Synthesis of ferrocenyl imidazolium salts and their novel PEPPSI-type N-heterocyclic carbene (NHC) palladium complexes

Article abstract of DOI:10.1016/j.ica.2020.119792

The novel PEPPSI-type palladium complexes of ferrocenyl-functionalized N-heterocyclic carbenes (NHCs) with different substituents were synthesized. The synthesis of these ferrocenyl-NHCs ligands involves the reaction of the alcohol 1-(ferrocenyl)ethanol s

Full text of DOI:10.1016/j.ica.2020.119792

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Research paper
Synthesis of ferrocenyl imidazolium salts and their novel PEPPSI-type N-het‐
erocyclic Carbene (NHC) palladium complexes
Betül Yenisarı, Rukiye Fırıncı, Namık Özdemir, M. Emin Günay
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DOI:
Reference:
S0020-1693(20)30991-9
https://doi.org/10.1016/j.ica.2020.119792
ICA 119792
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Inorganica Chimica Acta
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6 March 2020
28 May 2020
28 May 2020
Please cite this article as: B. Yenisarı, R. Fırıncı, N. Özdemir, M.E. Günay, Synthesis of ferrocenyl imidazolium
salts and their novel PEPPSI-type N-heterocyclic Carbene (NHC) palladium complexes, Inorganica Chimica
Acta (2020), doi: https://doi.org/10.1016/j.ica.2020.119792
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Synthesis of Ferrocenyl Imidazolium Salts and their Novel PEPPSI-type N-heterocyclic
Carbene (NHC) Palladium Complexes
Betül Yenisarı,a Rukiye Fırıncı,a Namık Özdemir,b M. Emin Günaya*
aDepartment of Chemistry, Faculty of Art and Science, Aydın Adnan Menderes University, 09100 Aydın, Turkey
bDepartment of Mathematics and Science Education, Faculty of Education, Ondokuz Mayıs University, 55139
Samsun, Turkey
*Corresponding author
E-mail address: megunay@adu.edu.tr (M. Emin Günay)
ABSTRACT
The novel PEPPSI-type palladium complexes of ferrocenyl-functionalized N-heterocyclic
carbenes (NHCs) with different substituents were synthesized. The synthesis of these ferrocenyl-
NHCs ligands involves the reaction of the alcohol 1-(ferrocenyl)ethanol successively with 1-
substituted imidazole in glacial acetic acid. Following that, the novel PEPPSI-type NHC
palladium complexes were prepared by heating their imidazolium salts with PdCl2, K2CO3 in neat
pyridine. In addition, deprotonation of N-ferrocenylethyl-N'-(2,4,6-trimethylphenyl)imidazolium
chloride (2a) and then its reaction with S8 gave imidazole-2-thione (5). All ligand precursors and
1
13
all palladium complexes were characterized by elemental analysis, H and C NMR, and X-ray
diffraction methods for two examples.
Keywords: N-heterocyclic carbene, ferrocenyl-imidazolium salts, PEPPSI-type NHC palladium
complexes, X-ray crystallography
1. Introduction
N-Heterocyclic carbenes (NHCs) and their metal complexes have been the subject of extensive
investigations owing to their successful applications in coordination chemistry and homogeneous
catalysis [1,2]. NHCs have several characteristics, which make them valuable for catalysis. Often,
they lead to air-stable compounds, in which the carbene ligands bind more strongly to the metal
than in comparable electron-rich phosphine/metal complexes. The strong -donor and

comparatively weak π-acceptor properties of NHCs sustain similarities to the coordination
characteristics of phosphines, and NHCs are in general more electron-donating than phosphines.
Ferrocenyl substituted NHCs have attracted interest because the ferrocenyl group has unique
electronic properties, and has an unusual cylindrical shape, and additional electron donation to
adjacent electron-deficient centers [3,4]. A number of NHC transition metal complexes bearing
ferrocenyl substituents have been synthesized and used in homogeneous catalysis or
electrochemical investigation in recent years [5]. The ferrocenyl groups are introduced to the
NHCs roughly through two manners, as pendant substituents attached to the side-arm of NHCs
[6-9], or as an integral part of the NHC backbone [10,11]. These ferrocenyl functionalized NHCs
and their derivatives exhibit spectacular reactivities [12,13] and electrochemical properties [10]
owing to the introduction of redox-active ferrocenyl groups. An additional advantage of the
ferrocenyl functionalization is that the catalytic activity and selectivity of complexes can be
effectively tuned by the redox-active moieties. Thus, NHCs with ferrocenyl substituents are
expected to act as very useful ligands for transition metals. In particular, the reason for the
synthesis of PEPPSI-type Pd(II)-NHC complexes is that such complexes have great potential in
the catalyst for organic transformations such as C-C bond formation and there are a few reports
related to especially ferrocenyl bearing PEPPSI-type Pd(II) complexes in the literature.
Herein, the synthesis and characterization of various ferrocenyl NHC palladium(II) complexes
were carried out successfully via the deprotonation of the ferrocenyl imidazolium salt by a base
followed by subsequent complexation by the palladium center. The compounds were
characterized by NMR, elemental analyses, and crystal structures of compounds 4 and 5 were
obtained.
2. Experimental
2.1. Materials and general methods
All manipulations except workup and purification were conducted under an inert atmosphere of
Ar using standard Schlenk techniques. Solvents were dried and freshly distilled prior to use. All
other chemicals were used as received. Acetyl ferrocene [3a,14], ferrocenyl ethanol [15], benzyl
bromide derivatives [16], and N-(aryl)-1H-imidazole [17] were prepared according to literature
1
13
procedures. H and C NMR spectra were recorded on a Varian Mercury AS 400 spectrometer
operating at 400 and 100 MHz, respectively. Chemical shifts are given in ppm with internal

