Preparation and reactions of base-free bis(1,2,4-tri-tert-butylcyclopentadienyl)uranium oxide, Cp′2UO

Article abstract of DOI:10.1021/om050406q

Reduction of the uranium metallocene [η⁵-1,2,4-Me ₃C)₃C₅H₂]₂UCl ₂ (1), Cp′₂UCl₂, in the presence of 2,2′-bipyridyl and sodium naphthalene gives the dark green metallocene complex Cp′2U(bipy) (6), which reacts with p-tolyl azide or pyridine-N-oxide to give Cp′₂U=N(p-tolyl) (7) or Cp′ ₂U(O)(py) (8), respectively. The Lewis acid BPh₃ precipitates Ph₃B(py) and gives the base-free oxo Cp′ ₂UO (10), which crystallizes from pentane. The oxometallocene 10 behaves as a nucleophile with Me₃SiX reagents, but it does not exhibit cycloaddition behavior with acetylenes, suggesting that the polar resonance structure Cp′₂U⁺-O^- dominates the double-bond resonance structure Cp′₂U=O.

Full text of DOI:10.1021/om050406q

Organometallics 2005, 24, 4251-4264
4251
Preparation and Reactions of Base-Free
Bis(1,2,4-tri-tert-butylcyclopentadienyl)uranium Oxide,
Cp′2UO
Guofu Zi, Li Jia, Evan L. Werkema, Marc D. Walter, Jochen P. Gottfriedsen, and
Richard A. Andersen*
Department of Chemistry and Chemical Sciences Division of Lawrence Berkeley National
Laboratory, University of California, Berkeley, California 94720
Received May 22, 2005
Reduction of the uranium metallocene [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1), Cp′2UCl2, in the
presence of 2,2′-bipyridyl and sodium naphthalene gives the dark green metallocene complex
Cp′2U(bipy) (6), which reacts with p-tolyl azide or pyridine-N-oxide to give Cp′2UdN(p-tolyl)
(7) or Cp′2U(O)(py) (8), respectively. The Lewis acid BPh3 precipitates Ph3B(py) and gives
the base-free oxo Cp′2UO (10), which crystallizes from pentane. The oxometallocene 10
behaves as a nucleophile with Me3SiX reagents, but it does not exhibit cycloaddition behavior
with acetylenes, suggesting that the polar resonance structure Cp′2U+-O- dominates the
double-bond resonance structure Cp′2UdO.
Introduction
the U-O group in a well-defined molecular compound
will provide molecular models for this reaction as well
as information about the nature of the multiple U-O
bond. A portion of this work has been previously
communicated.11
The U-O functional group is ubiquitous in uranium
chemistry, as shown by the prevalence of binary oxides
in the solid state and the uranyl ion UO22+ in solution,
which illustrates the thermodynamic stability of the
U-O bond.1 Although the rate of ligand substitution on
the uranyl ion is rapid in solution,2,3 the rate of oxygen
atom exchange in aqueous acid is very slow,4 but it is
rapid in basic solution.5 The gas phase ions UOxn+ have
been generated in a mass spectrometer, and their
reactions with hydrocarbons have been studied.6-9 In
addition to providing reactivity patterns, these gas
phase studies yield useful thermodynamic bond disrup-
tion enthalpies for the U-O bonds, which lie in the
Results and Discussion
Strategy. Our strategy is to use substituted cyclo-
pentadienyl ligands that are more heavily substituted
than the 1,3-(Me3E)2C5H3 (E ) C, Si) ligands, since
these less substituted cyclopentadienyl ligands yield
oxo-dimers of the type (η5-1,3-R2C5H3)4U2(µ-O)2 (R )
SiMe3, CMe3), which have been prepared by two syn-
thetic routes: the reaction of the corresponding dimethyl
derivatives with water or the thermal oxidative elimi-
nation of dihydrogen from the corresponding dimeric
hydroxides, eqs 1 and 2, respectively.12-14 The oxide
dimers give molecular ions in their mass spectra and
they do not undergo intermolecular exchange in solution
up to 130 °C, implying that dissociation to monomers
does not occur. As a consequence, the reaction chemistry
of the U-O functional group is nonexistent, although
the cyclopentadienyl rings can be removed by proton
sources, such as excess water. Clearly, preparation of a
monomeric oxometallocene derivative of uranium is
desirable, so the intrinsic reaction chemistry can be
explored.
range 120-190 kcal mol-1 6-9
.
This paper describes the synthesis of base-free [η5-
1,2,4-(Me3C)3C5H2]2UO (10), Cp′2UO, and some of its
reactions with silyl- and alkylhalides. These reactions
provide a molecular model for the heterogeneous reac-
tion of solid U3O8 and chlorocarbons that results in
complete destruction of the latter to COx and HCl.10 This
unusual and potentially useful reaction probably occurs
at the surface U-O functional group, which implies that
* To whom correspondence should be addressed. E-mail:
raandersen@lbl.gov.
(1) Gmelin Handbook of Inorganic Chemistry, U Suppl., Vol. A6;
Springer: Berlin, 1992.
(2) Farkas, I.; Ba´nyai, I.; Szabo´, Z.; Wahlgren, U.; Grenthe, I. Inorg.
Chem. 2000, 39, 799.
2(1,3-R2C5H3)2UMe2 + 2H2O f
(1,3-R2C5H3)4U2(µ-O)2 + 4CH4 (1)
(3) Vallet, V.; Szabo´, Z.; Grenthe, I. J. Chem. Soc., Dalton Trans.
2004, 3799.
(4) Gordon, G.; Taube, H. J. Inorg. Nucl. Chem. 1962, 19, 189.
(5) Clark, D. L.; Conradson, S. D.; Donohoe, R. J.; Keogh, D. W.;
Morris, D. E.; Palmer, P. D.; Rogers, R. D.; Tait, C. D. Inorg. Chem.
1999, 38, 1456.
(1,3-R2C5H3)4U2(µ-OH)2 f
(1,3-R2C5H3)4U2(µ-O)2 + H2 (2)
(6) Cornehl, H. H.; Heinemann, C.; Marc¸alo, J.; Pires de Matos, A.;
Schwarz, H. Angew. Chem., Int. Ed. Engl. 1996, 35, 891.
(7) Cornehl, H. H.; Heinemann, C.; Wesendrup, R.; Diefenbach, M.;
Schwarz, H. Chem. Eur. J. 1997, 3, 1083.
(8) Marc¸alo, J.; Leal, J. P.; Pires de Matos, A.; Marshall, A. G.
Organometallics 1997, 16, 4581.
(9) Gibson, J. K. Organometallics 1997, 16, 4214.
(10) Hutchings, G. J.; Heneghan, C. S.; Hudson, I. D.; Taylor, S. H.
Nature 1996, 384, 341.
Increasing the number of Me3C groups on the cyclo-
pentadienyl framework should increase the steric hin-
drance between the cyclopentadienyl groups in a hypo-
(11) Andersen, R. A.; Jia, L.; Blosch, L. L. Book of Abstracts; 215th
ACS National Meeting, Dallas, March 1998; INOR-061.
10.1021/om050406q CCC: $30.25 © 2005 American Chemical Society
Publication on Web 07/12/2005

4252 Organometallics, Vol. 24, No. 17, 2005
Zi et al.
Scheme 1
thetical oxo-dimer and perhaps yield monomers. This
is a useful strategy for preparation of the monomeric
cerium hydride [η5-1,2,4-(Me3C)3C5H2]2CeH, abbreviated
as Cp′2CeH,15 where Cp′ is used as the symbol for 1,2,4-
(Me3C)3C5H2 in this paper, while the 1,3-(Me3C)2C5H3
ligand yields the dimeric hydride [η5-1,3-(Me3C)2C5H3]4-
Ce2(µ-H)2.16 Accordingly, synthesis of Cp′2UCl2 (1), its
conversion to the dimethyl derivative Cp′2UMe2 (3), and
reaction of the latter with water is a synthetic objective.
Although the dimethyl derivative Cp′2UMe2 (3) can be
made, its reactions with water under various conditions
are not clean. The reaction mixtures always contain
large amounts of the free diene, (Me3C)3C5H3, and
therefore water is not a useful reagent for synthesis of
this oxometallocene derivative of uranium.
A new and successful strategy is derived from our
synthesis of (η5-C5Me5)2Ti(O)(py), which results from
exposure of (η5-C5Me5)2Ti(C2H4) to N2O in pyridine.17
Unfortunately, an analogous uranium complex, such as
Cp′2U(C2H4), is unavailable, but the isolable bipyridyl
derivative Cp′2U(bipy) (6), described below, is a useful
starting material. The literature contains two examples
of generating the (η5-C5Me5)2U fragment (and (η5-C5-
Me5)2UCl2), by valence disproportionation of (η5-C5Me5)2-
UCl, which is trapped by acetylenes or organic azides.18,19
In addition, the isolable benzene or toluene complexes
[(η5-C5Me5)2U]2(PhH) and {[(Me3C)(3,5-Me2C6H3)]N2U}2-
(PhMe) function similarly.20,21
Scheme 2
Cp′2UX2. The preparation of [η5-1,2,4-(Me3C)3C5H2]2-
UCl2 (1), Cp′2UCl2, has been reported,22 and a large-
scale preparation (20-30 g) is given in the Experimental
Section. The synthetic routes to the metallocenes de-
scribed in this paper are shown in Schemes 1 and 2,
and some of their physical properties are listed in Table
1. The halides and pseudohalide Cp′2UX2 (X ) F (4), Cl
(1), Br (2), N3 (17)) are all red or orange-red in color,
soluble in and readily crystallized from pentane, and
give monomeric molecular ions in their EI mass spectra.
The dibromide complex 2 is obtained from anion ex-
change between Me3SiBr and Cp′2UCl2 (1), but the
diiodide complex cannot be obtained pure by anion
exchange between 1 and Me3SiI, as a mixture of all
three possible metallocenes is obtained. The dimethyl
complex Cp′2UMe2 (3) is obtained from the reaction of
Cp′2UCl2 (1) with MeLi in diethyl ether in good yield.
Monitoring the reaction by 1H NMR spectroscopy in
Et2O-d10 shows that some Cp′Li is formed, the amount
(12) Lukens, W. W.; Beshouri, S. M.; Blosch, L. L.; Andersen, R. A.
J. Am. Chem. Soc. 1996, 118, 901.
(13) Lukens, W. W.; Allen, P. G.; Bucher, J. J.; Edelstein, N. M.;
Hudson, E. A.; Shuh, D. K.; Reich, T.; Andersen, R. A. Organometallics
1999, 18, 1253.
increasing with time, showing that the Cp′ ligands are
not substitutionally inert. Cp′2UMe2 (3) reacts with
ammonia to yield the yellow diamide Cp′2U(NH2)2 (5).
Exposure of 3 to BF3(OEt2) yields the difluoride Cp′2-
UF2 (4), a synthetic route also used to prepare (η5-1,3-
R2C5H3)2UF2.23
The solid-state crystal structures of 1, 3, 4, 5, and 17
have been determined. Crystal data for all of the
structures are shown in Table 2, and selected geo-
metrical parameters are shown in Table 3. ORTEP
diagrams for 4 and 17 are shown in Figures 1 and 2,
(14) Zalkin, A.; Beshouri, S. M. Acta Crystallogr. 1988, C44, 1826.
(15) Maron, L.; Werkerma, E. L.; Perrin, L.; Eisenstein, O.; Ander-
sen, R. A. J. Am. Chem. Soc. 2005, 127, 279.
(16) Gun’ko, Y. K.; Bulychev, B. M.; Soloveichik, G. L.; Belsky, V.
K. J. Organomet. Chem. 1992, 424, 289.
(17) Smith, M. R.; Matsunaga, P. T.; Andersen, R. A. J. Am. Chem.
Soc. 1993, 115, 7049.
(18) Fagan, P. J.; Manriquez, J. M.; Marks, T. J.; Day, C. S.; Vollmer,
S. H.; Day, V. W. Organometallics 1982, 1, 170.
(19) Warner, B. P.; Scott, B. L.; Burns, C. J. Angew. Chem., Int. Ed.
1998, 37, 959.
(20) Evans, W. J.; Kozimor, S. A.; Ziller, J. W.; Kaltsoyannis, N. J.
Am. Chem. Soc. 2004, 126, 14533.
(21) Diaconescu, P. L.; Arnold, P. L.; Baker, T. A.; Mindiola, D. J.;
Cummins, C. C. J. Am. Chem. Soc. 2000, 122, 6108.
(22) Duval, P. B.; Burns, C. J.; Clark, D. L.; Morris, D. E.; Scott, B.
L.; Thompson, J. D.; Werkema, E. L.; Jia, L.; Andersen, R. A. Angew.
Chem., Int. Ed. 2001, 40, 3358.
(23) Lukens, W. W.; Beshouri, S. M.; Blosch, L. L.; Stuart, A. L.;
Andersen, R. A. Organometallics 1999, 18, 1235.

