Unexpected fragmentation of phenyldithiobenzoate, formation and X-ray structure of [μ,η2(S,S)-1,2-(dithio)-1,2-(diphenylethylene)] diiron hexacarbonyl complex

Article abstract of DOI:10.1016/j.jorganchem.2010.01.005

The reaction of Fe₂(CO)₉ with phenyldithiobenzoate PhCS₂Ph 1 afforded four colored compounds: [(μ-η³(C,S,S)PhCS₂Ph)]Fe₂(CO) ₆ 2, (μ-S)₂Fe₃(CO)₉ 3, (μ-SPh)₂Fe₂(CO)₆ 4 and [μ-η²(S,S)][PhC(S){double bond, long}C(S)Ph]Fe₂(CO)₆ 5. Complex 5 was characterized by X-ray crystallography. The formation of complexes 4 and 5 was unexpected since it involved a fragmentation of the organic ligand 1 during its reaction with Fe₂(CO)₉. The electrochemical studies of 1, complexes 2 and 3 were undertaken in order to get information about the chemical behaviors of the intermediates generated by electron transfer. The results of cyclic voltammetry studies of 2 and 1 suggested that the reaction of 1 with Fe₂(CO)₉ involved two competitive reactions: (i) a thermal reaction which led to the expected compounds 2 and 3 and (ii) an electron transfer reaction involving a fragmentation of starting ligand 1 led to the unexpected complex 5. The required electrons may be provided by iron during the thermal decay of complexes 2 or 3 or Fe₂(CO)₉.

Full text of DOI:10.1016/j.jorganchem.2010.01.005

Journal of Organometallic Chemistry 695 (2010) 786–791
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Review
Unexpected fragmentation of phenyldithiobenzoate, formation and X-ray
structure of [
2(S,S)-1,2-(dithio)-1,2-(diphenylethylene)]
l,g
diiron hexacarbonyl complex
b
c
Hénia Mousser a, , André Darchen , Abdelhamid Mousser
*
a Département de Chimie Industrielle, Faculté des Sciences de l’Ingénieur, Université Mentouri Constantine, 25000 Constantine, Algeria
b UMR CNRS No. 6226, Sciences Chimiques de Rennes, ENSCR, Avenue du Général Leclerc, CS 50837, 35708 Rennes Cedex 7, France
c Département de Chimie, Faculté des Sciences Exactes, Université Mentouri Constantine, 25000 Constantine, Algeria
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of Fe2(CO)9 with phenyldithiobenzoate PhCS2Ph 1 afforded four colored compounds:
[(l-g (l-S)2Fe3(CO)9 3, (l-SPh)2Fe2(CO)6 4 and [l-g
3(C,S,S)PhCS2Ph)]Fe2(CO)6 2, 2(S,S)][PhC(S)
Received 4 November 2009
Received in revised form 24 December 2009
Accepted 4 January 2010
C(S)Ph]Fe2(CO)6 5. Complex 5 was characterized by X-ray crystallography. The formation of complexes
4 and 5 was unexpected since it involved a fragmentation of the organic ligand 1 during its reaction with
Fe2(CO)9. The electrochemical studies of 1, complexes 2 and 3 were undertaken in order to get informa-
tion about the chemical behaviors of the intermediates generated by electron transfer. The results of cyc-
lic voltammetry studies of 2 and 1 suggested that the reaction of 1 with Fe2(CO)9 involved two
competitive reactions: (i) a thermal reaction which led to the expected compounds 2 and 3 and (ii) an
electron transfer reaction involving a fragmentation of starting ligand 1 led to the unexpected complex
5. The required electrons may be provided by iron during the thermal decay of complexes 2 or 3 or
Fe2(CO)9.
Available online 11 January 2010
Keywords:
Dithioester
Diiron carbonyl
Diiron complex
Cyclic voltammetry
Electron transfer
Ó 2010 Elsevier B.V. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
2. Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
2.1. Physical measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
2.2. Reagents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
2.3. Preparations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
2.3.1. Reaction of PhCS2Ph 1 with diiron nonacarbonyl. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
2.3.2. Reaction of PhCS2Ph (1) with triiron dodecarbonyl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
2.3.2.1. Complex 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
2.3.2.2. Complex 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
2.3.2.3. Complex 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
2.3.2.4. Complex 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
3. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
3.1. Reaction of 1 with Fe2(CO)9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
3.2. X-ray crystal analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788
3.3. Thermal studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
3.4. Voltammetric studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 789
3.5. Proposed mechanism for the formation of complexes 4 and 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 790
4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 791
* Corresponding author. Tel.: +213 773 426 871.
