Depalladation of neutral monoalkyne- and dialkyne-inserted palladacycles and alkyne insertion/depalladation reactions of cationic palladacycles derived from N, N ′, N ″-triarylguanidines as facile routes for guanidine-containing heterocycles/carbocycles: Synthetic, structural, and mechanistic aspects

Article abstract of DOI:10.1021/om500837v

Depalladation of the monoalkyne-inserted cyclopalladated guanidines [κ²(C,N)Pd(2,6-Me₂C₅H₃N)Br] (I and II) in PhCl under reflux conditions and that of the dialkyne-inserted cyclopalladated guanidine [κ²(C,N):n²(C=C)PdBr] (III) in pyridine under reflux conditions afforded a guanidine-containing indole (1), imidazoindole (2), and benzazepine (3) in 80%, 67%, and 76%, yields, respectively. trans-[L₂PdBr₂] species (L = 2,6-Me₂C₅H₃N, C₅H₅N) were also isolated in the aforementioned reactions in 35%, 42%, and 40% yields. Further, the reaction of the cyclopalladated guanidine [κ²(C,N)Pd(μ-Br)]₂ (IV) with AgBF₄ in a CH₂Cl₂/MeCN mixture afforded the cationic pincer type cyclopalladated guanidine [κ³(C,N,O)Pd(MeCN)][BF₄] (4) in 85% yield and this palladacycle upon crystallization in MeCN and the reaction of [κ²(C,N)Pd(μ-Br)]₂ (V) with AgBF₄ in a CH₂Cl₂/MeCN mixture afforded the cationic palladacycles [{κ²(C,N)Pd(MeCN)₂][BF₄] (5 and 6) in 89% and 91% yields, respectively. The separate reactions of 4 with 2 equiv of methyl phenylpropiolate (MPP) or diphenylacetylene (DPA) and the reaction of 5 with 2 equiv of MPP in PhCl at 110 °C afforded the guanidine-containing quinazolinium tetrafluoroborate 7 in 25-32% yields. The reaction of 6 with 2 equiv of DPA under otherwise identical conditions afforded the unsymmetrically substituted guanidinium tetrafluoroborate 8, containing a highly substituted naphthalene unit, in 82% yield. Compounds 1-8 were characterized by analytical and spectroscopic techniques, and all compounds except 4 were characterized by single-crystal X-ray diffraction. The molecular structures of 2 and 3 are novel, as the framework in the former arises due to the formation of two C-N bonds upon depalladation while the butadienyl unit in the latter revealed cis,cis stereochemistry, a feature unprecedented in alkyne insertion chemistry. Plausible pathways for the formation of heterocycles/carbocycles are proposed. The influence of substituents on the aryl rings of the cyclopalladated guanidine moiety and those on alkynes upon the nature of the products is addressed. Heterocycles 1 and 7 revealed the presence of two rotamers in about a 1.00:0.43 ratio in CDCl₃ and in about a 1.00:0.14 ratio in CD₃OD, respectively, as detected by ¹H NMR spectroscopy while in CD₃CN and DMSO-d₆ (1) and CD₃CN and CDCl₃ (7), these heterocycles revealed the presence of a single rotamer. These spectral features are attributed to the restricted C-N single-bond rotation of the CN₃ unit of the guanidine moiety, which possibly arises from steric constraint due to the formation of a N-H···Cl hydrogen bond with CDCl₃ (1) and N-H···O and O-D···O hydrogen bonds with CD₃OD (7).

Full text of DOI:10.1021/om500837v

Article
pubs.acs.org/Organometallics
Depalladation of Neutral Monoalkyne- and Dialkyne-Inserted
Palladacycles and Alkyne Insertion/Depalladation Reactions of
Cationic Palladacycles Derived from N,N′,N″‑Triarylguanidines as
Facile Routes for Guanidine-Containing Heterocycles/Carbocycles:
Synthetic, Structural, and Mechanistic Aspects
†
,†
‡
Priya Saxena, Natesan Thirupathi,* and Munirathinam Nethaji
†
Department of Chemistry, University of Delhi, Delhi 110 007, India
‡
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, India
S Supporting Information
*
ABSTRACT: Depalladation of the monoalkyne-inserted cyclopalladated
2
guanidines [κ (C,N)Pd(2,6-Me C H N)Br] (I and II) in PhCl under reflux
2
5
3
conditions and that of the dialkyne-inserted cyclopalladated guanidine
2
2
[
κ (C,N):η (CC)PdBr] (III) in pyridine under reflux conditions afforded a
guanidine-containing indole (1), imidazoindole (2), and benzazepine (3) in
0%, 67%, and 76%, yields, respectively. trans-[L PdBr ] species (L = 2,6-
8
2
2
Me C H N, C H N) were also isolated in the aforementioned reactions in 35%,
2
5
3
5
5
4
2%, and 40% yields. Further, the reaction of the cyclopalladated guanidine
2
[
κ (C,N)Pd(μ-Br)] (IV) with AgBF in a CH Cl /MeCN mixture afforded the
2 4 2 2
3
cationic pincer type cyclopalladated guanidine [κ (C,N,O)Pd(MeCN)][BF ] (4)
4
in 85% yield and this palladacycle upon crystallization in MeCN and the reaction
2
of [κ (C,N)Pd(μ-Br)] (V) with AgBF in a CH Cl /MeCN mixture afforded
2
4
2
2
2
the cationic palladacycles [{κ (C,N)Pd(MeCN) ][BF ] (5 and 6) in 89% and
2
4
9
1% yields, respectively. The separate reactions of 4 with 2 equiv of methyl phenylpropiolate (MPP) or diphenylacetylene
(
DPA) and the reaction of 5 with 2 equiv of MPP in PhCl at 110 °C afforded the guanidine-containing quinazolinium
tetrafluoroborate 7 in 25−32% yields. The reaction of 6 with 2 equiv of DPA under otherwise identical conditions afforded the
unsymmetrically substituted guanidinium tetrafluoroborate 8, containing a highly substituted naphthalene unit, in 82% yield.
Compounds 1−8 were characterized by analytical and spectroscopic techniques, and all compounds except 4 were characterized
by single-crystal X-ray diffraction. The molecular structures of 2 and 3 are novel, as the framework in the former arises due to the
formation of two C−N bonds upon depalladation while the butadienyl unit in the latter revealed cis,cis stereochemistry, a feature
unprecedented in alkyne insertion chemistry. Plausible pathways for the formation of heterocycles/carbocycles are proposed. The
influence of substituents on the aryl rings of the cyclopalladated guanidine moiety and those on alkynes upon the nature of the
products is addressed. Heterocycles 1 and 7 revealed the presence of two rotamers in about a 1.00:0.43 ratio in CDCl and in
3
1
about a 1.00:0.14 ratio in CD OD, respectively, as detected by H NMR spectroscopy while in CD CN and DMSO-d (1) and
3
3
6
CD CN and CDCl (7), these heterocycles revealed the presence of a single rotamer. These spectral features are attributed to the
3
3
restricted C−N single-bond rotation of the CN unit of the guanidine moiety, which possibly arises from steric constraint due to
3
the formation of a N−H···Cl hydrogen bond with CDCl (1) and N−H···O and O−D···O hydrogen bonds with CD OD (7).
3
3
6
−9
2
INTRODUCTION
substituents. The ring size of the “[κ (C,N)Pd]” unit and the
steric/electronic properties of the C,N-chelate in this unit and
steric and electronic properties of the alkynes regulate the
mode and degree of insertion and course of depalladation and
thus the frameworks of the resulting organic products.
■
1
,1- and 1,2-insertion reactions of [C,N] palladacycles with
small molecules such as CO, isocyanide, allenes, alkenes,
alkynes, and arynes are some of the most important
methodologies in organometallic/organic chemistry for the
synthesis of a variety of hetero- and carbocycles through a
A variety of alkyne-inserted [C,N] palladacycles that contain
amino, imino, pyridyl, and azo functionalities have been
subjected to the insertion−depalladation sequence, and from
these reactions, numerous hetero- and carbocycles have been
1
−5
stoichiometric insertion and depalladation sequence.
The
hetero- and carbocycles prepared through a small molecule
insertion−depalladation sequence are difficult to prepare
through other routes. The alkyne insertion of [C,N] pallada-
cycles is the most widely studied insertion reaction, as alkynes
can act as electrophiles or nucleophiles depending upon the
Received: August 18, 2014
©
XXXX American Chemical Society
A
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1
0−14
24,25
isolated.
The palladium-catalyzed pathway involving
cyclic chemistry.
Line drawings of a few medicinally
alkyne and amine, imine, or amide partners that leads to the
formation of hetero- and carbocycles is also a rapidly growing
important guanidine-containing heterocycles are shown in
24a,b
Chart 2.
Herein, we report the synthesis and character-
1
5−18
field.
The structural and mechanistic information obtained
from the stoichiometric alkyne insertion−depalladation se-
quence is suggested to pave the way to a better understanding
of the mechanism of formation of hetero- and carbocycles in
Chart 2
16f
palladium-catalyzed reactions.
Depalladation of monoalkyne- and dialkyne-inserted [C,N]
palladacycles has been reported to form hetero- and carbocycles
more frequently than that of trialkyne-inserted [C,N] pallada-
6
−9
cycles.
