Hydrocarbonylation reactions using alkylphosphine-containing dendrimers based on a polyhedral oligosilsesquioxane core

Article abstract of DOI:10.1039/b200303a

Radical additions of HPR₂ (R = Et, Cy) onto alkenyl groups or nucleophilic substitution reactions on chlorosilanes by LiCH₂PR₂ (R = Me, Hex) are used to prepare first and second-generation alkylphosphine-containing dendrimers based on a polyhedral oligomeric silsesquioxane (POSS) core. The first generation dendrimers (G1) are built on 16 or 24 arms, which are chlorides, vinyl groups or allyl moieties. Hydrosilylation (chlorosilane) followed by vinylation or allylation of octavinyl-functionalised POSS gave these G1 dendrimers. Successive hydrosilylation/allylation followed by hydrosilylation/vinylation produce the framework for the second-generation dendrimer (G2). The phosphorus-containing dendrimers are used as ligands for the hydrocarbonylation of alkenes (hex-1-ene, oct-1-ene, non-1-ene, prop-1-en-2-ol) in polar solvents (ethanol or THF) using the complexes [Rh(acac)(CO)₂] or [Rh₂(O₂CMe)₄] as metal source. Linear to branched ratios up to 3:1 for the alcohol products are obtained for the diethylphosphine dendrimers. The reactions were found to proceed mainly via the formation of the corresponding aldehydes.

Full text of DOI:10.1039/b200303a

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Hydrocarbonylation reactions using alkylphosphine-containing
dendrimers based on a polyhedral oligosilsesquioxane core
Loïc Ropartz,a Douglas F. Foster,b Russell E. Morris,*a Alexandra M. Z. Slawina and
David J. Cole-Hamilton*a
a School of Chemistry, University of St. Andrews, Purdie Building, St. Andrews, UK KY16 9ST.
E-mail: rem1@st-and.ac.uk; djc@st-and.ac.uk
b Catalyst Evaluation and Optimisation Service (CATS), School of Chemistry,
University of St. Andrews, St. Andrews, Fife, Scotland, UK KY16 9ST
Received 8th January 2002, Accepted 18th February 2002
First published as an Advance Article on the web 3rd April 2002
Radical additions of HPR2 (R = Et, Cy) onto alkenyl groups or nucleophilic substitution reactions on chlorosilanes
by LiCH2PR2 (R = Me, Hex) are used to prepare first and second-generation alkylphosphine-containing dendrimers
based on a polyhedral oligomeric silsesquioxane (POSS) core. The first generation dendrimers (G1) are built on 16 or
24 arms, which are chlorides, vinyl groups or allyl moieties. Hydrosilylation (chlorosilane) followed by vinylation or
allylation of octavinyl-functionalised POSS gave these G1 dendrimers. Successive hydrosilylation/allylation followed
by hydrosilylation/vinylation produce the framework for the second-generation dendrimer (G2). The phosphorus-
containing dendrimers are used as ligands for the hydrocarbonylation of alkenes (hex-1-ene, oct-1-ene, non-1-ene,
prop-1-en-2-ol) in polar solvents (ethanol or THF) using the complexes [Rh(acac)(CO)2] or [Rh2(O2CMe)4] as
metal source. Linear to branched ratios up to 3 : 1 for the alcohol products are obtained for the diethylphosphine
dendrimers. The reactions were found to proceed mainly via the formation of the corresponding aldehydes.
drimer. Most dendrimers are based on tetravinylsilane, tetra-
allylsilane, pentaerythritol or propyl amino compounds with
Introduction
Dendrimers are well-defined macromolecules characterised by
the presence of a large number of functional groups on their
surface and by their ability to encapsulate guest species.1
Recently they have triggered interest in the field of homo-
geneous catalysis since they are relatively large molecules and
can be separated from reaction mixtures using ultra-filtration
techniques.2 Their application as ligands/catalysts ranges from
C–C coupling3–5 to hydrogenation6–8 reactions. Successful
recovery of the dendritic catalysts by ultra-filtration techniques
has been achieved in several research groups giving high expect-
ations for future industrial applications.3,9,10 In addition, the
diversity of functional groups, branching patterns, size and
crowding of dendrimers can affect the activity or selectivity of
the catalyst. Indeed, various ‘dendrimer effects’ from total
inhibition of the reaction11 to enhanced reactivity3,4,12,13 and
selectivity14 have been identified.
Jaffrès and Morris have previously developed a dendrimer
based on a polyhedral oligosilsesquioxane (POSS) core with up
to 72 arms.15 During this work, it became apparent that the
groups introduced in successive generations, i.e. chloro- and
vinyl-silane substituents, would be easily functionalisable by
phosphorus-containing species. Using simple organic/inorganic
reactions (nucleophilic substitution and radical addition) we
have introduced different phosphorus substituents (PR2, R =
Cy, Et, Hex, Me) on the periphery of the dendrimers. In this
way dendrimers of different generations with varying numbers
of peripheral functionality can be prepared in a relatively facile
manner. In general, the chemical properties of the dendrimers
are expected to be similar to their small molecule phosphine
complexes, modified only by the steric effects of the dendrimer
architecture itself.
only four such sites.16–19 Using the POSS cube as a framework,
the dendrimer can be built out in three dimensions leading to
a very globular structure which, by the second generation, has
72 end groups suitable for functionalisation with a catalytic
species.15 In contrast 2nd generation dendrimers based on
tetrahedral cores have a maximum of only 36 end groups. The
large number of catalytic species that can be supported on the
external surface of POSS-based dendrimers can lead to interest-
ing effects on catalytic activity and selectivity.14 In addition,
overcrowding on the periphery may also limit the extension of
the dendrimer, leading to globular, rigid dendrimers at lower
generation numbers than is seen for other dendrimer cores. The
relatively rigid dendrimers produced in this way should allow
better recovery of POSS-based dendrimers by ultrafiltration
techniques when compared to more deformable dendrimers.
Trialkylphosphines are effective ligands to rhodium catalysts,
and are used to prepare alcohols from terminal alkenes under
pressure of CO/H2. Using a protic solvent and mild conditions,
Cole-Hamilton and co-workers showed that this hydrocarbon-
ylation reaction did not necessarily proceed through aldehyde
intermediates.20,21 This reaction is suitable for testing the cat-
alytic ability of dendrimer bound alkyl phosphines, as simple
product analysis will be diagnostic as to whether the den-
drimers are bound to the catalytic metal or not. If the ligand
binds and a trialkylphosphine rhodium complex is formed,
alcohols (e.g. heptan-1-ol and 2-methylhexan-1-ol from hex-
1-ene) will be the hydrocarbonylation products. If binding
does not occur, the products will be aldehydes and acetals. In
addition, since hydrocarbonylation can give two different regio
isomers of the product (linear and branched), any changes in
the balance of the products brought about by the environment
of the dendrimer surface will be apparent.
The use of a silsesquioxane as the core of the dendrimer has
certain advantages. Above all, the R8Si8O12 POSS molecule has
an almost cubic shape, with a functional group at each corner,
and so there are eight sites from which to develop the den-
In preliminary communications, two of which relate to this
work,22 we have described the synthesis of a dendrimer struc-
ture based on a POSS core and introduced phosphine moieties
DOI: 10.1039/b200303a
J. Chem. Soc., Dalton Trans., 2002, 1997–2008
This journal is © The Royal Society of Chemistry 2002
1997

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at its periphery.14,22 First generation alkyl and arylphosphine
substituted dendrimers were shown to be excellent ligands for
the hydroformylation of alkenes, in some cases leading to
greatly increased selectivity compared with their parent mono-
mers.14 We report here a comparative study of the hydrocarbon-
ylation of various alkenes (hex-1-ene, oct-1-ene, non-1-ene,
prop-1-en-2-ol) by rhodium complexes of different alkylphos-
phine functionalised POSS dendrimers (R = PMe2, PEt2,
PHex2, PCy2).
24vinyl).15 The structure of G1-16vinyl is shown in Fig. 1 and
confirms that the POSS core remains intact. In addition, at least
in this crystal, all of the chlorides in G1-16Cl have been suc-
cessfully replaced with vinyl groups to give the fully substituted
vinyl dendrimer.
Results and discussion
Synthesis of POSS dendrimer cores
Polyhedral octavinyl oligosilsesquioxane (zeroth generation den-
drimer or G0) is commercially available or easily synthesised23
from hydrolysis of readily available trichlorovinylsilane. The
hydrosilylation of G0 under rigorously dry conditions by differ-
ent silanes (HSiCl3 or HSiMeCl2 in excess) catalysed by Speier’s
catalyst, H2PtCl6, introduces substituents on the dendrimer
with quantitative yield.15 The bulkiness and electronic proper-
ties of the POSS cube hinder unwanted β-addition to the vinyl
groups. Hydrosilylation using trichlorosilane or dichlorometh-
ylsilane yield 24 or 16 ‘reactive’ chlorosilane groups respectively
at the external surface of the first generation dendrimer.15
Chloro-functionalised G1 dendrimers can then be modified by
introduction of vinyl or allyl groups through nucleophilic sub-
stitution of the chloro groups by Grignard reagents as has been
done for many other carbosilane dendrimers. Compounds with
16- or 24-vinyl,15 or allyl groups (G1-16vinyl, G1-24vinyl, G1-
24allyl) were prepared in high yields. NMR techniques and
microanalysis were used to characterise the products, and G1-
16vinyl was partially characterised by single crystal X-ray dif-
fraction after crystals were obtained by recrystallisation from
cold light petroleum. However, only partial refinement was
obtained due to the extensive disorder of the carbon atoms of
the vinyl and methyl groups at the periphery of the dendrimer.
Similar problems of external group disorder have been seen in a
crystal structure determination of the 24-vinyl POSS (G1-
Fig. 1 X-Ray structure of G1-16vinyl. Si represented by diagonal
bottom left to top right lines, O by open circles C by partially shaded
circles. The hydrogen atoms are omitted for clarity.
Second generation POSS-based dendrimers (48 and 72
groups) were obtained from the reaction of G1-24vinyl or
G1-24allyl with HSiMeCl2 or HSiCl3. When starting from G1-
24vinyl, reaction with HSiCl3 as described previously gave the
compound G2-ethyl-72Cl as a white solid in 88% yield.15 From
the G1-24allyl POSS, different reaction conditions are neces-
sary as the solubility and reactivity of the starting materials and
product are different. Toluene was used as the solvent in the
hydrosilylation reaction (HSiMeCl2) as the use of diethyl ether
led to fast precipitation of partially functionalised product
while THF (in conjugation with some chlorosilane) was trapped
after reaction inside the dendritic structure. Longer reaction
times (up to 96 h) are also needed as the allyl groups are less
reactive toward hydrosilylation than their vinyl counterparts.
The 48-chloro compound, G1-propyl-48Cl, was isolated as a
white solid in quantitative yield (> 95%). The 1H NMR spectra
1998
J. Chem. Soc., Dalton Trans., 2002, 1997–2008

