Mercuration of ferrocenyl-p-tolyl sulfoxide and its conversion to 1,2-disubstituted ferrocenes

Article abstract of DOI:10.1016/j.jorganchem.2017.10.028

1-(p-Tolylsulfinyl)-2-(chloromercurio)ferrocene (2) was prepared by direct mercuration of ferrocenylsulfoxide (1). This reaction can be performed at room temperature in open air. Cross-coupling reactions of compound 2 and aryl halides especially aryl iodi

Full text of DOI:10.1016/j.jorganchem.2017.10.028

Journal of Organometallic Chemistry 853 (2017) 74e80
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Mercuration of ferrocenyl-p-tolyl sulfoxide and its conversion to
1,2-disubstituted ferrocenes
Venkatesan Sathesh 1, Ramu V. Ranga Naidu Chinta 1, Ramesh Mamidala,
Vanga Mukundam, Kunchala Dhanunjayarao, Krishnan Venkatasubbaiah*
School of Chemical Sciences, National Institute of Science Education and Research (NISER), HBNI, Bhubaneswar 752050, Orissa, India
a r t i c l e i n f o
a b s t r a c t
Article history:
1-(p-Tolylsulfinyl)-2-(chloromercurio)ferrocene (2) was prepared by direct mercuration of ferroce-
nylsulfoxide (1). This reaction can be performed at room temperature in open air. Cross-coupling re-
actions of compound 2 and aryl halides especially aryl iodides resulted in 1,2-disubstituted ferrocene
derivatives with moderate to good yields.
Received 2 August 2017
Received in revised form
18 October 2017
Accepted 19 October 2017
Available online 21 October 2017
© 2017 Elsevier B.V. All rights reserved.
Keywords:
Cyclomercurated ferrocene
1,2-disubstituted ferrocene
p-tolylsulfinyl ferrocene
1. Introduction
1,2-disubstituted ferrocenes synthesized using this methodology
involved organo lithium reagents for the deprotonation of the
Ferrocene and its derivatives are of great interest in the fields of
materials science, catalysis, biomedical research and so on [1e3].
The interest in ferrocene continues to grow owing to its versatility
in the synthesis of numerous derivatives, reversible redox proper-
ties and thermal stability [4e6]. Different approaches have been
utilized to make 1,10 (or) 1,2 (or) 1,3-disubstituted ferrocenes.
Among the different disubstituted ferrocenes, 1,2-disubstiuted
ferrocenes have gained interest, since the pioneering work of
Ugi's diastereoselective generation of planar chirality [7]. ortho-
Metallation introduced by different chiral auxiliaries such as oxa-
zolines [8,9], hydrazones [10,11], sulfoxides [12], sulfoximines [13],
pyrrolidines [14], and acetals [15,16] have been most widely used as
the synthetic tool to make 1,2-disubstituted ferrocenes.
The sulfoxide methodology introduced by Kagan and co-
workers has the advantage to act as (1) an excellent diaster-
eoselective ortho-directing group to make planar chiral com-
pounds, (2) the sulfoxide group can be replaced by different
substituents to make 1,2-disubstituted compounds and (3) the
absolute configuration of the resultant 1,2-substituted ferrocenes
are always predictable [12]. However most of the achiral and chiral
ortho-position of the ferrocenyl ring [16e24]. Here we report the
synthesis of 1-(aryl)-2-(p-tolylsulfinyl)ferrocenes using direct
mercuration of ferrocenyl p-tolyl sulfoxide followed by palladium-
catalyzed cross-coupling of 1-(p-tolylsulfinyl)-2-(chloromercurio)
ferrocene and aryl halides especially aryl iodides.
2. Experimental
2.1. Synthesis
2.1.1. General
All chemicals were used as received from commercially avail-
able sources. DL-menthol, ferrocene, tBu3SnCl were procured from
Sigma-Aldrich. All solvents were purified and dried according to
standard procedures. Ferrocenyl p-tolyl sulfoxide was prepared
according to literature procedure using menthyl-p-toluenesulfinate
prepared from DL-menthol [16,17]. NMR spectra were recorded on
Bruker 700 and ARX 400 spectrometers at room temperature. 1H
(700 MHz), 13C (176 MHz), 1H (400 MHz) and 13C (100 MHz) NMR
chemical shifts in ppm were referenced internally to its proton
resonance of incomplete deuterated solvent signals. In case of
compounds 2, 3c, 3d & 3h the splitting for Cp protons were not
observed due to fluxional behavior of the sulfoxide. Electrospray
ionization (ESI) mass spectra were recorded on a Bruker microTOF-
* Corresponding author.
E-mail address: krishv@niser.ac.in (K. Venkatasubbaiah).
These authors contributed equally.
1
https://doi.org/10.1016/j.jorganchem.2017.10.028
0022-328X/© 2017 Elsevier B.V. All rights reserved.

