Synthesis and structure of iron(iii) diamine-bis(phenolate) complexes

Article abstract of DOI:10.1039/b802274g

The structures and properties of six new iron(iii) diamine-bis(phenolate) complexes are reported. Reaction of anhydrous FeX₃ salts (where X = Cl or Br) with the diprotonated tripodal tetradentate ligands 2-pyridylamino-N,N-bis(2-methylene-4-met

Full text of DOI:10.1039/b802274g

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www.rsc.org/dalton | Dalton Transactions
Synthesis and structure of iron(III) diamine-bis(phenolate) complexes†
a
a
a
a
b
Kamrul Hasan, Candace Fowler, Philip Kwong, Angela K. Crane, Julie L. Collins and
a
Christoper M. Kozak*
Received 11th February 2008, Accepted 26th March 2008
First published as an Advance Article on the web 1st May 2008
DOI: 10.1039/b802274g
The structures and properties of six new iron(III) diamine-bis(phenolate) complexes are reported.
Reaction of anhydrous FeX
3
salts (where X = Cl or Br) with the diprotonated tripodal tetradentate
[L ], and
N,N-dimethyl-N ,N -bis(2-methylene-4-methyl-6-tert-butylphenol)ethylenediamine, H [L
]FeBr 4.
ligands 2-pyridylamino-N,N-bis(2-methylene-4-methyl-6-tert-butylphenol), H
2
1
ꢀ
ꢀ
2
2
], produces
the trigonal bipyramidal iron(III) complexes, [L
1
]FeCl 1, [L
1
]FeBr 2, [L
2
]FeCl 3 and [L
2
ꢀ
Reaction of FeX
methylphenol)-N,N -bismethyl-1,2-diaminoethane, H
3
with the related linear tetradentate ligand N,N -bis(4,6-tert-butyl-2-
ꢀ
2
[L
3
], generates square pyramidal iron(III)
complexes, [L
3
]FeCl 5 and [L
3
]FeBr 6. Complexes 1–6 have been characterized using electronic
absorption spectroscopy and magnetometry. Single crystal X-ray molecular structures have been
determined for complexes 1, 3, 5 and 6.
Introduction
bearing amine-bis(phenolate)-ether ligands, which effectively cat-
alyze the cross-coupling of aromatic Grignard reagents with alkyl
The use of chelating tetradentate amine-bis(phenolate) ligands has
recently played an increasingly important role in transition metal
catalyst design. They have been predominantly used with high-
valent early transition metals where they have been employed
as alternative auxiliary ligands to the cyclopentadienyl-based
systems. In combination with Group 4 and 5 metals they display
high activities towards olefin or cyclic ester polymerization.
Also, Group 3 and lanthanide metal complexes of these ligands
have been effective as catalysts or initiators for ring-opening
polymerization of lactide and e-caprolactone. By comparison,
there has been limited use of amine-bis(phenolate) ligands with
the first row late transition metals, whereas the chemistry of
monoanionic phenoxytriamine ligands with these metals is far
more developed. A number of Fe(III) complexes of this class
of ligand has been reported and studied as a result of their
close relationship to phenol-containing ligands found in non-
heme iron-containing metalloenzymes. Particularly interesting
is their similarity to catechol dioxygenases, iron proteins that
catalyze the oxidative cleavage of catechol or its derivatives with the
incorporation of molecular oxygen. Indeed, the principal focus of
amine-bis(phenolate) iron chemistry to-date has been with respect
13
halides possessing b-hydrogens. Here we report the synthesis,
structure and spectroscopic behaviour of a related class of iron(III)
complexes supported by diamine-bis(phenolate) ligands.
Results and discussion
1–3
Syntheses
The substituted amine-bis(phenol) compounds in Chart 1 were
prepared by modified literature procedures employing Mannich
condensation of the corresponding phenol, amine and formalde-
hyde. Previously, these compounds have been prepared in refluxing
4
5
2,3,14
methanol.
The use of water as a reaction medium proves to
6
be much more effective at generating the desired compounds in
15
higher yield and requires shorter heating time. In particular,
[L ], which is reported here for the first time, was prepared
H
2
1
7–11
by addition of 2-aminomethylpyridine and formaldehyde to an
t
aqueous suspension of 2- Bu-4-Me-C
6
3
H OH, (eqn (1)). Tetraden-
tate ligands H
2
[L
2
] and H
2
[L
3
] were prepared by the addition of
ꢀ
N,N-dimethylethylenediamine or N,N -dimethylethylenediamine,
respectively, to an aqueous mixture of formaldehyde and the corre-
12
t
to its use as a model for redox-active bioinorganic systems.
sponding 2,4-disubstituted phenol (namely 2- Bu-4-Me-C
6
3
H OH
t
We are interested in the development of new inexpensive
iron-based catalysts for organic synthesis. As a result, we have
recently begun exploring the catalytic potential of iron complexes
supported by various amine-bis(phenolate) ligands bearing an
additional pendant arm, such as an ether or amine group. For
example, we have recently reported novel iron(III) compounds
for H
2
[L
2
] and 2,4-di- Bu-C
6
H
3
OH for H
2
3
[L ]).
a
Department of Chemistry, Memorial University of Newfoundland, St.
(
1)
John’s, NL, Canada. E-mail: ckozak@mun.ca; Fax: +1-709-737-3702;
Tel: +1-709-737-8082
C-CART X-ray Diffraction Laboratory, Department of Chemistry, Memo-
rial University of Newfoundland, St. John’s, NL, Canada
This class of ligands can be complexed to transition metals
by several routes. Metallation with alkali metal reagents can
b
n
be accomplished using BuLi, NaH or KH to generate M
2
[L]
†
CCDC reference numbers 677420–677423. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b802274g
salts where M = Li, Na or K, respectively. Several structurally
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gave the analytically pure paramagnetic complexes in good yield.