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showed traces of β-substitution, although it was in such small
amounts that it was difficult accurately to quantify the relative
amount of this ‘side-reaction’. Subsequent addition of the vinyl
magnesium bromide in excess gave the corresponding G2-
propyl-48vinyl as a heavy oily product in 70% yield. NMR and
microanalysis showed high conversion (>95%) of the chloro
functionality to vinyl groups.
However, higher conversion was obtained after 36 hours
(>95%). The elimination of the LiCl salts was obtained by pre-
cipitation in dichloromethane. The 31P NMR spectrum shows a
single signal at Ϫ54.5 ppm attributed to the bound CH2P(Me)2.
The white product decomposed rapidly in air or non-degassed
solvent to form the oxide. The MALDI-TOF spectrum of the
compounds showed the high conversion of the product (>95%)
(m/z 2667 (broad), m/z expected 2667). However, due to the
sensitivity to moisture and air, low resolution was obtained.
Addition of LiCH2P(CH3)2 to the G2-ethyl-72Cl compound led
to slow precipitation (over 3 days) of the compound G2-ethyl-
72methylPMe2.
Functionalisation with alkylphosphine groups
Nucleophilic substitution. The first method used to introduce
alkylphosphine groups onto the surface of the dendrimer was
a nucleophilic substitution of the chlorine atoms of the Cl-
functionalised dendrimers. Deprotonation of different dialkyl-
phosphinomethyl compounds forms the corresponding lithium
dialkylphosphinomethyl salt. The first reaction used LiCH2-
P(CH3)2 as the nucleophile, which was prepared by reaction of
P(CH3)3 with ButLi.24 Stoichiometric additions of this reagent
to G1-24Cl and G2-ethyl-72Cl were carried out leading to
G1-24methylPMe2 and G2-ethyl-72methylPMe2 respectively.
Because of difficulties in determining the conversion of the sub-
strate to G1-24methylPMe2 by 1H NMR due to the overlapping
of the proton resonances, we used a subsequent reaction to
characterise the product. Addition of methyllithium after the
reaction had been going for 24 hours, revealed that ≈22 % of the
The substitution by di-n-hexylphosphine groups was achieved
by addition of LiCH2P(C6H13)2 to the G1-24Cl dendrimer.
LiCH2P(C6H13)2 was prepared by addition of the Grignard
C6H13MgBr to methyldichlorophosphine (PMeCl2) and sub-
t
sequent lithiation by BuLi.24 Addition of LiCH2P(C6H13)2 in
excess to G1-24Cl yielded a colourless low melting point solid
G1-24methylPHex2 after 3 days. The conversion reached 90%
to the desired dihexylphosphine POSS (as measured by 1H
NMR spectroscopy). The purification of the product was less
easy than for the dimethylphosphine dendrimer but a 40% yield
of the compound was obtained after removal of the LiCl. The
31P NMR spectrum of the reaction product showed a signal at
Ϫ36.3 ppm, which is attributed to the bound CH2P(C6H13)2.
1
chlorosilane groups of G1-24Cl were unreacted as H NMR
shows clearly the formation of methylsilane groups. The result
suggests that the steric bulk of the dendrimer (steric hindrance,
back-folded arms) hampers the reaction since both chlorosilane
and the phosphorus compound are highly reactive species.
Radical addition. The second type of reaction considered was
the radical reaction of dialkylphosphines onto the double bonds
of the vinyl-functionalised dendrimers. A radical reaction was
J. Chem. Soc., Dalton Trans., 2002, 1997–2008
1999

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performed to affect an anti-Markownikoff type addition of the
phosphine to the alkenes so that it would promote the form-
ation of the desired terminal phosphine groups. Similar work
had been previously carried out with the octavinyl oligosilses-
quioxane and diethylphosphine22 and dimethylphosphine25
leading to POSS compounds with eight phosphine moieties.
The 24-vinyl POSS molecules were reacted in this way with
HPEt2 in cyclohexane at 50–60 ЊC. The reaction was initiated by
AIBN (azoisobutyronitrile). The addition of an excess of
diethylphosphine (3 fold excess) gave conversion up to 96% for
the 24-branched compound G1-24ethylPEt2. The solvent and
the excess of phosphine were removed under vacuum to give an
oily colourless product. The product was characterised by
NMR (31P δ Ϫ15.9 ppm) and MALDI-TOF techniques.
ably caused by increased steric problems with the larger number
of vinyl groups.
A randomly dispersed diethyl- and dicyclohexyl-phosphine
functionalised POSS was synthesized by addition to G1-16vinyl
POSS of HPCy2 (phosphine/vinyl ratio of 1.5 : 1) followed by
the much smaller HPEt2 (1 equivalent to the vinyl groups) 3
days later. Excess of phosphines were removed under vacuum
with heating to give a quantitative yield of the derivatised
dendrimer as a colourless oil. The product contained 68%
of dicyclohexylphosphine groups and 32% of diethylphos-
phine substituents (determined by 1H and 31P NMR). No vinyl
1
groups were detected in the H NMR spectrum. When both
phosphines were added at the same time only the smaller
diethylphosphine groups were incorporated (conversion 99%).
Details of the phosphine-functionalised dendrimers are given in
Table 1.
1
Although no vinylic protons were detected by H NMR, the
mass spectrum seemed to indicate that on average between 23
and 24 of the arms were converted to diphosphine groups. Two
main broad signals in the MS spectrum were found at m/z 3582
(M Ϫ PEt2) and 3676 (m/z expected 3677). This may be due to a
small amount of fragmentation occurring during the MALDI-
TOF analysis as a similar phenomenon has been encountered
for a similar compound with PPh2 groups.26 The radical add-
ition was extended to the G1-24allyl POSS. The product
obtained G1-24propylPEt2 was a colourless oil in 98% yield
with a conversion reaching at least 87% after 15 days. The con-
version was calculated from the MALDI-TOF, which showed a
broad signal centered at m/z = 3730 corresponding to ≈21 arms
functionalised (m/z expected = 4014). Again this conversion
Preparation of Rh-dendrimer complexes
Upon addition of ethanol to a mixture of [Rh2(O2CMe)4] and
G1-24ethylPEt2 (P : Rh ratio = 3 : 1) a brown homogeneous
solution was obtained after 3–4 hours, whilst a yellow solution
was obtained with [Rh(acac)(CO)2] and the dendritic ligand
(<1 h). Although these solutions have not been investigated, it is
normal for phosphines to add to [Rh2(O2CMe)4] and to displace
one or more carbonyl ligands in [Rh(acac)(CO)2]. Under CO
and H2, however, both systems give the catalytically active
[RhH(CO)2(PR3)2].21 Interestingly lower phosphine/rhodium
ratios (below 3 : 1) led to the formation of gels when using the
rhodium-based complex [Rh(acac)(CO)2] or under CO/H2
atmosphere using [Rh2(O2CMe)4]. The gels precipitated with
time to form insoluble materials, which could not be dissolved
again even at higher temperature or on addition of excess lig-
ands. It is believed that cross-linking between two dendrimers,
(i.e. two phosphine groups of two different dendritic ligands
bind to the same rhodium atom) occurs under these conditions
leading to insoluble ‘oligomeric’ species. Steric hindrance
within such complexes would then prevent the new complex-
ation of a phosphine ligand on the metal centre on addition of
excess ligand.
1
differs with that suggested by the H NMR since no alkenyl
protons were detected and the integration indicating a high
phosphine loading (>94%). It is therefore, as discussed above,
difficult to determine the exact conversion. Interestingly various
31P chemical shifts were found at δ Ϫ22.1 (minor), Ϫ23.3
(minor), Ϫ23.5 (major), Ϫ23.7 (major), Ϫ24.2 (major), Ϫ28.2
(minor) and Ϫ29.3 ppm (minor). This may be due to back
folding of some of the outermost arms so that they are
encapsulated inside the dendrimer, and therefore in a different
environment to the ones remaining on the surface of the den-
drimer. This back folding is relatively well characterised for
other high generation POSS-based dendrimers.27 G1-16ethyl-
PEt2 and the 2nd generation dendrimer, G2-propyl-48ethyl-
PEt2, were prepared by a similar reaction from G1-16vinyl and
G2-propyl-48vinyl respectively. These G1 and G2 dendrimers
containing diethylphosphine functionality were isolated as oily
products (as expected the G2 dendrimer is the more viscous
of the two) in quantitative yields and with conversions of
The G1-16ethylPEt2 and G1-24propylPEt2 dendrimers were
readily complexed with [Rh(acac)(CO)2] in the ethanol solution
while the 2nd generation dendrimer necessitated stirring over-
night to obtain a homogeneous phase.
In order to clarify the mode of chelation of the dendritic
structure, i.e. whether or not bidendate or tridentate coordin-
ation of the phosphine to the rhodium centre occurred or if
bimetallic species were formed, a 31P NMR study of the
dendrimer rhodium complexes was carried out. The 31P NMR
spectrum of the solution formed under CO/H2 from the
[Rh(acac)(CO)2]/G1-24ethylPEt2 species (P/Rh = 4/1) shows
several species in solution. Two resonances were observed under
1 atmosphere of CO/H2 at room temperature in ethanol sol-
ution. One signal (δP Ϫ 16.0 ppm) was found corresponding to
the free P atoms (G1-24ethylPEt2 resonates at δP Ϫ16.0 ppm)
(width at half maximum = 50 Hz) and the other resonance
centred at δP 29.6 ppm (broad signal, width at half maximum =
660 Hz) was attributed to [RhH(CO)2(P)2] ([RhH(CO)2(PEt3)2]
resonates at δP 24.5 ppm)20 or [RhH(CO)(P)3] species
([RhH(CO)(PEt3)3] resonates at δP 26.2 ppm)20 (P = Dend-PR2,
Dend for dendrimer). At Ϫ50 ЊC, the resonance of the free P
atoms stayed unchanged while the rhodium complex species
showed some asymmetric broadening suggesting fluxionality
within the bound complex. The fact that the resonances for the
Rh bound P atoms are broad at all temperatures suggests that
there are different coordination environments, whilst the fact
that two resonances are observed at least up to room temper-
ature and the peak width for the free phosphine does not vary in
this temperature range suggests that the rhodium is fixed to
individual P atoms and is not migrating over the surface.
1
>99% (6 days, H NMR, MALDI-TOF) and >96% (12 days,
1H NMR) respectively. The MALDI-TOF spectrum of G1-
16ethylPEt2 showed a peak at m/z 2923 (m/z expected 2860)
possibly corresponding to partial oxidation of the phosphines
{M ϩ 3 × ‘O’}. However, the 2nd generation product could not
be characterised by MALDI-TOF as no peak in the expected
m/z 8502 is found. We suspect that this is due to more severe
fragmentation of this dendrimer than is seen for the smaller
ones. A single 31P chemical shift was found at δ Ϫ15.2 ppm for
the 16-branched product, while for the 48 arm molecule two
broad signals were detected at δ Ϫ15.8 and Ϫ16.1 ppm, again
indicating possible back folding of some arms. All these
diethylphosphine dendrimers showed high solubility except in
highly polar solvents (alcohols, etc.).
Dicyclohexyl phosphine was also reacted with G1-16vinyl.
After 10 days at 50 ЊC with an excess of diphosphine (3–4 fold)
and AIBN as radical initiator, an air sensitive product was
obtained. The compound, G1-16ethylPCy2, is a colourless low
melting point solid. A single 31P chemical shift was detected at
δ 4.1 ppm corresponding to the expected CH2P(Cy)2 group.
MALDI-TOF and 1H NMR show that only ≈12 of the 16 arms
(on average) had reacted.
Reaction of dicyclohexylphosphine with G1-24vinyl was
even less successful, with a very low conversion (≈55%), prob-
2000
J. Chem. Soc., Dalton Trans., 2002, 1997–2008

