Iridium-catalyzed preparation of silylboranes by silane borylation and their use in the catalytic borylation of arenes

Article abstract of DOI:10.1021/om800696d

Silylboranes are versatile reagents for transition metal-catalyzed reactions of unsaturated organic molecules. These reagents are typically prepared by the addition of a silyl lithium species to a boron electrophile. However, the need to generate anionic silane reagents limits the scope of silylboranes that can be readily obtained. Here, we describe the synthesis of trialkylsilylboranes by the borylation of silanes catalyzed by iridium complexes. The reaction of trialkylhydrosilanes with B₂pin ₂ catalyzed by the combination of [Ir(OMe)cod]₂ and 4,4′-di-tert-butylbipyridine forms trialkylsilylboronic esters. In addition, we show that these trialkylsilylboranes serve as boron sources for the iridium-catalyzed borylation of aryl C-H bonds. In contrast to diboron reagents, the silylboranes react with methylarenes at both the aryl and methyl C-H bonds.

Full text of DOI:10.1021/om800696d

Organometallics 2008, 27, 6013–6019
6013
Iridium-Catalyzed Preparation of Silylboranes by Silane Borylation
and Their Use in the Catalytic Borylation of Arenes
Timothy A. Boebel and John F. Hartwig*
Department of Chemistry, UniVersity of Illinois, 600 South Mathews AVenue, Urbana, Illinois 61801
ReceiVed July 22, 2008
Silylboranes are versatile reagents for transition metal-catalyzed reactions of unsaturated organic
molecules. These reagents are typically prepared by the addition of a silyl lithium species to a boron
electrophile. However, the need to generate anionic silane reagents limits the scope of silylboranes that
can be readily obtained. Here, we describe the synthesis of trialkylsilylboranes by the borylation of silanes
catalyzed by iridium complexes. The reaction of trialkylhydrosilanes with B2pin2 catalyzed by the
combination of [Ir(OMe)cod]2 and 4,4′-di-tert-butylbipyridine forms trialkylsilylboronic esters. In addition,
we show that these trialkylsilylboranes serve as boron sources for the iridium-catalyzed borylation of
aryl C-H bonds. In contrast to diboron reagents, the silylboranes react with methylarenes at both the
aryl and methyl C-H bonds.
compounds. Considering the utility of silylborane reagents,
improved methods for their preparation would contribute to their
utility.
Introduction
Transition metal-catalyzed reactions of silylboranes have
gained significant attention in recent years.1,2 Silylboranes
undergo metal-catalyzed additions to the unsaturated C-C bond
in substrates such as alkynes,3-9 alkenes,10,11 1,3-dienes,12-14
allenes,15-19 and alkylidenes,20,21 and the resulting difunction-
alized products possess orthogonal functionality for the diverse
reaction manifolds of organoboron22 and organosilicon23,24
The most commonly employed method for the preparation
of silylboranes involves the addition of silyllithium reagents to
boron electrophiles, such as haloboranes,25,26 trialkyborates, or
pinacolborane (HBpin).27 A significant limitation of these
methods is the need for silyl-metal reagents. Although aryl-
substituted silyl lithium reagents can be prepared from the
corresponding chlorosilanes, trialkylsilyl lithium reagents must
be prepared from disilanes, and few disilanes are commercially
available.28 In addition to these general methods, Berry has
reported a tantalum-mediated formation of Si-B bonds,29 and
Smith has described an isolated example of a rhodium-catalyzed
coupling of N-trimethylsilylpyrrole with HBpin.30
* Corresponding author. E-mail: jhartwig@scs.uiuc.edu.
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1229–1230.
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Our group has described catalytic methods for the direct C-H
borylation of alkanes31-34 and, in collaboration with Ishiyama
and Miyaura, the direct C-H borylation of arenes35,36 using
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10.1021/om800696d CCC: $40.75
2008 American Chemical Society
Publication on Web 10/17/2008

6014 Organometallics, Vol. 27, No. 22, 2008
Boebel and Hartwig
Table 1. Iridium-Catalyzed Hydrosilane Borylation
bis(pinacolato)diboron (B2pin2) or pinacolborane (HBpin), which
are both commercially available in bulk quantities, as the boron
source (eqs 1 and 2). We considered that a similar functional-
ization of Si-H bonds could convert hydrosilanes into silylbo-
ranes (eq 3). Furthermore, we wished to explore the reactivity
of silylboranes toward metal-catalyzed C-H functionalization
and to determine whether the borane or silane would be found
in the functionalized product (eq 4).
entry
R3SiH
Et3SiH
product
yield (%)a
1
1a
1a
1b
1c
1d
1e
1f
58 (76)
0
2b
3
Et3SiH
n-Pr3SiH
66 (71)
71 (84)
70 (90)
41 (61)
0
4
n-Bu3SiH
n-(pentyl)3SiH
t-BuMe2SiH
i-Pr3SiH
5
6c
7
a Yield based on 1 equiv of boron per B2pin2. Yield in parentheses is
GC yield. b HBpin (1 equiv) used in place of B2pin2. c 1% [Ir(cod)-
OMe]2 and 2% dtbpy used.
Furthermore, attempted borylations of aryl-functionalized hy-
drosilanes did not form the silylborane products, due to the
lability of the Ar-Si bond under the reaction conditions.37,38
Arene C-H Bond Functionalization with Borylsilanes.
Having developed the borylation of alkylhydrosilane Si-H
bonds, we explored the reactivity of silylboranes toward arene
C-H bond functionalization (eq 4). Substrates containing only
aryl C-H bonds were studied first. Accordingly, Et3SiBpin (1a,
1 equiv) was combined with [Ir(cod)OMe]2 (1%) and dtbpy
(2%) in neat benzene (10 equiv) and heated at 80 °C. This
reaction gave the aryl boronic ester 2 in 91% yield (entry 1,
Table 2), along with triethylsilane. No products from arene
silylation were observed. In addition to benzene, a range of
electron-rich and -deficient arenes were successfully borylated
when using 1a as the boron source. Monosubstituted arenes
provided mixtures of meta- and para-substituted products in
excellent yields (entries 2 and 3). Likewise, reactions of 1,3-
disubstituted arenes and symmetrically 1,2-disubstituted arenes
formed single products with high conversions of the silylborane
(entries 4-8). The yields and regioselectivities for reactions of
these substrates are comparable to those reported previously for
the iridium-catalyzed borylation of arenes with B2pin2 (eq 1).35,36
Despite the initial similarity of arene borylations conducted
with Et3SiBpin and with B2pin2, significant differences in the
reactivity of methylarenes with Et3SiBpin and B2pin2 were
observed. The reactions of silylborane 1a with methylarenes
are summarized in Table 3. The reaction of silborane 1a with
toluene under the standard reaction conditions formed a mixture
of three isomeric boronic esters in a combined 92% yield (entry
1, Table 3). The major product (10a) resulted from catalytic
borylation at the benzylic position.39 Similarly, the reaction of
electron-rich m-xylene with silborane 1a afforded products
resulting from benzylic and aryl C-H bond functionalization
in a 9:1 ratio and 86% yield (entry 2). The opposite preference
for formation of the two regioisomers was observed in the
reaction of 1a with the more electron-deficient 3-chlorotoluene.
