Hydroformylation of myrcene: Metal and ligand effects in the hydroformylation of conjugated dienes

Article abstract of DOI:10.1039/b207947j

The hydroformylation of myrcene catalyzed by Rh and Pt/Sn catalysts containing different P-donor ligands leads to the formation of a number of mono- and dialdehydes. Nine major products of the reaction have been characterized, showing that they arise from the n-alkyl and η³-allyl intermediates, formed through the reaction of the metal catalysts with the less substituted C=C bond of the substrate. Thus, 4-methylene-8-methyl-7-nonenal is the major aldehyde formed with Pt/Sn catalysts, regardless of the P-donor ligand used. This aldehyde is also the main product of the reaction catalyzed by the Rh/xantphos system (xantphos = 9,9-dimethyl-4,6-bis(diphenylphosphino)xantene). However, with ligands such as bisbi (bisbi = 2,2′-bis((diphenylphosphino)methyl)-1,1′-biphenyl), also with bite angles around 120°, but with more flexible backbones than xantphos, rhodium catalysts yield mainly cis- and trans-3-ethylidene-7-methyl-6-octenal. These two aldehydes are also formed in the reactions catalyzed by Rh and P-donor monodentate ligands or the bidentante ones with bite angles around 90° (dppe, dppp). For the last type of ligands, an increase in the flexibility of the backbone reduces the selectivity for the β,γ-unsaturated aldehydes.

Full text of DOI:10.1039/b207947j

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Hydroformylation of myrcene: metal and ligand effects in the
hydroformylation of conjugated dienes
a
Cl a´ udia M. Foca, Humberto J. V. Barros, Eduardo N. dos Santos, Elena V. Gusevskaya* and
b
b
b
a
J. Carles Bay o´ n*
a
Departament de Qu ı´ mica, Universitat Aut o` noma de Barcelona, Bellaterra, 08193 Barcelona,
Spain. E-mail: joancarles.bayon@uab.es
Departamento de Qu ı´ mica, Universidade Federal de Minas Gerais, 31270-901, Belo Horizonte,
MG, Brazil. E-mail: elena@dedalus.lcc.ufmg.br
b
Received (in London, UK) 14th August 2002, Accepted 19th December 2002
First published as an Advance Article on the web 3rd February 2003
The hydroformylation of myrcene catalyzed by Rh and Pt/Sn catalysts containing different P-donor ligands
leads to the formation of a number of mono- and dialdehydes. Nine major products of the reaction have been
3
characterized, showing that they arise from the n-alkyl and Z -allyl intermediates, formed through the reaction
of the metal catalysts with the less substituted C=C bond of the substrate. Thus, 4-methylene-8-methyl-7-
nonenal is the major aldehyde formed with Pt/Sn catalysts, regardless of the P-donor ligand used. This
aldehyde is also the main product of the reaction catalyzed by the Rh/xantphos system (xantphos ¼ 9,9-
0
dimethyl-4,6-bis(diphenylphosphino)xantene). However, with ligands such as bisbi (bisbi ¼ 2,2 -
0
ꢀ
bis((diphenylphosphino)methyl)-1,1 -biphenyl), also with bite angles around 120 , but with more flexible
backbones than xantphos, rhodium catalysts yield mainly cis- and trans-3-ethylidene-7-methyl-6-octenal. These
two aldehydes are also formed in the reactions catalyzed by Rh and P-donor monodentate ligands or the
ꢀ
bidentante ones with bite angles around 90 (dppe, dppp). For the last type of ligands, an increase in the
flexibility of the backbone reduces the selectivity for the b,g-unsaturated aldehydes.
Introduction
Hydroformylation of naturally occurring olefins represents a
versatile method for the production of aldehydes, which are
1
difficult to obtain by conventional synthetic pathways. Ter-
penes are an important family of natural products extensively
2
used in the perfume industry. Since aldehydes often show
3
interesting organoleptic properties, the hydroformylation of
terpenes has been quite extensively investigated and a consider-
able amount of information in this field is nowadays available,
4
,5
both in patents and in the open literature.
Myrcene 1 is a very abundant acyclic terpene available from
hops and other sources. It is used in the synthesis of a variety
of commercial products. Judging from the structure, the
6
hydroformylation of myrcene could result in a complex mix-
ture of saturated and unsaturated C11-monoaldehydes and
C
12-dialdehydes, arising from the hydroformylation (and,
eventually, from the isomerization and hydrogenation) of both
the 2-substituted butadiene fragment and trisubstituted double
bond. Probably for this reason, there has previously been only
7
one report on the hydroformylation of myrcene. In this work,
3
a Rh/PPh catalyst was used in a single experiment, and 3-
ethyl-7-methyl-6-octenal 9 (see Scheme 1), formally resulting
from the hydroformylation of the disubstituted double bond
and the hydrogenation of the monosubstituted double bond,
was obtained in a 40% selectivity, along with many secondary
products. According to this result and taking into account the
well-known reactivity of different substituted olefins in hydro-
formylation, it is expected that most of the products of the
hydroformylation of myrcene should arise from the addition
Scheme 1
as 1,3-butadiene, isoprene and 1,3-pentadiene. These sub-
strates are more reluctant to be hydroformylated than
mono-olefins. A recent study on the competitive hydrofor-
mylation of conjugated dienes and olefins shows that trace
of CO and H to the conjugated diene fragment.
