Novel synthetic strategy towards subphthalocyanine-functionalized acetylenic scaffolds: Via various dibromo-enynes

Article abstract of DOI:10.1039/d0ob00988a

Boron subphthalocyanine (SubPc) is a strong chromophore with interesting applications in the field of functional materials and can be synthetically modified in both the peripheral and axial positions, allowing tuning of optical and redox properties. Herei

Full text of DOI:10.1039/d0ob00988a

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DOI: 10.1039/D0OB00988A
ARTICLE
Novel synthetic strategy towards subphthalocyanine-
functionalized acetylenic scaffolds via various dibromo-enynes
Line Broløs,a Martin Drøhse Kilde a and Mogens Brøndsted Nielsen*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Boron subphthalocyanine (SubPc) is a strong chromophore with interesting applications in the field of functional materials
and can be synthetically modified in both the peripheral and axial positions, allowing tuning of optical and redox
properties. Herein we present novel acetylenic scaffolds where SubPc units are bridged via acetylenic moieties at the axial
boron. Specifically, we show that dibromo-functionalized enyne and enediyne units (vinylic dibromides) can be attached to
one or two SubPc boron atoms using an AlCl3-mediated alkynylation protocol of trimethylsilyl-protected alkynes, and such
compounds can conveniently be employed for further Sonogashira or Glaser-Hay coupling reactions. Thereby, new
tetraethynylethene (TEE) - SubPc scaffolds were obtained. The degree of communication between two SubPc units
incorporated in dimeric scaffolds was investigated by cyclic voltammetry. When bridged by one TEE unit, the oxidations of
the SubPc units occurred sequentially, while the two SubPc units behaved as independent redox centers when separated
by two TEE units.
acetylene-based moieties such as expanded radialenes and
radiaannulenes, which have previously demonstrated alluring
electron-accepting properties.9
Introduction
Boron subphthalocyanine (SubPc; Fig. 1A), discovered by
Meller and Ossko in 1972,1 is a π-conjugated, macrocyclic
chromophore of interest as a light harvester in materials for
optical applications such as organic photovoltaics and dye-
sensitized solar cells (DSSCs).2 One remarkable advantage of
the SubPc moiety as a dye is its facile one-step synthesis via
macrocyclization between phthalonitrile and BCl3 at 200 °C. In
contrast to e.g. porphyrin-based dyes, the SubPc macrocycle
furthermore has the advantage of taking a characteristic bowl-
like shape, which increases the solubility and facilitates
chromatographic purifications due to reduced aggregations.
While the macrocycle itself with an axial chlorine at the boron
(SubPc-Cl) is readily obtained, versatile methods for further
functionalization of the macrocycle are critical for
incorporation of the SubPc into functionalized dyes. Various
methods for functionalization of the precursor, SubPc-Cl, in
both peripheral and axial positions have been developed,3
including the direct attachment of an ethynyl to the central
boron atom via an AlCl3-mediated procedure by our group in
2016 (Fig. 1B).4 As a terminal alkyne functionality can work as a
handle for further metal-catalysed coupling reactions, such as
the Sonogashira coupling5 and the Glaser-Hay coupling,6 this
methodology opens up for incorporation of the SubPc
chromophore into larger, acetylenic scaffolds, which has been
of particular interest for our research in recent years.7,8 In
particular, linkage of the SubPc central boron atom to a
tetraethynylethene (TEE; Fig. 1A) unit has been pursued,8 as
the TEE is a versatile building block when synthesizing larger,
A
Axial
H
H
H
H
R
N
N
B
N
N
N
N
Peripheral
R
SubPc
TEE
B
R
TMS
AlCl3
R
Cl
N
N
B
N
N
N
B
N
N
N
N
N
o-DCB, rt
N
N
SubPc-Cl
TIPS
TIPS
TMS
C
Br
Br
a)
b)
O
TMS
TMS TMS
TMS TMS
Protected TEE
Dibromo-olefin
TIPS
TIPS
D
SubPc-TEE-SubPc
scaffold
N
N
B
N
N
N
B
N
N
N
N
N
N
N
Fig. 1 A) Boron subphthalocyanine (SubPc) chromophore and tetraethynylethene (TEE)
unit. B) AlCl3-mediated reaction between TMS-protected alkyne and SubPc-Cl to obtain
direct installation of alkyne on the central boron atom of SubPc. C) Synthesis of
a. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-
2100 Copenhagen Ø, Denmark. E-mail: mbn@chem.ku.dk
Electronic Supplementary Information (ESI) available: NMR and UV-Vis absorption
spectra. See DOI: 10.1039/x0xx00000x
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geminally substituted TEE, a) CBr4, PPh3, b) TIPS-acetylene, Pd(PPh3)4, CuI. D) Known
View Article Online
SubPc-TEE-SubPc scaffold. o-DCB = ortho-dichlorobenzene
DOI: 10.1039/D0OB00988A
H
N
N
B
N
N
N
B
N
One classical synthetic approach to obtain trialkylsilyl-
protected TEEs proceeds via
a dibromo-functionalized
N
N
N
N
diethynylethene, which is subjected to two-fold Sonogashira
couplings with terminal alkynes as pioneered by Diederich and
co-workers.10 One such example is shown in Fig. 1C, providing
a TEE with two geminal trimethylsilyl (TMS) groups and two
triisopropylsilyl (TIPS) groups. We have previously used this
TEE as a precursor for a SubPc-TEE-SubPc scaffold (Fig. 1D) via
AlCl3-mediated coupling of the two TMS-protected alkynes to
the boron atoms of two SubPcs.8 The TIPS-protected alkynes
were conveniently left un-reacted. This approach, however,
can only yield the dimer, as both the TMS-protected alkynes
react under the conditions. Furthermore, as SubPcs are known
to decompose in reaction with strong nucleophiles,
deprotection of the TIPS-protected alkynes for further reaction
was only possible using 10 equiv. of AgF,8 which is an
expensive procedure to use on larger scale. In comparison, it
was possible to remove TMS-groups from SubPc-functionalized
acetylenes using only 1 equiv. of AgF.
