σ-alkylpalladium intermediates in intramolecular Heck reactions: Isolation and catalytic activity

Article abstract of DOI:10.1002/chem.200902071

The isolation of σ-alkylpalladium Heck intermediates, possible when β-hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on Nallyl-2-halobenzylamines in the presence of [Pd(PPh₃)4], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding com- plexes. X-ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five-membered palladacycle with the metal center bearing a PPh₃ ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ-alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β-hydride elimination. Subsequently, the thus obtained bridged five-membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross-coupling processes such as Suzuki and Stille reactions.

Full text of DOI:10.1002/chem.200902071

DOI: 10.1002/chem.200902071
s-Alkylpalladium Intermediates in Intramolecular Heck Reactions:ACHTNUTGRNEUNGIsolation
and Catalytic Activity
Egle M. Beccalli,[b] Elena Borsini,[b] Stefano Brenna,[a] Simona Galli,[a]
Micol Rigamonti,[a] and Gianluigi Broggini*[a]
Abstract: The isolation of s-alkylpalla-
dium Heck intermediates, possible
when b-hydride elimination is inhibit-
ed, is a rather rare event. Performing
intramolecular Heck reactions on N-
allyl-2-halobenzylamines in the pres-
plexes. X-ray crystallographic analysis
of one of the indolyl derivatives re-
vealed the presence of a five-mem-
bered palladacycle with the metal
center bearing a PPh3 ligand and an
iodine atom in a cis position with re-
spect to the nitrogen atom. The stabili-
ty of the s-alkylpalladium complexes is
probably a consequence of the strong
constraint resulting from the bridged
junction that hampers the cisoid con-
formation essential for b-hydride elimi-
nation. Subsequently, the thus obtained
bridged five-membered palladacycles
were proven to be effective precata-
lysts in Heck reactions as well as in
cross-coupling processes such as Suzuki
and Stille reactions.
ence of [PdACHTUNGTRENNUNG(PPh3)4], we isolated and
characterized a series of stable bridged
palladacycles containing an iodine or
bromine atom on the palladium atom.
Indolyl substrates were also tested for
isolation of the corresponding com-
Keywords: Heck reaction · homo-
geneous catalysis · metallacycles ·
palladium · X-ray diffraction
Introduction
es,[4] this reaction has the practical and economical advan-
tages of being able to start from very simple and readily
available materials by substituting the organometallic cou-
pling partner with a simple unsaturated system. During the
past decades, the Heck reaction has been developed and im-
proved significantly with regard to scope and reactivity.[5] In
particular, proper catalyst and ligand design has led to a va-
riety of very efficient catalytic systems that provide high re-
action rates and turnover numbers (TON), often affording
good selectivity and product yields.
The standard catalytic cycle generally assumed for the
Heck reaction involves a homogeneous palladium catalyst
that cycles between the Pd0 and PdII oxidation states during
the course of the reaction.[6] As shown in Scheme 1, a Pd0
catalyst, which may also be obtained in situ by reduction of
a precatalyst in the PdII oxidation state, oxidatively adds to
the aryl halide to give a PdII intermediate. The olefin can
next bind to the PdII complex, with subsequent insertion
Palladium-catalyzed reactions represent one of the most val-
uable tools in organic synthesis over the last 30 years.[1] The
importance of these reactions is reflected by the numerous
reports of such reactivity in almost every issue of the jour-
nals dealing with organic synthesis. The broad utility of pal-
ladium in organic chemistry comes from the facile intercon-
version between the Pd0, PdII, and PdIV oxidation states
during the reaction course, because each oxidation state be-
haves differently.[2]
Among the different Pd-catalyzed reaction types, the Miz-
oroki–Heck reaction allows the direct coupling of activated
arenes/heteroarenes and olefins with an unactivated alkene
by a formal C–H activation creating a s bond between two
sp2 carbon centers.[3] Compared to cross-coupling process-
[a] Dr. S. Brenna, Dr. S. Galli, M. Rigamonti, Dr. G. Broggini
Dipartimento di Scienze Chimiche e Ambientali
Universitꢀ dellꢁInsubria, Via Valleggio 11, 22100 Como (Italy)
Fax : (+39)031-2386449
À
À
into the aryl Pd bond, forming a new carbon carbon bond.
b-Hydride elimination gives the product, with a [PdH(L)2X]
species generated in the process. According to the tradition-
ally proposed mechanism, the Pd0 species is then regenerat-
ed by deprotonating reductive action of the [PdH(L)2X]
complex in the presence of a base.
E-mail: gianluigi.broggini@uninsubria.it
[b] Prof. E. M. Beccalli, E. Borsini
DISMAB, Sezione di Chimica Organica “A. Marchesini”
Universitꢀ di Milano, Via Venezian 21, 20133 Milano (Italy)
Other plausible mechanisms of the Heck reaction based
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902071.
on cationic[3d] and anionic versions,[7] or on a PdII–PdIV se-
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FULL PAPER
Among the organopalladium complexes, palladacycles
have received special attention in the literature due to their
unique properties that make them suitable for a variety of
applications in many fields. Starting from the original work
of Herrmann and Beller,[8a] palladacycles have proven to be
convenient and efficient precatalysts for the construction of
[13]
À
À
C C and C heteroatom bonds. Noteworthy are the palla-
dacycles containing phosphorus ligands that can stabilize the
catalytically active Pd species usually involved in the catalyt-
ic cycle.
As a consequence of these aspects, and in light of our pre-
liminary results, we decided 1) to expand the scope to shed
light on the structural requirements of the substrates neces-
sary for the stability of the s-alkylpalladium intermediates,
and 2) to test the properties of the new palladium com-
Scheme 1. Typically accepted catalytic cycle for the Heck reaction.
À
plexes as precatalysts in C C bond-forming reactions.
quence[8] have been proposed, although the latter has been
demonstrated to be unlikely.
Results and Discussion
However, each of these mechanisms involves a s-alkylpal-
ladium complex, from which the different products evolve.
Despite the well-established assumption that such an inter-
mediate forms, the capture of s-alkylpalladium Heck inter-
mediates with inhibition of b-hydride elimination is an un-
common event. This has been described in only two publica-
tions concerning intramolecular reactions that recently ap-
Determination of structural features for isolation of s-alkyl
complexes: First, we wanted to determine the key frame-
work essential for assuring the
stability of s-alkylpalladium
Heck
intermediates.
