Metal-organic frameworks as efficient catalytic systems for the synthesis of 1,5-benzodiazepines from 1,2-phenylenediamine and ketones

Article abstract of DOI:10.1016/j.jcat.2017.08.009

Benzodiazepines and their derivatives are a very important class of nitrogen-containing heterocyclic compounds with biological activity that are widely used in medicine. In this study, we demonstrated synthesis of 1,5-benzodiazepines from 1,2-phenylenedia

Full text of DOI:10.1016/j.jcat.2017.08.009

Journal of Catalysis 354 (2017) 128–137
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Journal of Catalysis
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Metal-organic frameworks as efficient catalytic systems for the synthesis
of 1,5-benzodiazepines from 1,2-phenylenediamine and ketones
M.N. Timofeeva a,b, , V.N. Panchenko a,c, S.A. Prikhod’ko a,c, A.B. Ayupov a, Yu.V. Larichev a,b
,
⇑
Nazmul Abedin Khan d, Sung Hwa Jhung d,
⇑
a Boreskov Institute of Catalysis SB RAS, Prospekt Akad. Lavrentieva 5, 630090 Novosibirsk, Russian Federation
b Novosibirsk State Technical University, Prospekt K. Marksa 20, 630092 Novosibirsk, Russian Federation
c Novosibirsk State University, St. Pirogova 2, 630090 Novosibirsk, Russian Federation
d Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, Sankyuck-Dong, Buk-Ku, Daegu 41566, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Benzodiazepines and their derivatives are a very important class of nitrogen-containing heterocyclic
compounds with biological activity that are widely used in medicine. In this study, we demonstrated syn-
thesis of 1,5-benzodiazepines from 1,2-phenylenediamine and ketones (acetone, cyclohexanone, ace-
tophenone, methyl ethyl ketone) in the presence of isostructural porous metal-benzenetricarboxylates
of the families MIL-100(M) (M: V3+, Al3+, Fe3+ and Cr3+) and three porous aluminium trimesates Al-
BTCs (MIL-96(Al), MIL-100(Al) and MIL-110(Al)). A combination of catalytic, theoretical and physico-
chemical methods showed that reaction rates and yields of 1,5-benzodiazepines were adjusted by the
type of metal ions and accessibility of active sites. The yield of 1,5-benzodiazepines in the presence of
MIL-100(M) was comparable with zeolites, such as HY, H-ZSMꢀ5, b-zeolite and heulandite.
Ó 2017 Elsevier Inc. All rights reserved.
Received 27 April 2017
Revised 27 July 2017
Accepted 9 August 2017
Keywords:
Metal-organic framework
MIL-100
Acidity
1,5-Benzodiazepine
1,2-Phenylenediamine
Ketones
1. Introduction
metal-organic frameworks (MOFs), such as MOF-235(Fe), MOF-5
(Zn), Mn(BDC), MOF-199(Cu), and Ni2(BDC)2(DABCO), as heteroge-
1,5-Benzodiazepine derivatives have received significant atten-
tion as compounds with biological activity [1]. 1,5-Benzodiazepine
derivatives possess antifungal, antibacterial, antifeedant, anti-
inflammatory, analgesic and anticonvulsant activities. Moreover,
1,5-benzodiazepines are widely used as synthons for the synthesis
of triazole [2,3] and oxadiazole derivatives [4,5]. The traditional
approach for synthesis of 1,5-benzodiazepines is based on the
acid-catalysed reaction of 1,2-phenylenediamine (I) with ketones.
Various catalytic systems for this reaction have been reported in
the literature, a great number of which have appeared only very
recently [6-12]. Thus, synthesis of 1,5-benzodiazepines has been
achieved using different homogeneous catalysts, such as ZnCl2
neous catalysts for the cyclocondensation of acetone with different
1,2-diamines, including 1,2-phenylenediamine, 4-chloro-
1,2-phenylenediamine, 4-bromo-1,2-phenylenediamine, and
4-methyl-1,2-phenylenediamine, to the corresponding 1,5-
benzodiazepines. It was found that MOF-235(Fe) was highly active
compared with other studied MOFs. Unfortunately, the effects of
the structure of MOFs and the nature of active sites in the frame-
works of MOFs on the reaction rate and product distribution were
not investigated.
During last few years, metal-organic frameworks have attracted
significant interest as materials for catalytic applications due to
their unique structure and physicochemical properties [19–21].
Of material importance is that a large variety of structural types
and chemical compositions can be obtained by changing either
the organic linker or the metal. A large specific surface area, homo-
geneous distribution and high accessibility of active sites for reac-
tants also govern the catalytic properties of MOFs. The latest
investigations note that the type of metal ions in the framework
of MOFs affects their catalytic properties [22–24]. Thus, the effect
of the metal ion on catalytic properties of the isostructural MOFs
of the families MOF-74(Co, Cu, Mg, Ni) and MIL-100(Al, Cr, Sc, V)
was investigated in reactions of 3,4-dihydro-2 HApyran with
[10],
YbCl3
[11],
BF3-etherate
[13],
and
1-butyl-3-
methylimidazolium bromide (ionic liquid) [14]. As solid acid cata-
lysts, polyphosphoric acid on SiO2 [15], sulfated zirconia [7],
polymer-supported FeCl3 [12], H2SO4/SiO2 [8], Amberlyst-15 [9],
and zeolites [16,17] were used. Le et al. [18] suggested the use of
⇑
Corresponding authors at: Boreskov Institute of Catalysis SB RAS, Prospekt
Akad. Lavrentieva 5, 630090 Novosibirsk, Russian Federation (M.N. Timofeeva).