V. Sathesh et al. / Journal of Organometallic Chemistry 853 (2017) 74e80
75
QII spectrometer. Single crystal X-ray diffraction data were
collected on a Bruker APEX-II diffractometer. The data were
1.43 mmol) and Pd(PPh3)4 (0.012 g, 2.0 mol %). After refluxing for
2 h the title compound was purified by flash column chroma-
collected at 296 K using, Mo-K
a
radiation (0.71073 Å). Crystallo-
tography (n-hexane: EtOAc 4:1). Yield
¼
0.138
g
(90%),
graphic data for 2, 3a, & 5 and details of X-ray diffraction experi-
ments and crystal structure refinements are given in Table S1. Using
Olex2, the structures were solved with the ShelXS structure solu-
tion program using Direct Methods and refined with the ShelXL
refinement package using Least Squares minimization. All non-
hydrogen atoms were refined with anisotropic displacement co-
efficients. The H atoms were placed at calculated positions and
were refined as riding atoms. Crystallographic data for the struc-
tures of 2, 3a, & 5 have been deposited with the Cambridge Crys-
tallographic Data Center as supplementary publication no. CCDC-
1565373, 1565374, 1526742. Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax (þ44) 1223-336-033; email: deposit@ccdc.cam.ac.uk):
(Caution: Organomercurials are highly toxic, hence appropriate
handling should be followed for their generation and disposal).
mp ¼ 189e190 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 7.69 (d,
J ¼ 7.0 Hz, 2H, ArH), 7.44 (d, J ¼ 7.0 Hz, 2H, ArH), 7.01 (d, J ¼ 7.0 Hz,
2H, ArH), 6.73 (d, J ¼ 7.0 Hz, 2H, ArH), 4.22 (dd, J ¼ 2.7, 1.6 Hz, 1H,
Cp), 4.15 (dd, J ¼ 2.6, 1.6 Hz, 1H, Cp), 4.00 (s, 5H, Cp), 3.95 (t,
J ¼ 2.6 Hz,1H, Cp),1.85 (s, 3H, CH3). 13C NMR (176 MHz, Benzene-d6)
d
¼ 142.7, 142.2, 141.1, 132.2, 131.0, 129.9, 125.8, 119.6, 111.4, 95.5
(Cp), 86.6 (Cp), 73.6 (Cp), 72.4 (Cp), 72.3 (Cp), 70.3 (Cp), 21.5 (CH3).
HR-MS (ESI): calcd. for C23H19FeNOS ([MþH]þ): 426.0610, found:
426.0635.
Synthesis of 1-(4-cyanophenyl)-2-(p-tolylsulfinyl)ferrocene (3a)
from 4-bromobenzonitrile: The quantities involved are as follows.
Compound 2 (0.150 g, 0.27 mmol), 4-bromobenzonitrile (0.122 g,
0.67 mmol), sodium iodide (0.161 g, 1.07 mmol) and Pd(PPh3)4
(0.006 g, 2.0 mol%). After refluxing for 2 h the title compound was
purified by flash column chromatography (n-hexane: EtOAc 4:1).
Yield ¼ 0.055 g (48%).
2.1.2. Synthesis of 1-(p-tolylsulfinyl)-2-(chloromercurio)ferrocene
(2)
1-(Phenyl)-2-(p-tolylsulfinyl)ferrocene (3b): The quantities
involved are as follows. Compound 2 (0.200 g, 0.36 mmol), iodo-
benzene (0.182 g, 0.89 mmol), sodium iodide (0.214 g, 1.43 mmol)
and Pd(PPh3)4 (0.009 g, 2.0 mol %). After refluxing for 12 h the title
compound was purified by flash column chromatography (n-hex-
ane:EtOAc 4:1). Yield ¼ 0.110 g (76%), mp ¼ 163e164 ꢀC. 1H NMR
Ferrocenyl p-tolyl sulfoxide (1) (0.32 g, 1.0 mmol) was dissolved
in 5 mL of dichloromethane, in 100 mL two necked round bottom
flask fitted with a magnetic stirrer and an equilibrated addition
funnel. Hg(OAc)2 (0.32 g, 1.0 mmol) was dissolved in a sufficient
amount of MeOH. This solution was added dropwise to compound
1, over a period of 25 min in open air. Then, 0.08 g of LiCl (2.0 mmol)
dissolved in MeOH, was added through addition flask over 20 min
and the stirring was continued for 24 h. Finally the solvents were
evaporated under reduced pressure and the resulting crude
mixture was dissolved in dichloromethane (10 mL), filtered
through frit to remove the insoluble salts. The solution was trans-
ferred to a separating funnel, then 50 mL of water was added. The
organic layer was separated and the process was repeated twice.
