1-Aryl-3-(dimethylamino)propenones: Strong proton acceptors for hydrogen bonds

Article abstract of DOI:10.1002/ejoc.200390086

Because of the electron-donating effects of their terminal dimethylamino groups, the carbonyl units of 1-aryl-3-(dimethylamino)prop-2-en-1-ones are excellent proton acceptors. Intra- and intermolecular hydrogen bonds formed by these species were investigated by structural techniques (X-ray and neutron diffraction), spectroscopy, and density functional calculations. Co-crystallization of a derivative bearing three (dimethylamino)prop-2-en-1-one units attached at one center in the presence of different proton donors produced one- and two-dimensional H-bridged polymers. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200390086

FULL PAPER
1-Aryl-3-(dimethylamino)propenones: Strong Proton Acceptors for
Hydrogen Bonds
Anna-Katharina Pleier,[a] Eberhardt Herdtweck,[b] Sax A. Mason,[c] and Werner R. Thiel*[a]
Keywords: Aminopropenones / Density functional calculations / Hydrogen bonds / Self-assembly
Because of the electron-donating effects of their terminal di-
methylamino groups, the carbonyl units of 1-aryl-3-(di-
methylamino)prop-2-en-1-ones are excellent proton ac-
ceptors. Intra- and intermolecular hydrogen bonds formed by
these species were investigated by structural techniques (X-
tional calculations. Co-crystallization of a derivative bearing
three (dimethylamino)prop-2-en-1-one units attached at one
center in the presence of different proton donors produced
one- and two-dimensional H-bridged polymers.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ray and neutron diffraction), spectroscopy, and density func- Germany, 2003)
Introduction
counterpart, a 3-aminoprop-2-enone, changes the situation
completely. Whenever the nitrogen atom bears a proton, an
intramolecular hydrogen bond will be favored, due to the
formation of a stable six-membered ring (Scheme 1). Con-
sequently, intermolecular hydrogen bonds are disfavored.
Intermolecular interactions such as hydrogen bonding,
Lewis acid/base interactions, or aromatic π-stacking have
for a long time attracted the attention of researchers in
chemistry, biology, and materials sciences. Hydrogen bonds
in particular have been found to be of fundamental relev-
ance for the world we are living in. Starting from small
molecules such as water[1] and extending to large biopoly-
mers such as proteins[2] or DNA,[3] the chemical and phys-
ical properties of our environment are determined by hydro-
gen bonding. During the last few years, increasing efforts
have been made to gain better understanding of these phe-
nomena. An excellent review of hydrogen bonding in the
solid state was recently published by Steiner.[4]
Scheme 1
Use of the 3-aminoprop-2-enone fragment for the forma-
tion of intermolecular hydrogen bonds requires substitution
of the NH proton(s) by, for example, alkyl groups, which
obviously kills the proton donor site but on the other hand
enhances the proton-accepting properties of the carbonyl
function through the σ-donating effect of the alkyl groups.
In this paper we present a study on the proton-bonding
properties of 1-aryl-3-(dimethylamino)prop-2-en-1-ones
and their application for the formation of polymeric struc-
tures built up by hydrogen bonds.
The secondary structures of proteins are governed mainly
by the hydrogen-bonding properties of the amide units
[ϪC(O)ϪN(H)Ϫ], the oxygen atom of the carbonyl group
acting as a proton acceptor and the NH fragment as a pro-
ton donor. In this special case, the capability to form hydro-
gen bonds is enhanced by a cooperative effect, best de-
scribed by a second mesomeric form carrying charges at
both the oxygen (negatively polarized) and the nitrogen
atom (positively polarized). Owing to their importance for
the structural and functional features of proteins, the amide
group and its hydrogen bonds have long been a matter of
investigation. Switching from an amide to its vinylogue
Results and Discussion
[a]
Institut für Chemie, TU Chemnitz,
Straße der Nationen 62, 09111 Chemnitz, Germany
E-mail: werner.thiel@chemie.tu-chemnitz.de
Aromatic 3-(dimethylamino)prop-2-en-1-ones can be ob-
tained in high yields by heating the appropriate aromatic
acyl derivatives with N,N-dimethylformamide diethyl or di-
methyl acetals.[5] The reaction is best performed in a pres-
sure tube with microwave heating.[5b] Carrying out this pro-
cedure with 2-hydroxyacetophenone (1) as the starting mat-
[b]
Anorganisch-chemisches Institut, TU München,
Lichtenbergstr. 4, 85747 Garching, Germany
E-mail: eberhardt.herdtweck@ch.tum.de
[c]
Institute Max von Laue Ϫ Paul Langevin,
38042 Grenoble Cedex 9, France
E-mail: mason@ill.fr
Eur. J. Org. Chem. 2003, 499Ϫ506  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/03/0203Ϫ0499 $ 20.00ϩ.50/0
499

A.-K. Pleier, E. Herdtweck, S. A. Mason, W. R. Thiel
FULL PAPER
erial gives 1-(2-hydroxyphenyl)-3-(dimethylamino)prop-2- the solid state as obtained from neutron diffraction data
en-1-one (2, Scheme 2).
and a selection of characteristic bond lengths and angles.
Neither neutron nor X-ray diffraction experiments at dif-
ferent temperatures showed any significant temperature-de-
pendent changes of the structural parameters for the atoms
involved in hydrogen bonding.[6]
The molecules are packed in the unit cell by additional
weak interactions between O1 and the hydrogen atoms of
two CϪH units of a neighboring molecule [H···O distances:
C5aϪH51a···O1 2.405(3) and C8aϪH81a···O1 2.387(2)
A]. With these interactions, the solid-state structure of 2
can be described as an arrangement of parallel chains (Fig-
ure 2), within which the components are linked by CϪH···O
hydrogen interactions.
