Uranium(III)/(IV) nitrile adducts including UI4(N≡CPh) 4, a synthetically useful uranium(IV) complex

Article abstract of DOI:10.1021/ic050578f

The synthesis of complexes used to elucidate an understanding of fundamental An(III) and An(IV) coordination chemistry requires the development of suitable organic-soluble precursors. The reaction of oxide-free uranium metal turnings with 1.3 equivalents of elemental iodine in acetonitrile provided the U(III)/U(IV) complex salt, [U(N≡CMe)₉][UI₆][I] (1), in which the U(III) cation is surrounded by nine acetonitrile molecules in a tricapped trigonal prismatic arrangement, a [UI₆]^2- counterion, and a noncoordinating iodide. The U-N distances for the prismatic and capping nitrogens are 2.55(3) and 2.71(5) A, respectively. The same reaction performed in benzonitrile afforded crystalline UI₄(N≡ CPh)₄ (3) in 78% isolated yield. In the solid state, 3 shows an eight-coordinate U(IV) atom in a puckered square antiprismatic geometry with U-N and U-I distances of 2.56(1) and 3.027(1) A, respectively. This benzonitrile UI₄ adduct is a versatile U(IV) synthon that is soluble in methylene chloride, benzonitrile, and tetrahydrofuran, and moderately soluble in toluene and benzene, but decomposes in benzonitrile at 198°C to [UI(N≡CPh)₈][UI]₆ (4), a U(III)/U(IV) salt analogous to 1. A toluene slurry of 3 treated with 2.2 equiv of Cp*MgCl· THF (Cp* = pentamethylcyclopentadienide) provided Cp*₂UI₂(N≡CPh) (5) in low yields. Single-crystal X-ray structure determination shows that the iodide ligands in 5 are in a rare cis configuration with an acute I-U-I angle of 83.16(7)°. Treatment of a methylene chloride solution of 3 with KTp* (Tp* = hydridotris(3,5-dimethylpyrazolylborate)) formed green Tp*UI₃ (6) which was converted to yellow Tp*UI₃(N≡CMe) (7) by rinsing with acetonitrile. Addition of 2.2 equiv of KTp* to a toluene solution of 3 followed by heating at 95°C, filtration, and crystallization led to the isolation of the dinuclear species [Tp*UI(dmpz)] ₂[μ-O] (9) (dmpz = 3,5-dimethylpyrazolide), presumably formed by hydrolytic cleavage of excess KTp* by adventitious water. The Tp* complexes 6, 7, and 9 were characterized by single-crystal X-ray diffraction, NMR, FT-IR, and optical absorbance spectroscopies.

Full text of DOI:10.1021/ic050578f

Inorg. Chem. 2005, 44, 7403−7413
Uranium(III)/(IV) Nitrile Adducts Including UI4(NtCPh)4, a Synthetically
Useful Uranium(IV) Complex
Alejandro E. Enriquez, Brian L. Scott, and Mary P. Neu*
Actinide, Catalysis, and Separations Chemistry (C-SIC), Chemistry DiVision, Los Alamos National
Laboratory, Los Alamos, New Mexico 87545
Received April 14, 2005
The synthesis of complexes used to elucidate an understanding of fundamental An(III) and An(IV) coordination
chemistry requires the development of suitable organic-soluble precursors. The reaction of oxide-free uranium
metal turnings with 1.3 equivalents of elemental iodine in acetonitrile provided the U(III)/U(IV) complex salt,
[U(N
t
CMe)9][UI6][I] (1), in which the U(III) cation is surrounded by nine acetonitrile molecules in a tricapped trigonal
prismatic arrangement, a [UI6]2 counterion, and a noncoordinating iodide. The U
−N distances for the prismatic
-
and capping nitrogens are 2.55(3) and 2.71(5) Å, respectively. The same reaction performed in benzonitrile afforded
crystalline UI4(N CPh)4 (3) in 78% isolated yield. In the solid state, 3 shows an eight-coordinate U(IV) atom in a
“puckered” square antiprismatic geometry with U N and U I distances of 2.56(1) and 3.027(1) Å, respectively.
This benzonitrile UI4 adduct is a versatile U(IV) synthon that is soluble in methylene chloride, benzonitrile, and
tetrahydrofuran, and moderately soluble in toluene and benzene, but decomposes in benzonitrile at 198 C to
[UI(N CPh)8][UI]6 (4), a U(III)/U(IV) salt analogous to 1. A toluene slurry of 3 treated with 2.2 equiv of Cp*MgCl
THF (Cp* pentamethylcyclopentadienide) provided Cp*2UI2(N CPh) (5) in low yields. Single-crystal X-ray structure
determination shows that the iodide ligands in 5 are in a rare cis configuration with an acute I I angle of
83.16(7) . Treatment of a methylene chloride solution of 3 with KTp* (Tp* hydridotris(3,5-dimethylpyrazolylborate))
formed green Tp*UI3 (6) which was converted to yellow Tp*UI3(N CMe) (7) by rinsing with acetonitrile. Addition
of 2.2 equiv of KTp* to a toluene solution of 3 followed by heating at 95 C, filtration, and crystallization led to the
isolation of the dinuclear species [Tp*UI(dmpz)]2[ -O] (9) (dmpz 3,5-dimethylpyrazolide), presumably formed by
t
−
−
°
t
‚
)
t
−U−
°
)
t
°
µ
)
hydrolytic cleavage of excess KTp* by adventitious water. The Tp* complexes 6, 7, and 9 were characterized by
single-crystal X-ray diffraction, NMR, FT-IR, and optical absorbance spectroscopies.
Introduction
by oxidation of the actinide metal with molecular halides.
The anhydrous polymeric uranium trihalides are insoluble
in common organic solvents.1,2 Karraker has prepared slightly
more soluble AnI3(THF)x (An ) Pu, Np) by treatment of
actinide metals in THF suspensions with 1,2-diiodoethane
but noted that uranium was unreactive toward C2H4I2.3 The
more utilized An(III) reagents have been prepared through
oxidation of An metal turnings (An ) Np, Pu, and mercury-
coated U) by iodine in polar aprotic solvents to form AnI3-
(sol)4 (sol ) THF, py, or 1/2 dme).4 We recently reported an
We are studying low-valent early actinide (U-Cm)
complexes with the goals of enhancing our understanding
of fundamental An(III) and An(IV) coordination chemistry
and supporting the development of selective separation
agents. These efforts require a range of starting materials
with varying chemical and physical properties that will allow
us, for example, to prepare and structurally characterize
model complexes of operative species involved in actinide/
lanthanide separations. The synthesis of such compounds is,
in many cases, hindered by the paucity of suitable precursors.
(1) Taylor, J. C.; Wilson, P. W. Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 1974, 30, 2803-2805.
The anhydrous trivalent and tetravalent actinide halides
are important starting materials that are commonly prepared
(2) Levy, J. H.; Taylor, J. C.; Wilson, P. W. Acta Crystallogr., Sect. B:
Struct. Crystallogr. Cryst. Chem. 1975, 31, 880-882.
(3) Karraker, D. G. Inorg. Chim. Acta 1987, 139, 189-191.
(4) Avens, L. R.; Bott, S. G.; Clark, D. L.; Sattelberger, A. P.; Watkin, J.
G.; Zwick, B. D. Inorg. Chem. 1994, 33, 2248-2256.
* To whom correspondence should be addressed. E-mail: mneu@
lanl.gov. Fax: 505-667-9905. Phone: 505-667-7717.
10.1021/ic050578f CCC: $30.25
Published on Web 09/16/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 21, 2005 7403

Enriquez et al.
alternative to actinide metal oxidation with molecular halides
by using metal hexafluorophosphate salts as the oxidizing
agent. For example, plutonium metal suspended in acetoni-
trile is oxidized to the homoleptic acetonitrile complex [Pu-
(NtCMe)9][PF6]3 in the presence of either silver or thallium
hexafluorophosphate.5 Acetonitrile solutions of these hexaflu-
orophosphate salts will not oxidize uranium metal in the same
fashion as plutonium; however, access to an analogous
uranium triiodide, [U(NtCMe)9][I]3, is achieved by dis-
solution of purple UI3(THF)4 in acetonitrile.5 In contrast to
the green [U(NtCMe)9][I]3 product, direct oxidation of
uranium metal by iodine in acetonitrile has been reported to
give a dark brown crystalline material formulated as either
temperature oxidation of uranium metal by iodine in ben-
zonitrile solvent. During our investigations, we revisited the
analogous reactivity in acetonitrile solvent and were able to
isolate and structurally characterize a mixed-valence U(III)/
U(IV) product, [U(NtCMe)9][I][UI6], which has properties
similar to those of the trivalent compound UI3(NtCMe)4,
previously reported.7 A comparable mixed-valence adduct,
[UI(NtCPh)8][UI6], was isolated in low yield by refluxing
the crude reaction mixture of uranium oxidation by iodine
in benzonitrile. The synthetic utility of UI4(NtCPh)4 was
investigated by treating this UX4 synthon with Cp*MgCl‚
THF and KTp* under a variety of reaction conditions. The
products from these reactions are described herein.
6
UI4(NtCMe)4 or UI3(NtCMe)4,7 depending on the amount
Experimental Section
of iodine used for the oxidation.