Room temperature magnetic data were obtained using a Faraday
balance. All complexes exhibited solid state room temperature
5
magnetic moments consistent with high spin Fe(III) d centres
(
(
S = 5/2). The pyridine substituted compounds [L
1
]FeX (X = Cl
1), Br (2)) have effective moments of 5.9 and 6.0 l
B
, respectively,
while dimethylamine substituted compounds [L
Br (4)) show respective moments of 6.0 and 5.9 l . Complexes
2
]FeX (X = Cl (3),
B
[
L
3
]FeX (X = Cl (5), Br (6)) possess the sequentially arranged
diamine-bis(phenolate) ligand and show moments of 5.9 and 6.2
, respectively. MALDI-TOF mass spectrometry was conducted
using anthracene as the matrix. The mass spectra of compounds
–6 all showed molecular ion peaks and characteristic fragment
l
B
1
ions. The halide ligand is easily lost from the parent ion in all of
Chart 1
+
these compounds, that is, intense [M − X] (X = Cl or Br) peaks
were observed in all spectra.
characterized examples of dilithiated diamine-bis(phenolate) com-
pounds have recently been reported, both as Lewis base adducts
16
17
Structural characterization
with 1,4-dioxane and base-free. Reaction of these ligand pre-
cursors with transition metal or lanthanide halide salts produces
the desired coordination complex. The protonated ligands can be
Single crystal X-ray structural characterization was performed
on representative complexes 1, 3, 5 and 6. Crystallographic data
used directly with suitable metal precursors such as Zr(CH
2
Ph)
4
,
are given in Table 1. Ligands [L
bipyramidal geometry in the Fe(III) complexes, 1 (Fig. 1) and
(Fig. 2). The iron ion is bonded to two phenolate oxygen
1
2
] and [L ] enforce trigonal
Zr(NMe , La[N(SiHMe (THF) and Y(CH SiMe (THF)
2
)
4
2
)
2
]
3
2
2
3
)
3
2
in alkane and amine elimination reactions. For late transition
metal halide salts, such as anhydrous FeCl or FeBr , the
kinetically labile halide ligand can be easily displaced using the
protonated ligand as well.
3
3
3
atoms and the nitrogen atom of the pyridine group in 1 or the
dimethylamine fragment in 3, which define the trigonal plane
of the bipyramid. The central nitrogen atoms of the ligands
and the chloride ions occupy the apical sites. In complex 1
Six Fe(III) complexes were prepared by dropwise addition of
a methanol solution of anhydrous FeX
methanolic slurry of the ligand at room temperature (Scheme 1).
The resulting dark blue solution was neutralized using NEt and
evaporated to dryness. Extraction into an appropriate solvent,
such as toluene, followed by filtration and removal of solvent
3
(X = Cl or Br) to a
˚
the Fe(1)–O(1) distance of 1.8467(12) A and Fe(1)–O(2) length
˚
of 1.8655(16) A are similar to the Fe(1)–O(1) and Fe(1)–O(2)
3
˚
distances in 3 of 1.865(2) and 1.845(2) A, respectively. These
in turn are similar to the iron–phenolate oxygen donor lengths
observed in a related trigonal bipyramidal iron(III) complex
Fig. 1 Molecular structure (ORTEP) and numbering scheme of 1.
Ellipsoids are shown at 50% probability. Selected bond distances ( A˚ )
◦
and angles ( ): Fe(1)–Cl(1), 2.2894(5); Fe(1)–O(1), 1.8467(12); Fe(1)–O(2),
1
1
.8655(16); Fe(1)–N(1), 2.2706(15); Fe(1)–N(2), 2.142(2); O(1)–C(7),
.349(2); O(2)–C(19), 1.350(2); O(1)–Fe(1)–O(2), 116.70(7); O(1)–Fe(1)–
N(1), 86.49(5); O(1)–Fe(1)–N(2), 118.53(7); O(2)–Fe(1)–N(1), 88.46(6);
O(2)–Fe(1)–N(2), 120.91(6); N(1)–Fe(1)–N(2), 75.67(6); O(1)–Fe(1)–
Cl(1), 98.67(4); O(2)–Fe(1)–Cl(1), 97.21(4); N(1)–Fe(1)–Cl(1), 169.55(5);
N(2)–Fe(1)–Cl(1), 93.89(5); Fe(1)–O(1)–C(7), 135.20(12); Fe(1)–O(2)–
C(19), 128.34(12).