This reaction led to preferential functionalization at the mutually
meta-aryl C-H bond over the benzylic C-H bonds, but
significant amounts of benzylboronic ester product were still
formed (entry 3). The formation of benzyl-substituted products
in these examples stands in contrast with the essentially
exclusive aryl C-H functionalization that is observed when
B2pin2 is employed as the boron source for arene borylation in
the presence of this iridium catalyst.36,40,41
Herein, we describe the borylation of the Si-H bonds in
trialkylsilanes to provide trialkylsilyl(pinancolato)borane prod-
ucts. In addition, we demonstrate that silylboranes participate
in iridium-catalyzed borylation of arenes to form arylboronic
esters and silane as byproduct (eq 4, right). In some cases, the
use of R3SiBpin provides contrasting regioselectivity to that
observed when using B2pin2 as the boron source.
Results and Discussion
1. Discovery and Scope of the Borylation of Trialkylsi-
lane Si-H Bonds. Initial studies were conducted to identify
potential catalysts for the coupling of triethylsilane with B2pin2.
Complexes previously reported to catalyze the borylation of
aliphatic C-H bonds, [Cp*RuCl2]2 and Cp*Rh(C6Me6),31-34
did not lead to the formation of silylborane products. However,
the combination of [Ir(cod)OMe]2 and 4,4′-di-tert-butylbipyri-
dine (dtbpy), which catalyzes the borylation of arene C-H
bonds,35,36 afforded Et3SiBpin (1a) in good yield. Under opti-
mized reaction conditions, B2pin2 reacted with Et3SiH (4 equiv)
in the presence of [Ir(cod)OMe]2 (0.5%) and dtbpy (1%) in
cyclohexane solvent to give 1a in 58% yield after chromato-
graphic purification (entry 1, Table 1). When the reaction was
repeated with HBpin in place of B2pin2, no silylborane was
observed (entry 2). Several trialkylhydrosilanes also reacted to
form silylborane products in good yields (entries 3-6), although
the sterically hindered i-Pr3SiH did not react (entry 7). In
general, reactions of hydrosilanes bearing longer alkyl chains
occurred to higher conversions and gave higher isolated yields.
In contrast to the borylation of trialkyl hydrosilanes, the
attempted borylation of alkoxy- and dialkylamino-substituted
hydrosilanes, as well as dihydrosilanes, resulted in no reaction.
Other substrates underwent exclusive benzylic C-H bory-
lation. Mesitylene, a substrate that has not been reported to
(37) Castillo, I.; Tilley, T. D. Organometallics 2000, 19, 4733–4739.
(38) Boebel, T. A.; Hartwig, J. F. J. Am. Chem. Soc. 2008, 130, 7534–
7535.
(36) Ishiyama, T.; Takagi, J.; Ishida, K.; Miyaura, N.; Anastasi, N. R.;
Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 390–391.

Iridium-Catalyzed Preparation of Silylboranes
Organometallics, Vol. 27, No. 22, 2008 6015
Table 2. Catalytic Borylation of Arenes with Et3SiBpin
a Yield determined by GC. b Meta:para isomer ratios determined by 1H NMR. c 1% [Ir(cod)OMe]2 and 2% dtbpy were used over a 12 h reaction
time.
Table 3. Catalytic Borylation of Alkyl-Substituted Arenes with
Et3SiBpin
through direct cleavage of the benzylic C-H bonds without
initial reaction with an aromatic C-H bond. In contrast with
the borylation of toluene, the borylation of ethylbenzene formed
arylboronic esters (15) without evidence for any benzylic
functionalization (entry 6).
Mechanistic Considerations. The unexpected formation of
benzylboronic esters in the presence of reactive aryl C-H bonds
led us to consider how the mechanism would be altered by the
use of a silylborane in place of B2pin2. Previous studies on the
mechanism of arene borylation have demonstrated that the C-H
bond cleavage step occurs after dissociation of the alkene ligand
in the trisboryl complex 16 (eq 5, left).36,42 These studies have
also shown that the resting state of reactions initiated with
[Ir(cod)OMe]2, dtbpy, B2pin2, and coe is the version of complex
16 in which the alkene ligand is coe. In the absence of added
coe the olefin ligand in 16 can be cod, coe from reduction of
the cod, or a borylated derivative of cod. By analogy, the
combination of [Ir(cod)OMe]2/dtbpy and Et3SiBpin could
generate the related complex 17, and mixed silyl boryl complex
17 could react with distinct selectivity for reaction with benzylic
and aromatic C-H bonds. Although the silyl ligand of 17 would
alter the electronic properties of the metal center, the steric
differences between trisboryl complex 16 and the mixed silyl
boryl complex 17 seem more pronounced.
To probe the dependence of ligand size on the regioselectivity
of borylation, catalytic reactions between m-xylene and three
boron sources (XBpin, X ) pinB, t-BuMe2Si, and Bu3Si) in
addition to Et3SiBpin were conducted (entries 1-4, Table 4).
While the reaction with B2pin2 solely formed products resulting
a Yield determined by GC. b Benzyl:meta:para isomer ratios deter-
mined by 1H NMR. c 0.5% [Ir(cod)OMe]2 and 1% dtbpy were used over
a 4 h reaction time.
(39) Catalytic benzylic borylation has been previously noted. See: (a)
Ishiyama, T.; Ishida, K.; Takagi, J.; Miyaura, N. Chem. Lett. 2001, 1082–
1083. (b) Shimada, S.; Batsanov, A. S.; Howard, J. A. K.; Marder, T. B.
