FULL PAPER
slow cooling of a toluene solution of 2. 1H NMR (CDCl3): δ =
8.62 (d, J = 5.9 Hz, 2 H), 7.20 (d, J = 5.9 Hz, 2 H), 4.39 (dd, J =
Conclusion
Dative boron–nitrogen bonds are increasingly being used 11.3, 4.8 Hz, 2 H), 4.29 (t, J = 10.4 Hz, 2 H), 3.40 (m, 1 H) ppm.
13C NMR: not recorded due to low solubility. 11B NMR (CDCl3):
δ = 18.5 ppm. C14H9BF5NO2·0.5C7H8 (375.1): calcd. C 56.04, H
3.49, N 3.73; found C 56.19, H 3.45, N 3.96.
in the context of structural supramolecular chemistry and
crystal engineering. One synthetic strategy involves the utili-
zation of self-complementary building blocks that contain
Lewis acidic boron centers along with Lewis basic N-donor
ligands. We have explored the self-assembly of novel di-
Compound 3: A mixture of 2-(4-pyridyl)propan-1,3-diol (34.5 mg,
225 μmol) and [3,5-bis(trifluoromethyl)phenyl]boronic acid
oxaborinanes and benzodioxaboroles that contain pyridyl (58.0 mg, 225 μmol) in toluene (45 mL) was heated under reflux
conditions with a Dean Stark apparatus for 3 h. After this time,
the mixture was allowed to cool to room temperature, the solvent
was reduced to Ͻ5 mL, and pentane (10 mL) was added to induce
precipitation of the product. The product was filtered, washed with
pentane, and residual solvent was removed under vacuum to give
3 as an off-white solid (52 mg, 62%). Crystallization was ac-
complished by slow diffusion of pentane into a concentrated solu-
side chains. The modest Lewis acidity of the dioxaborinanes
was found to prevent significant aggregation in solution.
In the solid state, however, one-dimensional polymers were
obtained upon utilization of electron-withdrawing side
chains. The benzodioxaboroles, on the other hand, formed
dynamic mixtures of trimeric and tetrameric macrocycles in
solution. For one compound, we were able to confirm a
macrocyclic structure in the solid state by X-ray crystal-
lography. Overall, our results highlight the importance of
1
tion of 3 in chloroform. H NMR (CDCl3): δ = 8.65 (dd, J = 4.5,
1.6 Hz, 2 H), 8.26 (s, 2 H), 7.96 (s, 1 H), 7.22 (dd, J = 4.5, 1.6 Hz,
2 H), 4.42 (dd, J = 11.2, 4.8 Hz, 2 H), 4.30 (t, J = 10.6 Hz, 2 H),
electronic effects for the assembly of supramolecular struc- 3.38 (m, 1 H) ppm. 13C NMR (CDCl3): δ = 150.4, 145.9, 133.8 (br.
s), 130.8 (q, J = 33.0 Hz), 124.4 (m), 123.6 (q, J = 272.6 Hz), 122.9,
66.0, 42.2 (B–C was not observed) ppm. 19F NMR (CDCl3): δ =
–62.9 ppm. 11B NMR (CDCl3): δ = 26.7 ppm. C19H10BF6NO2
(409.09): calcd. C 51.24, H 3.22, N 3.73; found C 51.52, H 3.14, N
3.95.
tures by means of dative B–N bonds.
Experimental Section
General: The solvents were dried with a solvent purification system
from Innovative Technologies, Inc. All reactions were carried out
under an atmosphere of dry nitrogen using standard Schlenk tech-
niques. 1H, 13C, 11B, and 19F NMR spectra were obtained with
a Bruker Avance instrument (1H: 400 MHz, 13C: 100.6 MHz, 11B:
4-(3-Pyridyl)catechol: The ligand was synthesized by modification
of a published procedure.[15] A mixture of 4-bromoveratrole
(0.48 mL, 3.3 mmol), (3-pyridinyl)boronic acid (525 mg, 4.3 mmol),
[Pd(PPh3)4] (248 mg, 0.21 mmol), and Na2CO3 (3.5 g, 33 mmol) in
H2O/dioxane (1:1, 60 mL) was heated under reflux conditions for
1 h. Water (60 mL) and Et2O (60 mL) were added to the reaction
mixture, the organic layer was separated, and the water phase was
extracted with Et2O (60 mL) twice. The combined organic phase
was washed with water (20 mL), brine (20 mL), and then dried with
MgSO4. The solution was concentrated to approximately 1 mL,
and the residue was purified by chromatography (CH2Cl2/Et2O =
4:1) to give a light yellow oil, which was dissolved in HBr solution
(47%, 30 mL) and heated to reflux for 3 h. The solution was co-
oled, and the white precipitate was filtered, washed with acetone,
and then dried under vacuum to give 4-(3-pyridyl)catechol hydro-
1
128.4 MHz, 19F: 188.3 MHz) in CDCl3. H chemical shifts (δ) are
reported in parts per million referenced to internal CHCl3 (δ =
7.26 ppm). 13C chemical shifts are reported in ppm and referenced
to internal CHCl3 (δ = 77.0 ppm). All the NMR spectra were mea-
sured at 298 K unless mentioned otherwise. Combustion analyses
were performed with a Thermo Scientific Flash 2000 Organic Ele-
mental Analyzer.
