Synthesis, crystal structure, optical, electrochemical and thermal properties of the ynamide: Bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide

Article abstract of DOI:10.1016/j.molstruc.2016.03.026

The novel ynamide compound, bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide (3), was synthesized and characterized by single crystal X-ray diffraction, ¹H and ¹³C NMR, UV-fluorescence spectroscopy, cyclic voltammetry, TGA and DSC techniques. This first reported X-ray structure of a 1,3-butadiyne-1,4-diamide revealed that the amido substituents of 3 adopt a twisted conformation in the crystal with a torsion angle of 76.6° resulting in a molecule with axial chirality. The crystal structure of compound 3 is stabilized by intermolecular CH-π interactions that give pairs of stacked bis-alkyne-3 units. HOMO/LUMO energy levels of 3 were experimentally determined by means of electrochemical and optical methods to be??5.87/?1.98?eV respectively. The solid state polymerization of the title compound was investigated by differential scanning calorimetry (DSC) revealing that polymerization proceeded simultaneously to the phase transition assigned to the melting of 3. The solid state polymerization of 3 is discussed of being a topochemically initiated polymer chain reaction that proceeds with a non-topochemical chain growth.

Full text of DOI:10.1016/j.molstruc.2016.03.026

Accepted Manuscript
Synthesis, crystal structure, optical, electrochemical and thermal properties of the
ynamide: Bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide
Thu-Hong Doan, Imen Talbi, Jean-François Lohier, Soufiane Touil, Carole Alayrac,
Bernhard Witulski
PII:
S0022-2860(16)30221-6
10.1016/j.molstruc.2016.03.026
MOLSTR 22337
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 4 February 2016
Revised Date: 8 March 2016
Accepted Date: 9 March 2016
Please cite this article as: T.-H. Doan, I. Talbi, J.-F. Lohier, S. Touil, C. Alayrac, B. Witulski,
Synthesis, crystal structure, optical, electrochemical and thermal properties of the ynamide: Bis-(N-4-
methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide, Journal of Molecular Structure (2016),
doi: 10.1016/j.molstruc.2016.03.026.
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ACCEPTED MANUSCRIPT
Synthesis, crystal structure, optical, electrochemical and thermal properties of
the ynamide: Bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-
diamide
Thu-Hong Doan,a Imen Talbi,a,b Jean-François Lohier,a Soufiane Touil,b Carole Alayrac,a
Bernhard Witulski*,a
a
Laboratoire de Chimie Moléculaire et Thioorganique, CNRS UMR 6507, Normandie University, ENSICAEN & UNICAEN, 6
Bvd du Maréchal Juin, 14050 Caen, France.
b Laboratory of Heteroatom Organic Chemistry, University of Carthage, Faculty of Sciences of Bizerte, 7021 - Jarzouna, Tunisia.
HIGHLIGHTS
• The novel ynamide 3, having a 1,3-butadiyne-1,4-diamide moiety was prepared.
• First characterization of a 1,3-butadiyne-1,4-diamide by x-ray diffraction.
• The helical twisted molecular structure of diynamide 3 implies helical twisted MOs.
• The HOMO-LUMO energies of 3 were determined by optical and electrochemical methods.
• Probable topochemical ynamide polymerization was investigated.
ARTICLE INFO
Article history:
Received
Accepted
Available online
ABSTRACT
The novel ynamide compound, bis-(N-4-methylbenzenesulfonyl, N-n-
butyl)-1,3-butadiyne-1,4-diamide (3), was synthesized and
characterized by single crystal x-ray diffraction, 1H and 13C NMR,
UV-fluorescence spectroscopy, cyclic voltammetry, TGA and DSC
techniques. This first reported x-ray structure of a 1,3-butadiyne-1,4-
diamide revealed that the amido substituents of 3 adopt a twisted
conformation in the crystal with a torsion angle of 76.6° resulting in a
molecule with axial chirality. The crystal structure of compound 3 is
stabilized by intermolecular CH-π interactions that give pairs of
stacked bis-alkyne-3 units. HOMO/LUMO energy levels of 3 were
experimentally determined by means of electrochemical and optical
methods to be -5.87/-1.98 eV respectively. The solid state
polymerization of the title compound was investigated by differential
scanning calorimetry (DSC) revealing that polymerization proceeded
simultaneously to the phase transition assigned to the melting of 3.
The solid state polymerization of 3 is discussed of being a
topochemically initiated polymer chain reaction that proceeds with a
non-topochemical chain growth.
Keywords:
Diacetylenes
Ynamides
x-ray crystal structure
HOMO/LUMO energy levels
Polymerization of ynamides
Helical twisted MOs
1. Introduction
Functionalized acetylenes are versatile building blocks displaying widespread reactivity patterns
that result in a plethora of useful synthetic transformations and many of them found application in
the synthesis of natural products or material oriented research [1-6]. Especially nitrogen
functionalized alkynes, such as the electron-rich ynamines [7, 8], or their electron deficient and
* Corresponding author.
E-mail address: bernhard.witulski@ensicaen.fr

