Redox-controlled hydrogen bonding: Turning a superbase into a strong hydrogen-bond donor

Article abstract of DOI:10.1002/chem.201304882

Herein the synthesis, structures and properties of hydrogen-bonded aggregates involving redox-active guanidine superbases are reported. Reversible hydrogen bonding is switched on by oxidation of the hydrogen-donor unit, and leads to formation of aggregates in which the hydrogen-bond donor unit is sandwiched by two hydrogen-bond acceptor units. Further oxidation (of the acceptor units) leads again to deaggregation. Aggregate formation is associated with a distinct color change, and the electronic situation could be described as a frozen stage on the way to hydrogen transfer. A further increase in the basicity of the hydrogen-bond acceptor leads to deprotonation reactions. Hydrogen-bond sandwich, anyone? After oxidation of guanidinyl-functionalized aromatic compounds, the superbase is turned into a strong hydrogen-bond donor and forms hydrogen-bonded aggregates, which could be described as frozen stages on the way to hydrogen transfer (see figure).

Full text of DOI:10.1002/chem.201304882

DOI: 10.1002/chem.201304882
Full Paper
&
Hydrogen Bonds
Redox-Controlled Hydrogen Bonding: Turning a Superbase into
a Strong Hydrogen-Bond Donor
Ute Wild, Christiane Neuhꢀuser, Sven Wiesner, Elisabeth Kaifer, Hubert Wadepohl, and Hans-
Jçrg Himmel*[a]
Chem. Eur. J. 2014, 20, 1 – 13
1
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
Abstract: Herein the synthesis, structures and properties of
hydrogen-bonded aggregates involving redox-active guani-
dine superbases are reported. Reversible hydrogen bonding
is switched on by oxidation of the hydrogen-donor unit, and
leads to formation of aggregates in which the hydrogen-
bond donor unit is sandwiched by two hydrogen-bond ac-
ceptor units. Further oxidation (of the acceptor units) leads
again to deaggregation. Aggregate formation is associated
with a distinct color change, and the electronic situation
could be described as a frozen stage on the way to hydro-
gen transfer. A further increase in the basicity of the hydro-
gen-bond acceptor leads to deprotonation reactions.
Introduction
ing that oxidation of the hydrogen-bond donor or reduction of
the hydrogen-bond acceptor component strengthens the
bond. A variety of redox-active molecules were studied in
which hydrogen bonding is greatly enhanced upon electron
transfer, leading in some cases to “redox-controlled
switches”.[17–19] Redox-active metallocenes were used in some
reported receptors, in which hydrogen bonding is strength-
ened by oxidation. Two examples are shown in Scheme 2.[17]
Hydrogen-bonding[1–3] is considered as the master key of mo-
lecular recognition and is of extreme importance for supra-
molecular and biological assemblies.[4,5] Especially cooperativi-
ty, meaning the combination of several hydrogen-bonding in-
teractions, could lead to a strong total stabilization,[6] and con-
sequently much effort has been spent into synthesizing recep-
tor-type molecules with several sites suitable for hydrogen-
bonding.[7–11] Multiple hydrogen bonding can be used, for ex-
ample, to self-assemble guanine derivatives into macrocycles
or ribbon-like aggregates.[12,13] For a strong bonding in a hydro-
gen-bonded dimer it is obviously advantageous that the hy-
drogen-bond donor (D) and acceptor (A) sites are preorgan-
ized.[14,15] With relevance to this work, a guanidinium salt was
recently synthesized which contains four donor atoms for hy-
drogen bonding arranged in a linear array, and was combined
with a suitable molecule with four acceptor atoms, building
a AAAA-DDDD quadruple hydrogen-bond array (Scheme 1).[14]
A hydrogen bond is composed of electrostatic, induction,
charge-transfer and dispersion contributions, but electrostatic
interactions generally dominate.[16] Therefore, it is not surpris-
Scheme 2. Two literature examples for strengthening of hydrogen bonding
upon oxidation of the hydrogen-bond donor unit.
Scheme 1. Linear array of hydrogen bonding interactions involving guanidi-
nium salts.
One-electron oxidation of the ferrocenyl unit, but also one-
electron reduction of the flavine derivative sketched in
Scheme 2a strengthen the hydrogen bond by one order of
magnitude. Examples for receptors in which hydrogen bond-
ing is strengthened by reduction of the hydrogen-bond ac-
ceptor component include o-quinones, naphthalimide and also
nitrobenzene.[18] Using the same concepts it was also possible
to build electrochemically switchable hydrogen-bonded molec-
ular shuttles.[20] In a very recent publication, a molecular shuttle
was reported in which photolysis causes, in the presence of an
[a] U. Wild, Dr. C. Neuhꢀuser, S. Wiesner, Dr. E. Kaifer, Prof. Dr. H. Wadepohl,
Prof. Dr. H.-J. Himmel
Anorganisch-Chemisches Institut
Ruprecht-Karls Universitꢀt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
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/chem.201304882.
&
&
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
2
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
electron donor, reduction of a hydrogen acceptor unit initiat-
ing movement of a hydrogen-bond donor unit to this now
preferred site, and the authors show the influence of added
water on the rate of this process.[21]
Guanidines are known as strong bases, and have been inten-
sively used in the past,[22] especially for the synthesis of proton
sponges[23] and in coordination chemistry.[24,25] In the last years
we have developed guanidinyl-functionalized aromatic com-
pounds, such as 1,2,4,5-tetrakis(tetramethylguanidinyl)benzene
(1),[26,27] and 1,2,4,5-tetrakis(N,N’-dimethylethylene-guanidinyl)-
benzene (2),[28] as strong organic electron donors (Scheme 3).
We denoted this class of molecule GFA-n (GFA=guanidinyl-
functionalized aromatic compound, n being the number of
guanidinyl groups).[29] Compounds 1 and 2, which will both be
applied in this work, simultaneously lose two electrons at E1/2
(CH2Cl2)=À0.76 V versus Fc/Fc+ for 1 and À0.79 V for 2.[29–31]
In the oxidized form, the aromaticity is lost and the dication is
Figure 1. Molecular structure of 3. Vibrational ellipsoids are drawn at the
50% probability level. Hydrogen atoms attached to C atoms omitted for
clarity. Selected structural parameters (bond lengths in ꢂ, angles in deg):
N1–C2 1.423(5), N1–C4 1.283(5), N2–C4 1.374(5), N3–C4 1.369(5), N4–C3
1.405(5), N4–C11 1.310(5), N5–C11 1.350(5), N6–C11 1.375(5), C1–C2 1.400(5),
C2–C3 1.409(5), C3–C1’ 1.392(5), C2-N1-C4 119.9(3), C3-N4-C11 118.8(3).
Zn(OTf)2 as catalyst. Pale yellow
crystals of 3 precipitated from
CH3CN solutions, and its molecu-
lar structure is illustrated in
Figure 1. The molecules display
crystallographic inversion sym-
metry with two half-molecules in
the asymmetric unit. The N=C
bond lengths measure in aver-
age 1.299(5) ꢂ, and the N···N
separation (N1···N4) between the
imino N atoms of adjacent gua-
nidinyl
groups
measures
2.979(5) ꢂ. The crystal structure
data showed no sign of a signifi-
cant intermolecular interaction
in the solid state. The UV/Vis
Scheme 3. The two known GFA-4 compounds 1 (ttmgb) and 2 (tdmegb) and preparation of the new compound
spectra recorded for 3 in solu-
tion are similar to those of 1 and
3, which is oxidized to the dication and hydrogen-bond donor 32+
.
2, for which aggregation via hy-
best described as a pair of bisguanidinyl allyl cations connect-
ed by two CÀC single bonds. The positive charge is delocalized
into the guanidinyl groups. Moreover, GFAs are strong Brønst-
ed bases, and 2 was even shown to deprotonate CH3CN in the
presence of PhAuCl, resulting in formation of a gold–cyano-
methyl complex.[28] Herein we now report the construction of
a first redox-controlled switch with GFAs as hydrogen-bond
donor units. For this purpose, the dimethylamino groups
(NMe2) of the guanidinyl functions had to be replaced by NHR
groups (R=alkyl or aryl). We, therefore, prepared the new
redox-active GFA-4 compound 1,2,4,5-tetrakis(diisopropylguani-
dinyl)benzene (3; Scheme 3), which features in total eight NÀH
groups for hydrogen bonding.
drogen-bridges is not possible. Hence the molecules do not
aggregate in the solid state or in solution. Compound 3 was
subsequently oxidized with the two ferrocenium (Fc) salts
À
Fc[B(C6F5)4] and Fc[B(ArF)4] (where B(ArF)4
denotes
À
B[(3,5-(CF3)2C6H3]4 ). We crystallized the two salts [(3)(thf)2-
(dioxane)][B(C6F5)4]2 and [3(Et2O)4][B(ArF)4]2. In both structures,
solvent ether molecules are coordinated via hydrogen bonds
to the dications 32+, demonstrating already the hydrogen-
donor capacity of the oxidized GFA. The two structures are
shown in Figure 2a and b. Upon oxidation, two CÀC lengths
within the C6 ring (the C atoms which are directly bonded to
guanidinyl) increase from 1.409(5) ꢂ in neutral 3 to 1.503(3) ꢂ
in [(3)(thf)2(dioxane)]2+ and 1.506(3) ꢂ in [3(Et2O)4]2+. The other
CÀC lengths in the C6 ring shrink, in line with the description
of the dication as a pair of bis-guanidinyl-allyl cations connect-
ed by two CÀC single bonds (see the Lewis structure in
Scheme 3). Structural changes are also registered for the guani-
dinyl units. Hence, the shortest bond, the imino CN bond, is
elongated and the other CN bonds shrink, signaling delocaliza-
Results and Discussion
The new compound 1,2,4,5-tetrakis(N,N’-diisopropylguanidin-
yl)-benzene (3) was prepared by reaction between 1,2,4,5-tet-
raamino-benzene and diisopropylcarbodiimide with 2 mol% of
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
3
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
tion of the positive charge equally into all guanidinyl units. In
the olive-green colored salt [(3)(thf)2(dioxane)][B(C6F5)4]2, two of
the four guanidinyl groups are connected to a thf molecule,
leading to short NH···O distances of 1.83(4) ꢂ, and the other
two guanidinyl groups are connected to dioxane molecules,
which interconnect the 32+ dications. In the case of [3(Et2O)4]
[B(ArF)4]2, each guanidinyl group of 32+ establishes two NH···O
hydrogen bonds of 2.16(2) and 2.333(7) ꢂ length to a co-crys-
1
tallized Et2O molecule. In the H NMR spectrum (in CH3CN), the
NÀH protons give rise for a signal at d=5.95 ppm for both [(3)
(thf)2(dioxane)][B(C6F5)4]2 and [3(Et2O)4][B(ArF)4]2. The crystals of
[(3)(thf)2(dioxane)][B(C6F5)4]2 are green-colored. The green color
is typical for oxidized GFA compounds, and was also observed,
for example, in the case of 12+ and 22+. Interestingly, the
[3(Et2O)4][B(ArF)4]2 crystals are initially orange-colored and
change their color over time to green when kept for a week
under an Ar atmosphere or for 1 h under vacuum, leading to
evaporation of the hydrogen-bonded Et2O molecules. We have
included a photograph of a crystal after partial removal of the
Et2O molecules in the Supporting Information (Figure S1).