2
Several reports in the literature deal with the hydrofor-
mylation of conjugated dienes, mostly simple ones, such
quantities of dienes compete against an excess of olefins
for RhH(CO)
3
4
, forming Z -allyl complexes, while their
DOI: 10.1039/b207947j
New J. Chem., 2003, 27, 533–539
533
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hydroformylation usually occurs at a much slower rate than
that of simple olefins.
8
The homogeneous hydroformylation of conjugated dienes
was firstly reported by Natta and Adkins. Later, other
9
10
1
1
groups extensively investigated this reaction. In these studies,
a marked tendency for the formation of saturated monoalde-
hydes was observed. Because of the rather severe conditions
used in these reactions, selectivities for any specific product
were generally quite low. Only 1,3-butadiene was converted
to pentanal with over 90% selectivity using a Rh/dppe catalyst
1
1e
(
dppe ¼ 1,2-bis(diphenylphosphino)ethane). Some rhodium
catalytic systems have been also developed to produce b,g-
unsaturated aldehydes (which are attractive synthetic inter-
mediates) from various conjugated dienes. High chemo- and
regioselectivities for these products (80–96%) were attained
with a Rh vapour-mesitylene cocondensate/dppe system.
The hydroformylation of butadiene with a Rh/bubiphos
Chart 1
1
2
0
0
0
0
0
(
bubiphos ¼ bis(1,1 -biphenyl-2,2 -diyl)(1,1 -biphenyl-3,3 ,5,5 -tetra-
products resulting from the catalyst coordination to the less
hindered double bond, Scheme 2. In the subsequent migration
step, either n-alkyl (1b) or iso-alkyl (1c) intermediates are
formed. The first evolves to linear aldehyde 2, which can
2
further react with CO and H to selectively produce dialdehyde
3. No aldehydes resulting from the Markovnikov addition of
0
tert-butyl-2,2 diyl)diphosphite) catalyst was disclosed to yield
1
3
a 25% selectivity for 1,6-hexanedial. More recently, Ohgo-
mori et al. reported that 1,6-hexanedial and 4-pentenal can
be obtained in up to a 35% combined yield via the hydroformy-
lation of butadiene using Rh catalysts containing bidentate
phosphines with natural bite angles within the ‘‘intermediate
the metal hydride to the methylenic double bond were
observed. Instead, under certain reaction conditions (i.e., with
Pt/Sn catalysts), the methylenic double bond undergoes iso-
merization or hydrogenation, rendering products 4 and 5 or
6, respectively. Aldehyde 6 could also arise from the hydroge-
nation of the a,b-unsaturated aldehyde produced by further
isomerization of 5. However, this a,b-unsaturated aldehyde
was not detected in the reaction mixture.
ꢀ
14
region’’ (100–110 ). According to these authors, diphosphine
ligands coordinating the metal as apical-equatorial chelates
ꢀ
(
dinated at diequatorial positions, which favors the formation
ligands with bite angles near 90 ) allow butadiene to be coor-
3
of Z -allyl complexes leading to b,g-unsaturated aldehyde,
i.e., 3-pentenal. On the other hand, diphosphine ligands with
ꢀ
diequatorial coordination (bite angles near 120 ) induce an
apical–equatorial coordination of butadiene, which through
3
Z -Allyl intermediate 1d is formed by the rearrangement of
4
Z -butadiene rhodium complexes produces the g,d-unsatu-
iso-alkyl intermediate 1c. Since the aldehyde derived from the
iso-alkyl intermediate was not detected in reaction mixtures, it
should be inferred that this rearrangement is faster than the
CO insertion. This is consistent with the observation that Rh
rated aldehyde, i.e., 4-pentenal, and then dialdehyde. Good
to excellent regio- and enantioselectivities were obtained with
a Rh/binaphos catalyst (binaphos ¼ (2-diphenylphosphino-
0
0
0
0
1
,1 -dinaphthalen-2,2 -diyl)(1,1 -dinaphthalene-2,2 -diyl)phos-
catalyzed deuteroformylation of 1,3-butadiene has resulted in
the formation of 1,5-d -3-pentenal. Furthermore, it has been
1
5
12
phite)) in the hydroformylation of some conjugated dienes.
2
3
3
In this work we describe a systematic study on the hydrofor-
mylation of myrcene catalyzed by different Rh and Pt/Sn cat-
alysts, aiming to obtain new aldehydes of a potential interest
for the fine chemicals industry. The effect of the metal and
ligand nature on the reaction selectivity is analyzed.
3 2
found that [Rh(Z -allyl)(CO)(PPh ) ] complexes (Z -allyl
represents a substituted allyl ligand) showing a severely dis-
torted trigonal bipyramidal geometry are stable enough to be
1
characterized by X-ray diffraction. Aldehydes 7a and 7b seem
6
1
to be generated through the CO insertion into Z -allyl inter-
3
mediate 1e, instead of the direct carbonylation of Z -allyl inter-
3
mediate 1d. Z -Allyl rhodium complexes are known to be
rather resistant to CO insertion, but they can readily form
1
11e,15b
3
Z -allyl rhodium species.
allyl and acyl rhodium complexes have been recently observed
The formation of Z -allyl, s-
Results and discussion
The hydroformylation of myrcene was studied with the follow-
ing catalytic systems: Rh and monodentate P-donor ligands,
namely PPh , tris(o-tolyl)phosphine, tris(o-trifluoromethyl-
in an HPIR study on the hydroformylation of some conju-
gated dienes catalyzed by RhH(CO)4 .
