Phosphino carboxylic acid ester functionalized carbosilane dendrimers: Nanoscale ligands for the Pd-catalyzed hydrovinylation reaction in a membrane reactor

Article abstract of DOI:10.1021/jo000433k

Phosphino carboxylic acid ester terminated G₀ compounds Si{(CH₂)₃SiMe₂(C₆H₄ CH₂OC(O)(CH₂)_nCH₂PPh₂} ₄ (9a and 9b; n = 1, 2) and the carbosilane dendrimers Si{(CH₂)₃ Si((CH₂)₃SiMe₂(C₆H₄ CH₂OC(O)(CH₂)_nCH₂PPh₂) ₃}₄ (10a and 19b; n = 1, 2) have been prepared as hemilabile nanoscale ligands for the palladium-catalyzed codimerization of olefins. The hydrovinylation of styrene was carried out in a continuously operated nanofiltration membrane reactor. Under continuous conditions, the selectivity of the reaction is increased considerably. Monomeric model complexes and the dendritic catalysts were compared for their activity and selectivity in batch reactions. The Pd catalyst complexes were prepared in situ from the dendritic ligands and an (allyl)palladium(II) precursor.

Full text of DOI:10.1021/jo000433k

J . Org. Chem. 2000, 65, 8857-8865
8857
P h osp h in o Ca r boxylic Acid Ester F u n ction a lized Ca r bosila n e
Den d r im er s: Na n osca le Liga n d s for th e P d -Ca ta lyzed
Hyd r ovin yla tion Rea ction in a Mem br a n e Rea ctor
Eva B. Eggeling,† Neldes J . Hovestad, J ohann T. B. H. J astrzebski,‡ Dieter Vogt,*,† and
Gerard van Koten*,‡
Schuit Institute of Catalysis, Laboratory of Inorganic Chemistry and Catalysis, Eindhoven University of
Technology, 5600 MB Eindhoven, The Netherlands, and Debye Institute, Department of Metal-Mediated
Synthesis, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
d.vogt@tue.nl
Received March 22, 2000
Phosphino carboxylic acid ester terminated G0 compounds Si{(CH2)3SiMe2(C6H4CH2OC(O)(CH2)n-
CH2PPh2}4 (9a and 9b; n ) 1, 2) and the carbosilane dendrimers Si{(CH2)3Si((CH2)3SiMe2(C6H4-
CH2OC(O)(CH2)nCH2PPh2)3}4 (10a and 10b; n ) 1, 2) have been prepared as hemilabile nanoscale
ligands for the palladium-catalyzed codimerization of olefins. The hydrovinylation of styrene was
carried out in a continuously operated nanofiltration membrane reactor. Under continuous
conditions, the selectivity of the reaction is increased considerably. Monomeric model complexes
and the dendritic catalysts were compared for their activity and selectivity in batch reactions. The
Pd catalyst complexes were prepared in situ from the dendritic ligands and an (allyl)palladium(II)
precursor.
In tr od u ction
visaged, and several groups have started to explore the
potential of functionalized dendritic materials. Because
of their nanoscopic size these molecularly enlarged den-
dritic compounds have the potential to be removed from
the product mixture via ultra- or nanofiltration tech-
niques.13-15
C-C-coupling reactions that offer the opportunity to
convert cheap carbon feedstocks into valuable chemical
compounds are of high current interest. Major interest
focuses on homogeneous catalytic versions with their
adjustable regio- and stereoselectivity.16
For example, the hydrovinylation reaction (the codimer-
ization with ethylene) of olefins opens easy access to
building blocks for fine chemicals.17 Since the first report
of a hydrovinylation reaction with a RhCl3 catalyst,18
several metals were used as catalysts in hydrovinylation
reactions,19-20 among which nickel21-25 and palladium26-28
were the most successful ones.
It remains a crucial feature for the commercialization
of a catalytic process to separate catalysts from the
reaction mixture. For most of the applications seen in
industry today it was not until an efficient strategy for
catalyst recovery was developed that they were used in
chemical production. Depending on the productivity of
the catalyst, in fine chemicals synthesis the recycling of
sophisticated ligands can be as an important economic
factor as the separation of the noble metal used. There-
fore, there is currently considerable interest in the
development of organometallic catalysts anchored on
supports such as dendrimers.1-7 Taking into account the
enormous structural variety of these well-defined large
molecules, several potential applications in homogeneous
catalysis8-10 and supported synthesis11,12 have been en-
* Corresponding authors.
† Eindhoven University of Technology.
‡ Utrecht University.
(12) Hovestad, N. J .; J astrzebski, J . T. B. H.; van Koten, G. Polym.
Mater. Sci. Eng. 1999, 80, 53.
(13) Kragl, U.; Dreisbach, C. Angew. Chem., Int. Ed. Engl. 1996,
35, 642.
(14) Brinkmann, N.; Giebel, D.; Lohmer, G.; Reetz, M. T.; Kragl, J .
Catal. 1999, 183, 163.
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Int. Ed. Engl. 1990, 29, 138.
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Verlag: Berlin 1998.
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18, 2970.
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Leeuwen, P. W. M. N.; Wijkens, P., Grove, D. M.; van Koten, G. Nature
1994, 372, 659.
(15) Hovestad, N. J .; Eggeling, E. B.; Heidbu¨chel, H. J .; J astrzebski,
J . T. B. H.; Kragl, U.; Keim, W.; Vogt, D.; van Koten, G. Angew. Chem.,
Int. Ed. Engl. 1999, 38, 1655.
(16) Beller, M.; Bolm, C., Eds.; Transition Metals for Organic
Synthesis; Wiley-VCH: New York, 1998.
(17) J olly, W.; Wilke, G. In Applied homogeneous catalysis with
organometallic compounds; Cornils, B.; Herrmann, W. A., Eds.; VCH:
New York, 1992; pp 1024.
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10.1021/jo000433k CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/06/2000

8858 J . Org. Chem., Vol. 65, No. 26, 2000
Eggeling et al.
Sch em e 1. Hyd r ovin yla tion of Styr en e a n d Sid e
Rea ction s
F igu r e 1.
high activity and selectivity toward 3-phenylbut-1-ene 1
were observed applying various phosphino esters.37
However, at higher conversions isomerization of the
product to internal achiral olefins E/ Z-2 takes place.
Therefore, it would be useful to be able to run the reaction
continuously at lower conversion.
Herein we report on the synthesis of dendritic carbosi-
lanes38 functionalized with various diphenylphosphino
carboxylic acid ester end groups. These dendritic hemi-
labile ligands were applied in the palladium-catalyzed
hydrovinylation of styrene. The new Pd catalysts derived
from G0 compounds and G1 dendritic P,O ligands are
relatively stable under the reaction conditions, compared
to similar complexes of monodentate ligands that decom-
pose rapidly after formation to give palladium black. For
the first time, the hydrovinylation was carried out
continuously in a pressure membrane reactor using a
nanofiltration membrane, giving rise to the selective
formation of the desired, chiral 3-phenylbut-1-ene 1.
