Exploring the effects of reduction or lewis acid coordination on the U=O bond of the uranyl moiety

Article abstract of DOI:10.1021/ic802360y

Reaction of Li(ArNC(Ph)CHC(Ph)O) (^Aracnac; Ar ) 2,4,6-Me ₃C₆H₂) or Na(ArNC(Ph)CHC(Ph)O) (Ar ) 3,5- ^tBu₂C₆H₃) with 0.5 equiv of UO ₂Cl₂(THF)₃

Full text of DOI:10.1021/ic802360y

Inorg. Chem. 2009, 48, 3065-3072
Exploring the Effects of Reduction or Lewis Acid Coordination on the
UdO Bond of the Uranyl Moiety
Trevor W. Hayton* and Guang Wu
Department of Chemistry and Biochemistry, UniVersity of California Santa Barbara,
Santa Barbara, California 93106
Received December 10, 2008
Reaction of Li(ArNC(Ph)CHC(Ph)O) (Aracnac; Ar ) 2,4,6-Me3C6H2) or Na(ArNC(Ph)CHC(Ph)O) (Ar ) 3,5-tBu2C6H3)
with 0.5 equiv of UO2Cl2(THF)3 results in the formation of UO2(Aracnac)2 (Ar ) 2,4,6-Me3C6H2, 1; 3,5-tBu2C6H3, 2),
which were isolated as orange crystalline solids in good yields. The structure of 2 has been confirmed by X-ray
crystallography, while the solution redox properties of 1 and 2 have been measured by cyclic voltammetry. Complex
1 exhibits a reversible reduction feature at E1/2 ) -1.52 V (vs Fc/Fc+), while complex 2 exhibits a reduction
feature at -1.35 V (vs Fc/Fc+). Complexes 1 and 2 react with Cp*2Co to generate [Cp*2Co][UO2(Aracnac)2] (Ar )
2,4,6-Me3C6H2, 3; 3,5-tBu2C6H3, 4), in moderate to good yields. Both 3 and 4 have been fully characterized, while
the structure of 4 has also been determined by X-ray crystallography. Reaction of 2 with 2 equiv of B(C6F5)3 in
CH2Cl2 leads to the isolation of UO(OB{C6F5}3)(Aracnac)2 (Ar ) 3,5-tBu2C6H3) (5). Complex 5, generated in situ,
exhibits an irreversible reduction at -0.78 V (vs Fc/Fc+, 100 mV/s scan rate) which is considerably lower than the
reduction potential observed for 2, consistent with the removal of electron density from the uranyl moiety by
coordination of B(C6F5)3.
Introduction
induce much change in the U-O bond length.4-6 The uranyl
moiety can also be perturbed upon reduction to uranium(V).
For example, structural studies of [UO2(py)5][KI2(py)2],7,8
[UO2(OPPh3)4][OTf],9 and {[UO2(dbm)2]4[K6(py)10]}2+10 all
reveal slightly longer U-O(oxo) bonds than those observed
Uranyl (UO22+) is an exceptionally stable molecular
species, characterized by a linear OdUdO geometry, short
U-O bonds (ca. 1.78 Å), and substitutionally inert oxo
ligands.1 Because of this extraordinary stability, selective
functionalization of the uranyl oxo ligands is relatively rare.
However, several recent examples demonstrate that func-
tionalization is possible. For instance, coordination of two
potassium cations to one of the oxo ligands in a uranyl
macrocycle complex induces the reductive silylation of the
uranyl moiety,2 causing a notable lengthening of the func-
tionalized U-O bond. Coordination of the strong Lewis acid
B(C6F5)3 to one of the oxo ligands of uranyl also causes a
marked change to the uranyl fragment, increasing in the
U-O bond length of the coordinated oxo by about 0.1 Å.3
In contrast, the coordination of weaker Lewis acids to uranyl,
such as alkali metal cations or 3d transition metals, does not
1,11
2+
for UO2
;
however, the O-U-O angles are still 180°.
Processes that effect the complete substitution of the uranyl
oxo ligands are equally uncommon and are usually limited
to photochemical-mediated reactions,12 microbial activ-
ity,13-15 or powerful reducing agents.16
In this contribution we report the synthesis and characteriza-
tion of two uranyl(V) bis(ꢀ-ketoiminate) complexes, namely,
[Cp*2Co][UO2(Aracnac)2] (Ar ) 2,4,6-Me3C6H2, 3,5-tBu2C6H3).
These complexes contain the rare UVO2+ moiety, which has
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* To whom correspondence should be addressed. E-mail: hayton@
chem.ucsb.edu.
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10.1021/ic802360y CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 7, 2009 3065
Published on Web 03/05/2009

Hayton and Wu
recently been the focus of increased study.7,8,10,17-24 This
fragment readily disproportionates to UO22+ and U4+,25
ꢀ-ketoiminate complexes have been isolated,33 and this ligand
architecture has been successfully used to build Ti-based olefin
polymerization catalysts34 and Ni-based methyl methacrylate
polymerization catalysts.35 In addition, the related diphenyl-ꢀ-
diketonate ligand set has been previously used to stabilize U(V).
For example, the solid-state molecular structures of {[UO2-
(dbm)2]2[µ-K(py)2]2[µ8-K(py)]}22+ and {[UO2(dbm)2][K(18-
crown-6)]}2 were recently determined.10,22 Each complex is
built from the [UVO2(dbm)2]- fragment and held together with
bridging uranyl-oxo interactions. Furthermore, in situ reduction
of UO2(dbm)2(DMSO) leads to the formation of [UO2(dbm)2-
(DMSO)]-.36,37 These examples provide further justification for
using the ketoiminate ligand architecture.
Condensation of mesitylaniline or 3,5-di-tert-butylaniline
with dibenzoylmethane in refluxing toluene, using Zn(OTf)2
as a catalyst, results in the isolation of H(ArNC(Ph)CHC-
(Ph)O) (H(Aracnac); Ar ) 2,4,6-Me3C6H2, 3,5-tBu2C6H3), in
modest to good yields (eq 1). Alternately, the condensation
of 3,5-di-tert-butylaniline with dibenzoylmethane can also
be performed under solvent-less conditions. The condensation
of bulkier arylamines, such as 2,6-diisopropylaniline, with
dibenzoylmethane was not observed under these conditions,
presumably because of the steric bulk of the isopropyl
substitutents. In addition, we observe no evidence for the
formation of a ꢀ-diketimine.
a
property that has previously hampered its isolation and char-
acterization. We have also explored the reactivity of the
uranyl(VI) precursors, UO2(Aracnac)2, with B(C6F5)3. This has
provided us with the unprecedented opportunity to evaluate the
structural deformations of the uranyl moiety induced by either
reduction or Lewis acid coordination to an “yl” oxygen, while
keeping the equatorial ligand environment identical. These two
modes of reactivity may also provide a pathway by which
further functionalization of uranyl can be achieved. By studying
these interactions and discovering methods to effect the func-
tionalization of uranyl oxo ligands, we hope to develop novel
strategies for waste treatment and environmental remediation.
