Carbosilane dendrons containing a P-stereogenic phosphine at the focal point. Catalytic behavior of their allylpalladium complexes in the asymmetric hydrovinylation of styrene

Article abstract of DOI:10.1021/om800033k

Two carbosilane dendrons functionalized in the focal point by the P-stereogenic phosphine (S)-MePPh(2-biphenylyl) were synthesised and reacted with [Pd(μ-Cl)(η³-2-MeC₃H₄)]₂ to give the corresponding palladodendrons. The latter were tested as catalysts in the asymmetric hydrovinylation of styrene. The excellent catalytic results in terms of enantiomeric excesses were compared with those obtained with a model compound and with the related carbosilane dendrimers containing the palladium units on the periphery.

Full text of DOI:10.1021/om800033k

1328
Organometallics 2008, 27, 1328–1333
Carbosilane Dendrons Containing a P-Stereogenic Phosphine at the
Focal Point. Catalytic Behavior of Their Allylpalladium Complexes
in the Asymmetric Hydrovinylation of Styrene
Lara-Isabel Rodríguez, Oriol Rossell, Miquel Seco,* and Guillermo Muller
Departament de Química Inorgànica, UniVersitat de Barcelona, Martí i Franquès, 1-11, 08028 Barcelona, Spain
ReceiVed January 14, 2008
Two carbosilane dendrons functionalized in the focal point by the P-stereogenic phosphine (S)-MePPh(2-
biphenylyl) were synthesised and reacted with [Pd(µ-Cl)(η3-2-MeC3H4)]2 to give the corresponding
palladodendrons. The latter were tested as catalysts in the asymmetric hydrovinylation of styrene. The
excellent catalytic results in terms of enantiomeric excesses were compared with those obtained with a
model compound and with the related carbosilane dendrimers containing the palladium units on the
periphery.
of a metallodendron could depend on its particular generation.
In fact, several examples of a positive dendritic effect have been
reported.4
Here we describe the synthesis of two palladodendrons and
their good catalytic properties exhibited in the hydrovinylation
of styrene.
Introduction
Catalytic versions of asymmetric C-C coupling reactions are
attracting high current interest. In most of the cases, a transition-
metal complex containing chiral phosphines is required as a
catalyst, although an alternative method involving the use of
chiral dendrimers as ligands has emerged in the last few years.1
Dendrimers have some advantages as compared with their
monomeric catalysts. For example, they permit the regulation
of the number and location of the catalytic entities attached to
them and, significantly, they might favor the separation and reuse
of the catalysts from the products. In spite of this, relatively
few examples using metallodendrimers in stereoselective
carbon-carbon bond formation have been reported and the goal
of this paper is to increase the knowledge in this area.
Results and Discussion
The synthesis of the model compound 2 and the new reported
dendrons is shown in Schemes 1 and 2. As the core molecule
we chose trichlorophenylsilane (3), from which the dendron
growth was achieved by an alternating sequence of allylation
and hydrosilylation steps.5 The chloro-terminated dendrons
5 and 7 were then treated with BrMgMe to give the species
8 and 9, containing methyl end groups. The functionalization
of the latter molecules at the focal point was achieved by
using a previously successful method.6,7In this, the phenyl
group is selectively converted to a highly reactive triflato group,
which in turn is readily substituted by a number of nucleophiles.
The acidolytic cleavage of the Si-phenyl units in 8 or 9 was
carried out using trifluoromethanesulfonic acid in a 1:1 molar
ratio at 0 °C in CH2Cl2. Then the mixture was allowed to reach
room temperature. The quantitative conversion was monitored
Recently, we have described the first examples of carbosilane
dendrimers functionalized with P-stereogenic monophosphines
and the catalytic properties of their allylpalladium complexes
in the asymmetric hydrovinylation of styrene.2 The results
showed no dramatic differences in terms of conversion, selectiv-
ity, and enantiomeric excess among the different dendrimer
generations studied. This behavior is probably due to the almost
identical environment around the peripheral metal centers
throughout the dendrimer generations. In view of these results,
the aim of this work was the synthesis of carbosilane dendrons,
functionalized at the focal point with the P-stereogenic fragment
P(2-biphenylyl)PhCH2, capable of coordinating transition-metal
centers. We expected that the specific nanoenvironment of the
catalytic core site created by the dendritic structure could
modulate its catalytic behavior, because of the restricted access
to the metal center,3 and as a result, the reactivity and selectivity
1
by H NMR spectroscopy, which showed no traces of phenyl
resonances at the end of the reaction.
