Hydride route for the palladium-catalysed cyclocarbonylation of monoterpenes

Article abstract of DOI:10.1002/ejic.200500136

This paper focuses on the mechanism by which a monoterpene undergoes a cyclocarbonylation reaction catalysed by a palladium complex. Evidence is provided, based on intermediate species observed under pressure or with various ligands, that the catalytic cycle follows a hydride route starting from [Pd(H)(SnCl₃)L₂]. The [Pd(H)(SnCl₃)L ₂] complexes (L = PPh₃ or PCy₃) have been observed for the first time by multinuclear NMR spectroscopy. Cationic hydride complexes or palladium(0) precursors show either no or poor reactivity. Studies related to model platinum complex chemistry have detected an acylplatinum species. Most of the observations have been done on the cyclocarbonylation of isopulegol, dihydromyrcenol or isolimonene into the corresponding lactones or cyclopentanones. The use of dihydromyrcene allowed us to observe the acylplatinum complex and the corresponding elusive acylpalladium species. The co-catalytic role of SnCl₂ is also demonstrated. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200500136

FULL PAPER
Hydride Route for the Palladium-Catalysed Cyclocarbonylation of
Monoterpenes
Duc Hanh Nguyen,[a] Gábor Laurenczy,[b] Martine Urrutigoïty*[a] and Philippe Kalck*[a]
Keywords: Carbonylation / Hydrides / Palladium / Terpenes
This paper focuses on the mechanism by which a monoter-
pene undergoes a cyclocarbonylation reaction catalysed by
a palladium complex. Evidence is provided, based on inter-
mediate species observed under pressure or with various li-
gands, that the catalytic cycle follows a hydride route starting
from [Pd(H)(SnCl3)L2]. The [Pd(H)(SnCl3)L2] complexes (L =
PPh3 or PCy3) have been observed for the first time by multi-
nuclear NMR spectroscopy. Cationic hydride complexes or
palladium(0) precursors show either no or poor reactivity.
Studies related to model platinum complex chemistry have
detected an acylplatinum species. Most of the observations
have been done on the cyclocarbonylation of isopulegol, di-
hydromyrcenol or isolimonene into the corresponding lac-
tones or cyclopentanones. The use of dihydromyrcene al-
lowed us to observe the acylplatinum complex and the corre-
sponding elusive acylpalladium species. The co-catalytic role
of SnCl2 is also demonstrated.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
often the [PdCl2L2] precursor is introduced into the me-
dium. These reactions are promoted by the addition of a
Lewis acid such as SnCl2. Two catalytic pathways have been
considered, and are still proposed in the literature: the first
one involves an alkoxycarbonylpalladium intermediate [Pd-
COOR] to which the alkene coordinates and finally a cis-
migration produces an alkylpalladium moiety containing
the ester group,[6] whereas the second one starts from an
intermediate palladium hydride species [Pd–H] which gives
an alkylpalladium intermediate by successive coordination
of the alkene and subsequent hydride transfer.[1,7] The co-
polymerisation of ethylene and carbon monoxide catalysed
by the cationic [Pd(diphos)]2+ complexes in the presence of
methanol perfectly interconnects the two catalytic path-
ways[8] such that polymers with -CH2COOCH3 and
-CH2CH3 terminal functions are produced in equal pro-
portions. For the alkoxycarbonylation reaction of an al-
kene, Knifton has reported the [PdCl2(PPh3)2]/SnCl2 cata-
lytic system, with which he detected the presence of a ν(Pd–
H) stretching frequency.[7] In the literature, several papers
deal with evidence that the palladium hydride pathway op-
erates preferentially.[9,10] Particularly, in recent studies Hea-
ton and co-workers have synthesised cationic PdII hydride
complexes containing both a diphosphane ligand and a co-
ordinated solvent molecule, [Pd(H)(dtbpx)(MeOH)]+
[dtbpx = 1,2-(CH2PtBu2)2C6H4].[10] They demonstrated
that this complex is an essential intermediate in the catalytic
system for the formation of methyl propanoate by carbon-
ylation of ethene in methanol.
Introduction
Palladium chemistry is currently the workhorse of or-
ganic chemistry and is a versatile tool to perform carbon–
carbon coupling.[1] When appropriate building blocks are
introduced the substrate can follow a multistep function-
alisation so that tandem reactions open the way for the
preparation of rather sophisticated organic molecules.[2]
A
number of interesting compounds that show biological ac-
tivity contain a lactone moiety.[3] During the last few years
we have explored the introduction of a CO building block
into an unsaturated substrate to obtain such a backbone in
a one-pot synthesis.[4] We chose to follow an hemisynthetic
way starting from an abundant and cheap raw material like
monoterpenes. Thus, we functionalised isopulegol and dihy-
dromyrcenol into the corresponding lactones,[4] and then
extended this type of tandem reaction to the cyclocarbon-
ylation of isolimonene, which produces a cyclopentanone.[5]
All these reactions are an extension of the classical alkoxy-
carbonylation reaction by which a terminal alkene is car-
bonylated in the presence of an alcohol to provide an ester.
Generally, this reaction is catalysed by a palladium complex
containing a phosphane or a diphosphane ligand, and most
[a] Laboratoire de Catalyse, Chimie Fine et Polymères, Ecole Na-
tionale Supérieure des Ingénieurs en Arts Chimiques et Techno-
logiques,
118 route de Narbonne, 31077 Toulouse Cedex 04, France
Fax: +33-5-6288-5600,
E-mail: Philippe.Kalck@ensiacet.fr; Martine.Urrutigoity@ensi-
acet.fr
[b] Ecole polytechnique fédérale de Lausanne, Institut des sciences
et ingénierie chimiques,
The present study is concerned with spectroscopic evi-
dence obtained for various [Pd(H)(X)L2] and [Pd(H)L3]+
BCH-LCOM, 1015 Lausanne, Switzerland
Eur. J. Inorg. Chem. 2005, 4215–4225
DOI: 10.1002/ejic.200500136
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4215

D. H. Nguyen, G. Laurenczy, M. Urrutigoïty, P. Kalck
FULL PAPER
complexes under normal conditions or under CO pressure. Synthesis of [Pd(H)(X)L2] and [Pd(H)(L3)]+ Complexes
We demonstrate that the essential active species in the cy-
Complexes [PdCl2L2] were prepared in high yields by ad-
clocarbonylation reaction is [Pd(H)(SnCl3)L2].
