New ferrocene based dithiolate ligands

Article abstract of DOI:10.1016/j.jorganchem.2011.12.003

The preparation and characterization of the three ferrocene based dithiolane complexes [(η⁵-_C5H₅) Fe(η⁵-_C5H₄)NHC(O)(CH₂)4CHS ₂CH₂CH₂]1, [(η⁵- _C5H₅)Fe(η⁵-_C5H ₄)CH₂OC(O)(CH₂)4CHS₂CH ₂CH₂] 2 and [(η⁵-_C5H ₅)Fe(η⁵-_C5H₄)NHC(O)(CH ₂)CHS₂CH₂CH₂] 3, with different spacer groups between the ferrocenyl moiety and the dithiolane unit, are reported. The complexation of 1 and 2, using the oxidative addition of the S-S bonds to Pt(0), is also described, leading to the square planar Pt(II) complexes [Pt(PPh₃)₂(S₂CH₂CH ₂CH-κ²-S,S)(CH₂)₄C(O) NH(η⁵-C₅H₄)Fe(η⁵-C ₅H₅)] 4 and [Pt(PPh₃)₂(S ₂CH₂CH₂CH-κ²-S,S)(CH ₂)₄C(O)OCH₂(η⁵-C ₅H₄)Fe(η⁵-C₅H₅)] 5, respectively. The reduction of the S-S bond in 1 and 2 yields the corresponding dithiols; these can be deprotonated and treated with ClSiMe₃ to prepare [(η⁵-C₅H₅)Fe(η⁵- C₅H₄)NHC(O)(CH₂)₄CH(SSiMe ₃)CH₂CH₂(SSiMe₃)] 7 and [(η⁵-C₅H₅)Fe(η⁵-C ₅H₄)CH₂OC(O)(CH₂) ₄CH(SSiMe₃)CH₂CH₂(SSiMe ₃)] 9, respectively. The complexes were characterized via NMR and UV-Vis absorption spectroscopy, cyclic voltammetry and single crystal X-ray diffraction for 1 and 4.

Full text of DOI:10.1016/j.jorganchem.2011.12.003

Journal of Organometallic Chemistry 703 (2012) 16e24
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
New ferrocene based dithiolate ligands
*
Bahareh Khalili Najafabadi, Mahdi Hesari, Mark S. Workentin, John F. Corrigan
Department of Chemistry, The University of Western Ontario, Richmond St N, London, Ontario, Canada N6A 5B7
a r t i c l e i n f o
a b s t r a c t
Article history:
The preparation and characterization of the three ferrocene based dithiolane complexes
½ð
h
5-C5H5ÞFeðh5ꢀC5H4ÞNHCðOÞðCH2Þ4CHS2CH2CH2ꢁ1,
½ðh5ꢀC5H5ÞFeð
h
5-C5H4ÞCH2OCðOÞðCH2Þ4
Received 21 October 2011
Received in revised form
1 December 2011
CHS2CH2CH2ꢁ 2 and ½ðh5ꢀC5H5ÞFeðh5ꢀC5H4ÞNHCðOÞðCH2ÞCHS2CH2CH2ꢁ 3, with different spacer groups
between the ferrocenyl moiety and the dithiolane unit, are reported. The complexation of 1 and 2,
using the oxidative addition of the SeS bonds to Pt(0), is also described, leading to the square planar
Accepted 2 December 2011
Pt(II) complexes [Pt(PPh3)2(S2CH2CH2CH-
(S2CH2CH2CH-
2-S,S)(CH2)4C(O)OCH2( 5-C5H4)Fe(
bond in 1 and 2 yields the corresponding dithiols; these can be deprotonated and treated with
ClSiMe3 to prepare [(
5-C5H5)Fe( 5-C5H4)NHC(O)(CH2)4CH(SSiMe3)CH2CH2(SSiMe3)] 7 and [( 5-C5H5)
Fe(
5-C5H4)CH2OC(O)(CH2)4CH(SSiMe3)CH2CH2(SSiMe3)] 9, respectively. The complexes were charac-
k
2-S,S)(CH2)4C(O)NH(
h h
5-C5H4)Fe( 5-C5H5)] 4 and [Pt(PPh3)2
Keywords:
Ferrocene
Dithiolane
Dithiolate
k
h
h
5-C5H5)] 5, respectively. The reduction of the SeS
h
h
h
h
Chalcogen
terized via NMR and UVeVis absorption spectroscopy, cyclic voltammetry and single crystal X-ray
diffraction for 1 and 4.
Cyclic voltammetry
Platinum(II)
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
directly onto gold surfaces via oxidation of the SeS bond, or from
the corresponding tetrathiol after reduction of the two S2 units.
The synthesis of substituted bis(
h
5-cyclopentadienyl)iron(II)
More recently, Kraatz and co-workers have coupled lipoic acid to
the amine unit in [Fe(C5H4CO2Me)(C5H4NH2)], and oxidatively
added the SeS bond onto Au nanoparticles for the electrochemical
detection of HIV-1 reverse transcriptase [6]. It is possible to model
such metal/sulfur surface chemistry processes with molecular
coordination chemistry by the reactions of dithiolanes with
a zero-valent platinum complex [7]. One of the significant features
of disulfide redox chemistry is the oxidative addition of the SeS
bond to low-valent metal centers, which can play an important
role in different areas such as medicinal chemistry and transition
metal catalysis [8e10]. In this work, we describe the synthesis and
characterization of ferrocene based dithiolanes containing an alkyl
spacer between the ferrocenyl unit and the chalcogen center and
their reaction chemistry with Pt(0).
