Tuning the properties of redox-active guanidino-functionalized aromatic ligands by substitution: Experiment and theory

Article abstract of DOI:10.1002/ejic.201101366

Substitution of the aromatic hydrogen atoms in the electron donors 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1a) and 1,2,4,5-tetrakis(N,N'- dimethyl-N,N'-ethyleneguanidino)benzene (1b) by iodide (to give 2a and 2b) and nitro groups (to give 3a and 3b

Full text of DOI:10.1002/ejic.201101366

FULL PAPER
DOI: 10.1002/ejic.201101366
Tuning the Properties of Redox-Active Guanidino-Functionalized Aromatic
Ligands by Substitution: Experiment and Theory
Anastasia Peters,[a] Hendrik Herrmann,[a] Martin Magg,[a] Elisabeth Kaifer,[a] and
Hans-Jörg Himmel*[a]
Keywords: Redox chemistry / N ligands / Substituent effects / Coordination compounds / Electron donor / Guanidines
Substitution of the aromatic hydrogen atoms in the electron
donors 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1a)
tical spectra) have been analyzed and compared with the un-
substituted 1,2,4,5-tetrakis(guanidino)benzenes. The experi-
and 1,2,4,5-tetrakis(N,NЈ-dimethyl-N,NЈ-ethyleneguanidino)- mental results are supplemented by quantum chemical cal-
benzene (1b) by iodide (to give 2a and 2b) and nitro groups
(to give 3a and 3b) afforded new redox-active ligands. Their
properties (electron donor capacity, Brønsted basicity and op-
culations. The first late-transition metal complex of the push–
pull ligand 3a was prepared and characterized and its oxi-
dation studied.
[estimated pK(BH+) values in CH3CN solution of 25.3 for
1a and 23.8 for 1b] but is a superior electron donor
Introduction
1,4-Bis(dimethylamino)benzene and its derivatives are [E1/2(CH3CN) = –0.36 vs. SCE].[12]
well-known organic electron donors,[1] which can be easily
oxidized to their intensely blue radical monocations or di-
cations.[2] Wurster-type systems have also been integrated in
other architectures, which lead to, for example, crowns,[3,4]
cyclophanes[5] and oligoanilines.[6] 1,2,4,5-Tetraaminobenz-
ene is also well known,[7] and 1,2,4,5-tetrakis(dimethyl-
amino)benzene and other derivatives have been introduced
as even stronger electron donors.[8] These compounds are
generally oxidized directly to the dication. Recent work has
shown that ion pairing is responsible for the difficulty in
stabilizing the monocation radical,[9] and the preparation of
salts of the monocation has been made possible by the use
of weakly coordinating anions. We have introduced guan-
idino-functionalized aromatic (GFA) compounds where
Scheme 1.
several guanidino groups are in para positions to each other
The reactivity of 1a was assessed in several studies and
[GFA-n, where n (Ն 4) denotes the number of guanidino
groups] as a new class of strong organic electron donors
and chelating ligands.[10–15] The first compound of this class
was 1,2,4,5-tetrakis(tetramethylguanidino)benzene (1a,
Scheme 1).[10] Its oxidation potential (two-electron oxi-
dation) is –0.32 V vs. SCE (CH3CN), thus 1a clearly is a
stronger electron donor than 1,2,4,5-tetrakis(dimethyl-
amino)benzene [E1/2 (CH3CN) = –0.03 V vs. SCE].[9] The
related compound 1b (Scheme 1) is slightly less basic than 1a
some representative results are summarized in Figure 1.
Oxidation by I2 furnished the semiconducting salt
1a(I3)2.[10,17] Several examples of dinuclear complexes, such
as [1a{Cu(NCMe)4}2](BF4)6 and [1a{Cu(NO3)2}2][Cu-
(NO3)4],[11,16] showed that GFA-4 compounds are capable
of forming stable complexes even after two-electron oxi-
dation, in which they act as chelating ligands. Furthermore,
trapped in dinuclear CuII complexes, the radical monoca-
tion 1a·+ was stabilized.[16] Hence [1a{Cu(NO3)2}2]NO3 fea-
tures three strongly ferromagnetically coupled unpaired
electrons (one on each copper atom and one on the bridg-
ing guanidine ligand) in its ground electronic state.[16] Fi-
nally, 1a in [1a(CuI)2] was oxidized by I2 (two-electron oxi-
dation) to give the 1D polymer [{1a(CuI)2}(I3)2]n.[17] This
polymer was found to be an electrical semiconductor with
a low (indirect) band gap of 1.05 eV. More semiconducting
[a] Anorganisch-Chemisches Institut, Ruprecht-Karls-Universität
Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-545707
E-mail: hans-jorg.himmel@aci.uni-heidelberg.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201101366.
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Guanidino-Functionalized Aromatic Ligands
Figure 1. Some characteristic reactions of 1a.
1D coordination polymers have also been synthesized.[18]
For copper complexes, we were able to synthesize an almost
complete electron-transfer series with complexes of the type
[CuI–GFA-4–CuI], [CuI–GFA2+–CuI] (polymeric), [CuII–
GFA-4–CuII], [CuII–GFA-4·+–CuII] and [CuII–GFA-42+
CuII].
–
The introduction of electron-withdrawing groups should
lead to push–pull systems with distinct optical properties.
In this work, we report the substitution of the remaining
two aromatic hydrogen atoms in 1a and 1b by iodo or nitro
groups to give the new electron donors 2a, 2b, 3a and 3b
(Scheme 1). The synthesis, structure and electronic proper-
ties as well as some aspects of the reactivity of the new
organic electron donors will be discussed and compared to
those of 1a and 1b.
Scheme 2.
Another valuable indicator is the highest occupied mo-
lecular orbital (HOMO) energy, which is compared in
Table 1. According to this indicator, the trend 1b Ͼ 1a Ͼ
2b Ͼ 2aϾ 3b Ͼ 3a in the electron donor capacity was estab-
lished. The order again suggests that 1b is the strongest and
3a is the weakest electron donor, but 2a and 3b have
changed places in the series.
Results and Discussion
Quantum Chemical Calculations
Table 1. Calculated HOMO and LUMO energies, the HOMO–
LUMO energy gap (ΔE) and the calculated pK(BH+) value of the
corresponding acid in CH3CN.
Quantum chemical (DFT) calculations give an insight
into the effect substitution could have on the redox proper-
ties of the guanidine electron donors and the pK(BH+) val-
ues. For the estimation of the electron donor capacity, two
different indicators were considered, the first of which is
based on thermodynamic considerations. Several model
gas-phase electron transfer reactions between two of the six
guanidines were examined (Scheme 2), and their ΔG0 values
(calculated using B3LYP/6-311G**) were compared.
E(HOMO) [eV] E(LUMO) [eV]
ΔE [eV]
pK(BH+)
1a
1b
2a
2b
3a
3b
–4.12
–3.96
–4.42
–4.24
–4.62
–4.54
0.30
0.55
–0.37
–0.11
–1.73
–1.22
4.42
4.51
4.04
4.13
2.89
3.32
25.5
23.8
23.3
21.5
21.6
19.6
The ΔG0 indicator suggests that 1b is the strongest and
3a is the weakest electron donor. The electron donor ca-
A further parameter of importance for any application
pacity appears to decrease in the order 1b Ͼ 1a Ͼ 2b Ͼ 3b of the guanidine electron donors as building blocks in func-
Ͼ 2a Ͼ 3a.
tional materials, is the HOMO–lowest unoccupied molecu-
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FULL PAPER
lar orbital (LUMO) gap. The ability to control this gap over formed by the reaction of 1,2,4,5-tetraaminobenzene with
a large range through modification of the guanidine units two equivalents of the Vilsmeier salt 2-chloro-1,1,3,3-tet-
in a relatively simple way would add to the attractiveness ramethylformamidinium chloride, [(Me2N)2CCl]Cl.
of this class of compounds. Although the absolute LUMO
energy cannot be calculated accurately using simple DFT
methods, the relative LUMO energies can be treated with
more confidence. The HOMO–LUMO energy gaps are
summarized in Table 1, and the gap could indeed be modi-
fied over a large range. Hence it is 4.42 eV in 1a but only
2.89 eV in 3a. Figure 2 shows the HOMO and LUMOs of
1a, 2a and 3a. The HOMOs of all three guanidines look
similar, whereas the LUMOs are localized to a large extent
on the iodo and nitro groups in 2a and 3a.
Scheme 3.
Figure 2. Illustration of the HOMOs and LUMOs and their ener-
gies for 1a, 2a and 3a.
