Probing Peripheral H-Bonding Functionalities in BN-Doped Polycyclic Aromatic Hydrocarbons

Article abstract of DOI:10.1021/acs.joc.9b03202

The replacement of carbon atoms at the zigzag periphery of a benzo[fg]tetracenyl derivative with an NBN atomic triad allows the formation of heteroatom-doped polycyclic aromatic hydrocarbon (PAH) isosteres, which expose BN mimics of the amidic NH function

Full text of DOI:10.1021/acs.joc.9b03202

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Article
Probing peripheral H-bonding functionalities in
BN-doped polycyclic aromatic hydrocarbons
Jonathan Tasseroul, Maria Mercedes Lorenzo-Garcia, Jacopo Dosso, Francois
Simon, Simone Velari, Alessandro De Vita, Paolo Tecilla, and Davide Bonifazi
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b03202 • Publication Date (Web): 06 Feb 2020
Downloaded from pubs.acs.org on February 8, 2020
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The Journal of Organic Chemistry
Probing peripheral H-bonding functionalities in BN-doped polycyclic
aromatic hydrocarbons.
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Jonathan Tasseroul , M. Mercedes Lorenzo-Garcia§, ∥, Jacopo Dosso , François Simon , Simone
†
§
†
‡
#,‡
∥
†,§,*
Velari, Alessandro De Vita Paolo Tecilla and Davide Bonifazi
,
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†
§
Department of Chemistry, University of Namur (UNamur), Rue de Bruxelles 61, B-5000, Namur, Belgium; School of
Chemistry, Cardiff University, Park Place, Main Building, CF10 3AT, Cardiff, United Kingdom,
∥
bonifazid@cardiff.ac.uk; Department of Chemical and Pharmaceutical Science, University of Trieste, Piazzale Europa
‡
1
, 34127 Trieste, Italy; Department of Engineering and Architecture, University of Trieste, Piazzale Europa 1, 34127
#
Trieste, Italy; Department of Physics, King’s College London, Strand, London WC2R 2LS, United Kingdom
ABSTRACT: The replacement of carbon atoms at the zig-zag periphery of a benzo[fg]tetracenyl derivative with an NBN atomic
triad allows the formation of heteroatom-doped PAHs isosteres, which expose BN mimics of the amidic NH functions. Their ability
to form H-bonded complexes has never been touched so far. Herein we report the first solution recognition studies of peripherally
NBN-doped PAHs to form doubly H-bonded DD•AA and ADDA•DAAD-type complexes with suitable complementary H-bonding
-1
acceptor partners. The first determination of the K
a
in solution showed that the 1:1 association strength is around 27 ± 1 M for the
-1
DD•AA complexes in C , whereas it rises to 1820 ± 130 M for the ADDA•DAAD array in CDCl . Given the interest of BN-doped
6
D
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3
polyaromatic hydrocarbons in supramolecular and materials chemistry, it is expected that these findings will open new
possibilities to design novel materials, where the H-bonding properties of peripheral NH hydrogens could serve as anchors to
tailor the organizational properties of PAHs.
INTRODUCTION
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2
Following the vigorous synthetic developments of polycyclic aromatic hydrocarbons (PAHs), the substitution (i.e., doping) of sp -
carbon atoms with isoelectronic and isostructural BN couples is re-emerging as a versatile approach to tune the optoelectronic
properties of these materials.2–7In particular, borazines8,9 and BN-doped PAHs (e.g., azaborines,10,11borazapyrenes,12,13
borazaphenanthrenes12,14 borazanaphthalenes,15,16 borazaanthracene17,18 and boraazaperylene ) are now increasingly attracting the
attention of the physical and chemical community for their use in a broad spectrum of optoelectronic applications.20–22 When used
to decorate a periphery, non-substituted BN couples terminate with NH functions that, being more acidic than the CH analogues,
could engage into H-bonding interactions as observed with boronic acids.23 For instance, Liu and co-workers showed in a seminal
report that 1,2-dihydro-1,2-azaborine can act as an H-bonding donor in the solid state and engage into a H-bond with the C=O
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group of a glutamine side chain in a T4 lysozyme.24,25 However, to the best of our knowledge, no examples of studies describing
and measuring the strength of H-bonding interactions in solutions with BN-doped peripheries have been reported to date.
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While attempting different synthetic strategies to prepare hexabenzo-borazinocoronene,26 we prepared the NBN-doped isostere
of a benzo[fg]tetracenyl anion (Figure 1). Derivatives of the NBN-doped isostere were firstly prepared independently by the groups
of Hatekeyama27 and Feng . When looking at the NBN-doped zig-zag periphery, one notice that the unsubstituted HNBNH array
is a neutral H-bonding mimic of an amidinium moiety, known to establish doubly H-bonded DD-AA-type arrays. DFT calculations
(see SI for the details) on the all-carbon analogue (CCC) and its NBN-doped isostere suggest that the HOMO and LUMO
distributions are very similar on both molecules, with the NBN atomic triad negligibly contributing to the LUMO (Figure S39) in
line with the data reported by Hatekeyama27 and Feng . Remarkably, the lack of contribution from the B atom is observable for
the LUMO orbital, advocating a tenuous electrophilic character of the B atom center (Figure S39). On the other hand, a significant
contribution from the N atoms is noticeable for the HOMOs with the involvement of the B atom remaining negligible. As expected,
the NBN-doping results in a low-lying HOMO, the latter contributing significantly to the increase of the HOMO-LUMO gap with
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respect to the 22--e all-carbon benzo[fg]tetracenyl derivative (Figure S39).
Figure 1. Neutral NBN isosteres of polycyclic aromatic benzo[fg]tetracenyl anions. Charge density distribution for the A) CCC and
B) NBN-doped scaffold as calculated at the DFT theory level using the ab initio pseudopotential plane-wave method as
implemented in the PWSCF code of the Quantum ESPRESSO distribution (electron density accumulation is depicted in green,
depletion in orange).
DFT calculations also reveal a peculiar distribution of the electron density around the NH group as shown by the charge density
transfer plots (calculated as ρmol - Σρatom, where ρmol is the charge density of the molecule and ρatom the density of the single atoms)
in Figure 1b. The decreasing of charge density for the aminic H atoms is induced by the presence of the electronegative N atoms
and is clearly visible in the NBN-doped molecule while it is absent for the iso-positional H atoms of the CCC analogue (Figure 1a).
