Synthesis, structure, and catalytic activity of new μ-oxo-bridged diiron(III) complexes

Article abstract of DOI:10.1002/ejic.200200575

The preparation and characterisation of two dinuclear iron(III) complexes with tripodal ligands 1,3-bis(2′-pyridylimino)isoindoline (indH) are presented. The μ-oxo-bridged diiron(III) complex [{FeCl(ind)]₂O] (2) has been prepared by reacting FeCl₃·6H₂O with indH in methanol solution. Compound [{Fe(ind)(OAc)]₂O] (3) was obtained from the reaction of 2 with CH₃CO₂Ag in THF. Both compounds were characterised by elemental analysis and UV/vis, IR, and Moessbauer spectroscopy. The X-ray structure analysis of [Fe₂O(ind)₂Cl₂]·THF (2·THF) revealed a distorted trigonal bipyramidal (τ = 0.88) coordination geometry around the iron(III) ion. More importantly, 2 is a good functional model for the activation of small molecules as its 5-coordinate iron ions can easily coordinate such molecules. This is confirmed by the high catalase-like activity of 2, transforming 87% of the excess of H₂O₂ into O₂ in 1 min. The complexes exhibited monooxygenase-like activity using H₂O₂ as the oxidant and oxidise alkanes to alcohols and ketones in acetonitrile in moderate yields. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200200575

FULL PAPER
Synthesis, Structure, and Catalytic Activity of New µ-Oxo-Bridged Diiron(III
)
Complexes
´
[a]
[b]
[c]
[c]
Eva Balogh-Hergovich, G a´ bor Speier,* Marius R e´ glier, Michel Giorgi,
[d]
[d]
Ern o˝ Kuzmann, and Attila V e´ rtes
Keywords: Iron / Tripodal ligands / Peroxides / Oxidation
The preparation and characterisation of two dinuclear
iron(III) complexes with tripodal ligands 1,3-bis(2Ј-pyridylim-
ino)isoindoline (indH) are presented. The µ-oxo-bridged di-
iron(III) ion. More importantly, 2 is a good functional model
for the activation of small molecules as its 5-coordinate iron
ions can easily coordinate such molecules. This is confirmed
iron(III) complex [{FeCl(ind)}
acting FeCl ·6H O with indH in methanol solution. Com- the excess of H
pound [{Fe(ind)(OAc)} O] (3) was obtained from the reaction monooxygenase-like activity using H
of 2 with CH CO Ag in THF. Both compounds were charac- oxidise alkanes to alcohols and ketones in acetonitrile in
terised by elemental analysis and UV/vis, IR, and Mössbauer
spectroscopy. The X-ray structure analysis of
Fe O(ind) Cl ]·THF (2·THF) revealed a distorted trigonal bi-
2
O] (2) has been prepared by re- by the high catalase-like activity of 2, transforming 87% of
into O in 1 min. The complexes exhibited
as the oxidant and
3
2
2
O
2
2
2
2 2
O
3
2
moderate yields.
[
2
2
2
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
pyramidal (τ = 0.88) coordination geometry around the
Germany, 2003)
Introduction
using µ-oxo-diiron() complexes derived from various sup-
[
5]
[6]
porting ligands, and oxidants such as ROOH, H O , m-
2
2
[
7]
[8]
Oxo-bridged dinuclear FeIII complexes have been recently
chloroperbenzoic acid, and O (ϩ electron source). For
2
this class of iron complexes the reactivity can be tuned by
modifying the ligand around the metal centre.
extensively studied owing to their presence in a class of non-
heme iron proteins that include hemerythrin, ribonucleotide
reductase, methane monooxygenase and purple acid phos-
Hydrogen peroxide may be the best oxidant to func-
tionalise hydrocarbons as it is less expensive, and gives only
water as a by-product. However, its use is limited, since a
[
1]
phatase. The soluble methane monooxygenase, sMMO,
isolated from methanotropic organisms catalyses the trans-
formation of methane into methanol using molecular oxy-
[
9]
number of diiron complexes have catalase activity.
[
2]
We report here the preparation and characterisation of
µ-oxo-bridged diiron() complexes with the tripodal ligand
gen as the oxidant in the presence of a source of electrons.
Several intermediates in the catalytic cycle of sMMO have
been characterised but the mechanism of catalytic hydroxyl-
1,3-bis(2Ј-pyridylimino)isoindoline (1, indH) and their
[
3]
monooxygenase- and catalase-like activity.
ation of unactivated CϪH bonds is not fully understood.
