Synthesis of novel (NHC)Pd(acac)Cl complexes (acac=acetylacetonate) and their activity in cross-coupling reactions

Article abstract of DOI:10.1016/j.tet.2005.06.081

The synthesis and characterization of two new complexes (IPr)Pd(acac) ₂ (1) and (IPr)Pd(acac)Cl (2) (IPr=(N,N′-bis(2,6- diisopropylphenyl)imidazol)-2-ylidene, acac=acetylacetonate) are described. Complex 2 can be prepared in a one-pot protocol in high yield. A study detailing the versatility of 2 to effectively catalyze a series of cross-coupling reactions is discussed.

Full text of DOI:10.1016/j.tet.2005.06.081

Tetrahedron 61 (2005) 9716–9722
Synthesis of novel (NHC)Pd(acac)Cl complexes (acacZ
acetylacetonate) and their activity in cross-coupling reactions
a
Oscar Navarro, Nicolas Marion, Natalie M. Scott, Juan Gonz a´ lez, Dino Amoroso,
a
a
a
b
b
Andrew Bell and Steven P. Nolan
a,
*
a
Department of Chemistry, University of New Orleans, 2000 Lakeshore Dr, New Orleans, LA 70148, USA
b
Promerus LLC, 9921 Brecksville Rd, Brecksville, OH 44141-3289, USA
Received 4 April 2005; revised 28 May 2005; accepted 24 June 2005
Available online 21 July 2005
Abstract—The synthesis and characterization of two new complexes (IPr)Pd(acac) (1) and (IPr)Pd(acac)Cl (2) (IPrZ(N,N’-bis(2,6-
2
diisopropylphenyl)imidazol)-2-ylidene, acacZacetylacetonate) are described. Complex 2 can be prepared in a one-pot protocol in high yield.
A study detailing the versatility of 2 to effectively catalyze a series of cross-coupling reactions is discussed.
q 2005 Elsevier Ltd. All rights reserved.
1
. Introduction
precursors for NHC) and Pd(0) or Pd(II) sources to generate
catalytically active species in situ and these mediate
numerous organic reactions, principally cross-coupling
Research focusing on palladium compounds and their use in
catalysis at both industrial and laboratory scales has
exponentially increased during the last 10 years.
Although, ligandless systems are also known, it is well
understood that the ancillary ligation to the metal center
plays a crucial role in dictating the efficiency of a catalytic
7
8
reactions. These preliminary systems by us and others
1
,2
showed the importance of the NHC/Pd ratio on the
efficiency of the reactions, pointing to an optimum 1:1
ligand to metal ratio in most cases. From there, we aimed
our efforts on the development of monomeric NHC-bearing
Pd(II) complexes and the study of their catalytic activity.
Generally, shorter reaction times are observed in these well-
defined systems, since the carbene is already coordinated to the
palladium center. Also, the use of a well-defined pre-catalyst
allows for a better knowledge of the amount of ligand-
stabilized palladium species in solution, by reducing the
possibility of side reactions leading to ligand or palladium
precursor decomposition prior to the coordinationofthe ligand.
2
a
3
system. Bulky, electron-rich phosphines ligands such as
P(t-Bu) are now commonly used to stabilize the Pd(0)
intermediates thereby avoiding the precipitation of the metal
3
4
in homogeneous catalysis. However, the most common
phosphine ligands possess several drawbacks: (1) they often
are prone to air oxidation and therefore, require air-free
handling, (2) when these ligands are subjected to higher
temperatures, significant P–C bond degradation occurs and
require the use of an excess of the phosphine and (3) they
We have reported on the synthesis of monomeric (NHC)
and (NHC)Pd(carboxylate)
often react with Pd precursors such as Pd(OAc)2 in a
5
reduction process forming Pd(0)P and phosphine oxide.
n
7f,9
Pd(allyl)Cl complexes
10
11
complexes among many architectures, and have studied
activation mechanisms and catalytic activities. The syn-
thesis of most of these complexes is directly related to
successful in situ systems involving the use of NHC and the
corresponding palladium source. We reported on a catalytic
system for the Heck reaction involving the use of
6
N-Heterocyclic carbenes (NHC) have become increasingly
popular in the last few years as they represent an attractive
alternative to tertiary phosphines in homogeneous catalysis.
