Preparation and reactions of base-free bis(1,2,4-tri-tert- butylcyclopentadienyl)uranium methylimide, Cp′2U=NMe, and related compounds

Article abstract of DOI:10.1021/om050427k

The uranium metallocenes [η⁵-1,3-(Me₃E) ₂C₅H₃]₂UMe₂ (E = C, Si) react with NH₃ to give the dimers {[η⁵-1,3-(Me ₃E)₂C₅H₃]₂U} ₂(μ-NH)₂ (E = C (1), Si (2)) but with p-toluidine to give the monomeric diamides [η⁵-1,3-(Me₃E) ₂C₅H₃]₂U(NH-p-tolyl)₂ (E = C (3), Si (4)). The diamides η⁵-1,3-(Me₃E) ₂C₅H₃]₂U(NH-p-tolyl)₂ (E = C (3), Si (4)) do not eliminate p-toluidine but sublime intact at 140°C in a vacuum. The uranium metallocene [η⁵-1,2,4-(Me ₃C)₃C₅H₂]₂UMe ₂ reacts with RNH₂ to yield [η⁵-1,2,4- (Me₃C)₃C₅H₂]₂U(NHR) ₂ (R = Me (8), PhCH₂ (9), p-tolyl (10)), which are isolated as crystalline solids. In benzene solution these diamides are in equilibrium with [η⁵-1,2,4-(Me₃C)₃C ₅H₂]₂U=NR, which may be isolated pure when R is Me (11) or p-tolyl (12), and the primary amine. The monomeric imide [η⁵-1,2,4-(Me₃C)₃C₅H ₂]₂U = NMe (11) reacts with R′C≡CR′ to yield the cycloaddition products [η⁵-1,2,4-(Me₃C) ₃C₅H₂]₂U-[N(Me)C(R′)= C(R′)] (R′ = Me (15), Ph (16)), which react with excess MeNH ₂ to regenerate the diamide [η⁵-1,2,4-(Me ₃C)₃C₅H₂]₂U(NHMe) ₂ (8) and MeN=C(R′)CH(R′). The methylimide, [η⁵1,2,4-(Me₃C)₃C₅H ₂]₂U=NMe (11), does not react with Me₃SiX reagents; a model is proposed that rationalizes this reactivity pattern.

Full text of DOI:10.1021/om050427k

4602
Organometallics 2005, 24, 4602-4612
Preparation and Reactions of Base-Free
Bis(1,2,4-tri-tert-butylcyclopentadienyl)uranium
Methylimide, Cp′2UdNMe, and Related Compounds
Guofu Zi, Laura L. Blosch, Li Jia, and Richard A. Andersen*
Department of Chemistry and Chemical Sciences Division of Lawrence Berkeley National
Laboratory, University of California, Berkeley, California 94720
Received May 27, 2005
The uranium metallocenes [η5-1,3-(Me3E)2C5H3]2UMe2 (E ) C, Si) react with NH3 to give
the dimers {[η5-1,3-(Me3E)2C5H3]2U}2(µ-NH)2 (E ) C (1), Si (2)) but with p-toluidine to give
the monomeric diamides [η5-1,3-(Me3E)2C5H3]2U(NH-p-tolyl)2 (E ) C (3), Si (4)). The diamides
[η5-1,3-(Me3E)2C5H3]2U(NH-p-tolyl)2 (E ) C (3), Si (4)) do not eliminate p-toluidine but
sublime intact at 140 °C in a vacuum. The uranium metallocene [η5-1,2,4-(Me3C)3C5H2]2UMe2
reacts with RNH2 to yield [η5-1,2,4-(Me3C)3C5H2]2U(NHR)2 (R ) Me (8), PhCH2 (9), p-tolyl
(10)), which are isolated as crystalline solids. In benzene solution these diamides are in
equilibrium with [η5-1,2,4-(Me3C)3C5H2]2UdNR, which may be isolated pure when R is Me
(11) or p-tolyl (12), and the primary amine. The monomeric imide [η5-1,2,4-(Me3C)3C5H2]2Ud
NMe (11) reacts with R′CtCR′ to yield the cycloaddition products [η5-1,2,4-(Me3C)3C5H2]2U-
[N(Me)C(R′)dC(R′)] (R′ ) Me (15), Ph (16)), which react with excess MeNH2 to regenerate
the diamide [η5-1,2,4-(Me3C)3C5H2]2U(NHMe)2 (8) and MeNdC(R′)CH(R′). The methylimide,
[η5-1,2,4-(Me3C)3C5H2]2UdNMe (11), does not react with Me3SiX reagents; a model is proposed
that rationalizes this reactivity pattern.
Introduction
amines EtNH2 and Me3CNH2 behave similarly.8 Thus,
formation of decamethylmetalloceneuranium imides
depends in a very sensitive way on the steric bulk and,
perhaps, on the electronic effects of the substituents on
the primary amine. The formation of a metallocene
imide from a metallocene bis(amide) is an important
reaction since it is postulated to be a key step in the
catalytic hydroamination of terminal acetylenes re-
ported by Eisen.10
Several substituted cyclopentadienyl uranium-imido
derivatives of the type (η5-C5Me5)2U(NAr)2, (η5-C5Me5)2U-
(NAr)(O), (η5-MeC5H4)3UdNPh, and (η5-C5Me5)2UdNAr
have been prepared.1-10 When the arylamine has steri-
cally bulky substituents such as i-Pr and t-Bu in the
2,6-positions,3,4 the (η5-C5Me5)2UdNAr derivatives are
generally prepared by reaction of (η5-C5Me5)2UMe2 with
1 equiv of a primary arylamine, which presumably
forms (η5-C5Me5)2U(Me)(NHAr), which eliminates meth-
ane, forming the imidometallocene.3,4 When the sub-
stituents are somewhat less bulky, for example, 2,6-
dimethylaniline, the bis-amide derivative is formed,
which thermally eliminates the amine, forming (η5-
C5Me5)2U(NAr)(thf).8,9 However, the least bulky aryl-
amine, aniline, yields (η5-C5Me5)2U(NHPh)2, which is
stable to elimination of aniline.4 The primary alkyl-
The decamethylmetalloceneuranium fragment11 is
essential for the preparation of these monomeric f 2-
imido derivatives (with or without a coordinated Lewis
base), since for example, imides derived from (η5-
MeC5H4)2U or [(Me3Si)2N]2U fragments yield dimeric
derivatives, (η5-MeC5H4)4U2(µ-NR)212 or [(Me3Si)2N]4U2-
(µ-NR)2.13 Thus, steric effects seem to play a dominant
role in determining the degree of association of the
uranium imide.
The bulky 1,2,4-(Me3C)3C5H2 cyclopentadienyl
ligand has been shown to yield the base-free
oxo and p-tolylimido uranium derivatives, [η5-1,2,4-
(Me3C)3C5H2]2UdO (monomeric in the gas phase) and
[η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (12) (monomeric in
the gas and solid phase), respectively.14 In this paper,
we show that the [η5-1,2,4-(Me3C)3C5H2]2U fragment
yields a monomeric methylimido derivative that under-
goes irreversible cycloaddition reactions with internal
* To whom correspondence should be addressed. E-mail:
raandersen@lbl.gov.
(1) Brennan, J. G.; Andersen, R. A. J. Am. Chem. Soc. 1985, 107,
514.
(2) Arney, D. J. S.; Burns, C. J.; Smith, D. C. J. Am. Chem. Soc.
1992, 114, 10068.
(3) Arney, P. S. J.; Burns, C. J. J. Am. Chem. Soc. 1993, 115, 9840.
(4) Arney, P. S. J.; Burns, C. J. J. Am. Chem. Soc. 1995, 117, 9448.
(5) Warner, B. P.; Scott, B. L.; Burns, C. J. Angew. Chem., Int. Ed.
1998, 37, 959.
(6) Peters, R. G.; Warner, B. P.; Scott, B. L.; Burns, C. J. Organo-
metallics 1999, 18, 2587.
(7) Peters, R. G.; Warner, B. P.; Burns, C. J. J. Am. Chem. Soc. 1999,
121, 5585.
(11) Fagan, P. J.; Manriquez, J. M.; Maata, E. A.; Seyam, A. M.;
Marks, T. J. J. Am. Chem. Soc. 1981, 103, 6650.
(8) Straub, T.; Frank, W.; Reiss, G. J.; Eisen, M. S. J. Chem. Soc.,
Dalton Trans. 1996, 2541.
(12) Brennan, J. G.; Andersen, R. A.; Zalkin, A. J. Am. Chem. Soc.
1988, 110, 4554.
(9) Haskel, A.; Straub, T.; Eisen, M. S. Organometallics 1996, 15,
3773.
(13) Stewart, J. L.; Andersen, R. A. New J. Chem. 1995, 19, 587.
(14) Zi, G.; Jia, L.; Werkema, E. L.; Walter, M. D.; Gottfriedsen, J.
P.; Andersen, R. A. Organometallics 2005, 24, 4251.
(10) Straub, T.; Haskel, A.; Neyroud, T. G.; Kapon, M.; Botoshansky,
M.; Eisen, M. S. Organometallics 2001, 20, 5017.
