Efficient Water Reduction with sp3-sp3 Diboron(4) Compounds: Application to Hydrogenations, H–D Exchange Reactions, and Carbonyl Reductions

Article abstract of DOI:10.1002/anie.201709685

A series of crystalline sp³-sp³ diboron(4) compounds were synthesized and shown to promote the facile reduction of water with dihydrogen formation. The application of these diborons as simple and effective dihydrogen and dideuterium sources was demonstrated by conducting a series of selective reductions of alkynes and alkenes, and hydrogen–deuterium exchange reactions using two-chamber reactors. Finally, as the water reduction reaction generates an intermediate borohydride species, a range of aldehydes and ketones were reduced by using water as the hydride source.

Full text of DOI:10.1002/anie.201709685

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
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Accepted Article
Title: Efficient Water Reduction with sp3-sp3 Diboron(4) Compounds:
Application to Hydrogenations, H-D Exchange Reactions and
Carbonyl Reductions
Authors: Troels Skrydstrup, Mathias Flinker, Hongfei Yin, René Juhl,
Espen Eikeland, Jacob Overgaard, and Dennis Nielsen
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201709685
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10.1002/anie.201709685
Angewandte Chemie International Edition
COMMUNICATION
Efficient Water Reduction with sp3-sp3 Diboron(4) Compounds:
Application to Hydrogenations, H-D Exchange Reactions and
Carbonyl Reductions
Mathias Flinker, Hongfei Yin, René W. Juhl, Espen Z. Eikeland, Jacob Overgaard, Dennis U. Nielsen*
and Troels Skrydstrup*
Dedication: This paper is dedicated to the 50th anniversary of the Laboratoire Hétérochimie Fondamentale et Appliquée
Abstract: A series of crystalline sp3-sp3 diboron(4) compounds were
synthesized and shown to promote the facile reduction of water with
dihydrogen formation. The application of these diborons as simple
and effective dihydrogen and dideuterium sources was demonstrated
by conducting a series of selective reductions of alkynes and alkenes
and hydrogen-deuterium exchange reactions with two-chamber
reactors. Finally, as the water reduction reaction generates an
intermediate borohydride species, a range of aldehydes and ketones
could be reduced with water as the hydride source.
attributed to the role of the sp3-hybridized boron as the “sacrificial”
part of the diboron in boration chemistry. Nevertheless, these
types of compounds recently attracted our attention in attempts
for promoting the deoxygenation of CO2.[12] Although
unsuccessful in this respect,[13] we discovered that a series of
readily isolable and crystalline sp3-sp3 diboron(4) reagents proved
to be especially reactive for the reduction of water to dihydrogen.
As such we could exploit these reagents as a convenient and solid
dihydrogen source for the catalytic hydrogenation of a variety of
unsaturations, as well as D-H exchange reactions applying our
two-chamber technology. Furthermore, as an intermediate
borohydride reagent is formed in the initial reduction step, these
diboron reagents promote carbonyl reductions on a range of
aldehydes and ketones with water as the sole hydrogen source.
Recent years have witnessed a widespread increase for the
exploitation of sp2-sp2 diboron(4) reagents including B2pin2,
B2neop2 and B2cat2 (Figure 1) for 1,2- and 1,4-diborations, boryl
addition reactions, boryl substitutions and deoxygenations.[1]
Furthermore, several groups have demonstrated that the
combination of either B2(OH)4 or B2pin2 with water generates a
Pd-hydride species, which can be applied to the selective
hydrogenation of unsaturations.[2–4] Similarly, water was used as
a hydride source in Pd-catalyzed enantioselective reductive Heck
reactions applying B2(OH)4 or B2cat2.[5] There has been a growing
focus on the use of isolated sp2-sp3 diboron(4) compounds
(Figure 1).[6] Anionic adducts were extensively studied by Marder
and others, and used in boryl substitution reactions.[7] The
combined efforts of Santos and Marder prepared and investigated
a neutral sp2-sp3 diboron(4) compound (PDIPA) for the boration
of a,b-unsaturated carbonyls, whereby one of the two boron
atoms carries a diethanolamine linker.[8] And recently Aggarwal
sp2-sp2 diboron compounds
O
O
O
O
O
O
O
O
O
O
B
B
B B
B
B
O
O
B2pin2
B2neop2
B2cat2
sp2-sp3 diboron compounds
X
O
O
O
O
O
O
B
B
B
B
N
H
B B N
O
O
O
O
O
O
sp2-sp3 adduct
of B2pin2
PDIPA Diboron
pinacolato diisopropanol-
aminato diboron
PDTBMA Diboron
pinacolato ditertbutanol-
methylaminato diboron
(Marder)
(Santos)
(Aggarwal)
Figure 1. Common sp2-sp2 diboron(4) compounds (top) and recently reported
and co-workers reported on
a Rh-catalyzed Markovnikov
sp2-sp3 diboron adducts (bottom) applied in organic synthesis.