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therefore more stable variants - the ynamides (1-alkynylamides) [9-13] - gained considerable
interest in recent years. Since our first report of a reliable and up-scalable synthesis of ynamides,
[14] these versatile acetylenes found widespread use in organic chemistry. Particularly, transition
metal catalyzed transformations such as the Pauson-Khand reaction [15, 16], Ni(0)-, Rh(I)- and
Ru(II) catalyzed [4+2], [3+2] and [2+2+2] cycloadditions [17-22], as well as ring-closing
metathesis [23] and Au(I)-catalyzed reactions [24-27], highlighted the applicability of ynamides
as building blocks in organic synthesis. Many other reported transformations of ynamides took
likewise benefit of the slightly polarized alkyne moiety. Notably, first applications of the
chemistry of ynamides in step- and atom economic syntheses of natural products appeared [18,
20, 28-31]. In contrast to the chemistry of ynamides with just one alkyne moiety, only a small
number of examples exist with ynamides having a 1,3-diyne or larger conjugated alkyne skeleton
[32-39]. As a part of our efforts on the synthesis of ynamides with a conjugated oligoyne
structure that are of interest for non-linear optical materials [34] or as molecular wire for organic
electronics, we became interested in the study of symmetrical 1,3-diyne-1,4 amides.
Symmetrical amino alkynes of the type R2N-(C≡C)n-NR2 (n = 1, 2, 3, …) are less well described
although the parent compound with n = 1 was already reported by Viehe in the 60s [40].
However, detailed molecular properties including x-ray structure were only revealed by Tamm
recently [41]. Similar counts for the next higher homologues with n = 2 whose syntheses have
been reported by Ficini and Himbert [42-46] but a detailed molecular structure analysis was only
disclosed for two examples the N,N,N,N-tetraphenylbutadien-1,3-diyne-1,4-diamine 1 [47], and
the electronically more conjugated derivative, the bis(1-carbazolyl)buta-1,3-diyne 2 [48] (Figure
1). Both molecular structures belong to the electron-rich ynamine family. Here, we report on the
synthesis, the molecular structure and properties of the 1,3-buta-1,4-diynamide 3 – the electron
deficient and therefore more stable ynamide variant of 1 and 2.
Figure 1. The electron rich 1,3-butadiyne-1,4-diamines 1 and 2, and the here reported electron deficient ynamide variant 3.
Extended conjugated oligoynes like the title compound 3 are proposed to have axial chirality due
to a twisted conformation, like the one found in the allene family. The axial chirality has
furthermore impact on the topology of the frontier orbitals that resemble extended helices

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displaying non-linear π-interactions throughout the conjugated carbon rod. Such a helical twist of
conjugated frontier orbitals should have implications for structure stability, spectroscopy and
principle reaction pathways, as recently discussed by Aron Walsh et al. on the basis of quantum
chemical calculations [49]. Furthermore, 1,3-butadiynes gain considerable interest as monomers
in topochemical polymerization reactions as introduced by Wegner [50-52]. However, to the best
of our knowledge, the polymerization of ynamides or diynamides have not yet been reported.
2. Experimental
2.1.1. General procedure
Toluene was purified by an Innovative Technology Pure Solv. Device (activated alumina column
containing a copper catalyst and molecular sieves). Chromatographic purifications were
performed using Merck silica gel Si 60 (40-63 ꢀm) and TLC were developed on silica gel 60-
F254 plates (0.1 mm) with UV detection. 1H and 13C NMR spectra were recorded on a BRUKER
13
AVANCE III 400 or 500 spectrometer. 1H and C NMR chemical shifts are given in ppm using
the TMS signal (0 ppm) and the residual peak of chloroform-d (77.16 ppm) respectively as
internal reference. Coupling constants are reported in Hertz (Hz). Abbreviations are used as
follows: s = singlet, d = doublet, t = triplet, quint = quintuplet, sext = sextuplet, m = multiplet, br
= broad. Infrared (IR) spectra were recorded either on a “Perkin Elmer Spectrum One”
spectrometer equipped with an ATR device, or with a Perkin Elmer FT-IR Spectrometer 16PC
and only the strongest or structurally most important peaks are listed. Mass Spectrometry was
performed with a QTOF Micro WATERS spectrometer (ESI), or with a Finnigan MAT 90 for EI
(70eV). CHN analyses were performed with a Perkin-Elmer Elemental Analyzer EA 240 or with
a Perkin Elmer analyser 2400 CHN. Melting points (mp) were measured with a melting point
microscope and are not corrected. The amide
4
was obtained from 4-
methylbenzenesulfonylchloride and n-butylamine in dichloromethane and the alkynyliodonium
salts 5a and 5b were synthesized by literature proceedings [53].
2.1.2. Preparation of N-n-Butyl-N-trimethylsilanylethynyl-4-methylbenzenesulfonylamide (6)
Procedure A: To a solution of N-n-butyl-4-methylbenzenesulfonylamide (4) (690 mg, 3.04
mmol) in dry toluene (50 mL) was added n-BuLi (3.29 mmol; 2.19 mL of a 1.5 M solution in
hexane) at -78 °C. The solution was brought slowly to 0 °C and alkynyliodonium salt 5a (1.485
g, 3.30 mmol) was added. The resulting solution was stirred at room temperature for 12-14 h.
After completion of the reaction (TLC indicated complete consumption of 4) the solvents were
removed in vacuum and the remaining residue chromatographed on silica gel (SiO2, hexanes /
diethyl ether = 8:2 (v/v)) to give ynamide 6 (800 mg, 2.48 mmol, 82% yield); Rf: 0.6 (SiO2,
hexanes / ethyl acetate = 7:3 (v/v)); colorless crystals with mp. 54-55 °C (chloroform/pentane, -

