Preparation and crystal structures of manganese, iron, and cobalt complexes of the bis[di(2-pyridyl)methyl]amine (bdpma) ligand and its oxidative degradation product 1,3,3-tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin- 4-ium (tpip); Origin of the bdpma fragility

Article abstract of DOI:10.1002/(SICI)1521-3765(19990604)5:6<1766::AID-CHEM1766>3.0.CO;2-Z

The synthesis and structural characterization of manganese, iron, and cobalt complexes of bis[di(2-pyridyl)methyl]amine (bdpma) were investigated. The bdpma ligand can give rise to mono- or dimeric complexes. Moreover, bdpma can undergo oxidative degradation leading to 1,3,3-tris(2-pyridyl)-3H- imidazo[1,5-a]pyridin-4-ium (tpip) or to starting materials used for the preparation of bdpma. During attempts to prepare manganese, iron, or cobalt complexes of the tpip ligand, two classes of compounds were obtained. The first class corresponded to the tpip cation with a simple exchange of counterion and the second class led to a new type of complex, which involved a modification of tpip and contained the N-(di(2-pyridyl)methoxymethyl)(di(2- pyridyl)imine) (dpmmdpi) ligand. This work has allowed us to understand the fragility of the bdpma ligand, which is due to the easily activated benzylic C-H bonds in the α position to the heteroatom.

Full text of DOI:10.1002/(SICI)1521-3765(19990604)5:6<1766::AID-CHEM1766>3.0.CO;2-Z

FULL PAPER
Preparation and Crystal Structures of Manganese, Iron, and Cobalt
Complexes of the Bis[di(2-pyridyl)methyl]amine (bdpma) Ligand and Its
Oxidative Degradation Product 1,3,3-Tris(2-pyridyl)-3H-imidazo[1,5-a]-
pyridin-4-ium (tpip); Origin of the bdpma Fragility
Catherine Hemmert, Michael Renz, Heinz Gornitzka,
St e phanie Soulet, and Bernard Meunier*[a]
Abstract: The synthesis and structural
characterization of manganese, iron, and
cobalt complexes of bis[di(2-pyridyl)-
methyl]amine (bdpma) were investigat-
ed. The bdpma ligand can give rise to
mono- or dimeric complexes. Moreover,
bdpma can undergo oxidative degrada-
tion leading to 1,3,3-tris(2-pyridyl)-3H-
imidazo[1,5-a]pyridin-4-ium (tpip) or to
starting materials used for the prepara-
tion of bdpma. During attempts to
prepare manganese, iron, or cobalt com-
plexes of the tpip ligand, two classes of
compounds were obtained. The first
class corresponded to the tpip cation
with a simple exchange of counterion
and the second class led to a new type of
complex, which involved a modification
of tpip and contained the N-(di(2-pyr-
idyl)methoxymethyl)(di(2-pyridyl)im-
ine) (dpmmdpi) ligand. This work has
allowed us to understand the fragility of
the bdpma ligand, which is due to the
easily activated benzylic C�H bonds in
Keywords:
cobalt
´
iron
´
manganese ´ N ligands ´ oxidative
degradation
the a position to the heteroatom.
FePcS).[5] The latter complex has also been used in the
oxidative degradation of 2,4,6-trichlorophenol (TCP), a major
pollutant in the chlorine bleaching of wood pulp.[ The
catalytic oxidation of the poorly biodegradable catechol or
TCP substrates led not only to the corresponding benzoqui-
nones but also to ring cleavage products.[ However, little is
known about the potential use of nonheme mononuclear
complexes in the catalytic oxidation of such pollutants. In
order to investigate the activity of this category of catalysts,
we decided to prepare a new polypyridine ligand and to
determine the capacity of its iron or manganese complexes as
catalysts in TCP degradation (for a recent report on the
catalytic activity of an iron tetrapyridyl complex in alkane
oxidation, see ref. [7]).
Introduction
6]
Catechol dioxygenases, a class of nonheme iron enzymes, are
implicated in important metabolic reactions of environmental
relevance. This class of enzymes catalyzes the oxidative
[
1]
5, 6]
cleavage of intra- or extradiol C�C bonds of various catechols
[
1]
using molecular oxygen. Several synthetic functional models
have been described. Among these, iron(iii) complexes
Fe(L)(dbc)], where L is a tetradentate, tripodal ligand
[
(
for example L ˆ N,N'-dimethyl-2,11-diaza[3.3](2,6)pyridino-
[
2
]
[
3
]
phane or tris[(2-pypyridyl)methyl]amine; dbc ˆ 3,5-di-
tert-butylcatecholate dianion) react with dioxygen to afford
oxidative cleavage of dbc, mimicking the intradiol cleavage of
catechol dioxygenases. Funabiki et al. recently reported that
3
- and 4-chlorocatechols that contain an electron-withdrawing
We recently reported the synthesis of the new symmetric
polypyridine ligand bis[di(2-pyridyl)methyl]amine (bdpma,
Scheme 1). The bdpma ligand was designed in analogy to
substituent can also be oxidatively cleaved with molecular
oxygen, using a nonheme iron(iii) complex.
[
4]
[8]
In our group, we recently observed the oxidative degrada-
tion of different catechols using hydrogen peroxide and cobalt
or iron tetrasulfophthalocyanine complexes (CoPcS or
the N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine
(N4Py) ligand.[ bdpma was synthesized in a one-pot, two-
step reaction consisting of refluxing di(2-pyridyl)methylamine
7]
(
A) and di(2-pyridyl)ketone (B) in isopropanol in the
presence of molecular sieves and acetic acid, and subsequent
reduction with zinc dust (Scheme 1). The main advantages of
this synthesis are the good yield (70%) and the ability to
obtain bdpma in large amounts without using hazardous
reagents or potentially explosive materials (like perchlorate
salts).[ The coordination of pentadentate bdpma to transition
[
a] Dr. B. Meunier, Dr. C. Hemmert, Dr. M. Renz,
Dr. H. Gornitzka, S. Soulet
Laboratoire de Chimie de Coordination du CNRS
205 route de Narbonne, F-31077 Toulouse cedex 4 (France)
Fax : (‡ 33)5-61-55-30-03
8]
E-mail: bmeunier@lcc-toulouse.fr
1
766
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Chem. Eur. J. 1999, 5, No. 6

1
766±1774
our efforts to crystallize these different compounds we
discovered the versatile behavior of the bdpma ligand, which
gives rise to mono- or dimeric complexes. Moreover, the
bdpma ligand can also undergo oxidative degradation to form
the cationic species 1,3,3-tris-(2-pyridyl)-3H-imidazo[1,5-
[10]
a]pyridin-4-ium (tpip; for the structure see Scheme 1) or,
after hydrolysis, di-(2-pyridyl)ketone (B), one of the starting
materials used for the preparation of BDMPA. Finally, we
evaluated the ability of tpip to act as a ligand, using
manganese, iron, and cobalt salts. This work allowed us to
III
understand the low catalytic activity of the [Fe (bdpma)]-
(
NO ) complex and to discuss the origin of the fragility of the
3 3
bdpma ligand.
Results
Complexes containing the intact bdpma ligand. X-ray struc-
II
tures and characterizations of [Mn (bdpma)Cl ] (1) and
2
Scheme 1. Synthesis of bis[di(2-pyridyl)methyl]amine (bdpma) and 1,3,3-
tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin-4-ium (tpip) via the imine C.
