Palladium(II) complexes of 2-, 3-, and 4-quinolinyl(diphenyl)phosphane and di-(3-quinolinyl)phenylphosphane: Synthesis, characterization, and catalytic screening

Article abstract of DOI:10.1016/j.ica.2007.09.009

One previously known and three novel quinolinyl phosphanes were synthesized by either a reaction between a lithiated diphenylphosphane and the appropriate chloroquinoline or by a reaction between a lithiated haloquinoline and an arylchlorophosphane. The reaction of the quinolinyl phenylphosphane ligands with PdCl₂(cod) produced monomeric palladium complexes in diethyl ether and dimeric, chlorine-bridged complexes in dichloromethane. Crystal structures of the palladium complexes confirm that the quinolinyl phenylphosphanes do not form chelated structures while bonded to the metal centre. 2-Quinolinyl(diphenyl)phosphane has a tendency to form a cis-isomer while bonded to the metal centre in the mononuclear complex due to attractive interactions between two ligands. A catalytic study showed that the quinolinyl phenylphosphane ligands are moderately active in the Suzuki-Miyaura coupling of various aryl halides in air.

Full text of DOI:10.1016/j.ica.2007.09.009

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 1372–1380
www.elsevier.com/locate/ica
Palladium(II) complexes of 2-, 3-, and 4-quinolinyl(diphenyl)
phosphane and di-(3-quinolinyl)phenylphosphane:
Synthesis, characterization, and catalytic screening
a
a,
b
a
Juho Autio , Sauli Vuoti *, M. Haukka , J. Pursiainen
a
Department of Chemistry, University of Oulu, P.O. Box 3000, FIN-90014 Oulu, Finland
Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland
b
Received 20 June 2007; received in revised form 13 August 2007; accepted 3 September 2007
Available online 14 September 2007
Abstract
One previously known and three novel quinolinyl phosphanes were synthesized by either a reaction between a lithiated diphenylphos-
phane and the appropriate chloroquinoline or by a reaction between a lithiated haloquinoline and an arylchlorophosphane. The reaction
of the quinolinyl phenylphosphane ligands with PdCl2(cod) produced monomeric palladium complexes in diethyl ether and dimeric,
chlorine-bridged complexes in dichloromethane. Crystal structures of the palladium complexes confirm that the quinolinyl phenylphos-
phanes do not form chelated structures while bonded to the metal centre. 2-Quinolinyl(diphenyl)phosphane has a tendency to form a cis-
isomer while bonded to the metal centre in the mononuclear complex due to attractive interactions between two ligands. A catalytic study
showed that the quinolinyl phenylphosphane ligands are moderately active in the Suzuki–Miyaura coupling of various aryl halides in air.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Palladium complexes; Cross-coupling reactions; Quinolinyl phosphane ligands; Crystal structures
1. Introduction
plex. On the other hand, it has been reported that the
bidentate bonding of bulky aryl phosphanes [15] gave a
complete catalysis with very high yields in Suzuki coupling
reactions, when the appropriate substitutes had been intro-
duced to the phenyl ring. Furthermore, biphenyl moieties
among others have been a key factor in the success of these
catalysts [16]. In contrast with other catalytic reactions,
those involving ligands with quinoline moieties have not
yet been extensively tested as potential catalysts for the
Suzuki coupling reactions.
In this study we have prepared one previously known
and three novel quinolinyl phosphanes, and synthesized
their corresponding mono- and dinuclear palladium com-
plexes to study the coordination chemistry of the ligands.
The crystal structures of the palladium complexes have
been studied for possible bidentate bonding between the
Pd-atom and the phosphane. Furthermore, the quinolinyl
phosphanes have been screened as potential catalysts in
Quinoline and pyridine bearing moieties have been suc-
cessfully used as building blocks for phosphane ligands
working as catalysts in various reactions, such as polymer-
izations [1], hydroformylation reactions [2,3], alkyne addi-
tions [4,5], asymmetric synthesis [6,7] and phosphinations
[8]. Other types of bidentate, N–P chelating ligands have
been used as catalysts in asymmetric reactions [9], Suzuki
couplings [10] and Heck reaction [11], where the yields have
mostly been very high. However, other studies [2,3,8,12–14]
report that the chelating effects between a transition metal
complex and phosphane ligands with pyridine, quinoline
and other nitrogen bearing groups have inhibited catalytic
activity or describe a fast disintegration of the metal com-
*
Corresponding author. Tel.: +358 8 5531617; fax: +358 8 5531603.
E-mail address: sauli.vuoti@oulu.fi (S. Vuoti).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.09.009

J. Autio et al. / Inorganica Chimica Acta 361 (2008) 1372–1380
1373
Table 1
Crystal Data
the Suzuki–Miyaura coupling reactions of various aryl bro-
mides and chlorides under microwave irradiation.
