Palladium alkynyl and allenylidene complexes: Very efficient precatalysts for C-C coupling reactions

Article abstract of DOI:10.1021/om200862m

Oxidative addition of BrC≡CC(=O)O-menthyl (1a) to [Pd(PPh ₃)₄] affords the alkynyl complex trans-[Br(PPh ₃)₂Pd-C≡CC(=O)O-menthyl] (2a). Subsequent reaction of 2a with trifluoroacetate gives trans-[(F₃CCOO)(PPh ₃)₂Pd-C≡CC(=O)O-menthyl] (3a). Reaction of trans-[Br(PPh₃)₂Pd-C≡CC(=O)NC₄H ₈] (2b) with 10 equiv of NaI gives trans-[I(PPh₃) ₂Pd-C≡CC(=O)NC₄H₈] (4b). The efficiency of the new palladium complexes 3a and 4b as precatalysts is compared with that of recently published cationic palladium allenylidene complexes in C-C coupling reactions. Further trans-bis(alkynyl)palladium complexes, trans-[(PEt ₃)₂Pd(-C≡CC{=O}NR₂)₂] (NR ₂ = N(CH₂)₄ (9b), NMe₂ (9c), N(CH₂)₄O (9d), N(CH₂)₅ (9e)), trans-[(PⁱPr₃)₂Pd(-C≡CC{=O}NMe ₂)₂] (11c), and trans-[(PPh₃) ₂Pd(-C≡CC{=O}NR₂)₂] (NR₂ = N(CH₂)₄ (13b), NMe₂ (13c), N(CH ₂)₄O (13d)), were synthesized by treating HC≡CC(=O)NR₂ with AgNO₃ followed by transmetalation of the alkynyl ligand from silver to [PdCl₂(PEt₃) ₂], [PdCl₂(PⁱPr₃)₂], or [PdCl₂(PPh₃)₂], respectively. Methylation of complexes 9b-e with MeOTf yields dicationic bis(allenylidene) complexes of palladium, trans-[(PEt₃)₂Pd{=C=C=C(OMe)NR ₂}₂]²⁺(OTf)^-₂ (NR ₂ = N(CH₂)₄ (10b-OTf), NMe₂ (10c-OTf), N(CH₂)₄O (10d-OTf), N(CH₂) ₅ (10e-OTf). Alkylation of complex 9e with [Me₃O]BF ₄ or [Et₃O]BF₄ gave trans-[(PEt ₃)₂Pd{=C=C=C(OR)N(CH₂)₅} ₂]²⁺(BF₄)^-₂ (R = Me (10e-BF₄), Et (10e′-BF₄)). Complexes 11c and 13b-d were methylated accordingly to obtain the corresponding bis(allenylidene) complexes 12c-OTf, 12c-BF₄, 14b-OTf, 14c-OTf, and 14d-OTf. The catalytic activities of the new bis(alkynyl) and bis(allenylidene) complexes were investigated and compared with those of the mono(alkynyl) and mono(allenylidene) complexes. The palladium alkynyl and allenylidene complexes are both found to be very efficient precatalysts for Heck, Suzuki, and Sonogashira reactions. Even aryl chlorides were efficiently coupled in Heck and Suzuki reactions when complex 9e was used as precatalyst. Powder diffraction, TEM, and DLS measurements indicate that palladium nanoparticles are not formed during catalysis in the Heck reaction.

Full text of DOI:10.1021/om200862m

Article
pubs.acs.org/Organometallics
Palladium Alkynyl and Allenylidene Complexes: Very Efficient
Precatalysts for C−C Coupling Reactions†
Evelyn Wuttke, Bettina Nagele,‡ Bernhard Weibert, and Florian Kessler*,§
̈
Fachbereich Chemie, Universitat Konstanz, Fach 727. 78457 Konstanz, Germany
̈
S
* Supporting Information
ABSTRACT: Oxidative addition of BrCCC(O)O-
menthyl (1a) to [Pd(PPh3)4] affords the alkynyl complex
trans-[Br(PPh3)2Pd−CCC(O)O-menthyl] (2a). Subse-
quent reaction of 2a with trifluoroacetate gives trans-
[(F3CCOO)(PPh3)2Pd−CCC(O)O-menthyl] (3a). Re-
action of trans-[Br(PPh3)2Pd−CCC(O)NC4H8] (2b)
with 10 equiv of NaI gives trans-[I(PPh3)2Pd−CCC(
O)NC4H8] (4b). The efficiency of the new palladium
complexes 3a and 4b as precatalysts is compared with that
of recently published cationic palladium allenylidene com-
plexes in C−C coupling reactions. Further trans-bis(alkynyl)palladium complexes, trans-[(PEt3)2Pd(−CCC{O}NR2)2]
(NR2 = N(CH2)4 (9b), NMe2 (9c), N(CH2)4O (9d), N(CH2)5 (9e)), trans-[(PiPr3)2Pd(−CCC{O}NMe2)2] (11c), and
trans-[(PPh3)2Pd(−CCC{O}NR2)2] (NR2 = N(CH2)4 (13b), NMe2 (13c), N(CH2)4O (13d)), were synthesized by
treating HCCC(O)NR2 with AgNO3 followed by transmetalation of the alkynyl ligand from silver to [PdCl2(PEt3)2],
[PdCl2(PiPr3)2], or [PdCl2(PPh3)2], respectively. Methylation of complexes 9b−e with MeOTf yields dicationic
bis(allenylidene) complexes of palladium, trans-[(PEt3)2Pd{CCC(OMe)NR2}2]2+(OTf)− (NR2 = N(CH2)4 (10b-
2
OTf), NMe2 (10c-OTf), N(CH2)4O (10d-OTf), N(CH2)5 (10e-OTf). Alkylation of complex 9e with [Me3O]BF4 or [Et3O]BF4
gave trans-[(PEt3)2Pd{CCC(OR)N(CH2)5}2]2+(BF4)−2 (R = Me (10e-BF4), Et (10e′-BF4)). Complexes 11c and 13b−
d were methylated accordingly to obtain the corresponding bis(allenylidene) complexes 12c-OTf, 12c-BF4, 14b-OTf, 14c-OTf,
and 14d-OTf. The catalytic activities of the new bis(alkynyl) and bis(allenylidene) complexes were investigated and compared
with those of the mono(alkynyl) and mono(allenylidene) complexes. The palladium alkynyl and allenylidene complexes are both
found to be very efficient precatalysts for Heck, Suzuki, and Sonogashira reactions. Even aryl chlorides were efficiently coupled in
Heck and Suzuki reactions when complex 9e was used as precatalyst. Powder diffraction, TEM, and DLS measurements indicate
that palladium nanoparticles are not formed during catalysis in the Heck reaction.
described in the literature. Some of them, however, require high
temperatures for activation and others are not very stable at high
temperatures. Therefore, creating new organometallic catalyst
systems is a very challenging field of research and is often a
balancing act between activity and stability.
INTRODUCTION
■
Palladium-catalyzed carbon−carbon bond forming reactions are
among the most powerful tools in modern organic chemistry.1
While the Heck reaction usually is performed at high
temperatures, other C−C coupling reactions such as the Suzuki
reaction and the Sonogashira reaction (Scheme 1) can be
The synthesis of the first allenylidene complexes [LnMC
CC(R1)R2] was simultaneously reported in 1976 by Fischer et al.
(M = Cr, W)2 and Berke (M = Mn).3 Since then allenylidene
complexes of many transition metals have been prepared, including
complexes of titanium, chromium, tungsten, manganese, rhenium,
iron, ruthenium, osmium, rhodium, iridium, and platinum.4 Some of
these complexes have been used as catalyst precursors:5 for instance,
in ring-closing metathesis,6 in ring-opening metathesis,7 in
dehydrogenative dimerization of tin hydrides,8 and in selective
transetherification of substituted vinyl ethers.9 Allenylidene
complexes of palladium, however, have been unknown for a long
time. Only recently have the first palladium allenylidene and
bis(allenylidene) complexes been synthesized and isolated.10,11
Scheme 1
carried out at or even below room temperature. The temperature
is a very important parameter in catalytic applications. A large
number of catalytically active palladium complexes have been
Received: September 14, 2011
Published: November 1, 2011
© 2011 American Chemical Society
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We now report on the catalytic activity of some of these
palladium allenylidene complexes in C−C coupling reactions:
namely Heck, Suzuki, and Sonogashira reactions. For
comparison reasons new C(O)R-substituted palladium
alkynyl and allenylidene complexes as well as a broad range
of bis(alkynyl) and bis(allenylidene) complexes were addition-
ally synthesized and their catalytic activities in the same C−C
coupling reactions were studied.
Scheme 4
Scheme 5
RESULTS AND DISCUSSION
■
Synthesis of Palladium Mono(alkynyl) and Mono-
(allenylidene) Complexes. Recently, we developed an easy
to perform synthesis for O,N-substituted cationic palladium
allenylidene complexes. Oxidative addition of terminally
brominated N,N-dimethylpropiolamides 1b,c (Scheme 2) to
Scheme 2
[Pd(PPh3)4] gave the stable palladium(II) alkynyl complexes
trans-[Br(PPh3)2Pd−CCC(O)NR2]. Subsequent methyl-
ation with either MeOTf or [Me3O]BF4 yielded the first
cationic allenylidene complexes of palladium, [Br(PPh3)2Pd
CCC(OMe)NR2]+X− (X = OTf, BF4).10
Similarly, replacing brominated N,N-dimethylpropiolamide12
by bromoalkyne 1a in the oxidative addition reaction afforded
the stable palladium(II) alkynyl complex 2a in 99% yield
(Scheme 3). Bromoalkyne 1a was obtained by bromination of
of the alkynyl ligand. A high electron density at the metal center
should favor oxidative addition of aryl halides, which often
constitutes the rate-limiting step in palladium-catalyzed cross-
coupling reactions. Therefore, complex 2b with an O,N instead
of O,O substitution pattern was prepared. The iodo complex 4b
(Scheme 4), obtained by treating complex 2b10 with 10 equiv
of NaI at room temperature, was isolated in 81% yield.
In addition, for the catalytic studies several allenylidene com-
plexes (5c-BF4, 5c′-BF4, 7c-OTf, and 7c-BF4) and the alkynyl-
(trifluoroacetato) complex 6c were synthesized as summarized
in Scheme 5. Alkylation of 2c with [Me3O]BF4 and [Et3O]BF4
gave allenylidene complexes 5c-BF4 and 5c′-BF4, respectively.
Substitution of trifluorooacetate for the trans-bromo ligand in
2c gave alkynyl complex 6c; subsequent alkylation of 6c with
MeOTf or [Me3O]BF4 yielded the OTf¯ salt 7c-OTf and the
BF4¯ salt 7c-BF4.10
Scheme 3
The complexes 5b-OTf, 5b-BF4, 5b′-BF4, and 8b-OTf
(Chart 1) were prepared by analogous alkylation procedures
menthyl propiolate with N-bromosuccinimide (Scheme 2).
This reaction can also be perfomed with propiolamides to
obtain compounds 1b,c. Due to the low π-donor properties of
the terminal O,O-substitution pattern in 2a, the electron
density on the metal center is less than that in the recently
investigated O,N-substituted alkynyl complexes 2b,c (see
Schemes 4 and 5). To further decrease the electron density
at the metal, the trans-bromo ligand was replaced by electron-
withdrawing trifluoroacetate. When a solution of 2a in CH2Cl2
was treated with silver trifluoroacetate, AgBr quickly
precipitated from the reaction mixture. The trifluoroacetato
complex 3a was isolated in 88% yield as a yellow solid after
purification by column chromatography (Scheme 3).
