Hydrogenation of (1-phenylthiophene)Mn(CO)3 (thiophene = 3-methylthiophene and 3,4-dimethylthiophene) complexes: Formation of tetrakis(tricarbonyl-phenylthiomanganese)

Article abstract of DOI:10.1016/S0022-328X(99)00029-7

For the hydrogenation of (1-phenylthiophene)Mn(CO)₃ (2), the nature of the thiophene derivatives strongly affect the yields and distribution of reaction products. When 3-methyl- and 3,4-dimethylthiophene were used as thiophene derivatives, the dimer [Mn(CO)₄(SPh)]₂ (7) and the tetramer [Mn(CO)₃(SPh)]₄ (8) was obtained as major products and the hydrodesulfurized product, isoprene or 2,3-dimethyl-1,3-butadiene were obtained in a high yield. Structures of 7 and 8 were verified by X-ray diffraction studies.

Full text of DOI:10.1016/S0022-328X(99)00029-7

Journal of Organometallic Chemistry 579 (1999) 385–390
Hydrogenation of (1-phenylthiophene)Mn(CO)3
(thiophene=3-methylthiophene and 3,4-dimethylthiophene) complexes:
formation of tetrakis(tricarbonyl-phenylthiomanganese)
Dai Seung Choi, Soon Hyeok Hong, Su Seong Lee, Young Keun Chung *
Department of Chemistry and the Center for Molecular Catalysis, College of Natural Sciences, Seoul National Uni6ersity,
Seoul 151-742, South Korea
Received 14 October 1998; received in revised form 12 January 1999
Abstract
For the hydrogenation of (1-phenylthiophene)Mn(CO)3 (2), the nature of the thiophene derivatives strongly affect the yields and
distribution of reaction products. When 3-methyl- and 3,4-dimethylthiophene were used as thiophene derivatives, the dimer
[Mn(CO)4(SPh)]2 (7) and the tetramer [Mn(CO)3(SPh)]4 (8) was obtained as major products and the hydrodesulfurized product,
isoprene or 2,3-dimethyl-1,3-butadiene were obtained in a high yield. Structures of 7 and 8 were verified by X-ray diffraction
studies. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Thiophene; Manganese; Hydrodesulfurization; Cubane
1. Introduction
While 1 does not react with H2, complexes 2a and 2b
readily undergo hydrogenolysis of a CꢀS bond to afford
compounds 3–5, and diphenyl disulfide (2).
Due to the great importance of hydrodesulfurization
(HDS) in petroleum refining, a considerable amount of
research has been directed to the study of homogeneous
model systems that may mimic some of the chemical
steps occurring during the heterogeneously catalyzed
industrial process [1]. Thiophenic molecules are of par-
ticular interest in this regard due to their reluctance to
undergo desulfurization. Recently, we reported [2,3]
that neutral complexes 2a are formed via nucleophilic
addition of PhMgBr to the sulfur in (thio-
phene)Mn(CO)3+ (1) (1).
Such reactions may be relevant to the general problem
of HDS of thiophenic molecules. In order to more
thoroughly investigate this reaction, we report herein
the hydrogenation of (1-phenyl-2,5-dimethylthio-
phene)Mn(CO)3 (2c), (1-phenyl-3-methylthiophene)Mn-
(1)
* Corresponding author. Fax: +82-2-889-1568.
E-mail address: ykchung@plaza.snu.ac.kr (Y.K. Chung)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00029-7

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D.S. Choi et al. / Journal of Organometallic Chemistry 579 (1999) 385–390
(CO)3 (2d), and (1-phenyl-3,4-dimethylthiophene)Mn-
(CO)3 (2e). It is shown that two of the hydrogenation
products are the dimer [Mn(CO)4(SPh)]2 (7) and the
cubane-type molecule [Mn(CO)3(SPh)]4 (8). We also
report the X-ray crystal structures of 7 and 8.
(CO)3 (9) is the same type as 3 and 6. In addition to
these compounds, liberation of isoprene was confi-
rmed by GC-MS (mass number: 68; yield: 79%) [5].
