Thiazoline-Iridium (III) Complexes and Immobilized Nanomaterials as Selective Catalysts in N-Alkylation of Amines with Alcohols

Article abstract of DOI:10.1002/aoc.5970

In this research, a new series of thiazoline-iridium (III) complexes (4–7) derived from cysteine were prepared and fully characterized by conventional methods. The molecular structure of complex 5 was also determined by single-crystal X-ray diffraction. These complexes were evaluated as catalysts for hydrogen-borrowing reactions of amines with alcohols. In particular, complex 5 showed the best activity as catalyst. Various amines have been alkylated with alcohols affording moderate to good yield (33–99%). Moreover, the immobilized nanomaterials (M_1,2) were fabricated by sonication process from the best catalyst 5 with the multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO), respectively, and characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, and inductively coupled plasma-mass spectrometry (ICP-MS). The M_1,2 nanomaterials were also tested as catalysts in model catalytic reaction for N-alkylation. The M₁ nanomaterial showed significantly higher activity than the M₂ nanomaterial. The M₁ catalyst was recovered by filtration and reused for four catalytic cycles with high conversion (99%, 97%, 96%, and 86%).

Full text of DOI:10.1002/aoc.5970

Received: 25 April 2020
DOI: 10.1002/aoc.5970
Revised: 17 July 2020
Accepted: 20 July 2020
F U L L P A P E R
Thiazoline-Iridium (III) Complexes and Immobilized
Nanomaterials as Selective Catalysts in N-Alkylation of
Amines with Alcohols
Serpil Denizaltı1
| Serkan Dayan2
| Salih Günnaz1
| Ertan S¸ahin3
1Department of Chemistry, Ege
In this research, a new series of thiazoline-iridium (III) complexes (4–7)
derived from cysteine were prepared and fully characterized by conventional
methods. The molecular structure of complex 5 was also determined by single-
crystal X-ray diffraction. These complexes were evaluated as catalysts for
hydrogen-borrowing reactions of amines with alcohols. In particular, complex
5 showed the best activity as catalyst. Various amines have been alkylated with
alcohols affording moderate to good yield (33–99%). Moreover, the
immobilized nanomaterials (M1,2) were fabricated by sonication process from
the best catalyst 5 with the multi-walled carbon nanotubes (MWCNTs) and
graphene oxide (GO), respectively, and characterized by X-ray diffraction
(XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scan-
ning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectros-
copy, and inductively coupled plasma-mass spectrometry (ICP-MS). The M1,2
nanomaterials were also tested as catalysts in model catalytic reaction for
N-alkylation. The M1 nanomaterial showed significantly higher activity than
the M2 nanomaterial. The M1 catalyst was recovered by filtration and reused
for four catalytic cycles with high conversion (99%, 97%, 96%, and 86%).
_
University, Bornova-Izmir, 35100, Turkey
2Drug Application and Research Center,
Erciyes University, Kayseri, 38280, Turkey
3Department of Chemistry, Atatürk
University, Erzurum, 25400, Turkey
Correspondence
Serpil Denizaltı and Serkan Dayan,
Department of Chemistry, Ege University,
_
35100, Bornova-.Izmir, Turkey.
Email: serpil.denizalti@ege.edu.tr;
serkandayan@erciyes.edu.tr
Funding information
Ege University Research Fund, Grant/
Award Number: FGA-2019-20568
K E Y W O R D S
alkylation of amine, GO, iridium complex, MWCNT, nanomaterial
1 | INTRODUCTION
of homogeneous catalytic systems for this process have
been developed by many research groups.[11–18] Bifunc-
The synthesis of amines are widely used in the synthesis
of pharmaceuticals, agrochemicals, and biologically
active compounds.[1–3] Different procedures have been
used for their synthesis, such as reductive amination,[4,5]
hydroamination,[6] and reduction of nitriles.[7] The alkyl-
ation of amines with alcohols is known as “borrowing
hydrogen (BH)” or “hydrogen auto-transfer” reaction,
which offers an advantage over the other methods
because only water is generated as the by-product in this
alkylation reaction. Moreover, the starting materials are
less toxic and readily available alcohols.[8–10] A number
tional ligands and their complexes, which are capable of
protonating/deprotonating reactants and intermediates,
are successfully applied as catalysts. A few N,O-chelated
half-sandwich iridium complexes have been employed as
catalysts for transfer hydrogenation,[19,20] water
oxidation,[21–23] dehydrogenation of alcohols,[24] and
Friedel-Craft addition of indoles.[25] However, some
researchers used half-sandwich iridium (III) complexes
containing carboxylate or hydroxyl group in amination
reactions (Figure 1). Limbach and co-workers synthe-
sized aminoacidato Cp*Ir (III) complexes (A) and they
Appl Organomet Chem. 2020;e5970.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
1 of 12
https://doi.org/10.1002/aoc.5970

