Mechanistic insights into N - N bond cleavage in catalytic guanylation reactions between 1,2-diarylhydrazines and carbodiimides

Article abstract of DOI:10.1021/jo501865b

Cleavage of the N - N bond in 1,2-diarylhydrazine was achieved through an alkyllithium-catalyzed guanylation reaction of 1,2-diarylhydrazine with carbodiimide, affording guanidine and azo compounds. This N - N bond cleavage via thermal rearrangement was d

Full text of DOI:10.1021/jo501865b

Article
pubs.acs.org/joc
Mechanistic Insights into NN Bond Cleavage in Catalytic
Guanylation Reactions between 1,2-Diarylhydrazines and
Carbodiimides
Ling Xu,†,§ Yu-Chen Wang,†,§ Wangyang Ma,† Wen-Xiong Zhang,*,†,‡ and Zhenfeng Xi*,†
†Beijing National Laboratory for Molecular Sciences, MOE Key Laboratory of Bioorganic Chemistry and Molecular Engineering,
College of Chemistry, Peking University, Beijing 100871, China
‡State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
S
* Supporting Information
ABSTRACT: Cleavage of the NN bond in 1,2-diarylhydrazine was
achieved through an alkyllithium-catalyzed guanylation reaction of 1,2-
diarylhydrazine with carbodiimide, affording guanidine and azo
compounds. This NN bond cleavage via thermal rearrangement was
driven by an intramolecular proton shift. No reductants, oxidants, bases,
or external protons were needed. The proposed mechanism has been
well elucidated by the isolation, characterization, and reaction studies of
two important amido lithium intermediates and an ArHN-substituted
guanidine.
and azo compounds (Scheme 1). In this NN bond cleavage
INTRODUCTION
■
process, no additives including reductants, oxidants, bases, or
In recent years, there has been significant growth in the study of
external protons were required. The reaction mechanism was
investigated through the isolation, characterization, and
reaction studies of two important amido lithium intermediates
and an ArHN-substituted guanidine.
NN bond cleavage in hydrazines because of its importance in
biological nitrogen fixation1,2 and organic synthesis.3−5 In the
case of biological nitrogen fixation, evidence has shown that
only η1-coordinated hydrazines can be converted into ammonia
by NN bond cleavage, in which both the variable oxidation
RESULTS AND DISCUSSION
states on the Mo center and an external proton are required
(Scheme 1a).2 In organic synthesis, known methods for NN
bond cleavage of hydrazines mainly involve reductive cleavage,3
oxidative cleavage in which one of the substrate nitrogen atoms
is substituted by a carbonyl group,4 or base-promoted
eliminative cleavage (Schemes 1b−d).5 In all of these processes,
a stoichiometric amount of reductants, oxidants, and bases are
required. In addition, NN bond cleavage of hydrazines has
also been discovered and applied to Benzidine rearrangement6
and Fischer indole synthesis.7 In these two metal-free
transformations, NN bond cleavage is promoted by external
protons (Schemes 1e and 1f).
■
Catalytic Guanylation Reaction of 1,2-Diarylhydrazine
with Carbodiimide. a. Condition Screening. A 1:1 reaction
between 1,2-diphenylhydrazine (PhNHNHPh) and N,N′-
diisopropylcarbodiimide (DIC) was performed. No reaction
would take place without catalysts even at 110 °C for 24 h
(Table 1, entry 1). However, when the half-sandwich rare-earth
catalyst (1 mol %) [{Me2Si(C5Me4)(NPh)}Y(CH2SiMe3)-
(thf)2] (1)11i or [Cp4PrPhY(CH2SiMe3)3][Li(thf)3(OEt2)]
(2)11c was added to the mixture of 1,2-diphenylhydrazine and
DIC, the guanidine product PhNC(NHiPr2)2 (3a) and trans-
azobenzene (trans-PhNNPh) were obtained instead of the
i
expected product PrNC(NHiPr)NPhNHPh (4) (Table 1,
We have been interested in catalytic guanylation reactions of
various amines with carbodiimides to prepare guanidines.8−12
In this catalytic guanylation reaction, an amine that acts as a
nucleophile is added to a carbodiimide. Metal-catalyzed
aminoguanylation reactions between 1,1-disubstituted hydra-
zines and carbodiimides giving amino guanidines have been
reported;9g,10b however, we envisioned that 1,2-diarylhydra-
zines could be alternative nucleophiles for catalytic guanylation
reactions if cleavage of the NN bond in 1,2-diarylhydrazine
occurred. Herein, we report cleavage of the NN bond of 1,2-
diarylhydrazines in alkyllithium-catalyzed guanylation reactions
of 1,2-diarylhydrazines with carbodiimides to give guanidines
entries 2 and 3). Other rare-earth catalysts such as Y-
(CH2SiMe3)3(thf)2 or alkali-metal catalysts such as LiCH2TMS,
LiN(TMS)2, NaN(TMS)2, and KN(TMS)210g all could serve as
excellent catalyst precursors to give 3a and trans-azobenzene
(Table 1, entries 4−8, respectively). Other solvents such as
THF and toluene afforded similar results.