Scheme 1
2
992 | Dalton Trans., 2008, 2991–2998
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Table 1 Crystallographic data and refinements for 1, 3, 5 and 6
Compound
1
3
5
6
Chemical formula
Formula weight
T/K
C
549.94
153
30
H
38ClFeN
2
O
2
C
588.03
153
28
H
42ClFeN
2
O
2
·C
3
H
6
O
C
700.26
113
34
H
54ClFeN
2
O
2
·C
6
H
14
C
744.72
113
Blue, platelet
34
H
54BrFeN
2
O
2
·C
6 14
H
Colour, habit
Brown, block
Red, prism
Blue, prism
Crystal dimensions/mm
Crystal system
0.42 × 0.30 × 0.22
0.20 × 0.20 × 0.15
0.40 × 0.40 × 0.20
Monoclinic
C2/c (#15)
33.575(12)
13.954(5)
17.830(6)
90
102.144(8)
90
8166(5)
0.55 × 0.27 × 0.08
Monoclinic
C2/c (#15)
32.711(14)
14.027(6)
18.074(8)
90
101.330(8)
90
8166(5)
Triclinic
Monoclinic
¯
Space group
P 1 (#2)
P2 /c (#14)
1
a/A˚
9.0384(5)
12.5782(4)
13.4162(6)
67.583(4)
83.809(5)
78.145(5)
1379.18(11)
2
1.324
6.723
582.00
2.6 to 30.5
11430
17.059(4)
11.125(2)
16.676(4)
90
100.152(6)
90
3115.2(12)
4
1.254
b/A˚
c/A˚
◦
a/
b/
◦
◦
c /
V/A˚
3
Z
8
8
−
3
D
c
/g cm
1.139
4.672
3048.00
1.9 to 30.9
41294
1.217
13.894
3192.00
1.9 to 31.0
20292
−
1
l(Mo-Ka)/cm
F(000)
6.017
1260.00
2.2 to 30.8
20128
◦
h range for collection/
Reflections collected
Independent reflections
R(int)
5640
0.019
0.0430, 0.1025
0.0399, 0.1000
1.052
6405
0.048
0.0832, 0.1937
0.0737, 0.1841
1.131
8439
0.053
0.1095, 0.2831
0.0996, 0.2727
1.061
8344
0.040
0.1205, 0.3028
0.0972, 0.2732
1.043
R, wR2 (all)
R, wR2 [I > 2r(I)]
2
GOF on F
observed in the related complex containing 2,4-dimethylphenolate
˚
groups, while the Fe(1)–Cl(1) length of 2.2894(5) A in 1 is slightly
shorter. They are both only slightly shorter than Fe–Cl bonds
in octahedral iron(III) complexes possessing similar tetradentate
9
ligands, suggesting that the chloride ion should be labile in
solution. In 1, the pyridine nitrogen is quite strongly bound to the
˚
iron as shown by the short Fe(1)–N(2) bond length of 2.142(2) A;
the apical nitrogen is more weakly bound displaying a Fe(1)–
˚
N(1) bond distance of 2.2706(15) A. In 3 the Fe(1)–N(1) bond
˚
distance of 2.248(2) A is slightly shorter, whereas the Fe–N(2)
˚
length of 2.181(3) A is slightly longer than in both complex 1
ꢀ
MeMeNMe
8
III
2
and the previously reported FeCl[O
2
NN ]
. Typical Fe –
5,7,8
˚
N distances in octahedral systems are ∼2.15 A.
In 1 and
◦
◦
3
, the N(1)–Fe(1)–Cl(1) angles of 169.55(5) and 171.75(8) ,
respectively, are slightly distorted from the ideal linear geometry;
they are bent away from the phenolate groups and directed toward
the pendant nitrogen donors.
Fig. 2 Molecular structure (ORTEP) and numbering scheme of 3.
Ellipsoids are shown at 50% probability. Selected bond distances ( A˚ )
◦
and angles ( ): Fe(1)–Cl(1), 2.3051(10); Fe(1)–O(1), 1.865(2); Fe(1)–O(2),
◦
The Fe–O–C bond angles (Fe(1)–O(1)–C(7), 135.20(12) , and
1
.845(2); Fe(1)–N(1), 2.248(2); Fe(1)–N(2), 2.181(3); O(1)–C(3), 1.352(4);
O(2)–C(19), 1.353(4); O(1)–Fe(1)–O(2), 125.29(11); O(1)–Fe(1)–N(1),
7.94(10); O(1)–Fe(1)–N(2), 120.40(10); O(2)–Fe(1)–N(1), 86.97(10);
◦
◦
Fe(1)–O(2)–C(19), 128.34(12) , in 1; Fe(1)–O(1)–C(3), 129.3(2) ,
◦
8
and Fe(1)–O(2)–C(19), 138.3(2) , in 3) are larger than those ob-
served in the previously reported complex, FeCl[O NN ]
ꢀ
MeMeNMe
8
2
O(2)–Fe(1)–N(2), 112.08(11); N(1)–Fe(1)–N(2), 79.71(10); O(1)–Fe(1)–
Cl(1), 95.45(8); O(2)–Fe(1)–Cl(1), 97.11(7); N(1)–Fe(1)–Cl(1), 171.75(8);
N(2)–Fe(1)–Cl(1) 92.09(8); Fe(1)–O(1)–C(3), 129.3(2); Fe(1)–O(2)–C(19),
,
2
◦
which displays Fe–O–C bond angles of ∼122 . The angles in 1
and 3 are similar to or greater than those observed in octahedral
1
38.3(2).
◦
5,7,8
iron(III) complexes of phenolate ligands (∼128.5 ).
These
large bond angles suggest the O(1) and O(2) atoms possess
2
possessing diamine-bis(phenolate) ligands bearing 2,4-dimethyl-
smaller degrees of sp hybridization than their counterparts in
ꢀ
MeMeNMe
8
ꢀ MeMeNMe2
2
FeCl[O NN ]
. The six-membered chelate rings in 1 and 3
substituted aromatic groups (abbreviated FeCl[O
2
NN ]
).
2
These distances are shorter than the average octahedral Fe–O
are deviated from planarity further suggesting the out-of-plane
p-orbitals on O(1) and O(2) atoms are not ideally directed for
good overlap with the partially filled dp* orbital on the iron(III)
ion. The coordination geometry around iron(III) in both 1 and 3
is trigonal bipyramidal with the trigonality index s of 0.81 in 1
˚
bond length of 1.92 A suggesting relatively strong iron–oxygen
7–9
overlap, which is consistent with the lower coordination number.
The short Fe–O bond distance is also supported by the high
molar absorbtivity of the LMCT band (see below). The Fe(1)–
18
˚
and 0.86 in 3. As defined by Addison, Reedijk and co-workers,
Cl(1) bond distance of 2.3051(10) A in 3 is identical to that
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s = (b − a)/60, where b represents the N(1)–Fe(1)–Cl(1) angles
of 169.55 in 1 and 171.75 in 3, and a represents the angles
O(2)–Fe(1)–N(2) of 120.91 in 1 and O(1)–Fe(1)–N(2) of 120.40
overlap. Iron(III) bromide complex 6 displays shorter Fe–O bond
lengths of 1.836(5) A for Fe(1)–O(1) and 1.837(3) A for Fe(1)–
O(2) implying even stronger iron–oxygen overlap. The Fe(1)–Cl(1)
◦
◦
˚
˚
◦
◦
˚
in 3. For perfect trigonal bipyramidal and square pyramidal
geometries the s values are one and zero, respectively. Among
the structurally characterized five-coordinate trigonal bipyramidal
distance of 2.2392(13) A in 5 is shorter than that in the trigonal
bipyramidal complexes 1 and 3, above, but similar to the Fe–Cl
lengths observed in other square pyramidal iron(III) complexes
8,11
10,11
iron(III) complexes bearing a tetradentate ligand,
complexes
possessing salen or diamine-bis(phenolate) ligands.
