Uranium(IV) alkyl complexes of a rigid dianionic non-donor ligand: Synthesis and quantitative alkyl exchange reactions with alkyllithium reagents

Article abstract of DOI:10.1021/om301136f

Reaction of [(XA₂)UCl₃{K(dme)₃}] (XA ₂ = 4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9- dimethylxanthene) with 2 equiv of ((trimethylsilyl)methyl)lithium or neopentyllithium afforded red-orange [(XA₂)U(CH₂SiMe ₃)₂] (1) and dark red [(XA₂)U(CH ₂CMe₃)₂] (2), respectively. Reaction of 1 with an additional 1 equiv of LiCH₂SiMe₃ in THF yielded yellow [Li(THF)_x][(XA₂)U(CH₂SiMe₃) ₃] (3), and reaction of [(XA₂)UCl₃{K(dme) ₃}] with 3 equiv of methyllithium in dme afforded yellow [Li(dme)₃][(XA₂)UMe₃] (4). Reaction of 1 with 2.1 equiv of LiCH₂CMe₃ in benzene resulted in rapid conversion to 2, with release of 2 equiv of LiCH₂SiMe₃. Similarly, reaction of 1 with 3.3 equiv of MeLi in THF provided 4 as the [Li(THF)_x]⁺ salt, accompanied by 2 equiv of LiCH ₂SiMe₃. These unusual alkyl exchange reactions resemble salt metathesis reactions, but with elimination of an alkyllithium instead of a lithium halide. Addition of a large excess of LiCH₂SiMe₃ to 2 or 4 did not generate detectable amounts of 1 by NMR spectroscopy, suggesting that the equilibrium in these reactions lies far to the side of complexes 2 and 4. In contrast, the reaction of [(XA₂)Th(CH ₂SiMe₃)₂] (1-Th) with 2.2 equiv of LiCH ₂CMe₃ yielded an approximate 1:1:3:1 mixture of [(XA ₂)Th(CH₂CMe₃)₂] (2-Th), [(XA ₂)Th(CH₂SiMe₃)(CH₂CMe₃)] (5-Th), LiCH₂SiMe₃, and LiCH₂CMe₃.

Full text of DOI:10.1021/om301136f

Article
pubs.acs.org/Organometallics
Uranium(IV) Alkyl Complexes of a Rigid Dianionic NON-Donor
Ligand: Synthesis and Quantitative Alkyl Exchange Reactions with
Alkyllithium Reagents
Nicholas R. Andreychuk,† Sougandi Ilango,† Balamurugan Vidjayacoumar,† David J. H. Emslie,*,†
and Hilary A. Jenkins‡
†Department of Chemistry and Chemical Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1,
Canada
‡McMaster University Analytical X-ray Diffraction Facility, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S
4M1, Canada
S
* Supporting Information
ABSTRACT: Reaction of [(XA2)UCl3{K(dme)3}] (XA2
=
4,5-bis(2,6-diisopropylanilino)-2,7-di-tert-butyl-9,9-dimethyl-
xanthene) with 2 equiv of ((trimethylsilyl)methyl)lithium or
neopentyllithium afforded red-orange [(XA2)U(CH2SiMe3)2]
(1) and dark red [(XA2)U(CH2CMe3)2] (2), respectively.
Reaction of 1 with an additional 1 equiv of LiCH2SiMe3 in
THF yielded yellow [Li(THF)x][(XA2)U(CH2SiMe3)3] (3),
and reaction of [(XA2)UCl3{K(dme)3}] with 3 equiv of
methyllithium in dme afforded yellow [Li(dme)3][(XA2)-
UMe3] (4). Reaction of 1 with 2.1 equiv of LiCH2CMe3 in
benzene resulted in rapid conversion to 2, with release of 2 equiv of LiCH2SiMe3. Similarly, reaction of 1 with 3.3 equiv of MeLi
in THF provided 4 as the [Li(THF)x]+ salt, accompanied by 2 equiv of LiCH2SiMe3. These unusual alkyl exchange reactions
resemble salt metathesis reactions, but with elimination of an alkyllithium instead of a lithium halide. Addition of a large excess of
LiCH2SiMe3 to 2 or 4 did not generate detectable amounts of 1 by NMR spectroscopy, suggesting that the equilibrium in these
reactions lies far to the side of complexes 2 and 4. In contrast, the reaction of [(XA2)Th(CH2SiMe3)2] (1-Th) with 2.2 equiv of
LiCH2CMe3 yielded an approximate 1:1:3:1 mixture of [(XA2)Th(CH2CMe3)2] (2-Th), [(XA2)Th(CH2SiMe3)(CH2CMe3)]
(5-Th), LiCH2SiMe3, and LiCH2CMe3.
complexes, in particular cyclopentadienyl and cyclooctatetraen-
yl complexes.8 In contrast, actinide alkyl complexes supported
by multidentate noncarbocyclic ligand anions are scarce (Figure
1), despite the potential for such ligands to provide access to
complexes with unique and readily tunable steric and electronic
properties.
We have previously employed McConville’s BDPP ligand
and our own XA2 ligand for the synthesis of neutral
thorium(IV) bis((trimethylsilyl)methyl) and dibenzyl com-
plexes, and these complexes were shown to exhibit high thermal
s t a b i l i t y , c o m p a r a b l e t o t h a t o f b i s -
(pentamethylcyclopentadienyl) analogues.3,16,19 Reaction of
the neutral thorium dialkyls with B(C6F5)3 and [CPh3][B-
(C6F5)4] provided access to the first non-cyclopentadienyl
thorium alkyl cations, for example [(XA2)Th(CH2SiMe3)(η6-
benzene)][B(C6F5)4], and a rare example of a thorium dication,
[(XA2)Th{η6-PhCH2B(C6F5)3}2].17,19 We recently also pre-
INTRODUCTION
■
The early actinide elements occupy a unique position in the
periodic table where the f orbitals have sufficient radial
extension to interact with the ligands and can play an important
role in bonding. Additionally, uranium is able to gain ready
access to a significantly non-lanthanide-like range of oxidation
states, from III to VI.1 These attributes have the potential to
lead to organometallic reactivity inaccessible with transition-
metal and lanthanide complexes, ideally resulting in new and
productive applications for depleted uranium,2 a byproduct of
nuclear isotope enrichment that is currently stockpiled in large
quantities. However, the organometallic chemistry of the
actinide elements, relative to that of the transition metals and
lanthanides, has been slow to develop, despite very early
research efforts to prepare homoleptic actinide alkyl com-
plexes3−7 during the Manhattan project.7,8 Consequently, the
behavior of actinide organometallic complexes in fields such as
olefin polymerization, olefin hydroelementation, small-molecule
(e.g., carbon dioxide) activation, chemical vapor deposition
(CVD), and atomic layer deposition (ALD) remains
comparatively unexplored. Furthermore, the majority of
actinide alkyl chemistry has involved carbocyclic ligand
Special Issue: Recent Advances in Organo-f-Element Chemistry
Received: November 24, 2012
Published: February 19, 2013
© 2013 American Chemical Society
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(CH2SiMe3)2] (1) via unusual alkyl exchange reactivity. For the
purpose of comparison, the alkyl exchange reaction between
[(XA2)Th(CH2SiMe3)2] (1-Th) and LiCH2CMe3 was also
investigated.
RESULTS AND DISCUSSION
■
Reaction of [(XA2)UCl3{K(dme)3}] with 2 equiv of
LiCH2SiMe3 afforded highly soluble [(XA2)U(CH2SiMe3)2]
(1; Scheme 1), which was obtained as red-orange crystals in
64% yield after crystallization from hexanes at −30 °C. The
room-temperature 1H NMR spectrum of 1 in C6D6 or toluene-
d8 (Figure 2) shows only four signals: those for the tert-butyl
groups, the para positions of the 2,6-diisopropylphenyl rings,
and the CH1,8 and CH3,6 positions of the xanthene backbone.