Reagents and conditions: i) molecular sieves 3 Š, 1 h; ii) AcOH, reflux,
III
[
Fe (bdpma) (O)Cl ]Cl (MeOH) (2): Three different tran-
2 2 2 2 2
sition metals (manganese, iron, and cobalt) were used in the
present study, but only two complexes containing the intact
bdpma ligand were observed. Complex 1 was obtained on
5
2
± 6 h; iii) Zn; iv) MnO .
mixing methanolic solutions of MnCl and bdpma, followed
2
metals should leave one site free (in an octahedral geometry)
for catalytic oxidation activity. We thus compared the catalytic
activity of the mononuclear iron(iii) complex [Fe (bdpma)]-
by crystallization in a methyl tert-butyl ether atmosphere. By
III
III
the same method, under a nitrogen atmosphere, an Fe m-oxo
dimer (complex 2) was isolated when starting from FeCl
2
(
NO3)3 with macrocyclic complexes in the oxidation of
II
[
9]
and bdpma. The complexes [Mn (bdpma)Cl
2
] (1) and
pollutants. This complex catalyzed the oxidative degrada-
tion of polychlorophenols in the presence of potassium
monopersulfate as oxidant. Unfortunately, the oxidation
stopped at the quinone level without the formation of ring
cleavage products, and the catalyst was degraded after a few
III
[
Fe (bdpma) (O)Cl ]Cl (MeOH) (2) are depicted in
2
2 2 2 2
Scheme 2. Selected bond lengths and angles of complexes 1
and 2 are listed in Tables 1 and 2, respectively. The arrange-
ment of the BDMPA ligand around the metal centers is
similar in both complexes.
[
9]
catalytic cycles (22 ± 27).
The crystal structure of complex 1 consists of a mononu-
Here we report the synthesis and structural characteriza-
tion of manganese, iron, and cobalt complexes of bdpma. In
II
clear, neutral [Mn (bdpma)Cl ] entity in a distorted octahe-
2
Abstract in French: Nous avons synthØtisØ et caractØrisØ par
diffraction aux rayons X des complexes de mangan›se, fer et
cobalt utilisant le ligand bis[di(2-pyridyl)methyl]amine
(bdpma). Des complexes de type monom›re et dim›re ont ØtØ
respectivement isolØs avec le mangan›se et le fer. bdpma peut
Øgalement subir, en prØsence dꢀacides de Lewis, une dØgrada-
tion par oxydation conduisant soit au ligand cationique 1,3,3-
tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin-4-ium (tpip), soit aux
prØcurseurs utilisØs pour la prØparation de bdpma. Des essais
de complexation du ligand tpip par le mangan›se, le fer ou le
cobalt ont conduit à deux catØgories de composØs. La premi›re
correspond au cation tpip avec un simple Øchange de contre-
ion. La seconde est reprØsentØe par un nouveau complexe qui
implique une modification du composØ tpip conduisant au
ligand N-(di(2-pyridyl)mØthoxymØthyl)(di(2-pyridyl)imine)
(dpmmdpi). LꢀØtude dØtaillØe des diffØrents complexes et
composØs obtenus nous a permis de mettre en Øvidence la
fragilitØ du ligand bdpma, liØe à une activation des liaisons
Scheme 2. Complexes containing the intact bdpma ligand: X-ray struc-
�
H situØes en position a de lꢀatome dꢀazote de
II
III
2
benzyliques C
2
tures of [Mn (bdpma)Cl ] (1) and [Fe
(bdpma)
2
(O)Cl
]Cl
(MeOH)
(2)
2
2
2
lꢀamine secondaire.
(in the latter structure, two chlorides and the two methanol molecules have
been omitted for clarity).
Chem. Eur. J. 1999, 5, No. 6
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1767

B. Meunier et al.
FULL PAPER
II
Table 1. Selected bond lengths [Š] and angles [8] for [Mn (bdpma)Cl
2
] (1).
both iron centers are occupied by terminal chloride ligands at
an unusually short Fe ± Cl distance of 2.284(2) Š. The
chlorides are orientated cis to each other and trans to the
secondary amines. The Fe ± O and Fe ´´´ Fe distances of
Mn ± N(1)
Mn ± N(2)
Mn ± N(3)
2.326(2)
2.348(2)
2.337(3)
Mn ± N(4)
Mn ± Cl(1)
Mn ± Cl(2)
2.279(2)
2.413(1)
2.432(1)
N(4)-Mn-N(1)
N(4)-Mn-N(3)
N(1)-Mn-N(3)
N(4)-Mn-N(2)
N(1)-Mn-N(2)
N(3)-Mn-N(2)
N(4)-Mn-Cl(1)
N(1)-Mn-Cl(1)
72.03(8)
143.39(9)
72.09(8)
95.54(9)
70.38(9)
79.12(8)
98.01(7)
157.90(7)
N(3)-Mn-Cl(1)
N(2)-Mn-Cl(1)
N(4)-Mn-Cl(2)
N(1)-Mn-Cl(2)
N(3)-Mn-Cl(2)
N(2)-Mn-Cl(2)
Cl(1)-Mn-Cl(2)
118.19(6)
91.62(6)
90.28(7)
98.37(7)
87.87(7)
164.86(7)
101.41(6)
1
.782(1) and 3.563 Š respectively and the Fe ± O ± Fe angle
of 178.6(4)8 are typical values for linear (m-oxo)-diiron(iii)
core structures.[
11]
The Mössbauer spectrum of 2 recorded at 80 K consisted of
a single quadrupole doublet with an isomer shift d ˆ 0.46 mm/
s (relative to metallic iron at room temperature), character-
istic of two high-spin ferric centers. The quadrupole splitting,
�
1
DEq ˆ 1.37 mms , is small when compared to those generally
�
1
Table 2. Selected
bond
lengths
[Š]
and
angles
[8]
for
observed (in the range 1.5 ± 2.0 mms ) for oxo-bridged
III
[13]
[
Fe
2
(bdpma)
2
(O)Cl
2
]Cl
2
(MeOH)
2
(2).
dinuclear complexes.
Susceptibility data for complex 2
Fe(1) ± N(1)
Fe(1) ± N(2)
Fe(1) ± N(3)
Fe ´´´ Fe
2.323(5)
2.163(5)
2.148(6)
3.563
Fe(1) ± N(5)
Fe(1) ± Cl(1)
Fe(1) ± O(1)
2.203(5)
2.284(2)
1.782(1)
were recorded from 300 to 5 K, under a magnetic field of 5 T.
3
� 1
At 300 K, c T is equal to 0.81 cm Kmol . This value was
M
III
below that expected for two noninteracting Fe ions having g
3
� 1
values of 2.0 (8.75 cm Kmol ). When the temperature was
O(1)-Fe(1)-N(3)
O(1)-Fe(1)-N(2)
N(3)-Fe(1)-N(2)
O(1)-Fe(1)-N(5)
N(3)-Fe(1)-N(5)
N(2)-Fe(1)-N(5)
O(1)-Fe(1)-Cl(1)
N(3)-Fe(1)-Cl(1)
97.34(14)
94.68(14)
151.7(2)
95.4(2)
77.5(2)
75.9(2)
N(2)-Fe(1)-Cl(1)
N(5)-Fe(1)-Cl(1)
O(1)-Fe(1)-N(1)
N(3)-Fe(1)-N(1)
N(2)-Fe(1)-N(1)
N(5)-Fe(1)-N(1)
Cl(1)-Fe(1)-N(1)
Fe(1)-O(1)-Fe(2)
100.89(15)
161.80(13)
167.0(2)
82.66(18)
80.00(19)
71.83(18)
89.98(14)
178.6(4)
3
� 1
lowered, c T decreased to a value of 0.17 cm Kmol at 5 K.
M
This behavior is indicative of an antiferromagnetic interaction
III
between the two Fe ions. The experimental results obtained
from 5 to 300 K can be analyzed based on a spin Hamiltonian
for isotropic exchange H ˆ � JS ´ S . The experimental data
Fe
Fe
102.7(2)
101.30(16)
[14]
were fitted to the corresponding expression for two high-
III
spin Fe local spins (S ˆ 5/2), corrected for an uncoupled
impurity. The best fit yielded an interaction parameter J of
�
1
dral geometry. The square plane is formed by three nitrogen
donor atoms of bdpma, two pyridine nitrogens arising from
each di-(2-pyridyl)methyl moiety and the secondary amine
nitrogen, and a chloride. The equatorial Mn ± N bond lengths
are typical, ranging from 2.279(2) to 2.337(3) Š. The axial
positions, occupied by another pyridine nitrogen of the bdpma
ligand and a second chloride, have longer bonds, as expected
� 245 cm , g ˆ 2, z ˆ 0.045 (assuming that the impurity was a
III
high-spin Fe species; this was confirmed by the powdered
EPR spectrum which showed a signal of low intensity
centered at g ˆ 4.34) with an agreement factor R equal to
�
4
2
2
8  10 , R ˆ S(c T� c T) /S(c T) . All the previously
obs
calcd
obs
reported Fe ± O ± Fe complexes display rather similar mag-
netic properties with J values in the range � 170 to
�
1 [13, 15]
(
Mn ± N2 ˆ 2.348(2) and Mn ± Cl2 ˆ 2.432(1) Š).
