Sonogashira coupling in 3D-printed NMR cuvettes: synthesis and properties of arylnaphthylalkynes

Article abstract of DOI:10.1039/c6nj03614g

3D-Printing has been used to build hollow NMR tube/spinner combinations out of NMR-transparent polyamide. The whole 3D-print has been processed inside a glove box and during pauses of the 3D-printing process, all reactants for the palladium-catalyzed deca

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Jason B. Benedict et al.
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Sonogashira Coupling in 3D-Printed NMR Cuvettes: Synthesis and
Properties of Arylnaphthylalkynes
Received 00th January 20xx,
Accepted 00th January 20xx
Felix Lederle, Frederick Meyer, Christian Kaldun, Jan C. Namyslo and Eike G. Hübner*
DOI: 10.1039/x0xx00000x
3D-Printing has been used to build hollow NMR tube/spinner combinations out of NMR-transparent polyamide. The whole
3
D-print has been processed inside a glove box and during pauses of the 3D-printing process, all reactants for the
www.rsc.org/
palladium-catalyzed decarboxylative Sonogashira coupling of aryl halides with arylpropiolic acids have been inserted.
Within the totally gas tight and pressure resistant tubes, a set of arylnaphthylalkynes has been synthesized and the
progress of the reaction has been monitored via NMR spectroscopy. The (nonlinear) optical properties of the push-pull
substituted bis(aryl)alkynes have been investigated by fluorescence spectroscopy and DFT calculations. A significant
correlation between the intensity of the triple-bond stretching vibration and the calculated first hyperpolarizability is
reported.
1
4
objects. Herein, we now report on the development of
printed reaction flasks fabricated from polyamide which allows
the use of the most common organic solvents and was shown
to be invisible in NMR spectroscopy. Partly due to the
optimized layer adhesion achieved by printing within an inert
gas atmosphere, the mechanical properties of the printed
Introduction
3D-Printing technologies are rapidly improved and have found
various applications in chemical, physical and especially
1
biological research laboratories. From all 3D-printing
technologies, Fused Deposition Modeling (FDM) is probably
the most simple process. By adding layer by layer of the
1
5
objects are excellent. The whole printing procedure is
processed inside a glove box and reactants are filled into the
3D-printed tube/spinner combination during small pauses of
the print. Consequently, the 3D-printed NMR capsules are
capable to handle air-sensitive reaction mixtures for several
weeks. The printed NMR cuvettes were used for the synthesis
of a set of arylnaphthylalkynes via palladium catalyzed
Sonogashira-Hagihara coupling. The Sonogashira coupling is a
convenient method for the synthesis of tolane derivatives by
(
usually molten) polymer filament, the desired object is
2
constructed. Although other technologies such as laser
sintering can lead to printed parts with enhanced layer
adhesion and consequently comparably higher mechanical
load tolerance, the FDM process facilitates the printing of
hollow objects free of remaining powder or supporting
material. Consequently, reaction flask matrices have been
printed via the FDM process out of polypropylene (PP) and
1
6-27
3
,4
the coupling of aryl halides with acetylenes.
While
used for hydrothermal synthesis. 3D-Printing has become
rather popular in flow chemistry due to the possibility to print
virtually any reactor design and to control the product
symmetrical substituted acetylenes are readily accessible, the
synthesis of asymmetric tolane derivatives is more challenging.
5
-11
A side reaction of the Sonogashira coupling is the
2
formation by the geometry of the reactor.
With a
8
homocoupling of alkynes by the copper cocatalyst. Further
limitations are low reactive aryl halides, low catalyst efficiency
combination of PP and silicones, reaction cubes have been
designed, which act as multistep reactors with heterogeneous
2
9,30
1
2,13
and carefully optimized reaction conditions.
Consequently,
catalysts embedded into the silicone wall.
Recently, we
copper-free Sonogashira-conditions have been developed
demonstrated as a proof-of-concept, that the printing of
closed and gas-tight cuvettes fabricated from acrylonitrile
butadiene styrene (ABS) enables analytical measurements (IR,
UV/Vis and NMR spectroscopy) directly through the printed
31-36
which suppress homocoupled products.
