Palladacycles having normal and spiro chelate rings designed from bi- and tridentate ligands with an indole core: Structure, synthesis and applications as catalysts

Article abstract of DOI:10.1039/c7nj02116j

1-Pyridin-2-ylmethyl-1H-indole-3-carbaldehyde and 1-((1-benzyl-1H-1,2,3-triazol-4-yl)methyl)-1H-indole-3-carbaldehyde were synthesized. Their condensation with benzyl amine resulted in indole core containing Schiff bases benzyl-(1-pyridin-2-ylmethyl-1H-in

Full text of DOI:10.1039/c7nj02116j

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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ARTICLE
Palladacycles having normal and spiro chelate rings designed from
biꢀ and tridentate ligands with indole core: structure, synthesis
and applications as catalysts
Received
Accepted
Mahabir P. Singh, Fariha Saleem, Ram S. Pal and Ajai K. Singh*
DOI: 10.1039/x0xx00000x
1ꢀPyridinꢀ2ꢀylmethylꢀ1Hꢀindoleꢀ3ꢀcarbaldehyde and 1ꢀ((1ꢀbenzylꢀ1Hꢀ1,2,3ꢀtriazolꢀ4ꢀyl)methyl)ꢀ1Hꢀindoleꢀ3ꢀcarbaldehyde
were synthesized. Their condensation with benzyl amine resulted in indole core containing Schiff bases benzylꢀ(1ꢀpyridinꢀ2ꢀ
ylmethylꢀ1Hꢀindolꢀ3ꢀylmethylene)amine (L1) and benzylꢀ[1ꢀ(1ꢀbenzylꢀ1Hꢀ[1,2,3] triazoleꢀ4ꢀylmethyl)ꢀ1Hꢀindolꢀ3ꢀyl
methylene]amine (L2) respectively, unknown hitherto. The K2CO3 promoted sulfenylation of indole formed 3ꢀ(pyridinꢀ2ꢀ
ylsulfanyl)ꢀ1Hꢀindole (L3), also unknown so far. The yield of L1−L3 was 72ꢀ93%. The L1 and L2 on reaction with sodium
tetrachloropalladate(II) in the presence of CH3COONa give complexes [Pd(L1/L2−H)Cl] (1 / 2) in which they bind in a
tridentate (N,C−, N’) pincer mode. The L3 on reaction with [(MeCN)2PdCl2] results in a dimeric palladacycle [Pd(L3ꢀH)Cl]2
(3) with a spiro ring. The precursor aldehydes, L1ꢀL3 and Pd(II)ꢀcomplexes derived from them, were characterized using
1H, 13C{1H} NMR and HRꢀMS. The complexes 2 and 3, ligands L1 and L3 and precursor aldehydes of L1 and L2 were
authenticated with single crystal Xꢀray diffraction. The PdꢀC bond distances (Å) are 1.932(8) / 2.115(3) (2/3). The PdꢀN
bond lengths (Å) are: 2.063(7) and 2.028(7) for 2 and 2.053(3) and 2.019(3) for 3. These complexes have been found
efficient as a catalyst for SuzukiꢀMiyaura coupling of ArCl (3 as a catalyst) and ArBr and allylation of a variety of
aldehydes (1 and 2 as catalysts). The optimum loading of complexes as a catalyst is 0.001−0.01 and 1 mol% respectively for
the two reactions which appear to follow homogeneous pathway.
www.rsc.org/
antimicrobial,12 antitcancer,13 antioxidant,14 antiꢀinflammatory,15
antifungal16 and antihypertensive17 activities. The interest in metalꢀ
binding properties of indole ring known to coordinate via nitrogen
Introduction
Palladacycles of ligands having nitrogen as a coꢀdonor have got a lot
of attention in recent years.1,2 The ligands in such palladacycles are
generally biꢀ (N, C‾) or triꢀdentate (N, C‾, N). The chemistry of a
variety of (N, C‾, N) pincer type ligands and their metal
complexes,3,4 has been explored due to their versatile applications,
particularly of the complexes in chemical transformations (ranging
from stoichiometric to catalytic) with selectivity.5 The (N, C, N)
pincer ligands are stable towards oxidation6 and have two variants
symmetrical (N, C, N) and unsymmetrical (N, C, N’). However,
former ones are known,7,8 in much large number than the (N, C, N’)
type.9
Indole being a constituent of many biomolecules and natural
products10 is an important heterocyclic system. A number of indole
derivatives are part of functional cores in essential amino acid
tryptophan, growth regulating substance heteroauxin (indolylacetic
acid), serotonin etc.11 Several indole based compounds have
and carbon employing its tautomeric forms 1ꢀH and 3ꢀH
respectively, has arisen further due to its bio and clinical importance
cited above. However, complexes of the ligands based on this core,
having palladation at its Cꢀ2 and Cꢀ3(sp3) atom have been explored
scantly.18ꢀ19 It was thought, therefore, worthwhile to design new
complexes having coordinated 1Hꢀ or 3H–indole derivative, and
explore their chemistry. Thus benzylꢀ(1ꢀpyridinꢀ2ꢀylmethylꢀ1Hꢀ
indolꢀ3ꢀylꢀmethylene)amine (L1) and benzylꢀ[1ꢀ(1ꢀbenzylꢀ1Hꢀ
[1,2,3]triazoleꢀ4ꢀylmethyl)ꢀ1Hꢀindolꢀ3ꢀylmethylene]amine (L2) and
3ꢀ(pyridinꢀ2ꢀylsulfanyl)ꢀ1Hꢀindole (L3) were synthesized. The L1
and L2 having electronically different N donor atoms in the two
arms, undergo palladation at Cꢀ2 (1Hꢀindole form) and L3 at Cꢀ3
(Csp3of 3Hꢀindole form). In complexes [Pd(L1/L2−H)Cl] (1 / 2) the
ligand makes both five and six membered chelate rings. The pincers
forming two types of chelate rings, known so far, are fewer in
number20 than those which make two five or six membered
rings.3,5,21,22 In, [Pd(L3ꢀH)Cl]2, L3 forms a five membered chelate
ring (spiro type) due to palladation.
Palladium species are known to catalyze CꢀC coupling and
therefore 1−3 have been explored for catalysis of SuzukiꢀMiyaura
coupling (SMC) of ArCl /ArBr and allylation of several aldehydes.
The SMC continues to get attention of both industry and academia23
due to its importance in organic synthesis. Palladium complexes of
pincer ligands, were first reported by Szabό and coꢀworkers as
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efficient catalysts for allylation of aldehydes or activated imines.24
The homoallylic alcohols, resulting from allylation of aldehydes
have extensive use in the synthesis of biologically active compounds
and natural products.25 For both SMC and allylation of aldehydes no
complex of Pd(II) with ligand based on indole core, except
palladacycles of unsymmetrical (N, C‾,S/Se) pincers26 is in our
knowledge. The ligands in palladacycles 1 and 2 are the first
examples of unsymmetrical (N, C, N’) pincers with indole core
reported herein for the two catalytic reactons. The dimeric
palladacycle with a spiro ring, 3 has 3Hꢀindole core.
2 observed at 7.79 ppm is shielded by ∼0.71 ppm relative to the
corresponding signal of L2 at 8.50 ppm. Triazole being more basic
than pyridine makes Pd electron rich which causes shielding of CH
proton when imine nitrogen coordinates.
