The functionalization of benzene by boranes using trispyrazolylborate complexes

Article abstract of DOI:10.1016/j.poly.2021.115042

The catalytic C[sbnd]H activation and borylation of arenes by trispyrazolylborate complexes is reported. Trispyrazolylborate rhodium and iridium complexes have been previously shown to activate a variety of C[sbnd]H bonds. Here, we show the catalytic borylation of arenes by the trispyrazolylborate ethylene complexes Tp'Rh(C₂H₄)₂, and Tp'Ir(C₂H₄)₂.

Full text of DOI:10.1016/j.poly.2021.115042

Polyhedron 197 (2021) 115042
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
The functionalization of benzene by boranes using trispyrazolylborate
complexes
1
1
⇑
Andrew J. Vetter, Tarah A. DiBenedetto , Mikhaila D. Ritz , William D. Jones
Department of Chemistry, University of Rochester, Rochester, NY 14627, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The catalytic CAH activation and borylation of arenes by trispyrazolylborate complexes is reported.
Trispyrazolylborate rhodium and iridium complexes have been previously shown to activate a variety
of CAH bonds. Here, we show the catalytic borylation of arenes by the trispyrazolylborate ethylene com-
Received 22 October 2020
Accepted 13 January 2021
Available online 18 January 2021
2 4 2 2 4 2
plexes Tp’Rh(C H ) , and Tp’Ir(C H ) .
Ó 2021 Elsevier Ltd. All rights reserved.
Keywords:
Rhodium
Iridium
Trispyrazolylborate
Borylation
Arenes
1
. Introduction
Organoboron compounds are highly relevant in both the phar-
[8,9]. Direct arene borylation has since been catalyzed by rhodium,
platinum, and other iridium catalysts [10–13], as well as first row
transition metals such as cobalt [14], nickel [2], and iron [15,16].
Most recently, Farha has shown that an iridium catalyst can be
supported in a MOF to achieve arene borylation with B pin
2 2
(pin = pinacol) [17]. The development of these and other systems
has been reviewed in 2010 [3].
The direct borylation of arenes is a fundamental tool for syn-
thetic chemistry that is reliant on the activation of CAH bonds
[18]. Hartwig and coworkers have shown the catalytic borylation
maceutical and synthetic fields, as they are used in numerous
transformations such as metal catalyzed cross couplings, conjugate
additions, and oxidative aminations [1,2]. These boron containing
compounds are commonly synthesized from aryl halides via Grig-
nard or lithium reagents, or directly by the metal catalyzed reac-
tion of aryl or alkyl halides with boron reagents. While effective,
these methods increase synthetic overhead and rely on the acces-
sibility of halide precursors [3]. An alternative approach is the
direct borylation of CAH bonds, which avoids the need for prefunc-
tionalized starting materials and allows for a more atom econom-
ical strategy for the synthesis of borylated products [3].
of alkanes and arenes using a Cp*M(C
[19]. Previous work has shown that the isoelectronic Tp’Rh
(C and Tp’Ir(C complexes are able to activate both alkane
2 4 2
H ) (M = Rh, Ir) catalyst
H
2 4
)
2
2 4 2
H )
and arene CAH bonds [20-24], but have not been investigated for
the catalytic borylation of arenes. The success of the analogous
pentamethylcyclopentadienyl catalysts offers an opportunity for
the development of a catalytic borylation based on the trispyra-
zolylborate scaffold.
The importance of these compounds has driven the develop-
ment of new methodologies for direct arene borylation over the
last few decades. Hartwig reported in 1995 a photochemical bory-
lation of arenes and olefins using CpFe(CO)
and W(CO) (Bcat) (cat = catechol) [4]. This photochemistry was
extended to alkanes stoichiometrically using Cp*W(CO) )(Bcat)
5], and catalytically using Cp*Re(CO) [6]. In 1999, Smith and
2 5
(Bcat), Mn(CO) (Bcat),
5
3
[
3
2
. Results and discussion
coworkers reported the first catalytic borylation of arenes using
an iridium pentamethylcyclopentadienyl catalyst [7]. Further
improvements have been made by Ishiyama, Miyaura, and Hartwig
by using iridium precursors in combination with bidentate ligands
2
2
.1. Borylation with Tp’Rh(CNR)(g -PhN = CNR)
The borylation of benzene using various trispyrazolylborate
metal complexes was studied (Fig. 1). Our initial investigation
2
⇑
Corresponding author.
began
R = neopentyl), which when irradiated in the presence of benzene
is known to form the CAH oxidative addition product [25].
with
catalyst
1
Tp’Rh(CNR)(
g
-PhN
=
CNR)
(
E-mail address: jones@chem.rochester.edu (W.D. Jones).
