Catalytic Hydroboration of Organic Nitriles Promoted by Aluminum Complex

Article abstract of DOI:10.1002/adsc.201801252

We demonstrate an efficient protocol for the chemoselective hydroboration of organic nitriles with pinacolborane (HBpin) and catecholborane (HBcat) using aluminum alkyl complex [κ²-{2-F?C₆H₄NP(Se)Ph₂}₂Al?(Me)] as a pre-catalyst to afford diboryl amines under solvent-free and mild conditions (60 °C) in high yield. The aluminum complex was prepared by the reaction of [2-F?C₆H₄NHP(Se)Ph₂] and trimethylaluminum in toluene. The solid-state structure of Al complex is established. Nitriles with a wide array of electron-withdrawing and electron-donating functional groups were easily converted to the desired products through the formation of aluminum hydride as an active species. A kinetic study of the catalytic reaction is also reported. (Figure presented.).

Full text of DOI:10.1002/adsc.201801252

Title: Catalytic Hydroboration of Organic Nitriles Promoted by
Aluminum Complex
Authors: Tarun Kanti Panda, Adimulam Harinath, and Jayeeta
Bhattacharjee
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201801252
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Catalytic Hydroboration of Organic Nitriles Promoted by Aluminum
Complex
Adimulam Harinath,[a] Jayeeta Bhattacharjee,[a] and Tarun K. Panda*[a]
[aDepartment of Chemistry, Indian Institute of Technology Hyderabad, Kandi – 502 285, Sangareddy, Telangana, India
tpanda@iith.ac.in)]
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. We demonstrate an efficient protocol for the
chemoselective hydroboration of organic nitriles with
pinacolborane (HBpin) and catecholborane (HBcat) using
aluminum alkyl complex [2-{2-F-C6H4NP(Se)Ph2}2Al-
(Me)] as a pre-catalyst to afford diboryl amines under
solvent-free and mild conditions (60°C) in high yield. The
aluminum complex was prepared by the reaction of [2-F-
C6H4NHP(Se)Ph2] and trimethylaluminum in toluene. The
solid-state structure of Al complex is established. Nitriles
with a wide array of electron-withdrawing and electron-
donating functional groups were easily converted to the
desired products through the formation of aluminum
hydride as an active species. A kinetic study of the catalytic
reaction is also reported.
Keywords: nitriles, boranes, hydroboration, aluminum.
procedures require more or less effective catalysts
based on transition-metal complexes such as Co, Fe,
Ru,[15–23] alkaline earth metal (Mg),[24–35] but the
Introduction
Organoborane compounds, which act as crucial processes culminate in frustrated Lewis pairs.[36–38] On
organic intermediates in various natural syntheses, and the other hand, while the reduction of aryl and alkyl
also encountered as valuable synthons in a variety of nitriles can be achieved using stoichiometric quantities
chemical transformations, are very significant in the of main-group reducing agents such as LiAlH4 and
academic and industrial fields since these precursors NaBH4,[39] the combustible nature of these reagents and
are utilized in the production of commodities and large quantities of inorganic waste by-products they
agrochemicals as well as in material synthesis.[1–8] The generate render the process unattractive, and hence
hydroboration reaction is widely employed for the reductive hydroboration is preferable in order to
transformation of carbonyl moiety into alcohols as well provide further functionality to the resultant amine.[40]
as the functionalization of unsaturated compounds, Recently, Nakazawa et al. reported the use of an iron-
followed by reduction of organic nitriles to primary indium complex as a catalyst for the hydroboration of
amines with significant substance and regional aryl and alkyl nitriles,[41] while Nikonov et al.