� 230 cm .
The crystal structure of complex 2 exhibits a (m-oxo)-
The UV-visible spectrum of complex 2 did not show the
characteristic band (between 550 and 700 nm, blue-shifted to
diiron(iii) core with two lattice chloride anions and two
methanol molecules. The metal centers are arranged in an
approximate octahedral geometry. Each iron atom is coordi-
nated to four nitrogen donor atoms of bdpma (three
pyridines and the secondary amine), the bridging oxygen
atom, and one chloride. The m-oxo bridge was expected to
have a strong trans influence towards the weakest nitrogen
donor atom of bdpma, as in related complexes containing
ligands with both pyridyl and amine functions. However,
complex 2 shows a symmetric structure in which the
secondary amines of both bdpma ligands are in a cis position
with respect to the m-oxo bridge, with an Fe ± Namine distance of
III
a nearly 1808 angle for Fe ± O ± Fe) of an oxo to Fe charge-
transfer transition,[ strongly suggesting that the dimer core
is not maintained in solution. This is supported by IR
measurements. The solid-state IR spectrum of 2 exhibited
16]
�
1
an asymmetric Fe ± O stretching vibration at 840 cm , which
was not present in solution.
[
11]
Compounds obtained by oxidative degradation of BDMPA in
the presence of a transition metal salt. X-ray structure and
III
characterization of {[Co (dpkH) ](MeO)(MeOH)} (3): Dur-
2
ing attempts to crystallize a mononuclear iron(iii) complex
2
.203(5) Š, and are cis to each other. The (m-oxo)-diiron(iii)
involving the bdpma ligand and Fe(NO ) , a modified bdpma
ligand was obtained instead of the expected metal complex,
namely 1,3,3-tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin-4-ium,
3
3
III
complex of tris(2-pyridylmethyl)amine (TPA), [Fe2
2‡
[12]
(TPA) (O)Cl ] reported by Toftlund et al., also contains
2
2
such a symmetrical arrangement, with the two tertiary amines
of both TPA ligands located cis to the m-oxo bridge (and trans
to each other).
[tpip](NO ) (Scheme 3); see ref. [10] for a preliminary
communication on this structure). Selected bond lengths
3
and angles of [tpip](NO ) are given in Table 3. The tpip cation
3
In both complexes, steric constraints are involved and
strong stacking interactions between the pyridine rings
situated on each side of the m-oxo bridge are predominant.
The Fe ± Npyridine bond trans to the m-oxo bridge is longer
contains an imidazopyridinium entity, in which the positively
charged nitrogen (N2) is common to both the six- and five-
membered rings. The C7 ± N1 bond of the five-membered ring
has a short length of 1.293(5) Š, consistent with a double bond
conjugated to the pyridinium moiety through C6 ± C7 and to
the pyridine attached to C7. This is supported by the fact that
(Fe1 ± N1: 2.323(5) Š) than the Fe ± Npyridine bonds cis to the
bridge (mean value: 2.156 Š). The sixth coordination sites of
1
768
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Chem. Eur. J. 1999, 5, No. 6

bpdma and tpip Complexes
1766±1774
Table 4. Selected bond lengths [Š] and angles [8] for {[CoIII(dpkH)]
MeO)(MeOH)} (3).
-
2
(
Co ± N(1)
Co ± N(2)
Co ± O(1)
1.911(3)
1.915(3)
1.886(2)
O(1A)-Co-O(1)
O(1A)-Co-N(1)
O(1)-Co-N(1)
N(1)-Co-N(1A)
O(1A)-Co-N(2)
180
97.19(11)
82.81(11)
180
96.58(11)
O(1)-Co-N(2)
N(1)-Co-N(2)
N(1A)-Co-N(2)
N(2)-Co-N(2A)
83.42(11)
88.75(12)
91.25(12)
180
tridentate mode. The dpkH ligand stabilizes the high oxida-
tion state of the metal center better than bdpma (with four
pyridine ligands), owing to the presence of the s-donor
oxygen atom.
Two negative charges to neutralize the CoIII center were
provided by deprotonation of one hydroxy group of each
ketone hydrate. The crystal structure of 3 also displays one
methanolate anion, which provides the third negative charge,
and one methanol molecule, which are exchangeable by
symmetry. The structure depicted in Scheme 3 represents one
motif of the unit cell. In addition, two lattice-disordered ethyl
acetate molecules are present. The metal ± ligand bond
lengths are unusual because the axial Co ± O1 distance of
Scheme 3. Compounds obtained by the oxidative degradation of bdpma in
3
the presence of a transition metal salt: X-ray structures of [tpip](NO ) and
III
[
2
Co (dpkH)] (MeO)(MeOH) (3).
Table 3. Selected bond lengths [Š] and angles [8] for [tpip](NO
3
),
II
III
II
[
tpip]
2
[Mn Cl
4
] (4), [tpip][Fe Cl
4
] (5), and [tpip]
2
[Co Cl
4
] (6).
[
tpip](NO ) [tpip]
3
2
[MnCl
4
] [tpip][FeCl
4
] [tpip]
2
4
[CoCl ]
M(1) ± Cl(1)
M(1) ± Cl(2)
±
±
2.347(2)
2.366(1)
2.171(3)
2.191(8)
2.280(1)
2.272(1)
1.886(2) Š is shorter than the equatorial (Co ± N1: 1.911(3)
and Co ± N2: 1.915(3) Š) distances. The three angles O1 ±
Co ± O1A, N1 ± Co ± N1A, and N2 ± Co ± N2A are exactly
C(1) ± N(1)
C(1) ± N(2)
C(2) ± N(2)
C(2) ± C(3)
C(3) ± C(4)
C(4) ± C(5)
C(5) ± C(6)
C(6) ± C(7)
C(7) ± N(1)
1.457(4)
1.460(5)
1.447(4)
1.284(5)
1.346(4)
1.371(5)
1.374(5)
1.389(5)
1.371(5)
1.483(5)
1.284(5)
1.462(4)
1.498(4)
1.336(4)
1.374(5)
1.383(6)
1.388(5)
1.377(5)
1.471(5)
1.293(5)
1.488(6)
1.335(6)
1.372(7)
1.387(7)
1.389(7)
1.368(7)
1.475(6)
1.289(6)
1.498(3)
1.344(4)
1.373(4)
1.377(4)
1.391(4)
1.378(4)
1.477(4)
1.284(4)
1
808. The angle made by the off-axis coordination of the
oxygen atom with the line normal to the equatorial plane is
very small, with a value of 7.198. Several characterization
results, including the FAB mass spectrum, the 1H NMR
spectrum, and the absence of a magnetic susceptibility as
determined by the Faraday method, support the low-spin, ‡3
oxidation state of the cobalt center. Moreover, the X-ray
structure of the same complex has already been described by
N(1)-C(7)-C(6) 112.2(3)
N(1)-C(7)-C(8) 121.9(3)
N(1)-C(1)-N(2) 103.5(3)
N(1)-C(1)-C(13) 111.3(3)
N(1)-C(1)-C(18) 109.0(3)
N(2)-C(1)-C(18) 109.6(3)
N(2)-C(6)-C(5) 119.4(3)
N(2)-C(6)-C(7) 105.2(3)
N(2)-C(2)-C(3) 119.0(4)
C(6)-N(2)-C(1) 109.4(3)
C(2)-N(2)-C(1) 127.2(3)
C(2)-N(2)-C(6) 123.1(3)
C(7)-N(1)-C(1) 109.6(3)
112.3(4)
111.7(3)
122.9(3)
103.6(3)
111.1(3)
109.1(3)
112.1(3)
120.5(3)
105.2(3)
118.3(3)
109.4(3)
128.2(3)
122.5(3)
110.2(3)
112.5(2)
123.4(4)
103.7(3)
112.3(4)
109.4(3)
112.2(3)
119.3(4)
104.6(4)
118.8(4)
109.4(3)
128.0(4)
122.6(4)
110.0(3)
122.6(3)
103.5(2)
111.5(2)
109.8(2)
111.2(2)
119.5(3)
105.0(2)
118.4(3)
109.4(2)
127.6(2)
123.0(2)
109.6(2)
[17]
Sommerer et al., starting from [Co(NH ) CO ]NO and two
3
4
3
3
equivalents of di-(2-pyridyl)ketone in water. In this case, the
counterion was a nitrate and the substantiating evidence for a
III
Co was obtained from INDO geometry optimization
[17]
calculations.
