Halide, amide, cationic, manganese carbonylate, and oxide derivatives of triamidosilylamine uranium complexes

Article abstract of DOI:10.1021/ic201372a

Treatment of the complex [U(Tren^TMS)(Cl)(THF)] [1, Tren ^TMS = N(CH₂CH₂NSiMe₃)₃] with Me₃SiI at room temperature afforded known crystalline [U(Tren^TMS)(I)(THF)] (2), wh

Full text of DOI:10.1021/ic201372a

ARTICLE
pubs.acs.org/IC
Halide, Amide, Cationic, Manganese Carbonylate, and Oxide
Derivatives of Triamidosilylamine Uranium Complexes
Benedict M. Gardner, William Lewis, Alexander J. Blake, and Stephen T. Liddle*
School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, United Kingdom
S Supporting Information
b
ABSTRACT: Treatment of the complex [U(TrenTMS)(Cl)(THF)] [1,
TrenTMS = N(CH2CH2NSiMe3)3] with Me3SiI at room temperature
afforded known crystalline [U(TrenTMS)(I)(THF)] (2), which is re-
ported as a new polymorph. Sublimation of 2 at 160 ꢀC and 10À6 mmHg
afforded the solvent-free dimer complex [{U(TrenTMS)(μ-I)}2] (3),
which crystallizes in two polymorphic forms. During routine preparations
of 1, an additional complex identified as [U(Cl)5(THF)][Li(THF)4] (4)
was isolated in very low yield due to the presence of a slight excess of
[U(Cl)4(THF)3] in one batch. Reaction of 1 with one equivalent of
lithium dicyclohexylamide or bis(trimethylsilyl)amide gave the corre-
sponding amide complexes [U(TrenTMS)(NR2)] (5, R = cyclohexyl; 6,
R = trimethylsilyl), which both afforded the cationic, separated ion pair
complex [U(TrenTMS)(THF)2][BPh4] (7) following treatment of the
respective amides with Et3NH BPh4. The analogous reaction of 5 with Et3NH BArf4 [Arf = C6H3-3,5-(CF3)2] afforded, following
3
3
addition of 1 to give a crystallizable compound, the cationic, separated ion pair complex [{U(TrenTMS)(THF)}2(μ-Cl)][BArf4] (8).
Reaction of 7 with K[Mn(CO)5] or 5 or 6 with [HMn(CO)5] in THF afforded [U(TrenTMS)(THF)(μ-OC)Mn(CO)4] (9); when
these reactions were repeated in the presence of 1,2-dimethoxyethane (DME), the separated ion pair [U(TrenTMS)(DME)][Mn(CO)5]
(10) was isolated instead. Reaction of 5 with [HMn(CO)5] in toluene afforded [{U(TrenTMS)(μ-OC)2Mn(CO)3}2] (11). Similarly,
reaction of the cyclometalated complex [U{N(CH2CH2NSiMe2But)2(CH2CH2NSiMeButCH2)}] with [HMn(CO)5] gave
[{U(TrenDMSB)(μ-OC)2Mn(CO)3}2] [12, TrenDMSB = N(CH2CH2NSiMe2But)3]. Attempts to prepare the manganocene derivative
[U(TrenTMS)MnCp2] from 7 and K[MnCp2] were unsuccessful and resulted in formation of [{U(TrenTMS)}2(μ-O)] (13) and
[MnCp2]. Complexes3À13 have been characterized by X-ray crystallography, 1H NMR spectroscopy, FTIR spectroscopy, Evans method
magnetic moment, and CHN microanalyses.
’ INTRODUCTION
in the literature compared to the well-developed area of metalÀ
metal bonding in the d-block.6,7 We have found the TrenTMS
ligand to be an excellent ancillary ligand for complexes contain-
ing uraniumÀmetal bonds, as demonstrated by our use of the
complexes [U(TrenTMS)(X)(THF)] (X = Cl, 1; X = I, 2)27,29 to
prepare the first unsupported uraniumÀgallium27 and uraniumÀ
rhenium29 bonds, both of which are notable for containing σ- and
π-components in the uranium(IV)Àmetal bonds, although the
latter component is clearly weak. However, although 1 and 2 are
in principle clearly good precursors for constructing ura-
niumÀmetal bonds by salt elimination reactions, as evidenced
by the aforementioned UÀGa and UÀRe complexes, we have
found that some transition metal anions, especially carbonylate
anions, can exhibit sluggish reactivity that we ascribe to entrap-
ment of the alkali metal countercation by the carbonyl groups.32
This limitation can be overcome by thermolysis of reaction
mixtures, but this could clearly lead to decomposition and is
therefore undesirable.30 However, amide and separated ion pair
There is currently significant interest in the nonaqueous
coordination and organometallic chemistry of uranium.1À11 This
is motivated by the search for an improved understanding of the
differences in covalent bonding between the 5f and 4f elements
and for new reaction methodologies that might be applicable in
catalytic reactions.12 Although uranium complexes typically
exhibit more covalent character in their bonding than analogous
lanthanide complexes, it is necessary to precisely control the
nature of the coordination sphere to tailor the properties and
reactivity of the resultant complexes as electrostatic effects still
dominate the bonding picture. Since uranium is a large metal
(having a 1.70 Å single bond covalent radius according to
Pyykk€o)13 with many potential coordination sites, the use of
multidentate ligands represents an effective strategy for control-
ling the number of reactive sites at uranium, as exemplified by the
triamidoamine ligand {N(CH2CH2NSiMe3)}3À (TrenTMS),
which has been utilized to great effect in recent years.14À26
We recently embarked on a program of research to investigate
the structure, bonding, and reactivity of complexes that contain
uraniumÀmetal bonds;27À34 this was stimulated by their paucity
Received: June 27, 2011
Published: August 31, 2011
r
2011 American Chemical Society
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Inorganic Chemistry
ARTICLE
Scheme 1. Synthesis of 2, 3, 5, 6, 7, and 8
derivatives of 1 and 2 represent valuable alternative precursors to
uraniumÀmetal bonds. The former would enable uraniumÀ
metal bonds to be constructed from a uranium amide and
transition metal hydrides with concomitant elimination of
amine.35 The latter would provide the opportunity to conduct
salt elimination chemistry under less forcing conditions than
might be required with halide precursors, since the non/weakly
coordinating anion of a separated ion pair should be easier
to abstract and eliminate than a coordinated halide anion.36
The use of uranium precursors free of coordinated Lewis bases
such as ethers are potentially desirable, since the presence
of ethers such as THF could provide a mechanism for
decomposition by oxo-group abstraction.37 Lastly, a library
of Tren uranium precursor complexes is valuable in a broader
synthetic context as a basis for new nonaqueous uranium
chemistry.
Figure 1. Molecular structure of 2 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms are omitted for clarity.
Having successfully prepared UÀRe bonds previously,29
we investigated the possibility of preparing UÀMn bonds for
comparative purposes and also with a view to determining their
reactivity. Herein, we report the synthesis and characterization
of a range of solvated and solvent-free uranium halide, amide,
cationic, manganese carbonylate, and oxide complexes sup-
ported by TrenTMS and the more sterically demanding variant
TrenDMSB [TrenDMSB = N(CH2CH2NSiMe2But)3].
a new unit cell. Therefore, we carried out a full data collection to
ascertain the identity of the apparently new compound that was
subsequently found to be a polymorph of 2.
