Hydrogen bonding in 2,3-dithiolatoterephthaldiamide complexes of Cobalt(III), Nickel(II), and Iron(III)

Article abstract of DOI:10.1002/ejic.201000169

The synthesis and characterization of the novel 2,3- dithiolatoterephthaldiamide ligands C₆H₂{C(O)NHBn} ₂(SH)₂ (H₂-1a) and C₆H ₂{C(O)NH-iP:r}₂(SH)₂ (H₂-Ib) as well as their complexes with Ni^II, Co_III, and Fe^III is described. The molecular structures of the complexes (NEt ₄)[Co(1a)₂], (AsPh₄h₂[Ni(1b) ₂]·dmf, and (AsPh⁴)[Fe(1a)2]·CH ₂Cl₂ were determined by single-crystal X-ray diffraction. Electronic absorption spectroscopy and cyclic voltammetry were applied to investigate the electronic properties of the complex anions [M(L) ₂]^n-(M = Ni, Co; L = 1a, 1b; n = 1, 2). Comparison of the structural and electronic characteristics of the complexes with ligands 1a ^2- and 1b^2- to those of the corresponding complexes with related benzene-o-dithiolato ligands indicates a notable influence of intramolecular N-H... S hydrogen bonding between amide protons and coordinated sulfur atoms in 2,3-dithiolatoterephthalamide complexes.

Full text of DOI:10.1002/ejic.201000169

FULL PAPER
DOI: 10.1002/ejic.201000169
Hydrogen Bonding in 2,3-Dithiolatoterephthaldiamide Complexes of
Cobalt(III), Nickel(II), and Iron(III)
F. Ekkehardt Hahn,*[a] Thomas Eiting,[a] Wolfram W. Seidel,[a] and Tania Pape[a]
Dedicated to Professor Uwe Rosenthal on the occasion of his 60th birthday
Keywords: Dithiolenes / Hydrogen bonding / X-ray diffraction / Cobalt / Nickel / Iron
The synthesis and characterization of the novel 2,3-dithiol-
atoterephthaldiamide ligands C6H2{C(O)NHBn}2(SH)2 (H2-1a)
and C6H2{C(O)NH-iPr}2(SH)2 (H2-1b) as well as their com-
plexes with NiII, CoIII, and FeIII is described. The molecular
structures of the complexes (NEt4)[Co(1a)2], (AsPh4)2[Ni-
(1b)2]·dmf, and (AsPh4)[Fe(1a)2]·CH2Cl2 were determined by
single-crystal X-ray diffraction. Electronic absorption spec-
troscopy and cyclic voltammetry were applied to investigate
the electronic properties of the complex anions [M(L)2]n– (M
= Ni, Co; L = 1a, 1b; n = 1, 2). Comparison of the structural
and electronic characteristics of the complexes with ligands
1a2– and 1b2– to those of the corresponding complexes with
related benzene-o-dithiolato ligands indicates a notable in-
fluence of intramolecular N–H···S hydrogen bonding be-
tween amide protons and coordinated sulfur atoms in 2,3-
dithiolatoterephthalamide complexes.
In this contribution we present the first nickel(II), co-
balt(III), and iron(III) complexes with 2,3-dithiolatotere-
phthaldiamide ligands. The molecular structures as well as
the electronic properties of these complexes are compared
with the prototype complexes of the unsubstituted benzene-
o-dithiolato ligand (bdt2–). The goal of this work was to
investigate the influence of the amide substituents on the
molecular structures and the electronic properties of the re-
sulting (benzene-o-dithiolato)metal complexes.
Introduction
During the last decades (dithiolene)metal complexes have
attracted considerable interest owing to their distinctive
molecular and electronic structures.[1] In addition, their bio-
logical relevance[2] and potential applications in materials
science[3] with respect to photonics, electronic conductors
and magnetochemistry have stimulated further investi-
gations. Recent comprehensive studies of the electronic
structure of square-planar bis(benzene-o-dithiolato) com-
plexes confirmed the non-innocent nature of enedithiolato
ligands showing that they can form S,S-coordinated di-
thio(1–) π-radical anions by intramolecular redox pro-
cesses.[4]
Results and Discussion
Synthesis of Ligands and Complexes
Our research in the field of enedithiolates is driven by
attempts to incorporate the benzene-o-dithiolato binding
unit into larger polydentate ligands and to use these for the
generation of metallosupramolecular assemblies like triple-
stranded homo- and heterodimetallic helicates[5a–5j] or poly-
nuclear clusters.[5k–5m] In these efforts, 2,3-dimercapto-
terephthalic acid is a particularly valuable building block
due to the functionalization of the benzene-o-dithiol in
both ortho positions. In addition, intermolecular hydrogen
bonding has been shown to be of importance for the forma-
tion of solid-state networks from nickel complexes with
suitably functionalized dithiolene ligands.[6]
The ligands H2-1a and H2-1b were prepared by using a
protocol described previously (Scheme 1).[7] 2,3-Dimercap-
toterephthalic acid (2)[7a] was converted into the S,S-di-
alkylated derivative 3 in order to protect the thiol groups.
Subsequently, the terephthaldiamides 4a and 4b were pre-
[a] Institut für Anorganische und Analytische Chemie,
Westfälische Wilhelms-Universität Münster
Corrrensstraße 30, 48149 Münster, Germany
Fax: +49-251-833-3108
E-mail: fehahn@uni-muenster.de
Scheme 1. Synthesis of ligands H2-1 and H2-2.
Eur. J. Inorg. Chem. 2010, 2393–2399
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2393

F. E. Hahn, T. Eiting, W. W. Seidel, T. Pape
FULL PAPER
pared by conventional amide synthesis using either benzyl-
or isopropylamine. Cleavage of the S-isopropyl bonds in 4a
and 4b with sodium/naphthalene in thf yielded, after hy-
drolysis, the ligands H2-1a and H2-1b, respectively.[5,7]
Reaction of the metal salts CoCl2·6H2O or NiCl2·6H2O
with 2 equiv. of either H2-1a or H2-1b, respectively, in meth-
anol in the presence of 4 equiv. of LiOMe gave red-brown
solutions in all cases. For M = Co the solutions immediately
turned deep blue upon aerial oxidation, indicating the for-
mation of the CoIII complexes Li[Co(1a)2] and Li[Co(1b)2].