The NHC exhibit reaction behavior different than phosphine
especially displaying high thermal stability and tolerance to
oxidation conditions. We have developed several systems
based on the combination of imidazolium salts (air-stable
diazabutadiene ligands and Pd(OAc) , that also could use
2
1
Pd(acac)2 as palladium precursor. Using the same
2
approach as for (IPr)Pd(OAc) , we decided to test whether
2
analogous species using Pd(acac) as starting material was
2
possible. We report here the synthesis of (IPr)Pd(acac) (1)
2
Keywords: N-Heterocyclic carbenes; Palladium; Aryl amination; Ketone
arylation.
*
Corresponding author. Tel.: C1 504 286 6311; fax: C1 504 280 6860;
e-mail: snolan@uno.edu
and (IPr)Pd(acac)Cl (2) (IPrZ(N,N’-bis(2,6-diisopropyl-
phenyl)imidazol)-2-ylidene) complexes and preliminary
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.06.081

O. Navarro et al. / Tetrahedron 61 (2005) 9716–9722
9717
2
Scheme 1. Synthetic path leading to (IPr)Pd(acac) .
singlet signals were observed each at 2.63, 2.01, 1.63, and
1.31, together with two signals at 5.90 and 4.78 ppm. The
lowest-field methyl peaks are assigned to the carbon-bonded
acac, together with the lowest-field methenic hydrogen,
while the other three signals are assigned to the oxygen-
chelating ligand. It is of note that the PPh analogue showed
3
only one peak for the methyls of the carbon bound ligand,
1
8
due to free rotation. Clearly, the sterically demanding IPr
ligand inhibits this rotation. The disposition of the ligands
was unequivocally assigned when the crystal structure was
resolved by X-ray diffraction (Fig. 1). A square planar
configuration around the palladium center can be observed,
with nearly no distortion. As expected, the Pd–Ccarbenic
distance is in the range of a single Pd–C bond. The Pd–O
bond opposite to the NHC is elongated compared to the
other Pd–O bond due to a strong trans effect.
2
Figure 1. Ball and stick representation of (IPr)Pd(acac) (hydrogens
Preliminary tests on the activity of 1 for the Buchwald–
Hartwig reaction using KOtBu as base and DME as solvent
at 50 8C for the coupling of 4-chlorotoluene and morpholine
showed a moderate activity (43% product in 1 h with
˚
omitted for clarity). Selected bond distances (A): Pd1–C1: 1.982(6), Pd1–
C34: 2.073(6), Pd1–O1: 2.038(4), Pd1–O2: 2.081(4). Selected angles (deg):
O2–Pd1–O1: 90.70(15), O1–Pd1–C34: 86.4(2), C34–Pd1–C1: 90.4(2), C1–
Pd1–O2: 93.2(2).
1 mol% catalyst loading). The same moderate activity was
observed for the coupling of 4-chlorotoluene and propio-
phenone using NaOtBu as base and toluene as solvent at
studies on their catalytic activity in the Buchwald–Hartwig
aryl amination reaction and the a-ketone arylation reaction.
6
1
0 8C. The reaction required 2 h to reach completion using
mol% catalyst loading. We decided on modifying the
2
. Results and discussion
complex with the idea of increasing the activity in catalysis.
2,4-Pentadione (acetylacetonate, acac) and other b-carbonyl
compounds are very versatile and common ligands in
Kawaguchi reported on the reaction of (PPh )Pd(acac) with
3
benzoyl chloride to yield the new species(PPh )Pd(acac)Cl,
3
2
1
transition metal chemistry. 2,4-Pentadione typically binds
3
proposing a sequence of oxidative addition–reductive
1
2
metal ions in a h -O,O fashion, although some other
6a
elimination reactions.
reacts with 1 equiv of HCl at room temperature to produce
In a similar way, compound 1
coordination modes have been observed in platinum (II) and
palladium(II) complexes.
1
4,15
Previous work by Kawaguchi
the new species (IPr)Pd(acac)Cl (2) as a yellow powder in
nearly quantitative yield (Scheme 2). The loss of the
and co-workers focused on the reactivity of palladium(II)
acetylacetonate and related compounds with phosphines
leading to new complexes, but no catalytic applications
13
C
C-bound ligand is again clearly evidenced by NMR. In
NMR, only two carbonyl carbons (187.1, 184.1 ppm) and
1
6
were reported. Recently, Shmidt and co-workers have
performed a very extensive research on the use of such type
of complexes as hydrogenation catalysts.