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20 °C). 1H NMR (400 MHz, CDCl3) δ = 7.78 (d, J = 8.1 Hz, 2H), 7.34 (d, J = 8.2 Hz, 2H), 3.29
(t, J = 7.2 Hz, 2H), 2.45 (s, 3H), 1.60 (m, 2H), 1.33 (m, 2H), 0.90 (t, J = 7.4 Hz, 3H), 0.16 (s,
9H). 13C NMR (100 MHz, CDCl3) δ = 144.4 (s), 134.7 (s), 129.5 (d), 127.7 (d), 95.3 (s), 73.0 (s),
50.9 (t), 29.7 (t), 21.5 (q), 19.3 (t), 13.4 (q). IR (KBr) ν 2961, 2873, 2162, 1596, 1492, 1492,
1469, 1364, 1292, 1248, 1188, 1172, 1089, 1016, 985, 927 cm-1. MS (EI, 70 eV), m/z (%): 323
(100) [M+], 308 (55), 252 (26), 155 (21), 112 (18), 91 (33), 75 (38). C,H,N analysis for
C6H25NO2SSi (323.53); calc: C 59.40, H 7.79, N 4.33; found C 59.83, H 7.60, N 4.17. HRMS for
C16H25NO2SSi (323.53); calc. 323.1375; found 323.1380.
2.1.3 Desilylation of ynamide 6
To a solution of 6 (1.24 g, 3.83 mmol) in oxygen-free wet THF (145 mL) was slowly added a 1M
solution of TBAF in THF (4.72 mL, 1.2 equiv.) at 0 °C. After stirring for 15 min at 0 °C, TLC
indicated total consumption of 6 and the solvent was removed in vacuum. To the residue were
added CH2Cl2 and brine. After separation of the layers the organic phase was dried over MgSO4
and filtered. The solvents were removed in vacuum and the remaining residue was purified by
column chromatography on silica gel (SiO2, pentane / ethyl acetate = 95:5 (v/v)) to give ynamide
7 (710 mg, 2.82 mmol, 74% yield).
2.1.4 Preparation of N-n-Butyl-N-ethynyl-4-methylbenzenesulfonylamide (7)
Procedure B: To a solution of N-n-butyl-4-methylbenzenesulfonylamide (4) (300 mg, 1.30 mmol)
in dry toluene (30 mL) was added n-BuLi (1.43 mmol; 0.95 mL of 1.5 M solution in hexane) at -
78 °C. The solution was brought slowly to 0 °C and alkynyliodonium salt 5b (570 mg, 1.51
mmol) was added. The resulting solution was stirred at room temperature for 12-14 h. After
completion of the reaction (TLC indicated complete consumption of 4) the solvents were
removed in vacuum and the remaining residue chromatographed on silica gel (SiO2,
hexanes/diethyl ether = 8:2 (v/v)) to give ynamide 7 (250 mg, 1.00 mmol, 77% yield); Rf: 0.4
(SiO2, hexanes/ethyl acetate = 8:2 (v/v)); colorless crystals with mp. 43-45 °C (chloroform /
1
pentane, -20 °C). H NMR (500 MHz, CDCl3) δ = 7.80 (d, J = 8.3 Hz, 2H), 7.35 (d, J = 8.3 Hz,
2H), 3.30 (t, J = 7.2 Hz, 2H), 2.72 (s, 1H), 2.45 (s, 3H), 1.63 (m, 2H), 1.34 (m, 2H), 0.90 (t, J =
7.4 Hz, 3H). 13C NMR (125 MHz, CDCl3) δ = 144.8 (s), 134.7 (s), 129.9 (d), 127.8 (d), 76.2 (s),
59.1 (d), 51.0 (t), 29.8 (t), 21.8 (q), 19.5 (t), 13.7 (q). IR (KBr) ν 2961, 2875, 2133, 1595, 1303,
1169, 1120, 1089, 1026, 1016, 973, 939 cm-1. MS (EI, 70 eV), m/z (%) = 251 (8) [M+], 195 (22),
186 (27), 155 (36), 131 (45), 91 (100). C,H analysis C13H17NO2S (251.34): calc C 62.12, H 6.82,
N 5.57; found C 62.16, H 6.93, N 5.40. HRMS calc for C13H17NO2S: 251.0980; found 251.0972.

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2.1.5. Preparation of bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide (3)
To a suspension of CuI (36 mg, 0.19 mmol, 10 mol%) in dry acetone (10 mL) was added
TMEDA (58 µL, 0.19 mmol, 20 mol%). After 15 min of stirring at rt and under air condition a
solution of ynamide 7 (495 mg, 1.97 mmol) in dry acetone (10 mL) was added and the mixture
was vigorously stirred until complete consumption of the starting material (4 h, TLC monitoring).
The solvent was removed in vacuo and the residue was purified by silica gel column
chromatography using Pentane/EtOAc 8:2 as eluent to give the 1,3-butadiyne-1,4-diamide 3 in
92% yield (453 mg) as a white solid. Colorless crystals. Mp 109-110 °C (CHCl3/Pentane). Rf =
0.44 (Pentane/EtOAc 8:2 (v/v)). 1H NMR (400 MHz, CDCl3) δ 7.79 (d, J = 8.2 Hz, 4H, H-14/H-
18), 7.37 (d, J = 8.2 Hz, 4H, H-15/H-17), 3.34 (t, J = 7.3 Hz, 4H, H-5), 2.47 (s, 6H, H-19), 1.62
(quint, J = 7.4 Hz, 4H, H-6), 1.32 (sext, J = 7.4 Hz, 4H, H-7), 0.90 (t, J = 7.4 Hz, 6H, H-8). 13C
NMR (100 MHz, CDCl3) δ 145.0 (Cq, C-16), 134.8 (Cq, C-13), 130.0 (CH, C-15/C-17), 127.7
(CH, C-14/C-18), 75.4 (Cs, C-1), 59.6 (Cs, C-2), 51.6 (Ct, C-5), 30.0 (Ct, C-6), 21.8 (Cq, C-19),
19.6 (Ct, C-7), 13.7 (Cq, C-8). IR (ATR) ν 2960, 2933, 2874, 2169, 1596, 1492, 1456, 1361,
1184, 1163, 1087, 921, 811, 706 cm−1. HRMS (ESI) Calcd for C26H32N2O4NaS2 [M+Na]+:
523.1701. Found: 523.1717.
2.2 Physical measurements
UV absorption spectra in solution were recorded with a JASCO V-660 spectrometer and emission
spectra with a Perkin Elmer LS55 fluorescence spectrometer. Absolute photoluminescence
quantum yields in solution were recorded with the Hamamatsu CC9920 integration sphere set-up
at room temperature. For quantum yield measurements solutions of 3 were purged with argon
prior to measurement. Electrochemical studies were carried out at room temperature using a
GAMRY Ref600 potentiostat. The working electrode was a platinum electrode, and the auxiliary
electrode a platinum wire. The reference electrode was an aqueous saturated (KCl) calomel
electrode. Under the conditions used, the reversible potential for the ferrocenium/ferrocene
couple at 298 K is +0.46 V in CH2Cl2. A 10-3 M solution of 3 in a 1x10-1 M Bu4NPF6 /CH2Cl2
electrolyte solution was used. TGA measurements were recorded on a Perkin Elmer
Thermogravimetric Analyser TGA7. Differential Scanning Calorimetry measurements were
performed on a Perkin Elmer DSC7 analyser.
2.3 X-ray diffraction data for compound 3
Single crystals of ynamide 3 were grown by slow diffusion of pentane into a solution of 3 in
chloroform at room temperature. X-ray crystallographic data of the single crystals of 3 were
collected at 150 K on a Bruker Apex II Kappa CCD single-crystal diffractometer working with
monochromatic Mo Kα radiation and equipped with an area detector. The crystal structure was