Authors contributed equally to this work.
1
https://doi.org/10.1016/j.poly.2021.115042
277-5387/Ó 2021 Elsevier Ltd. All rights reserved.
0

A.J. Vetter, T.A. DiBenedetto, M.D. Ritz et al.
Polyhedron 197 (2021) 115042
2.2. Borylation with Tp’Rh(CNR)
2
We next examined catalysis using complex 2. Borylation of ben-
zene was attempted thermally at 130 °C for 5d [27]. Catalysis with
complex 2 led to a 20% consumption of B pin and GC showed a
newly formed peak corresponding to product 5a (Table 1, entry
). Borylation using HBpin resulted in a much faster reaction, with
2
2
4
just over 50% of HBpin consumed and the desired product 5a
observable by GC (Table 1, entry 5). Catalysis using 2 was
attempted at lower temperatures but no reaction was observed
at temperatures below 130 °C.
2.3. Borylation with Tp’Ir(C
2 4 2
H )
Fig. 1. Trispyrazolylborate catalysts.
From there, we began our investigation into the trispyrazolylb-
orate ethylene complexes, starting with the iridium complex 3.
Running the reaction neat at 115 °C showed ~ 40% consumption
of B
trace (Table 1, entry 6). When octane was added as a solvent, the
reaction showed 95% consumption of B pin and the formation of
product 5a, although the reaction was very slow (Table 1, entry
). Catalysis with HBpin showed a more rapid reaction when com-
pared to the reaction of B pin in neat benzene (Table 1, entry 6),
giving 50% consumption of HBpin and detection of the product
a (Table 1, entry 8). In all cases, the yield of 5a was not
2 2
pin and a new peak corresponding to product 5a in the GC
Catalyst 1 was irradiated at room temperature in the presence
of B pin (B pin = bis(pinacolato)diborane) and benzene for
0 min, resulting in the bleaching of the bright yellow solution.
However, no formation of desired product PhBpin (5a) was
observed by GC, and only starting materials were present. The
2
2
2
2
2
2
1
7
2
2
6 5
CAH activation product Tp’Rh(CNR)(C H )H (1a) was observed as
the only metal complex by NMR spectroscopy. Extended irradia-
tion also did not result in formation of any of the desired product.
Catalysis with 1 was also attempted thermally. A mixture of cat-
5
quantitative.
2 2
alyst 1, B pin , and benzene was heated for 4.5 h at 115 °C. Analo-
gous to the reaction that was irradiated, analysis by GC showed
only starting materials with no formation of desired product 5a,
and metal hydride 1a was again observed by NMR spectroscopy.
Further heating of the reaction also failed to give product 5a
2 4 2
2.4. Borylation with Tp’Rh(C H )
Next, borylation of benzene using the corresponding rhodium
complex Tp’Rh(C 4 was attempted. Initial conditions using
2 4 2
H )
(
Table 1, entry 2). Using HBpin gave similar results to the reaction
with B Pin . Only HBpin was visible in the GC trace and complex 1a
was the only metal complex in the H NMR spectra (Table 1, entry
). Note that stoichiometric activation of neat HBpin with the PMe
substituted version of 1 has been investigated previously, showing
an excess of benzene at 115 °C produced borylated product 5a in
a 76% isolated yield (Table 2, entry 1). Attempts at lowering the
number of equivalents of benzene and diluting the reaction with
n-heptane resulted in poor yields (Table 2, entries 2–3). It was
observed that the reaction with a lower loading of benzene
(Table 2, entry 2) performed slightly better than the reaction with
more benzene (Table 2, entry 3). This suggests that this transfor-
2
2
1
3
3
3
B-H oxidative addition to give Tp’Rh(PMe )(Bpin)H [26].
Table 1
Screen of benzene borylation with trispyrazolylborate complexes.