As observed by Liu and co-workers,29 this suggests that the NH groups are acidic, and thus possibly enabling the formation of
doubly H-bonding interactions in the presence of a suitable H-bond acceptor. ESP calculations showed that molecule 1 displays a
great charge depletion on the NH groups and B atoms, whereas the carbocyclic backbone remains slightly negatively charged
(
Figure 2). These results are consistent with the calculated electron density properties, further suggesting that this peculiar NBN
motif can be considered as a neutral isostere of substituted amidinium cations, known to behave as a H-bonding DD-type array.30
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This prompted us to study the H-bonding abilities of the NBN-doped moiety towards suitable complementary H-bonding
acceptors, such as fluoride ions and complementary AA-type H-bonding guests. Thus, we synthesized NBN-doped
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benzo[fg]tetracenyl derivatives 1 and 2, which should undergo formation of bifurcated and doubly H-bonds arrays with F ions and
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,8-naphthyridine, respectively (Figure 3). When comparing the H-bonding NBN-doped array with that of the amidinium, one can
hardly fail to notice that the amidinium is expected to present the strongest association due to the presence of charge-dipole
interactions. Building on this hypothesis, we conjectured that BN-doped scaffold 3, in which the lateral fused benzene rings have
been substituted by two pyridines, should behave as an ADDA-type H-bonding motif (Figure 3). In the presence of a suitable
complementary H-bonding DAAD-type partner, molecule 3 is expected to form quadruply H-bonded ADDA•DAAD arrays
featuring higher association constants than those hypothesized for DD•AA complexes. For this reason, we also prepared receptor
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and studied its H-bonding recognition properties in the presence ofdiacteyl-2,7-diaminonaphthyridine (Figure 3). All molecules
were equipped with either 2-phenylethyl chains (1) or mesitylene moieties (2 and 3) to increase solubility in organic solvents.
Figure 2.DFT calculations at the B3LYP/6-311G**level of theory of the structural and ESP properties of the NBN-doped
benzo[fg]tetracenyl derivatives exposing H-bonding recognition DD- (left) and ADDA-type (right) arrays.
Figure 3. H-bonded arrays and recognition modes studied in this work.
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RESULTS AND DISCUSSION
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Synthesis and structural characterization. We synthesized the NBN core starting from the relevant aniline bearing the chosen
solubilizing group instead of performing a post-synthetic functionalization of the NBN-doped benzo[fg]tetracenyle. This choice
allows to obtain differently substituted HNBNH derivatives without the need of protecting groups for the aminic moieties.
Moreover, to increase the synthetic versatility of the route, we decided to explore cyclisation conditions for the preparation of the
NBN-doped PAHs that start from an unsubstituted polyphenylene scaffold. The syntheses of the three aniline precursors are
reported in the insets of Scheme 1.The first step of the synthesis of 6 is the Pd/Cu-catalyzed Sonogashira cross-coupling of para-
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iodoaniline with phenylacetylene, yielding phenylacetylene-aniline 4.31.
Scheme 1. Synthetic routes towards aniline precursors 6, 9, and 11 (above) and NBN-doped scaffolds 1, 2, and 3 (below).
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Its reduction with Pd/C in MeOH afforded phenethylaniline 5, which was transformed into 3-bromoaniline 6 in quantitative yield
by bromination reaction with NBS at rt. Similarly, anilines 9 and 11 were obtained starting from Suzuki-Miyaura cross-coupling
reaction between 2,4,6-trimethylphenylboronic acid and either p-bromonitrobenzene or 2-amino-5-bromopyridineto give
intermediates 7 and 10 in 58% and 95% yield, respectively. Nitro-derivative 7 was reduced with AcOH/Zn (88% yield) and the
resulting amine brominated with NBS at rt to give substituted aniline 9 in quantitative yield. Analogously, bromination of 10 with
NBS gave final aniline 11 in excellent yield (84 %). The aniline precursors were then cross-coupled through Suzuki-Miyaura reaction
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with phenylene bisboronate 12 in the presence of Pd(OAc) , SPhos (or XPhos) and K PO , to give bis-aniline intermediates 13, 14
and 15 in 71%, 58%, 67% yield, respectively (Scheme 1). Our synthetic studies to prepare NBN-doped PAH by cyclization on an un-
substituted aromatic scaffold were commenced using bis-aniline 13 as substrate. Building on a general borylation procedure
following modified versions of the approaches previously described by Dewar and later by Hatakeyama,20 in a first attempt, we
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performed an intramolecular Friedel-Crafts cyclization reaction starting from the amino-BCl
in ODCB at 150°C. Unfortunately, these conditions were unsuccessful, and no conversion was observed. Similarly, deprotonation
of bis-aniline 13 with two equivalents of n-BuLi at -84°C followed by the addition of BCl at rt and Friedel-Crafts cyclization reaction
3 3
intermediate in the presence of AlCl
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did not lead to any transformation, and only starting material was recovered. On the other hand, changing the conventional oil-
bath heating to a microwave irradiation, 100% conversion was observed, affording desired molecule 1 in 49% yield after
3 3
purification. As expected, no reaction took place in the absence of AlCl , even when two equivalents of BCl were used. Subjecting
amino-precursors 14 and 15 to the same procedure, compounds 2 and 3 were obtained in 50% and 17% yield, respectively. All three
compounds exhibit an excellent chemical and thermal stability. The structure of all intermediates and products were
+
unambiguously identified by HR-MS through the detection of the peak corresponding to the molecular mass of the ion (M ) and
1
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by H-, C- and B-NMR, and IR spectroscopies (see SI, Figures S1-S29). Exemplary H-NMR spectra of NBN-doped derivatives 1 in
THF-d and 3 in CDCl are reported in Figure 4. Proton resonances H(a), H(b), and H(c) of structure 1 appear distinctively as triplet
8
3
at 7.67 ppm, doublet at 8.11 ppm, and broad singlet at 8.05 ppm, respectively. These three signals are highly deshielded, confirming
the polycyclic aromatic character of the structure. The signal of the NH protons appears as broad singlet centered at 7.31 ppm.
Similarly, for molecule 3 the H(a) and H(b) resonances appear at 8.31 ppm and 8.15 ppm, respectively. The H(c)- and H(b)- peaks
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are visible as doublet and triplet at 8.11 ppm and 7.79 ppm followed by the resonances of the NH(f) protons at 7.36 ppm. The B-
NMR spectrum of 1 (Figure 4, inset) displays a broad peak centered at 26.4 ppm, the chemical shift of which is in agreement with
that reported for similar NBN triads.32,33
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8 3
Figure 4. a) H- and B-NMR spectra for 1 in THF-d at 298 K and b) H-NMR spectra of 3 in CDCl .
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The photophysical properties of molecule 1 were investigated in THF solutions (see SI, Figure S30). Emission measurements display
a blue fluorescence with a fl value of 21% (reference anthracene, exc = 372 nm), with the spectrum displaying a mirror image of
the two lowest-energy absorption bands. The Stokes shift was as small as 27 nm, indicating a good rigidity of the structure, as
expected for a fully fused PAH. The optical gap (E00) of 1, deduced from the emission highest-energy peak, has been calculated to
be 3.22 eV. Cyclic voltammetry (Figures S33) of 1 in THF shows a clear reversible mono electronic oxidative wave at 0.4 V (vs.
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Fc/Fc ). This allowed us to calculate the HOMO and LUMO energy levels, which revealed to be -5.51 eV and -2.29 eV, respectively
(
the LUMO energy level was estimated from E00). Overall, these data are in agreement with those reported for the unsubstituted
NBN derivative in CH Cl
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and predicted by DFT Calculations (Figure S39).27,28
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Titration experiments and determination of the H-bonding recognition abilities. We started with the F ions as probes to
study the recognition properties of molecule 1 toward bifurcated H-bonded complexes. The interaction was studied in THF
solutions through spectroscopic UV-vis absorption titration experiments (Figure 5). In particular, a standard solution of TBAF was
added stepwise to a 4.43 × 10−5 M solution of 1 at 298 K and the steady-state UV-vis absorption spectra taken (Figure 5, above).