Finally, the pK(BH+) values in CH3CN were estimated
with the aid of an empirical formula introduced by Maksic´
et al.[19] Solvent effects were considered with the conductor-
like polarizable continuum model (CPCM). The resulting
pK(BH+) values in CH3CN for the corresponding acids are
listed in Table 1. The compounds with cyclic guanidino
groups exhibit lower values that their acyclic counterparts.
Substitution of the C–H groups at the aromatic C6 ring by
C–I or C–NO2 led to a marked decrease of the pK(BH+)
value; a maximum of 25.5 was calculated for 1a, and a mini-
mum of 19.6 was reached for 3b.
Synthesis and Characterization
Compounds 1a and 1b
Figure 3. a) Molecular structure of 4. Ellipsoids are drawn at the
Compounds 1a and 1b were synthesized according to a 50% probability level. Hydrogen atoms are omitted for clarity. Se-
lected bond lengths [pm]: N1–C2 140.14(16), N1–C4 133.05(17),
published procedure starting from 1,2,4,5-tetraaminobenz-
ene, which was generated in situ from its HCl adduct, and
N2–C1 139.41(16), N2–C4 136.68(16), N3–C4 136.17(16), C1–C2
141.24(19), C1–C3 138.44(17), C2–C3Ј 139.33(17), N4–C7
the corresponding activated urea (activation with oxalyl
139.34(16), N4–C10 136.97(17), N5–C8 140.02(16), N5–C10
chloride to give the Vilsmeier salts).[10,12] Experiments led
132.71(16), N6–C10 135.96(16), C7–C8 140.70(19), C7–C9
139.13(18), C8–C9Ј 139.18(17). b) Absorption and emission spec-
trum of 4 dissolved in MeOH. I denotes the normalized intensity.
to the isolation and characterization of a byproduct of this
reaction, the benzobisimidazole derivative 4 (Scheme 3 and
Figure 3, a). The yield of 4 varied from 10–32%. A possible
pathway is sketched in Scheme 3. According to this path-
The intermediate could either react with two further
way, the common intermediate to both products is 1,4-bis- equivalents of the Vilsmeier salt to give 1a or it could elim-
(tetramethylguanidino)-2,5-diaminobenzene, which is inate NMe2H at both “sides” of the molecule and undergo
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Guanidino-Functionalized Aromatic Ligands
a cyclization process to obtain 4. A similar second pathway to Me2SI+ and I–. Halogenation of the aromatic ring by
is not possible in the synthesis of 1b. Solutions of 4 were Me2SI+ leads to the product. In addition to 2a(I3)2 and
fluorescent, and Figure 3 (b) shows its absorption and emis- 2b(I3)2, small amounts of the monoiodated salts were iso-
sion spectra recorded in MeOH. In the absorption spectrum lated in crystalline form. Details of their molecular struc-
an intense band appeared at 324 nm, and the fluorescence tures can be found in the Supporting Information. Finally,
spectrum contains a large signal at 365 nm, which corre- 2a and 2b were synthesized by reduction with hydrazine in
sponds to a Stokes shift of 41 nm. The addition of HCl led N,N-dimethylformamide (DMF).[21]
to fluorescence quenching. Crystals of nonfluorescent
Both compounds crystallized from CH2Cl2 solutions
[4H2]Cl2 were grown from MeOH (see Supporting Infor- overlaid with Et2O, and their molecular structures are illus-
mation).
trated in Figure 4.
Compounds 2a and 2b
Compounds 3a and 3b
Scheme 4 outlines the pathways to 2a and 2b. In the first
step, the two-electron oxidation of 1a/b with I2 furnished
the triiodide salts.
Nitration of 1a with NO2BF4 in CH3CN solution at 0 °C
afforded 3a (Scheme 5). Different to 1a, which gave colour-
less crystals with a diamond-like shiny appearance (indicat-
ing a large refractive index), the push-pull system 3a was
isolated as deep red crystals.
Scheme 4.
Scheme 5.
The aromatic protons in these salts were substituted in
the second step by reaction with I2 in dimethylsulfoxide
(DMSO). This reaction can be explained as follows: the ad-
duct Me2S·I2 is formed by the I2-catalyzed disproportiona-
tion of DMSO,[20] and subsequently ionizes in polar DMSO
Figure 5 shows the molecular structure of 3a. A ball-and-
stick representation illustrates that the steric situation
around the benzene ring is relatively relaxed. The NO2
groups are not buried by the guanidino groups, but pro-
trude. However, at 147.34(2) pm the C–NO2 bond lengths
are relatively long. A further important structural difference
between 1a and 3a is the increase of the C1–C2–C3 angle
from 122.81(12)° in 1a to 126.11(12)° in 3a.
Figure 4. Molecular structures of 2a and 2b. Ellipsoids are drawn
at the 50% probability level. Selected bond lengths [pm] and angles
[°] for 2a: C3–I1 210.4(2), N1–C1 140.7(3), N4–C2 141.5(3), N1–
C4 130.0(3), N4–C9 129.0(3), N2–C4 137.9(3), N3–C4 137.6(3), Figure 5. a) Molecular structure of 3a. Thermal ellipsoids drawn at
N5–C9 138.1(3), N6–C9 139.0(3), C1–C2 141.3(3), C1–C3Ј the 50% probability level. Selected bond lengths [pm] and angles
139.8(3), C2–C3 140.4(3), C1–N1–C4 121.19(19), C2–N4–C9 [°]: O1–N7 122.51(16), O2–N7 122.80(16), N1–C1 140.42(17), N1–
121.50(19). Selected bond lengths [pm] and angles [°] for 2b: C2–
C4 129.77(18), N2–C4 137.72(19), N3–C4 137.37(19), N4–C3
I1 210.4(2), N1–C1 140.1(2), N4–C3 139.9(2), N1–C4 128.3(2), 139.90(17), N4–C9 130.46(17), N5–C9 137.29(18), N6–C9
N4–C9 128.3(2), N2–C4 139.2(3), N3–C4 138.8(2), N5–C9 137.48(18), N7–C2 147.34(18), C1–C2 139.64(19), C1–C3
137.9(3), N6–C9 138.9(2), C1–C2 139.7(2), C2–C3 140.6(2), C1– 140.97(19), O1–N7–O2 123.35(12), C1–N1–C4 120.43(12), C3–N4–
C1 142.4(4), C3–C3 142.3(4), C1–N1–C4 120.66(16). C3–N4–C9 C9 121.09(12), C1–C2–C3 126.11(12). b) Spacefilling model.
124.73(17).
c) View along the C6 ring.
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Similarly, 3b was prepared by the nitration of 1b with Protonation
NO2BF4, and its structure is shown in Figure 6. It also fea-
The protonation steps in the titration curves overlapped
tures relatively long C–NO2 bonds [147.3(3) and 147.6(3)
pm], and the C–C–C angle around the substituted C6/C3
atoms increases by 4°.
heavily (see Supporting Information for an example).
Therefore, the pK(BH+) values were estimated with the help
of quantum chemical calculations and empirical corre-
lations (Table 1). In most cases the protonated species were
crystallized and structurally analyzed. Figure 8 shows part
of the crystal structure of [3aH3]Cl3·3H2O as an example.
Figure 6. Molecular structure of 3b. Thermal ellipsoids drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths [pm] and angles [°]: N1–C1 140.2(3), N1–C7
129.9(3), N2–C7 136.0(3), N3–C7 136.9(3), N4–C2 141.0(3), N4–
C12 129.5(3), N5–C12 138.1(3), N6–C12 137.9(3), N7–C4 140.6(3),
N7–C17 128.6(3), N8–C17 136.9(3), N9–C17 138.6(3), N10–C5
140.1(3), N10–C22 129.4(3), N11–C22 138.6(3), N12–C22 137.2(3),
N13–O1 122.0(2), N13–O2 123.2(2), N13–C3 147.3(3), N14–O3
122.6(2), N14–O4 122.2(2), N14–C6 147.6(3), C1–C2 141.1(3), C1–
C6 139.5(3), C2–C3 139.1(3), C3–C4 139.2(3), C4–C5 141.3(3), C5–
C6 138.9(3), O1–N13–O2 123.58(19), O3–N14–O4 124.43(19), C2–
C3–C4 127.0(2), C1–C6–C5 127.1(2).
Optical Spectra
The UV/Vis spectra of all six guanidines contain intense
bands due to πǞπ* transitions localized on the benzene
ring and electronic transitions that involve the guanidino
groups (see Supporting Information). In the spectra of 3a
(Figure 7) and 3b, a very broad band centred at 475 nm in
3a and 448 nm in 3b appeared, which was absent in the
spectra of the other guanidines and most likely arises from
charge-transfer transitions that involve both the guanidino
donor and nitro acceptor groups.
