Synthesis, characterization, and cyclometalation studies of benzo[1,2-h: 5,4-h′]diquinolines with palladium and platinum

Article abstract of DOI:10.1016/j.jorganchem.2011.08.012

Benzo[1,2-h: 5,4-h′]diquinoline(1a) represents a new family of tridentate NCN pincer ligand. We report the synthesis of the parent ligand (1a) and its derivatives (1b R = Me, 1c R = t-Butyl, 1d R = Phenyl). The ligands were characterized by ¹H and ¹³C NMR, as well as mass spectral analysis, and X-ray structural determination. They readily undergo cyclometalation with LiPdCl₄, Pd(OAc)₂, and K ₂PtCl₄ to form the cyclometalated Pd(NCN)Cl (2a-c, 3a), and Pt(NCN)Cl (4a) pincer complexes. These complexes have been characterized through NMR, and mass spectrometry. PdNCNCl (2a) structure was determined by single crystal X-ray diffraction. Complex 2a has shown to catalyze the Heck coupling reaction between bromobenzene and n-butylacyrlate in NMP at 140 °C, TON of 2506 were observed.

Full text of DOI:10.1016/j.jorganchem.2011.08.012

Journal of Organometallic Chemistry 696 (2011) 3992e3997
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization, and cyclometalation studies of benzo[1,2-h: 5,4-h0]
diquinolines with palladium and platinum
*
Kenneth J.H. Young, Xianhui Bu, William C. Kaska
Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106, United States
a r t i c l e i n f o
a b s t r a c t
Benzo[1,2-h: 5,4-h0]diquinoline(1a) represents a new family of tridentate NCN pincer ligand. We report
the synthesis of the parent ligand (1a) and its derivatives (1b R ¼ Me, 1c R ¼ t-Butyl, 1d R ¼ Phenyl). The
ligands were characterized by 1H and 13C NMR, as well as mass spectral analysis, and X-ray structural
determination. They readily undergo cyclometalation with LiPdCl4, Pd(OAc)2, and K2PtCl4 to form the
cyclometalated Pd(NCN)Cl (2aec, 3a), and Pt(NCN)Cl (4a) pincer complexes. These complexes have been
characterized through NMR, and mass spectrometry. PdNCNCl (2a) structure was determined by single
crystal X-ray diffraction. Complex 2a has shown to catalyze the Heck coupling reaction between bro-
mobenzene and n-butylacyrlate in NMP at 140 ꢀC, TON of 2506 were observed.
Article history:
Received 22 April 2011
Received in revised form
13 August 2011
Accepted 16 August 2011
Keywords:
Pincer ligands
Benzodiquinolines
Cyclometalation
Heck reaction
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
modified Skraup synthesis [4], by heating aniline with a,b-unsatu-
rated aldehydes or ketones in sulfuric acid in the presence of an
oxidant. When aniline is replaced with 1,8-diaminoanthracene, benzo
[1,2-h: 5,4-h0]diquinoline is readily obtained. The electronic and steric
Organic transformations such as carbon-heteroatom and car-
bonecarbon bond formation have been shown to be catalyzed by
many different transition metals and ligand sets. One ligand set that
has received a lot of attention is the monoanionic tridentate pincer
ligands [1], due to their thermal stability [2] and reactivity of their
complexes. The trans directing donor atoms (P, N, S, or O), pre-
coordinates to the metal and brings it into proximity of the XeH
(X ¼ C, N, Si) backbone, allowing the metal to undergo electrophilic
properties of the ligand can be varied by changing the type of a,b-
unsaturated aldehyde or ketone and substiuents can be introduced
into the ortho, meta, or para position of the quinoline (Scheme 3).
We have synthesized a new family of NCN pincer ligands, benzo
[1,2-h: 5,4-h0]diquinoline (1a) and its derivatives (1bed). In this
paper we report the synthesis and characterization of these new
ligands and their metal complexes, the activity for the Heck reac-
tion, and methane oxidation.
substitution or oxidative addition to form a strong MeC
s bond and
rigid framework [1c]. The PCP, NCN, PCN, SCS, as well as the OCO
ligands are known (Scheme 1). These complexes have been shown
to act as sensors [1c], dehydrogenation/hydrogenation catalysts
[1,2], and Heck catalysts [1].
2. Results and discussion
2.1. Synthesis and characterization of benzo[1,2-h: 5,4-h0]
diquinoline and its derivatives (1aed)
Pd(NCN) complexes with aryl backbones such as 1,3-bis(2-pyridyl)
benzene have been challenging to synthesize. The corresponding
palladium complexes have been made by oxidative addition of
carbon-halogen bonds, by transmetallation, or by using ligands that
are stericly hindered [3]. Annulation of the 1,3-bis(2-pyridyl)benzene
to form benzo[1,2-h: 5,4-h0]diquinoline (Scheme 2) should allow
direct metalation of the C-2 carbon of the arene ring. Quinoline
and substituted quinolines can be readily synthesized through the
A new series of NCN pincer ligands have been synthesized using
a modified Skraup procedure in which a double cyclization is per-
formed on 1,8-diaminoanthracene. The 1,8-diaminoanthracene was
prepared in high yields by a three-step synthesis starting from
commercially available 1,8-dichloroanthraquinone (Scheme 3). The
parent ligand, benzo[1,2-h: 5,4-h0]diquinoline (1a) was obtained in
low to moderate yields upon heating 1,8-diaminoanthracene and
glycerol in 70 wt% sulfuric acid with an oxidant (Scheme 4). Ligand
1a is obtained as an off-white solid after purification with silica gel.
