Synthesis and structural analysis of 1,4-bis[n-(N,N-di-methylamino)phenyl]buta-1,3-diynes and charge-transfer complexes with TCNE

Article abstract of DOI:10.1002/poc.422

n-(N,N-Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between chloromethylene(triphenyl)phosphine ylide and the appropriate n-(N,N-dimethylamino)benzaldehyde, followed by dehydrochlorination with a strong base. The conjugate

Full text of DOI:10.1002/poc.422

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2001; 14: 859–868
DOI:10.1002/poc.422
Synthesis and structural analysis of 1,4-bis[n-ꢀN,N-di-
methylamino)phenyl]buta-1,3-diynes and charge-transfer
complexes with TCNE
J. Gonzalo RodrõÂguez,1* Antonio Lafuente,1 Rosa MartõÂn-Villamil1 and M. Paz MartõÂnez-Alcazar2
1Departamento de QuõÂmica Orga nica, Universidad Auto noma, Cantoblanco, 28049Madrid, Spain
2Departamento de Cristalogra®a, CSIC, Serrano 119, 28006 Madrid, Spain
Received 28 January 2001; revised 28 May 2001; accepted 7 June 2001
ABSTRACT: n-(N,N-Dimethylamino)phenylethynes were satisfactorily prepared by a Wittig reaction between
chloromethylene(triphenyl)phosphine ylide and the appropriate n-(N,N-dimethylamino)benzaldehyde, followed by
dehydrochlorination with a strong base. The conjugate dimers 1,4-bis[n-(N,N-dimethylamino)phenyl]buta-1,3-diyne
were obtained by oxidative dimerization with copper(I) chloride. X-ray molecular structure analysis of the dimer 1,4-
bis[2-(N,N-dimethylamino)phenyl]buta-1,3-diyne corroborated the resonance contribution of the o-dimethylamino
substituent, which was confirmed in the solid state by the molecular crystalline packing. Both o- and p-(N,N-
dimethylamino) conjugate dimers develop 1:1 charge-transfer complexes with TCNE and their structure was
identified by NMR, IR and UV–visible spectroscopic data. Differential scanning calorimetric analyses of the 1,3-
diynes showed an irreversible transformation to a thermopolymer as a unimolecular reaction. Copyright  2001 John
Wiley & Sons, Ltd.
KEYWORDS: 1,4-bis[n-(N,N-dimethylamino)phenyl]buta-1,3-diynes; TCNE; charge-transfer complexes; synthesis;
structural analysis
INTRODUCTION
diynes. This is because many of them are unreactive in
the solid state,4–6 although they do undergo liquid
crystal polymerization. Moreover, 4-aminophenyl-4-
nitrophenylbuta-1,3-diyne is solid-state reactive.6
The discovery of a one-dimensional metallic state in
the ion-radical solid formed from the p-donor tetra-
thiofulvalene and the acceptor tetracyanoquinodimethane
has stimulated interest in the structure–property relation-
ships of novel donors and acceptors.7 Although the
metallic conductivity and superconductivity of these
organic charge-transfer salts are the most important
properties, recently attention has also been directed to the
novel magnetic and optical properties which they can
display (review8).
Here we describe an efficient synthesis of o-, m- and
p-(N,N-dimethylamino)phenylacetylene units (3a–c),
the oxidative dimerization to 1,4-bis[n-(N,N-dimethyl-
amino)phenyl]buta-1,3-diynes (4a–c) and the synthesis
of charge-transfer complexes with acceptors, as well as
preliminary results concerning their conductive proper-
ties. The acetylene derivatives (3) were also obtained for
the synthesis of p-conjugated polyenes, and furthermore
serve for the synthesis of nanostructural molecules
containing these useful units (J. Gonzalo Rodr´ıguez et
al., in preparation).
The use of molecular organic materials as conductors and
in nonlinear optics is of considerable interest since such
materials have inherent synthetic flexibility which
permits the design of specific molecular properties.1
Solid-state polymerization of 1,3-diynes to form
crystalline conjugated polydiynes has attracted much
attention,1,2 often because of the large and fast non-linear
optical response of the latter, which suggests that they
can have potential applications.3 Although the electronic
and optical properties of poly-1,3-diynes are primarily
dominated by the p-conjugated backbone, the substituent
groups markedly influence both their topopolymerization
behaviour and physical and chemical properties. An
aspect of the substituent effect that has received little
attention is the influence of formally p-conjugated
substituents on the electronic properties of poly-1,3-
*Correspondence to: J. G. Rodr´ıguez, Departamento de Qu´ımica
Orga´nica, Universidad Auto´noma, Cantoblanco, 28049 Madrid, Spain.
E-mail: gonzalo.rodriguez@uam.es
Contract/grant sponsor: CICYT; Contract/grant number: PB97-0060.
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

´
860
J. G. RODRIGUEZ ET AL.
Scheme 1
Synthesis of 2-chloro-1-[2-ꢀN,N-dimethylamino)phe-
RESULTS AND DISCUSSION
nyl]ethene ꢀ2a). Compound 2a was prepared by the
Wittig reaction between chloromethylene(triphenyl)-
phosphine ylide and n-(N,N-dimethylamino)benzalde-
hyde in THF as a mixture of the E- and Z-isomers in
good yield.11
Synthesis of 1,4-bis[n-ꢀN,N-dimethylamino)phe-
nyl]buta-1,3-diynes, 4a±c ꢀn = 2, 3 and 4)
Good yields in the 2-chloroethenyl derivative were
obtained in all cases, as a mixture of the E- and Z-
isomers, which depends of the ylide stability, the solvent
and the base used for the preparation.12 Table 1 shows the
E/Z diastereoisomeric ratio of compounds 2a–c obtained
under the same reaction conditions (solvent and tem-
perature). For o- and p-(N,N-dimethylamino)benzalde-
hyde the Z-(2-chloroethenyl) form predominates whereas
for m-(N,N-dimethylamino)benzaldehyde the E-(2-
chloroethenyl) form predominates slightly in the mixture
of the two isomers.
Compounds 4a–c were synthesized from n-(N,N-di-
methylamino)benzaldehyde (1) and chloromethylene(tri-
phenyl)phosphine ylide to isolate the n-(2-chlorovinyl)-
N,N-dimethylaminobenzene (2) which, by dehydro-
chlorination with a strong base, gives the corresponding
n-(N,N-dimethylamino)phenylethyne (3) (Scheme 1).
Finally, the oxidative dimerization of 3 gives the 1,4-
bis[n-(N,N-dimethylamino)phenyl]buta-1,3-diyne (4) in
good yield.
