The retro-chloropalladation reaction of heterosubstituted alkynes

Article abstract of DOI:10.1016/S0277-5387(03)00324-3

The bridge-splitting reaction of dimeric palladacycles of the type {Pd[κ¹-C, κ¹-N-C(R) = C(Cl)CH₂NMe₂](μ-Cl)}₂ (R = Ph, Me, CH₂CH₂OH), derived from the chloropalladation of propa

Full text of DOI:10.1016/S0277-5387(03)00324-3

Polyhedron 22 (2003) 1665Á1671
/
www.elsevier.com/locate/poly
The retro-chloropalladation reaction of heterosubstituted alkynes
Mara L. Zanini a, Mario R. Meneghetti a, Gunter Ebeling a, Paolo R. Livotto a,
Frank Rominger b, Jairton Dupont a,*
a Laboratory of Molecular Catalysis Á
/
IQ Á UFRGS, Av. Bento Goncalves, 9500, Porto Alegre 91501-970 RS, Brazil
/
¸
b Organisch-Chemisches Institut der Universitat Heidelberg, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany
¨
Received 30 October 2002; accepted 15 April 2003
Abstract
The bridge-splitting reaction of dimeric palladacycles of the type {Pd[k1-C, k1-N-C(R)Ä
CH2CH2OH), derived from the chloropalladation of propargyl amines (RCÅCCH2NMe2), with pyridine (Py), triphenylphosphine
(PPh3) and tert-butylisonitrile (tBuNC) affords the monomeric compounds [PdC(R)Ä
/
C(Cl)CH2NMe2](m-Cl)}2 (Rꢀ
/
Ph, Me,
/
t
/
CCH2NMe2(Cl)L] (LꢀPy, PPh3, BuNC).
/
These monomeric compounds are not stable in solution and undergo retro-chloropalladation reactions yielding the propargyl
amines and [PdCl(L)-m-Cl]2. This process is strongly dependent upon the nature of the incoming nucleophile (L), the R group on the
metallated ligand and the temperature. The retro-halopalladation reaction is almost instantaneous in the case of the reaction of the
bromo derivative [PdC(Ph)ÄC(Br)CH2NMe2-m-Br]2 and pyridine at room temperature. These results can be rationalized in terms of
/
the stability of the PdÃ
/
C bond of the intermediate monomeric compound [PdC(R)Ä
/
C(X)CH2NMe2(X)L], that is directly related to
the nature of its substituents R (Ph, Me and CH2CH2OH), of ligands which are both cis and trans to it (Py, CNtBu, PPh3, Cl and
Br) and the temperature.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Retro-chloropalladation reaction; Monomeric compounds; Alkynes; Propargyl amines
1. Introduction
anion onto the activated triple CC bond (Scheme 1)
and that the stereochemical outcome (size of the formed
palladacycle) of this reaction is under thermodynamic
control.
The halopalladation reaction of alkynes leads to series
of very useful Pd-vinyl intermediate species for organic
While investigating the bridge-splitting reaction of
palladacycles derived from the chloropalladation of
propargyl amines we have observed the retro-chloro-
palladation reaction. Herein we show for the first time
the retro-chloropalladation of propargylamines and that
this reaction is highly dependent on the alkyne and the
other ligands around palladium.
synthesis. The PdÃ
/
C bond of these intermediates can be
selectively trapped with electrophilic reagents such as
allyl halides and dienes to afford highly functionalized
organic molecules [1]. The presence of potentially two
electron donor groups in the alkyne fragment, such as in
the case of propargyl amines and thioethers, allows the
isolation of these compounds in the form of pallada-
cycles [2]. Indeed, the halopalladation of heterosubsti-
tuted alkynes, is now emerging as a new alternative
method for the preparation of various types of pallada-
cycles [3]. It has been proposed that this halopallada-
tion, in particular chloropalladation, occurs via an
intermolecular nucleophilic addition of the chloride
2. Results and discussion
The reaction of 1a with a methanolic solution of
Li2PdCl4 at 5 8C affords almost instantaneously a
yellow solid (palladacycle 2a) that is isolated by filtra-
tion. It is interesting to note that prolonged reaction
times significantly reduce the yield of 2a that in solution
slowly decomposes forming among various products
PdCl2 and 1a (see below). Compound 2a was isolated as
* Corresponding author. Tel.: ꢁ
7304.
