Selenate and tellurate complexes of pentavalent uranium

Article abstract of DOI:10.1039/b819097f

Oxidation of (C₅Me₅)₂U(=N-2,6- ⁱPr₂-C₆H₃)(THF) with PhE-EPh yields the corresponding U^V-chalcogenate complexes (C₅Me ₅)₂U(=N-2,6-

Full text of DOI:10.1039/b819097f

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Selenate and tellurate complexes of pentavalent uraniumw
Christopher R. Graves, Brian L. Scott, David E. Morris* and Jaqueline L. Kiplinger*
Received (in Austin, TX, USA) 30th October 2008, Accepted 3rd December 2008
First published as an Advance Article on the web 15th January 2009
DOI: 10.1039/b819097f
Oxidation of (C5Me5)2U(QN–2,6-iPr2–C6H3)(THF) with
PhE–EPh yields the corresponding UV-chalcogenate complexes
(C5Me5)2U(QN–2,6-iPr2–C6H3)(EPh) (E = S, Se, Te) in
excellent (490%) isolated yields.
Heavy chalcogen (Se/Te) soft donor ligands have traditionally
been exploited to investigate trivalent actinide/lanthanide separa-
tion technologies1 and to address questions regarding covalency
in hard–soft interactions.2,3 Such studies have generated the
existing handful of structurally characterized trivalent1,4 and
tetravalent5,6 uranium–Se/Te complexes and a sole hexavalent
U–Se structure,7 with no corresponding pentavalent examples.
The absence of these high-valent uranium chalcogenate com-
plexes limits our understanding of bonding at the extremes of the
hard–soft continuum. Recent work by our group8 and others9,10
has shown that with appropriate supporting ligands uranium(V)
compounds are stable. Herein, we show that pentavalent uranium
thiolate, selenate, and tellurate complexes can be easily prepared
using readily available PhE–EPh (E = S, Se, Te) reagents.
Fig. 1 Molecular structure of 3 with thermal ellipsoids projected at the
50% probability level. Hydrogen atoms have been omitted for clarity.
(1)
Fig. 2 Molecular structure of 4 with thermal ellipsoids projected at the
50% probability level. Hydrogen atoms have been omitted for clarity.
Single crystals of complexes 3 and 4 suitable for X-ray
diffractionz were obtained from concentrated hexane solutions
at ꢀ30 1C. Fig. 1 and 2 show the molecular structures of
complexes 3 and 4, respectively, with select metrical parameters
As shown in eqn (1), reaction of (C5Me5)2U(QN–2,6-iPr2–C6H3)-
(THF) (1) with 0.5 equiv. of PhS–SPh overnight in toluene
solution provided the known8a UV-imido thiolate
complex (C5Me5)2U(QN–2,6-iPr2–C6H3)(SPh) (2) in 94%
yield after work-up. This protocol was conveniently
extended to the synthesis of the selenium and tellurium
derivatives (C5Me5)2U(QN–2,6-iPr2–C6H3)(SePh) (3) and
(C5Me5)2(QN–2,6-iPr2–C6H3)(TePh) (4), which were also
isolated in excellent yields (90% and 95%, respectively).z
Although RE–ER reagents have been used as oxidants for
low-valent uranium,5,11 the synthesis of 2–4 represents new
chemistry for uranium imido complexes and the first examples
of using dichalcogenide reagents to access the UV/UIV couple.
provided in Table 1. Both complexes feature
a bent-
metallocene framework with the imido and EPh ligand con-
tained within the metallocene wedge, similar in constitution to
the related pentavalent (C5Me5)2U(QN–2,6-iPr2–C6H3)(X/Y)
(X = Cl, Br, I; Y = OTf, SPh, NPh2, NQCPh2)8 complexes.
As noted for other high-valent uranium imido complexes,8b,d
all three complexes 2–4 have short UQN bond distances
(1.960(6)–1.984(4) A) and nearly linear UQN–Cipso bond
angles (170.6(6)–171.6(3)1), with no obvious trends present
on the basis of donating ability of the specific chalcogenide.