Preparation of o- and m-ꢀN,N-dimethylamino)ben-
zaldehyde. The preparation of o-(N,N-dimethylamino)-
benzaldehyde was carried out from o-fluorobenzaldehyde
by nucleophilic substitution with dimethylamine in
dimethyl sulfoxide.9
Synthesis of n-ꢀN,N-dimethylamino)phenylethynes
ꢀ3a±c). Compounds 3a–c were prepared by dehydro-
chlorination of the corresponding 2-chloro-1-[n-
(N,N-dimethylamino)phenyl]ethene, by treatment with
n-butyllithium (>3 equiv.) at room temperature in good
yield.13,14 A one-step synthesis of 3c starting from 1c has
recently been described.15
The synthesis of m-(N,N-dimethylamino)benzalde-
hyde, was carried out from m-nitrobenzaldehyde, in a
modification of the Cocker method (Scheme 2).10 In this
way, m-nitrobenzaldehyde was first transformed into the
dimethyl acetal and then the nitro group was satisfac-
torily reduced to the amino group with sodium sulfide and
transformed into the N,N-dimethylamino derivative by
treatment with dimethyl sulfate in an aqueous solution of
sodium carbonate; the monomethyl derivative was iso-
lated in low yield and re-used in the methylation step.
The m-(N,N-dimethylamino)benzaldehyde was finally
obtained by hydrolysis of the acetal with dilute sulfuric
acid (Scheme 2).
Synthesis of 1,4-bis[n-ꢀN,N-dimethylamino)phenyl]-
buta-1,3-diynes ꢀ4a±c). The synthesis of the 1,3-diynes
4a–c was carried out by an oxidative homocoupling
reaction of the appropriate n-(N,N-dimethylamino)-
phenylethyne (3a–c), catalysed by copper(I) chloride in
pyridine at 40°C, in good yield. Compounds 4a–c were
isolated as crystalline yellow solids which are stable to
sunlight.
The 1,4-bis[n-(N,N-dimethylamino)phenyl]buta-1,3-
diynes (4a–c) were analysed by differential scanning
calorimetry (DSC). The diagrams show an endothermic
Table 1. Wittig reaction of 2a±c: Z/E chlorovinyl stereo-
isomer ratio
Isomer
Z (%)
E (%)
Yield (%)
2a ortho
2b meta
2c para
58
48
60
42
52
40
96
86
90
Scheme 2
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

1,4-BIS[n-(N,N-DIMETHYLAMINO)PHENYL]BUTA-1,3-DIYNES
861
Table 2. Arrhenius equation from the DSC broad exothermic peak for 4a±c
Compound
m.p. (°C)
Exo-range DH (J gÀ1
)
LnZ (sÀ1
)
Ea (kJ molÀ1
)
n
4a
4b
4c
53.8
173.2
244.0
276–329
241–302
260–313
À632.5
À510.4
À619.8
29.9(5)
20.8(2)
25.0(1)
167(2)
118(1)
139(5)
1.23(2)
0.96(1)
1.20(5)
peak corresponding to the melting of the compound
followed by an irreversible broad exothermic peak.
Analysis of the Arrhenius equation of the broad range
of the exothermic peak in the DSC diagram indicated an
irreversible and practically unimolecular reaction (Table
2). In the solid state, the 1,3-diynes transform, under the
effect of the temperature, into an insoluble black solid.
A single crystal of the 1,3-diyne 4a was exposed to Cu
Ka x-radiation and the diffracted reflections were
recovered for crystallographic structure analysis. The
crystal was stable to the radiation and no topopolymer-
ization of the diyne 4a was observed.
assembled through its respective opposed dipole
(CH3)2N → Ph (Fig. 2).
Charge-transfer complexes of 1,4-bis[n-ꢀN,N-di-
methylamino)phenyl]buta-1,3-diynes ꢀ4a±c) with
TCNE
Some linear conjugated systems are already known to
give charge-transfer complexes with the acceptor TCNQ
having conductive properties.17 Compounds 4a and 4c
also yield charge-transfer complexes with TCNQ (J.
Gonzalo Rodr´ıguez et al., in preparation). The p-donor
character of 1,4-bis[n-(N,N-dimethylamino)phenyl]buta-
1,3-diyne (4a and 4c) was evaluated by cyclic voltam-
metry in acetonitrile with lithium perchlorate, giving
oxidation potentials of 0.79 mV for the ortho- and
0.72 mV for the para-dimer compound, while TCNE
has a potential of 0.15 mV.18
Crystal structure of 1,4-bis[2-ꢀN,N-dimethyl-
amino)phenyl]buta-1,3-diyne ꢀ4a)
Some selected bond lengths and angles for the buta-1,3-
diyne 4a are given in Table 3 and a view of the molecule
with the numbering scheme is shown in Fig. 1.
The preparation of the molecular complex between
In contrast to the isomer 4c the molecule is not
centrosymmetric, but the bond lengths and angles are in
agreement with those found there.16 The bond distances
˚
in the benzene rings are in the range 1.36–1.42 A, the
shortest being C-21—C-22 = 1.357(6), C-14—C-15 =
˚
1.362(6) and C-20—C-21 = 1.372 (6) A.
Moreover, in this molecular structure C-11—C-1 =
1.424(4), C-17—C-4 = 1.421(4), C-2—C-3 = 1.379(4)
˚
and N-5—C-18 and N-8—C-12 = 1.399(4) A show im-
portant double bond character. The benzene rings are
˚
nearly planar, with a maximum deviation of 0.016 (3) A
and a dihedral angle between the two rings of 8.2 (1)°.
The diyne unit shows small deviations from linearity with
C-2—C-1—C-11 = 177.5 (4), C-3—C-4—C-17 = 176.1
(4) and C-2—C-3—C-4 = 178.0 (4)°.