Spectroscopic studies implicate high-valent (µ-oxo)diiron
species as intermediates in the oxidation chemistry of the
diiron centres in methane monooxygenase.[ In the last dec-
ade several artificial sMMO systems have been developed
4]
[
a]
Research Group for Petrochemistry, Hungarian Academy of
Sciences,
8
201 Veszpr e´ m, Hungary
[
b]
Department of Organic Chemistry, University of Veszpr e´ m,
8
201 Veszpr e´ m, Hungary
Fax: (internat.) ϩ36-(0)88/427Ϫ492
E-mail: speier@almos.vein.hu
Results and Discussion
[
[
c]
Universit e´ d’Aix-Marseille 1 et 3, Facult e´ des Sciences et
Techniques de Saint-J e´ r oˆ me, Chimie, Biologie et Radicaux
Libres, UMR CNRS 6517, case 432,
Synthesis and Characterisation of the Complex
Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex
[
{FeCl(ind)} O]
2
1
3, France
d]
Research Group for Nuclear Techniques in Structural
Chemistry, Hungarian Academy of Sciences at Eötvös
University Budapest,
Complex [{FeCl(ind)} O] (2) was prepared from equimo-
2
lar amounts of the ligand and FeCl ·6H O. In its infrared
3
2
Ϫ1
Budapest, Hungary
spectrum the absorptions at 1638 and 1584 cm indicate
Eur. J. Inorg. Chem. 2003, 1735Ϫ1740
DOI: 10.1002/ejic.200200575
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1735

E. Balogh-Hergovich, G. Speier, M. R e´ glier, M. Giorgi, E. Kuzmann, A. V e´ rtes
FULL PAPER
that the complex contains the deprotonated isoindoline li- at the same time a lower s-electron density at the nucleus
[
10]
Ϫ1
III
gand.
The band at 792 cm
is characteristic of the of Fe (higher IS) and a higher symmetry around iron
asymmetric stretch of the FeϪOϪFe moiety, while the sym- atom than the trigonal bipyramidal coordination in
Ϫ1 [3a,11,12]
metric stretch occurs at 478 cm
.
In the electronic [{FeCl(ind)} O]. The later effect is the origin of the smaller
2
spectrum the band at 238 nm can be assigned to πϪπ* tran- quadrupole splitting in the complex [{Fe(ind)(OAc)} O].
2
sitions in the aromatic groups of the ligand, those in the oxo
dimer region (388, 473 nm) to a weak oxo-to-iron LMCT
transition. The less intense band at 473 nm is assigned to
6
4
the A Ǟ ( A , 4E) transition and is the signature of the
1
1
FeϪ(µ-O)ϪFe motif, independent of the bridging an-
gle.[
13,14]
Another important characteristic of the µ-oxo core
is expected in the 550Ϫ700 nm region, which is strongly de-
pendent on the FeϪ(µ-O)ϪFe angle: the lower the angle,
[
15]
the less energetic and/or the more intense the band. The
broad, weak band at 615 nm indicates a bent structure with
a low angle, in agreement with X-ray data.
Synthesis and Characterisation of the Complex
[
{Fe(ind)(OAc)} O]
2
Complex [{Fe(ind)(OAc)} O] (3) was prepared by the re-
2
action of [{FeCl(ind)} O] with CH CO Ag in THF. Infra-
2
3
2
Ϫ1
red spectrum absorptions at 1638 and 1577 cm indicate
that the complex contains the deprotonated isoindoline li-
2 N
Figure 1. Mössbauer spectra of [{FeCl(ind)} O]; T ϭ temperature
Ϫ1
gand (absence of a strong band at 1100 cm and absorp- of liquid nitrogen
Ϫ1
tions in the range 1600Ϫ1660 cm ). Complexes with the
deprotonated isoindoline ligand exhibit a weak band above
Ϫ1 [10]
Ϫ1
1600 cm
.
The band at 752 cm is characteristic of the Table 1. Mössbauer parameters for complexes 2 and 3
asymmetric stretch of the FeϪOϪFe moiety, the symmetric
Ϫ1 [3a,11,12]
stretch occurs at 510 cm
.
The ν(CO ) bands at
[{FeCl(ind)}
2
O]
2
Fe(ind)(OAc)] O
2
TN[
a]
TN
[a]
Ϫ1
room.
temp.
room.
temp.
1
570 and 1430 cm suggest a bridged coordination of the
acetate groups. In the electronic spectrum of 3, the band at
37 nm can be assigned to πϪπ* transitions in the aromatic
groups of the ligand, and bands in the oxo dimer region QS
385, 475 nm) assigned to an oxo-to-iron charge transfer Line width
2
IS
0.382
1.164
0.274
0.279
1.143
0.284
0.511
0.645
0.318
0.422
0.617
0.360
(
transition. Finally a broad, weak band was observed in the
low-energy visible region (720 nm). The considerable red-
shift of this band, compared with λmax assigned for the
transition in 2, indicates a smaller FeϪ(µϪO)ϪFe angle.
This supports the binding mode of the acetate as a biden-
tate bridging ligand between the two iron atoms. From the
spectroscopic data for compound 3 the [Fe(ind)(µ-O)(µ-
[
a]
N
T is the temperature of liquid nitrogen.
X-ray Crystal Structure of [{FeCl(ind)} O]·THF
2
The molecular structure of complex [{FeCl(ind)} O]·THF
2
is shown in Figure 2, and selected bond lengths and angles
are listed in Table 2. The complex is a µ-oxo dimer, the two
iron atoms have a distorted trigonal bipyramidal geometry
with τ ϭ 0.88. For perfect square pyramidal and trigonal
bipyramidal geometries the values of τ are zero and unity,
respectively; τ being an index of the degree of trigonality
within the structural continuum between square pyramidal
OAc) (ind)Fe] structure was proposed; however, the [Fe-
2
(ind)(OAc)(µ-O)(OAc)(ind)Fe] structure could not be
excluded.