Compound 1: A mixture of 2-(4-pyridyl)propan-1,3-diol (34.5 mg,
225 μmol) and (4-tert-butylphenyl)boronic acid (40.1 mg,
225 μmol) in toluene (45 mL) was heated under reflux conditions
with a Dean Stark apparatus for 3 h. After this time, the mixture
was allowed to cool to room temperature, the solvent was reduced
to Ͻ5 mL, and pentane (10 mL) was added to induce precipitation
of the product. The product was filtered, washed with pentane, and
residual solvent was removed under vacuum to give 1 as a white
solid (33 mg, 50%). Crystallization was accomplished by slow dif-
1
gen bromide salt (352 mg, 1.2 mmol, 39.8%). H NMR (CD3OD):
δ = 9.07 (s, 1 H), 8.83 (d, J = 8 Hz, 1 H), 8.73 (d, J = 6 Hz, 1 H),
8.12 (m, 1 H), 7.26 (d, J = 2.4 Hz, 1 H), 7.22 (d, J = 2.4 Hz, 1 H),
7.20 (d, J = 2.0 Hz, 1 H), 6.99 (d, J = 8 Hz, 1 H) ppm.
Compound 4: A mixture of 4-(3-pyridyl)catechol hydrobromide salt
(60.3 mg, 225 μmol) and silver acetate (37.6 mg, 225 μmol) in meth-
anol (6 mL) was stirred for 10 min before filtration. The solution
was dried by vacuum before toluene (45 mL) and [3,5-bis(trifluoro-
methyl)phenyl]boronic acid (58.0 mg, 225 μmol) were added. The
mixture was heated under reflux conditions with a Dean Stark ap-
paratus for 3 h. After this time, the mixture was filtered hot and
allowed to cool to room temp. The solvent was reduced to Ͻ5 mL,
and pentane (10 mL) was added to induce precipitation of the
product. The product was filtered, washed with pentane, and resid-
ual solvent was removed under vacuum to give 4 as a yellow solid
(31 mg, 35%). Crystallization was accomplished by slow diffusion
of pentane into a concentrated solution of 4 in benzene. NMR
spectroscopic measurements gave a mixture of trimer/tetramer in a
1:1.22 ratio at a monomer concentration of 10 mm. 1H NMR
(CDCl3): δ = 9.04 (s, 1 Htrimer), 8.97 (s, 1 Htetramer), 8.61 (s,
1 Htetramer), 8.26–8.22 (m, 2 Htrimer, 1 Htetramer), 8.10 (s, 2 Htrimer),
8.05 (s, 2 Htetramer), 7.83 (s, 1 Htrimer), 7.75 (s, 1 Htetramer), 7.71–
1
fusion of pentane into a concentrated solution of 1 in benzene. H
NMR (CDCl3): δ = 8.59 (dd, J = 4.5, 1.8 Hz, 2 H), 7.74 (d, J =
8.2 Hz, 2 H), 7.40 (d, J = 8.2 Hz, 2 H), 7.19 (dd, J = 4.5, 1.8 Hz,
2 H), 4.34 (dd, J = 11.1, 4.5 Hz, 2 H), 4.23 (t, J = 10.6 Hz, 2 H),
3.30 (m, 1 H) ppm. 13C NMR (CDCl3): δ = 154.1, 150.3, 146.7,
133.7, 124.6, 123.0, 65.8, 42.3, 34.8, 31.2 (B–C was not observed)
ppm. 11B NMR (CDCl3): δ = 27.9 ppm. C18H22BNO2 (295.19):
calcd. C 73.24, H 7.51, N 4.75; found C 73.25, H 7.43, N 4.86.
Compound 2: A mixture of 2-(4-pyridyl)propan-1,3-diol (34.5 mg,
225 μmol) and (2,3,4,5,6-pentafluorophenyl)boronic acid (47.7 mg,
225 μmol) in toluene (45 mL) was heated under reflux conditions
with a Dean Stark apparatus for 3 h. After this time, the mixture
was allowed to cool to room temperature. Compound 2 precipi-
tated in the form of an off-white solid. The product was filtered,
washed with pentane, and residual solvent was removed under vac-
uum to give 2 (54 mg, 73%). Crystallization was accomplished by
Eur. J. Inorg. Chem. 2013, 2558–2563
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