Minimisation of E-Factor in the synthesis of N-hydroxylamines: The role of silver(i)-based coordination polymers

Article abstract of DOI:10.1039/c2gc35076a

Among four different 2-D polymeric silver(i)-bpfb assemblies synthesized, [Ag(μ-bpfb)(N₃)]_n (4c) having an azide anion was shown to be the best catalyst for the partial oxidation of primary amines to N-monoalkylhydroxylamines with ur

Full text of DOI:10.1039/c2gc35076a

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Green Chemistry
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PAPER
Minimisation of E-Factor in the synthesis of N-hydroxylamines: the role of
silver(I)-based coordination polymers†‡
Mehdi Sheykhan, Zohreh Rashidi Ranjbar, Ali Morsali* and Akbar Heydari*
Received 16th January 2012, Accepted 19th April 2012
DOI: 10.1039/c2gc35076a
Among four different 2-D polymeric silver(I)–bpfb assemblies synthesized, [Ag(μ-bpfb)(N3)]n (4c)
having an azide anion was shown to be the best catalyst for the partial oxidation of primary amines to
N-monoalkylhydroxylamines with urea hydrogen peroxide (UHP). The method has supplied the
minimum E-Factor (which is in the range for bulk chemicals) amongst all of the presented methods.
More importantly, the catalyst could be easily recovered and reused for six reaction cycles without any
loss of activity.
introduced for assessing the environmental impacts of chemical
1. Introduction
processes.11
The development of clean and efficient oxidation methods for
fine chemical synthesis is a major goal of Green Chemistry.1
Due to the biological activities of α-N-hydroxyamino acids, the
synthesis of N-monoalkyl hydroxylamines has been a topic of
research interest.2 Hence, to date there have been many reports
of N-monoalkyl hydroxylamine preparation from primary amines
namely: oxidation of the amines with benzoyl peroxide,3 the
synthesis of corresponding nitroso and/or nitro or oxime com-
pounds followed by their reduction,4 oxidation of primary
amines by dimethyldioxirane,5 indirect oxidation of primary
amines, involving hydrolysis of oxaziridine,6 direct microwave-
induced oxidation of primary amines by oxone over silica gel or
alumina,7 cyanomethylation of primary amines, nitrone for-
mation, and hydroxyl aminolysis of the synthesized nitrones,8
the asymmetric hydrogenation of nitrones with an iridium cata-
lyst system9 and oxidation of primary amines to nitrones fol-
lowed by hydrolysis under acidic conditions, or treatment with
hydroxylamine to afford the desired N-alkylhydroxylamine.10
All reported reactions have significant drawbacks such as requir-
ing treatment of an intermediate (O-benzylatedhydroxylamine)
with a base in order to obtain the free hydroxylamine, over-
oxidation to nitroso and nitro compounds, inability for the
synthesis of optically active N-alkylhydroxylamines, and appli-
cability to a limited range of substrates. In fact, the most
fundamental problem of all these methods is their high E(nviron-
mental) Factor (kg waste/kg product) which Roger Sheldon
One of the great challenges in supramolecular chemistry is the
development of methods for the design and synthesis of topo-
logically innovative structures with increasing dimensionality.
Following design principles of complexes having regular two-
and three-dimensional (2&3-D) grid architectures which use
the relationship between functionality and stereochemistry, a
survey of metal–organic frameworks (MOFs) or coordination
polymers as two types of polymeric metal–ligand assemblies
has recently raised more and more interest.12 Some of the
potential applications of metal–ligand coordination polymers
with novel topologies are in the area of non linear optics
(NLO), gas storage, magnetism, catalysis, separations and extrac-
tions and applications related to zeolites such as anion
exchange.13
Although homogeneous catalysts in general have a high reac-
tivity, their applications are still quite limited. The recovery of
them is not easy, which increases cost and also leads to heavy-
metal pollution.14 Catalysis is one of important applications of
the metal–organic assemblies. The catalytic characteristic may
be caused by transition metals having catalytic activities. In
addition, assemblies can be designed in such a way as to offer
metal centers and specific organic groups to the reagents. To the
best of our knowledge, only a few examples of such materials
having efficient catalytic activity can be found in the literature.
