Highly selective iron-catalyzed synthesis of alkenes by the reduction of alkynes

Article abstract of DOI:10.1002/asia.201000941

Herein, the iron-catalyzed reduction of a variety of alkynes with silanes as a reductant has been examined. With a straightforward catalyst system composed of diiron nonacarbonyl and tributyl phosphane, excellent yields and chemoselectivities (>99 %) were obtained for the formation of the corresponding alkenes. After studying the reaction conditions, and the scope and limitations of the reaction, several attempts were undertaken to shed light on the reaction mechanism. Im Rahmen dieser Arbeit wird die Eisen-katalysierte Reduktion von Alkinen zu den entsprechenden Alkenen mit Hilfe von Silanen vorgestellt. Hierbei konnten exzellente Ausbeuten und Selektivitaeten (>99 %) durch die Modifikation des eingesetzten Eisenkatalysators mit Phosphanen beobachtet werden. Nach genauer Untersuchung verschiedenster Reaktionsparameter wurden die hervorragenden Eigenschaften des Katalysatorsystems in der Reduktion zahlreicher Alkine gezeigt. Zum besseren Verstaendnis der Reaktion wurden verschiedene mechanistische Experimente durchgefuehrt. Iron Made′m: In situ generated iron complexes catalyze the reduction of alkynes with silanes as a hydride source with excellent selectivity (>99 %). Copyright

Full text of DOI:10.1002/asia.201000941

DOI: 10.1002/asia.201000941
Highly Selective Iron-Catalyzed Synthesis of Alkenes by the Reduction of
Alkynes
[
a]
[a]
[b]
Stephan Enthaler,* Michael Haberberger, and Elisabeth Irran
Abstract: Herein, the iron-catalyzed reduction of a variety of alkynes with silanes
as a reductant has been examined. With a straightforward catalyst system com-
posed of diiron nonacarbonyl and tributyl phosphane, excellent yields and chemo-
selectivities (>99%) were obtained for the formation of the corresponding al-
kenes. After studying the reaction conditions, and the scope and limitations of the
reaction, several attempts were undertaken to shed light on the reaction mecha-
nism.
Keywords: alkynes · homogeneous
catalysis · iron · olefins · reduction
Introduction
duction processes, such as C=O, C=C, C=N, and NO reduc-
2
[3,4]
tions.
Indeed, iron catalysts have been applied for the re-
Alkenes have an extensive range of applications including,
as synthons for bulk chemicals, pharmaceuticals, agrochemi-
cals, polymers, in the syntheses of natural compounds, and
as key intermediates in organic syntheses. During the last
few decades, a number of methodologies have been estab-
lished to access alkenes; of these, the reduction of alkynes is
of great significance, because of the availability and low cost
of the starting materials (alkynes, hydrogen, and hydrogen
duction of alkynes to access alkenes using hydrogen as re-
[5]
ductant. However, problems can arise by over-reduction to
the corresponding alkane derivatives which reduce the
impact of the method. Apart from over-reduction the (E)/
(Z)-selectivity must be addressed by the catalysts. Here the
[6]
routes to (Z)-alkenes are of interest. On the other hand,
catalytic hydrosilylation is an alternative to hydrogenation,
because of mild reaction conditions and simplicity. Further-
more, the silane functionality in the obtained products (alke-
nylsilanes) can be the starting point for additional transfor-
[1]
sources). Catalytic hydrogenation is the most-direct route
to alkenes. In this regard, the application of transition metal
complexes has been demonstrated as useful reduction cata-
[7]
mations. Promising efforts were reported by the group of
Chirik, who applied well-defined iron-complexes modified
by tridentate nitrogen ligands to reduce alkynes with silanes
[2]
lysts to control the reaction. To date, several catalysts rely
on precious metals, such as rhodium, ruthenium, iridium, or
palladium. Owing to the high price and sometimes toxicity,
less-expensive “biological” metal-based catalysts are highly
[8]
to the corresponding alkene at ambient temperature. Even
if an excellent iron-based procedure is available, the devel-
opment of a general method to produce alkenes in an effi-
cient and selective manner is still a desirable objective. Re-
cently, we reported the reduction of sulfoxides in the pres-
ence of alkynyl groups to yield their corresponding sulfides,
[3]
desirable. Thus the use of iron is probably of great signifi-
cance. During the last few years, the potential use of iron in
synthetic transformations has been exhibited in various re-
[9,10]
with significant amounts of alkene side-products.
Based
[
a] Dr. S. Enthaler, M. Haberberger
Technische Universitꢀt Berlin
on these results, we wish to portray the application of a
robust and easy-to-adopt iron-based catalyst for the highly
selective reduction of alkynes to alkenes.
Department of Chemistry
Cluster of Excellence “Unifying Concepts in Catalysis”
Straße des 17. Juni 115
1
0623 Berlin (Germany)
Fax : (+49)3031429732
E-mail: stephan.enthaler@tu-berlin.de
Results and Discussion
[
b] Dr. E. Irran
Initial studies on the influence of the reaction conditions
were carried out with diphenylacetylene 1 as the model sub-
strate by using 5.0 mol% of diiron nonacarbonyl and various
Institute of Chemistry: Metalorganics and Inorganic Materials
Technische Universitꢀt Berlin
Straße des 17. Juni 135, Sekr. C2, 10623 Berlin (Germany)
Chem. Asian J. 2011, 6, 1613 – 1623
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1613

FULL PAPERS
silanes as reducing reagent in toluene at 1008C (Table 1, en-
tries 1–4). Afterwards, the reaction was quenched under
aqueous conditions. Best performance for the formation of
(Table 1, entry 12). Using tetrahydrofuran as solvent under
identical conditions resulted in 76% yield and 84% (Z)-se-
lectivity. Importantly, the catalyst demonstrated comparable
activity even when decreasing the temperature to 258C, with
stilbene was found for (EtO) SiH with yields of up to 80%
3
5
7% of (E)/(Z)-stilbene detected after one day (Table 1,
entry 13). Besides, the reduction of the catalyst loading to
Table 1. Iron-catalyzed reduction of diphenylacetylene 1.
1
mol% resulted in a diminished yield.
