Inter- and intramolecular hydroamination with a uranium dialkyl precursor

Article abstract of DOI:10.1021/om9006328

The same uranium dibenzyl complex supported by a ferrocene-diamide ligand was used as a precatalyst for both inter-and intramolecular hydroamination reactions. Mechanistic and reactivity studies were undertaken to determine whether the two types of reactions follow the same pathway. The experimental results indicate that more than one mechanism may be operating and that the change in mechanism may be dependent on the type of reaction (inter-versus intramolecular) and/or the type of substrate (primary versus secondary amine). In addition, the synthesis and characterization of a bridging-imide diuranium(IV) complex and of benzyl-and anilide-aryloxide uranium(IV) complexes are reported, and their role in hydroamination reactions is discussed.

Full text of DOI:10.1021/om9006328

3242 Organometallics 2010, 29, 3242–3251
DOI: 10.1021/om9006328
Inter- and Intramolecular Hydroamination with a Uranium
Dialkyl Precursor
Erin M. Broderick, Nathaniel P. Gutzwiller, and Paula L. Diaconescu*
Department of Chemistry & Biochemistry, University of California, Los Angeles, California 90095
Received July 18, 2009
The same uranium dibenzyl complex supported by a ferrocene-diamide ligand was used as a
precatalyst for both inter- and intramolecular hydroamination reactions. Mechanistic and reactivity
studies were undertaken to determine whether the two types of reactions follow the same pathway.
The experimental results indicate that more than one mechanism may be operating and that
the change in mechanism may be dependent on the type of reaction (inter- versus intramolecular)
and/or the type of substrate (primary versus secondary amine). In addition, the synthesis and
characterization of a bridging-imide diuranium(IV) complex and of benzyl- and anilide-aryloxide
uranium(IV) complexes are reported, and their role in hydroamination reactions is discussed.
Introduction
Hydroamination, the formal addition of an N-H bond
across a carbon-carbon unsaturation, can be achieved in
either an inter- or intramolecular fashion to produce nitrogen-
containing molecules such as amines, enamines, and imines
(Figure 1).1-8 The importance of the formation of the C-N
bond has led to a surge of research in this area.1 Hydro-
amination has been shown to occur with early9-15 or
*To whom correspondence should be addressed. E-mail: pld@
chem.ucla.edu.
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Figure 1. Intermolecular hydroamination reactions producing
amines, enamines, and imines.
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pubs.acs.org/Organometallics
Published on Web 07/01/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 15, 2010 3243
used constrained-geometry (CG) actinide amide complexes,
(CGC)An(NMe2)X (CGC = Me2Si(η5-Me4C5)(tBuN), X =
NMe2, OAr, Cl),39,40 while Eisen et al. used a bis(cyclopenta-
dienyl) actinide dialkyl complex, Cp*2UMe2 (Cp* = C5Me5).33
The complex Cp*2UMe2 has been used by the Marks group as
well, but mechanistic interpretations were extrapolated from
experiments using (CGC)An(NMe2)X.39,40
The goals of the present study are to use the same
uranium precatalyst for both inter- and intramolecular
hydroaminations and to determine if only one mechanism
is operating for a specific type of reaction. Group 4 metal
complexes are known to follow either an imido mechanism
if they are neutral41-48 or an amido mechanism if they are
cationic,49-51 with exceptions such as (CGC)M(NMe2)X
52
(M = Zr; X = NMe2, Cl, OAr)40 and Zr(NMe2)4 being
reported to adopt the amido mechanism. Only a few studies
have reported, on the basis of computational and experi-
mental data, both mechanisms to be possible for the same
group 4 metal complex.53,54 For actinide complexes, a compu-
tational study with thorium CGC complexes indicated that
in the intramolecular hydroamination/cyclization of (4E,6)-
heptadienylamine, the amido mechanism is favored over the
imido pathway.55 Herein, we report mechanistic studies of
inter- and intramolecular hydroamination reactions using
fc(NSitBuMe2)2U(CH2Ph)2, 1-(CH2Ph)2 (fc=1,10-ferro-
cenylene),56 as a precatalyst.
Results and Discussion
Synthesis and Characterization of Uranium Complexes.
The synthesis and characterization of the ferrocene-based
diamide uranium dialkyl compound 1-(CH2Ph)2 were pre-
viously reported by our group.56 The complex 1-(CH2Ph)2
was synthesized by the reaction of KCH2Ph with the ura-
nium diiodide complex fc(NSitBuMe2)2UI2(THF), which, in
turn, was obtained from UI3(THF)4.57
Figure 2. (a) Proposed mechanism for the hydroamination of
Me3Si-CtCH with aniline in the presence of Cp*2UMe2 (imido
mechanism).33 (b) Proposed mechanism for the reaction of 2,2-
diphenyl-4-penten-1-amine in the presence of (CGC)U(NMe2)X
(CGC=Me2Si(η5-Me4C5)(tBuN), X=Cl, OAr, amido mecha-
nism).40
Two groups, those of Eisen33 and of Marks,38-40 have
made contributions toward the mechanistic understanding
of hydroamination with actinide catalysts. The mechanism
proposed by Eisen33 for the intermolecular hydroamination
of alkynes (Figure 2a) involves the formation of a uranium
imido intermediate (imido mechanism), similar to group 4
metal examples,14,41,42 which then undergoes a [2þ2] cyclo-
addition with the olefin to generate an amido-vinyl uranium
complex. This complex is protonated by an incoming amine
and releases the product; isomerization from the enamine to
the imine is generally observed. The mechanism proposed by
Marks (Figure 2b) for the intramolecular hydroamination/
cyclization of aminoalkenes39 is similar to that proposed by his
group for the analogous reactions using lanthanide catalysts:29
the intermediate is a uranium amide, which undergoes an olefin
migratory-insertion reaction followed by subsequent protono-
lysis (amido mechanism).
Since a uranium terminal imide is proposed to be the cata-
lytically active species in the intermolecular hydroamination
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Although both groups show evidence for their proposed
mechanisms, the precatalysts used during the kinetics
studies are different from one group to the other. Marks et al.
€
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3244 Organometallics, Vol. 29, No. 15, 2010
Broderick et al.