referencing to the solvent peaks. Melting points were measured in open capillary tubes with an
Electrothermal-9200 melting point apparatus. Elemental analyses were performed by the
TÜBİTAK (Ankara, Turkey) Microlab.
2.2. Preparation of the imidazolium salts with ferrocenyl substituents, 2a-c.
1-Ferrocenylethanol (1.0 mmol) and N-substituted imidazole derivatives (1a-c, 1.1 mmol) were
dissolved in acetic acid (3.0 mL) and stirred at 60 °C for 7 h (Scheme 1). After removed most of
acetic acid, a solution of LiCl (4.0 mmol) in MeOH (20.0 mL) was added, and stirred for 24 h at
room temperature. After stirring for 24 h, the volatiles were removed under reduced pressure, and
residue extracted with CH2Cl2. The solution was filtered through Celite. Removal of solvent
under reduced pressure resulted in a liquid. As a result, all the salts synthesized (2a-c) were
obtained as oily.
Scheme 1. Synthesis of imidazolium salts with ferrocenyl substituents
2a: This compound was synthesized according to the literature procedure [18]. Yield: 62% (0.27
g). Anal. Calc. for C24H27ClFeN2 (MW = 434.78 g.mol-1): C, 66.30; H, 6.26; N, 6.44. Found: C,
1
66.41; H, 6.31; N, 6.48%. H NMR (400 MHz, DMSO-d6, TMS, ppm): δ = 1.89 (d, J = 7.0 Hz,
3H, FcCHCH3), 1.97 (s, 6H, C6H2(CH3)3-o-(CH3)), 2.30 (s, 3H, C6H2(CH3)3-p-(CH3)), 4.23 (s,
5H, Fc-H), 4.39 (s, 2H, Fc-H), 4.44 (s, 2H, Fc-H), 5.67-5.82 (m, 1H, FcCHCH3), 7.11 (d, J = 7.0
Hz, 2H, C6H2(CH3)3), 7.92 (s, 1H, NCHCHN), 8.18 (s, 1H, NCHCHN), 9.87 (s, 1H, NCHN). 13C
NMR (100 MHz, DMSO-d6, TMS, ppm): δ = 16.9 (FcCHCH3), 20.1 (C6H2(CH3)3), 20.5
(C6H2(CH3)3), 21.1 (C6H2(CH3)3), 55.8 (FcCHCH3), 65.9 (Fc-C), 67.3 (Fc-C), 68.1 (Fc-C), 68.6
(Fc-C), 68.8 (Fc-C), 78.8 (Fc-C), 79.1 (Fc-C), 79.4 (Fc-C), 87.3 (Fc-C), 121.4 (NCHCHN), 123.9
(NCHCHN), 128.9 (C6H2(CH3)3), 129.1 ((C6H2(CH3)3), 131.1 (C6H2(CH3)3), 134.0
(C6H2(CH3)3), 134.4 (C6H2(CH3)3), 136.3 (C6H2(CH3)3), 140.0 (NCHN).