The corresponding nickel compounds on the other hand
were isolated under anaerobic conditions as NiII complexes
Li2[Ni(1a)2] or Li2[Ni(1b)2]. After cation exchange with
either Et4NCl or Ph4AsCl in methanol solution, complexes
(Et4N)[CoIII(1a)2] (5a), (Ph4As)[CoIII(1b)2] (5b), (Et4N)2-
[NiII(1a)2] (6a), and (Ph4As)2[NiII(1b)2] (6b) were isolated
as blue solids in the case of the cobalt complexes and as
red solids in the case of the nickel complexes (Scheme 2).
Salts 5a and 6a with the N-benzylamide substituents are
only soluble in highly polar solvents such as dmf (dmf =
N,NЈ-dimethylformamide), whereas 5b and 6b with N-iso-
propylamide substituents are soluble in less polar solvents
like CH2Cl2 and CHCl3. Interestingly, the substitution
pattern at the amide functionality and the type of the coun-
terion has a stronger influence on the solubility than the
charge of the complex anions. The FeIII complex (Ph4As)-
[Fe(1a)2] (7), was prepared in an analogous procedure by
using FeCl3 as metal precursor (Scheme 2).
Figure 1. Molecular structure of the anion [Co(1a)2]– in 5a. Ther-
mal ellipsoids are drawn at the 50% probability level (hydrogen
atoms and cations have been omitted for clarity). Selected bond
angles [°]: S1–Co–S2 91.43(5), S1–Co–S3 179.72(7), S1–Co–S4,
88.45(5), S2–Co–S3 88.65(5), S2–Co–S4 178.15(6), S3–Co–S4
91.46(5), Co–S1–C1 105.05(15), Co–S2–C2 105.20(14), Co–S3–C23
104.72(14), Co–S4–C24 105.16(14).
Table 1. Selected bond lengths [Å] in 5a, 6b·dmf and 72·2CH2Cl2.
5a (M = Co) 6b (M = Ni1)[a] 6b (M = Ni2)[a] 7 (M = Fe)
M–S1[b]
M–S2[b]
M–S3
2.162(1)
2.172(1)
2.163(1)
2.169(1)
2.144(1)
2.148(1)
2.147(1)
2.139(1)
2.220(1)
2.231(1)
2.212(1)
2.244(1)
2.494(1)
1.748(4)
1.766(4)
1.757(4)
1.768(4)
1.408(6)
1.402(6)
M–S4
M–S4*
C1–S1[b]
C2–S2[b]
C23–S3
C24–S4
C1–C2[b]
C23–C24
1.758(4)
1.771(4)
1.750(4)
1.765(4)
1.401(6)
1.399(5)
1.764(4)
1.754(3)
1.759(3)
1.761(4)
1.415(5)
1.421(5)
[a] The asymmetric unit contains two crystallographically indepen-
dent halves of the formula unit of 6b, both nickel atoms reside on
crystallographic inversion centers. [b] For M = Ni2: C21, C22, S21
and S22.
Alternatively, cobalt(III) complexes bearing electron-
2–
withdrawing benzene-o-dithiolato ligands like S2C6Cl4 or
2–
S2C6H2(CN)2 have been reported to dimerize.[9] Such di-
Scheme 2. Preparation of the metal complexes.
mers are formed by µ2-coordination of a single sulfur atom
of an individual CoS4 moiety to the apical position of a
second CoS4 unit and vice versa. Surprisingly, in spite of
the electron-withdrawing nature of the amide substituents,
no such intermolecular interactions have been observed for
5a. In the solid state the anions of 5a are connected by
Molecular Structures
The molecular structures of 5a, 6b and 7 have been deter- intermolecular N–H···O hydrogen bonds between amide
mined by X-ray diffraction analysis. Single crystals of 5a groups (shortest N···O distance 2.75 Å). The CoS4 moieties
and 6b·dmf were obtained by vapor diffusion of diethyl are well separated, and the closest intermolecular Co···S
ether into saturated solutions of the complexes in dmf. distances measure more than 8 Å.
Vapor diffusion of diethyl ether into a concentrated dichlo-
romethane solution of 7 yielded crystals of 72·2CH2Cl2, 6b·dmf is shown in Figure 2, and selected bond lengths are
which were suitable for an X-ray diffraction study. listed in Table 1. The asymmetric unit of 6b·dmf contains
The molecular structure of the dianion [Ni(1b)2]2– in
The molecular structure of the complex anion [Co- two independent halves of the complex dianion, two
(1a)2]– in 5a is depicted in Figure 1, and selected bond Ph4As+ cations and one dmf molecule. Only one of the es-
lengths are listed in Table 1. The complex anion shows an sentially identical complex anions in the unit cell is depicted
overall square-planar coordination geometry. The Co–S in Figure 2. As expected, the nickel centers in the two inde-
and C–S distances fall in the typical range and match those pendent molecules of 6b are surrounded by two benzene-o-
reported for [Co(S2C6H4)2]–[8a] and [Co(S2C6H3CH3)2]–.[8b]
dithiolato ligands in a square-planar fashion. The Ni–S
2394
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2393–2399

2,3-Dithiolatoterephthaldiamide Complexes of CoIII, NiII, and FeIII
bond lengths, which fall in the range between 2.139(1) and 2.901 Å). Contrary to this observation, the cobalt(III) com-
2.148(1) Å, are somewhat shorter than those reported for plex anion [CoIII(1a)]– in 5a, possessing the same charge as
the comparable NiII complex dianions [Ni(bdt)2]2– [Fe(1a)2]–, shows no tendency for a dimerization by either
[2.168(4)–2.181(4)][10] and [Ni{S2C6H2(tBu2)}2]2– [2.172(1) intermolecular Co–S interactions or by N–H···O hydrogen
and 2.175(1)].[11] In addition, the chelate rings in [Ni- bonding.