A
further
development for the synthesis of asymmetric tolanes is the
decarboxylative Sonogashira coupling. In a first step, the aryl
halide is coupled with propiolic acid. The arylpropiolic acid is
subsequently treated with a second aryl halide in copper-free
conditions and yields the bis(aryl)alkyne upon decarboxylation
3
7-42
(which avoids the deprotonating step of the acetylene).
Especially combinations of electron-rich and electron-poor
substituted bis(aryl)alkynes are of interest. Predominantly
push-pull substituted tolanes show exceptional optical
properties, ranging from solvatochromic fluorescence due to
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Fig. 1 (a) Schematic representation of the 3D-printing and filling procedure of the
NMR tube/spinner combination. (b) Scale CAD drawing (cross-section) of the
NMR tube/spinner combination and inner structure of the NMR tube (insert).
Dimensions: NMR tube: 80.0 mm (length), 5.0 mm (diameter). Total length of the
tube/spinner combination: 131.1 mm. Diameter of the spinner (top): 24.9 mm.
Fig. 2 3D-Print of the NMR tube/spinner combination inside the glove box. The
reagents for the Sonogashira coupling have been inserted (dark solution).
further stops are performed and the print is finalized to obtain
a totally closed object filled with reactants and inert gas. The
total printing time for the NMR tube/spinner combination
presented here filled with all reagents is 3.5 h. During this
work, only one print led to an unusable NMR tube/spinner
combination due to a worn out extruder gear. After
discharging from the box, the tube/spinner combination is
1,55 suitable for NMR measurements. Polyamide has been chosen
as printing material. Since the whole print is processed within
an inert atmosphere, the temperature of the printer nozzle
can be increased up to 265 °C without degradation of the
polyamide by oxidation. As a consequence, the printed layers
intramolecular charge transfer up to nonlinear optical
4
3-54
properties caused by a large hyperpolarizability.
The
combination of common electron-rich bromoaromatic
reactants with alkynes bearing electron-withdrawing
substituents is one of the most challenging conditions for
Sonogashira couplings. Reasons are the comparably low
reactivity of bromoaryls as well as the low reactivity of
4
electron-rich aryl halides and electron-poor acetylenes.
Electron-rich aryl bromides are referred to as benchmark
5
5
conditions for Sonogashira reactions. Here, we present the
Sonogashira coupling with combinations of electron-rich aryl
bromides
-nitronaphthylpropiolic acid with the help of reaction
monitoring via NMR in 3D-printed NMR tube/spinner
combinations to yield push-pull substituted
with
naphthylpropiolic
acid
and
show a strong adhesion which leads to gas tight printed tubes.
To proof the usability of the printed NMR tubes for NMR
5
measurements, test substances in CDCl
13
3
were investigated and
1
revealed clean H-,
C- and 2D-NMR spectra (see
arylnaphthylalkynes and an investigation of their properties.
supplementary material for details and spectra). Fortunately,
the polyamide itself is virtually invisible in the NMR spectra,
probably due to massive line broadening of the solid phase.
According to the surface area, the wall thickness and the
permeability coefficients of polyamide, the printed flasks were
Results and discussion
A
hollow NMR tube/spinner combination has been
constructed by computer aided design (CAD) in accordance to
the outer dimensions given by the manufacturer (Fig. 1b). A
estimated to be sufficiently impermeable against the intrusion
56
of water and oxygen (O : 0.3 µmol/d; H O: 88 µmol/d). The
2 2
3D-printer with Fused Deposition Modeling technology (FDM)
residual water content of the dried polyamide was determined
has been operated inside a glove box to print the tube/spinner
combinations within an inert gas atmosphere (Fig. 2). In
deviation from a common NMR tube, vertical bars (shown in
the plot of the cross-section) had to be added to obtain a
seamless print (Fig. 1b). Otherwise, the comparably strong
adhesion of the molten polyamide to the printer nozzle leads
to irregularities at the nozzle lifting and reversal point. To fill
one or more reactants into the printed tube/spinner
combination, the print is stopped shortly, and solids or
to 0.033
±
0.005 wt-%. To proof the impermeability, a solution
Br
R1
Pd(OAc)2, X-Phos
R1
Cs2CO3, 80 °/ 90 °C
OH
O
+
R2
[D8]THF, N2
R2
in 3D-printed tube
R1 = H ( ), NO2 (
1
2
)
R2 = H, OMe, NMe2
solvents are inserted into the lower part of the tube/spinner Scheme 1 Sonogashira coupling in 3D-printed NMR tube/spinner combinations
as key step for the synthesis of arylnaphthylalkynes.