Results and Discussion
We have previously used a ꢀ-diketiminate ligand to stabilize
the UO2+ fragment.18,19 However, these complexes are ther-
mally unstable, possibly because of the relatively acidic methyl
protons on the ligand backbone.18,26-30 Thus, we have endeav-
ored to find a new ligand platform with similar electronic and
steric properties as the ꢀ-diketiminates but without the methyl
substituents attached to the ꢀ carbons of the ligand skeleton. In
this regard, the diphenyl-ꢀ-ketoiminate ligands are an attractive
option. This framework can be synthesized by condensation of
a substituted-aniline with dibenzoylmethane, under solventless
conditions,31 or in refluxing toluene.32 In this fashion we can
easily construct, in one step, a ꢀ-ketoimine with robust phenyl
substituents attached at the ꢀ-positions. Several transition-metal
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1991, 350, 413–416.
Deprotonation of the diphenyl-ꢀ-ketoimines is easily
achieved by reaction with either n-BuLi or NaN{SiMe3}2.
Subsequent addition of the alkali metal salt to 0.5 equiv of
UO2Cl2(THF)3 results in the formation of UO2(Aracnac)2 (Ar
) 2,4,6-Me3C6H2, 1; 3,5-tBu2C6H3, 2), which were isolable
as orange crystalline solids in good yields (eq 2).
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Complexes 1 and 2 are soluble in toluene, tetrahydrofuran
(THF), and CH2Cl2. Complex 1 exhibits two singlets in a
2:1 ratio at 2.23 and 2.42 ppm, respectively, in its 1H NMR
spectrum in CD2Cl2, which corresponds to the mesityl methyl
groups. 1 also exhibits a singlet at 6.15 ppm assignable to
the proton attached to the γ-carbon of the ketoiminate ring.
Similarly, complex 2 exhibits a singlet at 1.11 ppm in its 1H
NMR spectrum in CD2Cl2, which corresponds to the methyl
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3066 Inorganic Chemistry, Vol. 48, No. 7, 2009

Effects of Reduction on the UdO Bond of the Uranyl Moiety
Figure 2. Room temperature cyclic voltammogram for 1 in CH2Cl2 (vs
Fc/Fc+, 0.1 M [NBu4][PF6] as supporting electrolyte).
uranyl chromophore.41 Complex 1 also exhibits a strong
absorption at 355 nm (ε ) 31200 L · mol-1 · cm-1). This
absorption is red-shifted in complex 2 to 383 nm (ε ) 26000
L · mol-1 · cm-1). Both are probably attributable to a ligand-
to-metal charge transfer (LMCT) transition. The uncom-
plexed ligand, H(Aracnac) (Ar ) 3,5-tBuC6H3), also exhibits
a strong absorption in this region (386 nm, ε ) 13800
L · mol-1 · cm-1), but the molar absorptivity is considerably
lower.
Figure 1. Oak Ridge Thermal Ellipsoid Plot (ORTEP) diagram of
UO2(Aracnac)2 (Ar ) 3,5-tBu2C6H3) (2·2C7H8) with 50% probability
ellipsoids. Selected bond lengths (Å) and angles (deg): U1-O1 ) 1.755(5),
U1-O2 ) 2.255(5), U1-N1 ) 2.449(6), O1-U1-O1* ) 180, O2-U1-N1
) 73.4(2), O2-U1-N1* ) 106.6(2), O1-U1-O2 ) 89.7(2), O1-U1-N1
) 86.6(2).
groups of the tBu moieties, while the proton attached to the
γ-carbon of the ketoiminate ring is observed at 6.21 ppm.
The IR spectra of complexes 1 and 2 (as KBr mulls) exhibit
ν
asym(UdO) vibrations at 908 cm-1 and 911 cm-1, respec-
tively. These values are typical of uranyl(VI).38,39
The solution redox properties of complexes 1 and 2 have
been investigated by cyclic voltammmetry. The cyclic
voltammogram of 1 in CH2Cl2 reveals a reversible reduction
feature at E1/2 ) -1.52 V (vs Fc/Fc+) which we attribute to
j
Complex 2 crystallizes in the triclinic space group P1 as
a toluene solvate, 2 · 2C7H8, and its solid-state molecular
structure is shown in Figure 1. Complex 2 exhibits an
octahedral geometry with the two ꢀ-ketoiminate ligands
occupying the uranyl equatorial plane (O1-U1-O2 )
89.7(2)°, O1-U1-N1 ) 86.6(2)°). Moreover, the two N-aryl
substituents exhibit a trans orientation. The U-O(oxo) bond
length (U1-O1 )1.775(5) Å) is typical of the uranyl
fragment, while the U-O(acnac) and U-N bond lengths are
U1-O2 ) 2.255(5) Å and U1-N1 ) 2.449(6) Å, respec-
tively. The aryl substituents of the ꢀ-ketoiminate ligand lie
orthogonal to the uranyl equatorial plane, as is typically
observed with ꢀ-diketiminate complexes.40 The aryl substit-
uents are also tilted toward the uranyl moiety as indicated
by the relatively short U-Cipso contact (3.233(7) Å), provid-
ing excellent steric protection of the equatorial plane. The
N2O2 equatorial ligand environment provides a close match
to that observed in the previously isolated complex
UO2(Ar2nacnac)(acac).18 Not surprisingly, the U-N and
U-O bond lengths in 2 also mirror those observed in
UO2(Ar2nacnac)(acac).
+
the UO22+/UO2 redox couple (Figure 2). This potential is
similar to that observed for UO2(Ar2nacnac)(dbm) (dbm )
PhC(O)CHC(O)Ph).18 For complex 2, the cyclic voltammo-
gram in CH2Cl2 reveals a quasi-reversible reduction feature
at -1.35 V (vs Fc/Fc+). Notably, the difference in potential
between the cathodic and anodic waves is large (0.29 V at
100 mV/s), and increases with increasing scan rate. Similar
electrochemical behavior has been seen for other uranyl
complexes.42 When [NBu4][B{C6F5}4] is used as the sup-
porting electrolyte we observe a second reduction feature in
the cyclic voltammogram of 2 (see Supporting Information).