Preparation and Reactions of Base-Free Cp′2UO
Table 1. Physical Properties of Cp′2U(X)(Y), Cp′ ) 1,2,4-(CMe3)3C5H2
1H NMR (δ, 30 °C)a
Organometallics, Vol. 24, No. 17, 2005 4253
compound
mp (°C)
(CH3)3C
(CH3)3C
(CH3)3C
ring CH
other
Cp′2UCl2 (1)
192-194
9.8 (12)
12.2 (570)
3.3 (5)
0.64 (10)
5.4 (4)
1.1 (4)
9.8 (12)
12.2 (570)
3.3 (5)
0.64 (10)
-1.9 (5)
1.1 (4)
-20.2 (7)
-20.5 (40)
-7.5 (8)
-7.9 (3)
-1.9 (5)
-8.8 (3)
30.3 (110)
32.7 (850)
7.6 (25)
Cp′2UBr2 (2)
Cp′2UMe2 (3)
Cp′2UF2 (4)
205-206
143-144
160-162
165-167
271-276
UCH3, -98 (45)
8.6 (12)
Cp′2U(NH2)2 (5)
Cp′2U(bipy) (6)
14.1 (46)
1.4 (4)
UNH2, -34 (27)
bipyridyl
3-CHb 97.2 (12)
4-CHb -7.4 (d, J ) 7.2 Hz)
5-CHb -57.9 (11)
6-CHb -99.4 (16)
N-tolyl
Cp′2U[N(4-MeC6H4)] (7)
Cp′2U(O)(py) (8)
234-239
199-206
-6.1 (11)
-6.1 (11)
-22.5 (9)
22.2 (18)
o-CHb 29.4 (d, J ) 7.2 Hz)
m-CHb 24.7 (d, J ) 7.2 Hz)
p-CH3 23.7 (5)
23.4 (19)
26.3 (5)
-9.0 (300)
0.61 (37)
-9.0 (300)
-18.1 (34)
c
c
pyridinec
Cp′2U(O)(4-Me2NC6H4N) (9) 202-209
pyridined
N(CH3)2 -6.8 (17)
Cp′2UO (10)
178-180 (dec)
27.0 (9)
-12.2 (25)
-5.2 (48)
-5.8 (94)
-7.4 (261)
-6.5 (200)
-35.1 (7)
98.7 (23)
-90.5 (22)
Cp′2U(OSiMe3)(Cl) (11)
Cp′2U(OSiMe3)(Br) (12)
Cp′2U(OSiMe3)(I) (13)
Cp′2U(OSiMe3)(CN) (14)
248-250
271-273
288-290
267-268
9.1 (66)
-12.8 (50)
-13.1 (96)
-11.9 (347)
-14.2 (220)
14.8 (165) SiCH3, 24.3 (31)
-8.0 (232)
10.9 (136)
12.4 (408)
7.8 (280)
15.8 (190) SiCH3, 27.3 (30)
-15.9 (273)
8.0 (339) SiCH3, 31.2 (27)
-17.2 (683)
13.0 (346) SiCH3, 27.2 (91)
5.2 (404)
Cp′2U(OSiMe3)(OTf) (15)
Cp′2U(N3)2 (17)
210-212
193-194 (dec)
2.0 (3028)
5.9 (63)
2.0 (3028) -12.8 (627)
5.9 (63) -19.3 (9)
c
SiCH3, 31.5 (34)
28.8 (831)
a The chemical shifts are expressed in δ units with δ > 0 to downfield in C6D6 or C7D8 at 30 °C. The values in parentheses are the full
widths at half-maximum (Hz). b The specific assignments are uncertain, although the chemical shift values are not. c These resonances
are not observed at room temperature. d The ortho and meta resonances are not observed at room temperature.
and ORTEP diagrams for 1, 3, and 5 are in the
Supporting Information since the stereochemistry of the
latter three metallocenes is essentially identical to those
shown in Figures 1 and 2. The orientation of the
cyclopentadienyl rings in all five metallocenes is nearly
eclipsed, with the Me3C groups on each ring at the back
of the wedge located as far from each other as possible.
This orientation sets the disposition of the other four
Me3C groups such that two of them pointing toward the
open wedge are nearly eclipsed. The two X groups are
oriented on either side of the eclipsed Me3C groups such
that the molecule has idealized C2 symmetry.
The geometrical parameters for the five structures are
similar to each other, Table 3. The averaged U-C(Cp′)
distances range from 2.75 to 2.85 Å, the Cp′(cent)-U-
Cp′(cent) angles from 143° to 147°, and the X-U-X
angles from 97° to 104° in Cp′2U(N3)2 and Cp′2U(NH2)2,
respectively. The geometrical parameters for the other
three metallocenes lie within these extreme values. The
difference between the U-X distances in these metal-
locenes parallel the change in radius of the individual
X groups.24
so that at low temperature the Me3C resonances appear
as three equal intensity resonances, and the Cp′ ring
CH resonances appear as a pair of resonances of equal
intensity. A plot of δ vs T-1 for only the Me3C resonances
is shown for Cp′2UF2 (4) in Figure 3, which shows the
temperature dependence of the chemical shifts from
which a ring rotation barrier of approximately 12 kcal
mol-1 is calculated at the coalescence temperature of
233 K. The barriers for some of the other metallocenes
reported here are given in Table 4. The fluxional process
that gives rise to site exchange in the Cp′2UX2 metal-
locenes is nearly identical for the series 1, 4, and 17,
suggesting that the physical process that gives rise to
the barrier involves ring rotation of the Cp′ rings around
their pseudo-C5 axis. As the rings rotate about this axis,
they pass through several conformations, each of which
has a different free energy and symmetry, which are
related by different energy barriers.25,26 The largest
barrier presumably involves a conformation in which
the Me3C groups at the back of the wedge pass through
an eclipsed conformation. Since the Cp′(cent)-U-Cp′-
(cent) angles are essentially the same for 1, 4, and 17
(Table 3), it follows that the solution barriers should be
nearly identical. The barriers in [η5-1,2,4-(Me3C)3C5H2]2-
UX2 are about 3-4 kcal mol-1 larger than in [η5-1,3-
(Me3C)2C5H3]2UX2 for a given X group.23 The larger
rotational barrier and the more open Cp′(cent)-U-Cp′-
(cent) angle by about 20° are consistent with the notion
that the barrier is largely due to the steric hindrance
The 1H NMR spectra at room temperature of the Cp′2-
UX2 metallocenes show the Me3C groups in a 2:1
intensity ratio and, where located, a single Cp′ ring CH
resonance, Table 1. This pattern is consistent with
metallocenes that have idealized C2v symmetry in
solution. This implies that the Cp′ rings are fluxional,
since the solid-state structures have idealized C2 sym-
metry. Lowering the temperature of solutions in C7D8
results in decoalesence of the Me3C resonance of area 2
(25) Abel, E. W.; Long, N. J.; Orrell, K. G.; Osborne, A. G.; Sˇik, V.
J. Organomet. Chem. 1991, 403, 195.
(26) Okuda, J.; Herdtweck, E. Chem. Ber. 1988, 121, 1899.
(24) Pauling, L. The Nature of the Chemical Bond; Connell Univer-
sity Press: Ithaca, NY, 1960.

4254 Organometallics, Vol. 24, No. 17, 2005
Zi et al.
Table 2. Selected Crystal Data and Data Collection Parameters for 1, 3, 4, 5, 7, 9, 14, and 17
1
3
4
5
formula
fw
C
34H58Cl2U
C36H64
734.90
P21/n
10.337(1)
25.591(3)
13.151(2)
90
90.017(2)
90
3479.1(7)
4
U
C34H58F2U
C34H62N2U
736.91
P21/n
10.269(1)
25.460(1)
13.202(1)
90
90.100(1)
90
3451.7(2)
4
775.77
742.83
space group
a (Å)
Pca21
P212121
16.154(1)
10.219(1)
b (Å)
10.340(1)
17.012(2)
c (Å)
20.513(1)
19.282(2)
R (deg)
90
90
â (deg)
90
90
γ (deg)
90
90
V (Å3)
3426.4(3)
3351.9(6)
Z
4
4
Dcalc (g/cm3)
µ(Mo KR)calc (cm-1
size (mm)
temp (K)
diffractometer
scan type
2θ range (deg)
1.504
1.403
4.69
1.472
1.418
47.26
)
49.14
4.87
0.05 × 0.14 × 0.25
0.23 × 0.20 × 0.15
0.27 × 0.17 × 0.12
0.34 × 0.35 × 0.15
131(1)
120(2)
133(2)
161(1)
Bruker SMART CCD
SMART CCD
ω (0.3 deg per frame)
4.44 to 47.14
15 595
SMART CCD
ω (0.3 deg per frame)
4.86 to 49.22
14 989
Siemens SMART
ω (0.3 deg per frame)
4.00 to 46.50
16 178
ω (0.3 deg per frame)
3.00 to 45.00
14 508
no. of reflns, collected
no. of unique reflns
no of obsd reflns
3288 (Rint ) 0.075)
3765
333
5725 (Rint ) 0.0743)
4353
355
5534 (Rint ) 0.0466)
5089
353
6244 (Rint ) 0.030)
4704
334
no of variables
abs corr (Tmax, Tmin
)
1.00, 0.60
0.037
0.54, 0.41
0.036
0.56, 0.35
0.033
0.95, 0.63
0.032
R
Rw
Rall
gof
0.043
0.069
0.075
0.044
0.058
0.057
0.036
0.048
1.21
0.91
1.03
1.60
max. ∆/σ in final cycle
0.00
0.001
0.013
0.00
7
9
14
17
formula
fw
space group
a (Å)
b (Å)
c (Å)
C
41H65NU
C41H68N2OU
843.03
C38H67NOSiU
C34H58N6U
810.00
820.05
788.89
P21/n
P1h
P212121
P21/c
16.608(1)
12.174(1)
19.371(1)
90
10.773(1)
12.037(2)
16.180(2)
95.815(1)
102.558(1)
101.994(1)
1979.56(4)
2
12.786(2)
16.481(2)
17.319(3)
11.292(2)
18.007(3)
19.268(3)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
90
90
108.357(1)
90
3717.23(8)
4
1.447
43.95
90
90.216(2)
90
90
3987.3(11)
3586.2(8)
4
4
Dcalc (g/cm3)
1.414
41.32
1.366
1.461
µ(Mo KR)calc (cm-1
size (mm)
)
4.13
4.56
0.20 × 0.16 × 0.13
0.10 × 0.19 × 0.25
0.28 × 0.27 × 0.03
0.18 × 0.11 × 0.08
temp (K)
164(1)
140(2)
128(2)
110(2)
diffractometer
scan type
Siemens SMART
ω (0.3 deg per frame)
4.00 to 46.50
17110
6569 (Rint ) 0.049)
4164
388
Siemens SMART
ω (0.3 deg per frame)
4.00 to 46.50
11012
Bruker SMART CCD
ω (0.3 deg per frame)
4.56 to 49.0
17738
6535 (Rint ) 0.0453)
6007
400
Bruker SMART CCD
ω (0.3 deg per frame)
4.86 to 48.32
15572
5873 (Rint ) 0.0641)
4292
388
2θ range (deg)
no. of reflns, collected
no. of unique reflns
no of obsd reflns
6763 (Rint ) 0.025)
5761
no of variables
406
abs corr (Tmax, Tmin
)
0.5, 0.40
0.028
0.9, 0.7
0.89, 0.39
0.035
0.71, 0.49
0.041
R
0.027
Rw
Rall
gof
0.034
0.031
0.083
0.088
0.044
0.035
0.042
0.069
1.10
1.04
1.035
1.010
max. ∆/σ in final cycle
0.00
0.013
0.001
0.001
Table 3. Selected Distances (Å) and Angles (deg)
1
3
4
5
7
9
14
2.79(2)
17
C(Cp′)‚‚‚U (av)
C(Cp′)‚‚‚U (range)
2.78(5)
2.72(1)
2.84(1)
2.50
145
2.570(2)
2.80(7)
2.727(8)
2.894(8)
2.53
147
2.37(3)
2.76(3)
2.716(6)
2.806(6)
2.48
144
2.081(5)
2.85(6)
2.756(6)
2.926(7)
2.55
146
2.193(5)
2.80(5)
2.720(6)
2.912(6)
2.53
143
1.988(5)
2.87(3)
2.75(2)
2.714(7)
2.802(6)
2.48
2.841(4)
2.927(4)
2.61
2.695(6)
2.980(7)
2.51
Cp′(cent)‚‚‚U (av)
Cp′(cent)-U-Cp′(cent)
U‚‚‚X (av)
142
140
143
U‚‚‚O 1.860(3)
U‚‚‚N 2.535(4)
88.7(1)
U‚‚‚O 2.104(4)
U‚‚‚C 2.415(6)
86.6(2)
2.219(6)
2.244(6)
97.1(2)
X-U-X (av) or X-U-Y (av)
98.1(8)
97.6(3)
99.8(2)
104.4(2)
between the Me3C groups at the back of the metallocene
wedge and not directly due to the size of the X groups.23
Cp′2U(bipy). The bipyridyl complex Cp′2U(bipy) (6)
is prepared by the slow addition of 2 equiv of sodium
naphthalene to a 1:1 mixture of Cp′2UCl2 (1) and 2,2′-
bipyridyl in tetrahydrofuran, Scheme 1. The complex
is soluble in toluene, from which it may be crystallized
as large dark green crystals. The compound melts at

