Chemistry Letters 2001
1105
References and Notes
1
M. Yamashita, Y. Yamamoto, K.-y. Akiba, and S. Nagase, Angew.
Chem. Int. Ed., 39, 4055 (2000)
2
a) M. W. Haenel, D. Jakubik, C. Krüger, and P. Betz, Chem. Ber.,
1991, 333. b) M. W. Haenel, S. Oevers, J. Bruckmann, and C. Krüger,
Synlett, 1998, 301.
3
4
5
M. del R. Benites, F. R. Fronczek, R. P. Hammer, and A. W.
Maverick, Inorg. Chem., 36, 5826 (1997)
R. Biehl, K. Hinrichs, H. Kurreck, W. Lubitz, U. Mennenga, and K.
Roth, J. Am. Chem. Soc., 99, 4278 (1977)
THF (15 mL) was added to a mixture of 0.703 g (2.0 mmol) of 7 and
0.194 g (4.8 mmol) of NaH (60% in oil) at 0 °C under Ar. Me2SO4
(0.38 mL, 4 mmol) was added dropwise at 0 °C. The reaction mixture
was stirred for 20 h at 80 °C and filtered through Celite pad (Celite
545, Katayama Chemical Co. ltd.). Crude 8 was purified by column
chromatography (CH2Cl2:hexane = 1:15 – 1:7) to give 0.564 g (77%)
1
of 8 as a yellow solid; mp 179–181 °C; H NMR (400 MHz, CDCl3,
25 °C) δ 3.86 (s, 3H), 7.26 (dd, 2H, J = 8Hz, 8Hz), 7.86 (d, 2H, J =
8Hz), 7.93 (d, 2H, J = 8Hz), 8.25 (s, 1H); 13C NMR (99 MHz, CDCl3,
25 °C) δ 65.3, 116.3, 123.3, 124.0, 125.9, 128.4, 133.5, 133.9, 153.1;
MS (FAB+) M+ = 364, 366, 368.
6
n-BuLi in n-hexane solution (4.0 mL, 1.50 M, 6.0 mmol) was added to
the THF (30 mL) solution of 1.10 g (3.0 mmol) of 8 at –78 °C under
Ar. After the reaction mixture was stirred for 2 h at –78 °C, 0.954 mL
(6.0 mmol) of (i-Pr)2PCl was added to the solution at –78 °C. The
reaction mixture was allowed to warm to room temperature and stirred
for 2 h at room temperature. The crude product was treated with water
and then purified with column chromatography (SiO2; CH2Cl2:hexane
= 1:15 – 1:10 – 1:7) to give yellow solid of 9 (0.873 g, 63%); mp
observed in the 31P NMR. The peaks kept its sharpness and sym-
metrical pattern even at –80 °C. These NMR data indicate that
the very rapid bond switching process is taking place in solution
as illustrated in Scheme 3.
1
132–134 °C (dec.); H NMR (400 MHz, CDCl3, 25 °C) δ 0.81 (dd,
6H, J = 8 Hz, 8 Hz), 1.33 (dd, 6H, J = 8 Hz, 8 Hz), 1.24–1.31 (m,
12H), 1.80–1.98 (m, 2H), 2.28–2.42 (m, 2H), 3.84 (s, 3H), 7.40 (dd,
2H, J = 8 Hz, 8Hz), 7.58 (d, 2H, J = 8 Hz), 7.90 (d, 2H, J = 8 Hz),
8.22 (s, 1H); 31P NMR (99 MHz, CDCl3, 25 °C) δ 17.4.
7
THF (20 mL) was added to a mixture of 39.8 mg (5.0 mmol) of Li and
0.758 g (5.0 mmol) of di-tert-butylbiphenyl (DTBB) at 0 °C under Ar.
The mixture was stirred for 5 h at 0 °C to give lithium di-tert-butyl-
biphenylide (LDBB) solution. A cooled (–78 °C) THF solution of
0.887 g (2 mmol) of 9 was added to the LDBB solution at –78 °C
within 15 min. The reaction mixture was stirred for 15 min at –78 °C
and for 12 h at 0 °C. Then, 1.1 mL (5.0 mmol) of BrCF2CF2Br was
added dropwise to the solution at 0 °C. The reaction mixture was
stirred for 5 h at 0 °C. The crude product was purified by column
chromatography (CH2Cl2) to give 0.504 g (51%) of 5; mp 198–200 °C
1
(dec.); H NMR (400 MHz, CDCl3, 25 °C) δ 0.92 (d, 6H, J = 8 Hz),
Since the energy barrier of the P–B bond switching process in
12 was too small to measure by coalescence method, the energy
difference between the unsymmetrical tetracoordinate compound
12A and the pentacoordinate boron 12B, which should be the
transition state of the bond switching process, must be very small.