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Table 1 Preparation of phosphine-functionalised POSS
Dendrimer
31P NMR, δ/ppm
Conversion of end groups (%)
Chemical yield (%)
a
G1-24methylPMe2
Ϫ54.5
Ϫ54.4
>95c, d
97
80
40
99
97
96
98
98
95
95
a
G2-ethyl-72methylPMe2
G1-24methylPHex2
nde
90c
a
Ϫ36.3 (br)
Ϫ15.2 (br)
Ϫ15.9. Ϫ16
Ϫ15.8, Ϫ16.1
Ϫ23.6, Ϫ23.9, Ϫ24.3
4.1 (br)
b
G1-16ethylPEt2 b
>99c, d
>96c, d
>90c, d
>87c, d
75c
G1-24ethylPEt2
b
G2-propyl-48ethylPEt2
b
G1-24propylPEt2
b
G1-16ethylPCy2 b
G1-24ethylPCy2
4.1 (br)
Ϫ14.9, 4.8
55c
b
G1-16ethylPCy1.64Et0.36
98c
a Reaction of R2PCH2Li with –SiCl3 derivatised dendrimer. b Reaction of HPR2 with vinyl derivatised dendrimer. c 1H NMR. d MALDI-TOF.
e Not measured due to low solubility.
Table 2 Hydrocarbonylation reactions of hex-1-ene catalysed by Rh complexes of POSS derived dimethyl- and dihexyl-phosphine dendrimers
Ligand
[Rh]/10Ϫ3 mol dmϪ3
Time/h
Conversion (%)
Aldehydes (%)
Alcohols (%)
l : b ratio
PMe3
8
8
8
4.4
8
16
16
4
16
16
16
>99
—
tra
80
5c
2
99
98
14
94
97
99
2.4
2.1
2.2b
2.1
2.4
2.4
G1-24methylPMe2
G1-24methylPMe2
G1-24methylPMe2
G2-ethyl-72methylPMe2
G1-24methylPHex2
>99
>95
>99
>99
>99
8
tra
Reaction conditions: catalyst prepared in situ from [Rh2(O2CMe)4] and alkylphosphine species, batch autoclave, P/Rh = 3/1, substrate 8.3 × 10Ϫ3 mol,
ethanol (4 cm3), 120 ЊC, CO/H2 40 bar. a Traces not quantified. b Overall linear to branched ratio of alcohols and aldehydes. c Diethyl acetals of the
C7 aldehydes.
Catalysis
being hydrogenated faster as expected since the l : b ratios of
aldehydes and alcohols were not the same. The overall linear
to branched selectivity was 2.2 : 1, which is similar to that
obtained after the longer reaction time. This result is in contrast
with earlier studies showing the one-step formation of alcohol
products.20,21 The origins of this difference are currently being
investigated. Lower concentrations of Rh-dendrimer complexes
increase the amount of side products (i.e. diethyl acetals).
Indeed the hydrocarbonylation of hex-1-ene produced 5% of
diethyl acetals (from C7 aldehydes) when the concentration of
rhodium was reduced to 4.4 × 10Ϫ3 mol dmϪ3. Increased
amounts of aldehydes were also observed at lower catalyst
concentrations, when using PEt3 as the ligand.21
Use of the 72-dimethylphosphine functionalised POSS, G2-
ethyl-72methylPMe2, leads to the formation of C7 alcohols
(heptan-1-ol and 2-methylhexan-1-ol) and a small amount
of heptan-1-al diethyl acetal (2%). The catalytic solution was
partially heterogeneous (before and after reaction). Traces of
isomerisation products were also detected but not quantified.
The l : b ratio of the alcohols obtained was 2.4 : 1 (Table 2).
This regioselectivity is slightly higher than that found for the 1st
generation dendrimer, but similar to that seen when using PMe3
as the ligand.
Hydrocarbonylation of hex-1-ene in ethanol was also carried
out using the dendrimer G1-24methylPHex2 containing dihexyl-
phosphine moieties. After 16 hours (yellow clear solution), the
conversion of the substrate was higher than 99% (GC). As
expected the main products of reaction were heptan-1-ol and
2-methylhexan-1-ol in a ratio of 2.4 : 1. No trace of aldehydes
or side-products were detected.
Total conversion of the hex-1-ene was obtained using a cat-
alyst derived from G1-24ethylPEt2 after 16 hours in a batch
autoclave, while only 6 hours were necessary using a reactor,
which operates under constant pressure by feeding gas through
a mass flow controller from a ballast vessel and has more effi-
cient stirring leading to better transport across the gas–liquid
interface (Table 3). Interestingly the linear to branched ratio
(3.1 : 1) was slightly higher than for PEt3 (2.4 : 1) under identical
conditions, perhaps suggesting that the large dendrimer-based
Hydrocarbonylation of hex-1-ene, oct-1-ene, non-1-ene and
prop-2-en-1-ol catalysed by rhodium complexes formed from
[Rh2(O2CMe)4] or [Rh(acac)(CO)2] and dimethylphosphine
(G1-24methylPMe2, G2-ethyl-72methylPMe2), dihexylphos-
phine (G1-24methylPHex2) or diethylphosphine (G1-16ethyl-
PEt2, G1-24ethylPEt2, G1-24propylPEt2, and G2-propyl-48PEt2)
functionalised dendrimers was carried out at 120 ЊC and 40 bar
of CO/H2 in ethanol or THF.
Hydrocarbonylation of hex-1-ene. The rhodium complexes
formed with PMe3, G1-24methylPMe2, G2-ethyl-72methyl-
PMe2 and G1-24methylPHex2 show good activity for the cat-
alytic hydrocarbonylation of hex-1-ene to heptan-1-ol and
2-methylhexan-1-ol at the optimal conditions found previ-
ously21 (solvent ethanol, [Rh2(O2CMe)4] = 8.0 × 10Ϫ3 mol dmϪ3
,
phosphine/rhodium ratio of 3/1, 40 bar CO/H2 (1/1), 120 ЊC,
16 h, autoclave stirred using a stirrer bar) (Table 2). The use of
[Rh2(O2CMe)4] and [Rh(acac)(CO)2] as the Rh source at higher
P/Rh ratios (P/Rh = 4/1 to 6/1) gave similar results. The den-
drimers must be bound to the rhodium since only reactions
involving trialkylphosphine complexes give alcoholic products.
The hydrocarbonylation of hex-1-ene using [Rh2(O2CMe)4] and
G1-24methylPMe2 as catalyst complex in ethanol (batch
reactor) gave mainly C7 alcohols (over 94%) (Table 2) and the
substrate was totally converted to products after 16 hours.
Heptan-1-ol and 2-methylhexan-1-ol were the products of the
reaction (determined by gas chromatography (GC)) in a ratio
of 2.1 : 1. Traces of C7 aldehydes and diethyl acetals (formed
from C7 aldehydes and ethanol) were also detected in some
cases. The solutions recovered after reaction were clear yellow
although a small amount of yellow precipitate was sometimes
present. Interestingly, after 4 hours the conversion had reached
95% with 80% of the substrate converted to the aldehydes
(heptan-1-al and 2-methylhexan-1-al, l : b ratio of 1.8 : 1). The
other products were the alcohols (14%) with a l : b ratio of 4.6 : 1
(Table 2). This result suggests that the aldehydes are formed
initially, and then reduced to the alcohols, the linear isomer
J. Chem. Soc., Dalton Trans., 2002, 1997–2008
2001

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Table 3 Hydrocarbonylation reactions catalysed by Rh complexes of POSS derived 24-diethylphosphine dendrimer G1-24ethylPEt2
Substrate
Reaction time/h
Conversion (%)
Aldehydes (%)
Alcohols (%)
l : b ratio (alcohol)
Rate constant/10Ϫ4 sϪ1
Hex-1-ene
Non-1-ene
16a or 8b
16a
>99
>99
tr
tr
98
98
3.1
2.6
3.7b
—
Reaction conditions: catalyst prepared in situ from [Rh2(O2CMe)4] and dendrimer (Rh = 4.0 × 10Ϫ5 mol, P/Rh = 4/1), substrate 8.0 × 10Ϫ3 mol (hex-1-
ene 1 cm3, non-1-ene 1.4 cm3), ethanol 4 cm3, 120 ЊC, CO/H2 40 bar. a Batch autoclave. b Constant pressure apparatus.
ligand was exerting some steric control over the reaction. Small
amounts of isomerisation products (hex-2-ene and hex-3-ene
< 2%) were formed during the catalytic process. The graph
representing the consumption of syngas (CO/H2) during the
hydrocarbonylation of hex-1-ene is shown in Fig. 2. An inflec-
it is likely that the active complexes formed during hydro-
formylation are very similar. This result differs from those
obtained with the diphenylphosphine dendrimers, which give
different selectivities when using different spacers between the
two phosphorus atoms.14,21,26 For the first generation dendrimer
a decreasing rate (Table 4) was observed when using ligands
G1-24propylPEt2 (longer spacer atoms), G1-16ethylPEt2 (only
16 phosphine groups) and G1-24ethylPEt2 respectively. It is
possible that crowding at the dendrimer surface leads to a
slower reaction. However, the 48-branched diethylphosphine
POSS, G2-propyl-48ethylPEt2, leads to slightly higher reactiv-
ity than its 1st generation counterparts G1-16ethylPEt2 and
G1-24ethylPEt2 with a spacer of two carbons between the
silicon and phosphorus atoms. The reaction probably does not
proceed through direct formation of alcohols when using G1-
24propylPEt2 since aldehydes (6.1%, i.e. 10.5% of the total
amount of products) were found after 1 hour of reaction (con-
version 57.9%). In addition, since the linear to branched ratio
for the alcohols and the aldehydes were respectively 3.8 : 1 and
1 : 3, a two step reaction is more likely. The overall linear to
branched ratio (aldehyde and alcohols) was identical to that
obtained after a longer reaction time (2.9 : 1), when alcohols
were the only products.
Dendrimers G1-16ethylPCy2 and G1-16ethyl(PCy )
with
0.32(PEt2)0.68
2
dicyclohexylphosphine moieties were also used as ligands for
the hydroformylation/hydrocarbonylation of oct-1-ene (Table
5). Hydroformylation in toluene at 120 ЊC and 10 bar of syngas
by the complex formed from [Rh(acac)(CO)2] (2.0 × 10Ϫ5 mol)
and G1-24ethylPCy2 (P : Rh = 6/1) led to the formation of
nonan-1-al (57.2%) and 2-methyloctan-1-al (40.3%). A poor
selectivity to the linear aldehyde, l : b ratio of only 1.4 : 1, was
obtained. A likely explanation of this result is that the bis
ligand species responsible for the selectivity cannot form due
to the steric hindrance of such dicyclohexylphosphine ligands.
When using the di-substituted diethyl- and dicyclohexyl-
Fig. 2 Kinetics of the hydrocarbonylation of hex-1-ene in ethanol at
120 ЊC at 40 bar of CO/H2 catalysed by the complexes [Rh (CO)2(acac)]/
G1-24ethylPEt2.
tion at the beginning of the graph and a long tail at the end may
indicate that different reactions dominate at different times.
Based on the results obtained with G1-24methylPMe2 (see also
below), the hydrocarbonylation is probably a two step reaction
with hydroformylation followed by subsequent hydrogenation
of the aldehydes. Such a mechanism would explain the traces
of aldehydes found in the reaction products. A first order rate
constant for the rate of reaction was calculated for this reaction
(k = 3.7 × 10Ϫ4 sϪ1).
phosphine dendrimer (G1-16ethyl(PCy )
) as ligand of
0.32(PEt2)0.68
the rhodium-based catalyst derived 2 from [Rh(acac)(CO)2]
(4.0 × 10Ϫ5 mol) for the hydrocarbonylation of oct-1-ene, in
ethanol at 120 ЊC under 40 bar of syngas, the alcohols (59.9%
of nonan-1-ol and 32.4% of 2-methyloctan-1-ol) were the main
products of reaction. A slightly higher linear to branched ratio
was obtained (l : b = 1.8 : 1). This value is however low com-
pared to those obtained from the diethylphosphine dendrimers
showing that the catalytic active species were affected by the
bulky cyclohexyl substituents.
Hydrocarbonylation of oct-1-ene and non-1-ene. The hydro-
carbonylation of oct-1-ene catalysed by the complexes formed
from [Rh(acac)(CO)2] and the diethylphosphine-containing
dendrimers (G1-24ethylPEt2, G1-16ethylPEt2, G1-24propyl-
PEt2, G2-propyl-48ethylPEt2) led to the formation of nonan-1-
ol and 2-methyloctan-1-ol as the only products (Table 4). The
complexes were initially formed in a Schlenk tube and injected
into the autoclave when homogeneous solutions were obtained.
All complexes formed from ligands G1-24ethylPEt2 (5 atoms
between the phosphorus atoms, 3 P atoms/Si), G1-16ethylPEt2
(5 atoms between the P atoms, 2 P atoms/Si), G2-propyl-48PEt2
(2nd generation, 5 atoms between the P atoms, 2 P atoms/Si)
and G1-24propylPEt2 (7 atoms between the P atoms, 3 P atoms/
Si) showed similar selectivity to the linear alcohol nonan-1-ol
(ca. 73%), with a linear to branched ratio of ca. 3 : 1. Therefore,
The hydrocarbonylation of non-1-ene using G1-24ethylPEt2
as ligands led to the formation of decan-1-ol and 2-methyl-
nonan-1-ol in 98% yield (Table 3). A linear to branched ratio of
2.6 : 1 was obtained. Traces of aldehydes and 2- and 3-nonene
were also detected.
After reaction, the catalytic mixtures (all diethyl- and
dicyclohexyl-phosphine dendrimers) were bright yellow sol-
utions although the use of batch autoclaves occasionally led to
formation of a yellow precipitate, which was not further
analysed.
Hydrocarbonylation of prop-2-en-1-ol in protic solvents. The
synthesis of butane-1,4-diol is an important industrial process
since the diol is used as an intermediate in the formation of
tetrahydrofuran and of polyester resins.28 The preparation of
2002
J. Chem. Soc., Dalton Trans., 2002, 1997–2008

