Facile synthesis of σ,μ-iminoacyl bridged butterfly clusters (μ-RE)(σ,μ-ArC=NAr′)Fe2(CO)6 (E=S, Se)

Article abstract of DOI:10.1016/S0022-328X(99)00190-4

The reactive anionic salts [Et₃NH][(μ-RE)(μ-CO)Fe₂(CO)₆] (1) (RE=PhS, PhSe) reacted with N-arylbenzimidoyl chloride Ph(Cl)C=NAr′ (2) (Ar=Ph, 4-MeC₆H₄, 4-C₆H₄) in THF to give butterfly σ,μ-iminoacyl bridged hexacarbonyldiiron clusters (μ-RE)(σ,μ-PhC=NAr′)Fe₂(CO)₆ (3a-e) in moderate yields. The structure of the new clusters was characterized by elemental analyses, IR and ¹H-NMR spectroscopy. X-ray diffraction confirmed the crystal structure of (μ-PhSe)(σ,μ-PhC=NPh)Fe₂(CO)₆ (3a). It crystallizes in the triclinic space group P1 (no. 2) with a=11.224(3), b=13.542(4), c=8.9559(2) A, α=102.32(2), β=91.95(2), γ=70.20(2)°, V=1250.1(6) A³, Z=2 and D_calc=1.636 g cm^-3.

Full text of DOI:10.1016/S0022-328X(99)00190-4

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 585 (1999) 63–67
Facile synthesis of s,m-iminoacyl bridged butterfly clusters
(m-RE)(s,m-ArCꢀNAr%)Fe2(CO)6 (E=S, Se)
Chao-Guo Yan a,*, Jing Sun a, Jie Sun b
a Department of Chemistry, Yangzhou Uni6ersity, Yangzhou 225002, PR China
b Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Shanghai 200032, PR China
Received 3 December 1998; received in revised form 30 March 1999
Abstract
The reactive anionic salts [Et3NH][(m-RE)(m-CO)Fe2(CO)6] (1) (RE=PhS, PhSe) reacted with N-arylbenzimidoyl chloride
Ph(Cl)CꢀNAr% (2) (Ar=Ph, 4-MeC6H4, 4-C6H4) in THF to give butterfly s,m-iminoacyl bridged hexacarbonyldiiron clusters
(m-RE)(s,m-PhCꢀNAr%)Fe2(CO)6 (3a–e) in moderate yields. The structure of the new clusters was characterized by elemental
1
analyses, IR and H-NMR spectroscopy. X-ray diffraction confirmed the crystal structure of (m-PhSe)(s,m-PhCꢀNPh)Fe2(CO)6
,
(3a). It crystallizes in the triclinic space group P1 (no. 2) with a=11.224(3), b=13.542(4), c=8.9559(2) A, h=102.32(2),
3
i=91.95(2), k=70.20(2)°, V=1250.1(6) A , Z=2 and Dcalc=1.636 g cm−3. © 1999 Elsevier Science S.A. All rights reserved.
,
Keywords: Iminoacyl complex; Carbonyl–iron; Sulfur; Selenium; Crystal structure
1. Introduction
2. Results and discussion
Since Seyferth et al. first reported in 1985 [1], the
reactive anion [(m-RS)(m-CO)Fe2(CO)6]−1 and its sele-
nato-analog [(m-RSe)(m-CO)Fe2(CO)6]−1, mainly due to
the work of Seyferth et al. [2–4] and Song et al. [5–7],
they have become very useful reagents, synthesizing a
variety of carbonyl–iron clusters.
Our ongoing program is aimed at extending their
application to synthesize more novel clusters. As a
continuation of this project, we further investigated the
reactivity of the anions (m-RE)(m-CO)Fe2(CO)6 (E=S,
Se) toward an organic electrophile, N-arylbenzimidyl
chloride. We shall describe here the results of syntheses
of N-iminoacyl-bridged clusters (m-RE)(m-ArCꢀNAr%)-
Fe2(CO)6 from the reactions studied, and X-ray diffrac-
tion analysis for a representative cluster (m-PhSe)(m-
PhCꢀNPh)Fe2(CO)6.