Chart 1
An additional modification of the properties of the alkynyl
complex was achieved by variation of the terminal substituents
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Scheme 6
starting from trans-[Br(PPh3)2Pd−CCC(O)NC4H8] or
trans-[Br{P(C6H4OMe-p)3}2Pd−CCC(O)NC4H8].10
Synthesis of Palladium Bis(alkynyl) and Bis-
(allenylidene) Complexes. In 2010 we determined that
even dicationic bis(allenylidene) complexes are readily
accessible by alkylation of suitable alkynyl complexes (Scheme 6).
Transmetalation of the alkynyl ligand from silver13 to palladium
gives the stable palladium bis(alkynyl) complex 9c. Subsequent
alkylation with MeOTf yielded the dicationic allenylidene
complex 10c-OTf.11
in the 13C NMR spectra compare well with those of known
palladium alkynyl complexes.10,11 In comparison to the
corresponding mono(alkynyl) complexes the C1 resonances
of the bis(alkynyl) complexes are observed at lower field by
about 16 ppm. Variation of the phosphine ligands as well as
terminal substituents affects the signals of the alkynyl ligand
only marginally.
In the 31P NMR spectra the single signal for the phosphine
ligands shifts to higher field in the row PiPr3 (∼46 ppm) > PPh3
(∼25 ppm) > PEt3 (∼19 ppm). The same trends are observed
in the NMR spectra of the allenylidene complexes. The
formation of dicationic bis(allenylidene) complexes by
alkylation of bis(alkynyl) complexes is accompanied by a pro-
nounced shift of the C1 resonances to lower field (∼35 ppm)
and a shift of the C2 resonance to higher field (∼8 ppm).
The solid-state structures of bis(alkynyl) complexes 9e
(Figure 1) and 11c (Figure 2) and of the dicationic bis-
(allenylidene) complex 10e′-BF4 (Figure 3) were additionally
To extend the scope of our recently established synthetic
route (Scheme 6), we synthesized a broad range of new
palladium bis(alkynyl) and bis(allenylidene) complexes (Chart 2).
Chart 2
It is noteworthy to say that in addition to pyrrolidine (b) and
dimethylamine (c) also morpholine (d) and piperidine (e)
could be introduced as terminal N substituents, following the
same synthetic route. Furthermore, a variation of the phosphine
substituents from PEt3 to PiPr3 and PPh3 was successful using
[PdCl2(PiPr3)2] or [PdCl2(PPh3)2] instead of [PdCl2(PEt3)2]
as the alkynyl acceptor. Finally, different counterions (OTf
and BF4) and O substituents (Me and Et (see Chart 3)) of the
Figure 1. Structure of the bis(alkynyl) complex 9e in the crystal state
(ellipsoids drawn at the 50% probability level; hydrogen atoms
omitted for clarity).
Chart 3
bis(allenylidene) complexes were obtained by applying
[Me3O]BF4, [Et3O]BF4, and MeOTf as the alkylation agents.
All new complexes were characterized by spectroscopic
means; the purity of the compounds was established by elemental
analysis. The resonances of the alkynyl and allenylidene ligands
Figure 2. Structure of the bis(alkynyl) complex 11c in the crystal state
(ellipsoids drawn at the 50% probability level; hydrogen atoms
omitted for clarity).
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Table 2. Important Bond Distances (Å) and Angles (deg) in
9e, 11c, and 10e′-BF4
9e
11c
10e′-BF4
Pd−C1
Pd−P
C1−C2
C2−C3
C3−N
C3−O
Pd−C1−C2
C1−C2−C3
1.9990(16)
2.3009(8)
1.208(2)
1.996(2)
2.3306(6)
1.212(3)
1.455(3)
1.352(3)
1.235(3)
176.30(19)
177.7(2)
1.986(2)
2.3315(8)
1.209(3)
1.419(3)
1.308(3)
1.318(3)
176.1(2)
171.6(2)
1.456(2)
1.362(2)
1.2339(18)
174.69(12)
177.30(15)
Figure 3. Structure of the bis(alkynyl) complex 10e′-BF4 in the crystal
state (ellipsoids drawn at the 50% probability level; hydrogen atoms
and BF4 counterions are omitted for clarity).
slightly bent: Pd−C1−C2 = 174.69(12) (9e), 176.30(19)
(11c), 176.1(2)° (10e′-BF4) and C1−C2−C3 = 177.30(15)
(9e), 177.7(2) (11c), 171.6(2)° (10e′-BF4). However, a
modest deviation from linearity of the MCCC fragment in
allenylidene complexes is often observed.4 The Pd−C and
C1−C2 distances in the dicationic allenylidene complex 10e′-
BF4 (1.986(2) and 1.209(3) Å) compare well with the bond
lengths in the corresponding alkynyl complex 9e (1.9990(16)
and 1.208(2) Å). The four resonance forms of allenylidene
complexes can explain these similarities (Scheme 7). The
C2−C3 bond in 10e′-BF4 (1.419(3) Å) is significantly shorter
than in 9e (1.456(2) Å). As expected, alkylation results in an
elongation of the C3−O1 bond (9e, 1.2339(18) Å; 10e′-BF4,
1.318(3) Å) and, conversely, leads to a significant short-
ening of the C3−N bond (9e, 1.362(2) Å; 10e′-BF4,
1.308(3) Å).
established by X-ray structure analysis (Tables 1 and 2). In all
three complexes the metal has a square-planar coordination. As
already deduced from the appearance of only one phos-
phorus resonance in the 31P NMR spectra, the phosphine
ligands are mutually trans. The Pd−C1 distances of the
palladium bis(alkynyl) complexes (1.9990(16) Å (9e),
1.996(2) Å (11c)) are significantly longer than those of a
corresponding palladium mono(alkynyl) complex (1.947(3)
Å).10 In both bis(alkynyl) complexes the plane formed by the
atoms C3−O1−N1 (C3 plane) and the coordination plane of
palladium are almost perpendicular (87.9° (9e), 80.6° (11c)). In
contrast, in the palladium bis(allenylidene) complex 10e′-BF4
the C3 plane is strongly tilted against the coordination plane of
palladium (63.5°). In all three complexes the Pd−C3 chain is
Table 1. Crystallographic Data and Refinement Methods for 9e, 11c, and 10e′-BF4
9e
11c·2CH2Cl2
10e′-BF4
empirical formula
Mr
C28H50N2O2P2Pd
615.04
C30H58Cl4N2O2P2Pd
788.92
C32H60B2F8N2O2P2Pd
846.78
cryst syst
space group
a (Å)
triclinic
monoclinic
P21/c
monoclinic
P21/c
P1
̅
7.8879(16)
9.0249(18)
11.313(2)
96.64(3)
105.58(3)
96.99(3)
760.7(3)
2
11.614(2)
10.940(2)
16.303(6)
90
10.590(2)
15.586(3)
15.350(5)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
112.50(2)
90
129.296(19)
90
1913.7(9)
2
1960.7(8)
2
Z
cryst size (mm3)
0.5 × 0.4 × 0.3
1.343
0.5 × 0.4 × 0.3
1.369
0.50 × 0.45 × 0.40
1.434
ρcalcd (g cm−3
)
μ (mm−1
F(000)
T (K)
)
0.741
0.876
0.624
324
824
880
100(2)
100(2)
100(2)
max 2θ (deg)
53.40
53.56
53.58
index ranges
−9 ≤ h ≤ 9
−11 ≤ k ≤ 11
−14 ≤ l ≤ 14
10 741
−14 ≤ h ≤ 14
−13 ≤ k ≤ 13
−20 ≤ l ≤ 20
26 492
−13 ≤ h ≤ 13
−19 ≤ k ≤ 17
−19 ≤ l ≤ 19
25 256
no. of data
no. of unique data
R(int)
3174
4056
4165
0.0400
0.0493
0.0402
no. of params
160
187
223
goodness of fit on F2
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
largest diff peak/hole (e Å−3
1.088
1.146
1.017
0.0187, 0.0464
0.0203, 0.0469
0.328, −0.560
0.0293, 0.0639
0.0348, 0.0654
0.576, −0.599
0.0311, 0.0691
0.0387, 0.0717
0.787, −0.718
)
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was used as precatalyst. However, the bis(alkynyl) complex 9e
showed catalytic activity at this, for Heck type reactions, fairly
low temperature (Scheme 9). The lower temperature allowed
Scheme 7
Scheme 9
The conclusions drawn from the solid-state structures are
supported by the spectroscopic data. The formation of the
dicationic bis(allenylidene) complexes by alkylation of the
bis(alkynyl) complexes was accompanied by just a slight shift of
the ν(CCC) vibration to lower energy (∼6 cm−1). The
positions of the ν(CCC) vibration are dependent on the
phosphine ligands. With diminishing alkalinity of the phosphine
ligands we observe a shift to higher energy (PiPr3 > PEt3 >
PPh3).
Catalytic Investigations. Initial reactivity experiments
indicated that these alkynyl as well as the allenylidene
complexes are active catalyst precursors in carbon−carbon
coupling reactions. Therefore, the catalytic properties of the
palladium complexes presented were investigated in detail. The
activity in different types of C−C coupling reactionsHeck,
Suzuki and Sonogashira reactionswas explored. The neutral
alkynyl complexes and the cationic allenylidene complexes span
a rather broad range of electron density at the metal.
Consequently, significant differences in relative activity for
alkynyl and allenylidene complexes were observed in the three
types of carbon−carbon bond forming reactions.
Heck Coupling. First, we decided to test our complexes in a
Heck reaction14 to test not only their activity as precatalysts but
also their stability at the elevated temperatures needed for this
type of reaction. After some initial attempts bromobenzene
(1 equiv) could be successfully coupled with styrene (1.5 equiv)
at 130 °C using 0.4 mol % of complex 7c-OTf. To optimize the
reaction we screened 14 common bases (NaOAc, K2CO3,
Na2CO3, NaOtBu, KOtBu, K3PO4, Cs2CO3, NEt3, KOH,
NaOH, NaNH2, NaOMe, LiOAc, Na2HPO4) and found
NaOMe to give the highest conversion. Due to this
optimization the reaction temperature could be decreased to
110 °C and within 30 min 53% of the bromobenzene was
converted to stilbene using NaOMe as base, NMP as solvent,
and 0.4 mol % of 7c-OTf as precatalyst (Scheme 8). It is
us to use other solvents such as ethanol (36% conversion) and
an ethanol/water mixture (24% conversion). These results
indicate a high stability of the bis(alkynyl) complex 9e, even in
aqueous media. However, due to the highest conversion we
used NMP for our further investigations.
In the following study a reaction temperature of 110 °C was
chosen for mono(alkynyl) and mono(allenylidene) complexes
and 90 °C for bis(alkynyl) and bis(allenylidene) complexes.
