Allylpalladium complexes with P-stereogenic monodentate phosphines. Application in the asymmetric hydrovinylation of styrene

Article abstract of DOI:10.1021/om050421v

A group of P-stereogenic monodentate phosphines S-PPhRR' (R = 1-naphthyl, 9-phenan-thryl, or o-biphenylyl and R' = CH₃-, i-C₃R ₃-, and Ph₃SiCH₂-) have been prepared by succesive substitution reactions on the oxazaphospholidineborane obtained from (-)ephedrine and bis(N,N-diethylamino)phenylphosphine. The reaction with binuclear allyl compounds [Pd(μ-Cl)(allyl)]₂ gives neutral [PdCl(allyl)P*] complexes. When allyl = 2-CH₃-CsH₄ (5), two isomers appeared in solution due to the R- or S-geometry around the palladium atom. The discrimination effect of the phosphines is small and the maximum isomeric ratio is observed for PPh(o-Ph₂)(CH ₂SiPh₃). The molecular structure determined by X-ray diffraction of two complexes with P* = PPh(o-Ph₂)(i-Pr) and PPh(o-Ph₂)(OMe) showed a very similar nonsymmetric coordination of the allyl moiety according to the greater trans influence of the phosphorus atom. When allyl = 1-C₆H₅-C₃H₄ (6), the NMR spectroscopy showed up to four isomers due to the R- or S-geometry around palladium and the Z- or E-disposition of P* and the phenyl substituent of the allyl moiety. The E-isomers are the major species in solution, unique with PPh(o-Ph₂)(CH₂SiPh₃). The usual, well-defined dynamic exchanges by π-σ-π and pseudorotation of the allyl moiety have been observed. The codimerization reaction between styrene and ethylene has been tested using filtered CH₂Cl₂ solutions of [PdCl(2-CH₃-C₃H₄)P*] (5) complexes and AgBF₄ as catalytic precursors. Moderate activity (TOF < 225 h^-1 at 25 °C) and good selectivities to 3-Ph-l-butene (-90% at 80% conversion) are obtained. The ee is moderate (<40% ee) and different from the discrimination effects observed in the solutions of neutral complexes [PdCl(ally)P*]. The reaction carried out with deuterated styrene shows the clean C-H addition to the vinyl double bond of stryrene and confirms the irreversible nature of the insertion of styrene in the palladium hydride intermediate. The hydrovinylation reaction using substituted styrene with a potentially secondary coordination atom occurs only when the substitution is in the phenyl ring and without significant improvements of the ee.

Full text of DOI:10.1021/om050421v

Organometallics 2005, 24, 4961-4973
4961
Allylpalladium Complexes with P-Stereogenic
Monodentate Phosphines. Application in the Asymmetric
Hydrovinylation of Styrene
Arnald Grabulosa,† Guillermo Muller,*,† Juan I. Ordinas,† Antonio Mezzetti,‡
Miguel AÄ ngel Maestro,§ Merce` Font-Bardia, and Xavier Solans
Departament de Quı´mica Inorga`nica, Universitat de Barcelona, Martı´ i Franque`s 1-11,
E-08028 Barcelona, Spain, Department of Chemistry, Swiss Federal Institute of Technology,
ETH Ho¨nggerberg, CH-8093 Zu¨rich, Switzerland, AÄ rea de Quı´mica Orga´nica, Departamento
de Quı´mica Fundamental, Facultade de Ciencias, Campus da Zapateira, Universidade da
Corun˜a, E-15071 A Corun˜a, Spain, and Departament de Cristal‚lografia, Mineralogia i
Dipo`sits Minerals, Universitat de Barcelona, Martı´ i Franque`s s/n, E-08028 Barcelona, Spain
Received May 26, 2005
A group of P-stereogenic monodentate phosphines S-PPhRR′ (R ) 1-naphthyl, 9-phenan-
thryl, or o-biphenylyl and R′ ) CH3-, i-C3H8-, and Ph3SiCH2-) have been prepared by
succesive substitution reactions on the oxazaphospholidineborane obtained from (-)-
ephedrine and bis(N,N-diethylamino)phenylphosphine. The reaction with binuclear allyl
compounds [Pd(µ-Cl)(allyl)]2 gives neutral [PdCl(allyl)P*] complexes. When allyl ) 2-CH3-
C3H4 (5), two isomers appeared in solution due to the R- or S-geometry around the palladium
atom. The discrimination effect of the phosphines is small and the maximum isomeric ratio
is observed for PPh(o-Ph2)(CH2SiPh3). The molecular structure determined by X-ray
diffraction of two complexes with P* ) PPh(o-Ph2)(i-Pr) and PPh(o-Ph2)(OMe) showed a very
similar nonsymmetric coordination of the allyl moiety according to the greater trans influence
of the phosphorus atom. When allyl ) 1-C6H5-C3H4 (6), the NMR spectroscopy showed up to
four isomers due to the R- or S-geometry around palladium and the Z- or E-disposition of
P* and the phenyl substituent of the allyl moiety. The E-isomers are the major species in
solution, unique with PPh(o-Ph2)(CH2SiPh3). The usual, well-defined dynamic exchanges
by π-σ-π and pseudorotation of the allyl moiety have been observed. The codimerization
reaction between styrene and ethylene has been tested using filtered CH2Cl2 solutions of
[PdCl(2-CH3-C3H4)P*] (5) complexes and AgBF4 as catalytic precursors. Moderate activity
(TOF < 225 h-1 at 25 °C) and good selectivities to 3-Ph-1-butene (∼90% at 80% conversion)
are obtained. The ee is moderate (<40% ee) and different from the discrimination effects
observed in the solutions of neutral complexes [PdCl(ally)P*]. The reaction carried out with
deuterated styrene shows the clean C-H addition to the vinyl double bond of stryrene and
confirms the irreversible nature of the insertion of styrene in the palladium hydride
intermediate. The hydrovinylation reaction using substituted styrene with a potentially
secondary coordination atom occurs only when the substitution is in the phenyl ring and
without significant improvements of the ee.
Introduction
is also an alternative. The scope of the reaction is limited
by the nature of the olefin since excellent stereoselec-
tivity is achieved only with conjugated dienes or strained
olefins or in intramolecular reactions.3
The process shows a number of singularities, probably
the most important being the monodentate nature of
the unique stabilizing ligand supported by the catalytic
cycle on nickel and palladium systems. Allylic precur-
sors thus proved to be very useful since the metal/
phosphine ratio is 1/1. The basic mechanism is relatively
The reaction of hydrovinylation is a very effective and
highly stereoselective carbon-carbon bond forming
catalytic reaction that can be considered the addition
of a carbon-hydrogen bond from a vinyl group to an
olefin. The reaction, recently reviewed,1 is catalyzed by
a variety of transition metals, with nickel and palladium
compounds being the most used, although ruthenium2
* Corresponding author. E-mail: guillermo.muller@qi.ub.es.
† Departament de Qu´ımica Inorga`nica, Universitat de Barcelona.
‡ Swiss Federal Institute of Technology.
(2) (a) Yi, C. S.; He, Z.; Lee, D. W. Organometallics 2001, 20, 802.
(b) He, Z.; Yi, C. S.; Donaldson, W. A. Org. Lett. 2003, 5, 1567.
(3) (a) Boothe, U.; Rudbeck, H. C.; Tanner, D.; Johannsen, M. J.
Chem. Soc., Perkin Trans. 1 2001, 3305. (b) Dieno Buono, G.; Siv, C.;
Peiffer, G.; Triantaphylides, C.; Denis, P.; Mortreux, A.; Petit, F. J.
Org. Chem. 1985, 50, 1782. (c) Hilt, G.; du Mesnil, F. X.; Lu¨ers, S.
Angew. Chem., Int. Ed. 2001, 40, 387. (d) Kumareswaran, R.; Nandi,
M.; Rajanbabu, T. V. Org. Lett. 2003, 5, 4345. (e) Muller, G.; Ordinas,
J. I. J. Mol. Catal. 1997, 125, 97.
§ Universidade da Corun˜a.
Departament de Cristal‚lografia, Mineralogia i Dipo`sits Minerals,
Universitat de Barcelona.
(1) (a) Rajanbabu, T. V. Chem. Rev. 2003, 103, 2845. (b) Jolly, P.
W.; Wilke, G. In Applied Homogeneous Catalysis with Organometallic
Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH: New York,
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41, 3775.
10.1021/om050421v CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/16/2005

4962 Organometallics, Vol. 24, No. 21, 2005
Grabulosa et al.
Scheme 1
well defined and involves a cationic metal hydride
intermediate that initiates the heterodimerization. The
study of the stereoselectivity in this singular system
with a slightly crowded metal environment is attractive
since the use of prochiral olefins produces a stereogenic
center.
the reaction and all the species contained in the reaction
medium that could potentially operate as ligands. These
species are important in controlling the homo-hetero-
dimerization reaction and the possible isomerization of
the initial reaction product.
