Versatile behaviour of iron-arylcarbene complexes towards alkoxides: C-Cl and C-C bond activation reactions

Article abstract of DOI:10.1016/S0022-328X(01)00792-6

The Cp-containing carbene complexes [Fe(C₅H₅)(CO){κ²(C,O)C(OMe)C ₆H₄-o-OMe}][OTf] (2) and [Fe(C₅H₅)(CO)(CH₃CN){C(OMe)C₆H ₄-o-Cl}[OTf] (3) have been synthesised and characterised. Complex 2 has been characterised by a single-crystal X-ray diffraction analysis; the Fe-O distance of 2.045(5) A? suggests a rather strong bonding of the methoxy group. Substitution of one carbonyl ligand by PPh₃ allows the isolation of the chelate complex [Fe(C₅H₅)(PPh₃){κ ²(C,Cl)C(OMe)C₆H₄-o-Cl}][OTf] (4). The reaction of [Fe(C₅Me₅)(CO){κ²(C,Cl)C(OMe)C ₆H₄-o-Cl}][OTf] (5) with alkoxides RONa (R=Me, Et) affords the chelate complexes [Fe(C₅Me₅)(CO){κ²(C,O)C₆H ₄-o-C(OMe)(OR)(OR)}] 7 (R=Me) and 8 (R=Et), respectively. Similarly, the reaction of 3 with EtONa affords [Fe(C₅H₅)(CO){κ²(C,O)-C₆H ₄-o-C(OEt)(OEt)2}] (9), for which the Ar-Cl bond has been cleaved. No activation of the Ar-Cl bond is observed for the unchelated complex [Fe(C₅Me₅)(CO)₂{C(OMe)C₆H ₄-o-Cl}][OTf]. In contrast, treatment of the anisyl derivative [Fe(C₅Me₅)(CO){κ²(C,O)C(OMe)C ₆H₄-o-OMe}][OTf] (6) with EtONa gives selectively the carbene complex [Fe(C₅Me₅)(CO)(C₆H ₄-o-OMe){=C(OEt)₂}] (12). The Ar-OMe bond remains intact, but cleavage of the Cα-CAr bond occurs. This rearrangement process, i.e. α-elimination of the anisyl substituent, is favoured by the lability of the ortho-OMe group. Treatment of 2 with NaOEt gives as the only identified compound the ethyl ester [MeOC₆H₄-o-(CO)OEt]. Clean formation of the methyl ester derivative [MeOC₆H₄-o-(CO)OMe] is observed upon oxidation of 2 with C₆H₅I⁺O^-.

Full text of DOI:10.1016/S0022-328X(01)00792-6

Journal of Organometallic Chemistry 629 (2001) 19–27
www.elsevier.com/locate/jorganchem
Versatile behaviour of iron–arylcarbene complexes towards
alkoxides: CꢀCl and CꢀC bond activation reactions
a
Karine Ferre´ , Ge´raldine Poignant a, Loic Toupet b, Ve´ronique Guerchais a,*
a Institut de Chimie de Rennes, UMR 6509 CNRS, Uni6ersite´ de Rennes 1,
‘Organome´talliques et Catalyse: Chimie et Electrochimie Mole´culaires’, 1 Campus de Beaulieu, 35042 Rennes Cedex, France
b UMR 6626 CNRS, Groupe Matie`re Condense´e et Mate´riaux, Uni6ersite´ de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France
Received 5 January 2001; accepted 14 March 2001
Abstract
The
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
Cp-containing
carbene
complexes
[Fe(C5H5)(CO){k2(C,O)ꢀC(OMe)C6H4-o-OMe}][OTf]
(2)
and
[Fe(C5H5)(CO)(CH3CN){C(OMe)C6H4-o-Cl}[OTf] (3) have been synthesised and characterised. Complex 2 has been characterised
,
by a single-crystal X-ray diffraction analysis; the Fe–O distance of 2.045(5) A suggests a rather strong bonding of the methoxy
group. Substitution of one carbonyl ligand by PPh3 allows the isolation of the chelate complex
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5H5)(PPh3){k2(C,Cl)ꢀC(OMe)C6H4-o-Cl}][OTf] (4). The reaction of [Fe(C5Me5)(CO){k2(C,Cl)ꢀC(OMe)C6H4-o-Cl}]-
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[OTf] (5) with alkoxides RONa (R=Me, Et) affords the chelate complexes [Fe(C5Me5)(CO){k2(C,O)ꢀC6H4-o-C(OMe)(OR)-
(OR)}]
7
(R=Me) and
8
(R=Et), respectively. Similarly, the reaction of
3
with EtONa affords
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5H5)(CO){k2(C,O)ꢀC6H4-o-CO(Et)(OEt)2}] (9), for which the ArꢀCl bond has been cleaved. No activation of the ArꢀCl
bond is observed for the unchelated complex [Fe(C5Me5)(CO)2{C(OMe)C6H4-o-Cl}][OTf]. In contrast, treatment of the anisyl
derivative [F¸e(¹C¹5M¹¹e5¹)(¹C¹O¹){¹k¹2(¹C¹,O¹)¹ꢀC¹(¹O¹M¹e¹)C¹6¹H¹4-¹oº-OMe}][OTf] (6) with EtONa gives selectively the carbene complex
[Fe(C5Me5)(CO)(C6H4-o-OMe){ꢁC(OEt)2}] (12). The ArꢀOMe bond remains intact, but cleavage of the CaꢀCAr bond occurs.
This rearrangement process, i.e. a-elimination of the anisyl substituent, is favoured by the lability of the ortho-OMe group.
Treatment of 2 with NaOEt gives as the only identified compound the ethyl ester [MeOC6H4-o-(CO)OEt]. Clean formation of the
methyl ester derivative [MeOC6H4-o-(CO)OMe] is observed upon oxidation of 2 with C6H5I+O−. © 2001 Elsevier Science B.V.
