New electrochemlcally generated polymeric pd complexes as heterogeneous catalysts for Suzuki cross-coupling reactions

Article abstract of DOI:10.1002/ejoc.200900306

Electrochemically generated films of polymerized (diaminooligothiophene) palladium complexes as heterogeneous catalysts for Suzuki cross-coupling reactions are reported. The electrodeposition of these polymeric species onto porous graphite electrodes allows for easy removal of the organo-metallic species from the reaction mixture and convenient reuse in subsequent (up to 6) reactions.

Full text of DOI:10.1002/ejoc.200900306

FULL PAPER
DOI: 10.1002/ejoc.200900306
New Electrochemically Generated Polymeric Pd Complexes as Heterogeneous
Catalysts for Suzuki Cross-Coupling Reactions
Marco Bandini,*[a] Agostino Pietrangelo,[b] Riccardo Sinisi,[a] Achille Umani-Ronchi,[a] and
Michael O. Wolf[b]
Keywords: Cross-coupling / Electropolymerization / Heterogeneous catalysis / Palladium / Sulfur heterocycles
Electrochemically generated films of polymerized (diamino-
oligothiophene)palladium complexes as heterogeneous cata-
lysts for Suzuki cross-coupling reactions are reported. The
electrodeposition of these polymeric species onto porous
graphite electrodes allows for easy removal of the organo-
metallic species from the reaction mixture and convenient
reuse in subsequent (up to 6) reactions.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
An alternative approach is to covalently anchor the cata-
lytically active species to electrochemically deposited poly-
mer supports.[14] Direct electrodeposition of supported cat-
alysts onto inert electrodes avoids time-consuming
multistep syntheses that are required to introduce anchor-
ing sites and spacers to the molecular skeleton, while pro-
viding a simple means by which the catalyst can be removed
from the reaction system and recycled. Roglans and co-
workers have reported the synthesis and characterization of
modified electrodes prepared by electrodeposition of Pd0
complexes containing polypyrrole ligands.[15] These recover-
able systems were shown to exhibit moderate to good cata-
lytic activity in Suzuki cross-coupling reactions. More re-
cently, the electropolymerization of (thiophene-salen)chro-
mium derivatives afforded recoverable chiral polymers im-
mobilized onto inert surfaces that exhibit moderate
enantioselectivity in hetero-Diels–Alder (HDA) reac-
tions.[16] Thiophene-functionalized bipyridine ligands have
been previously reported as potential precursors to poly-
meric heterogeneous catalysts;[17] however, attempts to elec-
trochemically polymerize and co-polymerize these mono-
mers were unsuccessful.
In a recent communication, we described the synthesis
and characterization of a Pd-containing polythiophene
(poly-1, Figure 1)[18] obtained by electrochemically poly-
merizing the cationic complex 1 comprised of a chiral di-
amino ligand (DAT3) with linearly tethered terthienyl
groups.[19] These electrochemically modified electrodes
proved to be efficient catalysts for several intra- and inter-
molecular C–C cross-coupling reactions such as the Su-
zuki–Miyaura,[20a] Mizoroki-Heck,[20b] and Sonogashira[20c]
transformations with iodoarenes. Moreover, negligible Pd
leaching and no overall loss of polymer from the support
was observed after the reactions suggesting that the cataly-
sis was authentically heterogeneous.
Introduction
Green chemical processes will play a critical role in im-
proving the quality of life in an environmentally sustainable
fashion.[1] In the fine-chemical and pharmaceutical indus-
tries, homogeneous Pd-mediated cross-coupling reactions[2]
are widely employed[3] in the production of functionalized
oligoarenes, resulting in improved reaction yields, selectiv-
ity, turnover numbers (TON), and turnover frequencies
(TOF).[4] Immobilization of these catalysts onto solid inert
supports is a green alternative to homogeneous systems as
it enables the facile removal of the catalytically active spe-
cies from the reaction solution, thus avoiding time-consum-
ing and expensive workup processes that require additional
separation steps and larger volumes of hazardous materi-
als.[5,6]
To date, two main strategies have been used to immobi-
lize catalysts onto inert matrices, namely, (i) binding palla-
dium centres by van der Waals interactions to solid sup-
ports such as charcoal,[7] metal oxides,[8] zeolites/molecular
sieves,[9] organic polymers[10] or polymer capsules;[11] or (ii)
covalently binding palladium complexes to solid supports
such as silica[12] or organic polymers.[13] Unfortunately, cat-
alyst poisoning, limited accessibility to sterically encum-
bered active sites, and poor anchoring linkages are draw-
backs that prevent these heterogeneous catalytic systems
from being widely used on industrial scales.
[a] Dipartimento di Chimica “G. Ciamician”, Alma Mater Stu-
diorum – Università degli Studi di Bologna,
Via Selmi 2, 40126 Bologna, Italy
Fax: +39-051-2099456
E-mail: marco.bandini@unibo.it
[b] Department of Chemistry, University of British Columbia,
Vancouver, BC, V6T 1Z1, Canada
Fax: +1-604-822-2847
E-mail: mwolf@chem.ubc.ca
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900306.