(1b)2]2– are folded about the S–S vector (Figure 2, bottom).
For example, the angle between the planes S1–Ni1–S2 and
S1–C1–C2–S2 measures 16.7°. Such a folding is rather atyp-
ical for bis(benzene-o-dithiolato) group 10 metal complexes
but has been observed regularly for titanium complexes
bearing bdt2– ligands.[5] In contrast to the situation found
for 5a, the NH groups of the amide substituents in 6b are
directed towards the sulfur atoms. The intramolecular N···S
distances measure about 2.96 Å indicating an intramolecu-
lar N–H···S hydrogen-bond interaction. This observation
can be attributed to the higher charge of the [Ni(1b)2]2– di-
anion compared to the monoanion [Co(1a)2]– where no in-
dications for intramolecular N–H···S interactions have been
found in the solid state.
2–
Figure 3. Molecular structure of the dianion [Fe(1a)2]2
in
72·2CH2Cl2 formed from two formula units of 7. Thermal ellipsoids
are drawn at the 50% probability level (carbon-bound hydrogen
atoms, cations, solvent molecules and the phenyl groups of the
benzyl amide substituents have been omitted for clarity). Selected
bond angles [°]: S1–Fe–S2 88.71(5), S1–Fe–S3 87.60(5), S1–Fe–S4
164.31(5), S2–Fe–S3 155.53(5), S2–Fe–S4 89.01(5), S3–Fe–S4
88.07(5), S1–Fe–S4* 99.89(5), S2–Fe–S4* 103.95(5), S3–Fe–S4*
100.52(5), S4–Fe–S4*, 95.72(5), Fe–S4–Fe* 84.28(5), Fe–S1–C1
106.9(2), Fe–S2–C2 106.3(2), Fe–S3–C23 107.1(2), Fe–S4–C24
107.01(2).
The bond lengths and angles within the Fe2S8 core of the
2–
[Fe(1a)2]2 anion match those found in similar complexes
described in the literature.[13,14] The distinctively long Fe–
S4* bond in the apical position (Table 1) indicates the
weakness of the interaction, which is corroborated by the
recent isolation of the mononuclear, base-stabilized FeIII
complex [Fe(bdt)2(thf)]–.[15] The chelate rings in [Fe(1a)2]–
are essentially planar.
Figure 2. Molecular structure of the dianion [Ni(1b)2]2– in 6b·dmf.
Thermal ellipsoids are drawn at the 50% probability level (carbon-
bound hydrogen atoms, cations and solvent molecules have been
omitted for clarity). Selected bond angles [°] for molecule 1 [mole-
cule 2]: S1–Ni1–S2 89.57(4) [90.40(4)], S1–Ni1–S2* 90.43(4)
[89.60(3)], N1–S1–C1 107.14(12) [106.76(12)], N1–S2–C2
107.04(13) [106.39(12)].
Electronic Properties
Quasi-reversible electron-transfer waves (peak-to-peak
potential differences 82–107 mV) for the redox couples
[ML2]2–/[ML2]– with M = CoIII and NiII and L = 1a2– and
The X-ray analysis showed that the anions of compound 1b2– (Figure 4) allowed an estimation of the half-wave po-
7·CH2Cl2 dimerize in the solid state with formation of the tentials. The E1/2 values are listed in Table 2 together with
dinuclear dianion [Fe(1a)2]22–. This dianion resides on a those of related benzene-o-dithiolato complexes. The half-
crystallographic inversion center (Figure 3, Table 1). The di- wave potentials of the cobalt complexes in dmf were deter-
merization has been expected since bis(benzene-o-dithiol- mined as E1/2 = –1040 mV for 5a and E1/2 = –1080 mV for
ato)iron complexes are only monomeric with iron(II),[12] 5b (vs. Fc+/Fc in all cases). These half-wave potentials fall
whereas the corresponding iron(III) complexes dimerize[13] in between the E1/2 values reported for the redox couples of
regardless of the electron-withdrawing or -donating charac- [Co{S2C6H3C(O)NHR}2]2–/– bearing benzene-o-dithiolato
ter of the substituents at the benzene-o-dithiolato donor ligands with only one amide substituent[16] and
2–
groups.[14] The complex anion [Fe(1a)2]2 consists of two [Co(S2C6Cl4)2]2–/– bearing two tetrachloro-substituted ben-
FeS4 moieties, which are linked by two intermolecular Fe– zene-o-dithiolato ligands.[17] This observation can be ration-
S–Fe bridges leading to a distorted square-pyramidal coor- alized by the relative strength of the inductive effects of the
dination at each iron atom. In addition, the two [Fe(1a)2]– substituents at the benzene-o-dithiolato ligand. The formal
subunits are connected by hydrogen bonds between the addition of an amide substituent to the benzene-o-di-
amide groups (Figure 3; O2···N3* 2.854 Å, N1···O4* thiolato ligands causes a change of the potential of approxi-
Eur. J. Inorg. Chem. 2010, 2393–2399
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2395

F. E. Hahn, T. Eiting, W. W. Seidel, T. Pape
FULL PAPER
mately 0.12 V for the bis(benzene-o-dithiolato)cobaltate diamide-substituted benzene-o-dithiolato ligands) we be-
complexes. The whole potential range, marked by the came interested in the influence of the particular type of
electron-poor [Co{S2C6H2(CN)2}2]2–/– with two electron- amide, N-benzylamide in 1a2– and N-isopropylamide in
withdrawing cyano groups[9a] and the electron-rich 1b2–. For the cobaltate complexes 5a and 5b the half-wave
[Co(S2C6Me4)]2–/– with four electron-donating methyl potentials differed by 40 mV (Figure 4, Table 2). The same
groups,[17] spans more than 1.0 V, indicating the strong in- effect is observed with the nickel complexes where estimated
fluence of the ligand substitution on the redox potential in values of E1/2 = –660 mV for 6a and E1/2 = –710 mV for 6b
this type of complexes. The order of potentials in Table 2 were recorded (Figure 4, Table 2).