hydroboration of olefins employing a structurally similar sp2-sp3
diboron(4) (PDTBMA).[9,10]
In our initial attempts to prepare the sp3-sp3 diboron(4) 1 from
the reaction of tetrahydroxydiboron with diethanolamine in CH2Cl2
at 20 °C (Scheme 1), we immediately observed a change in the
heterogeneous mixture with first the disappearance of B2(OH)4
and then the appearance of a new crystalline material. After ca.
30 min of reaction time, gas evolution began, which was identified
as dihydrogen by GC-analysis. This was rationalized as a result
of H2O reduction by reaction between diboron 1 initially formed
and the expelled water upon its generation. Confirmation was
made by isolating 1 by filtration, and then resubmitting 1 to water,
resulting in immediate dihydrogen evolution. The structure of 1
was assigned to that depicted in Scheme 2, but indirect
confirmation was made by the following experiments. Due to its
low solubility in a variety of solvents, NMR characterization could
Whereas structurally different sp3-sp3 diboron(4) compounds
have been synthesized, their applications in organic synthesis
have not been investigated in great detail.[11] This can probably be
[*]
M. Flinker, Dr. H. Yin, R. W. Juhl, Dr. E. Z. Eikeland, Dr. J.
Overgaard, Dr. D. U. Nielsen, Prof. T. Skrydstrup
Carbon Dioxide Activation Center (CADIAC), Center for Materials
Crystallography (CMC), Department of Chemistry and the
Interdisciplinary Nanoscience Center (iNANO), Aarhus University
Gustav Wieds Vej 14, 8000 Aarhus C (Denmark)
E-mail: ts@chem.au.dk
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201709685
Angewandte Chemie International Edition
COMMUNICATION
Initial Results
HO
our two-chamber technology.[15] To test this approach, the
hydrogenation of ethyl cinnamate to ethyl 3-phenylpropanoate (4)
was examined to quantify the amount of H2 produced (See
Scheme 3).[16] An equimolar amount of diboron 1 to the olefin was
placed into one chamber with water, and the second chamber was
charged with the cinnamate and Pd/C in CPME/THF. Full
reduction to 4 was obtained after stirring for 18 h at 20 °C. A 3.5-
month-old sample of 1, which had been standing on the bench in
a closed vial, led to a similar activity (95% conversion to 4). The
reductions were set up in a glovebox, however, by simply flushing
the two-chamber system with argon prior to the reaction, the need
for a glovebox was not necessary providing only a slight drop in
the efficiency of the reduction (94% conversion).
O O
HO
HO
OH
OH
4 H2O
+
+
B
N
H
B
B
B
H
N
NH
CH2Cl2
20 o
O O
C
HO
2.0 equiv
1 (Formed in situ)
H2O
O O
Identified
by GC
H2
N
H
N
B
B
H
O O
1 (Isolated)
Scheme 1. a) Dihydrogen formation via water reduction with the sp3-sp3
diboron(4) compound formed in situ or as an isolated solid.
not be obtained. Nevertheless, suitable crystals for X-ray
structural analysis were obtained by recrystallization in hot
ethanol. Surprisingly, the crystal structure disclosed that each of
the diethanolamine ligands are bonded to both boron atoms in
fused 5- and 6-membered rings (compound 2, Scheme 2) instead
of the two fused 5-membered rings as in 1. This was unexpected
as the diboroxane remaining in the crude mixture after reaction of
the initial crystalline material with water, revealed only the
presence of two apparent broad triplets at 3.81 and 3.08 ppm in
the 1H NMR spectrum indicating a symmetrical molecule such as
1a. Furthermore, when diboron 2 was submitted to water, no
dihydrogen was formed, implying that compounds 1 and 2 are not
identical, but structural isomers. Hence, heating 1 in ethanol
resulted in rearrangement to the thermodynamically more stable
isomer 2.[8a,14] In order to suppress this rearrangement, the
bridged sp3-sp3 diboron(4) derivative 3 was prepared. X-ray
structural analysis of crystals obtained in ethanol revealed a
diboron structure without rearrangement. Importantly, subjecting
3 to water resulted in H2 formation, and the structure of the
diboroxane 3a was confirmed by HRMS and NMR analysis (See
Supporting Information).