Figure 8. a) Molecular structure of [3aH3]Cl3·3H2O. Thermal ellip-
soids drawn at the 50% probability level. Hydrogen atoms are omit-
ted for clarity. Selected bond lengths [pm] and angles [°]: N1–C1
140.9(3), N1–C7 136.6(3), N2–C7 132.5(3), N3–C7 133.5(3), N4–
C2 142.5(3), N4–C12 134.9(3), N5–C12 133.4(3), N6–C12 133.5(3),
N7–C4 141.2(3), N7–C17 135.0(3), N8–C17 133.8(3), N9–C17
133.4(3), N10–C5 137.6(3), N10–C22 131.8(3), N11–C22 136.3(3),
N12–C22 135.0(3), C1–C2 139.4(3), C1–C6 140.0(3), C2–C3
140.6(3), C3–C4 138.3(3), C4–C5 142.4(3), C5–C6 141.3(3), N13–
C3 148.1(3), N13–O1 120.8(3), N13–O2 122.4(3), N14–O3 123.6(2),
N14–O4 122.2(3), O1–N13–O2 124.6(2), O3–N14–O4 124.08(19),
C1–N1–C7 126.89(19), N2–C7–N3 121.7(2), C2–N4–C12
125.03(19), N5–C12–N6 119.8(2), C4–N7–C17 121.29(19), N8–
C17–N9 120.9(2), C5–N10–C22 121.42(19), N11–C22–N12
116.4(2). b) Illustration of the hydrogen-bonded network.
A hydrogen-bonded network, which involves cocrys-
tallized water molecules, was established. Illustrations of the
structures of other salts of protonated guanidines are in-
cluded in the Supporting Information. Selected structural
changes upon protonation are listed in Table 2. Protonation
leads to a significant increase (of more than 5 pm) in the
N=C bond lengths. At the same time, the C–NMe2 bond
lengths decrease.
Figure 7. Comparison of the UV/Vis spectra of 3a and (3a)I2 in
CH2Cl2.
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Guanidino-Functionalized Aromatic Ligands
Table 2. Average values of characteristic bond lengths [pm] in 1a, 2a, 3a, 1b, 2b and 3b before and after protonation.
1a
[1aH4]Cl4 [1aH2](PF6)2 2a
[2aH2]I2 3a
[3aH3]Cl3
1b
[1bH4]Cl4 [1bH2](PF6)2 2b
3b
N=C
(H)N=C
C–NMe2 138.9
128.9
–
–
130.0(3)
134.4(3)
137.4
129.5
–
138.2
130.6(2) 130.1 131.8(3)
130.1
–
128.2(2)
133.1(3)
139.4
128.3
–
138.7
129.4
–
138.7
135.9
–
135.7(2)
137.0
–
135.5
134.7
–
137.5 135.7
137.2
(H)C–
NMe2
–
133.4
133.7
–
133.3
–
133.4
133.63
133.2
–
–
Redox Properties
2a and 2b showed a one-electron wave due to oxidation to
the trications at positive potentials. The corresponding
waves for 3a and 3b are outside the window in which mea-
surements are possible in CH2Cl2. The two-electron wave
was relatively broad for 3a and 3b, which might suggest
differences in the speed of electron transfer. According to
the CV experiments, 1b is the strongest electron donor with
The cyclic voltammograms (CVs) of all six guanidine
electron donors in CH2Cl2 are shown in Figure 9 (0.1 m
Bu4NPF6 supporting electrolyte at a scan rate of 100 mV/
s).
E1/2 = –0.79 V vs. Fc/Fc+ and 3a is the weakest with E1/2
=
–0.54 V vs. Fc/Fc+ in CH2Cl2 solutions.
Table 3. Summary of the CV results (E values [V] relative to Fc/
Fc+).
First (two-electron) wave
Second (one-electron) wave
Eox
Ered
E1/2
Eox
Ered
E1/2
1a
1b
2a
2b
3a
3b
–0.71
–0.74
–0.54
–0.55
–0.27
–0.33
–0.82
–0.85
–0.64
–0.67
–0.54
–0.56
–0.76
–0.79
–0.59
–0.61
–0.41
–0.45
0.72
0.70
0.88
0.65
0.62
0.82
0.68
0.66
0.85
0.82
0.75
0.79
[a]
[a]
[a]
[a]
[a]
[a]
[a] Outside the solvent window.
This is in line with the calculated gas-phase electron do-
nor capacity. The electron donor capacity decreases in the
order 1b Ͼ 1a Ͼ 2b Ͼ 2a Ͼ 3b Ͼ 3a. The HOMOs (vide
supra) were shown to look similar for the unsubstituted and
substituted guanidines (Figure 2). Therefore, it is reasonable
to correlate the HOMO energies with the measured poten-
tials. The plot in Figure 10 indeed shows a linear relation-
Figure 9. CVs of 1a, 2a, 3a, 1b, 2b and 3b.
The E values (relative to Fc/Fc+, see Supporting Infor-
mation for curves relative to SCE) at the wave maxima are
included in Table 3. In all cases, a two-electron oxidation
wave was observed at negative potentials. Even on changing
the electrolyte (e.g. NBu4BPh4 and other salts of relatively
weakly coordinating anions), we were unable to distinguish
between the two one-electron events. Quantum chemical
calculations (B3LYP) of the gas-phase disproportionation
of two equivalents of the radical monocation into one
equivalent of the dication and the neutral guanidine re-
sulted in a very large estimate of ΔG0 of +253 kJmol–1.
More work is necessary to identify the reason for the insta-
Figure 10. E1/2 values [V] for oxidation to the dication as a function
bility of the radical cations. In addition, the CVs for 1a, 1b, of the HOMO energies [eV] of the neutral guanidines.
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A. Peters, H. Herrmann, M. Magg, E. Kaifer, H.-J. Himmel
FULL PAPER
ship between the calculated HOMO energies and the mea- the NC–CN bond lengths between the two adjacent carbon
sured E1/2 values. We found the relationship EHOMO [eV] = atoms in the central C6 ring that are attached to the guan-
–1.61·E1/2 [V] – 5.28.
idino groups. Two-electron oxidation resulted in an increase
Next, the twofold-oxidized electron donors were struc- of these bond lengths by more than 9 pm. The other four
turally characterized. To this end, salts were synthesized by C–C bond lengths within the C6 ring are similar, which
the reaction of the neutral guanidines with I2. The anions indicates the bisallylic character of the dication.
–
were either I3 or I–. Figure 11 displays the structures of
The delocalization of the positive charges on to the guan-
idino groups causes a significant increase of 5 pm or more
for the imino N=C bond lengths. Although the NC–CN
bond lengths increased, the separations between the N
atoms attached to two adjacent ring carbon atoms de-
creased sharply. Generally the effects were larger for the cy-
clic guanidines than for the acyclic ones. In the case of 1b,
the N···N separation was 297.7 pm before and 274.5 pm af-
ter two-electron oxidation.
2b(I3)2 and 3aI2 as examples.
Of particular interest are the changes in the optical prop-
erties upon oxidation. Two-electron oxidation was ac-
companied by intense colouration. For example, [3a]I2 is
dark red. The absorption spectrum of [3a]I2 in CH2Cl2 is
plotted with that of neutral 3a in Figure 7.
Ligand Properties
Finally, we probed the suitability of the push–pull system
3a as a ligand in preliminary experiments. The reaction of
3a with CuI furnished the dinuclear complex [3a(CuI)2]
(Scheme 6), and its structure is illustrated in Figure 12. The
two Cu ions are displaced from the C6 ring plane and adopt
a trans-type structure with one Cu below and the other
above the aromatic plane. The imino N=C bond lengths are
elongated upon coordination from 129.77(18)/130.46(17) to
132.9(3)/133.3(3) pm. The changes are slightly smaller than
those that occurred on protonation.
Figure 11. a) Molecular structure of 2b(I3)2. Ellipsoids are drawn
at the 50% probability level. Selected distances [pm] and angles [°]:
N1–C1 133.4(4), N1–C4 132.0(5), N2–C4 134.3(5), N3–C4
135.0(5), N4–C3 129.6(4), N4–C9 135.7(5), N5–C9 133.4(4), N6–
C9 132.5(5), C1–C2 137.8(5), C1–C3 151.5(5), C3–C2Ј 142.7(5),
C2–I1 210.0(4), I2–I3 291.38(9), I3–I4 290.96(10), I1···I2 385.6(1),
C1–N1–C4 128.0(3), C3–N4–C9 128.8(3), N2–C4–N3 110.1(3),
N5–C9–N6 112.5(3), I2–I3–I4 177.672(12). b) Molecular structure
of 3aI2. Ellipsoids are drawn at the 50% probability level. Selected
bond lengths [pm] and angles [°]: O1–N7 123.48(17), O2–N7
Scheme 6.