In
Figure 1, the features of the
basic skeleton that have been
modified for our purposes are
highlighted, namely 1) the type
of the benzylic carbon, 2) the
nature of the aryl halide, and 3)
the substitution pattern of the
aromatic ring.
peared in the literature.[9] Overman isolated [alkyl Pd(L)n]
À
palladacycles that were obtained by intramolecular trapping
+
À
À
of a cationic intermediate species [alkyl Pd(L)n] OTf
(Tf=trifluoromethylsulfonyl) by an internal nitrogen
atom.[9a,b] Balme obtained
a phosphine-coordinated [s-
Figure 1. Structural modifica-
tions of the basic skeleton
À
alkyl PdI] complex stabilized through chelation by the ni-
trogen atom of a proline moiety contained in the carbon
ligand backbone.[9c] Moreover, the literature cases of stable
s-alkylpalladium complexes having a hydrogen atom in the
b-position with respect to the metal are rare.[10]
First of all, we tried to change the nature of the benzylic
carbon, by considering an aryl iodide with an sp2-hybridized
carbon atom. Thus, diallylamide 4 was chosen as a substrate
Our contribution in the field of palladium-catalyzed pro-
cesses concerns studies to synthesize complex polyheterocy-
clic systems.[11] In the course of our investigations to obtain
4-spiroannulated tetrahydroisoquinolines by a one-pot se-
quential intramolecular Heck reaction/1,3-dipolar cycloaddi-
tion,[12] we disclosed that cyclization of allylamines 1 in the
for treatment with a catalytic amount of [PdACTHNGUTERN(NUG PPh3)4] and
Et3N in acetonitrile (Scheme 3). When the reaction was car-
ried out at room temperature, the formation of the Heck
product 6 and its isomerization derivative 7 occurred. The
corresponding s-Pd-complex intermediate 5 was neither iso-
1
lated, nor detected in the H NMR spectrum of the crude
presence of [Pd
ACHTUNGTRENNUNG(PPh3)4] and Et3N in acetonitrile gave rise to
the isolation of the s-alkylpalladium complexes
2
(Scheme 2), instead of the expected isoquinoline derivatives
3. These bridged palladacycles containing an iodine atom
and a triphenylphosphine ligand were found to be highly
stable towards air, moisture, heat, and bases.
Scheme 2. Previously reported behavior of allyl
(benzyl)amines 1 to give
Scheme 3. Reaction of allyl
ACHTUNGTRENUN(NG benzoyl)amine 4 in the presence of a catalyt-
s-alkyl complexes 2.
ic amount of [Pd(PPh3)4] and Et3N as a base.
ACHTUNGTRENNUNG
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1671

G. Broggini et al.
mixture. As expected, the use of a much higher amount of
[Pd(PPh3)4] (1 equiv) did not provide intermediate 5. It is
ACHTUNGTRENNUNG
worth noting that chromatographic separation of the crude
mixture provided only isoquinolin-2-one 7 in 58% yield,
whereas 4-exomethylene derivative 6 underwent degrada-
tion during the silica gel purification. According to this evi-
dence, an sp3-hybridized carbon atom in the benzylic posi-
tion seems to be necessary for the stability of the s-alkylpal-
ladium complex intermediate.
Subsequently, we modified the halide atom with the aim
to test the stability of s-alkyl
(benzyl)amine 8a was treated directly with a stoichiometric
amount of [Pd(PPh3)4] in the presence of Et3N in acetoni-
ACHTUNGTNER(NUNG bromo) complexes. Diallyl-
ACHTUNGTRENNUNG
Scheme 5. Synthesis of indole derivatives 12 by Mannich reactions with
alkyl
A
ACHTUNGTRENNUNG(allyl)-
ACHTUNGTRENNUNG
AHCTUNGRTENaGUNN mine, CH2O(aq) 37%, AcOH 60%, reflux; iii) BuLi, I2, Et2O, reflux.
trile (Scheme 4). Its conversion required heating at reflux to
situ preventive protection of the nitrogen atom in the pres-
ence of BuLi and CO2, whereas 1-methylindoles underwent
direct regioselective iodination at the 2-position.[15]
The behavior of iodosubstituted pseudobenzylamines
12a–d under our standard Heck conditions revealed close
similarities to the previous results involving benzylamines.
Compounds 12a–d were smoothly converted into s-alkylpal-
ladium complexes 13a–d at room temperature (Scheme 6),
and Heck products were not detected even after heating at
reflux.
Scheme 4. Preparation of aryl-s-alkyl bromo complexes as Heck inter-
mediates.
provide the bromide complex 9a as the sole product, al-
though isolated in lower yield than that obtained for 2b
from the corresponding precursor 1 (25 vs. 66%[12]). Similar
to iodide complex 2b, s-alkylACTHNUGRTNEUNG(bromo) complex 9a showed
high stability as well as a poor tendency for transforming
into the Heck product.
À
À
À
The stability of the s-alkyl Pd PPh3 bromo Heck inter-
mediate 9a encouraged us to extend the range of Pd com-
plexes by introducing a functional group on the benzene
ring. Starting from the commercially available 2-bromo-5-
methoxybenzyl bromide, diallylamine 8b was synthesized
and converted into bromo complex 9b through a reaction
outcome strictly closed to unfunctionalized compound 8a.
Intramolecular Heck coupling on heteroaromatic frame-
works was also investigated. We planned to construct com-
pounds with the iodine atom and the (allylamino)methyl
group tied to an indole nucleus. To this end, the series of
new 2-iodoindole derivatives 12a–d was prepared by iodina-
tion and Mannich condensation to introduce the [alkyl-
Scheme 6. Preparation of indolyl-s-alkyl iodo complexes as Heck inter-
mediates.
The structure of complexes 13a–d was confirmed by
means of an X-ray crystal structure analysis carried out on a
suitable single crystal of 13b.[16] As already observed in the
case of 2, the square-planar stereochemistry of the PdII
center is a consequence of the formation of a five-mem-
bered metallacycle and the presence of a PPh3 ligand and an
iodine atom cis with regard to the nitrogen atom of the met-
allacycle (Figure 2).
The results concerning the structural requirements for the
isolation of s-alkylpalladium complexes highlighted that an
sp3 benzylic carbon is an essential feature, while the nature
of the halide as well as the aromatic moiety may be varied.
The marked stability of the isolated complexes could be due
to the electronic nature of the nitrogen atom as well as the
strong constraint imposed by the bridged junction. The
latter hampers two essential requirements for b-hydride
elimination, namely, cisoid conformation and agostic inter-
actions. The two following explanations may account for the
ACHTUNGTRENNUNG(allyl)amino]methyl substituent to the 3-position of the
indole (Scheme 5). These functionalization reactions on an
indole nucleus were equally possible by both sequences
shown in Scheme 5, but the most convenient synthetic out-
come was strongly dependent on the allylamine. In the case
of diallylamine, the highest yields were obtained when the
Mannich reactions were performed in the presence of 37%
aqueous formaldehyde and 60% acetic acid (AcOH) on 2-
iodoindoles, while with methyl- and cyclohexylallylamines
the 3-aminomethyl functionalization was more conveniently
achieved on 1-methylindole with subsequent introduction of
the iodine atom. In the case of indole, the iodination was ac-
complished under Bergmanꢁs conditions,[14] which involve in
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s-Alkylpalladium Intermediates
FULL PAPER
Table 1. Palladacycle-catalyzed Heck reaction of aryl iodides and ethyl
acrylate.
