Aluminum-Catalyzed Selective Hydroboration of Nitriles and Alkynes: A Multifunctional Catalyst

Article abstract of DOI:10.1021/acs.joc.0c00234

The reaction of LH [L = {(ArNH)(ArN)-C=N-C=(NAr)(NHAr)}; Ar =2,6-Et₂-C₆H₃] with a commercially available alane amine adduct (H₃Al·NMe₂Et) in toluene resulted in the formation of a conjugated bis-guanidinate (CBG)-supported aluminum dihydride complex, i.e., LAlH₂ (1), in good yield. The new complex has been thoroughly characterized by multinuclear magnetic resonance, IR, mass, and elemental analyses, including single-crystal structural studies. Further, we have demonstrated the aluminum-catalyzed hydroboration of a variety of nitriles and alkynes. Moreover, aluminum-catalyzed hydroboration is expanded to more challenging substrates such as alkene, pyridine, imine, carbodiimide, and isocyanides. More importantly, we have shown that the aluminum dihydride catalyzed both intra- A nd intermolecular chemoselective hydroboration of nitriles and alkynes over other reducible functionalities for the first time.

Full text of DOI:10.1021/acs.joc.0c00234

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Article
Aluminum-Catalyzed Selective Hydroboration of
Nitriles and Alkynes: A Multifunctional Catalyst
Nabin Sarkar, Subhadeep Bera, and Sharanappa Nembenna
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.0c00234 • Publication Date (Web): 11 Mar 2020
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The Journal of Organic Chemistry
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Aluminum-Catalyzed Selective Hydroboration of Nitriles and
Alkynes: A Multifunctional Catalyst
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Nabin Sarkar, Subhadeep Bera and Sharanappa Nembenna*
School of Chemical Sciences, National Institute of Science Education and Research (NISER), Homi Bhabha National
Institute (HBNI), Bhubaneswar- 752 050 (India)
ABSTRACT: The reaction of LH [L= {(ArNH)(ArN)–C=N–C=(NAr)(NHAr)}; Ar =2,6-Et
2
-C
6
H
3
] with commercially available
alane amine adduct (H
formation of a conjugated bis-guanidinate (CBG) supported
aluminum dihydride complex, i.e., LAlH
new complex has been thoroughly characterized by multinuclear
magnetic resonance, IR, mass and elemental analyses, including
single-crystal structural studies. Further, we have demonstrated
the aluminum-catalyzed hydroboration of a variety of nitriles and
3 2
Al·NMe Et) in toluene resulted in the
H
Bpin
R
R'
R
C
N
Al
R
N(Bpin)2
R
R'
HBpin
HBpin
2
0 examples
(1) in good yield. The 19 examples
2
Cheap, abundant, less toxic
Solvent-free
Both inter and intramolecular
chemoselectivity
49 unsatuarted
Wide substrate scope
substrates screened
Multifunctional catalyst
alkynes. Moreover, aluminum-catalyzed hydroboration is expanded to more challenging substrates such as alkene, pyridine, imine,
carbodiimide, and isocyanides. More importantly, we have shown the aluminum dihydride catalyzed both intra- and intermolecular
chemoselective hydroboration of nitriles and alkynes over other reducible functionalities for the first time.
Therefore, the design of a sustainable catalyst is very
desirable because catalysts should be easily accessible,
efficient, and tolerance of more functional groups.
Moreover, to our knowledge, there are no reports on
INTRODUCTION
Aluminum is the third most abundant metallic element after
oxygen and silicon in the Earth's crust and also cheaper, less
1
7
aluminum catalyzed hydroboration of pyridine, and
toxic when compared to transition or lanthanide elements.
The sustainable and environmentally friendly aluminum-
based reagents/molecules are ideal for applications in
1
8
isonitrile functionalities. Thus, herein, we report well-
defined aluminum dihydride complex bearing conjugated
bis-guanidinate ligand catalyzed selective reduction of a
wide range of nitriles and alkynes. Moreover, this protocol
further extended to other reducible functionalities such as
alkene, carbodiimide, imine, isocyanide and pyridine. To the
best of our knowledge, this is the first report of aluminum-
based multifunctional catalysts for the hydroboration of
unsaturated organic substrates.
1
catalysis. Hence, the development of well-defined
2
aluminum-based catalysts is quite attractive. In recent years
there has been substantial progress in the development of the
main group- or transition metal-catalyzed hydroboration of
carbonyl compounds; however, relatively few examples of
the main group catalyzed nitrile and alkyne hydroboration
have been documented. Nonetheless, aluminum-catalyzed
reduction of organic nitriles has been rarely documented. In
3
,4
RESULTS AND DISCUSSION
Treatment of the free conjugated bis-guanidine (CBG), LH19
ligand with one equiv. of alane, H Al·NMe Et in toluene at
3 2
room temperature and followed by heating at 80 C cleanly
yields the CBG supported aluminum dihydride complex (1)
in good yield (84%) (Scheme 1).
2
016, Hill et al. reported the first main-group catalyzed,
5
Nacnac Mg alkyl catalyzed hydroboration of nitriles.
6
4i
7
o
Recently, Okuda, Thomas,
Ma research groups
independently reported the main group catalyzed
hydroboration of nitriles. During the preparation of this
8
9
manuscript, Yang, and Roesky and co-workers reported
Nacnac supported aluminum dialkyl and dihydride
complexes as (pre)catalysts for the hydroboration of nitriles
Scheme 1. Synthesis of Conjugated Bis-Guanidinate(CBG)
Supported Aluminum-Dihydride Complex (1).
10
and also, Panda et al. reported aluminum alkyl as a pre-
catalyst for the hydroboration of nitriles. There have been
Ar
Ar
Ar
Ar
4g,7,11
12
several reports on the main-group,
transition metal-
N
N
N
Alane (1.05 equiv.)
Toluene, 80 oC, 24 h
N
N
Al
(1)
N
catalyzed hydroboration of alkynes, while a few reports on
H
H
H
H
13
aluminum catalyzed hydroboration of alkynes. Moreover,
N
N
N
N
Ar
Ar
-H2
Ar
Ar
very few reports of aluminum catalyzed hydroboration of
H
4
i,13a,14
9,15
4g,16
H
alkene
carbodiimide and imines.
H
Ar = 2,6-Et2-C6H3
The reports mentioned above are having drawbacks such as
very limited substrate scope, high catalyst loading, ligand
containing elements other than C, H, and N, etc.
The new complex 1 was fully characterized by multinuclear
( H, C, and Al) NMR, infrared, mass, and elemental
analyses. In addition, the crystallographic analysis
1
13
27
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confirmed the solid-state structure of 1, which is monomeric under neat conditions (Table 1). Aryl nitriles with electron-
1
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(
Figure 1).
donating or electron-withdrawing groups undergo reduction
efficiently, yielding the corresponding 1,1-bis(boryl) amine
products. Functional groups such as OMe, Cl, and F were all
found to be tolerant under reaction conditions. Primary,
secondary, and tertiary alkyl nitriles were efficiently reduced
to corresponding 1,1-bis(boryl) amines in 52-80 % yields
(2m-2s). More importantly, we have explored the
intramolecular chemoselective hydroboration reaction by
1
The H NMR spectrum reveals a complete disappearance of
a free ligand N–H–N peak at 12.97 ppm, which indicates the
formation of complex 1. Moreover, a singlet resonance
displayed at 5.14 ppm, which corresponds to two protons of
side arm ArN–H moieties. Besides, other expected signals
for the CBG ligand were observed. The 13C{ H} NMR
spectrum exhibits a characteristic N C peak at 158.6 ppm,
which is downfield when compared to free ligand (155.0
ppm). The Al–H resonances were not obtained in H NMR
spectroscopy of compound (1) because of quadrupolar
broadening on the Al center (nuclear spin = 5/2).
Nonetheless, the existence of an Al−H bond was established
by IR spectroscopy, which shows two broad bands at 1813
1
3
choosing
1-cyanocyclohexene
(or
cyclohexene-1-
1
carbonitrile) substrate, as an example — the reaction of 1-
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cyanocyclohexene with two equiv. HBpin and catalyst 1 (3
o
1
2
7
20
mol %) in neat condition at 60 C was executed. The H
NMR analysis of this reaction mixture illustrated the
chemoselective hydroboration of nitrile with the quantitative
conversion over alkene (2t). Unsurprisingly, substrates
bearing reducible carbonyl functional group (2g and 2h)
were not tolerated under the conditions.
−
1
and 1926 cm , referred to the Al−H stretching
frequencies.
4
l,21
Table 1. Hydroboration of Nitriles Catalyzed by
a
2
LAlH Complex (1)
cat (1)
N
(
3 mol%)
+
2 HBpin
R
R
N(Bpin)2
a-2t
,1-bis(boryl)amine
neat, 12 h, 60 o
R = aliphatic / aromatic
C
2
1
Bpin
Bpin
Bpin
Bpin
Bpin
Bpin
Bpin
Bpin
N
N
N
N
MeO
2a, 83%
2b, 71%
2c, 74%
2d, 80%
Bpin
Bpin
Bpin
N
Bpin
Bpin
N
Bpin
N
Bpin
Bpin
N
Figure 1. Molecular structure of catalyst 1. Selected bond distances
Å) and angles (deg): C1-N2 1.332(4), C1-N5 1.351(4), C1-N3
.326(4), N3-Al1 1.894(3), N1-Al1 1.879(3), C2-N1 1.336(4), C2-
N2 1.342(4), C2-N4 1.355(4), Al1-H 1.411(3), Al1-HA 1.622(3).
N2-C1-N3 127.0(3), N2-C1-N5 113.7(3), N3-C1-N5 119.2(3), N1-
C2-N2 126.6(3), N2-C2-N4 114.5(3), N1-C2-N4 118.9(3), N3-
Al1-N1 94.73(12), N3-Al1-H 112.516(18), N1-Al1-H 113.93(9),
N3-Al1-HA 110.88(12), N1-Al1-HA 117.12(12), H-Al1-HA
Cl
F
(
1
OBpin
OBpin
2g,b 83%
2h,b 52%
2
e, 75%
2f, 74%
Bpin
N
Bpin
N
Bpin
Bpin
Bpin
N
Bpin
Bpin
Bpin
N
N
Bpin
Bpin
j,c 68%
1
07.220(21).