The collected organic fractions were dried over Na2SO4. The
resulting solution was evaporated in vacuo and subjected to a flash
column chromatography on silica gel, eluted with n-hexane/eth-
ylacetate (4:1 ratio). The first band was collected and afforded the
title compound 2 in 40% yield (0.22 g, 0.4 mmol). The crude yellow
solid was recrystallized from dichloromethane and n-hexane 1:0.2
ratio to afford the corresponding compound 2 as a reddish yellow
(700 MHz, Benzene-d6)
d
¼ 8.01 (m, 2H, ArH), 7.63 (d, J ¼ 8.1 Hz, 2H,
ArH), 7.18 (d, J ¼ 8.1 Hz, 2H, ArH), 7.06 (m, 1H, ArH), 6.79 (d,
J ¼ 8.1 Hz, 2H, ArH), 4.37 (dd, J ¼ 2.6, 1.5 Hz, 1H, Cp), 4.12 (dd, J ¼ 2.7,
1.5 Hz,1H, Cp), 4.01 (s, 5H, Cp), 3.96 (t, J ¼ 2.6 Hz,1H, Cp),1.91 (s, 3H,
CH3). 13C NMR (176 MHz, Benzene-d6)
d
¼ 142.6, 140.9, 137.3, 131.0,
129.8, 128.9, 127.9, 126.3, 94.6 (Cp), 90.0 (Cp), 72.6 (Cp), 72.1 (Cp),
71.7 (Cp), 69.6 (Cp), 21.6 (CH3). HR-MS (ESI): calcd. for C23H20FeOS
([MþH]þ): 401.0657, found: 401.0672.
Synthesis of 1-(phenyl)-2-(p-tolylsulfinyl)ferrocene (3b) from
bromobenzene: The quantities involved are as follows. Compound
2 (0.150 g, 0.27 mmol), bromobenzene (0.105 g, 0.67 mmol), sodium
iodide (0.161 g, 1.07 mmol) and Pd(PPh3)4 (0.006 g, 2.0 mol%). After
refluxing for 12 h the title compound was not observed.
1-(4-Florophenyl)-2-(p-tolylsulfinyl)ferrocene (3c): The quan-
tities involved are as follows. Compound 2 (0.280 g, 0.5 mmol), 1-
fluoro-4-iodobenzene (0.280 g, 1.25 mmol), sodium iodide
(0.300 g, 2.0 mmol) and Pd(PPh3)4 (0.012 g, 2.0 mol%). After
refluxing for 4 h the title compound was purified by flash column
chromatography (n-hexane: EtOAc 4:1). Yield ¼ 0.160 g (76%),
crystals. mp ¼ 159e160 ꢀC. 1H NMR (700 MHz, Benzene-d6)
¼ 7.38
d
(d, J ¼ 7.9 Hz, 2H, ArH), 6.76 (d, J ¼ 7.9 Hz, 2H, ArH), 4.32 (s, 1H, Cp),
4.05 (s, 5H, Cp), 3.96 (s, 1H, Cp), 3.62 (s, 1H, Cp), 1.86 (s, 3H, CH3). 13
NMR (176 MHz, Benzene-d6)
C
d
¼ 144.9, 141.1, 130.3, 123.9, 99.6 (Cp),
mp ¼ 148e149 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 7.80 (d,
76.6 (Cp), 75.1 (Cp), 73.0 (Cp), 70.8 (Cp), 69.0 (Cp), 21.2(CH3). HR-MS
(ESI): calcd. for C17H15ClFeHgSO ([M]þ): 559.9656, found: 559.9628.
J ¼ 8.4 Hz, 2H, ArH), 7.54 (d, J ¼ 7.7 Hz, 2H, ArH), 6.80 (d, J ¼ 8.4 Hz,
2H, ArH), 6.76 (d, J ¼ 7.7 Hz, 2H, ArH), 4.24 (s, 1H, Cp), 4.15 (s, 1H,
Cp), 4.03 (s, 5H, Cp), 3.94 (s, 1H, Cp), 1.88 (s, 3H, CH3). 13C NMR
2.1.3. General procedure: Cross-coupling reaction between 1-(p-
tolylsulfinyl)-2-(chloromercurio)ferrocene and electrophiles
catalyzed by Pd(0)
(176 MHz, Benzene-d6)
d
¼ 163.7 (d, J ¼ 246 Hz), 142.5, 140.9, 133.2
(d, J ¼ 3 Hz), 132.7 (d, J ¼ 8 Hz), 129.8, 126.3, 126.0, 115.5 (d,
J ¼ 21 Hz), 94.6 (Cp), 88.8 (Cp), 72.4 (Cp), 72.1 (Cp), 72.1 (Cp), 69.5
(Cp), 21.6 (CH3). HR-MS (ESI): calcd. for C23H19FFeOS ([MþH]þ):
419.6452, found: 419.6469.