Entry ArI
Palladacycle Proce- Solvent
T
[8C]
t
Yield
[mol%]
dure[a]
[h] [%][b]
1
2
3
4
5
6
7
8
9
PhI
PhI
PhI
PhI
PhI
PhI
PhI
PhI
PhI
PhI
PhI
2b (0.01)
2b (0.001)
2b (0.0001)
13a (0.0001)
13b (0.0001)
9a (0.1)
9a (0.01)
2b (0.1)
2b (0.1)
i
i
i
i
i
i
i
ii
ii
ii
ii
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
120
120
120
120
120
120
120
120
2
24
24
24
24
2
24
2
2
98
98
12
10
9
76
–
63
73
8
Figure 2. ORTEP representation (30% probability level) of the molecu-
lar structure of compound 13b.
CH3CN reflux
CH3CN reflux
CH3CN reflux
10
11
2b (0.01)
13b (0.1)
2
2
61
different behavior of species 5 compared to 2, 9, and 13: 1)
the carbonyl group imposes a geometry that favors b-elimi-
nation of the metal and 2) the stability of an intermediate
complex resulting from coordination of the metal with an
sp2-hybridized nitrogen is lower than that of an intermediate
arising from coordination with an sp3-hybridized nitrogen.
12
13
2b (0.001)
2b (0.001)
i
i
DMF
DMF
120
120
20
20
95
92
s-Alkyl complexes as precatalysts in Pd-promoted reactions:
Palladacycles are extensively investigated organometallic
compounds and some of them are efficient catalyst precur-
[a] Procedure i): Et3N (1 equiv); procedure ii) AcONa (1 equiv), Bu4NCl
(1 equiv). [b] Isolated yield.
À
sors for C C bond formation. However, these reactions
often have to be carried out under a controlled atmosphere
due to the air- and moisture-sensitivity of the palladacycles.
The high thermal stability of our palladacycles in the pres-
ence of air and moisture suggested a possible effective appli-
cation as precatalysts in Pd-catalyzed couplings such as
Heck, Suzuki, and Stille reactions.
First, we tested the catalytic efficacy of our palladacycles
in the Heck reaction between aryl iodides and ethyl acrylate
in the presence of Et3N as base in DMF as solvent at 1208C
or under “Jeffery conditions”[17] in the presence of sodium
acetate as base and Bu4NCl as additive in acetonitrile
heated under reflux or DMF at 1208C as solvent. Table 1
shows the results of the coupling reactions. Palladacycle 2b
was effective in the first procedure with iodobenzene as sub-
strate, giving ethyl cinnamate quantitatively after 2 h at a
tries 6 and 7 vs. 1–5), requiring a higher loading to accom-
plish the formation of ethyl cinnamate. The ability of palla-
dacycles 2 and 13 to operate as precursors of Heck catalysts
diminished in the presence of sodium acetate and Bu4NCl in
DMF or acetonitrile as the solvent. In these solvents, ethyl
cinnamate was obtained in satisfactory yields only in the
presence of complexes 2b and 13b at a loading of 0.1 mol%
(entries 8, 9, and 11). Palladacycle 2b was studied further in
the coupling of 4-nitro- and 4-methoxy-1-iodobenzene with
ethyl acrylate (entries 12 and 13). In both cases, the precata-
lyst performs well at 0.001 mol% giving the corresponding
cinnamates in good yields.
The catalytic efficacy of palladacycle 2b was also evaluat-
ed in the Heck reaction with aryl bromides as substrates
(Table 2). In general, more drastic conditions (higher preca-
talyst loading and/or activation under microwave irradia-
tion) were required compared to when the corresponding io-
dides were used as substrates.
loading of 0.01 mol% or after 24 h at
a loading of
0.001 mol% (entries 1 and 2). When the loading of 2b was
reduced to 0.0001 mol%, the Heck product was obtained in
12% yield (entry 3), corresponding to a turnover number
(TON) of 120000.
In the literature there are many examples of Heck reac-
tions of activated substrates such as aryl iodides in which
palladacycles act as a source of the catalytically active Pd0
species, usually with TONs in the order of 103–1010 cycles.
Among the reactions of iodobenzene with acrylates, com-
pound 2b is comparable to other catalytic systems such as
sulfur-[18] or rhenium-containing[19] and imine-[20] or oxime-
derived[21] palladacycles, even if there are other systems that
perform better.[22]
Ethyl cinnamate was produced in very low yield from
phenyl bromide and ethyl acrylate when 1 mol% of precata-
lyst was used with Et3N or AcONa as base in DMF or aceto-
nitrile as solvent (entries 1–3). Better results were obtained
when microwave activation was used, in particular under
“Jeffery conditions”, which led to the Heck product in 70%
yield (Table 2, entry 5 vs. 4). However, when the precatalyst
loading was reduced to 0.1 mol%, the reaction conversion
markedly decreased (entry 6). Subsequently, we tried the
coupling of different aryl and heteroaryl bromides with
ethyl acrylate under the conditions shown in entry 5. Bromo
derivatives with an activating group (including the pyridine
Similar catalytic activity was shown by iodo-
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G. Broggini et al.
Table 2. Heck reaction of aryl halides and ethyl acrylate catalyzed by
palladacycle 2b.
ploying phenylboronic acid and Cs2CO3 as a base in DMF/
H2O (4:1) as the solvent mixture. To our satisfaction, it was
found that 2b and 13b were active enough to promote the
À
C C bond formation under relatively mild conditions in air
Entry
ArX
2b
[mol%]
Proce-
dure[a]
Solvent
T
t
Yield
[%][c]
and in the presence of water. As shown in Table 3, in the
presence of 0.5 mol% of complex 2b, a series of electroni-
cally different (hetero)aryl iodides and bromides underwent
coupling to afford the corresponding biphenyls, although
full conversion was never observed (entries 1, 2, 4, and 6–9).
This means that as a catalyst precursor for Suzuki reactions
on activated aryl halides, palladacycle 2b cannot compete
with highly performing systems such as triaryl phosphite pal-
ladacycles capable of TONs on the impressive order of 107–
108.[23a] However, its behavior towards 4-bromoanisole
(entry 9) is similar to that of sulfur-[18,28] or hydrazone-con-
taining[29] palladacycles as well as imine-based palladium
complexes.[20]
G
[8C][b]
[h]
1
2
3
4
5
6
PhBr
PhBr
PhBr
PhBr
PhBr
PhBr
1
1
1
1
1
0.1
i
DMF
DMF
CH3CN
DMF
DMF
DMF
120
120
reflux
MW
MW
MW
24
48
48
1
25
8
–
27
70
<5
ii
ii
i
ii
ii
1
4
7
1
ii
DMF
MW
1
98
8
9
1
1
ii
ii
DMF
DMF
MW
MW
1
1
81
98
The behavior of indolyl complex 13b was very similar to
that of 2b (entries 3 and 5). Lowering the precatalyst load
affected the reaction course adversely. The attempt to im-
prove the yields by decreasing the reaction time by using
microwave activation did not give the desired results
(entry 10).[30]
Finally, we turned our attention to investigating our palla-
dacycles as precatalysts in Stille reactions.[31] In designing
our experiments with aryl halides in combination with two
different stannanes, we fixed iodide-bridged palladacycle 2b
10
1
ii
DMF
MW
1
62
11
12
1
1
ii
ii
DMF
DMF
MW
MW
1
1
87
Table 3. Palladacycle-catalyzed Suzuki coupling of aryl halides and phe-
nylboronic acid.
