Synthesis of luminescent BPh2-coordinated 2-(2′- hydroxyphenyl)benzoxazole (HBO)

Article abstract of DOI:10.1039/c3nj41052h

Triphenylborane (BPh₃) has been successfully coordinated to five π-conjugated aromatic systems containing a N^∧O bidentate 2-(2′-hydroxyphenyl)benzoxazole (HBO) ligand. Complexes 6-8 are directly substituted on the phenolic side of the HBO core while the structure of derivatives 9-10 includes a 4-dibutylaminophenyl module linked through an ethynyl fragment, at position 4 or 5. The crystal structure of complexes 8 and 10 reveals different solid-state molecular packing depending on the substitution, a herringbone molecular packing being observed for complex 8 while the dibutylamino fragment present in complex 10 is in favour of a lamellar structure. The optical properties are highly dependent on the nature and the position of substituents. Solvatochromic charge-transfer emissions are observed for substitution at position 3 or 5 while singlet emission is favoured when position 4 is functionalized. Solid-state fluorescence reveals that complex 8 possesses red-shifted emission when dispersed in a KBr matrix.

Full text of DOI:10.1039/c3nj41052h

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Synthesis of luminescent BPh2-coordinated
2-(20-hydroxyphenyl)benzoxazole (HBO)†
Julien Massue,*a Pascal Retailleau,b Gilles Ulrich*a and Raymond Ziessel*a
Cite this: NewJ.Chem., 2013,
37, 1224
Triphenylborane (BPh3) has been successfully coordinated to five p-conjugated aromatic systems
containing a N4O bidentate 2-(20-hydroxyphenyl)benzoxazole (HBO) ligand. Complexes 6–8 are directly
substituted on the phenolic side of the HBO core while the structure of derivatives 9–10 includes a
4-dibutylaminophenyl module linked through an ethynyl fragment, at position 4 or 5. The crystal
structure of complexes 8 and 10 reveals different solid-state molecular packing depending on the
substitution, a herringbone molecular packing being observed for complex 8 while the dibutylamino
fragment present in complex 10 is in favour of a lamellar structure. The optical properties are highly
dependent on the nature and the position of substituents. Solvatochromic charge-transfer emissions are
observed for substitution at position 3 or 5 while singlet emission is favoured when position 4 is
functionalized. Solid-state fluorescence reveals that complex 8 possesses red-shifted emission when
dispersed in a KBr matrix.
Received (in Montpellier, France)
19th November 2012,
Accepted 29th January 2013
DOI: 10.1039/c3nj41052h
www.rsc.org/njc
arise from the presence of a nearby decorated metallic centre
(Scheme 1).
Introduction
The 2-(20-hydroxyphenyl)benzoxazole (HBO) and benzothiazole
(HBT) derivatives1 are a class of fluorophores known for over
40 years that exhibit a bright emission in the solid state as
a consequence of an intrinsic Excited-State Intramolecular
Proton Transfer (ESIPT).2 This major reorganisation of the
molecule upon photoexcitation leads to improved Stokes shifts
and pronounced solvatochromism. These interesting features
have made these dyes emerge as promising luminescent materials
for pH and chemical sensing of cations3 or biologically relevant
anions.4 ESIPT displaying compounds have also successfully been
embedded in optoelectronic devices5 such as light-emitting
diodes or transistors or recently used as triplet-state sensitizers
in dyads for photodynamic therapy (PDT) applications.6
Numerous examples report their incorporation in the coordina-
tion sphere of metallic centres with the goal to create optically
tunable luminescent emitters.8 Among them, bis(2-(2-hydroxy-
phenyl)benzothiazolate)-zinc [Zn(BTZ)2] has been widely studied
as a white electroluminescent material that exhibits major
electron-transporting properties.9
Following a pioneer paper,10 we recently reported the synthesis
of several substituted HBO fragments coordinated to a boron
trifluoride moiety.11 These bright complexes thus obtained exhibit
emission properties that could be fine-tuned by introducing
relevant electronic substituents at different positions of the
phenolic side.12 p-Conjugated aromatic systems coordinated to
one or several boron biphenyl fragments (BPh2) have received
widespread interest for their use in electroluminescent devices.13
Several studies have also pointed out the fact that HBO- or
HBT-based fragments were excellent N4O chelating entities
towards a large variety of metals.7 ESIPT is consequently absent
but large Stokes shifts are usually maintained due to the non-
symmetric structure of HBO or HBT and new properties can
a
´
´
Laboratoire de Chimie Moleculaire et Spectroscopies Avancees (LCOSA),
´
´
`
ICEES-LCOSA, UMR CNRS 7515, Ecole Europeenne de Chimie, Polymeres et
´
Materiaux (ECPM), 25 rue Becquerel, 67087 Strasbourg Cedex 02, France.