Mössbauer Spectroscopy
[
18]
The Mössbauer spectrum of complex [{FeCl(ind)} O] is and trigonal bipyramidal geometries. Oxygen and chlor-
2
shown in Figure 1 and the parameters are given in Table 1. ine atoms and one N of the tridentate isoindolinate ligand
The relatively low value of the isomer shift (IS) of 2 is due are in basal positions, while two further N atoms of the
III
to the high population of 4s orbital of Fe and it can be ligand occupy apical positions. The metalϪmetal distance
III
˚
explained by the s bonding between Fe and N(1) and of 3.283 A is shorter than in other five-coordinated µ-oxo
[
12]
N(6) donor atoms. The large quadrupole splitting (QS) is monobridged diiron complexes.
Moreover, the
the consequence of the distorted trigonal bipyramidal ge- FeϪOϪFe angle is significantly shorter than is usually
ometry around the iron atom.[
16,17]
The Mössbauer param- found in similar complexes.
[5b,6a,12]
These values are close
eters of 3 represent a typical iron() with octahedral en- to those in µ-oxo complexes with an additional bridging
[
12]
[1a,1b,3a]
vironment (Table 1). Namely, the higher coordination num- ligand,
and also in dinuclear iron proteins.
The
ber results in a higher population of 3d orbital of iron and, FeϪO bond lengths are within the range reported for (µ-
1736
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 1735Ϫ1740

New µ-Oxo-Bridged Diiron(III) Complexes
FULL PAPER
oxo)diiron() complexes[12] and the FeϪN bond lengths ured by iodometric titration) was compared with the
[19]
are similar to those obtained for [FeCl (ind)]. The FeϪN amount of dioxygen formed and showed good agreement
2
distances involving the pyridine nitrogen atoms, N1 and with the stoichiometry of the dismutation reaction. Com-
N3, are significantly longer than for the pyrrole nitrogen plex 3 showed much lower dismutation activity.
atom, N5. The same bond length pattern has been observed
II [20]
II [21]
in Cu
and Ni
complexes of the isoindolinate li-
gand. The FeϪCl bond lengths are similar to those of
2
ϩ [5b]
[
Fe O(TPA) Cl ] .
2 2 2
Figure 3. Evolution of dioxygen from
2 2
H O catalysed by
Ϫ3
Ϫ3
[
2 2 2
{FeCl(ind)} O]; [2] ϭ 1.75 mol·dm , [H O ] ϭ 0.175 mol·dm
Kinetic measurements of H O2 decomposition in the
2
presence of 2 were performed in acetonitrile at 25 °C under
pseudo-first-order conditions. To determine the rate depen-
dence on the two reactants, runs were performed at various
[
{FeCl(ind)} O] and H O concentrations. The straight line
2 2 2
obtained by plotting the initial reaction rate against the in-
itial catalyst concentration indicates a reaction order of one
with respect to 2. The first-order dependence of the reaction
rate against [H O ] was established by plotting the initial
2
2
Figure 2. Molecular structure of [{FeCl(ind)}
2
O]·THF
reaction rate against the [H
O ]. On the basis of the kinetic
2 2
data the rate law (1) could be derived. The second-order
Ϫ1
3 Ϫ1
˚
rate constant k was found to be 9.2 Ϯ 0.6 mol ·dm ·s .
Table 2. Selected bond lengths [A] and angles [°] for
{FeCl(ind)} O]·THF
[
2
Reaction rate ϭ k·[H
2
O
2
][2]
(1)
Fe(1)ϪO(1)
Fe(1)ϪCl(1)
Fe(1)ϪN(1)
N(1)ϪC(5)
N(1)ϪC(1)
N(3)ϪC(18)
Fe(1)ϪO(1)ϪFe(1) 131.9(2)
N(5)ϪFe(1)ϪCl(1) 123.4(1)
N(3)ϪFe(1)ϪO(1)
N(1)ϪFe(1)ϪO(1)
N(5)ϪFe(1)ϪN(3)
N(5)ϪFe(1)ϪN(1)
1.792(1) Fe(1)ϪN(5)
2.272(1) Fe(1)ϪN(3)
2.145(3) N(3)ϪC(14)
1.341(7) N(5)ϪC(13)
1.362(5) N(5)ϪC(6)
1.352(5)
1.998(3)
2.161(3)
1.360(4)
1.406(5)
1.384(4)
UV/vis spectra of a solution of [{FeCl(ind)} O] recorded
2
immediately after addition of the oxidant show drastic
changes (Figure 4). The final spectrum is very similar to
that obtained in the reaction of some other (µ-oxo)dii-
O(1)ϪFe(1)ϪCl(1) 116.7(1)
O(1)ϪFe(1)ϪN(5) 119.8(1)
[
6b]
ron() complexes with H O .
This may indicate that in
2
2
91.2(1)
96.2(1)
86.3(1)
85.3(1)
N(3)ϪFe(1)ϪCl(1)
N(1)ϪFe(1)ϪCl(1)
92.3(1)
89.0(1)
the reaction with hydrogen peroxide the original bent µ-
oxo structure decomposes to form a linear µ-oxo type or a
mononuclear complex.
