Synthesis, characterization, and application of palladium complexes containing 8-quinolylphosphinite ligands

Article abstract of DOI:10.1139/V09-156

Palladium complexes containing 8-quinolylphosphinite ligands have been synthesized and characterized. Their solid state structures were determined by single-crystal X-ray diffraction. They were found to be active catalysts for Suzuki coupling reactions of

Full text of DOI:10.1139/V09-156

99
Synthesis, characterization, and application
of palladium complexes containing
8-quinolylphosphinite ligands
Earl Cook, Jason D. Masuda, and Aibing Xia
Abstract: Palladium complexes containing 8-quinolylphosphinite ligands have been synthesized and characterized. Their
solid state structures were determined by single-crystal X-ray diffraction. They were found to be active catalysts for Su-
zuki coupling reactions of phenylboronic acid and various aryl halides.
Key words: palladium complexes, unsymmetrical ligands, quinoline, the Suzuki reaction.
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Resume : On a effectue la synthese et caracterise des complexes du palladium avec des ligands 8-quinolylphosphiniques.
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On a determine leur structures a l’etat solide par diffraction des rayons X par un cristal unique. On a trouve qu’ils sont ac-
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tifs comme catalyseurs dans les reactions de couplage de Suzuki entre l’acide phenylboronique et divers halogenures
d’aryle.
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Mots-cles : complexes du palladium, ligands non symetriques, reaction de Suzuki.
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[Traduit par la Redaction]
Introduction
Experimental
Unsymmetrical ligands with two or more different donors
have attracted increasing attention due to their bonding ver-
satility and catalytic applications. The combination of a soft
donor and a hard donor induces different interactions be-
tween the metal centers and the unsymmetrical donors,
which may lead to hemilabile properties.1–3 The weak do-
nors in the hemilabile ligands can dissociate from the metal
center to facilitate substrate interaction, and rebind to the
metal center to stabilize the reactive intermediates during
catalytic cycles.
General
All experiments were performed under an argon atmos-
phere unless otherwise specified. All anhydrous solvents
were purchased from Sigma-Aldrich Canada Ltd. and stored
˚
over 4 A molecular sieves prior to use. 8-Hydroxyquinoline,
chlorodiphenylphosphine, chlorodiisopropylphosphine, po-
tassium hydride, and 4-N,N-dimethylaminopyridine (DMAP)
were purchased from Sigma-Aldrich Canada Ltd. Bis(benzo-
nitrile)dichloropalladium(II) and chlorodicyclohexylphos-
1
phine were purchased from Strem Chemicals, Inc. H and
31P NMR spectra were recorded on a Bruker Avance 500
spectrometer and referenced to SiMe4 and 85% H3PO4, re-
spectively. Infrared spectra were collected on a Nicolet Ava-
tar 330 FT-IR spectrometer. Elemental analyses were carried
out by Guelph Chemical Laboratories in Guelph, Ontario.
Melting points were recorded on a Mel-Temp (Electro-
thermal) Apparatus and were uncorrected.
P,N-type ligands, containing strong donors such as phos-
phines and weak donors such as amines,4–9 pyrazoles,10,11
and pyridines12–19 have been investigated in a variety of cat-
alytic transformations. Recently Walther and co-workers20
reported nickel complexes containing phosphinite ligands
i
based on 8-hydroxyquinoline (Fig. 1, R = Ph, Pr). The
nickel diisopropylphosphinite complex was isolated, yet the
diphenyl analogue was unstable and a tetrameric nickel
complex was obtained instead. Very recently Crociani et
al.21 reported the synthesis of quinolylphosphinite palladium
Complex 1
8-Hydroxyquinoline (0.145 g, 1.00 mmol) and DMAP
(0.122 g, 1.00 mmol) were dissolved in THF (10 mL).
Chlorodiphenylphosphine (0.221 g, 1.00 mmol) in THF
(5 mL) was added dropwise. The mixture was stirred over-
night and filtered. A solution of bis(benzonitrile)dichloropal-
ladium(II) (0.384 g, 1.00 mmol) in CH2Cl2 (5 mL) was
added to the filtrate. Yellow solids were formed after com-
pletion of the addition. The mixture was stirred overnight
and filtered. The yellow solids were washed with hexane
(2 Â 5 mL). Yield 0.470 g (93%), mp 209 8C (dec). IR
(KBr, cm–1) n: 2924 (m), 1655 (w), 1560 (w), 1508 (s),
1464 (m), 1437 (m), 1310 (m), 1253 (m), 1105 (s), 927 (w),
828 (m), 762 (w), 694 (w), 539 (w), 492 (w). 1H NMR
(500.13 MHz, CDCl3, ppm) d: 10.59 (dd, J = 1.5, 5.4 Hz,
1H, quinolyl), 8.44 (dd, J = 1.6, 8.3 Hz, 1H, quinolyl),
t
complexes containing di-tert-butyl groups (R = Bu) and
their catalytic applications. Here, we wish to report the syn-
thesis, characterization, and catalytic applications of three
new palladium complexes containing 8-quinolylphosphinites
i
(R = Ph, Pr, Cy).
Received 18 August 2009. Accepted 6 October 2009. Published
on the NRC Research Press Web site at canjchem.nrc.ca on
24 December 2009.
E. Cook and A. Xia.1 Department of Chemistry, Mount Saint
Vincent University, Halifax, NS B3M 2J6, Canada.
J.D. Masuda. Department of Chemistry, Saint Mary’s
University, Halifax, NS B3H 3C3, Canada.
1Corresponding author (e-mail: aibing.xia@msvu.ca).
Can. J. Chem. 88: 99–103 (2010)
doi:10.1139/V09-156
Published by NRC Research Press

