P-Stereogenic monophosphines in Pd-catalysed enantioselective hydrovinylation of styrene

Article abstract of DOI:10.1016/j.jorganchem.2011.02.034

Two groups of P-stereogenic monodentate phosphines containing pendant groups bearing functionalities capable of having secondary interactions, PArPhR (Ar = 2-[(2′,6′-dimethoxy)-1,1′-biphenylyl] and R = OMe (6) or Me (8)) and PMeR(CH₂R′) (13, R

Full text of DOI:10.1016/j.jorganchem.2011.02.034

Journal of Organometallic Chemistry 696 (2011) 2338e2345
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Journal of Organometallic Chemistry
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P-Stereogenic monophosphines in Pd-catalysed enantioselective hydrovinylation
of styrene
,
b
b
Arnald Grabulosa a, Alberto Mannu a, Guillermo Muller a , Teresa Calvet , Mercè Font-Bardia
*
a Departament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
b Departament de Cristal$lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Two groups of P-stereogenic monodentate phosphines containing pendant groups bearing functionalities
capable of having secondary interactions, PArPhR (Ar ¼ 2-[(20,60-dimethoxy)-1,10-biphenylyl] and
R ¼ OMe (6) or Me (8)) and PMeR(CH2R0) (13, R ¼ t-Bu or 14 R ¼ Fc and R0 ¼ SiMe3 (a), SiMe2Ph (b) or
CH2(2-naphthyl) (c)) have been prepared in enantiomerically pure form by the Jugé and Evans meth-
odologies and characterised, including the crystal structure for the borane adduct of 12b. Reaction of the
Received 17 December 2010
Received in revised form
9 February 2011
Accepted 11 February 2011
phosphines with the Pd dimer [Pd(
h m-Cl)]2 produced neutral allylic complexes C [PdCl
3-2-Me-allyl)(
Keywords:
Palladium
(
h
3-2-Me-C3H4)P*], which have been characterised in solution and shown to be a mixture of isomers
with different absolute configuration at the Pd atom. After abstraction of the chloride ligand by AgBF4,
the solutions of cationic complexes have been used as catalyst precursors in the hydrovinylation of
styrene under mild conditions. Very good activities (up to 1015 hꢀ1), moderate to good selectivities to
3-phenyl-1-butene and low to moderate enantioselectivities (<45% ee) have been found. Deep differ-
ences in the activity and enantioselectivity have been found depending on the structure of the ligand. In
spite of that the results did not permit to confirm the improvement of the selectivities of the reaction by
stabilization of the catalyst through secondary coordination with the potentially hemilabile ligands.
Ó 2011 Elsevier B.V. All rights reserved.
P-Stereogenic monophosphines
Allylic compounds
Asymmetric catalysis
Hydrovinylation
1. Introduction
route to 2-arylpropionic acids, the most important family of
nonsteroidal antiinflammatory drugs, including naproxen or
Catalytic activation and incorporation of simple inorganic and
organic molecules into complex organic frameworks without waste
generation constitutes one of the main research areas in chemistry.
In this context, the hydrovinylation reaction can be defined as an
heterodimerisation between ethylene gas and an activated olefin,
usually styrene (and other vinylarenes) or norbornene [1], cata-
lysed by a transition metal complex [2,3]. Scheme 1 shows the
hydrovinylation of the model substrate, styrene, and some of the
byproducts often encountered.
ibuprofen [6,7]. More recently it has also been employed in the
stereoselective construction of benzylic all-carbon quaternary
stereocentres [8e10], a structural motif present in pharmacologi-
cally important compounds, and in the short synthesis of natural
products [11,12]. In spite of its enormous potential and its long
history [13,14], hydrovinylation is still an underused reaction even
in the synthesis of fine chemicals. This is due to the presence of
many side reactions, as shown in Scheme 1, which requires a subtle
fine tuning of the catalyst to obtain good selectivity [3].
Typically encountered side reactions include dimerisation of
either ethylene or styrene and isomerisation of the 3-phenyl-1-
butene to the more stable 3-phenyl-2-butenes. The second process
can be minimised by stopping the reaction before total consump-
tion of styrene.
Since a stereogenic carbon atom is created, the reaction is
amenable to enantiocontrol [4,5]. Hydrovinylation has much
interest in enantioselective synthesis because it provides a short
Although some work has been carried out with complexes of
cobalt [15e20] and ruthenium [21], most of the studies on enantio-
selective hydrovinylation have beenperformed using Ni(II) and Pd(II)
organometallic precursors [3,5]. It has been traditionally accepted
that the mechanism involves an extremely reactive unsaturated
cationic nickel or palladium hydride as true catalyst, which coordi-
nates and inserts styrene, giving a
coordination, insertion into the metal-carbon bond and
h
3-benzylic intermediate. Ethylene
-elimina-
b
tion releases the product and regenerates the hydride closing the
catalytic cycle [3]. It must be noted, however, that the presence of the
metal hydride intermediate in nickel based systems has been
recently questioned by a theoretical study of RajanBabu and
* Corresponding author. Tel.: þ34 934039140; fax: þ34 934907725.
E-mail address: guillermo.muller@qi.ub.es (G. Muller).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.02.034

A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2011) 2338e2345
2339
potentially secondary coordination moieties could shed light on the
importance of the intramolecular secondarycoordination. Our recent
experience with phosphines bearing pendant functionalities, dis-
carded the use of isolated double bonds or carbonyl fragments [41].
2. Results and discussion
2.1. Ligand synthesis
Among the several methods available to prepare optically pure
P-stereogenic ligands [42], we selected the routes devised by Jugé
[43] and by Evans [44] to prepare two distinct sets of optically pure
P-stereogenic phosphines.
Scheme 1.
In previous studies on hydrovinylation [26,27,40] we found that,
among the diarylalkyl phosphines studied, those bearing a 2-
biphenylyl group led to the highest enantioselectivities. We
reasoned that phosphines with the same substituent but contain-
ing methoxy groups may improve these results by intramolecular
secondary coordination of the oxygen atom to the metallic centre.
To this aim, we prepared 2-bromo-(20,60-dimethoxy)-1,10-biphenyl
(1), following slightly modified procedures (Scheme 2) [45,46].
This compound was easily lithiated at low temperature and
installed at the phosphorus atom by nucleophilic attack on oxaza-
phospholidine 3, following the standard Jugé procedure (Scheme 3)
[43].