The best results were obtained when sodium iodide (catalytic
* Corresponding author.
E-mail addresses: kennethyoung87@gmail.com (K.J.H. Young), kaska@chem.
ucsb.edu (W.C. Kaska).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.08.012

K.J.H. Young et al. / Journal of Organometallic Chemistry 696 (2011) 3992e3997
3993
NHSO2R
Cl
Cl
NHSO2R
O
DR
NH2SO2R
Cu(OAc)2
O
2
amyl alcohol
R
MX L
m n
1
reflux
DR
2
O
O
R = C6H4CH3
Scheme 1. Pincer ligand motif.
amounts, 0.4 equiv.) or 3-nitrobenzenesulfonic acid were used as
oxidants. With the former, yields as high as 40% can be obtained,
and with the latter yields as high as 37% are obtained. Other
oxidants such as As2O5, I2 and nitrobenzene also worked but gave
lower yields (22 e 35%).
H2SO4
NH2
O
NH2
NH2
NH2
isoproponal
NaBH4
The product was fully characterized by 1H and 13C NMR,
elemental analysis, and high-resolution mass spectrometry. The 1H
NMR spectra of 1a showed 7 aromatic resonances consistent with
a symmetrical ligand with C2v symmetry. The hydrogen on the C-9
carbon of the anthracene is a singlet at 11.24 ppm which is highly
shifted downfield. The 13C NMR spectra are also consistent with the
proposed structure and all 11 aromatic carbons were observed
between 149 and 121 ppms. All of the proton and carbon reso-
nances were assigned based on 2D NMR experiments (g-COSY, g-
HSQC, and g-HMBC). The high-resolution electron impact mass
spectroscopy showed a parent ion peak at 280 (Δ ¼ 2.5 ppm), which
corresponds to the un-fragmented ligand.
reflux 24h
O
Scheme 3. Synthesis of 1,8-diaminoanthracene.
yelloweorange precipitate forms after 30 min. The precipitate is
then washed with ether and the cyclometalated products 2a is
obtained after reprecipitation. Complex 2a is poorly soluble in
CH2Cl2 but is soluble in polar solvents like DMSO and dmf.
Formation of 2a is supported by 1H NMR. Loss of the resonance at
11.24 ppm, corresponding to the hydrogen on the C-9 carbon of the
anthracene ring, and the shifting of the alpha proton to the nitrogen
supports that cyclometalation has occurred. The 1H NMR spectra of
complexes 2a is also consistent with a symmetrical complex. Mass
spectrometry also supports that metalation has occurred. Suitable
crystals for X-ray diffraction of 2a were grown from a CH2Cl2
solution at ꢁ5 ꢀC. The molecular structure is shown in Fig. 2.
Selected crystal data and refinement parameters can be found in
Table 1. As can be seen from the structure, the palladium forms
a distorted square planar geometry, with the palladium sitting in
the plane of the ligand. Selected bond lengths and angles can be
found in Table 2. The PdeN1 and PdeN2 distance of 2.125 and
2.133 Å are similar to Pd-N distances of other Pd NCN complexes
(2.019e2.146 Å) [3,6]. The Pd-C18 distance of 1.898 Å is also similar
to other Pd NCN complexes (1.85e2.018 Å). However the N1-Pd-N2
angle of 157.6ꢀ is slightly smaller than the previously reported
complexes (159.5e173.3ꢀ). Ligands 1b and 1c also undergo cyclo-
metalation with Li2PdCl4 to form Pd(NCN)Cl complexes 2b and 2c.
The solubility of 2b is poor in CH2Cl2, but 2c is readily soluble.
Ligand 1a also undergoes cyclometalation with Pd(OAc)2 and
the corresponding acetate complex 3a was formed upon refluxing
in acetic acid. Complex 3a was characterized by 1H NMR, 13C NMR
and mass spectroscopy. The solubility of complexes 3a is poor in
solvents like CH2Cl2, but is soluble in polar solvents like DMF and
DMSO.
Suitable crystals for x-ray diffraction of 1a were obtained by
slow evaporation of a CH2Cl2 solution. The molecular structure is
shown in Fig. 1. As can be seen from the structure, the ligand forms
a relatively flat ring system with the all the rings lying in the same
plane. Selected crystal data and refinement parameters can be
found in Table 1.