The overall structure of 2 (Figure 1 and Table 1) is identical to
the previously known polymorph in terms of connectivity; the
uranium center adopts a distorted octahedral geometry, being
coordinated by the four nitrogen centers of the quadridentate
Tren ligand, an iodide which is trans to the datively bound amine
center, and the oxygen donor of a THF molecule. The bond
lengths and angles in 2 exhibit similar values to those in the
previously reported polymorph, albeit with minor variations in
the UÀI, UÀN, and UÀO bond lengths, which are within
literature ranges.39
Realizing that an ether-free triamidoamine uranium(IV) io-
dide complex may prove to be a valuable and necessary precursor
to uraniumÀmetal bonds if ether cleavage/oxo-abstraction
reactions occurred with ether-coordinated uranium precursors,
we prepared [{U(TrenTMS)(μ-I)}2] (3) quantitatively by sub-
limation of 2 at 160 ꢀC and 10À6 mmHg. This afforded 3
as a pale yellow microcrystalline solid in quantitative yield
(Scheme 1). The 1H NMR spectrum of 3 spans the range +16 to
À46 ppm, which compares to a range of +28 to À44 ppm for 2.
’ RESULTS AND DISCUSSION
Halide, Amide, and Cationic Derivatives. The triamidoamine
uranium(IV) complex [U(TrenTMS)(Cl)(THF)] [1, TrenTMS
=
{N(CH2CH2NSiMe3)3}3À] is readily prepared from [Li3(TrenTMS)]
and UCl4 in THF and may be recrystallized in high yield as a
THF adduct on a multigram scale.27 Alternatively, 1 may be
sublimed to give the solvent-free dimeric form.14 In common with
related Tren and other uranium complexes,38 complex 1 may be
treated with Me3SiI and converted to the corresponding iodide
complex [U(TrenTMS)(I)(THF)] (2) in essentially quantita-
tive yield,29 with concomitant elimination of Me3SiCl, and 2 can
be recrystallized in excellent yields (Scheme 1). Although com-
plete characterization of 2 has been reported by us previously,29
during the course of routine crystallographic screening, we identified
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Inorganic Chemistry
ARTICLE
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 2,
3 2C7H8, and 3 0.5C7H8
3
3
2
U(1)ÀN(1)
U(1)ÀN(3)
U(1)ÀI(1)
2.283(8)
2.250(7)
3.1287(7)
U(1)ÀN(2)
U(1)ÀN(4)
U(1)ÀO(1)
2.225(8)
2.555(8)
2.558(6)
3 2C7H8
3
U(1)ÀN(1)
U(1)ÀN(3)
U(1)ÀI(1)
2.234(3)
2.224(2)
U(1)ÀN(2)
U(1)ÀN(4)
U(1)ÀI(1A)
U(1)ÀU(1B)
2.227(3)
2.567(2)
3.244(4)
3.241(4)
3.2902(5)
3.1832(4)
U(1)ÀI(1AA)
Figure 2. Molecular structure of 3 0.5C7H8 with selective atom label-
3
3 0.5C7H8
3
ing and probability ellipsoids set at 30%. Hydrogen atoms and minor
iodide disorder components omitted for clarity. Only the major com-
ponent of the disordered iodide and one of the two unique molecules are
U(1)ÀI(1)
3.2246(5)
3.328(6)
2.226(4)
2.211(5)
3.2095(5)
3.229(8)
2.233(4)
2.248(4)
U(1)ÀI(1A)
U(1)ÀI(1B)
U(1)ÀN(2)
U(1)ÀN(4)
U(2)ÀI(2A)
U(2)ÀI(2B)
U(2)ÀN(6)
U(2)ÀN(8)
3.261(6)
3.3768(5)
2.246(5)
2.570(4)
3.229(8)
3.3354(5)
2.228(4)
2.570(4)
U(1)ÀI(1AA)
U(1)ÀN(1)
U(1)ÀN(3)
U(2)ÀI(2)
shown for clarity. The structure of 3 2C7H8 is very similar.
3
Scheme 2. Preparation of A and Ba
U(2)ÀI(2AA)
U(2)ÀN(5)
U(2)ÀN(7)
Table 2. Room Temperature Magnetic Moment Data for
1À3 and 5À13a
compound
aggregation
μB
1
m
m
d
2.78
2.79
3.88
2.79
3.03
2.10
3.51
2.94
3.35
3.93
4.09
2.95
2
3
5
m
m
m
d
6
7
8
9
m
m
d
10
11
12
13
a See ref 30 for full details.
d
membered U2I2 ring, each uranium adopts a distorted octahedral
geometry defined by the four nitrogen centers of the Tren ligand
and the two bridging iodides. The UÀNamide distances average
2.228(5) Å, which compares to averages of 2.252(3), 2.253(8),
and 2.247(10) Å in 1,27 2,29 and the solvent-free chloride
analogue.14 Notably, the U(1)ÀN(2) bond length of 2.246(5) Å
is longer than the U(1)ÀN(1) and U(1)ÀN(3) bond dis-
tances of 2.226(4) and 2.211(5) Å, perhaps reflecting the
fact the former is trans to iodide whereas the latter pair are cis
to iodide. The U(1)ÀN(4) bond length of 2.570(4) Å com-
d
a m = monomeric; d = dimeric.
Spectroscopic and combustion analysis supported the proposed
formulation, and the magnetic moment in solution at room
temperature was found to be 3.88 μB (Table 2), which is
consistent with a 3H4 ground state of f2 uranium(IV).40
Complex 3 can be recrystallized in 80% yield as yellow-green
needles from toluene solution, and an X-ray diffraction study was
carried out to confirm the absence of coordinated THF (Figure 2
and Table 1). Two polymorphs of 3 were identified in the course
of these studies. In one polymorph, half a dimer resides in the
asymmetric unit and two molecules of toluene per dimer are
found in the lattice. In the other polymorph, the asymmetric unit
contains two half dimer molecules and half a molecule of toluene
pares to a UÀNamine distance of 2.567(9) Å in [{U(TrenTMS
)
(μ-Cl)}2].14 The UÀI bond distances fall within the literature
range of UÀI bond lengths but do not merit detailed discus-
sion because of positional disorder of the iodide ligands in
3 2C7H8 and 3 0.5C7H8.
3
3
On one occasion, we isolated a very small quantity (∼2% yield) of
per dimer. The two polymorphs are denoted as 3 2C7H8 and
pale green, almost colorless crystals from a preparation of 1, which
were subsequently identified as [U(Cl)5(THF)][Li(THF)4] (4),
and this is deposited in the Supporting Information.
3
3 0.5C7H8, and since they are generally similar with only minor
3
variations in bond lengths and angles, we confine our discussion
to one of the unique molecules in 3 0.5C7H8. In 3 0.5C7H8,
which is a centrosymmetric dimer constructed around a four-
We have previously shown that 2 reacts with benzyl
potassium to afford the tuck-in-tuck-over tuck-over dialkyl Tren
3
3
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ARTICLE
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
5À7
5
U(1)ÀN(1)
U(1)ÀN(3)
U(1)ÀN(5)
2.289(2)
2.272(2)
2.273(2)
U(1)ÀN(2)
U(1)ÀN(4)
2.267(2)
2.696(2)
6
U(1)ÀN(1)
U(1)ÀN(3)
U(1)ÀN(5)
2.247(6)
2.245(6)
2.329(6)
U(1)ÀN(2)
U(1)ÀN(4)
2.274(6)
2.698(7)
7•C7H8
U(1)ÀN(1)
U(1)ÀN(3)
U(1)ÀO(1)
2.246(3)
2.226(3)
2.544(3)
U(1)ÀN(2)
U(1)ÀN(4)
U(1)ÀO(2)
2.243(3)
2.542(3)
2.592(3)
Figure 3. Molecular structure of 5 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms omitted for clarity.
complex [U{N(CH2CH2NSiMe3)(CH2CH2NSiMe2CH2)2}-
U(TrenTMS)] (A, Scheme 2),30 and that treatment of A with
Et3NH BPh4 affords the metallocyclic complex [U{N(CH2CH2-
3
NSiMe3)2(CH2CH2NSiMe2C[H]BPh2)}(THF)] (B) rather than
the anticipated ion pair complex [(TrenTMS)U(THF)n][BPh4]
(Scheme 2).30 Since A and B have limited utility as precursors to
uraniumÀmetal bonds, we targeted amide derivatives. Amide deriva-
tives would not be expected to generate cyclometalated species such as
A from pKa considerations as the corresponding reaction of 2 with
benzyl potassium does. This would potentially enable the construction
of uraniumÀmetal bonds from a uranium amide and transition metal
hydrides with concomitant elimination of amine.
