Synthesis and Application of Silylene-Stabilized Low-Coordinate Ag(I)-Arene Cationic Complexes

Article abstract of DOI:10.1021/acs.organomet.1c00083

We report the first examples of N-heterocyclic silylene-stabilized monocoordinate Ag(I) cationic complexes weakly bound to the free arene rings (C6H6, C6Me6, and C7H8). Further, the application of these electrophilic Ag(I) complexes as catalysts has been investigated toward A3-coupling reactions, which afforded a series of propargylamines in good to excellent yields with low catalyst loading under a solvent-free condition (19 examples).

Full text of DOI:10.1021/acs.organomet.1c00083

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Article
Synthesis and Application of Silylene-Stabilized Low-Coordinate
Ag(I)−Arene Cationic Complexes
Nasrina Parvin, Nilanjana Sen, Srinu Tothadi, Shahila Muhammed, Pattiyil Parameswaran,*
and Shabana Khan*
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sı Supporting Information
ABSTRACT: We report the first examples of N-heterocyclic
silylene-stabilized monocoordinate Ag(I) cationic complexes
weakly bound to the free arene rings (C H , C Me , and C H ).
6
6
6
6
7
8
Further, the application of these electrophilic Ag(I) complexes as
3
catalysts has been investigated toward A -coupling reactions, which
afforded a series of propargylamines in good to excellent yields
with low catalyst loading under a solvent-free condition (19
examples).
he coinage metals (Cu, Ag, Au) in +1 oxidation states are
Chart 1. Silylene-Stabilized Monocoordinated M(I)−Arene
(M = Cu, Ag, Au) Cationic Complexes
T
important in catalysis, especially for various cross-
1
+
coupling reactions. In most of the cases, [L−M] [L =
monocoordinate ligands, M = Cu(I), Ag(I), and Au(I))] is
considered as the active catalytic species; although, such a type
of naked cations have not yet been isolated. A closely related
+
class of the complex [L−M−arene] , where arene is weakly
2
bound to the metal center, has some limited examples. To
date, there are only two reports of monocoordinate Ag(I)−
arene cationic complexes: one where phosphine ligands were
used to stabilize Ag(I)−toluene/m-xylene cationic complex-
3
a
es, and the other one is N-heterocyclic carbene (NHC)-
3b
stabilized Ag(I)−fluorobenzene/mesitylene cations. Being a
heavier congener of NHCs, silylenes have been widely used as
ligands in transition-metal-based catalysis due to their strong σ-
+
F
−
(
MeC H )] [BAr ] (4), respectively (Scheme 1). These are
6 5 4
the first reports of silylene-stabilized monocoordinated Ag(I)
cationic complexes weakly bound to benzene, hexamethylben-
zene , and toluene. All the complexes are well-characterized by
using routine NMR techniques and X-ray diffraction studies.
4
donation property. The current interest of our group is to
prepare well-defined coinage metal complexes stabilized by a
5
benz-amidinatosilylene ligand. Toward this end, we have
isolated a series of Si(II)−Cu(I)−arene (arene = toluene and
m-xylene) and Si(II)−Au(I)−arene (arene = benzene, m-
xylene) cationic complexes and further utilized them as
catalysts in click chemistry and glycosidation reactions,
Scheme 1. Syntheses of Silver Complexes 2−4
6
respectively (Chart 1). To complete the series, we have
turned our attention toward silver; however, due to its large
size, multiple coordination is feasible, which makes the
7
synthesis formidable. In this communication, we report the
synthesis of silylene-stabilized monocordinate Ag−arene
cationic complexes and their targeted use as catalysts.