Angew. Chem., Int. Ed. Engl. 2001, 40, 2168–2171.
undergo aryl C-H bond borylation, reacted with 1a to give
benzylboronic ester 13 in excellent yield (entry 4). Furthermore,
2,3,4,5,6-pentafluorotoluene underwent clean borylation of the
benzylic C-H bond (entry 5). This result indicates that the
benzylic C-H functionalization of alkylarenes can occur
(40) Takagi, J.; Sato, K.; Hartwig, J. F.; Ishiyama, T.; Miyaura, N.
Tetrahedron Lett. 2002, 43, 5649–5651.
(41) Ishiyama, T.; Nobuta, Y.; Hartwig, J. F.; Miyaura, N. Chem.
Commun. 2003, 2924–2925.
(42) Boller, T. M.; Murphy, J. M.; Hapke, M.; Ishiyama, T.; Miyaura,
N.; Hartwig, J. F. J. Am. Chem. Soc. 2005, 127, 14263–14278.

6016 Organometallics, Vol. 27, No. 22, 2008
Boebel and Hartwig
Table 4. Regioselectivity Dependence of Regioselectivity on Boron Source
entry
R
boron reagent
[Ir(cod)OMe]2, %
dtbpy, %
time, h
yield, %a (a:b)b
1
2
3
4
5
6
7
8
Me
Me
Me
Me
Cl
Cl
Cl
Cl
B2pin2
t-BuMe2SiBpin
Et3SiBpin
n-Bu3SiBpin
B2pin2
t-BuMe2SiBpin
Et3SiBpin
1
1
1
1
0.5
0.5
0.5
0.5
2
2
2
2
1
1
1
1
12
12
12
12
4
4
4
4
83 (0:1)
75 (70:30)
86 (89:11)
65 (93:7)
102 (0:1)
98 (10:90)
72 (40:60)
87 (60:40)
n-Bu3SiBpin
a Yield determined by GC. b 12a:12b isomer ratios determined by 1H NMR.
more of the product from benzylic borylation. Future efforts
will probe for the presence of silyl intermediates on the catalytic
reaction pathway and for a method to control the regioselectivity
of arene C-H functionalization in a synthetically valuable
fashion by judicious choice of boron source.
Experimental Section
from aryl C-H functionalization, the reactions of t-BuMe2-
SiBpin, Et3SiBpin, and n-Bu3SiBpin gave a mixture of benzyl-
and aryl-functionalized products in 70:30, 89:11, and 93:7 ratios,
respectively. For reactions of B2pin2, Et3SiBpin, and Bu3SiBpin,
there is a good correlation between the size of the X group and
the selectivity for benzylic C-H functionalization over aryl
C-H functionalization (X ) pinB < Et3Si < n-Bu3Si). The
same trend in selectivity was observed for the catalytic bory-
lation of 3-chlorotoluene (entries 5-8). The selectivity from
reactions of t-BuMe2SiBpin did not fit these trends, if one
considers the cone angle of t-BuMe2Si to be larger than that of
Et3Si, as based on Tolman’s parameters for phosphines.43
However, conformations of unsymmetrical substituents can
render them less hindered than would be expected from the
calculated angles.44
In addition to these steric effects on selectivity, the reactions
in Table 3 reveal the effect of arene electronics on regioselec-
tivity; the more electron-rich m-xylene forms more product from
benzylic functionalization than does the more electron-deficient
3-chlorotoluene. This trend fits with the slower rate of func-
tionalization of C-H bonds in electron-rich arenes than those
of electron-poor arenes.42
Reagents and Methods. All reactions, unless otherwise noted,
were performed in oven-dried 20 mL vials. Organic solutions were
concentrated either under high vacuum or by rotary evaporation.
Flash column chromatography was performed employing 230-400
mesh silica gel. Thin-layer chromatography was performed using
glass plates precoated to a depth of 0.25 mm with 230-400 mesh
silica gel impregnated with a fluorescent indicator (254 nm).
Compounds were visualized using iodine followed by ceric am-
monium molybdate stain. Anhydrous cyclohexane was purchased
from commercial sources. Arene and hydrosilane reagents were
degassed prior to use. All other reagents were obtained from
commercial sources and used without further purification. Proton,
carbon-13, and fluorine-19 nuclear magnetic resonance (1H NMR,
13C NMR, 19F NMR) spectra were recorded on a Varian 500, a
Varian VXR 500, or a Varian Inova 500 NMR spectrometer. Boron-
11 nuclear magnetic resonance (11B) spectra were recorded on a
Varian Unity Inova 300 or a Varian Unity Inova 600 NMR
spectrometer. Silicon-29 nuclear magnetic resonance (29Si) spectra
were recorded on a Varian Inova 600 NMR spectrometer. 1H
chemical shifts are expressed in parts per million (δ scale) downfield
from tetramethylsilane and are referenced to the residual protium
in the NMR solvent (δ ) 7.26 ppm). 13C NMR chemical shifts are
expressed in parts per million (δ scale) downfield from trimethyl-
silane and are referenced to the 13C resonance of CDCl3 (δ ) 77.00
ppm). In the 13C NMR spectra of arylboronic esters, the carbon
attached to boron was not observed. 11B, 19F, and 29Si NMR
chemical shifts are expressed in parts per million (δ scale) and are
referenced to external stardards: C6F6 in CDCl3 at δ ) -163.0
ppm, BF3 · OEt2 at δ ) 0.0 ppm, and SiMe4 at δ ) 0.0 ppm. Data
are presented as follows: chemical shift, multiplicity (s ) singlet,
d ) doublet, t ) triplet, q ) quartet, p ) pentet, m ) multiplet
and/or multiple resonances), integration, coupling constant in hertz
(Hz). GC/MS traces were acquired on an Agilent Technologies
6890N Network GC system with an Alltech EC-1 column and an
attached Agilent Technologies 5973 Network mass selective
detector. GC traces were acquired on a Hewlett-Packard 5890 Series
II GC system with a DB-1701 column and a FID detector.
n-Dodecane was used as an internal standard for the integration of
GC peaks. Elemental analyses were conducted by Robertson
Microlit Larboratories. High-resolution mass spectroscopy (HRMS)
was conducted by the University of Illinois at Urbana-Champaign
Mass Spectrometry Laboratory.