Preparation and Reactions of Base-Free Cp′2UO
Organometallics, Vol. 24, No. 17, 2005 4255
Figure 3. Plots of δ versus 1/T for [η5-1,2,4-(Me3C)3C5H2]2-
UF2 (4) in C7D8.
the complex is not a U(II) metallocene.29 For the purpose
of the present paper, however, the bipyridyl complex 6
is a useful starting material for the molecules described
next.
Cp′2UdN(p-tolyl). The bipyridyl complex Cp′2U(bipy)
(6) reacts with p-tolyl azide to give Cp′2UdN(p-tolyl) (7)
and N2, Scheme 2. The imide 7 is soluble in pentane,
from which it may be crystallized, gives a monomeric
molecular ion in its mass spectrum, and is a monomer
in the solid state as shown by the ORTEP diagram in
Figure 4. The orientation of the Cp′ rings is such that
the Me3C groups at the back of the wedge avoid each
other as much as possible, which results in an eclipsing
interaction between a Me3C group pointing toward the
open wedge and the N-p-tolyl group. The eclipsing
interaction results in a long U-C(3) distance, the carbon
atom of the cyclopentadienyl ring to which the eclipsed
Me3C group is attached, of 2.912(6) Å. This distance is
longer than the average U-C(Cp′) distance of 2.80(5)
Å. The eclipsing interaction results in bending of the
planar N-p-tolyl group toward the other Cp′ ring, so the
U-N-C(35) angle is 172.3(5)°. Related distortions are
apparent, as the [Cp′(C(18)-C(22))cent]-U-N and [Cp′-
(C(1)-C(5))cent]-U-N angles are 104° and 112°, re-
spectively. The p-tolylimido ligand is planar and ori-
ented so that the plane defined by the tolyl group is
nearly a perpendicular bisector (83°) of the plane that
contains the Cp′(cent)-U-Cp′(cent). The U-N distance
of 1.988(5) Å is in the range found in (η5-C5Me5)2U[N-
2,4,6-(t-Bu)3C6H2] (1.95(1) Å),30 (η5-C5Me5)2U(O)(N-2,6-
i-Pr2C6H3) (1.988(4) Å),31 (η5-C5Me5)2U(NPh)2 (1.952(7)
Å),32 (η5-C5Me5)2U[N-2,4,6-(t-Bu)3C6H2][N-NdCPh2]
(1.987(5) Å),33 and (η5-C5Me5)2Th[N-2,6-Me2C6H3][thf]
(2.045(8) Å).34
Figure 1. ORTEP drawing of [η5-1,2,4-(Me3C)3C5H2]2UF2
(4) with 35% thermal ellipsoids.
Cp′2UO(py) and Cp′2UO(dmap). Treatment of Cp′2-
UCl2 (1) with 2 equiv of potassium graphite in tetrahy-
drofuran, followed by addition of 2 equiv of pyridine-
N-oxide, gives the cluster Cp′4U6O13(bipy)2.22 In contrast,
reaction of Cp′2U(bipy) (6) with 1 equiv of pyridine-N-
oxide in diethyl ether gives a red solution from which
Figure 2. ORTEP drawing of [η5-1,2,4-(Me3C)3C5H2]2U-
(N3)2 (17) with 35% thermal ellipsoids.
271-276 °C and gives a molecular ion in its mass
1
spectrum, and the H NMR spectrum in C6D6 at 30 °C
(29) The electronic structure of the bipy complex
6 is under
shows resonances for all ring and bipyridyl resonances,
Table 1. The infrared spectrum shows strong absorp-
tions at 935, 955, and 1495 cm-1, features associated
with the bipyridyl radical anion,27,28 which implies that
investigation. The results of these physical studies will be published
at a later date.
(30) Arney, P. S. J.; Burns, C. J. J. Am. Chem. Soc. 1995, 117, 9448.
(31) Arney, P. S. J.; Burns, C. J. J. Am. Chem. Soc. 1993, 115, 9840.
(32) Arney, D. J. S.; Burns, C. J.; Smith, D. C. J. Am. Chem. Soc.
1992, 114, 10068.
(33) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J. Chem.
Commun. 2002, 30.
(34) Haskel, A.; Straub, T.; Eisen, M. S. Organometallics 1996, 15,
3773.
(27) Saito, Y.; Takemoto, J.; Hutchinson, B.; Nakamoto, K. Inorg.
Chem. 1972, 11, 2003.
(28) Schultz, M.; Boncella, J. M.; Berg, D. J.; Tilley, T. D.; Andersen,
R. A. Organometallics 2002, 21, 460.

4256 Organometallics, Vol. 24, No. 17, 2005
Table 4. Barriers to Me3C Group Site Exchange in Cp′2U(X)(Y)a
Zi et al.
Cp′2UCl2 (1)
Cp′2UF2 (4)
Cp′2U(O)(py) (8)
Cp′2U(O)(dmap) (9)
Cp′2U(N3)2 (17)
Tc
-40
12
-40
12
30
12
60
15
-33
12
∆Gq
a The free energy of activation was determined by the temperature dependence in C7D8 of only the Me3C groups and is expressed in
units of kcal mol-1, and Tc is in units of °C. When X ) Y ) Br (2) or Me (3), the resonance disappears at about -10 °C but does not
reappear as two sharp resonances by -70 °C.
Figure 4. ORTEP drawing of [η5-1,2,4-(Me3C)3C5H2]2Ud
N(p-tolyl) (7) with 35% thermal ellipsoids.
red crystals of Cp′2U(O)(py) (8) are isolated in 65% yield.
The crystal structure of a related metallocene oxo
adduct, (η5-C5Me5)2U(O)[C(NMeCMe)2], where C(NMeC-
Me)2 is an N,N′-heterocyclic carbene ligand, has been
reported recently.35 This, along with (η5-C5H5)2U(O)-
(thf),36 are the only other terminal oxometallocene
uranium(IV) derivatives of the general class (η5-C5R5)2U-
(O)(L), where L is a neutral ligand, that have been
reported. Ligand exchange in Cp′2U(O)(py) (8) occurs
on the chemical time scale since addition of 4-Me2-
NC5H4N (dmap) displaces pyridine in diethyl ether
solution and the complex Cp′2U(O)(dmap) (9) may be
crystallized as green-yellow blocks from that solution.
An ORTEP of 9 is shown in Figure 5, crystal data are
in Table 2, and selected geometrical parameters are
listed in Table 3. The orientation of the Cp′ rings is
nearly staggered, and the oxygen atom and the dmap
ligand lie in the open wedge of the bent metallocene.
The dmap ligand is nearly planar, the dihedral angle
defined by intersection of the planar pyridine ring and
the NMe2 group is 15°, and the planar pyridine ring is
twisted out of the plane defined by the UNO atoms.
Thus, the molecule has no symmetry in the solid state.
It is interesting to note that there is a short intermo-
lecular contact between O(1) and C(40), a methyl group
of the NMe2 group on the dmap ligand, of 3.321(6) Å.
The U(1)-N(1) distance of 2.535(4) Å is slightly shorter
than the average U-N distance of 2.65 Å in Cp2U-
Figure 5. ORTEP drawing of [η5-1,2,4-(Me3C)3C5H2]2U-
(O)(dmap) (9) with 35% thermal ellipsoids.
shorter than that found in (η5-C5Me5)2U(O)[C(NMeCMe)2]
of 1.917(6) Å,35 but slightly longer than that found in
(η5-C5Me5)2U(O)(N-2,6-i-Pr2C6H3) of 1.844(4) Å,30 and
identical to that found in (η5-C5Me5)2U(O)(O-2,6-i-
Pr2C6H3) of 1.859(6) Å.31 The U-O distance is rather
longer than that found in uranyl salts, which lies in the
range 1.70-1.76 Å.39 The infrared spectra of 8 and 9
show narrow, intense features at 760 and 765 cm-1
,
respectively, that are assigned to the U-O stretching
frequencies. Although this assignment is not supported
by labeling studies, the values are comparable to those
found in (η5-C5Me5)2U(O)(N-2,6-i-Pr2C6H3) of 751 cm-1
and (η5-C5Me5)2U(O)(O-2,6-i-Pr2C6H3) of 753 cm-1 31
,
which are supported by 18O labeling studies.30 In addi-
tion, the asymmetric U-O stretching frequency in
matrix-isolated UO2 is at 776 cm-1 40
.
1
The H NMR spectrum of Cp′2UO(py) (8) in C7D8 at
30 °C shows the Me3C resonances as a 1:2 pattern, but
the resonance of area 2 is very broad. The pyridine ring
and Cp′ ring CH resonances are not observed, Table 1.
Addition of free pyridine does not alter the appearance
of the spectrum except that resonances due to free
pyridine are observed. Heating the sample with added
pyridine sharpens the two Me3C resonances, and at
temperatures greater than 60 °C three resonances
appear at approximately 0, 5, and 10 ppm in an area
ratio of 2:1:2 due to the pyridine ring CH’s. A resonance
due to the Cp′ ring CH cannot be assigned with
(triflate)2(py)2 and (η5-MeC5H4)3U(4-Me2NC5H4N).38
37
The U(1)-O(1) distance of 1.860(3) Å is significantly
(35) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. Polyhedron 2004,
23, 2689.
(36) Villiers, C.; Adam, R.; Ephritikhine, M. Chem. Commun. 1992,
1555.
(37) Berthet, J. C.; Nierlich, M.; Ephritikhine, M. Eur. J. Inorg.
Chem. 2002, 850.
(39) Wells, A. F. Structural Inorganic Chemistry; Clarendon Press:
Oxford, 1984; p 1265.
(40) Jones, L. H. Spectrochim. Acta 1959, 11, 409.
(38) Zalkin, A.; Brennan, J. G. Acta Crystallogr. 1987, C43, 1919.