To improve the catalyst performance, the influence of var-
ious nitrogen-containing ligands were studied (Table 2, en-
tries 2–8). The highest (Z)-selectivity was detected for phe-
nanthroline 5 (92%) and 2,2ꢂ-bipyridine 4 (86%), but with
lower conversions. In addition, monodentate and bidentate
phosphane ligands were applied in combination with
Fe (CO) (Table 2, entries 9–14). Excellent (Z)-selectivity
[
a]
Entry
Iron source
mol%]
Silane
Conv. Yield of stil-
[%] bene [%]
(Z)-Selec-
tivity [%]
[
b]
[
1
2
3
4
5
6
7
8
9
Fe
Fe
Fe
Fe
2
2
2
2
(CO)
(CO)
(CO)
(CO)
9
9
9
9
PhSiH
PMHS
3
60
59
79
72
22
>99
>99
>99
>99
>99
>99
–
33
55
84
58
58
68
–
2
9
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO)
3
SiH
was observed for simple tributyl phosphane (96%) and
1,1’-bis(diphenylphosphino)ferrocene) (dppf; 92%). Fur-
Me
2
PhSiH
(
Fe(CO)
Fe (CO)12
FeCl ·4H
FeCl
Fe(ClO
[Fe(acac)
5
PMHS
PMHS
PMHS
PMHS
PMHS
PMHS
3
31
thermore, performing the reaction at room temperature im-
2
2
O
<1
<1
46
proved the cis-selectivity for the Fe (CO) /tributyl phos-
2
9
3
–
72
–
phane system to>99% (Table 2, entry 9). To identify the
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
4
)
3
52
52
84
62
86
–
role of the phosphane in the reaction, the phosphorus–sele-
10
11
12
13
14
15
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
]
47
76
82
57
<1
<1
>99
>99
>99
>99
–
[
[
[
[
c]
d]
e]
f]
1
31
77
Fe
Fe
Fe
Fe
2
2
2
2
(CO)
(CO)
(CO)
(CO)
–
9
9
9
9
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(EtO)
(EtO)
(EtO)
(EtO)
(EtO)
3
3
3
3
3
SiH
nium coupling constants [ J AHCTUNETGRNNUN(G P- Se)] were compared to es-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
SiH
SiH
SiH
SiH
timate the s-donor ability of the phosphanes. It has been re-
ported that the magnitude of the coupling constant can be
correlated to basicity, with an increase in the basicity of the
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
–
–
[11]
phosphanes leading to higher coupling constants. Howev-
[
0
a] Reactions were carried out with 0.036 mmol iron precursor (5 mol%),
.72 mmol diphenylacetylene, 0.79 mmol silane (1.1 equiv), 2.0 mL tolu-
ene, 24 h at 1008C. The yield was determined by GC analysis (30 m Rxi-
er, in the monodentate series, PBu3 (J=680 Hz), P-
A
H
U
G
R
N
U
G
ACHTUNGTRENN(UG MeO) Ph) (J=717 Hz), BuPAd (J=680 Hz), as well
2 3 2
5
8
ms column, 40–3008C, (Z)-stilbene: 8.02 min, (E)-stilbene: 9.12 min, 1
.83 min) with dodecane (7.84 min) as internal standard. In the case of
7
PMHS, 0.5 mL were used. [b] Combined yield of (E)- and (Z)-stilbene.
c] THF, 608C. [d] Toluene, 608C. [e] THF, RT. [f] MeOH, 608C.
[12]
served.
Moreover, the time-dependency of the (Z)-selectivity of
[
stilbene 1a was studied. Samples were taken over time, ac-
cording to the experiment stated in Table 2 entry 9 (608C).
No significant differences in (Z)-selectivity were observed
(>90% in all cases).
after 24 hours, with a (Z)-selectivity of 84%. Other silanes,
such as PhSiH , Me PhSiH, and PMHS [poly(methylhydrosi-
3
2
loxane)] gave similar yields, but with lower cis-selectivity.
Remarkably, the iron-catalyzed reduction of alkynes was
highly selective, as no over-reduction to the corresponding
To explore the scope and limitation of this iron catalyst
(Fe (CO) /PBu ), a variety of alkyne substrates were tested
2
9
3
1,2-diphenylethane was observed. Moreover, different iron
under the reaction conditions given in Table 2 entry 9
salts were tested (Table 1, entries 5–10), whilst in the ab-
sence of any iron salts no product was detected (Table 1,
entry 15). However, no progress was achieved with respect
to yield and (Z)-selectivity. Decreasing the reaction temper-
ature to 608C did not improve the reaction outcome
(608C). First, various substituted diphenyl acetylenes were
reacted with (EtO) SiH (Table 3). In all cases, the reaction
3
time was prolonged to 48 hours to ensure higher conversion.
No significant effect was observed in the presence of elec-
tron-withdrawing or electron-donating groups (Table 3, en-
tries 1-9). However, a decrease of the (Z)-selectivity was no-
ticed compared to the reduction of parent compound 1, but
the chemoselectivity for alkene formation was still excellent
(>99%). Difficulties were observed for compound 22 which
contained a nitro group at the para-position (Table 3,
entry 9); here, some reduction of the nitro group to the cor-
responding amine was found. Importantly, the reduction of
the nitro group decreases the reactivity of the alkenyl
moiety because only the (4-aminophenyl)-phenylacetylene
was detected, whilst the corresponding 4-amino stilbene was
not observed. Good performance was demonstrated for the
reduction of alkynes containing heteroaromatic groups
(Table 3, entry 10). Interestingly, the (E)-isomer was formed
as the major compound. Moreover, phenyl acetylene as the
Abstract in German: Im Rahmen dieser Arbeit wird die
Eisen-katalysierte Reduktion von Alkinen zu den entspre-
chenden Alkenen mit Hilfe von Silanen vorgestellt. Hier-
bei konnten exzellente Ausbeuten und Selektivitꢀten (>
99%) durch die Modifikation des eingesetzten Eisenkataly-
sators mit Phosphanen beobachtet werden. Nach genauer
Untersuchung verschiedenster Reaktionsparameter wurden
die hervorragenden Eigenschaften des Katalysatorsystems in
der Reduktion zahlreicher Alkine gezeigt. Zum besseren
Verstꢀndnis der Reaktion wurden verschiedene mechanisti-
sche Experimente durchgefꢃhrt.
1614
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 1613 – 1623

Iron-Catalyzed Synthesis of Alkenes by Alkyne Reduction
Table 2. Iron-catalyzed reduction of diphenylacetylene 1 in the presence of N- or P-ligands.
presence
of
Fe (CO)9
2
(
Table 4). Excellent chemose-
lectivity (>99%) was observed
for the reduction of alkynes in
the presence of aldehydes,
esters, amides, C=C double
bonds, and epoxides, whilst ke-
tones (43%) and sulfoxide
groups (7%) were reduced to
some extent.
Afterwards, competitive-re-
duction experiments of m/p-
substituted substrates were car-
ried out. Equimolar amounts
[
b]
[b]
Entry
Ligand
M/L
–
Conv. [%]
Yield of Stilbene [%]
(Z)-Selectivity [%]
1
2
–
–
76
85
>99
>99
84
48
2
1:1
3
4
3
4
1:1
42
52
>99
>99
76
86
1:1
1:1
5
6
5
6
63
>99
92
–
of
diphenylacetylene
(
0.72 mmol) and substituted di-
1:2
<1
–
phenylacetylene (0.72 mmol)
were reacted with triethoxysi-
lane (0.72 mmol) in the pres-
ence of the in situ generated
catalyst (Fe (CO) /PBu ).
[
[
11]
7
8
7
8
1:2
1:1
77
79
>99
>99
75
85
2
9
3
The reaction mixture was
hydrolyzed after 24 hours and
the yields of both compounds
and their corresponding iso-
mers was determined by GC
analysis and correlated with
c]
9
1
1
PBu
3
9
10
11
1:2
1:2
1:2
68 (64)
73
87
>99 (>99)
>99
>99
96 (>99)
88
72
0
1
P
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(2,6-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(MeO)
2
Ph)
3
BuPAd
2
[
c]
1
2
12
1:1
79 (59)
>99 (>99)
92 (88)
+
[13]
the Hammett s (Figure 1).
The values were correlated
1
3
4
13
14
1:1
1:1
85
45
>99
>99
81
76
+
after log CAHTUNGTRENUNG( k /k )=1s . Howev-
X H
er, no helpful information was
obtained for the single isomers.