However, there is a systematic difference in the U–E bond
distances in the order U–S (2.7230(13) A) o U–Se (2.8639(6) A) o
U–Te (3.0845(9) A) and the U–E–Cipso angles U–S–Cipso
(131.08(17)1) 4 U–Se–Cipso (126.41(15)1) 4 U–Te–Cipso
(121.5(2)1), which both track with increasing size of the
chalcogenide ion going down the group.12 Publication quality
X-ray data could not be obtained for the aryloxide complex 5;
however, the aryloxide ligand metrical parameters for the
(C5Me5)2U–OAr moiety are quite insensitive to uranium metal
Los Alamos National Laboratory, Los Alamos, NM 87544, USA.
E-mail: kiplinger@lanl.gov; Fax: +1 505 667 9905;
Tel: +1 505 665 9553
w Electronic supplementary information (ESI) available: General experi-
mental details, sample protocols, synthetic procedures, a plot of C5Me5 1H
NMR signal versus oxidation potential, and cyclic voltammograms and
crystallographic details for 3 and 4. CCDC numbers for 3 and 4 are
707530 and 707531, respectively. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b819097f
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Table 1 Selected characterization data for the (C5Me5)2U(QN–2,6-iPr2–C6H3)(EPh) complexes 2–5w
1H NMR data for
C5Me5
Structural data
Electrochemical dataa
d (ppm)
Dn1/2/Hz
UQN/A
UQN–C/1
U–E/A
U–E–C/1
N–U–E/1
E1/2 (UVI/UV)/V
E1/2 (UV/UIV)/V
Compound
2 (E = S)
3 (E = Se)
4 (E = Te)
5 (E = O)
a
4.57
4.57
4.36
3.33
83
147
172
71
1.976(4)
1.984(4)
1.960(6)
—
171.6(3)
171.4(3)
170.6(6)
—
2.7230(13)
2.8639(6)
3.0845(9)
—
131.08(17)
126.41(15)
121.5(2)
—
103.35(12)
102.17(11)
107.53(18)
—
0.00
0.00
ꢀ1.43
ꢀ1.43
ꢀ1.44
ꢀ1.75
ꢀ0.07
ꢀ0.22
In B0.1 M [Bu4N][B(3,5-(CF3)2–C6H3)4]–THF at room temperature vs. [(C5H5)2Fe]+/0 determined from the peak position in a square-wave
voltammogram.
oxidation state.13 For example, the geometric parameters
observed for (C5Me5)2U(–O–2,6-iPr2–C6H3)(I) (U–O
electronic spectral data (Fig. 3). The UV-visible region is
dominated by transitions derived from the (C5Me5)2UQN
core,8 and the changes that result as the EPh ligand varies
from E = O - S - Se - Te are manifest in both a
monotonic increase in the intensities of these bands and a
notable red-shift in the energy of the lowest energy set of
bands (E o 15 000 cmꢀ1) that have been attributed to the two
different spin components of the imido-to-metal charge-transfer
transition; 4(pMQN - nb5f) and 2(pMQN - nb5f), respectively
(nb = non-bonding). As shown in Fig. 3 inset, there are
also changes in the f–f spectral region that are most
pronounced as EPh changes from E = O - S, but are still
discernible for E = S - Se - Te. These spectral changes
closely parallel those seen for the halide series,8b and indicate
that these anionic wedge ligands do influence the electronic
energies and transition probabilities associated with both the
molecular (i.e., imido-based) and ligand-field states. Presum-
ably, the influence exerted on both classes of electronic states
derives from perturbations induced by the chalcogenide ligand
on the uranium(V) f-orbital manifold as previously noted for
the trivalent uranium and plutonium systems An[N(EPiPr2)2]3
(An = U, Pu; E = S, Se, Te) by Gaunt and co-workers.3
In summary, using PhE–EPh reagents we have provided a
convenient and high-yielding route for the synthesis of the first
pentavalent uranium selenate (U–SePh) and tellurate
(U–TePh) complexes. Spectroscopic comparisons of the penta-
valent uranium selenate and tellurate complexes with the
isostructural aryloxide (U–OPh) and thiolate (U–SPh) deriva-
tives reveal notable variations in electronic structure that can
=
2.114(6) A; U–O–Cipso = 166.6(6)1)13b are statistically indis-
tinguishable with those obtained for the structurally related
UV complex (C5Me5)2U(–O–2,6-iPr2–C6H3)(QO) (U–O =
2.135(5) A; U–O–Cipso = 169.7(5)1).13a As such, existing data
showing U–O { U–S and U–O–Cipso c U–S–Cipso can be
extrapolated for complex 5, which fits well within the above
trends observed for the UV-chalcogenide complexes.