Entry
B
2
Pin
2
equiv
HBpin equiv
5
Catalyst
Conversiona of B
Pin /HBpin
2 2
equiv
b
1
1
1
–
1
–
1
1
–
1
–
–
–
1
–
1
–
–
1
–
1
230
284
286
106
197
91
4
93
77
77
1
1
1
2
2
3
3
3
4
4
0%
0%
0%
~ 30%
~ 40%
~ 36%
~ 95%
~ 62%
~ 40%
~ 98%
c
2
c
3
d
4
c
5
e
6
f
7
g
8
g
9
1
0g
a
b
c
d
e
f
Conversion of borylating agent to PhBpin based on area ratios of GC peaks, no internal standard used, qualitative conversion.
Irradiated at RT for 5 h.
Heated at 115 °C for 4 h.
Heated at 110 °C for 4 d.
Heated at 115 °C for 24 h.
Heated at 120 °C for 3 d in 1.5 mL n-octane. 37% conversion after 24 h.
Heated at 115 °C for 3 h.
g
2

A.J. Vetter, T.A. DiBenedetto, M.D. Ritz et al.
Polyhedron 197 (2021) 115042
Table 2
2 4 2
Borylation of benzene using Tp’Rh(C H ) (4).
Entry
B
2
Pin
2
equiv
HBpin equiv
5 equiv
heptane mL
T °C
Yield
b
5
a
1a
1
1
1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1
1
1
2
1
1
1
1
1
1
1
76
0.5
2
76
4
4
1
1
2
4
20
4
3
20
–
115
115
115
115
100
90
100
115
100
100
115
100
100
100
76%
12%
5%
60%
73%
45%
6%
30%
69%
81%
80%
60%
70%
5%
a e,g
2
3
4
5
6
7
8
9
1
1
1
1
1
,
1.5
1.5
–
–
–
–
–
–
–
–
–
–
–
a,e,h
a
a
a
c,e
c
c
0c
1
2
3
c
d
c
f,e
4
a
b
c
0
.22 mmol scale, 5 mol % catalyst.
isolated yield.
0
0
.4 mmol scale, 4 mol % catalyst.
.4 mmol, 2 mol % catalyst.
d
e
f
NMR yield vs. dimethylsulfone as the internal standard.
Hg drop added, 0.4 mmol, 4 mol % catalyst, 0.81% of the doubly borylated product 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene was observed.
3
7
g
h
.5% of the doubly borylated product 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene was observed.
.4% of the doubly borylated product 1,3-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzene was observed.
mation relies heavily on having an excess of one substrate. In entry
the boron to benzene ratio is 2:0.5 while in entry 3 the boron to
benzene ratio is 1:1 (due to the fact that B pin contains two
equivalents of boron per molecule). Switching borylating agents
from B pin (Table 1, entry 1) to HBpin (Table 1, entry 4) gave
slightly lower yields. This is likely due to the fact that 1 equivalent
of each borylating agent was used, but B pin provides double the
equivalents of boron, manipulating the ratio of boron to benzene.
HBpin was used for further optimization for ease of reaction set
up. The temperature was able to be lowered to 100 °C without a
loss in yield, but upon lowering the temperature to 90 °C a drastic
reduction in yield was observed (Table 2, entry 6). The reaction,
when scaled from 0.22 mmol scale to a 0.4 mmol scale, resulted
in a slight increase in yield (Table 2, entries 5 & 10). Furthermore,
the equivalents of benzene were lowered to 4 equiv without a loss
in yield (Table 2 entries 10 & 11). It was seen when lowering the
equivalents of benzene below four, a reduction in yield was
observed (Table 2, entries 8,9, & 13). Specifically, reducing the
amount of benzene to 2–3 equivalents, led to a 10% decrease in
yield (Table 2, entries 9 & 13). A 1:1 ratio of substrates led to a
drastic drop in yield to 30% (Table 1, entry 8).