These signals are unaffected by the top−bottom symmetry of
the molecule, since they lie in the plane of the xanthene
backbone of the ligand. All other signals are broadened into the
baseline due to a fluxional process which exchanges the axial
and in-plane CH2SiMe3 groups. However, at low temperature, a
1
full complement of H NMR signals was observed, ranging
from +180 to −225 ppm at −60 °C (Figure 2), indicative of Cs
symmetry.
The X-ray crystal structure of 1·2(n-hexane) (Figure 3 and
Table 1) has two independent but structurally analogous five-
coordinate molecules in the unit cell, each with one CH2SiMe3
group in an axial position and one located approximately in the
plane of the ancillary ligand backbone. The four anionic donors
(we are not suggesting that 1 is four-coordinate) adopt a
distorted-tetrahedral arrangement with N−U−N, C−U−C, and
N−U−C angles of 123.7(2)−123.9(2), 102.7(3)−105.4(3),
and 101.1(2)−112.0(3)°, respectively. The neutral oxygen
donor is located 0.92 and 0.95 Å out of the NUN plane in the
direction of the axial alkyl group, and the complex has
approximate Cs symmetry, consistent with the low-temperature
1H NMR spectra.
Figure 1. Multidentate anionic ligands previously employed in the
synthesis of actinide alkyl9 complexes: (a) Tp,10 Tp′,11 and B(pz)4 (pz
= pyrazolate);12 (b) amidinate;13 (c) MesDABMe;6 (d) tBuNON;14,15 (e)
dippNCOCN;15 (f) BDPP;3,5,16,17 (g) NNfc;5,18 (h) XA2;3,17,19 (i) Et8-
calix[4]tetrapyrrole.20
The U−C distances of 2.368(7)−2.418(7) Å are comparable
with those observed for the other crystallographically
characterized neutral uranium(IV) (trimethylsilyl)methyl com-
plex, Leznoff’s [{(O(CH2CH2NAr)2}U(CH2SiMe3)2] (Ar =
2,6-diisopropylphenyl; U−C = 2.40(2) and 2.44(2) Å), but are
shorter than those in Hayton’s anionic [Li14(OtBu)12Cl][U-
(CH2SiMe3)5] (U−C = 2.445(6)−2.485(6) Å). The U−C−Si
pared an NSN-donor analogue of the XA2 ligand, TXA2, and
reported a study of U−O versus U−S covalency in tri- and
tetravalent uranium XA2 and TXA2 chloro complexes.21 Herein
we describe the synthesis of neutral uranium(IV) dialkyl and
anionic uranium(IV) trialkyl complexes prepared either from
[(XA2)UCl3{K(dme)3}] by salt metathesis or from [(XA2)U-
Scheme 1. Synthesis of Complexes 1 and 2
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Figure 2. 1H NMR spectra (500 MHz): (a) [(XA2)U(CH2SiMe3)2] (1) in toluene-d8 at room temperature; (b) complex 1 in toluene-d8 at −60 °C;
and (c) in situ generated [Li(THF)x][(XA2)U(CH2SiMe3)3] (3) in THF-d8 at −50 °C. In the figure, * denotes toluene-d8 and × denotes n-pentane.
Numbers below the baseline indicate the integration of each peak. Signals for U−CH2 protons, which are located at very high (>100 ppm) and very
low (<−100 ppm) frequencies in spectra b and c, are not shown. The CMe3 peaks are truncated in all three spectra, and the inset shows a portion of
spectrum c.
ether linkages, presumably due to steric constraints imposed by
the rigid ligand framework.
The geometry of 1 is analogous to that of the thorium
analogue, 1-Th,3,22 although the An−C, An−N, and An−O
distances in 1 are slightly shorter (Table 1), consistent with the
smaller size of uranium (the six-coordinate ionic radii for U4+
and Th4+ are 0.89 and 0.94 Å, respectively).23 In addition, the
xanthene backbone in 1 deviates further from planarity (the
angles between the two aryl rings of the xanthene backbone are
17.6 and 19.0° for 1 versus 9.0° for 1-Th), and uranium is
positioned further from the NON donor plane (0.64 and 0.65
Å for 1 versus 0.48 Å for 1-Th). However, the N1···N2 distance
in 1 is only slightly shorter than that in the thorium analogue
(4.00 and 4.02 Å in 1 versus 4.06 Å in 1-Th), and the extent to
which the 2,6-diisopropylphenyl groups are rotated away from
the axial alkyl group are similar in 1 and 1-Th (C(33)···C(42)
= 7.63 and 7.70 Å and C(30)···C(45) = 4.63 and 4.86 Å in 1;
the corresponding distances in 1-Th are 7.51 and 5.00 Å).
Addition of 2.1 equiv of LiCH2CMe3 to [(XA2)U-
(CH2SiMe3)2] (1) in C6D6 resulted in quantitative conversion
to [(XA2)U(CH2CMe3)2] (2) with release of 2 equiv of
LiCH2SiMe3 (Scheme 1). Treatment of complex 2 with up to
80 equiv of LiCH2SiMe3 in C6D6 did not re-form detectable
Figure 3. X-ray crystal structure of [(XA2)U(CH2SiMe3)2]·2(n-
hexane) (1·2(n-hexane)) with thermal ellipsoids at the 30% probability
level (collected at 173 K). Only one of the two independent molecules
in the unit cell is shown. Hydrogen atoms and hexane solvent are
omitted for clarity.