Preparation and Reactions of Base-Free Cp′2UO
Organometallics, Vol. 24, No. 17, 2005 4257
Figure 7. Plots of δ versus 1/T for [η5-1,2,4-(Me3C)3C5H2]2U-
(O) (10) in C7D8.
Figure 6. Plots of δ versus 1/T for [η5-1,2,4-(Me3C)3C5H2]2U-
(O)(dmap) (9) in C7D8.
resonances cannot be identified with certainty. The
∆Gq(Tc ) -49 °C) is 9.7 kcal mol-1 for the dmap
rotational barrier.
certainty. This change in line shape suggests that
exchange between free and bound pyridine is slow at
room temperature, but the individual pyridine ring
resonances are not resolved, and at higher temperature,
intermolecular exchange is rapid so that average chemi-
cal shifts are observed. As the temperature is decreased
below 30 °C, the Me3C groups decoalesce to a 1:1:1
pattern, but neither the pyridine nor Cp′ ring CH
resonances are visible, presumably due to their line
widths. Using the Me3C resonances, the barrier to Me3C
Cp′2UO. Although Cp′2U(O)(py) (8) exchanges with
dmap in solution, poorer donor ligands cannot compete
with these nitrogen heterocycles. To investigate the
intrinsic reactivity patterns of the U-O functional
group, and to compare them with those of base-free
imide 7, a synthetic route to the base-free oxo compound
is needed. This is accomplished by addition of BPh3,
which forms the insoluble BPh3(py) complex and leaves
the base-free oxo Cp′2UO (10) in toluene solution,
Scheme 2. Removal of toluene yields a brown-red solid
that may be crystallized as brown-red microcrystals
from pentane.41 The Lewis acid-base reaction is revers-
ible in solution, since addition of pyridine regenerates
the complex 8 quantitatively. The base-free metallocene
10 gives a monomeric molecular ion in its mass spec-
trum, but the 1H NMR spectrum is difficult to reconcile
with a simple monomeric species in solution.
site exchange is calculated to be 12 kcal mol-1
.
The 1H NMR spectrum of Cp′2UO(dmap) (9) provides
more information about the dynamic processes that
occur in solution. At 30 °C, the three chemically in-
equivalent Me3C resonances of the Cp rings and the
chemically equivalent Me2N resonances of the dmap
1
ligand are observed in the H NMR spectrum in C7D8,
Table 1. The Cp′ ring and pyridine ring CH resonances
are not conclusively identified due to their line widths,
as is the case in the pyridine complex 8. At 30 °C,
addition of free dmap to Cp′2UO(dmap) (9) does not
perturb the resonances due to the Me3C and Me2N
groups. Increasing the temperature of this mixture to
60 °C results in coalescences of the Me2N resonance of
the free and coordinated dmap. Thus at 30 °C, inter-
molecular exchange is slow, but by 60 °C, it is rapid on
the NMR time scale. A plot of the chemical shifts of the
Me3C and Me2N resonances as a function of T-1, in the
absence of added dmap, is shown in Figure 6. It is clear
that at 30 °C the three Me3C resonances are inequiva-
lent, as expected for a molecule of Cs symmetry; that
is, the individual Cp′ rings are related by a time-
averaged plane of symmetry, but a perpendicular plane
of symmetry and a C2 axis are absent. As the temper-
ature is raised, two Me3C resonances coalesce so that
time-averaged C2v symmetry is observed. As this process
occurs near the temperature where intermolecular
ligand exchange occurs, the physical process of ligand
dissociation that generates a metallocene of averaged
C2v symmetry is sufficient to cause the coalescence and
the barrier is about 15 kcal mol-1, Table 4. The Me2N
resonances are chemically equivalent at 30 °C, implying
that the planar pyridine ligand is free to rotate about
the U-N bond in solution. As the temperature is
lowered, the Me2N resonance decoalesces and two
distinct methyl resonances emerge, consistent with
slowing and stopping rotation about the U-N bond. This
assumes that the entire 4-Me2NC5H4N ligand rotates
rather than just the Me2N group since the pyridine ring
The 1H NMR spectrum of the base-free oxo 10 consists
of five resonances in either C7D8 or C7H14 at 99.0, 27.1,
-12.3, -35.1, and -90.8 ppm in area ratio 2:9:9:9:2 at
19 °C. The chemical shifts of the Me3C resonances in
10 are qualitatively similar to those in the dmap
complex 9 and imply that the two Cp′ rings are related
only by a plane of symmetry in a molecule of idealized
Cs symmetry. This requires that the Cp′ rings are not
free to oscillate about their pseudo-C5 axis in order to
generate a time averaged C2 axis, which is improbable
given the barriers shown in Table 4. The variable-
temperature 1H NMR spectra show that the 19 °C
spectrum in either solvent is deceptively simple. A plot
of δ vs T-1 in C7D8 solvent of the Me3C resonances is
shown in Figure 7. As the temperature is increased, the
total intensity of the three equal area Me3C resonances
at 27, -12, and -35 ppm, A set (A1, A2, and A3),
decrease as two new resonances in a 1:2 ratio appear
at -6.5 and -9.7 ppm, B set (B1 and B2). As the
temperature is increased, the A:B ratio decreases, and
at 100 °C the ratio is approximately 3:1. The relative
intensity of the individual components within the A and
B sets does not change with temperature, although their
chemical shifts are temperature dependent. Cooling to
19 °C regenerates the original spectrum without loss
in absolute intensity. The behavior on cooling is rather
(41) We have been unable to obtain single crystals of this material.
Further physical studies including EXAFS are in progress. The EXAFS
studies were essential in defining the molecular structure of other oxo
metallocenes described in ref 13.

4258 Organometallics, Vol. 24, No. 17, 2005
Zi et al.
more complex. As the temperature is decreased from 19
°C to -40 °C, the middle resonance (A2) in the A set of
resonances broadens and disappears into the baseline.
On further cooling to -70 °C, three equal area reso-
nances, C set (C1, C2, and C3), emerge from the
baseline, but their common parentage is not the middle
resonance (A2) of the A set; see Figure 7. In addition,
the deshielded resonance (A1) in the A set broadens and
disappears by -70 °C, while the upfield resonance (A3)
is still visible. During the cooling process the absolute
intensity of the A-set of resonances decreases by about
50%, but the new resonances that appear do not account
for the “lost” intensity. On warming to 19 °C, the
original spectrum is observed with the original absolute
intensity.
1
An interpretation of the high-temperature H NMR
spectrum is that a dimer-monomer equilibrium exists
in solution and the monomer concentration increases
with temperature. The 2:1 pattern of the Me3C reso-
nances suggests the monomer has C2v symmetry, as in
the high-temperature spectra of the pyridine complexes
8 and 9. Unfortunately, aromatic and aliphatic hydro-
carbon solvents are the only ones that are compatible
with the base-free oxometallocene 10, so using solvents
of different dielectric constant is not possible, and this
postulate cannot be tested. The low-temperature be-
havior is more difficult to interpret since the intensity
changes show that not all of the resonances are ob-
served. A postulate is that the dimer is largely present
at room temperature and below, and the dimer has
averaged C2h symmetry as in [η5-1,3-(Me3E)2C5H3]4U2-
(O)2 (E ) C, Si).12-14 Cooling slows Cp′ ring rotation and
some of the Me3C resonances disappear. Unfortunately,
single crystals of the base-free metallocene 10 cannot
be grown, which would be the ultimate test of this
proposition. EXAFS studies have been used to solve a
related structural dilemma, and such a study is con-
templated for Cp′2UO.13
Reactions of 10. The oxo 10 reacts with excess Me3-
SiCl rapidly to give Cp′2U(OSiMe3)(Cl) (11) cleanly at
room temperature in a mixing experiment in C6D6 in
an NMR tube. The reaction does not proceed further
unless heated. Heating at 65 °C slowly yields Cp′2UCl2
(1) and (Me3Si)2O; t1/2 is about 30 h at this temperature.
The Cp′2U(OSiMe3)(Cl) (11) is prepared on a synthetic
scale in two ways: reaction of Cp′2UO(py) (8) and Me3-
SiCl in toluene followed by crystallization from pentane,
or reaction of Cp′2UCl2 (1) with 1 equiv of LiOSiMe3 in
diethyl ether followed by crystallization from pentane.
Synthesis and characterization details for this and the
other metallocenes described in this section are given
in the Experimental Section, and some physical proper-
ties are listed in Table 1. In mixing experiments
monitored by 1H NMR spectroscopy, excess Me3SiX
reacts rapidly and cleanly to yield Cp′2U(OSiMe3)(X) (X
) Br (12), I (13), CN (14), OTf (15)). In the case of X )
Br, some Cp′2UBr2 (2) and (Me3Si)2O are formed, but
the rate is very slow; even at 65 °C, t1/2 is about 70 h.
In the case of X ) I, OTf, or CN, no resonances due to
Cp′2UX2 are detected when the solutions are kept at 65
°C for up to 3 days. In contrast, excess Me3SiN3 reacts
with 10 instantaneously to give Cp′2U(N3)2 (17) and
(Me3Si)2O; no resonances attributable to Cp′2U(OSiMe3)-
(N3) (16) are detected. However, upon addition of 1 equiv
Figure 8. ORTEP drawing of [η5-1,2,4-(Me3C)3C5H2]2U-
(OSiMe3)(CN) (14) with 35% thermal ellipsoids.
1
of Me3SiN3 to Cp′2UO (10) on a synthetic scale, the H
NMR spectrum of the crude products shows resonances
due to Cp′2U(N3)2 (17), unreacted Cp′2UO (10), and
three new resonances attributable to Cp′2U(OSiMe3)-
(N3) (16). The latter resonances disappear on addition
of more Me3SiN3. On a synthetic scale, the method of
choice is addition of excess Me3SiX to Cp′2U(O)(py) in
toluene followed by crystallization from pentane. The
1H NMR spectra of these compounds show the Me3C
resonances as a 1:1:1 pattern (except for the diazide)
consistent with a molecule of Cs symmetry. The infrared
spectrum of 14 shows a CN absorption at 2040 cm-1
,
which may be compared to a value of 2110 cm-1 found
in (η5-C5H5)3U(CN).42 The infrared spectrum of 17 shows
two N3 absorptions at 2100 and 2080 cm-1, close to
that found in [(ArO)3tacn]U(N3) ([(ArO)3tacn]3-
)
[1,4,7-tris(3,5-di-tert-butyl-2-oxybenzyl)-1,4,7-triazacy-
clononane]3-) of 2080 cm-1 43
.
An ORTEP diagram of the solid-state structure of 14
is shown in Figure 8. The orientation of the rings is
rather different from those observed for the molecules
shown in Figures 1 and 2. The rings are nearly stag-
gered, and the Me3C groups at the back of the wedge
are avoiding each other as much as possible. However,
the other four Me3C groups are oriented to the left and
right side of the open wedge, while the OSiMe3 and CN
groups occupy sites in the wedge. The U-O-SiMe3 and
U-C-N angles are not linear; U-O-Si is 160.6(3)° and
U-C-N is 164.5(7)°. A nonlinear U-O-Si angle is
common, while a U-C-N angle is not. Perhaps a reason
for the bending can be traced to the OSiMe3 group
avoiding the methyl groups on C(27), while the CN
group is avoiding those on C(11).
(42) Bagnall, K. W.; Plews, M. J. J. Chem. Soc., Dalton Trans. 1982,
1999.
(43) Castro-Rodriguez, I.; Olsen, K.; Gantzel, P.; Meyer, K. J. Am.
Chem. Soc. 2003, 125, 4565.

