Rhodium complexes stabilized by phosphine-functionalized phosphonium ionic liquids used as higher alkene hydroformylation catalysts: Influence of the phosphonium headgroup on catalytic activity

Article abstract of DOI:10.1039/c2dt31797d

Monodentate phosphine-functionalized phosphonium ionic liquids (PFILs) were employed as ligands for Rh complexes and used in the hydroformylation of higher alkenes. Three PFILs were designed by varying the length of the P-alkyl chain attached to the phosphonium moiety, for alkyl = methyl (1), butyl (2), octyl (3), in order to tune their solubility properties. In all PFILs, the phosphonium unit is linked to a diphenylphosphino functionality by an undecyl linker, with bis(trifluoromethylsulfonyl)imide as counter anion. These PFILs were combined with a Rh(i) precursor, [Rh(acac)(CO)₂], to provide a biphasic hydroformylation catalyst for the transformation of 1-octene, 1-decene and 1-dodecene using tetradecyltributylphosphonium bis(trifluoromethylsulfonyl) imide, [P_4,4,4,14]NTf₂ as a solvent. Good activities and excellent selectivities were obtained for these PFILs-Rh(i) complexes. Variation of the P-alkyl length in the PFIL ligand influenced the stability, catalytic activity and selectivity of the PFIL-stabilized catalyst.

Full text of DOI:10.1039/c2dt31797d

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PAPER
Rhodium complexes stabilized by phosphine-functionalized phosphonium
ionic liquids used as higher alkene hydroformylation catalysts: influence of
the phosphonium headgroup on catalytic activity†‡
Kylie L. Luska, Karl Z. Demmans, Samantha A. Stratton and Audrey Moores*
Received 7th August 2012, Accepted 13th September 2012
DOI: 10.1039/c2dt31797d
Monodentate phosphine-functionalized phosphonium ionic liquids (PFILs) were employed as ligands
for Rh complexes and used in the hydroformylation of higher alkenes. Three PFILs were designed by
varying the length of the P-alkyl chain attached to the phosphonium moiety, for alkyl = methyl (1), butyl
(2), octyl (3), in order to tune their solubility properties. In all PFILs, the phosphonium unit is linked to
a diphenylphosphino functionality by an undecyl linker, with bis(trifluoromethylsulfonyl)imide as
counter anion. These PFILs were combined with a Rh(I) precursor, [Rh(acac)(CO)2], to provide a biphasic
hydroformylation catalyst for the transformation of 1-octene, 1-decene and 1-dodecene using
tetradecyltributylphosphonium bis(trifluoromethylsulfonyl)imide, [P4,4,4,14]NTf2 as a solvent. Good
activities and excellent selectivities were obtained for these PFILs-Rh(I) complexes. Variation of the
P-alkyl length in the PFIL ligand influenced the stability, catalytic activity and selectivity of the
PFIL-stabilized catalyst.
which the nature of the phosphonium substitution was shown to
Introduction
have a dramatic influence on the activity and selectivity of the
catalyst.38 Olivier-Bourbigou and co-workers were the first to
The Ruhrchemie/Rhône-Poulenc biphasic process represents one
report the use of imidazolium ILs for hydroformylation.36,37
of the most important homogeneously catalyzed reactions in the
chemical industry.1,2 The hydroformylation of propene is cata-
Their initial study evidenced leaching of the Rh catalyst from the
lyzed using a water-soluble Rh catalyst stabilized by triphenyl-
phosphine trisulfonate (TPPTS). The Rh catalyst is retained in
the aqueous phase, which allows for facile removal of the
product and reuse of the catalyst.1,3 However, this process is less
successful for the conversion of long-chain olefins due to their
poor solubilities in the aqueous catalytic phase.3 Long chain
linear aldehyde are of major commercial importance and thus
various solutions have been explored to increase the reaction
rates of higher alkene hydroformylation including: (i) co-
solvents;4–6 (ii) addition of surfactants;7–15 (iii) amphiphilic
IL phase in the absence of an additional stabilizing ligand, such
as TPPTS.36 TPPTS allowed for complete retention of the cata-
lyst in the IL phase; however, the activity of the catalyst was dra-
matically reduced.36
In order to improve catalyst retention and stabilization in IL
biphasic systems, homogeneous catalysts have been stabilized by
functionalized ILs (FILs) – ILs featuring a metal binding
functionality.36,37,41–47 Several groups have reported phosphine
and phosphite based FILs as hydroformylation ligands that
improve the solubility of higher alkene reactants in the catalytic
phase, while simultaneously improving catalyst retention and
selectivity.33,35,42,45,46,48–54