Aminophosphine-borane 4 was obtained as a diastereomerically
pure compound according to NMR spectroscopy and was subjected
without purification to acidic methanolysis, affording phosphinite-
borane 5. From this precursor, methylphosphine-borane 7 was
easily obtained by substitution of the methoxy group by methyl-
lithium. Phosphinite-borane 5 and phosphine-borane 7 were
quantitatively deboronated by neat morpholine giving the desired
ligands 6 and 8 as white solids after column chromatography to
remove the morpholine-borane adduct.
In order to prepare electron-rich phosphines, we subjected
dimethylphosphine-boranes 9 and 10 to the desymmetrisation
protocol with s-BuLi/(ꢀ)-sparteine, a method originally developed
by Evans and coworkers [44] and already used by us (Scheme 4) [47].
With this procedure, we obtained phosphine-boranes 11 and 12
after electrophilic quenching of the carbanions with chlorosilanes.
HPLC analysis of the crude phosphine-boranes revealed very high
(>97%) enantiomeric excesses for compounds of the t-Bu series, 11.
In contrast, compounds 12a and 12b were formed in 80 and 82% ee
respectively, whereas 12c was found to be enantiopure. The optical
purity of 12b could be easily increased by recrystallisation. The
results suggest that the ferrocenyldimethylphosphine-borane (10)
is a less selective substrate for the enantioselective deprotonation
compared to 9 although the value of the enantioselectivity also
depends on the electrophile.
coworkers [22], who suggest a direct
b-H transfer instead of a
b-elimination. With palladium systems the isomerization of the
product of codimerization has been observed and therefore a metal
hydride intermediate fits adequately the experimental results. A
particularity of Ni and Pd systems is that active catalysts only admit
monodentate phosphorus ligands, since diphosphines and other
bidentate ligands inhibit the reaction. This implies that a single
monodentate ligand is responsible for the challenging task of
controlling both the chemo- and enantioselectivity.
To circumvent this difficulty, several approaches such as pure
steric shielding [1,23,24] or the dendritic effect [25e27] have been
applied but the most successful has been the use of ligands pos-
sessing pendant groups capable of interacting with and stabilising
the metal centre [28,29]. This strategy has been intensively pursued
by RajanBabu [1,22,30e33], Leitner [34e37] and Zhou [8,38]
employing Ni systems. A limitation of Ni-based systems is that to
obtain high chemo- and enantioselectivities the reactions have to
be carried out at very low temperatures, except for the less reactive
substrates [8]. It must be noted that a recent contribution of Leitner
and coworkers [37] describes a highly enantioselective Ni system
for the hydrovinylation of vinylarenes at room temperature with
a finely tuned phosphoramidite ligand, highlighting the impor-
tance of hemilabile interactions.
Pd-based catalysts have the advantage of operating at room
temperature, constituting a promising alternative. Our group
[24,26,27,39e41] and others [23] have been studying the hydro-
vinylation reaction using palladium
p-allylic complexes with
several types of monodentate P-stereogenic ligands as precatalysts.
This is an interesting class of ligands to be explored in hydro-
vinylation since the close proximity of the stereogenic phosphorus
to the metallic centre can provide high enantioselectivities as
shown by Vogt and coworkers [23] and by us [24,26,27].
With the aim of exploring the effect of potential secondary
interactions on Pd-catalysed enantioselective hydrovinylation of
styrene, in this contribution we describe the preparation of several
new P-stereogenic phosphines with different electronic properties
bearing functionalities capable of having secondary interactions, like
methoxy substituents or aryl groups. The comparison with the
catalytic results obtained using similar phosphines lacking the
We were able to obtain the crystal structure of optically pure
phosphine 12b, which confirmed the expected S configuration of
the phosphorus atom, as shown in Fig. 1.
The distances and angles of 12b are close to other reported
phosphine-boranes [26,40,48]. The Cp rings of the ferrocenyl
Scheme 2.

2340
A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2011) 2338e2345
Scheme 3.
substituent are present in eclipsed conformation as observed in
other ferrocenylphosphine-boranes [49,50].
determine the following order of s-donation capacity for the
ligands: 13a > 13c w 14a > 13b > 14c > 14b.
Given the electron-rich character phosphine-boranes 11 and 12,
the deprotection was carried out with tetrafluoroboric acid fol-
lowed by neutralisation [51], a procedure that worked efficiently
for 11a,11c,12a and 12c. In contrast, the eSiMe2Ph group present in
phosphine-boranes 11b and 12b was partially cleaved with the
acidic treatment giving back the starting material 9 and 10
respectively. For this reason, 11b and 12b were deprotected with
DABCO in refluxing toluene. The free phosphines 13 and 14 were
found to be very sensitive to oxidation and therefore they were
immediately complexed to palladium without isolation. Phos-
phines 13 and 14 were designed to incorporate pendant aryl
moieties susceptible to interact with the unsaturated Pd centre
during the catalysis. Phosphines 13a and 14a, without possibility of
such interactions were prepared for comparison purposes.
A list of the 31P NMR data of phosphine-boranes, free phos-
phines, phosphine selenides and Pd-allylic complexes (vide infra) is
given in Table 1.
2.2. Allylpalladium complexes
Neutral allylic Pd complexes [PdCl(
easily prepared by mixing 2 equivalents of the free phosphine with
one equivalent of dimer [Pd( -Cl-Cl)]2 (Scheme 5).
3-2-Me-C3H4)(
h
3-2-Me-C3H4)P*] were
h
m
After solvent removal, complexes C were obtained pure as solids
or oils, which were indefinitely stable in air. Complexes C13b and
C14b were contaminated with DABCO and DABCO$BH3 according to
1H NMR spectra. Complex C14b, dissolved in dichloromethane,
could be purified by treatment with diluted aqueous hydrochloric
acid, which removed DABCO, followed by column chromatography
(SiO2), which allowed the separation of DABCO$BH3. When the
same treatment was attempted with C13b, the complex decom-
posed to palladium black. Therefore, although the crude complex
could be characterised by NMR (vide infra), it was not used in
catalysis.
The most informative technique of characterisation was NMR
spectroscopy. 31P (Table 1) and 1H NMR spectra of C showed the
expected presence of two isomers (RPd and SPd) interconverting in
solution. The isomeric ratios as well as selected 1H NMR and 13C
NMR data are collected in Table 1S and Table 2S respectively (see
Supporting information).