E-mail: massue@unistra.fr, gulrich@unistra.fr, ziessel@unistra.fr
b
ˆ
Laboratoire de Cristallochimie, ICSN – CNRS Bat 27 – 1 avenue de la Terrasse,
91198 Gif-sur-Yvette Cedex, France
Scheme 1 (a) General structure of HBO/HBT dyes displaying the ESIPT process;
(b) use as N4O bidentate ligands.
† CCDC 891069 (complex 8) and CCDC 891070 (complex 10). For crystallographic
data in CIF or other electronic format see DOI: 10.1039/c3nj41052h
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For example, 8-hydroxyquinolinate diphenylboron (BPh2q)
was found to be an interesting alternative to the well-known
tris(8-hydroxyquinolinate)aluminum (Alq3) for organic light-
emitting diodes (OLEDs) because of its stability and high emission
quantum yield.14 It was thus interesting to study the impact of the
coordination of triphenylborane (BPh3) to substituted HBO ligands
on the chemical and photochemical stability and on the photo-
physical properties. The comparison of the optical properties
between the BPh2 and the BF2 complexes is likely to open the
way to subtle luminescence fine-tuning within this family of dyes.
Herein, we report the synthesis, crystal structures and
photoluminescence properties of five BPh2 HBO borate complexes,
either directly substituted with electron donating (ED) groups (tBu,
OMe, NEt2) or through an ethynyl fragment (–CRC-PhNBu2).
Results and discussion
Syntheses
HBO ligands 1–3 (ref. 11) and 4–5 (ref. 12) were synthesized
according to reported procedures. Targeted BPh2 complexes
6–8 and 9–10 were obtained by reacting the relevant ligand with
an excess of triphenylborane (6 equivalents) in toluene at 60 1C
for 1 hour. Note that a base is not required as BPh3 is used as a
proton scavenger releasing benzene as a side-product. Purification
by filtration on a basic Al2O3 column, eluting with CH2Cl2, afforded
the desired complexes 6–10 as beige to orange powders with yields
ranging from 66 to 95% (Scheme 2).
Fig. 1 (a) 1H NMR spectrum of ligand
3
in CDCl3 at room temperature
(300 MHz) and (b) 1H and 13C NMR spectra of BPh2 complex 8 in CDCl3 at room
temperature (300 and 75.4 MHz respectively).
to the H-bonded phenolic proton that disappears upon complexa-
tion to BPh3. The chelation of the BPh3 fragment is further
evidenced by a splitting of the multiplets corresponding to the
aromatic protons of the HBO core and the appearance of additional
multiplets for the BPh2 subunit. 13C spectra are in accordance with
expected signals for tertiary and quaternary aromatic carbons.
Finally, coordination to the boron centre leads to the appearance
of a broad signal in 11B spectroscopy between 5.5 and 6.1 ppm for
complexes 6–10.
1
These complexes were unambiguously characterized by H,
13C and 11B NMR spectroscopy in CDCl3 at room temperature.
A typical example is depicted in Fig. 1 with the 1H NMR of
1
ligand 3 along with the H and 13C NMR of the corresponding
BPh2 complex 8. HBO ligand 3 exhibits a distinctive downfield
1H signal resonating as a broad singlet at 11.5 ppm attributed
X-ray structures
Monocrystals of complexes 8 and 10 were grown by slow
diffusion of pentane in a concentrated CH2Cl2 solution at room
temperature. The X-ray molecular structures of 8 and 10 are
shown in Fig. 2 and 3, respectively, with selected geometric
values.15
In both structures, the boron has a similar distorted tetra-
hedral geometry with angles ranging from 105.7(3) to 116.1(2)1
and from 104.0(2) to 116.1(3)1 in 8 and 10, respectively. The
largest angle corresponds to the spreading of both phenyl
groups attached to the boron atom. A distortion of the tetra-
cyclic platform around the B–O bond is common for these types
of complexes. Both these atoms deviate significantly by 0.130(4)
and ꢀ0.105(3) Å from the least-squares mean plane defined by
the 15 other atoms with a root mean square deviation of 0.0128 Å
in 8. Unlike the non-substituted outer phenyl twisted known
structures,16 the overall planarity seems to be recovered by the
joint contribution of the syn-diethylamino substituent and the
relative B-phenyl orientation (dihedral angle of 56.41) deviating
from the usual orthogonality as observed for 10 (85.31).
