Synthesis, Characterization and Biological and Catalytic Activities of Propionitril: Ligated Transition Metal Complexes with [B(C6F5)4] as Counter Anion

Article abstract of DOI:10.1007/s10562-019-02804-9

Abstract: A series of new metal complexes of the general formula [M (NCCH₂CH₃)₆] [B (C₆F₅)₄]₂, where M: Cu, Fe, Co, Ni, Zn, Mn, have been synthesized. Resulting complexes have be

Full text of DOI:10.1007/s10562-019-02804-9

Catalysis Letters
https://doi.org/10.1007/s10562-019-02804-9
Synthesis, Characterization and Biological and Catalytic Activities
of Propionitril: Ligated Transition Metal Complexes with [B(C6F5)4]
as Counter Anion
Abdulaziz M. Ajlouni1 · Ahmed K. Hijazi1 · Ziyad A. Taha1 · Waleed Al‑Momani2 · Areen Okour1 · Fritz E. Kühn3
Received: 31 January 2019 / Accepted: 28 April 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
A series of new metal complexes of the general formula [M (NCCH2CH3)6] [B (C6F5)4]2, where M: Cu, Fe, Co, Ni, Zn, Mn,
have been synthesized. Resulting complexes have been characterized in diferent spectroscopic techniques such as: IR, TGA,
NMR and Elemental Analysis. GC–MS have been used to determine the purity of the reactions and the yield of the fnal
products. These complexes have been applied as catalysis on diferent olefns for cyclopropanation reaction in homogenous
phase. Complex 1 [Cu(CH3CH2CN)6][B(C6F5)4]2 which has the Cu as central atom has shown the highest activity on diferent
olefns. Their biological activities against a number of pathogenic bacteria have been screened and most of the complexes
have shown moderate activities against Gram positive and low activities against Gram negative.
Graphical Abstract
F
F
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M
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B
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Keywords Non-coordinating anions · Organonitrile · Cyclopropanation · Catalysts · Antimicrobial
Electronic supplementary material The online version of
1 Introduction
this article (doi:https://doi.org/10.1007/s10562-019-02804-9)
contains supplementary material, which is available to authorized
users.
Synthesis of metal organonitrile complexes has become
quite popular in organometallic chemistry because of their
beneficial applications such as inorganic materials and
catalysis [1–6]. The advantage of these complexes results
from the coordination mode of the nitrile ligands, which
can be easily replaced by more strongly coordinating ligands
therefore making the complexes proper starting materials
for the synthesis of other complexes. Many of these nitrile
complexes have been synthesized and found to be valuable
in many applications [7]. The acetonitrile complexes of the
type [MII(NCCH3)6][X]2 (M=Cu, Fe, Co, Ni, Zn, and Mn
and X=BF4−, B(C6F5)4 and B{C6H3(m-CF3)2}−4 ) have found
* Abdulaziz M. Ajlouni
amajlouni@just.edu.jo
1
Department of Chemical Sciences, Faculty of Science
and Arts, Jordan University of Science and Technology, P.O.
Box 3030, Irbid 22110, Jordan
2
Department of Basic Medical Sciences, Faculty of Medicine,
Yarmouk University, 21163 Irbid, Jordan
3
Molecular Catalysis, Department of Chemistry,
Catalysis Research Center, Technische Universität
München, Ernst Otto Fischer Str. 1, Lichtenbergstr. 4,
85747 Garching bei München, Germany
Vol.:(0123456789)
1 3

A. M. Ajlouni et al.
to be catalytically active towards many reactions such as
cyclopropanation and aziridination of olefns [8, 9], polym-
erization [10, 11], and aldehyde olefnation reaction [12–16].
Cyclopropanes are essential subunits of many natural
products, and a large number of synthetic compounds that
carry a cyclopropane unit possess biological activities [17,
18]. As a consequence, considerable eforts have been made
to develop efcient methods for the synthesis of these small
ring motifs and to incorporate them into pharmacologi-
cally active ingredients [19]. The most important strategy
for constructing three-membered rings start from olefns is
Michael-reaction-initiated ring closure (MIRC) [20]. This
method involves a sequence of a nucleophilic addition and a
ring closure and requires the presence of both electron-with-
drawing and leaving groups in the reaction partners [21].