In the context of IL-stabilized transition metal nanoparticles
(NPs),55–65 our group and others have studied the influence of
changing the parameters of FILs (i.e. alkyl chain length, counter
anion) on the catalytic properties of transition metal NPs.57,66–68
FILs represent a highly tunable class of ligands, in which sys-
tematic alterations to the FIL structure can be accomplished to
understand their influence on the stability, activity and selectivity
of a catalyst. For example, a series of imidazolium ILs functiona-
lized with a phosphine66,67 or a bipyridine68 moiety were
designed such that the alkyl linker between the cationic and
metal binding functionalities was used to tune catalytic activity
of transition metal NPs. Herein, we have applied this concept to
the design of new phosphine-functionalized ILs (PFILs) in order
phosphines;16–20 (iv) functionalized cyclodextrins;21–27 and (v)
28–35
alternative solvents, such as supercritical CO2
and ionic
liquids (ILs).36–40
Knifton was the first to report an IL-based hydroformylation
catalyst composed of a Ru and/or a Co carbonyl precursor dis-
solved in a phosphonium IL.39 Karodia et al. also reported the
use of phosphonium ILs as solvents for hydroformylation, in
Centre for Catalysis and Green Chemistry, Department of Chemistry,
McGill University, 801 Sherbrooke St. W., Montreal, Quebec, Canada,
H3A 2K6. E-mail: audrey.moores@mcgill.ca; Fax: +1 514 398 3797;
Tel: +1 514 398 4654
†Dedicated to David Cole-Hamilton, a patient supervisor, a passionate
mentor.
‡Electronic supplementary information (ESI) available: Additional
TEM data. See DOI: 10.1039/c2dt31797d
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 13533–13540 | 13533

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Fig. 1 Phosphine-functionalized phosphonium ionic liquids (PFILs)
1–3 used as ligands for the hydroformylation of long-chain alkenes.
Fig. 2 Synthesis of PFILs 1–3.
to better understand the impact of the PFIL on directing the
activity and selectivity in Rh(I) catalyzed hydroformylation.
The novel PFILs 1–3 (Fig. 1) were synthesized, in which the
P-alkyl chain length was varied, with R = methyl (1), butyl (2),
octyl (3). The coordination properties of these new ligands to
Rh(I) species was studied by 31P NMR. These PFILs were also
used as stabilizing ligands for Rh(I) complexes employed in the
biphasic hydroformylation of higher alkenes in a phosphonium
IL solvent, [P4,4,4,14]NTf2 (P4,4,4,14 = tetradecyltributylphospho-
nium, −NTf2 = bis(trifluoromethylsulfonyl)imide). Phosphonium
ILs impart several advantages to this system: (1) high chemical
and thermal stability;69 (2) lower cost alternatives to imidazolium
ILs;70 and (3) possess higher gas diffusivity than imidazolium
ILs of equal viscosity.60 Furthermore, the long chain alkyl
groups of the PFILs and the IL solvent could increase the solubi-
lity of the alkene substrate in the IL phase and facilitate the inter-
action of the substrate with the active metal sites. The
diphenylphosphino moiety of PFILs 1–3 was shown by NMR to
have similar electronic features upon coordination to a Rh(I)
centre, allowing to probe solely the steric and solubility proper-
ties. The activities and selectivities of the PFIL-stabilized Rh
catalysts in the hydroformylation of 1-octene, 1-decene and
1-dodecene were dependent on the nature of the phosphonium
headgroup. In general, the longer chain PFIL possessed superior
activities, while the shorter chain PFILs provided improved
selectivities.
Fig. 3 Precatalytic hydroformylation complexes stabilized by a mono-
dentate phosphine (L) responsible for the regioselectivity of the aldehyde
products.
nature of the catalytic complex has a crucial impact on both the
catalyst activity, and the selectivity towards the desired linear
aldehyde over the branched one, as described in Fig. 3.2 Phos-
phine disassociation leads to two unsaturated intermediates,
Rh(H)(CO)L2 and Rh(H)(CO)2L, which are responsible for the
formation of the aldehyde product. The bisphosphine species
Rh(H)(CO)L2 selectively produces the least hindered product,
the linear aldehyde, while Rh(H)(CO)2L yields both the linear
and branched product.2,71 Therefore, the hydroformylation regio-
selectivity can be tuned by controlling the concentration of
Rh(H)(CO)L2.
Results and discussion
Recently Klein Gebbink and co-workers used 31P NMR spec-
troscopy to demonstrate that charged phosphines were behaving
differently than neutral ones in respect to coordination to Rh(I)
species.71 A similar NMR experiment was performed to gain
insight into the coordination properties of PFIL 1–3 (Table 1).
