A R T I C L E S
Fortier et al.
t
°C for 24 h, resulting in the deposition of bright green crystals.
The solid was washed with hexanes (2 × 2 mL) and dried under
vacuum. 0.029 g, 38% yield. 1H NMR (500 MHz, 22 °C, C6D6): δ
-13.69 (s, 45H, CH2SiMe3), 1.12 (s, 72H, CCH3), 1.22 (s, 36H,
[Li(THF)4][U(CH2 Bu)5], [Li(TMEDA)]2[UMe6], and {[K-
(THF)]3[K(THF)2][U(CH2C6H5)6]2}x in good yields. The thermal
stability of these complexes, with the exception of [Li(TMEDA)]2-
[UMe6], is likely imparted by the steric saturation of the uranium
metal center via ‘ate’ formation and greatly contrasts with the
noted instability of “UR4”.2,3,15-17,19,20 Additionally, [Li(DME)3]-
7
CCH3), 18.42 (br s, 10H, CH2SiMe3). Li{1H} NMR (194 MHz,
22 °C, C6D6): δ -3.88 (s), -2.85 (s), -1.84 (s), -1.63 (s), -1.30
(s), -0.99 (s). Anal. Calcd for C68H163ClLi14O12Si5U: C, 48.49; H,
9.77. Found: C, 48.70; H, 9.91.
t
[U(CH2SiMe3)5], [Li(THF)4][U(CH2 Bu)5], and {[K(THF)]3[K-
(THF)2][U(CH2C6H5)6]2}x have been characterized by NIR
spectroscopy and SQUID magnetometry. Comparison of their
spectroscopic and magnetic properties with other homoleptic
uranium(IV) systems, such as [Li(THF)]2[U(OtBu)6], reveals that
their electronic structures are highly influenced by the nature
and number of ligands coordinated to the metal in a manner
that is reminiscent of the transition metals. We will continue to
investigate the coordination chemistry of these homoleptic
uranium(IV) alkyls to better understand the bonding and
reactivity of the uranium-carbon interaction in these high
symmetry complexes.
[Li(DME)3][U(CH2SiMe3)5] (2). To a cold, stirring solution
(-25 °C) of LiCH2SiMe3 (4.11 mL, 4.11 mmol, 1.0 M in pentane)
in Et2O (3 mL) was added a solution of UCl4 (0.312 g, 0.821 mmol)
in THF (2 mL) dropwise. The reaction mixture immediately turned
green concomitant with the precipitation of a white powder. The
solution was filtered through a Celite column (2 cm × 0.5 cm)
supported on glass wool, and the solvent was removed in vacuo to
provide a bright green solid. The solid was subsequently dissolved
in Et2O (4 mL) and DME (0.5 mL) and filtered through a Celite
column supported on glass wool. The filtrate was layered with
hexanes (10 mL) and stored at -25 °C for 24 h, resulting in the
formation of green crystals. The crystals were washed with hexanes
(2 × 2 mL) and dried under vacuum. 0.640 g, 82% yield. Crystals
of 2 turned opaque and pale green upon application of vacuum. 1H
NMR (400 MHz, 22 °C, C6D6/THF-d8): δ -2.15 (s, 45H,
CH2SiMe3), 2.98 (s, 18H, DME), 3.16 (s, 12H, DME), 17.80 (br s,
Experimental Section
General. All reactions and subsequent manipulations were
performed under anaerobic and anhydrous conditions under either
high vacuum or an atmosphere of argon or nitrogen. Diethyl ether,
hexanes, and THF were dried using a Vacuum Atmospheres DRI-
SOLV Solvent Purification system. DME was distilled from sodium
benzophenone ketyl. TMEDA was stored over activated 4 Å
molecular sieves for 24 h prior to use. All deuterated solvents were
purchased from Cambridge Isotope Laboratories Inc. and were dried
over activated 4 Å molecular sieves for 24 h prior to use.
7
10H, CH2SiMe3). Li{1H} NMR (194 MHz, 22 °C, C6D6/THF-
d8): δ -4.96 (s). 1H NMR (500 MHz, 22 °C, THF-h8): δ -2.32 (s,
45H, CH2SiMe3), 3.26 (s, 18H, DME), 3.42 (s, 12H, DME), 16.86
(br s, 10H, CH2SiMe3). 7Li{1H} NMR (194 MHz, 22 °C, THF-h8):
δ -0.02 (s). Anal. Calcd for C32H85LiO6Si5U: C, 40.39; H, 9.02.
Anal. Calcd for [Li(DME)2][U(CH2SiMe3)5], C28H75LiO4Si5U: C,
39.04; H, 8.79. Found: C, 39.16; H, 9.13. UV-vis/NIR (THF,
3.20 mM, 25 °C): 516 (ε ) 103 L · mol-1 · cm-1), 612 (ε ) 65.7
L · mol-1 · cm-1), 698 (ε ) 37.7 L · mol-1 · cm-1), 830 (ε ) 21.9
L · mol-1 · cm-1), 922 (ε ) 25.4 L · mol-1 · cm-1), 1012 (ε )
28.2 L · mol-1 · cm-1), 1042 (ε ) 29.1 L · mol-1 · cm-1), 1100 (ε
) 25.6 L · mol-1 · cm-1), 1224 (ε ) 33.4 L · mol-1 · cm-1), 1394
(ε ) 12.8 L · mol-1 · cm-1), 1456 (ε ) 12.7 L · mol-1 · cm-1), 1532
(ε ) 31.5 L · mol-1 · cm-1), 1892 (ε ) 75.2 L · mol-1 · cm-1).