In case of nickel, a nickel halide salt activated by a
Lewis acid together with a chiral azaphospholene ligand
reported by Wilke is still the most efficient system for
this reaction.29 But progress has been made recently:
RajanBabu et al. obtained good results using hemilabile
MOP ligands. By use of a weakly coordinating counter-
anion, the Lewis acid could be replaced.30,31 Via a similar
route, Leitner et al. were able to apply the successful
Wilke-system in supercritical CO2, yielding promising
results also in view of an immobilization of the catalyst.32
In case of palladium, for sufficient activity the halide
has to be abstracted by a silver salt of a noncoordinating
anion resulting in a cationic palladium complex. Due to
their lower reactivity, the use of palladium catalysts
allows moderate reaction conditions between 0 °C and
room temperature. We could obtain good results in the
asymmetric hydrovinylation of styrene (Scheme 1) using
a ligand bearing a stereogenic phosphorus atom as well
when applying bulky R-chiral (R)-tricarbonyl(η6-ethyl-
benzene)-chromium complexes as asymmetric ligands.33,34
Recently, the chiral benzylcyclohexylphenylphosphine
has been reported by Muller et al. to catalyze the
hydrovinylation of styrene with moderate selectivities
and the hydrovinylation of 2-vinylnaphthalene with good
selectivities.35
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of Mod el a n d
Den d r itic Liga n d s. Model studies were undertaken to
determine the most efficient reaction conditions for
periphery functionalization of the dendritic support.
Coupling of benzylic alcohol with phosphinoxy carboxylic
acid chlorides ClC(O)(CH2)nCH2P(O)Ph2 (n ) 1, 2)39 in
the presence of 4-(dimethylamino)pyridine in DMF af-
forded compounds 3a and 3b (Figure 1).
Compound 3a is a colorless crystalline solid, and 3b is
a slightly yellow viscous oil. Both were isolated in good
1
yields (57-95%). The H NMR spectrum of 3a shows a
It is known that phosphino carboxylic acid derivatives
lead to efficient and selective catalytic systems for C-C
coupling reactions.36 In the hydrovinylation of styrene
multiplet for the methylene protons C(O)(CH2)2P(O)Ph2
at 2.65 ppm, and the 1H NMR spectrum of 3b shows three
well-resolved resonances at 2.00, 2.37, and 2.52 ppm. The
13C and 31P NMR spectra show the respective resonances
at the expected chemical shifts. The GC-MS spectra of
3a and 3b show M+ peaks at respectively 364 and 378
mass units.
(23) Kitatsume, S.; Otaba, S. J pn. Kokai Tokkyo Koho J P 61 91,138,
1986; Chem. Abstr. 1986, 105, 227505d.
(24) Nozima, H.; Kawata, N.; Nakamura, Y.; Maruya, K.; Mizoroki,
T.; Ozaki, A. Chem. Lett. 1973, 1163.
(25) Ceder, R.; Muller, G.; Ordinas, J . I. J . Mol. Catal. 1994, 92,
127.
(26) Barlow, M. G.; Bryant, M. J .; Hazeldine, R. N.; Mackie, A. G.
J . Organomet. Chem. 1970, 21, 215.
(27) Kawamoto, K.; Imanaka, T.; Teranishi, S. Bull. Chem. Soc. J pn.
1970, 43, 2512.
(28) Hattori, S.; Munakata, H.; Tatsuoka, K.; Shimizu, T. US Pat.
3,803,254, 1974.
The compound Si{(CH2)3SiMe2(C6H4CH2OH)}4, G0-
(OH)4 (4), and first generation carbosilane dendrimer Si-
{(CH2)3Si((CH2)3SiMe2(C6H4CH2OH))3}4, G1-(OH)12 (5),
have been used as inert support material. Coupling of
the carbosilane supports 4 and 5 with ClC(O)(CH2)n-
(CH)2P(O)Ph2 (n ) 1, 2), under the same conditions as
described above, resulted in the formation of G0 phos-
phine oxides 6a ,b and dendritic G1 phosphine oxides 7a ,b
as viscous oils, which were isolated in 43-85% yield
(Schemes 2 and 3).
(29) Wilke, G. Angew. Chem. 1988, 100, 189.
(30) Nomura, N.; J in, J .; Park, H.; Rajanbabu, T. V. J . Am. Chem.
Soc. 1998, 120, 459-460.
(31) RajanBabu, T. V.; Nomura, N.; J in, J .; Radetich, B.; Park, H.;
Nandi, M. Chem. Eur. J . 1999, 5, 1963-8.
(32) Wegner, A.; Leitner, W. Chem. Commun. 1999, 16, 1583.
(33) Bayersdo¨rfer, R.; Ganter, B.; Englert, U.; Keim, W.; Vogt, D.
J . Organomet. Chem. 1998, 552, 187-194.
The methylene protons of the SiCH2CH2CH2Si units
appear as three well-resolved resonances for the G0
(34) Englert, U.; Haerter, R.; Vasen, D.; Salzer, A.; Eggeling, E. B.;
Vogt, D. Organometallics 1999, 18, 4390.
(35) 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.
(36) Keim, W.; Maas, H.; Mecking, S. Z. Naturforsch. 1995, 50 b,
430.
(37) Britovsek, G. J . P. Ph.D. Thesis, RWTH Aachen, Germany,
1993.
(38) Majoral, J .-P.; Caminade, A.-M. Chem. Rev. 1999, 99, 845-880.
(39) (a) Tsvetkov, E. N.; Bondarenko, N. A.; Malakhova, I. G.;
Kabachnik, M. I. Synthesis 1986, 198-208.

Carbosilane Dendrimers as Nanoscale Ligands
J . Org. Chem., Vol. 65, No. 26, 2000 8859
Sch em e 2a
a
Reagents and conditions: (i) 6.0 equiv. Ph2P(O)CH2(CH2)nC(O)Cl, 4-(dimethylamino)pyridine, DMF, 23 °C, 16 h; (ii) HSiCl3, NEt3,
benzene, reflux, 17 h. (iii) [(η3-C4H7)Pd(cod)]BF4, CH2Cl2, 0 °C, 1 h.
Sch em e 3a
a
Reagents and conditions: (i-iii) following similar procedures to those used for the synthesis of 6a ,b in Scheme 2.
compound (24 H) as well as for the G1 dendrimer (96 H).
In the 13C{1H} NMR spectra of 7a and 7b two of the inner
core methylene carbons of the G1 dendrimer are visible
while the third resonance occurs together with reso-
nances of one of the outer methylene carbons. MALDI-
TOF-MS spectra of 7a and 7b show signals at m/z
5974.1 and 6142.6 corresponding to [G1-(OC(O)(CH2)2-
P(O)Ph2)12 + 1Ag]+ (calcd 5974.2) and [G1-(OC(O)(CH2)3-
P(O)Ph2)12 + 1Ag]+ (calcd 6142.4), respectively. A solution
of silver(I) trifluoroacetate in THF was added to the
samples in order to improve the peak resolution.
The model compounds 3a ,b and the phosphine oxides
6a ,b and 7a ,b were converted into the phosphino com-
pounds 8a ,b, 9a ,b, and 10a ,b, respectively, by reduction
with trichlorosilane in benzene.
tively. Due to their air sensitivity, no elemental analysis
of the phosphines could be obtained.
The model and dendritic catalysts were prepared in
situ by treatment of the ligands with equimolar amounts
of [(η3-C4H7)Pd(cod)]BF4 (cod ) 1,5-cyclooctadiene) or
[(η3-C3H5)PdI]2/AgSbF6.
Ca ta lytic Hyd r ovin yla tion of Styr en e. High selec-
tivity to the codimers was observed when the resulting
catalysts 8a ,b, 9a ,b, and 10a ,b were applied in batch
reactions (Table 1).
The ligands derived from diphenylphosphino propionic
acid (n ) 1) forming a six-membered hemilabile Pd(P∧O)
chelate ring were generally less active than their diphen-
ylphosphino butyric acid analogues (n ) 2) forming a
seven-membered hemilabile Pd(P∧O) chelate ring (8a vs
8b, entries 1 and 5; 9a vs 9b, entries 3 and 8; 10a vs
10b, entries 4 and 10). The differences in activity are
supposed to be due to the higher lability of the seven-
membered chelate ring, which makes the catalysts more
active.