1
the carbenic carbon (156.4 ppm) appear, whereas in H
NMR, only one acac ligand can be assigned: singlet at
1
7
5.12 ppm, accounting for one hydrogen, and two methylic
singlets (1.84, 1.82 ppm). Again, the structural features
We have synthesized a NHC-bearing analogue to the
1
6a
reported (PPh )Pd(acac)
(
following a similar procedure
Scheme 1). Direct reaction of the free carbene IPr with
Pd(acac) at room temperature in anhydrous toluene yielded
3
2
2
(
The presence of one oxygen-chelating ligand and one
IPr)Pd(acac) (1) in very high yield as a yellow powder.
2
1
3
C-bound ligand in the complex was apparent by both
C
1
13
and H NMR. In the C NMR spectrum, 6 different signals
above 160 ppm: 207.5 (C-bound acac), 192.9, 188.1, 185.6,
183.3 (carbonyl carbons), and 161.2 (carbenic carbon) were
observed. In the H NMR spectrum, four methyl-proton
1
Scheme 2. Synthetic path leading to (IPr)Pd(acac)Cl.

9718
O. Navarro et al. / Tetrahedron 61 (2005) 9716–9722
were unequivocally assigned when the structure was
determined by single crystal X-ray diffraction (Fig. 2). For
this complex, the Pd–O distances are more similar (2.036,
˚
2.044 A), whereas the square planar coordination around the
palladium center becomes slightly more distorted.
The formation of 1 and subsequently 2 can be postulated to
occur by the pathway illustrated in Scheme 3. The
coordination of the sterically demanding IPr by palladium
is accompanied by the transition of one acac ligand from the
2
h -O,O-chelate to the O-monodentate form, with sub-
sequent transformation to the p-hydroxoallyl form and
further to the C-bonded form. A similar pathway has been
1
7b
proposed by Shmidt for the phosphine analogues.
Oxidative addition of HCl followed by reductive elimin-
ation of acacH yields 2.
Figure 2. Ball and stick representation of (IPr)Pd(acac)Cl (hydrogens
˚
omitted for clarity). Selected bond distances (A): C13–Pd1: 1.9694(17),
Pd1–O2: 2.0362(15), Pd1–O1: 2.0439(14), Pd1–C13: 2.2820(6). Selected
angles (deg): O2–Pd1–O1: 92.89(6), O1–Pd1–Cl1: 87.35(4), Cl1–Pd1–
C13: 93.89(5), C13–Pd1–O2: 86.21(2).
Scheme 3. Proposed mechanism for the formation of 1 and 2.
Table 1. Buchwald–Hartwig aryl amination of aryl chlorides using 2
a
Entry
1
Aryl chloride
Amine
Product
Time (h)
0.5
Yield (%)
97
2
3
0.5
1.5
98
90
4
5
6
4
99
95
6
2
Bu NH
b
93
10
a
Isolated yields, average of two runs.
2.1 equiv of aryl chloride were used.
b

O. Navarro et al. / Tetrahedron 61 (2005) 9716–9722
Table 2. a-Ketone arylation with aryl chlorides using 2
9719
a
Entry
1
Aryl chloride
Ketone
Product
Time (h)
1
Yield (%)
97
2
10
70
3
4
5
2
1
86
95
92
1.5
6
2
89
a
Isolated yields, average of two runs.
2
1
The activity of complex 2 for the Buchwald–Hartwig
coupling reaction of morpholine and 4-chlorotoluene in the
previously mentioned conditions was then tested. Using
bond formation,
catalysis,
homogeneous and heterogeneous
and nonlinear optical
2
2
23
DNA binding
2
4
materials. The formation of the double pyridilation
product was observed in good yield when 2.1 equiv of the
chloride were used (entry 6).