Scheme 2
The intense yellow compound 2 can be recrystallized
from ethyl acetate, whereupon single crystalline needles of
more than 1 cm length are formed. Initial investigation by
X-ray diffraction[6] showed a relatively short distance be-
tween the proton of the aromatic OH group and the neigh-
boring oxygen atom of the oxo function, indicating a strong
intramolecular hydrogen bond. This is due to the electron-
donating effect of the 3-(dimethylamino) group, which in-
creases the electron density at the carbonyl oxygen atom
according to the mesomeric form B (Scheme 3). For β-di-
oxo enols, equilibria between structures A and their tauto-
mers C are usually observed, though this should play a mi-
nor role in our case, since it would destroy the aromaticity
of the benzene ring.
[8]
˚
Figure 2. PLUTON[9] plot of the solid-state structure of 2, showing
the formation of parallel chains by CϪH···O hydrogen bonds
Scheme 3
Further structural investigation of 2 by neutron diffrac-
tion, by which hydrogen positions can be elucidated with
Up to now, only a handful of solid-state structures of 1-
much higher accuracy than with X-ray diffraction, con- aryl-3-(dimethylamino)prop-2-en-1-ones has been charac-
˚
firmed a long O1ϪH bond [1.032(3) A], a very short H···O2 terized by X-ray diffraction, and none by neutron diffrac-
distance [1.500(3) A], and a small C1ϪO1ϪH angle of tion.[5b,10] In all cases, hydrogen bonds between the car-
˚
103.1(2)°. Figure 1 shows the molecular structure of 2 in bonyl oxygen atom (acceptor) and sp3 or sp2 CϪH moieties
Figure 1. ORTEP[7] plot of the molecular structure of 2 in the solid state (from neutron diffraction); thermal ellipsoids are at the 90%
˚
probability level; selected bond lengths [A] and angles [°]: O1ϪC1 1.346(2), O2ϪC7 1.273(2), O1ϪH1 1.032(3), O2···H1 1.500(3), O1···O2
2.474(2), C1ϪC2 1.406(2), C1ϪC6 1.420(2), C2ϪC3 1.390(2), C3ϪC4 1.403(2), C4ϪC5 1.390(2), C5ϪC6 1.411(1), C6ϪC7 1.486(2),
C7ϪC8 1.428(2), C8ϪC9 1.384(2), NϪC9 1.326(1), NϪC10 1.458(1), NϪC11 1.458(1); C1ϪO1ϪH1 103.1(2), O1ϪH1···O2 154.9(2)
500
Eur. J. Org. Chem. 2003, 499Ϫ506

1-Aryl-3-(dimethylamino)propenones: Strong Proton Acceptors for Hydrogen Bonds
FULL PAPER
resulted in the formation of one-, two-, or three-dimen- O2 and H is promoted by the electron-donating effect of
sional networks. The dominating influence of the electron- the dimethylamino group, as depicted in Scheme 3, increas-
donating amino group on the distances in the OϭCϪCϭ ing the negative charge at O2 (and even at O1). This results
CϪN chain of 2 and related compounds becomes clear on in a moderate elongation of the O1ϪH distance and a pro-
comparison with 1-phenyl-3-[acetyl(phenyl)amino]prop-2- nounced shrinkage of the distance between O2 and H (relat-
en-1-one.[10a] Owing to its electron-withdrawing acetyl ive to compound 1). However, the OϪH distances obtained
group, the evidence of mesomeric structure B (Scheme 3) is from the neutron diffraction structure of 2 are not com-
reduced for this compound, as revealed by a pronounced pletely reproducible by quantum chemical calculations. This
shortening of the OϭC and the CϭC bonds and an elonga- might be due to the packing in the crystal, where the O1ϪH
tion of the CϪC and the CϪN bonds [OϭC: 1.228/ bond is weakened by the cooperative effects of two further
1.273(2), CϪC: 1.474/1.428(2), CϭC: 1.327/1.384(2), hydrogen bonds between O1 and the hydrogen atoms of two
CϪN: 1.392/1.326(1); data for 2 in italics]. Only one com- CϪH units of a neighboring molecule as described above.
pound {4-hydroxy-6-methyl-3-[3-(dimethylamino)acryloyl]-
Additionally, the 3-(dimethylamino)prop-2-en-1-ones 2
2H-pyran-2-one} forming an intramolecular OϪH···OϭC and 2a each show an increase in the charge at the carbonyl
hydrogen bond as in 2 has so far been reported.[10b] How- oxygen atom, of about 10% relative to 1 and 1a. This, and
ever, the exact position of the OH proton could not be loc- the strong intramolecular hydrogen bond found in com-
alized in this case, precluding any detailed discussion of the pound 2, stimulated further investigations of the proton ac-
hydrogen bond.
ceptor potential of other aromatic 3-(dimethylamino)prop-
To gain a deeper insight into the electronic situation of 2-en-1-ones. For this purpose we carried out quantum
the charge distribution in such compounds, we carried out chemical calculations on the hydrogen-bonded complexes
quantum chemical calculations on 2, 1-phenyl-3-(dimethyl- of 1-phenyl-3-(dimethylamino)prop-2-en-1-one (2a), aceto-
amino)prop-2-en-1-one (2a), 2-hydroxyacetophenone (1), phenone (1a), and N-methylbenzamide (1b) with water as
acetophenone (1a), and N-methylbenzamide (1b). Of a the proton donor (Scheme 4). The results are summarized
series of different methods (semiempirical, DFT, and ab in- in Table 2.
itio) and basis sets, the B3LYP method in combination with
a 6-311ϩG** basis set best reproduced the structural fea-
tures of 2.[11] The results are presented in Table 1, with the
atom numbering according to Figure 1.