t
T h e t r e a t m e n t o f [ { P h C ( N B u ) } S i { N -
2
5b
F
Received: February 10, 2021
Published: June 3, 2021
(
SiMe ) }] Ag (OTf) (1) with NaBAr 4 in a CH Cl −
arene (C H , C Me and MeC H ) mixture at room
3
2
2
2
2
2
2
6
6
6
6
6
5
temperature afforded monocoordinate Si(II) → Ag(I) cationic
t
2
complexes, [{PhC(N Bu) SiN(SiMe ) }Ag(η -
2
3
2
+
F
−
t
3
C H )] [BAr ] (2), [{PhC(N Bu) -SiN(SiMe ) }Ag(η -
C Me )] [BAr ] (3), and [{PhC(N Bu) SiN(SiMe ) }Ag-
6
6
4
2
3 2
+
F
−
t
6
6
4
2
3 2
©
2021 American Chemical Society
https://doi.org/10.1021/acs.organomet.1c00083
1
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Figure 1. Molecular structures of 2 (ellipsoids are shown at the
Figure 2. Molecular structures of 3 (left) and 4 (right) (ellipsoids are
F
−
probability level of 30%). Hydrogen atoms and the [BAr ] anion are
shown at the probability level of 30%). Hydrogen atoms and the
4
F
−
omitted for clarity. Selected bond lengths (Å) and bond angles (deg):
Si1−Ag1 2.37(2), Ag1−C25 2.43(8), Ag1−C24 2.54(1); Si1−Ag1−
C25 170.8(2), Si1−Ag1−C24 147.0(2).
[BAr ] anion are omitted for clarity. Selected bond lengths (Å) and
4
bond angles (deg) for 3: Si1−Ag1 2.35(7), Ag1−C1 2.50(2), Ag1−
C2 2.52(3); Si1−Ag1−C1 162.86(6), Si1−Ag1−C2 161.60(6); for 4:
Si1−Ag1 2.37(8), Ag1−C63 2.43(3), Ag1−C61 2.55(3); Si1−Ag1−
C63 174.99(7), Si1−Ag1−C61 151.94(7).
The coordination of the arene rings to the Ag(I) atom is
1
accompanied by a slight shift in the H NMR values: 3 shows a
sharp singlet at 2.34 ppm for 18 protons of the hexamethyl
2003, and after that, several research groups used either silver
salts or combined them with nanoparticles, nanocomposites,
group (free C Me : δ 2.22 ppm), 4 shows a peak at 2.45 ppm
6
6
3
for methyl group of toluene shifted downfield compared to the
free toluene (δ 2.36 ppm). The central Si(II) atom resonates at
δ −3.03 (2), −3.03 (3), and −3.97 (4) ppm in the respective
metal−organic frameworks, and polymers for the A -
12−16
coupling.
A variety of ligands have also been exploited
with silver metal to see the effect of the ligand in such
2
9
17
Si NMR spectrum, which are upfield-shifted relative to 1 (δ
transformations. Unlike copper and gold, silver is not much
F
−
8
.57 ppm). The presence of the [BAr ] anion was supported
explored, though it has advantages like (a) low cost, (b) low
catalyst loading, and (c) less reaction time.
4
1
9
by F NMR (δ) (−62.37 (2), −62.42 (3), and −62.40 (4)
1
1
3
ppm) and B NMR (δ) (−6.60 (2), −6.61 (3), and −6.60 (4)
The literature suggests that the A -coupling reaction involves
ppm) studies. 2 crystallizes in the monoclinic Cc space group.
the generation of the Ag(I) cations at first, which is weakly
2
The molecular structures of 2, 3, and 4 disclose an η
coordinated with the arene ring of the solvent or amine to
1
0
2
binding mode between the Ag(I) cation and arene ring. F
atoms are prone to manifest disorder in many crystal
structures, and we have also observed disorder of F in
complexes 3 and 4. Since the assignment of low hapticity is a
tough job, we followed the method of Alvarez and co-workers
generate an active catalyst. In this context, our [Ag(I)−η -
+
arene] complexes (2−4) would be the ideal catalysts for the
3
A -coupling reaction.