Palladium-mediated synthesis of heterocycles and
carbocycles was achieved by two different routes. In the first
route, monoalkyne- and dialkyne-inserted palladacycles were
depalladated at relatively high temperature, resulting in the
formation of hetero- and carbocycles through reductive
elimination of palladium accompanied by C−N bond formation
involving the coordinated nitrogen and carbon atoms. In the
second relatively milder route, alkyne insertion was performed
ization of three new cationic cyclopalladated guanidines, four
new heterocycles, and one carbocycle. Line drawings of the new
compounds 1−8 are shown in Chart 3. The determination of
2
+
−
on more reactive precursors, namely [κ (C,N)PdL ] [WCA]
2
2
and [κ (C,N)Pd(μ-I)] (C,N = cyclopalladated amine, imine,
2
pyridine; L = Lewis base; WCA = weakly coordinating anion)
to afford alkyne-inserted palladacycles in situ, which sub-
sequently undergo depalladation to afford hetero- and carbo-
the molecular structures of 1−3, 5−7, and 8·1.5H O by single-
2
crystal X-ray diffraction in conjunction with the knowledge
gained from alkyne insertion chemistry from the literature
allowed us to propose plausible mechanisms of the formation of
guanidine-containing heterocycles and the carbocycle.
6
−9
cycles as outlined in the first route.
Recently, we studied alkyne insertion reactions of cyclo-
2
palladated guanidines of the types [κ (C,N)Pd(μ-Br)] and
[
2
2
κ (C,N)Pd(Lewis base)Br] to afford a variety of alkyne-
RESULTS AND DISCUSSION
■
inserted palladacycles with unanticipated frameworks, mainly
due to ring contraction cum amine−imine tautomerization of
alkyne-inserted palladacyclic intermediates in conjunction with
the nature of the alkyne, coordinated anion, and other reaction
Syntheses. During the low-yield (23%) synthesis of I from
the insertion reaction of the 2,6-lutidine-coordinated mono-
meric analogue of V with MPP in CH Cl under ambient
2
2
conditions, we observed the formation of the adduct trans-
1
9,20
conditions.
We have chosen the monoalkyne- and dialkyne-
20
[
(2,6-Me C H N) PdBr ] in 36% yield. We speculated that
2 5 3 2 2
inserted cyclopalladated guanidines I−III for depalladation
reactions following the first route, as such an attempt would
afford guanidine-containing heterocycles/carbocycles (see
the low yield of I and the formation of the adduct are due to
spontaneous depalladation of I, and this information provided a
clue that palladacycle I could serve as a suitable precursor for
the heterocycle 1. Hence, palladacycle I was subjected to
depalladation in PhCl under reflux conditions for 10 h to afford
the indole 1 in 80% yield along with the formation of trans-
2
0
Chart 1). We have also used the cyclopalladated guanidines
Chart 1
[
(2,6-Me C H N) PdBr ] in 35% yield. Richeson and co-
2 5 3 2 2
workers synthesized a guanidine-containing indole from the
guanylation reaction of indole with N,N′-diisopropylcarbodii-
mide in the presence of catalytic amounts of LiN(SiMe ) /
3
2
26
TMEDA.
Palladacycle II was also subjected to depalladation in PhCl
under reflux conditions for 4.5 h, and the resulting mixture was
subjected to column chromatography to afford the imidazoin-
dole 2 in 67% yield along with the formation of trans-[(2,6-
2
7
Me C H N) PdBr ] in 42% yield and N,N′-bis(o-anisyl)urea
2
5
3
2
2
(
β form) in 16% yield. The formation of an imidazoindole
derivative such as 2 through depalladation of a monoalkyne-
inserted [C,N] palladacycle is unprecedented in the literature.
The diinserted palladacycle III was depalladated in pyridine
under reflux conditions for 5 h, and the resulting reaction
mixture upon workup afforded the benzazepine derivative 3 in
7
6% yield along with the formation of trans-[(C H N) PdBr ]
5 5 2 2
IV and V as starting materials for more reactive substrates of
in 40% yield. Upon perusal of the synthetic routes reported for
2
+
−
16g,28
the type [κ (C,N)PdL ] [WCA] , which would enable us to
benzazepine derivatives,
we conclude that the synthetic
2
isolate guanidine-containing hetero- and carbocycles through
route reported herein for 3 is an elegant, reliable route for
guanidine-containing benzazepine.
The successful isolation of heterocycles 1−3 following the
first route prompted us to explore the second route in order to
understand whether such a strategy would afford hetero- and
21,22
the second route, as outlined above (see Chart 1).
Nitrogen-containing heterocycles are medicinally important
2
3
compounds, and more importantly, guanidine-containing
heterocycles are considered as privileged scaffolds in hetero-
B
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Chart 3
carbocycles with distinct frameworks. Hence, palladacycle IV
was treated with AgBF in a CH Cl /MeCN mixture to afford a
4
2
2
solid, which upon crystallization in a CH Cl /n-hexane mixture
2
2
afforded the cationic pincer type palladacycle 4 in 85% yield.
Palladacycle 4 upon crystallization in MeCN afforded 5 in 89%
yield. Alternatively, the reaction of IV with AgBF in a CH Cl /
4
2
2
MeCN mixture and subsequent crystallization of the resulting
product from the same solvent combination afforded 5 in 90%
yield. Analogously, the reaction of V with AgBF in a CH Cl /
4
2
2
MeCN mixture readily afforded 6 in 91% yield. The separate
reactions of 4 with 2 equiv of MPP and DPA in PhCl under
reflux conditions for 5 h and the reaction of 5 with 2 equiv of
MPP under the aforementioned conditions followed by workup
of the reaction mixture afforded the quinazolinium derivative 7
in 25−32% yields. The reaction of 6 with 2 equiv of DPA in
PhCl under reflux conditions for 3 h afforded the annulated
guanidinium salt 8 in 82% yield.
Molecular Structures. The molecular structures of 1−3,
27a
5
−7, 8·1.5H O, and N,N′-bis(o-anisyl)urea were determined
2
by single crystal X-ray diffraction and are shown in Figures 1−6
and Figure S1 in the Supporting Information. There are two
molecules in an asymmetric unit of 1, 2, and 5 but the structural
features are discussed only for one molecule. The molecular
structure of 1 consists of an indole ring wherein the nitrogen
atom of the ring is simultaneously a part of the guanidine unit.
Both the amino nitrogen atoms and the central carbon atom of
the guanidine unit are planar. In 1, the C1−N1 distance
Figure 1. ORTEP representation of 1 at the 50% probability level.
Hydrogen atoms, except that on the amino nitrogen atom, are
removed for clarity. Selected bond distances (Å) and angles (deg):
C(1)−N(1) = 1.441(3), C(1)−N(2) = 1.263(3), C(1)−N(3) =
1
.370(3); N(1)−C(1)−N(2) = 125.8(2), N(2)−C(1)−N(3) =
124.1(2), N(1)−C(1)−N(3) = 110.2(2).
1.441(3) Å is longer than but the C1−N3 distance 1.370(3) Å
is comparable with the C−N single-bond distances of the CN
3
which was present in II has lost the OMe unit in the course of
the formation of the dihydroimidazole ring in 2. In 2, both the
C1−N1 distance 1.414(4) Å and the C1−N3 distance 1.417(4)
2‑tolyl
unit of N,N′,N′′-tri(2-tolyl)guanidine, LH
(1.377(4) and
2
2
9
1
.380(4) Å ), and the C1−N2 distance 1.263(3) Å in the
former is shorter than that reported for the latter (1.282(4) Å).
The lone pair on N1 is involved in π delocalization of the
indole ring to attain the aromatic character, and hence the lone
pair is not available for n−π conjugation with the CN π*
orbital of the guanidine unit, which explains the trend in bond
Å are longer than the C−N single-bond distances of the CN
3
2‑anisyl
unit of N,N′,N′′-tris(2-anisyl)guanidine, LH
(1.372(4)
2
29
and 1.384(4) Å ), and the C1−N2 distance 1.249(4) Å in the
former is shorter than that reported for the latter (1.272(4) Å).
The lone pair on N3 is involved in π-electron delocalization of
the indole ring, and that on N1 is involved in an interaction
with the CO π* orbital and π* orbitals of the o-anisyl ring to
which it is attached. Hence, n−π conjugation involving the lone
pair of the amino nitrogen atoms with the CN π* orbital of
the guanidine unit is minimal.
distances observed for the CN core.
3
The molecular structure of 2 consists of a dihydroimidazo-
[
1,5-a]indole framework wherein both the amino nitrogen
atoms of the guanidine unit are part of the dihydroimidazole
ring while the imino nitrogen atom is not. Interestingly, the
carbon atom C23 of the alkenyl unit of the central ring bears
one methyl ester substituent, whereas the second ester group
The molecular structure of 3 consists of a benzo[b]azepine
core wherein one of the amino nitrogen atoms of the guanidine
C
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the aromatic system in 1 and 2 but they are not in 3. The
seven-membered heterocyclic ring in 3 revealed a pseudo-boat
conformation with C16, C17, C33, and C36 forming the basal
plane (mean deviation 0.0377 Å), while C23, C26, and N1 lie
at 0.656(3), 0.728(3), and 0.663(2) Å, respectively, out of the
basal plane (see Figure 7). The angle between the mean plane
formed by the basal atoms of the boat and the CN unit of the
3
guanidine moiety is 70.42(8)°. To the best of our knowledge, 3
represents the first crystallographically characterized hetero-
cycle that possesses a butadienyl unit with cis,cis stereo-
chemistry obtained through the depalladation route (see later).
Diinserted [C,N] palladacycles upon depalladation or the
2
+
−
reaction of cyclopalldated [κ (C,N)PdL ] [WCA] with 2
2
equiv of alkynes are, on the basis of the literature, anticipated to
afford (i) heterocycles wherein the butadienyl unit possesses
cis,cis stereochemistry, (ii) heterocycles with a cyclobutene
1
1a,12a
unit
heterocycles with unanticipated frameworks.
cycles A and B are considered as valence isomers; the thermal
(see structures A and B in Chart 4), and (iii)
10g,11g
The hetero-
28a,30
conversion of the latter to the former
is known in the
literature, and thermal conversion of the former to the latter has
Figure 2. ORTEP representation of 2 at the 50% probability level.