Special Issue: Mechanisms in Metal-Based Organic Chemistry
Received: August 12, 2014
Published: October 14, 2014
© 2014 American Chemical Society
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Table 2. For isopropyl-, cyclohexyl-, phenyl-, and tolyl-
substituted carbodiimides, their corresponding guanidines
could all be obtained in moderate to good yields (Table 2).
Scheme 1. Different Modes of NN Bond Cleavage of
Hydrazines
Table 2. Substrate Scope of the Catalytic Guanylation
a
Reaction between ArNHNHAr and Carbodiimides
entry
R1
R2
Ar
yield (%)
1
iPr
Cy
Ph
iPr
Cy
Tol
iPr
iPr
iPr
iPr
iPr
Cy
Ph
iPr
Cy
Tol
iPr
iPr
iPr
iPr
Ph
3a: 89
3b: 93
3c: 71
3d: 82
3e: 88
3f: 96
3g: 85
3h: 93
3i: 64
3j: 46
2
Ph
3
Ph
4
Tol
Tol
Tol
5
6
7
o-MeC6H4
4-ClC6H4
4-BrC6H4
4-tBuC6H4
8
9
10
a
Conditions: ArNHNHAr, 1.0 mmol; carbodiimides, 1.0 mmol.
When the reaction of 1-methyl-1-phenylhydrazine or 1,1-
diphenylhydrazine with DIC was tested under the present
conditions, only amino guanidines, which were similar to those
of the work of Gade and Bergman, were observed. The present
reaction mode between 1,2-disubstituted arylhydrazines and
carbodiimides is different from that of catalytic amino-
guanylation reactions between 1,1-disubstituted hydrazines
and carbodiimides in which NN bond cleavage is not
observed.9g,10b
Table 1. Screening of the Catalytic Activity of the Reaction
between PhNHNHPh and DIC
a
Mechanistic Studies on NN Bond Cleavage. Cleavage
of the NN bond in 1,2-diarylhydrazine has apparently taken
place in the aforementioned catalysis process. However, the
reaction conditions applied in this study are totally different
from the known conditions that are used for the cleavage of
NN bonds in hydrazines. To explore this reaction
mechanism, a stoichiometric reaction was performed (Scheme
2). Initially, the reaction between LiCH2TMS and PhNHNHPh
in THF at room temperature yielded the lithium hydrazide
PhNHNPhLi (5). Recrystallization of 5 in THF/hexane
solution afforded the THF-coordinated complex 5′ in 97%
yield (Scheme 2a). 5′ was characterized by H and 13C NMR
1
b
spectra. Single crystal X-ray diffraction analysis indicated that 5′
was a solid-state, unsymmetric trimer (Figure 1). Li1 took a
five-coordinate mode bonded by one thf and four N atoms,
whereas Li2 adopted a four-coordinate fashion bonded by one
thf and three N atoms. In contrast, Li3 bonded to one thf and
two N atoms.