Scheme 2. Chemoselectivity of Catalyst 2
8
to assign the hapticity of the complexes 2, 3, and 4 (Table 1).
Table 1. Hapticity Calculation of 2 and 3 by Comparing the
Three Shortest Ag(I)−C
Distances, d < d < d , via the
arene
1 2 3
a
Distance Ratios ρ and ρ
1
2
a
M−C
distance ratio ρ1
distance ratio ρ2
η
d , d , d
3
1
2
2
3
4
2.43, 2.54, 2.88
2.50, 2.52, 2.74
2.43, 2.55, 2.76
1.04
1.00
1.04
1.18
1.09
1.13
2
2
2
We first performed a model reaction involving paraformal-
dehyde, phenylacetylene, and piperidine under microwave
irradiation (MW) with various catalysts under a solvent-free
condition (Tables 2 and S1). The neutral complexes LSi(II)−
AgOTf (1) and LSi(II)−AgBr (5) afforded moderate yields of
the products (48 and 53%, respectively, Table 2, entries 1 and
a
1
M = Cu, d < d < d , ρ = d /d , ρ = d /d . If ρ ≈ ρ ≫ 1, then η ,
if ρ > ρ ≈ 1, then η , and if ρ ≈ ρ ≈ 1, then η .
1
2
3
1
2
1
2
3
1
1
2
2
3
2
1
1
2
2
This method supports η coordination in 2, 3, and 4 with Ag−
benzene
bond distances of 2.50(2) and 2.52(3) Å, and Ag−C
bond distances of 2.43(3) and 2.55(3) Å. The central Si(II)
atom adopts distorted tetrahedral geometry in all the three
complexes. The lone pair of silylene is donated to the Ag(I)
center in 2, 3, and 4 with the bond distances of 2.37(2),
2
C
bond distances of 2.43(8) and 2.54(1) Å, Ag−C
2), whereas the η -coordinated Ag(I)−arene cationic com-
C6Me6
plexes 2, 3, and 4 give ∼90% product conversion (Table 2,
toluene
2
entries 3, 4 and 5). The higher efficiency of the Ag(I)−η -
arene cationic complexes could be explained by the strong
electrophilic cationic silver atom (presumably arising due to
the presence of the noncoordinating anion), which favors the
2
.35(3), and 2.37(8) Å, respectively. These bonds are in good
coordination of the Ag(I) center to alkyne and subsequently
7d,9
11b
agreement with 1 (2.337(2) Å) and other literature values.
the formation of the silver alkynide intermediate.
We
To explore the potential of 2, 3, and 4 as catalysts, we
noticed that changing the arene ring coordinated to the Ag(I)
center did not have a considerable effect in the formation of
the product (Table 2). We compared the efficiency of our
3
3
utilized them for the A -coupling reaction. A -coupling is well-
known for the synthesis of propargylamines, which involves a
multicomponent reaction of an aldehyde, an amine, and an
catalysts with the reported NHC−Ag(I) complexes (71−96%,
10
17c,d
alkyne in the presence of a transition-metal-based catalyst.
