1424
white crystalline solid (229 mg, 1.49 mmol; extraction yield:
58% yield based on PhBr or 149% yield based on NiCl2) whose
1H NMR and IR spectra indicated the extracted product was
almost pure biphenyl; accurate mass measurement also sup-
ported biphenyl.
1990, 23, 926. c) T. Yamamoto, K. Osakada, T. Wakabayashi, A.
CRC Handbook of Chemistry and Physics, 58th ed., ed. by
R. C. Weast, CRC Press, Cleveland, Ohio, 1977. Standard
electrode potential for reduction of M2+ to M: ¹2.38 and
¹0.76 V for magnesium and zinc, respectively.
Reaction of NiCl2 and bpy gives [NiCl2(bpy)] under various
conditions. Stirring a mixture of yellow NiCl2 and colorless
bpy in DMF at 70 °C gave a greenish yellow (color of
[NiCl2(bpy)]) dispersion.
7
16 Extraction-NMR yield of Ph(CH2)4Ph was 25%. 1H NMR
spectra (CDCl3) of extracts obtained in reactions of PhCH2Br
and PhCH2CH2Br showed a CH2 peak of PhCH2CH2Ph at ¤
2.90 (s) and CH2 peaks of Ph(CH2)4Ph at ¤ 2.62 (t, J = 7.1 Hz)
and 1.67 (multiplet) (cf. D. H. Richards, N. F. Scilly, J. Chem.
PhCH2CH2Ph (EI) m/z: 182.1092 (found), 182.1096 (calcd).
Accurate mass of extracted Ph(CH2)4Ph (EI) m/z: 210.1406
(found), 210.1409 (calcd). Extraction-NMR yield was deter-
mined by adding CHCl2CHCl2 as an internal reference.
17 A mixture of NiCl2 (260 mg, 2.0 mmol), bpy (620 mg,
4.0 mmol), Mg (110 mg, 4.5 mmol) in dry DMF (10 mL) was
stirred at 70 °C for about 10 min. CH3COC6H4Br-p (300 mg,
1.5 mmol) was added, and the reaction mixture was stirred at
70 °C for 7.5 h. After removal of volatile materials under
reduced pressure, hydrochloric acid (4 M, 15 mL) was added to
the residue, and the product was extracted with toluene.
Removal of toluene gave a solid whose IR spectrum essentially
agreed with that of standard CH3COC6H4COCH3. However, the
1H NMR spectrum showed some additional peaks and the
extraction-NMR yield was determined by adding CHCl2CHCl2
as an internal reference.
8
9
green DMF solution obtained by the reaction of a mixture of
NiCl2 and bpy with Mg gave rise to another UV-vis peak
at 428 nm; the energy difference between the two peaks at 428
¹1
and 600 nm was 6700 cm which was comparable to those
observed for Ni-bpy complexes.10a,10b
11 A. Misono, Y. Uchida, T. Yamagishi, H. Kageyama, Bull.
12 a) H. Kobayashi, Y. Kaizu, H. Matsuzawa, H. Sekino, Y. Torii,
Mg[Ni(bpy)2]2 are formed, occurrence of the reaction between
Mg[Ni(bpy)2]2 and RX to give R-R, MgX2, and [NiX2(bpy)n]
is conceivable.
13 An example for the preparation of biphenyl carried out using
standard Schlenk technique: A mixture of NiCl2 (260 mg,
2 mmol) and bpy (624 mg, 4 mmol) in dry DMF (10 mL) was
stirred for 5 min at 70 °C. After addition of Mg (75 mg,
3 mmol), the reaction mixture was stirred for 10 min. Magne-
sium turnings purchased from Kanto Chemical Co., Inc. were
used without activation. Then PhBr (310 mg, 2 mmol) was
added, and the reaction mixture was stirred for 7 h and 20 min at
70 °C. Volatile materials were removed by evaporation under
reduced pressure (50 °C under vacuum). Hydrochloric acid
(4 M, 15 mL) was added to the residue, and the product was
extracted with hexane. Drying up the hexane solution gave a
white crystalline solid (112 mg, 0.73 mmol; extraction yield:
19 a) [Ni(alkyl)2(bpy)] has high thermal stability.10a For [Ni(aryl)2-
(bpy)], ³-electron-³-electron interaction between the two aryl
groups is thought to enhance the aryl-aryl coupling;2b however,
the aryl-aryl coupling is retarded when the aryl group has an
electron-accepting group.2b,10b b) Similar effects of electron-
accepting substituents on reductive elimination of aryl-aryl
from [Pt(aryl)2Lm] have been reported: S. Shekhar, J. F.
20 A mixture of NiCl2 (270 mg, 2.08 mmol) and bpy (650 mg,
4.19 mmol) in dry DMF (40 mL) was stirred at 70 °C for
10 min. Mg (600 mg, 25 mmol) was added, and the mixture was
stirred at the temperature for several minutes. After addition of
M1 (1.17 g, 2.14 mmol), the reaction mixture was stirred at
70 °C for 18 h. The rection mixture was poured into water
(450 mL), and conc. hydrochloric acid (50 mL) was added.14
After stirring the mixture, the yellow precipitate was collected
by filtration, and the residue was washed with water and
methanol. Drying under vacuum gave P1 (800 mg, 96%). Gel
permeation chromatography (GPC) carried out at Tosoh Analy-
sis and Research Center Co., Ltd. showed Mw of 5700 (vs.
polystyrene standards). Addition of a smaller amount of M1
(1.0 mmol) to similar reaction mixtures gave analogous
polymers with Mw’s of about 7800; yields in two experiments
were 98 and 81%.
22 T. Yamamoto, R. Tokimitsu, T. Asao, T. Iijima, H. Fukumoto,
23 T. Yamamoto, T. Maruyama, Z.-H. Zhou, T. Ito, T. Fukuda, Y.
1
73%), whose H NMR and IR spectra indicated the extracted
product was almost pure biphenyl; accurate mass measurement
also supported biphenyl. During the removal process of the
volatile materials a part of biphenyl seemed to be lost because
standing biphenyl under vaccum at 50 °C caused a weight loss.
A separate experiment under similar conditions (NiCl2/PhBr =
1.3; bpy/NiCl2 = 2; Mg/PhBr = 2.9) showed an extraction
yield of 70% and a GC yield of 88% for biphenyl, supporting
the notion that a part of formed biphenyl in the extraction
process was lost during work-up.
14 When the reaction was carried out with excess Mg, Mg
remained after the reaction. Addition of hydrochloric acid13
caused evolution of a gas which was thought to be H2. This
should be cautioned.
15 A mixture of NiCl2 (130 mg, 1 mmol) and bpy (312 mg,
2 mmol) in dry DMF (10 mL) was stirred for 5 min at 70 °C.
After addition of Mg (120 mg, 4.9 mmol), the reaction mixture
was stirred for 10 min. Then PhBr (800 mg, 5.1 mmol) was
added, and the reaction mixture was stirred for 7 h and 20 min at
70 °C. Volatile materials were removed by evaporation under
reduced pressure (50 °C under vacuum). Hydrochloric acid
(4 M, 15 mL) was added to the residue, and the product was
extracted with hexane. Drying up the hexane solution gave a
Chem. Lett. 2012, 41, 1422-1424
© 2012 The Chemical Society of Japan
Yamamoto, Takakazu
