New synthesis and thermal studies of palladacycloalkanes and their precursors

Article abstract of DOI:10.1016/j.jorganchem.2007.10.025

A series of new palladacycloalkanes of formula cis-[PdL₂(CH₂)_n] (9. n = 6, L = PPh₃; 10. n = 6, L₂ = dppe; 11. n = 8, L = PPh₃; 12. n = 8, L₂ = dppe) have been prepared by two routes. In the first route, the precursor bis(1-alkenyl) complexes cis-[PdL₂((CH₂)_nCH{double bond, long}CH₂)₂] (1. n = 2, L = PPh₃, 2. n = 2, L₂ = dppe, 3. n = 3, L = PPh₃, 4. n = 3, L₂ = dppe) were allowed to react with Grubb's 2nd generation catalyst to give the palladacycloalkenes, cis-[PdL₂(CH₂)_nCH{double bond, long}CH(CH₂)_n] (5. n = 2, L = PPh₃, 6. n = 2, L₂ = dppe, 7. n = 3, L = PPh₃, 8. n = 3, L₂ = dppe), which were then hydrogenated to the palladacycloalkanes, 9-12. In the second route, the di-Grignard reagents BrMg(CH₂)_nMgBr (n = 6, 8) were reacted with the palladium complex [PdCl₂(COD)] followed by immediate ligand displacement to form the respective palladacycloalkanes 10 and 12. The complexes obtained were characterized by a range of spectroscopic and analytical techniques. Thermal decomposition studies were carried out on the palladacycloalkanes 9-12 and the main organic products shown to be 1-alkenes and 2-alkenes.

Full text of DOI:10.1016/j.jorganchem.2007.10.025

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 103–108
www.elsevier.com/locate/jorganchem
New synthesis and thermal studies of palladacycloalkanes
and their precursors
*
Tebello Mahamo, Feng Zheng, Akella Sivaramakrishna, John R. Moss , Gregory Smith
Department of Chemistry, University of Cape Town, Rondebosch 7701, Cape Town, South Africa
Received 7 September 2007; received in revised form 15 October 2007; accepted 16 October 2007
Available online 22 October 2007
Abstract
A series of new palladacycloalkanes of formula cis-[PdL2(CH2)n] (9. n = 6, L = PPh3; 10. n = 6, L2 = dppe; 11. n = 8, L = PPh3; 12.
n = 8, L2 = dppe) have been prepared by two routes. In the first route, the precursor bis(1-alkenyl) complexes cis-
[PdL2((CH2)nCH@CH2)2] (1. n = 2, L = PPh3, 2. n = 2, L2 = dppe, 3. n = 3, L = PPh3, 4. n = 3, L2 = dppe) were allowed to react with
Grubb’s 2nd generation catalyst to give the palladacycloalkenes, cis-[PdL2(CH2)nCH@CH(CH2)n] (5. n = 2, L = PPh3, 6. n = 2,
L2 = dppe, 7. n = 3, L = PPh3, 8. n = 3, L2 = dppe), which were then hydrogenated to the palladacycloalkanes, 9–12. In the second
route, the di-Grignard reagents BrMg(CH2)nMgBr (n = 6, 8) were reacted with the palladium complex [PdCl2(COD)] followed by imme-
diate ligand displacement to form the respective palladacycloalkanes 10 and 12. The complexes obtained were characterized by a range of
spectroscopic and analytical techniques. Thermal decomposition studies were carried out on the palladacycloalkanes 9–12 and the main
organic products shown to be 1-alkenes and 2-alkenes.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Palladacycloalkanes; Bis(1-alkenyl) precursors; Ring closing metathesis; Thermal decomposition
1. Introduction
the phosphine donor ligands. Using this methodology, we
now report the preparation, characterization and thermal
decomposition of novel palladacycloalkanes and their
precursors.