E-mail address: bouzidi_henia@yahoo.fr (H. Mousser).
0022-328X/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.01.005

H. Mousser et al. / Journal of Organometallic Chemistry 695 (2010) 786–791
787
1. Introduction
(CO)
Fe
9
2
3
4
5
PhCS2Ph
1
+
+
+
The thermal reaction of Fe2(CO)9 with organic substrates that
contain sulfur atoms is a general synthetic way to various hexa-
carbonyldiiron coordination compounds [1]. Some complexes con-
taining a Fe2S2 core attract interest of chemists because they have
a close resemblance to the diiron unit of the FeFe-hydrogenase
[2,3]. These complexes are easily synthesized and have been stud-
ied as structural and functional mimics of enzyme active site [4].
Hydrogenase enzymes catalyze the oxidation of dihydrogen and
the reduction of protons in nature. X-ray crystallography and IR
spectroscopy of [Fe]-only hydrogenases have shown the active
site to be comprised of a [2Fe–2S] subunit linked to a [4Fe–4S]
cluster by a cysteinyl-S bridge [5–10]. The two iron atoms in
the [2Fe–2S] subunit are linked by a bridging dithiolate ligand
and are bound to the biologically uncommon ligands like carbon
monoxide (CO) and cyanide (CN) [11]. Owing to the importance
of [2Fe–2S] hydrogenase model it is interesting to investigate
the coordination chemistry of organic compounds that contain
several sulfur atoms.
55°C
Fe
(CO)3
Ph
Ph
S
C
S
S
Fe
(OC)3
(CO)
Fe
3
(CO)
Fe
(OC)
3Fe
3
S
2
3
Ph
Ph
Ph
C
C
S
S
S
S
Ph
The reaction of iron carbonyl with numerous sulfur containing
compounds has been investigated. Dithioesters react with
(CO)
Fe
(OC)
(CO)
Fe
3Fe
(OC)
3
3Fe
3
Fe2(CO)9 to afford binuclear iron carbonyl complexes with a
r
metal–carbon bond in which the organic ligand gives 6 electrons
to the Fe2(CO)6 skeleton [12]. The starting organic ligand is linked
to the metal atoms without fragmentation and the overall reac-
tion may be rationalized by a stepwise replacement of three CO
ligand of Fe2(CO)9 by a six-electron ligand. X-ray structures of
these complexes show that coordination imposes important geo-
metrical constraints [13]. The reaction of Fe2(CO)9 with ethylene-
trithiocarbonate [12,13], 1,2-dithiol-3-thiones [14] or 2,3-
toluenedithiol and 1,3-propanedithiol [15] affords binuclear com-
plexes without a ligand fragmentation. However, in some cases
the thermal reaction of Fe2(CO)9 with sulfur containing substrates
leads to the formation of binuclear compounds including one or
several fragments arising from the organic substrates. For exam-
ple, the reaction with xanthates [16], linear trithiocarbonates
[17], S,S-substituted dithiocarbonates [18] or 1-thia-3-azabutadi-
ene bearing a thiobenzyl group [19] involves in all cases the frag-
mentation of the substrate or an intermediate organometallic
compound. S-Methyl O-methylene adamantane dithiocarbonate
reacts with Fe2(CO)9 [20] like a dithioester ligand [R1CS2R2]. At
first, it leads to an intermediate which undergoes a rearrangement
catalyzed by electron transfer and affords the final compound
containing the fragmented organic ligand [20,21]. However, the
reaction of R1CS2R2 (R1 = Me, R2 = Et or R1 = Ph, R2 = Me) with
Fe(CO)5 or Fe2(CO)9 under UV irradiation gives three compounds
[22]. In the first compound, the Fe atoms are doubly-bridged by
a C–S unit and the original bivalent S atom of the intact dithioest-
er in a well known structure [12]. The second one is a dimeric
compound in which there is no metal–metal bond but each coor-
dinated ligand forms an asymmetric dative S–metal bond to the
other iron atom. The third compound is the result of carbonyl
insertion into the C–SR2 bond of the ligand [22]. The reaction of
various O-alkyl aryl thioesters with diiron nonacarbonyl affords
an isomeric oxygen sulfur–donor diiron hexacarbonyl complex
as the major product [23].
