Benzene ring assembly promoted by a camphor derived palladium complex

Article abstract of DOI:10.1016/S0022-328X(03)00557-6

Trans -[PdCl₂L₂] (1, L=3-NNMe₂ C₁₀H₁₄O), under mild reaction conditions, acts as a catalyst for the cyclic trimerization of alkynes. The best performance is achieved for the reaction with PhC≡CMe that affords 1,3,5-trimethyl-2,4,6-triphenyl benzene with high activity and selectivity (ca. 99%). As a general trend the catalytic activity is higher for internal (PhC≡CMe, PhC≡CPh) than for terminal alkynes (HC≡CPh, HC≡C^tBu, HC≡CCO₂Me). Under more drastic experimental conditions the reaction of 1 with PhC≡CPh yields trans-[PdCl₂(PhC≡CPh)₂] and no catalytic activity is observed. The molecular structure of 1,3,5-trimethyl-2,4,6-triphenyl benzene was confirmed by X-ray diffraction analysis. The molecules were characterized by ¹H- and ¹³C-NMR spectroscopies, FAB-MS and, in some cases, elemental analyses.

Full text of DOI:10.1016/S0022-328X(03)00557-6

Journal of Organometallic Chemistry 679 (2003) 143ꢁ147
/
www.elsevier.com/locate/jorganchem
Benzene ring assembly promoted by a camphor derived palladium
complex
M. Fernanda N.N. Carvalho *, Fernanda M.T. Almeida, Adelino M. Galvao,
˜
Armando J.L. Pombeiro
Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
Received 30 April 2003; received in revised form 11 June 2003; accepted 12 June 2003
Abstract
Trans-[PdCl2L2] (1, Lꢀ
alkynes. The best performance is achieved for the reaction with PhCÅ
high activity and selectivity (ca. 99%). As a general trend the catalytic activity is higher for internal (PhCÅ
terminal alkynes (HCÅCPh, HCÅ CCO2Me). Under more drastic experimental conditions the reaction of 1 with PhCÅ
CtBu, HCÅ
CPh yields trans-[PdCl2(PhCÅ
/
3-NNMe2C10H14O), under mild reaction conditions, acts as a catalyst for the cyclic trimerization of
CMe that affords 1,3,5-trimethyl-2,4,6-triphenyl benzene with
CMe, PhCÅCPh) than for
/
/
/
/
/
/
/
/
CPh)2] and no catalytic activity is observed. The molecular structure of 1,3,5-trimethyl-2,4,6-triphenyl
benzene was confirmed by X-ray diffraction analysis. The molecules were characterized by 1H- and 13C-NMR spectroscopies, FAB-
MS and, in some cases, elemental analyses.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Catalysis; Cyclotrimerization; Palladium complexes; Camphorimine; CÃC coupling; Alkynes
/
1. Introduction
terminal alkynes mediated by camphorimine palladium
complexes.
The relevance of cyclo oligomerization processes to
organic syntheses encourages the search for efficient
catalysts and reinforces the interest in the study of the
mechanisms of alkyne trimerization in order to get
higher chemo- and regio-selectivity or to obtain multi-
functional aromatic compounds. Modern applications
of the Reppe’s alkyne cyclo-oligomerization [1] include
the syntheses of tetra-substituted benzenes by sequential
cycloaddition [2] or the selective synthesis of fulvenes [3].
The ability of some Pd(II) complexes to promote the
2. Results and discussion
Under mild conditions (room temperature and rela-
tively short reaction times) trans-[PdCl2L2] (Lꢀ
) (1) catalyses the cyclic trimerization of 1-
phenyl-1-propyne (MeCÅCPh) affording 1,3,5-tri-
methyl-2,4,6-triphenyl benzene (i), Eq. (1)
/
/
activation of alkynes towards cyclo-trimerization [4ꢁ8]
/
is known for more than 50 years, although the efficiency
of most of the processes is not very high, from the point
of view of practical applications. During our research we
verified that platinum and palladium camphor derived
ð1Þ
species are efficient in promoting CÃ
cesses that lead to ring expansion [9]. We now wish to
report the catalytic promotion of cyclic trimerization of
/
C coupling pro-
The formulation of i was based on data obtained by
1H-NMR, 13C-NMR, DEPT and FAB Mass Spectro-
metry. The structure was confirmed by X-ray diffraction
analysis, although the low number of observed reflec-
tions precluded a final R value lower than 0.079. The
asymmetric unit plus the twofold axis generated mole-
* Corresponding author. Tel./fax: ꢂ351-21-841-9165.