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solved by direct methods with SHELXS-97 [54] and refined against F2 with SHELXL-2014 [55],
with anisotropic thermal parameters for all non-hydrogen atoms. Idealized geometries were
assigned to the hydrogen atoms. Crystal data and refinement details for compound 3 are
summarized in Table 1.
Table 1. Crystal data and refinement details for ynamide 3 with Formula Sum C26H32N2O4S2 and Formula Weight 500.67 g mol-1.
Crystal system
Crystal size
Z
2
Triclinic
Dx (Mg/m3)
ꢀ (mm−1)
1.251
0.32 × 0.30 × 0.27
Colorless
P-1
Crystal color
Space group
0.23 (Mo Kα)
Theta range for data collection (°) 2.3–30.5
Limiting indices
−16 ⩽ h ⩽ 16, −16 ⩽ k ⩽ 15,
−18 ⩽ l ⩽ 17
a (Å)
11.3148(4)
b (Å)
c (Å)
a (°)
Reflections collected/unique
Reflections with I > 2σ(I)
Refined parameters/restrains
Goodness of fit on F2
R1, wR2
30969/8091 (Rint = 0.023)
11.4384(4)
12.8115(5)
64.9887(16)
6566
331/0
β (°)
1.04
73.5519(16)
62.8724(15)
g (°)
0.062, 0.185
V (Å3)
1328.90(9)
Largest diff. peak and hole (eÅ−3) 1.10 and −0.68
3. Results and discussion
3.1 Synthesis of bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide (3)
The synthesis of the title 3 was achieved by two complementary routes using alkynyliodonium
salts for a direct N-ethynylation following our previous procedure (Scheme 1) [14, 56].

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Procedure A:
n-BuLi (1.1 eq.)
followed by addition of
Me3Si
I
OTf
O
S
Ph
TBAF, THF
74%
5a
O
N
SiMe3
82%
O
O
S
S
6
O
O
N
H
NH
Procedure B:
n-BuLi (1.1 eq.) followed by addition of
H
I
OTf
4
7
Ph
5b
77%
O
CuI (10 mol%),TMEDA (20 mol%)
acetone, air, r.t.
S
O
N
N
O
92%
S
O
3
Scheme 1. Synthesis of bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide (3).
Accordingly, tosylamide 4 was deprotonated with n-butyl lithium in dry toluene and the resulting
amide was treated with the readily available silylated alkynyliodonium salt 5a to give ynamide 6
in 82% yield after work-up and column chromatography (Procedure A, Scheme 1). Thereafter, 6
was converted into the terminal ynamide 7 by desilylation with tetrabutyl ammonium fluoride
(TBAF) to give 7 in 74% yield. Alternatively, the terminal ynamide 7 was accessible by N-
ethynylation with the alkynyliodonium salt 5b (Procedure B, Scheme 1). This gave 7 in 77%
yield through an even more straightforward synthetic transformation. Finally, the oxidative
homo-coupling of ynamide 7 mediated by copper catalysis in acetone yielded title compound 3 in
92% yield after its isolation by column chromatography on silica gel as a colorless, air and
moisture stable solid.
3.2 1H and 13C NMR studies
With the aim to achieve the full assignment of the H and 13C NMR signals characterizing
1
1
ynamide 3, the H and 13C NMR spectra were measured together with more detailed 2D NMR
analyses including 1H-1H Cosy, HSQC and HMBC experiments. All NMR spectra were recorded
in CDCl3 solution at room temperature. The HMBC cross peaks and their assignment are shown
in Figure 2.

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Figure 2. HMBC spectra of bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide (3).
In the HMBC spectrum, the tosyl methyl group (H-19, 2.47 ppm) correlates with the quaternary
carbon atom at 145.0 ppm and is therefore assigned to C-16. Consequently, the signal at 134.8
ppm can be appointed to C-13, the other aromatic quaternary carbon atom. The 13C NMR signal
1
at 130.0 ppm can be endorsed to C-15 and C-17 because of its correlation with the H NMR
signal of H-19. Accordingly, the 13C NMR signal at 127.7 ppm corresponds to C-14 and C-18.
1
The assignment of the H NMR signals of H-14/H-18 and H-15/H-17 at 7.79 and 7.37 ppm
respectively can then be deduced from the analysis of the HSQC spectrum (see, supplement
material). Finally, the relaxation of the acetylenic carbon atoms C-1 and C-2 occurred at 75.4 and
59.6 ppm respectively, based on the HMBC spectrum analysis. Indeed a correlation spot is
observed between the triplet 1H NMR signal corresponding to H-5 at 3.34 ppm and the 13C NMR
peak at 75.4 ppm.
3.3 Molecular structure in the single crystal
Single crystals of diynamide 3 were obtained by slow diffusion of n-pentane into a chloroform
(3) solution through the vapor phase. The molecular structure of 3 as the result of a single crystal
x-ray analysis is shown in Figure 3 together with a listing of bond lengths and bond angles.
The amido substituents in 3 adopt a twisted orientation along the 1,3-diyne carbon rod resulting
in a molecule with axial chirality. The bond lengths of N1-C1 and N2-C4 are 1.345(4) Å and
1.348(3) Å, respectively, which are consistent with the reported lengths of the related compounds
1 and 2 [47, 48]. The distances of C1-C2, C2-C3 and C3-C4 are 1.199(4) Å, 1.365(4) Å and
1.199(4) Å, showing a clear bond alternation. The C1-C2/C3-C4 bond length is with 1.199(4) Å