Substituent’s can be added to the ortho, meta, and para posi-
tions of the pyridine ring to modify the solubility, steric bulk, or
electronic properties of the ligand. This was achieved by using
modified Skraup procedures. Alkyl and aryl groups were intro-
duced in the para position by replacing glycerol with the corre-
sponding
were obtained following the procedure of Gras [5]. Upon heating
the appropriate -unsaturated ketones with 1,8-
a,b-unsaturated ketones. t-butyl and phenyl vinyl ketone
a,b
diaminoanthracene the corresponding substituted benzo[1,2-h:
5,4-h0]diquinolines 1bed were obtained in low to moderate yields,
and were characterized by 1H and 13C NMR, and high-resolution
mass spectroscopy (Scheme 4). 1H and 13C NMR spectra’s of 1bed
show a symmetrical ligand, with substitution in the para position.
The doublets between 8.98 and 9.15 ppms for 1bed are consistent
for chemical shifts for a
a-quinoline proton. Both the ortho
substituted symmetrical and the ortho, para substituted unsym-
metrical ligand (Scheme 5) were also obtained as minor side
products.
Upon heating 1a with K2PtCl4 in glacial acetic acid, the cyclo-
metalated platinum complex Pt(NCN)Cl, 4a precipitated out as an
orange-red solid (Scheme 6). After reprecipiatation from DMF with
ether 4a was obtained in good yields (as high as 94%). The solubility
of 4a in CH2Cl2 is poor, but is soluble in DMF and DMSO. Cyclo-
metalation was confirmed by 1H NMR, and mass spectroscopy. Loss
of the proton at 11.24 ppm and the appearance of platinum
2.2. Cyclometalation studies with palladium and platinum
The NCN ligand 1a readily undergoes cyclometalation with
palladium, and the corresponding cyclometalated tridentate
palladium NCN complex Pd(NCN)Cl, 2a, was obtained upon
refluxing 1a with Li2PdCl4 (or K2PdCl4) in methanol (Scheme 6). A
ER2
ER2
ER2
E
E
O
R1
R1
R2
R3
R2
R3
R1
R3
NH2
NH2
N
N
R2
Oxidant
Scheme 4. Synthesis of NCN ligands.
ER2
Scheme 2. Ligand design.

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K.J.H. Young et al. / Journal of Organometallic Chemistry 696 (2011) 3992e3997
R
R
R
N
N
N
N
R
Scheme 5. Side products from synthesis of NCN ligands.
were unsuccesful. There have been other examples of catalysts
which form trisubsituted olefins. Beller et al. [8] reported the use of
a phosphine palladacyle to form trisubsituted olefins from dis-
ubsituted olefins. There have been some examples of Pd complexes
converting aryl halides and n-butylacrylate to the diphenyl sub-
situted product (phenyl-substituted cinnamate) [9].
3. Conclusion
Fig. 1. Molecular structure of 1a. Thermal ellipsoids are shown at 50% probability.
Hydrogen atoms have been eliminated for clarity.
A new class of NCN cyclometallated palladium and platinum
NCN complexes based on the benzo[1,2-h:5,4-h0]diquinoline motif
can be synthesized. The Pd(NCN)Cl complex shows activity for the
Heck coupling reaction between bromobenzene and n-butylacry-
late [17].
satellites (JPteH ¼ 21.93 Hz) for the alpha quinoline peak at
9.26 ppm support the formation of the Pt(NCN) complex.
2.3. Reactivity studies
Pincer complexes have been shown to be active catalysts for
several different organic transformations. Although most of the
Heck reactions have utilized Pd(PCP)X complexes, recent examples
using Pd(NCN)X complexes [7] have been reported. We tested the
catalytic ability of Pd(NCN)Cl, 2a, in the Heck coupling reaction
between bromobenzene and n-butylacrylate (Scheme 7).
After heating a solution of bromobenzene, n-butylacrylate, and
base in NMP with 0.02 mol% catalyst 2a at 140 ꢀC for 66 h, the
expected Heck coupling product, n-butyl cinnamate as well as the
unexpected double Heck product (b-phenyl-substituted cinna-
mate) were observed. The results are shown in Table 3. The product
distribution and % conversion were dependent on the base used. In
terms of % conversion, the best results were obtained when Na2CO3
(100% consumption), NaOAc only gave partial conversion (65.1%
conversion). Both base gave the double Heck product, however
Na2CO3 gave more of the diaryl product (70:30 ratio of mono:diaryl
product) than NaOAc (97:3). Attempts to activate chlorobenzene
4. Experimental section
4.1. General procedures
All reactions were performed under an argon-atmosphere using
Schlenck line techniques, and unless mentioned all workups were
performed in air. The argon was purified by passing through
columns containing Phillip’s catalyst and 4 Å molecular sieves. All
NMR spectra were collected on Varian Mercury 200 and Unity
Inova 400 and 500 MHz instruments. 1H and 13C chemical shifts
were referenced to TMS from residual solvent, and coupling
constants were reported in hertz. Shifts were assigned using COSY,
NOESY1D, APT, and HSQC experiments. Electron Impact (EI) mass
analysis were performed on a VG70 magnetic sector spectrometer.