Hence it appears that hydrogen bonding could change the
electronic properties (see Discussion below). In addition we
prepared the salt 3(dca)2 (dcaÀ =dicyanamide, N(CN)2À) as
product of the reaction between 3 and two equivalents of
Ag(dca). This salt again immediately gives green-colored crys-
tals. The crystal structure also shows hydrogen bonding, lead-
ing to chains (Figure 2c). The 1H NMR spectrum (measured
again in CH3CN) is similar to that of [3(Et2O)4][B(ArF)4]2, but the
NÀH protons occur at lower field (d=6.50 ppm). The com-
pound is a potential precursor to C,N materials (carbon, e.g.,
graphitic, network in which some C atoms are replaced by
N atoms),[32] and its thermogravimetric (TG) and differential
scanning calorimetric (DSC) curves are displayed and discussed
in the Supporting Information (Figure S2 and text). Subse-
quently, the [B(C6F5)4]À and [B(ArF)4]À salts of the oxidized GFA
3 were used as starting reagents for the synthesis of hydro-
gen-bonded aggregates.
First, we tested hydrogen-bond formation between dication-
ic and neutral 3. Experiments, in which the salt 3[B(C6F5)4]2 was
treated with slightly more than two equivalents of neutral 3,
indeed resulted in formation of the salt [(3)3][B(C6F5)4]2 (orange-
colored crystals). Hydrogen bonding, which is switched on by
oxidation, leads to an aggregate in which the hydrogen-bond
donor 32+ is sandwiched between two units of neutral 3. Fur-
ther oxidation leads to deaggregation (Scheme 4). The struc-
ture of the hydrogen-bonded cationic assembly as obtained
from XRD analysis is shown in Figure 3a. In total eight NH···N
interactions, involving the NH protons of 32+ and the imino
Figure 2. Crystal structures of: a) [(3)(thf)2(dioxane)][B(C6F5)4]2 (only the cat-
ionic portion is shown), b) [(3)(Et2O)4][B(ArF)4]2 (only one of the two inde-
pendent dications is shown), and c) 3(dca)2. Vibrational ellipsoids are drawn
at the 50% probability level. Hydrogen atoms attached to C atoms omitted
for clarity. Selected bond lengths (ꢂ) for [(3)(thf)2(dioxane)][B(C6F5)4]2: N1–C1
1.306(3), N1–C4 1.361(3), N2–C4 1.338(3), N3–C4 1.330(3), N4–C2 1.342(3),
N4–C11 1.344(3), N5–C11 1.340(3), N6–C11 1.336(3), C1–C2 1.503(3), C1–C3
1.418(3), C2–C3 1.378(3), N3H···O1 2.337(6), N5H···O3 1.883(4). Selected bond
lengths (ꢂ) for [(3)(Et2O)4][B(ArF)4]2: N1···N4 2.623(2), N1–C1 1.318(3), N1–C4
1.350(3), N2–C4 1.340(3), N3–C4 1.322(3), N4–C2 1.312(3), N5–C11 1.336(3),
N6–C11 1.346(3), C1–C2’ 1.506(3), C1–C3 1.397(3), C2–C3 1.395(3), N2H···O2
2.073(3), N3H···O2 2.28(1), N5H···O2 2.333(7), N6H···O2 2.16(2). Selected struc-
tural parameters (bond lengths in ꢂ, angles in deg) for 3(dca)2: N1–C1’
1.362(2), N1–C4 1.330(2), N2–C4 1.344(2), N3–C4 1.352(2), N4–C2 1.300(2),
N4–C11 1.367(2), N5–C11 1.329(2), N6–C11 1.322(2), N7–C18 1.310(2), N7–C19
1.311(3), N8–C18 1.154(2), N9–C19 1.167(2), C1–C2 1.503(2), C1–C3’ 1.364(2),
C2–C3 1.432(2), N5H···N8’ 2.156(3), N6H···N9 2.161(2), C18-N7-C19 121.23(16).
Scheme 4. Reversible formation of the hydrogen-bonded aggregate by elec-
tron transfer.
&
&
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
4
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Figure 3. Structures of the dications: a) [(3)3]2+, b) [(1)2(3)]2+, and c) [(2)2(3)]2+ (the anions B(C6F5)4À are not shown). Vibrational ellipsoids are drawn at the 50%
probability level. Hydrogen atoms attached to C atoms omitted for clarity. A list of bond lengths and angles for each structure can be found the Supporting
Information.
N atoms of neutral 3 stabilize the structure. Further experi-
ments showed that the dication 32+ could also form hydro-
gen-bonded aggregates with 1 and 2. The structures of the
two aggregates [(1)2(3)][B(C6F5)4]2 and [(2)2(3)][B(C6F5)4]2 (both
orange-colored solids), being the products of the reaction be-
tween (3)[B(C6F5)4]2 and slightly more than two equivalents of
neutral 1 or 2, are displayed in Figure 3b and c. Further details
of the structures and some bond parameters can be found in
Figures S3–S5 in the Supporting Information. The three dicat-
ions [(3)3]2+, [(1)2(3)]2+ and [(2)2(3)]2+ also formed in experi-
ments in which 3[B(ArF)4]2 was treated with two equivalents of
the neutral compounds 3, 1 or 2, but the crystals were of
poorer quality. Nevertheless, the structural parameters of the
dicationic aggregate units were very similar indicating that the
influence of the anions or crystal packing is small.
separations of 2.255(4) and 2.227(5) ꢂ between the relevant
hydrogen atoms of the central 32+ dicationic unit. Consequent-
ly, only three of the four guanidinyl groups of each neutral 3
unit are engaged in significant hydrogen bonding (Figure 3a).
There are still eight NH···N interactions, since one of the imino
N atoms of each hydrogen-bond acceptor unit is engaged in
two interactions. However, the average value of 2.242 ꢂ is
larger, and the bond lengths cover a larger range of 1.988–
2.592 ꢂ. Finally, in [(1)2(3)][B(C6F5)4]2, only two of the four guani-
dinyl groups in each neutral 1 unit are involved in hydrogen
bonding. The N···N distances between adjacent imino N atoms
in the two neutral units of 1 adopt values of 2.855(5) and
2.867(4) ꢂ, which do not fit with the separations of 2.155 and
2.210 ꢂ between the relevant hydrogen atoms of the central
32+ dicationic unit. Nevertheless, also in this case eight NH···N
interactions could be identified, now with an average value of
2.202 ꢂ, covering the range 2.029–2.363 ꢂ. The difference in
hydrogen bonding has consequences on the angle between
the C6 ring plane of the central 32+ donor unit and the C6 ring
plane of the neutral acceptor units. Hence this dihedral angle
decreases in the order: [(2)2(3)]2+ (94.58)>[(3)3]2+ (81.18)>
[(1)2(3)]2+ (33.78).
The optical properties of the aggregates clearly differ from
those of the components. As example, photographs of crystal-
line 3, green-colored 3[B(ArF)4]2 and orange-colored [(3)3]
[B(ArF)4]2 are shown in Figure 4a. In addition, the diffuse reflec-
tance spectra, recorded in a BaSO4 matrix, for the three com-
pounds are compared in Figure 4b. The spectrum of [3(Et2O)n]
[B(ArF)4]2 (n<4) is also included. In the case of pale-yellow 3,
the lowest energy band is located at 420 nm. Olive-colored
[3(Et2O)n][B(ArF)4]2 (n<4) gives a spectrum with a band at
433 nm, but in addition a band centered at 611 nm and
In all three aggregates [(3)3]2+, [(1)2(3)]2+ and [(2)2(3)]2+
,
eight NH···N interactions dominate and strongly connect the
central dication 32+ with the two neutral guanidine units. Nev-
ertheless, the structures show some differences. In [(2)2(3)]
[B(C6F5)4]2, all guanidinyl groups are involved in hydrogen
bonding, and the NH···N distances cover a relatively narrow
range of 2.030–2.282 ꢂ (average value: 2.128 ꢂ). This symmet-
ric structure is in line with the short N···N distances between
adjacent imino N atoms in the two neutral units of 2 (2.760(3)
and 2.753(3) ꢂ), which match relatively well the separations of
2.229(2) and 2.243(2) ꢂ between the relevant hydrogen atoms
of the central 32+ dicationic unit (see Figure 3c and the visuali-
zation of the hydrogen array in Figure S5 in the Supporting In-
formation). In [(3)3][B(C6F5)4]2, the N···N distances between adja-
cent imino N atoms in the two neutral units of 3 measure
2.864(5) and 2.803(5) ꢂ. This results in a more asymmetric
structure, since the values already do not ideally match the
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
5
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
gen bonding thus clearly significantly influences the energies
of the frontier orbitals. We interpret the situation as a frozen
stage on the way to deprotonation of 32+
.