Hydrogen atoms are removed for clarity. Selected bond distances (Å)
and angles (deg): C(1)−N(1) = 1.414(4), C(1)−N(2) = 1.249(4),
C(1)−N(3) = 1.417(4); N(1)−C(1)−N(2) = 131.8(3), N(2)−
C(1)−N(3) = 125.0(3), N(1)−C(1)−N(3) = 103.2(3).
12a
been proposed in the literature.
The formation of a
heterocycle such as 3 which possesses the framework A in
the depalladation reaction of diinserted [C,N] palladacycles has
never been reported in the literature, although Pfeffer and co-
workers erroneously claimed the formation of azacycloocta-
12a
triene from depalladation of a diinserted [C,N] palladacycle;
later this compound turned out to be a benzofulvene derivative,
as has been proven by Heck and co-workers through a
1
0e
structural determination.
Thus, 3 represents the first
heterocycle formed through a dialkyne insertion−depalladation
sequence leading to C−N bond formation with the [C,N]
chelate unit remaining intact during the depalladation reaction.
In 2013, the molecular structures of two benzazepines obtained
16g
through entirely different routes were reported. Further, to
the best of our knowledge, there exists no report of structural
characterization of indole, imidazoindole, and benzo[b]azepine
derivatives containing a guanidine unit. The noncovalent
interactions present in the crystal lattices of 1−3 are shown
in Figures S2−S6 in the Supporting Information.
The palladium atom in 5 and 6 is surrounded by the imino
nitrogen atom, the aryl carbon atom, and the nitrogen atoms of
two MeCN groups and thus revealed a distorted-square-planar
geometry (mean deviations 0.0284 Å (5) and 0.0220 Å (6)). As
anticipated, the Pd1−N5 distance 2.136(6) Å in 5 and the
corresponding distance in 6 (2.140(4) Å) are longer than the
Pd1−N4 distances in 5 (2.063(8) Å) and 6 (2.006(3) Å),
owing to greater trans influence of the aryl carbon. The degree
of n−π conjugation involving the lone pair of the amino
nitrogen atoms with the CN π* orbital of the guanidine unit
can be estimated from the values of Δ and Δ ′, which have
Figure 3. ORTEP representation of 3 at the 50% probability level.
Hydrogen atoms, except that on the amino nitrogen atom, are
removed for clarity. Selected bond distances (Å) and angles (deg):
C(1)−N(1) = 1.387(2), C(1)−N(2) = 1.281(2), C(1)−N(3) =
1
.375(2); N(1)−C(1)−N(2) = 117.6(1), N(2)−C(1)−N(3) =
31.1(2), N(1)−C(1)−N(3) = 111.3(1).
CN
CN
1
21
been defined in our previous publication. The values of Δ
CN
and Δ ′ in 5 (Δ ′ = 0.158(11) Å; Δ = −0.029(12) Å)
CN
CN
CN
moiety is part of the seven-membered heterocyclic ring. The
locations of the methyl ester and phenyl substituents on the
butadienyl part of the seven-membered heterocyclic ring in 3
are identical with those found in the butadienyl part of its
precursor III. Interestingly, the butadienyl unit in 3 revealed
cis,cis stereochemistry, while that in III revealed cis,trans
suggest a greater extent of n−π conjugation involving the lone
pair of the endocyclic amino nitrogen atom with the CN π*
orbital of the guanidine unit than that involves the lone pair of
the exocyclic amino nitrogen atom. In contrast, the values of
Δ
and Δ in 6 (Δ ′ = 0.054(8) Å; Δ = 0.054(7) Å) are
CN
CN
CN
CN
comparable with each other. It should be noted that two
crystallographically distinct molecules in 5 are linked to each
other via a pair of N−H···π interactions and, to improve this
interaction, the exocyclic N(H)Ar unit could have twisted (see
Figure S7 in the Supporting Information). This could result in a
stereochemistry. The C−N distances of the CN unit in 3
3
2
‑anisyl 29
are comparable with those reported for LH
.
These
2
features as opposed to those discussed for 1 and 2, are
attributed to the fact that amino nitrogen atom(s) are part of
D
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Figure 4. ORTEP representations of the cations of 5 (a) and 6 (b) at the 50% probability level. Hydrogen atoms, except those on the amino
nitrogen atoms and the anion, are removed for clarity. Selected bond distances (Å) and angles (deg) for 5/6: Pd(1)−N(1) = 1.981(6)/2.014(3),
Pd(1)−N(4) = 2.063(8)/2.006(3), Pd(1)−N(5) = 2.136(6)/2.140(4), Pd(1)−C(17) = 1.968(9)/1.982(4), C(1)−N(1) = 1.296(9)/1.297(5),
C(1)−N(2) = 1.454(7)/1.351(6), C(1)−N(3) = 1.267(8)/1.351(5); C(17)−Pd(1)−N(4) = 95.3(3)/90.6(2), N(4)−Pd(1)−N(5) = 88.2(3)/
8
6.8(1), N(1)−Pd(1)−N(5) = 91.9(2)/92.9(1), C(17)−Pd(1)−N(1) = 84.6(3)/89.8(2), C(17)−Pd(1)−N(5) = 174.9(3)/177.2(2), N(1)−
Pd(1)−N(4) = 179.2(4)/178.2(2).
Figure 5. ORTEP representation of the cation of 7 at the 50%
probability level. Hydrogen atoms, except those on the amino nitrogen
atom and the anion, are removed for clarity. Selected bond distances
(
1
Å) and angles (deg): C(1)−N(1) = 1.407(4), C(1)−N(2) =
.341(4), C(1)−N(3) = 1.302(4); N(1)−C(1)−N(2) = 115.5(3),
N(1)−C(1)−N(3) = 122.2(3), N(2)−C(1)−N(3) = 122.3(3).
Figure 6. ORTEP representation of the cation of 8·1.5H O at the 50%
2
poorer n−π conjugation involving the exocyclic amino nitrogen
atom with the CN π* orbital of the guanidine unit.
The molecular structure of 7 consists of a quinazolinium
cation and a BF4 anion. Interestingly, the exocyclic N(H)Ar
unit is coplanar with the quinazolinium ring (mean deviation
probability level. Hydrogen atoms, except those on the amino nitrogen
atoms, water molecule, and the anion, are removed for clarity. Selected
bond distances (Å) and angles (deg): C(1)−N(1) = 1.334(3), C(1)−
N(2) = 1.337(3), C(1)−N(3) = 1.336(3); N(1)−C(1)−N(2) =
−
1
1
22.2(2), N(2)−C(1)−N(3) = 119.8(2), N(1)−C(1)−N(3) =
17.9(2).
0.1034 Å), while the phenyl ring attached to C23 makes an
angle of 80.66(9)° and the o-anisyl ring attached to N1 makes
an angle of 78.00(9)°. The C1−N1 distance 1.407(4) Å is
longer than the C1−N2 distance 1.341(4) Å, due to n−π
conjugation only from the exocyclic amino nitrogen atom with
the CN π* orbital involving the C1−N3 bond, as there is no
lone pair on N1.
the nitrogen atoms of the guanidinium cation are linked to the
o-tolyl substituent, while the third nitrogen atom is linked to a
highly substituted naphthalene ring. The CN unit is planar, as
3
anticipated for a charge-delocalized guanidinium cation with
comparable C−N distances. The formation of highly
substituted naphthalene derivatives through dialkyne insertion
The salt 8·1.5H O is nothing but an unsymmetrically
2
−
substituted guanidinium cation with a BF4 anion. Two of
E
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also been proposed to explain the presence of two isomers for a
3
1
related 2-substituted amide-based dihydroindole derivative.
1
Surprisingly, the H NMR spectra of 1 in CD CN and
3
DMSO-d revealed the presence of only one species (see the
6
Experimental Section). The NH proton of the guanidine
moiety in 1 can form a hydrogen bond with all three of the
aforementioned deuterated solvents. However, the C−N single-
bond rotation is restricted only in CDCl , possibly due to its
3
greater steric bulk. Factors such as Lewis basicity, dielectric
constant, and steric bulk of the solvent have been shown to
3
2,33
affect the relative population of rotamers.
Thus, two
rotamers are observed in CDCl , while only one is observed in
3
CD CN and DMSO-d .
3
6
1
The H NMR spectrum of 4 revealed one singlet at δ 2.55
assignable to CH protons of MeCN and three downfield
3
shifted singlets at δ 3.78, 3.87, and 4.24 assignable to OCH3
protons of the guanidine unit. The estimated ratio of
Figure 7. Selected portion of the molecular structure of 3 illustrating
the pseudo-boat conformation of the seven-membered ring.
OCH :CH protons of 3:1 clearly indicated a pincer type
3
3
13
1
Chart 4
framework for the cation of 4. Moreover, the C{ H} NMR
spectrum of 4 revealed one singlet at δ 3.3 assignable to the
CH carbon of MeCN and three singlets at δ 56.0, 56.2, and
3
6
0.1 assignable to OCH carbons of the guanidine unit, which
3
further supported the pincer type framework for the cation of 4.
Previously, we identified the neutral pincer type palladacycle
3
[
(
Pd{κ (C,N,O)-C H (OMe)-3(NHC(NHAr)(NAr))-2}-
6
3
OAc)] as one of the species formed through the neighboring
group participation of the OMe group in the NAr unit of the
1
acetate analogue of IV through variable-temperature H NMR
2
1
measurements.
1
The H NMR spectrum of 5 revealed two singlets at δ 2.00
and 2.51 assignable to CH protons of two distinct MeCN
groups and three downfield-shifted singlets at δ 3.77, 3.87, and
3
of [C,N] palladacycles followed by depalladation of the
10a−c,e−h,11f
resulting product has been reported earlier,
two such carbocycles have been structurally characterized.