Displacement of the triflate ion from 10 and 12 by the chiral
phosphine was achieved by reaction of the dendrons with the
lithiated derivative Li[CH2P(BH3)(2-biphenylyl)Ph] in THF at
-78 °C (Scheme 2). The latter may be synthesized by direct
(4) (a) Fujita, K.; Muraki, T.; Hattori, H.; Sakakura, T. Tetrahedron
Lett. 2006, 47, 4831. (b) Fujita, K.; Muraki, T.; Sakurai, T.; Oishi, A.;
Taguchi, Y. Chem. Lett. 2005, 34, 1180. (c) Fujihara, T.; Obora, Y.;
Tokunaga, M.; Sato, H.; Tsuji, Y. Chem. Commun. 2005, 4526.
(5) (a) Seyferth, D.; Son, D. Y.; Rheingold, A. L.; Ostrander, R. L.
Organometallics 1994, 13, 2682. (b) Seyferth, D.; Kugita, T.; Rheingold,
A. L.; Yap, G. P. A. Organometallics 1995, 14, 5362. (c) Zhou, L. L.;
Roovers, J. Macromolecules 1993, 26, 963. (d) Benito, M.; Rossell, O.;
Seco, M.; Segalés, G. Inorg. Chim. Acta 1999, 291, 247. (e) van der Made,
A.; van Leeuwen, P. W. N. M. Chem. Commun. 1992, 1400.
* To whom correspondence should be addressed. E-mail: miquel.seco@
qi.ub.es.
(1) Caminade, A. M.; Servin, P.; Laurent, R.; Majoral, J. P. Chem. Soc.
ReV. 2008, 37, 56.
(2) Rodríguez, L. I.; Rossell, O.; Seco, M.; Grabulosa, A.; Muller, G.;
Rocamora, M. Organometallics 2006, 25, 1368.
(3) See, for example: (a) Ribourdouille, Y.; Engel, G. D.; Gade, L. H.
C. R. Chim 2003, 6, 1087. (b) Oosterom, E.; Reek, J. N. H.; Kamer, P. C. J.;
van Leeuwen, P. W. N. M. Angew. Chem., Int. Ed. 2001, 40, 1829. (c)
Caminade, A. M.; Majoral, J. P. Coord. Chem. ReV. 2005, 17/18, 1917. (d)
Caminade, A. M.; Maraval, A.; Majoral, J. P. Eur. J. Inorg. Chem. 2006,
887.
(6) (a) Tuchbreiter, A.; Werner, H.; Gade, L. H. Dalton Trans. 2005,
1394. (b) Meder, M. B.; Haller, I.; Gade, L. H. Dalton Trans. 2005, 1403.
(7) Andrés, R.; de Jesús, E.; de la Mata, J.; Flores, J. C.; Gómez, R.
Eur. J. Chem. 2005, 3742.
10.1021/om800033k CCC: $40.75
2008 American Chemical Society
Publication on Web 02/29/2008

Carbosilane Dendrons Containing a Phosphine
Organometallics, Vol. 27, No. 6, 2008 1329
Scheme 1
lithiation of P(BH3)(2-biphenylyl)PhMe with sec-BuLi.8 Depro-
tection of the resulting species with morpholine, followed by
purification with column chromatography, allowed us to obtain
11 in moderate yields. 13 was obtained in a similar manner,
although in this case the phosphinodendron was previously
isolated in its BH3-protected form as a white solid in good yield.
Both 11 and 13 were characterized by multinuclear NMR
palladium isomers, which are in equilibrium. The yellow
compounds were pure within the limits of the NMR spectro-
scopic detection. They are soluble in moderately polar and
nonpolar organic solvents and were characterized by NMR
spectroscopy, including HSQC H-13C and NOESY H-1H
experiments and electrospray mass spectrometry. The 1H NMR
of the palladium compounds 14 and 15 contained two sets of
signals due to the presence of the two isomers. The integration
showed isomeric ratios of 1:2, similar to those found for 2 and
for the palladodendrimers containing peripheral P*(PdCl(η3-2-
MeC3H4)) units,2 indicating the high steric hindrance induced
by the phosphine. The diastereotopic character of the methylene
protons SiCH2P was also evidenced by 1H NMR spectroscopy
by the presence of different signals for the two nuclei in each
isomer. Thus, for example, for 14, a proton signal for the major
and the minor isomers appeared overlapped in the region of
2.01–1.85 ppm with the anti-cis H signal of the allyl unit, while
the other proton signal appeared at 1.58 (dd, J ) 17.0 Hz, J )