Such a deprotonation is indeed possible if stronger bases
are applied. Hence, when 3[B(ArF)4]2 was treated with the su-
perbase and proton sponge 1,4,5,8-tetrakis(tetramethylguani-
dinyl)-naphthalene (4)[33,34] we observed, instead of formation
of a hydrogen-bonded aggregate, double proton abstraction
leading from the dication 32+ to the neutral compound 5
(Scheme 5). In this case the intramolecular NH···N bridges in
the protonated proton sponge 4 replace the NH···N bonds be-
tween the donor and acceptor units of the hydrogen-bonded
aggregate. Red-colored crystals of 5 were obtained after layer-
ing the CH2Cl2/Et2O solutions with petroleum ether 30/75. Its
structure is shown in Figure 5. The diffuse reflectance spectrum
of 5 displays in the visible region a broad band centered at
Figure 4. a) Photographs of crystals of 3, 3[B(ArF)4]2 and [(3)3][B(ArF)4]2. b) Dif-
fuse reflectance spectra for 3, [3(Et2O)n][B(ArF)4]2, 3[B(ArF)4]2, and [(3)3]
[B(ArF)4]2 in a BaSO4 matrix. To allow for a better comparison, the spectra
were plotted on top of each other by adding a constant to the diffuse re-
flectance values. The original spectra with the diffuse reflectance values
given in percentages are displayed in the Supporting Information.
Figure 5. Structure of 5. Selected bond lengths [ꢂ]: N1–C1 1.297(4), N1–C4
1.407(4), N2–C4 1.372(4), N3–C4 1.290(4), N4–C2 1.366(3), N4–C11 1.309(3),
N5–C11 1.367(4), N6–C11 1.362(3), C1–C2 1.502(4), C1–C3 1.443(4), C2–C3’
1.365(4).
a weaker extremely broad ab-
Table 1. Comparison between the diffuse reflectance data measured in BaSO4 matrices.
sorption in the region 750–
710 nm. If the material is kept
for several hours under vacuum
to remove all the Et2O mole-
cules, the color changes to in-
tense green and a very broad
absorption in the region 760–
710 nm gains in intensity. In the
aggregate [(3)3][B(ArF)4]2, a band
around 560 nm is found (in addi-
tion to a band at 409 nm). Simi-
lar results are obtained for the
other aggregate salts. A full list
of the absorptions for all rele-
vant compounds is given in
Table 1 (the original spectra are
displayed in Figure S6 in the
Supporting Information). Hydro-
Compound
Wavelength for maxima of absorption [nm]
3
2
1
5
420
421
431
416
433
430
433
434
429
410
409
412
413
419
411
340
340
350 (sh)
390 (sh)
291
292
320
280
266
277
292
295
305
325
320
335
335
338
330
260
270
530
611
625
600
601
605
560 (broad)
560 (broad)
565 (broad)
569 (broad)
575 (broad)
566 (broad)
[3(Et2O)n][B(ArF)4]2
3[B(ArF)4]2
[(3)(thf)2(dioxane)] [B(C6F5)4]2
3[B(C6F5)4]2
3(dca)2
[(3)3][B(ArF)4]2
[(3)3][B(C6F5)4]2
[(1)2(3)][B(ArF)4]2
[(1)2(3)][B(C6F5)4]2
[(2)2(3)][B(ArF)4]2
[(2)2(3)][B(C6F5)4]2
750–710 (broad)[a]
760–710 (broad)[a]
750–680 (broad)[a]
740–640 (broad)[a]
780–740 (broad)[a]
263
265
389 (sh)
388 (sh)
390 (sh)
390 (sh)
398 (sh)
389 (sh)
280
280
275
275
270
259
[a] Due to the large half-width of this band, the wavelength at the maximum of absorption could not be locat-
ed exactly. The band grows over time or when the compound is kept under vacuum (removal of the solvent
molecules, see Discussion).
&
&
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
6
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
S2 as well as Figure S8 in the
Supporting Information. In the
CV curve of 3, broad waves are
visible, in sharp contrast to the
sharp waves observed for 1 or 2,
indicating hydrogen-bond for-
mation (Figure S9 in the Sup-
porting Information). Electro-
spray ionisation (ESI) mass spec-
trometric analysis (in CH2Cl2)
showed evidence for weak sig-
nals due to [(3)2]+, [(1)(3)À4H]2+
Scheme 5. Double proton abstraction reaction leading to neutral 5.
530 nm, and another band at 416 nm. The spectrum clearly dif-
fers from that of the aggregate, and the lowest energy band
of the aggregate [(3)3]2+ is in between those of the dication
32+ and 5. Compound 5 could also be synthesized directly in
68% yield by treatment of 3·4HCl with an excess of KOtBu and
O2. The O2 is reduced in a two-proton-two-electron transfer re-
and [(2)(3)H2]2+ (see the Experimental Section).
However, a detailed analysis of the aggregation process in
solution was not possible for the following reasons. The solu-
bility of the aggregates turned out to be poor. More profound-
ly, the aggregates are not stable in solution, and are converted
with time to other species. We assume ring-closing reactions
leading to bis-imidazolium salts to slowly proceed (see the
Supporting Information and also related ring-closing processes
observed during synthesis of 1).[30] A similar ring-closing reac-
tion was observed when solutions of 32+ were treated with
NaOH, and it appears that the presence of strong bases ini-
tiates this reaction. Moreover, in the case of [(2)2(3)]2+, redox
reactions slowly occur, leading to 22+ and neutral 3. For solu-
tions of [(1)2(3)]2+, we also observed oxidation of the hydro-
gen-bond acceptor unit and formation of 12+, although this
process was slower. Nevertheless, the NMR and UV/Vis spectra
measured in solution point to strong hydrogen bonding in the
aggregates. Additional NMR experiments indicated that the ag-
gregation is reversible and that the aggregates can be annihi-
action. According to quantum chemical calculations (B3LYP/6-
1
311G*), the gas-phase reaction between 3 and = O2 to give 5
2
and H2O is exergonic (DG0 =À24 kJmolÀ1 at 1 bar).
The aggregates [(3)3]2+, [(1)2(3)]2+ and [(2)2(3)]2+ are also
present in solution. Hence, their CH3CN or CH2Cl2 solutions are
orange-colored, while solutions of salts of the dication 32+ are
green-colored. The UV/Vis spectra in CH3CN solution are com-
parable to those measured for the solid material in BaSO4 ma-
trices (all spectra are displayed in the Supporting Information).
The spectrum of [(3)3][B(ArF)4]2 contained a broad absorption
centered roughly at 389 nm with a tail to lower wavenumbers,
which should arise from another band around 565 nm, and
sharper features at 389 and 325 nm. The spectrum of [(1)2(3)]
[B(ArF)4]2 displayed a broad absorption at about 400 nm with
a shoulder at 585 nm, and sharper and stronger bands in the
UV region at 356, 328 and 270 nm. However, massive band
overlapping of the broad bands prohibited a more detailed
analysis.
+
lated both by oxidation with a salt of FeCp2 or by reduction
with CoCp2 (see Experimental Section).
Conclusions
The room temperature NMR spectra showed signals at posi-
tions which differ from those of the components. For example,
1H NMR spectra of CD3CN solutions of [(1)2(3)][B(ArF)4]2 showed
signals at d=2.70 (CH3) and 5.83 ppm (Harom.) assignable to the
hydrogen-bond acceptor units 1, and at 1.07 (CH3) and
3.59 ppm (CH) for the isopropyl groups of the hydrogen-bond
donor units 32+ (the aromatic protons and unfortunately also
the NH protons could not be detected, even at low tempera-
tures). The chemical shifts for 1 are in between those found for
unprotonated 1 (2.63 (CH3) and 5.54 ppm (Harom.)) and for the
diprotonated form [1H2]2+ (2.78 (CH3) and 6.11 ppm (Harom.)).
Also, the signals due to the hydrogen-bond donor component
32+ in [(1)2(3)][B(ArF)4]2 differ from those of 32+ in 3[B(ArF)4]2 sol-
utions (1.15 and 3.65 ppm), and are close to those observed
for 5. In no case did we observe signals due to protonated 1.
Thus, the NMR spectra are in line with the description of the
aggregates as frozen-stages on the way to hydrogen transfer.
Spectra recorded at various temperatures showed no evidence
for an equilibrium between the aggregate and the compo-
nents, indicating strong hydrogen bonding in the aggregates.
All NMR spectroscopy results are summarized in Tables S1 and
Strong and reversible hydrogen bonding could be switched on
by two-electron oxidation of the new redox-active guanidinyl-
functionalized aromatic compound (GFA) 1,2,4,5-tetrakis(diiso-
propylguanidinyl)benzene, which features eight hydrogen-
bond donor sites. Hydrogen bonding leads to the formation of
aggregates, in which the dication 32+ is sandwiched by two
neutral guanidine units. Three aggregates were structurally
characterized, which show that 32+ could not only form aggre-
gates with itself, but also with other guanidine bases. Aggrega-
tion is accompanied by a distinct change in the optical proper-
ties. Whereas crystals of neutral 3 are pale-yellow and crystals
of the dication 32+ green colored, the aggregate crystals are
orange. Further oxidation leads to deaggregation. If the
strength of the guanidine base is further increased, 32+ is de-
protonated and the neutral compound 5 formed. The electron-
ic situation in the aggregates could be described as a frozen-
stage on the way to hydrogen transfer. Ongoing and future
work in this area focuses on the synthesis of extended hydro-
gen-bonded structures with the dication 32+ as hydrogen-
bond donor component.
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
7
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
48608, independent: 11847, Rint =0.088. Final R indices [I>2s(I)]:
R1 =0.1005, wR2 =0.2308.
Experimental Section
General
[(3)(thf)2(dioxane)][B(C6F5)4]2: Compound 3 (20 mg; 0.031 mmol)
and Fc[B(C6F5)4] (49 mg; 0.057 mmol) were suspended in a mixture
of CH2Cl2 (2 mL) and dioxane (2 mL; C4H8O2). Then THF (3 mL) was
added until the solid is completely dissolved. The green-colored
solution was stirred for a period of 20 min at room temperature.
Crystals were obtained at À208C after layering the solution with
petroleum ether 40/60. Yield: 70 mg olive-green crystals
(0.028 mmol, 98%). Elemental analysis (%) for C82H66N12F40B2
(2001.05)·2CH2Cl2·2thf·2dioxane (2491.34): calcd: C 48.21, H 4.13, N
All reactions were carried out under inert gas atmosphere using
standard Schlenk techniques. The solvents were rigorously dried
prior to their use. Compounds 1, 2 and 4 were synthesized as de-
scribed previously.[26,28,32] Elemental analyses were carried out at
the Microanalytical Laboratory of the University of Heidelberg. UV/
Vis (in solution) and diffuse reflectance (of BaSO4 matrices) meas-
urements were carried out on a Cary 5000 spectrophotometer. In-
frared spectra were recorded using a BIORAD Excalibur FTS 3000.