dition of PPh3, PCy3 or the diphosphane dCypb [dCypb =
bis(dicyclohexylphosphanyl)butane] to the complex
[PdCl2(PhCN)2] according to the published pro-
cedures.[12,14,15] Addition of ten equivalents of the silane
HSiPh3 to these dichloro-, PPh3- or PCy3-containing com-
pounds gave the corresponding hydrido complexes
[Pd(H)(Cl)L2] (L = PPh3 1, PCy3 2) in 40% yields after
crystallisation.[16a] For the tricyclohexylphosphane ligand,
better yields can be obtained when [Pd(PCy3)2] is synthe-
sised by reduction of [PdCl2(PCy3)2]. Subsequent addition
of one equivalent of anhydrous HCl in diethyl ether affords
2 in 80% yield as a crystalline material.[16b] We did not suc-
ceed in preparing [Pd(H)(Cl)(dCypb)] (3) by reduction of
one chloro ligand in [PdCl2(dCypb)] by HSiPh3, since in all
experiments palladium black precipitated. As our attempts
with other diphosphanes also resulted in the precipitation
of abundant quantities of black materials, we suspect that
this absence of stability is due to the trans-position of the
incoming hydride ligand to a phosphorus atom. However,
starting from [Pd(PCy3)2] we succeeded in the exchange of
ligand dCypb, and addition in an NMR tube at 183 K of
one equivalent of HCl (in Et2O solution) produced the cor-
responding hydride [Pd(H)(Cl)(dCypb)] (3), which shows a
hydride signal at δ = –8.0 ppm (Table 1), a doublet of doub-
lets due to the coupling with a phosphorus in the trans-
Results and Discussion
Carbonylation of isopulegol A or isolimonene B, under
a CO pressure of 40 bar, in the presence of [PdCl2L2]/SnCl2
provides the lactone C or the cyclopentanone D, irrespec-
tive of whether the medium contains methanol or not
(Scheme 1).[4,11,12]
position (2J1H,31
= 200 Hz) and another one in the cis-
Ptrans
position (2J1H,31 = 10 Hz). However, we could not isolate
Pcis
Scheme 1. Cyclocarbonylation of isopulegol A and isolimonene B.
the hydride in the solid state.
Addition of one equivalent of SnCl2 to [D8]THF solu-
After catalysis, we never detected any alkoxycarbonylpal- tions of 1 or 2 gives [Pd(H)(SnCl3)L2] (L = PPh3 4, PCy3
ladium complex containing the isopulegyl moiety among 5). As shown in Table 1, these two derivatives are character-
1
the organometallic compounds. However, starting from iso- ised in their H NMR spectra by a hydride signal at δ =
limonene, small amounts of dehydro-D have previously –6.90 and –8.50 ppm, respectively, flanked by two satellites
2
been identified corresponding to a cyclopentenone resulting due to J1H,119 coupling (944 Hz and 1760 Hz, respec-
Sn
from the sacrificial formation of the palladium hydride spe- tively). The 1H-31P coupling is too small to be detected. The
cies.[5,11,13]
coupling between H and 119Sn was confirmed by a 2D-
1
During the present study, we carefully analysed the pro- HMQC sequence and is shown in Figure 1.
ducts resulting from the cyclocarbonylation of isopulegol
The 31P NMR spectra show a broad singlet at δ =
by GC/MS and we identified small amounts of the unsatu- 33.80 ppm for 4 and a singlet at δ = 52.26 ppm for 5 flanked
rated lactone dehydro-C, which leads to Equation (1). In by the two satellites due to the coupling with 119Sn
order to gain direct evidence of the involvement of this cata- (2J
= 138 Hz). In these compounds, the two phos-
31P,119Sn
lytic hydride route, we prepared a series of neutral and cat- phane ligands are in mutual trans positions and the ex-
ionic palladium hydride complexes, whose characterisation change of a Cl for an SnCl3 ligand results in a decrease of
is described below.
nearly 6 ppm for the chemical shift of the hydride ligand
(1)
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Palladium-Catalysed Cyclocarbonylation of Monoterpenes
FULL PAPER
Table 1. NMR spectroscopic data for hydridopalladium [Pd(H)(X)L2] complexes.[a]
Compound Hydridopalladium
complex
1H NMR
δ
31P NMR
δ
119Sn NMR
δ
2
2
1
2J
1
31P
31P,119Sn
119Sn
J H,
J H,
1*
2*
3
trans-[Pd(H)(Cl)(PPh3)2]
trans-[Pd(H)(Cl)(PCy3)2]
cis-[Pd(H)(Cl)(dCypb)]
trans-[Pd(H)(SnCl3)(PPh3)2] –6.90
trans-[Pd(H)(SnCl3)(PCy3)2] –8.50
–13.12
–14.32
–8.00
–
3
30.75
45.63
10; 200
–
–
4
33.80
52.30
–
138
–
154
944
1760
5
[a] T = 183 K (*: T = 298 K); solvent: [D8]THF; δ in ppm and J in Hz.
Figure 1. {1H-119Sn} HMQC spectra of complex 5 with an expansion of the two satellite signals on the right-hand side.
(6.22 ppm between 1 and 4 and 5.82 ppm between 2 and 5), isomer of 5 or a pentacoordinate species arising from the
thus showing that the addition of SnCl2 has a dramatic ef- coordination of SnCl2 to 2.
fect. Such a shift is certainly related to significant changes
It is worth mentioning that addition of SnCl2 to complex
and decreases in the electron density at the H ligand and 3, even at 183 K, does not result in the formation of the
thus its hydride character. Recent studies on [Mo(H)- expected Pd-SnCl3 species. The hydride signal of 3 disap-
(NO)(dmpe)2] [dmpe = bis(dimethylphosphanyl)ethane] pears, and several unassigned signals are detected in the 31
P
have shown that the hydridic character of the hydride ligand NMR spectrum. Decomposition into an orange material
is largely influenced by the nitrosyl ligand in the trans posi- occurs rapidly. Table 1 lists all the NMR spectroscopic data
tion. As a consequence, this complex presents a high pro- for complexes 1–5.
pensity to undergo hydride-transfer reactions.[17]
The synthesis of complexes containing the Pd(H)(SnBu3)
1
The H NMR spectrum of complex 5 at 183 K shows core was attempted in order to introduce another Lewis
the additional presence of a small amount of complex 2 acid into the coordination sphere of palladium. The syn-
(Figure 2). Increasing the temperature to 203 K leads to a thetic procedure is to add HSnBu3 directly to a palla-
large increase in the concentration of 2 due to decoordina- dium(0) species. In fact, [Pd(PPh3)n] (n = 2, 3, 4 in solution)
tion of SnCl2, complex 5 becoming the minor species. This reacts sluggishly, and at room temperature gives mainly the
2
31P,119Sn
observation does not mean that under the catalytic condi- complex [Pd(SnBu3)2(PPh3)2] (δ31P = 34.30 ppm, J
=
tions (348–373 K, PCO = 30–100 bar) only the chloro com- 113 Hz). Nevertheless, a ν(Pd–H) absorption is detected at
plex is operative. Indeed, the NMR spectra at room tem- 2046 cm–1 in the IR spectrum, which belongs presumably to
perature (under inert atmosphere) still show the presence of [Pd(H)(SnBu3)(PPh3)2]. The reaction proceeds cleanly with
5 but a fluxional process occurs, as detected by the broad- [Pd(PCy3)2], [Pd(diphos)(PCy3)] [diphos = 1,2-bis(dicy-
ening of its hydride signal, whereas that of 2 remains sharp. clohexylphosphanyl)ethane (dCype)], 1,4-bis(dicyclohexyl-
We did not observe the possible intermediates, i.e. the cis- phosphanyl)butane or 1,6-bis(diphenylphosphanyl)hexane
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D. H. Nguyen, G. Laurenczy, M. Urrutigoïty, P. Kalck
FULL PAPER
field than in 6. Provided the steric effects are ignored, the
31P
phosphorus atom PA in the trans position to SnBu3 [δ
31P,119Sn
= 27.36 ppm (t, J
= 1402 Hz] receives more electron
density from the metal centre than the second phosphorus
2
31P
31P,1H
=
atom PB trans to the hydride [δ = 43.96 ppm (t, J
166 Hz], which is not significantly affected by the presence
of the SnBu3 in the trans position. In the paragraph devoted
to catalysis, these electronic effects will be taken into ac-
count to explain the various catalytic activities observed.