To the precursor [Rh(COD)2][OTf], 1 to 4 equivalents of PFIL
(a) Synthesis of phosphine-functionalized ionic liquids
The synthesis of PFILs 1–3 followed a similar procedure to that
reported previously by our group for the synthesis of imidazo-
lium PFILs.66 The procedure involved a radical chain addition of
diphenylphosphine to alkene-functionalized ILs catalyzed by
1,1′-azobis(cyclohexanecarbonitrile) (ABCN) to introduce the
desired phosphines in almost quantitative yields (Fig. 2). Un-
decenyl phosphonium salts were synthesized through the quater-
nization of the desired phosphine (R = methyl, butyl, octyl) with
undecenyl bromide, followed by an anion exchange using
LiNTf2.
1–3 were added in d3-acetonitrile as solvent (COD
=
cyclooctadiene).
Stirring one equivalent of PFIL 1–3 with [Rh(COD)2][OTf] at
room temperature rapidly afforded the expected 1 : 1 complex
characterized by a doublet in 31P NMR (Fig. 4, Table 1, entries
4–6). Addition of a second equivalent gave rise to two signals, a
doublet of doublets and a doublet of triplets, which are character-
istic of a tri-phosphine-substituted rhodium species. This set of
signals correspond to an A2BX system, consistent with square
planar [Rh(MeCN)(PFIL)3][OTf]. No other peak was observed –
no free PFIL or mono-phosphine-substituted complex – but the
(b) NMR study of the Rh(I) complexes of PFILs 1–3
Monodentate phosphines are known to form with Rh(I) a variety
of coordination species under hydroformylation conditions. The
13534 | Dalton Trans., 2012, 41, 13533–13540
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base line was noisy: exchange is expected to happen between
these three species. The addition of a third equivalent of PFIL
confirms the full formation of the [Rh(MeCN)(PFIL)3][OTf]
complex (Fig. 4, Table 1, entries 7–9). Absence of coordinated
phosphonium) as solvent in the presence of [Rh(acac)(CO)2]
(acac = acetylacetonate) as pre-catalyst and a PFIL ligand
(Fig. 5). Initial studies employed PFIL 1 for the hydroformyla-
tion of 1-octene to optimize various reaction parameters. The
PFIL 1/Rh ratio influenced both the conversion and selectivity of
this reaction (Table 2, entries 1–4). The conversion of 1-octene
was >98% for 2, 4 and 8 eq. of PFIL 1, while the conversion
was decreased to 88% with 12 eq. of the phosphine ligand.
Further, the linear-to-branched (l/b) ratio for the aldehyde
product increased with an increase in the amount of PFIL 1
added to the reaction mixture. A PFIL 1/Rh ratio of 8 was
employed for further studies since these conditions were a
1
COD is also confirmed by H NMR. Addition of more PFIL led
to the appearance of a signal of free PFIL, confirming that 3 is
the maximum PFIL/Rh ratio for these species. PFILs 1–3 all
behaved in the same fashion. The chemical shifts of the PPh2
signals of [Rh(MeCN)(PFIL)3][OTf] complexes for PFIL 1–3
ranged from δ = 35.2 to 35.5 ppm (dt) and δ = 22.4 to 22.5 ppm
1
(dd) with coupling constants of JRh–P = 172 to 173 (dt) and
133 Hz (dd). These values are very similar and prove that PFILs
1–3 have essentially the same electronic behaviour towards
Rh(I). These properties are also close to those observed when PPh3
is used as the ligand under the same conditions (δ = 45.5 ppm,
1JRh–P = 174 Hz (dt), δ = 32.8 ppm, 1JRh–P = 137 Hz (dd)).71
(c) Hydroformylation catalysis
Hydroformylation tests were performed on long-chain
alkene substrates in [P4,4,4,14]NTf2 (P4,4,4,14 = tetradecyltributyl-
Fig. 5 Biphasic hydroformylation of higher alkenes catalyzed by
[Rh(acac)(CO)2] and PFILs 1–3 (for n = 5, 7, 9).
