New pyridine ONN-pincer gold and palladium complexes: Synthesis, characterization and catalysis in hydrogenation, hydrosilylation and C-C cross-coupling reactions

Article abstract of DOI:10.1002/adsc.200700209

The ONN-tridentate unsymmetrical pincer 2-[6-(pyrrolidin-1-ylmethyl) pyridin-2-yl]phenol and N-terf-butyl-1-{[6-(2-hydroxyphenyl)pyridin-2-yi] metriyl}pyrrolidine-2-carboxamide ligands were synthesized by an easy method in high purity and good yields. All the organic compounds were characterized by elemental analysis, mass spectrometry, IR and ¹H and ¹³C NMR spectroscopy. Palladium(II) and gold(III) complexes have been prepared as air-stable solids, with the ONN-tridentate ligand after deprotonation of the hydroxy group, the coordination of the metal ion is completely stereospecific and gives rise to only one diastereoisomer. These complexes were shown to be very active catalysts in the hydrogenation (80 % ee was achieved with the chiral gold complex), hydrosilylation and C-C coupling, Suzuki and Heck, reactions, under mild conditions.

Full text of DOI:10.1002/adsc.200700209

FULL PAPERS
DOI: 10.1002/adsc.200700209
New Pyridine ONN-Pincer Gold and Palladium Complexes:
Synthesis, Characterization and Catalysis in Hydrogenation,
À
Hydrosilylation and C C Cross-Coupling Reactions
N. Debono,a M. Iglesias,b,* and F. Sµncheza,*
a
Instituto de Química Orgµnica General, CSIC, C/Juan de la Cierva, 3, 28006 Madrid, Spain
Fax : (+34)-91-564-4872; e-mail: felix-iqo@iqog.csic.es
Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco, 28049 Madrid, Spain
b
Fax: (34)-91-372-0623; e-mail: marta.iglesias@icmm.csic.es
Received: April 24, 2007; Revised: July 25, 2007
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: The ONN-tridentate unsymmetrical pincer deprotonation of the hydroxy group, the coordina-
2-[6-(pyrrolidin-1-ylmethyl)pyridin-2-yl]phenol and tion of the metal ion is completely stereospecific and
N-tert-butyl-1-{[6-(2-hydroxyphenyl)pyridin-2-yl]meth- gives rise to only one diastereoisomer. These com-
yl}pyrrolidine-2-carboxamide ligands were synthe- plexes were shown to be very active catalysts in the
sized by an easy method in high purity and good hydrogenation (80% ee was achieved with the chiral
À
yields. All the organic compounds were character- gold complex), hydrosilylation and C Ccoupling,
ized by elemental analysis, mass spectrometry, IR Suzuki and Heck, reactions, under mild conditions.
and 1H and 13CNMR spectroscopy. Palladium(II)
and gold
A
stable solids, with the ONN-tridentate ligand after ladium; pincer complexes
Introduction
ity, and catalytic applications.[11,12] In the present
work, we have developed a series of novel conforma-
The use of gold compounds in homogeneous and het- tionally restricted ONN-pincer-type ligands (b) re-
erogeneous catalytic organic reactions has been un- sembling coordination environments present in previ-
dervalued for many years due to the preconceived ously described Schiff base ligands. The respective
idea that gold is chemically inert. However, recent re- Au(III) and Pd(II) complexes proved to be active and
U
ports have changed this assessment and gold com- selective for catalyzing the hydrogenation and hydro-
pounds are known to display high catalytic activity.[1] silylation reactions and Suzuki and Heck C Cbond
À
Indeed, Au(III) can act as a Lewis acid catalyst for a coupling.
A
large variety of reactions,[2,3] solid gold catalysts on
the other hand can be recycled, and when prepared in
the form of gold nanoparticles they are highly active
and selective for reactions such as hydrogenation,[4]
CO oxidation,[5] chemoselective reduction of substi-
tuted nitroaromatics by H2,[6] selective oxidation of al-
[8]
cohols[7] and some C Cbond forming reactions.
À
Moreover, the use of Au complexes in homogeneous
catalysis has undergone a renaissance and spectacular
achievements have been reported.[9]
Recently, we have shown that Au
with anionic linear Schiff ligands (a) exhibit excellent
A
catalytic activity in several reactions.[10] On the other We have developed the synthesis of new ONN-pincer-
hand, the Pincer-type ligand has become a valuable type ligands (b) in several steps starting from 2,6-di-
ligand class and their complexes play crucial roles bromopyridine as shown in Scheme 1. According to
with respect to unusual conformations, special reactiv- this pathway, mesylation of (6-bromopyridin-2-yl)me-
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New Pyridine ONN-Pincer Gold and Palladium Complexes
FULL PAPERS
Scheme 1. Synthesis of the ONN ligand, i) BuLi, ii) DMF, iii) NaBH4, iv) MsCl, Et3N, v) pyrrolidine, i-Pr2EtN,vi) 2-(tetrahy-
dropyran-2-yloxy)-phenylboronic acid, vii) p-TsOH.