selectivity. Hydroboration of organic nitriles, which introduced the Mo(IV) complex as a catalyst (5 mol %),
involves the reduction of organic nitriles to primary which resulted in the hydroboration of acetonitrile and
amines, is one of the most versatile and widely benzonitrile using the only catecholborane.[42–43] The
employed reactions, as the resultant amine is essential Szymczak working group and Gunanathan et al. have
for industrial processes such as the production of dyes, also reported that a ruthenium metal–based complex (1
polyesters, and as precursors of pharmaceutical as well mol %) catalyzed nitrile and imine hydroboration in
as agrochemical compounds.[9–14] As a result, preparing the corresponding diborylamines.[44–45] In
innumerable procedures have been evolved to addition, Hill et al. reported recently that Mg(II)- (10
accomplish the addition of boranes to nitriles. All these mol %) catalyzed the hydroboration of nitriles.[46]
1
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
mild and solvent-free conditions for the synthesis of
various diboryl amines.
Cobalt-catalyzed nitrile hydroboration has also been
reported by Fout et al. and Trovitch et al.[47–48] Further,
nitrile hydroboration with catecholboranes using
nickel salts as catalysts has been described by Shimada
et al. (Fig. 1).[49]
Results and Discussion
2-Flurophenyl(diphenylphosphinoselenoic)
amine
Indeed, although numerous metal complexes are
reported to have been used for the catalytic
hydroboration of organic nitriles, there are limited
examples of the main group–catalyzed hydroboration
of nitriles in the literature till date. Thus, developing an
active main group metal–based catalyst, which is
inexpensive, abundantly available, and less toxic, is
highly desirable as an alternative to using transition
metals and expensive lanthanide metals as catalysts for
ligand (L1) was prepared according to the procedure
described in the literature.[56] Complex 1 was prepared
in good yield as colorless crystals by the treatment of
L1 with trimethyl-aluminum, Al(CH3)3, in a 2:1 ratio
at room temperature in toluene (Scheme 1). The
characteristic singlet resonance at H -0.42 ppm in the
1H NMR spectra of complex 1 measured in C6D6
confirms the presence of one methyl group (-CH3)
attached to the Al ion (Figs FS 1–4 in ESI). The
molecular structure of complex 1 was confirmed by
single-crystal X-ray diffraction analysis. Complex 1
crystallizes in the triclinic space group, with two
molecules in the unit cell. Crystallographic and
refinement parameters are set out in Table TS1. The
molecular structure of complex 1 is shown in Figure 2.
The solid-state structure of complex 1 confirms the
ligation of two amidophosphin-selenoid ligands to the
Al ion through amido nitrogen and selenium atoms.
Additionally, one methyl group is attached to Al to
give a distorted trigonal bipyramidal geometry around
the metal ion with a geometric index  = 0.64.[57]
organic
transformations.[50]
Late
main-group
organometallic chemistry, such as catalysis based on
Al, B, or Sn, has been considerably explored for its
catalytic potential by various research groups
worldwide. Among the late main-group metals,
aluminum is abundantly available, which makes it
inexpensive, and its low toxicity and biocompatibility
render it attractive for various applications in chemical
synthesis. Additionally, it has been shown as a
versatile catalyst for a broad spectrum of reactions
including polymerization,[51] epoxidation of alkenes,[52]
and hydro functionalization. Roesky et al.[53] and
Nembenna et al.[28] have reported the hydroboration of
carbonyl compounds using active aluminum hydride,
whereas Thomas et al.[54] and Roesky et al.[55] have
reported the hydroboration of alkenes and alkynes
respectively. Interestingly, until now, there have been
no reports of hydroboration of organic nitriles
catalyzed by aluminum.
Scheme 1. Synthesis of aluminum (III) complex.
Figure 2. The molecular structure of complex 1 in the solid
state, after omitting hydrogen atoms for clarity. Selected
bond lengths [Å] and bond angles [°]: Al1–N1 1.901(3),
Al1–N2 1.901(3), Al1–C1 1.955(4), Al1–Se1 2.6651(11),
Al1-Se2 2.7612(2), P1–Se1 1.1340(9), P1–Se2 1.1327(9),
C19-F1 1.286(5). N1–Al1–N2 119.26(13), N1–Al1–C1
Figure 1. Reported metal catalysts for the hydroboration of
nitriles.