Table 1 31P NMR spectral data for the PFIL 1–3 and a series of PFIL
1–3: Rh(I) complexes
Table 2 Optimization of the reaction conditions for the biphasic
hydroformylation of 1-octene catalyzed by [Rh(acac)(CO)2] and PFIL 1
δPR3+
(ppm) (ppm)
δPPh2
1JP–Rh 2JP–P
Entry 31P species
(Hz)
(Hz)
c
PFIL
1/Rh
p[CO/H2]
(bar)
Conversiona
(%)
Sad
Entry
T (°C)
l/bb
(%)
1
2
3
4
5
6
7
PFIL 1
PFIL 2
PFIL 3
26.8
33.7
33.6
−17.0
−17.0
−17.0
23.0
23.0
23.0
35.4(dt) 173
22.4(dd) 133
35.2(dt) 172
22.5(dd) 133
35.5(dt) 173
22.5(dd) 133
—
—
—
143
143
143
—
—
—
—
—
—
42
42
43
42
43
43
1
2
3
4
5
6
7
8
2
4
8
12
8
8
8
8
100
100
100
100
75
50
75
40
40
40
40
40
40
20
10
100
98
98
88
91
28
91
57
1.8
2.3
2.2
2.8
2.8
3.0
3.7
3.6
88
86
85
84
[Rh(COD)(MeCN)(1)]+ 26.9
[Rh(COD)(MeCN)(2)]+ 33.6
[Rh(COD)(MeCN)(3)]+ 33.6
[Rh(MeCN)(1)3]+
[Rh(MeCN)(2)3]+
[Rh(MeCN)(3)3]+
26.9
33.6
33.6
95
100
100
88
8
9
75
Reaction conditions: [Rh(acac)(CO)2] = 0.05 mmol, [P4,4,4,14]NTf2
=
1.0 g, 1-octene/Rh = 100, CO/H2 = 1/1, t = 3 h. a Determined by GC
analysis employing dodecane as an internal standard. b Ratio linear/
Reaction conditions: [Rh(COD)2][OTf] = 0.05 mmol, PFIL/Rh = 1 or 3,
T = RT, t = 30 min. Note: in all Rh : PFIL complexes, the counter anion
is −OTf.
c
branched aldehyde. Sad = aldehyde selectivity (percentage [linear +
branched aldehydes]/[total conversion]).
Fig. 4 Coordination behaviour of PFIL 1–3 with [Rh(COD)2][OTf]. For R = methyl (PFIL 1); butyl (PFIL 2); octyl (PFIL 3).
This journal is © The Royal Society of Chemistry 2012 Dalton Trans., 2012, 41, 13533–13540 | 13535

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Table 3 Influence of PFIL structure on the biphasic hydroformylation
of higher alkenes catalyzed by [Rh(acac)(CO)2] and PFILs 1–3
Table 4 Catalyst recycling for the biphasic hydroformylation of
1-octene catalyzed by [Rh(acac)(CO)2] and PFILs 1–3
Entry
PFIL
Substrate
Conversiona (%)
l/bb
Sad c (%)
Entry
Ligand
Cycle
Conversiona (%)
l/bb
Sad c (%)
1
2
3
4
5
6
7
8
9
1
2
3
1
2
3
1
2
3
1-Octene
1-Octene
1-Octene
1-Decene
1-Decene
1-Decene
1-Dodecene
1-Dodecene
1-Dodecene
64
60
94
58
3.0
2.8
2.8
3.3
2.9
2.9
2.9
3.3
2.8
97
98
100
97
96
92
97
98
93
1
2
3
4
5
6
7
8
PFIL 1
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5
91
95
94
56
61
95
96
92
88
84
81
81
84
85
87
99
91
89
90
74
3.7
3.6
3.3
3.2
3.1
4.1
3.6
3.7
3.4
3.2
3.4
3.4
3.2
3.2
3.1
3.9
2.8
2.5
2.4
2.4
100
100
100
100
100
82
91
96
97
97
100
100
100
100
100
93
93
94
94
90
55
66
PFIL 2
PFIL 3
PPh3
53d
45d
70d
9
10
11
12
13
14
15
16
17
18
19
20
Reaction conditions: [Rh(acac)(CO)2] = 0.05 mmol, PFIL/Rh = 8,
[P4,4,4,14]NTf2 = 1.0 g, alkene/Rh = 250, CO/H2 = 1/1 (20 bar), T =
75 °C, t = 3 h. a Determined by GC analysis employing dodecane as an
internal standard. b Ratio linear/branched aldehyde. Sad = aldehyde
c
selectivity (percentage [linear + branched aldehydes]/[total conversion]).
d Decane used as an internal standard.
compromise between stability, activity and selectivity. Decreas-
ing the reaction temperature from 100 to 75 or 50 °C increased
the l/b ratio of the product mixture (Table 2, entries 1, 5, 6). A
reaction temperature of 75 °C was favoured as the 1-octene con-
version remained high, while the l/b ratio was increased from 2.2
at 100 °C to 2.8 at 75 °C. Lastly, a further increase in the l/b
ratio was obtained by altering the syngas pressure (Table 2,
entries 1, 7, 8). Decreasing the reaction pressure from 40 to 20
bar improved the l/b ratio to 3.7, an excellent selectivity for a
monodentate ligand. A further pressure decrease to 10 bar nega-
tively impacted the 1-octene conversion.