1
2
[
1
a] Reactions were carried out with 0.036 mmol Fe
0 mol%), 0.72 mmol diphenylacetylene, 0.79 mmol (EtO)
yield was determined by GC analysis (30 m Rxi-5 ms column, 40–3008C, (Z)-stilbene: 8.02 min, (E)-stilbene:
.12 min, 1: 8.83 min) with dodecane (7.84 min) as an internal standard. [b] Combined yield of (E)- and (Z)-
2
(CO)
9
(5 mol%), 0.036 mmol or 0.0072 mmol ligand (5–
SiH (1.1 equiv), 2.0 mL THF, 24 h at 608C. The
A value of R =0.82 was ach-
3
ieved for the summation of the
isomers. Linear regression
analysis led to a reaction con-
9
stilbene. [c] In parenthesis: 48 h at RT.
stant value of 0.99 for both iso-
mers. The positive Hammett
substrate yielded styrene in excellent yields (>99%) with
an alkene-selectivity of 95%, whilst the double reduced
product (ethyl benzene) was formed as a side-product
value indicated a partial negative charge in the transition
state in comparison with the starting substrates.
To gain additional insight into the reaction mechanism,
the carbonÀcarbon triple bond was applied as a probe. First,
(
2
Table 3, entry 12). The reduction of the conjugated system
6 showed as main transformation the reduction of one
1
3
the C NMR data can be of interest for studying the effect
of diphenyl-acetylene substitution and the electronic fea-
tures of the triple bond on the reaction outcome. DFT cal-
culations at the RB3LYP/6-31(d) level were carried out to
model the magnetic properties using the Gauge Independ-
triple bond (75%), whilst the reduction of both alkenyl
groups were observed with 15% (Table 3, entry 13). In addi-
tion, substrates containing functional groups attached to the
triple bond were subjected to catalysis (Table 3, entries 15–
[14,15]
18). In the case of ester functionalities, a mixture of the cor-
ent Atomic Orbital (GIAO) technique.
The accuracy of
responding esters of fumaric acid and maleic acid were ob-
tained in excellent yields. Worthy of note is that the reduc-
tion was highly selective to alkenyl reduction, whilst the
ester groups were not reduced under the described condi-
tions.
In order to study the selectivity of the process, different
substrates containing functional groups sensitive to reduc-
tion or a combination of the diphenylacetylene with an addi-
tional substrate were reacted with triethoxysilane in the
this method compared to experimental values has been re-
[16]
ported by Gevorgyan and co-workers. The GIAO shield-
ing was related to the obtained yields for both product iso-
mers (Figure 2 and Figure 3). Importantly, both triple-
bonded carbon atoms are non-equivalent owing to different
substitution patterns. As seen in Figure 2 and Figure 3, no
strong correlation between the GIAO shielding and the cat-
alytic results was found.
Chem. Asian J. 2011, 6, 1613 – 1623
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1615

S. Enthaler et al.
FULL PAPERS
Table 3. Scope and limitations of the iron-catalyzed reduction of alkynes.
[
a]
[b]
[
[c]
Entry
Substrate
Conv. [%]
cis/trans
d]
1
2
1
68 (>99)
58 (>99)
>99:<1
15
88:12
3
16
72 (>99)
75:25
4
5
17
18
57 (>99)
62 (>99)
80:20
61:39
6
7
8
9
19
20
21
53 (>99)
48 (>99)
63 (>99)
79:21
78:22
78:22
[
e]
22
23
89 (66)
63:37
36:64
1
0
1
55 (>99)
44 (>99)
Figure 1. Hammett correlation for the reduction of p/m-substituted di-
+
1
24
99:1
phenylacetylene [log(k(substituted)/k0(unsubstituted)]=1s ; 1=0.9857;
2
R =0.82 for summation of both isomers.
[
[
f]
1
1
2
3
25
26
>99 (95)
75 (60)
--
63:37
g]
[
h]
1
4
5
27
28
85 (76)
--
1
83 (>99)
19:81
16
17
18
29
30
31
>99 (>99)
80 (>99)
>99 (>99)
43:57
15:85
83:17
[
a] Reactions were carried out with 0.036 mmol Fe
2
(CO)
9
(5 mol%),
0
.072 mmol PBu
3 3
, 0.72 mmol substrate, 0.79 mmol (EtO) SiH (1.1 equiv),
2
.0 mL THF, 48 h at 608C. The conversion was determined by GC (30 m
1
Rxi-5 ms column, 40–3008C) and H NMR analysis. [b] Chemoselectivity
for alkene formation is given in parenthesis. [c] Determined by GC (30 m
1
Rxi-5 ms column, 40–3008C) and H NMR analysis. [d] 24h. [e] 4-H
2
N-
PhCCPh was observed as a side-product. [f] Phenylethane (5%) was ob-
served as a side-product. [g] The reduction of both triple bonds was ob-
served (15%) as a side-reaction. [h] Thiophenol was observed as a side
product (9%).
Secondly, the value for the stretch of the carbonÀcarbon
triple bond was correlated to the results. Owing to the weak-
ness of the stretch, the values were calculated using DFT at
the RB3LYP/6-31(d) level. Similar to the GIAO shielding,
no precious information were attained (Figure 4). Based on
the Hammett-plot and the calculations, the reaction is prob-
ably comprised of various reaction pathways, which lead to
an undefined picture.
Moreover, several iron complexes were synthesized by re-
acting equimolar amounts of monodentate phosphane 10 or
bidentate dppf 13 with diiron nonacarbonyl in refluxing di-
ethylether. In both cases, single-crystals suitable for X-ray
diffraction analysis were obtained by cooling the solution to
Figure 2. Correlation of the yield and the GIAO shielding of the alkenyl
a-carbon.
room temperature and slow evaporation of the solvent.
Thermal ellipsoid plots for the complexes are displayed in
Figure 5 and Figure 6. In case of the mononuclear complex
41, one monodentate phosphane is coordinated to the iron
center, whilst in case of the bidentate phosphane, both phos-
phorous donors are attached to the metal. Those coordina-
[17]
tion motifs have been reported recently. In complex 41,
four carbonyl ligands are coordinated to the iron center. For
the trans-positioned carbonyl ligand, with respect to the
1616
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 1613 – 1623

Iron-Catalyzed Synthesis of Alkenes by Alkyne Reduction
Table 4. Functional group tolerance of the iron-catalyzed reduction of alkynes.
that determined for the biden-
tate system (2.242–2.254 ꢄ).
[17]
The triaryl moiety of the mon-
odentate system is pyramidal
arranged and slightly distorted
owing to the influence of the
Entry
Substrate
Additive
Yield of Alkyne Reduction
Yield of Second Additive
[%]
Fe(CO) unit compared to sim-
[
b]
4
[%]
ilar complexes. The distortion
angles of the three phenyl
groups are 378, 448, and 658.
The PÀC bond distances are
[
c]
1
2
32
33
55 (>99)
61 (>99)
>99
43
nearly equal (1.842–1.848 ꢄ).
In complex 42, the cyclopen-
tadienyl rings (Cipso-P-P’-C’ipso
are eclipsed by an angle of
9.58 and the distances of FeÀ
bonds are nearly equal
2.242 and 2.254 ꢄ). Owing to
)
3
4
34
35
83 (>99)
67 (>99)
<1
<1
2
P
(
the bidentate coordination,
only three positions on the
metal are blocked by carbonyl
5
6
7
36
37
38
17 (>99)
98 (>99)
32 (>99)
<1
<1
7
ligands.
ligand spanned a bite angle of
9.98, which is in accordance to
the structure reported by Shim
Furthermore,
the
9
[18]
and co-workers.
