Tetraaryl tetradecahydroporphyrazins: Novel porphyrin derivatives featuring a cyclic benzene-ring tetramer

Article abstract of DOI:10.1002/chem.200901187

Treatment of tetramethylsuccinonitrile 1 with aryl lithium compounds and subsequent quenching with chlorotrimethylsilane yields 5-aryl3,3,4,4- tetramethyl-N-(trimethylsilyl)3,4-dihydropyrrol-2-imines 2a-c in 4971 % yield. Attempts to crystallise 2a-c in t

Full text of DOI:10.1002/chem.200901187

FULL PAPER
DOI: 10.1002/chem.200901187
Tetraaryl Tetradecahydroporphyrazins: Novel Porphyrin Derivatives
Featuring a Cyclic Benzene-Ring Tetramer
Simon Janich,[a] Roland Frçhlich,[a] Atsushi Wakamiya,[b] Shigehiro Yamaguchi,[b] and
Ernst-Ulrich Wꢀrthwein*[a]
Abstract: Treatment of tetramethylsuc-
cinonitrile 1 with aryl lithium com-
pounds and subsequent quenching with
chlorotrimethylsilane yields 5-aryl-
3,3,4,4-tetramethyl-N-(trimethylsilyl)-
3,4-dihydropyrrol-2-imines 2a–c in 49–
71% yield. Attempts to crystallise 2a–c
in the presence of wet air yielded the
tetraaryl tetradecahydroporphyrazins
3a–c in yields of 4–84% as single dia-
stereomers. X-ray diffraction studies of
3b and c showed that only the isomer
with four aryl substituents pointing in
the same direction was formed. The re-
sulting four-bladed pinwheel-like struc-
tures were characterised by four intra-
molecular aromatic interactions, in
which each phenyl ring points with its
edge towards the centre of a neigh-
bouring phenyl moiety, resembling the
arrangement of benzene molecules in
T-shaped dimers. Temperature-depen-
dent NMR spectra give insight into the
dynamic properties of the aryl substitu-
ents. Quantum chemical calculations
that included dispersion corrections in-
dicated the importance of aryl–aryl in-
teractions for the diastereoselectivity
of the reaction and for the structural
properties of the single isomers ob-
served.
Keywords: aromaticity
·
density
functional calculations · imines ·
porphyrins · tetramerisation
Introduction
and materials science. This relatively weak form of interac-
tion has a significant influence on the three-dimensional
structure of both small molecules and macromolecules of
biological and non-biological origin, and of supramolecular
systems. Furthermore, they affect the packing structure in
crystals of aromatic compounds.[5a] As a result, they have
been the focus of a multitude of theoretical[5] and experi-
mental[6] studies. Although examples of two interacting aro-
matic groups in larger systems are experimentally abun-
Hydroporphyrins, partly saturated derivatives of the macro-
cyclic tetrapyrrol derived porphins, are interesting for a vari-
ety of technical and analytical applications. They are confor-
mationally more flexible than their aromatic counterparts,
which affects not only their electronic properties but also
their ability to form coordination compounds with metals
and other guest ions.[1] This makes them applicable for
anion binding and recognition, for example.[2] However, the
synthesis of hydroporphyrin derivatives is usually not trivial,
comprising either the (often not very selective) modification
of porphyrins by reduction,[3] addition of substituents,[1a] or
by a multistep total syntheses.[4]
AHCTUNGTRENNUNG
dant,[6a–b,7] data on higher clusters consisting of more such
moieties are far more rare. Only recently, one of those rare
results was published by H. Furuta and co-workers. They re-
ported a supramolecular system, the formation of which was
modulated by the interaction of three phenyl substituents.[8]
Examples of structures with four mutually interacting aryl
groups are, to the best of our knowledge, unknown to date.
Herein, we report a new facile synthesis for hydropor-
phyrin derivatives of an unprecedented degree of saturation
and substitution, containing, in addition, a four-bladed pin-
wheel-shaped arrangement[9] of interacting phenyl moieties
as one of their most striking structural features.