120.19(15),
N2–Al1–C1
120.51(15),
Se1-Al1-Se2
158.57(4), P1-Se1-Al1 72.52 (3).
We are the first to report the aluminum-catalyzed
chemoselective hydroboration of aryl and alkyl nitriles
with pinacolborane as well as catecholborane under
2
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
Catalytic Hydroboration
groups such as -CH3, -t-Bu, -OMe (Table 2 entries 2b–
2e) or electron-withdrawing functional groups such as
-F, -Cl, -Br, -CF3 (2f–2i) reacted smoothly with HBpin
Initially, the hydroboration reaction was carried out to form the corresponding diboryl amine product
using 1 equivalent of benzonitrile (PhCN) with 2.2 ArCH2N(Bpin)2 with near-quantitative yields under
equivalents of pinacolborane (HBpin) at room optimum conditions. The hydroboration of 2-(4-
temperature in the presence of catalyst 1 (0.5 mol %) methoxyphenyl)acetonitrile and 2-(4-fluorophenyl)
under neat condition. After 24 hours of stirring at room acetonitrile as substrates furnished an excellent yield
temperature, only 50% conversion of PhCN was (80–92%) (Table 2, entries 2j–2k) under optimum
observed, with no by-product formation (Table 1 entry reaction conditions. When we switched from aryl to
1). However, when we carried out the same reaction alkyl nitrile as the substrate, the hydroboration reaction
with a higher loading of the catalyst (1 mol %) under occurred at a much faster rate, providing near-
room temperature, we were able to achieve a greater quantitative yields within a short period of time (95–
yield (90%) of diborylamine. To reduce the reaction 99%, Table 2 entries 2l–2p). Additionally, nitriles with
time, we performed the same reaction at a slightly electron-withdrawing (-Cl, -Br) and electron-donating
n
elevated temperature (60C) and to our delight, the (-OMe and - Bu) functional groups reacted with
yield from the reaction increased to 99% (Table 1 entry HBpin to produce the desired products in excellent
3) within 10 hours. However, the use of solvents such yield within five hours (Table 2, entries 2m–2p).
as THF and toluene resulted in a drastic decrease in the Under identical reaction conditions, 2-(thiophene-2-yl)
product (Table 1 entries 4–5). Thus, to ensure acetonitrile afforded an excellent yield (95%) of the
maximum efficiency and selectivity in a short time, product (2q). In contrast, 4-hydroxybenzonitrile
and based on the above observations, we decided to use converted to a tris-borylated product (2r) through the
2.2 equivalents of HBpin/HBcat in neat condition at cross-dehydrocoupling of -OH and HBpin, with the
60oC for the hydroboration reaction by loading 1 mol% hydroboration of -CN functional groups exhibiting
of catalyst 1.
greater reactivity toward hydroxy groups in the
substrate (Figs FS59–FS61 in ESI).
Table 1. Optimization table for hydroboration of nitriles
using catalyst 1
Table 2. Aluminum-catalyzed hydroboration of nitiles with
HBpin
Entry Cat1
(mol%)
Solvent T(C)
t(h)
yield
1
2
3
4
5
0.5
Neat
Neat
Neat
THF
Tol
r.t
r.t
60
60
60
24
24
10
10
10
50
90
99
30
40
1
1
1
1
The yield was calculated using 1H NMR (400 MHz)
integration of a characteristic product signal present in the
reaction mixture by using (HMB) as an internal standard.
With this optimized condition, we first investigated the
scope of the reaction in the presence of aromatic,
aliphatic as well as heterocyclic nitriles with
pinacolborane. All the results are summarized in Table
2 (2a–2r). In each case, the yield of the diboryl amine
1
product was calculated from the H NMR analysis of
the reaction mixtures using hexamethylbenzene
(HMB) as an internal standard. (Figs FS 5–61 in ESI).