2
i, 75%
2
2l, 70%
2k, 68%
Nitrile Hydroboration
Bpin
Bpin
Bpin
Bpin
N
N
3
D C
N
N
We began by examining the role of aluminum dihydride
compound (1) in the catalytic hydroboration of benzonitrile
Bpin
Bpin
Bpin
Bpin
2m, 52%
2p, 60%
2n, 60%
2o, 62%
with 2 equiv. HBpin. At a loading of 5 mol % of 1 in
Bpin
Bpin
Bpin
Bpin
o
N
N
N
N
benzene-d
6
at 60 C, benzonitrile was hydroborated to afford
Bpin
Bpin
Bpin
Bpin
1,1-bis(boryl) amine in 98 % yield within 12 h (Table S1,
Supporting Information). No reaction took place at similar
reaction conditions in the absence of catalyst 1, showing that
the aluminum dihydride compound is responsible for this
conversion. Also, the same reaction was carried out under
similar conditions by utilizing lower catalyst loadings (1 mol
2
q, 90%
2r, 82%
2s, 56%
2t, 65%
a
Reaction conditions: nitrile (1.0 mmol, 1.0 equiv.), pinacolborane
(2.0 mmol, 2.0 equiv.), catalyst (1) (3 mol%), 12 h at 60 C under
2. Reported numbers are the isolated yields. For 2g and 2h,
pinacolborane (3.0 equiv.) used and precursors 4-
Formylbenzonitrile and 4-Acetylbenzonitrile, respectively. For 2j
pinacolborane (4.0 equiv.).
o
b
N
c
%
and 3 mol %). We observed the formation of 1,1-
bis(boryl) amine in 50 % and 97 % yields, respectively.
However, the same reaction was accomplished under
solvent-free conditions by using 3 mol % catalyst; in this
case, we noticed the formation of the desired product in
quantitative yield.
All 1,1-bis(boryl)amine products were characterized by
1
13
11
multinuclear ( H, C, and B) NMR spectroscopy. HRMS
confirmed purity of new 1,1-bis(aryl) amines. Further,
compound 2i was confirmed by a single X-ray crystal
structural analysis (see Supporting Information). Notably,
this protocol also works for large scale synthesis as
Therefore, we investigated the reduction of a wide range of
organic nitriles with HBpin by using 3 mol % of catalyst 1
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established by 10 mmol scale reaction of benzonitrile under
optimized conditions producing corresponding 1,1-
selectivity was determined by NMR spectroscopy except for 3r and
3s, which show Z selectivity.
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1
1
1
1
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2
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bis(boryl) amine (2a) in 82% isolated yield (Scheme 2).
No conversion took place in the absence of catalyst 1.
Further, when the same reaction was performed at lower
catalyst loadings, lesser conversion observed (1 mol %, 70%
yield, and 3 mol %, 95 % yield). However, a quantitative
conversion was displayed when the same reaction operated
under solvent-free conditions by using a 3 mol % catalyst.
Scheme 2. Large-Scale Hydoboration of Benzonitrile with
HBpin
C
N
cat (1)
(3 mol%)
N(Bpin)2
HBpin
o
neat, 12 h, 60 C
With the optimized reactions conditions in hand, we
investigated the scope of the aluminum-catalyzed
hydroboration of terminal alkynes (Table 2). We began
examining different phenylacetylene derivatives and were
satisfied to see that substituents with electron-donating or
electron-withdrawing groups on the aromatic ring did not
influence the catalytic activity (3a-3e, 69-80 %). However,
a slightly lower yield obtained for the phenylacetylene
10 mmol
1.0 mL)
20 mmol
(3.0 mL)
2a
(2.9 g, 81%)
(
0
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0
1
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9
0
1
2
3
4
5
6
7
8
9
0
Alkyne Hydroboration
Next, we decided to explore the catalytic activity of
compound 1 for the hydroboration of alkynes. We chose
phenylacetylene as a substrate for the hydroboration with 1
equiv. HBpin. At a loading of 5 mol % catalyst 1 in benzene-
3
derivative 3f, containing CF at the para position of the
aromatic ring.
o
d6 at 60 C, phenylacetylene hydroborated to afford the cis-
hydroborated product, (E)-vinyl boronate ester in
quantitative yield within 12 h (Table S2, Supporting
Information).
Subsequently, we considered the scope of the transformation
by employing terminal alkynes bearing alkyl substituents
(3g-3o), which performed similarly to the corresponding
Table 2. Hydroboration of Alkynes Catalyzed by LAlH
2
phenylacetylene derivatives (60-80%). Hydroboration of
trimethylsilylacetylene took place, providing 3p in 40 %
yield. More importantly, another interesting intramolecular
chemoselective hydroboration of terminal alkyne by
choosing 1-ethynylcyclohexene, as an example was carried
out. Hydroboration took place smoothly, providing 3q in 71
% yield, in which C=C tolerated. To further broaden the
substrate scope, we decided to test the aluminum catalyzed
hydroboration of internal alkyne. Hydroboration of
unsymmetrical and symmetrical internal alkynes, like 1-
phenyl-1-propyne and diphenylacetylene, took place,
providing (Z)-vinyl boronate esters in 30% and 40 % yields,
respectively. It is interesting to note that CBG supported
aluminum dihydride catalyzes the challenging substrates
such as symmetrical and unsymmetrical internal alkynes, in
contrast to previously reported Nacnac AlH2, which is less
a
Complex (1)
cat (1)
R'
H
Bpin
R = aliphatic/aromatic
(
3 mol%)
+
HBpin
R
neat, 12 h, 60 o
R' = H; (E)- Vinylboronate ester
C
R
R'
R' = Me, Ph; (Z)- Vinylboronate ester
3a-3s
H
Bpin
H
Bpin
H
Bpin
H
Bpin
H
H
H
H
MeO
3b, 78%
3c, 80%
3d
3a, 75%
,
78%
H
Bpin
H
Bpin
H
Bpin
H
Bpin
H
H
H
H
1
3c
effective to reduce the internal alkynes.
Nitrile Intermolecular Chemoselectivity:
F
F3C
3e, 69%
3f, 55%
3g, 75%
3h, 69%
More importantly, we have displayed aluminum dihydride 1
catalyzed intermolecular chemoselective hydroboration of
nitriles over alkenes containing both electron-donating and
electron-withdrawing substituents, esters and isonitriles.
H
Bpin
H
Bpin
H
Bpin
H
Bpin
H
H
H
H
Scheme 3. Nitrile Intermolecular Chemoselective Reactions
Catalyzed by 1
3i, 82%
3j, 80%
3k, 80%
3l, 70%
H
Bpin
H
H
Bpin
H
Bpin
H
Bpin
N
cat (1)
a)
(
3 mol%)
N(Bpin)2
H
H
Si
H
HBpin
neat, 12 h, 60 o
C
R
R1
Cl
( 2.0 eq)
R
R1
>
99 %
unreacted
3m, 65%
3n, 60%
3o, 78%
3p, 40%
R = H (2a)
Me (2c)
F (2f)
R1 =
H
Me
Cl
N
O
O
cat (1)
H
Bpin
H
Bpin
H
Bpin
b)
c)
(3 mol%)
N(Bpin)2
O
HBpin
O
neat, 12 h, 60 o
C
H
Me
(
2.0 eq)
>99 %
2a)
unreacted
(
R1
R1
O
O
N
O
3q, 71%
3r, 30%
3s, 40%
cat (1)
(3 mol%)
neat, 12h, 60 o
N(Bpin)2
O
HBpin
( 2.0 eq)
C
R
R
a
Reaction conditions: alkyne (1.0 mmol, 1.0 equiv.), pinacolborane
1.0 mmol, 1.0 equiv.), catalyst (1) (3 mol%), 12 h at 60 C under
>99 %
unreacted
o
(
R = Me (2c)
(2f)
R1 = Me
NO2
F
N
2. Products are isolated after column chromatography. The E
N
C
cat (1)
(3 mol%)
neat, 12h, 60 o
C
N
d)
N(Bpin)2
N
HBpin
2.0 eq)
C
R
R1
R
R1
(
>
99 %
R = Me (2c)
(2f)
unreacted
3
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Initially, catalyst 1 reacts with the nitrile to form transition
1
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1
1
1
1
1
1
1
1
1
1
2
2
2
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2
2
2
2
2
2
3
3
3
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species (I), and followed by sigma bond metathesis to yield
the corresponding imine (II). This imine complex further
reacts with HBpin to produce the four-membered species
(III), which rearranges to give boryl amine (IV). Further, it
reacts with one more molecule of HBpin to yield
intermediate species (V), which undergoes sigma bond
metathesis to yield the product 1,1-bis(boryl) amine and
regeneration of the ligated aluminum dihydride catalyst
The reaction of 1 equiv. of benzonitrile, 1 equiv. styrene and
equiv. HBpin were mixed with catalyst 1 (3 mol %) under
solvent-free conditions at 60 C, which produced the
diborylated product 1,1-bis(boryl)amine in the quantitative
conversion of benzonitrile, in preference to the alkene
2
o
(Supporting Information). Similarly, either the reaction of
(
Scheme 5). Moreover, the aluminum imine species (II) was
aryl nitrile containing electron-donating group, 4-methyl
benzonitrile, or electron-withdrawing group, 4-Fluro
benzonitrile gives corresponding 1,1-bis(boryl) amine in
preference to the alkene. Moreover, the reaction of 1 equiv.
benzonitrile, 1 equiv. benzyl benzoate and 2 equiv. HBpin
were allowed to react with catalyst 1 (3 mol %) under
1
13
confirmed by H and
C NMR analyses by the
and
at 70 C. The H NMR
spectrum exhibits a characteristic imine, Al-N=CH-R peak
0
1
2
3
4
5
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2
3
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0
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9
0
stoichiometric reaction between catalyst
1
o
1
trimethylacetonitrile in CDCl
3
1
3
1
at 8.48 ppm, while the Al-H signal was silent. The C { H}
NMR spectrum displays a typical Al-N=C-HR peak at the
far downfield region at 160.4 ppm.
o
solvent-free conditions at 60 C, which yielded the
diborylated product 1,1-bis(boryl) amine in the quantitative
conversion of benzonitrile over benzyl benzoate. Similarly,
Scheme 5. Proposed Mechanism for Hydroboration of Nitrile.