All of the bands in the absorption spectrum (Figure 13)
experience a redshift upon coordination. Hence the bands
at 255 and 321 nm in the spectrum of 3a shift to 279 and
332 nm in that of [3a(CuI)2]. The broad charge-transfer
122.68(17), N1–C1 129.16(17), N1–C4 136.82(18), N2–C4 band at 474 nm shifts to 582 nm and increases in intensity.
132.81(18), N3–C4 134.62(19), N4–C2 132.02(17), N4–C9
The comparison between [1a(CuI)2] and [3a(CuI)2]
135.58(17), N5–C9 134.30(18), N6–C9 133.85(19), N7–C3
(Table 5) reveals some differences, which could explain their
146.56(17), C1–C3 142.27(19), C1–C2 151.21(18), C2–C3
different reactivities. All parameters indicate a weaker
138.81(18).
metal–ligand bond in [3a(CuI)2]. Hence the average Cu–N
Some important structural differences between the neu- distance is longer, and the imino N=C bond length is
tral and dicationic guanidines are highlighted in Table 4. shorter (closer to the value in the free ligand) in [3a(CuI)2]
The most remarkable structural change is the elongation of than [1a(CuI)2]. In addition, the shortest distance between
Table 4. Characteristic bond lengths [pm] of 1a, 2a, 3a, 1b, 2b and 3b and their changes upon two-electron oxidation [dication from the
–
triiodide or iodide (in the case of 3a) and PF6 (in the case of 1b) salts].
1a
1a2+
2a
2a2+
3a
3a2+
1b
1b2+
2b
2b2+
3b
3b2+
[a]
NCAr–CAr
N=C
N
140.87(2) 149.1(4) 141.3(3) 150.6(7) 140.97(2) 151.21(2) 141.34(2) 150.6(4) 142.4(4) 151.5(5) 141.1(3)
128.77(2)/ 133.9(3)/ 129.0(3)/ 133.7(6)/ 129.77(2)/ 135.58(2)/ 128.66(2)/ 133.7(3)/ 128.3(2)/ 132.0(5)/ 129.9(3)/
129.10(2) 136.4(4) 130.0(3) 135.5(7) 130.46(2) 136.82(2) 129.03(2) 135.4(3) 128.3(2) 135.7(5) 129.5(3)
[a]
[a]
N···N
287.5
275.6
281.1
273.1
287.3
272.2
297.7
274.5
284.0
271.6
293.0
[a] Not structurally characterized.
1626
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1620–1631

Guanidino-Functionalized Aromatic Ligands
Table 5. Characteristic bond lengths [pm] and torsion angles [°] of
[1a(CuI)2] and [3a(CuI)2].
[1a(CuI)2]
[3a(CuI)2]
N=C
141.5(2)
140.6(2)
201.60(18)
201.68(16)
244.15(7)
268.4
140.2(3)
135.5(3)
204.63(19)
204.08(18)
244.93(8)
266.1
Cu–N
Cu–I
N···N
Є(C6–N–Cu–N)
d(C6–Cu)
10.45
41.0
25.88
78.3
lated from the reaction between [3a(CuI)2] and I2 was (3a)
I2. The Lewis basicity of 3a seems to be too low to allow
copper coordination after two-electron oxidation. When a
solution of [3a(CuI)2] was exposed to air for several days at
r.t., we observed the formation of (3a)I2 again. In addition,
new mononuclear 5 was isolated, which consists of a C3N2
heterocycle (with two N=C double bonds) fused to a cyclo-
pentadiene derivative (Figure 14). Compound 5 features
three intact guanidino groups, two of which coordinate to
one CuI2. It was formed from [3a(CuI)2] by methane and
copper elimination. In future, we will continue the oxi-
dation experiments using different oxidation reagents (e.g.
AgPF6).
Figure 12. a) Molecular structure of [3a(CuI)2]. Thermal ellipsoids
drawn at the 50% probability level. Hydrogen atoms are omitted
for clarity. Selected bond lengths [pm] and angles [°]: Cu–I
244.93(8), Cu–N1 204.63(19), Cu–N4 204.08(18), N1–C1 140.2(3),
N1–C4 132.9(3), N2–C4 135.5(3), N3–C4 135.4(3), N4–C2
140.1(3), N4–C9 133.3(3), N5–C9 135.6(3), N6–C9 136.1(3), N7–
C3 147.5(3), N7–O1 123.5(2), N7–O2 123.4(2), C1–C2 142.1(3),
C1–C3Ј 140.4(3), C2–C3 140.5(3), N1–Cu–N4 81.26(7), N1–Cu–I
137.03(5), N4–Cu–I 141.60(5). b) View along the C6 ring.
Figure 14. Molecular structure of 5. Thermal ellipsoids drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity.
Selected bond lengths [pm] and angles [°]: C1–N1 132.7(4), C2–N4
129.6(4), N1–C7 136.3(4), N4–C12 138.0(4), N2–C7 132.1(4), N3–
C7 134.6(4), N5–C12 133.2(4), N6–C12 133.2(4), C6–N7 129.1(4),
C5–N14 138.6(4), C3–N13 136.8(4), C22–N10 128.6(4), C22–N12
142.8(4), C6–N12 135.6(4), C1–C2 151.0(4), C1–C5 138.9(4), C2–
C3 141.0(5), Cu1–I1 254.45(6), Cu1–N1 210.0(3), Cu1–N4
215.4(3), N13–O1 126.7(3), N14–O3 125.1(4), C1–N1–Cu1
114.6(2), C2–N4–Cu1 114.3(2), N1–Cu1–I2 113.85(8), N1–Cu1–I1
116.79(7), N4–Cu1–I2 114.07(7), N4–Cu1–I1 112.01(8), N1–Cu1–
Figure 13. The UV/Vis spectra of 3a and [3a(CuI)2] in CH2Cl2.
copper and the plane defined by the C6 ring, d(C6–Cu), and
the dihedral angle between the C6 and N–Cu–N planes,
Є(C6–N–Cu–N), are much larger in [3a(CuI)2] than N4 77.98(10), I1–Cu1–I2 116.32(2).
[1a(CuI)2] (Figure 12, b).
Having synthesized [3a(CuI)2], our next aim was its oxi-
dation. The oxidation of [1a(CuI)2] has previously been
Conclusions
showntogivethesemiconductingchainpolymer[{1a(CuI)2}-
(I3)2]n. In this case a molecular complex of the type [CuI–
The effect of substitution at the aromatic ring on the
GFA-4–CuI] was oxidized into a [CuI–GFA-42+–CuI]-type properties of guanidine electron donors was analyzed. The
coordination polymer. According to band structure calcula- optical properties, Brønsted basicity and electron donor ca-
tions, the already low band gap (experimental estimate pacity of six guanidines were compared. The HOMO–
1.1 eV, calcd. 1.5 eV) could be further reduced by NO2 sub- LUMO gap of the guanidines is substantially influenced by
stitution at the C6 rings.[18] However, the only product iso- substitution. Substitution with nitro groups led to intensely
Eur. J. Inorg. Chem. 2012, 1620–1631
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1627

A. Peters, H. Herrmann, M. Magg, E. Kaifer, H.-J. Himmel
FULL PAPER
coloured push–pull compounds. The estimated pK(BH+)
values of the corresponding acids could be modified in a
relatively large window by substitution [pK(BH+) = 19.6–
25.5]. The structural changes upon protonation were
studied and shown to affect the guanidino groups almost
exclusively. The half potentials for the first (two-electron)
oxidation/reduction waves varied between –0.76 and
–0.41 V relative to Fc/Fc+. The oxidation potentials
measured by cyclic voltammetry showed a linear correlation
and washed with CH3CN and Et2O. Compound 4 (0.280 g,
1.2 mmol, 32%) was obtained as a pale greenish-white solid. Upon
recrystallization from EtOH, colourless crystals were obtained.