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Polymeric Pd Complexes as Heterogeneous Catalysts
Figure 1. Synthesis of Pd-containing thiophene polymers by elec-
trochemical deposition of monomers 1a,b on graphite.
Results and Discussion
Synthesis of (Diamino-oligothiophene)Pd Complexes
Here, we expand our investigations to include two novel
conjugated polymers that possess the same catalytically
active Pd site as poly-1 but differ in the connectivity to the
polythiophene backbone. Due to the location of the di-
amino ligand site in 1, the conjugation pathway in poly-1
is short (a maximum of six rings if α–α coupling occurs
exclusively).
The new monomers investigated here have been designed
to afford polymers with larger conjugation lengths due to
the availability of both α-positions on the thiophene oligo-
meric moieties. Our objective here was to develop and inves-
tigate the electrochemical polymerizability and catalytic
performance of these new catalyst architectures. In the
novel C1-symmetric monomer 2, a terthienyl group is
tethered to the catalytically active (DAT2)Pd(allyl) complex
through an extended organic linker. Relative to 1a and 1b,
this Pd complex is anchored some distance from the oligo-
thiophene moiety rendering the catalytically active species
isolated from and sterically less confined by the polymer
chain. To prevent electrochemical coupling of the bithienyl
moiety and to improve the monomer solubility, a hexyl sub-
stituent on the αЈ position was used as an end-capping
group.
Monomer 2 was prepared according to a convergent syn-
thetic approach. The condensation of 1,2-cyclohexanedi-
amine hydrochloride (R,R)-4 with 5a[21] followed by a sec-
ond condensation with 5b[22] in the presence of TEA af-
forded diimine 7 (Scheme 1). The desired C1-symmetric
(R,R)-8 was prepared by the reduction of 7 with NaBH4 in
methanol and isolated with an overall yield of 29% after
purification by flash chromatography.
Scheme 1. Synthesis of the C1-symmetric ligand 8.
Compound 11 was prepared in 92% yield by the conden-
sation of 6-bromohexanoyl chloride (10) with the readily
available primary alcohol 9[23] (Scheme 2).
The cationic (DAT3b)Pd(allyl) complex 3 was designed
to evaluate the catalytic performance of an electrochemi-
cally generated cross-linked π-conjugated metal polymer
(poly-3) whereby both α positions on each terthienyl moiety
are available for polymerization. Cyclic voltammetry studies
on 2 and 3 and the catalytic efficiency of the subsequent
Scheme 2. Synthesis of ester 11.
Finally, the reaction of 11 with 8 under basic conditions
polymers in promoting Suzuki reactions with bromoarenes (Cs2CO3, DMF, 50 °C, 16 h) afforded 12 in 75% yield. Sub-
are reported.
sequent treatment of 12 with [Pd(η3-C3H5)Cl]2 followed by
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M. Bandini, A. Pietrangelo, R. Sinisi, A. Umani-Ronchi, M. O. Wolf
The cyclic voltammogram (CV) of a typical electrochem-
FULL PAPER
anion metathesis with NH4PF6 gave the Pd complex 2 as
an air-stable pale brown solid in high yield (98%, ical polymerization of 1a is shown in Figure 2a. The first
Scheme 3).
scan is characterized by the onset of monomer oxidation at
0.92 V reaching a maximum at +1.08 V. This is followed by
an associated weak reduction wave at +0.95 V on the return
sweep. Repeated cycling gave rise to a second broad redox
wave at lower potentials that is attributed to the elec-
trodeposited polymer. The CV trace of 3 (Figure 2c) is ne-
arly identical apart from the distinct shift in monomer oxi-
dation to higher potential, a feature that may be a conse-
quence of the connectivity between the Pd complex and the
oligothiophene units (i.e., α-connectivity vs. β-connectivity).
The UV/Vis spectrum of poly-3 grown on an ITO on glass
substrate (see Supporting Information) has a broad absorp-
tion band with a maximum at ca. 400 nm, 61 nm redshifted
from that of monomer 3.
Scheme 3. Synthesis of Pd complex 2.
Ligand 14 (DAT3b) was prepared by reductive amination
between (R,R)-1,2-cyclohexanediamine (R,R)-DACH and
(2,2Ј:5Ј,2ЈЈ-terthiophene)-3Ј-carboxaldehyde (13). Accord-
ing to an approach analogous to that used for the prepara-
tion of monomer 2, the corresponding monomer 3 was iso-
lated in 95% yield as an air-stable pale yellow solid
1
(Scheme 4). H NMR spectroscopy (CDCl3, room temp.)
was used to investigate the behaviour of 3 in solution. As
was the case for complex 1a, complex 3 exists in solution
as a mixture of three isomers in a ratio of ca. 1.15:1.92:1 (as
indicated by the three distinct sets of allylic proton signals),
suggesting the presence of dl and meso isomers that arise
from the amino stereocenters.[24]
Figure 2. Synthesis of Pd-containing thiophene polymers by elec-
trochemical deposition of (a) 1a, (b) 2 and (c) 3 on graphite.