actTiohnes mboetlweceuelnar NpMacek2inagndis —goCvꢀernCe—d btyhaptolgairveinrteisre-
Figure 1. Atomic numbering and the ellipsoids at 30%
probability for 4a
firstly to parallel layers to the ab plane which are
Table 3. Some bond lengths and angles for 4a
˚
˚
Bond length (A)
Bond length (A)
Bond angle (°)
N-5—C-18 1.399 (4)
N-5—C-7 1.452 (4)
N-5—C-6 1.447 (5)
N-8—C-12 1.399 (4)
N-8—C-10 1.452 (4)
N-8—C-9 1.450 (5)
C-1—C-2 1.204 (4)
C-1—C-11 1.424 (4)
C-2—C-3 1.379 (4)
C-3—C-4 1.179 (4)
C-4—C-17 1.421 (4)
C-2—C-1—C-11 177.5 (4)
C-1—C-2—C-3
C-4—C-3—C-2
178.4 (3)
178.0 (3)
C-3—C-4—C-17 176.1 (4)
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

´
J. G. RODRIGUEZ ET AL.
862
Table 4. 1H and 13C NMR data for 4a and 4a±TCNE complex
;ꢁ, ppm)
1,4-bis[2-(N,N-dimethylamino)phenyl]buta-1,3-diyne
(4a) and TCNE as the acceptor molecule was carried out
in a solution of acetonitrile. On the basis of the elemental
analysis and powder diffraction techniques, the ortho-
1,3-diyne 4a forms only a 1:1 molecular complex with
TCNE that was isolated as a dark-violet solid with a
strong, bright metallic appearance, which showed semi-
conductor properties. The electrical resistivity for 4c was
measured on compacted pellets by a standard four-probe
method under an argon atmosphere at room temperature,
4a–TCNE
4a–TCNE
Proton/carbon
4a
(complexed ring) (uncomplexed ring)
H-3
6.89
6.89
7.25
7.48
2.98
7.35
7.35
7.78
7.78
3.08
6.85
6.85
7.35
7.35
2.76
H-5
H-4
H-6
Me2N
C-1
C-2
C-3
C-4
C-5
C-6
113.2
112.7
112.1
the conductivity being ꢀ = 1.5 Â 10À5
ꢀ .
À1 cmÀ1
155.8
116.8
129.9
120.2
135.3
82.0
153.4
119.1
133.7
124.4
136.9
87.7
155.6
116.3
133.0
121.4
135.5
84.6
The DSC analysis of the molecular complex 4a–TCNE
exhibited a broad, irreversible exothermic peak at 178°C
but melting of the components was not detected.
On the basis of the elemental analysis and powder
diffraction results, the para-1,3-diyne 4c forms a 1:1
molecular complex with TCNE which was isolated as a
black solid with a strong, bright metallic appearance,
which showed conductor properties (as a pellet,
Ph—C
C—C
Me2N
ꢀ
ꢀ
79.4
43.6
92.2
44.5
84.4
43.5
ꢀ = 2.0 Â 10À2
ꢀ
À1 cmÀ1).
The DSC analysis of the molecular complex 4c–TCNE
showed a broad, irreversible exothermic peak at 203°C,
but melting of the components was not observed.
Structure of the 1,4-bis[2-ꢀN,N-dimethylamino)-
phenyl]buta-1,3-diyne±TCNE molecular complex
1
The H NMR spectrum of the 4a–TCNE complex in
solution of chloroform shows a general deshielding effect
on the protons of the TCNE complexed benzene ring
(Table 4). Thus, H-4 and H-6 appear at 7.78 ppm (7.25
and 7.48 ppm in the free diyne) as multiplets and H-3 and
H-5 at 7.35 ppm (6.89 ppm in the free diyne) as
multiplets. The deshielding effect for the uncomplexed
ring is more moderate; H-4 and H-6 appear at 7.35 and
H-3 and H-5 at 6.85 ppm. The methyl groups appear at
3.08 and 2.76 ppm as two singlets for the complexed and
uncomplexed rings, respectively (2.98 ppm as a singlet in
the free diyne).
The 13C NMR spectrum of the 4a–TCNE complex in a
solution of chloroform shows an important deshielding
effect for the carbons of the complexed ring. Thus, C-5
and C-4 appear at 124.4 and 133.7 ppm for the
complexed and at 121.4 and 133.0 ppm for the uncom-
plexed ring (120.2 and 129.9 ppm for the free diyne).
Moreover, a shielding effect was observed on C-2 and
C-1 (153.4 and 112.7 ppm and 155.6 and 112.1 ppm for
the complexed and uncomplexed rings, respectively
(155.8 and 113.2 ppm for the free diyne). This effect is
probably due to the resonance of the dimethylamino
group, which on the complexed ring has a deshielding
effect on the methyl substituents (44.5 ppm) whereas the
uncomplexed ring are practically unaffected (43.5 vs
43.6 ppm in the free diyne) (Table 4).
On the basis of the deshielding effect determined by
the difference in the carbon frequencies between the
complexed, uncomplexed and free diyne, the structure of
the charge-transfer complex 4a–TCNE can be defined as
an overlapping of the double bond of TCNE which is
closely parallel to the C-4—C-5 and C-3—C-6 bonds but
nearest to the former. The C-4—C-5 bond shows a
Figure 2. Packing of the molecules for 4a, showing the
intermolecular N,N-dimethyl contact
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

1,4-BIS[n-(N,N-DIMETHYLAMINO)PHENYL]BUTA-1,3-DIYNES
863
Scheme 4
Scheme 3
significant electron donor effect (important double bond
character) in the x-ray molecular structure of the free
diyne. Furthermore, in the 13C NMR spectrum, the TCNE
acceptor effect is higher than the donor effect of the
N,N-dimethylamino group, which was observed on the
6.75 ppm (meta and ortho to the N,N-dimethyl group,
respectively), as doublets in the complexed ring, and at
7.51 and 6.68 ppm, respectively, in uncomplexed ring
(7.40 and 6.63 ppm, respectively, in the free diyne)
(Table 5).
—C
87.7 ppm, respectively, for the complexed ring, but this
effect is of low intensity in the conjugate Ph—C C—
ꢀ
C—Ph bonds of the 1,3-diyne chain, 92.2 and
On the basis of the proton symmetry in the NMR
spectrum of the 4c–TCNE complex, and the deshielding
effect determined by the difference in the proton
frequencies between the complexed, uncomplexed and
free diyne, the structure of the charge-transfer complex
can be defined as a parallel molecular overlapping of the
double bond of TCNE on C-5—C-4 and C-3—C-6 bonds
on the diyne ring, forming an orthogonal angle with the
C-2—C-5 axis (Scheme 4).
ꢀ
bond that show these two carbon atoms at 84.6 and
84.4 ppm, respectively. The same effects were observed
1
by H NMR, despite the grouping of the H-4,H-6 and
H-3,H-5 signals (Scheme 3).