Aoyama et al. have studied anthracene bis-resorcinol (H4L)
based coordination polymers by treating with Zr(OtBu)4,
Al(CH3)3, Ti(OiPr)2Cl2, or La(OiPr)3.15 Additionally, many
metal–organic frameworks have lent themselves well to the
heterogeneous asymmetric catalysis.16 Providing cavities walled
with a chiral environment is the aim of such materials for
enantioselective catalysis. Sasai and Ding et al.17 designed chiral
metal–organic coordination polymers from 1,1′-2,2′-binaphthol
ligand and Al3+, Ti2+ ions. Furthermore, the compound
{[Ti2(μ-O)2(binol)]}n has found use as a catalyst in the asym-
metric ene-reaction.
Chemistry Department, Tarbiat Modares University, P.O. Box 14155-
4838, Tehran, Iran. E-mail: Akbar.heydari@gmx.de;
Fax: +9882883455; Tel: +9882883444
†Dedicated to the memory of Abbas Doran
‡Electronic supplementary information (ESI) available: Complete bond
lengths and angles, co-ordinates and displacement parameters. CCDC
780549 for compound [Ag(μ-bpfb)(NO3)]n (4a). For ESI and crys-
tallographic data in CIF or other electronic format see DOI:
10.1039/c2gc35076a
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−
Scheme 1 Preparation of [Ag(μ-bpfb)(X)]n (X– = NO3−, SCN−, N3
and ClO4−) (4a–d) nano-rods.
With respect to the compelling need for development of clean
and reusable catalysts, this research is concerned with the design
of a series of novel two dimensional brick-wall-shaped Ag(I)
based coordination polymers and their applications in the selec-
tive oxidation of primary amines to the corresponding hydroxy-
lamines as heterogeneous catalysts in the presence of a clean
oxidant. The effect of a new method in E-Factor minimisation
was evaluated and showed acceptable results.
Fig. 1 The IR spectra of compound [Ag(μ-bpfb)(NO3)]n (4a).
Table 1 Crystal data and structure refinements for [Ag(μ-bpfb)(NO3)]n
(4a)
Identification code
Moiety formula
Sum formula
Formula weight
Temperature
4a
C18H14AgN4O2,NO3(C18H14AgN4O2+,NO3
)
−
C
18H14AgN5O5
488.21
100 K
Wavelength
Crystal system
Space group
0.71073 Å
Monoclinic
P21/n
2. Results and discussion
Hall group
Unit cell parameters
−P2yn
In this study, nano-rods of silver complexed N,N′-bis(4-pyridyl
formamide)-1,4-benzenes (bpfb), denoted as 4 [Ag(μ-bpfb)(X)]n
where X is nitrate 4a, thiocyanate 4b, azide 4c and perchlorate
4d, anions were successfully synthesized with uniform mor-
phologies, nano dispersion and narrow distribution in sizes
(Scheme 1). The N,N′-bis(4-pyridyl formamide)-1,4-benzene can
be washed, dried and stored for long periods of time. The chemi-
cal compounds used for the preparation of these silver complexes
are cost-effective, easily available, and non-toxic. Moreover,
all processes involved are simple. Silver complexation in the
synthesis of 4a was accomplished by an ultrasonic agitation pro-
cedure. The Ag(I) ions were stabilized by electrostatic forces
on the ligand. The structures of the synthesized nano-structures
4a–d [Ag(μ-bpfb)(X)]n have been confirmed by spectroscopic
techniques. The single crystals of [Ag(μ-bpfb)(NO3)]n (4a)
were prepared by a three layer diffusion method. Nano-rods
of compound 4a have been used as precursor for the synthesis
of [Ag(μ-bpfb)(SCN)]n (4b), [Ag(μ-bpfb)(N3)]n (4c) and
[Ag(μ-bpfb)(ClO4)]n (4d).