The CV trace of 2 (Figure 2b) exhibits similar features to
that of 1a and 3; however, redox wave growth appeared to
plateau after only a few cycles during which time the solu-
tion turned green. Upon further inspection, it became ap-
parent that there was very little film growth on the surface
of the Pt disc working electrode. Multiple attempts with
different working electrodes (i.e., ITO on glass, Toray car-
bon paper) and higher monomer concentrations (i.e.,
0.2 m) yielded similar results, suggesting that either (1)
oxidative coupling is sluggish on the CV time scale, (2) the
polymer is soluble such that deposition does not occur, or
(3) the polymer does not adhere to the working electrode.
The UV/Vis absorption spectrum of poly-2 grown on an
ITO (see Supporting Information) has bands at 414 and
315 nm, the latter being consistent with those of monomer
2 (λmax = 317 nm) and terthiophene (λmax = 355 nm).[25]
Scheme 4. Synthesis of DAT3b 14 and the corresponding cationic
Pd complex 3.
Electropolymerization of (Diamino-oligothiophene)Pd
Complexes
Monomers 2 and 3 were oxidatively polymerized by
sweeping the working electrode for a total of 10 cycles be-
tween 0 and +1 V vs. SCE (for 2) and 0 to +1.7 V vs. SCE
(for 3). These experiments were carried out in CH2Cl2 solu-
Suzuki Cross-Coupling Catalyzed by Electrodeposited Pd-
Containing Polymers
The catalytic performances of monomeric precursors 2
tions containing 1 m of monomer and 0.1  [nBu4N]PF6 and 3 were investigated (loading 0.16 mol-%)[26] by selecting
in sealed glass three-electrode electrochemical cells.
4-bromobenzonitrile (14a) and PhB(OH)2 (15a) as the
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Polymeric Pd Complexes as Heterogeneous Catalysts
model reaction partners. The cross-coupling reactions were
carried out in a toluene/MeOH (3:1) mixture, in the pres-
ence of K2CO3 (2 equiv.), whereas the kinetic profiles were
obtained by gas chromatography by periodically with-
drawing aliquots from the reaction mixtures for analysis.
The corresponding curves are reported in Figure 3.
Figure 4. Reaction profiles of the model Suzuki cross-coupling cat-
alyzed by poly-2-graphite and poly-3-graphite/ITO. Reaction-rate
profiles were obtained by GC analysis of aliquots of the solution.
Secondly, the graphite-based catalysts showed an initial
induction time (30–45 min) that is absent in the profile of
poly-3-ITO catalyst. The lag phase observed for the reac-
tions with poly-2 or poly-3 on graphite may be related to
different rates of adsorption/diffusion of the reagents on the
supports. It is possible that during the lag phase recorded
for poly-2/3-graphite, the product is forming but retained
Figure 3. Reaction profiles of the model Suzuki cross-coupling cat-
alyzed by 2 and 3.
Pd complexes 2 and 3 were found to promote their re- on the porous support.
spective cross-coupling reactions efficiently with compar-
Thirdly, after the induction stage, poly-3-graphite pro-
able initial reaction rates; however, using complex 2 led moted the Suzuki cross-coupling to a greater extent with
to nearly complete conversion (Ͼ 98%) in a shorter reac- respect to poly-2-graphite and poly-3-ITO, leading to quan-
tion time (2.5 h vs. 7 h). This behaviour is consistent with titative coupling after 13 h. This trend is in contrast to the
previous experimental evidence on the stabilization/acti- relative performance of the monomeric species 2 and 3 (Fig-
vation effect of ancillary “non-innocent”[27] thienyl ligands ure 3). A possible explanation could be related to the evi-
in Pd-catalyzed transformations.[18,28]
dence that monomer 3 affords much better films than
In fact, hemilabile interactions of the terthienyl group monomer 2, hence there may be more catalytically active
with the metal center cannot be ruled out during the course sites in the poly-3 film resulting in higher conversion, which
of the reaction. For heterogeneous catalytic studies, com- is what is observed in Figure 4.
plexes 2 and 3 were electrochemically polymerized on car-
The scope of the heterogeneous catalyst poly-3-graphite
bon paper (Toray TGP-H-030) and ITO (indium tin oxide) was assessed by screening a range of reagent combinations
on glass electrodes. In order to assess the reactivity of poly- (Table 1). Tolerance towards many functional groups was
2-graphite, poly-3-ITO and poly-3-graphite as hetero- observed (i.e. alkyl, aryl, ketones, cyano, and alkoxy
geneous catalysts for Suzuki cross-coupling reactions, the groups). Excellent results in terms of conversion were ob-
experiments were run in the presence of the modified elec- tained with a variety of functionalized bromo- and iodoar-
trode with no stirring to avoid breaking of the inert support enes. For instance, 1,4-diiodobenzene (14d) underwent two
(carbon paper).