Although there have been reports of inorganic materials
with UV–Se or UV–Te interactions,14 complexes 3 and 4
represent the first structurally characterized pentavalent
uranium molecular systems featuring a U–Se or U–Te
bond, respectively. At 2.7230(13) A, the U–Se distance
observed in 3 agrees well with analogous parameters observed
for structurally characterized UIV metallocene complexes with
a U–Se linkage. For example, (C5Me5)2U(Me)(SePh) has a
U–Se distance of 2.8432(7) A,5d while (C5Me5)2U(SePh)2
has U–Se distances of 2.8011(7) and 2.7997(7) A.5c Likewise,
the U–Te distance observed for 4 (U(1)–Te(1) = 3.0845(9) A)
also compares well with the few structurally characterized UIV
metallocene complexes containing
a U–Te interaction:
(C5Me5)2U(TePh)2 has U–Te distances of 3.0383(6) and
3.0504(6) A,5d while the metallacycle (C5Me5)2U[Z2-(Te,C)-
(o-C6H4)Te] has a U–Te bond length of 2.9648(4) A.5d
Including the aryloxide complex (C5Me5)2U(QN–2,6-iPr2–
C6H3)(OPh) (5),8d the electrochemical and spectroscopic data
for this chalcogenide series of UV-imido complexes (2–4)
parallel those found for other UV-imido complexes, in particular
those of the corresponding halide series (F, Cl, Br, and I).8
All the chalcogenide complexes exhibit both UVI/UV and
UV/UIV redox couples (Table 1). While 1–4 are all stable in
neat THF, neither 3 nor 4 is stable in the supporting electrolyte
solution. Based on changes in the voltammetric behavior, it
appears that the decomposition proceeds to a UIV-imido
complex. Potential data cited in Table 1 were collected
within B2 min of preparation of fresh solutions. These
early-time voltammograms are included in the ESI.w
The correlation noted previously8d in the C5Me5 1H NMR
chemical shift vs. E1/2 (UVI/UV) is preserved for 3 and 4,
demonstrating that varying electron density at the metal center
is the primary influence on both observables. As such, the
lesser variability in the E1/2 values down the chalcogenide
series versus the halide series8a,d tracks with the smaller change
in electronegativity for the chalcogens versus the halogens.
Variations in electronic structure down the chalcogenide
series are most strongly reflected in the UV-visible-near IR
Fig. 3 UV-visible-near IR electronic absorption spectral data for the
(C5Me5)2U(QN–2,6-iPr2–C6H3)(EPh) complexes 2–5 in toluene solution.
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be ascribed to differing degrees of perturbation on the UV
f-orbital manifold down the O - S - Se - Te series. This
work demonstrates that soft dichalcogenide reagents are not
limited to chemistry with soft/low-valent actinide compounds
and can be used to access hard uranium complexes in high-
valent oxidation states. The understanding of bonding at these
hard–soft extremes will promote new separation schemes.
