Synthesis, electrochemical behavior and X-ray crystal and molecular structures of [Fe(diene)(CO)2PPh3] (diene = chalcone, sorbic acid)

Article abstract of DOI:10.1016/S0277-5387(01)00763-X

The compounds [Fe(ch)(CO)₂PPh₃] (1) (ch = chalcone) and [Fe(sba)(CO)₂PPh₃] (2) (sba = sorbic acid) were prepared by irradiating the tetracarbonyltriphenylphosphineiron(0) complex in benzene in the presence of ch or sba. The compounds were characterized by infrared and ³¹P NMR spectroscopies. Their electrochemical behavior was investigated by cyclic voltammetry and the results suggest that their oxidations occur by more than one electrochemical step, producing free ch and sba, free PPh₃ and solvated Fe(III). It was observed that sba ligand contributes more effectively to the stabilization of metal center in these complexes. The X-ray crystal and molecular structures of 1 and 2 were determined; it was shown that the Fe atom adopts a distorted octahedral coordinated geometry in which three of the sites are occupied by the ch or sba ligand. The [Fe(ch)(CO)₂PPh₃] complex is a monomer and the unit cell of complex 2 contains exist two identical and crystallographically independent molecules of [Fe(sba)(CO)₂PPh₃] which are linked by short hydrogen bonds O-H···O.

Full text of DOI:10.1016/S0277-5387(01)00763-X

Polyhedron 20 (2001) 1011–1016
www.elsevier.nl/locate/poly
Synthesis, electrochemical behavior and X-ray crystal and
molecular structures of [Fe(diene)(CO)2PPh3]
(diene=chalcone, sorbic acid)
K. Zutin a, V.M. Nogueira a,*, A.E. Mauro a, P. Melnikov a, A. Iluykhin b
a Instituto de Qu´ımica de Araraquara, UNESP, C.P. 355, 14800-900 Araraquara, Sao Paulo, Brazil
b Institute of General and Inorganic Chemistry, Moscow, Leninsky Prospekt 31, Moscow, Russian Federation
Received 1 October 1999; accepted 2 February 2001
Abstract
The compounds [Fe(ch)(CO)2PPh3] (1) (ch=chalcone) and [Fe(sba)(CO)2PPh3] (2) (sba=sorbic acid) were prepared by
irradiating the tetracarbonyltriphenylphosphineiron(0) complex in benzene in the presence of ch or sba. The compounds were
characterized by infrared and 31P NMR spectroscopies. Their electrochemical behavior was investigated by cyclic voltammetry
and the results suggest that their oxidations occur by more than one electrochemical step, producing free ch and sba, free PPh3
and solvated Fe(III). It was observed that sba ligand contributes more effectively to the stabilization of metal center in these
complexes. The X-ray crystal and molecular structures of 1 and 2 were determined; it was shown that the Fe atom adopts a
distorted octahedral coordinated geometry in which three of the sites are occupied by the ch or sba ligand. The [Fe(ch)(CO)2PPh3]
complex is a monomer and the unit cell of complex 2 contains exist two identical and crystallographically independent molecules
of [Fe(sba)(CO)2PPh3] which are linked by short hydrogen bonds OꢀH· · ·O © 2001 Published by Elsevier Science Ltd.
Keywords: Dicarbonyliron complexes; Chalcone; Sorbic acid; X-ray structures; Cyclic voltammetry
ligand under very mild conditions which is useful in
case of thermal or photochemical instability of the
diene ligand [9,14].
1. Introduction
Since the synthesis of butadiene-iron tricarbonyl [1] a
great deal of attention has been directed to the nature
of the very stable bonds between the diene group and
the iron atom [2–4]. The ability of heterodiene
molecules containing ꢀCꢁCꢀCꢁR (R=O, N, COOH)
units to coordinate to the iron tricarbonyl moiety has
been demonstrated in a series of papers [5–8].