The IR spectrum of the 4a–TCNE complex shows the
C
ꢀ
N group at 2220 cmÀ1 as a unique peak, whereas in
À1; the
The IR spectrum of the 4c–TCNE complex, in the solid
C
thꢀe fCreeboTnCdNapEpeitarasppatea2r1s4a0tc2m2À610 faonrdth2e22c0omcmplex and
state (KBr), shows the C
ꢀ
N group at 2210 cmÀ1 as a
2100 cmÀ1 in the free diyne; the conjugated C
=C bond
shows three absorption bands at 1590, 1535 and
1485 cmÀ1 whereas in the free diyne only one is ob-
served, at 1590 cmÀ1; finally, the C—H vibration dueÀt1o
uatniq2u2e60peaankd, w2h2e2r0eacsmthÀe1;frteheeTCCꢀNECexbhoinbditsatpwpoeabrasndast
2120 cmÀ1 in the free diyne; the conjugated C
=C bonds
show four absorption bands at 1600, 1535, 1505 and
1480 cmÀ1 (only two at 1600 and 1505 cmÀ1 in the the
free diyne) owing to the resonance of the dimethylamino
groups which are observed at 1380 cmÀ1 and assigned to
the greatest double bond character for the C—N bond
(1350 cmÀ1 in the free diyne). Finally, the C—H
ortho substitution shows two bands at 780 and 765 cm
,
.
whereas in the free diyne only one appears, at 745 cmÀ1
The UV–visible spectrum in CH2Cl2 (dark blue–violet
solution) shows a charge-transfer band at 559 nm (e =
730 l molÀ1 cmÀ1).
All the data indicated a p-complexed association of a
TCNE molecule with only one of the rings in the 1,3-
diyne donor, which shows an important resonance
contributions to the N,N-dimethylamino group to the
complexation.
vibration shows a new absorption band at 825 cmÀ1
.
Two signals at 815 and 810 cmÀ1 are attributed to para
substitution in the complex (810 and 800 cmÀ1 in the free
diyne).
Moreover, the UV–visible spectrum in CH2Cl2 (dark
Table 5. 1H and 13C NMR data for 4c and 4c±TCNE complex
Structure of the 1,4-bis[4-ꢀN,N-dimethylamino)-
phenyl]-1,3-butadiyne±TCNE molecular complex
4c–TCNE
4c–TCNE
Proton/carbon
4c
(complexed ring) (uncomplexed ring)
The structure of the 4c–TCNE molecular complex was
analysed by 1H and 13C NMR spectroscopy (Table 5). In
solution the complex exhibits a general deshielding effect
on the phenyl rings of the diyne derivative. Two signals
for methyl groups at 3.19 and 3.12 ppm for the
complexed and uncomplexed ring (2.98 ppm for the free
diyne) shows the p-bonding association of a molecule of
TCNE to only one of the aromatic rings in the diyne,
which involves a resonance contribution of the N,N-
dimethyl group to the complexation. This effect is more
evident when the aromatic protons are considered. Thus,
H-2,H-6 and H-3,H-5 are deshielded at 7.80 and
H-2
7.40
7.40
6.63
6.63
2.98
7.80
7.80
6.75
6.75
3.19
7.51
7.51
6.68
6.68
3.12
H-6
H-3
H-5
Me2N
C-1
108.4
112.6
111.4
C-2,C-6
C-3,C-5
C-4
133.5
111.6
150.2
82.2
136.1
111.9
148.2
92.3
132.5
111.7
150.0
83.9
Ph—C
C—C
Me2N
ꢀ
ꢀ
72.5
39.9
89.9
40.9
75.8
40.1
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

´
J. G. RODRIGUEZ ET AL.
864
violet solution) shows a charge-transfer band at 524 nm
(e = 749 1 molÀ1 cmÀ1).
All the data revealed a p-complexed association of a
TCNE molecule with only one of the rings in the 1,3-
diyne 4c, which exhibits an important resonance
contribution of its N,N-dimethyl group to the complexa-
tion.
dehyde, 7.8 g (72%), as a yellow oil. B.p. 115–120°C/
5.0 mmHg.9 IR (film, Nujol): 2800 (C—H, CH3), 1685
1
(C=
O), 1600 (C
=
C, conj.), 740 cmÀ1 (o-disubst.). H
NMR (CDCl3): ꢁ 10.22 (s, 1H, CHO), 7.75 (dd, 1H,
J = 8.0 and 2.0 Hz, H-6), 7.45 (td, 1H, J = 8.0 and 2.0 Hz,
H-4), 7.02 (m, 2H, H-3 and H-5), 2.9 (s, 6H, CH3). 13C
MNR (CDCl3): ꢁ 190.8 (C=O), 155.5 (C-2), 134.3 (C-4),
The conjugation of the donor N,N-dimethylamino
group is necessary for the complexation of 4a and 4c
because, under the same conditions of preparation of the
4a and 4c complexes, the 4b–TCNE complex was not
isolated.
130.5 (C-6), 126.7 (C-1), 120.3 (C-5), 117.3 (C-3), 45.2
(2C, CH3). MS (70 eV): m/z (%) 149 (70) [M ], 132 (51),
120 (88), 106 (89), 91 (50), 77 (100).
‡
3-ꢀN,N-Dimethylamino)benzaldehyde. m-Nitrobenz-
aldehyde dimethylacetal. A mixture of m-nitrobenz-
aldehyde (5 g, 33 mmol) and dimethyl sulfite (3.96 g,
36 mmol), methanol (20 ml) and p-toluensulfonic acid
(30 mg) was warmed at the reflux temperature for 8 h.
The mixture was hydrolysed with sodium hydroxide
(15%) and extracted with ethyl acetate (30 ml), washed
with water and dried with magnesium sulfate. Then the
mixture was filtered and the dimethylacetal derivative
was distilled under vacuum giving a yellow oil, 5.8 g
(90%). B.p. 159–162°C/20 mmHg. IR (film, Nujol):
2840 (C—H) 1535 and 1350 (NO2), 1060, 1120 and 1160
CONCLUSION
The N,N-dimethylamino conjugated diynes 4a–c can be
satisfactorily obtained by the Wittig reaction between the
appropriate aldehydes and chloromethylene(triphenyl)-
phosphine ylide, followed by elimination of hydrochloric
acid and oxidative dimerization of the corresponding
acetylene. DSC analysis of the 1,3-diynes 4a–c showed
an irreversible transformation to a thermopolymer as a
unimolecular reaction. The conjugated 1,3-diynes show
electronic donor character and give 1:1 charge-transfer
complexes with TCNE as acceptor. The association of the
TCNE with only one benzene ring of the diyne is
determined by the presence of the N,N-dimethylamino
group on the ring.