The use of complexes with the type of [MII(NCCH3)6][X]2
(M=Mn and Cu and X=BF4−, B(C6F5)4 and B{C6H3(m-
CF3)2}−4 ) can play a positive role on the catalytic activity
of cyclopropanation reactions. Several studies have been
reported using these types of complexes toward the decom-
position of ethyl diazoacetate (EDA) in the presence of both
terminal and internal olefns to yield cyclopropane products
[22–24]. It is generally accepted that transition metal cata-
lyzed cyclopropanation reactions involve the existence of a
metal-carbene complex, [25, 26]. Furthermore, many fuori-
nated compounds are synthesized routinely in pharmaceuti-
cal research and are widely used in the treatment of diseases
[27]. Introducing fuorine atoms into ligands would improve
metabolic stability, alter physicochemical properties because
of its electronegativity as well as increase the binding afn-
ity [28]. Herein, we report the synthesis and spectroscopic
characterization of propeonitrile complexes of the type [M
(C3H5N)6][B(C6F5)4]2, Where M = Cu(II),Mn(II),Ni(II),C
o(II),Zn(II),Fe(II). The synthesized compounds were also
examined for their catalytic cyclopropanation and biological
properties. The biological activities have been investigated
by evaluating the antibacterial behavior of the synthesized
complexes against various pathogenic bacterial strains.
tetramethylsilane (TMS) as an internal standard. Thermal
analyses were performed using a PCT-2 A thermo balance
analyser operating at a heating rate of 10 °C min−1 in the
range 30 to 800 °C under nitrogen atmosphere. Electron
paramagnetic resonance (EPR) spectra were recorded using
a JEOL JES-FA 200 spectrometer at X-band frequency.
The spectra were measured at a microwave frequency of
approximately 9.25 GHz with a microwave power of 5 mW,
modulation amplitude of 0.4 mT, sweep time of 4 min, time
constant of 0.1 s and modulation frequency of 100 kHz. The
microwave frequency was measured with a microwave fre-
quency counter (Advantest R5372). The temperature was
monitored with a JEOL ES DVT4 temperature controller
equipped with a calibrated thermocouple. Measurements
at 113 K were performed using liquid nitrogen for cool-
ing. The g values were determined using Mn2 + (nuclear
spin I=5/2) embedded in MgO as a standard; experimental
errors: Δg 0.001. GC–MS analyses were performed using
electronic impact ionization mode with a Varian Saturn
2000 ion trap spectrometer, interfaced with a Varian GC
CP-3800 apparatus. Microanalyses for carbon, hydrogen and
nitrogen were performed at the Microanalytical Laboratory
of the Technical University of Munich. Carbon, nitrogen
and hydrogen analyses were performed using aVario EL
elemental analyzer. GC–MS analyses were performed using
electronic impact ionization mode on a Varian Saturn 2000
ion trap spectrometer, interfaced with a Varian GC CP-3800
apparatus. The silver salt [B (C6F5)4]− was prepared accord-
ing to literature [29, 30].
2.1 Synthesis of Complexes
2.1.1 [Cu (NCC2H5)6][B (C6F5)4]2 (1)
CuCl2 (0.086 g, 0.64 mmol), was added to a solution of
Ag[B (C6F5)4] (1.00 g, 1.27 mmol) in (20 ml) dry acetoni-
trile, the resulting mixture was stirred overnight in the dark.
The precipitate was removed by fltration (used cannula fl-
ter) and the fltrate was concentrated by vacuum pump, then
the solid was dissolved in 20 ml propionitrile and stirred
overnight, the solution was concentrated by vacuum pump
and kept at − 35 °C. The desired product was obtained as a
light-green solid. Yield 0.78 g (87.5%). C66H30B2F40CuN6
(1751.1): calc. C 45.27, H 1.67, N 4.80; found C 45.20, H
1.73, N 4.67. Selected IR (KBr): 2291, 2319 [ν (CN)].1H:
1.11, 2.43 ppm. 11B: −19.27 ppm.