reveals that to date complex anion [Co(1a)2]– represents the
Intramolecular N–H···S hydrogen bonds, which have
upper potential limit for mononuclear [Co(S2C6X4)2]– com- been observed in the solid-state structure of [Ni(1b)2]2– in
plexes, since complexes with even more electron-poor ben- 6b·dmf most likely account for this difference. The higher
zene-o-dithiolato ligands such as [Co(S2C6Cl4)2]– or acidity of N-benzylamides relative to N-isopropylamides
[Co{S2C6H2(CN)2}2]– have been found to dimerize in the leads to a better hydrogen-donor ability of the former. The
solid state.[9]
underlying difference is evident, for instance, in the 1H
NMR spectra of the diamides 4a and 4b in CDCl3, in which
the signal of the amide protons appears at δ = 7.04 ppm for
the N-benzylamide and at δ = 6.35 ppm for the N-isoprop-
ylamide. The latter resonance is low-field-shifted to δ =
7.75 ppm for (Ph4As)2[Ni(1b)2] measured likewise in
CDCl3. Unfortunately, (Et4N)2[Ni(1a)2] is not soluble in
CDCl3 to allow a comparison. A stronger intramolecular
N–H···S interaction would stabilize the lower oxidation
state due to a charge reduction at the sulfur atoms. There-
fore, the bis(benzene-o-dithiolato) complexes with four N-
benzylamide substituents (5a and 6a) are easier to reduce
as indicated by the higher E1/2 values. The adjustment of
the redox potential by hydrogen bonding to sulfur atoms
has been found to be an essential property for the function
of iron–sulfur proteins.[19]
For the measurement of the electronic spectra, the nickel
complexes 6a and 6b were oxidized by air in order to ob-
serve the typical low-energy charge-transfer bands. The UV/
Vis spectroscopic data of (Et4N)[NiIII(1a)2], (Ph4As)-
[NiIII(1b)2] and those of the corresponding cobalt(III) com-
plexes 5a and 5b are compared with data of related com-
plexes from the literature in Table 2. From Table 2 it is evi-
dent that the position of the dominant charge-transfer
bands in the visible region varies only slightly with the li-
gand type. In addition, no clear trend can be derived, which
is in contrast to the trends observed for the redox poten-
tials. Recent comprehensive calculations by Neese and
Wieghardt et al. on bis(benzene-o-dithiolato) complexes led
to the conclusion that these 1b1uǞ2b2g transitions are li-
gand-to-ligand (LLCT) in character with nickel[4a] and of
mixed nature ligand-to-ligand (LLCT) and ligand-to-metal
(LMCT) with cobalt.[12a] These results corroborate our ob-
servation that a particular type of ligand influences the re-
dox potential, whereas the same does not apply to the
charge-transfer bands.
Figure 4. Cyclic voltammograms of 5a (gray line), 5b (gray dotted
line), 6a (black line), 6b (black dotted line), solvent dmf, scan rate
100 mV·s–1.
Table 2. Electronic data of bis(benzene-o-dithiolato)metal com-
plexes.
L in [ML2]–
E1/2 [V] vs. Fc/Fc+
λ (1b1uǞ2b2g) [nm]
M = Co
M = Ni
M = Co M = Ni
2–[7]
S2C6Me4
–1.48[a]
–1.15[a]
–1.10
680[b]
671[b]
660[b]
657[b]
653[b]
654[e]
662[e]
667[b]
926[b]
890[b]
860[c]
881[b]
860[d]
870[e]
864[e]
885[b]
2–[4a,17]
S2C6H2(tBu)2
S2C6H3Me2–[13a,17]
–1.31[a]
–1.28[a]
–0.97[a]
–0.95[a]
–0.78[d]
–0.66[d]
–0.71[d]
–0.43[a]
–0.02[f]
2–[17]
S2C6H4
S2C6H3C(O)NHR2–[16] –1.16[d]
1a2–
–1.04[d]
–1.08[d]
–0.75[f]
–0.31[f]
1b2–
2–[17]
S2C6Cl4
2–[9a]
S2C6H2(CN)2
[a] Adjusted according to ref.[18] to Fc/Fc+ standard; originally
measured vs. Ag/AgClO4 in dmf. [b] Dichloromethane solution. [c]
MeCN solution. [d] dmf solution. [e] MeOH solution. [f] Adjusted
according to ref.[18] to Fc/Fc+ standard; originally measured vs. Ag/
AgNO3 in MeCN.
Conclusions
In search for new transition metal complexes with ben-
Given the relative moderate potential changes caused by zene-o-dithiolato ligands we have synthesized the diamide-
addition of amide groups to the benzene-o-dithiolato li- functionalized derivatives H2-1a and H2-1b derived from
gands (120 mV for cobaltate complexes for the transition terephthalic acid. These ligands form bis(benzene-o-dithiol-
from monoamide-substituted benzene-o-dithilato ligands to ato) complexes with FeIII, CoIII, and NiII, which adopt the
2396
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2393–2399

2,3-Dithiolatoterephthaldiamide Complexes of CoIII, NiII, and FeIII
expected square-planar coordination geometry with NiII
and CoIII and a square-pyramidal geometry with FeIII due
to dimerization of the anion [Fe(1a)2]– to the dinuclear di-
anion [Fe(1a)2]22–. No such dimerization has been observed
for the CoIII congener. This observation indicates that the
dimerization for M = CoIII is restricted to complexes bear-
ing benzene-o-dithiolato ligands with strongly electron-
withdrawing substituents. In this context, cyclic voltamme-
try studies allowed the classification of the new 1,2-dithiol-
SOCl2 (1.5 mL) and a few drops of dmf was heated under reflux
for 2 h. The oily terephthalic dichloride obtained after removal of
the solvent was dissolved in thf (20 mL), and the resulting solution
was added to
a solution of either benzylamine (1.02 mL,
9.34 mmol) or isopropylamine (0.83 mL, 9.34 mmol) and NEt3
(2 mL, 14.35 mmol) in thf (20 mL). After stirring at room tempera-
ture for 12 h, the reaction mixture was filtered, and the filtrate was
concentrated to dryness in vacuo. The residue was washed with
water and diethyl ether (4a) or n-hexane (4b) to obtain a white
1
solid. 4a: Yield: 1.75 g (75%). H NMR (200 MHz, CDCl3 25 °C):
atoterephthaldiamide ligands on the redox scala of related δ = 7.43–7.18 (m, 12 H, Ar-H), 7.04 [t, 2 H, C(O)NH], 4.62 (d, 4
H, NCH2Ph), 3.42 (sept, 2 H, SCH), 1.13 (d, 12 H, CH3) ppm.