Metallacycloalkanes are an important class of com-
pounds [1] that can be key intermediates in various cata-
lytic reactions [2]. In spite of this importance of medium
to large metallacycloalkanes as intermediates, very little is
known about such compounds. Noteworthy, up to now,
no higher metallacycloalkanes containing more than 9-
membered rings are known [3]. On decomposition, various
metallacycloalkanes have shown an interesting organic
product distribution, depending on several factors [4].
Recently we have shown a novel route to the synthesis of
medium to large platinacycloalkanes from their bis(1-alke-
nyl) precursors by ring closing metathesis reaction using
Grubbs’ catalysts [5]. These platinacycloalkanes were
found to be stable at room temperature and the thermal
stability of these compounds depends on the nature of
2. Results and discussion
2.1. Synthesis and characterization of palladacycles
The preparation of the new palladacycloalkane com-
plexes (9–12) employed two reaction routes which are
shown in Scheme 1.
Route 1 is a new approach for the synthesis of metal-
lacycloalkane complexes using ring-closing metathesis
(RCM) with the Grubbs catalyst, which we have success-
fully used in making medium and large platinacycloalkanes
[5]. Herein, we applied this route to synthezis new medium
palladacycloalkane complexes.
*
The bis(1-alkenyl) complexes were prepared by the reac-
tion of [PdCl2(COD)] with the corresponding Grignard
Corresponding author. Fax: +27 21 689 7499.
E-mail address: John.Moss@uct.ac.za (J.R. Moss).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.10.025

104
T. Mahamo et al. / Journal of Organometallic Chemistry 693 (2008) 103–108
(CH ) CH=CH
2 n
2
2BrMg(CH2)nCH=CH2
(n = 2, 3)
(COD)Pd
PdCl2(COD)
(CH ) CH=CH
2 n
2
n = 2, 3
L = PPh3,
L2 = dppe
2nd generation Grubbs'
(CH ) CH=CH
2 n
2
L
Pd/C
H2
L
L
L
L
n
n
catalyst
Pd
Pd
Pd
(CH ) CH=CH
2 n
2
(5 mol%)
L
n
n
n = 2, L = PPh3, 1
L2 = dppe, 2
n = 3, L = PPh3, 3
L2 = dppe, 4
n = 2, L = PPh3, 9
L2 = dppe, 10
n = 3, L = PPh3, 11
L2 = dppe, 12
n = 2, L = PPh3, 5
L2 = dppe, 6
n = 3, L = PPh3, 7
L2 = dppe, 8
(a) Route 1
BrMg(CH2)mMgBr
m = 6, 8
n
PdCl2(COD)
Pd
Pd
(COD)
n
n = 2, 3
L2 = dppe
BrMg(CH2)mMgBr
m = 6, 8
L
L
n
PdCl2(dppe)
n
L2 = dppe,n = 2, 10
n = 3, 12
(b) Route 2
Scheme 1. Preparation of palladacycloalkanes.
reagents followed by ligand displacement as shown in
Scheme 1. Formation of the products was signaled by dis-
solution of the palladium species. The resulting complexes
were found to be unstable in the reaction mixture above
0 ꢁC, giving reductive elimination products, 1,7-octadiene
in the case of 1 and 2 and 1,9-decadiene in the case of 3
and 4, as well as some elemental palladium (palladium
black) and these observations are in agreement with the lit-
erature [6]. The reaction mixture was worked up immedi-
ately after the hydrolysis of the excess Grignard reagent
at 0 ꢁC. The left-over product, after decomposition, was
found to be relatively stable below room temperature.
The palladacycloalkenes were prepared from the bis(1-
alkenyl) complexes by the ring closing metathesis (RCM)
reaction using Grubbs’ 2nd generation catalyst in moderate
yields. Grubbs’ 2nd generation catalyst was used in all the
reactions as the longer reaction times were necessary with
the Grubbs’ 1st generation catalyst. Hydrogenation of
these palladacycloalkenes with Pd/C yielded the desired
saturated palladacycloalkanes in good yields.