For financial support of this work, we acknowledge LANL
(Director’s PD Fellowship to C.R.G.), the LANL LDRD
program and G. T. Seaborg Institute for Transactinium
Science (PD Fellowship to C.R.G.), and the Division of
Chemical Sciences, Office of Basic Energy Sciences, Heavy
Element Chemistry program. This work was carried out under
the auspices of the NNSA of the US Dept of Energy at LANL
under Contract DE-AC5206NA25396.
separations, see: A. J. Gaunt, B. L. Scott and M. P. Neu, Angew.
Chem., Int. Ed., 2006, 45, 1638–1641.
2 K. I. M. Ingram, N. Kaltsoyannis, A. J. Gaunt and M. P. Neu,
J. Alloys Compd., 2007, 444–445, 369–375.
3 A. J. Gaunt, S. D. Reilly, A. E. Enriquez, B. L. Scott, J. A. Ibers,
P. Sekar, K. I. M. Ingram, N. Kaltsoyannis and M. P. Neu, Inorg.
Chem., 2008, 47, 29–41.
4 For structurally characterized complexes with a UIII–Se bond, see:
A. J. Gaunt, B. L. Scott and M. P. Neu, Chem. Commun., 2005,
3215–3217.
5 For structurally characterized complexes with a UIV–Se bond, see:
(a) P. C. Leverd, M. Ephritikhine, M. Lance, J. Vigner and
M. Nierlich, J. Organomet. Chem., 1996, 507, 229–237;
(b) A. J. Gaunt, B. L. Scott and M. P. Neu, Inorg. Chem., 2006,
45, 7401–7407; (c) W. J. Evans, K. A. Miller, S. A. Kozimor,
J. W. Ziller, A. G. DiPasquale and A. L. Rheingold, Organo-
metallics, 2007, 26, 3568–3576; (d) W. J. Evans, K. A. Miller,
J. W. Ziller, A. G. DiPasquale, K. J. Heroux and A. L. Rheingold,
Organometallics, 2007, 26, 4287–4293.
6 For the two structurally characterized complexes with a UIV–Te
bond see: ref. 5d.
7 B. Zarli, R. Graziani, E. Forsellini, U. Croatto and G. Bombieri,
J. Chem. Soc. D, 1971, 1501–1502.
Notes and references
z All manipulations were performed in a recirculating vacuum atmo-
spheres NEXUS drybox (N2) with a 40CFM Dual Purifier NI-Train.
Complex 5 was prepared as previously reported.8d
8 (a) C. R. Graves, B. L. Scott, D. E. Morris and J. L. Kiplinger,
J. Am. Chem. Soc., 2007, 129, 11914–11915; (b) C. R. Graves,
P. Yang, S. A. Kozimor, A. E. Vaughn, D. L. Clark,
S. D. Conradson, E. J. Schelter, B. L. Scott, J. D. Thompson,
P. J. Hay, D. E. Morris and J. L. Kiplinger, J. Am. Chem. Soc.,
2008, 130, 5272–5285; (c) C. R. Graves, B. L. Scott, D. E. Morris
and J. L. Kiplinger, Organometallics, 2008, 27, 3335–3337;
(d) C. R. Graves, A. E. Vaughn, E. J. Schelter, B. L. Scott,
J. D. Thompson, D. E. Morris and J. L. Kiplinger, Inorg. Chem.,
2008, 47, 11879–11891.
9 For examples of pentavalent uranium complexes, see:
(a) C. Boisson, J.-C. Berthet, M. Lance, M. Nierlich, J. Vigner
and M. Ephritikhine, J. Chem. Soc., Chem. Commun., 1995,
543–544; (b) D. Gourier, D. Caurant, J.-C. Berthet, C. Boisson
and M. Ephritikhine, Inorg. Chem., 1997, 36, 5931–5936;
(c) T. Arliguie, M. Rourmigue and M. Ephritikhine, Organo-
metallics, 2000, 19, 109–111; (d) I. Castro-Rodriguez, K. Olsen,
P. Gantzel and K. Meyer, J. Am. Chem. Soc., 2003, 125,
4565–4571; (e) F. Burdet, J. Pecaut and M. Mazzanti, J. Am.