31P data of compounds 5e8 is very similar to analogous
compounds having an unsubstituted biphenylyl group [40]. The
value of the 31Pe77Se coupling constants of phosphine selenides are
used to compare the s-donor capacity of phosphorus ligands (for
example 712 Hz for PCy3 and 760.3 Hz for PPh3) [52e56], although
this method is not free from steric interference [55]. We easily
prepared the selenides of some of the trialkylphosphines by direct
treatment with elemental selenium. Comparison between JPeSe of
the selenides of 9-Se and 10-Se, 13a-Se and 14a-Se or 13b-Se and
14b-Se reflects the higher
s-donation of the phosphorus for
phosphines containing the tert-butyl group (9) compared to those
containing the ferrocenyl group (10). Given one of these substitu-
ents, the TMS group (a) is more
s-basic than the dimethylphe-
nylsilyl group (b). Taken together, the effect of both substituents
Fig. 1. ORTEP view (thermal ellipsoids drawn at the 50% probability level) of phos-
phine-borane 12b. Hydrogen atoms have been omitted for clarity. Selected distances
(Å): P1-B1, 1.910 (5); P1eC9, 1.799(4); P1eC10, 1.776(3); P1eC20, 1.810(4); SieC1, 1.892
(3), SieC7, 1.844(5); SieC8, 1.849(4). Selected angles (ꢁ): B1eP1eC9, 109.9(3);
B1eP1eC10, 111.5(2); B1eP1eC20, 113.4(2).
Scheme 4.

A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2011) 2338e2345
d in ppm, J in Hz) for phosphine-boranes, free
2341
Table 1
31P NMR dataa (CDCl3, 298 K, 101 MHz,
phosphines, phosphine selenides and Pd-allylic complexes.
Compound
d
(
31P)
d
(
31P)
d
(
31P)
JPeSe
d(
31P)
PeBH3
free P
P]Se
[Pd] Isomeric
ratio
5, 6, C6
7, 8, C8
9a, 9-Se
9b, 10-Se
107.2
(bs, d, 79.6)
10.7
(bs, d, 68.6)
20.5
(q, 58.8)
0.0
(q, 55.9)
23.6
(q, 63.6)
24.0
(q, 68.8)
25.2
(q, 54.7)
2.9e4.6
(m)
þ112.1
ꢀ33.9
ꢀ28.3
ꢀ56.9
ꢀ22.6
ꢀ23.2
ꢀ15.4
ꢀ51.3
ꢀ52.1
ꢀ46.1
eb
eb
120.8, 120.6
60/40
5.3
100/0
e
eb
eb
Fig. 2. Diastereotopic CH2 protons.
39.2
11.5
41.6
39.5
48.9
14.5
12.8
21.8
689.8
702.7
680.8
704.9
692.1
695.6
720.9
710.3
e
magnetically inequivalent, coupling to each other and to the
phosphorus atom (Fig. 2). An additional complication is the pres-
ence of two isomers of the complex, which duplicates the number
of signals. The observed patterns are listed in Table 3S.
11a, 13a,
21.2, 21.9
50/50
21.9, 21.8
62/38
28.7, 28.3
55/45
13a-Se, C13ac
11b, 13b,
13b-Se, C13b
11c, 13c, C13c
Phase-sensitive NOESY experiments on some of the complexes
were carried out to study the mechanism of interconversions
between isomers. The usual h3 h1 3 and the allyl pseudorotation
- - h
12a, 14a,
14a-Se, C14a
12b, 14b,
ꢀ4.9, ꢀ5.2
mechanisms were observed although interestingly for complex
53/47
C14b only the h3 h1 h3 mechanism could be detected.
-
-
4.6
ꢀ3.9, ꢀ4.6
57/43
1.0, 0.2
50/50
14b-Se, C14b
12c, 14c,
(q, 57.7)
1.7e2.3
(m)
2.3. Styrene hydrovinylation
14c-Se, C14cc
a
Multiplicity: bs, broad signal; d, doublet; m, multiplet; s, singlet; q, quadruplet.
Not measured.
Signals of both isomers of the complex not experimentally related.
Neutral allylic Pd complexes are suitable precatalysts for styrene
hydrovinylation [40,41]. The activation of these complexes was
carried out with one equivalent of AgBF4 in the presence of styrene,
b
c
giving solutions containing [PdL(
h
3-2-Me-C3H4)P*]BF4 (L ¼ styrene
Unexpectedly, a single set of signals was observed for complex
or solvent). These solutions were immediately introduced into an
autoclave and pressurised with ethylene. The results obtained after
GC analysis of at least two runs are listed in Table 2.
C8 at room temperature. It is possible that in this case both signals
appeared overlapped since in C6 they were observed at 120.8 and
120.6 ppm, furthermore an incomplete group of very small signals
were observed in the proton spectra probably accounting for the
minor isomer. For the rest of compounds, two 31P signals and
duplicity of allylic C and H resonances was observed. A moderate
discriminating effect is observed with similar ligand 6. In the case of
ligands 13 and 14, the highest discrimination is reached with
ligands 13b and 14b, bearing a dimethylphenylsilyl moiety.
The differences in the chemical shifts of allylic protons and
carbons between isomers in complex C6 reach 0.6 and 2.9 ppm in
1H and 13C NMR respectively. These differences are much smaller
for complexes C13 and C14. In 13C NMR the C1 carbon (trans to the
phosphine) is shifted downfield in complexes C6 and C8 compared
to complexes C13 and C14, in all cases highly deshielded
(w25 ppm) compared to the corresponding C3 carbon, cis to the
phosphine. As observed in similar complexes [28,40,57], both
the carbon and H atoms trans to the phosphorus were coupled to
the phosphorus atom.
Comparison between precatalysts containing diarylphosphines
(entries 1e4) and those with trialkylphosphines (entries 5e9)
shows that the latter are much more active, probably due to the
extra stabilisation of the cationic palladium hydride species by the
more bulky and basic trialkylphosphines.
Within the group of diarylphosphines (entries 1e4), the intro-
duction of methoxy groups in the biphenylyl substituent causes
a severe drop in the activity (cf. entry 1 with entry 2 and entry 3 with
entry 4), probably due to steric and secondary interaction effects.
More interesting are the differences on the enantioselectivity.
Whereas with the precursors bearing the methylphosphines the
presence of the methoxy groups completely destroys the chiral
induction (cf. entries 3 with 4), in the methylphosphinite pair the
Table 2
Hydrovinylation of styrene catalysed by [PdL(
h
3-2-Me-C3H4)P*]BF4 precursorsa.