Preparation and Reactions of Base-Free Cp′2UO
Organometallics, Vol. 24, No. 17, 2005 4259
Silicon tetrafluoride reacts instantaneously, as does
BF3(OEt2), with Cp′2UO (10) in C6D6 to give resonances
due to Cp′2UF2 (4) in the 1H NMR spectrum. The
conversion is quantitative, but the fate of the nonmetal
fragment is unknown. The difluoride Cp′2UF2 (4) is also
formed from the oxo 10 and Me3SiCF3. The binary
silicon halides SiX4 (X ) Cl, Br, I) give resonances
attributable to Cp′2U(OSiX3)(X) since their 1H NMR
spectra show three equal area resonances for the Me3C
groups, which over time evolve into the spectra of Cp′2-
UX2 (X ) Cl (1), Br (2)). In the case of the iodide, the
end point is a mixture that may contain Cp′2UI2, but
this deduction is uncertain since the diiodide complex
has not been prepared in pure form.
In contrast to the alkylsilyl halides, aryl and alkyl
halides do not react cleanly with Cp′2UO (10). Fluo-
robenzene does not react with 10, and the reactions of
chloro- and bromobenzene are not clean. Chlorobenzene
reacts rapidly in C6D6 as the resonances due to Cp′2UO
(10) disappear and nine new paramagnetic resonances
in approximately equal relative intensity (see Experi-
mental Section for details) along with resonances due
to Cp′H appear in an approximate area ratio of 2:1. The
intensity ratio does not change when the sample is
heated to 65 °C for 1 day, and resonances due to Cp′2-
UCl2 (1) are not observed. Repeating the experiment
with C6D5Cl gives the same results, showing that the
nine resonances are due to nine Me3C groups, which
implies that a mixture of compounds are formed. Bro-
mobenzene behaves similarly, but the chemical shifts
of the nine resonances are different, implying that a
halide or halides are attached to uranium. tert-Butyl
chloride reacts with Cp′2UO (10) in C6D6 to generate a
1H NMR spectrum that contains nine resonances whose
chemical shifts and relative intensities are identical to
those observed in the reaction of PhCl, and resonances
due to Cp′H and isobutene. Repeating the experiment
with (CD3)3CCl yields the same result and no Cp′D is
observed, implying that the source of H(D) is not the
alkyl chloride.
The oxo 10 reacts rapidly with AgF to give Cp′2UF2
(4) as the only paramagnetic compound observed in the
1H NMR spectrum along with the dimer Cp′2. Silver
chloride also reacts rapidly with the oxo 10, as reso-
nances due to Cp′2UO (10) disappear from the 1H NMR
spectrum and nine resonances with chemical shift and
intensity ratios identical to those in the PhCl reaction
appear along with resonances due to Cp′2. Adding more
AgCl results in the disappearance of the nine reso-
nances, while the resonances for Cp′2 increase in
intensity. Silver bromide behaves similarly, and the
chemical shifts and relative intensity of the nine reso-
nances are identical to those formed in reaction of PhBr.
A mixture of Cp′2UO (10) with Cp′2UF2 (4) gives a
1H NMR spectrum that contains only the resonances of
the individual starting compounds. However, mixing
Cp′2UO (10) and Cp′2UCl2 (1) in C6D6 gives resonances
due to Cp′2, Cp′2UCl,44 and nine resonances whose
chemical shifts and relative intensity are identical to
those in the reaction of PhCl or AgCl with Cp′2UO (10).
No change is observed over time or upon heating.
In summary, Me3SiX reacts with Cp′2UO (10) cleanly
to give addition products, which, in some cases, react
further to give the metathesis products. This implies
that the Cp′2UO (10) is an excellent nucleophile. The
other reactions described are more complex, but a
pattern is apparent. It seems reasonable to postulate
that halide atom transfer occurs and the resulting
Cp′2U(O)(X) metallocene decomposes by losing Cp′2 or
Cp′H fragments. Since these reactions are not clean,
they are not studied further.
Addition of pyridine-N-oxide to Cp′2UO (10) in C6D6
results in rapid disappearance of the resonances due to
Cp′2UO (10) and formation of resonances due to Cp′2 in
quantitative yield. It seems reasonable to suggest that
the initial reaction is oxygen atom transfer generating
“Cp′2U(O)2”, which eliminates Cp′2 and forms “UO2”. A
similar reaction occurs when the oxo 10 is mixed with
either Ph3PS or Ph3PSe, where the uranium-containing
products are therefore “U(O)(E)” (E ) S, Se).
As mentioned above, the oxo 10 forms isolable adducts
with pyridine and 4-(dimethylamino)pyridine. These two
adducts, 8 and 9, along with those formed with Ph3PO
and Ph2CO, are the only adducts that are stable in C6D6
solution. When the oxo 10 is exposed to other Lewis
bases, such as ethers (diethyl ether or tetrahydrofuran),
amines (Me(3-x)HxN, x ) 0-3), or azomethines, decom-
position occurs with formation of Cp′H. The decomposi-
tion rates vary from minutes to hours to days, but the
final organic product is always Cp′H. No reaction is
observed between the oxo 10 and dihydrogen, ethylene,
and acetylenes RCtCR (R ) Me, Ph, Me3Si). When the
acetylene is RCtCH, hydrogen atom transfer is ob-
served, and Cp′H is the final product.
Reactions of 7. In contrast to the rich reaction
chemistry of Cp′2UO (10), the reactions of the base-free
imide Cp′2UdN(p-tolyl) (7) are meager. The imide 7 does
not form adducts with ethers or pyridines. It does not
react with Me3SiX reagents except Me3SiN3, which gives
Cp′2U(N3)2 (17) in poor yield (20%). It does react with
SiF4 or BF3(OEt2), giving Cp′2UF2 (4) in quantitative
yield. Thus, the imido metallocene 7 is a poorer nucleo-
phile than the oxo metallocene 10. This result might
be due to steric or electronic effects of the p-tolyl group.
Experiments designed to test this proposition are un-
derway.
Although the imide 7 does not react with Ph3PE (E
) O, S, Se), it reacts rapidly and quantitatively with
pyridine-N-oxide to give Cp′2. The cyclopentadienyl ring
coupling product has been previously observed in the
reaction of (η5-C5Me5)2U(NPh)(py) with pyridine-N-
oxide, which gives a mixture of (η5-C5Me5)2U(NPh)2, (C5-
Me5)2, and “UO2”.30 More surprising, however, is the
reaction with Ph2CO, which yields Cp′2UO (10) and
Ph2CdN(p-tolyl) rapidly and cleanly in C6D6, Scheme
2. This reaction is important since it directly addresses
the question of the bond enthalpy of the uranium oxo
and imido bonds in these metallocenes. Information on
this question is available from the heat of formation of
ketones and azomethines, which suggests that the Cd
O bond is stronger than the CdNR bond by about 30
kcal mol-1 45,46
This difference implies that the UdO
.
bond is stronger than the UdN(p-tolyl) bond by at least
(45) Coates, G. E.; Sutton, L. E. J. Chem. Soc. 1948, 1187.
(46) Sandorfy, C. In The Chemistry of the C-N Double Bond; Patai,
S., Ed.; Interscience: London, 1970; Chapter 1.
(44) Zi, G.; Jia, L.; Gottfriedsen, J. P.; Andersen, R. A. Unpublished.

4260 Organometallics, Vol. 24, No. 17, 2005
Zi et al.
30 kcal mol-1. The ability of benzophenone to act as an
oxygen-atom transfer reagent has been observed previ-
ously.47,48
(C6D6): δ 6.42 (s, 1H, CH), 5.95 (s, 1H, CH), 2.95 (s, 1H, CH),
1.26 (s, 9H, C(CH3)3), 1.18 (s, 9H, C(CH3)3), 1.08 (s, 9H,
C(CH3)3). This sample was heated at 65 °C and monitored
periodically by 1H NMR spectroscopy; after 28 h the conversion
to the thermodynamic isomer was complete.
Conclusions
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1). To a
toluene (300 mL) suspension of [η5-1,2,4-(Me3C)3C5H2]2Mg
(25.0 g, 51 mmol) and UCl4 (19.0 g, 50 mmol) was added freshly
distilled pyridine (50 mL) dried with sodium. After the solution
was heated at reflux for 1 day with stirring, the solvent was
removed. The red residue was extracted with pentane (150 mL
× 3) and filtered. The volume of the filtrate was reduced to
200 mL and cooled to -20 °C. Two crops of dark red crystals
were collected by filtration. Yield: 26.4 g (68%). EI-MS [M+],
m/z (calcd, found): 774(100, 100), 775 (39, 38), 776 (71, 71),
777 (26, 25), 778 (15, 13), 779 (5, 4). Anal. Calcd for C34H58-
Cl2U: C, 52.7; H, 7.55. Found: C, 52.6; H, 7.55.
The bipyridyl complex Cp′2U(bipy) (6) is a useful
starting material for the oxo-metallocene and p-tolylimi-
dometallocene. The base-free oxo Cp′2UO (10) reacts
with Me3SiX reagents to yield addition products Cp′2U-
(OSiMe3)(X) and in some cases substitution products,
Cp′2UX2, as do (η5-C5Me5)2Zr(O)(py)49 and (η5-C5Me5)2-
Ti(S)(py).50 The oxo Cp′2UO (10) does not react with
dipolar molecules such as acetylenes, RCtCR, in con-
trast to (η5-C5Me5)2Ti(O)(py).51 The nucleophilic behav-
ior is consistent with the view that the uranium-oxygen
bond is better represented by the polar valence-bond
resonance structure U+-O-, rather than the double-
bond resonance structure UdO. Although the UdO
bond enthalpy is unknown, the exchange reaction
between Cp′2UdN(p-tolyl) (7) and Ph2CO indicates that
UdO is at least 30 kcal mol-1 stronger than UdN(p-
tolyl). Experiments that address the fundamental ques-
tion about the nature of the multiple bonds in these
uranium compounds are underway.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UBr2 (2). Me3SiBr
(0.22 mL, 1.68 mmol) was added to a pentane (20 mL) solution
of [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1; 0.65 g, 0.84 mmol) with
stirring at room temperature. After the mixture was stirred
for 12 h at room temperature, the volatile components were
removed. The resulting dark red solid was redissolved in
pentane (20 mL), and the above procedure was repeated twice
more. The dark red residue was extracted with pentane (15
mL × 2) and filtered. The volume of the filtrate was reduced
to 5 mL, and cooling to -20 °C yielded red crystals, which were
isolated by filtration. Yield: 0.62 g (85%). EI-MS [M+], m/z
(calcd, found): 862 (50, 48), 863 (19, 20), 864 (100, 100), 865
(38, 32), 866 (54, 52), 867 (19, 18), 868 (3, 3). Anal. Calcd for
C34H58Br2U: C, 47.2; H, 6.76. Found: C, 46.9; H, 6.85.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UMe2 (3). A di-
ethyl ether (11.6 mL) solution of MeLi (0.67 M in diethyl ether;
7.8 mmol) was slowly added to a diethyl ether (100 mL)
solution of [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1; 3.0 g, 3.9 mmol)
with stirring at room temperature. After the solution was
stirred for 1 h at room temperature, the solvent was removed.
The red residue was extracted with pentane (25 mL × 2) and
filtered. The volume of the filtrate was reduced to 10 mL and
cooled to -20 °C, yielding red crystals, which were isolated
by filtration. Yield: 2.4 g (85%). EI-MS [M+ - 15]: m/z 719.
Anal. Calcd for C36H64U: C, 58.8; H, 8.78. Found: C, 59.0; H,
8.98.
Experimental Section
General Procedures. All reactions and product manipula-
tions were carried out under dry nitrogen using standard
Schlenk and glovebox techniques. All organic solvents were
freshly distilled from sodium benzophenone ketyl immediately
prior to use. Me3SiX (X ) Cl, Br, I, CN, OTf, N3) were distilled
under nitrogen before using. 2,2′-Bipyridyl (bipy), pyridine-
N-oxide, Ph3B, 4-dimethyaminopyridine (dmap), and LiOSiMe3
were sublimed before using. [η5-1,2,4-(Me3C)3C5H2]2Mg22 and
52
p-CH3C6H4N3 were prepared according to the literature
methods. All other chemicals were purchased from Aldrich
Chemical Co. and used as received unless otherwise noted.
Infrared spectra were obtained as Nujol mulls. 1H NMR
spectra were recorded on Bruker AVB-400, AVQ-400, and AV-
300 spectrometers. All chemical shifts are reported in δ units
with reference to the residual protons of the deuterated
solvents, which are internal standards, for proton chemical
shifts. Melting points were measured on a Thomas-Hoover
melting point apparatus in sealed capillaries and are uncor-
rected. Electron impact mass spectra were recorded by the
mass spectroscopy laboratory, and elemental analyses were
performed by the analytical laboratories, both at the Univer-
sity of California, Berkeley.
Isomerization of (Me3C)3C5H3. To an NMR tube charged
with [η5-1,2,4-(Me3C)3C5H2]2Mg (30 mg) and C6D6 (0.5 mL) was
added one drop of degassed H2O. Two sets of resonances due
to the kinetic and thermodynamic isomers were observed by
1H NMR spectroscopy in an approximate area ratio of 2:1 at
20 °C. Kinetic isomer, 1H NMR (C6D6): δ 6.45 (s, 1H, CH),
3.09 (s, 2H, CH2), 1.37 (s, 9H, C(CH3)3), 1.30 (s, 9H, C(CH3)3),
1.16 (s, 9H, C(CH3)3). Thermodynamic isomer, 1H NMR
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UF2 (4). BF3‚OEt2
(1.0 mL, 7.9 mmol) was added to a pentane (50 mL) solution
of [η5-1,2,4-(Me3C)3C5H2]2UMe2 (3; 2.0 g, 2.72 mmol) with
stirring at room temperature. After the solution was stirred
at room temperature overnight, the solvent was removed. The
orange-red residue was extracted with pentane (25 mL × 2)
and filtered. The volume of the filtrate was reduced to 15 mL
and cooled to -20 °C, yielding orange-red crystals, which were
isolated by filtration. Yield: 1.4 g (70%). EI-MS [M+], m/z
(calcd, found): 742 (100, 100), 743 (37, 40), 744 (7, 10). Anal.
Calcd for C34H58F2U: C, 55.0; H, 7.87. Found: C, 54.7; H, 7.96.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(NH2)2 (5). In a
250 mL flask, [η5-1,2,4-(Me3C)3C5H2]2UMe2 (3; 1.0 g, 1.36
mmol) was dissolved in toluene (30 mL). The headspace of the
flask was evacuated and replaced with 1 atm of NH3 (dried
over sodium metal at -35 °C). After the solution was stirred
for 4 h at room temperature, the solvent was removed. The
yellow residue was extracted with pentane (25 mL × 2) and
filtered. The volume of the filtrate was reduced to 10 mL and
cooled to -20 °C, yielding yellow crystals, which were isolated
by filtration. Yield: 0.74 g (74%). EI-MS [M+], m/z (calcd,
found): 736 (100, 100), 737 (39, 40), 738 (8, 5). Anal. Calcd for
C34H62N2U: C, 55.4; H, 8.48; N, 3.80. Found: C, 55.8; H, 8.13;
N, 3.68.
(47) Hanna, T. E.; Keresztes, I.; Lobkovsky, E.; Bernskoetter, W.
H.; Chirik, P. J. Organometallics 2004, 23, 3448.
(48) Bryan, J. C.; Mayer, J. M. J. Am. Chem. Soc. 1990, 112, 2298.
This paper contains an excellent discussion of the thermodynamic
issues involved in the oxygen atom transfer reaction.
(49) Howard, W. A.; Trnka, T. M.; Waters, M.; Parkin, G. J.
Organomet. Chem. 1997, 528, 95.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(bipy) (6). A
green THF solution of sodium naphthalene, which was pre-
pared from naphthalene (3.3 g, 25.8 mmol) and sodium metal
(1.0 g, 43.5 mmol) in THF (200 mL) with stirring overnight at
(50) Sweeney, Z. K.; Polse, J. L.; Andersen, R. A.; Bergman, R. G.
J. Am. Chem. Soc. 1998, 120, 7825.
(51) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 5393.
(52) Ugi, I.; Perlinger, H.; Behringer, L. Chem. Ber. 1958, 91, 2330.