O
O
O
PhCH2N3, t-BuOH
Propargyl bromide
Sodium Ascorbate,
CuSO4
K2CO3, DMF, rt
N
H
N
N
N
N
B1
B
N
Ethanol
PhCH2NH2
Ph
25
22
Results and discussion
26
24
23
20
21
The syntheses of L1−L3 and their Pd(II) complexes (1−3) are
summarized in Schemes 1−3. 1ꢀPyridinꢀ2ꢀylmethylꢀ1Hꢀindoleꢀ3ꢀ
carbaldehyde (A in Scheme 1) was prepared by refluxing indoleꢀ3ꢀ
carbaldehyde with 2ꢀchloromethylpyridine hydrochloride in DMF
for 2 h, instead of reacting them for more than 10 h at room
temperature.27 Moreover, in lieu of extraction of both A and B
(Scheme 2) in dichloromethane,27 B was extracted into ethylacetate
and the remaining reaction mixture was cooled in refrigerator
overnight to isolate A.
19
19
N
17
N
15
15
17
16
16
11
MeOH,CH3COONa
70 °C, Na2PdCl4
14
13
14
13
Pd Cl
18
18
N
N
11
12
12
10
N
N
N
N
10
9
9
N
8
8
N
7
7
6
5
3
6
5
3
4
4
1
1
2
2
2
L2
Scheme 2 Synthesis of ligands L2 and its Pd (II) complex 2
O
O
K2CO3, DMF
2-(Chloromethyl)pyridine
.HCl
1
In H NMR spectrum of
3
, the NH signal of L3 (9.58 ppm)
form and
N
H
N
N
disappears impling that indole unit of L3 is in 3
H
A
coordinates with palladium via nitrogen and Cꢀ3. The signal of
proton ortho to nitrogen of pyridine ring (H1) in 1H NMR
spectrum of L3 appearing at 8.36 ppm can be considered
Ethanol
PhCH2NH2
19
19
18
18
20
21
17
20
21
deshielded by
the spectrum of
note that the aromatic region of H NMR spectrum of
nonꢀfirst order resonances. Overall the signals in 1H NMR
spectra of complexes , support the coordination of ligands
∼
0.51 ppm, presuming that signal at 8.87 ppm in
16
16
17
15
22
3
is also of the same proton. It is important to
N
N
22
15
N
11
12
11
8
1
13
13
12
7
3
has
10
9
10
9
MeOH,CH3COONa
70 °C, Na2PdCl4
14
Pd Cl
N
7
8
6
N
6
1–3
N
1
1
2
5
4
5
2
with Pd, as shown in Schemes 1–3.
4
3
3
L1
1
The scans of high resolution mass spectra (HRꢀMS) given
in ESI (Figs. S22ꢀS27) authenticate ligands and complexes. In
Scheme 1 Synthesis of ligands L1 and its Pd(II) complex 1
the spectra of L1–L3 peaks appearing at m/z = 326.1652,
406.2026 and 227.0642, respectively may be ascribed to
[L+H]+. The peaks of [M−Cl]+ have been observed in the
1,3ꢀDipolar cycloaddition of benzyl azide with B (having appended
terminal alkyne)27 gave B1 which on condensation with benzyl
amine resulted in L2 (Scheme 2). 3ꢀ(Pyridinꢀ2ꢀylsulfanyl)ꢀ1Hꢀindole
(L3) was synthesized by K2CO3 promoted sulfenylation of indole
with aldrithiol (Scheme 3).28 The L1−L3 and 1ꢀ2 have good
solubility in CH2Cl2, CHCl3, ethylacetate and DMF. The 3,
moderately soluble in the first three, has good solubility in DMSO
and DMF. The L1−L3 and 1−3, being air and moisture insensitive
can be stored for several months under ambient conditions.
spectra of Pd(II) complexes
and 696.8735 respectively.
1–3 at m/z = 430.0538, 510.0914
Crystal structures
The crystallographic and refinement data of L1, L3, 2 and
3 are
given in the ESI (Tables S1 S3). Their molecular structures
−
with selected bond lengths and angles, justifying the geometry
of central / donor atom are shown in Figs. 1–4. Some selected
bonding parameters for
S5 of ESI. The CH2Cl2 molecule present in the crystal of
omitted in Fig. 4 for clarity. The molecular structures of
aldehyde precursors and are given in the ESI (Figs. S1–S2)
with their selected bond lengths and angles. The L2 coordinates
in a (N, C−, N
) pincer mode forming fiveꢀ and sixꢀmembered
chelate rings with palladium whereas L3 binds in 3 ꢀindole
2
and
3
are also given in Tables S4 and
NMR and mass spectra
3
is
1
The H and 13C{1H} NMR spectra of A, B, B1, L1–L3 and their
A
B
palladacycles (ESI: Figs. S7–S21) were found consistent with their
structures given in Schemes 1−3. The CH15 (imine), signal (singlet)
at 8.61 ppm in 1H NMR spectrum of L1, probably appears as a
broad signal at 10.47 ppm in the spectrum of 1 (deshielded by 1.85
ppm). However the CH19 (imine), signal (singlet) in the spectrum of
′
H
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tautomeric form through N and tetrahedral Cꢀ3 of indole, CH2Cl2 participates in network building. The nonꢀcovalent
forming dimeric complex
3
with spiro ring.
interactions distances of ligands and their precursors are given
in Tables S6 and S7 of ESI.
3
S
4
Cl
N
6
2
5
1
Pd
S
N
S
13
8
N
1
Pd
N
2
7
Aldrithiol
PdCl2,K2CO3
6
N
9
Cl
13
K2CO3
DMSO
CH3CN
3
5
7
12
10
N
10
4
N
H
reflux,30 min
12
8
H
11
9
11
L3
3
Scheme 3 Synthesis of ligands L3 and the Pd (II) complex 3
The present spiro ring is different from the one reported
earlier19b. Here each Pd is a member of spiro ring and another 5
membered ring (having S), whereas in the earlier reported
one19b Pd is a part of two rings (one 5 membered and another 6
membered) apart from spiro ring. The geometry of palladium in
2
and
3 is distorted square planar with Cl and C(indolyl)
Fig.
1 Molecular structure of L1: Bond distances (Å):
N(2)−C(14) 1.339(4); N(2)−C(7) 1.380(4); N(2)−C(6)
1.466(4); N(3)–C(15) 1.262(4); N(3)−C(16) 1.461(4). Bond
angles (°): N(2)−C(6)−C(9) 113.3(3); C(15)−N(3)−C(16)
118.4(4).
disposed trans to each other. The Pd−C bond length of
2
(1.932(8) Å) is somewhat shorter than the values reported for
palladacycles of indole based (N, C, S/Se) ligand,26 1.957(8)
and
N
ꢀ(2ꢀnorbornyl)indole18a 2.0392(16) Å. This bond length
of 3, 2.115(3) Å is shorter relative to the value, 2.351(17) Å
reported for tetranuclear Pd(II) complex formed with Nꢀ
phenylindole and (Me)3CCOO‾.18b The Pd−C bond lengths of
2
and
reported for the [{Pd(C6F5)(
[PdCl(allyl) (Tripy)] (Tripy = [1,2,4]ꢀtriazolo[4,3ꢀ
ylidene)31 respectively. The Pd−N(amine) and Pd−N(triazole)
bond distances, in (2.063(7) and 2.028(7) Å respectively), are
3
are consistent with values, 1.932(5) and 2.115(6) Å
ꢀBuNC)(ꢁꢀPhNNNPh)}2]30 and
]pyridinꢀ3ꢀ
t
a
2
consistent with the lengths of such bonds, 2.056(4) and
2.005(4) Å, reported for palladacycle of (N, Se, C‒) pincer2d and
palladium complex of
respectively. The Pd−N bond distances of Pd(II) complexes of
pyridineꢀ2,6ꢀdicarboxylate,33 2.063(4) and terpyridine,34
2.028(7) Å are similar to those of . The Pd−N(pyridine) and
Pd−N(indole) of [2.053(3) and 2.019(3) Å respectively] are
consistent with the values reported for such bond distances of
Pd(II) complex of orthoꢀdiethylatedazobenzene35 (2.053(2) Å)
and [Pd2(en)2ꢀ(C5H4NO)2]2+ (2.019(3) Å).36 The Pd−Cl bond
a
1,2,3ꢀtriazole based ligand32
Å
2
Fig. 2 Molecular structure of L3. Bond distances (Å): S(1)–
C(6) 1.746(2); S(1)–C(1) 1.765(2). Bond angles (°): C(6)–S(1)–
C(1) 104.98(10).