It was found that using an excess of the arene rather than boron
source wascritical for reactivity; anexcess ofHBpin reducedthe yield
from 69% to 6% (Table 2, entries 7 & 9). The catalyst loading was low-
ered from 5 mol % to 4 mol % without a reduction in yield, but upon
lowering it further to 2 mol %, a 20% reduction in the yield of 5a
was observed. Final optimized conditions use a ratio of benzene to
HBpin of 4:1, a catalyst loading of 4 mol %, and heating the reaction
to 100 °C (Table 2, entry 10). Upon completion of a mercury drop test,
a large decrease in yield was observed suggesting this system is cat-
alyzed by Rh nanoparticles, which is something our group has seen
previously with similar catalysts (Table 2, entry 14) [28]. Monitoring
the reaction vs. time shows a smooth conversion to produce product
Further characterization by X-ray powder diffraction (XRD)
showed a crystalline material that was a mixture of Rh metal
and several different Rh oxides.We observed the Rh oxide forma-
tion in samples analyzed in air and samples analyzed under an
inert atmosphere. This suggests that the Rh oxides are forming
during the reaction. Additionally, transmission eletron microscopy
(TEM) was done showing the formation of 0.17 mm Rh oxide aggre-
gates and Rh metal nanoparticles (see Supporting Information for
more details).
2
2
2
2
2
2
2
2 4 2
2.5. Borylation of toluene and anisole with Tp’Rh(C H )
With optimizations in hand, we explored the effects of simple
electron withdrawing and donating substitution on the arene ring.
Fluorobenzene, chlorobenzene, anisole and toluene were submit-
ted to the reaction conditions (Scheme 1). Reaction with
chlorobenzene showed cleavage of the C-Cl bond, forming benzene
and a mixture of the borylated chlorobenzene and 5a in trace
yield. Fluorobenzene was chosen to avoid the C-X bond cleavage
and although it showed better reactivity than chlorobenzene the
yield remained below 10%. Unfortunately introducing any func-
tionality to the arene resulted in a drastic drop in yield under
our optimized conditions. Substrates 6a-7a worked best using
a much larger excess of arene, specifically 18–20 equiv. Toluene
was able to be borylated in a 75% yield when using a large excess
of arene, however lowering the arene to 4 equiv resulted in over
a 50% reduction in yield. Using a large excess of anisole did not
give the same increase in yield compared to the reaction at 4
equiv. The reaction with 20 equiv of anisole gave a 20% combined
yield of the meta and para products. The ortho isomer was
observed by GC–MS, with a ratio for the o/m/p isomers of
4:49:47, but the ortho isomer was not able to be observed by
NMR analysis.
5
a with no induction period (see Supporting Information).
3

A.J. Vetter, T.A. DiBenedetto, M.D. Ritz et al.
Polyhedron 197 (2021) 115042
3.3. Syntheses
Preparation of KTp’ [31], Tp’Rh(CNR)(g
2-PhN = CNR) (1) [32],
Tp’Rh(C H
2 4
)
2
2 4 2
[33], Tp’Ir(C H ) [34], and neopentylisocyanide (L)
[
35] have been previously reported.
3.4. Instrumentation
1
All H NMR spectra were recorded on a Bruker AMX400 or Bru-
ker AVANCE400 spectrometer and referenced using chemical shifts
of residual solvent resonances (C , d 7.16). TEM imaging was ran
on a FEI Tecnai F20 G2 scanning transmission electron microscope
S)TEM. All XRD data was collected using a Rigaku XtaLAB Synergy
diffraction system using Mo/Cu radiation.
6 6
D
(
Scheme 1. Substrate scope. areaction run with 4 equiv of benzene at 100 °C for
2
equiv of anisole at 100 °C for 24 h, NMR yield of meta and para products vs.
2
3
.5. Photolytic borylation of benzene using Tp’Rh(CNR)(
g -PhN = CNR)
4 h. breaction run with 18 equiv of toluene at 115 °C for 21 h. reaction run with 20
c
(
1) as the catalyst (Table 1, entry 1)
dimethylsulfone as the internal standard.