At a scan rates of 50 mV/s this feature is irreversible and is
centered at -2.06 V (vs Fc/Fc+). When the scan rate is
increased to 200 mV/s an anodic wave appears in the cyclic
voltammogram (ip,c/ip,a ) 1.64), suggesting that this feature
approaches electrochemical reversibility as the scan rate
increases.
In-line with the cyclic voltammetry results, 1 and 2 react
with Cp*2Co to generate tractable uranyl(V) complexes,
namely [Cp*2Co][UO2(Aracnac)2] (Ar ) 2,4,6-Me3C6H2, 3;
3,5-tBu2C6H3, 4), in moderate to good yields (eq 3). Both
complexes contain the paramagnetic uranyl(V) moiety, as
indicated by NMR spectroscopy. For instance, the 1H NMR
spectrum of 3 exhibits a broad resonance at -0.29 ppm,
which we attribute to the para methyl substituent of the
mesityl ring, while a broad resonance at 2.82 ppm is
The bright orange color of 1 and 2 can be attributed to
the prominent shoulders at 455 nm (ε ) 2330 L ·
mol-1 ·cm-1) and 493 nm (ε ) 1040 L ·mol-1 ·cm-1), in their
respective UV/vis spectra. These features may be due to the
(37) Mizuoka, K.; Tsushima, S.; Hasegawa, M.; Hoshi, T.; Ikeda, Y. Inorg.
Chem. 2005, 44, 6211–6218.
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Inorganic Chemistry, Vol. 48, No. 7, 2009 3067

Hayton and Wu
Figure 3. UV/vis spectra of 3 (1.6 × 10-3 M, blue line), and 4 (1.7 ×
10-3 M, pink line) in CH2Cl2.
assignable to the ortho methyl substituents. Similarly, the
1H NMR spectrum of 4 exhibits a broad resonance at -0.06
ppm, which we attribute to the tert-butyl substituents of the
aryl group.
Figure
4.
ORTEP
diagram
of
[Cp*2Co][UO2(Aracnac)2]
(4·2C6H14 ·4CH2Cl2) with 50% probability ellipsoids. Selected bond lengths
(Å) and angles (deg): U1-O1 ) 1.838(5), U1-O2 ) 2.364(6), U1-N1 )
2.513(6), O1-U1-O1* ) 180, O2-U1-N1* ) 109.6(2), O2-U1-N1
) 70.4(2), O1-U1-O2 ) 88.7(2), O1-U1-N1 ) 88.4(2).
shown in Figure 4. Complex 4 consists of discrete cation/
anion pairs: the closest intermolecular contact between the
uranyl complex and the decamethylcobaltocene cation is
C37-O1 ) 3.41 Å. Like 2, complex 4 possesses a distorted
octahedral geometry. The U-O(oxo) bond length is 1.838(5)
Å and the O1-U1-O1* angle is 180°. This distance is
longer than that observed in complex 2 but on par with those
observed in other uranyl(V) complexes.1,9,19 In addition, the
U-O(acnac) and U-N bond lengths are 2.364(6) Å and
2.513(6) Å, respectively. Both of these distances are also
longer than those observed in 2, which is consistent with
the presence of the larger U5+ ion. Complex 4 also exhibits
a short U-Cipso contact (3.21 Å).
Not surprisingly, complexes 3 and 4 are very air- and
moisture-sensitive. In addition, they are thermally unstable.
For instance, solutions of 4 in CD2Cl2 almost completely
decompose after standing for 24 h at room temperature.
Similar behavior is observed for the uranyl(V) Ar2nacnac
complexes, suggesting that changing the ꢀ substituents (from
Me to Ph) in the ligand backbone has no effect on the overall
stability of these species.18 Given the cyclic voltammogram
of complex 2 we have also explored the reduction of 4. Thus
reaction of 4 with Cp*2Co in CH2Cl2 results in a slow color
change to red; however, the only tractable product that can
be isolated from these reaction mixtures is the uncomplexed
ligand, H(Aracnac).
We have also studied the reactivity of our uranyl(VI)
ꢀ-ketoiminate complexes, 1 and 2, with B(C6F5)3. Addition
of 2 equiv of B(C6F5)3 to 1in CD2Cl2 results in no obvious
interaction between the two molecules, as determined by 1H
and 19F{1H} NMR spectroscopies. However, reaction of 2
(which contains tert-butyl substituents at the relatively remote
3 and 5 positions of the aryl ring) with 2 equiv of B(C6F5)3
in CH2Cl2 results is a rapid color change from orange to
brown (Scheme 1). Layering this solution with hexanes and
cooling to -25 °C leads to the isolation of UO(OB-
{C6F5}3)(Aracnac)2 (5) as a brown crystalline solid in good
The UV/vis spectra of complexes 3 and 4 in CH2Cl2 can
be found in Figure 3. The spectra exhibit absorptions that
are consistent with fff transitions and the presence of a 5f1
ion. For instance, complex 3 exhibits transitions in the visible
region, at 618 nm (ε ) 250 L · mol-1 · cm-1), 718 nm (ε )
460 L · mol-1 · cm-1), and 843 nm (ε ) 520 L · mol-1 · cm-1).
A nearly identical spectrum is observed for complex 4. Both
spectra mirror those observed for [Cp*2Co][U(Ar2nacnac)-
(acac)],18 and other uranyl(V) complexes.19,37 The IR spectra
of complex 3, recorded as a KBr pellet, is also consistent
with the presence of the uranyl(V) ion. For 3, the asymmetric
stretch of the uranyl group is assigned to the peak at 784
cm-1 (which is 124 cm-1 lower than the asymmetric stretch
observed for 1). However, no peak in the IR spectrum of 4
could be definitively identified as the νasym(UdO) stretch,
possibly because of overlap with the ligand vibrations.5 We
have also measured the magnetic susceptibility of complexes
3 and 4 in CD2Cl2 by Evans method.43,44 Complex 3 displays
an effective magnetic moment of 1.5 µB at room temperature,
which is less than the theoretical value calculated for a 5f1
ion using the L-S coupling scheme (µeff ) 2.57 µB).45
Complex 4 displays a similar effective magnetic moment
(µeff ) 1.6 µB). Both values are within the range of effective
22
+
magnetic moments previously measured for the UO2 ion.
Complex 4 was found to crystallize in the monoclinic
space group P21/c as a dichloromethane and hexane solvate,
4 · 2C6H14 · 4CH2Cl2. Its solid-state molecular structure is
(43) Evans, D. F. J. Chem. Soc. 1959, 2003–2005.
(44) Cai, S.; Walker, F. A.; Licoccia, S. Inorg. Chem. 2000, 39, 3466–
3478.