10.1021/om050427k CCC: $30.25 © 2005 American Chemical Society
Publication on Web 08/12/2005

Base-Free Uranium Methylimide
Organometallics, Vol. 24, No. 19, 2005 4603
acetylenes. In addition, we report that the less heavily
substituted derivatives derived from 1,3-(Me3E)2C5H3
(E ) C, Si) do not yield monomeric imido metallocenes.
diamide 3 or 4 and unreacted [η5-1,3-(Me3E)2C5H3]2UMe2,
implying that [η5-1,3-(Me3E)2C5H3]2U(Me)(NH-p-tolyl)
disproportionates. The diamides 3 and 4 melt without
decomposition about 150 °C, sublime without decom-
position in a vacuum in the temperature range 130-
140 °C, and give a molecular ion in their mass spectra.
Results and Discussion
Imides {[η5-1,3-(Me3E)2C5H3]2U}2(µ-NH)2 and
Amides [η5-1,3-(Me3E)2C5H3]2U(NH-p-tolyl)2. Addi-
tion of an excess of ammonia to a solution of either [η5-
[1,3-(Me3E)2C5H3]2UMe2 + 2p-tolylNH2 f
[1,3-(Me3E)2C5H3]2U(NH-p-tolyl)
E ) C (3), Si (4)
2 + 2CH4 (2)
15
1,3-(Me3C)2C5H3]2UMe215 or [η5-1,3-(Me3Si)2C5H3]2UMe2
in diethyl ether results in evolution of a gas, presumably
methane, and formation of red-purple precipitates, eq
1. The precipitates are insoluble in hexane, sparingly
soluble in toluene, but soluble in THF, from which they
may be crystallized as red-purple or purple blocks, {[η5-
1,3-(Me3E)2C5H3]2U}2(µ-NH)2 (E ) C (1), Si (2)). The
ammonia reaction is similar to the reaction of [η5-1,3-
(Me3E)2C5H3]2UMe2 with water that yields the oxo-
bridged dimers {[η5-1,3-(Me3E)2C5H3]2U}2(µ-O)2 (E ) C,
Si).16-18 The imido derivatives 1 and 2 do not melt up
to 300 °C, but both yield dimeric molecular ions in their
mass spectra. Thus, the isoelectronic functional groups
O and NH yield dimeric metallocene derivatives, which
presumably have similar structures.
1
The H NMR spectra of the diamides 3 and 4 at 20
°C are well resolved; all of the expected resonances are
observed and the doublet splitting between the ortho
and meta protons on the p-tolyl groups are resolved. The
observation of the coupling, along with the relative
intensities, allows all of the resonances to be assigned,
including a resonance tentatively assigned to the NH
group. Thus, [η5-1,3-(Me3C)2C5H3]2U(NH-p-tolyl)2 (3)
has two broadened absorptions of relative area 2 at -2.6
(ν1/2 ) 8 Hz) and -68 ppm (ν1/2 ) 24 Hz) due to either
the Cp-ring CH or the NH groups, respectively. To
distinguish between these two alternative assign-
ments, the dibenzyl derivatives [η5-1,3-(Me3E)2C5H3]2U-
(CH2Ph)2 (E ) C (5), Si (6)) were prepared. The benzylic
CH2 groups in 5 and 6 and the p-tolylamido NH groups
in 3 and 4 should have a similar chemical shift, since
the origin of the chemical shifts in these f-element
compounds is largely determined by the dipolar contri-
bution; that is, those protons that have similar geo-
metrical orientations relative to the paramagnetic cen-
ter will have similar chemical shifts.20-22 The di-
benzyl derivatives 5 and 6 may be prepared from the
benzyl-Grignard reagent and the dichlorides, [η5-1,3-
(Me3E)2C5H3]2UCl2 (E ) C, Si);15 see Experimental
Section for details. The 1H NMR spectra are well
resolved, the couplings for the phenyl CH resonances
allow them to be assigned, and the other resonances
may be assigned on the basis of their relative intensities.
In the spectrum of [η5-1,3-(Me3C)2C5H3]2U(CH2Ph)2 (5),
a resonance at -72 ppm (ν1/2 ) 32 Hz) is assigned to
the benzylic CH2 group, which by inference suggests
that the resonance at -68 ppm in 3 is due to the NH
group. Unfortunately, a resonance due to the benzylic
CH2 group in 6 cannot be observed, so the NH resonance
at -34.7 ppm in 4 is only a tentative assignment.
The difference in behavior between ammonia and
p-toluidine is rather striking and difficult to interpret,
but several possible reasons may be suggested. The
thermodynamics of imide formation from the diamide
may be endoergic, the rates of elimination of CH4 and
RNH2 may be greatly different, or the hypothetical
p-tolylimide metallocenes may be unstable. The experi-
ments described in the next section begin to address
these differences.
2[1,3-(Me3E)2C5H3]2UMe2 + 2NH3 f
{[1,3-(Me3E)2C5H3]2U}2(µ-NH)
E ) C (1), Si (2)
2 + 4CH4 (1)
The 1H NMR spectra of the imido dimers 1 and 2 are
similar to each other and to those of the oxo-bridged
dimers.16,19 Thus, at room temperature the Me3C or
Me3Si resonances appear as two equal area resonances
and the ring-CH resonances appear as a pair of A2B
resonances; see Experimental Section for details. A
structure in which the rings on each metallocene frag-
ment are inequivalent and the metallocene fragments
in the dimer are related so that the dimer has averaged
C2h symmetry at this temperature is consistent with the
1H NMR spectra. Increasing the temperature results in
coalescence of the two Me3Si resonances and the pair
of A2B subspectra in 2, with a barrier (∆Gq at Tc ) 100
°C) of 16.9 kcal mol-1. This barrier is similar to that
found in the analogous oxo-bridged dimer.16 The Me3C
resonances in 1 do not coalesce by 100 °C, although the
resonances are moving toward each other. An intra-
molecular process that is responsible for the site ex-
change is Cp-ring oscillations about their pseudo-C5
axes, generating a dimer with time-averaged D2d sym-
metry, as suggested for the oxo- and fluoride-bridged
dimer.19
Two equivalents of p-toluidine react rapidly with [η5-
1,3-(Me3E)2C5H3]2UMe2 (E ) C, Si)15 in hexane to yield
the red diamide metallocenes [η5-1,3-(Me3E)2C5H3]2U-
(NH-p-tolyl)2 (E ) C (3), Si (4)), which may be crystal-
lized from pentane, eq 2. Using 1 equiv of p-toluidine
results in a 1H NMR spectrum that consists of the
Amides [η5-1,2,4-(Me3C)3C5H2]2U(HNR)2. The reac-
tion of [η5-1,2,4-(Me3C)3C5H2]2UMe2 with an excess of
ammonia was shown recently to give the bis-amide [η5-
(15) Lukens, W. W.; Beshouri, S. M.; Blosch, L. L.; Stuart, A. L.;
Andersen, R. A. Organometallics 1999, 18, 1235.
(16) Lukens, W. W.; Beshouri, S. M.; Blosch, L. L.; Andersen, R. A.
J. Am. Chem. Soc. 1996, 118, 901.
(17) Zalkin, A.; Beshouri, S. M. Acta Crystallogr. 1988, C44, 1826.
(18) 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.
(19) Lukens, W. W.; Beshouri, S. M. Stuart, A. L.; Andersen, R. A.
Organometallics 1999, 18, 1247.
(20) NMR of Paramagnetic Molecules; La Mar, G. N., Horrocks, W.
D., Holm, R. H., Eds; Academic Press: New York, 1973; Chapters 4
and 13.
(21) Organometallics of the f-Elements; Marks, T. J., Fischer, R. D.,
Eds; D. Reidel: Dordrecht, 1979; p 337.
(22) Fundamental and Technological Aspects of Organo-f-Element
Chemistry; Marks, T. J., Fragala, I. L., Eds; D. Reidel: Dordrecht, 1985;
p 229.

4604 Organometallics, Vol. 24, No. 19, 2005
Zi et al.
1,2,4-(Me3C)3C5H2]2U(NH2)2 (7).14 Excess primary amines
react with [η5-1,2,4-(Me3C)3C5H2]2UMe2 to give the bis-
amide metallocenes [η5-1,2,4-(Me3C)3C5H2]2U(HNR)2 (R
) Me (8), PhCH2 (9), p-tolyl (10)), Scheme 1. The rates
of the reaction qualitatively follow the order MeNH2 >
PhCH2NH2 . p-tolylNH2. Primary amines with bulky
substituents, such as Me2CHNH2 or Me3CNH2, do not
react with [η5-1,2,4-(Me3C)3C5H2]2UMe2 even at 65 °C.
All three bis-amides are soluble in pentane, from which
they may be crystallized in colors that range from yellow
(8) to red (10). The bis-amides have moderately high
melting points, they do not sublime but decompose
about 200 °C, and give [M - NHR]+ molecular ions in
their mass spectra. The latter data suggest that the
metallocene imide derivatives are accessible, on a
synthetic scale, by thermal loss of an amine. This
inference is shown to be correct by the following experi-
ments.
Scheme 1
much, suggesting that a single isomer is present but
that the Cp rings are still related by a mirror plane of
symmetry at -80 °C.