a = 12.142(2) Å
b = 10.509(2) Å
c = 13.907(3) Å
α = 90°
β = 106.101(4)°
γ = 90°
Unit cell volume
Density
Z
Absorption coefficient
F000
F000′ (calculated)
Maximum theta for data 27.99°
collection
Reflections collected
Independent reflections 4059 [R(int) = 0.1102]
Minimum and
1705.0(6) Å3
1.902 g cm−1
4
1.228 mm−1
976
972
17 008
0.602 and 0.750
maximum transmission
Maximum indexes
h = 16
k = 13
l = 18
MULTI-SCAN
Least-squares on F2
4059/0/262
Correction method
Data/restraints/
parameters
Absorption correction
Data completeness
R indices (all data)
The IR spectrum of compound 4a shows the absorption bands
at around 3025 cm–1, corresponding to the stretching vibration of
aromatic C–H bonds in bpfb. The variable intensity absorption
bands in the frequency range of 1400–1580 cm–1 are attributable
to stretching vibrations of aromatic CvC bonds. The character-
istic band of the nitrate anion appears at 1336 cm−1. The broad
absorption band at 3340 cm−1 is assigned to the stretching
Semi-empirical from equivalents
0.989
R(reflections) = 0.0421(2480)
wR2(reflections) = 0.0956(4059)
1.044 and −0.587 e Å−3
Largest diff. peak, hole
1
vibration of N–H bonds (Fig. 1). The H NMR spectrum shows
distinct signals, 163.6, 150.2, 141.9, 134.7, 121.5 and
120.8 ppm, in which the signal at 163.6 is attributed to the
carbonyl group and others correspond to the aromatic carbon
atoms of bpfb ligand.
The structure of compound 4a was also determined by X-ray
crystallography (Table 1). The X-ray crystallography data shows
a broad signal at 10.51 ppm being assigned to the NH protons.
In the aromatic region, two doublet bands are observed at
8.78 ppm and 7.86 ppm both ascribing to protons of the pyridine
rings. The singlet signal at 7.77 ppm is assigned to four protons
of the middle aromatic ring. The 13C NMR spectrum shows six
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Fig. 3 The XRD patterns; (a) nano-size compound [Ag(μ-bpfb)-
(NO3)]n (4a); (b) simulated by extraction of data from single crystal
X-ray of compound [Ag(μ-bpfb)(NO3)]n (4a).
Fig. 2 (a) A fragment of the one-dimensional chain in compound 4a
along the crystallographic c axis [001]. (b) Hydrogen bonds form the 2D
coordination polymer (c) The π–π stacking interaction in supermolecule
structure (Ag = violet, O = red, C = gray, N = blue).
Ag(I) ions are connected by covalent bonds to the nitrogen
atoms (N1, N2) of the pyridyl groups. Therefore, this polymer
grows in one dimension along the c crystallography axis
(Fig. 2a). The hydrogen bonds connecting the chains and the
sheets are formed in the second dimension. Two distinct oxygen
atoms (O1s, O2s) of the nitrate groups are connected to the
amidic groups (N–H⋯O) of bpfb ligand (Fig. 2b) by hydrogen
bonding. The sheets are connected by π–π stacking interactions
and the structure grows as a three-dimensional supermolecule
(Fig. 2c).
Fig. 3a, b show X-ray powder diffraction (XRD) patterns of
the simulated X-ray crystallography data of compound 4a. Good
matches were observed between the patterns of simulated X-ray
crystallography data and the X-ray powder diffraction of com-
pound 4a.
Fig. 4 The SEM images of [Ag(μ-bpfb)(NO3)]n (4a).
microscopy. The morphology of compound 4a has been shown
by scanning electron microscopy (Fig. 4). The nano-rods of 4a
were used as precursor in the synthesis of 4b–d nanostructures.