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Table 4 Hydrocarbonylation reactions of oct-1-ene catalysed by Rh complexes of POSS derived diethylphosphine dendrimers
Ligand
Time/h
k/10Ϫ4 sϪ1
Conversion (%)
Isomerisation (%)
Nonan-1-ol (%)
l : b ratio
G1-16ethylPEt2
G1-24ethylPEt2
G1-24propylPEt2
G1-24propylPEt2
G2-propyl-48ethylPEt2
8
8
4
1
8
1.5
1.7
3.7
—
>99.9
3.1
2.1
1.4
0.6
2.6
73.5
73.2
72.8
40.3a
72.8
3.1
3.1
2.9
3.8
3.0
>99.9
>99.9
57.9
2.1
>99.9
Reaction conditions: [Rh(acac)(CO)2] = 4.0 × 10Ϫ5 mol, P/Rh = 6/1, ethanol (4 cm3) heated under CO/H2 (6 bar) for 1 h. Substrate oct-1-ene
(8.3 × 10Ϫ3 mol) injected and the pressure increased to and maintained at 40 bar by a constant supply of CO/H2, 120 ЊC. a Nonan-1-al 6.1 %, aldehyde
l : b = 0.33.
Table 5 Hydroformylation or hydrocarbonylation of oct-1-ene catalysed by [Rh(acac)(CO)2]/dicyclohexylphosphine-containing dendrimers
Ligand
Solvent
Time/h
k/10Ϫ4 sϪ1
Conversion (%)
Nonan-1-ol (%)
Nonan-1-al (%)
1 : b ratio
G1-16ethylPCy2
G1-16ethyl(PCy )
Toluenea
Ethanolb
5
8
1.9
2.4
>99.9
>99.9
—
59.9
57.2
—
1.4
1.8
0.32(PEt2)0.68
2
Reaction conditions: [Rh(acac)(CO)2], P/Rh = 6/1, substrate 8.3 × 10Ϫ3 mol, solvent (4 cm3), 120 ЊC. a Rh = 2.0 × 10Ϫ5 mol, CO/H2 10 bar. b Rh = 4.0 ×
10Ϫ5 mol, CO/H2 40 bar.
Table 6 Hydrocarbonylation of prop-2-en-1-ol catalysed by rhodium/G1-24ethylPEt2 complexes at 120 ЊC and 40 bar H2/CO
Solvent
Time/h
k1 a /10Ϫ3 sϪ1
k2 b /10Ϫ3 s1
Conversion (%)
BDO (%)
MPO (%)
MPD (%)
MPA (%)
HBA (%)
Ethanol
Ethanol
Ethanolc
THF
2
1.2
—
—
1.2
—
—
—
—
0.23
—
99.9
67.5
60.8
14.1
20.9
59.3
64.9
26.1
3.6
5.4
17.1
21.9
4.4
1.8
2.7
5.5
6.9
2.5
15.6
23.2
8.0
0.5
25.0
37.1
4.1
0.25
—
3
99.8
99.9
THF
9
1.1
0.2
Reaction conditions [Rh(acac)(CO)2] (4.0 × 10Ϫ5 mol), G1-24ethylPEt2 (1.0 × 10Ϫ5 mol), solvent 4 cm3, substrate 1 cm3 (14.7 × 10Ϫ3 mol), 120 ЊC,
40 bar H2/CO BDO = butane-1,4-diol, MPO = 2-methylpropan-1-ol, MPD = 2-methylpropane-1,3-diol, MPA = 2-methylpropan-1-al, HBA =
4-hydroxybutan-1-al. a k1 = rate constant for the hydroformylation step. b k2 = rate constant for the hydrogenation step. c After 0.25 h (as second entry
in this Table but the selectivity to the various products is shown for direct comparison with the first entry).
butane-1,4-diol by the hydrocarbonylation in a protic solvent
of prop-2-en-1-ol was also used to test the catalytic properties
of the dendrimer ligands. The products expected from prop-2-
en-1-ol are butane-1,4-diol and 2-methylpropane-1,3-diol if the
reaction follows a similar stepwise pathway to that of the
hydrocarbonylation of hex-1-ene.20,21 However the reaction car-
ried out in ethanol led to butane-1,4-diol in 60.8% yield and to
the branched alcohols 2-methylpropan-1-ol (26.1%) and only
4.4% of 2-methylpropane-1,3-diol (Fig. 3 and Table 6). The
The production of 2-methylpropan-1-ol as the major
branched product requires some interpretation since it cannot
be a direct product of the hydrocarbonylation of the substrate,
but must involve dehydration at some stage of the reaction
followed by hydrogenation. It was previously proposed that the
hydrocarbonylation of hex-1-ene and prop-2-en-1-ol in protic
solvents using PEt3 as ligand may involve a single step reaction
to the alcohols via a hydroxycarbene intermediate.20,21 The
2-methylpropan-1-ol was proposed to be formed from this
hydroxycarbene intermediate in the Markownikoff cycle by
dehydration followed by hydrogen transfer, η3-allyl formation, a
second hydrogen transfer to form the vinyl alcohol and taut-
omerisation to 2-methylpropan-1-al, which was then hydrogen-
ated to 2-methylpropan-1-ol (see Scheme 1).20 However in our
reaction using the dendrimer based ligand, after 15 minutes
more than 67% of the substrate had reacted, with the alde-
hydes being the major products. 37.1% of the product was the
linear aldehyde 4-hydroxybutan-1-al, while the main branched
product was 2-methylpropan-1-al. Only 20.9% and 5.4% of
the products were respectively butane-1,4-diol and 2-methyl-
propan-1-ol.
As shown in Fig. 4, corresponding to the gas consumption
during the hydroformylation of prop-2-en-1-ol in ethanol cat-
alysed by the complex formed between [Rh(acac)(CO)2] and
dendrimer G1-24ethylPEt2, two reaction regimes are visible.
Firstly, a hydroformylation reaction occurred with possibly a
concurrent hydrocarbonylation reaction (see below), followed
by a slower process, presumed to be hydrogenation. The first
step was first order in substrate (k1 = 1.2 × 10Ϫ3 sϪ1).
These results show that, for butane-1,4-diol, the reaction
proceeds, at least in part, through a sequential pathway (via
aldehyde), but for the branched pathway leading to 2-methyl-
propan-1-ol, this is less certain. The failure to observe more
Fig. 3 Distribution of the major products of the hydrocarbonylation
of prop-2-en-1-ol in ethanol catalysed by Rh dendritic complexes after
15 minutes and 2 hours (abbreviations used are given in Table 6).
other products detected were 2-methylpropan-1-al (2.5%),
propanol (1.4%), 2-methylprop-2-en-1-ol (0.3%), 4-hydroxy-
butan-1-al (0.5%) and 2-methylprop-2-en-1-al (0.2%). Traces
of propan-1-al, 2-methyl-3-hydroxypropan-1-al and the cyclic
products, γ-butyrolactone (0.4%) and 2,3-dihydrofuran, were
present with 3.4% of undetermined products. The linear to
branched ratio (taking account of all the different products)
was 1.8 : 1. This distribution of products is similar to those
obtained in earlier studies using PEt3.20
J. Chem. Soc., Dalton Trans., 2002, 1997–2008
2003