Isolation of the sp3-sp3 diborons 5 and 6 bearing alkyl
substituents on the nitrogen (N-methyl- or N-n-butyl) was not
possible due to their high reactivity with the water generated in
their formation in comparison to diboron 1.[17] However, their
efficiency for dihydrogen production could be assessed by in situ
generation in toluene and subsequent reaction with water. On the
other hand, the use of the corresponding triamines led to isolation
of the crystalline sp3-sp3-diboron species 7–9. These too provided
Chamber A
H2O
Toluene
(HO)2B B(OH)2
X X
1.0 equiv
B
N
R
N
B
R
Method1
Method 2 RN(CH2CH2XH)2
X X
2.0 equiv
1 (1.0 equiv)
H2 (1.0 equiv)
H
O
O
Pd/C (10 wt%)
CPME, rt, 18 h
Chamber B
Ph
OEt
Ph
OEt
0.5 mmol
H
4
Isolated salt (Method 1)
In situ formation (Method 2)
O O
O O
O O
nBu
N
B
B
N nBu
N
H
N
B
B
N
B
B
N
H
O O
O O
O O
5 72%
6 96%
1 100%
a)
H2O H2
O
O
O O
O
B N H
H
N
B
NH HN
H
NH HN
B
B
N
NH HN
H
N
O
O
N
N
B
B
H
N
B
B
N
H
O O
B
N
H
H
N
B
1a
HN
NH
NH HN
NH HN
7 100%
Characterized by
HRMS and NMR
1
8 100%
9 100%
H
Limitations (Method 2)
H
N
N
H2O
O
EtOH
reflux
Ph
N
Bn
N
tBu
H2
B
O
B
O
N
HO
OH
OH
HO
HO
OH
OH
O
2
HO
HO
OH
OH
12
11
10
Ts
Boc
N
b)
N
O
HO
13
14
15
O
H2O H2
O
O O
S
N
B
O
B
N
B
B
N
HO
OH
N
HO
OH
16
17
O
O
O O
3a
Characterized by
HRMS and NMR
3
Limitations (Method 1)
O O
O
O
B
O
O
O
O
Scheme 2. Characterization of sp3-sp3 diborons 1 and 3 and the corresponding
diboroxanes 1a and 3a.
N
B
N
H
Si Si
N
B
B
O
O
O
O
O O
19
20
18
Intrigued by the reactivity of 1, we prepared a small library of
different diboron derivatives. We recognized that such
compounds, representing practical sources of H2 and D2 by
simple addition to either H2O or D2O, could be exploited for
carrying out a number of catalytic hydrogenations of alkenes and
alkynes, as well as H-D exchange reactions in combination with
Scheme 3. Evaluation of a range of sp3-sp3 diboron compounds for dihydrogen
formation from the reduction of water. Reaction conditions: Chamber A, Method
1: Diboron (0.5 mmol, 1.0 equiv) and H2O (2.0 mL) at 20 °C for 18 h. Chamber
A, Method 2: Tetrahydroxydiboron (44.8 mg, 0.5 mmol, 1.0 equiv), diol/diamine
(1.0 mmol, 2.0 equiv) and toluene (3.0 mL) at 20 °C for 18 h. Chamber B: Ethyl
cinnamate (88.1 mg, 0.5 mmol, 1.0 equiv), Pd/C (8.8 mg, 10 wt%) and CPME
(2.0 mL) at 20 °C for 18 h. Yields refer to the formation of 4.