The monomeric model compounds PhCH2OC(O)CH2-
(CH2)nPPh2 (n ) 1, 2) showed a much higher activity than
the corresponding G0 and G1 dendritic phosphino esters
(compare 8a , 9a , and 10a , entries 2, 3, and 4; as well as
8b, 9b, and 10b, entries 5, 6, and 9). This effect might
be due to increasing steric hindrance at the catalytic
1
The H NMR spectra of the reduced compounds show
no significant shift of the benzylic protons. The aromatic
regions of the phosphino compounds 8a ,b, 9a ,b, and
10a ,b show one multiplet. The 31P{1H} NMR spectra of
the phosphino compounds 8a ,b, 9a ,b, and 10a ,b confirm
that quantitative reaction has occurred as indicated by
a shift of the phosphorus resonance to higher field, i.e.,
from 30 to -16 ppm. The FAB-MS spectra of compounds
9a and 9b show signals at m/z 1850 and 1889 corre-
sponding to [G0-(OC(O)(CH2)2PPh2)4 + 2O]+ (calcd 1851)
and [G0-(OC(O)(CH2)3PPh2)4 + 1O]+ (calcd 1889), respec-

8860 J . Org. Chem., Vol. 65, No. 26, 2000
Eggeling et al.
Ta ble 1. Hyd r ovin yla tion of Styr en e: Com p a r ison of Den d r itic Liga n d s a n d Mod el Com p ou n d sa
d
entry
ligand
t (h)
convb (%)
yieldc (%)
S(1+2) (%)
S(1)e (%)
1
2
3
4
5
6
7
8
9
C6H5CH2OC(O)(CH2)2PPh2 (8a )
C6H5CH2OC(O)(CH2)2PPh2 (8a )
G0-OC(O)(CH2)2PPh2 (9a )
G1-OC(O)(CH2)2PPh2 (10a )
C6H5CH2OC(O)(CH2)3PPh2 (8b)
G0-OC(O)(CH2)3PPh2 (9b)
G0-OC(O)(CH2)3PPh2 (9b)
G0-OC(O)(CH2)3PPh2 (9b)
G1-OC(O)(CH2)3PPh2 (10b)
G1-OC(O)(CH2)3PPh2 (10b)
3
17
17
17
3
20
97
68
1
100
3
40
100
2
14
50
57
1
4
3
36
<1
1
73
91
97
97
93
95
97
92
nd
100
98
56
86
93
<1
100
94
<1
100
89
3
10
17
3
10
17
72
57
a
b
Conditions: T ) 23 °C; initial pressure 30 bar; P/Pd ) 1; styrene/Pd ) 700, CH2Cl2 (20 mL), styrene (4 mL; 34.8 mmol). Conversion
of styrene. c Yield of 1. S(1+2) ) [(yield (1) + yield (2)/conv] × 100. S(1) ) [(yield (1)/(yield (1) + yield (2))] × 100. f t ) 3 h.
d
e
F igu r e 2. Dendritic catalyst complex 13b with ligand G1-(OC(O)(CH2)3PPh2)12 (10b).
sites, making access more difficult when going to higher
generations. But also an special dendritic effect must be
taken into account, leading to enhanced catalyst deacti-
vation. Because of the close proximity of a large number
of palladium centers, the formation of palladium black
could be facilitated.
For the ligands derived from diphenylphosphino bu-
tyric acid 8b and 9b (n ) 2) complete conversion and
almost complete isomerization of 3-phenylbut-1-ene 1 to
the E/ Z mixture of achiral 2-phenylbut-2-ene E/ Z-2 was
observed within 3 and 17 h, respectively (entries 5 and
8). However, as the isomerization is a consecutive reac-
tion that with the phosphino carboxylic acid ester type
of ligands occurs only at considerably high conversion,
it can be efficiently suppressed by limiting the conversion
(entry 7). This result suggests running the reaction at
lower conversion in a continuously operating reactor.
As a result of the stability of the six-membered chelate
ring, the G0 and G1 dendritic ligands 9a and 10a showed
only little activity in the hydrovinylation reaction. On the
other hand, ligands 9b and 10b were active enough to
be tested in the continuous catalysis.
Therefore the next step was to run the catalysis in a
continuously operated high-pressure-membrane-reactor
with the new dendritic phosphine Pd catalysts derived
from 9b and 10b. For the continuous catalysis a mem-
brane reactor was used which has been developed espe-
cially for reactions under high pressure (see Figure 2).
In preceding experiments the retention {defined as R )
1 - [permeate]/[retentate]} of the model compound G0-
(OSi(Me)2(tBu))4 in the membrane reactor was deter-
mined to be R ) 85%. Although this retention is still far
from being sufficient for practical purposes, the results
of the catalysis using the dendritic Pd catalyst derived

Carbosilane Dendrimers as Nanoscale Ligands
J . Org. Chem., Vol. 65, No. 26, 2000 8861
Ta ble 2. Hyd r ovin yla tion of Styr en e: G0 a n d Den d r itic
Liga n d s in a Con tin u ou s P r ocessa
Ch a r t 2. In d u ction P er iod in Ba tch Rea ction
Usin g G0-(OC(O)(CH2)3P P h 2)4 (9b)a
conv yield S(1+2) S(1)
entry
ligand
(%)b (%)c
(%)d (%)e
1
2
G0-OC(O)(CH2)3PPh2 (9b)f
8.1
7.6
27
96
80
98
85
G1-OC(O)(CH2)3PPh2 (10b)g 40
a
Conditions: T ) 23 °C; p ) 30 bar; P/Pd ) 1; flow rates:
ethene solution 2.5 mL h-1 (10 M), styrene solution 2.5 mL h-1
(1.8 M), MPF-60 NF membrane (Koch Int., Du¨sseldorf, Germany.
b
d
Conversion of styrene. c Yield of 1. S(1+2) ) [(yield (1) + yield
e
(2)/conv] × 100. S(1) ) [(yield (1)/(yield (1) + yield (2))] × 100.
f t ) 9 h. t ) 8 h.
g
Ch a r t 1. Con tin u ou s Hyd r ovin yla tion of Styr en e
in a Mem br a n e Rea ctor Usin g Liga n d
G0-(OC(O)(CH2)3P P h 2)4 (9b)a
a
Conditions: T ) 23 °C, 30 bar initial pressure; P/Pd ) 1;
styrene/Pd ) 700; styrene (4 mL, 34.8 mmol); 20 mL of CH2Cl2.
which can be ascribed to the formation of the active
species, depends on the type of ligand used.
Since the induction periods in the batch reaction and
in the continuous catalysis are of the same length, one
can postulate that the catalytic complex undergoes the
same activation steps in the membrane reactor as in the
autoclave. This is confirmed by the results obtained when
using a mononuclear phosphinite ligand.33
As a consequence of the results obtained with the G0
catalyst 9b, some conditions were changed applying the
G1-Pd12 catalyst 10b (see Figure 2). The catalytic complex
was not synthesized starting from the [(methallyl)Pd-
(cod)]BF4 precursor, but by reaction of the [(allyl)PdI]2
dimer with the phosphine ligand and subsequent ab-
straction of the iodide using silver hexafluoroantimonate.
This procedure ensures the formation of the hemilabile,
seven-membered P∧O-chelate ring. We assume that the
precipitation of palladium black is connected with a
double or multiple complexation of the phosphino groups
to the palladium, which would lead to a lack of ligand in
the catalytic solution. Using the presynthesized hemila-
bile chelate complex as the catalyst precursor, the neces-
sity of the displacement of the cyclooctadiene is avoided.