1-(4-Bromophenyl)-2-(p-tolylsulfinyl)ferrocene
quantities involved are as follows. Compound
In a Schlenk tube 0.5 mmol of compound 2, 1.25 mmol of ArI,
2.0 mmol of NaI and Pd(PPh3)4 (2 mol %) were placed. Subse-
quently, 3 mL of dry THF and 2 mL of dry acetone were added and
the reaction mixture was refluxed for the time mentioned in the
procedure. The reaction mixture was filtered through a pad of silica,
washed with 2 ꢁ 20 mL of THF and the resultant filtrate was
concentrated. The crude product was purified by flash column
chromatography using n-hexane and ethyl acetate as an eluent to
afford the desired 1,2-disubstituted ferrocenyl product.
(3d):
The
2 (0.400 g,
0.72 mmol), 1-bromo-4-iodobenzene (0.484 g, 1.78 mmol), sodium
iodide (0.430 g, 2.86 mmol) and Pd(PPh3)4 (0.017 g, 2.0 mol %). After
refluxing for 4 h the title compound was purified by flash column
chromatography (hexane: EtOAc 4:1). Yield ¼ 0.291 g (85%),
mp ¼ 155e156 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 7.69 (d,
J ¼ 8.0 Hz, 2H, ArH), 7.53 (d, J ¼ 7.8 Hz, 2H, ArH), 7.25 (d, J ¼ 8.0 Hz,
2H, ArH), 6.75 (d, J ¼ 7.8 Hz, 2H, ArH), 4.21 (s, 1H, Cp), 4.16 (s, 1H,
Cp), 4.01 (s, 5H, Cp), 3.93 (s, 1H, Cp), 1.87 (s, 3H, CH3). 13C NMR
2.1.4. 1,2-disubstituted p-tolylsulfinyl ferrocene derivatives
1-(4-Cyanophenyl)-2-(p-tolylsulfinyl)ferrocene (3a): The quan-
tities involved are as follows. Compound 2 (0.200 g, 0.36 mmol), 4-
iodobenzonitrile (0.204 g, 0.89 mmol), sodium iodide (0.214 g,
(176 MHz, Benzene-d6)
125.2, 121.0, 94.0 (Cp), 87.3 (Cp), 71.6 (Cp), 71.4 (Cp), 71.3 (Cp), 68.9
d
¼ 141.6, 140.2, 135.7, 131.7, 131.0, 129.0,

76
V. Sathesh et al. / Journal of Organometallic Chemistry 853 (2017) 74e80
(Cp), 20.7 (CH3). HR-MS (ESI): calcd. for C23H19BrFeOS ([MþH]þ):
478.9764, found: 478.9791.
Cp), 4.02 (s, 5H, Cp), 3.97 (s, 1H, Cp), 1.83 (s, 3H, CH3). 13C NMR
(176 MHz, Benzene-d6)
d
¼ 146.5, 144.2, 141.4, 140.3, 130.1, 129.1,
1-(4-Trifluoromethylphenyl)-2-(p-tolylsulfinyl)ferrocene (3e):
The quantities involved are as follows. Compound 2 (0.200 g,
0.36 mmol), 4-iodobenzotrifluoride (0.240 g, 0.89 mmol), sodium
iodide (0.214 g, 1.43 mmol) and Pd(PPh3)4 (0.012 g, 2.0 mol%). After
refluxing for 4 h the title compound was purified by flash column
chromatography (n-hexane: EtOAc 4:1). Yield ¼ 0.143 g (86%),
127.9, 124.9, 122.9, 95.0 (Cp), 85.0 (Cp), 73.2 (Cp), 71.7 (Cp), 71.5
(Cp), 69.5 (Cp), 20.6 (CH3). HR-MS (ESI): calcd. for C23H19FeNO3S
([MþH]þ): 446.0508, found: 446.0518.
