Enhanced Hydrogenation Activity and Recycling of Cationic Rhodium Diphosphine Complexes through the Use of Highly Fluorous and Weakly-Coordinating Tetraphenylborate Anions

Article abstract of DOI:10.1002/adsc.200202205

The effect of the nature of the anion on the performance of ionic rhodium catalysts has received little attention. Herein it is shown that the use of highly fluorous tetraphenylborate anions can enhance catalyst activity in both conventional and fluorous

Full text of DOI:10.1002/adsc.200202205

FULL PAPERS
Enhanced Hydrogenation Activity and Recycling of Cationic
Rhodium Diphosphine Complexes through the Use of Highly
Fluorous and Weakly-Coordinating Tetraphenylborate Anions
a
a
b,
a
Joep van den Broeke, Elwin de Wolf, Berth-Jan Deelman, * Gerard van Koten
a
Department of Metal-Mediated Synthesis, Debye Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht,
The Netherlands
b
ATOFINA Vlissingen B. V., P. O. Box 70, 4380 AB Vlissingen, The Netherlands
Fax: ꢀ ‡ 31)-113-612984, e-mail: Berth-Jan.Deelman@atofina.com
Received: December 13, 2002; Accepted: February 13, 2003
Abstract: The effect of the nature of the anion on the some perfluoroalkyl-substituents in the cation was
performance of ionic rhodium catalysts has received still required for achieving high partition coefficients.
little attention. Herein it is shown that the use of Therefore, [RhꢀCOD)ꢀAr PCH CH PAr )][X] {Arˆ
2
2
2
2
highly fluorous tetraphenylborate anions can enhance C H ꢀSiMe CH CH C F )-4,
X ˆ [B{C H ꢀC F ) -
6
4
2
2
2
6
13
6
3
6 13 2
À
catalyst activity in both conventional and fluorous 3,5}4] ꢀ3f); Arˆ C H ꢀSiMeꢀCH CH C F ) )-4 and
6
4
2
2
6 13 2
À
media. For hydrogenation catalysts of the type X ˆ [B{C H ꢀC F )-4} ] ꢀ2g)} were prepared, which
6
4
6
13
4
[
RhꢀCOD)ꢀdppb)][X] {COD ˆ 1,5-cis,cis-cycloocta- were active in the hydrogenation of 1-octene, 2g even
diene;
dppb ˆ 1,4-bisꢀdiphenylphosphino)butane; more so than 3f. Both these highly fluorous catalysts
could be recycled with 99% efficiency through
ꢀ1d), [B{C H ꢀSiMe - fluorous biphasic separation, whereas the correspond-
À
À
À
4
X ˆ BF ꢀ1a), [BPh ] ꢀ1b), [B{C H ꢀSiMe )-4} ]
4
4
6
4
3
À
ꢀ
1c), [B{C H ꢀCF ) -3,5} ]
6
3
3
2
4
6
4
2
À
À
À
CH CH C F )-4} ] ꢀ1e), [B{C H ꢀC F )-4} ] ꢀ1f) ing BF4 complex of 2g ꢀ2a) did not show any affinity
2
2
6
13
4
6
4
6
13
4
À
and [B{C H ꢀC F ) -3,5} ] ꢀ1 g)} the activity towards for the fluorous phase.
6
3
6
13
2
4
the hydrogenation of 1-octene in acetone increased in
the order 1c <1b <1e <1a <1d ~ 1f <1g with 1g
being twice as active as the commonly applied 1a. Keywords: fluorinated ligands; fluorous biphasic cat-
Despite the fluorophilic character introduced by the alyst separation; fluorous borate anions; homogene-
substituted tetraarylborate anions, the presence of ous catalysis; P ligands; phosphine; rhodium
Introduction
of a highly fluorous anion could enable the use of a
broad range of ionic catalysts in fluorous ꢀbiphasic)
The use of the unique properties of perfluorinated catalysis.
solvents for catalyst separation and recycling has been A further point to be considered is the often-observed
[
1]
demonstrated successfully. Fluorous biphasic catalyst reduction in catalyst activity under fluorous biphasic
separation ꢀFBCS) techniques have been employed in conditions in comparison with identical catalysts in
[
2a, c,6]
the immobilisation of a diverse range of transition-metal conventional solvents.
In the case of ionic catalysts,
complexes allowing their recovery with high efficiency, this is likely the result of the low polarity of the
the extent of catalyst leaching often being on the ppm perfluorinated solvent. This hampers dissociation of
[2]
level. The key to this success has been the introduction the catalystsꢁ ion pairs, since the separate charges cannot
of perfluoroalkyl substituents in the ligands surrounding be stabilised through solvation. As the formation of
the metal centre.[1±3] Although this approach has proved separated ion pairs is often essential for the creation of a
[
5a, b]
highly effective, it requires the design of a new fluorous vacant coordination site,
which allows the substrate
ligand for each new catalyst that is to be adapted for to bind to the catalytically active centre, this reduces the
FBCS. As the introduction of perfluoro substituents is availability of the catalyst for substrate binding and
[
4]
far from a trivial exercise, the development of a large consequently its activity. The introduction of a highly
library of fluorous catalysts entails a huge synthetic fluorous anion could enhance ion-separation in these
effort. In ionic catalysts an additional site for the apolar solvents, thereby improving catalyst perform-
introduction of fluorous character exists, namely the ance.
anion. As these counterions are less specific for partic-
ular catalysts or catalytic processes, the development as solubilising moieties for transition-metal catalysts in
The use of perfluoroalkyl-substituted tetraarylborates
[
5]
Adv. Synth. Catal. 2003, 345, 625 ± 635
DOI: 10.1002/adsc.200202205
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
625

FULL PAPERS
Joep van den Broeke et al.
apolar solvents has been reported,[7] with substituents does not affect the structural and electronic
À
[
B{C H ꢀCF ) -3,5} ] ꢀTFPB) being a well-known ex- properties of the cation. Using hydrogenation of 1-
6
3
3
2
4
[
5a, b,7a]
ample.
This anion has successfully been applied in octene in acetone as a model reaction, the effects of the
catalysis in supercritical carbon dioxide, where its highly various substituents on the performance of the catalyst
lipophilic character was used to solubilise ionic cata- were assessed ꢀTable 1).
lysts.[ The use of tetrakisꢀperfluoroaryl)borates in a-
8]
The use of complexes 1a ± 1g as pre-catalysts in the
[
9]
olefin polymerisation has also been well documented.
In this type of catalysis the borate anions are employed anion variation on the activity. Compared to BF , a
because of their weakly-coordinating nature, which reduction in catalyst activity was observed when [BPh4]
hydrogenation of 1-octene revealed a major influence of
À
4
À
helps in the creation of vacant coordination sites, and for was used. The introduction of a trimethylsilyl substitu-
[
7d,8c]
their lipophilic character.
fluorous enough to induce sufficient fluorous character an inactive catalyst, whereas the presence of ±Si-
for fluorous biphasic separation strategies ꢀvide infra). Me CH CH C F substituents in 1e yields a slightly
TFPB, however, is not ent in the tetraphenylborate anion ꢀ1c) even resulted in
2
2
2
6 13
Keeping these considerations in mind, we have enhanced activity compared with that of 1b. The reason
developed a range of highly fluorous tetraphenylborate for the inactivity of 1c was not investigated further. The
anions.[ Herein we report the use of these anions as introduction of electron-withdrawing substituents with-
counterions in ionic rhodium-catalysts in combination out spacer moieties in 1d, 1f and 1g results in signifi-
with both fluorous and non-fluorous diphosphine li- cantly enhanced hydrogenation activities, with the
gands. The partition behaviour of these complexes, and highly fluorous complex 1g being over ten times more
10]
[
11±15]
their application in the hydrogenation of olefins in both active than 1b and twice as active as 1a.
conventional and perfluorinated solvents, was studied. It is well known that the activity of cationic rhodium
Furthermore, the recovery and recycling of these diphosphine complexes in the hydrogenation of alkenes
complexes using FBCS is described.
is highly dependent on the coordinating behaviour of
[
16]
their anions. As the coordinating strength of the anion
diminishes, dissociation of the complexes into solvent-
separated ion pairs will become more pronounced,
which increases the availability of the catalytic centre
Results and Discussion
for substrate binding. The low activity observed for 1b,
Anion Effects in 1-Octene Hydrogenation Catalysed
by Rhodium Diphosphine Complexes
À
relative to 1a, is the result of the tendency of [BPh ] to
4
6
act as a h -coordinating ligand through one or more of its
[
5b,17]
phenyl groups.