E-mail address: dupont@iq.ufrgs.br (J. Dupont).
/
55-51-316-6321; fax: ꢁ55-51-316-
/
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00324-3

1666
M.L. Zanini et al. / Polyhedron 22 (2003) 1665Á
/1671
Scheme 1.
a yellow crystalline solid that is air and water stable,
soluble in polar organic solvents such as dichloro-
methane and acetone and slightly soluble in hexanes.
The 1H and 13C NMR spectra of 2a in CDCl3 show only
one set of signals suggesting that it is present as a single
isomer, that possesses the transoid-NMe2 geometry
through the chloro bridges (see later).
sphere around each Pd center can be considered as
essentially planar and this is also evident for the four-
membered Pd2Cl2 rings.
The palladacycles 2b and 2c have been prepared from
the chloropalladation of alkynes 1b and 1c as described
earlier [3c]. The reaction of 2b and 2c with pyridine in
dichloromethane at room temperature yields the corre-
sponding monomeric palladacycles 3b and 3c, respec-
tively, in almost quantitative yield (Scheme 2).
Compounds 3b and 3c are stable in solution at room
temperature. In contrast, the reaction of 2a with
pyridine, at room temperature, affords 1a and PdCl2Py2
after 1 h, and the monomeric compound 3a could not be
isolated or detected in pure form. The formation of
these products corresponds, formally, to the retro-
chloropalladation reaction. The reaction of 2a with an
The molecular structure of 2a has been ascertained by
means of an X-ray diffraction analysis. Although the
structure has a poor resolution (R1ꢀ0.152) the ob-
/
tained data can be used for the establishment of the
nuclearity connectivity and the type of 2a isomer
formed. A ball and stick drawing is shown in Fig. 1
together with selected bond distances and angles.
Crystallographic data and details of the structure
determination are presented in Table 1. Tables of atomic
coordinates, and thermal parameters are supplied as
supporting information.
1
excess of pyridine was monitored by H NMR spectro-
scopy at room temperature. Four compounds can be
1
clearly identified in the H NMR spectra immediately
after addition of pyridine to a solution of 2a in CDCl3:
The crystal structure of 2a contains discrete centro-
symmetric dimeric palladacycles. The coordination
˚
Fig. 1. Ball and stick drawing of 2a. Hydrogen atoms have been omitted for clarity. Selected bond distances (A) and angles (8): Pd(1)Ã
/
C(11): 1.96(2);
Pd(1)Ã
/
N(2): 2.05(2); Pd(1)Ã
N(2): 82.8 (9); N(2)Ã
/
C(11): 2.347(7); Pd(1)Ã
Pd(1)ÃC(l3): 96.6 (6); C(l3)Ã
/
C(13): 2.463(7); C(11)Ã
/
C(12): 1.32 (3); C(12)Ã
/
C(l4): 1.76(3). C(11)Ã
/
Pd(1)Ã
/
C(l1): 95.9 (7); C(11)Ã
/
Pd(1)Ã
/
/
/
/
Pd(1)ÃC(l1): 84.7 (2); C(l4)Ã
/
/
C(12)ÃC(13): 114 (2).
/

M.L. Zanini et al. / Polyhedron 22 (2003) 1665Á
/1671
1667
Table 1
Crystal data and structure refinement for 2a
structure of analogous compounds [4] and on theoretical
calculations (Gaussian) [5] which indicate that this
isomer is 5.14 kcal molꢂ1 more stable than the cis-
isomer (Fig. 2). Moreover, the trans isomer is always
obtained in the bridge-splitting reaction of dimeric
palladacycles upon reaction with L ligands such as
pyridines, phosphines and isonitriles [6]. This selectivity
can be explained by the antisymbiotic effect of the soft
Pd(II) center that will place the incoming ligand cis to
Empirical formula
Formula weight
Temperature (K)
C14H26Cl4N2O2Pd2
608.97
200(2)
˚
Wavelength (A)
0.71073
monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions
˚
a (A)
5.7319(1)
13.0459(2)
22.6404(4)
90
˚
b (A)
the PdÃ/C bond [7]. The structure of 4a was based on the
˚
c (A)
presence of a singlet at 2.73 ppm typical for a NMe2
coordinated to Pd(II) and a triplet for the CH2N at 3.60
ppm.