entry
catalyst
loading (mol %)
yield (%)
1
2
3
4
5
6
7
8
none
0
1
1
1
3
3
3
3
0
84
96
44
96
97
88
93
1
2
Y(CH2TMS)3(thf)2
LiCH2TMS
Heating the benzene solution of 5′ at 110 °C for 24 h did not
lead to any change in 1H NMR spectra, indicating that the N
N bond cleavage did not occur at this step. Then, 1 equiv of
DIC was added to the benzene solution of 5′ at room
temperature. After the sample had been mixed for 4 h, a large
amount of white powder 6 precipitated. Via evaporation of the
THF/hexane solution of 6, single crystals of 6′ were obtained
(Scheme 2b).13 X-ray analysis revealed that 6′ was a
centrosymmetric dimer (Figure 2). The bridged Li atom
adopted a distorted tetrahedral coordination environment and
LiN(TMS)2
NaN(TMS)2
KN(TMS)2
a
b
Conditions: PhNHNHPh, 0.20 mmol; DIC, 0.20 mmol. Yields were
determined by H NMR spectroscopy.
1
b. Substrate Scope. LiCH2TMS was chosen as the catalyst
precursor for the reaction between 1,2-diarylhydrazine and
various carbodiimides. Representative results are shown in
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Scheme 2. Mechanistic Studies
Figure 2. ORTEP drawing of 6′ with 30% thermal ellipsoids.
Hydrogen atoms, except those connected to N atoms, are omitted for
clarity.
The length of the C1N3 bond (1.292(2) Å) was significantly
shorter than that of the C1N5 bond (1.376(2) Å) or the
C1N2 bond (1.406(2) Å), which indicated that C1N3 was
a double bond. The formation of 6 could involve two steps: the
nucleophilic addition of lithium hydrazide from 5′ to the
central carbon of DIC, followed by proton transfer from the
i
PhNH moiety to the PrNC moiety. This process might be
driven by the increasing acidity of PhNH due to coordination
of the Lewis-acidic lithium and the stability of the fused [5.4.5]
ring. Both 5′ and 6 showed comparable catalytic activity with
LiCH2TMS in the aforementioned guanylation reaction.
The thermal stability of 6 was also examined by heating it in
1
THF solution at 110 °C for 24 h; no change in H NMR
spectra was detected. Then, the stoichiometric reaction
between 6 and PhNHNHPh was conducted in THF. After
24 h at room temperature, the mass spectrum data of the
reaction mixture showed the existence of both 4 and NN
bond cleaved product 3a. When the reaction between 6 and
PhNHNHPh was conducted at 110 °C for 24 h, 3a and trans-
PhNNPh were cleanly formed with a trace amount of 4 in
1
the H NMR spectrum. If 6 was treated with 1 equiv of
Et3NHCl at room temperature, 4 was obtained in 92% yield
(Scheme 2b and Figure 3). Being different from 5′ and 6, 4 was
Figure 3. ORTEP drawing of 4 with 30% thermal ellipsoids. Hydrogen
atoms, except those connected to N atoms, are omitted for clarity.
not stable at elevated temperatures. When 4 was heated at 110
°C for 24 h, it quantitatively transformed to 3a and trans-
PhNNPh. This experiment clearly showed that cleavage of
the NN bond should occur during further transformation of
4.
Figure 1. ORTEP drawing of 5′·C6H14 with 30% thermal ellipsoids.
Hexane and hydrogen atoms, except those connected to N atoms, are
omitted for clarity.
The catalytic reaction of unsymmetric hydrazine
(TolNHNHPh) and DIC was performed in the presence of
LiCH2TMS (3 mol %) at 110 °C for 24 h (Scheme 2c). In
was supported by one thf and two guanidino-amide ligands;
both of the guanidino-amide ligands adopted the η1:μ2 mode.
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addition to guanidines PhNC(NHiPr2)2 and TolNC-
(NHiPr2), only one azo complex (TolNNPh) was detected
by a GC/MS spectrometer. Furthermore, the crossover
experiment among PhNHNHPh, TolNHNHTol, and DIC
showed that TolNNPh was not observed (Scheme 2d).
These results showed that formation of the azo complex ArN
NAr should come from the proton abstraction of 0.5 equiv of
ArNHNHAr; the other half of ArNHNHAr should undergo
NN bond cleavage.
cleavage of 1,2-diarylhydrazine, which was driven by an
intramolecular proton shift, did not require a variable oxidation
state on a metal center and/or additives. The basicity of the
guanidino group played an important role in this cleavage
process. The isolation, characterization, and reaction studies of
two important amido lithium intermediates and an ArHN-
substituted guanidine give strong support to the proposed
mechanism.
