N-heterocyclic-carbene complexes readily prepared from Di-μ-hydroxopalladacycles catalyze the Suzuki arylation of 9-bromophenanthrene

Article abstract of DOI:10.1021/om501160n

New cyclometalated palladium complexes of general formula [Pd(Bmim)(X)(C^{^}N)] have been synthesized by a novel reaction route involving di-μ-hydroxo-palladacycles [{Pd(μ-OH)(C^{^}N)}₂] (C^{^}N = 2-benzoylpyridine (Bzpy

Full text of DOI:10.1021/om501160n

Article
pubs.acs.org/Organometallics
N‑Heterocyclic-Carbene Complexes Readily Prepared from Di-μ-
hydroxopalladacycles Catalyze the Suzuki Arylation of
‑Bromophenanthrene
9
,
†
†
†
‡
‡
§
́ ́ ́
J. Luis Serrano,* Jose Perez, Luis García, Gregorio Sanchez, Joaquín García, Pedro Lozano,
Vidya Zende, and Anant Kapdi*
∥
,∥
†
Departamento de Ingeniería Minera, Geolog
́
ica y Cartografi
́
ca, Regional Campus of International Excellence “Campus Mare
ica, 30203 Cartagena, Spain
́
ica and Departamento de Bioquímica y Biología Molecular B e Inmunología, Facultad de
́
Nostrum”, Universidad Politec
́
nica de Cartagena, Area de Química Inorgan
́
‡
§
Departamento de Química Inorgan
Química, Regional Campus of International Excellence “Campus Mare Nostrum”, Universidad de Murcia, 30071 Murcia, Spain
∥Department of Chemistry, Institute of Chemical Technology, Mumbai, Nathalal Road, Matunga, Mumbai 400019, India
*
S Supporting Information
ABSTRACT: New cyclometalated palladium complexes of
∧
general formula [Pd(Bmim)(X)(C N)] have been synthesized
by a novel reaction route involving di-μ-hydroxo-palladacycles
∧
∧
[
{Pd(μ-OH)(C N)} ] (C N = 2-benzoylpyridine (Bzpy), I,
2
∧
previously unreported, or C N = 2-phenylpyridine (Phpy),
II)] and 1,3-butylmethylimidazolium salts [HBmim]X (X: Cl,
Br, I, or saccharinate (Sacc); a, b, c, or d complexes,
respectively). This simple acid−base reaction could not be
achieved under identical conditions when corresponding di-μ-
acetate complexes were used as starting materials. An alternative pathway to NHC/imidate complexes has also been explored by
reacting IIb with [Ag(Phthal)(SMe )] (Phthal = phthalimidate, e) to obtain [Pd(Bmim)(Phthal)(Phpy)], IIe. Structural
2
2
characterization by X-ray diffraction of complexes Id, IIb, IId, and IIe has confirmed the proposed formulas. The mononuclear
complexes have shown to catalyze the scalable Suzuki−Miyaura cross-coupling of 9-bromophenanthrene with a wide scope of
aryl boronic acids, irrespective of their electronic properties and at a very low catalyst concentration of 0.01%.
INTRODUCTION
it does not work with some palladacycles, the use of hard to
remove dimethysulfoxide as solvent, and additional base is
required, in other examples, for azolium salt deprotonation with
■
The synthesis of carbene complexes has been developed since
1
1
968, when deprotonation of imidazolium salts was achieved
6
subsequent extra workup steps. Other routes to synthesize
using appropriate coordinatively unsaturated metal complexes
that provided both a ligand acting as a base and a metal center
able to stabilize the imidazolin-2-ylidene thus formed. Together
with this original method, the treatment of electron-rich
7
NHC-palladacycles use air-sensitive free carbenes or suggest a
one-pot reaction of imidazolium salts, PdCl , N,N-dimethyl-
2
8
benzylamine, and excess K CO in refluxing acetonitrile. Given
2
3
2
the enhanced catalytic activity of monocarbene palladium
complexes that combine the desirable electronic/sterical
properties of NHCs with the robustness of a palladacycle
enetetraamines with suitable transition metals or the use of
free and stable N-heterocyclic carbene ligands (NHCs available
3
from 1991) for direct preparation of complexes make up the
9
backbone, we envisaged the interest of designing a new route
main synthetic routes to these interesting compounds. Other
approaches, such as carbene transfer from silver NHC
complexes, have been profusely reported, as shown in the
excellent review of Hahn and Jahnke. However, the first
described in situ deprotonation of azolium salts with suitable
metal complexes, such as Pd(AcO) , or its modification by
adding an external base remains at present a very convenient
method.
to prepare them using cyclometalated binuclear hydroxo
10
complexes. Indeed, we have recently explored the usefulness
∧
4
of such [{Pd(μ-OH)(C N)} ] complexes in the preparation of
2
a wide variety of new derivatives by means of a simple acid−
11
base reaction, proving its superior performance against
2
specific ligands when compared to analogous di-μ-AcO
11b,g
precursors.
On the other hand, during the last 10 years we have studied
Regarding the synthesis of monocarbene cyclopalladated
12
11a,13
the applications of palladacycles in Stille, Suzuki,
and
complexes, it was assumed that acetate-bridged precursors
∧
Sonogashira reactions in the frame of wider research on
[
{Pd(μ-AcO)(C D)} ] would have a similar reactivity. In fact
2
they have been successfully employed to prepare a diverse
5
library of NHC-palladacycles with D = N, P, S, or O. Although
Received: November 17, 2014
this reaction has a wide scope, it still has noticeable drawbacks:
©
XXXX American Chemical Society
A
DOI: 10.1021/om501160n
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Article
complexes containing imidate ligands (a variety of pseudoha-
imidate/palladacyclic complexes that are the subject of our
study.
14
lides showing mixed σ-donating and π-accepting properties).
In our hands they have shown incredible potential for cross-
15
coupling reactions, far from just mimicking halide ligands.
That is the case of still scarce saccharinate-palladium
RESULTS
■
Synthesis and Characterization. Since the first descrip-
tion of 2-benzoylpyridine cyclopalladation in 1982 to form
1
6
complexes, in which the expanded coordinative possibilities
of saccharinate confer to this ligand additional interest in
several fields if compared with simple cyclic imides such as
succinimide or phthalimide, which still considerably differ from
halides. The possibility of including imidate ligands in the
coordination sphere of a palladacyclic complex that also
contains NHCs has not been explored to date, although an
interesting potential in catalysis for such species can be
anticipated, given the fact that subtle changes in the imidate
ligand structure have been claimed to have a pronounced effect
on the catalytic activity of related [Au(N-imidate)(NHC)]
27
dinuclear complexes with bridging chloride or acetate ligands,
28
only two articles about its reactivity can be found, one of
them displaying the only X-ray crystal structure reported to
date containing such a palladacyclic unit (refcode WOSYEI as
searched in the CSD version 5.35 updated Feb 2014). We have
moved one step beyond, and the hydroxo-complex [{Pd(μ-
OH)(Bzpy)} ] has been prepared by reaction of the related di-
2
μ-AcO precursor with NBu OH (Scheme 1) in the specific
4
conditions detailed in the Experimental Section.
1
7
complexes.
Scheme 1. Synthesis of Dimeric [{Pd(μ-OH)(Bzpy)}2]
The unquestionable performance of NHC-palladacyclic
complexes in Suzuki couplings using benchmark aryl bromide
5
b,8,9
and chloride substrates
targeting more specific and challenging compounds, such as the
-arylphenanthrene derivatives that we (aim for/work towards)
in this study. Since the initial isolation of phenanthrene from
encourages the study of reactions
9
1
8
coal tar, several synthetic procedures have been developed
over the years to address the growing need for phenanthrene-
1
9
The formation of I is evident through its IR spectra,
characterized by the appearance of a typical −OH stretching
absorption at 3433 cm− and considerable changes in the
carbonyl region due to the absence of the bridging acetate
based derivatives in a variety of fields. For example, some
1
20
phenanthrene derivatives have shown biological activity, and
others displayed promising photo- and electroluminescence
properties brought about by the subtle variation in the
electronic properties of the phenanthrene backbone, which
has resulted in their employment as potential organic light-
1
groups. The H NMR spectrum displayed a high-field
resonance (−1.60 ppm) characteristic of palladium hydroxo
11b,29
complexes.
Mass spectrometry (HPLC/MS TOF) also
21
contributed to the characterization of the new complex,
emitting diodes (OLEDs). Specifically, 9-arylphenanthrenes
are important phenanthrene-based derivatives that are
commonly employed as intermediates toward the synthesis of
+
displaying a fragment assigned to M .
The use of I and II as suitable basic precursors has been
explored making them react with 1,3-butylmethyl-imidazolium
salts in the mild conditions displayed in Scheme 2a.
2
0,21
OLEDs or bioactive phenanthrenes.
