Synthesis, structure, tautomerism, and reactivity of methanetrisamidines

Article abstract of DOI:10.1002/anie.201205030

Tout au contraire: Both tautomeric forms of a methanetrisamidine were structurally characterized for the first time by X-ray diffraction and by ab initio calculations (see structures; gray C, red H, blue N). Their reactivity as proton acceptors and multia

Full text of DOI:10.1002/anie.201205030

Angewandte
Chemie
DOI: 10.1002/anie.201205030
Methanetrisamidines
Synthesis, Structure, Tautomerism, and Reactivity of
Methanetrisamidines**
Benjamin Gutschank, Stephan Schulz,* Michael Marcinkowski, Georg Jansen,
Heinz Bandmann, Dieter Blꢀser, and Christoph Wçlper
N,N’-chelating monoanionic amidinate ligands have been
studied in detail over the last decades. The easy tunability of
their steric and electronic properties[1] allows the synthesis of
tailormade metal complexes for technical applications in
catalysis and materials sciences.[2] Surprisingly, multifunc-
tional ligands containing two or more amidine moieties, in the
following referred to as polyamidines, have been only scarcely
investigated. They are of potential interest for the synthesis of
(hetero)multimetallic complexes, which may show improved
catalytic properties. Moreover, neutral aromatic tetraami-
dines have been investigated in cancer research owing to their
antiproteinase activity.[3] Unfortunately, only very few poly-
amidines, almost all containing a central phenyl spacer, have
been synthesized and multidentate polyamidines, in which the
amidine moieties are bound to a single atom, are limited to
two Me2Si- and CH2-bridged derivatives.[4,5] In contrast,
Figure 1. Temperature-dependent 1H NMR spectra monitoring the
isoelectronic tetranitromethane C(NO2)4 and tetramethylme-
thanetetracarboxylate C(COOMe)4 are well known.[6]
~
&
*
hydrolysis of 1a with water in C6D6 (1a , 2a , C(NiPr)2 ).
We recently reported on the synthesis and reactivity of
tetraamidinatomethane complexes {C[C(NR)2ZnMe]4} (R =
iPr (1a), Ph (1b), Et (1c), Cy (1d); Cy = cyclohexyl) by
reactions of ZnMe2 with carbodiimides at elevated temper-
atures.[7,8] We now became interested in the neutral multi-
dentate ligands, which were expected to be formed by
kinetically controlled hydrolysis of the zinc complexes.
However, when we monitored the reaction of 1a with water
in C6D6 by temperature-dependent in situ 1H NMR spectros-
copy (Figure 1), we found a different reaction pathway.
Compound 1a is almost stable against hydrolysis at ambient
temperature, whereas at temperatures above 558C (iPrN)2C
and methanetrisamidine 2a are formed exclusively. Even
though the expected tetraamidine C[C(NR)N(R)H]4 was not
detected by NMR spectroscopy, its formation as a reaction
intermediate cannot be excluded. Comparable decomposition
reactions were found for the two isoelectronic compounds
C(NO2)4 and C(COOMe)4, which react under basic condi-
tions to form Ag+[C(NO2)3]À and HC(COOMe)3, respec-
tively.[9] However, an analogous carbodiimide elimination
reaction was only observed for metal amidinates (Cu, Al)
upon thermal treatment at temperatures higher than
2008C.[10] Considering the significantly lower reaction tem-
peratures in our experiments, the decomposition of 1a is
expected to proceed by a different reaction pathway, most
likely by an intramolecular hydrogen migration (see the
Supporting Information).