The excellent reaction yields using nickel systems
lead to the proposal of a protocol for the synthetic
application of the process.10 Catalyst recovery using
dendritic materials functionalized with P-O hemilabile
ligands has been studied in a pressure membrane
reactor.11 The hydrovinylation carried out with pal-
ladium systems in this way showed less activity than
the corresponding model molecular compounds.11,12 The
efficiency of supercritic CO2 or ionic liquid/CO2 systems
has also been tested.13
Recently, we investigated the model reaction (eq 1)
using nickel and palladium precursors.14,15 The initial
work provided evidence of the blocking effect of inert
bidentate ligands. Further research with allylic pal-
ladium precursors containing P-stereogenic phosphines
enabled the enantioselective version of the process to
be studied. The P-stereogenic phosphines could be
assumed to show good discrimination ability in the
coordination and insertion reaction (Scheme 1) since
they are close to the benzylic group in the allyl inter-
mediate.6 Precursor compounds [Pd(η3-2-Me-C3H4)ClP*]
containing the phosphines S-PBnMesPh and S-PBn-
CyPh gave S-3-Ph-1-butene with 40% and 60% ee,
respectively.15 Two diastereoisomers of the allylic pre-
cursors were observed in solution in a similar ratio (54-
53/46-47), so the discrimination ability of the phosphine
in the reaction could not be inferred from this ratio.
The model reaction of the process involves codimer-
ization between styrene or vinylnaphthalene and eth-
ylene (eq 1). When these types of vinylarenes are used
as prochiral olefins, the excellent regioselectivities
obtained originate in the allylic nature of the intermedi-
ate. However, the control of the reaction’s enantiose-
lectivity is more difficult, and it is probably an excellent
process for evaluating the hemilability or potential
secondary interactions of ligands anchored in one
coordination position around the metal.4 Impressive
enantioselectivities were initially obtained by Wilke5
(95.2% ee) and more recently by the groups of Vogt6
(86% ee), Gibson7 (92% ee), Rajanbabu (87% ee,8 91%
ee4d), and Leitner9 (94.8 ee) using phosphines, planar
chiral chromium phosphines, phosphinites, or phos-
phoramidites as stabilizing ligands with nickel systems.
However, the factors determining the discrimination
ability of the ligands in this reaction remain poorly
defined.
(10) (a) RajanBabu, T. V.; Nomura, N.; Jin, J.; Radetich, B.; Park,
H.; Nandi, M. Chem. Eur. J. 1999, 5, 1963. (b) Rajanbabu, T. V.;
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Chem., Int. Ed. 1999, 38, 1655. (b) Eggeling, E. V.; Hovestad, N. J.;
Jastrzebski, J. T. B. H.; Vogt, D.; van Koten, G. J. Org. Chem. 2000,
65, 8857.
(12) Benito, M.; Rossell, O.; Seco, M.; Muller, G.; Ordinas, J. I.; Font-
Bardia, M.; Solans, X. Eur. J. Inorg. Chem. 2002, 2477.
(13) (a) Wegner, A.; Leitner, W. Chem. Commun. 1999, 1583. (b)
Bo¨smann, A.; Francio`, G.; Janssen, E.; Solinas, M.; Leitner, W.;
Wasserscheid, P. Angew. Chem., Int. Ed. 2001, 40, 2697.
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127.
(15) (a) Albert, J.; Cadena, J. M.; Granell, J.; Muller, G.; Ordinas,
J. I.; Panyella, D.; Puerta, C.; San˜udo, C.; Valerga, P. Organometallics
1999, 18, 3511. (b) Albert, J.; Bosque, R.; Cadena, J. M.; Delgado, S.;
Granell, J.; Muller, G.; Ordinas, J. I.; Font Bardia, M.; Solans, X. Chem.
Eur. J. 2002, 8, 2279.
The final efficiency of the process is determined by
the delicate competition between the olefins present in
(4) (a) Britovsek, G. J. P.; Cavell, K. J.; Keim, W. J. Mol. Catal.
1996, 110, 77. (b) Nomura, N.; Jin, J.; Park, H.; RajanBabu, T. V. J.
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124, 736.

Allylpalladium Complexes
Organometallics, Vol. 24, No. 21, 2005 4963
Since the phosphines tested differed only in the mesityl
and cyclohexyl groups, in this work we obtained a group
of P-stereogenic phosphines by changing two different
substituents. Hence, we prepared organometallic pre-
cursors containing the η3-2-Me-C3H4 and the bulkier
nonsymmetric η3-1-Ph-C3H4 allyl ligands to see whether
it was possible to evaluate the efficiency of the phos-
phine ligand in the hydrovinylation reaction with the
isomer distribution of the allyl complexes in solution.
Perdeuterated styrene was used to support the proposed
mechanism. Some functionalized styrene derivatives
were also tested to check the effect of a secondary
coordination position in the substrate.
(NEt2)2. The crude solutions of the oxazaphospholidine
adducts showed a diastereomeric excess of 92% and
88%, respectively.22b,c,25 The solid compounds separated
were pure diastereomers. Since the use of the amino-
indanol did not represent any advantage, it was more
convenient to continue using the ephedrine as chiral
auxiliary.
The limitations of the Juge´ method in terms of the
type and order of the successive introduction of different
substituents preclude the preparation of a series of
ligands containing -Me, -i-Pr, and -t-Bu groups.
Although the t-Bu substituent can be introduced as the
first one over the ephedrine adduct, the subsequent
methanolysis does not occur.26 As the second substitu-
ent, the associative nature of the substitution reaction
blocked the process. Furthermore, the preparation of
isopropyl phosphines is very slow, about 12 h being
required to complete the reaction compared with 2 h
for methyl substitution. To overcome this problem, the
formation of P-Cl intermediates has been proposed.27
Selection of the groups to be attached to the phosphorus
atom seeks to increase regularly the steric hindrance
of the phosphine and also modify the conformation of
the biphenylyl substituent with respect to the P-B
bond. The methylphosphines S-PPhMeR (R ) o-Ph2 and
1-Naph) have been prepared before,28a,b although PPhMe-
(9-Phen) was obtained in racemic form.28c
The crystal structure of P-borane adducts 3bx, 3cx,
and 3cy (b ) 9-Phen, c ) o-Ph2, x ) Me, y ) i-Pr) was
determined to confirm the expected S-isomer geometry
of the stereogenic center. The distances and angles
measured (Table 1) were similar to those reported for
analogous molecules.28a,29 The disposition of the bi-
phenylyl group is not modified by changing the methyl
(3cx) for the i-Pr (3cy) alkyl substituents (Figure 1).
The relative steric hindrance of the three substituents
can be envisaged using the mean value of the three BPC
angles. Smaller angles should represent higher steric
hindrance, so the order proves to be 3cx ∼ 3cy > 3d >
3bx > 3ax (113.9°)28a (a ) Naph, b ) 9-Phen, c ) o-Ph2,
x ) Me, y ) i-Pr).
Results and Discussion
Phosphine Preparation. P-Stereogenic phosphines
have been prepared by several methods,16 such as the
resolution of racemates,15,17 stereoselective synthesis,
and asymmetric catalysis.18 In direct synthesis, the use
of stoichiometric chiral auxiliaries is needed. The re-
ported methods are based on the pairs (-)-menthol/
phosphine,19 sparteine/dimethylphosphines,20 dynamic
resolution with sparteine-n-BuLi,21 the adduct ephe-
drine/dihalophosphine,22 and the Michaelis-Arbuzov and
the Staudinger reaction to obtain P-stereogenic phos-
phine oxides.23
We used the method developed by Juge´22 and reported
by several groups24 (Scheme 1). Initially, the amino
alcohol (1R,2S)-ephedrine and the most rigid (1R,2S)-
1-amino-2-indanol were tested to achieve the best di-
astereomer discrimination in the reaction with PPh-
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nometallics 1997, 16, 3561.
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K. J. Am. Chem. Soc. 1990, 112, 5244. (b) Watanabe, T.; Gridnev, I.
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When the preparation of the isopropyl-phenanthryl-
protected phosphine was attempted using the standard
protocol, a new, different product was obtained (Scheme
2).
The addition of a slight excess of 2-propyllithium gave
a mixture of the starting protected phosphinite 2b (δP
(24) (a) Nettekoven, U.; Kamer, P. C. J.; Widhalm, M.; van Leeuwen,
P. W. N. M. Organometallics 2000, 19, 4596. (b) Nettekoven, U.;
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Chem. 2003, 68, 156.
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4964 Organometallics, Vol. 24, No. 21, 2005
Grabulosa et al.
Figure 1. ORTEP drawing of the molecular structures of the phosphine-boranes 3bx, 3cx, and 3cy (b ) 9-Phen; c )
o-Ph2; x ) Me; y ) i-Pr) shown at 50% probability. Hydrogen atoms omitted for clarity.
