Synthesis of catechol-, pinacol-, and neopentylglycolborane through the heterogeneous catalytic B-B hydrogenolysis of diboranes(4)

Article abstract of DOI:10.1002/chem.201302677

A new synthetic approach to hydroboranes catechol-, pinacol-, and neopentylglycolborane has been developed. Starting from diboranes(4) B ₂cat₂, B₂pin₂, or B ₂neop₂, the respective boranes were obtained by heterogeneously catalyzed cleavage of the B-B bond in the respective diboranes with hydrogen. Group10 metals were found to be effective catalysts for this reaction. Copyright

Full text of DOI:10.1002/chem.201302677

FULL PAPER
DOI: 10.1002/chem.201302677
Synthesis of Catechol-, Pinacol-, and Neopentylglycolborane through the
À
Heterogeneous Catalytic B B Hydrogenolysis of Diboranes(4)
[a]
Holger Braunschweig,* Frank Guethlein, Lisa Mailꢀnder, and Todd B. Marder*
Abstract: A new synthetic approach to hydroboranes catechol-, pinacol-, and neo-
pentylglycolborane has been developed. Starting from diboranes(4) B cat , B pin ,
Keywords: boron · cleavage reac-
tions · diboranes · heterogeneous
catalysis · hydrogenolysis
2
2
2
2
or B neop , the respective boranes were obtained by heterogeneously catalyzed
2
2
cleavage of the BÀB bond in the respective diboranes with hydrogen. Group 10
metals were found to be effective catalysts for this reaction.
Introduction
the BH moiety remains in the reaction product, whilst the
3
other two are lost as gaseous H . HBcat can also be ob-
2
As organoboronate esters grow in importance, owing to
their great utility in organic synthesis, interest in the re-
agents that are used in borylation reactions has increased
accordingly. Hydroboranes are commonly used compounds
tained from a ligand-scrambling reaction between B cat
2
3
[5]
and B H or BH ÀLewis base adducts.
2
6
3
Hydroboranes, such as HBcat and HBpin, are known to
[4b]
be air- and moisture-sensitive compounds
and they de-
[1]
in functionalization reactions, such as hydroboration, the
compose through disproportionation over time, even if they
are stored at low temperatures under an inert atmosphere.
Hydrogenolysis of the respective diboranes(4) could repre-
sent an attractive in situ method for the synthesis of hydro-
boranes to avoid such decomposition issues. This reaction
would make stable, solid diboranes simple synthons for hy-
droboranes.
[2]
borylation of arylhalides, and the catalytic CÀH activation
[3]
of aromatic hydrocarbons, alkenes, or even alkanes. By far
the most prominent of these hydroboranes are catecholbo-
ACHTUNGTRENNUNGr ane (HBcat) and pinacolborane (HBpin). The standard
synthesis of these boranes involves the reaction of BH À
3
Lewis-base adducts, such as BH ÀTHF or BH ÀSMe , with
3
3
2
[4]
the respective diol, that is, pinacol or catechol (Scheme 1).
A reductive procedure for the synthesis of diboranes was
first published by Brotherton et al. and Nçth and Meister in
the early 1960s and it has been improved and optimized a
number of times since then, thereby making these com-
During this reaction, only one of the reactive hydrides on
[6]
pounds available on a large scale. We recently developed a
new route to diboranes(4) that proceeded through a dehy-
drocoupling reaction under hetero- or homogeneous cataly-
[7]
sis. This development was based on the earlier observa-
tions of Marder and co-workers of the catalytic formation of
small amounts of B pin during the rhodium-catalyzed boryl-
2
2
[3e]
AHCTUNGTRENNUNG
[8]
by mechanistic studies, led us to attempt the synthesis of
hydroboranes through the hydrogenolysis of diboranes(4)
(
Scheme 2).
Scheme 1. Currently employed syntheses of HBcat and HBpin.