The magnetic properties of 12-(μ-NPh)2 were investigated
in order to determine whether the short uranium-uranium
distance is accompanied by the coupling of the uranium
unpaired electrons. Analyzing the magnetic moment for
12-(μ-NPh)2 in the temperature range 50-300 K (Figure 4),
it was noticed that the value corresponding to one uranium
was considerably less than that of [1-(CH2Ph)(OEt2)]-
[BPh4] and of 1-(CH2Ph)2 (ca. 1.9 versus 2.4 and 3.2 μB, res-
pectively, at 300 K).56 In general, for uranium compounds, a
smaller value of the room-temperature magnetic moment than
the one calculated for the free ion (3.58 μB) is a consequence of
partly quenching the orbital-angular momentum either be-
cause of lower symmetry or higher covalency than for the free
ion (3H4 for U(IV)).65 By extrapolation, the magnetic moment
value for 12-(μ-NPh)2 indicates a better orbital overlap (higher
degree of covalency) in 12-(μ-NPh)2 than in 1-(CH2Ph)2
and even in 1-(CH2Ph)(OEt2)][BPh4], a proposal that is con-
sistent with the short uranium-uranium and iron-uranium
distances in 12-(μ-NPh)2. Since 12-(μ-NPh)2 and 1-(CH2Ph)2
feature different coordination environments, however, the low
magnetic moment for 12-(μ-NPh)2 may be a consequence of
other factors as well. It is noteworthy that the plot of χT versus
1/T (Figure 4) does not show any unusual magnetic behavior
for 12-(μ-NPh)2, ruling out a magnetic exchange between the
two uranium centers.
The near-infrared (NIR) spectrum recorded at room
temperature for toluene solutions of 12-(μ-NPh)2 showed
absorption bands with ε ≈ 102 M-1 cm-1 (Figure 5). These
bands are consistent with f-f transitions;66,67 a similar
spectrum was reported by us for 1-(CH2Ph)2 (see the Sup-
porting Information for an overlay of the two spectra).56
Together with the other characterization data presented
here, the NIR spectrum of 12-(μ-NPh)2 indicates that the
two uranium centers behave as expected for uranium(IV)
complexes with no or little electronic communication be-
tween them.
Figure 3. Thermal ellipsoid (50% probability) representation
of 12-(μ-NPh)2. Hydrogen atoms were removed for clarity.
reactions,33 the synthesis and characterization of a uranium-
imide complex were attempted. The reaction between
1-(CH2Ph)2 and one equivalent of aniline at room tempera-
ture led to the isolation of a bridging-imide diuranium(IV)
complex, 12-(μ-NPh)2, in 56% yield after recrystallization
from n-pentane (eq 1). The complex 12-(μ-NPh)2 shows no
signals at room temperature in its 1H NMR spectrum,58 but
peaks become visible at 100 °C in toluene-d8. At this tempera-
ture, the chemical shifts are consistent with a symmetrical
structure, as inferred from one ancillary ligand environment
and one type of imide protons. The X-ray crystal structure of
12-(μ-NPh)2 (Figure 3), however, indicates an unsymmetrical
complex, with the phenyl groups of the two bridging imides
tilted toward one of the uranium atoms, whereas the other
uranium is relatively unobstructed. As a consequence, the
latter comes in close contact with the iron center of its
Because the 1H NMR spectrum of 12-(μ-NPh)2 at 100 °C
was consistent with a symmetrically dinuclear (likely a
consequence of enhanced rotation around σ bonds) or a
mononuclear complex in solution, but the crystallography
studies indicated a dinuclear structure in the solid state, a
pulse-gradient spin-echo 1H NMR spectroscopy experi-
ment was performed to probe the solution structure.68 The
˚
ferrocene-diamide ligand (U-Fe, 3.0839(6) A) and features
˚
shorter U-Nimide distances (2.1666(31) and 2.2449(30) A)
than those to the other uranium atom (2.3320(31) and
˚
2.2563(30) A). The canting toward one uranium atom is
not a consequence of crystal-packing effects (Figure SX1b in
the Supporting Information). It is interesting to note that the
˚
uranium-iron distance of 3.08 A in 12-(μ-NPh)2 is as short
˚
t
radius of 12-(μ-NPh)2 was estimated to be 6.8 A by measur-
ing its diffusion coefficient in a solution of toluene-d8 at
˚
as the uranium-iron distance (3.08 A) in [fc(NSi BuMe2)2-
U(CH2Ph)(OEt2)][BPh4] ([1-(CH2Ph)(OEt2)][BPh4]),56 indi-
cating a possible interaction59 between the two metals (the
100 °C. This value is close to that calculated from the X-ray
˚
sum of the covalent radii of uranium and iron is 3.28 A).60 The
˚
crystal structure, 6.9 A, indicating that 12-(μ-NPh)2 main-
tains its dinuclear structure in solution at 100 °C.
˚
uranium-uranium distance of 3.5464(3) A is also smaller than
the sum of the uranium covalent radii (3.92 A); such short
Next, the observation of a terminal-imide uranium com-
plex from 12-(μ-NPh)2 in the presence of donor molecules
was attempted. The reactions of THF, dimethylphenylphos-
phine, or 2,20-bipyridine with 12-(μ-NPh)2 were carried out,
but 12-(μ-NPh)2 remained unmodified after heating the
respective mixtures at 70 °C for several days. Another
attempt to isolate a terminal-imide complex was made by
˚
uranium-uranium distances were found for other bridging-
imide diuranium(IV) complexes as well.61-64
(58) Diaconescu, P. L.; Arnold, P. L.; Baker, T. A.; Mindiola, D. J.;
Cummins, C. C. J. Am. Chem. Soc. 2000, 122, 6108.
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verria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008,
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Cummins, C. C. J. Am. Chem. Soc. 2000, 122, 6108.
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Article
Organometallics, Vol. 29, No. 15, 2010 3245
Figure 4. Left: plot of the magnetic moment per uranium center (μeff) versus T for 12-(μ-NPh)2. Right: plot of the χT versus 1/T per
uranium center for 12-(μ-NPh)2.
Figure 5. UV-vis-NIR spectrum of 12-(μ-NPh)2 (0.1 mM,
toluene) with the inset showing the NIR spectrum of 12-(μ-
NPh)2 (5.0 mM, toluene).
Figure 6. Thermal ellipsoid (50% probability) representation
of 1-(CH2Ph)(OAr). Hydrogen atoms and disordered counter-
parts were removed for clarity.
using a bulkier amine than aniline, 2,6-di-iso-propylaniline.
The reaction between 1-(CH2Ph)2 and one equivalent of
2,6-di-iso-propylaniline afforded unreacted 1-(CH2Ph)2 and
the bis(amide) 1-(NH-2,6-iPr2C6H3)2 (structure assigned on
intramolecular hydroamination/cyclization reaction mecha-
nism for actinide complexes is similar to that for lanth-
anides,39,40 which cannot access an imido intermediate. The
use of phenols such as 2,6-dimethylphenol or 2,6-di-iso-
propylphenol produced the bis(aryloxide) products even when
only one equivalent of the phenol was used with 1-(CH2Ph)2.