The activity as precatalyst of the various cationic mono-
(allenylidene) complexes varied only slightly (50−68%); the
neutral mono(alkynyl) complexes 3a and 4b, however, gave
significantly slower conversions (Table 3). The efficiency as
Table 3. Influence of Alkynyl and Allenylidene Complexes
a
on the Heck Coupling of Bromobenzene with Styrene
b
entry
complex
conversn
1
2
3
4
5
6
7
8
3a
26
23
64
58
50
68
51
66
6
4b
5c-BF4
5c′-BF4
7c-OTf
7c-BF4
5b-BF4
8b-OTf
9b
c
9
c
10
9e
54
12
c
11
14c-OTf
a
Reaction conditions: 0.25 mmol of bromobenzene, 0.375 mmol of
styrene, 0.4 mol % of the Pd complex, 0.5 mmol of NaOMe, and 1 mL
b
of NMP; 110 °C; 0.5 h. GC conversion (%) of bromobenzene using
n-dodecane as internal standard. At 90 °C.
c
precatalyst turned out to be dependent on the anion (compare
entries 5 and 6); the BF4 salt gave a somewhat higher
conversion than the CF3SO3 salt. Changing the ligand in the
trans-position from trifluoroacetate (entry 6) to the less
electron-withdrawing bromo ligand (entry 3) did not affect
the catalytic activity. Variation of the substituent at the
allenylidene ligand (OMe versus OEt, NMe2 versus N(CH2)4)
influenced the activity only marginally. The same was true for
replacing PPh3 by the more basic phosphine P(C6H4OMe-p)3
and simultaneously BF4¯ by OTf¯ (increase in activity by about
30%; see entries 7 and 8). At lower temperature (90 °C), in
addition to complex 9e only complexes 9b and 14c-OTf
showed catalytic activity (Table 3). A significant difference in
activity was obtained within these complexes, with 9e being the
most active precatalyst under the applied conditions.
Scheme 8
noteworthy that a full conversion can be achieved by extending
the reaction time. In order to be able to detect higher or lower
conversions, we adjusted the reaction time to get approximately
50% conversion.
The reaction could not be improved by variation of the
solvent. In other high-boiling solvents such as DMA and
DMSO no conversion of the bromobenzene took place and in
1,4-dioxane a conversion of only 1.5% of the starting material
was observed. Under these optimized conditions we tried to
lower the reaction temperature to 90 °C; however, no
conversion of the bromobenzene was observed when 7c-OTf
With the highly active precatalyst 9e it was even possible to
perform the Heck coupling reaction of 4-chloroacetophenone
with styrene (ratio 1:1.5; Scheme 10). With NaOMe as the
base and N-methyl-2-pyrrolidone as the solvent over 18 h at
140 °C, 76% GC conversion of 4-chloroacetophenone was
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nanoparticles is in the diameter range 2−20 nm. Therefore, the
size distribution of the palladium and palladium oxide particles
in the reaction mixture was determined by dynamic light
scattering. As shown in Figure 5, the diameter of the particles
Scheme 10
obtained. Under these calm reaction conditions for none of the
commercially available complexes [PdCl2(PEt3)2],
[PdCl2(PiPr3)2], and [PdCl2(PPh3)2] was a coupling reaction
observed.
At the elevated temperatures (>100 °C) usually required for
catalyzing Heck coupling reactions, palladium nanoparticles
could be formed by decomposition of the Pd complexes.
Palladium nanoparticles have been suggested to be the
catalytically active species in palladium-catalyzed coupling
reactions.15 To determine whether or not such palladium
nanoparticles are formed from palladium allenylidene precata-
lysts, the coupling of bromobenzene with styrene catalyzed by
complex 8b-OTf (Table 3, entry 8) was studied in detail. First
we repeated this reaction but with a drop of mercury added and
the solution was vigorously stirred. This test has often been
successful in demonstrating the presence of homogeneous
catalysts when no poisoning of the catalyst was observed. In our
case the reaction got significantly poisoned by mercury, which
indicates that a heterogeneous or (not very well protected by
the ligands) homogeneous Pd(0) species is present in the
catalytic cycle.16 To further study the presence of Pd nano-
particles, we extended the reaction time from 30 min to 3 h to
get full conversion of the starting material. In this reaction the
desired product (trans-stilbene) was formed in 92% yield along
with 8% of 1,1-diphenylethene as a side product. After it was
cooled to ambient temperature, the reaction mixture was dried
in air and the resulting solid was analyzed by powder XRD (see
Figure 4). The observed reflections compare well to those
Figure 5. Size distribution of particles after catalysis measured by
dynamic light scattering (DLS).
formed in the reaction catalyzed by complex 8b-OTf was about
60−70 nm. This suggested that these particles were not the
catalytically active species. Also, we could not identify any
particles smaller than 50 nm by transition electron microscopy
(TEM). On the basis of these results it is likely that a molecular
species formed from the allenylidene precursor complex is the
catalytically active species.
In 2000 Amatore and Jutand showed that [PdIICl2(PPh3)2] is
reduced to [Pd0Cl(PPh3)2]− rather then the often expected
[Pd0(PPh3)2].17 On the basis of this mechanism we postulate
that a neutral Pd(0) spezies a is formed from the cationic
Pd allenylidene complex 8b-OTf, as despicted in Scheme 11.
Scheme 11. Postulated Mechanism for the Heck Reaction
Catalyzed with Precatalyst 8b-OTf
Figure 4. Powder XRD patterns of complex 8b-OTf, trans-stilbene,
and the reaction mixture after catalysis.
obtained from palladium and palladium oxide particles. From
the comparison of the XRD pattern with those of XRD powder
patterns of trans-stilbene and complex 8b-OTf it followed that
the observed reflections were due neither to trans-stilbene nor
to complex 8b-OTf.
The size of palladium particles is important for their catalytic
activity. Usually, the size of the catalytically active palladium
How this reduction (step A) exactly occurs remains unclear.
However, we expect the base to play a crucial role. In step B
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oxidative addition occurs, forming first a five-coordinate
species, which then converts to complex b in the preferred
square-planar geometry. Syn addition of an alkene (step C)
gives complex c, and β-hydride elimination (step D) forms
complex d. In this step the product is released. Finally the base
reduces the hydrido complex and the catalytic cycle is closed. In
conclusion, we think that formation of the catalyst from the
precatalyst (step A) is the main reason for different activities
within the series of complexes (Table 3). However, this
mechanism is only a postulation, and to draw a final conclusion
about the nature of the catalytically active species a more
detailed mechanistic study, including a three-phase test and
supporting theoretical calculations, will be needed.
Table 5. Influence of the Pd Complex on the Suzuki
Coupling of 1-Bromo-4-Butylbenzene with Phenylboronic
Acid
a
b)
entry
complex
conversn
1
3a
92
33
100
60
64
74
71
97
70
26
2
4b
3
5c-BF4
5c′-BF4
7c-OTf
7c-BF4
5b-OTf
5b-BF4
5b′-BF4
8b-OTf
4
5
6
7
8
Suzuki Coupling. The Suzuki coupling18 of 1-bromo-4-
butylbenzene with phenylboronic acid (ratio 1:1.5; Scheme 12)
9
10
a
Reaction conditions: 0.1 mmol of 1-bromo-4-butylbenzene, 0.15
mmol of phenylboronic acid, 1 mol % of the Pd complex, 0.2 mmol of
Scheme 12
b)
Cs2CO3, and 1 mL of THF; 50 °C; 1 h. GC conversion (%) of 1-
bromo-4-butylbenzene using n-dodecane as internal standard.
from 4 to 1 h. The differences in activity and the influence of
the substituents and ligands were more pronounced than in the
Heck reactions described before. As with the Heck coupling,
the anion in the allenylidene complexes exerted a small
influence, the OTf salts being slightly less active than the BF4
salts (entries 5 and 7 versus 6 and 8). Whereas replacing OMe
by OEt (entries 3 vs 4 and 8 vs 9) led to a significant decrease
in activity, the influence of substitution of NMe2 for N(CH2)4
was almost negligible.
When the trifluoroacetato ligand in a trans position was
replaced by the less electron-withdrawing bromo ligand, an
increase in activity was observed (entries 3 and 6). In contrast,
replacing PPh3 by the more basic P(C6H4OMe)3 in a cis
position and thus increasing the electron density at palladium
caused a drop in activity (complexes 5b-OTf and 8b-OTf,
entries 7 and 10).
was likewise studied in detail. The para-substituted bromo-
(butyl)benzene was chosen, since the heterocoupling product,
the homocoupling product of the phenylboronic acid (often
observed as the product of a side reaction), and reduction
products of the bromobenzene are easily differentiated.
Initially, 1 mol % of complex 7c-OTf as catalyst precursor,
2 equiv of potassium phosphate as base, and THF as solvent
were employed. At 50 °C the reaction was complete within
approximately 24 h. No reaction was observed without base and
without palladium catalyst. Decreasing the loading of complex
7c-OTf to 0.1 or 0.01 mol % resulted in a reduction of the
conversion to 58% or 33%, respectively. Analogously to the
Heck reaction described before, the Suzuki coupling proved to
be considerably base-dependent (Table 4). The highest
Table 4. Influence of the Base on the Suzuki Coupling of
1-Bromo-4-Butylbenzene with Phenylboronic Acid
Surprisingly different are the results obtained with alkynyl
complexes. In both neutral alkynyl complexes the palladium
atom is more electron rich than in the cationic allenylidene
complexes. Complex 4b, having a π-electron-donating iodide in
a trans position and the better π-donating pyrrolidinyl
substituent, gave a much lower conversion than complex 3a
(CF3COO¯ in trans position and O-menthyl as substituent at
Cγ). Since a high electron density on the metal center should
favor the oxidative addition step of the catalytic cycle, these
results suggest that the oxidative addition is not the rate-
limiting step in the catalytic cycle of the Suzuki coupling with
alkynyl or allenylidene complexes.
a
b
entry
base
K3PO4
conversn
1
53
34
3
2
K2CO3
3
Na2CO3
LiOtBu
4
0
5
NaOtBu
KOtBu
93
18
20
94
8
6
7
KOEt
8
Cs2CO3
LiNEt2
9
Under the aforementioned conditions (1 mol % of complex,
NaOtBu, THF, 50 °C, 4 h) no coupling product was formed
when bis(alkynyl) complex 9e was used as the precatalyst. Even
with the more reactive iodobenzene we had to increase the
temperature from 50 to 70 °C to get a 30% conversion (after 4 h)
using NaOtBu as base and THF as solvent. Under the same
conditions a change of solvent from THF to EtOH resulted in a
significant increase of reactivity. Full conversion (100%) was
observed in EtOH and also in the solvent mixtures THF/EtOH
and EtOH/water, while in some common solvents (NMP,
hexane, DMF, DMSO, 1,4-dioxane, toluene, acetonitrile,
benzene) no conversion of the starting material was observed.
For our further studies we used the EtOH/water mixture as a
“green” solvent. Under these optimized solvent conditions we
got a 73% conversion of 1-bromo-4-butylbenzene with
10
11
12
13
14
LDA
15
0
LiN(TMS)2
NaN(TMS)2
KN(TMS)2
NaNH2
0
0
8
a
Reaction conditions: 0.1 mmol of 1-bromo-4-butylbenzene, 0.15 mmol
of phenylboronic acid, 1 mol % of complex 7c-OTf, 0.2 mmol of base,
and 1 mL of THF; 50 °C; 4 h. GC conversion (%) of 1-bromo-4-
butylbenzene using n-dodecane as internal standard.
b
conversions were obtained after 4 h at 50 °C with NaOtBu
(93%) and Cs2CO3 (94%) (entries 5 and 8) as the base. Under
analogous conditions potassium phosphate gave 53% conversion.
Table 5 summarizes the activities of various alkynyl and
allenylidene complexes after the reaction time has been reduced
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phenylboronic acid using 9e as precatalyst (1 mol % of
complex, NaOtBu, EtOH/water, 50 °C, 4 h).
