Endo and exo cyclometallated iron carbonyl complexes derived from N-(N′-methyl-2-pyrrolylmethylidene)-2-thienylmethylamine

Article abstract of DOI:10.1016/j.jorganchem.2004.07.014

The reaction of N-(N′-methyl-2-pyrrolylmethylidene) -2-thienylmethylamine (1) with Fe₂(CO)₉ in refluxing toluene gives endo cyclometallated iron carbonyl complexes 2 and 5, exo cyclometallated iron carbonyl complex 3, and unexpected iron carbonyl complex 4. Complexes 2, 3, and 5 are geometric isomers. Complex 5 differs from complex 2 in the switch of the original substituent from α to β position of the pyrrolyl ring, and the pyrrolyl ring bridges to the diiron centers in μ-(3,2-η¹:η²) coordination mode in stead of μ-(2,3-η¹:η²). In complex 4, the pyrrolyl moiety of the original ligand 1 has been displaced by a thienyl group, which comes from the same ligand. Single crystals of 2, 3, and 5 were subjected to the X-ray diffraction analysis. The major product 2 undergoes: (i) thermolysis to recover the original ligand 1; (ii) reduction to form a hydrogenation product, 6, of the original ligand; (iii) substitution to form a monophosphine-substituted complex 7; (iv) chemical as well as electrochemical oxidation to produce a carbonylation product, γ-butyrolactam 8.

Full text of DOI:10.1016/j.jorganchem.2004.07.014

Journal of Organometallic Chemistry 689 (2004) 3173–3183
www.elsevier.com/locate/jorganchem
Endo and exo cyclometallated iron carbonyl complexes derived from
N-(N0-methyl-2-pyrrolylmethylidene)-2-thienylmethylamine
*
Shiau-Yi Jin, Chih-Yu Wu, Chen-Shiang Lee, Amitabha Datta, Wen-Shu Hwang
Department of Chemistry, National Dong Hwa University, 1, Sec.2, Da-Hsueh Rd., Shoufeng, Hualien 974, Taiwan, ROC
Received 4 June 2004; accepted 1 July 2004
Available online 12 August 2004
Abstract
The reaction of N-(N0-methyl-2-pyrrolylmethylidene)-2-thienylmethylamine (1) with Fe2(CO)9 in refluxing toluene gives endo
cyclometallated iron carbonyl complexes 2 and 5, exo cyclometallated iron carbonyl complex 3, and unexpected iron carbonyl com-
plex 4. Complexes 2, 3, and 5 are geometric isomers. Complex 5 differs from complex 2 in the switch of the original substituent from
a to b position of the pyrrolyl ring, and the pyrrolyl ring bridges to the diiron centers in l-(3,2-g1:g2) coordination mode in stead of
l-(2,3-g1:g2). In complex 4, the pyrrolyl moiety of the original ligand 1 has been displaced by a thienyl group, which comes from the
same ligand. Single crystals of 2, 3, and 5 were subjected to the X-ray diffraction analysis. The major product 2 undergoes: (i) ther-
molysis to recover the original ligand 1; (ii) reduction to form a hydrogenation product, 6, of the original ligand; (iii) substitution to
form a monophosphine-substituted complex 7; (iv) chemical as well as electrochemical oxidation to produce a carbonylation prod-
uct, c-butyrolactam 8.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Endo cyclometallation; Exo cyclometallation; Iron carbonyl complex; Carbonylation; c-butyrolactam
1. Introduction
tion. They are derivatives of 2,6-disubstituted N-
benzylideneamines, which contain substituents on the
ortho positions of the benzyl ring [1f,1i,1j,4b]. Usually,
the tendency to proceed endo cyclometallation is so
strong that, in the presence of Pd(AcO)2, an aliphatic
C–H bond of N-(2,4,6-trimethylbenzylidene)benzylam-
ine is activated in preference to the activation of an ar-
omatic C–H bond and results with the formation of a
six-membered endo metallacycle as the sole product
rather than a five-membered exo metallacycle [5]. Evi-
dence for a regiospecific endo cyclometallation was
therefore observed.
We report here, the interesting results from the action
of diiron nonacarbonyl on N-(N-methyl-2-pyrrolylme-
thylidene)-2-thienylmethylamine (1). During the course
of reaction, we observe products resulting from endo
cyclometallation followed by 1,3-hydrogen shift (2),
exo cyclometallation followed by 1,5-hydrogen shift
(3), substitution of the N-methyl-2-pyrrolylmethyl group
One of the prominent challenges in organometallic
chemistry in past decades has been the transition-metal
mediated activation of C–H bond. Cyclometallation is
one of the classical ways used to activate C–H bond in
hetero-substituted organic molecules [1].
It is well known that N-donor ligands have a strong
tendency to give metallacycle [2]. In systems, where there
is a possibility of choice between several modes of met-
allation, five-membered metallacyclic complexes are al-
ways the major compounds obtained [3]. It is also
known that, Schiff bases have a strong tendency to give
endo cyclometallated derivatives [4]. Only a few exo met-
allcycles of Schiff bases were obtained by C–H activa-
*
Corresponding author. Tel.: +886 3 8632001; fax: +886 3 8632000.
E-mail address: hws@mail.ndhu.edu.tw (W.-S. Hwang).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.07.014

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S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
of exo cyclometallated intermediate by a thienylmethyl
group (4), and endo cyclometallation which involved a
b to a azomethine group transformation (5).
ucts from the reaction are cyclometallated diiron hexa-
carbonyl complexes, in which the complexes 2, 3, and
5 are geometric isomers.
If the reaction was conducted in benzene, either at
room temperature or at reflux, only iron carbonyl com-
plex 2 was obtained with a much lower product yield
(12% and 27%, respectively). Obviously, higher temper-
ature would increase the rate of complex 2 formation
but solvent effect drives the formations of other three
minor products.
2. Results and discussion
The pyrrolyl Schiff bases N-(N-methyl-2-pyrrolylme-
thylidene)-2-thienylmethylamine (1), were prepared in
high yields by condensation of N-methyl-2-pyrrolecar-
boxaldehyde with 2-thiophenemethylamine in methanol
and was fully characterized spectrally.