Exploration of Ag(I) complexes as catalysts for the formation
Table 2, entries 10 and 11):
while the reported catalysts
−
1
give a low TOF (2.9−48 h ), our catalysts show a TOF of
11
−1
of propargylamine was initiated by Li and co-workers in
3320−3640 h (for 0.1 mol % catalyst loading) and 14 160−
1
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Article
3
3
d
Table 2. Catalyst Screening for the A -Coupling Reaction
Chart 2. Substrate Scope of the A -Coupling Reaction
a
and Comparison with the Previously Reported Catalysts
yield
d
TOF
−1
entry
catalyst
mol %
solvent
(%)
(h )
1
2
3
4
5
6
7
8
9
1
0.1
0.1
0.1
0.1
0.1
0.05
0.1
-
neat
neat
neat
neat
53
48
90
88
90
2120
1920
3600
3520
3600
15 360
950
Si(II)→AgBr (5)
2
3
4
neat
b
2
c
CH Cl
64
95
2
2
2
neat
-
-
neat
neat
neat
∼20
∼12
81−
-
-
48
c
-
1
7c,
1
0
NHC−Ag(I)
0.5−3
9
6
1
7d
1
1
1
2
PS−NHC−Ag(I)
MIL-101(Cr)−SO Ag
1
0.06
neat
neat
71
33
2.9
6600
3
15
(
MOF)
1
3
PS−PEG−BPy−CuBr
0.05
neat
88
7320
2
(
PS−PEG-
16b
supported)
a
Reaction conditions: alkyne (1.0 mmol), aldehyde (1.1 mmol),
amine (1.1 mmol), catalyst (0.1 mol %), neat reaction, 15 min, 100
b
°
C, microwave irradiation (MW). Catalyst (0.05 mol %), stock
solution in dichloromethane (DCM), 5 min, 150 °C. Conventional
c
d
heating, 60 min, 100 °C. Isolated yield (average of two runs).
1
9 200 h− upon reducing the catalyst loading to 0.05 mol %
1
(Table 2 and Table 3).
3
Table 3. A -Coupling Reaction with 0.05 mol % of Catalyst
a
2
product
catalyst
mol %
solvent
CH Cl
yield (%)
TOF (h−1)
I
2
2
2
0.05
0.05
0.05
64
59
80
15 360
14 160
19 200
2
2
XIV
XVIII
CH Cl
2
2
CH Cl
2
2
a
Catalyst (0.05 mol %) stock solution in DCM, 5 min, 150 °C.
Since the best yield is obtained with 0.1 mol % catalyst
a
b
Used 1 mol % of catalyst 2 (neat). Used 0.1 mol % of catalyst
loading, we performed the substrate scope with 0.1 mol %
catalyst. Nevertheless, we tried three reactions with 0.05 mol %
catalyst loading (stock solution), which demonstrated
satisfactory yields (Table 3). The efficiency of our catalyst is
even better than the Ag(I)-functionalized MOF (MIL-101−
c
(neat) 2. Used 0.05 mol % catalyst 2 (stock solution in DCM), 5
d
min, 150 °C. Reaction conditions: alkyne (1.0 mmol), aldehyde (1.1
mmol), amine (1.1 mmol), neat reaction, 15 min, 100 °C, in inert
atmosphere, Isolated yields (average of two runs).
1
5
SO Ag) and polymer-supported Cu(II)−bipyridine (PS−
3
16b
PEG−BPy−CuBr ) (Table 2, entries 12 and 13), which are
regarded as highly efficient catalysts for the A -coupling
alkynes featuring aromatic, deactivated aromatic, aliphatic, and
heterocyclic rings with cyclic and acyclic secondary amines in
the presence of paraformaldehyde. Gratifyingly, high yield
(∼81−99%) is observed for propargylamines containing
phenylacetylene (I, II, III, and IV) and heterocyclic alkynes
such as 3-ethynylthiophene (V, VI, VII, and VIII) and 2-
ethynylpyridine (XIII, XIV, XV, and XVI) with piperidine,
diisopropylamine, diethylamine, and dimethylamine. Similarly,
catalyst 2 efficiently activated aliphatic alkyne to give XVII in
82% yield. Of note, propargylamines IX, X, XI, and XII could
also be isolated in a good yield (∼74−89%) upon starting from
highly unactivated alkynes containing an electron-withdrawing
2
3
reactions. We have also examined the effect of various other
reaction parameters such as mol % of catalyst, temperature,
solvent, and reaction time (Table S1). It was observed that the
catalyst 2 is highly efficient in the solvent-free condition
compared to when used with toluene or acetonitrile (70 and
7
9%, Table S1, entries 5 and 6). The blank test experiment
gives a very small amount (∼20%) of product conversion even
after 1 h (Table 2, entry 8). The catalytic reaction in the
conventional method (without MW) at 100 °C yielded 95%
product conversion in 60 min (Table 2, entry 7). To probe the
substrate scope of catalyst 2, different types of alkynes and
amines were investigated (Chart 2). We have examined various
−CF moiety. The TOFs of all the complexes were calculated
and reached up to 19 200 h , reflecting the higher efficiency of
3
−
1
1
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our catalyst, comparable with highly efficient catalysts, PS−
complex I2. This step is slightly endothermic (5.0 kcal/mol)
and exergonic (−7.2 kcal/mol). The NBO charge analysis
indicates that the complexation increases the acidity of
acetylenic hydrogen in I2 (NBO charge = 0.27 e) as compared
to that in phenylacetylene (NBO charge = 0.22 e).