2 Æ (CH2Cl2)
43H34Cl4N2P2Pd
3
2. Experimental
Empirical formula
Fw
C
C42H32Cl4N2P2Pd2
981.24
888.86
Temperature (K)
k (A)
120(2)
120(2)
2.1. General details
˚
0.71073
monoclinic
P21
13.7378(3)
10.5523(2)
13.8307(3)
06.7670(10)
1919.73(7)
2
1.538
0.880
41388
8814
0.71073
monoclinic
P21/n
8.6887(5)
14.2099(9)
14.9357(8)
91.791(4)
1843.1(2)
2
1.768
1.388
27841
3571
Crystal system
Space group
The prepared phosphanes were air- and moisture sensi-
tive in their pure solid compound forms. In solution, and
without protection the phosphanes show observable oxida-
tion within a few hours, and in some cases even within a
few minutes. Therefore all reactions involving free phos-
phanes were carried out using standard Schlenk techniques
in a nitrogen or argon atmosphere. The palladium com-
plexes are stable in air both as solid compounds and in
solution, and were therefore isolated and characterized in
air. Diethyl ether was distilled over sodium-benzophenone
ketyl in nitrogen atmosphere before being used. Nitrogen
was bubbled through dichloromethane, ethanol and n-hex-
ane. Tetramethylethylenediamine (TMEDA) was distilled
prior to use. Other commercial reagents were used as
received. The characterization of the new phosphanes and
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
qcalc (Mg/m3)
l(Mo Ka) (mmꢀ1
Number of reflections
Unique reflections
)
a
R1 (I P 2r)
0.0275
0.0525
0.0466
0.0955
b
wR2 (IP 2r)
P
P
a
R1 = jjFoj ꢀ jFcjj/ jFoj.
P
P
2
2 1=2
b
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁꢁ
.
the palladium complexes was based on H, 31P–{1H} and
2.3. Synthesis of the ligands and starting materials
1
13C NMR spectroscopy. NMR spectra were recorded on
a Bruker DPX400 or DPX200 spectrometer at room tem-
perature in CDCl3 (99.8% D, 0.03% TMS); 85% H3PO4
was used as an external standard for 31P–{1H} NMR.
Exact mass peaks of the free ligands were determined on
a Micromass LCT, using an ESI+ method. C and H anal-
yses were performed with a Perkin–Elmer 2400 CHNS ana-
lyzer from the purified, solid metal complex powders. The
mass peaks for the coupling products were determined
using a Hewlett Packard HP 6890 Series GC-system cou-
pled with a 5973-MSD (Mass Selective Detector; quadru-
pole). Single crystals for X-ray crystallographical analyses
were obtained by a slow evaporation of the dichlorometh-
ane–hexane solvent mixture at room temperature.
2.3.1. Preparation of 2-diphenylphosphanequinoline (1a)
The following reaction was conducted in the dark to
prevent the decomposition of diphenylphosphane. A solu-
tion of n-buthyllithium in hexane (2.2 ml, 6.2 mmol) was
added slowly to diphenylphosphane (1.3 ml, 7.5 mmol) dis-
solved in THF (40 ml) at ꢀ115 ꢁC. The mixture was stirred
for 15 min at ꢀ115 ꢁC, and a solution of 2-chloroquinoline
(1.00 g, 6.11 mmol) in THF (20 ml) was added dropwise to
the mixture. The reaction mixture was then stirred at
ꢀ115 ꢁC for 2.5 h before it was allowed to gradually warm
to room temperature overnight. The liquid was separated
from the yellow precipitate by filtration and the precipitate
was washed with THF (3 · 20 ml). The THF extracts were
combined and the THF was removed in vacuo. The crude
product was purified by column chromatography using sil-
ica gel and CH2Cl2/hexane/MeOH (10:3:1) as the eluent.
The pure product 1a was obtained as a white solid. Yield:
0.35 g, 18%. Exact mass (Micromass LCT ESI+): 314.1108
2.2. X-ray crystal structure determinations
The crystals were immersed in cryo-oil, mounted in a
Nylon loop and measured at a temperature of 120 K.
The X-ray diffraction data were collected by means of a
Nonius KappaCCD diffractometer using Mo Ka radiation
1
(M+H)+ (calculated for C21H17NP, 314.1099). H NMR
(400 MHz, CDCl3, see Scheme 1 for numbering) dH
3
(k = 0.71073 A). The Denzo-Scalepack [17] program pack-
(ppm): 7.15 (d, JH–H = 8.4 Hz, 1H, H4), 7.2–7.3 (m, 6H,
˚
3
age was used for calculating cell refinements and data
reductions. All of the structures were solved by direct
methods using the SIR2004 [18] or SHELXS97 [19] with the
WINGX [20] graphical user interface. An empirical absorp-
tion correction was applied to all of the data (SADABS [21]
or XPREP in SHELXTL [22]). Structural refinements were car-
ried out using SHELXL97 [23]. All hydrogen atoms were
positioned geometrically and constrained to ride on their
parent atoms, with C–H length range being = 0.95–
H12, H13), 7.38 (t, JH–H = 7.6 Hz, 1H, H8), 7.4–7.5
3
(m, 4H, H11), 7.57 (t, JH–H = 7.8 Hz, 1H, H7), 7.62 (d,
3
3JH–H = 8.4 Hz, 1H, H9), 7.85 (d, JH–H = 8.4 Hz, 1H,
3
H3), 8.11 (d, JH–H = 8.8 Hz, 1H, H6). 13C{1H} NMR
2
(100 MHz, CDCl3) dC (ppm): 124.00 (d, JC–P
=
15.09 Hz, C4), 126.41 (s, C2), 126.48 (s, C8), 127.31 (s,
C9), 126.41 (d, JC–P = 7.04 Hz, C12), 128.70 (s, C13),
3
129.28 (s, C7), 129.30 (s, C6) 133.88 (d, JC–P = 20.12 Hz,
2
C11), 134.94 (s, C3), 136.11 (d, JC–P = 12.07 Hz, C10),
1
3
1
0.99 A and Uiso = 1.2 Ueq (parent atom). The crystallo-
148.30 (d, JC–P = 15.09 Hz, C1), 164.56 (d, JC–P
=
˚
graphic details are summarized in Table 1. Selected bond
lengths and angles are shown in the figure captions.
