The Journal of Organic Chemistry
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Na2SO4, the solvent was evaporated in vacuo, and the residue was
purified via recrystallization from ethyl acetate/heptane to give bright
yellow crystals in 90% (1.0 g) yield: mp 214 °C. 1H NMR (500 MHz;
CD2Cl2): δ 8.41−8.32 (m, 4H, -NC(‑)-ArH), 8.06 (t, JHH = 8.1 Hz,
1H, C5NHpara), 7.67−7.58 (m, 2H, -NC(‑)-ArHpara), 7.57−7.47 (m,
solvent was removed in vacuo. Purification of the residue on alumina
oxide B with 90% toluene and 10% ethyl acetate (Rf = 0.23) afforded
compound 2a in 47% (192 mg) yield as a yellow solid: mp 233 °C. 1H
NMR (500 MHz; CD2Cl2): δ 8.08−7.94 (m, 4H, -NC(‑)-ArHortho),
7.61 (t, JHH = 8.0 Hz, 1H, C5NHpara), 7.57−7.53 (m, 2H, -NC(‑)-
ArHpara), 7.51−7.45 (m, 4H, -NC(‑)-ArHmeta), 7.37 (dd, JHH = 7.9,
1.4 Hz, 2H, -B-ArHortho), 7.25−7.09 (m, 3H, -B-ArHmeta,para), 6.76 (d,
JHH = 8.0 Hz, 2H, C5NHortho), 6.30 (s, 2H, NH) ppm. 13C NMR (125
MHz; CD2Cl2): δ 162.4 (CN), 153.4 (Cq,Pyridin), 142.7
(CAr,Pyridin,para), 136.1 (-NC(‑)-Cq), 132.0 (-NC(‑)-CAr,para),
130.4 (-B-CAr,ortho), 129.2 (-NC(‑)-CAr,meta), 128.3, 127.9 (-B-
CAr,meta,para), 127.5 (-NC(‑)-CAr,ortho), 114.3 (CAr,Pyridin,meta) ppm.
(The B-Cq signal was not observed due to the quadrupolar relaxation
4H, -NC(‑)-ArH), 7.23 (d, JHH = 8.1 Hz, 2H, C5NHortho) ppm. 13
C
NMR (125 MHz; CD2Cl2): δ 165.5 (CN), 150.4 (Cq,Pyridin), 145.7
(CAr,Pyridin,para), 133.5 (-NC(‑)-CAr,para), 132.9 (-NC(‑)-Cq), 129.7,
128.8 (-NC(‑)-CAr), 117.5 (CAr,Pyridin,meta) ppm. 11B NMR (160
MHz; CD2Cl2): δ 1.3 (d, JBF ≈ 33 Hz, Bquart-F) ppm. 19F NMR (470
MHz; CD2Cl2): δ −123.36 (1:1:1:1 q, JFB ≈ 33 Hz, Bquart-F) ppm.
HRMS (ESI): calcd for C19H13BFN3O2Na ([M + Na]+) 368.0980,
observed 368.0978.
of the boron atom). 11B NMR (160 MHz; CD2Cl2): δ −1.2 (s, Bquart
)
Synthesis of 1b. A suspension of N,N′(pyridine-2,6-diyl)bis(4-
methylbenzamide) (13.8 g, 39.95 mmol, 1.0 equiv) in toluene (200
mL) was cooled to 0 °C, and BF3·OEt2 (15 mL, 119.0 mmol, 3.0
equiv) was added dropwise. After removal of the ice bath, the reaction
mixture was refluxed for 5 h. The reaction mixture was allowed to cool,
and a NaHCO3/DCM mixture (100/200 mL) was added to the
solution. The organic layer was collected and washed with NaHCO3
(3 × 100 mL), and the aqueous layer was extracted with DCM (3 ×
100 mL). After drying of the collected organic layers over Na2SO4, the
solvent was evaporated in vacuo, and the residue was purified via
alumina oxide B with 5% ethyl acetate and 95% toluene (Rf = 0.83) to
give a bright yellow solid in 85% (12.7 g) yield: mp 230 °C. 1H NMR
(500 MHz; CD2Cl2): δ 8.26−8.22 (m, 4H, -NC(‑)-ArHortho), 8.02
(t, JHH = 8.1 Hz, 1H, C5NHpara), 7.35−7.31 (m, 4H, -NC(‑)-
ArHmeta), 7.37 (d, JHH = 8.1 Hz, 2H, C5NHortho), 2.45 (s, 6H, CH3)
ppm. 13C NMR (125 MHz; CD2Cl2): δ 165.8 (CN), 150.7
(Cq,Pyridin), 145.7 (CAr,Pyridin,para), 144.8, 130.4 (-NC(‑)-Cq), 129.9,
129.8 (-NC(‑)-CAr), 117.3 (CAr,Pyridin,meta), 22.1 (CH3) ppm. 11B
NMR (160 MHz; CD2Cl2): δ 1.3 (d, JFB ≈ 33 Hz, Bquart-F) ppm. 19F
ppm. HRMS (ESI): calcd for C25H20BN5H ([M + H]+) 402.1889,
observed 402.1888.