All rights reserved.
Keywords: Iron; CꢀCl activation; CꢀC activation; Cleavage reactions; Carbene complexes
1. Introduction
[OTf] (5, X=Cl; 6, X=OMe) (OTfꢁCF3SO3)
and their related Cp complexes
[Fe(C5H5)(CO){k2(C,O)ꢀC(OMe)C6H4-o-OMe}][OTf]
(2) and [Fe(C5H5)(CO)(CH3CN){C(OMe)C6H4-o-
Cl}][OTf] (3), towards alkoxides. We hypothesised that
the combination of the Lewis acid character of the
organometallic fragment of these highly electrophilic
species and the presence of a potential vacant coordina-
tion site might promote new processes within the coor-
dination sphere of the metal. In this paper, we report
the bond activation reactions mediated by these car-
bene complexes leading to CꢀCl and CꢀC bond clea-
vage, selectively. Preliminary results from this work
have appeared [6].
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
The interest in Fischer-type carbene complexes has
intensified as such derivatives play an important role in
synthesis [1]. The reactivity of alkoxycarbene complexes
towards nucleophiles is dominated by a-addition at the
carbene carbon atom [2,3]. However, such reactions
frequently fail for iron complexes, principally due to the
occurrence of secondary O-dealkylation reactions [4].
The latter process is inhibited in the case of chelated
derivatives [5], and this allows us to study the reactivity
of the complexes containing labile or hemilabile li-
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
gands,i.e.[Fe(C5Me5)(CO){k2(C,X)ꢀC(OMe)C6H4-o-X}]-
* Corresponding author.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00792-6

20
K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
Table 1
2. Results and discussion
Selected bond lengths (A) and angles (°) a for the complexes
,
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5H5)(CO){k2(C,O)ꢀC(OMe)C6H4-o-OMe}][OTf] (2)
2.1. Synthesis of the Cp-containing carbene complexes
Bond lengths
FeꢀC7
FeꢀO3
C7ꢀO2
FeꢀC6
1.859(6)
2.045(5)
1.299(7)
1.769(7)
1.459(8)
C14ꢀO3
C7ꢀC9
C9ꢀC14
C6ꢀ01
1.367(7)
1.484(8)
1.380(8)
1.145(8)
1.457(8)
The preparation of the C5Me5-containing com-
plexes 5 and 6 has been previously described [5].
The
C5H5
complexes
[Fe(C5H5)(CO)2{C(OMe)-
O3ꢀC15
O2ꢀC8
C6H4-o-X}][OTf] (1,
a
X=Cl; X=OMe)
b
Bond angles
FeꢀC6ꢀO1
O3ꢀFeꢀC7
C6ꢀFeꢀC7
C6ꢀFeꢀO3
C9ꢀC7ꢀFe
are synthesised by classical procedures from the
172.9(6)
81.8(2)
91(7)
99.5(3)
114.6(4)
C14ꢀO3ꢀFe
C14ꢀC9ꢀC7
C9ꢀC14ꢀO3
C7ꢀO2ꢀC8
O3ꢀC14ꢀC13
114.2(4)
115.4(5)
113.3(5)
120.0(5)
124.8(5)
dimer [Fe(C5H5)(CO)2]2 [7]. The chelate complex
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5H5)(CO){k2(C,O)ꢀC(OMe)C6H4 -o -OMe}][OTf]
a There are three independent molecules per unit cell; the selected
data refer to one of them.
(2) is obtained upon photolysis (visible light) of 1b in
CH2Cl2 (Scheme 1). In contrast to the C5Me5 analogue,
coordination of the chlorine atom does not take place;
photolysis of 1a under the same conditions leads to
decomposition products. The chloroaryl fragment is a
weak donor and the cationic [Fe(C5H5)(CO)]+ unit is
not able to coordinate such a labile ligand. When
irradiation is performed in a coordinating solvent such
as CH3CN, the stable acetonitrile complex
[Fe(C5H5)(CO)(CH3CN){C(OMe)C6H4-o-Cl}][OTf] (3)
is then isolated (Scheme 1).
Substitution of one carbonyl ligand by PPh3
allows the isolation of the chelate complex
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5H5)(PPh3){k2(C,Cl)ꢀC(OMe)C6H4 - o - Cl}][OTf]
(4). This latter compound is obtained in one step upon
UV irradiation of 1a in the presence of one equivalent
of PPh3 in CH3CN. The coordination of the Cl atom is
indicated by the low-field chemical shift of the ArCl
carbon atom in the 13C{1H}-NMR spectrum (l 143.3),
whereas that of the non-chelated derivative 3 appears at
l 122.9. The downfield shift of the ArCl carbon reso-
nance upon complexation of the Cl atom to the iron
centre reflects a decrease in electronic density. This
Scheme 1.
feature has been already observed for the related com-
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
plex [Fe(C5Me5)(CO){k2(C,Cl)ꢀC(OMe)C6H4-o-Cl}]-
[OTf] (5), for which the X-ray crystal structure has been
established [5]. The phosphine ligand appears in this
context to have the same electronic effect as the perme-
thylation of the C5 ring.
The structure of complex 2 has been unequivocally
established by an X-ray crystal structure analysis (Fig.
1). Selected bond distances and angles are listed in
Table 1. The data show the classical pseudo-octahedral
geometry observed for three-legged piano-stool com-
plexes. There are three independent molecules per unit
cell. The FeꢀCa distances [1.859(6), 1.879(5), 1.870(5)
Fig. 1. ORTEP drawing of [¸F¹e¹(C¹5¹H¹5)¹(C¹O¹){¹k¹2(¹C¹,O¹)-¹C¹(O¹M¹¹e)¹C¹6H¹4¹-oº-O-
Me}][OTf] (2).
