Magneto-structural correlation of cyano-substituted 3-: Tert -butyl-1-phenyl-1,2,4-benzotriazin-4-yl: Spin transition behaviour observed in a 6-cyano derivative

Article abstract of DOI:10.1039/c7nj04534d

New cyano-substituted 3-tert-butylbenzotriazinyls, 7CN and 6CN, were synthesized and their spectroscopic properties and magneto-structural correlation were investigated. The radical 7CN formed a 1D columnar structure and displayed an antiferromagnetic interaction along the column (J = -15.8 cm^-1). The 6-cyano substituted radical 6CN also formed a 1D columnar structure and exhibited a reversible spin transition at ca. 284 K in the range of 6 K. The molecular arrangements in the high-temperature phase (300 K) and low-temperature phase (263 K) were evaluated by X-ray crystallographic analysis and the molecules slightly rotated while remaining in the 1D columnar structure, resulting in a phase transition. The spin transition behaviour was caused by the structural phase transition, which was consistent with the DSC and computational studies.

Full text of DOI:10.1039/c7nj04534d

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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ARTICLE
Magneto-structural Correlation of Cyano-substituted 3-tert-Butyl-
1-phenyl-1,2,4-benzotriazin-4-yl: Spin Transition Behavior
Observed in 6-Cyano Derivative
Received 00th January 20xx,
Accepted 00th January 20xx
Yusuke Takahashi, Naoya Tsuchiya, Youhei Miura and Naoki Yoshioka*
DOI: 10.1039/x0xx00000x
New cyano-substituted 3-tert-butylbenzotriazinyls, 7CN and 6CN, were synthesized and their spectroscopic property and
magneto-structural correlation were investigated. The radical 7CN formed a 1D columnar structure and displayed an
antiferromagnetic interaction along the column (J = -15.8 cm-1). The 6-cyano substituted radical 6CN also formed a 1D
columnar structure and exhibited a reversible spin transition at ca. 284 K in the range of 6 K. The molecular arrangements
in the high-temperature phase (300 K) and low-temperature phase (263 K) were evaluated by an X-ray crystallographic
analysis and the molecules slightly rotated while remaining in the 1D columnar structure, resulting in a phase transition.
The spin transition behavior was caused by the structural phase transition, which was consistent with the DSC and the
www.rsc.org/
computational
studies.
displaying those kinds of interesting properties.
Introduction
The 1,2,4-benzotriazin-4-yl radical analogue, which was
first reported by Blatter and Lukaszewski,5 has drawn attention
over the past two decades due to its enhanced stability against
air and moisture, the facile transformation of the functional
group6 and interesting physicochemical properties.7 In
addition, not only a computational study8 but also many kinds
of facile synthetic routes9 have been reported and various
derivatives have been prepared. Focusing on the
benzotriazinyl analogues, the planar benzotriazinyl radical
derivatives, which have a greater spin delocalization, exhibited
a ferromagnetic interaction in the 1D columnar structure,
providing a new basic skeleton for supramolecular chemistry.10
Therefore, the benzotriazinyls are promising spin centres for
multifunctional materials. Notably, 3CF3 showed a reversible
spin transition at ca. 58 K fully completed within 5 K caused by
the structural phase transition.11 To the best of our knowledge,
it is the only example of a benzotriazinyl exhibiting a spin
transition between the paramagnetic and diamagnetic phases.
Regarding the hydrazyl radical, 3-(4-cyanophenyl)-1,5-
Organic radicals have been investigated for developing
molecule-based multifunctional materials for electronics,
spintronics, as well as molecule-based magnets.1 If their
physicochemical properties are changed in response to
external stimuli, such as light, heat, and pressure, the material
can be used as a switching device by controlling their spin
state and molecular arrangement. In the field of magnetism,
many metal complexes exhibit
a spin crossover (SCO)
behaviour induced by thermal or light stimulus to control the
spin state of the metal ion.2 On the other hand, in organic
radical systems, the magnetic property of the organic radicals
significantly depends on their molecular arrangement,3 and
their structural phase transition is one of the triggers to exhibit
a
spin transition like SCO phenomena. Several radical
derivatives showing a phase transition by changing their
molecular assembly in a solid have been reported,4 whereas
almost all radicals do not demonstrate a spin transition.