2,8-11
The preparation of the tetrahalide uranium species UI4
General Comments. Oxide-free uranium turnings depleted in
235U were prepared in a fashion similar to that of Sattelberger and
co-workers;17 however, ongoing efforts to minimize mixed radioac-
tive hazardous waste disfavor the use of HgI2 to prepare the mercury
amalgamated uranium turnings described in their work. We prepared
oxide-free turnings in the following manner: 10 g of oxide-coated
U turnings were cut into 1-in. strips and then immersed in 100 mL
of concentrated nitric acid to remove the oxide coating. The turnings
remained in the acid until removal of the black oxide layer from
the metal visibly stopped, and then they were transferred to a beaker
containing 100 mL of fresh concentrated nitric acid. This nitric
acid rinsing process was repeated three or more times to produce
shiny metallic strips. Residual acid was removed by rinsing the
turnings with deionized water, and residual water was removed by
rinsing with copious amounts of dry THF. The turnings were then
transferred into the drybox antechamber where residual THF was
removed in vacuo; the metal was then used immediately. Safety
Note: Depleted uranium and its decay products are radioactiVe.
Uranium and other radioactiVe materials should be handled only
by trained and qualified workers in facilities equipped with
appropriate controls.
8,9
and UBr4 is laborious and tedious. Once UI4 is prepared,
it is unstable at room temperature and decomposes to
uranium triiodide and iodine.6,8,11,12 Iodine oxidation of
uranium metal suspended in a dichlormethane benzophenone
solution forms a putative UI4(OdCPh2)2 intermediate that
can be converted to UI4(NtCMe)4 upon dissolution in
acetonitrile in low yields; although neither of these products
has been characterized by single-crystal X-ray diffraction,
their structural assignments have been assigned using FT-
IR and optical-absorbance spectroscopies.6,12 In a recent
contribution, Berthet and co-workers were able to access
“UI4(NtCMe)4” in high yields through metathesis of UCl4
in acetonitrile using excess Me3SiI. However, crystallization
of the UI4(NtCMe)4 product yields the [UI2(NtCMe)7][UI6]
salt as the structurally characterized product.13
Uranium tetrachloride is the most common precursor for
the preparation of anhydrous uranium(IV) compounds. Even
though UCl4 can be prepared from the direct reaction of
chlorine gas with uranium metal, it is more conveniently
prepared by reducing uranium oxide in the chlorinating
solvent hexachloropropene. The reaction proceeds under
relatively harsh conditions (190 °C) and forms HCl and
phosgene as products.14-16 In this contribution, we report the
facile preparation of a stable uranium tetraiodide complex,
UI4(NtCPh)4, in multigram quantities from the room-
Hexanes, toluene, ether, and tetrahydrofuran solvents were dried
by using activated alumina columns (A2, 12 × 32, Purify).18,19
Anhydrous acetonitrile and benzonitrile were purchased from
Aldrich, distilled from CaH2, and stored over a 1:1 mixture of 3
and 4 Å molecular sieve pellets. All other solvents were purchased
as anhydrous grades from Aldrich and stored over a 1:1 mixture
of 3 and 4 Å molecular sieve pellets prior to use. Unless otherwise
noted, all reactions were performed in either a Vacuum Atmospheres
model HE-553-2 inert atmosphere drybox with a MO-40-2 Dri-
Train or an MBraun Labmaster 130 drybox under a He or N2
atmosphere. Infrared spectra were obtained on a Nicolet Magna-
IR 560 spectrometer equipped with a DTGS detector. Thin film
and Fluorolube mull IR spectra were obtained on CaF2 plates. The
Raman spectrum of UI4(NtCPh)4 was obtained with CH2Cl2
solution sealed in a 5 mm NMR tube by exciting from an Ar+
laser (Spectra Physics, model 2025) using the 514.5 nm line. The
scattered light was dispersed and analyzed on a SPEX model 1403
(5) Enriquez, A. E.; Matonic, J. H.; Scott, B. L.; Neu, M. P. Chem.
Commun. 2003, 1892-1893.
(6) Du Preez, J. G. H.; Zeelie, B. Inorg. Chim. Acta 1986, 118, L25-
L26.
(7) Drozdzynski, J.; du Preez, J. G. H. Inorg. Chim. Acta 1994, 218, 203-
205.
(8) Brown, D. Halides of the Lanthanides and Actinides; Wiley-Inter-
science: New York, 1968.
(9) Hussonnois, M.; Krupa, J. C.; Genet, M.; Brillard, L.; Carlier, R. J.
Cryst. Growth 1981, 51, 11-16.
(10) Levy, J. H.; Taylor, J. C.; Waugh, A. B. Inorg. Chem. 1980, 19, 672-
674.
(11) Bagnall, K. W.; Brown, D.; Jones, P. J.; du Preez, J. G. H. J. Chem.
Soc. 1965, 350-353.
(16) Herrmann, J. A.; Suttle, J. F.; Hoekstra, H. R. In Synthetic Methods
of Organometallic and Inorganic Chemistry Series; Herrmann, W. A.,
Edelmann, F. T., Eds.; Thieme: New York, 1997; Vol. 6, pp 156-
157.
(17) Clark, D. L.; Sattelberger, A. P. Inorg. Synth. 1997, 31, 307-315.
(18) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518-1520.
(19) Alaimo, P. J.; Peters, D. W.; Arnold, J.; Bergman, R. G. J. Chem.
Educ. 2001, 78, 64.
(12) du Preez, J. G. H.; Zeelie, B. J. Chem. Soc., Chem. Commun. 1986,
743.
(13) Berthet, J.-C.; Thue´ry, P.; Ephritikhine, M. Inorg. Chem. 2005, 44,
1142-1146.
(14) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J. Organome-
tallics 2002, 21, 5978-5982.
(15) Herrmann, J. A.; Suttle, J. F.; Hoekstra, H. R. Inorg. Synth. 1957, 5,
143-145.
7404 Inorganic Chemistry, Vol. 44, No. 21, 2005

Uranium(III)/(IV) Nitrile Adducts Including UI4(NtCPh)4
scanning double monochromator equipped with a 1800 groove/
mm grating and a single-photon-counting detection system. Scan
parameters were as follows: 1 cm-1 increments between points,
integration for 3 s at each point, 71 scans averaged for the final
spectrum, and a spectral resolution of 5 cm-1. An external standard
of Tylenol was used for energy calibration. Optical absorbance
spectra were obtained in airtight, Teflon-capped, 1 cm quartz
cuvettes on either a Varian Cary 6000i or a Varian Cary 500 UV-
vis near-IR spectrophotometer. All 1H, 13C, and 11B NMR samples
were prepared in 4 mm Teflon NMR tube liners that were inserted
into 5 mm NMR tubes to multiply contain the radioactive samples.
Spectra were obtained at room temperature on a Bruker Avance
300 MHz spectrometer equipped with a Bruker broadband probe.
connected to a nitrogen-flushed reflux condenser attached to a
Schlenk line. The dark red solution was stirred at room temperature
under continuous nitrogen flow for 12 h and then heated to reflux
for 5 min. This hot reaction flask was then transferred to the drybox,
and the contents were filtered through a 30-mL coarse porosity
glass fritted funnel. Unreacted U metal and a black microcrystalline
solid were collected. Manual separation of the uranium followed
by rinsing the black solid with 50 mL of toluene and removal of
residual solvent in vacuo provided 5.39 g of crystalline material
determined to be [UI(NtCPh)8][UI6] (2.46 mmol, 18% yield based
1
on uranium) by single-crystal X-ray diffraction. H NMR (CD2-
Cl2): δ (ppm) 8.82 (br, s, 8 Hpara), 8.15 (br s, 16 Hortho), 7.01 (br
s, 16 Hmeta). UV-vis-NIR (CH2Cl2): λ (nm) 683, 925, 1052, 1159,
1256. Anal. Calcd for C56H40I7N8U2: C, 30.72; H, 1.84; N, 5.12.
Found: C, 30.0; H, 1.65; N, 4.64.
1
The H and 13C spectra were referenced to the residual solvent
resonances, and 11B spectra were referenced to a BF3‚Et2O external
standard. The [U(NtCMe)9][I]3,5 KTp*,20 and Cp*MgCl‚THF21
complexes were prepared using published procedures. Elemental
and mass spectral analyses were performed by the Mass Spectrom-
etry and Micro-Mass group at the University of California at
Berkeley, Berkeley, CA.
[U(NtCMe)9][UI6][I] (1). Uranium turnings (0.102 g, 0.428
mmol) were added to a vial containing a magnetic stirbar and 4
mL of acetonitrile. A 4 mL suspension of iodine (0.149 g, 0.587
mmol) in acetonitrile was added to the vial containing the uranium,
and then the red solution was stirred overnight. Filtration of the
resulting turbid orange solution through a Whatman syringe filter
provided a dark orange filtrate that was placed in a freezer overnight.
The resulting large brown crystals (0.154 g, 50% isolated yield
based on iodine) were determined to be [U(NtCMe)9][UI6][I] by
single-crystal X-ray crystallography. UV-vis-NIR (MeCN): λ
(nm) 557, 649, 776, 925, 1115, 1264.
Cp*2UI2(NtCPh) (5). A 100 mL Schlenk tube was charged
with 3 (2.0 g, 1.72 mmol), Cp*MgCl‚THF (1.07 g, 4.0 mmol), 50
mL of toluene, and a stirbar. The tube was sealed, removed from
the drybox, immersed in a 95 °C oil bath, and heated for 15 h. The
flask was returned to the drybox, and the solution was filtered to
remove an uncharacterized gray solid that was rinsed with toluene.