3.02 Hz, C5). 31P{1H} NMR (161 MHz, CDCl3) dP
(ppm): ꢀ0.1.

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J. Autio et al. / Inorganica Chimica Acta 361 (2008) 1372–1380
13
13
12
11
12
11
10
10
6
9
1
P
N
P
5
4
1
2
7
8
2
3
N
5
3
4
9
6
7
1a
1b
8
13
13
12
11
12
11
8
10
9
2
7
10
6
1
P
P
3
1
2
3
N
N
4
5
N
5
4
9
6
7
1c
8
1d
Scheme 1. Structures of phosphanes 1a, 1b, 1d and 1d.
1
2.3.2. Preparation of 3-diphenylphosphanequinoline (1b),
4-diphenylphosphanequinoline (1c), and di-(3-quinolinyl)-
phenylphosphane (1d)
314.1099). H NMR (400 MHz, CDCl3, see Scheme 1 for
numbering) dH (ppm): 7.3–7.45 (m, 10H, H11, H12, H13),
7.53 (t, JH–H = 7.47 Hz, 1H, H8), 7.67–7.79 (m, 2H, H9,
3
3
3
A solution of n-buthyllithium in hexane (7.1 ml,
20 mmol) was added slowly to dry TMEDA (3.1 ml,
20 mmol). The solution was stirred for 15 min and then
cooled to ꢀ115 ꢁC by adding cold diethyl ether (50 ml). A
solution of 3-bromoquinoline (4.17 g, 20 mmol) in cold
diethyl ether (20 ml) was added dropwise to the reaction
mixture at ꢀ115 ꢁC. The colour of the solution turned from
yellow to orange and a white precipitate was formed. After
stirring for 5 min, chlorodiphenylphosphane (4.40 g,
20.0 mmol) in diethyl ether (20 ml) was added dropwise to
the mixture at ꢀ115 ꢁC. The colour of the reaction mixture
turned from orange to yellow and a white precipitate was
formed. The reaction mixture was then stirred at ꢀ115 ꢁC
for 2.5 h, before it was allowed to gradually warm to room
temperature overnight. The solution was then extracted by
H2SO4 (2 M, 3 · 10 ml) and the combined extracts were
made alkaline with the addition of NaOH (20%). The result-
ing aqueous phase was extracted by CH2Cl2(3 · 20 ml), and
the extracts were then combined and dried with MgSO4. The
solvent was removed in vacuo. The crude product was
washed with ethanol/n-hexane (1:1) solution and purified
by column chromatography using CH2Cl2/n-hexane/
MeOH (10:3:1) as the eluent. The crude solid was recrystal-
lized from CH2Cl2 to give 1b. The yield of the phosphane as
a white solid was 3.0 g, 9.4 mmol, 47%. Exact mass (Micro-
mass LCT ESI+): 314.1093 (M+H)+ (calc. for C21H17NP,
H7), 8.00 (d, JH–P = 6.76 Hz, 1H, H3), 8.09 (d, JH–H
= 8.31 Hz, 1H, H6), 8.81 (m, 1H, H1). 13C{1H} NMR
(100 MHz, CDCl3) dC (ppm): 126.90 (s, C8), 127.85 (s,
C9), 128.79 (d, JC–P = 7.19 Hz, C12), 129.20 (s, C13),
3
129.32 (s, C6), 130.11 (s, C7), 131.00 (d, JC–P = 16.08 Hz,
4
C5), 132.04 (d, JC–P = 9.97 Hz, C4), 133.77 (d, JC–P
=
3
2
19.78 Hz, C11), 135.78 (d, JC–P = 10.28 Hz, C10), 141.53
1
(d, 2JC–P = 17.74 Hz, C3), 147.79 (s, C2), 154.02 (d, 2JC–P
=
22.28 Hz, C1). 31P{1H} NMR (161 MHz, CDCl3) dP
(ppm): ꢀ10.0.
Phosphane 1c was synthesized by a similar method
as phosphane 1b by reacting n-buthyllithium (6.2 ml,
18 mmol), 4-chloroquinoline (2.95 g, 18 mmol) and
PR2R'
Cl
CH2Cl2
Pd
Cl
Cl
Pd
Cl
R'
P
PR2R'
PdCl2(cod)
+
Cl
R
R
(CH3CH2)2O
PR2R'
Pd
PR2R'
Cl
Scheme 2. A general reaction scheme for the preparation of the mono-
and dinuclear palladium complexes.

J. Autio et al. / Inorganica Chimica Acta 361 (2008) 1372–1380
1375
1.7 mmol) in diethylether (30 ml) yielded a yellow solid
product after purification by column chromatography.
The yield of the pure product was 0.745 g, 0.9 mmol,
57.9%. Anal. Calc. C42H32N2P2Cl2Pd: C, 62.74; H, 4.01.
Found: C, 62.29; H, 3.89%. 31P{1H} NMR (161 MHz,
CDCl3) dP (ppm): 23.8.