2 of 12
DENIZALTI ET AL.
FIGURE 1 Iridium (III) complexes
containing carboxylate or hydroxyl group
found that these catalysts were highly active for alkyl-
ation of amines with alcohols under mild conditions.[26]
Martin-Matute group also used alcohols in preparing irid-
ium catalyst (B) with chelating NHC-hydroxyl ligand
capable of amine alkylation. Although longer reaction
iridium complexes bearing thiazoline ligands and investi-
gations of their catalytic activities for the alkylation of
alcohols. To the best of our knowledge, it is the first exam-
ple that these thiazoline-Ir (III) complexes are used as cat-
alysts in the alkylation of amines with alcohols. The
fabricated immobilized nanomaterials M1,2 from the best
catalyst 5 were also tested for the same catalytic reaction.
times (48–60 hr) were needed, the quantitative yields were
[27]
ꢀ
also obtained at 50 C.
In 2014, Li0s research group
reported the synthesis of iridium complex bearing
2-hydroxypyridine ligands (C), which was already synthe-
sized by Fujita and Yamaguchi,[28] for N-alkylation of sul-
fonamides.[29] In these studies, the hydroxyl group played
an important role in the catalytic activity. Later, Chen and
colleagues developed iridium complexes (D and E).[17,30]
These complexes were used for methylation of ketones
and amines with methanol.[17] These are also used in
alkylation of aromatic amines with trialkylamines[30] by
hydrogen borrowing methodology. In 2019, Ke's group
reported the synthesis of N-heterocyclic carbene iridium
complex with bidentate 2-hydroxypyridine ligand (F),
which was successfully used in N-alkylation of anilines
and sulfonamides.[18] In light of this information, we
designed thiazoline–iridium complexes bearing carboxyl-
ate or hydroxyl group (Figure 1).
Although many homogeneous transition metals are
used as catalysts in N-alkylation reactions of amines
according to some researchers, recovery of the catalysts
from the reaction mixtures still remains a challenge.
Recently, works of combining material and molecular
structures with immobilization methods or covalent
bonds have been frequently observed.[31–34] Various het-
erogeneous catalysts have been employed in N-alkylation
of amines.[35–43] However, some of them suffer from low
turnover number (TON) or need high temperature and
high catalyst loading.
2 | EXPERIMENTAL SECTION
2.1 | Materials and instrumentation
Under argon (Ar) atmosphere, reactions involving air-
sensitive components were performed using high
vacuum-line technique and dichloromethane was dis-
tilled from P2O5. All reagents were purchased from com-
mercial sources and used as received. According to the
previous
4-carboxylic acid (1a) and 2-(2-hydoxyphenyl)-4,-
5-dihydrothiazole-4-carboxylic acid (1b) were
literature,
2-phenyl-4,5-dihydrothiazole-
prepared.[45–49] Using tetramethylsilane (TMS) as the
internal standard, 1H NMR (400 MHz) and 13C NMR
(100 MHz) spectra were measured on Varian AS 400 Mer-
cury spectrometer with CDCl3 as the solvent. All coupling
constants (J values) were reported in Hertz (Hz). High
resolution mass spectrometry (HRMS) analyses were per-
formed on Agilent 6,530 Accurate-Mass Q-TOF mass
spectrometer at Ege University Central Research Test and
Analysis Laboratory Application and Research Center.
2.2 | General synthesis of 2a and 2b
Acid (1a/1b) (9.65 mmol) was dissolved in the solution of
MeOH (100 ml) and concentrated H2SO4 (4.1 ml) was
added. The mixture was refluxed overnight under Ar
atmosphere. After cooling to room temperature, the sol-
vent was evaporated. The residue was diluted with water.
The aqueous suspension was extracted with CH2Cl2
In our previous study, the thiazoline carboxylate com-
plexes of ruthenium were prepared and used as catalysts.
The ruthenium catalysts showed better activity for a range
of substrates tested, and high yields were obtained in the
TH reaction.[44] Herein, we report on a novel family of