The low activity of 1b corresponds
[
18]
To investigate the influence of silyl- and perfluoroalkyl- with earlier reports,
where it was shown that a
substitution in tetraarylborate anions on catalyst per- zwitterionic species is formed that exhibits low activity
formance, complexes of the type [RhꢀCOD)ꢀdppb)][X] as a catalyst under similar, mild, reaction conditions. The
{
COD ˆ 1,5-cis,cis-cyclooctadiene, dppb ˆ 1,4-bisꢀdi- introduction of a large ±SiMe CH CH C F substituent
2
2
2
6 13
À
À
phenylphosphino)butane,
ꢀ
ꢀ
X ˆ [B{C H ꢀSiMe )-4} ]
ꢀFigure 2) on the tetraarylborate anion increases the
6
4
3
4
1c), TFPB ꢀ1d), [B{C H ꢀSiMe CH CH C F )-4} ]
activity of the corresponding catalyst ꢀ1e). This rate
6
À
4
2
2
2
6
13
4
1e), [B{C H ꢀC F )-4} ] ꢀ1f) and [B{C H ꢀC F ) - enhancement is most probably the result of the steric
6
4
6
13
4
6
3
6 13 2
À
3
,5} ] ꢀ1g)} were prepared ꢀFigure 1). Analysis of these bulk of the perfluoro tail, becausethe electronic effect of
4
31
1
complexes by P{ H} NMR spectroscopy revealed no this substituent is negligible as its Hammett parameter is
[
13]
significant variations between [RhꢀCOD)ꢀdppb)][BPh4] identical to that for a proton ꢀTable 1). According to
and 1c ± g, which indicates that the introduction of the electrostatic models describing ion association, an
X
P
Rh
P
P
1
1
1
1
1
1
1
a: X = BF4–
=
1,4-bis(diphenylphosphino)butane
b: X = [BPh4]–
P
c: X = [B{C6H4(SiMe3)-4}4]–
d: X = [B{C6H3(CF3)2-3,5}4]–
e: X = [B{C6H4(SiMe2CH2CH2C6F13)-4}4]–
f: X = [B{C6H4(C6F13)-4}4]–
g: X = [B{C6H3(C6F13)2-3,5}4]–
Figure 1. Rhodium diphosphine complexes used as catalysts in 1-octene hydrogenation in acetone.
626
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Adv. Synth. Catal. 2003, 345, 625 ± 635

Hydrogenation Activity and Recycling of Cationic Rh-Diphosphine Complexes
FULL PAPERS
[a]
Table 1. Hydrogenation of 1-octene with [RhꢀCOD)ꢀdppb)]BF ꢀ1a) and [RhꢀCOD)ꢀdppb)][BAr ] ꢀ1b ± 1g) in acetone.
4
4
Pre-catalyst
Ar
r ꢀnm)[b]
s[c]
TOF50[d]
1
1
1
1
1
1
1
c
b
e
a
f
d
g
ÀC H ꢀSiMe )-4
0.8
0.5
1.6
0.2
1.3
0.6
1.3
À 0.02
±
12
20
67
75
6
4
5
3
ÀC H
0.00
6
0.00[
±
e]
ÀC H ꢀSiMe CH CH C F )-4
6
4
2
2
2
6 13
±
0.52[
0.92[
0.94[
f]
ÀC H ꢀC F )-4
6
4
6 13
g]
ÀC H ꢀCF ) -3,5
80
140
6
3
3 2
f, g]
ÀC H ꢀC F ) -3,5
6
3
6 13 2
[
a]
Reaction conditions: 5 mL of acetone and 0.4 mL of n-decane, 2.12 mM [Rh], catalyst:1-octene ˆ 1: 200; Tˆ 428C; pH ˆ
2
1
.1 bar.
[
[
[
[
[
[
b]
[11]
Anion radius, Figure 2 and ref.
c]
d]
e]
f]
[12]
Hammett parameter, taken from ref.
À1
Average turn over frequency ꢀh ) at 50% yield of octane.
[13]
Taken from ref.
[2a]
and ref.[14]
The Hammett parameters for ±C F were used for ±C F , ref.
2
5
6 13
g]
[15]
The electronic effect of multiple substituents may be added up linearly, ref. The value denoted here is 2 Â sm.
Figure 2. Influence of perfluoro substitution on the radius ꢀr) of the anions.
increase in the distance between the two charges leads to 1d is four times as active as 1e, which contains a much
[
19]
a weakening of the electrostatic interaction. There- bulkier anion in which the perfluoro substituents cannot
fore, a reduced degree of association of the cation and affect its electronic properties. This indicates that charge
anion will result due to the increased anion size upon delocalisation is a more effective method for decreasing
[
20]
introduction of perfluoroalkyl substituents. Obvious- the ion-pairing properties of a tetraarylborate than
ly, this leads to an enhanced hydrogenation activity of 1e increasing its steric bulk.
compared to non-substituted 1b, because the cationic
An indication for the efficiency of the combination of
rhodium site has less and weaker interaction with the steric and electronic effects of perfluoroalkyl-substitu-
borate anion.[
21]
tion within a single anion is provided when 1f and 1g are
The introduction of electron-withdrawing substitu- compared with 1d. I n1f and 1g the size of the anion is
ents which are directly connected to the phenyl groups significantly larger than in the CF -substituted anion in
3
6
of the tetraarylborate helps to reduce its h -coordinating 1d ꢀFigure 2). As a C F -substituent is electronically
6
13
[
17a]
[12]
ability through delocalisation of the negative charge.
similar to a CF -substituent ꢀTable 1), the enhanced
3
This will result in a reduction in the strength of the ion- catalytic activity of 1g in comparison with 1d is the result
pairing, which in turn could explain the enhanced of the bulky perfluorohexyl substituents. The 2- to 3-fold
activity of the corresponding catalysts. For example, increase in the radius of the anion is accompanied by an
the radius of the anion in 1d is only slightly larger than increase in the catalytic activity by a factor two,[ an
20]
À
that of [BPh ] in 1b. Nevertheless, 1d is a much more effect similar in magnitude to that observed for 1b and
4
active hydrogenation catalyst. This indicates that the 1e. I n1f the number of fluorous tails is halved in
increase in hydrogenation rate observed for 1d is most comparison with 1d, nevertheless, very similar activities
likely connected to the electron-withdrawing properties are observed. Apparently, the increase in anion size by a
of the two CF -substituents in the anion. Furthermore, factor of two compensates for the electronic consequen-
3
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627

FULL PAPERS
Joep van den Broeke et al.
H2
for 1g the formation of 3- and 4-octenes started before
all 1-octene had been consumed and the maximum
concentration of 2-octenes achieved was lower ꢀ45%)
with respect to the initial 1-octene concentration.
Otherwise, the product distribution was similar to that
observed for 1a ± 1f.
H2
H2
Synthesis and Fluorous Biphasic Separation of
Rhodium Complexes Containing Fluorous Ligands
and Fluorous Borate Anions
Scheme 1.
ces of the reduction in the number of perfluoroalkyl
substituents. Thus, it can be concluded that both the After it had been observed that the introduction of
electronic and steric aspects of introducing substituents perfluoroalkyl substituents in the tetraphenylborate
in the tetraphenylborate anion have a significant impact anion affords catalysts with similar or enhanced hydro-
À
on its ion-pairing behaviour. A combination of these two genation activity compared to the corresponding BF -
4
effects is the most efficient in enhancing cation-anion based catalyst, their use in FBCS was investigated. As all
pair separation, and results in a more than 10-fold rhodium complexes, except 1g, proved insoluble in
increase in catalytic activity ꢀ1g) in comparison with the perfluorinated solvents, they were initially tested in the
À
[22]
corresponding [BPh ] -equipped catalyst.
lightly fluorous solvent a,a,a-trifluorotoluene ꢀBTF).