The results of the calculations are in agreement with the
special situation in 2, in which the hydrogen bond between
Table 1. Data from quantum chemical calculations for 2, 1-phenyl-
Scheme 4
3-(dimethylamino)prop-2-en-1-one (2a), 2-hydroxyacetophenone
(1), and acetophenone (1a)
Table 2. Data from quantum chemical calculations for the water
adducts of 1-phenyl-3-(dimethylamino)prop-2-en-1-one (2a), aceto-
phenone (1a), and N-methylbenzamide (1b)
2[a]
2a
1
1a
˚
Calcd. bond lengths [A]
2a·H2O
1a·H2O
1b·H2O
O1ϪH
O2···H
O1ϪC1
O2ϪC7
C6ϪC7
C7ϪC8
C8ϪC9
C9ϪN
0.996, 1.032(3)
1.614, 1.500(3)
1.339, 1.346(2)
1.254, 1.273(2)
1.486, 1.486(2)
1.451, 1.428(2)
1.365, 1.384(2)
1.349, 1.326(1)
Ϫ
Ϫ
Ϫ
0.988
1.686
1.339
1.236
1.472
1.513
Ϫ
Ϫ
Ϫ
Ϫ
1.217
1.502
1.518
Ϫ
∆HR [kcal·molϪ1 [a]
]
1.232
1.509
1.461
1.363
1.352
Bond angles [°]
Ϫ
Ϫ
Ϫ7.45
Ϫ4.74
Ϫ5.57
˚
Calcd. bond lengths [A]
CϭO1[b]
O1···H1
1.242, 1.232
1.817
0.979
1.223, 1.217
1.905
0.973
1.231, 1.224
1.874
0.974
0.961
Ϫ
Ϫ
H1ϪO2[c]
H2ϪO2[c]
0.961
0.961
C1ϪO1ϪH1
O1ϪH1···O2
105.9, 103.1(2)
149.3, 154.9(2)
107.0
146.8
Ϫ
Ϫ
Calcd. stretching frequencies [cmϪ1 [d]
]
ν(CϭO)[b]
1687, 1698
1725, 1746
3648
3893
1703, 1723
3638
3892
Mulliken charges
νsym(OϪH)[e] 3539
νasym(OϪH)[e] 3893
H
ϩ0.337
Ϫ0.337
Ϫ0.342
Ϫ0.405
ϩ2.446
Ϫ1.267
ϩ0.063
ϩ0.276
Ϫ0.018
Ϫ
ϩ0.319
Ϫ
Ϫ
O1
O2
C1
C6
C7
C8
C9
N
Ϫ
Ϫ0.289
Ϫ0.325
Ϫ0.647
ϩ1.785
Ϫ0.075
Ϫ0.484
Ϫ
Mulliken charges
Ϫ0.297
ϩ0.229
ϩ1.783
Ϫ1.246
ϩ0.092
Ϫ0.077
ϩ0.011
Ϫ0.265 CϭO[b]
ϩ0.287 CϭO[b]
ϩ1.214 H2O[f]
Ϫ0.218 H1ϪOϪH2
Ϫ0.483 H1ϪO-H2
Ϫ
Ϫ1.222, Ϫ1.246 Ϫ0.530, Ϫ0.218 Ϫ0.517, Ϫ0.427
Ϫ0.331, Ϫ0.297 Ϫ0.256, Ϫ0.265 Ϫ0.387, Ϫ0.345
Ϫ0.597
0.328
Ϫ0.542
0.275
0.247
Ϫ0.599
0.353
0.248
0.259
Ϫ
Ϫ
[a] For the reaction: A ϩ H2O Ǟ A···H2O (A ϭ acceptor) at 298 K.
[
b
]
[
c
]
Dipole moments [D]
5.318 3.494
In italics: values of pure compounds 2a, 1a, 1b. Calcd. bond
[d] [e]
˚
6.890
3.248
length in water: 0.962 A.
Without scaling.
Calcd. stretching
frequencies of water: νsym(OϪH) ϭ 3816 cmϪ1, νasym(OϪH) ϭ
[a]
[f]
Bond lengths and angles from neutron diffraction in italics.
3921 cmϪ1
.
Calcd. charges of water: H2O Ϫ0.506, H2O ϩ0.253.
Eur. J. Org. Chem. 2003, 499Ϫ506
501

A.-K. Pleier, E. Herdtweck, S. A. Mason, W. R. Thiel
FULL PAPER
The strength of the hydrogen bond increases in the order
1a Ͻ 1b Ͻ 2a, which is confirmed by the thermodynamic
data, the CϭO and OϪH stretching frequencies, and the
O···H distance. Additionally, there is an almost linear cor-
relation between ∆HR and the CϭO distances of the proton
acceptors, which might be usable in future for estimation of
the proton-binding properties of unknown carbonyl com-
pounds. In this context, it should not be forgotten that we
are discussing calculations of isolated compounds/com-
plexes in the gas phase, in which solvent or solid-state ef-
fects are excluded. Nevertheless, 1-aryl-3-(dimethylamino)-
propenones such as 2a seem to be better proton acceptors
than arylcarboxamides such as 1b, the aromatic model com-
pounds for peptide bonds.
With these results in mind we investigated the proton ac-
ceptor potential of 1,3,5-tris[3-(dimethylamino)-1-oxoprop-
2-enyl]benzene (3),[5b] which was expected to form hydrogen
bonds with one, two, or three of its 3-(dimethylaminoprop)-
2-en-1-one side chains. Depending on the nature of the pro-
ton donor used, this should give access to one- and two-
dimensional supramolecular structures. Hydrogen-bonded
polymers formed with 3 as the proton acceptor and para-
hydroquinone (4), 4,4Ј-dihydroxybiphenyl (5), and water (6)
are discussed below.
Figure 3. Hydrogen-bonded chains in the solid-state structure of 7
and packing of the chains (PLUTON[9] plot); all hydrogen atoms
not involved in hydrogen bonds are omitted for clarity; selected
˚
bond lengths [A]: O1ϪC11 1.252(2), O2ϪC21 1.243(2), O3ϪC31
1.252(2), O4ϪH41 0.94(2), O5ϪH51 0.93(2), O1···H51 1.75(2),
O3···H41 1.75(2), O1···O5 2.676(2), O3···O4 2.685(2)
Treatment of 4 or 5 with 3 in different molar ratios (from
5:1 to 1:2) exclusively affords the chain-type arrangements
7 and 8, with alternating proton donor and acceptor molec-
ules (Scheme 5). Figures 3 and 4 show the molecular struc-
tures of 7 and 8 in the solid state.