DENIZALTI ET AL.
3 of 12
(3 × 20 ml) and dried over Na2SO4. In the next step, the
organic phase was evaporated. The residue was purified
by column chromatography with hexane/CH2Cl2(1/1) as
eluent.[45–49] NaBH4 (15.0 mmol) was slowly added to the
solution of the obtained ester product (5.0 mmol) in
MeOH (50 ml) under Ar atmosphere. After being stirred
for 2 hr at room temperature, the mixture was refluxed
for 6 hr, cooled, and concentrated. The remaining solid
was dissolved in CH2Cl2 and washed with H2O. The
organic phase was dried over Na2SO4 and then concen-
trated. The purification by column chromatography with
CH2Cl2/MeOH gave the alcohol.
HRMS (ESI+): calcd. m/z for C20H23ClIrNO2S [M-Cl]+:
533.69; found: 534.12.
4: Ligand 1b and [IrCl2Cp*]2 were used. Yield: 36%.
1H NMR (400 MHz, CDCl3): δ = 7.24 (t, J = 6.8 Hz, 2 H,
Ar-H), 6.93 (d, J = 8 Hz, 1 H, Ar-H), 6.55 (t, J = 6.8 Hz,
1 H, Ar-H), 5.19–5.22 (m, 1 H, CH), 3.95–3.97 (m, 1 H,
SCH2), 3.60–3.65 (m, 1 H, SCH2), 1.61 (s, 15 H, CH3). 13
C
NMR (100 MHz, CDCl3): 9.1 (CH3), 34.0 (SCH2), 80.7
(CH), 83.7 (Cp-C), 116.1, 120.1, 122.6, 129.1, 134.1, 167.5
(Ar-C), 170.2 (C=N), 175.3 (C=O). HRMS (ESI+): calcd.
m/z for C20H22IrNO3S 548.68; found: 550.11.
5: Ligand 2a and [IrCl2Cp*]2 were used. Yield: 40%. 1H
NMR (400 MHz, CDCl3): δ = 7.77 (d, J = 8 Hz, 1 H, Ar-H),
7.41 (d, J = 8 Hz, 1 H, Ar-H), 7.20 (t, J = 8 Hz, 1 H, Ar-H),
7.01 (t, J = 8 Hz, 1 H, Ar-H), 4.64–4.69 (m, 1 H, CH),
4.28–4.33 (m, 1 H, CH2), 3.74–3.85 (m, 2 H, SCH2),
3.64–3.70 (m, 1 H, CH2), 1.72 (s, 15 H, CH3). 13C NMR
(100 MHz, CDCl3): 9.3 (CH3), 33.2 (SCH2), 63.9 (CH2), 73.7
(CH), 88.4 (Cp-C), 122.2, 127.7, 132.1, 135.2, 140.5 (Ar-C),
166.1 (C=N), 184.8 (Ar-C-Ir). HRMS (ESI+): calcd. m/z for
C20H25ClIrNOS [M-Cl]+: 519.71; found: 520.13.
2a: Yield: 75%. 1H NMR (400 MHz, CDCl3): δ = 7.78 (d,
J = 8 Hz, 2 H, Ar-H), 7.36–7.50 (m, 3 H, Ar-H), 4.73–4.80
(m, 1 H, CH), 3.98 (dd, J = 11.2 Hz, 1 H, CH2), 3.77 (dd,
J = 11.2 Hz, 1 H, CH2), 3.41 (t, J = 10.4 Hz, 1 H, SCH2),
3.30 (t, J = 10.4 Hz, 1 H, SCH2), 2.83 (bs, 1 H, OH). 13C
NMR (100 MHz, CDCl3): 31.5 (SCH2), 49.1 (CH2), 64.6
(CH), 128.6, 128.7, 131.6, 133.2 (Ar-C), 170.0 (C=N).
1
2b: Yield: 65%. H NMR (400 MHz, CDCl3): δ = 12.4
(bs, 1 H, Ar-OH), 7.40 (dd, J = 8 Hz, 1 H, Ar-H), 7.35 (td,
J = 7.6 Hz, 1 H, Ar-H), 7.00 (dd, J = 8 Hz, 1 H, Ar-H),
6.87 (td, J = 7.6 Hz, 1 H, Ar-H), 4.82–4.90 (m, 1 H, CH),
3.96 (dd, J = 11.2 Hz, 1 H, CH2), 3.83 (dd, J = 11.2 Hz,
1 H, CH2), 3.31–3.44 (m, 2 H, SCH2), 2.04 (bs, 1 H, OH).
13C NMR (100 MHz, CDCl3): 32.7 (SCH2), 64.1 (CH2),
77.7 (CH), 116.2, 117.0, 118.9, 130.6, 133.2, 158.9 (Ar-C),
173.4 (C=N).
6: Ligand 2b and [IrCl2Cp*]2 were used. Yield: 54%.
1H NMR (400 MHz, CDCl3): δ = 7.31(d, J = 8 Hz, 1 H,
Ar-H), 7.22 (td, J = 8.4 Hz, 1 H, Ar-H), 6.90 (d,
J = 8.4 Hz, 1 H, Ar-H), 6.41 (td, J = 8.4 Hz, 1 H, Ar-H),
4.59 (t, J = 8.4 Hz, 1 H, CH), 4.35–4.37 (m, 1 H, CH2),
4.06–4.10 (m, 1 H, OH), 3.69–3.71 (m, 1 H, CH2),
3.77–3.54 (m, 2 H, SCH2), 1.57 (s, 15 H, CH3). 13C NMR
(100 MHz, CDCl3): 9.3 (CH3), 31.6 (SCH2), 64.3 (CH2),
81.7 (CH), 84.8 (Cp-C), 115.5, 119.5, 123.9, 133.8, 165.3
(Ar-C), 170.1 (C=N). HRMS (ESI+): calcd. m/z for
C20H25ClIrNO2S [M-Cl]+: 535.71; found: 536.13.
2.2.1 | General synthesis of the complexes
(3–6)
To a solution of the ligand (1/2) (1.0 mmol), K2CO3
(1.0 mmol) in dry acetonitrile [IrCl2Cp*]2 (0.5 mmol) was
added. The reaction mixture was thoroughly degassed by
bubbling argon for 10 min and stirred for overnight at
ambient temperature. Then, the solution was filtered over
celite. The filtrate was removed under vacuum. The residue
was purified via column chromatography using CH2Cl2/
MeOH (99/1) as eluent, affording the yellow powder. The
complex was recrystallized from CH2Cl2 and Et2O.
2.2.2 | Preparation of [IrCp*ClL]
@MWCNTs (M1) and [IrCp*ClL]@GO (M2)
nanomaterials
The functionalized multi-walled carbon nanotubes
(MWCNTs-COOH) and graphene oxide (GO) materials
3: Ligand 1a and [IrCl2Cp*]2 were used. Yield: 64%.
1H NMR (400 MHz, CDCl3): δ = 8.19 (d, J = 8 Hz, 2 H,
Ar-H, maj.), 8.04 (d, J = 8 Hz, 2 H, Ar-H, min.),7.44–7.62
(m, 6 H, Ar-H, maj., min.), 5.90 (dd, J = 8 Hz, 1H, CH,
min.), 4.88 (dd, J = 8 Hz, 1 H, CH, maj.), 3.46–3.77 (m,
4 H, SCH2, maj., min), 1.40 (s, 15 H, CH3, maj.), 1.31 (s,
15 H, CH3, min.). 13C NMR (100 MHz, CDCl3): 8.8 (CH3,
min.), 8.9 (CH3, maj.), 33.9 (CH2, min.), 35.9 (CH2, maj.),
81.4(CH, min.), 82.5 (CH, maj.), 85.2 (Cp-C, maj.), 85.5
(Cp-C, min.), 128.3, 128.7, 129.3,132.1 (Ar-C, maj.), 130.1,
131.2, 132.6, 132.7 (Ar-C, min.), 175.2 (C=N, maj.), 176.4
(C=N, min.), 176.9 (C=O, maj.), 177.1 (C=O, min.).
SCHEME 1 Representative fabrication of nanomaterials (M1,2
)