Chem. Soc., 2006, 128, 16512–16513; (f) P. L. Arnold, D. Patel,
C. Wilson and J. B. Love, Nature, 2008, 451, 315–317.
10 C. J. Burns and M. S. Eisen, Organoactinide Chemistry Synthesis
and Characterization, in The Chemistry of the Actinide and Trans-
actinide Elements, ed. L. R. Morss, N. M. Edelstein and J. Fuger,
Springer, The Netherlands, 3rd edn, 2006, vol. 5, pp. 2799–2910,
and references therein.
General synthesis of (C5Me5)2U(QN–2,6-iPr2–C6H3)(E–Ph):
a
125 mL side-arm flask equipped with a stir bar was charged with
(C5Me5)2U(QN–2,6-iPr2–C6H3)(THF) (1) (0.50 g, 0.66 mmol) and
toluene (100 mL). PhE–EPh (0.33 mmol) was added to the dark brown
solution and the reaction mixture was stirred at room temperature.
After 12 h, the reaction mixture was filtered through a Celite-padded
coarse frit and volatiles were removed from the filtrate. The residue
was extracted into hexane (50 mL) and filtered through a Celite-
padded coarse porosity frit. The filtrate was collected and the volatiles
were removed under reduced pressure to give 2–4 as brown solids.
Characterization data for (C5Me5)2U(QN–2,6-iPr2–C6H3)(SPh) (2):
yield: 0.49 g, 0.62 mmol, 94%. Spectroscopic characterization of 2
matched the literature data:8a 1H NMR (C6D6, 300 MHz, 298 K):
d 51.33 (b, 1H, CH(CH3)2), 29.45 (1H, Ar-H), 24.18 (1H, Ar-H), 11.92
(6H, CH(CH3)2), 6.31 (2H, Ar-H), 4.57 (30H, (C5Me5), 1.42 (1H, Ar-H),
1.24 (1H, Ar-H), 0.89 (1H, Ar-H), ꢀ2.47 (6H, CH(CH3)2), ꢀ4.74
(1H, Ar-H), ꢀ7.95 (b, 1H, CH(CH3)2).
Characterization data for (C5Me5)2U(QN–2,6-iPr2–C6H3)(SePh)
(3): yield: 0.50 g, 0.60 mmol, 90%. 1H NMR (C6D6, 300 MHz,
298 K): d 49.62 (b, 1H, CH(CH3)2), 30.20 (1H, Ar-H), 25.44
(1H, Ar-H), 11.60 (6H, CH(CH3)2), 5.08 (3H, Ar-HSe–Ph), 4.57
(30H, (C5Me5), 3.74 (2H, Ar-HSe–Ph), ꢀ1.20 (6H, CH(CH3)2), ꢀ3.52
(1H, Ar-H), ꢀ6.78 (b, 1H, CH(CH3)2). Mp = 212–214 1C. MS
(EI, 70 eV): m/z 840 (M+). Anal. calcd for C38H52NSeU (mol. wt
839.82): C, 54.35; H, 6.24; N, 1.67. Found: C, 54.59; H, 6.20; N, 1.71.
Characterization data for (C5Me5)2U(QN–2,6-iPr2–C6H3)(TePh)
(4): yield: 0.55 g, 0.63 mmol, 95%. 1H NMR (C6D6, 300 MHz,
298 K): d 49.69 (b, 1H, CH(CH3)2), 30.90 (1H, Ar-H), 26.26
(1H, Ar-H), 11.73 (6H, CH(CH3)2), 4.85 (3H, Ar-HTe–Ph), 4.36
(30H, (C5Me5), 3.67 (2H, Ar-HTe–Ph), ꢀ0.76 (6H, CH(CH3)2), ꢀ2.75
(1H, Ar-H), ꢀ6.81 (b, 1H, CH(CH3)2). Mp = 205–207 1C. Anal. calcd
for C38H52NTeU (mol. wt 888.46): C, 51.37; H, 5.90; N, 1.58. Found:
C, 51.74; H, 5.90; N, 1.58.