4
For all catalysts investigated a reaction sequence Although all catalysts were found to be soluble in BTF,
involving direct hydrogenation of 1-octene to n-octane, no hydrogenation activity was observed. The non-
as well as isomerisation to internal octenes followed coordinating nature of this solvent is most likely
by hydrogenation to n-octane was observed responsible for this inactivity, as solvent coordination
ꢀ
Scheme 1).[
3,16]
The initial products of this isomerisa- is required to allow solvent-separated ion-pair forma-
tion were cis- and trans-2-octene, the trans-isomer being tion and to stabilise the cationic reaction intermedi-
the major component ꢀFigure 3). After full conversion ates.[
16,23]
Addition of 0.05 mL of THF to 2.12 mM
of 1-octene to a mixture of 2-octenes and n-octane, the catalyst solutions in 5.0 mL of BTF did not lead to
concentration of 2-octene in the reaction mixture hydrogenation activity.
declined steadily and the formation of 3- and 4-octenes
Catalyst 1g was then tested in perfluoro-a-butyltetra-
was detected. Ultimately, all internal octenes were hydrofuran ꢀFC-75), a fluorous solvent with an ether
hydrogenated to octane when the reaction was allowed functionality that is potentially coordinating. The sol-
to proceed for a sufficiently long period of time. For 1a ± ubility of 1g in this solvent was 0.21 mmol/L ꢀat 258C),
1
f no effect of the anion on the product distribution was which is only one order of magnitude below the catalyst
observed, all catalysts exhibiting reaction profiles as concentration we employed for the hydrogenations in
shown in Figure 3a. The highest concentration of 2- acetone. Despite this reasonable solubility and the
octenes, 50 ± 60% with respect to the initial concentra- possibility for ion-separation through solvent coordina-
tion of 1-octene, was observed at the moment that 1- tion, again no activity was observed towards the hydro-
octene was depleted. The combined concentration of 3- genation of 1-octene. It was then decided to prepare
and 4-octenes peaked at a level of approximately 10% complexes containing a fluorous diphosphine ligand in
relative to the initial octene concentration. In contrast, addition to a fluorous tetraarylborate. This combination
[
24]
Figure 3. Conversion vs. time plots of the hydrogenation of 1-octene using 1a ꢀA) or 1g ꢀB). Legend: ^ ˆ 1-octene;
octane; ~ ˆ 2-octenes; ˆ 3- and 4-octenes.
&
ˆ n-
628
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Adv. Synth. Catal. 2003, 345, 625 ± 635

Hydrogenation Activity and Recycling of Cationic Rh-Diphosphine Complexes
FULL PAPERS
+
2 S
2 S
+ Olefin
– Olefin
.
..
+
-
[(LL)Rh(Olefin)S] [BAr4]–
+
[
(LL)Rh] [BAr4]
[(LL)RhS2] + [BAr4]
–
close contact ion-pair
solvent separated ion-pair
ꢀ1)
LL = diphosphine
S = solvent molecule
BAr4 = tetraarylborate anion
Olefin = e.g. 1-octene
of a fluorous cation and a fluorous anion was expected to sufficient for efficient catalyst recovery. For these ionic
facilitate the formation of solvent-separated ion-pairs in rhodium diphosphine complexes the introduction of a
perfluorinated solvents ꢀcf. Equation 1). This approach highly fluorous anion alone is clearly insufficient to
did indeed prove successful ꢀvide infra).
obtain pronounced fluorophilicity. Its high aromatic
À
Using a procedure similar to that described for the character, especially in comparison with the BF4
synthesis of [Rhꢀdppb)ꢀCOD)][X], fluorous dppe com- complexes, may be held responsible for the moderate
plexes 2g and 3f were prepared ꢀFigure 4) as well as the partitioning of 1g as the presence of aryl groups is known
À
[3]
corresponding BF complexes 3a and 4a. Analysis of to have an adverse effect on fluorous phase solubili-
4
g and 3f by 31P NMR spectroscopy showed chemical ty.
[23a,27]
However, the introduction of a lightly fluorous
2
[
25]
shifts identical to those observed for 3a and 4a.
diphosphine ligand ꢀas in 2g) is sufficient to increase the
Attempts to prepare highly fluorous [RhꢀCOD)- partition coefficient by more than an order of magni-
Ar PCH CH Ar )][X]
{ArˆC H {SiMeꢀCH CH - tude, despite the fact that the volume percentage of
ꢀ
2
2
2
2
6
À
4
2
2
C F ) }-4,X ˆ[B{C H ꢀC F ) -3,5} ] }from[RhꢀCOD)- fluorine remains similar in comparison with 1g. The
6
13
2
6
3
6
13
2
4
ꢀ
acac)] and Na[B{C H ꢀC F ) -3,5} ] were unsuccessful contribution from the fluorous borate anion in 2g
6 3 6 13 2 4
À
as mixtures of [RhꢀLL)ꢀCOD)][X] and [RhꢀLL) ][X] becomes clear by comparison with BF4 complex 2a,
2
ꢀ
LL ˆ diphosphine) were obtained. Isolation of the which shows no solubility in the biphasic solvent
former complex from these mixtures proved impossible. systems. Significant preference for the fluorous phase
The use of [RhꢀCOD) ][X] ꢀX ˆ fluorous borate anion) can be achieved when at least, on average, 1.5 perfluoro-
2
[
3,26]
as an alternative starting compound
was not feasible, alkyl groups are present per aromatic moiety in the
as decomposition of the borate anions was observed complex. To reach this level of fluorous character, the
during attempts to prepare bis-cyclooctadiene com- use of a perfluoroalkyl-functionalised diphosphine,
plexes from [RhꢀCOD)Cl] , cyclooctadiene and Na[X] containing a minimum of four fluorous tails, is required.
2
or Ag[X].
Once a sufficient level of fluorous character has been
To get a general idea of the fluorophilicity of the reached, the distribution of the perfluoralkyl substitu-
complexes 1f, 1g, 2 g and 3f also in comparison with ents throughout the cation and the anion as well as the
literature data,[
1±3]
their partitioning in two typical nature of the anion are relatively unimportant, as
fluorous biphasic solvent systems THF/perfluorome- evidenced by the comparable partition coefficients for
thylcyclohexane ꢀPFMCH) and toluene/PFMCH was 2g, 3a and 3f. Nevertheless, the presence of perfluori-
examined and compared with that of the tetrafluorobo- nated substituents in both the cation and anion will
rate complexes 2a, 3a and 4a ꢀTable 2). The solubility of enhance ion-pair separation in fluorous solvents and
1
f and 2a in PFMCH was extremely low, which made the result in increased catalyst performance.
collection of relevant partitioning data impossible. The The partition coefficients of 2g, 3a, 3f and 4a are very
effect of a more fluorous anion became immediately similar, the only discrepancy being the high partitioning
clear, however, when the partitioning of 1g and 2g is displayed by 4a in the THF/PFMCH biphasic system.
compared with that of 1f and 2a, respectively. But This high partition coefficient could be the result of the
although 1g exhibits substantial affinity for the fluorous significantly higher fluorous volume of 4a, as this volume
phase in a toluene/PFMCH biphasic system, its almost fraction is the determining factor for the extent of
[28]
equal distribution over the two phases is still not partitioning in fluorous biphasic systems. However, a
X
(C6F13CH2CH2)nMe(3-n)Si
P
P
2 2 6 13 n
SiMe(3-n)(CH CH C F )
Rh
2
2
2
3
g: n = 1, X = [B{C6H3(C6F13)2-3,5}4]–
a: n = 2, X = BF4–
3
4
f: n = 2, X = [B{C6H4(C6F13)-4}4]–
a: n = 3, X = BF4–
Figure 4. Rhodium-diphosphine-complexes with fluorous ligands and fluorous borate counterions.
Adv. Synth. Catal. 2003, 345, 625 ± 635
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FULL PAPERS
Joep van den Broeke et al.
Table 2. Partition coefficients of fluorous rhodium diphosphine complexes.
Compound
Anion
Vol % F
No. of tails
P[b]
PFMCH/THF
PFMCH/toluene
À
4
[c]
[c]
[c]
1
2
1
2
3
3
4
f
[B{C H ꢀC F )-4} ]
22
25
31
32
32
33
37
4
4
8
12
8
12
12
±
±
±
±
6
4
6
13
À
[c]
a
g
g
a
f
BF4
[B{C H ꢀC F ) -3,5} ]
À
À
±2
<1 Â 10
0.7
34
6
3
6
13
2
4
[B{C H ꢀC F ) -3,5} ]
2.1
6
3
6
13
2
4
À
BF4
[B{C H ꢀC F )-4} ]
8.1
6.4
61
65
66
À
4
6
4
6
13
À
a
BF4
34
[
a]
Volume percentage of fluorine in the molecule, calculated from semi-empirical ꢀPM3ꢀtm)) optimised structures using the
Spartan 5.1.1 ꢀSGI) molecular modelling software package.
