Alkyl aluminum-catalyzed addition of amines to carbodiimides: A highly efficient route to substituted guanidines

Article abstract of DOI:10.1021/om801035t

The commercially readily available alkyl aluminums, such as AlMe ₃, AlEt₃, and AlEt₂Cl, can serve as excellent catalyst precursors for the catalytic addition of amines to carbodiimides, yielding quantitatively their corres

Full text of DOI:10.1021/om801035t

882
Organometallics 2009, 28, 882–887
Alkyl Aluminum-Catalyzed Addition of Amines to Carbodiimides: A
Highly Efficient Route to Substituted Guanidines
Wen-Xiong Zhang,*,†,‡ Dongzhen Li,† Zitao Wang,† and Zhenfeng Xi*,†
Beijing National Laboratory for Molecular Sciences (BNLMS), and Key Laboratory of Bioorganic
Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry, Peking UniVersity,
Beijing 100871, People’s Republic of China, and State Key Laboratory of Elemento-Organic Chemistry,
Nankai UniVersity, Tianjin, 300071, People’s Republic of China
ReceiVed October 28, 2008
The commercially readily available alkyl aluminums, such as AlMe3, AlEt3, and AlEt2Cl, can serve as
excellent catalyst precursors for the catalytic addition of amines to carbodiimides, yielding quantitatively
their corresponding trisubstituted guanidines. Aromatic C-X (X ) F, Cl, Br, and I) bonds, nitro NO2,
and terminal alkyne units can survive the reaction conditions. An aluminum guanidinate species has
been characterized by single-crystal X-ray structural analysis and has been confirmed to be a true catalyst
species.
cleophilic addition of some aromatic amines to carbodiimides.7
However, very few catalysts are known to promote the catalytic
Introduction
addition of amines to unactivated carbodiimides.1,2,8-10 The
catalytic addition of primary aromatic amines to carbodiimides
was reported by using titanium and vanadium imido complexes
to yield the corresponding guanidines, but secondary amines
could not be used in these reactions, because the catalytic
process required the regeneration of a “MdN” imido moiety.2
In 2006, a half-sandwich rare earth metal alkyl complex was
reported by Hou and co-workers to achieve the catalytic addition
of secondary amines to carbodiimides.1a-c In this catalytic
process, the nucleophilic addition of a rare earth metal-nitrogen
single bond to a carbodiimide meets the requirements for a
secondary amine, which is quite different from titanium and
vanadium imido catalysts. Similarly, lithium silyl amido com-
pound (Me3Si)2NLi,1f lanthanocene amido complexes,1d,e the
carboranyl-alkoxy-ligated titanium amido complex,1g and heavier
group 2 amides1j have been found to have high catalytic
activity, presumably through the same mechanism. The search
for a readily available catalyst system for efficient addition
of amines to carbodiimides is therefore of obvious interest
and importance.
Catalytic addition reaction of amine N-H bonds to carbo-
diimides (catalytic guanylation reaction of amines) is an atom-
economical and straightforward route to multisubstituted
guanidines, RNdC(NR′R′′)NHR,1,2 which are an important class
of N-containing compounds serving as building blocks for many
biologically relevant compounds3 and also as base catalysts in
synthetic organic chemistry.4 Generally, the reaction of an amine
with a suitable electrophilic guanylating reagent5 or function-
alization of a pre-existing guanidine core provide two typical
routes for the preparation of substituted guanidines.6 Tetrabu-
tylammonium fluoride was also reported to promote the nu-
* Corresponding authors. Fax: (+86)10-62759728. E-mail: wx_zhang@
pku.edu.cn; zfxi@pku.edu.cn.
† Peking University.
‡ Nankai University.
(1) For catalytic addition of amines to carbodiimides by M-N bond
complexes, see: (a) Zhang, W.-X.; Hou, Z. Org. Biomol. Chem. 2008, 6,
1720–1730. (b) Zhang, W.-X.; Nishiura, M.; Hou, Z. Chem.-Eur. J. 2007,
13, 4037–4051. (c) Zhang, W.-X.; Nishiura, M.; Hou, Z. Synlett 2006, 1213–
1216. (d) Zhou, S.; Wang, S.; Yang, G.; Li, Q.; Zhang, L.; Yao, Z.; Zhou,
Z.; Song, H.-B. Organometallics 2007, 26, 3755–3761. (e) Li, Q.; Wang,
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A.; Galindo, A. Organometallics 2006, 25, 4996–5002. (i) Du, Z.; Li, W.;
Zhu, X.; Xu, F.; Shen, Q. J. Org. Chem. 2008, 73, 8966–8972. (j) Lachs,
J. R.; Barrett, A. G. M.; Crimmin, M. R.; Kociok-Ko¨hn, G.; Hill, M. S.;
Mahon, M. F.; Procopiou, P. A. Eur. J. Inorg. Chem. 2008, 4173–4179.