Metal-mediated
coupling reactions have played a major role in accessing these
molecules, with palladium and nickel leading the way as the
Interestingly, our attempts to reproduce the same reactions
∧
22
using the corresponding [Pd(μ-AcO)(C N)} ] complexes
2
metals of choice. Suzuki−Miyaura cross-coupling reactions,
2
3
failed and the starting material was recovered, confirming the
superior performance of I and II and their specific usefulness in
the preparation of NHC-palladacycles. Again, noticeable
Hiyama coupling, and several other processes have been
routinely employed, although most of these processes suffer
from poor yields, high catalyst loadings, and harsh conditions.
2
4
C−H bond functionalization has also been recently
2
5
Scheme 2. (a) Preparation of Monocarbene Palladium
employed for the purpose of making the process environ-
mentally useful. However, the protocol produced low yields of
the desired products with the catalyst (Fe in this case)
concentration particularly higher than desired. A low-catalyst-
loading protocol for the Suzuki−Miyaura cross-coupling of 9-
bromophenanthrene with phenylboronic acid at 0.5 mol % Pd
concentration has been reported to give good yields of the
∧
Complexes [Pd(Bmim)(X)(C N)]; (b) Halide/Imidate
Exchange Using Labile Silver Complexes
26
cross-coupled product. However, the use of a phosphine
ligand in this case makes the protocol less attractive due to the
involvement of phosphine-related byproducts, as does the
employment of higher temperatures.
In this article we report a highly efficient, phosphine-free
Suzuki protocol to obtain 9-arylphenanthrene derivatives in
very good yields at low catalyst loading (0.01 mol %). We also
describe the synthesis of a new dinuclear hydroxo complex,
∧
∧
[
Pd(μ-OH)(C N)} ] (C N = 2-benzoylpyridine, I), that
2
together with its analogue with 2-phenylpyridine, II, have
proved to be convenient precursors in a novel route to prepare
the NHC-palladacyclic catalysts employed, [Pd(Bmim)(X)-
∧
(
C N)]. Halide/imidate substitution in the latter has also been
explored as a synthetic alternative to obtain the carbene/
B
DOI: 10.1021/om501160n
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Table 1. Selected Bond Lenghts (Å) and Angles (deg) Ib, IIb, IId, and IIe
b
bond/angle
Pd(1)−C(7)
Id
IIb
IId
IIe
1.9936(18)
Pd(1)−C(8)
1.9851(15)
Pd(1)−C(11)
Pd(1)−C(12)
2.012(10)
1.966(10)
2.0024(16)
2.0049(16)
Pd(1)−C(20)
Pd(1)−N(1)
Pd(1)−N(2)
Pd(1)−N(4)
1.9854(15)
2.0772(13)
2.1335(12)
1.9788(17)
2.0696(15)
2.0899(16)
2.080(7)
2.0912(13)
2.1263(14)
Pd(1)−Br(1)
2.5367(13)
90.0(4)
C(11)−Pd(1)−C(12)
C(11)−Pd(1)−N(1)
C(11)−Pd(1)−Br(1)
C(12)−Pd(1)−N(1)
C(12)−Pd(1)−Br(1)
N(1)−Pd(1)−Br(1)
C(11)−Pd(1)−N(4)
C(12)−Pd(1)−N(4)
N(1)−Pd(1)−N(4)
93.44(7)
80.54(6)
82.0(3)
178.4(3)
171.3(4)
91.5(3)
173.69(6)
96.5(2)
173.62(6)
91.44(6)
94.69(5)
a
C(7) −Pd(1)−C(20)
88.58(6)
90.05(6)
171.44(6)
176.78(6)
92.73(5)
88.20(5)
93.01(7)
81.44(7)
174.43(7)
173.82(7)
91.96(7)
93.70(6)
a
C(7) −Pd(1)−N(1)
a
C(7) −Pd(1)−N(2)
C(20)−Pd(1)−N(1)
C(20)−Pd(1)−N(2)
N(1)−Pd(1)−N(2)
a
b
C(8) in compound Id. Compound IIb presents four molecules in the asymmetric unit.
changes that were observed in the IR spectra as the −OH
stretching absorbances have now disappeared. Spectroscopic
1
13
characterization was completed by H and C NMR data,
which displayed typical carbene resonances, and HPLC/MS
+
TOF, where a common fragment at M −X was detected.
Another alternative route to the novel NHC/imidate
palladium complexes has been explored by reacting the silver
complex [Ag(Phthal)(SMe )] with [Pd(Bmim)(Br)(Phpy)],
2
2
IIb, to yield [Pd(Bmim)(Phthal)(Phpy)], IIe in Scheme 2b,
fully characterized as can be found in the Experimental Section.
This is an interesting possibility that expands the scope beyond
the limitations imposed by the availability of [HBmim]-
(Imidate) salts.
X-ray crystal structures of complexes Id, IIb, IId, and IIe
confirmed the proposed formulas of the new complexes. It is
worth highlighting that these are the first crystal structures
reported to date of palladacycles containing the Bmim carbene
ligand (CSD version 5.35 updated Feb 2014). Selected bond
distances and angles are listed in Table 1, and molecular
structures together with the atom-numbering scheme are
displayed in Figures 1, 2, 3, and 4, respectively.
Figure 1. Thermal ellipsoid plot of Id, drawn at the 50% probability
level. The hydrogen atoms have been omitted for clarity.
The arrangement of the Pd atoms in IIb, IId, and IIe can be
described as planar. For complex IIb w = −0.54° and w =
1
2
In complex Id the arrangement of the Pd atom can be
described as planar; its deviation from the planar coordination
geometry has been quantified by the measurement of improper
2
.13° in Pd1, w = −2.80° and w = −0.98° for IId, and for IIe
1
2
w = 1.68° and w = 1.72°. These values correspond to a
1
2
moderate square pyramidal (IIb) or tehtrahedral (IId and IIe)
distortion from the ideal square planar geometry. In these
complexes bite angles Pd−C−N are very similar and close to
81°. Complex IIb displays four molecules in the asymmetric
unit and exhibits very close structural parameters compared to
the analogous complex [Pd(Bzmim)(Br)(Phpy)] (Bzmim = 1-
methyl-3-(2,3,4,5,6- pentamethylbenzyl)-2,3-dihydro-1H-imida-
3
0
torsion angles w = 2.19° and w = −6.05° for Pd1. These
1
2
values correspond to a moderate square pyramidal distortion
from the ideal square planar geometry. The N−Pd−C bond
angle, 90.05(6)°, in the ortho-metalated moiety is slightly
higher than that found in the only previously reported
28b
structure, WOSYEI (87.4(3)°), while the distances Pd(1)−
C(8), Pd(1)−N(1), and carbonylic C(6)−O(1) are very similar
despite the different coligands involved. The conformation of
the six-membered ring Pd(1)−C(8)−C(7)−C(6)−C(5)−
32
zole, with refcode IGUVOW).
Supramolecular Description. We have recently reported
that phthalimidate and saccharinate ligands tend to adopt a
perpendicular conformation about the coordination plane in
31
N(1) is boat deformed 19° (B = 0.7312; SB = 0.2684).
C
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Table 2. Relevant Conformational Features
Id
IIb
IId
IIe
∧
a
Bmim C plane angle (deg)
86.23
70.00
73.39
85.72
87.60
88.55
83.86
∧
imidate C plane angle (deg)
a
Mean value for the four molecules in the asymmetric unit.
imidate results in IIb being the complex under study in which
Bmim is less perpendicular. In complexes Id and IId
saccharinate and Bmim can adopt two different relative
configurations, and each complex displays one of them.
Each molecule in complex Id interacts with the other 10
around it, but the most significant links take place with two of
them: (i) a C−H···OC and a C−H···OS hydrogen bond
and (ii) C−H···π by Bzpy ligands (omitted in Figure 5 for
clarity).
Figure 2. Thermal ellipsoid plot of IIb drawn at the 50% probability
level. The hydrogen atoms have been omitted.
Figure 5. Crystal packing in Id, displaying main interactions.
Complex IIb in the solid state can be described as a
“
tetramer” linked by C−H···π interactions between Phpy
ligands as shown in Figure 6. This fact could explain the four
Figure 3. Thermal ellipsoid plot of IId, drawn at the 50% probability
level. The hydrogen atoms have been omitted.
Figure 6. Crystal packing in IIb.
molecules in the asymmetric unit. Each Phpy ligand is nearly
perpendicular to the adjacent Phpy ligands (angles between
consecutive PhPy’s 83.68°, 85.26°, 82.09°, and 83.85°,
respectively). In spite of the fact that hydrogen atoms have
been added in calculated positions, the short H···C distances
inside the “tetramers” (Table 3, Figure 6) allow concluding that
Figure 4. Thermal ellipsoid plot of IIe, drawn at the 50% probability
level. The hydrogen atoms have been omitted.
33
their palladium complexes. The Bmim ligand also appears
perpendicular to the coordination plane, as can be seen in
Table 2. Probably a less steric impediment due to the lack of
34
they are strong C−H···π interactions. The most significant
interactions between “tetramers” are C−H···Br contacts.