The Fe(1)–
˚
1
and 3 display trigonality indices nearest to perfectly trigonal
Br(1) distance of 2.3683(11) A is shorter than that reported in
19
bipyramidal geometry.
other five-coordinate iron(III) bromide complexes. The nitrogen
donors in the ligand backbone exhibit bond lengths of 2.274(3)
and 2.161(3) A for Fe(1)–N(1) and Fe(1)–N(2), respectively, in 5,
The molecular structures of complexes 5 and 6 are shown in
˚
Fig. 3 and 4, respectively. Ligand [L
3
] enforces a square pyramidal
˚
geometry in the Fe(III) complexes. The iron atoms are bonded to
two phenolate oxygen atoms and two amine nitrogen atoms of
the ligand, which define the basal plane of the square pyramid.
The apical site is occupied by a chloride ion in 5 and a bromide
ion in 6. The Fe–O distances in 5 of 1.848(2) and 1.862(3) A for
Fe(1)–O(1) and Fe(1)–O(2), respectively, are consistent with those
and lengths of 2.154(4) and 2.264(4) A for Fe(1)–N(1) and Fe(1)–
N(2), respectively, in 6. The asymmetry in these bond distances
may be steric in nature, since the longer Fe–N interactions in
each molecule correspond to the nitrogen donor where the N-
methyl group is orientated cis to the halide ligand. Interestingly,
in both complexes 5 and 6 only the molecules where the methyl
groups of the ethylenediamine fragment are in trans orientation are
observed. The unit cell contains both trans enantiomers and none
of the cis isomer, in contrast to the structure reported by Girerd
and M u¨ nck and coworkers, which contains both trans isomers
and the cis isomer. The Fe–O–C bond angles in 5 are Fe(1)–O(1)–
C(10), 129.6(2) and Fe(1)–O(2)–C(22), 135.9(2) while 6 gives
angles for Fe(1)–O(1)–C(1) of 136.5(4) and Fe(1)–O(2)–C(22) of
29.1(3) . Hence, the degree of p
˚
observed in complexes 1 and 3, and suggest strong oxygen–iron
10
◦
◦
◦
◦
1
p
–dp* interaction in 5 and 6 is
similar to that in 1 and 3 with negligible effect resulting from
the geometry around the iron atom. The coordination geometry
around iron(III) in both 5 and 6 is square pyramidal with the
trigonality index s of 0.31 in 5 [b is given by O(2)–Fe(1)–N(1) and
a by O(1)–Fe(1)–N(2)] and 0.25 in 6 [b is given by O(1)–Fe(1)–N(2)
and a by O(2)–Fe(1)–N(1)].
Fig. 3 Molecular structure (ORTEP) and numbering scheme of 5.
Ellipsoids are shown at 50% probability. Selected bond distances ( A˚ )
◦
and angles ( ): Fe(1)–Cl(1), 2.2392(13); Fe(1)–O(1), 1.848(2); Fe(1)–O(2),
1
.862(3); Fe(1)–N(1), 2.274(3); Fe(1)–N(2), 2.161(3); O(1)–C(10), 1.358(4);
O(2)–C(22), 1.337(5); O(1)–Fe(1)–O(2), 94.13(13); O(1)–Fe(1)–N(1),
7.71(12); O(1)–Fe(1)–N(2), 139.37(13); O(2)–Fe(1)–N(1), 158.14(13);
Magnetic data
8
The magnetic susceptibility data for powdered samples of 1–6
were collected at room temperature using a Faraday balance.
O(2)–Fe(1)–N(2), 85.86(13); N(1)–Fe(1)–N(2), 78.75(12); O(1)–Fe(1)–
Cl(1), 112.29(10); O(2)–Fe(1)–Cl(1), 102.35(10); N(1)–Fe(1)–Cl(1),
9
1
/2
The magnetic moments [leff = (8v
between 5.9 and 6.0 l and thus were in the expected range for a
high-spin d ion, high-spin Fe(III). Complex 6, however, exhibited a
slightly elevated magnetic moment of 6.2 l at room temperature,
compared to 5.9 l observed for the related chloride complex, 5.
Although high-spin Fe(III) complexes sometimes exhibit magnetic
moments above 6.0 l , the high moment shown by the iron bro-
m
T) ] of complexes 1–5 were
7.03(10); N(2)–Fe(1)–Cl(1), 107.32(10); Fe(1)–O(1)–C(10), 129.6(2);
B
Fe(1)–O(2)–C(22), 135.9(2).
5
B
B
B
mide complex compared to the iron chloride derivative prompted
us to conduct further investigations into the magnetic behaviour of
these two compounds. Magnetic susceptibility data were acquired
for complexes 5 and 6 in the temperature range 2–300 K in an
applied magnetic field of 0.1 T (Fig. 5). Both complexes exhibit
only modest temperature dependent magnetic moments above
2
0 K. The magnetic behaviour of 5 and 6 show normal Curie–
Fig.
4
Molecular structure (ORTEP) and numbering scheme of
Weiss paramagnetism [v
m
= C/(T − h)]. The Weiss constants
6
.
Ellipsoids are shown at 50% probability. Selected bond dis-
for the two compounds are identical (h = −0.9 K) and indicate
◦
tances ( A˚ ) and angles ( ): Fe(1)–Br(1), 2.3683(11); Fe(1)–O(1),
antiferromagnetic independent iron(III) centres.