However, these compounds have been fortuitously discovered
in the study of the magnetic property for organic radicals. In
general, it is difficult to design a group of radical substances
dimethyl-6-oxoverdazyl radical exhibited
transition at 16 K.12
a
Spin-Peierls
exhibiting
a structural phase transition involving a spin
transition like the SCO. Therefore, in the investigation of the
physicochemical properties, such as the magneto-structural
correlation for the analogues of external stimuli-response
organic radical systems, is important to discover the molecules
Fig. 1 Molecular structures of 1,2,4-benzotriazine-4-yl derivatives.
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Scheme 1 Synthetic route of 3-tert-butyl benzotriazinyls.
In the examples where an organic radical exhibited spin
transition behaviour caused by a structural phase transition,
this was accompanied by packing motif changes between the
dimer and columnar structure. Therefore, the construction of a
columnar structure using a dimer with a weak π-π interaction
may be one of the methodologies to design an organic radical
exhibiting the spin transition behaviour. Keeping the size of
molecule small may also be beneficial. Based on this view
point, it is one of the good approaches to generate a dipole
moment by introducing electron donating or withdrawing
substituents for the formation of the π-dimer. For cancelling
the dipole moment between the molecules, dimerization of
the
the
π
-radicals can be promoted. In addition, the magnitude of
π-π interaction can be controlled by chemical modification
of the bulky group into the radical for formation of the dimer
and columnar structure. Recently, we investigated the
magneto-structural
correlation
of
the
3-tert-
butylbenzotriazinyls carrying an electron withdrawing group
and reported that 7CF3 forms an ideal 1D ferromagnetic
chain.13 As part of our investigation, in the present paper, the
synthesis, EPR spectroscopic study and magneto-structural
correlation in connection with the computational study of the
3-tert-butylbenzotriazinyls carrying a cyano group at the 7- or
6-position are described, and a reversible spin transition of
6CN at ambient temperature is demonstrated (Figure 1).
Fig. 2 Temperature dependence of χmT for 6CN;(a) The temperature range of 1.8-320 K
under the applied field of 50 kOe. The two arrows indicate the temperature’s changing
sign of the observed magnetization in the raw data. The solid line represents the best
fit to the Bleaney-Bowers model in the range of 284-320 K (2J = -122.8 cm-1, θ = -0.69 K,
2
correlation factor
R
= Σ[χmTobs-χmTcalcd]2/Σ[χmTobs
]
=
4.58×10-5
)
including
a
2.6%
uncoupled doublet species. (b) Temperature range of 260-290 K under the applied field
of 50 kOe. The measurement was carried out for the sample wrapped in paramagnetic
Al foil to avoid any discontinuity of the magnetization in the range of 3-250 K. The red
circle and blue triangle represent the heating and cooling processes, respectively.
Results and discussion
Synthesis
We first tried to synthesize the 7-cyano benzotriazinyl
radical 7CN by applying the Cu-catalyzed C-N coupling and
condensation in AcOH according to the literature methods,11,13
however, the radical 7CN was obtained in only 8% yield due to
the instability of the intermediate aniline. Thus, the cyano-
substituted benzotriazinyls were prepared according to
Scheme 1. The chlorination of pivalohydrazide proceeded in a
90% yield. Condensation between compound
corresponding aniline gave the hydrazonamides
3
and the
4a:82%,
Fig. 3 DSC measurement of 6CN (Heating rate: 10 K min-1).
4
(
4b:38%, 4c:61%). The radical precursor 4c was air-sensitive
and its appearance was changed from a yellow solid to orange
oil in the air. The palladium-catalysed oxidative cyclization9a
Magnetic property
The thermal behaviour of the magnetic susceptibility for the
polycrystalline sample of 7CN in the temperature range of 1.8
– 300 K is shown in Figure S1. The χmT value gradually
decreased with the decreasing temperature, which suggested
that the intermolecular antiferromagnetic interaction was
then afforded the benzotriazinyls (
The overall yield of the radicals using
:64%, 7CN:27%, 6CN:8%) was improved compared to that of
our previous report13
:34%).