D
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Article
Table 3. Relevant Supramolecular Interactions Found in the
New Crystal Structures
both molecules. With the second one there are anagostic Pd···H
and C−H···OS interactions. With the third one there are
hydrogen bonds of the type C−H···OS and C−H···OC
complex interaction type
geometrical parameters
(
this is the strongest hydrogen bond in this structure; the O
Id
hydrogen bonds D···A (Å)
H···A (Å)
D−H···A
deg)
C has been reported as the group producing the shortest
(
33
supramolecular interactions in the saccharinate ligand).
C−H···OC
C−H···OS
C−H···π
3.280
3.382
2.356
2.471
164.2
154.4
The more relevant interactions in compound IIe (Figure 8)
are (i) π···π interactions by Phpy ligands that define parallel
shortest H···C distances (Å)
.888, 2.891
shortest H···C distances (Å)
.750, 2.736, 2.723, 2.755
2
IIb
IId
C−H···π
π···π
2
plane−plane
centroid−
distance (Å)
centroid
distance (Å)
3
.384
3.604
hydrogen bonds D···A (Å)
H···A (Å)
D−H···A
(
deg)
C−H···OC
C−H···OS
C−H···OC
C−H···OS
3.630
3.453
3.282
3.375
Pd···H
2.714
2.664
2.337
2.691
162.29
140.86
172.35
129.45
anagostic
interaction
distance (Å)
.661
2
IIe
π···π
plane−plane
centroid−
centroid
distance (Å)
distance (Å)
3
.489
Pd···H
distance (Å)
.750
hydrogen bonds D···A (Å)
3.626
anagostic
Figure 8. Crystal packing in IIe.
interaction
2
planes (plane−plane distance of 3.489 Å). Again, like in IId,
both molecules are related by a center of symmetry (centroid−
centroid distance of 3.626 Å). The distance between planes in
IIe and IId is short according to the values reported in the
H···A (Å)
D−H···A
(
deg)
C−H···OC
C−H···OC
3.508
3.302
2.564
2.355
172.83
173.77
3
5
literature for π···π interactions; (ii) anagostic Pd···H
The most relevant supramolecular interactions in IId take
place with three molecules as displayed in Figure 7. With one of
interactions; this kind of interaction in IIe and IId is strong
3
6
according to metal···H distances reported; (iii) two
phthalimide ligands linked by two hydrogen bonds forming a
2
planar centrosymmetric ring, R (10); (iv) phthalimide also
2
interacting with a Phpy ligand by a hydrogen bond that can be
37
classified as moderate.
Catalytic Studies: Suzuki−Miyaura Cross-Coupling of
-Bromophenanthrene with Different Aryl Boronic
9
Acids. At the outset of our studies we first subjected the Pd
complexes Ia,b and IIa,b to the Suzuki−Miyaura cross-coupling
of 9-bromophenanthrene III with phenylboronic acid IVa in a
PhMe/H O system at 80 °C with Na CO as the base with a
2
2
3
Pd concentration kept at 1.0 mol % (much lower than most
22−25
examples reported in the literature;
once the superior
performance of phenylpyridine complexes was checked, the
whole series was tested, entries 1−6, Table 4).
It was observed that out of the six catalysts tested, complex
IId (entry 6, Table 4) gave an almost quantitative yield of the
cross-coupled product, although other catalysts were also found
to furnish the product in relatively similar yields with smaller
differences in reactivity.
Figure 7. Crystal packing in IId.
Optimum results for better product formation were obtained
at 80 °C, although at room temperature the reaction still
proceeded in good yield (entries 7 and 8, Table 4, respectively).
Catalyst loading experiments were also performed to reveal the
extent of catalytic activity of the Pd-NHC complexes (entries
9−13, Table 4). On reducing the catalyst loading from 1.0 mol
% to 0.1 mol %, it was still able to provide the cross-coupled
product in competitive yield (entries 9 and 10, Table 4,
the molecules relevant links are established by π···π and C−H···
OC interactions. Phpy ligands define parallel planes (plane−
plane distance of 3.384 Å). Both molecules are related by a
center of symmetry, so the py ring stacks over the Ph ring but
in a offset π-stacked geometry (centroid−centroid distance of
3
.604 Å, longer than the distance between planes). Two weak
C−H···OC hydrogen bonds strengthen the link between
E
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Table 4. Catalyst Screening Studies for Suzuki−Miyaura
Cross-Coupling of 9-Bromophenanthrene with Phenyl
Boronic Acid
chromatograph mass spectrometer using hexadecane as the
internal standard (with autosampler). The injections were done
at intervals of 0, 1, 2, 3, 6, 9, and 12 h to get enough data points.
The GC plot to a larger extent confirmed our initial findings
about the active nature of the Pd-NHC catalyst IId in
comparison to others (Figure 9). Depending on the type of
backbone, a marked difference in reactivity could be observed
between the complexes. Phenylpyridine-backbone-containing
Pd-NHC complexes converted at a faster rate than their
benzoylpyridine counterparts. Commercial NHC-based palla-
dium complexes [Pd(SIPr)(allyl)Cl] (A) and Pd-PEPPSI-SIPr
no.
complex temp (°C) catalyst conc (mol %) % yield
TON
(
B) got initiated at a much slower rate than IId (comparably
Complex Screening
better performing among the whole lot). With standard
phosphinated Pd complexes, namely, Pd(PPh3)4 (C) and
PdCl (PPh ) (D), an induction period is observed extending
1.
2.
3.
4.
5.
6.
Ia
80
80
80
80
80
80
1.0
1.0
1.0
1.0
1.0
1.0
81
87
88
95
92
96
Ib
2
3 2
IIa
IIb
IIc
Id
up to 2 h, after which these catalysts were found to convert,
although at a much slower rate than the others.
Scope Study. Next we turned our attention toward exploring
the scope of the catalytic reaction. A variety of arylboronic acids
were cross-coupled with 9-bromophenanthrene using a 0.01
mol % catalyst concentration of Pd-NHC complex IId at 80 °C
Temperature Study
7
.
.
IId
IId
80
r.t.
1.0
1.0
96
87
8
in a PhMe/H O system (Scheme 3). Electronic properties of
2
Catalyst Loading
the arylboronic acid were found to show less effect on the
activity of the catalytic system. Although lower product
formation was observed in the case of 3-nitrophenylboronic
acid, overall in most cases the arylated products were obtained
in good to excellent yields. It therefore highlights the activity of
the Pd-NHC complex IId to catalyze the transformation of
such synthetically important substrates at a very low catalyst
loading of 0.01 mol %.
Following the scope investigation, scale-up studies were
performed. The catalytic reaction was performed between 9-
bromoanthracene and phenylboronic acid on a 5.0 mmol scale.
It was observed that rather than performing the catalytic
reaction at 0.01 mol %, further reduction in the catalyst
concentration to 0.005 mol % also furnished the cross-coupled
product in excellent quantity (Scheme 4). Given the ease of
synthesis of the complexes as well as the mildness of the
protocol, such a synthetic route becomes highly attractive and
could be used successfully in obtaining good to excellent yields
of 9-arylated products on a larger scale for further applications.
9
1
1
1
1
.
IId
IId
IId
IId
IId
80
80
80
80
80
1.0
96
92
92
80
70
96
920
0.
1.
2.
3.
0.1
0.01
0.005
0.001
9200
40,000
70,000
respectively). Interestingly, at 0.01 mol % catalyst loading the
product could be obtained in very good yield, while any further
reduction resulted in slightly lower yields of the product (0.005
mol % gave 80% with a TON of 40 000, while reaction at 0.001
mol % gave 70% having a TON of 70 000).
Catalyst Comparison Study. To investigate the findings of
Table 4 regarding the difference in reactivity of the various Pd-
NHC complexes, gas chromatographic profiles were obtained
for all the complexes by injecting small aliquots of reaction
mixtures (in the conditions of entry 11 for the whole series)
quenched before injection and after regular time intervals.
Analysis was carried out on a Shimadzu Parvum 2 gas
Figure 9. GC profiles for the catalytic reaction of 9-bromophenanthrene III with phenylboronic acid IVa using different palladium catalysts. A =
Pd(SIPr)(allyl)Cl]; B = Pd-PEPPSI-SIPr; C = Pd(PPh ) ; D = PdCl (PPh ) . Hexadecane was used as an internal standard.
[
3
4
2
3 2
F
DOI: 10.1021/om501160n
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Scheme 3. Pd-Catalyzed Arylation of 9-Bromophenanthrene Using Pd-NHC Complex IId
a
Typically the reaction was performed on a 1.0 mmol scale of the 9-bromophenanthrene with 1.2 mmol of phenylboronic acid and 3.0 mmol of
Na CO in a PhMe/H O mixture (1:2) containing Pd-NHC complex IId in 0.01 mol % concentration. Isolated yields obtained after purification by
2
3
2
column chromatography.
Scheme 4. Scale-up Study for the Arylation of 9-
Bromophenanthrene
generating a cationic Pd species in situ. It should typically
catalyze the Suzuki−Miyaura cross-coupling reaction at a much
faster rate than the complex IId itself. A kinetic profile was
obtained for the catalytic reaction with the added AgNO and
3
was compared with the one obtained for complex IId (Figure
1
0).