angles of 128.2(3)−130.8(3)° are in line with previously
reported values (125.7(3)−130.6(3)°), and the U−N distances
are unremarkable.21 However, as previously discussed in the
context of [(XA2)UCl3{K(dme)3}], [(XA2)UCl(dme)]21 and
[(XA2)Th(CH2SiMe3)2] (1-Th),3 the An−Oxant distances in
XA2 actinide complexes (2.484(5) and 2.504(4) Å in 1) are
invariably shorter than might be expected for actinide−diaryl
1
amounts of 1 by H NMR spectroscopy; thus, the equilibrium
in this reaction must lie far to the side of complex 2. This
unusual reaction bears a resemblance to salt metathesis (both
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for XA2 Complexes 1, 2, and 4 as Well as the Previously Reported 1-Th
and [(XA2)UCl3{K(dme)3}]
(XA2)Th
(CH2SiMe3)2 (1-Th)
(XA2)U(CH2SiMe3)2
(XA2)U(CH2CMe3)2
(XA2)UMe3 anion
(1)
(2)
(4)
(XA2)UCl3K(dme)3
lattice solvent
ref
toluene
3
2 n-hexane
n-hexane
dme
none
this work
this work
this work
21
An−O
2.535(4)
2.484(5), 2.504(4)
2.528(5), 2.529(5)
2.517(5)
2.465(3)
An−N
2.291(4), 2.312(4) 2.261(5), 2.262(5),
2.272(5), 2.280(5)
2.260(6), 2.272(6),
2.279(5), 2.289(6)
2.363(6), 2.373(6)
2.297(4), 2.306(4)
An−Caxial or An−Claxial
2.467(6)
2.368(7), 2.380(7)
2.386(8), 2.396(7)
U−C48: 2.377(9)
U−C50: 2.493(8)
U−C49: 2.506(9)
U−Cl2:
2.620(2), 2.625(2)
U−Cl3:
2.629(2), 2.628(2)
An−Cin plane or An−Clin plane
2.484(6)
2.393(7), 2.418(7)
2.409(7), 2.417(7)
U−Cl1:
2.632(2), 2.619(3)
An−C−Caxial or An−C−Siaxial
An−C−Cin plane or An−C−Siin plane
C−An−C or Cl−An−Cl
126.8(3)
127.6(3)
111.9(2)
128.2(3), 130.4(3)
130.5(4), 130.8(3)
103.2(2), 105.0(2)
134.3(5), 134.4(5)
130.3(5), 130.3(5)
105.1(2), 106.6(3)
n/a
n/a
n/a
n/a
C48−U−C49:
Cl1−U−Cl2:
84.2(3)
89.91(6)
C49−U−C50:
Cl1−U−Cl3:
85.7(3)
88.25(6)
C48−U−C50:
Cl2−U−Cl3:
169.9(3)
177.07(6)
N−An−N
N−An−O
123.8 (2)
123.7(2), 124.0(2)
120.8(2), 120.9(2)
124.8(2)
129.1(1)
62.9(1), 63.0(1)
63.9(2), 64.0(2),
64.2(2), 64.4(2)
64.4(2), 64.5(2),
64.7(2), 65.1(2)
63.7(2), 63.8(2)
64.9(1), 65.5(1)
N−An−Caxial or N−An−Claxial
100.6(3), 100.8(2) 101.0(2), 101.6(2),
103.2(2), 103.3(2)
103.6(2), 105.5(2),
105.8(2), 108.5(2)
N−U−C48:
N−U−Cl2:
92.4(2), 93.1(2)
89.2(1), 92.5(1)
N−U−C50:
N−U−Cl3:
90.5(2), 93.3(2)
89.6(1), 90.3(1)
N−An−Cin plane or N−An−Clin plane
109.1(2), 109.7(2) 108.1(2), 110.8(2),
111.7(2), 112.5(2)
107.6(2), 108.3(2),
109.2(2), 109.8(2)
N−U−C49:
N−U−Cl1:
114.8(3), 120.3(3)
114.6(1), 116.2(1)
O−(N/An/N-plane)
An−(N/O/N-plane)
angle between xanthene aromatic rings 9.0
0.66
0.48
0.92
1.23, 1.29
0.84, 0.87
33.4, 34.2
4.16, 4.22
8.01, 8.07
3.95, 3.96
0.75
0.54
6.5
0.53
0.34
1.2
0.64, 0.65
17.6, 19.0
4.63, 4.86
7.63, 7.70
4.00, 4.02
C(30)···C(45) or analogous in 1-Th
C(33)···C(42) or analogous in 1-Th
N(1)···N(2)
4.00
7.30
6.11
4.20
6.87
6.35
4.16
7.51
4.06
alkyl exchange and salt metathesis are classes of transmetalation
reactions), but with elimination of LiCH2SiMe3 instead of a
lithium halide. It is not unique to uranium, since the reaction
between 1-Th and 15 equiv of LiCH2CMe3 cleanly provided
[(XA2)Th(CH2CMe3)2] (2-Th; Figure S5 (Supporting In-
formation)). However, addition of 2.2 equiv of LiCH2CMe3 to
1-Th yielded an approximate 1:1:3:1 mixture of 2-Th,
[(XA2)Th(CH2SiMe3)(CH2CMe3)] (5-Th), LiCH2SiMe3,
and LiCH2CMe3 (Scheme 2 and Figure S4 (Supporting
Information)). This product distribution was established within
5 min and did not change with extended reaction times (days),
consistent with a significantly smaller equilibrium constant for
the reaction of 1-Th with LiCH2CMe3, relative to the reaction
of uranium complex 1 with LiCH2CMe3. Complex 5-Th is the
mixed alkyl species that must form en route from 1-Th to 2-Th,
and both 2-Th and 5-Th were characterized in situ by 1H, 13C,
and 2D NMR spectroscopy (at low temperature for 2-Th).
Complex 2 could also be prepared by a traditional salt
metathesis reaction between [(XA2)UCl3{K(dme)3}] and 2
equiv of LiCH2CMe3 (Scheme 1), and dark red crystals of 2·(n-
hexane) were obtained from a concentrated hexanes solution at
−30 °C. Many of the peaks in the room-temperature 1H NMR
spectrum of 2 are extremely broad, indicative of a fluxional
process which exchanges the axial and in-plane alkyl groups, but
as for complex 1, a sharp spectrum consistent with Cs symmetry
was observed at low temperature (Figure 4).
Scheme 2. Reactions of 1-Th with 2.2 and 15 equiv of
LiCH2CMe3
The solid-state geometry of complex 2 (Figure 5 and Table
1) is analogous to that of 1, and as with 1, there are two
independent but structurally analogous molecules in the unit
cell. The U−C and U−N distances are comparable with those
in 1, despite the increased basicity of CH2CMe3 groups relative
to CH2SiMe3 groups,24 and the U−O distances are only
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Figure 4. 500 MHz 1H NMR spectra of [(XA2)U(CH2CMe3)2] (2) in toluene-d8 at temperatures from 25 to −50 °C. Numbers below the baseline
indicate the integration of each peak. Signals for U−CH2 protons, which are located at very high (>100 ppm) and very low (<−100 ppm)
frequencies, are not shown. The inset at the bottom shows a portion of the −50 °C spectrum.
mixture of unidentified paramagnetic products with concom-
itant evolution of SiMe4 or CMe4, respectively. Upon further
heating at 60−80 °C for 24−48 h, 1 and 2 were fully
decomposed to give spectra dominated by SiMe4 or CMe4 (at
1
this point, H NMR signals attributable to diamagnetic or
paramagnetic XA2 ligand-containing products were low in
intensity). We have previously reported similar behavior for the
decomposition of [(XA2)Th(CH2SiMe3)2] (1-Th) at 90 °C.3
The reaction to convert 1 to 2 presumably occurs via trialkyl
“ate” intermediates, as shown in Scheme 3. These intermediates
were not detected in the reaction of 1 with LiCH2CMe3 in
aromatic solvents, and reaction of complex 1 with up to 20
equiv of LiCH2SiMe3 in C6D6 did not provide any evidence for
the formation of [(XA2)U(CH2SiMe3)3]− by 1H NMR
Figure 5. X-ray crystal structure of [(XA2)U(CH2CMe3)2]·(n-hexane)
(2·(n-hexane)) with thermal ellipsoids at the 50% probability level
spectroscopy. However, trialkyl “ate” complexes did prove
(collected at 100 K). Only one of the two independent molecules in
the unit cell is shown. Hydrogen atoms and hexane solvent are omitted
for clarity. One tert-butyl group is disordered and so was refined
Scheme 3. Proposed Reaction Pathway for the Conversion
of 1 to 2
isotropically, and only one of the two orientations of the disordered
tert-butyl group is shown.
marginally longer than those in 1. However, due to the
increased steric presence of the neopentyl anion, uranium is
located further from the NON donor plane in complex 2 (0.84
and 0.87 Å versus 0.64 and 0.65 Å in 1), and the neutral oxygen
donor is located further (1.23 and 1.29 Å versus 0.92 and 0.95
Å in 1) from the NUN plane. In addition, the ligand backbone
deviates further from planarity (the angles between the
aromatic rings in the xanthene backbone are 33.4 and 34.2°
versus 17.6 and 19.0° in 1), and the 2,6-diisopropylphenyl
groups are more strongly rotated away from the axial alkyl
group so as to minimize unfavorable steric interactions:
C(33)···C(42) = 8.01 and 8.07 Å and C(30)···C(45) = 4.16
and 4.22 Å (cf. C(33)···C(42) = 7.63 and 7.70 Å and
C(30)···C(45) = 4.63 and 4.86 Å in 1).