1:87%, 7CN:78%, 6CN:15%).
2
as the starting material
(
1
(1
2 | J. Name., 2012, 00, 1-3
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dominant in the solid state. This observed behaviour was well 6CN
ARTICLE
,
1
(73.85(6)°) and 7CF3 (82.18(17)°)13 due to the crystal
described by the Bonner-Fisher equation14 taking into account packing effect. The crystal of 7CN belongs to the monoclinic
the molecular field and the best-fit result of J = -15.8 cm-1 and I2/a space group. In the
mean field term θ = -1.3 K. The crystallographic analysis also
supported the result; the radical 7CN is in close contact for the
intermolecular magnetic interaction along the column (See
below).
The temperature dependence of the χmT value for 6CN in
the temperature range of 1.8 – 320 K is shown Figure 2. The
χmT value at 300 K was 0.313 emu K mol-1, which was a lower
value than that of the estimated value of the isolated S = 1/2
spin (0.375 emu K mol-1). It implied the existence of the
intermolecular antiferromagnetic interaction. No change in
χmT occurred during cooling until 284 K, then an abrupt
Fig. 4 ORTEP drawing of (a) 7CN and (b) HT (300 K) phase of 6CN (50% thermal
decrease occurred and plateaued below 280 K. When heating,
ellipsoids).
the χmT exhibited a behaviour similar to the cooling process
and a sharp increase took place near 278 K. As shown in the
inset of Figure 2, the radical 6CN exhibited a fully reversible
transition during the heating and cooling processes in the
range of 6 K and the transition was completed in a small
thermal range around 280 K. The thermal behaviour of the χmT
in the range of 284-320 K can be reproduced by the Bleaney-
Bowers dimer model15 (equation 1) with 2J = -122.8 cm-1 and θ
= -0.71 K. The thermal behaviour of the χmT below 280 K can
be roughly reproduced by the Bleaney-Bowers model with -
485 cm-1 (Figure S2).
ꢄꢅꢆꢇꢆꢈ
ꢉꢈ
ꢊ
ꢊ
ꢀꢁ ꢂ ꢃ
∙
∙
(1)
ꢆꢔ
ꢋꢌꢍ
ꢎꢏꢐꢑꢒꢓꢌꢉꢈꢋꢕ
To confirm the change in the molecular packing, the DSC
measurement was carried out in the range of 250 – 320 K
(Figure 3). The DSC curve exhibited an endothermic peak at
283.9 K, which is the corresponding temperature of the spin
transition.
X-ray crystallographic analysis
Fig. 5 Molecular arrangement of (a) HT and (b) LT phases of 6CN. Hydrogen atoms and
some tert-butyl groups are omitted for clarity.
Single crystals of 7CN and 6CN suitable for
a
crystallographic analysis were obtained by slow evaporation
from the mix solvents of CH2Cl2 and n-hexane. As already
described, 6CN exhibited the spin transition at ca. 284 K. The
DSC measurement revealed the possibility of a structural
phase transition at the corresponding temperature. Thus, X-
ray crystallographic measurements were carried out at 263
and 300 K. It revealed that 6CN can form two polymorphs in
response to the temperature and these polymorphs are
referred to as the low-temperature (LT) and high-temperature
(HT) phases. Because of the rapid conversion from the HT/LT
phase to the LT/HT phase, the reflection data were obtained
using the same single crystal at 263 K (LT phase) and 300 K (HT
phase). The crystallographic data are shown in Table S1. The
ORTEP drawing of 7CN and 6CN are shown in Figure 4 and S3.
The bond lengths of the amidrazonyl ring (Table S2) are similar
to that of other benzotriazinyls, which suggest that an
unpaired electron is delocalized over the benzotriazinyl ring.
The dihedral angle between the phenyl ring and π-conjugated
system of 7CN is relatively smaller (45.236(80)°) than that of
Fig. 6 Proposed mechanism of phase transition from HT phase to LT phase for 6CN.