Based on this experimental evidence, a possible mechanism is
proposed in Scheme 3. Deprotonation of 1,2-diarylhydrazine by
EXPERIMENTAL SECTION
■
General Methods. All reactions were conducted under slightly
positive dry nitrogen pressure using standard Schlenk line techniques
or under a nitrogen atmosphere in a glovebox. The nitrogen in the
glovebox was constantly circulated through a copper/molecular sieves
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. Unless otherwise noted, all starting
materials were commercially available and were used without further
purifi ca tion. To lN HN HP h, To lN HN HT ol , and o -
MeC6H4NHNHC6H4Me-o were prepared according to known
procedures.14 Solvents were purified by a solvent purification system
and dried over molecular sieves in a glovebox. Organometallic samples
for NMR spectroscopic measurements were prepared in a glovebox by
Scheme 3. A Possible Mechanism for the Catalytic
Guanylation Reaction of 1,2-Diarylhydrazine with
Carbodiimides
the use of J. Young valve NMR tubes (Wilmad 528-JY). H and 13C
1
NMR spectra were recorded on a 500 MHz (FT, 500 MHz for 1H, 125
1
MHz for 13C) or 400 MHz (FT, 400 MHz for H, 100 MHz for 13C)
spectrometer at room temperature. Mass spectra (MS) were recorded
on a GC/MS spectrometer using an EI source. High-resolution mass
spectra (HRMS) were recorded on an FTMS mass spectrometer using
an ESI source.
Typical Procedures for the Catalytic Guanylation Reaction
between 1,2-Diarylhydrazine and Carbodiimides. a. NMR Tube
Reaction. In a glovebox, a J. Young valve NMR tube was charged with
catalyst (0.002 or 0.006 mmol), C6D6 (0.5 mL), PhNHNHPh (36.8
mg, 0.20 mmol), and DIC (25.3 mg, 0.20 mmol). The tube was taken
out of the glovebox and then heated at 110 °C in an oil bath for 24 h.
1
Formation of 3a was monitored by H NMR spectra.
b. Preparative Scale Reaction. In a glovebox, a benzene solution (1
mL) of LiCH2TMS (2.8 mg, 0.03 mmol) and a benzene solution (5
mL) of PhNHNHPh (184.2 mg, 1.00 mmol) were added to a Schlenk
tube. Then, a benzene solution (3 mL) of DIC (126.2 mg, 1.00 mmol)
was added to the above reaction mixture. The Schlenk tube was
removed from the glovebox, and the mixture was stirred at 110 °C for
24 h. After the solvent was removed under vacuum, an orange−red
residue was purified by silica-gel column chromatography using petrol
ether and EtOAc as eluents to give colorless solid 3a (196.0 mg, 0.89
mmol) in 89% yield. The NMR data of 3a−g were consistent with
previous reports.11c,f,15
3a: colorless solid11c (89% yield, 196 mg, 1 mmol scale); H NMR
1
(500 MHz, C6D6, Me4Si) δ 0.90 (d, J = 6.1 Hz, 12H), 3.65 (br, 4H),
6.92 (t, J = 7.3 Hz, 1H), 7.14 (d, J = 8.1 Hz, 2H), 7.25 (t, J = 7.6 Hz,
2H); 13C NMR (100 MHz, C6D6, Me4Si) δ 23.2, 43.3, 121.5, 123.7,
129.7, 149.8, 151.3.
LiCH2TMS affords lithium hydrazide A. Nucleophilic attack of
A on carbodiimide should give B. In the presence of
Ar1NHNHAr2, B is protonated to give guanidine C and
regenerate the active species A. Then, an intramolecular proton
shift in C gives D. This is likely driven by the strong basicity of
the guanidine unit. The intermolecular nucleophilic addition
between C and D should give the adduct E, which undergoes
proton transfer to yield F. An intramolecular rearrangement in
F gives the final products G1, G2, and the azo-compound H.
During the rearrangement of F, the NN bond from one
hydrazine unit is cleaved, whereas the NN bond from the
other hydrazine unit furnishes the NN bond of H.