These optimized catalytic conditions were employed to study
the influence of the PFIL stabilizer and the substrate in this reac-
tion. For this study the alkene/Rh ratio was increased to 250 eq.
while all other reaction conditions were held constant. For
1-octene, PFILs 1 and 2 possessed similar activities and selecti-
vities (Table 3, entries 1 and 2), while the activity of the PFIL
3-stabilized catalyst reached 94% conversion (Table 3, entry 3).
PFILs 1–3 also provided active catalysts for the hydroformyla-
tion of 1-decene and 1-dodecene. PFIL 1 and 2 showed moderate
activities for 1-decene and 1-dodecene (Table 3, entries 4, 5, 7,
8). Again PFIL 3 provided the most active catalyst for 1-decene
and 1-dodecene (Table 3, entries 6 and 9) achieving an alkene
conversion of ∼70% for both substrates, while maintaining
similar l/b selectivities. With both 1-octene and 1-decene, the
best selectivities were obtained for the short alkyl chain PFIL 1
(Table 3, entries 1 and 4), with a value up to 3.3, which is high
for a monodendate phosphine.71 The 31P NMR study did not
indicate significant impact of the higher steric hindrance of 2–3
on their coordination behaviour in acetonitrile. However, in the
phosphonium ionic liquid medium of catalysis, the difference in
l/b selectivities is a clear indication that the PFIL 1 may favour
Rh(H)(CO)(PFIL)2 over Rh(H)(CO)2(PFIL) more efficiently
than the bulkier PFILs 2 and 3. As both the charge and the elec-
tronic properties of the ligands PFIL 1–3 are essentially identi-
cal, these results demonstrate the impact of sterics and the
lipophilic character of the stabilizing species in homogeneous
catalysis.
Reaction conditions: [Rh(acac)(CO)2] = 0.05 mmol, PFIL/Rh = 8,
[P4,4,4,14]NTf2 = 1.0 g, 1-octene/Rh = 100, CO/H2 = 1/1 (20 bar), T =
75 °C, t = 3 h. a Determined by GC analysis employing dodecane as an
internal standard. b Ratio linear/branched aldehyde. Sad = aldehyde
c
selectivity (percentage [linear + branched aldehydes]/[total conversion]).
catalyst ratio of 100 (Table 4). Rh catalysts were prepared in situ
from the combination of [Rh(acac)(CO)2] and PFILs 1–3 in
[P4,4,4,14]NTf2. After catalysis, the product was extracted using
pentane and the recovered IL was dried in vacuo for 1 h. The cat-
alyst phase was recharged with substrate for a subsequent cataly-
tic cycle and employed for a total of five hydroformylation
cycles. As outlined in Table 4, the alkene conversion, l/b ratio
and aldehyde selectivity were dependent on the nature of the
PFIL stabilizer. PFILs 2 and 3 provided the most active catalysts
able to maintain a 1-octene conversion >84% over five catalytic
cycles. The stability of the catalyst based on PFIL 1 was reduced
compared to 2 and 3 as a significant decrease in 1-octene conver-
sion occurred after the third cycle. In terms of the l/b ratio,
PFILs 1 and 2 initially possessed l/b ratios of 3.7 and 4.1
respectively, which both decreased to 3.1 by the fifth cycle. PFIL
3 initially had a lower l/b ratio of 3.4; however, this catalyst did
not suffer from a significant decrease of the l/b ratio over the five
cycles. Lastly, PFILs 1 and 3 showed quantitative conversion of
1-octene to aldehyde products, whereas PFIL 2 catalyzed the iso-
merization of octene more readily as reflected in the Sad.