1
3
mol% of 2, the coupling occurred in 97% yield in only
0 min (entry 1, isolated yield). It is remarkable that the
product could be obtained in good yield using low catalyst
loading (0.1 mol%) or at room temperature if the reaction
time was increased. Results for the amination of aryl
chlorides using 2 as catalyst are shown in Table 1. Various
substrates were examined: heteroaromatic (entry 2),
sterically demanding (entry 3) and deactivated chlorides
As for the Buchwald–Hartwig reaction, 2 performed more
effectively than 1 for the a-ketone arylation reaction,
requiring half the time in the coupling of propiophenone
and 4-chlorotoluene (Table 2, entry 1). Using 2, the system
allowed for the coupling of aryl–aryl and aryl–alkyl ketones
with a variety of aryl chlorides.
(
entry 4). The coupling of the sterically demanding
dibutylamine with 4-chlorotoluene required a longer time
entry 5), and was the only reaction, in which dehalogena-
(
Since 2 displayed a higher activity than 1, we realized the
convenience of synthesizing 2 without the need of isolating
tion of the aryl chloride was observed (3% by GC). As the
synthesis of unsymmetrical tertiary amines starting from
the (IPr)Pd(acac)
synthesis of 2 is summarized in Scheme 4. Reaction of the
free carbene IPr with Pd(acac) in anhydrous 1,4-dioxane at
intermediate. A one-pot multigram
2
1
9
primary amines remains a challenge, we investigated the
reaction between aniline and 2-chloropyridine. One-pot
syntheses of N,N-bis(2-pyridyl)amino ligands, especially
2
room temperature, followed by the addition of an
equimolecular amount of HCl, leads to the formation of
the desired product.
2
0
with aryl chlorides, are attractive due to the number of
applications in which these compounds can take part: C–C
Scheme 4. One-pot protocol for the synthesis of (IPr)Pd(acac)Cl.

9720
O. Navarro et al. / Tetrahedron 61 (2005) 9716–9722
Scheme 5. Proposed mechanism for the activation of (IPr)Pd(acac)Cl.
A possible mechanism for the activation of 2 is depicted in
Scheme 5.
commercially available from Strem Chemicals Inc or
2
6
Sigma/Aldrich.
3.2. Synthesis of complexes
.2.1. (IPr)Pd(acac) (1). In a glovebox, a Schlenk flask
The activation pathway involves the chloride/tert-butoxide
anion exchange in a metathetical process followed by a
rearrangement of the acac moiety prior to a reductive
elimination step that yields the catalytically active [(IPr)
Pd(0)] species. Recently, Hartwig reported that sterically
demanding ancillary ligands promote the rearrangement of
3
2
equipped with a magnetic bar was loaded with free carbene
IPr (855 mg, 2.2 mmol), Pd(acac) (609 mg, 2 mmol) and
2
anhydrous toluene (30 mL), and sealed with a rubber cap.
The mixture was stirred at room temperature for 2 h. The
solvent was evaporated in vacuo and THF (25 mL) was
added. The solution was filtered and the solid washed with
THF (2!5 mL). The solvent was evaporated in vacuo; the
complex was then triturated with cold pentane (25 mL) and
the yellow precipitate was collected by filtration. Recrys-
tallization from chloroform/pentane (25:75) yielded 1.28 g
2
the k -O,O-bound ligands to the C-tautomers in Pd(II)
2
5
complexes with malonate or acetylacetonate anions. It
was also proposed that only complexes with these ligands in
a C-bound mode are able to undergo reductive elimination
in high yield. This fact not only supports the need of this
rearrangement for the activation of 2, but also for the
formation of 1 and its later transformation into 2 by the
addition of HCl (Scheme 3).
(93%) of the desired compound as a yellow microcrystalline
material. H NMR (400 MHz, C D ): d 7.28–7.24 (m, 2H),
1
6
6
We have described the synthesis of two new NHC-bearing
palladium complexes using Pd(acac) as the Pd precursor.
7
.18 (d, JZ8.0 Hz, 4H), 6.47 (s, 2H), 5.90 (s, 1H), 4.78 (s,
2
1H), 2.88 (q, JZ6.8 Hz, 4H), 2.63 (d, JZ0.8 Hz, 3H), 2.01
Complex 2 displays high activity for the Buchwald–Hartwig
reaction and a-ketone arylation in short reaction times and
very mild conditions. Both complexes are air- and moisture-
stable and can be prepared on multigram scale in high
yields. Studies focusing on the synthesis of related NHC-
bearing complexes and their activity in homogeneous
catalysis are currently ongoing in our laboratories.