1
.836(5); Fe(1)–O(2), 1.837(3); Fe(1)–N(1), 2.154(4); Fe(1)–N(2), 2.264(4);
O(1)–C(1), 1.347(7); O(2)–C(22), 1.352(5); O(1)–Fe(1)–O(2), 94.37(17);
O(1)–Fe(1)–N(1), 86.06(18); O(1)–Fe(1)–N(2), 158.0(2); O(2)–Fe(1)–N(1),
Electronic absorption data
1
42.86(17); O(2)–Fe(1)–N(2), 88.22(15); N(1)–Fe(1)–N(2), 78.88(16);
Electronic absorption spectra of all the present complexes show
multiple intense bands in the UV and visible regions. In complexes
1–6, the absorption maxima observed in the near-UV regions
O(1)–Fe(1)–Br(1), 101.78(16); O(2)–Fe(1)–Br(1), 110.48(11); N(1)–Fe(1)–
Br(1), 105.73(13); N(2)–Fe(1)–Br(1), 97.74(14); Fe(1)–O(1)–C(1), 136.5(4);
Fe(1)–O(2)–C(22), 129.1(3).
2
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Fig. 5 Magnetic moment measurements for complexes 5 and 6.
Fig. 7 Electronic absorption spectra of 2 in methanol, acetonitrile, THF
and toluene solutions.
(
below 300 nm) are caused by p → p* transitions involving the
bands located near 340 and 640 nm (Fig. 8). A third intense, high
energy, absorption appears in the UV region.
phenolate units. Intense, high energy bands are also observed in
the region between 330 and 450 nm, which are assigned to charge
transfer transitions from the out-of-plane p orbital (HOMO) of
p
the phenolate oxygen to the half-filled dx2−y2 /dz2 orbital of high-
spin Fe(III). The lowest energy bands (between 450 and 700 nm)
are proposed to arise from charge-transfer transitions from the
in-plane p orbital of the phenolate to the half-filled dp* orbital of
p
Fe(III). A shift of these LMCT bands is observed on changing the
solvent used. Electronic absorption spectra of 1 and 2 are shown in
Fig. 6 and 7, respectively. In complex 1, the lowest energy LMCT
band exhibits a noticeable solvent-dependant shift according to
the following trend: methanol < THF < toluene < acetonitrile,
where the absorption spectrum in acetonitrile shows this band at
lowest wavelength (496 nm) down from 607 nm in methanol. The
absorption spectra in toluene and THF display this LMCT band
at 500 and 530 nm, respectively. In complex 2, a similar trend in
solvent effect is observed giving LMCT bands at 602, 543, 503,
5
02 nm, respectively. Complexes 3 and 4 were very poorly soluble in
Fig. 8 Electronic absorption spectrum of 5 in methanol solution.
all of the above solvents, hence electronic absorption spectra were
acquired in acetone. Three strong absorption bands were observed
for each complex at ca. 335, 405, and 486 nm. Complexes 5 and
6
show virtually identical spectra in methanol with two intense
Conclusion
A
series of iron(III) complexes supported by diamine-
bis(phenolate) ligands has been prepared. All six complexes
reported are five-coordinate and exhibit either a mildly distorted
trigonal bipyramidal or square pyramidal geometry depending on
the ligand employed. Representative complexes 1, 3, 5 and 6 have
been structurally characterized by single crystal X-ray diffraction.
Additionally, all of the paramagnetic complexes have been ana-
lytically verified by elemental analysis and MALDI-TOF mass
spectrometry. Magnetic moment measurements confirm high-
5
spin d electronic configurations. Electronic absorption spectra
in the UV-vis range exhibit strong charge transfer bands which
are strongly solvent dependant and rapid exchange of the halide
(
chloride or bromide) ligand in solution with strongly coordination
solvents is expected.
Our own interest in these new complexes is directed towards
their use as inexpensive, relatively non-toxic catalysts for reactions
applicable to organic synthesis. For example, our use of related
Fe(III) complexes as catalysts for C–C cross coupling has recently
Fig. 6 Electronic absorption spectra of 1 in methanol, acetonitrile, THF
and toluene solutions.
This journal is © The Royal Society of Chemistry 2008
Dalton Trans., 2008, 2991–2998 | 2995

View Article Online
13
been communicated and further investigations of the reaction
chemistry of these complexes are currently in progress. Results
from these studies will be reported in due time.
(CH
IR (cm ): 3350 (OH); 2955 (C–H); 1603 (C=C, phenyl ring). Anal.
calcd for C30 : C, 78.22; H, 8.75; N, 6.08%. Found C, 78.30;
H, 8.89; N, 6.10%.
2
); 55.5 (CH
2
); 35.0 (C(CH
3
)
3
); 29.8 (C(CH
3
)
3
); 21.0 (ArCH ).
3
−
1
H
40
N
2
O
2
Experimental
[
L
1
]FeCl 1. To
a
methanolic slurry of recrystallized
ꢀ
BuMePy
H
2
[O
2
NN ]
, H
2
[L
1
] (3.00 g, 6.52 mmol) was added a solution
General experimental conditions
of anhydrous FeCl
3
(1.06 g, 6.52 mmol) in methanol resulting in
Unless otherwise stated, the handling of anhydrous FeX
3
salts was
an intense blue solution. To this solution was added triethylamine
(1.32 g, 13.0 mmol) and the resulting mixture was stirred for 2 h.
Solvent was removed under vacuum; the residue was extracted
with toluene and filtered through Celite. Removal of solvent
under vacuum yielded 3.19 g (89%) of analytically pure dark-blue
product. Crystals suitable for X-ray diffraction were obtained by
slow evaporation of a solution of 1 in a 1 : 1 mixture of hexanes
performed under an atmosphere of dry nitrogen by working in a
glove box. Best results were obtained using degassed methanol
and performing the syntheses under dry nitrogen using standard
Schlenk techniques. All manipulations of final products were
performed in air by using simple bench top techniques. Reagents
were purchased either from Aldrich or Alfa Aesar and used
3
2
without further purification. The syntheses of H
were conducted by modified literature procedure in water, as
described below for the synthesis of H [L ]. High purity anhydrous
FeCl (99.99+%) was purchased in ampoules from Aldrich. FeBr
99%) was purchased from Strem.