combination (Fig. 1a). The print is continued, if necessary
2
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coupling starts at 80 °C while the initial release of CO
2
is
caused by the deprotonation of the propiolic acid by Cs CO .
3
2
The consumption of the aryl bromide (according to the integral
value of the NMR spectra) is in good agreement with the
2
formation of CO . In both cases, the reaction was completed
after a surprisingly fast time of 3 h. The yield obtained after
workup (88%) is in good agreement with the expected yield
according to the consumption of bromobenzene (Fig. 3a).
Based on these results, the synthesis of the
arylnaphthylalkynes
spectroscopy (Fig. 3b). Naphthylpropiolic acid
with 9-bromoanthracene and is obtained in quantitative
yield after 20 h. As expected, the electron-poor
-nitronaphthylpropiolic acid ( ) is significantly less reactive
than . The direct comparison of the reaction from
4
–
8
has been monitored via NMR
1
reacts readily
4
5
2
1
1
and 2
Table 1 Summary of the optical properties of arylnaphthylalkynes
3
–
9
.
a
max
b
-30
c
-30
λ
/
Stokes shift
β
CT / 10
β
CC /10
Substance
-1
nm
/ cm
esu
esu
3
39
29
55
33
56
89
60
530
1050
4310
5970
6180
12 000
~
~
0
0
2
2
Fig. 3 Reaction monitoring of the Sonogashira coupling. (a) For the synthesis of
3
2
via consumption of bromobenzene and evolution of CO . (b) Progress of all
coupling reactions monitored via NMR spectroscopy and the consumption of aryl
bromide. *: Temperature has been increased by 10 K.
3
4
5
6
7
8
9
4
of tBuLi in [D18]octane was inserted into the tube/spinner
combination during the print. After 7 days, no decrease of the
tBuLi concentration could be noticed according to the NMR
spectra (see supplementary material). Pressure tests with 3D-
printed flasks with a wall thickness of 3 mm revealed a long-
term pressure stability of 10 bar (water pressure). Additional
impermeability tests have been performed with a basic
solution of pyrogallol in THF inside a 3D-printed reaction flask
with a printed UV/Vis cuvette and demonstrate the complete
absence of oxygen for several days. The spectroscopic
properties of polyamide enable the analysis of UV/Vis
measurements in the range from 900 to 400 nm and IR
d
3
4
3
3
3
-
15
32
47
104
5
13
13
>14
1
-1
measurements in the range from 1700 to 2700 cm through
the printed cuvettes. After these preliminary tests, the key
step for the synthesis of arylnaphthylalkynes has been
performed within printed reaction flasks. (Scheme 1).
5-Nitronaphthylpropiolic acid (2) has been synthesized in
common glassware following a procedure for the Sonogashira
e
coupling of naphthyl bromide with propiolic acid, which leads
4
1
to naphthylpropiolic acid
decarboxylative Sonogashira coupling of the propiolic acids
and with aryl halides follows procedure with
Pd(OAc) /X-Phos as catalytic system and Cs
cross-check the reaction monitoring procedure, the formation
of naphthyl(phenyl)ethyne ( ) by the coupling of with
(
1
)
in good yields.