Compounds obtained with tpip as a potential ligand. X-ray
II
structures and characterizations of [tpip] [Co Cl ] (6),
2
4
II
II
[
Fe (dpmmdpi)Cl ] (7), and [Co (dpmm) Cl ] (8): tpip was
2 2 2 4
prepared in a gram scale in order to study its behavior as a
potential ligand. It was efficiently synthesized from the imine
C by oxidation with MnO2 (Scheme 1; for the reaction
mechanism see the Discussion section). During attempts to
prepare tpip complexes using manganese, iron, or cobalt salts,
we obtained two different categories of compounds
(Scheme 4). The first category was obtained with MnCl2,
FeCl , and CoCl . In these cases, we were unable to get any
the pyridine plane containing N3 has a mean deviation of only
8 from the plane formed by the imidazopyridinium moiety.
The C2 ± N2 bond length of 1.344(4) Š is similar to those
observed in the pyridine rings (mean value: 1.340(4) Š), while
the C6 ± N2 bond is longer, with a distance of 1.368(4) Š.
Even less of the original bdpma structure remained when
5
this ligand reacted with Co(OAc) . Indeed, the crystal
2
3
2
III
structure of the resulting complex 3, which is depicted in
Scheme 3, showed a cobalt(iii) complex with two hydrates of
ketone B. Relevant bond lengths and angles are given in
complexation reaction and we observed [tpip][Fe Cl ] (5),
4
�
formed by the exchange of the initial anion (NO ) by
3
III
�
[Fe Cl ] , when using FeCl . MnCl and CoCl gave doubly
4
3
2�
2
2
II
Table 4. The geometry of the cationic complex
negatively charged [M Cl ] complexes and crystallized with
4
two molecules of tpip ([tpip] [Mn Cl ] (4) and [tpip] [Co Cl ]
2 4 2 4
(6), respectively). The crystal structure of [tpip] [Co Cl ] (6),
III
II
II
{
[Co (dpkH) ](MeO)(MeOH)} (3) is almost octahedral, as
2
III
II
would be expected for a Co species, with two di-(2-
pyridyl)ketone hydrate (dpkH) moieties coordinated in a
2 4
which illustrated this first class of compounds, is depicted in
1769
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B. Meunier et al.
FULL PAPER
molecule, methanol, has been incorporated into the initial
tpip and the imidazole ring has been opened (ligand E of
Scheme 5 in the Discussion section). The iron atom is in a
distorted square pyramidal environment, in which the square
plane is formed by one imine N5 and two pyridine (N1 and
N3) nitrogens and the chloride anion Cl1. The equatorial Fe ±
N bond lengths range from 2.133(5) to 2.147(5) Š. The second
chloride Cl2 occupies the axial position with a longer bond of
2
.325(2) Š. The major difference between the dpmmdpi and
bdpma ligands is the presence of an imine function linking the
dipyridyl entities of dpmmdpi. The corresponding short bond
length C6 ± N5 of 1.306(8) Š in complex 7 is in good agree-
ment with a carbon ± nitrogen double bond. In contrast, the
single C�N
bond of the bdpma ligand (C17 ± N1:
.467(9) Š) is slightly longer in complex 2. Another important
amine
1
feature of the dpmmdpi ligand is the presence of a methoxy
group at the C17 carbon connected to the imine function. This
provides an asymmetric center in complex 7 because of the
differentiation of the two pyridines by the coordination of
one. The molecule crystallizes in the centrosymmetric space
group P2 /n, and both enantiomers are present in the crystal
1
structure.
Other crystals 8 were obtained from the mother liquor of
II
[
tpip] [Co Cl ] (6) and revealed a totally different structure.
2
4
II
The complex [Co (dpmm) Cl ] (8) (dpmm ˆ di(2-pyridyl)-
2
2
4
methoxymethanol), the crystal structure of which is depicted
in Scheme 4, belongs to the second category of compounds
Scheme 4. Compounds obtained with tpip as potential ligand: X-ray
II
II
obtained with tpip. With CoCl as the starting material, the
structures of [Co Cl
4
][tpip]
2
(6), [Fe (dpmmdpi)Cl
2
]
(7), and
2
II
[
Co
2
(dpmm)
2
Cl
4
] (8).
degradation of tpip went further than for complex 7, resulting
in the crystallization of the cobalt complex 8, which contains
only fragments of the starting ligand (ligand G of Scheme 5 in
the Discussion section). Selected bond lengths and angles of
complex 8 are given in Table 6.
Scheme 4. Selected bond lengths and angles of compound 6
are listed in Table 3. The crystal structure of the ion pair 6
consists of two cationic tpip ligands arranged around a
tetrahedral tetrachlorocobaltate dianion.
In contrast to the unsuccessful complexation reactions
discussed above, a new type of complex (7) was synthesized
Table 6. Selected bond lengths [Š] and angles [8] for [Co I2 I(dpmm) Cl ] (8).
2
4
Co(1) ± N(1)
Co(1) ± N(2)
Co(1) ± Cl(1)
2.119(3)
2.124(3)
2.3626(13)
Co(1) ± O(1)
Co(1) ± Cl(2)
Co(1) ± Cl(3)
2.380(3)
2.416(1)
2.438(1)
when tpip and FeCl were used as starting materials. In this
2
case, we obtained a metal complex for the first time, namely
II
[
Fe (dpmmdpi)Cl ] (7; dpmmdpi ˆ N-(di(2-pyridyl)methoxy-
Co(1) ´´´ Co(1A)
N(1)-Co(1)-N(2)
N(1)-Co(1)-Cl(1)
N(2)-Co(1)-Cl(1)
N(1)-Co(1)-O(1)
N(2)-Co(1)-O(1)
Cl(1)-Co(1)-O(1)
N(1)-Co(1)-Cl(2)
N(2)-Co(1)-Cl(2)
Cl(1)-Co(1)-Cl(2)
3.574
2
87.47(13)
95.07(9)
93.63(9)
73.11(11)
70.39(11)
160.12(7)
158.80(9)
95.12(9)
105.72(13)
O(1)-Co(1)-Cl(2)
N(1)-Co(1)-Cl(3)
N(2)-Co(1)-Cl(3)
Cl(1)-Co(1)-Cl(3)
O(1)-Co(1)-Cl(3)
Cl(2)-Co(1)-Cl(3)
Co(1A)-Cl(2)-Co(1)
Co(1A)-Cl(3)-Co(1)
87.92(9)
89.53(10)
172.27(9)
93.74(3)
101.91(7)
85.14(4)
95.44(6)
94.27(6)
methyl)(di(2-pyridyl)imine)), which involves a modification
of tpip (Scheme 4). The crystal structure of complex 7 is
shown in Scheme 4, and selected bond lengths and angles are
given in Table 5. In the structure, the dpmmdpi ligand exhibits
a bdpma-like skeleton with four pyridine groups. A solvent
II
Table 5. Selected bond lengths [Š] and angles [8] for [Fe (dpmmdpi)Cl
2
]
(
7).
Fe(1) ± N(1)
Fe(1) ± N(3)
Fe(1) ± N(5)
Fe(1) ± Cl(1)
2.133(5)
2.133(5)
2.147(4)
2.307(2)
Fe(1) ± Cl(2)
C(6) ± N(5)
C(17) ± N(5)
N(3) ± N(4)
2.325(2)
1.306(8)
1.479(8)
3.93
The structure analysis of complex 8 shows a neutral dimeric
(di-m-chloro)dicobalt(ii) core. The two metal centers are
arranged in a very distorted octahedral geometry. The
cobalt(ii) ions are coordinated to two nitrogen donor atoms
and one oxygen atom of the methoxy group from the dpmm
ligand, and one terminal and two bridging chloride anions.