Figure 4. Hydrogen-bonded chains in the solid-state structure of 8
(PLUTON[9] plot); all hydrogen atoms not involved in hydrogen
˚
bonds are omitted for clarity; selected bond lengths [A]: O1ϪC11
1.254(2), O2ϪC21 1.236(2), O3ϪC31 1.255(2), O4ϪH41 0.96(3),
O5ϪH51 0.99(3), O1···H51 1.70(3), O3···H41 1.80(3), O1···O5
2.692(2), O3···O4 2.761(2)
is a little more complicated. In 7, two such chains, oriented
parallel to the diagonal of the ac plane of the unit cell, form
a zigzag arrangement. The resulting double chains are then
packed into planes. The polymer chains in 8 do not cross
each other, but form double layers parallel to the bc plane
of the unit cell. Here, the phenyl rings of the 4,4Ј-dihydroxy-
biphenyl units are twisted by 60°. In all cases, hydrogen
bonding increases the weight of the zwitterionic mesomeric
structure B (Scheme 3), which increases the bond lengths
O1ϪC11 and O3ϪC31 relative to O2ϪC21. The formation
of hydrogen bonds is expressed by a slight shift of the
CϭO stretching frequency of the proton acceptor to lower
energies and by a pronounced shift of the OϪH stretching
frequencies of the proton donors {KBr; νOϪH ϭ 3152 (7);
Scheme 5
Generally, the polymeric structures of 7 and 8 are pro- 3203 [hydroquinone (4)]; 3225, 3134 (8); 3384 cmϪ1 [4,4Ј-
duced by hydrogen bonding between two of the three car- dihydroxybiphenyl (5)]}.
bonyl oxygen atoms (O1, O3) of 3 and the two OH protons
To decrease the steric demand of the proton donor, water
of hydroquinone (4) and 4,4Ј-dihydroxybiphenyl (5), re- (6) was added. Crystallization of 3 from wet acetone results
spectively. When examined carefully, however, the situation in the two-dimensional hydrogen-bonded arrangement 9, in
502
Eur. J. Org. Chem. 2003, 499Ϫ506

1-Aryl-3-(dimethylamino)propenones: Strong Proton Acceptors for Hydrogen Bonds
FULL PAPER
which all three 3-(dimethylamino)prop-2-en-1-one side species. For data acquisition, 3 was dissolved in THF con-
chains are involved in hydrogen bonding (Figure 5).
taining a mixture of NaSCN and KSCN. The formation of
three 1:1 adducts was observed [m/z (obsd./calcd.)]: [3 ϩ
Hϩ] (370.253/370.216), [3 ϩ Naϩ] (392.236/392.195), and [3
ϩ Kϩ] (408.210/408.169). The signals of a whole series of
species containing more than one molecule of 3 in combina-
tion with one cation (charge ϩ1) can be assigned: [(3)2 ϩ
Hϩ] (739.515/739.418), [(3)2 ϩ Naϩ] (761.501/761.400),
[(3)2 ϩ Kϩ] (777.481/777.374), [(3)3 ϩ Naϩ] (1030.765/
1130.605), and [(3)4 ϩ Naϩ] (1500.001/1499.811). In addi-
tion, low-intensity signals corresponding to dications of the
type [(3)5 ϩ (Eϩ)2] were detectable.
Conclusion
In this paper we have demonstrated that the carbonyl
group of 1-aryl-3-(dimethylamino)prop-2-en-1-ones is a
strong proton acceptor, a feature that can be used to build
up hydrogen-bonded polymers. This is due to the π-donat-
ing effect of the dimethylamino group, which increases the
electron density (basicity) of the carbonyl oxygen atom, as
has been shown by quantum chemical calculations. Since
aromatic acyl compounds are easily available by standard
Figure 5. Hydrogen-bonded, two-dimensional polymeric structure
of 9 (PLUTON[9] plot), including the disordering of two water mo-
lecules; all hydrogen atoms not involved in hydrogen bonds are
˚
omitted for clarity; selected bond lengths [A]: O1ϪC11 1.259(2), organic synthesis techniques, a broad range of 1-aryl-3-(di-
O2ϪC21 1.246(2), O3ϪC31 1.242(2), O4ϪH1 0.91(2), H1···O1
1.92(2), O4···O1 2.826(2), O4ϪH2 0.94(2), H2···O3 1.85(2),
O4···O3 2.790(2), O5ϪH3 0.87(3), H3···O2 1.88(3), O5···O2
2.751(2), O5ϪH4A 0.93(5), H4A···O6 1.89(5), O5···O6 2.811(2),
O5ϪH4B 0.85(5), H4B···O5Ј 1.92(4), O5···O5Ј 2.759(2), O6ϪH5
0.85(3), H5···O1 1.97(3), O6···O1 2.808(2), O6ϪH6A 0.83(6),
H6A···O5 1.99(6)
methylamino)prop-2-en-1-ones bearing different types of
arene groups are accessible. This may include dyes, electron-
transferring groups such as ferrocene, or (transition)metal
coordination complexes, and opens up the door to new hy-
drogen-bonded materials with interesting electronic or spec-
troscopic properties.
The two-dimensional hydrogen-bonded polymeric struc-
ture in 9, in which the planes are oriented parallel to the bc
plane of the unit cell, is formed by the interaction of three
molecules of water with the three carbonyl oxygen atoms
O1, O2, and O3. Several different types of hydrogen bonds
are observed: while one water molecule (O4) acts as a pro-
ton-donating bridge between the carbonyl oxygen atoms O1
and O3, two further molecules of water (O5 and O6) build
up a chain of four water molecules around a crystallo-
graphic center of inversion, bridging the proton acceptors
O1, O2 and O1Ј, O2Ј (due to crystal symmetry). This im-
plies a disordering of the water molecules as depicted in
Scheme 6.
Experimental Section
General Information: The syntheses of compounds 2 and 3 are de-
scribed elsewhere,[5b] hydroquinone (4) and 4,4Ј-dihydroxybiphenyl
(5) are commercially available. The mass (Applied Biosystems Mar-
iner System 5229), and infrared spectra (PerkinϪElmer FT-IR
1000), as well as the elemental analyses were carried out at the
Institut für Chemie of the Technische Universität Chemnitz.