Study for Possible Cationic Pd Intermediates. The
noticeable activity of Pd-NHC complex IId was further
investigated toward the possible presence of cationic Pd
species. In the literature several studies have highlighted the
rate-enhancing effect of cationic Pd species formed either via
38
oxidative addition of the electrophilic partner to the Pd center
39
or via ligand displacement by a coordinating solvent. Our
initial assumption was based on the mass spectral analysis
results for the Pd-NHC complexes described here, which
showed the presence of the cationic Pd species as the base peak.
The presence of such species via ligand displacement has also
been shown to exist in the reactions using electrospray
39b
ionization mass spectrometry.
To verify this extent, we performed an experiment involving
40
the addition of silver salt (AgNO ) in an equimolar amount
Figure 10. Effect of Ag salt addition on the reactivity of the catalytic
3
to that of the Pd-NHC complex IId with the intention of
reaction.
G
DOI: 10.1021/om501160n
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
It seems that indeed the addition of silver salt helps to
accelerate the formation of the cationic Pd species, leading to
the faster conversion of the substrate to the product (complete
conversion was observed in around 3−6 h). In the case of IId
alone, the formation of cationic Pd species might take place at a
slower rate, which could explain the difference in reactivity.
Nevertheless, further ongoing studies to get better insight into
the possible mechanism acting in these types of coupling
reactions, including isolation and characterization of cationic
complexes, are needed and will be reported in due course.
NMR (200 MHz, CDCl
3
): δ 124.63, 125.45, 126.66, 128.15, 130.42,
1
30.93, 137.09, 138.58, 148.53, 150.43, 151.77, 192.35 CO. HPLC-
+
MS (positive mode) m/z: 610.17 (M ). Anal. Calcd for
C H N O Pd : C, 47.16; H, 2.97; N, 4.58. Found: C, 47.35; H,
24
18
2
4
2
3
.23; N, 4.63.
∧
Preparation of the Complexes [Pd(Bmim)(X)(C N)] (X = Cl a, Br b,
∧
I c, or saccharinate (sacc) d (C N = 2-benzoylpyridine (Bzpy) I
series; C N = 2-phenylpyridine (Phpy) II series). The new complexes
∧
were obtained by treating a CH Cl2 suspension (20 mL) of the
appropriate precursor [{Pd(μ-OH)(C N)}
2
∧
] (0.2 g) with the
2
corresponding 1,3-butylmethylimidazolium salt (molar ratio 1:2) in
dichloromethane (15 mL). The pale yellow solution thus formed was
stirred at room temperature for 1 h, passed through a short silica gel
column, and then concentrated under reduced pressure until ca. one-
fifth of the initial volume. Slow addition of hexane/diethyl ether (1:1)
caused the precipitation of the title complexes, which were filtered off
and air-dried.
CONCLUSION
A new and convenient route to obtain palladacyclic complexes
containing NHC ligands [Pd(Bmim)(X)(C N)] has been
■
∧
explored, exploiting the enhanced reactivity of di-μ-hydroxo
precursors. Novel NHC/imidate palladium complexes can also
be prepared by removing halide X in the former using a silver/
imidate source. Structural characterization by X-ray diffraction
of four complexes confirmed the proposed formula. In addition,
catalytic activity of the new complexes in Suzuki−Miyaura
cross-coupling of 9-bromoanthracene with aryl boronic acids at
very low catalyst loading has been disclosed. Faster conversion
−1
[Pd(Bzpy)(Bmim)Cl], Ia: 0.16 g, 53%;. IR (cm ): ν(Bzpy) 1660 vs,
1
1
1
(
6
603 vs, 772 vs. H NMR (400 MHz, CDCl ): δ 9.48 (d, J = 5.6 Hz,
3
2
5
4
H Bzpy), 8.13 (d, J = 8.0 Hz, 1H Bzpy), 7.97 (m, 1H Bzpy), 7.73
6
3
7
d, J = 7.6 Hz, 1H Bzpy), 7.52 (m, 1H Bzpy); 7.07 (m, 1H Bzpy);
8
.95 (m, 1H Bzpy); 6.90 (d, J = 1.6 Hz, 1H carbene), 6.87 (d, J = 1.6
α
Hz, 1H carbene), 6.55 (d, J = 7.6 Hz, 1H Bzpy), 4.29 (m, 1H N−
CH −), 4.03 (m, 1H N−CH −), 3.96 (s, 3H N−CH ), 1.76 (m, 1H
2
2
3
N−CH −CH −), 1.51 (m, 1H N−CH −CH −), 1.26 (m, 2H N−
2
2
2
2
of the substrate in the presence of AgNO suggests a key role of
3
CH −CH −CH −), 0.86 (t, J = 7.2 Hz, 3H N−CH −CH −CH −
2
2
2
2
2
2
13
intermediate cationic species.
CH ). C NMR (400 MHz, CDCl ): δ: 13.61 (N−CH −CH −
3
3
2
2
CH −CH ), 19.84 (N−CH −CH −CH −), 32.27 (N−CH −CH −),
2
3
2
2
2
2
2
EXPERIMENTAL SECTION
General Procedures. All catalytic reactions were conducted under
38.20 (N−CH
3
), 50.99 (N−CH
2
−CH
2
−CH −), 120.62 carbene,
2
■
1
1
22.01 carbene, 124.46, 124.57, 126.40, 129.19, 130.43, 137.03,
38.37, 138.88, 148.77, 151.87, 152.53, 170.44 [Pd−Ccarbene], 192.92
an inert atmosphere of N on a Schlenk line. Melting points were
2
+
CO. HPLC-MS (positive mode) m/z: 426.08 (M − Cl). Anal.
recorded on an electrothermal digital melting point apparatus and are
uncorrected. TLC analysis was performed on aluminum-backed silica
gel plates, and compounds were visualized by ultraviolet light (254
nm), phosphomolybdic acid solution (5% in EtOH), or 1% ninhydrin
Calcd for C H ClN OPd: C, 51.96; H, 4.80; N, 9.09. Found: C,
20
22
3
5
2.09; H, 5.06; N, 9.12.
Pd(Bzpy)(Bmim)Br], Ib: 0.23 g, 71%. IR (cm ): ν(Bzpy) 1663 vs,
−1
[
1
1
1590 vs, 772 vs. H NMR (400 MHz, CDCl ): δ 9.57 (d, J = 5.2 Hz,
3
in EtOH. NMR data ( H) were recorded on 200, 300, or 400
2
5
4
1
H Bzpy), 8.12 (d, J = 7.6 Hz, 1H Bzpy), 7.97 (m, 1H Bzpy), 7.73
spectrometers. ESI-MS analyses were performed on a mass
spectrometer. Chemical shifts are reported in parts per million
downfield from an internal tetramethylsilane reference. Coupling
constants (J values) are reported in hertz (Hz). IR spectra were
recorded on an FT-IR spectrophotometer, using Nujol mulls between
polyethylene sheets.
GC Parameters. GC analysis for the kinetic profile was done on a
Shimadzu GC-MS Parvum 2 equipped with an autosampler.
Separation was achieved using a Zebron ZB-1 capillary column (i.d.
6
3
7
(d, J = 7.6 Hz, 1H Bzpy), 7.49 (m, 1H Bzpy), 7.08 (m, 1H Bzpy),
8
10
11
6
.96 (m, 1H Bzpy), 6.91 (s, 1H carbene), 6.86 (s, 1H carbene),
α
6
.56 (d, J = 7.6 Hz, 1H Bzpy), 4.25 (m, 1H N−CH ), 4.03 (m, 1H
2
N−CH ), 3.97 (s, 3H N−CH ), 1.86 (m, 1H N−CH −CH −),1.44
2
3
2
2
(
(
m, 1H N−CH −CH −), 1.24 (m, 2H N−CH −CH −CH −), 0.84
2
2
2
2
2
13
t, J = 7.6 Hz, 3H N−CH −CH −CH −CH ). C NMR (300 MHz,
2
2
2
3
CDCl ): δ 13.62 (N−CH −CH −CH −CH ), 19.84 (N−CH −
3
2
2
2
3
2
CH −CH −), 32.27 (N−CH −CH −), 38.41 (N−CH ), 51.06 (N−
2
2
2
2
3
CH −CH −CH −), 120.61, carbene, 122.06 carbene, 124.55, 124.60,
0
1
.25 mm, length 30 m) with a temperature ramp from 50 to 250 °C at
2
2
2
−1
126.29, 129.16, 130.41, 137.94, 138.38, 138.86, 150.17, 152.13, 153.89,
70.20 [Pd−C
], 192.85 CO. HPLC-MS (positive mode) m/z:
0 °C min . The injection volume was 1 μL with a split ratio of 50.