The trans and cis isomers of 7 are obtained in a similar
proportion. The isomerization of these primary products pro-
duces a,b-unsaturated aldehyde 8, which is much more suscep-
tible to hydrogenation than to hydroformylation and readily
8
3
phenyl)phosphine,
tris(o-tert-butylphenyl)phosphite P(OPh*) ; Rh and bidentate
tris(p-trifluoromethylphenyl)phosphine,
3
P-donor ligands, namely dppe, 1,3-bis(diphenylphosphino)-
propane (dppp), 1,4-bis(diphenylphosphino)butane (dppb),
1
3
,2-bis[(diphenylphosphino)methyl]benzene (dppmb), (R,R)-2,
-o-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)-
butane (diop), bubiphos, 9,9-dimethyl-4,6-bis(diphenylpho-
0
sphino)xantene (xantphos), 2,2 -bis((diphenylphosphino)-
0
methyl)-1,1 -biphenyl (bisbi); Pt/SnCl
0
2
and PPh
3
or
diphosphines dppe, dppp, dppb and 2,2 -bis[(diphenylphosphi-
0
no)methyl]-1,1 -binaphtyl (naphos). The structures of some of
these ligands are depicted in Chart 1.
As expected, several concomitant transformations occur
under reaction conditions resulting in a complex mixture of
mono- and dialdehydes, as well as the products of the myrcene
hydrogenation. The reaction network and identified aldehydes
2–9 are represented in Scheme 1, with aldehydes 2–8 being new
compounds. In general, major hydroformylation products are
aldehydes 2, 7a and 7b. These aldehydes are primary reaction
Scheme 2
5
34
New J. Chem., 2003, 27, 533–539

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3
transformed into partially saturated aldehyde 9. The latter is
the major product found in the previous study on the hydro-
ligand coordination disfavors the formation of the Z -allyl
intermediate.
7
formylation of myrcene. However, under the conditions used
Interestingly, other ligands, such as bisbi and bubiphos,
which also coordinate the metal preferentially in equatorial–
equatorial positions (bite angles around 120 ), show very
low selectivity for aldehyde 2. As a matter of fact, in both
cases, the S(b/l) parameter is greater than 3, while it is only
0.5 for the xantphos catalyst. This is an unexpected result,
in the present work, both aldehydes 8 and 9 are always minor
components of the reaction mixture. Aldehyde 8, useful as
an intermediate for the synthesis of biologically active
ꢀ
20
1
7
compounds, can be quantitatively obtained from the mixture
of aldehydes 7 in the presence of the [Rh
2
(m-OMe)
, toluene, 6 h). The hydroformylation
2
(cod)
2
]/
ꢀ
ꢀ
PPh
3
catalyst (70 C, N
and isomerization of myrcene described here seems to be a
2
since the three ligands with bite angles near 120 are known
to yield similarly high ratios between linear and branched pro-
2
ducts in the hydroformylation of 1-alkenes. Furthermore,
1
more convenient synthetic path for aldehyde 8 than that
originally reported. Aldehyde 8 can be converted into aldehyde
ꢀ
catalysts containing diop and dppmb, bite angles near 100 ,
ꢀ
9
by hydrogenation (70 C, H
2
, 15 bar, toluene) in the pre-
produce an S(b/l) parameter of around 1. Thus, although
these two ligands show lower selectivity for linear aldehydes
than bubiphos or bisbi in the case of 1-alkenes, in the hydro-
formylation of myrcene, they render a higher ratio of the pro-
ducts arising from the n-alkyl intermediate than two large bite
angle ligands. These results indicate that, for the ligands coor-
dinating the metal in diequatorial positions in catalytically
active species, a flexible backbone (such as that of bisbi or
3
sence of the Rh/PPh catalyst mentioned above. However,
both the isomerization and hydrogenation of aldehydes 7 are
nearly suppressed under a CO atmosphere. This is the rea-
son for the low content of 8 and 9 in the hydroformylation
products.
The results on myrcene hydroformylation catalyzed by dif-
ferent rhodium and platinum/tin species are presented in
Tables 1–5. Most of the rhodium systems favor the formation
of 7a and 7b and then small amounts of 8 and 9, via the forma-
3
bubiphos) facilitates the formation of the Z -allyl intermediate,
while a rigid backbone disfavors this reaction path. Interest-
ingly, the opposite trend is observed for the ligands coordinat-
ing rhodium in axial–equatorial positions. It can be speculated
3
tion of the Z -allyl rhodium intermediate. On the contrary,
platinum catalysts give rise to aldehyde 2 and then to its deri-
vatives 3–6 through the n-alkyl intermediate.
ꢀ
that, for the ligands with bite angles near 120 , the flexibility of
the backbone is required to produce a low energy path, prob-
2
ably through a Berry or Meakin rearrangement, to convert
2
Rhodium catalysts
3
1
the Z -allyl intermediate into the Z -allyl complex, where the
CO insertion can take place. For instance, a square pyramidal
intermediate, where the ligand is coordinating in two trans
basal positions, should be easily accessible for the flexible
ligand, such as bisbi, as evidenced by the structure of [Fe(bis-
Table 1 collects the data on the hydroformylation of 1 cata-
lyzed by a series of Rh catalysts under the same reaction con-
ditions. The observed selectivity dramatically depends on the
1
8
ꢀ
ligand used. Thus, diphosphines with bite angle near 90
2
3
and very low ring flexibility, such as dppe, show a high selec-
tivity for aldehydes 7a and 7b, with small amounts of their iso-
merization and hydrogenation products 8 and 9 also being
formed. The molar ratio between the total amounts of pro-
bi)(CO) ], which adopts this geometry.