We find that the dibromo-olefin intermediate towards TEE
poses as an interesting alternative precursor for SubPc-
functionalized acetylenic scaffolds, as coupling this to the
SubPc core could avoid the TIPS protecting groups all together,
and thereby the harsh or expensive deprotection conditions.
The use of unsymmetrical dibromo-olefins could furthermore
facilitate a larger selectivity of the synthesis and thereby lead
to more complex SubPc-functionalized scaffolds. In this work
we pursue various, novel SubPc-functionalized dibromo-olefins
derived from ene- and diynes and investigate the reactivity of
these in further metal-catalysed coupling reactions.
N
N
Series A
Series B
N
N
B
N
N
N
B
N
N
N
N
N
N
N
Series C
Fig. 2. Series A, B and C elaborated in this work.
Gratifyingly, the three new dibromo-olefins 1a, 1b and 1c
were readily obtained via the previously reported AlCl3-
mediated protocol for alkynylation at the axial boron position
with the three known dibromo-olefins a,11 b10 and c10 (Scheme
1), and the three key building blocks were isolated as purple
solids. The notably lower isolated yield of 1c was attributed to
poor solubility of the compound, which resulted in tedious
purification on silica.
Br
Br
Br
Br
H
H
a
N
N
B
N
TMS
N
N
83%
N
1a
Br
Br
Br
Br
Cl
Br
N
N
B
N
b
TIPS
N
N
B
N
TMS
TIPS
N
N
N
N
88%
Results and Discussion
Three SubPc-functionalized dibromo-olefins were targeted in
N
N
1b
SubPc-Cl
Br
this work; A)
a monomer containing a dibromo-enyne
Br
Br
c
functionality, B) a monomer containing a dibromo-enediyne
functionality and C) a dimer containing a dibromo-enediyne
between two SubPc units. This led to evolution of three series
of SubPc-functionalized scaffolds (Fig. 2).
TMS
TMS
26%
N
N
N
N
N
B
N
B
N
N
N
N
N
N
1c
Scheme 1 Synthesis of dibromo-olefins 1a, 1b and 1c. Conditions: AlCl3, ortho-
dichlorobenzene, rt, 2 h.
2 | J. Name., 2012, 00, 1-3
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ARTICLE
TIPS
TIPS
SubPc dimer scaffold, of importance for further acetylenic
View Article Online
tBu
tBu
scaffolding under mild desilylation condiDtiOoIn: s1.0.1039/D0OB00988A
Me2N
NMe2
Br
Br
H
Br
Br
a)
N
N
B
N
N
N
N
68%
B
N
N
N
N
TIPS
a)
TIPS
N
N
B
N
N
N
N
N
N
B
N
N
N
N
1a
2a
94%
N
N
1b
2b
TIPS
b)
tBu
b)
Me2N
Me2N
74%
66%
I
II
II
TMS
TMS
N
Me2N
NMe2
CN
NC
NC
CN
Me2N
NMe2
Br
Br
NC
NC
CN
CN
N
N
B
N
N
N
B
c)
2
2
c)
N
N
N
N
25%
N
N
N
N
N
B
N
N
N
84%
B
N
N
N
N
3b
4b
N
N
Scgeme 3 Synthesis of functionalized SubPc Series B. Conditions: a) II, Pd2dba3, AsPh3,
CuI, toluene/Et3N, rt, 20 h; b) 1) AgF (10 equiv.), AcOH, CH2Cl2/MeCN, rt, 17 h, 2) CuCl,
TMEDA, CH2Cl2, rt, 2 h; c) TMS-acetylene, Pd2dba3, AsPh3, CuI, toluene/Et3N, rt, 17 h.
dba = dibenzylideneacetone. TMEDA = N,N,N’,N’-tetramethylethylenediamine.
3a
4a
Scheme 2 Synthesis of functionalized SubPc series A. Conditions: a) I, Pd2dba3, AsPh3,
CuI, toluene/Et3N, rt, 17 h; b) II, Pd2dba3, AsPh3, CuI, toluene/Et3N, rt, 17 h; c)
Tetracyanoethylene, ortho-dichlorobenzene, rt, 34 h.
Br
Br
Next, we investigated the ability of dibromo-olefin 1a to
undergo Sonogashira coupling reactions with the terminal
alkynes I and II (formed by protodesilylation of the
corresponding TMS-protected precursors). These coupling
reactions led to SubPc-functionalized scaffolds 2a and 3a,
respectively (Scheme 2). When stirred at room temperature
overnight, both reactions yielded the desired products in
highly acceptable yields, and compound 3a even proved
N
N
B
N
N
N
B
N
N
N
N
N
N
N
1c
TMS
N
TMS
N
N
N
N
B
N
further reactive in
tetracyanoethylene
a
[2+2] cycloaddition with
followed by
28%
B
N
N
N
N
(TCNE)
a
N
N
retroelectrocyclization reaction12 to give the product 4a. This
“click-like” reaction has previously proven useful when
synthesizing donor-acceptor systems containing SubPc.13
2c
Scheme 4 Synthesis of functionalized SubPc series C. Conditions: TMS-acetylene,
Pd2dba3, AsPh3, CuI, toluene/Et3N, 50 °C, 25 h.
The positive results from functionalizations of Series A
drove our interest towards the design of more elaborate
SubPc-functionalized acetylenic scaffolds starting from building
block 1b. To ensure the general reactivity of 1b in Sonogashira
coupling reactions, this compound was coupled to terminal
alkyne I, which successfully yielded the TEE product 2b
(Scheme 3). Furthermore, the reactivity of the second alkyne
of 1b was investigated by first removing the TIPS protecting
group using 10 equiv. of AgF and subsequently performing an
intermolecular Glaser-Hay coupling to achieve the tetra-
bromide 3b. Gratifyingly, this tetra-bromide was readily
further functionalized by a four-fold Sonogashira coupling with
an excess of TMS-acetylene resulting in dimer 4b in which the
The novel synthetic strategy in this work also allows us to
achieve a TEE-linked SubPc dimer with TMS protecting groups,
instead of TIPS groups that were present in the previously
published system, by conducting a Sonogashira coupling of
dimer 1c with TMS-acetylene (Scheme 4). The methodology
presented in this work hereby allows us to design and achieve
SubPc-functionalized systems with better selectivity using
milder conditions.