The hydroboration of unsubstituted benzonitrile
proceeded rapidly and a quantitative yield of
[PhCH2N(Bpin)2] was obtained within 10 hours (Table
2 entry 2a). Aryl nitriles with either electron-donating
3
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
ester group unperturbed (Scheme 2, 3m, Figs FS101–
FS106 in ESI). However, 4-acetyl-benzonitrile was
reacted with HBpin (2.2 equiv.) in presence of catalyst
1 to give hydroboration of both nitrile and ketone
functional groups indicating the higher reactivity of
ketone compare to nitrile group (Scheme 2, 2s) (FS126
- FS128 in SI).
Reaction conditions: catalyst 1 (1 mol%), nitrile (1 equiv.),
HBpin (2.2 equiv.), and reaction mixture was heated to 60C,
1
yield was calculated on the basis of H NMR (400 MHz)
integration of characteristic product signal present in the
reaction mixture using (HMB) as internal standard. In the
case of 2r, 3.2 equiv of HBpin was used.
Next, to expand our protocol, we investigated the
hydroboration reaction of nitriles with catecholborane
(HBcat). Initially, we carried out the reaction with
acetonitrile and HBcat while maintaining the same
reaction condition. We observed that the hydroboration
of acetonitrile with HBcat afforded the desired diboryl
amine product [CH3CH2N(Bcat)2] (3a) in quantitative
yield within three hours (Table 3 entry 3a). We
investigated the scope of the reaction further, and
representative results are summarized in Table 3. It is
noteworthy that the responses of alkyl nitriles with
both electron-donating -OMe and butyl groups and
electron-withdrawing -Cl, -Br groups continued easily,
giving an excellent yield of [RCH2CH2N(Bcat)2]
Table 3. Aluminum-catalyzed hydroboration of nitiles with
HBcat.
o
within four hours at 60 C (80–94 %, Table 3, entries
3b–3e).
In the case of an aryl nitrile such as benzonitrile, the
hydroboration resulted in the formation of a
quantitative amount of [PhCH2N(Bcat)2] (Table 3,
entry 3f). Similarly, the hydroboration of p-tolunitrile
and 2-(4-methoxyphenyl) acetonitrile resulted in the
formation of [p-CH3C6H4)CH2N(Bcat)2] and [(p-
MeOC6H4)CH2CH2N(Bcat)2] respectively in quanti-
tative yields under the same reaction conditions (Table
3 entries 3g, 3j). Interestingly, the hydroboration of
fluoro-, trifluoro-substituted benzonitrile and 2-(4-
fluorophenyl) acetonitrile brought about the formation
of corresponding diboryl amines in 92% yield (Table 3
entries 3h–3i, 3k). The hydroboration of 4-hydroxy-
benzonitrile with 3 equivalents of HBcat yielded the
tris-borylated product (3l), obtained through the
reaction of both -OH and -CN functional groups, which
was also observed in the case of HBpin (Table 3 entry
3l).
Reaction conditions: Cat 1 (1 mol%), nitriles (1 equiv.),
o
HBcat (2.2 equiv.); the reaction was carried out at 60 C.
1
Yield was caluculated on the basis of H NMR (400MHz)
integration of characteristic product signal present in the
reaction mixture. For 3l, 3.2 equivalents of HBcat was used.
Scheme 2. Chemoselective hydroboration of nitriles.