As a consequence, a positive influence on the length of
the induction period was expected.
Additionally, the amount of catalyst used was in-
creased by 2.5 times in case of a positive concentration
effect on the induction period. Due to both the higher
concentration and the higher expected retention of the
G1 catalyst 10b, the activity decrease caused by washout
should only be of minor importance. Chart 3 shows the
space-time yield obtained in the continuous catalysis in
the presence of the G1 dendritic catalyst 10b as a function
of time.
a
Conditions: T ) 23 °C, p ) 30 bar, 0.05 mmol Pd, L/Pd ) 1,
flow rates: ethylene solution 2.5 mL h-1 (10 M), styrene solution
2.5 mL h-1 (1.8 M), τ ) 4 h, MPF-60 NF membrane (Koch Int.,
Du¨sseldorf, Ger.). Y) space time yield (mg L-1h-1).
from ligand G0-(OC(O)(CH2)3PPh2)4 9b look promising
(Table 2, entry 1, Chart 1). It should be noted that the
actual catalyst is already much larger (MW ) 2867.97 g
mol-1) than the model compound 4 (MW ) 1314.62 g
mol-1). Chart 1 shows the space-time yield as a function
of time for a continuous run with the catalyst derived
from G0-(OC(O)(CH2)3PPh2)4 9b.
It takes about 9 h before the system reaches its
maximum productivity of 2.3 g L-1 h-1. The constant
decline after the maximum cannot exclusively be ex-
plained by the moderate retention of the catalyst: with
a residence time of τ ) 4 h after 80 h, at least 20% of the
catalyst should remain in the reactor. The effect of the
washout is amplified by the deactivation of the catalyst
visible by the precipitation of palladium black on the
surface of the membrane. Although the catalyst possesses
an acceptable stability in the batch reaction at low
catalyst loading, palladium black formation is favored
under continuous conditions.
However, although the retention of the G0 compound
is modest, the desired 3-phenylbut-1-ene 1 was produced
over a period of 80 h. Most important is the observation
that hardly any isomerization or other side products
could be detected in the product solution (Table 2,
entry 1).
Despite the use of a different catalyst precursor and
the higher retention of the G1 dendritic catalyst, the time
dependent product formation resembles almost perfectly
the one found with the G0 catalyst. The induction periods
are nearly identical. Therefore, this period cannot be due
to the displacement of the cyclooctadiene but to the
formation of the palladium hydride species. After 8 h,
the system achieves its maximum productivity of 7.5 g
L-1 h-1, which is 3.2 times higher than in the continuous
catalysis in the presence of the G0 ligand 9b. This does
not correspond completely to the increase in catalyst
concentration, but it can be assumed that by use of the
Under these conditions using a G0-Pd4 catalyst and a
continuous reaction mode, highly selective conversion is
achieved, though the yields are quite low due to the
decreased activity of this catalyst. Like in the continuous
catalysis, a significant induction period is also found in
the batch reaction (see Chart 2). The length of this period,

8862 J . Org. Chem., Vol. 65, No. 26, 2000
Eggeling et al.
Ch a r t 3. Con tin u ou s Hyd r ovin yla tion of Styr en e
in a Mem br a n e Rea ctor Usin g Den d r im er
a limited efficiency. Complete conversion is not achieved
under these conditions. As in the continuous runs, within
the first 10 h the catalyst reaches its maximum produc-
tivity. Afterward, the conversion falls off and after about
30 h no further conversion is obtained. With the G1
dendritic system a total turnover number of 3273 is
obtained, whereas with the mononuclear compound the
total turnover number comes to 6027. The dendritic
system therefore is even less stable than the mononuclear
compound. This is supposed to be due to the flexibility
of the dendritic arms bringing the phosphino end groups
close to each other. This facilitates the formation of
diphosphine complexes leading to a deactivation of the
catalyst followed by the precipitation of palladium black.
a
G1-(OC(O)(CH2)3P P h 2)12
Con clu d in g Rem a r k s
In conclusion, the model complexes used have a limited
efficiency resulting from a restricted lifetime. Despite the
stabilization by the hemilabile coordination, within 10 h
the dendritic catalyst complexes start to deactivate. This
is indicated by the precipitation of palladium black in
the reactor and on the membrane surface. The deactiva-
tion process must be ascribed to double or multiple
phosphine complexation. The multiple coordination surely
is facilitated by the low space-filling properties of the
diphenylphosphino groups. However, NMR investigations
with the freshly prepared catalyst solutions suggest that
independently of the precursor used, initially the pure
monophosphine complex is formed. The deactivation
process therefore occurs during the catalysis. Since the
deactivation process takes a similar course but different
turnovers are reached in the batch reaction as well as in
the continuous catalysis, it can be excluded that it is
correlated to the amount of converted styrene or solvent
contacted.
a
Conditions: T ) 23 °C, p ) 30 bar, 0.13 mmol Pd, L/Pd ) 1,
flow rates: ethylene solution 2.5 mLh-1 (10 M), styrene solution
2.5 mL h-1 (1.8 M), τ ) 4 h, MPF-60 NF membrane (Koch Int.,
Du¨sseldorf, Ger.). Y) space time yield (mg L-1h-1).
Ch a r t 4. Ma xim u m P r od u ctivity of th e Ca ta lyst
- a
[(a llyl)P d (G1)]+SbF 6
Exp er im en ta l Section
a
Conditions: T ) 23 °C, p ) 30 bar; P/Pd ) 1; styrene/Pd )
Gen er a l Da ta . All reactions were carried out using stan-
dard Schlenk techniques under an inert atmosphere of dry,
oxygen-free nitrogen unless otherwise stated. DMF was dried
on molecular sieves (4 Å) prior to use, Et2O, THF, and hexane
were carefully dried and distilled from Na/benzophenone prior
to use, and CH2Cl2 was distilled from CaH2. The carbosilane
functionalized compounds 4 and 5 were prepared according
to a literature procedure.12 Styrene was purchased from Fluka
and distilled from CaH2 under argon. The ethene used has a
purity of >99.5%. [(η3-C3H5)PdI]2 was prepared by a literature
procedure.40 All other standard chemicals were purchased from
ACROS Chimica or Aldrich Chemical Co. and used without
further purification. Catalytic experiments under pressure
were carried out in 75 mL stainless steel autoclaves equipped
with a magnetic stirring bar. Mass spectra obtained under
electron ionization (EI) conditions (70 eV) were recorded by
linear scanning from m/z 50-500. FAB-MS spectra were
recorded either on a (1) J EOL J MS SX/SX 102A four-sector
mass spectrometer, operated at 10 kV accelerating voltage,
equipped with a J EOL MS-FAB 10 D FAB gun operated at a
5 mA emission current, producing a beam of 6 keV xenon
atoms or a (2) J EOL J MS AX 505 spectrometer, operated at 3
kV accelerating voltage, equipped with a J EOL MS-FAB 10
D FAB gun operated at a 10 mA emission current, producing
a beam of 6 keV xenon atoms. The spectra were obtained from
the Analytical Chemical Department of the University of
Utrecht. MALDI-TOF-MS spectra were acquired using a
Voyager-DE BioSpectrometry Workstation (PerSeptive Bio-
10.400; styrene (30 mL, 260 mmol); 20 mL of CH2Cl2.
[(allyl)PdI]2/AgSbF6 system more active hydride species
are available. At the maximum, the chemoselectivity
amounts to 80% which is significantly lower than in the
catalysis using the G0 ligand 9b. The selectivity drop can
be ascribed to the different precursor system, as similar
observations were made in corresponding batch reactions.