Upon addition of increasing concentration of TBAF, the intensity of the band centered at 360 nm decreases and a new transition
develops at 390 nm. Similar red shift of the lowest-energy band had been previously observed when fluoride ions interact with
other DD-type H-bonding systems, like urea derivatives.34,35 Notably, no marked color changes were observed during the titration
experiments, suggesting that molecule 1 likely does not undergo deprotonation (see also Figures S31-32 for the color change and
UV-vis spectra of the mono- and bis-anionic species obtained upon addition of one and two equivalents of sec-BuLi).
1
−3
Complementary H-NMR titrations with a 1 × 10 M solution of 1 (Figure S38) showed a fast equilibrium, triggering a progressive
downfield shift of the NH protons from 7.30 to 10.60 ppm upon the incremental addition of TBAF. Together with the H(f)
resonances, also the signals of the aromatic peri-protons H(e) experience a progressive deshielding upon stepwise addition of
TBAF confirming the frontal arrangement of the H-bonded complex. However, the signal of the NH protons in presence of up to
2
equivalents of TBAF is rather broad, almost no detectable, and in the presence of larger excess of fluoride remains broad and
non-symmetric. This hampered a quantitative determination of the association constant (K ) in THF. Moreover, it is likely that
the equilibrium is made more complex by concurrent additional equilibria, such as the formation of the corresponding bihalide
specie (HF
-), which is known to take place in organic solvents.36
a
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Figure 5. UV-Vis titrations of 1 (c
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= 4.43 × 10−5 M) in THF at 298 K with TBAF.
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Complementary B-NMR studies showed that the chemical shift of the B resonance is unaffected by the incremental addition of
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further confirming the formation of H-bonded complex 1•F in solution. This is in line with the theoretical finding, which revealed
an elusive contribution of the B atom to the LUMO orbital of 1.
To further investigate H-bonding properties of the NBN-doped PAHs, we studied the binding of molecules 2 and 3 with 1,8-
naphthyridine (NAP) and diacteyl-2,7-diaminonaphthyridine (DAN).37 While NAP should form doubly H-bonded DD•AA arrays
with 2 and 3, DAN should undergo quadruply ADDA•DAAD complexes with 3 (Figure 3). Addition of increasing amount of NAP
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to an 8 mM solution of 3 in CD
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Cl
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up to 2.5 equivalents led to minor linear downfield shift of the H(f) resonances, suggesting the
value (Figure S34). This was confirmed by changing the solvent to less polar and
6 6
less competitive C D
, in which the formation of H-bonds is favored (Figure 6).38
formation of an H-bonded complex with a low K
a
1
= 9.30 × 10−3 M) with NAP in C
Figure 6. H-NMR (400 MHz) titration of 3 (c
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6
D
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at 298 K.
Upon addition of increasing amount of NAP (up to 8.6 equivalents) to a 9.30 × 10−3 M solution of 3 in C
D , a large downfield shift
6 6
(> 3.3 ppm) of the H(f) protons was observed typical of the formation of an H-bonded complex under a regime of fast equilibrium
exchange (Figure 6). Together with the H(f) resonances, also the peaks of the proton resonances of the lateral pyridyl moieties
revealed significant downfield shifts upon addition of NAP, confirming the frontal arrangement of the H-bonded DD•AA complex.
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The same picture is obtained by titrating molecule 2 with NAP in C
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D
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(see Figure S36). Fitting the chemical shift values of the
values of 25 ±
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H(f) resonances from the titration experiments of 3 and 2 with NAP to a 1:1 binding isotherm with Dynafit,39 gave K
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1 M-1 and 27 ± 1 M-1 for complexes 3•NAP and 2•NAP, respectively (Figures S35-36). Notably, these H-bonded DD•AA-type
complexes show association strengths considerably lower than those observed with a series of aromatic boronic acids that, in their
syn-syn conformation, showed 1:1 association in the range between 300 and 6900 M-1.23 Further evidences of the ability of the NBN
motif to undergo H-bonding recognition and form supramolecular complexes, came from the titration studies of molecule 3 with
complementary DAAD-type DAN derivative. As DAN is almost insoluble in benzene, the titration was performed in the more
polar and more competitive CDCl
of DAN, up to 3.36 equivalents, resulted in a large downfield shift (> 3.3 ppm) of the H(f) resonances. This suggested the formation
solvent. As shown in Figure 7, titration of a 4.94 × 10−3 M solution of 3 with increasing amounts
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
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8
9
0
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9
0
1
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3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-1
of a frontal H-bonded ADDA•DAAD complex. The calculated K
a
value for the 1:1 complex 3•DAN was found to be 1820±130 M in
. JOB’s analysis of the titration data confirmed
CDCl , which is more than 70 times higher than that measured for the 3•NAPin C D
3
6 6
the 1:1 stoichiometry of the quadruply H-bonded 3•DAN complex (Figure S37).
1
= 4.94 × 10−3 M) with DAN in CDCl
Figure 7. H-NMR (400 MHz) titration of receptor 3 (c
0
3
at 298 K.
Despite the numerous attempts, we could not grow suitable crystals for X-ray diffraction analysis of both the single components
1, 2 and 3) and H-bonded complexes (2•NAP, 3•NAP and 3•DAN). Therefore, we turned our attention to NOESY experiments to
(
1
1
-3
confirm the structure of the hypothesized hydrogen-bonded complex. The H− H NOESY spectrum of a 7.0 × 10 M solution of 3
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in the presence of 1.1 eq. of DAN was recorded (Figure 8). From this analysis, one can easily discern a through space interaction
Figure 8a) between protons H(b) and H(g) which allowed the unambiguous assignment of the resonances attributed to H(a) and
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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5
5
5
5
5
5
5
5
5
5
6
(
,
1
1
H(b). A clear peak assignment could not be made from H- H COSY spectra (Figure S16). Interestingly, the through space
interaction between protons H(i) of the Me groups of DAN and protons H(a) of 3 (Figure 8b) suggests that a close spatial proximity
exist for these atoms, unambiguously confirming the structure of the proposed frontal H-bonding arrangement for complex
3•DAN.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
= 7.0 × 10−3 M) with
Figure 8. a) Arrangement of hydrogen bonded aggregates; 2D H-NOESY NMR (600 MHz) of receptor 3 (c
0
3
DAN in CDCl at 298 K; ratio of 3 to DAN: 1:1.1. b) detail of aromatic part with through space interaction between H(b) and H(g)
highlighted; c) zoom on the through space interaction between H(a) and H(i).