Preparation and Reactions of Base-Free Cp′2UO
Organometallics, Vol. 24, No. 17, 2005 4261
room temperature, was slowly added to a THF (100 mL)
solution of [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1; 10 g, 12.9 mmol)
and 2,2′-bipyridyl (bipy; 2.1 g, 13.5 mmol) with stirring at room
temperature. After the green solution was stirred for 12 h,
solvent was removed. The dark green residue was extracted
with toluene (100 mL × 3) and filtered. The volume of the
filtrate was reduced to 100 mL and cooled to -20 °C. Two crops
of dark green crystals were collected by filtration. Yield: 7.2
g (65%). EI-MS [M+], m/z (calcd, found): 860 (100, 100), 861
(51, 57), 862 (13, 16), 863 (2, 3). Anal. Calcd for C44H66N2U:
C, 61.4; H, 7.73; N, 3.25. Found: C, 61.2; H, 7.82; N, 3.28.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7).
A hexane (1.9 mL) solution of p-CH3C6H4N3 (1.2 M in hexane;
2.3 mmol) was added to a hexane (100 mL) solution of [η5-
1,2,4-(Me3C)3C5H2]2U(bipy) (6; 2.0 g, 2.3 mmol) with stirring
at room temperature. During the course of the reaction, the
color of the solution changed from green to dark brown. After
the solution was stirred for 2 h at room temperature, solvent
was removed and the dark brown solid was exposed to vacuum
overnight at 50 °C in a water bath. The residue was extracted
with pentane (25 mL × 2) and filtered. The volume of the dark
brown solution was reduced to 20 mL and cooled to -20 °C,
yielding dark brown crystals, which were isolated by filtration.
Yield: 1.5 g (80%). EI-MS [M+], m/z (calcd, found): 809 (100,
100), 810 (47, 58), 811 (12, 14), 812 (2, 2). Anal. Calcd for
C41H65NU: C, 60.8; H, 8.09; N, 1.73. Found: C, 61.1; H, 8.40;
N, 1.84.
Method B. NMR Scale. Ph3B (5 mg, 0.02 mmol) was added
to an NMR tube charged with [η5-1,2,4-(Me3C)3C5H2]2U(O)-
(dmap) (9; 17 mg, 0.02 mmol) and C6D6 (0.5 mL). The color of
the solution immediately changed from yellow-green to brown-
red, and resonances due to [η5-1,2,4-(Me3C)3C5H2]2UO (10)
1
were observed by H NMR spectroscopy (100% conversion).
Method C. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7; 16 mg, 0.02 mmol) and
C6D6 (0.5 mL) was added benzophenone (3.6 mg, 0.02 mmol).
The color of the solution immediately changed from dark
1
brown to brown-red. The H NMR spectrum contained reso-
nances consistent with [η5-1,2,4-(Me3C)3C5H2]2UO (10) and
Ph2CdN-p-C6H4CH3 (1H NMR (C6D6): δ 7.97 (m, 2H, aryl H),
7.12 (m, 3H, aryl H), 6.98 (m, 2H, aryl H), 6.89 (m, 3H, aryl
H), 6.77 (m, 4H, aryl H), 1.97 (s, 3H, CH3)) (100% conversion).
10 cannot be isolated on a synthetic scale by this method, since
in the presence of Ph2CdN-p-C6H4CH3 the diene (Me3C)3C5H3
slowly results.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Pyri-
dine. NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was added a
drop of pyridine. The color of the solution immediately changed
from brown-red to red, and resonances due to [η5-1,2,4-
(Me3C)3C5H2]2U(O)(py) (8) were observed by 1H NMR spec-
troscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with dmap.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5 mL)
was added 4-(dimethylamino)pyridine (dmap; 2.5 mg, 0.02
mmol). The color of the solution immediately changed from
brown-red to yellow-green, and resonances due to [η5-1,2,4-
(Me3C)3C5H2]2U(O)(dmap) (9) were observed by 1H NMR
spectroscopy (100% conversion).
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(O)(py) (8). To
a diethyl ether (30 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2U-
(bipy) (6; 2.0 g, 2.3 mmol) was slowly added a diethyl ether
(20 mL) solution of pyridine-N-oxide (0.22 g, 2.3 mmol) with
stirring at room temperature. During the course of the
reaction, the color of the solution changed from green to red.
After the solution was stirred for 2 h at room temperature,
solvent was removed and the red solid was exposed to vacuum
overnight at 50 °C in a water bath. The residue was extracted
with diethyl ether (25 mL × 2) and filtered. The volume of
filtrate was reduced to 10 mL and cooled to -20 °C, yielding
red crystals, which were isolated by filtration. Yield: 1.2 g
(65%). IR: ν UO, 760(s) cm-1. Anal. Calcd for C39H63NOU: C,
58.6; H, 7.94; N, 1.75. Found: C, 58.6; H, 8.29; N, 1.92.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(O)(dmap) (9).
A diethyl ether (20 mL) solution of 4-(dimethylamino)pyridine
(dmap; 0.18 g, 1.48 mmol) was added to a diethyl ether (30
mL) solution of [η5-1,2,4-(Me3C)3C5H2]2U(O)(py) (8; 1.1 g, 1.38
mmol) with stirring at room temperature. During the course
of the reaction, the color of the solution changed from red to
yellow-green. After the solution was stirred for 2 h at room
temperature, solvent was removed. The yellow-green residue
was extracted with diethyl ether (25 mL × 2) and filtered. The
volume of the filtrate was reduced to 10 mL and cooled to -20
°C, yielding yellow-green crystals, which were isolated by
filtration. Yield: 0.75 g (65%). IR: ν UO, 765(s) cm-1. Anal.
Calcd for C41H68N2OU: C, 58.4; H, 8.13; N, 3.32. Found: C,
58.6; H, 8.52; N, 3.39.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(Cl)
(11). Method A. Me3SiCl (2.0 mL, 15.7 mmol) was added to a
toluene (20 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2U(O)(py) (8;
1.2 g, 1.5 mmol) with stirring at room temperature. After the
solution was stirred overnight at room temperature, solvent
was removed. The orange-red residue was extracted with
pentane (25 mL × 2) and filtered. The volume of the filtrate
was reduced to 10 mL and cooled to -20 °C, yielding orange-
red crystals, which were isolated by filtration. Yield: 1.1 g
(88%). EI-MS [M+], m/z (calcd, found): 828 (100, 100), 829 (47,
50), 830 (46, 49), 831 (18, 20); the parent ion is [M - 15]+.
Anal. Calcd for C37H67ClOSiU: C, 53.6; H, 8.15. Found: C,
53.2; H, 8.37.
Method B. To a diethyl ether (20 mL) solution of [η5-1,2,4-
(Me3C)3C5H2]2UCl2 (1; 2.0 g, 2.6 mmol) was added a diethyl
ether (10 mL) solution of Me3SiOLi (0.25 g, 2.6 mmol) with
stirring at room temperature. After the solution was stirred
at room temperature for one week, solvent was removed. The
orange-red residue was extracted with pentane (25 mL × 2)
and filtered. The volume of the filtrate was reduced to 10 mL
and cooled to -20 °C, yielding orange-red microcrystals, which
1
were identified as 11 by H NMR spectroscopy. Yield: 1.6 g
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UO (10). Method
A. To a toluene (20 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2U-
(O)(py) (8; 1.6 g, 2.0 mmol) was added a toluene (10 mL)
solution of Ph3B (0.49 g, 2.0 mmol) with stirring at room
temperature. During the course of the reaction, the color of
the solution changed from red to brown-red and a precipitate
(Ph3B‚py) appeared. After the solution was stirred for 2 h at
room temperature, solvent was removed. The brown-red
residue was extracted with pentane (25 mL × 2) and filtered.
The volume of the filtrate was reduced to 10 mL and cooled to
-20 °C, yielding brown-red microcrystals, which were isolated
by filtration. Yield: 1.2 g (83%). EI-MS [M+], m/z (calcd,
found): 720 (100, 100), 721 (39, 34), 722 (7, 6). Anal. Calcd for
C34H58OU: C, 56.6; H, 8.11. Found: C, 56.6; H, 7.95. This
compound cannot be prepared in THF or diethyl ether solution,
since in these solvents the diene, (Me3C)3C5H3 results.
(75%). Solvent has a large effect on this reaction; the conver-
sion is very low (below 10%) even at 65 °C for 3 days in THF
or toluene solution.
Method C. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL), an
excess of Me3SiCl was added. The color of the solution
immediately changed from brown-red to orange-red, and
resonances due to [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(Cl) (11)
were observed by 1H NMR spectroscopy (100% conversion). The
sample was maintained at 65 °C and monitored periodically
by 1H NMR spectroscopy. After 1 day, conversion to [η5-1,2,4-
(Me3C)3C5H2]2UCl2 (1) was 35% complete, and after 3 days,
conversion to [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1) was complete.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(Br)
(12). Method A. This compound was prepared as red crystals
from the reaction of [η5-1,2,4-(Me3C)3C5H2]2U(O)(py) (8; 1.2 g,