Quantum chemical calculations were performed with the program
Gaussian98W,[12] with the B3LYP gradient-corrected exchange-cor-
relation functional[13] in combination with the 6-311ϩG** basis
set.[14] Full geometry optimizations were carried out in C1 sym-
metry by using analytical gradient techniques and the resulting
structures were confirmed to be true minima by diagonalization of
the analytical Hessian matrix.
1,3,5-Tris[3-(dimethylamino)-1-oxoprop-2-enyl]benzene؊Hydro-
quinone and ؊4,4Ј-Dihydroxybiphenyl Adducts (7 and 8): 1,3,5-
Tris[3-(dimethylamino)-1-oxoprop-2-enyl]benzene
(3,
0.37 g,
1.00 mmol) was dissolved in CHCl3 (15 mL). This solution was
layered with a solution of 1 equiv. of the appropriate dihydroxy
species (4: 0.11 g; 5: 0.19 g), dissolved in 10 mL of acetone. Crystals
formed by slow diffusion within a few days. Analytical data for 7:
Yield: 0.48 g (quant.), orange crystals. M.p. 220 °C. IR (KBr): see
text. MS (ESI): see text. C27H33N3O5 (479.8): calcd. C 62.62, H
6.94, N 8.76; found C 67.32, H 7.10, N 8.67. Analytical data for 8:
Scheme 6
Mass spectrometric investigations (ESI-TOF) on com-
pound 3 confirmed its tendency to bind positively charged Yield: 0.56 g (quant.), orange crystals. M. p. 206 °C. IR (KBr): see
Eur. J. Org. Chem. 2003, 499Ϫ506 503

A.-K. Pleier, E. Herdtweck, S. A. Mason, W. R. Thiel
text. MS (ESI): see text. C33H37N3O5 (555.7): calcd. C 71.33, H All calculations were performed with a DEC 3000 AXP workst-
FULL PAPER
6.71, N 7.56; found C 77.11, H 6.62, N 7.06.
ation and an Intel Pentium II PC with the STRUX-V[23] system
including the programs PLATON,[7] SIR92,[21] and SHELXL-
97.[17] Details of the crystal data, intensity collection data and re-
finement parameters are given in Table 3. All hydrogen atoms were
found in the difference Fourier maps and refined with individual
isotropic thermal displacement parameters. Structure plots were
generated by PLATON[7] and PLUTON.[9]
1,3,5-Tris[3-(dimethylamino)-1-oxoprop-2-enyl]benzene Trihydrate
(9): 1,3,5-Tris[3-(dimethylamino)-1-oxoprop-2-enyl]benzene (3,
0.37 g, 1.00 mmol) was dissolved in acetone (15 mL), containing
5% water. This solution was left to concentrate slowly under ambi-
ent conditions, whereupon deep orange crystals were obtained.
Yield: 0.42 g (quant.). M.p. 103 °C (dec.), 249 °C. IR (KBr): ν˜ ϭ
3395 m, 3139 m, 1636 vs, 1594 vs, 1532 vs, 1495 s, 1411 vs, 1359
m, 1272 vs, 1227 m, 1195 m, 1145 s, 1117 m, 1086 m, 692 cmϪ1 m.
MS (ESI): see text. C21H33N3O6 (423.5): calcd. C 59.56, H 7.85, N
9.92; found C 59.54, H 8.00, N 9.81.
Data Collection and Refinement for 7: Intensity data were collected
at 173 K. Preliminary examination and data collection were carried
out with a kappa-CCD device (NONIUS MACH3) at the window
of a rotating anode (NONIUS FR591) with graphite-monochrom-
˚
ated Mo-Kα radiation (λ ϭ 0.71073 A). Data were corrected for
Single-Crystal Neutron Diffraction Study on 2: A single crystal suit-
able for the neutron diffraction study was grown at room temper-
ature from a solution of 2 in ethyl acetate. A well-formed, yellow
prism (3.6 ϫ 3.5 ϫ 1.8 mm) of the compound was fixed with a
two-component glue (Kwikfill) on a vanadium pin and then
mounted on the Eulerian cradle of the thermal neutron four-circle
diffractometer D19, equipped with a 2-stage Displex cryorefriger-
ator[15] and a 64° ϫ 4° position-sensitive detector.[16] A Ge(115)
monochromator in reflection geometry was used to select a neutron
Lorentz and polarization effects. Potential absorption effects and
decay of the crystal were corrected during the scaling procedure.[24]
Data collection was performed within the Θ range of 1.65° Ͻ Θ Ͻ
25.64° with an exposure time of 50 s per image (6 sets, 368 images,
∆ϕ/∆Ω ϭ 1.0°). A total of 11656 reflections were integrated. After
merging, a sum of 4684 independent reflections remained and were
used for all calculations. All non-hydrogen atoms were refined an-
isotropically.
Data Collection and Refinement for 8: The intensity data were col-
lected at 223 K. Preliminary examination and data collection were
carried out with an imaging plate diffraction system (IPDS; Stoe &
Cie.) at the window of a rotating anode (NONIUS FR591) with
˚
beam of wavelength 1.308 A. After indexing of three reflections at
room temperature, the sample was slowly cooled (2 K/min) to 20 K,
while a strong reflection was monitored. No splitting or change in
mosaicity of the peak was observed. Intensity data [θmax ϭ 58.92°,
h (Ϫ11/11),k (Ϫ12/13),l (Ϫ14/7)] were measured by ω-scans in
equatorial mode with a scan width between 2.4 and 3.2° and a
measuring time of about 2.8 s per step (7500 monitor counts/point,
31 points). Three strong reflections were monitored regularly
through the whole measurement and showed no significant vari-
ation. In addition, two ψ-scans clearly indicated that absorption
(µ ϭ 0.261 mmϪ1) and also extinction effects [ε ϭ 0.070(2)][17] had
to be accounted for in the final refinement. In all, 3137 reflections
were collected and integrated in three dimensions by use of the ILL
program Retreat.[18] The final unit cell parameters a ϭ 8.8807(2),
˚
graphite-monochromated Mo-Kα radiation (λ ϭ 0.71073 A). Data
were corrected for Lorentz and polarization effects.[25] No correc-
tions for decay and absorption effects were applied. Data collection
was performed within the Θ range of 2.10° Ͻ Θ Ͻ 25.72° with an
exposure time of 900 s per image (oscillation scan mode from ϕ ϭ
0° to 360° with ∆ϕ ϭ 2.0°). A total of 20191 reflections were col-
lected. After merging, a sum of 5181 independent reflections re-
mained and were used for all calculations. All non-hydrogen atoms
were refined anisotropically. Disorder of the hydrogen atoms of two
methyl groups (C15: two positions, 70:30; C25: two positions,
51:49) could be resolved clearly.