Scheme 2 Synthesis of BPh2 complexes 6–10.
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Fig. 2 (Left) Ortep view for 8 showing the atom-labelling scheme. Thermal
ellipsoids are plotted at the 30% level. (Right) Perpendicular view to highlight the
distortion at the B atom. B1–N1, B1–O1, B1–C14, B1–C20, C1–N1, N1–C7, and
C8–O1 bond lengths are 1.616(3), 1.502(3), 1.610(3), 1.611(3), 1.322(2), 1.403(2),
and 1.339(2), and the N–B–O, C–B–C, N–B–C, O–B–C, B–N–C, C1–N1–B1, C7–N1–
B1 and B–O–C angles are 105.66(16), 116.71(18), 106.95(16), 108.19(17),
108.22(17), 110.53(18), 121.98(17), 130.96(16) and 126.55(16)1.
Fig. 4 (a) A view part of the crystal structure of 8, showing the C–Hꢁ ꢁ ꢁp (dashed
lines) hydrogen bonds developed around a molecule (dark) at a general position.
In dark grey neighbouring molecules in front; in light grey, molecules in the back;
(b) view of the molecular packing down highlighting the herringbone molecular
packing.
the substituents, which can promote basically two types of
packing morphology, a ‘herring-bone’ structure (rather favoured
in the absence of side chains, Fig. 4) and a lamellar structure
(usually in the presence of linear alkyl side chains, Fig. 5).18
When viewed down the short molecular axis which is parallel to
the crystallographic a axis, complexes 8 appear to be stacked
pairwise in a herringbone-like structure, whereas complexes 10
stack along the crystallographic b axis forming infinite layers
along the a axis parallel to (0 ꢀ1 3) and (0 1 3) alternately every
distance corresponding to c/2. The stacks are canted relative to
the stack axis with an angle of ca. 651. In the crystal of complex 8,
despite a cofacial orientation with a distance of ca. 3.45 Å
between inversion-related pairwise molecules, there is little
p-overlap between them. The main cohesive forces are instead
provided by the C–Hꢁ ꢁ ꢁp non-conventional hydrogen bonds
involving the two orthogonal phenyl groups and the benzyl
moiety of the heterobicycle of a molecule at general positions
x, y, z and six neighbours (Fig. 4). As seen previously, the two
orthogonal phenyl groups interact with the conjugated main
groups; p–p interactions are present and involve the tetracycle of
one molecule at x, y, z and the part benzyl-ethynyl-phenyl moiety
of the adjacent molecule at 1/2 ꢀ x, ꢀ1/2 + y, z with an average
centroid–centroid distance of 3.69 Å.
Fig. 3 (Left) Ortep view for 10 showing the atom-labelling scheme. Thermal
ellipsoids are plotted at the 30% level. (Right) Perpendicular view to highlight the
distortion at the B atom. H-atoms are omitted for clarity. B1–N1, B1–O2, B1–C14,
B1–C20, C1–N1, N1–C7, and O2–C8 bond lengths are 1.614(4), 1.484(4),
1.612(4), 1.605(4), 1.319(3), 1.413(3) and 1.340(3), N–B–O, C–B–C, N–B–C,
O–B–C, C1–N1–B1/C7–N1–B1, and B–O–C angles are 104.0(2), 116.1(3),
108.3(2)/109.1(2), 110.8(2)/107.8(2), 119.3(2)/134.0(2) and 120.5(2)1.
With respect to 10, elongated ethynyl-phenyl substitution in C11
deforms again the tetracyclic platform, the outer phenyl making
a dihedral angle of 10.81 with the planar heterobicycle and the
maximum deviation of O and B atoms from this plane exceeds
0.3 Å.