thanol (2) with methanesulfonyl chloride in the pres- vents, with high purity and in high yields. The struc-
ence of DMAP in CH2Cl2 gave the corresponding me- tures of all the complexes were confirmed with ele-
1
sylate 3 in 96% yield. The substitution reactions with mental analysis (C, H, N), IR spectroscopy and H,
pyrrolidine and prolinamide were conducted in aceto- 13CNMR (data in Experimental Section). All these
nitrile in the presence of N,N-diisopropylethylamine complexes were characterized by electro-spray mass
at 608Cto afford products 4a and 4b, respectively, in spectrometry. Thus, the ES-MS of complexes show
65–70% yield. Suzuki cross-coupling reaction of bro- the ion peaks [M+] and peaks from the fragments due
mopyridine 4a or 4b with 2-(tetrahydropyran-2- to elimination of the ion acetate [M+ÀOAc] or the
yloxy)-phenylboronic acid using Pd
(PPh3)4 as a cata- molecular ion [AuLCl]+. All assignments were con-
G
lyst in presence of aqueous Na2CO3 gave 2-(pyrroli- firmed by good agreement between the observed and
din-1-ylmethyl)-6-[2-(tetrahydro-2H-pyran-2-yloxy)-
phenyl]pyridine (5a; 80% yield) or (2S)-N-tert-butyl-
1-({6-[2-(tetrahydro-2H-pyran-2-yloxy)phenyl]pyridin-
calculated isotopic distributions.
The absence of the n(OH) band (present in the
spectra of the free ligands at ca. 3430 cmÀ1) is in ac-
2-yl}methyl)pyrrolidine-2-carboxamide (5b; 75% cordance with loss of the OH proton. The IR spectra
yield). Finally cleavage of the THP group (using p- also shows strong bands at 1290 and ca. 1500 cmÀ1 as-
TsOH in MeOH) went smoothly to furnish 6a and 6b signed to the symmetric and asymmetric n(COO) vi-
G
with yields of 90–95%. Having succeeded in develop- brations, respectively, in agreement with those expect-
ing a flexible synthetic scheme for the preparation of ed for monocoordinate acetate ligands.[14] New bands
a broad variety of new ligands, we were interesting in in the 500–600 cmÀ1 region are ascribed to n
C
À
À
transition metal catalysis.
Cl).
Synthesis of Complexes
NMR spectra
For the synthesis of gold and palladium complexes we Diamagnetic palladium and gold complexes have
1
have followed the route developed for our Schiff base been characterized by H and 13CNMR spectroscopy.
complexes,[13] by addition of the divalent metal salt All assignments are based on several correlations in
Pd(OAc)2 or HAuCl4 to an ethanolic solution of the 2D spectra. They are fully consistent with the
G
ligand; one of the acetate groups or chloride was dis- structures depicted in Scheme 2. In all cases, the spec-
placed by the phenolic anion while the amine and pyr- tra show the simultaneous occurrence of two sets of
idine nitrogens were co-ordinated with the metal in a signals which are attributable on the one hand to the
square planar arrangement (Scheme 2). The com- substituted pyridine entity and on the other hand to
1
plexes, which precipitated in EtOH, were obtained as the aliphatic part of the ligand. In the H NMR spec-
microcrystalline stable solids, soluble in organic sol- tra all the resonances were high field shifted as com-
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Table 1. Turnover rates[a] for the catalytic hydrogenation of
diethyl benzylidenesuccinate with gold and palladium cata-
lysts.[b]
Catalyst
Conversion (%) [h]
TOF[a]
ee[c] [%]
(Schiff base)Au
6aAu
6bAu
(Schiff base)Pd
6aPd
100 (3)
92 (5)
96 (7)
100 (3)
93(6)
780
724
580
640
439
565
15 (S)
-
80 (S)
<10 (S)
-
6bPd
60(7)
15 (S)
[a]
TOF: mmol substrate/mmol catalayst min.
Conditions: 4 atm, 408C, catalyst: 0.1 mol%.
Average of three values.
[b]
[c]
The nature of the metal centre has an influence on
the catalytic activities. In general, the gold catalyst is
more active than the corresponding palladium ana-
logue. The results show that the Pd and Au systems
lead to quantitative conversion of olefins, under the
hydrogenation conditions. In all cases no gold or pal-
Scheme 2.
pared to the uncoordinated ligand and they were in ladium black has been formed during the hydrogena-
agreement with metallation of the ligand with coordi- tion reaction. Low enantiomeric excesses were ach-
nation of the metal atom via the pyridine nitrogen ieved with the Pd compound (<20%), but 6bAu
atom. The most noticeable shifts concern the CH2 be- shows an ee=80% for the hydrogenation of diethyl
tween the pyridine part and the pyrrolidine part 2-benzylidenesuccinate as we could detect from the
(about 0.5 ppm). Deprotonation of the OH group was HPLCanalysis of the reaction mixture.