The reactive intermediates [Et3NH][(m-PhS)(m-
CO)Fe2(CO)6]−1, prepared in situ from Fe3(CO)12,
Et3N and PhSH reacted smoothly with N-arylbenzimi-
doyl chloride (Aryl=phenyl, 4-methylphenyl) to yield
the expected m-iminoacyl bridged clusters 3a and 3b
(Scheme 1). This type of m-iminoacyl bridged carbonyl–
iron cluster has been synthesized by reaction of triiron
dodecarbonyl with thiomidates, or by the reaction of
[Et3NH][(m-RS)(m-CO)Fe2(CO)6] (R=alkyl) with N-
phenylbenzimidoyl chloride [8]. The selenato-bridged
intermediate [Et3NH][(m-ArSe)(m-CO)Fe2(CO)6]− reacts
similarly with benzimidoyl chloride to give clusters
3c–e in moderate yields. Mechanically, the formation
of the m-iminoacyl bridged cluster is apparently a nucleo-
philic substitution. The iron-centered anion attacks the
carbon atom of the benzimidoyl group and eliminates
the chloride ion. Then the nitrogen atom coordinates
the other iron atom while replacing the m-CO group to
complete the reaction.
Clusters 3a–e have been characterized by elemental
* Corresponding author.
analysis, IR and 1H-NMR spectroscopy, and like 3c, by
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00190-4

64
C.-G. Yan et al. / Journal of Organometallic Chemistry 585 (1999) 63–67
ORTEP representation of the molecule. As seen from
Fig. 1, the molecule exhibits a typical butterfly core
(Fe2SeCN) with Fe2Se and Fe2CN as two wings. The
dihedral angle between the two wing planes is 90.34°.
The six-coordinate atoms or groups around each iron
atom display as a distorted octahedron. The Fe–Fe
,
distance is 2.5799(8) A, which is similar to the
,
analogous selenato-bridged cluster 2.544(2) A in (m-
,
PhSe)(s,m-CHꢀCHPh)Fe2(CO)6 [11], 2.648(3) A in (m-
PhSe)(m-PhCH2SCꢀS)Fe2(CO)6 [9], and the two
Scheme 1.
,
selenato-bridged clusters 2.601(4), 2.575(4) A in [(m-
,
CH3C6H4Se)Fe2(CO)6]2(m4-Se) [10], 2.534 A in (m-
Table 1
SePhCꢀCHSe-m)Fe2(CO)6 [11].
Crystal data and refinement for complex 3c
The iminoacyl group is coordinated to Fe(2) via a
2
,
Fe–C s-bond (Fe(2)–C(7) 1.982(4) A, C(7) is in sp
form. The iminoacyl group coordinates to Fe(1) via the
donation of an unshared electron pair from the N atom
Empirical formula
Formula weight
Crystal system
Space group
C25H15O6NSeFe2
616.05
Triclinic
P1 (no. 2)
11.224(3)
13.542(4)
8.9559(2)
102.32(2)
91.95(2)
70.20(2)
1250.1(6)
2
1.636
612.00
26.55
20.0
v−2q
3641
3392 [Rint=0.018]
2688
377
,
(Fe(1)–N 2.000(3) A). This represents that the iminoa-
,
a (A)
cyl group is in s, n coordinate pattern. There are two
possible coordinate patterns for iminoacyl group as in
the A (s, p) and B (s, n) isomers. Since two isomers are
structurally very similar, differentiation between them
based on the spectroscopic data alone is very difficult.