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Scheme 2 Formation of 2-methylprop-2-en-1-al via dehydration of an
acyl intermediate.
the hydroxycarbene intermediate. The relative rate of proton-
ation of the acyl intermediate and oxidative addition of H2 to
the same intermediate determine which route will be followed
(Scheme 3). The branched acyl intermediate complex has its
Scheme 3 Proposed routes to the branched products from the
hydrocarbonylation of 2-propen-1-ol.
Scheme 1 Mechanism proposed in ref. 20 for the production of
2-methylpropan-1-ol from the hydrocarbonylation of prop-2-en-1-ol.
hydroxy proton in such a position that it may act to protonate
the carbonyl oxygen via a six membered transition state. This
may greatly enhance the rate of formation of the hydroxy-
carbene intermediate. For the linear acyl complex, the equiv-
alent intermediate would involve a seven membered ring, which
would not be expected to give such a rate enhancement. A
similar mechanism was proposed for the formation of 2-
methylpropan-1-ol in the hydrocarbonylation of 2-propen-1-ol
using PEt3 complexes of rhodium in toluene as solvent.20
If this explanation is correct, there is clearly a fine balance
between the “normal” hydroformylation mechanism and the
hydroxycarbene route. Further evidence for this comes from the
observation of 2-methyl-3-hydroxypropan-1-al (1.7% selectiv-
ity) after short reaction times, since this must come from the
“normal” hydroformylation pathway via the branched acyl
intermediate. This suggests that both pathways are occurring
for the branched aldehyde, but that the hydroxycarbene route
dominates.
The hydrocarbonylation of prop-2-en-1-ol in THF (Table 6)
gave similar results with the formation of butane-1,4-diol
(64.9% after 9 h), 2-methylpropan-1-ol (21.9%) and 2-methyl-
propane-1,3-diol (6.9%). Interestingly the selectivity (including
all the linear and branched products) was somewhat higher in
THF (l : b = 2.2 : 1 instead of 1.8 : 1 in ethanol). The rate of
formation of the desired alcohol products was much lower
(ca. half ) in the less polar solvent despite a similar rate of
Fig. 4 Kinetics of the hydrocarbonylation of prop-2-en-1-ol catalysed
by [Rh(CO2)(acac)]/G1-24ethylPEt2 at 120 ЊC and 40 bar (H2/CO) in
ethanol (k in 10Ϫ3 sϪ1).
than traces of the expected branched hydroxyaldehyde, 2-
methyl-3-hydroxypropan-1-al (selectivity of 1.4%),29 and of its
hydrogenated product, 2-methylpropane-1,3-diol (selectivity of
2.7%), after 15 min suggests that neither of these is an initial
product nor can they be intermediates in the formation of
2-methylpropan-1-ol (see Table 6). Similar conclusions were
drawn when using PEt3 as the ligand.20
Since dehydration of 2-methylpropane-1,3-diol would lead to
2-methyl prop-2-en-1-ol, which cannot easily give the observed
2-methylpropanal, this means that the dehydration must occur
from a rhodium bound intermediate. This cannot be the acyl
complex as this would give 2-methylprop-2-en-1-al (Scheme 2),
which is also probably not an intermediate (not observed after
15 min), so we propose that the branched cycle does go through
hydroformylation (k1 = 1.2 × 10Ϫ3
s
Ϫ1) being found (first order
reaction). The hydrogenation step was much slower in THF (k2
= 0.23 × 10Ϫ3 Ϫ1) (first order reaction). Similar results were
s
previously found with PEt3.20
The observation of 2-methylpropanol as the major branched
product (2-methylpropanal after shorter reaction time) for reac-
tions carried out in THF is consistent with the explanation
given in Scheme 3 for the production of these products. Since
the protonation occurs via a cyclic transition state from the
alcoholic proton of the allyl alcohol, this reaction should be
2004
J. Chem. Soc., Dalton Trans., 2002, 1997–2008

View Article Online
little affected by the reaction medium, as is observed. The
slightly higher yield of 2-methylpropane-1,3-diol (6.9% instead
of 4.4% in ethanol) at the expense of 2-methylpropan-1-ol and
other dehydrated products (23.1% instead of 29.1% in ethanol)
may indicate that the protonation is marginally less effective in
the aprotic solvent, THF.
were obtained using a micromass TOF Spec 2E mass spectro-
meter system equipped with a 337 nm N2 laser operating
in positive ion reflection mode. Samples were prepared by
addition of the matrix (α-cyano-4-hydroxycinnamic acid, 2.6-
dihydroxyacetophenone, or 2,5-dihydroxybenzoic acid). The
mixtures were then dissolved in a suitable solvent (THF, MeCN
or CH2Cl2) before being transferred to the sample holder
and dried. All mass measurements refer to peaks for the most
common isotopes (1H, 12C, 16O, 29Si, 31P).
Conclusion
1st and 2nd generation alkylphosphine dendrimers based on
POSS cores have been synthesised by two different routes. They
have then been successfully applied as ligands to rhodium for
the hydrocarbonylation of linear alkenes leading to alcohols as
the major products. In some cases slightly higher l : b ratios in
the alcohol products are obtained with the dendrimer based
phosphines (3.1 : 1) than with free triethylphosphine (2.4 : 1).
The reaction was shown to occur via formation of the aldehydes
and subsequent hydrogenation to the alcohols. This result con-
trasts with those obtained in previous studies using PEt3 as the
ligand.20,21
The hydrocarbonylation of propen-1-ol using the dendritic
ligand G1-24ethylPEt2 led to the formation of identical pro-
ducts (mainly butane-1,4-diol and 2-methylpropan-1-ol) to
those obtained with PEt3. However the formation of the linear
alcohol (butane-1,4-diol) clearly occurred via a two step reac-
tion i.e. hydroformylation to form 4-hydroxybutan-1-al and
subsequent hydrogenation to the diol. The formation of
2-methylpropan-1-ol (branched product) probably occurred via
a hydroxycarbene route, with intramolecular protonation of the
acyl intermediate.
All manipulations were carried out under dry, deoxygenated
(CrII on silica) argon, using standard Schlenk line and catheter
tubing techniques. Solvents were degassed before use having
been dried by distillation from sodium diphenyl ketyl (THF,
diethyl ether, light petroleum (boiling range 40–60 ЊC)), sodium
(toluene, cyclohexane), CaH2 (CH2Cl2) or magnesium alkoxide
(methanol, ethanol). Water was distilled and stored under
argon. Deuteriated solvents (Cambridge Isotope Laboratories)
were degassed by repeated freeze–pump–thaw cycles and stored
under argon over molecular sieves.
PMe3 (Strem), Et2PH (Strem), Cy2PH (Strem), vinylMgBr
(Aldrich), allylMgBr (Aldrich), BunLi (Aldrich), ButLi
(Aldrich), H2PtCl6 (Johnson Matthey), AIBN (Aldrich), 1-
bromohexane (Aldrich), PMeCl2 (Strem), [Rh2(OAc)4]
(Aldrich) and [Rh(acac)(CO)2] (Alfa) were all standard labor-
atory reagents and were used as received. HSiMeCl2 and HSiCl3
(both Aldrich) were distilled under argon before use.
G0-8vinyl,15 G1-24Cl,15 G1-24vinyl15 and Me2PCH2Li24 were
prepared by standard literature methods.
Syntheses
The different functionalised dendrimers show different prop-
erties depending upon the nature of the phosphine and the
complexity of the dendrimer itself. Hexyl and ethyl groups on
the phosphine promoted better solubility than their methyl
analogues (in toluene for example). Indeed, whichever diethyl-
phosphine dendrimer was used, its ability to form homo-
geneous systems with rhodium complexes was higher than that
for its dimethylphosphine counterpart. It seems that the longer
alkyl chains on the dendrimers increase the solubility of the
dendrimers in these solvents.
Understanding the effect of the dendrimer structure in the
rates and selectivity of hydroformylation reaction is not
straightforward since the different generation dendrimers may
show different properties depending on the phosphine end-
groups. Whilst the dendrimer generation did not seem to
modify the selectivity of the hydroformylation reaction, the
branching pattern had a large influence on the reaction rate.
Indeed, the number of functional groups and the length of
the bridge between the phosphines were determining factors in
the reactivity of the rhodium complexes.
1,3,5,7,11,13,15-Octakis[2-(dichloromethylsilyl)ethyl]penta-
cyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-16Cl). The com-
pounds HSiMeCl2 (6.7 cm3, 59.3 mmol) and H2[PtCl6] (0.1 mol
dmϪ3 in iPrOH, 10 drops) were added to a solution of G0-8vinyl
(1.0 g, 1.58 mmol) in diethyl ether (50 cm3). The resulting mix-
ture was heated under reflux for 8 h and stirred at 20 ЊC for 15 h.
The solvent was removed in vacuo to give 2.40 g (98%) of G1-
1
16Cl as a white solid. H NMR (CDCl3): δH (ppm) 1.52 (m,
16 H, CH2), 0.83 (m, 16 H, CH2), 0.80 (s, 24 H, CH3). 13C-{1H}
NMR (CDCl3): δC (ppm) 16.77 (CH2SiCl2), 14.53 (SiCH3), 3.41
(O3SiCH2).
1,3,5,7,11,13,15-Octakis[2-(divinylmethylsilyl)ethyl]penta-
cyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-16vinyl). Vinylmag-
nesium bromide (1.0 mol dmϪ3 in THF, 35 cm3) was added to
a solution of G1-16Cl (2.65 g, 1.71 mmol) in THF (40 cm3).
The resulting solution was stirred at room temperature for 17 h.
The mixture was slowly added to a cooled (ice bath) aqueous
solution of ammonium chloride (1.0 mol dmϪ3 in water, 50
cm3). The aqueous solution was extracted with petroleum (2 ×
80 cm3). The combined organic layers were washed with a sat-
urated aqueous solution of NaCl (20 cm3), dried over Na2SO4
and concentrated in vacuo. The residue was loaded onto a col-
umn of silica gel and eluted with petroleum to afford com-
pound G1-16vinyl (2.06 g, 85%). A crystalline compound was
obtained by recrystallisation in cold petroleum. Microanalysis
found C, 47.1; H, 7.3; Si16O12C56H104 requires C, 47.0; H, 7.3%.
Experimental
Microanalyses were carried out by the University of St.
Andrews Microanalysis service on a Carlo Erba 1110 CHNS
analyser. NMR spectra were recorded on a Bruker AM 300 or a
Varian 300 NMR spectrometer. The 1H and 13C NMR spectra
were recorded with reference to tetramethylsilane (external). 31
P
3
2
1H NMR (CDCl3): δH (ppm) 6.13 (dd, JHH = 19.5 Hz, JHH
=
NMR spectra were referenced externally to 85% H3PO4. 13C
and 31P NMR spectra were recorded with broad band proton
decoupling. Infrared spectra were recorded using either a
Perkin-Elmer 1710 or a Nicolet 460 Protege FTIR spectro-
meter. GC analyses were carried out using a Phillips PU4000
instrument fitted with a capillary column with nitrogen as the
carrier gas. GCMS analyses were carried out using a Hewlett-
Packard 5890 GC interfaced with an Incos quadrupole mass
spectrometer fitted with a SGE BP1 column or using a Hewlett-
Packard HP6890 GC with a 5973 mass selective detector fitted
with a 5% phenyl methyl siloxane capillary column. Matrix
assisted laser desorption/ionisation (MALDI) mass spectra
14.2 Hz, 24 H, CH ᎐), 6.02 (dd, 3JHH = 14.2 Hz, 3JHH = 4.4 Hz,
᎐
2
3
3
24 H, ᎐CH ), 5.71 (dd, J = 19.5 Hz, JHH = 4.4 Hz, 24 H,
᎐
2
HH
SiCH᎐), 0.62 (m, 16 H, SiCH ), 0.76 (m, SiCH , 16H), 13C-{1H}
᎐
2
2
NMR (CDCl ): δ (ppm) 136.65 (CH᎐CH ), 133.14 (CH᎐CH ),
᎐
᎐
3
C
2
2
5.35 (O3SiCH2CH2), 4.27 (O3SiCH2CH2), Ϫ5.90 (SiCH3).
1,3,5,7,11,13,15-Octakis[2-(diallylmethylsilyl)ethyl]penta-
cyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-16allyl). Allylmag-
nesium bromide (1.0 mol dmϪ3 in THF, 35 cm3) was added to a
solution of G1-16Cl (2.65 g, 1.71 mmol) in THF (40 cm3). The
resulting solution was stirred at room temperature for 17 h.
J. Chem. Soc., Dalton Trans., 2002, 1997–2008
2005