2 Experimental
All manipulations were carried out under nitrogen atmos-
phere using standard schlenk techniques. All solvents used
were dried, kept under inert gas atmosphere (N2 gas or Ar
gas) and molecular sieves prior to use. Acetonitrile and
propionitrile were pre dried over P2O5, distilled over CaH2
and were kept over 3A° molecular sieves. Nuclear magnetic
resonance spectra were recorded at 400 MHz on a Bruker
(FT-NMR advance 400 MHz) spectrometer. (Bruker Cor-
2.1.2 [Mn (NCC2H5)6][B (C6F5)4]2 (2)
Yield 0.83 g (84.3%). C66H30B2F40MnN6 (1742.5): calc.
C 45.49, H 1.68, N 4.82; found C 45.73, H 1.83, N 4.73.
Selected IR (KBr): 2281, 2322 [ν (CN)].1H: 1.14, 2.50 ppm.
11B: −16.67 ppm.
1
poration, United States). The H and 11B NMR spectra
were recorded on a Bruker Avance 400 MHz spectrometer.
The chemical shifts were measured in ppm in CDCl3 with
1 3

Synthesis, Characterization and Biological and Catalytic Activities of Propionitril: Ligated…
2.1.3 [Zn(NCC2H5)6][B (C6F5)4]2 (3)
Yield 0.79 g (88.7%). C66H30B2F40ZnN6 (1753): calc.
C 45.22, H 1.67, N 4.79; found C 45.4, H 1.80, N 4.71.
Selected IR (KBr): 2271, 2291 [ν (CN)].1H: 1.31, 2.42 ppm.
11B: −19.24 ppm.
2.1.4 [Co (NCC2H5)6][B (C6F5)4]2 (4)
Yield 0.76 g (85.4%). C66H30B2F40CoN6 (1746.5): calc.
Fig. 1 Proposed structure for the catalyst, M=Cu (complex 1), Zn
C 45.39, H 1.67, N 4.81; found C 45.61, H 1.75, N 4.76.
Selected IR (KBr): 2289, 2319 [ν (CN)].1H: 1.28, 2.63 ppm.
11B: − 19.07 ppm.
(complex 2), Mn (complex 3), Co (complex 4), Ni (complex 5), Fe
(complex 6)
2.1.5 [Ni (NCC2H5)6][B (C6F5)4]2 (5)
Yield 0.77 g (84.78%). C66H30B2F40NiN6 (1746.3): calc.
C 45.40, H 1.67, N 4.81; found C 45.62, H 1.91, N 4.79.
Selected IR (KBr): 2272, 2340 [ν (CN)].1H: 1.12, 2.44 ppm.
11B: − 19.23 ppm.
2.1.6 [Fe (NCC2H5)6][B (C6F5)4]2 (6)
Yield 0.65 g (76.1%). Selected IR (KBr): 2278, 2305 [ν
(CN)].1H: 1.14, 2.46 ppm. 11B: −19.25 ppm.
2.2 Antimicrobial Activity
Scheme 1 The synthetic route to complexes 1-6
The preparation of antimicrobial susceptibility cultures and
Minimum Inhibitory concentrations (MIC, µg/ml) testing for
the complexes were performed as described in previous work
[29]. The clinical isolates were Escherichia coli; Klebsiella
pneumonia; Proteus mirabilis; Pseudomonas aeruginosa (as
Gram-negative) and Staphylococcus aureus; Streptococcus
pyogenes (as Gram-positive).
solvent. The complexes are moderately air stable and can
be handled in laboratory atmosphere for brief periods of
time. For storage over longer periods, the compounds have
to be kept under an inert gas (N2 or Ar gas) atmosphere
at low temperature (− 30 °C). All synthesized compounds
were characterized by using IR spectroscopy, 1H-NMR 11
B
2.3 Cyclopropanation
NMR spectroscopy, Thermogravimmetry analysis (TGA),
Elemental analysis.