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in agreement with the presence of a C-C triple bond – albeit it is slightly longer than C-C triple
bonds reported for 1 and 2 with respectively 1.193(6) and 1.188(3) Å. This might be due to a
more favorable electronic conjugation along the 1,3-butadiyne-1,4-diamide moiety in 3. This
gains further support by the slightly shorter C2-C3 bond length of 3 with 1.365(4), compared to
those of 1 and 2 with 1.376(6) and 1.373(4) respectively.
Atoms
Bond
Length
(Å)
Atoms
Bond
Angle
(°)
N1-C1
C1-C2
C2-C3
C3-C4
C4-N2
N1-S1
N1-C5
N2-S2
N2-C9
-
1.345(4)
1.199(4)
1.365(4)
1.199(4)
1.348(3)
1.665(3)
1.492(3)
1.676(2)
1.490(3)
-
N1-C1-C2
C1-C2-C3
C2-C3-C4
C3-C4-N2
C5-N1-S1
S1-N1-C1
C1-N1-C5
C9-N2-S2
S2-N2-C4
C4-N2-C9
179.0(2)
178.5(2)
177.7(2)
177.2(2)
121.9(2)
117.7(2)
119.1(2)
118.8(1)
116.6(1)
118.9(2)
Figure 3. Asymmetric unit of 3 and table of bond length and angles. Displacement ellipsoids are drawn at the 50% probability
level.
The 1,3-butadiyne moiety curves slightly, where the angles of N1-C1-C2, C1-C2-C3, C2-C3-C4
and C3-C4-N2 are 179.0(2), 178.5(2), 177.7(2) and 177.2(2)°, respectively. The nitrogen atoms
have a trigonal planar environment as evidenced by both, the sum of the bond angles at N1/N2 =
358.7°/354.3° as well as the plane r.m.s. (root-mean-square) deviation of 0.0437 Å and 0.0899 Å
for the N1/C1/C5/S1 and the N2/C4/C9/S2 plane, respectively. Such a planar environment
around the nitrogen atoms is also due to the effective conjugation of the nitrogen lone pair with
the adjacent carbon-carbon triple bond. The torsion angle between the mean planes of
N1/C1/C5/S1 and N2/C4/C9/S2 is 76.6° underlining an orthogonal arrangement of the two amide
moieties throughout the spacing 1,3-butadiyne carbon rod (Figure S9 in supplementary material).
This orthogonal or twisted arrangement should not be solely understood as a conformation that is
stabilized by the crystal lattice – it is also reasoned by effective conjugations of the nitrogen lone
pairs with the adjacent 1,3-butadiyne moiety. The latter should be interpreted as being the origin
for extended helices of frontier molecular orbitals displaying non-linear π-interactions. Similar
twisted amino groups attached to a conjugated 1,3-diyne unit can be found in the 1,3-butadiyne-
1,4-diamines 1 and 2 with torsion angles of 60.2° and 85.2°, respectively. With 76.6° the torsion
angle of ynamide 3 is also in very good agreement with ab initio molecular geometry calculations
of a related diynamide, where a calculated torsion angle of 66.74° was reported [49].

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The crystal packing of diynamide 3 is shown in Figure 4 and 5. The molecular packing of 3 is
stabilized by weak CH-π intermolecular interaction: the distance between hydrogen H24 and Cg1
(Cg1 is centroid of C13-C19 benzene ring at 1-x, -y, -z symmetry code) is 2.914 Å (Figure 4).
Figure 4. CH-π intermolecular interaction within dimer units of 3 in the single crystal.
This interaction aligns molecules of 3 to pairs with an intermolecular spacing of 4.62 Å for the
shortest intermolecular distance between two 1,3-diyne units within these pairs – and about 7.89
Å for the translational distance between the two 1,3-diynes of adjacent pairs. Each pair of 3
consists of a right- and left-handed axial chiral carbon rod. The intermolecular distance of 4.62 Å
for two alkyne rods within such a pair is in the range to favor topochemical reactions; whereas
the spacing of the diyne pairs will make a topochemical chain polymerization less likely [57-60].
For example, for the topochemical chain polymerization of 1,3-diacetylenes the steric
requirements are one-dimensional stacking of the diacetylene units to translational positions
around 4.9 Å and inclination angles of the diacetylene axes to the packing axis about 45° [61].
Figure 5. Crystal packing of diynamide 3.

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Within the crystal packing of 3, there are short contacts (i.e. the distance between the atoms
involved is less than the sum of the van der Waals radii of these atoms) between protons H22 and
H25 of a benzene ring and the O atoms of the sulfonyl groups of adjacent molecules (Figure 5
and Table 2, and Figure S10 in supplementary material): 2.48 Å (CHO angle = 157°) and 2.60 Å
(CHO angle = 102°), respectively. These distances suggest the existence of relatively unusual C-
H…O hydrogen bonds.
Table 2. Hydrogen-bonding geometry (Å, °).
D—H···A
C(22)--H(22)···O(2)i
C(25)--H(25)···O(4)ii
D—H [Å]
0.95
H···A [Å]
2.48
D···A [Å]
3.380(3)
2.952(3)
D—H···A [°]
157
102
0.95
2.60
Symmetry code (i) : 1-x, 1-y, -z (ii) : -x, -y, -z
3.4 Photophysical and electrochemical properties
The photophysical properties of diynamide 3 were examined using UV-vis and fluorescence
spectroscopy in diluted (10-5 M) THF, CH2Cl2 and CH3CN solutions at room temperature. The
corresponding spectra are illustrated in Figure 6.
25000
THF
CH Cl
2
2
CH CN
20000
15000
10000
5000
0
3
240
260
280
300
320
340
360
380
400
Wavelength (nm)
Figure 6. UV-vis absorption spectra of 3 in THF (black), CH2Cl2 (red), and CH3CN (blue).
In agreement with the symmetrical molecular structure of diynamide 3, the solvatochromism is
negligible and the UV-vis spectra are almost identical in solvents of different polarity. The UV-
vis spectra have an onset value of λonset = 319 nm and shoulders at 295, 277, and 254 nm.
Photoluminescene measurements with 10-5 M solutions of diynamide 3 in THF, CH2Cl2 and
CH3CN at excitation wavelength of λex = 270, 280 and 290 nm respectively revealed that the
compound is non-emissive in these solvents and with our experimental setup.
Cyclic voltammetry experiments with 3 were carried out in the presence of Bu4NPF6 (0.1 M in
CH2Cl2) and with Fc/Fc+ (0.46 V vs SCE) [62] as the internal standard. Within the