(45) Cotton, S. Lanthanide and Actinide Chemistry; John Wiley & Sons
Ltd.: West Sussex, England, 2006.
3068 Inorganic Chemistry, Vol. 48, No. 7, 2009

Effects of Reduction on the UdO Bond of the Uranyl Moiety
Scheme 1
yield. When only 1 equiv of B(C6F5)3 is used in the reaction
with 2, complex 5 is still formed; however, the isolated yields
are markedly lower.
coordinated to an oxo ligand of uranyl. The U-O bond
length of the complexed oxo ligand is 1.890(4) Å, which is
0.135 Å longer than the U-O bond length observed in 2.
The other uranium oxo ligand exhibits a bond length of
U1-O1) 1.777(4) Å, demonstrating the coordination of
B(C6F5)3 has little effect on the uncomplexed oxo ligand. In
addition, the uranyl moiety in 5 remains linear (O1-U1-O2
) 177.2(2)°). The B(C6F5)3 unit exhibits the anticipated
tetrahedral coordination environment with a B1-O2 bond
length of 1.584(7) Å. Finally, the U-N bond lengths in 5
are U1-N1 ) 2.397(5) Å and U1-N2 ) 2.417(5) Å, while
the U-O(acnac) bond lengths are U1-O3 ) 2.192(4) Å and
U1-O4 ) 2.194(4) Å.
The metrical parameters of 5 are similar to those observed
in the previously reported B(C6F5)3-uranyl adduct, UO{OB-
(C6F5)3}(NCN)2 [NCN ) (Me3SiN)CPh(NSiMe3)].3 This
complex exhibits U-O bond lengths of 1.898(3) Å and
1.770(3) Å for the B(C6F5)3-complexed and uncomplexed
oxo ligands, respectively, while the B-O bond length was
found to be 1.545(6) Å. There are also several examples of
B(C6F5)3 coordinating to an oxo ligand of a transition-metal
oxo complex.48-51 In these molecules the MdO bond is
The 1H NMR spectrum of 5 is qualitatively similar to that
observed for 2, but it exhibits modest changes to the chemical
1
shifts. One notable feature of its H NMR spectrum is a
broadening of the signal associated with the ortho protons
of the 3,5-tBu2-C6H3 aryl substituent, possibly because of a
decreased rate of rotation caused by coordination of B(C6F5)3.
The 19F{1H} NMR spectrum of 5 in C6D6 consists of 3 peaks
in 2:1:2 ratio at -68.3, -94.0, -100.8, respectively,
consistent with the incorporation of B(C6F5)3 into the product.
In addition, the resonance at -94.0 ppm (attributable to p-F)
is considerably broadened relatively to that observed for the
p-F resonance in uncoordinated B(C6F5)3. For comparison,
the 19F{1H} NMR spectrum of B(C6F5)3 (in CD2Cl2) consists
of 3 peaks in 2:1:2 ratio at -64.2, -80.0, -96.8, respec-
tively; quite different from those observed for 5. No signal
was observed in the 11B{1H} NMR spectrum of 5. The IR
spectrum of 3 exhibits a medium intensity peak at 845 cm-1
which we have assigned to the νasym(UdO) vibration. This
is in-line with the IR spectrum observed for the other known
uranyl B(C6F5)3 adduct.3 Complex 5 quickly reacts with
equimolar amounts of THF in C6D6, generating 2 and
(THF)B(C6F5)3, as determined 1H NMR spectroscopy. This
reaction is accompanied by a rapid color change from brown
to orange as complex 2 is formed.
We have also measured the redox properties of 5 by cyclic
voltammetry. Complex 5 was generated in situ in an
electrochemical cell by addition of B(C6F5)3 to complex 2.
Before the addition of B(C6F5)3, we observe two redox
couples (one at -1.35 V and one at about -2.0 V), as
anticipated for complex 2. After addition of 2 equiv of
B(C6F5)3, the features characteristic of complex 2 disappear
and two new features appear: one at -0.78 V (vs Fc/Fc+,
100 mV/s scan rate) and another at 1.79 V (vs Fc/Fc+, 100
mV/s scan rate). Both features are irreversible up to scan
rates of 2 V/s. We attribute the feature at -0.78 V to the
one-electron reduction of complex 5, while we attribute the
feature at -1.79 V to the reduction of unreacted
B(C6F5)3.46,47 Interestingly, the reduction potential for com-
plex 5 is approximately 700 mV lower than that observed
for 2, consistent with the removal of electron density from
the uranyl moiety by coordination of B(C6F5)3.
Figure 5. ORTEP diagram of UO(OB{C6F5}3)(Aracnac)2 (5·C6H14) with
30% probability ellipsoids. Selected bond lengths (Å) and angles (deg):
U1-O1 ) 1.777(4), U1-O2 ) 1.890(4), U1-N1 ) 2.397(5), U1-N2 )
2.417(5), U1-O3 ) 2.192(4), U1-O4 ) 2.194(4), B1-O2 ) 1.584(7),
O1-U1-O2 ) 177.2(2), O3-U1-N1 ) 109.8(2), O4-U1-N2 )
106.0(2), N2-U1-O3 ) 73.0(2), N1-U1-O4 ) 71.2(2), O1-U1-O3
) 91.0(2), O1-U1-O4 ) 88.4(2), O1-U1-N1 ) 90.4(2), O1-U1-N2
) 86.3(2), B1-O2-U1 ) 163.7(4).
j
Complex 5 crystallizes in the triclinic space group P1 as
a hexane solvate, 5·C6H14. Its solid-state molecular structure
is shown in Figure 5. The uranium center in 5 exhibits an
octahedral coordination geometry, with one B(C6F5)3 moiety
Inorganic Chemistry, Vol. 48, No. 7, 2009 3069

Hayton and Wu
typically elongated by approximately 0.1 Å upon coordina-
tion of B(C6F5)3,49-51 while the B-O bond length is
approximately 1.53 Å.48-50
Experimental Section
General Procedures. All reactions and subsequent manipulations
were performed under anaerobic and anhydrous conditions under
either a high vacuum or an atmosphere of nitrogen or argon. THF,
hexanes, diethyl ether, and toluene were dried by passage over
activated molecular sieves using a Vacuum Atmospheres solvent
purification system. C6D6, CD2Cl2, and THF-d8 were dried over
activated 4 Å molecular sieves for 24 h before use. B(C6F5)3 was
made by the published procedure, except that pentafluoroiodooben-
zene was used in place of pentafluorobromobenzene.52 UO2Cl2-
(THF)353 and NBu4[B{C6F5}4]54 were synthesized by the published
procedures. Cp*2Co was recrystallized from hexanes before use,
while all other reagent were purchased from commercial suppliers
and used as received.