[
a] Prof. Dr. H. Braunschweig, Dr. F. Guethlein, L. Mailꢀnder,
Prof. Dr. T. B. Marder
Institut fꢁr Anorganische Chemie
Julius-Maximilians-Universitꢀt Wꢁrzburg
Am Hubland, 97074 Wꢁrzburg (Germany)
E-mail: h.braunschweig@mail.uni-wuerzburg.de
todd.marder@uni-wuerzburg.de
Scheme 2. Synthesis of HBcat, HBpin, and HBneop through the hydro-
genolysis of diboranes.
A
H
U
G
E
N
N
ACHTUNGTRENNUNG
Chem. Eur. J. 2013, 19, 14831 – 14835
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
14831

The hydrogenative cleavage of EÀE bonds has been dem-
onstrated in a number of different systems. Reactive GaÀ
Ga, InÀIn, and AlÀAl bonds can be broken without transi-
Table 1. Synthesis of HBcat and HBpin with Pt/C as a catalyst; reactions
were carried out in toluene, unless otherwise stated.
Entry Borane Catalyst loading
[mol%]
H
2
pressure
[bar]
T
t
TON
[9]
[8C] [h] (GC)
tion-metal (TM) catalysts, as can EÀE bonds in digermyl-
[10]
1
2
3
4
5
6
7
8
9
0
HBcat
HBpin
2.5
2.5
1
1
5
5
1
1
1
5
5
5
80
80
80
80
80
80
80
80
80
80
1
5
1
5
1
5
5
1
5
5
2
4
4
13
8
ACHTUNGTRENNUNGe nes and distannylenes. An example of the cleavage of a
more-stable EÀE bond is the hydrogenolysis of ClMe SiÀ
2
SiMe Cl. The SiÀSi bond is broken under homogeneous cat-
2
[11]
alytic conditions with [Pt
A
H
U
G
R
N
U
G
A
3
4
2
very similar reaction to the intended hydrogenolysis of
B cat /B pin is the deuterolysis of B pin reported by Hart-
15
10
11
21
18
[
a]
2
2
2
2
2
2
wig and co-workers. In that case, DBpin was generated in a
homogenous catalytic reaction with an iridium catalyst;
however, this technique was used only in one instance and
[a]
1
[
a] THF was used as the solvent.
[12]
was not developed further.
Hartwig et al. reported that the reductive elimination of
HBpin from [CpRhH (Bpin) ] was favored over the elimina-
A
H
U
G
R
N
U
G
measurements confirmed the formation of trace amounts of
2
2
[13]
+
tion of B pin .
Thus, we reasoned that the equilibrium
HBcat (m/z: 120 [M] ), which corresponded to a very small
2
2
should lead to the respective hydroborane on the introduc-
tion of dihydrogen gas to diboranes(4). Herein, we present
our results concerning the synthesis of hydroboranes Bpin,
HBcat, and HBneop through the hydrogenolysis of the BÀB
TON of 2. Prolonging the reaction time to 5 h doubled the
TON to 4. Under higher H pressure (5 bar), TONs of 4
2
(1 h) and 13 (5 h) were obtained.
For the synthesis of HBpin, slightly better results were ob-
tained with Pt/C (Table 1, entries 5–10). On heating the re-
bonds in their respective B (OR) compounds under hetero-
2
4
geneous catalysis.
action at 808C under 1 bar H pressure in toluene, the TON
2
was 8 after 1 h and 15 after 5 h. By increasing the hydrogen
pressure to 5 bar, the TON was improved to 11 (1 h) and 21
(5 h). The formation of HBpin was confirmed by the appear-
Results and Discussion
[4c,d]
ance of a doublet at d=28.4 ppm (J=173 Hz)
in the
1
1
Because our best dehydrocoupling results were obtained by
using heterogeneous Group 10 catalysts, such as platinum or
palladium, on charcoal or aluminum oxide,
B NMR spectra and by GCMS measurements (m/z: 128
+
[M] ). Because of its superior solubility, B pin could also be
2
2
[7a,b]
we used
reacted with H in other solvents; for example, reaction in
2
these catalysts in our initial attempts at the hydrogenolysis
of diboranes(4). These catalysts had the additional benefit
of being easily removable and reusable after the reaction.