C12H16N6 (244.30): calcd. C 59.00, H 6.60, N 34.40; found C 58.24,
1
H 6.62, N 34.21. H NMR (600.13 MHz, CD3OD): δ = 7.11 (s, 2
H), 3.10 (s, 12 H) ppm. 13C{1H} NMR (150.92 MHz, CD3OD): δ
= 157.76, 38.77 (CH ) ppm. IR (CsI): ν = 2951 (w), 2879 (w), 1590
˜
3
(vs), 1515 (m), 1456 (s), 1428 (vs), 1379 (m), 1314 (m), 1233 (m),
1154 (m), 1064 (w), 1026 (w), 922 (m), 881 (s), 837 (m), 694 (w),
591 (w) cm–1. UV/Vis (CH3OH, c = 2.78ϫ10–5 molL–1): λmax (ε,
with the calculated HOMO energies. The dications that re- dm3 mol–1 cm–1) = 324 (2.82ϫ104) nm. MS (FAB+): m/z (%) = 245
(100) [4H]+, 215 (12). Crystal data for C12H16N6·2EtOH:
sult from two-electron oxidation can be described in all
cases as a pair of bisguanidinoallyl cations connected by
two C–C single bonds. In preliminary experiments, the suit-
C16H28N6O2, Mr = 336.44, 0.20ϫ0.15ϫ0.15 mm3, monoclinic,
space group P21/c, a = 10.805(2), b = 13.699(3), c = 12.278(3) Å,
β = 99.28(3)°, V = 1793.6(6) Å3, Z = 4, dcalc = 1.246 Mgm–3, Mo-
ability of the guanidines as ligands was tested. The stability
Kα radiation (graphite-monochromated, λ = 0.71073 Å), T =
100 K, θrange 1.91 to 30.02°. Reflections measd. 10236, indep. 5236,
of [CuI–GFA-4–CuI]-type complexes were compared, and
the redox chemistry of such complexes was analyzed. The
Rint = 0.0458. Final R indices [IϾ2σ(I)]: R1 = 0.0499, wR2
=
results presented here demonstrate that the properties of the
guanidine electron donors could indeed be altered over a
large range by substitution at the aromatic ring system. The
possibility of tuning the properties adds to the interest in
these compounds for organic electronics and as building
blocks in polymeric networks and conducting coordination
polymers.
0.1130.
Synthesis of 1b(I3)2: To a solution of 1b (0.06 g, 0.12 mmol) in
CH2Cl2 (9 mL) was added a solution of I2 (0.09 g, 0.35 mmol) in
CH2Cl2 (10 mL). The colour of the mixture turned deep green.
After stirring for 20 min at r.t., the solvent was removed in vacuo
and the remaining green solid dissolved in CH3CN. Black crystals
of 2(I3)2 (0.09 g, 0.07 mmol, 64%) of a metallic appearance were
obtained from
a concentrated solution of CH3CN at r.t.
C26H42I6N12 (1284.10): calcd. C 24.32, H 3.30, N 13.09; found C
24.50, H 3.39, N 12.94. 1H NMR (399.89 MHz, CD3CN): δ = 5.26
(s, 2 H, CH), 3.70 (s, 8 H, CH2), 3.61 (s, 8 H, CH2), 2.74 (s, 24 H,
CH3) ppm. 13C{1H} NMR (100.56 MHz, CD3CN): δ = 165.38,
Experimental Section
General: All reactions were carried out under an Ar atmosphere
using standard Schlenk techniques. All solvents were dried prior
to use by standard methods. Compounds 1a, 1b and 2a(I3)2 were
prepared as described.[10–12] IR spectra were recorded with a
BIORAD Excalibur FTS 3000. NMR spectra were recorded with
BRUKER Avance II 400 or BRUKER Avance DPX AC200 instru-
ments. Elemental analyses were carried out at the Microanalytical
Laboratory of the University of Heidelberg. UV/Vis spectra were
measured with a Varian Cary 5000 spectrometer. Fluorescence
measurements were recorded with a Varian Cary Eclipse machine.
Electrochemical studies were carried out at r.t. using an EG&G
model 273A potentiostat/galvanostat. The auxiliary electrode was
a platinum wire and the working electrode was a glassy carbon
disk. The reference electrode was an aqueous saturated calomel
electrode. Calculations were carried out with the aid of the
Gaussian 09[22] program. Pure DFT calculations relied on the hy-
brid-method B3LYP (DFT using the Becke[23] exchange functional
and Lee–Yang–Parr[24] correlation functional) with the 6-
311G(d,p) basis set. Calculations on the solvent effect using
CH3CN (with static dielectric constant ε = 36.61 and dynamic di-
electric constant of 1.806) were carried out using the CPCM.[25]
158.47, 100.14 (CH), 48.67 (CH ), 33.24 (CH ) ppm. IR (CsI): ν =
˜
2
3
2940 (w), 2882 (w), 1623 (s), 1562 (vs), 1508 (vs), 1466 (vs), 1412
(s), 1374 (s), 1351 (vs), 1285 (s), 1239 (m), 1204 (m), 1088 (w), 1026
(vs), 971 (s), 898 (w), 825 (w), 781 (m), 744 (s), 653 (w), 616 (w),
583 (w), 556 (w) cm–1. UV/Vis (CH2Cl2, c = 1.43ϫ10–5 molL–1):
λmax (ε, dm3 mol–1 cm–1) = 294 (10.16ϫ104), 368 (5.84ϫ104), 592
(0.07ϫ104) nm. MS (ESI): m/z (%) = 648 (10) [1b + I]+, 324 (100)
[1b + I]2+, 261 (97) [1b]2+, 232 (92) [1b-C3H7N]2+, 174 (30) [1b]3+
.
Synthesis of 1b(PF6)2: Compound 1b (0.063 g, 0.121 mmol) was
dissolved in CH3CN (6 mL) and stirred for 1 d at r.t. in air. To the
resulting green solution was added NH4PF6 (0.039 g, 0.239 mmol).
After the addition of Et2O, dark crystals of 1b(PF6)2 (0.067 g,
0.082 mmol, 67%) were obtained. C26H42F12N12P2 (812.62): calcd.
C 38.43, H 5.21, N 20.68; found C 38.46, H 5.20, N 20.56. 1H
NMR (399.89 MHz, CD3CN): δ = 3.69–3.59 (m, 16 H, CH2), 2.73
(s, 24 H, CH3) ppm. 13C{1H} NMR (100.56 MHz, CD3CN): δ =
165.41, 158.47, 100.13 (CH), 48.62 (CH2), 33.17 (CH3) ppm. IR
(CsI): ν = 2924 (w), 1628 (m), 1571 (s), 1515 (vs), 1477 (s), 1411
˜
(w), 1355 (s), 1284 (m), 1240 (w), 1027 (m), 973 (m), 841 (vs), 799
(w), 734 (m), 557 (s) cm–1. UV/Vis (CH3CN,
c
=
Synthesis of 4: N,N,NЈ,NЈ-Tetramethylurea (2.2 mL, 18.4 mmol)
was dissolved in dry CHCl3 (12 mL), and oxalyl chloride (8.0 mL,
91.0 mmol, 4.9 equiv.) was added dropwise to this solution. The
reaction mixture was stirred for 16 h under reflux. The solvent was
removed under vacuum, and the remaining solid was washed with
Et2O. The obtained 2-chloro-1,1Ј,3,3Ј-tetramethylformamidium-
chloride was dissolved in CH3CN (48 mL) and added dropwise to
a CH3CN solution (20 mL) of 1,2,4,5-tetraaminobenzene (1.0 g,
3.5 mmol) and triethylamine (6.7 mL, 48.1 mmol) at 0 °C, and the
mixture was stirred for 75 min at 0 °C. The precipitate was collected
by filtration and washed with cold CH3CN before being redissolved
0.71ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1) = 225 (3.20ϫ104),
279 (1.40ϫ104), 419 (3.93ϫ104), 605 (0.05ϫ104) nm. MS (ESI):
m/z (%) = 667 (82) [1b + PF6]+, 261 (100) [1b]2+. Crystal data for
C26H42F12N12P2: Mr = 812.66, 0.35ϫ0.30ϫ0.30 mm3, monoclinic,
space group P21/c, a = 9.7430(19), b = 10.600(2), c = 17.158(3) Å,
β = 96.16(3)°, V = 1760.2(6) Å3, Z = 2, dcalc = 1.533 Mgm–3, Mo-
Kα radiation (graphite-monochromated, λ = 0.71073 Å), T =
100 K, θrange 2.06 to 29.49°. Reflections measd. 8286, indep. 4851,
Rint = 0.0557. Final R indices [IϾ2σ(I)]: R1 = 0.0684, wR2
=
0.1891.
in HCl (10%). After addition of NaOH (20%), a white precipitate Synthesis of 2b(I3)2: To a solution of 1b(I3)2 (0.043 g, 0.03 mmol)
was formed. The resulting precipitate was collected by filtration in DMSO (20 mL) was added I2 (0.007 g, 0.03 mmol). The reaction
1628
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© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1620–1631

Guanidino-Functionalized Aromatic Ligands
mixture was stirred for 1 h under reflux. The solvent was removed 345 (2.37ϫ104) nm. MS (ESI+): m/z (%) = 775 (100) [(2b)H]+, 388
under vacuum. Upon recrystallization from CH3CN, dark crystals
of 2b(I3)2 (0.031 g, 0.02 mmol, 66%) were obtained. C26H40I8N12
(1535.88): calcd. C 20.33, H 2.62, N 10.94; found C 20.41, H 2.62,
N 10.95. 1H NMR (600.13 MHz, CD3CN): δ = 3.72–3.61 (m, 16
(11) [(2b)2H]2+. Crystal data for C26H40I2N12: Mr = 774.50,
0.30ϫ0.30ϫ0.30 mm3, monoclinic, space group C2/c,
a =
12.663(3), b = 14.440(3), c = 16.619(3) Å, β = 98.06(3)°, V =
3008.8(0) Å3, Z = 4, dcalc = 1.710 Mgm–3, Mo-Kα radiation (graph-
H, CH2), 2.71 (s, 24 H, CH3) ppm. 13C{1H} NMR (150.92 MHz, ite-monochromated, λ = 0.71073 Å), T = 100 K, θrange 2.34 to
CD3CN): δ = 163.52, 157.17, 79.33, 48.46 (CH2), 33.15 (CH3) ppm.