Partition coefficients in a 1: 1 ꢀv/v) mixture of PFMCH and organic solvent at 08C ꢀP ˆ cfluorous phase/corganic phase) determined by
gravimetric methods and ICP/AAS for [Rh]. The average of these measurements is given here. The estimated error is Æ 1
in the last digit.
[
b]
[
c]
No partition coefficient could be determined due to poor solubility of the complex in PFMCH.
Table 3. Hydrogenation of 1-octene using pre-catalysts 2g and 3f.[a]
Catalyst precursor
Anion
Turn Over Frequency[b]
n-Hexane/FC-75 ꢀ2: 1)[c]
Acetone
n-Hexane/FC-75 ꢀ1: 1)[d]
À
4
3
2
f
g
[B{C H ꢀC F )-4} ]
4.2
19
1.2
5
0.7
2
6
4
6
13
À
[B{C H ꢀC F ) -3,5} ]
6 3 6 13 2 4
[
a]
Reaction conditions: 5 mL of acetone or FC-75 and 0.4 mL of n-decane, 2.12 mM catalyst with 200 equiv. of 1-octene;
Tˆ 428C; pH ˆ 1.1 bar. In the 1: 1 ꢀv/v) and 1: 2 ꢀv/v) systems, 5 mL and 10 mL hexane are added, respectively.
2
[
[
[
b]
À1
Average turn over frequency ꢀh ) for the conversion of 1-octene to octane after 24 h.
c]
Monophasic under reaction conditions.
Biphasic under reaction conditions.
d]
similar effect on the partition coefficient of 4a in the fluorous dppe derivatives in 2g and 3f displayed modest
toluene/PFMCH biphasic system was not observed. In the hydrogenation activity in 2:1 hexane/FC-75 mixtures
toluene/PFMCH biphasic system, the partition coeffi- ꢀv/v). This indicates that the use of a fluorous ligand
cients for all complexes were found to be superior to those facilitates ion separation in a reaction medium with low
observed for the THF/PFMCH solvent system. The lower polarity. When a 1:1 ratio of hexane and FC-75 is used,
partition coefficients in the latter biphase system could the reaction is performed under biphasic conditions.
originate from the fact that THFis capable of solvating the This leads to a decrease in activity, possibly due to mass
rhodium cation, whereas for toluene this is more difficult. transfer limitations between the two phases. When the
The solvation makes dissolution of the complexes in THF relative activity of 2g and 3f is compared, the complex
more favourable, thus hampering partitioning into the with 3,5-substituted borate anion ꢀ2g) was found to be
fluorous phase. As choosing an apolar organic solvent more active, as was also observed for the rhodium
eliminates the favourable solvent-solute interactions, complexes 1f and 1g with a non-fluorous diphosphine
preference for the fluorous phase increases.
ligand. Interestingly, 2g and 3f were less active than their
Complexes 2g and 3f were tested for catalytic dppb-analogues 1f and 1g in acetone. This is in agree-
performance under fluorous conditions towards the ment with earlier reports that showed that increased
hydrogenation of 1-octene. The THF/perfluoromethyl- catalyst activity can be expected when the chelate ring
cyclohexane ꢀPFMCH) and toluene/PFMCH biphasic size increases from five to seven atoms.[16] This rate
solvent systems that were used to determine the enhancement for the diphosphines with a longer alkane
fluorophilicity of the complexes were found to be bridge can be explained by an increase in flexibility of
unsuitable. However, in mixtures of FC-75 and hexane, the dichelating ligand, which lowers the relevant tran-
2
g and 3f were indeed found to be active catalysts sition state energies.
ꢀ
Table 3). Furthermore, their catalytic performance in Both 2g and 3f could be recycled efficiently through
acetone was determined for comparison with the other biphasic separation at 08C ꢀTable 4). Complex 3f could
fluorous catalytic species ꢀvide supra). Whereas 1g be recycled three times without loss of activity using
displayed no activity in FC-75, probably due to the both 1:1 ꢀv/v) and 2:1 ꢀv/v) mixtures of hexane and FC-
‡
fluorophobic nature of the [RhꢀCOD)ꢀdppb)] cation, 75. Leaching of the catalyst into the organic phase was
630
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2003, 345, 625 ± 635

Hydrogenation Activity and Recycling of Cationic Rh-Diphosphine Complexes
FULL PAPERS
Table 4. Efficiency of catalyst recycling for 2g and 3f in the hydrogenation of 1-octene in hexane/FC-75 biphasic systems.[a]
Catalyst precursor
Cycle
Turn Over Frequency[b]
n-Hexane/FC-75 ꢀ1: 1)[c] n-Hexane/FC-75 ꢀ1: 2)[d]
3f
1
2
3
0.7
0.7
0.7
0.5
1.2
1.4
1.5
e
5
Rh leaching[f]
0.5% ꢀ4 ppm)
0.5% ꢀ2 ppm)
2g
1
2
2.0
2.0
5.0
6.0
Rh leaching[f]
1% ꢀ4 ppm)
1% ꢀ2 ppm)
[
[
[
[
[
[
a]
b]
c]
d]
e]
f]
For reaction conditions, see Table 3. Phase separation performed at 08C.
Average turn over frequency ꢀh ) for the conversion of 1-octene to octane over 24 h.
Biphasic under reaction conditions.
Monophasic under reaction conditions.
Catalyst present as an oil, FC-75 had leached into the organic phase during the previous cycles.
Average leaching of Rh into the organic phase per cycle, determined by ICP-AAS.
À1
investigated by ICP-AAS analysis which revealed a loss borate anions. Significant affinity for perfluorinated
of 0.5% of catalyst per cycle. Complex 2g was recycled solvents was only achieved by the use of
À
once without loss of activity, catalyst leaching into the [B{C H ꢀC F ) -3,5} ] in combination with a lightly
6
3
6
13
2
4
organic phase amounting to 1.0% per cycle. For the 1:1 fluorous diphosphine ligand. This allowed efficient
hexene/FC-75 system, all fluorous solvent had been catalyst recycling through fluorous biphasic separation,
[
2d,3]
À
extracted after four recycles.
Nevertheless, 3f re- whereas the corresponding BF4 complex did not show
mained active in the absence of fluorous solvent, albeit at any affinity for fluorous solvents.
a somewhat lower level, the catalyst being present as an
emulsifiedoil. Whenthefluoroussolventwasreplenished
after the last cycle the catalyst did not regain its initial Experimental Section
activity, presumably because it had partly decomposed in
the absence of a coordinating solvent.
General
All reactions were performed under a dry N atmosphere using
2
Conclusions
standard Schlenk techniques. Hexane, tetrahydrofuran ꢀTHF)
and diethyl ether ꢀEt O) were distilled from sodium benzo-
2
phenone ketyl, CH Cl from CaH , acetone from CaCl and
As demonstrated explicitly in polymerisation catalysis,
the nature of the weakly-coordinating counterion can
have a major impact on the activity and selectivity of a
cationic catalyst. However, for rhodium-catalysed hy-
drogenation the role of the anion has hardly been
investigated. The results described show that cation-
anion separation plays a significant role in determining 4}4],[
2
2
2
2
toluene from sodium. FC-75 and a,a,a-trifluorotoluene were
degassed and stored over molecular sieves ꢀ3 Š). p-Bromo-
4b]
ꢀ
ꢀ
tridecafluorohexyl)benzene,[ Ar PCH CH PAr {ArˆC H -
2
2
2
2
6
4
[4a]
SiMe CH CH C F )-4 or C H [SiMeꢀCH CH C F ) ]-4},
2
2
2
6
13
6
4
2
2
6
13
2
[29]
[10a]
Na[B{C H ꢀCF ) -3,5} ],
Na[B{C H ꢀSiMe CH CH C F )-4} ],
Na[B{C H ꢀSiMe )-4} ]
and
6
3
3
2
4
6
4
3
4
[10a]
Na[B{C H ꢀC F )-
6
4
2
2
2
6
13
4
6
4
6 13
10a]
[10b]
[26]
Na[B{C H ꢀC F ) -3,5} ],
[RhꢀCOD) ]BF ,
6
3
6
13
2
4
2
4
activity of rhodium-diphosphine-complexes in the hy- [RhꢀCOD)ꢀacac)],[
30]
[RhꢀCOD)ꢀdppb)]BF
ꢀ1a),
PCH -
2 2
[31]
4
17c]
drogenation of 1-octene in acetone. These studies [RhꢀCOD)ꢀdppb)][BPh
]
4
ꢀ1b),[
[RhꢀCOD)ꢀAr
CH PAr )]BF {ArˆC H [SiMeꢀCH CH C F ) ]-4 ꢀ3a) or
indicate that the electronic properties of substituents
of a tetraarylborate anion exert a stronger effect on the
performance of the catalyst than their steric properties.