Optical properties
The optical properties of all new compounds were investigated
SubPc units are separated by a TEE dimer. This scaffold, with by UV-Vis absorption spectroscopy in CH2Cl2 at 25 °C (Fig. 3
the installed TMS protecting groups, would not be accessible
by the previously published8 AlCl3-mediated alkynation using a
TEE precursor. In other words, the new protocol has allowed
introduction of more labile TMS-protected alkynes in the
and Fig. 4). Absorption maxima and extinction coefficients are
listed in Table 1.
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Table 1. Absorption maxima (λmax) and extinction coefficients (ε) in CH2Cl2 at 25 °C
for monomers 1a, 2a, 3a, 4a, 1b and 2b, and dimers 3b, 4b, 1c and 2c. sh =
shoulder.
16
14
12
10
8
View Article Online
3b
DOI: 10.1039/D0OB00988A
4b
1c
2c
Compound

max / nm ( / 104 M-1 cm-1)
1a
2a
568 (8.33), 522 (sh) (2.51), 307 (5.31)
569 (8.00), 525 (sh) (2.44), 348 (2.90), 306 (7.22), 269
(6.25)
3a
4a
569 (8.00), 519 (sh) (2.44), 385 (4.36), 302 (8.34)
571 (5.79), 517 (3.14), 463 (3.60), 352 (sh) (2.53), 307 (6.18),
271 (538)
6

1b
2b
568 (7.77), 526 (sh) (2.40), 303 (5.21), 277 (4.44)
568 (7.56), 513 (2.54), 432 (5.04), 304 (8.46), 275 (sh)
(5.61)
567 (14.5), 528 (sh) (4.79), 357 (2.08), 307 (11.2), 269
(7.60)
4
2
3b
4b
0
570 (14.8), 527 (sh) (4.74), 438 (4.03), 405 (2.74), 378
(2.65), 306 (12.2), 273 (sh) (7.94)
300
400
500
600
700
800
 (nm)
1c
2c
564 (13.1), 529 (4.87), 305 (9.14), 272 (sh) (6.54)
568 (14.8), 528 (5.63), 309 (12.0), 267 (7.30)
Fig. 4 UV-Vis absorption spectra of dimers in Series B: 3b (black) and 4b (blue), and
Series C: 1c (green) and 2c (red) in CH2Cl2 at 25 °C.
The two monomeric dibromo-olefins 1a and 1b, as well as
π-extended monomer 2a, were observed to have similar
longest-wavelength absorption maxima and hence resemble in
this respect previously published axially functionalized
SubPcs.7 In general, the axial functionalizations did not alter
significantly the longest-wavelength absorption maximum for
monomer and dimers in all three series. Yet, introduction of
two tetracyanobuta-1,3-diene (TCBD) moieties, leading to
compound 4a, resulted in significant broadening of the SubPc
absorption band at 571 nm as well as the rise of a strong
absorption band at 463 nm, in accordance with observations
of similar systems in literature.13 Aniline-extension of the
systems resulted in an intense absorption band at 385 nm (3a)
and 432 nm (2b). The extended SubPc dimer 4b shows
additional absorption bands in the range between 350 and 450
nm, which is in accordance with the absorptions of the isolated
TEE dimer.14 As seen in Fig. 5, the functionalizations of the
various dibromo-olefins resulted in color changes clearly
visible by the naked eye.
2c
4b
2a
3a
4a
Fig. 5 Solutions of compounds 2c, 4b, 2a, 3a, and 4a in CH2Cl2 (all 0.05 mM).
Electrochemistry
Electrochemical studies of Series A and dimers 4b and 2c were
conducted in CH2Cl2 containing 0.1 M Bu4NPF6 as supporting
electrolyte, and the cyclic voltammograms are shown in Fig. 6
and Fig. 7. Redox potentials (reported as half-wave potentials)
are listed in Table
ferrocene/ferrocenium (Fc/Fc+) redox couple (recorded in a
separate experiment).
1a
2
referenced against the
2a
8
3a
4a
1b
6
Table 2. Oxidation potentials (Eox) and reduction potentials (Ered) for compounds
1a, 2a, 3a, 4a, 4b and 2c vs. Fc/Fc+ recorded in CH2Cl2 (+0.1 M Bu4NPF6).
Potentials are reported as half-wave potentials if not otherwise stated.
2b
4
Compound
Eox (V vs. Fc/Fc+)
+0.53*
Ered (V vs. Fc/Fc+)
1a
2a
3a
4a
4b
2c
-1.50
-1.54
-1.54

+0.56*
+0.32*
+0.61*
+0.54*
2
-0.60, -0.93, -1.23, -1.68
-1.73, -1.95
-1.60
+0.44*, +0.55*
0
300
400
500
600
700
800
* = irreversible (peak potential listed).
 (nm)
Fig. 3 UV-Vis absorption spectra of monomers in Series A: 1a (black), 2a (blue), 3a
(green) and 4a (red), and Series B: 1b (orange) and 2b (purple) in CH2Cl2 at 25 °C.
4 | J. Name., 2012, 00, 1-3
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View Article Online
DOI: 10.1039/D0OB00988A
4a
3a
2a
1a
4b
20
0
10
0
-10
-20
-30
-20
20
0
-20
2c
20
0
10
0
-10
-20
-20
20
0
-20
-30
-1.5
-1.0
-0.5
0.0
0.5
-2.0 -1.5 -1.0 -0.5 0.0
0.5
E (V vs. Fc/Fc+)
E (V vs. Fc/Fc+)
Fig. 6 Cyclic voltammograms of monomeric derivatives (from the bottom) 1a (0.72
mM), 2a (0.49 mM), 3a (0.64 mM) and 4a (0.80 mM); potentials vs. Fc/Fc+ (solvent:
CH2Cl2; supporting electrolyte: 0.1 M Bu4NPF6; scan rate: 0.1 V/s).