1
confirmed by the absence of OH resonances in the H
The accumulated evidence concerning the mecha-
1
spectra. The H NMR spectrum shows the signal of nisms of homogeneously catalyzed hydrogenation in-
the MeCOO protons as a singlet at d=2.10 ppm. The dicates that three principal modes of hydrogen activa-
13CNMR spectra showed the signals assigned to the
ligand OAc group for Pd complexes.
tion are suitable: oxidative addition, and homolytic or
heterolytic hydrogen cleavage. For Au complexes, het-
erolytic cleavage is preferred to give a hydride inter-
mediate which involves charge separation without any
oxidation of the metal. Heterolytic cleavage of hydro-
gen by Au complexes have been reinforced from our
Catalytic Activity
In order to evaluate the catalytic performances of experiments using more polar and protonic acid
these new soluble gold(III) and Pd(II) complexes, we media which produce a significant increase of reaction
AHCTREUNG
have tested them in hydrogenation, hydrosilylation, rate, probably favouring charge separation in the step
Suzuki cross-coupling and Heck reactions as shown in of formation of the intermediate.[15]
following paragraphs using experimental conditions
that could permit us to make a comparative study of
different catalysts and substrates, obviously for prepa- Catalytic C C Coupling: Suzuki and Heck Reactions
rative application a tuning of experimental conditions
À
would have to be done for each case.
The gold and palladium complexes were also studied
for the Suzuki cross-coupling of PhI with 4-bromo-
phenylboronic acids. The standard reaction conditions
were applied to gold and palladium catalysts and the
conversions are tabulated in Table 2. In our experi-
Catalytic Hydrogenation of Olefins
The structurally well defined Au(III) and Pd(II) com- ments, we have chosen K3PO4 as a mild base because
G
plexes enable us to explore the possibilities of these with K2CO3 longer reaction times were necessary to
complexes in hydrogenation. The hydrogenations of obtain reasonable conversions. Excellent yields (cal-
diethyl 2-benzylidenesuccinate with Au and Pd com- culated with respect to PhI) and 100% selectivity to-
plexes were carried out under standard conditions wards the cross-coupling product were found with Pd
(EtOH as the solvent, 4 atm. hydrogen pressure, complexes, gold complexes were inactive for this reac-
408C). Results are summarized in Table 1.
tion. For comparison purposes (Schiff base)-Pd com-
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New Pyridine ONN-Pincer Gold and Palladium Complexes
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Table 3. Gold-catalyzed hydrosilylation with Ph2SiH2.[a]
Catalyst
Table 2. Influence of ligands on Pd(II) reactivity for Suzuki
cross-coupling reactions.[a]
Catalyst
Suzuki reaction Pd(PPh3)4
t [min] Conversion [%][b]
A
90
71
6aAu
6bAu
90
80
70
50
50 (80)[b]
40 (70)[b]
(Schiff base)Pd 180
6aPd 180
Heck reaction (Schiff base)Pd 240
6aPd 15
68
100
75
[a]
The reactions were carried out with carbonyl compound
(1 mmol)/silane (2 mmol), and the gold catalyst (5%) in
toluene (1 mL) at 708Cunder a nitrogen atmosphere.
Yields quoted with respect to carbonyl consumed based
on GC-MS. Selectivity>98%.
100
[a]
Catalyst: 3%, IPh (1 mmol), arylboronic acid
K3PO4 (2 mmol).
A
[b]
Gold catalyst 10%.
plexes have also been prepared and tested under the
same reaction conditions (Table 2). Results show that
activity and selectivity are similar.
due to a significant aggregation of the particles under
In this work we have also studied the performance the reaction conditions. When the filtered solution
of Pd complexes for Heck reactions of iodobenzene was used as catalyst, it was observed that the transfor-
with n-butyl acrylate using the biphasic mixture tolu- mation of iodobenzene did not occur.
ene and ethylene glycol as solvent in the presence of
potassium acetate under phosphine-free conditions.[16]
The complexes are insensitive to oxygen or moisture Catalytic Hydrosilylation
and no change in their activity was observed when
the reaction was carried out in an open system.
Under a nitrogen atmosphere, in the presence of a
Among the various bases examined, 1.14 mmol of catalytic amount of gold compounds (5%), the reac-
NaOAc or KOAc proved to be most suitable in com- tion of the carbonyl compound (1 mmol) with diphe-
bination with catalyst (<3 mol%), and use of other nylsilane (2 mmol) in toluene at 708Cfor 15 h result-
bases resulted in lower yields: Et3N (<10%). In the ed in the formation of (benzyloxy)(diphenyl)silane in
A
biphasic vinylation system, the toluene phase contains 100% GCyield with >98% selectivity (Table 3).
the reactants and products, while metal complex and
potassium acetate are in the ethylene glycol phase.
