Note
Organometallics, Vol. 29, No. 21, 2010 5735
a cyclohexadiene analogue and not a benzene analogue. The
resulting π-conjugated system has a narrower HOMO-LU-
MO gap, giving rise to the bathochromically shifted absorption
and emission maxima, while maintaining high fluorescence
quantum yields in solution. These results well demonstrate the
features of the 1,2-dihydro-1,2-azaborine skeleton in the ex-
tended π-conjugated system.
NaHCO3 aqueous solution. After the usual aqueous workup,
the obtained mixture was dissolved in CH2Cl2 and passed
through an alumina column. Purification by recycling GPC
gave 26.1 mg (0.052 mmol) of 2 in 13% yield as yellow solids: mp
188-189 °C; 1H NMR (600 MHz, CDCl3) δ 8.40 (br s, 1H), 8.26
(br s, 1H), 8.07 (d, JHH = 7.3 Hz, 1H), 7.59 (d, JHH = 7.7 Hz,
2H), 7.47 (dd, JHH = 7.7, 7.3 Hz, 2H), 7.39 (t, JHH = 7.3 Hz,
1H), 7.24 (s, 2H), 7.17 (dd, JHH = 7.7, 7.3 Hz, 2H), 7.04 (t,
JHH = 7.3 Hz, 1H), 6.84 (d, JHH = 7.7 Hz, 2H), 6.82 (dd, JHH =
7.3, 2.2 Hz, 1H), 6.60 (quasi t, 1H), 6.50 (quasi t, 1H), 3.06 (sep,
JHH = 7.0 Hz, 1H), 2.82 (sep, JHH = 7.0 Hz, 2H), 1.42 (d,
Experimental Section
General Procedures. All experiments were carried out under
an argon atmosphere. Column chromatography was performed
using Fuji Silysia silica gel PSQ100B (100 μm). Recycling
preparative gel permeation chromatography (GPC) was per-
formed using polystylene gel columns (JAIGEL 1H and 2H,
Japan Analytical Industry) with chloroform as an eluent. Melt-
ing points (mp) were measured on a Stanford Research Systems
OptiMelt instrument. 1H, 11B, and 13C NMR spectra were
measured with JEOL AL-400 or A-600 spectrometer. UV-vis
absorption and fluorescence spectra were recorded at room
temperature with a Shimadzu UV-3150 spectrometer and a
Hitachi F-4500 spectrometer, respectively, in degassed solvents.
Absolute fluorescence quantum yields were determined with a
Hamamatsu C9920-02 calibrated integrating sphere system.
Fluorescence lifetimes were measured with a Hamamatsu
C4780 picosecond fluorescence measurement system. Cyclic
voltammograms were recorded on an ALS/CHI-617A electro-
chemical analyzer. The CV cell consisted of a glassy carbon
electrode, a Pt wire counter electrode, and a Ag/AgNO3 refer-
ence electrode. The measurements were carried out under an
argon atmosphere in THF or CH2Cl2 solutions with a sample
concentration of 1 mM and 0.1 M n-Bu4NPF6 as a supporting
electrolyte. The structural optimizations for 2, 5, and 6 were
performed using the Jaguar 6.5 program package22 at the
B3LYP/6-31G(d) level. The NICS calculations were carried
out using the Gaussian 03 program package23 at the HF/6-31
+G(d,p) level.
J
HH = 7.0 Hz, 6H), 1.21 (d, JHH = 7.0 Hz, 6H), 1.02 (d, JHH =
7.0 Hz, 6H); 13C NMR (150 MHz, CDCl3) δ 151.67, 150.30,
141.93, 137.40, 136.87, 136.61, 136.19, 132.43, 131.08, 130.85,
129.22, 128.62, 128.53, 125.43, 125.15, 122.24, 121.32, 109.73,
106.92, 105.21, 34.67, 34.54, 25.10, 24.30, 23.74; 11B NMR (192
MHz, CDCl3) δ 35.05. Anal. Calcd for C35H39BN2: C, 84.33; H,
7.89; N, 5.62. Found: C, 84.20; H, 7.90; N, 5.36.
2-Biphenyl-5-phenylpyrrole (2). To a mixture of 2-phenylpyr-
role (105 mg, 0.73 mmol) and NaH (17.6 mg, 0.73 mmol) was
added THF (3 mL) at room temperature. After the mixture was
stirred for 0.5 h, ZnCl2 (106 mg, 0.78 mmol) was added as a solid
at the same temperature, followed by stirring for an additional
0.5 h. To the mixture were added 4-bromobiphenyl (181 mg,
0.78 mmol), Pd2(dba)3 CHCl3 (7.7 mg, 7.4 μmol), and 2-(di-
3
tert-butylphosphino)biphenyl (4.4 mg, 15 μmol), and the result-
ing mixture was refluxed for 12 h. After cooling to room
temperature, the mixture was passed through a Celite pad.