The use of highly fluorous tetraarylborate anions
enhances the solubility of rhodium diphosphine com-
2
2
4
6
4
2
2
6 13 2
[
3]
C H [SiꢀCH CH C F ) ]-4 ꢀ4a)} were prepared according to
6
4
2
2
6 13 3
literatureprocedures.Allotherchemicalswereusedasreceived.
NMR spectra were recorded on Varian Mercury 200 ꢀ P) and
3
1
1
13
1
13
Varian Inova 300 ꢀ H and C)spectrometers with TMS ꢀ H, C)
31
and H PO ꢀ85%) ꢀ P) as external references. Gas chromatog-
3
4
plexes in apolar solvents. Furthermore, the use of
raphy was performed using a Perkin Elmer Autosystem XL
equipped with a 30 m PE-17 column. Elemental analyses were
À
[
B{C H ꢀC F ) -3,5} ] resulted in enhanced hydroge-
6
3
6
13
2
4
nation activity in acetone as well as in fluorous media in carried out by H. Kolbe, Mikroanalytisches Laboratorium,
comparison with catalysts equipped with less fluorous Mülheim an der Ruhr.
Adv. Synth. Catal. 2003, 345, 625 ± 635
asc.wiley-vch.de
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
631

FULL PAPERS
Joep van den Broeke et al.
Sodium Tetrakis[4-6perfluorohexyl)phenyl]borate
ꢀ0.44 mmol)
[RhꢀCOD)ꢀacac)],
0.94 g
and
ꢀ0.48 mmol)
188 mg
Na[B{C H ꢀSiMe CH CH C F )-4} ]
6
4
2
2
2
6
13
4
To p-bromoꢀperfluorohexyl)benzeneꢀ7.77 g, 16.3 mmol) inEt O
2
ꢀ
ꢀ
ꢀ
0.44 mmol) dppb this afforded an orange solid; yield: 0.82 g
ꢀ
100 mL) at À788C was slowly added n-BuLi ꢀ9.7 mL, 1.6 M in
1
73%); H NMR ꢀCDCl , 300.1 MHz): d ˆ 7.53 ꢀm, 20H), 7.42
3
hexanes, 15.5 mmol). The resulting solution was stirred for 1.5 h
3
m, 8H), 7.19 ꢀd, J ˆ 7.5 Hz, 8H), 4.44 ꢀs, 4H), 2.40 ꢀs, 4H),
HH
at À788C. BF ´Et O ꢀ0.34 mL, 2.7 mmol) was then added and
3
2
2
,23 ꢀm, 8H), 2.03 ꢀm, 8H, CH CF ), 1.61 ꢀs, 4H), 0.87 ꢀm, 8H,
2 2
the solution was allowed to reach room temperature over a
13
1
SiCH ), 0.21 ꢀs, 24H); C{ H} NMR ꢀCDCl , 75.5 MHz): d ˆ
2
3
period of 16 h. The solution was poured into H O and saturated
1
2
1
1
66.7 ꢀq, J ˆ 48.8 Hz, B-C), 137.1 ꢀs), 137.0 ꢀs), 133.5 ꢀs),
BC
with NaCl. After extraction of the aqueous layer with Et O ꢀ3Â
2
32.9 ꢀs), 132.4 ꢀs), 132.1 ꢀs), 131.7 ꢀs), 131.3 ꢀs), 130.6 ꢀm), 129.4
50 mL), the combined organic layers were washed with H O
2
ꢀ
ꢀ
s), 123.8 ꢀm), 122.3 ꢀm), 119.1 ꢀm), 115.7 ꢀs), 111.9 ꢀm), 110.3
m), 100.6 ꢀs), 76.1 ꢀd), 31.3 ꢀm), 30.1 ꢀs), 26.4 ꢀt), 24.6 ꢀs), 5.7 ꢀs,
ꢀ
50 mL) and dried over MgSO . Removal of the solvent and
4
washing with hexane afforded a white solid; yield: 3.69 g ꢀ84%);
31
1
SiCH ), 1.3 ꢀs), À 3.3 ꢀs, Si-CH ); P{ H} NMR ꢀCDCl ,
2
3
3
1
H NMR ꢀacetone-d , 300.1 MHz): dˆ7.48 ꢀm, 8H, Ar ), 7.35 ꢀd,
1
6
o
8
C
1.0 MHz): d ˆ 25.2 ꢀd,
J
ˆ 143.4 Hz); anal. calcd. for
RhP
3
13
1
J
ˆ8.1 Hz, 8H, Ar ); C{ H} NMR ꢀacetone-d , 75.5 MHz):
HH
m
6
H BF P RhSi : C 46.67, H 3.76, F 38.38, P 2.41; found: C
1
00 96
52 2 4
1
dˆ167.7 ꢀq, J ˆ49.3 Hz, Ar), 136.0 ꢀAr ), 124.0 ꢀAr ), 122.6
BC
i
o
m
4
6.82, H 4.79, F 38.26, P 2.49.
ꢀ
m, Ar ), 120.5 ꢀm), 117.7 ꢀm), 113.0 ꢀm), 112.6 ꢀm), 112.1 ꢀm),
p
1
10.6 ꢀm); anal. calcd. for C H BF Na: C 35.71, H 1.00, Na 1.42;
48 16 52
found: C 35.58, H 0.88, Na 1.57.
[
Rh6COD)6dppb)][B{C H 6C F )-4} ] 61f)
ꢀ 4 ꢀ 13 4
Preparation of 1f was carried out using a procedure similar to
that employed for the preparation of 1c. Starting from 72 mg
[
Rh6COD)6dppb)][B{C H 6SiMe )-4} ] 61c)
ꢀ 4 3 4
ꢀ
0.23 mmol)
[RhꢀCOD)ꢀacac)],
384 mg
ꢀ0.24 mmol)
Preparation of 1c was carried out using a procedure similar to
that employed for the preparation of 1d. Starting from 55 mg
Na[B{C H ꢀC F )-4} ] and 138 mg ꢀ0.23 mmol) dppb this
6
4
6
13
4
1
afforded an orange solid; yield: 0.40 g ꢀ77%); H NMR
ꢀ
0.18 mmol)
[RhꢀCOD)ꢀacac)],
122 mg
ꢀ0.19 mmol)
ꢀ
J
CDCl , 300.1 MHz): d ˆ7.49 ꢀm, 12H), 7.42 ꢀm, 8H), 7.24 ꢀd,
3
Na[B{C H ꢀSiMe )-4} ] and 76 mg ꢀ0.18 mmol) dppb this af-
forded an orange solid; yield: 0.17 g ꢀ77%); H NMR ꢀCDCl ,
3
6
3
6
4
3
4
ˆ8.0 Hz, 8H), 7.16 ꢀm, 5H), 7.06 ꢀm, 3H), 4.40 ꢀs, 4H), 2.36
HH
1
13 1
3
ꢀs, 4H), 2.19 ꢀm, 8H), 1.57 ꢀs, 4H); C{ H} NMR ꢀCDCl ,
3
3
00.1 MHz): dˆ7.51 ꢀm, 20H), 7.41 ꢀm, 8H), 7.15 ꢀd, J
ˆ
1
HH
75.5 MHz):d ˆ167.5ꢀq, J ˆ49.3 Hz,B-C),135.9ꢀs),133.1ꢀs),
BC
.3 Hz, 8H), 4.39 ꢀs, 4H), 2.35 ꢀs, 4H), 2,17 ꢀm, 8H), 1.54 ꢀs, 4H),
1
32.1 ꢀs), 129.7 ꢀs), 129.0 ꢀs), 124.2 ꢀs), 122.7 ꢀs), 121.4 ꢀm) 118.8
.13 ꢀs, 36H); 13C{ H} NMR ꢀCDCl , 75.5 MHz): d ˆ166.2 ꢀq,
1
0
3
ꢀm), 115.4 ꢀm), 114.8 ꢀm), 110.4 ꢀm), 107.5 ꢀm), 100.9 ꢀs), 31.8
1
JBC ˆ53.4 Hz, B-C), 137.0ꢀs), 136.2ꢀs), 135.0ꢀs), 134.1 ꢀs), 133.0
31
1
ꢀm), 30.5ꢀs), 24.9ꢀs); P{ H} NMR ꢀCDCl , 81.0 MHz): d ˆ25.7
3
ꢀ
s), 131.8 ꢀs), 131.2 ꢀm), 130.8 ꢀs), 129.4 ꢀs), 115.6 ꢀs), 100.6 ꢀs),
4.7 ꢀd), 31.0 ꢀm), 30.2 ꢀs), 28.5 ꢀs), 24.6 ꢀs), 1.2 ꢀs), À0.8 ꢀm, Si-
CH ); P{ H} NMR ꢀCDCl , 81.0 MHz): dˆ25.3 ꢀd, J
1
ꢀ
d, J ˆ142.4 Hz);anal. calcd. for C H BF P Rh:C 45.26, H
RhP
84 56
52 2
7
2
.53, F 44.32, P 2.78; found: C 45.10, H 2.58, F 44.28, P 2.71.