Table 1. Selected Distances (Å) and Angles (deg) of the P-Borane Adducts 3cx, 3cy, 3bx, and 3d
3cx
(o-Ph2)Me
3cy
(o-Ph2)(i-Pr)
3bx
(9-Phen)Me
3d (RPSS)
(9-PhenH2*)(i-Pr)
P(BH3)Ph(aryl)(alkyl)
P-alkyl
1.806(4)
1.801(5)
1.822(5)
1.919(8)
109.7(3)
111.8(3)
112.5(3)
111.33
1.829(2)
1.788(2)
1.816(2)
1.911(3)
111.49(13)
109.74(11)
112.93(12)
111.38
1.796(2)
1.817(2)
1.814(2)
1.934(2)
107.23(11)
117.74(12)
115.18(10)
113.38
1.939(5)
1.835(3)
1.815(3)
1.867(3)
110.4(2)
111.0(2)
117.5(2)
112.96
P-Ph
P-Aryl
P-B
Alkyl-P-B
Ph-P-B
Aryl-P-B
∑/3
dihedral
B-P-C(13)-C(14)
C(1)-C(6)-C(7)-C(12)
57.9(2)
82.3(2)
64.21(12)
92.3(3)
Scheme 2. Proposed Formation of 3d
phosphinite and the selective formation of the 3d
enantiomers could be interpreted as a concerted process
where the reactive 1,2 bond of the phenanthrene moiety
is initially attacked by the nucleophile, giving an
undetected active intermediate. The phosphorus race-
mization is probably produced in the second nucleophilic
attack assuming a P-C double bond as proposed in
Scheme 2.
Allyl Palladium Compounds, [PdCl(η3-allyl)(P)]
(5 and 6). Neutral allyl complexes [PdCl(η3-2-Me-C3H4)-
(P)] (5) and [PdCl(η3-1-Ph-C3H4)(P)] (6) were obtained
by reaction of the dinuclear complexes [Pd(η3-2-Me-
C3H4)(µ-Cl)]2 and [Pd(η3-1-Ph-C3H4)(µ-Cl)]2 with the
appropriate phosphine ligand as reported (see Scheme
3).30 1H NMR and 31P NMR spectra for allyl complexes
at room temperature showed broad signals for the
) 111.5 ppm) and a new compound (δP ) 10 ppm), and
after the addition of an excess of 2-propyllithium the
conversion to the new compound was complete. The final
washing with water changed the chemical shift to δP )
25 ppm. The proton NMR spectrum of the isolated white
solid showed the presence of two independent isopropyl
fragments, one coupled with the phosphorus atom. Two
new signals of aliphatic protons appeared at 3.75
(pseudotriplet, 4.0 Hz) and 2.78 (ddd, 3.2, 10.8, 34.8 Hz).
The integration of the signals and NOESY experiment
were coherent with the protected phosphine 3d. The 31P-
decoupled proton NMR spectrum modifies the signals
at 3.75 (d, ∼ 4 Hz), 2.78 (dd, 3.2, 10.8), and those of the
i-Pr group attached to the phosphorus atom. The signal
at 3.75 ppm disappears when D2O is used as the
washing solvent, and accordingly the signal at 2.78
reduced the multiplicity. Therefore, the initial signal at
10 ppm belongs to an anionic phosphine that captures
the necessary hydrogen atom from the solvent.
Crystals of sufficient quality to confirm the proposed
structure were obtained from mixtures of CH2Cl2 and
hexane. The unit cell contains two enantiomers, RPSS
and SPRR, of the phosphine-borane 3d ((BH3)PPh(9-
PhenH2*)(i-Pr)); Figure 2 shows the RPSS isomer.
Furthermore, optical rotation measurements of solu-
tions of the crude product gave values close to zero that
were consistent with the clean 1H and 13C NMR spectra
observed. Thus, the isomerization of the initial protected
Figure 2. ORTEP drawning, of the molecular structure
of the isomer RPSS of 3d ((BH3)PPh(9-PhenH2*)(i-Pr))
shown at 50% probability. Hydrogen atoms omitted for
clarity.

Allylpalladium Complexes
Organometallics, Vol. 24, No. 21, 2005 4965
Scheme 3. Allyl Compounds of Type 5 and 6 Obtained and Their Isomeric Composition in CDCl3
1
Table 2. 31P and Selected H NMR (CDCl3, 298 K, 101.2 and 500.0 MHz) Dataa (δ in ppm) for Complexes
[Pd(η3-(2-Me-C3H4)ClP] (5)
complex
5ax
31P δ
P-CHn
allyl-Me
syn-tP
anti-tP
syn-cP
anti-cP
P-X-CH3
major 1.1
minor 1
5ayb
3.62 2.19 (d, 9.0)
1.72
1.82
4.42 (m)
3.47 (d, 10.0) 2.66
3.43 (d, 10.0) 2.71
2.58
2.39
3.10 2.22 (d, 9.0)
23.72 3.05 (m)
22.71 3.05 (m)
4.42 (m)
4.32 (m)
4.32 (m)
isomer a 1.1
1.66
1.56
3.41 (d, 10.0) 2.61
3.34 (d, 10.0) 2.30
2.18
2.42
1.05, 1.31 (dd,
15.5, 7.0)
1.12, 1.39 (dd,
15.5, 7.0)
isomer b 1
5bx
major 1.1
minor 1
5cx
5.70 2.29 (d, 8.4)
4.50 2.22 (d, 8.8)
1.75
1.82
4.45 (m)
4.45 (m)
3.50 (d, 11.2) 2.75
3.45 (d, 12.0) 2.75
2.59
2.38
major 1.5
minor 1
5cy
6.21 1.88 (d, 8.0)
8.45 1.60 (d, 8.5)
1.72
1.85
4.22 (dd, 7.5, 2.5) 2.80 (d, 11.0) 2.68
4.37 (dd, 7.5, 2.5) 3.27 (d, 9.5) 2.97
1.66
2.08
major 1.7
33.46 2.49 (ds, 8.5, 6.5)
33.51 2.31 (ds, 8.0, 7.0)
1.85
1.86
4.36 (dd, 7.0, 3.0) 3.12 (d, 10.0) 3.00 (m)
1.87
2.24
0.94, 1.17 (dd,
18.5, 7.0)
0.93, 1.07 (dd,
19.0, 7.0)
minor 1
4.41 (dd, 6.5, 3.0) 3.22 (d, 9.5)
3.08 (m)
5cz
major 1.5
minor 1
5c′b
19.32 3.27, 2.30 (dd, 13.6, 11.2)
12.45 2.73, 2.59 (pt, 14.8)
1.79
1.39
4.26 (m)
4.26 (m)
2.77 (d, 9.6)
2.93 (d, 10.0) 3.00 (d, 2.5)
2.98 (d, 2.5)
1.64
1.61
isomer a 1
isomer b 1
122.25
118.07
1.81
1.84
4.36 (m)
4.36 (m)
3.09 (d, 11.0) 3.17
2.95 (d, 11.0) 2.96
1.88
1.95
3.53 (d, 14.0)
3.73 (d, 14.0)
a Multiplicity (b, broad; d, doublet; m, multiplet; q, quartet; s, septet; t, triplet, p pseudo), JPH and JHH coupling constants (in Hz). b 31P
and 1H signals of both isomers not experimentally related.
unsymmetrical allyl 6 complexes due to their dynamic
behavior. Only complexes 6cz and 5 (c ) o-Ph2, z ) CH2-
SiPh3) gave sharp signals at room temperature. On
cooling to 273 K the signals sharpened sufficiently and
spin-spin interactions could be observed.
The spectra of compounds 5 showed the presence of
two isomers, R and S-Pd, which are in equilibrium. The
31P and 1H data and isomeric composition are collected
in Table 2; the relative ratio of isomers was independent
of the temperature in chloroform. The discrimination
effect of the naphthyl- and phenanthryl-substituted
phosphines is negligible; only in those containing the
o-biphenylyl group is the discrimination moderate, and
even here it is not possible to establish any scale based
on steric factors, as shown in the group of complexes
containing PPh(o-Ph2)R (R ) Me, OMe, i-Pr).
31P NMR spectra of the complexes showed the pres-
ence of both isomers, but when the isomeric ratio is 1/1
1
the signals cannot be associated with those of the H
NMR spectra since the 31P-13C correlations have not
been carried out.
The 1H NMR spectra are more informative, with two
sets of signals for each pair of syn and anti protons being
observed for each pair of isomers of all compounds 5.
The assignations were carried out using the relative
amounts of the major and minor isomer, coupling with
31P in trans position, and NOESY measurements (Table
2). The diastereomeric nature of the methylene protons
P-CH2-Si in 5cz (c ) o-Ph2, z ) CH2SiPh3) is clearly
defined. NOE contacts between syn allyl protons and
the central methyl group and each pair of syn and anti
(30) (a) Kawatsura, M.; Uozumi, Y.; Hayashi, T. Chem. Commun.
1998, 217. (b) Mandal, S. K.; Gowda, G. A. N.; Krishnamurthy, S. K.;
Zheng, C.; Li, S.; Hosmane, N. S. J. Organomet. Chem. 2003, 676, 22.
(c) Boele, M. D. K.; Kamer, P. C. J.; Lutz, M.; Spek, A. L.; de Vries, J.
G.; Leeuwen, P. W. N. M.; van Strijdonck, G. P. F. Chem. Eur. J. 2004,
10, 6232.

4966 Organometallics, Vol. 24, No. 21, 2005
Grabulosa et al.