Seyferth suggested that the B-isomer is more consistent
with the observed IR spectrum [8]. From the crystal
structure we can conclude that the iminoacyl group
coordinated to the iron atom with a s, n pattern. The
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (g cm−3
F(000)
)
v (Mo–Ka) (cm−1
Temperature (K)
Scan type
)
,
CꢀN bond length (1.287(4) A) is identical within exper-
imental error to the values of 1.254(7) and 1.291(7) A
,
Total reflections measured
No. of unique reflections
Reflections observed [I\3.00|(I)]
No. variables
observed for the two independent CꢀN bonds in (m-
Me2CꢀN)(m-Me2CꢀN–O)Fe2(CO)6 [12]. This means
that the CꢀN bond in 3c is a normal bond value and
Residuals
R=0.026,
wR=0.033
1.90
0.04
0.30 and −0.36
,
falls in the range 1.24–1.29 A observed in ordinary
organic compounds. The angles of Fe(1)–Se–C(20) and
Fe(2)–Se–C(20) are 113.5(1) and 112.2(1)°; this reveals
that the phenyl group attached to the Se atom is at an
equatorial position, namely 3c is an E-type isomer,
which can be seen intuitively from Fig. 1.
Goodness-of-fit indicator
Max. shift/error in final cycle
Largest difference peak and hole (e A
−3
,
)
X-ray diffraction. The IR spectra of 3a–e showed four
to five strong absorption bands in the region of 1950–
2100 cm−1, which are the characteristic bands of the
terminal carbonyls attached to iron atoms. There is also
one medium absorption band at around 1540 cm−1 in
the IR spectra of the clusters, which was apparently
attributed to the iminoacyl CꢀN double band. This
band is shifted somewhat to a lower frequency when
compared to the parent thioimidates (wCꢀN 1610–1630
cm−1) [8], which is the result of the bridged coordina-
Table 2
,
Selected bond lengths (A) and angles (°)
Se–Fe(1)
Se–C(20)
Fe(1)–N
Fe(1)–C(2)
Fe(2)–C(4)
Fe(2)–C(6)
N–C(7)
2.3708(8)
1.931(4)
2.000(3)
1.805(4)
1.773(5)
1.811(5)
1.287(4)
1.482(5)
Se–Fe(2)
2.3724(8)
2.5799(8)
1.788(4)
1.791(5)
1.799(4)
1.982(4)
1.456(5)
Fe(1)–Fe(2)
Fe(1)–C(1)
Fe(1)–C(3)
Fe(2)–C(5)
Fe(2)–C(7)
N–C(14)
C(7)–C(8)
1
tion. The H-NMR spectra of 3a–e all exhibited the
presence of their respective organic groups.
Fe(1)–Se–Fe(2)
Fe(2)–Se–C(20)
Se–Fe(2)–Fe(1)
Fe(1)–Fe(2)–N
Fe(1)–Fe(2)–C(7)
Fe(1)–N–C(14)
Fe(2)–C(7)–N
N–C(7)–C(8)
65.90(3)
112.2(1)
57.02(2)
71.32(9)
70.76(10)
127.4(2)
110.3(2)
123.7(3)
Fe(1)–Se–C(20)
Se–Fe(1)–Fe(2)
Se–Fe(1)–N
Se–Fe(2)–C(7)
Fe(1)–N–C(7)
C(7)–N–C(14)
113.5(1)
57.08(2)
79.98(9)
80.3(1)
107.6(2)
124.7(3)
In order to further confirm the structure of such
m-iminoacyl bridged clusters, an X-ray diffraction anal-
ysis for 3c was undertaken. The data collection and
processing parameters, atomic coordinate equivalent
isotropic thermal parameters, and selected bond lengths
and angles are listed in Tables 1 and 2. Fig. 1 shows the
Fe(2)–C(7)–C(8) 125.8(3)

C.-G. Yan et al. / Journal of Organometallic Chemistry 585 (1999) 63–67
65
3.2. Reaction of [Et3NH][(v-PhS)(v-CO)Fe2(CO)6] (1)
with Ph(Cl)CꢀNPh
A 100 ml three-necked round-bottomed flask equipped
with a stir-bar, N2 inlet tube, and serum caps was charged
with 1.00 g (1.98 mmol) of Fe3(CO)12 and 40 ml of THF.