13.0 Hz; major isomer) and at 1.46–1.25 ppm as a multiplet
(minor isomer). The 13C NMR spectra in the aliphatic region
contained two doublets corresponding to CH2P of each isomer
at 14.4 ppm (1JC-P ) 10.6 Hz; minor isomer) and 12.2 ppm
1
1
1
spectroscopy, including HSQC H-13C experiments in order
to assign the aliphatic protons and the carbon signals. The
palladium allyl complexes were prepared in nearly quantitative
yield, following a well-established method,9 by stirring the
ligand 1, 11, or 13 with the dinuclear allyl complex [Pd(µ-
Cl)(η3-2-MeC3H4)]2 in CH2Cl2 at room temperature. The 31P
NMR of the reaction solution showed the disappearance of the
free phosphine signal at about –29 ppm and the emergence of
two singlets at 12.8 and 9.8 ppm for 14 and at 13.6 and 11.0
ppm for 15, which revealed the presence of two expected
(8) Grabulosa, A.; Muller, G.; Ordinas, J. I.; Mezzetti, A.; Maestro,
M. A.; Font-Bardia, M.; Solans, X. Organometallics 2005, 24, 4961.
(9) (a) Benito, M.; Rossell, O.; Seco, M.; Muller, G.; Ordinas, J. I.;
Font-Bardia, M.; Solans, X. Eur. J. Inorg. Chem. 2002, 2477. (b) Rossell,
O.; Seco, M.; Angurell, I. C. R. Chim. 2003, 6, 803.

1330 Organometallics, Vol. 27, No. 6, 2008
Rodríguez et al.
Scheme 2
(1JC-P ) 10.1 Hz; major isomer). The ESI mass spectrum
revealed the molecular peak in both cases, and Figure 1-S
(Supporting Information) gives the spectrum of 15 with the
expected and experimental isotopic distributions. Finally, the
phase-sensitive NOESY 1H-1H spectra of 14 and 15 at 298 K
with a mixing time of 500 ms showed the η3-η1-η3 dynamic
exchange and the pseudorotation mechanisms, typical for these
kinds of complexes10 (see the Supporting Information).
Catalytic Results. Palladium-catalyzed reactions using den-
drimer-based catalysts is an expanding area, due to the variety
of transformations they are able to catalyze, in particular the
possibilities offered for carbon-carbon formation.11 The hy-
drovinylation of styrene and ethylene to produce 3-phenyl-1-
butene is a well-known process. However, the asymmetric
version of the reaction has been much less studied,12 due
probably to the concomitant isomerization of the hydrovinylation
product to achiral species. In fact, the only report in the area of
dendrimers has been reported by our group, involving the use
(11) (a) Jolly, P. W.; Wilke, G. In Applied Homogeneous Catalysis with
Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH:
New York, 2002; Vol. 3, p 1164. (b) RajanBabu, T. V. J. Org. Chem. 2003,
68, 8431.
(10) Espinet, P.; Albéniz, A. C. In ComprehensiVe Organometallic
Chemistry III; Mingos, D. M. P., Crabtree, R. H., Eds.; Elsevier: Oxford,
U.K., 2007; Vol. 8, p 371.
(12) RajanBabu, T. V. Chem. ReV. 2003, 103, 2485.

Carbosilane Dendrons Containing a Phosphine
Organometallics, Vol. 27, No. 6, 2008 1331
Table 1. Catalytic Reactionsa
In conclusion, the combination of the palladium carbosilane
dendrons with NaBARF has been proved to be an active and
enantioselective system for the hydrovinylation reaction of
styrene. Thus, these materials have interesting potential as
catalysts in a continuous-pressure membrane reactor using a
nanofiltration membrane,15 although problems derived from
leaching of palladium metal can not be underestimated.
catalytic
run precursor t (h)
conversnb selectivityc dimers TOFd
(%)
(%)
(%)
(h-1
)
ee (%)
1
2
3
4
5
6
2
2
6
2
6
2
6
29.3
70.4
25.9
61.6
23.4
61.3
99.9
97.7
99.1
97.0
99.0
97.5
0.9
1.4
1.8
0.4
0.4
1.1
72
58
64
51
58
49
83(S)
83(S)
81(S)
82(S)
73(S)
73(S)
14
15
Experimental Section
a Conditions: reactions carried out at 25 °C, 15 bar of initial pres-
sure of ethylene, 10 mL of CH2Cl2, styrene/Pd/NaBARF ratio 500/1/2.
b Total amount of codimers formed. c Percent of 3-phenyl-1-butene with
respect to the codimers. d Calculated as the total amount of phenyl-
butenes formed.
General Data. All manipulations were performed under purified
nitrogen using standard Schlenk techniques. All solvents were
1
distilled from appropriate drying agents. H, 13C{1H}, 31P{1H},
19F{1H}, and 29Si{1H} NMR spectra were obtained on Bruker DXR
250, Varian Unity 300, and Varian Mercury 400 spectrometers.
Bidimensional NMR spectra (NOESY 1H-1H and HSQC 1H-13C)
were recorded on a Varian Mercury 400 spectrometer. Chemical
shifts are reported in ppm relative to external standards (SiMe4 for
1H, 13C, and 29Si, CF3COOH for 19F, and 85% H3PO4 for 31P),
and coupling constants are given in Hz. MS ESI(+) spectra were
recorded in a LC/MSD-TOF (Agilent Technologies) spectrometer.