4
-methyl benzonitrile and 4-Fluro benzonitrile gave the
Bnip
Bnip
H
H
corresponding 1,1-bis(boryl) amines in preference to the
esters (Scheme 3). Further, at similar reaction conditions, 4-
methyl benzonitrile and 4-fluoro benzonitrile yielded the
corresponding 1,1-bis(boryl) amines over aryl isonitriles.
N
R
N
R
LAlH2
O
O
B
H
H
H
R
L
H
N
Al
Alkyne Intermolecular Chemoselectivity:
L
Al
Bpin
H
H
N
C
R
V
I
The reaction of equimolar amounts of phenylacetylene,
HBpin
styrene, and HBpin was reacted together with catalyst 1 (3
o
mol %) under neat conditions at 60 C, which afforded the
Bnip
H
H
N
H
t
(E) vinyl boronate ester in preference to the alkene.
L
Al
IV
R
N
C
LAlH2: BuCN (1:1)
H
L
Al
R
1H NMR(CDCl3)
δ = 8.48 ppm
H
Similarly,
phenylacetylene,
hydroborated at the same reaction conditions over alkenes
Scheme 4).
4-methyl
phenylacetylene,
4-methoxy
II
m/z = 742 (M+H)+
4-fluoro
phenylacetylene
were
H
IR ν (cm-1) = 1613 (N=C)
L
N
O
C R
Al
B
H
HBpin
(
H
O
III
The reaction of equimolar amounts of phenylacetylene,
Mechanism
of
LAlH2 (1) Catalyzed
benzonitrile, and HBpin was reacted together with catalyst 1
Hydroboration of Alkyne:
o
under neat conditions at 60 C, which yielded the (E)-vinyl
Considering the previously established mechanisms of
boronate ester over nitrile functionality. Similarly,
equimolar amounts of aryl alkynes and aryl nitrile with
either electron-donating or electron-withdrawing groups,
and HBpin were reacted together, independently, in which
exclusively alkyne hydroborated over nitrile.
13a,c
aluminum-catalyzed hydroboration of terminal alkynes
we propose that the hydroboration reaction proceeds
according to the mechanism shown in Scheme 6. First, the
deprotonation of alkyne with aluminum-dihydride 1 leads to
the formation of aluminum acetylide (Int 1). Further, a
Scheme 4. Alkyne Intermolecular Chemoselective Reaction
Catalyzed by 1.
stoichiometric reaction of catalyst 1 and phenylacetylene in
o
C D at 70 C was carried out to confirm the formation of Int
6
6
1
13
1
. H and C NMR analyses confirmed the formation of
H
Bpin
a)
1
cat (1)
3 mol%)
aluminum acetylide, LAl(H)CCPh. The H NMR shows side
H
(
HBpin
arm ArNH resonance at 4.90 ppm, which upfield region
neat, 12 h, 60 o
C
1
3
1
R'
R'
R
R'
2
compared the LAlH (ArNH 5.13 ppm). The C { H} NMR
>
99 %
unreacted
displays two peaks at 77.4 and 83.5 ppm, which
corresponding to Al-CCPh carbon atoms, respectively. The
second step involves the cycloaddition reaction, in which the
B-H bond of HBpin adds to the C-C triple of Int 1 that leads
alkene Int 2. In the third step, Int 2 reacts with another
molecule of phenylacetylene, in which sigma bond
metathesis occurs that leads to the formation of product and
regeneration of the active catalyst Int 1.
R = H (3a)
Me (3c)
R' =
H
Me
OMe (3d)
F (3e)
OMe
Cl
N
H
Bpin
N
cat (1)
(3 mol%)
b)
H
HBpin
neat, 12 h, 60 o
C
R'
R
R'
R
>
99 %
unreacted
R = H (3a)
Me (3c)
F (3e)
R' =
H
Me
F
A different mechanism is operative for the internal alkynes,
which is previously reported by Thomas, Cowley and
1
3b
coworkers. Accordingly, we propose the catalytic cycle
starting with Al-H insertion in alkyne CC triple bond to form
Int 1, which undergoes transmetallation to regenerate the
2
Mechanism of LAlH (1) Catalyzed Hydroboration of
Nitrile:
4
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The Journal of Organic Chemistry
1
catalyst and (Z)-vinyl boronate ester. Further, a controlled
reaction was carried out to confirm the proposed reaction
on H NMR spectroscopy. For imine, the yield was determined by
b
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
using nitromethane as an internal standard. Isolated yield of alkene
hydroboration based on column chromatography.
mechanism. Thus, the treatment of catalyst 1 with 1-phenyl-
o
1-propyne in 1:1 ratio in C
6
D
6
at 80 C resulted in the
To our delight, compound 1 efficiently catalyzes the
hydroboration of imine, pyridine, alkene, carbodiimide, and
isonitrile substrates at neat and mild reaction conditions
Scheme 7). Hydroboration of imine was successfully
achieved for aldimines like N-Benzylideneaniline by 3 mol
1
13
formation of Int 1, which is confirmed by H and C NMR
spectroscopy analyses. The H NMR reveals two singlets at
1
1.85 and 5.25 ppm, which correspond to methyl and H
(
1
3
1
signals of Al-CMe=CHPh moiety. The C{ H} NMR
spectrum shows a typical signal at the upfield region at 3.2
ppm, which corresponds to the carbon atom of Al-
CMe=CHPh moiety.
o
%
of catalyst 1 at 70 C within 20 h. Similarly, other imines
t
such as benzyl, butyl, and methyl were also hydroborated at
the same reaction conditions (4a-4d). The reaction of
equimolar amounts of pyridine and HBpin were reacted
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Scheme 6. Proposed Mechanism for Hydroboration of Alkyne.
6
together with catalyst 1 in C D6, which afforded exclusively
LAlH2 +R
H
N-borylated 1,4- reduced product (5a). Next, using catalyst
1 (5 mol %) and HBpin (1.0 equiv), the hydroboration of
styrene proceeded in an 80 % yield to give the anti-
Markovnikov (linear) alkyl boronic ester (6a) within 12 h at
H
H
LAlH2
H
Bpin
R'
L
Al
R
R
R'
R
pinB
H
H
Int1
(Z)-Vinylboronate
H
R
13C NMR(C6D6)
δ = 77.4 ppm, 83.5 ppm
HBpin
ester
o
110 C. Further compound 1 catalyzed the more challenging
(
E)-Vinylboronate
ester
LAlH : PhCCH (1:1)
2
organic substrates such as carbodiimides and isonitriles has
been investigated. Aliphatic substrates such as N, N'-
diisopropyl carbodiimide and N, N'-ditertbutyl carbodiimide
reduced to corresponding monohydroborated ester (7a-7b)
when treated with 1eq. of HBpin. Following this, the inert
isocyanides such as acyclic and cyclic alkyl isonitriles, i.e.,
HBpin
R
H
pinB
H
L
H
Al
Al
H
R
H
L
1
6 6
H NMR(C D )
δ = 5.25 ppm
LAlH2: PhCCMe (1:1)
R'
Int2
R
Int1
Terminalalkyne
Internalalkyne
1
-pentylisoniitrile and cycloisonitrile and efficiently
Aluminum Catalyzed Hydroboration of Imines, Alkene,
Pyridine, Carbodiimides, and Isonitriles
converted to corresponding hydroborated amines (8a-8b).
CONCLUSION
To the best of our knowledge, there have been no reports on
aluminum-catalyzed hydroboration of heterocycles and
isonitriles. To further establish the relevance of this
procedure, we utilized aluminum-dihydride catalyzed
hydroboration to more challenging substrates.
In summary, we have demonstrated a newly synthesized β-
diketiminate analogue of well-defined conjugated bis-
guanidinate (CBG) supported aluminum dihydride (1)
catalyzed dihydroboration of
a
large number of
organonitriles with HBpin. We noticed that catalyst 1 is
more efficient for the hydroboration of nitriles than that of
β-diketiminate(Nacnac)supported aluminum dihydride
complex. Further, compound 1 catalyzed hydroboration of
both terminal and internal alkynes with HBpin has been
investigated. In contrast to Nacnac Al dihydride catalysis,
two different mechanisms are operative for CBG aluminum
dihydride catalyzed alkyne hydroboration reaction.
Scheme 7. Hydroboration of Imines, Alkene, Pyridine,
Carbodiimide, and Isonitriles by using Al Complex (1) as a
a
Catalyst.
A. Hydroboration of iminea
cat (1)
R
N
(3 mol%)
R
R =
Ph; 97% (4a)
PhCH2; 95% (4b)
(Me) C; 88% (4c)
Me; 94% (4d)
N
+
HBpin
neat, 20 h, 70 o
Bpin
C
3
>
99 %
B. Hydroboration of pyridinea
Further, compound 1 catalyzed hydroboration of alkene,
pyridine, imine, carbodiimide, and isocyanide substrates
with HBpin has been studied. Overall compound 1 was
found to be a highly efficient (low catalyst loadings and mild
reaction conditions) and multifunctional catalyst with a
broad substrate scope. Further studies on the aluminum-
dihydride catalyzed other organic transformations are
ongoing in our laboratory.
H
H
cat (1)
5 mol%)
neat, 12 h, 70 o
(
+
HBpin
C
N
N
Bpin
a, >99%
5
C. Hydroboration of alkeneb
cat (1)
5 mol%)
Bpin
(
+
HBpin
neat, 12 h, 110 o
C
EXPERIMENTAL SECTION
6
a, 80%
All air and moisture sensitive reactions were carried out by
using standard Schlenk line and glovebox techniques under
D. Hydroboration of carbodiimidea
R
cat (1)
5 mol%)
H
1
9
(
R
R
R
= iPr (7a)
tBu (7b)
an inert atmosphere of dinitrogen. The precursor LH [LH =
{(ArHN)(ArHN)C=N C= NAr(NHAr)}; Ar = 2, 6-Et
] was prepared by using method developed in our
N
C
N
HBpin
N
N
neat, 12 h, 70 0
C
R
2
-
Bpin
>
99%
6 3
C H
E. Hydroboration of isocyanidea
cat (1)
5 mol%)
neat, 16 h, 80 0
laboratory. Alane-N,N-dimethyl ethyl amine complex (0.5
M) in toluene were purchased from Sigma-Aldrich and used
as received. Anhydrous solvents such as toluene, benzene,
and n- hexane were collected from the MBraun solvent
purification system, degassed and stored under an
Bpin
(
R
N
C
2 HBpin
N
Bpin R = 1-C H (8a)
5 11
R
C
C
Cy (8b)
H2
>
99%
aReaction conditions: all reactions were done on 1.0 mmol scales.