3
Catalytic studies
lengths, 2.390(3) and 2.3360(10) Å of
2
and
3
respectively are
Application to SuzukiꢀMiyaura coupling
Suzuki Miyaura coupling (SMC) resulting biaryls important for
comparable with those of [(BL Pr)PdCl2] (BL
i
iPr = 1,2ꢀbis(1,3ꢀ
diisoꢀpropylꢀ4,5ꢀdimethylimidazolinꢀ2ꢀimino)ethane)
[2.3256(8)].37 The N−C(13) and C(6)–C(13) bond distances in
synthesis
of
agrochemicals,
natural
products
and
pharmaceutical ingredients23 was catalyzed with 1–3 (Scheme
4) under aerobic conditions. 4ꢀBromobenzaldehyde when
reacted with phenylboronic acid (for optimization of SMC) in
DMFꢀwater mixture (3 : 1) for 1 h at 90 °C in the presence of
L3 are 1.355(3) and 1.363(3) Å, respectively. In
distances have been found as 1.310(4) and 1.457(5)
respectively, indicating that in , N−C(13) bond acquires a
double character and C(6)–C(13) becomes a single bond. This
3 these bond
Å
3
0.01 mol% of
1 and K2CO3 as a base, a coupled product
may be attributed to coordination of L3 with Pd(II) in 3H
indole tautomeric form.
ꢀ
biphenylꢀ4ꢀcarboxaldehyde, was obtained in ~99% yield (Table
1 Entry 1). The yield of the product was low on using other
bases in the place of K2CO3 under similar reaction conditions
The nonꢀcovalent intermolecular interactions mainly
involved in the formation of 3ꢀD structural networks are:
C−HꢂꢂꢂO for aldehyde precursors, C–Hꢂꢂꢂπ for L1, C–H···S/N–
(Table 1, Entries 2
water mixture diminishes yield of the coupled product
considerably (Table Entries 9). The coupling of
phenylboronic acid with a variety of aryl chlorides/bromides
–4). The use of solvents other than DMFꢀ
1
5–
HꢂꢂꢂN for L3 and C−HꢂꢂꢂCl for
2
/
3
(Figs. 5 and 6 and Figs. S3
–
S6 given in ESI). In the case of
3
intramolecular C−HꢂꢂꢂCl
was catalyzed with
1
‒3
, in optimized solvent and base. The
interactions are also present. Further in this complex Cl of
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results for
1
2
and
2
are given in Table 2 and for
3
in Table 3. 4ꢀBromobenzaldehyde is coupled almost quantitatively in 1 h
as a catalyst (Table 3, Entry 1). With 4ꢀ
the yield was good even at 0.001 bromoanisole as substrate, yield of coupled product was 94%
with 0.02 mol% of . 4ꢀChlorobenzaldehyde gave coupled
product in 80% yield but in a 12 h reaction using 1.0 mol% of
. However, and failed to catalyze SMC of ArCl.
The
1
and
gave the product in good yield at 0.01 mol% using 0.001 mol% of 3
loading of Pd whereas for
mol% loading.
3
3
3
1
2
Fig. 6 Nonꢀcovalent C−HꢂꢂꢂꢂCl interaction in 3. Bond distances
(Å):1: C(13)—H(13)ꢂꢂꢂCl(2) 2.6963; 2: C(14)—H(14A)ꢂꢂꢂCl(1)
2.9123; 3: C(8)—H(8)ꢂꢂꢂCl(12) 2.829; 4: C(1)—H(1)ꢂꢂꢂCl(1)
2.6073.
[1/3]Pd Cat
Ar
X
Ar
+
B(OH)2
(0.001 to 1 mol%)
X= Cl, Br
Fig. 3 Molecular structure of 2. Bond distances (Å): Pd(1)–
Scheme 4 SMC catalyzed with 1–3
Table 1 Optimization of reaction conditionsa for SMC
C(16) 1.932(8), Pd(1)–N(3) 2.028(7), Pd(1)–N(1) 2.063(7),
Pd(1)–Cl(1) 2.390(3). Bond angles (°): C(16)–Pd(1)–N(3)
88.2(3), C(16)–Pd(1)–N(1) 78.9(3), N(3)–Pd(1)–N(1) 167.0(3),
C(16)–Pd(1)–Cl(1) 174.5(3), N(3)–Pd(1)–Cl(1) 96.8(2), N(1)–
Pd(1)–Cl1 96.2(2).
Entry
Solvent
Base
Yieldb
No.
1
DMF + Water
DMF + Water
DMF + Water
DMF + Water
DMF
K2CO3
Cs2CO3
CH3COONa
CH3ONa
K2CO3
99
47
2
28
18
3
4
5
50
22
65
<5
70
6
NMP
K2CO3
7
Toluene
K2CO3
8
THF
K2CO3
9
Ethanol + Water(3:1)
K2CO3
aReaction conditions: 1.0 mmol4ꢀbromobenzaldehyde, 1.5 mmol
phenylboronic acid, 2 mmol base, 0.01 mol% of catalyst . Solvent 4
1
mL, DMF:Water (3:1); reaction time 1 h; bath temperature 90 °C.
bNMR yield (%).
Fig. 4 Molecular structure of 3. Bond distances (Å): Pd(1)–
Table 2 Suzuki Miyaura coupling reaction catalyzed with 1–2a
N(2) 2.019(3), Pd(1)–N(1) 2.053(3), Pd(1)–C(6) 2.115(3),
Pd(1)–Cl(1) 2.3360(10). Bond angles (°): N(2)–Pd(1)–N(1)
173.15(11), N(2)–Pd(1)–C(6) 93.11(12), N(1)–Pd(1)–C(6)
84.34(12), N(2)–Pd(1)–Cl(1) 88.31(8), N(1)–Pd(1)–Cl(1)
94.82(9), C(6)–Pd(1)–Cl(1) 174.46(10).
Entry Aryl bromide
Catalyst
1
Catalyst
Yieldb
2
Mol
%
t
(h)
Yieldb
1
2
3
4
5
6
7
8
4ꢀBromobenzaldehyde
0.01
0.01
0.01
0.01
0.01
0.1
1
1
100
75
100
75
4ꢀBromobenzonitrile
4ꢀBromonitrobenzene
4ꢀBromoacetophenone
Bromobenzene
1
100
100
100
80
100
98
1
1
90
4ꢀBromotoluene
3
88
4ꢀBromoanisole
0.01
0.1
12
5
75
89
Fig. 5 Nonꢀcovalent C−HꢂꢂꢂꢂCl interaction in 2.Bond distances
(Å): 1: C(8)—H(8)ꢂꢂꢂCl(1)2.7564; 2:C(11)—H(11)ꢂꢂꢂCl(1)2.8769;
3:C(1)—H(1B)ꢂꢂꢂCl(1)2.8465
4ꢀBromoaniline
90
92
4 | J. Name., 2012, 00, 1-3
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ARTICLE
aReaction conditions: 1.0 mmol ArBr, 1.5 mmol phenylboronic acid, 2 mmol
K2CO3, solvent: 4 mL, DMF:Water (3:1), bath temperature 90 °C. bIsolated
yield in %.