The B1–O1 and B1–N1 distances are in the same range for 8
and 10 (1.502 Å vs. 1.484 Å for B1–O1 and 1.616 Å vs. 1.614 Å for
B1–N1) and are fairly similar to those in HBO borate complexes
reported in the literature.11,12 It is also noticeable that the B1–O1
and B1–N1 distances take intermediate values (ca. 1.61 Å
between 1.64 and 1.50 Å, and ca. 1.49 Å between 1.55 and
Photophysical properties
1.42(2) Å, respectively), in comparison with some reported Photophysical data of complexes 6–10 in various solvents are
boranil complexes substituted by either BPh2 or BF2 fragments.17 gathered in Table 1.
The solid-state packing of the conjugated planar platforms is
All BPh2 HBO borate complexes except 8 display unstruc-
affected by the nature, the size and the position of attachment of tured absorption spectra with a major band located between
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Fig. 6 Absorption (---) and emission (—) spectra of complexes 6–8 in CH2Cl2 at
room temperature. Excitation wavelengths were 380, 376 and 389 nm for
complexes 6, 7, and 8, respectively.
ranging between 427 and 556 nm and quantum yields from 7
to 82% (Table 1 and Fig. 6–8).
The absorption and emission spectra of the directly sub-
stituted BPh2 HBO borate complexes 6–8 in CH2Cl2 are shown
in Fig. 6. Complexes 6 and 7 bearing two Bu groups or a
Fig. 5 (a) Part of the crystal structure of 10 showing the p–p stacking as well as
the edge-to-face (cyan dotted lines) interactions; (b) view of the molecular
packing down the a axis with guidelines for the (0 ꢀ1 3) and (0 1 3) planes.
t
methoxy group at positions 5, 3 and 4, respectively, exhibit
similar photophysical characteristics such as a large, unstruc-
tured absorption band (labs = 390 nm for 6 and 366 nm for 7)
and a symmetrical emission band (lem = 472 nm for 6, F = 82%
and lem = 427 nm for 7, F = 44%). These features are consistent
with a weak internal charge-transfer (ICT). In the case of
complex 8, a structured, narrow, absorption band is observed
with an increased extinction coefficient (labs = 399 nm, e =
45 900 Mꢀ1 cmꢀ1). The emission band (lem = 414 nm for 8, F =
67%) mirrors the absorption band and features reduced Stokes
shift (900 cmꢀ1), consistent with a weakly polarized excited
state. These experimental observations are indicative of a
singlet state emission with a significant internal cyanine
character and are reminiscent of what was previously observed
on BF2 HBO borate complexes.11 The short lifetime (1.9 ns) is in
keeping with such a statement. Comparison of complexes 6–8
with their corresponding BF2 complexes11 shows in each case a
302 and 434 nm with extinction coefficients ranging between
9200 and 42 000 Mꢀ1 cmꢀ1, depending on the electronic
substitution on the hydroxyphenyl core. More intense bands
are observed below 300 nm, characteristic of the p–p* transitions
of the phenyl rings. In the case of dye 8, where the phenolic side
of the HBO core is directly substituted with a diethylamino
group, a structured, narrow absorption band is observed with
a higher extinction coefficient (45 900 Mꢀ1 cmꢀ1) with respect to
complexes 6 and 7. Note that all the absorption spectra are
centered in the UV region, regardless of the substitution, and do
not show pronounced solvatochromism.
Interestingly, irradiation in the lower energy absorption
band for complexes 6–10 leads to an intense emission band
located in the visible region with a maximum wavelength
Table
1
Optical data of complexes 6–10 measured in solution at room
temperature
labs
e
lem
D
t
Dye (nm) (Mꢀ1 cmꢀ1
)
(nm) (cmꢀ1
)
Ffa (ns) Solvent
6
7
8
9
390
366
399
423
434
324
430
331
340
302
9200
10 000
45 900
35 000
38 000
38 000
40 000
35 300
37 400
42 000
472
427
414
488
552
491
556
534
541
498
4500 0.82 8.4 CH2Cl2
3900 0.44 4.1 CH2Cl2
900 0.67 1.9 CH2Cl2
3100 0.79 1.8 Toluene
4900 0.63 2.5 CH2Cl2
10 500 0.08 2.1 CH2Cl2 + HClgas
5300 0.36 1.9 THF
11 500 0.08 1.4 Toluene
10 900 0.07 1.5 CH2Cl2
13 000 0.13 1.4 CH2Cl2 + HClgas
10
a
Quantum yields determined in solution, using quinine sulfate as
reference F = 0.55 in H2SO4 1 N, lex = 366 nm for dyes emitting below
480 nm, Rhodamine 6G F = 0.88 in ethanol, lex = 488 nm for dyes
emitting between 480 and 570 nm.