A J. Young NMR tube was charged with 2.5 mg (0.0036 mmol,
5
mol %) of 1 and dissolved in 1.5 mL (16.8 mmol, 230 equiv) of
2
.6. Conclusions
benzene. To the solution was added at once, 18.6 mg (0.073 mmol,
equiv) of B Pin . The sample was irradiated for 10 min at room
temperature, resulting in the bleaching of the bright yellow solu-
tion. Under inert conditions, 1 L of the solution was drawn into
a microsyringe and a GC trace was recorded immediately. The GC
trace showed only the starting B Pin and no formation of 5a. Irra-
1
2
2
In conclusion, four different trispyrazolylborate catalysts were
investigated for direct arene borylation. Catalysts 3 and 4 showed
the greatest reactivity out of all the catalysts, and further optimiza-
tion using catalyst 4 allowed for the direct borylation of benzene to
occur in 81% yield. Unfortunately, this methodology could not be
extended to functionalization of other arenes. A drastic drop in
yield is observed when simple functional groups are introduced,
and this system does not tolerate electron withdrawing substitu-
tion on the arene. Although trispyrazolylborate catalysts 3 and 4
are isoelectronic to their pentamethylcyclopentadienyl counter-
parts, the same reactivity is not observed, and nanoparticle cataly-
sis is indicated with rhodium. Also, complex 4 requires heating to
l
2
2
diation for an additional 5 h did not result in the formation of any
1
new products by GC. A H NMR spectrum of the mixture showed
6 5
Tp’Rh(CNR)(C H )H as the only metal complex.
2
3.6. Thermal borylation of benzene by B
PhN = CNR) (1) as the catalyst
2 2
Pin using Tp’Rh(CNR)(g -
A J. Young NMR tube was charged with 2.0 mg (0.0029 mmol,
5 mol %) of 1 and dissolved in benzene. B Pin /HBpin was then
added to the solution. The reaction was then heated in an oil bath
at 115 °C. A GC trace, using a 1 L aliquot of the solution, was taken
under inert conditions. No product was observed.
Table 1, entry 2) benzene, 1.5 mL (16.8 mmol, 284 equiv),
Pin , 15 mg (0.059 mmol, 1 equiv). Heated for 4 h, no consump-
tion of B Pin was observed by GC, and no peak corresponding to
1
00 °C to effect borylation, whereas one of the best systems
2
2
0
reported by Ishiyama, Miyaura, and Hartwig ([IrCl(COE)
di-t-butylbipyridine) operates at room temperature [29,30].
2
]
2
+ 4,4 -
l
(
B
2
2
3
. Experimental
.1. General
All operations were performed under a nitrogen atmosphere,
2
2
product 5a was observed. The solution was heated for an addi-
tional 24 h, showing no change.
3
(
Table 1, entry 3) benzene, 1.0 mL (11.2 mmol, 190 equiv),
HBpin, 7.5 mg (0.059 mmol, 1 equiv). Heated for 4 h, no consump-
tion of B Pin was observed by GC, and no peak corresponding to
either in a Vacuum Atmosphere Corporation Glove Box or on a high
vacuum line using modified Schlenk techniques.
2
2
product 5a was observed. The solution was heated for an addi-
tional 24 h, showing no change.
2
3.7. Borylation of benzene using Tp’Rh(CNR) (2) as the catalyst
3.2. Reagents
A J. Young NMR tube was charged with 2.3 mg (0.0040 mmol) of
2 and dissolved in benzene. B Pin /HBpin was then added to the
solution. The reaction was then heated in an oil bath. A GC trace,
using a 1 L aliquot of the solution, was taken under inert condi-
Benzene d
6
was purchased from the Cambridge Isotope Lab and
2
2
distilled under vacuum from dark purple solutions of benzophe-
none ketyl and stored in ampoules with Teflon sealed vacuum line
adaptors. Benzene and octane were purchased from Aldrich Chem-
ical Co. and distilled from dark purple solutions of benzophenone
ketyl (solvents for Table 1). Anhydrous benzene and toluene were
obtained from an Innovative Technology PS-MD-6 solvent purifica-
tion system and were degassed by freeze–pump–thaw cycles and
stored in a nitrogen glove box over 4Å molecular sieves (solvents
for Table 2 and substrate scope). n-heptane was purchased from
Sigma Aldrich and was degassed by freeze–pump–thaw cycles
and stored over 4Å molecular sieves. The following substrates were
used without further purification: chlorobenzene (Oakwood), ani-
sole (Sigma Aldrich), fluorobenzene (Sigma Aldrich)
l
tions as described in the text.
(Table 1, entry 4) benzene, 0.75 mL (8.39 mmol, 106 equiv),
B
2
Pin
2
, 20 mg (0.079 mmol, 1 equiv). Heated for 4 d at 110 °C,
Pin was observed in the GC trace, along
20% consumption of B
2
2
with a newly formed peak corresponding to product 5a. GCMS:
+
5a M , 204 m/z.