The 1H NMR spectral data of complexes 2–5 are
shown in the Section 3. The thienyl as well as pyrrolyl
protons in each complex can be easily assigned accord-
ing to their specific chemical shift and characteristic cou-
Each thienyl or pyrrolyl proton in the ligand can be
1
easily assigned from the H NMR spectrum according
1
to its specific position and the characteristic coupling
constant(s). The ligand is further identified by the pres-
ence of a singlet methine proton at d 8.24 ppm and an-
other singlet methylene resonance at 4.84 ppm. Ligand 1
also shows a characteristic C‚N stretching absorption
at 1640 cmꢀ1 in its IR spectrum and shows a molecular
ion peak in its mass spectrum.
pling constants. The most significant feature of the H
NMR spectrum of each of complexes is the disappear-
ance of methine proton resonance, which appears at d
8.28 ppm in free ligand 1, and the missing of either
one b-thienyl (3 and 4) or one b-pyrrolyl proton (2
and 5) relative to the free ligand 1. However, a new sin-
glet resonance representing a methylene group appears
at d 4.3–3.7 ppm in addition to the up-field shifted
vested methylene signal, indicating a hydrogen has been
transferred through an intramolecular hydrogen shift
from the b-carbon of the pyrrole (2 and 5) or thiophene
(3 and 4) ring towards the methine carbon during the
course of cyclometallation, thus producing a new meth-
ylene group. The lack of diastereotopicity of the methyl-
2.1. Complexes formation and characterization
The pyrrolyl schiff base 1 reacted with Fe2(CO)9 in re-
fluxing toluene for 12 h to give off a major product, 2
(46% yield), and three minor products, 3 (9%), 4 (8%),
and 5 (5%), as formulated in Scheme 1. All four prod-
Fe2(CO)9
+
C
H
N
C
S
N
H2
Toluene, reflux
CH3
1
CO CO
CO
CO
OC
OC
CO
Fe
CO
Fe
CO
CO
OC
OC
Fe
Fe
N
+
C
C
C
N
C
S
S
N
N
H2
H2
H2
H2
CH3
CH3
2
3
CO CO
CO CO
CO
CO
CO
CO
OC
OC
OC
CH3
Fe
Fe
Fe
Fe
OC
N
+
C
N
C
S
C
N
C
S
S
H2
H2
H2
H2
4
5
Scheme 1. ORTEP diagram of complex 5 at the 30% probability level.

S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
3175
ene protons in the azametallacycle of these complexes
indicates that a fluxional process, the so-called ‘‘wind-
shield-wiper type oscillation’’, of the ligand might occur
in these four complexes [6].
In their IR spectra, while the C‚N stretching is ab-
sent, there are sharp and intense CO stretches appearing
at 2066–1963 cmꢀ1, indicating the presence of terminal
carbonyl ligands on metal center. The mass spectra of
four products all show their own specific molecular
ion peak (M+), six fragments corresponding to the
sequential loss of six COs, and the ligand ion peak, in
accordance with the formulated structures.
The molecular structures of complexes 2, 3, and 5, as
determined by means of single-crystal X-ray diffraction
analysis, are shown in Figs. 1–3, respectively. Their crys-
tal and data collection parameters are tabulated in Table
1 and selected bond lengths and bond angles are summa-
rized in Table 2.
Fig. 2. ORTEP diagram of complex 3 at the 30% probability level.
Regarding the endo cyclometallated complex 2, it is
readily seen from Fig. 1 that C(3) of the pyrrolyl ring
is r bonded to Fe(2) with a bond distance of 1.977(6)
˚
A. C(2) and C(3) are p bonded to Fe(1) with bond dis-
˚
tances of 2.447(6) and 2.151(6) A, respectively, and the
bond distance between C(2) and C(3) is lengthened to
˚
1.401(10) A. The pyrrolyl ring serves as a three-electron
donor and bridges the two iron centers. The bond dis-
˚
tance from N(1) to C(1), 1.487(8) A, is in the single bond
range and is comparable to that of N(1)–C(7) distance,
˚
1.486(9) A. The nitrogen atom, N(1), acts as another
three-electron donor bridge and the bond distances to
˚
Fe(1) and Fe(2) are 1.958(5) and 1.997(6) A, respectively.
˚
An iron–iron distance of 2.4262(13) A is shorter than
usual for bridged diiron complexes [7]. The Fe(1)–
N(1)–Fe(2) angle is 75.68(20)ꢁ and Fe(1)–C(3)–Fe(2) an-
gle is 71.86(20)ꢁ. The compression of these two angles
from the tetrahedral value is a result of the ligand con-
Fig. 3. ORTEP diagram of complex 5 at the 30% probability level.
strains of double bridging, which also brings about the
shorter iron–iron distance.
The molecular structure of complex 3, as shown in
Fig. 2, clearly shows that the compound is an exo cycl-
ometallated product in which C(9) of the thienyl ring is
˚
r bonded to Fe(2) with a bond distance of 1.970(5) A.
C(9) and C(8) are p bonded to Fe(1) with bond distances
˚
of 2.169(5) and 2.341(5) A, respectively, and the bond
distance between C(8) and C(9) is lengthened to
˚
1.383(8) A. The thienyl ring acts as a three-electron do-
nor and bridges the two iron centers. The bond distances
˚
from N(1) to C(1) and C(7) are 1.486(7) and 1.484(6) A,
respectively, and both are in the single bond range. The
N(1) atom also serves as another three-electron bridge
and the bond distances from N(1) to Fe(1) and Fe(2)
Fig. 1. ORTEP diagram of complex 2 at the 30% probability level.