Fig. 7 Absorption and emission spectra of complex 9 in various solvents at
room temperature. Excitation wavelengths were 427, 315, 415 and 425 nm for
CH2Cl2, CH2Cl2 + HCl, toluene and THF respectively.
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respect to the maximum absorption wavelength in CH2Cl2
(labs = 324 nm vs. labs = 434 nm). Compared to the respective
maximum absorption of the corresponding BF2 complexes,12
all BPh2 complexes exhibit a significant red-shift (around
1900 cmꢀ1) in all solvents except in CH2Cl2 after protonation.
Irradiation of the maximum absorption band leads to an
intense emission band located in the visible region between
488 and 556 nm (F = 8 to 79%). In all solvents, the emission of
the BPh2 complexes is red-shifted with respect to their corres-
ponding BF2 analogues (around 1500 cmꢀ1). Protonation of the
lone electron pair of the nitrogen in CH2Cl2 with HClgas leads to
a significant blue-shift for both the absorption and the emis-
sion (labs = 434 nm, lem = 552 nm for 9 in CH2Cl2 vs. labs
=
Fig. 8 Absorption (---) and emission spectra (—) of complex 10 in various
solvents at room temperature. Excitation wavelengths were 335, 295 and
325 nm for CH2Cl2, CH2Cl2 + HCl and toluene.
324 nm, lem = 491 nm for 9 in CH2Cl2 + HClgas) and a dramatic
decrease of the quantum yield (F = 63% in CH2Cl2 vs. F = 8% in
CH2Cl2 + HClgas). No precipitation of the salts is observed; however,
the formation of soluble aggregates could not be excluded.
Complex 10 displays similar photophysical characteristics
bathochromic shift for both the absorption and emission
bands and an increase of the quantum yield. This observed with a major unstructured absorption band (labs = 302 to
red-shift is only moderate in the case of complex 8 (labs
340 nm, e = 35 000–42 000 Mꢀ1 cmꢀ1), which gives rise, upon
399 nm, lem = 414 nm, F = 67% compared to labs = 387 nm, irradiation, to an emission located in the visible region (lem
=
=
lem = 401 nm, F = 42% for the corresponding BF2 complex). 498 to 534 nm, F = 7 to 13%) (Fig. 8). This is a major
This shift increases as the electron donating ability decreases. improvement compared to its BF2 analogue whose fluorescence
t
Indeed, complex 6 bearing Bu groups is more strongly batho- was quenched in CH2Cl2 due to strong non-radiative deactiva-
chromically shifted (labs = 390 nm, lem = 472 nm, F = 82% for tions through ICT.12 ICT is similarly featured in complex 10 as
6 compared to labs = 359 nm, lem = 422 nm, F = 31% for the BF2 evidenced by the strong blue-shift and quantum yield increase
analogue) than complex 7 substituted by a methoxy fragment observed upon protonation of the nitrogen doublet using
(labs = 366 nm, lem = 427 nm, F = 44% for 7 compared to labs
339 nm, lem = 380 nm, F = 39% for the BF2 analogue). Switching due to the less electron accepting nature of the BPh2 fragment.
the BF2 fragment for a BPh2 reduces the strength of the ICT Monoexponential decays are observed for all compounds
which presumably decreases non-radiative deactivations and with lifetimes being on the nanosecond scale.20
is therefore responsible for an increased quantum yield. Never- Finally, solid-state emission and excitation were recorded
=
HClgas but is weaker than in its BF2 analogue, presumably
theless, BPh2 being less electron-attractor than BF2, the ICT for complex 8, in order to correlate with the molecular packing
is therefore weaker and the emission should not be batho- observed in the X-ray structure whereas complex 10 did not
chromically shifted as observed. One tentative explanation is exhibit any fluorescence in the solid state. As shown in Fig. 9,
that the electronic donation of the phenyl groups induces an complex 8 displays a broad intense emission band in the solid
increase of the energy level for the HOMO; whereas the energy state after irradiation at 390 nm.
level of the LUMO remains unaffected. As a consequence the
Optical data for complex 8 in the solid state are red-shifted
HOMO–LUMO gap decreases and the emission is therefore with respect to the CH2Cl2 solution (lexc = 427 nm, lem
=
bathochromically shifted. This case has already been observed 464 nm vs. labs = 399 nm, lem = 414 nm). The quantum yield,
on BODIPY dyes.19 It also seems that the nature of the emission
(ICT or singlet) has an influence on the amplitude of the
bathochromic shift observed for the BPh2 HBO borate complexes
compared to the BF2 ones; ICT emission seems to lead to
stronger red-shifts when switching from BF2 to BPh2 than singlet
emission. This is specifically the case for complexes 6 and 7.