Inter- and intramolecular non-bonding aromatic interac-
tions play an important role in various fields of chemistry
[a] Dr. S. Janich, Dr. R. Frçhlich, Prof. Dr. E.-U. Wꢀrthwein
Westfꢁlische Wilhelms-Universitꢁt
Corrensstrasse 40, 48149 Mꢀnster (Germany)
Fax : (+49)251-83-39772
E-mail: wurthwe@uni-muenster.de
[b] Dr. A. Wakamiya, Prof. Dr. S. Yamaguchi
Department of Chemistry, Graduate School of Science
Nagoya University, Nagoya 464-8602 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200901187.
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Results and Discussion
10 wt%. From NMR spectroscopy and mass spectrometry, it
appears that these by-products are also oligo- or even poly-
mers of the dihydropyrrol-2-imine, but their exact composi-
tion and structure could not be elucidated.
Part of our ongoing research on oligonitriles[10] was the syn-
thesis of 5-aryl-3,3,4,4-tetramethyl-N-(trimethylsilyl)-3,4-di-
hydropyrrol-2-imines 2[11] by treating an aryl lithium species
with tetramethylsuccinonitrile (1) and subsequently quench-
ing the reaction with chlorotrimethylsilane (Scheme 1).
It was possible to afford suitable crystals for X-ray crys-
tal-structure analysis from compounds 3b and c.[12] Both
compounds have many principal structural characteristics in
common. The most striking feature is the arrangement of
the four aryl substituents that are all pointing in the same
direction from the central heterocyclic system, regardless of
the partly significant structural bulk. Furthermore, the
phenyl groups proximal to the tetradecahydroporphyrazin
ring itself form a four-bladed pinwheel-like structure, in
which each phenyl ring points with its edge towards the
centre of a neighbouring phenyl moiety (Figure 1b). This
bears resemblance to the arrangement of benzene molecules
in T-shaped dimers. The observation of such an arrangement
of four benzene units has never been reported, and is dis-
tinctly different from the packing structure in crystalline
benzene II at high pressure.[13]
Scheme 1. Synthesis of 5-aryl-3,3,4,4-tetramethyl-N-(trimethylsilyl)-3,4-di-
hydropyrrol-2-imines 2.
The crystal structure of tetradecahydroporphyrazin 3b
contains two independent molecules A and B in the asym-
metric unit, each showing opposite stereodescriptors (Fig-
ure 1a). The centre to centre distances of the proximal
phenyl groups (inner phenyl groups of the biphenyl substitu-
ent) vary from 4.885 to 5.368 ꢃ, averaging at 5.122 ꢃ. The
planes of those phenyl groups are almost perpendicular to
each other, with angles averaging at 85.238 (Figure 1b). The
distal phenyl moieties (outer phenyl groups of the biphenyl
substituent) on the other hand are much farther apart, with
distances ranging from 6.0 to 7.2 ꢃ (Figure 1c). Taking the
apparently irregular arrangement of the planes of those
rings relative to each other additionally into account, it ap-
pears that no substantial direct interaction between these
distal phenyl groups exists.
The resulting compounds were solids in most cases, de-
pending on the aryl substituent, but not always crystalline.
The question arose of whether it is possible to obtain suita-
ble crystals for an X-ray analysis. To achieve this, a sample
of compound 2c was dissolved in dichloromethane. The so-
lution was subsequently slowly concentrated by gradual
evaporation of the solvent, and after a few days, cubic, col-
ourless crystals were acquired. However, these crystals un-
expectedly consisted of tetraaryl tetradecahydroporphyrazin
3c as a result of a tetramerisation of the starting material,
clearly after hydrolytic cleavage of the trimethylsilyl moiety
(Scheme 2). We could confirm that this method is reproduci-
A dichloromethane molecule is enclosed in a cavity
formed by the distal substituents. In the case of host mole-
cule A, it is significantly shifted away from the central axis
and is almost situated between two of the phenyl moieties
(Figure 1d and e).