16b
15
PEG−BPy−CuBr
and MIL-101−SO Ag. Interestingly,
2
3
catalyst 2 also shows selectivity for 2-ethynylbenzaldehyde
containing an alkyne group as well as aldehyde group to afford
XVIII (>99%) and XIX (86%), where the −CHO group
remains intact after the reaction. Based on NMR studies (of a
Concurrently, the amine and aldehyde react together to
form I3. The ΔE and ΔG for this reaction are −9.3 and 2.8
1
:1 reaction of the catalyst and substrates), a tentative
20
mechanism was proposed (Scheme 3): the first step involves
kcal/mol, respectively. The C−O bond length in I3 (1.47 Å)
is longer than the C−O bond length in alcohol (in the range of
1.41−1.43 Å), facilitating proton abstraction by coupling with
I2, resulting in the formation of I4. The intermediate I4 is a π-
complex formed between the Ag(I) center and the CC bond
of the product molecule. Note that the OH group in I3 has a
significantly high negative charge (−0.30 e), enabling the easy
abstraction of a proton from I2. The formation of I4 is
exothermic and exergonic (ΔE = −16.3 kcal/mol and ΔG =
3
Scheme 3. Mechanism for A -Coupling Reaction Calculated
at the M06/def2-TZVPP//BP86-D3BJ/def2-TZVPP Level
of Theory Using Catalyst 2 and Phenylacetylene,
a
Formaldehyde, and Diisopropylamine as Reactants
−
12.0 kcal/mol). The subsequent removal of the product by
coordinating with phenylacetylene regenerates the active
species I2, which can further react with I3 and continue the
catalytic cycle. This step has ΔE and ΔG vales of 5.4 and 2.3
kcal/mol, respectively.
We have also calculated the abstraction of proton from I2 by
amine (Scheme S1). The reaction energetics was found to be
highly endothermic and endergonic (ΔE = 33.6 kcal/mol and
ΔG = 32.7 kcal/mol). A hydroxyl ion alone abstracting the
proton from I2 was also considered as another possibility
(
Scheme S2), but the generation of a hydroxyl ion from an
aldehyde and amine was found to be highly endothermic and
endergonic (ΔE = 171.1 kcal/mol and ΔG = 179.3 kcal/mol).
In summary, we have reported the rare examples of
monocoordinate Ag(I)−arene cationic complexes (2−4)
stabilized by an N-heterocyclic silylene. The electrophilic
Ag(I) centers of 2−4 are involved in weak coordination with
free benzene, hexamethylbenzene, and toluene. Consequently,
a
Energies are in kcal/mol.
the displacement of the weakly coordinating arene upon the
addition of an alkyne, which leads to the formation of a π-
complex I. This increases the acidity of acetylenic hydrogen,
which is further attacked by an amine to give silver acetylide II.
The proton-assisted condensation between the amine and the
aldehyde generates a molecule of water and the iminium halide
III, which reacts with II to afford the final product. We have
also carried out the A -coupling reaction in the presence of
H O to check the stability of our catalyst, which gives 96%
product conversion (Table S1, entry 7, see SI).