For proof of principle, the catalyst was added in quite large
amounts (2–3 mol%) to a suspension of the diborane in tol-
uene. After degassing the mixture, hydrogen gas was intro-
duced and the pressure, reaction temperature, and reaction
time were varied. The reaction was monitored by GCMS
THF gave similar TONs (Table 1, entries 7 and 10).
In addition to the doublet signal for HBcat (29 ppm) and
[14]
the signal for B cat (30 ppm), another broad signal at d=
2
2
22 ppm was detected in every spectrum, which we assumed
to be the decomposition product B cat , as well as trace
2
3
[5b,15,16]
amounts of catBOBcat and/or HOBcat.
The genera-
tion of these side products is well-documented in cases in
which these diboranes and boranes are exposed to harsh re-
action conditions. The longer the reaction solutions were
11
and by B NMR spectroscopy; the latter technique con-
firmed the formation of the respective hydroborane by the
appearance of a doublet signal. Initial qualitative evaluation
of the progress of the reaction was made by assessment of
the relative intensities of the signals of the diborane, the
borane, and the decomposition products. The turnover num-
bers (TONs) were estimated by using GCMS measurements.
Our first attempts were performed by using Pt on alumi-
num-oxide pellets, which we had previously found to be the
most-effective catalyst for the synthesis of diborane(4). Be-
cause the reaction of B cat at 808C under 1 bar H pressure
stirred at 808C and the higher the H pressure, the more of
2
these side products that were formed. The same observa-
tions were made for the pinacol derivative. Aside from the
doublet signal for HBpin (d=28 ppm) and B pin (d=
2
2
[6d]
30 ppm),
a broad signal, which corresponded to B pin ,
2 3
pinBOBpin, and/or HOBpin, was observed at d=
[16,17]
21 ppm.
To improve on these results, analogous palladium catalysts
were applied to these reactions (Table 2). Under the same
conditions as implemented for Pt on charcoal, palladium on
charcoal gave much-better results for both boranes.
2
2
2
in toluene showed no formation of borane after 5 h or even
after a prolonged reaction time with a higher catalyst load-
ing, we used Pt on charcoal (10 wt.% Pt, 2.5 mol%) to in-
crease the surface area that was available for the reaction
and to ensure better mixing of the reactants (Table 1,
entry 1–4). After stirring for 1 h at 808C under an atmos-
1
1
B NMR spectra of the reaction solution showed the quan-
titative transformation of diborane into borane. After stir-
ring for 1 h at 808C with 1 bar H in toluene, a tenfold-
2
higher TON (48) was found for HBcat compared to the cor-
responding Pt-catalyzed reaction. A signal for B cat2 was
2
pheric pressure of H in toluene, a weak doublet signal at
d=28.8 ppm (J=192 Hz) was detected for HBcat. GCMS
not detected by GC. Longer reaction times decreased the
TON, owing to the increased formation of side products.
2
[5b]
14832
www.chemeurj.org
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 14831 – 14835

Synthesis of Catechol-, Pinacol-, and Neopentylglycolborane
FULL PAPER
Table 2. Synthesis of HBpin and HBcat with Pd/C as a catalyst; reactions
were carried out in toluene, unless otherwise stated.
Table 4. Synthesis of HBcat, HBpin, and HBneop with Pd/C.