4 of 12
DENIZALTI ET AL.
were
fabricated
with
conventional
literature
The number CCDC-1986245 contains the supplemen-
tary crystallographic data for this structure (5). These
data are provided free of charge by the joint CCDC and
FIZ Karlsruhe deposition service (www.ccdc.cam.ac.uk/
structures).
methods.[34,50,51] The corresponding nanomaterials (M1,2
)
were prepared using the following method (Scheme 1):
For the immobilization procedure, the best catalyst was
5 and the support materials were weighed as 20% (w/w)
and 80% (w/w), respectively, where the related ratio was
picked up to determine the amount of the metal ion used
in the alkylation reaction. The complex and the support
materials (MWCNTs-COOH or GO) were introduced in a
round-bottomed flask at specified rates (20% and 80%
w/w), and 10 ml of diethyl ether or 2-propanol solvent
mixture (1/3 v/v) and the suspension was sonicated with
a magnetic stirrer at ambient temperature until a stable
suspension formed. Then, the black suspension was fil-
tered, washed with the solvent mixture, and dried by a
vacuum system. The prepared nanomaterials (M1,2) were
characterized by XRD, FT-IR, FE-SEM, EDX, and ICP-
MS. The final iridium contents for M1,2 were found as
≈4.95% and ≈9,31%, respectively.
2.2.3 | X-ray diffraction study
To determine the crystal structure, a single-crystal of the
complex 5 was used for collecting data on a four-circle
Rigaku R-AXIS RAPID-S diffractometer (equipped with a
SCHEME 2 Synthesis of the ligands and iridium complexes (3–6)
two-dimensional
area
IP
detector).
Graphite-
monochromated Mo-Kα radiation with the wavelength of
0.71073 Å and oscillation scans technique with Δw = 5ꢀ
for one image were used for data collection. The lattice
parameters were determined using the least-squares
methods based on all reflections with F2 > 2 s(F2). Inte-
gration of the intensities, correction for Lorentz and
polarization effects, and cell refinement were performed
using CrystalClear software (Rigaku/MSC Inc., 2005).[52]
The structure was solved by direct methods using
SHELXS-97 program.[53] Non-hydrogen atoms were
refined using anisotropic displacement parameters by a
full-matrix least-squares procedure using the program
SHELXL-97.[53] H atoms were geometrically positioned
and refined using a riding model. The final difference
Fourier maps showed no peaks of chemical significance.
Crystal data for 5: C20H25Ir Cl N O S, crystal system,
space group: monoclinic, P21/c; (no. 14); unit cell dimen-
sions: a = 15.896(2), b = 7.7439(5), c = 16.175(2) Å,
α = 90ꢀ, β = 97.176(3), γ = 90ꢀ; volume 1975.6(3) Å3,
Z = 4; calculated density: 1.86 g/cm3; absorption coeffi-
cient: 7.00 mm−1; F(000): 1080; θ-range for data collec-
tion 1.6–18.4ꢀ; refinement method: full-matrix least-
square on F2; data/parameters: 4137/1226; goodness-of-fit
on F2: 0.997; final R-indices [I > 2σ(I)]: R1 = 0.093,
wR2 = 0.181; largest different peak and hole: 2.414 and
FIGURE 2 Molecular structure of the IrCp* complex 5.
Thermal ellipsoids are shown at the 30% probability level. Selected
bond lengths (Å) and angles (deg.) of 2: Ir − Cl, 2.423(3); Ir − N,
2.101(2); Ir1-C16, 2.046(3); Ir − C2, 2.146(3); Ir − C4, 2.158(3);
Ir − C5, 2.248(3); S − C17, 1.737(3); N − Ir − C1, 106.10(4);
N − Ir − Cl, 88.39(5); Cl − Ir − C16, 87.30(5); N − Ir − C4,
165.31(4); N − Ir2 − C2, 100.49(5); N − Ir − C16, 76.95(5)
−2.247 e Å−3
.

DENIZALTI ET AL.
5 of 12
FIGURE 3 Polyhedral representation of
IrCp*complex 5 with the unit cell viewed down
along the c-axis
2.2.4 | General procedure of alkylation of
amines with alcohols
A reaction tube was charged with the catalyst (1% mol),
amine (1 mmol), alcohol (1 mmol), KOtBu (0.5 mmol),
and toluene (100 μL). Then, the tube was charged with
Ar and sealed. The resulting mixture was heated at
ꢀ
110 C for 16 hr. This mixture was diluted with CH2Cl2
after cooling to room temperature, and filtered over a pad
1
of silica. The conversions were determined by H NMR
analysis. At the end of the catalytic reaction, petroleum
ether was added to the reaction mixture and stirred. The
catalyst was sedimented by centrifugation and the solvent
was decanted. The catalyst can be directly used for other
cycles after it was dried under vacuum.
3 | RESULTS AND DISCUSSION
3.1 | Synthesis and characterization of
Thiazoline-Ir (III) complexes
According to the previously published procedure,
2-Phenyl-4,5-dihydrothiazole-4-carboxylic acid (1a) and
2-(2-hydoxyphenyl)-4,5-dihydrothiazole-4-carboxylic acid
(1b) were prepared from cysteine.[44] The (2-phenyl-4,-
5-dihydrothiazol-4-yl)methanol (2a) and 2-(4-(hydroxyme
thyl)-4,5-dihydrothiazol-2-yl)phenol (2b) were synthe-
sized via reaction with H2SO4 in MeOH[45–48] and subse-
quent reduction of the corresponding ester derivative
FIGURE 4 FT-IR spectrums of MWCNTs, GO, [IrCp*ClL]
@MWCNTs (M1) and [IrCp*ClL]@GO (M2)

6 of 12
DENIZALTI ET AL.
(Scheme 2). The NMR data of the ligands are compatible
with the values given in the literature.[49]
diethyl ether and dichloromethane, the complex 5 could
be characterized by NMR spectroscopy and single-crystal
X-ray diffraction analysis (Figure 2).
When the ligands 1/2 were treated with the metal
precursors [IrCp*Cl2]2 in the presence of a base, the com-
plexes 3–6 were obtained as yellow or orange solids
(Scheme 2). The synthesized iridium complexes were
In the compound [Ir(C10H15)(C10H10NOS)(Cl)] (5),
the IrIII ion is coordinated by three anions:
pentamethylcyclopentadienyl
(Cp*−),
(2-phenyl-4,-
1
fully characterized by standard NMR techniques. The H
5-dihydrothiazol-4-yl)methanol (ptm−), and chlorine
(Cl−) ligands. The compound Ir(C10H15)(C10H10NOS)
(Cl) adopts a three-legged piano-stool geometry. The
coordination mode of Cl− is typical for Cp*IrIII-Cl com-
plexes, with an Ir-Cl bond length of 2.423 (2) Å.[54] For
the ptm− ligand, the bond lengths in Ir-C16 and Ir-N are
2.046(3) and 2.101(3) Å, respectively, which are rather
close to each other, compared to the related mononuclear
[Cp*Ir (ppy)X] complexes (X = Cl, I, MeCN4, etc.).[55–58]
The bond lengths in Ir-C (Cp*) vary in the range of 2.146
(2)–2.277 (2) Å, indicating a strong trans influence of
the cyclometallated C-donor atom of the ptm− ligand.
The Cp* ligand is symmetrically bound to the IrIII atom.
NMR spectrum of complex 3 showed two sets of signals
in the ratio of 2:1 at room temperature, which indicated
the complex 3 isolated from a mixture of two diastereo-
mers. The 13C NMR spectra of the complexes (3 and 4)
showed C=N and C=O resonances at around
170.2–175.2 ppm and 175.3–177.1 ppm, respectively. This
is consistent N,O-chelating character of the carboxylate
ligand.
We initially attempted to synthesize the alkoxide
complex. In spite of multiple attempts to prepare alkoxide
complex without a base, the complex 5 was always
formed. The ligand 2a was also treated with [IrCp*Cl2]2
in the presence of NaBF4 or AgBF4 in acetonitrile or dic-
hloromethane. Instead of the cationic complex, complex
5 was obtained. After recrystallization from a mixture of
FIGURE 5 XRD patterns of MWCNTs, GO, [IrCp*ClL]
@MWCNTs (M1) and [IrCp*ClL]@GO (M2)
FIGURE 6 SEM images (10.00 KX) of [IrCp*ClL]@MWCNTs
(M1) (a) and [IrCp*ClL]@GO (M2) (b) nanomaterials