PhCl
trace
[a] Procedure i): Et3N (1 equiv); procedure ii) AcONa (1 equiv), Bu4NCl
(1 equiv). [b] MW (microwave) conditions: 15–20 W, 1708C, 3.0 bar.
[c] Isolated yields.
Entry
ArX
PhI
Catalyst
T
[8C]
t
Yield
[%][a]
ring) were converted into the corresponding ethyl cinna-
mates in high yields (entries 7–9); 1-bromo-4-methoxyben-
zene and 2-bromothiophene gave the corresponding Heck
products in 62% and 87% yield, respectively (entries 10
and 11). Complex 2b was almost inactive when chloroben-
zene was used as substrate (entry 12).
[h]
1
2
2b
2b
50
18
73
50
18
81
3
4
13b
2b
50
50
18
18
78
66
When olefin arylations by use of palladacycles as precata-
lysts on aryl bromides are taken into account, the result of
entry 10 is the most appropriate to compare the effective-
ness of compound 2b with literature data, 4-bromoanisole
being the most suitable substrate to this end.[13b] Palladacy-
cle 2b shows a TON similar to the Herrmann–Beller cata-
lyst and its close analogues,[23] imine- and amine-derived pal-
ladacycles,[24] oxime-derived palladacycles,[22e,25] and sulfur-
containing palladacycles.[18] However, it should be men-
tioned that there are other systems with higher activity.[26]
On the basis of the results obtained by using s-alkylpalla-
dium–iodine complexes as effective precatalysts for Heck
reactions, we next examined whether they could also facili-
tate Pd-catalyzed cross-coupling reactions. In this field, the
Suzuki reaction is a method widely used for the construction
of biaryl or substituted aromatic moieties.[27]
5
6
7
13b
2b
50
100
100
18
24
24
60
48
67
PhBr
2b
8
9
2b
2b
2b
100
100
24
24
1
62
42
18
10
MW[b]
The impact of s-alkylpalladium–iodine complexes on the
performance of the Suzuki reaction was evaluated by em-
[a] Isolated yield. [b] MW conditions: 15–20 W, 1708C, 3.0 bar.
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s-Alkylpalladium Intermediates
FULL PAPER
as precatalyst, DMF as the solvent, and 808C as the reaction
temperature. The best results, collected in Table 4, were
always obtained at 0.01 mol% precatalyst loading. The
cross-coupling reactions also proceeded well when the load-
ing of 2b was decreased to 0.001 mol%, but the product
yields were lower (see yields in parentheses in Table 4).
The coupling between PhBu3Sn and iodo- or bromoben-
zene gave biphenyl in satisfactory yields (Table 4, entries 1
and 6). A variety of aryl halides containing electron-with-
drawing groups, including 3-bromopyridine, were converted
into coupling products with Me4Sn and PhBu3Sn in high
yields (entries 2, 3, and 7–10). For 4-methoxyphenyl iodide
and bromide the coupling products were obtained in 30–
59% yield (entries 4, 5, and 11).
pincer,[34] and works better than palladacyclopentadienyl
complexes.[35] However, its coupling ability is lower than
those of triaryl phosphite palladacycles, which are again
shown to be the best-performing precatalysts in cross-cou-
pling reactions.[36]
It is worth noting that all palladacycles retained their ac-
tivity even after being stored in air at room temperature for
a few months, and demonstrated excellent thermal stability,
decomposing only after being heated for more than 48 h in
the presence of a base. This means that they are much more
stable towards air, moisture, and heating than the [Pd-
AHCTUNGRTEG(NNNU PPh3)4] used for their generation.
Compared to Heck and Suzuki reactions, Stille coupling
has been under-investigated. Palladacycle 2b, reaching a
TON of 59000 in the reaction of 1-bromo-4-nitrobenzene, is
better than oxime–Pd complexes[32] and the Herrmann–
Beller catalyst[33] in coupling activated aryl bromides. The ef-
fectiveness of 2b towards 4-bromoanisole (TON 5100) also
reflects the behavior of other palladacycles such as the PCP
Conclusions
In summary, the development of stable s-alkylpalladium
Heck intermediates was well established. The present results
constitute the first example of the systematic isolation of the
s-alkylpalladium intermediates in Heck processes. Previous-
ly, only two cases led to the unusual isolation of Heck inter-
mediates containing a six-membered palladacycle in a fused-
ring structure[9a,b] or a five-membered palladacycle in a
bridged-ring structure.[9c] The allylamine nature of the in-
volved nitrogen atom in the starting substrate was proven to
be the key feature necessary for the isolation of stable Pd
complexes.
Table 4. Stille coupling of aryl halides and stannanes catalyzed by palla-
dacycle 2b.
Entry
1
ArX
PhI
Stannane
PhBu3Sn
Product
Yield [%][a]
83 (64)
Notably, this series of s-alkylpalladium complexes was
found to provide versatile and robust precatalysts suitable
À
for a wide range of C C bond-forming processes such as
Heck, Suzuki, and Stille reactions. Finally, these palladacy-
2
3
Me4Sn
98
cles offer an alternative to the use of traditional palladium
catalysts in C C bond-forming reactions in view of their ex-
À
cellent stability.
PhBu3Sn
99 (75)
4
5
6
7
Me4Sn
30
Experimental Section
PhBu3Sn
PhBu3Sn
PhBu3Sn
59
General: Melting points were determined by the capillary method on a
Bꢃchi B-540 apparatus and are uncorrected. NMR spectra were recorded
on an AVANCE 400 Bruker spectrometer at 400 MHz for 1H NMR,
100 MHz for 13C NMR, and 162 MHz for 31P NMR. Chemical shifts are
given as d values in ppm relative to the residual solvent peaks (CHCl3)
as the internal reference. 31P NMR spectra were recorded with external
H3PO4 as reference. 13C NMR spectra were 1H-decoupled and the multi-
plicities were determined by the APT pulse sequence. 31P NMR spectra
were decoupled. Mass spectra were determined on a VG-7070 EQ-HF in-
strument. Elemental analyses were carried out on a Perkin–Elmer CHN
Analyzer Series II 2400. Thin-layer chromatographic separations were
performed on precoated Merck silica gel 60 F254. Preparative separa-
tions were performed by flash chromatography on Merck silica gel
(0.035–0.070 mm).
PhBr
69
82 (59)
8
9
Me4Sn
83
93
96
51
PhBu3Sn
PhBu3Sn
PhBu3Sn
General procedure for N-alkyl-N-allyl-substituted 3-(aminomethyl)in-
doles 11 and 12: A mixture of a solution of the appropriate allylamine
(10.5 mmol, 1.2 equiv) and a 37% aq solution of formaldehyde (0.76 mL,
10.1 mmol, 1.2 equiv) in 60% acetic acid (2.11 mL, 22.6 mmol, 2.7 equiv)
10
11
was cooled at 08C.
A solution of the indolyl substrate (8.5 mmol,
1 equiv) in cold absolute EtOH (8 mL) was then added dropwise to the
preceding solution. The mixture was stirred for 30 min at room tempera-
ture and for 2 h under heating at reflux. After cooling of the mixture, 1n
[a] Isolated yield. Yields in parentheses were obtained when 0.001 mol%
of 2b was used.