In the conventional route 2, the pallacycloalkane com-
plexes with dppe ligand 10 and 12 were also prepared by
the reaction of di-Grignard reagents using the method
reported by Whitesides et al. for the synthesis of a series
of platinacyclopentanes and a platinacycloheptane [7]. By
treating a solution of [PdCl2(COD)] in diethyl ether with
the di-Grignard reagents {BrMg(CH2)6MgBr for 10 and
BrMg(CH2)8MgBr for 12} at ꢀ78 ꢁC, followed by ligand
displacement gave complexes 10 and 12 in very low yield
(<15%), respectively. This reaction had to be quenched in
a very short time (ca. 20 min when the reaction warmed
to ꢀ30 ꢁC) as the mixture easily decomposed even at low
temperature. The intermediates involved, palladacycloal-
kane with COD ligand, are soluble in any solvent and ther-
mally unstable at room temperature, this might be the
major reason to give the product in very low yields. Assum-
ing the absence of COD ligand would increase the product
yields, we then treated [PdCl2(dppe)], a much more stable
complex than [PdCl2(COD)], with the di-Grignard
reagents. The reaction mixture was stable at room temper-

T. Mahamo et al. / Journal of Organometallic Chemistry 693 (2008) 103–108
105
ature for more than 5 h and resulted in a moderate yield ca.
50% of the desired products.
pletely remove the solvent from the products resulted in the
complexes decomposing.
1
All new complexes were characterized by H and 31P
NMR spectroscopy as well as mass spectrometry. The
complexes were found to be unstable in air. Exposure of
the complexes to air at room temperature for a few hours
resulted in complex decomposition to give an intense red
product initially and then gradually turns to black residue
after longer periods (ca. 20 h). In contrast, the analogous
platinacycles and their precursors are quite stable to mod-
erate temperatures except in few cases when PPh3 ligand is
used [5b].
2.2. Thermal decomposition studies
Thermal decomposition of the palladacycloalkanes and
their corresponding bis(1-alkenyl) precursors were studied
directly, without any solvent in order to minimize any sol-
vent effects [4]. Thermolysis was carried out by dissolving
the freshly prepared complexes in dichloromethane, remov-
ing the solvent and drying at least for 3 h under vacuum,
then heating the complexes in a thermostatted bath. The
reaction mixture was quenched by cooling the tube at
ꢀ78 ꢁC. The volatile organic products were extracted by
pentane and analyzed by GC–MS. These results were com-
pared with the literature reports [4,5], especially with the
results for the platinum analogs.
1
The H NMR spectra of the bis(1-alkenyl) complexes,
(1–4), show characteristic signals for the protons in the
terminal alkenes (see Section 4 for details). The products
obtained from the RCM reaction showed broad alkene
1
proton shifts in the region 5.3–5.6 ppm in H NMR, sim-
ilar to their platinum analogs, which are due to the E
and Z isomers of the palladacycloalkenes and these iso-
mers could not be isolated. Formation of the ring-closed
complexes, 5–8, was indicated by the appearance of the
broad multiplet between 5 and 6 ppm, which is due to the
alkene protons in the palladacycloalkenes. Appearance
of this new peak was accompanied by the disappearance
of the terminal alkene protons in the bis(1-alkenyl)
precursors. The methylene protons attached to the metal
as well as other methylene protons in the metallacyclic
moiety appeared as broad multiplets together in the
region 1.1–2.5 ppm. The palladacycloalkanes were obtained
by the hydrogenation reaction of the palladacycloalkenes,
5–8. Reaction progress was monitored by 1H NMR. Product
formation was indicated by the reduction and eventual
disappearance of the alkene protons during the hydrogena-
tion reaction. 1H NMR spectra of complexes 1–12
show the same trends reported for analogous platinum
complexes [5].