Treatment of 1 with one equivalent of lithium dicyclohexyla-
mide, or one equivalent of lithium bis(trimethylsilyl)amide,
furnishes, after workup and recrystallization from hexane, yellow
crystals of the complexes formulated as [U(TrenTMS)(NR2)]
(5, R = Cy = cyclohexyl; 6, R = SiMe3) in 72% and 50% crystalline
yield, respectively (Scheme 1). The 1H NMR spectra of 5 and 6
span the ranges +89 to À17 and +17 to À7 ppm, respectively,
and together with the other spectroscopic and analytical data,
support the proposed formulations. The solution magnetic
moments of 2.79 and 3.03 μB for 5 and 6, respectively, compare
to moments of 2.78, 2.79, and 3.88 μB for 1,27 2,29 and 3, respectively,
and are consistent with uranium(IV) centers (Table 2).
Figure 4. Molecular structure of 6 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms omitted for clarity.
In 5 (Figure 3 and Table 3), the uranium center is 5-coordinate
and can be considered to adopt a distorted trigonal bipyramidal
geometry such that the N(4) and N(5) centers occupy the axial
sites but the N(1), N(2), and N(3) centers are distorted from the
equatorial plane by the constraints of the Tren ligand. The
U(1)ÀN(1), U(1)ÀN(2), and U(1)ÀN(3) bond lengths of
2.289(2), 2.267(2), and 2.272(2) Å, respectively, are surprisingly
longer overall than observed in 2,29 despite the 5-coordinate
nature of the uranium center in 5 compared to the 6-coordinate
uranium center in 2. The U(1)ÀN(4) bond length of 2.696(2) Å
is longer than the corresponding UÀN bond distance of
2.555(8) Å in 2 reflecting the fact the former is trans to a dialkyl
amide whereas the latter is trans to an iodide. The U(1)ÀN(5)
bond length of 2.273(2) Å in 5 is shorter than the other
UÀNamide distances as befits its dialkyl nature compared to the
alkyl-silyl nature of the N(1)ÀN(3) centers. Interestingly, the
UÀNCy2 bond length in 5 is longer than the UÀNCy2 bond
distance of 2.210(3) Å in [U(NCy2){HC(SiMe2NAr)3}(THF)]
(Ar = 3,5-Me2C6H3),31 which demonstrates the sterically de-
manding nature of Tren. The N(5) center adopts an essentially
Figure 5. Molecular structure of 7 C7H8 with selective atom labeling
and probability ellipsoids set at 30%. Hydrogen atoms and lattice toluene
solvent omitted for clarity.
3
trigonal planar geometry [Σ— = 359.97(17)ꢀ], which indicates that
it is likely acting as a π-base to the electrophilic uranium center.
Analogously to 5, complex 6 crystallizes with a 5-coordinate
uranium center due to the sterically demanding ligands (Figure 4
and Table 3). The U(1)ÀN(1), U(1)ÀN(2), U(1)ÀN(3), and
U(1)ÀN(4) bond lengths of 2.247(6), 2.274(6), 2.245(6), and
2.698(7) Å, respectively, compare well to 5. The U(1)ÀN(5)
bond distance of 2.329(6) Å is moderately longer than the other
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Inorganic Chemistry
ARTICLE
Scheme 3. Synthesis of 9À11
Table 4. Comparison of Selected FTIR Data for Free CO,
For example, the U(1)ÀN(1), U(1)ÀN(2), and U(1)ÀN(3)
bond lengths of 2.246(3), 2.243(3), and 2.226(3) Å, respectively,
give an average UÀNamide distance of 2.238(3) Å that com-
pares to an average UÀNamide distance of 2.253(8) Å in 2.29
The metrical parameters of the tetraphenylborate anion are
unremarkable.
K[Mn(CO)5], [HMn(CO)5], and 9À12 in Nujola
compound
FTIR vCO/cmÀ1
free CO
2143
1835, 1909a
K[Mn(CO)5]
1981, 2014a
Since the tetraphenylborate anion is potentially not an in-
nocent ligand and has precedent for mono-41À44 and double-
dearylation30 reactions in nonaqueous uranium chemistry,
we investigated the use of the more robust borate anion BArf4À
[Arf = C6H3-3,5-(CF3)2]45 as an alternative non/weakly coordi-
[HMn(CO)5]
9
1709, 1889, 1918, 1931
1859, 1892, 1921, 1939
1731, 1814, 1823, 1938, 1952
1734a, 1806a, 1956a
10
11
12
nating counteranion. Treatment of 5 with Et3NH BArf4 in THF
3
a Broad band that obscures other absorptions in these regions.
affords, after work up, an oily yellow-brown product (Scheme 1).
1
Although crude H NMR spectra were consistent with the
formation of the target complex [U(TrenTMS)(THF)2][BArf4],
a number of intractable and unidentifiable impurities were
observed that precluded the acquisition of further meaningful
characterization data. In an effort to isolate a product cleanly, we
added one equivalent of 1 to “[U(TrenTMS)(THF)2][BArf4]” in
the anticipation that 1 would displace a coordinated THF
molecule and bind via a bridging chloride to give an isolable
complex. Accordingly, the cationic separated ion pair complex
formulated as [{U(TrenTMS)(THF)}2(μ-Cl)][BArf4] (8) was
isolated as pale green crystals, and full details can be found in the
Supporting Information.
Carbonylate Derivatives. With the synthesis of 5À7 accom-
plished, we examined their reactivity toward the manganese
pentacarbonyl anion in an attempt to prepare uraniumÀmanga-
nese bonds. Treatment of either 7 with K[Mn(CO)5]46 or 5 or 6
with [HMn(CO)5]47 resulted in elimination of KBPh4 or HNCy2
and HN(SiMe3)2, respectively, to afford the complex formulated
as [U(TrenTMS)(THF)(μ-OC)Mn(CO)4] (9) (Scheme 3).
Complex 9 was isolated as yellow blocks in 54% crystalline yield.
Complex 9 could also be prepared by reaction of 2 with K[Mn-
(CO)5], but this required extended thermolysis and isolated
yields were much lower (∼15%), which demonstrates the utility
of 7. The 1H NMR spectrum covers the range +34 to À43 ppm,
and the solution magnetic moment of 9 of 2.94 μB (Table 2) is
comparable to those of 1 and 2. The FTIR spectrum of 9 exhibits
four strong carbonyl stretches at 1709, 1889, 1918, and
three UÀNamide bond lengths, which reflects the presence of its
silyl substituents. The N(5) center adopts an essentially trigonal
planar geometry [Σ— = 360.0(3)ꢀ], which indicates that it is
likely acting as a π-base to the electrophilic uranium center.
With complexes 5 and 6 in hand, we explored their conversion
to separated ion pair complexes. In light of the double-dearyla-
tion chemistry outlined in Scheme 2,30 we tested the reactivity of
5 and 6 with Et3NH BPh4. Accordingly, treatment of 5 or 6 with
3
Et3NH BPh4 in THF afforded, after work up, the separated ion
3
pair complex [U(TrenTMS)(THF)2][BPh4] (7) as a free-flowing
green powder from hexane in 95% yield (Scheme 1). The H
1
NMR spectrum of 7 exhibits resonances in the range +16 to À43
ppm, and the low solution magnetic moment of 2.10 μB
(Table 2) suggests that the orbital angular contribution at
uranium may be suppressed, which may be due to the cationic
nature of 7.40 All other spectroscopic and analytical data support
the proposed formulation. In order to assess whether complex 7
was a separated ion pair or a weakly associated contact ion pair,
we conducted a single crystal X-ray diffraction experiment on a
yellow-green crystal of 7 C7H8 grown from toluene.