EDA (0.114 g, 1.0 mmol) in (20 ml) propionitrile was slowly
added (addition time 1 h) to a 4.0 ml propionitrile solution of
an olefn (2.0 mmol) and catalyst (0.02 mmol). The reaction
was stirred for up to 24 h at room temperature. The course of
each reaction was monitored by GC–MS analysis.
3.2 Elemental Analysis
Table 1 lists the elemental analysis data and yields for all the
complexes. The elemental contents (C, H, N) of the com-
plexes are relatively close to those calculated based on the
proposed molecular formula.
3 Results and Discussion
3.3 Infrared Spectra
3.1 Synthesis of the Complexes
The infrared (IR) spectra of all the complexes are recorded
in a KBr matrix and listed in Table 2. Figure 2 shows the
IR spectra for [Mn (NCC2H5)6][B (C6F5)4]2 2 and [Co
(NCC2H5)6][B (C6F5)4]2 5 complexes. Complex 2 exhibits
two sharp ν(CN) absorptions at approximately 2291 cm−1
The metal complexes (Fig. 1) were synthesized by reacting
metal (II) halides with the silver salts of the corresponding
anion in acetonitrile (Scheme 1) [31]. The propionitrile is
exchanged with acetonitrile by adding excess of propionitrile
1 3

A. M. Ajlouni et al.
Table 1 Analytical data for the
Complexes
C (%) found (calc.)
H (%) found (calc.)
N (%) found (calc.)
Yields %
complexes 1–5
1
2
3
4
5
45.20 (45.27)
45.20 (45.22)
45.73 (45.49)
45.61 (45.39)
45.62 (45.40)
1.73 (1.67)
1.80 (1.67)
1.83 (1.68)
1.75 (1.67)
1.91 (1.67)
4.67 (4.80)
4.71 (4.79)
4.73 (4.82)
4.76 (4.81)
4.79 (4.81)
87.50
88.76
84.33
85.40
84.78
Table 2 Major infrared spectra
Complexes
v(CN)
v (Ar-(C=C))
v (Ar-(C-F))
1383
1383
1384
1383
1383
1384
data for the complexes 1–6
1 Cu
2 Mn
3 Zn
4 Ni
5 Co
6 Fe
2291
2271
2281
2289
2272
2278
2319
2291
2322
2319
2340
2305
1645
1646
1642
1643
1646
1645
1472
1264
1270
1271
1271
1272
1264
1082
1090
1081
1088
1089
1082
1518
1446
1474
1516
1471
CN group within all complexes. Higher energy for both types
of vibration modes observed for all examined compounds
in comparison to free propionitrile (ν (CN) = 2247 cm−1)
[33]. This energy change is due to the σ-donation of electron
density from the lone pair of the nitrogen, which has some
anti-bonding character [34].
3.4 Thermogravimmetric Analysis (TGA)
Thermogravimmetric (TG) and diferential Thermogravim-
metric (DTG) analysis for all complexes were carried out
within a temperature range from 30 °C up to 800 °C under
N2 fow.
Thermal gravimetric curves TG and DTG complexes 1–6
showed similar thermal decompositions (Figs. S1, S2). The
TGA/DrTG spectra of copper complex (Fig. 3) show that
the frst step decomposition started at 180 °C with 30.60
wt%, this mass loss back to loss six propionitrile ligands.
The second step occurred at 210 °C with an estimated mass
loss of 52.70% which may be due to decomposition of anion
fragmentation (B(C6F5)4)2. The fnal step involves the for-
mation of metal fuoride as a fnal residue [35].