DENIZALTI ET AL.
7 of 12
The distance between Ir and the least-squares plane of
the Cp* ring is 1.82 Å. This compares well with the values
for other iridium complexes containing Cp*.[59] The
structure contains one asymmetric carbon (C19) atom
and it is in (S) configuration. In the crystal structure,
there are no solvent molecules for crystallization. The Cl-
S distance between two adjacent molecules is 3.732(3) Å.
Moreover, any characteristic intermolecular interaction
was not observed in this crystal (Figure 3).
C=O stretching, –C=C– stretching, and –O–H stretching
were
1,500–1,600
assigned
between
1,100–1,350
cm−1
and
,
cm−1
,
1750–1850
cm−1
,
3,400–4,000 cm−1, respectively. Similarly for M2 nano-
material, the –C=O stretching, O–H bending, and –C–O–
vibration peaks were aligned between 1,650–1750 cm−1
,
1,550–1,650 cm−1, and 1,000–1,150 cm−1, respectively
(Figure 4). Moreover, the specific peaks from the complex
compound (5) were also detected in both nanomaterials
(M1,2), such as 2,800–3,100 cm−1 (Ar. C–H and Alip. C–H
stretching), 1,575–1,590 cm−1 (ring stretching),
1,470–1,525 cm−1 (ring stretching), 1,430–1,470 cm−1
(ring stretching), and 1,025–1,075 cm−1 (C–O stretching).
The XRD patterns of [IrCp*ClL]@MWCNTs (M1)
and [IrCp*ClL]@GO (M2), MWCNTs, and GO mate-
rials were demonstrated, assigned, and compared with
3.2 | Characterizations of M1 and M2
Figure 4 shows the FT-IR spectra of the prepared
[IrCp*ClL]@MWCNTs (M1) and [IrCp*ClL]@GO (M2).
For M1 nanomaterial, the related vibrations such as –
TABLE 1 Optimization studies for the alkylation of amines with alcohols
Entry
1
Catalyst
Base
Conversion (%)
Selectivity (I/A)
9/91
TON
15
74
58
97
34
80
76
95
12
55
50
59
83
60
134
95
92
-
3
4
5
6
5
5
5
5
5
5
5
5
5
5
5
5
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
Na2CO3
K2CO3
NaOH
KOH
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
15
74
58
97
34
80
76
95
12
55
50
59
83
60
67
95
92
2
2/98
3
5/95
4
1/99
5
6a
7b
8c
7/93
8/92
36/64
2/98
9
4/96
10
11
12
13d
14e
15f
16g
17h
3/97
4/96
1/99
>99
3/97
3/97
5/95
4/96
Reaction conditions: Aniline (0.5 mmol), benzyl alcohol (0.5 mmol), catalyst (1% mol), base (0.25 mmol), toluene (50 μL), 110 ꢀC, 16 h.
atoluene (150 μL).
btoluene (250 μL).
cbenzyl alcohol (1.2 eq., 0.6 mmol).
dbase (0.20 mmol).
ebase (0.125 mmol).
fcatalyst (0.5% mol).
g100 ꢀC.
h90 ꢀC.

8 of 12
DENIZALTI ET AL.
starting materials in Figure 5. The starting materials
The optimized rꢀeaction conditions were a reaction
temperature of 110 C with 1% mol of catalyst, aniline
(0.5 mmol), benzyl alcohol (0.5 mmol), KtOBu
(0.25 mmol), and toluene (50 μL). The scope of the reac-
tion was extended using a variety of aniline or benzyl
alcohol with the catalyst 5. The results were summarized
in Table 2. It was observed that N-alkylation of anilines
bearing either electron-donating or electron-withdrawing
groups at the para-position with benzylic alcohol gave
the corresponding products in 52%–95% yields (Table 2).
When ortho-substituted aniline derivatives were used,
MWCNT (JCDPS card no: 75–1,621) and GO indexed
as (002) plane (2θ
=
26.29o) and (200) plane
(2θ = 43.12o) and (001) plane (2θ = 11.26o)[60,61] and
the pattern peaks of M1 and M2 nanomaterials were
recorded as the major peaks 11.21ꢀ, 11.68ꢀ, 12.65ꢀ,
12.94ꢀ, 13.52ꢀ, 14.12ꢀ, 16.35ꢀ, 16.70ꢀ, 17.33ꢀ, 18.93ꢀ,
20.32ꢀ, 22.05ꢀ, 23.58ꢀ, 25.84ꢀ (MWCNTs) (002), 29.59ꢀ,
33.42ꢀ, 37.31ꢀ, 43.38ꢀ (MWCNTs) (200), and as the
major peaks 5.00–25.00o (broad peak), 10.84ꢀ
(GO) (001), 42.48ꢀ (Figure 5). When the data obtained
are examined, it is observed that materials [IrCp*ClL]
@MWCNTs (M1) and [IrCp*ClL]@GO (M2) include
the specific peaks of starting materials and the impreg-
nation methodology was successful in the preparation
of materials.
TABLE 2 Scope of the alkylation of amines with alcohols
The surface morphologies and mapping analyses of
[IrCp*ClL]@MWCNTs (M1) and [IrCp*ClL]@GO (M2)
nanomaterials were carried out by FE-SEM–EDX
(Figure 6) (10.00 KX). Figure S1,2 (Supporting informa-
tion) shows the mapping and EDX images. The specific
surface and physical structures of the nanomaterials are
evident as fiber-like structure for M1 and sheet-like struc-
ture for M2 (see SEM images). The presence of iridium
and other elements were confirmed by both EDX and
mapping analysis (Supporting information, Figure S1,2).
These results also represent the success of the fabrication
method.
3.3 | Catalytic studies
Initially, the reaction of aniline with benzyl alcohol was
chosen as a model system. The reactions were performed
with 1 mol% catalyst in toluene using an equimolar
amount of aniline (0.5 mmol) and benzyl alcohol
(0.5 mmol) in the presence of potassium tert-butoxide
(Table 1).
From Table 1, it is evident that complexes 3–6 are
active catalysts for the alkylation reaction. In the absence
of a catalyst, only a small amount of product was
obtained (Table 1, entry 1). Because of the higher activity,
catalyst 5 was selected for further optimization studies.
When solvent volume is increased, the yield decreases to
76% (Table 1, entries 6 and 7). Altering the ratio of benzyl
alcohol leads to slightly lower in both yield and selectiv-
ity (Table 1, entry 8). Other bases, such as Na2CO3,
K2CO3, NaOH, and KOH were also tested. In comparison
to KOtBu, the yield was lower, but selectivity did not
change using KOH (Table 1, entry 12). Decreasing the
catalyst loading, varying the amount of base, or reducing
Reaction conditions: Aniline (0.5 mmol), benzyl alcohol (0.5 mmol),
catalyst (1% mol), base (0.25 mmol), toluene (50 μL). Conversion
and selectivity (I/A) were determined by 1H NMR. * 48 h.
ꢀ
the temperature to 90 C gave rise to a drop in the yield
(Table 1, entries 13–17).