Table 7. Influence of the Solvent on the Sonogashira
Coupling of Iodobenzene with Phenylacetylene
a
With complex 9e it was even possible to perform the Suzuki
coupling reaction of 4-chloroacetophenone with phenylboronic
acid (ratio 1:1.5; Scheme 13). With NaOtBu as the base and
conversn
?b)
entry
solvent
1
2
3
4
5
6
7
8
THF
DMF
71
32
99
21
9
Scheme 13
DMSO
acetonitrile
toluene
propylene carbonate
diethyl carbonate
dimethyl carbonate
99
89
44
a
Reaction conditions: 0.1 mmol of iodobenzene, 0.12 mmol of
phenylacetylene, 5 mol % of complex 5b-OTf, 10 mol % of CuI,
0.2 mmol of NEt3, and 1 mL of solvent; room temperature; 1 h.
EtOH/H2O (1:1) as the solvent over 22 h at 70 °C a 51% GC
conversion of 4-chloroacetophenone was obtained. After the
reaction time was increased from 22 to 40 h and the catalyst
loading from 3 to 6%, full conversion of the aryl chloride was
observed. Under these calm reaction conditions for none of the
commercially available complexes [PdCl2(PEt3)2],
[PdCl2(PiPr3)2], and [PdCl2(PPh3)2] was a coupling reaction
observed.
Furthermore, we repeated the Suzuki coupling reaction with
complex 7c-OTf, except with a drop of mercury added and
vigorous stirring of the solution. Analogously to the Heck
reaction, the Suzuki reaction was significantly poisoned by
mercury.
b)
GC conversion (%) of iodobenzene using n-dodecane as internal
standard.
eight solvents (Table 7), DMSO and propylene carbonate gave
the best results.
In all subsequent reactions, DMSO was used as the solvent.
For a comparison of the relative activities of the various
complexes, the reaction time was reduced to 30 min. The
relative activities of the alkynyl and allenylidene complexes in
Sonogashira coupling reactions (Table 8) deviated strongly
Sonogashira Coupling. The coupling of iodobenzene with
phenylacetylene (ratio 1:1.2; R = H; Scheme 14), employing
Table 8. Influence of the Pd Complex on the Sonogashira
Coupling of Iodobenzene with Phenylacetylene
a
b
entry
complex
conversn
Scheme 14
1
2
3
4
5
6
7
8
9
3a
96
100
10
1
4b
5c-BF4
5c′-BF4
7c-OTf
7c-BF4
5b-OTf
5b-BF4
5b′-BF4
72
88
48
85
79
5 mol % of complex 7c-OTf as catalyst precursor, 10 mol %
of copper iodide as cocatalyst in THF, and 2 equiv of
triethylamine as base, went to completion at ambient
temperature within less than 3 h. In contrast, no reaction
took place without base and without palladium complex.
Secondary and tertiary amines are commonly used as bases
for Sonogashira coupling reactions.19 However, in some cases
the conversion could be significantly increased by changing
the base.20 The screening of some bases (Table 6) confirmed
a
Reaction conditions: 0.1 mmol of iodobenzene, 0.12 mmol of
phenylacetylene, 5 mol % of Pd complex, 10 mol % of CuI, 0.2 mmol
of NEt3, and 1 mL of DMSO; room temperature; 30 min. GC
b
conversion (%) of iodobenzene using n-dodecane as internal standard.
from those in Heck (Table 3) and Suzuki reactions (Table 5).
Whereas in Heck reactions the alkynyl complexes 3a and 4b
were the least active catalyst precursors, they turned out to be
the most active complexes in Sonogashira reactions. Both
complexes gave full or nearly full conversion of iodobenzene
and phenylacetylene to diphenylacetylene. Within the series of
allenylidene complexes, 5c-BF4 and 5c′-BF4 showed the least
activity (in contrast to the case for Suzuki reactions). Again, a
moderate dependence on the anion was observed, BF4 salts
giving slightly better results than OTf salts. Catalysis of the
Sonogahira reaction by nanoparticles formed by decomposition
of the alkynyl or allenylidene complexes seems unlikely, since
all Sonogahira reactions were performed at room temperature.
Under the reaction conditions employed, all complexes were
stable, even at elevated temperatures. Furthermore, TEM
measurements did not indicate formation of any nanoparticles.
When different substituted aryl iodides were employed in the
reaction with phenylacetylene, full or nearly full conversions
Table 6. Influence of the Base on the Sonogashira Coupling
of Iodobenzene with Phenylacetylene
a
b
entry
base
conversn
1
2
3
4
K2CO3
Cs2CO3
NEt3
47
6
67
8
KOH
a
Reaction conditions: 0.1 mmol of iodobenzene, 0.12 mmol of
phenylacetylene, 5 mol % of complex 5b-OTf, 10 mol % of CuI, 0.2
b
mmol of base, and 1 mL of THF; room temperature; 1 h. GC
conversion (%) of iodobenzene using n-dodecane as internal standard.
that the coupling of iodobenzene with phenylacetylene is
significantly base dependent. For our catalyst system, NEt3
gave the best results.
In addition to bases, the solvent likewise considerably
influences the activity of the complexes. In the screening of
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H3PO4 (31P). For the menthyl group the following labeling scheme
was used:
were observed within 1 h, although the catalyst loading was
reduced from 5 to 3 mol %. Only 4-iodoanisole gave a
somewhat lower conversion (80%). The reaction of 4-bromo-1-
iodobenzene with phenylacetylene yielded only (4-
bromophenyl)phenylacetylene. The corresponding (4-
iodophenyl)phenylacetylene was not formed, presumably due
to the lower reactivity of aryl bromides in comparison to aryl
iodides. The heterocoupling products (Table 9) were obtained
Table 9. Influence of the Para Substituent R on the
Sonogashira Coupling of the Aryl Iodides R-C6H4-I-p with
Phenylacetylene
a
IR spectra were obtained on a Biorad FTS 60 instrument and MS
on a Finnigan MAT 312 instrument . Elemental analysis was carried
out on Heraeus Elementar vario EL and Elementar vario MICRO
Cube instruments. The UV−vis spectra were recorded on a Hewlett-
Packard 8452A diode array spectrophotometer. GC/MS analyses were
made on an Agilent Technologies 5975C MSD interfaced to an
Agilent Technologies 7890A series GC.
b
b
entry
R
conversn
yield
1
2
3
4
H
100
99
95
94
75
95
COCH3
OMe
Br
80
100
1-Bromo-(−)-menthyl Propiolate (1a). A solution of 10 mmol
of menthyl propiolate in 40 mL of acetone was treated at ambient
temperature with 2.16 g (12 mmol) of N-bromosuccinimide and
150 mg (0.9 mmol) of AgNO3. After 80 min the reaction mixture was
poured onto 200 mL of ice water. The aqueous phase was extracted
three times with 50 mL portions of ethyl acetate. The combined
organic extracts were dried over MgSO4. The solid was filtered off and
the solvent removed in vacuo. The crude product was filtered over a
short plug of silica using CH2Cl2 as the eluent. Removal of the solvent
in vacuo gave 1a as a white solid. Yield: 2.56 g (89%). Mp: 85 °C.
a
Reaction conditions: 0.1 mmol of aryliodide, 0.12 mmol of
phenylacetylene, 3 mol-% of complex 4b, 10 mol-% of CuI, 0.2
b
mmol of NEt3 and 1 mL of DMSO; room temp.; 1 h. GC conversion
(%) of the aryliodide and GC yield (%) of diarylacetylene using
n-dodecane as internal standard.
in very high yield. Formation of homocoupling products of in
situ formed copper acetylide species (Glaser coupling) could
not be detected.
3
4
1H NMR (400 MHz, CDCl3): δ 4.71 (td, JHH = 11.1 Hz, JHH = 4.3
Hz, 1 H, H1), 1.95 (m, 2 H, H2), 1.83 (m, 2 H, H4), 1.62 (m, 1 H, H8),
1.36 (m, 1 H, H6), 0.99 (m, 2 H, H5), 0.96 (m, 1 H, H3), 0.85−0.83
In summary, the new neutral alkynyl as well as the cationic
allenylidene complexes of palladium are very active catalyst
precursors for several carbon−carbon bond-forming reactions.
These complexes are readily available by straightforward
syntheses and are remarkably stable. The relative reactivity
varies considerably, depending on the type of carbon−carbon
coupling reaction. In general, in comparison to the alkynyl
complexes 3a and 4b allenylidene complexes turned out to be
(a) more active catalyst precursors in Heck reactions and (b)
somewhat less active in Sonagashira reactions. In Suzuki C−C
coupling reactions the differences in activity between alkynyl
and allenylidene complexes are small; however, the activity
significantly depends on the substitution pattern. The high
activity allows for rather modest reaction temperatures: for
instance, room temperature in Sonogashira reactions. In Heck
and Suzuki reactions even aryl chlorides are efficiently coupled
when complex 9e was used as precatalyst. Under these calm
reaction conditions for none of the commercially available
complexes [PdCl2(PEt3)2], [PdCl2(PiPr3)2], and
[PdCl2(PPh3)2] was a coupling reaction observed.
3
(m, 6 H, H9, H10), 0.69 (d, JHH = 7.0 Hz, 3 H, H7) ppm. 13C NMR
(100.5 MHz, CDCl3): δ 177.5 (C(O)O), 152.1 (BrCC), 76.8
(C1), 46.7 (C6), 40.4 (C2), 34.0 (C4), 31.2 (C3), 29.5 (C8), 26.0 (C5),
23.2 (BrCC), 21.8 (C10), 20.6 (C9), 16.1 (C7) ppm. IR (CH2Cl2):
ν(CC) 2198 cm−1. EI-MS (70 eV): m/z (%) 287 (1) [M+], 207 (1)
[(M − Br)+], 138 (100) [(M − Br − CCC(O)O − H)+], 123
(59) [(M − Br − CCC(O)O − H − CH3)+], 95 (76) [(M −
Br − CCC(O)O − H − C3H7)+]. Anal. Calcd for C13H19BrO2
(287.20): C, 54.37; H, 6.67. Found: C, 54.09; H, 6.71.
trans-Bromo(3-((−)-menthoxy)-3-oxy-1-propynyl)bis-
(triphenylphosphine)palladium(II) (2a). A suspension of 1.16 g
(1.0 mmol) of [Pd(PPh3)4] in 25 mL of CH2Cl2 was treated with
0.43 g (1.5 mmol) of 1a at ambient temperature. The mixture was
stirred for 30 min. Then the solvent was removed in vacuo and the
crude product was purified by column chromatography using a
petroleum ether/CH2Cl2 mixture as the eluent. Removal of the solvent
1
gave 2a as a yellow solid. Yield: 0.91 g (99%). Mp: 174 °C dec. H
NMR (400 MHz, CD2Cl2): δ 7.73−7.68 (m, 12 H, o-CH), 7.49−7.40
(m, 18 H, m,p-CH), 4.30 (td, 3JHH = 10.9 Hz, 4JHH = 4.7 Hz, 1 H, H1),
1.63 (m, 2 H, H2), 1.56 (m, 2 H, H4), 1.47 (m, 1 H, H8), 1.34 (m, 1 H,
3
H6), 1.13 (m, 2 H, H5), 0.88 (d, JHH = 6.6 Hz, 3 H, H9), 0.80 (d,
3JHH = 6.6 Hz, 3 H, H10), 0.70 (m, 1 H, H3), 0.57 (d, 3JHH = 6.6 Hz, 3
H, H7) ppm. 13C NMR (100.5 MHz, CD2Cl2): δ 152.7 (C(O)OR),
135.2 (t, 2JPC = 6.4 Hz, o-C), 131.0 (p-C), 128.4 (t, 3JPC = 5.6 Hz, m-C),
74.0 (C1), 47.0 (C6), 41.3 (C2), 34.5 (C4), 31.7 (C3), 25.7 (C8), 23.3
(C5), 22.1 (C10), 20.9 (C9), 16.0 (C7) ppm; not observed Pd−CC,
i-C. 31P NMR (161.8 MHz, CD2Cl2): δ 24.6 ppm. IR (CH2Cl2): ν(C
C) 2115 cm−1; ν(CO) 1677 cm−1. UV−vis (CH2Cl2): λmax (nm)
(log ε) 301 (4.279). FAB-MS: m/z (%) 837 (4) [(M − Br)+], 633 (22)
[(M − CCC(O)O-menthyl − Ph)+], 367 (30) [(M − Br − C
CC(O)O-menthyl − PPh3)+]. Anal. Calcd for C49H49BrO2P2Pd
(918.20): C, 64.10; H, 5.38. Found: C, 64.03; H, 5.41.
trans-(3-(−)-Menthoxy-3-oxy-1-propynyl)trifluoroacetato-
{bis(triphenylphosphine)}palladium(II) (3a). A suspension of
0.63 g (0.69 mmol) of 2a and 0.15 g (0.69 mmol) of Ag[CF3CO2]
in 30 mL of dry CH2Cl2 was stirred for 30 min at room temperature.