1
(C—O), 850, 750 and 680 cmÀ1 (m-disubst.). H NMR
(CDCl3): ꢁ 8.35 (s br, 1H, H-2), 8.20 (m, 1H, H-4), 7.80
(d, 1H, J = 6.5 Hz, H-6), 7.55 (dd, 1H, J = 6.5 and 6.5 Hz,
H-5), 5.47 (s, 1H, HC—O), 3.34 (s, 6H, CH3).
m-Aminobenzaldehyde dimethylacetal. To a mixture of
Á
sodium sulfide (Na2S 9H2O) (15.79 g, 0.07 mol) in water
(16 ml) and hydrochloric acid (36%, 5.5 ml) was slowly
added the acetal prepared above (5.0 g, 25 mmol). The
mixture was warmed at the reflux temperature for 8 h and
finally extracted with ethyl acetate and dried with
magnesium sulfate. The m-aminobenzaldehyde di-
methylacetal was obtained as a yellow oil, 4.17 g
(87%). IR (film, Nujol): 3460 and 3380 (NH2), 2820
EXPERIMENTAL
General. Melting-points were determined with a Reich-
ert hot-stage microscope and are uncorrected. IR spectra
were recorded using a Perkin-Elmer Model 681 spectro-
photometer. UV–visible spectra were measured in
1
1
CH2Cl2, using a Unicam 8700 spectrometer. H NMR
(C—H), 885, 790 and 690 cmÀ1 (m-disubst.). H NMR
(200 MHz) and 13C NMR (50 MHz) spectra were
recorded with a Bruker WM-200-SY spectrometer;
chemical shifts are given on the ꢁ scale, using TMS as
internal reference. Mass spectra were recorded using a
Hewlett-Packard SP85 spectrometer. Elemental analyses
were performed with a LECO CHN-900 instrument.
(CDCl3): ꢁ 7.15 (dd, 1H, J = 8.0 Hz, H-5), 6.82 (m, 2H,
H-2 and H-6), 6.65 (m, 1H, H-4), 5.47 [s, 1H,
HC(OCH3)2], 3.70 (s br, NH2), 3.34 (s, 6H, CH3).
Dimethylacetal of m-ꢀN,N-dimethylamino)benzalde-
hyde. To a solution of m-aminobenzaldehyde dimethyl-
acetal (2.7 g, 16 mmol) in diethyl ether (10 ml) was
added a solution of sodium carbonate (7%, 50 ml) and
dimethyl sulfate in four portions during 4 days, with
stirring at room temperature. The mixture was hydrolysed
with ammonia solution, extracted with diethyl ether and
dried with magnesium sulfate. After filtration, the solvent
was removed, giving a residual oil which was treated
with dilute sulfuric acid (5%, 20 ml) for 1 h, with stirring
at the reflux temperature, extracted with dichloromethane
and dried with magnesium sulfate. After filtration, the
solvent was evaporated and the residual oil chromato-
graphed in a silica gel column using hexane–ethyl acetate
(3:1) as eluent. 3-(N,N-Dimethylamino)benzaldehyde
2-ꢀN,N-Dimethylamino)benzaldehyde. To a solution
of 2-fluorobenzaldehyde (9 g, 0.072 mol) in dry DMSO
(75 ml), under an argon atmosphere was added a
saturated solution of dimethylamine (40 ml) in dry THF
(20 ml) and K2CO3 (20 g). The mixture was warmed at
the reflux temperature for 3 h, then dimethylamine
(40 ml) in dry THF (20 ml) and DMSO (15 ml) was
newly added and warmed at the reflux temperature for a
further 3 h. The mixture was poured on to ice to give a
yellow oil, which was extracted with dichloromethane.
The solvent was removed and the residual oil distilled
under vacuum to obtain 2-(N,N-dimethylamino)benzal-
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

1,4-BIS[n-(N,N-DIMETHYLAMINO)PHENYL]BUTA-1,3-DIYNES
865
‡
was isolated as a yellow oil, 1.64 g (57%). IR (film,
MS (70 eV): m/z (%) 181 (72) [M ], 180 (100), 165 (8),
Nujol): 2780 (C—H); 1680 (C
=
O), 1590 (C
=
C, conj.),
144 (6), 130 (6).
890, 770 and 710 cmÀ1 (m-disubst.). 1H NMR (CDCl3): ꢁ
9.93 (s, 1H, CHO), 7.38 (dd, 1H, J = 8.8 and 8.8 Hz, H-5),
7.27–7.12 (m, 2H, H-2 and H-6), 6.95 (dd, 1H, J = 8.8
and 2.2 Hz, H-4), 2.99 (s, 6H, CH3). 13C NMR (CDCl3): ꢁ
ꢀE)-2-Chloro-1-ꢀ3-N,N-dimethylaminophenyl)ethene
ꢀ2b). IR (film, Nujol): 2790 (C—H), 1590 (C
=C, conj.),
990 (CH
=
CHCl, E), 840, 760 and 690 cmÀ1 (m-
1
192.9 (C=
O), 150.4 (C-3), 136.9 (C-1), 129.3 (C-5),
disubst.). H NMR (CDCl3): ꢁ 7.17 (dd, 1H, J = 7.8 Hz,
118.3 (C-4), 117.9 (C-6), 111.2 (C-2), 39.9 (2C, CH3).
MS (70 eV): m/z (%) 149 (77) [M ], 148 (100), 132 (8),
H-5), 6.73–6.65 (m, 3H, H-2, H-4 and H-6), 6.80 (AB,
1H, J = 13.6 Hz, CH=CHCl), 6.61 (AB, 1H, J = 13.6 Hz,
‡
120 (5), 105 (6), 91 (5), 77 (16).
CH
=
CHCl), 2.95 (s, 6H, CH3). MS (70 eV): m/z (%) 181
‡
(75) [M ], 180 (100), 165 (10), 144 (10), 130 (8).
2-Chloro-1-[2-ꢀN,N-dimethylamino)phenyl]ethene
ꢀ2a). To a suspension of chloromethylene(triphenyl)-
phosphine chloride11 (10.9 g, 31 mmol) in dry THF
(60 ml), under an argon atmosphere at 0°C, was slowly
added a solution of n-butyllithium (1.6 M in hexane,
22 ml, 34 mmol). The solution became red and after
being stirred for 30 min, 2-(N,N-dimethylamino)benz-
aldehyde (3.19 g, 21 mmol) was added. The mixture was
stirred at room temperature overnight after which the
solvent was evaporated to give a brown solid which was
Sohxlet extracted with hexane. The hexane was evapora-
ted and the residual yellow oil chromatographed in a
silica gel column with toluene as eluent to isolate (E)-2a
and (Z)-2a (luminescent) as pale-yellow oils 3.13 g
(96%) (E:Z, 58:42).
2-Chloro-1-[4-ꢀN,N-dimethylamino)phenyl]ethene
ꢀ2c). Following the above method, 4-(N,N-dimethyl-
amino)benzaldehyde gave a brown oil which was
chromatographed in a silica gel column (hexane–toluene,
1:1) to give 2c as a mixture of E- and Z-isomers (40:60),
yellow solid (13.16 g, 99%). IR (CH2Cl2): 3078, 2810,
1600 (C=C, conj.), 1360 (NMe2), 960 (E), 830
1
(p-subst.), 700 cmÀ1 (Z). H NMR (CDCl3): ꢁ 7.63–
6.70 (8H, m, H-2' and H-3', E and Z), 6.66 (1H, d,
J = 13.5 Hz, H-2, E), 6.50 (1H, d, J = 8.0 Hz, H-2, Z),
6.41 (1H, d, J = 13.5 Hz, H-1, E), 6.04 (1H, d, J = 8.0 Hz,
H-1, Z), 2.98 (6H, s, NMe2, E), 2.94 (6H, s, NMe2, Z). MS
‡
(70 eV): m/z (%) 183 (29), 181 (95) [M ], 180 (100), 165
(91).