Some p-(hetero-1,3-diene) tricarbonyl and tetracar-
bonyliron(0)complexes were synthesized and their reac-
tivity investigated. The [Fe(bda)(CO)2L] (bda=
benzylideneacetone; L=CO, phosphines, phosphites)
complexes were the more extensively investigated [5–
13]. These compounds have been described as effective
precursors for the synthesis of organometallic com-
pounds [14,15] as transfer reagents. Thus the
[Fe(CO)2L] group can be transferred to another diene
The X-ray crystal and molecular structures of the
complexes [Fe(h4-cyclodiene)(CO)2(PPh3)] [16] and
[Fe(h4 -bda)(CO)2L] (L=PPhMe2, PEt3) [11] were de-
termined; it was shown that the iron atom adopts a
distorted octahedral coordination geometry in which
three facial sites are being occupied by the diene or
enone ligand. In these complexes the two carbonyl
groups are cis to each other, while the phosphine is
approximately trans to midpoint of the internal CꢀC
bond of the diene or enone.
The first preparations of the compounds
[Fe(ch)(CO)3] [7] and [Fe(sba)(CO)3] [17,18] (ch=chal-
cone, sba=sorbic acid) were by thermal procedures.
Poor yields, air-sensible solids and mainly extensive
polymerization of free sorbic acid at temperatures
higher than approximately 50°C were observed.
Santos et al. [19] reported the preparation of the
[Fe(sba)(CO)2L] complexes, L=CO, P(OPh)3, PPh3
* Corresponding author. Fax: +55-16-2227032.
E-mail address: vaniamn@iq.unesp.br (V.M. Nogueira).
0277-5387/01/$ - see front matter © 2001 Published by Elsevier Science Ltd.
PII: S0277-5387(01)00763-X

1012
K. Zutin et al. / Polyhedron 20 (2001) 1011–1016
and PEt3. The complexes were obtained in good yields
by irradiating the corresponding Fe(CO)4L compounds,
in benzene, in the presence of sorbic acid.
that, after recrystallization from benzene/hexane, gave
orange crystals (25% yield based on ch).
2.3.2. [Fe(sba)(CO)2PPh3] (2) [19]
A
solution of sorbic acid (1.25 mmol) and
[Fe(CO)4PPh3] in benzene (100 cm3) was irradiated for
3 h. The resulting mixture was filtered and the solvent
was removed under vacuum. The resulting yellow-green
residue was recrystallized from methanol. After seven
days in the refrigerator, yellow crystals were obtained
(50% yield).
2. Experimental
2.1. Materials
The ligands ch and sba were purchased from Fluka
Chemika and Merck, respectively, and used without
further purification. [Fe(CO)4PPh3] was prepared in our
laboratory according to published procedures [9].
Dimethylformamide (Merck p.a.) was purified following
Brummer’s procedure [20]. Sodium perchlorate (Merck,
p.a.), recrystallized in ethanol and dried at 130°C for 24
h, was used as the supporting electrolyte.
2.4. X-ray diffraction structural study
Single crystals in form of needles were obtained on
recrystallization of compounds 1 and 2. The X-ray data
were collected on a Siemens SMART CCD detector
diffractometer using graphite monochromated Mo Ka
,
radiation (u=0.71073 A). The structures were solved by
direct methods and subsequent Fourier analysis. An-
isotropic displacement parameters were applied to non-
hydrogen atoms in full-matrix least-squares refinements
based on F2. Calculations of refinement were carried out
using the program SHELDRIX-97. Table 1 summarizes
the crystal data, data collection, structural solution and
refinement parameters for compounds 1 and 2.
2.2. General procedures
The IR spectra (4000–400 cm−1) were recorded on a
Nicolet Impact 400 spectrophotometer as KBr discs. 31
P
3. Results and discussion
NMR spectra were done on a Bruker AC-200 spec-
trophotometer, in CDCl3, using H3PO4 (85%) as exter-
nal standard. The voltammetric studies and coulometric
investigation were performed using a PAR model 273
potentiostat/galvanostat. All tests were carried out using
a conventional three-electrode cell. A platinum disk and
a platinum gauze, respectively, were used as working
electrodes in the cyclic voltammetric experiments and in
the coulometric experiments. An Ag/Ag+(10−2 M), 0.5
M NaClO4 in DMF electrode was used as the reference
electrode [21] and a platinum wire was used as the
auxiliary electrode. Electrochemical measurements were
performed under a dinitrogen atmosphere.