The
1
2
a
4
2
2
2 3
CO as base. To
f
6619
3
1
bromobenzene has been investigated first. Additionally to the
a
b
Longest wavelength absorption maximum measured in toluene. Measured in
reaction monitoring via NMR spectroscopy, the evolution of
c
d
-1
diethyl ether. Calcd. by DFT. Due to the absence of CT emission in less polar
CO
2
has been monitored via IR spectroscopy at 2350 cm
e
solvents a reasonable Lippert-Mataga plot could not be created. Measured in
inside a 3D-printed flask with a printed IR cuvette (see
f
methanol. Fluorescence emission in THF is weak. The slope of the Lippert-
supplementary material for details). The decarboxylative Mataga plot and consequently βCT is likely to be larger.
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Table 2 Plot of the calculated molecular orbitals of 4, 6, 8 and 9.
HOMO
LUMO
4
6
8
9
Fig. 4 Fluorescence emission of
irradiation with 405 nm.
3 – 8 in toluene (top) and THF (bottom) upon
shows weak IR fluorescence in THF and an IR cut filter
8
720 nm) has been used to filter visible light. 9 is shown in methanol.
(
with bromobenzene reveals an approx. 10 fold decrease in
reactivity for . After 40 h, a conversion of 60% was achieved.
2
Subsequently, no further progress of the reaction was
noticeable, even after 130 h reaction time and elevated
temperatures. It may be assumed, that the catalyst is
deactivated even in the absence of oxygen, for example by the
5
5
formation of palladium clusters. Consequently, all other
reactions have been stopped after 40 h.
The formation of 5-nitronaphthyl(anthracenyl)ethyne
(6)
proceeds slower, but to a comparable conversion as the
formation of 5. An increase of the temperature after 15 h
leads to a slightly faster reaction. The formation of the push-
pull substituted 5-nitronaphthyl(p-methoxyphenyl)ethyne (7)
is comparably slow, significantly speeds up with rising
temperature and leads to a maximal conversion of 60%.
Finally, the coupling of 1-bromo-4-N,N-dimethylaminobenzene
a
a
For 9, the HOMO-3 is shown.
emission in THF (Fig. 4). The Stokes shift (measured in diethyl
ether) increases from 7 nm ( ) and 14 nm ( ) for the unpolar
derivatives up to 280 nm for
in the same solvent for
with 5-nitronaphthylpropiolic acid (2) is as expected the
3
4
slowest and leads to a total conversion of 30%. Assuming a
slower reaction with increasing donor capability of the aryl
bromide (and consequently a limited yield due to limited
lifetime of the catalytic system), the aryl moieties can be
ordered according to their electron richness: Ph < anthracene
8
. The increase of the Stokes shift
5
–
8
(see Table 1) nicely resembles the
increasing donor strength of the substituents of the phenyl
ring. Interestingly, the anthracene moiety shows a comparable
57
donor strength as anisole according to the Stokes shift, which
~
Ph-OMe
2
< Ph-NMe which matches well with the
opens up the possibility for heteroatom-free donor-acceptor
expectation.
tolanes. The strongest donor, NMe2, can be switched into an
53
acceptor by alkylation. Consequently, 8 was treated with
All synthesized arylnaphthylalkynes show intense fluorescence
covering the full spectrum from intense blue to near infrared
58
methyl iodide following a standard procedure to obtain the
ionic species . The longest wavelength absorption maximum
shows a hypsochromic shift of 30 nm upon methylation and
shows intense blue fluorescence in methanol (Fig. 4). The
fluorescence emission maxima of are nearly independent of
the solvent. Consequently, the acceptor strength of the
-nitronaphthyl and the p-trimethylanilinium moiety can be
(
Fig. 4). The emission maxima of
independent from the solvent and the emission spectra reflect
the absorption spectra. In contrast, show predominantly
3 and 4 are nearly
9
9
5
– 8
broad and structureless fluorescence emission. This is in
agreement with a charge transfer (CT) in case of the push-pull
9
substituted arylnaphthylalkynes. Accordingly,
solvatochromic dependency of the fluorescence emission. In
the case of , a solution in toluene exhibits predominantly
non-CT emission ( em = 400 nm), while increasing the solvent
polarity to THF leads to a yellow CT emission ( em = 560 nm).