3
Complex 7 (Figure 5 and Table 3) crystallizes as a separated
ion pair complex. The uranium center is coordinated to the four
nitrogen centers of the Tren ligand and the oxygen centers of two
molecules of THF in a distorted octahedral geometry with no
contacts to the tetraphenylborate anion. The cationic nature of 7
is confirmed by inspection of the uranium-ligand bond lengths.
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Inorganic Chemistry
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Table 5. Selected Bond Lengths (Å) and Angles (deg) for 9À12
9
U(1)ÀN(1)
2.235(3)
2.225(3)
2.512(2)
1.759(4)
1.836(5)
1.824(5)
1.152(5)
1.135(4)
U(1)ÀN(2)
U(1)ÀN(4)
U(1)ÀO(1)
Mn(1)ÀC(17)
Mn(1)ÀC(19)
C(16)ÀO(1)
C(18)ÀO(3)
C(20)ÀO(5)
2.234(3)
2.570(3)
2.496(3)
1.830(5)
1.824(4)
1.182(4)
1.140(5)
1.154(5)
U(1)ÀN(3)
U(1)ÀO(6)
Mn(1)ÀC(16)
Mn(1)ÀC(18)
Mn(1)ÀC(20)
C(17)ÀO(2)
C(19)ÀO(4)
10
11
12
U(1)ÀN(1)
2.219(2)
2.222(2)
2.539(2)
1.824(3)
1.808(2)
1.808(3)
1.150(3)
1.161(3)
U(1)ÀN(2)
U(1)ÀN(4)
U(1)ÀO(2)
Mn(1)ÀC(21)
Mn(1)ÀC(23)
C(20)ÀO(3)
C(22)ÀO(5)
C(24)ÀO(7)
2.236(2)
2.603(2)
2.545(2)
1.820(3)
1.802(2)
1.153(3)
1.156(3)
1.154(3)
U(1)ÀN(3)
U(1)ÀO(1)
Figure 6. Molecular structure of 9 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms omitted for clarity.
Mn(1)ÀC(20)
Mn(1)ÀC(22)
Mn(1)ÀC(24)
C(21)ÀO(4)
C(23)ÀO(6)
1931 cmÀ1 that are consistent with substantial redistribution
of the anionic charge of the manganese pentacarbonyl fragment
to the carbonyl groups by manganeseÀcarbonyl backbonding
(Table 4). Based on a comparison with 10À12, we tentatively
assign the stretch at 1709 cmÀ1 to the isocarbonyl group. The
presence of four carbonyl stretches in the FTIR spectrum of 9 is
consistent with the approximate C2v symmetry of the coordinated
Mn(CO)5À anion in the solid state structure of 9 (vide infra).
The crystal structure of complex 9 confirms the presence of a
bridging isocarbonyl CO ligand between the uranium and
manganese centers (Figure 6 and Table 5), and this is reminis-
cent of [Yb(Cp*)2(THF)(μ-OC)Co(CO)3].48 The coordina-
tion geometry around uranium is best described as distorted
octahedral, with the TrenTMS ligand coordinating facially, occu-
pying four coordination sites. O(1) resides essentially trans to the
amine nitrogen N(4), and a molecule of THF completes the
coordination sphere. The geometry of the TrenTMS ligand is
unexceptional, with the UÀNamide and UÀNamine bond lengths
of 2.231(3) (av.) and 2.570(3) Å, respectively, being in line with
the Tren compounds described above. The U(1)ÀO(1) and
U(1)ÀO(6) bond lengths of 2.496(3) and 2.512(2) Å, respec-
tively, are also unexceptional. The Mn(1) atom adopts a slightly
distorted square pyramidal geometry, with MnÀC and CÀO
bond lengths lying within the range of those in previously
reported complexes.39 The formation of an isocarbonyl linkage
rather than a UÀMn bond highlights the oxophilicity of uranium
but also contrasts with the complex [(ButO)3TiMn(CO)5] that
contains a highly oxophilic titanium center but still forms a
TiÀMn bond.49 Given that three ButO groups at titanium can be
considered to present a fairly sterically congested coordination
environment, this suggests that the absence of a UÀMn bond in
9 might be attributed to the likely poor orbital overlap between
3d Mn and 5f/6d U rather than to steric factors, although the
latter could play a significant role. Of course, the nature of the
solvent could also affect the likelihood of UÀMn bond formation.
However, reactions were found to be sluggish in hydrocarbon
solvents. We therefore tried 1,2-dimethoxyethane (DME)
solvent.
U(1)ÀN(1)
2.201(3)
2.221(3)
2.640(2)
1.788(3)
1.838(4)
1.825(4)
1.146(4)
1.192(4)
U(1)ÀN(2)
U(1)ÀN(4)
2.211(3)
2.631(3)
2.534(2)
1.837(4)
1.762(3)
1.175(4)
1.144(4)
1.160(4)
U(1)ÀN(3)
U(1)ÀO(1)
U(1)ÀO(4A)
Mn(1)ÀC(17)
Mn(1)ÀC(19)
C(16)ÀO(1)
C(18)ÀO(3)
C(20)ÀO(5)
Mn(1)ÀC(16)
Mn(1)ÀC(18)
Mn(1)ÀC(20)
C(17)ÀO(2)
C(19)ÀO(4)
U(1)ÀN(1)
2.212(9)
2.227(9)
2.479(8)
1.752(11)
1.846(12)
1.853(13)
1.159(14)
1.165(13)
U(1)ÀN(2)
U(1)ÀN(4)
2.204(9)
2.599(9)
2.705(8)
1.833(11)
1.781(11)
1.193(13)
1.124(14)
1.143(15)
U(1)ÀN(3)
U(1)ÀO(1)
U(1)ÀO(4A)
Mn(1)ÀC(26)
Mn(1)ÀC(28)
C(25)ÀO(1)
C(27)ÀO(3)
C(29)ÀO(5)
Mn(1)ÀC(25)
Mn(1)ÀC(27)
Mn(1)ÀC(29)
C(26)ÀO(2)
C(28)ÀO(4)
spans the range +19 to À47 ppm, which is diagnostic of its
conversion from 9. The solution magnetic moment of 10 was
found to be 3.35 μB (Table 2), which is surprisingly high
compared to cationic 7, which underscores the complexity of
À
uranium orbital magnetism. The free Mn(CO)5 has D3h
symmetry and should only exhibit two FTIR active bands
according to Group Theory considerations. However, the FTIR
spectrum of 10 contains four carbonyl stretching bands at 1859,
1892, 1921, and 1939 cmÀ1 (Table 4). This phenomena most
likely arises from solid-state effects whereby the local symmetry
at manganese is lowered from D3h, for example, to C2v, which
facilitates the emergence of more FTIR active bands. This
postulate is supported by the crystal structure of 10 (vide infra).