To the resulting green solution were added 0.50 ml (3.00
mmol) of triethylamine and 0.21 ml (2.00 mmol) thiophe-
nol. The mixture was stirred at room temperature (r.t.)
for 30 min and the solution turned to red–brown. The
resulting [Et3NH][(m-PhS)(m-CO)Fe2(CO)6] (1) reagent
solution was cooled to 0°C and added by cannula, 0.65
g (3.00 mmol) N-phenylbenzimidoyl chloride dissolved in
a separate flask in 15 ml THF. The mixture was stirred
at r.t. for 24 h. Solvent was removed under vacuum to
leave a red residue, which was extracted with petroleum
ether and purified by filtration chromatography, then
purified further by TLC using petroleum ether as eluent.
The first red band gave 0.237
g (24%) of (m-
PhS)2Fe2(CO)6, which was identified by comparison of
its melting point and 1H-NMR spectrum with those given
in the literature [17]. The second red band gave 0.350 g
(31%) of (m-PhS)(s,m-PhCꢀNPh)Fe2(CO)6 (3a) as a red
solid. M.p. (dec.) 158–160°C. Anal. Calc. for
C25H15Fe2NO6S: C, 52.76; H, 2.66. Found: C, 52.38; H,
2.94%. 1H-NMR (CDCl3): l 6.60–7.60 (3 C6H5) ppm. IR
(KBr disc): w 2071(s), 2022(vs), 1992(vs), 1978(vs), 1945(s)
(CꢁO), 1535(m) (CꢀN) cm−1
.
Fig. 1. Molecular structure of cluster 3c.
3. Experimental
3.3. Reaction of [Et3NH][(v-PhS)(v-CO)Fe2(CO)6] (1)
with Ph(Cl)CꢀNC6H4CH3-p
3.1. General
The same procedure as for 3a was followed, but 0.690
g (3.00 mmol) of Ph(Cl)CꢀNC6H4CH3-p was used instead
of Ph(Cl)CꢀNPh. The first red band gave 0.219 g (22%)
of (m-PhS)2Fe2(CO)6, which was identified by comparison
All reactions were carried out under prepurified tank
nitrogen using standard Schlenk or vacuum line tech-
niques. THF and diethylether were distilled from sodium
benzophenone ketyl, while triethylamine was distilled
from potassium hydroxide under nitrogen. Thiophenol
was chemically pure. Triiron dodecacarbonyl [13], ben-
zeneselenol [14] and N-arylbenizimidoyl chloride
PhC(Cl)ꢀNAr [15,16] were all prepared according to the
literature.
The progress of all reactions was monitored by TLC.
Products were purified by column chromatography (30×
2.4 cm, 200–300 mesh silica gel) or by TLC (20×25×
0.025 cm, 10–40 mm silica gel G).The eluents were light
petroleum ether (60–90°C) and methylene chloride, used
without further purification. All the products were recrys-
tallized from CH2Cl2–hexane and characterized by ele-
mental analysis and IR, 1H-NMR spectroscopy.
Elemental analysis was performed by an Erba 1106
analyzer. IR spectra were recorded on a Nicolet FT-IR
5DX spectrometer with KBr discs. Proton-NMR spectra
were recorded on a Bruker 300 spectrometer with a CDCl3
solvent and a TMS internal standard.
1
of its melting point and H-NMR spectrum with those
given in the literature. The second red band gave 0.410
g (35%) of (m-PhS)(s,m-PhCꢀNC6H4CH3-p)Fe2(CO)6
(3b) as a red solid. M.p. (dec.) 146–148°C. Anal. Calc.
for C26H17Fe2NO6S: C, 51.55; H, 2.94. Found: C, 51.69;
H, 2.80%. 1H-NMR (CDCl3): l 2.15 (s, 3H, CH3), 6.61,
7.60 (d, d, J=7.0 Hz, 2H, 2H, C6H4), 6.89–7.39 (2 C6H5)
ppm. IR (KBr disc): w 2071(vs), 2022(vs), 1993(vs),
1978(vs), 1946(s) (CꢁO), 1535(m) (CꢀN) cm−1
.
3.4. Reaction of [Et3NH][(v-PhSe)(v-CO)Fe2(CO)6] (1)
with Ph(Cl)CꢀNPh
A 100 ml three-necked round-bottomed flask equipped
with a stir-bar, N2 inlet tube, and serum caps was charged
with 1.00 g (1.98 mmol) of Fe3(CO)12 and 40 ml of THF.