2b: Yield: 60% (1.07 g). Anal. Calc. for C25H29ClFeN2 (MW = 448.80 g.mol-1): C, 66.90; H,
6.51; N, 6.24. Found: C, 66.68; H, 6.73; N, 6.54%. 1H NMR (400 MHz, DMSO-d6, TMS, ppm):
δ = 1.30 (s, 9H, C6H4C(CH3)3), 1.95 (d, J = 7.0 Hz, 3H, FcCHCH3), 4.22 (s, 5H, Fc-H), 4.47 (s,
2H, Fc-H), 4.53 (s, 2H, Fc-H), 5.67-5.74 (m, 1H, FcCHCH3), 7.61 (d, J = 8.2 Hz, 2H,
C6H4C(CH3)3), 7.74 (d, J = 8.6 Hz, 2H, C6H4C(CH3)3), 8.10 (s, 1H, NCHCHN), 8.31 (s, 1H,
NCHCHN), 10.24 (s, 1H, NCHN). 13C NMR (100 MHz, DMSO-d6, TMS, ppm): δ = 19.9
(FcCHCH3), 30.9 (C6H4C(CH3)3), 34.5 (C6H4C(CH3)3), 55.9 (FcCHCH3), 66.2 (Fc-C), 67.9 (Fc-
C), 68.2 (Fc-C), 68.6 (Fc-C), 68.8 (Fc-C), 78.7 (Fc-C), 79.1 (Fc-C), 79.4 (Fc-C), 87.0 (Fc-C),
121.2 (NCHCHN), 121.3 (NCHCHN), 121.4 (C6H4C(CH3)3), 126.7 (C6H4C(CH3)3), 132.3
(C6H4C(CH3)3), 133.9 (C6H4C(CH3)3), 152.4 (NCHN).
2c: Yield: 58% (1.60 g). Anal. Calc. for C22H23ClFeN2O (MW = 422.72 g.mol-1): C, 62.51; H,
5.48; N, 6.63. Found: C, 62.65; H, 5.55; N, 6.76%. 1H NMR (400 MHz, DMSO-d6, TMS, ppm):
δ = 1.94 (d, J = 7.0 Hz, 3H, FcCHCH3), 3.81 (s, 3H, C6H4-p-(OCH3)), 4.22 (s, 5H, Fc-H), 4.45 (s,
2H, Fc-H), 4.51 (s, 2H, Fc-H), 5.62-5.71 (m, 1H, FcCHCH3), 7.14 (d, J = 8.0 Hz, 2H,
C6H4(OCH3)), 7.73 (d, J = 8.0 Hz, 2H, C6H4(OCH3)), 8.04 (s, 1H, NCHCHN), 8.22 (s, 1H,
NCHCHN), 10.05 (s, 1H, NCHN). 13C NMR (100 MHz, DMSO-d6, TMS, ppm): δ = 19.9
(FcCHCH3), 55.6 (C6H4-p-(OCH3)), 56.0 (FcCHCH3), 66.1 (Fc-C), 67.9 (Fc-C), 68.8 (Fc-C),
68.9 (Fc-C), 78.7 (Fc-C), 79.0 (Fc-C), 79.2 (Fc-C), 79.4 (Fc-C), 86.9 (Fc-C), 114.9 (C6H4(CH3)),
121.3 (NCHCHN), 123.3 (NCHCHN), 127.4 (C6H4(CH3)), 127.6 (C6H4(CH3)), 127.7
(C6H4(CH3)), 127.8 (C6H4(CH3)), 159.8 (NCHN).
2.3. Preparation of the ferrocenyl NHC-Palladium complexes.
A Schlenk flask was charged with imidazolium salts (2, 0.7 mmol), K2CO3 (5 mmol), PdCl2 (0.7
mmol), and 5 mL of pyridine (Scheme 2). The reaction mixture was heated with vigorous stirring
0
for 12 h at 75 C. The reaction mixture was diluted with CH2Cl2 then filtered through a pad of
celite and silica gel to remove the unreacted PdCl2 and imidazolium salt. The solvent was
removed under vacuum. The obtained yellow solid was recrystallized from CH2Cl2/Et2O.

Scheme 2. Synthesis of ferrocenyl NHC-Pd(II) complexes
o
3b: Yield: 65% (0.30 g). m.p.: 170-171 C. Anal. Calc. for C30H33Cl2FeN3Pd (MW = 668.77
1
g.mol-1): C, 53.88; H, 4.97; N, 6.28. Found: C, 53.72; H, 4.90; N, 6.42%. H NMR (400 MHz,
CDCl3, TMS, ppm): δ = 1.36 (s, 9H, C6H4C(CH3)3), 1.99 (d, J = 6.7 Hz, 3H, FcCHCH3), 4.07-
4.12 (m, 1H, Fc-H), 4.21 (d, J = 8.6 Hz, 1H, Fc-H),4.27 (s, 5H, Fc-H), 4.41 (s, 1H, Fc-H), 4.72
(s, 1H, Fc-H), 6.81 (s, 1H, NCHCHN), 6.87-6.92 (m, 1H, FcCHCH3), 7.0 (s, 1H, NCHCHN),
7.30-7.33 (d, J = 8.0 Hz, 1H, C5H5N), 7.53 (d, J = 7.8 Hz, 2H, C6H4C(CH3)3), 7.71-7.75 (m, 2H,
C5H5N), 7.91 (d, J = 7.8 Hz, 2H, C6H4C(CH3)3), 8.92 (d, J = 8.0 Hz, 2H, C5H5N). 13C NMR (100
MHz, CDCl3, TMS, ppm): δ = 20.8 (FcCHCH3), 31.3 (C6H4C(CH3)3), 57.0 (FcCHCH3), 65.8
(Fc-C), 67.8 (Fc-C), 69.1 (Fc-C), 70.1 (Fc-C), 87.1 (Fc-C), 118.7 (NCHCHN), 123.3
(NCHCHN), 124.4 (C5H5N), 125.3 (C6H4C(CH3)3), 126.2 (C6H4C(CH3)3), 137.9 (C5H5N), 147.4
(C6H4C(CH3)3), 151.3 (C5H5N), 151.4 (C6H4C(CH3)3), 153.3 (Pd-Ccarbene).
o
3c: Yield: 66% (0.29 g). m.p.: 160-161 C. Anal. Calc. for C27H27Cl2FeN3OPd (MW = 642.69
1
g.mol-1): C, 50.46; H, 4.23; N, 6.54. Found: C, 50.33; H, 4.16; N, 6.76%. H NMR (400 MHz,

