29Si NMR Spectra of Silicon-Containing Uranium Complexes

Article abstract of DOI:10.1021/om500512q

²⁹Si NMR spectra have been recorded for a series of uranium complexes containing silicon, and the data have been combined with results in the literature to determine if any trends exist between chemical shift and structure, ligand type, or oxidation state. Data on 52 paramagnetic inorganic and organometallic uranium complexes are presented. The survey reveals that, although there is some overlap in the range of shifts of U⁴⁺ complexes versus U³⁺ complexes, in general U³⁺ species have shifts more negative than those of their U⁴⁺ analogues. The single U²⁺ example has the most negative shift of all at -322 ppm at 170 K. With only a few exceptions, U⁴⁺ complexes have shifts between 0 and -150 ppm (vs SiMe₄), whereas U³⁺ complexes resonate between -120 and -250 ppm. The small data set on U⁵⁺ species exhibits a broad 250 ppm range centered near 40 ppm. The data also show that aromatic ligands such as cyclopentadienide, cyclooctatetraenide, and the pentalene dianion exhibit chemical shifts less negative than those of other types of ligands.

Full text of DOI:10.1021/om500512q

Article
pubs.acs.org/Organometallics
29Si NMR Spectra of Silicon-Containing Uranium Complexes
Cory J. Windorff and William J. Evans*
Department of Chemistry, University of California, Irvine, California 92697-2025, United States
*
S Supporting Information
ABSTRACT: 29Si NMR spectra have been recorded for a series of uranium complexes containing silicon, and the data have been
combined with results in the literature to determine if any trends exist between chemical shift and structure, ligand type, or
oxidation state. Data on 52 paramagnetic inorganic and organometallic uranium complexes are presented. The survey reveals
4
+
3+
3+
that, although there is some overlap in the range of shifts of U complexes versus U complexes, in general U species have
4
+
2+
shifts more negative than those of their U analogues. The single U example has the most negative shift of all at −322 ppm at
4
+
3+
1
70 K. With only a few exceptions, U complexes have shifts between 0 and −150 ppm (vs SiMe ), whereas U complexes
4
5+
resonate between −120 and −250 ppm. The small data set on U species exhibits a broad 250 ppm range centered near 40 ppm.
The data also show that aromatic ligands such as cyclopentadienide, cyclooctatetraenide, and the pentalene dianion exhibit
chemical shifts less negative than those of other types of ligands.
INTRODUCTION
9Si NMR spectroscopy has been used extensively to character-
complexes. We were particularly interested in correlations with
■
2
oxidation state, since the 3.62 and 3.58 μ calculated free ion
B
magnetic moments for U3+ and U , respectively, are too close
to be distinguished by room-temperature magnetic suscepti-
bility measurements. Moreover, in practice, the room-temper-
ature magnetic moments of complexes of U3+ and U exhibit
broad ranges that overlap considerably and variable-temper-
ature SQUID analysis is necessary to accurately assess the
4+
ize many types of silicon-containing molecules and materi-
1
−7
29
als.
Correlations of Si NMR chemical shifts with charge,
substitution pattern, ring size, coordination number, and π
interactions have been made.
2
−6
Typically, the range of shifts
4+
for a given structural type is large and the ranges overlap as the
structural type is varied, but trends can be discerned when
comparing mean chemical shifts for each structural type. This
has provided an additional analytical criterion for examining
new silicon-containing compounds.
29−37
oxidation state.
To explore the utility of 29Si NMR spectroscopy in uranium
chemistry, we obtained NMR data on our recently synthesized
complexes, as well as other previously reported inorganic and
organometallic uranium complexes with silicon-containing
One area of chemistry for which few 29Si NMR data have
been reported is that of silicon-containing complexes of
uranium. It is understandable that only a few reports of 29Si
NMR spectra of uranium compounds are given in the
8
−23
29
ligands. We also scanned the literature to find Si NMR data
literature,
since complexes of uranium in the +2, +3, +4,
8
−23
and +5 oxidation states are paramagnetic. To date, these data
serve only as a fingerprint of a specialized type for these
compounds.
already reported on uranium complexes.
The data obtained
so far show some interesting preliminary trends. We report this
information now to encourage a broader collection of data of
this type to determine how powerful this method of analysis
can become in the area of uranium chemistry.
We recently synthesized several series of silicon-containing
24−28
uranium complexes
that provide the opportunity to collect
2
9
a substantial amount of Si NMR data on closely related
2
9
complexes. We wondered if the Si NMR spectra would reveal
any correlations between the chemical shift and any aspect of
the composition, structure, or oxidation state of the uranium
Received: May 14, 2014
Published: July 15, 2014
©
2014 American Chemical Society
3786
dx.doi.org/10.1021/om500512q | Organometallics 2014, 33, 3786−3791

Organometallics
Article
RESULTS AND DISCUSSION
■
2
9
Data Collection. Si NMR spectroscopy is typically more
1
13
challenging than H or C NMR because of low natural
abundance (4.67%), a low negative gyromagnetic ratio
7
−1 −1
−4
(
−5.3146 × 10 rad T s ), low sensitivity (4 × 10 relative
1
1−6
to H), and long relaxation times.