11 For the use of RS-SR as an oxidant in uranium chemistry to give
IV-SR complexes, see: (a) P. L. Diaconescu, P. L. Arnold,
U
T. A. Baker, D. J. Mindiola and C. C. Cummins, J. Am. Chem.
Soc., 2000, 122, 6108–6109; (b) W. J. Evans, K. A. Miller,
W. R. Hillman and J. W. Ziller, J. Organomet. Chem., 2007, 692,
3649–3654; (c) W. J. Evans, E. Montalvo, S. A. Kozimor and
K. A. Miller, J. Am. Chem. Soc., 2008, 130, 12258–12259. Also see
ref. 5a and b.
12 F. A. Cotton, G. Wilkinson, M. Bochmann and C. Murillo,
& Sons, Inc.,
Crystal data for (C5Me5)2U(QN–2,6-iPr2–C6H3)(SePh) (3):
C38H52NSeU, M = 839.80, monoclinic, space group P21/n, a =
12.0348(10) A, b = 18.1721(16) A, c = 15.6860(14) A, a = 90.001,
Advanced Inorganic Chemistry, John Wiley
New York, 6th edn, 1998, p. 497.
13 (a) D. S. J. Arney and C. J. Burns, J. Am. Chem. Soc., 1993, 115,
9840–9841; (b) C. R. Graves, E. J. Schelter, T. Cantat, B. L. Scott
and J. L. Kiplinger, Organometallics, 2008, 27, 5371–5378.
14 A selection of inorganic materials with a UV–Se or UV–Te bond
have been reported. See: (a) J. Leciejewicz and A. Zygmunt, Phys.
Status Solidi A, 1972, 13, 657–660; (b) A. Zygmunt, A. Murasik,
S. Ligenza and J. Leciejewicz, Phys. Status Solidi A, 1974, 22,
75–79; (c) G. Amoretti, A. Blaise and P. Burlet, J. Less-Common
Met., 1986, 121, 233–248; (d) K. Stowe, Z. Anorg. Allg. Chem.,
1996, 622, 1423–1427; (e) Z. Henkie, T. Cichorek, A. Pietraszko,
R. Fabrowski, A. Wojakowski, B. S. Kuzhel, L. Kepinski,
L. Krajczyk, A. Gukasov and P. Wisniewski, J. Phys. Chem.
Solids, 1998, 59, 385–393; (f) J.-Y. Kim, D. L. Gray and
J. A. Ibers, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2006,
62, i124–i125.
b = 99.1150(10)1, g = 90.001, V = 3387.2(5) A3, Z = 4, Dc
=
1.647 mg mꢀ3, m = 5.893 mmꢀ1, F(000) = 1652, T = 120(1) K, 34 990
measured reflections, 6883 independent (Rint = 0.0816), R1 = 0.0347,
wR2 = 0.0633. for I 4 2s(I).
Crystal data for (C5Me5)2U(QN–2,6-iPr2–C6H3)(TePh) (4):
ꢀ
C38H52NTeU, M = 888.44, triclinic, space group P1, a = 10.078(2) A,
b = 10.161(2) A, c = 18.643(4) A, a = 76.745(2)1, b = 78.811(2)1,
g = 70.303(2)1, V = 1735.1(7) A3, Z = 2, Dc = 1.701 mg mꢀ3, m =
5.527 mmꢀ1, F(000) = 862, T = 120(1) K, 16 660 measured reflec-
tions, 6280 independent (Rint = 0.0572), R1 = 0.0469, wR2 = 0.1069
for I 4 2s(I).
1 For the sole structurally characterized complex with a UIII–Te
bond and a discussion regarding soft-donor ligands in actinide
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778 | Chem. Commun., 2009, 776–778