Chem. Eur. J. 2010, 16, 1670 – 1678
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1675

G. Broggini et al.
aq NaOH was added until an alkaline pH was obtained, and then the
mixture was extracted with Et2O (3ꢄ25 mL). The combined organic
layers were washed with brine, dried over Na2SO4, filtered, and evaporat-
ed under reduced pressure. The crude products were purified by flash
chromatography on silica gel.
3J=7.9 Hz, 3J=7.1 Hz, 1H; ArH), 6.00 (ddt, 3J=6.5, Jcis =10.2, Jtrans
17.2 Hz, 1H; =CHCH2), 5.24 (d, Jtrans =17.2 Hz, 1H; =CHHtrans), 5.17 (d,
cis =10.2 Hz, 1H; =CHHcis), 3.80 (s, 3H; CCNCH3), 3.67 (s, 2H;
=
J
NCH2Ar), 3.13 (d, 3J=6.5 Hz, 2H; NCH2CH=), 2.25 ppm (s, 3H;
CH2CH2NCH3); 13C NMR (100 MHz, CDCl3): d=139.1 (s, CAr), 137.0 (d,
CH2CH=CH2), 128.8 (s, CAr), 122.4 (d, CHAr), 120.1 (d, CHAr), 119.5 (d,
CHAr), 118.2 (s, CCH2N), 117.7 (t, CH=CH2), 110.4 (d, CHAr), 90,1 (s,
CI), 61.4 (t, CH2CH=CH2), 54.9 (t, NCH2Ar), 42.7 (q, CCNCH3),
34.7 ppm (q, CH2CH2NCH3); MS: m/z: 340 [M]+; elemental analysis
calcd (%) for C14H17IN2: C 49.43, H 5.04, N 8.23; found: C 49.57, H 4.88,
N 8.32.
N-Allyl-N-methyl-1-methyl-3-aminomethylindole (11c): Yield: 94%; Rf =
0.16 (petroleum ether/EtOAc 1:1, UV); colorless oil; 1H NMR
3
(400 MHz, CDCl3): d=7.74 (d, J=7.8 Hz, 1H; ArH), 7.12–7.35 (m, 3H;
ArH), 7.03 (s, 1H; =CHNCH3), 5.99 (ddt, 3J=6.3, Jcis =10.2, Jtrans
=
17.2 Hz, 1H; =CHCH2), 5.25 (d, Jtrans =17.2 Hz, 1H; =CHHtrans), 5.19 (d,
cis =10.2 Hz, 1H; =CHHcis), 3.80 (s, 3H; CCHNCH3), 3.74 (s, 2H;
J
NCH2Ar), 3.11 (d, 3J=6.3 Hz, 2H; NCH2CH=), 2.28 ppm (s, 3H;
CH2CH2NCH3); 13C NMR (100 MHz, CDCl3): d=137.7 (s, CAr), 136.8 (d,
CH2CH=CH2), 129.2 (d, CHAr), 129.1 (s, CAr), 122.2 (d, CHAr), 120.1 (d,
CHAr), 119.7 (d, CHAr), 118.1 (t, CH=CH2), 111.8 (s, CCH2N), 109.8 (d,
CHAr), 60.9 (t, CH2CH=CH2), 52.7 (t, NCH2Ar), 42.6 (q, CCHNCH3),
33.0 ppm (q, CH2CH2NCH3); MS: m/z: 214 [M]+; elemental analysis
calcd (%) for C14H18N2: C 78.46, H 8.47, N 13.07; found: C 78.32, H 8.58,
N 13.10.
N-Allyl-N-cyclohexyl-1-methyl-2-iodo-3-aminomethylindole (12d): Yield:
69%; Rf =0.68 (EtOAc, UV); colorless oil; 1H NMR (400 MHz, CDCl3):
3
d=7.85 (d, J=7.9, 1H; ArH), 7.30 (d, 3J=8.2, 1H; ArH), 7.23 (dd, 3J=
8.2 Hz, 3J=7.0 Hz, 1H; ArH), 7.11 (dd, 3J=7.9 Hz, 3J=7.0 Hz, 1H;
ArH), 5.89 (ddt, 3J=6.3, Jcis =10.1, Jtrans =17.2 Hz, 1H; =CHCH2), 5.19
(d, Jtrans =17.2 Hz, 1H; =CHHtrans), 5.05 (d, Jcis =10.1 Hz, 1H; =CHHcis),
3.79 (s, 2H; NCH2Ar), 3.78 (s, 3H; NCH3), 3.14 (d, 3J=6.3 Hz, 2H;
NCH2CH=), 2.48–2.62 (m, 1H; NCHcy), 1.15–1.92 ppm (m, 10H; cyH);
13C NMR (100 MHz, CDCl3): d=139.4 (s, CAr), 139.1 (d, CH2CH=CH2),
128.9 (s, CAr), 121.8 (d, CHAr), 120.0 (d, CHAr), 119.9 (d, CHAr), 119.8 (s,
CCH2N), 116.3 (t, CH=CH2), 109.8 (d, CHAr), 89.4 (s, CI), 58.6 (d,
NCHcy), 53.3 (t, CH2CH=CH2), 48.1 (t, NCH2Ar), 34.6 (q, NCH3), 29.2
(t, CH2cy), 27.1 (t, CH2cy), 22.8 ppm (t, CH2cy); MS: m/z: 408 [M]+; ele-
mental analysis calcd (%) for C19H25IN2: C 55.89, H 6.17, N 6.86; found:
C 55.78, H 6.25, N 6.94.
N-Allyl-N-cyclohexyl-1-methyl-3-aminomethylindole (11d): Yield: 70%;
Rf =0.36 (petroleum ether/EtOAc 2:1, UV); colorless oil; 1H NMR
(400 MHz, CDCl3): d=7.77 (d, 3J=7.9, 1H; ArH), 7.30 (d, 3J=8.2, 1H;
ArH), 7.23 (dd, 3J=8.2 Hz, 3J=6.9 Hz, 1H; ArH), 7.11 (dd, 3J=7.9 Hz,
3J=6.9 Hz, 1H; ArH), 6.98 (s, 1H; =CHNCH3), 5.89 (ddt, 3J=6.2, Jcis
=
10.2,
Jtrans =17.2 Hz, 1H; =CHCH2), 5.19 (d, Jtrans =17.2 Hz, 1H; =
CHHtrans), 5.07 (d, Jcis =10.2 Hz, 1H; =CHHcis), 3.82 (s, 2H; NCH2Ar),
3.77 (s, 3H; NCH3), 3.20 (d, 3J=6.3 Hz, 2H; NCH2CH=), 2.66 (tt, 3J=
General procedure for palladacycles 9 and 13: [PdACTHUNTRGNE(UNG PPh3)4] (1.154 g,
3
11.5 Hz, J=3.3 Hz, 1H; NCHcy), 1.87–1.92 (m, 2H; cyH), 1.78–1.83 (m,
1 mmol) and Et3N (0.42 mL, 3 mmol) in CH3CN (2 mL) were added to a
solution of 8 or 12 (1 mmol) in CH3CN (3 mL). The mixture was stirred
at room temperature (12) or under heating at reflux (8) for 2 h. After re-
moval of the solvent under reduced pressure, H2O (10 mL) was added
and the aqueous layer was extracted with CH2Cl2 (3ꢄ10 mL). The com-
bined organic layers were dried (Na2SO4) and eluted through a silica gel
column.