(k) Crimmin, M. R.; Barrett, A. G. M.; Hill, M. S.; Hitchcock, P. B.;
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2179.
The aluminum alkyls and amides are potential bifunctional
catalysts bearing a Lewis acidic Al(III) center and activated
Al-C/N bonds.11,12 Although nucleophilic addition of group
13 amides to carbodiimides giving the corresponding guanidi-
nate species is a well-established process,13,14 catalytic trans-
formation of a group 13 guanidinate species is rare and has
remained unknown until very recently.12d We report here such
a catalytic transformation of an aluminum guanidinate species
to prepare guanidines by alkyl aluminum catalyst precursors
such as AlMe3, AlEt3, and AlEt2Cl. Aromatic carbon-halogen
bonds, NO2, and terminal alkyne units survived the reaction
conditions. An aluminum guanidinate species has been char-
(2) For catalytic addition of amines to carbodiimides by MdN imido
complexes, see: (a) Ong, T.-G.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem.
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Organomet. Chem. 2004, 689, 993–996.
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10.1021/om801035t CCC: $40.75
2009 American Chemical Society
Publication on Web 01/14/2009

Efficient Route to Substituted Guanidines
Organometallics, Vol. 28, No. 3, 2009 883
Table 1. Catalytic Addition of an Aniline to a
acterized by X-ray single-crystal structural analysis and con-
firmed to be a true catalyst species.
N,N′-Diisopropylcarbodiimidea
Results and Discussion
Catalytic Addition of Primary Aromatic Amines to Carbo-
diimides. As a control experiment, N,N′-diisopropylcarbodiimide
iPrNdCdNiPr was heated with aniline in C6D5Cl at 140 °C,
but no reaction was observed in 24 h (Table 1, entry 1). In
contrast, addition of a small amount (1-2 mol %) of the readily
available alkyl aluminum complex AlMe3 at room temperature
entry cat. (mol %)
solvent
C6D6Cl
C6D6
temp (°C) time/h yield (%)b
1
2
3
4
5
6
7
8
9
0
140
rt
rt
rt
rt
rt
rt
rt
rt
24
0.5
0
>99
99
>99
>99
>99
>99
>99
59
AlMe3(2)
AlMe3(1)
AlMe3(2)
AlMe3(2)
AlMe3(2)
AlEt3(2)
AlEt2Cl(2)
AlCl3(2)
C6D6
0.5
0.5
0.5
0.5
0.5
0.5
2
[D8]toluene
[D8]THF
Et2O
C6D6
C6D6
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C6D6
a Conditions: aniline, 0.51 mmol; N,N′-diisopropylcarbodiimide, 0.50
b
1
mmol. Yields were determined by H NMR.
led to rapid addition of aniline to PrNdCdNiPr to give the
i
N,N′,N′′-trisubstituted guanidine 1 in high yields (Table 1, entries
2-6). The polarity of solvents did not show a significant
influence on the catalytic activity in the present reaction (Table
1, entries 3-6). Other alkyl complexes such as AlEt3 and
AlEt2Cl were also effective for this catalytic reaction, suggesting
that the activity of the present catalyst system is not significantly
affected by the initial alkyl group (Table 2, entries 7 and 8).
Compared with alkyl aluminum catalyst precursors, AlCl3
showed lower catalytic activity (Table 1, entries 2-9).
AlMe3 was then chosen as a catalyst for the addition reaction
between various primary amines and carbodiimides having
various substituents. Representative results are summarized in
Table 2. In the presence of 2 mol % of AlMe3, the reaction of
aniline with carbodiimides having N-aryl-N′-alkyl and N,N′-
dialkyl substituents was completed at room temperature to yield
the corresponding substituted guanidines 1-5 quantitatively
(Table 2, entries 1-5). In the case of the bulkier N,N′-di-tert-
butylcarbodiimide tBuNdCdNtBu, the reaction became a little
bit slower probably owing to its steric hindrance (Table 2, entry
4). A wide range of substituted anilines could be used for this
reaction. The reaction was not influenced by either electron-
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17, 1595–1601.