(Table 1, entry 5) benzene, 1.5 mL (16.8 mmol, 197 equiv),
HBpin, 11 mg (0.085 mmol, 1 equiv). Heated for 4 d at 115 °C,
50% consumption of HBpin was observed in the GC trace along
with a newly formed peak corresponding to product 5a. GCMS:
+
5a M , 204 m/z.
4

A.J. Vetter, T.A. DiBenedetto, M.D. Ritz et al.
Polyhedron 197 (2021) 115042
3
.8. Borylation of benzene by B
2
Pin
2
using Tp’Ir(C
2
H
)
4 2
(3) as the
(Table 2, entry 5) catalyst 4, 5 mg (5 mol %), benzene, 78.6 mL
(0.88 mmol, 4 equiv), HBpin, 31.9 mL (0.22 mmol, 1 equiv),
catalyst
1
00 °C. Spectroscopic data for product 5a matched the literature
[36].
(Table 2, entry 6) catalyst 4, 5 mg (5 mol %), benzene, 78.6 mL
A J. Young NMR tube was charged with 5.0 mg (0.0092 mmol,
mol %) of 3 and dissolved in benzene. B Pin /HBpin was then
added to the solution. The reaction was then heated in an oil bath.
5
2
2
(0.88 mmol, 4 equiv), HBpin, 31.9 mL (0.22 mmol, 1 equiv), 90 °C.
Spectroscopic data for product 5a matched the literature [36].
(Table 2, entry 7) catalyst 4, 7.3 mg (4 mol %), benzene, 35.7 mL
(0.4 mmol, 1 equiv), HBpin, 116 mL (0.8 mmol, 2 equiv), 100 °C.
Spectroscopic data for product 5a matched the literature [36].
(Table 2, entry 8) catalyst 4, 7.3 mg (4 mol %), benzene, 35.7 mL
(0.4 mmol, 1 equiv), HBpin, 58 mL (0.4 mmol, 1 equiv), 115 °C. Spec-
troscopic data for product 5a matched the literature [36].
(Table 2, entry 9) catalyst 4, 7.3 mg (4 mol %), benzene, 71.5 mL
(0.8 mmol, 2 equiv), HBpin, 58 mL (0.4 mmol, 1 equiv), 100 °C. Spec-
troscopic data for product 5a matched the literature [36].
(Table 2, entry 10) catalyst 4, 7.3 mg (4 mol %), benzene, 143 mL
(1.6 mmol, 4 equiv), HBpin, 58 mL (0.4 mmol, 1 equiv), 100 °C. Spec-
troscopic data for product 5a matched the literature [36].
(Table 2, entry 11) catalyst 4, 7.3 mg (4 mol %), benzene,
0.715 mL (8 mmol, 20 equiv), HBpin, 58 mL (0.4 mmol, 1 equiv),
115 °C. Spectroscopic data for product 5a matched the literature
[36].
A GC trace, using a 1
inert conditions.
lL aliquot of the solution, was taken under
(Table 1, entry 6) benzene, 1.5 mL (16.8 mmol, 91.2 equiv)
B
4
2
Pin
2
, 46.5 mg (0.183 mmol, 1 equiv). Heated for 24 h at 115 °C,
Pin was observed in the GC trace along
0% consumption of B
2
2
with a newly formed peak corresponding to product 5a. GCMS:
+
5
a M , 204 m/z.
Table 1, entry 7) benzene, 32.9 mL (0.368 mmol, 2 equiv),
Pin , 46.5 mg (0.183 mmol, 1 equiv), n-octane 1.5 mL (used as
Pin
2
(
B
2
2
solvent). Heated for 72 h at 120 °C, 95% consumption of B
2
was observed in the GC trace along with a newly formed peak cor-
+
responding to product 5a. GCMS: 5a M , 204 m/z.
(
Table 1, entry 8) benzene, 1.5 mL (16.8 mmol, 93.2 equiv),
HBpin, 23 mg (0.180 mmol, equiv), catalyst 3, 4.9 mg
0.009 mmol, 5 mol %). Heated for 3 h at 115 °C, 50% consumption
1
(
of HBpin was observed in the GC trace along with a newly formed
+
peak corresponding to product 5a. GCMS: 5a M , 204 m/z.