The square plane includes the two pyridines with a mean bond
length of 2.122 Š, and the two bridging chlorides with
significantly longer bond lengths (Co1 ± Cl2: 2.416(1) and
Co1 ± Cl3: 2.438(1) Š). The latter are especially long com-
N(1)-Fe(1)-N(3)
N(1)-Fe(1)-N(5)
N(3)-Fe(1)-N(5)
N(1)-Fe(1)-Cl(1)
N(3)-Fe(1)-Cl(1)
Fe(1)-N(1)-C(5)
N(1)-C(5)-C(6)
C(5)-C(6)-N(5)
C(6)-N(5)-Fe(1)
146.3(2)
N(5)-Fe(1)-Cl(1)
N(1)-Fe(1)-Cl(2)
N(3)-Fe(1)-Cl(2)
N(5)-Fe(1)-Cl(2)
Cl(1)-Fe(1)-Cl(2)
Fe(1)-N(3)-C(16)
N(3)-C(16)-C(17)
C(16)-C(17)-N(5)
C(17)-N(5)-Fe(1)
109.22(14)
97.13(14)
99.37(15)
144.19(15)
106.53(8)
119.7(4)
118.2(5)
106.1(5)
120.3(4)
74.89(19)
74.53(19)
99.80(14)
103.31(15)
116.7(4)
114.7(5)
115.4(5)
117.6(4)
1
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bpdma and tpip Complexes
1766±1774
pared to the axial Co ± Cl1 bond length of 2.362(1) Š. The
coordination sphere is completed by the axial methanolate
oxygen of the methoxy group, with a Co1 ± O1 bond length of
ly, only one C ± N double bond could be obtained by
dehydrogenation of the five-membered ring (step iii,
Scheme 5), and the pyridinium nitrogen remained positively
1
2.380(3) Š, the two coordinated oxygen atoms of both dpmm
charged. Traces of tpip were previously observed in H NMR
ligands being located trans to each other. The Co ´´´ Co
distance is 3.574 Š, and the deviation of the cobalt(ii) ion from
the least-squares plane defined by N1, N2, Cl2, and Cl3 is
spectra of imine C, suggesting that the oxidation of compound
D to tpip (step iii, Scheme 5) was also possible with molecular
oxygen. To prove that imine C was a potential intermediate in
the degradation of bdpma to tpip, we decided to prepare tpip
from C. After preparation of C according to literature[ and
0.28 Š.
8]
subsequent oxidation by MnO , tpip was obtained in 73%
2
yield. This showed unambiguously that C was an intermediate
in the transformation of bdpma to tpip and that the cyclization
occurred in high yield. In order to purify tpip, the crude
reaction mixture was dissolved in methanol and exposed to a
methyl tert-butyl ether atmosphere. After one day, crystal-
lization was complete and very clean tpip crystals were
collected. tpip is stable in methanol solution and no nucleo-
philic addition of methanol could be observed; this point will
be important in the discussion later.
Discussion
All structures of the complexes obtained with bdpma and
manganese, iron, or cobalt salts can be rationalized by
metal-catalyzed oxidative degradation of the bdpma ligand
as shown in Scheme 5 (when they did not contain the intact
bdpma). In the absence of transition metal ions bdpma is
highly stable, even in solution, and has been fully character-
[
8]
ized.
To understand the further
degradation
products
of
bdpma, tpip was employed as
a potential ligand instead of
bdpma. However, first attempts
with MnCl , FeCl , and CoCl
2
3
2
were unsuccessful: tpip re-
mained uncoordinated and
counterion exchange was ob-
served. The nitrate counterion
of tpip exchanged with the
chlorides of FeCl and the li-
3
berated chloride ions reacted
with excess FeCl to generate
3
the stable tetrachloroferrate
III
�
[
Fe Cl ] anion, which was
4
not able to undergo coordina-
tion by tpip. Probably, the ther-
Scheme 5. Proposed degradation mechanism of the polypyridine ligand bdpma via the cationic compound tpip to
di(2-pyridyl)ketone hydrate. i) Fe(NO ; ii) Zn, AcOH; iii) MnO or O ; iv) MeOH, FeCl or CoCl ; v) CoCl
vi) [Co(OAc) ].
modynamic
stability
of
3
)
3
2
2
2
2
2
;
II
2�
III
�
2
[Mn Cl ] , [Fe Cl ] , and
4
4
II
2�
[
Co Cl ] was the driving force
4
for the simple ion exchange and
In contrast, in the presence of iron or cobalt salts, several
degradation products of bdpma were observed, involving the
imine C as primary oxidation intermediate. Thereby, two
electrons and two protons are abstracted and the metal is
crystallization of tpip with the anionic metallate complexes as
counterion.
In contrast to these results, we did obtain a complex with
tpip when using FeCl . However, the tpip was not intact; a
2
[18]
reduced from the ‡3 to the ‡2 oxidation state.
The
methanol molecule attacked the imidazolium ring and opened
‡
coordination of the polypyridine ligands certainly facilitates
the redox reaction at the metal center by an inner-sphere
electron transfer. The imine C can be activated by protona-
it by cleaving the C�N bond of the pyridinium ring. This
addition is certainly metal-assisted, since tpip is stable in
methanol solution, as already mentioned in the description of
the purification procedure or as demonstrated by the crystal
[
19]
tion and can then be attacked by a pyridine nitrogen acting
as an internal nucleophile to produce a five-membered ring
II
III
structures of [M Cl ][tpip] and [Fe Cl ][tpip], which were
4
2
4
(
Scheme 5). Hydrolysis of the imine to the amine A and the
crystallized from methanol solutions. The first step should
thus be coordination of FeCl2 to two pyridyl moieties
connected to the imidazopyridinium unit in the 1 and 3
positions (see tpip numbering used for the NMR spectra, and
the imidazole nitrogen (structure H, Scheme 6). In conse-
quence, owing to the Lewis acidity of the metal center, the
LUMO level of the ring system was lowered, making it more
electrophilic and reactive with respect to nucleophilic attack
ketone B, the back-reaction of the bdpma synthesis (cf.
Scheme 1), should be possible but was not observed in the
present case. Cyclization is already known for pyridyl-
substituted imines, which are further oxidized to imida-
zo[1,5-a]pyridines after ring closure. This was not possible
in the present case because a quaternary carbon was created
during the cyclization (labeled C1 in Scheme 3). Consequent-
[
20]
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1771

B. Meunier et al.
FULL PAPER
analyses were consistent with the proposed formulas. Mass spectrometry
‡
analyses were performed on a Nermag R1010 apparatus (FAB /meta-
nitrobenzyl alcohol (MNBA) in DMSO) or on a Perkin ± Elmer SCIEX
Api100 spectrometer (ES in MeOH) by the Service de Spectrom e trie de
Masse de Chimie UPS-CNRS de Toulouse. UV-visible spectra were
obtained on a Hewlett-Packard 8452A diode array spectrophotometer,
with cuvettes of 1 cm pathlength. IR spectra were recorded on a Perkin ±
2 2
Elmer 983 spectrophotometer. Samples were run as KBr pellets or CH Cl
solutions. EPR spectra were recorded on a Bruker ESP 300 in X-Band, with
an ER035M gaussmeter (NMR probe) and a EIP 548 hyperfrequency-
meter. Powdered samples were loaded in 3 mm cylindrical quartz tubes.
Scheme 6. Metal-assisted opening of the imidazolium ring of tpip to
generate complex 7.
Mössbauer measurements were obtained on
a constant-acceleration
57
conventional spectrometer with a 25 mCi source of Co (Rh-matrix).
Magnetic susceptibilities were determined by the Faraday method at room
by a methanol molecule. Furthermore, the coordination of the
three nitrogens of tpip introduced a constraint into the
molecule which pinched the two coordinated pyridine rings
� 6
temperature, with a HgCo(SCN)
4
matrix (c/g ˆ 16.44 ´ 10 emucgs). Var-
iable-temperature magnetic susceptibility data were obtained with a
Quantum Design MPMS Squid susceptometer. The diamagnetism of the
ligands was corrected using Pascalꢁs constants. EPR, magnetism and
Mössbauer data were recorded by the Service de Mesures Magn e tiques du
Laboratoire de Chimie de Coordination.