Conclusion
We have demonstrated that [Ir(cod)OMe]2 and dtbpy gener-
ates a catalyst for the borylation of the Si-H bonds in
trialkylhydrosilanes to give silylborane products. Although the
reaction scope is limited to trialkylsilanes possessing modest
steric properties, this reaction provides access to materials that
would be more challenging to obtain by the more typical
reaction of silyl lithium reagents with boranes. In addition, we
have shown that silylboranes can serve as reagents for the
catalytic borylation of arenes. In contrast to reactions of B2pin2
with methylarenes, the reactions of silylboranes with methy-
larenes occurred with competitive aryl and benzyl C-H bond
functionalization. The ratio of benzyl to aryl C-H functional-
ization varied with arene electronics as well as the size of the
silyl group; reactions with more hindered silylboranes formed
(43) Tolman, C. A. Chem. ReV. 1977, 77, 313–348.
(44) Brown, T. L.; Lee, K. J. Coord. Chem. ReV. 1993, 128, 89–116.

Iridium-Catalyzed Preparation of Silylboranes
Organometallics, Vol. 27, No. 22, 2008 6017
General Procedure for Silane Borylation. Inside a nitrogen-
filled glovebox, an oven-dried vial was charged with [Ir(cod)OMe]2
(3.3 mg, 0.0050 mmol), dtbpy (2.7 mg, 0.010 mmol), B2pin2 or
HBpin, C6H12 (1.0 mL), n-dodecane (20 µL, 0.088 mmol), and
silane. The resulting dark brown solution was heated at 80 °C
outside the glovebox. After 6 h, the reaction was cooled to room
temperature. GC analysis was used to determine the yield of 1 by
integration against the n-dodecane standard. The crude reaction
mixture was concentrated under high vacuum. Purified product was
obtained by silica gel chromatography, using a hexane/ethyl acetate
gradient, 0%, to 2%, to 5% ethyl acetate.
26.98, 24.99, 16.20, -6.46; 11B NMR (CDCl3) δ 34.8; GC/MS
(EI) m/z (% relative intensity) M+ 242 (1), [M - Me]+ 227 (4)
[M - tBu]+ 185 (97), 101 (49), 83 (100), 69 (35), 55 (34); Anal.
Calcd for C12H27BO2Si: C, 59.50; H, 11.23. Found C, 59.23; H,
10.98.
Attempted Borylation of Tri-isopropylsilane. The reaction of
B2pin2 (253 mg, 1.00 mmol) with tri-isopropylsilane (820 µL, 4.00
mmol) resulted in no formation of silylborane product by GC and
GC/MS analysis.
General Procedure for Arene Borylation with Silylboranes.
Inside a nitrogen-filled glovebox, an oven-dried 20 mL vial was
charged with [Ir(cod)OMe]2, dtbpy, arene, n-dodecane (20 µL, 0.088
mmol), and silylborane. The resulting dark brown solution was
heated at 80 °C outside the glovebox. After heating, the reaction
was cooled to room temperature. GC analysis was used to determine
the yields of borylated products by integration against the n-
dodecane standard. Purified product was obtained by chromatog-
raphy on a short plug of silica gel, using a hexane/diethyl ether
gradient, 0 to 5% diethyl ether.
Borylation of Benzene with Et3SiBpin. The reaction of [Ir-
(cod)OMe]2 (6.6 mg, 0.010 mmol), dtbpy (5.2 mg, 0.019 mmol),
benzene (895 µL, 10.0 mmol), and 1a (270 µL, 0.992 mmol) gave
2 (91% by GC analysis) after 12 h. Purification on silica gel gave
2 (116.4 mg, 58%) as a pale pink oil. The spectroscopic charac-
terization of arylboronic ester 2 has been previously described.36
Borylation of Anisole with Et3SiBpin. The reaction of [Ir-
(cod)OMe]2 (6.5 mg, 0.0098 mmol), dtbpy (6.0 mg, 0.022 mmol),
anisole (1.09 mL, 10.0 mmol), and 1a (270 µL, 0.992 mmol) gave
3 (90% by GC analysis) after 12 h. Analysis of the crude reaction
mixture by 1H NMR spectroscopy showed meta- and para-borylated
products in a 4.3:1 ratio. Purification on silica gel gave 3 (148.4
mg, 64%) as a pale pink oil, in a 3.8:1 ratio of meta:para-substituted
products. The spectroscopic characterization of both isomers of
arylboronic ester 3 has been previously described.36
Borylation of Triethylsilane. The reaction of B2pin2 (254 mg,
1.00 mmol) with triethylsilane (640 µL, 4.01 mmol) gave 1a (76%
by GC analysis). Purification on silica gel gave 1a (140.0 mg, 58%)
1
as a colorless oil. Rf ) 0.56 in 5% EtOAc in hexane; H NMR
(CDCl3) δ 1.23 (s, 12H, Bpin-CH3), 0.96 (t, 9H, J ) 7.9 Hz,
CH2CH3), 0.59 (q, 6H, J ) 7.9 Hz, CH2CH3); 13C NMR (CDCl3)
δ 82.86, 25.00, 8.32, 2.91; 11B NMR (CDCl3) δ 34.9; 29Si NMR
(neat) δ -13.0; GC/MS (EI) m/z (% relative intensity) [M - Me]+
227 (2), [M - Et]+ 213 (28), 199 (5), 184 (6), 129 (7), 115 (10),
103 (19), 84 (100), 69 (34), 55 (16). Anal. Calcd for C12H27BO2Si:
C, 59.50; H, 11.23. Found: C, 59.28; H, 11.51.
Attempted Borylation of Triethylsilane with HBpin in Place
of B2pin2. The reaction of HBpin (145 µL, 1.00 mmol) with
triethylsilane (640 µL, 4.01 mmol) resulted in no formation of
silylborane product by GC and GC/MS analysis.
Borylation of Tri-n-propylsilane. The reaction of B2pin2 (253
mg, 0.995 mmol) with tri-n-propylsilane (835 µL, 4.00 mmol) gave
1b (71% by GC analysis). Purification on silica gel gave 1b (188.2
mg, 66%) as a colorless oil. Rf ) 0.64 in 5% EtOAc in hexane; 1H
NMR (CDCl3) δ 1.36 (m, 6H, CH2CH2CH3), 1.22 (s, 12H, Bpin-
CH3), 0.95 (t, 9H, J ) 7.3 Hz, CH2CH2CH3), 0.57 (m, 6H,
CH2CH2CH3); 13C NMR (CDCl3) δ 82.85, 24.96, 18.42, 18.31,
14.60; 11B NMR (CDCl3) δ 35.1; GC/MS (EI) m/z (% relative
intensity) [M - Me]+ 269 (1), [M - Pr]+ 241 (21), 199 (8), 159
(9), 115 (14), 84 (100), 69 (28), 55 (13). Anal. Calcd for
C15H33BO2Si: C, 63.37; H, 11.70. Found: C, 63.61; H, 11.98.