The crystal structure of 3c is highly symmetric, so that the
proximal phenyl groups form a perfect square with distances
of 5.03 ꢃ measured from ring centre to ring centre and
angles of 88.68 between the planes of the rings (Figure 2b).
The distances between the diphenylamino nitrogen atoms
are 5.99 ꢃ (Figure 2c), signifying that the large pendant
groups at the tetradecahydroporphyrazins are slanted out-
wards relative to the central molecule axis, giving the mole-
cule are slightly tapered appearance. Of the two phenyl
rings of the diphenylamine subunit, the phenyl rings I (Fig-
ure 2c) are again arranged in a pinwheel-like fashion. With
distances of 5.90 ꢃ, they are much farther apart than the
proximal phenyl groups. The planes of the phenyl rings I
form an angle of 87.68. The phenyl rings I and II of neigh-
bouring diphenylamino groups are in close vicinity to each
other with distances of 4.98 ꢃ in a similar interaction range
as the proximal phenyl groups. The angle between the ring
Scheme 2. Synthesis of tetraaryl tetradecahydroporphyrazins 3.
ble and applicable to other derivatives, so that we were able
to obtain also compounds 3a and b, which differ in the size
and nature of the aryl substituents.
In all three cases, only a single isomer has been isolated
in racemic form and unambiguously identified. For deriva-
tive 3c, an attempt was made to isolate other substances
from the oily residue of the synthesis. Apart from un-
changed starting material, several other compounds were
found, although only in very small amounts of less than
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Benzene Tetramers
FULL PAPER
planes is 58.38, which is much more acute than
the angle between the proximal phenyl groups.
The distal substituents again form a cavity
that is big enough to incorporate a dichloro-
methane molecule in the crystal structure,
which is disordered with regard to its orienta-
tion relative to the symmetry axis (Figure 3).
The NMR spectra of all three tetradecahy-
droporphyrazins 3 share most characteristics,
so it can be concluded that compound 3a, of
which no X-ray structure was obtained, has
comparable structural features. Especially the
proton NMR spectra show that the tetradeca-
hydroporphyrazins assume
a C2 symmetric
structure in solution, since eight equally sized
singlets for a total of sixteen methyl groups
can be found. Two signals corresponding to
two amino protons are visible, one at approxi-
mately 5.3 ppm, the other one at roughly
7.6 ppm. This signifies that of the four NH pro-
tons, two are bound to the dihydropyrrol nitro-
gen atoms, whereas the other two are situated
at the porphyrin meso nitrogen atoms.
The interactions between the proximal
phenyl moieties are also evident in the proton
NMR spectra, because the protons in the 2-po-
sition, which are pointing towards the neigh-
bouring phenyl ring, are experiencing addition-
al shielding by the aromatic ring current of
these groups. In all three cases, one multiplet
stands out that can be assigned to these ortho
protons. Variable-temperature NMR experi-
ments (see below) reveal that this signal ac-
tually consists of two signals with equal inten-
sity but somewhat different chemical shifts,
each corresponding to two protons. Thus, we
conclude that the proximal phenyl moieties in
tetradecahydroporphyrazins are not equally far
apart, but that two slightly differently distant
types of pairs exist, so that the proximal
phenyl groups do not form a perfect square
but a parallelogram-like shape.
On heating, the two signals exhibit a slightly
different dynamic behaviour (Figure 4).
Whereas the more low-field-shifted signal
broadens from 298 K onwards, the high-field
Figure 1. X-ray crystal structure of 3b of both independ-
ent molecules A and B. a) Central tetradecahydropor-
phyrazin ring, b) centre-to-centre distances and angles
between the planes of the proximal phenyl groups of the
biphenyl substituents, c) centre-to-centre distances be-
tween the distal phenyl moieties of the biphenyl substitu-
ents. (ORTEP plots with thermal ellipsoids at 50% prob-
ability level, hydrogen atoms omitted for clarity), d) in-
clusion of dichloromethane in the cavity formed by the
distal substituents, e) cavity with the CH2Cl2 molecule
omitted.