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solvent/electrolyte window diynamide 3 showed a non-reversible oxidation potential Eox1/2 = 1.51
V with a well pronounced oxidation half-wave at Eox = 1.54 V, respectively (Figure 7).
0,00006
Fc/Fc+
0,00004
0,00002
0,00000
-0,00002
-0,00004
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
Vf vs SCE (V)
Figure 7. Cyclic voltammetry study of compound 3 (10-3 M in CH2Cl2 / 0.1 M nBu4PF6) at room temperature measured versus
SCE. Scan rate 100 mV/s, values are corrected vs internal ferrocene (Fc/Fc+= 0.46 V vs SCE).
From the onset of the oxidation half-wave Eox
= 1.23 V, the energy level of the highest
onset
occupied molecular orbital (HOMO) of 3 was estimated to EHOMO = -5.87 eV; with EHOMO = -
(Eonset, ox vs Fc/Fc+ + 5.10) (eV) for measurements in dichloromethane solution with 0.1 M Bu4NPF6
as the supporting electrolyte. We choose -5.10 eV as the formal potential of the Fc+/Fc redox
couple in the Fermi scale as suggested by Bazan et al. and not the often used value of -4.8 eV for
0.0 V, because the calibration scale of -5.10 eV is based on a set of empirically obtained
electrochemical data and reflects best the stability of the redox species involved [63]. The energy
level of the lowest unoccupied molecular orbital (LUMO) was thereafter estimated by adding the
value of the optical band gap taken from the onset of the absorption spectra of 3 in CH2Cl2 (λonset
Gap
= 319 nm, 3.89 eV) providing ELUMO = -1.98 eV with ELUMO = EHOMO
+
E . The results of the
opt
photophysical and electrochemical investigation of diynamide 3 are summarized in Table 3.
Table 3. Experimental determination of the HOMO-LUMO energy levels of diynamide 3.
Gap
E
(eV) Eox (V) Eox1/2 (V) Eoxonset (V) HOMO (eV) LUMO (eV)
λonset (nm)
opt
319
3.89
1.54
1.51
1.23
-5.87
-1.98
3.5 Thermal properties
The thermal properties of compound 3 were investigated by thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) which are shown in Figure 8. Based on the TGA
analysis decomposition with mass loss proceeded slowly at 198 °C and the following
decomposition process was completed when the temperature was raised above 545 °C.

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198 °C
113 °C
100
80
60
40
20
0
98 °C
first heating
first cooling
545 °C
137 °C
second heating
100
200
300
400
500
600
700
60
80
100
120
140
160
180
Temperature (°C)
Temperature (°C)
Figure 8. Thermogravimetric analysis (TGA) [left] and Differential Scanning Calorimetry (DSC) [right] of diynamide 3.
A more detailed picture of the thermal transitions of diynamide 3 were obtained from DSC
analysis (Figure 8). The small endotherm transition at 98 °C can be assigned to an “alkyl chain
melting” process of the n-butyl groups of diynamide 3 in the crystal. This weakly endotherm
transition is followed by the endothermic melting with a maximum at 113 °C. Notably,
simultaneous to the melting of 3, an exothermic reaction was observed with a maximum at 137
°C that proceeded during the heating period of 110-180 °C and that is synonymous with a chain
polymerization. The occurrence of a polymerization reaction of 3 was furthermore verified by the
following cooling and a second heating scan. In the latter case, neither “alkyl chain melting” nor
the melting of 3 could be observed certainly demonstrating that discrete molecules of diynamide
3 were absent. This was sustained by the observation of film formation during continuous
increase of temperature during the heating process above the melting point. Based on the DSC
analysis, the spontaneous thermal polymerization of diynamide 3 in the solid state is less likely of
the sole topochemical type as it proceeds simultaneously with or shortly after the endothermic
phase transition assigned to melting. However, as the closest distances between the alkyne rods
of 3 in the single crystal are in the range of a topochemical reaction and the polymerization
process proceeds simultaneously to the disruptor of the regular crystal lattice, the results
presented here might be best interpreted as a topochemical initiated polymerization that is
induced by closely packed dimers of 3 in the crystal and that is continued by a non-topochemical
polymer chain growth of these dimers during the process of melting. Notably, the resulting
polymer gains thermal stability up to 198 °C without any mass loss by polymer fragmentation as
evidenced by TGA.
4. Conclusion
The new ynamide bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide (3)
was synthesized by direct N-ethynylation using alkynyliodonium salts followed by a subsequent
oxidative Glaser coupling. The molecular properties of the title compound 3 were characterized