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The mixture was slowly added to a cooled (ice bath) aqueous
solution of ammonium chloride (1.0 mol dmϪ3 in water,
50 cm3). The aqueous solution was extracted with petroleum
(2 × 80 cm3). The combined organic layers were washed with a
saturated aqueous solution of NaCl (20 cm3), dried over Na2SO4
and concentrated in vacuo. The residue was loaded onto a
column of silica gel and eluted with petroleum to afford 2.5 g
(90% yield) of the oily G1-16allyl. Microanalysis found C,
52.3; H, 8.3; Si16O12C72H136 requires C, 52.6; H, 8.3%. 1H NMR
(CDCl3): δH (ppm) 5.77 (m, 16 H, CH᎐CH ), 4.86 (m, 32 H,
1,3,5,7,11,13,15-Octakis{2-[bis(diethylphosphinoethyl)methyl-
silyl]ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-16-
ethylPEt2). G1-16vinyl (0.25 g, 0.176 mmol) was added to a dry
20 cm3 round bottomed Schlenk flask. AIBN (0.0078 g) was
added and the flask was charged with cyclohexane (5 cm3) and
diethylphosphine (1.0 g, 11.3 mmol). The flask was sealed and
heated to 60 ЊC for 8 days. The resulting solution was allowed to
cool and taken to dryness in vacuo. The resulting crude product
was a colourless oil (0.497 g, 99% yield for a conversion >96%).
MALDI-TOF: m/z 2923 (M ϩ 3 oxide)ϩ, (M expected 2860)
not found, small peak at 2645. 31P-{1H} NMR (CDCl3): δP
᎐
2
CH᎐CH ), 1.57 (d, 3J = 7.1 Hz, 32 H, SiCH CH᎐CH ), 0.59
᎐
᎐
2
HH
2
2
(m, 32 H, SiCH2CH2Si), 0.00 (SiCH3). 13C-{1H} NMR
(ppm) Ϫ15.2 (br). 1H NMR (CDCl3): δH (ppm) 1.44 (m, 3JH–H
=
(CDCl ): δ (ppm) 134.26 (CH᎐CH ), 113.86 (CH᎐CH ), 19.32
7.7 Hz, 96 H, PCH2–), 1.15 (dt, 3JH–H = 7.7 Hz, JP–H = 13.5 Hz,
96 H, PCH2CH3), 0.66 (br, 64 H, Si–CH2), 0.10 (s, 24 H,
᎐
᎐
3
C
2
2
(CH CH᎐CH ), 4.27 (O SiCH CH ), 2.75 (O CH CH ), Ϫ5.40
᎐
2
2
3
2
2
3
2
2
(SiCH3).
Si–CH3). 13C-{1H} NMR (CDCl3): δC (ppm) 19.45 (d, JC–P
=
15.0 Hz, SiCH2CH2P), 18.66 (d, JC–P = 12.7 Hz, PCH2CH3),
9.95 (d, JC–P = 12.7 Hz, PCH2CH3), 7.91 (d, JC–P = 6.0 Hz,
PCH2CH2Si), 5.16 (SiCH2CH2Si), 4.82 (SiCH2CH2Si), Ϫ5.52
(SiCH3). IR/cmϪ1 (KBr disc): 2956s, 2919s, 2873s, 1455vs,
1409vs (PCH2), 1260vs (SiCH2), 1120vs (SiCH2CH2Si), 1040vs
(SiOSi), 952s, 800m, 750vs, 707vs.
1,3,5,7,11,13,15-Octakis[2-(triallylsilyl)ethyl]pentacyclo-
[9.5.1.13,9.15,15.17,13]octasiloxane (G1-24allyl). Allylmagnesium
bromide (1.0 mol dmϪ3 in THF, 45 cm3) was added to a solution
of G1-24Cl (2.65 g, 1.54 mmol) in THF (40 cm3). The resulting
solution was stirred at room temperature for 17 h. The mixture
was slowly added to a cooled (ice bath) aqueous solution of
ammonium chloride (1.0 mol dmϪ3 in water, 50 cm3). The aque-
ous solution was extracted with petroleum (2 × 80 cm3). The
combined organic layers were washed with a saturated aqueous
solution of NaCl (20 cm3), dried over Na2SO4 and concentrated
in vacuo. The residue was loaded onto a column of silica gel and
eluted with petroleum to afford the desired compound G1-
24allyl (1.90 g, 81%) as an oil. Microanalysis found C, 56.6;
H, 8.8; Si16O12C88H152 requires C, 57.1; H, 8.3%. 1H NMR
1,3,5,7,11,13,15-Octakis{2-[tris(diethylphosphinoethyl)silyl]-
ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-24ethyl-
PEt2). G1-24vinyl (0.245 g, 0.162 mmol) was added to a dry
20 cm3 round bottomed Schlenk flask. AIBN (0.0078 g) was
added and the flask was charged with cyclohexane (7 cm3) and
diethylphosphine (1.40 g, 15.6 mmol). The flask was sealed and
heated to 60 ЊC for 10 days. The resulting solution was allowed
to cool and taken to dryness in vacuo. The resulting crude
product was a colourless oil (0.573 g, 97% yield for a conversion
>96%). MALDI-TOF: m/z 3676.3 (M expected 3677.4), other
peaks at m/z 3803 (M ϩ matrix), 3582.0 (M Ϫ PEt2), 3497.9
(M Ϫ {2 × PEt2}), 3406.2 (M Ϫ {3 × PEt2}), 3315.7 (M Ϫ {4 ×
PEt2}). If Naϩ is omitted from the matrix, two peaks are
observed at m/z 3808 (Mϩ matrix) and 3713 (M Ϫ PEt2 ϩ
matrix). Microanalysis found C, 51.7; H, 10.5;
C160H368O12P24Si16 requires C, 52.3; H, 10.9%. 31P-{1H} NMR
(CDCl3): δP (ppm) Ϫ15.9, Ϫ16.0. 1H NMR (CDCl3): δH (ppm)
1.34 (m, 122 H, PCH2–), 1.04 (dt, 3JPH = 14.0 Hz, 3JH–H = 7.7 Hz,
122 H, PCH2CH3), 0.66 (br, 80 H, Si–CH2). 13C-{1H} NMR
(CDCl3): δC (ppm) 19.21 (d, JC–P = 14.7 Hz, SiCH2CH2P), 18.66
(d, JC–P = 14.7 Hz, PCH2CH3), 9.95 (d, JC–P = 12.1 Hz,
PCH2CH3), 5.95 (d, JC–P = 6.0 Hz, PCH2CH2Si), 4.44 (SiCH2-
CH2Si), 3.07 (SiCH2CH2Si), Ϫ5.52 (SiCH3). IR/cmϪ1 (KBr
disc): 2957s, 2919s, 2874s, 1458vs, 1409vs (PCH2), 1259vs
(SiCH2), 1120vs (SiCH2CH2Si), 1040vs (SiOSi), 952s, 800m,
750vs, 706vs.
(CDCl3): δH (ppm) 5.79 (m, 24 H, CH᎐CH ), 4.90 (m, 48 H,
᎐
2
CH᎐CH ), 1.61 (d, 3J = 8.0 Hz, 48 H, SiCH CH᎐CH ), 0.63
᎐
᎐
2
HH
2
2
(m, 32 H, SiCH2CH2Si). 13C-{1H} NMR (CDCl3): δC (ppm)
134.28 (CH᎐CH ), 113.83 (CH᎐CH ), 19.06 (CH CH᎐CH ),
᎐
᎐
᎐
2
2
2
2
4.28 (O3SiCH2CH2), 2.76 (O3CH2CH2).
1,3,5,7,11,13,15-Octakis{2-{tris[2-(dichloromethylsilyl)-
propyl]silyl}ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane
(G2-propyl-48Cl). The compounds HSiMeCl2 (15 cm3, 0.15
i
mol) and H2[PtCl6] (0.1 mol dmϪ3 in PrOH, 15 drops) were
added to a solution of G1-24allyl (2.0 g, 1.08 mmol) in toluene
(50 cm3). The resulting mixture was heated at reflux for 96 h.
The solvent was removed in vacuo to give G2-propyl-48Cl as a
white solid (4.7 g, 95%). 1H NMR (CDCl3): δH (ppm) 1.84
(β hydrosilylation, MeCl2SiCH(CH3)CH2–) (<5%) 1.55 (m,
CH2CHMeSiCl2, CH2CH2SiCl2), 1.20 (m, 48 H, CH2CH2-
SiCl2), 0.78 (s, 72 H, SiCH3), 0.76–0.55 (m, 80 H, SiCH2). 13C-
{1H} NMR (CDCl3): δC (ppm) 28.36 (27.65), 17.37 (16.64),
14.71, 4.41 (br, O3SiCH2CH2Si).
1,3,5,7,11,13,15-Octakis{2-[tris(diethylphosphinopropyl)silyl]-
ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-24propyl-
PEt2). G1-24allyl (0.30 g, 0.162 mmol) was added to a dry
20 cm3 round bottomed Schlenk flask. AIBN (0.0078 g) was
added and the flask was charged with cyclohexane (7 cm3) and
diethylphosphine (1.40 g, 15.6 mmol). The flask was sealed and
heated to 60 ЊC for 10 days. The resulting solution was allowed
to cool and taken to dryness in vacuo. The resulting crude
product was a colourless oil (0.592 g, 98% yield for a conversion
>87%). MALDI-TOF: m/z 4012 (small) (M expected 4014.2),
other major peaks at m/z 3921 (M Ϫ{PEt2}); 3839 (M Ϫ 2 ×
{PEt2}); 3789; 3750 (M Ϫ 3 × {PEt2}) (major); 3660 (M Ϫ 4 ×
{PEt2}); 3632; 3569 (M Ϫ 5 × {PEt2}). 31P-{1H} NMR
1,3,5,7,11,13,15-Octakis{2-{tris[2-(divinylmethylsilyl)propyl]-
silyl}ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G2-prop-
yl-48vinyl). Vinylmagnesium bromide (1.0 mol dmϪ3 in THF,
60 cm3) was added to a solution of G2-propyl-48Cl (4.52 g,
0.98 mmol) in THF (50 cm3). The resulting solution was stirred
at room temperature for 48 h. The mixture was slowly added to
a cooled (ice bath) aqueous solution of ammonium chloride
(1.0 mol dmϪ3 in water, 50 cm3). The aqueous solution was
extracted with petroleum (2 × 80 cm3). The combined organic
layers were washed with a saturated aqueous solution of NaCl
(20 cm3), dried over Na2SO4 and concentrated in vacuo. The
residue was loaded onto a column of silica gel and eluted with
petroleum to afford compound G2-propyl-48vinyl as a colour-
less oil (3.83 g, 70%). Microanalysis found C, 59.3; H, 10.1;
(CDCl3): δP (ppm) Ϫ23.6, Ϫ23.9, Ϫ24.3. 1H NMR (CDCl3): δH
3
(ppm) 1.37 (m, 170 H, CH2CH2CH2, PCH2–), 1.04 (dt, JPH
=
3
Si40O12C208H392 requires C, 59.4; H, 9.3%. 1H NMR (CDCl3): δH
14.6 Hz, JH–H = 7.7 Hz, 122 H, PCH2CH3), 0.69 (br, 48 H,
SiCH2), 0.53 (br, 32 H, SiCH2CH2Si). 13C-{1H} NMR (CDCl3):
δC (ppm) 31.10 (br, CH2), 20.64 (d, 1JC–P = 13.4 Hz, CH2CH2P),
18.95 (d, JC–P = 10.7 Hz, PCH2CH3), 14.39 (d, 2JC–P = 10.7 Hz,
3
(ppm) 6.20–5.94 (m, 96 H, ᎐CH ), 5.73 (dd, J = 19.8 Hz,
᎐
2
HH
2JHH = 4.3 Hz, 48 H, SiCH᎐CH ), 1.80 (br, SiCH), 1.36 (m br,
᎐
2
CH2), 0.78–0.40 (m, SiCH2), 0.12 (br, 72 H, CH3Si). 13C-{1H}
1
NMR (CDCl ): δ (ppm) 137.23 (CH᎐CH ), 132.78 (CH᎐CH ),
PCH2CH2), 9.68 (d, JC–P = 12.1 Hz, PCH2CH3), 4.58 (SiCH2-
᎐
᎐
3
C
2
2
18.92, 18.47, 16.76, 4.57 (br, O3SiCH2CH2), Ϫ5.08 (CH3Si).
CH2Si), 4.05 (SiCH2CH2Si).
2006 J. Chem. Soc., Dalton Trans., 2002, 1997–2008