,
A] compare well with those reported for other iron–
,
carbene complexes (complex 5 — 1.857(6) A) [5,8]. The

K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
21
,
CaꢀO bond distances [1.299(7), 1.303(6), 1.299(7) A]
are typical for alkoxycarbene complexes [5,8]. The
A similar phenomenon is observed in bimetallic systems
bridged by Si(OSi(OMe)3)3 [10]. Concerning derivative
8, the two ethoxy groups are well-differentiated in the
1H- and 13C-NMR spectra. Moreover, the methylene
protons of one EtO substituent are diastereotopic (l
,
FeꢀO bonds [2.045(5), 2.043(4), 2.043(4) A)] are similar
to those found for other oxygen-containing iron com-
plexes [9]; for instance the FeꢀO bond distances of
[Fe(C5Me5)(dppe)(H2O)]+ [9a] and [Fe(C5Me5)(dppe)-
2
3.00, 2.78; JHꢀH=10 Hz); this could be attributed to
(OCMe2)]+ [9b] are 2.063(6) and 2.031(4) A, respec-
tively.
the coordination of this group to the stereogenic iron
centre.
,
Similarly, complex 9 is formed upon treatment of 3
with EtONa–EtOH; the methoxy group has been ex-
changed by an ethoxy substituent, a feature also ob-
served in the case of 6 (vide infra). The 1H-NMR
(toluene-d8, −20°C) spectrum shows two triplets at l
1.01 (6H) and 0.82 (3H) attributed to the methyl pro-
tons of the ethoxy groups, whereas all the methylene
protons are magnetically non-equivalent (see Section 3).
The 13C-NMR (CDCl3) spectrum displays two signals
for the methylene carbon at l 63.0 and 59.9.
The formation of 7–9 involves the cleavage of the
ArꢀCl bond, which could be promoted by the coordina-
tion of the chlorine atom or the presence of the poten-
tial vacant coordination site. In contrast, the ArꢀCl
bond cleavage does not occur for the dicarbonyl car-
2.2. Reacti6ity towards alkoxides
The reactivity of these complexes towards alkoxides
depends on the nature of the ortho-substituent X. Com-
plex 5 reacts with an excess of RONa (R=Me, Et) to
give in good yield (83–89%) the new chelate complexes
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5Me5)(CO){k2(C,O)ꢀC6H4-o-C(OMe)(OR)(OR)}]
(7, R=Me; 8, R=Et), which are isolated as dark
brown crystals (Scheme 2).
1
The H-NMR spectrum (C6D6, 25°C) of 7 exhibits
three broad signals for the methoxy groups at l 3.02,
2.88 and 2.73. Three different signals (l 56.3, 52.8 and
52.5), assigned to the magnetically non-equivalent OMe
groups, are also observed in the 13C{1H}-NMR
(CDCl3) spectrum. One methoxy is coordinated to the
iron centre, and the non-coordinated groups are
diastereotopic. Variable-temperature NMR studies
show that the signals coalesce at 42°C (300 MHz) and
give one signal at l 2.90 at 75°C; the exchange of the
OMe groups is therefore rapid on the NMR timescale.
bene
complex
[Fe(C5Me5)(CO)2{C(OMe)C6H4-o-
Cl}][OTf]. Here, the reaction with EtO− affords the
ketal complex [Fe(C5Me5)(CO)2{C(OEt)(OMe)(C6H4-o-
Cl}] (11), the formation of which results from addition
at the electrophilic carbene centre (Scheme 3). Complex
11 is stable in the solid state as a yellow powder at
−30°C, but undergoes thermal decomposition in solu-
tion above 0°C, even in an aprotic medium [11]. The
spectral properties of 11, recorded at −30°C, are in
1
agreement with the proposed structure. The H- and
13C{1H}-NMR spectra show two sets of signals, proba-
bly due to the presence of two geometric isomers. The
rotation about the CaꢀCAr bond would be hindered by
the presence of the ortho-substituent on the C6 ring.
For instance, in the 1H-NMR spectrum, the OCH3
resonances are observed at l 3.31 and 2.98 as singlets,
and the resonances of the OCH2CH3 group appear at l
3.55, 3.40 (CH2), and l 3.25, 3.05 (CH3). In the
13C{1H}-NMR spectrum, the Ca resonances are located
at l 116.5 and 114.9. These chemical shifts agree well
with that observed for related ketal complexes [11].
However, we were unable to characterise the expected
bis(methoxy) adduct [Fe(C5Me5)(CO)2{C(OMe)2(C6H4-
o-Cl}] (10), which is generated similarly by using
sodium methoxide. Therefore, this intermediate has
been chemically trapped as a carbene derivative. Addi-
tion of HBF4ꢀOEt2 (−80°C) to a solution of 10 quan-
titatively regenerates the starting carbene complex
[Fe(C5Me5)(CO)2{C(OMe)C6H4-o-Cl}]+ as a [BF4]−
salt (Scheme 3). The spectral data of this latter species
clearly show that the ArꢀCl bond is intact.
Scheme 2.
Although the formation of an ortho-ester group from
carbene species has already been reported [12], such a
Scheme 3.

22
K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
tion site would allow the formation of a p-benzyl
intermediate [15], since the benzyne intermediate is
speculative (Scheme 5). The p-benzyl species would
then rearrange into the s-benzyl derivative. A nucle-
ophilic attack of the alkoxide anion, followed by elimi-
nation of the chloride anion, and the migration of the
alkoxy group to the exocyclic double bond affords the
observed product. Both mechanisms could also be oper-
ative for 3, since the CH3CN ligand is labile. The
exchange of the alkoxy group in the presence of an
alkoxide has already been observed for carbene com-
plexes [16]. However, our results do not allow a distinc-
tion between these two pathways.