The IR spectra of 41 shows
three strong CO stretching
8
9
39 >99 (>99)
40 66 (57)
<1
<1
bands at 1981, 1908, and
À1
1
880 cm , whilst for 42, two
[
a] Reactions were carried out with 0.036 mmol Fe
2
(CO)
9 3
(5 mol%), 0.072 mmol PBu , 0.72 mmol 1,
strong CO stretching bands at
0
.72 mmol additional substrate, 0.79 mmol (EtO) SiH (1.1 equiv), 2.0 mL THF, 48 h at 608C. The yield was de-
3
À1
2
028 and 1912 cm and two
termined by GC (30 m Rxi-5 ms column, 40–3008C). [b] (Z)-selectivity is given in parentheses. [c] Undefined
side-products.
weak bands at 2186 and
À1
2
119 cm
were observed. In
1
phosphane ligand, a shorter FeÀC distance (2.920 ꢄ) were
the H NMR spectra of complex 41, a significant signal at
3.22 ppm was attributed to the methoxy-groups, whilst for
42, the characteristic cyclopentadienyl signals were found.
The isolated complexes were then subjected to the cata-
lytic reduction of diphenylacetylene 1 under the reaction
observed as for the cis-carbonyl ligands (2.928–2.938 ꢄ) be-
cause of the trans-effect of the FeÀP bond. In addition, the
FeÀP bond length is 2.338 ꢄ, which is slightly longer than
Figure 3. Correlation of the yield and the GIAO shielding of the alkenyl
b-carbon.
Figure 4. Correlation of the yield with triple bond stretch.
Chem. Asian J. 2011, 6, 1613 – 1623
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1617

S. Enthaler et al.
FULL PAPERS
Those undefined iron complexes presumably also display
catalytic activity. Unfortunately the side-products could not
be fully characterized.
In addition, complexes 41 and 42 were reacted with either
stoichiometric amounts of alkyne 1 or (EtO) SiH to try to
3
isolate the intermediate species. However, various attempts,
including heating, light irradiation, or the addition of
Me NO to replace a carbonyl ligand by alkyne or silane li-
3
gands.
Although the precise mechanism is still unknown, differ-
ent experiments were performed with the isolated com-
plexes to hopefully shed some light on the mechanism. Ini-
tial mechanistic investigations were dedicated to the activa-
tion of the silane by complex 42. The interaction of complex
4
2 with (EtO) SiH was studied in the absence of substrate
3
Figure 5. Molecular structure of (10)Fe(CO)
4
(41). Hydrogen atoms are
1
by H NMR spectroscopy. No signal was found for an iron-
hydride species in the expected region. Based on this result,
the formation of an iron-hydride species can be probably ex-
omitted. Thermal ellipsoids are drawn at the 50% probability level. Se-
lected bond distances [ꢄ]: Fe-C2: 1.762(2), Fe-C: 1.782(2)–1.793(3), Fe-
P: 2.3387(6).
[8]
cluded on the NMR time-scale. Furthermore, owing to the
paramagnetic abilities of the iron species, only broad signals
were observed in NMR studies, which did not allow any val-
uable analysis. Moreover, the reaction was studied by solu-
tion IR methods, by applying the CO-ligands coordinated to
the iron as a probe (Figure 7). First, Fe (CO) was dissolved
2
9
3
Figure 6. Molecular structure of (dppf)Fe(CO) (42). Hydrogen atoms
are omitted. Thermal ellipsoids are drawn at the 50% probability level.
Selected bond distances [ꢄ] and angles [8]: Fe1-C: 1.767(3)–1.782(3), Fe-
P: 2.2421(8)–2.2541(8), P1-Fe1-P2: 99.87(3).
conditions described in Table 2 (Scheme 1). Comparing the
results for the isolated- and well-defined complexes with the
in situ concept, an improved performance was noticed for
the in situ approach. In the case of complex 42, Kim, Shim
and co-workers reported the formation of various iron-con-
taining side-products during the preparation of complex 42.
Figure 7. IR spectroscopic investigation into the interaction of Fe
0, 1 and (EtO) SiH in THF.
2 9
(CO) ,
1
3
in tetrahydrofuran and the appearance of two bands at 2019
À1
and 1992 cm , which can be ascribed to the mode of the
carbonyl ligands. Next, ligand 10 was added and a spectrum
was acquired after 1 hour at 608C; the spectrum showed,
À1
aside from the bands at 2019 and 1992 cm , a band at
À1
1
925 cm that was probably caused by coordination of the
phosphane to the iron. The addition of either alkyne 1
(
10 equiv) or (EtO) SiH (10 equiv) to this solution did not
3
À1
affect the bands at 2019 and 1992 cm , while the band at
1
À1
925 cm disappeared. Finally, all components (Fe (CO) /
2
9
1
0/1/ ACHTUNGERTUNNNG( EtO) SiH) were reacted in tetrahydrofuran resulted in
3
À1
Scheme 1. Comparison of isolated complexes with the in situ approach.
the disappearance of the band at 1992 cm and a significant
1618
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 1613 – 1623

Iron-Catalyzed Synthesis of Alkenes by Alkyne Reduction
À1
decrease in the band at 2019 cm . The disappearance of
ing of the electronic structure of the metal. Furthermore,
the (E)-isomer is favored in the case of functional groups
closely connected to the triple bond, which could be ad-
dressed to a different coordination mode of the substrate to
the metal centre.
one carbonyl band can be probably attributed to the dissoci-
ation of carbonyl ligands to allow new coordination sides for
the alkyne or silane.
Based on our results, and previous reports we have pro-
posed a catalytic mechanism illustrated in Scheme 2. In the
initial step, one carbonyl ligand dissociates (see Figure 7)
Conclusions
In summary, we have demonstrated the value of iron as a
catalyst in the reduction of alkynes to generate the corre-
sponding alkenes. The simplicity of the procedure is outlined
by the application of the commercially available metal
source Fe (CO) , modified by simple PBu , and (EtO) SiH
2
9
3
3
as a hydride source under mild and non-inert conditions.
The outstanding selectivity of the system was shown by the
reduction of several substrates with excellent yields and a
broad functional-group tolerance.
Experimental Section
General
All manipulations with oxygen- and moisture-sensitive compounds were
performed under a nitrogen atmosphere using standard Schlenk tech-
niques. Toluene and tetrahydrofuran were distilled over sodium/benzo-
1
13
phenone ketyl under a nitrogen atmosphere. H and C NMR spectra
1
were recorded on a Bruker AFM 200 spectrometer ( H: 200.13 MHz;
1
3
19
C: 50.32 MHz, F: 188.33 MHz) using the proton signals of the deuter-
ated solvents as reference. Single-crystal X-ray diffraction measurements
were recorded on an Oxford Diffraction Xcalibur S Sapphire spectrome-
ter. IR spectra were recorded either on a Nicolet Series II Magna-IR-
System 750 FTR-IR or on a Perkin–Elmer Spectrum 100 FT-IR. Elec-
Scheme 2. Potential reaction pathways for the reduction of alkynes with
iron catalysts.
tron-impact mass spectra (EI-MS) were recorded on
MAT95S. GC-MS measurements were carried out on a Shimadzu GC-
010 gas chromatograph (30 m Rxi-5 ms column) linked with a Shimadzu
a Finnigan
2
and forms an unsaturated iron species that either coordi-
nates the alkyne or the silane (Scheme 2, cycle A and B).