The inorganic base added is partly soluble in the eth- Conclusions
ylene glycol phase. The reaction should occur in the
ethylene glycol phase and the ethylene glycol-toluene We have developed a general synthetic scheme which,
interface in which the base is partly soluble.
due to its modularity and efficiency, allows for the
In Table 2, we show the catalytic performance of synthesis of a broad variety of structurally related
Pd complexes for the Heck reaction. The reaction ONN-tridentate ligands with low effort. Treatment of
was successful using low Pd catalyst loadings (2–5 these ligands, with Pd
N
N
mol%), but the reactions did not proceed at concen- gave air-stable complexes. These complexes were
trations below 2 mol%. Analogous gold complexes shown to be active catalysts for hydrogenation and
do not react under the same reaction conditions. hydrosilylation reactions with high reactivity in mild
When using the palladium complexes, no palladium conditions (TOF up to 800 minÀ1) and ee=80% for
black was observed after more than 72 h. As shown in the Au compound. The palladium complexes are also
Table 2, under the optimized conditions, the Heck- active for Suzuki and Heck reactions. Studies on the
type olefination reactions of iodobenzene were readi- immobilization of these pincer complexes on a sup-
ly achieved with n-butyl acrylate. The initial green so- port such as silica or MCM-41 and their use as recov-
lution of homogeneous catalysts in N-methylpyrroli- erable catalyst are in progress.
done turned to red upon heating after addition of
base and particles of palladium black could be seen in
the flask. These observations led us to the hypothesis
Experimental Section
that palladium colloids will be generated upon addi-
tion of base to a solution of the homogeneous precur-
sor when heating the reaction mixture.[17] Indeed,
upon centrifugation of the reacted mixture we could
isolate palladium particles. These isolated particles
were used in a new reaction and they were catalytical-
General Remarks
All preparations of metal complexes were carried out under
dinitrogen by conventional Schlenk tube techniques. Sol-
vents were carefully degassed before use. Metal contents
ly inactive. The absence of reactivity is presumably were analyzed by atomic absorption using a Perkin–Elmer
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Analyst 300 atomic absorption apparatus and plasma ICP
Perkin–Elmer Optima 2100. IR spectra were recorded on a
Bruker IFS 66v/S spectrophotometer (range 4000–200 cmÀ1)
2-(Pyrrolidin-1-ylmethyl)-6-[2-(tetrahydro-2H-pyran-
2-yloxy)phenyl]pyridine[20] (5a)
1
in KBr pellets. H NMR, 13CNMR, spectra were taken on
A 25-mL 2-neck flask equipped with a reflux condenser was
charged with 2-(tetrahydropyran-2-yloxy)phenylboronic acid
(449 mg, 2.0 mmoles, 1.2 equivs.) and xylene (20 mL) under
argon. 2M aqueous Na2CO3 solution (2 mL, 2.3 equivs.),
Varian XR300 and Bruker 200 spectrometers. Gas chroma-
tography analyses were performed in a Hewlett–Packard
5890 II with a flame ionization detector or/and in a Hew-
lett–Packard G1800A with a quadrupole mass detector using
a cross-linked methylsilicone column. HPLCanalysis were
taken in an Agilent 1200 equipped with a chiralcel OD
column.
EtOH (2 mL), Pd(PPh3)4 (58 mg, 3 mol%) and the bromo-
G
pyridine 4a (406 mg, 1.69 mmol, 1 equiv.) were added. The
mixture was stirred for 15 h at 808C. The mixture was
quenched with 2M sodium carbonate solution and the aque-
ous phase extracted with toluene. The organic phase was
washed with water followed by saturated aqueous NaCl so-
lution. The organic layer was dried (MgSO4) and the solvent
was removed under reduced pressure. Yield: 79%; anal.