CONCLUSIONS
In conclusion, in this paper we describe the synthesis of a family of NBN isosteres of a full-carbon benzo[fg]tetracenyl anion with
improved solubility in different organic solvents. The NBN functional group could be inserted in a zig-zag topology allowing the
planarization of the three aryl rings. DFT calculations of the charge density showed significant charge depletion at the NH protons,
anticipating good H-bonding capabilities of this NBN functional group. This was for the first time demonstrated by spectroscopic
-
-
titration of molecule 1 with F ions, which clearly showed the formation of H-bonded complex 1•F excluding any interactions with
the B center. Titration of molecules 2 and 3 with complementary H-bonding NAP and DAN showed that heteromolecular H-
bonded complexes 2•NAP, 3•NAP and 3•DAN could be formed. In particular, complex 3•DAN presents a quadruply H-bonded
-1
a 3
array with a K value of 1820±130 M in CDCl . These findings open new applicative horizons for the BN-doping of polyaromatic
hydrocarbons in supramolecular chemistry, for which the ability to form H-bonding interactions at the periphery can be exploited
both in solution and at the solid state. 41 In addition, the ease of preparing these BN-doped PAHs makes these heterocycles
interesting to organic, supramolecular and materials chemists who are incessantly looking for programmable synthetic strategies
for digitizing molecules displaying multifunctional and self-organization properties exploitable in materials science and biology.42
EXPERIMENTAL PART
Instrumentation, materials and general methods
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Thin layer chromatography (TLC): performed on Machevery-Nagel Alugram SIL G/UV234 0.20 mm, visualized by UV light (254
or 366 nm). Micro-wave irradiation (MW Irr.): performed with a Biotage AB Initiator 2.5, in 2, 5 and 20 mL sealed tubes,
producing controlled irradiation at 2.450 GHz. The reactions temperature was monitored with an external surface sensor.
Adsorption silica chromatography columns (SCC): performed on Merck Gerduran silica gel 60 (40-63 μm), used with a Büchi
Sepacore X50 flash system. Melting points (M.P.): recorded on a Büchi Melting Point B-545 in open capillaries without correction.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
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4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
13
11
Nuclear magnetic resonance analysis ( H, C, B-NMR): spectra were recorded on a Jeol JNM EX-400, Jeol JNM ECZR-500,
1
3
1
Bruker Fourier 300 MHz spectrometer equipped with a dual ( C, H) probe, Bruker AVANCE III HD 400MHz NMR spectrometer
equipped with a Broadband multinuclear (BBFO) SmartProbe™, a Bruker AVANCE III HD 500 MHz Spectrometer or a Bruker 600
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
13
MHz Advance 3 equipped with Broardband multinuclear (BBO) Prodigy CryoProbe. For H and C, chemical shifts are reported in
ppm downfield from tetramethylsilane using the residual solvent signals as an internal reference (CDCl = 7.26 ppm, δ = 77.16
= 53.84 ppm. For B, chemical shifts are reported in ppm downfield from BF ·OEt as internal
3
δ
H
C
1
1
ppm; CD
2
Cl
2
δ
H
= 5.32 ppm, δ
C
3
2
reference, and analyses were performed in quartz tubes. Coupling constants (J) are given in Hz. The resonance multiplicity is
described as s singlet, d doublet, t triplet, q quartet, dd doublet of doublet, m multiplet and br broadened signal. All spectra were
recorded at 25°C unless specified otherwise. Ultraviolet-visible absorption spectroscopy (UV-Vis) and emission: UV-Vis
absorption spectra were recorded on Agilent Cary 5000 UV-Vis-NIR Spectrophotometer. All absorption measurements were
performed at 25 °C unless specified otherwise. The estimated experimental errors are 2 nm on the band maximum, 5% on the
molar absorption coefficient and 10% on the emission quantum yield in solution. Emission spectra were recorded on an Agilent
Cary Eclipse fluorescence spectrofluorimeter. All fluorimetric measurements were performed at 25 °C unless specified otherwise.
Quantum yield values in solution are calculated using anthracene in air equilibrated ethanol (Φ = 0.27),43 following the method of
Demas and Crosby.44 Infrared absorption spectra (IR): spectra were recorded on a) Perkin-Elmer Spectrum II FT-IR System
-1
UATR, mounted with a diamond crystal. Selected absorption bands are reported by wavenumber (cm ). b) Shimadzu IR Affinity
1S FTIR spectrometer in ATR mode with a diamond mono-crystal. Matrix-assisted laser desorption-ionisation time-of-flight
mass spectrometry analysis (MALDI-TOF): Performed by a) the Centre de spectrométrie de masse at the Université de Mons in
Belgium, using the following instrumentation: Waters QToF Premier mass spectrometer equipped with a nitrogen laser, operating
at 337 nm with a maximum output of 500 mW delivered to the sample in 4 ns pulses at 20 Hz repeating rate. Time-of-flight analyses
were performed in the reflectron mode at a resolution of about 10.000. The matrix solution (1 μL) was applied to a stainless-steel
target and air dried. Analyte samples were dissolved in a suitable solvent to obtain 1 mg/mL solutions. 1 μL aliquots of these
solutions were applied onto the target area already bearing the matrix crystals, and air dried. For the recording of the single-stage
MS spectra, the quadrupole (rf-only mode) was set to pass ions from 100 to 1000 THz and all ions were transmitted into the pusher
region of the time-of-flight analyser where they were analysed with 1 s integration time. Electron spray ionization time of flight
mass spectrometry analysis (ESI-TOF): Performed at Cardiff University using a Waters LCT HR TOF mass spectrometer in the
positive or negative ion mode for High-resolution ESI mass spectra.
Calculations:
DFT calculations were performed using the ab initio pseudopotential plane-wave method as implemented in the PWSCF code of
the Quantum ESPRESSO distribution,45 using Ultrasoft pseudopotentials from the publicly available repository.46 For the
exchange-correlation term, a GGA-BLYP approximation has been used.47,48 The valence electronic wave functions were expanded
onto a plane wave basis set with a kinetic energy cutoff of 544 eV. The Brillouin zone integration for the gas-phase systems
investigated has been limited to the Γ-point only. Ball and stick models are rendered using the XCrySDen software.49
Reagents and Solvents:
Reagents were purchased from Sigma-Aldrich, Acros Organics, Fisher Scientific, Tokyo Chemical Industry (TCI Europe), ABCR,
Carbosynth, and/or Apollo Scientific and used as received unless noted otherwise. NAP (1,8 naphthyridine) was acquired from
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fluorochem or TCI and used as received. Solvents were purchased from Sigma-Aldrich, while deuterated solvents from Eurisotop.
Anhydrous conditions were obtained by heating glassware in an oven at 120°C for 4 hours or by three cycles of heating with a heat
gun under argon or nitrogen flow and cooling down under vacuum. The inert atmosphere was maintained using argon or nitrogen-
filled balloons connected to a syringe and needle penetrating rubber stoppers used to close the flasks’ necks. Solutions were
degassed using freeze-pump-thaw technique: solutions were frozen using liquid nitrogen and kept under vacuum for 10’ before
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
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2
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3
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4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
thawing. ODCB (o-dichlorobenzene) was distilled from CaH with reduced pressure and stored over 5 Å molecular sieves. All
reactions were performed under anhydrous and inert gas conditions unless specified. Reactions were heated using silicon oil baths
and the temperature monitored with an external probe unless otherwise specified.