To check if these features are also present in ethynyl-
extended HBO borate complexes, the absorption and emission
spectra of the 4-dibutylaminophenyl ethynyl-extended HBO
borate complexes 9 and 10 were recorded in various solvents
(Fig. 7 and 8).
Complex 9 displays a major unstructured absorption band
located mostly in the UV region between 324 and 434 nm
(e = 35 000–40 000 Mꢀ1 cmꢀ1). This band is very mildly solvato-
Fig. 9 Solid-state excitation (---) and emission (—) recorded in KBr pellets of
chromic except after protonation of the nitrogen in CH2Cl2
using HCl gas where it undergoes a pronounced blue-shift with
complex 8 along with solution excitation in CH2Cl2 (grey scale, ---). Excitation
wavelength was 427 nm.
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calculated from a spectrometer fitted with an integrating (s, 3H, CH3). 13C NMR (75.4 MHz, CDCl3) d (ppm): 167.8, 165.6,
sphere, was found to be F = 13%. Biexponential decay is 161.5, 149.0, 133.4, 133.1, 127.4, 127.3, 126.8, 126.4, 125.7,
observed presumably due to the presence of various packing 117.1, 111.2, 109.0, 103.1, 101.2, 55.7. 11B NMR (128.38 MHz,
of the molecule in the KBr matrix (t1 = 2.4 ns, t2 = 5.6 ns).
CDCl3) d (ppm): 6.08. Anal. calculated for C26H20BNO3: C, 77.06;
H, 4.97; N, 3.46%; found C, 76.82; H, 4.69; N, 3.27%. EI-MS
(m/z): 405.0 (100).
Conclusion
HBO borate complex 8. Yellow crystals. 88%. 1H NMR
We have successfully coordinated a triphenylborane fragment (300 MHz, CDCl3) d (ppm): 7.59 (d, 1H, CH Ar, J = 9 Hz), 7.54
to differently substituted HBO pincer ligands. The substituents (d, 1H, CH Ar, J = 8.1 Hz), 7.47–7.50 (m, 4H, CH Ar), 7.15–7.31
are either directly linked to the hydroxyphenyl core or through (m, 8H, CH Ar), 6.88 (d, 1H, CH Ar, J = 7.8 Hz), 6.41 (d, 1H, CH
an ethynyl spacer. Two complexes were characterized by X-ray Ar, J = 2.7 Hz), 6.28 (dd, 1H, CH Ar, J = 6.6 Hz), 3.44 (q, 4H, CH2,
diffraction on single crystals. Depending on the electronic J = 7.2 Hz), 1.24 (t, 6H, CH3, J = 7.2 Hz). 13C NMR (75.4 MHz,
substitution and its position on the HBO core, different photo- CDCl3) d (ppm): 164.7, 161.7, 155.1, 148.8, 133.9, 133.1, 127.4,
physical behaviours were observed. The locally excited state is 127.2, 127.1, 126.4, 125.8, 124.5, 116.3, 110.7, 104.8, 99.7, 96.2,
either a charge-transfer or a singlet emission. In all cases, the 44.8, 12.7. 11B NMR (128.38 MHz, CDCl3) d (ppm): 5.54. Anal.
optical data recorded in solution and the solid-state showed a calculated for C29H27BN2O2: C, 78.04; H, 6.10; N, 6.28%; found
significant red-shift both for the absorption and emission with C, 77.74; H, 5.70; N, 5.88%. EI-MS (m/z): 446.2 (100).
respect to the BF2 analogues.