1
Variable-temperature H and 31P NMR studies of com-
plex 8 (Figure 3) show that a stereochemical non-rigidity
phenomenon occurs, and the square-planar complex does
1
not lose the SnBu3 ligand. The H NMR signal at room
temperature is consistent with a hydride ligand coupled to
two equivalent phosphorus atoms and to tin. A fast iso-
merisation process makes the PA and PB phosphorus atoms
equivalent. A similar phenomenon has recently been re-
ported for [Pd(H)(SiR3)(dCype)].[19] In addition, sophisti-
Figure 2. Evidence for a dynamic equilibrium between 2 and 4.
1
cated H-119Sn{31P} 2D-HMQC NMR experiments unam-
biguously show the 119Sn chemical shift at δ = 7.50 ppm.
(dpph) to give, according to 1H and 31P NMR analysis,
[Pd(H)(SnBu3)(PCy3)2] (6), [Pd(H)(SnBu3)(dCype)] (7),
Some authors consider that the main role of adding
[Pd(H)(SnBu3)(dCypb)] (8) or [Pd(H)(SnBu3)(dpph)] (9), SnCl2 is to provide the SnCl3– counterion, but this hypothe-
respectively, in which the two hydrido and SnBu3 ligands sis has been essentially confirmed in platinum chemistry.[20]
are in mutual trans (6) or cis (7–9) positions. Indeed, the We prepared the cationic hydrido complexes [Pd(H)L3]+ in
hydride signal of 6 is at δ = –14.32 ppm due to the large the presence of weakly coordinating anions such as
trans influence of the SnBu3 ligand. For 7–9, the hydride CF3COO– a, BF4– b, and TolSO3– c. Table 3 displays all the
signals are at δ = –2.67, –3.84 and –4.06 ppm, respectively. NMR spectroscopic data related to the complexes that were
All NMR spectroscopic data are displayed in Table 2. Simi- isolated and characterised by 1H and 31P NMR spec-
larly, the platinum analogue [Pt(H)(SnBu3)(PPh3)2] (10) was troscopy. They obey the general formula [Pd(H)(PCy3)L2]+,
prepared from [Pt(PPh3)4]. Here also addition of HSnBu3 except for [Pd(H)(PCy3)2]+ (11), for which the hydride sig-
provides [Pt(SnBu3)2(PPh3)2] directly, which was character- nal appears at δ = –18.8 ppm as a triplet with a small hy-
ised by 31P NMR spectroscopy (δ31P = 18.0 ppm). However, dride–phosphorus coupling of 3.5 Hz, consistent with a 14-
as already described in the literature[18] for the preparation electron palladium complex having the two PCy3 ligands in
of [Pt(H)(SnMe3)(PPh3)2], bubbling dihydrogen through the trans positions and the hydrogen atom cis to each phospho-
solution allows the isolation of 10.
rus atom.[9i–9k,21] For the 16-electron complexes
Comparison between the two SnCl3 and SnBu3 ligands [Pd(H)(PCy3)L2]+ {L2 = dCype 12, [1,2-bis(diphenylphos-
shows immediately that the trans influence of the tributyltin phanyl)ethane] (dppe) 13, [1,3-bis(diphenylphosphanyl)pro-
ligand is significantly stronger than that of SnCl3 and is pane] (dppp) 14, [1,4-bis(diphenylphosphanyl)butane]
rather similar to that of the chloro ligand. The hydridic (dppb) 15, [1,1Ј-bis(diphenylphosphanyl)ferrocene] (dppf)
character decreases significantly when SnCl2 is introduced 16}, the nature of the counterion is almost insignificant.
into the coordination sphere (the chemical shift is δ = For instance, when L2 = dppp, δ1H = –6.62 ppm with
–
–8.5 ppm for 5, whereas it is δ = –14.32 ppm for 2 and δ = CF3COO– or –6.84 ppm with BF4 . Variation of L2 (13–16)
–14.53 ppm for 6). When we consider complex 8, in which induces larger effects. For example, for 13a, 14a, 15a and
the hydrido and SnBu3 ligands are in mutual cis positions, 16a the shifts are δ = –5.58, –6.62, –6.12 and –7.87 ppm,
the situation is more contrasted. Indeed, the hydride signal respectively. The geometry is presumably square planar,
is found at δ = –3.84 ppm, i.e. roughly 10 ppm to lower with the PCy3 ligand being cis to the hydride ligand. The
Table 2. NMR spectroscopic data for the [Pd(H)(SnBu3)L2] complexes.[a]
Compound Hydridopalladium
complex
1H NMR
δ
31P NMR
δ
119Sn NMR
δ
2
2
1
2J
31P,119Sn
1
31P
119Sn
J H,
J H,
6
trans-[Pd(H)(SnBu3)(PCy3)2]
–14.5
–2.67
–3.84
–4.01
5.5
177
8, 166
200
2494
310
200
48.30
25.10, 45.20
27.36, 43.96 1402
40.70
7
cis-[Pd(H)(SnBu3)(dCype)]
cis-[Pd(H)(SnBu3)(dCypb)]
cis-[Pd(H)(SnBu3)(dpph)]
8*
9
7.50
–
–
[a] T = 298 K; solvent: C7D8; *: a coupling constant is observed between the two phosphorus atoms (2J
= 20 Hz).
31PA,31PB
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Palladium-Catalysed Cyclocarbonylation of Monoterpenes
FULL PAPER
Figure 3. a) Hydride section of the variable temperature 1H NMR spectra measured for 8; b) Variable temperature 31P NMR spectra
measured for 8.
Table 3. NMR spectroscopic data of [Pd(H)(PCy3)2]+(X)– and [Pd(H)(PCy3)L2]+(X)–.
2
δ (1H) [ppm][a]
J H, [Hz]
δ (31P) [ppm]
2J
1
31
P
31P,31
P
[Hz]
Complexes
[Pd(H)(PCy3)2]+
11a
11b
11c
–18.20
–18.84
–18.71
3.5
3.7
–
39.40
–
45.7
–
–
–
[Pd(H)(PCy3)(L2)]+(X)–
12a
12b
12c
13a
14a
14b
15a
16a
–6.29
–6.15*
–6.12
–5.58
–6.62
–6.90
–6.12
–7.87
7, 13, 179
–
9, 12, 177
20, 196
28, 189
12, 75
86.95, 65.43, 49.68
–
–
–
51.18, 9.16, 3.58
49.87, 7.66, 3.97
–
311, 18, 18
–
–
–
306, 48, 22
315, 51, 21
–
13, 185
10, 179
52.57, 24.94, 20.15
337, 31, 27
[a] T = 298 K; *: broad signal due to exchange phenomena at room temperature.
diphos ligand shows two phosphorus atoms in different Table 4. Catalytic activity for cyclocarbonylation of isopulegol in
the presence of [Pd(H)(Cl)L2/SnCl2/L].
magnetic environments, giving rise to an AMX system
(5R)-C (5S)-C de[a]
(Table 3).