1
The H NMR spectrum of [η5-1,2,4-(Me3C)3C5H2]2U-
(NH-p-tolyl)2 (10) at 20 °C in C7D8 shows the Me3C
groups in a 2:1 relative area ratio, the ortho and meta
tolyl CH resonances as a pair of doublets, and the
methyl group as a singlet, Table 1. The Cp-ring CH and
tolyl NH resonances are not apparent. The spectrum is
consistent with a metallocene with time-averaged C2v
symmetry, as found in derivatives of the general for-
mula [η5-1,2,4-(Me3C)3C5H2]2UX2.14 Increasing the tem-
perature alters the appearance of the spectrum in the
following manner. The chemical shifts of the Me3C
groups change slightly and a new set of resonances in
a 2:1 relative area ratio appear upfield of the original
set, which decreases in intensity such that the total
intensity of both sets is constant. The new set of
resonances is due to the Me3C groups of [η5-1,2,4-
(Me3C)3C5H2]2UdN(p-tolyl) (12).14 Inspection of the
spectrum at 100 °C shows the resonances due to the
ortho and meta CH, and the para-Me groups on the tolyl
groups of the diamide (10) and imide (12), but the
resonances for free p-toluidine are not visible, perhaps
due to the small amount formed or chemical exchange.
At 100 °C, the ratio of 10 to 12 is approximately 6:1.
Cooling to 20 °C yields the original spectrum without
1
The variable-temperature H NMR behavior of [η5-
1,2,4-(Me3C)3C5H2]2U(NHMe)2 (8) (labeled A in Figure
1) is similar to that of the p-tolyl derivative 10. The
chemical shifts of the Me3C groups in relative ratio of
2:1 shift as a function of temperature, and by about 70
°C, the resonances due to the Me3C groups of [η5-1,2,4-
(Me3C)3C5H2]2UdNMe (11) (labeled B in Figure 1)
appear. Increasing the temperature to 100 °C changes
the relative intensity of these resonances until the
amide (8) to imide (11) ratio is approximately 4:1.
Thus, the equilibrium illustrated by eq 3 also operates
1
in this case. The low-temperature H NMR spectrum
of the diamide (8) is well behaved like the [η5-1,2,4-
(Me3C)3C5H2]2UX2 derivatives;14 the Me3C resonance of
relative area 2 decoalesces into two equal-area reaso-
nances and ∆Gq(Tc ) -70 °C) ) 12 kcal mol-1, es-
sentially identical to the values observed for [η5-1,2,4-
(Me3C)3C5H2]2UX2 (X ) F, Cl, N3).14 In addition, the
methyl resonance in the MeNH group broadens and
disappears by -60 °C.
Imides [η5-1,2,4-(Me3C)3C5H2]2UdNR. The mono-
meric p-tolylimide, [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl)
(12), was originally prepared by reaction of [η5-1,2,4-
(Me3C)3C5H2]2U(bipy) with p-tolyl azide.14 The imide 12
may also be prepared by two alternative synthetic
methods, i.e., heating an equimolar mixture of [η5-1,2,4-
(Me3C)3C5H2]2UMe2 and either [η5-1,2,4-(Me3C)3C5H2]2U-
(NH-p-tolyl)2 or p-toluidine in methylcyclohexane for
periods of 3-4 days. For amines that are liquids or
solids, the reaction of [η5-1,2,4-(Me3C)3C5H2]2UMe2 and
the amine is the most convenient synthetic route. In this
way, the p-substituted benzene derivatives, [η5-1,2,4-
(Me3C)3C5H2]2UdNR (R ) p-MeOC6H4 (13), p-Me2NC6H4
(14)), are prepared. When the amine is a gas, for
example, MeNH2, the best synthetic route is heating an
equimolar mixture of [η5-1,2,4-(Me3C)3C5H2]2UMe2 and
[η5-1,2,4-(Me3C)3C5H2]2U(NHMe)2 (8) at reflux in cyclo-
hexane. When the amine is ammonia, exchange does
not occur between [η5-1,2,4-(Me3C)3C5H2]2UMe2 and [η5-
1,2,4-(Me3C)3C5H2]2U(NH2)2 (7), as shown by monitoring
the 1H NMR spectrum, up to a temperature of 65 °C, or
by heating an equimolar mixture of the two metallo-
cenes at reflux in methylcyclohexane for 4 days. Fur-
thermore, the amide [η5-1,2,4-(Me3C)3C5H2]2U(NH2)2 (7)
does not eliminate ammonia on heating in refluxing
1
loss in absolute intensity. The reversibility of the H
NMR spectrum is consistent with the equilibrium shown
in eq 3.
[1,2,4-(Me3C)3C5H2]2U(NHR)2 h
[1,2,4-(Me3C)3C5H2]2UdNR + H2NR (3)
1
The changes in the H NMR spectrum on lowering
the temperature are not so readily interpreted, since
Me3C resonances that appear in a 2:1 area ratio at 20
°C do not simply decoalesce into three equal area
resonances as found in [η5-1,2,4-(Me3C)3C5H2]2UX2.14
The Me3C resonance at -4.6 ppm of relative area 1 at
20 °C moves upfield and broadens, while the resonance
at 2.5 ppm of relative area 2 broadens and disappears
by -10 °C. By -50 °C, two broad, approximately equal
area resonances emerge. On further cooling to -80 °C,
the upfield resonance disappears and does not reappear,
while the downfield resonance is very broad and appears
to be on the verge of decoalescing into two equal-area
resonances. During this process, neither the chemical
shift of the p-Me resonance nor its line width changes

Base-Free Uranium Methylimide
Organometallics, Vol. 24, No. 19, 2005 4605
Table 1. Physical Properties of Cp′2U(X)(Y), Cp′ ) 1,2,4-(CMe3)3C5H2
1H NMR (δ, 20 °C)a
compound
mp (°C)
(CH3)3C
(CH3)3C
-1.6 (4)
(CH3)3C
-1.6 (4)
ring CH
other
Cp′2U(NHMe)2 (8)
144-146 (dec)
3.9 (3)
-14.9 (4)
NH, -87.8 (135)
NCH3, 36.9 (11)
Cp′2U(NHCH2C6H5)2 (9)
160-162 (dec)
9.4 (6)
-2.1 (124)
-2.1 (124) -43.0 (110) PhCH2NH
CH2, 68.6 (300)
o-CH, 7.2 (t, J ) 7.5 Hz)
m-CH, 5.9 (m)
p-CH, 6.7 (t, J ) 7.5 Hz)
NH, -12.9 (330)
NH-p-tolyl
Cp′2U(NH-p-tolyl)2 (10)
231-239 (dec)
2.5 (5)
2.5 (5)
-4.2 (3)
b
b
o-CH,c 3.1 (d, J ) 8 Hz)
m-CH,c -16.2 (d, J ) 8 Hz)
CH3, 3.3 (6)
NHb
NCH3, 23.2 (275)
Cp′2UdNMe (11)
Cp′2UdN(p-C6H4OCH3) (13)
205-207
192-194
-8.0 (42)
-8.0 (42)
-19.1 (59)
-6.1 (146) -6.1 (146) -22.6 (97)
22.7 (170) N(p-C6H4OMe)
o-CH,c 28.9 (13)
m-CHc 24.2 (15)
OCH3, 11.7 (4)
Cp′2UdN(p-C6H4NMe2) (14)
190-192
-6.2 (170) -6.2 (170) -22.6 (115)
23.0 (216) N(p-C6H4NMe2)
o-CH,c 29.0 (d, J ) 5.1 Hz)
m-CH,c 24.2 (d, J ) 5.1 Hz)
N(CH3)2, 12.1 (5)
NCH3, 58.8 (10)
Cp′2U[N(Me)C(Me)dC(Me)] (15) 250-252
-2.6 (14)
-0.8 (36)
-2.6 (14)
-3.8 (7)
-0.9 (73)
-1.5 (90)
CH3, 37.2 (7)
CH3, 17.1 (5)
Cp′2U[N(Me)C(Ph)dC(Ph)] (16)
172-174
-3.1 (400)
-7.4 (160)
15.9 (26)
15.8 (29)
NCH3, 56.9 (41)
phenyl (1)
o-CH 11.2 (t, J ) 7.5 Hz)
m-CH, 7.0 (m)
p-CH, 10.0 (t, J ) 7.5 Hz)
phenyl (2)
o-CH, 0.9 (t, J ) 7.2 Hz)
m-CH, 1.2 (m)
p-CH, 0.6 (t, J ) 7.5 Hz)
a The chemical shifts are expressed in δ units with δ > 0 to downfield in C6D6 or C7D8 at 20 °C. The values in parentheses are the full
widths at half-maximum (Hz). b These resonances are not observed at room temperature. c The specific assignments are uncertain, although
the chemical shift values are not.
(Me3C)3C5H2]2U(NH2)2 (7), which is consistent with the
steric argument advanced above. When the number of
Me3C groups on the cyclopentadienyl ring is reduced,
i.e., [1,3-(Me3C)2C5H3]2U(NH-p-tolyl)2 (3), amine elimi-
nation does not occur because the intramolecular crowd-
ing is less and the elimination barrier is higher. This
implies that the geometry of the transition state for the
proton transfer is very sensitive to the intramolecular
steric effects at uranium.
The imides are all dark brown-red, high melting solids
that crystallize from pentane. They do not sublime, but
they yield monomeric molecular ions in their mass
spectra. The 20 °C 1H NMR spectra of imide derivatives
are well resolved, and all of the expected resonances,
except those for ring CH’s, are observed for metallocenes
with C2v symmetry, Table 1. However, their variable-
temperature 1H NMR spectra show that the cyclo-
pentadienyl rings and the tolyl rings are fluxional.