884 Organometallics, Vol. 28, No. 3, 2009
Zhang et al.
Table 2. Catalytic Addition of Various Primary Anilines to Carbodiimidesa
a Conditions: amines, 2.02 mmol; carbodiimides, 2.00 mmol; AlMe3, 0.04 mmol; benzene, 5 mL. b Isolated yield. c Conditions: AlMe3 (5 mol %), 80
°C, 1 h. d Conditions: AlEt3 (5 mol %), 80 °C, 1 h. e THF, rt, 1 h.
withdrawing or -donating substituents or the position of the
substituents at the phenyl ring (Table 2, entries 1-16). Aromatic
C-F (Table 2, entry 6), C-Cl (Table 2, entry 7), C-Br (Table
2, entry 8), and C-I (Table 2, entry 9) bonds survived in the
present reactions. In the case of m-aminophenylacetylene,
the reaction took place selectively at the amino group, while
the terminal alkyne unit remained unchanged (Table 2, entry
10), possibly because the activation energy of a proton transfer
from an amine substrate to an aluminum guanidinate is lower
than that of an alkyne.15g The reaction of 4-nitroaniline with
iPrNdCdNiPr gave quantitatively product 15 in THF at room
temperature within 1 h; on the contrary, [ethylenebis(indenyl)]-
lanthanide(III) amides failed to produce the corresponding
guanidine product.1d
In the case of 2,6-dimethylaniline and 2,4,6-trimethylaniline,
AlEt3 was less efficient and afforded only a trace amount of
the corresponding guanidine products even at higher temperature
(80 °C) and in the presence of higher catalyst loading (5%).
The reaction of 2,6-dimethylaniline (Table 2, entry 13) and
i
2,4,6-trimethylaniline (Table 2, entry 14) with PrNdCdNiPr,
however, in the presence of 5 mol % of AlMe3 provided the
corresponding guanidine products at 80 °C in high yields,
respectively. These results are in sharp contrast with what was
observed above in the reaction of aniline with carbodiimides
(cf. Table 1, entries 3, and 7), showing that the effect of the
alkyl group of aluminum precursors on the catalytic activity
could depend on the reaction substrates. The reaction of the
i
bulkier 2,6-diisopropylaniline with PrNdCdNiPr in the pres-

Efficient Route to Substituted Guanidines
Organometallics, Vol. 28, No. 3, 2009 885
Table 3. Catalytic Addition of Heterocyclic Primary Amines to
Carbodiimidesa
Scheme 1. Formation of an Aluminum Guanidinate and Its
Reaction with Pyrazole 22
primary amines with the symmetric carbodiimides RNdCdNR
i
t
(R ) Pr, Cy, and Bu), all showed one set of signals for the
iPr, Cy, and Bu groups, suggesting that the two Pr, Cy, and
t
i
tBu groups in each guanidine product should be in a similar
environment. The H and 13C NMR spectra of the guanidine
1
products 3, 5, and 18, which resulted from the reactions with
the unsymmetrical carbodiimides EtNdCdNtBu and CyNd
CdNPh, also suggested the presence of only one isomer in
solution. The structure of 5 was confirmed by its X-ray single-
crystal structural analysis (Figure 1 and Table 2, entry 5).
Mechanistic Aspects. (a) Stoichiometric Addition of Amine
N-H Bonds to Carbodiimides. The 1:1:1 reaction of AlMe3,
i
PhNH2, and PrNdCdNiPr in C6D6 at room temperature was
first carried out to give quantitatively the aluminum guanidinate
complex [Me2Al{iPrNdC(NPh)(NHiPr)}]. However, in a 1:2:2
reaction of AlMe3, PhNH2, and iPrNdCdNiPr in C6D6 at room
temperature, the guanidine product PhNdC(NHiPr)2 (1) was
observed in addition to the aluminum guanidinate complex
[Me2Al{iPrNdC(NPh)(NHiPr)}], suggesting that the protonoly-
sis between the guanidinate unit {iPrNdC(NPh)(NHiPr)} and
PhNH2 became faster than that of the second Al-Me and PhNH2
in the present conditions. An attempt to obtain suitable crystals
of aluminum guanidinate [Me2Al{iPrNdC(NPh)(NHiPr)}], how-
ever, was unsuccessful owing to its good solubility in common
organic solvents. Then the 1:1:1 reaction of AlMe3, amino-
a Conditions: amines, 2.02 mmol; carbodiimides, 2.00 mmol; AlMe3,
0.04 mmol; benzene, 5 mL. b Isolated yield.