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1
by single crystal x-ray diffraction, 1- and 2D H and 13C NMR, UV-vis and fluorescence
spectroscopy, as well as cyclic voltammetry. The HOMO/LUMO energy levels of the diynamide
3 were experimentally estimated to be -5.87/-1.98 eV respectively by means of photophysical and
electrochemical investigations. In the single crystal, the amido substituents of 3 adopt a twisted
orientation with a torsion angle of 76.6°. Such a twist results in a molecule with axial chirality
where the lone-pairs of the nitrogen atoms conjugate effectively with the adjacent π-systems of
the alkyne motifs. Therefore, ynamide 3 is an example of a conjugated linear molecule displaying
helical frontier molecular orbitals with non-linear π-interactions. Intermolecular CH-π
interactions align molecules of 3 into pairs within the crystal lattice and as a result, the
intermolecular spacing of the 1,3-diyne units is with 4.62 Å in the range to favor topochemical
reactions. Based on TGA and DSC analyses, the thermally initiated solid state polymerization of
3 might be best described as a topochemical initiated polymer chain reaction that proceeds with a
non-topochemical chain growth.
Further studies on polymerization reactions of ynamides, diynamides and related alkynes
including polymerization in confined spaces are under investigation in our laboratory and will be
reported in due course.
Acknowledgement
Financial support of this work from the French Agence National de la Recherche (ANR) through
the program "Investissements d’Avenir” (ANR-10-LABEX-09-01) - EMC3 (energy materials
and clean combustion center) - and from the Ministère de l'Enseignement Supérieur et de la
Recherche of France for T.-H. Doan are gratefully acknowledged. I. Talbi is indebted to the
Ministry of Higher Education and Scientific Research of Tunisia for a scholarship allowing her
two short-term research stays at the LCMT in France.
Appendix A. Supplementary material
The supplementary crystallographic data for diynamide 3 have been deposited with the
Cambridge Crystallography Data Centre, 12 Union road, Cambridge CB22 1EZ, UK (Fax: +44
1223 336 033); E-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk and are available
free of charge on request quoting the deposition Number CCDC 1449990. Supplementary data
associated with this article can be found in the online version, at http://dx.doi.org/XX.XXX.
References
[1] Modern Acetylene Chemistry (Eds.: P.J. Stang, F. Diederich), VCH Weinheim (1995).
[2] Acetylene Chemistry-Chemistry, Biology and Material Science (Eds.: F. Diederich, P.J Stang,
R.R. Tykwinski), Wiley-VCH Weinheim (2005).

ACCEPTED MANUSCRIPT
[3] V. Maraval, R. Chauvin, Chem. Rev. 106 (2006) 5317-5343.
[4] B. Witulski, J. Grand, Application to the synthesis of natural products, in Transition-Metal-
Mediated Aromatic Ring Construction, (Ed. K. Tanaka); Wiley: Hoboken New Jersey
(2013), pp. 207-242.
[5] I.-T. Trotus, T. Zimmermann, F. Schüth, Chem. Rev. 114 (2014) 1761-1782.
[6] Carbon-Rich Compounds (Eds. M.M. Haley, R.R. Tykwinski), VCH Weinheim (2006).
[7] H.G. Viehe, Angew. Chem. Int. Ed. 6 (1967) 767-778.
[8] H.G. Viehe in Chemistry of Acetylenes (Ed.: H.G. Viehe), Marcel Dekker New York (1969)
pp. 861-912.
[9] A.M. Cook, C. Wolf, Tetrahedron Lett. 56 (2015) 2377-2392.
[10] K.A. DeKorver, H. Li, A.G. Lohse, R. Hayashi, Z. Lu, Y. Zhang, R.P. Hsung, Chem. Rev.
110 (2010) 5064-5106.
[11] G. Evano, A. Coste, K. Jouvin, Angew. Chem. Int. Ed. 49 (2010) 2840-2859.
[12] X.-N. Wang, H.-S. Yeom, L.-C. Fang, S. He, Z.-X. Ma, B.L. Kedrowski, R.P. Hsung, Acc.
Chem. Res. 47 (2014) 560-578.
[13] B. Witulski, C. Alayrac, N-Acyl- and N-Sulfonylalk-1-yn-1-amines, in: Science of Synthesis
– Compounds with Four and Three Carbon-Heteroatom Bonds, (Ed. A. de Meijere), Georg
Thieme Stuttgart, Germany, 2005, Vol. 24, pp. 1031-1058.
[14] B. Witulski, T. Stengel, Angew. Chem. Int. Ed. 37 (1998) 489-492.
[15] B. Witulski, M. Gößman, Chem. Commun. (1999) 1879-1880.
[16] B. Witulski, M. Gößman, Synlett (2000) 1793-1797.
[17] B. Witulski, J. Lumtscher, U. Bergsträßer, Synlett (2003) 708-710.
[18] C. Alayrac, B. Witulski, Angew. Chem. Int. Ed. 41 (2002) 3281-3284.
[19] V. Richard, M. Ipouck, D.S. Merel, S. Gaillard, R.J. Whitby, B. Witulski, J.L. Renaud,
Chem. Commun. 50 (2014) 593-595.
[20] F. Nissen, V. Richard, C. Alayrac, B. Witulski, Chem. Commun. 47 (2011) 6656-6658.
[21] S.K. Pawar, R.L. Sahani, R.-S. Liu, Chem. Eur. J. 21 (2015) 10843-10850.
[22] R. Liu, G.N. Winston-McPherson, Z.-Y. Yang, X. Zhou, W. Song, I. A. Guzei, X. Xu, W.
Tang, J. Am. Chem. Soc. 135 (2013) 8201-8204.
[23] H. Wakamatsu, M. Sakagami, M. Hanata, M. Takeshita, M. Mori, Macromol. Symp. 293
(2010) 5-9.
[24] Y. Tokimizu, M. Wieteck, M. Rudolph, S. Oishi, N. Fujii, A.S.K. Hashmi, H. Ohno, Org.
Lett. 17 (2015) 604-607.
[25] M.C.B. Jaimes, V. Weingand, F. Rominger, A.S.K. Hashmi, Chem. Eur. J. 19 (2013) 12504-
12511.