The variable-temperature 1H NMR spectra of the
series [η5-1,2,4-(Me3C)3C5H2]2UdN(p-RC6H4) (R ) Me
(12), OMe (13), Me2N (14)) are similar so only the Me2N
derivative, 14, is described in detail. In general, at 20
°C the Me3C resonances are in a 2:1 area ratio, and the
Cp-ring CH resonances are observed, as are the ortho
and meta benzene ring CHs’ and para R groups’
resonances, Table 1. In the case of R ) NMe2 (14), the
methyl groups (NMe2) appear as a single resonance,
indicating that all of the cyclopentadienyl and the imido
ligands are freely rotating and the molecule has aver-
Figure 1. Plots of δ versus 1/T for [η5-1,2,4-(Me3C)3C5H2]2U-
(NHMe)2 (8) in C7D8 (for Me3C, NH-Me, and N-Me groups).
cyclohexane or toluene. Thus, the simplest imido cannot
be made by these synthetic routes.
Formation of the imidometallocenes from the corre-
sponding diamide derivatives by elimination of an
amine, eq 3, is very dependent on the substituents on
the cyclopentadienyl ring and on the amide group. When
the cyclopentadienyl ligand is C5Me5, heating (η5-
C5Me5)2U(NHPh)2 does not yield an imide, whereas (η5-
C5Me5)2U(NH-2,6-xylyl)2 does.4,8 Thus, the thermal
elimination pathway presumably has a high kinetic
barrier that is lowered by increasing the steric bulk on
the aromatic ring in these C5Me5 derivatives. In the
metallocenes derived from 1,2,4-(Me3C)3C5H2, amine
elimination occurs for methyl- and phenyl-substituted
amides, but not with the simplest amide, [1,2,4-

4606 Organometallics, Vol. 24, No. 19, 2005
Zi et al.
Reactions of [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11).
Mixing experiments monitored by 1H NMR spectroscopy
at 20 °C were explored in order to compare the reaction
patterns of the methylimide 11 with those of the oxo-
metallocene [η5-1,2,4-(Me3C)3C5H2]2UO.14 The methyl-
imide 11 does not react with Me3SiX (X ) Cl, Br, I, CF3)
at 20 or 65 °C for time periods of up to 3 days. The lack
of reaction is in contrast with the instantaneous reaction
of the oxometallocene [η5-1,2,4-(Me3C)3C5H2]2UO with
these reagents. However, 11 reacts with Me3SiN3 to give
14
small amounts (20%) of [η5-1,2,4-(Me3C)3C5H2]2U(N3)2
over the course of 3 days at 65 °C. Imide 11 reacts
instantaneously with SiF4 or BF3(OEt2) to give [η5-1,2,4-
(Me3C)3C5H2]2UF214 as the only organometallic product
observed in the 1H NMR spectrum. The reactions of
SiCl4 or SiBr4 are much slower; the final product in each
case is [η5-1,2,4-(Me3C)3C5H2]2UX2 after 4 or 10 days
14
when X ) Cl or Br, respectively. A similar pattern is
observed for the oxometallocene, [η5-1,2,4-(Me3C)3C5H2]2-
UO,14 but the rates for the methylimide are much
slower. Thus, the nitrogen atom in 11 is a poorer nucleo-
phile than is the oxygen atom in the oxometallocene,
[η5-1,2,4-(Me3C)3C5H2]2UO.
As observed previously, [η5-1,2,4-(Me3C)3C5H2]2Ud
N(p-tolyl) (12) reacts on mixing with Ph2CO to give the
oxometallocene, [η5-1,2,4-(Me3C)3C5H2]2UO, and Ph2Cd
N(p-tolyl).14 The methylimide 11 behaves similarly,
giving the oxometallocene, [η5-1,2,4-(Me3C)3C5H2]2UO,
and Ph2CdNMe, eq 4. Addition of pyridine-N-oxide to
11 in C6D6 results in rapid disappearance of the
resonances due to 11 and formation of resonances due
to (2,3,5-(Me3C)3C5H2)2 in quantitative yield. A similar
pattern is observed for the oxometallocene, [η5-1,2,4-
(Me3C)3C5H2]2UO, and the imido metallocene 12.14 The
cyclopentadienyl ring coupling product was observed in
the reaction of (η5-C5Me5)2U(NPh)(py) with pyridine-N-
oxide, which gives a mixture of (η5-C5Me5)2U(NPh)2,
(C5Me5)2, and “UO2”.4 However, the methylimide 11 does
not react with Ph3PE (E ) O, S, Se) nor with pyridine,
4-Me2NC5H4N, or PhCl.
Figure 2. (a) Plots of δ versus 1/T for [η5-1,2,4-(Me3C)3-
C5H2]2UdN(p-Me2NC6H4) (14) in C7D8 (for Me3C groups).
(b) Plots of δ versus 1/T for [η5-1,2,4-(Me3C)3C5H2]2UdN(p-
Me2NC6H4) (14) in C7D8 (for Me2N, aryl, and Cp-ring CH
groups).
aged C2v symmetry. Increasing the temperature has the
usual effect; that is, the chemical shifts of all of the
resonances follow a Curie Law dependence. Lowering
the temperature is, however, more informative. A plot
of the chemical shift of the Me3C and Me2N resonances
as a function of T-1 for [η5-1,2,4-(Me3C)3C5H2]2UdN(p-
Me2NC6H4) (14) is shown in Figures 2a and 2b. On
cooling from 20 °C to -10 °C, the Me3C (labeled A in
Figure 2a) and the Cp′-ring CH resonances broaden and
disappear. By -40 °C, the Me3C resonances emerge as
three very broad equal-area resonances (labeled B in
Figure 2a). By -60 °C, all of the resonances are visible
and the Me3C resonances are well defined; however, the
three Me3C resonances do not have a common parent,
as illustrated in Figure 2a. At -60 °C and below, the
Cp-ring and benzene-CH’s are inequivalent, as are the
NMe2 resonances, as shown in Figure 2b. This behavior
is consistent with a molecule with time-averaged Cs
symmetry, where the plane of symmetry contains the
NC6H4NMe2 ligand in which the site exchange between
the ortho and meta CH’s and the NMe2’s is stopped. The
time-averaged plane of symmetry interconverts the two
1,2,4-(Me3C)3C5H2 rings, and these rings are still un-
dergoing oscillations about their pseudo-C5 axes, which
is presumably the reason the Me3C resonances do not
have a common parent. Cooling to -85 °C broadens the
Me3C and Cp′-ring CH resonances further, consistent
with slowing but not stopping the ring oscillations.
[1,2,4-(Me3C)3C5H2]2U)NMe + Ph2CO f
[1,2,4-(Me3C)3C5H2]2UO + Ph2CdNMe (4)
Neither the p-tolylimidometallocene, [η5-1,2,4-(Me3C)3-
C5H2]2UdN(p-tolyl) (12), nor the oxometallocene, [η5-
1,2,4-(Me3C)3C5H2]2UO, reacts with diphenyl- or di-
methylacetylene.14 In contrast, the methylimide 11
reacts on time of mixing to form the cycloaddition
products [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(R′)dC(R′)]
(R′ ) Me (15), Ph (16)), Scheme 2. The silylacetylene,
Me3SiCtCSiMe3, does not change the chemical shifts
of 11, but phenylacetylene yields (Me3C)3C5H3. The
cycloaddition products 15 and 16 may also be obtained
by addition of the acetylenes to [η5-1,2,4-(Me3C)3C5H2]2U-
(NHMe)2 (8), a reaction that is consistent with the
equilibrium illustrated in eq 3. The cycloaddition prod-
ucts 15 and 16 are soluble in pentane, and they may be
crystallized from that solvent. They are high-melting
solids, do not sublime, but yield molecular ions in their
mass spectra. An ORTEP diagram of 15 is shown in
Figure 3. The terminal MeN and MeC groups are
disordered (the disorder model is described in the
Experimental Section), but the crystal structure analy-
1
The variable-temperature H NMR behavior of [η5-
1,2,4-(Me3C)3C5H2]2UdNMe (11) in C7D8 is qualitatively
similar to that observed in the arylimide metallocenes.
Thus, the Me3C resonances broaden, disappear, and
then reappear as three equal-area resonances, without
a common parent, implying that the fluxional motion
is not stopped by -80 °C. The MeN resonance disap-
pears by -40 °C and does not reappear.

Base-Free Uranium Methylimide
Organometallics, Vol. 24, No. 19, 2005 4607
Scheme 2
sis shows that it is a cycloaddition product, not an
acetylene adduct of the imide 11.
The H NMR spectrum of [η5-1,2,4-(Me3C)3C5H2]2U-
1
Figure 4. (a) Plots of δ versus 1/T for [η5-1,2,4-(Me3C)3-
C5H2]2U[N(Me)C(Ph)dC(Ph)] (16) in C7D8 (for MeN, Me3C,
and Cp-ring CH groups). (b) Plots of δ versus 1/T for [η5-
1,2,4-(Me3C)3C5H2]2U[N(Me)C(Ph)dC(Ph)] (16) in C7D8 (for
phenyl CH groups).
[N(Me)C(Me)dC(Me)] (15) at 20 °C in C7D8 shows the
Me3C groups in a 2:1 area ratio, but the Cp-ring CH
groups are inequivalent, Table 1. The reason for this
apparent contradiction is that the Me3C resonance of
relative area 2 is composed of two equal-area resonances
that are accidentally degenerate at 20 °C. Increasing
the temperature removes this degeneracy, and at 35 °C
the Me3C resonances appear as three equal-intensity
resonances; the Cp-ring CH resonances are inequiva-
lent, as are the CMe resonances. Thus, the cycloaddition
product 15 has Cs symmetry, the MeC groups are not
undergoing site exchange, but the Cp rings are under-
going rotation or oscillation about their pseudo-C5 axes
that generates a time-averaged plane of symmetry.