i
substituted pyrazole 22, and PrNdCdNiPr in C6D6 at room
temperature was carried out to give the guanidinate complex
24 within 5 min at room temperature (Scheme 1). Single crystals
of 24 suitable for X-ray analysis were grown in ether at room
temperature overnight. This revealed that 24 adopts a monomeric
structure, in which the metal center is bonded to two methyl
ligands and one guanidinate unit (Figure 2). While the differing
guanidine substituents result in a small degree of asymmetry,
the X-ray structure clearly shows a delocalized monoanionic
guanidinate with roughly symmetric Al-N bonds. At room
temperature, a 1:1 mixture of 22 and 24 was observed to give
slowly the corresponding guanidine compound 19 and
23(Scheme 1). However, when excess 22 and iPrNdCdNiPr (1:
1) were added to 24 in C6D6 at room temperature, catalytic
formation of 19 was achieved (eq 1).
Figure 1. ORTEP drawing of 5 with 30% thermal ellipsoids.
Hydrogen atoms, except those on the nitrogen atoms, are omitted
for clarity. Selected bond lengths [Å] and angles [deg]: N(1)-C(1)
1.353(4), N(2)-C(1) 1.382(4), N(3)-C(1) 1.301(4), N(1)-C(1)-N(2)
112.4(3), N(1)-C(1)-N(3) 120.5(3), N(2)-C(1)-N(3) 127.0(4).
ence of AlMe3 did not occur to give the corresponding guanidine
even at higher temperatures (e.g., 110 °C), showing that the
steric effects of substituents on phenyl rings have a great
influence on the occurrence of catalytic reactions.
A variety of heterocyclic primary amines such as amino-
substituted isoxazoles, pyrozoles, thiazoles, and pyridines could
also be used for this reaction, as shown in Table 3. In the case
of the bulkier tert-butyl-3-ethylcarbodiimide, the reaction with
5-methylisoxazol-3-amine required a higher temperature (80 °C)
for completion in 1 h, probably due to steric hindrance (Table
3, entry 2). As far as amino-substituted thiazole and pyridine
were concerned, the reactions with iPrNdCdNiPr became a little
slower than that of amino-substituted isoxazoles and pyrozoles
(Table 3, entries 1, 4, and 5).
The 1H and 13C NMR spectra of the guanidine products 1, 2,
4, 6-17, and 19-21, formed by the reactions of aromatic
(b) Possible Mechanism. A possible catalytic cycle for the
addition reaction of primary aromatic amines to carbodiimides

886 Organometallics, Vol. 28, No. 3, 2009
Zhang et al.
leading to efficient formation of a series of guanidine derivatives
with a wide range of substituents on the nitrogen atoms.
Functional groups such as NO2, Ct CH, and aromatic C-X (X
) F, Cl, Br, I) bonds can survive the catalytic reaction
conditions. The isolation and reactivity investigation of the
aluminum guanidinate intermediate 24 suggest that the catalytic
formation of a guanidine compound proceeds through nucleo-
philic addition of an aluminum amido species, formed by
acid-base reaction between an Al-alkyl bond and an amine
N-H bond, to a carbodiimide, followed by amine protonolysis
of the resultant guanidinate species. These results have dem-
onstrated that a guanidinate unit, though being often used as a
supporting ligand for the aluminum complexes, can itself
participate in a reaction in a catalytic fashion under appropriate
conditions.
Figure 2. ORTEP drawing of 24 with 30% thermal ellipsoids.
Hydrogen atoms, except that on the nitrogen atom N2, are omitted
for clarity. Selected bond lengths (A) and angles (deg): Al(1)-N(1)
1.933(2), Al(1)-N(3) 1.950(2), Al(1)-C(1) 1.943(2), Al(1)-C(2)
1.945(3), N(1)-C(6) 1.318(3), N(2)-C(6) 1.341(3), N(3)-C(6)
1.388(3), N(1)-Al(1)-N(3) 69.22(9), N(1)-C(6)-N(3) 109.1(2),
N(1)-C(6)-N(2) 127.7(3), N(2)-C(6)-N(3) 123.1(3).