N(1)ϪFe(1)ϪN(3) 170.8(1)
Catalase-Like Activity
The H O dismutation activity of complexes 2 and 3 was
2
2
tested by measuring the dioxygen evolution in acetonitrile
with a complex/H O ratio of 1:100. As expected, H O de-
2
2
2
2
composed to give O gas and water, a reaction competing
2
with the oxidation of cyclohexane. As shown in Figure 3,
complex 2 exhibited rather high activity for the decompo-
sition of hydrogen peroxide with about 80 initial turnovers
per min at 25 °C (turnover is mmol of O per mmol of
2
complex). The yield of O was 87% based on H O after
2
2
2
Figure 4. UV/vis spectra of (a) [{FeCl(ind)} O], (b) 2 with 100
2
Ϫ5
Ϫ3
1
min of reaction. The residual hydrogen peroxide (meas- equiv. of H
2
O
2
added. [2] ؍ 4.02 10 mol·dm , CH
3
CN, 25 °C
Eur. J. Inorg. Chem. 2003, 1735Ϫ1740
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1737

E. Balogh-Hergovich, G. Speier, M. R e´ glier, M. Giorgi, E. Kuzmann, A. V e´ rtes
FULL PAPER
Table 3. Oxidation of cyclohexane
Catalyst[a]
Oxidant
Yield [%][b]
Cyclohexanone
TN[c][d]
Cyclohexanol
tBuO
2
/cyclohexane
[
[
[
[
[
[
[
{FeCl(ind)}
{FeCl(ind)}
{FeCl(ind)}
2
2
2
O]
O]
O]
H
H
H
H
H
tBuO
tBuO
2
2
2
2
2
O
O
O
O
O
2
2
2
2
2
14.6
15.3
12.2
4.5
4.3
7.2
14.8
13.8
13.6
8.4
6.6
7.2
Ϫ
Ϫ
Ϫ
Ϫ
Ϫ
0.5
0.6
29.4
[
[
d]
e]
29.1
25.8
12.9
10.9
14.9
15.2
{Fe(ind)(OAc)}
FeCl (ind)]
{FeCl(ind)}
{Fe(ind)(OAc)}
2
O]
O]
2
2
O]
2
H
H
2
2
7.2
7.4
[
a]
3
[b]
Reaction conditions: cyclohexane (3.5 mmol), oxidant (3.5 mmol), catalyst (35 µmol), acetonitrile (10 cm ), Ar, 25 °C, 10 h. Based
[
c]
on the oxidant.
TN (turnover numbers) ϭ mol of product per mol of catalyst. Total yield and TN values take into account that 2
[d]
[e]
3
equivalents of oxidant are required to make 1 equivalent of ketone. Under O
2
.
4
1 cm CCl added.
Oxygenation of Alkanes
this reaction (Table 2). When 2,6-di-tert-butyl-4-methylphe-
nol, as a free radical trap, was added to the oxidation of
cyclohexane prior to H O addition in the case of complex
The monooxygenase-like activity of complexes
2
2
[
{FeCl(ind)} O]
(2),
[{Fe(ind)(OAc)} O]
(3)
and
2
2
2
there was no significant lowering of the yields of oxidation
[
FeCl (ind)] was tested in the oxidation of alkanes. We
2
products. The oxidation reaction of cyclohexane was also
checked first the activity of (2) in the oxidation of cyclohex-
ane by different oxidants and in different solvents (MeOH,
CH Cl , CH CN). Catalytic oxidations were effective only
performed after addition of CCl to the reaction mixture.
4
No formation of bicyclohexyl and cyclohexyl chloride was
observed. Any free cyclohexyl radical present would un-
dergo dimerisation to give bicyclohexyl, and would also ab-
2
2
3
with H O and tBuO H. No oxidation products could be
2
2
2
detected with di-tert-butyl peroxide and iodosylbenzene.
The results (Table 3) show that the best yields were obtained
with H O in acetonitrile. Under our experimental con-
[23]
stract Cl from CCl to give cyclohexyl chloride.
4
2
2
2
Table 4. Oxygenation of alkanes catalysed by [{FeCl(ind)} O]
ditions the molar ratio of iron complex/hydrogen peroxide/
substrate is 1:100:100. The oxidation of cyclohexane yielded
cyclohexanol and cyclohexanone in a 2:1 ratio. The total
Substrate[a]
Yield [%][b]
TN[c]
Product
turnover number (mmol product per mmol catalyst) was Methylcyclohexane 1-methylcyclohexanol
2-methylcyclohexanol
4.2
0.4
1.8
6.2
2.8
9.2
6.3
1.2
2.5
13.6
29.4, and the alcohol ϩ ketone yield was 29.4% after 10 h.
3
3
4
-methylcyclohexanol
-methylcyclohexanone
-methylcyclohexanone
15.4
In comparison, the yield was 14.9% with tBuO H and a
2
small amount of tert-butyl cyclohexyl peroxide was also
formed. Moreover, the catalyst obtained by replacing the
chlorine ligands with acetate was less active. The mononu-
Adamantane[d]
1-adamantanol
2-adamantanol
adamantanone
1-phenylethanol
acetophenone
16.7
16.1
clear iron() complex, [FeCl (ind)], showed a catalytic ac-
2
Ethylbenzene
tivity similar to that of 2.