Borylation of Tri-n-butylsilane. The reaction of B2pin2 (254
mg, 1.00 mmol) with tri-n-butylsilane (1.03 mL, 4.00 mmol) gave
1c (84% by GC analysis). Purification on silica gel gave 1c (250.5
mg, 77%) as a colorless oil. Rf ) 0.70 in 5% EtOAc in hexane; 1H
NMR (CDCl3) δ 1.31 (m, 12H, CH2CH2CH2CH3), 1.22 (s, 12H,
Bpin-CH3), 0.87 (t, 9H, J ) 7.2 Hz, CH2CH2CH2CH3); 0.59 (m,
6H, CH2CH2CH2CH3); 13C NMR (CDCl3) δ 82.84, 27.04, 26.61,
24.94, 13.83, 11.44; 11B NMR (CDCl3) δ 35.2; GC/MS (EI) m/z
(% relative intensity) [M - Me]+ 311 (1), [M - Bu]+ 269 (22),
213 (18), 187 (6), 129 (18), 101 (18), 84 (100), 69 (20), 55 (13).
Anal. Calcd for C18H39BO2Si: C, 66.24; H, 12.04. Found: C, 66.31;
H, 12.10.
Borylation of Tri-n-pentylsilane. The reaction of B2pin2 (255
mg, 1.00 mmol) with tri-n-pentylsilane (1.23 mL, 4.01 mmol) gave
1d (95% by GC analysis). Purification on silica gel gave 1d (258.3
mg, 70%) as a pale pink oil. Rf ) 0.76 in 5% EtOAc in hexane;
1H NMR (CDCl3) δ 1.29 (m, 18H, CH2CH2CH2CH2CH3), 1.22 (s,
12H, Bpin-CH3), 0.86 (m, 9H, CH2CH2CH2CH2CH3), 0.58 (m, 6H,
CH2CH2CH2CH2CH3); 13C NMR (CDCl3) δ 82.83, 35.84, 24.96,
24.39, 22.33, 14.00, 11.66; 11B NMR (CDCl3) δ 35.2; GC/MS (EI)
m/z (% relative intensity) [M - Me]+ 353 (0.4), [M - pentyl]+
297 (10), 227 (15), 143 (12), 115 (10), 101 (11), 84 (100), 69 (20),
55 (10). Anal. Calcd for C21H45BO2Si: C, 68.45; H, 12.31. Found:
C, 68.21; H, 12.20.
Borylation of Chlorobenzene with Et3SiBpin. The reaction of
[Ir(cod)OMe]2 (3.4 mg, 0.0051 mmol), dtbpy (2.6 mg, 0.0097
mmol), chlorobenzene (1.02 mL, 10.0 mmol), and 1a (270 µL,
0.992 mmol) gave 4 (93% by GC analysis) after 4 h. Analysis of
the crude reaction mixture by 1H NMR spectroscopy showed meta-
and para-borylated products in a 4.4:1 ratio. Purification on silica
gel gave 4 (152.4 mg, 65%) as a pale pink oil, in a 3.3:1 ratio of
meta:para-substituted products. 4, meta-isomer: Rf ) 0.51 in 5%
1
EtOAc in hexane; H NMR (CDCl3) δ 7.78 (d, 1H, J ) 2.0 Hz,
Ar-H), 7.66 (td, 1H, J ) 1.1, 7.2 Hz, Ar-H), 7.42 (ddd, 1H, J )
1.3, 2.3, 8.0 Hz, Ar-H), 7.30 (t, 1H, J ) 7.6 Hz, Ar-H), 1.34 (s,
12H, Bpin-CH3); 13C NMR (CDCl3) δ 134.50, 133.96, 132.61,
131.21, 129.14, 84.06, 24.79; 11B NMR (CDCl3) δ 30.3; GC/MS
(EI) m/z (% relative intensity) M+ 238 (36), [M - Me]+ (77),
152(100), 139 (95). 4, para-isomer: Rf ) 0.51 in 5% EtOAc in
hexane; 1H NMR (CDCl3) δ 7.72 (d, 2H, J ) 8.4 Hz, Ar-H), 7.34
(d, 2H, J ) 8.3 Hz, Ar-H), 1.34 (s, 12H, Bpin-CH3); 13C NMR
(CDCl3) δ 137.46, 136.08, 127.94, 83.94, 24.65; 11B NMR (CDCl3)
δ 30.3; GC/MS (EI) m/z (% relative intensity) M+ 238 (36), [M -
Me]+ (77), 152(100), 139 (95). 4, mixture of isomers: HRMS (EI)
m/z calcd for C12H16BClO2 M+ 238.0931, found 238.0931. Anal.
Calcd for C12H16BClO2: C, 60.43; H, 6.76; N, 0.00. Found: C,
60.72; H, 7.09; N, <0.02.
Borylation of 1,2-Dichlorobenzene with Et3SiBpin. The reac-
tion of [Ir(cod)OMe]2 (3.3 mg, 0.0050 mmol), dtbpy (2.7 mg, 0.010
mmol), 1,2-dichlorobenzene (1.13 mL, 10.0 mmol), and 1a (270
µL, 0.992 mmol) gave 5 (89% by GC analysis) after 4 h.
Purification on silica gel gave 5 (135.6 mg, 50%) as a pale pink
oil. The spectroscopic characterization of arylboronic ester 5 has
been previously described.36
Borylation of 1,2-Dibromobenzene with Et3SiBpin. The reac-
tion of [Ir(cod)OMe]2 (3.2 mg, 0.0048 mmol), dtbpy (2.9 mg, 0.011
mmol), 1,2-bromobenzene (1.21 mL, 10.0 mmol), and 1a (270 µL,
Borylation of tert-Butyldimethylsilane. The reaction of B2pin2
(253 mg, 1.00 mmol) with tert-butyldimethylsilane (665 µL, 4.01
mmol) gave 1e (61% by GC analysis). Purification on silica gel
gave 1e (99.3 mg, 41%) as a white solid. Rf ) 0.57 in 5% EtOAc
1
in hexane; H NMR (CDCl3) δ 1.22 (s, 12H, Bpin-CH3), 0.91 (s,
9H, C(CH3)3), 0.01 (s, 6H, SiCH3); 13C NMR (CDCl3) δ 82.94,

6018 Organometallics, Vol. 27, No. 22, 2008
Boebel and Hartwig
0.992 mmol) gave 6 (86% by GC analysis) after 4 h. Purification
on silica gel gave 6 (229.8 mg, 64%) as a colorless oil. Rf ) 0.44
in 5% EtOAc in hexane; 1H NMR (CDCl3) δ 8.03 (d, 1H, J ) 1.4
Hz, Ar-H), 7.62 (d, 1H, J ) 7.9 Hz, Ar-H), 7.54 (dd, 1H, J ) 1.4,
7.9 Hz, Ar-H), 1.34 (s, 12H, Bpin-CH3); 13C NMR (CDCl3) δ
139.62, 134.38, 133.20, 128.12, 124.60, 84.28, 24.79; 11B NMR
(CDCl3) δ 29.92; GC/MS (EI) m/z (% relative intensity) M+ 362
(53), [M - Me]+ 347 (100), 276 (87), 263 (54); HRMS (EI) m/z
calcd for C12H15BBr2O2 M+ 359.9532, found 359.9533.