0
1
2
3
4
5
6
7
8
9
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2
3
4
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6
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9
0
S2. Experimental procedures
4
-(Phenylethynyl)aniline (4)
Diisopropylamine (80 mL) was degassed with 4 freeze-pump-thaw cycles in a flame-dried Schlenk. 4-iodoaniline (3.5 g, 16 mmol),
Pd(PPh Cl ] (112 mg, 0.16 mmol), CuI (61 mg, 0.32 mmol) and phenylacetylene (2.11 mL, 19.2 mmol) were added, and the
suspension stirred overnight at rt under argon. The black suspension was diluted with EtOAc (100 mL), washed with H O (3 × 100
mL) and brine (100 mL). The organic phase was dried on Na SO and evaporated to a dark brown solid, purification by SCC
(Cy/EtOAc 0 to 20%) afforded compound 4 as a white solid (3.5 g, 99%). M.P.: 119-121°C. H-NMR (400 MHz, CDCl
[
3
)
2
2
2
2
4
3
1
1
3
): δ 3.82 (br
): δ 87.4, 90.3,
12.4, 114.8, 123.9, 127.7, 128.4, 131.4, 133.0, 146.8. IR: 472, 498, 518, 535, 690, 756, 826, 846, 914, 966, 1068, 1137, 1179, 1290, 1317, 1371,
13
1
2 3
s, 2H), 6.64 (d, 2H, J = 8.8 Hz), 7.29-7.35 (m, 5H), 7.50 (dd, 2H, J= 8.0 Hz, J = 1.4 Hz). C{ H}-NMR (100 MHz, CDCl
1
-1
+
+
1440, 1486, 1513, 1591, 1615, 2210, 3036, 3377, 3475 cm . HRMS (EI-TOF) m/z: [M] calcd. for C14H11N 193.0886; found: 193.0888.
4
4
-Phenethylaniline (5)
-(phenylethynyl)aniline 4 (2.42 g, 12.5 mmol) was dissolved in MeOH (50 mL) under argon atmosphere, and Pd/C (10%, 267 mg,
and the suspension stirred at rt for 24 h. The reaction mixture was filtered on a
0.25 mmol) added. Argon was replaced with H
2
celite pad and evaporated to a yellow residue, purification on a silica plug (Cy/EtOAc 30%) afforded molecule 5 as a white solid
1
(
2.44 g, quant.). M.P.: 51-53°C. H-NMR (400 MHz, CDCl
3
): δ 2.65 (m, 4H), 3.48 (br, 2H), 6.63 (d, 2H, J = 8.4 Hz), 6.98 (d, 2H, J =
13
1
8
.4 Hz), 7.17-7.30 (m, 5H). C{ H}-NMR (100 MHz, CDCl
3
): δ 37.1, 38.3, 115.2, 125.8, 128.3, 128.5, 129.2, 131.8, 142.1, 144.4. IR: 523, 696,
-1
+
7
47, 764, 810, 858, 1027, 1065, 1143, 1175, 1261, 1451, 1491, 1512, 1616, 2849, 2912, 3023, 3348 cm . HRMS (AP-TOF) m/z: [M+H] calcd.
+
for C14
H
16N : 198.1283; found: 198.1285.
2-Bromo-4-phenethylaniline (6)
4
-phenethylaniline 5 (1.7 g, 8.6 mmol) was stirred in CH
3
CN (60 mL) with NBS (1.5 g, 8.6 mmol) overnight. The solution was
diluted with EtOAc (150 mL), washed with Na
2
S
2
O
3
sat. (100 mL), H
2
O (100 mL × 2), brine (100 mL), dried on MgSO and
4
evaporated. The residue was purified by SCC (Pet. Et/EtOAc 0 to 5%) to afford molecule 6 as a pale brown solid (2.0 g, 85%). M.P.:
1
4
7-49°C. H-NMR (400 MHz, CD
2
Cl
2
): δ 2.79-2.88 (m, 4H), 4.00 (bs, 2H), 6.69 (d, 1H, J = 8.0 Hz), 6.93 (dd, 1H, J= 8.0 Hz, J
Cl ): δ 36.6, 38.0, 108.9, 115.7, 125.9, 128.3, 128.5, 128.6, 132.2, 133.1, 141.8, 142.3.
IR:481, 498, 560, 602, 675, 696, 739, 814, 889, 1033, 1079, 1155, 1202, 1265, 1305, 1411, 1452, 1496, 1600, 1616, 1711, 2856, 2922, 3026, 3336,
2
= 1.4
1
3
1
Hz), 7.18-7.31 (m, 6H). C{ H}-NMR (100 MHz, CD
2
2
-1
+
+
3
420 cm . HRMS (EI-TOF) m/z: [M] calcd. for C14H14BrN 275.0304; found: 275.0307
1
,3-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene (12)
1
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2 2
Anhydrous DMF (20 mL) was degassed with 5 freeze-pump-thaw cycles in a flame dried Schlenk. B pin (6.5 g, 25.4 mmol),
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
[
Pd(dppf)Cl
1,3- dibromobenzene (2.0 g, 8.48 mmol) was added and the suspension heated at 90°C for 2 days under argon. The crude was then
quenched with H O (50 mL) and diluted with EtOAc (100 mL). The organic phase was washed with H O (3 × 100 mL), brine (100
mL), dried on Na SO and evaporated to a dark solid, purified by a silica plug (Cy/EtOAc 50%) to obtain molecule 12 as a yellow
pasty solid (2.8 g, quant.). M.P.: 111-113°C. H-NMR (400 MHz, CDCl
2 2 2
]·CH Cl (350 mg, 0.43 mmol) and AcOK (3.3 g, 33.6 mmol) were added and 3 freeze-pump-thaw cycles performed.
2
2
2
4
1
3
): δ 1.34 (s, 24H), 7.37 (t, 1H, J = 7.8 Hz), 7.90 (dd, 2H, J = 7.4
): 25.0, 83.9, 127.2, 137.8, 141.4 (signal for carbon atom attached to boron
atom absent due to quadrupolar relaxation). B{ H}-NMR (128 MHz, CDCl ): δ 29.5 (br). IR: 495, 519, 553, 578, 645, 653, 674, 685,
1
3
1
Hz J2= 1.4 Hz), 8.28 (s, 1H). C{ H}-NMR (100 MHz, CDCl
3
1
1
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
07, 807, 830, 845, 876, 951, 964, 983, 1009, 1079, 1110, 1138, 1214, 1270, 1305, 1328, 1370, 1456, 1474, 1602, 1669, 2934, 2978, 3436 cm-1.