In the present case, the initial substitution of the
halide group by the alkoxide is ruled out, as indicated
by the reactivity of the related anisyl derivative
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5Me5)(CO){k2(C,O)ꢀC(OMe)C6H4-o-OMe}][OTf]
Scheme 4.
rearrangement process is without precedent. Nucle-
ophilic attacks of Lewis bases at the halocarbon atom
have been described previously [13]. However, such a
process could not account for the formation of the
observed products. Other examples of arylꢀhalide acti-
vation have been previously described by Green et al.
[14]. For instance, the cleavage of the ArꢀF bond of
B(C6F5)3 by the iron complex [Fe(C5H5)(CO)2Me] is
proposed to involve a FeꢀF interaction. We suggest
that, in the first step, a k2(C,Cl) ketal derivative is
formed by the addition of an alkoxide group at the Ca.
This chelated species could be in equilibrium with the
coordinatively unsaturated species, due to the facile
decoordination of the chloro ligand (Schemes 4 and 5).
If one considers this equilibrium, two scenarios are
possible to explain the above results. The first would
involve an initial cleavage of the CꢀCl bond, as previ-
ously proposed by Green et al. [14]. The ketal deriva-
tive would rearrange into a benzyne complex. A
nucleophilic addition of RO− on the bis(alkoxy)-
carbene ligand affords the ortho-ester group (Scheme
4). Finally, the insertion of the benzyne ligand into the
metal–carbon bond gives the observed compound. Al-
ternatively, the presence of a potential vacant coordina-
Scheme 5.

K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
23
to spectroscopically identify or isolate any
organometallic species. Moreover, it is noteworthy that
the methoxy group has been exchanged by an ethoxy
one during the course of the reaction, as in the former
case. We assume that the bis(ethyl) ketal intermediate
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5H5)(CO){k2(C,O)ꢀC(OEt)2C6H4-o-OMe}]
is
formed, but again this species is too unstable to be
spectroscopically detected. In contrast, the ketal inter-
mediate does not evolve into a carbene species; the
lability of the chelate OMe group appears to depend on
the nature of the ancillary ligands (C5Me5 vs. C5H5).
Clean and quantitative formation of the free methyl
ester derivative MeOC6H4-o-(CO)OMe is observed
upon oxidation of complex 2 by iodosobenzene. The
formation of a Re–formaldehyde complex from the
corresponding methylene complex has already been re-
ported [20,21].
In conclusion, this work demonstrates that the reac-
tion pathways change dramatically, depending on the
nature of the ortho-substituent and the electron-rich-
ness of the organometallic fragment. The approach that
we have used — chelation assistance for a metal in
order to facilitate bond activation — should be appli-
cable more widely for selective organometallic
processes.
Scheme 6.
(6). Since methoxy groups are already present in the
molecule, the ethoxide anion was used. Addition of
EtONa (three equivalents) to a THF suspension of 6
(−80°C) gives, after work-up, a 93% yield of the
bis(ethoxy)carbene complex [Fe(C5Me5)(CO)(C6H4-o-
OMe){ꢁC(OEt)2}] (12) (Scheme 6). The structure of 12
has been established spectroscopically and the 13C-
NMR (CD2Cl2) spectrum exhibits the carbene carbon
resonance characteristically downfield at l 263.8.
Examples of selective activation of the ArꢀOMe
bond have been reported previously by Milstein and
co-workers [17] by using Rh(I) complexes. However,
the Lewis acid–base interaction in 6 appears not to
weaken the ArꢀOMe bond to the same extent as the
ArꢀCl bond in the chloroaryl derivative 5. Therefore, a
different rearrangement process takes place. We
assume that the mechanism involves the following
3. Experimental
All manipulations were carried out under an
Ar atmosphere with Schlenk techniques. Solvents
were dried and distilled under nitrogen before
use by standard methods. The compounds
[Fe(C5Me5)(CO)2{C(OMe)C6H4-o-X}][OTf]
and
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
steps: (i) formation of the ketal intermediate
[Fe(C5Me5)(CO){k2(C,X)ꢀC(OMe)C6H4-o-X}][OTf] (5,
X=Cl; 6, X=OMe) were prepared according to the
literature procedure [5]. NMR spectra were recorded on
Bruker DPX-200 and Bruker AC 300 (by S. Sinbandhit,
CRMPO, Universite´ de Rennes 1) spectrometers.
Chemical shifts (l) are given in ppm using SiMe4 as the
external standard (1H, 13C). Infrared spectra were ob-
tained with a Bruker IFS28 FTIR spectrometer. Mass
spectra were recorded on a Varian MAT 311 (70 eV)
instrument and FABMS on a Micromass ZABSpec
TOF spectrometer at the CRMPO. Microanalyses were
performed by the ‘Centre de Microanalyse du CNRS’
at Vernaison, France.
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5Me5)(CO){k2(C,O)ꢀC(OEt)2(C6H4 - o - OMe)}];
and (ii) spontaneous de-insertion/migration of the ani-
syl substituent to the metal, promoted by the presence
of a labile ligand. This final step corresponds to the
reverse pathway of insertion/migration of an alkyl or
aryl group to a carbene ligand (Scheme 6) [18]. When
an alkyl or aryl migrates to a carbene fragment, the
intramolecular CꢀC coupling reaction affords a coordi-
natively unsaturated complex, which usually rearranges
via b-hydrogen elimination or is captured by an incom-
ing ligand. The reverse process, i.e. migration of alkyl
or aryl groups to give a carbene complex, is less com-
mon and requires the presence of a vacant coordination
site [19]. The thermal instability of these ketal com-
plexes might well provide the driving force for these
clean rearrangement processes.