The time profiles of both complex
bromobenzaldehyde (under optimum reaction conditions)
shown in Fig. 7 are close and consistent with the fact complex
is more efficient than . Nearly 85 % conversion occurs in 40
min with 1/3. For substrate with electron donating group i.e 4ꢀ
bromotoluene the rate of SMC for both catalysts and under
optimum reaction condition was also found to be close. The
yield of coupled product increased with time and became
maximum after 3 h (Fig. 8). However 80% conversion was
achieved in 2 h.
1 and 3 for SMC of 4ꢀ
3
Table 3 Suzuki Miyaura coupling reaction catalyzed with 3a
1
Entry
Aryl halide
Catalyst
t (h)
3
Yieldb
1
3
Mol
%
1
2
3
4
5
4ꢀBromobenzaldehyde
4ꢀBromobenzonitrile
4ꢀBromonitrobenzene
4ꢀBromoacetophenone
Bromobenzene
0.001
0.001
0.001
0.001
0.02
0.005
0.02
0.005
0.02
1.0
1
3
97
95
92
95
96
54
95
45
94
80
92
3
3
Pd(II) complex of unsymmetrical (N, C, N’) pincer7 having
oxazoline and pyrazole in its two arms as a Nꢀdonor carry out
SMC of bromobenzene with a good yield, at its 0.1 mol%
12
8
6
7
4ꢀBromotoluene
4ꢀBromoanisole
3
loading (in ~7 h). The
1 gives same result with 0.01 mol% in 1
8
h. The 0.1 mol% loading at 120 °C reported optimum for Pd(II)
complex of unsymmetrical (N1,C, N2) pincer formed by
tandem reaction between 3ꢀ[(2,4,6ꢀtrimethylphenylimino)ꢀ
methyl]ꢀphenol8 and [Pd(NCPh)2Cl2] is higher than those of 1ꢀ
3. Palladacycles of Schiff bases resulting from 2ꢀ
(phenylthio/seleno)ethylamine and ferrocene carboxaldehyde38
3
8
9
4ꢀChlorobenzaldehyde
4ꢀBromoaniline
12
3
0.05
aReaction conditions: 1.0 mmol ArBr/ArCl, 1.5 mmol phenylboronic acid, 2
mmol K2CO3, solvent: 4 mL DMF:Water (3:1), bath temperature 90 °C.
bIsolated yield in %.
show good conversion (comparable to those of
0.01 mol% loading. The Pd complex of (N, C, N) pincer
(methyl ester of 3,5ꢀbisꢀ(5 ꢀpyrazolꢀ1ꢀylmethyl)benzoic acid
1 and 2) at their
H
having two pyrazole units as Nꢀdonor) shows good yield of
SMC in H2O at 100 °C when loading of Pd is 0.1 mol%,39
higher than the optimum loading of 1ꢀ3. The complexes
comparable to 1ꢀ3 are as follows. Pd complex of 1,3ꢀbisꢀ
phenylselanylmethylbenzene [(Se, C, Se) pincer]40 promotes
SMC at 0.001 mol% loading and 100 °C but reaction is slow
(20 h). The ligands which give palladacycles showing good
catalytic activity at 0.006ꢀ0.001 mol% loading are: (i) Schiff
bases41 made from 2ꢀthiophenemethylamine and 2ꢀ
hydroxybenzophenone/2ꢀhydroxyꢀ4ꢀmethoxybenzophenone,
(ii) 2−HO−4−H / OMe−C6H3−(C6H4)CHNHꢀ(CH2)3SPh (C−, N,
h
reaction time)42 (ii) 2,3ꢀbis[phenylꢀ
Fig.7 Time profile of catalytic SMC of 4ꢀbromobenzaldehyde
S)] pincer (15
thiomethyl]quinoxaline (12 h of reaction time)29 and (N, Se, C−)
(1.0 mmol) with
1 (0.01 mol%) and 3 (0.001 mol%)
pincer (shows conversion of 4ꢀbromo nitrobenzene like
3 but in
15h).2d The 5 mol% of Pd(II)ꢀbis(oxazolinyl)phenyl complex4d
is required for SMC of aryl iodide. The 5 mol% of palladacycle
of [Pd(Phbz)(mal)(PPh
)]2e is required to couple dibromoanthracene
3
(conversion is 70%). Palladium complex of 7ꢀferrocenylꢀmethylꢀ3ꢀ
methylꢀ3,7ꢀdiazabicyclo[3.3.1]nonane2f shows good conversion in
SMC of aryl bromides but only when catalyst loading is 0.5 mol%.
Palladacycles with Nꢀheterocyclic carbene were found to catalyze
SMC of aryl bromides with 1 mol% loading of the catalyst.2g
Fig. 8 Time profile of catalytic SMC of 4ꢀbromotoluene(1.0
mmol) with (0.1 mol%) and (0.02 mol%)
1
3
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Fig. 10 Time profile of allylation of 4ꢀbromobenzaldehyde (1.0
Fig.9 Reaction cycle of catalytic SMC of 4ꢀbromobenzaldehyde mmol) with 1 (1 mol%)
with (0.01 mol%) and (0.001 mol%)
The catalysis of SMC by 1ꢀ3 is fast in comparison to most of The
the examples cited above and catalyzes coupling of ArCl as allyltributylstannane in the presence of 1 was studied (Table 4) to
well, of course optimum loading required for good conversion optimize the reaction conditions of allylation. The DMF was found
is higher than that of ArBr. the most appropriate solvent (Table 4 ) and 1 mol% of 1 optimum to
1
3
coupling
reaction
of
4ꢀbromobenzaldehyde
with
3
To study reuse of the present catalysts, after completion of give good yield in 12 h. (Table 4 Entry 2). On lowering the catalyst
conversion in SMC of 4ꢀbromobenzaldehyde the reaction flask loading to half, conversion became 22% (Table 4 Entry 6). The N2
was replenished with a fresh lot of substrate, phenylboronic atmosphere was used as in the presence of air conversion reduced
acid (1.5 mmol) and K2CO3 (2 mmol) (See footnote of Table 3) significantly (Table 4, Entry 5), inspite the stability of catalysts in
and reaction was continued for 1h (optimum time). The catalyst air. The time profile of allylation of 4ꢀbromobenzaldehyde (1.0
was found active and yield of coupled product was ~ 100% mmol) with allyltributylstannane (1.2 mmol) with
1 (1 mol%)
(determined with 1H NMR) in the second reaction cycle (Fig 9). under optimum reaction conditions is shown in Fig. 10. The
The replenishing was repeated and ~50% conversion (Fig. 9) conversion steadily increases with time. The yield of allylated
was noticed in fifth reaction cycle in case of
respectively. In third and fifth run of SMC reaction catalyzed (Table 5). The activity enhances in the presence of electron
with the conversion to coupled product was 84 and 47% withdrawing groups on the ring. For deactivated 4ꢀ
1
and
3
product depends on the nature of substituents present on phenyl ring
1
respectively in 1 h. On continuing the reaction for 3 h the methoxybenzaldehyde, the reaction resulted in low conversion (51%
conversions became 100 and 70% respectively. In the fifth run and 54% for 1 and 2 respectively; Table 5: Entry 6). The hetero aryl
with catalyst
3 the conversion was 52%. It also became 84% halides have also been allylated successfully with good yield (Table
on increasing the reaction time to 3 h.