For isocyanide, 2.0 mmol of pinacolborane used. Conversion based
1
13
11
27
atmosphere of dinitrogen before use. The H, C, B & Al
5
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1
1
NMR spectra were acquired on 400 MHz (Bruker or JEOL)
and 700MHz Bruker spectrometers using dried deuterated
solvents with chemical shift given in parts per million. Dry
137.0, 128.5, 127.9, 126.9, 124.6, 82.1, 47.4, 24.3, 21.1. B
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
NMR (128 MHz, C D ) δ 29.92.
6
6
22
N-{B(OCMe
mg (74%, white solid). H NMR (400 MHz, C
.54 (d, J = 8.0 Hz, 2H, o-H), 7.10 – 7.08 (d, J = 8.0 Hz, 2H,
m-H), 4.63 (s, 2H, NCH ), 2.16 (s, 3H, PhCH ), 1.05 (s, 24H,
2 2 2
) } –p-tolylmethanamine (2c) . Yield: 277
deuterated benzene (C
6
D
6
), chloroform (CDCl
3
) solvents
1
6
6
D ) δ 7.56–
were used for NMR measurements; chemical shift values (δ)
were reported in parts per million (ppm) relatives to the
residual signals of their respective solvents. High-resolution
mass spectra (HRMS) were recorded on Bruker micrOTOF-
Q II spectrometer. IR spectrum of compound 1 was recorded
on the Perkin-Elmer FTIR spectrometer. Elemental analysis
for compound 1 was performed by EuroEA3000-CHNS-
Analyzer.
7
2
3
13
1
OC(CH
3
)
2
). C{ H} NMR (101 MHz, C
6
D
6
) δ 140.5, 135.3,
11
1
28.6, 127.7, 82.1, 47.2, 24.3, 20.7. B NMR (128 MHz,
) δ 29.68.
N-{B(OCMe
6 6
C D
23
2
)
2
}
2
–p-methoxymethanamine (2d) . Yield:
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
3
7
11 mg (80%, white solid). H NMR (400 MHz, CDCl
.19 – 7.17 (d, J = 8.0 Hz, 2H, o-H), 6.86 – 6.84 (d, J = 8.0
), 3.76 (s, 3H, PhOCH ),
3
). C{ H} NMR (101 MHz, CDCl )
3
) δ
2
Synthesis of LAlH (1): To a solution of LH (1.0 g, 1.58
Hz, 2H, m-H), 4.03 (s, 2H, NCH
2
3
mmol) in toluene (~30 mL) at room temperature was added
dropwise a solution of alane-N,N-dimethylethylamine
complex (0.5 M) in toluene (3.32 mL, 1.66 mmol). The
13
1
1
.24 (s, 24H, OC(CH
3
)
2
δ 158.3, 135.0, 127.9, 113.7, 82.1, 55.2, 44.6, 24.5.
24
N-{B(OCMe
2
)
2
}
2
–o-chlorobenzylamine (2e) . Yield: 294
o
reaction mixture was heated at 80 C and stirred for a further
1
mg (75%, colorless liquid). H NMR (400 MHz, C
.08 (d, J = 8.0 Hz, 1H,o-H), 7.03 (t, J = 8.0, 1H, o-H), 6.56
t, J = 8.0, 1H,p-H), 6.19 – 6.13 (m, 1H, o-H), 4.50 (s, 2H),
6 6
D ) δ
2
4 h. The reaction mixture was allowed to attain room
7
temperature and filtered through a Celite. Then volatiles
were removed in vacuo to yield a colorless solid. The residue
was extracted into toluene and colorless crystals suitable for
X-ray diffraction studies, were obtained from the storage of
(
1
13
1
.00 (s, 24H, OC(CH
3 2 6 6
) ). C{ H} NMR (101 MHz, C D ) δ
36.9, 130.5, 128.3, 127.2, 127.1, 126.4, 82.2, 65.0, 24.3.
B NMR (128 MHz, C
N-{B(OCMe –p-fluorobenzylamine (2f) . Yield: 277
mg (74%, white solid). H NMR (700 MHz, C D ) δ 7.38 (t,
J = 8.0, 2H, o-H), 6.87 (t, J = 8.0 Hz, 2H, m-H), 4.41 (s, 2H,
2 3 2
NCH ), 1.01 (s, 24H, OC(CH ) ). C{ H} NMR (176 MHz,
6 6
C D ) δ 162.4, 161.1, 139.1 (d, J = 3.0 Hz), 129.4 (d, J = 7.6
1
1
1
6 6
D ) δ 29.92.
o
a saturated solution in toluene at 5 C. A second crop of
5
2 2 2
) }
crystals was obtained on further concentration of the
1
o
1
supernatant solution at -30 C.(0.87 g, yield 84%). H NMR
6
6
3
6 6
(C D , 400 MHz, 273K): δ (ppm) 0.94 (t, JHH = 8 Hz, 12H,
13
1
3
PhCH
2
CH
.24 (m, 4H, PhCH
.84 – 2.86 (m, 4H, PhCH
CH ), 5.13 (s, 2H, Ar NH), 6.61– 6.63 (d, JHH = 8
Hz, 4H, ArH), 6.87 (t, JHH = 8 Hz, 2H, ArH), 7.00 – 7.05
m, 2H, ArH), 7.12 – 7.14 (m, 2H, ArH), 7.15 – 7.16 (m, 2H,
3
), 1.36 (t, JHH = 8 Hz, 12H, PhCH
CH ), 2.32 – 2.34 (m, 4H, PhCH
CH ), 3.33 – 3.37 (m, 4H,
2
CH
3
), 2.20 –
2
2
2
3
2
CH ),
3
Hz), 114.6 (d, J = 21.0 Hz), 82.2, 46.7, 24.3.
2
3
3
PhCH
2
3
N-{B(OCMe ) } –O-B(OCMe ) –(4-
2
2
2
2 2
3
23
(aminomethyl)phenyl)methanol (2g) . Yield: 428 mg (83%,
white solid). H NMR (400 MHz, C D ) δ 7.49 – 7.48(d, J =
6 6
1
(
13
1
ArH); C { H} NMR (101 MHz, C
6
D
6
, 273K): δ 14.4, 14.5,
4.0 Hz, 2H, o-H), 7.31 – 7.30(d, J = 4.0 Hz, 2H, p-H),4.92
(s, 2H, OCH ), 4.50 (s, 2H, NCH ), 1.04 (s, 12H, OC(CH ) ),
23.8, 25.1, 125.4, 126.8, 127.0, 127.5, 134.6, 138.0, 141.3,
2
2
3 2
2
7
13
1
141.3, 158.6. Al NMR (104 MHz, C
6
D
6
-1
, 273K) δ 56.35.
3 2 6 6
1.01 (s, 24H, OC(CH ) ). C{ H} NMR (101 MHz, C D )
δ 142.5, 137.6, 127.9, 126.6, 82.2, 82.1, 66.5, 47.2, 24.3,
o
Mp - 260 – 264 C. IR (Nujol mull) ν (cm ): 1813 and 1926
+
11
(br, Al-H). HRMS (ESI) m/z: [M+H] Calcd for C42
658.4797; Found 658.4424. Elemental analysis (%) for
: Calcd C 76.67 H 8.58 N 10.64; Found C 76.20
H
56AlN
5
24.3. B NMR (128 MHz, C D ) δ 28.32, 22.79.
6
6
2 2 2 2 2
N-{B(OCMe ) } -O-B(OCMe ) –(4-
C
42
H
56AlN
5
aminomethyl)phenyl)ethanol (2h)12d. Yield: 275 mg (52%,
(
H 8.42 N 10.86.
1
white solid). H NMR (700 MHz, C
6
D
6
) δ 7.57– 7.55 (d, J =
General Procedure for Catalytic Hydroboration of
Nitriles. In a sealed vial 19 mg (0.03 mmol) of catalyst 1,
304.7 μL (2.1 mmol) of pinacolborane was then added,
followed by 1.0 mmol of nitrile in a neat condition. This
8.0 Hz, 2H, o-H), 7.43 – 7.41 (d, J = 8.0 Hz, 2H, m-H), 5.47
– 5.43 (q, J = 8.0 Hz, 1H,PhCHCH ), 4.59 (s, 2H,NCH ),
3
2
1.49 – 1.47(d, J =8.0 Hz, 3H, CH ), 1.03 (s, 24H,
3
3
1
1
OC(CH ) ), 1.01 (s, 12H, OC(CH ) ). C{ H} NMR (176
3
2
3 2
o
mixture was then transferred to an oil bath at 60 C for 12 h.
6 6
MHz, C D ) δ 143.0, 142.2, 128.2, 125.1, 82.5, 82.1, 72.5,
The residue was redissolved in the minimum volume of n-
hexane and left to crystallize in the freezer overnight. The
product was isolated via filtration (2a–2t).
44.9, 25.3, 24.3, 24.2.