carbon–carbon coupling processes in good conversion (En-
The reaction profiles for the catalytic coupling reactions try 8). Moreover, the sterically congested o-tolylboronic
of 4-bromobenzonitrile and 15a by using the heterogeneous acid (15d) led to the corresponding adduct 16cd in reason-
catalysts are shown in Figure 4. The heterogeneous catalysts able conversion (50%, Entry 7) as a racemic mixture.
poly-2 and poly-3 require longer reaction times (13–24 h)
By using the same poly-3-graphite electrode in the model
relative to the corresponding homogeneous catalysts for 14a/15a cross-coupling reactions, six consecutive Suzuki re-
comparable conversion. The longer reaction times for the actions were carried out with conversions of 90–98% in
heterogeneous catalyst may be due to either the hetero- each case, demonstrating the reusability of the catalytic spe-
geneity of the system or to differences in the amount of cies (Figure 5).
catalyst present. As it is very difficult to accurately deter-
Several practical advantages of the use of these catalyst-
mine the amount of polymer on the electrode surface, it is modified surfaces can be highlighted. This type of engine-
not possible to directly compare the reactions with an iden- ered catalyst system allows for easy removal of the pro-
tical catalyst loading (by weight).
moter after each run without any appreciable contami-
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M. Bandini, A. Pietrangelo, R. Sinisi, A. Umani-Ronchi, M. O. Wolf
FULL PAPER
Table 1. Use of poly-3-graphite in the heterogeneous catalysis of
the Suzuki reaction.
Figure 5. Recovery and reusability of poly-3-graphite in model Su-
zuki reaction (14/15a).
same reaction by the addition of a second batch of reagents.
In this case, no appreciable formation of 16aa was observed
after 48 h. This demonstrates that the catalytic activity re-
quires the presence of the polymeric matrix, and no appreci-
able activity results from leaching from the films. A control
experiment with the unmodified electrode (80 °C, 40 h,
trace conversion) shows that the support does not partici-
pate in the catalysis.
Conclusions
We have presented a new class of electrochemically modi-
fied electrodes with (diamino-oligothienyl)palladium com-
plexes. The poly-3-graphite system proved to be efficient in
promoting the Suzuki reaction with bromoarenes. Advan-
tages of this approach include the ease of preparation of
the catalyst films by using electrochemical deposition and
the ease of recycling of the electrodes. This points to new
opportunities for carbon–carbon forming processes by
using heterogeneous, electrodeposited catalyst films.
Experimental Section
General Methods: All reagents were purchased from Aldrich Inc.
and used without further purification. All reactions were carried
out under anhydrous conditions unless otherwise specified. GC-
MS data was recorded by EI ionization at 70 eV with a Hewlett–
Packard 5971 instrument equipped with GC injection. LC electro-
spray ionization mass spectra were obtained with an Agilent Tech-
nologies MSD1100 single-quadrupole mass spectrometer. 1H NMR
spectra were recorded with either a Varian 200 (200 MHz) or Var-
ian 300 (300 MHz) spectrometer. Chemical shifts are reported in
ppm with respect to tetramethylsilane (TMS). Solution electronic
absorption spectra were obtained with a Varian Cary 5000 UV/
Vis/NIR spectrophotometer in dichloromethane (CH2Cl2), whereas
solid-state spectra were acquired from polymeric films grown on
an indium tin oxide (ITO) layer on glass. Fluorescence data was
obtained with a Photon Technology International QuantaMaster
fluorimeter. CH2Cl2 used for electrochemistry experiments was
purified by passing the solvent through an activated alumina tower.
[a] All the reactions were carried out in reagent grade solvent at
reflux for 16 h, unless otherwise specified. [b] Reaction time 48 h.
nation of the reaction product. Moreover, simple washing
of the supported catalyst with MeOH while sonicating for
30 min at room temp., followed by drying under vacuum
restores the initial catalytic performance.