5: Entry 7 and 9). The difference in catalytic activity of 1 and 2 is
not significant (Table 5).
Application in allylation of aldehydes
Palladium(II) complex of Nꢀisopropylꢀ1ꢀaminomethylꢀ3ꢀ(2ꢀ
pyridyloxyl)benzene43 (unsymmetrical (N, C, N’) pincer) catalyzes
allylation of pꢀnitrobenzaldehyde at 5 mol % loading and 50 ºC. The
1 and 2 do allylation of the same substrate at 1 mol % loading under
almost similar reaction conditions. Pd(II) complex of unsymmetrical
(C, N, N) pincer43 (Nꢀtolylꢀ2ꢀaminomethylꢀ6ꢀphenylpyridine) is
reported as a catalyst for allylation of 4ꢀbromobenzaldehyde but
requires, 5 mol % loading and reaction time of 24 h at 50 ºC, making
it less attractive than 1 and 2.
The 1 and 2 were explored for allylation of various aryl and
heteroaryl aldehydes with allyltributylstannane. To the best of our
knowledge, no Pd(II) complex of indole based unsymmetrical (N, C,
N’) pincer has been used to catalyze this reaction so far.
Table 4 Optimization of reaction conditionsa for allylation of aldehydes
Entry
Solvent
Yieldb
No.
1
Table 5 Allylation of aldehydes catalyzed with
1
and 2a
DMF + Water
DMF
75
95
2
28
18
3
DCM
4
THF
5
DMFc
DMFd
50
22
6
Complex
1
Complex 2
Entry
aReaction conditions: 1.0 mmol 4ꢀbromobenzaldehyde, 1.2 mmol
Aryl Aldehyde
No.
Yieldb
95
Yieldb
96
allyltributyl stannane, 2 mL solvent, 1 mol% of catalyst1. Reaction time
d
12 h, N2 atm, bath temperature 50 °C, bIsolated yield, Cwithout N2, 0.5
1
2
3
4
5
6
7
8
9
4ꢀBromobenzaldehde
2ꢀBromobenzaldehde
4ꢀChlorobenzaldehyde
Benzaldehyde
mol% catalyst.
98
72
78
90
76
92
4ꢀMethylbenzaldehyde
4ꢀMethoxybenzaldehyde
Furfural
90
91
51
54
94
95
4ꢀNitrobenzaldehyde
90
92
Pyridineꢀ2ꢀ carbaldehyde
92
96
aReaction conditions:1.0 mmol aryl
/ heteroaryl aldehyde , 1.2
6 | J. Name., 2012, 00, 1-3
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Conclusions
mmolallyltributylstannane, 2 mL DMF, 1 mol% complex as catalyst.
N2 atm., Reaction time 12 h, bath temperature 50 °C. bIsolated yield.
Palladium(II) complexes of ligands with indole core are known
scantly as catalyst for SMC and allylation of aldehydes. Thus
Palladium(II)ꢀcomplex of (S, C, S) pincer (1,3ꢀbisꢀphenylꢀ
sulfanylmethylꢀbenzene) catalyzes allylation of pꢀnitrobenzaldehyde
at 2 mol % loading25c, whereas the complex of (S, C, S) pincer25d
catalyzes allylation of the same substrate at 1 mol% loading, but in
24 h yield is 49%. The 5 mol% of palladacycle25e of (P, C‾) ligand
and 2 at 1 mol% loading catalyze allylation of benzaldehyde with
same efficiency. Palladacycle25f of (Se C Se) (1 mol%) allylates 4ꢀ
bromobenzaldehyde with 92% yield in 24 h. The 2.5 mol% loading
of palladium complex of tridentate phosphido diphosphine ligand
[(P, P, P) pincer] as a catalyst44 was found insufficient for allylation
of pꢀanisaldehyde. The 5 mol% of Pdꢀcomplexes of (P, C, P) pincer
ligands (1,3ꢀBisꢀ[diphenylphosphanyl)methyl]benzene/anthracene)45
and bis(phosphite)25g is optimum to obtain good conversion in
allylation catalyzed with them. Pd(II) complexes of Bis(NHC’s)25h
catalyze allylation of benzaldehyde with 1 mol% loading as with the
present catalyst but the reaction time is 36 h while it is 12 h with 1/2.
indole based unsymmetrical (N, C, N’) pincer ligands [L1
formed by condensation of benzyl amine with 1ꢀpyridinꢀ2ꢀ
ylmethylꢀ1 ꢀindoleꢀ3ꢀcarbaldehyde 1ꢀ((1ꢀbenzylꢀ1 ꢀ1,2,3ꢀ
triazolꢀ4ꢀyl)methyl)ꢀ1 ꢀindoleꢀ3ꢀcarbaldehyde have been
synthesized for the first time. 3ꢀ(Pyridinꢀ2ꢀylsulfanyl)ꢀ1
indole L3) was also afforded by K2CO3 promoted
sulfenylation of indole for the first time.
/ L2]
H
/
H
H
Hꢀ
(
Table 6 Mercury poisoning experiment for Suzuki Miyaura coupling with 1a
Entry Time
No. min at the time of Hg addition
% Conversion
% Conversionb after 6 h of
Hg addition
1
2
3
4
0
Nil
35
81
87
85
86
83
89
20
40
50
aReaction conditions: 1.0 mmol 4ꢀbromobenzaldehyde, 1.5 mmol
The πꢀallylpalladium complexes containing bidentate
Nꢀ
heterocyclic carbene ligands46 are reported for allylation of
benzaldehyde at 10 mol% loading (reaction time 1.5−17 h,
phenylboronic acid, 2.0 mmol K2CO3, 0.01 mol % of Complex 1. Solvent 4
b
mL, DMF +Water (3:1), bath temperature 90 °C. After standard workup of
the whole reaction mixture.
temperature 70 °C). In comparison to
1 and 2 their performance
Palladacycles [Pd(L1/L2−H)Cl]
(1 and 2) and dimeric
is poor. Thus and can be placed in the category efficient
1
2
palladacycle (palladation at tetrahedral Cꢀ3 atom of 3Hꢀ
3
catalysts known for allylation of aldehydes. The mechanism for
Pd(II) pincer ligand complex catalyzed allylation of aldehydes
reported by Szabό and coꢀworkers45 appears to be applicable in
our case also. First transmetalation of allylstannane with
catalyst results in η1ꢀallylꢀcoordinated pincer species. It is
followed by generation of nucleophilic σꢀallylpalladium species
and its addition to the aldehyde (via a cyclic transition state
indole) have been prepared and found suitable as catalyst at
their low loading (0.001 mol%) for SMC of various aryl
chlorides
catalyzing SMC the catalyst remains active and gives
reasonable yield in fifth to seventh run. Complexes and
/ bromides including deactivated ones. After
1
2
were found to be efficient catalyst for allyation of aldehydes
with 1 mol% of catalyst loading.
with the metal).
Finally alkoxideꢀcoordinated palladium
undergoes exchange reaction with SnBu3X to give homoallyl
alcohol.