The small activation energy in 12 indicates that our newly pre-
pared rigid anthracene ligand system stabilizes the 5-coordinate
boron transition state. The result is in contrast to the relatively
high energy barrier (∆G‡ = 13.4 kcal/mol) of the similar SN2 type
reaction of 13 with 2,6-bis(dimethylaminomethyl)phenyl ligand.11
0.95 (d, 6H, J = 8 Hz), 1.16 (d, 6H, J = 8 Hz), 1.18 (d, 6H, J = 8 Hz),
2.20–2.32 (m, 4H), 7.36 (dd, 2H, J = 8 Hz, 8 Hz), 7.84 (d, 2H, J = 8
Hz), 7.88 (d, 2H, J = 8 Hz), 8.30 (s, 1H); 31P NMR (99 MHz, CDCl3,
25 °C) δ 4.54 ; MS (FAB+) M+ = 489, 491.
8
n-BuLi (0.40 mL, 0.59 mmol) was added dropwise to a solution of
0.247 g (0.5 mmol) of 5 in 15 mL of THF at –78 °C under Ar. The
reaction mixture was stirred for 2 h at –78 °C and added to 83.1 mg
(0.53 mmol) of B-chlorocatecholborane in 5 mL of THF at –78 °C.
The reaction mixture was stirred for 3 h at –78 °C and for 1 h at room
temperature. The crude product was purified by preparative TLC
(CH2Cl2:hexane = 10:1) to give 32.2 mg (12%) of 12; mp 218–220 °C
(dec.); 1H NMR (400 MHz, CDCl3, 25 °C) δ 0.85–1.56 (m, 24H),
2.08–2.12 (m, 4H), 6.85–6.89 (m, 4H), 7.48 (dd, 2H, J = 8 Hz, 8 Hz),
7.72 (d, 2H, J = 8 Hz), 8.10 (d, 2H, J = 8 Hz), 8.52 (s, 1H); 31P NMR
(99 MHz, CDCl3, 25 °C) δ 0.97; 11B NMR (127 MHz, CDCl3, 25 °C)
δ 15.0–20.5 (br).
9
Data were collected at 298 K on a Mac Science DIP2030 imaging
plate equipped with graphite-monochromated Mo Kα radiation (λ =
0.710 73 Å). Unit cell parameters were determined by autoindexing
several images in each data set separately with program DENZO. For
each data set, rotation images were collected in 3° increments with a
total rotation of 180° about φ. Data were processed by using
SCALEPACK. The structure was solved using the teXsan system and
refined by full-matrix least-squares. Crystal data for 12: monoclinic
system, space group P21/a (no. 14), a = 10.440(1) Å, b = 12.4310(8)
Partial support of this work through Grant-in-Aid for
Scientific Research (Nos. 09239103, 09440218, 11166248,
11304044, 12304044) provided by the Ministry of Education,
Culture, Sports, Science and Technology of the Japanese
Government is heartily acknowledged.
Å, c = 23.664(3) Å, β = 90.462(4)°, V = 3071.0(5) Å3, Z = 4, ρcalc
=
1.143 g cm–3. R = 0.0716 (Rw = 0.1202) for 4029 observed reflections
(244 parameters) with I > 3σ(I). Goodness of fit = 1.320
10 J. A. Dean, “Lange’s Handbook of Chemistry,” 11th ed., McGraw-
Hill: New York (1973) pp 3-119 – 3-123.
11 a) S. Toyota, T. Futawaka, H. Ikeda, and M. Oki, J. Chem. Soc.,
Chem. Commun., 1995, 2499. b) S. Toyota, T. Futawaka, M. Asakura,
H. Ikeda, and M. Oki, Organometallics, 17, 4155 (1998).
Dedicated to Prof. Hideki Sakurai on the occasion of his
70th birthday.