(ferrocene) complexes continues to play an important role in
organometallic chemistry due in part to the ease of handling of
ferrocene complexes, the ease of functionalization and flexibility
of the cyclopentadienyl rings together with the accessible Fe(II)/
Fe(III) redox couple [1]. Because ferrocene displays greatly
adaptable synthetic chemistry, numerous functionalizations have
been incorporated for applications in different areas including
catalysis, sensing and biology [2]. For example, several successful
functionalizations of ferrocene have been reported by Beer and co-
workers for the selective sensing of both ionic and neutral species
[3]. Two factors are responsible for the recognition of anion or
neutral analytes by ferrocenyl compounds: H-bonding interactions
between the functional group (usually amide) on the ferrocene
based receptor and the analyte and, secondly, the electrostatic
attraction of the analyte to the oxidized form of ferrocene
(ferrocenium) [4]. In this vein, Beer, Davis and co-workers
2. Experimental
have illustrated that the bis(amido) ferrocene [Fe{(h
5-C5H4)
All syntheses were performed under a dinitrogen atmosphere
using standard Schlenk line and glove box techniques unless
otherwise stated. All chemicals were used as received from Strem
Chemicals and/or Aldrich. Tetrahydrofuran, diethyl ether, hexanes
and pentane purchased from Caledon were dried by passing
through packed columns of activated alumina using a commercially
available MBraun MB-SP Series solvent purification system.
Dichloromethane, chloroform and chloroform-d were purchased
NHC(O)(CH2)4CHS2CH2CH2}2] can be prepared from 1,10-dia-
minoferrocene and two equivalents of lipoic acid [5]. The disulfide
linkages can then be used to anchor the ferrocenylamido units
* Corresponding author. Tel.: þ1 519 661 2111x86387; fax: þ1 519 661 3022.
E-mail address: corrigan@uwo.ca (J.F. Corrigan).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.12.003

B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
17
from Caledon, and distilled over P2O5. Ferrocenyl amine, ferrocenyl
methanol and 2-(1,2-dithiolan-3-yl)acetic acid were prepared
following literature procedures [11e13]. Lipoic acid chloride was
prepared by modification of a published procedure using lipoic acid
and oxalyl chloride in toluene with DMF as a catalyst [14].
then diluted with 20 ml of dichloromethane and washed with 1 M
NaOH, saturated NaCl, 1 M HCl and NaCl aqueous solutions. The
organic layer was separated and dried over MgSO4. The solvent was
removed in vacuo yielding 0.27 g (86%) of compound 2 as an air-
stable orange oil.
1H and 13C{1H} NMR spectra were obtained on a Varian Mercury
400 MHz spectrometer and are reported in ppm. These spectra
were referenced internally to solvent peaks relative to SiMe4
1H NMR (400 MHz, CDCl3, 23 ꢂC)
d
¼ 4.87 (s, 2H), 4.24 (vt,
JHH ¼ 1.8 Hz, 2H), 4.15 (vt, JHH ¼ 1.8 Hz, 2H), 4.13 (s, 5H), 3.51 (m,
3
1H), 3.10 (m, 2H), 2.41 (m, 1H), 2.27 (t, JHH ¼ 7.2 Hz, 2H), 1.86 (m,
(
d
¼ 0 ppm). 31P{1H} NMR spectra were recorded on the same
1H), 1.64 (m, 4H), 1.41 (m, 2H). 13C{1H} NMR (100.5 MHz, CDCl3)
spectrometer and are referenced to 85% H3PO4
(d
¼ 0 ppm). An
d
¼ 172.8 (C(O)), 80.8 (CH2), 69.1 (CH), 68.4 (CH), 68.1 (Cp), 62.3 (C)
Autolab30 electrochemical workstation equipped with GPES 4.9
software was used for cyclic voltammetry (CV) experiments. A
homemade glassy carbon (GC, Tokai GC-20) working-electrode
3 mm in diameter was prepared by polishing over silicon carbide
papers (500, 1200, 2400 and 4000) followed by diamond paste
55.8 (CHS), 39.7 (CH2), 38.0 (CH2S), 34.1 (CH2), 33.6 (CH2), 28.2
(CH2), 24.2 (CH2). HRMS: Calcd for C19H24O2S2Fe (m/z): 404.0567
Found: 404.0562. Anal. Calc. (%) for C19H24O2S2Fe: C 56.38, H 5.94, S
15.83. Found: C 55.83, H 5.97, S 16.30.
(Struers, 1 and 0.25 mm). The GC electrodes were stored in ethanol
2.3. N-Ferrocenyl-rac-2-(1,2-dithiolane-3yl)ethylamide (3)
and polished before each set of experiments with the 0.25 mm
diamond paste (Struers), rinsed with dry ethanol (Commercial
Alcohols) and sonicated in dry ethanol for 5 min. An Ag wire and
a platinum wire served as the reference and counter electrodes,
respectively. Electrochemical experiments were carried out in dry
DCM (Caledon) containing 0.1 M tetrabutylammonium hexa-
fluorophosphate (TBAPF6) or tetrabutylammonium perchlorate
(TBAP) as the supporting electrolyte. Prior to each electrochemical
experiment, the solutions were saturated with 99.999% Ar gas for
15 min and the inert atmosphere was maintained during the
measurements.
Infrared (IR) absorption spectra were obtained on a Bruker
Vector 33 IR spectrophotometer in the solid state. A film of solid
was formed on the surface of a NaCl crystal cell by evaporating the
solvent of a concentrated solution of the compound of interest.
High-resolution mass spectra were recorded on a MAT8400 mass
spectrometer.
2-(1,2-Dithiolan-3-yl)acetic acid (0.14 g, 0.85 mmol) was dis-
solved in 10 ml of toluene to which DMF (0.01 ml, 20 mol %) was
added as a catalyst. Oxalyl chloride (0.09 ml, 1.02 mmol) in 3 ml of
toluene was added drop wise to the solution. It was stirred for
5e10 min (until no further gas was observed). This solution was
added to a mixture of ferrocenyl amine (0.14 g, 0.68 mmol) and
Et3N (0.12 ml, 0.85 mmol) in 10 ml of CH2Cl2 at 0 ꢂC. It was stirred at
0
ꢂC for 10 min and at room temperature for 25 h. After that the
solution was diluted with 15 ml of CH2Cl2, washed with 1 M NaOH,
saturated NaCl, 1 M HCl and NaCl aqueous solutions. The organic
layer was separated and the solvent was removed under vacuum.