Electro spray ionization (ESI) mass analysis were performed on
a VG Platform Benchtop quadropole spectrometer with a Michrom
LC System. Single crystal x-ray diffraction data were collected on
a Bruker Smart CCD diffractometer. Elemental analysis were
peformed by Desert Analytics, Inc.
Table 1
Selected crystal data and refinement parameters.
1a
2a
4.2. Materials
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
C20H12N2
280.32
293(2)
Monoclinic
C20H11ClN2Pd, 2H2O
457.19
293(2)
Monoclinic
P2(1)/c
1,8-Dichloroanthraquinone (Aldrich), p-toluenesulfonamide
(Acros), and all other reagents were used without further purifi-
cation. Isopropanol was dried by distilling over magnesium turn-
ings/I2 under argon. t-Butylvinylketone and Phenyl vinyl ketone
P2(1)/n
a ¼ 7.7237(17) Å,
alpha ¼ 90ꢀ
b ¼ 12.163(3) Å,
beta ¼ 101.940(4)o
c ¼ 15.237(3) Å,
gamma ¼ 90ꢀ
1400.5(5), 4
1.329
a ¼ 7.3844(11) Å,
alpha ¼ 90ꢀ
b ¼ 14.884(2) Å,
beta ¼ 101.593(3)o
c ¼ 15.781(2) Å,
gamma ¼ 90ꢀ
1699.1(4), 4
1.787
R
R
Volume (Å3), Z
N
N
N
Density (g cmꢁ3
)
MX
Crystal size (mm)
0.825 ꢂ 0.825 ꢂ 0.132
0.334 ꢂ 0.067 ꢂ 0.067
1.90 to 25.00
14719
2983 (Rint ¼ 0.1190)
25.00ꢀ 100.0%
2983/3/251
M
X
q
range for data collection 2.16 to 25.00ꢀ
Reflections collected
Independent reflections
6918
N
2462 (Rint ¼ 0.0889)
Completeness to
q
25.00ꢀ 100.0%
Data/restraints/parameters 2462/0/248
Goodness-of-fit on F2
0.969
0.888
R
R
Final R indices [I > 2s(I)]
R1 ¼ 0.0454,
wR2 ¼ 0.1190
R1 ¼ 0.0586,
wR2 ¼ 0.1287
R1 ¼ 0.0459,
wR2 ¼ 0.0918
R1 ¼ 0.0979,
wR2 ¼ 0.1053
MX = Li2PdCl4
PdOAc2
2a-c M=PdCl
3a
1a-c
R = H, Me, t-Bu
M=PdOAc
M=PtCl
R indices (all data)
K2PtCl4
4a
Largest diff. peak and hole 0.180 and ꢁ0.210 e Åꢁ3 0.915 and ꢁ0.601 e Åꢁ3
Scheme 6. Synthesis of NCN complexes.

K.J.H. Young et al. / Journal of Organometallic Chemistry 696 (2011) 3992e3997
3995
with CH2Cl2, and passed through an alumina plug with EtOAc. It
was then purified by passing through silica gel with (1% MeOH/
CH2Cl2)/ethyl acetate gradient. Yield (36% NMR yield). HREI-MS m/z
308.13101(5)
D
¼ 1.1 ppm. 1H NMR (400 MHz, CDCl3): 11.29(s, 1H,
3
benzo H-6), 8.98(d, 2H, J ¼ 4.34, quinoline H-2,20), 8.42(s, 1H,
3
benzo H-3), 8.01(d, 2H, J ¼ 9.16, quinoline H-6,60), 7.96(d, 2H,
3J ¼ 9.16, quinoline H-5,50), 7.41(d, 2H, 3J ¼ 4.58, quinoline H-3,30),
2.80(s, 6H, CH3). 13C{1H} (125 MHz, CDCl3): 148.77(quinoline C-
2,20), 147.46(quinoline), 143.96(quinoline C-4,40), 132.89(benzo C-
1,5), 130.92(benzo C-2,4), 127.45(quinoline C-6,60), 126.22(quino-
line C-7), 125.98(quinoline), 123.56(quinoline C-3,30), 122.35(quin-
oline C-5,50), 122.19(benzo C-6), 19.29(CH3).
4.3.3. Synthesis of benzo[1,2-h:5,4-h0]di(4-tertbutylquinoline) (1c)
NCNt-bu
1,8-Diaminoanthracene (200.0 mg, 0.960 mmol), NaI (37.5 mg,
0.250 mmol) was dissolved in dioxane (10 mL)/70 wt% H2SO4
(3 mL) solution. The suspension was stirred at 100 ꢀC, followed by
slow addition of t-butyl vinyl ketone (323.2 mg, 2.881 mmol) over
a 30-min period. After heating at 120 ꢀC for 8 h the dark brown
solution was diluted with water then neutralized with Na2CO3 (aq.).