Compound 2a was purified by sublimation at 808C. The
1H NMR spectrum shows
a
singlet (d = 5.37 ppm,
[D8]toluene) for the central CH group, whereas the NH
resonance (d = 4.63 ppm) occurs as a doublet on account of
3JHH coupling to CHiPr. Dynamic 1H NMR and DEPT experi-
ments (DEPT= distortionless enhancement by polarization
transfer) between À40 and + 1008C showed no CH–NH
tautomerization of the central C–H group. In contrast,
hydrolysis of 1b yielded both tautomeric forms, C[C-
(NPh)N(Ph)H]2[C(HNPh)2] 2b and HC[C(NHPh)NPh]3 2c,
which are the first structurally characterized CH–NH tauto-
mers of an acyclic amidine. Even though N,N’-tautomerism in
amidines has been investigated in detail,[11] up until now the
existence of an equilibrium between CH–NH tautomers has
been proven only indirectly for the short-lived ene-1,1-
diamine species, which could not be isolated.[12] In contrast,
a cyclic ene-1,1-diamine has been previously characterized by
NMR spectroscopy.[13] The postulated N–H tautomer of
acetamidine plays a crucial role in the Diels–Alder reaction
with tetrazine derivatives to form aminopyridazines.[14] In
addition, the cyclic ketene N,N-acetal is assumed as a key
[*] B. Gutschank, Prof. S. Schulz, M. Marcinkowski, Prof. G. Jansen,
Dipl.-Ing. H. Bandmann, D. Blꢀser, Dr. C. Wçlper
Fakultꢀt fꢁr Chemie, Universitꢀt Duisburg-Essen
Universitꢀtsstrasse 5–7, S07 S03 C30, 45117 Essen (Germany)
E-mail: stephan.schulz@uni-due.de
[**] S. Schulz gratefully acknowledges financial support by the Univer-
sity of Duisburg-Essen.
Supporting information for this article (including experimental
details) is available on the WWW under http://dx.doi.org/10.1002/
anie.201205030.
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!

.
Angewandte
Communications
intermediate in the synthesis of tetraazafulvalenes by oxida-
tive coupling.[15]
Colorless crystals were obtained by slow evaporation of
the solvent from a solution in cyclohexane/CH2Cl2 (2b) and
from a solution in CH3CN upon storage at À108C (2c).[16] The
central carbon atom C1 in 2b, which binds to three carbon
atoms in a trigonal-planar arrangement (root-mean-square
deviation of the four C atoms from the best plane is 0.0044 ꢀ),
2
À
À
can be considered to be sp hybridized. The C1 C2 and C1
C3 bonds are slightly shorter than typical single bonds
À
(1.54 ꢀ) and C1 C4 is longer than a common double bond
(1.34 ꢀ), indicating delocalization of the p-electrons. The
À
same is true for both C N bonds emerging from C4, which are
2
3
À
shorter than the expected length for a C(sp ) N(sp ) single
À
bond (1.43 ꢀ). In contrast, one C N bond at C2 and C3 shows
the typical length of a C N double bond (1.29 ꢀ), while the
other agree well with the mean C N single-bond length found
for R(H)N CR NR moieties in the CSD (1.372(28) ꢀ). The
structural parameters of the molecule agree well with the
hydrogen atom positions found in the difference Fourier
synthesis. The conformation of the molecule is supported by
two intramolecular hydrogen bonds.
À
À
À
=
The central carbon atom (C1) in 2c binds to three amidine
groups; one hydrogen position was found next to it in the
difference Fourier synthesis, which coincides with the other
À
structural parameters. The C C bond lengths are in the
À
typical range of C C single bonds and the C-C1-C bond
angles are about 1138. C1 deviates by 0.4180(12) ꢀ from the
C2/C3/C4 plane, indicating sp3 hybridization. The fact that the
angles are somewhat greater than the tetrahedral angle can be
explained by the steric demand of the residual amidine
Figure 2. Molecular structure of 2b (top) and of 2c (bottom); thermal
ellipsoids at the 50% probability level, hydrogen atoms shown as
spheres of arbitrary radius, phenyl hydrogen atoms omitted for clarity.
Bond lengths [ꢂ] and angles [8]:2b: C1–C2 1.486(2), C1–C3 1.476(2),
C1–C4 1.391(2), N1–C2 1.374(2), N2–C2 1.294(2), N5–C4 1.372(2),
N6–C4 1.373(2), H3···N3 1.93, H2···N2 1.97; C4-C1-C3 121.38(13),
C4-C1-C2 120.64(14), C3-C1-C2 117.97(14), N2-C2-N1 122.51(14),
N5-C4-N6 119.16(14), N5-H3···N3 138.6, N6-H2···N2 137.0; 2c: C1–C2
1.5356(14), C1–C3 1.5345(14), C1–C4 1.5341(15), N1–C2 1.2819(14),
N2–C2 1.3644(14), C4-C1-C3 113.04(8), C4-C1-C2 112.37(9), C3-C1-C2
113.21(9), N1-C2-N2 121.88(10).
À
groups. The C N bond lengths are typical for double and
single bonds (Figure 2).