The product was purified over a glass plate covered with silica gel in
2 steps, first with 1:4 ethylacetate/hexane solvent and then with
1:2.5 ethylacetate/hexane solvent for a better separation. Recrys-
tallization from CH2Cl2:heptane at ꢀ5 ꢂC yielded 3 as a microcrys-
talline orange solid (0.25 CH2Cl2 solvate from 1H NMR). Yield: 65%.
All reactions have been completed in subdued light due to the
sensitivity of SeS bonds in these compounds [15].
1H NMR (400 MHz, CDCl3, 23 ꢂC)
d
¼ 6.73 (br s, 1H), 4.69 (br s,
1H), 4.53 (br s, 1H), 4.18 (s, 5H), 4.14 (m, 1H), 4.02 (br s, 2H), 3.18 (m,
2H), 2.59 (m, 2H), 2.55 (m, 1H), 2.00 (m, 1H). HRMS: Calcd for
C15H17S2FeON (m/z): 347.0101 Found: 347.0101. Anal. Calc. (%) for
C15H17ONS2Fe$(CH2Cl2)0.25: C 49.70, H 4.79, N 3.80, S 17.40. Found:
C 50.71, H 4.63, N 3.89, S 17.97.
2.1. N-Ferrocenyl-rac-5-(1,2-dithiolan-3-yl)pentanamide (1)
Ferrocenyl amine (0.16 g, 0.77 mmol) was dissolved in 10 ml of
dichloromethane. Triethylamine (0.14 ml, 0.97 mmol) was added
and the yellow solution was cooled to 0 ꢂC. Freshly prepared lipoic
acid chloride (0.97 mmol) in toluene was added. The solution was
stirred at 0 ꢂC for 30 min and at room temperature for 20 h. It was
then diluted with 20 ml of dichloromethane and washed with 1 M
NaOH, saturated NaCl, 1 M HCl and NaCl aqueous solutions. The
organic layer was separated and dried over MgSO4. The solvent was
removed in vacuo yielding 0.20 g (66%) of compound 1 as an
orange-brown solid.
2.4. cis-(N-Ferrocenyl-rac-6,8-dithiolatooctaneamide)
bis(triphenylphosphine)platinum(II) (4)
0.20 g of [Pt(PPh3)4] (0.16 mmol) was dissolved in 15 ml of
benzene. 0.066 g of 1 (0.16 mmol) was added to the solution.
Compound 1 was completely dissolved after about 10 min of stir-
ring. The progress of the reaction was monitored by NMR spec-
troscopy. 1H and 31P NMR spectra indicated that the reaction was
complete after 20 h. The product was isolated by adding w15 ml of
pentane and removing the mother liquor from the purified product.
The dark orange solid was dissolved in a mixture of CHCl3 and
pentane (2:2.5) and cooled to ꢀ25 ꢂC to yield single crystals suit-
able for X-ray diffraction analysis. Yield ¼ 47%.
1H NMR (400 MHz, CDCl3, 5 mM, 23 ꢂC)
(vt, JHH ¼ 2.0 Hz, 2H), 4.14 (s, 5H), 3.98 (vt, JHH ¼ 2.0 Hz, 2H), 3.58
(m, 1H), 3.12 (m, 2H), 2.47 (m, 1H), 2.24 (td, 3JHH ¼ 7.4, 2JHH ¼ 1.6 Hz,
2H), 1.92 (m, 1H), 1.71 (m, 4H), 1.49 (m, 2H). 13C{1H} NMR
d
¼ 6.47 (br s, 1H), 4.57
(100.5 MHz, CDCl3)
d
¼ 170.9 (C(O)), 94.4 (CN), 69.1 (Cp), 64.5 (CH),
61.4 (CH), 56.4 (CHS), 40.2 (CH2), 38.5 (CH2S), 37.0 (CH2), 34.6 (CH2),
28.8 (CH2), 25.3 (CH2). HRMS: Calcd for C18H23ONS2Fe (m/z):
389.0570 Found: 389.0571. Anal. Calc. (%) for C18H23ONS2Fe: C
55.53, H 5.96, N 3.60, S 16.44. Found: C 55.65, H 5.90, N 3.56, S 16.41.
1H NMR (400 MHz, CDCl3, 23 ꢂC)
d
¼ 7.47 (t, 3JHH ¼ 7.6 Hz, 6H),
3
3
7.41 (t, JHH ¼ 7.6 Hz, 6H), 7.24 (m, 6H), 7.14 (t, JHH ¼ 7.6 Hz, 6H),
7.09 (t, 3JHH ¼ 7.6 Hz, 6H), 6.55 (s, 1H), 4.61 (s, 1H), 4.57 (s, 1H), 4.14
(s, 5H), 3.97 (s, 2H), 3.34 (m, 2H), 2.89 (m, 1H), 2.14 (m, 1H), 2.10 (t,
3JHH ¼ 7.8 Hz, 2H), 1.68 (m, 1H), 1.56 (m, 2H), 1.34 (m, 4H). 13C{1H}
2.2. Ferrocenemethyl rac-5-(1,2-dithiolane-3-yl)pentanoate (2) [16]
NMR (100.5 MHz, CDCl3)
127.5 (CH), 94.8 (CN), 69.1 (Cp), 64.2 (CH), 61.3 (CH), 39.6 (CHS),
d
¼ 171.6 (C(O)), 134.8 (CH), 130.0 (CH),
Ferrocenyl methanol (0.17 g, 0.77 mmol) was dissolved in 10 ml
of dichloromethane. Triethylamine (0.14 ml, 0.97 mmol) was added
and the yellow solution was cooled to 0 ꢂC. Freshly prepared lipoic
acid chloride (0.97 mmol) in toluene was added. The solution was
stirred at 0 ꢂC for 30 min and at room temperature for 20 h. It was
38.7 (CH2), 37.4 (CH2S), 27.5 (CH2), 26.0 (CH2), 25.3 (CH2), 24.5
2
(CH2). 31P{1H} NMR (CDCl3, 23 ꢂC)
d
¼ 24.8 (dd, JPP ¼ 21.0 Hz,
1JPPt ¼ 2865 Hz), 22.8 (dd, JPP ¼ 21.0 Hz, 1JPPt ¼ 2804 Hz). HRMS:
2
Calcd for C54H53FeNOP2PtS2 (m/z): 1108.2041 Found: 1108.2038.

