Complexes of 1,3-bis(2-thiazolylimino)isoindoline with middle and late first row transition metals

Article abstract of DOI:10.1016/j.inoche.2011.08.001

In this communication, we present a study that probes the middle and late first row transition metal chemistry of 1,3-bis(2-thiazolylimino)isoindoline, adding to the known Fe and Cu compounds. Complexes of this ligand with Mn, Co, Zn and a new Fe form are presented and all are structurally characterized by single crystal X-ray methods. The 1,3-bis(2-thiazolylimino)isoindoline ligand can potentially bind via the thiazolyl nitrogen or sulfur atoms; in all of the complexes presented in this report, the N,N,N binding mode is observed exclusively. The ligands bind in a planar configuration, similar to that seen for bis(2-iminopyridyl)isoindoline.

Full text of DOI:10.1016/j.inoche.2011.08.001

Inorganic Chemistry Communications 14 (2011) 1749–1752
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Inorganic Chemistry Communications
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Complexes of 1,3-bis(2-thiazolylimino)isoindoline with middle and late first row
transition metals
Goran Martić, James T. Engle, Christopher J. Ziegler ⁎
Department of Chemistry, University of Akron, Akron, OH 44325-3601, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
In this communication, we present a study that probes the middle and late first row transition metal chemistry of
Received 11 May 2011
Accepted 2 August 2011
Available online 22 August 2011
1
,3-bis(2-thiazolylimino)isoindoline, adding to the known Fe and Cu compounds. Complexes of this ligand with
Mn, Co, Zn and a new Fe form are presented and all are structurally characterized by single crystal X-ray methods.
The 1,3-bis(2-thiazolylimino)isoindoline ligand can potentially bind via the thiazolyl nitrogen or sulfur atoms; in
all of the complexes presented in this report, the N,N,N binding mode is observed exclusively. The ligands bind in
a planar configuration, similar to that seen for bis(2-iminopyridyl)isoindoline.
Keywords:
Diiminoisoindoline
Bis(imimoaryl)isoindoline
Late and middle first row transition metal
ions
©
2011 Elsevier B.V. All rights reserved.
Thiazole ligand
Homoleptic complexes
In the 1950s, Linstead and Elvidge presented a series of papers
reporting on the chemistry of the diiminoisoindoline (DII) heterocycle
of this ligand with copper has been examined by Meder and Gade [6],
Bröring and coworkers have explored the coordination chemistry of
this chelate with palladium [4,7], and very recently Pap et al. presented
a report on the Fe(III) complex of 1 [8]. Theoretically, compound 1 can
bind through NNN, SNN or SNS binding modes; in the iron and copper
complexes, the N,N,N mode is observed, but Bröring has reported a
SNN mode in the palladium complex of a sterically hindered form of
BTI [7]. In this report we present an extension of the coordination chem-
istry of 1 to additional late and middle first row transition metal ions, in-
cluding Mn(III), Co(III) and Zn(II) complexes. In addition, we have
isolated a variant of the previously reported Fe(III) complex and have
elucidated the structure of the free ligand. In all observed cases, the
NNN binding mode was adopted by the ligand. The ligand itself
binds to the metal ions in a planar configuration with slight deviations
of the thiazole rings. Both 2:1 and 1:1 ligand to metal complexes are
observed to form with chelate 1, as seen in the bis(2-iminopyridyl)
isoindoline.
[1]. This compound (Scheme 1), which can be considered as a subunit
of phthalocyanine, can be readily functionalized. Diiminoisoindoline
can be used to generate phthalocyanine analogs known as the hemipor-
phyrazines [2], as well as chelating ligands [3]. One method for modify-
ing diiminoisoindoline is via reaction with primary alkyl or aryl amines,
which results in bis(alkylimino) and bis(arylimino)isoindolines respec-
tively [1]. This reaction has been used to produce tridentate chelates,
and was first presented by Linstead and Elvidge in 1952 with the syn-
thesis of bis(2-iminopyridyl)isoindoline (BPI, Scheme 1) [1]. Initial in-
vestigations into the metal binding properties of this ligand were
presented in the same paper along with its synthesis. Over the decades
since its synthesis, the bis(2-iminopyridyl)isoindoline ligand has exhib-
ited rich metal chemistry, binding a variety of transition metal ions
[1,3,4]. These complexes have been used to model enzymatic active
sites [4,5] and as catalysts for organic transformations [4,6].
The chemistry observed with bis(2-iminopyridyl)isoindoline can
readily be extended to other coordinating heterocycles. However, to
date, little work has been carried out on chelating bis(arylimino)isoin-
dolines with groups other than pyridine. One metal binding aryl
group that has been incorporated into an isoindoline chelate is thiazole.
This ring is notable in that there are two potentially coordinating atoms
present in the ring: sulfur and nitrogen atoms. The resultant isoindoline
adduct is 1,3-bis(2-thiazolylimino)isoindoline (BTI, 1), which can act as
a monoanionic tridentate chelate (Scheme 1). Previously, the chemistry
The synthesis of 1 has been reported via two pathways: through a
modification of the original Linstead and Elvidge procedure in butanol
[1], and by the method developed by Siegl using the reaction of
2
phthalonitrile and aminothiazole with CaCl as the catalyst (Scheme 2)
[4]. We were able to generate compound 1 by use of the former method,
which resulted in analytically pure crystals from the reaction solution
without any observable phthalocyanine production. These crystals
were suitable for X-ray diffraction structure elucidation, and Fig. 1
shows the structure of 1. Table 1 contains crystal data and elucidation
parameters for the structure of 1. Globally, the structure of 1 resembles
that of the bis(2-iminopyridyl)isoindoline chelate. In the free ligand, the
nitrogen atoms face the interior of the chelate in a way such that the
NNN binding would be preferred. The reason for this orientation is
⁎
Corresponding author.
E-mail address: ziegler@uakron.edu (C.J. Ziegler).
1387-7003/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2011.08.001