HBO borate complex 9. Orange powder. 66%. 1H NMR
(300 MHz, CDCl3) d (ppm): 7.72 (d, 1H, CH Ar, J = 8.1 Hz),
7.60–7.65 (m, 2H, CH Ar), 7.43–7.47 (m, 5H, CH Ar), 7.39 (d, 2H,
Experimental
All reactions were performed under a dry atmosphere of argon. CH Ar, J = 9 Hz), 7.23–7.30 (m, 7H, CH Ar), 6.99 (d, 2H, CH Ar,
All chemicals were received from commercial sources and used J = 8.1 Hz), 6.59 (d, 2H, CH Ar, J = 9 Hz), 3.30 (t, 4H, CH2, J =
without further purification. Chromatographic purifications 7.8 Hz), 1.54–1.64 (m, 4H, CH2), 1.31–1.43 (m, 4H, CH2), 0.97
were conducted using 40–63 mm silica gel or basic aluminium (t, 6H, CH3, J = 7.5 Hz). 13C NMR (75.4 MHz, CDCl3) d (ppm):
oxide. 1H-, 13C- and 11B NMR spectra were acquired at 25 1C on 162.8, 161.2, 149.2, 148.5, 141.4, 133.8, 133.4, 133.1, 128.8,
either a Bruker AV 300 or a Bruker AV 400 spectrometer. 128.8, 127.3, 127.3, 127.2, 127.1, 126.8, 126.7, 126.3, 125.7,
Deuterated solvents were used as the lock and residual non- 122.5, 122.0, 117.5, 111.4, 111.2, 107.7, 106.7, 96.4, 87.5, 50.7,
deuterated solvents as the internal references.
29.4, 20.3, 14.0. 11B NMR (128.38 MHz, CDCl3) d (ppm): 5.41.
Anal. calculated for C41H39BN2O2: C, 81.72; H, 6.52; N, 4.65%;
found C, 81.50; H, 6.38; N, 4.41%. EI-MS (m/z): 602.2 (100).
HBO borate complex 10. Yellow crystals. 80%. 1H NMR
General procedure for the synthesis of HBO borate complexes
6–10
To a stirred solution of the corresponding HBO in toluene (300 MHz, CDCl3) d (ppm): 7.95 (d, 1H, CH Ar, J = 2.4 Hz),
(0.1 mL mgꢀ1), BPh3 (6 equivalents) was added as a powder 7.62–7.68 (m, 2H, CH Ar), 7.43–7.46 (m, 5H, CH Ar), 7.35 (d, 2H,
under argon. The resulting mixture was stirred at 60 1C for CH Ar, J = 9 Hz), 7.15–7.28 (m, 7H, CH Ar), 7.01 (d, 2H, CH Ar,
1 hour. The crude solution was then filtered through a column J = 8.1 Hz), 6.59 (d, 2H, CH Ar, J = 9 Hz), 3.29 (t, 4H, CH2, J =
of basic Al2O3, eluting with CH2Cl2, and the solvents were 7.8 Hz), 1.54–1.64 (m, 4H, CH2), 1.27–1.43 (m, 4H, CH2), 0.97
evaporated in vacuo. Pure BPh2 HBO borate complexes 6–10 (t, 6H, CH3, J = 7.2 Hz). 13C NMR (75.4 MHz, CDCl3) d (ppm):
were obtained as beige to orange powders after recrystallisation 161.4, 159.9, 148.2, 146.9, 139.4, 132.2, 132.0, 131.7, 128.0,
in pentane or cyclohexane.
127.5, 127.2, 126.4, 125.9, 125.8, 125.5, 124.3, 116.7, 114.2,
HBO borate complex 6. Beige powder. 95%. 1H NMR 110.5, 110.2, 107.5, 107.1, 89.2, 84.6, 49.7, 28.4, 19.3, 13.0. 11B
(300 MHz, CDCl3) d (ppm): 7.71 (d, 1H, CH Ar, J = 2.7 Hz), NMR (128.38 MHz, CDCl3) d (ppm): 5.74. Anal. calculated for
7.66 (d, 1H, CH Ar, J = 8.4 Hz), 7.63 (d, 1H, CH Ar, J = 2.4 Hz),
C41H39BN2O2: C, 81.72; H, 6.52; N, 4.65%; found C, 81.58; H,
7.47–7.50 (m, 4H, CH Ar), 7.38 (t, 1H, CH Ar, J = 8.4 Hz), 7.25– 6.37; N, 4.37%. EI-MS (m/z): 602.2 (100).