18
B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
Anal. Calc. (%) for C54H53FeNOP2PtS2: C 58.47, H 4.82, N 1.26, S 5.77.
Found: C 57.30, H 4.51, N 1.11, S 4.89.
room temperature for 2 h. 1 M HCl (0.77 ml, 0.77 mmol) was then
added and the solution was stirred for 15 min. The solution was
diluted with 20 ml of degassed water and extracted with
dichloromethane (2 ꢃ 20 ml). The organic layers were combined,
dried over MgSO4 and the solvent was evaporated in vacuo to yield
8 as an orange oil. Yield ¼ 64%.
2.5. cis-(Ferrocenemethyl rac-6,8-dithiolatooctanoate)
bis(triphenylphosphine)platinum(II) (5)
[Pt(PPh3)4] (0.20 g, 0.16 mmol) was dissolved in 15 ml of
benzene. Compound 2 (0.65 g, 0.16 mmol) was added to the solu-
tion. It was stirred at room temperature for 20 h and NMR spec-
troscopy confirmed the completion of the reaction. The product
was purified by washing with pentane several times to yield 5 as
a dark brown oil, which invariably contained traces of Ph3P/Ph3PO
(as determined by 31P{1H} NMR spectroscopy) which could not be
separated chromatographically due to the instability of 5 on silica/
alumina. Yield ¼ 51%.
1H NMR (400 MHz, CDCl3, 23 ꢂC)
d
¼ 4.89 (s, 2H), 4.26 (vt,
JHH ¼ 2.0 Hz, 2H), 4.17 (vt, JHH ¼ 1.8 Hz, 2H), 4.15 (s, 5H), 2.89 (m,
3
1H), 2.74e2.64 (m, 2H), 2.29 (t, JHH ¼ 7.3 Hz, 2H), 1.88 (m, 1H),
1.61e1.73 (m, 4H), 1.55e1.45 (m, 3H), 1.33 (t, 3JHH ¼ 8.2 Hz, 1H), 1.27
3
(d, JHH ¼ 7.6 Hz, 1H). HRMS: Calcd for C19H26O2S2Fe (m/z):
406.0724 Found: 406.0735.
2.9. Ferrocenemethyl rac-6,8-trimethylsilylsulfooctanoate (9)
1H NMR (400 MHz, CDCl3, 23 ꢂC)
d
¼ 7.52e7.08 (m), 4.88 (s, 2H),
ClSiMe3 (0.15 ml, 1.15 mmol) was added to a stirred solution of
C19H26FeO2S2 (8) (0.12 g, 0.30 mmol) dissolved in 15 ml of CH2Cl2
with NEt3 (0.16 ml, 1.15 mmol) at 0 ꢂC. The solution was stirred at
0 ꢂC for 15 min and at room temperature for 3 h. 20 ml of heptane
was added and the CH2Cl2 was removed under vacuum. The
heptane solution was filtered and the solvent was evaporated in
vacuo to yield compound 9 as an orange oil. Yield ¼ 82%.
4.27 (vt, JHH ¼ 1.8 Hz, 2H), 4.17 (vt, JHH ¼ 1.9 Hz, 2H), 4.16 (s, 5H),
3
3.30 (m, 2H), 2.88 (m, 1H), 2.18 (t, JHH ¼ 7.8 Hz, 2H), 2.11 (m, 1H),
1.64 (m, 1H), 1.49 (m, 2H), 1.30 (m, 4H). 31P{1H} NMR (CDCl3, 23 ꢂC)
d
¼ 24.9 (dd, 2JPP ¼ 21.0 Hz, 1JPPt ¼ 2860 Hz), 22.8 (dd, 2JPP ¼ 21.0 Hz,
1JPPt ¼ 2801 Hz).
2.6. N-Ferrocenyl-rac-6,8-dithioloctaneamide (6)
1H NMR (CDCl3, 23 ꢂC)
d
¼ 4.88 (s, 2H), 4.25 (vt, JHH ¼ 1.8 Hz, 2H),
4.16 (vt, JHH ¼ 1.8 Hz, 2H), 4.15 (s, 5H), 2.82 (m, 1H), 2.60 (m, 2H),
3
The orange-brown solid C18H23FeNOS2 (1) (0.15 g, 0.38 mmol)
was dissolved in 10 ml of THF and a degassed solution of NaBH4
(0.029 g, 0.77 mmol) in 4 ml of water was added. The solution was
stirred at room temperature for 2 h. 1 M HCl (0.77 ml, 0.77 mmol)
was then added and the solution was stirred for 15 min. The
solution was diluted with 20 ml of degassed water and extracted
with dichloromethane (2 ꢃ 20 ml). The organic layers were
combined, dried over MgSO4 and the solvent was evaporated in
vacuo to yield 6 as an orange oil. Yield ¼ 81%.
2.28 (t, JHH ¼ 7.2 Hz, 2H), 1.78 (m, 2H), 1.60 (m, 4H), 1.41 (m, 2H),
0.31 (s, 9H), 0.30 (s, 9H). HRMS: Calcd for C25H42FeO2S2Si2 (m/z):
550.1514 Found: 550.1520.
2.10. Crystallography
Single crystal X-ray diffraction measurements were performed on
a Bruker APEXII diffractometer, with the molecular structures
determined via direct methods using the SHELX suite of crystallo-
graphic programs [17]. Single crystals of the complexes were
selected, immersed in paraffin oil and mounted on a nylon loop.
Crystals were placed in a cold stream of N2. Multiple data sets for 1
were collected but all crystals weakly diffracting, a consequence of
theirplate-likemorphology. With the exceptionofdisorderedcarbon
atoms of the alkyl chain (beginning at C151) and C3S2 rings in both
independent molecules in 1, all non-hydrogen atoms were refined
anisotropically, while hydrogen atoms were kept at their calculated
distances and refined using a riding model. Disordered atoms were
refined with occupancy 0.66667:0.33333 and common CeC and CeS
bond distances were restrained with the SADI command in SHELXTL.
