A R T I C L E S
Boller et al.
and deuterated products. The same procedure was followed to determine
the kinetic isotope effect for a 1:1 mixture of 1,2-dichlorobenzene:1,2-
dichlorobenzene-d4 and 1,3,5-benzene-d3; the kinetic isotope effect was
determined by normalizing the MS peak intensities to the mass spectrum
of a sample of pure 2-(3,4-dichlorophenyl)-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane and 4,4,5,5-tetramethyl-2-phenyl-1,3,2-dioxaborolane,
respectively.
Independent Synthesis of 4,4,5,5-Tetramethyl-2-(thiophene-2-yl)-
1,3,2-dioxaborolane, 4,4,5,5-Tetramethyl-2-(furanyl-2-yl)-1,3,2-di-
oxaborolane, 4,4,5,5-Tetramethyl-2-(3,5-dimethylphenyl)-1,3,2-
dioxaborolane, and 2-(3,5-Bis(trifluoromethyl)phenyl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane. Representative Procedure for the
Synthesis of 4,4,5,5-Tetramethyl-2-(thiophene-2-yl)-1,3,2-dioxaboro-
lane. In a reaction vial equipped with a stir bar were combined [Ir-
(COD)(OMe)]2 (0.015 mmol, 0.0093 g), dtbpy (0.030 mmol, 0.0081
g), thiophene (2.00 mmol, 159 µL), and B2pin2 (0.500 mmol, 0.127 g).
Cyclohexane (approximately 2.0 mL) was added to the reaction vial,
and the reaction mixture was stirred at room temperature overnight.
The reaction mixture was monitored using GC. The product was purified
by column chromatography, eluting with 1:1 ethyl acetate:hexane. The
same procedure was also followed for the synthesis of 4,4,5,5-
tetramethyl-2-(3,5-dimethylphenyl)-1,3,2-dioxaborolane and 2-(3,5-bis-
(trifluoromethyl)phenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. The
4,4,5,5-tetramethyl-2-(furanyl-2-yl)-1,3,2-dioxaborolane was purchased
from Lancaster chemicals. The m-xylylBpin was isolated by column
chromatography, and the 1,3-bis(trifluoromethyl)phenylBpin was iso-
lated by Kugelrohr distillation. Spectroscopic data for 2-thienylBpin:
1H NMR (C6D6, 400 MHz): δ 7.87 (d, J ) 3.6 Hz), 6.89 (dd, J ) 3.6,
4.4 Hz, 1H), 1.07 (s, 12H). 11B (C6D6): δ 30.8 (br s). GC/MS (intensity,
m/z): 210 (97, M+), 195 (100, M - CH3+). 2-FuranylBpin: 1H NMR
(C6D6, 400 MHz): δ 7.29 (d, J ) 4.2 Hz), 7.20 (d, J ) 3.2 Hz, 1H),
6.08 (dd, J ) 3.2, 3.2 Hz, 1H), 1.05 (s, 12H). 11B (C6D6): δ 27.1 (br
s). GC/MS (m/z): 194 (100, M)+, 179 (90, M - CH3)+. 3,5-
dimethylphenylBpin: 1H NMR (CD3Cl, 400 MHz): δ 7.34 (s, 2H),
7.03 (s, 1H), 2.25 (s, 6H), 1.42 (s, 12H). 11B (C6D6): δ 30.8 (br s).
GC/MS (intensity, m/z): 232 (100, M+), 217 (77, M - CH3+). 1,3-
Bis(trifluoromethyl)phenylBpin: 1H NMR (C6D6, 400 MHz): δ 8.3
(s, 2H), 7.7 (s, 1H), 1.0 (s, 12H). 11B (C6D6): δ 31.4 (br s). GC/MS
(intensity, m/z): 340 (2, M+), 325 (100, M - CH3+).
Stoichiometric Reaction of 1 with Arene. Into an NMR tube was
placed complex 1 (10 mg, 0.011 mmol), cis-COE (3.0 µL, 0.023 mmol),
and an internal standard (TMS3Ph, 3 µL). These materials were
dissolved in a mixture of 0.32 mL of C6D12 and 0.25 mL of C7D14.
The sample was placed in a precooled spectrometer probe. An initial
1H NMR spectrum was recorded at -15 °C. 1,3-Bis(trifluoromethyl)-
benzene (32 µL, 0.21 mmol) was then added to the sample via
microsyringe and quickly returned to the spectrometer. The sample was
warmed to 0 °C, and the reaction was monitored by 1H NMR
spectroscopy. Trisboryl 1 reacted with the arene to produce an
equivalent of arylboronate ester and (dtbpy)(η2-COE)Ir(H)(Bpin)2 (2).
1H NMR (C6D12/C7D14, 0 °C): δ 9.51 (d, J ) 5.6 Hz, 2H, 6,6′), 7.91
(d, J ) 1.7 Hz, 2H, 3,3′), 7.13 (dd, J ) 6.1, 2.1 Hz, 2H, 5,5′), 3.38 (m,
2H, η2-COE CH), -4.81 (s, 1H, IrH). Subsequently, complex 2 reacted
with arene to afford an additional equivalent of arylboronate ester and
(dtbpy)(η2-COE)Ir(H)2(Bpin) (3). 1H NMR (C6D12/C7D14, 0 °C): δ 9.66
(d, J ) 6.1 Hz, 1H, 6 or 6′), 8.94 (d, J ) 5.6 Hz, 1H, 6 or 6′), -5.72
(d, J ) 5.3 Hz, 1H, IrH), -23.1 (d, J ) 5.3 Hz, 1H, IrH).