Dialkyl complexes 1 and 2 are thermally stable for days at
room temperature in aromatic solvents. However, over the
course of several days at 45 °C, 1 and 2 were converted to a
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accessible in THF; addition of 1.3 equiv of LiCH2SiMe3 to 1 in
THF yielded [Li(THF)x][(XA2)U(CH2SiMe3)3] (3), which
was characterized in situ by variable-temperature H NMR
spectroscopy (Figure 2), and addition of 3.3 equiv of MeLi to 1
in THF cleanly afforded [Li(THF)x][(XA2)UMe3] (4; Scheme
4 and Figure S6 (Supporting Information)). Hexane-insoluble
Å longer than those in complexes 1 and 2, and only the U−
C(48) distance of 2.377(9) Å falls within the range observed
for the U−C bonds in 1 and 2; the U−C(49) and U−C(50)
bonds in 4 are substantially longer at 2.493(8) and 2.506(9) Å.
The elongated uranium−ligand bond lengths in 4 can be
explained on the basis of an increased coordination number at
uranium and an overall anionic charge on the complex. The
geometry of complex 4 is analogous to that in six-coordinate
[(XA2)UCl3{K(dme)3}], which also exhibits a planar xanthene
backbone and a trigonal-bipyramidal arrangement of the
anionic donors. However, the U−O and U−N distances in 4
are substantially longer than those in [(XA2)UCl3{K(dme)3}]
(Table 1), most likely due to decreased Lewis acidity, increased
steric hindrance, and complete separation of the anionic
portion of the complex from the alkali-metal countercation in 4.
The extent to which the reactions of 1 with 2.1 equiv of
LiCH2CMe3 (in benzene) or 3.3 equiv of MeLi (in THF) lie
toward the side of the products (2 or 4 and LiCH2SiMe3) is
remarkable and likely25 reflects the increased basicity of
neopentyl and methyl anions in comparison with the
(trimethylsilyl)methyl anion,24 leading to stronger uranium−
alkyl bonds. The requirement for addition of more than 2 equiv
of LiCH2CMe3 to convert 1-Th to 2-Th is also intriguing in
that it highlights distinct differences in the reactivity of thorium
and uranium.
1
Scheme 4. Synthesis of Complexes 3 and 4
Previously reported alkyl exchange reactions at electro-
positive d- or f-element centers include (1) synthesis of [{o-
C6H4(N-Dipp)(PPh(C6H4)(N-Mes))}LuMe(THF)2] by
treatment of [{o-C6H4(N-Dipp)(PPh(C6H4)(N-Mes))}Lu-
(CH2SiMe3)(THF)] with 10 equiv of AlMe3 in THF,26 (2)
reaction of [Me2Si(2-Me-C9H5)2}YMe(THF)] with AlEt3
followed by addition of THF to yield an approximately 1:1
mixture of the starting methyl complex and [Me2Si(2-Me-
C9H5)2}YEt(THF)],27 and (3) exchange between a growing
polymer chain on a d- or f-element polymerization catalyst and
the alkyl group of an added trialkylaluminium,28−31 trialkylbor-
on,32 dialkylzinc30,31,33 or dialkylmagnesium34 reagent. This last
mode of reactivity is typically detrimental to olefin polymer-
ization activity35 but has found productive use in chain-
shuttling alkene polymerization33 and metal-catalyzed “Auf-
baureaktion” chemistry.28,31 Alkyl exchange reactions involving
alkyllithium reactions are more scarce but have been reported
for dialkylmercury compounds in combination with alkyl-
lithium reagents; these reactions proceed to completion when
the alkyllithium product is insoluble in the solvent employed.36
The alkyl exchange reactions in this work also bear
resemblance to salt metathesis-like reactions involving cyclo-
pentadienyl anion elimination from polar metallocenes. These
include the reaction of [{Cp*2U}2(μ-η6:η6-C6H6)] with MX
(M = K, X = N(SiMe3)2, OC6H2(CMe3)2-2,6-Me-4; M = Li, X
[Li(dme)3][(XA2)UMe3] (4; Scheme 4) could also be
prepared from the reaction of [(XA2)UCl3{K(dme)3}] with 3
equiv of MeLi in dme. In contrast, reactions of 1 or
[(XA2)UCl3{K(dme)3}] with 2 equiv of MeLi in dme or
THF yielded mixtures of unidentified products. Anionic 3 and
4 are less thermally stable than neutral 1 and 2, decomposing
over several days at room temperature in THF to produce a
mixture of unidentified paramagnetic products accompanied by
SiMe4 or CH4, respectively.
The room-temperature 1H NMR spectrum of 4 in THF-d8 is
consistent with a top−bottom-symmetric environment (C2v
symmetry) on the NMR time scale. Golden yellow X-ray-
quality crystals of 4·dme were obtained from dme/hexanes at
−30 °C; the ligand backbone in six-coordinate 4 (Figure 6) is
i
= CH(SiMe3)2, PrNCMeNiPr) to form [{Cp*XU}2(μ-η6:η6-
C6H6)],37 reaction of [MnCp2] with LiC2Ph in THF to provide
0.5 [{CpMn(μ-C2Ph)(THF)}2],38 reaction of [MnCp2] with 1
or 3 equiv of Li(hpp) to afford 0.5 [{CpMn(hpp)}2] or
[{LiMn(hpp)3}2],39 reaction of [VCp2] with 2 equiv of Li(hpp)
to give 0.25 [{V2(hpp)4}Li(μ-Cp)Li(μ-Cp)Li{V2(hpp)4}]-
[CpLi(μ-Cp)LiCp],40 and reaction of [CrCp2] with 2 equiv
of Li(MeNCHNMe) to yield 0.5 [Cr2(MeNCHNMe)4].41
Figure 6. X-ray crystal structure of [Li(dme)3][(XA2)UMe3]·dme
(4·dme) with thermal ellipsoids at 30% (collected at 173 K).
+
Hydrogen atoms, dme lattice solvent, and the Li(dme)3 cation are
omitted for clarity.
approximately planar (the angle between the two aryl rings of
the xanthene backbone is 6.5°), uranium is located 0.54 Å from
the NON donor plane, the five anionic donors in 4 form a
trigonal bipyramid (we are not suggesting that 4 is five-
coordinate) with methyl groups in axial positions, and the
neutral donor is located 0.75 Å out of the NUN plane in the
direction of C(50). The U−N distances are approximately 0.1
SUMMARY AND CONCLUSIONS
■
The preparation and crystallographic characterization of
[(XA2)U(CH2SiMe3)2] (1), [(XA2)U(CH2CMe3)2] (2), and
[(XA2)UMe3]− (4) and in situ syntheses of [(XA2)U-
1471
dx.doi.org/10.1021/om301136f | Organometallics 2013, 32, 1466−1474

Organometallics
Article
(CH2SiMe3)3]− (3), [(XA2)Th(CH2CMe3)2] (2-Th), and
[(XA2)Th(CH2SiMe3)(CH2CMe3)] (5-Th) are reported.
Reaction of 1 with 2.1 equiv of LiCH2CMe3 in benzene
resulted in rapid conversion to 2 and 2 equiv of LiCH2SiMe3.
This unusual exchange reaction resembles salt metathesis and
presumably proceeds via undetected trialkyl “ate” intermedi-
ates. Reactions of this type may find utility for clean in situ
generation of new alkyl complexes but are only likely to be of
preparative value if the solubility of the alkyllithium byproduct
permits its complete removal. The generality of this type of
alkyl exchange reaction also remains to be determined.
However, it is notable that while the reaction of 1 with 2.1
equiv of LiCH2CMe3 proceeds quantitatively to the dineopen-
tyl complex, the analogous reaction of [(XA2)Th(CH2SiMe3)2]
(1-Th) requires a significant excess of LiCH2CMe3 to reach
completion.