To elucidate the solvent dependency of the equilibrium
between 2b and 2c, temperature-dependent NMR experi-
ments were performed in C6D6 and CD3CN. The major form
in nonpolar C6D6 is 2b (more than 85%) over the whole
temperature range (25–758C). The 13C and DEPT90 spectra
only show four broadened phenyl resonances due to a fast
intramolecular proton exchange reaction between the amino
=
and imino groups. Consequently, the p-electrons of the C C
distances of 2.87 ꢀ (X-ray diffraction analysis (XRD): 2.98,
3.02, 3.13 ꢀ), proving the stabilizing effect of the three CH–p
contacts. The calculated C1–C2 distance (1.545 ꢀ) and C2-
C1-C3 angle (113.28) are in excellent agreement with the
crystal structure. The remaining three phenyl groups do not
show substantial CH–p or p–p stabilizations, but one of their
bond are delocalized within the planar C4 moiety, which
explains the enhanced stability of 2b. The 13C NMR spectrum
of 2b shows the characteristic resonances of the ene-1,1-
diamidine carbon atom (d = 84.96 ppm), the amidino back-
bone carbon atoms (d = 153.74 ppm), and the enediamine
carbon atom (d = 143.53 ppm). In contrast, the NMR spectra
of 2b in polar CD3CN show an increasing amount of 2c upon
heating from 25 to 758C. High temperatures are required
owing to the poor solubility of 2c. The formation of 2c points
to a solvent dependence (e.g. polarity) rather than to
a temperature dependence, hence it is possible to control
the equilibrium to some extent by the solvent polarity.[17]
Dispersion-corrected density functional theory (DFT+
D3) calculations were performed to evaluate the relative
stability of the N–H (2b) and C–H (2c) tautomers in more
detail.[18] Upon convergence of the geometry optimization, 2b
displays C2 symmetry, while 2c is C3-symmetric. Phenyl
groups surround the methine group in 2c with Hortho···Cmeta
Hortho atoms involved in a nearly planar six-membered H-C-C-
N-C-N ring is only 2.28 ꢀ away from the adjacent N atom. A
further stabilization of this geometry may be attributed to the
three NH···N contacts (2.55 ꢀ) between the different C-
(NHPh)(NPh) groups. In 2b only two CH–p contacts were
found, with a Hortho···Cpara distance of 2.87 ꢀ (XRD: 2.87,
2.90 ꢀ). On the other hand, one p–p contact in a typical
parallel-displaced arrangement of two phenyl rings of adja-
cent C(NHPh)(NPh) moieties and two short NH···N bonds of
1.80 ꢀ (XRD 1.93, 1.97 ꢀ) were found which help to stabilize
2b relative to 2c by 10.6 kJmolÀ1 according to DFT+ D3. The
calculated C1–C2 distance (1.475 ꢀ) agrees very well with
experimental values (C1–C2 1.486(2), C1–C3 1.476(2) ꢀ),
2
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
while the C1–C4 distance of 1.420 ꢀ points to slightly higher
single-bond character in the calculated structure than in the
crystal structure (1.391(2) ꢀ). The DFT+ D3 energy differ-
ence agrees well with the value of 12.3 kJmolÀ1 found in ab
initio calculations for the DFT+ D3 geometries using
valence-only second-order Møller–Plesset perturbation
theory (MP2).[19] In conjunction with an increase of the
dipole moment from 0.97 Debye (2b) to 2.42 Debye (2c) as
obtained from DFT+ D3, this energy difference is small
enough to explain why 2b is preferred but not exclusively
formed in nonpolar solvents whereas 2c dominates in polar
solvents (vide supra).