˚
b ϭ 10.0998(2), c ϭ 11.4354(2) A, β ϭ 109.6879(12)° were deter-
Data Collection and Refinement for 9: Intensity data were collected
at 173 K. Preliminary examination and data collection were carried
out with a kappa-CCD device (NONIUS MACH3) at the window
of a rotating anode (N FR591) with graphite-monochrom-
mined by use of the ILL program RAFD19. The data were cor-
rected for absorption by using ψ-scan data.[19] After merging, with
the program SHELXL-97,[17]
a sum of 2225 independent
reflections remained (Rint ϭ 0.0412) and were used for a full-mat-
rix, least-squares refinement by minimization of Σw(F2o Ϫ Fc2)2 with
a SHELXL-97 weighting scheme. The initial atomic coordinates
for the ‘‘heavy atoms’’ were taken from the X-ray structure deter-
mination and the neutron scattering lengths were taken as bc(C) ϭ
6.646, bc(H) ϭ Ϫ3.739, bc(N) ϭ 9.36, bc(O) ϭ 5.803 fm.[20] During
the refinement, difference Fourier maps clearly revealed all of the
hydrogen atom positions. All atoms of the asymmetric unit were
˚
ated Mo-Kα radiation (λ ϭ 0.71073 A). Data were corrected for
Lorentz and polarization effects. Potential absorption effects and
decay of the crystal were corrected during the scaling procedure.[24]
Data collection was performed within the Θ range of 2.13° Ͻ Θ Ͻ
25.67° with an exposure time of 20 s per image (8 sets, 535 images,
∆ϕ/∆Ω ϭ 1.0°). A total of 12627 reflections were integrated. After
merging, a sum of 4030 independent reflections remained and were
used for all calculations. All non-hydrogen atoms were refined an-
isotropically. Disorder of the hydrogen atoms of two methyl groups
(C15: two positions, 50:50; C35: two positions, 50:50) could be re-
solved clearly. All three water molecules are involved in a two-di-
mensional hydrogen bonded network (see text). The hydrogen
atoms of two water molecules (O4: two positions, 50:50; O5: two
positions, 50:50) are disordered about a crystallographic center of
inversion. The well-resolved disorder is a superposition of the two
possible ‘‘homodromic’’ arrangements of the hydrogen bonds.[4]
refined anisotropically, giving a final R value of 0.0385 [R1, Io
Ͼ
2σ(Io)] and 0.0948 (wR2, all data), respectively (GOF ϭ 1.229).
Details of the crystal data, intensity collection data, and refinement
parameters are given in Table 3.
Single-Crystal X-Ray Structure Determinations. General Remarks:
The preparation of the single crystals is described above. Selected
crystals were coated with perfluorinated diethyl ether, fixed in a
capillary, transferred to the diffractometer, and cooled in a nitrogen
stream (Oxford Cryosystems). All structures were solved by a com-
bination of direct methods[21] and difference Fourier syntheses. CCDC-195156 (2؊100K),[6] -195150 (2؊150K),[6] -195154
Full-matrix, least-squares refinements were carried out by minim-
(2؊200K),[6] -195152 (2؊250K),[6] -195155 (2؊300K),[6] -195149
ization of Σw(F2o Ϫ Fc2)2 with SHELXL-97 weighting scheme and (2؊20K), -195153 (7), -195148 (8) and -195151 (9) contain the
stopped at shift/err Ͻ 0.001. Neutral atom scattering factors for all
atoms and anomalous dispersion corrections for the non-hydrogen
atoms were taken from International Tables for Crystallography.[22]
supplementary crystallographic data for this paper. These data can
be obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html or from the Cambridge Crystallographic Data Centre, 12
504
Eur. J. Org. Chem. 2003, 499Ϫ506

1-Aryl-3-(dimethylamino)propenones: Strong Proton Acceptors for Hydrogen Bonds
FULL PAPER
Table 3. Summary of the crystallographic data for compounds 2, 7, 8, and 9
2[a]
7
8
9
Empirical formula
Formula mass
Crystal system
Space group
C11H13NO2
191.23
C21H27N3O3, C6H6O2 C21H27N3O3, C12H10O2 C21H27N3O3, 3(H2O)
479.56
555.66
423.50
monoclinic
P21/n (no. 14)
8.8807(2)
10.0998(2)
11.4354(2)
90
109.6879(12)
90
965.72(3)
4
monoclinic
C2/c (no. 15)
24.2378(3)
14.4836(3)
14.7336(3)
90
105.512(1)
90
4983.8(2)
8
triclinic
triclinic
¯
¯
P1 (no. 2)
P1 (no. 2)
˚
a [A]
9.217(1)
11.838(2)
14.343(2)
99.16(2)
108.04(2)
92.20(2)
1462.6(4)
2
7.6206(2)
9.6569(2)
15.1088(4)
95.449(1)
92.491(2)
96.848(2)
1097.27(5)
2
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
3
˚
V [A ]
Z
ρcalcd. [g cmϪ3
]
1.315
0.261
20
1.278
0.089
1.262
0.085
1.282
0.094
µ [mmϪ1
Τ [K]
]
173
223
173
Reflections collected
3137
11656
20191
12627
Independent reflections [Io Ͼ 2σ(Io)/all data/Rint] 2176/2225/0.0412 4265/4684/0.0239
4076/5181/0.0392
5181/0/528
0.0366/0.0490
0.0940/0.1029
1.027
3401/4030/0.0217
4030/0/435
0.0397/0.0505
0.0934/0.0986
1.012
Data/restraints/parameter
R1 [Io Ͼ 2σ(Io)/all data]
wR2 [Io Ͼ 2σ(Io)/all data]
GOF
2225/0/245
0.0385/0.0399
0.0939/0.0948
1.229
4684/0/448
0.0379/0.0420
0.1037/0.1067
1.037
Weights a/b
∆ρmax/min [e·A
0.0422/4.8163
0.0579/2.8303
0.25/-0.19
0.0637/0.1266
0.20/-0.15
0.0407/0.3264
0.18/-0.18
Ϫ3
]
0.86/-0.94[b]
˚
[a]
Ϫ3
Neutron diffraction data. For X-ray experiments see ref.[6] [b] Unit: fm A
˚
individual isotropic displacement parameters. Full-matrix, le-
ast-squares refinements[17] were carried out by minimization of
Σw(F2o Ϫ w(F2c)2 and converged with shift/error Ͻ 0.001. a) T ϭ
Union Road, Cambridge CB2 1EZ, UK [Fax: (internat.) ϩ 44-
1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
˚
103 K: a ϭ 8.8928(3), b ϭ 10.1874(3), c ϭ 11.4130(4) A, β ϭ
Acknowledgments
We wish to thank the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for financial support and Dr.