As shown in Table 4, complex 2 also catalyses the oxygen-
ation of methylcyclohexane, adamantane, and ethylbenzene.
[a]
Reaction conditions: substrate (3.5 mmol), oxidant (3.5 mmol),
3
[b]
With methylcyclohexane as substrate, the reactivity at the 2 (35 µmol), acetonitrile (10 cm ), Ar, 25 °C, 10 h. Based on the
oxidant. [ TN (turnover numbers) ϭ mol of product per mol of
c]
tertiary position is 6 times higher than that at the secondary
catalyst. Total yield and TN values take into account that 2 equiv.
of oxidant are required to make 1 equiv. of ketone. 20 cm aceto-
nitrile.
position, and no oxygenation was observed at the primary
position. The normalised reactivity ratio of the tertiary
CϪH to secondary CϪH in the oxygenation of adamantane
is 4.0. The adamantane C3/C2 selectivity ratio is in the
range found for other systems, including model studies of
[d]
3
[5a]
sMMO by using dinuclear iron complexes,
and also for
the MMO enzyme (3.0, normalised).[ These results show
22]
that the regio-selectivity in the alkane hydroxylation cata-
lysed by [{FeCl(ind)} O] follows the order tertiary Ͼ sec-
2
ondary Ͼ primary carbon. From the time dependence of the
reaction (Figure 5) it seems that cyclohexanone and cyclo-
hexanol were always formed in approximately constant ra-
tios, showing that cyclohexanol is not the precursor of cyclo-
hexanone. Experiments were also performed under dioxygen
Figure 5. Yields of the products versus reaction time for the oxy-
to elucidate the role of O . The almost constant yields of
2
genation of cyclohexane, catalyst [{FeCl(ind)} O]; (·) cyclohexanol,
2
the oxidation products, whether the reaction was carried out
Ϫ3
(
o) cyclohexanone; [cyclohexane] ϭ 0.35 mol·dm , [H
2
O
2
] ϭ 0.35
Ϫ3
3
Ϫ3
3
under argon or dioxygen, suggest that O is not involved in mol·dm , [2] ؍ 3.5 10Ϫ mol·dm , CH
3
CN 10 cm , Ar, 25 °C
2
1738
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 1735Ϫ1740

New µ-Oxo-Bridged Diiron(III) Complexes
FULL PAPER
In our study the coordinatively unsaturated iron() in with a column identical to that used for GC analyses. UV/vis spec-
tra were recorded on a Shimadzu UV-160 spectrophotometer by
using quartz cells. The Mössbauer spectroscopy measurements
were carried out at room temp. or at liquid nitrogen temperature
[
{FeCl(ind)} O] can easily bind H O , and an iron-peroxo
2
2
2
species, observed also during other H O dependent
reactions,
based oxidative species. Our observations suggest that the
reaction proceeds via heterolytic scission of the peroxide
bond, resulting in high-valent oxo metal intermediates,
rather than via a radical mechanism. The same reaction
2
2
[
24Ϫ26]
may be a transient precursor of a metal-
(
T
N
) and in zero applied magnetic field using a conventional
Mössbauer spectrometer in constant acceleration mode. The γ-rays
57
9
were provided by a Co(Rh) source of 10 Bq activity. All isomer
shift data are given relative to α-Fe. For the spectrum evaluation
[30]
we used the MössWinn program package.
also occurs with [FeCl (ind)]. It is likely that the mononu-
2
Synthesis of [{FeCl(ind)} O] (2): FeCl ·6H O (0.270 g, 1 mmol) was
2
3
2
clear [FeCl (ind)] in solution is converted into the oxo-
2
3
bridged dimer (2), the thermodynamic sink for the FeIII
dissolved in methanol (10 cm ), then 1,3-bis(2Ј-pyridylimino)isoin-
3
doline (0.299 g, 1 mmol) in methanol (20 cm ) was added and the
state, and this will be the active catalyst of the reaction.
reaction mixture stirred under argon at 60° for 8 h. After cooling,
Compound 2 could also be prepared by stirring [FeCl (ind)]
2
a dark brown powder of [{FeCl(ind)}
filtered off, washed with acetonitrile and dried under vacuum
0.34 g, 85%). Recrystallisation of the product from THF gave dark
2
O] precipitated, which was
in hot methanol. In [{Fe(ind)(OAc)} O], obtained by re-
2
placing chlorine ligands by acetate bridges, the six-coordi-
(
nated iron() has no vacant site for the coordination of brown crystals. M.p. 354Ϫ356 °C. IR (KBr): ν˜ ϭ 1638 w, 1602 w,
H O , which results in lower activity. Further spectroscopic 1584 s, 1549 m, 1536 s, 1468 s, 1428 m, 1360 w, 1306 w, 1265 m,
2
2
studies are needed to elucidate the structure of the inter- 1197 m, 1150 w, 1095 w, 1061 s, 1007 m, 898 w, 851 w, 792 m, 783
Ϫ1
s, 722 m, 702 m, 641 w, 539 w, 514 w, 478 w, 437 w cm . UV/vis
mediate complexes.