ACCEPTED MANUSCRIPT
[26] E. Rettenmeier, A.M. Schuster, M. Rudolph, F. Rominger, C.A. Gade, A.S.K. Hashmi,
Angew. Chem. Int. Ed. 52 (2013) 5880-5884.
[27] P.W. Davies, A. Cremonesi, L. Dumitrescu, Angew. Chem. Int. Ed. 50 (2011) 8931-8935.
[28] C. Alayrac, D. Schollmeyer, B. Witulski, Chem. Commun. (2009) 1464-1466.
[29] B. Dassonneville, B. Witulski, H. Detert, Eur. J. Org. Chem. (2011) 2836-2844.
[30] N. Saito, T. Ichimaru, Y. Sato, Org. Lett. 14 (2012) 1914-1917.
[31] X.Y. Mak, A.L. Crombie, R.L. Danheiser, J. Org. Chem. 76 (2011) 1852-1873.
[32] J.R. Dunetz, R.L. Danheiser, Org. Lett. 5 (2003) 4011-4014.
[33] D. Rodriguez, L. Castedo, C. Saa, Synlett (2004) 377-379.
[34] B. Witulski, T. Schweikert, D. Schollmeyer, N.-A. Nemkovich, Chem. Commun. 46 (2010)
2953-2955.
[35] S. Kramer, J.L.H. Madsen, M. Rottländer, T. Skrydstrup, Org. Lett. 12 (2010) 2758-2761.
[36] T.R. Hoye, B. Baire, D. Niu, P.H. Willoughby, B.P. Woods, Nature 490 (2012) 208-212.
[37] S.Y. Yun, K.-P. Wang, N.-K. Lee, P. Mamidipalli, D. Lee, J. Am. Chem. Soc. 135 (2013)
4668-4671.
[38] R. Kamakar, P. Mamidipalli, S.Y. Yun, D. Lee, Org. Lett. 15 (2013) 1938-1941.
[39] M. Ide, K. Ohashi, S. Mihara, T. Iwasawa, Tetrahedron Lett. 55 (2014) 2130-2133.
[40] H.G. Viehe, M. Reinstein, Angew. Chem. Int. Ed. 3 (1964) 582-583.
[41] A.R. Petrov, C.G. Daniliuc, P.G. Jones, M. Tamm, Chem. Eur. J. 16 (2010) 11804-11808.
[42] J. Ficini, C. Barbara, J. d’Angelo, A. Duréault, Bull. Soc. Chim. Fr. (1974) 1535-1537.
[43] M. Feustel, G. Himbert, Tetrahedron Lett. 24 (1983) 2165-2168.
[44] G. Himbert, D. Faul, M. Barz, Z. Naturforsch. B: Chem. Sciences 46 (1991) 955-968.
[Erratum: Z. Naturforsch. B: Chem. Sciences 13 (1991) 12798.].
[45] M. Barz, M. Feustel, G. Himbert, G. Maas, Liebigs Ann. (1987) 221-226.
[46] M.S. Paley, D.O Frazier, H. Abeledeyem, S.P. McManus, S.E. Zutaut, J. Am. Chem. Soc.
114 (1992) 3247-3251.
[47] Y. Tokutome, T. Okuno, J. Mol. Struct. 1047 (2013) 136-142.
[48] J.J. Mayerle, M.A. Flandera, Acta Cryst. B34 (1978) 1374-1376.
[49] C.H. Hendon, D. Tiana, A.T. Murray, D.R. Carbery, A. Walsh, Chem. Sci. 4 (2013) 4278-
4284.
[50] G. Wegner, Z. Naturforsch. B. 24b (1969) 824-832.
[51] Wegner, Pure & Appl. Chem. 49 (1977) 443-454.
[52] P.C.M. Grim, S. De Feyter, A. Gesquière, P. Vanoppen, M. Rücker, S. Valiyaveettil, G.
Moessner, K. Müllen, F.C. De Schryver, Angew. Chem. Int. Ed. 36 (1997) 2601-2603.
[53] P.J. Stang, Alkynyliodonium Salts: Electrophilic Acetylene Equivalents, in Modern
Acetylene Chemistry, (Eds.: P.J. Stang, F. Diederich, VCH-Weinheim, 1995, pp. 67-98.

ACCEPTED MANUSCRIPT
[54] G.M. Sheldrick SHELXS-97 and SHELXL-97, Program for the Solution of Crystal
Structures University of Gottingen, Germany (1997).
[55] G.M. Sheldrick, Acta Cryst. A64 (2008) 112-122.
[56] B. Witulski, N. Buschmann, U. Bergsträßer, Tetrahedron 56 (2000) 8473-8480.
[57] K. Sada, T. Ishiwata, K. Kokado, Topochemical polymerizations and crystal cross-linking of
metal organic frameworks, in Advances in Organic Crystal Chemistry, (Eds.: R. Tamura, M.
Miyata), Springer, 2015, pp. 517-530.
[58] R. Jelinek, M. Ritenberg, RSC Adv. 3 (2013) 21192-21201.
[59] J.W. Lauher, F.W. Fowler, N.S. Goroff, Acc. Chem. Res. 41 (2008) 1215-1229.
[60] A. Sun, J.W. Lauher, N.S. Goroff, Science 312 (2006) 1030-1034.
[61] V. Enkelmann, Adv. Polym. Sci. 63 (1984) 91-136.
[62] N.G. Connelly, W.E. Geiger, Chem. Rev. 96 (1996) 877-910.
[63] C.M. Cardona, W. Li, A.E. Kaifer, D. Stockdale, G.C. Bazan, Adv. Mater. 23 (2011) 2367-
2371.

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Graphical Abstract
Synthesis, crystal structure, optical, electrochemical and thermal properties of the ynamide:
Bis-(N-4-methylbenzenesulfonyl, N-n-butyl)-1,3-butadiyne-1,4-diamide
Thu-Hong Doan,a Imen Talbi,a,b Jean-François Lohier,a Soufiane Touil,b Carole Alayrac,a Bernhard Witulski*,a
113 °C
98 °C
first heating
first cooling
137 °C
second heating
60
80
100
120
140
160
180
Temperature (°C)