100
Can. J. Chem. Vol. 88, 2010
Table 1. Crystal data and structure refinement data for 1.
Fig. 1. 8-Quinolylphosphinites.
Formula
C21H16Cl2NOPPd
506.62
Formula weight
Crystal size (mm3)
Space group
0.368Â0.242Â0.216
P2(1)/n
˚
a (A)
10.5513(4)
11.3256(4)
17.0524(6)
99.2349(4)
2011.35(13)
4
˚
b (A)
˚
c (A)
b (8)
V (A )
3
˚
Z
Dcalcd. (g/cm3)
1.673
1.279
m (mm–1)
Scheme 1. Synthesis of palladium 8-quinolylphosphinite com-
plexes.
F(000)
1008
q for data collection (8)
No. of total reflns.
No. of unique reflns.
R1 (I > 2s(I))a
Rw (all data)b
2.17–25.50
13594
3731
0.0234
0.0636
aR = S|(|Fo| – |Fc|)| / S|Fo|.
bRw = [Sw(Fo2 – Fc2)2/S(Fo)4]1/2 where w = 1/[s2(Fo ) + (0.0324
2
 P)2 + (0.6790  P)] where P = (Fo + 2Fc2)/3.
2
˚
Table 2. Selected bond lengths (A) and angles (8) for 1.
˚
Bond lengths (A)
Pd(1)—N(1)
Pd(1)—P(1)
Pd(1)—Cl(1)
Pd(1)—Cl(2)
Pd(1)—N(1)
2.0803(18)
2.1765(6)
2.2880(7)
2.3809(6)
2.0803(18)
Fig. 2. Molecular structure of 1.
Bond angles (8)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
N(1)–Pd(1)–Cl(2)
P(1)–Pd(1)–Cl(2)
Cl(1)–Pd(1)–Cl(2)
N(1)–Pd(1)–P(1)
N(1)–Pd(1)–Cl(1)
P(1)–Pd(1)–Cl(1)
86.28(5)
175.48(5)
91.65(2)
93.00(5)
170.84(2)
89.68(2)
86.28(5)
175.48(5)
91.65(2)
was added slowly. The mixture was stirred for 10 min and
filtered to afford a fluorescent green solution. Chlorodiiso-
propylphosphine (0.155 g, 1.00 mmol) in THF (5 mL) was
added dropwise. The mixture was stirred for 1 h. Bis(benzo-
nitrile)dichloropalladium(II) (0.384 g, 1.00 mmol) in CH2Cl2
(5 mL) was added. The mixture was stirred overnight and fil-
tered through celite. The volatiles were removed under vac-
uum to afford yellow solids. Yield 0.400 g (91%), mp 204–
206 8C. IR (KBr, cm–1) n: 3448 (w), 2921 (m), 1590 (w),
1508 (s), 1465 (s), 1385 (m), 1310 (w), 1252 (m), 1104 (s),
932 (m), 842 (s), 825 (s), 758 (m), 667 (m). 1H NMR
(500.13 MHz, CDCl3, ppm) d: 10.49 (dd, J = 1.5, 5.4 Hz,
1H, quinolyl), 8.45 (dd, J = 1.4, 8.2 Hz, 1H, quinolyl), 7.75–
7.72 (dd, J = 1.4, 8.2 Hz, 1H, quinolyl), 7.64 (t, J = 7.9 Hz,
1H, quinolyl), 7.58–7.55 (m, 2H, quinolyl), 2.87 (sept, J =
6.7 Hz, 2H, CH(CH3)2), 1.56 (d, J = 6.7 Hz, 6H,
CH(CH3)’(CH3)@), 1.33 (d, J = 6.7 Hz, 6H, CH(CH3)’(CH3)@).
7.97–7.93 (m, 4H, Ph), 7.74 (dd, J = 2.2, 7.6 Hz, 1H, qui-
nolyl), 7.62–7.56 (m, 5H, overlapping quinolyl and Ph),
7.51–7.47 (m, 4H, overlapping quinolyl and Ph). 31P NMR
(202.47 MHz, CDCl3, ppm) d: 115.24. Anal. Calcd. for
C21H16Cl2NOPPd: C 49.78, H 3.18, N 2.76; found: C 50.16,
H 3.38, N 2.77.
Complex 2
8-Hydroxyquinoline (0.145 g, 1.00 mmol) was dissolved in
THF (10 mL). Potassium hydride (KH, 0.080 g, 2.00 mmol)
Published by NRC Research Press