/
E-mail address: fearvalho@ist.utl.pt (M.F.N.N. Carvalho).
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00557-6

144
M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 679 (2003) 143ꢁ147
/
CDCl3 solution of 1, new signals were detected at d
values (0.95, 0.99 and 1.09) that are slightly different
from those of the original methyl groups (0.97, 1.03 and
1.10) of the camphor skeleton. Concomitantly, a new
signal (d 3.03) appeared in the region attributed to the
methyl signal of the hydrazone group on complex 1 (d
3.25). However, on a preparative scale, the only complex
recovered is the starting complex 1. The reaction is
complete within 2 h.
The catalytic activity (A) of complex 1, per hour (2 h
were considered as the average effective reaction time),
towards the cyclic trimerization of 1-phenyl-1-propyne
104 gT/(mol [Pd]ꢃ
/
Fig. 1. X-ray structure of 1,3,5-trimethyl-2,4,6-triphenyl benzene (i)
showing the atom labelling scheme.
was tentatively calculated [1.1ꢃ
/
[(CÅC)]ꢃh)] on the basis of the mass (g) of cyclic
/
/
trimer species (gT) per mol of palladium per molar
concentration of alkyne. Since the catalytic experimental
conditions were not optimized this is a promising value.
In addition, the reaction is very selective, since, just
cule is depicted in Fig. 1. The X-ray structure shows that
the phenyl groups occupy perpendicular positions to the
plane of the benzene ring and are approximately parallel
to each other.
The selected bond distances and angles are displayed
on Table 1.
In order to study the interaction of 1-phenyl-1-
propyne with 1 the reaction was followed by 1H-
NMR. Soon after the addition of the alkyne to the
traces (B
The reactions of 1 with other internal alkynes [e.g.
diphenyl acetylene (PhCÅCPh), dimethyl acetylenedi-
carboxylate (MeCO2CÅCCO2Me)] or terminal [phenyl
acetylene (PhCÅCH), methyl propiolate (MeCO2CÅ
CH)] followed by
/1%) of other organic products were detected.
/
/
/
/
CH), 3,3-dimethyl-1-butyne (tBuCÅ
/
1H-NMR display a pattern similar to that mentioned for
1-phenyl-1-propyne. However, the isolated yield and
selectivity are dependent on the alkyne.
Table 1
Selected bond lengths and angles for compound 1,3,5-trimethyl-2,4,6-
triphenyl benzene (i)
The reaction of complex 1 with diphenyl acetylene
affords hexaphenyl benzene (ii) as the main product,
although other species also form. The yield (46%)
calculated relative to the alkyne is lower than that
obtained in the reaction with 1-phenyl-1-propyne (74%),
˚
Bond lengths (A)
Bond angles (8)
C1Ã
C1Ã
C3Ã
C3Ã
C3Ã
/
C2
C5
C2
C4
C6
1.388(7)
1.512(11)
1.399(8)
1.389(7)
1.521(9)
1.496(9)
1.378(9)
1.372(10)
1.487(11)
1.366(8)
1.380(10)
1.379(10)
1.391(10)
1.367(12)
1.361(10)
1.378(11)
0.960(9)
0.960(8)
0.960(8)
0.930(11)
0.930(9)
0.930(10)
0.960(4)
0.960(4)
0.960(4)
0.930(10)
0.930(11)
0.930(10)
0.930(13)
0.94(4)
C2Ã
C2Ã
C2Ã
C4Ã
C2Ã
C2Ã
C22Ã
C1ÃC2Ã
C1ÃC2Ã
C3ÃC2Ã
C3ÃC4Ã
C4Ã
C21Ã
C21Ã
C11Ã
C22Ã
C26Ã
C23Ã
C12Ã
/
C1Ã
C3Ã
C3Ã
C3Ã
C21Ã
C21Ã
/
C5
C4
C6
C6
119.3(6)
120.6(5)
118.6(5)
120.8(5)
120.7(6)
120.8(6)
118.5(6)
118.9(5)
119.9(5)
121.2(5)
120.2(6)
120.9(6)
119.9(6)
120.6(7)
121.8(7)
121.6(7)
121.3(6)
118.1(7)
118.9(7)
/
/
/
/
/
/
/
/
/
but the catalytic activity is similar [1.1ꢃ
/
104 gT/(mol
/
/
/C22
C21Ã
C21Ã
C21Ã
C4Ã
C11Ã
C22Ã
C26Ã
C12Ã
C23Ã
C25Ã
C13Ã
/
C2
/
/C26
[Pd]ꢃ[(CÅC)]ꢃh)].