3
It seems to be expected that rhodium catalysts with PPh
ꢀ
3
(cone angle of 145 ) and similar phosphines, which can be con-
2
sidered as equatorial–equatorial ligands with complete flex-
4
3
3
ducts 7–9, arising from Z -allyl intermediate 1d, and those aris-
ibility, yield mainly the products derived from the Z -allyl
intermediate in high selectivity. Finally, monodentate ligands
ing from linear s-alkyl intermediate 1b, i.e., products 2–6, is
indicated as S(b/l) in Tables 1–4. This parameter reaches a
value close to eight for the dppe catalyst, indicating that
ligands coordinating only as axial–equatorial chelates favor
with high cone angles, such as tris(o-tert-butylphenyl)pho-
ꢀ
sphite (cone angle of 175 ), tris(o-trifluoromethylphenyl)pho-
ꢀ
sphine (cone angle of 231 ) and tris(o-tolyl)phosphine (cone
ꢀ
3
the formation of the Z -allyl rhodium intermediate. An
increase in the flexibility of the backbone of the ligands with
angle of 194 ), as well as the [RhH(CO) ] catalyst, show low
or no activity in myrcene hydroformylation, under the reaction
conditions of Table 1.
4
ꢀ
bite angle angles around 90 (i.e., going from dppe to dppb),
significantly decreases the S(b/l) parameter. On the other
We have further investigated the effect of the reaction condi-
tions on the selectivity of rhodium catalysts with three repre-
sentative ligands, with respect to their behavior in this
reaction, namely xantphos, dppe and PPh . Results are
3
summarized in Tables 2, 3 and 4, respectively. For the Rh/
ꢀ
hand, ligands with a bite angle near 120 and with a rigid back-
1
9
bone, such as xantphos, show preferential selectivities for
aldehyde 2 and for the other products originating from n-alkyl
intermediate 1b. This suggests that the equatorial–equatorial
a
Table 1 Hydroformylation of myrcene (1) catalyzed by Rh/P-donor ligands
b
c
d
e
f
g
Ligand
L/Rh
Con.(%) (t/h)
2 (%)
3 (%)
7 (%)
Ot. (%)
H. (%)
S(b/l)
dppe
2
2
2
2
2
2
2
2
6
6
3
94(24)
43(24)
75(24)
62(24)
75(24)
99(24)
99(17)
64(24)
99(24)
16(72)
29(24)
9
12
31
48
49
17
2
1
0
73
78
63
48
47
77
60
28
73
65
54
14
6
3
4
7.8
6.2
1.9
1.0
1.0
4.3
3.2
0.5
4.4
6.2
5.0
dppp
dppb
dppmb
2
2
2
1
< 1
1
3
(R, R)-diop
bisbi
0
3
2
3
1
bubiphos
xantphos
20
3
8
5
62
6
3
4
PPh
P(OPh*)
3
10
0
10
5
1
3
11
11
19
30
P(p-CF
3
C
6
H
4
)
3
0
5
a
ꢂ2
ꢀ
b
Reaction conditions: 3.75 ꢁ 10 mmol of Rh as [Rh
2
(m-OMe)
2
(cod)
2
] in 7.5 ml of toluene; [1]/[Rh] ¼ 200; [CO]/[H
2
] ¼ 1; 45 bar; 70 C. See
c
Chart 1. [Ligand]/[Rh]. Conversion determined by gas chromatography for the time indicated in parentheses. Other aldehydes, including 4, 5,
d
e
f
, 8 and 9. Products of hydrogenation of 1. Ratio between the products arising from allylic intermediate 1d and n-alkyl intermediate 1b:
g
6
(
7 + 8 + 9)/(2 + 3 + 4 + 5 + 6) (see text).
New J. Chem., 2003, 27, 533–539
535

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a
Table 2 Hydroformylation of myrcene (1) catalyzed by Rh/xantphos
ꢀ
b
c
d
e
P/bar
T/ C
Con. (%) (t/h)
2 (%)
3 (%)
7 (%)
Ot. (%)
H. (%)
S(b/l)
45
45
45
30
30
60
60
50
70
17(40)
64(24)
100(24)
58(65)
95(24)
81(24)
91(20)
64
62
11
58
44
63
8
0
3
28
28
13
33
39
27
17
0
3
8
4
0.4
0.5
1.1
0.6
0.8
0.4
0.8
f
100
50
8
65
3
1
0
5
2
8
70
70
5
78
4
4
28
f
100
46
< 1
a
b
Reaction conditions: 3.75 ꢁ 10ꢂ2 mmol of Rh as [Rh
2
(m-OMe)
2
(cod)
2
] in 7.5 ml of toluene; [xantphos]/[Rh] ¼ 2; [1]/[Rh] ¼ 200; [CO]/[H ] ¼ 1.
2
c
Conversion determined by gas chromatography for the time indicated in parentheses. Other aldehydes, including 4, 5, 6, 8 and 9. Products of
d
e
hydrogenation of 1. Ratio between the products arising from allylic intermediate 1d and n-alkyl intermediate 1b: (7 + 8 + 9)/(2 + 3 + 4 + 5 + 6)
f
see text). Mainly unidentified dialdehydes along with 6–10% of 9.
(
2
6
xantphos catalyst, little effect of pressure on the reaction selec-
tivity was observed at pressures above 45 bar. However, on
raising the temperature from 70 to 100 C, the selectivity for
ligand. The strong trans-activation effect of the tin ligand
favors the required ligand-exchange reactions.