E-mail addresses: timofeeva@catalysis.ru (M.N. Timofeeva), sung@knu.ac.kr
(S.H. Jhung).
http://dx.doi.org/10.1016/j.jcat.2017.08.009
0021-9517/Ó 2017 Elsevier Inc. All rights reserved.

M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
129
alcohols [24]. It was found that the yield of tetrahydropyranyl
ether decreased in the following orders:
cage). The amount of Lewis acid sites (LAS) in MIL-100(M) and
Al-BTCs was measured by EPR spectroscopy using the 2,20,6,60-tet
ramethyl-1-piperidinyoxyl radical (TEMPO) as the probe molecule.
Earlier, we successfully used this technique in the analysis of coor-
dinatively unsaturated sites (Al3C+US) in Al-BTCs, such as MIL-100(Al),
MIL-96(Al) and MIL-110(Al) [22]. This method is based on the reac-
tion of TEMPO with only one acid site [29–31]. According to this
property, the maximum amount of radicals adsorbed (until the
EPR spectrum of the TEMPO radical appears in the solution) corre-
sponds to the concentration of acid sites. Analysis of the main factors
that affect the reaction rate and the isomer selectivity was based on
a combination of catalytic, theoretical and physicochemical meth-
ods. Another purpose of our investigation was to demonstrate the
catalytic potential of the studied MOFs as heterogeneous catalysts
for this reaction. To this end, we investigated cyclocondensation of
(I) with other ketones, such as cyclohexanone, acetophenone and
methyl ethyl ketone, to obtain the corresponding 1,5-
benzodiazepines.
MIL-100(V) > MIL-100(Sc) > MIL-100(Cr) > MIL-100(Al)
MOF-74(Mg) > MOF-74(Ni) > MOF-74(Cu) > MOF-74(Co)
The main reasons for these trends are related to the accessibility
and strength of open metal sites. The dependence of catalytic prop-
erties on the type of metal ions was also demonstrated for the
isostructural MOFs of the families MIL-100(M) and MIL-53(M)
(M = V, Al, Fe and Cr) and mixed MIL-53(Al,V) (Al/V – 100/0,
75/25, 50/50, 25/75 and 0/100 atom/atom) in the synthesis of
solketal from acetone and glycerol (I) [23]. According to this
investigation, glycerol conversion decreased in the following order
V3+ > Al3+ > Fe3+ > Cr3+, which was in agreement with the value of
the zero point of charge of the surface (pHPZC). Reasonably, the type
of metal ions in the framework of MOFs should also be important
for the reaction between (I) and ketones.
As a part of a systematic study on the catalytic behaviour of
MOFs and with a view to increase knowledge about the depen-
dence of their catalytic properties on the type of metal ions, we
report for the first time on variable catalytic activity of isostruc-
tural MOFs of the families MIL-100(M) (M: V3+, Al3+, Fe3+and
Cr3+) and three porous aluminium trimesates Al-BTCs (MIL-96
(Al), MIL-100(Al) and MIL-110(Al)) in the cyclocondensation of (I)
with acetone to 2,3-dihydro-2,2,4-trimethyl-1H-1,5-benzodiaze
pine (1,5-benzodiazepine, (III)) (Scheme 1). We suggested that
the type of metal ions in the MOFs should allow to adjust the cat-
alytic activity of MIL-100(M). Moreover, three porous aluminium
trimesates Al-BTCs are good candidates for our investigation
because their textural properties are different, important for
analysis of the effect of the amount of active sites and their
accessibility to the reactants. Thus, the structure of MIL-96(Al)
([Al12O(OH)18(H2O)3(Al2(OH)4)[BTC]6ꢁ24H2O]) has three types of
cages. The pore-opening diameters of these cavities are in the
range of 2.5–3.5 Å [25]. MIL-110(Al) (Al8(OH)12{(OH)3(H2O)3}
[BTC]3ꢁ42H2O) also has a honeycomb topology. MIL-110(Al)’s
structure is built up from the connection of an octahedrally coordi-
nated aluminium octameric unit through trimesate ligands delim-
iting one-dimensional, large hexagonal channels (16 Å) [26]. At the
same time, mesoporous MIL-100(Al) ([Al3O(OH)(H2O)2[BTC]ꢁ
24H2O]) possesses a three-dimensional framework structure with
two types of cavities [27,28]. The first type of cavity is delimited
by 12 pentagonal windows with a size of 5.5 Å (dodecahedral
cage); the second cavity is delimited by 12 pentagonal windows
and 4 hexagonal windows with a size of 8.6 Å (hexadodecahedral
2. Experimental
2.1. Materials
Commercial methanol, acetone (Acros Organics), 1,2-
phenylenediamine (Acros Organics), cyclohexanone (99+ %, Acros
Organics), acetophenone (98%, Acros Organics), 2-butanone
(99+ %, Acros Organics), 2,20,6,60-tetramethyl-1-piperidinyoxyl rad-
ical (TEMPO) (Aldrich), Al(NO3)3 9H2O (98 wt%, Junsei), 1,3,5-
benzenetricarboxylic acid (H3BTC) and 1,3,5-trimethyl-benzenetri
carboxylate (Me3-BTC, 98%, Aldrich), ortho-phosphoric acid
(H3PO4, 85 wt%, Merck), sodium hydroxide (NaOH, 4 M), nitric acid
(HNO3, 60 wt%), iron powder (Fe0, 99%, DC Chemical Co.), CrO3
(98%, Junsei) and hydrofluoric acid (HF, 48%, OCI Company Ltd.) were
used without any further purification. Beta zeolite (Si/Al 30, frame-
work type BEA) and H-ZSM-5 (Si/Al 28, framework type MFI) were
synthesized in a way similar to reported methods [16,32].