NMR spectra were recorded on a Varian INOVA 400 or Varian
INOVA 500 spectrometer. 1H and 13C{1H} NMR spectra are
referenced to external SiMe4 using the residual protio solvent peaks
as internal standards (1H NMR experiments) or the characteristic
resonances of the solvent nuclei (13C NMR experiments). 19F{1H}
NMR spectra were referenced to external R,R,R-trifluorotoluene.
Elemental analyses were performed by the Microanalytical Labora-
tory at UC Berkeley. UV-vis spectra were recorded on an Ocean
Optics USB4000 UV-vis spectrometer equipped with a USB-DT
light source and IR spectra were recorded on a Mattson Genesis
FTIR spectrometer.
The structural characterization of complexes 2, 4, and 5
permits a thorough comparison of the metrical parameters
of the uranyl moiety after coordination of a Lewis acid or
after reduction to U(V). In both modes of reactivity, we see
that the two oxo ligands of the uranyl fragment do not deviate
from their usual trans arrangement, while the acnac ligands
are not displaced out of the equatorial plane. However in
both 4 and 5, the U-O(oxo) bond lengths diverge from their
typical values. For instance, the U-O(oxo) bond length in
4 is about 0.08 Å longer that observed in 2, while the
U-O(B(C6F5)3) bond length in 5 is about 0.14 Å longer than
the U-O bond length of the parent complex. Interestingly,
we also observe a slight decrease in the U-O(acnac)
distances upon coordination of B(C6F5)3. In particular, the
U-O(acnac) distances in 5 are about 0.05 Å shorter than
that observed in 2, which we attribute to the removal of
electron density from the uranyl center by B(C6F5)3.
Summary
The successful isolation of complexes 3 and 4 demon-
strates that a ꢀ-ketoiminate ligand set is capable of supporting
the reactive uranyl(V) moiety. However, even with our
carefully tailored ligand set, both 3 and 4 are still thermally
unstable, a characteristic they share with most of the
uranyl(V) complexes isolated thus far. However, the stability
Cyclic Voltammetry (CV) Measurements. CV experiments
were performed with a CH Instruments 600c Potentiostat, and the
data were processed using CHI software (version 6.29). All
experiments were performed in a glovebox using a 20 mL glass
vial as the cell. The working electrode consisted of a platinum disk
embedded in glass (2 mm diameter), the counter electrode was a
platinum wire, and the reference electrode consisted of AgCl plated
on Ag wire. Solutions employed during CV studies were typically
3 mM in the uranium complex and 0.1 M in [Bu4N][PF6]. All
potentials are reported versus the [Cp2Fe]0/+ couple. For all trials
ip,a/ip,c ) 1 for the [Cp2Fe]0/+ couple, while ip,c increased linearly
with the square root of the scan rate (i.e., ꢀV). Redox couples which
exhibited behavior similar to the [Cp2Fe]0/+ couple were thus
considered reversible.
{2,4,6-Me3C6H2}NHC(Ph)dCHC(Ph)O. A round-bottom flask
was charged with dibenzoylmethane (3.20 g, 14.3 mmol), mesity-
laniline (1.98 g, 14.6 mmol), and Zn(OTf)2 (50 mg). Toluene (25
mL) was added, and the resulting solution was refluxed for 72 h.
The volatiles were removed by distillation to provide an orange
oil, which was subsequently dissolved in hexanes (20 mL). This
solution was washed successively with 1 M NaOH (20 mL) and 1
M HCl (20 mL) and then dried over MgSO4. The volatiles were
then removed in vacuo to provide a yellow oil. 1.06 g, 21% yield.
1H NMR (CDCl3, 25 °C, 500 MHz): δ 2.14 (s, 6H, Me), 2.19 (s,
3H, Me), 6.10 (s, 1H, γ-CH), 6.74 (s, 2H, meta CH), 7.18-7.27
(m, 5H, aryl CH), 7.44 (m, 3H, aryl CH), 7.98 (m, 2H, ortho CH),
12.68 (s, 1H, NH). 13C{1H} NMR (CDCl3, 25 °C, 125 MHz): δ
18.7 (Me), 20.8 (Me), 93.8 (γ-C), 127.1, 127.7, 127.9, 128.2, 128.9,
129.5, 130.9, 134.3, 134.4, 136.1, 136.2, 140.1, 164.9 (ꢀ-CN), 189.0
(ꢀ-CO). ESI-MS: m/z 342 (M+H)+.
+
of 3 and 4 is greatly improved relative to that of UO2 (aq),
likely because of the bulky, substitutionally inert equatorial
ligand environment. The protection of the uranyl equatorial
plane by the aryl substituent of Aracnac is readily demon-
strated by the short U-Cipso carbon distances observed in
the solid-state molecular structures of 2, 4, and 5. Moreover,
the lack of reactivity between 1 and B(C6F5)3 confirms that
a bulky aryl substitutent (which projects bulk above and
below the uranyl equatorial plane) can curtail the ability of
a Lewis acid to interact with the uranyl oxygen atoms. This
lack of reactivity is most likely a steric phenomenon as
B(C6F5)3 can interact with the uranyl oxo ligands in the less
sterically encumbered analogue 2. Finally, inspection of the
solid-state molecular structures of 4 and 5, suggest that their
oxo ligands are more activated toward substitution than those
of the parent complex. Future studies will focus on attempts
+
to functionalize the oxo ligands in UO2 , particularly efforts
to cleave the U-O bond in a well-defined manner.
(46) Kwaan, R. J.; Harlan, C. J.; Norton, J. R. Organometallics 2001, 20,
3818–3820.
(47) Harlan, C. J.; Hascall, T.; Fujita, E.; Norton, J. R. J. Am. Chem. Soc.
1999, 121, 7274–7275.
(48) Sa´nchez-Nieves, J.; Royo, P.; Mosquera, M. E. G. Eur. J. Inorg. Chem.
2006, 2006, 127–132.
(49) Galsworthy, J. R.; Green, M. L. H.; Mu¨ller, M.; Prout, K. Dalton Trans.
1997, 1309–1314.
(50) Doerrer, L. H.; Galsworthy, J. R.; Green, M. L. H.; Leech, M. A.
Dalton Trans. 1998, 2483–2488.
(51) Doerrer, L. H.; Galsworthy, J. R.; Green, M. L. H.; Leech, M. A.;
Mu¨ller, M. Dalton Trans. 1998, 3191–3194.
(52) Chernega, A. N.; Graham, A. J.; Green, M. L. H.; Haggit, J.; Lloyd,
J.; Mehnert, C. P.; Metzler, N.; Souter, J. Dalton Trans. 1997, 2293–
2303.