Formation of 7 and 8 was confirmed by the X-ray
structure determinations. Compound 7 can be com-
pletely converted into 8 by heating in THF. However,
neither 5 nor 9 is converted to 8 when heated or
treated with CO or H2. This means that the origin of
8 is from 7 and not from 5 or 9 and that 7 (or 8)
and 9 may come from different intermediates. Treat-
ment of 7 with H2 did not produce a noticeable
amount of 5. Compound 9 is derived from the C5ꢀS
cleavage. The C2ꢀS cleaved product, presumably
{h1:h3-PhSCHCHC(CH3)2}-Mn(CO)3 (A) was not ob-
served presumably due to the gem-dialkyl effect [6].
2. Results and discussion
The manganese thiophene complexes were prepared
by the reaction of the appropriate thiophene with
Mn(CO)5BF4 in dichloromethane [2–4]. Nucleophilic
addition of PhMgBr to the sulfur in the manganese
thiophene complexes led to reasonable yields of com-
plexes 2c, 2d and 2e.
Treatment of 2c in THF with 10 atm of H2 at
room temperature for 7 days led to the isolation of 6
in 81% yield (3).
Instead of A, 7 and 8 were obtained. We can envis-
age that 7 and 8 may come from A. However, we do
not have any evidence to support the relation be-
tween A and 7 (or 8). Nevertheless, in addition to the
C5ꢀS cleavage there should be other reaction routes
to explain formation of 7 and 8.
(3)
Compound
(CO)3 (6) is the same type as 3.
{h1:h3-PhSC(CH3)CHCHCH2CH3}Mn-
Treatment of 2d in THF with 10 atm of H2 at
room temperature for 2 days afforded 5, 7, 8, 9,
PhSSPh and isoprene (4).
We have determined the X-ray crystal structures of
7 and 8. Figs. 1 and 2 show the structures of 7 and 8
and Tables 1 and 2 give a summary of the crystallo-
graphic data and selected bond lengths and angles of
7 and 8. Recently, [Mn(CO)4(SC6H4CH3-p)]2 was
characterized crystallographically [4]. The crystal
structure of 7 is essentially the same as that of
[Mn(CO)4(SC6H4CH3-p)]2. The MnꢀS bond distances
˚
are between 2.395(2) and 2.401(2) A and the SꢀC
˚
bond distances are between 1.784(7) and 1.793(9) A.
Compound 8 has no metal–metal bonds, with the
sulfur lying off the centers of the triangular faces.
˚
The Mn1ꢀMn2 distance is 3.763(1) A, longer than the
sum of covalent radii. The average MnꢀS bond dis-
˚
tance is 2.393 A, slightly longer than those in tricar-
bonyl[(methylsulfidomethyl)phenyl-2-C,S]triphenylpho-
sphinemanganese: C6H4CH2SCH3Mn(CO)3PPh3 (2.310
˚
(4) A) [7], trialkylphosphinedithiocarboxylato complex
˚
[Mn2(CO)6(m-S2CPCy3)] (2.282(2) and 2.335(2) A) [8],
the terminal thiolate complex (h6-C6H6)Mn(CO)2SPh
(2.350(3) A), the bridging thiolate {[(h6-1,3,5-
˚
C6Me3H3)(CO)2Mn]2(SPh)}+ (2.347(2) and 2.358(2)
A) [9], and the bridging thietane complex
Two of the isolated products are the dimer
[Mn(CO)4(SPh)]2 (7) (13%) and the tetrameric cubane
[Mn(CO)3(SPh)]4 (8) (41%). These compounds are
newly characterized in this reaction. Compounds [(m-
H)(m-SPh)Mn2(CO)8] (5) and diphenyl disulfide were
previously generated by the hydrogenation of 2a and
2b [3]. Compound {h1:h3-PhSCHC(CH3)CHCH3}Mn-
˚
Mn2(CO)8[m-SCH2CMe2CH2] (2.207(1) and 2.211(1)
˚
A) [10]. Each manganese has an octahedral coordina-
tion geometry.
Hydrogenation of 2e led to the isolation of various
products (6).