2.2. Synthesis of metal-benzenetricarboxylates
Al-BTCs were synthesized from Al(NO3)3ꢁ9H2O, 1,3,5-
benzenetricarboxylic acid (H3BTC)
or
trimethyl 1,3,5-
benzenetricarboxylate (Me3-BTC), sodium hydroxide (NaOH,
4 M), nitric acid (HNO3, 60%) and deionized water similar to the
reported methods for MIL-100(Al) [27,28], MIL-110(Al) [27] and
MIL-96(Al) [25] under autogenous pressure at 210 °C. The reactant
compositions for the desired phases are shown in Table S1 (Sup-
O
C
CH3
CH3
O
CH3
CH3
H
N
C
N
NH2
H3C
CH3
H3C
C
CH3
NH2
NH2
N
CH3
(II)
(I)
(III)
H
N
CH3
CH3
C
N
H
(IIa)
Scheme 1. The cyclocondensation of 1,2-phenylenediamine with acetone.

130
M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
porting Information (SI)). MIL-100(Fe) was synthesized according
to a reported procedure [33]. MIL-100(Cr) was synthesized in a
way similar to a reported method [34]. MIL-100(V) was synthe-
sized in a way similar to a reported method [35]. The designation
of the samples, chemical composition and textural data of samples
are presented in Table 1 and Figs. S1–S2 (SI).
recorded at 20 dB attenuation with a typical microwave power of
3 mW.
2.5. Catalytic tests
The reaction of (I) with acetone was carried out at 30–50 °C in a
jacketed glass reactor (10 mL) equipped with a magnetic stirrer
and connected to thermostat. The temperature control was 1 °C.
Methanol was used as solvent. Before reaction, all catalysts were
activated at 200 °C for 2 h in air in order to remove adsorbed water.
The standard procedure was as follows: 0.1 mmol of (I), 4 mL of
solvent (methanol, ethanol, acetonitrile or 1,2-dichloroethane),
2.5–4 mmol of acetone and 5–20 mg of catalyst were added into
the reactor. At different time intervals, aliquots were taken from
the reaction mixture and analysed by GC and GC–MS analysis
(SI). A gas chromatograph (Agilent 7820) with a flame ionization
detector and an HP-5 capillary column was used to analyse prod-
ucts quantitatively. n-Decane was used as the internal standard.
The GC–MS analysis of the organic phase was performed with a
GC–MS-QP2010 Ultra gas chromatography-mass spectrometer.
Analysis conditions were as follows: GC: Injection port tempera-
ture 250 °C, capillary column GsBP1-MS 30 m ꢂ 0.32 mm, pro-
grammed heating: 50 °C (7.5 min)–20 °C/min–300 °C (10 min),
and carrier gas – He (linear velocity of 50 cm/s); MS: Determined
2.3. Instrumental measurements
The porous structure of the materials was determined from the
adsorption isotherm of N2 at ꢀ196 °C using a Micromeritics ASAP
2400. The specific surface area (SBET) was calculated from the
adsorption data over the relative pressure range between 0.05
and 0.20. The total pore volume (V ) was calculated from the
R
amount of nitrogen adsorbed at a relative pressure of 0.99. The
X-ray diffraction patterns were measured on a X-ray diffractome-
ter (ThermoARL) with Cu-K (k = 1.5418 Å) radiation.
a
2.4. Lewis surface acidity investigation by EPR spectroscopy
All samples for EPR measurements were prepared using ‘‘break
seal” techniques. For this, 0.015–0.020 g of sample (Al-BTC, MIL-
100(Al), MIL-100(Cr)) was loaded into a quartz cell and evacuated
at 200 °C until an absolute pressure of 20 mTorr was reached and
maintained for 3 h. MIL-100(V) and MIL-100(Fe) were loaded into
a quartz cell and calcinated at 200 °C in air for 3 h, and air was
blown out with N2. After cooling to room temperature under vac-
uum conditions, 1 mL of 3.2 ꢁ 10ꢀ5–6.2 ꢁ 10ꢀ4 M TEMPO in toluene
was added to the sample. The EPR spectra were recorded at room
temperature. The concentration of TEMPO was calculated after
the calibration procedure (error 10%).
m/z 35–500, detector voltage 0.8 kV, emission current 60
ion source temperature 250 °C.
lA, and
3. Results and discussion
3.1. The choice of reaction medium
It is well-known [36,37] that in the presence of MOF-235, MOF-
5, Mn(BDC), MOF-199, and Ni2(BDC)2 (DABCO) the reaction rate
and yield of (III) depend on solvent type. Therefore the effect of
The EPR spectra were measured with an ERS-221 EPR spectrom-
eter working in the X-band (
m
= 9.3 GHz). The EPR spectra were
Table 1
Textural properties of M-BTC materials.