2
[L
2
] and H
2
[L
3
]
and acetone. Anal. calcd for C30
H
38ClFeN
2
2
O : C, 65.52; H, 6.96;
N, 5.09%. Found C, 65.83; H, 6.92; N, 4.93%. MS (MALDI-TOF)
+
+
m/z (%, ion): 548.98 (20, [M] ); 514.05 (100, [M − Cl] ). UV-vis
2
1
kmax, nm (e): (methanol) 607 (1097), 345 (1450); (acetonitrile) 496
3
3
(
(1110), 332 (1840); (THF) 530 (940), 335 (1910); (toluene) 500
◦
(
1000), 327 (1840). leff (solid, 25 C): 5.9 l
B
.
Instrumentation
[
L
1
]FeBr 2. An identical procedure to that described for 1,
above, was employed using FeBr (1.93 g 6.52 mmol). Yield: 3.22 g
83%). Anal. calcd for C30
MALDI-TOF MS spectra were recorded on an Applied Biosys-
tems Voyager DE-PRO equipped with a reflectron, delayed ion
extraction and high performance nitrogen laser (337 nm). Samples
were prepared at a concentration of 0.03 mg L in methanol.
Anthracene was used as the matrix, which was mixed at a
concentration of 0.03 mg L . UV-vis spectra were recorded
on an Ocean Optics USB4000+ fiber optic spectrophotometer.
Room temperature magnetic moments were determined by using a
Metler BE 21 Faraday balance and variable temperature magnetic
moments were measured on powdered samples at 1000 G using
a Quantum Design MPMS-5S SQUID Magnetometer. The data
were corrected for background and for the diamagnetism of all
atoms. Elemental analyses were carried out by Guelph Chemical
Laboratories, Guelph, ON, Canada. Crystal structures were solved
on an AFC8-Saturn 70 single crystal X-ray diffractometer from
Rigaku/MSC, equipped with an X-stream 2000 low temperature
system.
3
(
H
38BrFeN
2
O
2
: C, 60.62; H, 6.44; N,
4
.71%. Found C, 60.85; H, 6.71; N, 4.67%. MS (MALDI-TOF)
+
+
−
1
m/z (%, ion): 593.03 (20, [M] ), 514.18 (100, [M − Br] ), 461.26
+
(
(
(
10, [M − FeBr] ). UV-vis kmax, nm (e): (methanol) 602 (2120), 345
−
1
2650); (acetonitrile) 502 (1600), 405 (1690), 339 (2630); (THF) 543
1980), 346 (3490); (toluene) 503 (1600), 409 (1870), 340 (2670).
eff (solid, 25 C): 6.0 l
◦
l
B
.
[
L
2
]FeCl 3. To
a
methanolic slurry of recrystallized
] (2.00 g, 4.54 mmol) was added a
(736 mg, 4.54 mmol) in methanol
ꢀ
BuMeNMe
2
H
2
[O
2
NN ]
, H
2
[L
2
solution of anhydrous FeCl
3
resulting in an intense blue solution. To this solution was added
triethylamine (919 mg, 9.08 mmol) and the resulting mixture was
stirred for 10 h. A dark precipate formed, which was collected
on a glass frit, washed with cold methanol and dried in vacuo to
yield 1.85 g (85%) of analytically pure dark-blue product. Crystals
suitable for X-ray diffraction were obtained by slow evaporation
of a solution of 3 in acetone. Anal. calcd for C28
H
42ClFeN
2
O
2
: C,
Synthesis of compounds
6
3.46; H, 7.99; N, 5.29%. Found C, 63.72; H, 8.28; N, 5.33%. MS
+
ꢀ
BuMePy
(MALDI-TOF) m/z (%, ion): 528.84 (55, [M] ), 493.91 (100, [M −
H
2
[O
2
NN ]
(H
2
[L ]). A solution of 2-tert-butyl-4-
1
+
+
Cl] ), 439.25 (32, [M − FeCl] ). UV-vis kmax, nm (e): (acetone) 482
methylphenol (20.236 g, 0.1232 mol), aminomethylpyridine
6.61 g, 0.0616 mol), and 37% aqueous formaldehyde (9.17 mL,
.1232 mol) in water (50 mL) was stirred and refluxed for 12 h.
◦
(4494), 397 (4247), 334 (7157). leff (solid, 25 C): 6.0 l
B
.
(
0
[
L
2
]FeBr 4. An identical procedure to that described for 3,
above, was employed using FeBr (1.34 g 4.54 mmol). Yield: 1.92 g
81%). Anal. calcd for C28
Upon cooling, a large quantity of beige solid formed. The solvents
were decanted, and the remaining solid residue was washed with
cold methanol to give a pure, white powder (26.95 g, 95% yield).
3
(
H
42BrFeN
2
O
2
: C, 58.55; H, 7.37; N,
4
.88%. Found C, 58.72; H, 7.50; N, 4.88%. MS (MALDI-TOF)
Crystalline product was obtained by slow cooling of a hot diethyl
+
+
m/z (%, ion): 575.05 (30, [M] ), 494.18 (100, [M − Br] ), 439.26
1
ether solution. H NMR (500 MHz, CDCl
3
, 298 K): d 10.47 (s,
+
(
(
15, [M − FeBr] ). UV-vis kmax, nm (e): (acetone) 490 (4436), 411
3
3
–
OH, 2H); 8.69 (d, JH1–H2 = 5.8 Hz, PyH, 1H); 7.70 (ddd, JH3–H4
=
◦
5288), 337 (7051). leff (solid, 25 C): 5.9 l
B
.