DENIZALTI ET AL.
9 of 12
the yield was 35% or 70% after 48 hr. This finding indi-
cates that sterically demanding substrates are less active
than para- or meta-substituted ones.[62] Transformations
of benzylamine, 2-naphthylamine, and 2-aminopyridine
afforded the desired products in 42%, 43%, and 99%
yields, respectively. Catalytic alkylation of aniline with
different benzyl alcohols was moderate to good yielding
(31%–84%) (Table 2). Aliphatic alcohols, n-butanol,
cyclohexanol, and hexanol reacted with aniline, resulting
in 76%–99% yield (Table 2).
The methodology of combining different materials
with complexes by immobilization or covalent bonding is
one of the methods used by scientists. Herein, we selected
the complex 5 from the synthesized iridium (III) com-
plexes, which showed the best activity result in the N-
alkylation reaction of amines with alcohols, and this
complex was immobilized to carbon-based materials
(MWCNTs and GO). As a result of this type of immobili-
zation process, some synergistic effects or performance
increases can be seen. We used these new materials
because of this property. In a model reaction, the cata-
lytic effects of M1 and M2 nanomaterials were tested
using aniline and benzyl alcohol. The results of
MWCNTs, GO, M1, and M2 are summarized in Table 3.
When 2 mg of MWCNTs, GO, M1, and M2 were used,
the yields were obtained as 14%, 12%, 31%, and 19%,
respectively. The catalytic activities of M1 and M2 are
higher than those of the bare support materials
(MWCNTs and GO). It was determined that M1 nano-
material showed higher activity than other materials, and
the tests were carried out by increasing the amount of
catalyst. It was observed that the yield also increased.
Although, complex M2 contains more amount of iridium
according to ICP-MS results, the catalytic performance of
the nanomaterials including MWCNT (M1) is obviously
higher. This situation can also be considered as an indica-
tor of a synergistic effect. The best results were obtained
in presence of 6 mg catalyst. The yields of M1 and M2 cat-
alysts were 99% and 27%, respectively. Under the same
reaction conditions, the yields of 3–6 catalysts were
recorded as 74%, 58%, 97%, and 34%. It was seen that the
performance of M1 was better, when compared those
results of the fabricated M1 nanomaterials (TON = 330)
from immobilization of the complex 5 (TON = 99) with
other catalysts under the same reaction conditions. The
obtained catalytic results are also comparable or even
higher than the other heterogeneous iridium complexes
according to the reported literature.[37,43,63,64] For exam-
ple, TON value of heterobimetallic-iridium complex was
85.[43,63]
The recyclability of M1 was also investigated
(Figure 7). After each run, petroleum ether was added to
FIGURE 7 The recyclability of M1 in the N-alkylation of
aniline with benzyl alcohol reaction
TABLE 3 N-alkylation of aniline with benzyl alcohol using catalysts M1 and M2
Entry
Catalyst (mg)
MWCNTs (2 mg)
GO (2 mg)
M1 (2mg)
Conversion (%)
Selectivity (I/A)
12/88
TON
14
1
2
3
4
5
6
7
8
14
12
31
19
53
23
99
27
15/85
12
9/91
310
97.9
257.3
60.5
330
46.6
M2 (2mg)
11/89
M1 (4mg)
4/96
M2 (4mg)
14/86
M1 (6mg)
4/96
M2 (6mg)
6/94
Reaction conditions: Aniline (0.5 mmol), benzyl alcohol (0.5 mmol), base (0.25 mmol), toluene (50 μL).

10 of 12
DENIZALTI ET AL.
SCHEME 3 A possible mechanism for the N-
alkylation of amines with alcohols
the reaction mixture and stirred. The catalyst sedimented
by centrifugation and the solvent was decanted. The cata-
lyst can be directly used for other cycles after drying
under vacuum. Figure 7 shows the excellent yields of
96%–99% in the first three runs. In the fourth run, the
yield slightly decreased to 86%.
4 | CONCLUSIONS
In this study, we have synthesized new thiazoline-
iridium (III) complexes (4–7) derived from cysteine. Their
catalytic activities were evaluated for alkylation of
amines with alcohols. As complex 5 showed the best
activity, its immobilized nanomaterials (M1 and M2)
were prepared with MWCNTs and GO, respectively. The
new catalysts (M1 and M2) were also tested for the alkyl-
ation of aniline with benzyl alcohol. It was found that
MWCNTs immobilized iridium complex M1 gave the
product in 99% yield with low catalyst loading. The recy-
clability of M1 was also investigated. The good yields
(99–86%) of M1 were obtained even after the fourth run.
After catalytic cycles, when the FT-IR spectrum of the
catalyst was examined, the 3,500–2,700 (–OH), 3,055
(Ar. C–H), 3,023 (Ar. C–H), 1,622 (–C=C– stretching),
1,592 (–C=C– stretching), 1,543 (–C=C– stretching),
1,381 (−C=O stretching), 1,065, 1,020, 833, 764, 699, and
674 cm−1 peaks were assigned (Supporting information,
Figure S3). These peaks represented the specific regions
of both the carbon nanotube structure and the complex,
and shown the stability of the structure.
In accordance with the previous reports,[18,27,65,66]
a
ACKNOWLEDGMENTS
plausible mechanism for the N-alkylation of amines
with alcohols is proposed as shown in Scheme 3. The
reaction initiated by the formation of I, which is
formed via the elimination of HCl. Iridium-hydride
intermediate (II) occurred after the dissociation of alde-
hyde. The aldehyde reacts with an amine to form an
imine for subsequent coordination to species III. In the
last step, reduction of imine takes place to produce
amine. The hydroxyl group plays an important role in
participating throughout the catalytic cycle by donating
or accepting protons to or from the substrates and
facilitating the reaction.[27,66]
The authors thank Ege University Research Fund (FGA-
2019-20568) for the financial support of this work. We
are also grateful to Ege University Planning and Monitor-
ing Coordination of Organizational Development and
Directorate of Library and Documantaion for their sup-
port in editing and proofreading service of this study.
AUTHOR CONTRIBUTIONS
Serkan Dayan: Data curation; investigation; methodol-
ogy; supervision; validation; visualization. Salih Gün-
naz: Data curation; visualization. Ertan S¸ahin: Data
curation; validation; visualization.