M content (wt.%)
Textural data
SBET (m2/g)
V
(cm3/g)
V
(cm3/g)
l
R
MIL-100(V)
MIL-100(Fe)
MIL-100(Cr)
MIL-100(Al)
MIL-110(Al)
MIL-96(Al)
19.5
24.3
19.5
15.9
17.3
17.6
1628
1794
1653
1486
679
0.82
1.56
0.91
0.70
0.58
0.14
0.34
0.35
0.35
0.38
0.27
0.13
315
Table 2
Effect of solvent on reaction of 1,2-phenylenediamine with acetone in presence of MIL-100(V).a
Solvent
Relative polarityb
Time (min)
Conversion of (I) (%)
Selectivity (%)
(II)
(III)
(Other)
MIL-100(V)
Methanol
0.672
10
30
70
30
180
30
180
60
87
96
100
37
74
43
64
29
41
19
13
5
69
27
73
67
82
75
77
81
93
21
67
18
25
3
4
6
2
10
6
9
8
15
16
Ethanol
0.654
0.460
0.269
Acetonitrile
1,2-Dichlorethane
180
9
MIL-100(Al)
Methanol
0.672
90
92
100
63
33
15
74
4
69
79
84
17
92
20
5
9
4
11
16
13
180
180
180
180
Ethanol
Acetonitrile
1,2-Dichlorethane
0.654
0.460
0.269
3
a
Reaction conditions: 0.1 mmol of (I), 0.25 mmol of acetone, 0.015 g of catalyst, 4 mL of solvent, 50 °C.
Data are from Ref. [38].
b

M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
131
leads to the formation of (II), which then reacts with the second
molecule of acetone to give (III).
The yield of (III) depends on the type of metal and decreases in
the following order (Fig. 3A, Table 3):
MIL-100(V) > MIL-100(Fe) > MIL-100(Cr) > MIL-100(Al).
Scheme 2. The interaction of alcohol with LAS of MIL-100(M) (s – metal atom, d –
oxygen atom).
This order can be explained both by impact of acidity and the com-
plexing ability of active sites.
It is well-known that both Brønsted and Lewis acids can be used
as catalysts for these reactions [4,7,9,13,16,17]. Since MIL-100(M)
possesses both type acid sites, we considered their effects on the
reaction rate and yield of (III).
solvent on conversion of (I) and yield of (III) was investigated in
the presence of MIL-100(V) and MIL-100(Al) at an acetone/(I)
molar ratio of 2.5 and 50 °C. The main results are shown in Table 2
and Fig. S3 (SI). According to experimental data, the conversion of
(I) and yield of (III) decreased with decreasing solvent polarity (rel-
ative polarity [38]) in the following order:
Effect of Brønsted acid sites (BAS). The high activity of MIL-
100(M) can be related to the Brønsted acidity, which is associated
with the existence of structural M-OH groups and BAS formed by
guest molecules (water, alcohols, etc.) adsorbed onto Lewis acid
sites (Scheme 2) [40,41]. Previously, in the condensation of glycerol
with acetone, we demonstrated that the activity of MIL-100(M)
correlated with surface acidity, which was determined as zero
point of charge of the surface (pHPZC) by the method of mass titra-
tion in aqueous solution [23]. According to these data, surface acid-
ity decreases in the following order (pHPZC values):
Methanol > Ethanol > Acetonitrile > 1,2-Dichloroethane
The maximal efficiency was observed in methanol with its large
relative polarity (0.672). Most likely, the application of polar sol-
vent affects the formation and the spatial arrangement and config-
uration of intermediates. Moreover, Vimont et al. [39]
demonstrated that alcohols favour a change in the surface acidity
of MIL-100(Cr) due to the formation of the Brønsted acid sites
(BAS) (Scheme 2). Amount and strength of BAS decrease with an
increase in the size of the alcohol. We can assume that similar
BAS is formed due to the interaction of methanol and ethanol with
LAS of MIL-100(V) and MIL-100(Al). Thus, methanol was preferred
as a reaction medium for the investigations.
MIL-100(V) (3.41) > MIL-100(Al) (3.95) > MIL-100(Fe) (4.11)
> MIL-100(Cr) (4.41).
The comparison of orders of pHPZC and activity of MIL-100(M) does
not reveal clear trend in the cyclocondensation of (I) with acetone.
In spite of the high surface acidity, the yield of (III) in the presence
of MIL-100(Al) was lower as compared with MIL-100(Cr) and MIL-
100(Fe) (Table 3).
Effect of Lewis acid sites (LAS). The amount of LAS in MIL-100
(M) was determined by a spin probe EPR spectroscopy using a
bulky probe molecule, such as 2,20,6,60-tetramethylpiperidine-1-o
xyl (TEMPO). Typical EPR spectra of the TEMPO complex
(3.18ꢁ10ꢀ4 mol/L) before and after adsorption on MIL-100(Cr) and
the TEMPO complex adsorbed on MIL-100(Al) (0.98 mmol/g and
0.05 mmol/g) are shown in Figs. S5–S6 (SI). The main results of
The reaction has heterogeneous character in the presence of
MIL-100(M) samples in methanol as reaction medium. One can
be seen from Fig. 1, the reaction does not proceed after catalyst
separation from the reaction mixture.