The reactions of [Fe(CO)4PPh3] with the diene ligand
(ch or sba) afforded compounds 1 and 2. These com-
plexes were characterized by IR and 31P NMR spectro-
scopies. The electrochemical behavior of the compounds
was investigated by cyclic voltammetry and coulometry.
The structure of the complexes was determined by X-ray
diffractometry. The data obtained from these techniques
are presented below.
3.1. Spectral data
Infrared and 31P NMR spectroscopic data are sum-
marized in Table 2.
2.3. Preparation of the compounds
The infrared spectra of the dicarbonyl derivatives
showed two strong and sharp wCꢁO bands in the region
2005–1915 cm−1 typical of [Fe(diene)(CO)2L] com-
plexes [3,9,22] and one wCꢀO band at 1655 cm−1, as-
signed to the carbonyl group of the coordinated sorbic
acid. For the free ligand sba the wCꢀO occurred at 1690
2.3.1. [Fe(ch)(CO)2PPh3] (1)
This complex, not yet reported in the literature, was
prepared was follows. Tetracarbonyl(triphenylphos-
phine)iron (1.55 mmol) and chalcone (1.55 mmol) were
dissolved in benzene (200 cm3) and the resulting solution
was irradiated for 8 h using a 125 W medium-pressure
mercury lamp. The resulting red solution was filtered,
the solvent was removed under vacuum and the residue
was cromatographed on silica gel. Elution with benzene
gave some unchanged [Fe(CO)4PPh3] and a red solid
cm−1
.
The 31P NMR spectra of 1 and 2 were obtained in
order to better characterize these complexes. In this way
a unique signal on the 31P resonance spectra con-
firmed the molecular formulae of complexes 1 and 2.
Furthermore the chemical shift values indicated clearly

K. Zutin et al. / Polyhedron 20 (2001) 1011–1016
1013
a lesser electronic density on the phosphorus nucleus
for complex 2.
Table 1
Crystal
data
and
structure
refinement
for
complexes
[Fe(ch)(CO)2PPh3] and [Fe(sba)(CO)2PPh3]
Complex
[Fe(ch)(CO)2PPh3]
[Fe(sba)(CO)2PPh3]
486.2861
Formula weight 582.4173
(
(
Space group
Unit cell
P1
P1
dimensions
,
a (A)
8.6222(7)
16.1887(13)
17.6625(14)
81.0890(10)
78.4070(10)
75.1280(10)
2320.2(6)
2
10.579(2)
10.821(2)
14.395(3)
104.04(3)
103.64(3)
107.58(3)
1436.4(4)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Fig. 1. The structure of the complex [Fe(ch)(CO)2PPh3].
Z
Dcalc (g cm−3
Absorption
coefficient
)
1.392
0.749
1.347
0.615
3.2. Structure determination
(mm−1
F(000)
)
The molecular structure of [Fe(ch)(CO)2PPh3] is illus-
trated in Fig. 1 and that of [Fe(sba)(CO)2PPh3] in Fig.
2. The selected bond lengths and interbond angles for
the two complexes are listed in Tables 3 and 4.
1008
604
q Range for
data
collection (°)
1.18–23.27
1.55–23.43
In solid state the [Fe(ch)(CO)2PPh3] complex exists as
a discrete, neutral, monomeric molecule. In the unit cell
of [Fe(sba)(CO)2PPh3] there exists two identical and
crystallographically independent molecules [Fe(sba)-
(CO)2PPh3] which are linked into dimers by two short
hydrogen bonds OꢀH· · ·O (Table 5) extending from the
hydroxyl hydrogen of the carboxyl group of one sorbic
acid ligand to the carbonyl oxygen of the second. In
addition crystallochemical structures analogous to 2
have been recently described [23–25].