Borylation of 3-Chloroanisole with Et3SiBpin. The reaction
of [Ir(cod)OMe]2 (3.6 mg, 0.0054 mmol), dtbpy (2.6 mg, 0.0097
mmol), 3-chloroanisole (1.22 mL, 9.96 mmol), and 1a (270 µL,
0.992 mmol) gave 7 (99% by GC analysis) after 4 h. Purification
of silica gel gave 7 (140.5 mg, 53%) as a pale orange oil. Rf )
0.37 in 5% EtOAc in hexane; 1H NMR (CDCl3) δ 7.37 (dd, 1H, J
) 0.7, 2.0 Hz, Ar-H), 7.19 (dd, 1H, J ) 0.6, 2.5 Hz), 6.98 (t, 1H,
J ) 2.2 Hz, Ar-H), 3.82 (s, 3H, OCH3), 1.34 (s, 12H, Bpin-CH3);
13C NMR (CDCl3) δ 159.82, 134.52, 126.79, 117.66, 117.35, 84.12,
55.45, 24.78; 11B NMR (CDCl3) δ 30.1; GC/MS (EI) m/z (%
relative intensity) M+ 268 (78), [M - Me]+ 253 (46), 182 (100),
168 (78); HRMS (EI) m/z calcd for C13H18BClO3 M+ 268.1038,
found 268.1036. Anal. Calcd for C13H18BClO3: C, 58.14; H, 6.76;
N, 0.00. Found: C, 58.25; H, 6.42; N, <0.02.
Borylation of 3-Chlorotoluene with Et3SiBpin. The reaction
of [Ir(cod)OMe]2 (3.2 mg, 0.0048 mmol), dtbpy (2.7 mg, 0.010
mmol), 3-chlorotoluene (1.18 mL, 9.99 mmol), and 1a gave 12
(88% by GC analysis) after 4 h. Analysis of the crude reaction
mixture by 1H NMR spectroscopy showed benzyl- and meta-
borylated products in a 1:1.5 ratio. Purification on silica gel gave
12 (180.4 mg, 72%) as a pale pink oil, in a 1:1.7 ratio of benzyl:
meta-substituted products. 12a: Rf ) 0.35 in 5% EtOAc in hexane;
1H NMR (CDCl3) δ 7.18 (m, 1H, Ar-H), 7.16 (t, 1H, J ) 7.8 Hz,
Ar-H), 7.10 (m, 1H, Ar-H), 7.06 (m, 1H, Ar-H), 2.27 (s, 2H, CH2-
Bpin), 1.24 (s, 12H, Bpin-CH3), 1.24 (t, 3H, J ) 7.5 Hz, CH2CH3);
13C NMR (CDCl3) δ 133.86, 133.77, 129.56, 129.01, 127.15,
125.02, 83.54, 24.65, 19.64 (br s); 11B NMR (CDCl3) δ 32.4; GC/
MS (EI) m/z (% relative intensity) M+ 252 (48), [M - Me]+ 237
(31), 166 (71), 152 (74), 117 (63), 83 (100), 59 (29). 12b: Rf )
1
0.46 in 5% EtOAc in hexane; H NMR (CDCl3) δ 7.59 (m, 1H,
Ar-H), 7.49 (m, 1H, Ar-H), 7.25 (m, 1H, Ar-H), 2.33 (s, 3H, Ar-
CH3), 1.34 (s, 12H, Bpin-CH3); 13C NMR (CDCl3) δ 140.73,
139.19, 133.37, 131.83, 131.48, 84.02, 24.79, 20.91; 11B NMR
(C6D6) δ 30.4; GC/MS (EI) m/z (% relative intensity) M+ 252 (32),
[M - Me]+ 237 (39), 166 (100), 153 (85), 117 (37); HRMS (EI)
m/z calcd for C13H18BClO2 M+ 252.1088, found 252.1089. Anal.
Calcd for C13H18BClO2: C, 61.83; H, 7.18; N, 0.00. Found: C,
61.83; H, 7.01; N, <0.02.
Borylation of 1,3-Dichlorobenzene with Et3SiBpin. The reac-
tion of Ir(cod)OMe]2 (3.2 mg, 0.0048 mmol), dtbpy (2.8 mg, 0.010
mmol), 1,3-dichlorobenzene (1.14 mL, 9.99 mmol), and 1a (270
µL, 0.992 mmol) gave 8 (96% by GC analysis) after 4 h.
Purification of silica gel gave 8 (150.3 mg, 56%) as a pale pink
Borylation of 1,3,5-Trimethylbenzene with Et3SiBpin. The
reaction of [Ir(cod)OMe]2 (6.6 mg, 0.010 mmol), dtbpy (5.3 mg,
0.020 mmol), 1,3,5-trimethylbenzene (1.39 mL, 9.99 mmol), and
1a (270 µL, 0.992 mmol) gave 13 (95% by GC analysis) after 12 h.