The decrease of the activity in the continuous catalysis
using the G1 dendritic ligand 10b is as rapid as with the
G0 ligand 9b. Therefore, after 80 h the product fraction
in the solution is minimal. Due to the similarity of the
results obtained with the G0 compound and the G1
dendrimer, the activity drop can only secondarily be
connected to the washout. The drastic decrease must
rather be ascribed to a catalyst deactivation, which is
independent of the precursor and starts within the first
10 h of the catalysis.
A total turnover number of 260 is obtained in the
continuous catalysis. The next step was the correlation
of this value to the maximum efficiency of the system
obtained in the batch reaction. For this reason, catalytic
runs with a high catalyst loading (styrene/palladium )
10400) were conducted with both the G1 dendritic ligand
10b and the mononuclear model compound 8b. The
courses of conversion and yield are given in Chart 4. The
graph shows clearly that also these systems possess only
(40) White, D. A. Inorg. Synth. 1972, 13, 55.

Carbosilane Dendrimers as Nanoscale Ligands
J . Org. Chem., Vol. 65, No. 26, 2000 8863
systems Inc., Framingham, MA) mass spectrometer equipped
with nitrogen laser emitting at 337 nm. The instrument was
operated in the linear mode at an accelerating voltage in the
range 23000-25000 V. External calibration was performed
using insulin (bovine), and detection was done by means of a
linear detector and a digitizing oscilloscope operating at 500
MHz. Sample solutions with (30 mg/mL) in THF were used,
and the matrix was 3,5-dihydroxybenzoic acid in THF (34 mg/
mL). A solution of silver(I) trifluoroacetate in THF was added
in order to improve the peak resolution. The sample solution
(0.2 mL) and the matrix solution (0.2 mL) were combined and
placed on a gold MALDI target and analyzed after evaporation
of the solvents. Elemental microanalyses were obtained from
Dornis und Kolbe Mikroanalytisches Laboratorium, Mu¨lheim
a.d. Ruhr, Germany.
(d, J CP ) 11.9, 16C), 127.4 (s, 8C), 66.7 (s, 4C), 26.4 (s, 4C),
24.9 (d, 1J CP ) 72.6, 4C), 20.4 (s, 4C), 18.4 (s, 4C), 17.3 (s, 4C),
-3.0 (s, 8C). 31P{1H}-NMR: (CDCl3; 298 K): δ ) 32.1 (s). FAB-
MS: (rel intensity): m/z 1906 (G0(CH2)2P(O)Ph2 + Na)+, 1883
(G0(CH2)2P(O)Ph2 + H)+. IR (CHCl3): 1732 cm-1 (CdO), 1179
cm-1 (PdO). Anal. Calcd for C108H128O12P4Si5 (mw: 1882.54):
C, 68.91; H, 6.85; P, 6.58; Si, 7.46. Found: C, 68.78; H, 6.88;
P, 6.66; Si, 7.41.
G0-(OC(O)(CH2)3P (O)P h 2)2, Si{(CH2)3SiMe2(C6H4CH2OC-
(O)(CH2)3P (O)P h 2}4 (6b). The synthetic procedure was iden-
tical to that described for 3a , starting from diphenylphosphi-
noxy butyric acid chloride (2.30 g, 7.5 mmol), 4-(dimethyl-
amino)pyridine (1.23 g, 10.0 mmol), and 4 (1.08 g, 1.26 mmol).
A slightly yellow oil was obtained. Yield: 1.29 g, 0.67 mmol,
1
53%. H NMR (CDCl3, 298 K): δ ) 7.74 (m, 16H), 7.53-7.43
Syn th esis of P h osph in e Oxide Ligan ds. Diph en ylph os-
p h in oxy ca r boxylic a cid s were prepared following a litera-
ture procedure.39 These were then converted to the acid
chlorides by treatment with a 0.5 M solution of thionyl chloride
in THF. The acid chlorides were not isolated but used directly
after evaporation to dryness.
(m, 32H), 7.27 (d, J ) 8.1, 8H), 5.05 (s, 8H), 2.49 (t, J ) 7.0,
8H), 2.31 (m, 8H), 1.97 (m, 8H) 1.29 (m, 8H), 0.75 (t, J ) 8.0,
8H), 0.52 (t, 8H), 0.20 (s, 24H). 13C{1H}-NMR: (CDCl3, 298
K): δ ) 172.7 (s, 4C), 140.2 (s, 4C), 136.4 (s, 4C), 134.0 (s,
8C), 133.0 (d, 1J CP ) 100.6, 8C), 131.9 (d, 4J CP ) 2.4, 8C), 131.0
(d, J CP ) 9.2, 16C), 128.9 (d, J CP ) 12.0, 16C), 127.7 (s, 8C),
66.5 (s, 4C), 34.9 (d, 3J CP ) 14.3, 4C), 29.2 (d, 1J CP ) 71.8, 4C),
Dip h en ylp h osp h in oxy P r op ion ic Ben zyl Ester (3a ). To
a solution of 4-(dimethylamino)pyridine (0.63 g, 5.16 mmol)
in DMF (15 mL) was added a solution of diphenylphosphinoxy
propionyl chloride (1.50 g, 5.13 mmol) in DMF (10 mL) at room
temperature. Subsequently, a solution of benzylic alcohol (0.4
g, 3.7 mmol) in DMF (10 mL) was added to the orange solution.
The mixture was stirred overnight and filtered. Ice-water was
added, and the mixture was extracted with Et2O. The com-
bined organic layers were washed with water and dried over
Na2SO4. The solvent was removed in vacuo, and after purifica-
tion by column chromatography (silica/CH2Cl2) colorless crys-
tals were obtained. Yield: 1.27 g, 3.5 mmol, 95%. Mp: 96 °C.
1H NMR (CDCl3, 298 K): δ ) 7.74 (m, 4H), 7.49 (m, 6H), 7.32
(m, 5H), 5.07 (s, 2H), 2.65 (m, 4H). 13C{1H}-NMR: (CDCl3, 298
2
20.7 (s, 4C), 18.8 (s, 4C), 17.6 (d, J CP ) 4.1, 4C), 17.5 (s, 4C),
-2.6 (s, 8C). 31P{1H}-NMR: (CDCl3; 298 K): δ ) 33.1 (s). FAB-
MS: (rel intensity): m/z 1961.0 (G0(CH2)3P(O)Ph2 + Na)+,
1939.0 (G0(CH2)3P(O)Ph2 + H)+. IR (CHCl3): 1749 cm-1 (Cd
O), 1171 cm-1 (PdO). Anal. Calcd for C112H136O12P4Si5 (mw:
1938.64): C, 69.39; H, 7.07; Si, 7.24. Found: C, 69.19; H, 7.02;
Si, 7.36.