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E.-U. Wꢀrthwein et al.
Figure 3. a) Inclusion of a four-fold disordered dichloromethane molecule
in a cavity formed by the distal substituents of 3c. b) Cavity with the
CH2Cl2 molecule omitted.
Figure 4. Temperature-dependent behaviour of the 1H NMR signals of
the ortho protons of the proximal phenyl groups in 3b.
by steric hindrance. We quantified the kinetics of these dy-
namic processes by line-shape analysis for tetradecahydro-
porphyrazin 3b in which the signals in question are best visi-
ble and resolved, and could thus determine the activation
energy required breaking the pairs of phenyl groups. Corre-
sponding to the observed differing behaviour, two different
energy values were found, namely, DH1 =14.0 kcalmolÀ1 for
the low-field signal and DH2 =15.3 kcalmolÀ1 for the high-
field signal. This means that the pairs of phenyl rings with a
shorter distance require about 1.3 kcalmolÀ1 more than the
pairs with a longer distance to surmount the interaction and
become mobile. However, note that the determined enthal-
pies not only contain the isolated interaction energy of the
phenyl moieties, but also the required energy for geometry
changes of the whole molecular framework. Furthermore,
cooperative effects between the phenyl rings can also be as-
Figure 2. X-ray crystal structure of 3c. a) Overview. Centre-to-centre dis-
tances and angles between the planes of the b) proximal and c) distal
phenyl substituents. (ORTEP plots with thermal ellipsoids at 50% proba-
bility level, hydrogen atoms omitted for clarity).
signal remains sharp for longer and only begins to show line
broadening at temperatures higher than 323 K. This line
broadening can be assumed to be caused by a breaking of
the fairly rigid pairings of the phenyl groups, leading to a
mobilisation of the aryl groups, which is somewhat limited
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Benzene Tetramers
FULL PAPER
sumed to play a role because it appears to be plausible that
the breaking up of one pair of interacting phenyl groups af-
fects the whole molecular geometry in its vicinity.
To validate our experimental observations and to find a
plausible explanation for the prevalence of a single observed
isomer of the tetradecahydroporphyrazins, we used quantum
chemical calculations. Because traditional methods such as
the popular B3LYP density functional either tend to esti-
mate the strength of weak dispersion interactions incorrectly
or require unaffordable amounts of calculation time and re-
sources, we employed the recently developed B97-D density
functional that includes a long-range dispersion correc-
tion.[14] The relatively small phenyl-substituted tetradecahy-
droporphyrazin 3a has been chosen as model compound for
the calculations, which have been performed with TURBO-
MOLE.[15]
Scheme 3. Potential diastereomers of compound 3a and hypothetical
model compound 4.
Table 1. Relative energies of the potential diastereomers of compounds
3a and 4 (B97-D/TVZP) [kcalmolÀ1].
Compound
all S
SSSR
SSRR
SRSR
The formation reaction of the tetradecahydroporphyra-
zins, starting from the dihydropyrrol-2-imine (after hydro-
3a
4
0.0
0.0
13.9
4.5
16.7
5.2
15.3
1.3
ACHTUNGTRENNUNGlytic desilylation of 2a), is very exothermic with a reaction
enthalpy of À67.6 kcalmolÀ1 calculated on the B97-D/TZVP
level, thus explaining why these macrocycles form under
such mild conditions.
appears to be the case, considering the long reaction time
and conditions) only the single observed diastereomer
forms.
The structure resulting from a geometry optimisation is in
accordance with the one deduced from the spectroscopic
data with two types of phenyl pairs at distances that differ
by 0.33 ꢃ (Figure 5).