Test
t
[h]
PCO
[bar]
T
[°C]
Yield
[%]
[%]
[%]
[%]
R1
R2
R3
16
16
40
16
68
16
30
30
20
10
10
10
60
40
60
60
50
60
100
62
100
100
68
60
35
60
66
45
78
40
27
40
44
23
22
20
13
20
22
22
56
Catalytic Activity in Carbonylation of Isopulegol
The catalytic activity of [Pd(H)(SnCl3)(PPh3)2] {formed R4
R5
from [Pd(H)(Cl)(PPh3)2] by addition of an excess of SnCl2
R6[b]
100
in situ with a P/Pd ratio of 4} was examined in the cyclocar-
bonylation of isopulegol in toluene, exclusively with CO as
a reactant (A giving C in Scheme 1). Conversion of the sub-
strate is 100% within 16 h at 60°C (see Table 4, run R1).
One more experiment was carried out at the same pressure
[a] de = {R(%) – S(%)}/{R(%) + S(%)}. [b] dppb was used as li-
gand.
The two diastereomers of lactone C were obtained in a
but at lower temperature (40°C, run R2): the yield was nearly 60:40 proportion (runs R1, R3 and R4). In fact, as
62%. The effect of the temperature appears to be promi- noted by Knifton in his early studies, the promoting role of
nent, since when the pressure was decreased from 30 bar to the SnCl2 co-catalyst is essentially to increase the regioselec-
20 bar and even 10 bar the yields were not affected (com- tivity of the alkoxycarbonylation of the terminal alkene into
pare runs R1, R3 and R4 at 60°C).
the corresponding linear ester.[7] In the present case, the re-
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D. H. Nguyen, G. Laurenczy, M. Urrutigoïty, P. Kalck
FULL PAPER
action with [Pd(H)(Cl)(PPh3)2] is slower and less diastereo- [PtCl2(PPh3)2][22] and treated with dihydromyrcene at
selective.[11] Increasing the electron density on palladium by 100°C under a CO pressure of 40 bar. Microcrystalline ma-
substituting the PPh3 ligands with PCy3 results in the com- terial precipitated at the end of the reaction. After separa-
plete absence of reactivity under the same reaction condi- tion and dissolution of the solid, analysis by multinuclear
tions irrespective of whether the complex is prepared and NMR showed that its structure corresponds to the square-
isolated or generated in
situ. Formation
of planar acyl complex trans-[PtCl{C(O)CH2CH2CH(CH3)-
[Pd(H)(SnCl3)(dppb)] from [Pd(H)(Cl)(PPh3)2] (1), dppb CH2CH2CHC(CH3)2}(PPh3)2] (18), as shown in Equa-
and SnCl2 leads to lower reaction rates but improved dia- tion (2).
A signal with two satellites is observed in the 31P NMR
stereomeric ratios (78:22). On the contrary, producing the
cationic hydrido precursor 15a by direct addition of
CF3COOH to [Pd(PCy3)(dppb)] gives a poor yield of C
(17%). Similarly, [Pd(H)(PCy3)(dppf)]+[CF3COO]– (16a)
leads to a 21% yield. All the other prepared cationic com-
plexes were examined in the carbonylation of isopulegol:
the results are similarly deceiving.
Moreover, the effect of the introduction of SnBu3 in the
coordination sphere of palladium was analysed. In the pres-
ence of [Pd(H)(SnBu3)(PPh3)2], prepared in situ by addition
of HSnBu3 to [Pd(PPh3)n], or cis-[Pd(H)(SnBu3)(dCypb)],
the carbonylation reaction gives only traces of lactone. The
important difference in the chemical shift − δ = –14.50 ppm
for 6 and δ = –8.50 ppm for 5 − is presumably related to
the significant differences in reactivity of the two complexes.
Indeed, 6 presents a high hydridic character and its intras-
phere nucleophilic attack of the olefin should be easy, this
transfer producing the alkyl species, but the coordination
of the olefin to the metal centre is presumably retarded.
Moreover, we cannot exclude that in the subsequent step
the CO migratory insertion could be disfavoured due to the
steric hindrance of SnBu3 and/or the electronic effects on
palladium.
spectrum at δ = 23.18 ppm due to the coupling with 195Pt
(1J
= 3186 Hz), and a triplet is observed for the 195Pt
31P,195Pt
signal at δ = –3933 ppm due to the coupling with two equiv-
alent phosphorus atoms. Furthermore, in the 13C NMR
spectrum the acyl carbon atom appears as a triplet at δ =
219.45 ppm (2J
= 6 Hz) flanked by satellites with
31P,13
C
1J
= 458 Hz. A similarly high chemical shift value of
195Pt,13
C
δ = 243.9 ppm has been found for the C(O)Me carbon in
the anionic acylplatinum() complex [Li][(η2-TpЈ)Pt(CO-
Me)(Me)] [TpЈ
= hydridotris(3,5-dimethylpyrazolyl)bo-
rate].[23]
Thus, under a CO atmosphere the platinum complex that
separates from the medium as a solid contains the acyl moi-
ety trans to the chloro atom. We supposed that, in fact, the
formation of the SnCl3 ligand is reversible, so we decided
to add one equivalent of SnCl2 to the acyl chloro complex.
All the analyses show that we unambiguously produced the
acylplatinum SnCl3 complex trans-[Pt(SnCl3){C(O)-
CH2CH2CH(CH3)CH2CH2CHC(CH3)2}(PPh3)2] (19), as
given by Equation (3).
The 31P NMR spectrum of this complex shows that the
two phosphane ligands are equivalent and give a signal,
with two satellites, at δ = 18.95 ppm (1J
= 3186 Hz).
195Pt,31
P
The 195Pt NMR signal at δ = –4466 ppm is a triplet due to
the coupling with the two equivalent phosphorus atoms.
The 119Sn NMR spectrum contains a signal at δ =
55.61 ppm (t) with a 31P-119Sn coupling constant of 296 Hz
that we obtained from 31P-119Sn INEPTND and 31P-119Sn
Mechanistic Proposal
Characterisation of an Acylplatinum Species
Platinum complexes are often used to mimic the reactiv- HMQC experiments. Finally, the 13C NMR spectrum pres-
2
13C,31
P
ity of palladium because they are less labile and they lead ents an acyl signal at δ = 224.80 ppm (t), with J
=
2
13C,195Pt
to more stable pentacoordinate species. The complex trans- 5 Hz, the J
coupling constant being difficult to de-
[Pt(H)(SnCl3)(PPh3)2] (17) was therefore prepared from cis- termine due to the low signal-to-noise ratio.