4262 Organometallics, Vol. 24, No. 17, 2005
Zi et al.
1.5 mmol) and Me3SiBr (2.0 mL, 15 mmol) in toluene (20 mL)
by procedures similar to those used in the synthesis of [η5-
1,2,4-(Me3C)3C5H2]2U(OSiMe3)(Cl) (11). Yield: 1.1 g (85%). EI-
MS [M+], m/z (calcd, found): 872 (89, 90), 873 (42, 40), 874
(100, 100), 875 (44, 40), 876 (13, 15); the parent ion is [M -
15]+. Anal. Calcd for C37H67BrOSiU: C, 50.9; H, 7.74. Found:
C, 50.7; H, 7.80.
Method B. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was
added an excess of Me3SiBr. The color of the solution im-
mediately changed from brown-red to orange-red, and reso-
nances due to [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(Br) (12) were
observed by 1H NMR spectroscopy (100% conversion). The
sample was maintained at 65 °C and monitored periodically
by 1H NMR spectroscopy. After 1 day, conversion to [η5-1,2,4-
(Me3C)3C5H2]2UBr2 (2) was 15% complete, and after 10 days,
conversion to [η5-1,2,4-(Me3C)3C5H2]2UBr2 (2) was complete.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(I) (13).
Method A. This compound was prepared as red crystals from
the reaction of [η5-1,2,4-(Me3C)3C5H2]2U(O)(py) (8; 1.2 g, 1.5
mmol) and Me3SiI (2.0 mL, 14 mmol) in toluene (20 mL) by
procedures similar to those used in the synthesis of [η5-1,2,4-
(Me3C)3C5H2]2U(OSiMe3)(Cl) (11). Yield: 1.2 g (87%). EI-MS
[M+], m/z (calcd, found): 920 (100, 100), 921 (47, 35); the parent
ion is [M - 15]+. Anal. Calcd for C37H67IOSiU: C, 48.2; H,
7.34. Found: C, 48.0; H, 7.31.
Method B. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was
added an excess of Me3SiI. The color of the solution im-
mediately changed from brown-red to red, and resonances due
to [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(I) (13) were observed by
1H NMR spectroscopy (100% conversion). The sample was
monitored periodically by 1H NMR spectroscopy, and the
spectrum did not show any change when heated at 65 °C for
3 days.
and the spectrum did not show any change when heated at
65 °C for 3 days.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(N3)2 (17). Meth-
od A. Me3SiN3 (2.0 mL, 15 mmol) was added to a toluene (20
mL) solution of [η5-1,2,4-(Me3C)3C5H2]2U(O)(py) (8; 1.2 g, 1.5
mmol) with stirring at room temperature. After the solution
was stirred overnight at room temperature, solvent was
removed. The orange-red residue was extracted with pentane
(25 mL × 2) and filtered. The volume of the filtrate was
reduced to 10 mL and cooled to -20 °C, yielding orange-red
crystals, which were isolated by filtration. Yield: 1.0 g (85%).
IR: ν UN3, 2100, 2080 cm-1. EI-MS [M+], m/z (calcd, found):
788 (100, 100), 789 (41, 45), 790 (8, 10). Anal. Calcd for
C34H58N6U: C, 51.7; H, 7.41; N, 10.7. Found: C, 51.7; H, 7.32;
N, 10.7.
Method B. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was
added an excess of Me3SiN3. The color of the solution im-
mediately changed from brown-red to orange-red, and reso-
nances due to [η5-1,2,4-(Me3C)3C5H2]2U(N3)2 (17) were observed
1
by H NMR spectroscopy (100% conversion). Reaction of [η5-
1,2,4-(Me3C)3C5H2]2UO (10) or [η5-1,2,4-(Me3C)3C5H2]2U(O)(py)
(8) with 1 equiv of Me3SiN3 gave resonances due to [η5-1,2,4-
(Me3C)3C5H2]2U(N3)2 (17) and resonances attributable to [η5-
1,2,4-(Me3C)3C5H2]2U(OSiMe3)(N3) (16; 1H NMR (C6D6): δ 18.6
(9H, (CH3)3Si), 5.6 (18H, (CH3)3C), -4.6 (18H, (CH3)3C), -11.7
(18H, (CH3)3C); the protons of the rings were not observed).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Pyri-
dine-N-oxide. NMR Scale. To an NMR tube charged with
[η5-1,2,4-(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6
(0.5 mL) was added pyridine-N-oxide (2.0 mg, 0.02 mmol). The
color of the solution immediately changed from brown-red to
black, and resonances due to (2,3,5-(Me3C)3C5H2)253 (1H NMR
(C6D6): δ 6.48 (4H, CH), 1.38 (36H, (CH3)3C), 1.01 (18H,
(CH3)3C)) were observed by 1H NMR spectroscopy (100%
conversion). (2,3,5-(Me3C)3C5H2)2 can be isolated in 70% yield
(0.33 g) from the reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10;
0.72 g, 1.0 mmol) and pyridine-N-oxide (0.10 g, 1 mmol) in
pentane solution.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(CN)
(14). Method A. This compound was prepared as red crystals
from the reaction of [η5-1,2,4-(Me3C)3C5H2]2U(O)(py) (8; 1.2 g,
1.5 mmol) and Me3SiCN (2.0 mL, 15 mmol) in toluene (20 mL)
by procedures similar to those used in the synthesis of [η5-
1,2,4-(Me3C)3C5H2]2U(OSiMe3)(Cl) (11). Yield: 1.1 g (89%).
IR: ν UCN, 2040(s) cm-1. EI-MS [M+], m/z (calcd, found): 819
(100, 100), 820 (49, 50), 821 (15, 15), 822 (2, 2); the parent ion
is [M - CN]+. Anal. Calcd for C38H67NOSiU: C, 55.6; H, 8.24;
N, 1.71. Found: C, 55.4; H, 8.12; N, 2.01.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Ph3PE
(E ) S, Se). NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5
mL) was added Ph3PE (E ) S, Se) (6 mg, 0.02 mmol). The color
of the solution immediately changed from brown-red to black,
and resonances due to (2,3,5-(Me3C)3C5H2)2 were observed by
1H NMR spectroscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with SiF4
or BF3(OEt2). NMR Scale. To an NMR tube charged with
[η5-1,2,4-(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was
added an excess of SiF4 or BF3(OEt2). The color of the solution
immediately changed from brown-red to orange-red, and
resonances due to [η5-1,2,4-(Me3C)3C5H2]2UF2 (4) were ob-
Method B. NMR Scale. An excess of Me3SiCN was added
to an NMR tube charged with [η5-1,2,4-(Me3C)3C5H2]2UO (10;
15 mg) and C6D6 (0.5 mL). The color of the solution im-
mediately changed from brown-red to red, and resonances due
to [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(CN) (14) were observed
by 1H NMR spectroscopy (100% conversion). The sample was
monitored periodically by 1H NMR spectroscopy, and the
spectrum did not show any change when heated at 65 °C for
3 days.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(OTf)
(15). Method A. This compound was prepared as orange-red
microcrystals from the reaction of [η5-1,2,4-(Me3C)3C5H2]2U-
(O)(py) (8; 1.2 g, 1.5 mmol) and Me3SiOTf (2.0 mL, 11 mmol)
in toluene (20 mL) by using the procedures similar to those
used in the synthesis of [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(Cl)
(11). Yield: 1.2 g (86%). EI-MS: m/z 927 [M+ - CH3]. Anal.
Calcd for C38H67F3O4SSiU: C, 48.4; H, 7.16. Found: C, 48.2;
H, 7.24.
1
served by H NMR spectroscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Me3-
SiCF3. NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was added
an excess of Me3SiCF3. The color of the solution immediately
changed from brown-red to orange-red, and resonances due
to [η5-1,2,4-(Me3C)3C5H2]2UF2 (4; 60% conversion) and reso-
nances due to other unidentified uranium containing com-
1
pounds were observed by H NMR spectroscopy. The sample
was monitored periodically by 1H NMR spectroscopy, and the
spectrum did not show any change when heated at 65 °C for
3 days.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with SiCl4.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was added
an excess of SiCl4. The color of the solution immediately
changed from brown-red to orange-red, and resonances at-
Method B. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was
added an excess of Me3SiOTf. The color of the solution
immediately changed from brown-red to orange-red, and
resonances due to [η5-1,2,4-(Me3C)3C5H2]2U(OSiMe3)(OTf) (15)
were observed by 1H NMR spectroscopy (100% conversion). The
1
sample was monitored periodically by H NMR spectroscopy,
(53) Sitzmann, H.; Wolmersha¨user, G. Chem. Ber. 1994, 127, 1335.