The resulting dark red/orange filtrate was then twice passed through
Celite-545 padded coarse glass fritted funnels, and the volume was
reduced to ∼25 mL in vacuo. This dark red solution was triturated
with 25 mL of hexane, stirred for 24 h, and filtered twice through
a Celite-545 padded coarse fritted funnel to remove the fine white
precipitate (presumably Mg salts) that formed. The collected red
filtrate was placed in a freezer at -35 °C, and the dark brown
crystals that formed within 24 h were collected and determined by
single-crystal X-ray crystallography to be Cp*2UI2(NtCPh) (0.535
1
g, 36% yield). H NMR (0.3 mL PhCN/0.1 mL CD2Cl2 solution):
δ (ppm) 14.00 (30 Cp* H). MS: [M - C7H5N]+ 762. Anal. Calcd
for C27H35I2NU: C, 37.47; H, 4.08; N, 1.62. Found: C, 39.62; H,
4.39; N, 1.67.
UI4(NtCPh)4 (3). Uranium turnings (2.08 g, 8.74 mmol) were
added to a 250 mL Erlenmeyer flask containing a stirbar and 40
mL of benzonitrile. This suspension was stirred as iodine (2.66 g,
10.5 mmol) was added over 5 min. Within 20 min after the addition
of iodine, the color of the suspension changed to dark orange/black.
A red precipitate formed as this suspension was stirred overnight.
Filtration through a coarse porosity glass fritted funnel provided a
small amount of red microcrystalline material, unreacted U, and a
red filtrate. The unreacted U was manually separated from the red
crystalline material and reclaimed for later use. A 100 mL portion
of hexanes was added to the red filtrate, and a red microcrystalline
material precipitated. Isolation of the microcrystalline material by
filtration, rinsing with three 20 mL portions of hexane, and removal
of residual solvent in vacuo provided 4.514 g (74% yield based on
iodine) of analytically pure red UI4(NtCPh)4. Crystals suitable for
X-ray crystallography were obtained from a saturated benzonitrile
solution that was gently heated, filtered, and cooled to room
Tp*UI3 (6). A 50 mL sidearm flask was charged with 3 (1.35
g, 1.17 mmol), 20 mL of CH2Cl2, and a magnetic stirbar. The
resulting red solution was stirred as KTp* (0.485 g, 1.44 mmol)
was added in 3 portions over a period of 5 min. After 1 h of stirring,
the solution color gradually turned green-yellow and was filtered
through a Celite 545 padded coarse glass fritted funnel. The filter
plug was washed with 20 mL of dichloromethane, and the green
filtrate was isolated. Removal of solvent from the filtrate in vacuo
yielded a green solid that was rinsed with toluene, benzene, or ether.
Residual solvent was removed in vacuo, and a bright green Tp*UI3
solid (0.652 g, 61% yield) was isolated. Green-yellow crystals were
obtained as Tp*UI3‚(toluene)3 by cooling a saturated toluene
1
solution of Tp*UI3 to -38 °C. H NMR (CD2Cl2): δ (ppm) 7.80
(s, 3 Tp* C-H), 5.49 (s, 9 Tp* CH3), -7.71 (s, 9 CH3). 13C NMR
(CD2Cl2): δ (ppm) 164.4 (s, Tp* C-CH3), 136.5 (d, 1JCH ) 177.4
1
3
temperature. H NMR (CD2Cl2): δ (ppm) 6.44 (t, JHH ) 7.0 Hz,
4 Hpara), 4.22 (br s, 8 Hmeta), 0.80 (br s, 8 Hortho). Raman: νNC 2250
1
Hz, Tp* C-H), 134.8 (s, Tp* C-CH3), 20.16 (q, JCH ) 129.8
cm-1 (CH2Cl2). UV-vis-NIR (CH2Cl2): λ (nm) (ꢀ, M-1‚cm-1
)
1
Hz, Tp* C-CH3), -0.31 (q, JCH ) 129.8 Hz, Tp* C-CH3). 11B
NMR (CD2Cl2): δ (ppm) 21.97 (d, 1JH ) 141 Hz, Tp* -H). UV-
vis-NIR (CH2Cl2): λ (nm) (ꢀ, M-1‚cm-1) 498 (46), 599 (17), 632
(11), 658 (73), 677 (82), 747 (10), 783 (10), 815 (10), 910 (14),
959 (13), 999 (10), 1114 (46), 1131 (42), 1164 (12), 1266 (16).
MS: M+ 916. IR (Fluorolube mull): νH 1538 cm-1. Anal. Calcd
for C17H25N6I3U: C, 21.34; H, 2.63; N, 10.25. Found: C, 21.27;
H, 2.31; N, 10.34.
690 (140), 825 (23), 877 (22), 962 (25), 1051 (43), 1165 (130).
IR: νNC 2254 cm-1 (thin film from CH2Cl2 solution evaporation
on CaF2 plates). Anal. Calcd for C28H20I4N4U: C, 29.04; H, 1.74;
N, 4.84. Found: C, 29.08; H, 1.71; N, 4.70.
[UI(NtCPh)8][UI6] (4). Iodine (9.16 g, 36.1 mmol) was added
to a 500 mL Schlenk flask containing uranium turnings (6.70 g,
28.15 mmol), 200 mL of benzonitrile, and a stirbar. The flask was
capped with a ground-glass stopper, removed from the drybox, and
Tp*UI3(NtCMe) (7). Rinsing either crude 6 after filtration
through Celite or pure 6 with MeCN results in quantitative
conversion to golden brown Tp*UI3(NtCMe). Crystals were
obtained from vapor diffusion of hexane into a CH2Cl2 solution of
(20) Trofimenko, S. Scorpionates: Polypyrazolylborate Ligands and Their
Coordination Chemistry; Imperial College Press: London, 1999.
(21) Fagan, P. J.; Manriquez, J. M.; Maatta, E. A.; Seyam, A. M.; Marks,
T. J. J. Am. Chem. Soc. 1981, 103, 6650-6667.
1
Tp*UI3(NtCMe). H NMR (CD2Cl2): δ (ppm) 7.81 (s, 3 Tp*
Inorganic Chemistry, Vol. 44, No. 21, 2005 7405

Enriquez et al.
Table 1. Crystallographic Parameters for Complexes 1, 3-7, and 9
complex
empirical formula
fw
T (K)
λ (Å)
space group
a (Å)
b (Å)
1
3
C
4
5
6
7
9
C18H27I7N9U2
1733.85
203(2)
0.71073
P6hc2 (No. 188)
10.9169(19)
10.9169(19)
21.622(5)
90
90
90
2231.6(8)
2
2.580
112H80I16N16U4
C56H40I7 N8U
1951.29
203(2)
0.71073
P4/m
12.221(3)
12.221(3)
10.806(4)
90
90
90
1613.8(9)
1
2.008
C27H35I2NU
865.39
203(2)
0.71073
P21/c
17.021(6)
8.725(3)
19.189(7)
90
104.294(6)
90
2761.3(17)
4
C36H46I3N6U
1192.33
203(2)
0.71073
P21/c
17.943(9)
18.658(9)
20.265(10)
90
116.276(6)
90
6083(5)
8
C17H25I3N7U
956.98
203(2)
0.71073
P21/c
14.538(4)
10.323(3)
17.448(5)
90
99.301(5)
90
2584.0(13)
4
C20H29IN8O0.5
765.25
203(2)
0.71073
C2/c
18.520(4)
11.972(3)
24.861(5)
90
107.242(4)
90
U
4632.44
203(2)
0.71073
I4h
16.898(5)
16.898(5)
11.615(3)
90
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å)3
Z
90
90
3316.6(16)
1
2.319
5264.5(18)
8
1.931
F
calcd (g/cm3)
2.082
8.128
1.2-25.1
0.0820
0.2522
2.604
8.424
1.3-23.3
0.0606
0.0751
2.460
9.883
1.4-28.0
0.0353
0.0852
µ (mm-1
)
12.109
1.9-25.3
0.0694
0.2141
8.639
5.901
7.364
æ range (deg)
1.7-28.4
0.0571
0.1429
1.7-22.4
0.0811
0.1195
1.7-28.1
0.0672
0.1701
Ra
a
Rw
2
2
2
2
a R ) σ||Fo| - |Fc||/σ|Fo| and Rw ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2. The parameter w ) 1/[σ2(Fo ) + (aP)2].
C-H), 5.50 (s, 3 NtCCH3), 1.94 (s, 9 Tp* CH3), -7.71 (s, 9 CH3).
13C NMR (CD2Cl2): δ (ppm) 163.9 (s, Tp* C-CH3), 135.93 (d,
1JCH ) 177.3 Hz, Tp* C-H), 134.2 (s, Tp* C-CH3), 19.66 (q,
1JCH ) 129.8 Hz, Tp* C-CH3), 1.71 (1JCH ) 135.8 Hz, NtCCH3),
-0.89 (q, 1JCH ) 129.8 Hz, Tp* C-CH3). 11B NMR (CD2Cl2): δ
tion corrections, and final cell parameter calculations were carried
out using SAINT23 software. The data were corrected for absorption
using the SADABS24 program. Decay of reflection intensity was
monitored via analysis of redundant frames. The structure was
solved using Direct methods (SHELXS-97) and difference Fourier
techniques. All hydrogen atom positions were idealized and rode
on the atom to which they were attached. The final refinement
included anisotropic temperature factors on all non-hydrogen atoms
(SHELXL-97). Structure solution, refinement, graphics, and creation
of publication materials were performed using SHELXTL 5.10.25
Additional details of data collection and structure refinement are
listed in Table 1.