Lowering the temperature results in disappearance of
Cp-ring CH resonances as the Me3C resonances broaden.
Broadening of the latter resonances increases with
decreasing temperature until three approximately equal
area resonances appear with widely different line
widths at -75 °C. The MeN resonance and both of the
MeC resonances remain sharp, which implies that a
single isomer is present, which further implies that the
oscillations of the Cp rings about their pseudo-C5 axes
are slowed but not stopped at -75 °C.
The cycloaddition product 15 does not undergo intra-
molecular site exchange to 100 °C, since the individual
MeC resonances do not coalesce. Intermolecular site
exchange is also slow since addition of dimethylacet-
ylene or diphenylacetylene does not lead to exchange
up to 100 °C. Hence, the dynamic behavior described
above is due to intramolecular fluxions of the cyclopen-
tadienyl rings. This fluxional motion is clarified by
examination of the low-temperature 1H NMR spectrum
of the diphenylacetylene cycloaddition product 16.
1
The 20 °C H NMR spectrum of 16 in C7D8 shows
three equal-area Me3C resonances (labeled A in Figure
4a) and two inequivalent Cp-ring CH resonances. The
two chemically inequivalent phenyl rings are freely
rotating, since the ortho and meta CH’s are equivalent;
the chemical shifts are given in Table 1. On cooling, the
three Me3C resonances broaden and decoalesce, and by
-80 °C, they appear as five resonances in a 9:9:18:9:9
Figure 3. ORTEP drawing of [η5-1,2,4-(Me3C)3C5H2]2U-
[N(Me)C(Me)dC(Me)] (15) with 35% thermal ellipsoids.
Selected bond lengths (Å) and angles (deg): Cp′(cent)-U1
2.55 and 2.56, U1-N1/C40 2.202(6), U1-C3/N2 2.270(6),
C2-N1/C40 1.410(9), C2-C3/N2 1.390(9), Cp′(cent)-U1-
Cp′(cent) 138.7, N1/C40-U1-C3/N2 65.1(2), N1/C40-C2-
C3/N2 118.5(7).

4608 Organometallics, Vol. 24, No. 19, 2005
Zi et al.
Scheme 3
area ratio (labeled B in Figure 4a). The ring CH
resonances broaden, shift downfield, and emerge as a
pair of broadened singlets with the relative area ratio
2:2, which implies that their chemical shift difference
is small. This behavior is shown graphically in Figure
4a. The Cp rings are inequivalent, and only a single
isomer is observed since the MeN resonance is a sharp
singlet throughout the temperature study. The benzene
ring CH groups are also resolved into eight resonances
in a 1:1:1:1:1:1:2:2 area ratio by -80 °C (Figure 4b),
consistent with a molecule without symmetry. Ten
equal-area resonances should be observed, but two are
accidentally degenerate. Thus, the diphenylacetylene
cycloaddition product 16 is sufficiently sterically crowded
that the intramolecular barriers to Cp-ring fluxions and
C-Ph rotations are sufficiently high that these motions
are stopped by -80 °C.
followed by two successive proton transfer reactions that
liberate the azomethines and form [η5-1,2,4-(Me3C)3-
C5H2]2U(NHMe)2 (8), Scheme 3. Since the diamide 8 is
in equilibrium with the imide 11, the diamide 8 is a
catalyst for the hydroamination of an internal acetylene.
This reaction pattern was discovered by Eisen, using
(η5-Me5C5)2U(NHR)2 and terminal acetylenes, though
the cycloaddition product was not observed.10 Replacing
the (η5-Me5C5)2U fragment with [η5-1,2,4-(Me3C)3C5H2]2U
yields the diamide (8), imide (11), and the cycloaddition
products with RCtCR (R ) Me (15), Ph (16)) as isolable,
crystalline solids. The essential steps in the hydro-
amination of internal acetylene are established by
In summary, the different reactivity patterns ob-
served for [η5-1,2,4-(Me3C)3C5H2]2UO14 and [η5-1,2,4-
(Me3C)3C5H2]2UdNMe (11) are striking, given the fact
that O and NMe are isolobal, but with different electro-
negativities and steric effects. Steric differences should
be minor, but this difference is difficult to evaluate and
steric effects could be the principle reason that [η5-1,2,4-
(Me3C)3C5H2]2UdN(p-tolyl) (12) does not react with
internal acetylenes whereas [η5-1,2,4-(Me3C)3C5H2]2Ud
NMe (11) does. Our current qualitative model traces the
different reactivity patterns to the nature of the multiple
bond between the metallocene uranium and the O/NMe
fragments. The general reactivity pattern is that the
oxometallocene, [η5-1,2,4-(Me3C)3C5H2]2UO, reacts rap-
idly with electron-poor substrates, such as Me3SiX, to
yield addition products, but does not react with internal
acetylenes.14 In contrast, the methylimidometallocene,
[η5-1,2,4-(Me3C)3C5H2]2UdNMe (11), does not react with
Me3SiX (except Me3SiN3) but does react with more
electron-rich reagents, such as internal acetylenes.
A model that rationalizes this behavior is that the
uranium-oxygen bond is better represented by the
polar resonance structure U+-O-, which emphasizes
the electronegativity of the oxygen atom and therefore
nucleophilicity,14 whereas the uranium-nitrogen bond
is better represented by the double-bond resonance
structure UdNMe, consistent with the lower electro-
negativity of the NMe group, and therefore lower
nucleophilicity. These resonance structures emphasize
the differences in local charges on the atoms in their
ground states, but the general concept of atom electro-
negativity in conjugation with the electroneutrality
principle23 is a qualitatively useful model that accounts
for the reactivity patterns observed for [η5-1,2,4-
(Me3C)3C5H2]2UE (E ) O, NMe).
1
monitoring the H NMR spectra of the isolated solid 8
as it proceeds to 11 and then to 15 and the azomethine.
The suggested mechanism for the reaction of the cyclo-
addition product 15 with MeNH2 is shown in Scheme
3. On the right-hand side is the pathway suggested by
Eisen,10 and on the left-hand side is a pathway origi-
nally suggested by Bergman for the catalytic reaction
between (η5-C5H5)2Zr(NHR)2 and an acetylene,26 which
is adapted for the uranium metallocenes. We have no
information to distinguish between these two pathways
1
since these intermediates are not observed in the H
NMR spectra. Unfortunately, the simplest diamide, [η5-
1,2,4-(Me3C)3C5H2]2U(NH2)2 (7), does not react with
either acetylene, presumably because the equilibrium
illustrated in eq 3 lies to the left.
Conclusions
Amine elimination occurs from [1,2,4-(Me3C)3C5H2]2U-
(NHMe)2 (8) and [1,2,4-(Me3C)3C5H2]2U(NH-p-tolyl)2
(10), while not from [1,2,4-(Me3C)3C5H2]2U(NH2)2 (7)
and [1,3-(Me3C)2C5H3]2U(NH-p-tolyl)2 (3). These results
show that formation of the imidometallocenes from the
corresponding diamide derivatives by elimination of an
amine is very sensitive to the intramolecular steric
effects at uranium. The equilibrium illustrated in eq 3,
which was discovered by examining the variable-
temperature behavior of the 1H NMR spectra of the
diamides, is the key discovery, since it leads to a simple
synthesis of the imide [η5-1,2,4-(Me3C)3C5H2]2UdNMe
(11), which in turn leads to the development of the
catalytic hydroamination of the internal acetylenes.27
Hydroamination. In mixing experiments monitored
by 1H NMR spectroscopy at 20 °C, the resonances of the
cycloaddition products [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C-
(R′)dC(R′)] (R′ ) Me (15), Ph (16)) disappear when
excess MeNH2 is added, while resonances due to [η5-
1,2,4-(Me3C)3C5H2]2U(NHMe)2 (8) and the azomethine
derivatives MeNdC(R′)CH2R′ (R ) Me, Ph)24,25 appear
in the spectra. The azomethine derivatives result from
the addition of methylamine to the cycloaddition product
(23) Pauling, L. The Nature of the Chemical Bond; Connell Univer-
sity Press: Ithaca, NY, 1960; pp 64 and 172.
(24) Karabatsos, G. J.; Lande, S. S. Tetrahedron 1968, 24, 3907.
(25) Ahlbrecht, H.; Fischer, S. Tetrahedron 1970, 26, 2837.
(26) Walsh, P. J.; Baranger, A. M.; Bergman, R. G. J. Am. Chem.
Soc. 1992, 114, 1708.
(27) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673, and
references therein.

Base-Free Uranium Methylimide
Organometallics, Vol. 24, No. 19, 2005 4609
NH, 3335 (s) cm-1. Anal. Calcd for C44H86N2Si8U2: C, 39.3; H,
6.45; N, 2.08. Found: C, 39.3; H, 6.15; N, 1.98.
The methylimidometallocene [η5-1,2,4-(Me3C)3-
C5H2]2UdNMe (11) does not show nucleophilic behavior,
in contrast to [η5-1,2,4-(Me3C)3C5H2]2UO,14 but it does
undergo cycloaddition reactions that [η5-1,2,4-(Me3C)3-
C5H2]2UO does not.14 This implies that the uranium-
nitrogen bond is better represented by the double-bond
resonance structure UdNMe, whereas the uranium-
oxygen bond is better represented by the polar reso-
nance structure U+-O-.14 Further studies designed to
test this model are underway.
Preparation of [η5-1,3-(Me3C)2C5H3]2U(NH-p-tolyl)2 (3).