2.2.1. Thermolysis of bis(1-alkenyl)palladium(II)
complexes, 1–4
Bis(1-pentenyl)palladium(II) complex, 4, was initially
decomposed at room temperature during the synthesis
and the decomposition was also carried out at 170 ꢁC in
solid phase to give 1,9-decadiene as the major product
(95%) in both the cases via the reductive elimination reac-
tion. These organic products were confirmed by NMR
spectra and GC–MS. n-Decane was also found as the
minor product.
Ph2
P
1,9-decadiene, 95%
Pd
+
P
Ph2
4
decane, 5%
ð1Þ
The 31P NMR spectra of the bis(1-alkeny), pall-
dacycloalkene and palladacycloalkane complexes all show
a similar pattern. The signals in the 31P NMR appeared
in the region 25.5–29.7 ppm for the PPh3 complexes and
30.1–33.5 ppm for the dppe complexes. For the palla-
dacycloalkanes, the 31P NMR spectra showed a small sig-
nal close to the main singlet, indicating the possible
presence of different conformational isomer.
The mass spectra of the complexes show molecular ion
peaks corresponding to the molecular masses of the
expected products. The fragmentation patterns of the com-
plexes also show peaks corresponding to the loss of the
ligands as well as the hydrocarbon fragments. It is interest-
ing to note that higher molecular masses, i.e., beyond the
molecular ion peaks were observed in all the palladacycles.
This could be due to either the formation of various prod-
ucts under the experimental conditions with FAB or the
presence of dimeric species. C, H analysis of the bis(1-alke-
nyl) complexes showed that solvent (hexane) molecules
were trapped in the products. The number of trapped sol-
vent molecules ranged between 2 and 5. Attempts to com-
Even though no decomposition studies have been
reported on bis(1-alkenyl)palladium(II) complexes, the
possible decomposition pathways of this class of complexes
have been summarized, in which the long chain diene prod-
ucts are formed by reductive elimination [5c]. The forma-
tion of 1,9-decadiene in the thermolysis of 4 is consistent
with the reductive elimination pathway and also agrees
with the findings by Ozawa and Yamamoto [8]. They
observed that thermal decomposition of cis-PdEt2L2 com-
plexes afforded reductive elimination products exclusively.
The small amount of n-decane could be the result of reduc-
tive elimination followed by hydrogenation. The source of
hydrogen could be either the activation of solvent or the
phenyl groups in phosphine ligands by the zerovalent metal
species under those experimental conditions.
In contrast to the reductive elimination reaction that
occurred for 4, the thermolysis of complexes 1–3 in solid
state indicated the formation of mixture of products
through the b-hydride elimination as well as reductive elim-
ination reactions. For example, bis(1-pentenyl)palla-
dium(II) complex with PPh3 ligand, 3, decomposed to

106
T. Mahamo et al. / Journal of Organometallic Chemistry 693 (2008) 103–108
Table 1
the Grubbs catalyst route, the new precursor complexes,
bis(1-alkenyl)palladium(II) and palladacycloalkenes, have
also been prepared. These complexes exhibit low stability
at room temperature and are sensitive to moisture and
air. It appeared that the RCM methodology is better than
the di-Grignard route in terms of yields of the
palladacycloalkanes.
Products for the thermal decomposition of the palladacycloalkanes 9–12
Complex
Products observed (%)
1-Alkene
2-Alkenes
Diene
n-Alkane
Cycloalkane
9
10
11
12
43
52
33
17
17
24
32
71
6
11
17
2
18
6
15
10
16
7
3
<1
Although the palladacycloalkane complexes 9–11 pres-
ent different distribution of the decomposition products,
their decomposition demonstrates that the b-hydride elim-
ination to form 1-alkene is the major decomposition path-
way. Due to the effect of ring size and ancillary ligands, the
thermal decomposition of complex 12 gives 2-alkenes as
major products easily. In addition, the possible pathways
for the formation of the minor products are also proposed.