3.2. The effect of the metal ion on catalytic properties of MIL-100(M)
Effect of the type of metal ions on reaction rate and distribution
product was investigated for MIL-100(M) (M = V, Al, Fe and Cr). The
main results are presented in Table 3, Figs. 2–3 and S4 (SI). From
the kinetic data, one can see that the reaction proceeds via two
steps (Scheme 1). In the first step, reaction between (I) and acetone
the estimation of the amount of LAS in MIL-100(M) are given in
3+
Table 3. One can see from these data that the amount of LAS (Al
)
CUS
MIL-100(V)
MIL-100(Al)
100
100
75
75
Catalyst was separated
50
50
Catalyst was separated
25
25
o
o
40 C
30 C
0
0
0
30
60
90
0
20
40
60
Time, min
Time, min
Fig. 1. The cyclocondensation of 1,2-phenylenediamine with acetone in the presence of MIL-100(V) and MIL-100(Al) (Experimental conditions: 4 mL of MeOH, 0.1 mmol of
(I), 0.25 mmol of acetone, 0.010 g of catalyst).

132
M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
Table 3
Surface acidity and catalytic properties of MIL-100(M) materials in reaction of 1,2-phenylenediamine with acetone.
Amount of LASb
Mtotal (mmol/g)
Catalytic propertiesc
Time (min)
a
Catalyst
pHPZC
3+
M
(mmol/g)
MC3+US/Mtotal (mol/mol)
Yield of (III) (%)
CUS
1
2
3
4
MIL-100(Al)
MIL-100(Cr)
MIL-100(Fe)
MIL-100(V)
3.95
4.41
4.11
3.41
5.89
3.75
4.34
3.84
0.98
2.64
2.28
2.44
0.17
0.70
0.52
0.63
100
100
100
70
47
69
92
93
a
b
c
pHPZC - zero point of charge of the surface was estimated by the method of mass titration in aqueous solution [23].
Amount of LAS in MIL-100(M) materials was determined by EPR spectroscopy using TEMPO as probe molecul.
0.1 mmol of (I), 0.25 mmol of acetone, 0.015 g of catalyst, 4 mL of MeOH, 50 °C.
MIL-100(Al)
MIL-100(V)
100
75
50
25
0
100
75
50
25
0
(III)
(II)
(IIa)
(I)
(I)
(III)
(II)
(IIa)
0
30
60
90
0
30
60
90
Time, min
Time, min
Fig. 2. Kinetic curves of the cyclocondensation of (I) with acetone in the presence of MIL-100(V) and MIL-100(Al) (Experimental conditions: 4 mL of MeOH, 0.1 mmol of (I),
0.25 mmol of acetone, 0.015 g of catalyst, 50 °C).
100
75
50
25
0
100
75
50
25
0
B
A
MIL-100(V)
MIL-100(V)
MIL-100(Fe)
MIL-100(Fe)
MIL-100(Cr)
MIL-100(Cr)
MIL-100(Al)
90 min
MIL-100(Al)
10 min
0
30
60
90
4,6
4,8
5,0
5,2
5,4
Time, min
Z/r
Fig. 3. (A) Kinetic curve of yield of (III) in the cyclocondensation of (I) with acetone in the presence of MIL-100(M). (B) Correlations between Z/r and yield of (III).
(Experimental conditions: 4 mL of MeOH, 0.1 mmol of (I), 0.25 mmol of acetone, 0.015 g of catalyst, 50 °C).
3+
and (Cr ) are 0.98 and 2.64 mmol/g for MIL-100(Al) and MIL-100
LAS in MIL-100(Fe) is 2.28 mmol/g, which is also lower in compar-
CUS
(Cr) calcined at 200 °C, respectively. These values are lower than that
determined by IR spectroscopy using CO (2180–2220 cm–1) as the
probe molecule (MIL-100(Al) approximately 1.7 mmol/g [41] and
MIL-100(Cr) approximately 3.5 mmol/g [39,40]). The amount of
ison with the value determined by CO adsorption [42]. Total
3+
amounts of Fe2+/Fe
in MIL-100(Fe) calcinated at 150 and 250 °C
CUS
were 1.94 and 3.66 mmol/g, respectively. We can suggest that
these differences are related to the difference in the size of the probe

M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
133
molecule, which affects the accessibility of LAS. Interestingly, the
amount of LAS in MIL-100(V) (2.44 mmol/g) determined by the spin
probe method is close to that determined by CD3CN adsorption
(approximately 2.3 mmol/g) [24].
According to EPR data, the amount of LAS decreases in the order
(Table 3):
MOFs for their adsorptive removal. Most likely, this parameter can
play a key role in reaction between (I) and acetone. According to
the chemistry of coordination complexes [45], the bonding
strength between the NH2-group of (I) and M3+ ion, i.e., the com-
plexing ability of M3+ ion to NH2-groups in (I), should depend on
the ionic potential
u
¼ Zr, where Z and r are charge and the radius
of the metal ion, respectively. The radius of the metal ion decreases
in the order [46]:
MIL-100(Cr) > MIL-100(V) > MIL-100(Fe) > MIL-100(Al)
V3+(0.63 0.003 Å) > Fe3+(0.62 0.003 Å) > Cr3+(0.61 0.001 Å)
> Al3+(0.52 0.005 Å)
The catalytic properties of MIL-100(M) are slightly dependent on
the amount of LAS. The low conversion of (I) and yield of (III) in
the presence of MIL-100(Al) are not surprising due to the lower
amount and accessibility of active sites for reactants as compared
with other MIL-100(M).