DENIZALTI ET AL.
11 of 12
[26] A. Wetzel, S. Wöckel, M. Schelwies, M. K. Brinks,
F. Rominger, P. Hofmann, M. Limbach, Org. Lett. 2013, 2, 266.
[27] A. Bartoszewicz, R. Marcos, S. Sahoo, A. K. Inge, X. Zou,
B. Martín-Matute, Chem. – Eur. J. 2012, 18, 14510.
[28] R. Kawahara, K.-i. Fujita, R. Yamaguchi, J. Am. Chem. Soc.
2012, 134, 3643.
[29] P. Qu, C. Sun, J. Ma, F. Li, Adv. Synth. Catal. 2014, 356, 447.
[30] D. Deng, B. Hu, Z. Zhang, S. Mo, M. Yang, D. Chen, Organo-
metallics 2019, 38, 2218.
[31] N. K. M. Subodh, K. Chaudhary, G. Kumar, D. T. Masram,
ACS Omega 2018, 3, 16377.
[32] N. K. M. Subodh, K. Chaudhary, K. Prakash, D. T. Masram,
Appl. Surf. Sci. 2020, 509, 144902.
ORCID
Serpil Denizaltı https://orcid.org/0000-0001-7354-3098
Serkan Dayan https://orcid.org/0000-0003-4171-7297
Salih Günnaz https://orcid.org/0000-0002-7422-6593
REFERENCES
[1] C. Chiappe, D. Pieraccini, Green Chem. 2003, 5, 193.
[2] K.-i. Fujita, Y. Enoki, R. Yamaguchi, Tetrahedron 2008, 64,
1943.
[3] X. Ma, C. Su, Q. Xu, N-Alkylation by Hydrogen Autotransfer
Reactions, Springer International Publishing, Switzerland
2016 291.
[4] O. I. Afanasyev, E. Kuchuk, D. L. Usanov, D. Chusov, Chem.
Rev. 2019, 119, 11857.
ꢁ
[33] S. Dayan, C. Altınkaynak, N. Kayacı, S. D. Dogan,
N. Özdemir, N. K. Özpozan, Appl. Organomet. Chem. 2020, 34,
[5] C. Li, B. Villa-Marcos, J. Xiao, J. Am. Chem. Soc. 2009, 131,
6967.
[6] J. S. Yadav, A. Antony, T. S. Rao, B. V. S. Reddy, J. Organomet.
Chem. 2011, 696, 16.
[7] S. Das, S. Zhou, D. Addis, S. Enthaler, K. Junge, M. Beller,
Top. Catal. 2010, 53, 979.
[8] A. Corma, J. Navas, M. J. Sabater, Chem. Rev. 2018, 118, 1410.
[9] R. Kawahara, K.-i. Fujita, R. Yamaguchi, Adv. Synth. Catal.
2011, 353, 1161.
e5381.
[34] S. Dayan, N. Özdemir, N. K. Özpozan, Appl. Organomet.
Chem. 2019, 33, e4710.
[35] U. Mandi, S. K. Kundu, N. Salam, A. Bhaumik, S. M. Islam,
J. Colloid Interface Sci. 2016, 467, 291.
[36] P. Paul, P. Bhanja, N. Salam, U. Mandi, A. Bhaumik,
S. M. Alam, S. M. Islam, J. Colloid Interface Sci. 2017, 493, 206.
[37] D. Wang, X.-Q. Guo, C.-X. Wang, Y.-N. Wang, R. Zhong, X.-
H. Zhu, L.-H. Cai, Z.-W. Gao, X.-F. Hou, Adv. Synth. Catal.
2013, 355, 1117.
[10] Q. Yang, Q. Wang, Z. Yu, Chem. Soc. Rev. 2015, 44, 2305.
[11] Y. Watanabe, Y. Tsuji, H. Ige, Y. Ohsugi, T. Ohta, J. Org.
Chem. 1984, 49, 3359.
[38] S. P. Shan, T. T. Dang, A. M. Seayad, B. Ramalingam,
ChemCatChem 2014, 6, 808.
[12] S. Bähn, S. Imm, K. Mevius, L. Neubert, A. Tillack,
J. M. J. Williams, M. Beller, Chem. – Eur. J. 2010, 16, 3590.
[13] A. Martínez-Asencio, D. J. Ramón, M. Yus, Tetrahedron 2011,
67, 3140.
[14] S. Michlik, T. Hille, R. Kempe, Adv. Synth. Catal. 2012,
354, 847.
[15] A. B. Enyong, B. Moasser, J. Org. Chem. 2014, 79, 7553.
[16] K. O. Marichev, J. M. Takacs, ACS Catal. 2016, 6, 2205.
[17] D. Deng, B. Hu, M. Yang, D. Chen, Organometallics 2018, 37,
3353.
[18] M. Huang, Y. Li, J. Liu, X.-B. Lan, Y. Liu, C. Zhao, Z. Ke,
Green Chem. 2019, 21, 219.
[39] L. He, B. Lou, J. Ni, Y. Cao, H. Y. He, K. N. Fan, Chem. –
Eur. J. 2010, 16, 13965.
[40] J. W. Kim, K. Yamaguchi, N. Mizuno, J. Catal. 2009, 263, 205.
[41] X. Cui, Y. Zhang, F. Shi, Y. Deng, Chem. – Eur. J. 2011, 17,
1021.
[42] C. M. Wong, R. T. McBurney, S. C. Binding, M. B. Peterson,
V. R. Gonçales, J. J. Gooding, B. A. Messerle, Green Chem.
2017, 19, 3142.
[43] K.-i. Shimizu, Catal. Sci. Technol. 2015, 5, 1412.
[44] S. Denizaltı, B. S¸en, A. G. Gökçe, B. Çetinkaya, Appl. Organo-
metal. Chem. 2016, 30, 373.
[45] R. J. Bergeron, J. Wiegand, J. B. Dionis, M. Egli-Karmakka,
J. Frei, A. Huxley-Tencer, H. H. Peter, J. Med. Chem. 1991, 34,
2072.
[19] D. Carmona, F. J. Lahoz, R. Atencio, L. A. Oro, M. P. Lamata,
ꢀ
F. Viguri, E. S. José, C. Vega, J. Reyes, F. Joó, A. Kathó, Chem.
– Eur. J. 1999, 5, 1544.
[46] Y. Lu, C. Li, Z. Wang, J. Chen, M. L. Mohler, W. Li,
J. T. Dalton, D. D. Miller, J. Med. Chem. 2011, 54, 4678.
[47] R. J. Bergeron, J. Wiegand, J. S. McManis, B. H. McCosar,
W. R. Weimar, G. M. Brittenham, R. E. Smith, J. Med. Chem.
1999, 42, 2432.
[48] P. Chen, L. B. Horton, R. L. Mikulski, L. Deng, S. Sundriyal,
T. Palzkill, Y. Song, Bioorg. & Med. Chem. Lett. 2012, 22, 6229.
[49] K. L. Rinehart, A. L. Staley, S. R. Wilson, R. G. Ankenbauer,
C. D. Cox, J. Org. Chem. 1995, 60, 2786.
[50] S. Sabater, J. A. Mata, E. Peris, Organometallics 2015, 34, 1186.
[51] S. Sabater, J. A. Mata, E. Peris, ACS Catal. 2014, 4, 2038.
[52] Rigaku/MSC, Inc., 9009 new Trails Drive, The Woodlands, TX
77381.
[53] G. M. Sheldrick, SHELXL-97 Program for Crystal Structure
Solution and refinement, University of Gottingen, Göttingen,
Germany 1997.
[20] G. Zhou, A. H. Aboo, C. M. Rebertson, R. Liu, Z. Li,
K. Luzyanin, N. G. Berry, W. Chen, J. Xiao, ACS Catal. 2018,
8, 8020.
[21] D. L. Huang, R. Beltrán-Suito, J. M. Thomsen, S. M. Hashmi,
K. L. Materna, S. W. Sheehan, B. Q. Mercado, G. W. Brudvig,
R. H. Crabtree, Inorg. Chem. 2016, 55, 2427.
[22] N. D. Schley, J. D. Blakemore, N. K. Subbaiyan,
C. D. Incarvito, F. D' Souza, R. H. Crabtree, G. W. Brudvig,
J. Am. Chem. Soc. 2011, 133, 10473.
[23] E. V. Sackville, G. Kociok-Köhn, U. Hintermair, Organometal-
lics 2017, 36, 3578.
[24] A. M. Royer, T. B. Rauchfuss, S. R. Wilson, Inorg. Chem. 2008,
2, 395.
[25] D. Carmona, P. Lamata, A. Sánchez, P. Pardo, R. Rodríguez,
P. Ramírez, F. J. Lahoz, P. García-Orduña, L. A. Oro, Organo-
metallics 2014, 33, 4016.
[54] L. Ma, W.-J. Zhao, K. Lu, Acta Cryst 2006, E62, m2524.