The noncovalent interactions present in the crystal lattices of 6,
and 8·1.5H O are shown in Figures S8−S10 in the
and
4
.18 assignable to OCH protons of three distinct anisyl
1
0a,11f
3
substituents of the guanidine moiety. The estimated ratio of
OCH /CH protons of 3/2 clearly indicated a chelate type
framework for the cation of 5. Moreover, the C{ H} NMR
3
3
7
13
1
2
Supporting Information.
spectrum of 5 revealed two singlets at δ 1.70 and 3.17
1
NMR Studies. The H NMR spectrum of 1 in CDCl3
revealed the presence of two isomers in about a 1.00:0.43 ratio,
and this ratio was found to be independent of the
concentration. Further, the presence of two isomers of 1 in
assignable to the CH carbon of two distinct MeCN groups and
3
three singlets at δ 55.87, 55.92, and 57.81 assignable to OCH3
carbons of the guanidine unit, and this spectral feature further
1
supported a chelate type framework for the cation of 5. The H
1
3
1
CDCl was supported by C{ H} NMR spectroscopy. The two
13
1
3
and C{ H} NMR spectra of 6 indicated a chelate type
framework such as that present in 5.
solution species are ascribed to the presence of two rotamers, C
and D, which interconvert via C−N
single-bond rotation of
the CN unit, as this bond is longer than the remaining two C−
1
indole
H NMR spectra of 7 in CDCl and CD CN revealed the
3
3
3
presence of one species, while that in CD OD revealed the
3
N bonds (see above and also Scheme 1). In an ideal
presence of two isomers in about a 1.00:0.14 ratio. Further, the
presence of two isomers of 7 in CD OD was supported by
C{ H} NMR spectroscopy. The observed spectral behavior of
3
Scheme 1
13
1
7
is possibly ascribed to the ability of CD OD to form
3
intermolecular N−H···O and O−D···O hydrogen bonds with
the proton of the N(H)Ar moiety and the oxygen atom of the
o-OMe group of the anisyl ring of the same moiety. As a result,
the C−N(H)Ar single bond of the CN unit restrictively rotates
3
on the NMR time scale, resulting in the formation of two
rotamers, namely E and F, as shown in Scheme 2.
Mechanistic Aspects of Depalladation. The formation
of 1 involves C−N bond formation through nucleophilic attack
of the imino nitrogen atom on the palladated carbon followed
representation, in the major rotamer indicated as C, the C
NAr unit and the phenyl group on the pyrrole ring are located
on the same side, while in the minor isomer indicated as D, the
aforementioned units are located on the opposite side. In
solution, the C−N bond rotation may be restricted due to steric
constraints. Such a C−N single-bond rotation in solution has
0
by reductive elimination of palladium in the form of Pd L
accompanied by the loss of HBr. Oxidative addition of HBr to
0
Pd L species could form “PdHBr(L)” species, and this hydrido
species subsequently recombines with itself to form trans-
[L PdBr ] (L = 2,6-Me C H N), Pd(0), and H , as discussed
2
2
2
5
3
2
F
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Scheme 2
Scheme 4
34
20
by Vicente and co-workers and subsequently by us. The
formation of 2 from II is believed to occur in two steps, as
shown in Scheme 3. The first step involves the formation of the
Scheme 3
the formation of a diradical intermediate in the formation of an
1
1
intermediate G, the structural analogue of 1, and this
intermediate subsequently loses MeOH intramolecularly to
afford 2. N,N′-Bis(o-anisyl)urea is believed to form through
partial hydrolysis of the guanidine moiety present in II. It
should also be noted that depalladation of cyclopalladated
unusual dimer of the type [μ -κ :κ (C,N)Pd(PPh )Br] from
2 3 2
the bridge-splitting reaction of an eight-membered mono-
2
alkyne-inserted cyclopalladated amine of the type [κ (C,N)Pd-
36
(μ-Br)] with PPh . The aforementioned literature prece-
2
3
dence and cis,trans stereochemistry of the butadienyl unit in III
versus cis,cis stereochemistry of the same unit in 3 indirectly
support the decoordination and recoordination pathway
proposed in Scheme 4.
1
0g,11a,12a
10a,b,m,13
11b,j
14
amine,
imine,
pyridyl,
and azo com-
pounds in the presence of alkyne afforded six- or seven- rather
than five-membered nitrogen-containing heterocycles or their
salts. Only Pfeffer and co-workers reported the formation of
Indirect evidence for the formation of the intermediate K
stems from the fact that Heck and co-workers also suggested a
cis,cis-diene-containing [C,N] palladacycle as the intermediate
in the formation of a tetrasubstituted naphthalene derivative
from depalladation of a diinserted [C,N] palladacycle that
2
,3-disubstituted indoles from the alkyne insertion−depallada-
tion sequence involving cyclopalladated N-phenyl-2-pyridyl-
amine of the types [{κ (C,N)Pd(MeCN) ] [BF ] and
2
+
−
2
4
2
11i
[
{κ (C,N)Pd(μ-I)] in the presence of alkynes. However,
2
10e
neither the molecular structures nor the probable mechanism of
formation of the 2,3-disubstituted indoles was reported. The
gross resemblance of our work to that reported by Pfeffer and
contains the diene in cis,trans stereochemistry. Moreover, the
molecular structure of one diinserted palladacycle wherein the
butadienyl unit revealed cis,cis stereochemistry is known which
further supports the proposed structure for the intermediate
co-workers is ascribed to the presence of an endocyclic amino
2
37
(
NH) functionality in the six-membered “[κ (C,N)]Pd” ring of
K.
the precursors from which indoles have been obtained.
A plausible mechanism of formation of 7 is illustrated in
Scheme 5. This mechanism is somewhat analogous to that
invoked by Pfeffer and co-workers to explain the formation of a
benzo[b]quinolizinium salt from the insertion reaction of
cationic cyclopalladated 2-benzylpyridine with ethyl 3-phenyl-
propiolate followed by depalladation. Insertion of MPP or
DPA into the Pd−C bond of 4 or 5 can give rise to the eight-
membered palladacyclic intermediate L, which can subse-
quently undergo Pd−N bond cleavage followed by C−N bond
formation involving the β carbon atom of the olefinic unit and
subsequent migration of π electrons from the olefinic unit to
the Pd−C single bond to afford the six-membered
palladacarbene intermediate M. The intermediate M upon
losing the proton, Pd(0), and other byproducts can give rise to
the heterocycle 7. Pfeffer and co-workers explained the
A plausible pathway for the formation of 3 is outlined in
Scheme 4. In the presence of an excess of boiling pyridine,
palladacycle III dechelates through Pd−N bond cleavage to
afford the acyclic intermediate H. This intermediate upon
homolytic cleavage of one of the π bonds of the butadienyl unit
can give rise to the diradical intermediate I. This intermediate
upon C−C bond rotation can give rise to the more ordered
diradical intermediate J. Thereafter, re-formation of the double
bond and recoordination of the imino nitrogen atom to the
palladium can give rise to the intermediate K, which upon
reductive elimination, as occurred in the formation of 1 and 2,
can give rise to 3. Palladium is recovered as the previously
11e
35
known adduct trans-[(C H N) PdBr ] during the formation
5
5
2
2
of 3. It should be noted that Vicente and co-workers invoked
G
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a
Scheme 5. Plausible Mechanism of Formation of 7
which are neutral analogues of O, from the monoalkyne
insertion reactions of six-membered cyclopalladated guanidines,
20
cis-/trans-[(C,N)PdBrL]. The intermediate O upon insertion
with a second molecule of DPA can give rise to the
intermediate P. The intermediate P transforms to 8 via the
spirocyclic intermediate Q and the intermediate R, as
previously suggested in the formation of annulated products
10a−c,e,f
from dialkyne-inserted [C,N] palladacycles.
The insertion reactions of 4 or 5 with DPA afforded 7, albeit
in low yield, while the insertion reaction of 6 with DPA
afforded 8 in good yield. The difference in the nature of the
depalladated products can be explained by invoking greater
steric pressure in the intermediate N than in the intermediate L
due to the presence of the sterically more hindered o-tolyl
substituent of the guanidine unit in the former. Thus, steric
factor appears to facilitate ring contraction cum amine−imine
tautomerism to afford the guanidinium salt 8 (see Schemes 5
and 6). These examples illustrate the influence of aryl
substituents of the guanidine moieties in 4/5 and 6 upon the
nature of depalladated products.
a
Only the cation is shown for clarity.
formation of the benzo[b]quinolizinium salt in low yield due to
its formation from the minor regioisomer of the alkyne-inserted
1
1e
palladacycle. An analogous explanation can be invoked for
the low yield of 7 from the insertion reaction of 4 or 5 with
MPP. However, the low yield of 7 from the reaction of 4 or 5
with DPA can be attributed to our inability to isolate the
crystallized product from the mother liquor after the isolation
of the first crop of crystals due to the gradual transformation of
the mother liquor to a sticky form.
CONCLUSION
■
Mono- and diinserted palladacycles I−III upon depalladation
followed by C−N bond formation resulted in the formation of
heterocycles 1−3 in high yield. The cationic pincer type
palladacycle 4 and chelate type palladacycles 5 and 6 were
isolated in high yield, and these palladacycles upon an alkyne
insertion−depalladation sequence afforded the heterocycle 7 in
low yield and the carbocycle 8 in high yield. Synthetic routes
reported herein are believed to enrich the chemistry of
nitrogen-containing heterocycles in general and guanidine-
containing heterocycles in particular. The new compounds have
been characterized by analytical and spectroscopic techniques.