CDCl3, TMS, ppm): δ = 1.21 (s, 3H, FcCHCH3), 3.80 (s, 3H, C6H4-p-(OCH3)), 4.07 (s, 5H, Fc-
H), 4.12 (s, 2H, Fc-H), 4.22 (s, 1H, Fc-H), 4.39 (s, 1H, Fc-H), 6.97 (d, J = 2.0 Hz, 2H,
NCHCHN), 7.05-7.08 (m, 1H, FcCHCH3), 7.25-7.27 (m, 1H, C6H4(OCH3), 7.30-7.35 (m, 2H,
C5H5H, 1H, C6H4(OCH3)), 7.54 (m, 1H, C6H4(OCH3), 7.78 (t, J = 7.6 Hz, 1H, C5H5N), 8.27-8.29
(m, 1H, C6H4(OCH3), 8.82 (d, J = 4.0 Hz, 2H, C5H5N).13C NMR (100 MHz, CDCl3, TMS, ppm):
δ = 28.9 (FcCHCH3), 55.5 (FcCHCH3), 68.8 (C6H4-p-(OCH3)), 78.5 (Fc-C), 78.8 (Fc-C), 79.0
(Fc-C), 79.2 (Fc-C), 93.2 (Fc-C), 114.8 (C6H4(CH3)), 122.7 (NCHCHN), 125.3 (NCHCHN),
127.4 (C6H4(CH3)), 127.6 (C6H4(CH3)), 127.8 (C6H4(CH3)), 128.9 (C6H4(CH3)), 129.6 (C5H5N),
137.2 (C5H5N), 152.9 (C5H5N), 158.9 (Pd-Ccarbene).
4: Yield: 44% (0.24 g). m.p.: 165-166 oC. Anal. Calc. for C36H40Cl2FeN4Pd (MW = 761.90 g.mol-
1): C, 56.75; H, 5.29; N, 7.35. Found: C, 56.85; H, 5.46; N, 7.43%. 1H NMR (400 MHz, CDCl3,
TMS, ppm): δ = 1.95 (s, 6H, C6H2(CH3)3-p-(CH3)), 1.98 (d, J = 6.7 Hz, 3H, FcCHCH3), 2.21 (s,
3H, C6H2(CH3)3-o-(CH3)), 2.26 (s, 3H, C6H2(CH3)3-p-(CH3)), 2.29 (s, 3H, C6H2(CH3)3-o-(CH3)),
2.33 (s, 3H, C6H2(CH3)3-o-(CH3)), 4.19 (s, 2H, Fc-H), 4.26 (s, 5H, Fc-H), 4.40 (s, 1H, Fc-H),
4.75 (s, 1H, Fc-H), 6.72 (d, J = 4.0 Hz, 1H, NCHCHN), 6.86 (d, J = 4.0 Hz, 1H, NCHCHN), 6.90
(s, 2H, C6H2(CH3)3), 6.95 (s, 1H, NCHCHN), 6.98 (s, 2H, C6H2(CH3)3), 7.14-7.18 (m, 1H,
13
FcCHCH3), 7.66 (s, 1H, NCHCHN), 8.03 (s, 1H, NCHN). C NMR (100 MHz, CDCl3, TMS,
ppm): δ = 15.4 (FcCHCH3), 18.6 (C6H2(CH3)3-o-(CH3)), 18.7 (C6H2(CH3)3-o-(CH3)), 20.7
(C6H2(CH3)3-p-(CH3)), 21.2 (C6H2(CH3)3-p-(CH3)), 51.36 (FcCHCH3), 66.0 (Fc-C), 67.8 (Fc-C),
69.5 (Fc-C), 70.1 (Fc-C), 87.6 (Fc-C), 116.8 (NCHCHN), 119.8 (NCHCHN), 122.8 (NCHCHN),
125.2 (C6H2(CH3)3-o-(CH3)), 131.3 (C6H2(CH3)3-o-(CH3)), 134.1 (C6H2(CH3)3-o-(CH3)), 135.7
(NCHCHN), 136.5 (C6H2(CH3)3-o-(CH3)), 137.2 (Fc-CCHCH3N), 139.1 (C6H2(CH3)3-o-(CH3)),
140.1 (C6H2(CH3)3-o-(CH3)), 140.4 (NCHN), 144.4 (C6H2(CH3)3-o-(CH3)), 145.0 (C6H2(CH3)3-
o-(CH3)), 154.1 (Pd-Ccarbene).
2.3. Preparation of the N-ferrocenylethyl-N’-(2,4,6-trimethylphenyl)imidazole-2-thione, 5.
A Schlenk flask was charged with imidazolium salt (3a, 1.0 mmol), KtOBu (1.4 mmol), and 15
0
mL dry THF. After this mixture was stirred at 25 C for one hour, S8 (2.0 mmol) was added
(Scheme 3). After two hours, H2O (10.0 mL) was added to the reaction mixture, and the organic
phase was extracted with Et2O (10.0 mLx2). Subsequently, the organic phase was dried with