To the resulting green solution were added 0.50 ml (3.00

66
C.-G. Yan et al. / Journal of Organometallic Chemistry 585 (1999) 63–67
mmol) of triethylamine and 0.21 ml (2.00 mmol) ben-
zeneselenol. The mixture was stirred at r.t. for 30 min
and the solution turned to red–brown. The resulting
[Et3NH][(m-PhSe)(m-CO)Fe2(CO)6] (1) reagent solution
was cooled to 0°C and added by cannula 0.65 g (3.00
mmol) N-phenylbenzimidoyl chloride dissolved in a
separate flask in 15 ml THF. The mixture was stirred at
r.t. for 24 h. The solvent was removed under vacuum to
leave a red residue, which was extracted with petroleum
ether and purified by filtration chromatography, then
purified further by TLC using petroleum ether as elu-
ent. The first red band gave 0.271 g (23%) of (m-
PhSe)2Fe2(CO)6, which was identified by comparison of
its melting point and 1H-NMR spectrum with those
given in the literature [5]. The second red band gave
0.347 g (28%) of (m-PhSe)(s,m-PhCꢀNPh)Fe2(CO)6 (3c)
as a red solid. M.p. (dec.) 140–141°C. Anal. Calc. for
C25H15Fe2NO6Se: C, 48.74; H, 2.45. Found: C, 48.44;
H, 2.76%. 1H-NMR (CDCl3): l 6.55–7.70 (3 C6H5)
ppm. IR (KBr, disc): w 2069(s), 2021(vs), 1991(vs),
3.7. Crystal structure determination of 3c
A red prismatic crystal of C25H15O6NSeFe2 having
approximate dimensions of 0.20×0.20×0.30 mm was
mounted on a glass fiber. All measurements were made
on a Rigaku AFC7R diffractometer with graphite
monochromated Mo–Ka radiation and a 12 kW rotat-
ing anode generator. Cell constants and an orientation
matrix for data collection, obtained from a least-
squares refinement using the setting angles of 18
carefully centered reflections in the range 18.333°B
2qB24.42° corresponded to a primitive triclinic cell.
The data were collected at a temperature of 2091°C
using the ꢀ−2q scan technique to a maximum 2q
value of 50.0°. ꢀ scans of several intense reflections,
made prior to data collection, had an average width at
half-height of 0.10 with a take-off angle of 6.0°. Scans
of (1.21+0.30 tan q) were made at a speed of 16.0
min−1 (in ꢀ). The weak reflections [IB13.0|(I)] were
rescanned (maximum of four scans) and the counts
were accumulated to ensure good counting statistics.
Stationary background counts were recorded on each
side of the reflection. The ratio of peak counting time
to background counting time was 2:1. The diameter of
the incident beam collimator was 1.0 mm, the crystal to
detector distance was 235 mm, and the computer con-
trolled detector aperture was to 9.0×13.0 mm (hori-
zontal×vertical). Of the 3641 reflections that were
collected, 3392 were unique [Rint=0.018]. The intensi-
ties of three representative reflection were measured
after every 200 reflections. Over the course of data
collection, the standards decreased by −1.1%. A linear
correction factor was applied to the data to account for
this phenomenon. The linear absorption coefficient v
for Mo–Ka radiation is 26.6 cm−1. An empirical ab-
sorption correction based on azimuthal scans of several
reflections was applied which resulted in transmission
factors ranging from 0.58 to 1.00. The data were cor-
rected for Lorentz and polarization effects. A correc-
tion for secondary extinction was applied where the
coefficient=2.433296e-06.
1975(vs), 1950(s) (CꢁO), 1530(m) (CꢀN) cm−1
.
3.5. Reaction of [Et3NH][(v-PhSe)(v-CO)Fe2(CO)6] (1)
with Ph(Cl)CꢀNC6H5CH3-p
The same procedure as for 3c was followed, but 0.690
g (3.00 mmol) of Ph(Cl)CꢀNC6H4CH3-p was used in-
stead of Ph(Cl)CꢀNPh. The first red band gave 0.209 g
(18%) of (m-PhSe)2Fe2(CO)6, which was identified by
comparison of its melting point and 1H-NMR spectrum
with those given in the literature [5]. The second red
band gave 0.350
PhCꢀNC6H4CH3-p)Fe2(CO)6 (3d) as a red solid. M.p.