There is also an inherent
resonance from the glass in the NMR tube and probe that
extends from −80 to −130 ppm and has the potential to
obstruct signals. Due to these considerations, concentrated
samples were needed (≥20 mg/0.5 mL) and data were
collected with an acquisition time of 0.5 s and a t value of ≥2 s.
1
A reviewer suggested a t value of 1 s should be adequate for
1
paramagnetic samples and we have confirmed that spectra with
acceptable signal to noise ratios can be obtained in less time
Figure 1. Plot of chemical shift (δ) vs T−1 for [K(2.2.2-crypt)]-
with this shorter t value. Initial experiments were conducted
1
[
(C H SiMe ) U].
5 4 3 3
with a large window, from 200 to −400 ppm, since it was
uncertain how much the paramagnetic uranium would shift the
signal. Each experiment was followed by a second experiment
with a smaller window, typically 250 ppm. Data collection
C D at 293−303 K, except where noted. For convenience, the
6
6
29
data are presented as a graph of the Si resonances in Figure 2.
Correlations of chemical shift and the distance of silicon
from uranium in the solid state X-ray crystal structures were
also examined. These are presented in the Supporting
required 1−3 h per sample with the 2 s t value. Typical
1
examples of spectra are given in the Supporting Information
(
Figures S1−S9).
Information, since the plots show no consistent correlations
All samples in this study used C D as the solvent, except for
6
6
4+
(
Figure S10). For example, for U complexes, a scatter plot is
(
C Me SiMe )MgCl(THF), [K(THF) ][(C Me SiMe ) -
5
4
3
x
5
4
3
2
3+
observed (Figure S11). For U complexes, 4 compounds with
close U···Si distances have larger shifts than 13 compounds
with longer U···Si distances, but within these two groups there
is no correlation of shift and the U···Si distance in the solid-
state structure (Figure S12). Correlations were also examined
within a ligand set (Figures S13 and S14). Three U complexes
of [N(SiMe ) ] show a correlation (Figure S15), as do four
complexes of Tren ligands (Figure S16), but two pairs of
complexes with similar U···Si distances have shifts that vary
by 100 ppm (Figure S13). A correlation for 4 U complexes of
cyclopentadienyl, cyclooctatetraenyl, and pentalenyl ligands
looks better than that for 11 U complexes of the same types
UMe ], [K(2.2.2-crypt)][(C H SiMe ) UH], and [K(2.2.2-
2
5
4
3 3
crypt)][(C H SiMe ) U], which are insoluble in C D and
5
4
3 3
6
6
were measured in either C H O or C D O. Previous studies
4
8
4
8
2
9
have shown that the solvent does not have a large effect on Si
NMR shifts. Several samples were examined in both C D6
2
,4
6
3+
and C H O (THF) to test this generalization with uranium-
−
4
8
3
2
containing species, and a similarly small solvent effect was again
5+
4+
U
U
observed: complex (shift in C D , shift in C H O in ppm)
6
6
4
8
(
(
(
C Me SiMe ) UCl (−51, −50); (C Me SiMe ) UMeCl
4+
5
4
3
2
2
5
4
3 2
−67, −66); (C Me SiMe ) UMe (−84, −84); [C H -
5
4
3
2
2
5
3
SiMe ) ] U, (−162, −163); (C H SiMe ) U, (−165, −158).
3+
3
2 3
5
4
3 3
Exceptions to this solvent independence were observed in the
case of a solvated cation such as [K(THF) ]{U[N(SiMe ) ] },
of ligands (Figure S14), but we are reluctant to overinterpret
these correlations with so few data. Perhaps more insight can be
gained with these plots as more data are added. The difficulty of
finding correlations in the NMR shifts of paramagnetic species
6
3 2 4
which has chemical shifts of −192 and −142 ppm in C D and
6
6
C H O, respectively.
4
8
All newly reported data were collected at room temperature
3
has been pointed out. Competing factors can affect the shift
2
+
except for the U
complex [K(2.2.2-cryptand)]-
(
e.g., contact and pseudocontact effects) and distances and
23
[
(C H SiMe ) U], which has limited stability in solution at
5
4
3 3
geometries in solution may not reflect data obtained in the solid
state.
2
9
room temperature. To obtain Si NMR data on this complex,
it was synthesized at low temperature in an NMR tube. The
chemical shift of this complex as a function of 1/T is plotted in
Figure 1. The data follow a typical Curie−Weiss dependence
on temperature.
Ligand Effects. A ligand-based trend discernible from the
data in Table 1 is that uranium complexes with ligands such as
triamidoamine (Tren) and amide exhibit chemical shifts more
negative than those with aromatic ligands such as cyclo-
pentadienide, cyclooctatetraenide, and the pentalene dianion.
This is exemplified by the U3+ complexes [C H (SiMe ) ]U-
29Si NMR Data. The most common types of silicon-
containing ligands in the uranium complexes are the bulky
8
6
3 2
−
trimethylsilyl-substituted amide and alkyl ligands [N(SiMe ) ]
and [CH(SiMe ) ] and trimethylsilyl-substituted cyclopenta-
3
2
(C Me ), and [C H (SiMe )] U, which resonate at −145 and
5
5
5
3
3
3
−
12
TIPS
3
2
−162 ppm, respectively, whereas (Tren )U and U[N-
−
−
17
dienyl groups (C Me SiMe ) , (C H SiMe ) , and
(SiMe ) ] resonate at −178 and −219 ppm, respectively.