Synthesis of 2b. A stirred suspension of phenyl boronic acid
(135.3 mg, 1.11 mmol, 1.0 equiv) and N,N′-(pyridine-2,6-diyl)bis(4-
methylbenzenecarboximidamide) (381.1 mg, 1.11 mmol, 1.0 equiv)
was refluxed in toluene for 5 h. After cooling to room temperature, the
solvent was removed in vacuo. Purification of the residue on alumina
oxide B with 90% toluene and 10% ethyl acetate (Rf = 0.30) afforded
compound 2b in 67% (319 mg) yield as a yellow solid: mp 240 °C. 1H
NMR (500 MHz; CD2Cl2): δ 7.92−7.87 (m, 4H, -NC(‑)-ArHortho),
7.57 (t, JHH = 8.0 Hz, 1H, C5NHpara), 7.35 (dd, JHH = 7.9, 1.4 Hz, 2H,
-B-ArHortho), 7.31−7.27 (m, 4H, -NC(‑)-ArHmeta), 7.20−2.11 (m,
3H, −B-ArHmeta,para), 6.70 (d, JHH = 8.0 Hz, 2H, C5NHmeta), 6.46 (s,
2H, NH), 2.42 (s, 6H, −CH3) ppm. 13C NMR (125 MHz; CD2Cl2): δ
162.1 (CN), 153.5 (Cq,Pyridin), 142.6 (CAr,Pyridin), 142.5 (Cq), 133.3
(Cq), 130.4, 129.8, 128.2, 127.7, 127.5 (CAr), 114.3 (CAr,Pyridin), 21.8
(CH3) ppm. (The B-Cq signal was not observed due to the
quadrupolar relaxation of the boron atom). 11B NMR (160 MHz;
CD2Cl2): δ −1.3 (s, Bquart) ppm. HRMS (ESI): calcd for C27H24BN5H
([M + H]+) 430.2202, observed 430.2208.
Synthesis of 2c. A stirred suspension of phenyl boronic acid (179
mg, 1.47 mmol, 1.0 equiv) and N,N′-(pyridine-2,6-diyl)-
dicyclohexanecarboximidamide (481 mg, 1.47 mmol, 1.0 equiv) was
refluxed in toluene for 5 h. After cooling to room temperature, the
solvent was removed in vacuo. Purification of the residue on alumina
oxide B with 80% hexane and 20% ethyl acetate (Rf = 0.72) afforded
compound 2c in 43% (261 mg) yield as a light yellow solid: mp 180
°C. 1H NMR (600 MHz; C6D6): δ 7.72−7.45 (m, 2H, ArHortho), 7.32
(t, JHH = 7.6 Hz, 2H, ArHmeta), 7.20−7.16 (m, 1H, ArHpara), 6.83 (t,
JHH = 8.0 Hz, 1H, C5NHpara), 6.58 (d, JHH = 8.0 Hz, 2H, C5NHortho),
5.15 (s, 2H, NH), 2.11 (tt, JHH = 11.9, 3.4 Hz, 2H, CyCH), 1.95 (d,
JHH = 11.9 Hz, 4H, CyCH2), 1.74−1.61 (m, 4H, CyCH2), 1.61−1.48
(m, 6H, CyCH2), 1.22−0.98 (m, 6H, CyCH2) ppm. 13C NMR (150
MHz; C6D6): δ 172.0 (CN), 153.6 (Cq,Pyridin), 142.5 (CAr,Pyridin),
130.2, 128.1, 127.6 (CAr), 112.9 (CAr,Pyridin), 47.1 (CyCH), 31.4, 31.1,
26.6, 26.5, 26.5 (CyCH2) ppm. (The B-Cq signal was not observed due
to the quadrupolar relaxation of the boron atom). 11B NMR (192
MHz; C6D6): δ −2.7 (s, Bquart) ppm. HRMS (ESI): calcd for
C25H32BN5H ([M + H])+ 414.2828, observed 414.2827.
NMR (470 MHz; CD2Cl2): δ −123.78 (1:1:1:1 q, JFB ≈ 33 Hz, Bquart
-
F) ppm. HRMS (ESI): calcd for C21H17BFN3O2Na ([M + Na]+)
396.1294, observed 396.1287.