Experimental
Materials and instrumentation
Nature of catalysis with Pd(II) complex 1
Sodium tetrachloropalladate, allyltributylstannane, propargyl
bromide, sodium borohydride and palladium(II) chloride were
To understand the nature of catalyst in both SMC and
allylation of aldehydes, Hg and PPh3 poisoning tests47 were
carried out. 4ꢀBromobenzaldehyde was used as a substrate and
procured
(Chloromethyl)pyridine hydrochloride, 2,2′ꢀdipyridyl disulfide,
indole, indoleꢀ3ꢀcarboxaldehyde, benzyl bromide,
from
SigmaꢀAldrich
(USA).
2ꢀ
complex
1 as a catalyst Under optimum reaction conditions
SMC is not quenched in the presence of Hg(0)/PPh3, but yield
is reduced by 10ꢀ15 % after running reaction for 6 h, indicating
that contribution of heterogeneous pathway to catalysis is
small. Absence of blackening of reaction mixture or colloidal
Pd formation rules out substantial role heterogeneous pathway.
In the case of allylation conversion was not inhibited even after
18 h of reaction. Thus, both catalytic reactions with 1ꢀ3 appear
to be predominantly homogeneous. In SMC of 4ꢀ
bromobenzaldehyde with phenylboronic acid under optimum
conditions Hg was added at different time intervals to the
reaction as given in Table 6. The reaction continued in each
case with vigorous stirring after addition of Hg up to 6 h. The
conversion into coupled product (monitored with 1H NMR), did
not reduce significantly on the addition of Hg at different stages
also and almost reached to maximum after a reaction of 6 h.
These results (Table 6) further support that the process
catalyzed with the present complexes is largely homogeneous.
phenylboronic acid, bases, aldehydes, aryl halides and solvents
were procured locally. All these chemicals were used as
received, except solvents which were dried and purified by
standard methods.48 The reported methods were used for the
synthesis of azidomethylbenzene.49 The picolyl or propargyl
appended indoleꢀ3ꢀcarbaldehyde was prepared using reported
procedures27 modified suitably. Commercial nitrogen gas was
used after passing it successively through traps containing
solutions of alkaline anthraquinone, sodium dithionite, alkaline
pyrogallol, concentrated H2SO4 and KOH pellets. Yields
reported are of isolated coupled products which have purity ≥
95% [established by 1H NMR]. The products of Suzukiꢀ
Miyaura coupling and allylation reactions were authenticated
by matching their spectroscopic data with those reported in the
literature.
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The 1H, and 13C{1H}, NMR spectra were recorded on a C, 78.67; H, 4.95; N, 7.65%. 1H NMR (CDCl3, 25 °C, TMS):
Bruker Spectrospin DPX 300 NMR spectrometer at 300.13, δ (ppm): 2.56 (s, 1H, H1), 4.94 (s, 2H, H3), 7.26 (s, 1H), 7.35–
75.47 and 57.24 MHz, respectively. Carbonꢀ13 DEPT NMR 7.44 (m, 2H), 7.90 (s, 1H), 8.34(d, 1H), 10.02 (s, 1H, C12)
experiments were used routinely to determine the number of .13C{1H} NMR (CDCl3, 25 °C, TMS): δ (ppm): 36.4, 75.4,
hydrogen atoms linked to a carbon. Melting points were 75.7, 109.8, 118.2, 121.9, 123.1, 124.0, 125.2, 136.5, 137.6,
determined in an electrically heated apparatus by taking the 184.4.
sample in a glass capillary sealed at one end. Elemental
Synthesis of 1ꢀ(1ꢀBenzylꢀ1
indoleꢀ3ꢀcarbaldehyde (B1)
Hꢀ[1,2,3]ꢀtriazoleꢀ4ylmethyl)ꢀ1Hꢀ
analyses were carried out with a PerkinꢀElmer 2400 Series II C,
H, analyzer. Highꢀresolution mass spectral (HRꢀMS)
N
measurements were performed with a Bruker Micro TOFꢀQ II In a round bottom flask azidomethylbenzene (0.266 g, 2 mmol)
machine based on electron spray ionization (10 eV, 180 °C and 1ꢀpropꢀ2ꢀynylꢀ1 ꢀindoleꢀ3ꢀcarbaldehyde (0.366 g,
source temperature, and sodium formate as a calibrant), taking mmol) were taken in 5 mL of ꢀBuOH. Each of CuSO4.5H2O
H
2
t
the sample in CH3CN. Xꢀray diffraction data for the single (10 mol%, 0.050 g) and sodium ascorbate (20 mol%, 0.078 g)
crystals were collected with a Bruker AXS SMART Apex CCD dissolved separately in 2 mL of distilled water were quickly
diffractometer at 298(2) K using MoꢀKα (0.71073 Å) radiation. added to the reaction flask. The reaction mixture was stirred at
Frames were collected by
ω, φ, and 2θꢀrotations with full 80 °C for 12 h. It was cooled and tꢀBuOH removed on a rotary
quadrant data collection strategy (four domains each with 600 evaporator. The residue was mixed with cold water (40 mL)
frames) at 10s per frame with SMART. The measured and extracted with ethylacetate (4 × 25 mL). The combined
intensities were reduced to F2 and corrected for absorption with organic layer was washed successively with brine (2 × 25 mL),
SADABS.50 Structure solution and refinement were carried out 20% ammonia solution (2 × 25 mL) and water (20 mL).
with the SHELXTL package by direct methods.51 Nonꢀ Anhydrous sodium sulfate was used to dry the organic phase
hydrogen atoms were refined anisotropically. All hydrogen and its solvent evaporated off under reduced pressure on a
atoms were included in idealized positions and a riding model rotary evaporator to get brown solid, B1
.
was used for the refinement. Images were created with the B1: Brown solid; Yield: 0.568 g, 1.7 mmol (90)%; m.p. 110 °C.
program Diamond.
Anal. Found: C, 72.11; H, 5.11; N, 17.70%. Calcd for
C19H16N40: C, 72.13; H, 5.10; N, 17.71%. 1H NMR (CDCl3,
25 °C, TMS): δ (ppm): 5.40 (s, 2H), 5.43 (s, 2H), 7.20–7.21 (d,
2H), 7.25–7.34 (m, 6H), 7.39–7.41 (s, 1H), 7.75(s, 1H), 8.26(t,
1ꢀPyridinꢀ2ꢀylmethylꢀ1Hꢀindoleꢀ3ꢀcarbaldehyde (A)
The indoleꢀ3ꢀcarbaldehyde (0.943 g, 6.5 mmol), 2ꢀ 1H
J
= 8.7 Hz), 9.91 (s, 1H) .13C{1H} NMR (CDCl3, 25 °C,
(chloromethyl)pyridine hydrochloride (1.06 g, 6.5 mmol), TMS): δ (ppm): 42.4, 54.2, 110.0, 118.5, 122.0, 122.1, 123.0,
potassium carbonate (0.898 g, 6.5 mmol) and 15 mL of DMF 124.1, 125.3, 128.0, 128.8, 129.1, 134.0, 136.9, 138.1, 142.9,
placed in a 250 mL roundꢀbottom flask was refluxed for 2 h 184.5.