MS MALDI-TOF spectra were recorded with a Voyager DE-RP
(Perspective Biosystems) spectrometer using DTH (dithranol; 1,8,9-
trihydroxianthracene) or DBH (2,5-dihydroxybenzoic acid) as a
matrix. The routine GC analyses were performed on a Hewlett-
Packard 5890 Series II gas chromatograph (50 m Ultra 2 capillary
column, 5% phenylmethylsilicone and 95% dimethylsilicone) with
an FID detector. 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.
[Pd(η3-2-Me-C3H4)(µ-Cl)]2, P-BH3, 2, 4-6, and 12 were prepared
as previously described.1,6,7 Other reagents were used as received
from commercial suppliers.
of carbosilane dendrimers functionalized peripherally with the
chiral ligands (S)-MePPh(2-biphenylyl) and (S)-MePPh(9-
phenanthryl).2 The best results in terms of enantiomeric excess
(79%) were obtained by using the third-generation carbosilane
dendrimer functionalized with (S)-MePPh(2-biphenylyl) in the
presence of NaBARF (BARF ) B[3,5-(CF3)2C6H3]4) as a halide
abstractor.
These precedents prompted us to investigate the catalytic
properties of the palladium compounds reported here. It is
generally accepted that the key intermediate is a cationic Pd(II)
hydride complex, which reacts with the olefin to afford a
metal-alkyl bond stabilized, in the case of vinyl aromatic
derivatives, in the form of an η3-benzylic complex. This is the
step where the asymmetric discrimination operates.13 Conse-
quently, since the active catalysts are cationic species, they were
prepared in this work in situ from 2, 14, and 15 by reaction
with NaBARF in CH2Cl2. In a typical experiment, after filtration
of the NaCl formed, the solution was introduced immediately
into the reactor and the reactor was pressurized with ethylene,
whereupon the active hydride catalyst was formed. In no case
were the cationic precursors previously isolated. The styrene/
Pd/NaBARF ratio was 500/1/2, and we used 15 bar of initial
ethylene pressure and a reaction temperature of 25 °C. The
conversion was monitored by GC. The results given in Table 1
were obtained as a mean of at least three runs.
All the palladium complexes were catalytically active, and
(S)-3-phenyl-1-butene was the species obtained in excess. A
decrease in the TOF was clearly observed on going from the
mononuclear model compound 2 to the palladodendrimers 14
and 15; this change might be due to the increasing steric bulk
of the dendron, hindering the attack of the nucleophile on the
palladium center, as found by other groups.4 Interestingly, the
selectivity was good and the formation of styrene dimers was
in all cases very low. Moreover, the enantiomeric excesses found
were better than those found for the dendrimers containing the
palladium allyl units on the periphery.2 The best results were
obtained with the model compound 2 (83%) and the dendrimer
14 (81–82%). A negative effect was detected on going to 15
(73%). It is clear that the increase of the dendron generation
strongly affects the catalytic activity, as expected, in contrast
with our observations based on their palladodendrimer conge-
ners. However, in terms of ee value, the results reported here
are better than or comparable with those reported for the best
palladium systems described so far.14
Synthesis of 7. To a solution in thf (25 mL) of 6 (1.95 g, 2.99
mmol) were added an excess of HSiMeCl2 (6.2 mL, 1.105 g/mL,
99%, 59.2 mmol) and 3 drops of the Karstedt catalyst. After the
solution was stirred for 4 h at 50 °C, the volatiles were removed.
A colorless oil was obtained in quantitative yield (4.89 g). 1H NMR
(400.1 MHz, CDCl3, 298 K; δ (ppm)): 7.49–7.42 (m, o-C6H5, 2H),
7.36–7.31 (m, m-C6H5 + p-C6H5, 3H), 1.55–1.46 (m, C5H2, 18H),
3
1.40–1.30 (m, C2H2, 6H), 1.16 (t, JHH ) 8.0 Hz, C6H2, 18H),
0.95–0.82 (m, C1H2, 6H), 0.76 (s, CH3Si, 27H), 0.64–0.60 (m, C3H2
+ C4H2, 24H). 13C{1H} NMR (100.6 MHz, CDCl3, 298 K; δ
(ppm)): 137.7 (s, i-C6H5), 134.2 (s, o-C6H5), 129.1 (s, p-C6H5),
128.0 (s, m-C6H5), 26.1 (s, C6H2), 18.7 (s, C2H2), 17.7 (s, C1H2),
17.6 (s, C5H2), 17.4 (s, C3H2), 16.2 (s, C4H2), 5.7 (s, CH3Si).
29Si{1H} NMR (49.7 MHz, CDCl3, 298 K; δ (ppm)): 32.1 (s, Si2),
1.2 (s, Si1), -4.0 (s, Si0).
(13) Angermund, K.; Eckerle, A.; Lutz, A. Z. Naturforsch., B 1995, 50,
488.