Radiation (Mo 0.71073
0.71073
Ka)
Index ranges
−95h57,
−115h510,
−125k511,
−155l515
0.56
−175k512,
−195l519
0.56
Max. [sin q/l]
−1
,
(A
)
Reflections
collected
8625
5291
Independent
observations
6211 [Rint=0.348]
3787 [Rint=0.1233]
Reflections used 6211 (all)
3787 (all)
empirical
The structural features of such complexes are com-
Absorption
correction
Max./min.
transmission
Refinement
method
empirical
mon for
a number of compounds of the type
[FeL(CO)2PR3] with L containing a coordinated frag-
ment CꢁCꢀCꢁO [26–28]. The coordination geometry
around the iron atom in the two complexes may be
regarded as octahedral. The bond angles between the
carbonyls and the phosphine at iron close to idealized
octahedral angle. A pseudo-octahedral symmetry was
previously suggested for [Fe(CO)2L(diene)] (L=CO or
Group V ligands) [10,16] with the iron atom in a
formally d2sp3 hybridization. Two sites of the octahe-
dral are occupied by two carbonyl groups cis to each
other. The other site is occupied by triphenylphosphine
that is approximately trans to the midpoint of the
central C(25)ꢀ(C(27) bond of complex 1 and trans to
the midpoint of the central C(21)ꢀC(22) and
C(47)ꢀC(48) bonds of complex 2.
0.841, 0.386
full-matrix
0.802, 0.529
full-matrix least-squares
least-squares on F2 on F2
Final R indices R1=0.0590,
R1=0.0803, wR2=0.1508
[Iꢀ2|(I)]
R indices (all
data)
wR2=0.1016
R1=0.0807,
wR2=0.1183
715
R1=0.1537, wR2=1745
Data
361
parameters
Max. shift/error 0.001
0.005
Table 2
IR and 31P NMR data for [Fe(ch)(CO)2PPh3] (1) and
[Fe(sba)(CO)2PPh3] (2) compounds (w in cm−1, l in ppm)
Complex
wCꢀO
wCꢀO
l
The others two sites in complex 1 are occupied by the
O(1) atom and the C(25) atom of the chalcone ligand.
For complex 2 the sites are occupied by C(46) and
C(49) or C(20) and C(23) of the sorbic acid ligand.
1
2
2005, 1920
1990, 1915
52.20
67.90
1655

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K. Zutin et al. / Polyhedron 20 (2001) 1011–1016
Fig. 2. The structure of the complex [Fe(sba)(CO)2PPh3].
As suggested for [Fe(bda)(CO)2L] (L=PEt3 and
PPhMe2) [10], the C(26)ꢀC(27) bond on
[Fech(CO)2PPh3] should exhibit multiple bond charac-
ter since the higher donor capacity of the trans P atom
should increase the flow of the metal electron density
into the antibonding ‘‘diene’’ orbitals. An analogous
behavior was observed for [Fe(sba)(CO)2PPh3].
Table 6 shows the comparison of selected distances
(A) and angles (°) for [Fe(ch)(CO)2PPh3] and in the
,
related compounds. In recent cases the FeꢀC(34) dis-
tance, trans to O(1), is shorter than the corresponding
values for the coordinate FeꢀC(35), trans to C(25).
Table 3
,
Select bond lengths (A) and angles (°) for [Fe(ch)(CO)2PPh3]
3.3. Electrochemical studies
Bond lengths
Fe(1)ꢀC(34)
Fe(1)ꢀC(35)
Fe(1)ꢀC(25)
Fe(1)ꢀC(26)
Fe(1)ꢀC(27)
1.750(10)
1.836(10)
2.160(7)
2.035(8)
2.075(7)
Fe(1)ꢀO(1)
Fe(1)ꢀP(1)
O(2)ꢀC(34)
O(3)ꢀC(35)
2.002(5)
2.268(3)
1.141(9)
1.117(9)
The electrochemical oxidation of the complexes
[Fe(ch)(CO)2PPh3] and [Fe(sba)(CO)2PPh3] was studied
by cyclic voltammetry and controlled potential electrol-
ysis in 0.5 M NaClO4 (DMF). No anodic and cathodic
peaks were observed in the absence of complexes in the
potential range studied.