5
4
Scheme 1. Reaction and structures of isolated compounds.
this reaction, we investigated the electrochemical behavior of
dithioester 1, complexes 2 or 3 and 5 and we report here our
results.
2. Experimental
2.1. Physical measurements
1H and 13C NMR spectra were recorded at 60 and 20.115 MHz,
respectively, in CDCl3 with TMS as internal standard. Mass spectra
were recorded with a Varian MAT 311 spectrophotometer at 70 eV
at CRMPO (Rennes, France). Elemental analyses were carried out by
Service Central d’Analyse (Vernaison, France). The electrochemical
experiments were carried out in a three-electrode thermostated
cell with a PAR 362 potentiostat coupled to a Kipp and Zonen XY
recorder. Pt micro disc and a saturated calomel electrode (SCE)
were used as working and reference electrodes, respectively. Dif-
fraction measurements of single crystals of complex 5 were made
at 293 K on a kappa CCD diffractometer (Bruker AXS BV, 1997-
2004) equipped with a graphite monochromatic using Mo Ka radi-
ation (k = 0.71073 Å). Crystal data collection, reduction and refine-
ment were accomplished with COLLECT (Nonius, 1998), SCALEPACK
and DENZO [24] programs. The structure was solved by SIR2002
[25] and refined by using SHELXL-97 [26]. The hydrogen atoms were
located in Fourier maps but introduced in calculated positions and
treated as riding on their parent C atom, with 0.95 (aromatic) and
with Uiso(H) = 1.2 Ueq (aromatic C atoms). The molecular graphi-
cal was showed with ORTEP-3 [27] program and material for publi-
cation was prepared with WinGX 1.7 Software [28,29].
It is remarkable that, despite some structural analogies with lin-
ear trithiocarbonates or xanthates, the dithioesters are generally
stable during their thermal reaction with Fe2(CO)9 [12,13]. Surpris-
ingly, we have observed an unusual fragmentation of phen-
yldithiobenzoate PhC(S)SPh (1) during its thermal reaction with
Fe2(CO)9 leading to the expected complexes 2 and 3, and to com-
plexes 4 and 5 of which the formation involved a fragmentation
reaction of the starting ligand (Scheme 1). In order to understand
2.2. Reagents
The supporting electrolyte Bu4NBF4 (Fluka, Purum) was recrys-
tallized in a mixture of methanol and water (1/1), dried at 120 °C
and used at 0.1 M concentration. Diiron nonacarbonyl and triiron
dodecarbonyl (Strem Chemical, 99%), trimethylphosphite (Fluka
purum, 97%) and diphenylacetylene (Aldrich, 99%) were used as

788
H. Mousser et al. / Journal of Organometallic Chemistry 695 (2010) 786–791
received. Toluene, acetone, CH2Cl2 and DMF (SDS, analytical grade)
were stored over 4 Å molecular sieves before use.
scribed during its thermal reaction with Fe2(CO)9. The formation
of 3 is the proof of both reagent fragmentations. The formation of
binuclear compounds 4 and 5 is also the proof of a fragmentation
of the phenyldithiobenzoate during its thermal reaction with
Fe2(CO)9. During this reaction 93% of the phenyldithiobenzoate
were transformed into iron carbonyl complexes. Complexes 4
and 5 or analogous one were unexpected compounds and were
never observed during reaction of Fe2(CO)9 with dithioesters.