‡
and lengthened the C�N bond. The distance between N3 and
N4 in the Fe complex 7 was 3.93 Š (Table 5), but in the
relaxed tpip molecule the corresponding distance was around
X-ray measurements of 1 ± 8: Crystal data for all structures are presented in
1
Š longer (4.95 Š taken from the distance between C9 and
Table 7. All data were collected at low temperatures from an oil-coated
[
21]
C14 of a tpip salt in Scheme 4). The Lewis acidity and the
pinching effect synergetically assisted the methanol addition
shock-cooled crystal on a Stoe-IPDS with MoKa (l ˆ 0.71073 Š) radia-
tion. The structures were solved by direct methods by means of SHELXS-
97 and refined with all data on F 2 by means of SHELXL-97. All non-
[
22]
[23]
‡
and the cleavage of the C�N bond of the imidazolium ring.
hydrogen atoms were refined anisotropically. The hydrogen atoms of the
Consequently, a non-alkylated pyridine was obtained. With
bdpma as ligand, we obtained only a complex with an iron(iii)
ion, even starting from an iron(ii) salt. The most interesting
feature of complex 7 was the stabilization of the ‡2 oxidation
state of the iron center by the modified tpip ligand. In
contrast, the cobalt analogue of 7 probably exists but was not
stable enough to be fully characterized by X-ray analysis. The
corresponding red crystals were too small to be correctly
analyzed, but the cell parameters were similar to that of the
iron complex 7. From the mother liquor, violet crystals were
isolated and analyzed by X-ray studies (complex 8, Scheme 4).
This compound is a further modified tpip ligand correspond-
ing to a hemiacetal of dipyridyl ketone with a methanol
molecule (see ligand F in Scheme 5).
molecules were geometrically idealized and refined using a riding model.
Refinement of an inversion twin parameter[24] [x ˆ� 0.02(4); x ˆ 0 for
the correct absolute structure and ‡1 for the inverted structure] confirmed
the absolute structure of 2. Selected bond lengths and angles of 1 ± 8
can be found in Tables 1 ± 6. Crystallographic data (excluding structure
factors) for the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC-108596 ± 108603 (1 ± 8). Copies of the data can
be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB21EZ (UK) (fax: (‡44)1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk).
1
,3,3-Tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin-4-ium (tpip), nitrate form:
Di(2-pyridyl)ketone (3.72 g, 20.0 mmol) and di(2-pyridyl)methylamine
3.71 g, 20.0 mmol) were dissolved in absolute isopropanol (120 mL) and
dried over 3 Š molecular sieves for 1 h at room temperature. Glacial acetic
acid (4.3 mL, 75.0 mmol) was added under N atmosphere and the reaction
mixture refluxed for 5 h. MnO (17.40 g, 200 mmol) was then added (the oil
(
2
2
bath was removed for the addition). After 1 h heating was switched off and
the reaction mixture allowed to cool slowly. After 16 h, solids were
removed by filtration. The solvent was evaporated (508C, 30 Torr) and the
Conclusion
residue dissolved in CH
The crude reaction mixture was purified by column chromatography (SiO
MeOH with 2 vol% of HNO Ðthis acid provides the counterion for the
2
Cl
2
(100 mL) and washed with brine (2 Â 30 mL).
2
,
While attempting to prepare different complexes with the
tetrapyridyl ligand bdpma and manganese, iron, and cobalt
salts, we were able to trap different degradation products of
the bdpma ligand. By identification and preparation of the
intermediate product tpip, we showed that the benzylic C�H
3
tpip cation). The resulting brown oil was dissolved in MeOH and exposed
to a methyl tert-butyl ether atmosphere. 6.02 g (14.6 mmol, 73%) of yellow
1
crystals were obtained. H NMR (300 MHz, CDCl
3
, 258C): d ˆ 7.38 (ddd,
3
4
5
J(H,H) ˆ 7.5 Hz, J(H,H) ˆ 4.8 Hz, J(H,H) ˆ 0.9 Hz, 2H, 18-H), 7.60
(
7
1
ddd, 3J(H,H) ˆ 7.6 Hz, J(H,H) ˆ 4.8 Hz, J(H,H) ˆ 0.9 Hz, 1H, 12-H),
4
5
bonds in the a-position to a heteroatom are the weak point of
this polypyridine ligand. This detailed work on polypyridine
ligand degradation will be useful in the development of more
robust nonheme ligands based on polypyridine units. Such
work is in progress in our group.
3
3
4
.72 (d, J(H,H) ˆ 7.9 Hz, 2H, 20-H), 7.85 (td, J(H,H) ˆ 7.8 Hz, J(H,H) ˆ
3
4
.7 Hz, 2H, 19-H), 8.01 (td, J(H,H) ˆ 7.8 Hz, J(H,H) ˆ 1.7 Hz, 1H, 13-H),
3
8.55 (m, 4H, 6-H, 17-H, 14-H), 8.84 (dq, J(H,H) ˆ 4.9 Hz, J(H,H) ˆ
3
3
0.8 Hz, 1H, 11-H), 9.05 (t, J(H,H) ˆ 7.7 Hz, 1H, 7-H), 9.64 (d, J(H,H) ˆ
3
13
8
,0 Hz, 1H, 8-H), 10.08 (d, J(H,H) ˆ 6.0 Hz, 1H, 5-H); C NMR (75 MHz,
CDCl
, 258C): d ˆ 105.1 (s, C-3), 124.8 (d, 2C, C-20), 125.2 (d, C-14), 126.1
d, 2C, C-18), 127.8 (d, C-8), 128.1 (d, C-6), 128.3 (d, C-12), 138.5 (d, C-13),
3
(
1
39.1 (d, 2C, C-19), 145.5 (s, C-8a), 146.2 (d, C-5), 149.4 (d, C-7), 149.6 (s,
C-9), 150.7 (d, C-11), 150.8 (d, 2C, C-17), 153.3 (s, 2C, C-15), 162.5 (s, C-1).
The structure of [tpip](NO ) was determined by X-ray crystallography (see
Experimental Section
3
text, Scheme 3, and Tables 3 and 7).
General: Commercially available reagents and all solvents were purchased
from standard chemical suppliers and used without further purification.
Bis[di(2-pyridyl)methyl]amine (bdpma) and di(2-pyridyl)methyl amine
II
Dichloro{bis[di(2-pyridyl)methyl]amine}manganese(ii)
([Mn (bdpma)-
´ 4H (26 mg,
�
4
Cl
2
], 1): bdpma (50 mg, 1.41 Â 10 mol) and MnCl
2
2
O
were synthesized according to literature procedures.[ H NMR spectra
8]
1
1.30 Â 10 mol) were dissolved separately in MeOH (total volume of
3 mL). The resulting solution was stirred for 15 min and then allowed to
stand in a diethyl ether bath for one week. After washing with diethyl ether
and drying under vacuum, the solution yielded 10 mg (15%) of colorless
� 4
were recorded on a Bruker AM 250 (250 MHz) spectrometer with CDCl
as solvent; d
ˆ 7.26. Elemental analyses were carried out by the Service de
Microanalyse du Laboratoire de Chimie de Coordination and all elemental
3
H
1
772
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Chem. Eur. J. 1999, 5, No. 6

bpdma and tpip Complexes
1766±1774
Table 7. Crystal structure data for compounds 1 to 8.