Experimental Section
General Procedures. Unless otherwise noted, all starting
materials were commercially available and were used without
further purification. All reactions were carried out under a dry
and oxygen-free nitrogen atmosphere by using Schlenk tech-
niques or under a nitrogen atmosphere in a Mikrouna Super
(1220/750) glovebox. The nitrogen in the glovebox was con-
stantly circulated through a copper/molecular sieve catalyst unit.
The oxygen and moisture concentrations in the glovebox
atmosphere were monitored by an O2/H2O Combi-Analyzer to
ensure both were always below 1 ppm. Solvents were distilled
fromsodium/benzophenoneketyl,degassedbythefreeze-pump-thaw
method (three times), and dried over fresh Na chips in the
glovebox. [D6]Benzene, [D8]toluene, and [D8]THF (all 99+ atom
% D) were obtained from Acros and were dried over fresh Na
chips in the glovebox for NMR reactions. 1H and 13C NMR
spectra were recorded on a JEOL-AL400 spectrometer (FT, 400
MHz for 1H; 100 MHz for 13C) or a JEOL JNM-AL300
Scheme 2. Possible Mechanism of Catalytic Addition of
Primary Aromatic Amines to Carbodiimides
1
spectrometer (FT, 300 MHz for H; 75 MHz for 13C) at room
temperature, unless otherwise noted. Organometallic samples for
NMR spectroscopic measurements were prepared in the glovebox
by use of J. Young valve NMR tubes (Wilmad 528-JY).
Typical Procedures for the Catalytic Reaction of Primary
Aromatic Amines to Carbodiimides. (i) NMR Tube Reaction.
In the glovebox, a J. Young valve NMR tube was charged with
AlMe3 (10 µL, 0.01 mmol), C6D6 (0.5 mL), aniline (48 mg, 0.51
mmol), and N,N′-diisopropylcarbodiimide (63 mg, 0.50 mmol). The
tube was taken outside the glovebox, and the reaction was carried
out at room temperature. Formation of 1 was easily monitored by
1H NMR spectroscopy. The reaction was quantitative and finished
within 1 h.
is proposed in Scheme 2. The acid-base reaction between
an aluminum alkyl and a primary amine N-H bond yields
straightforwardly an amido species such as A. Nucleophilic
addition of the amido species A to a carbodiimide would
first afford the guanidinate species B, which could then
quickly be rearranged to the guanidinate species C at room
temperature through the intramolecular 1,3-hydrogen shift
(path a).1a,b In the case of the formation of C, nucleophilic
attack of the amido species A at the central carbon atom of
the carbodiimide followed by 1,3-hydrogen migration from
the aryl amido moiety to the more basic uncoordinated
nitrogen leading to the formation of C (path b) could not be
ruled out. Protonolysis of C by another molecule of primary
amine would regenerate the amido A and release the
guanidine D. Intramolecular 1,3-hydrogen shift in D could
give the more stable, final product E. Protonolysis of B by
another molecule of primary amine giving the final product
E is also a possible route.13c
(ii) Preparative Scale Reaction. In the glovebox, a solution of
aniline (188 mg, 2.02 mmol) in benzene (3 mL) was added to a
solution of AlMe3 (0.04 mL, 0.04 mmol) in a Schlenk tube. N,N′-
Diisopropylcarbodiimide (252 mg, 2.00 mmol) was then added to
the above reaction mixture. The Schlenk tube was taken outside
the glovebox, and the reaction was carried out at room temperature
for 1 h. After the solvent was removed under reduced pressure,
the residue was extracted with ether and filtered to give a clean
solution. After removing the solvent under vacuum, the residue was
recrystallized in ether to provide a colorless solid, 1.