3.1. [Fe(C5H5)(CO)2{C(O)C6H4-o-X}] (X=Cl, OMe),
general procedure
The parent Cp complex 2 was treated under the same
reaction conditions with an excess of EtONa–EtOH;
however, no carbene complex was formed. The only
product that has been characterised is the ethyl ester
derivative MeOC6H4-o-(CO)OEt, but we were unable
A suspension of 3 mmol (1 g) of [Fe(C5H5)(CO)2]2
and 7 mmol (210 mg) of potassium in 20 ml of THF
was refluxed for 2 h. To the resulting orange mixture
were added, at room temperature (r.t.), 7 mmol of the
appropriate acid chloride X-o-C6H4C(O)Cl. The solu-

24
K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
tion was stirred for 30 min, and the solvent removed in
vacuo. The residue was extracted with ether (3×20 ml)
and chromatography on alumina (eluent, pentane–
CH2Cl2 4:1) afforded a yellow crystalline solid.
red powder. Crystallisation in CH2Cl2–EtO2 at −20°C
gave red microcrystals (219 mg, 71%). 1H-NMR
3
(CDCl3): l=7.89 (d, J(HꢀH)=8 Hz, 1H, Ar), 7.69 (t,
3J(HꢀH)=7.7 Hz, 1H, Ar), 7.22 (m, 2H, Ar), 5.27 (s,
5H, C5H5), 4.78 (s, 3H, OMe), 4.27 (s, 3H, OMeAr).
13C{1H}-NMR (CDCl3): l=316.8 (ꢁC), 212.2 (CO),
168.9 (ArOMe), 137.9 (Ar), 133.8 (Ar), 124.3 (Aripso),
120.7 (Ar), 113.3 (Ar), 84.4 (C5H5), 70.9 (OMe), 70.7
(OMe). IR (CH2Cl2): 2004 (s, wCO). Anal. Found: C,
42.81; H, 3.40. Calc. for C16H15O6FeSF3: C, 42.88; H,
3.37%.
[Fe(C5H5)(CO)2{C(O)C6H4-o-Cl}] (80% yield). 1H-
NMR (CDCl3): l=7.38–7.16 (m, 3H, Ar), 6.92 (dd,
4
3J(HꢀH)=7.3 Hz, J(HꢀH)=1.9 Hz, 1H, Ar), 5.01 (s,
5H, C5H5). 13C{1H}-NMR (CDCl3): l=256.8 (CꢁO),
213.8 (CO), 154.3 (Aripso), 130.2 (Ar), 128.6 (Ar), 127.3
(Ar), 124.4 (ArCl), 122.7 (Ar), 87.6 (C5H5). IR
(CH2Cl2): 1625 (s, wCꢁO), 1970 (s, wCO), 2025 (s,
wCO). Anal. Found: C, 53.32; H, 3.07. Calc. for
C14H9O3FeCl: C, 53.13; H, 2.87%.
3.4. Crystal structure analysis of 2
[Fe(C5H5)(CO)2{C(O)C6H4-o-OMe}] (80% yield).
1H-NMR (CDCl3): l=7.25 (td, 3J(HꢀH)=7.8 Hz,
4J(HꢀH)=1.6 Hz, 1H, Ar), 7.00–6.80 (m, 3H, Ar),
4.95 (s, 5H, C5H5), 3.87 (s, 3H, OMe). 13C{1H}-NMR:
(CDCl3) l=258.1 (CꢁO), 214.4 (CO), 151.6 (Aripso),
146.4 (ArOMe), 129.0 (Ar), 122.0 (Ar), 120.8 (Ar), 111.7
(Ar), 87.2 (C5H5), 55.7 (OMe). IR (CH2Cl2): 1618 (s,
wCꢁO), 1966 (s, wCO), 2022 (s, wCO). Anal. Found: C,
57.89; H, 3.85. Calc. for C15H12O4Fe: C, 57.73; H,
3.88%.
C15H15O3Fe,CF3SO3, M 448.19 g mol−1, colour red,
crystal size 0.42×0.23×0.20 mm, crystal system mon-
oclinic, space group P21/c, a=13.4766(2), b=
,
23.4767(3),
c=16.8954(3)
A,
i=94.304(1)°,
V=5330.4(1) A−3, Z=12, z=1.675 g cm−3, T=110
K, v=10.28 cm−1, F(000)=2736. The sample was
studied on a Nonius Kappa CCD with graphite
,
,
monochromatised Mo–Ka radiation, u=0.71073 A.
The data collection (2qmax=60°) gave 63 738 integrated
reflections (hkl: −0.17, 0.30, −22.22). The data reduc-
tion with Denzo and Scalepack [22] led to 12 672 inde-
pendent reflections (10 157 with I\2.0|(I)). The
structure was solved with SIR-97 [23], which reveals all
the non-hydrogen atoms of the three complexes of the
asymmetric unit. After anisotropic refinement, the three
anions appeared disordered. The whole structure was
refined with SHELXL97 [24] by the full-matrix least-
squares techniques (use of F2 magnitude; x, y, z, iij for
Fe, C and O atoms, and riding mode for H atoms;
isotropic mode for the anions; 683 variables and 10 157
3.2. [Fe(C5H5)(CO)2{C(OMe)C6H4-o-X}][CF3SO3] (1,
a X=Cl, b X=OMe), general procedure
A
CH2Cl2 solution (15 ml) of 1.1 mmol of
[Fe(C5H5)(CO)2{C(O)C6H4-o-X}] (X=Cl, OMe) was
treated with 1.43 mmol (0.16 ml) of CH3OSO2CF3. The
mixture was stirred overnight and the solution was then
concentrated under vacuum to ca. 3–5 ml. Compound
1 was washed with diethylether (3×10 ml). 1a (yellow
powder, 65%). 1H-NMR (CDCl3): l=7.63–7.14 (m,
3
3H, Ar), 6.91 (dm, J(HꢀH)=7 Hz, 1H, Ar), 5.46 (s,
observations with I\2.0|(I).
w
calc=1/[|2(F2o)+
5H, C5H5), 4.38 (s, 3H, OMe). 13C{1H}-NMR (CDCl3):
l=327.5 (ꢁC), 208.1 (CO), 207.5 (CO), 147.4 (Ar),
132.6 (Ar), 130.5 (Ar), 128.9 (Ar), 123.9 (Ar) 122.9
(ArCl), 91.0 (C5H5), 70.7 (OMe). IR (CH2Cl2): 2029 (s,
wCO), 2074 (s, wCO). Anal. Found: C, 39.89; H, 2.49.