1750
G. Martić et al. / Inorganic Chemistry Communications 14 (2011) 1749–1752
acid nature of the metals and oxidation states presented in this report,
and the weak basicity of the sulfur of the thiazole ring.
We were able to isolate complexes of 1 by reaction of the free base
ligand with various metal salts in methanol solution. In all cases, crys-
talline products formed upon concentration of the reaction solution
and, with the exception of the nickel complex, the crystals were suit-
able for single crystal X-ray structure elucidation. Table 1 contains the
X-ray data and elucidation parameters for these structures. Fig. 2
shows the structures of the Mn, Fe, Co, and Zn complexes of 1. The
middle transition metal adducts (1Mn, 1Fe and 1Co) are all 2:1 ligand
to metal complexes, whereas the complex 1Zn has a 1:1 ligand to
metal ratio as seen in the previously elucidated Cu(II) complex. In
Scheme 1. The structures of DII (left), BPI (center) and compound 1 (right).
1
Zn, the remainder of the coordination sphere is occupied by solvent
molecules. Previous work on the bis(2-iminopyridyl)isoindoline li-
gand has shown that control of reactant stoichiometry can be used
to generate 1:1 complexes with metals such as manganese [4].
In all of the metal complexes of 1, there are several common charac-
teristics observed in the ligand binding geometries. First, the ligand binds
in an asymmetric fashion to metals, resulting in different M\Nthiazole and
M\Nindoline lengths. Table 2 lists the M\N bond lengths for the metal
complexes presented in this report. As expected, the M\Nindoline bonds
are appreciably shorter than the M\Nthiazole bonds; this primarily
results from the negative charge on the isoindoline nitrogen versus
the lack of charge on the azole nitrogen. Similar bond length
disparities are observed in the bis-pyridine hemiporphyrazines [2] and
in bis(2-iminopyridyl)isoindoline complexes, where the M\Nisoindoline
bonds are markedly shorter than the M\Npyridyl bonds. The bis-ligand
complexes 1Mn, 1Fe and 1Co adopt distorted octahedral geometries,
with compression along the axis that is aligned with the M\Nindoline
bonds. As can be seen in Fig. 2, all three homoleptic complexes exhibit
nearly identical coordination environments. As mentioned above, the
M\Nisoindoline are shorter than the M\Npyridine bonds, however in the
Fig. 1. The structure of 1 with 35% thermal ellipsoids. Hydrogen atoms have been omit-
ted for clarity.
1
Mn complex the difference between these bond lengths is much great-
er than the other two, on the order of b0.25 Å. We can readily deter-
mine the oxidation states in these three compounds as Mn(III), Fe(III)
and Co(III) respectively by the charges of the ligand (monoanionic)
and the presence of an anion in the asymmetric units of 1Mn and 1Fe.
The anion in the Co(III) complex 1Co was disordered and difficult to lo-
cate on the difference map, and the overall quality of the dataset was
limited by twinning problems, but the presence of a normal 1H NMR
spectrum along with the observed bond lengths led to an unambiguous
Co(III) assignment. Susceptibility measurements as well as bond
lengths can also be used to determine the spin states of these three
compounds. For the Fe(III) complex, we observed short bond lengths
and a susceptibility (μeff=3.91 BM) that correlate with an intermediate
spin system (S=3/2), whereas in the Mn(III) compound we observed a
due to hydrogen bonding interactions between the nitrogen atoms on
the thiazole ring and the isoindoline NH group; the N\N distances
measure ~2.72 and ~2.70 Å. Although in the free base this is the pre-
ferred orientation, the thiazole can potentially rotate such that the sul-
fur would be oriented toward a chelated metal, affording the S-bound
coordination isomers. Bröring discusses such coordination isomerism
in the palladium complexes of bis(4-tert-butylthiazolyl)indoline, bis
(
2-iminopicolinyl)isoindolines [7] and bis(2-iminobromopyridinyl)iso-
indoline [4]. However, as will be shown below, compound 1 was found
to chelate to first row transition metals exclusively in the N,N,N binding
mode. The preference for this mode most likely results from the hard
Table 1
X-ray data collection and structure parameters for the compounds presented in this report. All structures were collected at 100(2) K.
Compound
1
1Mn
1Fe
1Co
1Zn
Empirical formula
C
12
H
9
N
5
S
2
C
30
H
18
C
l6
N
11
O
3
S
4
Mn
C
30
H
24
N
11
O
S
5 4
Fe
C
28
H
16
N
10
4
S Co
17 20 5 7 2
C H N O S ZnCl
Formula weight
311.38
976.43
802.69
679.68
571.36
Crystal system space group
a, Å
b, Å
c, Å
α, °
β, °
γ, °
V, Å [3]
Monoclinic, P2(1)/c
14.678(3)
4.6240(10)
20.047(4)
90
102.146(3)
90
1330.2(5)
4
Monoclinic, P2(1)/c
11.5686(15)
28.696(4)
11.2240(15)
90
92.523(2)
90
3722.4(9)
4
Monoclinic, P2(1)/c
12.0797(10)
15.4733(12)
17.5335(14)
90
91.5210(10)
90
3276.1(5)
4
Monoclinic, Pc
14.513(4)
15.229(5)
16.749(5)
90
115.431(5)
90
3343.1(18)
4
Triclinic, P-1
9.371(4)
10.272(5)
12.285(5)
98.442(7)
95.652(7)
109.691(7)
1087.3(8)
2
Z
D
calc, mg m−
3
1.555
1.742
1.627
1.35
1.745
Unique reflections
10054
30923
26292
27618
8907
DataN2σ/parameters/restraits
2861/190/0
0.0558, 0.1235
1.036
8112/498/0
0.0426, 0.1014
0.951
7119/464/0
0.0393, 0.1056
1.093
13950/775/8
0.472, 0.0844
0.806
4636/313/0
0.0516, 0.1102
0.821
R
1
[F2N2σ (F2)], wR
2
(F2)
Goodness of fit