HO
OH
K CO
3
Br
Pd-catalyst, DMF,
B
2
MW, 150ο C, 30 min
+
Scheme 3. A standard reaction scheme for the couplings showing the
reaction used for the optimization for the amount of the Pd-catalyst.
2.4.2. Di-l-chlorodichlorobis(2-diphenylphosphane-
quinoline)di-palladium (3)
chlorodiphenylphosphane (3.96 g, 18 mmol). The yield of
1c, a white solid, was 2.94 g, 9.4 mmol, 52%. Exact mass
(Micromass LCT ESI+): 314.1080 (M+H)+ (calc. for
An overnight reaction between 2-diphenylphosphane-
quinoline1a (0.986 g, 3.2 mmol) and PdCl2(cod) (0.941 g,
3.4 mmol) in dichloromethane (20 ml) yielded an orange
solid product after purification by column chromatogra-
phy. The yield of the pure product was 1.101 g, 1.1 mmol,
70.1%. Anal. Calc. C42H32N2P2Cl4Pd2: C, 51.40; H, 3.29.
Found: C, 51.13; H, 3.26%. dP (ppm): 31.0.
C21H17NP, 314.1099). 1H NMR (400 MHz, CDCl3, see
3
Scheme 1 for numbering) dH (ppm): 6.82 (t, JH–H
=
2.25 Hz, 1H, H5), 7.25–7.43 (m, 11H, H8, H11, H12, H13),
7.62–7.75 (m, 1H, H7) 8.13 (d, JH–H = 8.42 Hz, 1H, H6),
3
8.20–8.25 (m, 1H, H9), 8.76 (d, JH–H = 4.30 Hz, 1H,
3
H4).13C{1H} NMR (100 MHz, CDCl3) dC (ppm): 125.24
2.4.3. Dichlorobis(3-diphenylphosphanequinoline)palladium
(4)
(s, C5), 126.01 (d, JC–P = 22.24 Hz, C9), 126.62 (s, C8),
3
128.79 (d, JC–P = 7.5 Hz, C12), 129.41 (s, C13), 129.82 (d,
3
An overnight reaction between 3-diphenylphosphane-
quinoline (0.985 g, 3.2 mmol) 1b and PdCl2(cod) (0.469 g,
1.7 mmol) in diethylether (30 ml) yielded a yellow solid
product after purification by column chromatography.
The yield of the pure product was 0.819 g, 1.0 mmol,
63.7%. Anal. Calc. C42H32N2P2Cl2Pd: C, 62.74; H, 4.01.
Found: C, 62.43; H, 3.71%. 31P{1H} NMR (161 MHz,
CDCl3) dP (ppm): 28.2.
2
3JC–P = 19.19 Hz, C2), 130.04 (s, C6), 134.27 (d, JC–P
=
20.23 Hz, C11), 134.29 (d, JC–P = 8.65 Hz, C10), 146.56
1
(d, JC–P = 20.83 Hz, C1), 147.59 (s, C3), 149.59 (s, C4).
2
31P{1H} NMR (161 MHz, CDCl3) dP (ppm): ꢀ13.8.
Phosphane 1d was synthesized by a similar method as
phosphanes 1b and 1c by reacting n-buthyllithium
(10.7 ml, 30 mmol), 3-bromoquinoline (6.24 g, 30 mmol)
and dichlorophenylphosphane (2.68 g, 15 mmol). The yield
of 1d, a white solid, was 3.17 g, 8.7 mmol, 58%. Exact mass
(Micromass LCT ESI+): 365.1217 (M+H)+ (calc. for
2.4.4. Di-l-chlorodichlorobis(3-diphenylphosphane-
quinoline)di-palladium (5)
1
C24H17N2P, 365.1208). H NMR (400 MHz, CDCl3, see
An overnight reaction between 3-diphenylphosphane-
quinoline 1b (0.985 g, 3.2 mmol) and PdCl2(cod) (0.940 g,
3.4 mmol) in dichloromethane (20 ml) yielded an orange
solid product after purification by column chromatogra-
phy. The yield of the pure product was 1.008 g, 1.0 mmol,
63.9%. Anal. Calc. C42H32N2P2Cl4Pd2: C, 51.40; H, 3.29.
Found: C, 51.13; H, 3.26%. dP (ppm): 36.1.
Scheme 1 for numbering) dH (ppm): 7.35–7.50 (m, 5H,
3
H11, H12, H13), 7.53 (t, JH–H = 7.53 Hz, 2H, H8), 7.7 (d,
3JH–H = 8.71 Hz, 2H, H9), 7.73–7.75 (m, 2H, H7), 8.00
3
3
(d, JH–P = 8.07 Hz, 2H, H3), 8.12 (d, JH–H = 8.46 Hz,
2H, H6), 8.9 (m, 2H, H1). 13C{1H} NMR (100 MHz,
CDCl3) dC (ppm): 127.07 (s, C8), 127.80 (s, C9), 129.03
3
(d, JC–P = 7.41 Hz, C12), 129.31 (s, C6), 129.48 (d,
3JC–P = 15.6 Hz, C5), 129.64 (s, C13), 130.37 (s, C7),
131.91 (d, JC–P = 10.28 Hz, C4), 133.75 (d, JC–P
=
3
3
2.4.5. Dichlorobis(4-diphenylphosphanequinoline)palladium
(6)
20.16 Hz, C11), 134.31 (d, JC–P = 9.77 Hz, C10), 141.85
3
3
(d, JC–P = 23.84 Hz, C3), 147.00 (s, C2), 153.58 (d,
An overnight reaction between 4-diphenylphosphane-
quinoline (0.985 g, 3.2 mmol) 1c and PdCl2(cod) (0.470 g,
1.7 mmol) in diethylether (30 ml) yielded a yellow solid
product after purification by column chromatography.