2H; cyH), 1.60–1.68 (m, 1H; cyH), 1.13–1.38 ppm (m, 5H; cyH);
13C NMR (100 MHz, CDCl3): d=139.0 (d, CH2CH=CH2), 137.9 (s, CAr),
128.8 (s, CAr), 128.4 (d, CHAr), 122.0 (d, CHAr), 120.5 (d, CHAr), 119.2 (d,
CHAr), 116.3 (t, CH=CH2), 114.3 (s, CCH2N), 109.6 (d, CHAr), 58.9 (d,
NCHcy), 53.5 (t, CH2CH=CH2), 45.6 (t, NCH2Ar), 33.1 (q, NCH3), 29.4
(t, CH2cy), 27.2 (t, CH2cy), 26.9 ppm (t, CH2cy); MS: m/z: 282 [M]+; ele-
mental analysis calcd (%) for C19H26N2: C 80.80, H 9.28, N 9.92; found:
C 80.95, H 9.15, N 9.90.
Palladacycle 9a: Yield: 25%; Rf =0.12 (petroleum ether/EtOAc 8:2,
UV); brown solid; m.p. 145–1478C (diisopropyl ether); 1H NMR
(400 MHz, CDCl3): d=7.25–7.36 (m, 18H; ArH), 6.97 (d, 3J=7.3 Hz,
1H; ArH), 6.64–6.69 (m, 1H; =CHCH2), 5.44 (d, Jcis =11.5 Hz, 1H; =
CHHcis), 5.40 (d, Jtrans =17.3 Hz, 1H; =CHHtrans), 5.07 (d, 2J=14.7 Hz,
1H; ArCHHN), 4.71 (dd, 2J=3.7 Hz, 3J=11.4 Hz, 1H; NCHHCH=),
3.78 (dd, 3J=5.5 Hz, 2J=14.7 Hz, 1H; ArCHHN), 3.20 (d, 3J=11.4 Hz,
1H; NCHHCH=), 3.04–3.11 (m, 1H; NCHHCH), 2.58 (s br, 1H;
NCHHCH), 2.40–2.42 (m, 1H; ArCHCH2), 1.72 (dd, 3J=3.2 Hz, 2J=
12.5 Hz, 1H; PdCHHCH), 1.58–1.60 ppm (m, 1H; PdCHHCH);
13C NMR (100 MHz, CDCl3): d=141.3 (s, CAr), 135.0 (d, CHAr), 134.9 (d,
CH2CH=CH2), 134.8 (d, CHArPPh3), 134.4 (d, CHAr), 132.9 (s, CAr), 132.8
(s, CAr), 132.2 (s, CAr), 131.7 (s, CAr), 130.4 (d, CHArPPh3), 128.4 (d,
CHArPPh3), 128.3 (d, CHArPPh3), 128.1 (d, CHAr), 127.4 (d, CHAr), 127.2
(d, CHAr), 126.6 (d, CHAr), 121.0 (t, CH2CH=CH2), 63.8 (t, CH2CH=
CH2), 60.8 (t, NCH2CH), 60.3 (t, ArCH2N), 45.9 (t, PdCH2CH), 45.0 ppm
(d, ArCHCH2); 31P NMR (162 MHz, CDCl3): d=34.5 ppm (s); MS: m/z:
633 [M]+ (calculated for the most abundant Pd isotope, 106Pd); elemental
analysis calcd (%) for C31H31BrNPPd: C 58.65, H 4.92, N 2.21; found: C
58.56, H 5.13, N 2.17.
General procedure for 3-(aminomethyl)-substituted 2-iodoindoles 12:
The products were prepared according to literature procedures.[14]
N,N’-Diallyl-2-iodo-3-aminomethylindole (12a): Yield: 52%; Rf =0.32
(petroleum ether/EtOAc 85:15, UV); colorless oil; 1H NMR (400 MHz,
CDCl3): d=8.06 (br s, 1H; NH), 7.82 (d, 3J=7.7 Hz, 1H; ArH), 7.30 (d,
3J=7.8 Hz, 1H; ArH), 7.15 (dd, 3J=7.7 Hz, 3J=6.3 Hz, 1H; ArH), 7.11
(dd, 3J=7.8 Hz, 3J=6.3 Hz, 1H; ArH), 5.96 (ddt, 3J=6.4, Jcis =10.2,
J
trans =17.2 Hz, 2H; =CHCH2), 5.23 (d, Jtrans =17.2 Hz, 2H; =CHHtrans),
5.16 (d, Jcis =10.2 Hz, 2H; =CHHcis), 3.69 (s, 2H; NCH2Ar), 3.14 ppm (d,
3J=6.4 Hz, 4H; NCH2CH=). 13C NMR (100 MHz, CDCl3): d=139.2 (s,
CAr), 136.8 (d, CH2CH=CH2), 128.9 (s, CAr), 122.4 (d, CHAr), 119.8 (d,
CHAr), 119.7 (d, CHAr), 119.6 (s, CCH2N), 117.8 (t, CH=CH2), 110.7 (d,
CHAr), 89.8 (s, CI), 57.1 (t, CH2CH=CH2), 51.8 ppm (t, NCH2Ar); MS:
m/z: 352 [M]+; elemental analysis calcd (%) for C15H17IN2: C 51.15, H
4.86, N 7.95; found: C 51.36, H 4.75, N 8.04.