Reductive elimination of cycloalkane appears to be a
favorable reaction in the complex with easily dissociated
ligand, and the formation of n-butane could involve inter-
molecular or intramolecular hydrogen abstraction reac-
tions. In addition, we are currently performing insertion
reactions of small molecules such as carbon monoxide
and carbon dioxide into the metal carbon bonds of the pal-
ladacycloalkane compounds.
give n-pentane (17%), 1,4-pentadiene (54%) and 1-decene
(30%). A similar trend was observed in the decomposition
of bis(1-butenyl) complexes (1,2).
2.2.2. Thermolysis of palladacycloalkane complexes, 9–12
Thermal decomposition of palladacycloalkanes in the
solid phase at 170 ꢁC gave the alkene products presented
as a mixture of isomers as well as n-alkanes (Table 1).
The decomposition is accompanied by the formation of a
black residue, which could be palladium metal and some
[L4Pd] complex shown as [9].
(CH2)n
L2Pd
L4Pd + 1-alkenes + 2-alkenes + dienes +
n-alkanes + cycloalkanes
n = 6, 8
L2 = dppe, L = PPh3
4. Experimental
ð2Þ
1-Alkene and 2-alkenes are the major products in all cases
whereas 1-alkene predominates except for complex 12. The
formation of 1-alkene might go through the b-hydride elim-
ination and the occurrence of isomerization either during or
after decomposition could give the 2-alkenes.
For complex 12, the isomerization to 2-alkenes is much
easier than for other complexes, and there might be two
factors influenced the decomposition pathway here. One
is the effect of ring size. It appears that the conformation-
ally flexible larger size rings have lower thermal stability
[10], which could make the decomposition via b-hydride
elimination/isomerization more easy for the 9-membered
ring. Another one is the effect of the ancillary ligand. Com-
pared to their analogues, the complexes with the chelating
ligand dppe formed higher yields of 2-alkenes (24% for 10
and 71% for 12).
The observation of cycloalkanes as minor decomposi-
tion products is consistent with the palladacyclopentane
system [9]. It was suggested that the production of cycloal-
kane is favoured only when the ancillary ligand dissociates
easily. For instance, complexes 9 (16%) and 11 (3%) gave
higher yield than their analogues with dppe ligand. In addi-
tion, n-alkane was also found as the minor product, which
could be formed by intermolecular reactions involving a
hydridopalladium(II) species [11], or intramolecular hydro-
gen abstraction from the ancillary ligand [12].
4.1. General
All reactions were carried out under nitrogen or argon
atmosphere using a dual vacuum/nitrogen line and stan-
dard Schlenk line techniques. PdCl2 was obtained from
Johnson Matthey. All other reagents were obtained com-
mercially from Aldrich and, unless otherwise stated, were
used as received without further purification. The reagents
PdCl2(COD) [13], PdCl2(dppe) [14], BrMg(CH2)nCH@CH2
(n = 2, 3) and BrMg(CH2)nMgBr (n = 6, 8) [15] were pre-
pared as previously reported. Solvents were dried and dis-
tilled, and all procedures were carried out under nitrogen.
Microanalysis was carried out using a Fisons EA 1108
CHNS Elemental Analysis apparatus. Melting points were
recorded using a Kofler hot stage microscope (Riechert
Thermovar). NMR spectra were recorded on Varian
XR300 MHz and XR400 MHz spectrometers using deuter-
ated benzene as a solvent. Gas chromatographic analyses
were performed on a Varian 3900 instrument and GC–
MS analyses were carried out with an Agilent 5973
instrument.