3b: colorless solid11c (93% yield, 277 mg, 1 mmol scale); H NMR
1
(400 MHz, CDCl3, Me4Si) δ 1.04−1.20 (m, 6H), 1.30−1.40 (m, 4H),
1.58−1.62 (m, 2H), 1.66−1.71 (m, 4H), 1.99−2.02 (m, 4H), 3.41 (br,
2H), 6.85 (d, J = 8.0 Hz, 2H), 6.92 (t, J = 7.3 Hz, 1H), 7.24 (t, J = 7.6
Hz, 2H); 13C NMR (100 MHz, C6D6, Me4Si) δ 25.2, 25.9, 34.0, 50.4,
121.4, 123.8, 129.6, 149.4, 151.8.
3c: colorless solid15 (71% yield, 204 mg, 1 mmol scale); H NMR
1
(400 MHz, CDCl3, Me4Si) δ 7.03 (t, J = 7.3 Hz, 3H), 7.18 (d, J = 7.5
Hz, 6H), 7.28 (t, J = 7.8 Hz, 6H); 13C NMR (100 MHz, CDCl3,
Me4Si) δ 121.4, 123.1, 129.2, 142.2, 145.0. The NH signal was not
1
observed in the H NMR spectrum.
3d: colorless solid11f (82% yield, 191 mg, 1 mmol scale); H NMR
1
CONCLUSIONS
■
(400 MHz, CDCl3, Me4Si) δ 1.15 (d, J = 6.3 Hz, 12H), 2.28 (s, 3H),
3.57 (br, 2H), 3.74−3.77 (m, 2H), 6.74 (d, J = 7.9 Hz, 2H), 7.04 (d, J
= 7.8 Hz, 2H); 13C NMR (100 MHz, CDCl3, Me4Si) δ 20.8, 23.4,
43.3, 123.3, 129.9, 130.5, 147.4, 150.4.
In summary, we have disclosed the first alkyllithium-catalyzed
guanylation reaction of 1,2-diarylhydrazine with carbodiimides
to give guanidine and azo compounds. The NN bond
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3e: colorless solid11f (88% yield, 276 mg, 1 mmol scale); H NMR
(400 MHz, CDCl3, Me4Si) δ 1.04−1.19 (m, 6H), 1.29−1.38 (m, 4H),
1.57−1.69 (m, 6H), 1.98−2.00 (m, 4H), 2.27 (s, 3H), 3.40 (br, 2H),
3.65 (br, 2H), 6.74 (d, J = 7.8 Hz, 2H), 7.03 (d, J = 7.8 Hz, 2H); 13C
NMR (100 MHz, CDCl3, Me4Si) δ 20.8, 24.9, 25.7, 33.8, 50.2, 123.4,
129.8, 130.5, 147.5, 150.3.
analysis could be grown from THF/hexane for 2 days at room
temperature.
1
Preparation of 4. Et3NHCl (275 mg, 2.0 mmol) was added to a
THF solution (5 mL) of 6 (633 mg, 2.0 mmol) at room temperature.
The mixture was stirred overnight, and the solvent was removed under
reduced pressure. The residue was extracted with toluene three times.
Then, the extract was dried under vacuum. The residual solid was
washed by hexane. 4 was obtained as a white solid (573 mg, 1.84
mmol, 92% yield) after any remaining hexane was removed under
reduced pressure. Single crystals of 4 suitable for X-ray analysis could
3f: colorless solid11f (96% yield, 317 mg, 1 mmol scale); H NMR
1
(400 MHz, C6D6, Me4Si) δ 2.08 (s, 9H), 5.68 (br, 2H), 6.90 (d, J = 7.8
Hz, 6H), 7.04 (d, J = 6.7 Hz, 6H); 13C NMR (100 MHz, C6D6, Me4Si)
δ 20.7, 121.8, 130.0, 132.2, 140.8, 145.5.
3g: colorless solid11f (85% yield, 99.5 mg, 0.50 mmol scale); H
1
1
be grown from THF/hexane at room temperature: H NMR (500
NMR (400 MHz, CDCl3, Me4Si) δ 1.15 (d, J = 6.3 Hz, 12H), 2.15 (s,
3H), 3.53−3.76 (m, 4H), 6.78 (d, J = 7.7 Hz, 1H), 6.88 (t, J = 7.2 Hz,
1H), 7.08 (t, J = 7.0 Hz, 1H), 7.14 (d, J = 7.4 Hz, 1H); 13C NMR (100
MHz, CDCl3, Me4Si) δ 18.1, 23.4, 43.4, 122.1, 123.3, 126.7, 130.5,
131.7, 147.5, 149.5.