N-{B(OCMe –2-phenylethanamine (2i) . Yield: 280
mg (75%, white solid). H NMR (400 MHz, C
22
2 2 2
) }
1
6
6
D ) δ 7.29 –
2
2
N-{B(OCMe
mg (83%, white solid). H NMR (400 MHz, C
7.59 (m, 2H, o-H), 7.25 (t, J = 8.0 Hz, 2H, m-H), 7.15 – 7.12
2
)
2
}
2
–phenylmethanamine(2a) . Yield: 298
7.27(d, J = 8.0 Hz, 2H, o-H), 7.18 – 7.14 (m, 3H, m-H, p-H),
1
6
D
6
) δ 7.60 –
3.67 (t, J = 8.0 Hz, 2H, NCH ), 2.99 (t, J = 8.0 Hz, 2H,
2
1
3
1
PhCH ), 1.04 (s, 24H, OC(CH ) ). C{ H} NMR (101
2
3 2
(
d, J = 8.0 Hz, 1H, p-H), 4.62 (s, 2H, NCH
2
), 1.03 (s, 24H,
) δ 143.4, 131.6,
6 6
28.4, 126.2, 82.2, 47.5, 24.3. B NMR (128 MHz, C D ) δ
6 6
MHz, C D ) δ 140.7, 129.7, 129.0, 126.1, 82.3, 46.0, 40.2,
1
3
1
11
OC(CH
1
3
)
2
). C{ H} NMR (101 MHz, C
6
D
6
6 6
24.7. B NMR (128 MHz, C D ) δ 29.85.
1
1
[N-{B(OCMe
2
)
2
}
2
-O-B(OCMe
(2j) . Yield: 454 mg (68%, white solid). H NMR (400
MHz, C D ) δ 7.23 (s, 4H, ArH), 3.67 – 3.63 (m, 4H,
2 2
)–(4-(aminoethylphenyl)]
2
9.45.
23
1
2
2
N-{B(OCMe
2
)
2
}
2
–m-tolylmethanamine (2b) . Yield: 264
6
6
1
NCH CH ), 3.00 – 2.93(m, 4H, NCH CH ), 1.04 (s, 48H,
mg (71%, white solid). H NMR (400 MHz, C
.43 (m, 1H, o-H), 7.29 – 7.25 (m, 1H, p-H), 7.04 – 6.95 (m,
2H, m-H), 4.60 (s, 2H, NCH ), 2.30 (s, 3H, PhCH ), 1.14 (s,
). C{ H} NMR (101 MHz, C ) δ 143.2,
6
D
6
) δ 7.47 –
2
2
2
2
1
3
1
3 2 6 6
OC(CH ) ). C{ H} NMR (101 MHz, C D ) δ 137.7, 129.1,
7
8
1.9, 45.8, 39.6, 24.3. Reaction has been performed for 48 h
2
3
1
3
1
in dry benzene.
24H, OC(CH
3
)
2
6 6
D
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5
N-{B(OCMe
2
)
2
}
2
–diphenylacetoamine (2k) . Yield: 305
2 2 2
NCH ), 2.87 – 2.77 (m, 2H, CH ), 2.15 – 2.12 (m, 2H, CH ),
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1
mg (68%, white solid) H NMR (400 MHz, C
.40 (d, J = 8.0 Hz, 4H, o-H), 7.07 – 7.02 (m, 4H, m-H), 6.95
– 6.93 (m, 2H, p-H), 4.62 (t, J = 8.0 Hz, 1H, Ph CH), 4.09 –
4.07(d, J = 8.0 Hz, 2H, NCH ), 1.01 (s, 24H,
). C{ H} NMR (101 MHz, C ) δ 143.9, 129.2,
6
D
6
) δ 7.42 –
2 2
1.85 – 1.80 (m, 2H, CH ), 1.55 – 1.54 (m, 2H, CH ,), 1.00
13
1
7
3 2 6 6
(s, 24H, OC(CH ) ). C{ H} NMR (101 MHz, C D ) δ
2
141.71, 132.3, 122.9, 82.3, 48.11, 24.2, 23.9, 23.9, 21.82.
1
1
2
6 6
B NMR(128 MHz, C D ) δ 29.85. HRMS (ESI) m/z:
1
3
1
+
OC(CH
3
)
2
6
D
6
19 35 2 4
[M+H] Calcd for C H B NO 364.2793; Found 364.2832.
128.6, 126.4 82.9, 54.8, 49.2, 24.8. Reaction has been
performed for 48 h in dry benzene.
General Procedure for Catalytic Hydroboration of
Alkynes. In a sealed vial, 19 mg (0.03 mmol) of catalyst 1,
145μL (1.0 mmol) of pinacolborane was then added,
followed by 1.0 mmol of alkyne in a neat condition. This
5
N-{B(OCMe
2
)
2
}
2
–cyclohexylmethanamine (2l) . Yield:
1
255 mg (70%, white solid). H NMR (400 MHz, C
6
D
6
) δ
), 1.90 – 1.87(m, 2H,
CH),1.73 – 1.30 (m, 10H, Cy-H), 1.07 (s, 24H,
o
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3.31 – 3.29 (d, J = 8.0 Hz, 2H, NCH
NCH
3 2 6 6
OC(CH ) ). C{ H} NMR (101 MHz, C D ) δ 82.2, 50.5,
mixture was then transferred to an oil bath at 60 C for 12 h.
2
2
The reaction mixture was concentrated and purified by
column chromatography over silica gel (100–200 mesh)
with n-hexane/ethyl acetate (1:5) mixture as an eluent,
which provided the pure product which was visualized by
UV light at 254 nm (3a–3s).
1
3
1
1
1
40.9, 31.2, 27.2, 26.6, 24.7. B NMR (128 MHz, C
6 6
D ) δ
29.48.
2
2
N-{B(OCMe
(52%, white solid). H NMR (400 MHz, C
(q, J = 8.0 Hz, 2H, NCH ), 1.33 (t, J = 8.0 Hz, 3H, CH
1.15 (s, 24H, OC(CH
δ 81.7, 38.6, 24.3, 18.6. B NMR (128 MHz, C
2 2 2
) } –ethanamine (2m) . Yield: 155 mg
1
6
D
6
) δ 3.48 – 3.43
CH ),
). C{ H} NMR (101 MHz, C
(E)-4,4,5,5-teteramethyl-2-styryl-1,3,2-dioxaborolane
(3a)1 . Yield: 172mg (75%, pale yellow oil). H NMR (700
3b
1
2
2
3
1
3
1
3
)
2
6 6
D )
MHz, C D ) δ 7.79 – 7.75(d, J = 18.5 Hz, 1H, CH), 7.33 –
6
6
1
1
6
D
6
) δ 28.80.
7.32 (m, 2H, ArH ), 7.03 – 7.01(m, 3H, ArH), 6.48 – 6.45
1
3
1
23
3 2
(d, J = 18.5 Hz, 1H, CH), 1.12 (s, 12H, OC(CH ) ). C{ H}
N-{B(OCMe
(60%, white solid). H NMR (400 MHz, C
2
)
2
}
2
–ethanamine(D3) (2n) . Yield: 180 mg
1
6 6
NMR (176 MHz, C D ) δ 149.9, 137.7, 128.6, 128.5, 127.0,
116.6 (br, C-B), 82.8, 24.6.
6
D
6
) δ 3.32 (s, 2H,
1
3
1
NCH ), 1.02 (s, 24H, OC(CH ) ). C{ H} NMR (101 MHz,
) δ 82.1, 38.8, 24.6, 18.3– 17.7 (m, CD
2 3 2
1
1
C
6
D
6
3
). B NMR
(E)-4,4,5,5-teteramethyl-2-(3-methylstyryl)-1,3,2-
dioxaborolane (3b) . Yield: 190 mg (78%, colorless oil). H
2
6
1
(128 MHz, C
6
D
6
) δ 29.75.
22
NMR (400 MHz, CDCl ) δ 7.42 – 7.37 (d, J = 18.4 Hz, 1H,
N-{B(OCMe
2
)
2
}
2
–propan-1-amine (2o) . Yield: 195 mg
3
1
CH), 7.33 – 7.25 (m, 3H, ArH), 7.14 – 7.12 (d, J = 8.0 Hz,
(
62%, pale yellow solid). H NMR (400 MHz, C
(t, J = 8.0 Hz, 2H, NCH ), 1.68 – 1.63 (m, 2H, CH
1.02 (s, 24H, OC(CH ), 0.88 (t, J = 8.0 Hz, 3H, CH
C{ H} NMR (101 MHz, C
6 6
D ) δ 3.30
1
H, ArH), 6.20 – 6.15 (d, J = 18.4 Hz, 1H, CH), 2.37 (s, 3H,
2
2
CH
CH
3
),
).
1
3
1
3 3 2
CH ), 1.34 (s, 12H, OC(CH ) ). C{ H} NMR (101 MHz,
3 2
)
2
3
1
3
1
CDCl ) δ 149.6, 138.0, 137.4, 129.7, 128.4, 127.7, 124.2,
D
6
) δ 81.7, 45.6, 26.3, 24.3,
3
6
1
1
83.3, 24.8, 21.4, one resonance not located (C-B).
11.0. B NMR (128 MHz, C
N-{B(OCMe –butan-1-amine (2p) . Yield: 195 mg
60%, white solid). H NMR (400 MHz, CDCl
= 8.0 Hz, 2H, NCH ), 2.66 – 2.62(m, 2H, CH
1.44 (m, 2H, CH CH ), 1.10 (s, 24H, OC(CH
= 8.0 Hz, 3H, CH CH
81.6, 40.6, 35.5, 24.3, 19.9, 13.6.
N-{B(OCMe –2-methylpropan-1-amine (2q) . Yield:
93 mg (90%, pale yellow oil). H NMR (400 MHz, C
δ 3.20 – 3.18 (d, J = 8.0 Hz, 2H, NCH ), 2.02 – 1.95 (m, 1H,
CH(CH ), 1.07 (s, 24H, OC(CH ), 0.98 – 0.96 (d, J = 8.0
Hz, 6H, CH(CH ). C{ H} NMR (101 MHz, C ) δ 82.5,
52.0, 31.4, 25.0, 20.6. B NMR (128 MHz, C ) δ 29.53.
N-{B(OCMe –2-methylbutan-1-amine (2r). Yield:
77 mg (82%, pale yellow solid). H NMR (400 MHz, C
δ 3.27 – 3.09(m, 2H, NCH ), 1.79 – 1.72 (m, 1H,
CH(CH )(CH CH )), 1.03 (s, 24H, OC(CH ), 0.95 – 0.87
(m, 8H, CH(CH )). C{ H} NMR (101 MHz,
) δ 81.8, 49.8, 37.4, 26.8, 24.3, 16.8, 10.8. B NMR
6 6
D ) δ 29.31.