Table 3. 13C NMR (CDCl3, 298 K, 100.6 MHz) Dataa (δ in ppm) for Complexes [Pd(η3-(2-Me-C3H4)ClP] (5)
complex
P-CHn
Callyl-Me
C1-tP
C3-cP
P-X-CH3
5axb
major 1.1
minor 1
5ay
isomer a 1
isomer b 1
5bx
major 1.1
minor 1
5cx
major 1.5
minor 1
5cy
major 1.7
minor 1
5cz
major 1.5
minor 1
5c′
isomer a 1
isomer b 1
13.30 (d, 27.0)
23.15
23.15
76.90c (d, 34.4)
58.65
59.15
13.85 (d, 27.0)
75.65c (d, 34.2)
26.44 (d, 22.9)
25.75 (d, 23.0)
23.01
22.91
78.58 (d, 31.5)
78.15 (d, 31.4)
59.40
60.45
18.55, 20.70 (d, 8.5)
18.70, 20.96 (d, 7.6)
13.50 (d, 26.8)
14.00 (d, 26.8)
23.00
23.12
76.60 (d, 33.0)
76.80 (d, 35.5)
58.85
59.45
15.00 (d, 26.8)
15.70 (d, 26.0)
23.47
23.56
76.15 (d, 34.5)
76.70 (d, 34.5)
59.50
56.90
26.00 (d, 21.4)
26.85 (d, 21.4)
23.22
23.22
77.95 (d, 32.3)
78.55 (d, 31.4)
58.45
58.59
19.32, 20.58 (d, 6.8)
19.00, 20.30 (d, 7.6)
14.58 (d, 12.3)
13.18 (d, 10.7)
23.07
22.56
∼76.8 ov
∼77.2 ov
58.30
56.70
23.44
23.44
79.85 (d, 36.0)
79.30 (d, 36.0)
58.50
56.60
57.26
56.16
c
a Multiplicity (d, doublet; m, multiplet; ov, overlapped), coupling constants JPC in Hz). b Measured at 50.3 MHz. In acetone-d6.
protons attached to one carbon allowed us to assign the
complete set of signals. The phase-sensitive NOESY
spectra at 298 K with a mixing time of 500 ms showed
the well-known η3-η1-η3 isomerization process. The
exchange between syn/anti allyl methylene proton pairs
was observed selectively with the pair cis to the phos-
phorus atom. The pair that is trans only exchange
between syn-syn and anti-anti protons, in accordance
with a selective opening of the allyl ligand trans to the
phosphorus atom as observed in analogous com-
pounds.30c,31 Less important cross-peaks that could be
assigned to the whole apparent allyl rotation were also
observed. Thus, for instance, the pair syn-anti trans
to phosphorus of one isomer exchanges with the same
pair trans to the chloride ligand of the other isomer. The
signals of the alkyl groups of the phosphine and the
methyl group of the allyl group showed the exchange
between both isomers.
complex 5cy (c ) o-Ph2, y ) i-Pr) and the inverse, R-Pd
S-P, for the phosphinite complex 5c′ (c ) o-Ph2, ′ )
OMe). In both structures, the palladium atom showed
a distorted square-planar coordination. Bond distances
and angles are similar to those reported for related allyl
compounds, and the longer Pd-C length trans to the
phosphorus atom is in agreement with the stronger
trans influence of the phosphorus ligand relative to the
chloro ligand. The difference of the C-C distances in
the allyl moiety is more pronounced, showing greater
double-bond character in the trans position to the
phosphorus atom in both complexes, although this
difference could be reversed on changing from S-Pd to
R-Pd isomers as reported.15b,33 However, the difference
between the phosphine and the phosphinite complexes
is rather small and similar to crystal structures of
analogous phosphinite6b or phosphine complexes.34
More interestingly, the o-biphenylyl arm in 5c′ is
directed toward the allyl group, but the substituents at
the phosphorus atom are not large enough to favor
clearly this type of disposition that can be seen in 5cy.
Therefore, in 5c′ the allyl ligand is pushed out of the
plane defined by the Pd-Cl-P atoms (C2 at 0.611 Å in
5c′ and 0.401 Å in 5cy from the plane).
Although complexes containing a terminally mono-
phenyl-substituted allyl can give rise to several isomers
depending on the position occupied by the allyl phenyl
group (syn/syn, syn/anti), NMR spectroscopy (I to IV
in Scheme 3) reveals that complexes 6 appear as a
mixture of four syn/syn isomers, and those with the
phosphine and the phenyl allyl arm in opposite positions
are the most favorable. In this type of allyl complex it
is necessary to define the relative position of the
asymmetric allyl substituent with respect to the two
opposing and different ligands, the syn-anti allyl
geometry of the allyl fragment and the inherent stereo-
genicity of the [M(allyl)AB] complex. Here, the E,Z
13C chemicals shifts for allylic carbons showed that
the carbon atom located in trans position to phosphorus
is more deshielded than the cis one, which usually
coupled to the phosphorus atom as reported (Table 3).32
The central atom resonates at a lower field than the
terminal atoms but was not assigned. The methyl allyl
group appears in nearly an almost identical position,
showing a very small steric differentiation between the
R- and S-Pd environment produced by the chiral phos-
phine.
Suitable monocrystals of 5cy (c ) o-Ph2, y ) i-Pr) and
5c′ (c ) o-Ph2, ′ ) OMe) for X-ray diffraction measure-
ments were obtained by slow diffusion of hexane over a
dichloromethane solution of the complex. The molecular
structure and selected bond lengths and angles are
shown in Figure 3.
The selected crystals from which the structure deter-
mination has been carried out contain only one dia-
stereomer, the configuration S-Pd R-P for the phosphine
(31) Kollmar, M.; Steinhagen, H.; Janssen, J. P.; Goldfuss, B.;
Malinovskaya, S. A.; Va´zquez, J.; Rominger, F.; Helmchen, G. Chem.
Eur. J. 2002, 8, 310.
(32) (a) Åkermark. B.; Krakenberger, B.; Hansson, S.; Vitagliano,
A. Organometallics 1987, 6, 620. (b) Kumar, P. G. A.; Dotta, P.;
Hermatschweiler, R.; Pregosin, P. S.; Albinati, A.; Rizzato, S. Orga-
nometallics 2005, 24, 1306.
(33) Boele, M. D. K.; Kamer, P. C. J.; Lutz, M.; Spek, A. L.; de Vries,
J. G.; van Leeuwen, P. W. N. M.; van Strijdonck, G. P. F. Chem. Eur.
J. 2004, 10, 6232.
(34) (a) Andrieu, J.; Camus, J. M.; Dietz, J.; Richard, P.; Poli, R.
Inorg. Chem. 2001, 40, 1597. (b) Leznoff, D. B.; Rancurel, C.; Sutter,
J. P.; Rettig, S. J.; Pink, M.; Kahn, O. Organometallics 1999, 18, 5097.

Allylpalladium Complexes
Organometallics, Vol. 24, No. 21, 2005 4967
Figure 3. Molecular structures of complexes 5cy and 5c′ and selected bond distances (Å) and structural parameters R
(angle between planes C1C2C3 and PdClP) and τ (dihedral angle PClC3C1).66
1
Table 4. 31P and Selected H NMR Dataa for Complexes [Pd(η3-(1-Ph-C3H4)ClP] (6)
complex
6ay (273 K)
31P δ
H-central
anti-tP
syn-cP
anti-cP
P-CHn
P-X-CH3
major 1 (50%) 93% 35.52 5.47 (ddd, 12.0, 4.87 (dd, 13.0, 2.83 (d, 6.0)
2.34 (d, 12.0) 2.37 (m)
2.42 (d, 12.0) 2.77 (m)
1.08, 0.99 (dd, 7.0, 20.0)
1.17, 0.95 (dd, 7.0, 20.0)
12.0, 7.0)
JPH ) 10.0)
major 2 (43%)
36.42 5.34 (ddd, 12.0, 4.91 (dd, 13.0, 2.86 (d, 6.0)
12.0, 7.0)
JPH ) 10.0)
minor 1 (5%) 7%
minor 2 (2%)
6cy (273 K)
30.36
28.94
major 1 (43%) 82% 27.9 5.75 (m)
5.11 (dd, 10.2, 2.50 (d, 6.0)
JPH ) 13.2)
5.19 (dd, 10.2, 2.81 (d, 6.0)
JPH ) 13.2)
2.65 (d, 12.0) 3.14 (m)
2.27 (d, 12.0) 3.08 (m)
1.15, 1.44 (dd, 6.5, 19.8)
1.08, 1.35 (dd, 6.5, 19.8)
major 2 (39%)
27.6 5.75 (m)
minor 1 (12%) 18% 32.4
minor 2 (6%)
29.8
6cz (293 K)
major 1 (75%) 100% 14.76 4.96 (ddd, 12.8, 4.18 (dd, 11.0, 2.48 (d, 6.8)
1.61 (d, 11.6) 3.42, 2.56 (pt, 12.0)
(dd, 23.2, 16.8)
∼1.55 (ov)
12.0, 5.0)
JPH ) 12.4)
4.62 (pt, 10.8) 2.76 (dd, 6.8)
major 2 (25%)
15.14 4.90 (m, ov)
2.92, ∼1.55 (pt, ov,
12.4)
6ax (273 K)
major 1 (41%) 75%
major 2 (34%)
8.90 5.78 (m)
9.30 5.89 (ddd, 12.5, 5.21 (pt, 10.0) 2.94 (dd, 7.0, 1.5)
5.23 (pt, 10)
2.69 (d, 8.5)
2.69 (d, 8.5) 2.19 (d, 8.5)
2.50 (d, 12.0) 2.26 (d, 8.5)
12.0, 7.0)
H-central
syn-tP
anti-tP
anti-cP
P-CHn
minor 1 (13%) 25%
minor 2 (12%)
4.75
4.60
5.80 (m)
5.95 (m)
4.75 (pt, 10.0)
4.73 (pt, 10.0)
3.82 (d, 10.0) 4.05 (d, 11.5)
3.79 (d, 10.0) 3.99 (d, 11.5)
2.04 (d, 8.5)
1.72 (d, 8.5)
a δ in ppm, CDCl3; multiplicity (d, doublet; t, triplet; m, multiplet; p pseudo; ov, overlapped), coupling constants (in Hz), JPH and JHH
.