1
1b
3
we have investigated them as catalysts in the A -coupling
reactions for a range of substrates and found them as a highly
efficient catalyst in the solvent-free condition with a
significantly higher TOF than the previously reported catalysts
for this reaction. Our results will spur further interest in
developing silylene-stabilized well-defined coinage metal
complexes as catalysts for other organic transformations.
3
2
We performed quantum mechanical calculations at the
M06/def2-TZVPP//BP86-D3BJ/def2-TZVPP level of theory
to explore the reaction mechanism for the A -coupling reaction
EXPERIMENTAL SECTION
■
3
All experiments were carried out under an atmosphere of dry argon or
in vaccuo using a standard Schlenk technique and in a dinitrogen-
filled MBRAUN MB 150-G1 glovebox. The solvents used were
purified by the MBRAUN solvent purification system MB SPS-800.
using catalyst 2 and phenylacetylene, formaldehyde, and
19
diisopropylamine as reactants. The overall reaction is highly
exothermic (ΔE = −20.2 kcal/mol) and slightly exergonic
5b
The starting materials 1 were prepared as reported in the literature.
All other chemicals purchased from Aldrich were used without further
(
ΔG = −6.7 kcal/mol). Among the several possible reaction
pathways, the most feasible pathway is shown in Scheme 3.
1
13
29
11
19
purification. H, C, Si, B, and F NMR spectra were recorded
2
The benzene ring is η -coordinated to the silylene-stabilized
with a Bruker 400 MHz spectrometer, using CDCl as the solvent
3
Ag(I) center in catalyst 2, and the corresponding bonding
1
13
29
11
with an external standard (SiMe for H, C, Si; BF ·OEt for B;
4
3
2
6
1
9
interaction is rather weak. The calculated energy for the
and CHF for F).
3
dissociation of benzene from catalyst 2 is ΔE = 21.2 kcal/mol
and ΔG = 10.1 kcal/mol. The first step of the reaction
mechanism is the formation of intermediate I1, wherein both
phenylacetylene and arene (benzene here) are coordinated to
Synthesis of 2. First, 1 (0.270 g, 0.200 mmol) in 10 mL of
benzene was added into another flask containing NaBArF (0.354g,
.400 mmol) in 25 mL of DCM. After overnight stirring at room
temperature, NaOTf was precipitated out from the reaction mixture
and was filtered off. The volume was reduced to 15 mL and kept at 0
4
0
the silylene-stabilized Ag(I) center. The Ag−C
bond
arene
°
C. The colorless, block-shaped crystals suitable for X-ray analysis
were observed after 1 day. Yield: 0.385 g (65%). Mp: 133−136 °C.
(
2.699 and 2.762 Å) and CC bond (1.229 Å) are
significantly elongated as compared to those in catalyst 2
2.386 and 2.683 Å) and phenylacetylene (1.215 Å). The
1
H NMR (400 MHz, CDCl , 298 K): δ 0.31 (s, 9H, SiMe ), 0.34 (s,
3
3
(
9
H, SiMe ), 1.13 (s, 18H, CMe ), 7.01 (d, J = 7.5 Hz, 1H, Ph), 7.37
3
3
reaction energy and Gibbs free energy for the formation of I1
are −8.3 and 5.6 kcal/mol, respectively. The subsequent
dissociation of the benzene molecule from I1 results in π-
(
d, J = 7.6 Hz, 1H, Ph), 7.48−7.53 (m, 2H, Ph), 7.57−7.64 (m, 9H,
13 1
Ph), 7.74−7.82 (m, 10H, Ph) ppm. C{ H} NMR (100.613 MHz,
CDCl , 298 K): δ 3.44 (SiMe ), 4.82 (SiMe ), 30.60 (CH , toluene),
3
3
3
3
1
629
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3
1.70 (CMe ), 54.10 (CMe ), 116.70, 122.10, 124.81, 126.47, 126.88,
the triple-ζ valence type and augmented with two sets of polarization
24
3
3
1
27.35, 127.72, 127.92, 128.25, 128.65, 130.53, 131.49, 133.69 (Ph−
functions, was used for geometry optimization. The single-point and
2
9
1
25
C), 168.49 (NCN) ppm. Si{ H} NMR (79.495 MHz, CDCl , 298
natural bond orbital (NBO) calculations were done using the meta-
3
26
K): δ 6.36 (SiMe ), 4.84 (SiMe ), −3.03 (SiN(SiMe ) ) ppm.