The suspension was filtered, washed with water, and extracted
with CH2Cl2. The extract was then passed through an alumina plug
with EtOAc, then through silica gel with CH2Cl2 then ether yielding
1c as a beige solid (112 mg, 29.7% yield) mp 227e229 ꢀC HRESI-
Fig. 2. Molecular structure of 2a. Thermal ellipsoids are shown at 50% probability. The
two water molecules have been removed for clarity.
[11], 1,8-bis-p-toluenesulfonamide anthraquinone [12], 1,8 dia-
minoanthraquinone [12], and 1,8-diaminoanthracene [13] were
prepared following literature procedure.
MS m/z 393.2342
D
¼ 2.9 ppm Rf (CH2Cl2, Silica) ¼ 0.23 1H NMR
4.3. Synthesis of NCN ligands
(400 MHz, CDCl3): 11.38(s, 1H, benzo H-6), 9.02(d, 2H, 3J ¼ 4.94,
quinoline H-2,20), 8.40(d, 2H, 3J ¼ 9.71, quinoline H-5,50), 8.38(s, 1H,
4.3.1. Synthesis of benzo[1,2-h:5,4-h0]diquinoline (1a)
3
benzo H-3), 7.96(d, 2H, J ¼ 9.71, quinoline H-6,60), 7.56(d, 2H,
1,8-diaminoanthracene (100 mg, 0.480 mmol), oxidant [NaI
(30 mg, 0.200 mmol), or 3-nitrobenzenesulfonicacid (195.1 mg,
0.960 mmol)], and glycerol (354 mg, 1.921 mmol) were dissolved in
70 wt% H2SO4 (1.5 mL). The mixture was heated at 120 ꢀC for 2 days,
cooled and neutralized with NaOH (aq). The brown suspension was
filtered and washed with water. The product was isolated by
Soxhlet extraction with CH2Cl2, and passed through an alumina
plug with EtOAc. It was further purified by passing through silica
gel with CHCl3. Rf (CH2Cl2, Silica) ¼ 0.13. Isolated yield: NaI 50 mg
(37.1%); 3-nitrobenzenesulfonic acid 49.7 mg (36.9%) HREI-MS m/
3J ¼ 4.94, quinoline H-3,30), 1.70(s, 18H, C(CH3)3) 13C{1H} (125 MHz,
CDCl3): 155.66(quinoline C-4,40), 148.89(quinoline) 148.82(quino-
line C-2,20), 132.19(benzo C-1,5), 131.43(benzo C-2,4), 126.01(quin-
oline
C-6,60),
125.33(benzo
C-3),
125.21(quinoline),
124.90(quinoline C-5,50), 123.06(benzo C-6), 119.42(quinoline C-
3,30), 36.31(C(CH3)3), 31.72(C(CH3)3).
4.3.4. Synthesis of benzo[1,2-h:5,4-h0]di(4-phenylquinoline) (1d)
NCNphen
1,8-diaminoanthracene (30 mg, 0.144 mol), NaI (10 mg), and
phenyl vinyl ketone (95 mL) were stirred together for a short period
z ¼ 280.09933(9)
D
¼ 2.5 ppm. 1H (500 MHz, CDCl3): 11.24 (s, 1H,
benzo H-6), 9.13 (dd, 2H, 3J ¼ 4.39 4J ¼ 1.46, quinoline H-2,20), 8.43
(s,1H, benzo H-3), 8.20 (dd, 2H, 3J ¼ 7.81, 4J ¼ 1.47, quinoline H-4,40),
followed by addition of 1 mL of 70 wt% H2SO4. The solution was
heated at 120 ꢀC for 2 days. The resultant black solution was
neutralized with NaOH(aq), and the suspension was filtered and
washed with water. The product was isolated by Soxhlet extraction
with CH2Cl2. It was purified by passing through silica gel with
CHCl3. Isolated yield 18.7 mg (30.0%). ESI-MS m/z 432(NCNphen). 1H
NMR (400 MHz, CDCl3): 11.40(s, 1H, benzo H-6), 9.15(d, 2H,
3J ¼ 4.58, quinoline H-2,20), 8.40(s, 1H, benzo H-3), 7.92(d, 2H,
3J ¼ 9.16, quinoline H-6,60), 7.86 (d, 2H, 3J ¼ 9.34, quinoline H-5,50),
3
7.98 (d, 2H, J ¼ 8.79, quinoline H-6,60), 7.74 (d, 2H, 3J ¼ 9.28,
quinoline H-5,50), 7.59 (dd, 2H, J ¼ 8.3, 4.4, quinoline H-3,30) 13C
3
{1H}(125 MHz, CDCl3) 149.22(quinoline C-2,20), 147.82(quinoline),
135.81(quinoline C-4,40), 133.31(benzo C-1,5), 130.58(benzo C-2,40),
127.91(quinoline C-6,60), 126.69(quinoline), 126.55(benzo C-3),
126.45(quinoline C-5,50), 122.31(quinoline C-3,30), 121.42(benzo C-
6). Elemental analysis found; C 85.64, H 4.38, N 9.81 Calc. C, 85.69;
H, 4.31; N, 9.99. Mp. 157e160 ꢀC.
