. McGrady,
N. Kaltsoyannis, A.J. Downs, C.Y. Tang, J.F.C. Turner, Inorg. Chem. 41 (2002)
6646.
ꢁ52.3 (s, 2H)
ꢁ62.8 (s, 6H)
[17] R.R. Rietz, A. Zalkin, D.H. Templeton, N.M. Edelstein, L.K. Templeton, Inorg.
Chem. 17 (1978) 653.
[18] A. Zalkin, R.R. Rietz, D.H. Templeton, N.M. Edelstein, Inorg. Chem. 17 (1978)
661.
dramatically to a lower field: d 727, compared to the reported
value of d 753 for U2( -H)2(BH4)6(dme)2. We do suggest that the
l
assignments of the two BH4 resonances should be reversed,
however: the resonance at d ꢁ115 integrates to four protons in
our spectrum (versus eight reportedꢁpreviously), and thus this
resonance is best assigned to the BH4 group that is trans to the
bridging oxo ligand. We could not obtain an accurate integral for
the resonance at d 727 owing to its large shift and line width.
Integrations and chemical shifts for the dme resonances match
those reported previously.
[19] R.R. Rietz, N.M. Edelstein, H.W. Ruben, D.H. Templeton, A. Zalkin, Inorg. Chem.
17 (1978) 658.
[20] A. Zalkin, S.M. Beshouri, Acta Crystallogr., Sect. C44 (1988) 1826.
[21] J.C. Berthet, J.F. Le Marechal, M. Nierlich, M. Lance, J. Vigner, M. Ephritikhine, J.
Organomet. Chem. 408 (1991) 335.
[22] J.-C. Berthet, M. Ephritikhine, M. Lance, M. Nierlich, J. Vigner, J. Organomet.
Chem. 460 (1993) 47.
[23] C. Villiers, P. Thuery, M. Ephritikhine, Inorg. Chem. Commun. 10 (2007) 891.
[24] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.