MgSO4. The Et2O phase was concentrated in vacuum and the product precipitated by addition of
hexane.
Yield: 40% (0.172 g). m.p.: 137-138 oC. Anal. Calc. for C24H26FeN2S (MW = 430.38 g.mol-1): C,
1
66.98; H, 6.09; N, 6.51. Found: C, 66.86; H, 6.03; N, 6.75%. H NMR (400 MHz, DMSO-d6,
TMS, ppm): δ = 1.67 (d, J = 7.0 Hz, 3H, FcCHCH3), 1.90 (d, J = 8.0 Hz, 6H, C6H2(CH3)3-o-
(CH3)), 2.27 (s, 3H, C6H2(CH3)3-p-(CH3)), 4.14-4.16 (m, 1H, Fc-H), 4.18-4.19 (m, 1H, Fc-H),
4.21 (s, 5H, Fc-H), 4.26 (s, 1H, Fc-H), 4.36 (s, 1H, Fc-H), 5.91 (q, J = 4.0 Hz, 1H, FcCHCH3),
6.96 (s, 2H, C6H2(CH3)3), 7.15 (s, 2H, NCHCHN). 13C NMR (100 MHz, CDCl3, TMS, ppm): δ =
17.4 (FcCHCH3, C6H2(CH3)3-o-(CH3)), 19.7 (C6H2(CH3)3-o-(CH3)), 20.5 (C6H2(CH3)3-p-(CH3)),
66.2 (FcCHCH3), 68.6 (Fc-C), 78.5 (Fc-C), 78.9 (Fc-C), 79.1 (Fc-C), 79.2 (Fc-C), 88.9 (Fc-C),
127.4 (NCHCHN), 127.6 (NCHCHN), 127.9 (C6H2(CH3)3), 128.5 (C6H2(CH3)3), 133.9
(C6H2(CH3)3), 135.2 (C6H2(CH3)3), 135.3 (C6H2(CH3)3), 137.9 (C6H2(CH3)3), 160.9 (Ccarbene-S).
Scheme 3. Synthesis of N-ferrocenylethyl-N’-(2,4,6-trimethylphenyl)imidazole-2-thione, 5.
2.4. X-ray crystallography
Intensity data of the compounds were collected on a STOE IPDS II diffractometer at room
temperature using graphite-monochromated Mo Kα radiation by applying the -scan method.
Data collection and cell refinement were carried out using X-AREA [19] while data reduction
was applied using X-RED32 [19]. The structure was solved by direct methods using SHELXS-
2013 [20] and refined with full-matrix least-squares calculations on F2 using SHELXL-2014 [21]
implemented in WinGX [22] program suit. All carbon bound H atoms were positioned
geometrically and treated using a riding model, fixing the bond lengths at 0.93, 0.98 and 0.96 Å
for aromatic CH, methine CH and CH3 atoms, respectively. The displacement parameters of the
H atoms were fixed at Uiso(H) = 1.2Ueq (1.5Ueq for CH3) of their parent atoms. Crystal data, data
collection and structure refinement details are summarized in Table 1 while important bond