G. Martić et al. / Inorganic Chemistry Communications 14 (2011) 1749–1752
1751
Table 2
M\N bond distances in compounds 1Mn, 1Fe, 1Co, and 1Zn.
M\Nindoline (Å)
Mn\Nthiazole (Å)
1
1
1
1
Mn 1.968(2), 1.967(2)
2.143(2), 2.165(2), 2.134(2), 2.141(2)
Fe
Co
Zn
1.9283(15), 1.9216(16) 1.9849(16), 1.9912(15), 1.9831(15), 1.9707(15)
1.913(4), 1.931(4)
2.056(4)
1.955(4), 1.954(4), 1.962(4), 1.964(4)
2.092(4), 2.096(4)
a perchlorate, is non-coordinating. The compound is in the divalent
oxidation state, as evinced by the presence of a counter ion in the
crystal structure, bond length distances and by a diamagnetic NMR
spectrum observed in 1Zn. The structure of this compound is very
similar to that seen in the Cu(II) complex of 1 reported by Meder
and Gade [6].
Scheme 2. Synthetic pathways for compound 1.
In conclusion, we present an investigation into the synthesis of the
first row transition metal complexes of the 1,3-bis(2-thiazolylimino)
isoindoline ligand, 1. This compound can be readily generated via the
reaction of aminothiazole with diiminoisoindoline in butanol solution,
resulting in the formation of pure crystals of 1 without phthalocyanine
contamination. Compound 1 readily forms complexes with first row
transition metal ions in both 1:1 and 2:1 stoichiometries, but in all
cases chelates via the nitrogen atoms rather than the thiazole sulfur
atoms. As in other bis(2-iminoaryl)isoindoline ligands, compound 1
binds to metal ions in a tridentate, planar fashion. We are continuing
larger susceptibility that corresponds to an S=2 spin system. Notably,
the Mn\N bonds in 1Mn are longer than those seen in 1Fe.
The 1:1 complex 1Zn (Fig. 2) has the remainder of the coordina-
tion sphere occupied by solvent methanol molecules. 1Zn adopts an
octahedral coordination environment, with three meridonal positions
occupied by neutral methanol solvent molecules. The Zn\O bond dis-
tances in 1Zn are 2.193(3), 2.116(4), and 2.157(3)Å, which correlate
well with neutral methanol binding to Zn(II). The counter ion in 1Zn,
Fig. 2. Structures of 1Mn, 1Fe, 1Co, and 1Zn with 35% thermal ellipsoids. Hydrogen atoms and anions have been omitted for clarity.

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G. Martić et al. / Inorganic Chemistry Communications 14 (2011) 1749–1752
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CCDC 824820–824824 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif. Supplementary materials related to this article
can be found online at doi: 10.1016/j.inoche.2011.08.001.
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