3
4
8
.2 Hz, JH3–H2 = 7.0 Hz, JH3–H1 = 1.8 Hz, PyH, 1H); 7.28 (dd,
3
3
3
J
H2–H1 = 5.8 Hz, JH2–H3 = 7.0 Hz, PyH, 1H); 7.11 (d, JH4–H3
=
[L
[N
3
]FeCl 5. To a methanolic slurry of recrystallized
BuBu
8
.2 Hz, PyH, 1H); 7.00 (s, ArH, 2H); 6.74 (s, ArH, 2H); 3.81 (s,
H
2
2
O
2
]
, H
2
[L
3
], (2.00 g, 3.81 mmol) was added a solution
(0.62 g, 3.81 mmol) in methanol resulting in
CH
2
, 2H); 3.75 (s, CH
2
, 4H); 2.24 (s, CH
3
, 6H); 1.39 (s, C(CH
3
)
3
,
of anhydrous FeCl
3
1
3
1
1
1
1
8H). C{ H} NMR (125 MHz, CDCl
3
, 298 K): d 156.3 (Py);
an intense blue solution. To this solution was added triethylamine
(771 mg, 7.62 mmol) and the resulting mixture was stirred for 2 h.
Solvent was removed under vacuum; the residue was extracted
54.1 (ArC–OH); 148.3 (Py); 137.8 (Py); 137.3 (Ar); 129.2 (Ar);
27.4 (Ar); 127.2 (Ar); 124.1 (Py); 122.8 (Py); 122.3 (Ar); 56.4
2
996 | Dalton Trans., 2008, 2991–2998
This journal is © The Royal Society of Chemistry 2008

View Article Online
with methanol and filtered through Celite. Removal of solvent
under vacuum yielded a powdered dark-blue product. Removal of
solvents yielded 2.07 g (89%) of analytically pure product. Crystals
suitable for X-ray diffraction were obtained by slow evaporation
of a solution of 5 in a 1 : 1 mixture of hexanes and acetone. Anal.
Research Awards to P. K. and A. K. C.). P. K. also thanks the
Canadian Inorganic Chemistry Exchange (ICE) Program for a
summer work term placement. We thank Prof. F. M. Kerton for
use of a UV-vis spectrometer (acquired with the aid of an NSERC
RTI-I grant).
calcd for C34
H
54ClFeN
2
2
O : C, 66.50; H, 8.86; N, 4.56%. Found
C, 66.57; H, 9.05; N, 4.13%. MS (MALDI-TOF) m/z (%, ion):
Notes and references
+
+
+
6
13.20 (40, [M] ), 578.24 (100, [M − Cl] ), 525.34 (32, [L
3
] ). UV-
◦
vis (CH
3
OH) kmax, nm (e): 638 (4834), 343 (4828). leff (solid, 25 C):
1 S. Groysman, I. Goldberg, M. Kol, E. Genizi and Z. Goldschmidt,
Inorg. Chim. Acta, 2003, 345, 137; E. Y. Tshuva, S. Groysman, I.
Goldberg, M. Kol and Z. Goldschmidt, Organometallics, 2002, 21, 662;
A. Yeori, I. Goldberg and M. Kol, Macromolecules, 2007, 40, 8521; A.
Yeori, I. Goldberg, M. Shuster and M. Kol, J. Am. Chem. Soc., 2006,
5
.9 l .
B
[L
3
]FeBr 6. An identical procedure to that described for 5,
above, was employed using FeBr (1.13 g, 3.82 mmol). Yield: 2.47 g
98%). Crystals suitable for X-ray diffraction were obtained by
slow evaporation of a solution of 6 in a 1 : 1 mixture of hexanes
and acetone. Anal. calcd for C34 : C, 62.01; H, 8.26;
N, 4.25%. Found C, 62.34; H, 8.45; N 4.22%. MS (MALDI-TOF)
3
1
28, 13062; S. Gendler, S. Segal, I. Goldberg, Z. Goldschmidt and
(
M. Kol, Inorg. Chem., 2006, 45, 4783; S. Segal, I. Goldberg and M.
Kol, Organometallics, 2005, 24, 200; S. Groysman, E. Y. Tshuva, I.
Goldberg, M. Kol, Z. Goldschmidt and M. Shuster, Organometallics,
H
54BrFeN
2
O
2
2
004, 23, 5291; C. Lorber, F. Wolff, R. Choukroun and L. Vendier,
Eur. J. Inorg. Chem., 2005, 2850; A. J. Chmura, M. G. Davidson,
M. D. Jones, M. D. Lunn, M. F. Mahon, A. F. Johnson, P. Khunkam-
choo, S. L. Roberts and S. S. F. Wong, Macromolecules, 2006, 39,
7250.
+
+
m/z (%, ion): 656.89 (25, [M] ), 578.04 (100, [M − Br] ), 525.16
+
(
18, [L
3
] ). UV-vis (CH
3
OH) kmax, nm (e): 634 (5602), 343 (4888).
◦
l
eff (solid, 25 C): 6.2 l
B
.
2
E. Y. Tshuva, I. Goldberg and M. Kol, J. Am. Chem. Soc., 2000, 122,
1
0706.
X-Ray crystallography
3 Y. Sarazin, R. H. Howard, D. L. Hughes, S. M. Humphrey and M.
Bochmann, Dalton Trans., 2006, 340.
Crystallographic data for compounds 1, 3, 5 and 6 are summarized
in Table 1. All data collections were performed on a Rigaku AFC8-
Saturn 70 equipped with a CCD area detector, using graphite
4 F. M. Kerton, A. C. Whitwood and C. E. Willans, Dalton Trans., 2004,
2
237; H. E. Dyer, S. Huijser, A. D. Schwarz, C. Wang, R. Duchateau
and P. Mountford, Dalton Trans., 2008, 32; F. Bonnet, A. R. Cowley
and P. Mountford, Inorg. Chem., 2005, 44, 9046; A. Amgoune, C. M.