1
(ppm) 22.16 (d, JH ) 89.5 Hz, Tp* -H). UV-vis-NIR (CH2-
Cl2): λ (nm) 700, 953, 1112. IR (Fluorolube mull): νH 1538 cm-1
,
νCN 2269 cm-1. Anal. Calcd for C17H25N7I3U: C, 21.34; H, 2.63;
N, 10.25. Found: C, 21.27; H, 2.31; N, 10.34.
[Tp*]2[UI6] (8). Crystals of 8 were obtained by vapor diffusion
of hexanes into a pyridine solution of Tp*UI3(NtCMe).
[Tp*UI(dmpz)]2[µ-O] (9). A 100 mL Schlenk tube was charged
with 3 (1.42 g, 0.986 mmol), KTp* (0.734 g, 2.18 mmol), 40 mL
of toluene, and a stirbar and then heated at 95 °C, as in 5, to produce
a yellow-brown solution after 15 h. A tan solution and an
uncharacterized brown solid were isolated after filtration through
a coarse porosity glass fritted funnel. The brown solid was
discarded, and the tan solution was filtered through a Celite padded
coarse fritted funnel. The volume of collected grayish-yellow filtrate
solution was reduced to 10 mL in vacuo, transferred to a scintillation
vial, and stored in a -35 °C freezer for 1 month. Dull green crystals
were isolated and assayed by single-crystal X-ray crystallography.
Removal of solvent in vacuo provided analytically pure [Tp*UI-
(dmpz)]2[µ-O] as a gray-green solid (0.688 g, 91% yield). 1H NMR
(CD2Cl2): δ (ppm) 70.22, 20.12, -2.74, -8.09, -14.10, -18.06,
-39.18 (3 H each from either Tp* C-CH3 or dmpz C-CH3). UV-
vis-NIR (CH2Cl2): λ (nm) (ꢀ) (M-1‚cm-1) 476 (113), 512 (60),
662 (103), 688 (123), 943 (61), 1050 (138), 1115 (137), 1275 (55).
Anal. Calcd for C40H582I2N16OU2: C, 31.39; H, 3.82; N, 14.64.
Found: C, 31.73; H, 4.01; N, 14.64.
The crystal structures of all compounds were determined as
follows, with exceptions noted in subsequent paragraphs: A crystal
was mounted onto a glass fiber using a spot of silicone grease.
Because of air sensitivity, the crystal was mounted from a pool of
mineral oil under argon gas flow. The crystal was placed on a
Bruker P4/CCD diffractometer and cooled to 203 K using a Bruker
LT-2 temperature device. The instrument was equipped with a
sealed, graphite, monochromatized Mo KR X-ray source (λ )
0.71073 Å). A hemisphere of data was collected using æ scans
with 30 s frame exposures and 0.3° frame widths. Data collection
and initial indexing and cell refinement were handled using
SMART22 software. Frame integration, including Lorentz polariza-
Compound 1. Hydrogen atom positions were not modeled on
the acetonitrile methyl carbon atom C2; this methyl group was
disordered across a mirror plane. The anisotropic refinement of
carbon atom C2 was constrained to approximate isotropic behavior.
The structure was refined as a racemic twin, with the batch scale
factor converging to 0.10(3). A lattice void of 92.00 Å3 was
observed in the unit cell, but because the residual electron density
in the void was less than 2 e-/Å3, a disordered solvent molecule
was not modeled.
Compound 3. The structure was refined as a racemic twin, with
the batch scale factor converging to 0.46(1).
Compound 4. The molecule was disordered across a site of 4/m
crystallographic symmetry, and all atomic positions were refined
at one-half occupancy. Hydrogen atom positions were not modeled
on the one-half occupancy phenyl groups. The phenyl groups were
restrained to be rigid bodies.
Compound 6. The electron density of 24 disordered toluene
molecules (299 e-/cell and 1721 Å3) was removed from the unit
cell using PLATON/SQUEEZE.26
Results and Discussion
Oxidation of Uranium Metal with Iodine in Acetoni-
trile. We revisited the reactivity of uranium metal toward
oxidation by iodine in acetonitrile solvent. Our attempts to
isolate UI3(NtCMe)4 from the oxidation of uranium metal
by 1.3 equivalents of iodine in acetonitrile were not suc-
(23) SAINT-NT 5.050; Bruker AXS, Inc.: Madison, WI, 1998.
(24) Sheldrick, G. M. SADABS, first release; University of Go¨ttingen:
Go¨ttingen, Germany.
(25) SHELXTL-NT, version 5.10; Bruker AXS, Inc.: Madison, WI, 1997.
(26) Spek, A. L. Acta Crystallogr., Sect. A 1990, 46 (supplement), C34.
(22) SMART-NT 4; Bruker AXS, Inc.: Madison, WI, 1996.
7406 Inorganic Chemistry, Vol. 44, No. 21, 2005

Uranium(III)/(IV) Nitrile Adducts Including UI4(NtCPh)4
Figure 1. Thermal ellipsoid plot of [U(NtCMe)9][UI6][I] (1) at the 35%
probability level. Selected bond lengths (Å): U(2)-N(1) ) 2.71(5); U(2)-
N(2) ) 2.55(3); U(1)-I(1) ) 2.987(1); U(2)-I(2) ) 6.303(1); N(2)-C(3)
) 1.16(4); N(1)-C(1) ) 1.13(6). Selected bond angles (deg): N(1B)-
U(2)-N(1A) ) N(1A)-U(2)-N(1) ) N(1)-U(2)-N(1B) ) 120.000(5).
The dashed lines are a visual aid showing the terminal faces of the trigonal
prism.
Figure 2. Superimposed NIR optical absorption spectra for complexes
with a trivalent uranium cation containing bound nitrile ligands: [U-
(NtCMe)9][UI6][I] (1) in MeCN, [U(NtCMe)9][I]3 (2) in MeCN, and
[UI(NCPh)8][UI6] (4) in CH2Cl2.
Oxidation of Uranium Metal with Iodine in Benzoni-
trile. Given the difficulty in preparing both UI4 and UCl4,
alternative routes to obtaining uranium tetrahalides under
mild conditions and in high yields would be synthetically
useful. Other than UI4, UI4(NtCMe)4 is the only character-
ized tetraiodide uranium complex prepared from the oxida-
tion of uranium metal. UI4(NtCMe)4 can be prepared via
direct oxidation in MeCN; however, multiple intractable
products form, and the desired UI4(NtCMe)4 product is
difficult to isolate and is yet to be structurally characterized
by X-ray crystallography.6 If the iodine oxidation is per-
formed in CH2Cl2 in the presence of benzophenone, then
UI4(OdCPh2)2 is isolated as the putative intermediate. The
addition of MeCN followed by cooling to -18 °C ultimately
affords UI4(NtCMe)4 in an overall yield of 36%.6,12
Unfortunately, UI4(NtCMe)4 is insoluble in most useful
organic solvents except THF, where it decomposes to a
haloalkoxide product from ring opening of THF.28 Similar
reactivity is observed for UI4.29 Other uranium nitrile adducts
of the type UX4(NtC-R)4 (X ) Cl or r; R ) Me, Et, n-Pr,
n-Bu, and Ph) have been prepared by dissolution of UX4
into the appropriate nitrile.30 The only structurally character-
ized UX4(nitrile)x adduct prepared using this synthetic
methodolgy is UCl4(NtCMe)4.31,32
cessful. Instead, we were able to isolate brown crystals of
the mixed U(III)/U(IV) compound [U(NtCMe)9][UI6][I] (1)
as the only product. The crystal structure of 1 (Figure 1) is
a complex U(III)/U(IV) salt that contains a U(III) atom
surrounded by nine acetonitrile solvent molecules. A non-
coordinating [UI6]-2 anion and a noncoordinating iodide
anion flank the symmetric U(III) nitrile adduct. The [UI6]-2
anion and the U(III) cation respectively occupy positions of
D3 and C3h crystallographic site symmetry. The coordination
geometry around the U(III) cation is an ideal tricapped
trigonal prism with nine N-bound acetontrile molecules. The
U(2)-N(2) distance of 2.55(3) Å for the prismatic nitrogens
is 0.13 Å shorter than the U(2)-N(1) distance of 2.71(5) Å
observed for the three capping nitrogens. These distances
are within errors of the U-Nprismatic, 2.60(2) Å, and U-
N
capping, 2.65(2) Å, distances reported for the cation in the
compound [U(NtCMe)9][I]3 (2).5
Complex 1 is insoluble in nonpolar organic solvents and
1
CH2Cl2 and soluble in THF and acetonitrile. The H NMR
in THF-d8 shows a single resonance for free acetonitrile,
indicating complete displacement of bound acetonitrile by
THF-d8. The optical absorbance spectrum of an orange
acetonitrile solution of [U(NtCMe)9][UI6][I] in the NIR
region contains Laporte forbidden f f f bands.4,27 The
superimposed spectra of three trivalent uranium nitrile
compounds are shown in Figure 2. The similarity of the
complex 1 (green solution in acetonitrile) and complex 2
(orange solution in acetonitrile) spectra in the NIR region
suggests that the optical transition arises from the [U(Nt
CMe)9]3+ chromophore. These data, along with the solid-
state structures for complexes 1 and 2, underscore the poor
U(III) coordinating ability of iodide in the presence of excess
acetonitrile.