G1-(OC(O)(CH2)2P (O)P h 2)12, Si{(CH2)3Si((CH2)3SiMe2-
(C6H4CH2OC(O)(CH2)2-P (O)P h 2)3}4 (7a ). The synthetic pro-
cedure was identical to that described for 3a , starting from
diphenylphosphinoxy propionic acid chloride (1.34 g, 4.58
mmol), 4-(dimethylamino)pyridine (0.61 g, 5.00 mmol), and 5
(0.71 g, 0.25 mmol). A slightly yellow oil was obtained. Yield:
1.27 g, 0.22 mmol, 85%. 1H NMR (CDCl3, 298 K): δ ) 7.72
(m, 48H), 7.59-7.31 (m, 96H), 7.24 (d, J ) 7.8, 24H), 5.00 (s,
24H), 2.62 (m, 48H), 1.29 (m, 32H), 0.77 (m, 24H), 0.54 (m,
40H), 0.17 (s, 24H). 13C{1H}-NMR: (CDCl3, 298 K): δ ) 172.3
3
K): δ ) 172.1 (d, J CP ) 17.1, 1C), 135.5 (s, 1C), 132.1 (d,
4
1J CP ) 99.8, 2C), 131.9 (d, J CP ) 2.8, 2C), 130.7 (d, J CP ) 9.4,
4C), 128.7 (d, J CP ) 11.6, 4C), 128.5 (s, 2C), 128.2 (s, 1C), 128.1
1
(s, 2C), 66.7 (s, 1C), 26.4 (d, 2J CP ) 1.8, 1C), 25.0 (d, J CP
)
72.6, 1C). 31P{1H}-NMR: (CDCl3; 298 K): δ ) 31.9 (s). GC-
MS: (rel intensity): m/z 364 (<1%, M+; 257 (10), 230 (15), 202
(100), 183 (10), 155 (10), 91 (40). IR (CHCl3): 1740 cm-1 (CdO),
1179 cm-1 (PdO). Anal. Calcd for C22H21O3P (mw: 364.38):
C, 72.52; H, 5.81; P, 8.50. Found: C, 72.35; H, 5.83; P, 8.38.
(d, J CP ) 17.1, 12C), 140.2 (s, 12C), 136.2 (s, 12C), 134.3 (s,
3
1
4
24C), 132.2 (d, J CP ) 101.3, 24C), 132.2 (d, J CP ) 2.7, 24C),
131.0 (d, J CP ) 9.2, 48C), 129.0 (d, J CP ) 11.5, 48C), 127.7 (s,
1
24C), 66.9 (s, 12C), 26.7 (s, 12C), 25.2 (d, J CP ) 73.2, 12C),
20.7 (s, 12C), 18.9 (s, 16C), 18.4 (4C), 18.1 (4C), 17.7 (s, 12C),
-2.6 (s, 24C). 31P{1H}-NMR: (CDCl3; 298 K): δ ) 32.8 (s).
MALDI-TOF-MS: m/z 5974.1 [G1(CH2)2P(O)Ph2 + Ag]+ (calcd
5974.2). IR (CHCl3): 1738 cm-1 (CdO), 1175 cm-1 (PdO). Anal.
Calcd for C108H128O12P4Si5 (mw: 1882.54): C, 68.73; H, 7.00;
P, 6.33; Si, 8.13. Found: C, 68.79; H, 6.99; P, 6.26; Si, 8.21.
Dip h en ylp h osp h in oxy Bu tyr ic Ben zyl Ester (3b). The
synthetic procedure was identical to that described for 3a ,
starting from benzyl alcohol (0.65 g, 6.0 mmol), 4-(dimethyl-
amino)pyridine (1.46 g, 12.0 mmol) and diphenylphosphinoxy
butyric acid chloride (2.75 g, 9.00 mmol). A slightly yellow oil
1
was obtained. Yield: 1.28 g, 3.4 mmol, 57%. H NMR (CDCl3,
G1-OC(O)(CH2)3P (O)P h 2, Si{(CH2)3Si((CH2)3SiMe2(C6H4-
CH2OC(O)(CH2)3-P (O)P h 2)3}4 (7b). The synthetic procedure
was identical to that described for 3a , starting from diphen-
ylphosphinoxy butyric acid chloride (1.27 g, 4.13 mmol),
4-(dimethylamino)pyridine (0.61 g, 5.00 mmol), and 5 (0.64 g,
0.23 mmol). A slightly yellow oil was obtained. Yield: 1.12 g,
298 K): δ ) 7.74 (m, 4H, ortho PArH), 7.47 (m, 6H), 7.32 (m,
5H), 5.08 (s, 2H), 2.48 (t, J ) 6.8, 2H), 2.32 (m, 2H), 1.97 (m,
2H). 13C{1H}-NMR: (CDCl3, 298 K): δ ) 172.7 (s, 1C), 136.1
4
(s, 1C), 133.0 (d, 1J CP ) 105.6, 2C), 132.0 (d, J CP ) 3, 2C),
131.0 (d, J CP ) 9.2, 4C), 128.9 (d, J CP ) 11.1, 4C), 128.8 (s,
3
1
2C), 128.5 (s, 1C), 128.5 (s, 2C), 66.5 (s, 1C), 34.9 (d, J CP
)
0.19 mmol, 81%. H NMR (CDCl3, 298 K): δ ) 7.75 (m, 48H),
1
2
14.3, 1C), 29.2 (d, J CP ) 71.9, 1C), 17.6 (d, J CP ) 3.7, 1C).
31P{1H}-NMR: (CDCl3; 298 K): δ ) 33.2 (s). GC-MS: (rel
intensity): m/z 378 (10), M+; 271 (20), 243 (40), 215 (100), 202
(70), 183 (10), 155 (10), 91 (70). IR (CHCl): 1745 cm-1 (CdO),
1188 cm-1 (PdO). Anal. Calcd for C23H23O3P (mw: 378.41):
C, 73.00; H, 6.13; P, 8.19. Found: C, 73.18; H, 6.20; P, 8.06.
7.60-7.34 (m, 96H), 7.24 (d, J ) 6.6, 24H), 5.02 (s, 24H), 2.42
(t, J ) 7.1, 24H), 2.30 (m, 8H), 1.97 (m, 8H), 1.31 (m, 32H),
0.75 (m, 24H), 0.54 (m, 40H), 0.18 (s, 24H). 13C{1H}-NMR:
(CDCl3, 298 K): δ ) 172.7 (s, 12C), 140.1 (s, 12C), 136.6 (s,
1
12C), 133.9 (s, 24C), 133.0 (d, J CP ) 97.6, 24C), 132.0 (d,
4J CP ) 2.8, 24C), 131.0 (d, J CP ) 9.2, 48C), 128.9 (d, J CP ) 11.5,
2
48C), 127.7 (s, 24C), 66.4 (s, 12C), 34.8 (d, J CP ) 14.3, 12C),
G0-(OC(O)(CH2)2P (O)P h 2)4, Si{(CH2)3SiMe2(C6H4CH2OC-
(O)(CH2)2P (O)P h 2}4 (6a ). The synthetic procedure was iden-
tical to that described for 3a , starting from diphenylphosphi-
noxy propionic acid chloride (5.18 g, 17.7 mmol), 4-(dimethyl-
amino)pyridine (2.47 g, 20.2 mmol), and 4 (2.13 g, 2.48 mmol).
A slightly yellow oil was obtained. Yield: 2.0 g, 1.1 mmol, 43%.
1H NMR (CDCl3, 298 K): δ ) 7.69 (m, 16H), 7.53-7.41 (m,
32H), 7.27-7.25 (d, J ) 7.6, 8H), 5.05 (s, 8H), 2.65 (m, 16H)
1.27 (m, 8H), 0.77 (m, 8H), 0.54 (m, 8H), 0.18 (s, 24H). 13C-
1
29.2 (d, J CP ) 71.9, 12C), 20.8 (s, 12C), 18.9 (s, 16C), 18.5 (s,
2
4C), 18.1 (s, 4C), 17.7 (s, 12C), 17.6 (d, J CP ) 3.3, 12C), -2.5
(s, 24C). 31P{1H}-NMR: (CDCl3; 298 K): δ ) 32.9 (s). MALDI-
TOF-MS: m/z 6142.6 [G1(CH2)3P(O)Ph2 + Ag]+ (calcd 6142.4).
IR (CHCl3): 1754 cm-1 (CdO), 1186 cm-1 (PdO). Anal. Calcd
for C112H136O12P4Si5 (mw: 1938.64): C, 69.19; H, 7.20; P, 6.15.