The precipitate (AgBr) that formed was filtered off. The solvent of the
crude reaction mixture was removed in vacuo. The crude product was
EXPERIMENTAL SECTION
■
General Considerations. All operations were performed under
an inert gas atmosphere using standard Schlenk techniques. Solvents
were dried by distillation from CaH2 (CH2Cl2), LiAlH4 (petroleum
ether, hexane), or sodium (THF, Et2O). The silica gel used for
chromatography (Baker, silica for flash chromatography) was nitrogen-
saturated. The yields refer to analytically pure compounds and were
not optimized. The propiolamides,12 the bromoalkynes 1b,c, the
complexes 2b,c, 5c-BF4, 5c′-BF4, 6c, 7c-OTf, 7c-BF4, 5b-OTf, 5b-
BF4, 5b′-BF4, and 8b-OTf,10 the silver acetylides,13 complexes 9b,c,
10b-OTf, and 10c-OTf,11 and [Me3O]BF4 and [Et3O]BF4 were
21
prepared according to literature procedures. All other chemicals were
commercial products and were used as supplied. H, 13C, 19F, and 31P
1
NMR spectra were recorded with Bruker Avance 400 and Varian Inova
400 spectrometers at ambient temperature. Chemical shifts are relative
to the residual solvent peaks or tetramethylsilane (1H, 13C) or 100%
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purified by column chromatography on silica using a CH2Cl2/acetone
mixture as eluent. Removal of the solvent in vacuo gave 3a as a yellow
solid. Yield: 0.58 g (88%). Mp: 85 °C. 1H NMR (400 MHz, CD2Cl2):
δ 7.73−7.63 (m, 12 H, o-CH), 7.45−7.35 (m, 18 H, m,p-CH), 4.22
(t, J = 5.3 Hz, 4 H, NCH2CH2CH2), 1.95 (m, 12 H, PCH2CH3),
1.60−1.49 (m, 12 H, NCH2CH2CH2), 1.13 (m, 18 H, PCH2CH3)
ppm. 13C NMR (100.5 MHz, CDCl3): δ 154.1 (s, Cγ), 118.8 (t, 2JPC
=
3
16.7 Hz, Cα), 104.5 (t, JPC = 3.2 Hz, Cβ), 47.9 (s, NCH2CH2CH2),
41.7 (s, NCH2CH2CH2), 26.5 (s, NCH2CH2CH2), 25.5 (s,
3
4
(td, JHH = 10.9 Hz, JHH = 4.7 Hz, 1 H, H1), 1.62 (m, 5 H, H2, H4,
H8), 1.35 (m, 1 H, H6), 1.14 (m, 2 H, H5), 0.79 (d, 3JHH = 6.6 Hz, 3 H,
H9), 0.70 (d, 3JHH = 6.6 Hz, 3 H, H10), 0.54 (m, 1 H, H3), 0.45 (d, 3JHH
= 6.6 Hz, 3 H, H7) ppm. 13C NMR (100.5 MHz, CD2Cl2): δ 134.6 (t,
1
NCH2CH2CH2), 24.8 (s, NCH2CH2CH2), 16.8 (t, JPC = 14.4 Hz,
PCH2CH3), 8.4 (s, PCH2CH3) ppm. 31P NMR (161.8 MHz, CDCl3):
δ 19.6 ppm. IR (CH2Cl2): ν(CC) 2089 cm−1. UV−vis (CH2Cl2):
λmax (nm) (log ε) 235 (4.623). FAB-MS: m/z (%) 615 (100) [M+],
497 (14) [(M − PEt3)+], 363 (29) [(M − PEt3 − CCC(
O)N(CH2)5)+]. Anal. Calcd for C28H50N2O2P2Pd (615.08): C, 54.68;
H, 8.19; N, 4.55. Found: C, 54.50; H, 8.25; N, 4.56%.
1
2JPC = 6.7 Hz, o-C), 130.8 (p-C), 129.0 (t, JPC = 25.5 Hz, ipso-C),
3
128.4 (t, JPC = 5.3 Hz, m-C), 74.0 (C1), 46.8 (C6), 40.7 (C2), 34.1
(C4), 31.2 (C3), 25.5 (C8), 23.1 (C5), 22.0 (C10), 20.8 (C9), 16.1 (C7)
ppm; not observed Pd−CCC, F3CCO. 31P NMR (161.8 MHz,
CD2Cl2): δ 23.5 ppm. IR (CH2Cl2): ν(CC) 2123 cm−1; ν(CO)
1680 cm−1. UV−vis (CH2Cl2): λmax (nm) (log ε) 299 (4.417). FAB-
MS: m/z (%) 838 (54) [(M − CF3COO)+], 760 (8) [(M − CF3COO −
Ph)+], 655 (45) [(M − PPh3)+], 552 (18) [(M − CF3COO − Ph − C
CC(O)O-menthyl)+], 470 (100) [(M − PPh3 − C(O)O-
menthyl)+]. Anal. Calcd for C51H49F3O4P2Pd (951.31): C, 64.39; H,
5.19. Found: C, 64.38; H, 5.58.
t r a n s - [ B i s ( 3 - ( N - m o r p h o l i n o ) - 3 - m e t h o x y - 1 , 2 -
propadienylidene)bis(triethylphosphine)palladium(II)] Trifluoro-
methanesulfonate (10d-OTf). A solution of 0.60 g (0.1 mmol) of
9d in 10 mL of CH2Cl2 was treated with 0.24 μL (0.2 mmol) of
MeOTf at ambient temperature. The mixture was stirred for 2.5 h.
Removal of the solvent gave 10d-OTf as a yellow solid. Yield: 0.20 g
1
(99%). Mp: 93 °C. H NMR (400 MHz, CD2Cl2): δ 4.29 (s, 6 H,
OCH3), 4.01 (t, J = 4.8, 4 H, N(CH2CH2)2O), 3.91−3.81 (m, 12 H,
N(CH2CH2)2O), 2.05−1.94 (m, 12 H, PCH2CH3), 1.26−1.14 (m, 18
H, PCH2CH3) ppm. 13C NMR (100.5 MHz, CD2Cl2): δ 156.6 (t,
2JPC = 15.3 Hz, Cα), 153.6 (s, Cγ), 121.5 (q, JCF = 322.4 Hz, SO3CF3),
trans-Iodo(3-(N,N-tetramethyleneamino)-3-oxy-1-propynyl)-
bis(triphenylphosphine)palladium(II) (4b). A solution of 0.41 g
(0.49 mmol) of 2b and 0.74 g (4.9 mmol) of NaI in 30 mL of dry
CH2Cl2 was stirred for 5 h at room temperature. The precipitate was
filtered off. The solvent of the crude reaction mixture was removed in
vacuo. The crude product was purified by column chromatography on
silica using a CH2Cl2/acetone mixture as the eluent. Removal of the
solvent in vacuo gave 4b as a yellow solid. Yield: 0.35 g (81%). Mp:
145 °C dec. 1H NMR (400 MHz, CD2Cl2): δ 7.72−7.70 (m, 12 H, o-
3
97.3 (t, JPC = 3.4 Hz, Cβ), 66.2 (s, N(CH2CH2)2O), 65.8 (s,
N(CH2CH2)2O), 62.5 (s, OCH3), 51.1 (s, NCH2), 46.9 (s, NCH2),
1
17.6 (t, JPC = 15.0 Hz, PCH2CH3), 8.85 (s, PCH2CH3) ppm. 31P
NMR (161.8 MHz, CD2Cl2): δ 22.0 ppm. 19F NMR (376 MHz,
CD2Cl2): δ −78.8 (SO3CF3) ppm. IR (CH2Cl2): ν(CCC) 2082 cm−1.
UV−vis (CH2Cl2): λmax (nm) (log ε) 281 (4.578). Anal. Calcd for
C30H52F6N2O10P2PdS2 (947.23): C, 38.04; H, 5.53; N, 2.96. Found: C,
37.84; H, 5.82; N, 2.84.
3
CH), 7.39−7.26 (m, 18 H, m,p-CH), 3.03 (t, JHH = 6.8 Hz, 2 H,
NCH2), 2.23 (t, 3JHH = 6.8 Hz, 2 H, NCH2), 1.57 (m, 2 H, CH2), 1.38
(m, 2 H, CH2) ppm. 13C NMR (100.5 MHz, CD2Cl2): δ 152.8
(C(O)NC4H8), 135.4 (m, o-C), 132.6 (p-C), 130.9 (t, 1JPC = 19.6 Hz,
trans-[Bis(3-(pentamethyleneamino)-3-methoxy-1,2-
propadienylidene)bis(triethylphosphine)palladium(II)] Tri-
fluoromethanesulfonate (10e-OTf). A solution of 0.05 g (0.1
mmol) of 9e in 10 mL of CH2Cl2 was treated with 0.22 μL (0.2 mmol)
of MeOTf at ambient temperature. The mixture was stirred for 1 h.
Removal of the solvent gave 10e-OTf as a yellow solid. Yield: 0.08 g
3
i-C), 128.3 (t, JPC = 5.4 Hz, m-C), 108.2 (br, Pd−CC), 104.0 (br,
Pd−CC), 47.2 (NCH2), 44.5 (NCH2), 25.4 (CH2), 25.0 (CH2)
ppm. 31P NMR (161.8 MHz, CD2Cl2): δ 22.1 ppm. IR (CH2Cl2):
ν(CC) 2114 cm−1; ν(CO) 1677 cm−1. UV−vis (CH2Cl2): λmax
(nm) (log ε) 297 (4.302). FAB-MS: m/z (%) 880 (71) [M+], 751
(82) [(M − I − 2H)+], 491 (72) [(M − I − PPh3)+]. Anal. Calcd for
C43H38INOP2Pd (880.05): C, 58.69; H, 4.35; N, 1.59. Found: C,
58.69; H, 4.74; N, 1.48.