/
/
/
/
C22
C26
/
C21ÃC26
/
The molecular structure of ii (see Fig. 2) obtained by
X-ray analysis is in full agreement with that previously
reported [10,11].
/
/
/
C3
/
C11
/
/
C21
C21
C11
/
C12
C23
C25
C13
C24
C24
C14
/
/
/
/
/
Hydrolysis, possibly due to traces of moisture in the
alkyne, conceivably accounts for the formation of 1,3,5-
trihydroxy-2,4,6-triphenyl benzene (iii) as a by-product.
The high melting point (283 8C) suggests extended
hydrogen bonding through the unit cell.
/
/
C11Ã
C22Ã
C26Ã
C12Ã
C23Ã
C25Ã
C24Ã
C13Ã
/C12
/
/
/C23
/
/
/
C25
C13
C24
C24
C25
C14
/
/
/
/
/
/
C6Ã
C6Ã
C6Ã
/
H6A
H6B
H6C
/
/
/
/
/
/
/
/
C22Ã
C26Ã
C12Ã
/
H22
H26
H12
/
/
C5Ã
C5Ã
C5Ã
/
H5A
H5B
H5C
/
/
C23Ã
C25Ã
C24Ã
C13Ã
C14Ã
/
H23
H25
H24
H13
H14
/
/
/
/
Fig. 2. Trimerization products.

M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 679 (2003) 143ꢁ
/147
145
As with 1-phenyl-1-propyn, compound 1 is the only
complex recovered from the reaction at room tempera-
ture. However, under reflux conditions, the replacement
of the camphor derived ligand by the alkyne affords a
product, highly soluble in all common solvents, that
1
appears to be paramagnetic in view of the H-NMR
spectrum. In this case, the FAB-MS data were incon-
clusive.
The yellow oily species vi obtained from reaction of
dark red compound that is formulated as [PdCl2(PhCÅ
/
tBuCÅ
/
CH with complex 1 was characterized by 1H-
CPh)2] (2) based on elemental microanalyses, conduc-
tivity measurements and NMR spectroscopic data (see
Section 3). Under these experimental conditions, just
traces of the cyclic trimer ii were detected and no other
organic products were obtained.
NMR and 13C-NMR as the cyclic trimer. The attribu-
tion of the 13C-NMR chemical shifts was confirmed by
DEPT. In this case, the yield and catalytic activity could
not be accurately calculated. However, the selectivity is
high i.e. comparable with that observed in the case of i.
The benzene ring assembly catalysed by palladium(II)
is not unique. More than 20 years ago it was reported
that PdCl2 or [PdCl2(NCPh)2] could promote the
catalytic cyclization of alkynes [4,12].
In CH2Cl2, complex 2 displays by cyclic voltammetry
a reversible reduction wave (Er1e/2dꢀ
/
ꢄ0.28 V) but no
/
oxidation process was found within the available
potential range, in contrast with the behaviour reported
for complex 1 [13] which exhibits irreversible cathodic
and anodic processes.