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S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
Table 1
Crystal and data collection parameters for compounds 2, 3, and 5
Compound
2
3
5
Formula
C17H12Fe2N2O6S
484.04
C17H12Fe2N2O6S
484.06
Triclinic
C17H12Fe2N2O6S
484.04
Formula weight
Crystal system
Space group
Monoclinic
P21/c
Monoclinic
P21/c
ꢀ
P1
Unit cell dimensions
˚
a (A)
˚
7.7944(11)
11.8488(13)
20.5274(18)
7.9844(25)
10.2069(19)
11.869(3)
98.529(19)
95.226(25)
94.989(21)
974.6(4)
2
7.983(3)
11.614(4)
20.735(10)
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
91.319(9)
93.61(4)
3
˚
Volume (A )
1939.1(4)
4
1.658
1918.6(13)
4
1.676
Z
Dcalc (g/cm3)
1.696
Crystal size (mm)
Temperature (K)
2hmax(ꢁ)
0.30 · 0.12 · 0.10
293
0.45 · 0.25 · 0.20
293
49.8
0.60 · 0.50 · 0.36
293
49.8
h/2h
49.8
h/2h
Scan type
h/2h
No. of reflections measured
Total unique
No. of observed reflections
No. of variables
F000
3507, 3406
3499, 3324
3477, 3376
2709 (I > 2.00r(I))
254
976
2876 (I > 2.00r(I))
253
488
2952 (I > 2.00r(I))
254
976
l (Mo Ka) (cmꢀ1
)
16.4
0.046
0.049
16.8
0.046
0.053
16.6
0.038
0.040
R1
Rw
˚
are 1.971(4) and 1.982(4) A, respectively. The iron–iron
˚
distance, 2.4370(2) A, is longer than that in complex 2.
ring and led to the formation of complex 5. At this
stage, we do not have any idea concerning with the
transformation.
The Fe(1)–N(1)–Fe(2) bond angle, 76.13(15)ꢁ, and
Fe(1)–C(9)–F(2) angle, 71.95(17)ꢁ, are very closely re-
semble that of complex 2 described above. It seems that,
after the coordination of the azomethine nitrogen to one
of the iron centers, a C–H activation occurs at the b-car-
bon of the thienyl ring instead of pyrrolyl ring to form a
five-membered exo metallacycle and then the methine
carbon adopts the hydrogen originated from the b-car-
bon of the thienyl ring to form the complex 5. This is
a consecutive process of coordination, exo cyclometalla-
tion, and 1,5-hydrogen shift.
2.2. Formation of complex 4
Complex 4 had been obtained from the reaction of N-
(2-thienylmethylidene)-2-thienylmethylamine with Fe2
(CO)9 and its molecular structure had been confirmed
by single crystal X-ray diffraction analysis [6]. It is an
unexpected product from this reaction. Although the
original Schiff base contains a N-methylpyrroly unit, it
is interesting to find that the N-methylpyrrolyl group
of the original Schiff base has been displaced with a thie-
nyl ring in 4. The Schiff base in the complex has there-
fore undergone a chemical transformation. Since the
Schiff base itself is very thermally stable, obviously, a
C–N bond cleavage or a C–C bond cleavage must be in-
volved during the course of complex formation. In terms
of bond energies of C‚N, C–N, and C–C bonds, it is
most likely that a C–N bond cleavage occurs on 2 and
3. The thienyl group that was cleaved from endo cyclo-
metallated product 2 might substitute the N-methyl-2-
pyrrolylmethyl moiety of the exo cyclometallated
product 3, thus directed to the formation of complex 4.
It is interesting to find that, if the reaction time for the
reaction of Schiff base 1 with Fe2(CO)9 was prolonged
The molecular structure of complex 5, as shown in
Fig. 3, is similar to that of complex 2. However, the pyr-
rolyl ring in 5 is arranged up-side-down relative to that
in 2 and the a-substituted group is found to migrate to
the b-position of the pyrrolyl ring. The a-carbon, C(2),
of the pyrrolyl ring, instead of b-carbon, C(3), in
that of complex 2, is r bonded to Fe(2) with a bond dis-
˚
tance of 1.977(6) A, which is about same value as that of
Fe(2)–C(3) bond distance in 2. Other corresponding
structure parameters in complex 5, as shown in Table
2, closely resemble that in complex 2. Since the free Shiff
base itself was stable to the blank experiment, the iron
center must be responsible for the migration of the
substituent from the b- to the a-position of the pyrrolyl

S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
3177
Table 2
˚
Selected bond lengths (A) and bond angles (ꢁ) for complexes 2, 3, and 5
Complex 2
Fe(1)–Fe(2)
2.4262(13)
2.447(6)
2.151(6)
1.487(8)
1.486(9)
52.88(16)
50.73(17)
74.31(24)
51.43(14)
77.5(3)
Fe(1)–N(1)
Fe(2)–N(1)
1.958(5)
1.997(6)
1.977(6)
Fe(1)–C(2)
Fe(1)–C(3)
Fe(2)–C(3)
C(2)–C(3)
C(4)–C(5)
N(1)–C(1)
N(1)–C(7)
1.401(10)
1.345(11)
70.57(15)
60.59(22)
34.7(3)
Fe(2)–Fe(1)–N(1)
Fe(2)–Fe(1)–C(3)
N(1)–Fe(1)–C(3)
Fe(1)–Fe(2)–N(1)
N(1)–Fe(2)–C(3)
Fe(1)–N(1)–C(1)
Fe(2)–N(1)–C(1)
C(1)–N(1)–C(7)
Fe(1)–C(2)–C(1)
C(1)–C(2)–C(3)
Fe(1)–C(3)–C(2)
Fe(2)–Fe(1)–C(2)
N(1)–Fe(1)–C(2)
C(2)–Fe(1)–C(3)
Fe(1)–Fe(2)–C(3)
Fe(1)–N(1)–Fe(2)
Fe(1)–N(1)–C(7)
Fe(2)–N(1)–C(7)
N(1)–C(1)–C(2)
Fe(1)–C(2)–C(3)
Fe(1)–C(3)–Fe(2)
Fe(2)–C(3)–C(2)
57.42(18)
75.68(20)
127.8(4)
120.5(4)
99.3(5)
103.2(4)
113.1(4)
111.6(5)
83.6(4)
61.0(3)
71.86(20)
111.8(5)
119.5(6)
84.3(4)
Complex 3
Fe(1)–Fe(2)
2.4370(13)
2.341(5)
2.169(5)
1.486(7)
1.484(6)
52.14(12)
50.22(14)