Although several reports in literature41–49 have
described the catalytic hydroboration of aryl nitriles
with lower conversion to the desired diboryl amine
products even after prolonged reaction times, the
current protocol demonstrates that we can achieve the
target compounds in very good yields under mild
conditions and in shorter reaction times. To extend the
synthetic scope of this response, we also tested the
chemoselective hydroboration of nitriles. Methyl 4-
cyanobenzoate, having both nitrile and ester
functionalities, was reacted with HBpin (2.2 equiv.) to
chemo selectively reduce the nitrile group and afforded
a quantitative yield, leaving the ester group intact
(Scheme 2, 2t). Replacing HBpin with HBcat (2.2
equiv.) also provided a similar result at the nitrile
center under the same reaction conditions, leaving the
Reaction conditions: Cat 1 (1 mol%) methyl 4-
cyanobenzoate (1.0 equiv.), pinacol/catecholborane (2.2
equiv.). The yield calculated on the basis of 1H NMR (400
4
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
MHz) integration of a characteristic product signal
present in the reaction mixture.
order. Thus, we can only represent the kinetics
analysis of alkyl nitriles with electron donating
group such as 2-methoxy acetonitrile to achieve a
significant result in the presence of HBpin and
catalyst 1 using hexa-methylbenzene (HMB) as an
internal standard to calculate the amounts of
starting material and product present in the
reaction mixture. Initial reactions were performed
at 333 K and the rate of the reaction was monitored
Two separate control reactions were carried out
using 4-triflurobenzonitrile and HBpin in presence
only ligand L1 in set 1 and using AlMe3 in set 2.
From the NMR spectra (Figure FS129 - FS135 in
SI), it was observed that in presence of the ligand L1
even at higher loading of ligand 50 mol%, no traces
of product was formed. However, the hydroboration
reaction in the presence of only AlMe3 (10 mol%),
40% conversion of nitrile to diborylamine was
achieved in 10 h. It is noted that the pyrophoric
nature of the AlMe3 is considered as a major
disadvantage for its use as a catalyst also it have
tendency to produce mixture of products.
Additionally, a blank reaction with t-butyl
benzonitrile with HBpin and thiophene 2-
carbonitrile with HBpin were performed in absence
of the catalyst and no traces of product formation
under these conditions was observed (Figure FS136
- FS140 in SI).
1
by H NMR spectroscopy utilizing the 1:2.4
proportion of 2-methoxy-acetonitrile (0.25 M) to
HBpin (0.6 M) in the presence of various
concentrations of catalyst 1 (1–5 mol %).
0.018
0.016
0.014
y = 0.01664x - 0.0002
R2 = 0.99
0.012
0.010
0.008
0.006
0.004
0.002
0.000
Table 4. Hydrolysis of diborylamines to give primary
amines.
0.0
0.2
0.4
0.6
0.8
1.0
HBpin / M
Figure 3. Kinetics plots of kobs vs [HBpin] for the reaction
of [CH3OCH2CN] with [HBpin]. Reaction conditions:
[CH3OCH2CN]=0.25 M, [{(Ph2P(=Se)N(C6H4F)}2Al(CH3)]
= 2.5 mM) and [HBpin] = 0.5 M to 0.9 M] in CDCl3 (0.4
mL).
Additionally, to isolate the end-product of the
hydroboration reaction of organic nitriles, we
treated the diboryl amine product using aqueous
HCl (0.05 M) at room temperature for two hours,
which gave a fine white powder of substituted
benzyl ammonium chloride in moderate yield
(Table 4, 4a–4d).
Further, to evaluate the mechanistic implications
of hydroboration of nitriles, we carried out a
kinetics study. Kinetic studies highlight variations
in mechanism for the catalytic dihydroboration of
alkyl nitriles, aryl nitriles bearing either electron
withdrawing {Ar(EWG)CN/Alk(EWG)CN} or
electron donating {Ar(EDG)CN/Alk(EDG)CN}
substitution patterns that already well reported by
Hill et al.[35] Aryl nitrile bearing electron
withdrawing group shows zero order with respect
to HBpin and first order with respect to both nitrile
Under these reaction conditions, the rate was observed
to be first-order with respect catalyst, keeping both the
concentrations of 2-methoxyacetonitrile and HBpin
constant (Figs FS107–FS109 in ESI). In addition, a
first-order dependence was also obtained with respect
to the concentrations of both the substrates i.e. 2-
methoxyacetonitrile and HBpin, by keeping the
concentration of either one substrate along with the
catalyst concentration unchanged (Figs FS112–FS115
in ESI). Thus, the empirical rate law may be written as:
rate = k[catalyst][methoxyacetonitrile][HBpin]
and
catalyst
concentrations.