ꢀZ)-2-Chloro-1-[2-ꢀN,N-dimethylamino)phenyl]ethene
2-ꢀN,N-Dimethylamino)phenylethyne ꢀ3a). To a solu-
tion of the (E,Z)-chloroethenyl derivative 2a (1.25 g,
6.9 mmol) in dry THF (40 ml) under an argon atmosphere
at 0°C was slowly added a solution of n-butyllithium
(1.6 M in hexane, 12.9 ml, 20.7 mmol) and the mixture
was stirred for 3 h at room temperature. Then a saturated
solution of ammonium chloride (25 ml) was added,
extracted with dichloromethane and dried over magne-
sium sulfate. After filtration, the solvent was removed,
giving a brown oil that was purified by silica gel column
chromatography using toluene as eluent to give the
ꢀ2a). IR (film, Nujol): 2800 (C—H), 1600 (C=C, conj.),
1
740 (o-disubst.), 660 cmÀ1 (CH
=CHCl, Z). H NMR
(CDCl3): ꢁ 7.84–7.80 (m, 1H, H-6), 7.24–7.13 (m, 1H,
H-4), 7.06–6.90 (m, 2H, H-3 and H-5), 6.85 (d, 1H,
J = 7.9 Hz, CH=CHCl), 6.28 (d, 1H, J = 7.9 Hz,
CH
=
CHCl), 2.70 (s, 6H, CH3). MS (70 eV): m/z (%)
‡
181 (14) [M ], 166 (1), 146 (72), 131 (100).
ꢀE)-2-Chloro-1-[2-ꢀN,N-dimethylamino)phenyl]ethene
ꢀ2a). IR (film, Nujol): 2800 (C—H), 1600 (C=C, conj.),
1
960 (CH=
CHCl, E), 740 cmÀ1 (o-disubst.). H NMR
(CDCl3): ꢁ 7.33–7.18 (m, 2H, H-4 and H-6), 7.07–6.93
(m, 2H, H-3 and H-5), 7.12 (AB, 1H, J = 13.7 Hz,
a(ficelmty,lenNeudjoelr)i:va3ti3v2e03a(ꢀ(0.C8—5 gH, )8,5%28)0a0s a(Cye—lloHw),oi2l.1I0R0
1
(C
ꢀ
C), 1600 (C
=
C, conj.), 760 cmÀ1 (o-disubst.). H
CH
=
CHCl), 6.62 (AB, 1H, J = 13.7 Hz, CH
=
CHCl),
NMR (CDCl3): ꢁ 7.45 (m, 1H, H-6), 7.25 (dd, d, 1H,
JH=-57),.33,.74.23(asn, d1H1.,7ꢀHzC,HH)-,42),.963.9(3s–, 66.H82, C(mH,32).H1,3HC-M3 aNnRd
‡
2.73 (s, 6H, CH3). MS (70 eV): m/z (%) 181 (5) [M ],
166 (1), 146 (88), 131 (100).
(CDCl ): ꢁ 155.5 (C-2), 134.8 (C-6), 129.6 (Cꢀ-4)),, 12802..63
3
(
(ꢀC-5C)H, )1, 1473..05 ((2CC-,3C),H13)1.4M.5S ((C70-1e)V, )8: 3m.1/z ((%C) 145 (50)
2-Chloro-1-[3-ꢀN,N-dimethylamino)phenyl]ethene
ꢀ2b). Following the above method, 3-(N,N-dimethyl-
amino)benzaldehyde gives a mixture of (E)-2b and (Z)-
2b as a yellow oil, 2.0 g (76%) (E:Z, 48:52).
‡
[M ], 144 (100), 129 (14), 115 (19), 101 (9). C10H11N
(145.21): calcd C, 82.71; H, 7.64; N, 9.65; found C,
82.47; H, 7.45; N, 9.30%.
ꢀZ)-2-Chloro-1-[3-ꢀN,N-dimethylamino)phenyl]ethene
ꢀ2b). IR (film, Nujol): 2790 (C—H), 1590 (C
=
C, conj.),
3-ꢀN,N-Dimethylamino)phenylethyne ꢀ3b). Following
the above procedure, a solution of (E,Z)-chloroethenyl
840, 760 and 690 (m-disubst.), 710 cmÀ1(CH
=
CHCl, Z).
1H NMR (CDCl3): ꢁ 7.24 (dd, 1H, J = 7.8 Hz, H-5), 7.09–
derivative 2b gave 3b as a paꢀle-CyeHll)o,w28o1i0l, (1C1—5 Hm)g,
J = 8.2 Hz, CH=CHCl, Z), 6.73–6.65 (m, 1H, H-4), 6.22
2110 (C
ꢀ
C), 1600 (C
(70%). IR (film, Nujol): ꢀ3300 (
C, conj.), 850, 780 and
7.07 (m, 1H, H-2), 7.03–6.99 (m, 1H, H-6), 6.60 (AB, 1H,
1
(AB, 1H, J = 8.2 Hz, CH
=CHCl, Z), 2.95 (s, 6H, CH3).
690 cmÀ1 (m-disubst.). H MNR (CDCl3): ꢁ 7.17 (td,
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

´
J. G. RODRIGUEZ ET AL.
866
1H, J = 8.1 and 0.8 Hz, H-5), 6.90–6.82 (m, 2H, H-2 and
(38). Calcd for C20H20N2: C, 83.30; H, 6.99; N, 9.71;
found C, 83.15; H, 6.85; N, 9.62%.