Fig. 3 shows the cyclic voltammograms for 1 and 2,
obtained on a platinum electrode at a potential scan
rate w=100 mV s−1 and 25°C. In the range from
−0.50 to +0.50 V (vs Ag/Ag+) an anodic current
peak (1a) was observed for the compounds, but no
corresponding cathodic current peak is observed. At
more negative potentials, a cathodic current peak (2c)
was observed and repetitive scanning revealed a second
anodic peak (2a) which corresponds to the cathodic
peak (2c). The data obtained from cyclic voltam-
mograms are given in Table 7. The pair 2a/2c is not
Bond angles
C(35)ꢀFe(1)ꢀO(1)
C(34)ꢀFe(1)ꢀC(25)
C(35)ꢀFe(1)ꢀP(1)
C(35)ꢀFe(1)ꢀP(1)
91.9(3)
96.0(3)
99.3(2)
100.6(3)
O(2)ꢀC(34)ꢀFe(1)
O(3)ꢀC(35)ꢀFe(1)
177.2(7)
178.4(8)
Table 4
,
Selected bond lengths (A) and angles (°) for [Fe(sba)(CO)2PPh3]
Bond lengths
Fe(1)ꢀC(20)
Fe(1)ꢀC(21)
Fe(1)ꢀC(22)
Fe(1)ꢀC(23)
Fe(1)ꢀC(25)
Fe(1)ꢀC(26)
Fe(1)ꢀP(1)
2.140(5)
2.039(5)
2.070(5)
2.169(5)
1.753(6)
1.777(6)
2.2410(15) Fe(2)ꢀP(2)
1.153(6)
1.145(6)
Fe(2)ꢀC(46)
Fe(2)ꢀC(47)
Fe(2)ꢀC(48)
Fe(2)ꢀC(49)
Fe(2)ꢀC(51)
Fe(2)ꢀC(52)
2.123(5)
2.029(6)
2.064(6)
2.182(5)
1.759(6)
1.762(6)
2.2522(15)
1.151(6)
1.157(6)
Table 5
O(3)ꢀC(25)
O(4)ꢀC(26)
O(7)ꢀC(51)
O(8)ꢀC(52)
,
Distances (A) of atoms and bond angles (°) for the hydrogen bonds
in [Fe(sba)(CO)2P Ph3]
Bond angles
Bond OꢀH· · ·O
Bond distance
OꢀH H· · ·O OꢀH· · ·O
Bond angle
C(25)ꢀFe(1)ꢀC(23)
C(26)ꢀFe(1)ꢀC(20)
C(25)ꢀFe(1)ꢀP(1)
C(26)ꢀFe(1)ꢀP(1)
O(3)ꢀC(25)ꢀFe(1)
O(4)ꢀC(26)ꢀFe(1)
88.6(2)
98.4(2)
C(51)ꢀFe(2)ꢀC(49)
C(52)ꢀFe(2)ꢀC(46)
92.0(2)
96.4(2)
103.01(18)
104.09(18)
175.3(5)
173.0(5)
99.90(19) C(51)ꢀFe(2)ꢀP(2)
103.10(17) C(52)ꢀFe(2)ꢀP(2)
177.4(5)
173.2(5)
O(1)ꢀH(1)· · ·O(6) 0.98(6)
O(5)ꢀH(5)· · ·O(2) 0.926(6) 1.68(6) 2.603(5)
1.69(6) 2.655(5)
166(5)
174(5)
O(7)ꢀC(51)ꢀFe(2)
O(8)ꢀC(52)ꢀFe(2)

K. Zutin et al. / Polyhedron 20 (2001) 1011–1016
1015
Table 6
Comparison of selected distances (A) and angles (°) in [Fe(ch)(CO)2PPh3] and in the related compounds
,
Compound
FeꢀC(34)
FeꢀC(35)
C(34)ꢀFeꢀO(1)
C(35)ꢀFeꢀC(25)
Ref.