To obtain information about the contribution of the aro-
matic interactions to the stability of the tetraaryl-tetradeca-
hydroporphyrazins, the single-point energy of a benzene
tetramer with the individual molecules arranged exactly like
the proximal phenyl groups in the optimised structure of
compound 3a has been calculated. On the B97-D/TZVP
level of theory, such a cyclic benzene tetramer is favoured
by 11.8 kcalmolÀ1 in comparison with four single benzene
molecules, thus amounting to approximately 3 kcalmolÀ1 per
interaction.[5,14b,16] On the other hand, the macrocyclic
system itself only slightly favours the all S diastereomer, in-
dicated from calculations without the phenyl substituents
(Table 1, model compound 4).[16] Based on these results, it is
clear that the interactions between the aryl moieties essen-
tially contribute to the formation and stabilisation of the
whole macrocylic structure.
Conclusion
In summary, we have discovered a simple method to synthe-
sise highly saturated and substituted porphyrazin derivatives
with excellent diastereoselectivity. The structures of the ob-
tained compounds have been elucidated in solid phase and
solution by X-ray crystallography and NMR spectroscopy,
respectively, and have been found to contain four aryl moi-
eties in close contact, arranged in a cyclic fashion. In solu-
Figure 5. Structure of 3a optimised on the B97-D/TZVP level of
theory.[14]
Comparison with the optimised structures of the other
three hypothetically diastereomers of the tetradecahydro-
porphyrazins in which the aryl substituents are differently
aligned (Scheme 3) reveals that the observed diastereomer
with all four substituents pointing in the same direction is in
fact the energetically most favourable one (Table 1). Thus, it
is safe to assume that under thermodynamic control (which
tion, the tetradecahydroporphyrazins prefer
a slightly
oblong C2 symmetric structure with two types of pairs of
phenyl groups at different distances and of different interac-
tion strengths. Quantum chemical calculations employing
the new B97-D density functional with dispersion correc-
tion[14] are in good agreement with the experimentally deter-
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E.-U. Wꢀrthwein et al.
(s, 2H; NH); 13C NMR (75.47 MHz, CDCl3): d=16.3, 18.2, 20.2, 21.1,
23.1, 24.7, 25.1, 26.2 (CH3), 47.1, 48.1, 50.3, 51.1, 79.5, 90.6 (Cquat.), 124.5,
125.4, 125.8, 126.4, 126.6, 126.8, 127.3, 127.5, 127.8, 128.5, 128.6, 128.6,
128.7, 128.8, 130.5, 144.9, 148.1 (Carom), 162.4, 169.0 ppm (C=N); IR: n˜ =
3372 (vw), 3061 (w), 2974 (w), 2938 (w), 2909 (w), 2870 (w), 2569 (vw),
2500 (vw), 1668 (s), 1628 (s), 1599 (w), 1582 (w), 1493 (w), 1464 (m),
1445 (m), 1404 (m), 1393 (m), 1375 (m), 1362 (m), 1342 (m), 1288 (w),
1261 (w), 1250 (w), 1225 (w), 1198 (w), 1173 (w), 1148 (m), 1124 (w),
1088 (m), 1061 (m), 1051 (m), 1032 (w), 1003 (w), 957 (m), 939 (w), 910
(m), 849 (w), 824 (vw), 756 (s), 733 (m), 704 (vs), 679 (w), 664 (m), 650
(w), 640 (w), 617 (w), 592 (w), 579 cmÀ1 (w); ESI-MS [M+H]: calcd:
857.5953; found: 857.5936; elemental analysis (for C56H72N8·CDCl3):
calcd: C 70.03 H 7.63 N 11.46; found: C 69.64 H 7.63 N 11.31.
mined structure and confirm the preference of the found
diastereomer.
The clear application of the porphyrazin macrocycle of
these new compounds is its use as a valuable coordination
ligand for metal complexation. Additionally, the hydropho-
bic cavity formed by the aryl substituents, which is expected
to be variable in diameter, could be interesting for selective
interactions with suitable molecules of appropriate size and
polarity. Furthermore, the synthetic pathway discovered for
this new class of compounds allows controlled functionalisa-
tion at the walls of the cavity as exemplified in compound
3c, in which the diphenylamine substituent may serve as an
example of Brønsted or Lewis base activity. Thus, we expect
that this new class of compounds, owing to its unique struc-
tural and reactive properties, could serve as a basic frame-
work for catalysts, supramolecular structures and container
molecules.