To a hexane (30 mL) solution of [η5-1,3-(Me3C)2C5H3]2UMe2
(2.0 g, 3.2 mmol) was added a hexane (20 mL) solution of
p-toluidine (0.69 g, 6.4 mmol) with stirring at room temper-
ature. The solution was stirred for 12 h at room temperature
and filtered. The volume of the filtrate was reduced to 5 mL
and cooled to -80 °C, yielding orange-red microcrystals, which
were isolated by filtration. Yield: 1.9 g (74%). The product
sublimed at 145 °C in diffusion pump vacuum. 1H NMR
(C6D6): δ 5.2 (d, J ) 7 Hz, 4H, tolyl H), 4.6 (6H, ν1/2 ) 3 Hz,
CH3), 0.32 (36H, ν1/2 ) 8 Hz, (CH3)3C), -2.6 (2H, ν1/2 ) 8 Hz,
Experimental Section
ring CH), -14.2 (d, J ) 7 Hz, 4H, tolyl H), -16.0 (4H, v1/2
)
8 Hz, ring CH), -68.1 (2H, ν1/2 ) 24 Hz, NH). Mp: 152-153
°C. EI-MS [M+], m/z (calcd, found): 804 (100, 100), 805 (46,
39), 806 (10, 10). IR: ν NH, 3358 (s) cm-1. Anal. Calcd for
C40H58N2U: C, 59.7; H, 7.26; N, 3.48. Found: C, 59.4; H, 7.25;
N, 3.25.
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. MeCtCMe was freshly distilled from sodium
immediately prior to use. Me3SiX (X ) Cl, Br, I, N3) were dis-
tilled under nitrogen before using. PhCtCPh, p-MeC6H4NH2,
p-MeOC6H4NH2, and p-Me2NC6H4NH2 were sublimed before
using. [η5-1,3-(Me3C)2C5H3]2UCl2,15 [η5-1,3-(Me3Si)2C5H3]2-
UCl2,15 [η5-1,3-(Me3C)2C5H3]2UMe2,15 [η5-1,3-(Me3Si)2C5H3]2-
UMe2,15 [η5-1,2,4-(Me3C)3C5H2]2UMe2,14 and [η5-1,2,4-(Me3C)3-
C5H2]2U(NH2)214 (7) were prepared according to the literature
methods. All other chemicals were purchased from Aldrich
Chemical Co. used as received unless otherwise noted. Infrared
spectra were obtained as Nujol mulls on CsI windows. 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.
Preparation of [η5-1,3-(Me3Si)2C5H3]2U(NH-p-tolyl)2 (4).
This compound was prepared as orange-red microcrystals from
the reaction of [η5-1,3-(Me3Si)2C5H3]2UMe2 (2.0 g, 2.9 mmol)
and p-toluidine (0.62 g, 5.8 mmol) in hexane (50 mL) by
procedures similar to those used in the synthesis of [η5-1,3-
(Me3C)2C5H3]2U(NH-p-tolyl)2 (3). Yield: 2.0 g (79%). 1H NMR
(C6D6): δ 4.5 (d, J ) 7 Hz, 4H, tolyl H), 4.3 (6H, ν1/2 ) 3 Hz,
CH3), 0.41 (36H, ν1/2 ) 4 Hz, (CH3)3Si), -9.9 (2H, ν1/2 ) 6 Hz,
ring CH), -15.0 (4H, ν1/2 ) 4 Hz, ring CH), -18.0 (d, J ) 7
Hz, 4H, tolyl H), -34.7 (2H, ν1/2 ) 19 Hz, NH). Mp: 156-158
°C. EI-MS [M+], m/z (calcd, found): 868 (100, 100), 869 (62,
58), 870 (32, 28), 871 (11, 9), 872 (3, 2). IR: ν NH, 3358 (s)
cm-1. Anal. Calcd for C36H58N2Si4U: C, 49.7; H, 6.73; N, 3.22.
Found: C, 49.5; H, 6.67; N, 3.15.
Reaction of [η5-1,3-(Me3C)2C5H3]2U(NH-p-tolyl)2 (3) or
[η5-1,3-(Me3Si)2C5H3]2U(NH-p-tolyl)2 (4) with Tetrahydro-
furan or Me3PO. NMR Scale. To an NMR tube charged with
[η5-1,3-(Me3C)2C5H3]2U(NH-p-tolyl)2 (3) or [η5-1,3-(Me3Si)2-
C5H3]2U(NH-p-tolyl)2 (4) (15 mg) and C6D6 (0.5 mL) was added
an excess of tetrahydrofuran or Me3PO. In each case, the
1
Preparation of {[η5-1,3-(Me3C)2C5H3]2U}2(µ-NH)2 (1). In
a 250 mL flask, [η5-1,3-(Me3C)2C5H3]2UMe2 (1.0 g, 1.6 mmol)
was dissolved in diethyl ether (50 mL). The headspace of the
flask was evacuated and replaced with 1 atm of NH3 (dried
over sodium metal at -35 °C). During the course of the
reaction, the color of the solution changed from red to brown-
red and a purple-red precipitate formed. After the solution was
stirred for 12 h at room temperature, the solvent was removed.
The purple-red residue was extracted with tetrahydrofuran
(25 mL × 2) and filtered. The volume of the filtrate was
reduced to 10 mL and cooled to -20 °C, yielding purple-red
microcrystals, which were isolated by filtration. Yield: 0.88 g
sample was monitored periodically by H NMR spectroscopy,
and the spectrum did not show any change when heated at
65 °C for 3 days.
Preparation of [η5-1,3-(Me3C)2C5H3]2U(CH2C6H5)2 (5).
To a diethyl ether (100 mL) solution of [η5-1,3-(Me3C)2C5H3]2-
UCl2 (3.0 g, 4.5 mmol) was added a diethyl ether (8.8 mL)
solution of PhCH2MgCl (1.05 M in diethyl ether; 9.2 mmol)
with stirring at room temperature. After the solution was
stirred for 12 h at room temperature, the solvent was removed.
The dark residue was extracted with pentane (25 mL × 2) and
filtered. The volume of the filtrate was reduced to 25 mL and
cooled to -80 °C, yielding black microcrystals, which were
1
1
(91%). H NMR (C6D6): δ 35.5 (1H, ν1/2 ) 110 Hz, ring CH),
isolated by filtration. Yield: 2.2 g (64%). H NMR (C6D6): δ
33.2 (1H, ν1/2 ) 100 Hz, ring CH), 20.0 (2H, ν1/2 ) 45 Hz, ring
CH), 10.0 (2H, ν1/2 ) 50 Hz, ring CH), -10.9 (18H, ν1/2 ) 25
Hz, (CH3)3C), -11.4 (18H, ν1/2 ) 30 Hz, (CH3)3C); protons of
NH were not observed. Mp: > 300 °C. EI-MS [M+], m/z (calcd,
found): 1213 (60, 58), 1214 (100, 100), 1215 (20, 18), 1216 (6,
4). IR: ν NH, 3321 (s) cm-1. Anal. Calcd for C52H86N2U2: C,
51.4; H, 7.13; N, 2.31. Found: C, 51.2; H, 7.10; N, 1.98.
Preparation of {[η5-1,3-(Me3Si)2C5H3]2U}2(µ-NH)2 (2).
This compound was prepared as purple microcrystals from the
reaction of [η5-1,3-(Me3Si)2C5H3]2UMe2 (1.0 g, 1.46 mmol) and
excess NH3 in diethyl ether (50 mL) by procedures similar to
those used in the synthesis of {[η5-1,3-(Me3C)2C5H3]2U}2(µ-
NH)2 (1). Yield: 0.91 g (93%). 1H NMR (C6D6): δ 40.5 (1H, ν1/2
) 72 Hz, ring CH), 33.1 (2H, ν1/2 ) 59 Hz, ring CH), 23.0 (1H,
ν1/2 ) 62 Hz, ring CH), 15.0 (2H, ν1/2 ) 85 Hz, ring CH), -9.78
(18H, ν1/2 ) 43 Hz, (CH3)3Si), -11.6 (18H, ν1/2 ) 48 Hz,
(CH3)3Si); protons of NH were not observed. Mp: > 300 °C.
EI-MS [M+], m/z (calcd, found): 1342 (100, 100), 1343 (91, 92),
1344 (67, 55), 1345 (35, 29), 1346 (15, 11), 1347 (6, 4). IR: ν
33.0 (2H, ν1/2 ) 26 Hz, ring CH), 8.16 (t, J ) 7 Hz, 4H, phenyl
H), 2.08 (t, J ) 7 Hz, 2H, phenyl H), 0.26 (36H, ν1/2 ) 5 Hz,
(CH3)3C), -2.56 (d, J ) 7 Hz, 4H, phenyl H), -36.4 (4H, ν1/2
)
46 Hz, ring CH), -72.2 (4H, ν1/2 ) 32 Hz, PhCH2). Mp: 113-
114 °C. EI-MS: m/z 683 [M - PhCH2]+. Anal. Calcd for
C40H56U: C, 62.0; H, 7.28. Found: C, 61.9; H, 7.24.
Preparation of [η5-1,3-(Me3Si)2C5H3]2U(CH2C6H5)2 (6).