lengths and angles are collected in Table 2. PLATON [23] was used for the structure analysis.
Molecular graphics were generated by using ORTEP-3 [22].
Table 1. Crystal data and structure refinement parameters for 4 and 5.
Parameter
4
5
CCDC depository
Color/shape
1472057
Yellow/plate
1472056
Yellow/plate
Chemical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
[FePdCl2(C5H5)(C19H21N2)(C12H14N2)] [Fe(C5H5)(C19H21N2S)]
761.87
430.38
296
296
0.71073 Mo Kα
Monoclinic
P21/c (No. 14)
0.71073 Mo Kα
Triclinic
̅
Space group
P1 (No. 2)
Unit cell parameters
a, b, c (Å)
19.6604(11), 8.7608(3), 20.8479(11)
7.3883(5), 12.1643(8), 13.4322(9)
α, β, γ (°)
90, 100.266(4), 90
3533.4(3)
4
1.432
1.101
63.974(5), 74.630(5), 78.015(4)
1040.16(13)
2
1.374
0.837
Volume (Å3)
Z
Dcalc (g/cm3)
μ (mm−1)
Absorption correction
Tmin, Tmax
F000
Integration
0.6943, 0.9487
1560
Integration
0.6592, 0.9741
452
Crystal size (mm3)
Diffractometer/measurement method
Index ranges
0.53 × 0.17 × 0.07
STOE IPDS II/ω scan
−23 ≤ h ≤ 22, −10 ≤ k ≤ 10, −24 ≤ l ≤ 24 −9 ≤ h ≤ 9, −16 ≤ k ≤ 16, −17 ≤ l ≤ 17
0.58 × 0.22 × 0.04
STOE IPDS II/ω scan
θ range for data collection (°)
Reflections collected
Independent/observed reflections
Rint
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
Δρmax, Δρmin (e/Å3)
1.985 ≤ θ ≤ 25.247
22832
6408/2564
1.721 ≤ θ ≤ 28.419
18785
5203/3809
0.1278
0.100
Full-matrix least-squares on F2
6408/0/403
Full-matrix least-squares on F2
5203/0/257
0.804
1.001
R1 = 0.0524, wR2 = 0.0637
R1 = 0.1663, wR2 = 0.0825
0.347, −0.318
R1 = 0.0426, wR2 = 0.0887
R1 = 0.0685, wR2 = 0.0968
0.310, −0.295

Table 2. Selected geometric parameters for 4 and 5.
Parameter
4
Parameter
5
Bond lengths (Å)
S1─C10
N1─C6
N1─C10
N1─C11
N2─C10
N2─C12
N2─C13
C11─C12
2.3021(19) Pd1─Cl1
2.3021(19) Pd1─Cl2
1.685(2)
1.432(3)
1.361(3)
1.393(3)
1.364(3)
1.389(3)
1.468(3)
1.331(4)
2.068(5)
1.949(7)
1.445(8)
1.350(7)
1.368(7)
1.318(7)
1.361(7)
1.375(8)
1.377(7)
1.442(8)
1.339(8)
1.376(8)
1.481(8)
1.345(8)
1.306(10)
Pd1─N2
Pd1─C24
N1─C1
N1─C10
N1─C12
N2─C10
N2─C11
N3─C22
N3─C24
N3─C13
N4─C24
N4─C23
N4─C25
C11─C12
C22─C23
Bond angles (°)
N1─C10─S1
N2─C10─S1
N1─C10─N2
C12─C11─N1
C10─N1─C11
C10─N1─C6
C11─N1─C6
C11─C12─N2
C10─N2─C12
C10─N2─C13
C12─N2─C13
175.8(3)
88.72(19)
90.27(16)
89.81(19)
91.06(17)
177.49(9)
112.9(6)
104.2(6)
105.1(6)
127.8(6)
126.9(6)
104.4(6)
108.6(6)
125.4(6)
126.0(6)
111.7(6)
125.0(6)
123.3(7)
107.2(6)
110.4(7)
109.2(7)
106.2(8)
C24─Pd1─N2
C24─Pd1─Cl1
N2─Pd1─Cl1
C24─Pd1─Cl2
N2─Pd1─Cl2
Cl1─Pd1─Cl2
N2─C10─N1
N4─C24─N3
C10─N1─C12
C10─N1─C1
C12─N1─C1
C10─N2─C11
C22─N3─C24
C22─N3─C13
C24─N3─C13
C24─N4─C23
C24─N4─C25
C23─N4─C25
C11─C12─N1
C12─C11─N2
C23─C22─N3
C22─C23─N4
126.66 (15)
127.87 (17)
105.46 (17)
107.3 (2)
109.83 (18)
124.97 (17)
125.14 (19)
107.72 (19)
109.66 (19)
123.96 (18)
126.32 (18)