Purification of silica gel gave 13 (186.5 mg, 78%) as a pale yellow
1
oil. Rf ) 0.46 in 5% EtOAc in hexane; H NMR (CDCl3) δ 7.65
1
(d, 1H, J ) 2.1 Hz, Ar-H), 7.43 (t, 1H, J ) 2.0 Hz, Ar-H), 1.34 (s,
12H, Bpin-CH3); 13C NMR (CDCl3) δ 134.7, 132.7, 131.06, 84.48,
24.81; 11B NMR (CDCl3) δ 29.8; GC/MS (EI) m/z (% relative
intensity) M+ 272 (44), [M - Me]+ 257 (82), 186 (100), 173 (52);
HRMS (EI) m/z calcd for C12H15BCl2O2 M+ 272.0542, found
272.0542.
oil. Rf ) 0.40 in 5% EtOAc in hexane; H NMR (CDCl3) δ 6.80
(s, 2H, Ar-H), 6.76 (s, 1H, Ar-H), 2.26 (s, 6H, Ar-CH3), 2.21 (s,
2H, CH2-Bpin), 1.24 (s, 12H, Bpin-CH3); 13C NMR (CDCl3) δ
138.28, 137.55, 126.80, 126.52, 83.30, 24.66, 21.23, 19.74 (br s);
11B NMR (CDCl3) δ 32.8; GC/MS (EI) m/z (% relative intensity)
M+ 246 (89), [M - Me]+ 231 (27), 160 (42), 146 (100), 131 (22),
119 (62), 105 (29), 83 (28); HRMS (EI) m/z calcd for C15H23BO2
M+ 246.1791, found 246.1793. Anal. Calcd for C15H23BO2: C,
73.19; H, 9.42; N, 0.00. Found: C, 73.44; H, 9.68; N, <0.02.
Borylation of 2,3,4,5,6-Pentafluorotoluene with Et3SiBpin. The
reaction of [Ir(cod)OMe]2 (6.6 mg, 0.010 mmol), dtbpy (5.4 mg,
0.020 mmol), 2,3,4,5,6-pentafluorotoluene (1.26 mL, 9.96 mmol),
and 1a (270 µL, 0.992 mmol) gave 14 (79% by GC analysis) after
12 h. Purification of silica gel gave 14 (194.4 mg, 64%) as a pale
pink oil. Rf ) 0.21 (compound streaks on TLC plate) in 5% EtOAc
in hexane; 1H NMR (CDCl3) δ 2.25 (br s, 2H, CH2), 1.24 (s, 12H,
Bpin-CH3); 13C NMR (CDCl3) δ 144.82 (d of m, J ) 243.5 Hz),
138.86 (ttd, J ) 4.8, 13.7, 250.2 Hz), 137.37 (d of m, J ) 248.6
Hz), 112.71 (dt, J ) 3.7, 19.6 Hz), 84.17, 24.54, 6.02 (br s), 0.97;
11B NMR (CDCl3) δ 32.2; 19F NMR (CDCl3) δ -144.4 (dd, J )
8.8, 22.9 Hz), -161.1 (t, J ) 21.0 Hz), -165.0 (dt, J ) 7.7, 21.3
Hz); GC/MS (EI) m/z (% relative intensity) M+ 308 (7), [M -
Me]+ 293 (56), 235 (19), 208 (30), 202 (57), 189 (23), 181 (34),
85 (100), 59 (50); HRMS (EI) m/z calcd for C13H14BF5O2 (M -
H)+ 308.1007, found 308.1008.
Borylation of 1,3-Bis(trifluoromethyl)benzne with Et3SiBpin.
The reaction of [Ir(cod)OMe]2(3.6 mg, 0.0054 mmol), dtbpy (2.7
mg, 0.010 mmol), 1,3-bis(trifluoromethyl)benzene (1.55 mL, 9.98
mmol), and 1a (270 µL, 0.992 mmol) gave 9 (88% by GC analysis)
after 4 h. Purification of silica gel gave 9 (181.4 mg, 54%) as a
white solid. The spectroscopic characterization of arylboronic ester
9 has been previously described.45
Borylation of Toluene with Et3SiBpin. The reaction of [Ir-
(cod)OMe]2 (6.5 mg, 0.0098 mmol), dtbpy (5.6 mg, 0.021 mmol),
toluene (1.06 mL, 9.95 mmol), and 1a (270 µL, 0.992 mmol) gave
10 (92% by GC analysis) after 12 h. Analysis of the crude reaction
mixture by 1H NMR spectroscopy showed benzyl-, meta-, and para-
borylated products in a 2.6:1.8:1 ratio. Purification of silica gel gave
10 (140.0 mg, 65%) as a colorless oil, in a 2.7:2.0:1 ratio of benzyl:
meta:para-substituted products. The spectroscopic characterization
of benzylboronic ester 10a46 and both isomers of arylboronic ester
10b36 has been previously described.
Borylation of meta-Xylene with Et3SiBpin. The reaction of
[Ir(cod)OMe]2 (6.5 mg, 0.0098 mmol), dtbpy (5.9 mg, 0.022 mmol),
meta-xylene (1.22 mL, 9.97 mmol), and 1a (270 µL, 0.992 mmol)
gave 11 (86% by GC analysis) after 12 h. Analysis of the crude
reaction mixture by 1H NMR spectroscopy showed benzyl- and
meta-borylated products in a 8:1 ratio. Purification on silica gel
gave 11 (163.9 mg, 71%) as a pale pink oil, in a 7:1 ratio of benzyl:
meta-substituted products. The spectroscopic characterization of
benzylboronic ester 11a46 and arylboronic ester 11b36 has been
previously described.
Borylation of Ethylbenzene with Et3SiBpin. The reaction of
[Ir(cod)OMe]2 (6.6 mg, 0.010 mmol), dtbpy (5.6 mg, 0.021 mmol),
ethylbenzene (1.22 mL, 9.96 mmol), and 1a (270 µL, 0.992 mmol)
gave 15 (71% by GC analysis) after 12 h. Analysis of the crude
reaction mixture by 1H NMR spectroscopy showed meta- and para-
borylated products in a 2.3:1 ratio. Purification on silica gel gave
15 (138.0 mg, 60%) as a pale pink oil, in a 2.4:1 ratio of meta:
para-substituted products. 15, meta-isomer: Rf ) 0.38 in 5% EtOAc
1
in hexane; H NMR (CDCl3) δ 7.65 (s, 1H, Ar-H), 7.63 (m, 1H,
Ar-H), 7.30 (m, 1H, Ar-H), 2.65 (q, 2H, J ) 7.6 Hz, CH2CH3),
1.35 (s, 12H, Bpin-CH3), 1.24 (t, 3H, J ) 7.5 Hz, CH2CH3); 13C
NMR (CDCl3) δ 143.43, 134.19, 132.06, 130.83, 127.72, 83.63,
28.77, 24.80, 15.71; 11B NMR (CDCl3) δ 30.7; GC/MS (EI) m/z
(45) Cho, J.-Y.; Iverson, C. N.; Smith, M. R., III. J. Am. Chem. Soc.
2000, 122, 12868–12869.
(46) Murata, M.; Oyama, T.; Watanabe, S.; Masuda, Y. Synth. Commun.