By grinding the compound 4a with KSCN, NaN3 and NaClO4
in the solid phase, nano-structures of 4b–d were obtained. The
IR spectra of compounds 4b–d show the absorption bands of the
aromatic C–H bonds, the vibrations of aromatic rings, and
stretching vibration of N–H bonds. The characteristic band of the
nitrate anion at 1336 cm−1 completely disappeared. The presence
of a signal at 2100 cm−1 in compound 4b is assigned to the pres-
ence of thiocyanate anion (Fig. 5a). Also, the absorption band at
2029 cm−1 is assigned to the vibration mode of the azide anion
in compound 4c (Fig. 5b). The vibration mode of perchlorate
The nanorods of compound 4a were synthesized by ultrasound
irradiation with a power of 138 W and characterized by IR
spectroscopy, X-ray powder diffraction and scanning electron
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Fig. 5 The IR spectra of compounds (a) Ag(μ-bpfb)(SCN)]n (4b), (b)
[Ag(μ-bpfb)(N3)]n (4c) and (c) [Ag(μ-bpfb)(ClO4)]n (4d).
Fig. 6 The XRD patterns of (a) nanostructure of [Ag(μ-bpfb)(SCN)]n
(4b), (b) nanostructure of [Ag(μ-bpfb)(N3)]n (4c); and (c) nanostructure
of [Ag(μ-bpfb)(ClO4)]n (4d).
anion is appeared at 1083 cm−1 in the IR spectrum of compound
4d (Fig. 5c).
Fig. 6 shows that compounds 4b–d have different XRD pat-
terns and therefore have specific structures. The scanning elec-
tron microscopy (SEM) images of synthesized nanoparticles are
shown in Fig. 7 and confirm that all of the synthesized materials
have nano-rod motifs, smooth surface morphology and uniform
particles. In addition, the histogram obtained for 45 random
nanoparticles in the SEM images with mean diameters and
standard deviations for each nanomaterial are summarized in
Table 2. Histograms confirm the narrow size distribution of the
synthesized nanoparticles. Amongst these materials, [Ag(μ-bpfb)-
(NO3)]n has the least mean diameter as well as a small standard
deviation in particle size. It has a 78 nm average diameter and
a 16 nm standard deviation. The theoretical curves of standard
distributions from our studies were calculated by means of
Microsoft Excel.
Using [Ag(μ-bpfb)(NO3)]n as catalyst, the reaction was carried
out for 1-phenylethylamine. The results demonstrated that
1 mol% of catalyst at room temperature in diethyl ether provide
the optimum conditions for giving the corresponding mono-
alkylated hydroxylamine in 80% yield after 2 h. In the absence
of [Ag(μ-bpfb)(NO3)]n no product was observed even after
1 week, so it can be deduced that Ag(I) has a key role as a
catalyst. In the presence of the catalyst the only product was
N-hydroxyl amine. Avariety of primary amines such as aliphatic,
aromatic and amino esters were investigated to bear out the
scope and diversity of the [Ag(μ-bpfb)(NO3)]n catalyzed oxi-
dation reaction (Scheme 2, Table 3).
The anion effect analysis: The reaction was effected using
[Ag(μ-bpfb)(NO3)]n (0.010 g, 0.02 mmol, 1 mol %) as catalyst,
2.0 mmol UHP as oxidant and 0.242 g (2mmol) of 1-phenyl-
ethylamine as substrate under an Ar atmosphere. Having stirred
for 2 h at room temperature, the resulting suspension was filtered
through a pad of celite, and the filtrate concentrated on a rotary
evaporator which resulted in the hydroxylation of 1-phenyl-
ethylamine in 80% yield. The catalyst was washed with diethyl
ether to remove the residual product, and then dried to be reused
in the next run. For comparison of all materials we repeated the
reaction with [Ag(μ-bpfb)(ClO4)]n, [Ag(μ-bpfb)(SCN)]n and
[Ag(μ-bpfb)(N3)]n under the same conditions. The results are
listed in Table 4. All of the prepared catalysts promoted the reac-
tion in high isolated yields and all of them were separated and
reused for six runs. Analyses revealed that the presence of the
‘azide’ anion in the complex leads to the best catalytic results.