(2)
(3)
4220
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Palladium-Catalysed Cyclocarbonylation of Monoterpenes
1
FULL PAPER
Observations by H NMR carried out over a period of the square-planar pyramid structure 21b represented in Fig-
several days showed that the acyl complex 19 evolves to- ure 5.
ward the starting complex [Pt(H)(SnCl3)(PPh3)2] (17). Di-
hydromyrcene was also unambiguously detected. Thus, we
can deduce that the equilibrium between these two com-
plexes involves the intermediate alkyl species 20 shown in
Figure 4. Indeed, decarbonylation of complex 19 would
give 20, which produces the pentacoordinate species
[Pt(H)(SnCl3)(dihydromyrcene)(PPh3)2] by β-elimination.
This latter complex would give 17 by loss of dihydromyr-
cene.
Figure 5. Two possible geometries for the pentacoordinate species
[Pd(H)(SnCl3)(CO)(PCy3)2] (21a) and 21b.
The hydrido and carbonyl ligands in 21a occupy the axial
positions of the tbp geometry. Although such pentacoordi-
nate hydrido species have already been proposed in the lit-
erature,[27] no such characterisation has been reported in
palladium chemistry. However, it is worth mentioning that
a palladium atom with five ligands in tbp or sp environ-
Figure 4. Alkylplatinum species 19 resulting from the addition of
ments
is
known
for
[Pd(CH2CMe2-o-C6H4)-
dihydromyrcene.
(PMe3)2(SO2)],[28] or for a cationic palladium complex con-
taining a triphosphane ligand and an imine ligand in the o-
position of an aryl group.[29a]
In situ Characterisation of Palladium Species under CO
Pressure
Although we did not reach the slow exchange limit for
Zudin and al.[24] have previously shown that the cationic complex 21a, we suggest that a Berry pseudo-rotation
hydridopalladium complex [Pd(H)(PPh3)3]+[CF3COO]–, mechanism occurs in solution which exchanges the axial
prepared in situ, reacts with CO to afford the dinuclear and equatorial ligands. In this way the dynamic equilibrium
complex [Pd2(µ-H)(µ-CO)(PPh3)4]+[CF3COO]– in which the shown in Figure 6 should occur. In this case, the second tbp
hydrido and carbonyl ligands occupy the two bridging posi- isomer contains the CO and SnCl3 ligands in mutual cis
tions. A similar monocationic dinuclear complex has been positions with regard to the two PCy3 ligands (Figure 6).
prepared with the diphosphane ligand 1,3-bis[di(isopropyl)-
phosphanyl]propane.[25] Moreover, Elsevier and Tóth
started from the mononuclear neutral acyl complex
[Pd(Cl)(COMe)(bdppp)] [bdppp is (2S,4S)-2,4-bis(diphen-
ylphosphanyl)pentane] and observed that a methanolysis
reaction occurs under a CO atmosphere to provide the elus-
Figure 6.
[Pd(H)(SnCl3)(CO)(PCy3)2] (21a).
Axial–equatorial
ligand
exchange
in
ive intermediate [Pd(H)(Cl)(bdppp)], which leads to a mix-
ture of [PdCl2(bdppp)] and [Pd2(µ-H)(µ-CO)(bdppp)2]+-
[Cl]–.[26]
In addition to these observations, we detected a weak
signal in the H NMR spectrum at δ = –14.5 ppm corre-
1
Introduction of SnCl2 into the Palladium Hydride
Coordination Sphere
sponding to a weak signal in the 13C NMR spectrum at δ
= 194.6 ppm. Such a value for the hydride ligand recalls the
shift of [Pd(H)(Cl)(PCy3)2] (2) (δ1H = –14.32 ppm) and we
suggest that these signals should correspond to the species
[Pd(H)(CO)(Cl)(PCy3)2] (22) (21/22 = 65:35). As we pre-
viously observed (see above) the equilibrium between
[Pd(H)(SnCl3)(PCy3)2] (5) and [Pd(H)(Cl)(PCy3)2] (2) +
SnCl2, and since removing SnCl2 from a pentacoordinate
species is rather uncommon, we propose that the complex
[Pd(H)(Cl)(CO)(PCy3)2] (22) results from the direct coordi-
nation of a CO ligand to the square-planar complex
[Pd(H)(Cl)(PCy3)2] (2).
[Pd(H)(SnCl3)(PCy3)2] (5), prepared in situ in an NMR
tube by addition of one equivalent of SnCl2 to
[Pd(H)(Cl)(PCy3)2] (2), was pressurised with 3 bar 13CO.
The 1H NMR spectra present a broad signal at δ =
–8.70 ppm and even at 183 K no 1H-31P nor 1H-119Sn coup-
ling constants could be determined due to an exchange phe-
nomenon. However, the 13C NMR spectra clearly reveal a
2
13C,31
P
triplet at δ = 232.4 ppm with a J
coupling constant
of 3.7 Hz, the CO ligand thus being cis to two equivalent
phosphorus atoms. The same spectra also show two satel-
lites due to 13C-119Sn coupling (2J = 144.6 Hz), such a value
being in agreement with a mutual cis arrangement of the
CO and SnCl3 ligands. In the 31P NMR spectrum, a signal
is detected at δ = 50.80 ppm with two satellites due to a
NMR Monitoring of the Reactivity of the Substrate with
[Pd(H)(SnCl3)(PCy3)2] (5)
We carried out the same type of experiments, main-
small coupling with 119Sn (2J = 148 Hz), consistent with the taining the same temperature and concentrations, but now
SnCl3 ligand being cis with regard to the two equivalent four equivalents of dihydromyrcene were added and the
phosphorus atoms. Thus, we can assign to this pentacoordi- 13CO/12CO pressure was increased to 10 bar. In less than
nate species either the trigonal bipyramid geometry 21a or one hour, still at 183 K, the main hydride peak at δ =
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D. H. Nguyen, G. Laurenczy, M. Urrutigoïty, P. Kalck
FULL PAPER
–8.7 ppm and the weak signal at δ = –14.5 ppm disap- scribed in which the coordination sphere contains the di-
peared, presumably due to the formation of the correspond- phosphane dppe, CO, methyl and methoxy ligands.[29b]
ing alkyl species. In the 13C NMR spectrum two CO signals
The CO migratory insertion is presumably the rate-de-
were detected at δ = 232.6 ppm (complex 23) and δ = termining step, since at 183 K the coordination of the al-
194.7 ppm (complex 24) as two triplets with relative inten- kene followed by the hydride transfer are relatively fast
2
13C,31
P
sities of 70:30 and J
coupling constants of 4.5 and steps. Such an observation parallels the reactivity of
3.2 Hz, respectively; this ratio was found to be 75:25 for the [Pd(H)(SnCl3)(PPh3)2] (4) in catalytic tests, since at 40°C
hydride signals of [Pd(H)(SnCl3)(PCy3)2] (5) and and 30 bar the conversion rate is near to 60% in 16 h,
[Pd(H)(Cl)(PCy3)2] (2) in the 1H NMR spectrum. The prox- whereas at 60°C and even at 10 bar the reaction reaches
imity of the two chemical shifts and the coupling constants completion overnight (see Table 4).