Entry Precursor Time, Conversionb, Codimersc, Selectivityd TOFe, ee, %
Complexes C13 or C14 present one or two methylene groups in
the phosphine part. Due to the stereogenic phosphorus atom, the
protons of each group are diastereotopic and hence chemically and
h
%
%
hꢀ1
29 45 (R)
1
C6
C15
C8
C16
C13a
C13c
C14a
C14b
C14c
3
1
3
1
3
1
3
3
3
8.5
8.4
99.1
95.9
96.3
97.2
83
67
74
84
92
2f
3
18.1
10.7
10.5
96
17.7
10.6
10.0
94
99
85
178 12 (R)
35 <5 (ꢀ)
100 23 (S)
322 <5 (ꢀ)
1015 35 (R)
283 20 (R)
241 35 (R)
145 17 (R)
4f
5
6
100
7g
8
85
72
50
71
49
9
a
Conditions: 25 ꢁC, 15 bar of initial pressure of ethylene in 10 ml of CH2Cl2. Ratio
styrene/Pd: 1000/1.
b
Conversion of starting styrene.
Total amount of codimers.
% of 3-phenyl-1-butene/codimers.
TOF calculated as the total amount of phenylbutenes formed.
c
d
e
f
Complexes C15 and C16 are similar to C6 and C8 respectively but bearing an
unsubstituted 2-biphenylyl group in the phosphine, the data has been taken from
our previous report [40].
g
Scheme 5.
The phosphine used to prepare the complex had a 80% ee.

2342
A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2011) 2338e2345
effect is inverse (cf. entries 1 with 2), enhancing the enantiomeric
excess and making C6 a moderately enantioselective catalyst. The
absolute configuration of the 3-phenyl-1-butene in entries 1 and 2 is
opposite to that of entry 4 as expected due to the opposite absolute
configuration at the phosphorus atom.
performed on a HewlettePackard 5890 Series II gas chromato-
graph (50-m Ultra 2 capillary column 5% phenylmethylsilicone and
95% dimethylsilicone) with a FID detector. The GC/MS analyses
were performed on a HewlettePackard 5890 Series II gas chro-
matograph (50-m Ultra 2 capillary column) interfaced to a Hew-
lettePackard 5971 mass selective detector. HPLC analyses were
carried out in a Waters 717 plus autosampler chromatograph with
a Waters 996 multidiode array detector, fitted with a Chiralcel OD-
H chiral column. The eluent, in all the determinations, was
a mixture n-hexane/i-PrOH 95:5. Optical rotations were measured
on a Perkin Elmer 241 MC spectropolarimeter at 23 ꢁC. Enantio-
meric excesses were determined by GC on a HewlettePackard
5890 Series II gas chromatograph (30-m Chiraldex DM column)
with a FID detector. Elemental analyses were carried out by the
Serveis Cientificotècnics of the Universitat Rovira i Virgili and of
Universitat de Barcelona. Phosphine-borane 13c had already been
reported by us [47].
In the trialkylphosphine series, precursor and C14a (entry 7),
without possibility of secondary interactions, is faster than the other
catalysts bearing the ferrocenyl substituent. Precursor C13c (entry
6), which is extraordinarily active, quantitatively consumes the
styrene in 1 h and leads to noticeable isomerisation. We do not have
any explanation for this fact. Although all the systems favour the R
enantiomer of 3-phenyl-1-butene, some interesting observations
can be made. Entries 5 and 6 show that while C13a, bearing
a pendant TMS group, is a very poor chiral inductor, C13c, with
a pendant 2-naphthyl group, gives much better enantioselectivity. In
contrast, entries 7e9 show that both C14a and C14c are equivalent
in terms of enantioselectivity, a result that is improved by C14b. All
the trialkylphosphines have the same absolute configuration at the P
atom leading to the same sense in the chiral induction due to the
preferential coordination of styrene by one of its enantiotopic faces.
In spite of that, an interesting modulation of the enantioselectivity is
observed possibly due to secondary coordination interactions
between the Pd centre and aromatic rings. This effect is more
pronounced in the phosphines bearing the tert-butyl group.
4.2. Synthesis of ligands
4.2.1. 2-Bromo-20,60-dimethoxybiphenyl (1)
m-dimethoxybenzene (4.00 ml, 4.22 g, 30.6 mmol) was dissolved
in 60 ml of dry THF and cooled to ꢀ5 ꢁC. n-BuLi (19.2 ml of 1.6 M
solution, 30.8 mmol) was added by syringe and after 15 min the
solution was allowed to warm to room temperature. After 5 h of
3. Conclusions
stirring, the suspension was cooled to 0
ꢁC and o-bromo-
chlorobenzene (3 ml, 4.96 g, 25.6 mmol), dissolved in 20 ml of THF,
was slowly added during a period of 30 min and the resulting
solution was stirred for 15 min. Methanol (0.5 ml) was added and
the brownish solution immediately became yellow. This solution
was concentrated under reduced pressure and diethyl ether
(100 ml) and water (100 ml) were added. The layers were separated
and the aqueous phase was extracted with diethyl ether (2 ꢂ 50 ml).
The combined organic extracts were washed once with brine
(50 ml), dried with anhydrous sodium sulphate and concentrated
under reduced pressure to yield a yellow solid. This solid was
recrystallised in CH2Cl2/diethyl ether to yield the desired product.
A family of [PdCl(
h
3-2-Me-C3H4)P*] complexes containing two
types of new enantiopure P-stereogenic ligands have been prepared
and characterised. The cationic derivatives obtained after extraction
of the coordinated chloride by a silver salt have been used in the
catalytic hydrovinylation of styrene. Good activities and regiose-
lectivities towards 3-phenyl-1-butene have been found. In contrast,
the enantioselectivities have remained low to moderate, which
requires further work on ligand design. Some interesting trends in
the enantioselectivities have been identified. In general, except for
C13a, the increase of the bulkiness of the ligands diminishes the
activity of the catalysts, an effect that is more pronounced in the
diarylphosphine series. For the diarylphosphines, either enhance-
ment (C6) or destruction (C8) of the enantioselectivity has been
observed whereas for the trialkylphosphines a low to moderate
increase on the enantioselectivity has been found.
Yield: 3.7 g (49%). 1H NMR (400.1 MHz, CDCl3, 298 K):
d
¼ 3.73 (s,
6H), 6.65 (d, 2H, J ¼ 8.4 Hz), 7.19e7.25 (m, 2H), 7.31e7.36 (m, 2H),
7.65 (dd,1H, J ¼ 8.0 Hz,1.2 Hz) ppm. 13C{1H} NMR (100.6 MHz, CDCl3,
298 K):
d
¼ 56.8 (CH3), 104.9 (CH), 126.0e158.5 (C, CH, Ar) ppm.
Therefore, the results did not allow to confirm the improvement
of the selectivities of the reaction by stabilization of the catalyst
through secondary coordination with the methoxy groups or aryl
fragments in the ligands prepared.