Thomas and J. F. Carpentier, Pure Appl. Chem., 2007, 79, 2013; A.
Amgoune, C. M. Thomas, T. Roisnel and J. F. Carpentier, Chem.–
Eur. J., 2005, 12, 169; Y. Yao, M. Ma, X. Xu, Y. Zhang, Q. Shen and
W. T. Wong, Organometallics, 2005, 24, 4014.
˚
monochromated Mo-Ka radiation (k = 0.71073 A). Suitable
crystals were selected and mounted on glass fibers using Paratone-
◦
N oil and freezing to either −120 or −160 C. In each case the
20
data were processed and corrected for Lorentz and polarization
5
6
For late transition metal complexes of amine-bis(phenolate) ligands
see: T. Nagataki and S. Itoh, Chem. Lett., 2007, 36, 748; L. Rodriguez,
E. Labisbal, A. Sousa-Pedrares, J. A. Garcia-Vazquez, J. Romero, M.
Luz Duran, J. A. Real and A. Sousa, Inorg. Chem., 2006, 45, 7903;
A. Philibert, F. Thomas, C. Philouze, S. Hamman, E. Saint-Aman and
J.-L. Pierre, Chem.–Eur. J., 2003, 9, 3803; O. Rotthaus, F. Thomas, O.
Jarjayes, C. Philouze, E. Saint-Aman and J.-L. Pierre, Chem.–Eur. J.,
2
1
effects and absorption. Neutral atom scattering factors for all
non-hydrogen atoms were taken from the International Tables
2
2
for X-ray Crystallography. All structures were solved by direct
2
3
methods using SIR92 and expanded using Fourier techniques
24
(
DIRDIF99). All non-hydrogen atoms were refined anisotropi-
2
006, 12, 6953.
cally. Hydrogen atoms were refined using the riding model.
For metal complexes of phenoxytriamine ligands see: W. A. Chomitz,
S. G. Minasian, A. D. Sutton and J. Arnold, Inorg. Chem., 2007, 46,
7199; H. Adams, N. A. Bailey, I. K. Campbell, D. E. Fenton and Q. Y.
He, J. Chem. Soc., Dalton Trans., 1996, 2233; M. C. B. de Oliveira,
M. Scarpellini, A. Neves, H. Terenzi, A. J. Bortoluzzi, B. Szpoganics,
A. Greatti, A. S. Mangrich, E. M. de Souza, P. M. Fernandez and
M. R. Soares, Inorg. Chem., 2005, 44, 921; S. Ito, S. Nishino, H. Itoh,
S. Ohba and Y. Nishida, Polyhedron, 1998, 17, 1637; I. A. Koval, M.
Huisman, A. F. Stassen, P. Gamez, M. Lutz, A. L. Spek and J. Reedijk,
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Troeltzsch, Inorg. Chim. Acta, 2004, 357, 619; N. Reddig, D. Pursche
and A. Rompel, Dalton Trans., 2004, 1474; N. Reddig, D. Pursche, B.
Krebs and A. Rompel, Inorg. Chim. Acta, 2004, 357, 2703; N. Reddig,
D. Pursche, M. Kloskowski, C. Slinn, S. M. Baldeau and A. Rompel,
Eur. J. Inorg. Chem., 2004, 879; S. Sarkar, A. Mondal, J. Ribas, M. G. B.
Drew, K. Pramanik and K. K. Rajak, Eur. J. Inorg. Chem., 2004, 4633;
Y. Shimazaki, S. Huth, S. Karasawa, S. Hirota, Y. Naruta and O.
Yamauchi, Inorg. Chem., 2004, 43, 7816.
25
Anomalous dispersion effects were included in Fcalc
;
the
values for Df ꢀ and Df were those of Creagh and McAuley.
ꢀꢀ
26
The values for the mass attenuation coefficients are those of
27
Creagh and Hubbell. All calculations were performed using the
28
CrystalStructure crystallographic software package except for
29
refinement, which was performed using SHELXL-97. The struc-
ture of 3 contains one molecule of acetone per asymmetric unit. In
the structures of 5 and 6, no suitable point model could be found
for a region of diffuse electron density in the asymmetric unit
that corresponded to a partial occupancy n-hexane molecule. The
30
31
Platon Squeeze procedure was applied in the solution of 5 to
recover 142 electrons per unit cell in two voids (total volume
3
˚
1
946 A ); this represents 17.75 electrons per asymmetric unit.
In 6, it was applied to recover 342 electrons per unit cell in
two voids (total volume 2032 A ); this represents 42.75 electrons
per asymmetric unit. Structural illustrations were created using
ORTEP-III for Windows.
CCDC reference numbers 677420–677423. For crystallographic
data in CIF or other electronic format see DOI: 10.1039/b802274g
7
E. Safaei, T. Weyhermuller, E. Bothe, K. Wieghardt and P. Chaudhuri,
Eur. J. Inorg. Chem., 2007, 2334; T. Weyhermuller, T. K. Paine, E.
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M. Velusamy, R. Mayilmurugan and M. Palaniandavar, Inorg. Chem.,
3
˚
3
2
2
004, 43, 6284; M. Merkel, F. K. Muller and B. Krebs, Inorg. Chim.
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Adsetts, E. W. Ainscough, A. M. Brodie and M. J. Morris, Inorg. Chem.,
2
005, 44, 3070.
Acknowledgements
8
9
M. Velusamy, M. Palaniandavar, R. S. Gopalan and G. U. Kulkarni,
Inorg. Chem., 2003, 42, 8283.
R. Viswanathan, M. Palaniandavar, T. Balasubramanian and T. P.
Muthiah, Inorg. Chem., 1998, 37, 2943.
We thank Memorial University and the NSERC of Canada for
funding (Discovery Grant to C. M. K. and Undergraduate Student
This journal is © The Royal Society of Chemistry 2008
Dalton Trans., 2008, 2991–2998 | 2997

View Article Online
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