Iron Se-bonded mono-selenocarbonates CpFe(CO)2SeCO2R: The first selenocarbonate complexes

Article abstract of DOI:10.1016/j.ica.2004.01.023

The reactivity of the iron selenide complex (μ-Se)[CpFe(CO) ₂]₂ toward chloroformates, ROCOCl, has been studied and the products CpFe(CO)₂SeCO₂R [R=Me (1), Et (2), iso-Bu (3), Ph (4), 2-C₆H₄

Full text of DOI:10.1016/j.ica.2004.01.023

Inorganica Chimica Acta 357 (2004) 4341–4344
www.elsevier.com/locate/ica
Note
Iron Se-bonded mono-selenocarbonates CpFe(CO)2SeCO2R: the first
selenocarbonate complexes
*
Mohammad El-khateeb
Chemistry Department, Jordan University of Science and Technology, Irbid 22110, Jordan
Received 15 October 2003; accepted 9 January 2004
Available online 26 February 2004
Abstract
The reactivity of the iron selenide complex (l-Se)[CpFe(CO)2]2 toward chloroformates, ROCOCl, has been studied and the
products CpFe(CO)2SeCO2R [R ¼ Me (1), Et (2), iso-Bu (3), Ph (4), 2-C6H4Cl (5), 4-C6H4Cl (6), and 4-C6H4NO2 (7)] have been
obtained. The novel complexes, 1–7, have been characterized by elemental analyses, IR and 1H NMR spectroscopy. The solid state
structure of CpFe(CO)2SeCO2Et, 2, was determined by an X-ray crystal structure analysis.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Iron; Cyclopentadienyl; X-ray structure; Selenocarbonates; Carbonyl; Selenium-ligands
1. Introduction
plexes were synthesized by treatment of 1,2,3-selen-
adiazoles with low-valent transition metal compounds
such as CpꢀCoL2 (L ¼ CO, PPh3), Pd(PPh3)4 and
Fe2(CO)9 [30,31].
There has been great interest in organometallic sele-
nium compounds in recent years [1–5]. The interest
stems not only from the bonding diversity [6–10] and
reactivity [11–15] of these compounds but also from the
applications of such complexes in material science
[2,16,17] and biochemistry [18–21]. The structure of
NiFeSe-hydrogenase (isolated from Desulfovibrio
baculatus) showed that the Ni-center is bonded to one
Se-atom [20].
Selenolate complexes, M–SeR, are among the most
studied complexes of organometallic compounds con-
taining selenium-ligands. The preparation of these
complexes involves oxidative addition of organodisele-
nides to low-valent transition metal centers [15,22,23],
metathesis of organotransition metal halide with alkali-
metal organoselenolates [24] or by selenium insertion
into alkali metal–transition–metal bonds and sub-
sequent reactions with organohalides [25–28].
Recent work in this laboratory has shown that the
iron selenosulfonate complexes, CpFe(CO)2SeSO2R,
have been synthesized by the reaction of the iron sele-
nide (l-Se)[CpFe(CO)2]2, with sulfonyl chlorides [32].
Iron selenocarboxylates CpFe(CO)2SeCOR have also
been prepared by treatment of (l-Se)[CpFe(CO)2]2 with
acid chlorides [33]. Photolysis of these thiocarboxylates
in the presence of EPh3 (E ¼ P, As, Sb) gave
CpFe(CO)(EPh3)SeCOR as sole reaction products [34].
Although, thiocarbonate complexes are very common
in the literature, the analogous selenocarbonates are
relatively uncommon. In this paper, the preparation and
characterization of iron monoselenocarbonate com-
plexes, CpFe(CO)2SeCO2R, are discussed.
Transition metal complexes containing diselenolene
ligands are known in the literature [29–31]. Such com-
2. Results and discussion
2.1. Synthesis and characterization
* Corresponding author. Tel.: +962-2-7201000x23644; fax: +962-2-
7095014.
E-mail address: kateeb@just.edu.jo (M. El-khateeb).
The novel complexes CpFe(CO)2SeCO2R [R ¼ Me
(1), Et (2), iso-Bu (3), Ph (4), 2-C6H4Cl (5), 4-C6H4Cl
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.01.023