5
4
3
5
4
3
3 2 3
−
[
C H (SiMe ) ] . The prevalence of the trimethylsilyl
Comparison of the −247 ppm shift for (C Me ) U[N(SiMe ) ]
5
3
3
2
5
5 2
3 2
substituent in this study provides some uniformity in the
versus the −158 ppm shift of (C Me ) U[CH(SiMe ) ] shows
5
5 2
3 2
immediate environment of the silicon.
the amide to resonate at a shift more negative than that for the
corresponding alkyl. The order of the resonances in these two
complexes is reversed from what is observed in the free ligands.
For example, CH (SiMe ) resonates at −0.12 ppm, whereas
2
9
Table 1 shows Si NMR data collected in this study on
3
+
4+
inorganic and organometallic U and U complexes with
silicon-containing ligands, along with other data found in the
2
3 2
2
+
literature. A single example of U is also given in Table 1. Data
HN(SiMe ) resonates at 1.95 ppm.
3 2
on U5 and U complexes are given in Table 2. For reference,
data on free ligands and derivatives are shown in Table 3. The
data are arranged according to decreasing chemical shift in
+
6+
The data show that cyclopentadienide ligands resonate at
shifts less negative than those for cyclooctatetraenyl ligands
2−
i
(C H R -1,4) (R = SiMe , Si Pr ,). For example, three of the
8
6
2
3
3
3
787
dx.doi.org/10.1021/om500512q | Organometallics 2014, 33, 3786−3791

Organometallics
Article
Table 1. 29Si NMR Chemical Shifts of Un+ Complexes (n =
Table 2. Si NMR Chemical Shifts of U Complexes (n = 5,
29
n+
2−4)
6)
2
9
29
Si chem shift δ
Si chem shift δ
a
b
a
b
compound
n
(ppm)
ref
compound
n
(ppm)
ref
22
2
2
c
{
U[OSi(Mes) ] } (μ-η :η -N )
4
4
4
4
4
4
4
4
4
4
64
23
20
20
17
14
19
14
(ROUO) (L)
5
5
6
6
5
160
152
3
3
2
2
2
[
(TrenTIPS)U(THF)][BPh4]
36
(PhMe SiOUO) (L)
22
15
21
19
2
2
(
(
[
(
[
(
(
[
TrenTIPS)U(PH2)
TrenTIPS)UCl
21
(BIPM)UOCl2
−0.69
−8.28
−13
13
(BIPM)U(NMes)(O)(DMAP)2
2
(TrenTIPS)U(μ-N)[μ-Na(15-crown-
κ -C H N(2-NR)] UI
−11
−11
−41
−51
−67
5; −74
5
4
3
TrenTIPS)UN
2
5)]
3
(TrenTIPS)UN
6
5
5
5
5
−21.70
−37
−58
19
κ -C H N(2-NR)] UCl
5
4
3
(
TrenTIPS)UNAd
TrenTIPS)UNR
19
C Me R) UCl
2
this work
this work
19
5
4
2
(
17, 19
18
C Me R) UMeCl
5
5
4
2
(TrenTIPS)UO
−71
i
κ -(NHCMe Si Pr NCH CH )
2
2
2
2
2
2
c
N(CH CH NR′) ]U
[(C H R )(C Me )U] (μ-η :η -
−90
12
2
2
2
8
6
2
5
5
2
C O )
(
C Me R) UMe
4
4
4
4
4
4
4
−84
this work
4
4
5
4
2
2
a
i
2
U(NR ) (κ -CH SiMe NR)
−74; −83; −152
−90
−97
−101; −134
−108; −185
this work
Abbreviations: R = SiMe
3
, R′ = Si Pr , L = Pacman-like binucleating
3
2
2
2
2
TrenTIPS)UNH2
TrenTIPS)UF
Schiff-base calixpyrrole macrocycle, BIPM = bis(iminophosphorano)-
(
(
(
19
19
8
methanediide = C(PPh NSiMe ) , Mes = mesityl, DMAP = 4-
2
3 2
TIPS
i
c
dimethylaminopyridine, Tren
= N(CH CH NSi Pr ) , Ad =
2 2 3 3
c
C H R′ ) U
8
4
2
2
b
2
2
adamantyl. In C
6
D
6
unless noted otherwise. In C
7
D
8
.