30.21°. Reflections measd. 8512, indep. 4394, Rint = 0.0220. Final
R indices [IϾ2σ(I)]: R1 = 0.0266, wR2 = 0.0716.
IR (CsI): ν = 2925 (w), 2866 (w), 1643 (s), 1567 (vs), 1507 (vs),
˜
1409 (s), 1373 (m), 1330 (vs), 1293 (s), 1266 (s), 1233 (m), 1169 (w),
1087 (w), 1033 (s), 954 (w), 843 (w), 749 (m), 705 (w), 663 (w), 634
Synthesis of 3a: NO2BF4 (0.398 g, 3.0 mmol) was dissolved in
CH3CN (24 mL) at 0 °C and added dropwise to a suspension of 1a
(0.362 g, 0.68 mmol) in CH3CN (11 mL). The reaction mixture was
stirred for 0.5 h at 0 °C. Removal of the solvent in vacuo led to a
brown-red solid, which was redissolved in water and HCl (10%).
After addition of NaOH (20%), the solution was extracted three
times with CH2Cl2. The combined CH2Cl2 phases were dried with
K2CO3, and the solvent was removed under vacuum. Upon
recrystallization from CH3CN, deep red crystals of [C6(NO2)2-
{NC(NMe2)2}4] (0.062 g, 0.1 mmol, 14%) were obtained.
C26H48N14O4 (620.75): calcd. C 50.31, H 7.79, N 31.59; found C
(w), 569 (m), 547 (w) cm–1. UV/Vis (CH2Cl2,
c
=
1.02ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1) = 294 (8.11ϫ104),
368 (4.86ϫ104) nm. MS (ESI): m/z (%) = 774 (100) [2b]+, 387 (66)
[2b]2+
.
Crystal data for C26H40I8N12: Mr
=
3071.80,
3
¯
0.30ϫ0.20ϫ0.20 mm , triclinic, space group P1, a = 10.027(2), b
= 10.361(2), c = 11.286(2) Å, α = 65.68(3)°, β = 81.27(3)°, γ =
84.36(3)°, V = 1055.3(4) Å3, Z = 1, dcalc = 2.417 Mgm–3, Mo-Kα
radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K,
θrange 2.00 to 29.99°. Reflections measd. 23683, indep. 6160, Rint
0.0458. Final R indices [IϾ2σ(I)]: R1 = 0.0325, wR2 = 0.0697.
=
1
50.02, H 7.69, N 31.31. H NMR (600.13 MHz, CD2Cl2): δ = 2.65
Synthesis of 2a: To a solution of 2a(I3)2 (0.103 g, 0.067 mmol) in
DMF (2 mL) was added hydrazine monohydrate (0.1 mL) under
an argon atmosphere. The mixture was stirred at r.t. for 1 h. The
resulting precipitate was collected by filtration and washed with
(s, 48 H, CH3) ppm. 13C NMR (150.90 MHz, CD2Cl2): δ = 160.22,
140.18, 130.61, 39.56 (CH ) ppm. IR (CsI): ν = 2990 (w), 2928 (w),
˜
3
2889 (w), 2808 (w), 1569 (vs), 1516 (vs), 1474 (s), 1457 (s), 1426
(s), 1378 (vs), 1213 (s), 1144 (vs), 1059 (m), 1025 (m), 968 (s), 917
CH3CN. The resulting yellow solid was dissolved in HCl (10%). (m), 801 (s), 720 (m), 676 (w), 644 (w) cm–1. UV/Vis (CH2Cl2, c =
After addition of NaOH (20%), the solution was extracted three
times with CH2Cl2. The combined organic phases were dried with
K2CO3, and the solvent was removed under vacuum to yield 2a
2.80ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1) = 255 (3.81ϫ104),
321 (1.73ϫ 104), 394 (0.12ϫ 104), 474 (0.12ϫ 104) nm. MS
(FAB+): m/z (%) = 621 (100) [3a + H]+. Crystal data for 3a
(0.034 g, 0.044 mmol, 65%) as a yellow powder. C26H48I2N12 (C26H48N14O4): Mr = 620.78, 0.30ϫ0.25ϫ0.25 mm3, monoclinic,
(782.55): calcd. C 39.91, H 6.18, N 21.48; found C 39.76, H 6.08,
space group P21/n, a = 8.3330(17), b = 18.865(4), c = 10.629(2) Å,
1
N 21.35. H NMR (600.13 MHz, CD2Cl2): δ = 2.68 (s, 48 H, CH3) β = 97.83(3)°, V = 1655.3(6) Å3, Z = 2, dcalc = 1.245 Mgm–3, Mo-
ppm. 13C{1H} NMR (150.92 MHz, CD2Cl2): δ = 158.98, 138.80,
Kα radiation (graphite-monochromated, λ = 0.71073 Å), T =
100 K, θrange 2.16 to 30.03°. Reflections measd. 9548, indep. 4825,
96.63, 39.85 (CH ) ppm. IR (CsI): ν = 2919 (w), 2801 (w), 1584
˜
3
(vs), 1499 (m), 1452 (m), 1422 (m), 1407 (m), 1366 (s), 1235 (w),
Rint = 0.0405. Final R indices [IϾ2σ(I)]: R1 = 0.0502, wR2 =
1189 (m), 1135 (s), 1065 (w), 1042 (w), 1015 (m), 949 (w), 910 (m), 0.1247.
809 (m), 756 (w), 723 (w), 687 (w), 610 (w) cm–1. UV/Vis (CH2Cl2,
Synthesis of 3b: NO2BF4 (0.095 g, 0.72 mmol) was dissolved in
CH3CN (10 mL) at 0 °C and added dropwise to 1b (0.091 g,
0.17 mmol) in CH3CN (8 mL). The reaction mixture was stirred
for 0.5 h at 0 °C. Removal of the solvent in vacuo led to a brown-
red solid, which was redissolved in water and HCl (10%). After
addition of NaOH (20%), the solution was extracted three times
with CH2Cl2. The combined CH2Cl2 phases were dried with
K2CO3, and the solvent was removed under vacuum. Upon
recrystallization from CH3CN, orange crystals of 3b (0.009 g,
0.012 mmol, 7%) were obtained. C26H40N14O4 (612.70): calcd. C
c = 1.8ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1) = 255 (4.77ϫ104),
339 (0.99ϫ104) nm. MS (FAB+): m/z (%) = 783 (100) [(2a)H]+, 737
(69) [2a-HN(CH3)2]+. Crystal data for C26H48I2N12: Mr = 782.56,
0.30ϫ0.20ϫ0.20 mm3, monoclinic, space group P21/n,
a =
9.900(2), b = 16.157(3), c = 11.044(2) Å, β = 113.29(3)°, V =
1622.6(6) Å3, Z = 2, dcalc = 1.602 Mgm–3, Mo-Kα radiation (graph-
ite-monochromated, λ = 0.71073 Å), T = 100 K, θrange 2.34 to
30.21°. Reflections measd. 27257, indep. 4763, Rint = 0.0525. Final
R indices [IϾ2σ(I)]: R1 = 0.0285, wR2 = 0.0654.
1
Synthesis of 2b: To a solution of 2b(I3)2 (0.152 g, 0.099 mmol) in
DMF (2 mL) was added hydrazine monohydrate (0.07 mL) under
an argon atmosphere. The mixture was stirred at r.t. for 1 h. The
resulting precipitate was collected by filtration and washed with
CH3CN. The resulting yellow solid was dissolved in HCl (10%).