The imino moieties of the methanetrisamidines are proton
acceptors as was shown by the reaction of 2b with two
equivalents of acetic acid, yielding [C(C(HNPh)2)3]2+
-
{[CH3COO]À}2 3 (see the Supporting Information). Crystals
¯
of 3, which crystallizes in the triclinic space group P1, were
obtained from a solution in Et2O at À308C. The most notable
structural difference between 2b and the methanetrisamidi-
À
nium dication in 3 is reflected by the almost equal C C bond
lengths within the trigonal-planar C4 moiety (C1–C2
1.417(2) ꢀ, C1–C3 1.4440(19) ꢀ, C1–C4 1.4464(19) ꢀ). The
shorter C1–C2 bond can be explained by the orientation of
the N-C-N unit relative to the central C4 unit. The N1/C2/N2
plane is almost coplanar to the C1/C2/C3/C4 plane
(26.51(15)8), which allows a more effective p-electron deloc-
alization than that with the other two amidinate groups
(40.27(13)8, 43.38(10)8) and explains the slightly elongated
Replacement of the phenyl groups by H atoms followed
by geometry optimization and calculation of the vibrational
frequencies at the DFT+ D3 level again shows the C2-
symmetrical N–H and the C3-symmetrical C–H tautomeric
forms to be true minima on the potential energy surface.[20]
The N–H tautomer is preferred by 23.8 kJmolÀ1, in good
agreement with the MP2 energy difference of 22.1 kJmolÀ1
obtained for the DFT+ D3 geometries, which changes only
slightly to 23.1 kJmolÀ1 when the structures are reoptimized
at the MP2 level of theory. The p–p contact between adjacent
C(NHPh)(NPh) groups observed in 2b is now replaced with
two NH···N contacts with an N···H distance of 2.38 ꢀ, while
CH–p contacts obviously no longer exist, which rationalizes
the increased energy difference between the tautomeric
forms. When the C3-symmetry constraint was released,
a second, lower-lying minimum with C1 symmetry for the
C–H tautomer was found (see the Supporting Information).
This structure is 20.9 kJmolÀ1 higher in energy than the N–H
tautomer at the DFT+ D3 level of theory, while an anergy
difference of only 16.1 kJmolÀ1 was obtained at the MP2 level
(17.1 kJmolÀ1 after MP2 reoptimization of both structures).
To determine the energy difference between the (unob-
served) N–H and C–H (2a) tautomers of the iPr-substituted
trisamidine, a molecular mechanics force field conformer scan
was carried out for both tautomers. The lowest-energy 12 N–
H tautomeric and 15 C–H tautomeric structures were then
reoptimized at the DFT+ D3 level with a small basis set of
split-valence quality. Then for each tautomer the two lowest-
energy conformers were reoptimized at the DFT+ D3 level
with a triple-zeta basis set. A C1-symmetrical conformer of 2a
was found to be 1.9 kJmolÀ1 lower in energy than any
conformer of the N–H tautomer, the lowest of which was
found to display C2 symmetry. The next conformer of 2a (C1
symmetry) was found at 2.0 kJmolÀ1, while the next confor-
mer (C1 symmetry) of the N–H tautomer is 5.6 kJmolÀ1 higher
in energy than the lowest conformer of 2a. The energy
difference between the lowest-energy conformers of the two
tautomers increases to 3.3 kJmolÀ1 on the MP2 level of theory
(without reoptimization of the DFT+ D3 structures), which is
too small to explain why only 2a has been experimentally
observed. However, the dipole moment of 2a is 2.42 Debye
(DFT+ D3), while that of the two conformers of the N–H
tautomer is only 1.02 and 1.07 Debye, respectively. Interac-
tions with neighboring dipole molecules or a polarizable
environment may have a stabilizing effect, subsequently
favoring the C–H tautomeric form 2a.
À
À
C2 N bonds and the slightly shorter C1 C2 bond.
In addition, the ampholytic compounds 2a–c are powerful
reagents for the synthesis of multinuclear organometallic
complexes owing to the presence of acidic N–H groups.
Reactions of 2a with AlMe3 and iBu2AlH occurred with
elimination of methane and H2, respectively, and subsequent
formation of HC[C(NiPr)2AlR2]3 (R = Me (4a), iBu (4b)), in
quantitative yields. Threefold deprotonation was proven by
the disappearance of the NH resonances in the 1H NMR
spectra (C6D6), whereas the characteristic CH group signal
was preserved. Crystals of 4a and 4b of low quality were
obtained from different solvents, from which the connectivity
within the molecules was proven. The models suggest a sp3
hybridization of the central carbon atom and a chelating
coordination of the amidinate groups to the AlR2 units.