NMR spectra were taken on a BRUKER Avance III 600, a BRUKER
Avance II 400 or on a BRUKER Avance DPX AC200 spectrometer. A
Bruker ApexQe FT-ICR (ESI) machine was used for mass spectrome-
try (MS). 1,2,4,5-Tetraaminobenzene-tetrahydrochloride and N,N’-
diisopropylcarbodiimide were purchased from Aldrich and used as
delivered. Ag(dca) and the two salts Fc[B(C6F5)4] and Fc[B(ArF)4]
(Fc=FeCp2, [B(ArF)4]À =[B{C6H3(CF3)2}4]À) were prepared according
to the literature.[32,35,36]
1
6.75; found: C 47.98, H 4.20, N 6.21; H NMR (399.89 MHz, CD3CN,
295.5 K): d=5.95 (bs, 8H, NH), 5.23 (s, 2H, CHarom.), 3.64 (m, 8H,
CHisopropyl), 1.15 ppm (d, J=6.47 Hz, 48H, CH3); 13C NMR
(150.56 MHz, CD3CN, 297.6 K): d=98.63 (CHarom.), 45.54 (CHisopropyl),
22.68 ppm (CH3); 11B NMR (128.30 MHz, CD3CN, 295.9 K): d=
À16.71 ppm; 19F NMR (376.23 MHz, CD3CN, 295.9 K): d=À133.79,
À163.91, À168.42 ppm; IR (CsI): v˜ =3426 (w), 3305 (w), 2971 (w),
2920 (w), 2863 (w), 1668 (sh), 1626 (m), 1605 (m), 1586 (m), 1565
(m), 1514 (s), 1463 (s), 1379 (m), 1368 (m), 1330 (w), 1319 (m), 1280
(m), 1256 (m), 1216 (w), 1173 (m), 1158 (sh), 1115 (sh), 1091 (s), 980
(vs), 873 (m), 865 (s), 775 (m), 757 (s), 726 (w), 685 (s), 662 (s), 611
(m), 578 (w), 504 (w), 430 cmÀ1 (w); diffuse reflectance (BaSO4
matrix): lmax =750–680 (broad), 600, 433, 292, 263 nm. UV/Vis (c=
2.770·10À5 mollÀ1, d=1 cm, CH3CN): lmax (e)=597 (0.089ꢃ104), 422
(3.218ꢃ104), 280 (1.99ꢃ104), 266 nm (2.049ꢃ104 LmolÀ1 cmÀ1). MS
(ESI, CH2Cl2,): m/z (%): 907 (100) [3(dioxane)3]+, 935 (42) [3H4(thf)4]+
, 951 (24) [3H4(thf)3(dioxane)]+, 967 (12) [3H4(dioxane)2(thf)2]+, 979
(11) [3(dioxane)3(thf)]+. Crystal data for C98H98B2F40N12O6, Mr =
1,2,4,5-Tetrakis(N,N’-diisopropylguanidinyl)benzene (3): 1,2,4,5-
Tetraaminobenzene-tetrahydrochloride (0.28 g, 1.00 mmol) was sus-
pended in THF (10 mL) together with 2 mol% of Zn(OTf)2 (7 mg).
Then, N,N’-diisopropylcarbodiimid (0.50 g, 4.00 mmol; 0.62 mL) was
added. The reaction mixture was stirred at room temperature for
a period of 6 d. Then the precipitate was separated by filtration,
washed three times with 5 mL portions of diethylether, and dried
under vacuum. Yield of 3·4HCl: 0.58 g (74%, 0.74 mmol). Crystals
of 3·4HCl were obtained at room temperature from CH3CN.
C34H70Cl4N12 (788.81 gmolÀ1) calcd: C 51.77, H 8.94, N 21.31; found:
C 48.98, H 8.80, N 19.50. The deviation is most likely caused by
traces of the zinc salt, which cannot be removed completely at this
2321.50, 0.40ꢃ0.40ꢃ0.20 mm3, triclinic, space group P1, a=
¯
11.535(2), b=13.629(3), c=17.890(4) ꢂ, a=112.16(3)8, b=
103.25(3)8,
g=91.42(3)8,
V=2515.9(9) ꢂ3,
Z=1,
1calcd =
1.532 MgmÀ3
, MoKa radiation (graphite monochromated, l=
1
stage. H NMR (600.13 MHz, D2O): d=7.30 (s, 2H, CHarom), 3.77 (br,
0.71073 ꢂ), T=100 K, qrange 2.29 to 30.068. Reflections measured:
25414, independent: 14521, Rint =0.0405. Final R indices [I>2s(I)]:
R1 =0.0553, wR2 =0.1315.
8H, CH), 1.14 ppm (d, 3J=6.12 Hz, 48H, CH3); 13C{1H} NMR
(150.92 MHz, D2O): d=154.55 (CN), 135.23 (Carom), 133.43 (CHarom),
47.90 (CH), 24.47 ppm (CH3); MS (ESI+): m/z (%): 322.3 (100)
[MÀ2H]2+; UV/Vis (H2O, c=2.28ꢃ10À5 molLÀ1, d=1 cm): lmax (e)=
213 (3.263ꢃ104), 238 nm (3.407ꢃ104 LmolÀ1 cmÀ1). Then 0.8 mL of
a 1m NaOH solution was added to 0.12 g (0.15 mmol) of 3·4HCl
dissolved in H2O (6 mL). The reaction mixture was extracted three
times with 6 mL portions of CH2Cl2. Subsequently the combined or-
ganic phases were dried over K2CO3. Then the solvent was re-
moved under vacuum, yielding 0.09 g pale-yellow colored product
3 (93%, 0.14 mmol). Recrystallization from CH3CN afforded crystals
[3(Et2O)n][B(ArF)4]2 (nꢀ4): Compound 3 (23 mg; 0.036 mmol) and
Fc[B(ArF)4] (75 mg; 0.071 mmol) were dissolved in a mixture of Et2O
(2 mL) and CH2Cl2 (2 mL). The green-colored solution was stirred at
room temperature for a period of 10 min. Then the solution was
layered by 10 mL petroleum ether 35/70 and the orange-colored
product was crystallized at À208C. Yield: 61 mg (0.023 mmol,
65%), upon removal of the solvent in the form of green-colored
crystals.
Elemental
analysis
(%)
for
C98H90N12F48B2
1
of 3 suitable for an XRD analysis. H NMR (600.13 MHz, CD2Cl2): d=
(2369.40 gmolÀ1)·2CH2Cl2·Et2O calcd: C 47.80, H 4.01, N 6.43;
found: C 47.91, H 4.19, N 6.89; 1H NMR (399.89 MHz, CD3CN,
295.7 K): d=7.69, 7.67 (bs, 24H, CHarom. B(ArF)4), 5.95 (bs, 8H, NH),
5.22 (s, 2H, CHarom), 3.65 (m, 8H, CHisopropyl), 1.15 ppm (d, J=6.49 Hz,
48H, CH3); 13C NMR (150.56 MHz, CD3CN, 296.2 K): d=163.44,
163.26, 162.27, 161.77, (CN), 129.98, 129.63, 129.43, 126.73, 124.02
6.31 (s, 2H, CHarom), 4.01 (br, 8H, NH), 3.71 (br, 8H, CH), 1.12 ppm
(d, 3J=6.23 Hz, 48H, CH3); 13C{1H} NMR (150.92 MHz, CD2Cl2): d=
149.77 (CN), 136.56 (Carom), 119.22 (CHarom), 43.69 (CH), 23.60 ppm
(CH3); MS (HR-EI+): m/z (%): [C34H66N12]+ calcd 642.5533 [3]+, exptl
642.5581 (88), [C17H29N7]+ calcd 331.2579 [MÀC17H37N5]+, exptl
331.2532 (40), [C14H20N6]+ calcd 272.1750 [MÀC20H46N6]+, exptl
272.1764 (100); IR (CsI): v˜ =3454 (w), 3381 (m), 3333 (m), 2969 (s),
2933 (m), 2870 (w), 1631 (vs), 1601 (vs), 1543 (s), 1486 (s), 1381 (s),
1363 (s), 1330 (m), 1287 (m), 1259 (w), 1179 (s), 1126 (m), 1063 (w),
1031 (w), 896 (m), 874 (w), 803 (w), 709 (w), 574 (w), 492 cmÀ1 (w);
(Carom), 135.57, 118.61 (Carom.
,
B(ArF)4), 97.88 (CHarom.), 45.53
(CHisopropyl), 22.68 ppm (CH3); 11B NMR (128.30 MHz, CD3CN, 295.2 K):
d=À6.71 ppm; 19F (376.24 MHz, CD3CN, 295 K): d=À63.24 ppm;
IR (CsI): v˜ =3450 (w), 3431 (w), 2984 (w), 2946 (w), 2880 (w), 1643
(sh), 1610 (m), 1568 (m), 1520 (s), 1469 (w), 1356 (s), 1279 (vs), 1164
(sh), 1126 (vs), 1096 (sh), 932 (w)„ 898 (w), 888 (m), 839 (s), 744 (w),
716 (vs), 683 (vs), 669 (vs), 586 (w), 503 (w), 448 cmÀ1 (w); diffuse
reflectance (BaSO4 matrix): lmax =750–710 (broad), 611, 433,
266 nm. UV/Vis (c=2.304ꢃ10À5 molLÀ1, d=1 cm, CH2Cl2/Et2O 1:1):
lmax (e)=797 (0.029ꢃ104), 606 (0.076ꢃ104), 422 (2.705ꢃ104), 278
(2.421ꢃ104), 270 nm (2.549ꢃ104 LmolÀ1 cmÀ1); MS (ESI, CH3CN,
MeOH): m/z (%): 321 (100) [3]2+, 753 (60) {[3][B(ArF)4]}2+, 1505 (10)
{3-H[B(ArF)4]}+. Crystal data for [3(Et2O)4][B(ArF)4]2, C114H130B2F48N12O4,
UV/Vis (CH3CN, c=3.92ꢃ10À5 molLÀ1
, d=1 cm): lmax (e)=370
(0.394ꢃ104), 324 (0.896ꢃ104), 241 nm (2.063ꢃ104 LmolÀ1 cmÀ1);
diffuse reflectance (BaSO4 matrix): lmax =420, 340, 291 nm. Crystal
data for C34H66N12, Mr =642.99, 0.19ꢃ0.11ꢃ0.04 mm3, triclinic,
¯
space group P1, a=10.8873(8), b=13.5200(12), c=14.350(2) ꢂ, a=
75.621(10)8, b=74.886(10)8, g=89.997(7)8, V=1970.5(4) ꢂ3, Z=2,
1calcd =1.084 MgmÀ3, Cu radiation (graphite monochromated, l=
0.71073 ꢂ), T=110 K, qrange 2.108 to 33.3988. Reflections measured:
&
&
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
8
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
Mr =2665.92, 0.40ꢃ0.30ꢃ0.30 mm3, monoclinic, space group P21/
n, a=13.050(3), b=27.005(5), c=21.075(4) ꢂ, b=104.51(3)8, V=
7190(2) ꢂ3, Z=2, 1calcd =1.231 MgmÀ3, MoKa radiation (graphite
monochromated, l=0.71073 ꢂ), T=100 K, qrange 1.78 to 27.498. Re-
flections measured 32306, independent 16455, Rint =0.0399. Final
R indices [I>2s(I)]: R1 =0.0627, wR2 =0.1608.