13C NMR (50.32 MHz, CDCl3, 25 °C): δ = 167.7 [C(O)NH], 143.6,
138.0, 137.6, 129.0, 128.7, 128.2, 127.6 (Ar-C), 44.2 (NCH2Ph),
41.4 (SCH), 22.8 (CH3) ppm. 4b: Yield: 1.56 g (84%). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 7.49 (s, 2 H, Ar-H), 6.35 [d, 2 H,
C(O)NH], 4.20 (sept, 2 H, NCH), 3.44 (sept, 2 H, SCH), 1.20 (d,
12 H, CH3), 1.15 (d, 12 H, CH3) ppm. 13C NMR (50.32 MHz,
CDCl3, 25 °C): δ = 166.8 [C(O)NH], 143.6, 137.5, 128.6 (Ar-C),
41.8 (NCH), 41.0 (SCH), 22.7 (CH3), 22.3 (CH3) ppm.
benzene-o-dithiolato ligands. In addition, our studies re-
vealed an influence of the particular amide type on the re-
dox potential of the coordinated metal center. This effect
can be attributed to intramolecular N–H···S hydrogen inter-
actions, which are evident in the solid-state structure of
(Ph4As)2[Ni(1b)2].
Experimental Section
N,NЈ-Dibenzyl-2,3-dimercaptoterephthalamide (H2-1a) and N,NЈ-
Diisopropyl-2,3-dimercaptoterephthalamide (H2-1b): Compound 4a
(1.5 g, 3.06 mmol) and naphthalene (1.18 g, 9.18 mmol) were dis-
solved in thf (80 mL), and pieces of sodium (420 mg, 18.36 mmol)
were added. The mixture was stirred at ambient temperature for
12 h, and then methanol (10 mL) was added dropwise. After
10 min, the solvents were removed in vacuo, the residue was dis-
solved in degassed water (20 mL), and the mixture was filtered. The
aqueous filtrate was washed with diethyl ether (3ϫ 10 mL) and
acidified with hydrochloric acid (37%) to afford a white solid. The
precipitate was filtered off and washed with water (2ϫ 20 mL) and
diethyl ether (2ϫ 10 mL). Drying in vacuo yielded H2-1 as a white
powder (0.85 g, 68%). 1H NMR (200 MHz, CDCl3, 25 °C): δ =
9.15 [t, 2 H, C(O)NH], 7.77–7.44 (m, 12 H, Ar-H), 4.62 (d, 4 H,
NCH2Ph), 3.98 (s br, 2 H, SH) ppm. 13C NMR (50.32 MHz,
CDCl3, 25 °C): δ = 169.5 [C(O)NH], 139.9, 136.4, 133.8, 127.6,
127.2, 124.9 (Ar-C), 43.7 (NCH2Ph) ppm. The same procedure for
4b (0.8 g, 2.0 mmol) gave H2-1b (0.54 g, 86%). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 8.52 [d, 2 H, C(O)NH], 7.87 (s, 2
H, Ar-H), 4.92 (br. s, 2 H, SH), 4.03 (sept, 2 H, NCH), 1.16 (d, 12
H, CH3) ppm. 13C NMR (50.32 MHz, CDCl3, 25 °C): δ = 167.3
[C(O)NH], 136.0, 132.1, 124.0 (Ar-C), 41.0 (NCH), 22.0 (CH3)
ppm.
Materials and Methods: If not stated otherwise, all manipulations
were performed under dry argon by means of standard Schlenk
techniques. Solvents were dried by standard methods and freshly
distilled prior to use. N,N,NЈ,NЈ-Tetramethylethylenediamine
(TMEDA) was purified by vacuum distillation from Na/benzophe-
none. 1H and 13C NMR spectra were recorded with a Bruker
AC200 NMR spectrometer. Mass spectra were obtained with a
Bruker Reflex IV spectrometer. UV/Vis spectra were measured with
a Varian Cary 50 spectrometer. Cyclic voltammetry data were ac-
quired with an ECO/Metrohm PGSTAT30 potentiometer with a
platinum working electrode, an Ag/AgCl double-junction electrode
(3  KCl solution) as the reference electrode and Bu4NBF4 as the
supporting electrolyte. Benzene-o-dithiol was prepared according
to a literature procedure.[20] Consistend microanalytical data for
complex 5–7 were difficult to obtain. However, all complexes have
been fully characterized by either NMR spectroscopy or mass spec-
trometry in addition to X-ray diffraction studies on 5a, 6b·dmf and
7·CH2Cl2.