Fig. 7. Cyclic voltammograms of dimeric derivatives (from the bottom) 2c (0.48 mM)
and 4b (0.51 mM); potentials vs. Fc/Fc+ (solvent: CH2Cl2; supporting electrolyte: 0.1 M
Bu4NPF6; scan rate: 0.1 V/s).
For monomers 1a and 2a an irreversible one-electron
oxidation is observed at +0.53 and +0.56 V, respectively, and a
reversible one-electron reduction at -1.50 and -1.54 V,
respectively. For aniline-extended derivative 3a, the one-
electron oxidation is seen to occur at lower potential (+0.32 V)
due to the electron-rich aniline moiety, while the reversible
one-electron reduction is found at similar potential to the
other monomers (-1.54 V). Derivative 4a incorporating two
TCBD moieties is, in addition to an irreversible one-electron
oxidation at +0.61 V, found to undergo four reductions at -
0.60, -0.93, -1.23 and -1.68 V.
Dimer 2c is found to have similar electrochemical
properties to the previously synthesized TIPS-protected TEE-
linked SubPc dimer shown in Fig. 1D.8 The oxidations of the
two SubPc units of 2c are seen to occur sequentially, indicating
communication between these. On the contrary, oxidation of
the SubPc units of dimer 4b is observed as one two-electron
oxidation, suggesting that the additional TEE spacer between
the SubPc units results in diminished electronic
communication between the SubPcs presumably due to the
longer boron-boron distance. Simultaneously, the TEE-dimer
bridge results in reactive reduced species, leading to
irreversible reductions of 4b, in contrast to a reversible two-
electron reduction of mono-TEE bridged compound 2c.
Conclusions
In this work we have presented a novel synthetic strategy
towards SubPc-functionalized acetylenic scaffolds by attaching
dibromo-enyne/enediyne units to the axial position of SubPc.
The vinylic dibromide unit could conveniently withstand the
alkynylation conditions, and the procedure proved to work
readily to provide products in high yields. The resulting
products were easily further functionalized by both
Sonogashira and Glaser-Hay coupling reactions as well as a
[2+2]
cycloaddition
with
TCNE
followed
by
retroelectrocyclization. Furthermore, we have achieved a new
SubPc-TEE-TEE-SubPc dimer, which contains four TMS-
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protected alkynes that may be deprotected and employed for (Fc/Fc+) redox couple measured before andViewaAfrttieclre Ontlhinee
DOI: 10.1039/D0OB00988A
further acetylenic scaffolding. This elongation of the bridge experiment on a 0.1 mM solution of Fc. All solutions were
resulted in a single two-electron oxidation of the two SubPc purged with solvent saturated argon prior to measurement.
units rather than two sequential one-electron oxidations as The concentrations of the electroactive compounds were: 0.72
observed when only one TEE unit is present in the bridge. Our mM (1a), 0.49 mM (2a), 0.64 mM (3a), 0.80 mM (4a), 0.48 mM
new synthetic route contributes to the expansion of the SubPc (2c) and 0.51 mM (4b). The voltammograms of the compounds
functionalization toolbox and may allow construction of even were recorded in CH2Cl2 (HPLC grade) containing 0.1 M
more elaborate acetylenic scaffolds containing SubPc in the Bu4NPF6 supporting electrolyte. The iR-compensation was
future.
applied in order to compensate for the solvent resistance.
Compound 1a. Compound a (400 mg, 1.42 mmol) and SubPc-
Cl (710 mg, 1.65 mmol) were suspended in o-DCB (5 mL) in a
small vial and exposed to ultrasound at 25 C for 30 min after
Conflicts of interest
There are no conflicts to declare.
ᵒ
which AlCl3 (500 mg, 3.75 mmol) was added; the vial was
sealed, and the reaction mixture was stirred violently at rt for
2 h. The reaction mixture was quenched with pyridine (1.0
mL), stirred for 10 min and filtered through a plug of neutral
Brockman I Al2O3 (50% EtOAc/toluene), and the filtrate was
concentrated in vacuo. Purification by flash column
chromatography (SiO2 0.43–0.63 µm, 2% EtOAc/toluene,
loading: toluene) gave 1a (713 mg, 1.18 mmol, 83%) as a
Acknowledgements
The Independent Research Fund Denmark | Natural Sciences
(#8021-00009B) is acknowledged for financial support.
Experimental
General methods
1
purple solid. TLC (2% EtOAc/toluene): Rf = 0.25. H NMR (500
MHz, CDCl3) δ 8.86 (dd, J = 5.9, 3.1 Hz, 6H), 7.90 (dd, J = 5.9,
3.1 Hz, 6H), 5.76 (s, 1H) ppm. 13C NMR (126 MHz, CDCl3) δ
150.51, 130.98, 129.88, 122.28, 119.01, 101.95 ppm (2 signals
missing, presumably due to overlap). HRMS (MALDI FT-ICR,
Anhydrous MeOH was obtained by drying over 3Å sieves. All
remaining anhydrous solvents were obtained from a solvent
drying tower (IT model PS-MD-05). HPLC solvents were used.
Elevated reaction temperatures were obtained by use of an
aluminium heating mantle. Purification by chromatography
was performed using silica gel (flash: 40-63 µm). TLC was
performed using aluminium sheets covered with silica gel
coated with fluorescent indicator. NMR spectra were recorded
+
dithranol) m/z = 604.97108 [M+H]+, calcd. for (C28H14BBr2N6 )
m/z = 604.97138.