The / value increases in this order can point to the decreasing
the strength of complexing. According to this trend, active sites
formed by Al3+ in MIL-100(Al) should possess lower complexing
ability to NH2-groups in (I) in compared with active sites formed
It is well-known that MIL-100(M) possesses a very high affinity
for S- and N-containing materials [43,44] that allows to the use of
(A)
NH2
R
+
M3
Hδ+
R
O
:
+
NH2
M3
H
:
O
O
C
NH2
step 2
O
δ+
δ+
-
-
CH3
CH3
-
C
-
CH3 CH
3
=
-
N
C CH3
ste
p
1
H
R
CH3
+
M3
:
O
Hδ+
+
M3
:
O
R
H
N
O
H
C
3
-
-
CH3 C CH3
NH2
NH2
CH3
H
2O
+
H
2O
+
δ+
Hδ+
R
step 3
= -
C CH3
=
-
N
N
C CH3
+
M3
N
:
O
CH3
H
R
H
C
CH3
3
+
M3
:
O
(B)
NH2
NH2
O
CH3
CH3
M3+
C
M3+
H2N
CH3
CH3
M3+
N=C
H2N
NH2
- H2O
O
CH3 - C - CH3
Intermediate 1
Surface reaction
CH3
CH3
O
CH3
NH
N
N=C
CH3 - C - CH3
CH3
CH3
M3+
CH3
CH3
N=C
CH3
CH3
N=C
H2N
Diimine
1,5-benzodiazepine
CH3
N=C
N
N
NH
1,3-proton
transfer
CH3
CH3
CH3
CH3
CH3
Intermediate 1
NH2
NH
H
H
Dihydrobenzimidazole
Scheme 3. Possible mechanism of the cyclocondensation of 1,2-phenylenediamines with acetone.

134
M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
by V3+, Fe3+and Cr3+. One can see from Fig. 3B the yield of (III)
decreases with increasing / value:
MIL-100(Al) > MIL-110(Al) > MIL-96(Al)
This order is proportional to the total amount of LAS (Fig. 4). The
larger the amount of LAS, the higher the yield of (III). Another
explanation for this trend can be the difference in their structures.
The large cavities and channels in the MIL-100(Al) structure ensure
the free access to active sites for reagent molecules, which leads to
an increase in the reaction rate.
Most likely, the distribution of LAS in the structure of Al-BTCs
can also affect their activity. This effect can be estimated from
the difference in TON calculated using Eq. (1):
MIL-100(V) > MIL-100(Fe) > MIL-100(Cr) > MIL-100(Al)
The radius of metal ion and strength of interaction between
metal ions and reactants are strongly important in terms of the
reaction mechanism. The mechanism of benzodiazepine formation
via condensation of 1,2-phenylenediamines with ketones was con-
sidered in [13,47-50]. We can suggest that both acetone and (I)
coordinate on the LAS, simultaneously, and interaction of acetone
with LAS leads to the activation of the carbonyl group (Scheme 3A).
At the same time, the NH2-groups of (I) attacks the carbonyl group
of the acetone, giving intermediate 1. Then, this intermediate can
attack the carbonyl group of a second activated acetone molecule
giving diimine, which after intramolecular imine enamine cycliza-
tion forms the seven-membered 1,5-benzodiazepine ring. More-
over, intermediate 1 can transform to dihydrobenzoimidazole
(IIa) due to the inside cyclization. We can assume that the radius
of the metal ion is one of the crucial parameters for the simultane-
ous coordination of acetone and (I). Active sites formed by V3+ with
D
NLAS
ðIIIÞ
TON ¼
ð1Þ
where
D(III) is the amount of (III) (mmol), NLAS is the amount of LAS
(mmol). According to experimental data, the efficiency of Al-BTCs
for the first of 10 min decreases in the order (TON):
MIL-110(Al) (7.3) > MIL-100(Al) (5.4) >> MIL-96(Al) (2.2)
This result notes that active sites (LAS) of MIL-110(Al) are
located on the surface and their density is higher as compared with
MIL-100(Al). The low activity of MIL-96(Al) can be related to high
microporosity (Table 1) that affects the accessibility of the active
sites for the reactants.
its large radius ion are more preferable than that formed by Al3+
.
3.4. The catalytic properties of MIL-100(M) under solvent free
conditions
3.3. Effect of structure and Lewis acidity on catalytic properties of Al-
BTCs
Catalytic properties of MIL-100(M) were also investigated in the
reaction of (I) with acetone at a 4/1 M ratio of acetone/(I) and 50 °C
under solvent free conditions. The results given in Table 4 show
The effect of structure of M-BTCs and amount of LAS on reaction
rate and yield of (III) was investigated in the presence of Al-BTCs,
such as MIL-100(Al), MIL-110(Al) and MIL-96(Al). Application of
identical precursor reactants and control of the pH of the starting
mixture and/or the reaction time allow us to synthesize Al-BTCs
having three different structures [26,27]. Earlier, we estimated
concentration of LAS (Al3C+US) on the surface of these solids by the
spin probe method, i.e., EPR spectroscopy using TEMPO as the probe
molecule [22]. It was found that the amount of LAS (Al3C+US) in MIL-
100(Al), MIL-110(Al) and MIL-96(Al) calcined at 200 °C are 0.98,
0.62 and 0.14 mmol/g, respectively. The differences in the amount
of LAS are in agreement with differences in their structure and tex-
tural properties.