4.2.2. (1R,2S)-2-{[(S)-(2-(20,60-Dimethoxybiphenylyl))phenyl-
phosphanyl] methylamino}-1-phenylpropan-1-ol-P-borane (4)
1 (10.11 g, 34.5 mmol) was dissolved in 100 ml of dry THF and
cooled to ꢀ78 ꢁC. n-BuLi (22.5 ml of 1.6 M solution, 36.0 mmol) was
added by syringe. After 2 h, to ensure the complete lithiation, the
suspension was warmed to ꢀ20 ꢁC and cooled again to ꢀ78 ꢁC. A
solution of 3 (8.55 g, 30.0 mmol) was dissolved in 30 ml of THF,
cooled to ꢀ78 ꢁC and added slowly to the suspension of 2. The
mixture was allowed to warm to room temperature overnight.
Water (25 ml) was added and the organic solvents were removed in
vacuo. The obtained suspension was extracted with dichloro-
methane (3 ꢂ 30 ml) and the combined organic fractions were
washed with water (100 ml). The final organic fraction was dried
with sodium sulphate, filtered and concentrated. The desired
product was obtained as a white powder. Yield: 13.51 g (90%). 31P
4. Experimental section
4.1. General data
All compounds were prepared under
a purified nitrogen
atmosphere using standard Schlenk and vacuum-line techniques.
The solvents were purified by standard procedures and distilled
under nitrogen. The routine 1H, 13C, and 31P NMR spectra were
recorded on either a Varian XL-500 or Mer-400 MHz (1H, standard
SiMe4), Varian Inova 300 (13C, 75.4 MHz, 1H, standard SiMe4) and
Bruker DRX-250 (31P, 101.2 MHz) spectrometers in CDCl3 unless
otherwise specified. Chemical shifts were reported downfield from
standards. The two-dimensional experiments were carried out
with a Bruker DMX-500 or a Varian XL-500 instrument. IR spectra
were recorded on the spectrometers: FT-IR Nicolet 520 and FT-IR
Nicolet 5700; only the stretching bands assigned to the allyl group
are given [58]. FAB mass chromatograms were obtained on
a Fisons V6-Quattro instrument. The routine GC analyses were
{1H} NMR (101.3 MHz, CD3COCD3, 298 K):
NMR (250.1 MHz, CDCl3, 298 K):
d
¼ þ70.4 (bs) ppm. 1H
d
¼ 0.00e1.80 (m, bs, 3H), 0.97 (d,
3H, J ¼ 6.9 Hz), 2.65 (d, 3H, J ¼ 7.8 Hz), 3.50 (s, 3H), 3.70 (s, 3H), 3.90
(m, 1H), 4.84 (d, 1H, J ¼ 3.6 Hz), 6.33 (d, 1H, J ¼ 8.3 Hz), 6.42 (d, 1H,
J ¼ 8.3 Hz), 6.65 (d, 1H, J ¼ 8.3 Hz), 7.13e7.48 (m, 14H, Ar) ppm. 13C
{1H} NMR (50.0 MHz, CDCl3, 298 K):
d
¼ 9.6 (d, CH3, JCP ¼ 4.6 Hz),
30.6 (s, CH3), 56.6 (d, CH, JCP ¼ 9.1 Hz), 53.9 (s, CH3), 54.3 (s, CH3),
77.7 (d, CH, JCP ¼ 2.3 Hz), 102.0e156.7 (m, C, CH, Ar) ppm.

A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2011) 2338e2345
2343
4.2.3. (R)-(2-(20,60-Dimethoxybiphenylyl))methoxy-
phenylphosphine-P-borane (5)
23.6 mmol) was added by syringe and the mixture stirred for
30 min at ꢀ78 ꢁC. A solution of dimethylphosphine-borane 9
(23.6 mmol) was added by syringe and the mixture was stirred for
3 h at ꢀ78 ꢁC. At the same temperature, the solution was quenched
with the desired electrophile (35.4 mmol). The reaction mixture
was allowed to warm to room temperature overnight and then
hydrolysed with 20 ml of water. The mixture was washed with
a solution of HCl (0.5 M, 3 ꢂ 10 ml). The combined organic layers
were dried with sodium sulpate, filtered, and the resulting solution
concentrated in vacuo. The remaining residue was purified by
chromatography on silica gel and/or by recrystallisation.
Compound 4 (13.50 g, 27.0 mmol) was dissolved in 200 ml of dry
methanol and cooled to 0 ꢁC. Sulphuric acid (1.51 ml, 2.78 g,
27.0 mmol) was rapidly added and the mixture was left stirring
overnight. Removal of the solvent furnished a pasty solid, which was
suspended in 100 ml of ethyl acetate causing the precipitation of
(ꢀ)-ephedrine sulphate, which was filtered out. The solvent was
removed and the oil obtained was treated several times with diethyl
ether, which dissolved the desired compound. Concentration fur-
nished again a pasty solid, which was recrystallised in CH2Cl2/
ethanol to yield the title product as a white solid. Yield: 3.08 g (30%).
31P{1H} NMR (101.3 MHz, CDCl3, 298 K):
d
¼ þ107.2 (d, bs,
4.2.8. (S)-Tert-butyl(2,2-dimethyl-2-sila-1-propyl)
methylphosphine-P-borane (11a)
The crude product was purified by recrystallisation in
dichloromethane/diethyl ether to afford the title compound as
a white powder. Yield: 3.85 g (80%). 31P{1H} NMR (101.3 MHz,
J ¼ 79.6 Hz) ppm. 1H NMR (400.1 MHz, CDCl3, 298 K):
d
¼ 0.25e1.20
(m, bs, 3H), 3.33 (s, 3H), 3.41 (s, 3H), 3.57 (d, 3H, J ¼ 12.0 Hz), 6.26 (d,
1H, J ¼ 8.4 Hz), 6.38 (d, 1H, J ¼ 8.0 Hz), 7.11e7.58 (m, 9H, Ar),
8.13e8.19 (m, 1H, Ar) ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 298 K):
d
¼ 53.9 (d, CH3, JCP ¼ 4.6 Hz), 55.1 (s, CH3), 55.2 (s, CH3),102.7e158.1
CDCl3, 298 K):
d
¼ þ23.6 (q, JPB ¼ 63.6 Hz) ppm. 1H NMR
(m, C, CH, Ar) ppm. C21H24BO3P: calcd. C 68.88, H 6.61; found C 68.63,
H 6.57. [a]D (c ¼ 0.9, CH2Cl2): þ28.4ꢁ.