[a]
Entry Borane
Catalyst loading
[mol%]
H
2
pressure
[bar]
T
t
TON
Entry Borane Catalyst loading
H
2
pressure
[bar]
T
t
TON
[8C] [h]
[mol%]
[8C] [h] (GC)
[b]
1
2
3
HBcat
HBpin
HBneop
0.27
0.18
0.41
1
1
1
RT
RT
80,
RT
21 196
20 504
13,
30
[
b]
1
2
3
4
5
6
7
8
9
0
1
HBcat
HBpin
2.5
1
1
1
5
5
1
1
1
1
5
5
40
80
80
40
80
40
80
80
80
40
80
1
1
5
1
1
1
1
5
5
1
1
32
48
44
32
35
24
24
31
0
[c]
86
[
[
a] TON for the isolated borane. [b] Pentane was used as the solvent.
c] Benzene was used as the solvent.
2.5
[
a]
After stirring the suspension for 21 h at room temperature
under a hydrogen atmosphere (1 bar) with a catalyst loading
of only 0.27 mol%, HBcat was isolated by distillation, with
a TON of 196. Hartwig’s synthesis of DBpin through the ho-
mogeneous Ir-catalyzed deuteration of B pin with the same
1
1
27
33
[
a] THF was used as the solvent.
2
2
[12]
When the temperature was lowered to 408C, a TON of 32
was obtained after 1 h. Performing the hydrogenolysis reac-
tion at higher H2 pressures (5 bar) did not improve the
TONs.
Comparable results were obtained for the synthesis of
HBpin (Table 2, entries 6–11). Under a H2 atmosphere
catalyst loading gave a TON of 155. HBpin could also be
isolated in the same way. Stirring B pin in pentane for 20 h
2
2
under a H atmosphere with Pd/C allowed HBpin to be ob-
2
tained by distillation. The TON reached 504 with a catalyst
loading of 0.18 mol%. This result was more than twice as
high as that for HBcat and more than three times higher
[12]
(
1 bar) at 408C, a TON of 24 was obtained for the hydro-
than for the synthesis of DBpin by deuterolysis.
Similarly, bis(neopentylglycolato)diborane(4)
was examined for cleavage of its BÀB bond by hy-
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
genolysis of B pin in toluene after 1 h. The same TON was
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(B2-
2
2
[14a]
obtained when the temperature was increased to 808C and
prolonging the reaction time to 4 h caused the TON to in-
crease to 31. When THF was used as the solvent for the syn-
thesis of HBpin, only decomposition products, which were
presumably due to ring-opening of the THF, were observed,
whereas the reaction in n-hexane afforded comparable
TONs to those in toluene.
ACHTUNGTRENNUNGn eop )
2
[
18]
drogenolysis to form neopentylglycolborane (HBneop).
Reaction of B neop in toluene for 1–5 h under a hydrogen
2
2
atmosphere of 1 bar at 808C in the presence of Pt/C or Pd/C
resulted in a doublet signal at d=25.6 ppm (J=172 Hz) in
1
1
the B NMR spectra. GCMS measurements also confirmed
+
the formation of HBneop (m/z: 114 [M] ). The synthesis of
To complete the comparison of Group 10 metals, Raney
nickel was applied as a heterogeneous catalyst in the BÀB
HBneop was more successful with Pd as the catalyst than
with Pt, as already observed for the synthesis of HBcat and
1
1
hydrogenolysis reaction (Table 3). Thus, Raney nickel
HBpin. However, the B NMR spectra indicated that the
transformation of HBneop proceeded much more slowly
than those of HBcat and HBpin. HBneop was isolated by
using Pd/C as the catalyst (Table 4, entry 3). Because
B neop was not very soluble in either pentane or n-hexane,
Table 3. Synthesis of HBpin and HBcat catalyzed by Raney nickel; reac-
tions were carried out in toluene.
2
2
Entry Borane Catalyst loading
H
2
pressure
[bar]
T
t
TON
benzene was used as the solvent. After stirring the solution
for 13 h at 808C and then for 30 h at room temperature
under a hydrogen atmosphere of 1 bar, HBneop was ob-
tained. At a catalyst loading of 0.41 mol%, the TON was
[mol%]
[8C] [h] (GC)
1
2
HBcat
HBpin
5.50
4.30
1
1
80
80
5
5
10
3
8
6.