Determination of the Half-Life of the Reaction of 1 with Benzene.
In a reaction vial were placed 1 (0.011 mmol, 0.010 g) and DHT (0.050
mmol, 0.014 g). Cyclohexane-d12 (0.5 mL) was added to the reaction
vial, and the solution was mixed until 1 and DHT were dissolved.
Benzene (0.144 mmol, 13.0 µL) was added, and the solution was then
transferred to a screw-capped NMR tube. The tube was removed from
the glovebox, and 1H NMR spectra of the reaction mixture were
obtained once every 60 min for 6 h. The borylated product was
monitored by the appearance of a peak at δ 1.26, corresponding to the
methyl groups of the phenyl pinacol boronate ester. The decay of 1
was monitored by integrating the doublet at δ 9.44, which corresponded
to the bound dtbpy ligand on 1.
Reaction of [Ir(COD)(OMe)]2 with Phenanthrene. In a reaction
vial equipped with a stir bar were placed [Ir(COD)(OMe)]2 (0.002
mmol, 0.001 g), dtbpy (0.003 mmol, 0.001 g), phenanthrene (0.20
mmol, 0.034 g), B2pin2 (0.10 mmol, 0.026 g), and DHT (0.10 mmol,
0.026 g). Cyclohexane (approximately 0.6 mL) was added to the
reaction vial, and the reaction mixture was stirred at room temperature
overnight. The reaction mixture was monitored by GC and GC/MS.
Reactions of 1 with a mixture of two Arenes. In a reaction vial
equipped with a stir bar were placed complex 1 (0.015 mmol, 0.010 g)
and dodecahydrotriphenylene (DHT) (0.10 mmol, 0.023 g). Into a
second reaction vial were mixed benzene (3.0 mmol, 0.27 mL) and
thiophene (3.0 mmol, 0.24 mL); the diluted arene was then added to
the vial that contained 1 and DHT. The reaction mixture was stirred at
room temperature overnight in the glovebox. After 24 h, an aliquot of
the reaction mixture was removed, and a GC trace of the reaction
mixture was obtained. The identity of each product was determined
by comparison of the GC/MS to that of authentic material prepared
independently (vide infra) or purchased from chemical suppliers, and
the yield of each product was determined by using GC. The same
procedure was also followed for the reactions of a mixture of benzene
and furan, and m-xylene and 1,3-bis(trifluoromethyl)benzene.
Independent Synthesis of 9-Phenanthryl-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane. To a solution of tert-butyllithium (1.4 M, 3.2
mL, 4.48 mmol) in 15 mL of THF was added a solution of
9-bromophenanthrene (575 mg, 2.24 mmol) in 4 mL of THF at -78
°C via syringe in small portions. The mixture was stirred for a further
1.5 h at -78 °C to give a green suspension. 2-Isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (1.9 mL, 11.2 mmol) was added in one
portion. The reaction mixture was allowed to warm to room temperature
over 24 h, at which time the solution was clear yellow. The reaction
mixture was poured into water and extracted several times with
dichloromethane, and the combined organic phases were subsequently
washed with water and brine and dried over MgSO4. After evaporation
of the solvent, the crude product was obtained as an oil. This crude
material was purified by column chromatography on silica gel with
Reactions of B2pin2 with a Mixture of Two Arenes Catalyzed
by 1. In a reaction vial equipped with a stir bar were placed catalyst 1
(1 mol %, 0.001 g), B2pin2 (0.005 mmol, 0.003 g), and dodecahydrot-
riphenylene (DHT) (0.050 mmol, 0.011 g). Into a second reaction vial,
benzene (0.10 mmol, 9.0 µL) and thiophene (0.10 mmol, 8.0 µL) were
mixed; the diluted arene was then added to the vial that contained 1,
B2pin2, and DHT. The reaction mixture was stirred at room temperature
overnight in the glovebox. After 24 h, an aliquot of the reaction mixture
was removed, and a GC trace of the reaction mixture was obtained.
The identity of each product was determined by comparison of the
GC/MS to authentic material (see the next paragraph), and the yield of
each product was determined by GC. The same procedure was also
followed for the reactions with the combination of benzene and furan,
and m-xylene and 1,3-bis(trifluoromethyl)benzene.
1
n-hexane/ethyl acetate (30:1 v/v) as eluent to give a white solid. H
NMR (CDCl3, 500 MHz): δ 8.86-8.84 (m, 1H), 8.71 (dd, J ) 3.5,
9.6 Hz, 1H), 8.69 (d, J ) 8.2 Hz, 1H), 8.41 (s, 1H), 7.90 (d, J ) 7.9
Hz, 1H), 7.69 (ddd, J ) 1.3, 7.1, 8.2 Hz, 1H), 7.66-7.64 (m, 2H),
7.60 (ddd, J ) 0.9, 7.0, 7.9 Hz, 1H). The position of the boryl group
was confirmed by 1H-1H COSY spectroscopy. 13C NMR (CDCl3, 125.8
MHz): δ 138.3, 134.7, 132.1,131.2, 130.2, 129.5, 129.3, 128.0, 126.9,
126.6, 126.3, 122.8, 122,7, 84.1, 25.2 (the carbon atom attached to the
boron could not be detected). 11B (CDCl3, 160.4 MHz): δ 31.6 (br s).
GC/MS (m/z) (intensity, fragment): 304 (100, M+), 289 (10, M+
-
CH3), 204 (100, M+ - C6H12O). Anal. Calcd for C20H21BO2: C, 78.97;
H, 6.96. Found: C, 78.74; H, 7.12.
9
14276 J. AM. CHEM. SOC. VOL. 127, NO. 41, 2005