1H measured at 400.0 or 500.0 MHz, 31P measured at 101.2 MHz.
convention, the syn-anti description, and the R-S
convention used recently by Faller35 enable each isomer
to be described. Unfortunately, it was not possible to
obtain any crystals of sufficient quality to perform X-ray
diffraction measurements. Isomers III and IV were not
detected with the phosphine containing the SiPh3 group,
and only compound 6ax (a ) Naph, x ) Me) displayed
four sets of clear signals that could be assigned to the
four isomers described in Scheme 3. The combined use
of two-dimensional COSY and NOESY (τmix ) 500 ms,
273 K) experiments enabled the relevant proton signals
to be assigned and the dynamic behavior to be investi-
gated (Table 4). By way of an example, the pattern of
NOE contacts and exchange processes observed are
displayed in Figure 4. Isomers I and II exchange by the
η3-η1-η3 mechanism, which is consistent with the
interconversion between protons Ha′ and the pair Hs and
Ha. This exchange was not detected between isomers
III and IV. The conversion between major and minor
isomers occurs in pairs, I with III and II with IV. The
mechanism is a pseudorotation according to the inter-
conversions observed between the same type of protons.
(35) Faller, J. W.; Sarantopoulos, N. Organometallics 2004, 23, 2008.

4968 Organometallics, Vol. 24, No. 21, 2005
Grabulosa et al.
Table 5. Hydrovinylation of Styrene Catalyzed by [PdL(allyl)(PPhRR′)]BF4 Precursorsa
isomer ratio
selectivity toward
3-Ph-1-butene
PPhRR′
conversion %
codimers %
TOF h-1
ee %
5
6b
Ph2, i-Pr
16.1
59.0
98.8
10.5
8.0
18.1
99.9
94.0
28.5
25.0
64.0
61.5
95.0
16.0
58.8
98.6
10.0
7.8
17.7
93.0
92.0
24.0
22.5
98.9
96.2
70.6
97.2
98.6
95.9
10.2
80.5
96.3
94.4
92.5
98.0
160
120
40 (S)
40 (S)
40 (S)
23 (S)
38 (S)
12 (R)
63/37
63/37
63/37
60/40
60/40
50/50
50/50
50/50
53/47
53/47
43/39
43/39
43/39
Ph2, i-Prc
Ph2, i-Prd
Ph2, Me
125
100
Ph2, SiPh3
Ph2, OMe
Naph, i-Pre
Naph, i-Pre,f
Naph, Me
Phen, Me
Bn, Mes15b
Bn, Cy15a
Menth, t-Bu6
77
75/25
178
>2800
2780
240
50/43
50/43
41/34
22 (S)
∼0 (-)
20 (S)
40 (S)
60 (S)
86 (S)
225
625
56.0
1290
a Reaction carried out at 25 °C, and 15 bar of initial pressure of ethylene, 1 h, in 10 mL of CH2Cl2; ratio styrene/Pd 1000/1; TOF/h
calculated as the total amount of phenylbutenes formed. Conversion: conversion of starting styrene. Codimer: total amount of codimers.
Selectivity: % of 3-phenyl-1-butene with respect to the codimers. bOnly relative amounts of the more stable Z-isomers are represented.
e
f
c5 h. d8 h. 20 min. 15 °C.
Chart 1
of 2-phenyl-2-butene isomers were formed at about 20%
conversion of ethylene, suitable conditions to compare
the discrimination ability of the phosphines avoiding
kinetic resolution in the consecutive isomerization reac-
tion.36 However, the hydrovinylation was followed at
higher conversions with precursor 5cy (c ) o-Ph2, y )
i-Pr) to check the efficiency of this type of catalyst. The
catalytic system remains similarly selective toward S-3-
Ph-1-butene at high conversion (run at 5 h). At almost
total conversion (run at 8 h) the codimers are present
in a relative composition of A/B/C ) 70.5/23.8/4.2% (eq
1), similar to other systems,6 and the ee drops by about
5%, showing the inverse effect to that already re-
ported.36 The catalytic system remains stable since
similar TOF values were obtained until almost total
conversion.
The subtle difference in coordinating ability between
styrene and 3-Ph-1-butene could be varied by changing
the phosphine substituents, as shown in Table 5. The
better selectivity of the codimer toward 3-Ph-1-butene
may be associated with the increased steric hindrance
of the phosphine.
Examples reported in the literature show that when
nickel complexes, containing not very labile bidentate
ligands (Chart 1), were activated with MAO and used
as precursors in the hydrovinylation reaction, the
isomers of 3-phenyl-1-butene or styrene dimers were not
obtained; however, at complete conversion of styrene,
around 70% of trimers and tetramers were obtained.
This ilustrates that with these ligands a second inser-
tion of ethylene competes well with the â-elimination
after formation of the heterodimer.37
Figure 4. NOE contacts and exchange peaks observed for
6ax (a ) Naph, x ) Me).
The pattern showed that the accessibility of the η3-η1-
η3 mechanism is limited to the opening of the allyl
carbon bond trans to the phosphorus atom when it
contains the phenyl substituent. This path is less
favorable for the minor isomers because the rotation on
the η1-carbon cis to the phosphine requires the displace-
ment of the phenyl ring, giving the anti isomer.
Hydrovinylation Reactions. Hydrovinylation Re-
sults. [PdL(η3-2-Me-C3H4)(PPhRR′)]BF4 precursors were
prepared in situ from compounds 5 and AgBF4 in CH2-
Cl2 solution, where L may be solvent or styrene. The
solution was introduced immediately into the reactor
and was pressurized with ethylene. The results obtained
as a mean value of at least three runs are shown in
Table 5. Good reproducibility and excellent selectivity
toward codimers at low conversions were obtained, in
accordance with previous research.15 Only with the
precursor containing the phosphine 4ay (a ) Naph, y
) i-Pr) did a very fast reaction occur, thus preventing
direct comparison of the activity with the other precur-
sors. Despite the slightly faster reactions with the
similar naphthyl or phenanthryl phosphines, this huge
difference cannot be discussed without further struc-
tural data. Thus, the activity observed is difficult to
relate to a single steric parameter.
The ee’s obtained here are moderate, showing a range
of enantioselectivities from 10% to 40% ee that can be
related to pure steric discrimination since secondary
Some features may, however, to be highlighted. For
example, under ethylene pressure dimerization of sty-
rene is negligible and palladium black appears only
after total conversion of styrene. Very small amounts
(36) (a) Englert, U.; Haerter, R.; Vasen, D.; Salzer, A.; Eggeling, E.
B.; Vogt, D. Organometallics 1999, 18, 4390. (b) Shi, W. J.; Xie, J. H.;
Zhou, Q. L. Tetrahedron: Asymmetry 2005, 16, 705.
(37) Faissner, R.; Huttner, G. Eur. J. Inorg. Chem. 2003, 2239.

Allylpalladium Complexes
Scheme 4
Organometallics, Vol. 24, No. 21, 2005 4969
Scheme 5
interactions are not expected with this type of phosphine
substituent.38
The ortho-biphenylyl phosphines are slightly better
than the naphthyl and phenanthryl analogues. The
increased steric hindrance of the alkyl groups attached
to the phosphorus atom also induced greater discrimi-
native power in the phosphine. Major discriminative
power could be expected for biphenylyl-containing phos-
phines, but crystal structures of the allyl precursors
showed that the differences in size of the different
substituents, methyl or isopropyl groups, are not enough
to direct the biphenylyl arm toward the metal center;
thus, the environments generated by this group of
phosphines are similar.
Although the relative amounts of epimers in the
substituted 6 allyl precursors provide accurate informa-
tion about the discriminative power of the palladium-
phosphine unit, the discrimination ability of the phos-
phine ligands in the hydrovinylation of styrene cannot
be deduced from the isomer ratio of the palladium
complexes. Neither is it possible to obtain a reasonable
precise match with the ee’s of the reaction from the
compounds 5, whose allyl moiety is small and too
symmetric to be an effective reporter group, nor from
the isomers of compounds 6. When the substrate used
contains a second potentially coordinating atom, the
hydrovinylation reactions were observed to some extent
only with the aryl-substituted styrene. The results
shown in Scheme 4 do not suggest any important
secondary coordination of the substrate that could
improve the ee.