D.S. Choi et al. / Journal of Organometallic Chemistry 579 (1999) 385–390
387
pressure of CO. Treatment of 2e with 30 atm of H2 for
5 days led to ca. 91% of 2,3-dimethyl-1,3-butadiene.
The liberation of 2,3-dimethyl-1,3-butadiene was de-
1
tected by GC-MS and H-NMR [11].
The results for hydrogenation of 2d and 2e are quite
different from the hydrogenation of 2a, 2b and 2c.
Hydrogenation products are quite dependent upon the
nature of thiophene derivatives, e.g. the position(s) of
the substituent(s) on the thiophene ring. We envision
that the stability of the CꢀS cleaved product(s) de-
pend(s) upon the position of substituent(s). Thus, when
the substituent is located at the 2-position, the C2ꢀS
cleaved product 3 is stable, and when the substituent is
situated at the 3-position, the C5ꢀS cleaved product 9 is
stable, but the C2ꢀS cleaved products (presumably A)
may be quite unstable to be isolated. When the sub-
stituents are at the 3- and 4-positions, we failed to
observe the presence of the C2ꢀS or C5ꢀS cleaved
product (presumably B). When the C2ꢀS or C5ꢀS
cleaved product seems to be unstable, formation of 7
and 8 is observed. Thus, we envisage that there will be
a relation between formation of 7 and 8 and the
stability of CꢀS cleaved product(s). One notable thing
in the hydrogenation for 2d and 2e is the high yield
generation of the hydrodesulfurized organic com-
pounds, i.e. isoprene and 2,3-dimethyl-1,3-butadiene.
For the hydrogenation of 2a, 2b and 2c we failed to
detect hydrodesulfurized organic compounds. Right
now we do not have any plausible mechanisms to
explain the generation of the hydrodesulfurized organic
compound. To firmly establish the mechanism, further
investigation is needed.
When 2e was treated with the 10 atm of H2, the
hydrogenation reaction did not go to completion. At 30
atm of H2, the reaction went to completion and com-
pounds 5, 7, 8 and diphenyl disulfide were isolated as
products. It is almost the same result as the hydrogena-
tion products of 2d, but the distribution of products is
quite different: a considerable amount of diphenyl
disulfide was isolated for the hydrogenation of 2e.
Furthermore, formation of {(h1:h3-PhSCHC(Me)-
C(Me)2}Mn(CO)3 (B), which may be akin to the 9, was
not observed, presumably, due to the gem-dialkyl effect
[6].
These observations imply that there will be a relation
between the yield of diphenyl sulfide and B. Treatment
of 2e with a mixture of H2 and CO (30 and 10 atm,
respectively) led to an increase in the yield of 7 from 12
to 38% and to a decrease in the yield of 8 from 26 to
12%, respectively. This suggests that the yields of 7 and
8 are correlated to each other and depend upon the
In conclusion, we have demonstrated that for the
hydrogenation of 2, the nature of thiophene derivatives
Fig. 1. ORTEP drawing and atomic numbering scheme for 7.

388
D.S. Choi et al. / Journal of Organometallic Chemistry 579 (1999) 385–390
Fig. 2. ORTEP drawing and atomic numbering scheme for 8.
strongly affect the yields and distribution of reaction
products. When 3-methyl- or 3,4-dimethylthiophene
was used as thiophene derivatives, 7 and 8 were
obtained as major products and formation of
hydrodesulfurized organic compounds, such as isoprene
and 2,3-dimethyl-1,3-butadiene, was confirmed by
GC-MS and 1H-NMR. Structures of 7 and 8 were
solved by X-ray diffraction studies.
(CO)3]BF4 (thiophene=3-methylthiophene, 2,5-dim-
ethylthiophene and 3,4-dimethylthiophene: 2a, 2b and
2d, respectively) were previously reported [2–4].
Table 1
Crystal data for 7 and 8
7
8
Formula
C20H10Mn2O8S2
C36H20Mn4O12S
4
3. Experimental
Formula weight
552.28
992.52
˚
u(Mo–Ka) (A)
0.71073
0.7×0.4×0.3
P1
0.71073
0.3×0.3×0.2
C2/c
11.524(2)
22.018(2)
16.514(2)
90
108.231(13)
90
3979.7(10)
4
Crystal size (mm3)
3.1. General
Space group
˚
a (A)
7.7353(14)
9.2820(7)
15.552(2)
90.709(8)
96.634(13)
101.727(11)
1085.2(3)
2
1.690
4.48–50.00
3809
289
0.0785
All solvents were purified by standard methods and
all synthetic procedures were done under a nitrogen
atmosphere. Reagent grade chemicals were used with-
out further purification.