7
+
+
29 2 4
HRMS (ESI-TOF) m/z: [M+H] calcd. for C18H B O 331.2253; found: 331.2252. Characterization in accordance with data reported
in the literature.40
5
,5”-Diphenethyl-[1,1’:3’,1”-terphenyl]-2,2”-diamine (13)
2
-bromo-4-phenethylaniline 6 (1.89 g, 6.87 mmol), diboronic ester 12 (754 mg, 2.28 mmol), Pd(OAc)
2
(26 mg, 0.11 mmol), SPhos
O (6 mL). The
solution was degassed by 5 freeze-pump-thaw cycles and stirred at 80°C for 48 h under argon. The reaction mixture was allowed
to cool down to rt, diluted with EtOAc (50 mL) and washed with H O (50 mL × 3) and brine (100 mL). The organic layer was dried
(94 mg, 0.23 mmol) and KOAc (968 mg, 9.86 mmol) were dissolved in a 5:1 mixture of 1,4-dioxane (30 mL) and H
2
2
and the solvent evaporated under reduced pressure. The black residue was purified by SCC (Cy/EtOAc 0 to 15%) to yield compound
1
1
3 as a light yellow powder (770 mg, 71%) M.P.: 120-122°C. H-NMR (400 MHz, CD
2
Cl
2
): δ 2.80-2.91 (m, 8H), 3.76 (br s, 4H), 6.70
1
3
1
(
d, 2H, J = 7.6 Hz), 6.97-6.99 (m, 4H), 7.13-7.27 (m, 10H), 7.40-7.52 (m, 4H). C{ H}-NMR (100 MHz, CD
2
Cl ): δ 37.6, 38.8, 116.2,
2
126.3, 127.6, 128.1, 128.8, 129.0, 129.1, 129.6, 130.2, 131.0, 132.4, 140.9, 142.2, 142.7. IR: 477, 499, 573, 617, 632, 695, 711, 741, 758, 817, 839,
-1
8
95, 896, 908, 1029, 1089, 1154, 1251, 1269, 1299, 1307, 1386, 1451, 1469, 1504, 1601, 1617, 2854, 2920, 3025, 3354, 3440 cm . HRMS (EI-
+
+
32 2
TOF) m/z: [M] calcd. for C34H N 468.2560; found.468.2567.
5
,12-Diphenethyl-8H,9H-8,9-diaza-8a-borabenzo[fg]tetracene (1)
A solution of BCl
3
(1.0 M in heptane, 250 μL, 0.25 mmol) was added to a solution of terphenyldiamine 6 (100 mg, 0.21 mmol) in
before adding AlCl (3 mg, 0.023 mmol) and
anhydrous ODCB (6 mL). The reaction mixture was stirred for 15 min at rtunder N
2
3
then heated at 150°C under microwave irradiation for 16 h. The solution was allowed to cool down to rt and the solvent removed
from the deep brown solution under reduced pressure. The residue was purified by SCC (Cy/EtOAc 0 to 10%) to yield molecule 1
1
as a white powder (50 mg, 49%). M.P.: 194-196°C. H-NMR (400 MHz, DMSO-d6, 50°C): δ 2.96 (m, 8 H), 7.14-7.29 (m, 14H) 7.76
13
1
(
t, 1H, J = 7.9 Hz), 8.00 (s, 2H), 8.09 (s, 2H), 8.17 (d, 2H, J = 7.9 Hz). C{ H}-NMR (100 MHz, DMSO-d6): δ 37.4, 38.2, 118.8, 119.1,
21.5, 124.3, 126.3, 128.8, 129.0, 129.2, 131.2, 132.5, 139.3, 140.1, 142.5.(signal for carbon atom attached to boron atom absent due to
1
1
1
1
quadrupolar relaxation). B{ H}-NMR (128 MHz, DMSO-d6): δ26.5. IR: 531, 580, 628, 649, 670, 699, 750, 750, 798, 849, 875, 916,
-1
+
+
1
029, 1075, 1288, 1319, 1340, 1420, 1444, 1453, 1468, 1497, 1560, 1603, 2918, 3292 cm . HRMS (EI-TOF) m/z: [M] calcd. for C34
H29BN
2
4
76.2418; found.476.2413.
5
-Mesitylpyridin-2-amine (10)
2
2-amino-5-bromopyridine(1.0 g, 5.8 mmol), 2,4,6-trimethylphenylboroni acid(1.1 g, 6.7 mmol), Pd(OAc) (70 mg, 0.31 mmol), XPhos
(
429 mg, 0.90 mmol) and K
PO
3 4
(3.7 g, 17.4 mmol) were dissolved in a 5:1 mixture of 1,4-dioxane (10 mL) and H
2
O (2 mL). The
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solution was degassed by 3 freeze-pump-thaw cycles and stirred at 90°C for 48 h under nitrogen. The reaction mixture was allowed
to cool down to rt, diluted with EtOAc (50 mL), washed with H O (50 mL × 3) and brine (100 mL). The organic layer was dried
over MgSO and the solvent evaporated under reduced pressure. The black residue was purified by SCC (Pet. Et/EtOAc 0 to 30%)
to yield compound 10 as an orange powder (1.17 g, 95%).M.P.: 92-94°C; H-NMR (300 MHz, CDCl
.50 (bs, 2H), 6.59 (d, 1H, J = 8.7 Hz), 6.94 (s, 2H), 7.25 (dd, 1H,J = 8.7 Hz, J = 1.2 Hz), 7.87 (d, 1H, J = 1.2 Hz). C{ H}-NMR (75 MHz,
CDCl ): δ 21.0, 21.1, 108.5, 126.8, 128.3, 135.5, 137.0, 137.1, 139.2, 148.2, 157.1. IR: 407, 421, 571, 754, 835, 847, 912, 1011, 1057, 1146, 1234,
315, 1387, 1439, 1468, 1624, 2913, 3140, 3285, 3464. HRMS (EI-TOF) m/z: [M] calcd. for C14
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
4
1
3
): δ 2.04 (s, 6H), 2.32 (s, 3H),
1
3
1
4
1
2
3
+
+
1
16 2
H N 212.1308; found 212.1313.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
-Bromo-5-mesitylpyridin-2-amine (11)
5-mesitylpyridin-2-amine 10 (260 mg, 1.22 mmol) was stirred in CH
solution was diluted in CH Cl (30 mL), washed with sat. Na (50 mL), H
evaporated. The resulting residue was purified by SCC (Pet. Et/EtOAc 0 to 30%) to afford molecule 11 as a pale yellow solid (310
3
CN (20 mL) with NBS (220 mg, 1.23 mmol) overnight. The
2
2
2
S
2
O
3
2
O (50 mL × 3), brine (50 mL), dried over MgSO and
4
1
mg, 87%). M.P.: 138-140°C; H-NMR (300 MHz, CDCl
3
): δ 2.05 (s, 6H), 2.32 (s, 3H), 5.02 (br s, 2H), 6.94 (s, 2H), 7.50 (d, 1H, J = 1.2
Hz), 7.83 (d, 1H, J = 1.2 Hz). C{ H}-NMR (75 MHz, CDCl ): δ 21.0, 21.2, 104.4, 128.2, 128.6, 134.2, 137.1, 137.6, 141.5, 147.5, 154.2. IR:
413, 422, 434, 498, 534, 579, 625, 710, 745, 754, 853, 881, 912, 939, 951, 1011, 1057, 1234, 1267, 1288, 1389, 1441, 1468, 1489, 1533, 1593,
1
3
1
3
+
+
1
2
632, 2853, 2916, 3136, 3285, 3470. HRMS (EI-TOF) m/z: [M+H] calcd. for C14H16BrN 291.0491; found: 291.0499.
3,3'-(1,3-Phenylene)bis(5-mesitylpyridin-2-amine) (15)
3
-bromo-5-mesitylpyridin-2-amine 11 (200 mg, 0.69 mmol), diboronic ester 12 (113 mg, 0.34 mmol), Pd(OAc)
XPhos (32 mg, 0.07 mmol) and K PO (437 mg, 2.06 mmol) were dissolved in a 5:1 mixture of 1,4-dioxane (5 mL) and H
The solution was degassed by 5 freeze-pump-thaw cycles and stirred at 90°C for 20 h under argon. The reaction mixture was
allowed to cool down to rt, diluted with CH Cl (50 mL) and washed with H O (40 mL × 3) and brine (50 mL). The organic layer
2
(4 mg, 0.02 mmol),
3
4
2
O (1 mL).