1
1: colorless solid, yield >99%. H NMR (400 MHz, C6D6): δ
0.91 (d, J ) 6.4 Hz, 12H, CH3), 3.52 (br, 2H, NH), 3.64-3.69 (m,
2H, CH), 6.90 (t, J ) 7.6 Hz, 1H, p-C6H5), 7.10 (d, J ) 7.6 Hz,
2H, o-C6H5), 7.25 (t, J ) 7.6 Hz, 2H, m-C6H5). 13C NMR (100
MHz, C6D6): δ 23.4, 43.4, 121.3, 123.7, 129.6, 149.7, 151.6.1b
Conclusion
1
3: colorless solid, yield >99%. H NMR (400 MHz, C6D6): δ
Readily available alkyl aluminums such as AlMe3, AlEt3, and
AlEt2Cl can serve as excellent catalyst precursors for the
catalytic addition of amine N-H bonds to carbodiimides,
0.71 (t, J ) 7.2 Hz, 3H, CH2CH3), 1.29 (s, 9H, C(CH3)3), 2.70-2.73
(m, 2H, CH2CH3), 3.48 (br, 2H, NH), 6.91 (t, J ) 7.2 Hz, 1H,
p-C6H5), 7.06 (d, J ) 7.2 Hz, 2H, o-C6H5), 7.23-7.26 (m, 2H,

Efficient Route to Substituted Guanidines
Organometallics, Vol. 28, No. 3, 2009 887
m-C6H5). 13C NMR (100 MHz, CDCl3): δ 15.0, 29.9, 37.1, 50.7,
121.2, 123.6, 129.6, 150.0, 151.6.
X-ray Crystallographic Studies. Crystals for X-ray analyses
of 5 and 24 were obtained as described in the preparations. The
crystals were manipulated in the glovebox and were sealed in thin-
walled glass capillaries. Data collections were performed at -110
°C on a Bruker CCD APEX diffractometer with a CCD area
detector, using graphite-monochromated Mo KR radiation (λ )
0.71069 Å). The determination of crystal class and unit cell
parameters was carried out by the SMART program package. The
raw frame data were processed using SAINT and SADABS to yield
the reflection data file.16 The structures were solved by use of the
SHELXTL program.17 Refinement was performed on F2 anisotro-
pically for all the non-hydrogen atoms by the full-matrix least-
squares method. The hydrogen atoms were placed at the calculated
positions and were included in the structure calculation without
further refinement of the parameters. Crystal data, data collection,
and processing parameters for 5 and 24 are given only in the
Supporting Information. Crystallographic data (excluding structure
factors) have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication nos. CCDC-706408 (5)
and CCDC-706407 (24). Copies of these data can be obtained free
of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
1
4: colorless solid, yield >99%. H NMR (400 MHz, C6D6): δ
1.20 (s, 18H, C(CH3)3), 3.67 (br, 2H, NH), 6.92 (t, J ) 7.2 Hz,
1H, p-C6H5), 7.02 (d, J ) 7.2 Hz, 2H, o-C6H5), 7.21-7.25 (m,
2H, m-C6H5). 13C NMR (100 MHz, CDCl3): δ 30.0, 50.6, 121.4,
123.5, 129.5, 149.9, 151.5.
5: Single crystals suitable for X-ray analysis were grown in
benzene at room temperature for two days; colorless crystals, yield
93%. 1H NMR (400 MHz, C6D6): δ 0.77-1.98 (m, 10H, Cy), 3.87
(br, 2H, NH and CH), 5.67 (br, 1H, NH), 6.86-7.36 (m, 10H,
C6H5). 13C NMR (100 MHz, CDCl3): δ 25.2, 25.9, 33.4, 50.0,
122.7(br), 123.8, 125.0, 129.1, 129.2, 129.6, 146.8, 150.4, 151.7.
1
6: colorless solid, yield >99%. H NMR (300 MHz, C6D6): δ
0.88 (d, J ) 6.3 Hz, 12 H, CH3), 3.26-3.67 (br, 4H, 2NH and
2CH), 6.84-7.16 (br, 4H, CH). 13C NMR (75 MHz, C6D6): δ 23.2,
43.2, 116.1 (d, J ) 21.6 Hz), 124.5 (d, J ) 7.43 Hz), 147.6 (d, J
) 2.48 Hz), 150.0 (d, J ) 1.28 Hz), 160.08.
10: colorless solid, yield >99%. 1H NMR (300 MHz, C6D6): δ
0.89 (d, J ) 6.0 Hz, 12 H, CH3), 2.82 (s, 1H, CH), 3.54-3.67 (br,
4H, 2NH and 2CH), 6.99-7.17 (br, 4H, CH). 13C NMR (75 MHz,
C6D6): δ 23.1, 43.2, 77.2, 84.6, 123.6, 124.6, 125.0, 127.1, 129.6,
150.1, 151.7.