Molecular structures of seven new compounds have been
determined by single-crystal X-ray diffraction. The molecular
structures of 2 and 3 are novel, as the framework in the former
arises due to the formation of two C−N bonds upon
depalladation, while the butadienyl unit in the latter revealed
cis,cis stereochemistry, a feature unprecedented in alkyne
insertion chemistry. Heterocycles 1 and 7 revealed the presence
of two rotamers in solution due to the restricted C−N single-
A plausible mechanism for the formation of 8 is illustrated in
Scheme 6. Palladacycle 6 undergoes an insertion reaction with
a
Scheme 6. Plausible Mechanism of Formation of 8
bond rotation of the CN unit, depending on the steric bulk
3
and hydrogen bond forming capability of the solvents. Plausible
mechanisms for the formation of heterocycles 1−3 and 7 and
the carbocycle 8 have been outlined. The nature of substituents
in the alkynes as well as those on the nitrogen atoms of the
guanidine moiety in 4/5 and 6 influence the course of the
insertion/depalladation process and hence nature of the
depalladated products (compare 2 versus 3 and 7 versus 8).
EXPERIMENTAL SECTION
■(
E)-Methyl 1-(N,N′-Bis(o-tolyl)carbamimidoyl)-7-methyl-2-
phenyl-1H-indole-3-carboxylate (1). Palladacycle I (100 mg,
a
Only the cation is shown for clarity.
0
.128 mmol) was dissolved in chlorobenzene (15 mL) in a 25 mL
round-bottom flask to give a clear solution. The round-bottom flask
was fitted to a condenser-guard tube setup, and the solution was
simultaneously stirred and refluxed for 10 h and then cooled. The
blackish yellow solution thus obtained was filtered, and the filtrate was
left undisturbed. Yellow crystals of the adduct trans-[(2,6-
Me C H N) PdBr ] were obtained after 1 day. The crystals were
DPA to afford the eight-membered palladacyclic intermediate
N, which upon ring contraction followed by amine−imine
tautomerization can give rise to the intermediate O. Ring
contraction and amine−imine tautomerization or only amine−
imine tautomerization is frequently invoked to explain the
formation of small molecule inserted products in stoichio-
2
5
3
2
2
washed with several aliquots of n-hexane and subsequently recrystal-
lized from CH Cl . Yield (adduct·1.5CH Cl ): 35% (27 mg, 0.044
2
2
2
2
1
9−22,38
39
metric
and catalyzed reactions mediated by palladium.
mmol). The volatiles from the mother liquor were removed under
In the past, we have isolated palladacycles such as I and II,
vacuum to afford a light yellow solid, which was crystallized from a
H
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Article
CHCl /heptane mixture to afford 1 as white cuboidal crystals over a
yellow solid was crystallized from a CH Cl /toluene mixture under
3
2
2
span of several days. Yield: 80% (50 mg, 0.102 mmol). The
ambient conditions to afford 2 as yellow cuboidal crystals and N,N′-
bis(o-anisyl)urea as white flaky crystals. The two types of crystals were
separated with the aid of a brush. The yellow crystals were washed
with a minimum amount of methanol and dried. Yields: 67% (80 mg,
0.164 mmol; 2); 16% (11 mg, 0.040 mmol; N,N′-bis(o-anisyl)urea).
Characterization Data for 2. Mp (DSC): 221.23 °C. Anal. Calcd
for C H N O (mol wt 485.49): C, 66.80; H, 4.77; N, 8.66. Found:
composition of the adduct was confirmed by comparing its 1
H
NMR data and melting point with those of the authentic sample
20
reported in the literature.
Characterization Data for 1. Mp (DSC): 201.91 °C. Anal. Calcd
for C H N O (mol wt 487.59): C, 78.82; H, 5.99; N, 8.62. Found:
3
2
29
3
2
−1
C, 78.66; H, 6.03; N, 8.49. IR (KBr, cm ): ν(NH) 3380 (m); ν(C
27
23
3
6
1
−1
O) 1686 (s); ν(CN) 1663 (vs). H NMR spectra of 1 in CDCl
C, 66.47; H, 5.04; N, 8.74. IR (KBr, cm ): ν(CO) 1764 (s), 1718
3
solution at 20.0 × 10−3 mM and 273 × 10 mM concentrations
revealed the presence of two isomers, hereafter indicated as isomers 1
and 2 in about a 1.00:0.43 ratio, as estimated from the integrals of alkyl
−3
1
(vs); ν(CN) 1708 (vs). H NMR (CDCl , 400 MHz): δ 3.60, 3.65,
3
3.93 (each s, 3 × 3H, OCH ), 3.99 (s, 3 H, C(O)OCH ), 6.30 (d, J
HH
3
3
=
8.1 Hz, 1 H, ArH), 6.45 (d, JHH = 8.0 Hz, 1 H, ArH), 6.61−6.69 (m,
1
protons. H NMR (CDCl , 400 MHz): δ 1.43 (s, 3 H, CH , isomer 2),
3
3
2 H, ArH), 6.72−6.79 (m, 2 H, ArH), 7.01 (d, J = 8.0 Hz, 1 H,
ArH), 7.05 (apparent t, J = 7.3 Hz, 1 H, ArH), 7.11 (d, JHH = 7.3
HH
1
.58 (br, 3 H, CH , isomer 1), 2.19 (s, 3 H, CH , isomer 2), 2.25 (br, 3
3
3
HH
H, CH , isomer 1), 2.69 (s, 3 H, CH , isomer 1), 2.85 (s, 3 H, CH ,
3
3
3
Hz, 1 H, ArH), 7.36 (t, J = 8.1 Hz, 1 H, ArH), 8.03 (d, JHH = 8.0 Hz,
HH
isomer 2), 3.66 (s, 3 H, OCH , isomer 1), 3.68 (s, 3 H, OCH , isomer
13
1
3
3
1 H, ArH). C{ H} NMR (CDCl , 100.5 MHz): δ 52.00
3
2
), 6.01 (br, 1 H, isomer 2), 6.04 (d, JHH = 8.0 Hz, 1 H, isomer 1), 6.35
s, 1 H, isomer 2), 6.45 (s, 1 H, isomer 1), 6.67 (br, 1 H, isomer 1),
.74 (t, JHH = 7.7 Hz, 1 H, isomer 2), 6.86 (t, JHH = 7.0 Hz, 2 H,
isomer 1), 6.91 (d, JHH = 6.6 Hz, 2 H, isomer 1), 6.96 (d, JHH = 8.0 Hz,
(C(O)OCH ), 54.78 (OCH ), 55.04 (OCH ), 57.34 (OCH ),
3
3
3
3
(
6
1
09.22 (C), 109.72 (CH), 110.31 (CH), 110.97 (CH), 116.28
(CH), 119.37 (CH), 119.44 (CH), 120.66 (C), 120.96 (CH), 124.08
(CH), 125.75 (CH), 129.73 (CH), 130.71 (CH), 131.24 (C), 133.03
(C), 133.33 (C), 133.40 (C), 148.14 (C), 148.27 (C), 154.64 (C),
157.54 (CO), 163.43 (CO). MS (HRMS) m/z (relative intensity
2
× 1 H, isomers 1 and 2), 7.02 (t, JHH = 7.0 Hz, 2 × 1 H, isomers 1
and 2), 7.13 (t, JHH = 7.3 Hz, 2 × 1 H, isomer 2), 7.22 (q, JHH = 7.6
Hz, 3 H (isomer 1), 6H (isomer 2)), 7.31 (t, JHH = 7.7 Hz, 2 H, isomer
+
%) [ion]: found, 486.1646 (100) [M + H] ; calcd, 486.1665.
1), 7.37 (t, JHH = 7.3 Hz, 1 H (isomer 1), 2H (isomer 2)), 8.17 (d, JHH
27
Characterization Data for N,N′-Bis(o-anisyl)urea (β Form).
=
8.0 Hz, 2 × 1 H, isomers 1 and 2), 8.42 (br, 2 × 1 H, isomers 1 and
Anal. Calcd for C H N O (mol wt 272.30): C, 66.16; H, 5.92;
1
15 16
2
3
2) (ArH and NH). H NMR (CD CN, 400 MHz): δ 1.46, 2.28, 2.72
1
3
N,10.29%. Found: C, 65.89; H, 6.21; N, 9.97. H NMR (CDCl , 400
3
(
each s, 3 × 3 H, CH ), 3.60 (s, 3 H, OCH ), 5.95 (d, J = 7.4 Hz, 1
3 3 HH
MHz): δ 3.88 (s, 2 × 3 H, OCH ), 6.89 (dd, J = 7.3, 1.5 Hz, 2 × 1
3
HH
H, ArH), 6.58 (t, JHH = 7.3 Hz, 1 H, ArH), 6.80 (t, JHH = 7.3 Hz, 1 H,
H, ArH), 7.00 (dquint, JHH = 8.1, 1.8 Hz, 2 × 2 H, ArH), 7.11 (br, 2 ×
H, NH), 8.12 (dd, JHH = 7.7, 1.8 Hz, 2 × 1 H, ArH).
E)-Dimethyl 1-(N,N′-Bis(3-methoxyphenyl)carbamimidoyl)-
ArH), 6.99−7.05 (m, 4 H, ArH), 7.18 (t, J = 7.9 Hz, 1 H, ArH), 7.23
HH
1
(
7
d, J = 7.3 Hz, 2 H, ArH), 7.28 (dt, J = 7.8, 2.0 Hz, 3 H, ArH),
HH HH
(
.41 (t, JHH = 7.6 Hz, 1 H, ArH), 7.73 (s, 1 H, NH), 8.08 (d, J = 7.9
HH
9-methoxy-2,4-diphenyl-1H-benzo[b]azepine-3,5-dicarboxy-
late (3). Palladacycle III (200 mg, 0.226 mmol) was dissolved in
pyridine (15 mL) in a 25 mL round-bottom flask to afford a clear
solution. The round-bottom flask was fitted to a condenser-guard tube
setup, and the solution was simultaneously stirred and refluxed for 5 h.