In contrast, the reaction of 2b with 4 equiv of AlMe3 gave
C[C(NPh)2AlMe2]2[C(N(Ph)AlMe2)2] 4c in quantitative
yield. Yellow crystals of 4c were obtained from a solution in
toluene at À308C. Compound 4c crystallizes in the mono-
clinic space group C2/c with C1 and C2 on a twofold axis
(Figure 3). One amidinate group (N1-C1-N1#1) adopts
a bridging position, while two serve as chelating units. The
C atoms of the amidinate groups bind to trigonal-planar-
À
coordinated C1 with two short bonds and one long C C bond,
showing a delocalized p-electron system within the N3-C3-
À
C1-C3#1-N3#1 unit. The C N bond lengths within these two
amidinate groups differ owing to different coordination
À
numbers of the N atoms, whereas the C N bond lengths
within the N1-C2-N1#1 unit indicate delocalized p-electrons.
To
{HC[C(NR)NHR]3 (R = iPr (2a), Ph (2c)) and ene-1,1-
diamidine-2,2-diamine {C[C(NPh)NHPh)2]2[C(NHPh)2]}
summarize,
the
methanetrisamidines
(2b) were formed by an unforeseen carbodiimide elimination
reaction upon hydrolysis of the corresponding tetranuclear
zinc complexes. The crystal structures of the N–H and C–H
tautomers 2b and 2c provide structural evidence of N,C
tautomerism in amidines for the first time. In solution, the
equilibrium between 2b and 2c depends to some extent on
the polarity of the solvent. Quantum chemical calculations
revealed the N–H tautomers to be energetically favored over
the C–H tautomers for Ph- and H-substituted trisamidines,
whereas the C–H tautomer of the iPr-substituted complex is
slightly lower in energy than the N–H tautomer. Reactivity
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
3
These are not the final page numbers!

.
Angewandte
Communications
Cordes, R. C. Haddon, R. G. Hicks, R. T. Oakley, T. T. M.
Palstra, L. F. Schneemeyer, J. V. Waszczak, J. Am. Chem. Soc.
1992, 114, 5000; f) R. T. Boerꢁ, R. T. Oakley, R. W. Reed, J.
Organomet. Chem. 1987, 331, 161; g) J. Grundy, M. P. Coles, P. B.
Hitchcock, J. Organomet. Chem. 2002, 662, 178; h) J. R. Haga-
dorn, J. Arnold, Angew. Chem. 1998, 110, 1813; Angew. Chem.
Int. Ed. 1998, 37, 1729; i) H. Kawaguchi, T. Matsuo, Chem.
Commun. 2002, 958; j) J. F. Li, L. H. Weng, X. H. Wei, D. S. Liu,
Dalton Trans. 2002, 1401; k) C. T. Chen, L. H. Rees, A. R.
Cowley, M. L. H. Green, Dalton Trans. 2001, 1761; l) H. A.
Jenkins, D. Abeysekera, D. A. Dickie, J. A. C. Clyburne, Dalton
Trans. 2002, 3919; m) S.-D. Bai, J.-P. Guo, D.-S. Liu, W.-Y. Wong,
Eur. J. Inorg. Chem. 2006, 4903; n) J. R. Babcock, C. Incarvito,
A. L. Rheingold, J. C. Fettinger, L. R. Sita, Organometallics
1999, 18, 5729.
[6] a) F. D. Chattaway, J. Chem. Soc. Trans. 1910, 97, 2099 – 2102;
b) R. Scholl, W. Egerer, Liebigs Ann. Chem. 1913, 397, 301.
[7] a) M. Mꢂnch, U. Flçrke, M. Bolte, S. Schulz, D. Gudat, Angew.
Chem. 2008, 120, 1535; Angew. Chem. Int. Ed. 2008, 47, 1512;
b) S. Schmidt, S. Gondzik, S. Schulz, D. Blꢃser, R. Boese,
Organometallics 2009, 28, 4371; c) S. Schmidt, B. Gutschank, S.
Schulz, D. Blꢃser, R. Boese, C. Wçlper, Eur. J. Inorg. Chem.
2011, 4464.
[8] a) B. Gutschank, S. Schulz, U. Westphal, D. Blꢃser, R. Boese,
Organometallics 2010, 29, 2093; b) B. Gutschank, S. Schulz, D.
Blꢃser, R. Boese, C. Wçlper, Organometallics 2010, 29, 6133.
[9] a) M. Gçbel, T. M. Klapçtke, P. Mayer, Z. Anorg. Allg. Chem.
2006, 632, 1043; b) R. Scholl, W. Egerer, Liebigs Ann. Chem.
1913, 397, 301.