31
1
1
ˆ
3
3
RhP
1
43.4 Hz); anal. calcd. for C H BF P RhSi : C 69.43, H 7.45,
100 96 52 2 4
P 4.97, Si 9.02; found: C 69.26, H 7.41, P 4.96, Si 9.61.
[
Rh6COD)6dppb)][B{C H 6C F ) -3,5} ] 61g)
ꢀ 3 ꢀ 13 2 4
Preparation of 1g was carried out using a procedure similar to
that employed for the preparation of 1c. Starting from 56 mg
[
Rh6COD)6dppb)][B{C H 6CF ) -3,5} ] 61d)
ꢀ 3 3 2 4
ꢀ
0.18 mmol)
[RhꢀCOD)ꢀacac)],
0.58 g
ꢀ0.20 mmol)
To a solution of 51 mg ꢀ0.16 mmol) [RhꢀCOD)ꢀacac)] and
81 mg ꢀ0.21 mmol) Na[B{C H ꢀCF ) -3,5} ] in THF ꢀ25 mL)
Na[B{C H ꢀC F ) -3,5} ] and 77 mg ꢀ0.18 mmol) dppb this
6
3
6
13
2
4
1
1
afforded an orange oil; yield: 0.5 g ꢀ76%); H NMR ꢀCDCl ,
6
3
3
2
4
3
at 08C was dropwise added 70 mg ꢀ0.16 mmol) dppb in THF
10 mL) over 15 min. After stirring the solution for an addi-
300.1 MHz): d ˆ 7.62 ꢀbs, 8H, B-Ar ), 7.52 ꢀm, 20H, P-Ar), 7.42
o
ꢀ
ꢀs, 4H, B-Ar ), 4.42 ꢀbs, 4H), 2.42 ꢀbs, 4H), 2,23 ꢀm, 8H), 1.58
p
1
3
1
tional 15 min, the solvent was removed under vacuum. Toluene
was added and solids were filtered off using a glass sinter. The
resulting solution was evaporated to dryness affording a yellow
ꢀm, 4H); C{ H} NMR ꢀCDCl , 75.5 MHz): d ˆ 167.5 ꢀq,
3
1
JBC ˆ 49.3 Hz, B-C), 137.5 ꢀs), 135.3 ꢀs), 133.7 ꢀs), 132.9 ꢀs),
131.6 ꢀs), 130.2 ꢀs), 127.9 ꢀs), 127.0 ꢀs), 119.3 ꢀs), 117.0 ꢀs), 115.8
ꢀm), 115.2 ꢀm), 110.9 ꢀm), 110.5 ꢀm), 110.0 ꢀm), 108.2 ꢀm), 100.0
1
solid; yield: 0.09 g ꢀ62%); H NMR ꢀCDCl , 300.1 MHz): d ˆ
3
3
1
1
7
8
.72 ꢀm, 8H), 7.52 ꢀm, 24H), 4.42 ꢀs, 4H), 2.42 ꢀs, 4H), 2.22 ꢀs,
ꢀs), 31.8 ꢀm), 30.5 ꢀs), 24.9 ꢀs); P{ H} NMR ꢀCDCl ,
3
13
1
1
H), 1.62 ꢀs, 4H); C{ H} NMR ꢀCDCl , 75.5 MHz): d ˆ 161.9
81.0 MHz): d ˆ 25.4 ꢀd, JRhP ˆ 142.4 Hz); anal. calcd. for
3
1
ꢀ
ꢀ
q, J ˆ 49.9 Hz, B-C), 135.6 ꢀs), 134.4 ꢀs), 133.8 ꢀm), 132.6
C H BF P Rh: C 37.05, H 1.50, F 56.43, P 1.77; found: C
108 52 104 2
BC
m), 130.2 ꢀs), 129.3 ꢀs), 128.9 ꢀs), 128.5 ꢀs), 126.6 ꢀs), 123.0 ꢀs),
36.91, H 1.41, F 56.46, P 1.77.
1
18.2 ꢀs), 117.1 ꢀs), 101.8 ꢀs), 100.1 ꢀs), 31.8 ꢀs), 30.5 ꢀt), 24.9 ꢀs);
31
1
1
P{ H} NMR ꢀCDCl3, 81.0 MHz): d ˆ 25.4 ꢀd, JRhP
ˆ
1
4
43.0 Hz); anal. calcd. for C H BF P Rh: C 54.42, H 3.49, P
6
8
52
24 2
[
Rh6COD)6Ar PCH CH PAr )][B{C H 6C F ) -3,5} ]
2 2 2 2 ꢀ 3 ꢀ 13 2 4
.13; found: C 54.15, H 3.74, P 4.37.
{
Arˆ C H 6SiMe CH CH C F )-4} 62g)
ꢀ
4
2
2
2
ꢀ
13
Preparation of 2g was carried out using a procedure similar to
that employed for the preparation of 1c. Starting from 40 mg
[
6
Rh6COD)6dppb)][B{C H 6SiMe CH CH C F )-4} ]
ꢀ 4 2 2 2 ꢀ 13 4
1e)
ꢀ
0.13 mmol)
[RhꢀCOD)ꢀacac)],
and
0.38 g
0.26 g
ꢀ0.13 mmol)
ꢀ0.13 mmol)
Na[B{C H ꢀC F ) -3,5} ]
6
3
6
13
2
4
Preparation of 1e was carried out using a procedure similar to
that employed for the preparation of 1c. Starting from 137 mg
Ar PCH CH PAr {Arˆ C H ꢀSiMe CH CH C F )-4} this
2
2
2
2
6
4
2
2
2
6 13
yielded a red oil. This was dissolved in MeOH ꢀ5 mL) and
632
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2003, 345, 625 ± 635

Hydrogenation Activity and Recycling of Cationic Rh-Diphosphine Complexes
FULL PAPERS
extracted with FC-75 ꢀ3 Â 5 mL). The FC-75 fractions were Determination of Partitioning Coefficients
combined and all volatiles removed under vacuum, leaving a
1
A known amount of rhodium complex was dissolved in
PFMCH ꢀ2.00 mL). A biphasic system was created by the
addition of toluene ꢀ2.00 mL) or THF ꢀ2.00 mL). The mixture
was stirred and then allowed to equilibrate at 08C. When two
clear layers were obtained, an aliquot of 0.5 mL was removed
from each layer, and its weight was determined ꢀÆ0.5 mg).
After removal of all volatiles under vacuum, the weight of the
residue was determined ꢀÆ0.5 mg). Furthermore, for each
layer examined this way, a sample was analysed by ICP-AAS.
red oil; yield: 0.34 g ꢀ49%); H NMR [C D :FC-75 ꢀ1:1),
6
6
3
4
00.1 MHz]: dˆ7.90 ꢀm, 8H), 7.54 ꢀm, 4H), 7.40 ꢀm, 16H),
.72 ꢀs, 4H), 1.95 ꢀm, 16H), 1.00 ꢀm, 12H), 0.16 ꢀs, 24H);
3
1
1
1
P{ H} NMR [C D :FC-75 ꢀ1:1), 81.0 MHz]: d ˆ56.2 ꢀd,
6
6
J
ˆ148.4 Hz); anal. calcd. for C H BF P RhSi : C 34.45,
RhP
138 72
156
2
4
H 1.66, F 58.23, P 1.22; found: C 34.52, H 1.78, F 58.16, P, 1.25.