The step forward provided by this research is that, in
contrast with the former systems, complex 1 provides
good catalytic activity and high selectivity (ca. 100%, in
some cases) under mild conditions. The turnover
The reaction of complex 1 with dimethyl acetylenedi-
1
carboxylate was followed by H-NMR which reveals a
pattern comparable to that observed for the aromatic
alkynes. However, no cyclic or other organic products
were detected. This result was unexpected for two
reasons. First, there is evidence by NMR for the
interaction of the alkyne with the metal centre; second,
the reaction of dimethyl acetylenedicarboxylate with
[PdCl2(NCPh)2] proceeds towards cyclic trimerization,
although through a different intermediate [4]. Hence, the
catalytic activity of our system is strongly dependent on
the characteristics of the alkyne.
number for i (TONꢀ7.4) is not very high, but under
/
the experimental conditions used (30-fold molar excess
of alkyne) the maximum value that could be reached is
10. Moreover, TON is calculated on the basis of the
weight of the isolated product and would have a large
error in this present case due to the small quantities used
in the reactions.
One favourable characteristic of this system for
scaling up is that in the solvent, CH2Cl2, the aryl
derived trimers, separate out thus making their separa-
tion easy.
Terminal alkynes such as PhCÅ
/
CH, MeCO2CÅ
/
CH or
tBuCÅ
sponding cyclic trimer, species iv, v or vi, that were
/
CH react with complex 1 affording the corre-
In order to try to ascertain the generality of the alkyne
cyclization process using palladium camphor-type de-
?
rived complexes we studied the reaction of cis-[PdCl2L2]
formulated on the basis of FAB-MS and H- or 13C-
1
NMR spectroscopies. The 1H- or 13C-NMR spectra
were not fully conclusive in the case of iv and v. As
expected, in compound iv the resonances appear as a
complex multiplet in the aromatic region from which a
few signals emerge but no clear structure could be
ascertained. By FAB-MS, compound iv displays an
t
(L?ꢀ
/
) (3) with MeCÅ
/
CPh and BuCÅ
/CH under
similar experimental conditions to those used for com-
plex 1. In the case of 1-phenyl-1-propyne no trimeriza-
tion was detected. However, in the reaction of 3 with
3,3-dimethyl-1-butyne there is evidence for the forma-
tion of an organic product that was tentatively char-
intense signal (m/z (%)ꢀ306 (100)) that is attributed
/
to the molecular ion of the cyclic trimer. The fragmenta-
tion pattern suits this formulation. The isolated yield for
compound iv is low (20%, relative to the alkyne) and the
acterized by FAB-MS (m/zꢀ
/
789 (B1)) as an
/
103 gT/(mol [Pd]ꢃ
/
[(CÅ
/
C)]ꢃ
/
oligomeric species. The NMR data, although not fully
conclusive, support the formulation. In this reaction,
traces of the oily cyclic trimer vi were also detected.
The linear oligomerization of 3,3-dimethyl-1-butyne
could in-principle involve the formation of an inter-
catalytic activity [(3.1ꢃ
h)] is one order of magnitude lower than that measured
for the internal alkynes. The selectivity is also lower and
/
species with higher molecular weight such as (m/z (%)ꢀ
/
408 (2)), possibly a tetrameric species, are detected by
FAB-MS.
mediate of the type {Pd Ã
/
C(tBu)Ä
/
CHCHÄ
/
C(tBu)Cl}
CtBu with
formerly proposed [4] for the reaction of HCÅ
/
In the reaction of MeCO2CÅ/CH with 1 at least two
[PdCl2(NCPh)2].
products are formed. One is whitish, poorly soluble in
common solvents and formulated as the cyclic trimer v
The substantial differences observed for the appar-
ently similar complexes 1 and 3 for benzene ring
assembly possibly result from both geometric and
electronic factors. In 1 the trans geometry and the lower
dimension of L compared to L? in 3 can impose lower
steric constraints. Moreover, a previously reported
based mostly on FAB-MS (m/z (%)ꢀ252 (26)). The
/
NMR data mentioned in Section 3 were obtained in
solution during the reaction, previously to precipitation.
The activity was calculated as 1.8ꢃ
/
103 gT/(mol [Pd]ꢃ
/
[(CÅC)])ꢃh). The other species is a dark brownish-grey
/
/

146
M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 679 (2003) 143ꢁ147
/
cyclic voltammetry study [13] revealed that the electro-
nic properties of the camphorimine and camphorsul-
phonimine in complexes 1 and 3, respectively, are
considerably different, i.e., camphorimine is a weak
net electron donor whereas camphorsulphonimine is a
slightly p-electron withdrawing ligand.