Compound 1b. Compound b (600 mg, 1.30 mmol) and SubPc-
Cl (736 mg, 1.71 mmol) were suspended in o-DCB (4 mL) in a
at 500 MHz and 126 MHz for H- and 13C-NMR, respectively
(using an instrument with
1
ᵒ
small vial and exposed to ultrasound at 25 C for 30 min after
a
cryoprobe). Deuterated
which AlCl3 (450 mg, 3.38 mmol) was added; the vial was
sealed, and the reaction mixture was stirred violently at rt for
2 h. The reaction mixture was quenched with pyridine (1.0
mL), stirred for 10 min and then filtered through a plug of
neutral Brockman I Al2O3 (50% EtOAc/toluene), and the filtrate
was concentrated in vacuo. Purification by flash column
chromatography (SiO2 0.43–0.63 µm, 5–20% EtOAc/toluene,
loading: o-DCB/toluene) gave 1b (893 mg, 1.14 mmol, 88%) as
chloroform (CDCl3, δH = 7.26 ppm, δC = 77.16 ppm) was used as
solvent (and reference for calibration). The CDCl3 was filtered
through activated Al2O3 prior to use. Chemical shift values are
referenced to the ppm scale and coupling constants are
expressed in Hertz (Hz). In 13C-APT (Attached Proton Test)
NMR spectra, negative signals correspond to CH and CH3,
positive signals correspond to C and CH2. High-resolution mass
spectrometry (HRMS) was performed using MALDI with
dithranol as matrix or using ESP on an FT-ICR instrument
equipped with a 7-T Magnet. Melting points are not corrected.
UV/Vis absorption spectra were recorded by scanning
between 800 and 200 nm. All spectra were recorded in CH2Cl2
(HPLC grade) at 25 C in a 1-cm quartz cuvette. The
concentrations of the compounds were: 0.017 mM (1a),
0.0092 mM (2a), 0.012 mM (3a), 0.010 mM (4a), 0.015 mM
(1b), 0.015 mM (2b), 0.0090 mM (3b), 0.0076 mM (4b), 0.0047
(1c) and 0.014 mM (2c).
Cyclic voltammograms (CV) were obtained using a scan
rate of 0.1 V/s. A silver wire was used as the reference
electrode, a Pt wire was used as the counter electrode, and a
glassy-carbon disk electrode (3 mm) was used as the working
electrode. The reference electrode was separated from the
solution containing the substrate by a ceramic frit. Measured
potentials were referenced to the ferrocene/ferrocenium
1
a purple solid. TLC (10% EtOAc/toluene): Rf = 0.64. H NMR
(500 MHz, CDCl3) δ 8.86 (dd, J = 5.9, 3.1 Hz, 6H), 7.90 (dd, J =
5.9, 3.1 Hz, 6H), 1.56 (s, 3H), 0.90 (s, 18H) ppm. 13C NMR (126
MHz, CDCl3) δ 150.48, 130.98, 129.86, 122.28, 113.83, 108.73,
101.56, 99.35, 18.58, 11.12 ppm (2 signals missing, presumably
due to overlap and/or low intensity). HRMS (ESP) m/z =
785.10642 [M+H]+, calcd. for (C39H34BBr2N6Si+) m/z
=
785.10481.
Compound 1c. Compound c (201 mg, 0.531 mmol) and SubPc-
Cl (454 mg, 1.05 mmol) were suspended in o-DCB (5 mL) in a
small vial and exposed to ultrasound at 25 ᵒC for 1 h after
which AlCl3 (268 mg, 2.01 mmol) was added; the vial was
sealed, and the reaction mixture was stirred vigorously at rt for
1 h. The reaction mixture was quenched with pyridine (1.0 mL)
and stirred for an additional 10 min before it was filtered
through a plug of neutral Brockman I Al2O3 (o-DCB), and the
6 | J. Name., 2012, 00, 1-3
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ARTICLE
filtrate was concentrated in vacuo. Purification by flash column column chromatography (SiO2 0.43–0.63 µm, toluene to 5%
View Article Online
chromatography (SiO2 0.43–0.63 µm, 0–20% EtOAc/toluene, EtOAc/toluene, loading on column: toluDenOeI:)10g.a10v3e9/2Db0O(2B40309m88gA,
loading: o-DCB) gave 1c (282 mg, 0.276 mmol, 26%) as a purple 0.266 mmol, 94%) as
a purple, shiny solid. TLC (5%
1
1
solid. TLC (20% EtOAc/toluene): Rf = 0.31. H NMR (500 MHz, EtOAc/toluene): Rf = 0.27. H NMR (500 MHz, CDCl3) δ 8.86
CDCl3) δ 8.74 (dd, J = 5.8, 3.0 Hz, 12H), 7.80 (dd, J = 5.8, 3.0 Hz, (dd, J = 5.8, 3.1 Hz, 6H), 7.87 (dd, J = 5.8, 3.1 Hz, 6H), 7.20 (d, J
12H) ppm. 13C NMR (126 MHz, CDCl3) δ 150.35, 130.82, = 9.0 Hz, 2H), 6.94 (d, J = 8.8 Hz, 2H), 6.50 (d, J = 9.0 Hz, 1H),
129.72, 122.19 ppm (4 signals missing, presumably due to low 6.39 (d, J = 8.8 Hz, 1H), 3.06 (s, 6H), 2.92 (s, 6H), 0.93 (s, 21H)
intensity). HRMS (MALDI FT-ICR, dithranol): m/z = 1023.08964 ppm. 13C NMR (126 MHz, CDCl3) δ 150.62, 150.62, 150.46,
+
[M+H]+, calcd. for (C54H24B2N12Br2 ) m/z = 1023.08520.
150.40, 133.25, 133.18, 131.06, 129.65, 122.29, 119.00,
112.16, 111.76, 111.54, 109.61, 109.44, 104.19, 100.30,
Compound 2a. Protodesilylation: To
a solution of the 100.10, 86.60, 86.05, 40.49, 40.23, 18.71, 11.39 (2 signals
corresponding TMS-protected alkyne of I (275 mg, 1.27 mmol) missing, presumably due to overlap and/or low intensity) ppm.
in THF (15 mL) and MeOH (15 mL) was added K2CO3 (887 g, HRMS (MALDI FT-ICR, dithranol) m/z = 913.43291 [M+H]+,
6.42 mmol). The reaction mixture, in which I is generated, was calcd. for (C59H53BN8Si+) m/z = 913.43283.