4.2. Synthesis of palladacycloalkanes and their precursors
4.2.1. cis-[Pd{(CH2)2CH@CH2}2(PPh3)2] (1)
BrMg(CH2)2CH@CH2 (2.3 ml of 2.39 M diethyl ether
solution, 5.36 mmol) was slowly added to a suspension of
PdCl2(COD) (0.51 g, 1.79 mmol) in diethyl ether (15 ml)
at ꢀ78ꢁC. The suspension was stirred for 40 min, then
warmed to room temperature and stirred for another
20 min. The reaction was quenched by adding a saturated
3. Conclusions
New palladacycloalkane complexes have been prepared
by two routes. In the ring-closing metathesis (RCM) with

T. Mahamo et al. / Journal of Organometallic Chemistry 693 (2008) 103–108
107
1
solution of NH4Cl (5 ml). The product was extracted with
hexane and the organic layer was collected and dried over
anhydrous MgSO4. Excess solvent was removed under
reduced pressure and the product was obtained as a bright
yellow oil, which was then dried under vacuum. The yellow
oil obtained was dissolved in Et2O and PPh3 (0.47 g,
1.78 mmol) was added. The solution was stirred for 1 h at
room temperature, after which the solvent was removed
and the product was obtained as bright yellow oil (0.67 g,
50%). Anal. Calc. for C59H80P2Pd (with 2.5 mol. of
80%). H NMR: 7.44–7.71 (m, 30 H, Ph), 5.44 (br m, 2H,
@CH), 2.31 (m, 4H, CH2), 1.62 (m, 4H, Pd–CH2). 31P
NMR: 29.3 (PPh3). Mass spec. (FAB): m/z 712.1 [M]+,
629.1 [MꢀC6H10]+, 449.8 [MꢀPPh3]+, 188.9 [Mꢀ2PPh3]+.
Complexes 6–8 were prepared in a similar manner. All of
the complexes are yellow brown oils at 70–80% yields.
4.2.6. Palladacycloheptene (L2 = dppe) (6)
1H NMR: 7.46–8.01 (m, 20H, Ph), 5.40 (br m, 2H,
@CH), 2.54 (t, 4H, P–CH2), 2.05 (m, 4H, CH2), 1.79 (m,
4H, Pd–CH2). 31P NMR: 32.9 (–PPh2). Mass spec.
(FAB): 585.9 [M]+, 503.8 [MꢀC6H10]+, 189.4 [Mꢀdppe]+.
1
C6H14): C, 74.00; H, 8.42. Found: C, 73.51; H, 7.67%. H
NMR: 7.47–7.70 (m, 30H, Ph), 5.84 (m, 2H, @CH), 4.94–
5.07 (m, 4H, @CH2), 1.43–2.34 (m, 8H, CH2). 31P NMR:
29.2 (PPh3). Mass spec. (FAB): m/z 740.1 [M]+, 687.1
4.2.7. Palladacyclononene (L = PPh3) (7)
[MꢀCH2CH2CH@CH2]+,
629.8
[Mꢀ2CH2CH2
1H NMR: 7.47–7.90 (m, 30H, Ph), 5.45 (br m, 2H,
@CH), 1.70–2.27 (br m, 8H, CH2), 1.51 (m, 4H, Pd–
CH2). 31P NMR: 28.6 (PPh3). Mass spec. (FAB): m/z
740.2 [M]+, 628.9 [MꢀC8H14]+, 477.8 [MꢀPPh3]+, 217.1
[Mꢀ2PPh3]+.
CH@CH2]+, 477.8 [MꢀPPh3]+, 215 [Mꢀ2PPh3]+.
Complexes 2–4 were prepared in a similar manner. All
of the complexes were found to be yellow oils with moder-
ate yields (ca. 50%). Microanalyses of these oils showed the
presence of solvent molecules.
4.2.8. Palladacyclononene (L2 = dppe) (8)
4.2.2. cis-Pd(CH2CH2CH@CH2)2(dppe)] (2)
1H NMR: 7.45–7.76 (m, 20H, Ph), 5.41 (br m, 2H,
@CH), 2.58 (t, 4H, P–CH2), 2.01–2.38 (br m, 8H, CH2),
1.87 (m, 4H, Pd–CH2). 31P NMR: 32.9 (–PPh2). Mass spec.
(FAB): m/z 614.1 [M]+, 503.9 [MꢀC8H14]+, 216.9
[Mꢀdppe]+.