1-(Tolyl)-2-(p-tolylsulfinyl)ferrocene (3i): The quantities
involved are as follows. Compound 2 (0.400 g, 0.72 mmol), 1-iodo-
4-methyl benzene (0.389 g, 1.78 mmol), sodium iodide (1.067 g,
2.86 mmol) and Pd(PPh3)4 (0.016 g, 2.0 mol%). After refluxing for
4 h the title compound was purified by flash column chroma-
mp ¼ 135e136 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 7.86 (d,
J ¼ 8.1 Hz, 2H), 7.50 (d, J ¼ 8.0 Hz, 2H), 7.32 (d, J ¼ 8.1 Hz, 2H), 6.73
(d, J ¼ 8.0 Hz, 2H), 4.23 (dd, J ¼ 2.6, 1.5 Hz, 1H, Cp), 4.21 (dd, J ¼ 2.6,
1.5 Hz,1H, Cp), 4.02 (s, 5H, Cp), 3.96 (t, J ¼ 2.6 Hz,1H, Cp),1.85 (s, 3H,
tography (n-hexane: EtOAc 3:1). Yield
¼
0.052
g
(17%),
mp ¼ 120e130 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 7.95 (d,
CH3). 13C NMR (176 MHz, Benzene-d6)
d
¼ 142.4, 141.8, 141.0, 131.1,
J ¼ 8.0 Hz, 2H), 7.67 (d, J ¼ 7.8 Hz, 2H), 7.03 (d, J ¼ 7.8 Hz, 2H), 6.81
(d, J ¼ 8.0 Hz, 2H), 4.41 (d, J ¼ 2.0 Hz,1H), 4.11 (t, J ¼ 2.1 Hz,1H), 4.02
(s, 5H), 3.97 (t, J ¼ 2.6 Hz, 1H), 2.10 (s, 3H), 1.91 (s, 3H). 13C NMR
129.8, 129.6, 129.4, 126.4, 125.9, 125.6 (q, J ¼ 3 Hz), 124.9, 95.3 (Cp),
87.4 (Cp), 73.0 (Cp), 72.5 (Cp), 72.3 (Cp), 70.0 (Cp), 21.5 (CH3). HR-
MS (ESI): calcd. for C24H19F3FeOS ([MþH]þ): 469.0531, found:
469.0521.
(176 MHz, Benzene-d6)
d
¼ 142.0, 140.3, 136.7, 133.6, 130.2, 129.2,
128.9, 125.7, 93.6 (Cp), 89.7 (Cp), 72.0 (Cp), 71.4 (Cp), 70.8 (Cp), 69.0
(Cp), 21.0 (CH3), 20.9 (CH3). HR-MS (ESI): calcd. for C24H22FeOS
([MþNa]þ): 437.0557, found: 437.0633.
Synthesis of 1-(4-trifluoromethylphenyl)-2-(p-tolylsulfinyl)
ferrocene (3e) from 4-bromobenzotrifluoride: The quantities
involved are as follows. Compound 2 (0.150 g, 0.27 mmol), 4-
bromobenzotrifluoride (0.151 g, 0.67 mmol), sodium iodide
(0.161 g, 1.07 mmol) and Pd(PPh3)4 (0.006 g, 2.0 mol %). After
refluxing for 4 h the title compound was purified by flash column
chromatography (n-hexane: EtOAc 4:1). Yield ¼ 0.036 g (28%).
1-(3-Trifluoromethylphenyl)-2-(p-tolylsulfinyl)ferrocene (3f):
The quantities involved are as follows. Compound 2 (0.200 g,
0.36 mmol), 3-iodobenzotrifluoride (0.240 g, 0.89 mmol), sodium
iodide (0.240 g, 1.4 mmol) and Pd(PPh3)4 (0.012 g, 2.0 mol %). After
refluxing for 12 h the title compound was purified by flash column
chromatography (n-hexane: EtOAc 4:1). Yield ¼ 0.125 g (75%),
Control Experiment (Synthesis of compound 5): In a Schlenk
tube, 0.280 g (0.50 mmol) of compound 2 and 0.300 g (2.0 mmol) of
NaI were placed. Subsequently 3 mL of dry THF and 2 mL of dry
acetone were added and the reaction mixture was refluxed for 12 h.
The reaction mixture was filtered through a pad of silica, washed
with 2 ꢁ 20 mL of THF and the resultant filtrate was concentrated.
The crude product was purified by flash column chromatography
using n-hexane and ethyl acetate as an eluent to afford the desired
product in 85% yield (0.23 g). mp. >230 ꢀC (decomposes). 1H NMR
(400 MHz, Benzene-d6):
d
¼ 7.58 (d, J ¼ 8 Hz, 2H, ArH), 6.84 (d,
J ¼ 8 Hz, 2H, ArH), 4.77 (s, 5H), 4.60 (s, 1H), 4.39 (s, 1H), 4.29 (s, 1H),
mp ¼ 138e140 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 8.16 (s, 1H,
4.05 (ferrocene impurity),1.90 (s, 3H, CH3) ppm. 13C NMR (100 MHz,
ArH), 8.12 (d, J ¼ 7.8 Hz, 1H, ArH), 7.47 (d, J ¼ 7.2 Hz, 2H, ArH), 7.20
(d, J ¼ 7.8 Hz, 1H, ArH), 6.95 (t, J ¼ 7.8 Hz, 1H, ArH), 6.73 (d,
J ¼ 7.2 Hz, 2H, ArH), 4.26 (dd, J ¼ 2.8,1.6 Hz,1H, Cp), 4.19 (dd, J ¼ 2.8,
1.6 Hz, 1H, Cp), 4.05 (s, 5H, Cp), 3.95 (t, J ¼ 2.8, 1H, Cp), 1.86 (s, 3H,
Benzene-d6):
d
¼ 146.2,140.1, 129.7, 124.2,102.7 (Cp), 95.4 (Cp), 77.5
(Cp), 72.6 (Cp), 70.6 (Cp), 69.7 (Cp), 21.0 (CH3) ppm. HR-MS (ESI):
calcd. for C34H30Fe2HgO2S2 ([MþH]þ): 849.0169, found: 849.0157.