For both pathways, Chirik and co-workers were able to char-
acterize the iron-alkyne and iron-silane complexes. Un-
fortunately, suitable intermediates could be isolated for nei-
ther the coordination of the silane nor the coordination of
the alkyne. Activation of the CÀC triple bond, owing to the
GCMA-QP 2010 Plus mass spectrometer.
Safety Considerations
[8]
During our studies we used triethoxysilane as a reducing reagent without
incident. However, Berk and Buchwald reported difficulties when work-
[
21]
ing with triethoxysilane.
General Procedure for the Synthesis of Alkynes (Method A)
coordination of the alkyne, allows interactions with the
silane and finally the formation of the alkene (Scheme 2,
cycle B). Furthermore, the reactions of both the iron–alkyne
and iron–silane complexes can be seen as possible pathways
to afford the hydrosilylated product. Same fact can be as-
sumed for the iron–silane complex (Scheme 2, cycle A). Be-
cause no iron–hydride species was detected, we assume a
concerted mechanism for the transfer of the SiÀH function-
Reactions were carried out in accordance with the procedure reported by
[
19a]
Liu and co-workers with small variations.
(10 mol%, 0.8 mmol) and PPh (20 mol%, 1.6 mmol) was stirred for
0 min at room temperature. This mixture was added to an aqueous solu-
An aqueous solution of CuI
3
1
tion of phenylacetylene (9.6 mmol), KOH (16.0 mmol), and the corre-
sponding substituted iodoarene (8.0 mmol). The flask was sealed and
heated to 1208C. After four days, the mixture was cooled to room tem-
perature and the aqueous layer was extracted with diethyl ether (3ꢅ
5
0 mL). The organic layer was washed with water, brine, and dried over
Na SO . The solvent was removed under vacuum and the residue was
2
4
ality via a four-membered transition state (Scheme 2). Two
possibilities can be envisaged: For the (Z)-addition, the acti-
vated alkyne and silane are horizontal to each other in the
transition state, whilst for the (E)-addition, the alkyne and
the silane are positioned orthogonal to one another
either purified by column chromatography on silica gel (n-hexane/ethyl
[19]
acetate 98:2 to 4.5:1) or by crystallization.
(
4-Methoxyphenyl)phenylacetylene (18)
Yield 92% (colorless crystals obtained by crystallization from diethyl
1
3
ether); H NMR (200 MHz, CDCl , 258C): d=7.30–7.64 (7H, m, Ar),
(
Scheme 2). As seen in Table 1 and Table 2, the (Z)/(E)-
1
3
6
.90–6.98 (2H, m, Ar), 3.87 ppm (s, 3H, OCH
3
); C NMR (50.32 MHz,
ratio is strongly depended on the addition of a ligand and
the nature of the ligand; disfavoring of the (E)-addition was
probably derived from the creation of a pocket and chang-
CDCl
3
, 258C): d=159.6, 133.0, 131.4, 128.3, 127.9, 123.6, 115.3, 114.0,
8
9.4, 88.0, 55.2 ppm; IR (KBr): n˜ =3055 (w), 2994 (w), 2958 (w), 2936
(w), 2835 (w), 2216 (w), 1604 (m), 1594 (m), 1510 (s), 1486 (m), 1465
Chem. Asian J. 2011, 6, 1613 – 1623
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1619

S. Enthaler et al.
FULL PAPERS
(
(
m), 1454 (m), 1440 (m), 1288 (m), 1246 (s), 1180 (m), 1139 (w), 1108
(3-Methylphenyl)phenylacetylene (16)
À1
m), 1070 (w), 833 (s), 813 (m), 779 (w), 755 (s), 692 (s), 523 cm (m);
1
+
Yield 89%; H NMR (200 MHz, CDCl
3
, 258C): d=7.50–7.61 (m, 2H),
MS (70 eV, EI) m/z (%)=208 (100, M ), 193 (70), 165 (47), 139 (12),
1
1
3
7
.08–7.44 (m, 10H), 2.37 ppm (s, 3H, CH
3
); C NMR (50.32 MHz,
04 (14).
CDCl
3
, 258C): d=138.0, 132.2, 131.6, 123.4, 123.1, 129.1, 128.7, 128.3,
1
28.2, 128.1, 89.6, 89.0, 21.2 ppm; IR (KBr): n˜ =3056 (w), 2912 (w), 1601
(
4-Fluorophenyl)phenylacetylene (20)
(
m), 1493 (s), 1442 (m), 1070 (w), 913 (w), 783 (s), 755 (s), 689 (s),
Yield 89% (colorless crystals obtained by crystallization from diethyl
À1
+
5
8
44 cm (w); MS (70 eV, EI) m/z (%)=192 (100, M ), 165 (18), 95 (15),
2 (12). R =0.66 (n-hexane/ethyl acetate 4.5:1).
1
ether); H NMR (200 MHz, CDCl
.18–7.29 (m, 3H, Ar), 6.86–6.99 ppm (m, 2H, Ar);
50.32 MHz, CDCl , 258C): d=164.9, 160.0, 133.5, 133.3, 131.5, 128.32,
3
, 258C): d=7.35–7.47 (m, 4H, Ar),
f
1
3
7
(
C NMR
(4-tert-Butylphenyl)phenylacetylene (17)
3
1
3
28.28, 123.1, 119.4, 119.3, 115.8, 115.4, 89.0, 88.3 ppm; IR (KBr): n˜ =
1
Yield 73%; H NMR (200 MHz, CDCl
3
, 258C): d=6.7.30–7.69 (m, 9H,
, 258C):
d=151.4, 131.5, 131.3, 128.2, 128.0, 125.3, 123.5, 120.2, 89.5, 88.7, 34.7,
049 (w), 1594 (m), 1509 (s), 1217 (s), 1157 (m), 1098 (w), 911 (w), 843
1
3
À1
3 3 3
Ar), 1.44 ppm (s, 9H, C ACHTUNGTRENNNU(G CH ) ); C NMR (50.32 MHz, CDCl
(
s), 815 (w), 792 (m), 755 (s), 688 (s), 516 (s), 493 cm (s); MS (70 eV,
+
EI) m/z (%)=196 (100, M ), 175 (13), 170 (15), 98 (19), 85 (14).
3
1
5
1.1 ppm; IR (KBr): n˜ =2963 (s), 1595 (m), 1504 (m), 1442 (m), 1396 (w),
363 (m), 1268 (w), 1103 (w), 1069 (w), 913 (w), 836 (s), 754 (s), 690 (s),
62 cm (m); MS (70 eV, EI) m/z (%)=234 (68, M ), 219 (100), 203
(17), 191 (19), 178 (12), 96 (27); R =0.53 (n-hexane/ethyl acetate 4.5:1).