1
(100%). Mp: 97 °C. H NMR (400 MHz, CD2Cl2): δ 4.24 (s, 6 H,
OCH3), 3.99 (s, 4 H, N(CH2CH2)2CH2), 3.81 (s, 4 H, N(CH2CH2)2CH2),
2.05−1.93 (m, 12 H, PCH2CH3), 1.76 (s, 12 H, N(CH2CH2)2CH2),
1.27−1.11 (m, 18 H, PCH2CH3) ppm. 13C NMR (100.5 MHz,
trans-Bis(3-(N-morpholino)-3-oxy-1-propynyl)bis-
(triethylphosphine)palladium(II) (9d). A suspension of 0.25 g
(1.0 mmol) (3-(N-morpholino)-3-oxy-1-propynyl)silver(I) in 20 mL
of CH2Cl2 was treated with 0.16 g (0.4 mmol) of [PdCl2(PEt3)2] at
ambient temperature. The mixture was stirred for 14 h. After filtration
through Celite the solvent was removed in vacuo. The residue was
chromatographed on silica at −20 °C using a CH2Cl2/acetone mixture
as the eluent. Removal of the solvent gave 9d as a beige solid. Yield:
0.14 g (58%). Mp: 115 °C. 1H NMR (400 MHz, CDCl3): δ 3.82−3.58
(m, 16 H, N(CH2)4O), 1.95 (m, 12 H, PCH2CH3), 1.14 (m, 18 H,
PCH2CH3), ppm. 13C NMR (100.5 MHz, CDCl3): δ 154.3 (s, Cγ),
CD2Cl2): δ 154.4 (t, 2JPC = 15.6 Hz, Cα), 152.6 (s, Cγ), 99.5 (t, 3JPC
=
3.0 Hz, Cβ), 61.9 (s, OCH3), 52.9 (s, N(CH2CH2)2CH2), 47.7 (s,
N(CH2CH2)2CH2), 26.6 (s, N(CH2CH2)2CH2), 25.8 (s, N-
1
(CH2CH2)2CH2), 23.7 (s, N(CH2CH2)2CH2), 17.6 (t, JPC = 14.8
Hz, PCH2CH3), 8.88 (s, PCH2CH3) ppm; not observed SO3CF3. 31P
NMR (161.8 MHz, CD2Cl2): δ 21.7 ppm. 19F NMR (376 MHz,
CD2Cl2): δ −78.9 (SO3CF3) ppm. IR (CH2Cl2): ν(CCC) 2083 cm−1.
UV−vis (CH2Cl2): λmax (nm) (log ε) 275 (4.830). FAB-MS: m/z (%)
629 (100) [(M − 2BF4 − CH3)+], 374 (50) [(M − 2BF4 − 2PEt3)+].
Anal. Calcd for C32H56F6N2O8P2PdS2 (943.28): C, 35.09; H, 5.22; N,
2.34. Found: C, 35.19; H, 5.46; N, 2.78.
2
3
120.7 (t, JPC = 16.5 Hz, Cα), 104.2 (t, JPC = 3.3 Hz, Cβ), 67.0 (s,
NCH2CH2O), 66.7 (s, NCH2CH2O), 47.2 (s, NCH2), 41.6 (s,
trans-[Bis(3-(pentamethyleneamino)-3-methoxy-1,2-
propadienylidene)bis(triethylphosphine)palladium(II)] Tetra-
fluoroborate (10e-BF4). A solution of 0.19 g (0.3 mmol) of 9e in
10 mL of CH2Cl2 was treated with 0.11 g (0.8 mmol) of [Me3O]BF4
at ambient temperature. The mixture was stirred for 1 h. Removal of
the solvent gave 10e-BF4 as a yellow solid. Yield: 0.25 g (98%). Mp:
1
NCH2), 16.9 (t, JPC = 14.6 Hz, PCH2CH3), 8.5 (s, PCH2CH3) ppm.
31P NMR (161.8 MHz, CDCl3): δ 19.6 ppm. IR (CH2Cl2): ν(CC)
2090 cm−1. UV−vis (CH2Cl2): λmax (nm) (log ε) 237 (4.783). FAB-
MS: m/z (%) 619 (100) [M+], 503 (15) [(M − PEt3)+], 363 (38)
[(M − PEt3 − CCC(O)N(CH2)4O)+]. Anal. Calcd for
C26H46N2O4P2Pd (619.02): C, 50.45; H, 7.49; N, 4.53. Found: C,
50.40; H, 7.09; N, 4.66.
1
120 °C. H NMR (400 MHz, CD2Cl2): δ 4.20 (s, 6 H, OCH3), 3.94
(s, 4 H, N(CH2CH2)2CH2), 3.76 (s, N(CH2CH2)2CH2), 1.98−1.89
(m, 12 H, PCH2CH3), 1.78−1.64 (m, 12 H, N(CH2CH2)2CH2),
1.21−1.09 (m, 18 H, PCH2CH3) ppm. 13C NMR (100.5 MHz,
trans-Bis(3-oxy-3-(pentamethyleneamino)-1-propynyl)bis-
(triethylphosphine)palladium(II) (9e). A suspension of 0.24 g
(1.0 mmol) of (3-oxy-3-(pentamethylenamino)-1-propynyl)silver(I)
in 20 mL of CH2Cl2 was treated with 0.16 g (0.4 mmol) of
[PdCl2(PEt3)2] at ambient temperature. The mixture was stirred for
16 h. After filtration through Celite the solvent was removed in vacuo.
The residue was chromatographed on silica at −20 °C using a
CH2Cl2/acetone mixture as the eluent. Removal of the solvent gave
CD2Cl2): δ 154.1 (t, 2JPC = 15.7 Hz, Cα), 152.3 (s, Cγ), 96.8 (t, 3JPC
=
3.2 Hz, Cβ), 61.9 (s, OCH3), 52.3 (s, N(CH2CH2)2CH2), 47.3 (s,
N(CH2CH2)2CH2), 26.3 (s, N(CH2CH2)2CH2), 25.5 (s, N-
1
(CH2CH2)2CH2), 23.4 (s, N(CH2CH2)2CH2), 17.3 (t, JPC = 15.1 Hz,
PCH2CH3), 8.56 (s, PCH2CH3) ppm. 31P NMR (161.8 MHz,
CD2Cl2): δ 21.6 ppm. 19F NMR (376 MHz, CD2Cl2): δ −152.5
(BF4), −152.5 (BF4) ppm. IR (CH2Cl2): ν(CCC) 2083 cm−1. UV−vis
(CH2Cl2): λmax (nm) (log ε) 276 (4.532). FAB-MS: m/z (%) 629
1
9e as a beige solid. Yield: 0.19 g (78%). Mp: 140 °C dec. H NMR
(400 MHz, CDCl3): δ 3.73 (t, J = 5.3 Hz, 4 H, NCH2CH2CH2), 3.52
6279
dx.doi.org/10.1021/om200862m|Organometallics 2011, 30, 6270−6282

Organometallics
Article
(76) [(M − 2OTf − CH3)+], 528 (64) [(M − 2OTf − PEt3)+], 408
Removal of the solvent gave 12c-BF4 as a white solid. Yield: 0.10 g
(75%). Mp: 200 °C dec. 1H NMR (400 MHz, CD2Cl2): δ 4.13 (s, 6 H,
OCH3), 3.38 (s, 6 H, NCH3), 3.19 (s, 6 H, NCH3), 2.67 (m, 6 H,
CH(CH3)2), 1.31 (m, 36 H, CH(CH3)2) ppm. 13C NMR (100.5 MHz,
(100) [(M
− 2OTf −
2PEt3 )+ ]. Anal. Calcd for
C30H56B2F8N2O2P2Pd·0.9CH2Cl2 (818.75): C, 41.85; H, 6.57; N,
3.17. Found: C, 41.96; H, 6.25; N, 3.39.
2
CD2Cl2): δ 155.8 (t, JPC = 13.4 Hz, Cα), 153.0 (s, Cγ), 98.1 (s, Cβ),
trans-[Bis(3-(pentamethyleneamino)-3-ethoxy-1,2-
propadienylidene)bis(triethylphosphine)palladium(II)] Tetra-
fluoroborate (10e′-BF4). A solution of 0.19 g (0.3 mmol) of 9e
in 10 mL of CH2Cl2 was treated with 0.12 g (0.6 mmol) of [Et3O]BF4
at ambient temperature. The mixture was stirred for 1 h. Removal of
the solvent gave 10e′-BF4 as a yellow solid. Yield: 0.25 g (97%). Mp:
1
60.8 (s, OCH3), 41.2 (s, NMe2), 37.3 (s, NMe2), 25.0 (t, JPC = 12.0
Hz, CH(CH3)2), 19.1 (s, CH(CH3)2) ppm. 31P NMR (161.8 MHz,
CD2Cl2): δ 50.1 ppm. 19F NMR (376 MHz, CD2Cl2): δ −153.54
(BF4), −153.59 (BF4) ppm. IR (CH2Cl2): ν(CCC) 2080 cm−1. UV−
vis (CH2Cl2): λmax (nm) (log ε) 236 (4.139). FAB-MS: m/z (%) 649
(5) [(M − 2BF4)+], 634 (50) [(M − 2BF4 − CH3)+], 475 (9) [(M −
2BF4 − CH3 − PiPr3)+], 429 (100) [(M − 2BF4 − 2OCH3 − PiPr3)+].
Anal. Calcd for C30H60B2F8N2O2P2Pd (822.79): C, 43.79; H, 7.35; N,
3.40. Found: C, 43.63; H, 7.32; N, 3.56.
1
130 °C dec. H NMR (400 MHz, CD2Cl2): δ 4.58 (q, 6 H, J = 7.0,
OCH2CH3), 3.94 (s, 4 H, N(CH2CH2)2CH2), 3.76 (s, N(CH2CH2)2CH2),
2.00−1.87 (m, 12 H, PCH2CH3), 1.75−1.65 (m, 12 H, N(CH2CH2)2CH2),
1.41 (t, 6 H, J = 7.5, OCH2CH3), 1.20−1.10 (m, 18 H, PCH2CH3) ppm.
2
13C NMR (100.5 MHz, CD2Cl2): δ 152.7 (t, JPC = 15.6 Hz, Cα), 151.4
trans-Bis(3-(tetramethyleneamino)-3-oxy-1-propynyl)bis-
(triphenylphosphine)palladium(II) (13b). A suspension of 0.23 g
(1.0 mmol) of (3-(tetramethyleneamino)-3-oxy-1-propynyl)silver(I)
in 20 mL of CH2Cl2 was treated with 0.28 g (0.4 mmol) of
[PdCl2(PPh3)2] at ambient temperature. The mixture was stirred for
60 h. After filtration through Celite the solvent was removed in vacuo.
The residue was chromatographed on silica at −20 °C using a
CH2Cl2/acetone mixture as the eluent. Removal of the solvent gave
3
(s, Cγ), 97.0 (t, JPC = 3.0 Hz, Cβ), 72.5 (s, OCH2CH3), 52.1 (s,
N(CH2CH2)2CH2), 47.2 (s, N(CH2CH2)2CH2), 26.3 (s, N-
(CH2CH2)2CH2), 25.5 (s, N(CH2CH2)2CH2), 23.4 (s, N(CH2CH2)2CH2),
1
17.3 (t, JPC = 15.1 Hz, PCH2CH3), 14.6 (s, OCH2CH3), 8.52 (s,
PCH2CH3) ppm. 31P NMR (161.8 MHz, CD2Cl2): δ 21.6 ppm. 19F NMR
(376 MHz, CD2Cl2): δ −152.5 (BF4), −152.5 (BF4) ppm. IR (CH2Cl2):
ν(CCC) 2083 cm−1. UV−vis (CH2Cl2): λmax (nm) (log ε) 275 (4.935).