PPh3 was also employed as a stabilizer to compare a neutral
phosphine to PFILs 1–3 (Table 4, entries 16–20). The catalytic
activity of the PPh3-stabilized catalyst was >90% over the first
four cycles; however, the conversion decreased during the fifth
cycle (74%). The l/b ratio also decreased upon recycling from
3.9 during the first cycle to 2.4 during the fifth cycle. Isomeriza-
tion of 1-octene was more readily catalyzed in this system as the
Sad was <94%. The stability of the PPh3 catalyst was reduced
compared to that of the PFILs. Qualitatively, the IL phase trans-
formed from a bright orange solution to a dark brown suspension
after the second catalytic cycle, signifying the formation of
Rh(0) NPs.72
The recyclability of the PFIL-stabilized catalysts was investi-
gated for the hydroformylation of 1-octene with a substrate/
13536 | Dalton Trans., 2012, 41, 13533–13540
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A transmission electron microscopy (TEM) study was under-
taken to better understand the nature of the catalyst for each
PFIL 1/Rh ratio after catalysis (Fig. S1, see ESI‡ for additional
TEM data). Small Rh(0) NPs with diameters ∼2 nm were
formed for PFIL 1/Rh ratios higher than 8; however, ratios lower
than 8 resulted in the formation of a mixture of heterodispersed
particles of sizes ranging from 2 to several hundreds of nm. The
catalysis data proved that 8 eq. of PFIL was also required to
form a selective catalyst by favouring the formation of the
bisphosphine complex and to enhance the stability of the Rh(I)
catalyst under catalytic conditions. TEM analysis of the IL phase
with each PFIL and PPh3 was also obtained after five cycles of
catalysis and showed the presence of NPs ranging from
∼2–10 nm (Fig. S2‡). The NP size and concentration was depen-
dent on the nature of the phosphine stabilizer. PFILs 1 and 2 pro-
vided the most stable catalysts as only a low concentration of
∼2 nm NPs were observed, while PFIL 3 showed the presence
of NPs ranging from ∼2–10 nm. The PPh3-stabilized catalyst
showed a higher concentration of NPs compared to PFILs 1–3
and could result from the insolubility of PPh3 in the IL sol-
ution.67 Further, the PPh3 catalyst solution turned from an
orange to a dark brown colour, signifying the formation of a
high concentration of Rh NPs,72 while the solutions containing
PFILs 1–3 remained orange throughout the recycling exper-
iments. It should be noted that Dupont and co-workers have
employed Rh(0) NPs synthesized in imidazolium ILs as hydro-
formylation catalyst precursors.72 These Rh NPs acted as a reser-
voir for the formation of catalytically active Rh(I) mononuclear
complexes; however, possessed low l/b ratios for the aldehyde
products in the absence of an additional stabilizing ligand.72 In
our system, Rh NPs were also formed, but unlike the results
reported by Dupont, the inclusion of these PFIL ligands allowed
the catalyst system to maintain high l/b ratios. It is reasonable to
assume that our NPs may also act as a reservoir in the formation
of Rh(I) monomeric complexes, while the PFIL effectively co-
ordinates Rh(I) species to afford excellent selectivity. In order to
test the catalytic properties of the Rh NPs themselves, an experi-
ment was performed where Rh NPs were created in the presence
of PFIL 2 in situ before addition of 1-octene. In this test, the l/b
ratio dropped to 1.8, while the conversion (78.4%) and aldehyde
selectivity (94%) was also adversely affected. This is consistent
with the idea that Rh NPs may serve as a source of Rh, but that
they do not explain the catalysis itself.71
Experimental
(a) General
All syntheses were carried out under an argon atmosphere
employing Schlenk techniques. Tetradecylmethanesulfonate,73
65
[P4,4,4,14]OMs65 and [P4,4,4,14]NTf2 was prepared following a
known literature procedure. Dichloromethane (Grubbs apparatus)
and triethylamine (distillation over CaH2) were purified prior to
use. All other chemicals and solvents were purchased from com-
mercial sources and used without further purification. 1-Octene,
1-decene and 1-dodecene were degassed prior to use and storage
under an inert atmosphere. Melting points (mp) were determined
on a Gallenkamp melting point apparatus and are uncorrected.
Nuclear magnetic resonance (NMR) spectra were recorded on a
200 or 300 MHz Varian Mercury spectrometer. 1H and 13C
NMR spectra were calibrated to TMS using the residual solvent
signal and 31P NMR spectra were calibrated using 85% H3PO4.
Mass spectra (MS) were recorded in positive electrospray mode
with LTQ Orbitrap ESI/APCI (Thermo Scientific). Transmission
electron microscopy (TEM) was performed on a Phillips CM
200 microscope. High-pressure experiments were performed
employing a Parr Instruments 5000 Series Multiple Reactor
System equipped with 100 mL reaction vessels. Gas chromato-
graphy (GC) was performed on an Agilent 7890A Gas Chromato-
graph equipped with an Agilent HP-5MS column.
(b) Synthesis of phosphine-functionalized ionic liquids
Synthesis of trialkyl(undec-10-enyl)phosphonium bromide.
Trialkylphosphine (23.0 mmol) and 11-bromo-1-undecene
(23.0 mmol) were combined in a Schlenk flask and dissolved in
CH3CN (20 mL). The reaction mixture was refluxed for 18 h.
The solvent was removed to yield the product, which was
washed with pentane (3 × 50 mL) and removed by decantation.
The product was dried in vacuo overnight at 60 °C.