2,3-Bis(isopropylmercapto)terephthalic Acid (3): Benzene-o-dithiol
(4 mL, 34.8 mmol) was added to a solution of TMEDA (26 mL,
174 mmol) and nBuLi (10  solution in n-hexane) (17.4 mL,
174 mmol) in n-hexane (100 mL) at 0 °C. After stirring at room
temperature for 90 h, dry CO2 was passed through the mixture at
0 °C for 2 h. After evaporation of the solvent, the residue was dis-
solved in methanol (100 mL), and isopropyl bromide (9.8 mL,
104.4 mmol) was added. The mixture was heated under reflux for
24 h. After evaporation of the methanol, the residue was dissolved
in water and acidified with hydrochloric acid (37%) to pH = 2. The
aqueous solution was extracted with diethyl ether (3ϫ 50 mL), and
the combined organic layers were dried with MgSO4. Volatiles were
removed in vacuo to afford a brown oil. Isolation of 3 was achieved
by column chromatography on SiO2 using diethyl ether/petroleum
ether/acetic acid (3:1:0.2) as the eluent. Compound 3 was obtained
as a pale yellow powder (2.3 g, 7.3 mmol, 21%). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 9.78 (s, 2 H, CO2H), 7.95 (s, 2 H,
Ar-H), 3.59 (sept, 2 H, SCH), 1.26 (d, 12 H, CH3) ppm. 13C NMR
(50.32 MHz, CDCl3, 25 °C): δ = 169.2 (CO2H), 140.6, 139.8, 130.3
(Ar-C), 42.8 (SCH), 31.0 (CH3) ppm.
(Et4N)[Co(1a)2] (5a): A solution of H2-1a (340 mg, 0.83 mmol) and
LiOCH3 (1.7 mmol, 1.7 mL of a 1  solution in methanol) in meth-
anol (15 mL) was added to a solution of CoCl2·6H2O (100 mg,
0.42 mmol) in methanol. The mixture was stirred at ambient tem-
perature for 12 h, and the color changed to red-brown. Aerial oxi-
dation of the reaction mixture resulted in a color change to blue.
Addition of Et4NCl (70 mg, 0.42 mmol) in methanol (5 mL)
yielded a blue precipitate. After filtration and drying in vacuo, com-
plex 5a was isolated as blue powder. Vapor diffusion of diethyl
ether into a concentrated dmf solution of 5a yielded crystals suit-
able for an X-ray diffraction study. Yield: 320 mg (76%). MS-
MALDI (negative ions): m/z = 872 [M – Et4N+]–. UV/Vis
(CH3OH): λmax (ε) = 324 (12.6), 369 (12.4), 654 nm.
(Ph4As)[Co(1b)2] (5b): A solution of H2-1b (312 mg, 1.0 mmol) and
LiOCH3 (2 mmol, 2 mL of a 1  solution in methanol) in methanol
(15 mL) was treated as described for 5a. Addition of Ph4AsCl
(209 mg, 0.5 mmol) in methanol (5 mL) yielded a blue solution.
After removal of the solvent, the solid residue was washed exten-
sively with diethyl ether and dried in vacuo to give 5b a blue pow-
N,NЈ-Dibenzyl-2,3-bis(isopropylmercapto)terephthalamide (4a) and
N,NЈ-Diisopropyl-2,3-bis(isopropylmercapto)terephthalamide (4b): A
mixture of compound 3 (1.47 g, 4.68 mmol), CHCl3 (20 mL),
Eur. J. Inorg. Chem. 2010, 2393–2399
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2397

F. E. Hahn, T. Eiting, W. W. Seidel, T. Pape
FULL PAPER
der. Yield: 260 mg (49%). MS-MALDI (negative ions): m/z = 680
[M – Ph4As+]–. UV/Vis (CH3OH): λmax (ε) = 324 (13.2), 371 (13.6),
662 nm.
b = 17.410(2), c = 28.357(4) Å, V = 4746.2(11) Å3, ρ = 1.403 gcm–3,
µ = 0.590 mm–1, Z = 4, 33702 measured reflections, 7023 unique
reflections (Rint = 0.0684), 6593 observed reflections [IՆ2σ(I)], 628
parameters, R(all) = 0.0538, wR(all) = 0.0944, GOF = 1.167,
largest peak/hole 0.386/–0.394 e– Å–3.
(Et4N)2[Ni(1a)2] (6a): A solution of H2-1 (409 mg, 1.0 mmol) and
LiOCH3 (2 mmol, 2 mL of a 1  solution in methanol) in methanol
(15 mL) was added to a solution of NiCl2·H2O (119 mg, 0.5 mmol).
The mixture was stirred at ambient temperature for 12 h, and the
color changed to red. Addition of Et4NCl (166 mg, 1.0 mmol) in
methanol (5 mL) caused the formation of a red precipitate. After
filtration and drying in vacuo, compound 6a was isolated as a red
Crystal Data for (Ph4As)2[Ni(1b)2]·dmf: C79H83As2N5NiO5S4, M =
–1
¯
1519.29 gmol , red plates, space group P1, a = 13.351(3), b =
13.548(3), c = 23.883(6) Å, α = 93.579(5), β = 103.481(5), γ =
114.970(5)°, V = 3744(2) Å3, ρ = 1.348 gcm–3, µ = 1.301 mm–1, Z
= 2, 30413 measured reflections, 13173 unique reflections (Rint
=
1
0.0586), 9390 observed reflections [IՆ2σ(I)], 878 parameters,
R(all) = 0.0755, wR(all) = 0.1078, GOF = 0.990, largest peak/hole
0.821/–0.368 e– Å–3.
solid. Yield: 340 mg (60%). H NMR (200 MHz, [D7]dmf, 25 °C):
δ = 9.86 [t, 4 H, C(O)NH], 7.6–7.25 (m, 24 H, Ar-H), 4.64 (d, 8
H, NCH2Ph) 3.31 (q, 16 H, NCH2CH3), 1.24 (t, 24 H, CH2CH3)
ppm. MS-MALDI (negative ions): m/z = 1002 [M – Et4N+]–. UV/
Vis (CH3OH): λmax (ε) = 315 (27.9), 385 (6.9), 870 nm.
Crystal Data for (Ph4As)[Fe(1a)2]·CH2Cl2: C69H58AsCl2FeN4O4S4,
–1
¯
M = 1337.10 gmol , brown plates, space group P1, a = 14.161(3),
b = 15.192(3), c = 16.041(4) Å, α = 97.954(5), β = 100.902(5), γ =
110.294(4)°, V = 3099.5(12) Å3, ρ = 1.433 gcm–3, µ = 1.047 mm–1,
Z = 2, 25317 measured reflections, 10894 unique reflections (Rint
= 0.0819), 6847 observed reflections [IՆ2σ(I)], 782 parameter,
R(all) = 0.1051, wR(all) = 0.1225, GOF = 0.979, largest peak/hole
0.511/–0.553 e– Å–3.