FAB-MS: m/z (%) 643 (75) [(M − 2BF4 − CH3)+], 553 (60) [(M −
2BF4 − PEt3)+], 435 (100) [(M − 2BF4 − 2PEt3)+]. Anal. Calcd for
C32H60B2F8N2O2P2Pd·0.66CH2Cl2 (836.81): C, 43.43; H, 6.84; N,
3.10. Found: C, 43.51; H, 6.88; N, 3.36.
1
13b as a beige solid. Yield: 0.28 g (80%). Mp: 145 °C dec. H NMR
(400 MHz, CDCl3): δ 7.71 (m, 12 H, o-CH), 7.37 (m, 18 H, m,p-CH),
3.09 (t, J = 6.9 Hz, 4 H, NCH2), 2.40 (t, J = 6.9 Hz, 4 H, NCH2), 1.59
(p, J = 6.9 Hz, 4 H, NCH2CH2), 1.41 (p, J = 6.9 Hz, 4 H, NCH2CH2)
ppm. 13C NMR (100.5 MHz, CDCl3): δ 153.5 (s, Cγ), 134.9 (t, 2JPC
=
trans-Bis(3-(dimethylamino)-3-oxy-1-propynyl)bis-
(triisopropylphosphine)palladium(II) (11c). A suspension of
0.51 g (2.5 mmol) of (3-(dimethylamino)-3-oxy-1-propynyl)silver(I)
in 40 mL of CH2Cl2 was treated with 0.62 g (1.2 mmol) of
[PdCl2(PiPr3)2] at ambient temperature. The mixture was stirred for
25 h. After filtration through Celite the solvent was removed in vacuo.
The residue was chromatographed on silica at −20 °C using a
CH2Cl2/acetone mixture as the eluent. Removal of the solvent gave
11c as a white solid. Yield: 0.31 g (40%). Mp: 130 °C. 1H NMR (400
MHz, CDCl3): δ 3.10 (s, 6 H, NCH3), 2.84 (s, 6 H, NCH3), 2.75 (m,
6 H, CH(CH3)2), 1.32 (m, 36 H, CH(CH3)2) ppm. 13C NMR (100.5
1
6.5 Hz, o-C), 131.5 (t, JPC = 25.4 Hz, i-C), 130.4 (s, p-C), 128.0 (t,
2
3
3JPC = 5.4 Hz, m-C), 118.8 (t, JPC = 16.4 Hz, Cα), 109.3 (t, JPC
=
3.7 Hz, Cβ), 47.1 (s, NCH2), 44.2 (s, NCH2), 25.1 (s, NCH2CH2),
24.7 (s, NCH2CH2) ppm. 31P NMR (161.8 MHz, CDCl3): δ 25.7
ppm. IR (CH2Cl2): ν(CC) 2101 cm−1. UV−vis (CH2Cl2): λmax
(nm) (log ε) 274 (3.597). FAB-MS: m/z (%) 876 (86) [M+], 613
(25) [(M − PPh3)+], 369 (100) [(M − PPh3 − 2CCC(
O)NMe2)+]. Anal. Calcd for C50H46N2O2P2Pd · CH2Cl2 (875.28):
C, 66.09; H, 5.16; N, 3.05. Found: C, 66.45; H, 5.27; N, 3.21.
trans-Bis(3-(dimethylamino)-3-oxy-1-propynyl)bis-
(triphenylphosphine)palladium(II) (13c). A suspension of 0.20 g
(1.0 mmol) (3-(dimethylamino)-3-oxy-1-propynyl)silver(I) in 20 mL
of CH2Cl2 was treated with 0.28 g (0.4 mmol) of [PdCl2(PPh3)2] at
ambient temperature. The mixture was stirred for 20 h. After filtration
through Celite the solvent was removed in vacuo. The residue was
chromatographed on silica at −20 °C using a CH2Cl2/acetone mixture
as the eluent. Removal of the solvent gave 13c as a white solid. Yield:
MHz, CDCl3): δ 155.8 (s, Cγ), 121.4 (t, 2JPC = 14.5 Hz, Cα), 106.9 (t,
1
3JPC = 2.6 Hz, Cβ), 38.1 (s, NCH3), 33.7 (s, NCH3), 25.1 (t, JPC
=
11.3 Hz, CH(CH3)2), 20.1 (s, CH(CH3)2) ppm. 31P NMR (161.8
MHz, CDCl3): δ 46.1 ppm. IR (CH2Cl2): ν(CC) 2086 cm−1. UV−
vis (CH2Cl2): λmax (nm) (log ε) 236 (4.150). FAB-MS: m/z (%) 620
(100) [M+], 459 (13) [(M − PiPr3)+], 364 (37) [(M − PiPr3 −
CCC(O)NMe2)+]. Anal. Calcd for C28H54N2O2P2Pd (619.11): C,
54.32; H, 8.79; N, 4.52. Found: C, 54.08; H, 8.87; N, 4.70.
1
0.10 g (30%). Mp: 150 °C dec. H NMR (400 MHz, CDCl3): δ 7.71
(m, 12 H, o-CH), 7.37 (m, 18 H, m,p-CH), 2.58 (s, 6 H, NCH3), 2.22
(s, 6 H, NCH3) ppm. 13C NMR (100.5 MHz, CDCl3): δ 155.3 (s, Cγ),
134.9 (t, 2JPC = 6.5 Hz, o-C), 132.2 (s, p-C), 131.5 (t, 1JPC = 25.3 Hz,
t r a n s - [ B i s ( 3 - ( d i m e t h y l a m i n o ) - 3 - m e t h o x y - 1 , 2 -
propadienylidene)bis(triisopropylphosphine)palladium(II)]
Trifluoromethanesulfonate (12c-OTf). A solution of 0.05 g (0.1
mmol) 11c in 10 mL of CH2Cl2 was treated with 0.20 μL (0.2 mmol)
of MeOTf at ambient temperature. The mixture was stirred for 1 h.
Removal of the solvent gave 12c-OTf as a white solid. Yield: 0.08 g
(99%). Mp: 210 °C dec. 1H NMR (400 MHz, CD2Cl2): δ 4.21 (s, 6 H,
OCH3), 3.46 (s, 6 H, NCH3), 3.28 (s, 6 H, NCH3), 2.74 (m, 6 H,
CH(CH3)2), 1.40 (m, 36 H, CH(CH3)2) ppm. 13C NMR (100.5 MHz,
3
2
i-C), 128.1 (t, JPC = 5.3 Hz, m-C), 119.8 (t, JPC = 16.1 Hz, Cα),
107.9 (s, Cβ), 37.6 (s, NCH3), 33.3 (s, NCH3) ppm. 31P NMR (161.8
MHz, CDCl3): δ 25.4 ppm. IR (CH2Cl2): ν(CC) 2095 cm−1. UV−
vis (CH2Cl2): λmax (nm) (log ε) 275 (3.714). FAB-MS: m/z (%) 824
(48) [M+], 726 (32) [(M − CCC(O)NMe2)+], 464 (32) [(M −
PPh3 − CCC(O)NMe2)+], 371 (100) [(M − PPh3 − 2CCC(
O)NMe2)+]. Anal. Calcd for C46H42N2O2P2Pd·0.25CH2Cl2 (823.21):
C, 65.78; H, 5.07; N, 3.32. Found: C, 66.11; H, 5.08; N, 3.45.
trans-Bis(3-(N-morpholino)-3-oxy-1-propynyl)bis-
(triphenylphosphine)palladium(II) (13d). A suspension of 0.12 g
(0.5 mmol) of (3-(N-morpholino)-3-oxy-1-propynyl)silver(I) in 10
mL of CH2Cl2 was treated with 0.16 g (0.2 mmol) of [PdCl2(PPh3)2]
at ambient temperature. The mixture was stirred for 14 h. After
filtration through Celite the solvent was removed in vacuo. The
residue was chromatographed on silica at −20 °C using a CH2Cl2/
acetone mixture as the eluent. Removal of the solvent gave 13d as a
CD2Cl2): δ 157.1 (t, 2JPC = 13.4 Hz, Cα), 154.4 (s, Cγ), 121.6 (q, JCF
=
3
322.9 Hz, SO3CF3), 99.5 (t, JPC = 2.3 Hz, Cβ), 62.1 (s, OCH3), 42.5
1
(s, NMe2), 38.7 (s, NMe2), 26.3 (t, JPC = 11.8 Hz, CH(CH3)2), 20.4
(s, CH(CH3)2) ppm. 31P NMR (161.8 MHz, CD2Cl2): δ 50.3 ppm.
19F NMR (376 MHz, CD2Cl2): δ −78.7 (SO3CF3) ppm. IR (CH2Cl2):
ν(CCC) 2080 cm−1. UV−vis (CH2Cl2): λmax (nm) (log ε) 274
(3.504). FAB-MS: m/z (%) 638 (100) [(M − 2OTf − Me)+], 488
(14) [(M − 2OTf − PiPr3)+], 473 (28) [(M − 2OTf − PiPr3 − Me)+],
380 (30) [(M − 2OTf − PiPr3 − CCC(OMe)NMe2)+]. Anal.
Calcd for C32H60F6N2O8P2PdS2 (947.32): C, 40.57; H, 6.38; N, 2.96.
Found: C, 40.52; H, 6.38; N, 3.06.
1
white solid. Yield: 0.17 g (82%). Mp: 170 °C dec. H NMR (400
MHz, CDCl3): δ 7.70 (m, 12 H, o-CH), 7.40 (m, 18 H, m,p-CH), 3.36
(t, J = 4.7 Hz, 4 H, NCH2CH2O), 3.26 (p, J = 4.7 Hz, 4 H,
NCH2CH2O), 3.01 (t, J = 4.7 Hz, 4 H, NCH2), 2.71 (t, J = 4.7 Hz, 4
H, NCH22), ppm. 13C NMR (100.5 MHz, CDCl3): δ 153.7 (s, Cγ),
t r a n s - [ B i s ( 3 - ( d i m e t h y l a m i n o ) - 3 - m e t h o x y - 1 , 2 -
propadienylidene)bis(triisopropylphosphine)palladium(II)]
Tetrafluoroborate (12c-BF4). A solution of 0.10 g (0.2 mmol) of
11c in 10 mL of CH2Cl2 was treated with 0.05 g (0.3 mmol) of
[Me3O]BF4 at ambient temperature. The mixture was stirred for 2 h.
1
134.9 (t, JPC = 6.5 Hz, o-C), 131.4 (t, JPC = 25.2 Hz, i-C), 130.6
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Article
3
2
(s, p-C), 128.2 (t, JPC = 5.7 Hz, m-C), 121.3 (t, JPC = 16.3 Hz, Cα),
δ 25.2 ppm. 19F NMR (376 MHz, CD2Cl2): δ −78.7 (SO3CF3) ppm.