(
Table 2, entry 12) catalyst 4, 3.6 mg (2 mol %), benzene, 143 mL
1.6 mmol, 4 equiv), HBpin, 58 mL (0.4 mmol, 1 equiv), 100 °C. Spec-
troscopic data for product 5a matched the literature [36].
Table 2, entry 13) catalyst 4, 7.3 mg (4 mol %), benzene, 107 mL
(
2 4 2
3.9. Borylation of benzene using Tp’Rh(C H ) (4).
(
In a glovebox a J. Young NMR tube was charged with catalyst 4,
benzene and borylating reagent (HBpin/B Pin ). The reaction was
(1.2 mmol, 3 equiv), HBpin, 58 mL (0.4 mmol, 1 equiv), 100 °C. Spec-
troscopic data for product 5a matched the literature [36].
(Table 2, entry 14) catalyst 4, 7.3 mg (4 mol %), benzene,
0.715 mL (8.0 mmol, 20 equiv), HBpin, 58 mL (0.4 mmol, 1 equiv),
a drop of Hg, 100 °C. The Hg drop test was run using the same gen-
eral procedure and workup described in the previous entries. Spec-
troscopic data for product 5a matched the literature [36].
2
2
then removed from the glovebox and placed in a metal heating
block for 24 h. After 24 h, the reactions were allowed to cool to
room temperature. Once cool, the reactions were diluted with
dichloromethane (1 mL) and transferred to a scintillation vial. An
additional 9 mL of dichloromethane was used to rinse the NMR
tube and the washings were added to the scintillation vial. A GCMS
of the crude reaction mixture was then recorded. The reaction was
then worked up using a celite/silica plug. The plug was made out of
a 30 mL syringe with a needle on the bottom. A glass fiber filter
was placed in the bottom of the syringe and 10 mL of celite was
added; the celite was packed with dichloromethane. Silica (3 mL)
was added on top of the celite (to remove the decomposed cata-
lyst) and was also packed with dichloromethane. The reaction mix-
ture was then loaded onto the plug and the product was eluted
with 200 mL of dichloromethane. The product was concentrated
on a rotovap and further dried under vacuum overnight.
2 4 2
3.10. Functionalization of toluene using Tp’Rh(C H ) (4)
Catalyst 4, 6.1 mg (3.9 mol %), toluene, 0.667 mL (6.27 mmol, 18
equiv), HBpin, 50 mL (0.344 mmol, 1 equiv), 115 °C, 21 h. Benzyl
1
and ortho products were too small to be observed by H NMR spec-
troscopy.
4,4,5,5-Tetramethyl-2-m-tolyl-1,3,2-dioxaborolane:
Spectroscopic data for the meta product of 6a matched the litera-
1
3
ture [36] H NMR (400 MHz, CDCl ) d 7.67 (s, 1H), 7.64 (t,
For reactions with an NMR yield the same workup was fol-
lowed. Then once the reaction was fully concentrated, dimethyl-
sulfone was added as an internal standard before taking the NMR
spectrum.
J = 4.4 Hz, 1H), 7.18–7.22 (m, 2H), 2.38 (s, 3H) 1.36 (s, 12H).
4,4,5,5-Tetramethyl-2-p-tolyl-1,3,2-dioxaborolane: Spectroscopic
data for the para product of 6a matched the literature [36]. 1
H
3
NMR (400 MHz, CDCl ) d 7.73 (d, J = 7.6 Hz, 2H), 7.29–7.30 (m,
(
Table 2, entry 1) catalyst 4, 5 mg (5 mol %), benzene, 1.5 mL
16.8 mmol, 76.3 equiv), B Pin , 55.8 mg (0.22 mmol, 1 equiv).
15 °C. Spectroscopic data for product 5a matched the literature
2H), 2.38 (s, 3H) 1.37 (s, 12H).
(
1
[
2
2
1
36] H NMR (400 MHz, CDCl
J = 7.2 Hz, 1H), 7.37 (t, J = 7.2 Hz, 2H), 1.35 (s, 12H).
Table 2, entry 2) catalyst 4, 5 mg (5 mol %), benzene, 9.8 mL
0.11 mmol, 0.5 equiv), B Pin , 55.8 mg (0.22 mmol, 1 equiv), n-
heptane 1.5 mL (solvent), 115 °C. Spectroscopic data for product
a matched the literature [36].