(
d, JZ0.8 Hz, 3H), 1.63 (s, 3H), 1.35 (d, JZ6.8 Hz, 12H),
.31 (s, 3H), 0.97 (d, JZ6.8 Hz, 12H). C NMR (100 MHz,
1
3
1
C D ): 207.5, 192.9, 188.1, 185.6, 183.3, 161.2, 146.9,
1
1
2
6
6
6
35.9, 131.2, 130.4, 125.7, 125.2, 124.7, 124.5, 104.8,
00.3, 47.2, 31.9, 31.5, 29.3, 29.0, 28.9, 28.1, 27.0, 26.5, 26.2,
5.1, 24.0, 23.8, 23.4. Elemental analysis: Anal. Calcd: C,
4.11; H, 7.27; N, 4.04. Found: C, 63.89; H, 7.06; N: 3.86.
3
.2.2. One-pot synthesis of (IPr)Pd(acac)Cl (2). In a
glovebox, a Schlenk flask equipped with a magnetic bar was
loaded with the free carbene IPr (2.73 g, 7 mmol), Pd(acac)2
3. Experimental
(1.53 g, 5 mmol) and anhydrous dioxane (50 mL), and
3
.1. General remarks
sealed with a rubber cap. The mixture was stirred at room
temperature for 2 h. After that time, 1.25 mL of HCl 4 M in
dioxane was injected in the solution and the mixture allowed
stirring at room temperature for another 2 h. The solvent
was then evaporated in vacuo and diethyl ether was added
until no more solid dissolved (20 mL). The solution was
filtered and the solid washed with diethyl ether (2!10 mL).
The solvent was evaporated in vacuo and the powder
obtained dried under vacuum overnight to yield 2.85 g
1
13
H and C nuclear magnetic resonance spectra were
recorded on a Varian-300 or Varian-400 MHz spectrometer
at ambient temperature in CDCl3 (Cambridge Isotope
Laboratories, Inc), unless otherwise noted. Elemental
analyses were performed at Robertson Microlit Labora-
tories, Inc., Madison, NJ. IPr$HCl was synthesized
according to literature procedures but is also now

O. Navarro et al. / Tetrahedron 61 (2005) 9716–9722
9721
(
90%) of the desired product as a yellow microcrystalline
3.4.1.3. 4-(2,6-Dimethylphenyl)morpholine (Table 1,
entry 3). The procedure afforded 170 mg (90%) of the
title compound.
1
29
material. H NMR (400 MHz, CDCl ): d 7.51 (t, JZ7.6 Hz,
2
3
H), 7.35 (d, JZ8.0 Hz, 4H), 7.12 (s, 2H), 5.12 (s, 1H), 2.95
(
6
q, JZ6.4 Hz, 4H), 1.84 (s, 3H), 1.82 (s, 3H), 1.34 (d, JZ
.4 Hz, 12H), 1.10 (d, JZ6.4 Hz, 12H). C NMR
1
3
3.4.1.4. 4-(4-Methoxyphenyl)morpholine (Table 1,
entry 4). The procedure afforded 190 mg (99%) of the
title compound.
3
0
(
1
2
100 MHz, CDCl ): 187.1, 184.1, 156.4, 147.0, 135.5,
34.8, 130.9, 125.7, 124.7, 124.6, 99.9, 29.1, 30.0, 27.6,
6.8, 23.7, 23.5. Elemental analysis: Anal. Calcd: C, 61.05;
3
3
1
H, 6.88; N, 4.45. Found: C, 60.78; H, 7.15; N: 4.29.
3.4.1.5. N,N-Dibutyl-p-toluidine (Table 1, entry 5).
The procedure afforded 207 mg (95%) of the title
compound.