CH3). 13C NMR (176 MHz, Benzene-d6)
d
¼ 142.0, 140.4, 138.3, 134.0,
3. Results and discussion
130.7, 130.6, 130.4, 129.4, 127.5, 127.1 (q, J ¼ 4 Hz), 126.0,125.3,123.9
(q, J ¼ 3 Hz), 94.4 (Cp), 86.7 (Cp), 72.3 (Cp), 71.4 (Cp), 71.4 (Cp), 69.0
(Cp), 20.6 (CH3). HR-MS (ESI): calcd. for C24H19F3FeOS ([MþH]þ):
469.0531, found: 469.0599.
3.1. Synthesis and characterization of compound 2
Ortho-mercuration of substituted ferrocenes [25], attract a great
deal of interest owing to the fact that they can be used a) to syn-
thesis other organometallic compounds through trasmetallation
and b) as reagents in organic synthesis. Although, synthesis of
ortho-mercury ferrocene using different functionalities like azo-
benzenes, benzylideneanilines, phenylhydrazenes etc. have been
reported [25]; however, to the best of our knowledge, there are no
reports on the ortho-mercuration of ferrocenyl p-tolyl sulfoxide.
The starting compound ferrocenyl p-tolyl sulfoxide (1) has been
synthesized using the well-established Kagan and co-workers
methodology [15]. Ortho-mercuration of the sulfinyl ferrocene
proceeded smoothly to produce 2-chloromercurated ferroce-
nylsulfoxide (2) in moderate yield (Scheme 1). The 1H NMR of
compound 2 shows three signals of equal intensity for the
1-(2-Trifluoromethylphenyl)-2-(p-tolylsulfinyl)ferrocene (3g):
The quantities involved are as follows. Compound 2 (0.200 g,
0.36 mmol), 2-iodobenzotrifluoride (0.240 g, 0.89 mmol), sodium
iodide (0.214 g, 1.4 mmol) and Pd(PPh3)4 (0.012 g, 2.0 mol %). After
refluxing for 12 h the title compound was purified by flash column
chromatography (n-hexane: EtOAc 4:1). Yield ¼ 0.040 g (27%),
mp ¼ 135e136 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 8.70 (d,
J ¼ 7.8 Hz, 1H, ArH), 7.24 (t, J ¼ 7.7 Hz, 1H, ArH), 7.20 (d, J ¼ 7.9 Hz,
1H, ArH), 7.10 (d, J ¼ 7.9 Hz, 2H, ArH), 6.88 (t, J ¼ 7.7 Hz, 1H, ArH),
6.66 (d, J ¼ 7.9 Hz, 2H, ArH), 4.46 (dd, J ¼ 2.6 Hz, 1H, Cp), 4.37 (dd,
J ¼ 2.6 Hz, 1.5 Hz, 1H, Cp), 4.26 (s, 5H, Cp), 3.96 (t, J ¼ 2.6 Hz, 1H, Cp),
1.89 (s, 3H, CH3). 13C NMR (176 MHz, Benzene-d6)
d
¼ 141.7, 139.7,
138.3,134.1, 130.6,130.1, 128.9,127.7,125.0 (q, J ¼ 6 Hz),124.3, 123.9,
96.8 (Cp), 87.9 (Cp), 73.1 (Cp), 71.8 (Cp), 71.6 (Cp), 68.3 (Cp), 21.0
(CH3). HR-MS (ESI): calcd. for C24H19F3FeOS ([MþH]þ): 469.0531,
found: 469.0477.
1-(4-Nitrophenyl)-2-(p-tolylsulfinyl)ferrocene (3h): The quan-
tities involved are as follows. Compound 2 (0.280 g, 0.5 mmol), 1-
iodo-4-nitrobenzene (0.310 g, 1.25 mmol), sodium iodide
(0.300 g, 2.0 mmol) and Pd(PPh3)4 (0.012 g, 2.0 mol%). After
refluxing for 4 h the title compound was purified by flash column
chromatography (n-hexane: EtOAc 3:1). Yield ¼ 0.17 g (76%),
mp ¼ 205e206 ꢀC. 1H NMR (700 MHz, Benzene-d6)
d
¼ 7.84 (d,
J ¼ 8.7 Hz, 2H, ArH), 7.74 (d, J ¼ 8.7 Hz, 2H, ArH), 7.46 (d, J ¼ 7.9 Hz,
2H, ArH), 6.72 (d, J ¼ 7.9 Hz, 2H, ArH), 4.26 (s, 1H, Cp), 4.18 (s, 1H,
Scheme 1. Synthesis of 1-(p-tolylsulfinyl)-2-(chloromercurio)ferrocene (2).