2.3. Preparations
2.3.1. Reaction of PhCS2Ph 1 with diiron nonacarbonyl
The organic substrate PhCS2Ph was prepared according to the
literature [30]. Fe2(CO)9 (1.5 mmol) was added to PhCS2Ph
(1.0 mmol) in dry toluene (40 mL). The mixture, in the dark and
under nitrogen, was heated at 55 °C for 0.5 h. The progress of the
reaction was followed by thin layer chromatography. After filtra-
tion and distillation of the solvent, the residue was dissolved in
10 mL of diethyl ether. The reaction products were separated by
chromatography on thin layer of silica gel and elution with petro-
leum ether. The isolated complexes, with decreasing polarity were:
3 (6%), 4 (20%), 5 (24%) and 2 (43%). They were purified by crystal-
lization from ethanol solution. All yields are based on PhCS2Ph.
3.2. X-ray crystal analysis
ꢀ
Crystals of complex 5 were triclinic with space group P1. The X-
ray study of 5 established that it was a binuclear iron complex. The
two iron atoms are maintained at a distance from 2.56 Å with a
dithiodiphenylethylene group. It was identical to the compound
2.3.2. Reaction of PhCS2Ph (1) with triiron dodecarbonyl
Fe3(CO)12 (1.0 mmol) was added to PhCS2Ph (1.0 mmol) in dry
toluene (40 mL). The mixture, in the dark and under nitrogen,
was stirred at room temperature for 72 h or heated at 55 °C for
1 h. After filtration, distillation of the solvent and chromatography
on silica gel the complexes 2 and 3 were isolated with 60% and 10%,
respectively.
2.3.2.1. Complex 2. [l-g
3(C,S,S)PhCS2Ph]Fe2(CO)6, m.p. 152 °C. 1H
NMR d: 7.25(m) ppm. 13C NMR d: 211.0; 208.5 (CO); 146.9;
139.2; 129.9; 129.6; 128.5; 127.5; 126.7; 122.2 (Ph); 69.1 (CS2)
ppm. IR (C2Cl4):
m CO = 1970; 1980; 2000; 2010; 2040;
2080 cmÀ1 Mass spectrum: M+ found 509.8622; M+ calc.
.
509.8617. Anal. Calc. for C19H10Fe2O6S2: C, 44.70; H, 1.96; S,
12.54; Fe, 21.95; O, 18.82. Found: C, 45.75; H, 1.88; S, 13.08; Fe,
20.83%. Cyclic voltammetry: EpC1: À1.00; EpC2: À1.55 V versus
SCE EpC1: À0.85; EpC2: À1.40 V versus SCE.
2.3.2.2. Complex 3. (
(Nujol):
CO = 2040; 2060; 2080 cmÀ1. Mass spectrum: M+ found
483.7019; M+ calc. 483.7031.
l-S)2Fe3(CO)9, m.p. 114 °C; (114 °C [31]). IR
Fig. 1. Molecular structure of complex 5 with thermal ellipsoids at 30% probability.
Hydrogen atoms are omitted for clarity.
m
Table 1
2.3.2.3. Complex 4. (
ppm. IR (C2Cl4):
CO = 2000; 2010; 2040; 2080; cmÀ1. Mass spec-
trum: M+ found 497.8599; M+ calc. 497.8617.
l
-PhS)2Fe2(CO)6, m.p. 130 °C.1H NMR d: 7.4(m)
Crystal data and refinement details for X-ray structure determination of 5.
m
Molecular formula
C20H10Fe2O6S2
Formula weight (g molÀ1
)
522.1
T (K)
293 (2)
Triclinic
2.3.2.4. Complex 5. [
1H NMR d: 7.2(m) ppm. 13C NMR d: 207.8 (CO); 150.2 (C@C); 135.2;
l-g
2(S,S)PhC(S)@C(S)Ph]Fe2(CO)6, m.p. 140 °C.
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢀ
P1
9.2280 (6)
14.9718 (10)
17.5488 (10)
108.622 (3)
91.688 (3)
107.939 (2)
2163.83 (34)
4
128.9; 128.4; 127.3 (Ph) ppm. IR (C2Cl4):
m CO = 2000; 2040;
2080 cmÀ1
493.866.
.