The red solution thus obtained was filtered, and the filtrate was left
undisturbed. The formation of a yellow crystalline solid was observed
after 1 day. The solid was separated, washed with several aliquots of n-
hexane, and subsequently recrystallized from CH Cl to afford the
1
Hz, 1 H, ArH), 8.18 (d, JHH = 7.9 Hz, 1 H, ArH). H NMR (DMSO-
d , 400 MHz): δ 1.38, 2.29, 2.74 (each s, 3 × 3 H, CH ), 3.54 (s, 3 H,
OCH ), 5.84 (d, J = 8.0 Hz, 1 H, ArH), 6.57 (d, JHH = 7.3 Hz, 1 H,
6
3
3
HH
ArH), 6.75 (t, JHH = 7.3 Hz, 1 H, ArH), 6.96−7.04 (m, 4 H, ArH), 7.15
(
7
t, JHH = 7.3 Hz, 1 H, ArH), 7.20−7.31 (m, 5 H, ArH), 7.43 (t, J
=
HH
.6 Hz, 1 H, ArH), 7.83 (d, J = 8.0 Hz, 1 H, ArH), 8.03 (d, J = 6.7
HH HH
13
1
Hz, 1 H, ArH), 9.42 (s, 1 H, NH). The C{ H} NMR assignments of
the signals of isomers 1 and 2 were made wherever possible. 13C{ H}
NMR (CDCl , 100.5 MHz): δ 17.29 (CH , isomer 2), 18.23 (CH ),
1
2
2
3
3
3
adduct trans-[(C H N) PdBr ]. Yield: 40% (33 mg, 0.078 mmol). The
5
5
2
2
1
5
8.27 (CH ), 18.48 (CH ), 20.39 (CH , isomer 2), 50.91 (OCH ),
3 3 3 3
volatiles from the mother liquor were removed under vacuum to afford
a reddish yellow solid. The solid was subjected to column
chromatography over alumina. A yellow band was eluted with an
ethyl acetate/n-hexane (3/97, v/v) mixture, and the eluent was
evaporated under vacuum to afford a yellow solid. The solid was
crystallized from a CH Cl /toluene mixture at ambient temperature
0.98 (OCH ), 107.33 (C, isomer 1), 107.93 (C, isomer 2), 118.78
3
(CH), 119.01 (CH), 119.13 (CH), 120.30 (CH), 120.43 (CH), 121.32
(C), 121.87 (C), 123.04 (CH), 123.19 (CH), 123.87 (CH), 124.24
(CH), 124.53 (CH), 126.27 (CH), 127.00 (CH), 127.20 (CH), 127.35
(CH), 127.46 (CH), 127.60 (CH), 128.16 (C), 129.08 (CH), 129.23
(CH), 129.80 (CH), 130.19 (C), 130.52 (CH), 131.28 (CH), 131.70
(CH), 134.01 (C), 135.44 (C), 135.89 (C), 136.90 (C), 137.08 (C),
2
2
over a span of several days to afford 3 as irregular yellow crystals.
Yield: 76% (120 mg, 0.172 mmol).
Characterization Data for 3. Mp (DSC): 208.39 °C. Anal. Calcd
142.30 (C), 143.87 (C), 144.51 (C), 144.79 (C), 145.07 (C) (ArC,
ArCH, CN, CC), 165.14 (CO, isomer 1), 165.25 (CO,
+
for C42
H N O (mol wt 695.76): C, 72.50; H, 5.36; N, 6.04. Found:
37 3 7
isomer 2). MS (ESI ) m/z (relative intensity %) [ion]: 488 (100)
−1
+
C, 72.73/72.50; H, 5.41/5.59; N, 6.00/5.83. IR (KBr, cm ): ν(NH)
[
M] .
1
3
323 (m); ν(CO) 1734 (s, sh), 1720 (vs); ν(CN) 1627 (vs). H
(
Z)-Methyl 5-Methoxy-2-(2-methoxyphenyl)-3-(2-methoxy-
NMR (CDCl , 400 MHz): δ 3.20, 3.36 (each s, 2 × 3 H, C(O)OCH ),
3
3
phenylimino)-1-oxo-2,3-dihydro-1H-imidazo[1,5-a]indole-9-
carboxylate (2). Palladacycle II (200 mg, 0.246 mmol) was dissolved
in chlorobenzene (15 mL) in a 25 mL round-bottom flask to give a
clear yellow solution. The round-bottom flask was fitted to a
condenser-guard tube setup, and the solution was refluxed for 4.5 h.
The blackish yellow solution thus obtained was filtered, and the filtrate
was left undisturbed. The formation of yellow crystals of the adduct
trans-[(2,6-Me C H N) PdBr ] was observed after 1 day. The crystals
3
6
7
.66, 3.68, 3.82 (each s, 3 × 3 H, OCH ), 6.37 (t, J = 7.3 Hz, 1 H),
3
HH
.49 (d, JHH = 7.3 Hz, 2 H), 6.54 (t, JHH = 7.0 Hz, 2 H), 6.60 (d, JHH
.3 Hz, 1 H), 6.66 (d, JHH = 7.3 Hz, 1 H), 6.75 (br, 2 H), 6.90 (d, JHH
=
=
=
(
7.4 Hz, 1 H), 7.28 (br, 4 H), 7.34 (d, JHH = 7.7 Hz, 1 H), 7.39 (t, JHH
7.3 Hz, 2 H), 7.56 (d, JHH = 8.0 Hz, 1 H), 7.76−7.79 (m, 2 H), 7.82
d, JHH = 7.3 Hz, 2 H) (ArH and NH). 13C{ H} NMR (CDCl , 100.5
1
3
MHz): δ 51.71 (C(O)OCH ), 52.07 (C(O)OCH
55.63 (OCH ), 55.93 (OCH ), 109.48 (CH), 110.76 (CH), 111.64
3
), 55.16 (OCH ),
3 3
2
5
3
2
2
3
of the adduct were washed with several aliquots of n-hexane and
3
subsequently recrystallized from CH Cl . Yield: 42% (50 mg, 0.104
(CH), 119.58 (CH), 120.02 (CH), 120.26 (CH), 120.52 (CH), 120.59
(CH), 121.68 (CH), 122.66 (CH), 127.50 (CH), 127.75 (CH), 128.11
(CH), 128.31 (CH), 128.95 (CH), 129.23 (C), 129.66 (CH), 129.88
(C), 130.03 (CH), 132.20 (C), 133.41 (C), 135.18 (C), 137.08 (C),
139.04 (C), 141.77 (C), 145.29 (C), 147.67 (C), 150.51 (C), 150.76
(C), 150.99 (C), 155.62 (C), 167.62 (CO), 169.22 (CO). MS
2
2
mmol). The volatiles from the mother liquor were removed under
vacuum to afford a reddish yellow solid. The solid was purified by
column chromatography over alumina. A pale yellow band was eluted
with an ethyl acetate/n-hexane (4/96, v/v) mixture. The volatiles from
the eluent were evaporated to dryness to afford a yellow solid.
1
+
+
Amount: 96 mg. The H NMR spectrum of the solid revealed that it is
(ESI ) m/z (relative intensity %) [ion]: 718 (40) [M + Na − H] , 696
+ + 2‑tolyl +
a mixture of 2 and N,N′-bis(o-anisyl)urea in about a 4:1 ratio. The
(100) [M] , 638 (19) [M + H − C(O)OMe] , 378 (8) [LH
] .
3
I
dx.doi.org/10.1021/om500837v | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Characterization Data for trans-[(C H N) PdBr ]. Mp (DSC):
period of several days to afford 6 as light yellow-green cuboidal
5
5
2
2
2
50.32 °C. Anal. Calcd for C H N Br Pd (mol wt 424.43): C, 28.30;
crystals. Yield: 91% (213 mg, 0.353 mmol).
1
0
10
2
2
1
(Ω cm2
−1
H, 2.37; N, 6.60. Found: C, 28.62; H, 2.77; N, 6.61. H NMR (CDCl ,
Characterization Data for 6. Mp (DSC): 134.20 °C. Λ
M
3
−
1
−3
4
00 MHz): δ 7.33 (t, JHH = 7.0 Hz, 2 H, m-PyH), 7.77 (t, J = 7.7
mol ) = 143.1 (10 M). Anal. Calcd for C26
H N BF Pd (mol wt
28 5 4
HH
Hz, 1 H, p-PyH), 8.89 (d, JHH = 5.1 Hz, 2 H, o-PyH). 13C{ H} NMR
1
603.76): C, 51.72; H, 4.67; N, 11.60. Found: C, 51.40; H, 4.71; N,
−1
(
CDCl , 100.5 MHz): δ 125.2, 138.5, 154.5 (PyCH).
11.49. IR (KBr, cm ): ν(NH) 3413 (m), 3200 (m); ν(CN) 1629
, 400 MHz): δ 1.71 (s, 3
4 3
3
−
1
Palladacycle 4. To a solution of IV (200 mg, 0.178 mmol) in
(vs); ν(BF
H, CH ), 1.95 (s, 3 H, CH
2.43 (s, 3 H, CH CN), 5.86, 6.55 (each s, 2 × 1 H, NH), 6.72 (t, JHH
) 1060 (br, vs). H NMR (CDCl
CH Cl (25 mL) was added an MeCN solution (5 mL) of AgBF (70
3
3
CN), 2.16, 2.42 (each s, 2 × 3 H, CH
3
),
=
2
2
4
mg, 0.360 mmol), and the resulting solution was stirred at ambient
temperature for 20 min in the absence of light. The formation of a
light yellow precipitate was observed in the reaction mixture. The
solution was filtered, and the volatiles from the filtrate were removed
under vacuum to afford a light yellow solid. The solid was crystallized
from a CH Cl /n-hexane mixture under ambient conditions over a
3
7.7 Hz, 1 H), 6.87 (d, JHH = 7.3 Hz, 1 H), 7.13 (d, JHH = 7.4 Hz, 1 H),
7.19 (d, JHH = 6.6 Hz, 1 H), 7.29 (d, JHH = 7.3 Hz, 2 H), 7.31−7.39
13
1
(m, 5 H) (ArH). C{ H} NMR (CDCl , 100.5 MHz): δ 1.8
3
(
(
(
(
CH CN), 3.2 (CH CN), 16.9 (CH ), 17.7 (CH ), 18.4 (CH ), 117.8
3 3 3 3 3
C), 118.5 (C), 120.6 (C), 122.1 (C), 122.3 (CH), 127.2 (CH), 127.6
CH), 127.8 (CH), 128.0 (CH), 128.2 (CH), 128.6 (CH), 129.7
CH), 131.9 (CH), 132.1 (CH), 132.7 (C), 133.3 (C), 134.9 (C),
2
2
period of several days to afford 4 as a light green powder. Yield: 85%
(
185 mg, 0.303 mmol).