Satisfactory refinement of the data for 1 was completed with the use
of a TWIN command and resultant BASF value of 0.12315. A summary
of the crystallographic data is presented in Table 1.
1H NMR (400 MHz, CDCl3, 23 ꢂC)
d
¼ 6.46 (br s, 1H), 4.61 (br s,
2H), 4.16 (s, 5H), 4.02 (vt, JHH ¼ 1.8 Hz, 2H), 2.94 (m, 1H), 2.75e2.65
(m, 2H), 2.24 (t, 3JHH ¼ 7.4 Hz, 2H), 1.88 (m, 1H), 1.76e1.65 (m, 4H),
1.60e1.48 (m, 3H), 1.34 (t, 3JHH ¼ 7.9 Hz, 1H), 1.30 (d, 3JHH ¼ 8.2 Hz,
1H). 13C{1H} NMR (100.5 MHz, CDCl3)
d
¼ 170.8 (C(O)), 94.5 (CN),
69.2 (Cp), 64.5 (CH), 61.4 (CH), 42.8 (CHS), 41.8 (CH2), 39.3 (CH2S),
38.8 (CH2), 37.1 (CH2), 26.6 (CH2), 25.22 (CH2). HRMS: Calcd for
C18H25ONS2Fe (m/z): 391.0727 Found: 391.0716.
2.7. N-Ferrocenyl-rac-6,8-trimethylsilylsulfooctanamide (7)
ClSiMe3 (0.15 ml, 1.15 mmol) was added to a stirred solution of
C18H25FeNOS2 (6) (0.11 g, 0.30 mmol) which was dissolved in 15 ml
of CH2Cl2 with NEt3 (0.16 ml, 1.15 mmol) at 0 ꢂC. The solution was
stirred at 0 ꢂC for 15 min and at room temperature for 3 h. 20 ml of
heptane was added and the CH2Cl2 was removed under vacuum.
The heptane solution was filtered and the solvent was evaporated
in vacuo to yield compound 7 as an orange oil. Yield ¼ 90%.
3. Results and discussion
3.1. Synthesis
1H NMR (400 MHz, CDCl3, 23 ꢂC)
d
¼ 6.53 (br s, 1H), 4.57 (m, 2H),
4.14 (s, 5H), 3.98 (vt, JHH ¼ 2.0 Hz, 2H), 3.55 (m, 1H), 2.86 (m, 2H),
Under exposure to light or with heat, the five-membered ring in
lipoic acid opens at the SeS junction and undergoes a polymeriza-
tion reaction [15]. Thus all reactions involving five-membered
dithiolane ring in the starting reagents and products were carried
out under subdued lighting conditions, and high reaction temper-
atures have been avoided. Ligands were synthesized via a coupling
reaction between a ferrocenyl unit and an acid chloride. Lipoic acid
chloride was synthesized using oxalyl chloride and DMF as a cata-
lyst. It has been shown previously that DMF can act as a catalyst in
the synthesis of acid chlorides using oxalyl chloride [18].
3
2.61 (m, 3H), 2.23 (t, JHH ¼ 7.6 Hz, 2H), 1.86 (m, 1H), 1.68 (m, 2H),
1.52 (m, 2H), 0.31(s, 9H), 0.30(s, 9H). 13C{1H} NMR (100.5 MHz,
CDCl3)
d
¼ 111.0 (CN), 69.1 (Cp), 64.5 (CH), 62.6 (CH), 61.4 (CHS), 41.4
(CH2), 38.2 (CH2S), 37.2 (CH2), 32.7 (CH2), 26.4 (CH2), 25.6 (CH2), 1.7
(CH3), 1.0 (CH3). HRMS: Calcd for C24H41FeNOS2Si2 (m/z): 535.1517
Found: 535.1525.
2.8. Ferrocenemethyl rac-6,8-dithioloctanoate (8)
The orange oil C19H24FeO2S2 (2) (0.15 g, 0.38 mmol) was dis-
solved in 10 ml of THF and a degassed solution of NaBH4 (0.029 g,
0.77 mmol) in 4 ml of water was added. The solution was stirred at
The ferrocenyl complex 1 was obtained as an air stable orange
solid in 66% yield, starting from ferrocenyl amine [11] and lipoic
acid chloride (Scheme 1) and fully characterized.

B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
19
Table 1
Compound 2 was synthesized following a similar procedure
using freshly prepared lipoic acid chloride, ferrocenyl methanol [12]
and triethylamine. The ferrocenyl ester has previously been re-
ported using a N,N0-dicylcohexylcarbodiimide coupling procedure,
although yields were not reported [16]. Here, the product was ob-
tained as an air-stable, orange oil in 86% yield. For the synthesis of 3,
2-(1,2-dithiolan-3-yl)acetic acid [13] was converted to the related
acid chloride and a coupling reactionwas completed with ferrocenyl
amine yield the shorter chain ferrocenyl amide in 66% yield.
The first example of the oxidative addition of a disulfide linkage to
Pt(0) was reported in 1964 by Davison et al. [19] and this is nowawell
developed strategy for the complexation of thiolate ligands onto
electron rich platinum metal centers [7,20e22]. Recently, Weigand
and co-workers published the reaction of a 1,2-dithiolane derivative
with a Pt(0) source leading to the cis mononuclear complex of plat-
inum [(Ph3P)2Pt(eSeCH2eCHPheCH2eSe)] [21] and we success-
fully targeted reactions of the disulfide complexes 1 and 2 with Pt(0).
The oxidative addition of 1 and 2 (Scheme 2) was carried out by
dissolving [Pt(PPh3)4] in benzene followed by the addition of the
disulfide reagents. The progress of these reactions was easily fol-
lowed by 31P NMR spectroscopy, which indicated the reactions were
complete after w20 h of stirring at room temperature.
Selected crystal data, data collection and refinement parameters for 1 and 4.