Synthesis of 1c. A mixture of N,N′-(pyridine-2,6-diyl)bis(4-
methoxybenzamide) (383 mg, 1.01 mmol, 1.0 equiv) and triethyl-
amine (1.42 mL, 10.15 mmol, 10 equiv) in toluene (25 mL) was
cooled to 0 °C, and BF3·OEt2 (1.9 mL, 10.15 mmol, 10 equiv) was
added dropwise. After removal of the ice bath, the reaction mixture
was refluxed for 5 h. The reaction mixture was allowed to cool, and a
H2O/DCM mixture (50/100 mL) was added to the solution. The
organic layer was collected and washed with H2O (3 × 50 mL), and
the aqueous layer was extracted with DCM (3 × 50 mL). After drying
of the collected organic layers over Na2SO4, the solvent was
evaporated in vacuo, and the residue was recrystallized from a ethyl
acetate/heptane mixture to give bright yellow crystals in 72% (295
mg) yield. 1H NMR (600 MHz; CD2Cl2): δ 8.32−8.28 (m, 4H, -N
C(‑)-ArHortho), 7.99 (t, JHH = 8.1 Hz, 1H, C5NHpara), 7.12 (d, JHH = 8.1
Hz, 2H, C5NHortho), 7.02−6.9 (m, 4H, -NC(‑)-ArHmeta), 3.90 (s,
6H, CH3) ppm. 13C NMR (150 MHz; CD2Cl2): δ 165.2 (CN),
164.3 (Cq-OMe), 150.6 (Cq,Pyridin), 145.4 (CAr,Pyridin,para), 131.8 (-N
C(‑)-CAr), 125.2 (-NC(‑)-Cq), 116.6 (CAr,Pyridin,meta), 114.2 (-N
C(‑)-CAr), 55.9 (O-CH3) ppm. 11B NMR (192 MHz; CD2Cl2): δ 1.2
(d, JFB ≈ 33 Hz, Bquart-F) ppm. 19F NMR (564 MHz; CD2Cl2): δ
−124.67 (1:1:1:1 q, JFB ≈ 33 Hz, Bquart-F) ppm. HRMS (ESI): calcd
for C21H17BFN3O4Na ([M + Na]+) 428.1192, observed 428.1199.
Synthesis of Boron Compounds 2a−2d Based on NNN-
Tridentate Ligands. General Procedures. The boron complexes
based on NNN-tridentate ligands can be obtained by either reacting
one equivalent of the respective ligand 4a-4c with an equimolar
amount of boronic acid or by reacting one equivalent of the respective
ligand 4a-4c with an equimolar amount of triphenylborane. The
reaction mixture is refluxed for approximately four hours in toluene in
both cases. The purification method used for each compound is given
in in the respective experimental section.
Synthesis of 2d. A stirred suspension of 4-(octadecyloxy)phenyl
boronic acid (423.0 mg, 1.08 mmol, 1.0 equiv) and N,N′-(pyridine-
2,6-diyl)dibenzenecarboximidamide (342.0 mg, 1.08 mmol, 1.0 equiv)
was refluxed in toluene for 4 h. After cooling to room temperature, the
solvent was removed in vacuo. Purification of the residue on alumina
oxide B with 90% cyclohexane and 10% ethyl acetate (Rf = 0.12)
afforded compound 2d in 65% (470 mg) yield as a yellow solid: mp
1
160 °C. H NMR (500 MHz; CD2Cl2): δ 8.03−7.96 (m, 4H, -N
C(‑)-ArH), 7.59 (t, JHH = 8.0 Hz, 1H, C5NHpara), 7.57−7.52 (m, 2H,
-NC(‑)-ArH), 7.52−7.46 (m, 4H, -NC(‑)-ArH), 7.30−7.25 (m,
2H, -B-ArHortho), 6.74 (d, JHH = 8.0 Hz, 2H, C5NHortho), 6.73−6.69
(m, 2H, -B-ArHmeta), 6.28 (s, 2H, NH), 3.85 (t, JHH = 6.6 Hz, 2H,
- O C H 2 C H 2 C H 2 ( C H 2 ) 1 4 C H 3 ) , 1 . 7 4 − 1 . 6 3 ( m , 2 H ,
- O C H 2 C H 2 C H 2 ( C H 2 ) 1 4 C H 3 ) , 1 . 4 3 − 1 . 3 4 ( m , 2 H ,
-OCH2 CH2 CH2 (CH2 )1 4 CH3 ), 1. 34−1. 22 (m, 28H,
- O C H 2 C H 2 C H 2 ( C H 2 ) 1 4 C H 3 ) , 0 . 9 5 − 0 . 7 8 ( m , 3 H ,
-OCH2CH2CH2(CH2)14CH3) ppm. 13C NMR (125 MHz; CD2Cl2):
Synthesis of 2a. A stirred suspension of phenyl boronic acid (124
mg, 1.02 mmol, 1.0 equiv) and N,N′-(pyridine-2,6-diyl)-
dibenzenecarboximidamide (322 mg, 1.02 mmol, 1.0 equiv) was
refluxed in toluene for 5 h. After cooling to room temperature, the
H
dx.doi.org/10.1021/jo4003745 | J. Org. Chem. XXXX, XXX, XXX−XXX