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1,3,5,7,11,13,15-Octakis{2-{tris{3-[bis(diethylphosphinoethyl)-
methylsilyl]propyl}silyl}ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octa-
siloxane (G2-propyl-48ethylPEt2). G2-propyl-48vinyl (0.22 g,
5.2 × 10Ϫ5 mol) was added to a dry 20 cm3 round bottomed
Schlenk flask. AIBN (0.008 g) was added and the flask was
charged with cyclohexane (5 cm3) and diethylphosphine (0.9 g,
0.01 mol). The reaction mixture was heated to 50 ЊC for 12 days.
The resulting solution was allowed to cool and taken to dry-
ness in vacuo. The resulting crude product was a colourless oil
(0.411 g, 96% yield for a conversion >90%). Microanalysis
found C, 54.0; H, 12.2; C400H920O12P48Si40 requires C, 56.3;
H, 10.9%. 31P-{1H} NMR (CDCl3): δP (ppm) Ϫ15.8, Ϫ16.1. 1H
NMR (CDCl3): δH (ppm) 1.30 (m, 3JH–H = 7.7 Hz, 96 H, PCH2–),
sealed and heated to 60 ЊC for 10 days. The resulting solution
was allowed to cool and the excess phosphine was removed by
vacuum distillation (100 ЊC, 0.1 mmHg). The resulting crude
product was a colourless solid (0.621 g, 95% yield for a conver-
1
sion 55%). 31P -{1H} NMR (CDCl3): δP (ppm) 4.1. H NMR
(CDCl ): δ (ppm) 6.10 (m, 22 H, ᎐CH ), 5.45 (m, 11 H, SiCH᎐),
᎐
᎐
3
H
2
1.70 (br, H, CH2), 1.52 (br, CH2), 1.26 (br, CH2 and CH3),
0.75–0.45 (br, 58 H, Si–CH2). 13C-{1H} NMR (CDCl3): δC
(ppm) 33.45 (d, JC–P = 13.4 Hz, CH2P), 30.47 (d, JC–P = 12.1 Hz,
CH2P), 29.38, 27.04, 26.66, 4.44 (br, SiCH2CH2Si).
1,3,5,7,11,13,15-Octakis{2-[tris(dimethylphosphinomethyl)-
silyl]ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-24-
methylPMe2). LiCH2PMe2 24 (0.272 g, 3.32 mmol) was dissolved
at Ϫ78 ЊC in a flask containing THF (20 cm3). The solution was
transferred via cannula to a Schlenk flask containing G1-24Cl
(0.218 g, 0.127 mmol) in THF (10 cm3). The mixture was stirred
for 60 hours. The solvent was removed in vacuo. Dichlorometh-
ane was added (40 cm3). After LiCl had settled, the liquid was
transferred via cannula to another flask and taken to dryness
in vacuo. The solid was washed twice with hexane. The resulting
product was a white solid (0.329 g, 97%). MALDI-TOF m/z
2677 (very broad) (m/z expected 2667.5). Other peak at m/z
2603 (M Ϫ {CH2PMe2}). Microanalysis found C, 32.7; H, 7.5;
C88H24O24P16Si16 requires C, 36.9; H, 8.5%. 31P-{1H} NMR
(CD2Cl2): δP (ppm) Ϫ54.5. 1H NMR (CD2Cl2): δH (ppm) 1.0 (br,
144 H, P(CH3)2), 0.78 (br, 48 H, –CH2P(CH3)2), 0.66 (m,
32 H,Si–CH2CH2–Si). 13C-{1H} NMR (CD2Cl2): δC (ppm) 18.5
(br, P–CH3), 13.8 (br, P–CH2), 5.0 (br, SiCH2CH2Si). IR/cmϪ1
(KBr disc): 2951m, 2892m, 1428m (SiCH2P), 1417m (PCH3),
1292m (PCH3), 1274m–1262m (SiCH2P), 1143vs (SiCH2-
CH2Si), 1097vs (SiOSi), 938m (PCH3), 895m (PCH3), 761s
(PCH3), 707m, 665m.
3
1.03 (dt, JH–H = 7.7 Hz, JP–H = 13.7 Hz, 96 H, PCH2CH3),
0.66 (br, 68 H, Si–CH2), 0.10 (s, 24 H, Si–CH3). 13C-{1H} NMR
(CDCl3): δC (ppm) 19.55 (d, JC–P = 15.0 Hz, CH2CH2P),
18.73 (d, JC–P = 12.7 Hz, PCH2CH3), 10.08 (d, JC–P = 11.5 Hz,
PCH2CH3), 8.75 (CH2CH2CH2), 6.38 (d, JC–P = 7.0 Hz,
CH2CH2P), 5.5 (br, SiCH2), 4.90 (br, SiCH2), 1.34, Ϫ5.34 9 (br,
SiCH3).
1,3,5,7,11,13,15-Octakis{2-[(dicyclohexylphosphinoethyl)-
(diethylphosphinoethyl)methylsilyl]ethyl}pentacyclo-
[9.5.1.13,9.15,15.17,13]octasiloxane (G1-16ethyl(PCy )
). G1-
0.32(PEt2)0.68
2
16vinyl (0.133 g, 0.0939 mmol) was added to a dry 20 cm3 round
bottomed Schlenk flask. AIBN (0.007 g) was added and the
flask was charged with cyclohexane (5 cm3) and dicyclohexyl-
phosphine (0.446 g, 2.25 mmol). The flask was sealed and
heated to 60 ЊC for 3 days. Diethylphosphine (0.270 g, 3.0
mmol) was then added. The flask was heated to 60 ЊC for 5
further days. The resulting solution was allowed to cool and the
excess phosphine was removed by vacuum distillation (100 ЊC,
0.1 mmHg). The resulting crude product was a colourless solid
(0.360 g, 95% yield for a conversion >98%). 31P-{1H} NMR
1
(CDCl3): δP (ppm) 4.8, Ϫ14.9. H NMR (CDCl3): δH (ppm)
1,3,5,7,11,13,15-Octakis{2-{tris{2-[tris(dimethylphosphino-
methyl)silyl]ethyl}silyl}ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octa-
siloxane (G2-ethyl-72methylPMe2). LiCH2P(Me)2 (0.202 g,
2.47 mmol) was dissolved at Ϫ78 ЊC in a flask containing THF
(20 cm3). The solution (room temperature) was transferred via
cannula to a Schlenk flask containing POSS G2-ethyl-72Cl
(0.25 g, 0.0052 mmol) in THF (10 cm3). The mixture was stirred
for 60 h (a precipitate appeared). The solid (precipitate) was
collected by filtration and washed twice with THF. The result-
ing product was a white solid (80%) with poor solubility. IR/
cmϪ1 (KBr disc): 2952m, 2893m, 1416s (SiCH2P and PCH3),
1289w (PCH3), 1260m (SiCH2P), 1140vs (SiCH2CH2Si), 1097vs
(SiOSi), 1027m, 946w (PCH3), 894m (PCH3), 758s Ϫ743s
(PCH3), 712s, 465m.
1.86 (br, 96 H, CH2), 1.70–1.20 (br m, CH3 and CH2), 1.15 (dt,
3JH–H = 7.7 Hz, JP–H = 13.7 Hz, 30 H, PCH2CH3), 0.90–0.55 (br,
64 H, Si–CH2), 0.20–0.02 (br, 24 H, Si–CH3). 13C-{1H} NMR
(CDCl3): δC (ppm) 33.48 (d, JC–P = 13.4 Hz, CH2P), 30.47 (d,
JC–P = 12.1 Hz, CH2P), 29.38, 27.04, 26.66, 19.50 (d, JC–P
=
15.0 Hz, SiCH2CH2P), 18.66 (d, JC–P = 12.6 Hz, PCH2CH3),
9.95 (d, JC–P = 12.5 Hz, PCH2CH3), 7.80 (d, JC–P = 6.0 Hz,
PCH2CH2Si), 5.5–4.8 (br, SiCH2CH2Si), Ϫ5.45 (SiCH3).
1,3,5,7,11,13,15-Octakis{2-[(dicyclohexylphosphinoethyl)-
methylsilyl]ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane
(G1-16ethylPCy2). G1-16vinyl (0.133 g, 0.0939 mmol) was
added to a dry 20 cm3 round bottomed Schlenk flask. AIBN
(0.007 g) was added and the flask was charged with cyclohexane
(5 cm3) and dicyclohexylphosphine (0.446 g, 2.25 mmol). The
flask was sealed and heated to 60 ЊC for 10 days. The resulting
solution was allowed to cool and the excess phosphine was
removed by vacuum distillation (100 ЊC, 0.1 mmHg). The result-
ing crude product was a colourless solid (0.356 g, 98% yield for
a conversion >75%). MALDI-TOF: m/z 3746 (very broad)
(ca. 12 arms substituted due to poor quality G1-16vinyl),
M expected 4591.5. 31P-{1H} NMR (CDCl3): δP (ppm) 4.1.
1H NMR (CDCl3): δH (ppm) 1.75 (br, 120 H, CH2), 1.53 (br, 32
H, CH2), 1.26 (br, 158 H, CH2 and CH3), 0.75–0.45 (br, 64 H,
Si–CH2), 0.20–0.02 (br, 24 H, Si–CH3). 13C-{1H} NMR
(CDCl3): δC (ppm) 33.45 (d, JC–P = 13.4 Hz, CH2P), 30.47 (d,
JC–P = 12.1 Hz, CH2P), 29.38, 27.04, 26.66, 4.44 (br, SiCH2-
CH2Si), Ϫ5.40 (br, SiCH3).
Di-n-hexylmethylphosphine (ref. 24). Magnesium turnings
(3.5 g, 0.144 mol) were charged into a three neck Schlenk flask
fitted with a reflux condenser and a gas bubbler. Diethyl ether
(250 cm3) was added, followed dropwise by 1-bromohexane
(17 cm3, 0.121 mol) causing an exothermic reaction (reflux).
After completion of the addition, the grey reaction mixture was
stirred at room temperature for 1 hour, and then the unreacted
magnesium was allowed to settle. The solution was filtered to
give a Grignard solution of C6H13MgBr. Dichloromethylphos-
phine (5 cm3, 55.7 mmol) was added to a Schlenk flask contain-
ing diethyl ether. The flask was then cooled (ice bath) and
C6H13MgBr was added slowly (1 hour) to the well-stirred sol-
ution. A white precipitate of magnesium halides was formed.
The solution mixture was stirred overnight. The liquid was fil-
tered into another flask. The precipitate was twice washed with
petroleum (20 cm3) and the washings added to the second flask.
The liquid was distilled under vacuum (10Ϫ2 mmHg, 120 ЊC) to
give a colourless liquid (3.3 g, 26%). 31P-{1H} NMR (CDCl3): δP
(ppm) Ϫ41.4. 1H NMR (CDCl3): δH (ppm) 1.46–1.20 (m, 26 H,
1,3,5,7,11,13,15-Octakis{2-[tris(dicyclohexylphosphinoethyl)-
silyl]ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-24-
ethylPCy2). G1-24vinyl (0.245 g, 0.162 mmol) was added to a
dry 20 cm3 round bottomed Schlenk flask. AIBN (0.0078 g) was
added and the flask was charged with cyclohexane (7 cm3) and
dicyclohexylphosphine (3.08 g, 15.5 mmol). The flask was
2
hexyl CH2), 0.95 (d, JPH = 1.8 Hz, 3 H, PCH3), 0.74 (m, 4 H,
CH2P). 13C-{1H} NMR (CDCl3): δC (ppm) 31.67, 31.15 (d,
J. Chem. Soc., Dalton Trans., 2002, 1997–2008
2007