ꢀ
The hydroformylation of myrcene in all platinum/tin sys-
tems studied is accompanied by the hydrogenation and, to a
lesser extent, dimerization of the substrate. The product selec-
tivity is strongly influenced by the nature of phosphorous
ligand, the phosphine/Pt molar ratio and reaction conditions.
The best selectivity was obtained with the PPh ligand. For
3
instance, at 80 C, 45 bar and PPh
for aldehyde products reaches 87%. From these aldehydes,
85% corresponds to aldehyde 2. Small amounts of aldehydes
4, 5 and 6, resulting from the isomerization and hydrogenation
of 2, were also observed. The structures of minor aldehydes 4,5
aldehydes 2 and 3 reduces because of the formation of several
unidentified products. This effect seems to be related to the
increase in the thermal flexibility of xantphos. For the Rh/
dppe catalyst, the S(b/l) ratio also increases with temperature,
with the yield of the products originating from the s-alkyl
ꢀ
ꢀ
intermediate being significantly lower at 100 C. Interestingly,
the Rh/PPh catalyst shows the opposite effect, since the tem-
3
/Pt ¼ 4, the selectivity
3
perature increase clearly reduces the proportion of aldehydes 7
with respect to aldehydes 2 and 3. It should be mentioned also
that at a higher P/Rh ratio (15 vs. 6), a marked increase in the
relative amounts of dialdehyde 3 at the expense of aldehydes 7
is observed, while the reaction becomes slower.
and 6 have been proposed based on GC/MS data and addi-
ꢀ
tionally confirmed by the isomerization (50 C, N
ꢀ
2
, toluene)
, 30 bar, toluene)
and hydrogenation (10% Pd/C, 50 C, H
2
ꢀ
of 2. On raising the temperature to 100 C, the rate increases
but the chemoselectivity drops drastically due to the extensive
hydrogenation and dimerization of the substrate. Surprisingly,
the reaction rate and chemoselectivity virtually do not depend
on the pressure. Only a slight increase in the relative amounts
of minor aldehydes 4, 5 and 6 at the expense of aldehyde 2 is
Platinum/tin catalysts
The results on the hydroformylation of myrcene with Pt/SnCl
2
catalysts and different P-donor ligands are collected in Table 5.
The most distinctive feature of these catalytic systems is an
exceptionally high regioselectivity for aldehyde 2 and its deri-
vatives regardless of the P-donor used. Not even trace amounts
of b,g-unsaturated aldehydes 7 have been observed in platinum
observed. The best rates were observed at PPh
P/Pt ratio, the reaction occurs under relatively mild conditions
3
/Pt ¼ 2. At this
ꢀ
for Pt catalysts (45 bar, 70 C), although the selectivity is worse
than that at PPh /Pt ¼ 4.
catalyzed reactions. The steric bulk of both the phosphine
(
ꢂ
3
diphosphine) and SnCl3 ligands in the platinum complex
We have also tested the hydroformylation of myrcene with
should favor an anti-Markovnikov H addition, with the for-
mation of less sterically crowded straight-chain s-alkyl plati-
num intermediate 1b leading to aldehyde 2. Furthermore, the
2
Pt/SnCl in the presence of various diphosphines: dppe, dppp,
dppb and naphos. All these catalysts produce exclusively alde-
hyde 2 and its derivatives, but they render much lower rates
than that with PPh . The addition of diphosphines also
3
increases the amounts of hydrogenation products, which leads
to a drop in the aldehyde selectivity compared to the catalyst
3
formation of Z -allyl complexes 1d, which further give alde-
hydes 7, requires more coordination positions and seems to
be also sterically disfavored in Pt/Sn/phosphine systems.
In the absence of SnCl
ity in the hydroformylation of myrcene. A synergetic effect of
SnCl and Pt(II) on hydroformylation has been thoroughly
2
, platinum complexes show no activ-
3
with PPh .
2
2
5
investigated. A recent theoretical study proposes that the
ꢂ
Conclusions
most important effect of the [SnCl
3
]
ligand is to stabilize pen-
tacoordinated Pt(II) intermediates and facilitate the olefin
insertion due to weakening of the Pt–H bond trans to this
We have achieved a good control of the chemo- and regioselec-
tivity of the hydroformylation of myrcene 1, through the
a
Table 3 Hydroformylation of myrcene (1) catalyzed by Rh/dppe
ꢀ
b
c
d
e
P/bar
T/ C
Con. (%) (t/h)
2 (%)
3 (%)
7 (%)
Ot. (%)
H. (%)
S(b/l)
45
45
30
60
70
100
70
94(24)
96(9)
9
3
5
9
1
< 1
0
73
75
61
70
14
19
3
3
3
6
7.8
30.3
15.2
8.3
f
39(24)
83(24)
31
15
70
0
a
b
Reaction conditions: 3.75 ꢁ 10ꢂ2 mmol of Rh as [Rh
2
(m-OMe)
2
(cod)
2
] in 7.5 ml of toluene; [dppe]/[Rh] ¼ 2; [1]/[Rh] ¼ 200; [CO]/[H
2
] ¼ 1.
c
Conversion determined by gas chromatography for the time indicated in parentheses. Other aldehydes, including 4, 5, 6, 8 and 9. Products
d
e
of hydrogenation of 1. Ratio between the products arising from allylic intermediate 1d and n-alkyl intermediate 1b: (7 + 8 + 9)/(2 + 3 + 4 + 5 + 6)
f
see text). Mainly of 8 (17%) along with other monoaldehydes.