This compound was prepared as black microcrystals from the
reaction of [η5-1,3-(Me3Si)2C5H3]2UCl2 (1.0 g, 1.37 mmol) and
PhCH2MgCl (2.7 mL, 1.05 M in diethyl ether; 2.8 mmol) in
diethyl ether (50 mL) by procedures similar to those used in
the synthesis of [η5-1,3-(Me3C)2C5H3]2U(CH2C6H5)2 (5). Yield:
1
0.62 g (54%). H NMR (C6D6): δ 19.9 (4H, ν1/2 ) 19 Hz, ring
CH), 7.83 (t, J ) 7 Hz, 4H, phenyl H), 0.40 (t, J ) 7 Hz, 2H,
phenyl H), -0.75 (36H, ν1/2 ) 15 Hz, (CH3)3Si), -5.72 (d, J )
7 Hz, 4H, phenyl H), -37.0 (2H, ν1/2 ) 35 Hz, ring CH); protons
of PhCH2 were not observed. Mp: 116-118 °C. EI-MS: m/z
747 [M - PhCH2]+. Anal. Calcd for C36H56Si4U: C, 51.5; H,
6.73. Found: C, 51.2; H, 6.60.

4610 Organometallics, Vol. 24, No. 19, 2005
Zi et al.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(NHMe)2 (8). In
a 250 mL flask, [η5-1,2,4-(Me3C)3C5H2]2UMe2 (1.0 g, 1.36 mmol)
was dissolved in toluene (50 mL). The headspace of the flask
was evacuated and replaced with 1 atm of MeNH2 (dried over
sodium metal at -5 °C). During the course of the reaction,
the color of the solution changed from red to yellow. 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: 0.75 g (72%).
EI-MS: m/z 734 [M - CH3NH]+. Anal. Calcd for C36H66N2U:
C, 56.5; H, 8.70; N, 3.66. Found: C, 56.2; H, 8.74; N, 3.37.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(NHCH2C6H5)2
(9). C6H5CH2NH2 (0.30 mL, 2.72 mmol) was added to a toluene
(20 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2UMe2 (1.0 g, 1.36
mmol) with stirring at room temperature. After the solution
was stirred overnight at 40 °C in a water bath, the solvent
was removed. The brown-yellow residue was extracted with
pentane (25 mL × 2) and filtered. The volume of the filtrate
was reduced to 5 mL and cooled to -20 °C, yielding brown-
yellow crystals, which were isolated by filtration. Yield: 0.80
g (64%). EI-MS: m/z 811 [M - C6H5CH2NH]+. Anal. Calcd for
C48H74N2U: C, 62.9; H, 8.13; N, 3.05. Found: C, 62.6; H, 8.41;
N, 2.98.
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: 0.81 g (75%). EI-MS [M+], m/z
(calcd, found): 825 (100, 100), 826 (47, 45), 827 (10, 10), 828
(2, 1). Anal. Calcd for C41H65NOU: C, 59.6; H, 7.93; N, 1.70.
Found: C, 59.3; H, 8.00; N, 1.64.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-C6H4NMe2)
(14). This compound was prepared as dark brown crystals from
the reaction of [η5-1,2,4-(Me3C)3C5H2]2UMe2 (1.0 g, 1.36 mmol)
and p-Me2NC6H4NH2 (0.18 g, 1.32 mmol) in toluene (30 mL)
by procedures similar to those used in the synthesis of [η5-
1,2,4-(Me3C)3C5H2]2UdN(p-C6H4OCH3) (13). Yield: 0.77 g
(70%). EI-MS [M+], m/z (calcd, found): 838 (100, 100), 839 (48,
48), 840 (11, 10), 841 (2, 2). Anal. Calcd for C42H68N2U: C,
60.1; H, 8.17; N, 3.34. Found: C, 59.7; H, 8.36; N, 3.34.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Me)d
C(Me)] (15). Method A. 2-Butyne (2.0 mL, 26 mmol) was
added to a toluene (20 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2U-
(NHMe)2 (8; 1.0 g, 1.3 mmol) with stirring at room tempera-
ture. During the course of the reaction, the color of the solution
changed from yellow to brown-red. After the solution was
stirred for 3 days at room temperature, the 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
crystals, which were isolated by filtration. Yield: 0.77 g (75%).
EI-MS [M+], m/z (calcd, found): 787 (100, 100), 788 (44, 45),
789 (10, 10), 790 (1, 1); the parent ion is [M - Me2C2]+. Anal.
Calcd for C39H67NU: C, 59.5; H, 8.58; N, 1.78. Found: C, 59.3;
H, 8.69; N, 1.71.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U(NH-p-tolyl)2
(10). To a hexane (30 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2-
UMe2 (2.0 g, 2.72 mmol) was added a hexane (20 mL) solution
of p-toluidine (0.61 g, 5.7 mmol) with stirring at room tem-
perature. The solution was heated at reflux for 1 day with
stirring 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: 1.6 g (65%). EI-MS: m/z 811
[M - tolylNH]+. IR: ν NH, 3280 (s), 3260 (s) cm-1. Anal. Calcd
for C48H74N2U: C, 62.9; H, 8.13; N, 3.05. Found: C, 62.7; H,
8.36; N, 3.21.
Method B. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UdNMe (11; 15 mg, 0.02 mmol) and C6D6
(0.5 mL) was added an excess of 2-butyne. The color of the
solution immediately changed from dark brown to brown-red,
and resonances due to 15 were observed by 1H NMR spectros-
copy (100% conversion).
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UdNCH3 (11). To
a cyclohexane (20 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2UMe2
(1.0 g, 1.36 mmol) was added a cyclohexane (20 mL) solution
of [η5-1,2,4-(Me3C)3C5H2]2U(NHCH3)2 (8; 1.04 g, 1.36 mmol)
with stirring at room temperature. After the solution was
heated at reflux for 4 days with stirring, the solvent was
removed. The dark brown residue was extracted with pentane
(25 mL × 2) and filtered. The volume of the dark brown
solution was reduced to 5 mL and cooled to -20 °C, yielding
dark brown crystals, which were isolated by filtration. Yield:
1.4 g (70%). EI-MS [M+], m/z (calcd, found): 733 (100, 100),
734 (40, 38), 735 (8, 8), 736 (1, 2). Anal. Calcd for C35H61NU:
C, 57.3; H, 8.38; N, 1.91. Found: C, 56.9; H, 7.99; N, 1.65.
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl)14
(12). Modified Method A. To a methylcyclohexane (20 mL)
solution of [η5-1,2,4-(Me3C)3C5H2]2UMe2 (0.81 g, 1.1 mmol) was
added a methylcyclohexane (20 mL) solution of [η5-1,2,4-
(Me3C)3C5H2]2U(NH-p-tolyl)2 (10; 1.0 g, 1.1 mmol) with stirring
at room temperature. After the solution was heated at reflux
for 4 days with stirring, the solvent was removed. The dark
brown 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 identified as 12 by 1H NMR spectroscopy.14 Yield:
1.0 g (56%).
Preparation of [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Ph)d
C(Ph)] (16). Method A. To a toluene (10 mL) solution of [η5-
1,2,4-(Me3C)3C5H2]2UdNMe (11; 1.8 g, 2.45 mmol) was added
a toluene (10 mL) solution of diphenylacetylene (0.44 g, 2.47
mmol) with stirring at room temperature. After the solution
was stirred overnight at 40 °C in a water bath, the solvent
was removed. The brown-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 brown-
red microcrystals, which were isolated by filtration. Yield: 1.65
g (74%). EI-MS [M+], m/z (calcd, found): 911 (100, 100), 912
(56, 54), 913 (15, 15), 914 (3, 3); the parent ion is [M - Ph2C2]+.
Anal. Calcd for C49H71NU: C, 64.5; H, 7.85; N, 1.54. Found:
C, 64.2; H, 8.14; N, 1.84.
Method B. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2U(NHMe)2 (8; 15 mg, 0.02 mmol) and C6D6
(0.5 mL) was added diphenylacetylene (6 mg, 0.03 mmol). The
color of the solution slowly (2 h) changed from yellow to brown-
1
red at 40 °C, and resonances due to 16 were observed by H
NMR spectroscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Me)d
C(Me)] (15) with MeNH2. NMR Scale. To an NMR tube
charged with [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Me)dC(Me)]
(15; 16 mg, 0.02 mmol) and C6D6 (0.5 mL) was added an excess
of MeNH2. The color of the solution immediately changed from
brown-red to yellow, and resonances due to [η5-1,2,4-(Me3C)3-
C5H2]2U(NHMe)2 (8) along with MeNdC(Me)(CH2Me)24 were
Method B. [η5-1,2,4-(Me3C)3C5H2]2UMe2 (2.0 g, 2.72 mmol)
and p-toluidine (0.28 g, 2.6 mmol) were heated together in
methylcyclohexane (30 mL) as in the above method, which
gave 12 in 68% yield (1.4 g).
1
observed by H NMR spectroscopy (100% conversion).