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10.1002/anie.201709685
Angewandte Chemie International Edition
COMMUNICATION
Chamber B
high efficiency for dihydrogen formation with water and were even
more reactive than 1 as measured from the rates of gas evolution
(See Supporting Information). To obtain a better understanding of
a)
R2
R2
Pd/C (10 mol%)
D/H
R1
R3
R3
R1
THF, rt, 18 h
H/D
R4
H/D
R4
R2
the reactivity of these diborons,
a
range of different
H2O
or
D2O
b)
Ru(PPh3)3CO(Cl)H
(2.5 mol%)
diethanolamines 10–14 bearing other N-substituents were
examined including a t-Bu, Bn, Ph, Ts and Boc group. None of
these led to the formation of their respective diboron derivative
with B2(OH)4. Assessment of their propensity to reduce water with
subsequent reduction of ethyl cinnamate were in all cases
unrewarding. Furthermore, replacing the nitrogen of
diethanolamine with oxygen or sulfur or even with CH2 (diols 15–
17) did not lead to water reduction. All of these experiments point
towards the crucial role of nitrogen for activating these diboron(4)
compounds.
O O
R2
B
N
H
H
N
B
H2/D2
R1
R1
THF, 45 ºC, 18 h
(2.0 mL)
O O
H/D
Chamber A
c)
DG
DG
H
D
Ir-Cat (5.0 mol%)
CH2Cl2, rt, 72 h
a) Hydrogenation of alkenes
H
H
H
H
O
H
OH
OEt
H
O
H
H
4 99%
21 99%
22 99%
23 96%
Next, we tested whether the water activation could be
extended to include disilanes as well. Indeed, disilane 18 was
prepared (see Supporting Information) and a modest reduction of
ethyl cinnamate was observed (26% conversion) under similar
reaction conditions as for the diborons. Interestingly, neither
disilane 18 nor any of the tested sp3-sp3 diborons were effective
in reducing CO2 to CO (results not shown). Finally, a set of control
experiments were conducted applying an sp2-sp2 diboron (B2pin2)
and an sp2-sp3 diboron (PDIPA) compound (19 and 20). In neither
case, was dihydrogen evolution observed upon stirring in water,
which is consistent with similar experiments conducted by Santos
and co-workers. [18]
H/D
H
H
MeO
MeO
H/D
H
H
(HO)2B
AcO
24 99%
25 97%
26 96%, 26-d2 93%
O
O
H
H
H
H
H
H
HO
H
H
D/H
H/D 27 99%, 27-d2 99%
28 99%
29 89%
b) Semi-hydrogenation of alkynes
O
N
O
H
H
H
O
Having employed ethyl cinnamate as a model substrate, the
reduction of a range of olefins was investigated using 1 as the
reductant (Scheme 4). Similar to ethyl cinnamate, 4-phenyl-3-
butenoic acid could be reduced quantitatively to 21, and 1,1- and
mono-substituted styrenes were suitable substrates, providing
22–26. Employing D2O instead allowed for full deuterium
incorporation into 26 via the generation of D2. Structurally more
elaborate molecules, such as cholesterol, vitamin K and a tetra-
substituted alkene afforded compounds 27–29 in high yield. The
high deuterium incorporation observed in the reduction of
cholesterol suggests that the nitrogen-bound protons in 1 do not
exchange or this event is slow with respect to D2 formation.
H
H
H
30 96%
31 90%
32 81%
O
c) Hydrogen-deuterium exchange
F
[85%]
D
N
Mes
PF6
N
N
N
N
H
O
Ir
[85%] D
N
Mes
PPh3
NH
34
33
100% Recovered
material
100% Recovered
material
“Ir-cat”
[64%]
D
O
Scheme 4. Utilization of ex situ produced H2 in the hydrogenation of alkenes,
trans-selective semi-hydrogenation of alkynes and hydrogen-deuterium
exchange reactions. Reactions conditions for the hydrogenation of alkenes (a):
Chamber A: 1 (148.1 mg, 0.63 mmol, 1.3 equiv) and H2O (2.0 mL) at 20 °C for
18 h. Chamber B: Alkene (0.5 mmol), Pd/C (10 wt%) and THF (2.0 mL) at 20 °C
for 18 h. Reactions conditions for the semi-hydrogenation of alkynes (b):
Chamber A: 1 (113.9 mg, 0.5 mmol, 2.5 equiv) and H2O (2.0 mL) at 20 °C for
18 h. Chamber B: Alkyne (0.2 mmol), Ru(PPh3)2CO(Cl)H (4.8 mg, 0.005 mmol,
2.5 mol%) and THF (1.0 mL) at 45 °C for 18 h. Reactions conditions for
hydrogen-deuterium exchange (c): Chamber A: 1 (478.8 mg, 2.1 mmol, 30
equiv) and D2O (2.0 mL) at 20 °C for 72 h. Chamber B: Arene (0.07 mmol), Ir-
cat (3.5 mg, 0.0035 mmol, 5.0 mol%) and CH2Cl2 (1.0 mL) at 20 °C for 72 h.