69
105
106
[Li(THF)]2[U(OtBu)6], UCl4,66 LiCH2 Bu, and KCH2C6H5
t
were synthesized according to the published procedures. All other
reagents were obtained from commercial sources and used as
received.
NMR spectra were recorded on a Varian UNITY INOVA 400
1
or a Varian UNITY INOVA 500 spectrometer. H NMR spectra
are referenced to external SiMe4 using the residual protio solvent
peaks as an internal standard. 7Li{1H} NMR spectra are referenced
to an external saturated solution of LiCl in deuterium oxide.
UV-vis/NIR spectra were recorded on a UV-3600 Shimadzu
spectrophotometer. Elemental analyses were performed by the
Micro-Mass Facility at the University of California, Berkeley.
Magnetism Measurements. Magnetism data were recorded
using a Quantum Design MPMS 5XL SQUID magnetometer. All
experiments were performed using a 1 T field between 2 and 295
K. Crystalline, powdered samples containing ca. 50-100 mg of
compound were loaded, under an inert atmosphere, into a Teflon-
lined gelatin capsule and packed with approximately 20 mg of
quartz wool. The sample was positioned within a plastic straw for
analysis. The data were not corrected for the contribution of the
gelatin capsule/straw sample holder. Diamagnetic corrections (ꢀdia
) 5.70 × 10-4 cm3 ·mol-1 for 2, 5.55 × 10-4 cm3 ·mol-1 for 3,
5.85 × 10-4 cm3 ·mol-1 for 5, and 4.71 × 10-4 cm3 ·mol-1 for
[Li(THF)]2[U(OtBu)6]) were made using Pascal’s constants.107
[Li14(OtBu)12Cl][U(CH2SiMe3)5] (1). To a stirring mixture of
[Li(THF)]2[U(OtBu)6] (0.077 g, 0.092 mmol) and LiCl (0.006 g,
0.142 mmol) in Et2O (2 mL) was added a solution of LiCH2SiMe3
(0.415 mL, 0.415 mmol, 1.0 M in pentane) dropwise. The resulting
pale green solution was stirred for 5 min, and the solvent was
removed in vacuo affording a bright green oil. The oil was dissolved
in hexanes (2 mL), and the solution was filtered through a Celite
column (2 cm × 0.5 cm) supported on glass wool. The volume of
the filtrate was reduced in vacuo, and the solution cooled to -25
t
[Li(THF)4][U(CH2 Bu)5] (3). To a cold, stirring solution (-25
t
°C) of LiCH2 Bu (0.333 g, 4.27 mmol) in Et2O (3 mL) was added
a solution of UCl4 (0.320 g, 0.843 mmol) in THF (2 mL) dropwise.
The reaction mixture immediately turned dark orange concomitant
with the formation of a white powder. The solution was filtered
through a Celite column (2 cm × 0.5 cm) supported on glass wool,
and the solvent was removed in vacuo to provide a dark orange
solid. This solid was subsequently dissolved in Et2O (4 mL) and
filtered through a Celite column supported on glass wool. The filtrate
was layered with hexanes (10 mL) and stored at -25 °C for 24 h
resulting in the formation of dark orange crystals. The crystals were
washed with hexanes (2 × 2 mL) and dried under vacuum. 0.548 g,
73% yield. Crystals of 3 turned opaque upon application of vacuum.
1H NMR (500 MHz, 22 °C, THF-d8): δ 2.77 (s, 45H, CH2CMe3),
7
26.44 (s, 10H, CH2CMe3). Li{1H} NMR (194 MHz, 22 °C, THF-
d8): δ 0.15 (s). Anal. Calcd for C41H87LiO4U: C, 55.38; H, 9.88. Anal.
Calcd for [Li(THF)2][U(CH2tBu)5], C33H71LiO2U: C, 53.20; H, 9.63.
Found: C, 53.56, H, 9.93. UV-vis/NIR (THF, 5.22 mM, 25 °C): 622
(ε ) 85.2 L ·mol-1 ·cm-1), 704 (ε ) 52.1 L ·mol-1 ·cm-1), 826
(ε ) 35.5 L ·mol-1 ·cm-1), 916 (ε ) 33.4 L ·mol-1 ·cm-1), 966 (ε )
35.3 L ·mol-1 ·cm-1), 992 (ε ) 34.0 L · mol-1 · cm-1), 1052 (ε )
36.3 L · mol-1 · cm-1), 1098 (ε ) 32.8 L · mol-1 · cm-1), 1222 (ε
) 32.3 L · mol-1 · cm-1), 1412 (ε ) 16.7 L · mol-1 · cm-1), 1532
(ε ) 34.6 L · mol-1 · cm-1), 1904 (ε ) 46.0 L · mol-1 · cm-1).
[Li(TMEDA)]2[UMe6] (4). To a cold, stirring solution (-25 °C)
of MeLi (0.48 mL, 1.44 mmol, 3.0 M in diethoxymethane) and
TMEDA (0.25 mL) in Et2O (3 mL) was added a solution of UCl4
(0.090 g, 0.238 mmol) in THF (1 mL) dropwise. The reaction
mixture immediately turned orange concomitant with the deposition
of a white powder. The solvent was quickly removed in vacuo
affording an orange solid. The solid was dissolved in cold Et2O (5
(105) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc. 1978, 100, 3359–
3370.
(106) Schlosser, M.; Hartmann, J. Angew. Chem., Int. Ed. 1973, 12, 508–
509.
(107) Bain, G. A.; Berry, J. F. J. Chem. Educ. 2008, 85, 532–536.
9
15520 J. AM. CHEM. SOC. VOL. 131, NO. 42, 2009