C
Hꢀ-6)C, H6).7, 12.9(d4 (bsr,, 61HH, ,CJH=3)8. .M1 HSz(,70He-4V)),: 3m.0/z1(%(s,) 114H5,
‡
(84) [M ], 144 (100), 129 (14), 101 (22). C10H11N
1,4-Bis-[4-ꢀN,N-Dimethylamino)phenyl]buta-1,3-
(145.21): calcd C, 82.71; H, 7.64; N, 9.65; found C,
82.66; H, 7.35; N, 9.42%.
diyne ꢀ4c). Following the above procedure, the acetylene
dme.rpi.va2t3iv3e°C3b. IgRav(eKtBher)d:iy2n9e304,c2(16200%)(Caꢀs aCy)e,ll1o6w00soalindd,
4-ꢀN,N-Dimethylamino)phenylethyne ꢀ3c). Following
the above procedure, a solution of (E,Z)-chloroethenyl
derivative 2c gave 3c (60%) as a yellow solid, m.p. 51–
10 52–53°C). IR (CH2Cl2): 3300 (C—H), 2100
1505 (C=C, conj.), 1430 (CH3), 1350 (NMe2), 810 and
1
800 cmÀ1 (p-subst.). H NMR (CDCl3): ꢁ 7.40 (4H, d,
J = 8.2 Hz, H-2'), 6.63 (4H, d, J = 8.2 Hz, H-3'), 2.98
(12H, s, NMe2). 13C NMR (CDCl3): ꢁ 150.2 (2C, C-4'),
133.5 (4C, C-2' and C-6'), 111.6 (4C, C-3' and C-5'),
108.4 (2C, C-1'), 82.2 (2C, C-1 and C-4), 72.5 (2C, C-2
and C-3), 39.9 (4C, NMe2). MS (70 eV): m/z (%) 288
(5C2ꢀ°CC()li,t.1615 and 1520 (C
=C, conj.), 1360 (N(CH3)2),
1
820 cmÀ1 (p-subst.). H NMR (CDCl3): ꢁ 7.37 (2H, d,
J = 8.6 Hz, H-2'), 6.62 (2H, d, J = 8.6 Hz, H-3'), 3.00 (1H,
s, H-1), 2.99 (6H, s, N-Me2). MS (70 eV): m/z (%) 145
‡
(M , 100), 272 (16), 144 (13); UV–visible (CH2Cl2):
‡
(M , 100), 144 (99), 129 (25), 101 (18). C10H11N
lmax 377 nm (e = 55 000 1 molÀ1 cmÀ1). Calcd for
C20H20N2: C, 83.30; H, 6.99; N, 9.71; found C, 83.25;
H, 6.72; N, 9.55%.
(145.21): calcd C, 82.71; H, 7.64; N, 9.65; found C,
82.38; H, 7.29; N, 9.66%.
1,4-Bis[2-ꢀN,N-Dimethylamino)phenyl]buta-1,3-
diyne ꢀ4a). To a solution of copper(I) chloride (0.31 g,
1.57 mmol) in pyridine (10 ml) in an oxygen atmosphere
was added a solution of 3a (0.63 g, 4.3 mmol) in pyridine
(10 ml). The mixture was stirred for 4 h at 40°C. The
pyridine was removed by distillation and the crude
product was washed with ammonia solution until the blue
colour disappeared and then extracted with dichloro-
methane (30 ml) and dried with magnesium sulfate. After
filtration, the solvent was removed giving a brown solid
that was chromatographed in a silica gel column with
hexane–ethyl acetate (6:1) as eluent to leave 4a (0.38 g,
Charge-transfer complex of 1,4-bis[2-ꢀN,N-dimethyl-
amino)phenyl]buta-1,3-diyne ꢀ4a) with TCNE ꢀ1:1).
To a hot solution of the 1,3-butadiyne 4a (80 mg,
0.28 mmol) in acetonitrile (27 ml) was slowly added a
solution of TCNE (36 mg, 0.28 mmol) in acetonitrile
(3 ml). The yellow solution became violet. Slow solvent
evaporation at room temperature gave a molecular
charge-transfer complex 4a-TCNE as crystalline black–
v2i2o2l0et p(Claꢀtes with a bright metallic appearance. IR (KBr):
N), 2140 (C
ꢀ
C), 1590, 1535 and 1485
(C=
C, conj.), 1350 (NMe2), 780 and 765 cmÀ1 (o-
disubst.). 1H NMR (CDCl3): ꢁ 7.78 (m, 2H, H-4 and H-6,
complexed), 7.35 (m, 4H, H-3 and H-5, complexed; H-4
and H-6, uncomplexed ring), 6.85 (m, 2H, H-3 and H-5,
uncomplexed ring), 3.08 (s, 6H, NMe2, complexed), 2.76
(s, 6H, N-Me2, uncomplexed ring). 13C NMR (CDCl3): ꢁ
155.6 (C-2', uncomplexed ring), 153.4 (C-2', com-
plexed), 136.9 (C-6', complexed), 135.5 (C-6', uncom-
plexed ring), 133.7 (C-4', complexed), 133.0 (C-4',
uncomplexed ring), 124.4 (C-5', complexed), 121.4
(C-5', uncomplexed ring), 119.1 (C-3', complexed),
116.3 (C-3', uncomplexed ring), 112.7 (C-1', com-
plexed), 112.1 (C-1', uncomplexed ring), 92.2 (C-2 and
C-3, complexed), 87.7 (C-1 and C-4, complexed) and
84.6 (C1 and C-4, uncomplexed ring), 84.4 (C-2 and C-3,
complexed), 44.4 (2C, NMe2, complexed), 43.5 (2C,
NMe2, uncomplexed ring). UV–visible (CH2Cl2): lmax
559 nm (e = 730 1 molÀ1 cmÀ1). DSC: irreversible broad
exothermic peak at 178°C. Calcd for C26H20N6: C,
74.98; H, 4.84; N, 20.18; found C, 75.36; H, 4.66; N,
19.82%.
6N1u%jo)l)a:s2a92y0e,llo2w100sol(iCdꢀ, m.p. 65°C (decomp.). IR (film,
C), 1590 (C
=
C, conj.), 1370
1
(NMe2), 745 cmÀ1 (o-subst.). H NMR (CDCl3): ꢁ 7.48
(dd, 2H, J = 8.3 and 1.8 Hz, H-6), 7.25 (td, 2H, J = 8.3
and 1.8 Hz, H-4), 6.89 (m, 4H, H-3 and H-5), 3.00 (s,
12H, CH3). 13C NMR (CDCl3): ꢁ 155.9 (2C, C-2), 135.3
(2C, C-6), 129.9 (2C, C-4), 120.2 (2C, C-5), 116.8 (2C,
C-3); 113.4 (2C, C-1), 82.0 (2C, Ph—C
ꢀ
), 79.4 (2C,
‡
ꢀ
C), 43.6 (4C, NMe2). MS (70 eV): m/z (%) 288 (M ,
68), 287 (73), 271 (100), 200 (4), 144 (66), 143 (65). UV–
visible (CH2Cl2): lmax 369 nm (e 28 000 l molÀ1 cmÀ1).
Calcd for C20H20N2: C, 83.30; H, 6.99; N, 9.71; found C,
82.92; H, 7.15; N, 9.47%.