(Ph4As)2[Ni(1b)2] (6b): A solution of H2-1b (312 mg, 1.0 mmol) and
LiOCH3 (2 mmol, 2 mL of a 1  solution in methanol) in methanol
(15 mL) was treated as described for 6a. Addition of Ph4AsCl
(418 mg, 0.5 mmol) in methanol (5 mL) gave a red solution. After
removal of the solvent, the mixture was washed extensively with
diethyl ether. Compound 6b was obtained after drying in vacuo as
1
a red powder. Yield: 250 mg (35%). H NMR (200 MHz, CDCl3,
25 °C): δ = 7.83 (m, 8 H, Ar-H), 7.75 (m, 24 H, Ar-H + NH), 7.56
(m, 16 H, Ar-H), 4.03 (sept, 2 H, CH), 1.16 (d, 24 H, CH3) ppm.
MS-MALDI (negative ions): m/z = 1063 [M – Ph4As+]–. UV/Vis
(CH3OH): λmax (ε) = 310 (26.9), 370 (6.9), 864 nm. Vapor diffusion
of diethyl ether into a concentrated dmf solution of 6b yielded red
crystals of 6b·dmf, which were suitable for an X-ray diffraction
study.
Acknowledgments
We thank the Deutsche Forschungsgemeinschaft (IRTG 1444) for
financial support.
[1] a) C. L. Beswick, J. M. Schulman, E. I. Stiefel, Prog. Inorg.
Chem. 2004, 52, 55–110; b) M. L. Kirk, R. L. McNaughton,
M. E. Helton, Prog. Inorg. Chem. 2004, 52, 111–212.
[2] S. J. Nieter Burgmayer, Prog. Inorg. Chem. 2004, 52, 491–537.
[3] C. Faulmann, P. Cassoux, Prog. Inorg. Chem. 2004, 52, 399–
489.
[4] a) K. Ray, T. Weyhermüller, F. Neese, K. Wieghardt, Inorg.
Chem. 2005, 44, 5345–5360; b) K. Ray, T. Weyhermüller, A.
Goossens, M. W. J. Crajé, K. Wieghardt, Inorg. Chem. 2003,
42, 4082–4087; c) B. S. Lim, D. V. Fomitchev, R. H. Holm, In-
org. Chem. 2001, 40, 4257–4262.
[5] a) F. E. Hahn, C. Schulze Isfort, T. Pape, Angew. Chem. Int.
Ed. 2004, 43, 4807–4810; b) F. E. Hahn, T. Kreickmann, T.
Pape, Dalton Trans. 2006, 769–771; c) T. Kreickmann, C. Died-
rich, T. Pape, H. V. Huynh, S. Grimme, F. E. Hahn, J. Am.
Chem. Soc. 2006, 128, 11808–11819; d) C. Schulze Isfort, T.
Kreickmann, T. Pape, R. Fröhlich, F. E. Hahn, Chem. Eur. J.
2007, 13, 2344–2357; e) F. E. Hahn, B. Birkmann, T. Pape, Dal-
ton Trans. 2008, 2100–2102; f) F. E. Hahn, M. Offermann, C.
Schulze Isfort, T. Pape, R. Fröhlich, Angew. Chem. Int. Ed.
2008, 47, 6794–6797; g) B. Birkmann, A. W. Ehlers, R.
Fröhlich, K. Lammertsma, F. E. Hahn, Chem. Eur. J. 2009, 15,
4301–4311; h) B. Birkmann, W. W. Seidel, T. Pape, A. W.
Ehlers, K. Lammertsma, F. E. Hahn, Dalton Trans. 2009,
7350–7352; i) J. S. Gancheff, R. O. Albuquerque, A. Guerrero-
Martínez, T. Pape, L. De Cola, F. E. Hahn, Eur. J. Inorg. Chem.
2009, 43, 4043–4051; j) F. Hupka, F. E. Hahn, Chem. Com-
mun., in press; k) F. E. Hahn, T. Kreickmann, T. Pape, Eur. J.
Inorg. Chem. 2006, 535–539; l) B. Birkmann, R. Fröhlich, F. E.
Hahn, Chem. Eur. J. 2009, 15, 9325–9329; m) for a review on
supramolecular structures with benzene-o-dithiolato ligands,
see: T. Kreickmann, F. E. Hahn, Chem. Commun. 2007, 1111–
1120.
(Ph4As)[Fe(1a)2] (7): A solution of H2-1a (340 mg, 0.83 mmol) and
LiOCH3 (1.7 mmol, 1.7 mL of a 1  solution in methanol) in meth-
anol (15 mL) was added to a solution of FeCl3 (68 mg, 0.42 mmol)
in methanol. The mixture was stirred at ambient temperature for
12 h, and the color changed to red-brown. Addition of Ph4AsCl
(176 mg, 0.42 mmol) in methanol (5 mL) yielded a red-brown pre-
cipitate. After filtration and drying in vacuo, complex 7 was iso-
lated as a red-brown powder. Yield: 350 mg (66%). MS-MALDI
(negative ions): m/z = 869 [M – Ph4As+]–. UV/Vis (CH3OH): λmax
(ε) = 320 (16.2), 391 (18.4), 491 nm. Vapor diffusion of diethyl ether
into a concentrated dichloromethane solution of 7 yielded crystals
of 7·CH2Cl2, which were suitable for an X-ray diffraction study.