Table 2, entry 3) catalyst 4, 5 mg (5 mol %), benzene, 39.3 mL
0.44 mmol, 2 equiv), B Pin , 55.8 mg (0.22 mmol, 1 equiv), n-hep-
3
) d 7.81 (d, J = 6.8 Hz, 2H), 7.46 (t,
2 4 2
3.11. Functionalization of anisole using Tp’Rh(C H ) (4)
(
(
2
2
Catalyst 4, 7.3 mg (4 mol %), anisole, 0.869 mL (8.0 mmol, 20
equiv), HBpin, 58 mL (0.4 mmol, 1 equiv), 100 °C. Ortho product
was too small to be observed by H NMR spectroscopy. 2-(4-meth-
1
5
(
oxyphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane:
Spectro-
(
2
2
scopic data for the para product of 7a matched the literature
1
tane 1.5 mL (solvent), 115 °C. Spectroscopic data for product 5a
3
[37]. H NMR (400 MHz, CDCl ) d 7.76 (d, J = 8.7 Hz, 2H), 6.90 (d,
matched the literature [36].
J = 8.7 Hz, 2H), 3.83 (s, 3H), 1.35 (s, 12H). 2-(3-methoxyphenyl)-
4,4,5,5-tetramethyl-1,3,2-dioxaborolane: Spectroscopic data for
the meta product of 7a matched the literature [38]. 1H NMR
(
Table 2, entry 4) catalyst 4, 5 mg (5 mol %), benzene, 1.5 mL
16.78 mmol, 76.3 equiv), HBpin, 31.9 mL (0.22 mmol, 1 equiv),
15 °C. Spectroscopic data for product 5a matched the literature
36].
(
1
[
(400 MHz, CDCl
3
) d 7.45 – 7.20 (m, 3H), 7.08 – 6.91 (m, 1H), 3.83
(s, 3H), 1.35 (s, 12H).
5

A.J. Vetter, T.A. DiBenedetto, M.D. Ritz et al.
Polyhedron 197 (2021) 115042
3.12. Preparation of nanoparticle samples
Appendix A. Supplementary data
In a glovebox a J. Young NMR tube was charged with catalyst 4,
.3 mg (4 mol %), benzene, 143 mL (1.6 mmol, 4 equiv), and HBpin,
8 mL (0.4 mmol, 1 equiv). The reaction was then removed from the
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.poly.2021.115042.
7
5
glovebox and placed in a metal heating block at 100 °C for 24 h.
Atmospheric work-up. In a separate experiment, after 24 h, the
reaction was allowed to cool to room temperature. Once cool, the
reaction was diluted with dichloromethane (1 mL) and transferred
to a scintillation vial open to the atmosphere. An additional 9 mL of
dichloromethane was used to rinse the NMR tube and the wash-
ings were added to the scintillation vial. The crude reaction mix-
ture was then added in 1 mL aliquots to an Eppendorf tube and
spun down in a centrifuge for 5 mins. Once finished, the mother
liquor was decanted and more crude reaction mixture was added.
When all of the reaction mixture had been spun down, 1 mL ali-
quots of DCM were added, centrifuged down, and then decanted
off 3 separate times to wash the pellet completely.
Air free work-up. In a separate experiment, after 24 h, the reac-
tion was allowed to cool to room temperature. Once cool, the reac-
tion was brought back into the gloveback and diluted with
dichloromethane (1 mL) and transferred to a scintillation vial. An
additional 9 mL of dichloromethane was used to rinse the NMR
tube and the washings were added to the scintillation vial. The
crude reaction mixture was then added in 1 mL aliquots to an
Eppendorf tube, brought outside the glovebox spun down in a cen-
trifuge for 5 mins. Once finished, the Eppendorf was returned to
the glovebox, the mother liquor was decanted off and more crude
reaction mixture was added. The Eppendorf was then brought out-
side of the glovebox to be spun down in the centrifuge again. When
all of the reaction mixture had been centrifuged, 1 mL aliquots of
DCM were added 3 separate times inside the glovebox, centrifuged
down outside the glovebox, and decanted off inside the glovebox to
wash the pellet completely.
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