An excess of oxide-free uranium metal turnings suspended
in benzonitrile reacts with iodine to yield microcrystalline,
red UI4(NtCPh)4 (3) in 74% isolated yield after overnight
stirring. This compound is easily prepared on a synthetically
useful 5-g scale, and the mild conditions are preferable to
the high-temperature furnace techniques that yield UI4 and
(28) Avens, L. R.; Barnhart, D. M.; Burns, C. J.; McKee, S. D. Inorg.
Chem. 1996, 35, 537-539.
(29) Collin, J.; Pires de Matos, A.; Santos, I. J. Organomet. Chem. 1993,
463, 103-107.
(30) Gans, P.; Marriage, J. J. Chem. Soc., Dalton Trans. 1972, 46-48.
(31) Van den Bossche, G.; Rebizant, J.; Spirlet, M. R.; Goffart, J. Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 1986, 42, 1478-1480.
(32) Cotton, F. A.; Marler, D. O.; Schwotzer, W. Acta Crystallogr., Sect.
C: Cryst. Struct. Commun. 1984, 40, 1186-1188.
(27) Cohen, D.; Carnall, W. T. J. Phys. Chem. 1960, 64, 1933-1936.
Inorganic Chemistry, Vol. 44, No. 21, 2005 7407

Enriquez et al.
Figure 3. Thermal ellipsoid plot of UI4(NtCPh)4 (3) at the 35% probability level (left) and the intimate coordination geometry about the central U(IV)
atom (right). Selected bond lengths: (Å) U(1)-N(1) ) 2.56(1); U(1)-I(1) ) 3.027(1); N(1)-C(1) ) 1.15(1). Selected bond angles (deg): I(1)-N(1)-
I(1C) ) 81.1(1). The dashed lines are a visual aid representing the puckered terminal faces of the distorted square antiprism.
the multistep synthesis that generates UI4(NtCMe)4. Unlike
UI4, which decomposes via I2 loss to UI3 at room temper-
ature, complex 3 is stable for months at room temperature
in an inert atmosphere drybox. The air-sensitive compound
is soluble in benzonitrile, CH2Cl2, and THF; moderately
soluble in benzene and toluene; and insoluble in hexanes
and ether. The structure of the UI4(NtCPh)4 crystalline
material was determined by single-crystal X-ray diffraction
and is shown in Figure 3.
The crystal structure of 3 shows an eight-coordinate U(IV)
atom in a “puckered” square antiprismatic geometry. The
uranium atom is bound to one N atom from each of the four
benzonitrile ligands and four iodides. The U-N and U-I
distances are 2.56(1) and 3.027(1) Å, respectively. The planes
of an ideal square antiprism defined by either I(1C)-N(1)-
I(1)-N(1C) or I(1B)-N(1B)-I(1A)-N(1A) are puckered
by a unique 81.1(1)° angle between each I(1)-N(1)-I(1).
Complex 3 has S4 molecular symmetry and is more sym-
metric than UCl4(NtCMe)4 which has C2 symmetry.31,32
Figure 4. Optical absorption spectra of UI4(NtCPh)4 (3), Tp*UI3 (6),
and [Tp*UI(dmpz)]2[µ-O] (9) in CH2Cl2 solutions.
to the 28-cm-1 increase in νNC observed for acetonitrile
coordination to UCl4.33
The 1H NMR of 3 in CD2Cl2 shows three paramagnetically
broadened resonances at δ ) 0.80, 4.22, and 6.44 ppm for
each of the ortho, meta, and para hydrogens, respectively,
of the equivalent benzonitrile ligands coordinated to the
U(IV) center. The resonance at 6.44 ppm is broad (∼20 Hz);
The UV-vis-NIR spectrum of complex 3 dissolved in
methylene chloride is shown in Figure 4. The absorption
maxima at 690 and 1165 nm are typical for U(IV) observed
in 1 M perchloric acid (deuterated) solution27 and also agree
favorably with absorption maxima of structurally character-
ized U(IV) iodide coordination complexes derived from UI4-
(NtCPh)4 dissolved in methylene chloride (vide infra). A
cyclic voltammogram of 3 in the noncoordinating ionic liquid
2-ethyl-5-methylimidazolium bis(trifloumethanesulfon)imide
shows a reduction wave at -0.40 V (vs silver wire). The
reoxidation wave is not observed, indicating that the U(III)
complex is unstable in the ionic liquid.
During one preparation of 3, we attempted to dissolve the
crude UI4(NtCPh)4 product by heating the benzonitrile
suspension to reflux. After 5 min at 191 °C, the red UI4-
(NtCPh)4 precipitate disappeared and a black precipitate
formed. Filtration of this solution resulted in the isolation
3
however, it appears as a triplet with JHH ) 7 Hz and is
assigned as the resonance for the four equivalent para
hydrogens of each benzonitrile ligand. The remaining two
resonances integrate for eight hydrogens each. The broadest
resonance (∼45 Hz) at 0.80 ppm is assigned to the ortho
hydrogens because they are closest to and most influenced
by the paramagnetic U(IV) center; the next broadest reso-
nance (∼25 Hz) at 4.22 ppm is assigned to the meta
hydrogens. The FT-IR spectrum of 3, obtained as a thin film,
shows an absorption band corresponding to the vibrational
frequencies of bound nitriles at νNC ) 2254 cm-1; the Raman
spectrum in CH2Cl2 solution shows a similar band at νNC
)
2250 cm-1. This ∼25-cm-1 increase in the nitrile CtN
stretching frequency (compared to νNC ) 2228 cm-1 for free
benzonitrile) is expected after coordination of the nitrile
nitrogen to the electropositive U(IV) center and is similar
(33) Bagnall, K. W.; Brown, D.; Jones, P. J. J. Chem. Soc. A 1966, 1763-
1766.
7408 Inorganic Chemistry, Vol. 44, No. 21, 2005

Uranium(III)/(IV) Nitrile Adducts Including UI4(NtCPh)4
Scheme 1. Oxidation of Uranium Metal by Iodine in Nitrile
Solventsa
a
Equations are not balanced and reflect the reaction conditions used to
prepare each uranium nitrile adduct.
Figure 5. Structure of the [UI(NtCPh)8]2+ cation in 4 (left) with thermal
ellipsoids at the 35% probability level shown for the N, U, and I atoms,
and the intimate coordination geometry about the central U(III) atom (right).
Selected bond lengths (Å): U(2)-N(1) ) 2.64(1); U(2)-N(2) ) 2.54(1);
U(2)-I(4) ) 3.209(3); [N2-N(2A)-N(2B)-N(2C)]centroid-U(2) ) 0.05-
(1) Å; [N1-N(1E)-N(1F)-N(1G)]centroid-U(2) ) 1.70(1) Å. Selected bond
angles (deg): I(4)-U(2)-N(2) ) 78.62(5); N(1)-U(2)-I(4) ) 130.4(3).
The dashed lines are a visual aid representing the terminal faces of the
square antiprism.
closest to and most influenced by the paramagnetic U(III)
center. The remaining two signals at 7.01 and 8.82 ppm are
equally broad (∼30 Hz) and correspond to meta and para
hydrogens, respectively, but the upfield resonance at 7.01
ppm is twice as intense as the downfield resonance at 8.82
ppm. The simplicity of the 1H NMR spectrum may arise from
the weak coordinating ability of iodide toward U(III) in
solution.5,34 Iodide likely dissociates from [UI(NtCPh)8]+
to form an ion paired [U(NtCPh)8]2+ cation that is sym-
metric on the NMR time scale. An overall scheme of the
products obtained by uranium oxidation by iodine in nitrile
solvents is shown in Scheme 1.
Reactivity of UI4(NtCPh)4. A. Addition of Cp*MgCl‚
THF. Uranium(IV) bis-metallocene chemistry is dominated
by the Cp*2UCl2 (Cp* ) pentamethylcyclopentadienide)
starting material21,35-37 because of its ready preparation from
UCl4 and Cp*MgCl‚THF. The lack of a useful UI4-type
starting material presumably has precluded isolation of the
analogous Cp*2UI2 compound, which has been characterized
spectroscopically as a product from the in situ oxidative
addition reactions of Cp*2UCl‚THF with either iodine or
alkyl iodides and by iodide transfer from I3 to Cp*2UCl2.38
We attempted the preparation of Cp*2UI2 by treating 3 with
Cp* reagents.
Addition of 2.4 equiv of Cp*MgCl‚THF to a slurry of 3
in toluene, followed by overnight heating, leads to the
isolation of Cp*2UI2(NtCPh) (5) in 36% isolated yield.
Unfortunately, treatment of 3 with excess KCp* under
identical conditions yielded intractable products. The crystal
structure of 5, shown in Figure 6, is of the Cp2MX2Y type,
with uranium coordinated by two pentamethylcyclopenta-
dienides, two iodides, and the nitrogen of benzonitrile. This
is an uncommon coordination geometry for Cp*2U com-
pounds, with the most similar being Cp*2UCl2(L) (L ) HNd
PPh3,39 HNdSPh2,40 and pyrazole41). However, unlike the
latter compounds where the N-donor ligand binds to the
of a black microcrystalline material, determined by single-
crystal X-ray crystallography to be [UI(NtCPh)8][UI6] (4)
in 18% yield and likely formed by thermally induced iodide
loss from 3. This decomposition suggests that, although
complex 3 is much more stable than UI4, UI4(NtCPh)4
decomposes through a pathway similar to that observed for
UI4. The structure of the cation in the mixed U(III)/U(IV)
salt [UI(NtCPh)8][UI6] is shown in Figure 5.
The thermal ellipsoid plot of 4 shows a nine-coordinate
U(III) complex ion and a noncoordinating [UI6]-2 counterion.