The reaction between one equivalent of 2,6-di-tert-butyl-
phenol and 1-(CH2Ph)2, however, led to the isolation of
1-(CH2Ph)(OAr) (Ar = 2,6-di-tert-butyl-C6H3) in 97% yield
(eq 2). The complex 1-(CH2Ph)(OAr) was characterized
1
the basis of its H NMR spectrum). This complex did not
produce any free 2,6-di-iso-propylaniline upon heating at
85 °C for two days, indicating that the formation of an imido
complex was unlikely under those conditions. Finally, excess
aniline was added to 12-(μ-NPh)2 in order to mimic, in part,
the hydroamination reaction conditions (see below). It
was found that when both aniline and Me3Si-CtCH were
added to 12-(μ-NPh)2, hydroamination occurred; in the
presence of aniline alone, four equivalents at 100 °C for
0.5 h, or one equivalent at room temperature for three days,
12-(μ-NPh)2 decomposed (the formation of the free ferrocene
diamine was observed). Although all the attempts to isolate a
mononuclear uranium complex from 12-(μ-NPh)2 were un-
successful, the transformation of 12-(μ-NPh)2 to the corres-
ponding terminal imide or uranium bis(amide) may still occur
under the hydroamination reaction conditions.
1
by elemental analysis, H NMR spectroscopy, and single-
crystal X-ray diffraction (Figure 6).
A mixed anilide-aryloxide uranium(IV) complex was also
synthesized in order to compare its behavior with that of the
corresponding benzyl-aryloxide complex. The reaction of
aniline (one equivalent) with 1-(CH2Ph)(OAr) at 70 °C, for four
hours, in toluene, led to the expected product, 1-(NHPh)(OAr)
(eq 3). This complex was characterized by elemental analysis
and 1H NMR spectroscopy. At 70 °C, in C6D6, 1-(NHPh)(OAr)
is stable for up to four days, exhibiting minimal decomposi-
tion (<1%).
A mixed benzyl-aryloxide uranium(IV) complex was tar-
geted in addition to the uranium imide because such a
complex may have only one site available for the protono-
lysis reaction with amines and would not be able to access an
imide catalyst. Marks et al. used analogous mixed alkyl-
aryloxide complexes to support their hypothesis that the
Intermolecular Hydroamination Reactions. The reactions
between various alkynes, including terminal and internal
alkynes, and olefins with anilines were conducted in the

3246 Organometallics, Vol. 29, No. 15, 2010
Table 1. Substrate Scope for Intermolecular Hydroaminations with 1-(CH2Ph)2
Broderick et al.
a
a Reactions were performed in C6D6 at 70 °C with 10 mol % 1-(CH2Ph)2; [catalyst] = 4.0 mM, [alkyne] = 0.40 M, [amine] = 0.04 M. b Room
temperature. c [catalyst] = 1.7 mM, [alkyne] = 0.34 M, [amine] = 0.034 M.
presence of catalytic amounts of 1-(CH2Ph)2 to give the
expected hydroamination products (Table 1). Several reac-
tions between Me3Si-CtCH and aniline derivatives were
successful (entries 1-4), as well as the reaction with n-butyl-
amine (entry 6). A large-scale hydroamination reaction of ani-
line and Me3Si-CtCH with 1-(CH2Ph)2 led to the isolation of
the product 2 in 74% yield, indicating that only one of the two
possible regioisomers is formed in this reaction. When the
alkyne was changed to nBu-CtCH, the reaction with aniline
required three days to obtain a 48% conversion to the imine
product (entry 7). Similarly, when the alkyne was replaced by
tBu-CtCH, only a low conversion with either n-butylamine
(entry 8) or aniline (entry 10) was observed after three days. No
hydroamination products were observed in the reactions of
aniline with styrene, norbornene, phenylacetylene, 2-phenyl-
propyne, 2-butyne, or diphenylacetylene or in the reaction of n-
butylamine with diphenylacetylene, but such results are not
surprising given that these are difficult substrates in inter-
molecular hydroaminations. The formation of alkyne oligomers
was observed in the reactions that did not lead to hydroamina-
tion products, similarly to the results reported by Eisen et al.33
The alkyne-oligomerization products were also obtained in-
dependently from the reactions of 1-(CH2Ph)2 with alkynes,
such as Me3Si-CtCH and 1-hexyne (see the Supporting
Information for details).
tered for intermolecular hydroaminations with group 4
metal complexes involving anilines and alkynes, which, in
general, required temperatures above 100 °C and prolonged
heating.69-80 The scope of the intermolecular hydroamina-
tions performed by us was limited by the fact that
1-(CH2Ph)2 was not stable above 70 °C for long periods of
time56 and decomposed when the reaction mixtures were
heated above that temperature.
Next, it was observed that there was no reaction between
Me3Si-CtCH and N-methylaniline (entry 5) or dibutyl-
amine (entry 9), suggesting that in those reactions a termi-
nal uranium(IV) imide81-86 may be the catalytically active
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(79) Bexrud, J. A.; Li, C.; Schafer, L. L. Organometallics 2007, 26,
6366.
(80) Lorber, C.; Choukroun, R.; Vendier, L. Organometallics 2004,
23, 1845.
(81) Arney, D. S. J.; Burns, C. J. J. Am. Chem. Soc. 1995, 117, 9448.
(82) Arney, D. S. J.; Burns, C. J.; Smith, D. C. J. Am. Chem. Soc.
1992, 114, 10068.
It is worth mentioning that the Eisen group reported all the
intermolecular hydroaminations catalyzed by uranium com-
plexes to occur between unhindered aliphatic (as opposed to
aromatic) amines and terminal acetylenes.33 Only one ex-
i
ample of a reaction between Pr-CtCH and aniline was
reported that was catalyzed by Cp*2ThMe2; that reaction
mixture converted 95% to the corresponding imine after
170 h of heating at 78 °C. A similar situation was encoun-
(83) Arney, D. S. J.; Burns, C. J. J. Am. Chem. Soc. 1993, 115, 9840.

Article
Organometallics, Vol. 29, No. 15, 2010 3247
(80 equivalents) were added to 1-(CH2Ph)(OAr), no conver-
sion to 2 was observed after one day at 70 °C in C6D6. This
finding is consistent with two mechanistic scenarios: (1) the
precatalyst 1-(CH2Ph)2 accesses the imido mechanism for
intermolecular-hydroamination reactions and (2) either type
of reaction (imido or amido mechanism) is suppressed with
1-(CH2Ph)(OAr) because the steric bulk of the aryloxide
ligand prevents the coordination of the two substrates.
Furthermore, it was investigated whether a migratory inser-
tion of the alkyne into the U-N bond of 12-(μ-NPh)2 may
occur. The addition of excess Me3Si-CtCH to 12-(μ-NPh)2
and heating of the reaction mixture at 70 °C for one day
resulted in no change to the bridging-imide uranium complex,
indicating that the intermolecular hydroamination reactions
do not initiate with the alkyne substrate.
Figure 7. Determination of the reaction order in amine concen-
tration for the hydroamination of Me3Si-CtCH and aniline
catalyzed by 1-(CH2Ph)2 (left) and 12-(μ-NPh)2 (right) at 70 °C
in C6D6.