Mass spectrum: (MÀCO)+ found 493.867.; calc.
a
(°)
b (°)
c
(°)
3. Results and discussion
V (Å3)
Z
Color
Red
1.60
15.67
2.27–25.37
13 748
3.1. Reaction of 1 with Fe2(CO)9
qcalc (g cmÀ3
)
l
Hmin
(cmÀ1
–
)
Hmax
An excess of Fe2(CO)9 reacted with PhCS2Ph (1) and afforded
four colored compounds: 2 (43%); 3 (6%); 4 (20%) and 5 (24%).
Compound 2 was the expected product containing the starting
dithioester ligand linked to Fe2(CO)6. It was fully characterized
by mass spectrometry and by spectroscopic methods. Trinuclear
cluster 3 was frequently obtained in low yield by reaction of
Fe2(CO)9 with organic substrates that contain thiono group
[13,16,23,32,33]. This cluster has been obtained, from the reaction
of organic sulfide with Fe3(CO)12 [34], the thienyl Schiff base with
Fe2(CO)9 [35] and its molecular structure is well known [36]. To
date, no fragmentation of a dithioester compound has been de-
Measured data
Reflexions used
F000
Radiation
Wave length (Å)
No. data with I > 2
Number of parameters
Rint
R1(I > 2
wR2
GOF
7431
1048
Mo ka (graphite monochromated)
0.71073
4884
542
0.0689
0.0397
0.0976
1.013
r
r)

H. Mousser et al. / Journal of Organometallic Chemistry 695 (2010) 786–791
789
already described in the literature [37] which was synthesized by
(CO)12
Fe3
2
3
4
5
reaction of the tetraphenyldithine [38] or the diphenylthiirene-1-
oxide [39] with Fe2(CO)9. The ORTEP plot is given in Fig. 1. Its crys-
tal and collection parameters are shown in Table 1, and selected
bond distances and angles are tabulated in Table 2.
PhCS2Ph
1
+
+
+
55°C
Scheme 2. Reaction of 1 with Fe3(CO)12
.
3.3. Thermal studies
ible than 2 and 1 [40], Fe3(CO)12 acted as an electron trap and
inhibited the formation of 4 and 5.
The reaction of 1 with Fe2(CO)9 or Fe3(CO)12 in toluene or ace-
tone gave a variety of results. The conditions and yields are listed
in Table 3. When Fe2(CO)9 reacted with 1 at room temperature, 5
was not obtained. At 55 °C, the yield of 5 did not increase with
longer reaction time or by using acetone instead of toluene solvent.
At 110 °C, 4 and 5 were not isolated. When Fe3(CO)12 reacted with
1 at room temperature or at 55 °C, 4 and 5 were not obtained
(Scheme 2). TLC analysis showed that 2 slowly decayed during
its heating in toluene at 55 °C. After one day, trace amount of 5
was detected. After four days, the TLC analysis revealed the pres-
ence of free phenyldithiobenzoate, complex 3 and diphenylacety-
lene. These two last compounds suggest the occurrence of a
fragmentation of 2 or 1 but the intermediate complex 5 was not
isolated.
The main conclusion of these results was that 4 and 5 did not
arise from a fast thermal reaction involving complex 2. The forma-
tion of 4 and 5 during the reaction of Fe2(CO)9 with 1 at 55 °C was
an indication of the occurrence of a more efficient activation than
the thermal one. As for the fragmentation of xanthate ligand [12]
we suggest that this efficient activation could be the result of an
electron transfer involving 2 or 3 or 1. The origin of the transferred
electrons may be found in the decomposition of the iron carbonyl
Fe2(CO)9 or one of complexes 2 or 3 leading to species containing
iron at low oxidation state. The overall transformation of 2 impli-
cated a fragmentation followed by a dimerization of mononuclear
entities. It was very important to note that when the complexation
of 1 was carried out at 55 °C with Fe3(CO)12, which is more reduc-
3.4. Voltammetric studies
In DMF solution, at room temperature, complex 2 underwent
two one-electron reduction steps. The first one was quasi-revers-
ible (E1/2 = À0.75 V versus SCE) and gave the corresponding radical
anion 2À, which was observed as a stable compound at the voltam-
metric time scale (Fig. 2a). The further reduction of 2À to 22À due to
the follow-up 22À chemical reaction’s, was observed at À1.45 V
versus SCE and was irreversible. The difference
D
Ep = Epa À Epc
(0.5 V for the first reduction) showed a slow heterogeneous charge
transfer. The heating of the solution increased the lability of 2À.