(400.1 MHz, CDCl3, 298 K),
d
¼ 0.18 (s, 9H), 0.72e0.85 (m, 2H), 1.11
(d, 9H, J ¼ 13.6 Hz), 1.20 (d, 3H, J ¼ 10.0 Hz) ppm. 13C{1H} NMR
(100.6 MHz, CDCl3, 298 K),
d
¼ 0.8 (s, CH3), 7.7 (d, CH3, JCP ¼ 57.5 Hz),
4.2.4. (S)-(2-(20,60-Dimethoxybiphenylyl))methylphenyl-
phosphine-P-borane (7)
7.8 (s, CH2), 25.5 (s, CH3) ppm. C9H26BPSi (204.17): calcd. C 52.94, H
12.83; found C 50.93, H 13.55. [
(c ¼ 0.3, CHCl3): ꢀ8.9.
a]
D
Compound 5 (0.732 g, 2.0 mmol) was dissolved in 20 ml of dry
diethyl ether and cooled to ꢀ20 ꢁC. Methyllithium (2.00 ml of 1.6 M
solution, 3.2 mmol) was added rapidly by syringe and the mixture
was left stirring for 30 min and then allowed to warm to room
temperature. Water was carefully added and the mixture was
extracted with diethyl ether (3 ꢂ 30 ml). The combined organic
extracts were washed with water (100 ml), the final organic frac-
tion was dried with anhydrous sodium sulphate, filtered and
concentrated to dryness furnishing the product as a white powder.
Yield: 0.271 g (39%). 31P{1H} NMR (101.3 MHz, CDCl3, 298 K):
4.2.9. (S)-Tert-butyl(2-methyl-2-phenyl-2-sila-1-propyl)
methylphosphine-P-borane (11b)
The crude oil was purified by column chromatography (flash
SiO2, hexane/ethyl acetate 95:5) to afford the title compound as
a white powder. Yield: 5.65 g (90%). 31P{1H} NMR (101.3 MHz,
CDCl3, 298 K),
CDCl3, 298 K):
d
¼ þ24.0 (q, JPB ¼ 68.8 Hz) ppm. 1H NMR (400.1 MHz,
d
¼ 0.50 (s, 3H), 0.56 (s, 3H), 1.00 (d, 3H, J ¼ 11.2 Hz),
1.05 (d, 2H, J ¼ 13.2 Hz), 1.13 (d, 9H, J ¼ 13.2 Hz), 7.36e7.40 (m, 3H,
Ar), 7.55e7.59 (m, 2H, Ar) ppm. 13C{1H} NMR (100.6 MHz, CDCl3,
d
¼ þ10.7 (d, bs, J ¼ 68.6 Hz) ppm. 1H NMR (400.1 MHz, CDCl3,
298 K):
d
¼ ꢀ1.5 (s, CH3), ꢀ0.4 (d, CH3, JCP ¼ 2.0 Hz), 7.2 (d, CH3,
298 K):
d
¼ 0.20e2.10 (m, bs, 3H), 1.53 (d, 3H, J ¼ 10.0 Hz), 3.21 (s,
JCP ¼ 35.2 Hz), 7.6 (d, CH2, JCP ¼ 20.1 Hz), 24.5 (d, CH3, J ¼ 2.0 Hz),
28.2 (d, C, JCP ¼ 33.2 Hz), 127.9 (Ar), 129.3 (Ar), 133.4 (Ar), 138.38
(Ar), 138.42 (Ar) ppm. MS (HR-ESI(þ)): m/z 265.1699 [M ꢀ H]þ;
289.1678 [M þ Na]þ. HPLC (hexane:2-propanol, 90:10), tR: 7.95 min
C14H28BPSi (266.24): calcd. C 63.16, H 10.60; found C 62.95, H 11.43.
3H), 3.58 (s, 3H), 6.27 (d, 1H, J ¼ 8.4 Hz), 6.49 (d, 1H, J ¼ 8.4 Hz),
7.07e7.55 (m, 9H, Ar), 8.07e8.13 (m, 1H, Ar) ppm. 13C{1H} NMR
(100.6 MHz, CDCl3, 298 K):
CH3), 55.4 (s, CH3), 103.1e158.0 (m, C, CH, Ar) ppm. C21H24BO2P:
d
¼ 10.8 (d, CH3, JCP ¼ 41.3 Hz), 55.1 (s,
calcd. C 72.02, H 6.91; found C 72.43, H 7.05.
[a
]
D (c ¼ 0.6, CHCl3): þ4.3ꢁ.
4.2.5. (R)-(2-(20,60-Dimethoxybiphenylyl))methoxy-
4.2.10. (S)-Ferrocenyl(2,2-dimethyl-2-sila-1-propyl)
phenylphosphine (6)
methylphosphine-P-borane (12a)
Phosphinite-borane 5 was dissolved in degassed morpholine
and stirred for 14 h at room temperature. The morpholine was
removed in vacuo and the pasty residue was dissolved into a small
amount of toluene and eluted through a short column of alumina,
with toluene as eluent. Concentration to dryness quantitatively
furnished the desired phosphinite as a colourless oil. 31P{1H} NMR
The crude product was purified by column chromatography
(flash SiO2, hexane/ethyl acetate 9:1 as eluent) to afford the title
compound as an orange powder. Yield: 3.53 g (45%). 31P{1H} NMR
(101.3 MHz, CDCl3, 298 K):
298 K):
d
¼ þ3.8 (bs) ppm. 1H (400.1 MHz, CDCl3,
d
¼ 0.06 (s, 9H), 1.07 (d, 2H, J ¼ 15.0 Hz), 1.56 (d, 3H,
J ¼ 10.1 Hz), 4.28 (s, 5H), 4.30e4.32 (m, 1H), 4.40e4.42 (m, 2H),
(101.3 MHz, CDCl3, 298 K):
CDCl3, 298 K):
6.41 (d, 1H, J ¼ 8.4 Hz), 6.66 (d, 1H, J ¼ 8.2 Hz), 7.14e7.44 (m, 9H, Ar),
7.68e7.70 (m, 1H, Ar) ppm.
d
¼ þ112.1 ppm 1H NMR (250.1 MHz,
4.49e4.51 (m, 1H) ppm. 13C{1H} NMR (100.6 MHz, CDCl3, 298 K):
d
¼ 3.24 (s, 3H), 3.52 (d, 3H, J ¼ 15.0 Hz), 3.81 (s, 3H),
d
¼ 0.4 (s, CH3), 15.2 (d, CH3, JCP ¼ 40.1 Hz), 17.3 (d, CH2,
JCP ¼ 22.2 Hz), 69.5 (s, Cp), 69.75 (m, Cp), 70.9 (d, Cp, JCP ¼ 8.1 Hz),
71.1 (d, Cp, JCP ¼ 6.1 Hz), 72.1 (d, Cp, JCP ¼ 14.2 Hz) ppm.