Figure 3. Molecular structure of 4c (thermal ellipsoids at the 50%
probability level, hydrogen atoms omitted for clarity, asymmetric unit
shown in dark bonds, C1 and C2 located on a twofold axis). Bond
lengths [ꢂ] and angles [8], #1Àx+1, y, Àz+1/2: C1–C2 1.506(2),
C1–C3 1.4191(15), N2–C3 1.4470(15), N3–C3 1.3257(16), N1–C2
1.3404(13), Al1–N1 1.9199(11), Al1–N2 1.9984(11), Al2–N3
1.9268(11), Al2–N2 1.9967(11), C3#1-C1-C3 120.55(16), C3#1-C1-C2
119.73(8), C3-C1-C2 119.73(8), N1-C2-N1#1 125.02(16), N1-C2-C1
117.49(8), N3-C3-C1 132.19(12), N3-C3-N2 105.46(10), C1-C3-N2
122.29(11), C2-N1-C4 120.32(11), C2-N1-Al1 125.64(9), C4-N1-Al1
113.22(8), C3-N2-C(10) 120.94(10), C3-N2-Al2 89.32(7), C(10)-N2-Al2
112.40(8), C3-N2-Al1 101.14(7), C(10)-N2-Al1 112.80(8), Al2-N2-Al1
118.29(5), C3-N3-C(16) 132.96(11), C3-N3-Al2 96.09(8), C(16)-N3-Al2
129.65(8), N1-Al1-N2 90.67(5), N3-Al2-N2 68.46(4).
[10] a) T. Whitehorne, J. P. Coyle, A. Mahmood, W. H. Monillas, G.
Yap, S. Barry, Eur. J. Inorg. Chem. 2011, 3240; b) A. L. Brazeau,
Z. Wang, C. N. Rowley, S. T. Barry, Inorg. Chem. 2006, 45, 2276.
[11] a) C. Berndt, T. Kaempchen, Chem. Ber. 1986, 119, 1101; b) J.
Oszczapowicz, E. Raczynska, J. Osek, J. Magn. Reson. Chem.
´
1986, 24, 9; c) E. Raczynska, Perkin Trans. 2 1986, 1189; d) E.
Raczynska, R. Gawinecki, Trends Org. Chem. 1998, 7, 85.
[12] a) M. Pfau, M. Chiriacescu, G. Revial, Tetrahedron Lett. 1993,
34, 327; b) K. Sung, S.-H. Wu, R.-R. Wu, S.-Y. Sun, Org. Chem.
2002, 67, 4298; c) K. Ito, Y. Kizuka, Y. Hirano, J. Heterocycl.
Chem. 2005, 42, 583.
[13] J. Goerdeler, R. Sappelt, Chem. Ber. 1967, 100, 2064.
[14] H. P. Figeys, A. Mathy, A. Dralants, Synth. Commun. 1981, 11,
655.
studies showed that these novel ligands can be either
protonated at the Lewis basic N centers or metalated by
organometallic complexes at the N–H moieties.
Received: June 27, 2012
Published online: && &&, &&&&
[15] a) J. Brandenburg, C. Kꢃpplinger, R. Beckert, Synthesis 1996,
1302; b) D. Mꢂller, R. Beckert, J. Weston, W. Gꢂnther, H. Gçrls,
M. Friedrich, Eur. J. Org. Chem. 2001, 4551.
Keywords: ab initio calculations · structure determination ·
.
[16] Bruker AXS D8 Kappa diffractometer with APEX2 detector
(MoKa radiation, l = 0.71073 ꢀ; T= 100(1) K). The structures
were solved by Direct Methods (SHELXS-97, G. M. Sheldrick,
Acta Crystallogr. Sect. A 1990, 46, 467) and refined by full-matrix
least-squares on F2. Absorption corrections were performed
semiempirically from equivalent reflections on basis of multi-
scans (Bruker AXS APEX2). All non-hydrogen atoms were
refined anisotropically, methyl hydrogen atoms as rigid groups
and others by a riding model. NH and OH hydrogen atoms were
taken from the difference Fourier synthesis and constrained.
(SHELXL-97, Program for Crystal Structure Refinement, G. M.
Sheldrick, Universitꢃt Gçttingen, 1997 and shelXle, A Qt GUI
for SHELXL. See also: G. M. Sheldrick, Acta Crystallogr. Sect.