[
Rh6COD)6Ar PCH CH PAr )][B{C H 6C F )-4} ]
2 2 2 2 ꢀ 4 ꢀ 13 4
{
Arˆ C H 6SiMe6CH CH C F ) )-4} 63f)
ꢀ
4
2
2
ꢀ 13 2
Preparation of 3f was carried out using a procedure similar to References and Notes
that employed for the preparation of 1c. Starting from 29.4 mg
ꢀ
0.095 mmol) [RhꢀCOD)ꢀacac)], 153 mg ꢀ0.095 mmol)
[1] a) E. de Wolf, G. van Koten, B.-J. Deelman, Chem. Soc.
Rev. 1999, 28, 37 ± 41; b) E. G. Hope, A. M. Stuart, J.
Fluorine Chem. 1999, 100, 75 ± 83; c) I. T. Horv a th, Acc.
Chem. Res. 1998, 31, 641 ± 650; d) D. P. Curran, Angew.
Chem. Int. Ed. 1998, 37, 1175 ± 1196; e) B. Cornils,
Angew. Chem. Int. Ed. Engl. 1997, 36, 2057 ± 2059.
Na[B{C H ꢀC F )-4} ] and 317 mg ꢀ0.095 mmol)
6
4
6
13
4
Ar PCH CH PAr ꢀArˆ C H ꢀSiMeꢀCH CH C F ) )-4) this
2
2
2
2
6
4
2
2
6
13 2
yielded a red oil. This was dissolved in MeOH ꢀ5 mL) and
extracted with FC-75 ꢀ3 Â 5 mL). The FC-75 fractions were
combined and all volatiles removed under vacuum, leaving a
1
red oil; yield: 0.58 g ꢀ71%); H NMR [C D :FC-75 ꢀ1:1),
3
ꢀ
ꢀ
C
6
6
[2] a) I. T. Horv a th, G. Kiss, R. A. Cook, J. E. Bond, R. A.
00.1 MHz]: d ˆ 7.72 ꢀm, 8H), 7.52 ꢀm, 24H), 4.42 ꢀs, 4H), 2.42
Stevens, J. R a bai, E. J. Mozeleski, J. Am. Chem. Soc.
3
1
1
s, 4H), 2.22 ꢀs, 8H), 1.62 ꢀs, 4H); P{ H} NMR [C D :FC-75
6
6
1
998, 120, 3133 ± 3143; b) J. J. J. Juliette, D. Rutherford,
I. T. Horv a th, J. A. Gladysz, J. Am. Chem. Soc. 1999, 121,
696 ± 2704; c) E. G. Hope, R. D. W. Kemmit, D. R.
Paige, A. M. Stuart, J. Fluorine Chem. 1999, 99, 197 ±
00; d) B. Richter, A. L. Spek, G. van Koten, B.-J.
1
1:1), 81.0 MHz]: d ˆ 56.2 ꢀd, J ˆ 148.1 Hz); anal. calcd. for
RhP
H BF P RhSi : C 35.01, H 1.80, F 57.59; found: C 34.88, H
156 2 4
150 92
2
1
.71, F 57.42.
2
Deelman, J. Am. Chem. Soc. 2000, 122, 3945 ± 3951;
e) T. Nishimura, Y. Maeda, N. Kakiuchi, S. Uemura, J.
Chem. Soc. Perkin Trans. 1 2000, 4301 ± 4305.
3] E. de Wolf, A. L. Spek, B. W. M. Kuipers, A. P. Philipse,
J. D. Meeldijk, P. H. H. Bomans, P. M. Frederik, B.-J.
Deelman, G. van Koten, Tetrahedron 2002, 58, 3911 ±
Hydrogenation of 1-Octene in Acetone
[
[
Hydrogenation reactions were carried out under the following
conditions: 5 mL of catalyst solution ꢀ2.1 mM [Rh]) were
vigorously stirred ꢀusing a cross-shaped Spinplus magnetic
3
922.
stirring bar at 1250 rpm) at 428C under 1.1 bars of H for
2
4] For various procedures for introducing perfluoroalkyl
substituents, see: a) E. de Wolf, B. Richter, B.-J. Deel-
man, G. van Koten, J. Org. Chem. 2000, 65, 5424 ± 5427;
b) P. Bhattacharyya, D. Gudmunsen, E. G. Hope,
R. D. W. Kemmitt, D. R. Paige, A. M. Stuart, J. Chem.
Soc. Perkin Trans. 1 1997, 3609 ± 3612; c) T. Mathivet, E.
Monflier, Y. Castanet, A. Mortreux, J.-L. Couturtier,
Tetrahedron Lett. 1999, 40, 3885 ± 3888; d) W. Chen, L.
Xu, J. Xiao, Tetrahedron Lett. 2001, 42, 4275 ± 4278; e) S.
30 min. Then, 1-octene ꢀ0.40 mL, 0.49 M) was added and the
progress of the reaction was followed using GC by taking
samples after regular intervals. n-Decane ꢀ0.40 mL) was added
at the start of the reaction as internal reference for GC analysis.
Hydrogenation of 1-Octene under Fluorous Biphasic
Conditions
Darses, M. Pucheault, J.-P. Gene
Ãt, Eur. J. Org. Chem.
2
001, 1121 ± 1128.
Hydrogenation reactions were carried out under the following
conditions: to a solution of catalyst in FC-75 ꢀ5 mL, 2.1 mM
[
5] a) Applied Homogeneous Catalysis with Organometallic
Compounds, ꢀEds.: B. Cornils, W. Herrmann), Wiley-
VCH, Weinheim, 199ꢀ; b) S. H. Strauss, Chem. Rev. 1993,
[Rh]) was added 1-octene ꢀ0.40 mL, 0.49 M) and n-decane
ꢀ
0.40 mL). This was followed by the addition of n-hexane
9
±
3, 927 ± 942; c) A. J. Lupinetti, S. H. Strauss, Chemtracts
Inorg. Chem. 1998, 11, 565 ± 595.
ꢀ
5 mL or 10 mL) and the resulting mixture was vigorously
stirred ꢀusing a cross-shaped Spinplus magnetic stirring bar at
250 rpm) at 428C under 1.1 bars of H . The progress of the
[
6] a) D. Rutherford, J. J. J. Juliette, C. Rocaboy, I. T.
Horv a th, J. A. Gladysz, Catal. Today 1998, 42, 381 ±
1
2
reaction was followed using GC by taking samples after regular
intervals. When n-hexane ꢀ5 mL) was added the reaction was
run in emulsion, whereas the addition of 10 mL resulted in a
homogeneous system under the reaction conditions. After 24 h
the reaction mixture was cooled to 08C, the upper layer
removed and new batches of 1-octene, n-decane and n-hexane
were added and the reaction was continued.
388; b) L. V. Dinh, J. A. Gladysz, Tetrahedron Lett.
1
999, 40, 8995 ± 8998; c) I. T. Horv a th, J. R a bai, Science
1994, 266, 72 ± 75; d) D. C. Smith, E. D. Stevens, S. P.
Nolan, Inorg. Chem. 1999, 38, 5277 ± 5281; e) S. Saito, Y.
Chounan, T. Nogami, O. Ohmori, Y. Yamamoto, Chem.
Lett. 2001, 444 ± 445.
Adv. Synth. Catal. 2003, 345, 625 ± 635
asc.wiley-vch.de
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
633

FULL PAPERS
Joep van den Broeke et al.
[
7] a) H. Kobayashi, J. Fluorine Chem. 2000, 105, 201 ± 203;
b) K. Fujiki, M. Kashiwagi, H. Miyamoto, A. Sonoda, J.
Ichikawa, H. Kobayashi, T. Sonoda, J. Fluorine Chem.
[17] a) M. Aresta, E. Quaranta, I. Tommasi, New J. Chem.
1997, 21, 595 ± 613; b) Z. Zhou, G. Facey, B. R. James, H.
Alper, Organometallics 199ꢀ, 15, 2496 ± 2503.
[18] R. R. Schrock, J. A. Osborn, J. Am. Chem. Soc. 197ꢀ, 98,
2134 ± 2143.
