Photosubstitution of the halide ligands (X-) in (ν5-C5H5)Fe(CO)(PPh3)X

Article abstract of DOI:10.1016/S0022-328X(01)01447-4

Irradiation of CpFe(CO)(PPh₃)X, (Cp = η⁵-cyclopentadienyl, X = Cl, Br or I), 1a-c, with white or red (λ > 600 nm) light with maleimide or succinimide and di-iso-propyl amine (dipa) or ethyldi-iso-propyl amine (edipa) in dichlorometha

Full text of DOI:10.1016/S0022-328X(01)01447-4

Journal of Organometallic Chemistry 648 (2002) 293–296
www.elsevier.com/locate/jorganchem
Photosubstitution of the halide ligands (X−) in
(h5-C5H5)Fe(CO)(PPh3)X
Bogna Rudolf, Joanna Walendowska, Janusz Zakrzewski *
Department of Organic Chemistry, Uni6ersity of Łodz, 90-136 Łodz, Narutowicza 68, Poland
Received 11 October 2001; accepted 24 November 2001
Abstract
Irradiation of CpFe(CO)(PPh3)X, (Cp=h5-cyclopentadienyl, X=Cl, Br or I), 1a–c, with white or red (u\600 nm) light with
maleimide or succinimide and di-iso-propyl amine (dipa) or ethyldi-iso-propyl amine (edipa) in dichloromethane leads to the
efficient formation of CpFe(CO)(PPh3)(h1-N-imidato) complexes 2a–b. Irradiation with white light of CpFe(CO)(PPh3)Br in
dichloromethane in the presence of an excess of Br− (as tetrabutylammonium bromide) yields CpFe(CO)(PPh3)Br. These results
are discussed in terms of possible photoinduced heterolysis of the iron–halide bond in 1a–c. © 2002 Elsevier Science B.V. All
rights reserved.
Keywords: Halide ligands; Imidato ligands; Photosubstitution
propyl amine (dipa) in benzene leads to efficient photo-
substitution of iodide by the corresponding N-anions
[5–14]. Initially for these reactions, a mechanism in-
volving electron transfer between amine and the
organometallic substrate has been suggested [8], but
later indirect (via CO-dissociation) halide exchange
mechanism was put forward [9]. Finally, in the recent
work by Lees et al. [5] a possibility of direct heterolysis
of the FeꢀI bond was considered, especially when red
light (u=647 nm) was used for irradiation.
In contrast to CpFe(CO)2X complexes their mono
carbonyl derivatives CpFe(CO)(L)X, where L is a neu-
tral 2 e donor ligand, have attracted only little attention
of photochemists. Only one report has appeared
devoted to photochemical transformations of these
complexes [15]. It has been found that irradiation
CpFe(CO)(PPh3)Br in pyridine or dmso leads to forma-
tion (in low yield)of [CpFe(CO)2]2 when L=P(OPh)3
and [CpFe(CO)2(L)]Br when L=PPh3. Although these
reactions proceed with the disruption of the ironꢀhalide
bond, their mechanism does not seem to be simple (the
isolated products contain two CO ligands) and there is
no evidence that this disruption occurs in the first,
photochemical step.
1. Introduction
Photochemistry of cyclopentadienylmetal carbonyl
complexes containing halide ligands has been exten-
sively studied, especially for CpM(CO)3X (Cp=h5-cy-
clopentadienyl, M=Mo, W, X=halide) and
CpM(CO)2X (M=Fe, Ru) [1–14]. It has been found
that photoexcited states of these compounds undergo a
variety of chemical reactions including dissociation of
the carbonyl ligand, homolytic or heterolytic cleavage
of the metal halide bond, intramolecular isomerization
and intraligand rearangements. Photolysis of
CpFe(CO)2X (X=Br or I) in the presence of PPh3
leads to the formation of covalent complexes
CpFe(CO)(PPh3)X with high quantum efficiency, indi-
cating that CO dissociation is a dominant reaction
pathway [1]. This has been confirmed by IR studies in
low-temperature matrices, indicating exclusive forma-
tion of the 16-electron species CpFe(CO)X [3]. How-
ever, other studies have revealed that photoprocesses
involving heterolysis of the FeꢀX bond are also possi-
ble. For example, upon irradiation of CpFe(CO)2X, the
dimer [CpFe(CO)2]2 is formed [4]. Irradiation of
CpFe(CO)2I in the presence of an NꢀH acid and di-iso-
In this paper we would like to report the first exam-
ple of the straightforward photochemical substitution
of the halide ligand in CpFe(CO)(PPh3)X complexes
* Corresponding author.
E-mail address: janzak@krysia.uni.lodz.pl (J. Zakrzewski).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01447-4