Calc. for C16H12O6F3SFeCl: C, 39.99; H, 2.52%. 1b
(brown oil, 63%). 1H-NMR (CDCl3): l=7.52 (t,
3J(HꢀH)=8.6 Hz, 1H, Ar), 7.28 (m, 2H, Ar), 7.05 (d,
3J(HꢀH)=8.6 Hz, 1H, Ar), 5.46 (s, 5H, C5H5), 4.43 (s,
3H, OMe), 3.95 (s, 3H, OMeAr). IR (CH2Cl2): 2028 (s,
wCO), 2071 (s, wCO). HRMS; m/z: Found 327.0318
[M+]. Calc. for C16H15O4Fe: 327.0320 [M+].
(0.094P)2+29.9P] where P=(Fo2 +2F2c)/3, with the re-
sulting R=0.088, Rw=0.232 and Sw=1.12 (residual
DzB1.6 e A−3).
,
3.5. [Fe(C5H5)(CO)(CH3CN){C(OMe)C6H4-o-Cl}]-
[CF3SO3] (3)
A CH3CN solution of 0.62 mmol (308 mg) of 1a was
irradiated (visible light) overnight. The yellow solution
became orange. After evaporation of the solvent, the
residue was washed with diethylether (2×10 ml) to
1
afford a red oil (228 mg, 74%). H-NMR (CD3CN):
l=7.53 (m, 3H, Ar), 7.18 (m, 1H, Ar), 5.06 (s, 5H,
C5H5), 4.37 (s, 3H, OMe). 13C{1H}-NMR (CDCl3):
l= (ꢁC not observed due to coalescence), 214.9 (CO),
147.6 (Aripso), 134.6 (CN), 131.0 (Ar), 129.6 (Ar), 128.2
(Ar), 124.4 (Ar), 122.9 (ArCl), 88.8 (C5H5), 67.4 (OMe),
5.2 (CH3CN). IR (CH2Cl2): 2019 (s, wCO). HRMS;
m/z: Found: 344.0148 [M+]. Calc. for C16H15O2FeCl:
344.0141 [M+].
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
3.3. [Fe(C5H5)(CO){k2(C,O)ꢀC(OMe)C6H4-o-OMe}]-
[CF3SO3] (2)
A CH2Cl2 solution of 0.7 mmol (330 mg) of 1b was
irradiated (visible light) overnight. The yellow solution
became red. After evaporation of the solvent, the
residue was washed with ether (2×10 ml), affording a

K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
25
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
3.8. [Fe(C5H5)(CO){k2(C,O)ꢀC6H4-o-C(OEt)(OEt)2}]
(9)
3.6. [Fe(C5H5)(PPh3){k2(C,Cl)ꢀC(OMe)C6H4-o-Cl}]-
[CF3SO3] (4)
A THF suspension of 1 mmol (490 mg) of 3 was
treated at −80°C with a freshly prepared EtOH solu-
tion of EtONa (4 mmol). After stirring for 1 h, the
solution was warmed up to −30°C and evaporated to
dryness. The brown residue was extracted with pentane
(2×15 ml), and evaporation to dryness gave a brown
oil (310 mg, 83%). 1HꢀNMR (toluene-d8, −20°C):
l=7.62 (d, 3J(HꢀH)=7 Hz, 1H, Ar), 7.20 (t,
3J(HꢀH)=7 Hz, 1H, Ar), 7.04 (m, 2H, Ar), 4.09 (s,
5H, C5H5), 3.75, 3.32, 3.12, 2.88, 2.82, 2.45 (6×m, 1H,
To a solution of 4 mmol (1.92 g) of 1a in CH3CN
(200 ml) was added 5 mmol (1.3 g) of PPh3. The
solution was photolysed under UV for 16 h. The sol-
vent was evaporated, and crystallisation of the residue
in a CH2Cl2–ether mixture provided 2.7 g (90%) of a
1
yellow-green powder. H-NMR (CDCl3): l=8.11–7.12
(m, Ar/Ph) 4.92 (s, 5H, C5H5), 4.45 (s, 3H, OMe).
13C{1H}-NMR (CDCl3): l=319.15 (d, 2J(PꢀC)=23
Hz, ꢁC), 146.0 (Aripso), 143.5 (ArCl), 135.3–121.7 (Ar/
Ph), 80.9 (C5H5), 67.8 (OMe). 31P{1H}-NMR (CDCl3,
H3PO4 ext): l=57.86 (PPh3). HRMS; m/z: Found:
537.0835 [M+]. Calc. for C31H27OFePCl: 537.0838 [M+].
3
OCH2CH3), 1.01 (t, J(HꢀH)=7 Hz, 6H, OCH2CH3),
0.82 (t, 3J(HꢀH)=7 Hz, 3H, OCH2CH3). 13C{1H}-
NMR (CDCl3): l=222.0 (CO), 165.9 (FeꢀAr), 143.5
(Ar), 139.7 (ArC), 127.4 (Ar), 124.3 (Ar), 122.6 (Ar),
114.3 (C(OEt)3), 80.9 (C5H5), 63.0 (OCH2CH3), 59.9
(OCH2CH3), 15.2 (OCH2CH3). IR (CH2Cl2): 1925 (s,
wCO). HRMS; m/z: Found: 372.1014 [M+]. Calc. for
C19H24O4Fe: 372.1024 [M+].