Acknowledgements
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG, IRTG 1143 Mꢀnster–Nagoya, SFB 424) and the Fonds der Chemi-
schen Industrie, Frankfurt. We thank Prof. Dr. S. Grimme, Mꢀnster, for
helpful discussions.
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General procedure for the synthesis of 2: Aryl halide (10.0 mmol) was
dissolved in anhydrous THF (10.0 mL) in a Schlenk flask that had been
dried and flushed with argon. The solution was cooled to À788C and n-
butyllithium (11.0 mmol; 6.9 mL of an 1.6m solution in n-hexane) was
added. After stirring for one hour at À788C, 2,2,3,3-tetramethylsuccinoni-
trile (11.0 mmol, 1.50 g) dissolved in anhydrous THF (10.0 mL) was
slowly added. The reaction mixture was stirred at À788C for 30 min,
warmed to 08C and stirred for additional 30 min. Then, the solution was
cooled to À788C again and chlorotrimethylsilane (11.0 mmol, 1.20 g,
1.4 mL) was added. The reaction mixture was slowly warmed to room
temperature and stirred for one hour. The crude product was obtained
by removing the solvent under vacuum and was subsequently purified by
Kugelrohr distillation.
Compound 2a: By using bromobenzene (1.57 g, 1.05 mL, 10.0 mmol) as
the starting material, compound 2a was synthesised by using the general
procedure. The product was obtained after purification as a yellow solid
in 71% yield (2.02 g, 7.1 mmol). B.p. 1228C (1.9ꢄ10À2 mbar); 1H NMR
(300.13 MHz, CDCl3): d=0.27 (s, 9H; SiCH3), 1.06 (s, 6H; CH3), 1.27 (s,
6H; CH3), 7.41–7.49 (m, 3H), 7.95–7.98 ppm (m, 2H; CHarom); 13C NMR
(75.47 MHz, CDCl3): d=1.3 (SiCH3), 22.7 (CH3), 23.3 (CH3), 50.5 (Cquat.),
53.0 (Cquat), 128.5, 129.3, 131.3, (Carom), 134.3 (Cipso), 183.2, 191.3 ppm (C=
N); IR: n˜ =3053 (vw), 2997 (w), 2976 (w), 2965 (m), 2897 (w), 2868 (w),
2361 (w), 2336 (w), 1717 (w), 1682 (s), 1584 (w), 1545 (s), 1497 (w), 1474
(w), 1458 (w), 1447 (m), 1396 (m), 1377 (w), 1371 (w), 1362 (w), 1315
(m), 1298 (m), 1269 (m), 1238 (s), 1165 (w), 1144 (m), 1126 (w), 1103 (s),
1076 (m), 1034 (w), 1013 (w), 928 (w), 881 (vs), 843 (vs), 829 (vs), 785
(m), 770 (s), 758 (m), 743 (s), 702 (vs), 692 (s), 662 (m), 631 (m), 617
(w) cmÀ1 ; ESI-MS [MÀTMS+H]: calcd: 215.1543; found: 215.1541.
General procedure for the synthesis of the tetraaryl tetradecahydropor-
phyrazins 3: The tetradecahydroporphyrazins were synthesised by dis-
solving N-silylated dihydropyrrol imine 2 (1.0 mmol) in dichloromethane
(1 mL). This solution was slowly concentrated by evaporation of the sol-
vent over the course of several days. To increase the yield, the residue
was re-dissolved in dichloromethane and again slowly evaporated several
times. The resulting crystals were collected, washed repeatedly with small
amounts of pentane or hexane and dried under vacuum.