Table 4
Reaction of 1,2-phenylenediamine with acetone in presence of different catalytic
systems under solvent-free conditions.a
Catalyst
Time (min)
Yield of (III) (%)
1
2
3
4
5
6
7
8
MIL-100(V)
180 (300)
180 (300)
180 (300)
180 (300)
180
300
300
300
85 (95)
76 (88)
72 (81)
68 (75)
82
81
39
32
MIL-100(Fe)
MIL-100(Cr)
MIL-100(Al)
HY [16]
Heulandite [16]
Beta Zeolite
H-ZSM-5
The catalytic properties of these materials were investigated at
60 °C at an acetone/(I) molar ratio of 2.5. The kinetic profiles in the
presence of Al-BTCs are shown in Fig. S7 (SI). According to the
experimental data, the activity of Al-BTCs decreases in the order
(Fig. 4)
H-ZSM-5 [16]
1.7%Fe-MMM [51]
6.5%Fe-VSB-5 [51]
420
300
300
52
86
64
10
11
a
0.1 mmol of (I), 0.4 mmol of acetone, 0.02 g of catalyst, 50 °C.
100
100
MIL-100(Al)
MIL-100(Al)
75
50
25
0
MIL-110(Al)
MIL-96(Al)
75
MIL-110(Al)
50
25
MIL-96(Al)
0
0,0
0
30
60
90
120
0,3
0,6
0,9
1,2
Al3+CUS, (mmol/g)
Time, min
Fig. 4. Kinetic curves of yield of (III) and correlation between amount of LAS and yield of (III) for 60 min in the cyclocondensation of (I) with acetone in the presence of Al-
BTCs. (Experimental conditions: 4 mL of MeOH, 0.1 mmol of (I), 0.25 mmol of acetone, 0.015 g of catalyst, 60 °C.)

M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
135
Table 5
Reaction of 1,2-phenylenediamine with ketones in presence of MIL-100(V) and MIL-100(Al).a
Ketone
Gas basicityb (kJ/mol)
782.1
Product
Catalyst
Time (min)
Yield (%)
1
MIL-100(V)
MIL-100(Al)
70
180
93
92
2
3
795.5
829.3
MIL-100(V)
MIL-100(Al)
180
300
89c
79c
MIL-100(V)
MIL-100(V)
180
180
49 (68)d
69 (82)d
4
811.2
a
b
c
Reaction conditions: 0.1 mmol of (I), 0.25 mmol of ketone, 0.015 g of catalyst, 4 mL of MeOH, 50 °C.
Data are from Ref. [52].
Overall yield by two isomers.
60 °C.
d
that yield of (III) is adjusted by the nature of the metal ion. The
maximal yield of (III) was observed in the presence of MIL-100
(V). In the presence of MIL-100(V), yields of (III) were 85 and
95% after 3 and 5 h, respectively (Table 4, run 1). The comparison
of the catalytic properties of MIL-100(M) with that of zeolites
reported in the literature [16] notes that the activity of MIL-100
(V) is comparable to that of zeolite HY (Si/Al 2.5, framework type
FAU) (Table 4, runs 1 and 5). At the same time, zeolites such as zeo-
lite heulandite (Si/Al 5, framework type HEU), H-ZSM-5 (Si/Al 28,
framework type MFI) and b-zeolite (Si/Al 30, framework type
BEA), show lower activity than MIL-100(V) (Table 4, runs 1, 6–9),
which probably can be explained by the difference in surface acid-
ity. Moreover, the low activity of zeolites can also be related to
their high microporosity. Mesoporosity and the unique structure
of MIL-100(M) are major parameters that likely affect their cat-
alytic properties. Thus, the activity of MIL-100(Fe) is comparable
with that of Fe-containing mesoporous mesophase silica material
(1.7%Fe-MMM) [51] (Table 4, runs 2 and 10) and is strongly higher
than that of Fe-containing microporous nickel phosphate molecu-
lar sieves (6.5%Fe-VSB-5) (Table 4, runs 2 and 11).
Noteworthy that in the presence of MIL-100(M) (M-Al, Cr, Fe)
the yields of (III) under solvent free conditions were slightly differ-
ent from those in methanol solvent (Tables 3–4). This phenomenon
can be related to the formation of BAS due the interaction of
methanol with LAS of MIL-100(M). These sites may contribute as
active sites for the activation of carbonyl group of the acetone
(Scheme 3B, step 1) which then reacts with the amine group of (I).
3.5. Synthesis of different 1,5-benzodiazepines
The catalytic activity of the most active MIL-100(V) was inves-
tigated in the condensation of (I) with other ketones (cyclohex-
anone, acetophenone, ethyl methyl ketone). Similarly, for these
ketones, we used excess amounts (ketone/(I), 2.5/1.0) in the reac-
tion mixture and methanol as solvent. One can see from Table 5
that reaction of (I) with ethyl methyl ketone gave the correspond-
ing 1,5-benzodiazepines (two isomers) in 89% overall yield at 50 °C
for 180 min. Note that the corresponding 1,5-benzodiazepines
(two isomers) also can be obtained in the presence of MIL-100
(Al). Their overall yield was 79% after 300 min. At the same time
MIL-100(V)
MIL-100(Al)
Yield of (III), %
Yield of (III), %
100
100
75
50
25
0
75
50
25
0
le
cle
ycle
cy
cle
cycle
2 c
3 cycle 4 cycle 5 cycle 6 cyc
2 cycle
3 cy
1
1
Fig. 5. Recycling test in cyclocondensation of (I) with acetone in the presence of MIL-100(V) and MIL-100(Al) (Experimental conditions: (A) - 40 mL of MeOH, 1 mmol of (I),
2.5 mmol of acetone, 0.100 g of MIL-100(V), 30 °C, 60 min; (B) - 40 mL of MeOH, 1 mmol of (I), 2.5 mmol of acetone, 0.150 g of MIL-100(Al), 50 °C, 300 min). The amount of the
reactants was corrected based on reaction conditions.