Apart from the different reactivities of complexes 1
and 3, the specific characteristics of the alkyne also play
a role in the activity and selectivity towards cyclic
trimerization. In terms of activity, internal alkynes
provide better results than terminal ones and aryl
groups apparently favour the process. The relevance of
the presence of an aryl group at the alkyne for the
Table 2
Crystallographic data for compound 1,3,5-trimethyl-2,4,6-triphenyl
benzene (i)
Empirical formula
Formula weight
Temperature (K)
C27H24
348.46
293(2)
˚
Wavelength (A)
0.71069
Monoclinic
I21/a
Crystal system
Space group
Unit cell dimensions
˚
a (A)
10.557(5)
14.882(2)
12.818(2)
90.00
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
99.80
90.00
promotion of alkyne CÃ
stressed [14] in the case of a ruthenium azavinylidene
trinuclear system. Furthermore, in that system the MÃ
/C insertion was formerly
3
˚
Volume (A )
1984.4(10)
4
1.166
Z
/
N
Dcalc (g cmꢄ3
)
bound ligand was not completely innocent [14], allowing
the stabilization of the system. That could also be the
case, in our system, although the detailed mechanism of
cyclization of alkynes has not been elucidated.
Absorption coefficient (mmꢄ1
F(0 0 0)
)
0.066
744
Crystal size (mm3)
0.25ꢃ
25
125
05k 5
155l 5
1750
/0.25ꢃ
/0.40
u Range for data collection (8)
Index ranges
ꢄ
/
/
h 5
17,
15
/0,
/
/
ꢄ/
/
/
3. Experimental
Reflections collected/unique
Refinement method
Full-matrix least-squares on F2
All the manipulations were carried out under dinitro-
gen atmosphere using standard Schlenk glassware
techniques. The solvents were dried before use by
standard methods. Palladium(II) chloride was pur-
chased from Aldrich and the camphor derived com-
plexes were prepared by published methods [13].
The compounds were dissolved in CDCl3 and the
NMR spectra were recorded on a Varian UNITY 300
spectrometer. FAB-Mass spectra were measured with
Varian CH5 (EI mode, 70 eV) and LCQ Finnigan (ESI)
instruments using 4-nitrobenzyl alcohol as matrix.
Conductivity measurements were made using a Schott
Konduktometer CG 855 provided with a Cell Schott
Gerate LF 1100. Melting and sublimation points were
measured using a Leica Galen III Microscope.
Data/restraint/parameters
Final R (observed)
1291/1/127
0.0788
86 [16], and was found to have a binary axis bisecting
the molecule and passing through one methyl group and
two carbon atoms of the central six membered ring. The
atomic positions and thermal parameters were refined
by least-squares on F2 using SHELXL 93 [17], with all the
non-hydrogen atoms refining with anisotropic thermal
motion parameters. The hydrogen atoms were included
in calculated positions, constrained to ride at fixed
distances of the parent carbon atom. Atomic scattering
factors and anomalous dispersion terms were as in
SHELXL 93 [17]. The ORTEP drawings were made with
ORTEX [18].