Synthesis of 8. This product was prepared by following literature
procedures6,7 with some experimental modifications. To a stirred
(14) (a) Bayersdörfer, R.; Ganter, B.; Englert, U.; Keim, W.; Vogt, D.
J. Organomet. Chem. 1998, 552, 187. (b) Albert, J.; Cadena, J. M.; Granell,
J.; Muller, G.; Ordinas, J. I.; Panyella, D.; Puerta, C.; Sañudo, C.; Valerga,
P. Organometallics 1999, 18, 3511. (c) 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.
(15) (a) Hovestad, N. J.; Eggeling, E. B.; Heidbüchel, H. J.; Jastrzebski,
J. T. B. H.; Kragl, U.; Keim, W.; Vogt, D.; van Koten, G. Angew. Chem.,
Int. Ed. 1999, 38 (11), 1655. (b) Eggeling, E. V.; Hovestad, N. J.; Jastrzebski,
J. T. B. H.; Vogt, D.; van Koten, G. J. Org. Chem. 2000, 65, 8857.

1332 Organometallics, Vol. 27, No. 6, 2008
Rodríguez et al.
solution in thf of MeMgCl (3 M, 50 mL, 150.0 mmol) at 0 °C, a
solution of 5 (6.70 g, 10.6 mmol, 100 mL of thf) was added, drop
by drop, for 30 min. The mixture was stirred and warmed to room
temperature overnight. A saturated aqueous solution of NH4Cl (100
mL) was added to hydrolyze MeMgCl in excess, and thf was
removed in vacuo. The remaining suspension was extracted with
CH2Cl2 (3 × 30 mL), and the combined organic portions were dried
with anhydrous sodium sulfate. After the CH2Cl2 was evaporated
to dryness, the product was purified by column chromatography
(SiO2, hexane) and it was obtained as a colorless oil. Yield: 3.47 g
(73%). 1H NMR (400.1 MHz, CDCl3, 298 K; δ (ppm)): 7.51–7.47
(m, o-C6H5, 2H), 7.37–7.33 (m, m-C6H5 + p-C6H5, 3H), 1.44–1.36
under N2 on a silica gel column with hexane/thf (100/1) as eluent.
The desired compound was obtained as a colorless oil. Yield: 0.352
g (31%). 31P{1H} NMR (101.3 MHz, CDCl3, 298 K; δ (ppm)):
-29.1 (s). 1H NMR (400.1 MHz, CDCl3, 298 K; δ (ppm)):
7.49–7.16 (m, Ar, 14H), 1.20–1.07 (m, C2H2 + CH2P, 8H), 0.39
(t, 3JHH ) 8.2 Hz, C3H2, 6H), 0.35–0.31 (m, C1H2, 6H), -0.06 (s,
CH3Si, 27H). 13C{1H} NMR (100.6 MHz, CDCl3, 298 K; δ (ppm)):
3
147.7–127.0 (m, Ar), 21.7 (s, C3H2), 18.5 (s, C2H2), 18.3 (d, JCP
) 4.0 Hz, C1H2), 10.9 (d, 1JCP ) 32.7 Hz, CH2P), -1.3 (s, CH3Si).
MS (MALDI-TOF, DBH; m/z): 649.2 (649.2 calcd) [M]•+
.
(m, 2CH2, 6H), 0.87 (t, 3JHH ) 8.4 Hz, C1H2, 6H), 0.60 (t, 3JHH
)