1
Materials and Methods. The cyclometalated precursor [{Pd(μ-
carbene
+
∧
∧
426.08 (M − Br). Anal. Calcd for C H BrN OPd: C, 47.40; H,
4
OH)(C N)} ] (C N = 2-phenylpyridine (Phpy), II) was prepared as
20 22
3
2
2
9b
.38; N, 8.29. Found: C, 47.50; H, 4.61; N, 8.31.
described previously.
HBmim]X (X: Cl, Br, I) were obtained from IoLiTec GmbH
Germany). [HBmim](Sacc) was prepared adapting a method
The 1,3-butylmethylimidazolium salts
−1
[
Pd(Bzpy)(Bmim)I], Ic: 0.20 g, 55%. IR (cm ): ν(Bzpy) 1665 vs,
[
(
1
1
1
603 vs, 772 vs. H NMR (200 MHz, CDCl ): δ 10.10 (d, J = 4.4 Hz,
3
2
5
41
H Bzpy), 8.70 (d, J = 7.0 Hz, 1H Bzpy), 8.02 (m, 2H Bzpy), 7.56
previously described. Other commercially available chemicals such
as arylboronic acids, 9-bromophenanthrene, and AgNO3 were
purchased from Aldrich Chemical Co. and were used without further
purification, and all the solvents were dried by standard methods
before use.
α
(
4
m, 3H Bzpy), 6.86 (m, 3H carbene+H ), 4.32 (m, 1H N−CH −),
2
.10 (m, 1H N−CH −), 3.94 (s, 3H N−CH ), 1.94 (m, 2H N−CH −
2
3
2
CH −), 1.37 (m, 2H N−CH −CH −CH −), 0.98 (t, J = 7.0 Hz, 3H
2
2
2
2
1
3
N−CH −CH −CH −CH ,). C NMR (300 MHz, CDCl ): δ 13.71
2
2
2
3
3
∧
∧
(
N−CH −CH −CH −CH ), 20.03 (N−CH −CH −CH −), 32.09
Preparation of Complex [{Pd(μ-OH)(C N)} ] (C N = 2-benzoyl-
2
2
2
3
2
2
2
2
pyridine (Bzpy), I). To a solution of [{Pd(Bzpy)(μ-AcO)} ] (348 mg,
(N−CH
2
−CH
2
−), 38.44 (N−CH
3
), 50.87 (N−CH
2
−CH
2
−CH −),
2
2
0
.5 mmol) in 10 mL of acetone was added 20% NBu OH(aq) (1.45
120.98, carbene, 122.27 carbene, 124.50, 124.61, 126.17, 128.14,
4
mL, 1.1 mmol). After 1 h stirring at room temperature the solvent was
partially evaporated under reduced pressure. Addition of water
followed by vigorous stirring and filtration afforded a yellow solid,
which was air-dried. The complex was recrystallized from acetone/
diethyl ether.
130.92, 137.06, 138.41, 138.92, 150.27, 152.63, 153.99, 170.15 [Pd−
+
C
carbene], 192.82 CO. HPLC-MS (positive mode) m/z: 426.08 (M
− I). Anal. Calcd for C20
Found: C, 43.51; H, 4.20; N, 7.67.
H22IN
OPd: C, 43.38; H, 4.00; N, 7.59.
3
−1
Pd(Bzpy)(Bmim)(Sacc)], Id: 0.23 g, 58%. IR (cm ): ν(Bzpy) 1666
vs, 1594 vs, 782 vs ν(Sacc) 1660 vs, 1285s, 1168s, 968vs, 679s. H
−
1
1
[
{Pd(μ-OH)(Bzpy)} ], I: 0.275g, 90%. IR (cm ): ν(OH) 3434,
2
1
2
ν(Bzpy) 1660, 1596, 1550, 766. H NMR (200 MHz, CDCl ): δ 9.07
d, J = 5.0 Hz, 2H Bzpy), 8.17 (d, J = 8.0 Hz, 2H Bzpy), 7.97 (m,
H Bzpy), 7.75 (d, J = 7.6 Hz, 2H Bzpy), 7.46 (m, 2H Bzpy), 7.19−
.15 (m, 4H Bzpy); 6.93 (m, 2H Bzpy), −1.60 (s, 2H, OH).
NMR (400 MHz, CDCl ): δ 9.10 (d, J = 5.2 Hz, 1H Bzpy), 8.19 (d, J
3
3
2
5
5
4
6
(
2
7
= 7.6 Hz, 1H Bzpy), 7.92 (m, 1H Bzpy), 7.65 (d, J = 7.6 Hz, 1H
4
6
3
3
7
Bzpy), 7.54 (m, 2H Sacc), 7.38 (m, 1H Bzpy), 7.10 (m, 1H Bzpy),
α
13
8
10
11
C
6.99 (m, 1H Bzpy), 6.90 (s, 1H carbene), 6.81 (s, 1H carbene),
H
DOI: 10.1021/om501160n
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
α
6
.75 (d, J = 7.6 Hz, 1H Bzpy), 4.55 (m, 1H N−CH ), 4.18 (s, 3H N−
127.88 Sacc, 128.33 Sacc, 129.42, 131.98, 132.38 Sacc, 132.93 Sacc,
2
CH ), 4.04 (m, 1H N−CH ), 1.44 (m, 2H N−CH −CH −), 1.18 (m,
136.67, 138.51, 147.02, 149.88 Sacc, 154.16, 164.18, 167.40 Sacc,
3
2
2
2
+
2
H N−CH −CH −CH −), 0.78 (t, J = 7.6 Hz, 3H N−CH −CH −
171.93 [Pd−C
]. HPLC-MS (positive mode) m/z: 398.08 (M −
2
2
2
2
2
carbene
13
CH −CH ). C NMR (300 MHz, CDCl ): δ 13.66 (N−CH −CH −
Sacc). Anal. Calcd for C H N O PdS: C, 53.75; H, 4.51; N, 9.64; S,
2
3
3
2
2
26 26 4 3
CH −CH ), 19,68 (N−CH −CH −CH −), 31.99 (N−CH −CH −),
5.52. Found: C, 53.92; H, 4.65; N, 9.84; S, 5.75.
2
3
2
2
2
2
2
3
8.38 (N−CH ), 51.05 (N−CH −CH −CH −), 119.81 Sacc, 120.37
Preparation of Complex [Ag(Phthal)(SMe )] . To a 20 mL solution
3
2
2
2
2 2
carbene, 122.09 carbene, 123.37 Sacc, 124.61, 124.76, 126.66, 129.35,
of Ag(CH COO) (500 mg, 3.0 mmol) in CH Cl were added
3
2
2
1
1
C
30.23, 131.98 Sacc, 132.67 Sacc, 137.13, 138.03, 138.92, 142.64 Sacc,
phthalimide (440 mg, 3 mmol) and 0.222 mL (3.0 mmol) of SMe2.
After 1 h of stirring at room temperature the solvent was partially
evaporated under reduced pressure. Addition of diethyl ether afforded
a white solid, which was filtered, air-dried, and recrystallized from
acetone/hexane.
48.18 Sacc, 151.83, 152.48, 153.86, 167.35 Sacc, 169.41 [Pd−
+
], 192.30 CO. HPLC-MS (positive mode) m/z: 426.08 (M
carbene
−
Sacc). Anal. Calcd for C H N O PdS: C, 53.63; H, 5.14; N, 8.93;
28 32 4 4
S, 5.11. Found: C, 53.65; H, 5.40; N, 9.12; S, 5.23.
−
1
−1
[
Pd(Phpy)(Bmim)Cl], IIa: 0.21 g, 66%. IR (cm ): ν(Phpy) 1604 vs,
[Ag(Phthal)(SMe )] : 0.743g, 79%. IR (cm ): ν(Phthal) 1702,
2
2
1
2
1
7
52 vs. H NMR (400 MHz, CDCl ): δ 9.30 (d, J = 1.6 Hz, 1H
1644, 3434, ν(SMe ) 1052, 1034. H NMR (200 MHz, CDCl ): δ
3
2
3
4
5
Phpy), 7.79 (m, 1H Phpy), 7.69 (d, J = 7.9 Hz, 1H Phpy), 7.53 (d, J
7.86 (m, 4H Phthal); 7.75 (m, 4H Phthal); 2.18 (s, 12H SMe ). Anal.
2
6
3
8
=
7.9 Hz, 1H Phpy), 7.21 (m, 1H Phpy), 7.05 (m, 1H Phpy), 7.00
Calcd for C H Ag N O S : C, 37.99; H, 3.19; N, 4.43. Found: C,
20
20
2
2
4 2
7
α
(
s, 2H carbene), 6.87 (m, 1H Phpy), 6.10 (d, J = 7.2 Hz, 1H Phpy),
38.18; H, 3.22; N, 4.53.
4
.37 (m, 1H N−CH −), 4.31 (m, 1H N−CH −), 3.96 (s, 3H N−
Preparation of Complex [Pd(Phpy)(Bmim)(Phthal)], IIe. To a 20
2
2
CH ), 1.89 (m, 2H N−CH −CH −, 1.31 (m, 2H N−CH −CH −
mL CH Cl solution of [Pd(Phpy)(Bmim)Br] (250 mg, 0.521 mmol)
3
2
2
2
2
2
2
1
3
CH −), 0.84 (t, J = 7.3 Hz, 3H N−CH −CH −CH −CH ).