(53) Wilkerson, M. P.; Burns, C. J.; Paine, R. T.; Scott, B. L. Inorg. Chem.
1999, 38, 4156–4158.
(54) LeSuer, R. J.; Buttolph, C.; Geiger, W. E. Anal. Chem. 2004, 76, 6395–
6401.
3070 Inorganic Chemistry, Vol. 48, No. 7, 2009

Effects of Reduction on the UdO Bond of the Uranyl Moiety
{3,5-tBu2C6H3}NHC(Ph)dCHC(Ph)O. To a vial charged with
a stir bar was added dibenzoylmethane (0.1792 g, 0.80 mmol), 3,5-
di-tert-butylaniline (0.1652 g, 0.80 mmol), and Zn(OTf)2 (10 mg).
The mixture of the two solids was warmed to 70 °C on a hot plate
resulting in the formation of an orange oil. After stirring for 18 h
the orange oil had solidified. Water (2 mL), and CH2Cl2 (2 mL)
were added to the solid to give an orange organic solution below
a colorless aqueous layer. The organic layer was then isolated and
dried with MgSO4, and all volatiles were removed in vacuo to
providing 0.1062 g. A further 0.041 g of powder was collected by
concentrating the original reaction mixture and cooling to -25 °C
for 24 h. Total yield: 0.1472 g, 36% yield. Anal. Calcd for
C58H64N2O4U·C7H8: C, 65.98; H, 6.13; N, 2.37. Found: C, 66.59;
1
H, 5.97; N, 2.22. H NMR (CD2Cl2, 25 °C, 500 MHz): δ 1.11 (s,
36H, Me), 6.21 (s, 2H, γ-H), 7.03 (s, 4H, ortho aryl CH), 7.27-7.34
(m, 12H, aryl CH), 7.43 (m, 6H, aryl CH), 7.53 (d, JHH ) 7.0 Hz,
4H, ortho CH). 13C{1H} NMR (CD2Cl2, 25 °C, 125 MHz): δ 31.4
(Me), 35.4 (CMe3), 100.7 (γ-C), 121.0, 122.6, 128.0, 128.6, 128.7,
128.8, 129.5, 130.9, 139.5, 141.5, 142.1, 152.9, 173.1 (ꢀ-CN), 178.8
(ꢀ-CO). UV/vis (CH2Cl2, 2.8 × 10-5 M): 285 nm (sh, ε ) 17100
L·mol-1 ·cm-1), 383 nm (ε ) 26000 L ·mol-1 ·cm-1), 493 nm (sh,
ε ) 1040 L ·mol-1 ·cm-1). IR (KBr pellet, cm-1): 1590(s), 1556(s),
1497(s), 1483(s), 1450(m), 1383(s), 1371(m), 1298(m), 1247(w),
1073(w), 1025(w), 932(w), 911(m) νasym(UdO), 905(w), 873(w),
759(w), 737(w), 715(w), 697(m), 609(w), 577(w).
1
provide an orange oil, 0.306 g, 93% yield. H NMR (CDCl3, 25
°C, 500 MHz): δ 1.06 (s, 18H, Me), 5.99 (s, 1H, γ-CH), 6.55 (d,
2H, JHH ) 1.5 Hz, ortho CH), 6.96 (s, 1H, para CH), 7.21-7.39
(m, 6H, meta and para CH), 7.90 (m, 4H, ortho CH), 12.98 (s, 1H,
NH). 13C{1H} NMR (CDCl3, 25 °C, 125 MHz): δ 31.1 (Me), 34.5
(CMe3), 96.3 (γ-C), 109.9, 117.4, 127.0, 128.1, 128.2, 128.4, 129.3,
131.0, 136.1, 138.2, 139.9, 151.0, 151.7 (ꢀ-CN), 161.6 (ꢀ-CO).
ESI-MS: m/z 412 (M+H)+. UV/vis (CH2Cl2, 7.8 × 10-5 M): 386
nm (ε ) 13800 L ·mol-1 ·cm-1).
[Cp*2Co][UO2(Aracnac)2] (Ar ) 2,4,6-Me3C6H2) (3). To a
stirring solution of 1 (0.0582 g, 0.061 mmol) in CH2Cl2 was added
Cp*2Co (0.0207 g, 0.063 mmol). The solution immediately turned
green-brown. After 10 min of stirring the solution was filtered
through a Celite column supported on glass wool (0.5 cm × 2 cm).
The supernatant was then layered with an equal volume of hexanes.
Storage of this solution at -25 °C for 48 h resulted in the deposition
of a yellow-brown powder, which was collected by decanting off
the supernatant (0.0462 g, 59% yield). Anal. Calcd for
C68H74CoN2O4U: C, 63.79; H, 5.83; N, 2.19. Found: C, 63.38; H,
5.74; N, 2.52. 1H NMR (CD2Cl2, 25 °C, 400 MHz): δ -0.29 (br s,
6H, Me), 2.22 (s, 30H, C5Me5), 2.82 (br s, 12H, Me), 3.33 (br s,
4H, aryl CH), 3.59 (br s, 2H, γ-CH), 4.41 (br s, 4H, aryl CH),
5.27 (br s, 4H, aryl CH), 5.59 (br s, 4H, aryl CH), 6.32 (br s, 2H,
aryl CH), 6.68 (br s, 2H, aryl CH), one set or aryl resonances was
not observed. UV/vis (CH2Cl2, 1.6 × 10-3 M): 501 nm (sh, ε )
710 L·mol-1 ·cm-1), 618 nm (ε ) 250 L·mol-1 ·cm-1), 718 nm
(ε ) 460 L ·mol-1 ·cm-1), 843 nm (ε ) 520 L ·mol-1 ·cm-1). IR
(KBr pellet, cm-1): 1586(m), 1558(m), 1497(s), 1474(s), 1415(s),
1384(m), 1328(w), 1309(w), 1298(w), 1272(w), 1213(m), 1121(w),
1077(w), 1060(w), 1025(m), 908(w), 899(w), 858(w), 834(w),
784(s) νasym(UdO), 746(m), 695(m), 629(w).