25
(E)-4,4,5,5-teteramethyl-2-(4-methylstyryl)-1,3,2-
2 2 2
) }
2
6
1
1
dioxaborolane (3c) . Yield: 195 mg (80%, yellow oil). H
NMR (700 MHz, C ) δ 7.82– 7.80 (d, J = 18.5 Hz, 1H,
(
3
) δ 2.75 (t, J
CH ), 1.52 –
), 0.80 (t, J
). C{ H} NMR (101 MHz, CDCl ) δ
6
D
6
2
2
3
CH), 7.30 – 7.28 (d, J = 8.0 Hz, 2H, ArH), 6.86 – 6.85 (d, J
= 8.0 Hz, 2H, ArH), 6.49 – 6.46 (d, J = 18.5 Hz, 1H, CH),
2
3
3 2
)
1
3
1
2
3
3
1
3
1
2
.02 (s, 3H, CH
3
), 1.14 (s, 12H, OC(CH
3 2
) ). C{ H}
NMR(176 MHz, C
6
D
6
) δ 150.0, 138.5, 135.1, 129.2, 127.1,
22
2 2 2
) }
8
2.8, 24.6, 20.8, one resonance not located (C-B).
E)-2-(4-methoxystyryl)-4,4,5,5-tetramethyl-1,3,2-
1
2
6 6
D )
(
2
2
6
1
dioxaborolane (3d) . Yield: 202 mg (78%, colorless oil). H
NMR (400 MHz, C D ) δ 7.78 – 7.73 (d, J = 18.5 Hz, 1H,
3
)
2
3 2
)
1
3
1
)
2
6
D
6
6
6
3
1
1
CH), 7.29 – 7.27 (d, J= 8.0 Hz, 2H, ArH), 6.63 – 6.61 (d, J
8.0 Hz, 2H, ArH), 6.36 – 6.32 (d, J = 18.5 Hz, 1H, CH),
6
D
6
=
2 2 2
) }
1
3
1
3
.23 (s, 3H, OCH
3 3 2
), 1.15 (s, 12H, OC(CH ) ). C{ H} NMR
1
2
6 6
D )
(
101 MHz, C ) δ 160.8, 149.9, 130.9, 128.8, 114.3(C-B),
6 6
D
2
8
3.1, 54.7, 25.0.
3
2
3
3 2
)
1
3
1
(E)-2-(4-fluorostyryl)-4,4,5,5-tetramethyl-1,3,2-
3
2 3
)(CH CH
1
3b
1
1
dioxaboralane (3e) . Yield: 171 mg (69%, colorless oil).
6 6
C D
1
+
H NMR (700 MHz, C D ) δ 7.63– 7.60 (d, J = 18.5 Hz, 1H,
(128 MHz, C
NO
N-{B(OCMe
Yield: 190 mg (56%, white solid). H NMR (400 MHz,
) δ 3.27 (s, 2H, NCH ), 1.12 (s, 24H, OC(CH ), 1.03
) δ 82.1,
) δ 29.57.
6
D
6
) δ 29.48. HRMS (ESI) m/z: [M+H] Calcd
340.2054; Found: 340.2892.
–2,2-dimethylpropan-1-amine
6
6
CH), 7.05 – 7.04 (m, 2H, ArH), 6.64 (t, J = 8.7 Hz, 2H, ArH),
for C17
H
35
B
2
4
6
.29 – 6.26 (d, J = 18.5 Hz, 1H, CH), 1.13 (s, 12H,
2
2
2
)
2
}
2
(2s) .
1
3
1
3 2 6 6
OC(CH ) ). C{ H} NMR (176 MHz, C D ) δ 163.8, 162.4,
1
1
48.5, 133.8 (d, J = 3.2 Hz),128.7 (d, J = 8.2 Hz),115.4 (d,
J = 21.0 Hz, C-B), 82.9, 24.6.
(E)-4,4,5,5-tetramethyl-2(4-(trifluoromethyl)styryl)-
C
6
D
6
2
3 2
)
1
3
1
(s, 9H, C(CH
54.9, 33.6, 28.0, 24.8. B NMR (128 MHz, C
N-{B(OCMe
Yield: 235 mg (65%); white solid; H NMR (400 MHz,
) δ 6.69 – 6.67 (d, J = 18.1 Hz, 1H, CH), 4.78 (s, 2H,
3
)
3
). C{ H} NMR (101 MHz, C
6
D
6
1
1
6
D
6
2
6
1
,3,2-dioxaborolane (3f) . Yield: 149 mg (55%, colorless
2 2 2
) } –cyclohex-1-en-1-ylmethylamine (2t).
1
6 6
oil). H NMR (700 MHz, C D ) δ 7.57 – 7.54 (dd, J = 17.8
1
Hz, 1H, CH), 7.19 – 7.16(d, J = 8.0 Hz, 2H, ArH), 7.05 –
6 6
C D
7
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 11
7
.04 (d, J = 8.0 Hz, 2H, ArH), 6.38 – 6.34 (m, 1H, CH), 1.12 1.10 (s, 12H,OC(CH ) ), 0.79 (t, J = 7.3 Hz, 3H,
3
2
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
13
1
13
1
(s, 12H, OC(CH
3
)
2
). C{ H} NMR (176 MHz, C
6
D
6
) δ
3 6 6
CH ). C{ H} NMR (176 MHz, C D ) δ 154.6,119.2 (br, C-
1
47.9, 140.7, 130.34 (q, J = 32 Hz), 127.08, 125.4 (q, J = 4.0
B), 82.5, 35.8, 31.3, 28.0, 24.6, 22.4, 13.7.
Hz), 83.1, 24.5, one resonance not located (C-B).
(
E)-2-(oct-1-en-1-yl)-4,4,5,5-tetramethyl-1,3,2-
13b
(
E)-2-(4-phenylbut-1-en-1-yl)-4,4,5,5-Tetramethyl-1,3,2-
dioxaborolane (3n) . Yield: 142mg (60%, colorless oil).
H NMR (700 MHz, C D ) δ 6.97 – 6.96 (d, J = 17.8 Hz, 1H,
26
1
1
dioxaborolane (3g) . Yield: 193mg (75%); colorless oil; H
NMR (400 MHz, CDCl ) δ 7.31 (t, J = 8.0 Hz, 2H,ArH),
.23 – 7.21 (d, J = 8.0 Hz, 3H, ArH), 6.75 (dt, J = 17.9, 5.8
Hz, 1H, CH), 5.57 – 5.53 (d, J = 18.0 Hz, 1H,CH), 2.78 (t, J
= 8.0 Hz, 2H, CH ), 2.52 (dd, J = 15.3, 6.9 Hz, 2H, CH ),
1.31 (s, 12H, OC(CH
6
6
3
CH), 5.79 – 5.77(d, J = 17.8 Hz, 1H, CH), 2.07 – 2.04 (q, J
= 7.0 Hz, 2H, CH ), 1.31 – 1.28 (m, 4H, CH ), 1.18 – 1.16
7
2
2
(m, 4H, CH ), 1.10 (s, 12H, OC(CH ) ), 0.83 (t, J = 7.3 Hz,
2
3 2
1
3
1
2
2
3 6 6
3H, CH ). C{ H} NMR (176 MHz, C D ) δ 154.6,
1
3
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
)
2
). C{ H} NMR (101 MHz, CDCl
)
119.3(br, C-B), 82.5, 35.86, 31.6, 28.8, 28.3, 24.6, 22.5,
3
3
δ 153.4, 141.7, 128.4, 125.8, 83.0, 37.5, 34.6, 24.8, one
resonance not located (C-B).
13.9.
(
E)-2-(5-chloropent-1-en-1-yl)-4,4,5,5-tetramethyl-1,3,2-
26
1
(
E)-4,4,5,5-teteramethyl-2-(5-methylhex-1-en-1-yl)-
dioxaborolane (3o) . Yield: 179mg (78%, colorless oil). H
NMR (700 MHz, C D ) δ 6.75 – 6.73(d, J = 17.8 Hz, 1H,
12d
1
,3,2-dioxaborolane (3h) . Yield: 154mg (69%, colorless
6
6
1
oil). H NMR (400 MHz, CDCl
Hz, 1H, CH), 5.43 – 5.38 (d, J = 17.9 Hz, 1H, CH), 2.16 (dd,
J = 14.7, 7.1 Hz, 2H, CH ), 1.59 – 1.50 (m, 1H, CH), 1.31 –
1.27 (m, 2H, CH ), 1.24 (s, 12H, OC(CH ), 0.86 – 0.84 (d,
J = 6.6 Hz, 6H, CH ). C{ H} NMR (101 MHz, CDCl ) δ
3
) δ 6.65 (dt, J = 17.9, 6.4
CH), 5.72 – 5.69 (m, 1H, CH), 2.97 (t, J = 7.3 Hz, 2H, CH2),
1.98 – 1.95 (m, 2H, CH ), 1.46 – 1.42 (m,2H,CH ), 1.09 (s,
12H, OC(CH ) ). C{ H} NMR (176 MHz, C D ) δ 152.2,
3 2 6 6
2
2
1
3
1
2
2
3
)
2
121.1 (br, C-B), 82.6, 43.7, 32.5, 30.9, 24.5.
1
3
1
3
3
(
E)-trimethyl(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-
154.9, 82.9, 37.3, 33.6, 27.4, 24.7, 22.4, one resonance not
located (C-B).
11f
2
-yl)vinyl)silane (3p) . Yield: 90mg (40%); colorless oil;
1
H NMR (700 MHz, C
6 6
D ) δ 6.64 – 6.61 (d, J = 19.1 Hz, 1H,
(E)-2-(2-cyclopropylvinyl)-4,4,5,5-tetramethyl-1,3,2-
CH), 5.93 – 5.87 (d, J = 19.1 Hz, 1H,CH ), 1.09 (s, 12H,
OC(CH ) ), 0.03 (s, 9H, Si(CH ) ). C{ H} NMR (176
3 2 3 3
1
3b
1
13
1
dioxaborolane (3i) . Yield: 159mg (82%, colorless oil). H
NMR (700 MHz, C ) δ 6.40 – 6.36 (dd, J= 17.8, 9.3 Hz,
1H, CH), 5.87 – 5.84 (d, J = 17.8 Hz, 1H, CH), 1.30 – 1.28
(m, 1H, CH ), 1.10 (s, 12H, OC(CH ), 0.47 – 0.46 (m, 2H,
CH ), 0.29 – 0.28(m, 2H, CH
) δ 158.6, 116.0 (br, C-B), 82.4, 24.6, 16.9, 7.61.