3.1. X-ray crystallographic analysis
3.2. Catalytic reactions
X-ray data were collected from white crystals
mounted in thin-walled glass capillaries at room tem-
As a typical procedure for the catalytic experiments,
the reaction of complex 1 with 1-phenyl-1-propyne is
perature on Enrafꢁ
graphite-monochromatized Moꢁ
vꢁ 2u scan mode. The data and refinement parameters
/
Nonius MACH3 diffractometer with
/
Ka radiation, using an
indicated as follows: PhCÅ
/
CCH3 (0.65 cm3, 5.2 mmol)
/
was added to a solution of complex 1 (0.10 g, 0.17
mmol) in CH2Cl2 (44 cm3) and stirred for ca. 20 h,
although the process is complete within 2 h (as verified
by NMR). The solvent was then evaporated approxi-
mately to 1/3 to afford a yellowish abundant precipitate
that flocculates from the solution. Upon filtration and
are displayed in Table 2. Unit cell dimensions were
obtained by least-squares refinement of the setting
angles of 25 reflections. The crystal was found to
crystallise in the monoclinic I21/a space group with
˚
aꢀ
99.80(2)8, Vꢀ
m(MoꢁKa)ꢀ
33 cmꢄ1. The data were corrected [15] for
/
10.557(5), bꢀ
/
14.882(2), cꢀ
/
12.818 A, bꢀ
/
3
˚
/
1984(10) A , Zꢀ
/
4, Dcꢀ
/
1.17 g cmꢄ3
,
washing with Et2O (2ꢃ
/
5 cm3), ((i) 0.45 g, 1.29 mmol;
/
/
74% yield relatively to the alkyne) a white precipitate is
1
Lorentz-polarization effects and linear decay. The
structure was solved by direct methods using SHELXS
obtained. H-NMR: d 7.47ꢁ
/
6.95 (m, 15H, C6H5), 2.04
(s, 3H, CH3), 1,72 (s, 6H, CH3). 13C-NMR: d 142.2,

M.F.N.N. Carvalho et al. / Journal of Organometallic Chemistry 679 (2003) 143ꢁ
/147
147
139.8, 133.2 (s, quaternary), 130.3, 129.4, 128.5, 127.3,
126.5, 125.7 (s, C6H5), 19.4 (s, CH3). FAB-MS: m/z
PdCl2C28H20. 1/20 (C14H10): Calc. C, 63.5; H, 3.8.
Found: C, 63.6; H, 4.2%. Conductivity: 2.4 Vꢄ1 cm2
molꢄ1 (in CH2Cl2).
(%)ꢀ348 (62). Sublimation point: 192 8C. The sharp
/
and weak (1600 cmꢄ1) and the sharp and strong (702
cmꢄ1) IR bands are characteristics of the product.
From the mother-liquor traces of the starting complex
3.4. Crystallographic data
and of other organic products (B1%) were obtained.
Under similar experimental conditions the main
organic product of the reaction of complex 1 with
/
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC 208927 for compound i. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge CB2
PhCÅ
/
CPh is hexaphenyl benzene (iiꢀ46% yield rela-
/
tively to the alkyne). H-NMR: d 6.82 (s, C6H5). 13C-
NMR: d 140.5, 140.2 (s, quaternary), 131.3, 126.4, 125.0
1
1EZ, UK (Fax: ꢂ44-1223-336033; e-mail: deposit@
/
(s, C6H5). FAB-MS: m/z (%)ꢀ/360 (100). In the process,
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
1,3,5-trihydroxy-2,4,6-triphenyl benzene (iii, 2% yield
1
relatively to the alkyne) also forms (m.p.ꢀ283 8C). H-
/
NMR: d 7.51 (s, 6H, C6H5), 7.32 (s, 9H, C6H5), 1.54 (s,
3H, OH). 13C-NMR: d 162.2, 153.7, 101.0 (s, quatern-
ary), 131.4, 129.1 (s, C6H5). C24H18O3 (354): Calc. C,
81.4; H, 5.1. Found: C, 81.2; H, 5.2%. FAB-MS: m/z
Acknowledgements
We are grateful to Dr M.T.D. for help with the
confirmation of hexaphenyl benzene structure. This
work was partially supported by Fundacao para a
¸˜
(%)ꢀ
Reaction of complex 1 with ca. 30-fold molar excess
of HCÅCPh affords 1,3,5-triphenyl benzene (iv, 20%
yield relatively to the alkyne). H-NMR: d 7.72ꢁ
(m, 18H, CH, C6H3Rꢂ
C6H5). 13C-NMR: d 129.7ꢁ
125.6 (m, CH, C6H3RꢂC6H5). FAB-MS: m/z (%)ꢀ
/354 (5).
Cieˆncia e Tecnologia (Project POCTI 36125/2000/QUI).
/
1
/
7.16
/
/
References
/
/
306 (100). In the same reaction conditions, HCÅ
/
[1] (a) W. Reppe, O. Schlichting, K. Klager, T. Toepel, Liebigs Ann.
Chem. 560 (1948) 3;
CCO2Me affords 1,3,5-trimethylcarboxylate benzene
(v, 21% yield relatively to the alkyne) in addition to a
(b) W. Reppe, W.J. Schweckendiek, Liebigs Ann. Chem. 560
(1948) 104.