[(XA2)U(CH2SiMe3)2] (1). A mixture of [(XA2UCl3{K(dme)3}]
(0.150 g, 0.11 mmol) and LiCH2SiMe3 (0.022 g, 0.24 mmol) in
hexanes (20 mL) was stirred at −78 °C and then warmed slowly to
room temperature; stirring was continued for a total of 12 h. The
orange-red solution was evaporated to dryness in vacuo, and the solid
residue was extracted with a minimum amount of hexanes. The
suspension was centrifuged to remove insoluble KCl and LiCl, and the
red mother liquors were cooled to −30 °C. After a few days, X-ray-
quality bright red crystals of 1·2(n-hexane) were collected in two
batches and dried in vacuo to provide 0.079 g of 1 (0.072 mmol, 64%
yield). Alternatively, crystallization from a minimum amount of n-
pentane at −30 °C followed by drying in vacuo provided 1·(n-
1
pentane) in comparable yield. H NMR (C6D6, 200 MHz, 298 K): δ
12.30, 7.32 (broad s, 2 × 2H, CH1,8 and CH3,6), 7.25 (t, 3JH,H = 8 Hz,
1
2H, Aryl-para), 2.82 (s, 18H, CMe3). H NMR (toluene-d8, 500.1
MHz, 298 K): δ 11.41, 8.27 (broad s, 2 × 2H, CH1,8 and CH3,6), 7.56
(t, 3JH,H = 9.3 Hz, 2H, Aryl-para), 2.87 (s, 18H, CMe3). UCH2 protons
1
were not observed at room temperature. H NMR (toluene-d8, 500.1
MHz, 213 K): δ 178.2, −222.3 (extremely broad s, 2 × 2H, UCH2),
25.00, 13.51 (broad s, 2 × 3H, CMe2), 17.93, 4.71 (broad s, 2 × 2H,
CH1,8 and CH3,6), 17.69, −2.08 (broad s, 2 × 9H, SiMe3), 6.45 (broad
s, 2H, Aryl-para), 5.54, 1.33 (broad s, 2 × 2H, Aryl-meta), 3.40 (s,
18H, CMe3), −3.14, −14.47, −16.61, −26.85 (broad s, 4 × 6H,
CHMe2), −29.86, −96.02 (v broad s, 2 × 2H, CHMe2). Anal. Calcd
for C55H84N2OSi2U: C, 60.97; H, 7.81; N, 2.59. Found: C, 61.05; H,
8.06; N, 2.38.
[(XA2)U(CH2CMe3)2] (2). Method 1. A mixture of [(XA2UCl3{K-
(dme)3}] (0.250 g, 0.19 mmol) and LiCH2CMe3 (0.031 g, 0.39
mmol) in hexanes (25 mL) was stirred at −78 °C and then warmed
slowly to room temperature; stirring was continued for a total of 12 h.
The deep red solution was evaporated to dryness in vacuo, and the
solid residue was extracted with a minimum amount of n-pentane. The
suspension was centrifuged to remove insoluble KCl and LiCl, and the
deep red mother liquors were cooled to −30 °C. After a few days, deep
red crystals were collected in two batches and dried in vacuo to
provide 0.146 g of 2·(n-pentane) (0.13 mmol, 69% yield).
Alternatively, crystallization from a minimum amount of hexanes at
−30 °C provided X-ray-quality crystals of 2·(n-hexane) in comparable
yield.
EXPERIMENTAL SECTION
■
General Details. General synthetic procedures have been reported
elsewhere.3,16,17,19,42 Deuterated solvents were purchased from ACP
Chemicals. Neopentyl chloride was purchased from Strem Chemicals.
LiCH2SiMe3 (1.0 M in n-pentane) and MeLi (1.60 M in OEt2)
solutions were purchased from Sigma-Aldrich, and prior to use, solid
LiCH2SiMe3 and MeLi were obtained by removal of solvent in vacuo.
H2[XA2],3 UCl4,43 [(XA2)UCl3{K(dme)3}],21 [(XA2)Th-
(CH2SiMe3)2] (1-Th),3 and LiCH2CMe3 were prepared using
44
literature procedures. In situ reactions to form 2 (method 2), 3, 4
(method 2), and 5-Th involved the use of small amounts (3.0−0.7
mg) of alkyllithium reagents. These reagents were weighed out as
accurately as possible using an analytical balance (accurate to 0.1 mg),
but the actual reported stoichiometries of these reactions were
determined by 1H NMR integration. Sonication was employed in
several NMR tube reactions in lieu of stirring. If sonication was
continued for extended periods of time, the water in the sonicator was
changed periodically (approximately every 30 min) to prevent
undesired heating of the reaction.
Combustion elemental analyses were performed on a Thermo
EA1112 CHNS/O analyzer by Ms. Meghan Fair or Dr. Steve Kornic
of this department. X-ray crystallographic analyses were performed on
suitable crystals coated in Paratone oil and mounted on a SMART
APEX II diffractometer with a 3 kW sealed-tube Mo generator at the
McMaster Analytical X-ray (MAX) Diffraction Facility. Three of four
molecules of n-hexane in the unit cell of 1·2(n-hexane) (Z = 2), and
two molecules of n-hexane in the unit cell of 2·(n-hexane) (Z = 2)
were highly disordered and could not be modeled satisfactorily and so
were treated using the SQUEEZE routine.45 1H, 13C{1H}, DEPT-q,
COSY, HSQC, and HMBC NMR spectroscopy was performed on
Method 2. Complex 2 was generated in situ by reaction of 1·(n-
pentane) (0.015 g, 0.013 mmol) with 2.1 equiv of LiCH2CMe3
(0.0021 g, 0.027 mmol) in C6D6. After approximately 1 h of
1
sonication, H NMR indicated complete conversion of 1 to 2 (the
reaction was usually complete after 20 min) with concomitant release
of LiCH2SiMe3. Method 2 was not pursued as a means to isolate pure
1
2, since both 2 and LiCH2SiMe3 are highly soluble in hexanes. H
NMR (C6D6, 500.1 MHz, 298 K): δ 141.1, −142.1 (extremely broad s,
2 × 2H, UCH2), 20.02, −2.43 (v broad s, 2 × 9H, CH2CMe3), 17.51,
10.17 (v broad s, 2 × 3H, CMe2), 14.71, 4.05 (s, 2 × 2H, CH1,8 and
CH3,6), 5.57 (t, 3JH,H = 8 Hz, 2H, Aryl-para), 4.42, 2.02 (v broad s, 2 ×
2H, Aryl-meta), 2.61 (s, 18H, CMe3), −3.89, −9.21, −18.84 (v broad
s, 4 × 6H, CHMe2), −27.15, −49.21 (v broad s, 2 × 2H, CHMe2). 1H
NMR (toluene-d8, 500.1 MHz, 298 K): δ 134.5, −138.8 (extremely
broad s, 2 × 2H, UCH2), 18.78, −2.77 (v broad s, 2 × 9H, CH2CMe3),
16.66, 9.80 (v broad s, 2 × 3H, CMe2), 14.26, 4.63 (s, 2 × 2H, CH1,8
and CH3,6), 5.71 (t, 3JH,H = 8.6 Hz, 2H, Aryl-para), 4.88, 2.29 (v broad
s, 2 × 2H, Aryl-meta), 2.66 (s, 18H, CMe3), −3.43, −8.48, −8.92,
−16.73 (v broad s, 4 × 6H, CHMe2), −24.98, −48.17 (v broad s, 2 ×
1
Bruker AV-200, DRX-500, and AV-600 spectrometers. All H NMR
spectra were referenced relative to SiMe4 through a resonance of the
employed deuterated solvent or protio impurity of the solvent: C6D6
(7.16 ppm), C7D8 (7.09, 7.01, 6.97, 2.08 ppm), and THF-d8 (3.58,
1.73 ppm) for 1H NMR, and C6D6 (128.0 ppm), C7D8 (137.48,
128.87, 127.96, 125.13, 20.43 ppm), and THF-d8 (67.57, 25.37 ppm)
for 13C NMR.