calcd. for C21H26N2O2 (338.4): C74.5, H 7.7, N 8.3; found: C
Synthesis of Ligands
General Method for the Substitution Reaction of
Mesylate 3 with Pyrrolidines[18]
1
74.1, H 8.1, N 8.7%; H NMR (CDCl3, 300 MHz): d=7.55
(m, 3H, CH), 7.23 (m, 3H, CH), 7.05 (td, 1H, CH), 5.39 (br
s, 1 H, CHTHP), 3.76 (m, 1H, CH2THP), 3.47 (m, 1H, CH2THP),
2.58 (m, 5H, CH2Pyr, CH2THP), 2.47 (m, 1H, CH2THP), 1.76
(m, 5H, CH2Pirr, CH2THP), 1.51 (m, 3H, CH2THP); 13CNMR
(CDCl3, 300 MHz): d=161.4 (Cq), 158.8 (Cq) 155.3 (Cq),
135.7 (CH), 131.1 (CH), 130.2 (Cq), 129.6 (CH), 123.2 (CH),
122.2 (CH), 120.6 (CH), 115.5 (CH), 96.7 (CHTHP), 62.3
2-Bromo-6-(pyrrolidin-1-ylmethyl)pyridine (4a): A carefully
degassed mixture of (6-bromopyridin-2-yl)methyl methane-
sulfonate[19] (1 g, 3.8 mmol, 1,0 equiv.), pyrrolidine (373 mL,
4.5 mmol, 1.2 equivs.) and N,N-diisopropylethylamine
(2.6 mL, 15.1 mmol, 4.0 equivs.) in acetonitrile (15 mL) was
heated at 50–608Cunder an argon atmosphere. After 4 h,
the heating bath was removed and the solvent was evaporat-
ed under reduced pressure. Dichloromethane was added
and the mixture was washed with a 3% solution of NaOH
(20 mL). The organic layer was dried over MgSO4 and con-
densed. The residual oil was purified by flash column chro-
matography on silica gel (AcOEt/hexane: 1/1) to give the
product as a yellow liquid; yield: 67%; anal. calcd. for
C10H13BrN2 (240): C49.8, H 5.4, N 11.6; found: C49.9, H
5.2, N 11.5; 1H NMR (CDCl3, 300 MHz): d=7.50 (t, 3J=
(CH2N), 61.8 (CH2THP), 54.2 (CH2Pyr
,
CH2THP), 25.1
(CH2THP), 23.6 (CH2Pirr), 18.6 (CH2THP).
(2S)-N-tert-Butyl-1-({6-[2-(tetrahydro-2H-pyran-2-
yloxy)phenyl]pyridin-2-yl}methyl)pyrrolidine-2-
carboxamide (5b)
Following the general procedure employed for the synthesis
of 5a, starting from 4b (227 mg, 0.67 mmol), we have ob-
tained 5b; yield: 116 mg (49%) [two products were ob-
tained, (RS, SS)]; anal. calcd. for C26H35N3O3 (437): C71.4,
H 8.1, N 9.6; found: C, 71.0, H 8.1, N 9.7%; 1H NMR
(CDCl3, 300 MHz): d=7.79 (t, 2H, CH), 7.65 (m, 2H, CH),
7.49 (NH), 7.31 (m, 1H, CH), 7.21 (m, 1H, CH), 7.08 (t,
3
7.72 Hz, 1H, p-CH), 7.40 (d, J=7.72 Hz, 1H, m-CH), 7.33
3
(d, J=7.72 Hz, 1H, m-CH), 3.76 (s, 2H, CCH2N), 2.57 (m,
4H, CH CH2N), 1.79 (m, 4H, CH2CH2N); 13CNMR
2
(CDCl3, 300 MHz): d=161.3 (C-Br), 141.1 (C-NPy), 138.7 (p-
CHPy), 126.1 (m-CHPy), 121.5 (m-CHPy), 61.5 (CCH2N), 54.2
(CH2CH2N), 23.6 (CH2CH2N); MS (EI): m/z (%)=171–173;
84; 70.
2
1H, CH), 5.46 (2 s, 1H, CHTHP), 3.98 (2d, J=13.19 Hz, 1H,
2
CCH2), 3.84 (m, 1H, CH2OTHP), 3.74 (2d, J=13.19 Hz, 1H,
CCH2), 3.58 (m, 1H, CH2OTHP), 3.22 (m, 1H, NCHCO),
3.13 (m, 1H, CH2CH2N), 2.50 (m, 1H, CH2CH2N), 2.22 (m,
1-[(6-Bromopyridin-2-yl)methyl]-N-tert-
butylpyrrolidine-2-carboxamide (4b)
1H, CH2CHN), 1.69 (m, 9H, CH2CHOTHP, CH2CH2CHOTHP
CH2CH2OTHP, CH2CHN, CH2CH2N); 1.23 (2 s, 9H, CH3);
13CNMR (DClC
3, 300 MHz): d=173.60 (C=O), 157.99
,
Following the general procedure employed for the synthesis
of 4a, the residue was purified by flash column chromatogra-
phy (AcOEt/hexane: 1/1). The product was obtained as a
white solid; yield: 64%; mp 89–938C; anal. calcd. for
C15H22BrN3O (339): C52.9, H 6.5, N 12.3; found: C52.5, H
6.1, N 12.7; 1H NMR (CDCl3, 300 MHz): d=7.50 (t, 3J=
7.63 Hz, 1H, p-CH), 7.43 (br s, 1H, NH), 7.37 (d, 3J=
(Cq), 155.76 (Cq), 154.32 (Cq), 135.68 (CH), 131.84(CH),
131.21–131.17 (CH), 129.67 (CH), 128.42–128.26 (CH),
123.53–123.49 (CH), 121.71(CH), 120.40–120.36 (CH),
115.25–115.20 (CH), 96.67–96.57 (CHOTHP), 67.82–67.76
(NCHCO), 61.77–61.73 (CH2OTHP), 61.43–61.38 (CCH2N),
54.19–54.09 (CH2CH2N), 49.92–49.87 (C-t-Bu), 30.50–30.45
(CH2CHN), 30.16 (CH2CHOTHP), 28.55–28.52 (CH3), 25.01
3
7.92 Hz, 1H, CH), 7.19 (d, J=7.35 Hz, 1H, CH), 3.85 (d,
2
2J=13.38 Hz, 1H, CCH2), 3.64 (d, J=13.38 Hz, 1H, CCH2),
(CH2CH2OTHP),
23.98–23.95
(CH2CH2N),
18.56
3.09 (m, 2H, CHN, CH2N), 2.43 (m, 1H, CH2N), 2.20 (m,
1H, CH2CHN), 1.86 (m, 1H, CH2CHN), 1.74 (m, 2H,
CH2CH2N), 1.30 (s, 9H, CH3); 13C NMR (CDCl3, 300 MHz):
d=173.4 (C=O), 160.1 (CBr), 142.1 (CCH2), 138.8 (p-CH),
126.8 (CH), 121.6 (CH), 67.9 (CHN), 60.7 (CCH2), 54.3
(CH2N), 50.2 (C-t-Bu), 30.6 (CH2CHN), 28.7 (CH3), 24.1
(CH2CH2N); MS (EI): m/z (%)=239–241, 170–172.