However,
hydroboration of aryl nitrile with electron
donating group provides different dependence
towards the rate determining process during
catalysis and ultimately does not show any proper
5
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
Schlenk technique or argon-filled glove box. CDCl3 was
1
distilled and stored in the glove box. H NMR (400 MHz),
13C{1H} NMR (100 MHz), and 11B{1H} (128.3 MHz)
spectra were measured on a BRUKER AVANCE III-400
spectrometer. 1H NMR spectra were recorded on a 400 MHz
spectrometer at 298 K in CDCl3; chemical shifts (δ ppm) and
coupling constants (Hz) are reported in standard fashion
with reference to either internal standard tetramethylsilane
(TMS) (δH = 0.00 ppm) or hexamethylbenzene (HMB) (δH =
2.22 ppm). 13C NMR spectra were recorded on a 100 MHz
spectrometer at 298 K in CDCl3; chemical shifts (δ ppm) are
reported relative to CHCl3 [δC = 77.00 ppm (central line of
1
the triplet)]. In the H-NMR, the following abbreviations
were used throughout: s = singlet, d = doublet, t = triplet, q
= quartet, qui = quintet, sept = septet, dd = doublet of doublet,
m = multiplet and br. s = broad singlet. Elemental analyses
were performed on a BRUKER EURO EA at the Indian
Institute of Technology Hyderabad. All the starting
materials:
2-fluro-aniline,
chlorodiphenylphosphine,
trimethyl aluminum, and organic nitriles were purchased
from Sigma Aldrich India and used without further
purification. Pinacolborane and catecholborane were
purchased from Sigma Aldrich India and distilled prior to
use.
Scheme 3. The most plausible mechanism for catalytic
hydroboration reaction of nitriles with HBpin.
In light of this outcome and those previously reported
in the literature, [53–55] the most plausible mechanism
for the catalytic hydroboration of nitriles with HBpin
is shown in Scheme 3. Initially, aluminum pre-catalyst
1 reacts with HBpin to form the active aluminum
hydride species (I), which further reacts with the nitrile
and affords the corresponding imine (III) via sigma
bond metathesis. The imine complex (III) further
reacts with another molecule of HBpin to yield a four-
membered species (IV) which eventually rearranges to
give boryl amine (V) and subsequently reacts with
another HBpin molecule to give diboryl amine
aluminum species (VI). In the final step, the active
Preparation of [2-{2-F-C6H4NP(Se)Ph2}2Al(Me)] (1)[58]
To a solution of LH [L= (C6H4FNP{Se}Ph2)] (200 mg, 0.53
mmol) in toluene (15 mL), a solution of Al(CH3)3 (0.63 mL
0.5 M, 0.027mmol) in toluene was added at room
temperature. Immediate evolution of CH4 was observed and
the reaction mixture was further stirred for 12 hours. The
resulting solution was evaporated under reduced pressure to
give a white solid residue. The residue was further purified
by washing with cold hexane and recrystallized from a
toluene/n-pentane mixture (4:1) at -35C.
aluminum hydride species is regenerated by emitting Yield: 384 mg (92%). 1H NMR (400 MHz, C6D6): δH 7.80 -
7.75 (m, 8H, ArH), 7.51 - 7.41 (m, 12H, ArH), 6.98 - 6.93
(m, 2H, ArH), 6.65 - 6.57 (m, 4H, ArH), 6.31 (t, J = 8 MHz,
2H, ArH), -0.42 (s, 3H, CH3). 13C{1H} NMR (100 MHz,
C6D6): δc 154.4 (Ar-C attached to F), 133.9 (Ar-C), 132.6
(Ar-C), 131.9 (Ar-C),131.8 (Ar-C), 129.0 (Ar-C), 128.9,
124.3 (Ar-C), 120.3 (Ar-C), 115.12 (Ar-C), -5.3 (CH3) ppm.