[
[
(C H R′ )(C Me )U] (μ-η :η -N )
9
8
4
2
5
5
2
2
c
(C H R )(C Me R)U] (μ-
−108; −143
12
8
6
2
5
4
2
Table 3. 29Si NMR Chemical Shifts of Diamagnetic
Derivatives of Ligands
1
1 13
η :η - C O )
2
2
c
[
[
(
(C H R′ )(C Me Et)U] (μ-
4
4
−113
12
10
8
6
2
5
4
2
1
1 13
η :η - C O )
2
2
2
9
c
Si chem shift δ
(C H R′ )(C Me )U] (μ-
−115
a
b
8
6
2
5
5
2
1
1 13
compound
(ppm)
ref
η :η - C O )
2
2
C H R′ ) U(κ -TpMe2)
3
c
,
g
RCl
30.11
2, this work
3
4
3
4
3
3
3
4
3
3
3
3
3
3
3
3
3
3
3
−116
−121
−124 (C H R′ )
11
8
6
2
K(2.2.2-crypt)][(TrenTIPS)U(PH)]
R2CHCl
4.40/3.43
4.19
2, this work
[
20
c
K [C H R′ ]
8
(
C H R′ )(C Me R)U
12
2
8
4
2
8
6
2
5
4
8
6
2
TIPS
Li (Tren
3
)
2.60
17
U(NR2)4
−127
−133
−137
−145
−149
−154
−154
−155
−158
−159
−162
this work
12
c
i
4
c
HNR2
1.95−2.22
1.32
2, this work
(
(
(
C H R′ )(C Me Pr)U
8
6
2
5
c
C Me RH
this work
C H R′ )(C Me Et)U
12
5
4
8
6
2
5
4
d
CH2R
2
0.50/−0.12
−0.56
−4.01
−6.06
−8.52
−8.55
−9.9
−11.75
2, this work
C H R )(C Me )U
12
8
6
2
5
5
(TrenDMSB)U] (μ-η :η -C O )
1
1
HC[SiMe N(Li)Ar]3
38
[
[
(
(
(
(
(
(
(
(
(
(
16
2
2
2
2
e
c
HC[SiMe N(Li)Ar′] (OEt )
38
K(2.2.2-crypt)][(C H R) UH]
this work
12
2
3
2 2
5
4
3
HC[SiMe N(Li)Ar] (OEt )
38
C H R )(C Me R)U
2
3
2
8
6
2
5
4
K[C H N(2-NR)](THF)
14
C Me R) U
this work
this work
11
5
4
0.25
5
4
3
Li[C H N(2-NR)](THF)
2
14
C Me ) U(CHR )
5
4
5
5
2
2
d
C H R′ )U(κ -TpMe2)
3
c
C H (SiPh )
3 2
27
8
6
8
4
2
e
(
(
(
C Me R)MgCl(THF)
this work
15
C H R ) U
this work
this work
9, 13
12
5
4
5
3 2 3
e
RNPPh ) CC(H)Ph
−12.02; −12.51
−12.47; −13.36
−14.43
C H R) U
−165 (−158 )
−173 (−295
−176
−178
2 2
5
4
3
ch
,
RNPPh ) CC(H)R″
39
C H R′ )(C Me )U
)
2 2
8
4
2
5
5
c
K(C H R)
this work
this work
40
C H R )(C Me )U(THF)
5
4
8
6
2
5
5
TrenTIPS)U
K(C H R )
−14.59
−17.22
−20.49
−21.82
17
5
3 2
(
RNPPh ) CCPh
C Me R) U(CHR )
−137; −181;
this work
2
2
2
5
4
2
2
−
198
KNR2
this work
16
e
[
K(THF) ][U(NR ) ]
3
3
3
3
3
4
2
−192 (−142 )
−206; −231
−219
−237
−247
−255
this work
this work
this work
this work
this work
this work
this work
bis(trimethylsiloxy)furanone
bis(dimethylphenylsiloxy)furanone
6
2 4
(
C Me R) U(NR )
−21.94
16
5
4
2
2
U(NR2)3
a
i
TIPS
R = SiMe , R′ = Si Pr , R″ = anthracene, C H , Tren
=
6
3
3
14
9
c
i
b
[
K(THF) ][(C Me R) UMe ]
x
5
4
2
2
N(CH CH NSi Pr ) , Ar = 3,5-Me C H , Ar′ = 4-MeC H In C D
2
2
3
3
2
6
3
6
4
6
c d e
(
C Me ) U(NR )
unless noted otherwise. In C H . In CDCl . In C H O.
6 6 3 4 8
5
5
2
2
5
1
[
(η :η -C Me SiMe CH ) U]
5 4 2 2 2
,
fi
[
a
K(2.2.2-crypt)][(C H R) U]
−322
5
4
3
[
C H (SiMe ) ] U, and (C H SiMe ) U resonate at −155,
5
3
3 2 3
5
4
3 3
i
TIPS
Abbreviations: R = SiMe , R′ = Si Pr , Tren
CH CH NSi Pr ) , Tren
= N-
3
3
−162, and −165 ppm, respectively.
i
DMSB
t
Me2
(
= N(CH CH NSiMe Bu) , Tp
=
2
2
3
3
2
2
2
3
Oxidation State Analysis. As can be seen in Table 1 and
Figure 2, there is a general trend of U complexes occurring at
values more negative than those for U complexes. The range
b
hydridotris(3,5-dimethylpyrazolyl)borate. In C D unless noted
3+
6
6
c
d
e
f
g
otherwise. In C D . In C D . In C H O. In C D O. At 328 K.
4+
7
8
6
12
4
8
4
8
h
i
At 201 K. At 170 K.