a (8)
b (8)
g (8)
96.317(1)
90
3
˚
The monomeric compounds 5aÁ
/
5c and 6aÁ6b could
/
V (A )
2067.12(6)
4
1.96
be observed in solution (1H NMR spectroscopy) by the
Z
Dcalc (g cmꢂ3
Absorption coefficient (mmꢂ1
Crystal shape
)
t
addition of BuNC and PPh3 to an NMR tube contain-
)
2.27
polyhedron
ing a CDCl3 solution of the dimers 2aÁ2c (Scheme 4). In
/
the case of the reaction of 2c with PPh3 only free alkyne
1c and the signals corresponding to PPh3 were observed.
Crystal size (mm)
u Range for data collection (8)
Index ranges
0.28ꢃ
0.9Á24.7
65h 5
265l 5
/
0.18ꢃ
/
0.05
/
ꢂ
ꢂ/
/
/
/6, ꢂ
/185
/
k 518,
/
Compounds 5aÁ
/
5c and 6aÁ6b are relatively stable at
/
/
/26
room temperature but eventually undergo retro-chlor-
opalladation upon heating in CDCl3 solution affording
Reflections collected
17 422
Observed reflections [I ꢀ2s(I)]
/
3090
3574 [Rint
the free alkynes 1aÁ
isonitrile products resulting from the insertion of the
isonitrile into the PdÃC bond have been observed [8]. It
/
1c and [Pd(L)Cl(m-Cl)]2. Note that
Independent reflections
Absorption correction
Refinement method
ꢀ0.1015]
/
none
full-matrix least-squares on F2
3574/0/98
/
Data/restraints/parameters
is also important to note that 2b undergoes retro-
chloropalladation even in the solid state at temperatures
above 150 8C. Moreover, the retro-chloropalladation
reaction also takes place almost instantaneously in the
reaction of the bromo palladacycle 7b (prepared by
bromopalladation of alkyne 1b) with pyridine at room
temperature (Scheme 5).
Final R indices [I ꢀ
/
2s(I)]
R1ꢀ
3.37
7.03 and ꢂ2.99
/
0.152, wR2ꢀ0.414
/
Goodness-of-fit on F2
Largest difference peak and hole
ꢂ3
/
˚
(e A
)
It is also of note that attempts to prepare palladacycle
7b by oxidative addition of (E)-1,2-dibromo-3-dimethy-
lamino-1-phenyl-1-propene [9] with Pd2(dba)3 in CHCl3
affords the alkyne 1b and PdBr2, among other uni-
dentified products (Scheme 6). This result can be
rationalized in terms of the formation of palladacycle
7b followed by retro-bromopalladation to generate
alkyne 1b and PdBr2. Indeed, heating a CDCl3 solution
of the palladacycle 7b (prepared by reaction of 1b with
Li2PdBr4) generated the alkyne 1b and PdBr2. In
contrast the chloro analogue 2b does not undergo the
retro-chloropalladation reaction under identical reac-
tion conditions.
Scheme 2.
alkyne 1a, monomeric compound 3a, PdCl2Py2 and
(PdCl2(1a)Py) 4a (Scheme 3).
The evolution of this reaction with time is summar-
ized in Fig. 3. The presence of alkyne 1a, monomeric
palladacycle 3a and PdCl2Py2 in the reaction mixture
1
was easily assigned in the H NMR spectrum of the
reaction mixture. The location of the pyridine ligand
trans to the NMe2 group in 3a is based on the X-ray
These results clearly indicate that the retro-halopalla-
dation reaction is strongly dependent on the stability of
Scheme 3.

1668
M.L. Zanini et al. / Polyhedron 22 (2003) 1665Á1671
/
Fig. 2. Full optimized geometries of the cis and trans isomers of 3a (H atoms have been omitted for clarity).
which are in a relative cis or trans position (Py, CNtBu,
PPh3, Cl and Br), and the temperature (Scheme 7).