−1
135.6 (CH), 136.4 (C), 143.2 (C), 146.0 (C) (ArC, ArCH, CN,
Characterization Data for 4. Mp (DSC): 176.85 °C dec. Λ (Ω
M
+
2
−1
−3
CH CN). MS (ESI ) m/z (relative intensity %) [ion]: 475 (94) [M −
cm mol ) = 159.3 (10 M). Anal. Calcd for C H N O BF Pd
3
24
25
4
3
4
+
+
MeCN, H] , 460 (35) [M − MeCN, Me, H] , 434 (96) [M −
2MeCN, H] , 328 (100) [LH
(
mol wt 610.70): C, 47.20; H, 4.13; N, 9.17. Found: C, 47.00/46.91;
+
2‑tolyl +
−1
] , where M is the cation of 6.
H, 4.17/4.01; N, 8.78/8.77. IR (KBr, cm ): ν(NH) 3400 (br, w),
−
1
8-Methoxy-3-(2-methoxyphenyl)-2-(2-methoxyphenylami-
no)-4-phenylquinazolin-3-ium Tetrafluoroborate (7). Method 1.
To a suspension of 4 (200 mg, 0.327 mmol) in chlorobenzene (25
mL) was added a chlorobenzene solution (5 mL) of MPP (105 mg,
3
(
3
373 (m); ν(CN) 1616 (vs); ν(BF ) 1060 (br, vs). H NMR
4
CDCl , 400 MHz): δ 2.55 (s, 3 H, CH CN), 3.78, 3.87, 4.24 (each s,
3
3
× 3 H, OCH ), 6.68 (d, J = 8.0 Hz, 1 H), 6.74 (d, JHH = 7.4 Hz, 1
3 HH
H), 6.83−6.87 (m, 2 H), 6.95−7.00 (m, 1 H), 7.02−7.09 (m, 2 H),
0
.656 mmol) in a 50 mL round-bottom flask. The round-bottom flask
7
.14 (d, J = 3.6 Hz, 2 H), 7.31−7.36 (m, 2 H), 7.43 (d, J = 8.1
HH
HH
13
1
was attached to a condenser guard tube setup, and the turbid green
suspension was simultaneously stirred and heated at 110 °C for 5 h.
During the course of the reaction, the suspension became a clear green
solution and gradually transformed into a red solution. The solution
was filtered, and the volatiles from the filtrate were removed under
Hz, 1 H) (ArH and NH), 8.05 (s, 1H, NH). C{ H} NMR (CDCl ,
3
1
(
1
(
%
[
00.5 MHz): δ 3.3 (CH CN), 56.0 (OCH ), 56.2 (OCH ), 60.1
3 3 3
OCH ), 109.2, 111.6, 112.0, 112.8, 121.3, 122.4, 122.8, 123.9, 124.2,
3
24.4, 124.5, 126.5, 127.1, 128.0, 133.2, 145.7, 146.8, 152.3, 152.8
+
ArC, ArCH, CN and CH CN). MS (ESI ) m/z (relative intensity
3
vacuum to afford a red solid. The solid was crystallized from a CHCl3/
toluene mixture under ambient conditions over a span of several days
+
+
) [ion]: 523 (100) [M − H] , 510 (47) [M + H − Me] , 482 (75)
+ 2‑anisyl +
M − H, MeCN] , 376 (79) [LH
Palladacycle 5. Method 1. To a solution of IV (200 mg, 0.178
mmol) in CH Cl (25 mL) was added an MeCN solution (5 mL) of
] , where M is the cation of 4.
to afford 7 as red cuboidal crystals. Yield: 30% (54 mg, 0.098 mmol).
No more crystals could be further isolated from the mother liquor, as
it turned sticky with time.
Methods 2 and 3. The heterocycle 7 was also obtained from the
reaction of 4 (200 mg, 0.327 mmol) with DPA (117 mg, 0.655 mmol)
in chlorobenzene following the aforementioned procedure in 25%
yield (45 mg, 0.082 mmol). The reaction of 5 (200 mg, 0.307 mmol)
with MPP (100 mg, 0.624 mmol) in chlorobenzene following the
aforementioned procedure also afforeded 7 in 32% yield (55 mg, 0.100
2
2
AgBF (70 mg, 0.360 mmol), and the resulting solution was stirred at
4
ambient temperature for 20 min in the absence of light. The formation
of a light yellow precipitate was observed in the reaction mixture. The
solution was filtered, and the filtrate was concentrated under vacuum
to about 5 mL to afford 5 as light green crystals over a span of several
days. Yield: 90% (210 mg, 0.322 mmol).
Method 2. Palladacycle 4 (100 mg, 0.164 mmol) was dissolved in
MeCN (10 mL) and stored under ambient conditions to afford 5 as
light green crystals over a span of several days. Yield: 89% (95 mg,
mmol).
Characterization Data for 7. Mp (DSC): 288.98 °C. Λ (Ω−1 cm2
M
−1
−3
mol ) = 131.6 (10 M). Anal. Calcd for C H N O BF (mol wt
29
26
3
3
4
0
.146 mmol).
5
51.34): C, 63.18; H, 4.75; N, 7.62. Found: C, 63.09/63.20; H, 4.48/
−1
Characterization Data for 5. Mp (DSC): 160.63 °C dec. Λ (Ω
−1
M
4.58; N, 7.50/7.44. IR (KBr, cm ): ν(NH) 3366 (m); ν(CN) 1624
(vs); ν(BF ) 1062 (s), 1017 (s). H NMR (CDCl , 400 MHz): δ
4 3
2
−1
−3
cm mol ) = 154.6 (10 M). Anal. Calcd for C H N O BF Pd
−
1
26
28
5
3
4
(
4
mol wt 651.76): C, 47.91; H, 4.33; N, 10.74. Found: C, 47.52; H,
3
.62, 3.78, 4.15 (each s, 3 × 3 H, OCH ), 6.82−6.84 (m, 1 H), 7.05 (d,
3
−1
.73; N, 10.35. IR (KBr, cm ): ν(NH) 3400 (br, w), 3379 (m);
J
= 8.8 Hz, 2 H), 7.11−7.13 (m, 2 H), 7.16 (s, 1 H), 7.19 (d, J
=
HH
HH
−
1
ν(CN) 1612 (s); ν(BF ) 1060 (br, vs). H NMR (CDCl , 400
4
3
8.8 Hz, 2 H), 7.30−7.48 (m, 4 H), 7.51−7.55 (m, 1 H), 7.78−7.80 (m,
MHz): δ 2.00, 2.51 (each s, 2 × 3 H, CH CN), 3.77, 3.87, 4.18 (each
3
1 H), 7.88, 7.90 (each s, 2 × 1 H), 8.84−8.87 (m, 1 H) (ArH and
s, 3 × 3 H, OCH ), 6.68 (d, J = 8.0 Hz, 1 H), 6.78 (d, JHH = 8.1 Hz,
1
3
HH
NH). H NMR (CD CN, 400 MHz): δ 3.67, 3.79, 4.11 (each s, 3 × 3
3
1
1
7
(
(
1
1
H), 6.82−6.86 (m, 2 H), 6.98−7.06 (m, 3 H), 7.12 (d, JHH = 8.0 Hz,
H), 7.20 (t, JHH = 8.1 Hz, 1 H), 7.27−7.32 (m, 2 H), 7.40 (d, J
H, OCH ), 7.02−7.05 (m, 2 H, ArH), 7.14 (apparent q, J = 7.4 Hz,
3
HH
=
HH
2 H, ArH), 7.19 (d, J = 8.8 Hz, 1 H, ArH), 7.23 (dt, J = 8.0, 1.5
HH HH
13
1
.3 Hz, 1 H) (ArH and NH), 8.03 (s, 1 H, NH). C{ H} NMR
Hz, 1 H, ArH), 7.37−7.41 (m, 1 H, ArH), 7.43 (dd, J = 4.4, 2.2 Hz,
HH
CDCl , 100.5 MHz): δ 1.70 (CH CN), 3.17 (CH CN), 55.87
3
3
3
2 H, ArH), 7.46 (br, 1 H, ArH), 7.48 (s, 1 H, ArH), 7.50−7.55 (m, 2
OCH ), 55.92 (OCH ), 57.81 (OCH ), 107.68, 111.89, 112.02,
3
3
3
H, ArH), 7.60 (m, 2 H, ArH), 7.91 (s, 1 H, NH), 8.55 (dd, J = 8.1,
HH
1
17.68, 118.24, 121.04, 122.17, 122.91, 123.46, 124.07, 124.82, 126.84,
1
.5 Hz, 1 H, ArH). The H NMR spectrum of 7 in CD OD revealed
3
27.46, 128.36, 133.77, 145.50, 146.34, 151.88, 153.06 (ArC, ArCH,
the presence of two isomers, hereafter indicated as isomers 1 and 2, in
+
CN and CH CN). MS (ESI ) m/z (relative intensity %) [ion]: 523
about a 1.00:0.14 ratio, as estimated from the integrals of OCH
3
3
+
+
1
(
[
33) [M − MeCN, H] , 510 (49) [M + H − MeCN, Me] , 483 (100)
protons. H NMR (CD OD, 400 MHz): δ 3.63 (s, 3H, OCH , isomer
3
3
+
2‑anisyl +
(C,N)Pd] , 376 (94) [LH
Palladacycle 6. To a solution of V (200 mg, 0.194 mmol) in
CH Cl (25 mL) was added an MeCN solution (5 mL) of AgBF (76
] , where M is the cation of 5.