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crystal, 7CN formed a 1D columnar structure due to the π-π antiferromagnetic interaction was mainly derived from the
interaction between the phenyl ring and -conjugated system interaction along the column.
with an ca. 3.6 separation (Figure S4). In the column, the Regarding the radical 6CN, there were two kinds of
π-π
π
molecules formed an antiparallel stacked arrangement to contacts in both the HT and LT phases and the J values were
cancel the dipole moment. On the other hand, the crystal of also
the HT phase of 6CN belongs to the monoclinic I2/a space
group and formed a 1D columnar structure along the b axis
due to the weak
π
benzo rings with an ca. 3.3
-
π
interaction between the functionalized
separation. There is an
antiparallel stacked structure in the column to cancel the
dipole moment. There was a negligible intermolecular contact
without a columnar direction. In contrast, the LT phase
belongs to the triclinic P-1 space group and exhibits crystal
twinning. The observed data were analysed by the TWINABS
program16 with the volume fraction parameter = 0483. The
bond lengths and dihedral angle are almost the same values as
those of the HT phase. Regarding the contacts of the
molecules, the intermolecular distance between the π-
conjugated systems is ca. 3.3 which is slightly shorter than
,
that of the HT phase (Figure 5). The molecules were slightly
slipped while maintaining the columnar structure due to the
rotation of the molecules arising from the weak π-π interaction
Fig. 7 (a) SOMO and (b) spin density distributions of 7CN(left) and 6CN (HT: middle, LT:
(The longitudinal slippage ϕ1 and latitudinal slippage ϕ2 are
shown in Table S3; these slippages are defined according to
the literature11). The ϕ2 slightly changed with the structural
phase transition, however, the ϕ1 increased 6.4° for the Pair I-
II and decreased 4.0° for the Pair II-I’. Therefore, a structural
phase transition of 6CN was induced by the small rotation of
the molecules (Figure 6).
right) at UB3LYP/6-31G(d) level of theory.
Table 1 The calculation results of 6CN at U3LYP/6-31G(d) level. BS and T represent
broken symmetry singlet and triplet state.
Pair (Phase) Spin state
Energy / a.u.
<S2>
2J / cm-1
BS
-1828.7783900 0.996173
-1828.7782979 2.008510
-1828.7934835 0.737716
-1828.7906151 2.008629
-1828.7760002 1.003631
-1828.7759894 2.008553
-1828.7940379 0.934801
-1828.7932765 2.008723
I-II(HT)
T
-40.9
Computational study
BS
I-II(LT)
T
-1600
-4.8
The DFT calculations using crystallographic geometry were
performed at the UB3LYP/6-31G(d) level of theory to estimate
the distributions of the singly-occupied molecular orbitals
(SOMO) and spin density. The SOMO and spin density
distributions for 7CN and 6CN are shown in Figure 7. The
SOMO and spin density mainly distributed over the molecules
include the substituent and the spin density slightly distributed
BS
II-I’(HT)
T
BS
II-I’(LT)
T
-358.9
estimated (Table 1, S5). The magnetic property of the HT and
LT phases was reproduced by the UBLYP function. The
magnitude of the 2J values of the LT phase is much larger than
those of the HT phase, indicating that the strong
antiferromagnetic interaction was dominant in the pair I-II and
pair II-I’ of the LT phase, whereas there was a weak
antiferromagnetic interaction in the HT phase. Focusing on the
molecular arrangement, there are small structural changes in
the overlaps of the molecules between the HT and LT phases,
however, the contact and overlap of the SOMOs significantly
changed (Figure S5(b, c)). The existence of large overlaps of
the SOMO in the LT phase lead to an increase in the bonding
character and diamagnetic behaviour.