The central uranium atom in the cation adopts a highly
distorted monocapped square antiprismatic geometry where
eight N atoms of the coordinating benzonitrile molecules
form the square antiprism, with iodide as the capping ligand.
The U(III) and U(IV) ions occupy positions of C4h and 4-fold
crystallographic symmetry, respectively. The central U(III)
atom is nine-coordinate, as observed in the U(III) iodide
organonitrile species 1 and 2. However, in this case, an iodide
ligand is situated in the pocket formed by the four benzoni-
trile molecules that form the square antiprism face instead
of in the one formed by nine N-bound nitriles and all outer
sphere iodides. If the square antiprismatic portion of the
U(III) cation is considered, then the distortion arises from
the position of the central U(III) atom with respect to the
centroids of the square planes that form the terminal faces
of the antiprism. In fact, the uranium atom is almost coplanar
with all four N(2) atoms and sits only 0.05(1) Å below the
centroid of the N(2)-N(2A)-N(2B)-N(2C) plane as com-
pared to the 1.70(1) Å above the centroid of the plane defined
by the four N(1) atoms.
(34) Berthet, J.-C.; Miquel, Y.; Iveson, P. B.; Nierlich, M.; Thue´ry, P.;
Madic, C.; Ephritikhine, M. J. Chem. Soc., Dalton Trans. 2002, 3265-
3272.
Complex 4 is insoluble in the nonpolar solvents toluene,
ether, and hexane but is soluble in methylene chloride. The
optical absorbance spectrum of a brown methylene chloride
solution of 4 is similar to those for the homoleptic U(III)
acetonitrile adducts, as shown in Figure 1, confirming the
presence of U(III).
(35) Manriquez, J. M.; Fagan, P. J.; Marks, T. J.; Day, C. S.; Day, V. W.
J. Am. Chem. Soc. 1978, 100, 7112-7114.
(36) Marks, T. J. In Fundamental and Technological Aspects of Organo-
f-Element Chemistry; Marks, T. J., Fragala, I. L., Eds.; Dordrecht,
Holland, 1985; pp 115-157.
(37) Fischer, R. D. In Fundamental and Technological Aspects of Organo-
f-Element Chemistry; Marks, T. J., Fragala, I. L., Eds.; Dordrecht,
Holland, 1985; p 277.
1
The H NMR spectrum of 4 in CD2Cl2 shows three
(38) Finke, R. G.; Hirose, Y.; Gaughan, G. J. Chem. Soc., Chem. Commun.
1981, 232-234.
(39) Cramer, R. E.; Roth, S.; Gilje, J. W. Organometallics 1989, 8, 2327-
2330.
paramagnetically broadened resonances at δ ) 8.82, 8.15,
and 7.01 ppm in a 1:2:2 ratio. The broadest resonance (∼80
Hz) at 8.15 ppm is assigned to the ortho hydrogens that are
Inorganic Chemistry, Vol. 44, No. 21, 2005 7409

Enriquez et al.
1
that the bound benzonitrile of 5 is labile and that the H
NMR spectrum obtained in C6D6 reflects an equilibrium
between Cp*2UI2 and 5. We tentatively assign the downfield
resonance at 18.0 ppm to the 30 Cp* hydrogens of Cp*2-
UI2, in reasonable agreement with the 16.8 ppm resonance
reported for the in-situ preparation of Cp*2UI2.38 Because
of the overwhelming presence of the coordinating benzoni-
1
trile solvent, the H NMR spectrum of 5 in CD2Cl2-spiked
benzonitrile shows the Cp* resonance for 5 exclusively. The
EI mass spectrum of crystals of complex 5 dissolved in
toluene shows a molecular ion peak at m/z ) 762 for Cp*2-
UI2 and a peak at m/z ) 103 for free benzonitrile, supporting
the theory that benzonitrile binds weakly to Cp*2UI2.
B. Addition of KTp* to UI4(NtCPh)4 Solutions. Poly-
pyrazolyl borate derivatives of uranium have been
studied29,41,44-59 for the last three decades, and like uranium
cyclopetadienide compounds, these complexes are generally
prepared from UCl4. Two notable exceptions are the reactions
of UI4 with Tp (Tp ) hydridotris(pyrazolyl)borate)47 and Tp*
(Tp* ) hyridotris(3,5-dimethylpyrazolyl)borate).29 In both
cases, dissolution of UI4 in THF followed by addition of
the pyrazolylborate ligand results in the isolation of 4-iodo-
butoxide U(IV) species Tp2UI(O(CH2)4I) and Tp*UI2-
(O(CH2)4I), respectively, because of ring opening of THF
by UI4. The increased solubility of 3 in organic solvents
relative to the insolubility of both UI4 and UI4(NtCMe)4
prompted reactivity studies of 3 with KTp* in methylene
chloride and toluene solutions.
Figure 6. Thermal ellipsoid plot of Cp*2UI2(NtCPh) (5) at the 35%
probability level. Selected bond lengths (Å): U(1)-Cp*(centroid) ) 2.48-
(2) and 2.45(2); U(1)-N(1) ) 2.53(1); U(1)-I(1) ) 2.942(3); U(1)-I(2)
) 3.092(2); N(1)-C(2) ) 1.14(2). Selected bond angles (deg): Cp*-
(centroid)-U(1)-Cp*(centroid) ) 136.7(5); N(1)-U(1)-I(2) ) 70.6(4);
N(1)-U(1)-I(1) ) 153.8(4); I(2)-U(1)-I(1) ) 83.16(7).
uranium center inside the ∼150° Cl-U-Cl “wedge” formed
by the chlorides, the iodides in 5 are cis to each other,
forming an acute I-U-I angle of 83.16(7)°. In fact, the acute
I-U-I angle is almost 15° smaller than the 97.9° Cl-U-
Cl angle in Cp*2UCl2.42
The two U-Cp* centroid distances of 2.45(2) and 2.48-
(2) Å and the Cp*(centroid)-U-Cp*(centroid) angle of
136.7(5)° are similar to known Cp*An complexes, and the
Cp* rings are arranged in the sterically favored staggered
arrangement. The three atoms in the equatorial positions are
in the same plane because the sum of the N(1)-U(1)-I(2)
and I(2)-U(1)-I(1) angles, 70.6(4) and 83.16(7)°, respec-
tively, equals the 153.8(4)° N(1)-U(1)-I(1) angle. The
U(1)-N(1) bond length of 2.53(1) Å is similar to the U-N
bond length observed in UI4(NtCPh)4. There are two U-I
distances in 5, 2.942(3) and 3.092(2) Å, which are 0.3-0.4
Å longer than the U-Cl bonds in the analogous Cp*2UCl2-
(L) complexes but similar to the 2.954 Å lengths reported
for Cp′2UI2 (Cp′ ) 1,3-bis(trimethylsilyl)cyclopentadienide),
the only structurally characterized bis(cyclopentadienido)
uranium diiodide reported;43 the U-I distances in UI4(Nt
CPh)4; and the [UI6]-2 counterions observed in the mixed-
valent U(III)/U(IV) nitrile compounds (vide supra).
Treatment of a red methylene chloride solution of 3 with
1.2 equiv of KTp* produces a yellow-green solution within
1 h of stirring at room temperature. Filtration to remove KI
and excess KTp* followed by evaporation of the filtrate
solution and washing with toluene, benzene, or ether to
(44) Antunes, M. A.; Ferrence, G. M.; Domingos, A.; McDonald, R.; Burns,
C. J.; Takats, J.; Marques, N. Inorg. Chem. 2004, 43, 6640-6643.
(45) Bagnall, K. W.; Beheshti, A.; Edwards, J.; Heatley, F.; Tempest, A.
C. J. Chem. Soc., Dalton Trans. 1979, 1241-1245.
(46) Carvalho, A.; Domingos, A.; Gaspar, P.; Marques, N.; Pires de Matos,
A.; Santos, I. Polyhedron 1992, 11, 1481-1488.
(47) Campello, M. P. C.; Domingos, A.; Santos, I. J. Organomet. Chem.
1994, 484, 37-46.
(48) Bagnall, K. W.; Edwards, J.; Preez, J. G. H. d.; Warren, R. F. J. Chem.
Soc., Dalton Trans. 1975, 140-143.
(49) Bagnall, K. W.; Edwards, J. J. Less-Common Met. 1976, 48, 159-
1
The H NMR spectrum of complex 5 in C6D6 displays
165.
(50) Silva, M.; Marques, N.; Pires de Matos, A. J. Organomet. Chem. 1995,
493, 129-132.
resonances at 18.0 and 15.6 ppm in approximately a 2:1 ratio
and displays benzonitrile resonances between 6.8 and 6.5
ppm. Addition of a single drop of benzonitile to the sample
results in the disappearance of the 15.6 ppm resonance and
the appearance of a 14.2 ppm resonance. The intensities of
the 18.0 ppm resonance and the 14.2 ppm resonance are
equal in the benzonitrile-spiked C6D6 solution of 5. When
the spectrum of 5 is obtained in CD2Cl2-spiked benzonitrile,
a single resonance at 14.0 ppm is observed. We postulate
(51) Domingos, A.; Marques, N.; De Matos, A. P. Polyhedron 1990, 9,
69-74.
(52) Ball, R. G.; Edelmann, F.; Matisons, J. G.; Takats, J.; Marques, N.;
Marcalo, J.; Pires de Matos, A.; Bagnall, K. W. Inorg. Chim. Acta
1987, 132, 137-143.