3
7.54e7.59(m, 10H, phenyl), 7.53(d, 2H, J ¼ 4.58, quinoline H-3,30).
13C{1H} (100 MHz, CDCl3): 148.63, 148.34, 148.26, 138.70, 133.09,
130.82, 129.94, 128.81, 128.49, 127.71, 126.15, 124.59, 124.10, 122.89,
122.4.
4.3.2. Synthesis of benzo[1,2-h:5,4-h0]di(4-methylquinoline) (1b)
NCNMe
1,8-Diaminoanthracene (50 mg, 0.240 mmol) and methylvinyl
ketone (40 mL, 0.480 mmol) were dissolved in nitrobenzene (2 mL).
After adding 2 drops of glacial acetic acid the mixture was heated at
110 ꢀC for 1 day then at 180 ꢀC for 1 day. The solution was then
neutralized with NaOH (aq), and the suspension was filtered and
washed with water. The product was isolated by soxhlet extraction
4.4. Structure determination and refinement of NCN (1a)
Suitable crystals of 1a were obtained by slow evaporation from
a concentrated solution in CH2Cl2 from an NMR tube and were
Table 2
Selected bond lengths and angles for 2a.
Pd(1)-C(18) ¼ 1.899(6)
Pd(1)-N(1) ¼ 2.126(5)
Pd(1)-Cl(1) ¼ 2.4304(17)
C(18)-Pd(1)-N(1) ¼ 78.9(3)
C(18)-Pd(1)-Cl(1) ¼ 177.21(19)
Pd(1)-N(2) ¼ 2.133(5)
C(18)-Pd(1)-N(2) ¼ 78.7(3)
N(1)-Pd(1)-N(2) ¼ 157.6(2)
N(1)-Pd(1)-Cl(1) ¼ 100.23(15)
N(2)-Pd(1)-Cl(1) ¼ 102.17(14)

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K.J.H. Young et al. / Journal of Organometallic Chemistry 696 (2011) 3992e3997
3
8.91(d, 2H, J ¼ 5.48, quinoline H-2,20), 8.24(d, 2H,
Catalyst
base
500 MHz)
d
3J ¼ 9.14, quinoline H-5,50), 7.93(s, 1H, benzo H-3), 7.86(d, 2H,
3J ¼ 9.14, quinoline H-6,60), 7.54(d, 2H, 3J ¼ 4.87, quinoline H-3,30),
1.68(s, 18H, C(CH3)3). 13C{1H} NMR: (500 MHz, CD2Cl2)
Br
NMP
140oC
O
O
170.49(benzo C-6), 159.84(quinoline C-4,40), 158.44(quinoline)
O
O
d
O
O
151.90(quinoline C-2,20), 136.61(benzo C-1,5), 132.43(benzo C-2,4),
127.59(quinoline C-6,60), 126.16(quinoline), 126.15(quinoline C-
5,50), 120.32(quinoline C-3,30), 115.92(benzo C-3), 37.16(eC(CH3)3),
31.21(eC(CH3)3)
Scheme 7. Heck coupling reaction.
mounted on a glad fiber with 5-min epoxy. The data was collected
at room temp with a Bruker SMART CCD Defractometer with
4.6. Structure determination and refinement of PdNCNCl (2a)
a normal focus 2.4 kW sealed tube X-ray source (Mo K
ation ¼ 0.71073 Å) operating at 45 kV, 35 mA. A hemisphere of
intensity data was collected with
scans (width of 0.30ꢀ, exposure
a radi-
A suitable crystal of 2a was obtained from CH2Cl2 at ꢁ5 ꢀC, and
was mounted on a glass fiber with epoxy. The data were collected at
room temp with a Bruker SMART CCD Defractometer with a normal
u
of 30 s). The number of reflections used for the least squares
refinement of the unit cell parameters was 850. The data frames
were processed using the SAINT program [14]. Absorption and
beam corrections were performed using the program SADABS [15].
The structure was solved using SHELXTL-97 [16] and refined by full
matrix least squares on F2. The non-hydrogen atoms were found
directly by successive Fourier calculations and refined anisotropi-
cally. The hydrogen atoms were calculated on the basis of geometric
criteria and allowed to ride on their respective atoms.
focus 2.4 kW sealed tube X-ray source (Mo
radiation ¼ 0.71073 Å) operating at 45 kV, 35 mA. A hemisphere of
intensity data was collected with
scans (width of 0.30ꢀ, exposure
Ka
u
of 30 s). The number of reflections used for the least squares
refinement of the unit cell parameters was 2410. The data frames
were processed using the SAINT program. Absorption and beam
corrections were performed using the program SADABS. The
structure was solved using SHELXTL-97 and refined by full matrix
least squares on F2. The non-hydrogen atoms were found directly
by successive Fourier calculations and refined anisotropically. The
hydrogen atoms were calculated on the basis of geometric criteria
and allowed to ride on their respective atoms.