All NMR spectra were obtained at room temperature unless
otherwise specified. Herein, Aryl = 2,6-diisopropylphenyl, and the
numbering scheme (CH1,8, C2,7, CH3,6, C4,5, C10/13, and C11,12) for the
xanthene ligand backbone is shown in Scheme 1. Most peaks in the 1H
NMR spectra of paramagnetic uranium(IV) complexes could be
assigned on the basis of integration. The para aryl, CH1,8, CH3,6, and
tert-butyl signals were also readily identified, since they are unaffected
by the presence/absence of top−bottom symmetry on the NMR time
scale. Furthermore, the para Ar signal always appeared as a triplet at
room temperature, allowing definite assignment. The broad signals
integrating to 2H and located between −25 and −100 ppm in the
spectra of 1 and 2 were speculatively assigned as the isopropyl methine
protons (rather than the meta aryl protons), given their close
proximity to the paramagnetic U(IV) center.
1
2H, CHMe2). H NMR (toluene-d8, 500.1 MHz, 223 K): δ 223.3,
−221.5 (extremely broad s, 2 × 2H, UCH2), 33.64, −2.39 (broad s, 2
× 9H, CH2CMe3), 28.61, 15.47 (broad s, 2 × 3H, CMe2), 20.13, 0.81
(broad s, 2 × 2H, CH1,8 and CH3,6), 4.45 (broad t, 2H, Aryl-para),
3.02 (s, 18H, CMe3), 1.81, −1.12 (broad s, 2 × 2H, Aryl-meta), −7.35,
−16.10, −16.48, −25.70 (broad s, 4 × 6H, CHMe2), −46.92, −84.92
(v broad s, 2 × 2H, CHMe2). Anal. Calcd for C62H96N2OU: C, 66.28;
H, 8.61; N, 2.49. Found: C, 66.76; H, 8.01; N, 2.39.
[Li(THF)x][(XA2)U(CH2SiMe3)3] (3; in Situ). A mixture of
[(XA2)U(CH2SiMe3)2]·(n-pentane) (1·(n-pentane); 0.010 g, 0.009
mmol) and 1.3 equiv of LiCH2SiMe3 (0.0011 g, 0.011 mmol) were
taken up in THF-d8 to afford a yellow solution. Five minutes after
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Organometallics
Article
mixing, 1H NMR revealed new signals corresponding to 3, with
concomitant loss of 1. H NMR (THF-d8, 500.1 MHz, 298 K): δ
[(XA2)Th(CH2SiMe3)(CH2CMe3)] (5-Th; in Situ). A mixture of
[(XA2)Th(CH2SiMe3)2]·0.5O(SiMe3)2 (1-Th·0.5O(SiMe3)2) (0.020
g, 0.017 mmol) and 2.2 equiv of LiCH2CMe3 (0.0030 g, 0.04 mmol)
were taken up in toluene-d8 to afford a colorless solution. Five minutes
after mixing, 1H NMR revealed new signals corresponding to an
approximate 1:1:3:1 mixture of 5-Th, 2-Th, free LiCH2SiMe3, and
remaining LiCH2CMe3, with concomitant loss of 1-Th. 1H NMR of 5-
1
314.6, 268.8, −161.0 (extremely broad s, 3 × 2H, UCH2), 35.08,
23.20, −14.20 (v broad s, 3 × 9H, CH2SiMe3), 28.34, −9.54, −11.39,
−24.50 (v broad s, 4 × 6H, CHMe2), 5.85, −12.40 (v broad s, 2 × 2H,
Aryl-meta), 4.70, −9.50 (v broad s, 2 × 3H, CMe2), 0.19 (t, 3JH,H = 7
Hz, 2H, Aryl-para), −1.49, −28.03 (s, 2 × 2H, CH1,8 and CH3,6),
−1.65, −56.37 (v broad s, 2 × 2H, CHMe2), −5.34 (s, 18H, CMe3).
1H NMR (THF-d8, 500.1 MHz, 223 K): δ 451.0, 378.0, −236.9
(extremely broad s, 3 × 2H, UCH2), 49.48, 30.58, −21.27 (broad s, 3
× 9H, CH2SiMe3), 39.69, −12.53, −13.32, −30.85 (broad s, 4 × 6H,
CHMe2), 5.68, −13.68 (broad s, 2 × 3H, CMe2), 4.07, −20.03 (broad
s, 2 × 2H, Aryl-meta), −0.86, −60.16 (v broad s, 2 × 2H, CHMe2),
−3.37 (broad s, 2H, Aryl-para), −5.28, −40.72 (broad s, 2 × 2H,
CH1,8 and CH3,6), −8.04 (s, 18H, CMe3).
[Li(dme)3][(XA2)UMe3] (4). Method 1. A mixture of
[(XA2UCl3{K(dme)3}] (0.150 g, 0.11 mmol) and MeLi (0.008 g,
0.37 mmol) in dme (20 mL) was stirred at −78 °C and then warmed
slowly to room temperature; stirring was continued for a total of 12 h.
The yellow solution was evaporated to dryness in vacuo, and the solid
residue was extracted with toluene (20 mL). The suspension was
filtered to remove insoluble KCl and LiCl, and the yellow filtrate was
evaporated to dryness in vacuo. The solid residue was taken up in
minimal dme and layered with hexanes. After a few days at −30 °C, X-
ray-quality crystals of 4·dme were obtained and dried in vacuo to
provide 0.046 g of 4·dme (0.035 mmol, 31% yield). The low yield
likely results from losses during extraction as a consequence of poor
solubility in toluene.
3
Th (toluene-d8, 600.1 MHz, 298 K): δ 7.29, 7.21 (dd, JH,H = 7.7 Hz;
3
4JH,H = 1.7 Hz, 2 × 2H, Aryl-meta), 7.26 (t, JH,H = 7.7 Hz, 2H, Aryl-
para), 6.77, 6.04 (d, 4JH,H = 2 Hz, 2 × 2H, CH1,8 and CH3,6), 3.83, 3.32
3
(broad sept, JH,H = 7 Hz, 2 × 2H, CHMe2), 1.70, 1.64 (s, 2 × 3H,
CMe2), 1.50, 1.32, 1.25, 1.08 (d, 3JH,H = 7 Hz, 4 × 6H, CHMe2), 1.19
(s, 18H, CMe3), 0.74 (s, 9H, ThCH2CMe3), 0.21 (broad s, 2H,
ThCH2CMe3), 0.05 (s, 9H, ThCH2SiMe3), −0.11 (broad s, 2H,
ThCH2SiMe3). 13C{1H} NMR of 5-Th (toluene-d8, 150 MHz, 298 K):
δ 148.36, 147.86 (2 × Aryl-Cortho), 148.23 (C2,7), 145.92 (C4,5), 142.0
(C11,12), 135.66 (Aryl-Cipso), 129.79 (C10,13), 128.26 (Aryl-Cpara),
125.55, 125.48 (2 × Aryl-Cmeta), 110.49, 110.19 (CH1,8 and CH3,6),
37.44 (ThCH2CMe3), 35.54 (ThCH2CMe3), 35.26 (CMe2), 35.12
(CMe3), 33.87, 28.33 (2 × CMe2), 31.63 (CMe3), 29.43, 28.47 (2 ×
CHMe2), 26.92, 25.91, 25.46, 24.77 (4 × CHMe2), 3.48
(ThCH2SiMe3).