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B. Rudolf et al. / Journal of Organometallic Chemistry 648 (2002) 293–296
Table 2
1a–c (X=Cl (a), Br (b) and I (c)).We have found that
irradiation of these complexes with red light in the
presence of cyclic imides (maleimide, succinimide) and
dipa or ethyldiisopropyl amine (edipa) in dichloro-
methane brings about substitution of the halide ligands
Photoinduced reaction of CpFe(CO)(PPh3)X with imides in the pres-
ence of an amine
Complex
X
Imide
Base
Product (yield)
1a
1b
1c
1c
1c
Cl
Br
I
I
I
Maleimide
Maleimide
Maleimide
Succinimide
Maleimide
dipa
dipa
dipa
dipa
edipa
2a (45%)
2a (60%)
2a (77%)
2b (45%)
2a (95%)
by h1-N-imidato ligands. Furthermore, irradiation of
1c in dichloromethane in the presence of bromide an-
ions leads to a fast halide exchange.
2. Results and discussion
The solutions CpFe(CO)(L)X (1a–c) in benzene and
dichloromethane are green and show in the visible
region two absorption bands (Fig. 1, Table 1).
Taking into consideration the weak molar absorptivi-
ties of these bands and the absence of solvatochromism
we assign them to the orbitally forbidden ligand-field
(LF) transitions [16].
Fig. 1. Electronic absorption spectra of 1a–c in dichloromethane
(c=5×10−4 M).
It has been found that irradiation with visible light of
a solution of 1a–c in dichloromethane containing a
cyclic imide (maleimide, succinimide) and dipa or edipa
leads to the formation of red 2a–b, isolated in 45–95%
yield (Scheme 1, Table 2).
Complex 2b, was earlier obtained by the CO–PPh3
exchange in CpFe(CO)2(h1-N-succinimidato) [7].
Analogously, for we have prepared 2a from
CpFe(CO)2(h1-N-maleimidato). It has been found that
complexes prepared by a photochemical route have the
same spectral data and TLC properties as those ob-
tained by the CO–PPh3 exchange.
Table 1
Electronic absorption spectra of CpFe(CO)(L)X, 1a–c, in the visible
region
Solvent
CH2Cl2
X
umax (nm) (mmax (l mol−1 cm−1))
Cl (1a)
Br (1b)
I (1c)
440 (510); 615 (90)
443 (1010) 619 (140)
444 (880); 619 (150)
C6H6
Cl (1a)
Br (1b)
I (1c)
443 (860); 618 (270)
446 (1370);618 (260)
442 (900); 620 (200)
Using an appropriate cut-off filter it has been found
that reaction occurs at irradiation with the red (u\600
nm) light. We have found that solvent plays a very
important role and the photoreaction does not takes
place in less polar benzene. This fact may indicate that
a polar transition state is involved which is in favor of
direct photoinduced heterolysis of the FeꢀI bond in the
organometallic substrate. An additional argument for
that is provided by the fact that the CO ligand in
CpFe(CO)(PPh3)X is more tightly bound to iron than
these ligands in CpFe(CO)2X (compare the wCO fre-
quencies in CpFe(CO)2I, 2039 and 1995 cm−1, with
that in CpFe(CO)(PPh3)I, 1948 cm−1 [2]).
Despite the fact that photolysis of CpFe(CO)2X in
low temperature matrices produces only the 16 e
CpFe(CO)X as a result of the CO dissociation, Lees
and co-workers suggest that photoreaction CpFe(CO)2I
with NH acids in the presence of an amine involves
heterolysis if the FeꢀI bond [5]. They emphasize a
Scheme 1.