Kinetics studies were conducted with Me3Si-CtCH, ani-
line, and 1-(CH2Ph)2 at 70 °C in C6D6 and monitored by 1H
NMR spectroscopy. In order to determine the order in amine,
the catalyst concentration was held constant, while the alkyne
to amine ratio was held at a value greater than 12:1 to mini-
mize amine inhibition and maintain pseudo-first-order con-
ditions. Although the reaction was followed until 90% con-
version of aniline, the kinetics data were only considered
until 60% conversion because the plot of [aniline] versus time
curved around that value. It is possible that two different
mechanisms operate during the two time ranges, although
most reports indicate that product inhibition occurs toward
the end of hydroamination reactions. In order to probe
whether product inhibition takes place in the above reactions,
two experiments were carried out:
(1) The reaction of 1-(CH2Ph)2 with 1400 equivalents of
Me3Si-CtCH and 80 equivalents of aniline was performed,
and then another 80 equivalents of aniline was added. The
first reaction occurred fast until ca. 60% conversion of
aniline, and then it slowed down. The addition of fresh
aniline caused the reaction rate to increase, but the product
formation was about 10% slower than in the initial reaction.
(2) The reaction between 1-(CH2Ph)2 and 1400 equivalents
of Me3Si-CtCH and 80 equivalents of aniline was carried
out in the presence of 80 equivalents of the product 2. It was
observed that the reaction proceeded slower in its presence
than in its absence (after 20 min, the reaction without 2
present showed 30% conversion, while the reaction with 2
present had 20% conversion), indicating that the product
may be inhibiting the reaction.
species (an intermolecular hydroamination reaction bet-
ween Me3Si-CtCH and Et2NH, catalyzed by [(Et2N)3-
(Et2NH)3U]þ, was reported, but a detailed mechanistic study
was not carried out).34 In order to probe whether this hypo-
thesis extends to the reaction of 1-(CH2Ph)2 with Me3Si-
CtCH and aniline, the reaction between those substrates was
carried out using 12-(μ-NPh)2 as a precatalyst (1.2 mol %).
Even though a terminal-imide uranium(IV) complex could
not be obtained from 12-(μ-NPh)2, the product 2 (78%
conversion) was obtained after 38 min at 70 °C, similar to
what was found when 1-(CH2Ph)2 was used as a precatalyst.
Furthermore, the observed reaction rate of 6.8 ꢀ 10-5 M s-1
(Figure 7) was the same as that determined for 1-(CH2Ph)2
(6.0 ꢀ 10-5 M s-1, see below). The reactions of 2-butyne with
aniline or di-n-butylamine with Me3Si-CtCH in the pre-
sence of 12-(μ-NPh)2 gave the same results as those conducted
in the presence of 1-(CH2Ph)2 (no reaction), indicating that
1-(CH2Ph)2 and 12-(μ-NPh)2 are proceeding through a similar
mechanism in these reactions and that a terminal-imide
uranium complex is likely the catalytically active species. It
is also noteworthy that the reaction of Me3Si-CtCH and
aniline mediated by 1-(CH2Ph)2 occurred faster when lower
concentrations of aniline were used than when higher con-
centrations of aniline were employed, consistent with the
formation of a terminal imide as the active catalyst, although
these results are also consistent with the interpretation that
aniline may inhibit a σ-bond migratory-insertion step (that is
part of the amido mechanism).
The reaction between aniline and Me3Si-CtCH in the
presence of 1-(CH2Ph)(OAr) was also attempted because it
was reasoned that this precatalyst would not be able to form a
uranium imide. As described earlier, 1-(CH2Ph)(OAr) reacts
with one equivalent of aniline to give the anilide-aryloxide
complex 1-(NHPh)(OAr) (eq 3). Even when three equivalents
of aniline were used, 1-(NHPh)(OAr) was the only product
after the reaction mixture was heated for several days at
70 °C. The latter experiment was performed because it was
observed that aniline can protonate aryloxides smaller than
2,6-di-tert-butylphenol (see above). These experiments indi-
cate that the anilide-aryloxide complex can be formed from
1-(CH2Ph)2, but the bis(amide) complex cannot. Conse-
quently, when Me3Si-CtCH (1800 equivalents) and aniline
The disappearance of the aryl-proton resonances for the
aniline was normalized to an internal standard, hexaethylben-
zene. The kinetics data plot in Figure 7 shows a linear depen-
dence of [aniline] versus time, indicating a zero-order depen-
dence on amine concentration. Given that 1-(CH2Ph)2 forms
12-(μ-NPh)2 within minutes at room temperature, the zero-
order dependence on amine concentration is not surprising.
Although an inverse order in amine concentration was re-
ported by the Eisen group in analogous reactions, a kinetics
analysis of the imido mechanism indicates that the rate law
obtained here is in agreement with a fast pre-equilibrium or
irreversible formation of the imide intermediate, followed by a
fast [2þ2] cycloaddition reaction with the alkyne.40,42
In order to determine the order in catalyst, the initial con-
centrations of the alkyne and amine were held constant, while
the concentration of 1-(CH2Ph)2 was varied over a 6-fold
range. Outside of this range, reactions were inconsistent,
possibly due to catalyst decomposition as a consequence of
(84) Haskel, A.; Straub, T.; Eisen, M. S. Organometallics 1996, 15,
3773.
(85) Zi, G.; Blosch, L. L.; Jia, L.; Andersen, R. A. Organometallics
2005, 24, 4602.
(86) Barros, N.; Maynau, D.; Maron, L.; Eisenstein, O.; Zi, G.;
Andersen, R. A. Organometallics 2007, 26, 5059.

3248 Organometallics, Vol. 29, No. 15, 2010
Broderick et al.
Table 2. Substrate Scope for the Intramolecular Hydroamination/
a
Cyclization Reaction with 1-(CH2Ph)2
a Reactions were performed in C6D6 at 70 °C. b [catalyst] = 11.2 mM,
[3a/b] = 0.45 M. c [catalyst] = 6.0 mM, [3c] = 0.45 M, roomtemperature.
Figure 8. Determination of the reaction order in catalyst concen-
tration for the intermolecular hydroamination of Me3Si-CtCH
and aniline in the presence of 1-(CH2Ph)2 in C6D6 at 70 °C.
Figure 10. Determination of the reaction order in amine (left)
and catalyst (right) for the reaction of 2,2-diphenyl-4-penten-1-
amine (3a) with 1-(CH2Ph)2 in C6D6 at 70 °C.
Figure 9. Eyring plot for the hydroamination of Me3Si-CtCH
with aniline in the presence of 7.5 mol % of 1-(CH2Ph)2 in C6D6.
the large amount of aniline present. A plot of the reaction rate,
kobs, versus precatalyst concentration indicates a first-order
dependence on [1-(CH2Ph)2] (Figure 8). Finally, when the
concentrations of the amine and precatalyst were held con-
stant and the concentration of the alkyne was changed over
a 6-fold range, the rate of the reaction stayed the same.
Therefore, the ratelaw for the intermolecular hydroamination
of Me3Si-CtCH with aniline in the presence of 1-(CH2Ph)2
is ν = k[1-(CH2Ph)2]1[alkyne]0[amine]0. Consistent with the
fact that the amine is not present in the rate law and that the
N-H bond does not participate in the rate-determining step,
the observed reaction rate when C6H5ND2 was used in a
reaction with Me3Si-CtCH and 1-(CH2Ph)2 was similar to
the rate for the aniline reaction (kH/kD = 1.03).