IR (CH2Cl2): ν(CCC) 2092 cm−1. UV−vis (CH2Cl2): λmax (nm) (log
ε) 283 (4.904). FAB-MS: m/z (%) 922 (38) [(M − 2OTf − Me)+],
822 (100) [(M − 2OTf − 2Me − N(CH2CH2)2O)+], 674 (31) [(M
− 2OTf − PPh3)+], 414 (94) [(M − 2OTf − 2PPh3)+]. Anal. Calcd
for C54H52F6N2O10P2PdS2·1.5CH2Cl2 (1235.49): C, 51.33; H, 4.27; N,
2.16. Found: C, 51.35; H, 4.30; N, 2.22.
Heck Coupling. In a typical run, a test tube containing a stirring
bar was charged with sodium methoxide (41.0 mg, 0.50 mmol) and
the palladium catalyst (0.001 mmol, 0.4 mol %). The test tube fitted
with a screw cap having a pierceable Teflon septum was then
evacuated and refilled with nitrogen. NMP (1 mL), bromobenzene
(26.3 μL, 0.25 mmol), and styrene (42.9 μL, 0.375 mmol) were then
added via syringe. The mixture was heated at 110 °C. After 0.5 h the
solution was quenched with water, diluted with ethyl acetate, and
analyzed by GC using n-dodecane as the internal standard.
3
106.9 (t, JPC = 3.9 Hz, Cβ), 66.8 (s, NCH2CH2O), 66.5 (s,
NCH2CH2O), 46.2 (s, NCH2), 41.2 (s, NCH2) ppm. 31P NMR (161.8
MHz, CDCl3): δ 25.5 ppm. IR (CH2Cl2): ν(CC) 2099 cm−1. UV−
vis (CH2Cl2): λmax (nm) (log ε) 274 (3.486). FAB-MS: m/z (%) 908
(50) [M+], 645 (16) [(M − PPh3)+], 509 (24) [(M − PPh3
−
CCC(O)NMe2)+]. Anal. Calcd for C50H46N2O4P2Pd·0.25CH2Cl2
(907.28): C, 65.00; H, 5.05; N, 3.02. Found: C, 65.16; H, 5.12; N,
3.09.
trans-[Bis(3-(tetramethylenamino)-3-methoxy-1,2-
propadienylidene)bis(triphenylphosphine)palladium(II)] Tri-
fluoromethanesulfonate (14b-OTf). A solution of 0.10 g (0.1
mmol) of 13b in 10 mL of CH2Cl2 was treated with 0.25 μL (0.2
mmol) of MeOTf at ambient temperature. The mixture was stirred for
1 h. Removal of the solvent gave 14b-OTf as a beige solid. Yield: 0.13
1
g (98%). Mp: 175 °C dec. H NMR (400 MHz, CD2Cl2): δ 7.70 (m,
12 H, o-CH), 7.56 (m, 18 H, m,p-CH), 3.39 (s, 6 H, OCH3), 3.35 (t,
J = 7.2 Hz, 4 H, NCH2), 2.79 (t, J = 6.9 Hz, 4 H, NCH2), 1.89 (p, J =
7.2 Hz, 4 H, NCH2CH2), 1.76 (p, J = 7.2 Hz, 4 H, NCH2CH2) ppm.
Suzuki Coupling. In a typical run, a test tube containing a stirring
bar was charged with phenylboronic acid (18.3 mg, 0.15 mmol),
cesium carbonate (65.2 mg, 0.20 mmol), and the palladium catalyst
(0.001 mmol, 1 mol %). The test tube fitted with a screw cap having a
pierceable Teflon septum was evacuated and then refilled with
nitrogen. THF (1 mL) and 1-bromo-4-butylbenzene (17.6 μL, 0.10
mmol) were added via syringe. The mixture was heated to 50 °C. After
1 h the solution was quenched with water, diluted with ethyl acetate,
and analyzed by GC using n-dodecane as internal standard.
Sonogashira Coupling. In a typical run, a test tube containing a
stirring bar was charged with CuI (0.01 mmol, 10 mol %) and the
palladium catalyst (0.005 mmol, 5 mol %). The test tube fitted with a
screw cap having a pierceable Teflon septum was evacuated and then
refilled with nitrogen. DMSO (1 mL), phenyl iodide (11.2 μL, 0.10
mmol), phenylacetylene (13.2 μL, 0.12 mmol), and triethylamine (20.8
μL, 0.15 mmol) were added via syringe. The mixture was stirred at room
temperature. After 1 h the solution was quenched with water, diluted with
ethyl acetate, and analyzed by GC using n-dodecane as internal standard.
X-ray Structural Analysis of 9e, 11c, and 10e′-BF4. Single
crystals suitable for an X-ray structural analysis of 9e, 11c, and 10e′-
BF4 were grown from CH2Cl2/hexane, CH2Cl2/petroleum ether, and
CH2Cl2/Et2O, respectively. The measurements were performed at
100(2) K with a crystal mounted on a glass fiber on a Stoe IPDS II
diffractometer (graphite monochromator, Mo Kα radiation, λ = 0.710
73 Å). The structures were solved by direct methods using the
SHELX-97 program package.22 The positions of the hydrogen atoms
were calculated by assuming an ideal geometry, and their coordinates
were refined together with those of the attached carbon atoms as the
riding model. All other atoms were refined anisotropically.
2
13C NMR (100.5 MHz, CD2Cl2): δ 154.8 (t, JPC = 15.0 Hz, Cα),
2
151.5 (s, Cγ), 134.9 (t, JPC = 6.5 Hz, o-C), 132.4 (s, p-C), 129.9 (t,
3
1JPC = 26.0 Hz, i-C), 129.4 (t, JPC = 5.7 Hz, m-C), 121.5 (q, JCF
=
307.6 Hz, SO3CF3), 98.81 (t, 3JPC = 4.0 Hz, Cβ), 61.3 (s, OCH3), 52.2
(s, NCH2), 49.3 (s, NCH2), 24.8 (s, NCH2CH2), 24.6 (s, NCH2CH2)
ppm. 31P NMR (161.8 MHz, CD2Cl2): δ 25.7 ppm. 19F NMR (376 MHz,
CD2Cl2): δ −78.7 (SO3CF3) ppm. IR (CH2Cl2): ν(CCC) 2096 cm−1.
UV−vis (CH2Cl2): λmax (nm) (log ε) 281 (4.646). FAB-MS: m/z (%)
892 (8) [(M − 2OTf − Me)+], 791 (91) [(M − 2OTf − 2Me −
N(CH2)4)+], 645 (14) [(M − 2OTf − PPh3)+], 380 (100) [(M −
2OTf − 2PPh3)+]. Anal. Calcd for C54H52F6N2O8P2PdS2·2CH2Cl2
(1203.49): C, 48.98; H, 4.11; N, 2.04. Found: C, 49.33; H, 3.58; N,
2.35.
t r a n s - [ B i s ( 3 - ( d i m e t h y l a m i n o ) - 3 - m e t h o x y - 1 , 2 -
propadienylidene)bis(triphenylphosphine)palladium(II)] Tri-
fluoromethanesulfonate (14c-OTf). A solution of 0.09 g (0.1
mmol) of 13c in 10 mL of CH2Cl2 was treated with 0.25 μL (0.2
mmol) of MeOTf at ambient temperature. The mixture was stirred for
1 h. Removal of the solvent gave 14c-OTf as a beige solid. Yield:
0.11 g (98%). Mp: 160 °C dec. 1H NMR (400 MHz, CD2Cl2): δ 7.70
(m, 12 H, o-CH), 7.56 (m, 18 H, m,p-CH), 3.36 (s, 6 H, OMe), 2.96
(s, 6 H, NCH3), 2.72 (s, 6 H, NCH3) ppm. 13C NMR (100.5 MHz,
CD2Cl2): δ 155.9 (t, 2JPC = 15.3 Hz, Cα), 154.2 (s, Cγ), 135.0 (t, 2JPC
=
1
6.4 Hz, o-C), 132.7 (s, p-C), 130.0 (t, JPC = 26.5 Hz, i-C), 129.6 (t,
3JPC = 5.7 Hz, m-C), 121.6 (q, JCF = 321.7 Hz, SO3CF3), 98.0 (t, 3JPC
=
4.0 Hz, Cβ), 62.9 (s, OCH3), 42.2 (s, NCH3), 38.1 (s, NCH3) ppm.
31P NMR (161.8 MHz, CD2Cl2): δ 25.4 ppm. 19F NMR (376 MHz,
CD2Cl2): δ −78.7 (SO3CF3) ppm. IR (CH2Cl2): ν(CCC) 2094 cm−1.
UV−vis (CH2Cl2): λmax (nm) (log ε) 227 (4.619). FAB-MS: m/z (%)
738 (100) [(M − 2OTf − CCC(OMe)NMe2)+], 630 (29)
[(M − 2OTf − 2CCC(OMe)NMe2)+], 479 (43) [(M − 2OTf −
PPh3 − CCC(OMe)NMe2)+], 372 (71) [(M − 2OTf − PPh3 −
2CCC(OMe)NMe2)+]. Anal. Calcd for C50H48F6N2-
O8P2PdS2·0.5CH2Cl2 (1151.41): C, 50.81; H, 4.14; N, 2.35. Found:
C, 50.73; H, 4.28; N, 2.39.
ASSOCIATED CONTENT
* Supporting Information
■
S
CIF files giving crystallographic data for the complexes 9e, 11c,
and 10e′-BF4. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: florian.kessler@epfl.ch. Tel: +4121-6939822. Fax:
+4121-6934111.
■
t r a n s - [ B i s ( 3 - ( N - m o r p h o l i n o ) - 3 - m e t h o x y - 1 , 2 -
propadienylidene)bis(triphenylphosphine)palladium(II)] Tri-
fluoromethanesulfonate (14d-OTf). A solution of 0.17 g (0.2
mmol) of 13d in 10 mL of CH2Cl2 was treated with 0.44 μL (0.4
mmol) of MeOTf at ambient temperature. The mixture was stirred for
2 h. Removal of the solvent gave 14d-OTf as a beige solid. Yield: 0.22
PRESENT ADDRESSES
■
‡E-Bau, Universitat Tubingen, Auf der Morgenstelle 28, 72076
1
g (99%). Mp: 170 °C dec. H NMR (400 MHz, CD2Cl2): δ 7.72 (m,
̈
̈
12 H, o-CH), 7.58 (m, 18 H, m,p-CH), 3.55 (t, J = 4.8 Hz, 4 H,
NCH2CH2O), 3.51 (t, J = 4.8 Hz, 4 H, NCH2CH2O), 3.44 (s, 6 H,
OCH3), 3.36 (t, J = 4.8 Hz, 4H, NCH2), 3.12 (t, J = 4.8 Hz, 4H,
NCH2) ppm. 13C NMR (100.5 MHz, CD2Cl2): δ 157.5 (t, 2JPC = 15.1
Tubingen, Germany.
̈
§Laboratory of Photonics and Interfaces, Institute of Chemical
Sciences and Engineering, School of Basic Sciences, Swiss
Federal Institute of Technology, CH-1015 Lausanne, Switzerland.
2
Hz, Cα), 152.8 (s, Cγ), 135.0 (t, JPC = 6.7 Hz, o-C), 132.7 (s, p-C),
1
3
130.0 (t, JPC = 26.7 Hz, i-C), 129.7 (t, JPC = 5.5 Hz, m-C), 121.6
NOTES
3
■
(q, JCF = 321.5 Hz, SO3CF3), 97.5 (t, JPC = 3.9 Hz, Cβ), 66.4
Dedication
(s, NCH2CH2O), 65.9 (s, NCH2CH2O), 62.1 (s, OCH3), 50.5
(s, NCH2), 46.5 (s, NCH2) ppm. 31P NMR (161.8 MHz, CD2Cl2):
†Dedicated to Helmut Fischer.
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̈
ACKNOWLEDGMENTS
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We are grateful to Carlos Lizandara (XRD), Michael Krumm
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concerning the Pd nanoparticles. Support of this work by the
Wacker-Chemie AG (gift of chemicals) is gratefully acknowl-
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