Elemental analyses were done at the Chemical Ana-
lytic Center, College of Engineering, Seoul National
University. 1H-NMR spectra were obtained with a
Bruker BPX-300 or AMX-500. Infrared spectra were
recorded on a Shimadzu IR-470 spectrometer. GC-MS
spectra were recorded on a HP 6890 Series GC system
with HP 5973 mass selective detector.
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
3
˚
V (A )
Z
zcalc (g cm−3
2q range
Data
)
1.657
3.70–49.90
1952
Parameters
R (all data)
253
0.0476
0.1041
1.109
wR2 (all data)
0.2346
1.238
3,4-Dimethylthiophene was prepared by the pub-
lished procedure [12]. Compounds [(thiophene)Mn-
S

D.S. Choi et al. / Journal of Organometallic Chemistry 579 (1999) 385–390
389
Table 2
˚
Selected bond distances (A) and angles (°) for 7 and 8
7
Mn1ꢀS
C02ꢀMn1ꢀS
2.389(2)
177.0(3)
Mn2ꢀS2
C1ꢀS1ꢀMn1
2.401(2)
114.2(3)
S1ꢀC1
C7ꢀS2ꢀMn2
1.793(9)
113.7(3)
8
Mn1ꢀC02
Mn2ꢀS2
S2ꢀC7
C02ꢀMn1ꢀC03
S1ꢀMn1ꢀS2
C1ꢀSꢀMn(2)
1.794(8)
2.393(2)
1.800(7)
93.6(3)
76.18(6)
117.0(2)
Mn1ꢀS1
Mn2ꢀS1
C01ꢀO01
C02ꢀMn1ꢀS1
C05ꢀMn2ꢀC04
Mn1ꢀS1ꢀMn2
2.391(2)
2.395(2)
1.126(8)
171.6(3)
91.5(4)
Mn1ꢀS2
S1ꢀC1
C02ꢀO02
C03ꢀMn1ꢀS1
C05ꢀMn2ꢀS2
C1ꢀS1ꢀMn1
2.395(2)
1.805(6)
1.144(8)
92.2(2)
171.7(3)
117.0(2)
103.66(7)
3.2. Synthesis of [(3,4-dimethylthiophene)Mn(CO)3]BF4
reactor. The reactor was charged with 10 atm of H2.
The solution was stirred at room temperature for 5
days. After releasing the pressure, the solution was
filtered and the filtrate was evaporated to dryness.
Chromatography on a silica gel column eluting with
hexane gave 0.122 g of 6 (81%). IR (hexane) w(CO):
AgBF4 (1.42 g, 7.3 mmol) was added to Mn(CO)5Br
(2.0 g, 7.3 mmol) in CH2Cl2 (40 ml), and the mixture
was stirred for 1 min at room temperature in the
absence of light. At this stage 3,4-dimethylthiophene
(0.98 g, 8.76 mmol) was added and the mixture was
heated at reflux for 12 h. The volume was then reduced
to 5 ml, and the product was precipitated as the BF4−
salt by addition of Et2O. Yield: 65% (1.61 g). IR
2050, 1933, 1921 cm−1
;
1H-NMR (CDCl3): one
diastereomer l 7.56 (m, 2H, Ph), 7.44 (m, 1H, Ph), 7.39
(m, 2H, Ph), 4.80 (d, 9.3 Hz, 1H), 2.24 (s, 3H, CH3),
2.01 (m, 1H), 1.90 (m, 1H), 1.32 (m, 1H), 1.19 (t, 7.4
Hz, 3H, CH3); other diastereomer l 7.24 (m, 1H, Ph),
7.19 (m, 2H, Ph), 6.98 (m, 2H, Ph), 5.09 (d, 9.5 Hz,
1H), 2.69 (s, 3H, CH3), 1.92–1.87 (m, 2H), 1.23 (m,
1H), 0.96 (t, 7.4 Hz, 3H, CH3) ppm; Anal. Found: C,
54.32; H, 4.41; S, 10.11. Calc. for C15H15MnO3S: C,
54.55; H, 4.58; S, 9.71.