Anal. Calc. for C46H66P2Pd (with 2 mol. of C6H14): C,
70.17; H, 8.45. Found: C, 70.12; H, 9.76%. 1H NMR:
7.44–7.68 (m, 20H, Ph), 5.82 (m, 2H, @CH), 4.96–5.10
(m, 4H, @CH2), 1.72–2.36 (m, 8H, CH2), 3.44 (t, 4H, P–
CH2). 31P NMR: 31.0 (–PPh2). Mass spec. (FAB): m/z
614.0 [M]+, 560.0 [MꢀCH2CH2CH@CH2]+, 502.9
[Mꢀ2CH2CH2CH@CH2]+, 215.4 [Mꢀdppe]+.
4.2.9. Palladacycloheptane (L = PPh3) (9)
Ten percent of Pd/C (20 mg) was added to the solution
of 5 (0.21 g, 0.29 mmol) in Et2O (20 ml). The solution was
stirred under 1 atm hydrogen gas for 46 h. The mixture was
then filtered and excess solvent was removed under reduced
pressure and the product was obtained as a brownish yel-
4.2.3. cis-[Pd(CH2CH2CH2CH@CH2)2(PPh3)2] (3)
Anal. Calc. for C76H118P2Pd (with 5 mol. of C6H14):
C, 76.06; H, 9.91. Found: C, 76.84; H, 10.66%. 1H
NMR: 7.01–7.88 (m, 30H, Ph), 5.80 (m, 2H, @CH),
4.86–4.96 (m, 4H, @CH2), 1.63–2.10 (m, 12H, CH2).
31P NMR: 29.7 (PPh3). Mass spec. (FAB): m/z
767.9 [M]+, 698.1 [MꢀCH2CH2CH2CH@CH2]+, 629.8
[Mꢀ2CH2CH2CH2CH@CH2]+, 505.9 [MꢀPPh3]+, 243.5
[Mꢀ2PPh3]+, 135.1 [2CH2CH2CH2CH@CH2]+, 68.2
[CH2CH2CH2CH@CH2]+.
1
low solid (0.19 g, 90%), m.p. 48–59 ꢁC (dec.); H NMR:
7.35–7.82 (m, 30H, Ph), 2.30 (m, 8H, CH2), 2.05 (m, 4H,
Pd–CH2). 31P NMR: 27.3 (PPh3). Mass spec. (FAB): m/z
714. 2 (M+), 451.8 (MꢀPPh3)+, 189.7 (ꢀ2PPh3)+, 629.1
(MꢀC6H12)+. Complexes 10–12 were prepared in a similar
fashion. All of the complexes were obtained in good yields
as pale yellow brown solids (80–90%).
4.2.4. cis-[Pd(CH2CH2CH2CH@CH2)2(dppe) (4)
4.2.10. Palladacycloheptane (L2 = dppe) (10)
Anal. Calc. for C60H98P2Pd (with 4 mol. of C6H14): C,
M.p. 65–73 ꢁC (dec.); 1H NMR: 7.44–7.71 (m, 20H, Ph),
3.36 (t, 4H, P–CH2), 2.50 (m, 8H, CH2), 2.01 (m, 4H, Pd–
CH2). 31P NMR: 32.7 (–PPh2). Mass spec. (FAB): m/z
587.9 [M]+, 503.8 [MꢀC6H12]+, 189.9 [Mꢀdppe]+.
1
72.96; H, 10.06. Found: C, 73.11; H, 9.67%. H NMR:
7.45–7.89 (m, 20H, Ph), 5.81 (m, 2H, @CH), 4.94–5.01
(m, 4H, @CH2), 2.52 (t, 4H, P–CH2), 1.31–2.37 (m, 12H,
CH2). 31P NMR: 30.1 (–PPh2). Mass spec. (FAB): m/z
642.1 [M]+, 572.9 [MꢀCH2CH2CH2CH@CH2]+, 503.8
[Mꢀ2CH2CH2CH2CH@CH2]+, 243.6 [Mꢀdppe]+.