(
5
36
New J. Chem., 2003, 27, 533–539

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a
3
Table 4 Hydroformylation of myrcene (1) catalyzed by Rh/PPh
ꢀ
b
c
d
e
f
P/bar
T/ C
P/Rh
Con. (%) (t/h)
2 (%)
3 (%)
7 (%)
Ot. (%)
H. (%)
S(b/l)
45
45
45
30
60
45
50
70
6
6
91(24)
99(24)
99(24)
98(24)
97(24)
93(40)
13
6
0
10
14
5
83
73
42
78
76
51
3
10
1
1
6.5
4.4
g
100
70
6
5
38
21
2
2.7
6
3
12
16
12
10.2
10.7
1.5
70
70
6
15
2
5
37
21
0
0
a
b
ꢂ2
Reaction conditions: 3.75 ꢁ 10 mmol of Rh as [Rh
2
(m-OMe)
2
(cod)
2
] in 7.5 ml of toluene; [PPh
3
]/[Rh] ¼ 2; [1]/[Rh] ¼ 200; [CO]/[H
2
] ¼ 1.
c
d
[
3
PPh ]/[Rh]. Conversion determined by gas chromatography for the time indicated in parentheses. Other aldehydes, including 4, 5, 6, 8
e
and 9. Products of hydrogenation of 1. Ratio between the products arising from allylic intermediate 1d and n-alkyl intermediate 1b:
f
g
7 + 8 + 9)/(2 + 3 + 4 + 5 + 6) (see text). Mainly unidentified dialdehydes
(
appropriate combination of the metal and ligands. Thus, the
preferential syntheses of a mixture of cis- and trans-3-ethyli-
dene-7-methyl-6-octenal 7a/7b and 4-methylene-8-methyl-7-
nonenal 2 were attained, both with 75% selectivity, with Rh
and Pt/Sn, respectively. 3-Ethyl-7-methyl-2,6-octadienal 8,
(5890/Series II or G1800A) instrument operating at 70 eV
and fitted with a HP-5 capillary column.
Hydroformylation experiments were carried out in home-
made autoclaves with magnetic stirring. To prevent a direct
contact with stainless steel, the reaction solution was kept in
a glass vessel and the autoclave cap was Teflon-covered. The
reaction products were separated by column chromatography
(silica) using mixtures of hexane, CH Cl and methanol as elu-
1
7
useful for the synthesis of biologically active compounds,
and 3-ethyl-7-methyl-6-octenal 9, previously described as the
7
major product of myrcene hydroformylation, are formed only
2
2
1
13
in small amounts under our conditions. Both 8 and 9 can be,
however, readily obtained from aldehydes 7. Furthermore,
unsaturated nonanals, i.e., 4,8-dimethyl-4,7-nonadienal 4,
ent. The products were identified by MS, H, and C-NMR.
The assignment of H and C-NMR signals was made using
bidimensional techniques.
1
13
4
,8-dimethyl-3,7-nonadienal 5 and 4,8-dimethyl-7-nonenal 6,
can be prepared from aldehyde 2. Finally, 3-(4-methyl-3-pente-
nyl)hexanedial 3 is also accessible through the hydroformyla-
tion of 1, although the rate for this reaction is low.
4
-Methylene-8-methyl-7-nonenal 2
PtCl (PhCN) (0.05 mmol), SnCl ꢃ2H O (0.05 mmol), PPh
2
2
2
2
3
(0.20 mmol), myrcene (3.75 mmol) and toluene (7.5 ml) were
transferred under nitrogen into the autoclave, which was pres-
surized to 45 bar total pressure (CO/H
ꢀ
2
¼ 1/1), placed in an
oil bath (80 C) and stirred with a magnetic stirrer. After carry-
ing out the reaction for 48 h and cooling to room temperature,
the excess CO and H were slowly vented. Aldehyde 2 was
Experimental
All chemicals were purchased from commercial sources and
used as received, unless otherwise indicated. [Rh(m-OMe)-
2
separated by column chromatography (silica) using mixtures
of hexane, CH Cl and methanol as eluents and identified by
2
7
28
19
29
30
(
dppmb, P(p-CF
cod)]2 , [Rh(m-Cl)(cod)]2 , xantphos, bisbi, bubiphos,
2
2
1 13
GC/MS and H and C-NMR spectroscopy. GC yield 40%.
3
1
32
3
C
6
4
H )
3
and P(o-CF
3
C
6
4
H )
3
and P(O-
were prepared by published methods or by
+
MS (m/z/rel.int.): 166/1 (M ); 133/1; 123/26; 122/18; 107/
t
o- BuC
33
6
H
4
)
3
1 13
; 69/100; 41/50. For H and C NMR data see Fig. 1.
8
slight modifications of them. Naphos was kindly donated by
Prof. B. Hanson (Virginiatech, US). Toluene was purified
under reflux with sodium wire–benzophenone for 6 h and then
distilled under nitrogen. Myrcene was distilled before use.