12 of 12
DENIZALTI ET AL.
[55] Y. Boutadla, O. Al-Duaij, D. L. Davies, G. A. Griffith, K. Singh,
Organometallics 2009, 28, 433.
[56] L. S. Park-Gehrke, J. Freudenthal, W. Kaminsky,
A. G. DiPasquale, J. M. Mayer, Dalton Trans. 2009, 1972.
[57] A. Takayama, T. Suzuki, M. Ikeda, Y. Sunatsuki, M. Kojima,
Dalton Trans. 2013, 42, 14556.
SUPPORTING INFORMATION
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
[58] K. Ariyoshi, T. Suzuki, Acta Cryst. 2013, E69, m566.
[59] J.-Q. Wang, C.-X. Ren, G.-X. Jin, Chem. Commun. 2005, 4738.
[60] J. H. Wu, G. T. Yue, Y. M. Xiao, M. L. Huang, J. M. Lin,
L. Q. Fan, Z. Lan, J. Y. Lin, Acs. Appl. Mater. Inter. 2012, 4,
6530.
[61] C. Nagavolu, K. Susmitha, M. Raghavender, L. Giribabu,
K. B. S. Rao, C. T. G. Smith, C. A. Mills, S. R. P. Silva, V. V.
S. S. Srikanth, Sol. Energy. 2016, 137, 143.
How to cite this article: Denizaltı S, Dayan S,
Günnaz S, S¸ahin E. Thiazoline-Iridium (III)
Complexes and Immobilized Nanomaterials as
Selective Catalysts in N-Alkylation of Amines with
Alcohols. Appl Organomet Chem. 2020;e5970.
https://doi.org/10.1002/aoc.5970
[62] J. Neumann, S. Elangovan, A. Spannenberg, K. Junge,
M. Beller, Chem. – Eur. J. 2017, 23, 5410.
[63] H. Ohta, Y. Yuyama, Y. Uozumi, Y. M. A. Yamada, Org. Lett.
2011, 13, 3892.
[64] A. M. Rasero-Almansa, A. Corma, M. Iglesias, F. Sánchez,
ChemCatChem 2014, 6, 1794.
[65] M. V. Jiménez, J. Fernández-Tornos, M. González-Lainez,
B. Sánchez-Page, F. J. Modrego, L. A. Oro, J. Pérez-Torrente,
Catal. Sci. Technol. 2018, 8, 2381.
[66] A. Bartoszewicz, G. G. Miera, R. Marcos, P.-O. Norrby,
B. Martín Matute, ACS Catal. 2015, 5, 3704.