In order to ascertain whether the catalysis is authenti-
cally heterogeneous, an aliquot (50 µL) from the Suzuki re-
Electrochemistry: Cyclic voltammetry experiments were carried out
action (14a/15a) run to completion was subjected to the with an Autolab potentiostat. The working electrode was either a
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Polymeric Pd Complexes as Heterogeneous Catalysts
Pt disk, an indium tin oxide (ITO) thin film on glass, or Toray
carbon paper (TGP-H-030). The counter electrode was a Pt mesh
and the reference electrode a silver wire. An internal reference, de-
camethylferrocene, was added to correct the measured potentials
with respect to saturated calomel electrode (SCE). [nBu4N]PF6 was
used as a supporting electrolyte and was purified by triple
recrystallization from ethanol and dried at 90 °C under vacuum for
3 d. All experiments were carried out in 1 m CH2Cl2 solutions of
monomer (0.1  electrolyte) in sealed glass three-electrode electro-
chemical cells at a scan rate of 100 mV/s. All monomers were oxi-
datively polymerized by sweeping the working electrode between
0 V and the onset of current for a total of 10 cycles.
116.4(C-Ar), 120.8 (C-Ar), 122.3(C-Ar), 123.0 (C-Ar), 124.6 (C-
Ar), 125.4 (C-Ar), 125.9 (C-Ar), 126.9 (C-Ar), 134.8 (C-Ar), 134.9
(C-Ar), 136.9 (C-Ar), 137.1 (C-Ar), 141.4 (C-Ar), 141.5 (C-Ar),
142.4 (C-Ar), 144.1 (C-Ar), 144.9 (C-Ar) ppm. C32H40N2OS3
(564.23): calcd. C 68.04, H 7.14, N 4.96; found C 67.99, H 7.10, N
4.85.
Synthesis of 11: To a solution of 9[23] (2.08 mmol, 578 mg) and TEA
(4.16 mmol, 578 µL) in CH2Cl2, 6-bromohexanoyl chloride
(2.28 mmol, 340 µL) was added dropwise at 0 °C. The mixture was
stirred for 24 h. The solvent was removed under reduced pressure
and the crude mixture purified by flash chromatography with cy-
clohexane/AcOEt (9:1) as the eluent. The product was isolated as
1
a yellow oil (865 mg, 92% yield). H NMR (300 MHz, CDCl3): δ
Synthesis of 8: In a 50 mL two-necked flask, the ammonium salt 4
(1 mmol, 150 mg) and 5Ј-n-hexyl-2,2Ј-bithienyl-5-carbaldehyde
(1 mmol, 278 mg) were dissolved in EtOH/MeOH (1:1) (20 mL).
The reaction mixture was stirred at room temperature for 24 h and
the solvent removed under reduced pressure to leave the crude im-
ine salt 6 as a brown solid. The solid was washed with Et2O
(3ϫ10 mL), and collected by filtration. The crude product (chemi-
cal purity Ͼ 95% by HPLC and NMR) was used in the next step
without further purification. 1H NMR (200 MHz, DMSO): δ =
0.85 (br., 3 H, CH3), 1.27 (br., 8 H, CH2), 1.61–1.85 (m, 6 H, CH2),
2.07 (br., 2 H, CH2), 2.78 (br., 2 H, CH2), 3.03 (br., 1 H, CH), 3.23
(br., 1 H, CH), 3.37 (br., 3 H, NH3), 6.84 (br. s, 1 H, Ar-H), 7.23
(s, 2 H, Ar-H), 7.43 (br. s, 1 H, Ar-H), 8.47 (br., 4 H, Ar-H) ppm.
13C NMR (50 MHz, DMSO): δ = 14.7 (CH3), 22.8 (CH2), 23.6
(CH2), 24.3 (CH2), 28.8 (CH2), 29.6 (CH2), 30.1 (CH2), 31.7 (CH2),
31.8 (CH2), 33.5 (CH2), 52.1 (CHN), 70.4 (CHNH3+), 124.0 (C-
Ar), 125.7 (C-Ar), 126.6 (C-Ar), 133.8 (C-Ar), 134.4 (C-Ar), 140.8
= 1.43–1.57 (m, 2 H, CH2), 1.65–1.75 (m, 2 H, CH2), 1.83–1.93
(m, 2 H, CH2), 2.41 (t, J = 7.5 Hz, 2 H, CH2CO), 3.40 (t, J =
6.9 Hz, 2 H, CH2Br), 5.16 (s, 2 H, CH2OCO), 7.03 (dd, J = 3.6,
5.1 Hz, 1 H, Ar-H), 7.10 (dd, J = 3.6, 5.1 Hz, 1 H, Ar-H), 7.19–
7.21 (m, 3 H, Ar-H), 7.25 (dd, J = 1.2, 5.1 Hz, 1 H, Ar-H), 7.37
(dd, J = 1.2, 5.1 Hz, 1 H, Ar-H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 23.9 (CH2), 27.5 (CH2), 32.2 (CH2), 33.4 (CH2), 33.9 (CH2Br),
59.8 (CH2O), 123.9 (C-Ar), 124.8 (C-Ar), 126.3 (C-Ar), 126.4 (C-
Ar), 126.7 (C-Ar), 127.8 (C-Ar), 127.8 (C-Ar), 132.8 (C-Ar), 134.1
(C-Ar), 134.2 (C-Ar), 135.8 (C-Ar), 136.4 (C-Ar), 173.0 (CO) ppm.