74.35(19)
51.73(12)
78.75(19)
127.1(3)
121.8(3)
113.1(4)
85.5(3)
Fe(1)–N(1)
Fe(2)–N(1)
1.971(4)
1.982(4)
1.970(5)
1.383(8)
1.331(8)
71.69(13)
62.48(17)
34.45(19)
57.82(15)
76.13(15)
100.4(3)
112.5(3)
99.0(4)
Fe(1)–C(8)
Fe(1)–C(9)
Fe(2)–C(9)
C(8)–C(9)
C(10)–C(11)
N(1)–C(1)
N(1)–C(7)
Fe(2)–Fe(1)–N(1)
Fe(2)–Fe(1)–C(9)
N(1)–Fe(1)–C(9)
Fe(1)–Fe(2)–N(1)
N(1)–Fe(2)–C(9)
Fe(1)–N(1)–C(1)
Fe(2)–N(1)–C(1)
C(1)–N(1)–C(7)
Fe(1)–C(8)–C(7)
C(7)–C(8)–C(9)
Fe(1)–C(9)–C(8)
Fe(2)–Fe(1)–C(8)
N(1)–Fe(1)–C(8)
C(8)–Fe(1)–C(9)
Fe(1)–Fe(2)–C(9)
Fe(1)–N(1)–Fe(2)
Fe(1)–N(1)–C(7)
Fe(2)–N(1)–C(7)
N(1)–C(7)–C(8)
Fe(1)–C(8)–C(9)
Fe(1)–C(9)–Fe(2)
Fe(2)–C(9)–C(8)
65.5(3)
71.95(17)
112.0(4)
119.1(4)
79.1(3)
Complex 5
Fe(1)–Fe(2)
2.4227(12)
2.122(4)
2.534(4)
1.476(5)
1.474(5)
52.84(9)
70.13(14)
60.00(14)
51.89(9)
75.74(15)
103.76(23)
113.03(23)
110.6(3)
90.1(3)
Fe(1)–N(1)
Fe(2)–N(1)
1.971(3)
1.996(3)
1.976(4)
1.382(6)
1.364(8)
51.03(11)
73.05(14)
33.05(15)
56.58(12)
75.27(12)
123.98(23)
124.86(24)
101.9(3)
80.9(3)
Fe(1)–C(2)
Fe(1)–C(3)
Fe(2)–C(2)
C(2)–C(3)
C(4)–C(5)
N(1)–C(1)
N(1)–C(7)
Fe(2)–Fe(1)–N(1)
Fe(2)–Fe(1)–C(3)
N(1)–Fe(1)–C(3)
Fe(1)–Fe(2)–N(1)
N(1)–Fe(2)–C(2)
Fe(1)–N(1)–C(1)
Fe(2)–N(1)–C(1)
C(1)–N(1)–C(7)
Fe(1)–C(2)–C(3)
C(1)–C(3)–C(2)
Fe(1)–C(3)–C(2)
Fe(2)–Fe(1)–C(2)
N(1)–Fe(1)–C(2)
C(2)–Fe(1)–C(3)
Fe(1)–Fe(2)–C(2)
Fe(1)–N(1)–Fe(2)
Fe(1)–N(1)–C(7)
Fe(2)–N(1)–C(7)
N(1)–C(1)–C(3)
Fe(1)–C(3)–C(1)
Fe(1)–C(2)–Fe(2)
Fe(2)–C(2)–C(3)
115.5(3)
56.9(34)
72.38(13)
114.9(3)
from 12 to 24 h in refluxing toluene, only 2 and 4 two
complex products were isolated. While the yield of prod-
uct 4 increases to 17%, the yield of 2 was found decreases
to 41%. The increment of 9% for product 4 is exactly the
amount of disappeared 3 and is about the sum of the dec-
rement of product 2 and the amount of disappeared 5.
On the other hand, if the reaction was stopped after six
hours of reaction under the same reaction condition,
32% of complex 2, 4% of complex 3, and 3% of com-
plex 5 were obtained accompanying with 10% of com-
plex 4. Therefore, the formation of product 3 might be
tentatively proposed to follow the underlying process.

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S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
CO CO
CO
CO
OC
OC
CO
Fe
CO
Fe
CO
CO
Fe
Fe
OC
OC
+
C
N
C
S
C
N
C
S
N
H2
H2
N
H2
H2
CH3
CH3
2/5
3
CO CO
CO
CO
OC
OC
Fe
Fe
C
N
C
S
S
H2
H2
4
There are two potential sites, the b-position of pyr-
rolyl ring and the b-position of thienyl ring, in the
Schiff base 1 that might involve in the cyclometallation
and leads to the formation of endo and exo five-mem-
bered metallacycle. The products and yields distribu-
tion clearly show that the C–H activation that occurs
at the b-position of pyrrolyl ring, which directs to the
endo cyclometallation, is relatively more favorable than
that of thienyl ring (with ꢁ77/23 ratio). The minor exo
cyclometallated intermediate 3 thus formed might react
further with excess amount of endo cyclometallated
product 2 (product 5 might also be involved) and led
to the formation of net product 4. A reaction of equi-
molar quantities of complex 2 and complex 3 was con-
ducted under exactly the same reaction condition.
More than 90% of complex 4, 78% of N-methyl-2-
methylpyrrole, and 73% of N-methyl-2-(aminomethyl)-
pyrrole were obtained and no thienyl-contained
complex was found, confirming the substitution process
suggested.
2.4. Reactions of complex 2
Thermolysis of complex 2 in a refluxing n-heptane,
acetonitrile, or toluene solution led to the decomposi-
tion of the complex and the recovery of the original
Schiff base 1 in more than 80% after 48 h. If the reaction
was proceeded in a deuterated solvent such as d8-toluene
or d3-acetonitrile, similar result was obtained and there
was no deuterium atom attached Schiff base 1 observed.
This is a reverse process of the consecutive reactions of
coordination, cyclometallation and 1,3-hydrogen shift.
Hydrogen from the inner methylene group transferred
back to the b-carbon of the pyrrolyl ring and led to
the de-cyclometallation of the pyrrole group from the
iron center. If the thermal reaction was proceeded under
carbon monoxide atmosphere, only a few percent of
complex 2 decomposed after four days under the same
reaction condition. Since the methylene hydrogen might
act as a b-hydrogen, the thermal reaction of complex 2
might proceed through the following consecutive proc-
esses: dissociation of a carbonyl ligand, b-hydrogen
elimination, reductive elimination, and the Schiff base
1 released from the metal centers.
2.3. Electrochemical properties of complexes 2–5
Reduction of complex 2 by lithium aluminum
hydride led to the formation of high yield of the
corresponding secondary amine, N-(N0-methyl-2-pyrro-
lylmethyl)(2-thienylmethyl)amine (6), which is a hydro-
genation product of the original Schiff base 1. Product
6 was identified by its NMR, IR, and Mass spectra.