1
4. 3.5 CHCl3
Formula
Mr
T [K]
C18H23FeNOS2
389.34
150(2)
0.71073
Orthorhombic
Pca2(1)
10.0366(10)
11.1816(11)
31.259(3)
90
90
90
3508.1(6)
8
1.474
1.101
1632
0.09 ꢃ 0.08 ꢃ 0.03
1.82e28.72
ꢀ13ꢄhꢄ13,
ꢀ15ꢄkꢄ15,
ꢀ42ꢄlꢄ42
80,156
C57.5H56.5Cl10.5FeNOP2PtS2
1526.76
150(2)
0.71073
Triclinic
l
(MoKa) [Å]
Crystal system
Space group
A [Å]
B [Å]
C [Å]
P ꢀ 1
16.910(3)
20.310(4)
20.370(4)
90.122(9)
103.733(6)
111.205(5)
6306(2)
a
b
g
[ꢂ]
[ꢂ]
[ꢂ]
V [Å3]
Z
4
rcaled (g cmꢀ3
)
1.608
3.047
3044
m
[mmꢀ1
]
F (000)
Crystal size mm3
range [ꢂ]
0.10 ꢃ 0.06 ꢃ 0.05
1.03e31.70
ꢀ24ꢄhꢄ24, ꢀ29ꢄkꢄ29,
ꢀ30ꢄlꢄ29
2
q
Index ranges
Collected reflections
Unique reflections
Rint
Restraints
Parameters
GOF
353,324
42,107
0.1624
0
1369
1.007
9059
0.0548
63
424
As reported by Beer et al. for ½Fefð
h
5-C5H4ÞNHCðOÞðCH2Þ4
CHS2CH2CH2g2ꢁ [5], reduction of the disulfide linkages in 1 and 2 can
be carried out with NaBH4 to yield the corresponding dithiols after
acidic work-up (Scheme 3). The formation of dithiols [(
C5H4)NHC(O)(CH2)4CH(SH)CH2CH2(SH)] 6 and [( h
h -
5-C5H5)Fe(h5
1.086
h
5-C5H5)Fe( 5-C5H4)
R1 [I > 2
s
(I)]
R1 ¼ 0.0608,
wR2 ¼ 0.1442
R1 ¼ 0.0764,
wR2 ¼ 0.1519
1.057 and ꢀ1.194
R1 ¼ 0.0550, wR2 ¼ 0.1094
CH2OC(O)(CH2)4CH(SH)CH2CH2(SH)] 8 was indicated by the appear-
ance of peaks assigned to eSH at w1.30 ppm in their 1H NMR spectra
(seediscussionbelow). Thedithiols couldalsobereacted with ClSiMe3
in the presence of base to yield the corresponding silylated reagents
wR2 all
R1 ¼ 0.1275, wR2 ¼ 0.1393
2.805 and ꢀ1.791
Max/min electron
density (e Åꢀ3
)
[(
h
5-C5H5)Fe(
h 7
5-C5H4)NHC(O)(CH2)4CH(SSiMe3)CH2CH2(SSiMe3)]
and [(
h
5-C5H5)Fe( 5-C5H4)CH2OC(O)(CH2)4CH(SSiMe3)CH2CH2(SSi-
h
Me3)] 9, respectively (Scheme 3).
S
S
H
N
S
S
NH2
Cl
1
O
Toluene/CH2Cl2
+
Fe
Fe
+
under N2/in dark
20 hr.
O
[NEt3H][Cl]
+ Et3N
S
S
S
CH2OH
S
O
Cl
+
Toluene/CH2Cl2
Fe
Fe
O
2
under N2/in dark
20 hr.
O
+ Et3N
+
[NEt3H][Cl]
H
N
NH2
Cl
Toluene/CH2Cl2
+
+
[NEt3H][Cl]
O
S
Fe
Fe
S
under N2/in dark
20 hr.
O
S
S
3
+ Et3N
Scheme 1. Synthesis of 1e3.

20
B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
PPh3
S
Ph3P
Pt
S
S
S
H
N
H
N
C6H6
O
O
+ Pt(PPh3)4
Fe
Fe
4
20 hr.
at r.t.
+ 2 PPh3
O
O
O
O
C6H6
S
+ Pt(PPh3)4
S
Fe
S
Fe
S
5
20 hr.
at r.t.
Pt
Ph3P
PPh3
+ 2 PPh3
Scheme 2. Oxidative addition of 1 and 2 to [Pt(PPh3)4].
S
S
SH
SH
H
N
H
N
O
+
+
2NaBH4
2HCl
THF/water
O
Fe
6
2NaCl +
B2H6+H2
Fe
+
in dark/2 hr.
SH
SH
SSiMe3 SSiMe3
H
H
N
N
O
7
CH2Cl2
O
Fe
Fe
+
Fe
+
at r.t./3 hr.
2 [NEt3H][Cl]
2ClSiMe3 + 2NEt3
S
S
SH
SH
O
O
+
+
2NaBH4
2HCl
THF/water
Fe
O
2NaCl +
B2H6+H2
+
in dark/2 hr.
O
8
SH
SH
SSiMe3 SSiMe3
O
O
Fe
CH2Cl2
at r.t./3 hr.
Fe
O
+ 2ClSiMe3 + 2NEt3
+
O
2 [NEt3H][Cl]
9
Scheme 3. Synthesis of 6e9.

B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
21
Fig. 1. 1H NMR spectrum of 5 mM of 1 in CDCl3.
3.2. Characterization
The 1H NMR spectrum of 2 displays similar pattern in the
aliphatic region to those reported for 1, with a very slight shift in the
chemical shifts due to the presence of an ester linkage versus the
amide functional group. The two hydrogen atoms in the CH2 spacer
bonded to the cyclopentadienyl ring and eC(O)Oe group are
assigned to the signal at 4.87 ppm (singlet). The peaks for the
hydrogen atoms in the ferrocenyl group are assigned in Fig. S1. The
1H NMR spectrum of 3 was analyzed using gcosy techniques and
assigned via comparison with values reported for similar
compounds [13]. The assigned 1H NMR spectrum of 3 is shown in
Fig. S2.