MHz, CD2Cl2, Me4Si) δ 1.02 (br, 12H), 3.57 (br, 2H), 3.66 (br, 1H),
6.85 (t, J = 7.3 Hz, 1H), 6.94 (d, J = 7.9 Hz, 2H), 6.98 (t, J = 7.4 Hz,
1H), 7.19−7.23 (m, 4H), 7.25 (t, J = 7.9 Hz, 2H); 13C NMR (125
MHz, CD2Cl2, Me4Si) δ 24.2, 46.1, 114.8, 119.0, 120.8, 122.8, 129.1,
1
129.3, 148.9, 149.9. One signal of NH was not observed in the H
3h: colorless solid11f (93% yield, 119.7 mg, 0.50 mmol scale); 1H
NMR (400 MHz, C6D6, Me4Si) δ 0.86 (d, J = 6.4 Hz, 12H), 3.35 (br,
2H), 3.57 (br, 2H), 6.86 (d, J = 8.6 Hz, 2H), 7.17 (d, J = 8.8 Hz, 2H);
13C NMR (100 MHz, C6D6, Me4Si) δ 23.2, 43.2, 124.9, 126.3, 129.7,
149.8, 150.2.
NMR spectrum, and one signal of carbon was not observed in the 13C
NMR spectrum. HRMS m/z: [M + H]+ calcd for C19H27N4, 311.2230;
found, 311.2234.
X-ray Crystallographic Studies. Crystals of 4, 5′, and 6′ suitable
for X-ray analysis were grown as described above. The crystals were
wrapped in mineral oil and then frozen at low temperature. Data
collections for 4 were performed at 180 K on a SuperNova
diffractometer using graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). Data collections for 5′ and 6′ were performed at 100 K on
a SuperNova diffractometer using graphite-monochromated Mo Kα
radiation (λ = 0.71073 Å). Using Olex2,16a the structures of 4, 5′, and
6′ were solved with the Superflip structure solution program using
Charge Flipping16b and refined with the XL refinement package using
least-squares minimization. Refinement was performed on F2
anisotropically for all of the non-hydrogen atoms by the full-matrix
least-squares method. The hydrogen atoms connected to N atoms in
5′ were identified according to difference electron density. Other
hydrogen atoms were placed at the calculated positions and were
included in the structure calculation without further refinement of
their parameters. Crystallographic data (excluding structure factors)
have been deposited with the Cambridge Crystallographic Data Centre
with supplementary publication numbers: CCDC 1017747 (4),
CCDC 1017748 (5′·C6H14), and CCDC 1017749 (6′). These data
can be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif. The thermal
ellipsoid plots in the figures were drawn by Ortep-3 v1.08.16c
3i: colorless solid11f (64% yield, 95.0 mg, 0.50 mmol scale); H
1
NMR (400 MHz, C6D6, Me4Si) δ 0.85 (d, J = 6.4 Hz, 12H), 3.34 (br,
2H), 3.56 (br, 2H), 6.81 (d, J = 8.6 Hz, 2H), 7.31 (d, J = 8.6 Hz, 2H);
13C NMR (100 MHz, C6D6, Me4Si) δ 23.2, 43.3, 113.9, 125.4, 132.6,
149.8, 150.6.
3j: colorless solid11c (46% yield, 63.0 mg, 0.50 mmol scale); H
1
NMR (400 MHz, C6D6, Me4Si) δ 0.92 (d, J = 6.3 Hz, 12H), 1.27 (s,
9H), 3.70 (br, 4H), 7.09−7.13 (m, 2H), 7.30−7.34 (m, 2H); 13C
NMR (100 MHz, C6D6, Me4Si) δ 23.2, 31.7, 34.2, 43.3, 123.2, 126.4,
143.6, 148.6, 149.9.