Crystal Structure Determinations: Single crystals suitable for X-ray
diffraction analyses were coated in perfluoro polyether oil and
mounted on glass fibers. Diffraction data were collected at T =
123(2) K (for 5a and 7·CH2Cl2) or at 153(2) K (for 6b·dmf) with a
Bruker AXS APEX CCD diffractometer equipped with a rotation
anode using graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å) Diffraction data were collected over the full sphere and
were corrected for absorption. The data reduction was performed
with the Bruker SMART[21] program package. Structures were
solved with the SHELXS-97[22] package by using direct methods
and were refined with SHELXL-97[22] against |F2| by using first
isotropic and later anisotropic thermal parameters for all non-hy-
drogen atoms. Hydrogen atoms were added to the structure models
in calculated positions. CCDC-768615 (5a), -768616 (6a·dmf), and
-768617 (7·CH2Cl2) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
[6] S. A. Baudron, N. Avarvari, P. Batail, Inorg. Chem. 2005, 44,
3380–3382.
[7] a) H. V. Huynh, W. W. Seidel, T. Lügger, R. Fröhlich, B. Wib-
beling, F. E. Hahn, Z. Naturforsch., Teil B 2002, 57, 1401–1408;
b) W. W. Seidel, F. E. Hahn, T. Lügger, Inorg. Chem. 1998, 37,
Crystal Data for (Et4N)[Co(1a)2]: C52H56CoN5O4S4,
M =
1002.19 gmol–1, blue needles, space group P212121, a = 9.6136(13),
2398
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 2393–2399

2,3-Dithiolatoterephthaldiamide Complexes of CoIII, NiII, and FeIII
6587–6596; c) F. E. Hahn, W. W. Seidel, Angew. Chem. Int. Ed.
Engl. 1995, 34, 2700–2703.
Giménez-Saiz, V. Gama, J. C. Waerenborgh, R. T. Henriques,
M. Almeida, Polyhedron 2003, 22, 2481–2486.
C.-M. Lee, C.-H. Hsieh, A. Dutta, G.-H. Lee, W.-F. Liaw, J.
Am. Chem. Soc. 2003, 125, 11492–11493.
a) W. W. Seidel, F. E. Hahn, J. Chem. Soc., Dalton Trans. 1999,
2237–2241; b) H. V. Huynh, C. Schulze-Isfort, W. W. Seidel, T.
Lügger, R. Fröhlich, O. Kataeva, F. E. Hahn, Chem. Eur. J.
2002, 8, 1327–1335.
a) K. Wang, Prog. Inorg. Chem. 2004, 52, 267–314; b) M. J.
Baker-Hawkes, E. Billig, H. B. Gray, J. Am. Chem. Soc. 1966,
88, 4870–4875.
N. G. Connelly, W. E. Geiger, Chem. Rev. 1996, 96, 877–910.
a) A. Dey, F. E. Jenney Jr., M. W. W. Adams, E. Babini, Y. Tak-
ahashi, K. Fukuyama, K. O. Hodgson, B. Hedman, E. I. Solo-
mon, Science 2007, 318, 1464–1468; b) A. Dey, C. L. Roche,
M. A. Walters, K. O. Hodgson, B. Hedman, E. I. Solomon, In-
org. Chem. 2005, 44, 8349–8354; c) M. A. Walters, C. L. Roche,
A. L. Rheingold, S. W. Kassel, Inorg. Chem. 2005, 44, 3777–
3779; d) T. Glaser, I. Bertini, J. J. G. Moura, B. Hedman, K. O.
Hodgson, E. I. Solomon, J. Am. Chem. Soc. 2001, 123, 4859–
4860.
ˇ
[8] a) K. Mrkvová, J. Kamenícˇek, Z. Sindelárˇ, L. Kvítek, Transi-
[15]
[16]
tion Met. Chem. 2004, 29, 238–244; b) R. Eisenberg, Z. Dori,
H. B. Gray, J. A. Ibers, Inorg. Chem. 1968, 7, 741–748.
[9] a) H. Alves, D. Simão, I. C. Santos, V. Gama, R. T. Henriques,
H. Novais, M. Almeida, Eur. J. Inorg. Chem. 2004, 1318–1329;
b) M. J. Baker-Hawkes, Z. Dori, R. Eisenberg, H. B. Gray, J.
Am. Chem. Soc. 1968, 90, 4253–4259.
[10] D. Sellmann, S. Fünfgelder, F. Knoch, M. Moll, Z. Natur-
forsch., Teil B 1991, 46, 1601–1608.
[11] D. Sellmann, H. Binder, D. Häußinger, F. W. Heinemann, J.
Sutter, Inorg. Chim. Acta 2000, 300–302, 829–836.
[12] a) K. Ray, A. Begum, T. Weyhermüller, S. Piligkos, J. van Slag-
eren, F. Neese, K. Wieghardt, J. Am. Chem. Soc. 2005, 127,
4403–4415; b) D. Sellmann, T. Becker, F. Knoch, Chem. Ber.
1996, 129, 509–519; c) D. Sellmann, U. Kleine-Kleffmann, L.
Zapf, G. Huttner, L. Zsolnai, J. Organomet. Chem. 1984, 263,
321–331.
[13] a) D. T. Sawyer, G. S. Srivatsa, M. E. Bodini, W. P. Schaefer,
R. M. Wing, J. Am. Chem. Soc. 1986, 108, 936–942; b) B. S.
Kang, L. H. Weng, D. X. Wu, F. Wang, Z. Guo, L. R. Huang,
Z. Y. Huang, H. Q. Liu, Inorg. Chem. 1988, 27, 1128–1130.
[14] a) K. Ray, E. Bill, T. Weyhermüller, K. Wieghardt, J. Am.
Chem. Soc. 2005, 127, 5641–5654; b) D. Sellmann, K. P. Peters,
R. M. Molina, F. W. Heinemann, Eur. J. Inorg. Chem. 2003,
903–907; c) H. Alves, D. Simão, H. Novais, I. C. Santos, C.
[17]
[18]
[19]
[20]
[21]
[22]
D. M. Giolando, K. Kirschbaum, Synthesis 1992, 451–452.
Bruker AXS, 2000.
G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
Received: February 11, 2010
Published Online: April 23, 2010
Eur. J. Inorg. Chem. 2010, 2393–2399
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2399