2-[(E)-2-cyclopentylethenyl]-4,4,5,5-tetramethyl-1,3,2-
6
D
6
6 6
MHz, C D ) δ 157.5, 141.0 (C-B), 82.8, 24.5, -2.20(Si – C).
(
E)-2-(2-(cyclohex-1-en-1-yl)vinyl)-4,4,5,5-tetramethyl-
2
3
)
2
1
13b
1
,3,2-dioxaborolane (3q) . Yield: 166mg (71%, pale
yellow oil). H NMR (700 MHz, C D ) δ 7.51 – 7.48 (d, J =
6 6
1
3
2
2
). C{ H} NMR (176 MHz,
1
6 6
C D
18.1 Hz, 1H, CH), 5.84 – 5.80 (m, 2H, CH), 2.08 – 2.06 (m,
2H, CH ), 1.87 – 1.84 (m, 2H, CH ), 1.41 – 1.40 (m, 2H,
2
2
1
2g
dioxaborolane (3j) . Yield: 182 mg (80%, colorless oil).
2 2
CH ), 1.33 – 1.32 (m, 2H, CH ), 1.12 (s, 12H,
1
13
1
H NMR (400 MHz, CDCl
3
) δ 6.60 (dd, J = 17.9, 7.3 Hz,
3 2 6 6
OC(CH ) ). C{ H} NMR (176 MHz, C D ) δ 153.5, 137.3,
1H, CH), 5.38 – 5.33 (d, J = 18.2 Hz, 1H, CH), 2.50 (dd, J
=
–
133.5, 112.5 (br, C-B), 82.5, 25.9, 24.6, 23.7, 23.0, 22.2
15.7, 7.8 Hz, 1H, CpH), 1.75 – 1.73 (m, 2H, CpH ), 1.60
1.50 (m, 4H, CpH), 1.33 – 1.32 (m, 2H, CpH), 1.22 (s,
(Z)-4,4,5,5-tetramethyl-2-(1-phenylprop-1-en-2-yl)-
11f
1,3,2-dioxaborolane (3r) . Yield: 73mg (30%, colorless
1
3
1
1
8
2H, OC(CH
3
)
2
). C{ H} NMR (101 MHz, CDCl
3
) δ 158.8,
1
oil). H NMR (400 MHz, CDCl
3
) δ 7.53 – 7.51 (d, J = 8.0
2.9, 46.1, 32.3, 25.2, 24.7, one resonance not located (C-
Hz, 2H, ArH), 7.36 – 7.30 (m, 1H, ArH), 7.28 – 7.27 (m, 2H,
ArH), 5.40 (s, 1H, CH), 2.05 (s, 1H, CH ), 1.30 (s, 12H,
OC(CH ) ). C{ H} NMR (101 MHz, CDCl ) δ 149.1,
B).
3
1
3
1
(E)-2-(2-Cyclohexylvinyl)-4,4,5,5-tetramethyl-1,3,2-
3
2
3
2
6
1
dioxaborolane (3k) . Yield: 188mg (80%, colorless oil). H
NMR (400 MHz, CDCl ) δ 6.58 (dd, J = 18.2, 6.2 Hz, 1H,
CH), 5.36 – 5.32 (d, J = 18.0 Hz, 1H, CH), 2.06 – 1.96 (m,
H, CyH), 1.70 (t, J = 8.0 Hz, 4H, CyH), 1.63 – 1.60 (m, 1H,
CyH), 1.23 (s, 12H, OC(CH ), 1.07 (t, J = 11.6 Hz, 5H,
CyH). C{ H} NMR (101 MHz, CDCl ) δ 159.7, 82.9, 43.2,
1.9, 26.1, 25.9, 24.7, one resonance not located (C-B).
E)-2-(hex-1-en-1-yl)-4,4,5,5-tetramethyl-1,3,2-
136.4, 131.3, 129.9, 126.7, 123.8, 122.3, 83.3, 24.9, 3.1, one
3
resonance not located (C-B).
(Z)-2-(1,2-diphenylvinyl)-4,4,5,5-tetramethyl-1,3,2-
1
11f
1
dioxaborolane (3s) . Yield: 122mg (40%, colorless oil). H
NMR (700 MHz, C ) δ 8.17 (s, 1H, CH), 7.37 – 7.33 (m,
2H, ArH), 7.23 (s, 3H, ArH), 7.18 (d, J = 2.0 Hz, 3H, ArH),
.12 (d, J = 2.0 Hz, 1H, ArH), 7.10 (d, J = 2.0 Hz, 1H, ArH),
3 2
)
6
D
6
1
3
1
3
3
7
1
3
1
(
3 2 6 6
1.11 (s, 12H, OC(CH ) ). C{ H} NMR (176 MHz, C D ) δ
1
2d
1
dioxaborolane (3l) . Yield: 147mg (70%, colorless oil). H
NMR (700 MHz, C ) δ 6.97– 6.94 (d, J = 17.8 Hz, 1H,
CH), 5.80 – 5.77 (d, J = 17.8 Hz, 1H, CH), 2.05 – 2.02(q, J
7.0 Hz, 2H, CH ), 1.26 – 1.25(m, 2H, CH ), 1.16 – 1.15
m, 2H, CH ), 1.10 (s, 12H,OC(CH ), 0.76 (t, J = 7.3 Hz,
). C{ H} NMR (176 MHz, C ) δ 154.5, 119.2
143.7, 140.1, 135.0, 131.2, 129.6, 128.3, 125.4, 83.3, 24.6,
6
D
6
one resonance not located (C-B).
General procedure for intermolecular chemoselective
catalytic hydroboration. In a sealed vial, 19 mg (0.03
mmol) of catalyst 1, 1.0 mmol (or 2.0 mmol (for nitrile)) of
pinacolborane and 1.0 mmol of reactants were added
=
(
2
2
2
3 2
)
1
3
1
3
H, CH
3
6 6
D
(br, C-B), 82.5, 35.5, 30.4, 24.6, 22.1, 13.6.
successively. The progress of the reaction was monitored by
1
(
E)-2-(hept-1-en-1-yl)-4,4,5,5-tetramethyl-1,3,2-
H
NMR analyses, which marked the complete
1
3c
dioxaborolane (3m) . Yield: 145 mg (65%, colorless oil).
hydroboration of alkyne over unreacted alkene or nitrile and
also complete hydroboration of nitrile over unreacted
alkene, ester and isocyanide (final spectra are provided) in
individual cases.
1
H NMR (700 MHz, C
H,CH), 5.81 – 5.79(d, J = 17.8 Hz, 2H, CH), 2.06 – 2.03(q,
J =7.0 Hz, 2H, CH ), 1.29(m,2H, CH ), 1.14 (m, 4H, CH ),
6 6
D ) δ 6.99– 6.97 (d, J = 17.8 Hz,
2
2
2
2
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The Journal of Organic Chemistry
General procedure for catalytic hydroboration of
imines. In a sealed vial, 19 mg (0.03 mmol) of catalyst 1,
45 μL (1.0 mmol) of pinacolborane was then added,
4,4,5,5-tetramethyl-2-phenylethyl-1,3,2-dioxaborolane
(6a) . Yield: 185 mg (80%, colorless oil). H NMR (400
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
4i
1
1
MHz, CDCl ) δ 7.26 – 7.21 (m, 4H, Ar), 7.17 – 7.13 (m, 1H,
3
followed by 1.0 mmol of imine in a neat condition. This
Ar), 2.75 (t, J = 8.0 Hz, 2H, CH ), 1.22 (s, 12H, OC(CH ) ),
2
13
3 3
o
1
mixture was then transferred to an oil bath at 70 C for 20 h.
1.15 (t, J = 8.0 Hz, 2H, CH ). C{ H} NMR (101 MHz,
2
1
The
H
NMR spectrum confirms the complete
CDCl ) δ 144.4, 128.1, 128.0, 125.5, 83.1, 29.9, 24.8.
3
disappearance of the starting material and the appearance of
a new CH peak. The yield was determined by using
General procedure for catalytic hydroboration of
carbodiimides. In a sealed vial, 32 mg (0.05 mmol) of
catalyst 1, 145 μL (1.0 mmol) of pinacolborane, was then
added, followed by 1.0 mmol of carbodiimide in a neat
condition. This mixture was then transferred to an oil bath at
2
nitromethane as an internal standard (4a–4d).
N-benzyl-4,4,5,5-tetramethyl-N-phenyl-1,3,2-
2
7
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
dioxaborolan-2-amine (4a) . NMR Yield: (97%, colorless
1
o
1
oil). H NMR (400 MHz, CDCl
3
) δ 7.17 (s, 6H, ArH), 7.14
70 C for 12 h. The H NMR spectrum confirms the
complete disappearance of the starting material and the
appearance of a new CH peak. The yield was determined by
– 7.12 (m, 2H, ArH), 7.09 – 7.05 (m, 2H, ArH), 4.75 (s, 2H,
1
3
1
NCH
MHz, CDCl
20.5, 82.9, 51.2, 24.6.
N,N–dibenzyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
2
), 1.08 (s, 12H, B{OC(CH
3 2 2
) } ). C{ H} NMR (101
1
3
) δ 146.3, 140.5, 128.5, 128.3, 126.4, 121.3,
H NMR spectroscopy (7a–7b).
1
(E)-N,N’-diisopropyl-N-(4,4,5,5-tetramethyl-1,3,2-
1
5
dioxaborolan-2-yl)formimidamide (7a) . NMR Yield:
2
7
1
1
amine (4b) . NMR Yield: (95%, yellow oil). H NMR (400
MHz, CDCl ) δ 7.88 – 7.80 (m, 2H, ArH), 7.78 – 7.74 (m,
4H, ArH), 7.70 – 7.66 (m, 5H, ArH), 4.70 (s, 4H, NCH ),
). C{ H} NMR (101 MHz,
) δ 140.1, 128.2, 128.0, 126.7, 82.5, 48.3, 24.6.