4342
M. El-khateeb / Inorganica Chimica Acta 357 (2004) 4341–4344
(6), 4-C6H4NO2 (7)] were obtained in good yield when
slight excess of chloroformates was reacted with (l-
Se)[CpFe(CO)2]2 (Eq. 1). The side product CpFe-
(CO)2Cl, which produced from this reaction and similar
ones [32–35], can be easily separated from the desired
products by column chromatography.
2.2. Crystal structure
A perspective view of CpFe(CO)2SeCO2Et, 2, is dis-
played in Fig. 1 along with the atom numbering scheme.
The coordination around the Fe-atom can be described
as three-legged piano stool. The values of C11–Fe–C12,
C11–Fe–Se and C12–Fe–Se are 93.9(2)°, 88.72(14)° and
93.01(14)°, respectively. It can be seen that the seleno-
carbonate ligand is bonded to the iron atom in a
monodentate fashion through the selenium atom.
Compound 2 possesses an Fe–Se bond distance of
CO
O
CO
R
Fe Se
Fe
+
Cl
O
OC
OC
ꢀ
2.3829(8) A, which is similar to that observed for
ꢀ
CpFe(CO)2SeSO2C6H5 (2.394(3) A) [32]. The C(1)–O(1)
ꢀ
bond length of 1.192(5) A is also similar to that obtained
ð1Þ
ꢀ
for CpFe(CO)2SCO2Et (1.197(3) A [35] and CpFe-
O
ꢀ
(CO)2SCO-2-C6H4NO2 (1.209(5) A [36]. The Se–C(1)–
Fe
R
Fe
+
O(2) bond angle of 107.0(3)° is smaller than the
corresponding S–C–O angle in CpFe(CO)2SCO2Et
(108.2 (2)°).
OC
Se
O
OC
Cl
OC
OC
1-7
To the best of our knowledge, complexes (1–7) are the
first selenocarbonate complexes known. These com-
plexes (1–7) are air stable as solids and in solutions.
They are soluble in most common organic solvents such
as THF, and CH2Cl2 but insoluble in hydrocarbons.
These complexes were isolated as red-brown solids and
3. Experimental
3.1. General
All reactions and manipulations were performed un-
der a nitrogen atmosphere using Schlenk techniques.
Diethyl ether, hexane and benzene were purified by re-
flux over sodium and distillation under nitrogen. Di-
chloromethane was heated under reflux over P2O5 and
distilled under nitrogen. Chloroformates, iron dimer,
and selenium were obtained from Acros and were used
1
characterized by elemental analysis, IR and H NMR
1
spectroscopy. The H NMR spectra of 1–7, in deuter-
ated chloroform, exhibit a singlet due to the five cyclo-
pentadienyl ligand protons in the range 4.98–5.09 ppm.
This peak falls within the same range observed for the
selenocarboxylates, CpFe(CO)2SeCOR (5.08–5.11 ppm)
[33] and thiocarbonate complexes, CpFe(CO)2SCO2R
(4.98–5.12 ppm) [35]. The chemical shifts for the protons
of the selenocarbonate ligands are observed in the ex-
pected ranges and multiplicity.
The solution IR spectra of 1–7 (in CH2Cl2) show the
characteristic absorptions m(CO, terminal) in the ranges
2036–2043 and 1988–1993 cmꢁ1. These bands are higher
than those observed for the selenocarboxylate analog,
CpFe(CO)2SeCOR (2030–2035 and 1965–1973 cmꢁ1
[33] and lower than those of thiocarbonates,
CpFe(CO)2SCO2R (2044–2045 and 1997–1979 cmꢁ1
)
)
[35]. This shift may be attributed to weaker p-accepting
properties of selenocarbonate ligands relative to thio-
carbonate ligands. This result is in agreement with re-
ported results of thio- vs. selenocarboxylate complexes
[33,35]. The spectra also contain a band in the range
1655–1678 cmꢁ1 for the carbonyl group of the seleno-
carbonate ligand. The frequency of this band is higher
than that of the corresponding selenocarboxylate com-
plexes (1590–1615 cmꢁ1) [33], in agreement with re-
ported results. These spectroscopic results reflect a
relatively higher electron density around the iron-center
in complexes 1–7 compared to analogous thiocarbonate
complexes.
Fig. 1. ORTEP drawing of CpFe(CO)2SeCO2Et (2). Selected bond
ꢀ
length (A) and angles (°): Fe–Se ¼ 2.3829(8); Fe–C11 ¼ 1.766(5); Fe–
C12 ¼ 1.774(4);
Fe–C31 ¼ 2.081(4);
Fe–C32 ¼ 2.087(5);
Fe–C33 ¼ 2.090(5); Fe–C34 ¼ 2.099(5); Fe–C35 ¼ 2.100(5); Se–
C1 ¼ 1.914(4); C1–O1 ¼ 1.192(5); C1–O2 ¼ 1.333(5); C11–
O11 ¼ 1.141(6); C12–O12 ¼ 1.133(5); C11–Fe–C12 ¼ 93.9(2); C11–Fe–
Se ¼ 88.72(14);
C12–Fe–Se ¼ 93.01(14);
C1–Se–Fe ¼ 105.78(13);
O1–C1–O2 ¼ 125.4(4); O1–C1–Se ¼ 127.6(3); O2–C1–Se ¼ 107.0(3);
C1–O2–C3 ¼ 116.1(3).