stirred at rt for 3 h before it was passed through a short plug of
silica (SiO2, CH2Cl2), after which toluene (20 mL) and 1a (175 Compound 2c. To a N2 degassed suspension of 1c (169 mg,
mg, 0.290 mmol) were added, and the solution was 0.255 mmol) in anhydrous toluene (20 mL) and Et3N (0.5 mL)
concentrated in vacuo until the total volume was ca. 5 mL were added N2 degassed TMS-acetylene (0.40 mL, 2.81 mmol),
(toluene). Sonogashira coupling: To this mixture were added Pd2dba3 (125 mg, 0.137 mmol), CuI (25 mg, 0.131 mmol) and
additional toluene (25 mL) and Et3N (15 mL), and the solution AsPh3 (444 mg, 1.45 mmol), and the mixture was heated to 50
was thoroughly degassed with argon. Then Pd2dba3 (53 mg, °C in a sealed vial and stirred for 25 h before it was filtered
0.058 mmol), AsPh3 (143 mg, 0.467 mmol, 4 equiv. per Pd) and through a SiO2 plug (EtOAc/CH2Cl2) and concentrated in vacuo.
CuI (8 mg, 0.04 mmol) were added, and the reaction mixture The crude mixture was dissolved in o-DCB (20 mL) and purified
was stirred at rt for 15 h. The reaction mixture was passed by flash column chromatography (SiO2, 20-30% EtOAc/toluene)
through
a plug of silica (SiO2 0.43–0.63 µm, 50% followed by trituration of the solid compound with MeOH (3 x
EtOAc/toluene). Purification by flash column chromatography 4 mL) to give 2c (75 mg, 28%) as a purple solid. TLC (30%
1
(SiO2 0.43–0.63 µm, toluene to 5% EtOAc/toluene, loading on EtOAc/toluene): Rf = 0.29. H NMR (500 MHz, CDCl3) δ 8.61
column: toluene) gave 2a (349 mg, 0.312 mmol, 68%) as a pink (dd, J = 5.9, 3.1 Hz, 12H), 7.59 (dd, J = 5.9, 3.1 Hz, 12H), -0.02
metallic solid. 1H NMR (500 MHz, CDCl3) δ 8.84 (dd, J = 5.9, 3.1 (s, 18H) ppm. 13C NMR (126 MHz, CDCl3) δ 150.44, 130.68,
Hz, 6H), 7.89 (dd, J = 5.9, 3.1 Hz, 6H), 7.41 (d, J = 1.9 Hz, 1H), 129.42, 122.04, 117.23, 104.09, 100.36, -0.26 ppm (3 signals
7.34 (d, J = 1.9 Hz, 1H), 7.19–7.14 (m, 3H), 7.10 (dd, J = 8.2, 2.1 missing, presumably due to low intensity). HRMS (MALDI FT-
Hz, 1H), 6.88 (d, J = 8.2 Hz, 1H), 5.39 (s, 1H), 1.43 (s, 9H), 1.23 ICR, dithranol): m/z
=
1057.34514 [M+H]+, calcd. for
+
(s, 9H), 0.96 (app. s, 21H), 0.92 (app. s, 21H) ppm. 13C NMR (C64H43B2N12Si2 ) m/z = 1057.34528.
(126 MHz, CDCl3) δ 151.56, 151.41, 150.59, 132.96, 132.18,
131.00, 129.77, 129.36, 129.30, 125.54, 125.41, 125.26, Compound 3a. Protodesilylation: To
a solution of the
125.23, 122.84, 122.64, 122.49, 122.29, 116.05, 105.48, corresponding TMS-protected alkyne of II (275 mg, 1.27
105.46, 94.60, 94.50, 93.76, 90.82, 89.69, 88.63, 34.96, 34.77, mmol) in THF (15 mL) and MeOH (15 mL) was added K2CO3
31.37, 31.08, 18.73, 18.72, 11.33, 11.32 ppm (2 signals missing, (887 mg, 6.42 mmol). The reaction mixture, in which II is
presumably due to overlap). HRMS (MALDI FT-ICR, dithranol) generated, was stirred at rt for 3 h, before it was passed
+
m/z = 1119.60537 [M+H]+, calcd. for (C74H80BN6Si2 ) m/z = through a short plug of silica (SiO2, CH2Cl2), after which toluene
1119.60706.
(20 mL) and 1a (175 mg, 0.290 mmol) was added and the
solution was concentrated in vacuo until the total volume was
Compound 2b. Protodesilylation: To
a
solution of the ca. 5 mL (toluene). Sonogashira coupling: To this mixture were
corresponding TMS-protected alkyne of II (275 mg, 1.27 added additional toluene (25 mL) and Et3N (15 mL), and the
mmol) in THF (15 mL) and MeOH (15 mL) was added K2CO3 solution was thoroughly degassed with argon. Then Pd2dba3
(1.02 g, 7.38 mmol). The reaction mixture, in which II is (53 mg, 0.058 mmol), AsPh3 (143 mg, 0.467 mmol, 4 equiv. per
generated, was stirred at rt for 2 h, after which it was passed Pd) and CuI (8 mg, 0.04 mmol) were added, and the reaction
through a short plug of silica (SiO2, CH2Cl2), toluene (20 mL) mixture was stirred at rt for 15 h. The reaction mixture was
and 1b (223 mg, 0.284 mmol) was added ,and the solution was passed through a plug of silica (SiO2 0.43 – 0.63 µm, CH2Cl2).