The products were analyzed by gas chromatography (GC)
using Carbowax 20 M or HP-5 capillary columns and a
3
-(4-Methyl-3-pentenyl)hexanedial 3
This product was isolated and characterized as its 2,4-dinitro-
phenylhydrazone. A catalytic mixture enriched in aldehyde 3
was treated with 2,4-dinitrophenylhydrazine following a
FID. NMR spectra were obtained in CDCl
00, 400 and 250 MHz spectrometers, with TMS as internal
standard. Mass spectra were obtained on a Hewlett-Packard
3
using Bruker
3
4
5
described procedure. The product was recrystallized in EtOH
and purified by preparative chromatography (silica) to yield an
a
Table 5 Hydroformylation of myrcene (1) catalyzed by Pt/SnCl
2
/P-donor ligand
b
c
ꢀ
d
e
f
g
Ligand
P/Pt
P/bar
T/ C
Con. (%)
2 (%)
(4 + 5) (%)
6 (%)
H. (%)
Ot (%)
S
al
PPh
PPh
PPh
PPh
PPh
PPh
PPh
3
3
3
3
3
3
3
2
4
4
4
4
2
2
2
2
2
4
45
45
45
45
80
60
80
45
45
45
45
70
70
80
100
70
70
70
70
70
70
80
60
20
55
85
18
60
52
28
30
28
15
66
68
74
43
53
63
66
21
32
34
54
6
9
7
16
6
19
7
2
< 1
6
79
93
87
54
94
77
84
48
53
53
81
7
7
5
6
40
6
6
17
6
24
8
< 1
< 1
1
23
15
62
47
47
16
8
10
11
13
12
21
dppe
dppp
dppb
6
< 1
< 1
< 1
3
8
7
naphos
6
a
ꢂ2
b
Reaction conditions: 5.0 ꢁ 10 mmol of PtCl
2
(PhCN)
2
in 7.5 ml of toluene; [SnCl
Phosphorus to platinum atomic ratio. Conversion for 48 h, determined by gas chromatography. Products of hydrogenation of 1. Other
2
ꢃ2H
2
O]/[Pt] ¼ 1; [1]/[Pt] ¼ 75; [CO]/[H
2
] ¼ 1. See Chart 1.
c
d
e
f
g
products, mainly those of dimerization of 1. Selectivity for aldehydes.
New J. Chem., 2003, 27, 533–539
537

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Fig. 1
1 13
orange powder, which was analyzed by H and C NMR. See
ꢀ
50 C under N
ture of 4 and 5 was observed by GC/MS.
2
for 4 h. A partial conversion of 2 into a mix-
+
data in Fig. 2. MS of 3 (m/z/rel.int.): 196/1 (M ); 178/8; 163/
8
1
; 152/9; 135/14; 134/31; 121/23; 109/30; 95/30; 83/38; 69/
00; 55/45; 41/89.
4
,8-Dimethyl-3,7-nonadienal 5
+
MS (m/z/rel.int.): 166/4 (M ); 148/4; 137/22; 123/10; 109/
2
5; 108/28; 95/30; 83/26; 69/100; 67/21; 41/76.
4
,8-Dimethyl-4,7-nonadienal 4
+
MS (m/z/rel.int.): 166/4 (M ); 148/7; 133/8; 122/58; 107/28;
9
3
3/32; 91/24; 81/33; 80/43; 79/100; 68/33; 67/60; 55/54; 53/
2. A catalytic mixture enriched in aldehyde 2 was heated at
4
,8-Dimethyl-7-nonenal 6
+
MS (m/z/rel.int.): 153/1 (M -CH
3
); 135/1; 125/10; 109/13;
1
hyde 2 in toluene was heated at 50 C under H
07/7; 79/10; 69/100; 68/14; 55/7; 53/8. The solution of alde-
ꢀ
2
(30 bar) for 12
h, in the presence of 5%Pd/C (2 wt%). A partial conversion of
2
into 6 was observed by GC/MS.
3
-Ethylidene-7-methyl-6-octenal trans 7a and cis 7b
[
Rh
2
(m-OMe)
7.50 mmol) and toluene (7.5 ml) were transferred under nitro-
2 2 3
(cod) ] (0.02 mmol), PPh (0.24 mmol), myrcene
(
gen into the autoclave, which was pressurized to 45 bar total
ꢀ
pressure (CO/H ¼ 1/1), placed in an oil bath (70 C) and stir-
2
red with a magnetic stirrer. After carrying out the reaction for
2
4 h and cooling to room temperature, the excess CO and H2
were slowly vented. Aldehydes 7a and 7b were separated as a
mixture (ꢄ1/1) by column chromatography (silica) using mix-
2 2
tures of hexane, CH Cl and methanol as eluents and identified
1
by GC/MS and H and C-NMR spectroscopy. GC com-
13
+
bined yield 72%. 7a: MS (m/z/rel.int.): 166/5 (M ); 151/8;
1
4
2
23/17; 122/18; 107/2; 95/4; 81/3; 69/100; 67/8; 53/6; 41/
+
6. 7b: MS (m/z/rel.int.): 166/3 (M ); 151/8; 123/15; 122/
1
2; 107/3; 95/4; 81/3; 69/100; 67/8; 53/6; 41/46. For
1
H
3
Fig. 2
and C NMR data see Fig. 1.
5
38
New J. Chem., 2003, 27, 533–539

View Article Online
3
-Ethyl-7-methyl-2,6-octadienal 8
P. N. Rylander, H. Greenfield and R. L. Augustine, Marcel
Dekker, New York, 1988, vol. 22, p. 43.
The Chemistry of Fragances, ed. D. H Pybus and C. S. Sell, RSC
Paperbacks, Cambridge, 1999.
J. C. Chalchat, R. Ph. Garry, E. Lecomte and A. Michet, Flavour
Fragrance J., 1991, 6, 178.
G. Liu and M. Garland, J. Organomet. Chem., 2000, 608, 76.
G. Natta and M. Beatti, Chim. Ind. (Milan), 1945, 27, 84.
H. Adkins and J. L. R. Williams, J. Org. Chem., 1952, 17, 980.
A solution was prepared with 1.0 g of a mixture of aldehydes
7
mmol) and 64.0 mg of PPh (0.24 mmol) in 10 ml of toluene.