Fig. 2 FT-IR spectrum of [Mn (NCC2H5)6][B (C6F5)4]2 2 and [Co
3.5 NMR Characterization
(NCC2H5)6][B(C6F5)4]2 5
1
The H-NMR spectra of the complexes were obtained
and 2271 cm−1 and this is for stretching mode ν2-CN and a
combination mode (ν3 +ν4) for complex respectively. Com-
plex 5 also shows two sharp ν(CN) absorptions at approxi-
mately 2340 cm−1 and 2272 cm−1 [32]. For complexes 1,
3,4 and 6, the absorptions bands assigned to stretching mode
ν2-CN at 2319, 2322, 2319 and 2305 cm−1, respectively, and
bands for combination mode (ν3 +ν4) at 2291, 2281, 2289
and 2278 cm−1, respectively. These results indicate that the
in DMSO-d6 solution in the range 0–12 ppm. Figure 4
shows the chemical shifts of the propionitrile protons of
[Zn(NCC2H5)6][B (C6F5)4]2 complex which are observed
as quartet and triplet peaks at 2.36 (q, 12H, CH2) and 1.20
(t, 18H,CH3) ppm, respectively. The 11B-NMR spectra of all
complexes were recorded in deuterium oxide (D2O), in the
range (−20, −10) ppm. Figure 5 shows the spectra for the
Fe complex, a singlet peak observed at δ=−19.25 ppm is
1 3

Synthesis, Characterization and Biological and Catalytic Activities of Propionitril: Ligated…
Fig. 3 TGA/DTG spectra of [Cu (NCC2H5)6][B (C6F5)4]2 1
Fig. 6 UV–Vis absorption spectra for [Cu(NCC2H5)6][B (C6F5)4]2 1
assigned to boron of [B(C6F5)4] [36]. The same peaks were
observed in the same region for the other metal complexes.
3.6 UV–Visible Spectroscopy
The UV–Vis absorption spectra of the complexes 1–6
were carried out in methanol solvent at room tempera-
ture. Figure 6 shows the UV–Vis absorption spectra for
[Cu(NCC2H5)6][B (C6F5)4]2 1. The absorption band centered
at 293 nm may be attributed to the π–π* transitions in the
aromatic ring and the absorption bands between 326 and
340 nm corresponds to the n–π* transitions.
Fig. 4 1H NMR for structure of [Zn(NCC2H5)6][B (C6F5)4]2 3
3.7 Determination of MIC
The minimum inhibition concentration (MIC) of the com-
plexes against diferent types of Gram-positive and Gram-
negative bacteria, as well as fungi were determined and
tabulated in Table 3. The synthesized complexes possessed
poor antimicrobial activity against all the Gram-negative
bacteria tested. The complexes showed moderate antimi-
crobial activity against S. aureus and S. pyogenes. The anti-
fungal activities for all complexes were highly active against
C. tropicalis and moderate activities against C. albicans.
Ni complex has less active against S. aureus and moderate
activity against C. tropicalis and poor activity against C.
albicans. All complexes have similar geometry; its apparent
from the present results that the nature of the coordinating
ligands, this enhancement in the activity can be explained
Fig. 5 11B NMR for structure of [Fe(NCC2H5)6][B (C6F5)4]2 6
1 3

A. M. Ajlouni et al.
Table 3 Minimum inhibitory
concentrations (MIC, μg/ml) of
all complexes against clinical
isolates of some bacterial and
Candida albicans using agar
well difusion
Gram (−) bacteria
Gram (+) bac-
teria
Antifungal
Ec
Pm
Pa
Sp
Sa
Cr
Ca
Ct
Tested compounds
1
2
3
4
5
DMSO (−ve control)
Oxytetracycline (+ve control)
Fluconazole (+ve control)
256
256
256
256
256
N
256
256
256
256
256
N
512
512
256
512
512
N
64
128
64
128
64
N
32
32
32
64
256
N
N
N
N
N
N
–
64
64
32
128
256
–
4
8
8
8
32
–
8
8
16
–
16
–
4
–
–
–
–
4
–
–
4
4
Ec Escherichia coli, Pm Proteus mirabilis, Pa Pseudomonas aeruginosa, Sa Staphylococcus aureus; pyo-
genes, Sp Streptococcus pyogenes, Cc Candida cruzi, Ct Candida tropicalis, Ca Candida albicans, Flu-
conazole antifungal positive control for Candida albicans
on the basis of chelation theory [37]. Chelation increases
the lipophilic nature of the central metal atom, and the type
of counter anion maybe responsible for a number of specifc
interactions with selected microorganisms, which enhances
the penetration of the complexes into the lipid membrane of
the microorganism cell wall and thus raising the activity of
the complex and restricts the further growth of the organism
[38]. The activity observed against the Gram positive bacte-
ria can be explained by considering the efect on lipopoly-
saccharide (LPS), a major component of the surface of Gram
positive [39]. LPS is an important entity in determining the
outer membrane barrier function and the virulence of Gram
negative pathogens. The complexes can permeate the bacte-
rial cell membrane by coordination to LPS and this leads to
the spoilage of outer cell membrane and inhibits the growth
of the bacteria. However the chance of such coordination is
low in Gram negative bacteria which contain a thin pepti-
doglycan layer adjacent to the cytoplasmic membrane.