for 21a and 23 led us to propose that we observe the penta-
coordinate species in which CO is coordinated as shown in
Figure 7. Similarly, we propose that 24, with the chloro li-
Conclusions
gand, is characterised by the shift at δ = 194.7 ppm. Penta-
In this paper, the identification of various neutral, cat-
coordinated platinum species have previously been de-
ionic, square-planar and pentacoordinate (under CO pres-
sure) hydridopalladium complexes has been described. It
appears that the co-catalyst role of SnCl2 is crucial because
it produces an active palladium–SnCl3 species. Preparation
of [Pd(H)(SnCl3)(PPh3)2], as shown by multinuclear NMR
spectroscopy, leads to an active complex which catalyses the
alkoxycarbonylation reaction of an alkene efficiently. Thus,
we propose a catalytic cycle exclusively based on the hy-
dride route, with the two L phosphorus ligands in trans po-
sitions (Figure 8).
Recent studies reported by van Leeuwen and Heaton[30]
are consistent with the coordination of methanol to explain
Figure 7. Representation of the two pentacoordinate acyl species
23 and 24 observed under CO pressure in HP/NMR spectroscopy. the last step of the alcoholysis, provided the two phosphane
Figure 8. Proposed hydridopalladium route for alkoxycarbonylation reaction.
4222
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Eur. J. Inorg. Chem. 2005, 4215–4225

Palladium-Catalysed Cyclocarbonylation of Monoterpenes
FULL PAPER
diethyl ether; the final product was pale yellow and was isolated in
80% yield.
ligands are mutually cis. Our preliminary observations that
isomerisation occurs for the monophosphane ligands
prompted us to explore and investigate the final step of the
catalytic reaction in the present system.
[Pd(H)(Cl)(PPh3)2] (1): IR: ν(Pd–H) = 2050 cm–1. 1H NMR
(250 MHz, 293 K, CDCl3): δ = –13.12 ppm. 31P NMR (250 MHz,
293 K, CDCl3): δ = 30.75 ppm.
[Pd(H)(Cl)(PCy3)2] (2): IR: ν(Pd–H) = 2046 cm–1. 1H NMR
(250 MHz, 293 K, CDCl3): δ = –14.32 ppm. 31P NMR (250 MHz,
293 K, CDCl3): δ = 46.63 ppm.
Experimental Section
General Considerations: All reactions and manipulations were car-
ried out in dried and distilled solvents under argon using standard
Schlenk techniques. All NMR measurements were performed on
Bruker AM250, AMX400 or DRX400 spectrometers using 5-mm
triple resonance inverse probes with a dedicated 31P channel. All
chemical shifts for 1H and 13C are relative to TMS using 1H (resid-
ual) or 13C chemical shifts of the solvent as a secondary standard.
The chemical shifts were referenced to external H3PO4 (85%) for
31P, SnMe4 for 119Sn and H2PtCl6 for 195Pt. High-pressure NMR
experiments in situ were carried out in special sapphire tubes with
a diameter of 10 mm (for more details concerning the setup and
procedure see ref.[31]). IR spectra were recorded on a Perkin–Elmer
1710 FT-IR spectrophotometer. Gas chromatography analyses
were performed on a Perkin–Elmer instrument equipped with a
DB-5GC column (30 m×0.25 mm×0.25 µm) and a flame ionis-
ation detector. Mass spectrometric measurements were performed
at the Service de Spectrométrie de Masse de l’Université Paul Sab-
atier on a NERMAG R 10-10 apparatus for organometallic com-
pounds and on a Perkin–Elmer TURBO MASS instrument
equipped with a DB-5MS 30 m×0.25 mm×0.25 µm column for or-
ganic products. Elemental analysis (C,H,O) was performed at the
Ecole Nationale Supérieure des Ingénieurs en Arts Chimiques et
Technologiques de Toulouse. Several compounds are unstable, so
mass spectrometry or elemental analyses were not always possible.
Preparation of [Pd(H)(Cl)(dCypb)] (3): A solution of [Pd(PCy3)2]
(0.1 mmol) in 1 mL of [D8]THF was treated with 0.1 mmol of 1,4-
bis(dicyclohexylphosphanyl)butane at room temperature. After 1 h,
one equivalent of HCl (in Et2O solution) was added and the solu-
tion was stirred for 1 h at 183 K. Then, 1H NMR spectra were
recorded, and revealed the presence of [Pd(H)(Cl)(dCypb)] (3)
along with small amounts of [Pd(H)(Cl)(PCy3)2] (2) and traces of
1
unidentified hydridopalladium complexes. H NMR (400.13 MHz,
183 K): δ = –8.0 ppm (2J1H,31P = 10 and 200 Hz). From the integra-
1
tion of the H signals, the yield of 3 was estimated to be 40%.
Preparation of [Pd(H)(SnCl3)L2] (L = PPh3, 4; PCy3, 5): A solution
of [Pd(H)(Cl)L2] (0.1 mmol) in 1 mL of [D8]THF was treated with
one equivalent of anhydrous SnCl2 at 183 K for 2 h, and the 1H,
31P and 119Sn NMR spectra were recorded; the spectra indicated
the presence of a mixture of [Pd(H)(SnCl3)L2] and [Pd(H)(Cl)L2]
with relative intensities 1/4 = 20:80 and 2/5 = 75:25.
[Pd(H)(SnCl3)(PPh3)2] (4): 1H NMR (400.13 MHz, 183 K): δ =
–6.90 ppm (2J1H,119 = 944 Hz). 31P{1H} NMR (161.98 MHz,
Sn
183 K): δ = 33.80 ppm.
[Pd(H)(SnCl3)(PCy3)2] (5): 1H NMR (400.13 MHz, 183 K): δ =
–8.50 ppm. 31P{1H} NMR (161.98 MHz, 183 K): δ = 52.3 ppm
(2J
= 138.1 Hz). 1H-119Sn HMQC NMR (400.13 MHz,
31P,119Sn
All the chemical products were purchased from Aldrich Chemical
Co., except for the following complexes, which were prepared by
the methods reported in the literature: [PdCl2(PhCN)2],[15] cis-
149.21 MHz, 183 K): δ = 154 ppm (2J1H,119 = 1760 Hz).
Sn
Synthesis of [Pd(H)(SnBu3)(dCypb)] (8): A solution of [Pd(PCy3)2]
(0.2 mmol) in 5 mL of toluene was treated with 0.2 mmol of 1,4-
bis(dicyclohexylphosphanyl)butane at room temperature. After 1 h,
one equivalent of tri(n-butyl)tin hydride was added and the solution
was stirred for 1 h. Then, the solvent was removed under reduced
pressure and the remaining solid with 75% yield was dissolved in
[PdCl2(dppb)],[12,15]
[Pt(H)(SnBu3)(PPh3)2]
cis-[PdCl2(dCypb)],[12,15]
(6),[18] cis-[PtCl2(PPh3)2],[22]
trans-
trans-
[Pt(H)(SnCl3)(PPh3)2] (17),[22] trans-[PdCl2(PPh3)2],[14] trans-
[PdCl2(PCy3)2],[12,32] [Pd(PPh3)n],[14] [Pd(PCy3)2].[32] 12CO and 13CO
(99%) were purchased from Air Liquide.