2
2
2
was dried over MgSO
4
and the solvent evaporated under reduced pressure. The black residue was purified by SCC (Pet. Et./EtOAc
*
1
3
0 to 90%) to yield compound 15 as a light brown solid (230 mg, 67%). M.P.: 248-250 °C; H-NMR (300 MHz, CDCl
3
): δ 2.09 (s,
13
1
1
2H), 2.32 (s, 6H), 4.65 (br s, 4H), 6.95 (s, 4H), 7.25 (d, 2H, J = 2.1 Hz), 7.53-7.61 (m, 4H), 7.90 (d, 2H, J = 2.1 Hz). C{ H}-NMR (75
MHz, CDCl ): δ 21.2, 121.2, 127.6, 128.2, 128.4, 129.2, 130.0, 135.1, 137.0, 137.2, 139.2, 139.4, 147.6, 154.4. (one signal not visible due to
overlapping). IR: 411, 426, 494, 538, 573, 635, 714, 793, 849, 912, 1005, 1229, 1391, 1454, 1491, 1558, 1622, 2918, 3140, 3283, 3493. HRMS
3
+
+
*
(
EI-TOF) m/z: [M] calcd. for C34
34 4 3
H N 498.2778; found 498.2783. 5% Et N was added to the final eluent to recover the product
from the column.
5
,12-Dimesityl-8H,9H-7,8,9,10-tetraaza-8a-borabenzo[fg]tetracene (3)
A solution of BCl
3
(1.0 M in heptane, 210 μL, 0.21 mmol) was added to a solution of terphenyldiamine 15 (100 mg, 0.20 mmol) in
before adding AlCl (3 mg, 0.023 mmol) and
anhydrous ODCB (6 mL). The reaction mixture was stirred for 15 min at rt under N
2
3
heating at 150°C under microwave irradiation for 16 h. The solution was allowed to cool down to rt and the solvent removed from
*
the deep brown solution under reduced pressure. The residue was purified by SCC (Pet. Et./EtOAc 30 to 60%) to yield molecule
1
3
as a white powder (17 mg, 17%). M.P.: 196-198 °C H-NMR (300 MHz, CDCl
3
): δ 2.11 (s, 12H, CH
), 8.11 (d, 2H, J = 7.9 Hz, CH ), 8.15 (d, 2H, J = 2.0 Hz, CH
): δ 21.2, 117.4, 120.3, 128.5, 129.5, 131.5, 133.5, 135.4, 137.1, 137.6, 138.4, 148.3, 150.9. (signal for
c
), 2.37 (s, 6H, CH
e
), 7.02 (s, 4H,
CH
d
), 7.44 (bs, 2H, NH
f
), 7.79 (t, 1H, J = 7.9 Hz, CH
h
g
a
), 8.31 (d, 2H, J = 2.0
13
1
Hz, CH
b
). C{ H}-NMR (126 MHz, CDCl
3
carbon atom attached to boron atom absent due to quadrupolar relaxation, one signal for CH
c
CH
e
not visible due to overlapping).
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1
1
1
3
B{ H}-NMR (160 MHz, CDCl ): δ: 27.7. IR: 581, 822, 851, 910, 1233, 1281, 1387, 1447, 1576, 1611, 2853, 2920, 2955, 3059, 3221, 3364.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
+
+
HRMS (ESI-TOF) m/z: [M+H] calcd. for C34
4
H32BN 507.2709; found 507.2710 *Addition of 5 % MeOH to the last eluent was
required to remove all product from the column.
2
,4,6-Trimethyl-4'-nitro-1,1'-biphenyl (7)
4
-bromonitrobenzene (500 mg, 2.49 mmol), 2,4,6-trimethylphenylboronic acid (447 mg, 2.72 mmol), [Pd(PPh
CO (1.03 g, 7.46 mmol) were dissolved in a 5:1 mixture of 1,4-dioxane (10 mL) and H O (2 mL). The solution was
degassed by 3 freeze-pump-thaw cycles and stirred at 90°C for 48 h under nitrogen. The reaction mixture was allowed to cool
down to rt, diluted with CH Cl (50 mL), washed with H O (100 mL × 3) and brine (100 mL). The organic layer was dried over
3 4
) ](287 mg, 0.25
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
mmol), and K
2
3
2
2
2
2
MgSO
4
2 2
and the solvent evaporated under reduced pressure. The residue was purified by SCC (Pet. Et/CH Cl 0 to 20%) to yield
1
compound 7 as a yellow powder (350 mg, 58%). H-NMR (300 MHz, CDCl
3
): δ 2.01 (s, 6H), 2.36 (s, 3H), 6.99 (s, 2H), 7.35 (d, 2H, J
): δ 20.7, 21.1, 123.9, 128.5, 130.6, 135.4, 136.9, 137.8, 147.0, 148.7. IR:
09, 440, 471, 511, 525, 571, 579, 594, 700, 731, 739, 760, 827, 851, 959, 1005, 1028, 1067, 1098, 1105, 1177, 1283, 1312, 1344, 1385, 1396, 1472,
1
3
1
=
4
8.8 Hz), 8.31 (d, 2H, J = 8.8 Hz). C{ H}-NMR (75 MHz, CDCl
3
+
+
1
2
514, 1599, 1927, 2849, 2947, 3013, 3104. HRMS (EI-TOF) m/z: [M] calcd for C15H15NO 241.1097; found 241.1108.
2
,4,6-Trimethyl-4'-amino-1,1'-biphenyl (8)
Compound 7 (350 mg, 1.45 mmol) was suspended in a EtOH (15 mL) AcOH (3 mL) solution and stirred for 2 h at rt in the presence
of Zn (948 mg, 14.5 mmol).The suspension was filtered through celite to remove the excess of Zn while washing with EtOAc (100
2 3 4
mL). The organic layers were washed with Sat. K CO (100 mL × 2), brine (100 mL) dried over MgSO , filtered and evaporated
under reduced pressure. The yellowish residue was purified by SCC (Pet. Et/EtOAc 20 to 60%) to yield compound 8 as a pale
1
yellow powder (270 mg, 88%) H-NMR (300 MHz, CDCl
3
): δ 2.03 (s, 6H), 2.32 (s, 3H), 3.92 (br s, 2H), 6.77 (d, 2H, J = 8.5 Hz), 6.92-
): δ 21.0, 21.1, 115.5, 128.1, 130.3, 131.7, 136.3, 136.7, 139.1, 144.4. IR: 415, 440, 511, 540, 579,
02, 739, 760, 851, 1005, 1098, 1105, 1177, 1283, 1312, 1344, 1385, 1474, 1514, 1599, 2851, 2918, 2949, 3011, 3352, 3431. HRMS (EI-TOF) m/z:
1
3
1
6.98 (m, 4H). C{ H}-NMR (75 MHz, CDCl
3
7
+
+
[
M+H] calcd. for C15H18N 212.1432; found 212.1435.