Schiff bases derived from aromatic aldehyde are
known to yield lactam products such as N-phenylphtha-
limidine on carbonylation at high temperature and high
carbon monoxide pressure in the presence of metal car-
bonyl [9]. Carbonylation of an organic ligand from its
metalcarbonyl complex could be achieved by treating
the complex with a variety of Lewis bases such as
Cyclic voltammetry experiments on complexes 2–5
showed a well-defined cathodic wave with a peak poten-
tial of 0.75, 0.94, 0.94, and 0.74 V vs. Ag–AgCl elec-
trode, respectively, at 100 mV/s sweep rate. The
maximum currents are directly proportional to the
square root of the sweep rate in the investigated range
of 50-800 mV/s. No reduction wave in the reverse ca-
thodic sweep was observed, demonstrating a totally irre-
versible overall process [8]. The voltammetry curve is
consistent with an ErCi mechanism [8a,d], i.e., heteroge-
neous electron transfer followed by an irreversible chem-
ical reaction.

S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
3179
phosphines [10,11], by oxidation, or by photochemical
reaction [11]. However, treatment of cyclometallated
complex 2 with excess amount of triphenylphosphine
(1:5 molar ratio) results only in substitution of one car-
bonyl ligand from complex 2 to give a pentacarbonyl-
phosphinodiiron complex 7 in 82% yield. In its 1H
NMR spectrum, there are two multiplet signals appear-
ing at d 7.38 and 7.00 ppm and showing a total of fifteen
phenyl protons, in additional to the three thienyl and
two pyrrolyl protons in the aromatic region. There also
exists one set of methylene resonance consisting of two
well-separated doublets, a typical AB spin pattern, with
a coupling constant of JH–H = 14.4 Hz at d 4.18 and
3.46 ppm, representing the inner methylene group. An-
other singlet signal representing the outer methylene
moiety appears at 3.80 ppm. The IR spectrum of com-
plex 7 shows four sharp and intense C‚O stretches at
2024, 1968, 1946, and 1922 cmꢀ1, which are lower
energy shifted relative to that of complex 2 (2055,
2011, 1963 cmꢀ1) due to the substitution of a more r
donor triphenylphosphine ligand. The mass spectrum
shows a molecular ion peak at m/z 718 and the entirely
loss of five COs and a PPh3 group in a sequential
manner, in accordance with the formulated structure.
On the other hand, from the reaction of complex 2
with nitrosonium salt, we obtained a novel bi-heterocy-
clic lactam, N-2-thienylmethyl-N0-methyl-2-methylpyr-
rolo[2,3b]-c-butyrolactam (8), in 66% yield, instead of
the expected nitrosyl substituted diiron complex. Com-
pound 8 shows a characteristic IR stretching absorption
might serve as an oxidant that not only promotes the
carbonyl insertion but also accelerates the reductive
elimination as a result of iron oxidation.
CO
ON
CO
CO CO
CO
O
C
Fe
Fe
8
2
C
N
C
S
N
H2
H2
CH3
9
In order to obtain some evidences for the pathway of
the oxidation induced carbonylation, we have conducted
the direct chemical and electrochemical oxidation of
complex 2. Chemical oxidation of complex 2 by anhy-
drous ferric chloride in ethyl alcohol afforded 53% yield
of carbonylation product 8 while by ceric ammonium ni-
trate in acetone resulted in only 37% yield of the same
product 8.
Control potential bulk electrolysis of complexes 2
was conducted in acetonitrile solution containing 0.10
M of tetraethylammonium perchlorate (TEAP) with
platinum gauze electrode at 0.95 (vs. Ag–AgCl reference
electrode), respectively. The process is a one-electron ox-
idation from the iron metal. Isolation and characteriza-
tion of the product from the electrochemical oxidation
of complex 2 showed an identical lactam 8 (89% yield)
to that obtained by chemical oxidation. The electro-
chemical experiment is strongly indicative that the car-
bonylation process involves cationic intermediate.
Since both the cyclometallation and subsequent oxida-
tion induced carbonylation proceed in good yields, this
two-step sequence is a very convenient and useful entry
into the bicyclic c-lactam ring system.
1
at 1687 cmꢀ1. In its H NMR spectrum, while the two
pyrrolyl protons up-field shift to d 6.95 and 6.18 ppm
and the two methylene groups down-field shift to d
4.93 and 4.32 ppm, the thienyl protons do not show a
significant shift relative to that of complexes 2. The mass
spectrum and elemental analysis clearly indicate the
structure formulated.
During the course of working up, we also isolated
trace among of unstable intermediate (9), which decom-
posed rapidly to form compound 8. The IR spectrum of
the intermediate shows two extra absorption bands at
1788 and 1660 cmꢀ1 in addition to the terminal carbonyl
stretching frequencies that appear in the range of 2100–
2000 cmꢀ1, indicating that the intermediate complex
might contain a linear nitrosyl ligand and an inserted
carbonyl group. Therefore, the formation of compound
8 might be suggested by assuming that on addition of a
nitrosonium cation to one of the iron centers in complex
2, a carbonyl ligand inserted into the Fe–C bond con-
comitantly to form the unstable intermediate 9, and fol-
lowed by a ring closure process via a reductive
elimination of the chelating organic ligand to form a lac-
tam. The intermediate 9 bears some resemblance to the
carbonyl inserted complex from diphenylthioketon re-
ported by Alper [10], which led to the formation of a
thiolacton. In this reaction, the nitrosonium cation
3. Experimental
Diiron nonacarbonyl was prepared through the pho-
tolysis of iron pentacarbonyl (Aldrich) in glacial acetic
acid [12]. Solvents were dried (sodium/benzophenone,
P4O10) and distilled under nitrogen prior to use. N-Me-
thyl-2-pyrrolecarboxaldehyde (Acros) and 2-thiophene-
methylamine (Aldrich) were distilled by a Kugelrohr
distillation apparatus under reduced pressure (0.1
mmHg) prior to use. All other chemicals were reagent
grade and used without further purification. The
NMR spectra were recorded on a Bruker DX-300
NMR spectrometer (1H, 299.95 MHz; 13C, 75.43
MHz). Chemical shifts were referenced to TMS and deu-
terated acetone (Janssen) was used as a solvent and as a

3180
S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
secondary reference. Mass spectra were obtained from a
Micromass Platform II spectrometer. IR spectra were
recorded employing a Mattson Genesis FTIR spectro-
photometer. Elemental analyses were performed using
a Perkin–Elmer 2400, 2400II elemental analyzer. Crys-
tals for X-ray diffraction were obtained from ethyl ace-
JH–H = 5.1 Hz, 1H), 7.17 (d, JH–H = 2.7 Hz, 1H), 7.12
(d, JH–H = 3.3 Hz, 1H), 7.03 (dd, JH–H = 5.1, 3.6 Hz,
1H), 6.49 (d, JH–H = 2.7 Hz, 1H), 4.26 (s, 2H), 3.88 (s,
2H), 3.74 (s, 3H). ppm. 13C NMR (CD3COCD3): d
211.9, 147.3, 140.4, 131.9, 128.3, 126.6, 126.3, 126.1,
110.8, 66.0, 62.7, 34.7 ppm. IR (KBr film) mmax (CO)
2055, 2011, 1963 cmꢀ1. MS (FAB): m/z 484 (M+), 456
(M+ ꢀ CO), 428 (M+ ꢀ 2CO), 400 (M+ ꢀ 3CO), 372
(M+ ꢀ 4CO), 344(M+ ꢀ 5CO), 316 (M+ ꢀ 6CO), 260
(M+ ꢀ 6CO ꢀ Fe), 204 (L+). Anal. Calc. for C17H12Fe2-
N2O6S: C, 42.14; H, 2.47; N, 5.78; S, 6.61. Found: C,
42.30; H, 2.68; N, 5.68; S, 6.70%.