(
92 wt.% Ni) and the respective diborane(4) were stirred in
toluene for 5 h at 808C under 1 bar hydrogen pressure.
B NMR analysis indicated that both reactions produced
Conclusion
11
the desired hydroborane products. The TONs were compa-
rable to those with Pt/C, but, because Raney Ni is much
more sensitive towards water and air, the other two
Group 10 metals were preferred as catalysts for this reac-
tion.
To demonstrate the applicability of this reaction, the syn-
theses of HBcat and HBpin were conducted on a larger
scale with palladium on charcoal as the catalyst (Table 4).
Owing to the very similar boiling points of toluene and
HBcat, pentane was used for the synthesis of this borane.
We have shown that the synthesis of hydroboranes, such as
HBcat and HBcat, is possible through the hydrogenolysis of
diboranes(4) under heterogeneous catalysis. All of the
Group 10 catalysts (Pt/C, Pd/C, Raney Ni) that were tested
were able to catalyze the hydroborane formation. For Pt/C
and Raney Ni, only low TONs were obtained. The most-
active catalyst for this reaction by far was palladium on
charcoal, with which the boranes could be synthesized under
mild conditions (room temperature, atmospheric H2 pres-
sure). Reactions on a larger scale were carried out by using
Chem. Eur. J. 2013, 19, 14831 – 14835
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14833

H. Braunschweig, T. B. Marder et al.
this catalyst and all three boranes (HBcat, HBpin, HBneop)
were isolated as pure materials. The TONs were estimated
to be 196 for HBcat, 504 for HBpin, and 86 for HBneop.
lowed by 19 h at RT. After degassing the solution again, another portion
of H gas (1 bar) was introduced. After stirring for 13 h at 908C and 32 h
2
at RT, Pd/C was separated from the solution and the solvent was re-
moved by distillation under an argon atmosphere (1 bar). HBneop
(
(
429 mg, 3.76 mmol, 18% yield) was obtained as a clear, colorless liquid
1
b.p. 1028C) with a TON of 86 (Table 4, entry 3). H NMR (400.1 MHz,
1
C
6
D
6
): d=0.51 (s, 6H), 3.20 (s, 4H), 4.51 ppm (br q, J=172 Hz, 1H);
Experimental Section
1
1
1
6 6
B NMR (128.4 MHz, C D ): d=25.6 ppm (d, J=172 Hz; BH); MS
+
(
EI): m/z: 114 [M] .
General procedures and materials: Reactions were carried out under a
dry argon atmosphere by using standard Schlenk techniques. Reactions
under increased H pressure were carried out in an autoclave that was
2
purchased from BASF. The solvents were dried by distillation over ap-
propriate drying agents and stored over molecular sieves. Diboranes(4)
were provided by AllyChem Co. Ltd. and used without further purifica-
tion. Pd/C and Pt/C were purchased from commercial suppliers and
Acknowledgements
We are grateful to the Deutsche Forschungsgemeinschaft (DFG) and the
Fonds der Chemischen Industrie (FCI) for financial support. L.M. thanks
the FCI for a doctoral scholarship. The generous gift of diboranes from
AllyChem Co. Ltd. is also gratefully acknowledged.
[
19]
Raney nickel was synthesized according to a literature procedure. Hy-
drogen gas was purchased from Linde (purityꢀ99.9992%). NMR spectra
1
were recorded on
4
a
Bruker Avance 400 NMR spectrometer ( H:
1
1
00.130 MHz, B: 128.385 MHz). Chemical shifts are given in ppm and
are referenced to internal Me Si ( H) and BF ·OEt ( B). Turnover num-
4 3 3
1
11
[
1] a) H. C. Brown, J. Chandrasekharan, J. Org. Chem. 1983, 48, 5080–
bers were determined by GCMS analysis on an Agilent Technologies
GCMS system (GC 7890A, MSD 5975 C) with n-dodecane as an internal
standard.