UO2(Aracnac)2 (Ar ) 2,4,6-Me3C6H2) (1). To a stirring toluene
suspension (3 mL) containing UO2Cl2(THF)3 (0.1803 g, 0.32 mmol)
was added Li[{2,4,6-Me3C6H2}NC(Ph)dCHC(Ph)O] (0.225 g, 0.64
mmol), which was prepared by deprotonation of {2,4,6-Me3C6H2}-
NHC(Ph)dCHC(Ph)O with 1 equiv of n-BuLi. This resulted in the
immediate formation of an orange solution concomitant with the
formation of an orange powder. After stirring for 1 h, the volatiles
were removed in vacuo and the resulting oil was dissolved in
CH2Cl2 (10 mL). This mixture was filtered through a Celite column
supported on glass wool (0.5 cm × 2 cm). The volume of the filtrate
was reduced in vacuo, and the solution was layered with an equal
volume of hexanes. Storage of this solution at -25 °C for 1 week
resulted in the deposition of an orange powder, which was collected
by decanting off the supernatant (0.1496 g). Further concentration
of the supernatant resulted in the deposition of a further 0.0295 g
of orange powder, for a total of 0.1791 g, 58% yield. Anal. Calcd
for C48H44N2O4U: C, 60.63; H, 4.66; N, 2.95. Found: C, 59.13; H,
1
4.42; N, 3.41. H NMR (C6D6, 25 °C, 400 MHz): δ 2.20 (s, 6H,
Me), 2.23 (s, 12H, Me), 6.08 (s, 2H, γ-CH), 6.77 (s, 4H, meta
CH), 7.00 (m, 6H, aryl CH), 7.26 (m, 6H, aryl CH), 7.34 (m, 4H,
aryl CH), 7.75 (d, 4H, JHH ) 7.2 Hz, ortho CH). 1H NMR (CD2Cl2,
25 °C, 400 MHz): δ 2.23 (s, 12H, Me), 2.42 (s, 6H, Me), 6.15 (s,
2H, γ-CH), 6.97 (s, 4H, meta CH), 7.29-7.35 (m, 6H, aryl CH),
7.45-7.52 (m, 10H, aryl CH), 7.85 (d, 4H, JHH ) 7.2 Hz, ortho
CH). 13C{1H} NMR (CD2Cl2, 25 °C, 125 MHz): δ 19.1 (Me), 21.3
(Me), 100.9 (γ-C), 127.9, 128.0, 128.5, 128.8, 130.2, 131.1, 134.7,
137.2, 138.6, 139.5, 173.5 (ꢀ-CN), 178.1 (ꢀ-CO). UV/vis (CH2Cl2,
1.2 × 10-5 M): 288 nm (sh, ε ) 19300 L ·mol-1 ·cm-1), 355 nm
(ε ) 31200 L ·mol-1 ·cm-1), 455 nm (sh, ε ) 2330 L ·mol-1 ·cm-1).
IR (KBr pellet, cm-1): 1587(m), 1557(s), 1495(s), 1469(s), 1439(s),
1380(s), 1297(m), 1278(m), 1213(m), 1185(w), 1159(w), 1116(w),
1063(m), 1024(m), 908(s) νasym (UdO), 857(m), 832(w), 811(w),
777(m), 767(m), 720(m), 693(m), 627(m), 574(m), 533(m).
UO2(Aracnac)2 (Ar ) 3,5-tBu2C6H3) (2). To a stirring Et2O
solution (3 mL) of {3,5-tBu2C6H3}NHC(Ph)dCHC(Ph)O (0.306 g,
0.74 mmol) was added NaN{SiMe3}2 (0.138 g, 0.75 mmol). After
10 min of stirring, UO2Cl2(THF)3 (0.207 g, 0.37 mmol) was added,
and the solution was stirred for a further 2 h, resulting in the
deposition of an orange powder. The solution was decanted off,
and the powder was dissolved in toluene (5 mL). This mixture was
filtered through a Celite column supported on glass wool (0.5 cm
× 2 cm). The solution was then layered with an equal volume of
hexanes, and the volume of the solution was reduced in vacuo
resulting in the deposition of an orange microcrystalline powder.
The powder was collected by decanting off the supernatant,
[Cp*2Co][UO2(Aracnac)2] (Ar ) 3,5-tBu2C6H3) (4). To a stirring
solution of 2 (0.0384 g, 0.027 mmol) in CH2Cl2 was added Cp*2Co
(0.0125 g, 0.037 mmol). The solution immediately turned bright
green. The solution was filtered through a Celite column supported
on glass wool (0.5 cm × 2 cm), and the supernatant was then
layered with an equal volume of hexanes. Storage of this solution
at -25 °C for 24 h resulted in the deposition of a large green blocks,
which were collected by decanting off the supernatant (0.0361 g,
72% yield). Anal. Calcd for C78H94CoN2O4U: C, 65.95; H, 6.67;
N, 1.97. Found: C, 65.73; H, 6.58; N, 2.14. 1H NMR (CD2Cl2, 25
°C, 400 MHz): δ -0.06 (br s, 36H, CMe3), 0.09 (br s, 4H, aryl
CH), 0.57 (br s, 2H, aryl CH), 1.64 (br s, 4H, aryl CH), 2.47 (s,
30H, C5Me5), 3.46 (br s, 2H, γ-CH), 4.20 (br s, 4H, aryl CH), 4.88
(br s, 4H, aryl CH), 5.41 (br s, 4H, aryl CH), 6.12 (br s, 2H, aryl
CH), 6.42 (br s, 2H, aryl CH). UV/vis (CH2Cl2, 1.7 × 10-3 M):
620 nm (ε ) 250 L · mol-1 · cm-1), 725 nm (ε ) 460 L ·
mol-1 ·cm-1), 846 nm (ε ) 520 L ·mol-1 ·cm-1). IR (KBr pellet,
cm-1): 1588(s), 1567(m), 1498(s), 1482(s), 1455(s) 1392(m),
1327(m), 1295(m), 1249(m), 1214(w), 1182(w), 1134(w), 1072(m),
1056(m), 1025(m), 988(w), 889(br m), 837(w), 758(sh), 714(m),
697(m), 617(w), 574(w).