2002, 32, 2513–2517.

Iridium-Catalyzed Preparation of Silylboranes
Organometallics, Vol. 27, No. 22, 2008 6019
(% relative intensity) M+ 232 (47), [M - Me]+ 217 (57), 146 (100),
133 (100), 117 (38). 15, para-isomer: Rf ) 0.43 in 5% EtOAc in
hexane; 1H NMR (CDCl3) δ 7.74 (d, 1H, J ) 8.0 Hz, Ar-H), 7.21
(d, 1H, J ) 7.9 Hz, Ar-H), 2.66 (q, 2H, J ) 7.6 Hz, CH2CH3),
1.34 (s, 12H, Bpin-CH3), 1.23 (t, 3H, J ) 7.5 Hz, CH2CH3); 13C
NMR (CDCl3) δ 147.66, 134.86, 127.29, 83.53, 29.06, 24.80, 15.44;
11B NMR (CDCl3) δ 30.7; GC/MS (EI) m/z (% relative intensity)
M+ 232 (41), [M - Me]+ 217 (53), 146 (80), 133 (100), 117 (31).
15, mixture of isomers: HRMS (EI) m/z calcd for C14H21BO2 M+
232.1635, found 232.1638. Anal. Calcd for C14H21BO2: C, 72.44;
H, 9.12; N, 0.00. Found: C, 72.16; H, 9.38; N, <0.02.
Borylation of m-Xylene with B2pin2. The reaction of [Ir-
(cod)OMe]2 (6.7 mg, 0.010 mmol), dtbpy (5.6 mg, 0.021 mmol),
B2pin2 (254 mg, 1.00 mmol), and m-xylene (1.22 mL, 9.97 mmol)
gave 11b (83% by GC analysis) after 12 h. Analysis of the crude
reaction mixture by 1H NMR spectroscopy showed 11b as the only
isomeric product. Purification of silica gel gave 11b (352.1 mg,
76%) as a pale pink oil.
the only isomeric product. Purification on silica gel gave 12b (348.2
mg, 69%) as a white solid.
Borylation of 3-Chlorotoluene with t-BuMe2SiBpin. The
reaction of [Ir(cod)OMe]2 (3.4 mg, 0.0051 mmol), dtbpy (2.8 mg,
0.010 mmol), 3-chlorotoluene (1.18 mL, 9.99 mmol), and 1e (243
mg, 1.00 mmol) gave 12 (98% by GC analysis) after 4 h. Analysis
1
of the crude reaction mixture by H NMR spectroscopy showed
benzyl- and meta-borylated products in a 1:9.3 ratio. Purification
on silica gel gave 12 (163.4 mg, 65%) as a pale pink oil, in a 1:6.2
ratio of benzyl:meta-substituted products.
Borylation of 3-Chlorotoluene with n-Bu3SiBpin. The reaction
of [Ir(cod)OMe]2 (3.4 mg, 0.0051 mmol), dtbpy (2.6 mg, 0.0097
mmol), 3-chlorotoluene (1.18 mL, 9.99 mmol), and 1c (375 µL,
1.01 mmol) gave 12 (87% by GC analysis) after 4 h. Analysis of
the crude reaction mixture by 1H NMR spectroscopy showed
benzyl- and meta-borylated products in a 1.5:1 ratio. Purification
on silica gel gave 12 (158.7 mg, 62%) as a pale pink oil, in a 1.1:1
ratio of benzyl:meta-substituted products.
Borylation of 3-Chlorotoluene with Et3SiBpin. Evaluation
of Ratio of Benzylic vs Aryl C-H Functionalization over
Time. Inside a nitrogen-filled glovebox, an oven-dried 20 mL vial
was charged with [Ir(cod)OMe]2 (3.3 mg, 0.0050 mmol), dtbpy
(2.7 mg, 0.010 mmol), 3-chlorotoluene (1.18 mL, 9.99 mmol),
n-dodecane (20 µL, 0.088 mfmol), and 1a (270 µL, 0.992 mmol).
The resulting dark brown solution was heated at 80 °C inside the
glovebox. Reaction aliquots (5 µL) were removed at 10 min
intervals and diluted with diethyl ether (1.5 mL) for subsequent
GC analysis. After 120 min, GC analysis indicated complete
conversion of 3-chlorotoluene to 12a and 12b, in a 1:1.6 ratio.
Borylation of m-xylene with t-BuMe2SiBpin. The reaction of
[Ir(cod)OMe]2 (6.4 mg, 0.0097 mmol), dtbpy (5.4 mg, 0.020 mmol),
m-xylene (1.22 mL, 9.97 mmol), and 1e (201 mg, 0.829 mmol)
gave 11 (75% by GC analysis) after 12 h. Analysis of the crude
reaction mixture by 1H NMR spectroscopy showed benzyl- and
meta-borylated products in a 2.3:1 ratio. Purification on silica gel
gave 11 (143.2 mg, 74%) as a pale pink oil, in a 2.1:1 ratio of
benzyl:meta-substituted products.
Borylation of m-Xylene with n-Bu3SiBpin. The reaction of
[Ir(cod)OMe]2 (6.8 mg, 0.010 mmol), dtbpy (5.6 mg, 0.021 mmol),
m-xylene (1.22 mL, 9.97 mmol), and 1c (375 µL, 1.01 mmol) gave
11 (65% by GC analysis) after 12 h. Analysis of the crude reaction
mixture by 1H NMR spectroscopy showed benzyl- and meta-
borylated products in a 13.3:1 ratio. Purification on silica gel gave
11 (142.2 mg, 61%) as a pale pink oil, in a 11.3:1 ratio of benzyl:
meta-substituted products.
Acknowledgment. We thank the NSF (CHE-0606685) for
funding. We thank Frontier Scientific and AllyChem for the
gift of bis(pinacolato)diboron. We thank Johnson Matthey for
the gift of 1,5-cyclooctadiene(µ-methoxy)iridium(I) dimer.
Borylation of 3-Chlorotoluene with B2pin2. The reaction of
[Ir(cod)OMe]2 (3.3 mg, 0.0050 mmol), dtbpy (2.8 mg, 0.010 mmol),
B2pin2 (253 mg, 1.00 mmol), and 3-chlorotoluene (1.18 mL, 9.99
mmol) gave 12b (102% by GC analysis) after 4 h. Analysis of the
Supporting Information Available: 1H and 13C NMR spectra
of compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
1
crude reaction mixture by H NMR spectroscopy showed 12b as
OM800696D