A 2008, 64, 112; C. B. Hꢂbschle, G. M. Sheldrick, B. Dittrich, J.
Appl. Crystallogr. 2011, 44, 1281 – 1284). 2b: [C40H34N6], M =
598.73, colorless crystal (0.42 ꢄ 0.32 ꢄ 0.26 mm); monoclinic,
space group Cc; a = 18.1738(16) ꢀ, b = 10.3046(9) ꢀ, c =
18.983(2) ꢀ; a = 908, b = 113.163(3)8, g = 908, V= 3268.4(6) ꢀ3;
Z = 4; m = 0.073 mmÀ1; 1calcd = 1.217 gcmÀ3; 37607 reflections
(2qmax = 598), 8129 unique (Rint = 0.0333); 415 parameters, Flack
parameter x = À0.7(15); largest max./min. in the final difference
tautomerism · X-ray diffraction
[1] a) J. Barker, M. Kilner, Coord. Chem. Rev. 1994, 133, 219;
b) F. T. Edelmann, Adv. Organomet. Chem. 2008, 57, 183;
c) M. P. Coles, Dalton Trans. 2006, 985.
[2] a) K. A. Schug, W. Lindner, Chem. Rev. 2005, 105, 67; b) M. W.
Hosseini, Coord. Chem. Rev. 2003, 240, 157.
[3] a) C. Nastruzzi, R. Gambari, Cancer Lett. 1990, 50, 93 – 102;
b) R. R. Tidwell, L. L. Fox, J. D. Geratz, Biochim. Biophys. Acta
Enzymol. 1976, 445, 729 – 738.
[4] a) J.-A. Gautier, M. Miocque, C. C. Farnoux, The Chemistry of
Amidines and Imidates, Vol. 1 (Eds.: S. Patai), Wiley, London,
1975, pp. 283 – 348; b) R. L. Shriner, F. W. Neumann, Chem. Rev.
1944, 35, 351.
[5] a) A. Kraft, R. Frçhlich, Chem. Commun. 1998, 1085; b) A.
Kraft, Perkin Trans.
1 1999, 705; c) S. K. Mandal, L. K.
Thompson, M. J. Newland, E. J. Gabe, F. L. Lee, Chem.
Commun. 1989, 744; d) S. S. Tandon, L. K. Thompson, J. N.
Bridson, J. C. Dewan, Inorg. Chem. 1994, 33, 54; e) A. W.
4
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!

Angewandte
Chemie
Fourier synthesis 0.249 eꢀÀ3/À0.245 eꢀÀ3; max./min. transmis-
sion 0.75/0.68; R1 = 0.0435 (I > 2s(I)), wR2 (all data) = 0.1076.
Due to the high standard deviation of x, the absolute structure
could not be determined reliably. 2c: [C40H34N6·C2H3N], M =
639.79, colorless crystal (0.24 ꢄ 0.18 ꢄ 0.13 mm); triclinic, space
CCDC 868842 (2c), CCDC 868841 (3), and CCDC 868840
(4c)” contain the supplementary crystallographic 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.
¯
group P1; a = 12.3438(7) ꢀ, b = 13.3509(7) ꢀ, c = 13.4235(8) ꢀ;
a = 60.586(2)8, b = 67.453(3)8, g = 66.088(3)8, V=
1713.77(17) ꢀ3; Z = 2; m = 0.075 mmÀ1 1calcd = 1.240 gcmÀ3
[17] Detailed information is given in the Supporting Information.
[18] Starting from the crystal structures the molecule geometries of
2b and 2c were optimized with tightened convergence thresh-
olds and an improved DFT integration grid at the DFT level
;
;
28355 reflections (2qmax = 618), 10184 unique (Rint = 0.0234);
442 parameters; largest max./min. in the final difference Fourier
synthesis 0.394 eꢀÀ3/À0.222 eꢀÀ3; max./min. transmission 0.75/
0.67; R1 = 0.0460 (I > 2s(I)), wR2 (all data) = 0.1192. 3:
[C40H36N6·2(C2H3O2)·2(H2O)], M = 754.87, pale yellow crystal
including
a third-generation dispersion energy correction
(DFT+ D3; a) S. Grimme, J. Antony, S. Ehrlich, H. Krieg, J.