A temperature-dependent study (Figure 9) allowed the
determination of the activation parameters ΔH# = 11.0(1)
kcal/mol, ΔS#=-30(3) eu, and Ea=11.7(1) kcal/mol for the
reaction of Me3Si-CtCH with aniline in the presence of
1-(CH2Ph)2. These values are similar to those reported by the
Eisen group for the hydroamination of Me3Si-CtCH and
EtNH2 mediated by Cp*2UMe2 (ΔH#=11.7(3) kcal/mol and
ΔS#=-44.5(8) eu).33 Therefore, on the basis of all the data
presented above, the difference in the order of the amine
concentration notwithstanding, the mechanism proposed by
us is analogous to that proposed by Eisen et al. for the
intermolecular hydroamination of alkynes.33 Since 12-(μ-
NPh)2 was very reluctant to form monomeric adducts, it is
proposed that the rate-determining step in the reaction of
Me3Si-CtCH with aniline in the presence of 1-(CH2Ph)2 is
the formation of the terminal imide from the dinuclear
complex 12-(μ-NPh)2, consistent with a zero-order depen-
dence on both the amine and alkyne substrate and a first-
order dependence on precatalyst concentration.
Intramolecular Hydroamination/Cyclization Reactions.
The complex 1-(CH2Ph)2 was also used as a precatalyst for the
intramolecular hydroamination/cyclization of 2,2-diphenyl-
4-penten-1-amine (3a) to give the corresponding cyclic pro-
duct 4a in 22 min at 70 °C in C6D6 (Table 2). A large-scale
reaction of 3a with 1-(CH2Ph)2 (18 mol %) resulted in the
isolation of 4a in a 70% yield.
Unlike what was found for the intermolecular hydroami-
nation (see above), when the secondary amine N-methyl-2,2-
diphenyl-4-penten-1-amine (3b) was used, the formation of
the cyclized product 4b was observed, although the reaction
had to be heated at 70 °C in C6D6 for three days to achieve an
80% conversion. Similar observations have been reported
for analogous reactions catalyzed by actinide complexes.40
In order to compare directly the reactions of alkyne sub-
strates, the reaction between 2,2-diphenyl-4-pentyn-1-amine
(3c) and 1-(CH2Ph)2 (Table 2) was also carried out, leading
to the formation of the expected product, 3d, at room
temperature within minutes.
Kinetics studies were conducted for the reaction between
3a and 1-(CH2Ph)2. The disappearance of the peak for the
terminal olefinic protons, at 5.2 ppm, was monitored by 1H
NMR spectroscopy (the peaks were normalized to the inter-
nal standard hexaethylbenzene). The plot of [3a] versus time
indicated a zero-order dependence for the substrate concen-
tration (Figure 10). To determine the order in catalyst, [3a]
was kept constant and the concentration of 1-(CH2Ph)2 was
varied over a 2.5-fold range. A linear plot of the rate versus
[1-(CH2Ph)2] indicated a first-order dependence on the pre-
catalyst concentration (Figure 10). Therefore, the rate law
for the intramolecular hydroamination/cyclization of 3a
in the presence of 1-(CH2Ph)2 is ν= k[3a]0[1-(CH2Ph)2]1.

Article
Organometallics, Vol. 29, No. 15, 2010 3249
that 12-(μ-NPh)2 may form an amide or bis(amide) species
under these reaction conditions that acts as a catalyst, a
hypothesis supported by the fact that the reaction of 3a with
12-(μ-NPh)2 showed a large induction period (3% conver-
sion after one hour). The induction period is consistent with
the fact that, in the reaction of 1-(CH2Ph)2 with aniline,
12-(μ-NPh)2 forms immediately and a bis(amide) complex
could not be isolated (see above). Therefore, on the basis of
all the data presented above, there are two possibilities:
(1) The mechanism for the intramolecular hydroamina-
tion of 3a-c with 1-(CH2Ph)2 is analogous to that proposed
by Marks et al. for the intramolecular hydroamination/
cyclization of aminoalkenes mediated by lanthanide and
actinide complexes.40
Figure 11. Eyring plot for the hydroamination of 2,2-diphenyl-
4-penten-1-amine (3a) with 1-(CH2Ph)2 (1.4 mol %) in C6D6.
(2) The imido mechanism operates for the reactions of
1-(CH2Ph)2 and 12-(μ-NPh)2 with 3a and 3c, and a change in
mechanism occurs with 3b.
Consistent with this rate law, when 2,2-diphenyl-4-penten-1-
amine-d2 was used, only a small difference in the rate of its
reaction with 1-(CH2Ph)2 was observed by comparison to the
On the basis of our experimental data, it is not possible to
distinguish between the two situations.
rate for the reaction between 3a and 1-(CH2Ph)2 (kH/kD =
1.36). These data are consistent with either one of the two
situations:
Conclusions
(1) The turnover-limiting step is the intramolecular amide
migratory insertion into the CdC bond, analogous to the
reaction pathway proposed previously for aminoalkene
hydroamination/cyclization by uranium complexes (amido
mechanism).39,40 The fact that 3b reacted with 1-(CH2Ph)2
supports this mechanism.
(2) The turnover-limiting step is the metallacycle formation
([2þ2] cycloaddition with a uranium imide), analogous to the
reaction pathway proposed above for the intermolecular
hydroamination. The fact that 3b required a significantly
longer time than 3a to react with 1-(CH2Ph)2 indicates that
the mechanisms of the two reactions may be different.
The uranium complex 1-(CH2Ph)2 acts as a precatalyst for
both inter- and intramolecular hydroamination reactions.