[PdR(CH3CN)P2]BF4 precursors are readily activated in
the presence of ethylene. Consequently, it seems that
ethylene is unable by itself to substitute certain phos-
phines or induce the η3-η1 shift on the allyl moiety.
Two reactions were carried out with deuterated
styrene under standard conditions using the [PdCl(2-
MeC3H4)PPh(o-Ph2)(i-Pr)] (5cy) complex as the precur-
sor, the first at low conversion, and the second at total
conversion to study the isomerization of 3-Ph-1-butene.
At low conversion the partially deuterated 3-phenyl-1-
butene obtained showed an extremely clean C-H ad-
dition of the ethylene (Scheme 5). The proton NMR
spectra obtained after standard workup and evaporation
of the solvent confirmed the expected isotopomer. Mass
spectroscopy confirmed the isotopic pattern without any
H-D scrambling due to an equilibrium of insertion-â-
elimination between species [A] and [B]. Accordingly,
the insertion reaction of styrene is not reversible under
the reaction conditions.
Isomerization of 3-phenyl-1-butene takes place at
total conversion. The proton NMR spectrum of the crude
product mainly showed the isomer E-2-Ph-2-butene [F]
partially deuterated (Scheme 6). After initiation (reac-
tion a of Scheme 6), the isomerization process must
exclusively transfer the deuterium located in carbon 3
to carbon 1 in the 3-Ph-1-butene (reaction b of Scheme
6). However, the isotopomer obtained showed the trans-
fer of hydrogen alone. Thus, it must be assumed that
the scrambling of hydrogen between the palladium
hydride and the free ethylene is very fast compared with
the isomerization process (reaction c of Scheme 6), since
The Mechanism. Nickel and palladium compounds
are usually used as catalysts in the hydrovinylation of
styrene.
Nonlabile bidentate ligands are known to inhibit the
reaction, so only monodentate or hemilabile ligands are
used to stabilize the catalytic system. Consequently,
allyl palladium complexes [Pd(Allyl)ClP] containing one
monodentate ligand are convenient reaction precursors.
The transition to the active hydride species involves two
steps, initial generation of the cationic species using
silver salts or NaBARF-type halide abstractors, followed
by the insertion and â-elimination of either ethylene or
styrene in the sigma form of the allyl ligand, giving the
active hydride intermediate (Scheme 5).
The cationic precursors [Pd(Allyl)PP]BF4, where PP
is a bidentate phosphine or two monodentate phos-
phines,39 were recovered unaltered after treatment with
ethylene under the same catalytic conditions. However,
(38) (a) Faller, J. W.; Sarantopoulos, N. Organometallics 2004, 23,
2008. (b) Dotta, P.; Kumar, P. G. A.; Pregosin, P. S.; Albinati, A. Helv.
Chim. Acta 2004, 87, 272.
(39) Ceder, R. M.; Garc´ıa, C.; Muller, G.; Rocamora, M. Manuscript
in preparation.

4970 Organometallics, Vol. 24, No. 21, 2005
Grabulosa et al.
Scheme 6
[F] is the only derivative detected. This fact has already
been stated by Ozaki et al.,40 who observed fast inter-
change of deuterium between mixtures of ethylene and
deuterated ethylene using nickel precursors. The comple-
mentary results of the hydrovinylation reaction using
deuterated ethylene could be rationalized in the same
way.41
Scheme 7
The presence of neutral or anionic species in the
reaction medium can compete with ethylene4c,10b for the
open coordination position. This kind of competition
alters either the activity of the reaction or the selectivity
between codimers. In this study the counterion was
always BF4-, so this effect was not investigated. There-
fore, in this case the nature of the anchored phosphine
is the primary element that modifies the pattern of the
free coordination position at the palladium center.
The enantioselectivity depends only on the discrimi-
nation ability between the stereoheterotopic faces of the
olefin generated by the chiral phosphine if the subse-
quent ethylene insertion is faster than the reequilibra-
tion of the benzylic intermediate. The formally enanti-
oselective step of the proposed mechanism, from [A] to
[B], is nonreversible under the reaction conditions, so
what needs to be clarified is the configuration stability
of the benzylic complex [η3C] responsible for the excel-
lent regioselectivity of the reaction. This control must
be complex in a system containing only one monodentate
phosphine, so hemilabile ligands may play an important
role in this reaction, as reported.4
All the experimental data suggest that the intermedi-
ate responsible for the enantioselectivity contains an η3-
benzylic group, one monodentate phosphine, and eth-
ylene ([C] of Scheme 5), so Scheme 7 enables discussion
of the process. The complex dynamics of these particular
allyl complexes includes the well-known η3-η1 exchange
and the pseudorotation of the allyl ligand, as well as a
2,6-suprafacial allyl shift, which is likely to be relatively
faster.42 The 2,6-shift can be considered as a natural
alternative available for the σ-intermediate of the η3-
η1 exchange accessible by the benzylic system. However,
analysis of the different exchange between isomers
showed that only the standard η3-η1 mechanism can
modify the geometry of the final 3-Ph-1-butene product.
The direct insertion of ethylene into the allyl moiety
has been proposed by computational studies43 in pal-
ladium allyl complexes containing one monodentate
phosphine and ethylene, and in this case the insertion
process would take place from the Z-isomers.
It remains unclear which benzylic disposition is the
most stable, the methyl fragment in syn or anti position.
The determined crystal structures containing similar
allylic moieties in palladium compounds gave a syn
disposition in tol-BINAP44 or 2,2′-bipyridyl45 stabilized
(40) Maruyama K.; Kuroki T.; Mizoroki T.; Ozaki A. Bull. Chem.
Soc. Jpn. 1971, 44, 2002.
(41) Kawakami, K.; Kawata, N.; Maruya, K.; Mizoroki, T.; Ozaki,
A. J. Catal. 1975, 39, 134.
(43) Ca´rdenas, D. J.; Alcam´ı, M.; Cossio´, F.; Me´ndez, M.; Echavar-
ren, A. M. Chem. Eur. J. 2003, 9, 96.
(44) Nettekoven, U.; Hartwig, J. F. J. Am. Chem. Soc. 2002, 124,
1166.
(42) (a) Mann, B. E.; Shaw, S. D. J. Organomet. Chem. 1987, 326,
C13. (b) Mann, B. E.; Keasey, A.; Sonoda, A.; Maitlis, P. M. J. Chem.
Soc., Dalton Trans. 1979, 338.

Allylpalladium Complexes
Organometallics, Vol. 24, No. 21, 2005 4971
Bruker DMX-500 or a Varian XL-500 instrument. IR spectra
were recorded on the following spectrometers: FT-IR Nicolet
520, FT-IR Nicolet Impact 400, FT-IR Avatar 330, and FT-IR
Nicolet 5700. FAB mass chromatograms were obtained on a
Fisons V6-Quattro instrument. The routine GC analyses were
performed on a Hewlett-Packard 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 Hewlett-Packard 5890 Series
II gas chromatograph (50-m Ultra 2 capillary column) inter-
faced to a Hewlett-Packard 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 Chiracel OD-H chiral column. The
eluent, in all the determinations, was a mixture of n-hexane/
iPrOH, 95:5. Optical rotations were measured on a Perkin-
Elmer 241MC spectropolarimeter at 23 °C. Enantiomeric
excesses were determined by GC on a Hewlett-Packard 5890
Series II gas chromatograph (30 m Chiraldex DM column) with
a FID detector. Elemental analyses were carried out by the
Serveis Cientificote`cnics of the Universitat Rovira i Virgili in
an Eager 1108 microanalyzer.
complexes and an anti disposition in a methylstyrene
moiety stabilized by 1,10-phenanthroline.46 Analogous
platinum diphosphine species stabilized the benzyl
ligand in anti conformation.47
Furthermore, the anti conformation is proposed as the
most probable isomer following careful NMR analysis
of a series of palladium and platinum η3-methylbenzyl
diphosphine complexes.48 The isomers of type E with
the bulkier phosphine and the phenyl ring in opposing
positions are expected to be preferred.
Conclusions
A group of allyl [PdCl(allyl)P*] complexes (allyl )
2-CH3-C3H4 (5) and 1-C6H5-C3H4 (6)) containing P-
stereogenic phosphines has been obtained. The discrimi-
nation power of the phosphines was reflected in the
relative amounts of diastereoisomers present in solution.
The cationic derivatives [PdS(2-CH3-C3H4)P*]+ were
used as catalyst precursors in the hydrovinylation of
styrene. However, the enantiomeric excess observed in
the reactions were different compared to the isomeric
proportions observed in the solutions of complexes 5 and
6. The control of the enantioselectivity in the hydrovi-
nylation reaction of vinylarenes seems to be done in
benzylic intermediates, a particular type of allylic
intermediates. Reactions carried out using deuterated
styrene showed that the formation of the benzylic
species by insertion of styrene is not reversible under
the reaction conditions ([B] in Scheme 5). The dynamics
of the benzylic intermediates is complex but only the
η3-η1-η3 exchange is able to modify the isomer ratio
of the reaction products.