After azide, thiocyanate and nitrate, in turn, provide the best
results. It seems that the active center of the catalyst is the Ag(I)
Lewis acid. The coordination of hydrogen peroxide from its
oxygen to the silver(I) appears to be the first step of oxidation
process and the Lewis acidity of Ag(I) reduces the activation
barrier for the oxygen transfer process. The basic strength of the
azide anion promotes this step (by deprotonation of hydrogen
peroxide) more efficiently than do the others.
With regard to the mild reaction conditions including tempera-
ture, pressure, time and the use of moderate oxidant in the pres-
ence of the efficient catalytic system, the chemoselectivity of
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Scheme 2 The synthesis of N-monoalkylated hydroxylamine with
UHP in the presence of 4a.
Table 3 Partial oxidation of primary amines using [Ag(μ-bpfb)(NO3)]n
(4a) as a recoverable and high efficient catalyst
Entry
A
Amine
Product 6
Isolated yield (%)
80
B
C
D
77
75
83
E
F
81
86
Table 4 Counter ion effect on catalytic performance
Yield (%)
4a 4b
80 83
Fig. 7 The SEM images of compounds (a) [Ag(μ-bpfb)(SCN)]n (4b),
(b) [Ag(μ-bpfb)(N3)]n (4c) and (c) [Ag(μ-bpfb)(ClO4)]n (4d)
nanostructures.
Amine
Product
Time
2 h
Mol%
1
4c
4d
5a
6a
89
62
Table 2 Size properties of synthesized materials using SEM images
yields in six consecutive runs (Fig. 8). This means that the
average yield of the reaction is 86.3% and there is no consider-
able loss of activity. Also, the turnover number is about 89.
Although, the turnover number is lower, in comparison with
[γ-Fe2O3@HAp-Ag], but [Ag(μ-bpfb)(N3)]n catalyst shows the
better E-Factor. To rule out any contribution of homogeneous
catalysis, the reaction of phenylalanine methyl ester and UHP
was conducted for 15 min in the presence of [Ag(μ-bpfb)(N3)]n
to obtain a conversion of 15%. The catalyst was then filtered off
and the supernatant followed for 24 h. Experiment shows that
the reaction completely stopped and no further product was
obtained from catalyst-free solution. This confirmed that the
Ag(I) species on the surface is a heterogeneous catalyst.
[Ag(μ-bpfb)(X)]n
Mean diametera (nm) Standard deviation (nm)
[Ag(μ-bpfb)(NO3)]n
[Ag(μ-bpfb)(SCN)]n 343
[Ag(μ-bpfb)(N3)]n 121
78
16
79
30
15
[Ag(μ-bpfb)(ClO4)]n 106
a For observed 45 nanoparticles in SEM.
reactions can be described. Also, the catalyst’s ability for being
reused was tested. For instance, the reaction of 1-phenylethyl-
amine and UHP in the presence of [Ag(μ-bpfb)(N3)]n quenched
after 2 h and resulted in the desired monoalkylated hydroxyl-
amine product in 89%, 87%, 87%, 85%, 85% and 85% isolated
The efficiency of the [Ag(μ-bpfb)(N3)]n in comparison with
other catalytic systems is shown in Table 5 which compares
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Table 6 Role of coordination polymers in E-Factor minimisation
The method
E-Factor
170.2
Oxidation of primary amines by
dimethyldioxirane5
Indirect oxidation of primary
amines, involving hydrolysis of
oxaziridine6
Direct microwave-induced
oxidation of primary amines by
oxone over silica gel or alumina7
The asymmetric hydrogenation of
nitrones with an iridium catalyst
system9
Oxidation of primary amines to
nitrones followed by hydrolysis
under acidic conditions, or
treatment with hydroxylamine10
Current study
(8.78 + 27.88 + 173) = 209.7
401.8
29.6 (only in the hydrogenation
step, 2 to 3, without regarding
transformation to the nitrone)
149 (until the nitrone 11 and
without regarding the aqueous
hydrolysis step by HCl to
N-hydroxylamine 12)
Fig. 8 Recyclability of the catalyst ([Ag(μ-bpfb)(N3)]n) in the
N-hydroxylation of 1-phenylethylamine by UHP quenched after 2 h.