All complexes were characterized by NMR spectroscopy and
chemical shift data were obtained at room temperature in CDCl3.
Due to the complex aliphatic region in their 1H NMR spectra, 2D
NMR spectroscopic methods were used for the assignment of the
signals. All peaks in the 1H NMR spectra were assigned
completely using gcosy and gHSQC techniques. The 1H NMR
spectrum of 1 (Fig. 1) shows a slight downfield shift of the proton
peaks of the substituted cyclopentadienyl ring versus those of
ferrocenyl amine [11]. The peak for the amino group in FcNH2 at
2.60 ppm has disappeared and a signal at 6.47 ppm is readily
assigned to the presence of the amide. All assigned peaks are
illustrated in Fig. 1.
31P NMR spectroscopy was particularly useful for confirming the
formation of 4 and 5. 1H and 13C{1H} NMR spectra of 4 and 5 show
similar patterns to the spectra of 1 and 2 with slight shift in the
Fig. 2. 31P{1H} NMR spectrum of 4 in CDCl3.

22
B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
spectrum of 4 is shown in Fig. 2. The observed coupling constant
values are in close agreement with those reported for related
square planar Pt(II) complexes with two cis-phosphine ligands
trans to two ligands with different trans influences [7,21,23,24].
The formation of 6e9 was also followed by NMR spectroscopy.
Formation of the dithiols was confirmed by the appearance of
signals assigned to eSH groups. These were observed at 1.34 (t,
3JHH ¼ 7.9 Hz, 1H) and 1.30 (d, 3JHH ¼ 8.2 Hz, 1H) ppm for 6 and at
3
3
1.33 (t, JHH ¼ 8.2 Hz, 1H) and 1.27 (d, JHH ¼ 7.6 Hz, 1H) ppm for
8. The proton signals for those H centers closest to the thiols
shifted w0.5 ppm to the lower chemical shifts relative to their
position in the 1H NMR spectra of 1 and 2 upon opening of the
C3S2 ring. The position of eCH signal in the C3S2 ring was the
most shifted, from 3.58 ppm for 1 to 2.94 ppm for 6 and, similarly,
from 3.52 ppm in 2 to 2.89 ppm for 8. Deprotonation of the
dithiols with Et3N and treatment with ClSiMe3 results in the
signals for the thiol peaks replaced with 2 peaks centered around
w0.3 ppm and assigned to eSSiMe3. The 1H NMR spectra of 6 and
7 are shown in supporting information, respectively (Figs. S3 and
S4).
Fig. 3. Absorption spectra of 1, 2 and 3 in CH2Cl2.
The absorption spectra of compounds 1e3 are presented in
Fig. 3. They all display a maximum between 440 and 450 nm with
molar absorption coefficients (
) of 184, 102 and 37 Mꢀ1 cmꢀ1
3
respectively, the absorption assigned to the symmetry forbidden
ded transition and consistent with spectra of related ferrocenyl
amides [11]. Compound 2 shows a well-resolved maximum at
330 nm with
from the highest
3
¼ 255 Mꢀ1 cmꢀ1 which is assigned to the transition
p
-orbital to the antibonding s-orbital in the SeS
bond [25]. This transition is not resolved for 1 and 3 and is not
present for the Pt complexes 4 and 5.
IR spectroscopy identified the amide and ester functional groups
in the synthesized ferrocenyl complexes. Three characteristic
amide peaks are present in the IR spectra of 1 and 3. These peaks
are at 3294 cmꢀ1 (NeH stretching), 1654 cmꢀ1 (C]O
stretching þ NeH bending þ CeN stretching), 1560 cmꢀ1 (NeH
bending þ CeN stretching) for 1 and at 3277 cmꢀ1 (NeH stretch-
ing), 1675 cmꢀ1 (C]O stretching þ NeH bending þ CeN stretch-
ing), 1573 cmꢀ1 (NeH bending þ CeN stretching) for 3. These
assignments were completed according to values reported for other
ferrocenyl amides [11]. The IR spectrum of 2 displays 3 character-
istic peaks for the ester functional group at 1734 cmꢀ1 (C]O
stretching), 1176 and 1243 cmꢀ1 (CeO stretching).
Fig. 4. Cyclic voltammograms for 2.25 mM solutions of 1 (dashed lines) and 4 (solid
lines) in 0.1 M TBAP/dichloromethane. The potential is referenced relative to ferrocene
oxidation at 0.68 V under the same conditions.
position of the peaks of the ferrocenyl unit in addition to the
presence of signals for PPh3. The peak assigned to the lone CH in the
C3S2 ring is shifted from 3.58 ppm in the 1H NMR spectrum of 1 to
3.32 ppm for 4. A similar shift in the corresponding CH resonance
(3.52 ppm) was observed in the 1H NMR spectrum of 2 versus 5
(3.30 ppm). In the 31P{1H} NMR spectra of 4 and 5 two peaks are
present at w25 and 23 ppm. These peaks display 195Pt satellites
with 1JPtP values in the range of 2801 and 2865 Hz and 2JPP values of
21 Hz for the two inequivalent phosphorus nuclei. The 31P{1H} NMR
3.2.1. Cyclic voltammetry
The electrochemistry of 1 and 4 were investigated by cyclic vol-
tammetry as 2.25 mM solutions in 0.1 M TBAP/dichloromethane at
room temperature using a glassy carbon working-electrode (Fig. 4).
Fig. 5. The molecular structure of 1 (molecule 1). Selected bond lengths (Å) and angles (degrees): N11eC111 1.333(7), N11eC11 1.428(7), O11eC111 1.228(6), S11eC161 1.881(9),
S11eS21 2.005(7), S21eC181 1.8051(4), C161eC171 1.5351(2), C171eC181 1.4821(4), C161eS11eS21 98.8(4); C181eS21eS11 95.6(7), C151eC161eC171 112.0(8), C151eC161eS11
107.4(7), C171eC161eS11 107.4(7), C181eC171eC161 113.61(2), C171eC181eS21 110.01(1).