C
was added 165 mg (0.521 mmol) of complex [Ag(phthal)(SMe )].
2
2
2
2
3
2
NMR (400 MHz, CDCl ): δ 13.59 (N−CH −CH −CH −CH ),
After 1 h of stirring at room temperature a yellow solid was obtained.
The solvent was then partially evaporated under reduced pressure, and
slow addition of diethyl ether caused complete precipitation of a white
solid, which was filtered, air-dried, and recrystallized from CH Cl /
3
2
2
2
3
1
9.75 (N−CH −CH −CH −), 32.44 (N−CH −CH −), 38.46 (N−
2
2
2
2
2
CH ), 51.05 (N−CH −CH −CH −), 117.87 carbene, 120.90
3
2
2
2
carbene, 122.06, 122.02, 123.55, 123.92, 129.56, 136.51, 138.42,
46.49, 149.60, 154.66, 164.09, 173.15 [Pd−Ccarbene]. HPLC-MS
2
2
1
ether.
+
−1
(
positive mode) m/z: 398.08 (M − Cl). Anal. Calcd for
[Pd(Phpy)(Bmim)(Phthal)], IIe: 0.15 g, 52%. IR (cm ): ν(Phpy)
C H ClN Pd: C, 52.55; H, 5.11; N, 9.68. Found: C, 52.76; H,
1605 vs, 1570 vs, 755 vs ν(Phthal) 1721s, 1643 vs, 1298s, 1127s, 849s.
1
9
22
3
1
2
5
7
.36; N, 9.69.
Pd(Phpy)(Bmim)Br], IIb: 0.23 g, 71%. IR (cm ): ν(Phpy) 1605 vs,
H NMR (400 MHz, CDCl ): δ 8.26 (d, J = 5.2 Hz, 1H Phpy), 7.74
3
−
1
5
6
[
(m, 1H Phpy), 7.65 (m, 2H Phthal), 7.56 (m, 1H Phpy), 7.49 (m,
1
2
3
52 vs. H NMR (200 MHz, CDCl ): δ 9.49 (d, J = 5.6 Hz, 1H
2H, Phthal), 7.05 (m, 1H Phpy), 6.95 (d, J = 2.1 Hz, 1H carbene),
3
6
7
Phpy), 7.79 (m, 2H Phpy), 7.53 (d, J = 7.8 Hz, 1H Phpy), 7.23 (m,
6.91 (d, J = 2.1 Hz, 1H carbene), 6.88 (m, 1H Phpy), 6.11 (d, J = 7.0
3
8
7
α
1
H Phpy), 7.06 (m, 1H Phpy), 7.00 (s, 2H carbene), 6.90 (m, 1H
Hz 1H Phpy), 4.67 (m, 1H N−CH -), 4.21 (m, 1H N−CH -), 4.10
2
2
α
Phpy), 6.08 (d,, J = 7.6 Hz, 1H Phpy), 4.37 (m, 2H N−CH −), 3.95
(s, 3H N−CH ), 1.71 (m, 2H, N−CH −CH ), 1.32 (m, 2H N−CH −
2
3
2
2
2
(
s, 3H N−CH ), 1.87 (m, 2H N−CH −CH −), 1.28 (m, 2H N−
CH −CH −), 0.80 (t, J = 7.5 Hz, 3H, N−CH −CH −CH −CH ).
3
2
2
2
2
2
2
2
3
13
CH −CH −CH −), 0.82 (t, J = 7.3 Hz, 3H, N−CH −CH −CH −
C NMR (400 MHz, CDCl ): δ 13.66 (N−CH −CH −CH −CH ),
2
2
2
2
2
2
3
2
2
2
3
13
CH ). C NMR (200 MHz, CDCl ): δ 13.61 (N−CH −CH −CH −
3
3
2
2
2
19.80 (N−CH −CH −CH −), 32.41 (N−CH −CH −), 38.65 (N−
2
2
2
2
2
CH ), 19.80 (N−CH −CH −CH −), 32.24 (N−CH −CH −), 38.54
3
2
2
2
2
2
CH ), 50.88 (N−CH −CH −CH −), 118.21 carbene, 120.25
3
2
2
2
(
N−CH ), 51.13 (N−CH −CH −CH −), 117.99 carbene, 120.92
3
2
2
2
carbene, 120.93, 122.06, 122.19, 123.40, 123.57, 123.83 Phthal,
29.33, 131.35, 136.95, 137.55 Phthal, 138.43, 147.10, 149.59 Phthal,
164.92, 173.45 [Pd−C
], 181.41 CO. HPLC-MS (positive
carbene, 122.07, 122.34, 123.63, 124.03, 129.63, 136.18, 138.29,
1
1
46.54, 151.14, 155.62, 164.11, 172.83 [Pd−Ccarbene]. HPLC-MS
carbene
+
+
(
positive mode) m/z: 398.08 (M − Br). Anal. Calcd for
mode) m/z: 398.08 (M − Phthal). Anal. Calcd for C H N O Pd: C,
27
26
4
2
C H BrN Pd: C, 47.67; H, 4.63; N, 8.78. Found: C, 47.95; H,
1
9
22
3
59.51; H, 4.81; N, 10.28. Found: C, 59.72; H, 4.65; N, 10.36.
4
7
.76; N, 8.91.
Pd(Phpy)(Bmim)I], IIc: 0.20 g, 55%. IR (cm ): ν(Phpy) 1603 vs,
General Procedure for Suzuki−Miyaura Cross-Coupling of
9-Bromophenanthrene with Aryl Boronic Acids Using Pd-NHC
Complex II. In a dry Schlenk tube, Pd-NHC complex IId solution in
PhMe was taken via syringe (to obtain a 0.01 mol % catalyst
concentration a stock solution of 1.0 mol % IId was prepared in PhMe
as solvent by dissolving 5.8 mg of IId in 100 mL of PhMe under
nitrogen in a Schlenk tube from which 1.0 mL of the solution was
taken out to provide the catalyst in the desired concentration for the
−
1
[
1
2
52 vs. H NMR (200 MHz, CDCl ): δ 9.70 (d, J = 5.0 Hz, 1H ,
3
6
Phpy), 7.75 (m, 2H Phpy), 7.53 (d, J = 7.9 Hz, 1H Phpy), 7.26−6.86
α
(
(
m, 5H 3H Phpy + 2H carbene), 5.98 (d, J = 7.4 Hz, 1H Phpy), 4.34
m, 2H N−CH −), 3.95 (s, 3H N−CH ), 1.85 (m, 2H N−CH −
2
3
2
CH −), 1.31 (m, 2H N−CH −CH −CH −); 0.87 (t, J = 7.4 Hz, 3H
N−CH −CH −CH −CH ,). C NMR (200 MHz, CDCl ): δ 13.56
(
(
1
1
2
2
2
2
13
2
2
2
3
3
N−CH −CH −CH −CH ), 19.80 (N−CH −CH −CH -), 31.98
N−CH −CH -), 38.59 (N-CH ), 51.12 (N-CH −CH −CH −),
reaction) and was stirred under a N atmosphere. To this was added 9-
2
2
2
3
2
2
2
2
bromophenanthrene III (1.0 mmol, 0.255 g), and the resultant
solution was stirred at 80 °C for 5 min. The reaction mixture was
cooled, and to this was added phenylboronic acid IVa (1.2 mmol,
0.145 g) as well as Na CO (3.0 mmol, 0.318 g). Finally H O (2 mL)
2
2
3
2
2
2
18.19 carbene, 120.95 carbene, 122.21, 122.68, 123.68, 124.16,
29.68, 135.41, 138.05, 146.59, 153.89, 157.15, 164.06, 171.92 [Pd−
+
C
]. HPLC-MS (positive mode) m/z: 398.08 (M − I). Anal.
carbene
2
3
2
Calcd for C H IN Pd: C, 43.41; H, 4.22; N, 7.99. Found: C, 43.54;
H, 4.37; N, 8.01.
Pd(Phpy)(Bmim)(Sacc)], IId: 0.23 g, 58%. IR (cm ): ν(Phpy)
was added, and the resultant mixture was stirred at 80 °C for 12 h. At
the end of the reaction, solvent was removed in vacuo, and the
resultant crude product was purified using column chromatography
(hexane) to give the product Va in 96% yield.