C15H26FePBSi (332.09): calcd. C 54.25, H 7.89; found C 53.90, H 7.94.
4.2.6. (S)-(2-(20,60-Dimethoxybiphenylyl))methylphenylphosphine (8)
The same method used to deboronate 5 was employed. The
desired product was obtained quantitativelyas awhite solid. 31P{1H}
HPLC (hexane:2-propanol, 95:5), tR: 10.66 min [
CHCl3): ꢀ10.0.
a
]
(c ¼ 0.3,
D
NMR (101.3 MHz, CDCl3, 298 K):
CDCl3, 298 K):
(d,1H, J ¼ 8.4 Hz), 6.64 (d,1H, J ¼ 8.4 Hz), 7.17e7.41 (m,10H, Ar) ppm.
d
¼ ꢀ33.9 ppm 1H NMR (400.1 MHz,
4.2.11. (S)-Ferrocenyl(2-methyl-2-phenyl-2-sila-1-propyl)
methylphosphine-P-borane (12b)
d
¼1.44 (d, 3H, J ¼4.4 Hz), 3.43(s, 3H), 3.76 (s, 3H), 6.48
The crude product was purified by recrystallisation in
dichloromethane/hexane to afford the title compound as an orange
powder. Yield: 8.37 g (90%). 31P{1H} NMR (101.3 MHz, CDCl3,
4.2.7. General procedure for enantioselective deprotonation of
dimethylphosphine-boranes 9e10
298 K):
298 K):
d
¼ þ4.59 (q, JPB ¼ 57.7 Hz) ppm. 1H NMR (400.1 MHz, CDCl3,
¼ 0.30 (s, 3H), 0.45 (s, 3H), 1.30 (d, 2H, J ¼ 14.8 Hz), 1.41 (d,
(ꢀ)-Sparteine (5.53 g, 23.6 mmol) was dissolved in diethyl ether
d
(20 ml) and cooled to ꢀ78 ꢁC. s-BuLi (18.2 ml of a 1.3 M solution,
3H, J ¼ 10.1 Hz), 4.26 (bs, 6H), 4.38 (bs, 2H), 4.46 (bs, 1H), 7.35 (bs,

2344
A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2011) 2338e2345
3H), 7.46e7.47 (m, 2H) ppm. 13C{1H} NMR (100.6 MHz, CDCl3,
298 K):
5.08. MS (HR-ES(þ)): m/z 513.0818 [M ꢀ Cl]þ. MS (HR-ES(þ)): calcd.
for [M ꢀ Cl]þ m/z 513.0811, found 513.0818.
d
¼ ꢀ1.29 (s, CH3), ꢀ1.22 (s, CH3), 14.72 (d, CH3,
JCP ¼ 40.8 Hz), 17.0 (d, CH2, JCP ¼ 25.4 Hz), 69.5 (bs, Cp), 69.7e69.8
(m, Cp), 70.9e71.1 (m, Cp), 72.0e72.2 (m, Cp), 127.9 (Ar), 129.3 (Ar),
133.4 (Ar), 138.3 (m, Ar) ppm. C20H28BFePSi (394.15): calcd. C 60.95,
H 7.16; found C 59.86, H 7.49. HPLC (hexane:2-propanol, 90:10), tR:
4.3.2. [PdCl(
The same procedure used to prepare C6 but using 8 was
employed. Yield 80%. IR (KBr),
(cmꢀ1): 1471, 1434. C25H28ClO2PPd
h
3-C4H7)(8)] (C8)
n
11.91 min [
a
]
D
(c ¼ 0.6, CHCl3): ꢀ3.4ꢁ.
(533.33): calcd. C 56.30, H 5.29; found C 56.60, H 5.10. MS (HR-ES
(þ)): calcd. for [M ꢀ Cl]þ m/z 497.0862, found 497.0871.
4.2.12. Crystal structure determination of 12b
Orange crystals, suitable to perform X-ray diffraction studies,
were obtained by slow diffusion of hexane over a solution of 12b in
4.3.3. [PdCl(
The same procedure used to prepare C6 but using 13a was
employed. Yield 90%. IR (KBr),
(cmꢀ1): 1463, 1422. C13H30ClPPdSi
(387.31): calcd. C 40.31, H 7.81; found C 41.10, H 8.14.
h
3-C4H7)(13a)] (C13a)
dichloromethane
at
room
temperature.
C20H28BFePSi
n
Mr ¼ 394.14 gmolꢀ1, monoclinic, a ¼ 9.014(6) Å, b ¼ 11.641(7) Å,
c ¼ 10.499(4) Å,
b
¼ 109.55(2), U ¼ 1038.2(10) Å3, T ¼ 298(2) K,
space group P21, Z ¼ 2, 7736 reflections measured, 4669 unique
(Rint ¼ 0.0407), which were used in all calculations. The final wR
(F2) was 0.1196 (all data).
4.3.4. [PdCl(h
3-C4H7)(13b)] (C13b)
The same procedure used to prepare C6 but using 13b
(impurified with DABCO and DABCO$BH3) was employed. The
crude complex was rapidly dissolved in anhydrous CDCl3 and
analysed by NMR. Attempts of purification resulted into deposition
of Pd black.
4.2.13. (S)-Ferrocenyl(2-(2-naphthyl)methyl)methylphosphine-P-
borane (12c)
The crude oil was purified by column chromatography (flash
SiO2, hexane/ethyl acetate 1:9 as eluent) to afford the title
compound as an orange solid. Yield: 5.67 g (60%). 31P{1H} NMR
4.3.5. [PdCl(h
3-C4H7)(13c)] (C13c)
The same procedure used to prepare C6 but using 13c was
(101.3 MHz, CDCl3, 298 K),
CDCl3, 298 K):
d
¼ þ1.7e2.3 (m) ppm. 1H (400.1 MHz,
employed. The title product was recovered as an orange oil after
d
¼ 1.56 (d, 3H, J ¼ 10.0 Hz), 2.01e2.15 (m, 2H),
concentration to dryness. IR (Nujol), n
(cmꢀ1): 1462. C21H30ClPPd,
2.82e3.00 (m, 2H), 4.31 (s, 6H), 4.40e4.47 (m), 4.55e4.57 (m, 1H),
7.24e7.27 (dd, 1H, J ¼ 8.0, 1.6 Hz), 7.40e7.47 (m, 2H), 7.57 (bs, 1H),
MS (HR-ES(þ)): calcd. for [M ꢀ Cl]þ m/z 419.1120, found 419.1126.