Complex 10 (Figure 7 and Table 5) crystallizes as a separated
ion pair complex. The uranium center is 6-coordinate and adopts
a distorted octahedral geometry due to the bite angle of the DME
ligand [63.94(5)ꢀ]. The coordinated molecule of DME occupies
two coordination sites at uranium, with O(2) residing axially,
Repeating reactions of 7 with K[Mn(CO)5] in DME or 5 or 6
with [HMn(CO)5] or adding DME to 9 resulted in formation
of the separated ion pair complex [U(TrenTMS)(DME)]-
[Mn(CO)5] (10, Scheme 3). Complex 10 was isolated in 24%
crystalline yield as yellow blocks. The 1H NMR spectrum of 10
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Scheme 4. Synthesis of 12
Figure 7. Molecular structure of 10 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms omitted for clarity.
carbonyl groups in the solid state (vide infra). In common with
9, we tentatively assign the carbonyl stretch at 1731 cmÀ1 to an
isocarbonyl group.
Complex 11 crystallizes as a centrosymmetric, THF free,
dimer with distorted octahedral uranium centers (Figure 8
and Table 5) and is reminiscent of [Yb(Cp*)2(μ-OC)2Mn-
(CO)3]2.50 The UÀNamide bond distances span the range 2.201-
(3)À2.221(3) Å. These distances can be considered relatively
short, perhaps reflecting that the coordination sphere of each
uranium center is completed by two oxygen atoms from iso-
carbonyl groups that must be considered as weakly bound
considering DME and THF are capable of displacing them.
The U(1)ÀO(1) and U(1)ÀO(4) bond lengths are 2.640(2)
and 2.534(2) Å, respectively, which reflects the fact the former is
trans to an anionic amide whereas the latter resides trans to a
neutral, dative amine center. This is reflected in the MnÀC bond
lengths. For example, the longer U(1)ÀO(1) bond compared to
the U(1)ÀO(4) suggests there is less formal negative charge on
O(1) compared to O(4), which implies that the backbonding
from manganese to carbon is less. Therefore, the Mn(1)ÀC(16)
bond length [1.788(3) Å] should be longer than the Mn(1)ÀC-
(19) distance [1.762(3) Å], which is indeed the case. Further-
more, increased backbonding from manganese to carbon as a
consequence of charge polarization toward the electropositive
uranium center is evidenced by longer Mn(1)ÀC(17), Mn-
(1)ÀC(18), and Mn(1)ÀC(20) bond lengths of 1.837(4),
1.838(4), and 1.825(4) Å compared to the Mn(1)ÀC(16) and
Mn(1)ÀC(19) distances. Within the latter three MnÀC bonds,
the axial pair [C(17) and C(18)] appear to be elongated
compared to C(20) as observed in 10. Lastly, the expected
lengthening of the OÀCcarbonyl bond distances in the bridging
isocarbonyls, as a result of increased MnÀC backbonding, is
evident in 11. For example, the isocarbonyl C(16)ÀO(1) and
C(19)ÀO(4) bond lengths are 1.175(4) and 1.192(4) Å,
respectively, and are longer than the terminal C(17)ÀO(2),
C(18)ÀO(3), and C(20)ÀO(5) bond distances of 1.146(4),
1.144(4), and 1.160(4) Å, respectively.
Figure 8. Molecular structure of 11 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms omitted for clarity.
essentially trans to the amine nitrogen N(4) and O(1) in an
equatorial location. The geometry of the TrenTMS ligand is
unexceptional, and the UÀNamide and UÀNamine bond lengths
of 2.2255(18) (av) and 2.6031(17) Å, respectively, are relatively
short and compare well to the corresponding values in cationic 7. The
U(1)ÀO(1) and U(1)ÀO(2) bond lengths of 2.5388(14) and
2.5454(14) Å, respectively, are unexceptional. The manganese center
adopts a distorted, axially elongated, trigonal bipyramidal geometry as
evidenced by equatorial Mn(1)ÀC(22), Mn(1)ÀC(23), and Mn-
(1)ÀC(24) distances of 1.808(2), 1.802(2), and 1.808(3) Å,
respectively, and longer axial Mn(1)ÀC(20) and Mn(1)ÀC(21)
bond lengths of 1.824(3) and 1.820(3) Å, respectively. This axial
elongation is rationalized by simple crystal field considerations and is
consistent with the observed FTIR spectrum for 10.
Reasoning that donor solvent might be precluding formation
of a UÀMn bond, as found in 10, we examined the reaction
between solvent free 5 and 6 with [HMn(CO)5] in nondonor
solvent. Accordingly, yellow [{U(TrenTMS)(μ-OC)2Mn(CO)3}2]
(11) was isolated in 73% crystalline yield (Scheme 3). Despite
the dimeric formulation determined in the solid state (vide infra),
the 1H NMR spectrum contains only three resonances spanning
the range +20 to À45 ppm. Variable temperature NMR was
not investigated due to the low solubility of 11 in arene solvents,
and the addition of THF afforded 9. The solution magnetic
moment of dimeric 11 is 3.93 μB (Table 2). The FTIR spectrum
of 11 exhibits five carbonyl bands at 1731, 1814, 1823, 1938,
and 1952 cmÀ1 (Table 4), which reflects the relatively low
symmetry at manganese and the presence of two bridging
For completeness, we investigated the reaction of the known
cyclometalated, tuck-in complex [U{N(CH2CH2NSiMe2But)2-
(CH2CH2NSiMeButCH2)}] (C),20 with [HMn(CO)5] in to-
luene. Accordingly, yellow-green crystals of [{U(TrenDMSB
)
(μ-OC)2Mn(CO)3}2] [12, TrenDMSB =N(CH2CH2NSiMe2But)3]
were isolated in 60% yield (Scheme 4). Thus, formal salt, amine,
and alkane elimination methods provide accessto uranium manga-
nese carbonylate complexes. Like 11, the 1H NMR spectrum of
12 is relatively simple and exhibits four resonances over the range
+16 to À38 ppm despite the dimeric formulation in the solid
state, and variable temperature NMR experiments were not
practicable due to the poor solubility of 12 in arene solvents.
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Figure 10. Molecular structure of 13 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms omitted for clarity.
Figure 9. Molecular structure of 12 with selective atom labeling and
probability ellipsoids set at 30%. Hydrogen atoms omitted for clarity.
although the reaction of 7 with K[MnCp2] proceeds under a
variety of reaction conditions with elimination of potassium
tetraphenylborate, significant quantities of manganocene were
isolated from reaction mixtures, and fractional crystallization
afforded the oxo complex [{U(TrenTMS)}2(μ-O)] (13) as
yellow plates in 82% isolated yield (Scheme 5). The oxo-group
abstraction most likely originates from the coordinated THF
solvent in 7,53 and we propose that, following salt elimination, a
putative [U(TrenTMS)MnCp2] complex is formed but homolytic
bond cleavage occurs to yield 17 valence electron manganocene
and [U(TrenTMS)]. This would necessarily require inner-sphere
electron transfer, but we also cannot rule out an outer-sphere
electron transfer mechanism. The latter complex would be highly
reactive by virtue of its uranium(III) formulation, resulting in
oxo-abstraction and favorable oxidation of uranium from a III to
IV state.
Scheme 5. Synthesis of 13
The solution magnetic moment of 12 was found to be 4.09 μB
(Table 2), which is comparable to that of 11. The FTIR spectrum
of 12 contains only three clear-cut carbonyl absorptions at 1734,
1806, and 1956 cmÀ1 (Table 4), compared to five absorptions for
11, but these bands are broad and clearly obscure other absorÀp1-
tions in this region. The isocarbonyl stretching band at 1734 cm
for 12, assigned on the basis of 9 and 11, is shifted only 3 cmÀ1
from the corresponding band in 11.
The structure of 12 (Figure 9 and Table 5) is very similar to
that of 11. Indeed, regarding the manganese pentacarbonyl
fragment, exactly the same trends are observed regarding the
MnÀC and CÀO bond lengths. Specifically, the isocarbonyl
groups exhibit shorter MnÀC bonds and longer CÀO bonds
compared to the terminal carbonyl groups, as a result of increased
backbonding to facilitate charge polarization toward the electro-
philic uranium centers, and within the latter group, the axial
carbonyls show elongated MnÀC bonds compared to the
equatorial carbonyl.