The higher trans-influence of the bromo ligand than
the chloro analogue can explain the difference of
palladacycles 2b and 7b towards the retro-halopallada-
tion reaction. The greater stabilization of the PdÃ
/
C
Scheme 4.
bond in compounds 5a and 6a indirectly induced by the
more effective back-donation properties of CNR and
PPh3 than Py in 3a can account for the observed results.
The influence of the R group linked to the PdÃ
/
C(vinyl)
group (CH2CH2OH, Ph and Me) in 3aÁ3c is not
/
straightforward but it is reasonable to assume that the
alcohol function in 3a can provide anchimeric assistance
during the C-halogen bond breaking step.
All these results strongly suggest that the retro-
halopalladation reaction of alkynes occurs through a
concerted mechanism identical to the one previously
proposed for the halopalladation reaction. Moreover,
Scheme 5.
the PdÃ
/
C bond which is directly related to the nature of
its substituents (Ph, Me and CH2CH2OH), to ligands
Fig. 3. The evolution of the reaction of 2a with an excess of pyridine at room temperature in CDCl3.

M.L. Zanini et al. / Polyhedron 22 (2003) 1665Á
/1671
1669
Program at a HF/B3LYP [11] level of theory, using a
DunningÁHuzinaga D95 [12] basis set for the non-metal
atoms and a DZ valence basis set plus an effective core
/
potential for the palladium [13].
Scheme 6.
3.3. X-ray structure analysis of 2a
this process can explain why these palladacycles do not
easily undergo insertion reactions with unsaturated
substrates such as alkynes and isonitriles even at
temperatures above 25 8C [10].
In summary the stability of palladacycles derived
from the halopalladation of propargylamines in solution
is strongly dependent upon the type of the alkyne
substituents, halogen and temperature. Moreover, the
retro-halopalladation is facilitated by the addition of
nucleophiles such as pyridine, triphenylphosphine or
tert-butylisonitrile.
Crystals were mounted on a glass fiber with perfluor-
opolyether. The measurements were carried out on a
Bruker SMART-CCD diffractometer with graphite
monochromated Mo Ka radiation. For 2a, frames
corresponding to a sphere of data were collected using
the v-scan technique, 20 s exposures of 0.38 in v were
taken. No absorption correction was applied, due to the
bad quality of data. The data were corrected for Lorentz
and polarization effects. The structure was solved by
direct methods and expanded using Fourier techniques,
all non-hydrogen atoms were refined with isotropic
displacement parameters, hydrogen atoms were not
considered. The full-matrix least-squares refinement
against F2 converged. All calculations were performed
using the SHELXTL crystallographic software package of
Bruker (G.M. Sheldrick, SHELXTL V5.10, Bruker REM
AXS, Inc., Madison, WI, 1997).
3. Experimental
3.1. General methods
All reactions involving organometallic compounds
were carried out under argon or nitrogen atmosphere
in oven dried Schlenk tubes. The alkynols were prepared
according to known procedures [14]. Solvents were dried
with adequate drying agents and distilled under argon
prior to use. All the other chemicals were purchased
from commercial sources (Acros or Aldrich) and used
without further purification. The following compounds
were prepared according to the published procedures: 1a
[3d]; 1b, 1c, 2b, 2c [3c]. Elemental analyses were
performed by the Analytical Central Service of IQ-
USP (Brazil). NMR spectra were recorded on a Varian
Inova 300 spectrometer. Infrared spectra were per-
formed on a Bomem B-102 spectrometer. Mass spectra
were obtained using a GC/MS Shimadzu QP-5050 (EI,
70 eV). Gas chromatography analyses were performed
3.4. Synthesis of palladacycle 2a
A Li2PdCl4 solution was prepared by dissolving PdCl2
(1.06 g, 6.00 mmol) and LiCl (0.63 g, 15.0 mmol) in hot
methanol (20 ml), under vigorous stirring. After dis-
solution of the solids, this solution was cooled to 0 8C
and a solution of 1-dimethylamino-2-pentyn-5-ol 1a
(0.76 g, 6.00 mmol) was added. The resulting yellow
suspension was stirred at 0 8C for 15 min. Filtration and
washing of the resulting solid with cold MeOH and
drying under reduced pressure afforded the desired
palladacycle (yellow solid, 1.18 g, 64% yield). M.p.:
105 8C (dec.). Anal.: (C7H13Cl2NOPd)2 (609.02) requires
C, 27.61; H, 4.30; N, 4.60. Found: C, 27.41; H, 4.12; N,
with a HewlettÁPackard-5890 Gas Chromatograph with
/
a FID and 30 m capillary column with a dimethylpo-
lysiloxane stationary phase.