10266, independent: 5233, Rint =0.0487. Final R indices [I>2s(I)]:
R1 =0.0532, wR2 =0.1266.
[(3)3][B(ArF)4]2: Compound 3 (30 mg; 0.047 mmol) and Fc[B(ArF)4]
(20 mg; 0.019 mmol) were dissolved in a mixture of Et2O (2 mL)
and CH2Cl2 (2 mL). The orange-colored solution was stirred at room
temperature for a period of 5 min. Then it was layered by 10 mL of
petroleum ether 35/70 and the product was crystallized at a tem-
perature of À208C. Yield: 30 mg orange-colored crystals
(0.0082 mmol, 86%). Elemental analysis for C166H222N36F48B2
(3655.34 gmolÀ1) calcd: C 54.54, H 6.12, N 13.79; found: C 54.81, H
6.06, N 14.68; IR (CsI): v˜ =3452 (w), 3400 (w), 2972 (m), 2927 (w),
2872 (w), 1636 (sh), 1609 (s), 1517 (s), 1479 (m), 1464 (m), 1429 (w),
1394 (w), 1387 (sh), 1355 (s), 1278 (vs), 1163 (sh), 1126 (vs), 937 (w),
887 (m), 840 (m), 790 (w), 713 (m), 683 (s), 669 cmÀ1 (m); diffuse re-
flectance (BaSO4 matrix): lmax =560 (broad), 410, 389 (sh), 325,
280 nm; UV/Vis (CH3CN, c=3.59ꢃ10À5 molLÀ1, d=1 cm): lmax (e)=
565 (sh, 0.130ꢃ104), 389 (1.724ꢃ104), 325 nm (3.152ꢃ
104 LmolÀ1 cmÀ1); MS (ESI, CH2Cl2): m/z (%): 643 (100) [3]+, 322
(12)[3H]2+, 1507 (3) {3H[B(ArF)4]}+, 1285 (1) [(3)2]+.
[3(Et2O)n][B(C6F5)4]2: Compound 3 (30 mg; 0.047 mmol) was dis-
solved together with Fc[B(C6F5)4] (77 mg; 0.089 mmol) in CH2Cl2
(2 mL) and Et2O (2 mL). The green-colored solution was stirred at
room temperature for a period of 20 min. Then the solvent was re-
moved under vacuum. The green-colored residue was redissolved
in a small portion of Et2O, and then precipitated again upon addi-
tion of petroleum ether 40/60. The solution was separated with
a cannula, and the green-colored solid was washed several times
with petroleum ether 40/60. Yield: 73 mg green-colored powder,
0.034 mmol, 76%. Elemental analysis (%) for C82H66N12F40B2
(2001.05 gmolÀ1)·2CH2Cl2 calcd: C 46.47, H 3.25, N 7.74; found: C
46.28, H 3.15, N 7.76; 1H NMR (399.89 MHz, CD3CN, 295.0 K): d=
5.87 (bs, 8H, NH), 5.22 (s, 2H, CHarom.), 3.66 (m, 8H, CHisopropyl),
1.15 ppm (d, J=6.48 Hz, 48H, CH3); 13C NMR (150.56 MHz, CD3CN,
295.0 K): d=153.69 (CN), 98.50 (CHarom.), 45.54 (CHisopropyl),
22.65 ppm (CH3); 19F NMR (376.23 MHz, CD3CN, 295.0 K): d=
À133.76, À163.92, À168.43 ppm; 11B NMR (128.30 MHz, CD3CN,
295.0 K): d=À16.71 ppm; IR (CsI): v˜ =3426 (w), 3409 (w), 2977 (w),
2928 (w), 2868 (w), 1643 (m), 1607 (m), 1587 (m), 1564 (sh), 1514
(s), 1462 (s), 1379 (w), 1373 (m), 1316 (w), 1273 (m), 1251 (m), 1170
(w), 1156 (m), 1116 (sh), 1084 (s), 980 (vs), 912 (w), 851 (w), 775 (s),
757 (s), 684 (m), 661 (m), 612 (w), 572 (w), 500 cmÀ1 (w); diffuse re-
flectance (BaSO4 matrix): lmax =740–640 (broad), 601, 434, 295,
265 nm. UV/Vis (c=3.095ꢃ10À5 molLÀ1, d=1 cm, CH3CN): lmax (e)=
673 (0.045ꢃ104), 597 (0.079ꢃ104), 422 (2.880ꢃ104), 281 (1.777ꢃ
104), 266 nm (1.834ꢃ104 LmolÀ1 cmÀ1). MS (ESI, CH2Cl2): m/z (%):
[(3)3][B(C6F5)4]2: Compound 3 (19 mg; 0.030 mmol) was suspended
in Et2O (2 mL). Then a solution of Fc[B(C6F5)4] (47 mg; 0.054 mmol)
in CH2Cl2 (2 mL) was added dropwise. The green-colored solution
was stirred at room temperature for a period of 10 min, and then
another 42 mg of 3 (0.065 mmol) was added in solid form. The
orange-colored solution was layered by 10 mL of petroleum ether
35/70, and the product was crystallized at a temperature of
À208C. Yield: 70 mg orange-colored crystals (0.021 mmol, 79%). El-
emental analysis for C150H198N36F40B2 (3286.99 gmolÀ1)·CH2Cl2 calcd:
C 53.79, H 5.98, N 14.95; found: C 53.29, H 6.06, N 14.96; IR (CsI):
v˜ =3450 (w), 3397 (w), 2970 (m), 2927 (w), 2871 (w), 1627 (sh),
1609 (s), 1514 (s), 1464 (s), 1371 (m), 1368 (m), 1330 (w), 1270 (m),
1171 (m), 1103 (w), 1085 (s), 980 (vs), 902 (w), 780 (w), 775 (m), 757
(m), 707 (w), 690 (w), 684 (m), 662 (m), 602 (w), 573 (w), 473 cmÀ1
(w); diffuse reflectance (BaSO4 matrix): lmax =560 (broad), 409, 388
(sh), 320, 280 nm; MS (ESI, CH2Cl2): m/z (%): 322 (100) [3H]2+, 643
(6) [3H]+, 1323 (4) {3H[B(C6F5)4]}+. Crystal data for [(3)3]
[B(C6F5)4]2·2.6CH2Cl2, C152.60H203.20B2Cl5.20F40N36, Mr =3507.87, 0.60ꢃ
322 (100) [3H]2+, 643 (11) [3]+
.
3(dca)2: Ag(dca) (63 mg; 0.36 mmol) and 3 (116 mg; 0.181 mmol)
were dissolved in CH3CN (10 mL) and stirred for a period of 20 h in
the dark. The green-colored solution was filtrated and the solvent
was removed under vacuum. The green-colored residue was
washed three times with Et2O. Yield: 101 mg (0.13 mmol, 72%).
Single crystals suitable for single-crystal X-ray analysis were ob-
0.40ꢃ0.40 mm3, triclinic, space group P1, a=15.063(3), b=
¯
17.303(4), c=18.676(4) ꢂ, a=86.05(3)8, b=76.13(3)8, g=83.71(3)8,
V=4692.7(16) ꢂ3, Z=1, 1calcd =1.241 MgmÀ3
,
MoKa radiation
(graphite monochromated, l=0.71073 ꢂ), T=100 K, qrange 2.08 to
tained from
a concentrated CH3CN solution. For purification
27.508. Reflections measured: 86597, independent: 21514, Rint
0.0829. Final R indices [I>2s(I)]: R1 =0.0784, wR2 =0.2251.
=
a CH2Cl2 solution was layered with Et2O and the resulting green-
colored needles used for the analytical measurements. C38H66N18
(775.05 gmolÀ1): calcd: C 58.89, H 8.58, N 32.53; found: C 58.13, H
8.26, N 32.49; 1H NMR (399.89 MHz, CD3CN, 295.2 K): d=6.50 (bs,
8H, NH), 5.31 (s, 2H, CH), 3.72 (m, 8H, CH), 1.17 ppm (d, 48H, J=
6.47, CH3); 13C NMR (100.56 MHz, CD3CN, 296.0 K): d=160.42,
158.32, 154.46 (CN), 123.40, 120.70, 120.35 (CN, dca), 99.50, 97.54
(Carom), 45.47 (CH), 22.69 ppm (CH3); MS (ESI, CH3CN): m/z (%): 321
General procedure for the synthesis of the other hydrogen-
bonded aggregates
Compound 3 and approximately 1.9 equiv of the ferrocenium salt
were dissolved in a mixture of Et2O (2 mL) and CH2Cl2 (2 mL). The
green-colored solution was stirred at room temperature for
a period of 10 min. Then approximately 2.2 equiv of 1 or 2 were
added. The reaction mixture was layered by 10 mL petroleum
ether 35/70, and the product was crystallized at a temperature of
À208C in the form of orange-colored crystals.