3
Ϫ1
Ϫ1
(CH
3
CN): λmax (log ε/dm ·mol ·cm ) ϭ 238 (4.78), 282 (4.65),
3
88 (4.51), 473 (3.99), 615 (3.57) nm. C36H24Cl Fe N10O (795.2):
2 2
calcd. C 54.36, H 3.04, Cl 8.91, Fe 14.04, N 17.61; found C 54.68,
H 3.12, Cl 8.54, Fe 13.44, N 17.34.
Conclusion
Two new µ-oxo-diiron() complexes with 1,3-bis(2Ј- Synthesis of [{Fe(ind)(OAc)} O] (3): [{FeCl(ind)} O] (1.067 g,
2
2
3
pyridylimino)isoindoline ligands, [{FeCl(ind)} O] (2), 1.34 mmol) in THF (80 cm ) was treated with CH CO Ag (0.447 g,
2
3
2
[
{Fe(ind)(OAc)} O] (3), have been prepared and then charac- 2.68 mmol) at 60 °C for 8 h. The resultant light brown precipitate
2
was filtered off and the solution condensed under vacuum to 30
terised by elemental analysis and UV/vis, IR, and Mössbauer
spectroscopy. X-ray structure analysis of the complex
Fe O(ind) Cl ]·THF revealed that the coordination ge-
ometry around the iron() ion is distorted trigonal bipyr-
amidal (τ ϭ 0.88). In complex 3 the iron() has an octa-
hedral environment. Moreover 2 is a good functional model
for the activation of small molecules, since each iron ion is
3
cm . Upon cooling (Ϫ10 °C), a dark brown solid was deposited,
which was filtered off, washed with acetonitrile and dried under
vacuum (0.75 g, 65%). M.p. Ͼ 320 °C. IR (KBr): ν˜ ϭ 1638 w, 1597
w, 1577 s, 1570 s, 1530 s, 1468 s, 1430 s, 1367 w, 1272 m, 1190 m,
150 w, 1061 s, 1000 m, 878 w, 802 m, 797 s, 752 m, 539 w, 510 w,
30 w cm . UV/vis (THF): λmax (log ε/dm ·mol ·cm ) ϭ 237
[
2 2 2
1
4
(
Ϫ1
3
Ϫ1
Ϫ1
4.51), 363 (4.32), 385 (4.35), 409 (4.28), 475 (3.84) 720 (2.45) nm.
five-coordinate and, thus, small substrate molecules can be C H Fe N O (842.4): calcd. C 57.02, H 3.58, Fe 13.25, N 16.63;
4
0
30
2
10
5
coordinated easily. Both complexes were effective catalysts found C 56.74, H 3.60, Fe 12.97, N 16.57.
for the oxidation of alkanes utilising hydrogen peroxide as
oxygen source; however, their use is limited due to their
ability to dismutate H O . Complex 2 exhibits a rather high
activity for the decomposition of hydrogen peroxide, trans-
2
2
Table 5. Crystallographic data of [{FeCl(ind)}
2
O]·THF
forming 87% of the excess of H O into O in 1 min.
Empirical formula
Formula mass
Crystal size [mm ]
C H N OFe Cl ·THF
2
2
2
36 24 10
867.36
2
2
3
0.7 ϫ 0.2 ϫ 0.1
orthorhombic
Pccn
12.727(1), 90
13.460(1), 90
21.516(1), 90
3685.8(4)
4
1840
1.621
0.992
2.90, 26.36
4014
3632
2243
254
1.027
0.0502 (0.1028)
0.1047 (0.1253)
0.577
Crystal system
Space group
Experimental Section
˚
a [ A], α [°]
General Remarks: All manipulations were performed under a pure
˚
b [ A], β [°]
dinitrogen or argon atmosphere unless otherwise stated, using
c [ A˚ ], γ [°]
[27]
˚
3
standard Schlenck-type inert-gas techniques. 1,3-Bis(2Ј-pyridyli-
V [ A ]
Z
[
28]
[19]
mino)isoindoline,
and [FeCl
2
(ind)]
were prepared according
F(000)
to literature methods. Methanol and acetonitrile were purified in
the usual manner and stored under argon.[
29]
ρ
calcd. [g cmϪ3]
All other chemicals
Ϫ1
µ [mm
]
were commercial products and were used as received without
further purification.
Θmin., Θmax. [°]
Reflections collected
Reflections total
Reflections unique
Parameters
Physical Measurements: Infrared spectra were recorded on a Spe-
cord 75 IR (Carl Zeiss) spectrophotometer using samples mulled
in Nujol between KBr plates or in KBr pellets. GC analyses were
performed on a HP 583OA gas chromatograph equipped with a
flame ionisation detector and a 25 m (0.2 mm i.d., 0.25 µm FT)
CP-SIL-8CB fused silica capillary column. GC-MS analyses were
performed on a HP 5890II/5971 GC/MSD apparatus equipped
2
GOF on F
R [I Ն 2σ(I)] (all data)
R
w
(all data)
˚
3
Max. resd. density [e/A ]
Eur. J. Inorg. Chem. 2003, 1735Ϫ1740
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1739

E. Balogh-Hergovich, G. Speier, M. R e´ glier, M. Giorgi, E. Kuzmann, A. V e´ rtes
FULL PAPER
hedron Letters 1994, 35, 6287Ϫ6290. [5d] M. Costas, K. Chen,
L. Que, Jr., Coord. Chem. Rev. 2000, 200Ϫ202, 517Ϫ544.
6] [6a]
X-ray Structure Determination of 2: Suitable crystals of
{FeCl(ind)} O]·THF were obtained from THF. The intensity data
were collected with a Nonius Kappa CCD single-crystal dif-
[
2
[
S. Ito, T. Okuno, H. Matsushima, T. Tokii, Y. Nishida, J.
Chem. Soc., Dalton Trans. 1996, 4479Ϫ4484. [ T. Okuno, S.