tate/dichloromethane (1/3).
A
single crystal was
mounted on a glass fiber and the X-ray diffraction inten-
sity data were measured on a Kappa CCD XRD.
3.1. Syntheses of pyrrolyl Schiff bases N-(N0-methyl-2-
pyrrolylmethylidene)-2-thienylmethylamine (1)
Compound 3: 0.175 g (0.362 mmol), 9.0% yield; m.p.
142–143 ꢁC. 1H NMR (CD3COCD3): d 7.70 (d,
JH–H = 5.1 Hz, 1H), 7.39 (d, JH–H = 5.1 Hz, 1H), 6.88
The synthesis of Schiff base employed the usual ap-
proach of condensation in alcohol [13]. Equimolar
quantities of N-methyl-2-pyrrolecarboxaldehyde (1.09
g, 10.0 mmol) and 2-thiophenemethylamine (1.13 g,
10.0 mmol) were stirred in 50 ml methanol for 8 h at
room temperature. The reaction mixture was then fil-
tered and the solvent as well as unreacted starting mate-
rials were removed in vacuo over night to yield pure
orange–yellow product 1 (1.86 g, 9.12 mmol, 91.2%
yield); m.p. 121–122 ꢁC. 1H NMR (CD3COCD3): d
8.28 (s, 1 H), 7.31 (d, JH–H = 5.1 Hz, 1H), 7.01 (d,
JH–H = 3.6, 1H), 6.96 (dd, JH–H = 3.6, 5.1 Hz), 6.86 (d,
JH–H = 2.4 Hz, 1H), 6.51 (dd, JH–H = 3.6 Hz, 1H), 6.09
(JH–H = 2.7, 3.9 Hz, 1H), 4.84 (s, 2H), 3.96 (s, 3H).
ppm. 13C NMR (CD3COCD3): d 153.6, 144.1, 129.5,
128.3, 126.6, 124.1, 123.7, 116.9, 107.8, 59.5, 36.0 ppm.
IR (KBr film) mmax (CN) 1640 cmꢀ1. MS (FAB): m/z
204 (M+). Anal. Calc. for C11H12N2S: C, 64.70; H,
5.88; N, 13.72; S, 15.68. Found: C, 64.95; H, 5.88; N,
13.77; S, 15.59%.
(s, 1H), 6.23 (d, JH–H = 3.6 Hz, 1H), 6.05 (dd, JH–H
=
2.7, 3.6 Hz, 1H ), 3.96 (s, 2H), 3.95 (s, 2H), 3.68 (s,
3H) ppm. 13C NMR (CD3COCD3): d 207.4, 154.9,
139.3, 131.7, 129.9, 122.9, 117.8, 110.4, 106.9, 67.2,
60.7, 33.4 ppm. IR (KBr film) mmax (CO) 2063, 2026,
1981 cmꢀ1. MS (FAB): m/z 484 (M+), 456 (M+ ꢀ CO),
428 (M+ ꢀ 2CO), 400 (M+ ꢀ 3CO), 372 (M+ ꢀ 4CO),
344 (M+ ꢀ 5CO), 316 (M+ ꢀ 6CO), 260 (M+ ꢀ 6CO
ꢀ Fe), 204 (L+). Anal. Calc. for C17H12Fe2N2O6S: C,
42.14; H, 2.47; N, 5.78; S, 6.61. Found: C, 42.26; H,
2.71; N, 5.71; S, 6.67%.
Compound 4: 0.158 g (0.324 mmol), 8.1% yield; m.p.
d 7.69 (d,
96–97 ꢁC. 1H NMR (CD3COCD3):
JH–H = 5.1 Hz, 1 H), 7.48 (d, JH–H = 5.1 Hz, 1H), 7.40
(d, JH–H = 5.1 Hz, 1H), 7.14 (d, JH–H = 3.3 Hz, 1H),
7.04 (dd, JH-H = 5.1, 3.6 Hz, 1H), 4.20 (s, 2H), 3.96 (s,
2H) ppm. 13C NMR (CD3COCD3): d 210.4, 154.7,
139.3, 131.8, 128.6, 126.5, 126.2, 117.3, 115.2, 67.9,
65.2 ppm. IR (CH2Cl2) mmax (CO) 2066, 2024, 1975
cmꢀ1. MS (FAB): m/z 487 (M+), 459 (M+ ꢀ CO), 431
(M+ ꢀ 2CO), 403 (M+ ꢀ 3CO), 375 (M+ ꢀ 4CO),
347(M+ ꢀ 5CO), 319 (M+ ꢀ 6CO), 263 (M+ ꢀ 6CO ꢀ
Fe), 207 (L+). Anal. Calc. for C16H9Fe2NO6S2: C,
39.42; H, 1.85; N, 2.88; S, 13.14. Found: C, 39.52; H,
1.95; N, 2.93; S, 13.06%.