(100) [3]2+ 708 (42) [3+dca]+, 641 (13) [3ÀH]+; IR (CsI): v˜ =3348
,
(w), 3248 (w), 3161 (sh), 2977 (m), 2932 (w), 2912 (w), 2872 (w),
2845 (w), 2247 (s), 2202 (s), 2142 (vs), 1620 (sh), 1606 (vs), 1575 (s),
1523 (s), 1467 (m), 1437 (m), 1368 (w), 1344 (w), 1325 (m), 1244
(m), 1169 (m), 1074 (sh), 1068 (m), 1018 (sh), 866 (w), 802 (m), 764
(w), 716 (w), 669 (w), 504 (m), 470 cmÀ1 (m); diffuse reflectance
(BaSO4 matrix): lmax =780–740 (broad), 605, 429, 305 nm. UV/Vis
(CH3CN, c=3.59ꢃ10À5 molLÀ1, d=1 cm): lmax (e)=678 (0.037ꢃ104),
[(1)2(3)][B(ArF)4]2: Compound 3 (23 mg; 0.036 mmol), Fc[B(ArF)4]
(75 mg; 0.071 mmol), 1 (48 mg; 0.09 mmol). Yield: 50 mg product
(0.015 mmol, 42%). Elemental analysis for C150H196N36F48B2
(3436.96 gmolÀ1) calcd: C 52.42, H 5.75, N 14.67; found: C 52.22, H
5.42, N 14.69; IR (CsI): v˜ =2961 (w), 2928 (m), 2872 (w), 1608 (s),
1584 (s), 1515 (m), 1457 (w), 1381 (m), 1354 (s), 1278 (vs), 1154 (sh),
1125 (vs), 1062 (w), 1019 (w), 928 (w), 886 (w), 840 (w), 713 (m),
682 (s), 670 cmÀ1 (m); diffuse reflectance (BaSO4 matrix): lmax =565
(broad), 412, 390 (sh), 335, 275 nm; UV/Vis (CH3CN, c=3.67ꢃ
598
(0.073ꢃ104),
422
(2.856ꢃ104),
279 nm
(1.802ꢃ
104 LmolÀ1 cmÀ1). Crystal data for C38H66N18, Mr =775.09, 0.40ꢃ
0.20ꢃ0.20 mm3, monoclinic, space group C2/c, a=17.703(4), b=
21.007(4), c=15.555(3) ꢂ, b=124.39(3)8, V=4773.6(16) ꢂ3, Z=4,
1calcd =1.078 MgmÀ3, MoKa radiation (graphite monochromated, l=
0.71073 ꢂ), T=100 K, qrange 2.51 to 27.088. Reflections measured:
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
9
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
10À5 molLÀ1, d=1 cm): lmax (e)=ca. 585 (sh, 0.069ꢃ104), ca. 400
(1.257ꢃ104), 356 (sh, 3.308ꢃ104), 328 (4.385ꢃ104), 270 nm (7.603ꢃ
104 LmolÀ1 cmÀ1); MS (ESI, CH2Cl2): m/z (%): 531 (100) [1]+, 266 (45)
[1H]2+, 322 (30) [3H]2+, 641 (11) [3-H]+, 1395 (8) {1H[B(ArF)4]}+, 584
(5) [(1)(3)-4H]2+, 1505 (1) {3[B(ArF)4]}+.
were added. The red-colored reaction mixture was layered by
10 mL petroleum ether 35/70. Red colored crystals were grown at
a temperature of À208C. Yield: 16 mg, 0.024 mmol, 95%.
Alternative route: KOtBu (94 mg, 0.82 mmol) was added over
5 min in portions to a suspension of 3·4HCl (109 mg, 0.14 mmol)
in THF (15 mL) under an argon gas atmosphere. The dark solution
was stirred for an additional 5 min. Then compressed dry air was
passed via a glass tube into the solution until a clear, orange-red
colored solution was obtained. After partial removal of the solvent
(until clouding was observed) the solution was filtrated over Celite
under an argon gas atmosphere, and the residue was rinsed with
a small amount of THF. The solvent was removed from the filtrate
under vacuum, and the remaining orange-colored solid was dis-
solved in some THF. Unfortunately, it was not possible to free the
product completely from KCl. Yield: 61 mg (0.095 mmol, 68%). Ele-
mental analysis (%) for C34H64N12 (640.96 gmolÀ1)·0.75KCl calcd: C
58.62, H 9.27, N 24.14; found: C 58.38, H 9.21, N 23.92. Red crystals
were obtained from THF at À208C. 1H NMR (600.13 MHz,
[D6]acetone, 295 K): d=5.83 (bs, 1H, NH or CH), 3.80, 3.58 (m, 8H,
CH), 1.12, 1.05 ppm (br, 48H, CH3); 13C NMR (150.92 MHz, CD3CN,
295.1 K): d=45.3–44.3 (CH), 24.67 ppm (CH3); weak NMR signals
[(1)2(3)][B(C6F5)4]2: Compound 3 (35 mg; 0.055 mmol), Fc[B(C6F5)4]
(86 mg; 0.099 mmol), 1 (64 mg; 0.12 mmol). Yield: 133 mg crystal-
line product (0.043 mmol, 88%). Elemental analysis for
C134H166N36F40B2 (3062.57 gmolÀ1) calcd: C 52.55, H 5.46, N 16.47;
found: C 53.35, H 5.62, N 16.05; IR (CsI): v˜ =2953 (w), 2922 (m),
2864 (w), 2788 (w), 1632 (sh), 1594 (m), 1570 (m), 1510 (s), 1460 (s),
1422 (m), 1393 (w), 1381 (m), 1331 (w), 1273 (m), 1237 (w), 1174
(w),1156 (s), 1137 (s), 1085 (s), 1063 (w), 1017 (m), 980 (vs), 923 (w),
878 (m), 795 (w), 757 (s), 726 (w), 684 (s), 662 (s), 610 (w), 572 (w),
500 cmÀ1 (w); diffuse reflectance (BaSO4 matrix): lmax =569 (broad),
413, 390 (sh), 335, 275 nm; MS (ESI, CH2Cl2): m/z (%): 266 (100)
[1H]2+ 531 (87) [1]+, 1211 (9) {1H[[B(C6F5)4]}+, 321 (4) [3]2+, 641 (1)
,
[3-H]+, 1060 (1) [(1-H)2]+. Crystal data for [(1)2(3)]
[B(C6F5)4]2·1.7CH2Cl2, C135.70H169.40B2Cl3.40F40N36, Mr =3207.02, 0.40ꢃ
0.30ꢃ0.30 mm3, triclinic, space group P1, a=16.946(3), b=
¯
17.141(3), c=18.680(4) ꢂ, a=78.76(3)8, b=66.92(3)8, g=60.71(3)8,
due to a low solubility; MS (ESI, CH3OH): m/z (%): 321 (100) [5H]2+
,
V=4353.4(15) ꢂ3, Z=1, 1calcd =1.223 MgmÀ3
,
MoKa radiation
641 (17) [5]+. IR (CsI): v˜ =3431 (w), 3280 (w), 2970 (m), 2931 (w),
2872 (w), 1628 (s), 1595 (s), 1522 (s), 1489 (sh), 1465 (sh), 1385 (w),
1364 (w), 1324 (w), 1240 (m), 1194 (w), 1168 (w), 1127 (w), 1062
(w), 1043 (w), 855 (w), 839 (w), 797 (w), 730 cmÀ1 (w); diffuse reflec-
tance (BaSO4 matrix): lmax =530, 416, 390, 280 nm; UV/Vis (CH3CN,
c=5.37ꢃ10À5 molLÀ1, d=1 cm): lmax (e)=500 (0.125ꢃ104), 420
(0.608ꢃ104), 358 (1.309ꢃ104), 332 (1.376ꢃ104), 253 nm (1.584ꢃ
104 LmolÀ1 cmÀ1). Crystal data for 5·4CH2Cl2, C38H72Cl8N12, Mr =
980.68, 0.40ꢃ0.30ꢃ0.25 mm3, monoclinic, space group P21/n, a=
14.375(3), b=11.336(2), c=16.775(3) ꢂ, b=110.64(3)8, V=
2558.2(9) ꢂ3, Z=2, 1calcd =1.273 MgmÀ3, MoKa radiation (graphite
monochromated, l=0.71073 ꢂ), T=100 K, qrange 2.22 to 27.508. Re-
flections measured: 11669, independent: 5874, Rint =0.0465. Final R
indices [I>2s(I)]: R1 =0.0611, wR2 =0.1508.
(graphite monochromated, l=0.71073 ꢂ), T=100 K, qrange 2.19 to
27.508. Reflections measured: 83975, independent: 19949, Rint
0.0842. Final R indices [I>2s(I)]: R1 =0.0653, wR2 =0.1559.
=
[(2)2(3)][B(ArF)4]2: Compound 3 (23 mg; 0.036 mmol), Fc[B(ArF)4]
(75 mg; 0.071 mmol), 2 (47 mg; 0.09 mmol). Yield: 80 mg crystalline
product (0.023 mmol, 66%). Elemental analysis for C150H180N36F48B2
(3420.84 gmolÀ1) calcd: C 52.67, H 5.30, N 14.74; found: C 52.84, H
5.35, N 16.29; IR (CsI): v˜ =2950 (m), 2914 (m), 2913 (m), 2856 (sh),
2848 (m), 1631 (s), 1624 (s), 1577 (sh), 1513 (m), 1464 (m), 1451 m),
1449 (m), 1391 (w), 1365 (w), 1355 (s), 1277 (vs), 1154 (sh) 1124
(vs), 1035 (m), 971 (w), 884 (m), 885 (m), 840 (m), 799 (m), 744 (w),
711 (m), 682 (s), 669 (m), 634 (w), 500 cmÀ1 (w); diffuse reflectance
(BaSO4 matrix): lmax =575 (broad), 419, 398 (sh), 338, 270 nm; MS
(ESI, CH2Cl2): m/z (%): 523 (100) [2]+, 322 (53)[3H]2+, 643 (12) [3]+,
1045 (2) [(2)2]+, 1164 (<1) [(2)(3)-H]+, 1388 (<1) {2H2[B(ArF)4]}+,
1507 (<1) {3H[B(ArF)4]}+.