(
4-Methylphenyl)phenylacetylene (15)
À1
+
1
Yield 77%; H NMR (200 MHz, CDCl
3
, 258C): d=7.38–7.66 (m, 7H,
f
1
3
Ar), 7.20–7.28 (m, 2H, Ar), 2.45 ppm (s, 3H, CH
50.32 MHz, CDCl , 258C): d=138.3, 131.51, 131.46, 129.1, 128.3, 128.0,
23.5, 120.2, 89.6, 88.7, 21.4 ppm; IR (KBr): n˜ =3049 (w), 2912 (w), 1594
m), 1509 (s), 1440 (m), 1106 (w), 1070 (w), 916 (w), 818 (s), 754 (s), 690
3
);
C NMR
Phenyl(2-pyridinyl)acetylene (23)
(
1
3
Yield 88% (colorless crystals obtained by crystallization from diethyl
ether); H NMR (200 MHz, CDCl
.35–7.57 (m, 4H, Ar), 7.18–7.28 (m, 3H, Ar), 7.04–7.13 ppm (m, 1H,
Ar); C NMR (50.32 MHz, CDCl
(
(
(
1
3
, 258C): d=8.46–8.52 (m, 1H, Ar),
À1
+
s), 515 cm (s); MS (70 eV, EI) m/z (%)=192 (100, M ), 165 (18), 95
12); R =0.41 (n-hexane/ethyl acetate 4.5:1).
7
f
13
3
, 258C): d=149.8, 143.2, 135.9, 131.8,
1
2
28.8, 128.2, 126.9, 122.9, 122.0, 88.5, 89.0 ppm; IR (KBr): n˜ =3049 (w),
(
4-Nitrophenyl)phenylacetylene (22)
214 (m), 1595 (w), 1579 (s), 1561 (m), 1491 (s), 1441 (m), 1426 (s), 1153
À1
Yield 81% (colorless crystals obtained by crystallization from diethyl
ether); H NMR (200 MHz, CDCl
(m), 777 (m), 756 (m), 688 cm (m); MS (70 eV, EI) m/z (%)=179 (100,
M ), 151 (16), 76 (17); R =0.29 (n-hexane/ethyl acetate 4.5:1).
f
1
+
3
, 258C): d=8.06–8.15 (m, 2H, Ar),
7
7
1
.60–7.51 (m, 2H, Ar), 7.40–7.50 (m, 2H, Ar), 7.24–7.33 (m, 3H, Ar),
1
3
General Procedure for the Reduction of Alkynes
.13–7.18 ppm (m, 1H, Ar); C NMR (50.32 MHz, CDCl
3
, 258C): d=
46.8, 132.2, 131.8, 130.2, 129.2, 128.5, 123.6, 122.1, 94.7, 87.5 ppm; IR
A pressure tube was charged with diiron nonacarbonyl (0.036 mmol, 5.0
mol%). The catalyst was dissolved in freshly distilled tetrahydrofuran
(
(
KBr): n˜ =2925 (w), 2851 (w), 1592 (m), 1510 (s), 1345 (s), 1105 (m), 921
w), 856 (m), 765 (m), 689 cm (m); MS (70 eV, EI) m/z (%)=223 (100,
À1
(
2.0 mL). To this solution diphenylacetylene (0.72 mmol), (EtO)
3
SiH
+
M ), 193 (30), 176 (62), 165 (20), 151 (25), 88 (15); R
ethyl acetate 4.5:1).
f
=0.49 (n-hexane/
(
0.79 mmol) were added via syringe. The reaction mixture was stirred in
a preheated oil bath at 608C for 24 h. The mixture was cooled down in
an ice bath and was treated with dodecane (10 mL) as GC standard (for
GC-analysis), and aqueous sodium hydroxide solution (1.0 mL) with stir-
ring. The reaction mixture was stirred for 60 min at RT and was then ex-
tracted with diethyl ether (2ꢅ10.0 mL). The combined organic layers
General procedure for the synthesis of alkynes (Method B)
To a solution of phenyl acetylene (10.7 mmol) and the corresponding
bromoarene (9.8 mmol) in dioxane (2.0 mL) was added palladium(II)
chloride (5 mol%, 0.49 mmol), PPh
amine (21.4 mmol). The mixture was stirred for 3 days at 608C. After-
3
(10 mol%, 0.98 mmol), and triethyl
2 4
were washed with brine, dried over anhydrous Na SO , filtered (an ali-
quot was removed for GC-analysis), and concentrated in vacuum. The
wards, the mixture was cooled to room temperature and dichloromethane
yield was monitored by GC (30 m Rxi-5 ms column, 40–3008C) and by
H NMR spectroscopy. The crude product was purified over a short plug
1
(
50 mL) was added. The organic layer was washed with water, brine, and
dried over Na SO . The solvent was removed under vacuum and the resi-
due was purified by column chromatography on silica gel (n-hexane/ethyl
of silica gel (eluent: ethyl acetate). The analytical data for all products
2
4
[
20]
are in agreement with literature reports.
[
19]
acetate 98:2 to 4.5:1).
1
-(4-Methylphenyl)-2-phenyl ethene (15a)
(
3-Methoxyphenyl)phenylacetylene (19)
1
H NMR (200 MHz, CDCl
.52 (s, 2H, C(H)=C(H)), 2.27 (s, 3H, CH
3
, 258C): d=Selected data for the (Z) isomer:
), Selected data for the (E)
6
3
Yield 86% (colorless crystals obtained by crystallization from diethyl
ether); H NMR (200 MHz, CDCl
1
isomer: 2.35 (s, 3H, CH ) ppm; MS (70 eV, EI) m/z (%) for the (Z)
isomer: 194 (87, M ), 179 (100), 165 (11), 152 (11), 115 (13), 96 (14); (E)
isomer: 194 (84, M ), 188 (10), 179 (100), 165 (11), 152 (11), 115 (14),
1
3
, 258C): d=7.49–7.58 (m, 2H, Ar),
.02–7.40 (m, 6H, Ar), 6.86–6.93 (m, 1H, Ar), 3.81 ppm (s, 3H, OCH );
, 258C): d=159.3, 131.6, 129.4, 128,3, 128.2,
24.2, 124.1, 123.2, 116.3, 114.9, 89.3, 89.2, 55.2 ppm; IR (KBr): n˜ =3049
3
3
+
7
3
+
1
3
C NMR (50.32 MHz, CDCl
3
05 (12), 92 (12), 89 (15), 76 (12); GC (30 m Rxi-5 ms column, 40–
008C) for the (Z)-isomer 8.492 min, (E)-isomer 9.725 min.
1
(
1
(
w), 3005 (w), 2950 (w), 2829 (w), 1598 (s), 1580 (s), 1492 (s), 1464 (s),
440 (m), 1418 (m), 1321 (m), 1234 (s), 1036 (w), 924 (w), 862 (m), 793
1
-(3-Methylphenyl)-2-phenyl ethene (16a)
À1
+
s), 768 (s), 686 cm (s); MS (70 eV, EI) m/z (%)=208 (100, M ), 178
29), 165 (17). R =0.69 (n-hexane/ethyl acetate 4.5:1).