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
3.7. [Fe(C5Me5)(CO){k2(C,O)ꢀC6H4-o-C(OMe)(OR)-
(OR)}] (7, R=Me; 8, R=Et)
A suspension of 1.5 mmol (785 mg) in 25 ml of THF
of 5 was treated at −80°C with a freshly prepared
ROH (R=Me, Et) solution of RONa (three equiva-
lents). After stirring for 1 h, the solution was warmed
up to r.t. and evaporated to dryness. The residue was
extracted with pentane and crystallisation at −20°C
gave dark brown crystals. 7 (539 mg, 89%, dark brown
crystals): 1H-NMR (C6D6): l=7.84 (dd, 3J(HꢀH)=7.5
3.9. Formation of [Fe(C5Me5)(CO)2{C(OMe)-
(C6H4-o-Cl)}][BF4] 6ia [Fe(C5Me5)(CO)2{C(OMe)2-
(C6H4-o-Cl)}] (10)
A
THF suspension of
1
mmol (551 mg) of
was
[Fe(C5Me5)(CO)2{C(OMe)C6H4-o-Cl}][OTf]
4
3
Hz, J(HꢀH)=0.8 Hz, 1H, Ar), 7.35 (td, J(HꢀH)=
7.4 Hz, 4J(HꢀH)=1.6 Hz, 1H, Ar), 7.10 (td,
treated at −80°C with a freshly prepared MeOH solu-
tion of MeONa (3 mmol). After stirring for 1 h at
−80°C, the solution was evaporated to dryness. The
yellow residue was extracted with pentane (2×15 ml)
at −80°C. Addition of 1 mmol of HBF4ꢀOEt2 (150 ml,
85% in Et2O) to the resulting solution caused precipita-
tion of a yellow powder (400 mg, 81%). 1H-NMR
(CDCl3): l=7.59–7.42 (m, 3H, Ar), 7.28 (dd,
3J(HꢀH)=7.6 Hz, 1H, Ar), 4.49 (s, 3H, OMe), 2.00 (s,
15H, C5Me5). 13C{1H}-NMR (CDCl3): l=210.8 (CO),
147.6 (Aripso), 132.0 (Ar), 130.4 (Ar), 128.8 (Ar), 123.2
(ArCl), 122.5 (Ar), 103.9 (C5Me5), 70.7 (OMe), 9.8
(C5Me5). IR (Nujol): 2052 (s, wCO), 2008 (s, wCO),
1054 (s, wBF4). HRMS; m/z: Found: 401.0628 [M+].
Calc. for C20H22O3FeCl: 401.0607 [M+].
3J(HꢀH)=7.4 Hz, J(HꢀH)=1 Hz, 1H, Ar), 6.99 (dd,
4
3J(HꢀH)=7.5 Hz, J(HꢀH)=1.5 Hz, 1H, Ar), 3.02 (br
4
s, 3H, OMe), 2.88 (br s, 3H, OMe), 2.73 (br s, 3H,
OMe), 1.42 (s, 15H, C5Me5). 13C{1H}-NMR (CDCl3):
l=221.7 (CO), 174.6 (FeꢀAr), 140.2 (Ar), 136.5 (ArC),
127.9 (Ar), 126.8 (C(OMe)3), 123.9 (Ar), 121.9 (Ar),
89.6 (C5Me5), 56.3 (OMe), 52.7 (OMe), 52.5 (OMe),
10.8 (C5Me5). IR (pentane): 1917 (s, wCO). Anal.
Found: C, 62.78; H, 7.12. Calc. for C21H28O4Fe: C,
63.01; H, 7.05%. 8 (530 mg, 83%, dark brown crystals).
3
1H-NMR (CDCl3): l=7.57 (d, J(HꢀH)=7.5 Hz, 1H,
Ar), 7.17 (t, 3J(HꢀH)=6.7 Hz, 1H, Ar), 6.96 (t,
3J(HꢀH)=7 Hz, 1H, Ar), 6.84 (d, 3J(HꢀH)=7 Hz,
1H, Ar), 3.31 (q, 3J(HꢀH)=7 Hz, 2H, OCH2CH3),
3.15 (s, 3H, OMe), 3.00 (m, 1H, OCH2CH3), 2.79 (m,
1H, OCH2CH3), 1.60 (s, 15H, C5Me5), 1.14 (t,
3.10. [Fe(C5Me5)(CO)2{C(OEt)(OMe)C6H4-o-Cl}] (11)