The voltammograms did not show the formation of complexes 4
or 5. The relative peak currents and the loss of quasi-reversibility
at 55 °C (Fig. 2b) suggest that the reduction of 2 followed an ECE
mechanism, where the chemical step C occurring at 2À allowed
the transfer of a second electron at the same potential. The chem-
ical reversibility of the reductions and the absence of following
fragmentation led us to conclude that the extra electrons in 2À
and 22À were located on the metal atoms and not on the dithioest-
er ligand.
However, the lability of 2À may be disclosed in the presence of a
donor ligand and confirm the electron localization on the metal
center. When a ligand P(OMe)3 was added into solution of 2 in
DMF, the cyclic voltammogram (Fig. 3) showed the typical behav-
ior of a ligand substitution catalyzed by an electron transfer which
occurred at the cathode surface [13,18,41]. The cathodic peak C1
(Epc = À1.0 V versus SCE) of 2 decreased while the peak C3, corre-
Table 2
Selected bond lengths (Å) and angles (°) for complex 5.
Bond lengths (Å)
Angles (°)
sponding to the reduction of the substituted complex
g
[l-
3(C,S,S)PhCS2Ph]Fe2(CO)5L (L = P(OMe)3), appeared at more nega-
Fe(1)–Fe(2)
Fe(1)–C(1)
Fe(2)–C(4)
C(1)–O(1)
C(4)–O(4)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(2)–S(1)
Fe(2–S(2)
S(1)–C(13)
S(2)–C(14)
C(13–C(14)
C(13)–C(23)
C(14)–C(17)
2.4821(8)
1.772(5)
1.783(4)
1.146(5)
1.139(5)
2.2629(11)
2.2666(11)
2.2642(11)
2.2640(11)
1.816(4)
1.8144(4)
1.326(5)
1.481(5)
Fe(1)–(S1)–Fe(2)
Fe(1)–S(2)–Fe(2)
C(1)–Fe(1)–Fe(2)
C(1)–Fe(1)–C(3)
C(5)–Fe(2)–Fe(1)
C(5)–Fe(2)–C(4)
S(1)–Fe(1)–S(2)
S(1)–Fe(1)–C(1)
S(1)–Fe(2)–S(2)
S(1)–Fe(2)–C(6)
Fe(1)–S(1)–C(13)
Fe(2)–S(2)–C(14)
C(23)–C(13)–C(14)
C(13)–C(14)–C(17)
66.50(3)
66.44(3)
tive potentials (Epc = À1.2 V versus SCE).
100.85(14)
100.6(2)
105.46(13)
91.04(18)
79.53(4)
89.93(15)
79.56(4)
104.47(13)
102.85(13)
101.95(13)
129.2(3)
1.486(5)
129.1(3)
Table 3
Reactions of PhCS2Ph with iron carbonyl.
Iron
carbonyl
Temperature
(°C)
Time
(h)
Solvent
Yields of products (%)
2
3
4
5
Fe2(CO)9
Fe2(CO)9
Fe2(CO)9
Fe2(CO)9
Fe2(CO)9
Fe3(CO)12
Fe3(CO)12
Fe3(CO)12
55
55
0.5
1
1
1
1
72
1
4
Toluene 43
Toluene 35
6
8
0
20
25
0
24
30
0
110
Toluene
0
20–25a
55
Toluene 60 N.C. N.C. 18
Acetone 30 N.C. N.C. 18
Toluene 65
Toluene 60 10
Acetone 47 N.C.
20–25a
55
0
0
0
0
0
0
0
Fig. 2. Cyclic voltammetry of 2 mM of complex 2 in DMF 0.1 M Bu4N+ BF4À; Pt
electrode; scan rate 0.2 V sÀ1. (a) At 20 °C; (b) at 55 °C; - - - - - reverse scan after the
first reduction.
20–25a
a
With ultrasonic activation; N.C.: not calculated.