Found: C, 69.25; H, 7.16; P, 6.06.
Syn th esis of th e P h osp h in e Liga n d s. Dip h en ylp h os-
p h in o P r op ion ic Ben zyl Ester (8a ). To a solution of 3a (0.89
g, 2.44 mmol) in C6H6 (20 mL) were added degassed triethyl-
amine (0.7 mL, 5.1 mmol) and trichlorosilane (2.3 mL, 23
3
{1H}-NMR: (CDCl3, 298 K): δ ) 172.1 (d, J CP ) 17.1, 4C),
140.0 (s, 4C), 135.8 (s, 4C), 133.7 (s, 8C), 132.1(d, 1J CP ) 99.8,
4
8C), 131.9 (d, J CP ) 2.8, 8C), 130.7 (d, J CP ) 9.4, 16C), 128.7

8864 J . Org. Chem., Vol. 65, No. 26, 2000
Eggeling et al.
mmol). The mixture was heated under reflux overnight and
the solvent removed in vacuo. After addition of Et2O (50 mL),
a yellow suspension was obtained which was filtered under a
nitrogen atmosphere. The filtrate was diluted with degassed
water and extracted with Et2O. The combined organic layers
were dried over Na2SO4 and concentrated in vacuo to yield a
24H). 13C{1H}-NMR: (CDCl3, 298 K): δ ) 173.1 (d, 3J CP ) 14.7,
1
4C), 140.1 (s, 12C), 138.0 (d, J CP ) 12.4, 24C), 136.5 (s, 12C),
133.9 (s, 24C), 132.7 (d, J CP ) 18.9, 24C), 127.7 (s, 24C), 128.7
2
(m, 96C), 66.7 (s, 12C), 31.0 (d, J CP ) 19.4, 4C), 23.2 (d,
1J CP ) 12.0, 4C), 20.8 (s, 12C), 18.9 (s, 16C), 18.5 (s, 4C), 18.1
(s, 4C), 17.7 (s, 12C), -2.5 (s, 24C). 31P{1H}-NMR: (CDCl3;
298 K): δ ) -14.8 (s). IR (CHCl3): 1730 cm-1 (CdO).
1
pale yellow oil (0.5 g, 1.4 mmol, 60%). H NMR (C6D6, 298 K):
δ ) 7.31 (m, 4H), 7.15 (m, 11H), 4.99 (s, 2H), 2.31 (m, 4H).
G1-(OC(O)(CH2)3P P h 2)4, Si{(CH2)3Si((CH2)3SiMe2(C6H4-
CH2OC(O)(CH2)3P P h 2)3}4 (10b). The synthetic procedure
was identical to that described for 8a , starting from 7b (0.13
g, 2.15 × 10-5 mol), degassed triethylamine (0.1 mL, 7.22 ×
10-4 mol), and trichlorosilane (0.26 mL, 2.58 mmol). A colorless
3
13C{1H}-NMR: (C6D6, 298 K): δ ) 172.7 (d, J CP ) 15.0, 1C),
1
4
139.2 (s, 1C), 137.9 (d, J CP ) 95.9, 2C), 133.4 (d, J CP ) 18.8,
2C), 129.2 (s, 4C), 129.0 (d, J CP ) 7.3, 4C), 129.0 (s, 2C), 128.8
2
(s, 1C), 128.6 (s, 2C), 66.8 (s, 1C), 31.4 (d, J CP ) 20.0, 1C),
23.9 (d, J CP ) 13.1, 1C). 31P{1H}-NMR: (CDCl3; 298 K): δ )
1
1
oil was obtained. Yield: 0.10 g, 1.7 × 10-5 mol, 80%. H NMR
-15.1 (s). IR (CHCl3): 1732 cm-1 (CdO). Anal. Calcd for
C22H21O2P (mw: 348.38): C, 75.85; H, 6.08; P, 8.89. Found:
C, 75.72; H, 6.00; P, 8.66.
(CDCl3, 298 K): δ ) 7.58-7.16 (m, 168H), 5.04 (s, 24H), 2.45
(t, J ) 7.0, 24H), 2.04 (m, 24H), 1.76 (m, 24H) 1.31 (m, 32H),
0.77 (m, 24H), 0.55 (m, 40H), 0.19 (s, 24H). 13C{1H}-NMR:
(CDCl3, 298 K): δ ) 173.1 (s, 12C), 140.0 (s, 12C), 138.5 (d,
1J CP ) 12.4, 24C), 136.7 (s, 12C), 133.9 (s, 24C), 132.9 (d,
4J CP ) 18.9, 24C), 128.7 (m, 96C), 127.7 (s, 8C), 66.3 (s, 12C),
Dip h en ylp h osp h in o Bu tyr ic Ben zyl Ester (8b). The
synthetic procedure was identical to that described for 8a ,
starting from 3b (0.81 g, 2.14 mmol), degassed triethylamine
(0.6 mL, 4.3 mmol), and trichlorosilane (2.2 mL, 21.4 mmol).
A slightly yellow oil was obtained. Yield: 0.58 g, 1.6 mmol,
3
1
35.5 (d, J CP ) 13.4, 12C), 27.8 (d, J CP ) 12.0, 12C), 21.8 (d,
2J CP ) 18.4, 12C), 20.8 (s, 12C), 18.9 (s, 16C), 18.5 (4C), 18.1
(4C), 17.7 (s, 12C), -2.5 (s, 24C). 31P{1H}-NMR: (CDCl3; 298
K): δ ) -15.7 (s). IR (CHCl3): 1725 cm-1 (CdO).
1
60%. H NMR (CDCl3, 298 K): δ ) 7.59-7.30 (m, 15H), 5.17
(s, 2H), 2.55 (t, J ) 7.0, 2H), 2.15 (m, 2H), 1.88 (m, 2H).
13C{1H}-NMR: (CDCl3, 298 K): δ ) 173.1 (s, 1C), 138.7 (d,
1J CP ) 12.9, 2C), 136.3 (s, 1C), 133.0 (d, J CP ) 18.4, 4C), 128.8
(m, 6C), 128.8 (s, 2C), 128.7 (s, 1C), 128.5 (s, 2C), 66.5 (s, 1C),
P r ep a r a tion of th e Ca tion ic [(m eth a llyl)P d P ]+BF 4
-
Com p lexes. A solution of 1.00 equiv of the phosphorus P∧O
ligand (0.05 mmol) in CH2Cl2 was added to a solution of 0.05
mmol of [(η3-C4H7)Pd(cod)]BF4[13] in CH2Cl2. After stirring for
60 min at 0 °C, the resulting solution was used for catalysis.
12+
3
1
35.7 (d, J CP ) 13.4, 1C), 27.8 (d, J CP ) 12.0, 1C), 21.9 (d,
2J CP ) 18.4, 1C). 31P{1H}-NMR: (CDCl3; 298 K): δ ) -15.8
(s). IR (CHCl3): 1732 cm-1, (CdO). Anal. Calcd for C23H23O2P
(mw: 362.41): C, 76.23; H, 6.40; P, 8.55. Found: C, 76.09; H,
6.54; P, 8.39.
P r ep a r a tion of th e Ca tion ic [(G1-P 12) {(a llyl)P d }12
(SbF 6 )12 Com p lex for th e Con tin u ou s P r ocess. A solution
]
-
-
of 1.00 equiv of the phosphorus P∧O ligand (0.011 mmol) in
CH2Cl2 was added to a solution of 0.065 mmol of [(η3-C3H5)-
PdI]2 in 5 mL of CH2Cl2. After stirring for 30 min the solution
was transferred to a flask containing 1.03 equiv of AgSbF6 in
2 mL of CH2Cl2. Subsequently, the mixture was stirred for 5
min and filtered over Celite. The solvents were removed in
vacuo, 2 mL of CH2Cl2 was added, and the mixture was
injected in the membrane reactor.