(CH2CH2CHOTHP); MS (EI): m/z (%)=437; 337; 253; 185;
85.
2-[6-(Pyrrolidin-1-ylmethyl)pyridin-2-yl]phenol (6a)
To a solution of 5a (112 mg, 0.26 mmoles, 1 equiv.) in
MeOH (5 mL) was added p-TsOH (54 mg, 0.28 mmoles,
1.1 equivs.). The mixture was stirred 6 h. The solvent was re-
moved under reduced pressure. The residue was purified by
column chromatography on silica gel (CH2Cl2/i-PrOH: 50/
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New Pyridine ONN-Pincer Gold and Palladium Complexes
FULL PAPERS
1); yield: 95%; anal. calcd. for C16H18N2O (254.3): C75.6, H
7.1, N 11.0; found: C75.2, H 7.5, N 11.2%; 1H NMR
(CDCl3, 300 MHz): d=7.70 (m, 2H, CH), 7.25 (m, 3H,
CH), 6.93 (d, 1H, CH), 6.81 (t, 1H, CH), 3.68 (s, 2H,
CCH2N), 2,46 (m, 4H, CH2Pyrr), 1,67 (m, 4H, CH2Pyrr); 13C
NMR (CDCl3, 300 MHz): d=159.9 (Cq), 156.9 (Cq), 156.3
(Cq), 138.2 (CH), 131.2 (CH), 126.1 (CH), 122.3 (Cq), 121.2
(CH), 120.7 (CH), 118.6 (CH), 117.1 (CH), 61.4 (CCH2N),
54.2 (CH2Pyrr), 23.8 (CH2Pyrr).
1H, NCHCO), 3.37 (m, 2H, NCH2CH2), 2.06 (s, 3H, CH3),
1.85 (m, 4H, CH2), 0.99 (s, 9H, CH3-t-Bu); 13CNMR
(CDCl3, 300 MHz): d=179.5 (C=O), 165.3 (C=O), 163.8
(Cq), 161.0 (Cq), 152.8 (Cq), 138.1 (CH), 131.9 (CH), 128.5
(CH), 122.5 (CH), 120.7 (Cq), 119.8 (CH), 115.8 (CH), 115.7
(CH), 70.5 (NCHCO), 62.8 (CCH2N), 62.7 (NCH2CH2), 51.5
(C-t-Bu), 27.9 (CH3-t-Bu), 24.1 (CH3), 21.7 (CH2), 20.4
(CH2); MS: m/z (%)=474 (M+ÀAcO, for 106Pd).
[Au(6a)Cl]Cl (6aAu): Yield: 60%; anal. calcd. for
C16H17N2AuCl 2O (521.2): C36.8, H 3.3, N 5.4; found: C
36.6, H 3.6, N 5.1%; IR (KBr): n=1614–1600 (C=C , C=N),
N-tert-Butyl-1-{[6-(2-hydroxyphenyl)pyridin-2-
yl]methyl}pyrrolidine-2-carboxamide (6b)
337 cmÀ1 (Au Cl); UV-vis: l=225, 270, 310, 440 nm; 1H
À
NMR (DMSO, 300 MHz): d=8.44 (d, 3J=7.9 Hz 1H,
3
Following the general procedure employed for the synthesis
of 6a, the product was obtained with a yield of 80%; anal.