Trimethyl(undec-10-enyl)phosphonium bromide. The reaction
provided an off-white solid (79%). mp 171–173 °C. H NMR
1
(300 MHz, CDCl3) δ 5.77 (ddt, J = 16.9, 10.1, 6.7 Hz, 1H),
5.01–4.87 (m, 2H), 2.53–2.36 (m, 2H), 2.19 (d, J = 14.2 Hz,
9H), 2.07–1.89 (m, 2H), 1.62–1.39 (m, 4H), 1.39–1.15 (m,
10H). 13C NMR (75.5 MHz, CDCl3) δ 139.3 (s), 114.4 (s), 34.0
(s), 30.7 (d, JCP = 15.6 Hz), 29.5 (s), 29.4 (s), 29.2 (s), 29.2 (s),
29.1 (s), 24.0 (d, JCP = 52.1 Hz), 21.9 (d, JCP = 4.6 Hz), 9.2 (d,
JCP = 55.1 Hz). 31P NMR (81 MHz, CDCl3) δ 28.1 (s). ESI/MS
(+) m/z calc. for [C14H30P]+ 229.2080, found 229.2086.
Conclusions
Tributyl(undec-10-enyl)phosphonium bromide. The reaction pro-
vided a yellow liquid (97%). 1H NMR (300 MHz, CDCl3) δ
5.60 (ddt, J = 16.9, 10.1, 6.7 Hz, 1H), 4.91–4.62 (m, 2H),
2.41–2.10 (m, 8H), 1.83 (q, J = 6.8 Hz, 2H), 1.50–1.22 (m,
16H), 1.22–1.01 (m, 10H), 0.78 (t, J = 6.9 Hz, 9H). 13C NMR
(75.5 MHz, CDCl3) δ 138.9 (s), 113.9 (s), 33.5 (s), 30.6 (d, JCP
= 14.7 Hz), 29.1 (s), 29.0 (s), 28.8 (s), 28.7 (s), 28.6 (s),
23.9–23.5 (m, 2C), 21.7 (d, JCP = 4.7 Hz), 19.1 (d, JCP = 46.8
Hz), 18.9 (d, JCP = 47.6 Hz), 13.3 (s). 31P NMR (81.0 MHz,
CDCl3) δ 33.8 (s). ESI/MS(+) m/z calc. for [C23H48P]+
355.3499, found 355.3494.
Phosphine-functionalized phosphonium ILs 1–3, possessing
variable P-alkyl chain lengths, were effective stabilizing species
in the preparation of higher alkene hydroformylation catalysts.
The nature of the PFIL phosphonium headgroup influenced the
coordination modes, stability, catalytic activity, selectivity and
recyclability of the corresponding Rh catalysts. Long alkyl
chains on the phosphonium headgroup favoured conversion by
improving high alkene solubility, while short chains favoured
selectivity by maintaining a higher concentration of the bisphos-
phine Rh(I) complex. PFILs were also compared to PPh3 and
were shown to improve the catalytic activity and selectivity of
the hydroformylation catalyst. Future studies will include the
design of bidentate phosphine functionalized ILs for catalysis.
Trioctyl(undec-10-enyl)phosphonium bromide. The reaction pro-
vided a yellow liquid (99%). 1H NMR (300 MHz, CDCl3) δ
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 13533–13540 | 13537

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PFIL 1. The reaction provided a pale yellow liquid (100%).
1H NMR (300 MHz, (CD3)2SO) δ 7.45–7.30 (m, 10H),
2.23–1.96 (m, 4H), 1.80 (d, J = 14.8 Hz, 9H), 1.57–1.10 (m,
18H). 13C NMR (75.5 MHz, (CD3)2SO) δ 138.7 (d, JCP = 13.9
5.66 (ddt, J = 16.9, 10.2, 6.7 Hz, 1H), 4.94–4.61 (m, 2H),
2.46–2.15 (m, 8H), 1.90 (q, J = 7.0 Hz, 2H), 1.50–1.05 (m,
50H), 0.74 (t, J = 6.7 Hz, 9H). 13C NMR (75.5 MHz, CDCl3) δ
139.0 (s), 114.1 (s), 33.7 (s), 31.6 (s), 30.7 (d, JCP = 14.6 Hz),
29.4–28.7 (m, 10C), 22.5 (s), 21.9 (d, JCP = 4.8 Hz), 19.3 (d,
Hz), 132.3 (d, JCP = 18.9 Hz), 128.5 (m, 2C), 119.5 (q, JCF
=
J
CP = 46.8 Hz), 14.0 (s). 31P NMR (81 MHz, CDCl3) δ 33.7 (s).