Reversibility tests
[(2)2(3)][B(C6F5)4]2: Compound 3 (20 mg; 0.031 mmol), Fc[B(C6F5)4]
(49 mg; 0.057 mmol), 2 (37 mg; 0.071 mmol). The crystals were
washed several times with Et2O to remove impurities. Yield: 30 mg
crystalline product (0.0098 mmol, 35%). Elemental analysis for
C134H150N36F40B2 (3046.44 gmolÀ1) calcd: C 52.83, H 4.96, N 16.55;
found: C 52.84, H 5.35, N 16.29; IR (CsI): v˜ =2980 (w), 2941 (w),
2965 (w), 1669 (sh), 1646 (s), 1617 (sh), 1517 (s), 1462 (s), 1401 (m),
1394 (m), 1369 (w), 1336 (w), 1289 (m), 1279 (m), 1246 (w), 1198
(w), 1160 (w), 1093 (s), 1039 (s), 982 (vs), 938 (w), 898 (w), 802 (w),
775 (s), 756 (s), 729 (w), 684 (s), 661 (s), 638 (w), 611 (w), 578 (w),
502 cmÀ1 (w); diffuse reflectance (BaSO4 matrix): lmax =566 (broad),
411, 389 (sh), 330, 259 nm; MS (ESI, CH2Cl2): m/z (%): 523 (100) [2]+,
262 (62) [2H]2+, 322 (11) [3H]2+, 584 (4) [(2)(3)H2]2+, 641 (1) [3-H]+,
1201 (1) {2[B(C6F5)4]}+, 1045 (<1) [(2)2]+, 1324 (<1) {3H2[B(C6F5)4]}+.
Crystal data for C134H150B2F40N36, Mr =3046.52, 0.35ꢃ0.30ꢃ
0.25 mm3, monoclinic, space group P21/c, a=16.415(3), b=
A) [(3)3][B(C6F5)4]2·CH2Cl2 (15 mg; 0.0044 mmol) was dissolved in an
NMR tube in [D8]THF (0.4 mL). Then 0.1 mL of a solution of CoCp2
(0.009 mmol; 17 mg CoCp2 in 1 mL [D8]THF) was added dropwise.
The color change and NMR spectrum indicated the reduction to 3.
B) In an NMR tube, [(3)3][B(C6F5)4]2·CH2Cl2 (15 mg; 0.0044 mmol)
and Fc[B(C6F5)4] (14 mg; 0.016 mmol) were dissolved in [D8]THF
(0.5 mL). The color change and NMR spectrum indicated oxidation
to 3[B(C6F5)4]2.
X-ray crystallographic study
Suitable crystals were taken directly out of the mother liquor, im-
mersed in perfluorinated polyether oil and fixed on top of a glass
capillary. Measurements were made with a Nonius-Kappa CCD dif-
fractometer with low-temperature unit using graphite-monochro-
mated MoKa radiation. The temperature was set to 100 K. The data
collected were processed using the standard Nonius software.[37]
All calculations were performed using the SHELXT-PLUS software
package. Structures were solved by direct methods with the
SHELXS-97 program and refined with the SHELXL-97 program.[38,39]
Graphical handing of the structural data during solution and refine-
ment was performed with XPMA.[40] Atomic coordinates and aniso-
tropic thermal parameters of nonhydrogen atoms were refined by
full-matrix least-squares calculations. Hydrogen atoms were placed
at calculated positions and refined with a riding model. In the case
18.911(4), c=24.238(5) ꢂ, b=90.48(3)8, V=7524(3) ꢂ3, Z=2, 1calcd
1.345 MgmÀ3
MoKa radiation (graphite monochromated, l=
=
,
0.71073 ꢂ), T=100 K, qrange 2.00 to 27.438. Reflections measured:
61666, independent: 17154, Rint =0.0753. Final R indices [I>2s(I)]:
R1 =0.0634, wR2 =0.1480.
Compound 5: Compound 3 (20 mg; 0.031 mmol) and Fc[B(ArF)4]
(57 mg; 0.054 mmol) were dissolved in a mixture of Et2O (2 mL)
and CH2Cl2 (2 mL). The green-colored solution was stirred at room
temperature for a period of 20 min. Then 38 mg of 4 (0.066 mmol)
&
&
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
10
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
[14] a) B. A. Blight, C. A. Hunter, D. A. Leigh, H. McNab, P. T. Thomson, Nat.
Chem. 2011, 3, 244–248; b) D. A. Leigh, C. Robertson, A. M. Z. Slawin,
P. I. T. Thomson, J. Am. Chem. Soc. 2013, 135, 9939–9943.
[15] a) S. H. M. Sçntjens, R. P. Sijbesma, M. H. P. van Genderen, E. W. Meijer, J.
Am. Chem. Soc. 2000, 122, 7487–7493; b) T. Park, E. M. Todd, S. Nakashi-
ma, S. C. Zimmerman, J. Am. Chem. Soc. 2005, 127, 18133–18142;
c) H. C. Ong, S. C. Zimmerman, Org. Lett. 2006, 8, 1589–1592.
[16] K. Morokuma, Acc. Chem. Res. 1977, 10, 294–300.
[17] C. Bourgel, A. S. F. Boyd, G. Cooke, H. Augier de Cremiers, F. M. A. Du-
clairoir, V. M. Rotello, Chem. Commun. 2001, 1954–1955.
[18] J. Bu, N. D. Lilienthal, J. E. Woods, C. E. Nohrden, K. T. Hoang, D. Truong,
D. K. Smith, J. Am. Chem. Soc. 2005, 127, 6423–6429.
of 3, full shells of intensity data were collected at low temperature
(110 K) with an Agilent Technologies Supernova-E CCD diffractome-
ter (CuKa radiation, l=1.5418 ꢂ, microfocus tube, multilayer mirror
optics). Data were corrected for air and detector absorption, Lor-
entz and polarization effects;[41] absorption by the crystal was treat-
ed with a semiempirical multiscan method.[42] The crystal was
found to be a two-component twin (twin fractions 0.54:0.46). After
de-twinning, the structure was solved by the charge-flip proce-
dure.[43] Refinement was carried out against all observations involv-
ing singles and composites of both twin domains by full-matrix
least-squares methods based on F2 against all unique reflections.[44]
All nonhydrogen atoms were given anisotropic displacement pa-
rameters. Hydrogen atoms were generally input at calculated posi-
tions and refined with a riding model. Hydrogen atoms on N were
refined with all NÀH bonds restrained equal with an esd of 0.02 ꢂ.
CCDC 913085 (3), 974356 ([(3)(thf)2(dioxane)][B(C6F5)4]2), 972541
([3(Et2O)4][B(ArF)4]2), 913084 (5), 940651 (3(dca)2), 972542 ([(3)3]
[B(C6F5)4]2·2.6CH2Cl2), 972543 ([(1)2(3)][B(C6F5)4]2·1.7CH2Cl2), 972544
[(2)2(3)][B(C6F5)4]2), and 913086 (5·4CH2Cl2) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
[19] G. Cooke, Y.-M. Legrand, V. M. Rotello, Chem. Commun. 2004, 1088–
1089.
[20] A. Altieri, F. G. Gatti, E. R. Kay, D. A. Leigh, D. Martel, F. Paolucci, A. M. Z.
Slawin, J. K. Y. Wong, J. Am. Chem. Soc. 2003, 125, 8644–8654.
[21] M. R. Panman, B. H. Bakker, D. den Uyl, E. R. Kay, D. A. Leigh, W. J. Buma,
A. M. Brouwer, J. A. J. Greenevasen, S. Woutersen, Nat. Chem. 2013, 5,
929–934.
[22] a) F. T. Edelmann, Coord. Chem. Rev. 1994, 137, 403–481; b) J. Barker, M.
Kilner, Coord. Chem. Rev. 1994, 133, 219–300; c) P. J. Bailey, S. Price,
Coord. Chem. Rev. 2001, 214, 91–141; d) H. E. Abdou, A. A. Mohamed,
J. P. Fackler, Inorg. Chem. 2005, 44, 166–168; e) M. P. Coles, Dalton
Trans. 2006, 985–1001; f) F. T. Edelmann, Adv. Organomet. Chem. 2008,
57, 183–352; g) A. A. Mohamed, H. E. Abdou, A. Mayer, J. P. Fackler, Jr.,
J. Cluster Sci. 2008, 19, 551–559; h) M. P. Coles, Chem. Commun. 2009,
3659–3676; i) S. Herres-Pawlis, Nachr. Chem. 2009, 57, 20–23; j) C.
Jones, Coord. Chem. Rev. 2010, 254, 1273–1289; k) H.-J. Himmel, in
Modeling of Molecular Properties (Ed.: P. Comba), Wiley-VCH, Weinheim,
2011.
Details of the quantum chemical calculations
The density functional calculations used the B3LYP functional[45] in
combination with the 6-311G** basis set.[46] The calculations were
performed with the program Gaussian09.[47]
´
ˇ
´
[23] a) Z. B. Maksic, B. Kovacevic, J. Org. Chem. 2000, 65, 3303–3309; b) V.
Raab, J. Kipke, R. M. Gschwind, J. Sundermeyer, Chem. Eur. J. 2002, 8,
ˇ
´
´
1682–1693; c) B. Kovacevic, Z. B. Maksic, Chem. Eur. J. 2002, 8, 1694–
ˇ
´
´
1702; d) V. Raab, K. Harms, J. Sundermeyer, B. Kovacevic, Z. B. Maksic, J.
Org. Chem. 2003, 68, 8790–8797; e) A. Singh, B. Ganguly, New J. Chem.
2008, 32, 210–213; f) U. Wild, O. Hꢄbner, A. Maronna, M. Enders, E.
Kaifer, H. Wadepohl, H.-J. Himmel, Eur. J. Inorg. Chem. 2008, 4440–4447;
g) M. P. Coles, P. J. Aragꢅn-Sꢆez, S. H. Oakley, P. B. Hitchcock, M. G. David-
Acknowledgements
The authors gratefully acknowledge financial support from the
Deutsche Forschungsgemeinschaft (DFG). We thank Prof. Dr. R.
Altherr (Institut fꢄr Geowissenschaften, Universitꢀt Heidelberg)
and T. Ludwig for help with the crystal photographs.
´
son, Z. B. Maksic, R. Vianello, I. Leito, I. Kaljurand, D. C. Apperley, J. Am.
Chem. Soc. 2009, 131, 16858–16868; h) T. Ishikawa, Superbases for Or-
ganic Synthesis, Wiley, 2009; i) A. Maronna, O. Hꢄbner, M. Enders, E.
Kaifer, H.-J. Himmel, Chem. Eur. J. 2013, 19, 8958–8977.