concentrated in vacuo until the total volume was ca. 5 mL. Purification by flash column chromatography (SiO2 0.43–0.63
Sonogashira coupling: To this mixture was added toluene (25 µm, toluene to 7% EtOAc/toluene, loading on column:
mL) and Et3N (15 mL), and the solution was thoroughly toluene) gave 3a (156 mg, 0.213 mmol, 74%) as a purple,
1
degassed with argon. Next, Pd2dba3 (45 mg, 0.049 mmol), shimmering solid. TLC (5% EtOAc/toluene): Rf = 0.28. H NMR
AsPh3 (121 mg, 0.395 mmol, 4 equiv. per equiv. of Pd) and CuI (500 MHz, CDCl3) δ 8.87 (dd, J = 5.9, 3.1 Hz, 6H), 7.89 (dd, J =
(9 mg, 0.047 mmol) were added, and the reaction mixture was 5.9, 3.1 Hz, 6H), 7.19 (d, J = 9.2 Hz, 2H), 7.00 (d, J = 8.9 Hz, 2H),
stirred at rt for 20 h after which it was passed through a plug 6.52 (d, J = 8.9 Hz, 2H), 6.45 (br d, J = 8.3 Hz, 2H), 5.25 (s, 1H),
of silica (SiO2 0.43–0.63 µm, CH2Cl2). Purification by flash 3.07 (s, 6H), 2.91 (s, 6H) ppm. 13C NMR (126 MHz, CDCl3) δ
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150.62, 150.62, 150.37, 150.31, 133.37, 133.00, 131.08, concentrated in vacuo. Purification by flash column
View Article Online
DOI: 10.1039/D0OB00988A
129.70, 129.19, 128.37, 122.31, 118.60, 116.63, 111.81, chromatography (SiO2, 1-10% EtOAc/toluene) yielded 4b (46
111.72, 93.30, 85.89, 85.26, 40.53, 40.25 ppm (2 signals mg, 25%) as a purple solid. TLC (10% EtOAc/toluene): Rf = 0.25.
missing, presumably due to overlap). HRMS (MALDI FT-ICR, 1H NMR (500 MHz, CDCl3) δ 8.82 (dd, J = 5.9, 3.1 Hz, 12H), 7.88
+
dithranol) m/z = 733.29900 [M+H]+, calcd. for (C48H34BN8 ) m/z (dd, J = 5.9, 3.1 Hz, 12H), 0.06 (s, 18H), -0.05 (s, 18H) ppm. 13C
= 733.29940.
NMR (126 MHz, CDCl3) δ 150.48, 131.01, 129.77, 122.23, -0.29,
-0.41 ppm (10 signals from double and triple bond carbon
Compound 3b. To a solution of 1b (220 mg, 0.280 mmol) in atoms missing, presumably due to low intensity of the signals
CH2Cl2 (15 mL) and MeCN (5 mL) covered from light under an and/or low solubility of the compound). HRMS (MALDI FT-ICR,
Ar atmosphere was added AcOH (2 ml, 1.4 mmol, equiv. 5, 0.7 dithranol): m/z
M in CH2Cl2) followed by AgF (179 mg, 1.41 mmol, 5 equiv), (C80H61B2N12Si4 ) m/z = 1323.43998.
and the reaction mixture was stirred at rt for 17 h. The
=
1323.44704 [M+H]+, calcd. for
+
reaction mixture was quenched with HCl (10 mL, 1 M), stirred
for 10 min; H2O (0.5 L) was added, and the mixture was
Notes and references
subjected to numerous extractions with CH2Cl2 (a total volume
of 500 mL). The combined organic phase was dried over
MgSO4, filtered, and concentrated to ca. 50 mL in vacuo. A
solution of CuCl (21 mg, 0.21 mmol) and TMEDA (0.5 mL) in
CH2Cl2 (10 mL) was added, and the reaction mixture was
stirred violently for 2 h at rt. Then the reaction mixture was
passed through a plug of silica (SiO2 0.43–0.63 µm, 50%
EtOAc/toluene), and the filtrate was concentrated in vacuo.
Purification by flash column chromatography (SiO2 0.43–0.63
µm, 2% EtOAc/toluene to 4% EtOAc/toluene, loading: toluene)
gave 3b (231 mg, 0.184 mmol, 66%) as a purple solid. TLC (10%
1
2
A. Meller and A. Ossko, Monatsh. Chem., 1972, 103, 150.
C. G. Claessens, D. González-Rodríguez, M. S. Rodríguez-
Morgade, A. Medina and T. Torres, Chem. Rev., 2014, 114,
2192; J. S. Castrucci, D. S. Josey, E. Thibau, Z.-H. Lu and T.
Bender, J. Phys. Chem. Lett., 2015, 6, 3121; C. Zhang, K.
Nakano, M. Nakamura, F. Araoka, K. Tajima and D. Miyajima,
J. Am. Chem. Soc., 2020, 142, 3326.
J. Guilleme, D. González-Rodríguez and T. Torres, Angew.
Chem. Int. Ed., 2011, 50, 3506; G. E. Morse and T. P. Bender,
Inorg. Chem., 2012, 51, 6460; J. Guilleme, L. Martínez-
Fernández, I. Corral, M. Yáñez, D. González-Rodríguez and T.
Torres, Org. Lett., 2015, 17, 4722.
H. Gotfredsen, M. Jevric, S. L. Broman, A. U. Petersen and M.
B. Nielsen, J. Org. Chem., 2016, 81, 1.
K. Sonogashira, Y. Tohda and N. Hagihara, Tetrahedron Lett.,
1975, 16, 4467.
C. Glaser, Ber. Dtsch. Chem. Ges., 1869, 2, 422; A. S. Hay, J.
Org. Chem., 1960, 25, 1275-1276; A. S. Hay, J. Org. Chem.,
1962, 27, 3320.
H. Gotfredsen, M. Jevric, A. Kadziola and M. B. Nielsen, Eur.
J. Org. Chem., 2016, 17.
H. Gotfredsen, L. Broløs, T. Holmstrøm, J. Sørensen, A. V.
Muñoz, M. D. Kilde, A. B. Skov, M. Santella, O. Hammerich
and M. B. Nielsen, Org. Biomol. Chem., 2017, 15, 9809.
R. R. Tykwinski and F. Diederich, Liebigs Ann., 1997, 649; J.-P.
Gisselbrecht, N. N. P. Moonen, C. Boudon, M. B. Nielsen, F.
Diederich and M. Gross, Eur. J. Org. Chem., 2004, 2959; M. B.
Nielsen and F. Diederich, Chem. Rev., 2005, 105, 1837; F.
Diederich and M. Kivala, Adv. Mater., 2010, 22, 803; M. D.
Kilde, A. H. Murray, C. L. Andersen, F. E. Storm, K. Schmidt, A.