790
H. Mousser et al. / Journal of Organometallic Chemistry 695 (2010) 786–791
Fig. 3. Cyclic voltammetry of 2 mM complex 2 in DMF 0.1 M Bu4N+ BF4À; Pt electrode; scan rate 0.5 V sÀ1. — Complex 2 alone; - - - - - and Á Á ÁÁ Á Á first and second scanning in
the presence of an excess of P(OMe)3.
The cyclic voltammetry of complex 5 was performed in CH2Cl2
solution (Fig. 4). The electronic effect of the bridging ligand influ-
ences the reduction potential which was observed at À0.99 V ver-
sus SCE, The reduction was a two-electron reversible process. For
similar propane dithiolate iron carbonyl complex, the reduction
is a two-electron quasi-reversible reaction [21].
The cyclic voltammetry of the phenyldithiobenzoate 1 showed
three peaks. The first was attributed to the reduction of 1 leading
to the corresponding anion 1À. The second was the reduction of an-
ion 1À. The third was due to the reduction of phenylacetylene. As
reported by Lund et al. [42], the first reduction (Epc = À1.12 V ver-
sus SCE) is irreversible and shows a heterogeneous electron trans-
fer involving dimerization of anion radical 1À followed by an
elimination reaction (Scheme 3). We were able to confirm the
elimination of the PhC(S)SÀ by observing its irreversible oxidation
at +0.4 V versus SCE.
3.5. Proposed mechanism for the formation of complexes 4 and 5
The formation of 4 and 5 during the reaction of Fe2(CO)9 with 1
at 55 °C requires an activation more efficient than the thermal one.
We suggest that the reaction involves an electron transfer mecha-
nism. We propose that the reaction of 1 with Fe2(CO)9 follows two
competitive pathways (Scheme 4). The first one would be a step-
wise replacement of three carbonyls of Fe2(CO)9 by a ligand 1 with
the formation of 2 and 3. In this pathway 49% of the phen-
yldithiobenzoate have been transformed.
However the second pathway would be a reduction of 1 leading
to the elimination of PhC(S) and PhSÀ fragments. These last two
species or their dimerized forms would be trapped by Fe2(CO)9
and this reaction should consume 44% of PhCS2Ph. The electrons
required in the reduction of 1 may arise from the thermal decom-
position of Fe2(CO)9, 2 or 3. It is useful to recall that when the reac-
tion of 1 was carried out with Fe3(CO)12 (Table 3), we obtained only
complexes 2 and 3. In the presence of Fe3(CO)12, this compound
acted as an electron trap since it is more easy to reduce than 1.
So, complexes 4 and 5 could not be formed.
The mechanism of the second competitive pathway suggested
above can be explained by the following reactions. First, the
decomposition of iron carbonyl compounds (Fe2(CO)9, 2 or 3) af-
fords Fe(0) which reduces the starting dithioester 1. Then, the re-
duced form of dithioester is involved in a cleavage leading to
sulfur containing fragments or their dimers [42]. Finally, these
compounds react with Fe2(CO)9 and lead to 4 and 5 (Scheme 4).
+ e
.
1
1
.
.
1
2 PhS
2
PhC(S)C(S)Ph
+
Fig. 4. Cyclic voltammetry of 2 mM of complex 5 in CH2Cl2 0.1 M Bu4N+ BF4À; Pt
electrode; scan rate 0.5 V sÀ1
.
Scheme 3. Electrochemical reduction of 1.

H. Mousser et al. / Journal of Organometallic Chemistry 695 (2010) 786–791
791
Fe2(CO)9
Fe3(CO)12
2 +
3
+
4
+ 5
1
2 + 3
Fe(0)
Fe2(CO)9
1
Fe3(CO)12
Fe2(CO)9
Fe2(CO)9
PhSSPh
+
PhC(S)
C(S)Ph
=
Scheme 4. Formation of complexes in reaction of 1 with iron carbonyl.
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By taking into account the yields in each pathway, we can estimate
that the kinetic constant ratio of the two competitive reactions
(electron transfer and replacement of three carbonyls) is equal to
0.89.
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The fragmentation occurring during the reaction of phen-
yldithiobenzoate is a new example of the intricacy of Fe2(CO)9
reactivity under thermal activation. Owing to the fact that the reac-
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organic ligand.
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