1
mixture of not characterized species. H-NMR: d 7.31
(s, 3H, C6H3R), 3.5ꢁ
3.4 (s, br, 9H, CH3CO2). 13C-
NMR: d 165.1 (s, CO2Me), 140.8 (s, quaternary), 134.3
(s, CH, C6H3R), 52.4 (m, br, OCH3). The reaction of
/
[2] V. Gevorgyan, U. Radhakrishan, A. Takeda, M. Rubina, M.
Rubin, Y. Yamamoto, J. Org. Chem. 66 (2001) 2835.
[3] U. Radhakrishnan, V. Gevorgyan, Y. Yamamoto, Tetrahedron
Lett. 41 (2000) 1971.
compound 1 with HCÅ
/
CtBu affords 1,3,5-tri-tert-butyl
benzene (vi) as the sole organic species. FAB-MS: m/z
[4] P.M. Maitlis, J. Organometal. Chem. 200 (1980) 161.
[5] (a) N.E. Schore, Chem. Rev. 88 (1988) 1081;
(b) M. Lautens, W. Klute, W. Tam, Chem. Rev. 96 (1996) 49.
[6] S. Saito, Y. Yamamoto, Chem. Rev. 100 (2000) 2901.
[7] K.P.C. Vollhardt, Angew. Chem. Int. Ed. Engl. 23 (1984) 539.
[8] J.H. Hardesty, J.B. Koerner, T.A. Albright, G.-Y. Lee, J. Am.
Chem. Soc. 121 (1999) 6055.
1
(%)ꢀ252 (29). H-NMR: d 7.28 (s, 3H, C6H3R), 1.31
/
t
(s, 27H, Bu). 13C-NMR: d 149.8 (s, quaternary), 119.4
(s, CH, C6H3R), 34.9 (s, CMe3), 31.5 (s, CH3).
t
The reaction of complex 3 with BuCÅ
/
CH affords
789
[9] M.F.N.N. Carvalho, R. Herrmann, B. Pedersen, A.J.L. Pom-
beiro, G. Wagner, Z. Naturforschung. 54b (1999) 725.
[10] Data obtained by Dr. M.T. Duarte.
traces of vi and oligomeric species, FAB-MS: m/zꢀ
/
(B1).
/
[11] J.C.J. Bart, Acta Crystallogr. Sect. B: Struct. Crystallogr. Cryst.
Chem. 24 (1968) 1277.
3.3. Syntheses of the complexes
[PdCl2(PhCÅCPh)2] (2)*Complex 1 (100 mg, 0.17
[12] H. Dietl, H. Reinheimer, J. Moffat, P.M. Maitlis, J. Am. Chem.
Soc. 92 (1970) 2276.
[13] M.F.N.N. Carvalho, L.M.G. Costa, A.J.L. Pombeiro, A. Schier,
/
/
mmol) reacts with diphenyl acetylene (300 mg, 1.7
mmol) under reflux in CH2Cl2 (20 cm3) for 2 days
affording an orange solution that upon evaporation of
the solvent to half the volume and addition of Et2O (3
cm3) affords 2 (40 mg, 44% yield). Further addition of
Et2O to the solution leads to the precipitation of traces
of a mixture of 2 and cyclic trimer. 1H-NMR: d 7.84 (d,
W. Scherer, S.K. Harbi, U. Verfurth, R. Herrmann, Inorg. Chem.
¨
33 (1994) 6270.
[14] J.A. Cabeza, I. del Rio, F. Grepioni, M. Moreno, V. Riera, M.
Sua´rez, Organomentallics 20 (2001) 4190.
[15] C.K. Fair, MOLEN, Enrafꢁ/Nonius, Delft, 1990.
[16] G.M. Sheldrick, SHELXS 86, Program for the Solution of Crystal
Structure, University of Gottingen, 1986.
¨
[17] G.M. Sheldrick, SHELXL 93, Program for the Refinement of
Crystal Structure, University of Gottingen, 1993.
8.0 Hz, 2H), 7.68 (t, 8.0, 1H), 7.53ꢁ
/
7.43 (m, 2H); 13C-
¨
[18] P. McArdle, J. Appl. Crystallogr. 28 (1995) 65.
NMR d 167.3, 131.6, 130.7, 129.8, 128.4, 128.3.