Kadziola, K. V. Mikkelsen, F. Hampel, O. Hammerich, R. R.
Tykwinski and M. B. Nielsen, Nat. Comm., 2019, 10, 3714.
3
4
5
6
1
EtOAc/toluene): Rf = 0.45. H NMR (500 MHz, CDCl3) δ 8.85
(dd, J = 5.9, 3.1 Hz, 12H), 7.90 (dd, J = 5.9, 3.1 Hz, 12H) ppm.
13C NMR (126 MHz, CDCl3) δ 150.49, 130.96, 129.89, 129.19,
128.38, 122.31, 112.48, 112.05, 79.65, 78.94 ppm. HRMS
(MALDI FT-ICR, dithranol) m/z = 1254.91859 [M+H+], calcd. for
(C60H24B2Br4N12+) m/z = 1254.91983.
7
8
Compound 4a. To a solution of 3a (30 mg, 0.041 mmol) in o-
DCB (5 mL) was added TCNE (110 mg, 0.859 mmol), and the
reaction mixture was stirred for 34 h at rt. The reaction
mixture was subjected directly to purification by flash column
chromatography (SiO2 0.43–0.63 µm, toluene to 10%
EtOAc/toluene to 25% EtOAc/toluene, loading on column: o-
DCB), which gave 4a (34 mg, 0.034 mmol, 84%) as a dark
9
1
purple metallic solid. TLC (25% EtOAc/toluene): Rf = 0.37. H
NMR (500 MHz, CDCl3) δ 8.9–8.82 (m, 6H), 8.02–7.90 (m, 6H),
7.25–7.13 (m, 2H), 7.04–6.90 (m, 2H), 6.62–6.48 (m, 2H), 6.46–
6.32 (m, 2H), 5.72 (br s, 1H), 3.16–2.94 (m, 12H) ppm. 13C NMR
(126 MHz, CDCl3) δ 162.01, 159.74, 158.18, 157.15, 154.74,
154.65, 150.47, 138.87, 132.87, 132.04, 130.96, 130.32,
129.17, 128.36, 127.51, 122.55, 113.92, 113.87, 113.37,
112.35, 112.07, 110.17, 109.79, 97.30, 94.39, 90.50, 40.27,
40.17 ppm (6 signals missing, presumably due to overlap
and/or low intensity). HRMS (ESP) m/z = 989.32503 [M+H]+,
calcd. for (C60H34BN16+) m/z = 989.32399.
10 J. Anthony, A. M. Boldi, Y. Rubin, M. Hobi, V. Gramlich, C. B.
Knobler, P. Seiler and F. Diederich, Helv. Chim. Acta, 1995,
78, 13.
11 N. P. Bowling, N. J. Burrmann, R. J. Halter, J. A. Hodges and R.
J. McMahon, J. Org. Chem., 2010, 75, 6282.
12 M. I. Bruce, J. R. Rodgers, M. R. Snow and A. G. Swincer, J.
Chem. Soc., Chem. Comm., 1981, 271; M. I. Bruce, M. E.
Smith, B. W. Skelton and A. H. White, J. Organomet. Chem.,
2001, 637-639, 484; T. Mochida and S. Yamazaki, J. Chem.
Soc., Dalton Trans, 2002, 3559; T. Michinobu, J. C. May, J. H.
Lim, C. Boudon, J.-P. Gisselbrecht, P. Seiler, M. Gross, I.
Biaggio and F. Diederich, Chem. Commun. 2005, 737; T.
Michinobu, C. Boudon, J.-P. Gisselbrecht, P. Seiler, B. Frank,
N. N. P. Moonen, M. Gross and F. Diederich, F. Chem. Eur. J.,
2006, 12, 1889; T. Michinobu, H. Kumazawa, K. Noguchi and
K. Shigehara, Macromolecules, 2009, 42, 5903; S.-i. Kato, M.
Kivala, W. B. Schweizer, C. Boudon, J.-P. Gisselbrecht and F.
Diederich, Chem. Eur. J., 2009, 15, 8687; A. R. Lacy, A. Vogt,
C. Boudon, J.-P. Gisselbrecht, W. B. Schweizer and F.
Compound 4b. To a N2 degassed solution of 3b (170 mg, 0.135
mmol) in anhydrous toluene (10 mL) and Et3N (5 mL) were
added N2 degassed TMS-acetylene (0.50 mL, 3.51 mmol),
Pd2dba3 (69 mg, 0.075 mmol), CuI (17 mg, 0.089 mmol) and
AsPh3 (204 mg, 0.666 mmol). The mixture was stirred at rt for
7.5 h before it was filtered through a SiO2 plug (EtOAc) and
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Diederich, Eur. J. Org. Chem., 2013, 869; T. Shoji, M.
Maruyama, A. Maruyama, S. Ito, T. Okujima and K. Toyota,
Chem. Eur. J., 2014, 20, 11903; M. Betou, N. Kerisit, E.
Meledje, Y. R. Leroux, J.-F. Halet, J.-C. Guillemin and Y.
Trolez, Chem. Eur. J., 2014, 20, 9553; A. T. Bui, C. Philippe, M.
Beau, N. Richy, M. Cordier, T. Roisnel, L. Lemiègre, O.
Mongin, F. Paul and Y. Trolez, Chem. Commun., 2020, 56,
3571.
View Article Online
DOI: 10.1039/D0OB00988A
13 K. A. Winterfeld, G. Lavarda, J. Guilleme, M. Sekita, D. M.
Guldi, T. Torres and G. Bottari, J. Am. Chem. Soc., 2017, 139,
5520; A. V. Muñoz, H. Gotfredsen, M. Jevric, A. Kadziola, O.
Hammerich and M. B. Nielsen, J. Org. Chem., 2018, 83, 2227.
14 M. B. Nielsen, M. Schreiber, Y. G. Baek, P. Seiler, S. Lecomte,
C. Boudon, R. R. Tykwinsky, J.-P. Gisselbrecht, V. Gramlich, P.
J. Skinner, C. Bosshard, P. Günter, M. Gross and F. Diederich,
Chem. Eur. J., 2001, 7, 3263.
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