G0-(OC(O)(CH2)2P P h 2)4, Si{(CH 2)3SiMe2(C6H 4CH 2OC-
(O)(CH2)2P P h 2}4 (9a ). The synthetic procedure was identical
to that described for 8a , starting from 6a (0.67 g, 0.36 mmol),
degassed triethylamine (0.40 mL, 2.9 mmol), and trichlorosi-
lane (0.7 mL, 7.0 mmol). A colorless oil was obtained. Yield:
1
0.34 g, 0.19 mmol, 52%. H NMR (C6D6, 298 K): δ ) 7.46 (d,
J ) 8.1, 8H), 7.33 (m, 16H), 7.27 (d, J ) 7.8, 8H), 7.03 (m,
24H), 5.00 (s, 8H), 2.34 (m, 16H), 1.47 (m, 8H), 0.85 (m, 8H),
0.63 (t, J ) 8.3, 8H), 0.26 (s, 24H). 13C{1H}-NMR: (C6D6, 298
Hyd r ovin yla tion Rea ction
Ba tch Rea ction . The cold catalyst solution (0.05 mmol of
[(η3-C4H7)Pd(P∧O)]BF4 in 20 mL of CH2Cl2) was transferred
into a 75 mL stainless steel autoclave via a syringe with a
stainless steel needle. The autoclave was cooled in an ice bath.
Chilled styrene (4 mL: 34.8 mmol) was added, and the
autoclave was pressurized with ethene (30 bar initial pres-
sure). After the reaction, the autoclave was slowly vented, and
the reaction mixture separated from the catalyst and higher
oligomers by flash chromatography over basic alumina. Prod-
ucts were analyzed by GC.
Con tin u ou s Ca ta lysis. The membrane (MPF-60 NF mem-
brane, Koch Int., Du¨sseldorf, Germany), stored in ethanol, was
rinsed with acetone and carefully transferred into the mem-
brane reactor. After the membrane had been thoroughly
flushed by several 100 mL portions of CH2Cl2, the reactants
3
K): δ ) 172.8 (d, J CP ) 14.6, 4C), 140.0 (s, 4C), 139.1 (d,
4
1J CP ) 14.0, 8C), 137.7 (s, 4C), 134.4 (s, 8C), 133.4 (d, J CP
)
18.9, 8C), 129.2 (s, 8C), 129.1 (m, 32C), 66.7 (s, 4C), 31.4 (d,
2J CP ) 20.1, 4C), 23.8 (d, 1J CP ) 13.1, 4C), 21.2 (s, 4C), 19.5
(s, 4C), 18.2 (s, 4C), -2.4 (s, 8C). 31P{1H}-NMR: (C6D6; 298
K): δ ) -17.3 (s). FAB-MS: (rel intensity): m/z 1850 (M +
2O)+, 1834 (M + O)+, 1819 (M + H)+. IR (CHCl3): 1730 cm-1
(CdO).
G0-(OC(O)(CH2)3P P h 2)4, Si{(CH 2)3SiMe2(C6H 4CH 2OC-
(O)(CH2)3P P h 2}4 (9b). The synthetic procedure was identical
to that described for 8a , starting from 6b (0.61 g, 0.31 mmol),
degassed triethylamine (0.40 mL, 2.9 mmol), and trichlorosi-
lane (0.65 mL, 6.5 mmol). A colorless oil was obtained. Yield:
1
0.36 g, 0.19 mmol, 62%. H NMR (CDCl3, 298 K): δ ) 7.61-
7.23 (m, 56H), 5.07 (s, 8H), 2.47 (t, J ) 7.4, 8H), 2.11 (m, 8H),
1.80 (m, 8H) 1.26 (m, 8H), 0.80 (t, J ) 7.8, 8H), 0.52 (t, J )
8.2, 8H), 0.21 (s, 24H). 13C{1H}-NMR: (CDCl3, 298 K): δ )
173.1 (s, 4C), 140.1 (s, 4C), 138.6 (d, 1J CP ) 12.4, 8C), 136.6 (s,
(ethylene solution 1.8 M in CH2Cl2, flow rate 2.5 mLh-1
;
styrene solution 10 M in CH2Cl2, flow rate 2.5 mLh-1) were
pumped through the reactor. The catalyst solution (0.05 mmol
in 2 mL of CH2Cl2) was injected via an HPLC injection valve.
Samples of the outcoming product solution were taken con-
tinuously and analyzed by GC.
4
4C), 134.0 (s, 8C), 132.9 (d, J CP ) 18.4, 8C), 128.7 (m, 32C),
3
127.7 (s, 8C), 66.4 (s, 4C), 35.6 (d, J CP ) 13.3, 4C), 27.8 (d,
1J CP ) 12.0, 4C), 21.8 (d, 2J CP ) 18.4, 4C), 20.8 (s, 4C), 18.8 (s,
4C), 17.7 (s, 4C), -2.6 (s, 8C). 31P{1H}-NMR: (CDCl3; 298 K):
δ ) -15.9 (s). FAB-MS: (rel intensity): m/z 1888.7 (M + O)+.
IR (CHCl3): 1725 cm-1 (CdO). Anal. Calcd for C112H136O8P4-
Si5 (mw: 1874.65): C, 71.76; H, 7.31; P, 6.61, Si, 7.49. Found:
C, 71.84; H, 7.38; P, 6.49, Si, 7.38.
Ack n ow led gm en t. The authors thank Mrs. A. van
der Kerk and Mr. K. Versluis from the Analytical
Chemical Department for measuring the FAB-MS spec-
tra. Dr. J . Verweij (DSM/Gist) and Prof. J . G. de Vries
(DSM) are kindly acknowledged for stimulating discus-
sions. Prof. D. Vogt and E. Eggeling thank Prof. W.
Keim from the Institute of Technical and Macromolecu-
lar Chemistry (ITMC) of the RWTH Aachen for excellent
working conditions. Mr. S. Schwerdt (RWTH Aachen)
is gratefully acknowledged for his contributions to the
construction of the membrane reactor. This work was
G1-(OC(O)(CH2)2P P h 2)12, Si{(CH2)3Si((CH2)3SiMe2(C6-
H4CH2OC(O)(CH2)2P P h 2)3}4 (10a ). The synthetic procedure
was identical to that described for 8a , starting from 7a (0.22
g, 3.75 × 10-5 mol), degassed triethylamine (0.13 mL, 9.4 ×
10-4 mol), and trichlorosilane (0.45 mL, 4.5 mmol). A colorless
oil was obtained. Yield: 0.17 g, 0.030 mmol, 80%. 1H NMR
(CDCl3, 298 K): δ ) 7.61-7.20 (m, 168H), 5.00 (s, 24H), 2.46
(m, 48H), 1.25 (m, 32H), 0.75 (m, 24H), 0.53 (m, 40H), 0.17 (s,

Carbosilane Dendrimers as Nanoscale Ligands
J . Org. Chem., Vol. 65, No. 26, 2000 8865
Su p p or tin g In for m a tion Ava ila ble: Experimental part
with all NMR peak assignments. This material is available
free of charge via the Internet at http://pubs.org.org.
supported by the Council for Chemical Sciences of The
Netherlands Organization for Scientific Research
(CW-NWO), the Dutch Technology Foundation (STW)
with financial aid from DSM Gist, and the Deutsche
Forschungsgemeinschaft (DFG, SFB 380).
J O000433K