Chem. Phys. 2010, 132, 154104). The BLYP exchange correlation
functional b) P. A. M. Dirac, Proc. R. Soc. London Ser. A 1929,
123, 714; c) J. C. Slater, Phys. Rev. 1951, 81, 385; d) A. D. Becke,
Phys. Rev. A 1988, 38, 3098; e) C. Lee, W. Yang, R. G. Parr, Phys.
Rev. B 1988, 37, 785) and a basis set of triple-zeta-valence quality
(def2-TZVP; f) F. Weigend, R. Ahlrichs, Phys. Chem. Chem.
Phys. 2005, 7, 3297) were used along with the corresponding
auxiliary basis set (g) F. Weigend, Phys. Chem. Chem. Phys.
2006, 8, 1057) in the resolution-of-the-identity (RI) approxima-
tion as implemented in Turbomole V6.3 (TURBOMOLE V6.3
2009, University of Karlsruhe and Forschungszentrum Karlsruhe
GmbH, 1989 – 2007, TURBOMOLE GmbH, since 2007; avail-
able from http://www.turbomole.com; h) R. Ahlrichs, M. Bꢃr, M.
Hꢃser, H. Horn, C. Kçlmel, Chem. Phys. Lett. 1989, 162, 165;
i) O. Treutler, R. Ahlrichs, J. Chem. Phys. 1995, 102, 346; j) M.
von Arnim, R. Ahlrichs, J. Chem. Phys. 1999, 111, 9183.).
[19] Valence-only MP2 calculations were performed in the RI
approximation with a larger orbital basis set (def2-TZVPP)
and the corresponding auxiliary basis set (F. Weigend, M. Hꢃser,
H. Patzelt, R. Ahlrichs, Chem. Phys. Lett. 1998, 294, 143).
[20] P. Deglmann, K. May, F. Furche, R. Ahlrichs, Chem. Phys. Lett.
2004, 384, 103.
¯
(0.18 ꢄ 0.15 ꢄ 0.12 mm); triclinic, space group P1; a =
10.5079(11) ꢀ, b = 13.5325(15) ꢀ, c = 16.2636(19) ꢀ; a =
110.849(5)8, b = 92.152(5)8, g = 111.876(5)8, V= 1966.6(4) ꢀ3;
Z = 2; m = 0.086 mmÀ1; 1calcd = 1.275 gcmÀ3; 33622 reflections
(2qmax = 508), 6990 unique (Rint = 0.0405); 505 parameters;
largest max./min. in the final difference Fourier synthesis
0.229 eꢀÀ3/À0.263 eꢀÀ3
; max./min. transmission 0.75/0.69;
R1 = 0.0355 (I > 2s(I)), wR2 (all data) = 0.0883. The hydrogen
atoms of C72 and C82 were refined as idealized disordered
methyl group over two positions. 4c: [C48H54AL4N6], M =
822.89, yellow crystal (0.25 ꢄ 0.10 ꢄ 0.08 mm); monoclinic,
space group C2/c; a = 17.4755(9) ꢀ, b = 15.5339(8) ꢀ, c =
18.5007(11) ꢀ; a = g = 908, b = 116.831(2)8, V= 4481.6(4) ꢀ3;
Z = 4; m = 1.145 mmÀ1; 1calcd = 1.220 gcmÀ3; 23163 reflections
(2qmax = 618), 6861 unique (Rint = 0.0334); 263 parameters;
largest max./min. in the final difference Fourier synthesis
0.499 eꢀÀ3/À0.235 eꢀÀ3
; max./min. transmission 0.75/0.66;
R1 = 0.0398 (I > 2s(I)), wR2 (all data) = 0.1087. The crystallo-
graphic data (without structure factors) were deposited as
“supplementary
publication
no.
CCDC 868839
(2b),
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

.
Angewandte
Communications
Communications
Methanetrisamidines
Tout au contraire: Both tautomeric forms
of a methanetrisamidine were structurally
characterized for the first time by X-ray
diffraction and by ab initio calculations
(see structures; gray C, red H, blue N).
Their reactivity as proton acceptors and
multianionic ligands was demonstrated.
B. Gutschank, S. Schulz,*
M. Marcinkowski, G. Jansen,
H. Bandmann, D. Blꢁser,
C. Wçlper
&&&& — &&&&
Synthesis, Structure, Tautomerism, and
Reactivity of Methanetrisamidines
6
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 1 – 6
These are not the final page numbers!