IR (neat): ν = 3104, 2938, 2863, 1731, 1461, 1415, 1371, 1349, 1246,
˜
1159, 1078, 1047, 957, 882, 696, 637 cm–1. ESI-MS: m/z = 478 [M
+ Na]. C19H19BrO2S3 (453.97): calcd. C 50.10, H 4.20; found C
50.01, H 4.15.
Synthesis of 12: To a solution of 11 (0.2 mmol, 93 mg) in dry THF/
DMF (7.0:0.7 mL) stirred under nitrogen, cesium carbonate
(0.41 mmol, 134 mg) and 8 (0.20 mmol, 116 mg) were added. The
mixture was heated to reflux for 24 h. The reaction mixture was
cooled to room temperature and then quenched with water (3 mL).
The aqueous layer was extracted with CH2Cl2 (3ϫ10 mL). Evapo-
ration of the volatiles afforded a crude product that was purified
by flash chromatography with CH2Cl2/MeOH (98:2 Ǟ 95:5). The
product was isolated as a yellow oil (158 mg, 75% yield). 1H NMR
(200 MHz, CDCl3): δ = 0.89 (t, J = 5.8 Hz, 3 H CH3), 1.32 (br., 8
H, CH2), 1.52–1.84 (m, 10 H, CH2), 2.18 (br., 4 H), 2.32–2.36 (m,
2 H, CHNH), 2.44 (t, J = 7.4 Hz, 2 H, CH2CO), 2.76 (t, J = 7.6 Hz,
2 H, NH), 3.87 (dd, J = 5.6, 14.2 Hz, 2 H, 2 CHNH), 3.94 (t, J =
6.2 Hz, 2 H, CH2O), 4.09 (dd, J = 5.6, 14.2 Hz, 2 H, 2 CHNH),
5.17 (s, 2 H, CH2OCO), 6.61 (dd, J = 3.6 Hz, 1 H, Ar-H), 6.82 (dd,
J = 3.6, 12.4 Hz, 4 H, Ar-H), 6.90 (t, J = 3.4 Hz, 2 H, Ar-H), 7.00–
7.03 (m, 2 H, Ar-H), 7.09 (dd, J = 3.6, 3.8 Hz, 1 H, Ar-H), 7.17–
7.23 (m, 4 H, Ar-H), 7.35 (d, J = 4.8 Hz, 1 H, Ar-H), 7.46 (d, J =
8.8 Hz, 2 H, Ar-H) ppm. 13C NMR (50 MHz, CDCl3): δ = 14.0
(CH3), 22.5 (CH2), 24.7 (CH2), 24.8 (CH2), 25.6 (CH2), 28.7 (CH2),
28.9 (CH2), 29.7 (CH2), 30.1 (CH2), 31.1 (CH2), 31.2 (CH2), 31.5
(CH2), 34.1 (CH2), 45.4 (CH2), 59.9 CHN, 2 C, (), 60.1 (CH2N),
60.2 (CH2N), 67.6 (CH2O), 77.2 (CH2O), 114.7 (2 C, C-Ar), 121.3
(C-Ar), 122.3 (C-Ar), 122.9 (C-Ar), 124.0 (C-Ar), 124.6 (C-Ar),
124.8 (C-Ar), 125.2 (C-Ar), 125.7 (C-Ar), 126.3 (C-Ar), 126.5 (C-
Ar), 126.7 (C-Ar), 126.8 (2 C, C-Ar), 127.3 (C-Ar), 127.8 (C-Ar),
127.9 (C-Ar), 132.9 (C-Ar), 134.1 (C-Ar), 134.3 (C-Ar), 135.0 (C-
Ar), 135.9 (C-Ar), 136.5 (C-Ar), 136.9 (C-Ar), 142.6 (C-Ar), 142.9
(C-Ar), 143.3 (C-Ar), 144.9 (C-Ar), 158.4 (C-Ar), 173.3 (CO) ppm.
(C-Ar), 140.9 (C-Ar), 146.8 (C-Ar), 156 (C=N) ppm. IR (neat): ν
˜
= 3423, 2088, 1643, 1444, 1091 cm–1. ESI-MS: m/z = 373 [M –
HCl]. Compound 6 (1 mmol, 410 mg) was dissolved in anhydrous
CH2Cl2 (15 mL) followed by the addition of TEA (2 mmol,
278 µL), aldehyde 5b (1 mmol, 204 mg) and MgSO4 (3 mmol,
360 mg). The mixture was stirred at room temperature for 24 h.