calcd. for C21H27N3O2 (353.5): C71.4, H 7.7, N 11.9; found:
Harom), 8.21 (m, 1H, Harom), 8.06 (d, J=7.8 Hz, 1H, Harom),
3
7.97 (m, 1H, Harom), 7.71 (d, J=7.8 Hz, 1H, Harom), 7.36 (m,
1H, Harom), 6.98 (m, 1H, Harom), 4.52 (br s, 2H, CCH2N),
3.41 (m, 1H, CH2), 3.02 (m, 1H, CH2), 1.86 (m, 1H, CH2),
1.07 (m, 1H, CH2); 13CNMR (DMSO, 300 MHz): d=164.0
(Cq), 158.6 (Cq), 153.0 (Cq), 138.0 (CHPh), 132.1 (CHPy),
128.1 (CHPy), 123.0 (CHPh), 121.8 (Cq), 120.0 (CHPh), 116.5
(CHPh), 115.3 (CHPy), 67.1 (CCH2N), 60.0 (NCH2CH2), 22.0
(NCH2CH2); MS: m/z (%)=485 (M+ÀCl), 449 ([AuL]).
[Au(6b)Cl]Cl (6bAu): Yield: 65%; anal. calcd. for
C21H26N3AuCl 2O2 (620.3): C40.7, H 4.2, N 6.8; found: C
40.6, H 4.6, N 7.1%; IR (KBr): n=1664–1610 (C=C , C=O,
À
C71.2, H 7.5, N 11.6%; IR (KBr): n=3200 (O H), 1650,
(C=O), 1608 cmÀ1 (C=C); UV-vis: l=299, 366 nm; 1H
NMR (CDCl3, 300 MHz): d=7.79 (m, 2H, CH, OH), 7.66,
7.47, 7.30 (m, Harom.), 7.23 (br, s, 1H, NH), 7.16 (m, Harom.),
2
7.00 (d, 1H, CH), 6.90 (t, 1H, CH), 3.98 (d, J=14.04 Hz,
2
1H, CCH2), 3.72 (d, J=14.04 Hz, 1H, CCH2), 3.16 (m, 2H,
NCHCO, CH 2CH2N), 2.43 (m, 1H, CH2CH2N), 2.25 (m,
1H, CH2CHN), 1.85 (m, 3H, CH2CHN, CH2CH2N), 1.23 (s,
9H, CH ); 13C NMR (CDCl3, 300 MHz): d=173.3 (C=O),
3
C=N), 335 cmÀ1 (Au Cl); UV-vis: l=240, 265, 310, 450 nm;
159.9 (Cq), 157.6 (Cq), 155.2 (Cq), 138.4 (CH), 131.9 (CH),
128.3 (CH), 121.7 (CH), 120.3 (CH), 118.7 (CH), 118.5 (Cq),
117.5 (CH), 68.5 (NCHCO), 60.4 (CCH2N), 54.5
(CH2CH2N), 50.1 (C-t-Bu), 30.7 (CH2CHN), 28.5 (CH3-t-
Bu), 24.0 (CH2CH2N); MS (EI:) m/z (%)=353, 253, 185.
À
1H NMR (DMSO, 300 MHz): d=7.60 (m, 2H, Harom.), 7.40
(m, 1H, Harom.), 7.00 (m, 1H, Harom.), 6.93 (m, 1H, Harom.),
6.80 (m, 1H, Harom.), 6.49 (m, 1H, Harom.); 4.390 (d, 2J=
2
18.2 Hz, 1H, CCH2N); 3.96 (d, J=18.2 Hz, 1H, CCH2N);
3.82 (m, 1H, NCHCO), 3.40 (m, 2H, NCH2CH2), 2.10 (s,
3H, CH ), 1.95 (m, 4H, CH2), 1.00 (s, 9H, CH3-t-Bu); 13C
Preparation of Metal Complexes; General Method
3
NMR (CDCl3, 300 MHz): d=166.0 (C=O), 163.7 (Cq), 161.3
(Cq), 153.0 (Cq), 138.4 (CH), 132.1 (CH), 128.7 (CH), 122.8
(CH), 120.9 (Cq), 119.6 (CH), 115.5 (CH), 115.9 (CH), 70.2
(NCHCO), 62.6 (CCH2N), 62.3 (NCH2CH2), 51.1 (C-t-Bu),
27.7 (CH3-t-Bu), 24.3 (CH3), 21.9 (CH2), 20.2 (CH2); MS:
m/z (%)=585 (M+ÀCl), 550 ([AuL]).
To a solution of ligand (1 equiv.) in EtOH (15 mL), at room
temperature, was added 1 equiv. of KOH. The mixture was
stirred for 15 min. An ethanolic solution of Pd(OAc)2 or
G
KAuCl4 (0.5 mmol/15 mL) was added. The resulting mixture
was stirred overnight at room temperature, and concentrat-
ed under vacuum. The residue was washed several times
with diethyl ether, dried and filtered to afford the respective
complexes in almost quantitative yields.