3
3
.3. Crystallographic data
.3.1. (IPr)Pd(acac) (1). Single crystals were grown by
2
3.4.1.6. N-Phenyl-N-(pyridin-2-yl)pyridin-2-amine
3
2
slow evaporation at room temperature of a concentrated
methylene chloride/hexanes solution. C H N O Pd, MZ
6
bZ13.3836(7) A, cZ22.6493(12) A, VZ3562.6(3) A ;
D (ZZ4)Z1.292 g cm ; mMoZ0.560 mm ; specimen:
(Table 1, entry 6). The procedure with 2-chloropyridine
(2.1 mmol, 200 mL), aniline (1.0 mmol, 93 mL), KOtBu
(2.2 mmol, 248 mg), (IPr)Pd(acac)Cl (1.0 mol%, 12.6 mg)
and DME (2 mL) afforded 230 mg (93%) of the title
3
7 50 2 4
˚
93.2. Orthorhombic, space group P2 2 2 , aZ11.7529(6) A,
1 1 1
3
˚
˚
˚
K3
K1
1
compound as a white solid. H NMR (400 MHz,
(CD ) CO): d 8.22 (d, JZ4 Hz, 2H), 7.61 (m, 2H), 7.38
c
0
.6!0.5!0.3 mm; Tmin/maxZ0.88; 2qmaxZ408; N Z22450,
t
3 2
N Z3318; RZ0.0340, R Z0.0737.
(t, JZ8.1 Hz, 2H), 7.24–7.16 (m, 3H), 7.00 (d, JZ8.4 Hz,
o
w
1
3
H), 6.97–6.94 (m, 2H). C NMR (100 MHz, ((CD ) CO)):
2
3 2
3.3.2. (IPr)Pd(acac)Cl (2). Single crystals were grown by
slow evaporation at room temperature of a concentrated
159.5 (C), 149.4 (CH), 146.6 (C), 138.6 (CH), 130.7 (CH),
128.9 (CH), 126.6 (CH), 119.3 (CH), 118.0 (CH). Elemental
analysis: Anal. Calcd for C H N (M 247.29): C, 77.71;
methylene chloride/hexanes solution. C H N O Pd, MZ
3
2
43
2
2
16 13
3
W
˚
6
29.53. Monoclinic, space group P2 /c, aZ10.957(2) A,
H, 5.30; N, 16.99. Found: C, 77.79; H, 5.57; N, 16.93.
1
˚
˚
bZ17.431(3) A, cZ16.814(3) A, bZ106.162(4) VZ
3
084.4(10) A ;
K3
˚
3
0
2
D (ZZ4)Z1.356 g cm
c
;
mMo
Z
3.4.2. a-Ketone arylation of alkyl or aryl ketones
K1
.718 mm ; specimen: 0.6!0.6!0.4 mm; Tmin/maxZ0.77;
qmaxZ458; N Z30901, N Z4006; RZ0.0259, R Z0.0576.
General procedure: In a glovebox, 2 (1 mol%, 6 mg),
sodium tert-butoxide (1.5 mmol, 144 mg) and toluene
(1 mL) were added in turn to a vial equipped with a
magnetic bar, and sealed with a screw cap fitted with a
septum. Outside the glovebox, the ketone (1.1 mmol) and
the aryl chloride (1.0 mmol) were injected in turn through
the septum. The vial was then placed in an oil bath at 60 8C
and the mixture stirred on a stirring plate. The reaction was
monitored by gas chromatography. When reaction reached
completion, or no further conversion could be observed, the
vial was allowed to cool to room temperature. Water was
added to the reaction mixture; the organic layer was
extracted with diethyl ether and dried over magnesium
sulfate. The solvent was then evaporated in vacuo. When
necessary the product was purified by flash chromatography
on silica gel (pentane/ethyl acetate: 9:1). The reported yields
are the average of two runs:
t
o
w
CCDC reference numbers 263919-263920.
See http://www.rsc.org/suppdata/dt/b4/b4125540a/ for
crystallographic data in CIF or other electronic format.
3
3
.4. Cross-coupling reactions
.4.1. Buchwald–Hartwig reaction of aryl chlorides with
primary and secondary amines. General procedure: In a
glovebox, 2 (1 mol%, 6 mg), potassium tert-butoxide
(
1.1 mmol, 124 mg) and DME (1 mL) were added in turn to
a vial equipped with a magnetic bar, and sealed with a screw
cap fitted with a septum. Outside the glovebox, the amine
(
1.1 mmol) and the aryl chloride (1 mmol) were injected in
turnthroughtheseptum. Thevialwasthenplacedinanoilbath
at50 8C and the mixture stirred ona stirring plate. Thereaction
was monitored by gas chromatography. When the reaction
reached completion, or no further conversion could be
observed, the vial was allowed to cool down to room
temperature. Water was added to the reaction mixture; the
organic layer was extracted with diethyl ether and dried over
magnesium sulfate. The solvent was then evaporated invacuo.