GGA functional M06 and def2-TZVPP basis set.
3
3
3 2
19
1
11
1
F{ H} NMR (376.49 MHz, CDCl , 298): δ −62.37 ppm. B{ H}
3
NMR (128.387 MHz, CDCl , 298): δ −6.60 ppm.
ASSOCIATED CONTENT
sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.1c00083.
3
■
Synthesis of 3. First, 1 (0.270 g, 0.200 mmol), hexamethylben-
*
zene (0.065 g, 0.400 mmol), and NaBArF (0.354 g, 0.400 mmol)
4
were added into a flask containing 25 mL of DCM. After overnight
stirring at room temperature, NaOTf was precipitated out from the
reaction mixture and was filtered off. Then, 3 was crystallized in a
DCM−pentane mixture and kept at 0 °C. The colorless, block-shaped
Experimental details, X-ray data, DFT data, and NMR
spectra (PDF)
crystals suitable for X-ray analysis were observed after 1 day. Yield:
1
Accession Codes
0
.439 g (70%). Mp: 126−130 °C. H NMR (400 MHz, CDCl , 298
3
CCDC 2056511−2056513 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
K): δ 0.20 (s, 9H, SiMe ), 0.25 (s, 9H, SiMe ), 1.04 (s, 18H, CMe ),
3
3
3
2
.27 (s, 18H, CH3,C6Me6), 7.26−7.28 (m, 1H, Ph), 7.41−7.49 (m, 7H,
13 1
Ph), 7.63 (bs, 9H, Ph) ppm. C{ H} NMR (100.613 MHz, CDCl ,
3
2
98 K): δ 3.36 (SiMe ), 4.41 (SiMe ), 16.28 (CH , C Me ), 30.62
3 3 3 6 6
(CMe ), 54.04 (CMe ), 116.53, 122.13, 124.84, 127.02, 127.42,
3
3
2
9
1
1
30.64, 131.42, 133.75 (Ph−C), 160.24 (NCN) ppm. Si{ H} NMR
(
79.495 MHz, CDCl , 298 K): δ 4.62 (SiMe ), 4.60 (SiMe ), −3.03
3
3
3
19 1
(
SiN(SiMe ) ) ppm. F{ H} NMR (376.49 MHz, CDCl , 298): δ
3 2 3
62.42 ppm. B{ H} NMR (128.387 MHz, CDCl , 298): δ −6.61
AUTHOR INFORMATION
Corresponding Authors
11
1
■
−
ppm.
3
Shabana Khan − Department of Chemistry, Indian Institute of
Science Education and Research Pune, Pune 411008, India;
orcid.org/0000-0002-6844-3954; Email: shabana@
iiserpune.ac.in
Synthesis of 4. First, 1 (0.270 g, 0.200 mmol) in 10 mL of
toluene was added into another flask containing NaBArF (0.354 g,
4
0
.400 mmol) in 25 mL of DCM. After overnight stirring at room
temperature, NaOTf was precipitated out from the reaction mixture
and was filtered off. The volume was reduced to 12 mL and kept at 0
Pattiyil Parameswaran − National Institute of Technology
Calicut, Kozhikode 673601, Kerala, India; orcid.org/
°
C. The colorless, block-shaped crystals suitable for X-ray analysis
were observed after 1 day. Yield: 0.420 g (70%). Mp: 140−143 °C.