After addition of NaOH (20%), the solution was extracted three
times with CH2Cl2. The combined organic phases were dried with
K2CO3, and the solvent was removed under vacuum to yield 2b
(0.053 g, 0.068 mmol, 69%) as a yellow powder. C26H40I2N12
(774.49): calcd. C 40.32, H 5.21, N 21.70; found C 40.53, H 5.17,
N 21.40. 1H NMR (399.89 MHz, CD2Cl2): δ = 3.24–3.14 (m, 16
50.97, H 6.58, N 32.01; found C 51.04, H 6.43, N 32.18. H NMR
(600.13 MHz, CD2Cl2): δ = 3.25–3.16 (m, 16 H, CH2), 2.65 (s,
24 H, CH3) ppm. 13C NMR (150.90 MHz, CD2Cl2): δ = 155.19,
141.28, 128.81, 48.68 (CH ), 34.11 (CH ) ppm. IR (CsI): ν = 2937
˜
2
3
(w), 2872 (w), 2827 (w), 1628 (s), 1523 (s), 1488 (s), 1450 (m), 1394
(s), 1280 (vs), 1245 (m), 1220 (s), 1138 (w), 1120 (w), 1075 (w),
1060 (w), 1035 (m), 955 (vs), 861 (w), 815 (m), 752 (m), 720 (w),
707 (w), 640 (m), 628 (m), 586 (w), 544 (w) cm–1. UV/Vis (CH2Cl2,
c
= = 252
4.90ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1)
(3.31ϫ104), 328 (1.14ϫ 104), 448 (0.14ϫ 104) nm. MS (FAB+):
m/z (%) = 613 (100) [3b + H]+. Crystal data for 3b·4CH3CN:
H, CH2), 2.62 (s, 24 H, CH3) ppm. 13C{1H} NMR (100.55 MHz, C34H52N18O4, Mr = 776.94, 0.30ϫ0.20ϫ0.15 mm3, triclinic, space
CD2Cl2): δ = 153.55, 137.18, 98.39, 48.85 (CH2), 34.50 (CH3) ppm. group P1, a = 10.823(2), b = 10.984(2), c = 17.317(4) Å, α =
¯
IR (CsI): ν = 2924 (w), 2846 (w), 1636 (vs), 1488 (m), 1439 (w),
100.64(3)°, β = 91.06(3)°, γ = 90.91(3)°, V = 2022.5(7) Å3, Z = 2,
˜
1418 (m), 1390 (m), 1285 (m), 1244 (m), 1236 (m), 1194 (w), 1167 dcalc = 1.276 Mgm–3, Mo-Kα radiation (graphite-monochromated,
(m), 1048 (m), 1033 (w), 991 (w), 968 (w), 939 (s), 825 (w), 739 (w), λ = 0.71073 Å), T = 100 K, θrange 2.04 to 27.49°. Reflections measd.
659 (w), 637 (w), 608 (w) cm–1. UV/Vis (CH2Cl2,
c
=
16880, indep. 9176, Rint = 0.0494. Final R indices [IϾ2σ(I)]: R1 =
7.0ϫ10–6 molL–1): λmax (ε, dm3 mol–1 cm–1) = 254 (12.13ϫ104), 0.0698, wR2 = 0.1987.
Eur. J. Inorg. Chem. 2012, 1620–1631
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1629

A. Peters, H. Herrmann, M. Magg, E. Kaifer, H.-J. Himmel
FULL PAPER
Synthesis of [(3a)H3]Cl3: Et2O·HCl (0.1 mL, 2 m) was added to 3a
dm3 mol–1 cm–1) = 256 (3.01ϫ104), 295 (7.97ϫ 104), 372 (6.73ϫ
(0.016 g, 0.02 mmol) dissolved in CH2Cl2 (10 mL). After stirring 104) nm. MS (ESI+): m/z (%) = 306 (100) [3b]2+
.
for 20 min at r.t., the resulting yellow precipitate was collected by
Synthesis of [3a(CuI)2]: Compound 3a (0.022 g, 0.036 mmol) and
CuI (0.015 g, 0.081 mmol) in CH3CN (10 mL) were stirred for 1 h
at r.t. The resulting dark blue precipitate was collected by filtration
and washed with CH3CN and Et2O to afford [3a(CuI)2] (0.022 g,
0.022 mmol, 61%). C26H48Cu2I2N14O4 (1001.65): calcd. C 31.18, H
4.83, N 19.58; found C 31.11, H 4.88, N 18.93. 1H NMR
filtration and washed with CH2Cl2. Upon recrystallization from
CH3CN/Et2O, orange crystals of [(3a)H3]Cl3·3H2O (0.012 g,
0.015 mmol, 61%) were obtained. C26H51Cl3N14O4·3H2O (784.18):
calcd. C 39.82, H 7.33, N 25.01; found C 39.88, H 7.11, N 24.92.
1H NMR (600.13 MHz, CD3CN): δ = 2.85 (s, 48 H, CH3) ppm.
13C NMR (150.90 MHz, CD3CN): δ = 40.44 (CH3) ppm. IR (CsI):
(200.13 MHz, CD Cl ): δ = 2.81 (s, 48 H, CH ) ppm. IR (CsI): ν
˜
2
2
3
ν = 3402 (w), 2936 (w), 1636 (vs), 1542 (vs), 1474 (m), 1423 (m),
˜
= 2938 (w), 2876 (w), 1521 (vs), 1466 (s), 1417 (s), 1406 (s), 1391
(s), 1346 (w), 1240 (w), 1207 (s), 1152 (s), 1113 (w), 1066 (w), 1037
(m), 991 (s), 909 (m), 800 (m), 733 (w), 711 (m), 696 (w), 643 (w),
610 (w) cm–1. UV/Vis (CH2Cl2, c = 1.42ϫ 10–5 molL–1): λmax (ε,
dm3 mol–1 cm–1) = 279 (3.16ϫ104), 332 (2.81ϫ 104), 582 (0.30ϫ
104) nm. MS (FAB+): m/z (%) = 811 (14) [(3a)CuI + H]+, 621 (32)
[3a + H]+, 460 (60) [(3a)H–HNC{N(CH3)2}2–HN(CH3)2]+. Crystal
1395 (m), 1360 (w), 1341 (w), 1302 (w), 1241 (m), 1228 (m), 1170
(m), 1161 (m), 1147 (w), 1065 (w), 1041 (w), 1020 (w), 910 (w), 895
(w), 799 (w), 780 (w) cm–1. UV/Vis (CH2Cl2,
c
=
0.77ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1) = 307 (2.68ϫ104),
456 (0.28ϫ 104) nm. MS (FAB+): m/z (%) = 621 (100) [3a + H]+,
311 (30) [3a
+ . Crystal data for [(3a)H3]Cl3·3H2O:
2H]2+
C26H57Cl3N14O7, Mr = 784.21, 0.25ϫ0.20ϫ0.20 mm3, triclinic,
data for [3a(CuI)2]: C26H48Cu2I2N14O4, Mr
=
1001.66,
¯
space group P1, a = 11.059(2), b = 12.725(3), c = 16.208(3) Å, α =
3
¯
0.20ϫ0.20ϫ0.16 mm , triclinic, space group P1, a = 7.595(2), b =
10.824(2), c = 11.725(2) Å, α = 90.52(3)°, β = 91.21(3)°, γ =
103.67(3)°, V = 936.3(6) Å3, Z = 1, dcalc = 1.776 Mgm–3, Mo-Kα
radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K,
84.57(3)°, β = 87.80(3)°, γ = 66.23(3)°, V = 2078.0(7) Å3, Z = 2,
dcalc = 1.253 Mgm–3, Mo-Kα radiation (graphite-monochromated,
λ = 0.71073 Å), T = 100 K, θrange 2.07 to 27.90°. Reflections measd.
18077, indep. 9860, Rint = 0.0427. Final R indices [IϾ2σ(I)]: R1 =
0.0577, wR2 = 0.1449.
θrange 2.58 to 30.05°. Reflections measd. 9893, indep. 5471, Rint
0.0242. Final R indices [IϾ2σ(I)]: R1 = 0.0282, wR2 = 0.0658.
=
Synthesis of (3a)I2: I2 (0.005 g, 0.039 mmol) was dissolved in
CH2Cl2 (2 mL) and added dropwise to 3a (0.007 g, 0.012 mmol) in
CH2Cl2 (5 mL). The mixture was stirred for 2 h at r.t. The solvent
was removed under vacuum, and the resulting solid was redissolved
in CH3CN. On addition of Et2O, dark red crystals of (3a)I2 (0.01 g,
0.011 mmol, 92%) were obtained. C26H48I2N14O4 (874.56): calcd.