4.54%. IR (KBr, cmꢂ1): 3304 (nOÃH), 1617 (nCÄC). H
1
3
NMR (CDCl3): d 3.78 (t, 2H, JHH
ꢀ6.6 Hz, CH2O);
/
3.2. Theoretical calculations
3.54 (s, 2H, CH2N); 2.83 (s, 6H, NMe2); 2.10 (t, 2H,
3JHH C). 13C{1H} NMR (CDCl3): d
6.6 Hz, H2CÃCÄ
142.0, 117.4 (CÄC); 74.6 (CH2N); 62.3 (CH2O); 53.5
(NMe2); 37.9 (H2CÃCÄC).
ꢀ
/
/
/
The energy of all calculated species was obtained by
full geometry optimization without any constraint. The
calculations were performed with the GAUSSIAN-98’ [5]
/
/
/
Scheme 7.

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M.L. Zanini et al. / Polyhedron 22 (2003) 1665Á1671
/
3.5. Synthesis of palladacycles 3aÁ
/
c, 5aÁ
/
c and 6a,b
74.4 (CH2N); 51.4 (NMe2); 29.4 (Me3C); C quat tBu and
isonitrile carbon: not observed.
General procedure. The dimeric palladacycle (2a, 2b
or 2c; 0.05 mmol) was dissolved in CDCl3 (1.1 ml) and
3.11. Palladacycle 5c
t
the required ligand (Py, BuNC or Ph3P; 0.05 mmol),
dissolved in CDCl3 (1 ml), was added and the 1H NMR
spectra recorded immediately.
1H NMR (CDCl3): d 3.55 (q, JHH
ꢀ
ꢀ
/
2.0 Hz, 2H,
5
CH2N); 2.83 (s, 6H, NMe2); 1.96 (t, 5JHH
/2.0 Hz, 3H,
CH3); 1.55 (s, 9H, tBu). 13C{1H} NMR (CDCl3): d
t
C); 74.0 (CH2N); 58.5 (C quat Bu);
3.6. Palladacycle 3a
143.2, 119.1 (CÄ
/
51.5 (NMe2); 30.3 (Me3C); 26.0 (Me); isonitrile carbon:
not observed.
3
1H NMR (CDCl3): d 8.77 (d, 2H, JHH
ꢀ5.4 Hz, H
/
py); 7.79 (1H, 3JHH
ꢀ7.6 Hz, H py); 7.36 (m, 2H, H py);
/
3.60 (s, 2H, CH2N); 3.38 (t, 3JHH
ꢀ
ꢀ
/
6.6 Hz, 2H, CH2O);
6.6 Hz, 2H, H2CÃ
3.12. Palladacycle 6a
3
2.91 (s, 6H, NMe2); 1.77 (t, JHH
/
/
CÄ/C).
This reaction was performed in C6D6, although the
1
1
signals were broad in the H NMR spectrum. H NMR
(C6D6): d 8.10Á7.90 (m, 6H, H arom); 7.15Á6.95 (m,
9H, H arom); 3.58 (br s, 2H, CH2O); 3.44 (br s, 2H,
3.7. Palladacycle 3b
/
/
This compound could be isolated from the NMR tube
by addition of hexanes. Anal.: C16H18Cl2N2Pd (415.66)
requires C, 46.23; H, 4.36; N, 6.74. Found: C, 46.61; H,
4.37; N, 6.54%. 1H NMR (CDCl3): d 8.30 (d, 2H,
CH2N); 2.48 (br s, 6H, NMe2); 2.33 (br s, 2H, H2CÃ
C).