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Figures giving H NMR spectra of 1 (variable temperature), 3
(variable temperatue), 4, 1-Th, 2-Th, and 5-Th and CIF files
giving crystallographic data for 1, 2, and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
Method 2. Complex 4 can be prepared cleanly in situ by reaction of
1·(n-pentane) (0.010 g, 0.009 mmol) and MeLi (0.0007 g, 0.03 mmol)
1
in THF-d8 to afford a yellow solution. After 30 min of sonication, H
NMR revealed new signals corresponding to 4 with concomitant loss
of 1. 1H NMR (THF-d8, 500.1 MHz, 298 K): δ 6.29, −7.04 (broad s, 2
× 12H, CHMe2), −1.53 (t, 3JH,H = 6 Hz, 2H, Aryl-para), −2.26 (s, 6H,
CMe2), −2.44, −28.86 (s, 2 × 2H, CH1,8 and CH3,6), −4.59 (v broad
AUTHOR INFORMATION
Corresponding Author
*Tel: 905-525-9140. Fax: 905-522-2509. E-mail: emslied@
mcmaster.ca.
■
3
s, 4H, CHMe2), −5.69 (s, 18H, CMe3), −5.84 (d, JH,H = 5 Hz, 4H,
Aryl-meta). Signals corresponding to the UCH3 protons were not
located between +400 and −400 ppm. Anal. Calcd for
C62H101N2O7LiU prepared using method 1: C, 60.47; H, 8.27; N,
2.27. Found: C, 60.79; H, 7.73; N, 2.08.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
[(XA2)Th(CH2CMe3)2] (2-Th; in Situ). A mixture of [(XA2)Th-
(CH2SiMe3)2]·0.5O(SiMe3)2 (1-Th·0.5O(SiMe3)2) (0.020 g, 0.017
mmol) and 15 equiv of LiCH2CMe3 (0.022 g, 0.26 mmol) were taken
up in toluene-d8 to afford a colorless solution. Five minutes after
mixing, 1H NMR revealed new signals corresponding to 2-Th and free
■
D.J.H.E. thanks the NSERC of Canada for a Discovery Grant,
and N.R.A. thanks the Government of Ontario for an Ontario
Graduate Scholarship (OGS) and McMaster University for a
Richard Fuller Memorial Scholarship.
1
LiCH2SiMe3, with concomitant loss of 1-Th. H NMR (toluene-d8,
600.1 MHz, 298 K): δ 7.25 (broad s, 6H, Aryl-meta and Aryl-para),
6.76, 6.03 (d, 4JH,H = 2 Hz, 2 × 2H, CH1,8 and CH3,6), 3.63 (v broad s,
4H, CHMe2), 1.66 (s, 6H, CMe2), 1.41, 1.15 (broad s, 2 × 12H,
CHMe2), 1.32 (broad s, 4H, ThCH2), 1.18 (s, 18H, CMe3), 0.90
REFERENCES
■
(1) Burns, C. J.; Neu, M. P.; Boukhalfa, H.; Gutowski, K. E.; Bridges,
N. J.; Rogers, R. D., Chapter 3.3: The Actinides. In Comprehensive
Coordination Chemistry II; Parkin, G. F. R., Ed.; Elsevier: San Diego,
CA, 2004; Vol. 3, p 189.
(2) Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C. Nature 2008,
455, 341.
(3) Cruz, C. A.; Emslie, D. J. H.; Harrington, L. E.; Britten, J. F.;
Robertson, C. M. Organometallics 2007, 26, 692.
(4) (a) Fortier, S.; Melot, B. C.; Wu, G.; Hayton, T. W. J. Am. Chem.
Soc. 2009, 131, 15512. (b) Fortier, S.; Walensky, J. R.; Wu, G.; Hayton,
T. W. J. Am. Chem. Soc. 2011, 133, 11732.
1
(broad s, 18H, ThCH2CMe3). H NMR (toluene-d8, 500.1 MHz, 213
3
K): δ 7.28 (m, JH,H = 7 Hz, 4H, Aryl-meta and Aryl-para), 7.16 (d,
3JH,H = 7 Hz, 2H, Aryl-meta), 6.79, 6.14 (s, 2 × 2H, CH1,8 and CH3,6),
3
4.19, 3.20 (broad sept, JH,H = 6.3 Hz, 2 × 2H, CHMe2), 1.74, 1.54
3
(broad s, 2 × 3H, CMe2), 1.60, 1.36, 1.22, 1.10 (broad d, JH,H = 6.2
Hz, 4 × 6H, CHMe2), 1.29, 0.71 (broad s, 2 × 9H, ThCH2CMe3), 1.17
(broad s, 18H, CMe3) 0.97, −0.30 (broad s, 2 × 2H, ThCH2CMe3).
13C{1H} NMR (toluene-d8, 150 MHz, 298 K): δ 148.14 (C2,7), 147.86
(Aryl-Cortho), 146.24 (C4,5), 141.93 (C11,12), 136.32 (Aryl-Cipso), 130.02
(C10,13), 128.04 (Aryl-Cpara), 125.38 (Aryl-Cmeta), 110.56, 109.89
(CH1,8 and CH3,6), 37.94 (ThCH2CMe3), 35.66 (ThCH2CMe3),
35.24 (CMe2), 35.03 (CMe3), 31.67 (CMe3), 29.0 (CHMe2), 26.25,
25.17 (CHMe2). 13C{1H} NMR (toluene-d8, 150 MHz, 213 K): δ
147.96, 147.32 (2 × Aryl-Cortho), 147.78 (C2,7), 146.06 (C4,5), 142.24
(C11,12), 135.81, 120.59 (2 × ThCH2CMe3), 135.02 (Aryl-Cipso),
129.91 (C10,13), 128.18, 125.40 (Aryl-Cpara and Aryl-Cmeta), 110.33,
109.37 (CH1,8 and CH3,6), 39.11, 36.37 (2 × ThCH2CMe3), 36.05,
23.96 (2 × CMe2), 35.97, 35.35 (2 × ThCH2CMe3), 35.13 (CMe2),
34.90 (CMe3), 31.43 (CMe3), 29.44, 28.08 (2 × CHMe2), 27.03,
25.77, 25.36, 24.33 (4 × CHMe2).
(5) Duhovic,
46, 3390.
́
S.; Khan, S.; Diaconescu, P. L. Chem. Commun. 2010,
(6) Kraft, S. J.; Fanwick, P. E.; Bart, S. C. J. Am. Chem. Soc. 2012, 134,
6160.
(7) Seaman, L. A.; Walensky, J. R.; Wu, G.; Hayton, T. W. Inorg.
Chem. 2012, DOI: 10.1021/ic300867m.
(8) (a) Takats, J. Organoactinide Complexes Containing Classical
Ligands. In Fundamental and Technological Aspects of Organo-f-Element
Chemistry; Marks, T. J., Fragala, I. L., Eds.; D. Reidel: Dordrecht, The
̀
Netherlands, 1985; NATO Science Series C, Vol. 155, p 159.
(b) Marks, T. J.; Day, V. W. Actinide Hydrocarbyl and Hydride
1473
dx.doi.org/10.1021/om301136f | Organometallics 2013, 32, 1466−1474

Organometallics
Article
Chemistry. In Fundamental and Technological Aspects of Organo-f-
Element Chemistry; Marks, T. J., Fragala, I. L., Eds.; D. Reidel:
̀
Dordrecht, The Netherlands, 1985; NATO Science Series C, Vol. 155,
p 115. (c) Burns, C. J.; Clark, D. L.; Sattelberger, A. P., Actinides:
Organometallic Chemistry. In Encyclopedia of Inorganic Chemistry;
King, R. B., Lukehart, C. M., Eds.; Wiley: Chichester, England, 2005;
Vol. 1, p 33.