8.2 Hz, C3H2, 6H), -0.02 (s, CH3Si, 27H). 13C{1H} NMR (100.6
MHz, CDCl3, 298 K; δ (ppm)): 138.5 (s, i-C6H5), 134.3 (s, o-C6H5),
128.8 (s, p-C6H5), 127.8 (s, m-C6H5), 21.8 (s, C3H2), 18.7 (s, C2H2),
17.5 (s, C1H2), -1.3 (s, CH3Si). 29Si{1H} NMR (49.7 MHz, CDCl3,
298 K; δ (ppm)): 0.6 (s, Si1), -3.9 (s, Si0).
Synthesis of 13. A 40 µL portion of HOTf (1.696 g/mL, 99%,
0.499 mmol) was added at 0 °C to a solution of 9 (0.800 g, 1.774
mmol) in CH2Cl2 (10 mL). After 20 min at 0 °C, the stirring was
maintained for other 40 min at room temperature. Volatiles were
removed in vacuo. 12 was obtained quantitatively as a colorless
oil. On the other hand, the phosphine-borane P-BH3 (0.195 g, 0.672
mmol) was dissolved in 10 mL of thf, and the solution was cooled
to -78 °C. sec-Butyllithium (485 µl, 1.3 M cyclohexane/hexane
solution, 0.630 mmol) was added slowly. After the violet mixture
that formed was stirred for 2 h, a precooled solution of 12 (0.600
g, 0.421 mmol) in thf (5 mL) was added. The temperature was
maintained at -78 °C for 4 h, and after that the mixture was stirred
for 14 h, slowly achieving room temperature. Afterward, 25 mL
of a 0.5 M aqueous HCl solution was added and the thf was
removed in vacuo. The remaining suspension was extracted with
CH2Cl2 (3 × 30 mL), and the combined organic portions were dried
with anhydrous sodium sulfate. After the CH2Cl2 was evaporated
to dryness, the crude product was extracted with 5 mL of cool
hexane and the soluble fraction was purified by flash chromatog-
raphy (SiO2, starting with hexane and increasing the polarity to
100/5 hexane/thf). The protected phosphine-borane dendron was
obtained as a colorless oil. Yield: 0.312 g (47%). 31P{1H} NMR
(101.3 MHz, CDCl3, 298 K; δ (ppm)): 18.1 (s (br)). 1H NMR (400.1
MHz, CDCl3, 298 K; δ (ppm)): 8.09–6.73 (m, Ar, 14H), 1.38–1.22
(m, C5H2, 18H), 1.17–1.00 (m, C2H2 + CH2P, 8H), 0.62–0.50 (m,
C4H2 + C6H2, 36H), 0.46–0.37 (m, C1H2 + C3H2, 12H), -0.03
(s, CH3Si, 81H). 13C{1H} NMR (100.6 MHz, CDCl3, 298 K; δ
Synthesis of 9. This product was prepared using the same
procedure as for 8, starting from 5.05 g (2.93 mmol) of 7 and 30
mL of a 3 M solution of MeMgCl in thf (90.0 mmol). The desired
1
product was obtained as a colorless oil. Yield: 2.79 g (70%). H
NMR (4001 MHz, CDCl3, 298 K; δ (ppm)): 7.47–7.43 (m, o-C6H5,
2H), 7.32–7.30 (m, m-C6H5 + p-C6H5, 3H), 1.39–1.21 (m, C2H2
+ C5H2, 24H), 0.85–0.78 (m, C1H2, 6H), 0.59–0.50 (m, C3H2 +
C4H2 + C6H2, 42H), -0.04 (s, CH3Si, 81H). 13C{1H} NMR (100.6
MHz, CDCl3, 298 K; δ (ppm)): 138.4 (s, i-C6H5), 134.2 (s, o-C6H5),
128.8 (s, p-C6H5), 127.8 (s, m-C6H5), 21.9 (s, C4H2/C6H2), 18.8 (s,
C2H2 + C5H2), 18.1 (s, C3H2), 17.9 (s, C1H2), 17.6 (s, C4H2/C6H2),
-1.3 (s, CH3Si). 29Si{1H} NMR (49.7 MHz, CDCl3, 298 K; δ
(ppm)): 0.6 (s, Si2), -4.2 (s, Si1), -4.7 (s, Si0).
Synthesis of 11. A 158 µL portion of HOTf (1.696 g/ml, 99%,
1.774 mmol) was added at 0 °C to a solution of 8 (0.800 g, 1.774
mmol) in CH2Cl2 (10 mL). After 20 min at 0 °C, the stirring was
maintained for a further 40 min at room temperature. Volatiles were
removed in vacuo. 10 was obtained quantitatively as a colorless
oil. On the other hand, the phosphine-borane P-BH3 (0.618 g,
2.129 mmol) was dissolved in 20 mL of thf, and the solution was
cooled to -78 °C. sec-Butyllithium (1.50 mL, 1.3 M cyclohexane/
hexane solution, 1.951 mmol) was added slowly. After the violet
mixture that formed was stirred for 2 h, a precooled, recently
prepared solution of 7 (0.246 g, 0.482 mmol) in thf (5 mL) was
added. The temperature was maintained at -78 °C for 4–5 h, and
after that the mixture was stirred for 14 h, slowly achieving room
temperature. Afterward, 25 mL of a 0.5 M aqueous HCl solution
was added and the thf was removed in vacuo. The remaining
suspension was extracted with CH2Cl2 (3 × 30 mL), and the
combined organic portions were dried with anhydrous sodium
sulfate. After the CH2Cl2 was evaporated to dryness, the crude
product was dissolved in morpholine (20 g, 20 mL) and the solution
was stirred for 14 h at room temperature. Morpholine was then
removed by vacuum, and the crude product was passed through a
short column of alumina with toluene as eluent. A mixture of the
dendron 11 and the free phosphine was obtained after the toluene
was evaporated. The product was purified by flash chromatography
(ppm)): 146.8–127.4 (m, Ar), 21.9 (s, C4H2/C6H2), 18.9 (d, 3JCP
)
1.5 Hz, C1H2), 18.8 (s, C5H2), 18.6 (s, C2H2), 18.2 (s, C3H2), 17.6
1
(s, C4H2/C6H2), 7.6 (d, JCP ) 24.0 Hz, CH2P), -1.2 (s, CH3Si).