The yield of the pure product was 0.801 g, 1.0 mmol,
62.3%. Anal. Calc. C42H32N2P2Cl2Pd: C, 62.74; H, 4.01.
Found: C, 62.39; H, 3.88%. 31P{1H} NMR (161 MHz,
CDCl3) dP (ppm): 19.9.
3JC–P = 23.29 Hz, C1). 31P{1H} NMR (161 MHz, CDCl3)
dP (ppm): ꢀ13.9.
2.4. Synthesis of the palladium complexes
All palladium complexes were prepared by a substitution
of cyclooctadiene (cod) in PdCl2 (cod) with a preferred
phosphane ligand in dichloromethane or diethyl ether, See
Scheme 2 and purification by silica gel and dichlorometh-
ane/hexane (1:2) solvent mixture as reported previously [24].
2.4.6. Di-l-chlorodichlorobis(4-diphenylphosphane-
quinoline)di-palladium (7)
An overnight reaction between 4-diphenylphosphane-
quinoline 1c (0.983 g, 3.2 mmol) and PdCl2(cod) (0.938 g,
3.4 mmol) in dichloromethane (20 ml) yielded an orange
solid product after purification by column chromatogra-
phy. The yield of the pure product was 0.996 g, 1.0 mmol,
2.4.1. Dichlorobis(2-diphenylphosphanequinoline)palladium
(2)
An overnight reaction between 2-diphenylphosphane-
quinoline (0.988 g, 3.2 mmol) 1a and PdCl2(cod) (0.472 g,

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J. Autio et al. / Inorganica Chimica Acta 361 (2008) 1372–1380
63.2%. Anal. Calc. C42H32N2P2Cl4Pd2: C, 51.40; H, 3.29.
Found: C, 51.06; H, 3.07%. dP (ppm): 28.7.
7.82–7.75 (m, 1H), 7.75–7.65 (m, 1H), 7.6–7.4 (m, 5H)
ppm; 13C NMR (CDCl3) d 157.31, 136.73, 129.70, 129.61,
129.27, 128.81, 127.53, 127.42, 127.11, 126.24,
118.96 ppm. GC–MS: m/z 205 (M+).
2.4.7. Dichlorobis(di-(3-quinolinyl)phenylphosphane)
palladium (8)
An overnight reaction between di-(3-quinolinyl)phenyl-
phosphane (0.915 g, 2.5 mmol) 1d and PdCl2(cod)
(0.359 g, 1.3 mmol) in diethylether (30 ml) yielded a yellow
solid product after purification by column chromatogra-
phy. The yield of the pure product was 0.819 g, 0.9 mmol,
72.3%. Anal. Calc. C48H34N2P2Cl2Pd: C, 63.62; H, 3.78.
Found C, 63.40; H, 3.55%. 31P{1H} NMR (161 MHz,
CDCl3) dP (ppm): 17.2.
2.5.3. 2-Isopropylbiphenyl
1
White solid, mp 80 ꢁC (lit. 82 ꢁC). H NMR (CDCl3) d
7.75–7.4 (m, 7H), 7.3–7.4 (m, 2H), 3.05 (sep, J = 6.80 Hz,
1H), 1.15 (d, J = 6.80 Hz, 6 H) ppm; 13C NMR (CDCl3)
d 146.286, 142.059, 141.040, 129.912, 129.273, 127.934,
127.631, 126.651, 125.485, 125.257, 29.309, 24.261 ppm.
GC–MS m/z 196 (M+).
2.5.4. 2,4,5-Trimethylbiphenyl
1
2.4.8. Di-l-chlorodichlorobis(di-(3-quinolinyl)
phenylphosphane)di-palladium (9)
Yellow oil. H NMR (CDCl3) d 7.42–7.35 (m, 2H),
7.35–7.22 (m, 3H), 7.05–7.02 (m, 2H), 2.22–2.28 (m, 9H)
ppm; 13C NMR (CDCl3) d 141.972, 139.402, 135.452,
133.755, 132.438, 131.695, 131.108, 129.253, 127.975,
126.497, 22.724, 19.309, 19.180 ppm. GC–MS m/z 196
(M+).
An overnight reaction between di-(3-quinolinyl)phenyl-
phosphane 1d (0.914 g, 2.5 mmol) and PdCl2(cod)
(0.360 g, 1.3 mmol) in dichloromethane (20 ml) yielded an
orange solid product after purification by column chroma-
tography. The yield of the pure product was 0.615 g,
0.6 mmol, 45.4%. Anal. Calc. C48H34N2P2Cl4Pd2: C,
53.21; H, 3.16. Found C, 53.06; H, 3.02%. dP (ppm): 23.8.