1
2
3
4
5
6
7
8
formula
C
22
H
19Cl
2
MnN
5
C
22
H
19Cl
2
FeN
5
O
0.5- C26H
29CoN
4
O
7
C
22
H16Cl
2
Mn0.5N
5
C
22
H
16Cl
4
FeN
5
C
22
H
16Cl
2
Co0.5
N
5
C
23 2 5 2 2 2
H19Cl FeN O C12H12Cl CoN O
(
CH
3
OH)0.75
M
T [K]
crystal system
space group
a [Š]
b [Š]
c [Š]
a [8]
b [8]
r
479.26
173(2)
511.95
173(2)
tetragonal
568.46
193(2)
monoclinic
448.77
173(2)
monoclinic
I2/a
14.626(4)
14.511(3)
19.709(7)
90
103.40(4)
90
548.05
193(2)
triclinic
P1
8.343(1)
10.249(2)
14.394(2)
82.74(2)
78.62(2)
86.99(2)
1196.4(3)
2
450.76
173(2)
monoclinic
I2/a
14.600(2)
14.404(2)
19.818(2)
90
102.85(1)
90
508.18
173(2)
346.07
173(2)
monoclinic
C2/c
14.273(3)
15.937(2)
13.364(3)
90
112.17(2)
90
monoclinic
P2 /n
monoclinic
P2 /n
Å
1
P4
3
2
1
2
P2
1
/c
1
11.145(2)
16.462(2)
12.041(2)
90
90.30(2)
90
2202.9(6)
4
1.445
13.079(1)
13.079(1)
27.921(4)
90
90
90
4776.2(9)
8
1.424
2106
11.603(2)
7.990(1)
15.186(2)
90
96.40(2)
90
1399.1(4)
2
1.349
8.237(1)
17.347(2)
15.388(1)
90
90.17(1)
90
2198.7(4)
4
1.535
g [8]
V [Š ]
3
4069(2)
8
1.465
4063.3(9)
8
1.474
2815.1(9)
8
1.633
Z
1
calcd [Mgm 3
�
]
1.521
554
F(000)
cryst. size [mm]
980
592
1836
1844
1040
1400
0.6 Â 0.5 Â 0.1 0.7 Â 0.5 Â 0.2
0.7 Â 0.1 Â 0.1 0.5 Â 0.4 Â 0.1
0.5 Â 0.4 Â 0.1 0.5 Â 0.4 Â 0.1
0.4 Â 0.4 Â 0.1
0.7 Â 0.4 Â 0.3
2
q
max [8]
46
46
46
45
46
46
45
46
refl. collected
indep. refl.
17908
3028
0.0539
38511
3214
0.0970
numerical
11343
1991
0.0393
numerical
0.8541, 0.9505
237
8006
2632
0.1427
none
±
8809
3229
0.0356
none
±
16457
2916
0.0748
numerical
0.7038, 0.8779
267
14520
2857
0.1099
numerical
0.7807, 0.8934
290
11312
2014
0.0672
numerical
0.6200, 0.8088
178
R
int
absorption correct. numerical
T
min,
T
max
0.6803, 0.8631 0.7744, 0.8985
281
parameters
319
268
335
R (I > 2s(I))
0.0300
0.0669
� 0.341
0.249
0.0549
0.1381
� 0.502
0.703
0.0482
0.1299
� 0.390
0.677
0.0610
0.1668
� 0.540
0.379
0.0489
0.1377
� 0.467
0.805
0.0326
0.0687
� 0.480
0.241
0.0502
0.1296
0.0362
0.0927
� 0.642
0.353
[
a]
wR2 (all data)
�
3
(
(
D/1)min [eŠ
]
]
� 0.452
D/1)max [eŠ 3
�
0.423
a] wR2 ˆ {[Sw(Fc � Fo ) ]/[Sw(Fo ) ]}1/2.
2
2
2
2 2
[
I
]‡; 1H NMR (250 MHz, [D
[
Co (dpk)
2
6
]DMSO, 258C): d ˆ 7.58 (dd, 2H),
7
.98 (d, 2H), 8.20 (t, 2H), 8.33 (d, 2H) (further analysis by two-dimensional
1
13
H NMR or C NMR was impossible because the complex decomposed in
solution after minutes). The structure of 3 was determined by X-ray
crystallography (see text, Scheme 3, and Tables 4 and 7).
Bis[1,3,3-tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin-4-ium] tetrachloroman-
II
� 4
ganate ([tpip]
MnCl ´ 4H
(
2
[Mn Cl
4
], 4): [tpip](NO
3
) (50 mg, 1.21 Â 10 mol) and
�
4
2
2
O (30 mg, 1.52 Â 10 mol) were dissolved separately in MeOH
total volume of 2 mL). The resulting solution was stirred for 15 min and
then allowed to stand in a methyl tert-butyl ether bath. After two weeks,
II
II
‡
15 mg (24%) of pale red-brown crystals of [tpip] [Mn Cl ] were obtained.
crystals 1. FAB-MS: m/z (%) ˆ 443 (100) [Mn (bdpma)Cl] ; UV/Vis
2
4
‡
�
3
� 1
� 1
FAB-MS: m/z (%) ˆ 350 (100) [tpip] . The structure of 4 was determined
by X-ray crystallography: selected bond lengths and angles are given in
Table 3 and X-ray data in Table 7.
(
MeOH): lmax (e  10
M
cm ) ˆ 264 nm (9.2), 318 (3.9). The structure
of 1 was determined by X-ray crystallography (see text, Scheme 2, and
Tables 1 and 7).
Dichloro-m-oxo{bis{bis[di(2-pyridyl)methyl]amine}}diiron(iii) dichloride
1,3,3-Tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin-4-ium
tetrachloroferrate
III
III
� 4
(
[Fe
2
(bdpma)
2
(O)Cl
2
]Cl
2
, 2): By the double-ended needle technique,
([tpip][Fe Cl
4
], 5): [tpip](NO
3
)
(50 mg, 1.21 Â 10 mol) and FeCl
3
´
�
4
� 4
FeCl
2
´ 4H
2
O (195 mg, 9.79 Â 10 mol) in degassed MeOH (2 mL) was
6H
2
O (40 mg, 1.48 Â 10 mol) were dissolved separately in MeOH (total
�
4
added under nitrogen to a solution of bdpma (346 mg, 9.79 Â 10 mol) in
degassed MeOH (2 mL). The resulting solution was stirred for 15 min
under nitrogen and then allowed to stand in a degassed methyl tert-butyl
ether atmosphere for 3 d. Red crystals of 2 were washed with methyl tert-
butyl ether and dried under vacuum. The iron centers were probably
oxidized by diffusion of molecular oxygen during this 3-day work-up. The
volume of 3 mL). The resulting solution was stirred for 15 min and then
allowed to stand in a methyl tert-butyl ether bath. After two weeks, 47 mg
(71%) of pale brown crystals were obtained. FAB-MS: m/z (%) ˆ 350
‡
(100) [tpip] . Under anaerobic conditions, the same crystals of [tpip]-
III
4 3 2 2
[Fe Cl ] were obtained when [tpip](NO ) and the ferrous salt FeCl ´ 4H O
were used in stoichiometric amounts as starting materials (in contrast,
complex 7 was obtained when a 2:1 mixture of tpip and FeCl was
employed). The structure of 5 was determined by X-ray crystallography:
selected bond lengths and angles are given in Table 3 and X-ray data in
Table 7.
III
2
�
‡
yield was 246 mg (48%). ES-MS: m/z ˆ 940.91 [Fe
(bdpma)
2
(O)(Cl )
3
] ,
2
III
2
� 1
�
‡
9
1
04.45 [Fe
(bdpma)
2
(O)(Cl )
3
� HCl] ; UV/Vis (MeOH):
l
max (e Â
�
3
� 1
0
M
cm ) ˆ 244 nm (15.4), 260 (18.1), 320 (11.2). The structure of 2
was determined by X-ray crystallography (see text, Scheme 2, and Tables 2
and 7).