View Article Online
JPC = 11.6 Hz), 29.87 (d, JPC = 9.7 Hz), 25.79 (d, JPC = 12.6 Hz),
22.59, 14.08, 11.65 (d, JPC = 14.5 Hz, PCH3).
0.71073 Å), Dc = 1.078 Mg mϪ3, F(000) = 1520, 18587 measured
reflections (minimum and maximum transmission factors
0.448671 and 1.0000), 6252 independent [Rint = 0.1085] and
1940 observed data (I > 2σ(I )) to give R = 0.1343, Rw = 0.3871
with goodness-of-fit on F 2 0.951.
CCDC reference number 177248.
See http://www.rsc.org/suppdata/dt/b2/b200303a/ for crystal-
lographic data in CIF or other electronic format.
Dihexylphosphinomethyllithium. PMe(C6H13)2 (3.23 g,
14.9 mmol) was dissolved in petroleum (40 cm3). ButLi (8.8 cm3,
14.9 mmol) (1.7 M in pentane) was added at room temperature
and the reaction mixture was stirred for 5 days. The solvent was
removed in vacuo to give a pale yellow heavy liquid. The conver-
sion was only 78% (determined by 31P NMR). 31P-{1H} NMR
1
(C6D6): δP (ppm) Ϫ24.9 (LiCH2P), Ϫ43.2 (CH3P). H NMR
Acknowledgements
(C6D6): δH (ppm) 1.8–1.10 (m, 26 H, CH2), 0.95 (m, PCH3), 0.82
(br, 6 H, CH2CH3), Ϫ0.35 (br, PCH2Li).
We thank the University of St. Andrews for a studentship
(L. R.). R. E. M. thanks the Royal Society for the provision
of a University Research Fellowship.
1,3,5,7,11,13,15-Octakis{2-[tris(dihexylphosphinomethyl)-
silyl]ethyl}pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxane (G1-24-
methylPHex2). LiCH2P(C6H13)2 (0.3236 g, 1.09 mmol) was
dissolved at Ϫ78 ЊC in a Schlenk flask containing THF
(20 cm3). The solution (room temperature) was transferred via
cannula to a Schlenk flask containing G1-24Cl (0.0778 g,
0.0453 mmol) in THF (10 cm3). The mixture was stirred for
60 h. The solvent was removed in vacuo. Dichloromethane was
added (20 cm3). After settling overnight, the liquid was trans-
ferred via cannula and taken to dryness in vacuo. The product
was washed with diethyl ether (3 × 5 cm3) and dried in vacuo.
The resulting product was a white solid (yield 40%). 31P-{1H}
References
1 G. R. Newcome, E. F. He and C. N. Morefield, Chem. Rev., 1999, 99,
1689.
2 For recent reviews see: G. E. Oosterom, J. N. H. Reek, P. C. J. Kamer
and P. W. N. M. van Leeuwen, Angew. Chem., Int. Ed., 2001, 40,
1828; D. Astruc and F. Chardac, Chem. Rev., 2001, 101, 2991.
3 N. Brinkmann, D. Giebel, G. Lohmer, M. T. Reetz and U. Kragl,
J. Catal., 1999, 83, 1655.
4 V. Maraval, R. Laurent, A.-M. Caminade and J.-P. Marjoral,
Organometallics, 2000, 19, 4025.
5 V. Maraval, R. Laurent, B. Donnadieu, M. Mauzac, A.-M.
Caminade and J.-P. Marjoral, J. Am. Chem. Soc., 2000, 122, 2499.
6 R. Schneider, C. Köllner, I. Weber and A. Togni, Chem. Commun.,
1999, 2415.
1
NMR (CDCl3): δP (ppm) Ϫ36.3. H NMR (CDCl3): δH (ppm)
1.64–1.20 (m, 384 H, hexyl CH2), 0.95 (br, 115 H, CH3), 0.74
(br, SiCH2P), 0.7–0.45 (m, 32 H, Si–CH2CH2–Si). 13C-{1H}
NMR (CDCl3): δC (ppm) 31.7, 31.2 (d, JPC = 11.5 Hz), 29.8
(d, JPC = 10 Hz), 25.79 (d, JPC = 12.3 Hz), 22.6, 14.1, 10.3 (d,
JPC = 14.5 Hz, PCH2Si).
7 Q.-H. Fan, Y.-M. Chen., D.-Z. Jiang, F. Xi and A. S. C. Chan,
Chem. Commun., 2000, 789.
8 M. Petrucci-Samija, V. Guillemette, M. Dasgupta and A. K.
Kakkar, J. Am. Chem. Soc., 1999, 121, 1968.
9 D. de Groot, E. B. Eggeling, J. C. de Wilde, H. Kooijman, R. J.
van Haaren, A. W. van der Made, A. L. Spek, D. Vogt, J. N. H. Reek,
P. C. J. Kamer and P. W. N. M. van Leeuwen, Chem. Commun., 1999,
1623.
10 N. J. Hovestad, E. B. Eggeling, H. J. Heidbüchel, J. T. B. H.
Jastrzebski, U. Kragl, W. Keim., D. Vogt and G. van Koten, Angew.
Chem., Int. Ed., 1999, 38, 1655.
11 A. W. Kleij, R. A. Gossage, J. T. B. H. Jastrzebski, J. Boersma and
G. van Koten, Angew. Chem., Int. Ed., 2000, 39, 176.
12 R. Breinbauer and E. R. Jacobsen, Angew. Chem., Int. Ed., 2000, 39,
3604.
13 C. Francavilla, M. D. Drake, F. V. Bright and M. R. Detty, J. Am.
Chem. Soc., 2001, 123, 57.
14 L. Ropartz, R. E. Morris, D. F. Foster and D. J. Cole-Hamilton,
Chem. Commun., 2001, 361.
15 P.-A. Jaffrès and R. E. Morris, J. Chem. Soc., Dalton Trans., 1998,
2767.
16 L. L. Zhoo and J. Roovers, Macromolecules, 1993, 26, 963.
17 A. W. van der Made and P. W. N. M. van Leeuwen, J. Chem. Soc.,
Chem. Commun., 1992, 1400.
18 D. Seyferth, D. Y. Son, A. L. Rheingold and R. L. Ostrander,
Organometallics, 1994, 13, 2682.
19 F. J. Feher and T. A. Budzichowski, Polyhedron, 1995, 14, 3239.
20 M. C. Simpson, A. W. S. Currie, J. A. Andersen, M. J. Green and
D. J. Cole-Hamilton, J. Chem. Soc., Dalton Trans., 1996, 1793.
21 J. K. MacDougall, M. C. Simpson, M. J. Green and D. J.
Cole-Hamilton, J. Chem. Soc., Dalton Trans., 1996, 1161.
22 L. Ropartz, R. E. Morris, G. P. Schwarz, D. F. Foster and D. J.
Cole-Hamilton, Inorg. Chem. Commun., 2000, 3, 714; L. Ropartz,
R. E. Morris, D. F. Foster and D. J. Cole-Hamilton J. Mol. Catal. A,
in the press.
Catalytic reactions
The functionalised POSS dendrimer, the rhodium source
([Rh2(O2CMe)4] or [Rh(CO)2(acac)]) (amounts are shown in
the Tables) and ethanol or THF (4 cm3) were charged into a
Schlenk tube and stirred until complexation of the rhodium
with the phosphine species had occurred. The catalytic solution
and substrate were then injected into a degassed autoclave and
pressurised/heated to the desired pressure and temperature.
When using the CATS rig the catalytic solution was heated
under CO/H2 (6 bar) for 1 h. The substrate was injected and the
pressure of CO/H2 was increased to 40 bar, 120 ЊC. The pressure
was kept constant through a mass flow controller and fed from
a ballast vessel (pressure drop in ballast vessel monitored every
5 s). After reaction, the products were analysed by GC-MS.
Crystallography
X-Ray diffraction studies on crystals of G1-16vinyl were per-
formed at 293 K using a Bruker SMART diffractometer with
graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å).
The structure was solved by direct methods. The carbon atoms
were refined isotropically, with the geometries of the terminal
Si-vinyl and methyl carbon atoms having been refined in mod-
elled positions with fixed isotropic thermal positions. The inner
ethyl carbon atoms were not modelled, but allowed to refine
isotropically. All other non-hydrogen atoms were refined with
anisotropic displacement parameters. Hydrogen atoms were
refined in idealised positions. Structural refinements were by
the full-matrix least-squares method on F 2 using the program
SHELXTL30 with absorption corrected data.30
23 T. N. Martynova and V. P. Korchkov, Zh. Obshch. Khim., 1982, 52,
1585.
24 H. H. Karsch, Z. Naturforsch., Teil B, 1979, 34, 1178.
25 S. Lücke, K. Stoppek-Langner, J. Kuchinke and B. Krebs,
J. Organomet. Chem., 1999, 584, 11.
26 L. Ropartz, K. J. Haxton, R. E. Morris, D. F. Foster and D. J.
Cole-Hamilton, to be published.
27 X. Zhang, K. J. Haxton, L. Ropartz, D. J. Cole-Hamilton and
R. E. Morris, J. Chem Soc., Dalton Trans, 2001, 3261.
28 A. M. Brownstein, CHEMTECH, 1991, 506.
29 C. U. Pittman and W. D. Honnick, J. Org. Chem., 1980, 45, 2132.
30 SHELXTL, version 5.10, Bruker AXS, Madison, WI, USA, 1997.
Crystal data and structure refinement. G1-16vinyl. C56H104
-
O12Si16, colourless crystal 0.12 × 0.1 × 0.1 mm, M = 1418.8,
space group P21/c, a = 13.6425(7), b = 13.8802(6), c = 23.2237(8)
Å, β = 96.445(3)Њ, U = 4369.9(3) Å3, Z = 2 (the molecule was
located about a centre of symmetry), µ = 0.277 mmϪ1 (λ =
2008
J. Chem. Soc., Dalton Trans., 2002, 1997–2008