0000-0003-2065-2463; Email: param@nitc.ac.in
1
H NMR (400 MHz, CDCl , 298 K): δ 0.31 (s, 9H, SiMe ), 0.35 (s,
3
3
9
7
7
H, SiMe ), 1.15 (s, 18H, CMe ), 2.45 (s, 3H, CH , toluene), 7.01−
3
3
3
Authors
.03 (d, 1H, Hz, Ph), 7.34.7.38 (m, 2H, Ph), 7.42−7.53 (m, 5H, Ph),
Nasrina Parvin − Department of Chemistry, Indian Institute of
1
3
1
.57 (s, 5H, Ph), 7.75 (s, 9H, Ph) ppm. C{ H} NMR (100.613
Science Education and Research Pune, Pune 411008, India
Nilanjana Sen − Department of Chemistry, Indian Institute of
Science Education and Research Pune, Pune 411008, India
Srinu Tothadi − Organic Chemistry Division, CSIR-National
Chemical Laboratory, Pune 411008, India; orcid.org/
0000-0001-6840-6937
MHz, CDCl , 298 K): δ 4.58 (SiMe ), 5.79 (SiMe ), 21.49 (CH ,
toluene), 31.64 (CMe ), 55.09 (CMe ), 117.88, 123.07, 125.78,
3
3
3
3
3
3
1
1
6
27.15, 127.94, 128.41, 128.74, 129.20, 131.57, 134.70 (Ph−C),
29 1
69.47 (NCN) ppm. Si{ H} NMR (79.495 MHz, CDCl , 298 K): δ
3
.50 (SiMe ), 4.81 (SiMe ), −3.97 (d, J = 567.3 Hz,
3
3
Si−Ag
1
9
1
SiN(SiMe ) ) ppm. F{ H} NMR (376.49 MHz, CDCl , 298): δ
3
2
3
11
1
−
62.40 ppm. B{ H} NMR (128.387 MHz, CDCl , 298): δ −6.60
Shahila Muhammed − National Institute of Technology
Calicut, Kozhikode 673601, Kerala, India
3
ppm.
General Reaction Procedure for Propargylamine Synthesis.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.1c00083
Alkyne (1.00 mmol), amine (1.10 mmol), and aldehyde (1.10 mmol)
were taken into a sealed tube. The catalyst (neat or stock solution in
CH Cl ) was added into the mixture. The suspension was heated
2
2
under microwave irradiation at 100 °C for 15 min. After cooling to
room temperature, the mixture was purified by flash column
chromatography over a silica gel to afford desired propargylamines.
The amount of product shown is the average of two runs. A
Author Contributions
The manuscript was written through contributions of all
authors.
Notes
concentrated solution of the samples in CDCl was sealed off in an
3
The authors declare no competing financial interest.
NMR tube for measurement. Mass spectra were recorded using AB
Sciex, 4800 plus MALDI TOF/TOF.
ACKNOWLEDGMENTS
Crystallographic Details. Crystal data for 2−4 were collected on
a Bruker Smart Apex Duo diffractometer at 100 K using Mo Kα
radiation (λ = 0.71073 Å). The absorption correction was done using
a multiscan method (SADABS). The structures were solved by direct
methods and refined by full-matrix least-squares methods against F2
■
S.K. thanks BRNS and SERB (India) for the financial support.
S.K. also thanks DST-FIST for single-crystal X-ray diffrac-
tometer. N.P. thanks to UGC for providing the fellowships.
P.P. thanks DST, India, for the financial support, and S.M.
thanks NIT Calicut for the fellowship.
1
8
(
SHELXL-2014/6). The crystallographic data file (including
structure factors) for 2, 3, and 4 has been deposited with the
Cambridge Crystallographic Data Centre: 2056511 (2), 2056512 (3),
and 2056513 (4).
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