/
CÄ
/
3JHH
6.95Á
ꢀ
/
4.9 Hz, H py); 7.42 (t, 1H, 3JHH
6.82 (m, 7H, H arom and H py); 3.69 (s, 2H,
ꢀ6.1 Hz, H py);
/
3.13. Palladacycle 6b
/
1H NMR (CDCl3) d 7.80Á
/
7.20 (m, 15H, H arom);
CH2N); 3.03 (s, 6H, NMe2). 13C{1H} NMR (CDCl3): d
153.3, 138.4, 137.0, 131.7, 128.2, 127.6, 127.3, 125.2,
125.0, 124.3 (CH arom and CH py); 146.1, 142.3 (C
3
6.80 (t, 1H, JHH
ꢀ7.5 Hz, H arom); 6.61 (t, 2H,
/
3
7.5 Hz, H arom); 6.48 (d, 2H, JHH
3JHH
H arom); 3.87 (d, 2H, JPH
ꢀ
/
ꢀ7.5 Hz,
/
4
ꢀ1.8 Hz, CH2N); 2.97 (d,
/
arom quat and CÄ
/
C); 117.4 (CÄ
/
C); 75.2 (CH2N); 53.0
4
6H, JPH
ꢀ
/
2.7 Hz, NMe2). 13C{1H} NMR (CDCl3): d
(NMe2).
3
143.4 (d, JPC
2
C); 120.6 (d, JPC
C); 135.4, 135.3, 135.2, 135.1, 134.9, 134.5, 134.4,
ꢀ
/
5.0 Hz, CÄ
/
ꢀ4.0 Hz,
/
CÄ
/
3.8. Palladacycle 3c
132.1, 131.1, 130.8, 130.4, 130.3, 130.1, 128.7, 128.6,
128.4, 128.3, 128.2, 126.9, 124.9 (CH arom); 74.8 (d,
3
1H NMR (CDCl3): d 8.77 (dd, JHH
ꢀ
ꢀ
/
6.3 Hz,
7.5 Hz,
6.3 and 7.5
2.0 Hz,
2.0 Hz,
CH3). 13C{1H} NMR (CDCl3): d 152.8, 137.8, 125.3
3JPC
ꢀ
/
3.0 Hz, CH2N); 50.4 (d, JPC
ꢀ2.5 Hz, NMe2).
/
3
3
4JHH
4JHH
ꢀ
/
1.5 Hz, 2H, H py); 7.79 (tt, 1H, JHH
/
31P{1H} NMR (CDCl3): d 35.1.
ꢀ
/
1.5 Hz, H py); 7.36 (ddd, 2H, 3JHH
ꢀ
/
4
5
Hz, JHH
ꢀ
/
1.5 Hz, H py); 3.53 (q, 2H, JHH
ꢀ
ꢀ
/
CH2N); 2.93 (s, 6H, NMe2); 1.18 (t, 3H, 5JHH
/
3.14. Synthesis of palladacycle 7b
(CH py); 141.8, 116.2 (CÄ
/
C); 74.6 (CH2N); 52.9
A Li2PdBr4 solution was prepared by dissolving
PdBr2 (1.59 g, 6.00 mmol) and LiBr (1.56 g, 18.0
mmol) in hot methanol (20 ml), under vigorous stirring.
After dissolution of the solids, this solution was cooled
to 5 8C and a solution of 1-phenyl-3-dimethylamino-1-
propyne 1b (1.00 g, 6.30 mmol) was added. The resulting
brown suspension was stirred at 5 8C for 15 min.
Filtration and washing of the resulting solid with cold
MeOH and drying under reduced pressure afforded the
desired palladacycle (brown solid, 1.70 g, 64% yield).
Anal.: (C11H13Br2NPd)2 (850.92) requires C, 31.05; H,
(NMe2); 20.0 (CH3).
3.9. Palladacycle 5a
1H NMR (CDCl3): d 3.75 (t, 2H, JHH
ꢀ6.9 Hz,
/
3
CH2O); 3.56 (s, 2H, CH2N); 2.83(s, 6H, NMe2); 2.48 (t,
C); 1.54 (s, 9H, tBu).
C); 73.8
3
2H, JHH
ꢀ
/
6.9 Hz, H2CÃ
/
CÄ
/
13C{1H} NMR (CDCl3): d 143.9, 121.7 (CÄ
(CH2N); 61.5 (CH2O), 58.5 (C quat Bu); 51.2 (NMe2);
29.8 (Me3C); isonitrile carbon: not observed.