on the tert-butyl group. For 6CN
, there are negligible
differences in the SOMO and spin density distributions
between the HT and LT phases. To evaluate the contribution of
the intermolecular magnetic interaction, the magnitude of
interaction J was estimated at the UB3LYP and UBLYP levels
and 6-31G(d) basis set. The J value was calculated using
equation J = (EBS-ET)/(<S2>T-<S2>BS), where E and S2 are the
total energy and total spin angular momentum, respectively,
reported by Yamaguchi and co-workers.17 For 7CN
, the
estimated J values within the column using both the UB3LYP (J
= -3.4 cm-1) and UBLYP (J = -8.7 cm-1) functions were negative,
suggesting that there was an antiferromagnetic interaction in
the column (Table S4). It is consistent with the experimental
result. Focusing on the contact of the SOMO, there were large
overlaps of the SOMO and overlap integral, leading to the
antiferromagnetic behaviour (Figure S5(a)). The magnitude of
the J value of the intermolecular magnetic interaction within
and between columns was well reproduced by the UBLYP
function. The computation also implied that the
EPR spectroscopic study
The EPR spectra of 7CN and 6CN in toluene are shown in
Figure S6 and exhibited complex patterns derived from the
non-equivalent nitrogen and hydrogen nuclei. The spectra
showed a seven-line hyperfine splitting attributed to the three
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nitrogen nuclei of the benzotriazinyl ring, and the hyperfine spectra were recorded by a JEOL JNM-LA 300 spectrometer
splitting of the hydrogen nuclei and nitrogen nucleus of the using tetramethylsilane as the internal reference in CDCl3. The
cyano group were also observed. However, the hyperfine chemical shifts and coupling constants were expressed in ppm
coupling constants (hfccs) derived from the hydrogen nuclei of and Hz, respectively. The mass spectroscopy was carried out
the tert-butyl group cannot be assigned. The spin density can using a Bruker Ultraflex II(MALDI-TOF, sinapic acid was used as
be estimated by comparing the hfcc, which is proportional to the matrix) and JEOL GC-mate(EI). The IR spectra were
the spin density. The hfcc values were determined by the recorded using a JASCO FT/IR-4100 (KBr method) and Bruker
Winsim program18 and assigned according to the result of the ALPHA FTIR spectrometer (ATR method). The crystal data were
ENDOR measurement19 (Table S6). This result indicated that collected using a Bruker D8 Venture with MoKα (0.71073 Å)
the spin density is distributed over the molecule without the radiation. For the radical 7CN, the structures were solved by
tert-butyl group, which was consistent with the computational the direct method using SHELXT-2013 and refined by the F2 full
study. Comparing the hfccs of the nitrogen nuclei on the matrix least squares using SHELXL-2013 in the Bruker APEX-II
benzotriazinyl ring, the hfccs of N2 and N3 for 7CN, and N1 for program package. For the radical 6CN, the structures were
6CN were smaller than that of the corresponding nitrogen solved by the Intrinsic Phasing method using SHELXT-2013 and
nuclei for radical
cyano group on the 7-position affected the spin density of N2 the Bruker APEX-III program package.21 The magnetic
and N3, which is similar to the 7CF3 system. On the other susceptibility measurements were performed using
hand, the substituent on the 6-position mainly affected the Quantum Design MPMP-XL SQUID magnetometer. The
1
. This implied that the electron withdrawing refined by the F2 full matrix least squares using SHELXL-2014 in
a
spin density of N1, which was smaller than that of
1
.
diamagnetic contribution from the sample holder and samples
Therefore, the spin density of the nitrogen nuclei can be estimated using the Pacault method22 (-1.82×10-4 emu mol-1)
modulated by introducing a substituent on the para-position were corrected. The X-band EPR spectra were recorded using a
of the nitrogen nuclei.
Bruker E500 spectrometer. The signal positions were
calibrated by a Bruker ER035M teslameter. The samples were
degassed by the freeze-pump-thaw method. The elemental
analyses were carried out at the Central Laboratory of the
Faculty of Science and Technology, Keio University.
Computational studies were carried out using the Gaussian 09
program package.23
Conclusions
The 3-tert-butyl benzotriazinyls carrying the cyano group at
the 7- or 6-position were prepared and their physicochemical
properties
discussed.