4+
of most of the U complexes in Table 1 is between 0 and −150
ppm. In contrast, most of the U3+ complexes have resonances
between −120 and −250 ppm. The low-temperature spectrum
U3+ complexes containing the [(C H R -1,4)](C Me R′)U (R
8
6
2
5
4
i
i
2+
=
−
Si Pr , R′ = Pr, Et; R = SiMe , R′ = Me) structure resonate at
of the U example had the most negative chemical shift of all,
3
3
1
2
133, −137, and −145 ppm, respectively, whereas the
−322 ppm at 170 K, but extrapolation of the data in Figure 1
gives an estimated shift of −216 ppm at 298 K, at the low end
tris(cyclopentadienyl) complexes , (C Me SiMe ) U,
5
4
3 3
3
788
dx.doi.org/10.1021/om500512q | Organometallics 2014, 33, 3786−3791

Organometallics
Article
exhibit more negative shifts. The lower the oxidation state of
2
9
the uranium in the series +4, +3, and +2, the lower the Si
NMR chemical shift.
EXPERIMENTAL SECTION
■
All manipulations and syntheses described below were conducted with
the rigorous exclusion of air and water using standard Schlenk line and
glovebox techniques under an argon or dinitrogen atmosphere.
Solvents were sparged with UHP argon and dried by passage through
columns containing Q-5 and molecular sieves prior to use. Deuterated
NMR solvents were dried over sodium benzophenone ketyl or
sodium/potassium alloy, degassed by three freeze−pump−thaw cycles,
1
13
29
and vacuum-transferred before use. H, C, and Si NMR spectra
were recorded on a Bruker GN 500 MHz spectrometer operating at
4
99.3, 125.6, and 99.2 MHz, respectively, at 298 K unless otherwise
4
+/3+
Figure 2. Graphical representation of the U
data, where purple
1
stated. H NMR spectra were referenced internally to residual protio
solvent resonances, C NMR spectra were referenced internally to
solvent, and Si NMR spectra were referenced externally to SiMe4.
The following compounds were prepared following literature
4+
lines represent the shift of a U complex and yellow lines represent
complexes. Not shown are the resonances at positive chemical
shifts for {U[OSi(Mes) ] } (μ-η :η -N ) at 64 ppm, [Tren U-
THF)][BPh ] at 36 ppm, (Tren )U(PH ) at 21 ppm,
Tren )UCl at 13 ppm, and one of the resonances for [κ -
13
3+
U
29
2
2
23
TIPS
3
3
2
2
2
0
TIPS
20
5
(
(
(
24
24
4
2
procedures: C Me SiMe MgCl(THF), (C Me SiMe ) UMe
5 4 3 5 4 3 2 2,
24 25
TIPS
17
5
1
(
η :η -C Me SiMe CH ) U,
(C Me SiMe ) UMe K,
5 4 3 2 2
28
5
4
2
2
2
i
19
2
5
NHCMe Si Pr NCH CH )N(CH CH NR′) ]U at 5 ppm.
2
2
2
2
2
2
2
(C Me SiMe ) U,
(C H SiMe ) U,
[K(2.2.2-crypt)]-
5
4
3
3
5
4
3 3
2
8
41
[
(C H SiMe ) UH], (C Me ) U[N(SiMe ) ], [(C Me ) U][(μ-
5
4
3
3
5
5
2
3
2
5
5 2
4
2
37
37
37
of the U3+ range. This calculated room-temperature resonance
is significantly shifted from that of the neutral (C H SiMe ) U-
THF) compound (at −159 ppm) and is more negative than
those for most cyclopentadienyl complexes. All of these shifts
are substantially more negative than the +30 to −25 ppm range
found for the ligands in diamagnetic compounds such as
C Me SiMe H, K[C H (SiMe ) ], and KN(SiMe ) and the
three examples of U compounds in Tables 2 and 3. The U
compounds, on the other hand, exhibit the widest range of
Ph
2
)BPh
3
2
], KU[N(SiMe
3
)
2
]
4
,
U[N(SiMe
3
)
2
]
4
,
and U[N-
2
(SiMe ) ] (κ -CH SiMe NSiMe ). The following compounds were
2
2
2
2
3
5
4
3 3
prepared following the literature, but with the exceptions noted:
(
43
(
(
C Me SiMe ) UMeCl was made analogously to (C Me H)UMeCl,
5 4 3 2 5 4
24
C Me SiMe ) UCl was recrystallized from toluene at −35 °C after
5
4
3
2
2
2
5
filtration, [(C Me SiMe ) U][(μ-Ph )BPh ] was washed with
5
4
3
2
2
2
methylcyclohexane and hexane and then extracted in benzene, and
U[N(SiMe ) ] was sublimed under vacuum at 10 Torr at 80 °C
for 6 h before use. (C Me SiMe ) U[N(SiMe ) ] and
4
2 3
4
−7
3
5
4
3
5
3
3 2
3 2
6
+
5+
5 4 3 2 3 2
(
C Me SiMe ) U[CH(SiMe ) ] were prepared following the method
5 4 3 2 3 2
41
of (C Me ) U[N(SiMe ) ]. The syntheses of (C Me SiMe ) U[N-
5
5
2
3
2
5
4
3 2
shifts: +160 to −90 ppm. However, to date there have only
been seven examples for which Si NMR data on U
(SiMe ) ] and (C Me SiMe ) U[CH(SiMe ) ] can be found in the
2
9
5+
3 2 5 4 3 2 3 2
Supporting Information.
1
2,17−19,22
compounds are reported.