1), 3.90, 3.91 (each s, 2 × 3 H, OCH , isomer 2), 3.92, 3.94 (each s, 2
3
× 3 H, OCH , isomer 1), 3.99 (s, 3 H, OCH , isomer 2), 6.25 (dd, J
3
3
HH
2
2
4
= 8.0, 1.6 Hz, 1 H, ArH, isomer 2), 6.35−6.40 (m, 1 H, ArH, isomer
1), 6.56 (dq, J = 7.8, 1.4 Hz, 2 H, ArH, isomer 2), 6.71 (d, J = 7.8
mg, 0.390 mmol), and the resulting solution was stirred at ambient
temperature for 20 min in the absence of light. The formation of a
light yellow precipitate was observed in the reaction mixture. The
solution was filtered, and the volatiles from the filtrate were removed
under vacuum to afford a light yellow solid. The solid was crystallized
from a CH Cl /n-hexane mixture under ambient conditions over a
HH
HH
Hz, 1 H, ArH, isomer 1), 6.91 (t, JHH = 7.8 Hz, 1 H, ArH, isomer 1),
7.03−7.12 (m, 2 × 4 H, ArH, isomers 1 and 2), 7.14 (d, J = 2.3 Hz,
HH
2 × 1 H, ArH, isomers 1 and 2), 7.15 (s, 1 H, NH, isomer 1), 7.16 (s, 1
H, NH, isomer 2), 7.19−7.32 (m, 2 × 5 H, ArH, isomers 1 and 2),
7.34−7.36 (m, 2 × 1 H, ArH, isomers 1 and 2), 7.39−7.46 (m, 2 × 2
2
2
J
dx.doi.org/10.1021/om500837v | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
H, ArH, isomers 1 and 2). 13C{ H} NMR (CD OD, 100.5 MHz): δ
5
1
3
ACKNOWLEDGMENTS
N.T. acknowledges the Department of Science and Technol-
ogy, Delhi, India, for a research grant (grant no. SR/S1/IC-04/
■
5.84 (OCH ), 55.87 (OCH ), 56.54 (OCH ), 56.58 (OCH ), 57.05
3 3 3 3
(
OCH ), 57.09 (OCH ), 95.70 (C, isomer 1), 96.37 (C, isomer 2),
12.21 (CH, isomer 2), 112.39 (CH, isomer 1), 112.91 (CH), 113.76
CH), 120.81 (CH), 121.42 (CH), 121.57 (CH), 121.79 (CH), 122.58
CH), 122.71 (C), 123.14 (C), 123.62 (C), 126.65 (CH), 127.78
CH), 128.25 (CH), 129.26 (CH), 129.47 (CH), 129.60 (CH), 130.12
CH), 131.63 (CH), 131.78 (CH), 132.83 (CH), 141.08 (C, isomer
), 144.65 (C, isomer 2), 147.25 (C, isomer 1), 147.70 (C, isomer 2),
50.84 (C, isomer 1), 150.98 (C, isomer 2), 155.73 (C, isomer 1),
55.82 (C, isomer 1), 157.83 (C, isomer 2). MS (ESI ) m/z (relative
intensity %) [ion]: 465 (100) [M] , where M is the cation of 7.
3 3
1
2
010), and P.S. acknowledges the Council of Scientific and
(
(
(
(
Industrial Research for a fellowship. We also acknowledge the
University Science Instrumentation Center, University of Delhi,
for infrastructure facilities.
1
1
1
REFERENCES
+
■
+
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-(2-Methyl-5,6,7,8-tetraphenylnaphthalen-1-yl)-1,3-bis(o-
tolyl)guanidinium Tetrafluoroborate (8). To a suspension of 6
200 mg, 0.331 mmol) in chlorobenzene (25 mL) in a 50 mL round-
2
608.
(
́
(2) (a) Vicente, J.; Saura-Llamas, I.; Garcıa-Lopez, J.-A.; Calmuschi-
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bottom flask was fitted to a condenser-guard tube setup, and the
suspension was simultaneously stirred and refluxed for 3 h. During the
course of the reaction, the suspension turned into a red solution
accompanied by the formation of palladium black. The reaction
mixture was filtered, and the volatiles from the filtrate were removed
under vacuum to afford an orange-yellow solid. The solid was
crystallized from a CH Cl /n-hexane mixture under ambient
Saura-Llamas, I.; Garcı
a
́
-Lop
́
́
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́
́
́
́
́
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2
2
conditions over a span of several days to afford 8·CH Cl as light
2
2
yellow irregular crystals. Yield: 82% (233 mg, 0.272 mmol).
Characterization Data for 8. Mp (DSC): 214.66 °C. Λ (Ω cm2
−1
́
́
M
−1
−3
mol ) = 141.9 (10 M). Anal. Calcd for C H N BF ·CH Cl (mol
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50
42
3
4
2
2
wt 771.69 + 84.93): C, 71.51; H, 5.18; N, 4.91. Found: C, 71.72/
−
1
7
1.55; H, 4.83/5.00; N, 4.91/4.89. IR (KBr, cm ): ν(NH) 3324 (m,
−
1
br); ν(CN) 1628 (vs); ν(BF ) 1084 (s, br). H NMR (CDCl , 400
(7) Pfeffer, M. Pure Appl. Chem. 1992, 64, 335.
4
3
MHz): δ 2.04, 2.25, 2.59 (each s, 3 × 3 H, CH ), 6.46 (br, 1 H, NH),
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Weinheim, Germany, 2008; Chapter 5, p 87.
3
6
6
1
.59 (d, JHH = 6.6 Hz, 1 H, ArH), 6.67 (d, JHH = 7.4 Hz, 1 H, ArH),
.73 (s, 2 H, ArH), 6.78 (br, 2 H, ArH), 6.81 (apparent t, JHH = 1.5 Hz,
H, ArH), 6.86 (apparent t, JHH = 9.2 Hz, 5 H, ArH), 6.93 (br, 4 H,
ArH), 7.00−7.03 (m, 2 H, ArH), 7.10−7.23 (m, 11 H, ArH), 7.31 (t,
HH
(10) (a) Wu, G.; Rhelngold, A. L.; Heck, R. F. Organometallics 1986,
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Rheingold, A. L.; Heck, R. F. Organometallics 1989, 8, 2550.
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A.; Fisher, J. New J. Chem. 1990, 15, 551. (g) Beydoun, N.; Pfeffer, M.;
DeCian, A.; Fischer, F. Organometallics 1991, 10, 3693. (h) Pfeffer, M.;
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1992, 48, 2427. (i) Sutter, J.-P.; Pfeffer, M.; De Cian, A.; Fischer, J.
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13
1
J
= 7.0 Hz, 1 H, ArH), 7.38, 8.52 (each br, 2 × 1 H, NH). C{ H}
NMR (CDCl , 100.5 MHz): δ 17.58 (CH ), 18.00 (CH ), 19.52
3
3
3
(
CH ), 124.82, 125.72, 125.77, 126.73, 126.82, 126.87, 126.93, 127.11,
27.24, 127.46, 128.04, 128.28, 128.68, 128.88, 129.10, 129.79, 130.56,
30.76, 130.92, 131.06, 131.34, 132.06, 132.58, 132.80, 134.05, 134.20,
3
1
1
1
38.90, 139.26, 139.57, 139.90, 141.93, 142.17, 153.21 (ArC, ArCH,
+
CN). MS (ESI ) m/z (relative intensity %) [ion]: 686 (100) [M +
+
+
2‑tolyl +
H] , 670 (24) [M − Me] , 330 (23) [LH
] , where M is the
3
cation of 8. Crystals suitable for X-ray diffraction were grown from a
CHCl /petroleum ether mixture at 10 °C over a span of several days
3
to afford 8·1.5H O as light yellow irregular crystals.
2
ASSOCIATED CONTENT
Supporting Information
■
*
S
Text giving full experimental and crystallographic details
pertinent to general considerations, crystallographic parameters
of structurally characterized palladacycles (Tables S1 and S2),
Figure S1 for molecular structure of N,N′-bis(o-anisyl)urea,
Figures S2−S10 for hydrogen bond interactions, Figures S11−
1
13
13
S32 for H− C HETCOR and C DEPT 90 NMR spectra of
13
1
−3 and 7 and C DEPT 90 NMR spectrum of 6, and Figure
S33 for the HRMS spectrum of 2, and CIF files giving
crystallographic data for 1−3, 5−7, 8·1.5H O, and N,N′-bis(o-
2
anisyl)urea. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
E-mail for N.T.: tnat@chemistry.du.ac.in, thirupathi_n@
yahoo.com.
■
*
(i) Maassarani, F.; Pfeffer, M.; Spencer, J.; Wehman, E. J. Organomet.
Chem. 1994, 466, 265. (j) Spencer, J.; Pfeffer, M. Tetrahedron:
Asymmetry 1995, 6, 419.
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Notes
1987, 6, 2029. (b) Spencer, J.; Pfeffer, M.; Kyritsakas, N.; Fischer, F.
The authors declare no competing financial interest.
Organometallics 1995, 14, 2214.
K
dx.doi.org/10.1021/om500837v | Organometallics XXXX, XXX, XXX−XXX

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