Bjørn Pedersen (TU München), Peter Sirsch (TU München), and
Dr. Gerd Rheinwald (TU Chemnitz) for experimental help with X-
ray (B. P., P. S., G. R.) and neutron (B. P., P. S.) diffraction.
3
109.683(2)°, V ϭ 973.54(6) A ; ρcalcd. ϭ 1.305 g·cmϪ3, µ ϭ
˚
0.090 mmϪ1, R1 ϭ 0.0328 [Io Ͼ 2σ(Io)], wR2 ϭ 0.0910 (all
data), GOF ϭ 1.042. A total of 4244 reflections were collected
within the Θ range of 2.53°Ͻ Θ Ͻ 26.33°. After merging
(Rint
ϭ 0.0269), 1981 [1781: Io Ͼ 2σ(Io)] independent
reflections remained and all were used to refine 179 parameters.
b) T ϭ 153 K: a ϭ 8.9079(3), b ϭ 10.2644(4), c ϭ 11.4024(4)
3
A, β ϭ 109.619(2)°, V ϭ 982.05(6) A ; ρcalcd. ϭ 1.293 g·cmϪ3
,
˚
˚
µ ϭ 0.089 mmϪ1, R1 ϭ 0.0355 [Io Ͼ 2σ(Io)], wR2 ϭ 0.0978
(all data), GOF ϭ 1.052. A total of 4292 reflections were col-
lected within the Θ range of 2.53°Ͻ Θ Ͻ 26.39°. After merging
[1]
R. Ludwig, Angew. Chem. 2001, 113, 1856Ϫ1876; Angew.
Chem. Int. Ed. 2001, 40, 1808Ϫ1827.
[2] [2a]
L. Pauling, R. B. Corey, H. R. Branson, Proc. Natl. Acad.
[2b]
(Rint
ϭ 0.0275), 2001 [1781: Io Ͼ 2σ(Io)] independent
Sci. U.S.A. 1951, 37, 205Ϫ211.
G. Walsh, Proteins Ϫ Bio-
reflections remained and all were used to refine 179 parameters.
chemistry and Biotechnology, 2nd ed., John Wiley & Sons, New
York, 2001.
c) T ϭ 203 K: a ϭ 8.9236(3), b ϭ 10.3445(4), c ϭ 11.4081(4)
3
A, β ϭ 109.606(2)°, V ϭ 992.03(6) A ; ρcalcd. ϭ 1.280 g·cmϪ3
,
˚
˚
[3] [3a]
J. D. Watson, F. H. C. Crick, Nature 1953, 171, 737Ϫ738.
J. D. Watson, F. H. C. Crick, Nature 1953, 171, 964Ϫ967.
µ ϭ 0.088 mmϪ1, R1 ϭ 0.0385 [Io Ͼ 2σ(Io)], wR2 ϭ 0.1041
(all data), GOF ϭ 1.034. A total of 4336 reflections were col-
lected within the Θ range of 2.53°Ͻ Θ Ͻ 26.36°. After merging
[3b]
[3c]
F. H. C. Crick, J. D. Watson, Proc. R. Soc. 1954, A223,
[3d]
80Ϫ96.
K. Drlica, Understanding DNA and Gene Cloning,
(Rint
ϭ 0.0280), 2017 [1742: Io Ͼ 2σ(Io)] independent
3rd ed., John Wiley & Sons, New York, 2001.
T. Steiner, Angew. Chem. 2002, 114, 50Ϫ80; Angew. Chem. Int.
Ed. 2002, 41, 48Ϫ76.
[4]
reflections remained and all were used to refine 179 parameters.
d) T ϭ 253 K: a ϭ 8.9377(3), b ϭ 10.4253(4), c ϭ 11.4243(4)
3
A, β ϭ 109.639(2)°, V ϭ 1002.57(6) A ; ρcalcd. ϭ 1.267 g·cmϪ3
,
˚
˚
[5] [5a]
H. Brunner, T. Scheck, Chem. Ber. 1992, 125, 701Ϫ709. [5b]
µ ϭ 0.087 mmϪ1, R1 ϭ 0.0412 [Io Ͼ 2σ(Io)], wR2 ϭ 0.1154
(all data), GOF ϭ 1.042. A total of 4365 reflections were col-
lected within the Θ range of 2.52°Ͻ Θ Ͻ 26.35°. After merging
A.-K. Pleier, H. Glas, M. Grosche, P. Sirsch, W. Thiel, Syn-
thesis 2001, 55Ϫ62.