The
magnetic
susceptibility
measurement revealed that 7CN forms a 1D antiferromagnetic
chain with J = -15.8 cm-1 and mean field term of θ = -1.3 K,
which was derived from the overlap between the SOMOs. The
Preparation of N, N'-diphenylpivalohydrazonamide (4a)
A mixture of N-phenylpivalohydrazonoyl chloride (277 mg,
1.31 mmol), aniline (0.120 mL, 1.31 mmol) and triethylamine
(0.201 mL, 1.44 mmol) in EtOH(2.0 mL) was stirred for 16 h at
room temperature under a nitrogen atmosphere. The reaction
mixture was extracted with CH2Cl2, washed with water, dried
over Na2SO4 and evaporated under reduced pressure. The
residue was purified by column chromatography on SiO2
(CH2Cl2 / n-hexane = 2 / 3 as eluent) to afford a colourless
solid. Yield: 287 mg, 1.07 mmol, 82%; mp: 76-78 °C; 1H
NMR(CDCl3, 300 MHz) δ: 7.25-7.16(m, 4H), 6.96-6.94(m, 3H),
6.88(t, 1H, J = 7.2 Hz), 6.77(t, 1H, J = 7.2 Hz) 6.62(d, 2H, J = 7.8
Hz), 5.34(s, 1H), 1.26(s, 9H); 13C NMR(CDCl3, 75 MHz) δ:
145.57, 143.14, 141.12, 129.20, 129.00, 120.33, 119.14,
115.67, 112.70, 37.90, 27.77; HRMS(EI): Calcd. for
C17H21N3[M]+: m/z = 267.1735, Found 267.1735; IR(KBr pellet,
cm-1): 3378, 3338, 3050, 2966, 1598.
crystallographic study revealed that 7CN formed
a 1D
columnar structure due to the π-π interaction. The
computations supported the experimental results. Surprisingly,
in contrast, 6CN exhibited a spin transition at ca. 284 K in the
range of 6 K between the paramagnetic HT and diamagnetic LT
phases. The spin transition was fully reversible. The DSC
measurement implied a structural phase transition at ca. 284
K. The crystallographic analysis revealed that 6CN exhibited a
structural phase transition at ambient temperature due to the
small rotation of the molecules. The computation using the
UBLYP/6-31G(d) level reproduced the observed spin transition
behaviour and implied that the phenomena were derived from
a transformation of the overlap between the SOMOs and spin
density of 6CN due to the structural phase transition. The EPR
study and the computations showed delocalization of the spin
density over the molecule.
Preparation of 3-tert-Butyl-1,4-dihydro-1-phenyl-1,2,4-
benzotriazin-4-yl (1)
To a solution of N, N'-diphenylpivalohydrazonamide (325 mg,
1.22 mmol) and a catalytic amount of 10% Pd/C in CH2Cl2(4.5
mL) was added DBU (0.182 mL, 1.22 mmol) and stirred for 16 h
at room temperature. The reaction mixture was concentrated
and the residue was purified by column chromatography on
neutral alumina (CH2Cl2 / n-hexane = 1 / 3 as eluent) and
recrystallized from n-hexane to afford a reddish-black crystal.
Experimental
General information
Acetonitrile and dichloromethane were distilled from calcium
hydride. N-phenylpivalohydrazonoyl chloride (3) was prepared
according to the literature.20 The other chemicals were
purchased from Wako, TCI Chemicals, Junsei Chemical and
Sigma-Aldrich and used as received. The 1H and 13C NMR
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Yield: 280 mg, 1.06 mmol, 87%; mp: 107-109 °C (lit.13 106-108
°C), identical to the authentic sample.
Preparation of 3-tert-Butyl-6-cyano-1,4-dihydro-1-phenyl-1,2,4-
Preparation of N-(4-cyanophenyl)-N'-phenylpivalohydrazonamide
benzotriazin-4-yl (6CN)
(4b)
To
a
solution
of
N-(3-cyanophenyl)-N'-
A mixture of N-phenylpivalohydrazonoyl chloride (297 mg, phenylpivalohydrazonamide (393 mg, 1.34 mmol) and
a
1.41 mmol), 4-aminobenzonitrile (167 mg, 1.41 mmol) and catalytic amount of 10% Pd/C in CH2Cl2 (5.0 mL) was added
triethylamine (0.216 mL, 1.55 mmol) in EtOH(2.0 mL) was DBU (0.250 mL, 1.37 mmol) and stirred for 23 h at room
stirred for 1 d at room temperature under a nitrogen temperature. The reaction mixture was concentrated and the
atmosphere. The reaction mixture was extracted with CH2Cl2, residue was purified by column chromatography on SiO2
washed with water, dried over Na2SO4 and evaporated under (EtOAc / n-hexane = 1 / 10 as eluent) and recrystallized from
reduced pressure. The residue was purified by column CH2Cl2 / n-hexane to afford a black crystal. Yield: 57 mg, 15%;
chromatography on SiO2 (CH2Cl2 / n-hexane = 2 / 1 as eluent) mp: 180-181 °C; LRMS(MALDI): Calcd. for C18H17N4[M]+: m/z =
to afford an orange solid. Yield: 158 mg, 0.540 mmol, 38%; mp: 289.2, Found: 289; IR (ATR, cm-1): 2958, 2217, 1590; Elem.