The mixture was heated at 70 C. The reaction evolution was
followed by GC. After 6–8 h, a nearly complete conversion
was obtained. The oily product was purified by distillation in
a kugelrohr apparatus at 75 C (1 mm of Hg). Yield 75%.
MS (m/z/rel.int.): 166/4 (M ); 151/4; 137/16; 123/7; 108/
6
7
a and 7b (6.00 mmol), 9.0 mg of [Rh(m-OMe)(cod)] (0.02
3
ꢀ
8
9
0
1
ꢀ
+
11 (a) B. Fell and H. Bahrmann, J. Mol. Catal., 1977, 7, 211; (b)
H. Bahrmann and B. Fell, J. Mol. Catal., 1980, 8, 329; (c) B. Falk
and B. Fell, J. Mol. Catal., 1983, 18, 127; (d ) P. W. N. M. van
Leeuwen and C. F. Roobeek, Eur. Pat. Appl. 81-200033 to Shell,
1981; (e) P. W. N. M. Van Leeuwen and C. F. Roobeek, J. Mol.
Catal., 1985, 31, 345; ( f ) C. Botteghi, M. Branca and A. Saba,
J. Organomet. Chem., 1980, 184, C17; (g) C. Botteghi, M. Branca
and A. Saba, J. Organomet. Chem., 1987, 332, 229.
1
obtained as a mixture of trans and cis isomers (88% trans/
4; 95/11; 98/16; 83/19; 69/100; 41/57. Aldehyde 8 is
1
2% cis) as shown by NOESY experiments. For H and
13
1
NMR data for the major (trans) isomer see Fig. 1.
C
1
2
S. Bertozzi, N. Campigli, G. Vitulli, R. Lazzaroni and
P. Salvadori, J. Organomet. Chem., 1995, 487, 41.
3
-Ethyl-7-methyl-6-octenal 9
An autoclave was charged with 0.50 g of aldehyde 8, 9.0 mg of
13 D. L. Packett, US 5,312,996 to Union Carbide, 1994.
14 Y. Ohgomori, N. Suzuki and N. Sumitani, J. Mol. Catal. A, 1998,
[
mmol) dissolved in 7.5 ml of toluene. The autoclave was closed
Rh(m-OMe)(cod)] (0.02 mmol) and 64.0 mg of PPh (0.24
3
1
33, 289.
ꢀ
15 (a) T. Horiuchi, T. Ohta, K. Nozaki and H. Takaya, Chem. Com-
mun., 1996, 155; (b) T. Horiuchi, T. Ohta, E. Shirakawa, K.
Nozaki and H. Takaya, Tetrahedron, 1997, 53, 7795.
and pressurized with 15 bar of H
pressure was released and the product was purified by distilla-
2
at 60 C. After 4 h, the gas
ꢀ
tion in a kugelrohr apparatus at 77 C (1 mm of Hg). Yield
9
1
6
(a) K. Osakada, J. C. Choi, T. Koimuzi, I. Yamaguchi and
T. Yamamoto, Organometallics, 1995, 14, 4962; (b) J. C. Choi,
K. Osakada and T. Yamamoto, Organometallics, 1998, 17, 3044.
+
0%. MS (m/z/rel.int.): 168/7 (M ); 153/7; 150/8; 125/21;
1
21/26; 95/63; 83/47; 69/100; 67/32; 55/50; 41/80. For H
1
and C NMR data see Fig. 1.
1
3
17 M. I. Dawson, P. D. Hobbs,Kuhlmann, V. A. Fung, C. T. Helmes
and W. R. Chao, J. Med. Chem., 1980, 23, 1013.
1
8
(a) C. P. Casey and G. T. Whiteker, Isr. J. Chem., 1990, 30, 299;
b) P. Dierkes and P. W. N. M. van Leeuwen, J. Chem. Soc.,
Dalton Trans., 1999, 1519.
(
Acknowledgements
1
9
0
M. Kranenburg, Y. E. M. van der Burgt, P. C. J. Kamer and
P. W. N. M. van Leeuwen, Organometallics, 1995, 14, 3081.
(a) C. P. Casey, G. T. Whiteker, M. G. Melville, L. M. Petrovich,
J. A. Gavney Jr. and D. R. Powell, J. Am. Chem. Soc., 1992, 114,
5535; (b) P. W. N. M. van Leeuwen, G. J. H. Buisman, A. van
Rooy and P. C. J. Kamer, Recl. Trav. Chim. Pays-Bas, 1994,
Financial support from DGSIC (PB98-0913), DGI (BQU2002-
0
4070), CNPq and FAPEMIG is gratefully acknowledged. We
2
also thank CYTED (Red VD and project V9) for providing a
scholarship (C. M. F.) to start this project, DGSIC for a doc-
toral scholarship (C. M. F.), and CNPq for a scholarship (H. J.
V. B.). The authors wish to thank Dr Teodor Parella (NMR
Service of UAB) and Ms. Ivana Silva Lula (NMR Service of
UFMG) for their assistance in the NMR characterization of
the products.
1
See reference 1a, chapters 3 and 4.
13, 61.
2
2
1
2
(a) E. L. Muetterties, Acc. Chem. Res., 1970, 3, 266; (b) P.
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2
3
4
C. P. Casey, G. T. Whiteker, C. F. Campana and D. R. Powell,
Inorg. Chem., 1990, 29, 3376.
J. M. Brown and A. G. Kent, J. Chem. Soc., Perkin Trans. 2,
2
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New J. Chem., 2003, 27, 533–539
539