[6]
Temperature-dependent single-crystal X-ray structure analyses
of 2: C11H13NO2, Mr ϭ 191.23, monoclinic, space group P21/n,
F000 ϭ 408, Z ϭ 4. Preliminary examination and data collec-
tion were carried out with a kappa-CCD device (NONIUS
MACH3) at the window of a rotating anode (NONIUS
FR591) with graphite-monochromated Mo-Kα radiation (λ ϭ
(Rint
ϭ 0.0282), 2037 [1688: Io Ͼ 2σ(Io)] independent
reflections remained and all were used to refine 179 parameters.
e) T ϭ 303 K: a ϭ 8.9544(3), b ϭ 10.5148(4), c ϭ 11.4575(4)
3
A, β ϭ 109.706(2)°, V ϭ 1015.59(6) A ; ρcalcd. ϭ 1.251 g·cmϪ3
,
˚
˚
µ ϭ 0.086 mmϪ1, R1 ϭ 0.0437 [Io Ͼ 2σ(Io)], wR2 ϭ 0.1228
(all data), GOF ϭ 1.047. A total of 4457 reflections were col-
lected within the Θ range of 2.52°Ͻ Θ Ͻ 26.38°. After merging
˚
0.71073 A). The structure was solved by a combination of dir-
ect methods[21] and difference Fourier syntheses. All non-hy-
drogen atoms were refined anisotropically. All hydrogen atoms
were located in the difference Fourier maps and refined with
(Rint
ϭ 0.0299), 2074 [1614: Io Ͼ 2σ(Io)] independent
reflections remained and all were used to refine 179 parameters.
Eur. J. Org. Chem. 2003, 499Ϫ506
505

A.-K. Pleier, E. Herdtweck, S. A. Mason, W. R. Thiel
FULL PAPER
[7]
[14] [14a]
A. L. Spek, PLATON, A Multipurpose Crystallographic Tool,
R. Krishnan, J. S. Binkley, R. Seeger, J. A. Pople, J. Chem.
[14b]
Utrecht University, Utrecht, The Netherlands, 2000.
Phys. 1980, 72, 650Ϫ654.
T. Clark, J. Chandrasekhar, G.
[8]
The program PLATON[7] detects two further very weak
W. Spitznagel, P. v. R. Schleyer, J. Comput. Chem. 1983, 4,
˚
CϪH···O interactions: C10aϪH103a···O(2) 2.503(3) A and
294Ϫ301.
[15]
[16]
˚
C3bϪH31b···O2 2.530(3) A.
A. L. Spek, PLUTON, A program for plotting molecular and
J. Archer, M. S. Lehmann, J. Appl. Crystallogr. 1986, 19,
456Ϫ458.
[9]
crystal structures, University of Utrecht, The Netherlands,
1995.
M. Thomas, R. F. D. Stansfield, M. Berneron, A. Filhol, G.
Greenwood, J. Jacobe, D. Feltin, S. A. Mason, Position-Sensit-
ive Detection of Thermal Neutrons (Eds.: P. Convert, J. B. For-
syth), Academic Press, London, UK, 1983, p. 344ff.
G. M. Sheldrick, SHELXL-97, Universität Göttingen,
Göttingen, Germany, 1998.
C. Wilkinson, H. W. Khamis, R. F. D. Stansfield, G. J. McIn-
tyre, J. Appl. Crystallogr. 1988, 21, 471Ϫ478.
J. C. Matthewman, P. Thompson, P. J. Brown, J. Appl. Crys-
tallogr. 1982, 15, 167Ϫ173.
International Tables for Crystallography, vol. C (Ed.: A. J. C.
Wilson), Kluwer Academic Publishers, Dordrecht, 1992,
Table 4.4.4.1.
SIR92: A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagli-
ardi, M. C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr.
1994, 27, 435Ϫ436.
[10] [10a]
S. M. Aldoshin, L. O. Atovmyan, O. A. Dyachenko, V. I.
Minkin, V. A. Bren, G. D. Palai, Zh. Strukt. Khim. 1984, 25,
[10b]
[17]
[18]
[19]
[20]
131Ϫ132.
O. Carugo, C. B. Castellani, M. Rizzi, Polyhed-
[10c]
ron 1990, 9, 2061Ϫ2069.
E. Bejan, H. A. Haddou, J. C.
[10d]
Daran, G. G. A. Balavoine, Synthesis 1996, 1012Ϫ1018.
H. Karlsen, P. Kolsaker, C. Romming, E. Uggerud, Acta Chem.
Scand. 1998, 52, 391Ϫ398.
The mesomeric form B is slightly overestimated by the
quantum chemical calculations.
[11]
[12]
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.
A. Robb, J. R. Cheeseman, V. G. Zakrzewski, J. A. Montgom-
ery, Jr., R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Mil-
lam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J.
Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Po-
melli, C. Adamo, S. Clifford, J. Ochterski, G. A. Petersson, P.
Y. Ayala, Q. Cui, K. Morokuma, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. Cioslowski, J. V. Ortiz, B.
B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.
Gomperts, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham,
C. Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe,
P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, J. L. Andres,
C. Gonzalez, M. Head-Gordon, E. S. Replogle, J. A. Pople,
Gaussian 98, Revision A.3, Gaussian, Inc., Pittsburgh, 1998.
[21]
[22]
[23]
International Tables for Crystallography, vol. C (Ed.: A. J. C.
Wilson), Kluwer Academic Publishers, Dordrecht, 1992, Tables
6.1.1.4, 4.2.6.8, and 4.2.4.2.
G. Artus, W. Scherer, T. Priermeier, E. Herdtweck, STRUX-
V, A Program System to Handle X-ray Data, TU München,
München, Germany, 1997.
[24] [24a]
Data Collection Software for Nonius kappa-CCD devices,
Delft, The Netherlands, 1997. [24b]Z. Otwinowski, W. Minor,
Methods Enzymol. 1997, 276, 307.
IPDS Operating, System Version 2.8., Stoe & Cie. GmbH,
Darmstadt, Germany, 1997.
[13] [13a]
[25]
C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37,
[13b]
785Ϫ789.
A. D. Becke, Phys. Rev. 1988, A38, 3098Ϫ3100.
[13c]
B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys.
Received September 9, 2002
Lett. 1989, 157, 200Ϫ206.
[O02515]
506
Eur. J. Org. Chem. 2003, 499Ϫ506