[Fe(ch)(CO)2PPh3]
1.750
1.739
1.740
1.739
1.750
1.750
1.836
1.786
1.791
1.767
1.790
1.784
161.6
167.8
168.1
165.6
165.5
165.5
163.1
161.7
163.4
157.9
158.1
162.8
[Fe(bda)(CO)2PEt3]
[Fe(bda)(CO)2 PPh(Me)2]
[Fe(cin)(CO)2PPh3]
[Fe(bda)(CO)2PPh3]
[Fe(bda)(CO)2 P(Bu)3]
[10]
[10]
[23]
[24]
[25]
observed when the scanning is inverted before the oxi-
dation of the original compound. The separation of the
pairs of peaks 2a/2c is around 60 mV and the peak
current radio is unity, as expected for a one-electron
reversible process. The peak potentials for 2a/2c are the
same for the complexes, within experimental error.
However, the peak 1a potential value is influenced
strongly by the nature of the diene.
The number of electrons obtained from the con-
trolled potential electrolysis for the compounds (1) and
(2) studied was 2.6 and 2.9, respectively. After exhaus-
tive electrolysis at the potential peak (1a), only the pair
of peaks 2a/2c was observed.
In previous papers [12,13] we have described the
electrochemical oxidation of some [Fe(bda)(CO)2L]
(L=CO, phosphines and phosphites), studied by cyclic
voltammetry and controlled potential electrolysis. The
cyclic voltammograms showed the 1a, 2a and 2c peaks,
analogous to complexes 1 and 2. The analysis of the
electrolysis products of [Fe(bda)(CO)2L] showed the
presence of free bda, identified by infrared and ultravio-
let spectra. The pair of peaks 2a/2c was ascribed to the
solvated Fe3+/Fe2+ pair and the current peak 1a corre-
sponds to the global process where Fe(0) complex goes
to Fe3+ (solvated).
Fig. 3. Cyclic voltamograms for 0.5 M NaClO4 in DMF solution with
1.0×10−3 M of: (a) [Fe(ch)(CO)2PPh3]; and (b) [Fe(sba)(CO)2PPh3]
at a platinum electrode, at 25°C and w=100 mV s−1
.
The electrochemical behavior observed for complexes
1 and 2 is similar to that of [Fe(bda)(CO)2L] complexes
[13]. The results suggest that the electrode process
involves a complicated mechanism, the species formed
in the first oxidation step being highly unstable and its
decomposition producing free diene ligand, free phos-
phine and solvated iron(II) species. The oxidation
Fe(0)“Fe+3 (solvated) occurs by more than one elec-
trochemical step, as a three electron process in a single
step is not common. Consequently, we can propose that
the global electrode process for the oxidation of 1 and
2 may be represented as is showed in the scheme for the
chalcone complex:
Table 7
Data obtained from cyclic voltammograms for [Fe(ch)(CO)2PPh3] (1)
and [Fe(sba)(CO)2PPh3] (2) in DMF at 25°C (w=100 mV s−1
)
Complex
E1pa (V)
E2pc (V)
E2pa (V)
1
2
+0.08
+0.37
−0.15
−0.16
−0.09
−0.08
When we compare the values of oxidation peak
potentials (1a) for [Fe(ch)(CO)2PPh3] (+0.09 V) and
[Fe(bda)(CO)2PPh3] [13] (+0.08 V) obtained in identi-
cal conditions, we can observe that are the same for the
two complexes, within experimental error. However the
peak potential (1a) occurred at +0.37 V for the sba
complex. These data indicate that the sba ligand con-
tributes more effectively for the stabilization of metal
center, probably by decreasing the electronic density at

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K. Zutin et al. / Polyhedron 20 (2001) 1011–1016
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(1977) 1180.
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