5
1
082; b) K. Burgess, M. J. Ohlmeyer, Chem. Rev. 1991, 91, 1179–
191; c) S. A. Westcott, H. P. Blom, T. B. Marder, R. T. Baker, J.
Am. Chem. Soc. 1992, 114, 8863–8869; d) K. Burgess, W. A. Van der
Donk, S. A. Westcott, T. B. Marder, R. T. Baker, J. C. Calabrese, J.
Am. Chem. Soc. 1992, 114, 9350–9359; e) I. Beletskaya, A. Pelter,
Tetrahedron 1997, 53, 4957–5026; f) C. M. Crudden, D. Edwards,
Eur. J. Org. Chem. 2003, 4695–4712.
General procedure for the synthesis of HBcat with Pd/C or Pt/C: B
Pd/C or Pt/C (10 wt.%, 10–20 mmol, 2–3 mol%), and n-dodecane were
suspended in toluene (8 mL). After degassing the mixture, H gas (1 or
bar) was introduced and the mixture was stirred for several hours at
the chosen temperature (Table 1 and Table 2). The formation of HBcat
2 2
cat ,
2
5
1
1
[2] a) M. Murata, S. Watanabe, Y. Masuda, J. Org. Chem. 1997, 62,
458–6459; b) M. Murata, T. Oyama, S. Watanabe, Y. Masuda, J.
was confirmed by GCMS, as well as by B NMR spectroscopy.
6
2 2
General procedure for the synthesis of HBcat with Raney Ni: B cat ,
Org. Chem. 1999, 65, 164–168; c) O. Baudoin, D. Guꢃnard, F. Guꢃ-
ritte, J. Org. Chem. 2000, 65, 9268–9271; d) K. C. Lam, T. B.
Marder, Z. Lin, Organometallics 2010, 29, 1849–1857.
Raney Ni (92 wt.%, 70 mmol, 15 mol%), and n-dodecane were suspended
in toluene (8 mL). After degassing the mixture, H gas (1 or 5 bar) was
2
introduced and the mixture was stirred for 1–5 h at 40 or 808C (Table 3).
[
3] a) S. A. Westcott, T. B. Marder, R. T. Baker, Organometallics 1993,
The formation of HBcat was confirmed by GCMS measurements, as well
1
9
2, 975–979; b) S. Pereira, M. Srebnik, J. Am. Chem. Soc. 1996, 118,
09–910; c) M. Murata, T. Oyama, S. Watanabe, Y. Masuda, J. Org.
1
1
as by B NMR spectroscopy.
Isolation of HBcat: cat
9.7 mg, 27.9 mmol, 0.27 mol%) were suspended in pentane (15 mL).
After degassing the mixture, H gas (1 bar) was introduced and the mix-
B
2
2
(2.50 g, 10.5 mmol) and Pd/C (10 wt.%,
Chem. 2000, 65, 164–168; d) H. Chen, S. Schlecht, T. C. Semple, J. F.
Hartwig, Science 2000, 287, 1995–1997; e) S. Shimada, A. S. Batsa-
nov, J. A. K. Howard, T. B. Marder, Angew. Chem. 2001, 113, 2226–
2229; Angew. Chem. Int. Ed. 2001, 40, 2168–2171; f) J.-Y. Cho, K.
Tse Man, D. Holmes, R. E. Maleczka, Jr., M. R. Smith III, Science
2002, 295, 305–308; g) I. A. I. Mkhalid, R. B. Coapes, S. N. Edes,
D. N. Coventry, F. E. S. Souza, R. L. Thomas, J. J. Hall, S.-W. Bi, Z.
Lin, T. B. Marder, Dalton Trans. 2008, 0, 1055–1064; h) I. A. I.