19
22
3
−1
[
1
1
602 vs, 1567 vs, 752 vs ν(Sacc) 1661 vs, 1288s, 1151s, 964vs. H
2
1
NMR (400 MHz, CDCl ): δ 8.47 (d, J = 5.2 Hz, 1H Phpy), 7.87 (m,
1
Sacc), 7.46 (m, 1H Phpy), 7.12 (m, 2H Phpy), 6.99 (d, J = 2.0 Hz,
1
6
Phenylphenanthrene (Va): 96%, 0.243 g. Mp: 100−102 °C. H
3
5
6
H Phpy), 7.77 (m, 2H Sacc), 7.61 (m, 1H Phpy), 7.54 (m, 2H
NMR (400 MHz, CDCl ): δ 8.83 (d, J = 8.2 Hz, 1H), 8.77 (d, J = 8.2
3
3
Hz, 1H), 7.99−7.94 (m, 2H), 7.74−7.70 (m, 3H), 7.68−7.65 (m, 1H),
7
13
H carbene); 6.97 (d, J = 2.0 Hz, 1H carbene), 6.89 (m, 1H Phpy),
7.62−7.50 (m, 6H). C NMR (100 MHz, CDCl ): δ 140.9, 138.9,
3
α
.07 (d, J = 7.2 Hz, 1H Phpy), 4.74 (m, 1H N−CH −), 4.21 (m, 1H
131.7, 131.3, 130.8, 130.2, 130.1, 128.8, 128.4, 127.6, 127.5, 127.1,
2
N−CH −), 4.06 (s, 3H N−CH ), 1.77 (m, 2H N−CH −CH −), 1.33
127.0, 126.7, 126.6, 126.5, 123.0, 122.7. MS (EI, m/z): 254 (100).
2
3
2
2
(
m, 2H N−CH −CH −CH −), 0.82 (t, J = 7.3 Hz, 3H, N−CH −
Anal. Calcd (%) for C H : C, 94.45; H, 5.55. Found: C, 94.32; H,
2
2
2
2
20 14
13
CH −CH −CH ). C NMR (400 MHz, CDCl ): δ 13.64 (N−CH −
5.41.
2
2
3
3
2
CH −CH −CH ), 19.79 (N−CH −CH −CH −), 32.26 (N−CH −
9-(2-Naphthyl)phenanthrene (Vb): 94%, 0.285 g. Mp: 141−143
2
2
3
2
2
2
2
1
CH −), 38.63 (N−CH ), 51.00 (N−CH −CH −CH −), 118.20
°C. H NMR (400 MHz, CDCl ): δ 8.83 (d, J = 8.2 Hz, 1H), 8.78 (d,
2
3
2
2
2
3
carbene, 119.90 carbene, 120.59, 122.18, 122.51, 123.57, 124.28,
J = 8.2 Hz, 1H), 8.06 (s, 1H), 8.01−7.93 (m, 5H), 7.82 (s, 1H), 7.72−
I
DOI: 10.1021/om501160n
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
3
7.51−7.49 (m, 2H), 7.42−7.40 (m, 2H). 13C NMR (100 MHz,
7
1
1
1
.65 (m, 4H), 7.60−7.55 (m, 3H). C NMR (100 MHz, CDCl ): δ
3
38.8, 138.5, 133.6, 132.8, 131.7, 131.4, 130.8, 130.2, 128.8, 128.6,
28.2, 128.0, 127.9, 127.8, 127.1, 127.0, 126.8, 126.7, 126.6, 126.5,
26.2, 123.1, 122.7. MS (EI, m/z): 304 (100). Anal. Calcd (%) for
CDCl ): δ 138.3, 137.8, 137.7, 131.7, 131.2, 130.8, 130.6, 130.1, 128.8,
3
127.6, 127.0, 126.9, 126.8, 126.7, 126.6, 126.5, 123.1, 122.7, 16.0. MS
(EI, m/z): 300 (100). Anal. Calcd (%) for C H S: C, 83.96; H, 5.37;
21
16
C H : C, 94.70; H, 5.30. Found: C, 94.63; H, 5.26.
S, 10.67. Found: C, 83.74; H, 5.23.
2
4
16
5
-(Phenanthren-9-yl)benzo[d][1,3]dioxole (Vc): 93%, 0.277 g. Mp:
9-(3-Nitrophenyl)phenanthrene (Vk): 49%, 0.146 g. Mp: 122−124
1
1
9
8
7−99 °C. H NMR (400 MHz, CDCl ): δ 8.81 (d, J = 8.2 Hz, 1H),
.75 (d, J = 8.2 Hz, 1H), 8.05 (d, J = 8.2 Hz, 1H), 7.93 (dd, J = 7.8, 0.8
°C. H NMR (400 MHz, CDCl ): δ 8.81 (d, J = 8.4 Hz, 1H), 8.74 (d,
3
3
J = 8.4 Hz, 1H), 8.44 (s, 1H), 8.34−8.32 (m, 1H), 7.93−7.91 (m, 1H),
Hz, 1H), 7.73−7.64 (m, 4H), 7.62−7.59 (m, 1H), 7.11−7.01 (m, 3H),
7.89−7.87 (m, 1H), 7.78 (d, J = 8.2 Hz, 1H), 7.74−7.64 (m, 5H),
.09 (s, 2H). 13C NMR (100 MHz, CDCl ): δ 147.6, 147.1, 138.4,
34.7, 131.6, 131.3, 130.7, 130.0, 128.7, 127.6, 127.0, 126.9, 126.7,
26.6, 126.5, 123.5, 123.0, 122.6, 110.8, 108.4. MS (EI, m/z): 298
7.59−7.56 (m, 1H). C NMR (100 MHz, CDCl ): δ 148.5, 142.6,
13
6
1
1
3
3
136.3, 136.2, 131.3, 130.9, 130.4, 129.4, 129.0, 128.4, 127.4, 127.3,
127.1, 127.0, 126.2, 125.0, 123.3, 122.8, 122.6. MS (EI, m/z): 299
(100). Anal. Calcd (%) for C H NO : C, 80.25; H, 4.38; N, 4.68.
(
100). Anal. Calcd (%) for C H O : C, 84.54; H, 4.73. Found: C,
21 14 2
20 13
2
8
4.37; H, 4.59.
-(3,5-Dimethylphenyl)phenanthrene (Vd): 98%, 0.276 g. Mp:
Found: C, 80.02; H, 4.43; N, 4.75.
9
9-(4-Fluorophenyl)phenanthrene (Vl): 88%, 0.238 g. Mp: 148−150
1
1
1
1
1
54−156 °C. H NMR (400 MHz, CDCl ): δ 8.81 (d, J = 8.3 Hz,
°C. H NMR (400 MHz, CDCl ): δ 8.82 (d, J = 8.2 Hz, 1H), 8.76 (d,
3
3
H), 8.76 (d, J = 8.3 Hz, 1H), 8.04−8.01 (m, 2H), 7.94−7.92 (m,
J = 8.2 Hz, 1H), 7.93−7.91 (m, 1H), 7.74−7.65 (m, 4H), 7.61−7.53
13
H), 7.74−7.57 (m, 5H), 7.24 (d, J = 5.0 Hz, 2H), 7.16 (s, 1H), 2.48
(m, 3H), 7.28−7.25 (m, 2H). C NMR (100 MHz, CDCl ): δ 163.4,
3
(
s, 6H). 13C NMR (100 MHz, CDCl ): δ 140.8, 139.2, 137.9, 131.7,
161.5, 137.8, 136.8, 131.8, 131.7, 131.6, 131.2, 130.8, 130.1, 128.8,
127.8, 127.1, 126.9, 126.8, 126.7, 126.6, 123.1, 122.7, 115.5, 115.3. MS
(EI, m/z): 272 (100). Anal. Calcd (%) for C H F: C, 88.21; H, 4.81.
3
1
1
31.4, 130.7, 130.0, 129.1, 128.7, 128.0, 127.4, 127.2, 126.9, 126.6,
26.5, 123.0, 122.6, 21.5. MS (EI, m/z): 282 (100). Anal. Calcd (%)
20
13
for C H : C, 93.57; H, 6.43. Found: C, 93.47; H, 6.48.
Found: C, 88.04; H, 4.65.
22
18
9
-(4-Phenoxyphenyl)phenanthrene (Ve): 96%, 0.332 g. Mp: 116−
Scale-up Studies for Suzuki−Miyaura Cross-Coupling of 9-
Bromophenanthrene with Aryl Boronic Acids Using Pd-NHC
Complex IId. In a dry 50 mL Schlenk tube, a Pd-NHC complex IId
solution in PhMe was taken via syringe (to obtain a 0.005 mol %
catalyst concentration, a stock solution of 5.0 mol % IId was prepared
in PhMe as solvent by dissolving 29 mg of IId in 100 mL of PhMe
under nitrogen in a Schlenk tube, from which 5.0 mL of the solution
was taken out and further diluted to 50 mL using dry PhMe under a
nitrogen atmosphere; 5.0 mL of this stock solution provides the
catalyst in the desired concentration for the 5.0 mmol reaction) and
was stirred under a N2 atmosphere. To this was added 9-
bromophenanthrene III (5.0 mmol, 0.1.275 g), and the resultant
solution was stirred at 80 °C for 5 min. The reaction mixture was
cooled, and to this was added phenylboronic acid IVa (6.0 mmol,
1
1
(
7
18 °C. H NMR (400 MHz, CDCl ): δ 8.81 (d, J = 8.2 Hz, 1H), 8.76
d, J = 8.2 Hz, 1H), 7.99 (d, J = 7.7 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H),
.73−7.53 (m, 7H), 7.45−7.42 (m, 1H), 7.21−7.15 (m, 4H).