Table 3. Hydrogen bonding geometry for 4 and 5.
D—H···A
D—H (Å)
H···A (Å)
D···A (Å)
D—H···A (°)
4
C19─H19A···Cl1
C21─H21A···Cl2
C10─H10···Cl1
C12─H12···Cl1i
5
0.96
0.96
0.93
0.93
2.70
2.74
2.65
2.72
3.656(9)
3.631(8)
3.163(7)
3.642(7)
176
154
115
170
C13─H13···S1
0.98
2.68
3.220(2)
115
Symmetry code: i x, y+1, z.
3. Results and discussion
3.1. Synthesis of ferrocenyl imidazolium salts (2a-c)
The ferrocenyl imidazolium salts can be efficiency synthesized starting from ferrocene according
to the literature method [3a,24] (Scheme 1). The reduction of acetylferrocene prepared by
Friedel-Crafts acylation reaction of ferrocene gave 1-ferrocenylethanol in excellent yield.
Treatment of 1-ferrocenylethanol with 1-substituted imidazole in acetic acid at 60 0C for 7 h gave
an imidazolium salt with the acetate as a counter anion. Subsequently, addition of excess LiCl to
the reaction mixture resulted in anion exchange to give ferrocenyl imidazolium chlorides. The
1
new compounds were characterized by their spectroscopic data and elemental analyses. The H
NMR signals of the C(2)-H protons were observed as sharp singlets at chemical shifts of 9.87,
10.24, and 10.05 and ppm for 2a-c ligands, respectively. In the 13C-NMR spectra of 2a-c, the
characteristic signals of the imino carbon (NCHN) were detected as typical singlets at 140.0,
152.4, and 159.8 ppm, respectively.
3.2. Synthesis of ferrocenyl-NHC palladium complexes (3b,3c,4)
The synthesis of ferrocenyl NHC-palladium complexes (3b,3c,4) is achieved by refluxing of the
corresponding imidazolium salt 2a–c, with palladium chloride (1.0 eq.) in presence of K2CO3 in
pyridine in an argon atmosphere, as shown in Scheme 2. All of these palladium complexes are air
and moisture stable and can be stored under air in solid-state without any decomposition. This
complex 4 was fully characterized by NMR spectroscopy, elemental analyses, and X-ray
diffraction method. The proton signal of NCHN from the imidazolium chlorides at ca. 9–10 ppm
1
was absent in the H NMR of palladium complexes, confirming carbene generation. In addition,

the formation of the metal complexes was evident from the distinctive Pd–Ccarbene peak 150–160
ppm.
The general method for the preparation of PEPPSI-type Pd(II)-NHC complexes by reacting PdCl2
with imidazolium salts in the presence of excess K2CO3 worked well for 3b and 3c derivatives.
However, the reaction of the sterically hindered N-mesitylene substituted imidazolium salt 2a
under similar reaction conditions gave the N-coordinated mesityl-imidazole ligand, which
presumably resulted from N-C cleavage of the N-mesityl group under these reaction conditions
[25]. We do not have any data at this stage on whether there is such a situation in other
substituents. It is understood that the main product in the synthesis of PEPPSI-type Pd complexes
of 4-tert-butyl- and 4-methoxyphenyl substituted imidazolium salts are complexes of type [PdCl2
(NHC)py], 3b,c.
3.3. Synthesis of N-ferrocenylethyl-N’-(2,4,6-trimethylphenyl)imidazole-2-thione (5)
N-ferrocenylethyl-N’-(2,4,6-trimethylphenyl)imidazole-2-thione 5 was synthesized via the
reaction of the corresponding imidazolium salt 2a with potassium tert-butoxite and elemental
sulphur in tetrahydrofuran in moderate yield. The (Ccarbene-S) resonance of this complex in the 13C
NMR spectra appeared at 160.9 ppm.
3.4. Description of crystal structures
The structures of compounds 4 and 5 were unambiguously determined by single-crystal X-
ray diffraction. Compound 4 crystallizes in the monoclinic space group P21/c with four molecules
in the unit cell, and is shown in Fig. 1. The central palladium atom is tetracoordinated with one
carbene carbon atom, one imidazole nitrogen atom and two chlorine atoms to adopt a slightly
distorted trans-square-planar geometry. In the square-planar coordination, atoms Pd1, Cl1, Cl2,
N2 and C24 deviate by 0.0454(6), 0.004(2), 0.004(2), −0.026(6) and −0.027(8) Å, respectively,
from the mean plane through these five atoms. The Pd─N and Pd─C distances are 2.068(5) and
1.949(7) Å, respectively, comparable to those in other palladium(II)-NHC analogues [26,27]. The
Cl1─Pd1─Cl2 and C24─Pd1─N2 arrays are almost linear with the bond angles of 177.49(9) and
175.8(3)°, respectively. The angle sum about the divalent Pd atom is 359.86°, the greatest
deviation from orthogonality being 88.72(19)° for C24─Pd1─Cl1. As shown in Fig. 1, the