3.2. Reaction of 1 with Fe2(CO)9 in refluxing anhydrous
toluene to yield [l-N-(((2,3-g1:g2)-N0-methyl-2-pyrro-
lyl)methyl)-g1:g1(N) -2-thienylmethylamino]hexacarbo-
nyldiiron (2), [l-N-(((2,3-g1:g2)-2-thienyl)methyl)-
g1:g1(N)–N0-methyl-2pyrrolymethylamino]hexacarbonyl-
diiron (3), [l-N-(((2,3-g1:g2)-2-thienyl)methyl)-g1:g1
(N)-2-thienylmethylamino]hexacarbonyldiiron (4), and
[l-N-(((2,3-g1:g2)-N0-methyl-3-pyrrolyl)methyl)-g1:g1
(N)-2-thienylmethylamino]hexacarbonyldiiron (5)
Compound 5: 0.100 g (0.207 mmol), 5.2% yield; m.p.
142–143 ꢁC. 1H NMR (CD3COCD3): d 7.77 (d,
JH-H = 2.4 Hz, 1H), 7.48 (d, JH–H = 5.1 Hz, 1H), 7.13
(d, JH–H = 3.6 Hz, 1H), 7.03 (dd, JH–H = 5.1, 3.6 Hz,
1H), 6.27 (d, JH–H = 2.4 Hz, 1H), 4.30 (s, 2H), 3.77 (s,
3H), 3.69 (s, 2H). ppm. 13C NMR (CD3COCD3): d
211.8, 144.5, 140.3, 138.2, 136.7, 128.4, 126.3, 126.1,
103.7, 65.7, 64.8, 37.7 ppm. IR (CH2Cl2) mmax (CO)
2056, 2018, 1974 cmꢀ1. MS (FAB): m/z 484 (M+), 456
(M+ ꢀ CO), 428 (M+ ꢀ 2CO), 400 (M+ ꢀ 3CO), 372
(M+ ꢀ 4CO), 344(M+ ꢀ 5CO), 316 (M+ ꢀ 6CO), 260
(M+ ꢀ 6CO ꢀ Fe), 204 (L+). Anal. Calc. for C17H12Fe2-
N2O6S: C, 42.14; H, 2.47; N, 5.78; S, 6.61. Found: C,
42.26; H, 2.61; N, 5.72; S, 6.56%.
0.820 g (4.02 mmol) of ligand 1 and 12.0 mmol of
Fe2(CO)9 were heated at reflux in 80 ml of anhydrous
toluene solution in the dark under nitrogen for 12 h.
The reaction mixture was filtered through Celite 545
and the solvent was removed under reduced pressure.
The residue was chromatographed on a silica gel column
with ethyl acetate/n-hexane (1/3) as eluent to separate
the resulting red product 2 from the rest of other prod-
ucts. The column was further treated with n-hexane as
eluent to obtain other three red products 3, 4, and 5.
Compound 2: 0.895 g (1.85 mmol), 46.0% yield; m.p.
142–143 ꢁC. 1H NMR (CD3COCD3): d 7.48 (d,
If the reaction time was prolonged from 12 to 24 h
under the same reaction conditions, only 41% of

S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
3181
complex 2 and 17% of complex 4 were isolated. On the
other hand, if the reaction was stopped after six hours of
reaction under the same reaction conditions, 32% of
complex 2, 4% of complex 3, 10% of complex 4, and
3% of complex 5.
3.5. Reaction of complex 2 with triphenylphosphine to give
[l-N-(((2,3-g1:g2)-N0-methyl-2-pyrrolyl)methyl)-g1:g1-
(N)-2-thienylmethylamino]pentacarbonyltiphenylphospi-
nodiiron (7)
If the reaction was carried out at r.t. in benzene for
12 h, only complex 2, in 12% yield, was produced. Even
if the reaction temperature was raised up to the reflux
temperature in benzene, we still obtained complex 2, in
30% yield, as the sole organometallic product.
A mixture of complex 2 (0.42 g, 0.87 mmol), triphe-
nylphosphine (1.23 g, 4.30 mmol), and trimethylamine
N-oxide Æ 2H2O (0.80 g) in 80 ml of acetonitrile was stir-
red at room temperature under nitrogen atmosphere for
48 h. The reaction mixture was filtered and the solvent
was removed in vacuo. The residue was washed with
several portions of n-hexane and was then dissolved in
ethyl acetate. After the filtration, the filtrate was concen-
trated under reduced pressure to give deep red product 7
3.3. Thermolysis of complex 2
0.87 g (1.8 mmol) of complex 2 was dissolved in 50 ml
of solvent (n-heptane, acetonitrile, or toluene) and the
solution was refluxed under N2 atmosphere for 48 h.
The solution was cooled and filtered, and the filtrate
was flash evaporated in vacuo. The residue was chroma-
tographed on a silica gel column with ethyl acetate/n-
hexane (1:20) as eluent. Compound 1 (0.31 g, 1.5 mmol,
83% yield if the solvent is n-heptane and 0.35 g, 1.7
mmol, 94% yield if the solvent is acetonitrile or toluene)
and compound 6 (0.14 mmol, 7.8% yield if the solvent is
n-heptane) were isolated. Compound 6: 1H NMR
(CD3COCD3): d 7.21 (d, JH–H = 5.1 Hz, 1H), 6.75 (d,
JH–H = 3.3 Hz, 1H), 6.71 (dd, JH–H = 3.6, 5.1 Hz, 1H),
6.47 (dd, JH–H = 2.7 Hz, 1H), 5.80 (d, JH–H = 3.6 Hz,
1H), 5.55 (JH–H = 2.7, 3.9 Hz, 1H), 4.86 (b, 1H), 4.34
(s, 2H), 4.01 (s, 2H), 3.61 (s, 3H). ppm. IR (KBr film)
mmax (NH) 3421 cmꢀ1. MS (FAB): m/z 206 (M+). Anal.
Calc. for C11H14N2S: C, 64.07; H, 6.80; N, 13.59; S,
15.53. Found: C, 64.31; H, 6.98; N, 13.71; S, 15.67%.
Similar results were obtained if the thermolysis was
proceeded in d3-acetonitrile or d8-toluene solvent.