2.5.5. 2,5-Dimethyl-30,50-dimethylbiphenyl
1
Colorless oil. H NMR (CDCl3, 400 MHz) d (ppm): 2.2
(s, 3H), 2.33 (s, 3H), 2.34–2.37 (m, 6H), 6.91–6.94 (m, 2H),
7.02–7.07 (m, 4H), 7.11–7.16 (m 1H). 13C{H} NMR
(CDCl3, 100 MHz) d (ppm): 19.97, 20.89, 21.35, 125.10,
126.98, 127.71, 128.25, 130.14, 130.46, 132.08, 135.01,
137.42, 141.94, 142.03. GC–MS: m/z 210 (M+).
2.5. A general procedure for the Suzuki–Miyaura coupling
reactions
A microwave pressure vessel (2–5 ml) was charged with
the aryl halogen, phenylboronic acid, K2CO3 and the cor-
responding palladium complex. DMF (2.5 ml) (and in
some cases H2O (0.5 ml)) were added to the vessel, and
the vessel was pre-stirred for 5 min. The resulting solution
was warmed at 150 ꢁC for 30 min under standard irradia-
tion mode. The reaction mixture was cooled to room tem-
perature, and water (30 ml) was added to the mixture. The
organic layer was separated, and the water extracted by
diethyl ether (30 ml) three times. The ether extracts were
combined with the organic layer and dried with MgSO4,
and the solvent was removed in vacuo. The remaining res-
idue was separated by column chromatography using silica
gel and dichloromethane/hexane (1:3) mixture. Each exper-
iment was repeated twice and the yields were reported as an
average of the two measurements. The coupling products
were identified by 1H and 13C NMR spectroscopy and
gas chromatography. See Scheme 3.
2.5.6. 2,5-Dimethylbiphenyl
1
White solid, mp 105–107 ꢁC (lit. 107–109 ꢁC). H NMR
(CDCl3, 400 MHz) d (ppm): 2.2 (s, 3H), 2.30 (s, 3H), 7.0–
7.05 (m, 2H), 7.09–7.17 (m, 2H), 7.23–7.3 (m, 2H), 7.3–7.4
(m, 2H). 13C{H} NMR (CDCl3, 100 MHz) d (ppm): 19.90,
20.85, 126.60, 127.80, 127.89, 127.96, 130.20, 130.48,
132.05, 135.03, 141.71, 142.05. GC–MS: m/z 182 (M+).
2.5.7. 3-Methylbiphenyl
Colorless oil. 1H NMR (CDCl3) d 7.6–7.5 (m, 2H), 7.45–
7.35 (m, 3H), 7.35–7.19 (m, 2H), 7.18–7.0 (m, 2H), 2.39 (s,
3H) ppm; 13C NMR (CDCl3) d 141.289, 141.168, 138.245,
128.642, 128.619, 127.948, 127.918, 127.118, 124.222,
21.50 ppm. GC–MS: m/z 168 (M+).
2.5.8. 3,4-Dimethyl-30,50-dimethylbiphenyl
Colorless oil. 1H NMR (CDCl3, 400 MHz) d (ppm): 2.27
(s, 3H) 2.30 (s, 3H), 2.35 (s, 6H), 6.94 (s, 1H), 7.1–7.24 (m,
3H), 7.27–7.33 (m, 1H), 7.34 (s, 1H). 13C{H} NMR
(CDCl3, 100 MHz) d (ppm): 19.39, 19.89, 21.39, 124.52,
124.91, 128.41, 128.53, 129.92, 135.42, 136.69, 138.07,
139.05, 141.28. GC–MS m/z 210 (M+).
2.5.1. 2,3-Dimethylbiphenyl
White solid, mp 97–99 ꢁC (lit. 98–100 ꢁC). 1H NMR
(CDCl3) d 7.5–7.35 (m, 2H), 7.35–7.25 (m, 3H), 7.2–7.05
(m, 3H), 2.33 (s, 3H); 2.15 (s, 3H) ppm; 13C NMR (CDCl3)
d 142.560, 142.244, 137.134, 133.969, 129.385, 128.821,
127.955, 127.660, 126.580, 125.211, 20.690, 16.947 ppm.
GC–MS m/z 182 (M+).
2.5.9. 3,4-Dimethylbiphenyl
Colorless oil. 1H NMR (CDCl3, 400 MHz) d (ppm): 2.28
(s, 3H) 2.30 (s, 3H), 7.16–7.19 (m, 1H), 7.25–7.34 (m, 2H),
7.34–7.45 (m, 3H), 7.53–7.58 (m, 2H). 13C{H} NMR
(CDCl3, 100 MHz) d (ppm): 19.39, 19.88, 124.46, 126.83,
2.5.2. 2-Phenylquinoline
White solid, mp 81–83 ꢁC (lit. 82–84 ꢁC). 1H NMR
(CDCl3) d 8.24–8.1 (m, 4H), 7.87 (d, J = 8.57 Hz, 1H),

J. Autio et al. / Inorganica Chimica Acta 361 (2008) 1372–1380
1377
126.93, 128.37, 128.61, 130.00, 135.60, 136.81, 138.80,
2.5.11. 2,6-Dimethyl-o-terphenyl
141.22. GC–MS m/z 182 (M+).
White solid, mp 40–42 ꢁC. 1H NMR (CDCl3, 400 MHz)
d (ppm): 1.92 (s, 6H), 6.85–7.00 (m, 2H), 7.00–7.22 (m,
4H), 7.22–7.50 (m, 4H), 7.50–7.65 (m, 2H). 13C{H}
2.5.10. 4-Methyl-o-terphenyl
White solid, mp 60–62 ꢁC. 1H NMR (CDCl3) d 7.5–7.25
(m, 7H), 7.25–7.06 (m, 4H), 7.06–6.95 (m, 2H), 2.29 (s, 3H)
ppm; 13C NMR (CDCl3) d 141.614, 140.442, 138.454,
130.548, 129.799, 129.662, 128.540, 127.790, 127.388,
126.303, 21.04 ppm. GC–MS m/z 244 (M+).