Cook et al.
101
Table 3. Suzuki–Miyaura couplings using palladium complexes 1–3.
Entry
1
2
3
4
5
6
7
8
Pd complex
Solvent
1,4-Dioxane
1,4-Dioxane
1,4-Dioxane
Toluene
THF
DMF
DMF
DMF
DMF
Base
K3PO4
R
X
Yield (%)a
77
57
88
65
50
96
47
1
1
1
1
1
1
1
3
1
2
3
1
2
3
1
2
3
CH3O
CH3O
CH3O
CH3O
CH3O
CH3O
NO2
NO2
NO2
NO2
NO2
CH3
CH3
CH3
COCH3
COCH3
COCH3
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
K2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
K2CO3
K2CO3
44
9
97b
92b
88b
Trace
Trace
Trace
5c
10
11
12
13
14
15
16
17
DMF
DMF
DMF
DMF
DMF
Toluene
Toluene
Toluene
61c
60c
Note: Reaction conditions: 1.0 mmol aryl halide, 1.5 mmol phenyl boronic acid, 2.0 mmol base, 1 mol% palladium complex, 3 mL solvent, 100 8C,
18 h.
aGC yields based on aryl halides.
b2 mol% palladium complex used.
c110 8C, 2 h.
31P NMR (202.47 MHz, CDCl3, ppm) d: 162.13. Anal. Calcd.
for C15H20Cl2NOPPd: C 41.07, H 4.60 N 3.19; found: C
41.16, H 4.88, N 3.13.
nonhydrogen atoms were refined anisotropically. Hydrogen
atoms were placed in calculated positions using an appropri-
ate riding model and coupled isotropic temperature factors.
Thermal ellipsoid diagrams (50% probability level) were
produced using Ortep-3 for Windows.23
Complex 3
In a procedure similar to the preparation of 2, complex 3
was obtained as yellow solids. Yield 0.490 g (94%), mp
235 8C (dec). IR (KBr, cm–1) n: 2931 (s), 2850 (m), 1593
(w), 1510 (m), 1465 (w), 1448 (w), 1388 (w), 1311 (w),
1258 (m), 1170 (w), 1101 (m), 1043 (w), 1002 (w), 933
(w), 886 (w), 856 (w), 831 (m), 762 (w), 726 (w), 696 (w),
Suzuki coupling reaction
General procedures for Suzuki reactions: a 20 mL reac-
tion tube was charged with an aryl halide, phenylboronic
acid, the palladium complex, and a base in 3 mL of solvent
under argon and heated to 100 8C for 18 h. The mixture was
then cooled to room temperature. The volatiles were re-
moved under a reduced pressure. The organic product was
extracted with ether and analyzed on an Agilent 6890 GC-
FID instrument. The GC yield was calculated based on un-
reacted aryl halide and calibrated relative to standards con-
taining aryl halide starting material and biphenyl product.
1
571 (w), 560 (w), 531 (w). H NMR (500.13 MHz, CDCl3,
ppm) d: 10.48 (dd, J = 1.5, 5.4 Hz, 1H, quinolyl), 8.44 (dd,
J = 1.4, 8.3 Hz, 1H, quinolyl), 7.72 (dd, J = 1.4, 8.2 Hz, 1H,
quinolyl), 7.64 (t, J = 7.9 Hz, 1H, quinolyl), 7.58–7.55 (m,
2H, quinolyl), 2.69–2.61 (m, 2H, Cy), 1.91–1.72 (m, 12H,
Cy), 1.41–1.25 (m, 6H, Cy). 31P NMR (202.47 MHz,
CDCl3, ppm) d: 155.82. Anal. Calcd. for C21H28Cl2NOPPd:
C 48.62, H 5.44, N 2.70; found: C 48.35, H 5.22, N 2.35.
Results and discussion
Synthesis
X-ray crystallography
The syntheses of 8-quinolylphosphinite ligands and their
palladium complexes were outlined in Scheme 1. Deproto-
nation of 8-hydroxyquinoline with DMAP or potassium hy-
dride, followed by reactions with chlorophosphines, gave the
phosphinites. Due to their air-sensitive nature,21 the phos-
phinites were used directly without further purification to re-
act with bis(benzonitrile)dichloropalladium(II) to afford the
corresponding palladium quinolylphosphinite complexes (1–
3). All the complexes are air stable and can be stored and
handled in air. They were also thermally robust, showing no
Crystals of 1–3 were grown by slow evaporation of solu-
tions in CH2Cl2/hexane at room temperature. Single crystals
were mounted in thin-walled capillaries. The data were col-
lected using the Bruker APEX2 software package22 on a
Siemens diffractometer equipped with an APEXII CCD de-
tector, a graphite monochromator, and MoKa radiation (l =
˚
0.71073 A). A hemisphere of data was collected in 1664
frames with 10 s exposure times. Data processing and ab-
sorption corrections were applied using the APEX2 software
package.22 The structure was solved (direct methods) and all
Published by NRC Research Press