The interpretation of results from both kinetics and reactivity
studies is consistent with more than one mechanism in the
two types of reactions: uranium can behave similarly to group
4 metal complexes and access an imido mechanism or to
lanthanides and access an amido mechanism. It is possible
that (1) for the intermolecular hydroamination, the reaction
between 1-(CH2Ph)2 and aniline forms the bridging-imide
diuranium(IV) complex 12-(μ-NPh)2 in a fast pre-equilibrium,
the rate-determining step is the formation of the terminal
imide, and a fast [2þ2] cycloaddition reaction between the
imide and the alkyne follows; (2) fortheintramolecular hydro-
amination/cyclization, the reaction between 1-(CH2Ph)2 and
the aminoalkene forms a bis(amide) fast, it is followed by a
slow migratory-insertion step, and it concludes with a fast
protonolysis reaction to give the cyclized product. Specific
behaviors, such as the reaction between 1-(CH2Ph)2 and a second-
ary aminoalkene in an intramolecular hydroamination/
cyclization, or the lack of reactivity of 1-(CH2Ph)2 with
secondary amines and a terminal alkyne in an intermolecular
hydroamination, signal that a change in mechanism could
take place between the two types of reactions. A change in
the mechanism, however, may occur as a response to steric
factors. In favor of the first scenario (change in mechanism
from the inter- to the intramolecular hydroamination) is the
fact that the bridging-imide diuranium(IV) precursor (12-(μ-
NPh)2) behaved similarly to 1-(CH2Ph)2 toward aniline or
secondary amines and Me3Si-CtCH, while the benzyl-aryl-
oxide complex 1-(CH2Ph)(OAr) did not react with aniline and
Me3Si-CtCH. On the other hand, 1-(CH2Ph)(OAr) did allow
the complete conversion to the respective products of the
intramolecular hydroamination/cyclization substrates 3a and
3c, indicating that the formation of a uranium-imide inter-
mediate was not required for those reactions. Unfortunately,
kinetics data, deuterium-labeling studies, and reactivity results
were not sufficient to distinguish between all the reasonable
pathways. The results of several experiments carried out to
support the proposal that the mechanism changes based on the
type of reaction (inter- versus intramolecular) were weakened
by an abrupt change in the reactivity of the respective uranium
An Eyring plot shows ΔH# = 19.5(1) kcal/mol, ΔS# =
-22(2) eu, and Ea = 20.3(1) kcal/mol for the reaction of
3a with 1-(CH2Ph)2 (Figure 11). These values are similar
to those reported for the reaction of the dimethyl analogue
of 3a with (CGC)An(N[SiMe3]2)Cl (ΔH#=16(3) kcal/mol,
ΔS#=-18(9) eu, and Ea=17(3) kcal/mol) and in the range
of those observed for intramolecular hydroamination reac-
tions catalyzed by lanthanide catalysts.40 It is important to
note, however, that the activation parameters are relatively
similar for the two types of reactions (intra- and inter-
molecular).
The complexes 1-(CH2Ph)(OAr) and 12-(μ-NPh)2 were also
employed in intramolecular hydroamination/cyclization reac-
tions. The reactions of3a and 3c in the presence of 1-(CH2Ph)-
(OAr) led to the formation of the products 4a and 4c after two
days and one hour, respectively. The complex 1-(CH2Ph)-
(OAr) (10 mol %) also reacted with 3b, and 10% conversion
was achieved after four days at 70 °C in C6D6. All reactions
required longer times than when 1-(CH2Ph)2 was used to
achieve similar conversions, indicating that either the results
are a consequence of the sterically hindered aryloxide ligand
or that a change in mechanism occurs from 1-(CH2Ph)(OAr)
to 1-(CH2Ph)2.
When 12-(μ-NPh)2 (1.8 mol %) was used as a precatalyst in
reactions with 3a and 3c, the results were surprising: the
substrate 3a was 70% converted in 7.5 h at 70 °C in C6D6,
while a 99% conversion of 3c was achieved within 10 minutes
at room temperature. The complex 12-(μ-NPh)2 also con-
verted 3b (11% in four days). The conversion of 3b indicates

3250 Organometallics, Vol. 29, No. 15, 2010
Broderick et al.
precursors and by the fact that the kinetics data are consistent
with either possibility operating for both types of reactions.
DFT calculations may be able to distinguish between these
possibilities, although the paramagnetic nature of the catalytic
species involved will complicate the interpretation of the
results. It is interesting to point out that the ability to access
multiple reaction mechanisms makes uranium an especially
versatile catalyst for hydroamination reactions.
removed again to give an analytically pure solid. Yield: 0.220
g, 97%. 1H NMR (300 MHz, 25 °C, C6D6), δ (ppm): 54.62
(s, 6H, SiCH3), 45.75 (s, 6H, SiCH3), 35.17 (s, 18H, CCH3),
-2.17 (t, 1H, OC6H3 or C6H5), -5.60 (s, 2H, OC6H3 or C6H5),
-6.68 (s, 1H, OC6H3 or C6H5), -7.47 (t, 1H, OC6H3 or C6H5),
-8.65 (s, 1H, OC6H3 or C6H5), -17.20 (s, 2H, OC6H3 or C6H5),
-18.66 (d, 4H, C5H4), -31.31(s, 9H, CCH3), -36.37 (s, 2H,
C5H4), -38.95 (s, 2H, C5H4), -42.73 (s, 9H, CCH3); Ph-CH2
was not observed in the spectrum. Anal. Calcd for C43H66Fe-
N2OSi2U: C, 52.86; H, 6.81; N, 2.87. Found: C, 52.63; H, 6.97;
N, 2.62.
Experimental Section
Synthesis of 1-(NHPh)(OAr). Aniline (0.021 g, 0.23 mmol)
was added to 1-(CH2Ph)(OAr) (0.233 g, 0.23 mmol) in toluene
at room temperature, and the reaction mixture was stirred for
4 h at 70 °C. The volatiles were removed under reduced pressure,
the product was extracted with hexanes, and the volatiles were
removed again. The resulting solid was recrystallized from con-
centrated hexanes at -36 °C. Yield: 0.162 g, 72.9%. 1H NMR
(300 MHz, 25 °C, C6D6), δ (ppm): 36.57 (s, 6H, SiCH3), 32.06
(s, 6H, SiCH3), 24.61 (s, 18H, CCH3), 2.42 (t, 1H, OC6H3 or
NC6H5), -0.56 (d, 2H, OC6H3 or NC6H5), -1.92 (t, 1H, OC6H3
or NC6H5), -2.99 (s, 2H, OC6H3 or NC6H5), -9.82 (s, 2H,
OC6H3 or NC6H5), -13.89 (s, 2H, OC6H3 or NC6H5), -14.62
(s, 2H, OC6H3 or NC6H5), -25.73(s, 18H, CCH3), -27.86 (s,
2H, OC6H3 or NC6H5), -37.03 (s, 2H, OC6H3 or NC6H5) Anal.
All experiments were performed under a dry nitrogen atmo-
sphere using standard Schlenk techniques or an MBraun inert-gas
glovebox. Solvents were purified using a two-column solid-state
purification system by the method of Grubbs87 and transferred
to the glovebox without exposure to air. NMR solvents were
obtained from Cambridge Isotope Laboratories, degassed, and
stored over activated molecular sieves prior to use. Compounds
1-(CH2Ph)2,56 2,2-diphenyl-4-penten-1-amine (3a),88 N-methyl-
2,2-diphenyl-4-penten-1-amine (3b),39 2,2-diphenyl-4-pentyn-1-
amine (3c),88 C6H5ND2,89 and 3a-d289 were synthesized accord-
ing to published procedures. Aniline, N-methylaniline, nBu2NH,
Me3Si-CtCH, styrene, methylphenylacetylene, phenylacety-
lene, 2-butyne, n-butylamine, 1-hexyne, tert-butylacetylene, di-
phenylacetylene, 2,6-di-isopropylphenol, 2,6-dimethylphenol,
and dimethylphenylphosphine were distilled under argon over
CaH2 and stored over sieves in the glovebox prior to use.