M. El-khateeb / Inorganica Chimica Acta 357 (2004) 4341–4344
4343
as received. The iron selenide was prepared by published
procedure [33].
3H, C6H5), 7.37 (m, 2H, C6H5). IR (CH2Cl2, cmꢁ1):
2039 (s), 1992 (s) (m(CBO)), 1690 (w) (m(C@O)).
Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker 200 MHz spectrometer. Chemical
shifts are in ppm relative to TMS at 0 ppm. Infrared
(IR) spectra were recorded on Nicolat-Impact 410 FT-
IR spectrometer. Elemental analyses were done in
3.2.5. CpFe(CO)2SeCO2-2-C6H4Cl (5)
Yield: 95%. M.p.: 130–132 °C. Anal. Calc. for
C14H9ClFeO4Se: C, 40.87; H, 2.20. Found: C, 40.19; H,
1.98%. H NMR (CDCl3): 5.06 (s, 5H, C5H5), 7.15 (m,
2H, C6H4), 7.43 (m, 2H, C6H4). IR (CH2Cl2, cmꢁ1):
1
ꢁ
Laboratoire DÕAnalyse Elementaire, Universite de
ꢁ
ꢁ
ꢁ
Montreal, Montreal, Quebec, Canada. Melting points
were reported on a Staurt Melting point apparatus
(SMP3) and are uncorrected.
2039 (s), 1993 (s) (m(CBO)), 1695 (w) (m(C@O)).
3.2.6. CpFe(CO)2SeCO2-4-C6H4Cl (6)
Yield: 83%. M.p.: 108–110 °C. Anal. Calc. for
C14H9ClFeO4Se: C, 40.87; H, 2.20. Found: C, 40.22; H,
3.2. General procedure for the preparation of
CpFe(CO)2SeCO2R, 1–7
1
2.05%. H NMR (CDCl3): 5.01 (s, 5H, C5H5), 7.04 (d,
2H, C6H4), 7.33 (d, 2H, C6H4). IR (CH2Cl2, cmꢁ1):
2039 (s), 1992 (s) (m(CBO)), 1697 (w) (m(C@O)).
A diethyl ether solution (100 mL) of the iron selenide
(l-Se)[CpFe(CO)2]2 (0.43 g, 1.00 mmol) and chlorofor-
mate (1.20 mmol) was stirred overnight. The volatiles
were removed under vacuum and the resulting solid was
redissolved in a minimum amount of dichloromethane
and introduced to a silica gel column made up in hex-
ane. Elution with hexane removes the unreacted chlo-
roformates. Elution with hexane/dichloromethane
solution (1:1 v:v ratio) gave a brown band which was
collected and identified as CpFe(CO)2SeCO2R, followed
by a red band which was also collected and identified as
CpFe(CO)2Cl. The CpFe(CO)2SeCO2R were recrystal-
lized from dichloromethane/hexane.
3.2.7. CpFe(CO)2SeCO2-4-C6H4NO2 (7)
Yield: 86%. M.p.: 101–103 °C. Anal. Calc. for
C14H9FeNO6Se: C, 39.84; H, 2.15; N, 3.32. Found: C,
1
40.51; H, 2.50, N, 3.76%. H NMR (CDCl3): 5.09 (s,
5H, C5H5), 7.54 (d, 2H, C6H4), 8.40 (d, 2H, C6H4). IR
(CH2Cl2, cmꢁ1): 2034 (s), 1996 (s) (m(CBO)), 1695 (w)