NMR (CDCl3, 100 MHz) d (ppm): 126.60, 126.97,
127.17, 127.21, 127.29, 127.37, 127.48, 127.65, 128.80,
128.83, 130.20, 130.40, 136.13, 139.00, 140.81, 140.85,
141.29, 141.32. GC–MS m/z 258 (M+).
3. Results and discussion
3.1. Ligand syntheses
The synthesis of 2-diphenylphosphanequinoline (1a) See
Scheme 1 has been previously described in the literature,
but using a different method and obtaining a different yield
[25]. In our study phosphane 1a was prepared by lithiating
diphenylphosphane followed by an overnight reaction with
2-chloroquinoline. The starting material for ligand 1d, 4-
chloroquinoline, was prepared according to the method
involving the chlorination of 4-quinoline by phosphorous
oxychloride [26]. The novel phosphane ligands 1b, 1c and
1d were prepared according to a modification of a method
reported in the literature. This involved lithiating the halo-
quinolines by n-butyl lithium followed by an overnight
reaction between the matching dichlorophenyl or diphenyl-
chlorophosphane [2]. The phosphanes were characterized
1
by H, 13C, 31P–{1H} NMR and mass spectroscopy.
3.2. Palladium(II) complex syntheses
The mononuclear palladium(II) complexes were pre-
pared by a 1:2 substitution reaction of cyclooctadiene
(cod) in PdCl2(cod) with a preferred phosphane ligand in
diethyl ether. The dinuclear, chlorine-bridged palladium
complexes were prepared by a 1:1 similar reaction in dichlo-
Fig. 1. Thermal ellipsoid plot (50% probability level) of 2. The CH2Cl2
solvent molecule has been omitted for clarity. Selected bond lengths (A)
and angles (deg.): Pd1–P1 2.2631(6), Pd1–P2 2.2711(6), Pd1–Cl2
2.3428(6), Pd1–Cl1 2.3617(6), P1–Pd1–P2 94.83(2), Cl1–Pd1–Cl2 90.86(2).
˚
˚
Fig. 2. Thermal ellipsoid plot (50% probability level) of 3. Selected bond lengths (A) and angles (deg.): Pd1–P1 2.2383(14), Pd1–Cl1 2.2671(14), Pd1–Cl2
2.3235(14), P1–Pd1–Cl1 88.75(5), Cl2–Pd1–Cl2# 84.58(5), Pd1–Cl2–Pd1# 95.42(5). Symmetry transformations used to generate equivalent atoms: # ꢀx,
ꢀy + 1, ꢀz.

1378
J. Autio et al. / Inorganica Chimica Acta 361 (2008) 1372–1380
Table 2
romethane. We have previously reported that ortho-alkyl
substituted arylphosphanes form mono- or dinuclear palla-
dium complexes regardless of stoichiometric factors and the
nuclearity of the complexes depends on the solvent used
[24]. The same occurs with the prepared quinolinyl phos-
phanes; dinuclear complexes were formed in dichlorometh-
ane and mononuclear complexes in diethyl ether regardless
of the Pd:P ratio. Interestingly, phosphane 1a forms a cis-
isomer (see Fig. 1) in the synthesis of the mononuclear com-
plex 2 but a trans-isomer (see Fig. 2) in the synthesis of the
dinuclear complex 3. It has been previously shown that var-
ious pyridyl phosphanes behave similarly and tend to form
cis-isomers in tungsten carbonyl complexes. This is due to
the attractive interactions within the molecules [27]. The
crystal structure of the mononuclear palladium complex 2
revealed an offset p-stacking interaction between the quin-
olinyl and phenyl moieties. The centroid to centroid contact
Coupling of aryl halides with phenyl boronic acida
Entry
Aryl halide
Pd-catalyst
Yield (%)
3-Br-o-xylene
1
2
3
4
5
6
7
6
4
2
5
9
3
8
75
70
69
51
35
20
10
2-Chloroquinoline
8
9
10
11
6
4
2
8
80
72
55
46
2-Isopropylbromobenzene
12
13
14
15
16
17
18
6
2
4
2
4
3
8
81
80b
71b
59
˚
between the rings being 3.831 A and the angle between the
planes 10.86ꢁ. The typical distance range between two p-
˚
54
50
16
stacked rings is 3.3 and 3.8 A, and contact angles usually
lie from parallel displacement up to 40ꢁ [28]. The palladium
complexes were characterized by 31P–{1H} NMR, elemen-
tal analysis and X-ray crystal diffraction (where applicable).
The palladium complexes are not soluble enough to pro-
duce proper 1H NMR spectra. However, overnight 1H
NMR measurements of complexes 2, 3 and 4 showed that
the shifts of the hydrogen atoms had moved downfield only
slightly; therefore the measurements were not repeated for
the other complexes.