Ito, S. Ohba, Y. T. Nishida, J. Chem. Soc., Dalton Trans.
6b]
fractometer, using graphite-monochromated Mo-K
α
radiation (λ ϭ
˚
0
.71073 A) and ϕ scan technique at 293 K. Details of the crystal
structure determination are shown in Table 5. The structure was
1
997, 3547Ϫ3551.
M. Kodera, H. Shimakoshi, K. Kano, Chem. Commun. 1996,
737Ϫ1738.
[7]
[8]
[
31]
solved by direct and difmap methods (SIR92),
and refined on
CCDC-195083
1
2
[32,33]
F by using full-matrix least-squares methods.
S. M e´ nage, J. B. Galey, J. Dumats, G. Hussler, M. Seit e´ , I.
Gautier, G. Chottard, M. Fontecave, J. Am. Chem. Soc. 1998,
120, 13370Ϫ13382.
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html or from Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK [Fax: (in-
ternat.) ϩ 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
[
9] [9a]
R. Tahn, A. Schrodt, L. Westerheide, R. van Eldik, B.
Krebs, Eur. J. Inorg. Chem. 1999, 1537Ϫ1543. [ S. M e´ nage,
J. M. Vincent, C. Lambeaux, M. Fontecave, J. Chem. Soc., Dal-
ton Trans. 1994, 2081Ϫ2084.
9b]
[
10]
Oxidation Reactions: Standard oxidation reactions were carried out
under an inert atmosphere of argon. The complex (35 µmol) was
dissolved in acetonitrile (10 cm ) containing 3.5 mmol of substrate.
R. R. Gagn e´ , D. N. Marks, Inorg. Chem. 1984, 23, 65Ϫ74.
J. E. Plowman, T. M. Loehr, C. K. Schauer, O. P. Anderson,
Inorg. Chem. 1984, 23, 3553Ϫ3559.
D. M. Kurtz, Jr., Chem. Rev. 1990, 90, 585Ϫ606.
R. Hazell, K. B. Jensen, C. J. McKenzie, H. Toftlund, J. Chem.
Soc., Dalton Trans. 1995, 707Ϫ717.
R. C. Reem, J. M. McCormick, D. E. Richardson, F. J. Devlin,
P. J. Stephens, R. L. Musselman, E. I. Solomon, J. Am. Chem.
Soc. 1989, 111, 4688Ϫ4704.
R. E. Norman, R. C. Holz, S. M e´ nage, C. J. O’Connor, J. H.
Zhang, L. Que, Jr., Inorg. Chem. 1990, 29, 4629Ϫ463.
R. R. Berrett, B. W. Fitzsimmons, A. Owusu, J. Chem. Soc.
[
11]
3
[
[
12]
13]
The reaction was then started by adding 3.5 mmol of H
2 2
O or
tBuO H. After stirring for 10 h at 25 °C the products were deter-
2
mined by GC analysis. The structures of the products were con-
firmed by GC-MS spectrometry, and by comparison with auth-
entic samples.
[14]
[
[
15]
16]
Catalase-Like Reactions: All reactions were carried out at 25 °C
under an argon atmosphere in a thermostatted reactor with stir-
ring. To start the reaction hydrogen peroxide (0.875 mmol, 97 µL)
was added through a septum to a stirred solution of the complex
8.75 mmol, 7 mg) in acetonitrile (5 cm ). The volume of evolved
(
A) 1968, 1575Ϫ1579.
[17]
G. M. Bancroft, A. G. Maddock, R. P. Randl, J. Chem. Soc.
3
(
(A) 1968, 2939Ϫ2944.
[
18]
dioxygen was read periodically by using a gas burette. In the kinetic
A. W. Addison, T. N. Rao, J. Reedijk, J. Rijn, van, G. C. Ver-
measurements the hydrogen peroxide concentration was first kept
shoor, J. Chem. Soc., Dalton Trans. 1984, 1349Ϫ1356.
Ϫ3
[19]
´
constant ([H
2
O
2
] ϭ 0.175 mol·dm ) and the concentration of 2
E. Balogh-Hergovich, G. Speier, B. Tapodi, M. R e´ glier, M.
Ϫ3
Giorgi, Z. Kristallogr. 1999, 214, 579Ϫ580.
was varied from 0.525 to 3.52 mol·dm . To determine the rate
dependence on the H , the catalyst concentration was kept con-
2
stant ([2] ϭ 1.75 mol·dm ) and the [H O ] varied in the range
[
[
[
20]
21]
22]
´
E. Balogh-Hergovich, J. Kaizer, G. Speier, G. Huttner, A. Ja-
2
O
2
Ϫ3
cobi, Inorg. Chem. 2000, 39, 4224Ϫ4229.