MS (MALDI-TOF, DBH; m/z): 1565.8 (1565.0 calcd) [M + H]+,
1550.8 (1551.0 calcd) [M - BH3]•+
.
The protected phosphine-borane dendron (0.300 g, 0.192 mmol)
was dissolved in morpholine (10 g, 10 mL), and the solution was
stirred for 14 h at room temperature. The morpholine was then
removed in vacuo, and the crude product was passed through a
short column of alumina with toluene as eluent. Evaporation of
the solvent furnished 13 as a colorless oil. Yield: 0.200 g (67%).
31P{1H} NMR (101.3 MHz, CDCl3, 298 K; δ (ppm)): -28.5 (s).
1H NMR (400.1 MHz, CDCl3, 298 K; δ (ppm)): 7.52–7.12 (m,
Ar, 14H), 1.35–1.26 (m, C5H2, 18H), 1.18–1.06 (m, C2H2 + CH2P,
3
8H), 0.57–0.50 (m, C4H2 + C6H2, 36H), 0.38 (t, JHH ) 8.0 Hz,
3
C3H2, 6H), 0.31 (t, JHH ) 8.0 Hz, C1H2, 6H), -0.03 (s, CH3Si,
81H). 13C{1H} NMR (100.6 MHz, CDCl3, 298 K; δ (ppm)):
147.8–127.0 (m, Ar), 21.9 (s, C4H2/C6H2), 18.8 (s, C5H2), 18.6 (s
(br), C1H2 + C2H2), 18.1 (s, C3H2), 17.7 (s, C4H2/C6H2), 10.7 (d,
1JCP ) 32.7 Hz, CH2P), -1.2 (s, CH3Si). MS (MALDI-TOF, DBH;
m/z): 1549.9 (1551.0 calcd) [M]•+
.
Synthesis of 14. The dendron 11 (0.319 g, 0.491 mmol) was
dissolved in 15 mL of CH2Cl2, and the palladium dimer [Pd(η3-
2-Me-C3H4)(µ-Cl)]2 (0.097 g, 0.246 mmol) was added. After the

Carbosilane Dendrons Containing a Phosphine
Organometallics, Vol. 27, No. 6, 2008 1333
Hsyn-cP, both isomers), 3.21 (d, J ) 9.9 Hz, Hanti-tP, major isomer),
2.57 (s, Hanti-cP, minor isomer), 2.01 (s, allyl Me, minor isomer),
2.01–1.85 (m, CH2P both isomers + Hanti-cP, major isomer), 1.90
(s, allyl Me, major isomer), 1.58 (dd, J ) 17.0 Hz, J ) 13.0 Hz,
CH2P, major isomer), 1.46–1.40 (m, CH2P, minor isomer), 1.35–1.22
(m, C5H2, both isomers), 1.18–0.94 (m, C2H2, both isomers),
0.58–0.46 (m, C4H2 both isomers + C6H2 both isomers + C1H2
both isomers), 0.39–0.31 (m, C1H2 both isomers + C3H2 both
isomers), -0.03 (s, CH3Si, major isomer), -0.03 (s, CH3Si, minor
isomer). 13C{1H} NMR (100.6 MHz, CDCl3, 298 K; δ (ppm)):
146.2–127.0 (m, Ar + allyl Cq, both isomers), 77.7–76.9 (m, allyl
CtP, both isomers), 57.3 (s (br), allyl CcP, minor isomer), 56.4 (s
(br), allyl CcP, major isomer), 23.8 (s, allyl Me, major isomer), 23.3
(s, allyl Me, minor isomer), 21.9 (s, C4H2/C6H2, both isomers),
mixture was stirred for 20 min, the solvent was removed. The
product was obtained quantitatively as a yellow oil (0.416 g).
31P{1H} NMR (101.3 MHz, CDCl3, 298 K; δ (ppm)): 12.8 (s, minor
isomer), 9.8 (s, major isomer). 1H NMR (400.1 MHz, CDCl3, 298
K; δ (ppm)): 7.95–6.92 (m, Ar, both isomers), 4.47 (dd, J ) 6.6
Hz, J ) 2.9 Hz, Hsyn-tP, minor isomer), 4.40 (dd, J ) 7.0 Hz, J )
2.8 Hz, Hsyn-tP, major isomer), 3.49 (d, J ) 9.6 Hz, Hanti-tP, minor
isomer), 3.38 (s (br), Hsyn-cP, both isomers), 3.21 (d, J ) 9.9 Hz, H
3
3
19.2 (d, JCP ) 3.3 Hz, C1H2, minor isomer), 19.0 (d, JCP ) 2.7
Hz, C1H2, major isomer), 18.8 (s, C5H2, both isomers), 18.7 (s,
C2H2, minor isomer), 18.6 (s, C2H2, major isomer), 18.3 (s, C2H2,
minor isomer), 18.2 (s, C2H2, major isomer), 17.6 (s, C4H2/C6H2,
H
anti-tP, major isomer), 2.59 (s, H Hanti-cP, minor isomer), 2.01 (s,
1
allyl Me, minor isomer), 2.01–1.85 (m, CH2P both isomers + Hanti-cP
major isomer), 1.90 (s, allyl Me, major isomer), 1.58 (dd, J ) 17.0
Hz, J ) 13.0 Hz, CH2P, major isomer), 1.46–1.25 (m, CH2P minor
isomer + C2H2 major isomer), 1.22–0.80 (m, C2H2 + C1H2, minor
isomer), 0.65–0.28 (m, C1H2 major isomer + C3H2 both isomers),
-0.08 (s, CH3Si, minor isomer), -0.09 (s, CH3Si, major isomer).