(dec.) 142–144°C. Anal. Calc. for C26H17Fe2NO6Se: C,
g
(28%) of (m-PhSe)(s,m-
1
49.56; H, 2.72. Found: C, 50.02; H, 3.04%. H-NMR
(CDCl3): l 2.13 (s, 3H, CH3), 6.74, 7.38 (d, d, J=7.0
Hz, 2H, 2H, C6H4), 6.89–7.37 (2 C6H5) ppm. IR (KBr,
disc): w 2069(vs), 2020(vs), 1991(vs), 1975(vs), 1944(s)
(CꢁO), 1535(m) (CꢀN) cm−1
.
3.6. Reaction of [Et3NH][(v-PhSe)(v-CO)Fe2(CO)6] (1)
with Ph(Cl)CꢀNC6H5Cl-p
The structure was solved by direct methods and
expanded using Fourier techniques. The non-hydrogen
atoms were refined anisotropically. Hydrogen atoms
were refined isotropically. The final cycle of full-matrix
least-squares refinement was based on 2688 observed
reflections [I\3.00|(I)] and 377 variable parameters
and converged (largest parameter was 0.04 times its
estimated S.D.) with unweighted and weighted agree-
ment factors of R=0.026, Rw=0.033. The standard
deviation of an observation of unit weight [Sw(ꢀFoꢀ−
ꢀFcꢀ)/(No−Nv)]1/2=1.29 (No=number of observations,
Nv=number of variables). The weighting scheme was
based on counting statistics and included a factor (p=
0.030) to downweight the intense reflections. Plots of
Sw(ꢀFoꢀ−ꢀFcꢀ) versus ꢀFoꢀ, reflection order in data col-
The same procedure as for 3c was followed, but 0.615
g (3.00 mmol) of Ph(Cl)CꢀNC6H4Cl-p was used instead
of Ph(Cl)CꢀNPh. The first red band gave 0.313 g (26%)
of (m-PhSe)2Fe2(CO)6, which was identified by compari-
1
son of its melting point and H-NMR spectrum with
those given in the literature. The second red band gave
0.514
g
(40%) of (m-PhSe)(s,m-PhCꢀNC6H4Cl-
p)Fe2(CO)6 (3e) as a red solid. M.p. (dec.) 124–126°C.
Anal. Calc. for C25H15ClFe2NO6S: C, 46.16; H, 2.17.
1
Found: C, 46.35; H, 2.56%. H-NMR (CDCl3): l 6.53–
7.53 (2 C6H5, C6H4) ppm. IR (KBr, disc): w 2067(vs),
2020(vs), 1992(vs), 1978(vs), 1945(s) (CꢁO), 1540(m)
(CꢀN) cm−1
.

C.-G. Yan et al. / Journal of Organometallic Chemistry 585 (1999) 63–67
67
(1985) 398.
lection, sin q/u and various classes of indices showed no
unusual trends. The maximum and minimum peaks on
the final difference Fourier map corresponded to 0.30
and −0.36 e A−3, respectively. Neutral atom scattering
factors were taken from Cromer and Waber [18]. Anoma-
lous dispersion effects were included in Fcac [19]; the
values for Df % and Df %% were those of Creagh and Mcauley
[20]. The values for the mass attenuation coefficients are
those of Creagh and Hubbell [21]. All calculations were
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Further details of the crystal structure investigation
may be obtained from the Fachinformationszentrum
Karsruhe, D-76344 Eggenstein-Leopoldshafen, Ger-
many, on quoting the depository number CSD-410428.
[14] D.G. Foster, Organic Syntheses, vol. III, Wiley, New York,
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Acknowledgements
The authors would like to thank the State Key
Laboratory of Organometallic Chemistry at Shanghai
Institute of Organic Chemistry for financial support of
this work.
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