The mixture was purified by silica gel column chromatography
and washed with hexane to give 144 mg (0.49 mmol) of 2 in 67%
yield as pale yellow solids: mp 214-215 °C; 1H NMR (400 MHz,
CDCl3) δ 8.62 (br s, 1H), 7.68-7.60 (m, 6H), 7.55 (d, JHH = 7.6
Hz, 2H), 7.49-7.32 (m, 5H), 7.23 (d, JHH = 7.6 Hz, 1H), 6.63
(quasi d, 2H); 13C NMR (150 MHz, CDCl3) δ 140.57, 139.03,
133.30, 132.75, 132.41, 131.38, 128.97, 128.82, 127.60, 127.25,
126.81, 126.44, 124.07, 123.80, 108.16, 108.07. Anal. Calcd for
C22H17N: C, 89.46; H, 5.80; N, 4.74. Found: C, 89.47; H, 5.87;
N, 4.74.
Bis(N-tert-butoxycarbonyl-5-phenylpyrrol-2-yl )(2,4,6-triisopropyl-
phenyl)borane (3). To a LiTMP (15.3 mmol) solution, freshly
prepared from tetramethylpiperidine (2.6 mL, 15.3 mmol) and
n-BuLi (1.6 M in hexane solution, 9.6 mL, 15.3 mmol) in THF
(15 mL), was added N-(tert-butoxycarbonyl)-2-phenylpyrrole
(3.73 g, 15.3 mmol) dropwise at -78 °C. After stirring for 1.5 h,
(2,4,6-triisopropylphenyl)dimethoxyborane (TipB(OMe)2) (1.92 g,
6.95 mmol) was added, and the mixture was gradually warmed to
room temperature. The mixture was poured into a saturated NH4Cl
aqueous solution. After usual aqueous workup, the mixture was
dissolved in toluene and passed through an alumina column.
Recrystallization from hot hexane gave 2.83 g (4.05 mmol) of 3 in
58% yield as colorless solids: mp 135-136 °C; 1H NMR (400 MHz,
CDCl3) δ 7.39-7.28 (m, 10H), 6.88 (s, 2H), 6.51 (d, JHH = 3.2 Hz,
2H), 6.22 (d, JHH = 3.2 Hz, 2H), 2.82 (sep, JHH = 6.8 Hz, 1H), 2.76
(sep, JHH = 6.8 Hz, 2H), 1.21 (d, JHH = 6.8 Hz, 6H), 1.07 (br s,
12H), 1.03 (s, 18H); 13C NMR (100 MHz, CDCl3) δ 151.19, 150.14,
148.21, 143.17, 140.77, 138.01, 133.96, 128.64, 127.72, 127.37,
X-ray Crystallographic Analysis of 1. Single crystals of 1
suitable for X-ray crystallographic analysis were obtained by
recrystallization from a hot hexane solution. Intensity data were
collected at 173 K on a Rigaku Single Crystal CCD X-ray
diffractometer (Saturn 70 with MicroMax-007) with Mo KR
˚
radiation (λ = 0.71070 A) and graphite monochromator. A total
of 20 026 reflections were measured at a maximum 2θ angle of
50.0°, of which 10 209 were independent (Rint = 0.0580). The
structure was solved by direct methods (SHELXS-97)24 and
refined by full-matrix least-squares on F2 (SHELXL-97).24 All
non-hydrogen atoms were refined anisotropically, and all hydro-
gen atoms were placed using AFIX instructions. The crystal data
are as follows: C35H39BN2; fw = 498.49, crystal size 0.10 Â 0.10 Â
3
0.10 mm , triclinic, P1, a= 11.83(2) A, b= 16.30(3) A, c= 16.90(2)
˚
˚
3
˚
˚
A, R= 76.02(18)°, β= 70.03(16)°, γ= 80.22(18)°, V= 2958(9) A ,
Z = 4, Dc = 1.119 g cm-3. The refinement converged to R1 =
0.0667, wR2 = 0.1389 (I > 2σ(I)), GOF = 1.029.
126.98, 119.84, 112.73, 83.60, 34.34, 34.06, 26.92, 24.40, 24.11; 11
B
Acknowledgment. This work was partially supported by
a Grant-in-Aid(19675001)from the Ministryof Education,
Culture, Sports, Science, and Technology, Japan.
NMR (128 MHz, CDCl3) δ 52.11. Anal. Calcd for C45H55BN2O4:
C, 77.35; H, 7.93; N, 4.01. Found: C, 77.35; H, 8.10; N, 3.95.
6-Phenyl-3-(5-phenylpyrrol-2-yl)-2-(2,4,6-triisopropylphenyl)-
1,2-dihydro-1,2-azaborine (1). A solution of dipyrrorylborane 3
Supporting Information Available: A CIF file of 1, Cartesian
coordinates of the optimized structures for 2, 5, and 6, and the
complete ref are available free of charge via the Internet at
(200 mg, 0.29 mmol) and BF3 OEt2 (7.3 μL, 0.057 mmol) in
THF (28 mL) was refluxed for 16 h. After cooling to room
temperature, the reaction mixture was poured into a saturated
3
23
€
(22) Jaguar, version 6.5; Schrodinger, LLC: New York, NY, 2005.
(23) Frisch, M. J.; et al. et al. Gaussian 03, Revision C.02; Gaussian,
Inc.: Wallingford, CT, 2004.
(24) Sheldrick, G. M. SHELXL-97, Program for the Refinment of
€
€
Crystal Structures; University of Gottingen: Gottingen, Germany, 1997.