13C{1H} NMR (100.6 MHz, CDCl3, 298 K; δ (ppm)): 146.2–127.0
(m, Ar + allyl Cq, both isomers), 77.7–76.9 (m, allyl CtP, both
isomers), 57.5 (s (br), allyl CcP, minor isomer), 56.5 (d, 2JCP ) 2.0
Hz, allyl CcP, major isomer), 23.8 (s, allyl Me, major isomer), 23.3
(s, allyl Me, minor isomer), 21.9 (s, C3H2, minor isomer), 21.7 (s,
C3H2, major isomer), 18.9 (d, 3JCP ) 3.4 Hz, C1H2, minor isomer),
18.7 (s (br), C1H2 major isomer + C2H2 minor isomer), 18.6 (s,
C2H2, major isomer), 14.4 (d, 1JCP ) 10.6 Hz, CH2P, minor isomer),
both isomers), 14.3 (d (br), JCP ≈ 10 Hz, CH2P, minor isomer),
12.2 (d, 1JCP ) 9.4 Hz, CH2P, major isomer), -1.2 (s, CH3Si, both
isomers). MS (ESI(+); m/z): 1710.0 (1710.0 calcd) [M - Cl]+.
Hydrovinylation Reactions. Hydrovinylation reactions were
performed in a stainless-steel autoclave fitted with an external jacket
connected to an isobutyl alcohol bath, and the temperature was
controlled using a thermostat to (0.5 °C. The internal temperature
was monitored using a thermopar coupled to a digital recorder,
whereas the internal pressure was continuously measured as a
function of time with a Linseis L-200 recorder.
A mixture of the suitable neutral palladium complex (4.0 × 10-5
mol), styrene (0.02 mol), and NaBARF (8.0 × 10-5 mol) in 10
mL of dry and freshly distilled CH2Cl2 was stirred for 20 min in
the dark. After the NaCl that formed was filtered off, the solution
was placed in the autoclave, which had previously been purged by
successive vacuum/nitrogen cycles and thermostated at 25 °C.
Ethylene was admitted until a pressure of 15 bar was reached. After
the time indicated for each reaction (2 or 6 h), the autoclave was
slowly depressurized and aqueous HCl 10% solution (10 mL) 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 values were
determined by GC analysis.
1
12.2 (d, JCP ) 10.1 Hz, CH2P, major isomer), -1.3 (s, CH3Si,
minor isomer), -1.3 (s, CH3Si, major isomer). MS (ESI(+); m/z):
809.3 (809.3 calcd) [M - Cl]+.
Acknowledgment. We acknowledge support from the
Ministerio de Ciencia y Tecnología (Projects CTQ2006-
02362/BQU and CTQ2007-61058/BQU). L-I.R. is indebted
to the Ministerio de Ciencia y Tecnología for a scholarship.
Synthesis of 15. This complex was obtained in the same way as
for 14. With 13 (0.159 g, 0.103 mmol) and [Pd(η3-2-Me-C3H4)(µ-
Cl)]2 (0.020 g, 0.051 g) as starting materials, a yellow oil was
obtained in quantitative yield (0.180 g). 31P{1H} NMR (101.3 MHz,
CDCl3, 298 K; δ (ppm)): 13.6 (s, minor isomer), 11.0 (s, major
isomer). 1H NMR (400.1 MHz, CDCl3, 298 K; δ (ppm)): 7.94–6.93
Supporting Information Available: A figure giving ESI mass
1
spectra of compound 15 and tables giving NOESY H-1H cross-
peaks between the isomers of compounds 14 and 15. This material
is available free of charge via the Internet at http://pubs.acs.org.
(m, Ar, both isomers), 4.47 (dd, J ) 6.4 Hz, J ) 2.6 Hz, Hsyn-tP
,
minor isomer), 4.40 (dd, J ) 7.0 Hz, J ) 2.6 Hz, Hsyn-tP, major
isomer), 3.49 (d, J ) 9.5 Hz, Hanti-tP, minor isomer), 3.39 (s (br),
OM800033K