/
t
1
3.08; N 3.29. Found: C, 29.87; H, 2.89; N, 3.11%. H
3.10. Palladacycle 5b
NMR (CDCl3): d 7.55Á
2H, CH2N), 2.51 (s, 6H, NMe2). H NMR (CDCl3ꢁ
Pyd5): d 7.50Á7.40 (m, 2H, H arom), 7.35Á7.25 (m, 3H,
H arom), 2.50 (s, 2H, CH2N), 2.38 (s, 6H, NMe2) (This
spectrum is identical to the one recorded with an
authentic sample of 1b).
/
7.35 (m, 5H, Harom), 3.78 (s,
1
/
1H NMR (CDCl3): d 7.45Á
3.70 (s, 2H, CH2N); 2.92 (s, 6H, NMe2); 1.07 (s, 9H,
tBu). 13C{1H} NMR (CDCl3): d 146.5, 145.9, 120.2 (C
/
7.10 (m, 5H, H arom);
/
/
arom quat and CÄ
/
C); 127.9, 127.2, 125.7 (CH arom);

M.L. Zanini et al. / Polyhedron 22 (2003) 1665Á
/1671
1671
Burrow, M. Horner, Organometallics 16 (1997) 2386;
3.15. Attempted synthesis of palladacycle 6c
(d) G. Ebeling, M.R. Meneghetti, F. Rominger, J. Dupont,
Organometallics 21 (2002) 3221.
The reaction of palladacycle 2c with PPh3, performed
in CDCl3 solution, affords almost instantaneously a
yellow solid, identified as PdCl2(PPh3)2. The presence of
alkyne 1c in the remaining solution was confirmed by
[4] G.R. Newkome, W.E. Puckett, V.K. Gupta, G.E. Kiefer, Chem.
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Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V.
Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q.
Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Raghava-
chari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, B.B Stefanov, G.
Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L.
Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y Peng, A.
Nanayakkara, C. Gonzalez, M. Challacombe, P.M.W. Gill, B.
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Head-Gordon, E.S. Replogle, J.A. Pople, GAUSSIAN-98, Revision
A.5, Gaussian, Inc., Pittsburgh, PA, 1998.
CGÁMS.
/
4. Supplementary material
Further details of the crystal structure investigation
are available from CCDC quoting the deposition
number 195545. These data can be obtained free of
charge via www: http://www.ccdc.cam.ac.uk/conts/re-
trieving.html (or from CCDC, 12 Union Road, Cam-
[6] A.D. Ryabov, L.G. Kuzmina, V.A. Polyakov, G.M. Kazankov,
E.S. Ryabova, M. Pfeffer, R. Vaneldik, J. Chem. Soc., Dalton
Trans. (1995) 999 (and references therein).
bridge CB2 1EZ, UK; fax: ꢁ44 1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
/
[7] (a) R.G. Pearson, Inorg. Chem. 12 (1973) 712;
(b) C.K. Jorgensen, Inorg. Chem. 3 (1964) 1201.
[8] The action of isonitriles with palladacycles usually results in
Acknowledgements
insertion of these unsaturated molecules into the PdÃC bond. See
/
for example: (a) J. Dupont, M. Pfeffer, J.C. Daran, Y. Jeannin,
Organometallics 6 (1987) 899. (b) J. Dupont, M. Pfeffer, J. Chem.
Soc., Dalton Trans. (1990) 3193.
This work was supported by grants from FAPERGS
and CNPq (Brazil). Dr. MRM thanks the CNPq for a
visiting scientific grant.
[9] E. Turgunov, M.K. Sadikov, T. Nurmakhmedova, T.S. Sirlibaev,
Rus. J. Org. Chem. 35 (1999) 1131.
[10] The PdÃC of ‘classical’ palladacycles usually undergoes insertion
/
reactions with these unsaturated reagents. See for example: (a) J.
Dupont, M. Pfeffer, J.C. Daran, J. Gouteron, J. Chem. Soc.,
Dalton Trans. (1988) 2421. (b) M. Pfeffer, Rec. Trav. Chim. Pay.-
Bas. 109 (1990) 567.
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