Consequently, it seems that in order to confirm the
origin of the enantioselectivity in the hydrovinylation
reaction, it is necessary to conduct further studies of
η3-methylbenzyl complexes in an asymmetric environ-
ment. The goal would be to ensure that the ethylene
insertion reaction is faster than the η3-η1-η3 exchange,
to control the enantioselectivity just at the coordination
of the olefin ([A] in Scheme 5). Here, the presence of an
efficient hemilabile ligand could be the determining
factor.4,49
Detailed synthetic procedures and characterization data of
the P-stereogenic phosphines are collected in the Supporting
Information. Only PPh(1-Naph)Me (4ax) has been obtained
by the method of Juge´,28a but the phosphinites (R)-methoxy-
(9-phenanthryl)phenylphosphine-P-borane(1/1) (2b), and (R)-
(2-biphenylyl)methoxyphenylphosphine-P-borane(1/1) (2c) are
already known.
Synthesis. Chloro(η3-2-methylallyl)[(R)-methyl(1-naph-
thyl)phenylphosphine]palladium(II), 5ax. The phosphine
4ax (0.501 g, 2.0 mmol) was dissolved in 20 mL of dichlo-
romethane, and [Pd(η3-2-Me-C3H4)(µ-Cl)]2 (0.394 g, 1.0 mmol)
was added in one portion. The yellow solution was stirred for
1 h. The dichloromethane was then removed, and the addition
of ether (10 mL) caused the precipitation of the 5ax complex
as a pale yellow solid. This solid was filtrated and washed with
ether and pentane. Yield: 0.800 g (90%). Anal. Calcd for C21-
ClH22PPd: C 56.40, H 4.96. Found: C 56.20, H 5.24. IR νj
(cm-1): 3055 ν(C-H), 2977 ν(C-H), 2958 ν(C-H), 2914 ν(C-
H), 1386, 1099, 900, 883, 801, 779, 725, 693, 456.
Chloro[(R)-isopropyl(1-naphthyl)phenylphosphine]-
(η3-2-methylallyl)palladium(II), 5ay. This complex was
prepared with the same method used for 5ax. From 4ay (0.100
g, 0.36 mmol) and the dimer [Pd(η3-2-Me-C3H4)(µ-Cl)]2 (0.07
g, 0.18 mmol) a pale yellow solid was obtained. Yield: 0.100 g
(60%). Anal. Calcd for C23ClH26PPd: C 58.12, H 5.51. Found:
C 58.09, H 5.71. IR νj (cm-1): 3052 ν(C-H), 2955 ν(C-H), 2926
ν(C-H), 2908 ν(C-H), 2854 ν(C-H), 1504, 1435, 1381, 1031,
798, 776, 754, 703, 697, 634, 520, 479.
Experimental Section
Chloro[(R)-(2-biphenylyl)methylphenylphosphine](η3-
2-methylallyl)palladium(II), 5cx. The procedure used was
the same as for 5ax. Starting from the phosphine 4cx (0.379
g, 1.37 mmol) and the palladium dimer [Pd(η3-2-Me-C3H4)(µ-
Cl)]2 (0.237 g, 0.60 mmol) a pale yellow solid was obtained.
Yield: 0.270 g (48%). Anal. Calcd for C23ClH24PPd: C 58.37,
H 5.11. Found: C 58.27, H 5.46. IR νj (cm-1): 3061 ν(C-H),
3042 ν(C-H), 2987 ν(C-H), 2959 ν(C-H), 1438, 891, 884, 751,
734, 699, 508.
Chloro[(R)-(2-biphenylyl)isopropylphenylphosphine]-
(η3-2-methylallyl)palladium(II), 5cy. This compound was
prepared following the procedure used to obtain 5ax. Starting
from 4cy (0.304 g, 1.0 mmol) and [Pd(η3-2-Me-C3H4)(µ-Cl)]2
(0.197 g, 0.5 mmol) a pale yellow solid was obtained. Yield:
0.350 g (70%). Anal. Calcd for C25ClH28PPd: C 59.90, H 5.63.
Found: C 59.42, H 5.84. IR νj (cm-1): 3049 ν(C-H), 2970 ν-
(C-H), 2925 ν(C-H), 2864 ν(C-H), 1463, 1436, 1380, 1097,
1043, 786, 765, 753, 701, 676, 631, 524, 462.
General Data. All compounds were prepared under a
purified nitrogen atmosphere using standard Schlenk and
vacuum-line techniques. The solvents were purified by stan-
dard procedures and distilled under nitrogen. [Pd(η3-2-Me-
C3H4)(µ-Cl)]2 and [Pd(η3-1-Ph-C3H4)(µ-Cl)]2 were prepared
as previously described. The routine 1H, 13C, and 31P NMR
spectra were recorded on either a Varian XL-500 or Mer-400
MHz (1H, standard SiMe4), Varian Gemini (13C, 50.3 MHz,
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 generally carried out with a
50
51
(45) Gatti, G.; Lopez, J. A.; Mealli, C.; Musco, A. J. Organomet.
Chem. 1994, 483, 77.
(46) Rix, F. C.; Brookhart, M.; White, P. S. J. Am. Chem. Soc. 1996,
118, 2436.
(47) Crascall, L. E.; Litster, S. A.; Redhouse, A. D.; Spencer, J. L. J.
Organomet. Chem. 1990, 394, C35.
(48) Crascall, L. E.; Spencer, J. L. Dalton Trans. 1992, 3445.
(49) Ho¨lscher, M.; Francio`, G.; Leitner, W. Organometallics 2004,
23, 5606.
X-ray Diffraction. Yellow crystals were grown, at 4 °C,
by slow diffusion of hexane over a solution of the complex in
dichloromethane.
(50) Dent, W. T.; Long, R.; Wilkinson, A. J. J. Chem. Soc. 1964, 1585.

4972 Organometallics, Vol. 24, No. 21, 2005
Grabulosa et al.
Chloro(η3-2-methylallyl)[(R)-methyl(9-phenanthryl)-
phenylphosphine]palladium(II), 5bx. The procedure used
was the same as for 5ax. Starting from the phosphine 4bx
(0.400 g, 1.33 mmol) and the palladium dimer [Pd(η3-2-Me-
C3H4)(µ-Cl)]2 (0.210 g, 0.53 mmol) a pale yellow solid was
obtained. Yield: 0.305 g (58%). Anal. Calcd for C25ClH24PPd:
C 60.38, H 4.86. Found: C 60.10, H 5.22. IR νj (cm-1): 3065
ν(C-H), 3046 ν(C-H), 3023 ν(C-H), 1489, 1436, 1427, 1108,
793, 748, 726, 711, 700, 642.
Chloro[(R)-(2-biphenylyl)phenyl(2,2,2-triphenyl-2-si-
laethyl)phosphine](η3-2-methylallyl), 5cz. The phosphine
4cz (0.107 g, 0.2 mmol) was dissolved in 10 mL of dichlo-
romethane, and the palladium dimer [Pd(η3-2-Me-C3H4)(µ-Cl)]2
(0.039 g, 0.1 mmol) was added. After 1 h of stirring the solvent
was removed and the pasty solid obtained was washed and
stirred several times with pentane until the yellow solid 5cz
was obtained after filtration. Yield: 0.110 g (75%). Anal. Calcd
for C41ClH38PPdSi: C 67.31, H 5.23. Found: C 67.72, H 5.54.
IR νj (cm-1): 3046 ν(C-H), 3018 ν(C-H), 2957 ν(C-H), 2922
ν(C-H), 1427, 1108, 726, 711, 698, 515.
Chloro[(S)-(2-biphenylyl)methoxyphenylphosphine]-
(η3-2-methylallyl)palladium(II), 5c′. This complex was pre-
pared with the same method used for 5ax. Starting from 2c′
(0.333 g, 1.14 mmol) and the palladium dimer [Pd(η3-2-Me-
C3H4)(µ-Cl)]2 (0.195 g, 0.49 mmol), the product was obtained
as a very pale yellow solid. Yield: 0.323 g (67%). Anal. Calcd
for C23ClH24OPPd: C 56.46, H 4.94. Found: C 56.49, H 5.35.
IR νj (cm-1): 3052 ν(C-H), 2971 ν(C-H), 2926 ν(C-H), 2835
ν(C-H), 1433, 1099, 1034, 776, 737, 704.
CH), 27.0 (s, CH), 55.3 (s, CH2), 56.8 (s, CH2), 99.6 (d, CH, JCP
) 27.6 Hz), 100.4 (d, CH, JCP ) 27.6 Hz), 124.9-136.7 (m, C,
CH, Ar).
Chloro[(R)-(2-biphenylyl)phenyl(2,2,2-triphenyl-2-si-
laethyl)phosphine](η3-phenylallyl)palladium(II), 6cz. This
complex was obtained through the same procedure as for 5cz.
From the phosphine 4cz (0.200 g, 0.37 mmol) and the pal-
ladium dimer [Pd(η3-1-Ph-C3H4)(µ-Cl)]2 (0.088 g, 0.17 mmol),
a bright yellow solid was isolated. Yield: 0.151 g (56%). Anal.