B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
23
disulfide moiety [26]. The shape of the anodic peak arising from the
oxidation is indicative of an absorption process, suggesting that
upon oxidation the resulting intermediate is reacting with the
electrode. A similar, yet smaller the anodic peak caused by the
oxidative process is also observed in the CV of 4. This additional
oxidative process in 4 is not due impurities in the sample, as the
purity was established by NMR spectroscopy prior to the electro-
chemical experiment both in the absence and presence of the sup-
porting electrolyte. As mentioned above the complex 4 is slightly
reactive under oxidative conditions leading to what appears to be
some disulfide (or PteS oxidative products) formation that is
responsible for the higher Ia/Ic.
3.2.2. X-ray crystallography
Orange crystals of 1 were obtained by recrystallization from
CH2Cl2/heptane, and the structure determined using single crystal
X-ray diffraction techniques. Complex 1 crystallizes in the non-
Fig. 6. Molecular structure of 1 with hydrogen bonding interactions.
centrosymmetric, orthorhombic space group Pca2(1) with
8
molecules in the unit cell. There are two independent molecules in
the asymmetric unit, reflecting the presence of the enantiomeric
pair. Each of the C3S2 rings exhibited some site disorder which was
satisfactorily refined with 0.66667:0.33333 occupancy and a figure
representing the refined model is provided in the Supporting
information (Fig. S5). A summary of the pertinent bond lengths and
angles for molecule 1 is listed in the caption of Fig. 5. Within the
experimental deviation, the SeS bond length in 1 is similar to that
found in lipoic acid (2.053(4)) [27]. The Cp rings are almost
perfectly parallel. The molecular structure of 1 is shown in Fig. 5
(molecule 1).
As expected each show a quasi-reversible wave at 0.52 V (DEp at
50 mV/s is 68 mV) that can be assigned to the oxidation of the
ferrocene moiety (oxidation of ferrocene is at 0.65 V under the same
conditions;
D
Ep ¼ 73 mV, Ia/Ic ¼ 1.0). The ratio of anodic and cathodic
currents (Ia/Ic), one measure of the chemical reversibility of the
oxidation, is one for 1 but slightly larger for 4 (ranges from 1.1 to 1.3
for scan rates 500 mV/s and 50 mV/s, respectively) suggesting that
the latter is slightly unstable to oxidation. Unlike in the cyclic vol-
tammetry of ferrocene, for 1 there is an additional single electron
oxidation peak at 1.35 V that can be assigned to the oxidation of the
Fig. 7. Molecular structure of 4 (molecule 1). Selected bond lengths [Å] and angles [ꢂ] for 4: Pt11eS11 2.360(1), Pt11eS21 2.339(1), Pt11eP11 2.287(1), Pt11eP21 2.306(1), S11eC161
1.842(6); S11ePt11eS21 91.73(5), S11ePt11eP11 179.10(5), P11ePt11eP21 97.50(5), S21ePt11eP11 87.41(5), S21ePt11eP21 174.92(5), C171eC161eS11 109.4(4).

24
B. Khalili Najafabadi et al. / Journal of Organometallic Chemistry 703 (2012) 16e24
As illustrated in Fig. 6, compound 1 displays H-bonding inter-
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
actions in the crystal. Each molecule of 1 displays two hydrogen
bonding interactions with two neighboring molecules via the
amide protons (N/O ¼ 3.026 Å).
Appendix. Supplementary material
Dark
S,S)(CH2)4C(O)NH(
orange
crystals
of
5-C5H5)]
[Pt(PPh3)2(S2CH2CH2CH-k2
-
h
5-C5H4)Fe(
h
4
were obtained by
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.12.003.
recrystallization from CHCl3/pentane. The ligated complex 4 crys-
ꢀ
tallizes in the triclinic space group P 1 (Z ¼ 4) and the molecular
structure of one of the two independent (chiral) molecules present
in the asymmetric unit is shown in Fig. 7. As for 1, both enantiomers
are found in the asymmetric unit although unlike 1, complex 4
crystallizes in a centrosymmetric space group. Bond lengths and
angles discussed in the text refer to molecule 1. The coordination
geometry of platinum center is a slightly distorted square planar
with two phosphines and one dithiolate ligand that coordinates in
a bidentate fashion to yield a six-membered ring. The PteS
(2.339(1)e2.3603(1) Å) and PteP bond lengths (2.287(1)e
2.306(1)) and SePteS (average of 91.73(5)ꢂ) and PePteP angles
(97.50(5)ꢂ) compare well with those reported for related complexes
[7,21]. Notably, the eSeCHeCH2e bond angle is markedly
increased in 4 (112.6(4)ꢂ) compared to that in 1 (107.4(7)ꢂ),
a consequence of the ring opening and consistent with the change
in 1H NMR chemical shifts. The Cp rings defined by C11eC51 and
C61eC101 are almost perfectly parallel. Selected bond lengths and
angles are summarized in the caption of Fig. 7. Unlike for the crystal
packing observed in 1 there is no H-bonding observed in 4 and can
perhaps be attributed to the sterics of the PPh3 ligands and the large
number of CHCl3 present in the lattice.
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Thepreparationandcharacterizationof threenewferrocenebased
dithiolane compounds are reported. These were designed to contain
an amide or ester functional group in their structure. The synthesis
and purification of these materials was a challenging one because of
thesensitivity of the SeS bond in these compoundsand theformation
of insoluble polymers when compounds are exposed to light or heat.
Theircyclicvoltammograms displaya reversibleoxidationassigned to
the ferrocenyl unit and one quasi-reversible oxidation related to the
dithiolane ring. Complexation of these ligands was studied using
oxidative addition of their SeSbondstoplatinum(0)centers,resulting
in cis mononuclear platinum(II) complexes.
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We thank the Natural Sciences and Engineering Research
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for equipment funding.
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Appendix A. Supplementary material
CCDC 848844 and 848845 contain the supplementary crystal-
lographic data for 1 and 4 respectively in this paper. These data can