45
C Me SiMe H. As a variation from the literature method,
5
4
3
The ranges for most U and U3+ complexes do not overlap,
but there are some exceptions. The two U complexes that
have resonances more negative than those for the other
examples each contain cyclometalated silicon-containing
ligands. In the U complex (η :η -C Me SiMe CH ) U, in
which the only silicon is in the ring of a cyclometalated ligand, a
4
+
Me SiCl (0.83 g, 7.6 mmol) in toluene (10 mL) was added dropwise
over 5 min to a stirred suspension of KC Me H (1.23 g, 7.67 mmol).
3
4
+
5
4
The solution was stirred for 48 h, and the solvent was removed under
reduced pressure. Hexane (60 mL) was added to the reaction mixture,
which was then filtered on a 60 mL medium-porosity frit and washed
with 2 × 10 mL of hexane. The hexane was removed under reduced
4
+
5
1
5
4
2
2 2
2
pressure to yield C
5
Me
4 3
SiMe H as a colorless liquid (0.850 g, 57%).
chemical shift at −255 ppm is observed. U[N(SiMe ) ] (κ -
45
3
2 2
1
H NMR (C D ): δ 2.67 (s, 1H, C Me SiMe H), 1.90 (s, 6H,
6
6
5
4
3
CH SiMe NSiMe ) has three observable resonances at −74,
2
2
3
C Me SiMe H), 1.79 (s, 6H, C Me SiMe H), −0.04 (s, 9H,
C Me SiMe H). C NMR (C D ): δ 135.4 (C Me SiMe ), 133.0
5
4
3
5
4
3
−
83, and −152 ppm. The latter resonance is outside the
13
5
4
3
6
6
5
4
3
normal range and is attributed to the silicon in the
(
C Me SiMe ), 55.3 (i-(C Me SiMe ), 11.3 (C Me SiMe ), −1.6
5
4
3
5
4
3
5
4
3
2
9
29
cyclometalated ring. Si NMR shifts in cyclic silanes are
known to be sensitive to ring size and ring strain;
there is precedence for these silicon resonances to be shifted
outside the expected range.
(C Me SiMe ). Si NMR (C D ): δ 1.32 (C Me SiMe ).
5 4 3 6 6 5 4 3
46
1
−7
therefore,
(C Me ) U[CH(SiMe ) ]. This complex was prepared following
5 5 2 3 2
41
the method of (C
synthesis. LiCH(SiMe ) (37 mg, 0.22 mmol) was added to a stirred
slurry of [(C Me ) U][(μ-Ph )BPh ] (170 mg, 0.206 mmol) in
Me
5
)U[N(SiMe
5
)
2
]
rather than the literature
3
3
2
5
5
2
2
2
benzene (5 mL). After 20 h, an aliquot was drawn for NMR
spectroscopy to ensure the reaction had gone to completion, following
CONCLUSION
■
Recently obtained 29Si NMR spectra on uranium complexes
containing silicon and a review of the known literature has
revealed some general trends among chemical shift, composi-
tion, and oxidation states that should prove to be useful for
further studies. These trends should not be considered
which white solids (presumably LiBPh ) were removed by
4
centrifugation and the solvent was removed under reduced pressure
to yield (C Me ) U[CH(SiMe ) ] as a dark brown solid (104 mg,
5
5
2
3 2
1
46 29
75%). The product was confirmed by H NMR spectroscopy.
NMR (C ): δ −158 [CH(SiMe ].
C H (SiMe ) ] U. This synthesis is an alternative to that given in
Si
D
)
3 2
6
6
4
7
2
9
[
definitive at this stage, since Si NMR shifts are often variable
and data on only 52 paramagnetic uranium complexes are
collected here. Therefore, the following correlations should be
further tested in future studies. Complexes containing non-
aromatic ligands resonate at shifts lower than those with
aromatic ligands. Complexes containing ligands with silicon
bound to nitrogen resonate at values more negative than those
with silicon bound to carbon. Silicon in cyclic ligands tends to
5
3
3 2 3
the literature. KC H (SiMe ) (321 mg, 1.29 mmol) was tapped into a
5
3
3 2
stirred slurry of UI (264 mg, 0.427 mmol) in Et O (10 mL). An
3
2
immediate color change from purple to green was observed, and the
volume was increased to 20 mL. After 1 h, white solids (presumably
KI) were removed by centrifugation and the solvent was removed
under reduced pressure. The product was dissolved in 15 mL of
hexane and the solution stirred for 4 h. More white solids (presumably
KI) were removed by centrifugation, and the solvent was removed
3
789
dx.doi.org/10.1021/om500512q | Organometallics 2014, 33, 3786−3791

Organometallics
Article
under reduced pressure to give [C H (SiMe ) ] U as a green solid
(12) Tsoureas, N.; Summerscales, O. T.; Cloke, F. G. N.; Roe, S. M.
Organometallics 2013, 32, 1353.
(13) Tsoureas, N.; Kilpatrick, A. F. R.; Summerscales, O. T.; Nixon, J.
F.; Cloke, F. G. N.; Hitchcock, P. B. Eur. J. Inorg. Chem. 2013, 2013,
4085.
5
3
3 2 3
1
(
262 mg, 70%). The product was confirmed by H NMR
47
29
spectroscopy.
Si NMR (C D ): δ −162 (C H (SiMe ) ).