B. Rudolf et al. / Journal of Organometallic Chemistry 648 (2002) 293–296
295
different nature of the lowest excited state of the iodo
3.1. Synthesis of CpFe(CO)(PPh3)(p1-N-maleimidato)
(2a)
complex, in comparison with its bromo- and chloro
counterparts, and the possibility of the assistance of
dipa in the cleavage of the FeꢀI bond. However, we
have found that CpFe(CO)2Br displays similar photore-
activity toward cyclic imides–amine as CpFe(CO)2I
[17]. On the other hand, the replacement of dipa by
edipa improves significantly the yield of CpFe(CO)-
(PPh3)X (Table 2). The latter amine does not form
hydrogen bond with iodide and cannot, therefore, facil-
itate the leave of I− as it was suggested [5].
The results obtained in this work suggest that irradi-
ation of CpFe(CO)(PPh3)X brings about a heterolysis
of the ironꢀhalide bond, forming CpFe(CO)(PPh3)+
and X−. To confirm this we irradiated CpFe(CO)-
(PPh3I in the presence of excess Br− (as tetrabutylam-
monium bromide). We have observed efficient halide
exchange yielding CpFe(CO)(PPh3)Br. The reaction oc-
curs in the absence of amine, indicating that its role is
presumably limited to deprotonation of imide (free or
bound to Fe) Scheme 2.
In conclusion, it has been found that the halide
ligands in CpFe(CO)(PPh3)X complexes (1a–c) un-
dergo substitution by h1-N-imidato ligands a upon
irradiation with red light with cyclic imides and an
amine in dichloromethane solvent. The reaction did not
take place in less polar benzene. This fact, together with
the observed halide exchange suggest that these reac-
tions may proceed via photoinitiated heterolysis of the
ironꢀhalide bond, forming CpFe(CO)(PPh3)+ and X−.
Obviously, photophysical studies (e.g. photolysis in
low-temperature matrices) are now required to confirm
this hypothesis.
A solution of CpFe(CO)2(h1-N-maleimidato) [9]
(300mg, 1.1 mmol) and triphenylphosphine (343 mg,
1.3 mmol) in benzene (10 ml) was refluxed for 3 h.
Evaporation to dryness and column chromatography
gave red–brown 2a (515 mg, 92%). An analytical sam-
ple was prepared by recrystallization from Et2O–n-hep-
tane. 1H-NMR (200 MHz, CDCl3, l) 7.35–7.3 (m 15H,
aromatic H’s), 6.18 (s, 2H, olefinic), 4, 62 (s, 5H, Cp).
IR (CHCl3, cm−1): 1968, 1641. Elemental analysis:
Anal. Calc. for C28H22FeNO3P: C, 66.28; H, 4.38; N,
2.73; P, 6.10. Found: C, 66.56; H, 4.44; N, 2.43; P,
5.94%.
3.2. Photoinduced reaction of CpFe(CO)(PPh3)X with
imides in the presence of an amine
A solution of CpFe(CO)(PPh3)X (0.56 mmol), imide
(0.56 mmol) in dichloromethane (17 ml) and amine
(1 ml) was photolyzed for 3 h. The green color of the
photolyte gradually turned to brown. After filtration
and evaporation to dryness the residue was chro-
matographed. The deep red band of the product, which
followed
a
small green band of unreacted
CpFe(CO)(PPh3)X was collected. The products were
recrystallized from chloroform–hexane·and identified
by comparison of their spectral and TLC properties
with those of authentic samples. The yields are given in
Table 1.
3.3. Photoinduced halide exchange in CpFe(CO)(PPh3)I
An argon-saturated solution of 1c (54 mg, ꢀ0.1
3. Experimental
mmol) and Bu4N+Br− (322 mg,
1
mmol) in
dichloromethane (10 ml) was photolyzed for 1 h. Evap-
oration to dryness and chromatography (SiO2–chloro-
form) gave 32 mg (65%) of 1b, identified by comparison
with an authentic sample.
Compounds 1a–c and 2b were prepared according to
earlier published procedures [7,18].
The photolyses were carried out under argon using
4×150 W domestic tungsten lamps, The photolytes
were magnetically stirred and externally cooled with
water–ice. Dichloromethane was distilled over CaH2
and benzene from sodium-benzophenone. Other sol-
vents were reagent-grade and were used without prior
purification. Silica gel 60 (230–400 mesh ASTM), pur-
chased by Merck was used for chromatography. Chlo-
roform was used as eluent.
Acknowledgements
This research was financially supported by the grant
505/471 from the University of Łodz.
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