The derivatives show intense charge transfer in toluene
5 – 8 show a
5
assumed to be quite equivalent. To further investigate the
donor-acceptor substitution pattern, density functional theory
5
λ
(
DFT) calculations were performed and contour plots of
59,60
λ
selected HOMO/LUMOs are given in Table 2.
In the cases
6
– 8
of 3 - 8, the longest wavelength absorption maximum was
and a strong solvent dependency of the CT emission
maximum. In case of 8, the bathochromic shift of the
fluorescence is large enough to lead to a weak infrared
confirmed to be the allowed HOMO/LUMO transition by time-
dependent DFT calculations. As expected, the electron density
of the HOMO and the LUMO are located at the anthracene
4
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moiety in case of
4, which is in accordance with the absence of
charge transfer. The orbital plots of
6
reveal the donor
strength of the anthracene moiety if an appropriate acceptor is
present and show a complete charge transfer from the
anthracene to the naphthalene unit, which again is in
accordance with the fluorescence spectra. Obviously,
complete charge transfer is observed for
possession of the strongest donor, too. The calculations of the
cation of instead resulted in a contrary situation with a
8, which is in
9
strong charge transfer from nitronaphthalene as donor and
trimethylanilinium as acceptor. This is in contrast to the
observed absence of solvatochromism. The calculation of the
contact ion pair (see Table 2) revealed a minimum energy at a
distance of the iodine anion d(N-I) = 4.3 Å from the cationic
nitrogen center. This corresponds with an overall decrease of
the charge (NBO) of the cation of
9 from +1 to +0.8, which is in
accordance with the charge distribution at the energy
6
1,62
minimum for calculated ion pairs.
The decrease of the
positive charge reduces the electron-pull character of the
trimethylanilinium moiety. The first allowed UV transition of
the contact-ion pair is calculated via time-dependent DFT as
the HOMO-3/LUMO transition (HOMO/-1/-2 are located at the
iodine anion). The orbital plots of the contact-ion pair reveal
this transition to be located at the naphthalene unit and
charge-transfer is nearly absent, which is in accordance with
the fluorescence spectra and again demonstrates the electron
deficiency of nitronaphthalene and trimethylanilinium
moieties to be nearly equivalent.
For tolanes, the hyperpolarizability β is a well known and
highly interesting feature. The static part of the
hyperpolarizability β0 can be estimated for compounds with an
intense charge-transfer via the solvatochromic method:
6
3-68
Fig. 5 Correlation of the calculated hyperpolarizability
β
CC with (a) the chemical
]THF (*: measured in [D ]methanol)
and (b) the intensity of the C-C-triple bond vibrational band CC in ATR-IR
spectroscopy.
1
3
13
shift difference ꢀδ
(
C
α
-
C
β
) measured in [D
8
4
2
A
3
| Meg | ꢀµ
eg
(1)
β
CT
=
2
2
2h ν
eg
with νeg=frequency of the CT absorption, M =transition dipole
eg
been evaluated experimentally to 25 esu for 4-methoxy-4’-
nitrodiphenylacetylene (MONA) which is roughly twice as
moment of the CT absorption and
dipole moment between ground and CT excited state.
Consequently, fluorescence spectra of have been
measured in cyclohexane, toluene, diethyl ether and THF. With
the help of Lippert-Mataga plots to determine µeg, βCT has
ꢀµeg=difference of the
5
4
much compared to
same level of theory reveal
to 47 esu for . One reason for a lower
lower oscillator strength of the HOMO/LUMO transition which
7.
In accordance, calculations on the
CC=104 esu for MONA compared
CT may be found in a
3
– 8
β
7
β
ꢀ
been evaluated (see supplementary material for details).