4.2.11. Palladacyclononane (L = PPh3) (11)
M.p. 39–49ꢁC (dec.); 1H NMR: 7.64–7.98 (m, 30H, Ph),
1.22–1.62 (m, 12H, CH2), 0.87 (m, 4H, Pd–CH2). 31P
NMR: 25.5 (PPh3). Mass spec. (FAB): m/z 742.9 [M]+,
630.0 [MꢀC8H16]+, 489.9 [MꢀPPh3]+, 216.9 [Mꢀ2PPh3]+.
4.2.5. Palladacycloheptene (L = PPh3) (5)
Grubbs’ 2nd generation catalyst was added a solution of 1
(0.32 g, 0.45 mmol) in benzene (30 ml). The mixture was
refluxed with stirring at 50 ꢁC for 18 h, then cooled to room
temperature. The solvent was removed under reduced pres-
sure gave a maroon residue which was extracted with hexane
(4 · 5 ml). The product was obtained as brown oil (0.25 g,
4.2.12. Palladacyclononene (L2 = dppe) (12)
M.p. 55–67ꢁC (dec.); 1H NMR: 7.10–7.85 (m, 20H, Ph),
2.24 (t, 4H, P–CH2), 1.33 (br m, 8H, CH2), 0.90 (br m, 8H,
Pd–CH2–CH2). 31P NMR: 33.5 (–PPh2). Mass spec.

108
T. Mahamo et al. / Journal of Organometallic Chemistry 693 (2008) 103–108
(FAB): m/z 616.0 [M]+, 503.4 [MꢀC8H16]+, 217.5
[Mꢀdppe]+.
The oven was programmed to hold at 50 ꢁC for 2 min
and then ramp to 250 ꢁC at 10ꢁ/min and hold 8 min.
4.3. Synthesis of palladacycloalkanes by di-Grignard route
Acknowledgements
A
twofold excess solution of BrMg(CH2)nMgBr
We are thankful to AngloPlatinum Corporation, DST
Centre of Excellence in Catalysis, C* Change, UCT, The
UCT Chemistry EDP programme and Johnson Matthey
for their support.
(n = 6, 8) in anhydrous THF was slowly added to a sus-
pension of PdCl2(COD) (0.50 g, 1.75 mmol) in Et2O
(30 ml) at ꢀ78ꢁC. The mixture was stirred for 30 min,
then warmed to room temperature and stirred for
another 30 min. Pentane (5 ml) was then added to the
tube and excess di-Grignard reagent precipitated out of
solution. The supernatant was filtered and the solvent
was removed under reduced pressure to form the yellow
oil of the COD complexes, cis-[Pd(CH2)n(COD)] (when
n = 6, yield: 0.31 mmol, 18%; when n = 8, 0.28 mmol,
16%), which were then dissolved in Et2O (20 ml) and
an excess of dppe was added. The product immediately
precipitated out of solution. The mixture was stirred
for a further 30 min and the supernatant was removed.
The pale yellow solid obtained was washed with diethyl
ether (4 · 5 ml). The solid was dried under vacuum for
half an hour. The same procedure was followed for the
preparation of other complexes. Complex 10: (0.15 g,
15%), complex 12: (0.12 g, 11%). These two complexes
were also prepared (yield ca. 48%) from the reaction of
di-Grignard reagents with PdCl2(dppe).
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30 m · 0.32 mm CP-Wax 52 CB column (0.25 lm film
thickness). The carrier gas was helium at 5.0 psi. The oven
was programmed to hold at 32 ꢁC for 4 min and then to
ramp to 200 ꢁC at 10ꢁ/min and hold 5 min.
GC–MS analyses for peak identification were performed
using an Agilent 5973 gas chromatograph equipped with
MSD and a 60 m · 0.25 mm Rtx-1 column (0.5 lm film
thicknesses). The carrier gas was helium at 0.9 ml/min.