Catalytic Guanylation Reaction of Unsymmetric 1,2-Diary-
lhydrazine and DIC. In a glovebox, a benzene solution (1 mL) of
LiCH2TMS (0.6 mg, 0.006 mmol) and a benzene solution (3 mL) of
TolNHNHPh (39.7 mg, 0.20 mmol) were added to a Schlenk tube.
Then, a benzene solution (3 mL) of DIC (25.2 mg, 0.20 mmol) was
added to the above reaction mixture. The Schlenk tube was removed
from the glovebox, and the mixture was stirred at 110 °C for 24 h. The
reaction was monitored by GC/MS spectrometry; for azo complexes,
1
only the peak of m/z = 196 was observed. The H NMR and 13C
NMR spectra of the isolated azo complex also indicated the formation
of TolNNPh.
Preparation of 5′. A THF solution (∼1 mL) of LiCH2TMS
(282.6 mg, 3.0 mmol) was added to a THF solution (15 mL) of
PhNHNHPh (552.6 mg, 3.0 mmol); the solution turned light green
immediately. The mixture was stirred for 4 h at room temperature.
Evaporation of volatiles gave a light green powder. The powder was
washed with hexane and recrystallized in THF/hexane at −20 °C.
After the sample had been dried under a vacuum, 5′·C6H14 was
obtained as a white powder (848 mg, 0.97 mmol, 97% yield). Single
crystals of 5′·C6H14 suitable for X-ray analysis could be grown from
ASSOCIATED CONTENT
■
S
* Supporting Information
Additional NMR data, copies of H NMR and 13C NMR
1
spectra of all new compounds, crystallographic tables, and X-ray
crystallographic data in cif format. This material is available free
of charge via the Internet at http://pubs.acs.org.
1
THF/hexane for 2 days at room temperature: H NMR (500 MHz,
C6D6, Me4Si) δ 0.88 (t, J = 7.0 Hz, 6H), 1.19−1.21 (m, 12H), 1.23−
1.27 (m, 8H), 3.31 (t, 12H), 5.66 (br, 3H), 6.71 (br, 18H), 7.09−7.12
(m, 12H); 13C NMR (125 MHz, C6D6, Me4Si) δ 14.3, 23.0, 25.3, 31.9,
68.7, 113.3, 116.7, 129.7, 155.3. The hexane in the unit cell was
partially pumped away, and therefore, the hexane integral was not
accurate. The aromatic carbon may degenerate in solution.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: wx_zhang@pku.edu.cn.
*E-mail: zfxi@pku.edu.cn.
Preparation of 6. A benzene solution (10 mL) of 5′ (848 mg, 0.97
mmol) was added to a benzene solution of DIC (367 mg, 2.9 mmol).
After the sample had been stirred for 4 h, a large amount of white
powder precipitated; then, the solvent was decanted. The residual
white solid was washed by benzene three times. Any residual solvent
was removed under vacuum. 6 was obtained as a white powder (787
Author Contributions
§L.X. and Y.-C.W. contributed equally.
Notes
The authors declare no competing financial interest.
1
mg, 2.49 mmol, 86% yield): H NMR (400 MHz, THF-d8) δ 1.08−
1.13 (m, 24H), 3.41−3.58 (m, 2H), 3.90 (br, 2H), 4.56 (d, J = 6.9 Hz,
2H), 5.80 (br, 2H), 6.21 (br, 2H), 6.35 (br, 2H), 6.64−6.67 (m, 6H),
6.99 (t, J = 7.6 Hz, 4H), 7.13 (d, J = 7.4 Hz, 4H); 13C NMR (100
MHz, THF-d8) δ 19.8, 21.8, 43.4, 43.7, 104.8, 108.9, 115.7, 116.8,
125.4, 126.7, 148.9, 156.4, 161.4. Single crystals of 6′ suitable for X-ray
ACKNOWLEDGMENTS
■
This work was supported by the “973” program from the
National Basic Research Program of China (2011CB808601)
and the Natural Science Foundation of China (NSFC).
12008
dx.doi.org/10.1021/jo501865b | J. Org. Chem. 2014, 79, 12004−12009

The Journal of Organic Chemistry
Article
́ ́
F.; Garces, A.; Otero, A.; Lopez-Solera, I.; Rodríguez, A. M.; Antinolo,
̃
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