We have recently reported on the trans-selective semi-
hydrogenation of alkynes.[19] This methodology could be easily
transferred to the developed conditions to obtain the stilbenes 30–
32. As a final demonstration, the methodology was connected to
a hydrogen-deuterium exchange reaction (HDE)[20] exploiting the
Kerr catalyst.[21] With this in hand, selective HDE was observed
for the anti-cancer drug olaparib (33) (64% deuterium
incorporation), and both ortho-hydrogen atoms on a phenyl ring
guided by a pyridyl directing group (85% incorporation in 34). Both
of these results are consistent with previous reports.[16,21b]
alcohol (37) after work up (Scheme 6). As such, a range of
aldehydes and ketones were tested including substituted
benzaldehydes and heteroaromatic derivatives 38–44 leading to
the corresponding alcohols in high yields. THF or methanol were
added as co-solvents for the reduction of aldehydes with a more
extended p-system, affording 45–47 in good yields. Aliphatic
aldehydes could also be employed leading to primary alcohols 48
and 49. In the case of (±)-citronellal, replacement of water with
D2O led to 49-d. Both aryl and aliphatic ketones were reduced to
A possible mechanism for dihydrogen formation is depicted in
Scheme 5. Reaction of diboron 1 with water produces the
borohydride 35 and borinic acid derivative 36, which react
together to form dihydrogen and the diboroxane 1a. If indeed
borohydride 35 is formed, we speculated whether it may be
possible to intercept this species in the reduction of carbonyl
containing compounds. As such benzaldehyde was added to 1 in
water, which gratifyingly led to the quantitative formation of benzyl
This article is protected by copyright. All rights reserved.

10.1002/anie.201709685
Angewandte Chemie International Edition
COMMUNICATION
O
O
ketones were generally even less water-soluble, and indeed by
taking a 1:1 mixture of each of the hydrophobic aldehydes and
ketones and treatment with 8 equiv. of diboron 1, reduction of the
former was highly selective (58–62). Conducting the same
experiment in MeOH with 2 equiv. of NaBH4 led to complete
reduction of both the aldehydes and ketones.[23]
O
H2
O
H2O
+
O
B N H
B
Diboron 1
H
N
B
H
HO
B
N
H
H
N
O
O
O
O
1a
35
36
Scheme 5. Proposed mechanism for the diboron-mediated water reduction.
the corresponding alcohols (50–52). Subjecting an unsymmetrical
1,3-diketone to the reaction conditions resulted in the desired 1,3-
diol 53 with a good dr (7:1). On the other hand, functional groups
such as an ester or an amide remained untouched as for
compounds 54 and 55, and heteroaromatic rings proved tolerant
to the conditions (compounds 56 and 57).[22]
In conclusion, we have reported on a series of crystalline sp3-
sp3 diboron(4) compounds, which are capable of reducing water
to dihydrogen without the need for additives or transition metal
complexes for activation. The role of the pendant nitrogen atoms
and the sp3-hybridization of both boron atoms were shown to be
crucial for obtaining the desired reactivity. The applicability of
these compounds in synthesis as a simple H2 or D2 source was
demonstrated in a range of hydrogenations of olefins, semi-
hydrogenations of alkynes and hydrogen-deuterium exchange
reactions. The intermediacy of a borohydride species could be
exploited for aldehyde/ketone reductions with the hydride source
originating from water. Further studies on these intriguing
molecules are currently underway.
HO H/D
O O
O
H2O or D2O
+
H
B
N
N
B
H
R1 R2
R1 R2
rt, 18 h
O O
(0.25 mmol)
1 (2.0 equiv)
H
H
H
H
Aldehydes
OH
OH
OH
MeS
38 (meta) 80%
39 (para) 76%
OH
MeO
O2N
41 92%[a]
40 78%
37 99%
Acknowledgements
H
H
H
Br
H
OH
OH
OH
We are deeply appreciative of the generous financial support from
the Danish National Research Foundation (Grant No. DNRF118
and DNRF93) and Aarhus University for generous financial
support.