After removal of the CH2Cl2 under reduced pressure, the crude
product was triturated with Et2O and the liquid removed under
reduced pressure. The crude product 7 was isolated as a yellow
solid and used in the next step without further purification. 1H
NMR (200 MHz, CDCl3): δ = 0.89 (br., 3 H, CH3), 1.26–1.45 (m,
5 H, CH2), 1.66 (br., 2 H, CH2), 1.86 (br., 2 H, CH2), 2.78 (t, J =
7.2 Hz, 2 H, CH2), 3.10–3.15 (m, 2 H, CH-N), 6.67 (br., 2 H, Ar-
H), 6.83–7.02 (m, 8 H, Ar-H), 8.18 (s, 1 H, N=CH), 8.24 (s, 1 H,
N=CH) ppm; OH signal not observed. ESI-MS: m/z = 561 [M +
H]. Compound 7 (1 mmol, 596 mg) was dissolved in MeOH
(15 mL) followed by the dropwise addition of NaBH4 (7 mmol,
266 mg) at 0 °C. The ice bath was then removed and the mixture
stirred at room temperature overnight. Water (8 mL) was added to
quench the reaction and the product extracted with CH2Cl2
(3ϫ10 mL). Removal of any volatile compounds by evaporation
afforded a crude product that was purified by flash chromatog-
raphy with CH2Cl2/MeOH (99:1) as the eluent. Product 8 was iso-
lated as a pale yellow solid (158 mg, 29% overall yield for three
steps from 4). 1H NMR (300 MHz, CDCl3): δ = 0.89 (br., 4 H,
CH3, CH), 1.31 (br., 8 H, CH2), 1.65 (br., 2 H, CH2), 1.80 (br., 2
H, CH2), 2.19–2.38 (m, 2 H, CH2), 2.49 (br., 2 H, CH2), 2.75 (br.,
3 H, CH2, CH), 3.84 (d, J = 14.4 Hz, 2 H, 2 CHNH), 4.08 (d, J =
14.4 Hz, 2 H, 2 CHNH), 6.61–6.90 (m, 6 H, Ar-H), 7.27 (br., 4 H,
IR (neat): ν = 3423, 2924, 2853, 1727, 1640, 1547, 1512, 1461, 1377,
˜
1261, 1117, 1073, 794, 697 cm–1. ESI-MS: m/z = 940 [M + 1].
C50H56N2O3S6 (924.26): calcd. C 64.90, H 6.10, N 3.03; found C
64.85, H 6.01, N 2.95.
Ar-H) ppm; OH and NH signals not observed. IR (neat): ν = 3410,
˜
2926, 2853, 1693, 1667, 1608, 1453, 1270, 1202, 1173, 1132,
794 cm–1. 13C NMR (75 MHz, CDCl3): δ = 14.0 (CH3), 22.5 (CH2),
24.7 (2 C, CH2), 28.7 (2 C, CH2), 30.1 (2 C, CH2), 30.9 (CH2), Synthesis of [12-(Pdallyl)PF6] Complex (2): In a Schlenk flask,
31.5(CH2), 45.1 (2 C, CHN), 59.9 (2 C, CH2N), 116.0 (C-Ar), flame-dried and flushed with nitrogen, 12 (0.03 mmol, 28 mg) was
Eur. J. Org. Chem. 2009, 3554–3561
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3559

M. Bandini, A. Pietrangelo, R. Sinisi, A. Umani-Ronchi, M. O. Wolf
dissolved in THF/CH2Cl2 (1:1) (3.6 mL). [Pd(η3-C3H5)Cl]2 (634.07): calcd. C 60.53, H 4.76, N 4.41; found C 60.45, H 4.68, N
FULL PAPER
(0.015 mmol, 5.5 mg) was added and the mixture stirred at room
temperature for 4 h. NH4PF6 (0.03 mmol, 4.9 mg) was added and
the mixture stirred in the dark overnight. The mixture was then
filtered and the solvent removed under reduced pressure. The prod-
uct was dried under vacuum. The residue was washed with Et2O
(5 mL) and the desired Pd complex recovered as an air-stable dark
4.35.