Calcd for C46ClH40PPdSi: C 69.61, H 5.08. Found: C 69.85, H
5.47. IR νj (cm-1): 3065 ν(C-H), 3046 ν(C-H), 3023 ν(C-H),
1489, 1461, 1427, 1107, 793, 748, 727, 700, 492. 13C{1H} NMR
(100.6 MHz, CDCl3, 298 K), δ (ppm, major isomer): 15.9 (d,
CH2, JCP ) 12.2 Hz), 52.7 (s, CH2), 97.7 (d, CH, JCP ) 29.7
Hz), 110.5 (d, CH, JCP ) 5.4 Hz), 127.2-146.4 (C, CH, Ar). δ
(ppm, minor isomer): 13.9 (br, CH2), 52.1 (s, CH2), 98.9 (m,
CH), 110.0-110.1 (m, CH), 127.2-146.4 (m, C, CH, Ar).
Structural Characterization. Suitable crystals of phos-
phine-borane adducts 3bx, 3cy, and 3d and complexes 5c′ and
5cy for X-ray characterization were mounted in a Bruker
SMART CCD diffractometer. The data were collected using
graphite-monochromated. Mo KR radiation (λ ) 0.71073 Å).
SHELXTL software was used for solution and refinement.52
Absortion corrections were made with the SADABS program.53
The structures were refined by full-matrix least-squares on
F2.
Hydrovinylation Reactions. Hydrovinylation reactions
were performed in a stainless steel autoclave fitted with an
external jacket connected to an isobutanol bath, and the
temperature was controlled using a thermostat to (0.5 °C.
Internal temperature and pressure were recorded as a function
of time with a Linseis L-200 recorder.
X-ray Diffraction. Yellow crystals were grown, at 4 °C,
by slow diffusion of hexane over a solution of the complex in
dichloromethane.
A mixture of the suitable neutral palladium complex 5
(0.045 mmol), AgBF4 (around 8.9 mg, 0.045 mmol), and styrene
(4.7 g, 45 mmol) in 10 cm3 of dry and freshly distilled CH2Cl2
was stirred for 5 min in the dark. After filtering off the AgCl
formed, the solution was placed in the autoclave, which had
previously been purged by successive vacuum/nitrogen cycles
and thermostated at the desired temperature. Ethylene was
admitted until a pressure of 15 bar was reached. After the time
indicated in Table 4 for each reaction, the autoclave was slowly
depressurized and NH4Cl 10% solution (10 cm3) was added.
The mixture was stirred for 10 min in order to quench the
catalyst. The CH2Cl2 layer was decanted off and dried with
Na2SO4. The quantitative distribution of products and their
ee were determined by GC analysis. Major components were
Chloro[(R)-methyl(1-naphthyl)phenylphosphine](η3-
1-phenylallyl)palladium(II), 6ax. The procedure was the
same as that used to prepare the complex 5cz. From the
phosphine 4ax (0.525 g, 2.1 mmol) and the dimer [Pd(η3-1-
Ph-C3H4)(µ-Cl)]2 (0.518 g, 1.0 mmol) the title product was
obtained as a bright yellow solid. Yield: 0.605 g (60%). Anal.
Calcd for C26ClH24PPd: C 61.32, H 4.75. Found: C 61.63, H
5.20. IR νj (cm-1): 3050 ν(C-H), 2969 ν(C-H), 2917 ν(C-H),
2852 ν(C-H), 1505, 1488, 1435 1385, 1101, 892, 800, 775, 751,
691, 522, 453. 13C{1H} NMR (100.6 MHz, CDCl3, 298 K), δ
(ppm): 11.5 (CH3), 14.7 (CH3), 15.5 (CH3), 53.6 (CH), 55.2 (CH),
55.4 (CH), 98.0 (CH), 99.1 (CH) 111.2 (CH), 111.4 (CH), 114.6
(CH), 124.8-136.8 (m, C, CH).
Chloro[(R)-isopropyl(1-naphthyl)phenylphosphine]-
(η3-1-phenylallyl)palladium(II), 6ay. This complex was
obtained in the same way as 5cz. Using the phosphine 4ay
(0.165 g, 0.59 mmol) and the dimer [Pd(η3-1-Ph-C3H4)(µ-Cl)]2
(0.154 g, 0.29 mmol) a bright yellow solid was obtained.
Yield: 0.239 g (75%). Anal. Calcd for C28ClH28PPd: C 62.59,
H 5.25. Found: C 61.83, H 5.42. IR νj (cm-1): 3050 ν(C-H),
2959 ν(C-H), 2926 ν(C-H), 2866 ν(C-H), 1504, 1435, 1386,
1097, 1029, 800, 776, 751, 699, 522, 480. 13C{1H} NMR (100.6
MHz, CDCl3, 298 K), δ (ppm): 18.6 (CH3), 18.7 (CH3), 20.5
(CH3), 20.9 (CH3), 26.7 (s, CH), 27.0 (s, CH), 55.3 (s, CH2), 56.8
(s, CH2), 99.6 (d, CH, JCP ) 27.6 Hz), 100.4 (d, CH, JCP ) 27.6
Hz), 124.9-136.7 (m, C, CH).
1
characterized by H NMR.
Characterization of Hydrovinylation Products. 3-Phen-
1
yl-1-butene. H NMR (200.0 MHz, CDCl3, 298 K): δ (ppm)
1.36 (d, J ) 7.0 Hz, 3H), 3.47 (m, 1H), 5.03 (dd, J ) 10.5 Hz,
J ) 1.4 Hz, 1H), 5.05 (dd, J ) 17.0 Hz, J ) 1.4 Hz, 1H), 6.01
(ddd, J ) 17.0 Hz, J ) 10.5 Hz, J ) 6.8 Hz, 1H), 7.10-7.35
(m, 5H). 13C{1H} NMR (50.3 MHz, CDCl3): δ (ppm) 20.7, 43.2,
113.1, 126.1, 127.2, 128.4, 143.2, 145.5.
(E)-2-Phenyl-2-butene. 1H NMR (200.0 MHz, CDCl3, 298
K): δ (ppm) 1.77 (d, J ) 6.9 Hz, 3H), 2.01 (s, 3H), 5.85 (q, J )
6.9 Hz, 1H), 7.10-7.40 (m, 5H). 13C{1H} NMR (50.3 MHz,
CDCl3): δ (ppm) 14.3, 15.4, 122.4, 125.5, 126.4, 128.1, 135.5,
144.0.
The absolute configuration of the major enantiomer of
3-phenyl-1-butene was assigned by measuring the optical
Chloro[(R)-(2-biphenylyl)isopropylphenylphosphine]-
(η3-1-phenylallyl)palladium(II), 6cy. This complex was
obtained using the same procedure as for 5cz. Starting from
the phosphine 4cy (0.205 g, 0.67 mmol) and the palladium
dimer [Pd(η3-1-Ph-C3H4)(µ-Cl)]2 (0.163 g, 0.32 mmol), a bright
yellow solid was obtained. Yield: 0.320 g (51%). Anal. Calcd
for C30ClH30PPd: C 63.96, H 5.37. Found: C 63.72, H 5.83.
IR νj (cm-1): 3051 ν (C-H), 2964 ν(C-H), 2960 ν(C-H), 2928
ν(C-H), 2924 ν(C-H), 2908 ν(C-H), 1434, 761, 695, 522, 513,
495. 13C{1H} NMR (100.6 MHz, CDCl3, 298 K), δ (ppm): 18.6
(s, CH3), 18.7 (s, CH3), 20.5 (s, CH3), 20.9 (s, CH3), 26.7 (s,
(51) Auburn, P.; Mackenzie, P. B.; Bosnich, B. J. Am. Chem. Soc.
1985, 107, 2033.
(52) (a) Sheldrick, G. M. SHELXS 97: A Computer Program for
Crystal Structure Determination; University of Go¨ttingen: Germany,
1997. (b) Sheldrick, G. M. SHELXL 97: A Computer Program for
Crystal Structure Refinement; University of Go¨ttingen: Germay, 1997.
(53) Sheldrick, G. M. SADABS: A Program for Empirical Absorption
Correction of Area Detector Data; University of Go¨ttingen: Germany,
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Allylpalladium Complexes
Organometallics, Vol. 24, No. 21, 2005 4973
rotation of a reaction mixture and comparing the sign with
the literature.54
Supporting Information Available: Experimental de-
tails and characterization data for P-stereogenic phosphines,
crystallographic data for palladium complexes 5cy and 5c′,
1H and 13C NMR spectra of the aromatic region of palladium
complexes 5, NMR spectra of partially deuterated 3-Ph-1-
butene and 2-Ph-2-butene, and CIF files of phosphines 3bx,
3cy, and 3d and complexes 5cy and 5c′. This material is
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. This work was supported by the
Spanish Ministerio de Ciencia y Tecnolog´ıa (BQU2001-
3358). Financial support from MEC (AP2000-2866) is
gratefully acknowledged by A.G.
(54) (a) Lardicci, L.; Salvadori, P.; Caporusso, A. M.; Menicagli, R.;
Belgodere, E. Gazz. Chim. Ital. 1972, 102, 64. (b) Menicagli, R.; Piccolo,
O.; Lardicci, L.; Wis, M. L. Tetrahedron 1979, 35, 1301.
OM050421V