6
6
5
3
3 2
2
8
Small-Scale Synthesis of [K(2.2.2-crypt)][(C H SiMe ) U]
5
4
3 3
for Low-Temperature NMR Studies. (C H SiMe ) U (85 mg,
5
4
3 3
0
1
.13 mmol) and 2.2.2-cryptand (59 mg, 0.16 mmol) were dissolved in
mL of d -THF to form a red-brown solution and placed into a −35
(
14) King, D. M.; Lewis, W.; Liddle, S. T. Inorg. Chim. Acta 2012,
380, 167.
15) Mills, D. P.; Cooper, O. J.; Tuna, F.; McInnes, E. J. L.; Davies, E.
8
°
C freezer for 2 h along with a pipet packed with ∼45 mg of KC , an
8
(
NMR tube, and a scintillation vial filled with hexane. Once removed
S.; McMaster, J.; Moro, F.; Lewis, W.; Blake, A. J.; Liddle, S. T. J. Am.
Chem. Soc. 2012, 134, 10047.
from the freezer, the NMR tube was placed in the hexane bath and the
KC column was placed above the NMR tube. The red-brown solution
8
(
16) Gardner, B. M.; Stewart, J. C.; Davis, A. L.; McMaster, J.; Lewis,
W.; Blake, A. J.; Liddle, S. T. Proc. Natl. Acad. Sci. U.S.A. 2012, 109,
265.
17) King, D. M.; Tuna, F.; McInnes, E. J.; McMaster, J.; Lewis, W.;
was quickly added to the column and pushed through to yield a very
dark green solution. The NMR tube was capped, removed from the
glovebox, sealed with Parafilm, frozen in liquid nitrogen, and taken to
the NMR facility. The NMR spectrometer was locked and shimmed
9
(
Blake, A. J.; Liddle, S. T. Science 2012, 337, 717.
(18) King, D. M.; Tuna, F.; McMaster, J.; Lewis, W.; Blake, A. J.;
McInnes, E. J. L.; Liddle, S. T. Angew. Chem., Int. Ed. 2013, 52, 4921.
using pure d -THF at low temperature. The sample was thawed in
8
1
29
water and placed into the precooled probe. H and Si NMR spectra
were recorded at 170 K, and spectra were then taken from 183 to 233
K in 10 K increments.
(
19) King, D. M.; Tuna, F.; McInnes, E. J.; McMaster, J.; Lewis, W.;
Blake, A. J.; Liddle, S. T. Nat. Chem. 2013, 5, 482.
20) Gardner, B. M.; Balazs, G.; Scheer, M.; Tuna, F.; McInnes, E. J.
(
́
ASSOCIATED CONTENT
■
L.; McMaster, J.; Lewis, W.; Blake, A. J.; Liddle, S. T. Angew. Chem.,
*
S
Supporting Information
Int. Ed. 2014, 53, 4484.
(21) Lu, E.; Cooper, O. J.; McMaster, J.; Tuna, F.; McInnes, E. J. L.;
Lewis, W.; Blake, A. J.; Liddle, S. T. Angew. Chem., Int. Ed. 2014, 53,
Details for the synthesis of additional compounds examined for
2
9
29
the survey, sample Si NMR spectra, graphs of Si NMR
6
696.
chemical shifts vs U···Si distances by uranium oxidation state,
29
(22) Arnold, P. L.; Jones, G. M.; Odoh, S. O.; Schreckenbach, G.;
graphs of Si NMR chemical shifts vs U···Si distances by ligand
2
9
Magnani, N.; Love, J. B. Nat. Chem. 2012, 4, 221.
23) Mansell, S. M.; Farnaby, J. H.; Germeroth, A. I.; Arnold, P. L.
Organometallics 2013, 32, 4214.
24) Evans, W. J.; Siladke, N. A.; Ziller, J. W. Chem. Eur. J. 2010, 16,
96.
25) Siladke, N. A.; Ziller, J. W.; Evans, W. J. Z. Anorg. Allg. Chem.
010, 636, 2347.
26) Siladke, N. A.; Ziller, J. W.; Evans, W. J. J. Am. Chem. Soc. 2011,
33, 3507.
27) Lorenz, V.; Schmiege, B. M.; Hrib, C. G.; Ziller, J. W.;
set, and a table of Si NMR chemical shifts and their U···Si
distances. This material is available free of charge via the
Internet at http://pubs.acs.org.
(
(
7
(
2
(
1
(
AUTHOR INFORMATION
■
Corresponding Author
E-mail for W.J.E.: wevans@uci.edu.
*
Notes
The authors declare no competing financial interest.
Edelmann, A.; Blaurock, S.; Evans, W. J.; Edelmann, F. T. J. Am. Chem.
Soc. 2011, 133, 1257.
(
28) MacDonald, M. R.; Fieser, M. E.; Bates, J. E.; Ziller, J. W.;
Furche, F.; Evans, W. J. J. Am. Chem. Soc. 2013, 135, 13310.
29) Castro-Rodriguez, I.; Nakai, H.; Zakharov, L. N.; Rheingold, A.
L.; Meyer, K. Science 2004, 305, 1757.
30) Castro-Rodriguez, I.; Meyer, K. Chem. Commun. 2006, 1353.