Bis[1,3,3-tris(2-pyridyl)-3H-imidazo[1,5-a]pyridin-4-ium] tetrachloroco-
Bis[di(2-pyridyl)ketonehydrate}cobalt(iii) methanolate ({[CoIII(dpkH)
]-
II
� 5
{
2
baltate ([tpip]
CoCl ´ 6H
2
[Co Cl
4
], 6): [tpip](NO
3
)
(25 mg, 6.1 Â 10 mol) and
�
5
(
(
1
MeO)(MeOH)}, 3): An ethanolic solution (2 mL) of Co(OAc)
2
´ 4H
2
O
2
2
O (19 mg, 7.5 Â 10 mol) were dissolved separately in MeOH
�
4
71 mg, 2.83 Â 10 mol) was added to a solution of bdpma (100 mg, 2.83 Â
(total volume of 2 mL). The resulting red solution was stirred for 15 min
�
4
0
mol) in CH
3
CN (2 mL). The resulting dark blue solution was stirred
and then allowed to stand in a methyl tert-butyl ether bath. After 3 weeks, a
II
for 5 d at room temperature and then allowed to stand in an ethyl acetate
small quantity of dark green crystals of [tpip]
2
[Co Cl
4
] (5 mg, yield ˆ 18%)
bath. 51 mg (37%) of red crystals of 3 were collected and dried under
were filtered off and dried under vacuum. FAB-MS: m/z (%) ˆ 350 (100)
III
‡
‡
vacuum after two months. FAB-MS: m/z (%) ˆ 461 (100) [Co (dpkH)
2
] ,
[tpip] . The structure of 6 was determined by X-ray crystallography (see
II
‡
4
44 (16) [Co (dpkH)(dpk)] (dpk: di(2-pyridyl)ketone), 427 (4)
text, Scheme 4, and Tables 3 and 7).
Chem. Eur. J. 1999, 5, No. 6
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
0947-6539/99/0506-1773 $ 17.50+.50/0
1773

B. Meunier et al.
FULL PAPER
Dichloro{N-[di(2-pyridyl)methoxymethyl][di(2-pyridyl)imine]}iron(ii)
1995, 34, 1512; b) G. Roelfes, M. Lubben, S. W. Leppard, E. P.
Schudde, R. M. Hermant, R. Hage, E. C. Wilkinson, L. Que, Jr., B. L.
Feringa, J. Mol. Catal. A 1997, 117, 223.
II
(
4
[Fe (dpmmdpi)Cl
2
], 7): By the double-ended needle technique, FeCl
2
´
�
4
H
2
O (28 mg, 1.43 Â 10 mol) in degassed MeOH (2 mL) was added under
nitrogen atmosphere to a solution of two equivalents of [tpip](NO
(
3
)
[8] M. Renz, C. Hemmert, B. Meunier, Eur. J. Org. Chem. 1998, 1271.
[9] C. Hemmert, M. Renz, B. Meunier, J. Mol. Catal. A 1998, 137,
205.
[10] M. Renz, C. Hemmert, B. Donnadieu, B. Meunier, J. Chem. Soc.
Chem. Commun. 1998, 1635.
[11] a) A. Hazell, K. B. Jensen, C. J. McKenzie, H. Toftlund, J. Chem. Soc.
Dalton Trans. 1993, 3249; b) E. C. Wilkinson, Y. Dong, L. Que, Jr., J.
Am. Chem. Soc. 1994, 116, 8394.
�
4
99 mg, 2.85 Â 10 mol) in degassed MeOH (2 mL). The resulting solution
was stirred for 1 h under nitrogen and then allowed to stand under
anaerobic conditions in a methyl tert-butyl ether atmosphere. After one
week, a small quantity of dark blue crystals of 7 (7 mg, yield ˆ 10%) were
filtered off and dried under vacuum. FAB-MS: m/z (%) ˆ 472 (100)
II
‡
[
Fe (dpmmdpi)Cl] . The structure of 7 was determined by X-ray crystal-
lography (see text, Scheme 4, and Tables 5 and 7).
[
12] A. Hazell, K. B. Jensen, C. J. McKenzie, H. Toftlund, Inorg. Chem.
Dichloro-m-dichloro{bis[di(2-pyridyl)methoxymethanol]}dicobalt(ii)
II
1994, 33, 3127.
(
[Co
2
(dpmm)Cl
4
], 8): After two further weeks, an additional crop of violet
II
[13] S. Yan, D. D. Cox, L. L. Pearce, C. Juarez-Garcia, L. Que, Jr., J. H.
Zhang, C. J. OꢁConnor, Inorg. Chem. 1989, 28, 2507.
[14] O. Kahn, Molecular Magnetism, VCH, New York, 1993.
[15] C. J. OꢁConnor, Prog. Inorg. Chem. 1982, 29, 203.
[
[
[
crystals was obtained from the mother liquor of [tpip]
2
[Co Cl
4
]. These were
washed with methyl tert-butyl ether and dried under vacuum. 5 mg (24%)
II
‡
of 8 was obtained. FAB-MS: m/z (%) ˆ 462 (47) [Co (dpk)
2
Cl] , 278 (100)
II
‡
[
Co (dpk)Cl] . The structure of 8 was determined by X-ray crystallography
16] R. E. Norman, R. C. Holz, S. M e nage, C. J. OꢁConnor, J. H. Zhang, L.
(
see text, Scheme 4, and Tables 6 and 7).
Que, Jr., Inorg. Chem. 1990, 29, 4629.
17] S. O. Sommerer, J. D. Baker, W. P. Jensen, A. Hamza, R. A. Jacobson,
Inorg. Chim. Acta 1993, 210, 173.
Acknowledgments
II
18] The further evolution of the Fe species was not investigated, but a
reoxidation with molecular oxygen seemed very likely. Starting from
III
We are grateful to the CNRS for financial support, especially M.R. for a
postdoctoral fellowship. We are indebted to Dr. Jean-Pierre Costes (LCC-
CNRS) for his contribution to the interpretation of the magnetic measure-
ments, and we thank Alain Mari (LCC-CNRS) for magnetic measurements.
2
FeCl , the Fe dimer 2 was probably obtained as a result of slow
diffusion of molecular oxygen (Scheme 2). In the cobalt case, the
metal oxidation step should be the first one to generate a reducible
III
III
II
Co species and to enter the Co /Co oxidation system. In contrast,
II
III
for manganese the oxidation of the metal from Mn to Mn by
molecular oxygen is less favorable, even for a polypyridine complex.
Consequently, a stable Mn complex 1 could be isolated (Scheme 2)
II
[
[
1] L. Que, Jr., R. Y. N. No, Chem. Rev. 1996, 96, 2607.
2] W. O. Koch, H.-J. Krüger, Angew. Chem. 1995, 107, 2928; Angew.
Chem. Int. Ed. Engl. 1995, 34, 2671.
and no ligand degradation was detected.
[
19] This protonated species may be generated directly from the bdpma
ligand by abstraction of 2 electrons and 1 proton. As tpip has been
synthesized from the imine, the formula of the neutral form with
subsequent protonation is the preferred presentation in Scheme 5.
20] A. P. Krapcho, J. R. Powell, Tetrahedron Lett. 1986, 27, 3713.
21] D. Stalke, Chem. Soc. Rev. 1998, 27, 171.
22] G. M. Sheldrick, Acta Crystallogr. Sect. A. 1990, 46, 467.
23] G. M. Sheldrick, SHELXL-97, Program for Crystal Structure Refine-
ment, Universität Göttingen, 1997.
[
[
3] H. G. Jang, D. D. Cox, L. Que, Jr., J. Am. Chem. Soc. 1991, 113, 9200.
4] T. Funabiki, T. Yamazaki, A. Fukui, T. Tanaka, S. Yoshida, Angew.
Chem. 1998, 110, 527; Angew. Chem. Int. Ed. 1998, 37, 513.
5] A. Sorokin, L. Fraisse, A. Rabion, B. Meunier, J. Mol. Catal. A 1997,
[
[
[
[
[
[
117, 103.
6] a) A. Sorokin, J. L. S e ris, B. Meunier, Science 1995, 268, 1163; b) A.
Sorokin, S. De Suzzoni-Dezard, D. Poullain, J.-P. No eÈ l, B. Meunier, J.
Am. Chem. Soc. 1996, 118, 7410; c) A. Sorokin, B. Meunier, Acc.
Chem. Res. 1997, 30, 470; d) A. Hadasch, A. Sorokin, A. Rabion, B.
Meunier, New J. Chem. 1998, 22, 45.
[
24] H. D. Flack, Acta Crystallogr. Sect. A. 1983, 39, 876.
[
7] a) M. Lubben, A. Meetsma, E. C. Wilkinson, B. L. Feringa, L.
Que, Jr., Angew. Chem. 1995, 107, 1610; Angew. Chem. Int. Ed. Engl.
Received: November 20, 1998 [F1454]
1
774
ꢀ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
0947-6539/99/0506-1774 $ 17.50+.50/0
Chem. Eur. J. 1999, 5, No. 6