(m(C@O)).
3.3. X-ray structure analysis
X-ray diffraction measurements for 2 were performed
on a Nonius CAD-4 diffractometer with Cu Ka radia-
tion. The crystallographic data are shown in Table 1.
The cell parameters were determined from 5095 reflec-
tions collected in the range 3:25 < h < 72:53°. There
were 2348 independent reflections with 1919 observed
3.2.1. CpFe(CO)2SeCO2Me (1)
Yield: 67%. M.p.: 99–100 °C. Anal. Calc. for
C9H8FeO4Se: C, 34.32; H, 2.56. Found: C, 34.33; H,
1
2.53%. H NMR (CDCl3): 3.64 (s, 3H, CH3), 5.00 (s,
5H, C5H5). IR (CH2Cl2, cmꢁ1): 2036 (s), 1988 (s)
(m(CBO)), 1676 (w) (m(C@O)).
Table 1
Selected crystal data and refinement parameters for CpFe(CO)2-
SeCO2Et (2)
3.2.2. CpFe(CO)2SeCO2Et (2)
Yield: 75%. M.p.: 92–94 °C. Anal. Calc. for
C10H10FeO4Se: C, 36.51; H, 3.06. Found: C, 36.57; H,
Empirical formula
Formula weight
Crystal size (mm)
Crystal system
C10H10FeO4Se
328.99
1
3.07%. H NMR (CDCl3): d 1.16 (t, 3H, CH3), 3.76 (q,
0.58 ꢂ 0.24 ꢂ 0.20
orthorhombic
Pbca
2H, CH2), 5.02 (s, 5H, C5H5). IR (CH2Cl2, cmꢁ1): 2036
Space group
Unit cell dimensions
(s), 1989 (s) (m(CBO)), 1672 (w) (m(C@O)).
ꢀ
a (A)
13.6195 (2)
11.6029 (2)
15.2003 (2)
2402.04 (6)
8
ꢀ
b (A)
3.2.3. CpFe(CO)2SeCO2CH2CH(CH3)2 (3)
Yield: 78%. M.p.: 82–83 °C. Anal. Calc. for
C12H14FeO4Se: C, 40.37; H, 3.95. Found: C, 40.28; H,
ꢀ
c (A)
3
ꢀ
V (A )
Z
Index ranges
1
4.38%. H NMR (CDCl3): 0.94 (d, 6H, CH3), 1.92 (m,
ꢁ16 < h < 15, ꢁ13 < k < 13,
ꢁ16 < l < 18
1.819
1H, CH), 3.80 (d, 2H, CH2), 4.98 (s, 5H, C5H5). IR
(CH2Cl2, cmꢁ1): 2036 (s), 1990 (s) (m(CBO)), 1678 (w)
(m(C@O)).
Dcalc (mg mꢁ3
Radiation type
l (mmꢁ1
)
Cu Ka
12.088
1.54178
)
ꢀ
k (A)
3.2.4. CpFe(CO)2SeCO2Ph (4)
Yield: 87%. M.p.: 109–110 °C. Anal. Calc. for
C14H10FeO4Se: C, 44.60; H, 2.67. Found: C, 44.32; H,
h range (°)
3.25–72.53
0.0456
0.1350
R½F 2 > 2rF 2Þꢃ
a
xRðF 2Þ
2
1
2.48%. H NMR (CDCl3): 5.02 (s, 5H, C5H5), 7.13 (m,
a x ¼ 1=½r2ðF02Þ þ ð0:0693PÞ ꢃ, where P ¼ ðF02 þ 2Fc2Þ=3.

4344
M. El-khateeb / Inorganica Chimica Acta 357 (2004) 4341–4344
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
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Copies of this information may be obtained free of
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