C 35.71, H 5.53, N 22.42; found C 35.69, H 5.52, N 22.44. 1H
NMR (600.13 MHz, CD2Cl2): δ = 3.04 (s, 48 H, CH3) ppm. 13C
NMR (150.90 MHz, CD2Cl2): δ = 166.14, 146.37, 127.25, 41.73
Synthesis of 5: In contrast to that of [1a(CuI)2], the oxidation of
[3a(CuI)2] with I2 led to decomposition of the complex. In the case
of [3a(CuI)2], only oxidized ligand (3a)I2 was obtained. The slow
oxidation of [3a(CuI)2] in CH2Cl2 or CH3CN solutions at r.t. in air
led quantitatively in 3 d to (3a)I2 and 5, which was crystallized from
CH2Cl2/hexane. 1H NMR (200.13 MHz, CD3CN): δ = 3.10 (s, 3
H), 3.00 (s, 12 H), 2.95 (s, 12 H), 2.93 (s, 12 H), 2.81 (s, 6 H) ppm.
IR (CsI): ν = 2930 (w), 1645 (s), 1603 (s), 1578 (s), 1516 (m), 1459
˜
(m), 1410 (s), 1352 (w), 1315 (m), 1292 (m), 1258 (w), 1225 (m),
1169 (m), 1144 (w), 1065 (w), 1036 (w), 928 (m), 901 (w) cm–1. UV/
Vis (CH2Cl2, c = 1.10ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1) =
377 (1.87ϫ104), 457 (0.87ϫ 104) nm. MS (ESI+): m/z (%) = 605
(100) [5 – Cu – 2I]+. Crystal data for 5·2CH2Cl2: C27H49Cl4Cu-
I2N14O4, Mr = 1092.94, 0.20ϫ0.20ϫ0.20 mm3, monoclinic, space
group P21/n, a = 9.542(2), b = 39.561(8), c = 11.920(2) Å, β =
106.31(3)°, V = 4318.5(15) Å3, Z = 4, dcalc = 1.681 Mgm–3, Mo-Kα
radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K,
θrange 2.06 to 27.92°. Reflections measd. 20337, indep. 10326, Rint
= 0.0224. Final R indices [IϾ2σ(I)]: R1 = 0.0341, wR2 = 0.0839.
(CH ) ppm. IR (CsI): ν = 2934 (w), 1636 (m), 1593 (s), 1545 (vs),
˜
3
1514 (vs), 1498 (s), 1470 (s), 1429 (m), 1402 (s), 1381 (s), 1334 (w),
1305 (m), 1282 (s), 1189 (m), 1169 (m), 1077 (w), 988 (w), 921 (w),
899 (w), 801 (w), 756 (w), 713 (w), 653 (w) cm–1. UV/Vis (CH2Cl2,
c
=
1.14ϫ10–5 molL–1): λmax (ε, dm3 mol–1 cm–1)
= 269
(4.49ϫ104), 390 (4.13ϫ 104), 532 (0.30ϫ 104) nm. MS (FAB+):
m/z (%) = 621 (100) [3a + H]+, 531 (12) [3a-2NO2], 469 (62).
Crystal data for (3a)I2: C26H48I2N14O4, Mr
=
874.58,
3
¯
0.35ϫ0.30ϫ0.30 mm , triclinic, space group P1, a = 9.5230(19), b
= 10.351(2), c = 10.837(2) Å, α = 75.73(3)°, β = 81.95(3)°, γ =
63.26(3)°, V = 924.0(4) Å3, Z = 1, dcalc = 1.572 Mgm–3, Mo-Kα
radiation (graphite-monochromated, λ = 0.71073 Å), T = 100 K,
X-ray Crystallographic Study: Suitable crystals were taken directly
out of the mother liquor, immersed in perfluorinated polyether oil
and fixed on top of a glass capillary. Measurements were made
with a Nonius-Kappa CCD diffractometer with low-temperature
unit using graphite-monochromated Mo-Kα radiation. The tem-
perature was set to 100 K. The data collected were processed using
the standard Nonius software.[26] All calculations were performed
using the SHELXT-PLUS software package. Structures were
solved by direct methods with the SHELXS-97 program and re-
fined with the SHELXL-97 program.[27,28] Graphical handing of
the structural data during solution and refinement was performed
with XPMA.[29] Atomic coordinates and anisotropic thermal pa-
rameters of non-hydrogen atoms were refined by full-matrix least-
squares calculations.
θrange 2.25 to 32.92°. Reflections measd. 12246, indep. 6785, Rint
0.0215. Final R indices [IϾ2σ(I)]: R1 = 0.0271, wR2 = 0.0619.
=
Synthesis of (3b)(I3)2: I2 (0.014 g, 0.11 mmol) was dissolved in
CH2Cl2 (2 mL) and added dropwise to 3b (0.011 g, 0.018 mmol) in
CH2Cl2 (6 mL). The mixture was stirred for 2 h at r.t. The resulting
precipitate was collected by filtration and washed with CH2Cl2.
Upon recrystallization from CH3CN, dark crystals of (3b)2I3
(0.02 g, 0.015 mmol, 80%) were obtained. C26H40N14O4I6
(1374.10): calcd. C 22.73, H 2.93, N 14.27; found C 23.16, H 3.04,
N 14.34. 1H NMR (600.13 MHz, CD3CN): δ = 3.68–3.65 (m, 16 H,
CH2), 2.76 (s, 24 H, CH3) ppm. 1H NMR [600.13 MHz, (CD3)2-
SO]: δ = 3.72–3.65 (m, 16 H, CH2), 2.76 (s, 24 H, CH3) ppm. 13C
NMR [150.90 MHz, (CD3)2SO]: δ = 162.57, 147.19, 125.36, 47.80
(CH2), 32.38 (CH ) ppm. IR (CsI): ν = 2958 (w), 2881 (w), 1669
CCDC-848628 (for 4), -848623 [for 1b(PF6)2], -770431 [for
˜
3
(s), 1578 (vs), 1551 (vs), 1504 (s), 1474 (m), 1412 (m), 1373 (m), 2b(I3)2], -770441 (for 2a), -848627 (for 2b), -848621 (for 3a),
1341 (s), 1291 (s), 1236 (w), 1198 (w), 1077 (w), 1005 (m), 966 (w), -848624 (for 3b), -848622 (for [3aH3]Cl3), -848625 [for (3a)I2], and
926 (w), 815 (w), 776 (w), 745 (m), 648 (w), 580 (w), 496 (w), 454 -848626 (for [3a(CuI)2]) contain the supplementary crystallographic
(w) cm–1. UV/Vis (CH2Cl2, c = 1.44ϫ10–5 molL–1): λmax (ε,
data for this paper. These data can be obtained free of charge from
1630
www.eurjic.org
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2012, 1620–1631

Guanidino-Functionalized Aromatic Ligands
[13] V. Vitske, C. König, E. Kaifer, O. Hübner, H.-J. Himmel, Eur.
J. Inorg. Chem. 2010, 115–126.
[14] V. Vitske, P. Roquette, S. Leingang, C. Adam, E. Kaifer, H.
Wadepohl, H.-J. Himmel, Eur. J. Inorg. Chem. 2011, 1593–
1604.
[15] A. Maronna, E. Bindewald, E. Kaifer, H. Wadepohl, H.-J.
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[16] C. Trumm, O. Hübner, E. Kaifer, H.-J. Himmel, Eur. J. Inorg.
Chem. 2010, 3102–3108.
[17] D. Emeljanenko, A. Peters, N. Wagner, J. Beck, E. Kaifer, H.-
J. Himmel, Eur. J. Inorg. Chem. 2010, 1839–1846.
[18] C. Trumm, S. Stang, B. Eberle, E. Kaifer, N. Wagner, J. Beck,
T. Bredow, N. Meyerbröker, M. Zharnikov, O. Hübner, H.-J.
Himmel, Eur. J. Inorg. Chem., DOI: 10.1002/ejic.201101325.
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
Supporting Information (see footnote on the first page of this arti-
cle): Molecular structures of [(4)H2]Cl2, [(1a)H2](PF6)2, [(1b)-
H2](PF6)2, [(1b)H4]Cl4, [(2a)H2]I2 and monoiodated salts of 1a and
1b. Titration curve of 1b. UV/Vis spectra and CVs of the six GFAs
vs. Fc/Fc+. CVs for 3a at different scan rates. Synthetic details for
[(4)H2]Cl2, [(1b)H4]Cl4 and [(1b)H2](PF6)2.
Acknowledgments
The authors gratefully acknowledge financial support by the Deut-
sche Forschungsgemeinschaft (DFG). We although thank Ute Wild
for help with syntheses.
[19] B. Kovacevic, Z. B. Maksic, Org. Lett. 2001, 3, 1523–1526.
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´
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[20]
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We also tested the reduction of the dicationic guanidines with
various reducing agents, which included piperidine in DMF
and potassium bis(trimethylsilyl)amide in toluene. However,
the product yield was smaller.
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Received: December 7, 2011
Published Online: February 9, 2012
Eur. J. Inorg. Chem. 2012, 1620–1631
© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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