with vigorous stirring. It was cooled, poured in ice cold water
Synthesis of Ligand L1/L2
and kept in refrigerator for overnight. The settled light brown
precipitate was filtered on Buchner funnel, washed (3 × 10 mL) In a round bottom flask 1ꢀ(pyridinꢀ2ꢀylmethyl)ꢀ1
with water and dried in vacuo. Its recrystallization with hot carbaldehyde (0.472 g, 2.0 mmol)/ 1ꢀ((1ꢀbenzylꢀ1
ethanol afforded as a white solid. triazolꢀ4ꢀyl)methyl)ꢀ1 ꢀindoleꢀ3ꢀcarbaldehyde (0.633 g, 2.0
: White solid; Yield: 1.41 g, 5.97 mmol (92%); m.p. 70 °C. mmol) was taken in 5 mL of ethanol and stirred at room
Hꢀindoleꢀ3ꢀ
Hꢀ1,2,3ꢀ
A
H
A
Anal. Found: C, 76.20; H, 5.10; N, 11.84%. Calcd for temperature for 0.5 h. Benzylamine (0.214 g, 2.0 mmol)
1
C15H12N2O: C, 76.25; H, 5.12; N, 11.86%. H NMR (CDCl3, dissolved in ethanol (2 mL), was added drop wise to the flask
25 °C, TMS): δ (ppm): 5.48 (s, 2H, H6), 6.93 (d, 1H), 7.20–7.33 with stirring. The mixture was stirred further at room
(m, 4H), 7.58–7.63 (m, 1H), 7.86 (s, 1H), 8.31(d, 1H), 8.61 (d, temperature for 12 h. Its solvent was removed under reduced
1H), 10.20 (s, 1H, C15) .13C{1H} NMR (CDCl3, 25 °C, TMS): δ pressure on a rotary evaporator resulting L1 as a white solid
(ppm): 52.6, 110.3,118.6, 121.1, 122.2, 123.1, 124.2, 125.4, and L2 as red viscous oil. The white solid L1 on
137.2, 137.3, 138.9, 149.7, 155.3, 184.6.
recrystallization from EtOH gave white colored single crystals
of L1.
L1: White Solid; Yield: 0.604 g, 1.8 mmol (93%); m.p. 80 °C.
Synthesis of 1ꢀPropꢀ2ꢀynylꢀ1 ꢀindoleꢀ3ꢀcarbaldehyde (B)
H
Indoleꢀ3ꢀcarbaldehyde (0.942 g, 6.5 mmol) and K2CO3 (0.897 Anal. Found: C, 81.21; H, 5.27; N, 12.90%. Calcd for
1
g, 6.5 mmol) were dissolved in DMF (15 mL). Propargyl C22H19N3: C, 81.20; H, 5.89; N, 12.91%. H NMR (CDCl3, 25
bromide (0.996 g, 6.5 mmol) was added and the mixture stirred ºC, TMS):
δ
(ppm): 4.87 (s, 2H, H16), 5.47 (s, 2H, H6), 6.80 (d,
= 7.8 Hz, 1H), 7.18−7.22 (m, 1H), 7.25−7.31 (m, 4H), 7.38 (t,
= 7.5 Hz, 2H), 7.46 (d, = 6.9 Hz, 2H), 7.57 (t, = 6.9 Hz,
at room temperature for 12 h. It was poured into water and
extracted with ethylacetate (3 × 25 mL). The organic layer was
J
J
J
J
dried with anhydrous Na2SO4. Its solvent was evaporated off on 1H), 7.62 (s, 1H), 8.43−8.47 (m, 1H), 8.61−8.63 (m, 2H,
rotary evaporator resulting as (ppm):52.2
white solid. The H1+H15). 13C{1H} NMR (CDCl3, 25 ºC, TMS):
recrystallization with hot EtOH afforded its single crystals. (C16), 65.2 (C6), 109.8, 115.0 (Cq), 120.8, 121.4, 122.2, 122.7,
: White solid; Yield: 1.09 g, 5.98 mmol (92%); m.p. 55 °C. 123.3, 126.4 (Cq), 126.6, 127.8, 128.3, 132.6, 137.1, 137.2 (Cq),
a
B
a
δ
B
+
Anal. Found: C, 78.65; H, 4.94; N, 7.64%. Calcd for C12H9N0: 140.3 (Cq), 149.5 (C15), 155.9, 156.5 (C5).HRꢀMS [M+H]
8 | J. Name., 2012, 00, 1-3
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1
(
m/z) = 326.1652; calcd. value for C22H20N3 = 326.1652 (ppm C22H18N3PdCl: C, 56.67; H, 3.89; N, 9.01%. H NMR (CDCl3,
error
L2: Red viscous oil; Yield: 0.729 g, 1.8 mmol (90%). H NMR 1H), 7.09−7.20 (m, 2H), 7.34−7.71 (m, 8H), 7.94−8.05 (m,
(CDCl3, 25 ºC, TMS): (ppm): ) = 430.0538; calcd
4.78 (s, 2H, H20), 5.36 (s, 4H, 1H), 10.47 (b, 1H). HRꢀMS [M−Cl]+ (
H7+H10), 7.12 (s, 1H), 7.16−7.17 (m, 2H), 7.20−7.25 (m, 3H), value for C22H18N3Pd = 430.0539 ( :0.2 ppm).
7.30−7.32 (m, 5H), 7.34−7.38 (m, 3H), 7.44 (s, 1H), 8.34−8.36 : Yellow solid; Yield: 0.100 g, 0.18 mmol (92%); m.p. 172 °C
(m, 1H), 8.50 (s, 1H, H19). 13C{1H} NMR (CDCl3, 25 ºC, (d). Anal. Found: C, 57.19; H, 4.10; N, 12.86%. Calcd for
TMS):
(ppm):42.2 (C20), 54.2, 65.5, 109.6, 115.1 (Cq), 121.4, C26H22N5PdCl: C, 57.16; H, 4.06; N, 12.82%. 1H NMR
121.7, 122.2, 123.2, 126.3 (Cq), 126.6, 127.7, 128.0, 128.3, (CDCl3, 25 °C, TMS): (ppm): 5.05 (s, 2H), 5.21 (s, 2H), 5.72
128.8, 129.1, 131.6, 134.2 (Cq), 136.8 (Cq), 140.4 (Cq), 144.2 (s, 2H), 6.99−7.01 (m, 2H), 7.27−7.31 (m, 4H), 7.38 (s, 2H),
δ
: ꢀ0.1).
25 °C, TMS): δ (ppm): 5.10 (br, 2H), 6.00 (br, 1H), 6.41 (br,
1
δ
δ
m/z
δ
2
δ
δ
+
(Cq), 155.8 (C19). HRꢀMS [M+H]
(
m/z) = 406.2026; calcd. 7.45 (s, 4H), 7.59−7.61 (m, 2H), 7.79 (s, 1H). HRꢀMS [M−Cl]+
value for C26H24N5 = 406.2026 (ppm error
δ
: 0.0).
(m/z) = 510.0887; calcd value for C26H22N5Pd = 510.0914 (δ:
5.3 ppm).