31P (1H) NMR (161.9 MHz, C6D6) δ 38.1 (1J PSe = 534 Hz)
ppm. 19F {1H} NMR (376.4 MHz, C6D6) δF -127.0 ppm.
Elemental Analysis: C37H31AlF2N2P2Se2 (788.50): Calcd. C
56.36, H 3.96, N 3.55. Found C 56.13, H 3.68, N 3.38.
the corresponding free diboryl amine product. The
reaction of species (III) with HBpin is much slower
than that of aluminum hydride (I) with nitrile and
considered as the rate determining step of the
hydroboration reaction. No decomposition of HBpin
was observed during the reaction.
To summarize, we have reported here the aluminum-
catalyzed hydroboration of organic nitriles under
solvent-free conditions. A number of organic nitriles,
bearing a wide cluster of electron-withdrawing and
electron-donating functional groups, can experience
effective hydroboration with pinacolborane as well as
catecholborane under mild conditions to give near-
quantitative yields. The reaction proceeds through the
formation of metal hydride species.
General procedure for the synthesis of diboryl amine
compounds (2a–2s and 3a–3m)
Catalyst 1 (1 mol %), nitriles (2a–2s or 3a–3m 0.5 mmol)
and boranes such as pinacolborane/catecholborane (2.2
mmol) were placed in a 25 mL Schlenk flask equipped with
a magnetic stir bar inside the glove box. The reaction
mixture was stirred at 60°C for 1–6 hours depending on the
nature of the starting materials. The progress of the reaction
was monitored by 1H NMR spectroscopy using
hexamethylbenzene (10 mol %) as an internal standard.
After the reaction was complete, the excess of pinacolborane
EXPERIMENTAL SECTION
All manipulations involving air- and moisture-sensitive
compounds were carried out with argon, using the standard
6
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
or catecholborane was evaporated under reduced pressure to [13] J. S. Carey, D. Laffan, C. Thomson, M. T. Williams,
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[14] A. Ricci, Modern Amination Methods; Wiley:
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[16] T. D. Nixon, M. K. Whittlesey and J. M. J. Williams,
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Supporting Information
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[17] S. R. Tamang and M. Findlater, J. Org. Chem., 2017
82, 12857–12862.
[18] D. A. Evans and G. C. Fu, J. Org. Chem., 1990
2138, 2280–2282.
[19] R. Arévalo, C. M. Vogels, G. A. MacNeil, L. Riera,
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7750–7757.
This material is available free of charge via the Internet at
http://pubs.acs.org. 1H and 13C{1H}, 11B{1H}, 19F{1H},
NMR spectra, and mass spectra, and combustion analysis of
all the diboryl amine and substituted benzyl ammonium
chloride 2a-2s, 3a-3m, 4a-4d are given in Supporting
Information.
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ACKNOWLEDGMENTS
This work was supported by the Japan International Cooperation
Agency (JICA) FRIENDSHIP Project under the Collaboration
Kick-starter Program (CKP) ARC2016-2. A.H. and J.B. thank
CSIR and UGC India respectively for their Ph.D. fellowships. We
also thank Prof. Kazushi Mashima and Dr. Hayato Tsurugi, Osaka
University, Japan, for their generous support.
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10.1002/adsc.201801252
Advanced Synthesis & Catalysis
UPDATE
Catalytic Hydroboration of Organic Nitriles
Promoted by Aluminum Complex
Adv. Synth. Catal. Year, Volume, Page – Page
Adimulam Harinath,[a] Jayeeta Bhattacharjee,[a] and
Tarun K. Panda*[a]
9
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