2.36–4.29
Table 5 The comparison of various methods for the oxidation of
1-phenylethyl amine
contribution of coordination polymers to design environmentally
benign processes. The simplicity of operation, reduction in the
time and cost and reusability of the catalyst once prepared, intro-
duce a green and sustainable catalyst for fine chemical synthesis.
Entry
1
Catalyst
Time
6 h
Yield
70%
TON
7
Na2WO4/UHP
(unrecoverable)18
Ag nanoparticle/UHP
Ag2O/UHP
2
3
4
5
2 h
72 h
2 h
85%
0%
85%
89% (87, 87,
85, 85, 85)a
0%
4.25
0
425
89
[γ-Fe2O3@HAp-Ag]19
[Ag(μ-bpfb)(N3)]n
2 h
4. Experimental section
6
Without catalyst
1 week
0
4.1. Synthesis of N,N′-bis(4-pyridyl formamide)-1,4-benzene
(bpfb) 3
a Isolated yields after sequenced runs.
At room temperature, 1 g of 1,4-phenylenediamine 1 (9.2 mmol)
was dissolved in 50 mL of dry THF. 5 g of the commercially
available hydrochloride salt of isonicotinoyl chloride 2 was
added to this solution. After stirring for 30 min, 10 mL of
triethylamine was added and the mixture was stirred overnight.
After evaporation to dryness, the yellow residue was poured into
an aqueous solution (50 mL) of Na2CO3 (1.2 M) and then
filtered the product 3. The precipitant was washed with distilled
water and a yellowish powder was obtained after drying at
ambient temperature in 75% yield.20
this catalyst with Na2WO4,18 Ag nanoparticle, Ag2O and
[γ-Fe2O3@HAp-Ag]19 with respect to reaction times and yields.
Regarding green chemistry, in which the guiding principles
are the design of environmentally benign products and processes
(benign by design), the ideal E-Factor is zero, that more clearly
reflects the ultimate goal of zero waste.11 As is clear from
Table 6, the method used has a minimum E-Factor from all the
presented methods for synthesis of N-hydroxylamines.
Minimisation of organic solvents and synthetic steps, utilizing
a clean oxidant (that produces only water as by-product) and an
efficient catalytic system are our main green contexts leading to
a reduction of the E-Factor.
IR (cm−1) selected bands: 3340 (s), 3025(s), 1646 (s),
1542 (w), 1443 (br), 1407 (w), 1314 (w), 840 (w), 661 (w).
1H NMR (500 MHz, DMSO): δ 10.54 (s, 2H, NH); 8.77 (d, 4H,
H-py); 7.87 (d, 4H, H-Py); 7.78 (s, 4H, H-Ar) ppm.
3. Conclusions
4.2. Synthesis of [Ag(μ-bpfb)(NO3)]n (4a)
In summary, we have devised a simple grinding method to
produce a coordination polymer system having oxidizing be-
haviours in the presence of UHP as an environmentally clean
oxidant. SEM, IR, XRD and X-ray crystallography techniques
were used to confirm the chemical structures of synthesized
materials. The system showed high catalytic activity in chemo-
selective oxidation of primary amines to monoalkylated
hydroxylamines. The activity of the azide anion (compound 4c)
revealed the best results, giving a maximum yield of the product.