12: colorless solid, yield >99%. 1H NMR (300 MHz, C6D6): δ
0.91 (d, J ) 6.3 Hz, 12 H, CH3), 1.32 (d, J ) 6.9 Hz, 6H, CH3),
3.36-3.63 (br, 5H, 2NH and 3CH), 6.94-7.33 (br, 4H, CH). 13C
NMR (75 MHz, C6D6): δ 23.3, 23.4, 28.6, 43.3, 122.1, 123.0, 126.2,
126.7, 142.2, 148.5, 148.8.
Acknowledgment. This work was supported by the
Natural Science Foundation of China (20702003, 20632010,
and 20521202) and the Major State Basic Research Develop-
ment Program (2006CB806105). Cheung Kong Scholars
Programme, Qiu Shi Science & Technologies Foundation,
BASF, Dow Corning Corporation, and Eli Lilly China are
gratefully acknowledged.
Isolation of the Guanidiate Complex 24. In the glovebox, a
benzene solution (3 mL) of 3-methyl-1-phenyl-1H-pyrazol-5-amine
(22) (173 mg, 1 mmol) was added to a benzene solution (2 mL) of
AlMe3 (0.5 mL, 2 mol/L in toluene, 1 mmol) in a flask. Then N,N′-
diisopropylcarbodiimide (126 mg, 1 mmol) was added to the above
reaction mixture. The mixture was stirred at room temperature for
5 min. After the solvent was removed under reduced pressure, the
residue was extracted with ether and filtered to give a clean solution.
The solution volume was reduced under vacuum to precipitate 24
as a colorless crystalline powder in 93% yield. Single crystals of
24 suitable for X-ray analysis were grown in ether at room
Supporting Information Available: Experimental details, X-ray
data for 5 and 24, and scanned NMR spectra of all new products
(PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
OM801035T
(15) (a) Liu, Y.; Nishiura, M.; Wang, Y.; Hou, Z. J. Am. Chem. Soc.
2006, 128, 5592–5593. (b) Zhang, W.-X.; Nishiura, M.; Hou, Z. J. Am.
Chem. Soc. 2005, 127, 16788–16789. (c) Nishiura, M.; Hou, Z. J. Mol.
Catal. A 2004, 213, 101>106. (d) Nishiura, M.; Hou, Z.; Wakatsuki, Y.;
Yamaki, T.; Miyamoto, T. J. Am. Chem. Soc. 2003, 125, 1184–1185. (e)
Hou, Z. Bull. Chem. Soc. Jpn. 2003, 76, 2253–2266. (f) Zhang, W.-X.;
Nishiura, M.; Hou, Z. Angew. Chem., Int. Ed. 2008, 47, 9700–9703. See
also: (g) Rowley, C. N.; Ong, T.-G.; Priem, J.; Richeson, D. S.; Woo, T. K.
Inorg. Chem. 2008, 47, 12024–12031.
(16) Sheldrick, G. M. SADABS, Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Go¨ttingen,
Germany, 1996.
(17) Sheldrick, G. M. SHELXTL 5.10 for Windows NT, Structure
Determination Software Programs; Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 1997.
1
temperature overnight. H NMR (400 MHz, C6D6): δ -0.54 (s,
6H, AlMe2), 0.64 (d, J ) 6.0 Hz, 6H, CH(CH3)2), 0.90 (d, J ) 6.0
Hz, 6H, CH(CH3)2), 2.27 (s, 3H, Me), 2.94-3.01 (m, 1H,
CH(CH3)2), 3.49-3.58 (m, 1H, CH(CH3)2), 4.07 (d, 1H, J ) 9.6
Hz, NH), 5.62 (s, 1H, CH(pyrazolyl)), 6.96 (t, J ) 7.6 Hz, 1H,
p-C6H5), 7.13-7.18 (m, 2H, m-C6H5), 7.80 (d, J ) 7.6 Hz, 2H,
o-C6H5). 13C NMR (100 MHz, CDCl3): δ -9.5, 14.5, 23.0, 24.0,
44.0, 44.1, 44.9, 96.1, 124.6, 126.6, 129.1, 140.2, 145.0, 148.8,
160.8. Anal. Calcd for C19H30AlN5: C, 64.20; H, 8.51; N, 19.70.
Found: C, 64.30; H, 8.76; N, 19.45.