Synthesis of Ligand L3
Synthesis of complex 3
A 25 mL round bottom flask equipped with a magnetic stirring
bar was charged with indole (0.469 g, 4.0 mmol), 2,2′ꢀdipyridyl To a solution of ligand L3 (0.045 g, 0.2 mmol) made in
disulfide (0.440 g, 2.0 mmol) and potassium carbonate (0.553 acetonitrile (20 mL) was added PdCl2 (0.056 g, 0.2 mmol) and
g, 4.0 mmol) dissolved in DMSO (5 mL). The mixture was the mixture heated at 70 °C for 30 min with stirring. Potassium
o
stirred at 100 C for 12 h. The EtOAc (20 mL) was added after carbonate (0.069 g, 0.5 mmol) was added to it and stirring of
cooling the reaction mixture. The organic phase was separated mixture continued further for 20 min. The clear red coloured
and the aqueous phase further extracted with EtOAc (2
mL). The organic phases were combined and treated with 10 filtrate reduced to ~2 mL. It was mixed with 30 mL of diethyl
mL of 10% HCl solution. The resulting mixture was stirred for ether to obtain complex as a red precipitate. The complex was
10 min and mixed with 20 mL of distilled water. The aqueous filtered, washed with diethyl ether and dried in air. Single
layer of mixture was separated and neutralized with 10% NaOH crystals of were obtained by diffusion of hexane into its
solution and extracted with (2 30 mL) of EtOAc. The solution made in 4 mL of CH2Cl2.
organic extracts were combined, dried with anhydrous sodium : Red solid; Yield: 0.129 g, 0.17 mmol (88%) ; m.p. 202 °C
× 20 solution was filtered through a celite pad and volume of the
3
3
×
3
sulfate and the solvent evaporated off on a rotary evaporator to (d). Anal. Found: C, 42.58; H, 2.40; N, 7.69 %. Calcd for
get a light brown product, which on recrystallization from EtOH C26H18N4S2Pd2Cl2: C, 42.53; H, 2.47; N, 7.63%. 1H NMR
gave white colored single crystals of L3
L3: Light brown solid; Yield: 0.650 g, 2.8 mmol (72%); m.p. 7.36−7.49 (m, 2H), 7.59 (t, 1H), 7.85ꢀ7.94 (m, 1H), 7.98−8.07
135 °C. Anal. Found: C, 69.01; H, 4.46; N, 12.39%. Calcd for (m, 1H), 8.43 (d, 1H), 8.87 (d, 1H, H1). HRꢀMS [M−Cl] +
m/z
C13H10N2S: C, 69.00; H, 4.45; N, 12.38%. 1H NMR (CDCl3, = 696.8798; calcd. value for C26H18ClN4Pd2S2 = 696.8735 (
25 ºC, TMS): (ppm): 6.80 (d, = 8.1 Hz, 1H), 6.90−6.94 (m, 9.2 ppm).
1H), 7.12−7.18 (m, 1H), 7.20−7.25 (m, 1H), 7.29−7.41 (m,
3H), 7.60 (d, = 7.8 Hz, 1H), 8.36 (d, = 4.8 Hz, 1H), 9.58 (s,
1H, NH). 13C{1H} NMR (CDCl3, 25 ºC, TMS):
(ppm): 100.2 In a round bottom flask degased with nitrogen, aldehyde (1
(Cq), 111.9, 119.2, 119.4, 120.0, 120.8, 122.9, 128.8 (Cq), mmol) and complex (1.0 mol%) were taken in 2 mL of
131.5, 136.7, 136.8 (Cq), 148.9, 162.8 (Cq). HRꢀMS [M+H] + DMF and the mixture stirred for 10 min. Allyltributylstannane
m/z) = 227.0642; calcd. value for C13H11N2S = 227.0637 (ppm (1.2 mmol) was added drop wise and the reaction mixture
.
(DMSOꢀd6, 25 °C, TMS): δ (ppm): 6.85 (s, 1H), 7.12 (d, 1H),
(
)
δ
:
δ
J
General procedure for allylation of aldehydes
J
J
δ
1/2
(
error
δ
: 2.3).
stirred at 50 °C further for 12 h. It was allowed to cool, mixed
with 10% aqueous KF solution (30 mL) and stirred at 25 °C for
3 h. The mixture was extracted with ethyl acetate (2 × 25 mL).
Synthesis of Complex 1 and 2
In 20 mL of methanol, L1 (0.065g, 0.2 mmol) or L2 (0.081 g, The organic layer was washed with water (2 × 50 mL), dried
0.2 mmol) was heated at 70 °C for 15 min. Anhydrous sodium over Na2SO4 and its solvent evaporated off on a rotary
acetate (0.02 g, 0.24 mmol) was added to it with stirring and the evaporator. The crude product obtained as a residue was
mixture
further
stirred
for
15
min.
Sodium purified by column chromatography on silica gel using ethyl
tetrachloropalladate(II) (0.059 g, 0.2 mmol) was added and the acetate and hexane mixture as an eluent.
reaction mixture heated at 70 °C for 5 h with stirring. The
General procedure for SuzukiꢀMiyaura coupling
resulting solution was filtered through celite pad, and the
volume of the filtrate reduced (
and the concentrate mixed with 50 mL of hexane to obtain condenser and charged with ArX (1.0 mmol), phenylboronic
complex as a precipitate. It was filtered and dried in vacuo acid (1.5 mmol), K2CO3 (2.0 mmol), aqueousꢀ DMF (1.0 + 3.0
Single crystals of were grown by slow diffusion of hexane mL) and a complex from as a catalyst. The flask was
into its solutions made in 4 mL of CH2Cl2. placed on an oil bath maintained at 90 °C. The reaction mixture
∼5 mL) with a rotary evaporator A 50 mL round bottom flask was equipped with a reflux
.
2
1−3
1: Yellow solid; Yield: 0.083 g, 0.17 mmol (90%); m.p. 210 °C was stirred until maximum conversion of aryl halide to product
(d). Anal. Found: C, 56.70; H, 3.80; N, 9.08%. Calcd for occurred. It was extracted with diethyl ether (2 × 20 mL). The
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extract was washed with water (2 × 25 mL) and dried over R. J. M. K. Gebbink, guest editors, Pincers and other Hemilabile
anhydrous Na2SO4. Its solvent was removed with a rotary ligands, Dalton Trans., 2011, 40, 8731–8732; (d) D. MoralesꢀMorales
evaporator. The pure product from the resulting residue was and C. M. Jensen, Eds. The Chemistry of Pincer Compounds; Elsevier
obtained by column chromatography on silica gel and Science: Amsterdam, 2007
.
authenticated with 1H NMR spectra.2d
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Poisoning test for coupling reactions
An excess of poisoning agent (Hg, 400 times to Pd or 5 Angew. Chem., Int. Ed., 2001, 40, 3750–3781; (d) T. Takemoto, S. Iwasa, H.
equivalents of PPh3) was taken in a reaction flask. A mixture of Hamada K. Shibatomi, M. Kameyama, Y. Motoyamac and H. Nishiyama;
4ꢀbromobenzaldehyde (1 mmol) and phenylboronic acid (1.2 Tetrahedron Lett., 2007, 48, 3397–3401.
mmol) for SMC /allyltributylstannane (1.2 mmol) for allylation
was added. The reaction was carried out under optimum 12024−12087; (b) N. Selander and K. J. Szabo´, Chem. Rev., 2011, 111
reaction conditions in the presence of complex (0.01/1 mol%) 2048–2076; (c) J. Choi, A. H. R. MacArthur, M. Brookhart and Alan S.
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Acknowledgments
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6 S. Iyer, G. M. Kulkarni and C.Ramesh, Tetrahedron,2004, 60, 2163–2172.
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A.K.S thanks Department of Science and Technology
(Nanomission) and Department of Atomic Energy (BRNS),
India for financial support. M.P.S thanks to University Grants
Commission (UGC), India for Senior Research Fellowship. F.S.
thanks BRNS for Research Associateship.
8 X. ꢀQ. Hao, Y. –X. Xu, M. –J. Yang, L. Wang, J. –L. Niu, J. –F. Gong
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New Journal of Chemistry
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DOI: 10.1039/C7NJ02116J
Palladacycles having normal and spiro chelate rings designed from bi- and
tridentate ligands with indole core: structure, synthesis and applications as
catalysts
Mahabir P. Singh, Fariha Saleem, Ram S. Pal and Ajai K. Singh*
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India
Palladacycles with normal and spiro ring catalyze Suzuki-Miyaura coupling of ArBr/ArCl /
allylation of aldehydes at 0.001/ 1 mol % loading.