Mkhalid, J. H. Barnard, T. B. Marder, J. M. Murphy, J. F. Hartwig,
Chem. Rev. 2010, 110, 890–931.
2
2
ture was stirred for 21 h at RT. Pd/C was separated from the solution and
the solvent was removed by distillation under an argon atmosphere
(
1 bar). HBcat (700 mg, 5.47 mmol, 26% yield) was obtained as a clear,
colorless liquid (b.p. 120–1258C) with a TON of 196 (Table 4, entry 1).
1
1
6 6
H NMR (400.1 MHz, C D ): d=4.57 (br q, J=192 Hz, 1H), 6.98 (m,
1
1
2
H), 6.75 ppm (m, 2H); B NMR (128.4 MHz, C D ): d=28.8 ppm (d,
6 6
1
+
J=192 Hz; BH); MS (EI): m/z: 120 [M] .
General procedure for the synthesis of HBpin with Pd/C or Pt/C: HBpin
[4] a) H. C. Brown, S. K. Gupta, J. Am. Chem. Soc. 1971, 93, 1816–
1818; b) H. C. Brown, S. K. Gupta, J. Am. Chem. Soc. 1975, 97,
5249–5255; c) C. E. Tucker, J. Davidson, P. Knochel, J. Org. Chem.
was prepared as described above for HBcat, by using B
ing material (Table 1 and Table 2).
2 2
pin as the start-
1
992, 57, 3482–3485; d) T. Kikuchi, Y. Nobuta, J. Umeda, Y. Yama-
Synthesis of HBpin with Raney Ni: HBpin was prepared as described
above for HBcat, by using B pin as the starting material (Table 3).
Isolation of HBpin: B pin (2.00 g, 7.74 mmol) and Pd/C (10 wt.%,
5.2 mg, 14.4 mmol, 0.18 mol%) were suspended in pentane (15 mL).
After degassing the mixture, H gas (1 bar) was introduced and the mix-
moto, T. Ishiyama, N. Miyaura, Tetrahedron 2008, 64, 4967–4971.
5] a) D. Mꢀnnig, H. Nçth, J. Chem. Soc. Dalton Trans. 1985, 1689–
1
2
2
[
2
2
692; b) J. V. B. Kanth, M. Periasamy, H. C. Brown, Org. Process
1
Res. Dev. 2000, 4, 550–553.
2
[
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(
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1
1
H NMR (400.1 MHz, C
73 Hz, 1H); B NMR (128.4 MHz, C
6
D
6
): d=0.99 (s, 12H), 4.27 ppm (br q, J=
1
1
1
1
6
D
6
): d=28.4 ppm (d, J=173 Hz;
+
BH); MS (EI): m/z: 128 [M] .
[
General procedure for the synthesis of HBneop with Pd/C or Pt/C:
1
2824; Angew. Chem. Int. Ed. 2011, 50, 12613–12616; b) F. Gueth-
HBneop was prepared as described above for HBcat, by using B
as the starting material.
2 2
neop
lein, Dissertation, Julius-Maximilians Universitꢀt Wꢁrzburg, 2012;
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Isolation of HBneop: Bis(neopentylglycolato)diborane(4) (2.40 g,
0.6 mmol) and Pd/C (10 wt.%, 46.4 mg, 43.6 mmol, 0.41 mol%) were
suspended in benzene (27 mL). After degassing the mixture, H gas
1 bar) was introduced and the mixture was stirred for 4 h at 808C, fol-
1
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2
(
14834
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ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 14831 – 14835

Synthesis of Catechol-, Pinacol-, and Neopentylglycolborane
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2
cat
3
, catBOBcat, and HOBcat cannot be distinguished in the
1
1
2 3
B NMR spectra due to the broadened signal. B cat forms through
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Published online: September 20, 2013
Chem. Eur. J. 2013, 19, 14831 – 14835
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
14835