Oxo Derivative. The formation of 9À12 suggested that the
formation of uraniumÀmanganese bonds is unlikely to occur in
the presence of carbonyl groups due to isocarbonyl bonding
being favored for oxophilic uranium(IV). Since we have had
significant success with the rhenocene fragment, we investigated
the use of manganocene, since the 18-electron potassium com-
plex K[MnCp2]51 is known. However, we did not investigate the
potential use of [HMnCp2] due to its unstable nature.52
Although K[MnCp2] is accessible, it is also relatively unstable
and easily decomposes to the 17-electron parent manganocene.
Therefore, we selected complex 7 for this reaction because we
surmised that any sluggish reactivity could not be countered with
thermolysis due to the instability of K[MnCp2]. However,
The identity of 13 was confirmed by X-ray diffraction
(Figure 10). Complex 13 crystallizes with N(2)ÀU(1)ÀO(1)
aligned along a crystallographic 3-fold axis, and O(1) resides on
an inversion center. The U(1)ÀN(1) and U(1)ÀO(1) bond
lengths of 2.263(2) and 2.13197(19) Å, are unremarkable and
consistent with the uranium(IV) formulation of 13.
’ SUMMARY AND CONCLUSIONS
To summarize, we have reported a series of halide, amide, and
cationic separated ion pair derivatives of a triamidoamine ur-
anium complex that represent valuable precursors for nonaqu-
eous uranium chemistry. Whereas the use of alkyl derivatives
gives cyclometalation chemistry and fragmentation of tetraphe-
nylborate anion, the corresponding amide derivatives yield the
anticipated separated ion pair derivatives in a straightforward
manner. The potential utility of the halide, amide, and cationic
complexes is demonstrated by the synthesis of a range of
manganese carbonylate complexes. No uraniumÀmanganese
bonds were formed, and instead, isocarbonyl linkages dominate
in the products formed from a variety of routes and precursors.
Therefore, we conclude that, in these Tren systems, the valence
orbital on manganese is possibly too contracted to make bonding
with oxophilic 5f/6d uranium(IV) favorable when isocarbonyl
linkages are available. Additionally, sterics are likely to play a role
in the preferential formation of isocarbonyl linkages. Attempts to
prepare a uraniumÀmanganese bond with the manganocene
anion were unsuccessful, which possibly suggests that the
formation of such linkages is inherently unfavorable. We are
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currently investigating the reactivity of 9À12 and will report on
by filtration and washed with cold pentane (2 Â 2 mL). Yield: 0.76 g,
50%. Anal. Calcd for C21H57N5Si5U: C, 33.27; H, 7.58; N, 9.24%.
Found: C, 33.18; H, 7.53; N, 9.39%. 1H NMR: (C6D6, 298 K) δ À6.88
(s, 18H, {N(SiMe3)2}), À3.85 (s, 27H, SiMe3), À1.83 (6H, s, CH2),
17.08 (s, 6H, CH2). FTIR ν/cmÀ1 (Nujol): 1725 (w), 1658 (w), 1258
(s), 1246 (s), 1180 (w), 1146 (m), 1137 (m), 1056 (s), 1028 (m), 1018
(m), 933 (vs), 898 (m), 838 (vs), 773 (s), 740 (m), 723 (m), 672 (m),
609 (m), 588 (w), 566 (w), 550 (w), 522 (w), 465 (w), 437 (m). μeff
(Evans method, d8-THF, 298 K): 3.03 μB.
this work in due course.
’ EXPERIMENTAL SECTION
General. All manipulations were carried out using standard Schlenk
techniques, or an MBraun UniLab glovebox, under an atmosphere of dry
nitrogen. Solvents were dried by passage through activated alumina
towers and degassed before use. All solvents were stored over potassium
mirrors, with the exception of THF and DME, which were stored over
activated 4 Å molecular sieves. Deuterated solvents were distilled from
potassium, degassed by three freezeÀpumpÀthaw cycles and stored
Preparation of [U(TrenTMS)(THF)2][BPh4] (7). THF (40 mL)
was added to a cold (À78 ꢀC) mixture of 5 (1.94 g, 2.50 mmol) and
Et3NH BPh4 (1.05 g, 2.50 mmol). The resulting suspension was
3
under nitrogen. Compounds 1,27 2,28 C,20 [Li(NCy2)],31 Et3NH BPh4,54
allowed to warm to ambient temperature while being stirred over 1 h,
before being stirred at ambient temperature for a further 16 h. Volatiles
were removed in vacuo to yield a yellow-green oil. Toluene (50 mL) was
added and gently warmed to 60 ꢀC while stirring, before being allowed
cool to ambient temperature to yield a yellow-brown solution and green
oil. The solution was decanted from the oil, reduced to 25 mL in vacuo
and was stored at ambient temperature for 21 days to yield a small crop
3
Et3NH BArf4,45 K[Mn(CO)5],46 [HMn(CO)5],47 and K[MnCp2]51
were prepared according to published procedures.
3
1H NMR spectra were recorded on a Bruker 400 spectrometer
operating at 400.2 MHz; chemical shifts are quoted in parts per million
and are relative to TMS. FTIR spectra were recorded on a Bruker Tensor
27 spectrometer. Elemental microanalyses were carried out by Medac
Ltd., U.K. The very small yield of 4 precluded any analysis other than its
crystal structure. Satisfactory CHN data could not be obtained for 10;
of yellow-green crystals of 7 C7H8 suitable for single-crystal X-ray
3
crystallography. Alternatively, the oil was vigorously stirred in 80 mL
of hexane for 7 days to yield a pale green free-flowing precipitate.
Yield: 0.29 g, 10% (crystalline); 2.73 g, 95% (powder). The synthesis of
7 from 6 is analogous. Anal. Calcd for C47H75BN4O2Si3U: C, 53.19; H,
7.12; N, 5.28%. Found: C, 52.90; H, 6.78; N, 5.35%. 1H NMR: (d8-THF,
298 K) δ À42.90 (s, 6H, CH2), À0.07 (m, 12H, ArÀH), 1.77 (m, 8H,
ArÀH), 3.84 (s, 8H, THF), 4.10 (s, 8H, THF), 7.53 (s, 27H, SiMe3),
15.54 (s, 6H, CH2). 11B NMR: (d8-THF, 298 K) δ À10.17. FTIR ν/
cmÀ1 (Nujol): 1949 (s), 1882 (w), 1819 (w), 1766 (w), 1658 (w), 1580
(s), 1304 (w), 1250 (s), 1182 (w), 1142 (w), 1069 (m), 1054 (m), 1032
(m), 1012 (m), 931 (s), 898 (s), 837 (s), 792 (m), 776 (m), 739 (m),
731 (m), 706 (s), 681 (w), 607 (m). μeff (Evans method, d8-THF, 298
K): 2.10 μB.
1
the H NMR spectrum of 10 is therefore included in the Supporting
Information (Figure S3).
Preparation of [{U(TrenTMS)(μ-I)}2] (3). Compound 2 (3.16 g,
3.97 mmol) was sublimed at 160 ꢀC at 10À6 mmHg for 8 h to yield a
yellow crystalline solid in quantitative yield. This was dissolved in hot
(70 ꢀC) toluene (5.0 mL), filtered while hot, and then stored at À30 ꢀC
for 72 h to yield yellow-green crystals of 3 (3 0.5C7H8 and 3 2C7H8
3
3
from different batches) suitable for single-crystal X-ray crystallography.