Additionally, the first hyperpolarizability tensor has been
calculated along the axis of the C-C-triple-bond (βCC) with DFT
is calculated to f = 1.0 for MONA compared to f = 0.3 for
7
8
(measured in toluene: f = 0.2). As expected, alkylation of
massively decreases the hyperpolarizability and
βCC of the
9 is calculated to 5 esu, which is in the range
calculations on the LACVP*/PBE0 level of theory. For
the calculated hyperpolarizability CC is very weak and
due to the absence of solvatochromic fluorescence. The
donor-acceptor substituted arylnaphthylalkynes show
large values. Again, p-methoxybenzene and anthracene
appear to be rather comparable donor moieties according to
the calculated and experimentally determined
hyperpolarizability. N,N-Dimethylaminobenzene as the
strongest donor leads to the largest calculated CC of 100 esu.
Due to the weak infrared emission, eg and consequently
could not be estimated more accurate for . Overall, the
measured hyperpolarizabilities are comparable to donor-
3 and 4,
contact ion pair
β
βCT ≈ 0
for the unpolar derivatives
estimated experimentally.
3
and
4
and in accordance with
β
CT
5
– 8
The polarization of the triple-bond of tolanes has been
extensively studied. Especially, the correlation between the
β
1
3
13
shift difference ꢀδ ( C
atoms has been observed as a useful parameter to quantify
α β
- C ) of the two acetylenic carbon
6
9,70
the polarization.
Para, ortho and meta subsituted tolanes
β
must be discussed separately, due to an influence of the
substitution pattern on the chemical shift. Since the
ꢀ
µ
β
CT
8
7
1.72
polarization is connected to the hyperpolarizability,
1
we
3
13
investigated the correlation of βCC vs. ꢀδ ( C - C ) (Fig. 5a).
α β
0
acceptor substituted bis(phenyl)alkynes. For example, β has
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The series of naphthyl(phenyl)alkynes
3
,
5
,
7
,
8
(black line) observed. Overall, the fluorescence emission of the
) to near infrared ( ).
had to be measured in a more The solvatochromic fluorescence could be explained by an
polar solvent and is excluded from the correlation. The intense charge-transfer which was investigated by DFT
reveal a nice dependency of
difference. The ionic species
β
CC on the chemical shift arylnaphthylalkynes ranges from blue (
3
8
9
+
-
anthracenyl(naphthyl)alkynes
3
4 and 6 (grey line) have to be calculations. Interestingly, the contact ion pair Aryl-NR I
discussed separately in accordance with the ortho-substitution showed up to be comparably electron withdrawing as Aryl-
7
0
effect.
Since the polarization should directly affect the intensity of an substituted arylnaphthylalkyne
IR vibrational band, we investigated the correlation of the switched off by alkylation ( ). The solvatochromic fluorescence
was used to estimate the hyperpolarizability of the
CC. Fortunately, an effect of the arylnaphthylalkynes and found to be in the range of
ortho-substitution on the intensity of the IR vibration is not push-pull substituted bis(phenyl)alkynes. The calculated
noticeable here and we are able to correlate the full set of hyperpolarizability cc along the C-C triple bond was correlated
substances with phenyl and anthracenyl substituents, with the chemical shift difference of the ethyne carbon atoms
including the ionic species (Fig. 5b). According to the IR in accordance with literature. Finally, a good correlation of
spectra, the polarization is by far the largest for the with the intensity of the IR vibrational band CC has been
dimethylamino-species , followed by the anisole and with a observed and allows an extremely fast prediction of the optical
noticeable lower intensity the anthracene derivate 6. properties.
Subsequently, is the least polarized pull-substituted
arylnaphthylalkyne. As expected, the unpolar derivates
show only very weak IR intensities. Again, the methylation of
NO
2
.