When necessary the product was purified by flash chroma-
tography on silica gel (pentane/ethyl acetate: 9:1). Reported
yields are the average of two runs:
3.4.2.1. 2-(4-Methylphenyl)-1-phenyl-1-propanone
(Table 2, entry 1). The procedure afforded 216 mg
(97%) of the title compound.
3
3
3.4.2.2. 1-(Naphthyl)-2-phenylethanone (Table 2, entry
2). The procedure afforded 173 mg (70%) of the title
compound.
3
4
3
3.4.2.3. a-Phenylcyclohexanone (Table 2, entry 3). The
5
procedure afforded 150 mg (86%) of the title compound.
3.4.1.1. 4-(4-Methylphenyl)morpholine (Table 1,
entry 1). The procedure afforded 171 mg (97%) of the
title compound.
2
7
3.4.2.4. 2-(2,6-Dimethylphenyl)-1-phenylethanone
(Table 2, entry 4). The procedure afforded 212 mg (95%)
1
of the title compound as a white compound. H NMR
3.4.1.2. 4-(2-Pyridinyl)morpholine (Table 1, entry
). The procedure afforded 160 mg (98%) of the title
(400 MHz, CD Cl ): d 8.09 (d, JZ7.2 Hz, 2H), 7.64 (t, JZ
2
2
2
8
2
compound.
7.2 Hz, 1H), 7.54 (t, JZ8.0 Hz, 2H), 7.14–7.06 (m, 3H),
13
4.40 (s, 2H), 2.21 (s, 6H). C NMR (100 MHz, CD Cl ):
2
2

9722
O. Navarro et al. / Tetrahedron 61 (2005) 9716–9722
1
1
2
97.5 (C), 137.7 (C), 133.7 (CH), 133.4 (C), 129.2 (CH),
28.5 (CH), 128.3 (CH), 127.3 (CH), 114.0 (C), 40.2 (CH2),
0.6 (CH ). Elemental analysis: Anal. Calcd for C H O
10. Viciu, M. S.; Stevens, E. D.; Petersen, J. L.; Nolan, S. P.
Organometallics 2004, 23, 3752–3755.
11. (a) Viciu, M. S.; Kelly, R. A., III; Stevens, E. D.; Naud, F.;
Studer, M.; Nolan, S. P. Org. Lett. 2003, 5, 1479–1482. (b)
Viciu, M. S.; Kissling, R. M.; Stevens, E. D.; Nolan, S. P. Org.
Lett. 2002, 4, 2229–2231.
3
16 16
(
MW 224.30): C, 85.68; H, 7.19. Found: C, 85.36; H, 7.23.
3.4.2.5. 2-(p-Methoxyphenyl)-acetophenone (Table 2,
entry 5). The procedure afforded 208 mg (92%) of the
title compound.
3
6
12. Grasa, G. A.; Singh, R.; Stevens, E. D.; Nolan, S. P.
J. Organomet. Chem. 2003, 687, 269–279.
1
3. Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry,
5th ed.; Wiley: New York, 1998.
3.4.2.6. 1-Phenyl-2-(3-pyridinyl)-1-propanone (Table 2,
entry 6). The procedure afforded 188 mg (89%) of the
title compound.
3
7
14. Kawaguchi, S. Coord. Chem. Rev. 1986, 70, 51–84.
15. (a) Shriver, D. F.; Atkins, P. W. Inorganic Chemistry, 3rd ed.;
Freeman: New York, 1988. (b) Fackler, J. P., Jr. Prog. Inorg.
Chem. 1966, 7, 361–425.
Acknowledgements
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974, 47, 665–668. (b) Kanda, Z.; Nakamura, Y.; Kawaguchi,
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The authors would like to thank the National Science
Foundation and the Louisiana Board of Reagents for
financial support of this work and Boehringer Ingelheim
Pharmaceuticals Inc. for an unrestricted grant. O. N.
acknowledges the International Precious Metal Institute
for a Student Award.
17. (a) Belykh, L. B.; Goremyka, T. V.; Shmidt, F. K. Russ. J.
Appl. Chem. 2004, 77, 770–774. (b) Shmidt, F. K.; Belykh, L. B.;
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