Yield: 2.59 g, 80%. Anal. Calcd for C30H78I2N8Si6U2: C, 24.86; H, 5.42;
N, 7.73%. Found: C, 24.21; H, 5.36; N, 6.93%. 1H NMR: (C6D6, 298 K)
δ À45.17 (s, 12H, CH2), 12.35 (s, 54H, SiMe3), 15.19 (s, 12H CH2).
FTIR v/cmÀ1 (Nujol): 1726 (w), 1260 (m), 1248 (m), 1141 (m), 1083
(m), 1053 (m), 927 (m), 896 (m), 839 (s), 800 (m), 743 (w), 723 (w),
678 (m), 623 (m). μeff (Evans method, 298 K): 3.88 μB.
Preparation of [{U(TrenTMS)(THF)}2(μ-Cl)][BArf4] (8). THF
(40 mL) was added to a cold (À78 ꢀC) mixture of 5 (0.62 g, 0.73 mmol)
and Et3NH BArf4 (0.70 g, 0.73 mmol). The resulting suspension was
Preparation of [U(TrenTMS)(NCy2)] (5). Toluene (30 mL) was
added to a cold (À78 ꢀC) mixture of 1 (0.71 g, 1.00 mmol) and lithium
dicyclohexylamide (0.19 g, 1.00 mmol). The resulting suspension was
allowed to warm to ambient temperature while being stirred over 1 h,
before being stirred at ambient temperature for a further 16 h. Volatiles
were removed in vacuo from the yellow-brown turbid reaction mixture
to yield a brown solid. Hexane (20 mL) was added, and the resulting
suspension was allowed to settle. The brown solution was filtered away
from the off-white precipitate, before the solvent was reduced in volume
to 10 mL in vacuo and stored at À80 ꢀC for 18 h to yield yellow crystals
of 5 suitable for single-crystal X-ray crystallography. Yield: 0.56 g, 78%.
Anal. Calcd for C35H61N5Si3U: C, 41.68; H, 7.90; N, 9.00%. Found: C,
40.87; H, 8.49; N, 9.21%. 1H NMR: (C6D6, 298 K) δ À16.07 (s, 27H,
SiMe3), À6.10 (s, 6H, CH2), 5.86 (4H, s, CyÀCH2), 5.98 (s, 4H,
CyÀCH2), 7.87 (s, 4H, CyÀCH2), 12.03 (s, 4H, CyÀCH2), 14.36 (s,
4H, CyÀCH2), 36.17 (s, 6H, CH2), 88.07 (s, 2H, CH). FTIR v/cmÀ1
(Nujol): 1590 (w), 1258 (m), 1244 (m), 1142 (w), 1110 (w), 1067 (m),
1025 (m), 926 (m), 899 (w), 835 (s), 770 (m), 742 (m), 722 (m), 693
(m), 677 (w). μeff (Evans method, 298 K): 2.79 μB.
3
allowed to warm to ambient temperature while being stirred over 1 h,
before being stirred at ambient temperature for a further 16 h. Volatiles
were removed in vacuo to yield a yellow-brown oil that could not be
purified. A solution of 1 (0.56 g, 0.73 mmol) in THF (10 mL) was then
added, and the mixture allowed to stir for 16 h. Volatiles were removed in
vacuo to afford a sticky brown-green solid. Toluene (40 mL) was added
and briefly warmed to 60 ꢀC, and the turbid mixture was allowed to cool
to ambient temperature while stirring before being stirred at ambient
temperature for a further 16 h. The brown suspension was allowed to
settle before the solution was filtered away from the fine precipitate,
reduced in volume to 1 mL and stored at À30 ꢀC for 12 h to yield pale
green crystals of 5 suitable for single-crystal X-ray crystallography. Yield:
0.61 g, 37%. Anal. Calcd for C70H106BClF24N8O2Si6U2: C, 37.56; H,
4.77; N, 5.01%. Found: C, 37.25; H, 4.42; N, 4.73%. 1H NMR: (C6D6,
298 K) δ À40.15 (s, 6H, CH2), À27.45 (s, 6H CH2), À25.80 (s, 6H
CH2), À19.91 (s, 6H CH2), 0.22 (m, 27H, SiMe3), 0.99 (m, 27H,
SiMe3), 4.60 (s, 8H, THF), 8.21 (m, 3H, ArÀH), 13.82 (s, br, 8H,
THF). FTIR ν/cmÀ1 (Nujol): 3403 (w), 1609 (w), 1280 (s), 1260 (m),
1164 (m), 1130 (s), 1058 (w), 1018 (w), 984 (w), 929 (w), 919 (w), 889
(w), 839 (m), 772 (w), 744 (w), 719 (m), 682 (w). μeff (Evans method,
298 K): 3.51 μB.
Preparation of [U(TrenTMS){N(SiMe3)2}] (6). THF (20 mL)
was added to a cold (À78 ꢀC) mixture of 2 (1.59 g, 2.0 mmol) and
[KN(SiMe3)2] (0.40 g, 2.0 mmol). The resulting suspension was
allowed to warm to ambient temperature while being stirred (1 h),
before being stirred at ambient temperature for a further 16 h. The dark
yellow turbid reaction mixture was filtered, and volatiles were removed
in vacuo to yield a pale yellow solid. Hexane (15 mL) was added, and the
resulting suspension was allowed to settle and was filtered. The dark
yellow solution was reduced in volume to 3 mL in vacuo and stored at
À30 ꢀC for 18 h to yield yellow crystals, which were collected at À30 ꢀC
Preparation of [U(TrenTMS)(THF)(μ-OC)Mn(CO)4] (9). THF
(30 mL) was added to a cold (À78 ꢀC) mixture of 7 (1.15 g, 1.00 mmol)
and K[Mn(CO)5] (0.234 g, 1.00 mmol). The mixture was allowed to
warm to room temperature and was stirred for 12 h. The mixture was
allowed to settle (1 h), and the solution was filtered from the white
precipitate. Volatiles were removed at reduced pressure, and the
resulting yellow-brown solid was extracted into warm toluene (10 mL).
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Inorganic Chemistry
ARTICLE
The volume of toluene was reduced to ∼1 mL, and 9 crystallized as
yellow blocks at À30 ꢀC over a period of 48 h. Yield: 54%. Anal. Calcd
for C24H47MnN4O6Si3U: C, 33.33; H, 5.48; N, 6.48%. Found: C, 34.11;
H, 5.67; N, 6.60%. 1H NMR (C6D6, 295 K): δ À42.25 (6H, s, br, CH2),
3.53 (4H, s, THF), 5.73 (27H, s, SiMe3), 15.65 (6H, d, br, CH2), 33.90
(4H, s, THF). FTIR v/cm-1 (Nujol): 1931 (s), 1918 (s), 1889 (s), 1709
(s), 1249 (m), 1082 (m), 1061 (m), 1018 (m), 928 (s), 907 (s), 836 (s),
775 (m), 718 (m), 675 (m). μeff (Evans method, C6D6, 295 K): 2.94 μB.
Preparation of [U(TrenTMS)(DME)][Mn(CO)5] (10). DME
(30 mL) was added to a cold (À78 ꢀC) mixture of 7 (1.15 g, 1.00
mmol) and K[Mn(CO)5] (0.234 g, 1.00 mmol). The clear green
reaction mixture was heated to ∼75 ꢀC for 3 h, whereupon the color
of the solution gradually changed from green to yellow-brown. The
solution was allowed to cool to ambient temperature (1 h), and volatiles
were removed in vacuo to yield a brown solid. Toluene (∼ 30 mL) was
added, and the resulting suspension was gently warmed to ∼60 ꢀC while
stirring, before being allowed to settle and cool to ambient temperature
(30 min). The yellow-brown solution was filtered away from the white
precipitate, before the solvent was reduced in volume to 1 mL in vacuo
and stored at À30 ꢀC for 72 h to yield yellow crystals of 10. Yield: 0.21 g,
24%. Anal. Calcd for C24H49MnN4O7Si3U: C, 32.65; H, 5.59; N, 6.34%.