The solvatochromism of the N,N-dimethylamino-
8
consequently could be
9
-1
absorbance ACC of the triple bond vibration around 2200 cm
in ATR-IR-spectroscopy with
β
3 – 9
β
9
β
cc
ν
8
7
5
3
and
4
8
Acknowledgements
is confirmed to lead to a nearly unpolarized tolane. Overall,
the extremely fast measurement of an ATR-IR spectrum in
solid phase allows to evaluate the polarization of tolanes and
We thank PD Dr. J. Adams and K. Hillrichs of the Institute of
Physical Chemistry for help with fluorescence measurements,
Dr. G. Dräger of the Institute of Organic Chemistry of the
Leibniz University Hannover for the measurement of the high-
resolution mass spectra, M. Heinz and U. Köcher of the
Institute of Technical Chemistry for SEC and DSC
measurements.
CC
consequently to estimate β .
Conclusions
In summary, we demonstrated 3D-printed cuvettes to be a
useful tool in synthetic inert gas chemistry. The use of
polyamide as printing material led to totally gas-tight and
pressure resistant reaction vessels. Additionally, solid
polyamide was found to be nearly transparent in NMR
spectroscopy. Further work will concentrate on taking an
advantage of the 3D-printing process to generate virtually any
desired structure and consequently use 3D-printed devices for
the determination of reaction mechanism by controlled
addition of reactants during the NMR measurements.
Experimental
General procedure for the synthesis of arylnaphthylalkynes in
3
D-printed NMR tube/spinner combinations
On a small weighing boat, 1 eq. of the appropriate
-(naphthalene-1-yl)propiolic acid, 1 eq. dry Cs CO , 1 mol-%
Pd(OAc) and 2 mol-% X-Phos were weighed in with a balance
3
2
3
2
installed in the glove box and mixed thoroughly. In a small
flask, a solution of 0.85 eq. of the appropriate dry aryl halide in
The 3D-printed tube/spinner combinations presented here
have been used to synthesize arylnaphthylalkynes via
decarboxylative Sonogashira coupling. With the help of
reaction-monitoring via NMR, each reaction was performed
only once and proceeded to the best possible conversion.
Additionally, information about the reaction rate was
gathered. Due to the design of the NMR cuvette, a sufficient
amount of substance for subsequent investigations could be
isolated from the same experiment after the reaction had
been completed. The donor capability of different aryl
bromides could be correlated with the speed of the reaction.
The combination of 5-nitronaphthylpropiolic acid with push-
substituted aryl bromides were challenging conditions for the
Sonogashira coupling and led to a set of new push-pull
substituted arylnaphthylalkynes. The fluorescence properties
8
dry [D ]THF (40 eq.) was prepared separately.
The print of the tube/spinner combination was started inside
the glove box with polyamide as printing material. After half of
the print of the spinner section had been completed, the solid
mixture prepared before was inserted during a short first
pause of the print. The print was continued, until the spinner
had been printed completely. The solution of the aryl halide in
8
[D ]THF was inserted into the spinner via a syringe during a
second short pause of the print. The print was continued until
the tube/spinner combination was complete. After finishing
the print, the flask was discharged from the glove box and
1
3
carefully checked for irregularities. An initial
C-NMR
spectrum was recorded directly after discharging from the box.
The tube/spinner combination was heated with an aluminium
bead bath at 90 °C (bead bath temperature). Regularly, the
tube/spinner combination was cooled down and subsequent
of
3 – 9 were investigated in detail and the donor strength of
anthracene was found to be comparable to anisole.
Dependent from the donor-substituent and the solvent
polarity, a large Stokes shift of the fluorescence emission was
1
3
C-NMR spectra were recorded. If necessary, the bead bath
6
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NP lee wa s eJ od uo r nn oa tl aod fj uC s ht em ma ri sg it nr sy
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temperature was increased to 100 °C. After completion of the 27 A. C. Götzinger and T. J. J. Müller, Org. Biomol. Chem., 2016,
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2
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removed at reduced pressure. The remaining dark brown oil
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New Journal of Chemistry
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DOI: 10.1039/C6NJ03614G
A set of push-pull substituted arylnaphthylalkynes has been synthesized under inert gas
conditions in 3D-printed cuvettes out of NMR-transparent polyamide and their optical
properties were investigated.