136
M.N. Timofeeva et al. / Journal of Catalysis 354 (2017) 128–137
in the presence of MIL-100(V) the high yield of 1,5-
benzodiazepines from cyclohexanone and acetophenone were
obtained at 60 °C for 180 min. In the reaction mixtures of (I) with
ethyl methyl ketone and cyclohexanone, we observed also the cor-
responding diimines as minor products. It can be assumed that,
since the imine formation reaction is in equilibrium, these prod-
ucts are subsequently converted to the desired 1,5-diazepines.
Basicities (gas basicity [52]) of studied ketones are different one
another (Table 5), which can be important for their activation
on active sites (BAS) and water removal (Scheme 3B). Results
In the presence of Al-BTCs, the reaction rate and yield of
1,5-benzodiazepine were in agreement with the amount of LAS
and decreased in the order:
MIL-100(Al) > MIL-110(Al) > MIL-96(Al).
The accessibility of active sites for the reactants was also important
for reactivity of Al-BTCs.
Synthesis of other 1,5-benzodiazepines from (I) and cyclohex-
anone, acetophenone and ethyl methyl ketone in the presence of
MIL-100(V) and MIL-100(Al) was also demonstrated. Gas basicity
of ketones affects the yield of 1,5-benzodiazepines. The higher
gas basicity, the lower yield of 1,5-benzodiazepines.
in Table
5 show that gas basicity affects the yield of
1,5-benzodiazepines. The higher gas basicity, the lower yield of
1,5-benzodiazepines.
The efficiencies of MIL-100(V) and MIL-100(Fe) were compared
with that of zeolites and zeotype materials reported in the litera-
ture. It was found that activity of MIL-100(V) is comparable to that
of HY, while the activities of H-ZSM-5, b-zeolite and zeolite heulan-
dite were much lower than MIL-100(V) or HY. At the same time,
the activities of MIL-100(Fe) and mesoporous mesophase silica
material 1.7%Fe-MMM were similar to each other, while the activ-
ity of microporous 6.5%Fe-VSB-5 was low.
Recycling experiments point that yield of (III) does not change
during at least three and six catalytic cycles for MIL-100(V) and
MIL-100(Al), respectively. According to XRD data, structure of
MIL-100(Al) was stable for cyclic test, while the structure transfor-
mation of MIL-100(V) was observed after the first cycle.
3.6. Stability of MIL-100(M): Recycling test
Stability of catalysts in the reaction mixture is the important
property for their application. The stability of high-active MIl-
100(V) and low-active MIL-100(Al) samples was investigated by
means of recycling tests at an acetone/(I) molar ratio of 2.5 in
methanol medium. After each catalytic test, the sample was sepa-
rated from the reaction mixture by filtration, washed with acetone
and used in the next cycles.
It was found that MIL-100(Al) can be used repeatedly without
significant loss in catalytic activity during at least 6 catalytic cycles
(Fig. 5). The yield of (III) was 81–86% in each cycle. According to
the XRD data, structure of MIL-100(Al) after 6 cycles is not much
different from that of fresh sample (Fig. S8, SI). The yield of (III) also
does not change during 3 catalytic cycles (78–80%) in the presence
of MIL-100(V). However, XRD patterns of the fresh MIL-100(V) and
MIL-100(V) after first cycle are different each other (Fig. S8, SI), i.e.
MIL-100(V) is not very stable under the reaction conditions. Prob-
ably, the high efficiency of MIL-100(V) might be related to the
structure transformation, which needs further study.
Acknowledgments
This work was conducted within the framework of budget pro-
ject No. 0303-2016-0007 for Boreskov Institute of Catalysis and by
the National Research Foundation of Korea (NRF) grant funded by
the
Korea
government
(MSIP)
(grant
number:
2017R1A2B2008774). The authors also thank Dr. A.V. Toktarev
for synthesis of H-ZSM-5 and b-zeolite.
4. Conclusions
Appendix A. Supplementary material
The catalytic behaviour of isostructural MOFs of the families
MIL-100(M) (M: V3+ Al3+ Fe3+ and Cr3+
, , ) and three porous
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2017.08.009.
aluminium trimesates Al-BTCs (MIL-96(Al), MIL-100(Al) and MIL-
110(Al)) was investigated in the cyclocondensation of (I) with ace-
tone to provide 1,5-benzodiazepine. Reactions were carried out at
50 °C with an acetone/(I) molar ratio of 2.5 and 4.0 in different sol-
vents (methanol, ethanol, acetonitrile, 1,2-dichloroethane) and
under solvent free conditions. It was found that yield of 1,5-
benzodiazepine decreases with decreasing solvent polarity. The
maximal yield of 1,5-benzodiazepine was observed in methanol,
a solvent with large relative polarity.
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