(CH3NO2) w(CO): 2065, 1966 cm−1
;
1H-NMR
(CD3NO2): l 6.60 (s, 2H), 2.49 (s, 6H) ppm; Anal.
Found: C, 31.63; H, 2.06. Calc. for C9H8BF4MnO3S: C,
31.99; H, 2.39.
3.3. Synthesis of 2
3.5. Reaction of 2d with H2
These complexes were prepared by a procedure previ-
ously described for 2a,b,d [3]. In a typical synthesis of
Compound 2d (0.10 g, 0.32mmol) and THF (10 ml)
were put in a 100 ml stainless steel high pressure
reactor. The reactor was charged with 10 atm of H2.
The solution was stirred at room temperature for 5
days. After releasing the pressure, the solution was
filtered and the filtrate was evaporated to dryness.
Chromatography on a silica gel column eluting with
hexane gave the hydride (trace), diphenyl disulfide
(trace), the dimer (23 mg, 13%), {h1:h3-
PhSCHC(CH3)CH(CH3)}Mn(CO)3 (10 mg, 10%), and
2e, to
a
solution of [(3,4-dimethylthiophene)-
Mn(CO)3]BF4 (0.91 g, 2.69 mmol) in 30 ml of THF,
PhMgBr (1.2 equivalents, 3.48 mmol) was added at 0°C
under N2. The reaction mixture was stirred for 30 min
and allowed to warm to room temperature. To this
solution diethyl ether (30 ml) and saturated aq. NH4Cl
(30 ml) were added. The organic layer was collected,
dried over MgSO4, concentrated, and chromatographed
on a silica gel column with n-hexane and diethyl ether
(v/v, 10:1) as eluant to give the product 2e as a yellow
solid. Yield: 55% (0.49 g). IR (CH2Cl2) w(CO): 1984,
the
PhSCHC(CH3)CH(CH3)}Mn(CO)3: IR (hexane) w(CO)
2010, 1933, 1920 cm−1 1H-NMR (CDCl3) of one
cubane
(32
mg,
41%).
{h1:h3-
1899 cm−1 1H-NMR (CDCl3): l 7.36 (m, 3H, Ph),
;
;
7.18 (m, 2H, Ph), 2.57 (s, 2H), 2.20 (s, 6H, CH3) ppm;
Anal. Found: C, 54.82; H, 3.68; S, 9.88. Calc. for
C15H13MnO3S: C, 54.88; H, 3.97; S, 9.77. For 2c: Yield:
isomer: l 7.3–7.0 (m, 5H, Ph), 5.11 (s, 1H), 2.03 (s, 3H,
CH3), 1.61 (d, 6.1 Hz, 3H, CH3), 1.36 (q, 6.1 Hz, 1H)
1
1
31%. IR (hexane) w(CO): 1975, 1869 cm−1; H-NMR
ppm; H-NMR (CDCl3) of the other isomer: l 7.6–7.3
(m, 5H, Ph), 5.29 (s, 1H), 2.06 (s, 3H, CH3), 1.69 (d, 6.1
Hz, 3H, CH3), 1.11 (q, 6.1 Hz, 1H) ppm; Anal. Found:
C, 52.98; H, 4.23; S, 10.02. Calc. for C14H13MnO3S: C,
53.17; H, 4.14; S, 10.14. Dimer: IR (hexane) w(CO)
(CD2Cl2): l 7.6–7.5 (m, 5H, Ph), 5.12 (s, 2H), 1.79 (s,
6H, CH3) ppm; Anal. Found: C, 54.79; H, 4.12. Calc.
for C15H13MnO3S: C, 54.89; H, 3.96.