Synthesis of [14-(Pdallyl)BF4] (3): In a flame-dried Schlenk tube
flushed with N2, 14 (0.08 mmol, 50 mg) was dissolved in THF/
CH2Cl2 (6:1) (7 mL). [Pd(η3-C3H5)Cl]2 (0.04 mmol, 14 mg) was
added and the mixture stirred at room temperature for 4 h. Silver
tetrafluoroborate (AgBF4, 0.08 mmol, 15.6 mg) was added to the
reaction mixture and stirred in the absence of light overnight. The
mixture was filtered and the solvent removed under reduced pres-
sure. The resulting product was dried under vacuum. The residue
was washed with Et2O (5 mL) and the desired Pd complex isolated
as a yellow solid by filtration (61 mg, yield 95%). 1H NMR
(300 MHz, CDCl3, fluxional, mixture of three isomers): diagnostic
signals: (a) δ = 5.60–5.70 (m, 1 H, allyl-CH), 4.24 (d, J = 6.3 Hz,
2 H, allyl-CH), 3.21 (d, J = 11.7 Hz, 2 H, allyl-CH) ppm; (b) 5.12–
5.35 (m, 1 H, allyl-CH), 3.67 (d, J = 9.0 1 H, allyl-CH), 3.52 (br.,
1 H, allyl-CH); c) 4.80–4.95 (m, 1 H, allyl-CH), 3.30 (d, J = 6.9 Hz,
1 H, allyl-CH), 3.02 (d, J = 13.6 Hz, 1 H, allyl-CH), 2.86 (d, J =
6.9 Hz, 1 H, allyl-CH), 2.60 (d, J = 13.6 Hz, 1 H, allyl-CH) ppm.
1
yellow solid by filtration (40 mg, yield 98%). H NMR (300 MHz,
CDCl3, fluxional, mixture of three isomers): diagnostic signals: (a)
δ = 5.78–5.58 (m, 1 H, allyl-CH), 3.74 (br., 2 H, allyl-CH), 3.40–
3.35 (m, 1 H, allyl-CH), 3.04 (d, J = 12.0 Hz, 1 H, allyl-CH) ppm;
(b) 5.48–5.38 (m, 1 H, allyl-CH), 4.12 (br., 2 H, allyl-CH), 3.04 (d,
J = 12.0 Hz, 1 H, allyl-CH) ppm; (c) 5.17 (br., 1 H, allyl-CH), 2.91
(d, J = 13.2 Hz, 1 H, allyl-CH), 2.79 (br., 2 H, allyl-CH) ppm. 13C
NMR (75 MHz, CDCl3): diagnostic signals: δ = 14.0 (CH3), 15.2
(CH2), 22.5 (CH2), 23.7 (CH2), 24.6 (CH2), 25.6 (CH2), 26.8 (CH2),
28.8 (CH2), 29.6 (CH2), 30.1 (CH2), 31.5 (CH2), 34.1 (CH2), 38.7
(CH2), 59.9 (2 C, CHN), 65.8 (2 C, CH2N), 67.7 (CH2O), 77.1
(CH2O), 114.9 (C-Ar), 124.0 (C-Ar), 124.8 (C-Ar), 126.3 (C-Ar),
126.5 (C-Ar), 126.7 (C-Ar), 127.8 (C-Ar), 132.9 (C-Ar), 135.9 (C-
Ar), 136.5 (C-Ar), 173.3 (CO). UV/Vis (CH2Cl2): λmax (ε) = 317 nm
ESI-MS: m/z
=
783 [Pd(η3-C3H5)(14)]+. C35H35BF4N2PdS6
(868.02): calcd. C 48.36, H 4.06, N 3.22; found C 48.28, H 4.00, N
3.45.
(35000 Lmol–1 cm–1). IR (neat): ν = 2932, 2857, 1729, 1608, 1511,
˜
1432, 1251, 1179, 1166, 1024, 829, 699, 559 cm–1.
C54H63F6N2O3PPdS6 (1230.18): calcd. C 52.65, H 5.15, N 2.27;
found C 52.30, H 5.25, N 2.21.
Supporting Information (see footnote on the first page of this arti-
cle): Typical experimental procedure for the Suzuki reaction, ana-
lytical characterization of biaryls 16 [Table 1 (SI)] and photophysi-
cal characterization of 2/poly-2 and 3/poly-3 [Figures 1 and 2 (SI)].
Synthesis of N,NЈ-Bis[(2,2Ј:5Ј,2ЈЈ-terthiophen-3Ј-yl)methyl]cyclohex-
ane-1,2-diamine (14): In a 25 mL two-necked flask, 2,2Ј:5Ј,2ЈЈ-ter-
thiophene-3Ј-carbaldehyde (13) (0.47 mmol, 130 mg) and (1R,2R)-
diaminocyclohexane (DACH, 0.23 mmol, 27 mg) were dissolved in
dry CH2Cl2 (8 mL) under N2. Magnesium sulfate (MgSO4,
1.18 mmol, 142 mg) was added and the mixture stirred at room
temperature for 48 h. The crude reaction mixture was filtered and
the solvent evaporated under reduced pressure to afford 116 mg of
the intermediate imine (DIT3b) as a yellow oil (purity Ͼ 90% by
1H NMR). The crude product was used without further purifica-
Acknowledgments
This work was supported by M. I. U. R. (Rome), the University of
Bologna and the Natural Sciences and Engineering Research
Council of Canada. We thank also Pasquale Olivelli (University
of Bologna) for part of the Experimental Section. Thanks also to
Fondazione del Monte di Bologna e Ravenna for financial support.
1
tion. H NMR (200 MHz, CDCl3): δ = 1.38–1.65 (m, 2 H, CH2),
1.67–1.75 (m, 2 H, CH2), 1.88 (br., 4 H, CH2), 3.27–3.41 (m, 2 H,
CH=N), 6.90 (q, J = 3.0 Hz, 4 H, Ar-H), 7.02 (dd, J = 3.6, 3.8 Hz,
2 H, Ar-H), 7.17–7.27 (m, 6 H, Ar-H), 7.58 (s, 2 H, Ar-H), 8.30 (s,
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˜
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Received: March 21, 2009
Published Online: June 16, 2009
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