(53) Maier, R.; Mueller, J.; Kanellakopulos, B.; Apostolidis, C.; Domingos,
A.; Marques, N.; Pires De Matos, A. Polyhedron 1993, 12, 2801-
2808.
(54) Marcalo, J.; Marques, N.; Pires de Matos, A.; Bagnall, K. W. J. Less-
Common Met. 1986, 122, 219-224.
(55) Marques, N.; De Matos, A. P.; Bagnall, K. W. Inorg. Chim. Acta 1984,
95, 75-77.
(56) Marques, N.; Marcalo, J.; Almeida, T.; Carretas, J. M.; Pires de Matos,
A.; Bagnall, K. W.; Takats, J. Inorg. Chim. Acta 1987, 139, 83-85.
(57) Marques, N.; Marcalo, J.; Pires de Matos, A.; Bagnall, K. W.; Takats,
J. Inorg. Chim. Acta 1987, 139, 79-81.
(58) Marques, N.; Marcalo, J.; De Matos, A. P.; Santos, I.; Bagnall, K. W.
Inorg. Chim. Acta 1987, 134, 309-314.
(59) Sun, Y.; McDonald, R.; Takats, J.; Day, V. W.; Eberspacher, T. A.
Inorg. Chem. 1994, 33, 4433-4434.
(40) Cramer, R. E.; Ariyaratne, K. A. N. S.; Gilje, J. W. Z. Anorg. Allg.
Chem. 1995, 621, 1856-1864.
(41) Eigenbrot, C. W., Jr.; Raymond, K. N. Inorg. Chem. 1982, 21, 2653-
2660.
(42) Spirlet, M. R.; Rebizant, J.; Apostolidis, C.; Kanellakopulos, B. Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 1992, 48, 2135-2137.
(43) Blake, P. C.; Lappert, M. F.; Taylor, R. G.; Atwood, J. L.; Hunter,
W. E.; Zhang, H. J. Chem. Soc., Dalton Trans. 1995, 3335-3341.
7410 Inorganic Chemistry, Vol. 44, No. 21, 2005

Uranium(III)/(IV) Nitrile Adducts Including UI4(NtCPh)4
Figure 7. Thermal ellipsoid plot of Tp*UI3 (6) (left) and coordination
geometry of U(IV) center (right) at the 35% probability level. Three
cocrystallized toluene molecules are omitted. Selected bond lengths (Å):
U(1)-N(2) ) 2.446(9); U(1)-N(4) ) 2.422(9); U(1)-N(6) ) 2.425(9);
U(1)-I(1) ) 2.960(1); U(1)-I(2) ) 2.973(1); U(1)-I(3) ) 2.969(1).
Selected bond angles (deg): I(1)-U(1)-I(2) ) 93.54(4); I(2)-U(1)-I(3)
) 94.96(5); I(3)-U(1)-I(1) ) 95.91(4); N(2)-U(1)-N(6) ) 77.2(3);
N(6)-U(1)-N(4) ) 78.2(3); N(4)-U(1)-N(2) ) 78.8(3).
Figure 8. Thermal ellipsoid plot of Tp*UI3(NtCMe) (7) at the 35%
probability level. Selected bond lengths (Å): U(1)-N(2) ) 2.463(5); U(1)-
N(4) ) 2.455(5); U(1)-N(6) ) 2.513(5); U(1)-I(1) ) 2.9980(8); U(1)-
I(2) ) 3.0238(9); U(1)-I(3) ) 3.3036(7); U(1)-N(1) ) 2.557(6); N(1)-
C(1) ) 1.143(8). Selected bond angles (deg): I(1)-U(1)-I(2) ) 101.89(1);
I(2)-U(1)-I(3) ) 117.44(2); I(3)-U(1)-I(1) ) 115.42(2); I(1)-U(1)-
N(1) ) 73.3(1); I(2)-U(1)-N(1) ) 73.2(1); I(3)-U(1)-N(1) ) 72.2(1);
N(2)-U(1)-N(6) ) 77.2(3); N(6)-U(1)-N(4) ) 78.2(3); N(4)-U(1)-
N(2) ) 78.8(3). The dashed lines are a visual aid representing two faces of
the monocapped octahedron.
remove benzonitrile from the crude reaction mixture results
in the isolation of Tp*UI3 (6) in 61% isolated yield as a
brilliant green powder.
Analogous to the two Tp*UCl3(L) (L ) THF,52 OdP(O-
C2H3)353) complexes which have been structurally character-
ized, the crystal structure of 7 contains a central uranium
atom with monocapped octahedral geometry. The three
N-donor atoms of Tp* and the three iodide atoms coordinate
facially to the central uranium atom, and the acetonitrile N
atom caps the face formed by the iodides. Despite the small
size and the linear profile of the acetonitrile, the U(1)-N(1)
distance of 2.557(6) Å is longer than either U-O distance
of 2.546(4) or 2.373(7) Å from Tp*UCl3(THF) and Tp*UCl3-
(OdP(O-C2H3)3), respectively, likely because of the oxo-
philicity of uranium. The average U-I distance in Tp*UI3
of 2.967(1) Å increases by 0.14-3.109(8) Å upon coordina-
tion of acetonitrile; however, it should be noted that the
U(1)-I(3) distance is much longer, by ∼0.3 Å, than the two
3.0 Å U-I distances in 7. The average U-I distance increase
from 6 to 7 is double that of the average 0.05 Å U-Cl
distance increase observed upon coordination of the O-atom
donors THF and OdP(O-C2H3)3 to Tp*UCl3. The 0.05 Å
lengthening of the average Tp* U-N distance appears to
increase uniformly upon coordination of the Lewis bases to
either Tp*U(X)3 compound.
Dissolution of 6 in toluene and cooling to -38 °C produces
crystals of Tp*UI3‚3(toluene), and the crystal structure of
Tp*UI3 is shown in Figure 7. The coordination environment
of the uranium (IV) atom is approximately octahedral, with
the three nitrogen donor atoms from the Tp* ligand forming
one trigonal face of the octahedron and the three iodides
forming another. The compound is almost isostructural to
that of the previously reported Tp*UCl3, except for the
expected longer U-X distances for U-I’s which range
between 2.957(1) and 2.971(1) Å, relative to the U-Cl’s
which range between 2.548(3) and 2.68(3) Å.51 The 1H NMR
of complex 6 in CD2Cl2 is consistent with a C3V symmetric
paramagnetic complex in solution. The resonances at δ )
7.80, 5.49, and -7.71 ppm exist in a 1:3:3 ratio and agree
with the resonances reported for spectroscopically character-
ized 6 formed by oxidation of Tp*UI2(THF) with iodine in
toluene.29 In addition, the 13C NMR spectrum shows five
resonances for the five inequivalent carbon environments in
the bound Tp* ligand. The 11B NMR spectrum shows a well-
resolved doublet at δ ) 22.0 ppm (1JB-H ) 141 Hz) for the
Tp* B-H moiety. The UV-vis-NIR spectrum of Tp*UI3
in CH2Cl2 is shown in Figure 4.
Treatment of either crude or pure 6 with acetonitrile results
in a rapid quantitative conversion to a mustard-yellow
material. Crystals of Tp*UI3(NtCMe) (7) were obtained by
vapor diffusion of hexanes into a CH2Cl2 solution of this
mustard-yellow material, and the crystal structure is shown
in Figure 8. Attempts to prepare t-Bu-NtC and pyridine
adducts of Tp*UI3 in a similar fashion were unsuccessful.
When we attempted to prepare the pyridine adduct of 6 by
dissolution in pyridine followed by vapor diffusion of
hexanes, we isolated crystals which were analyzed as a
[Tp*B]2[UI6] (8) decomposition product by X-ray diffraction.
Similar degradation of the Tp* ligand to form 3,5-dimeth-
ylpyrazole-bridged dibora cations has been observed during
the synthesis of electrophilic early transition-metal com-
plexes.52,60 The thermal ellipsoid plot of decomposition
product 8 is included in the Supporting Information.
The Tp* hydrogen signals of 7 in CD2Cl2 resonate at the
same frequencies in the H NMR spectrum as those for
1
Tp*UI3, with the only difference in these spectra being a
three-hydrogen singlet assigned to the methyl resonance of
acetonitrile in 7, which appears at 1.94 ppm. The 13C NMR
spectrum of 7 also differs by the appearance of a quartet
carbon resonance assigned to the methyl carbon of the
acetonitrile centered at 1.71 ppm. No resonance for the nitrile
carbon was observed. Optical absorbance spectra of com-
plexes 6 and 7 in CH2Cl2 solutions are superimposable. The
11B NMR spectrum of 7 has a single resonance which appears
as a doublet centered at δ ) 22.2 ppm with 1JH ) 89.5 Hz.
1
We postulate that the 51 Hz difference between the JB-H
(60) Boncella, J. M.; Cajigal, M. L.; Gamble, A. S.; Abboud, K. A.
Polyhedron 1996, 15, 2071-2078.
Inorganic Chemistry, Vol. 44, No. 21, 2005 7411

Enriquez et al.
Figure 9. Thermal ellipsoid plot of [Tp*UI(dmpz)]2[µ-O] at the 35%
probability level. Selected bond length (Å): U(1)-O(1) ) 2.098(1). Selected
bond angle (deg): U(1)-O(1)-U(1A) ) 166.7(5).