Norbornylene was sublimed under argon and stored in the
glovebox. 2,6-Di-tert-butylphenol was recrystallized from con-
centrated hexanes at -36 °C. 1H NMR spectra were recorded on
Bruker300 or Bruker500 spectrometers at room temperature
in C6D6 (the UCLA NMR spectrometers are supported by the
NSF grant CHE-9974928). Chemical shifts are reported with
respect to internal solvent, 7.16 ppm (C6D6). UV-vis-NIR
spectra were recorded on a Varian Carey 5000 spectrophoto-
meter from 200 to 1800 nm using matched, 1 cm quartz cells; all
spectra were obtained using a solvent reference blank in a
cuvette fitted with an air-free Teflon adapter. High-resolution
mass spectrometry, ESI, was performed by the UCLA MIC
Mass Spectrometry Laboratory on an IonSpec Ultima 7T FT-
ICR-MS. CHN analyses were performed by UC Berkeley
Micro-Mass facility, 8 Lewis Hall, College of Chemistry, Uni-
versity of California, Berkeley, CA 94720.
Synthesis of 12-(μ-NPh)2. Aniline (0.0077 g, 0.0827 mmol) was
added to 1-(CH2Ph)2 (0.068 g, 0.079 mmol) in hexanes, at room
temperature, and the reaction was stirred for 2 h. The volatiles
were removed under reduced pressure, and hexanes was added
to the resulting solid. The volatiles were removed again under
reduced pressure, and recrystallization from a concentrated
n-pentane solution at -36 °C afforded the product. Yield: 0.035
g, 56%. There are no observable peaks at room temperature in the
1H NMR spectrum. 1H NMR (500 MHz, 100 °C, toluene-d8), δ
(ppm): 8.12 (s, 8H, C5H4), 4.87 (s, 36H, CCH3), -2.73 (s, 24H,
SiCH3), -3.46 (s, 4H, NC6H5), -4.93 (s, 2H, NC6H5), -13.18
(s, 4H, C5H4), -35.88 (s, 4H, C5H4); the o-NC6H5 peaks were
not observed in the spectrum. Anal. Calcd (%) for C56H86Fe2-
Calcd for C42H65FeN3OSi2U 0.33(C6H14): C, 52.49; H, 6.97; N,
3
4.17. Found: C, 52.41; H, 7.00; N, 3.79.
Synthesis of 2,2-Diphenyl-4-pentyn-1-amine (3c). Diphenyl-
acetonitrile (4.0 g, 20.7 mmol) in DMF was added to a stirring
DMF slurry of NaH (0.521 g, 21.7 mmol) at room temperature,
under argon. After 1 h, the solution was cooled to 0 °C, and
propargyl bromide (1.78 mL, 20.7 mmol) was added. The
reaction was allowed to warm to room temperature and stirred
overnight. The product was extracted with benzene, washed
with water, and dried over MgSO4. The volatiles were then
removed under reduced pressure, yielding a slightly yellow oil
(4.2 g, 18.2 mmol, 89% yield). The product was added to a
stirring diethyl ether slurry of LiAlH4 (1.05 g, 27.6 mol) under
argon, at 0 °C. After stirring at room temperature overnight,
the reaction mixture was cooled to -78 °C and quenched with
6 M NaOH. The product was extracted with diethyl ether (2.9 g,
12.3 mmol) and purified by column chromatography using a
3:1 ethyl acetate/hexanes mixture by volume. The product was
dried overnight, resulting in a white powder, which was recrys-
tallized from diethyl ether/hexanes at -36 °C (1.0 g, 4.5 mmol,
24% yield). 1H NMR (500 MHz, 25 °C, CDCl3), δ (ppm):
7.3-7.2 (m, 10H, C6H5), 3.54 (s, 2H, NH2CH2), 3.11 (d, 2H,
CHCH2), 1.94 (t, 1H, CHCH2), 0.99 (s, 2H, CH2NH2). 13C
NMR (75 MHz, 25 °C, CDCl3), δ (ppm): 145.24 (Ph-C), 128.08
(meta-Ph-CH), 128.01 (ortho-Ph-CH), 126.38 (para-Ph-CH),
81.42 (HCCCH2), 71.48 (HCCCH2), 51.28 (NH2CH2), 49.13
(NH2CH2C), 27.74 (HCCCH2). HRMS, ESI: calcd 236.1439,
found 236.1434.
X-ray Crystal Structures. The X-ray data collections were
carried out on a Bruker AXS single-crystal X-ray diffractometer
using Mo KR radiation and a SMART APEX CCD detector.
The data were reduced by SAINTPLUS, and an empirical
absorption correction was applied using the package SADABS.
The structures were solved and refined using SHELXTL
(Bruker 1998, SMART, SAINT, XPREP, AND SHELXTL,
Bruker AXS Inc., Madison, WI).90 All atoms were refined ani-
sotropically, and hydrogen atoms were placed in calculated
positions unless specified otherwise. Tables with atomic coordi-
nates and equivalent isotropic displacement parameters, with all
the bond lengths and angles, and with anisotropic displacement
parameters are listed in the Supporting Information.
N6Si4U2 0.5(C5H12): C, 44.48; H, 5.87; N, 5.32. Found: C, 44.36;
3
H, 5.64; N, 5.40.
Synthesis of 1-(CH2Ph)(OAr). 2,6-Di-tert-butylphenol (0.048
g, 0.23 mmol) was added to 1-(CH2Ph)2 (0.068 g, 0.079 mmol) in
toluene at room temperature, and the reaction was stirred for 4 h
at 70 °C. The volatiles were removed under reduced pressure, the
product was extracted with hexanes, and the volatiles were
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1070.
X-ray Crystal Structure of 12-(μ-NPh)2. X-ray quality crystals
were obtained from a concentrated n-pentane solution placed in
(89) Gagne, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992,
114, 275.
(90) Sheldrick, G. Acta Crystallogr. A 2008, 64, 112.

Article
Organometallics, Vol. 29, No. 15, 2010 3251
1
a -35 °C freezer in the glovebox. Inside the glovebox, the cry-
stals were coated with oil (STP Oil Treatment) on a microscope
slide, which was brought outside the glovebox. A total of 62937
reflections (-35 e h e 35, -26 e k e 25, -18 e l e 18) were
collected at T = 100(2) K with 2θmax = 61.66°, of which 18594
were unique (Rint = 0.0321). The unit cell contained solvent
molecules that were too disordered to model. As a consequence,
the PLATON SQUEEZE program was used to remove the
solvent from the unit cell. The residual peak and hole electron
densitywere 1.60 and-1.01 e A-3, respectively. The least-squares
refinement converged normally with residuals of R1 = 0.0295
and GOF=1.048. Crystal and refinement data for 12-(μ-NPh)2:
formula C56H85N6Fe2Si4U2, space group P2(1)/c, a = 25.323(3)
in a 70 °C oil bath, and the reactions were monitored by H
NMR spectroscopy. The 1H NMR spectra of the products were
compared with those reported in the literature.33,36,52,91
Kinetics Studies. In the glovebox, 1-(CH2Ph)2, the alkyne, the
amine, and the internal standard, hexaethylbenzene, were added
to a Teflon-sealed NMR tube in C6D6. The NMR tube was
inserted into the instrument (Bruker AV300) and heated to
70 °C. The reactions were monitored until ca. 90% conversion.