R. J. Letcher, W. Zhang, C. Bensimon, R. J. Crutchley, Inorg.
Chim. Acta 1993, 210, 183Ϫ191.
M. Kodera, K. Kano, T. Funabiki, in Oxygenases and Model
Systems (Ed.: T. Funabiki), Kluwer Academic Publishers, Dor-
drecht, 1997, vol. 19, (Catalysis by Metal Complexes), p.
2
Ϫ3
0.0618Ϫ0.3088 mol·dm .
Acknowledgments
The financial support of the Hungarian National Research Fund
OTKA T-7443, T-016285, T-30400 and T-034839) is gratefully
acknowledged.
2
83Ϫ343.
(
[23]
R. H. Crabtree, Chem. Rev. 1985, 85, 245Ϫ269.
[24]
H. Zheng, S. J. Yoo, E. Münck, L. Que, Jr., J. Am. Chem. Soc.
2
000, 122, 3789Ϫ3790.
[
1] [1a]
[25]
[26]
D. M. Kurtz, Jr., J. Biol. Inorg. Chem. 1997, 2, 159Ϫ167.
1b]
K. Chen, L. Que, Jr., J. Am. Chem. Soc. 2001, 123, 6327Ϫ6337.
Y. Mekmouche, S. M e´ nage, C. Toia-Duboc, M. Fontecave, J.
B. Galey, C. Lebrun, J. P e´ caut, Angew. Chem. Int. Ed. 2001,
40, 949Ϫ952.
[
J. B. Vincent, G. L. Olivier-Lilley, B. A. Averill, Chem. Rev.
990, 90, 1447Ϫ1467. [ S. -Y. Choi, P. E. Eaton, D. A. Kopp,
1c]
1
S. J. Lippard, M. Newcomb, R. Shen, J. Am. Chem. Soc. 1999,
[27]
121, 12198Ϫ12199.
D. F. Shriver, M. A. Drezdzon, The Manipulation of Air-sensi-
tive Compounds, John Wiley & Sons, New York, 1986.
W. O. Siegel, J. Org. Chem. 1977, 42, 1872Ϫ1878.
D. D. Perrin, W. L. Armarego, D. R. Perrin, Purification of
Laboratory Chemicals, 2nd ed., Pergamon, New York, 1990.
Z. Klencs a´ r, E. Kuzmann, A. V e´ rtes, J. Rad. Nucl. Chem. Lett.
1996, 210, 105Ϫ118.
A. Altamore, G. Cascarano, C. Giacovazzo, A. Guagliardi, M.
C. Burla, G. Polidori, M. Camalli, J. Appl. Cryst. 1994, 27,
435Ϫ436.
S. Mackay, C. J. Gilmore, C. Edwards, M. Tremayne, N. Ste-
wart, K. Shankland, maXus: A Computer Program for the Solu-
tion and Refinement of Crystal Structures from Diffraction
Data, University of Glasgow, Scotland, UK, Nonius BV, Delft,
The Netherlands and MacScience Co. Ltd., Yokohama, Ja-
pan, 1998.
G. M. Sheldrick, SHELXL-97: Program for the Refinement of
Crystal Structures, University of Göttingen, Germany, 1997.
Received October 16, 2002
[
[
2] [2a]
B. J. Wallar, J. D. Lipscomb, Chem. Rev. 1996, 96,
[
2b]
[28]
29]
2
625Ϫ2658.
ara, C. A. Frederick, S. J. Lippard, Chem. Biol. 1995, 2,
09Ϫ418.
A. C. Rosenzweig, P. Nordlund, P. M. Takah-
[
4
3] [3a]
[30]
[31]
J. Sanders-Loehr, W. D. Wheeler, A. K. Shiemke, B. A. Av-
erill, T. M. Loehr, J. Am. Chem. Soc. 1989, 111, 8084Ϫ8093.
[
3b]
A. M. Valentine, S. J. Lippard, J. Chem. Soc., Dalton Trans.
997, 3925Ϫ3931. [ A. M. Valentine, S. S. Stahl, S. J. Lippard,
3c]
1
J. Am. Chem. Soc. 1999, 121, 3876Ϫ3887.
[
[
4] [4a]
[32]
K. E. Liu, A. M. Valentine, D. Wang, B. H. Huynh, D. E.
Edmondson, A. Salifoglou, S. J. Lippard, J. Am. Chem. Soc.
[4b]
1
995, 117, 10174Ϫ10185.
Kauffmann, E. Münck, J. D. Lipscomb, L. Que, Jr., Science
997, 275, 515Ϫ518.
L. Shu, J. C. Nesheim, K.
1
5] [5a]
R. A. Leising, R. E. Norman, L. Que, Jr., Inorg. Chem.
990, 29, 2553Ϫ2555. [ T. Kojima, R. A. Leising, S. Yang,
5b]
[33]
1
[5c]
L. Que, Jr., J. Am. Chem. Soc. 1993, 115, 11328Ϫ11335.
J.
M. Vincent, S. M e´ nage, C. Lambeaux, M. Fontecave, Tetra-
1740
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 1735Ϫ1740