Repetition of the thermolysis under carbon monoxide
atmosphere afforded only trace amount of compound 1
after 4 days of reaction and more than 95% of un-
changed complex 2 was recovered.
1
(0.61 g, 85% yield). H NMR d 7.48 (d, JH–H = 5.1 Hz,
1H), 7.29 (m, 5H), 7.17 (d, JH–H = 2.4 Hz, 1H), 7.12
(d, JH–H = 3.6 Hz, 1H), 7.03 (m, 1H), 6.96 (m, 10H),
6.49 (d, JH–H = 2.4 Hz, 1H), 4.26 (d, JH–H = 14.4 Hz,
1H), 4.08 (d, JH–H = 14.4 Hz, 1H ), 3.88 (s, 2H), 3.74
(s, 3H). IR (CHCl3) mmax (CO) 2030, 1961, 1934, 1906
cmꢀ1. MS (EI): m/z 718 (M+), 690 (M+ ꢀ CO), 662
(M+ ꢀ 2CO), 634 (M+ ꢀ 3CO), 606 (M+ ꢀ 4CO), 578
(M+ ꢀ 5CO), 262 (PPh3+), 204 (L+). Anal. Calc. for
C34H27Fe2N2O5PS: C, 56.82; H, 3.76; N, 3.90; S, 4.46.
Found: C, 57.01; H, 3.80; N, 3.87; S, 4.38%.
3.6. Reaction of complex 2 with nitrosonium tetrafluo-
roborate to give N-2-thienylmethyl-N0-methyl-2-methyl-
pyrrolo[2,3b]-c-butyrolactam (8)
A mixture of complex 2 (0.42 g, 0.78 mmol) and nitr-
osonium tetrafluoroborate (0.10 g, 0.86 mmol) in 80 ml
of acetonitrile was stirred at room temperature under ni-
trogen atmosphere for 72 h. The reaction mixture was
filtered and the solvent was removed under reduced
pressure. The residue was washed with several portions
of n-hexane and was then dissolved in diethyl ether. Af-
ter the filtration, the filtrate was concentrated under re-
duced pressure to give 8 (0.12 g, 0.52 mmol, 66% yield).
1H NMR d 7.58 (d, J = 5.1 Hz, 1H), 7.18 (d, J = 3.6 Hz,
1H), 7.06 (dd, J = 3.6, 5.1 Hz, 1H), 6.95 (d, JH–H = 2.4
Hz, 1H), 6.18 (d, JH–H = 2.4 Hz, 1H), 4.93 (s, 2H),
4.23 (s, 2H), 4.01 (s, 3H). IR (CHCl3) mmax (CO) 1687
cmꢀ1. MS (EI): m/z 232 (M+), 204 (M+ ꢀ CO). Anal.
Calc. for C12H12N2SO: C, 62.07; H, 5.17; N, 12.07; S,
13.79. Found: C, 61.92; H, 5.26; N, 12.22; S, 13.64%.
3.4. Lithium aluminum hydride reduction of complex 2
0.97 g (2.0 mmol) of complex 2 in 20 ml of THF was
added drop wise with stirring to a 50 ml of ice-cold THF
solution containing 0.16 g of suspension LiAlH4. After
the reaction mixture was stirred for 2 h, excess of LiAlH4
was decomposed by the addition of 20 ml ethyl acetate.
The reaction mixture was filtered and the solvent was re-
moved in vacuo. The residue was chromatographed on a
silica gel column with ethyl acetate/n-hexane (1:20) as
eluent to give N-(N0-methyl-2-pyrrolylmethyl)(2-thienyl-
methyl)amine (6) (0.29 g, 1.4 mmol, 70% yield) and
unchanged complex 2 (0.46 mmol, 23%).
3.7. Oxidation of complex 2 with ferric chloride/ceric
ammonium nitrate
The complex 2 (0.35 g, 0.72 mmol) in 30 ml of ethyl
alcohol was added drop wise with stirring to a 30 ml
ethyl alcohol solution of anhydrous ferric chloride
(0.25 g, 1.5 mmol). The reaction mixture was stirred at
room temperature for 3 h and then at 60 ꢁC for 4 h. It
A sample obtained similarly, but with lithium alumi-
num deuteride, was shown by NMR and Mass spectra
to contain one derterium atom attached to the b-carbon
of the pyrrolyl ring.

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S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
was filtered and evaporated under reduced pressure. The
residue was washed with several portions of n-hexane
and was then dissolved in diethyl ether. After the filtra-
tion, the filtrate was concentrated in vacuo to give 8
(0.088 g, 0.38 mmol, 53% yield). Similar procedure
was performed for the oxidation of complex 2 with ceric
ammonium nitrate in acetone solution to afford the
same product 8 (0.064 g, 0.28 mmol, 37% yield).
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3.8. Electrochemical experiment
Cyclic voltammetry was performed at room temper-
ature in acetonitrile solution containing 0.1 M tetra-
ethylammonium perchlorate (TEAP) as supporting
electrolyte. The single sweep cyclic voltammogram
(CV) of the complex of ꢁ10ꢀ3 M in a three-compart-
ment cell was recorded with stationary platinum
microelectrode. The peak potential Ep of the com-
pound was independent of the concentration in the
range between 10ꢀ2 and 10ꢀ4 M in acetonitrile solu-
tion and was always reproducible to within 50 mV.
Repeated CV scans did not affect the appearance of
the voltammogrames.
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3.8.1. Control potential bulk coulometry of complex 2
0.20 mmol of complex 2 in an acetonitrile solution
containing 0.1 M of TEAP was exhaustively oxidized
with platinum gauze electrode at 0.95 V vs. Ag–AgCl
reference electrode. The electrolysis showed that the
process is a 1.03 electron oxidation. After the electroly-
sis, the solution was filtered and the solvent was re-
moved in vacuo. The residue was dissolved in diethyl
ether. After the filtration, the filtrate was concentrated
under reduced pressure to give pure 8 product in 92%
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Crystallographic data for the structural analysis have
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5). Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: +44-1223-336033;
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The authors express their appreciation to the
National Science Council (Taiwan, ROC) and National
Dong Hwa University for providing the financial
support necessary to carry out this study.

S.-Y. Jin et al. / Journal of Organometallic Chemistry 689 (2004) 3173–3183
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