Preparation of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-C6H4OCH3)
(13). To a toluene (20 mL) solution of [η5-1,2,4-(Me3C)3C5H2]2-
UMe2 (1.0 g, 1.36 mmol) was added a toluene (10 mL) solution
of p-anisidine (0.16 g, 1.30 mmol) with stirring at room
temperature. After the solution was heated at reflux for 4 days
with stirring, the solvent was removed. The dark brown
Reaction of [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Ph)d
C(Ph)] (16) with MeNH2. NMR Scale. To an NMR tube
charged with [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Ph)dC(Ph)]
(16; 18 mg, 0.02 mmol) and C6D6 (0.5 mL) was added an excess
of MeNH2. The color of the solution immediately changed from
brown-red to yellow, and resonances due to [η5-1,2,4-(Me3C)3-

Base-Free Uranium Methylimide
Organometallics, Vol. 24, No. 19, 2005 4611
C5H2]2U(NHMe)2 (8) along with MeNdC(Ph)(CH2Ph)25 were
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (12)
with RCtCR (R ) Me, Ph, Me3Si). NMR Scale. To an NMR
tube charged with [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (12; 16
mg, 0.02 mmol) and C6D6 (0.5 mL) was added an excess of RCt
CR (R ) Me, Ph, Me3Si). In each case, 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
observed by H NMR spectroscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Me)d
C(Me)] (15) or [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Ph)d
C(Ph)] (16) with RCtCR (R ) Me, Ph). NMR Scale. To
an NMR tube charged with [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C-
(Me)dC(Me)] (15) or [η5-1,2,4-(Me3C)3C5H2]2U[N(Me)C(Ph)d
C(Ph)] (16) (16 mg) and C6D6 (0.5 mL) was added an excess of
RCtCR (R ) Me, Ph). In each case, the sample was monitored
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11) with
Pyridine-N-Oxide. NMR Scale. To an NMR tube charged
with [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11; 15 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)214 were observed by 1H NMR spectroscopy (100%
conversion).
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]2UdNMe (11) with
MeNH2. NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UdNMe (11; 15 mg, 0.02 mmol) and C6D6 (0.5
mL) was added an excess of MeNH2. The color of the solution
immediately changed from dark brown to yellow, and reso-
nances due to [η5-1,2,4-(Me3C)3C5H2]2U(NHMe)2 (8) were
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11) with
Me3SiN3. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UdNMe (11; 15 mg, 0.02 mmol) and C6D6
(0.5 mL) was added an excess of Me3SiN3, and resonances due
to [η5-1,2,4-(Me3C)3C5H2]2U(N3)214 (20% conversion) along with
other uranium-containing unidentified compounds were ob-
1
observed by H NMR spectroscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (12)
with p-Toluidine. NMR Scale. To an NMR tube charged
with [η5-1,2,4-(Me3C)3C5H2]2UdN(p-tolyl) (12; 16 mg, 0.02
mmol) and C6D6 (0.5 mL) was added p-toluidine (2 mg, 0.02
mmol). The color of the solution immediately changed from
dark brown to red, and resonances due to [η5-1,2,4-(Me3C)3-
C5H2]2U(NH-p-tolyl)2 (10) were observed by 1H NMR spectros-
copy (100% conversion).
1
served by H NMR spectroscopy. The sample was monitored
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]2UdNMe (11) with
SiF4 or BF3(OEt2). NMR Scale. To an NMR tube charged
with [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11; 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]2UF214 were
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UMe2 with [η5-1,2,4-
(Me3C)3C5H2]2(NH2)2 (7). NMR Scale. To an NMR tube
charged with [η5-1,2,4-(Me3C)3C5H2]2UMe2 (15 mg, 0.02 mmol)
and C6D6 (0.5 mL) was added [η5-1,2,4-(Me3C)3C5H2]2(NH2)2
(7; 15 mg, 0.02 mmol). 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
observed by H NMR spectroscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11) with
SiCl4. NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UdNMe (11; 15 mg) and C6D6 (0.5 mL) was
added an excess of SiCl4. The color of the solution slowly (2 h)
changed from dark brown to brown-red, and resonances
attributable to [η5-1,2,4-(Me3C)3C5H2]2U(N(Me)(SiCl3))(Cl) (1H
NMR (C6D6): δ 51.8 (3H, NCH3), 14.5 (18H, (CH3)3C), -4.8
(18H, (CH3)3C), -6.9 (18H, (CH3)3C); the protons of the rings
were not observed) were observed by 1H NMR spectroscopy
(100% conversion). This 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 was 30% complete,
and after 4 days, conversion to [η5-1,2,4-(Me3C)3C5H2]2UCl2 was
complete.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2U(NH2)2 (7) with
RCtCR (R ) Me, Ph, Me3Si). NMR Scale. To an NMR tube
charged with [η5-1,2,4-(Me3C)3C5H2]2U(NH2)2 (7; 15 mg, 0.02
mmol) and C6D6 (0.5 mL) was added an excess of RCtCR (R
) Me, Ph, Me3Si). In each case, the sample was monitored
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]2UdNMe (11) with
PhCtCH. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UdNMe (11; 15 mg, 0.02 mmol) and C6D6
(0.5 mL) was added an excess of PhCtCH. The color of the
solution immediately changed from dark brown to brown,
14
and resonances due to (Me3C)3C5H3 and other unidentified
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11) with
SiBr4. NMR Scale. To an NMR tube charged with [η5-1,2,4-
(Me3C)3C5H2]2UdNMe (11; 15 mg) and C6D6 (0.5 mL) was
added an excess of SiBr4. The color of the solution slowly (4 h)
changed from dark brown to brown-red, and resonances
attributable to [η5-1,2,4-(Me3C)3C5H2]2U(N(Me)(SiBr3))(Br) (1H
NMR (C6D6): δ 48.2 (3H, NCH3), 15.8 (18H, (CH3)3C), -4.3
(18H, (CH3)3C), -6.8 (18H, (CH3)3C); the protons of the rings
were not observed) were observed by 1H NMR spectroscopy
(100% conversion). This sample was maintained at 65 °C and
monitored periodically by 1H NMR spectroscopy. After 2 days,
conversion to [η5-1,2,4-(Me3C)3C5H2]2UBr2 was 30% complete,
and after 10 days, conversion to [η5-1,2,4-(Me3C)3C5H2]2UBr2
was complete.
uranium-containing compounds were observed by 1H NMR
spectroscopy.
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11) with
Ph2CdO. NMR Scale. To an NMR tube charged with [η5-
1,2,4-(Me3C)3C5H2]2UdNMe (11; 15 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 brown to
brown-red, and resonances due to [η5-1,2,4-(Me3C)3C5H2]2Ud
O14 along with Ph2CdNMe28 were observed by 1H NMR
spectroscopy (100% conversion).
Reaction of [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11) with
Me3SiCtCSiMe3, CH2dCH2, Me3SiX (X ) Cl, Br, I, CF3),
Ph3PE (E ) O, S, Se), Diethyl Ether, Tetrahydrofuran,
Pyridine, 4-Me2NC5H4N, or C6H5Cl. NMR Scale. To an
NMR tube charged with [η5-1,2,4-(Me3C)3C5H2]2UdNMe (11;
15 mg, 0.02 mmol) and C6D6 (0.5 mL) was added an excess of
Me3SiCtCSiMe3, CH2dCH2, Me3SiX (X ) Cl, Br, I, CF3),
Ph3PE (E ) O, S, Se), diethyl ether, tetrahydrofuran, pyridine,
4-Me2NC5H4N, or C6H5Cl. In each case, 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.
X-ray Crystallography. Crystal data for [η5-1,2,4-(Me3C)3-
C5H2]2U[N(Me)C(Me)dC(Me)] (15): a red blocklike crystal
(0.10 × 0.13 × 0.14 mm) was mounted from Paratone N oil
onto a glass fiber and immediately placed on a Bruker SMART
CCD diffractometer. A hemisphere of data was collected by
using ω scans, with 10-s frame exposures and 0.3° frame
widths. A total of 15 749 reflections were measured at T )
123 K in the 2θ range of 5.0-49.0°, of which 6277 were unique
(Rint ) 0.060); Mo KR radiation (λ ) 0.71069 Å). C39H67NU, M
) 787.99, monoclinic, space group P21/c (no. 14), a ) 10.220(3)
Å, b ) 16.419(5) Å, c ) 22.098(6) Å, â ) 100.818(4)°, V )
(28) Moretti, I.; Torre, G. Synthesis 1970, 141.

4612 Organometallics, Vol. 24, No. 19, 2005
Zi et al.
3642(1) Å3, Dcalc ) 1.437 g cm-3, Z ) 4, F(000) ) 1600, µ(Mo
KR) ) 44.83 cm-1, F2 refinement, R ) 0.037, Rw ) 0.041, Rall
) 0.063, gof ) 1.22, 4387 observed reflections (I > 2.50σ(I)),
361 parameters. The MeNC(Me)CMe ligand is disordered by
an approximate 2-fold rotation, interchanging the terminal N
and C atoms. The disorder was modeled with constrained C
and N atoms in the two positions, refined with identical
position and isotropic thermal parameters, and the sum of
occupancies was constrained to equal 1.0. The majority oc-
cupancy refined to 0.70 rather than 0.50. N1, C2, and C3 form
the majority backbone and C40, C2, and N2 form the minority
backbone. The distances from C2 to the two terminal atoms
are approximately equal, but the U-X distances are 2.202(6)
Å to (N1/C40) and 2.270(6) Å to (C3/N2). The thermal
parameters of the MeNC(Me)CMe ligand are substantially
larger than those of the 1,2,4-(Me3C)3C5H2 ligands due to the
cumulative effects of the disorder. Detailed information is
available in the Supporting Information.
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, and we thank
Marc D. Walter, Evan L. Werkema, and Wayne W.
Lukens, Jr. for discussions.
Supporting Information Available: Crystallographic
data (also deposited with the Cambridge Crystallographic
Data Centre; copy of the data (CCDC 270596) 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 Rd.,
Cambridge CB2 1EZ, UK; fax +44 1223 336033); labeling
diagrams, tables giving atomic positions and anisotropic
thermal parameters, bond distances, and angles, and least-
squares planes for 15 are available free of charge via the
Internet at http://pubs.acs.org. Structure factor tables are
available from the authors.
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-
OM050427K