N,N’-Diallyl-1-methyl-2-iodo-3-aminomethylindole (12b): Yield: 72%;
Rf =0.78 (petroleum ether/EtOAc 1:1, UV); colorless oil; 1H NMR
(400 MHz, CDCl3): d=7.83 (d, 3J=7.9, 1H; ArH), 7.32 (d, 3J=8.2, 1H;
ArH), 7.20 (dd, 3J=8.2 Hz, 3J=7.2 Hz, 1H; ArH), 7.11 (dd, 3J=7.9 Hz,
Palladacycle 9b: Yield: 28%; Rf =0.16 (petroleum ether/EtOAc 8:2,
UV); brown solid; m.p. 156–1588C (diisopropyl ether); 1H NMR
(400 MHz, CDCl3): d=7.27–7.37 (m, 15H; ArH), 6.88 (d, 3J=8.3 Hz,
1H; ArH), 6.82 (dd, 4J=2.5 Hz, 3J=8.3 Hz, 1H; ArH), 6.76 (d, 4J=
2.3 Hz, 1H; ArH), 6.63–6.67 (m, 1H; =CHCH2), 5.44 (d, Jcis =11.6 Hz,
1H; =CHHcis), 5.40 (d, Jtrans =17.2 Hz, 1H; =CHHtrans), 5.02 (d, 2J=
14.7 Hz, 1H; ArCHHN), 4.69 (dd, 2J=3.9 Hz, 3J=12.6 Hz, 1H;
NCHHCH=), 3.88 (s, 3H; CH3), 3.75 (dd, 3J=5.5 Hz, 2J=14.7 Hz, 1H;
ArCHHN), 3.18 (d, 3J=10.3 Hz, 1H; NCHHCH=), 3.03–3.10 (m, 1H;
NCHHCH), 2.52 (br s, 1H; NCHHCH), 2.37–2.40 (m, 1H; ArCHCH2),
1.71 (dd, 3J=3.2 Hz, 2J=9.2 Hz, 1H; PdCHHCH), 1.53–1.59 ppm (m,
1H; PdCHHCH); 13C NMR (100 MHz, CDCl3): d=158.5 (s, CAr), 135.0
(d, CHArPPh3), 134.9 (d, CHArPPh3), 134.4 (d, CH2CH=CH2), 133.9 (s,
CAr), 133.5 (s, CAr), 132.2 (s, CAr), 131.7 (s, CAr), 131.6 (s, CAr), 130.5 (d,
3
3J=7.2 Hz, 1H; ArH), 5.98 (ddt, J=6.4, Jcis =10.2, Jtrans =17.2 Hz, 2H; =
CHCH2), 5.24 (d, Jtrans =17.2 Hz, 2H; =CHHtrans), 5.18 (d, Jcis =10.2 Hz,
2H; =CHHcis), 3.79 (s, 3H; NCH3), 3.75 (s, 2H; NCH2Ar), 3.15 ppm (d,
3J=6.4 Hz, 4H; NCH2CH=). 13C NMR (100 MHz, CDCl3): d=139.2 (s,
CAr), 136.8 (d, CH2CH=CH2), 128.8 (s, CAr), 122.4 (d, CHAr), 119.8 (d,
CHAr), 119.6 (d, CHAr), 118.4 (s, CCH2N), 117.6 (t, CH=CH2), 109.8 (d,
CHAr), 89.7 (s, CI), 57.0 (t, CH2CH=CH2), 51.8 (t, NCH2Ar), 34.7 ppm
(q, NCH3); MS: m/z: 366 [M]+; elemental analysis calcd (%) for
C16H19IN2: C 52.47, H 5.23, N 7.65; found: C 52.56, H 5.14, N 7.51.
N-Allyl-N-methyl-1-methyl-2-iodo-3-aminomethylindole (12c): Yield:
1
34%; Rf =0.38 (petroleum ether/EtOAc 7:3, UV); colorless oil; H NMR
(400 MHz, CDCl3): d=7.75 (d, 3J=7.9 Hz, 1H; ArH), 7.32 (d, 3J=
8.2 Hz, 1H; ArH), 7.19 (dd, 3J=8.2 Hz, 3J=7.1 Hz, 1H; ArH), 7.10 (dd,
1676
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ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1670 – 1678

s-Alkylpalladium Intermediates
FULL PAPER
2
CHArPPh3), 129.0 (d, CHAr), 128.4 (d, CHArPPh3), 128.3 (d, CHArPPh3),
121.0 (t, CH2CH=CH2), 114.4 (d, CHAr), 111.1 (d, CHAr), 63.7 (t,
CH2CH=CH2),60.9 (t, NCH2CH), 60.6 (t, ArCH2N), 55.8 (q, CH3), 46.4
(t, PdCH2CH), 44.2 ppm (d, ArCHCH2); 31P NMR (162 MHz, CDCl3):
d=36.5 ppm (s); MS: m/z: 663 [M]+ (calculated for the most abundant
Pd isotope, 106Pd); elemental analysis calcd (%) for C32H33BrNOPPd: C
57.80, H 5.00, N 2.11; found: C 57.97, H 4.86, N 2.33.
3.37 (s, 3H; NCH3), 3.30 (br s, 1H; NCHHCH), 3.08 (d, J=8.1 Hz, 1H;
NCHHCH), 2.71 (br s, 1H; ArCHCH2), 2.24 (d, 2J=10.7 Hz, 1H;
PdCHHCH), 1.90–1.99 (m, 2H; PdCHHCH, cyH), 1.20–1.37 ppm (m,
9H; cyH); 13C NMR (100 MHz, CDCl3): d=140.2 (s, CAr), 137.4 (s, CAr),
135.2 (d, CHArPPh3), 135.0 (d, CHArPPh3), 134.9 (d, CHArPPh3), 134.8 (d,
CHArPPh3), 133.3 (s, CAr), 132.8 (s, CAr), 130.4 (d, CHArPPh3), 128.4 (d,
CHArPPh3), 128.3 (d, CHArPPh3), 128.1 (d, CHArPPh3), 127.9 (d,
CHArPPh3), 126.0 (s, CAr), 121.4 (d, CHAr), 120.0 (d, CHAr), 119.1 (d,
CHAr), 114.7 (s, CAr), 109.3 (d, CHAr), 106.0 (s, CAr), 65.5 (d, NCHcy),
56.0 (t, NCH2CH), 53.3 (t, ArCH2N), 44.7 (t, PdCH2CH), 39.5 (d,
ArCHCH2), 30.1 (t, CH2cy), 29.2 (q, NCH3), 26.9 (t, CH2cy), 26.1 ppm (t,
CH2cy); 31P NMR (162 MHz, CDCl3): d=36.5 ppm (s); MS: m/z: 776
[M]+ calculated for the most abundant Pd isotope, 106Pd; elemental anal-
ysis calcd (%) for C37H40IN2PPd: C 57.19, H 5.19, N 3.61; found: C 57.37,
H 5.16, N 3.48.
Palladacycle 13a: Yield: 45%; Rf =0.37 (petroleum ether/EtOAc 2:1,
UV); brown solid; m.p. 79–818C (diisopropyl ether); 1H NMR
(400 MHz, CDCl3): d=7.12–7.76 (m, 20H; ArH, NH), 6.74–6.79 (m, 1H;
=CHCH2), 5.48 (d, Jcis =11.5 Hz, 1H; =CHHcis), 5.43 (d, Jtrans =18.1 Hz,
1H; =CHHtrans), 5.31 (d, 2J=12.8 Hz, 1H; ArCHHN), 4.93 (dd, 3J=
11.6 Hz, 1H; NCHHCH=), 3.86 (dd, 3J=6.9 Hz, 2J=12.8 Hz, 1H;
ArCHHN), 3.23–3.35 (m, 2H; NCHHCH, NCHHCH=), 2.59–2.66 (m,
2H; NCHHCH, ArCHCH2), 1.84–1.87 (m, 1H; PdCHHCH), 1.44–
1.61 ppm (m, 1H; PdCHHCH); 13C NMR (100 MHz, CDCl3): d=139.0
(s, CAr), 136.2 (s, CAr), 135.6 (d, CHArPPh3), 135.5 (d, CHArPPh3), 135.2
(d, CHArPPh3), 135.0 (d, CHArPPh3), 134,9 (d, CH2CH=CH2), 132.8 (s,
CAr), 132.3 (s, CAr), 130.5 (d, CHArPPh3), 128.6 (d, CHArPPh3), 128.4 (d,
CHArPPh3), 128.3 (d, CHArPPh3), 128.1 (d, CHArPPh3), 126.3 (s, CAr),
122.0 (d, CHAr), 120.8 (t, CH2CH=CH2), 120.4 (d, CHAr), 119.1 (d, CHAr),
114.5 (s, CAr), 111.2 (d, CHAr), 106.8 (s, CAr), 64.7 (t, CH2CH=CH2), 61.0
(t, NCH2CH), 57.1 (t, ArCH2N), 47.3 (t, PdCH2CH), 40.3 ppm (d,
ArCHCH2); 31P NMR (162 MHz, CDCl3): d=34.8 ppm (s); MS: m/z: 720
[M]+ (calculated for the most abundant Pd isotope, 106Pd); elemental
analysis calcd (%) for C33H32IN2PPd: C 54.98, H 4.47, N 3.89; found: C
54.77, H 4.56, N 3.68.