7.74e7.80 (m, 3H) ppm. 13C{1H} (100.6 MHz, CDCl3, 298 K):
d
¼ 10.8
4.3.6. [PdCl(h
3-C4H7)(14a)] (C14a)
The same procedure used to prepare C6 but using 14a was
employed. The title product was recovered as an orange oil after
(d, CH3, JCP ¼ 40.1 Hz), 29.4 (s, CH2), 30.8 (d, CH2, JCP ¼ 35.4 Hz), 69.6
(s, Cp), 71.3e71.5 (m, Cp), 72.6 (s, Cp), 72.8 (s, Cp), 125.4 (s, Ar), 126.1
(d, Ar, JCP ¼ 3.3 Hz), 126.6 (s, Ar), 127.4 (s, Ar), 127.5 (s, Ar), 128.2 (s,
Ar), 132.1 (s, Ar), 133.5 (s, Ar) ppm. C23H26FeBP (400.08): calcd. C
69.05, H 6.55; found C 68.99, H 6.77. HPLC (hexane:2-propanol,
concentration to dryness. IR (Nujol),
n
(cmꢀ1): 1460.
C19H30ClFePPdSi, MS (HR-ES(þ)): calcd. for [M ꢀ Cl]þ m/z 479.0239,
found 479.0237.
95:5), tR: 8.27 min [
a]
D (c ¼ 0.6, CHCl3): ꢀ5.4ꢁ.
4.3.7. [PdCl(h
3-C4H7)(14b)] (C14b)
4.2.14. Deprotection of phosphine-boranes 11 and 12
The same procedure used to prepare C6 but using a solution of
14b (impurified with DABCO and DABCO$BH3) in toluene was
employed. The crude complex was dissolved in dichloromethane
and rapidly washed with aqueous 10% solution of hydrochloric acid.
The organic layer was separated, dried with Na2SO4, filtered and
concentrated to dryness. The residue was purified by column
chromatography (flash SiO2, hexane/ethyl acetate 9:1 as eluent),
yielding the title product as an orange oil after concentration to
Method A: The phosphine-borane (11a, 11c, 12a or 12c) was
dissolved in dichloromethane and the solution cooled to ꢀ10 ꢁC. 5
equivalents of HBF4$OEt2 were added and the mixture was stirred
for 1 h at room temperature. The completion of the deboronation
and formation of the phosphonium salt was checked by 31P NMR
spectroscopy. The solution was treated with degassed, aqueous
saturated solution of NaHCO3 and stirred vigorously during 30 min
31P NMR spectroscopy confirmed complete formation of the
phosphine. The organic layer was separated, dried with sodium
sulphate and filtered. This solution, containing the free phosphine,
was immediately treated with the Pd dimer to form complexes C.
Method B: The phosphine-borane (11b or 12b) and DABCO
(10 equivalents) were dissolved in degassed toluene and heated to
90 ꢁC during 6 h. The completion of the reaction was confirmed by
31P NMR spectroscopy. Once cold, this solution was treated with
a CH2Cl2 solution of the Pd dimer to obtain the neutral complexes C.
dryness. IR (KBr),
n
(cmꢀ1): 1459. The value of the given elemental
analysis is the best of several runs C24H32ClFePPdSi (577.29): calcd.
C 49.93, H 5.59; found C 46.13, H 5.89. MS (HR-ES(þ)): calcd. for
[M ꢀ Cl]þ m/z 541.0395, found 541.0400.
4.3.8. [PdCl(
The same procedure used to prepare C6 but using 14c was
employed. Yield 65%. IR (KBr),
(cmꢀ1): 1413. C27H27ClFePPd
h
3-C4H7)(14c)] (C14c)
n
(580.19): calcd. C 55.90, H 4.69; found C 55.93, H 5.18.
4.3. Synthesis of palladium complexes
4.4. General procedure for the enantioselective hydrovinylation of
styrene
4.3.1. [PdCl(
Phosphinite 6 (0.197 g, 0.56 mmol) was dissolved in 10 ml of
anhydrous CH2Cl2. The dimer [PdCl( -Cl)(
3-C4H7)]2 (0.181 g,
h
3-C4H7)(6)] (C6)
Hydrovinylation reactions were performed in a stainless-steel
autoclave fitted with an external jacket connected to an ethanol
bath and the temperature controlled using a thermostat to ꢃ0.5 ꢁC.
Internal temperature was controlled with a termopar.
m
h
0.27 mmol) was added and the mixture was stirred for 1 h. The
solvent was removed in vacuo and the remaining yellowish powder
was washed several times with pentane. Finally, the obtained
powder was filtered and dried under vacuum. NMR data of C6 and
the rest of Pd complexes are listed in Tables 1Se3S (Supporting
A
mixture of the suitable neutral palladium complex C
(0.045 mmol), AgBF4 (8.8 mg, 0.045 mmol) and styrene (4.7 g,
45 mmol) in 10 ml of dry and freshly distilled dichloromethane was
stirred for 5 min in the dark. After filtering off the AgCl formed, the
solution was placed into the autoclave (which had been purged by
information). Yield 0.28 g (91%). IR (KBr),
C25H28ClO3PPd (548.05): calcd. C 54.66, H 5.14; found C 54.33, H
n
(cmꢀ1): 1473, 1430.

A. Grabulosa et al. / Journal of Organometallic Chemistry 696 (2011) 2338e2345
2345
successive vacuum/nitrogen cycles and thermostated to 25 ꢁC) by
syringe. Ethylene was admitted until a pressure of 15 bar was
reached. After the desired time, the autoclave was slowly depres-
surised and 10 ml of a 10% aqueous NH4Cl solution was added. The
mixture was stirred for 10 min in order to quench the catalyst. The
organic layer was separated, dried with Na2SO4, filtered through
a plug of SiO2 and subjected to GC analysis to determine the
product distribution and the ee using 30 m (0.320 mm) Agilent HP5
and 30 m (0.25 mm) Astec Chiraldex DM Columns. The major
components were also characterised by 1H NMR.
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The authors thank the Ministerio of Educación y Ciencia, (MEC,
grant number CTQ2007-61058/BQU) for financial support of this
work. Financial support from MEC (FPI 2008-002758) is gratefully
acknowledged by A.M.
Appendix A. Supplementary material
CCDC-786189 contains the supplementary data for 12b. These
data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.02.034.
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