1,4-Bis[3-ꢀN,N-Dimethylamino)phenyl]buta-1,3-
diyne ꢀ4b). Following the above procedure, the acetylene
derivative 3b gave the diyne 4b (60%) as a pale-yellow
solid, m.p. 162–165°C. IR (KBr): 2930, 1590 and 1570
(C=
C, conj.), 1370 (NMe2), 830, 770 and 680 cmÀ1 (m-
subst.). 1H NMR (CDCl3): ꢁ 7.19 (t, 2H, J = 8.3 Hz, H-5),
6.87 (m, 4H, H-2 and H-6), 6.73 (m, 2H, H-4), 2.97 (s,
12H, NMe2). 13C NMR (CDCl3): ꢁ 150.1 (2C, C-3),
129.0 (2C, C-5), 122.1 (2C, C-1), 120.5 (2C, C-6), 115.8
Charge-transfer complex of 1,4-bis[4-ꢀN,N-dimethyl-
amino)phenyl]buta-1,3-diyne ꢀ4c) with TCNE ꢀ1:1).
Following the above procedure, 1,3-butadiyne 4c gave a
black solid with a bright metallic appearance as a charge-
transfer complex, which was recrystallized from hexane.
H(2-CC,ꢀC-2), 113.5 (2C, C-4), 82.5 (2C, PhC
), 40.3 (4C, CH3). MS (70 eV): m/z (%) 288 (M ,
ꢀ
), 72.9 (2C,
‡
100), 287 (55), 271 (25), 258 (6), 200 (7), 144 (14), 143
IR (KBr): 2210 (CN), 2120 (C
ꢀ
C), 1600, 1535, 1505
Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868

1,4-BIS[n-(N,N-DIMETHYLAMINO)PHENYL]BUTA-1,3-DIYNES
867
and 1480 (C
=
C, conj.), 1380 (NMe2), 825, 815 and
maps and then the coordinates were refined. Thereafter,
several cycles of full-matrix least-squares calculations
were carried out with anisotropic thermal parameters for
heavy atoms and the H-atoms were included as fixed
contributors,20 and convergence was reached at R = 0.036
and Rw = 0.084 with a weighting scheme to prevent
trends in wD2F vs kFol and vs ksinꢂ/ll.21 The final
810 cmÀ1 (p-subst.). H NMR (CDCl3): ꢁ 7.80 (2H, d,
J = 8.4 Hz, H-2 and H-6, complexed), 7.51 (2H, d,
J = 8.4 Hz, H-2 and H-6, uncomplexed ring), 6.75 (2H,
d, J = 8.4 Hz, H-3 and H-5, complexed), 6.68 (2H, d,
J = 8.4 Hz, H-3 and H-5, uncomplexed ring), 3.19 (6H, s,
N-Me2, complexed), 3.12 (6H, s, N-Me2, uncomplexed
ring). 13C NMR (CDCl3): ꢁ 150.0 (C-4', uncomplexed
ring), 148.2 (C-4', complexed), 136.1 (C-2' and C-6',
complexed), 132.5 (C-2' and C-6', uncomplexed ring),
112.6 (C-1', complexed), 111.4 (C-1', uncomplexed
ring), 111.9 (C-3' and C-5', complexed), 111.7 (C-3'
and C-5', uncomplexed ring), 92.3 (C-2 and C-3,
complexed), 83.9 (C-2 and C-3, uncomplexed ring),
89.9 (C-1 and C-4, complexed) and 75.8 (C-1 and C-4,
uncomplexed ring), 40.9 (2C, NMe2, complexed), 40.1
(2C, NMe2, uncomplexed ring). UV–visible (CH2Cl2):
lmax 524 nm (e = 749.1 molÀ1 cmÀ1). -DSC: irreversible
broad exothermic peak up to 200°C (200–250°C). Calcd.
for C26H20N6: C, 74.98; H, 4.84; N, 20.18; found C,
74.56; H, 4.88; N, 19.91%.
1
difference synthesis showed no peaks exceeding 0.11 e
˚
A
À3. The atomic scattering factors and the anomalous
dispersion correction were taken from the literature.22
Acknowledgement
We are greatly indebted to CICYT, Spain, for financial
support (Project No. PB97-0060).
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X-ray analysis of 1,4-bis[2-ꢀN,N-dimethylamino)phe-
nyl]buta-1,3-diyne ꢀ4a). Caramel needle crystals of the
diyne 4a for x-ray analysis were obtained from slow
evaporation of a dilute ethyl acetate solution. A crystal of
0.16 Â 0.10 Â 0.73 mm dimensions was used for the
crystallographic study. Accurate cell dimensions were
determined by least-squares analysis of setting angles of
25 reflections (2 < ꢂ < 35°), using graphite mono-
˚
chromated Cu Ka radiation (l = 1.5418 A) automatically
located and centred on a Seifert XRD 3000S four-circle
diffractometer. The crystal is orthorhombic, space group
˚
Pca21, with a = 14.447(2), b = 7.909(1), c = 14.672(2) A,
3
˚
a = b = ꢃ = 90°, V = 1.676.4(4) A . The molecular for-
mula is C20H20N2, molecular weight 288.38, Dc =
1.143(2) mg mÀ3, Z = 4, F(000) = 616. Correction by
absorption was neglected, m = 0.515 (4) mmÀ1. Data
collection: two standard reflections were measured every
90 min to ascertain the crystal stability, and no significant
variation was observed. All the reflections were corrected
for Lorentz and polarization effects, but no absorption
correction was applied. For the intensity measurement,
reflections were surveyed in the range 5 < ꢂ < 67°; from
1471 independent reflections measured, 1059 were con-
sidered as observed, satisfying the criterion I > 2s(I) in
the range h 0–17, k 0–8, l 0–17, and were used in the
subsequent calculations. The crystallographic data for 4a
(excluding structure factors), have been deposited with
the Cambridge Crystallographic Data Centre as supple-
mentary publication No. CCDC-151589. A copy of the
data can be obtained free of charge on application to
the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK
(E-mail: deposit@ccdc.cam.ac.uk).
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19. Altomare A, Cascarano G, Giacovazzo C, Guagliardi A.
Dipartimento Geomineralogico, University of Bari; M Burla, G.
Polidori Dipartimento Science della Terra, University of Perugia;
M. Camalli SIR92. Ist. Strutt. Chimica, CNR, Monterrotondo
Stazione, Rome.
The crystal structure was partially elucidated by direct
methods.19 After preliminary adjustment of the heavy
atoms, H-atoms were positioned from difference Fourier
20. Hall SR, Crystallography Centre, University of Western Australia.
Copyright  2001 John Wiley & Sons, Ltd.
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Copyright  2001 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2001; 14: 859–868