7.31 (m, 7H, CH Ar), 7.06 (d, 1H, CH Ar, J = 8.4 Hz), 1.47 (s, 9H,
CH3), 1.38 (s, 9H, CH3). 13C NMR (75.4 MHz, CDCl3) d (ppm):
162.5, 160.2, 149.1, 140.5, 140.0, 133.5, 133.3, 132.8, 129.1,
Notes and references
128.3, 127.1, 126.5, 126.4, 125.9, 125.3, 119.5, 117.3, 111.1,
106.5, 35.3, 34.4, 31.3, 29.7. 11B NMR (128.38 MHz, CDCl3) d
(ppm): 6.13. Anal. calculated for C33H34BNO2: C, 81.31; H,
7.03; N, 2.87%; found C, 81.04; H, 6.72; N, 2.51%. EI-MS
(m/z): 487.2 (100).
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HBO borate complex 7. Beige powder. 94%. 1H NMR
(300 MHz, CDCl3) d (ppm): 7.73 (d, 1H, CH Ar, J = 8.7 Hz),
7.63 (d, 1H, CH Ar, J = 8.1 Hz), 7.50–7.53 (m, 4H, CH Ar),
7.24–7.41 (m, 8H, CH Ar), 7.01 (d, 1H, CH Ar, J = 7.8 Hz), 6.74
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Paper
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and Y. Pang, Chem. Commun., 2010, 46, 4070; (c) M. Santra,
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446.34, colourless block, 0.39 ꢂ 0.35 ꢂ 0.18 mm, mono-
clinic, space group P21/c (no 14), a = 14.4020(2) Å, b =
8.9147(1) Å, c = 18.3569(12) Å, b = 92.158(7)1, V =
2355.16(16) Å3, Z = 4, rcalcd = 1.259 g cmꢀ3, 2qmax
=
136.481, 12 222 measured reflections, 4253 independent,
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ꢀ17 r h r 14, ꢀ10 r k r 6, ꢀ22 r l r 19, R(int)
=
0.0474, m = 0.615 mmꢀ1, multi-scan absorption correction,
Tmin = 0.751 and Tmax = 0.895, 310 parameters were refined
against all reflections, R1 = 0.0735, wR2 = 0.1296 based on all
observed F values, R1 = 0.0530, wR2 = 0.1119 (3059 reflec-
tions with I > 2s(I)), Drmin and rmax = ꢀ0.216 and 0.185 eꢀ3
,
extinction coefficient 0.00214(18), GOF = 1.126 based on F2.
Crystallographic data for complex 10: C41H39BN2O2, Mr =
7 (a) T. E. Keyes, D. Leane, R. J. Forster, C. G. Coates,
C. G. Mcgarvey, M. N. Nieuwenhuyzen and E. Figgemeier, Inorg.
Chem., 2002, 41, 5721; (b) M. A. Katkova, T. V. Balashova,
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602.55, pale yellow triangular plate, 0.58
ꢂ
0.26
ꢂ
0.12 mm, orthorhombic, space group Pbca (no 61), a =
18.9987(3) Å, b = 14.3343(3) Å, c = 25.2809(17) Å, V =
6884.8(5) Å3, Z = 8, rcalcd = 1.163 g cmꢀ3, 2qmax = 136.51,
20 818 measured reflections, 6262 independent, ꢀ22 r h r
22, ꢀ8 r k r 17, ꢀ22 r l r 29, R(int) = 0.0274, m =
0.547 mmꢀ1, multi-scan absorption correction, relative Tmin
= 0.719 and Tmax = 0.936, 437 parameters were refined
against all reflections, R1 = 0.0980, wR2 = 0.2191 based on
all observed F values, R1 = 0.0612, wR2 = 0.1641 (3965
reflections with I > 2s(I)), 87 soft restraints on bond lengths,
Drmin and rmax = ꢀ0.279 and 0.401 eꢀ3, GOF = 1.165 based
on F2. CCDC 891069 (complex 8) and CCDC 891070
(complex 10)†.
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13 (a) Z. Zhang, H. Bi, Y. Zhang, D. Yao, H. Gao, Y. Fan, 20 Luminescence lifetimes were measured on an Edinburgh
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Instruments spectrofluorimeter equipped with a R928
photomultiplier and a PicoQuant PDL 800-D pulsed diode
connected to a GwInstec GFG-8015G delay generator.
No filter was used for the excitation. Lifetimes were decon-
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voluted with FS-900 software using
solution (LUDOX) for instrument response.
a light-scattering
c
1230 New J. Chem., 2013, 37, 1224--1230
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013