4.5. Synthesis of Pd(NCN)Cl complexes 2aec
4.5.1. Synthesis of PdNCNCl (2a)
Palladium chloride (6.3 mg, 3.55 ꢂ 10ꢁ2 mmol), lithium chloride
(3.0 mg, 7.11 ꢂ 10ꢁ2 mmol), and NCN ligand 1a (12.0 mg,
3.55 ꢂ 10ꢁ2 mmol) were dissolved in methanol (9 mL) under argon.
The mixture was refluxed for 3 days, during which a yellow
precipitate formed. The solution was filtered and washed with
water, then ether. It was then purified by dissolving in DMF,
filtering through celite, and then reprecipitating with ether.
Complex 2a was obtained as a yellow solid. Yield: 7.5 mg (50%).
FAB-MS (NBA matrix) m/z 385(Mþ ꢁ Cl). 1H NMR (dmso-d6,
200 MHz) 8.91(dd, 2H, 3J ¼ 5.43, 4J ¼ 1.01 quinoline H-2,20), 8.73(d,
4.7. Synthesis of Pd(NCN)OAc complexes 3a
Palladium acetate (39.8 mg, 0.177 mmols), and 1a (49.7 mg,
0.177 mmols) were dissolved in glacial acetic acid (7 mL) under
argon and was heated at 80 ꢀC for 2 days during which time
a yellow precipitate formed. The solvent was then removed, and the
residue was redissolved in methanol and filtered through celite.
The product was isolated by dissolving in CH2Cl2 and reprecipi-
tating with ether. Isolated yield: 70.2 mg (89.0%). 1H NMR (CDCl3,
200 MHz) 8.83(bs, 2H, quinoline H2,20), 8.21(d, 2H, 3J ¼ 7.9, quin-
oline H-4,40), 7.76(s, 1H, benzo H-3), 7.69(d, 2H, 3J ¼ 9.2, quinoline
H-6,60), 7.53(d, 2H, 3J ¼ 9.2, quinoline H-5,50), 7.46(bs, 2H, quinoline
H-3,30). 13C{1H} NMR (dmso-d6, 125 MHz) 176.08, 166.93, 154.60,
150.18, 136.90, 133.46, 130.94, 127.64, 125.67, 125.33, 122.64, 115.84.
4
2H, 3J ¼ 8.15 J ¼ 1.01, quinoline H-4,40), 8.27(s, 1H, benzo H-3),
3
8.11(d, 2H, J ¼ 8.82, quinoline H-6,60), 7.98(d, 2H, 3J ¼ 4.97, quin-
3
oline H-5,50), 7.86(dd, 2H, J ¼ 8.14, 5.43, quinoline H-3,30).
4.5.2. Synthesis of PdNCNMeCl (2b)
Palladium chloride (5.2 mg, 2.92 ꢂ 10ꢁ2 mmol), lithium chloride
(2.5 mg, 5.84 ꢂ 10ꢁ2 mmol), and NCNMe ligand 2b (9.0 mg,
2.92 ꢂ 10ꢁ2 mmol) were refluxed in methanol (40 mL) under argon
for 2 days during which time an orange-yellow precipitate formed.
Workup is same as 2a. Yield: 11.4 mg (87%). ESI-Ms m/z 413
(M ꢁ Cl)þ. 1H NMR (dmso-d6, 400 MHz) 8.53(d, 2H, 3J ¼ 4.56,
quinoline H-2,20), 7.94(s, 1H, benzo H-6), 7.84(d, 2H, 3J ¼ 8.60,
quinoline H-6,60), 7.80(d, 2H, 3J ¼ 8.60, quinoline H-5,50), 7.54(d, 2H,
3J ¼ 4.82, quinoline H-3,30), 2.77(s, 6H, CH3).
4.8. Synthesis of Pt(NCN)Cl complex 4a
Synthesis of PtNCNCl (9a). Potassium tetrachloroplatinate
(27.7 mg, 0.067 mmols), and 1a (15.6 mg, 0.056 mmols) were
heated in glacial acetic acid (5 mL) at 90 ꢀC for 1 day and at 110 ꢀC
for 3 days during which time an orange-red precipitate had formed.
The solvent was then removed under reduced pressure and the
residue was washed with water, methanol, then ether. It was then
dissolved in dmf and filtered through celite, then reprecipitated
with ether. Isolated yield 26.8 mg 94.4% yield. HRFAB-MS m/z
473.052771 (4.5 ppm). Dec >394 ꢀC. 1H NMR (CDCl3, 400 MHz)
4.5.3. Synthesis of PdNCNt-buCl (2c)
Palladium chloride (1.8 mg, 0.0102 mmols), lithium chloride
(0.9 mg, 0.0204 mmols), and NCNtbu ligand 2c (4.0 mg,
0.0102 mmols) were refluxed in methanol (5 mL) under argon for 2
days during which time a yellow precipitate formed. Workup is
similar to 2a, extracted with CH2Cl2. Yield: 4 mg (74.1%). ESI-MS: m/
z 497(Mþ ꢁ Cl), 534(Mþ), 1031(2Mþ ꢁ Cl). 1H NMR (CD2Cl2,
d
9.26(dd, 2H, 3J ¼ 5.49 4J ¼ 1.28 JPteH ¼ 21.93, quinoline H-2,20),
8.42(dd, 2H, 3J ¼ 8.06 4J ¼ 1.10, quinoline H-4,40), 8.05(s, 1H, benzo
H-3), 7.95(d, 2H, J ¼ 8.97, quinoline H-6,60), 7.72(d, 2H, 3J ¼ 8.98,
3
quinoline H-5.50).