1
(
f
3
H NMR (200 MHz, CDCl , 258C): d=Selected data for the (Z)-isomer:
6
.53 (s, 2H, C(H)=C(H)), 2.28 (s, 3H, CH
isomer: 2.36 (s, 3H, CH ) ppm; MS (70 eV, EI) m/z (%) for (Z) isomer:
194 (89, M ), 179 (100), 165 (10), 115 (12), 96 (11), 89 (11); (E) isomer:
3
), Selected data for the (E)-
(
2-Fluorophenyl)phenylacetylene (21)
3
+
1
Yield 73%; H NMR (200 MHz, CDCl
Ar); C NMR (50.32 MHz, CDCl ,
3
1
1
2
1
3
, 258C): d=7.01–7.62 ppm (m,
258C): d=165.1, 160.1, 133.41,
33.39, 131.7, 130.0, 129.8, 128.5, 128.3, 123.94, 123.87, 122.9, 115.7, 115.3,
+
1
3
194 (92, M ), 179 AHCUTNGTERNNUN(G 100), 165 (11), 115 (15), 96 (18), 89 (15); GC (30 m
Rxi-5 ms column, 40–3008C): (Z)-isomer 8.650 min, (E)-isomer 9.783
min.
1
9
3
12.1, 111.7, 94.43, 94.36, 82.6 ppm; F NMR (188.33 MHz, CDCl ,
58C): d=À106 - À109.8 ppm (m); IR (KBr): n˜ =3061 (w), 1595 (m),
1
-(4-tert-Butylphenyl)-2-phenyl ethene (17a)
270 (m), 1497 (s), 1443 (s), 1263 (m), 1221 (s), 1098 (m), 1028 (m), 943
À1
(
w), 916 (w), 858 (w), 795 (m), 755 (s), 689 (s), 580 cm (w); MS (70 eV,
Selected data for the (Z)-isomer: 1.49 (s, 9H, CH ), Selected data for the
(E)-isomer: 1.37 (s, 9H, CH ) ppm; MS (70 eV, EI) m/z (%) for isomer
1: 236 (50, M ), 221 (100), 178 (12), 91 (26); isomer 2: 236 (49, M ), 221
3
+
EI) m/z (%)=196 (100, M ), 170 (11), 98 (13); R
acetate 4.5:1).
f
=0.66 (n-hexane/ethyl
3
+
+
1620
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 1613 – 1623

Iron-Catalyzed Synthesis of Alkenes by Alkyne Reduction
(
100), 178 (11), 96 (11), 91 (22). Isomer 1: 9.808 min, isomer 2:
(26), 77 (16), 72 (11), 69 (19), 65 (45), 51 (22); GC (30 m Rxi-5 ms
1
1.025 min.
column, 40–3008C): 5.892 min.
1
-(4-Methoxyphenyl)-2-phenyl ethene (18a)
Ethyl cinnamate (28a)
1
H NMR (200 MHz, CDCl
.75 (s, 3H, CH ), Selected data for the (E)-isomer: 3.79 (s, 3H, CH
ppm; MS (70 eV, EI) m/z (%) for isomer 1: 210 (100, M ), 195 (24), 179
3
, 258C): d=Selected data for the (Z)-isomer:
1
H NMR (200 MHz, CDCl
3
, 258C): d=Selected data for the (Z)-isomer:
), Selected data for the (E)-
isomer: 6.41 (d, 2H, C(H)=C(H)), 7.66 (d, 2H) ppm; MS (70 eV, EI) m/z
3
3
3
)
+
6.95 (d, 2H, C(H)=C(H)), 2.27 (s, 3H, CH
3
+
(
(
18), 165 (33), 152 (25), 89 (12); isomer 2: 210 (100, M ), 195 (18), 179
129, 165 (22), 152 (14). Isomer 1: 9.575 min, isomer 2: 10.633 min.
+
(
(
%) for the (Z)-isomer: 176 (25, M ), 148 (14), 131 (100), 103 (60), 77
39), 51 (18); (E)-isomer: 176 (26, M ), 148 (14), 131 (100), 103 (56), 77
+
1
-(3-Methoxyphenyl)-2-phenyl ethene (19a)
(36), 51 (17); GC (30 m Rxi-5 ms column, 40–3008C): (Z)-isomer 7.042
min, (E)-isomer 7.633 min.
1
H NMR (200 MHz, CDCl
.63 (s, 3H, CH ), Selected data for the (E)-isomer: 3.75 (s, 3H, CH
ppm; MS (70 eV, EI) m/z (%) for isomer 1: 210 (100, M ), 194 (26), 179
3
, 258C): d=Selected data for the (Z)-isomer:
3
3
3
)
2
-Butenedioic acid dimethyl ester (29a)
+
+
1
(
(
39), 167 (18), 152 (17), 89 (10); isomer 2: 210 (100, M ), 194 (22), 179
32), 165 (26), 152 (13), 105 (21). Isomer 1: 9.350 min, isomer 2:
H NMR (200 MHz, CDCl , 258C): d=Selected data for the (Z)-isomer:
3
6.22 (s, 2H, -C(H)=C(H)-), 3.76 (s, 3H, OCH ), Selected data for the
3
1
0.508 min.
(E)-isomer: 6.87 (s, 2H, -C(H)=C(H)-), 3.81 (s, 3H, OCH ) ppm; MS
3
+
(
(
70 eV, EI) m/z (%) for the (Z)-isomer: 144 (2, M ), 113 (100), 59 (55);
E)-isomer: 143 (1, M ), 126 (28), 113 (100), 99 (70), 85 (38) 82 (27), 59
1
-(4-Fluorophenyl)-2-phenyl ethene (20a)
+
1
3
(35), 55 (35); GC (30 m Rxi-5 ms column, 40–3008C): (Z)-isomer 4.283
min, (E)-isomer 4.925 min.
C NMR (50 MHz, CDCl
3
, 258C): d=Selected data for the (Z)-isomer:
1
63.4, Selected data for the (E)-isomer: 162.4 ppm; MS (70 eV, EI) m/z
+
(
1
%) for isomer 1: 198 (100, M ), 183 (37), 176 (30), 98 (11); isomer 2:
+
98 (100, M ), 183 (37), 177 (29), 98 (29), 85 (12). Isomer 1: 7.967 min,
2-Butenedioic acid diethyl ester (30a)
isomer 2: 9.100 min.
1
3
H NMR (200 MHz, CDCl , 258C): d=Selected data for the (Z)-isomer:
1
-(2-Fluorophenyl)-2-phenyl ethene (21a)
6.26 (s, 2H, C(H)=C(H)), Selected data for the (E)-isomer: 6.83 (d, 2H,
C(H)=C(H)) ppm; MS (70 eV, EI) m/z (%) for the (Z)-isomer: 172 (1,
1
3
C NMR (50 MHz, CDCl
3
, 258C): d=Selected data for the (Z)-isomer:
+
+
M ), 127 (30), 99 (100); (E)-isomer: 172 (1, M ), 127 (100), 99 (77), 82
16), 71 (15), 55 (31); GC (30 m Rxi-5 ms column, 40–3008C): (Z)-iso-
1
62.2, Selected data for the (E)-isomer: 158.3 ppm; MS (70 eV, EI) m/z
(
+
(
%) for isomer 1: 198 (100, M ), 183 (35), 177 (30), 98 (14); 198 (100,
+
mer 5.442 min, (E)-isomer 5.550 min.
M ), 183 (34), 177 (22), 120 (10), 98 (27), 89 (12), 85 (17). Isomer 1:
7
.967 min, isomer 2: 9.075 min.