Preparation and Reactions of Base-Free Cp′2UO
Organometallics, Vol. 24, No. 17, 2005 4263
tributable to [η5-1,2,4-(Me3C)3C5H2]2U(OSiCl3)(Cl) (1H NMR
(C6D6): δ 14.6 (18 H, (CH3)3C), -5.1 (18H, (CH3)3C), -14.8
(18H, (CH3)3C); the protons of the rings were not observed)
were observed by 1H NMR spectroscopy (100% conversion). The
sample was maintained at 65 °C and monitored periodically
by 1H NMR spectroscopy. After 1 day, conversion to [η5-1,2,4-
(Me3C)3C5H2]2UCl2 (1) was 30% complete, and after 4 days,
conversion to [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1) was complete.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with SiBr4.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was added
an excess of SiBr4. The color of the solution immediately
changed from brown-red to orange-red, and resonances at-
tributable to [η5-1,2,4-(Me3C)3C5H2]2U(OSiBr3)(Br) (1H NMR
(C6D6): δ 15.6 (18H, (CH3)3C), -4.7 (18H, (CH3)3C), -14.8
(18H, (CH3)3C); the protons of the rings were not observed)
were observed by 1H NMR spectroscopy (100% conversion). The
sample was maintained at 65 °C and monitored periodically
by 1H NMR spectroscopy. After 1 day, conversion to [η5-1,2,4-
(Me3C)3C5H2]2UBr2 (2) was 20% complete, and after 10 days,
conversion to [η5-1,2,4-(Me3C)3C5H2]2UBr2 (2) was complete.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with SiI4.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg) and C6D6 (0.5 mL) was added
an excess of SiI4. The color of the solution immediately changed
from brown-red to orange-red, and resonances attributable to
[η5-1,2,4-(Me3C)3C5H2]2U(OSiI3)(I) (1H NMR (C6D6): δ 15.4
(18H, (CH3)3C), -3.3 (18H, (CH3)3C), -14.5 (18H, (CH3)3C);
the protons of the rings were not observed) were observed by
1H NMR spectroscopy (100% conversion). The sample was
monitored periodically by 1H NMR spectroscopy, and the
spectrum did not show any change when heated at 65 °C for
3 days.
(9H, (CH3)3C), -25.5 (9H, (CH3)3C), -26.0 (9H, (CH3)3C), -28.0
(9H, (CH3)3C), -33.5 (9H, (CH3)3C)) were observed by 1H NMR
spectroscopy. The sample was monitored periodically by 1H
NMR spectroscopy. After 1 day at 65 °C or 10 days at room
temperature, the nine resonances disappeared, and resonances
due to [η5-1,2,4-(Me3C)3C5H2]2UCl2 (1) were observed (30%
conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with AgF.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5 mL)
was added an excess of AgF. The color of the solution
immediately changed from brown-red to orange-red, and
resonances due to (2,3,5-(Me3C)3C5H2)2 along with [η5-1,2,4-
(Me3C)3C5H2]2UF2 (4) were observed by 1H NMR spectroscopy
(100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with AgCl.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5 mL)
was added an excess of AgCl. The color of the solution
immediately changed from brown-red to brown, and reso-
nances due to (2,3,5-(Me3C)3C5H2)2 and new nine resonances
(1H NMR (C6D6): δ 26.6 (9H, (CH3)3C), 23.4 (9H, (CH3)3C), 12.9
(9H, (CH3)3C), 1.6 (9H, (CH3)3C), -20.4 (9H, (CH3)3C), -25.5
(9H, (CH3)3C), -26.0 (9H, (CH3)3C), -28.0 (9H, (CH3)3C), -33.5
1
(9H, (CH3)3C)) were observed by H NMR spectroscopy. The
1
sample was monitored periodically by H NMR spectroscopy.
After 1 day at 65 °C or 10 days at room temperature, the nine
resonances disappeared, and only resonances due to (2,3,5-
(Me3C)3C5H2)2 were observed (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with AgBr.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5 mL)
was added an excess of AgBr was added. The color of the
solution immediately changed from brown-red to brown, and
resonances due to (2,3,5-(Me3C)3C5H2)2 and new nine reso-
nances (1H NMR (C6D6): δ 28.2 (9H, (CH3)3C), 22.5 (9H,
(CH3)3C), 16.7 (9H, (CH3)3C), 4.3 (9H, (CH3)3C), -19.9 (9H,
(CH3)3C), -27.8 (9H, (CH3)3C), -28.6 (9H, (CH3)3C), -29.6 (9H,
(CH3)3C), -33.0 (9H, (CH3)3C)) were observed by 1H NMR
spectroscopy. This NMR sample was monitored periodically
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with C6H5Cl
or C6D5Cl. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5
mL) was added an excess of C6H5Cl or C6D5Cl. The color of
the solution immediately changed from brown-red to brown,
and resonances due to (Me3C)3C5H3 and nine new resonances
(1H NMR (C6D6): δ 26.6 (9H, (CH3)3C), 23.4 (9H, (CH3)3C), 12.9
(9H, (CH3)3C), 1.6 (9H, (CH3)3C), -20.4 (9H, (CH3)3C), -25.5
(9H, (CH3)3C), -26.0 (9H, (CH3)3C), -28.0 (9H, (CH3)3C), -33.5
1
by H NMR spectroscopy. After 1 day at 65 °C or 10 days at
room temperature, the nine resonances disappeared, and only
resonances due to (2,3,5-(Me3C)3C5H2)2 were observed (100%
conversion).
1
(9H, (CH3)3C)) were observed by H NMR spectroscopy. The
1
sample was monitored periodically by H NMR spectroscopy,
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with [η5-
1,2,4-(Me3C)3C5H2]2UF2 (4). NMR Scale. To an NMR tube
charged with [η5-1,2,4-(Me3C)3C5H2]2UO (10; 15 mg, 0.02
mmol) and C6D6 (0.5 mL) was added [η5-1,2,4-(Me3C)3C5H2]2-
UF2 (4; 15 mg, 0.02 mmol). The sample was monitored
and the spectrum did not show any change when heated at
65 °C for 3 days.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with C6H5Br.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5 mL)
was added an excess of C6H5Br. The color of the solution
immediately changed from brown-red to brown, and reso-
nances due to (Me3C)3C5H3 and nine new resonances (1H NMR
(C6D6): δ 28.2 (9H, (CH3)3C), 22.5 (9H, (CH3)3C), 16.7 (9H,
(CH3)3C), 4.3 (9H, (CH3)3C), -19.9 (9H, (CH3)3C), -27.8 (9H,
(CH3)3C), -28.6 (9H, (CH3)3C), -29.6 (9H, (CH3)3C), -33.0 (9H,
(CH3)3C)) were observed by 1H NMR spectroscopy. The sample
was monitored periodically by 1H NMR spectroscopy, and the
spectrum did not show any change when heated at 65 °C for
3 days.
1
periodically by H NMR spectroscopy, and the spectrum did
not show any change when heated at 65 °C for 3 days.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with [η5-
1,2,4-(Me3C)3C5H2]2UCl2 (1). NMR Scale. To an NMR tube
charged with [η5-1,2,4-(Me3C)3C5H2]2UO (10; 15 mg, 0.02
mmol) and C6D6 (0.5 mL) was added [η5-1,2,4-(Me3C)3C5H2]2-
UCl2 (1; 15 mg, 0.02 mmol). The color of the solution im-
mediately changed from brown-red to black. Resonances due
to [η5-1,2,4-(Me3C)3C5H2]2UCl (1H NMR (C6D6): δ -7.8 (36H,
v1/2 ) 45 Hz, (CH3)3C), -24.9 (18H, v1/2 ) 45 Hz, (CH3)3C);
protons of the rings were not observed),44 (2,3,5-(Me3C)3C5H2)2,
and new nine resonances (1H NMR (C6D6): δ 26.6 (9H,
(CH3)3C), 23.4 (9H, (CH3)3C), 12.9 (9H, (CH3)3C), 1.6 (9H,
(CH3)3C), -20.4 (9H, (CH3)3C), -25.5 (9H, (CH3)3C), -26.0 (9H,
(CH3)3C), -28.0 (9H, (CH3)3C), -33.5 (9H, (CH3)3C)) were
observed in the 1H NMR spectrum. The sample was monitored
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Me3CCl
or (CD3)3CCl. NMR Scale. To an NMR tube charged with
[η5-1,2,4-(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6
(0.5 mL) was added an excess of Me3CCl or (CD3)3CCl. The
color of the solution immediately changed from brown-red to
brown, and resonances due to (Me3C)3C5H3, Me2CdCH2 (1H
NMR (C6D6): δ 4.74 (s, 2H, CH2), 1.58 (s, 6H, CH3)),54 and
new nine resonances (1H NMR (C6D6): δ 26.6 (9H, (CH3)3C),
23.4 (9H, (CH3)3C), 12.9 (9H, (CH3)3C), 1.6 (9H, (CH3)3C), -20.4
1
periodically by H NMR spectroscopy, and the spectrum did
not show any change when heated at 65 °C for 3 days.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Ph3PO.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5 mL)
was added Ph3PO (6 mg, 0.02 mmol). The color of the solution
(54) Jordan, A. Y.; Meyer, T. Y. J. Organomet. Chem. 1999, 591,
104.

4264 Organometallics, Vol. 24, No. 17, 2005
Zi et al.
immediately changed from brown-red to brown, and reso-
nances attributable to [η5-1,2,4-(Me3C)3C5H2]2U(O)(OPPh3) (1H
NMR (C6D6): δ 8.8 (36H, (CH3)3C), 5.4 (18H, (CH3)3C); the
with [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7; 16 mg, 0.02
mmol) and C6D6 (0.5 mL) was added pyridine-N-oxide (2 mg,
0.02 mmol). The color of the solution immediately changed
from dark brown to black, and resonances due to (2,3,5-
(Me3C)3C5H2)2 were observed by 1H NMR spectroscopy (100%
conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7) with
Me3SiN3. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7; 16 mg, 0.02 mmol) and
C6D6 (0.5 mL) was added an excess of Me3SiN3. Resonances
due to [η5-1,2,4-(Me3C)3C5H2]2U(N3)2 (17; 20% conversion)
along with other unidentified uranium-containing compounds
were observed by 1H NMR spectroscopy. The sample was
monitored periodically by 1H NMR spectroscopy, and the
spectrum did not show any change when heated at 65 °C for
3 days.
1
protons of the rings were not observed) were observed by H
NMR spectroscopy (100% conversion). This compound was not
isolated on a synthetic scale, since it is poorly soluble in
nonpolar solvents, and it decomposes to (Me3C)3C5H3 in polar
solvents.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Ph2CO.
NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5 mL)
was added Ph2CO (4 mg, 0.02 mmol). The color of the solution
immediately changed from brown-red to brown, and reso-
nances attributable to [η5-1,2,4-(Me3C)3C5H2]2U(O)(OCPh2) (1H
NMR (C6D6): δ 26.2 (18H, (CH3)3C), -8.0 (36H, (CH3)3C); the
1
protons of the rings were not observed) were observed by H
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7) with
SiF4 or BF3(OEt2). NMR Scale. To an NMR tube charged
with [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7; 15 mg) and C6D6
(0.5 mL) was added an excess of SiF4 or BF3(OEt2). The color
of the solution immediately changed from dark brown to
orange-red, and resonances due to [η5-1,2,4-(Me3C)3C5H2]2UF2
(4) were observed by 1H NMR spectroscopy (100% conversion).
Crystallographic data were deposited with the Cam-
bridge Crystallographic Data Centre; copies of the data
(CCDC 262849-262856) can be obtained free of charge
via www.ccdc.cam.ac.uk/ data_request/cif, by e-mailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax +44 1223 336033.
NMR spectroscopy (100% conversion). When the sample was
heated at 65 °C and monitored periodically by 1H NMR
spectroscopy, decomposition to (Me3C)3C5H3 and other uni-
dentified uranium containing compounds was observed.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with Amines
or PhCtCH. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UO (10; 15 mg, 0.02 mmol) and C6D6 (0.5
mL) was added an excess of amine (NH3, MeNH2, Me2NH,
Me3N) or PhCtCH. The color of the solution immediately
changed from brown-red to brown, and resonances due to
(Me3C)3C5H3 and resonances due to other unidentified uranium-
containing compounds were observed.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UO (10) with C6H5F,
RCtCR (R ) Me, Ph, Me3Si), H2 or C2H4. NMR Scale. To
an NMR tube charged with [η5-1,2,4-(Me3C)3C5H2]2UO (10; 15
mg, 0.02 mmol) and C6D6 (0.5 mL) was added an excess of
C6H5F, RCtCR (R ) Me, Ph, Me3Si), H2, or C2H4. The sample
was monitored periodically by 1H NMR spectroscopy, and the
spectrum did not show any change when heated at 65 °C for
3 days.
Acknowledgment. This work was supported by the
Director, Office of Basic Research, Office of Basic Energy
Sciences, Chemical Sciences Division, of the U.S. De-
partment of Energy under contract No. DE-AC03-
76SF00098. We thank Dr. Fred Hollander and Dr. Allen
Oliver (at CHEXRAY, the UC Berkeley X-ray facility)
for their help with the crystallography.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7) with
Me3SiX (X ) Cl, Br, I), Ph3PE (E ) O, S, Se), Diethyl
Ether, Tetrahydrofuran, Pyridines, 4-Me2NC5H4N, or
PhCl. NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UdN(p-tolyl) (7; 16 mg, 0.02 mmol) and C6D6
(0.5 mL) was added an excess of Me3SiX (X ) Cl, Br, I), Ph3-
PE (E ) O, S, Se), diethyl ether, tetrahydrofuran, pyridines,
4-Me2NC5H4N, or PhCl. The sample was monitored periodi-
cally by 1H NMR spectroscopy, and the spectrum did not show
any change when heated at 65 °C for 3 days.
Supporting Information Available: Crystallographic
data, labeling diagrams, tables giving atomic positions and
anisotropic thermal parameters, bond distances and angles,
and least-squares planes for each structure. This material is
available free of charge via the Internet at http://pubs.acs.org.
Structure factor tables are available from the authors.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (7) with
Pyridine-N-Oxide. NMR Scale. To an NMR tube charged
OM050406Q