2,4,5-Trimethylbromobenzene
19
20
21
22
23
4
2
6
8
7
82b
79b
70
60
58
4-Br-o-xylene
24
25
26
27
28
29
30
4
6
2
5
8
9
6
80b
66b
62b
50
45
40
3.3. Catalytic testing
As a starting point, we utilized the widely used K2CO3
as the base and DMF as the solvent for our catalytic
screening. In some cases a small amount of water was
added to the reaction mixture to enhance further the yield
and the purity of the coupling products [29]. The amount
of the Pd-catalyst was optimized to 0.5%. The catalyst sys-
tem is extremely simple and the reactions can be done in air
due to the stability of the palladium (II) complexes. Addi-
tionally, the palladium(II) complexes allow strict control
for the palladium/ligand ratio and therefore an excess of
the ligands is not required.
19
2-Br-p-xylene
31
32
33
a
2
6
4
84b
78b
77b
Standard reaction conditions: aryl halide (1.45 mmol, 1.0 equiv),
phenyl boronic acid (1.65 mmol, 1.15 equiv), K2CO3 (3.0 mmol,
2.0 equiv), DMF (2.5 ml), 0.5 mol% of Pd-catalyst.
b
0.5 ml H2O added into the reaction mixture.
Microwave heating was chosen as the heating method in
our studies for practical reasons. Microwave heating is an
adaptable heating method, which shortens the reaction
times and increases yields [30]. The results for each individ-
ual aryl halide are presented in Tables 2–4. All yields have
been reported as isolated yields after separation of the
products by column chromatography.
Early on in our studies we observed that the dinuclear
palladium(II) complexes produced only low to mediocre
yields in the simplest coupling reactions. Apparently the
dinuclear palladium complex decomposes under the reac-
tion conditions. Therefore these catalysts were not tested
in more complicated coupling reactions. Similarly, the
mononuclear complex 8 seemed to produce only low yields,
which was probably due to the bulky, highly sterically hin-
dered structure. For this reason, it was not further tested.
Our preliminary testing showed that the mononuclear
palladium(II) complexes 2, 4 and 6 produced average to
high yields in most coupling reactions. In our screening
the reactions between biphenyl boronic acid and 4-bromo-
toluene, or 2-bromo-m-xylene were the most demanding
reactions involving aryl bromides. The complexes only pro-
duced low to mediocre yields in these reactions. We
observed that some of the biphenyl boronic acid remained
unreactive in these reactions. Therefore coupling reactions
with even more complex aryl bromides were not conducted.
The differences in the catalytic efficiencies of complexes
2, 4 and 6 were mostly insignificant as all the ligands

J. Autio et al. / Inorganica Chimica Acta 361 (2008) 1372–1380
1379
Table 3
phosphane by lithiating either. The quinolinyl phenyl and
diphenylphosphane complexes readily coordinate with pal-
ladium(II) under standard reaction conditions. It is possible
to prepare either mono- or dinuclear palladium complexes
with these ligands depending on the choice of solvent. The
mononuclear palladium complex of 2-quinolinyl diphenyl-
phosphane forms a cis-isomer due to the attractive forces
between the two ligands. The nitrogen atoms in the quino-
line rings of the quinolinyl phenylphosphane ligands do not
form a bond with the palladium atom and the structures
remain non-chelated, which is also reflected in the catalytic
activity of the complexes. The prepared mononuclear palla-
dium complexes are moderately active in the Suzuki–Miya-
ura coupling of various simple and moderately demanding
aryl halides and phenyl boronic acids. They also produce
high yields in most reactions. The reaction setup is simple
and can be conducted in air using low catalyst loadings.
Microwave heating enables fast reaction times. The addi-
tion of a small amount of water to the reaction mixture fur-
ther increases the yields in all coupling reactions. No
reaction, or only a small yield is observed when bulky sub-
strates or inactivated aryl chlorides are used.
Coupling of aryl halides with 3,5-dimethylphenyl boronic acida
Entry
Aryl halide
Pd-catalyst
Yield (%)
4-Br-o-xylene
1
2
3
4
2
6
86b
80b
79b
2-Br-p-xylene
4
5
6
7
8
9
a
4
2
6
3
8
6
85b
84b
68b
40b
40
27
Reaction conditions: aryl halide (1.50 mmol, 1.0 equiv), 3,5-dimethyl
phenyl boronic acid (1.65 mmol, 1.1 equiv), K2CO3 (3.0 mmol, 2.0 equiv),
DMF (2.5 ml), 0.5 mol% of Pd-catalyst.
b
0.5 ml H2O added into the reaction mixture.
Table 4
Coupling of aryl halides with 2-biphenyl boronic acida
Entry
Aryl halide
Pd-catalyst
Yield (%)
4-Bromotoluene
1
2
3
4
5
2
4
6
6
8
68b
51b
49b
35
Appendix A. Supplementary material
CCDC 650409 and 650410 contain the supplementary
crystallographic data for 2 and 3. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via http://www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this
article can be found, in the online version, at
doi:10.1016/j.ica.2007.09.009.
8b
2-Br-m-xylene
6
7
8
a
2
4
6
49b
39b
38b
Reaction conditions: aryl halide (1.45 mmol, 1.0 equiv), 2-biphenyl
boronic acid (1.65 mmol, 1.15 equiv), K2CO3 (3.0 mmol, 2.0 equiv), DMF
(2.5 ml), 0.5 mol% of Pd-catalyst.
b
0.5 ml H2O added into the reaction mixture.
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