PdCNCl2 coordination plane is almost oriented perpendicularly to the N3/N4/C22-24 ring plane
with a dihedral angle of 76.8(4)°, and is twisted from the N1/N2/C10-12 ring plane by 20.9(4)°.
The Fe─C distances are as expected for a ferrocene derivative, changing from 1.975(10) to
2.038(11) Å. The cyclopentadienyl (Cp) rings are roughly eclipsed, with a twist angle τ =
6.3(14)°, and they are slightly tilted with respect to each other, forming a dihedral angle of
1.8(8)°. The Fe-to-centroid distances are 1.6313(12) Å (Cg3) and 1.6374(12) Å (Cg4), and the
Cg3─Fe1─Cg4 angle is 179.06(8)° (Cg3 and Cg4 are the centroids of the C27-C31 and C32-C36
rings, respectively).
In the molecular structure of 4, intramolecular C19─H19A···Cl1, C21─H21A···Cl2 and
C10─H10···Cl1 contacts lead to the formation of eight- and five-membered rings with graph-set
descriptor S(8) for the first two, and S(5) for the last one [28]. In the crystal structure, atom C12
in the molecule at (x, y, z) acts as hydrogen-bond donor to the Cl1 atom in the molecule at (x,
y+1, z), forming a C(6) [27] chain running parallel to the b axis (Fig. 2).
Figure 1. A view of 4 showing the atom-numbering scheme. Displacement ellipsoids are drawn
at the 30% probability level and H atoms have been omitted for the sake of clarity.

Figure 2. Part of the crystal structure of 4, showing a C(6) chain along [010]. For the sake of
clarity, H atoms not involved in H-bonds have been omitted.
̅
Compound 5 crystallizes in the triclinic space group P1 with two molecules in the unit cell,
and is shown in Fig. 3. The C═S bond length of 1.685(2) Å is intermediate between the single-
bond value of 1.81 Å and the double-bond value of 1.61 Å [29]. The shortening of the two
adjacent N1─C10 and N2─C10 bonds also confirms the existence of some partial double-bond
character [1.361(3) and 1.364(3) Å]. The bond angle sums about N1 and N2 both sum to 359.94°,
indicating sp2 hybridization. The C11─C12 bond length of 1.331(4) Å in the five-membered
imidazole ring (sum of pentagonal internal angles ≅ 540.0°) is the same with the average for a
non-delocalized olefinic C═C grouping (1.331 Å) [30]. These data show that the major
contributors to the resonance hybrid for 5 mainly involve the electrons of N1, N2, C10 and S1
atoms, and this is a normal feature for the thiourea systems [3a, 31-34].
The Fe─C distances fall within the expected range, ranging from 2.035(3) to 2.049(3) Å,
which agree well with those reported for ferrocene derivatives [35-37]. Similar to 4, the Cp rings
are roughly eclipsed, with a twist angle τ = 8.0(2)°, and they are slightly tilted with respect to
each other, forming a dihedral angle of 1.4(2)°. The Fe-to-centroid distances are 1.6434(4) Å
(Cg1) and 1.6527(4) Å (Cg2), and the Cg1─Fe1─Cg2 angle is 178.82(3)° (Cg1 and Cg2 are the
centroids of the C15-C19 and C20-C24 rings, respectively).
In the molecular structure of 5, a weak intramolecular contact between the methine H and
sulphur atoms leads to the formation of a five-membered ring with graph-set descriptor S(5) [28].
In the crystal structure, there are no important interactions between the molecules, other than van

der Waals contacts. Full details of the hydrogen-bonding geometries in 4 and 5 are given in Table
3.
Figure 3. A view of 5 showing the atom-numbering scheme. Displacement ellipsoids are drawn
at the 30% probability level and H atoms have been omitted for the sake of clarity.
4. Conclusions
In this study, ferrocenyl-substituted novel PEPPSI-type Pd(II)-NHC complexes (3a,b), mesityl-
imidazole bearing Pd(II)-NHC complex (4), and thione derivative (5) have been prepared. All
synthesized complexes have been characterized by 1H- and 13C-NMR, and elemental analyses. In
addition, the structures of synthesized compounds 4 and 5 were described by the X-ray
diffraction analysis method. The syntheses of Pd(II)-NHC complexes were performed at the
presence of excess K2CO3 which was necessary to detach proton at C2 of imidazolium salts. In
these reaction conditions, it is seen that the C-N bond in the imidazolium salt (2a) is cleavage,
and a compound of 4 is formed.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was financially supported by the Scientific Research Unit (BAP, project number: FEF-
13021) of Aydın Adnan Menderes University and Ondokuz Mayıs University (Project No:
PYO.FEN.1906.19.001).

Appendix A. Supplementary data
CCDC 1472056 and 1472057 contain the supplementary crystallographic data for the
compound reported in this article. These data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: +44 1223 336 033, e-mail:
deposit@ccdc.cam.ac.uk, https://www.ccdc.cam.ac.uk/structures/].
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Highlights
 The ferrocenyl-functionalized N-heterocyclic carbene (NHCs) precursors were
synthesized.
 The novel ferrocenyl-bearing PEPPSI-type palladium complexes were synthesized.
 Imidazole-2-thione derivative was synthesized via the deprotonation method.
 The excess base play a role in cleavage the C-N bond in the imidazole salt.

Author Statement
Betil Yenisarı: Investigation, MSc. Student.
Rukiye Fırıncı: Investigation, visualization.
Namık Özdemir: Software, X-ray analysis.
M. Emin Günay: Supervision, writing-reviewing and editing,