[Pd(6a)
A
Catalytic Activity
C18H20N2O3Pd (418.8): C51.6, H 4.8, N 6.7; found: C51.6, H
4.6,
N
6.3%; IR (KBr): n=1614–1600 (C=C , =CN),
Hydrogenation of alkenes: The catalytic properties, in the
hydrogenation of diethyl benzylidenesuccinate, of the com-
plexes were examined under conventional conditions for
batch reactions in a reactor (Autoclave Engineers) of
100 mL capacity at 408Ctemperature, 4 atm dihydrogen
pressure and 1/1000 metal/substrate molar ratio. The evolu-
tion of the hydrogenated reaction product was monitored by
gas chromatography.
557 cmÀ1 (Pd O); UV-vis: l=235, 259, 289, 420 nm; 1H
NMR (CDCl3, 300 MHz): d=7.70 (m, 2H, CHPh), 7.50 (m,
À
3
1H, CHPy), 7.07 (m, 3H, CHPy, CHPh), 6.61 (t, J=6.53 Hz,
1H, CHPy), 4.16 (s, 2H, CCH2N), 3.61 (m, 2H, NCH2CH2),
2.69 (m, 2H, NCH2CH2), 1.98 (m, 7H, CH3, NC HCH2); 13C
2
NMR (CDCl3, 300 MHz): d=178.4 (C=O), 164.2 (Cq), 158.3
(Cq), 152.9 (Cq), 138.2 (CHPh), 131.9 (CHPy), 128.4 (CHPy),
122.8 (CHPh), 121.6 (Cq), 120.2 (CHPh), 116.3 (CHPh), 115.6
(CHPy), 67.5 (CCH2N), 59.9 (NCH2CH2), 23.9 (CH3), 22.1
(NCH2CH2); MS: m/z (%)=419 (M+, for 106Pd), 359
(M+<M->OAc, for 106Pd).
À
Suzuki C C Coupling: The reaction was carried out in a
25-mL vessel, at 1308Cduring a time period time from 20 to
180 min. In
a typical run, a mixture of aryl halide
(10 mmol), boronic acid (15 mmol), aqueous potassium car-
bonate or phosphate (20 mmol) and catalyst (3.3%) in 3 mL
of o-xylene was stirred for the desired time. The solution
was allowed to cool, and a 1:1 mixture of ether/water
(20 mL) was added. The organic layer was washed, separat-
ed, further washed with another 10 mL portion of diethyl
ether, dried with anhydrous MgSO4 and filtered. The solvent
and volatiles were completely removed under vacuum to
give the crude product which wassubjected to column chro-
[Pd(6b)(AcO)] (6bPd): Yield: 75%; anal. calcd. for
C23H29N3O5Pd (534.0): C51.7, H 5.5, N 7.9; found: C51.6,
G
H 5.6, N 8.1%; IR (KBr): n=1654–1600 (C=C , C=O, C=N),
557 cmÀ1 (Pd O); UV-vis: l=235, 259, 289, 420 nm; 1H
À
NMR (CDCl3, 300 MHz): d=7.63 (m, 2H, Harom.), 7.47 (m,
1H, Harom.), 7.08 (m, 1H, Harom.), 6.95 (m, 1H, Harom.), 6.82
(m, 1H, Harom.), 6.54 (m, 1H, Harom.), 4.34 (d, J=18.2 Hz,
1H, CCH2N), 3.90 (d, J=18.2 Hz, 1H, CCH2N), 3.79 (m,
2
2
Adv. Synth. Catal. 2007, 349, 2470 – 2476
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
2475

N. Debono et al.
FULL PAPERS
matographic separation, resulting in pure compounds. The
reaction was followed by GC-MS.
A. A. Herzing, M. Watanabe, C. J. Kiely, D. W. Knight,
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Heck Reaction: In a typical experiment, catalyst (3–
5 mmol%) was suspended in a mixture of ethylene glycol
and toluene (1:1, 6 mL). Then iodobenzene (1 mmol), n-
butyl acrylate (1 mmol) and potassium acetate (1.14 mmol)
were added with stirring. The mixture was refluxed and the
reaction progress was monitored by gas chromatography.
Catalytic Hydrosilylation: In a 5-mL Schlenk tube, a so-
lution of the catalyst compound in dry toluene (2 mL) was
allowed to equilibrate for 5 min with stirring, at which point,
styrene (343 mL, 3 mmol), a-methylstyrene (390 mL,
3 mmol), acetophenone (114 mL, 1 mmol), or benzaldehyde
(101 mL, 1 mmol) was added. The resultant mixture was
stirred for an additional 5–10 min, after which H2SiPh2,
(1 mmol for styrenes, 2 mmol for benzaldehyde, acetophe-
none) was added. The reaction mixture was stirred at 708C
for 1–15 h and the reaction course was monitored by GC-
MS analysis. The mixture was filtered through a short
column (celite) from which clear, colourless solutions
eluted. Products of each reaction were identified by use of
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Financial support by the Dirección General de Investigación
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Adv. Synth. Catal. 2007, 349, 2470 – 2476