C7D8 for characterisation by NMR spectroscopy. 1H NMR
Catalytic Tests: A mixture of triphenylphosphane (0.4 mmol) and
tin() chloride (0.5 mmol) was introduced into a 150 mL stainless
steel autoclave with magnetic stirring. A nitrogen-saturated mixture
of palladium complex [chlorobis(triphenylphosphanyl)palladi-
um() hydride or dichlorobis(triphenylphosphanyl)palladium
(0.2 mmol)] and isopulegol (10 mmol) in toluene (10 mL) was in-
troduced into the evacuated autoclave by aspiration. It was heated
(40–60°C) under pressure (10–30 bar) of carbon monoxide. After
16 h, the autoclave was cooled and then slowly depressurized. The
obtained solution was analysed by gas chromatography.
2
(400.13 MHz, 213 K): δ = –3.84 ppm (2J1H,31 = 8.4, J1H,31
=
Pcis
Ptrans
2
165.9, J1H,119
=
110 Hz). 1H-119Sn {31P} HMQC NMR
Sn
(400.13 MHz, 149.22 MHz, 253 K): δ = 7.50 ppm. 31P{1H} NMR
2
(161.99 MHz, 233 K): δ = 27.36 ppm (31PA, J
= 1402 Hz),
31PA,119Sn
2
43.96 (31PB, J
Ͻ 20 Hz).
31PB,119Sn
Identification of Neutral and Cationic Complexes: A similar pro-
cedure to the preceding one was adopted. solution of
A
[Pd(PCy3)2] (0.1 mmol) in 2 mL of [D8]toluene was treated with
0.1 mmol of ligand L (L = dCype, dppe, dppp, dCypb, dppb, dpph,
dppf) at room temperature. After 1 h, one equivalent of HX (HX
= HSnBu3, CF3COOH, HBF4, TolSO3H) was added and the solu-
tion was stirred for 1 h. The solution was filtered and transferred
to a 5-mm NMR tube for NMR measurements. Only the most
relevant shifts are given below. In addition, after removal of the
solvent, the resulting solids were tested in cyclocarbonylation reac-
tion.
Synthesis of [Pd(H)(Cl)L2] (L = PPh3 1; PCy3 2): A 100 mL ben-
zene solution of [PdCl2L2] (0.57 mmol) and HSiPh3 (11.44 mmol)
was heated at 70–80°C for 2 h. The resultant red solution was con-
centrated to ca. 30 mL, and addition of hexane afforded a powder
of trans-[Pd(H)(Cl)L2] which was dissolved in benzene and precipi-
tated with hexane three times; the final product was white and was
isolated in 40% yield.
[Pd(H)(SnBu3)(PCy3)2] (6): 1H NMR: δ = –14.5 ppm (2J1H,31P = 5.5,
Alternative Method for the Synthesis of 2: A pale-green solution of
[Pd(PCy3)2] (1 mmol) in 10 mL of toluene was slowly treated with
one equivalent of 2  HCl in diethyl ether solution at room tem-
perature. The resultant pale-yellow solution was evaporated under
reduced pressure. The obtained solid was washed three times with
(2J1H,119 = 2494 Hz). 31P NMR: δ = 48.30 ppm.
Sn
[Pd(H)(SnBu3)(dCype)] (7): 1H NMR: δ = –2.67 ppm (2J1H,119
=
Sn
2
310, J1H,31
= 177 Hz). 31P NMR: δ = 25.10 ppm, 45.20
Ptrans
(2J1H,31
= 200 Hz), 40.70.
Ptrans
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D. H. Nguyen, G. Laurenczy, M. Urrutigoïty, P. Kalck
FULL PAPER
[Pd(H)(SnBu3)(dpph)] (9): 1H NMR: δ = –4.01 ppm (exchange phe-
nomena at room temperature).
anhydrous SnCl2 at 183 K. After 2 h, this solution was transferred
to a sapphire tube and the solution was charged with 3 bar of 13CO
at the same temperature. The 1H, 31P and 13C spectra indicated the
presence of [Pd(H)(13CO)(SnCl3)(PCy3)2] (21; 65%) and
[Pd(H)(13CO)(Cl)(PCy3)2] (22; 35%).
[Pd(H)(PCy3)(dCype)]+(CF3COO)– (12a): 1H NMR: δ = –6.29 ppm
(2J1H,31 = 7, 13, 179 Hz). 31P NMR: δ = 86.95, 65.43, 49.68 ppm
P
(2J
= 18, 311 and 18 Hz).
31P,31
P
[Pd(H)(13CO)(SnCl3)(PCy3)2] (21): 1H NMR: δ = –8.70 ppm. 31P
[Pd(H)(PCy3)(dCype)]+(BF4)– (12b): 1H NMR: δ = –6.15 ppm. (ex-
change phenomena at room temperature).
NMR: δ = 50.80 ppm (2J
= 148 Hz). 13C NMR: δ =
13C,119Sn
= 144.6 Hz).
31P,119Sn
2
2
13C,31
P
232.4 ppm (CO; J
= 3.7, J
[Pd(H)(PCy3)(dCype)]+(TolSO3)– (12c): 1H NMR: δ = –6.12 ppm
[Pd(H)(13CO)(Cl)(PCy3)2] (22): 1H NMR: δ = –14.50 ppm. 13C
NMR: δ = 194.6 ppm (CO).
(2J1H,31 = 9, 12 and 177 Hz).
P
1
[Pd(H)(PCy3)(dppe)]+(CF3COO)– (13a): H NMR: δ = –5.58 ppm
Observation of Mixtures of [Pd(Alkyl)(CO)(SnCl3)(PPh3)2] (23) and
(2J1H,31 = 20, 196 Hz.
P
[Pd(Alkyl)(CO)(Cl)(PPh3)2] (24):
A solution of [Pd(H)(Cl)L2]
1
[Pd(H)(PCy3)(dppp)]+(CF3COO)– (14a): H NMR: δ = –6.62 ppm
(0.1 mmol) in 2 mL of [D8]THF was treated with one equivalent of
anhydrous SnCl2 at 183 K. After 2 h, this solution was transferred
to a sapphire tube and the solution was charged with four equiva-
lents of dihydromyrcene and 3 bar of 13CO at the same tempera-
ture. Multinuclear NMR analyses indicated the formation of a mix-
ture of 23 and 24, with a 23/24 ratio of 70:30. 23: 13C NMR: δ =
(2J1H,31P = 28, 189 Hz). 31P NMR: δ = 51.18, 9.16, 3.58 ppm 2J
31P,31
P
= 306, 48 and 22 Hz).