2064, 2002, 1994, 1959 cm−1 1H-NMR (CDCl3): l
;
3.4. Reaction of 2c with H2
7.58 (d, 8.0 Hz, 4H), 7.32 (dd, 7.2 Hz, 8.0 Hz, 4H), 7.25
(t, 7.2 Hz, 2H) ppm; Anal. Found: C, 43.19; H, 1.80; S,
11.91. Calc. for C20H10Mn2O8S2: C, 43.50; H, 1.83; S,
Compound 2c (0.150 g, 0.457 mmol) and THF (10
ml) were put in a 100 ml stainless steel high pressure

390
D.S. Choi et al. / Journal of Organometallic Chemistry 579 (1999) 385–390
11.61. Cubane: IR (hexane) w(CO) 2010, 1942 cm−1
;
and refined by full-matrix least-squares with SHELXL-
1H-NMR (CDCl3): l 8.0 (d, 7.2 Hz, 8H), 7.53 (dd, 7.2
Hz, 8H), 7.44 (t, 7.2 Hz, 4H) ppm; Anal. Found: C,
43.42; H, 1.84. Calc. for C36H20Mn4O12S4: C, 43.56; H,
2.03.
93. All non-hydrogen atoms were refined with an-
isotropic temperature factors; hydrogen atoms were
refined isotropically using a riding model with 1.2 times
the equivalent isotropic temperature factors of the
atoms to which they are attached. Supplementary mate-
rials for 7 and 8 (tables of atomic coordinates, bond
lengths and angles, anisotropic displacement parame-
ters, hydrogen atom positional and displacement
parameters, and observed and calculated structure fac-
tors) have been deposited with the Cambridge Crystal-
lographic Data Center.
3.6. Reaction of 2e with H2
Compound 2e (0.10 g, 0.296 mmol) and THF (10 ml)
were put in a 100 ml stainless steel high pressure
reactor. The reactor was charged with 30 atm of H2.
The solution was stirred at room temperature for 5
days. After releasing the pressure, the solution was
filtered and the filtrate was evaporated to dryness.
Chromatography on a silica gel column eluting with
hexane gave the hydride (trace), diphenyl disulfide
(0.011 g, 35%), and the dimer (0.011 g, 7%) and eluting
with hexane/diethyl ether (v/v, 60:1) gave cubane (0.019
g, 26%).
Acknowledgements
The authors thank the Korea Science and Engineer-
ing Foundation (96-0501-03-01-3), the Ministry of Edu-
cation (BSRI 97-3415), and the KOSEF through the
Center for Molecular Catalysis for financial support.
3.7. Reaction of 2e with H2 and CO
Compound 2e (0.10 g, 0.29 mmol) and THF (10 ml)
were put in a 100 ml stainless steel high pressure
reactor. The reactor was charged with 30 atm of H2 and
10 atm of CO. The solution was stirred at room tem-
perature for 5 days. After releasing the pressure, the
solution was filtered and the filtrate was evaporated to
dryness. Chromatography on a silica gel column eluting
with hexane gave the hydride (trace), diphenyl disulfide
(13 mg, 40%), and the dimer (31 mg, 38%) and eluting
with hexane/diethyl ether (v/v, 60:1) gave cubane (9 mg,
12%).
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3.8. Synthesis of 8 from 7
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Compound 7 (70 mg) in 10 ml of THF was vigor-
ously refluxed for 8 h. The solution was cooled and
concentrated, and chromatographed on a silica gel
column eluting with hexane and diethyl ether (v/v,
60:1). Yield: 59 mg (94%).
3.9. X-ray structure determination of 7 and 8
Diffraction was measured by an Enraf–Nonius
CAD4 diffractometer with a ꢀ–2q scan method. Unit
cells were determined by centering 25 reflections in the
approximate 2q range. Other relevant experimental de-
tails are given in the Supporting Information. The
structure was solved by direct method using SHELXS-86
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4104.
[11] The yield was calculated by comparison of the GC-MS chro-
matogram of the 2,3-dimethyl-1,3-butadiene with that of an
internal standard anisole. 1H-NMR(C6D6): l 5.03 (s, 2H), 4.92
(s, 2H), 1.83 (s, 6H) ppm.
[12] J.M. Tour, R. Wu, Macromolecules 25 (1992) 1901.
.