4.9. Heck studies
Table 3
Heck reaction with 2a.
A stock solution of catalyst (1.8 mg in 4 mL NMP), bromo-
benzene (5.27 mL (50 mmol) þ 4.73 mL of NMP), n-butylacyrlate
(8.54 mL (60 mmol) þ 1.46 mL NMP) were made. For the trials with
Catalyst ArX [Pd] ꢂ 10ꢁ3 mmol Base
% conversion Mono:Di TON [10]
2a
2a
PhBr 1.068
PhBr 1.068
NaOAc
Na2CO3 100
65.1
97:3
1726
2506
70:30
bromobenzene
1 ml catalyst-solution, 1 ml Bromobenzene-

K.J.H. Young et al. / Journal of Organometallic Chemistry 696 (2011) 3992e3997
3997
[3] (a) J. Hurtado, A. Ibañez, R. Rojas, M. Valderrama, Inor. Chem. Comm. 13
(2010) 1025;
solution, 1 ml Butylacrylate-solution, NMP (1.4 mL) and base
(6 mmol, Na2CO3 or NaOAc) were mixed and stirred at 140 ꢀC for
66 h under argon-atmosphere. After cooling to room-temperature,
0.1 ml n-decane (internal standard), 0.27 ml n-hexadecane
(internal standard) and 1 ml THF were added. The mixture was
stirred at room temperature for 1 h. The clear solution was dec-
anted from the base and analyzed by gas chromatography (HP 6890
with a FID detector, 30 m Rtx-5 column). A1 ml catalyst-solution of
chlorobenzene (0.51 mL, 5 mmol), Butylacrylate (0.85 mL, 6 mmol),
NMP (2 mL) and Na2CO3 (0.64 g) were mixed and stirred at 140 ꢀC
for 66 h under argon-atmosphere. The workup was the same. There
was no visual evidence of palladium metal formation in the reac-
tion studies.
(b) B. Soro, S. Stoccoro, G. Minghetti, A. Zucca, M. Agostina Cinellu,
M. Manassero, S. Gladiali, Inorganica Chim. Acta 359 (2006) 1879;
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Acknowledgment
[7] (a) M. Hirotsu, Y. Tsukahara, I. Kinoshita, Bull. Chem. Soc. Jpn. 83 (2010) 1058;
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(2008) 1585;
We thank James Pavlovich for the mass spectral data, Professor
Mathias Haenel and Frank Sedletzek at the Max-Planck-Institut für
Kohlenforschung, Mülheim an der Ruhr, Germany for the use of
facilities and helpful discussions, and University of California, Santa
Barbara for financial support.
(c) K. Takenaka, M. Minakawa, Y. Uozumi, J. Am. Chem. Soc. 127 (2005) 12273;
(d) I.G. Jung, S.U. Son, K.H. Park, K.-C. Chung, J.W. Lee, Y.K. Chung, Organo-
metallics 22 (2003) 4715;
(e) Q.-L. Luo, J.-P. Tan, Z.-F. Li, Y. Qin, L. Ma, D.-R. Xiao, Dalton Trans. 40 (2011) 3601;
(f) J. Hurtado, A. Ibañez, R. Rojas, M. Valderrama, Inor. Chem. Comm. 13 (2010)
1025;
(g) B. Soro, S. Stoccoro, G. Minghetti, A. Zucca, M. Agostina Cinellu, M. Manassero,
S. Gladiali, Inorganica Chim. Acta 359 (2006) 1879;
Appendix A. Supplementary material
(h) K. Takenaka, Y. Uozumi, Adv. Synth. Catal. 346 (2004) 1693;
(i) B. Soro, S. Stoccoro, G. Minghetti, A. Zucca, M.A. Cinellu, S. Gladiali, M. Manassero,
M. Sansoni, Organometallics 24 (2005) 53.
CCDC 838937 and 838938 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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(b) E. Mieczynska, A. Gnieweka, I. Pryjomska-Raya, A.M. Trzeciaka,
H. Grabowskab, M. Zawadzkib, Green Chem. 12 (2010) 804;
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Appendix. Supplementary material
ꢀ
(d) A. Skarzynska, A.M. Trzeciak, M. Siczek, Inorganica Chim. Acta 365 (2011)
204e210.
[10] TON ¼ (mol of product/mol of catalyst), based off of GC quantification of
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.08.012.
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References
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180e200 ꢀC for 30 min. After the addition of acetic acid (5
mL) the solution
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