Figure 10. Thermal ellipsoid plot of the U(IV) coordination environment
in [Tp*UI(dmpz)]2[µ-O] (9). Selected bond lengths (Å): U(1)-O(1) )
2.098(1); U(1)-I(2) ) 3.0650(9); U(1)-N(1) ) 2.509(8); U(1)-N(3) )
2.543(8); U(1)-N(5) ) 2.526(9); U(1)-N(7) ) 2.390(8); U(1)-N(8) )
2.331(8); N(7)-N(8) ) 1.38(1); [N(7)-N(7)center]-U(1) ) 2.257. Selected
bond angles (deg): N(8)-U(1)-N(7) ) 34.0(3); [N(8)-N(7)center]-U(1)-
N(1) ) 99.9(3); [N(8)-N(7)center]-U(1)-N(3) ) 166.1(3); [N(8)-N(7)center]-
U(1)-N(5) ) 87.8(3); [N(8)-N(7)center]-U(1)-O(1) ) 98.1(3); [N(8)-
N(7)center]-U(1)-I(2) ) 95.9(3); N(1)-U(1)-I(2) ) 156.5(2); N(5)-U(1)-
O(1) ) 163.8(4). The dashed line represents the pseudoaxis of the distorted
octahedron passing through U(1) and the centroid of atom positions N(7)
and N(8).
coupling constants observed for Tp*UI3 and Tp*UI3(Nt
CMe) implies that the acetonitrile is coordinated to Tp*UI3
in CD2Cl2 solution. However, the acetonitrile ligand of
complex 7 is labile and can be removed from the uranium
coordination sphere by repeated rinsing with ether to form
6.
We attempted the addition of 1.2 equiv of KTp* to a
toluene slurry of 3 at room temperature in a drybox and
isolated Tp*UI3 in low yield. We also performed the reaction
using 2.2 equiv of KTp* in a Schlenk tube and heated the
reaction for 12 h at 95 °C. The initially red slurry became
brown with heating, and after several filtrations in a drybox,
a grayish yellow filtrate was collected and placed in a freezer
at -38 °C for 1 month. Large green crystals formed and
were determined by single-crystal X-ray crystallography to
be the oxo-bridged dinuclear uranium species [Tp*UI-
(dmpz)]2[µ-O] (9) (dmpzH ) 3,5-dimethylpyrazole). The
residual filtrate was evaporated in vacuo, and 9 was isolated
in 92% yield. We believe that this product forms because of
the presence of adventitious water. Hydrolysis of the Tp*
ligand has been observed during the preparation of analogous
lanthanide(III) compounds of the type Tp*LnCl2(THF)61 to
form Tp*LnCl2(dmpzH) (dmpzH ) 3,5-dimethylpyrazole;
Ln ) Y,62 Yb,63 or Lu61). We postulate that Tp*UI3 facilitates
the hydrolysis of an excess Tp* ligand present in the reaction
to form Tp*UI3(dmpzH), the uranium analogue of Tp*LnCl2-
(dmpzH). A Tp*UI3(dmpzH) intermediate could then un-
dergo a series of formal HI elimination and hydrolysis
reactions to ultimately form the dinuclear compound 9.64
The crystal structure of 9 (Figure 9) shows the meso (R,S)
stereoisomer of the dinuclear U(IV) complex with oxygen
bridging two chiral centers. The µ-O is located at an inversion
center; thus, both U atoms are symmetry related, with each
binding to three nitrogen atoms from tridentate Tp*, two
nitrogen atoms from the bidentate 3,5-dimethypyrazolide
ligand, an iodide, and the bridging oxygen atom. If the dmpz
ligand is considered to occupy a single coordination site,
then the coordination environment around each U(IV) atom
in 9 can be described as a distorted octahedron with the center
of the dmpz N-N bond located 2.26(1) Å away from the
U(IV) atom (Figure 10).
Few simple oxo-bridged dinuclear uranium species have
been reported.65-68 The 2.098(1) Å U-O distance in 9 is
most comparable to the shorter 2.075(1) Å U-O distance
reported for [Tp*UCl2]2[µ-O].65 The 0.023(1) Å increase in
U-O bond length can be ascribed to the larger steric
encumbrance imparted by the dmpz and both iodides relative
to three chlorides. The U-O-U angle of 166.7(5)° is almost
identical to the 167.1(5)° angle found in [Cp*2UCl]2[µ-O]68
which, coincidently, has a comparable U-O distance of
2.13 Å.
The 1H NMR spectrum of complex 9 is paramagnetically
broadened and complicated. For the meso isomer of 9, each
“half” of the molecule is identical and one would expect to
observe 12 resonances: three for each unique pyrazole ring
of two equivalent Tp* ligands and three for each of the two
equivalent dmpz ligands. We could assign only seven
(61) Marques, N.; Sella, A.; Takats, J. Chem. ReV. 2002, 102, 2137-2159.
(62) Long, D. P.; Chandrasekaran, A.; Day, R. O.; Bianconi, P. A.;
Rheingold, A. L. Inorg. Chem. 2000, 39, 4476-4487.
(63) Apostolidis, C.; Carvalho, A.; Domingos, A.; Kanellakopulos, B.;
Maier, R.; Marques, N.; De Matos, A. P.; Rebizant, J. Polyhedron
1998, 18, 263-272.
(64) One helpful referee correctly pointed out that there are many equally
plausible mechanistic pathways to forming the µ-O complex 9. For
example, initial formation of (κ3-Tp*)UI3(κ2-Tp*) could undergo
hydrolysis to give (κ3-Tp*)UI2(OH)(κ2-Tp*). Subsequent B-N cleav-
age would then give (κ3-Tp*)(UI2)(dmpz). Once some Tp*- has
undergone B-N cleavage, any number of possible pathways could
generate the final µ-O complex.
(65) Domingos, A.; Marques, N.; Pires de Matos, A.; Santos, I.; Silva, M.
Polyhedron 1992, 11, 2021-2025.
(66) Beeckman, W.; Goffart, J.; Rebizant, J.; Spirlet, M. R. J. Organomet.
Chem. 1986, 307, 23-37.
(67) Berthet, J. C.; Le Marechal, J. F.; Nierlich, M.; Lance, M.; Vigner, J.;
Ephritikhine, M. J. Organomet. Chem. 1991, 408, 335-341.
(68) Evans, W. J.; Seibel, C. A.; Forrestal, K. J.; Ziller, J. W. J. Coord.
Chem. 1999, 48, 403-410.
7412 Inorganic Chemistry, Vol. 44, No. 21, 2005

Uranium(III)/(IV) Nitrile Adducts Including UI4(NtCPh)4
resonances of equal intensity at δ ) 70.22, 20.12, -2.74,
-8.09, -14.10, -18.06, and -39.18 ppm to three hydrogens
each of either a Tp* methyl group or a dmpz methyl group.
The NMR sample could contain either or both of the (R,R)-9
or (S,S)-9 diastereomers of (R,S)-9. Either one of these
asymmetric stereoisomers would provide up to 24 different
additional resonances in the spectrum. The electronic absorp-
tion spectrum of 9 is shown in Figure 4 for comparison to
the other U(IV) iodides we have prepared.
precusor. Treatment of a toluene solution of UI4(NtCPh)4
with excess Cp*MgCl‚THF provided Cp*2UI2(NtCPh), and
treatment with KTp* in CH2Cl2 solution cleanly provided
both Tp*UI3 and Tp*UI3(NtCMe) depending on workup
conditions. Addition of 2.2 equiv of KTp* to a toluene
solution of UI4(NtCPh)4 followed by prolonged heating at
95 °C, filtration, and crystallization led to the isolation of
[Tp*UI(dmpz)]2[µ-O], which presumably resulted from the
presence of adventitious water.
Conclusion
Acknowledgment. We thank the Heavy Element Chem-
istry Research Program, Chemical Sciences Division of the
Office of Basic Energy Sciences, U.S. Department of Energy,
for funding. The University of California operates LANL
for the U.S. DOE under contract W-7405-ENG-36. We also
thank the following generous colleagues: Dr. C. Drew Tait
(Raman spectrum of UI4(NtCPh)4), Dr. Warren Oldham
(CV of UI4(NtCPh)4), Dr. Jeffery Golden (Cp*MgCl‚THF),
UNCsChapel Hill Professor Joseph Templeton (KTp*), and
Dr.’s Carol Burns and Jaqueline Kiplinger for liberal use of
their equipment.
Characterization of products from the oxidation of uranium
metal with 1.3 equiv of iodine in nitrile solvents has been
presented. When this reaction is carried out in acetonitrile,
the mixed-valent U(III)/U(IV) complex [U(NtCMe)9][UI6]
is isolated. In contrast, the same reaction in benzonitrile
provides UI4(NtCPh)4 as the only product. This U(IV)
tetraiodide complex was prepared in synthetically useful
quantities and characterized by single-crystal X-ray crystal-
lography, NMR, Raman, FT-IR, and UV-vis-NIR spec-
troscopies. Heating UI4(NtCPh)4 in benzonitrile solution to
reflux generates [UI(NtCPh)8][UI6], a U(III)/U(IV) salt
analogous to the product obtained by iodine oxidation in
acetonitrile, as a decomposition product. The facile high-
yield synthesis of UI4(NtCPh)4, compared with the high-
temperature furnace methods used to prepare UI4 and UBr4
or the harsh reducing conditions used to prepare UCl4, and
its solubility in organic solvents make it a useful UX4
Supporting Information Available: Tables of crystallographic
data, structure solution and refinement, atomic coordinates, bond
lengths and angles, and anistotropic thermal parameters for
compounds 1 and 3-9. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC050578F
Inorganic Chemistry, Vol. 44, No. 21, 2005 7413