Compound 3a: Compound 3a was synthesised from 2a (247 mg,
0.86 mmol), following the general procedure and was obtained as colour-
less a crystalline solid in 26% yield (47 mg, 0.06 mmol). M.p. 1518C;
1H NMR (300.13 MHz, CDCl3): d=À0.11 (s, 6H), À0.02 (s, 6H), 0.99 (s,
6H), 1.01 (s, 6H), 1.05 (s, 6H), 1.18 (s, 6H), 1.30 (s, 6H), 1.31 (s, 6H,
CH3), 5.27 (s, 2H; NH), 6.06 (d, 2H), 6.09 (d, 2H; o-CHarom), 6.88–7.05
(m, 5H), 7.07–7.20 (m, 9H), 7.36 (d, 3J=7.2 Hz, 2H; CHarom), 7.54 ppm
10462
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Chem. Eur. J. 2009, 15, 10457 – 10463

Benzene Tetramers
FULL PAPER
floth, S. Warzeska, E.-U. Wꢀrthwein, Eur. J. Inorg. Chem. 1999,
1189–1192; e) E. Marihart, J.-B. Greving, R. Frçhlich, E.-U.
Wꢀrthwein, Eur. J. Org. Chem. 2007, 5071–5081.
[13] G. J. Piermarini, A. D. Mighell, C. E. Weir, S. Block, Science 1969,
165, 1250–1255.
[14] a) S. Grimme, J. Comput. Chem. 2006, 27, 1787–1799; b) S.
Grimme, Angew. Chem. 2008, 120, 3478–3483; Angew. Chem. Int.
Ed. 2008, 47, 3430–3434.
[11] S. Janich, R. Frçhlich, A. Wilken, J. von Zamory, A. Wakamiya, S.
Yamaguchi, E.-U. Wꢀrthwein, Eur. J. Org. Chem. 2009, 2077–2087.
[12] Crystallographic data for 3b: C81.5H91Cl3N8, Mr =1288.97; triclinic;
[15] TURBOMOLE, R. Ahlrichs, M. Bꢁr, H.-P. Baron, S. Bauernschmitt,
S. Bçcker, M. Ehrig, K. Eichkorn, S. Elliott, F. Furche, F. Haase, M.
Hꢁser, H. Horn, C. Huber, U. Huniar, M. Kattannek, C. Kçlmel, M.
Kollwitz, K. May, C. Ochsenfeld, H. ꢈhm, A. Schꢁfer, U. Schneider,
O. Treutler, M. von Arnim, F. Weigend, P. Weis, H. Weiss, Universi-
tꢁt Karlsruhe, Karlsruhe, 2003, (see also: http://www.turbomole.-
com).
[16] Geometry optimisations on the B97-D/TZVP-level of theory result-
ed in a tetramerisation energy of 15.6 kcalmolÀ1 for the formation
of a slightly distorted pinwheel-like tetramer (very flat energy hy-
perface). These results are in contrast with those of O. Engkvist, P.
Hobza, H. L. Selze, E. W. Schlag, J. Chem. Phys. 1999, 110, 5758–
5762. They did not localise a minimum of such an arrangement on
the energy hyperface.
¯
space group P1; a=14.1518(4), b=19.8854(5), c=26.4582(8) ꢃ; a=
94.046(1), b=90.867(1), g=101.212(2)8; V=7282.2(4) ꢃ3; Z=4;
1calcd =1.176 gcmÀ3; T=À508C; 108369 reflections collected; 25673
unique reflections (Rint =0.061); R=0.0796;
RW =0.1982; GOF=
1.022; Crystallographic data for 3c: C105H110Cl2N12; Mr =1610.95;
tetragonal; space group P4/ncc; a=17.208(3), b=17.208(3), c=
30.208(6) ꢃ; a=90, b=90, g=908; V=8945(3) ꢃ3; Z=4, 1calcd
=
1.196 gcmÀ3; T=À1508C; 56073 reflections collected; 3953 unique
reflections (Rint =0.1043); R=0.1240;
RW =0.2343; GOF=1.379.
The quality of the measured data did not allow further refinement.
CCDC 729167 (3c) and 729168 (3b) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif
Received: May 5, 2009
Published online: August 28, 2009
Chem. Eur. J. 2009, 15, 10457 – 10463
ꢂ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
10463