Compared with other catalytic systems, ours shows advantages
in selectivity, efficiency and reusability leading to the smallest
E-Factor that has been reported for synthesis of biologically
important hydroxylamines. This is the first report of significant
The N,N′-bis(4-pyridylformamide)-1,4-benzene (bpfb)
3
(0.159 g, 0.50 mmol) was dissolved in DMF (5 mL) and this sol-
ution was poured into a test tube. A mixture having equal
amounts (1 : 1) of DMF and acetonitrile (5 mL) was very slowly
and dropwise layered on top of a solution of 3; then a solution of
AgNO3 (0.085 g, 0.5 mmol) in acetonitrile (5 mL) was carefully
added dropwise on top of the mesosphere layer without disturb-
ing it. Gray single crystals were obtained after a month in the
mesosphere layer, d.p. > 300 °C.21
IR (cm−1) selected bands: 3340 (s), 3025 (s), 1656 (s), 1555
(w), 1513 (br), 1415 (w), 1340 (w), 1310 (s), 840 (w), 661 (w),
1
522 (w). H NMR (500 MHz, DMSO): δ 10.51 (s, 2H, NH);
8.78 (d, 4H, H-py); 7.86 (d, 4H, H-Py); 7.77 (s, 4H, H-Ar) ppm.
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13C NMR (125 MHz, DMSO): δ 163.6, 150.2, 141.9, 134.7,
121.5, 120.8 ppm.
4.6. The catalytic activity of silver complexed synthesized
[Ag(μ-bpfb)(X)]n (X− = NO3−, SCN−, N3− and ClO4−) 4a–d
nano-structures
10 mg of the [Ag(μ-bpfb)(NO3)]n (4a) (0.02 mmol, 1 mol%)
was added to 0.208 g (2 mmol) UHP in 1 mL of ether and the
system was kept under an Ar atmosphere. After 5 min, 0.358 g
(2 mmol) of phenylalanine methyl ester was added and the
mixture was stirred for 2 h at room temperature. The resulting
suspension was filtered through a pad of celite, and the filtrate
concentrated on a rotary evaporator resulting in the desired
N-monoalkylated hydroxylamine in 81% yield. The catalyst was
washed with diethyl ether to remove residual product and dried
to be reused in the next run. All isolated products gave satisfac-
tory spectral data (FT-IR and 1H NMR) and compared with
those reported in literature.
4.3. Synthesis of [Ag(μ-bpfb)(NO3)]n (4a′) nano-rods by a
sonochemical process
An ultrasonic bath (138 W, 1 h) was used to prepare the nano-
rods of compound 4a′ by a sonochemical process. A solution of
AgNO3 (0.3 mmol, 0.05 g) in acetonitrile (30 mL) was poured
dropwise into a prepared solution of bpfb 3 (0.3 mmol, 0.095 g)
in DMF (30 mL), under ultrasonic irradiation. The obtained
precipitate was filtered, washed with ethanol and then dried,
d.p. > 300 °C.
IR (cm−1) selected bands: 3340 (s), 3025 (s), 1656 (s), 1555
(w), 1513 (br), 1415 (w), 1340 (w), 1310 (s), 840 (w), 661 (w),
1
6a: White crystals, mp 69–71 °C; IR (KBr): 3000–3500 (br),
522 (w). H NMR (500 MHz, DMSO): δ 10.51 (s, 2H, NH);
3064, 1487, 1439, 1369, 1298, 1154, 1074 cm−1 1H NMR
.
8.78 (d, 4H, H-py); 7.86 (d, 4H, H-Py); 7.77 (s, 4H, H-Ar) ppm.
13C NMR (125 MHz, DMSO): δ 163.6, 150.2, 141.9, 134.7,
121.5, 120.8 ppm.21
(500 MHz, MeOD): δ 7.27–7.41 (m, 5H, ArH), 4.18 (q, 1H, J =
6.6 Hz), 1.91 (bs, 2H, NHOH), 1.46 (d, 3H, J = 6.6 Hz).23
6b: White crystals, mp 158–159 °C; IR (KBr): 3370, 1727,
1432, 1189, 1010 cm−1; 1H NMR (500 MHz, MeOD): δ 3.87 (d,
1H, 5.0 Hz), 3.78 (s, 3H), 2.23 (m, 1H), 1.00 (m, 6H).5
6c: White crystals, mp 65–67 °C; IR (KBr): 3355, 2925,
1727, 1431, 1193 cm−1. 1H NMR (500 MHz, MeOD): δ 4.02 (d,
1H, J = 5.5 Hz), 3.83 (s, 3H), 1.78 (m, 2H), 1.68 (m, 1H), 0.97
(m, 6H).19
4.4. Synthesis of the nano-structure [Ag(μ-bpfb)(X)]n
(X− = SCN−, N3− and ClO4−) 4b–4d from nano-rods of
[Ag(μ-bpfb)(NO3)]n (4a) by solid-state reaction
(a) 0.2 g of the 4a nano-rods and an excess quantity of KSCN
were added as solids and ground for 1 h. The generated nano-
structure 4b was washed with ethanol and dried in air.