B.; Kempe, R. Dalton Trans. 2010, 39, 6847. (c) Kretschmer, W. P.;
Meetsma, A.; Hessen, B.; Schmalz, T.; Qayyum, S.; Kempe, R. Chem.
Eur. J. 2006, 12, 8969. (d) Hey, T. W.; Wass, D. F. Organometallics
2010, 29, 3676.
(30) Ni Bhriain, N.; Brintzinger, H. H.; Ruchatz, D.; Fink, G.
Macromolecules 2005, 38, 2056.
(31) Wei, J.; Zhang, W.; Sita, L. R. Angew. Chem., Int. Ed. 2010, 49,
1768.
(32) Lin, W. T.; Niu, H.; Chung, T. C. M.; Dong, J. Y. J. Polym. Sci.,
Polym. Chem. 2010, 48, 3534.
(9) Only terminal alkyl complexes are included in Figure 1.
Metalated ligand complexes or complexes of ylide, aryl, alkynyl, or
π-allyl ligands are not included.
(10) Campello, M. P. C.; Calhorda, M. J.; Domingos, A.; Galvao, A.;
Leal, J. P.; de Matos, A. P.; Santos, I. J. Organomet. Chem. 1997, 538,
̂
(33) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.;
Wenzel, T. T. Science 2006, 312, 714.
̃
(34) Pelletier, J. F.; Mortreux, A.; Olonde, X.; Bujadoux, K. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1854.
(35) (a) Hartwig, J. F., Organotransition Metal Chemistry: From
Bonding to Catalysis; University Science Books: Sausalito, CA, 2010.
(b) Crabtree, R. H., The Organometallic Chemistry of the Transition
Metals, 3rd ed.; Wiley: Toronto, 2001.
(36) (a) Schlenk, W.; Holtz, J. Chem. Ber. 1917, 262. (b) Zieger, H.;
Perri, C.; Bharucha, K. Tetrahedron Lett. 1987, 28, 5989.
(37) Evans, W. J.; Traina, C. A.; Ziller, J. W. J. Am. Chem. Soc. 2009,
131, 17473.
(38) Soria Alvarez, C.; Boss, S. R.; Burley, J. C.; Humphry, S. M.;
Layfield, R. A.; Kowenicki, R. A.; McPartlin, M.; Rawson, J. M.;
Wheatley, A. E. H.; Wood, P. T.; Wright, D. S. Dalton Trans. 2004,
3481.
223.
(11) (a) Silva, M.; Marques, N.; de Matos, A. P. J. Organomet. Chem.
̂
1995, 493, 129. (b) Domingos, A.; Marques, N.; de Matos, A. P.;
Santos, I.; Silva, M. Organometallics 1994, 13, 654. (c) Matson, E. M.;
Forrest, W. P.; Fanwick, P. E.; Bart, S. C. J. Am. Chem. Soc. 2011, 133,
4948. (d) Matson, E. M.; Forrest, W. P.; Fanwick, P. E.; Bart, S. C.
Organometallics 2012, 31, 4467.
̂
(12) Campello, M. P. C.; Domingos, A.; Galvao, A.; de Matos, A. P.;
Santos, I. J. Organomet. Chem. 1999, 579, 5.
(13) Wedler, M.; Knosel, F.; Edelmann, F. T.; Behrens, U. Chem. Ber.
̈
1992, 125, 1313.
(14) Jantunen, K. C.; Batchelor, R. J.; Leznoff, D. B. Organometallics
2004, 23, 2186.
(15) (a) Jantunen, K. C.; Haftbaradaran, F.; Katz, M. J.; Batchelor, R.
J.; Schatte, G.; Leznoff, D. B. Dalton Trans. 2005, 3083. (b) Hayes, C.
E.; Leznoff, D. B. Organometallics 2010, 29, 767. (c) Hayes, C. E.;
Platel, R. H.; Schafer, L. L.; Leznoff, D. B. Organometallics 2012, 31,
6732.
(16) Cruz, C. A.; Emslie, D. J. H.; Jenkins, H. A.; Britten, J. F. Dalton
Trans. 2010, 39, 6626.
(17) Cruz, C. A.; Emslie, D. J. H.; Robertson, C. M.; Harrington, L.
E.; Jenkins, H. A.; Britten, J. F. Organometallics 2009, 28, 1891.
(18) (a) Monreal, M. J.; Diaconescu, P. L. Organometallics 2008, 27,
1702. (b) Duhovic, S.; Monreal, M. J.; Diaconescu, P. L. J. Organomet.
́
Chem. 2010, 695, 2822.
(19) Cruz, C. A.; Emslie, D. J. H.; Harrington, L. E.; Britten, J. F.
Organometallics 2008, 27, 15.
(20) Korobkov, I.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int.
Ed. 2003, 42, 814.
́
(39) Brinkmann, C.; Garcıa, F.; Morey, J. V.; McPartlin, M.; Singh,
S.; Wheatley, A. E. H.; Wright, D. S. Dalton Trans. 2007, 1570.
́
́
(40) Fernandez-Cortabitarte, C.; Garcıa, F.; Morey, J. V.; McPartlin,
M.; Singh, S.; Wheatley, A. E. H.; Wright, D. S. Angew. Chem., Int. Ed.
2007, 46, 5425.
(41) Haywood, J.; Stokes, F. A.; Less, R. J.; McPartlin, M.; Wheatley,
A. E. H.; Wright, D. S. Chem. Commun. 2011, 47, 4120.
(42) Cruz, C. A.; Chu, T.; Emslie, D. J. H.; Jenkins, H. A.;
Harrington, L. E.; Britten, J. F. J. Organomet. Chem. 2010, 695, 2798.
(43) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J.
Organometallics 2002, 21, 5978.
(44) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100,
3359.
(45) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(21) Vidjayacoumar, B.; Ilango, S.; Ray, M. J.; Chu, T.; Kolpin, K. B.;
Andreychuk, N. R.; Cruz, C. A.; Emslie, D. J. H.; Jenkins, H. A.;
Britten, J. F. Dalton Trans. 2012, 41, 8175.
(22) In 1-Th, α-agostic interactions were confirmed by small J
1
13C,1H
coupling constants for the ThCH2 groups. The An−CH2−SiMe3
angles in 1-Th were 126.8(3) and 127.6(3)°. In paramagnetic 1 and
1
13
1
2, J C, H coupling constants could not be measured; therefore, it is not
possible to draw any definite conclusions from the expanded U−C−E
(E = Si, C) angles.
(23) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.
(24) (a) Wetzel, D. M.; Brauman, J. I. J. Am. Chem. Soc. 1988, 110,
8333. (b) Damrauer, R.; Kass, S. R.; Depuy, C. H. Organometallics
1988, 7, 637.
(25) The thermodynamic driving force for conversion of 1 to 2 and 4
could alternatively be related to different levels of aggregation for the
LiCH2CMe3 and MeLi reactants versus the LiCH2SiMe3 product in
solution. However, this explanation seems unlikely, given that the
reaction to form 2 was performed in an aromatic solvent while the
reaction to form 4 was performed in THF, and the extent of
alkyllithium aggregation in THF can be expected to be significantly
less than that in benzene or toluene.
(26) Liu, B.; Liu, X. L.; Cui, D. M.; Liu, L. Organometallics 2009, 28,
1453.
(27) Klimpel, M. G.; Eppinger, J.; Sirsch, P.; Scherer, W.; Anwander,
R. Organometallics 2002, 21, 4021.
(28) Mani, G.; Gabbai, F. P. Angew. Chem., Int. Ed. 2004, 43, 2263.
(29) (a) Samsel, E. G; Eisenberg, D. C. (Ethyl Corporation, USA).
US Patent 5,276,220, 1994. (b) Kretschmer, W. P.; Bauer, T.; Hessen,
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