ACKNOWLEDGMENTS
■
We thank Dr. Philip R. Dennison for his helpful discussions and
the Chemical Sciences, Geosciences, and Biosciences Division
of the Office of Basic Energy Sciences of the Department of
Energy (DE-SC0004739) for support.
(
(
(31) Lam, O. P.; Anthon, C.; Heinemann, F. W.; O’Connor, J. M.;
Meyer, K. J. Am. Chem. Soc. 2008, 130, 6567.
(
32) Graves, C. R.; Vaughn, A. E.; Schelter, E. J.; Scott, B. L.;
Thompson, J. D.; Morris, D. E.; Kiplinger, J. L. Inorg. Chem. 2008, 47,
1879.
33) Graves, C. R.; Yang, P.; Kozimor, S. A.; Vaughn, A. E.; Clark, D.
L.; Conradson, S. D.; Schelter, E. J.; Scott, B. L.; Thompson, J. D.;
Hay, P. J.; Morris, D. E.; Kiplinger, J. L. J. Am. Chem. Soc. 2008, 130,
REFERENCES
■
(
1) Iggo, J. A. NMR Spectroscopy in Inorganic Chemistry; Oxford
University Press: New York, 1999; Vol. 83.
1
(
(
2) Marsmann, H. NMR Basic Principles and Progress; Springer-
Verlag: New York, 1981; Vol. 17.
3) Harris, R. K.; Mann, B. E. NMR and the Periodic Table; Academic
Press: San Francisco, 1978.
4) Schraml, J. The Chemistry of Organic Silicon Compounds; Wiley:
New York, 2001; Vol. 3.
5) Coleman, B. Chemically and Biochemically Important Elements;
Academic Press: New York, 1983; Vol. 2.
6) Kennedy, J. D.; McFarlane, W. Multinuclear NMR; Plenum
Publishing: New York, 1987.
7) Kupce, E.; Wrackmeyer, B. Advanced Application of NMR to
Organometallic Chemistry; Wiley: New York, 1996.
8) Cloke, F. G. N.; Green, J. C.; Jardine, C. N. Organometallics 1999,
8, 1080.
9) Cloke, F. G. N.; Hitchcock, P. B. J. Am. Chem. Soc. 2002, 124,
352.
10) Frey, A. S.; Cloke, F. G. N.; Hitchcock, P. B.; Day, I. J.; Green, J.
C.; Aitken, G. J. Am. Chem. Soc. 2008, 130, 13816.
11) Farnaby, J. H.; Cloke, F. G. N.; Coles, M. P.; Green, J. C.;
Aitken, G. C. R. Chim. 2010, 13, 812.
(
5
272.
34) Kraft, S. J.; Fanwick, P. E.; Bart, S. C. Inorg. Chem. 2010, 49,
103.
35) Matson, E. M.; Forrest, W. P.; Fanwick, P. E.; Bart, S. C.
Organometallics 2012, 31, 4467.
36) Fortier, S.; Brown, J. L.; Kaltsoyannis, N.; Wu, G.; Hayton, T.
W. Inorg. Chem. 2012, 51, 1625.
37) Lewis, A. J.; Williams, U. J.; Carroll, P. J.; Schelter, E. J. Inorg.
Chem. 2013, 52, 7326.
38) Patel, D.; Lewis, W.; Blake, A. J.; Liddle, S. T. Dalton Trans.
(
1
(
(
(
(
(
(
(
(
(
1
(
9
2010, 39, 6638.
(39) Cooper, O. J.; Mills, D. P.; McMaster, J.; Moro, F.; Davies, E. S.;
Lewis, W.; Blake, A. J.; Liddle, S. T. Angew. Chem. 2011, 123, 2431.
(40) Cooper, O. J.; Mills, D. P.; Lewis, W.; Blake, A. J.; Liddle, S. T.
Dalton Trans. 2014, DOI: 10.1039/C4DT00909F.
(41) Evans, W. J.; Kozimor, S. A.; Ziller, J. W.; Kaltsoyannis, N. J. Am.
Chem. Soc. 2004, 126, 14533.
(
(
3
790
dx.doi.org/10.1021/om500512q | Organometallics 2014, 33, 3786−3791

Organometallics
Article
(
42) Evans, W. J.; Nyce, G. W.; Forrestal, K. J.; Ziller, J. W.
Organometallics 2002, 21, 1050.
43) Evans, W. J.; Kozimor, S. A.; Hillman, W. R.; Ziller, J. W.
Organometallics 2005, 24, 4676.
(
(
(
44) Andersen, R. A. Inorg. Chem. 1979, 18, 1507.
45) Horacek, M.; Gyepes, R.; Cisarova, I.; Polasek, M.; Varga, V.;
Mach, K. Collect. Czech. Chem. Commun. 1996, 61, 1307.
46) Fagan, P. J.; Manriquez, J. M.; Marks, T. J.; Day, C. S.; Vollmer,
S. H.; Day, V. W. Organometallics 1982, 1, 170.
47) del Mar Conejo, M.; Parry, J. S.; Carmona, E.; Schultz, M.;
(
(
Brennann, J. G.; Beshouri, S. M.; Andersen, R. A.; Rogers, R. D.;
Coles, S.; Hursthouse, M. B. Chem. Eur. J. 1999, 5, 3000.
3
791
dx.doi.org/10.1021/om500512q | Organometallics 2014, 33, 3786−3791