6d: Pale yellow crystals, mp 140–142 °C; IR (KBr): 3210
(br), 1726, 1431, 1196, 1008 cm−1 1H NMR (500 MHz,
.
IR (cm−1) selected bands: 3340 (s), 3025 (s), 2143 (s), 2100
(s), 1656 (s), 1555 (w), 1513 (br), 1415 (w), 840 (w), 661 (w),
MeOD): δ 7.47–7.49 (m, 5H, ArH), 5.21 (s, 1H), 3.80 (s, 3H),
2.70 (bs, 2H, NHOH).4
1
522 (w). H NMR (500 MHz, DMSO): δ 10.52 (s, 2H, NH);
6e: White crystals, mp 69–71 °C; IR (KBr): 3000–3500 (br),
3064, 1487, 1439, 1369, 1298, 1154, 1074 cm−1 1H NMR
.
8.78 (d, 4H, H-py); 7.86 (d, 4H, H-Py); 7.77 (s, 4H, H-Ar) ppm.
13C NMR (125 MHz, DMSO): δ 163.6, 150.2, 141.9, 134.7,
121.5, 120.8 ppm.
(500 MHz, MeOD): δ 7.31–7.43 (m, 5H, ArH), 4.38 (m, 1H),
3.83 (s, 3H), 3.23–3.36 (m, 2H).5,6
(b) 0.2 g of 4a nano-rods and an excess amount of solid NaN3
were ground for 1 h in the solid-phase. The nano-structure com-
pound 4c was washed with ethanol and dried in air.
IR (cm−1) selected bands: 3340 (s), 3025 (s), 2029 (s), 1656
(s), 1555 (w), 1513 (br), 1415 (w), 840 (w), 661 (w), 522 (w).
1H NMR (500 MHz, DMSO): δ 10.52 (s, 2H, NH); 8.78 (d, 4H,
H-py); 7.86 (d, 4H, H-Py); 7.77 (s, 4H, H-Ar) ppm. 13C NMR
(125 MHz, DMSO): δ 163.6, 150.2, 141.9, 134.7, 121.5,
120.8 ppm.
(c) 0.2 g of 4a nano-rods and an excess amount of solid
NaClO4 were ground for 1 h in the solid-phase. The nano-struc-
ture compound 4d was washed with ethanol and dried in air.
IR (cm−1) selected bands: 3340 (s), 3025 (s), 1656 (s), 1555
(w), 1513 (br), 1415 (w), 1083 (s), 840 (w), 661 (w), 522 (w).
1H NMR (500 MHz, DMSO): δ 10.52 (s, 2H, NH); 8.78 (d, 4H,
H-py); 7.86 (d, 4H, H-Py); 7.77 (s, 4H, H-Ar) ppm. 13C NMR
(125 MHz, DMSO): δ 163.6, 150.2, 141.9, 134.7, 121.5,
120.8 ppm.
6f: Pale yellow crystals, mp 82 °C; IR (KBr): 3340 (br), 1719,
1
1430, 1200 cm−1; H NMR (500 MHz, MeOD): δ 1.7–2.0 (bs,
2H, NHOH), 3.2 (q, J = 5.5 Hz, J = 7.2 Hz, 2H, CH2), 3.5–4.0
(m, 4H, CH, OCH3), 7.0–7.7 (m, 5H, ArH), 8.5 (br, 1H, NH).24
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