O
S
OH
Br
42 84%
43 71%
44 86%
45 75%[c]
OH
H
OH
H
OH
H
CbzHN
OH
H/D
49 85%, 49-d 90%[e]
48 60%
Keywords: water • dihydrogen • diboron • reductions • hydride
46 80%[a,d]
47 87%[a,d]
OH
OH
HO
H
HO
H
H
Ketones
HO
H
[1]
For reviews on the utility of diboron reagents in organic synthesis, see a)
E. C. Neeve, S. J. Geier, I. A. I. Mkhalid, S. A. Westcott, T. B. Marder,
Chem. Rev. 2016, 116, 9091–9161; b) T. Ishiyama, N. Miyaura, Chem.
Rec. 2004, 3, 271–280; c) G. J. Irvine, M. J. G. Lesley, T. B. Marder, N.
C. Norman, C. R. Rice, E. G. Robins, W. R. Roper, G. R. Whittel, L. J.
Wright, Chem. Rev. 1998, 98, 2685–2722; d) J. Cid, H. Gulyás, J. J.
Carbó, E. Fernández, Chem. Soc. Rev. 2012, 41, 3558–3570; e) A. B.
Cuenca, R. Shishido, H. Ito, E. Fernández, Chem. Soc. Rev. 2017, 46,
415–430.
H
NC
50 82%[b]
O
H
51 68%[b]
52 89%[d]
53 62% (dr = 7:1)
Ph
O
HO
H
HO
HO
H
O
HO
H
N
OEt
N
N
N
57 88%[a]
54 62%
Carbonyl selectivity
55 91%
HO
56 90%
HO
[2]
S. P. Cummings, T.-N. Le, G. E. Fernandez, L. G. Quiambo, B. J. Stokes,
J. Am. Chem. Soc. 2016, 138, 6107–6110.
R
H
H
OH
H
R
[3]
[4]
[5]
[6]
Q. Xuan, Q. Song, Org. Lett. 2016, 18, 4250–4253.
R
D. P. Ojha, K. Gadde, K. R. Praphu, Org. Lett. 2016, 18, 5062–5065.
W. Kong, Q. Wang, J. Zhu, Angew. Chem. Int. Ed. 2017, 56, 3987–3991.
For an excellent and recent account on the history, synthesis and
applicability of isolated sp2-sp3 diboron(4) compounds, see: R. D.
Dewhurst, E. C. Neeve, H. Braunschweig, T. B. Marder, Chem. Commun.
2015, 51, 9594–9607.
47 (R = H) 46%[f]
62 (R = Me) < 5%[f]
60 (R = H) 50%[f]
61 (R = Me) < 5%[f]
58 (R = H) 88%[f]
59 (R = Me) < 5%[f]
Scheme 6. Reduction of aldehydes and ketones by intercepting the
intermediary borohydride. Reaction conditions for separate reduction: Aldehyde
or ketone (0.25 mmol), 1 (113.9 mg, 0.5 mmol, 2.0 equiv) and H2O (1.0 mL) at
20 °C for 18 h. Reaction conditions for combined reduction: Aldehyde (0.25
mmol), ketone (0.25 mmol) and H2O (2.0 mL) at 20 °C for 18 h. [a] Solvent:
THF/H2O (1:1, 1.0 mL). [b] MeOH/H2O (1:1, 1.0 mL). [c] 10% reduction of the
double bond was observed. [d] 1 (227.8 mg, 1.0 mmol, 4.0 equiv). [e] D2O (1.0
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Entry for the Table of Contents
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(B)reaking (B)onds: sp3-sp3
Mathias Flinker, Hongfei Yin, René W.
Juhl, Espen Z. Eikeland, Jacob
Overgaard, Dennis U. Nielsen* and
Troels Skrydstrup*
Diboron(4) compounds are capable of
reducing water to dihydrogen. The
produced gas was utilized in a variety
of reductive transformations.
Page No. – Page No.
Furthermore, a selection of aldehydes
and ketones can be reduced in the
presence of such diboron compounds
in water through an intermediary
borohydride species.
Efficient Water Reduction with sp3-
sp3 Diboron(4) Compounds:
Application to Hydrogenations, H-D
Exchange Reactions and Carbonyl
Reductions
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