UO(OB{C6F5}3)(Aracnac)2 (Ar ) 3,5-tBu2C6H3) (5). To a
stirring solution of 2 (0.0517 g, 0.047 mmol) in CH2Cl2 (2 mL)
was added B(C6F5)3 (0.0477 g, 0.093 mmol). The solution im-
mediately turned brown. Hexanes (4 mL) was added, and the
Inorganic Chemistry, Vol. 48, No. 7, 2009 3071

Hayton and Wu
Table 1. X-ray Crystallographic Data for Complexes 2·2C7H8, 4·2C6H14 ·4CH2Cl2, and 5·C6H14
2·2C7H8 4·2C6H14 ·4CH2Cl2
C72H80N2O4U
5·C6H14
empirical formula
crystal habit, color
crystal size (mm)
crystal system
space group
volume (Å3)
a (Å)
C94H130CoCl8N2O4U
C82H78BF15N2O4U
block, orange
0.15 × 0.10 × 0.06
triclinic
block, green
cube, brown
0.25 × 0.20 × 0.15
triclinic
0.20 × 0.15 × 0.08
monoclinic
j
j
P1
P1
P21/c
1540.6(5)
10.234(2)
11.042(2)
15.124(3)
70.187(3)
88.089(3)
73.812(3)
1
4778(2)
13.376(1)
15.880(2)
22.599(2)
90
92.861(3)
90
2
3783.6(7)
12.327(1)
13.855(2)
22.295(2)
86.873(2)
85.589(2)
86.192(2)
2
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
Z
formula weight (g/mol)
1275.4
1.375
2.684
650
1932.6
1.339
2.130
1990
1689.3
1.483
2.233
1696
density (calculated) (Mg/m3)
absorption coeff. (mm-1
F000
)
total no. reflections
unique reflections
final R indices [I > 2σ(I)]
largest diff. peak and hole (e- Å-3
GOF
12036
5795
39651
9947
33066
15422
R1 ) 0.059, wR2 ) 0.139
1.42 and -1.71
0.968
R1 ) 0.080, wR2 ) 0.225
3.27 and -3.07
1.080
R1 ) 0.061, wR2 ) 0.145
4.01 and -2.11
1.016
)
volume of the solution was reduced in vacuo until incipient
precipitation was observed. The solution was then layered with
another aliquot of hexanes (2 mL). Storage of this solution at -25
°C for 24 h resulted in the deposition of a brown microcrystalline
powder, which was collected by decanting off the supernatant
(0.0617 g, 81% yield). Anal. Calcd for C76H64BF15N2O4U: C, 56.94;
H, 4.02; N, 1.75. Found: C, 55.49; H, 4.08; N, 1.85. 1H NMR (C6D6,
25 °C, 500 MHz): δ 1.07 (s, 36H, Me), 5.92 (s, 2H, γ-H), 6.81 (t,
JHH ) 7.5 Hz, 2H, para CH), 6.89 (t, JHH ) 7.5 Hz, 4H, meta CH),
7.03 (br s, 4H, ortho aryl CH), 7.17-7.22 (m, 12H, aryl CH), 7.34
(d, JHH ) 7.5 Hz, 4H, ortho CH). 19F{1H} NMR (C6D6, 25 °C, 276
MHz): δ -68.3 (br s, 6F, ortho CF), -94.0 (br s, 3F, para CF),
-100.8 (br s, 6F, meta CF). 13C{1H} NMR (C6D6, 25 °C, 125
MHz): δ 31.3 (Me), 35.4 (CMe3), 104.5 (γ-C), 123.0, 123.5, 128.0,
128.6, 129.3, 129.4, 132.0, 136.8 (br s, CF), 138.1, 138.8 (br s,
CF), 140.5, 142.9, 147.4 (br s, CF), 149.3 (br s, CF), 153.1, 174.0
(ꢀ-CN), 178.1 (ꢀ-CO). IR (KBr pellet, cm-1): 1647(m), 1597(m),
1558 (s), 1518(s), 1471(vs), 1365(s), 1298(s), 1247(m), 1211(w),
1192(w), 1095(s), 1025(m), 980(s), 921(m), 895(m), 845(m)
refinement included anisotropic temperature factors on all non-
hydrogen atoms. Structure solution, refinement, graphics, and creation
of publication materials were performed using SHELXTL or WinGX.58
For complex 4·2C6H14 ·4CH2Cl2, because of severe disorder in
the molecules of solvation (identified as CH2Cl2 and hexane), the
SQUEEZE function in PLATON was applied. However, one
dichloromethane could be adequately modeled. For this molecule,
the C-Cl bond lengths were fixed to 1.70(1) Å, and the Cl-Cl
distance was fixed to 3.00(1) Å. The carbons of cyclopentadienyl
ring of the [Cp2*Co]+ moiety also displayed a significant amount
of thermal motion. For complex 5·C6H14, one tert-butyl group was
found to be disordered between two positions about the tertiary
carbon, in a 50:50 ratio. Restraints were applied to the disordered
tert-butyl groups by fixing the C-C bond lengths between the
tertiary and methyl carbons to 1.54(1) Å. In addition, a disordered
molecule of hexanes was found in the crystal lattice. It was modeled
in two different positions, in a 75:25 ratio. However, because of
disorder, some of the carbon atoms could not be located. For this
structure, the atoms of the solvent molecule were refined isotro-
pically, while the hydrogen atoms were not assigned. A summary
of relevant crystallographic data for 2·2C7H8, 4·2C6H14 ·4CH2Cl2,
and 5·C6H14 is presented in Table 1.
ν
asym(UdO), 811(w), 705(s), 601(m), 577(m).
X-ray Crystallography. The solid-state molecular structures of
complexes 2·2C7H8, 4·2C6H14 ·4CH2Cl2, and 5·C6H14 were deter-
mined similarly with exceptions noted in the following paragraph.
Crystals were mounted on a glass fiber under Paratone-N oil. Data
collection was carried out a Bruker 3-axis platform diffractometer with
SMART-1000 CCD detector. The instrument was equipped with
graphite monochromatized Mo KR X-ray source (λ ) 0.71073 Å).
All data were collected at 150(2) K using Oxford nitrogen gas
cryostream system. A hemisphere of data was collected using ω scans,
with 15 s frame exposures and 0.3° frame widths. SMART55 was used
to determine the cell parameters and data collection. The raw frame
data were processed using SAINT.56 The empirical absorption cor-
rection was applied based on Psi-scan for 2·2C7H8 and 5·C6H14 or
SADABS for 4·2C6H14 ·4CH2Cl2. Subsequent calculations were
carried out using SHELXTL.57 The structures were solved using Direct
methods and difference Fourier techniques. All hydrogen atom
positions were idealized and rode on the atom of attachment. The final
Acknowledgment. We thank the University of California,
Santa Barbara and the University of California Energy
Institute for financial support of this work.
Supporting Information Available: X-ray crystallographic
details (as CIF files) of 2·2C7H8, 4·2C6H14 ·4CH2Cl2, and 5·C6H14;
tabulated cyclic voltammetry data for 1, 2, and 5; UV/vis spectra
for 1 and 2; 1H NMR spectra for complexes 1-5. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC802360Y
(56) SAINT Software Users Guide, Version 5.1, Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1999.
(57) Sheldrick, G. M. SHELXTL, Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 2001.
(58) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
(55) SMART Software Users Guide, Version 5.1; Bruker Analytical X-ray
Systems, Inc.: Madison, WI, 1999.
3072 Inorganic Chemistry, Vol. 48, No. 7, 2009