3
-Bromo-2',4',6'-trimethyl-[1,1'-biphenyl]-4-amine (9)
4
-mesitylaniline 8 (270 mg, 1.28 mmol) was dissolved in CHCl
3
(10 mL) and NBS (228 mg, 1.28 mmol) added at 0°C. The reaction
sat. (50 mL),
4
and evaporated. The orange residue was purified by SCC (Pet. Et/EtOAc 0 to
was allowed to reach r.t. and stirred overnight. The solution was diluted in EtOAc (100 mL), washed with Na
O (100 mL × 3), brine (100 mL), dried over MgSO
%) to afford molecule 9 as a viscous transparent oil (277 mg, 75%). H-NMR (300 MHz, CDCl
2 2 3
S O
H
2
1
5
3
): δ 2.02 (s, 6H), 2.31 (s, 3H), 4.57
): δ 20.9, 21.1, 109.4, 115.8, 128.1, 129.5,
32.5, 133.1, 136.5, 136.7, 137.7, 142.5. IR: 407, 434, 527, 577, 615, 658, 696, 731, 818, 851, 883, 908, 1015, 1040, 1153, 1240, 1267, 1288, 1302,
1
3
1
(
br s, 2H), 6.88-6.89 (m, 2H), 6.92 (s, 2H), 7.21 (d, J = 1.8 Hz, 1H). C{ H}-NMR (75 MHz, CDCl
3
1
1
+
+
375, 1395, 1474, 1508, 1616, 2855, 2916, 3011, 3375, 3472. HRMS (EI-TOF) m/z: [M+H] calcd. for C15H17BrN , 290.0539; found
290.0544.
2
,2'''',4,4'''',6,6''''-Hexamethyl-[1,1':3',1'':3'',1''':3''',1''''-quinquephenyl]-4',6'''-diamine (14)
3
-bromo-2',4',6'-trimethyl-[1,1'-biphenyl]-4-amine9 (500mg, 1.72 mmol), diboronic ester 12 (260 mg, 0.78 mmol), Pd(OAc)
2
(13 mg,
0.06 mmol), XPhos (47 mg, 0.10 mmol) and K PO (470 mg, 2.21 mmol) were dissolved in a 5:1 mixture of 1,4-dioxane (15 mL) and
3
4
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H
2
O (3 mL). The solution was degassed by 5 freeze-pump-thaw cycles and stirred at 80°C for 48 h under argon. The reaction
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
2
mixture was allowed to cool down to rt, diluted with EtOAc (50 mL), washed with H O (50 mL × 3) and brine (100 mL). The organic
layer was dried over MgSO
4
and the solvent evaporated under reduced pressure. The black residue was purified by SCC (Pet.
1
Et./EtOAc 30 to 90%) to yield compound 14 as a white-yellow powder (500 mg, 58%). M.P.: 112-114 °C; H-NMR (300 MHz, CDCl
3
):
13
1
δ 2.09 (s, 12H), 2.32 (s, 6H), 3.86 (br s, 4H), 6.83 (d, 2H, J = 7.4 Hz), 6.92-6.97 (m, 8H), 7.48-7.53 (m, 3H), 7.61 (s, 1H). C{ H}-NMR
(75 MHz, CDCl
3
): δ 21.1, 21.1, 116.0, 127.5, 127.9, 128.2, 129.3, 129.7, 129.9, 131.4, 131.6, 136.3, 136.7, 139.0, 140.4, 142.0. IR: 573, 633, 729,
+
8
22, 907, 1013, 1030, 1152, 1287, 1375, 1472, 1508, 1616, 2857, 2916, 2947, 3015, 3368, 3460. HRMS (EI-TOF) m/z: [M+H] calcd. for
+
36 36 2
C H N 497.2951; found 497.2950.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
5
,12-Dimesityl-8H,9H-8,9-diaza-8a-borabenzo[fg]tetracene (2)
A solution of BCl
3
(1.0 M in heptane, 210 μL, 0.21 mmol) was added to a solution of terphenyldiamine 14 (100 mg, 0.20 mmol) in
before adding AlCl (3 mg, 0.023 mmol) and
anhydrous ODCB (6 mL). The reaction mixture was stirred for 15 min at rt under N
2
3
heating at 150 °C under microwave irradiation for 16 h. The solution was allowed to cool down to rt and the solvent removed from
the deep brown solution under reduced pressure. The residue was purified by SCC (Pet. Et./EtOAc 30 to 60%) to yield molecule 2
1
as a white powder (50 mg, 50%). M.P.: 156-158°C; H-NMR (300 MHz, CDCl
3
): δ 2.12 (s, 12H, CH
), 8.04 (s, 2 H, CH ), 8.10 (d, 2 H, J = 7.9 Hz, CH
): δ 21.15, 21.21, 118.4, 119.2, 122.5, 125.3, 128.3, 129.6, 131.2, 132.7, 136.7, 136.8, 139.2, 139.2, 139.3. (signal for carbon
c e
), 2.38 (s, 6H, CH ), 6.33 (bs, 2H,
13
1
NH
NMR (126 MHz, CDCl
atom attached to boron atom absent due to quadrupolar relaxation) B{ H}-NMR (160 MHz, CDCl
38, 673, 750, 822, 851, 889, 1028, 1076, 1138, 1188, 1221, 1256, 1283, 1298, 1321, 1375, 1406, 1447, 1460, 1572, 2853, 2916, 2953, 3007, 3385.
f
), 7.01 (s, 4H, CH
d
) 7.08-7.13 (m, 4H, CHai), 7.74 (t, 1 H, J = 8.0 Hz, CH
h
b
g
). C{ H}-
3
1
1
1
3
): δ 27.0. IR: 405, 490, 581, 619,
6
+
2
H 504.2851; found 504.2833.
3410BN
+
HRMS (AP-TOF) m/z: [M+H] calcd. for C36
ASSOCIATED CONTENT
Supporting Information
Synthetic protocols and spectroscopic data for all molecules, computational studies, electrochemical characterization and titration
experiments. The Supporting Information is available free of charge on the ACS Publications website at DOI: TO DE ADDED.
AUTHOR INFORMATION
Corresponding Author* E-mail: bonifazid@cardiff.ac.uk
ACKNOWLEDGMENTS
The authors gratefully acknowledge the EU through the ERC Starting Grant “COLORLANDS” and the FRS-FNRS. JT thanks the
FRIA (FNRS) for his doctoral fellowship. DB is grateful to the RW through the FLYCOAT project and to Cardiff University for
generous funding. DB and PT thank the EU for the MC-RISE INFUSION research project. We thank T. Battisti at Cardiff University
for the ESP calculations.
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K.; Shiren, K. Ultrapure Blue Thermally Activated Delayed Fluorescence Molecules: Efficient HOMO-LUMO Separation
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Efficient Single-Component White Light-Emitting Electrochemical Cells. Adv. Funct. Mater. 2020, DOI:
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0.1002/adfm.201906830.
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Georgiou, I.; Kervyn, S.; Rossignon, A.; De Leo, F.; Wouters, J.; Bruylants, G.; Bonifazi, D. Versatile Self-Adapting Boronic
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