[24] a) D. Petrovic, T. Bannenberg, S. Randoll, P. G. Jones, M. Tamm, Dalton
Trans. 2007, 2812–2822; b) D. Petrovic, L. M. R. Hill, P. G. Jones, W. B.
Tolman, M. Tamm, Dalton Trans. 2008, 887–894; c) J. Bçrner, U. Flçrke,
K. Huber, A. Dçring, D. Kuckling, S. Herres-Pawlis, Chem. Eur. J. 2009, 15,
2362–2376; d) P. Roquette, A. Maronna, A. Peters, E. Kaifer, H.-J.
Himmel, C. Hauf, V. Herz, E.-W. Scheidt, W. Scherer, Chem. Eur. J. 2010,
16, 1336–1350; e) J. Bçrner, I. dos Santos Vieira, A. Pawlis, A. Doering,
D. Kuckling, S. Herres-Pawlis, Chem. Eur. J. 2011, 17, 4507–4512; f) J.
Bçrner, I. dos Santos Vieira, M. D. Jones, A. Dçring, D. Kuckling, U.
Flçrke, S. Herres-Pawlis, Eur. J. Inorg. Chem. 2011, 4441–4456; g) B. M.
Day, N. E. Mansfield, M. P. Coles, P. B. Hitchcock, Chem. Commun. 2011,
47, 4995–4997; h) I. dos Santos Vieira, S. Herres-Pawlis, Eur. J. Inorg.
Chem. 2012, 765–774.
[25] a) C. Wꢄrtele, E. Gaoutchenova, K. Harms, M. C. Holthausen, J. Sunder-
meyer, S. Schindler, Angew. Chem. 2006, 118, 3951–3954; Angew. Chem.
Int. Ed. 2006, 45, 3867–3869; b) D. Maiti, D.-H. Lee, K. Gaoutchenova, C.
Wꢄrtele, M. C. Hothausen, A. A. N. Sarjeant, J. Sundermeyer, S. Schindler,
K. D. Karlin, Angew. Chem. 2008, 120, 88–91; Angew. Chem. Int. Ed.
2008, 47, 82–85; c) M. P. Lanci, V. V. Smirnov, C. J. Cramer, E. V. Gauche-
nova, J. Sundermeyer, J. P. Roth, J. Am. Chem. Soc. 2007, 129, 14697–
14709; d) R. L. Peterson, J. W. Ginsbach, R. E. Cowley, M. F. Qayyum, R. A.
Himes, M. A. Siegler, C. D. Moore, B. Hedman, K. O. Hodgson, S. Fukuzu-
mi, E. I. Solomon, K. D. Karlin, J. Am. Chem. Soc. 2013, 135, 16454–
16467.
Keywords: aggregation
oxidation · self-assembly
· guanidine · hydrogen bonds ·
[1] a) T. S. Moore, T. F. Windmill, J. Chem. Soc. 1912, 101, 1635–1676; b) L.
Pauling, The Chemical Bond: A Brief Introduction to Modern Structural
Chemistry, Cornell University Press, Ithaca, 1967.
[2] M. Meot-Ner (Mautner), Chem. Rev. 2005, 105, 213–284; see also M.
Meot-Ner (Mautner), Chem. Rev. 2012, 112, PR22–PR103.
[3] M. Olschewski, S. Knop, J. Lindner, P. Vçhringer, Angew. Chem. 2013,
125, 9814–9836; Angew. Chem. Int. Ed. 2013, 52, 9634–9654.
[4] a) E. D. Głowacki, M. Irimia-Vladu, S. Bauer, N. S. Sariciftci, J. Mater. Chem.
B 2013, 1, 3742–3753; b) K. Liu, Y. Kang, Z. Wang, X. Zhang, Adv. Mater.
2013, 25, 5530–5548.
[5] A. J. Wilson, Nat. Chem. 2011, 3, 193–194.
[6] W. Xu, X.-C. Li, H. Tan, G.-J. Chen, Phys. Chem. Chem. Phys. 2006, 8,
4427–4433.
[7] W. L. Jorgensen, J. Pranata, J. Am. Chem. Soc. 1990, 112, 2008–2010.
[8] S.-K. Chang, D. Van Engen, E. Fan, A. D. Hamilton, J. Am. Chem. Soc.
1991, 113, 7640–7645.
[9] G. Cooke, V. M. Rotello, Chem. Soc. Rev. 2002, 31, 275–286.
[10] X. Zhang, Q. Zeng, C. Wang, RSC Adv. 2013, 3, 11351–11366.
[11] A. J. Wilson, Soft Matter 2007, 3, 409–425.
[12] J. T. Davis, Angew. Chem. 2004, 116, 684–716; Angew. Chem. Int. Ed.
2004, 43, 668–698.
[13] T. Giogi, F. Grepioni, I. Manet, P. Mariani, S. Masiero, E. Mezzina, S. Pierac-
cini, L. Saturni, G. P. Spada, G. Gottarelli, Chem. Eur. J. 2002, 8, 2143–
2152.
[26] A. Peters, E. Kaifer, H.-J. Himmel, Eur. J. Org. Chem. 2008, 5907–5914.
[27] A. Peters, C. Trumm, M. Reinmuth, D. Emeljanenko, E. Kaifer, H.-J.
Himmel, Eur. J. Inorg. Chem. 2009, 3791–3800.
[28] D. Emeljanenko, A. Peters, V. Vitske, E. Kaifer, H.-J. Himmel, Eur. J. Inorg.
Chem. 2010, 4783–4789.
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
11
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
[29] H.-J. Himmel, Z. Anorg. Allg. Chem. 2013, 639, 1940–1952.
[30] A. Peters, E. Kaifer, H.-J. Himmel, Eur. J. Inorg. Chem. 2012, 1620–1631.
[31] See also the detailed analysis for the related compound 1,2,4,5-tetrakis-
(dimethylamino)benzene in: C. J. Adams, R. C. da Costa, R. Edge, D. H.
Evans, M. F. Hood, J. Org. Chem. 2010, 75, 1168–1178.
[32] B. Eberle, H. Herrmann, E. Kaifer, H.-J. Himmel, Eur. J. Inorg. Chem. 2013,
3671–3679.
[43] a) L. Palatinus, SUPERFLIP, EPF Lausanne, Switzerland, 2007; b) L. Palati-
nus, G. Chapuis, J. Appl. Crystallogr. 2007, 40, 786–790.
[44] a) G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112–122; b) G. M.
Sheldrick, SHELXL-2012, University of Gçttingen, Germany, 2012.
[45] a) P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys.
Chem. 1994, 98, 11623–11627; b) A. D. Becke, J. Chem. Phys. 1993, 98,
5648–5652; c) A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100; d) C. Lee,
W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
[46] a) K. Raghavachari, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem. Phys.
1980, 72, 650–654; b) A. D. McLean, G. S. Chandler, J. Chem. Phys. 1980,
72, 5639–5648.
[33] V. Vitske, C. Kçnig, E. Kaifer, O. Hꢄbner, H.-J. Himmel, Eur. J. Inorg. Chem.
2010, 115–126.
[34] V. Vitske, H. Herrmann, M. Enders, E. Kaifer, H.-J. Himmel, Chem. Eur. J.
2012, 18, 14108–14116.
[47] Gaussian 09 (RevisionA.02), M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Men-
nucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Ko-
bayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyen-
gar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg,
S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cio-
slowski, D. J. Fox, Gaussian, Inc., Wallingford, CT, 2009.
[35] I. Chꢆvez, A. Alvarez-Carena, E. Molins, A. Rooig, W. Maniukiewicz, A.
Arancibia, V. Arancibia, H. Brand, J. M. Manrꢇquez, J. Organomet. Chem.
2000, 601, 126–132.
[36] C. Gerdes, Dissertation, Carl von Ossietzky Universitꢀt Oldenburg, 2012.
[37] DENZO-SMN, Data processing software, Nonius, 1998, http://www.
nonius.com.
[38] a) G. M. Sheldrick, SHELXS-97, Program for Crystal Structure Solution, Uni-
versity of Gçttingen, Germany, 1997, http://shelx.uni-ac.gwdg.de/
SHELX/index.html; b) G. M. Sheldrick, SHELXL-97, Program for Crystal
Structure Refinement, http://shelx.uni-ac.gwdg.de/SHELX/index.html.
[39] International Tables for X-ray Crystallography, Vol. 4, Kynoch, Birming-
ham, 1974.
[40] L. Zsolnai, G. Huttner, XPMA, University of Heidelberg, Germany, 1994;
http://www.uni-heidelberg.de/institute/fak12/AC/huttner/soft-ware/
software.html.
[41] CrysAlisPro, Agilent Technologies UK Ltd., Oxford 2011.
[42] a) R. H. Blessing, Acta Crystallogr. Sect. A 1995, 51, 33–38; b) SCALE3 AB-
SPACK, CrysAlisPro, Agilent Technologies UK Ltd., Oxford, 2011.
Received: December 13, 2013
Revised: February 24, 2014
Published online on && &&, 0000
&
&
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
12
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Hydrogen-bond sandwich, anyone?
After oxidation of guanidinyl-functional-
ized aromatic compounds, the super-
base is turned into a strong hydrogen-
bond donor and forms hydrogen-
bonded aggregates, which could be de-
scribed as frozen stages on the way to
hydrogen transfer (see figure).
&
Hydrogen Bonds
U. Wild, C. Neuhꢀuser, S. Wiesner,
E. Kaifer, H. Wadepohl, H.-J. Himmel*
&& – &&
Redox-Controlled Hydrogen Bonding:
Turning a Superbase into a Strong
Hydrogen-Bond Donor
Redox-Controlled Hydrogen Bonding
Hydrogen bonding can be greatly enhanced by oxidation of
the hydrogen-bond donor component or reduction of the
hydrogen-bond acceptor component, a strategy which
could be applied for the design of “redox-controlled
switches”. In their Full Paper on page && ff. H.-J. Himmel
et al. present the synthesis of a new redox-active
guanidinyl-functionalized aromatic compound (GFA). Its
oxidation turns the highly Brønsted basic molecule into
a strong hydrogen-bond donor. Orange-colored aggregates
are formed by reaction of the green-colored oxidized GFA
with neutral GFAs. Reduction initiates deaggregation. A
further increase of the basicity of the hydrogen-bond
acceptor leads to deprotonation.
Chem. Eur. J. 2014, 20, 1 – 13
www.chemeurj.org
13
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