V. Sathesh et al. / Journal of Organometallic Chemistry 853 (2017) 74e80
77
substituted Cp ring (
the unsubstituted Cp ring at
d
¼ 4.33, 3.96, & 3.62 ppm) and one signal for
¼ 4.05 ppm, which is consistent with
been reported in the literature [19,28e30]. We believe that this
oxygen-mercury interaction is responsible for the ortho-mercura-
tion of compound 1 into compound 2.
d
1,2-disubstituted ferrocenes. Single crystal X-ray diffraction anal-
ysis was carried out to confirm the formation of compound 2. As
shown in Fig. 1, the oxygen (O) atom points towards the mercury
(Hg) atom. The distance between O and Hg atom (2.875 (5) Å) is
shorter than the sum of the van der Waals radii (for Hg 1.73e2.00 Å
[26]; for O 1.54 Å [27]), thus indicating an interaction between the
oxygen and the mercury atom. Such type of weak interactions have
3.2. Reaction of compound 2 to form compound 3
Inspired by Beletskaya and co-workers [31] work, we tested
cross-coupling of 1-(p-tolylsulfinyl)-2-(chloromercurio)ferrocene
(2) with 4-iodobenzonitrile as the model substrate. We first
studied the reaction using 1.5 equivalents of CuO as an oxidant in
the presence of
5 mol % PdCl2(dppf) in anhydrous dime-
thylformamide (DMF) at 100 ꢀC under argon atmosphere but failed
to get the desired product (Table 1, entry 1). Various palladium
based catalysts, solvents, additives were screened and found that
the reaction proceeded smoothly with 2 mol % of Pd(PPh3)4
(Table 1, entry 6) in mixture of solvents (THF/acetone) at reflux
condition. To our delight, the desired product was isolated in 90%
yield. Under the above optimized reaction conditions, the scope
of substrates were investigated. As shown in Table 2, various
substituted aryl iodides bearing electron withdrawing groups were
converted to the corresponding products with good to moderate
isolated yields. The reaction of 4-iodobromobenzene with com-
pound 2 resulted in 1-(4-bromophenyl)-2-(p-tolylsulfinyl)ferro-
cene (3d) in high yield. p, m, o-Iodobenzotrifluorides were
converted to the corresponding products (3e, 3f & 3g) with mod-
erate yields. However, the o-iodobenzotrifluoride afforded only
low yield (27%). Reaction of 1-iodo-4-methylbenzene resulted in
the corresponding product 3i in low yield (17%). Aryl bromides
such as 4-bromobenzonitrile and 4-bromobenzotrifluoride got
converted to their respective products in 48% and 28% yields
respectively, however bromobenzene was not active enough to
give the desired product under the experimental conditions.
Moreover, aryl chlorides failed to afford the respective products
under the optimized conditions.
All coupled products (3a-3i) were confirmed using 1H, 13C and
HRMS. Product 3a, was further confirmed using single crystal X-ray
analysis (Fig. 2). The X-ray analysis revealed one molecule in the
asymmetric unit. The Cp//Cp tilt angle is 0.89ꢀ. The angle between
cyclopentadienyl (Cp) and the CN-phenyl group is 37.68ꢀ. The ox-
ygen atom on sulfur (-SO-) points upwards and the tolyl points
away from the CN-Phenyl (see Fig. 2).
Fig. 1. Molecular structure of compound 2 (ORTEP, 50% probability). Hydrogen atoms
are removed for clarity. Selected bond lengths (Å) and bond angles (ꢀ): Hg1-C1
2.035(5), Hg1-Cl1 2.308(1), S1-O1 1.489(3), C1-Hg1-Cl1 178.9(1).
Table 1
Cross-coupling reaction between 4-iodobenzonitrile and compound 2.a
CN
Cl
p-Tol
Hg
I
catalyst
O
S
p-Tol
Fe
+
solvent
O
S
Fe
CN
2
3a
S. No
Catalyst
Cat. Loading (mol %)
Additives (eq.)
Solventsb
Temp. (ꢀC)
Yield (%)c
1
2
3
4
5
6
PdCl2(dppf)
Pd(dba)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
5
5
5
5
5
2
CuO (1.5)
ZnCl2 (1.5)
K2CO3 (4)
NaI (4)
e
DMF
THF
THF
THF/Acetone
THF/Acetone
THF/Acetone
100
80
80
80
80
80
e
e
e
95
e
NaI (4)
90
a
Reaction conditions: Compound 2 (0.50 mmol), 4-iodobenzonitrile (1.25 mmol).
All reactions were carried out under inert atmosphere.