N-benzyl-N-(tert-butyl)-4,4,5,5-tetramethyl-1,3,2-
(>99%, white solid). H NMR (400 MHz, CDCl ) δ 7.74 (s,
3
3
1H, NCHN), 4.41 – 4.34 (dt, J = 13.0, 6.4 Hz, 1H,
CH(CH ) ), 3.26 – 3.20 (dt, J = 12.0, 5.8 Hz, 1H, CH(CH ) ),
2
3
2
3 2
1
3
1
1.76 (s, 12H, B{OC(CH
CDCl
3
)
2
}
2
1.16 (s, 12H, NBpin), 1.14 – 1.12 (d, J = 8.0 Hz, 6H,
CH(CH ) ), 1.03 – 1.02 (d, J = 4.0 Hz, 6H, CH(CH ) ).
3 2 3 2
3
1
3
1
C{ H} NMR (101 MHz, CDCl
56.7, 42.8, 25.1, 24.3, 21.3.
(E)-N,N’-di-tert-butyl-N-(4,4,5,5-tetramethyl-1,3,2-
3
) δ 150.2 (NCHN), 82.4,
2
7
dioxaborolan-2-amine (4c) . NMR Yield: (88%, white
1
solid). H NMR (400 MHz, CDCl
Hz, 4H, ArH), 7.27– 7.26 (d, J = 4.0 Hz, 1H, ArH), 4.34 (s,
2H, NCH ), 1.33 (s, 12H, B{OC(CH ), 1.29 (s, 9H,
) δ 144.2, 127.9,
3
) δ 7.37– 7.35 (d, J = 8.0
1
5
dioxaborolan-2-yl)formimidamide (7b) . NMR Yield:
(>99%, white solid). H NMR (400 MHz, CDCl ) δ 7.83 (s,
1
2
3
)
2
}
2
3
1
3
NC(CH
26.7, 125.8, 81.4, 53.0, 48.3, 30.6, 24.5.
N-benzyl-N-4,4,5,5-pentamethyl-1,3,2-dioxaborolan-2-
3
)
3
). C NMR (101 MHz, CDCl
3
1H, NCHN), 1.30 (s, 12H, NBpin), 1.22 (s, 9H,
1
3
1
1
N(CH ) ). C{ H} NMR (101 MHz,
CDCl3)
δ
3 2
1
48.5(NCHN), 81.9, 54.4, 30.1, 24.4.
2
8
1
amine (4d) . NMR Yield: (94%, yellow oil); H NMR (400
MHz, CDCl ) δ 7.38 – 7.37 (m, 2H, ArH), 7.36 – 7.35 (d, J
= 4.0 Hz, 2H, ArH), 7.33 – 7.29 (m, 1H, ArH), 4.11 (s, 2H,
NCH ), 2.54 (s, 3H, NCH ), 1.32 (s, 12H,
B{OC(CH ). C{ H} NMR (101 MHz, CDCl ) δ 140.2,
28.2, 127.6, 126.6, 82.2, 52.8, 33.2, 24.6.
General procedure for catalytic hydroboration of
General procedure for catalytic hydroboration of
3
isocyanide. In a sealed vial, 32 mg (0.05 mmol) of catalyst
1, 290 μL (2.0 mmol) of pinacolborane, was then added,
followed by 1.0 mmol of isocyanide in a neat condition. This
2
3
1
3
1
o
3
)
2
}
2
3
mixture was then transferred to an oil bath at 80 C for 16 h.
1
1
The
H
NMR spectrum confirms the complete
disappearance of the starting material and the appearance of
1
2
a new CH peak. The yield was determined by H NMR
pyridine. In a sealed vial, 32 mg (0.05 mmol) of catalyst 1,
145 μL (1.0 mmol) of pinacolborane, was then added,
followed by 1.0 mmol of pyridine in a neat condition. This
spectroscopy (8a–8b).
4,4,5,5-tetramethyl-N-pentyl-N-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)methyl)-1,3,2-dioxaborolan-2-
o
mixture was then transferred to an oil bath at 70 C for 12 h.
1
18
1
The course of the reaction was determined by H NMR
amine (8a) . NMR Yield: (>99%, white solid). H NMR
spectroscopy, which explains the complete conversion of
pyridine.
(400 MHz, CDCl ) δ 2.85 (t, J = 8.0 Hz, 2H,
3
CH (CH ) NBpinCH Bpin),
3
2 4
2
2.45
1.36–1.30
1.25–1.20
1.18
(s,
(m,
(m,
(s,
(s,
2H,
2H,
4H,
12H,
12H,
2
9
1
CH (CH ) NBpinCH Bpin),
1,4-dihydropyridine (5a) . H NMR (400 MHz, C
6
D
6
) δ
3
2 4
2
CH
3
(CH
2
)
4
NBpinCH
2
Bpin),
6
2
.53 – 6.52 (m, 2H, ArH), 4.58 – 4.55 (m, 2H, ArH), 2.82 –
1
3
1
CH (CH ) NBpinCH Bpin),
.81 (m, 2H, CH
) δ 127.1, 102.4, 83.0, 24.2, 22.4.
General procedure for catalytic hydroboration of
2
), 1.01 (s, 12H, OC(CH
3
)
2
). C{ H} NMR
3
3
3
3
2 4
2
2
2
2
CH
CH
CH
(CH
(CH
(CH
2
2
2
)
4
)
4
)
4
NBpinCH
NBpinCH
NBpinCH
Bpin),
1.12
6 6
(101 MHz, C D
Bpin), 0.81 (t, J = 8.0 Hz, 3H,
Bpin). C{ H} NMR (101 MHz,
1
3
1
alkene. In a sealed vial, 32 mg (0.05 mmol) of catalyst 1,
145 μL (1.0 mmol) of pinacolborane, was then added,
followed by 1.0 mmol of the alkene in a neat condition. This
CDCl
4.0.
N-Cyclohexyl-4,4,5,5-tetramethyl-N-((4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)methyl)-1,3,2-
3
) δ 83.0, 81.6, 48.5, 28.5, 28.0, 24.7, 24.7, 24.4, 22.4,
1
o
mixture was then transferred to an oil bath at 110 C for 12
1
h. The course of the reaction was checked by H NMR. Upon
1
8
dioxaborolan-2-amine (8b) . NMR Yield: (>99%, white
completion, the reaction mixture was filtered and
evaporated, and the residue was purified by column
chromatography over silica gel (100−200 mesh) with ethyl
acetate/hexane (1:5).
1
solid). H NMR (400 MHz, CDCl
CyH), 2.37 (s, 2H, CyH), 1.66 – 1.63 (m, 2H, CyH), 1.56 –
.52 (m, 2H, CyH), 1.36 – 1.30 (m, 4H, CyH), 1.17 (s, 12H,
3
) δ 2.95 – 2.89 (m, 1H,
1
CyNBpinCH
2
Bpin), 1.12 (s, 12H, CyNBpinCH
2
Bpin), 0.96
9
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The Journal of Organic Chemistry
Page 10 of 11
(
8
m, 2H, CyH). 13C{ H} NMR (101 MHz, CDCl
1
3
) δ 82.9,
M.;Ma, X.;De, S.;Anusha, C.;Parameswaran, P.;Roesky, H.W. An
Aluminum Hydride That Functions like a Transition-Metal Catalyst.
Angew. Chem., Int. Ed. 2015, 54 (35), 10225-10229.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
1.3, 55.7, 31.8, 26.0, 25.7, 24.7, 24.4, 22.5.
(
5) Weetman, C.; Anker, M. D.; Arrowsmith, M.; Hill, M. S.; Kociok-
ASSOCIATED CONTENT
Kohn, G.; Liptrot, D. J.; Mahon, M. F. Magnesium-catalysed nitrile
hydroboration. Chem. Sci. 2016, 7 (1), 628-641.
Detailed optimizations, NMR spectra of the products, and
crystallographic data and structure refinement summary
(PDF).
(6) Mukherjee, D.; Shirase, S.;Spaniol, T.P.;Mashima, K.;Okuda, J.
Magnesium hydridotriphenylborate [Mg(thf)
hydroboration catalyst. Chem. Commun. 2016, 52 (89), 13155-13158.
7) Li, J.; Luo, M.; Sheng, X.; Hua, H.; Yao, W.; Pullarkat, S.A.;
Xu, L.; Ma, M. Unsymmetrical β-diketiminate magnesium(I)
complexes: syntheses and application in catalytic hydroboration of
alkyne, nitrile and carbonyl compounds. Org. Chem. Front. 2018, 5
6 3 2
][HBPh ] : a versatile
(
Crystallographic information files (CIF)
AUTHOR INFORMATION
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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(24), 3538-3547.
Corresponding Author
(8) Liu, W.; Ding, Y.; Jin, D.; Shen, Q.; Yan, B.; Ma, X.; Yang, Z.
*
E-mail: snembenna@niser.ac.in. Tel: 0091-6742494174.
Organic aluminum hydrides catalyze nitrile hydroboration. Green
Chem. 2019, 21 (14), 3812-3815.
(9) Ding, Y.; Ma, X.; Liu, Y.; Liu, W.; Yang, Z.; Roesky, H. W.
Alkylaluminum Complexes as Precatalysts in Hydroboration of
Nitriles and Carbodiimides. Organometallics 2019, 38 (15), 3092-
ORCID
Sharanappa Nembenna: 0000-0001-8856-4561
Notes
3
097.
(10) Harinath, A.; Bhattacharjee, J.; Panda, T.K. Catalytic
The authors declare no competing financial interest.
Hydroboration of Organic Nitriles Promoted by Aluminum Complex.
Adv. Synth. Catal. 2019, 361 (4), 850-857.
ACKNOWLEDGMENT
(11) (a) Feng, X.; Ji, P.; Li, Z.; Drake, T.; Oliveres, P.; Chen, E.Y.;
The authors thank the National Institute of Science Education and
Research (NISER), HBNI, Bhubaneswar, Department of Atomic
Energy (DAE), Govt. of India.
Song, Y.; Wang, C.; Lin, W. Aluminum Hydroxide Secondary
Building Units in a Metal–Organic Framework Support Earth-
Abundant Metal Catalysts for Broad-Scope Organic Transformations.
ACS Catal. 2019,
9 (4), 3327-3337; (b) Magre, M.;Maity,
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