NMR (100 MHz, CDCl ): δ 157.0. 156.7, 138.0, 135.5, 131.5, 131.3,
31.1, 130.6, 129.8, 129.7, 128.5, 127.5, 126.7, 126.5, 126.4, 126.3,
23.4, 122.9, 122.4, 119.1, 118.4. MS (EI, m/z): 346 (100). Anal.
Calcd (%) for C H O: C, 90.14; H, 5.24. Found: C, 90.21; H, 5.28.
3
13
C
3
1
1
26
18
9
-(4-Methylphenyl)phenanthrene (Vf): 94%, 0.251 g. Mp: 90−92
1
°
C. H NMR (400 MHz, CDCl ): δ 8.81 (d, J = 7.7 Hz, 1H), 8.75 (d,
3
J = 8.8 Hz, 1H), 7.97 (d, J = 7.7 Hz, 1H), 7.92 (dd, J = 7.8, 0.8 Hz,
1
7
H), 7.70−7.68 (m, 3H), 7.66−7.66 (m, 1H), 7.58−7.55 (m, 1H),
.48 (d, J = 7.7 Hz, 2H), 7.36 (d, J = 7.7 Hz, 2H), 2.51 (s, 3H). 13
C
NMR (100 MHz, CDCl ): δ 138.7, 137.8, 137.0, 131.6, 131.2, 130.6,
29.8, 128.9, 128.5, 127.3, 126.9, 126.7, 126.4, 126.3, 122.8, 122.4,
3
0
.725 g) as well as Na CO (15.0 mmol, 1.59 g). Finally H O (10 mL)
1
2
3
2
was added, and the resultant mixture was stirred at 80 °C for 12 h. At
the end of the reaction, solvent was removed in vacuo, and the
resultant crude product was purified using column chromatography
(hexane) to give the product Va in 80% yield.
2
1.2. MS (EI, m/z): 268 (100). Anal. Calcd (%) for C H : C, 93.99;
21
16
H, 6.01. Found: C, 93.84; H, 5.83.
9-(4-Biphenyl)phenanthrene (Vg): 79%, 0.260 g. Mp: 215−218 °C.
1
H NMR (400 MHz, CDCl ): δ 8.81 (d, J = 8.3 Hz, 1H), 8.76 (d, J =
3
Crystal Structure Determination of [Pd(Bzpy)(Bmim)(Sacc)],
Id, [Pd(Phpy)(Bmim)Br], IIb, [Pd(Phpy)(Bmim)(Sacc)], IId, and
[Pd(Phpy)(Bmim)(Phthal)], IIe. Data collection for Id, IIb, IId, and
IIe was performed at 100 K on a Bruker Smart CCD diffractometer
with a nominal crystal to detector distance of 4.5 cm. Diffraction data
were collected based on a ω scan run. A total of 2524 frames were
collected at 0.3° intervals and 10 s per frame. The diffraction frames
8
7
7
1
1
.0 Hz, 1H), 8.03 (d, J = 7.3 Hz, 1H), 7.93 (dd, J = 7.8, 0.8 Hz, 1H),
.78−7.63 (m, 10H), 7.61−7.57 (m, 1H), 7.54−7.50 (m, 2H), 7.43−
.40 (m, 1H). 13C NMR (100 MHz, CDCl ): δ 141.0, 140.4, 139.9,
3
38.5, 131.7, 131.2, 130.8, 130.6, 130.1, 129.0, 128.8, 127.7, 127.5,
27.3, 127.2, 127.1, 127.0, 126.8, 126.7, 126.6, 123.1, 122.7. MS (EI,
m/z): 330 (100). Anal. Calcd (%) for C H : C, 94.51; H, 5.49.
26
18
Found: C, 94.39; H, 5.33.
-(3-Methoxyphenyl)phenanthrene (Vh): 92%, 0.269 g. Mp: 92−
42
were integrated using the SAINT package and corrected for
9
43
1
absorption with SADABS. The structures were solved by direct
4 °C. H NMR (400 MHz, CDCl ): δ 8.79 (d, J = 8.2 Hz, 1H), 8.74
44
3
methods and refined by full-matrix least-squares techniques using
anisotropic thermal parameters for non-H atoms (Table 5 included as
Supporting Information).
1
7
3
1
1
H), 7.71−7.67 (m, 3H), 7.65−7.61 (m, 1H), 7.57−7.54 (m, 1H),
.46−7.43 (m, 1H), 7.16−7.11 (m, 2H), 7.04−7.01 (m, 1H), 3.88 (s,
H). 13C NMR (100 MHz, CDCl ): δ 159.7, 142.3, 138.8, 131.6,
3
31.2, 130.7, 130.1, 129.4, 128.8, 127.5, 127.1, 127.0, 126.8, 126.7,
26.6, 123.0, 122.7, 122.6, 115.7, 113.1, 55.5. MS (EI, m/z): 284
ASSOCIATED CONTENT
■
*
S
Supporting Information
(
100). Anal. Calcd (%) for C H O: C, 88.70; H, 5.67. Found: C,
21 16
8
8.61; H, 5.49.
-(4-Methoxyphenyl)phenanthrene (Vi): 78%, 0.221 g. Mp: 157−
The X-ray coordinates (cif files) are available for complexes Id,
IIb, IId, and IIe. Table 5 with crystal data and structure
refinement for complexes Id, IIb, IId, and IIe is also included
9
1
1
59 °C. H NMR (400 MHz, CDCl ): δ 8.80 (d, J = 8.3 Hz, 1H), 8.74
3
(
d, J = 8.2 Hz, 1H), 7.99 (d, J = 7.6 Hz, 1H), 7.91 (d, J = 7.5 Hz, 1H),
1
13
as Supporting Information. H and C NMR spectra for all the
-arylphenanthrenes are also available. This material is available
7
7
1
1
.70−7.62 (m, 4H), 7.57 (t, J = 7.5 Hz, 1H), 7.52−7.50 (m, 2H),
9
1
3
.10−7.07 (m, 2H). C NMR (100 MHz, CDCl ): δ 159.2, 138.5,
3
free of charge via the Internet at http://pubs.acs.org.
33.3, 131.8, 131.5, 131.3, 130.8, 130.0, 128.7, 127.6, 127.1, 126.9,
26.6, 126.5, 123.0, 122.7, 113.9, 55.5. MS (EI, m/z): 284 (100). Anal.
Calcd (%) for C H O: C, 88.70; H, 5.67. Found: C, 88.53; H, 5.46.
AUTHOR INFORMATION
21
16
■
9
-(4-Thiomethylphenyl)phenanthrene (Vj): 86%, 0.257 g. Mp:
1
Corresponding Authors
*E-mail: jose.serrano@upct.es.
*E-mail: ar.kapdi@ictmumbai.edu.in.
1
1
1
54−156 °C. H NMR (400 MHz, CDCl ): δ 8.79 (d, J = 8.2 Hz,
3
H), 8.73 (d, J = 8.2 Hz, 1H), 7.95 (d, J = 8.2 Hz, 1H), 7.92−7.90 (m,
H), 7.70−7.67 (m, 3H), 7.64−7.62 (m, 1H), 7.57−7.54 (m, 1H),
J
DOI: 10.1021/om501160n
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Notes
(14) Adams, H.; Bailey, N.; Briggs, T. N.; McCleverty, J. N.;
Colquhoun, H. M.; Williams, D. G. J. Chem. Soc., Dalton Trans. 1986,
The authors declare no competing financial interest.
8
(
13.
15) (a) Fairlamb, I. J. S.; Taylor, R. J. K.; Serrano, J. L.; Sanchez, G.
ACKNOWLEDGMENTS
We thank Fundacio
■
New J. Chem. 2006, 30, 1695. (b) Fairlamb, I. J. S.; Kapdi, A. R.;
Lynam, J. M.; Taylor, R. J. K.; Whitwood, A. C. Tetrahedron 2004, 60,
́
́
eca (project 08670/PI/08) for
financial support. A.R.K. would like to acknowledge the
Department of Science and Technology for the DST Inspire
Faculty award (IFA12-CH-22). The Alexander von Humboldt
Foundation is also thanked for the equipment grant to A.R.K.
5
711. (c) Chaignon, N. M.; Fairlamb, I. J. S.; Kapdi, A. R.; Taylor, R. J.
K.; Whitwood, A. C. J. Mol. Catal. A: Chem. 2004, 219, 191.
d) Crawforth, C. M.; Burling, S.; Fairlamb, I. J. S.; Kapdi, A. R.;
(
Taylor, R. J. K. Tetrahedron 2005, 61, 9736. (e) Burns, M. J.; Fairlamb,
I. J. S.; Kapdi, A. R.; Taylor, R. J. K.; Sehnal, P. Org. Lett. 2007, 9, 5397.
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(
(
011.
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(
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