1
992, 57, 307 ± 321; c) K. Fujiki, J. Ichikawa, H. Kobaya-
shi, A. Sonoda, T. Sonoda, J. Fluorine Chem. 2000, 102,
93 ± 300; d) L. Jia, X. Yang, C. L. Stern, T. J. Marks,
[19] The Eigen±Denison
ÀRamsey±Fuoss Model describes the
2
Organometallics 1995, 14, 3135 ± 3137.
association of an ion pair in solution as follows: Kass
ˆ
3
b
‡
±
2
[
[
8] a) S. Kainz, A. Brinkmann, W. Leitner, A. Pfaltz, J. Am.
Chem. Soc. 1999, 121, 6421 ± 6429; b) M. J. Burk, S. Feng,
M. F. Gross, W. Tumas, J. Am. Chem. Soc. 1995, 117,
[4pN
A
r /3000]e , where b ˆ ꢀ j z z j e )/4pree
0
kT, rˆ the
centre to centre distance of the ions in contact, e is the
dielectric constant of the solvent, see: J. E. Gordon, The
Organic Chemistry of Electrolyte Solutions, ꢀEd.: G. A.
Olah), Wiley, New-York, 1975, p. 372.
8
277 ± 8278; c) T. J. de Vries, R. Duchateau, M. A. G.
Vorstman, J. T. F. Keurentjes, Chem. Commun. 2000,
63 ± 264.
9] a) E. Y.-X. Chen, T. J. Marks, Chem. Rev. 2000, 100,
391 ± 1434; b) F. A. R. Kaul, G. T. Puchta, H. Schneider,
[
20] From
semi-empirical
ꢀPM3TM)
optimised
2
‡
[
Rhꢀdppb)ꢀCOD)] using the Spartan 5.1.1 ꢀSGI) mo-
lecular modelling software package, the shortest radius
from Rh to the periphery of the cation was estimated at
1
M. Grosche, D. Mihalios, W. A. Herrmann, J. Organo-
met. Chem. 2001, 621, 177 ± 183; c) J. Zhou, S. J. Lancas-
ter, D. A.; Walker, S. Beck, M. Thornton-Pett, M.
Bochmann, J. Am. Chem. Soc. 2001, 123, 223 ± 237;
d) R. Taube, J. Langlotz, J. Sieler, T. Gelbrich, K. Tittes,
J. Organomet. Chem. 2000, 597, 92 ± 104; e) S. D. Ittel,
L. K. Johnson, M. Brookhart, Chem. Rev. 2000, 100,
4
Š. Using the Eigen±DenisonÀRamsey±Fuoss model
the difference in ion association between the complexes
can be estimated. For example, in acetone Kass 1b/Kass 1e
ˆ
1
.5 and Kass 1c/Kass 1g ˆ 1.7.
[
21] A similar reduction of cation-anion interactions was
±
observed for [BPh ] and TFPB in cationic palladium
4
catalysts active in co-polymerisation of CO and styrene.
Enhanced catalyst activity for TFPB was supported by
HOESY and NOESY NMR which confirmed a weak-
ening of the inter-ionic interactions: A. Macchioni, G.
Bellachioma, G. Cardaci, M. Travaglia, C. Zuccacia,
Organometallics 1999, 18, 3061 ± 3069.
1
169 ± 1203; f) L. Li, M. V. Metz, T. J. Marks, L. Liable-
Sands, A. L. Rheingold, Polymer Preprints 2000, 41,
912 ± 1913.
1
[
10] a) J. van den Broeke, M. Lutz, H. Kooijman, A. L. Spek,
B.-J. Deelman, G. van Koten, Organometallics 2001, 20,
2
114 ± 2117; b) J. van den Broeke, B.-J. Deelman, G.
[
22] This solvent has a polarity similar to that of CH Cl : A.
2
2
van Koten, Tetrahedron Lett. 2001, 42, 8085 ± 8087.
11] The ion radius r denotes the longest distance from the
boron atom to the periphery of the anion: TFPB taken
Ogawa, D. P. Curran, J. Org. Chem. 1997, 62, 450 ± 451.
23] a) L. P. Barthel-Rosa, J. A. Gladysz, Coo. Chem. Rev.
[
[
1
999, 190 ± 192, 587 ± 605; b) B. Betzemeier, P. Knochel,
from J. H. Golden, P. F. Mutolo, E. B. Lokovsky, F. J.
Topics in Current Chemistry 1999, 206, 61 ± 78.
±
DiSalvo, Inorg. Chem. 1994, 33, 5374 ± 5375; BF ,
4
[
[
24] Reaction conditions: 3.7 mg ꢀ1.0 mmol) 1g was dissolved
in 5 mL FC-75. To this solution 0.02 mL ꢀ0.2 mmol) 1-
octene was added and the resulting homogeneous
±
±
[
BPh ] ,
[B{C H ꢀSiMe )-4} ] ,
[B{C H ꢀSiMe -
4
6
±
4
3
4
6
±
4
2
CH CH C F )-4} ] ,
[B{C H ꢀC F )-4} ]
and
2
2
6
13
4
6
4
6
13
4
±
[
ꢀ
ꢀ
B{C H ꢀC F ) -3,5} ] calculated for semi-empirical
6 3 6 13 2 4
solution was stirred for 24 h under 1 bar of H at 408C.
2
TM
PM3 ) optimised structures using the Spartan 5.1.1
SGI) molecular modelling software package.
31
25] P NMR chemical shifts in CDCl for [Rhꢀdppe)-
3
ꢀ
5
4
COD)]BF4 ꢀd ˆ 56.5), [Rhꢀdppe)ꢀCOD)][BPh ] ꢀd ˆ
4
[
[
[
[
12] C. Hansch, A. Leo, Substituent Constants for Correlation
Analysis in Chemistry and Biology, John Wiley & Sons,
New York, 1979.
13] E. de Wolf, A. J. M. Mens, O. L. J. Gijzemans, J. H.
van Lenthe, L. W. Jenneskens, B.-J. Deelman, G. van Ko-
ten, Inorg. Chem., accepted.
14] H. Jiao, S. Le Stang, T. So o s, R. Meier, K. Kowski, P.
Rademacher, L. Jafarpour, J.-B. Hamard, S. P. Nolan,
J. A. Gladysz, J. Am. Chem. Soc. 2002, 124, 1516 ± 1523.
15] J. A. S. Howell, N. Fey, J. D. Lovatt, P. C. Yates, P.
McArdle, D. Cunningham, E. Sadeh, H. E. Gottlieb, Z.
Goldschmidt, M. B. Hursthouse, M. E. Loght, J. Chem.
Soc. Dalton Trans. 1999, 3015 ± 3028.
6.2), 3a ꢀd ˆ 56.5) and in C D /CF C H 1:1 ꢀv/v) for
6
6
3
6
5
[3]
a ꢀd ˆ 56.8) are reported in ref. 3f ꢀd ˆ 56.2) and 2g
ꢀ
d ˆ 56.2) were measured in C D :FC-75 1:1 ꢀv/v).
6
6
[
[
26] T. G. Schenk, J. M. Downes, C. R. C. Milne, P. B. Mack-
enzie, H. Boucher, Inorg. Chem. 1985, 24, 2334 ± 2337.
27] As indicated by the significantly lower partition coef-
ficients observed for 1g in comparison with 3a, despite
the fact that both have a comparable fluorous volume.
[28] a) L. E. Kiss, I. Kövesdi, J. R a bai, J. Fluorine Chem.
2001, 108, 95 ± 109; b) E. de Wolf, PhD Thesis, Utrecht
University, 2002, Chapter 7.
[29] M. Brookhart, B. Grant, A. F. Volpe, Organometallics
1992, 11, 3920 ± 3922.
[16] a) C. R. Landis, J. Halpern, J. Organomet. Chem. 1983,
[30] R. Cramer, J. Am. Chem. Soc. 19ꢀ4, 86, 217 ± 219.
2
50, 485 ± 490; b) J. Reiss, J. Hetflejs, React. Kinet. Catal.
[31] Adapted from [RhꢀCOD)ꢀdppe)]BF : M. Green, T. A.
4
Lett. 198ꢀ, 31, 309 ± 313.
Kuc, S. H. Taylor, J. Chem. Soc. A 1971, 2334 ± 2337.
634
ꢂ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2003, 345, 625 ± 635

Hydrogenation Activity and Recycling of Cationic Rh-Diphosphine Complexes
FULL PAPERS
Adv. Synth. Catal. 2003, 345, 625 ± 635
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635