102
Can. J. Chem. Vol. 88, 2010
sign of decomposition under 200 8C in air. They were char-
acterized by 1H and 31P NMR spectroscopy and infrared
(IR) spectroscopy. The solid state structures of the palladium
complexes (1–3) were determined through X-ray diffraction
studies. The elemental analysis results matched well with
the expected values.
and larger steric hindrance, which are beneficial factors for
the Suzuki reactions of more challenging aryl chlorides.25,26
Conclusion
In summary, we have synthesized and characterized three
palladium complexes containing 8-quinolylphosphinite li-
gands. The palladium complexes were easy to synthesize
and stable in air. They were investigated in the Suzuki cou-
pling reaction and showed excellent activity towards a deac-
tivated aryl bromide but lower activity towards aryl
chlorides.
Characterization
1
The H NMR spectra of the three palladium complexes
contained chemical shifts for the quinolyl hydrogen around
10.5 ppm. This reflected a downfield shift of 1.5 ppm from
the signal in the reported free ligands.20,21 Other quinolyl
hydrogens showed smaller shifts. The methyl groups in the
isopropyl moieties in complex 2 became nonequivalent, re-
flecting the restriction of rotation of the isopropyl in the pal-
ladium complexes. The 31P signals ranged from 115 to
162 ppm.
Suitable crystals of 1–3 for X-ray analysis were grown
from slow evaporation of solutions of dichloromethane and
hexane. The molecular structures of the complexes were al-
most identical. A representative structure of 1 is shown in
Fig. 2. The structural data of 2 and 3 were included in the
Supplementary data. Selected bond lengths and angles are
listed in Table 1. Crystal data and structure refinement data
are listed in Table 2. The structure of 1 showed a distorted
square-planar geometry around the palladium ion, which
bonded to the quinolylphosphinite P and N atoms as well as
two Cl atoms. The bond angles of N–Pd–Cl(1) and P–Pd–
Cl(2) are 175.58 and 170.88, respectively. The bond lengths
Supplementary data
Supplementary data for this article are available on the
journal Web site (canjchem.nrc.ca) or may be purchased
from the Depository of Unpublished Data, Document Deliv-
ery, CISTI, National Research Council Canada, Ottawa, ON
K1A 0R6, Canada. DUD 5317. For more information on ob-
taining material, refer to cisti-icist.nrc-cnrc.gc.ca/cms/
unpub_e.shtml. CCDC 743458–743460 contain the X-ray
data in CIF format for seven complexes for this manuscript.
These data can be obtained, free of charge, via www.ccdc.
cam.ac.uk/conts/retrieving.html (or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge
CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.
cam.ac.uk).
Acknowledgements
˚
˚
for Pd–P (2.177 A), Pd–N (2.080 A), and Pd–Cl (2.288 and
˚
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) and the Canada Foundation for
Innovation (CFI) for financial support.
2.381 A) are comparable to the reported values in related di-
tert-butyl quinolylphosphinite palladium complexes.21 The
Pd–Cl(2) distance trans to the phosphorus is slightly longer
than the Pd–Cl(1) distance trans to the nitrogen atom, sug-
gesting a stronger trans effect of the phosphinite donor.
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