For the intermolecular reaction, the aniline concentration was
0.16 M, and for the intramolecular reaction the 3a concentration
was 0.42 M. Errors for the activation parameters were calcu-
lated as reported in the literature.92,93
Large-Scale Reaction of Aniline and Me3Si-CtCH with
1-(CH2Ph)2. 1-(CH2Ph)2 (0.023 g, 0.027 mmol) in 4 mL of tolu-
ene was added to aniline (0.200 g, 2.14 mmol) and Me3Si-
CtCH (0.263 g, 2.67 mmol) in 8 mL of toluene in a Schlenk
˚
˚
˚
A, b = 18.607(2) A, c = 13.5646(14) A, β = 97.009(1)°, V =
3
6343.6(11) A , Z = 4, μ = 5.652 mm-1, F(000) = 3020, R1 =
˚
0.0443 and wR2 = 0.0703 (based on all 18 594 data).
1
X-ray Crystal Structure of 1-(CH2Ph)(OAr). X-ray quality
crystals were obtained from a concentrated Et2O solution
placed in a -35 °C freezer in the glovebox. Inside the glovebox,
the crystals were coated with oil (STP Oil Treatment) on a
microscope slide, which was brought outside the glovebox. A
total of 40 674 reflections (-16 e h e 16, -31 e k e 31, -21 e l
e 20) were collected at T = 100(2) K with 2θmax = 58.13°, of
which 11 371 were unique (Rint = 0.0390). The residual peak and
hole electron density were 0.85 and -0.61 e A-3, respectively.
The least-squares refinement converged normally with residuals
of R1=0.0268 and GOF=1.011. Crystal and refinement data
for 1-(CH2Ph)(OAr): formula C43H66N2FeSi2OU, space group
tube. The reaction was heated at 70 °C and monitored by H
NMR spectroscopy by analyzing aliquots from the reaction.
When the conversion to product was at least 90%, the volatiles
were removed under reduced pressure and the product 2 was
isolated by Kugelrohr distillation. Yield: 0.306 g, 74.4%.
Large-Scale Reaction of 3a with 1-(CH2Ph)2. 1-(CH2Ph)2
(0.024 g, 0.028 mmol) in 1 mL of toluene was added to 3a
(0.350 g, 1.56 mmol) in 2.5 mL of toluene in a Schlenk tube. The
reaction was heated at 70 °C and monitored by 1H NMR
spectroscopy by analyzing aliquots from the reaction. When
the conversion to product was at least 90%, the volatiles were
removed under reduced pressure and the product 4a was
isolated by Kugelrohr distillation. Yield: 0.276 g, 79.0%.
Kinetic-Isotope Effect for the Intermolecular-Hydroamination
Reaction. In the glovebox, 1-(CH2Ph)2 (0.85 mg, 9.8 ꢀ 10-4
mmol), aniline (6.5 mg, 0.069 mmol), Me3Si-CtCH (110 mg,
1.12 mmol), and hexaethylbenzene (0.75 mg, 3.04 ꢀ 10-3 mmol)
in a total volume of 0.4 mL of C6D6 were added to a J.-Young
tube. Another J.-Young tube was set up identically and simul-
taneously to the previous reaction using C6H5ND2. The reac-
tions were monitored by 1H NMR spectroscopy.
˚
˚
˚
P2(1)/n, a=12.1124(13) A, b = 23.245(3) A, c = 15.3884(17) A,
˚
3
-1
β = 98.859(1)°, V = 4280.9(8) A , Z = 4, μ = 4.206 mm
F(000) = 1968, R1 = 0.0391 and wR2 = 0.0579 (based on all
11 371 data).
,
Magnetic-Susceptibility Measurements. Measurements for
12-(μ-NPh)2 were carried out on batches obtained indepen-
dently until at least two different experiments gave superimpo-
sable results. Magnetic susceptibility measurements were recor-
ded using a SQUID magnetometer at 5000 G. The samples were
prepared in the glovebox (ca. 50 mg), loaded in a gelatin capsule
that was positioned inside a plastic straw, and carried to the
magnetometer in a tube under N2. The sample was quickly
inserted into the instrument and centered, and data were ob-
tained from 5 to 300 K. The contribution from the sample
Kinetic-Isotope Effect for the Intramolecular-Hydroamination
Reaction. In the glovebox, 1-(CH2Ph)2 (2.6 mg, 3 ꢀ 10-3 mmol),
3a (40 mg, 0.069 mmol), and hexaethylbenzene (3.0 mg, 0.012
mmol) in a total volume of 0.4 mL of C6D6 were added to a
J. Young tube. Another J. Young tube was set up identically and
simultaneously to the previous reaction using 3a-d2. The reac-
tions were monitored by 1H NMR spectroscopy.
holders was not accounted for. Effective magnetic moments
for non-
1/2
were calculated by using the formula 2.828(Tχmol
)
Curie-Weiss behavior.
Diffusion-Coefficient Experiment. The pulse-gradient, spin-
echo (SE: 90°-t1-180°-t1-echo) technique was used to mea-
sure the self-diffusion coefficient of 12-(μ-NPh)2 in toluene-d8 at
100 °C on a Bruker DRX-500 NMR spectrometer. The gradient
strength was measured running the pulse-gradient spin-echo
experiment on H2O and using the literature value of 2.3 ꢀ 10-9
m2/s for the self-diffusion coefficient. The gradient strength was
found to be 51.0 G/cm. The time during which the diffusion
process occurred was varied from 50 μs to 5 ms. The duration of
the gradient pulse (δ) was set to 1 ms. The hydrodynamic radius
was obtained by using the Stokes-Einstein equation.68
Acknowledgment. The authors thank Marisa J. Monreal
for help with the SQUID experiments, Gregory Kuzmanich
for help with the absorption-spectroscopy experiments, Dr.
Robert Taylor for assistance with the diffusion-coefficient
experiment, and Prof. Kai Hultzsch (Rutgers University)
for insightful discussions. This work was supported by the
UCLA, Sloan Foundation, and DOE (Grant ER15984).
Supporting Information Available: Details of the NMR
spectroscopy experiments, DFT calculations, and full crystallo-
graphic descriptions (in cif format) are available free of charge
via the Internet at http://pubs.acs.org.
Hydroamination Reactions. In the glovebox, 1-(CH2Ph)2, the
alkyne, the amine, and the internal standard, hexaethylbenzene,
were added to C6D6 and transferred to a Teflon-sealed NMR
tube, which was taken out of the glovebox. The tube was placed
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