Found: C, 31.84; H, 5.81; N, 8.62%. 1H NMR: (C6D6, 298 K) δ À46.14
(s, 6H, CH2); À40.41 (s, 2H, OCH2); 6.47 (s, 6H, OMe); 12.61 (s, 27H
SiMe3); 13.21 (s, 6H, CH2); 18.76 (s, 2H, OCH2). FTIR ν/cmÀ1
(Nujol): 2726 (w), 2045 (m), 2013 (m), 1982 (w), 1971 (w), 1960 (w),
1939 (s), 1921 (s), 1892 (s), 1859 (s), 1840 (m), 1261 (s), 1248 (s),
1020 (m), 927 (m), 839 (s), 773 (w), 722 (m), 684 (m). μeff (Evans
method, C6D6, 298 K): 3.35 μB.
v/cm-1 (Nujol): 2730 (w), 1956 (s), 1806 (s), 1734 (s), 1614 (w), 1259
(m), 1250 (m), 1078 (m), 1030 (m), 936 (w), 828 (m), 802 (m), 776
(m), 744 (w), 712 (w), 696 (w), 679 (m), 669 (m), 565 (w), 549 (m),
455 (m). μeff (Evans method, C6D6, 298 K): 4.09 μB.
Preparation of [{U(TrenTMS)}2(μ-O)] (13). THF (∼30 mL)
was added to a cold (À78 ꢀC) mixture of 7 (1.15 g, 1.00 mmol) and
K[MnCp2] (0.16 g, 1.00 mmol). The mixture was allowed to warm to
room temperature and was stirred for 12 h. The mixture was allowed to
settle (1 h), and the solution was filtered from the off-white precipitate.
Volatiles were removed at reduced pressure, and the resulting red-brown
solid was extracted into warm toluene (10 mL). The volume of toluene
was reduced to ∼1 mL, and 13 crystallized as yellow plates at À30 ꢀC
over a period of 48 h. Yield: 0.99 g, 82%. Anal. Calcd for C30H78N8O-
Si6U2: C, 29.74; H, 6.49; N, 9.25%. Found: C, 30.96; H, 6.50; N, 9.10%.
1H NMR (C6D6, 295 K): δ À25.59 (12H, s, CH2), À23.25 (54H, s,
SiMe3), 76.40 (12H, s, CH2). FTIR ν/cmÀ1 (Nujol): 1605 (w), 1550
(w), 1330 (m), 1247 (s), 1069 (s), 1059 (s), 926 (s), 893 (m), 771 (s),
721 (s), 685 (w), 673 (w), 548 (s), 432 (m), 412 (m). μeff (Evans
method, C6D6, 295 K): 2.95 μB.
X-ray Crystallography. Crystal data for compounds 2À13 are
given in the Supporting Information. Bond lengths are listed in Tables 1,
3, and 5. Crystals were examined variously on Bruker AXS SMART 1000
or SMART APEX CCD area detector diffractometers using graphite-
monochromated MoKα radiation (λ = 0.71073 Å). Intensities were
integrated from a sphere of data recorded on narrow (0.3ꢀ) frames by ω
rotation. Cell parameters were refined from the observed positions of all
strong reflections in each data set. Semiempirical absorption corrections
based on symmetry-equivalent and repeat reflections were applied. The
structures were solved by direct methods and were refined by full-matrix
least-squares on all unique F2 values, with anisotropic displacement
parameters for all non-hydrogen atoms, and with constrained riding
hydrogen geometries; Uiso(H) was set at 1.2 (1.5 for methyl groups)
times Ueq of the parent atom. The largest features in final difference
syntheses were close to heavy atoms and were of no chemical signifi-
cance. Highly disordered solvent molecules of crystallization in
Preparation of [{U(TrenTMS)(μ-OC)2Mn(CO)3}2] (11).
[Mn(CO)5H] (0.20 g, 1.00 mmol) in toluene (10 mL) was added to
a cold (À78 ꢀC) solution of 5 (0.78 g, 1.00 mmol) in toluene. The
resulting solution was allowed to warm to ambient temperature while
being stirred (1 h), before being stirred at ambient temperature for a
further 16 h. Volatiles were removed in vacuo to yield a yellow-brown
solid. Hexane (40 mL) was added, and the resulting suspension was
gently warmed to ∼50 ꢀC while stirring, before being allowed to settle
and cool to ambient temperature (30 min). The yellow-brown solution
was filtered away from the small amount of precipitate, before the
solvent was removed in vacuo. To the yellow-brown residue was added
hexane (2 mL) and toluene (1.25 mL), the suspension was warmed to
60 ꢀC, allowed to cool to ambient temperature, and stored at À30 ꢀC for
18 h to yield yellow crystals of 11 suitable for single-crystal X-ray
crystallography. Yield: 0.58 g (73%). Anal. Calcd for C40H78Mn2N8O10-
Si6U2: C, 30.30; H, 4.96; N, 7.07%. Found: C, 30.16; H, 5.01; N, 5.17%.
1H NMR: (C6D6, 298 K) δ À45.21 (s, 12H, CH2); 11.03 (s, 54H,
SiMe3); 19.25 (s, 12H CH2). FTIR ν/cmÀ1 (Nujol): 2361 (w), 2343
(w), 2062 (w), 2035 (m), 2014 (w), 1952 (s), 1938 (s), 1823 (s), 1814
(s), 1731 (s), 1590 (w), 1303 (w), 1260 (m), 1248 (m), 1180 (w), 1142
(w), 1074 (m), 1061 (m), 1020 (m), 928 (m), 903 (m), 870 (m), 834
(s), 772 (m), 747 (w), 723 (m), 682 (m), 669 (m), 617 (w), 589 (w),
571 (w), 547 (w). μeff (Evans method, C6D6, 298 K): 3.93 μB.
5 2C7H8, could not be modeled and were treated with the PLATON
3
SQUEEZE procedure.55,56 Programs were Bruker AXS SMART
(control) and SAINT (integration),57 and SHELXTL was employed
for structure solution and refinement and for molecular graphics.58
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic details for
b
2À13. This material is available free of charge via the Internet
at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: stephen.liddle@nottingham.ac.uk.
Preparation of [{U(TrenDMSB)(μ-OC)2Mn(CO)3}2] (12).
[Mn(CO)5H] (0.20 g, 1.00 mmol) in toluene (10 mL) was added to
a cold (À78 ꢀC) solution of C (0.72 g, 1.00 mmol) in toluene (10 mL).
The resulting solution was allowed to warm to ambient temperature
while being stirred (1 h), before being stirred at ambient temperature for
a further 16 h. Volatiles were removed in vacuo to yield a yellow-green
solid. To this was added toluene (∼ 10 mL), the suspension was warmed
to ∼60 ꢀC, allowed to cool to ambient temperature, and stored at
À30 ꢀC for 18 h to yield yellow-green crystals of 12 suitable for single-
crystal X-ray crystallography. Yield: 0.55 g (60%). Anal. Calcd for
C29H57MnN4O5Si3U: C, 37.89; H, 6.26; N, 6.10%. Found: C, 37.87;
H, 6.17; N, 6.36%. 1H NMR: (C6D6, 298 K) δ À38.24 (s, 12H, CH2);
’ ACKNOWLEDGMENT
We thank the Royal Society for a University Research Fellow-
ship (S.T.L.), the EPSRC, ERC, University of Nottingham, and
the U.K. National Nuclear Laboratory for generously supporting
this work, and Mr. A. J. Wooles (University of Nottingham) for
obtaining the FTIR spectra of K[Mn(CO)5] and [HMn(CO)5]
in Nujol.
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