[Pd(H)(PCy3)(dppp)]+(BF4)– (14b): 1H NMR:
δ = –6.90 ppm
(2J1H,31P = 12, 75 Hz). 31P NMR: δ = 49.87, 7.66, 3.97 ppm (2J
31P,31
P
= 315, 51 and 21 Hz).
232.6 ppm (2J
= 4.5 Hz). 24: 13C NMR: δ = 194.7 ppm
13C,31
P
1
[Pd(H)(PCy3)(dppb)]+(CF3COO)– (15a): H NMR: δ = –6.12 ppm
(2J
= 3.2 Hz).
13C,31
P
(2J1H,31 = 13, 185 Hz).
P
Characterisation of Compound (5R)-C: MS: m/z (%) = 95( 100), 81
(62), 96(41), 122 (30), 183 (18) [M + 1], 138 (7). 1H NMR
(250.13 MHz, CDCl3): δ = 3.75 (ddd, J = 4.2, 10.5 and 10.5 Hz, 1
H, H1), 2.55 (dd, J = 6.8 and 18 Hz, 1 H, H4ax), 1.96 (dd, J = 9.4
and 17.8 Hz, 1 H, H4eq), 1.8 (m, 1 H, H10eq), 1.84 (m, 1 H, H7eq),
1.54 (m, 1 H, H8ax), 1.45 (m, 1 H, H5), 1.34 (m, 1 H, H9), 1.10
(m, 1 H, H7ax), 0.92 (m, 1 H, H8eq), 0.82 (d, J = 6.2 Hz, 3 H, CH3
1
[Pd(H)(PCy3)(dppf)]+(CF3COO)– (16a): H NMR: δ = –7.87 ppm
(2J1H,31 = 10, 179 Hz). 31P NMR: δ = 52.57, 24.94, 20.15 ppm
P
(2J
= 337, 27, 31 Hz). FAB+/MS: m/z = 941.3; mode FAB–/
31P,31
P
MS: m/z = 113.1.
Synthesis of
[(CH3)2C=CH(CH2)2CH(CH3)CH2CH2C(O)-
PtCl(PPh3)2] (18): Complexes 18 and 19 were prepared according
to the methods previously reported by Gómez et al.[27] A mixture
of trans-[Pt(H)(Cl)(PPh3)2] (0.473 g, 0.5 mmol), PPh3 (0.118 g,
0.45 mmol), dihydromyrcene (6.90 g, 50.0 mmol) and ethanol
(25 mL) was charged in an autoclave. The autoclave was purged of
air under reduced pressure and was then pressurised with 50 bar of
CO, heated to 100°C and stirred for 4 h. Then, the reactor was
cooled to room temperature and depressurised. The resulting green
solution was cooled to –30°C to give 18 as a white solid, which
was washed three times with cool ethanol, diethyl ether and finally
dried under vacuo. Yield: 55%.
11), 0.80 (m, 1 H, H6), 0.77 (d, J = 6.5 Hz, 3 H, CH3 12) ppm. 13
C
NMR (62.9 MHz, CDCl3): δ = 171.3 (C3), 82.3 (C1), 44.6 (C6),
40.4 (C10), 38.0 (C4), 33.7 (C8), 31.7 (C5), 30.9 (C9), 27.7 (C7),
21.8 (C12), 19.0 (C11) ppm.
Characterisation of Compound (5S)-C: MS: m/z (%) = 96 (100), 81
1
(85), 122 (31), 183 (12) [M + 1], 138 (6). H NMR (250.13 MHz,
CDCl3): δ = 4.13 (ddd, J = 4.3, 11, and 11 Hz, 1 H, H1), 2.69 (dd,
J = 6.6 and 17.6 Hz, 1 H, H4ax), 2.41 (dd, J = 2.8 and 17.6 Hz, 1
H, H4eq), 2.13 (ddd, J = 1.6, 12, and 12 Hz, 1 H, H10eq), 2.07 (m,
1 H, H5), 1.73 (m, 2 H, H8ax and H8eq), 1.66 (m, 1 H, H7eq), 1.60
(m, 1 H, H6), 1.48 (m, 1 H, H9), 1.27 (ddd, J = 3.5, 12.9, and
12.9 Hz, 1 H, H7ax), 1.16 (ddd, J = 3.0, 12, and 12 Hz, 1 H, H10ax),
1.00 (d, J = 7.2 Hz, 3 H, CH3 11), 0.97 (d, J = 6.6 Hz, 3 H, CH3
12). 13C NMR (62.9 MHz, CDCl3): δ = 171.2 (C3), 77.8 (C1), 41.7
(C6), 40.9 (C10), 38.9 (C4), 33.9 (C8), 30.8 (C9), 28.8 (C5), 27.2
(C7), 21.7 (C12), 14.7 (C11) ppm. C11H18O2 (182.12): calcd. C 71.5,
H 10, O 17.6; found C 71.8, H 9.8, O 18.3.
18: 31P{1H} NMR (161.98 MHz, CDCl3, 298 K): δ = 23.2 ppm
(2J
= 3510.7 Hz). 195Pt{1H} NMR (85.68 MHz, CDCl3,
31P,195Pt
298 K): δ = –3933 ppm. 13C{1H}bb+{31P} NMR (100.63 MHz,
CDCl3, 298 K): δ = 219.4 (2J P = 6, 1J
Pt = 457.8 Hz), 135.4,
13C,31
13C,195
134.5, 131.3, 131.3, 130.8, 125.4, 57.1, 37.4, 32.1, 31.4, 26.2, 25.9,
19.5, 15.7 ppm.
Synthesis
Pt(SnCl3)(PPh3)2] (19):
of
[(CH3)2C=CH(CH2)2CH(CH3)CH2CH2C(O)-
mixture of complex 18 (0.0922 g,
Characterisation of Dehydro-C: MS: m/z (%) = 181 (14) [M + 1],
138 (12), 123 (40), 109 (13), 95 (66), 81 (100), 67 (69), 55 (30), 41
(55), 29 (13).
A
0.10 mmol), SnCl2 (0.019 g, 0.1 mmol) and CHCl3 (2 mL) was
placed in a Schlenk tube and stirred for 15 min at room tempera-
ture. The solution was filtered and multinuclear NMR analysis was
carried out. After removal of the solvent 19 was obtained as a
yellow compound in 50% yield. 31P-119Pt HMQCND {1H}bb
NMR (161.98 MHz, 85.63 MHz, CDCl3, 233 K) and 31P{1H}
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31P,119Sn
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195Pt HMQCND {1H}bb NMR, 195Pt{1H,31P} NMR (85.68 MHz,
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–4466 ppm (1J
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195Pt,31
P
134.2, 132.5, 132.2, 129.9, 125.1, 37.3, 32.0, 30.5, 26.6, 25.7, 18.5,
15.1 ppm.
Observation of Mixtures of [Pd(H)(13CO)(SnCl3)(PCy3)2] (21) and
[Pd(H)(13CO)(Cl)(PCy3)2] (22):
A
solution of [Pd(H)(Cl)L2]
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4224
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www.eurjic.org
Eur. J. Inorg. Chem. 2005, 4215–4225

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Received: February 16, 2005
Published Online: September 5, 2005
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www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4225