1
54-57 °C; H NMR(CDCl3, 300 MHz) δ: 7.50(d, 2H, J = 8.7 Hz), Anal.: Calcd. for C18H17N4: C 74.72, H 5.92, N 19.36, Found: C
7.22(t, 2H, J = 7.8 Hz) 6.97(d, 2H, J = 7.8 Hz), 6.93(s, 1H), 6.83(t, 74.65, H 5.89, N 19.05; CCDC number: 1524671(300 K),
1H, J = 7.5 Hz), 6.61(d, 2H, J = 8.7 Hz), 1.25(s, 9H); 13C 1524669(263 K).
NMR(CDCl3, 75 MHz) δ: 145.22, 145.00, 141.31, 133.67,
129.16, 120.00, 119.47, 115.25, 112.95, 102.67, 38.11, 27.67;
HRMS(EI): Calcd. for C18H20N4[M]+: m/z = 292.1688, Found
292.1686; IR(KBr pellet, cm-1): 3330, 2966, 2363, 2219, 1601.
Conflicts of interest
There are no conflicts to declare.
Preparation of 3-tert-Butyl-7-cyano-1,4-dihydro-1-phenyl-1,2,4-
benzotriazin-4-yl (7CN)
Acknowledgements
To
a
solution
of
N-(4-cyanophenyl)-N'-
This work was partly supported by the MEXT Supported Pro-
gram for the Strategic Research Foundation at Private
Universities, 2012–2016. Authors thank to Dr. K. Yoza (Bruker
AXS K. K.) for the discussion about crystallographic analysis. Y.
T. thanks to JSPS Grant-in-Aid for JSPS Research Fellow
16J05998.
phenylpivalohydrazonamide (90 mg, 0.308 mmol) and
a
catalytic amount of 10% Pd/C in CH2Cl2(2.0 mL) was added
DBU (0.046 mL, 0.308 mmol) and stirred for 16 h at room
temperature. The reaction mixture was concentrated and the
residue was purified by column chromatography on neutral
alumina (CH2Cl2 / n-hexane = 1 / 3 as eluent) and recrystallized
from CH2Cl2 / n-hexane to afford a greenish-black crystal. Yield:
69 mg, 0.238 mmol, 78%; mp: 117-119 °C; LRMS(MALDI):
Calcd. for C18H17N4[M]+: m/z = 289.2, Found: 289; IR(ATR, cm-
1): 2956, 2222, 1581; Elem. Anal.: Calcd. for C18H17N4: C 74.72,
H 5.92, N 19.36, Found: C 74.87, H 5.95, N 18.98; CCDC
number: 1524670.
Notes and references
1
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Preparation of N-(3-cyanophenyl)-N'-phenylpivalohydrazonamide
(4c)
A mixture of N-phenylpivalohydrazonoyl chloride (526 mg,
2.50 mmol), 3-aminobenzonitrile (296 mg, 2.51 mmol) and
triethylamine (0.383 mL, 2.75 mmol) in EtOH (2.5 mL) was
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washed with water, dried over Na2SO4 and evaporated under
reduced pressure. The residue was purified by column
chromatography on SiO2 (EtOAc / n-hexane = 1 / 4 as eluent)
to afford a yellow solid which turn orange oil in the air. Yield:
2
3
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cm-1): 3350, 2965, 2229, 1600.
6 | J. Name., 2012, 00, 1-3
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