Scheme 2 Catalytic cyclopropanation of alkenes
Table 4 Catalytic cyclopropanation of trans-stilbene mediated by
complexes 1–6
Entry
Catalyst
Yielda
Cis:transb
1
2
3
4
5
6
1
2
3
4
5
6
82
66
72
71
73
70
28:72
30:70
32:68
31:69
30:70
38:62
Reactions performed at room temperature with 2.0 mmol of EDA
aPercentage of the product, based in EDA, determined by GC
bDetermined by GC–MS
3.8 Application to Catalytic Olefn
Cyclopropanation
Weakly coordinated complexes based are easily displaceable
ligands and have a positive efect on the catalytic activity, by
rendering the intermediate species more accessible to sub-
strate coordination [40]. Complexes 1–6 were evaluated as
catalysts for cyclopropanation using trans-stilbene with ratio
catalyst/olefn 1:250 using EDA in a propionitrile as a sol-
vent at room temperature yielding a mixture of cis and trans
isomers (Scheme 2). The catalytic runs of the complexes
1–6 with the trans-stilbene are summarized in Table 4. Com-
pounds 1–6 exhibited to be active in internal olefn cyclo-
propanation as well. In fact, Complex 1 [Cu(CH3CH2CN)6]
[B(R)4]2 exhibited the best among other metal catalysts
toward the decomposition of ethyl diazoacetate, and the
subsequent transfer of the carbene moiety to the C=C double
bond [41]. As reported the literature in catalytic cyclopro-
panation reactions, Cu(II) complexes are reduced to Cu(I)
derivatives during the catalytic cycle, lead to the general
agreement that the active species is a Cu(I) species regard-
less the oxidation state of the copper complex used as a pre
catalyst. A large excess of the olefn is not required for the
reaction to proceed: even if equimolar amounts of EDA and
olefn were used the cyclopropane products were obtained
in reasonable yields. The cis:trans ratio is not afected to a
large extent by changing the conditions and the cis:trans
ratio ranging from 40:60 to 20:80. Several alkenes were
employed to determine the substrate scope of the complex
1 3

Synthesis, Characterization and Biological and Catalytic Activities of Propionitril: Ligated…
[Cu(CH3CH2CN)6][B(R)4]2 as cyclopropanation catalyst.
At a 1/EDA/olefn ratio of 1:1:250 at room temperature,
the complex catalyzed the cyclopropanation of a range of
substrates with quantitative conversion ranging from 68 to
89% Table 4. Styrene and α and β methyl styrene derivatives
are employed as substrates. The catalyst could successfully
convert these substrates to the desired cyclopropanes in good
yields (entry 2, 3 and 7, Table 5). Steric hindrance at the
position α does not hamper the reaction and good yields are
obtained even with 1 α methyl styrene (entry 2, Table 5).
Aliphatic double bonds are generally less reactive towards
cyclopropanation, even though they gave good results (entry
4 and 6 Table 5).
complexes are structurally similar with six propionitrile
ligand coordinated to M(II) in octahedral arrangement.
All compounds are easily accessible and can be obtained
in good yields. The antimicrobial and antifungal activities
of all complexes were studied against diferent pathogens.
The complexes have shown moderate activities against
Gram positive and low activities against Gram negative.
The catalytic results indicate that these types of com-
plexes are potentially interesting for cyclopropanation
reaction. The copper(II) complex showed excellent cata-
lytic activity in for various olefns at room temperature.
Acknowledgements We gratefully acknowledge fnancial support from
Jordan University of Science and Technology (Project No. 533/2015).
4 Conclusions
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