Acknowledgements
The authors thank the Ministero dellꢁIstruzione, dellꢁUniversitꢀ e della
Ricerca for financial support and for the Ph.D. fellowships to M.R. (Pro-
getto Giovani 2006).
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Palladacycle 13b: Yield: 27%; Rf =0.25 (petroleum ether/EtOAc 4:1,
UV); brown solid; m.p. 179–1818C (diisopropyl ether); 1H NMR
(400 MHz, CDCl3): d=7.12–7.73 (m, 19H; ArH), 6.75–6.80 (m, 1H; =
CHCH2), 5.49 (d, Jcis =10.4 Hz, 1H; =CHHcis), 5.45 (d, Jtrans =17.2 Hz,
1H; =CHHtrans), 5.31 (d, 2J=12.5 Hz, 1H; ArCHHN), 4.93 (d, 3J=
13.3 Hz, 1H; NCHHCH=), 3.84–3.89 (m, 1H; ArCHHN), 3.39 (s, 3H;
CH3), 3.30–3.41 (m, 2H; NCHHCH=, NCHHCH), 2.67 (br s, 1H;
NCHHCH), 2.60 (d, 3J=10.3 Hz, 1H; ArCHCH2), 1.88–1.91 (m, 1H;
PdCHHCH), 1.51–1.56 ppm (m, 1H; PdCHHCH); 13C NMR (100 MHz,
CDCl3): d=140.3 (s, CAr), 137.4 (s, CAr), 135.6 (d, CHArPPh3), 135.3 (d,
CHArPPh3), 135.2 (d, CHArPPh3), 135.0 (d, CHArPPh3), 134.9 (d, CH2CH=
CH2), 133.0 (s, CAr), 132.5 (s, CAr), 130.5 (d, CHArPPh3), 128.8 (d,
CHArPPh3), 128.6 (d, CHArPPh3), 128.3 (d, CHArPPh3), 128.2 (d,
CHArPPh3), 125.7 (s, CAr), 121.5 (d, CHAr), 120.8 (t, CH2CH=CH2), 120.0
(d, CHAr), 119.1 (d, CHAr), 114.8 (s, CAr), 109.3 (d, CHAr), 105.6 (s, CAr),
64.6 (t, CH2CH=CH2), 61.2 (t, NCH2CH), 57.2 (t, ArCH2N), 46.0 (t,
PdCH2CH), 39.0 (d, ArCHCH2), 29.2 ppm (q, NCH3); 31P NMR
(162 MHz, CDCl3): d=35.2 ppm (s); MS: m/z: 734 [M]+ (calculated for
the most abundant Pd isotope, 106Pd); elemental analysis calcd (%) for
C34H34IN2PPd: C 55.56, H 4.66, N 3.81; found: C 55.42, H 4.84, N 3.61.
Palladacycle 13c: Yield: 64%; Rf =0.59 (petroleum ether/EtOAc 1:1,
UV); brown solid; m.p. 132–1338C (diisopropyl ether); 1H NMR
(400 MHz, CDCl3): d=7.11–7.56 (m, 19H; ArH), 5.25 (d, 2J=13.5 Hz,
1H; ArCHHN), 3.64–3.69 (m, 1H; ArCHHN), 3.36–3.41 (m, 6H; NCH3,
NCH3), 3.12 (d, 2J=10.3 Hz, 1H; NCHHCH), 2.89 (d, 2J=10.3 Hz, 1H;
NCHHCH), 2.68 (br s, 1H; ArCHCH2), 1.89–1.92 (m, 1H; PdCHHCH),
1.54–1.66 ppm (m, 1H; PdCHHCH); 13C NMR (100 MHz, CDCl3): d=
139.8 (s, CAr), 137.5 (s, CAr), 135.1 (d, CHArPPh3), 135.0 (d, CHArPPh3),
134.9 (d, CHArPPh3), 134.8 (d, CHArPPh3), 132.9 (s, CAr), 132.4 (s, CAr),
130.5 (d, CHArPPh3), 128.6 (d, CHArPPh3), 128.4 (d, CHArPPh3), 128.3 (d,
CHArPPh3), 128.2 (d, CHArPPh3), 125.6 (s, CAr), 121.5 (d, CHAr), 120.0 (d,
CHAr), 119.1 (d, CHAr), 114.7 (s, CAr), 109.3 (d, CHAr), 105.4 (s, CAr), 66.5
(t, NCH2CH), 58.5 (t, ArCH2N), 53.1 (q, CCNCH3), 46.5 (t, PdCH2CH),
39.1 (d, ArCHCH2), 29.2 ppm (q, CH2CH2NCH3); 31P NMR (162 MHz,
CDCl3): d=37.2 ppm (s); MS: m/z: 708 [M]+ (calculated for the most
abundant Pd isotope, 106Pd); elemental analysis calcd (%) for
C32H32IN2PPd: C 54.22, H 4.55, N 3.95; found: C 54.07, H 4.69, N 4.06.
Palladacycle 13d: Yield: 66%; Rf =0.43 (petroleum ether/EtOAc 2:1,
UV); brown solid; m.p. 68–708C (diisopropyl ether); 1H NMR
(400 MHz, CDCl3): d=7.11–7.57 (m, 19H; ArH), 5.17 (d, 2J=13.1 Hz,
1H; ArCHHN), 4.36–4.41 (m, 1H; ArCHHN), 4.01 (br s, 1H; NCHcy),
Chem. Eur. J. 2010, 16, 1670 – 1678
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[16] Crystal data for 13b: C34H34IN2PPd; Mr =734.9 gmolÀ1; triclinic, P1;
¯
a=9.305(1), b=12.529(2), c=14.220(3) ꢇ; a=84.25(2), b=72.87(2),
g=83.07(1)8;
V=1569.0(4) ꢇ3,
Z=2,
F
(000)=732,
1calc =
1.556 gcmÀ3, m
ACHTUNGTRENNUNG
1.054 for 5035 observed [I>2s(I)] reflections and 353 parameters;
highest peak and deepest hole=0.72 and À0.85 eꢇÀ2
. CCDC-
740279 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
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Received: July 24, 2009
Published online: December 18, 2009
1678
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ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1670 – 1678