Bis-(trimethylsilyl)ethylene (31a)
1
-(4-Nitrophenyl)-2-phenyl ethene (22a)
1
H NMR (200 MHz, CDCl
(CH ), Selected data for the (E)-isomer: 0.06 (s, 18H, Si-
), ppm; MS (70 eV, EI) m/z (%) for the (Z)-isomer: 172 (2, M ),
3
, 258C): d=Selected data for the (Z)-isomer:
1
H NMR (200 MHz, CDCl
3
, 258C): d=Selected data for the (Z)-isomer:
0.13 (s, 18H, Si
(CH
A
T
N
T
E
N
N
3 3
)
+
8
.04 (m, 2H), Selected data for the (E)-isomer: 8.20 (m, 2H) ppm; MS
A
H
U
G
R
N
U
G
3 3
)
+
+
(
70 eV, EI) m/z (%)=(Z)-isomer: 225 (100, M ), 178 (73), 152 (18);
125 (12), 99 (12), 73 (100), 59 (15); (E)-isomer: 172 (5, M ), 157 (13), 99
(13), 73 (100); GC (30 m Rxi-5 ms column, 40–3008C): (Z)-isomer 3.042
min, (E)-isomer 3.533 min.
+
isomer 2: 225 (86, M ), 178 (100), 152 (30), 89 (19), 76 (20); (Z)-isomer:
1
0.650 min, isomer 2: 11.733 min.
1
-Phenyl-2-(2-pyridinyl) ethylene (23a)
General Synthesis of Iron Phosphane Complexes
1
3
C NMR (50 MHz, CDCl
3
, 258C): d=Selected data for the (Z)-isomer:
A solution of the corresponding phosphine ligand (761 mmol) and diiron
nonacarbonyl (761 mmol) in diethyl ether (30 mL) was refluxed for 1–2 h.
The solution was allowed to cool to room temperature. The volatiles
were removed under vacuum to yield a brown foam. The products were
purified by extraction and filtration through a pad of aluminum oxide.
Colored crystals were obtained by crystallization from diethyl ether.
1
56.2, Selected data for the (E)-isomer: 155.8 ppm; MS (70 eV, EI) m/z
+
+
(
%) for isomer 1: 180 (100, M ), 152 (10); isomer 2: 180 (100, M ), 152
(
10); isomer 1: 8.425 min, isomer 2: 9.408 min.
1
-Phenyl-1-hexene (24a)
1
H NMR (200 MHz, CDCl
3
, 258C): d=Selected data for the (Z)-isomer:
5
.67 (m, 1H) ppm; MS (70 eV, EI) m/z (%) for the (Z)-isomer: 160 (27,
Compound 41
+
M ), 117 (100), 104 (79), 91 (32); GC (30 m Rxi-5 ms column, 40–
008C): (Z)-isomer: 6.242 min.
3
Reaction time: 1 h, deep-red crystals obtained from diethyl ether;
1
6 6
H NMR (200 MHz, C D , 258C): d=7.98–7.82 (m, Ar), 7.10–6.94 (m,
Styrene (25a)
MS (70 eV, EI) m/z (%)=150 (100, M ), 135 (94), 117 (72), 109 (58), 91
Ar), 4.29 (s, 4H, Cp), 3.83 ppm (s, 4H, Cp); IR (KBr): n˜ =3056 (w), 1981
(s), 1907 (s), 1879 (s), 1480 (m), 1434 (m), 1309 (w), 1162 (w), 1089 (m),
+
1
4
5
038 (w), 821 (w), 750 (w), 697 (m), 634 (m), 610 (w), 544 (w), 499 (w),
67 cm (w); MS (70 eV, EI) m/z (%)=694 (M ), 638 (10), 610 (100),
54 (27), 425 (35), 304 (18).
(
26), 77 (16), 72 (11), 69 (19), 65 (45), 51 (22); GC (30 m Rxi-5 ms
À1
+
column, 40–3008C): 5.892 min.
1
,4-Diphenyl-1-buten-3-yne (26a)
1
Compound 42
H NMR (200 MHz, CDCl
3
, 258C): d=Selected data for the (Z)-isomer:
.92 (d, 1H, J=12.0 Hz, C(H)=C(H)), Selected data for the (E)-isomer:
.40 (d, 1H, J=16.1 Hz, C(H)=C(H)) ppm; MS (70 eV, EI) m/z (%) for
5
6
Reaction time: 2 h, deep-red crystals obtained from diethyl ether.
1
6 6
H NMR (200 MHz, C D , 258C): d=7.15–6.88 (m, Ar), 6.46–6.05 (m,
+
the (Z)-isomer: 204 (100, M ), 101 (31), 89 (12), 76 (12); (E)-isomer: 204
(
3
Ar), 3.22 ppm (brs, 18H, OMe); IR (KBr): n˜ =3001 (w), 2970 (w), 2940
m), 2839 (m), 2536 (w), 2028 (s), 1912 (s), 1580 (s), 1468 (s), 1427 (s),
+
100, M ), 101 (38), 89 (17), 76 (18); GC (30 m Rxi-5 ms column, 40–
008C): (Z)-isomer 10.117 min, (E)-isomer 10.667 min.
(
1
251 (s), 1182 (w), 1171 (w), 1149 (w), 1105 (s), 1029 (m), 899 (w), 776
À1
(
s), 757 (m), 719 (m), 627 (s), 604 (w), 531 (m), 484 cm (m); MS (70 eV,
Phenyl allyl thioether (27a)
EI) m/z (%)=526 (46), 498 (62), 442 (62), 411 (36), 396 (27), 365 (12),
291 (25), 249 (14), 167 (14), 151 (100), 138 (28), 91 (18), molecular ion
peak was not detectable.
1
3
C NMR (50 MHz, CDCl
3 2
, 258C): d=37.5 (SCH ), 118.0 (C=C) ppm;
+
MS (70 eV, EI) m/z (%): 150 (100, M ), 135 (94), 117 (72), 109 (58), 91
Chem. Asian J. 2011, 6, 1613 – 1623
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1621

S. Enthaler et al.
FULL PAPERS
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2
[
Oxford Diffraction Xcalibur S Sapphire spectrometer at 150(2) K (MoKa
radiation, l=0.71073 ꢄ). The structures were solved by direct methods
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[22]
and refined on F with the SHELX-97 software package. The positions
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1
1.1565(3) ꢄ; a=908, b=105.316(3)8, g=908; V=2771.94(14) ꢄ ; Z=4;
calc =1.462 mgm ; Absorption coefficient 0.659 mm ; F AHCTUNGTRENNUN(G 000) 1264; Re-
À3
À1
flections collected: 20394; Independent reflections: 4872 [Rint =0.0402];
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and 0.8422; Goodness-of-fit on F 0.963; Final R indices [I>2s(I)]: R1=
2
0
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Largest diff. peak and hole 0.381 and À0.279 eꢄ
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2
009, 131, 1394–1395; g) C. Sui-Seng, F. N. Haque, A. Hadzovic, A.-
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1
1
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Acknowledgements
1
977, 18, 3947–3950.
This work was supported by the Cluster of Excellence “Unifying Con-
cepts in Catalysis” (sponsored by the Deutsche Forschungsgemeinschaft
and administered by the Technische Universitꢀt Berlin). The authors
thank M. Weidner (TU Berlin) for technical support. Dr. K. Junge (Leib-
niz Institut fꢃr Katalyse e.V. an der Universitꢀt Rostock) is acknowl-
edged for the kind donation of ligand 11.
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Received: December 29, 2010
Published online: May 19, 2011
Chem. Asian J. 2011, 6, 1613 – 1623
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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