Isolated yield.
b
c

78
V. Sathesh et al. / Journal of Organometallic Chemistry 853 (2017) 74e80
Table 2
Cross-coupling reaction between different aryl halides and compound 2.
Cl
p-Tol
Hg
Ar
p-Tol
Pd(PPh3)4 (2 mol%)
O
S
O
S
Fe
Fe
3
+
ArI
NaI (4 eq.), THF/Acetone
2
CN
F
p-Tol
p-Tol
p-Tol
O
S
O
S
O
S
Fe
Fe
Fe
yieldb :76 %
: 0d %
yieldb : 90 %
: 48c %
yieldb : 76 %
3b
3a
3c
CF3
Br
F3C
p-Tol
p-Tol
p-Tol
O
S
O
S
O
S
Fe
Fe
Fe
yieldb : 85 %
yieldb : 75 %
yieldb : 86 %
3f
3d
3e
: 28e
%
NO2
F3C
p-Tol
p-Tol
p-Tol
O
O
S
S
O
S
Fe
Fe
Fe
yield b: 17 %
yieldb : 27 %
yield b: 76 %
3h
3i
3g
aReaction conditions: Compound 2 (0.10 mmol), aryl iodides (0.25 mmol), Pd(PPh3)4 (2 mol%), and NaI (0.40 mmol) in 1 mL dry acetone and 2 mL of dry THF at reflux condition.
bIsolated yield after flash column chromatography. c4-Bromobenzonitrile is used. dBromobenzene is used. e4-Bromobenzotrifluoride is used.
Fig. 2. Molecular structure of 3a (ORTEP, 50% probability). Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and bond angles (ꢀ): C1-S1 1.776(3), S1-
O1 1.494(2), C1-C2 1.449(3), C24-N1 1.139(4), C1-S1-O1 105.7(1), C1-S1-C11 106.9(1),
C2-C1-S1 123.3(2), N1-C24-C21 177.2(3).
Fig. 3. Molecular structure of 5 (ORTEP, 50% probability). Hydrogen atoms are omitted
for clarity. Selected bond lengths (Å) and bond angles (ꢀ): Hg1-C1 2.051(6), Hg1-C18
2.056(6), S1-O1 1.493(5), S2-O2 1.478(5), C1-Hg1-C18 173.7(2), Cpcentroid-Hg-C1 176.5,
Cpcentroid-Hg-C18 177.7.

V. Sathesh et al. / Journal of Organometallic Chemistry 853 (2017) 74e80
79
Scheme 2. Proposed mechanism for the palladium-catalyzed cross-coupling of compound 2 with aryl halides.
3.3. Proposed mechanism
Acknowledgements
We propose a plausible mechanism based on LC/MS, X-ray
analysis and based on the previous literature [31]. As shown in
Scheme 2, the mechanism for the cross-coupling of aryl halide and
compound 2 is analogous to other organometallic coupling re-
actions. To examine the species involved during transformation,
we recorded the ESI of the reaction mixture of one of the reactions
and found fragment ion of m/z ¼ 651.9037 and m/z ¼ 848.0237
which corresponds to compound 4 and 5 respectively (supporting
information).
KV thanks the Department of Science and Technology (DST),
New Delhi (SR/S2/RJN-49/2011 and SR/S1/IC-58/2012) and NISER
for financial support. RVRNC, RM, VM, KD thank CSIR, New Delhi for
research fellowship.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.jorganchem.2017.10.028.
We have found the formation of symmetrized (Fc-SO-tolyl))2Hg
(5) as a side product under our optimized reaction conditions
without the use of aryl iodide and palladium catalyst. It has been
reported in literature [32] that treatment of chloromercury organic
compounds in the presence of sodium iodide results in symme-
trization or dimerization or cyclization depending on the starting
materials. To know the role of compound 5, a control experiment
was carried out using compound 5 as the substrate and 4-
fluorophenyl iodide as the arylating agent. We found a higher
yield of product 3c under similar conditions discussed vide supra.
We are lucky enough to have the crystal structure of 5 also. As
shown in Fig. 3, two (tolyl sulfoxide) ferrocenyl moieties are linked
through a mercury atom. The Hg1-C1 (2.051 (6) Å) and Hg1-C18
(2.056(6) Å) bond lengths are comparable to those found in related
organomercury compounds [19,29,30]. The molecular structure of
compound 5 also shows the coordination to one of the oxygen
atoms with mercury atom. The Hg1/O1 (2.824(4) Å) bond length is
shorter than the sum of the van der Waals radii of Hg and O, where
as the Hg1/C18 bond length (3.374(6) Å) shows a very weak
interaction between O and Hg. The Cpcentroid-Hg-C angles of 176.5ꢀ
and 177.7ꢀ indicates almost linear coordination geometry at Hg,
however C1-Hg2-C18 angle of 173.6ꢀ reveals a slight tilting toward
O1 atom associated with binding of the eSO ligand.
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