3
3J(HꢀH)=7 Hz, 3H, OCH2CH3), 0.98 (t, J(HꢀH)=7
A suspension of 1 mmol (551 mg) of [Fe(C5Me5)-
(CO)2{C(OMe)C6H4-o-Cl}][OTf] in 20 ml of THF was
treated at −80°C with a freshly prepared EtOH solu-
tion of EtONa (three equivalents). After stirring for 1
h, the solution was evaporated to dryness. The residue
was extracted at −20°C with pentane (3×15 ml), and
evaporation of the solvent gave a yellow powder (390
mg, 93%). The solid decomposes at r.t. 1H-NMR
(CDCl3, −30°C): l=7.58, 7.47, 7.17, 6.98 (m, Ar),
3.55, 3.40 (br m, OCH2CH3), 3.31 (s, OMe), 3.25, 3.05
Hz, 3H, OCH2CH3). 13C{1H}-NMR (CDCl3): l=
221.4 (CO), 173.5 (FeꢀAr), 139.7 (Ar), 137.4 (ArC),
127.4 (Ar), 125.8 (C(OMe)(OEt)2), 123.4 (Ar), 121.5
(Ar), 89.2 (C5Me5), 60.2 (OCH2CH3), 59.8
(OCH2CH3), 55.8 (OMe), 15.3 (OCH2CH3), 14.8
(OCH2CH3), 10.1 (C5Me5). IR (pentane): 1914 (s,
wCO). HRMS; m/z: Found 428.1641 [M+]. Calc. for
C23H32O4Fe: 428.1649 [M+]. Anal. Found: C, 64.82; H,
7.47. Calc. for C23H32O4Fe: C, 64.49; H, 7.53%.

26
K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
(br m, OCH2CH3), 2.98 (s, OMe), 1.73, 1.64 (s, C5Me5),
1.35, 1.17 (br m, OCH2CH3). 13C{1H}-NMR (CDCl3,
−30°C): l=219.1, 218.8, 218.2 (CO), 149.6, 147.9
(ArC), 131.3, 130.9 (Ar), 129.8, 129.2 (ArCl), 128.0,
126.9, 126.5, 125.9, 125.6 (Ar), 116.5, 114.9 (Ca), 97.9,
96.6 (C5Me5), 58.9, 57.1 (OCH2CH3), 51.5, 50.8 (OMe),
15.5, 15.0 (OCH2CH3), 10.0, 9.8 (C5Me5). IR (pentane):
1997 (s, wCO), 1947 (s, wCO). Two isomers were ob-
served at −30°C, resulting from a hindered C*a ꢀAr
rotation at the low temperature. However, decomposi-
tion at 0°C prevents the observation of any coalescence
of the signals.
3.13. Preparation of [o-(OMe)ꢀC6H4ꢀC(O)OMe] from
¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
[Fe(C5H5)(CO){k2(C,O)ꢀC(OMe)(C6H4-o-OMe)}]-
[CF3SO3] (2) with C6H5I+ꢀO−
To a solution of 1.4 mmol (630 mg) in 15 ml of
CH2Cl2 was added at r.t., 1.7 mmol (370 mg) of
C6H5IO. The reaction mixture was stirred overnight.
After evaporation to dryness, the residue was extracted
with pentane. Evaporation gave a brown oil (100 mg,
1
3
43% yield). H-NMR (CDCl3): l=7.85 (d, J(HꢀH)=
3
7.2 Hz, 1H, Ar), 7.53 (t, J(HꢀH)=7.5 Hz, 1H, Ar),
7.04 (m, 2H, Ar), 3.96 (s, 3H, OMe), 3.95 (s, 3H, OMe);
13C{1H}-NMR (CDCl3): l=167.2 (CꢁO), 159.6
(ArOMe), 134.0 (Ar), 132.1 (Ar), 120.6 (Ar), 120.4
(ArCO), 112.4 (Ar), 56.4 (OMeAr), 52.5 (OMe). IR
(CH2Cl2): 1725 (s, wCꢁO).
3.11. [Fe(C5Me5)(CO)(C6H4-o-OMe){=C(OEt)2}] (12)
A suspension of 0.7 mmol (363 mg) of 6 in 15 ml of
THF was treated at −80°C with a freshly prepared
EtOH solution of EtONa (three equivalents). After
stirring for 2 h, the solution was warmed up to r.t. and
evaporated to dryness. The residue was extracted with
pentane and crystallisation at −20°C gave yellow crys-
tals (285 mg, 95%). 1H-NMR (C6D6): l=7.75 (d,
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 155024 for compound 2.
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;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
3
3J(HꢀH)=6.6 Hz, 1H, Ar), 7.11 (t, J(HꢀH)=7.5 Hz,
3
1H, Ar), 6.96 (t, J(HꢀH)=7 Hz, 1H, Ar), 6.59 (d,
3J(HꢀH)=6.6 Hz, 1H, Ar), 4.05 (br m, 2H,
OCH2CH3), 3.92 (br m, 2H, OCH2CH3), 3.48 (s, 3H,
OMe), 1.61 (s, 15H, C5Me5), 0.92 (br m, 6H,
OCH2CH3). 13C{1H}-NMR (CD2Cl2): l=263.8 (ꢁC),
=226.6 (CO), 166.7 (FeꢀAr), 154.3 (ArOMe), 143.9
(Ar), 122.5 (Ar), 119.8 (Ar), 108.2 (Ar), 95.5 (C5Me5),
66.7 (br s, OCH2CH3), 55.1 (OMe), 14.6 (OCH2CH3),
9.7 (C5Me5). IR (pentane): 1936 (s, wCO). HRMS; m/z:
Found: 383.1314 [M+−OEt], 355.1355 [M+−OEt−
CO]. Calc. for C21H27O3Fe: 383.1310 [M+−OEt],
355.1361 [M+−OEt−CO]. Anal. Found: C, 64.82; H,
7.47. Calc. for C23H32O4Fe: C, 64.49; H, 7.53%.
Acknowledgements
We thank Dr Matts Tilset for helpful discussions.
References
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¸¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹¹º
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3
4
7.46 (td, 1H, J(HꢀH)=7 Hz, J(HꢀH)=1.2 Hz, Ar),
7.00 (m, 2H, Ar), 4.36 (d, 2H, 3J(HꢀH)=7 Hz, OCH2),
3
3.91 (s, 3H, OMe), 1.38 (t, 3H, J(HꢀH)=7 Hz, CH3).
13C{1H}-NMR (CDCl3): l=166.2 (CꢁO), 159.1
(ArOMe), 133.3 (Ar), 131.5 (Ar), 120.5 (Aripso), 120.1
(Ar), 112.1 (Ar), 60.8 (CH2CH3), 56.0 (OMe), 14.3
(CH2CH3). IR (CH2Cl2): 1720 (s, wCꢁO).
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K. Ferre´ et al. / Journal of Organometallic Chemistry 629 (2001) 19–27
27
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