322.4 Hz), 30.4 (d, JCP = 12.1 Hz), 30.0 (d, JCP = 15.9 Hz),
28.9 (s), 28.8 (s), 28.7 (s), 28.7 (s), 28.3 (s), 26.7 (d, JCP = 10.6
Hz), 25.5 (d, JCP = 15.9 Hz), 22.2 (d, JCP = 52.1 Hz), 20.5 (d,
JCP = 3.8 Hz), 7.1 (d, JCP = 53.6 Hz). 31P NMR (81 MHz,
(CD3)2SO) δ 29.0 (s), −16.4 (s). ESI/MS(+) m/z calc. for
[C26H41P2]+ 415.2678, found 415.2687.
ESI/MS(+) m/z calc. for [C35H72P]+ 523.5366, found 523.5372.
Synthesis of trialkyl(undec-10-enyl)phosphonium bis(trifluoro-
methylsulfonyl)
imide. Trialkyl(undec-10-enyl)phosphonium
bromide (17.0 mmol) was dissolved in H2O (50 mL). Bis(tri-
fluoromethanesulfonimide) lithium salt (17.9 mmol) was added
in portions and the mixture was stirred vigorously at rt for 18 h.
The mixture was extracted with CH2Cl2 (50 mL), washed with
H2O (3 × 50 mL) and dried over MgSO4. Upon solvent removal,
the product was dried in vacuo overnight at 60 °C.
PFIL 2. The reaction provided a pale yellow liquid (100%).
1H NMR (300 MHz, (CD3)2SO) δ 7.44–7.31 (m, 10H),
2.25–2.10 (m, 8H), 2.04 (t, J = 7.5 Hz, 2H), 1.54–1.14 (m,
30H), 0.91 (t, J = 7.0 Hz, 9H). 13C NMR (75.5 MHz,
(CD3)2SO) δ 138.6 (d, JCP = 14.0 Hz), 132.3 (d, JCP = 18.1 Hz),
Trimethyl(undec-10-enyl)phosphonium bis(trifluoromethylsulfo-
nyl)imide. The reaction provided an amber liquid (90%). 1H
NMR (300 MHz, CDCl3) δ 5.77 (ddt, J = 17.1, 10.2, 6.7 Hz,
1H), 5.05–4.80 (m, 2H), 2.18–1.94 (m, 4H), 1.80 (d, J = 14.0
Hz, 9H), 1.61–1.12 (m, 14H). 13C NMR (75.5 MHz, CDCl3) δ
139.3 (s), 119.9 (q, JCF = 321.6 Hz), 114.3 (s), 33.9 (s), 30.5 (d,
JCP = 16.0 Hz), 29.4 (s), 29.3 (s), 29.2 (s), 29.2 (s), 29.0 (d, JCP
= 0.8 Hz), 23.3 (d, JCP = 52.1 Hz), 21.6 (d, JCP = 4.6 Hz), 7.9
(d, JCP = 54.4 Hz). 31P NMR (81 MHz, CDCl3) δ 27.6 (s). ESI/
MS(+) m/z calc. for [C14H30P]+ 229.2080, found 229.2085.
128.5 (s), 128.4 (s), 119.5 (q, JCF = 322.4 Hz), 30.3 (d, JCP
=
12.1 Hz), 30.0 (d, JCP = 15.1 Hz), 28.8 (d, JCP = 2.3 Hz), 28.6
(s), 28.1 (s), 26.7 (d, JCP = 11.1 Hz), 25.5 (d, JCP = 15.9 Hz),
23.3 (d, JCP = 15.6 Hz), 22.6 (d, JCP = 4.4 Hz), 20.5 (d, JCP
=
4.3 Hz), 17.8 (s), 17.6 (s), 17.1 (s), 17.0 (s), 13.2 (s). 31P NMR
(81 MHz, (CD3)2SO) δ 34.9 (s), −16.3 (s). ESI/MS(+) m/z calc.
for [C35H59P2]+ 541.4087, found 541.4085.
1
PFIL 3. The reaction provided a pale yellow liquid (87%). H
NMR (300 MHz, (CD3)2SO) δ 7.43–7.28 (m, 10H), 2.24–2.08
(m, 8H), 2.04 (t, J = 7.5 Hz, 2H), 1.55–1.15 (m, J = 54H), 0.85
(t, J = 7.6 Hz, 9H). 13C NMR (75.5 MHz, (CD3)2SO) δ 138.6
(d, JCP = 14.0 Hz), 132.3 (d, JCP = 18.4 Hz), 128.5–128.3 (m,
2C), 119.5 (q, JCF = 322.4 Hz), 31.2 (s), 30.4 (d, JCP = 12.8
Hz), 30.2–29.8 (m, 2C), 29.0–28.0 (m, 9C), 26.8 (d, J = 11.3
Hz), 25.5 (d, J = 16.0 Hz), 22.1 (s), 20.5 (d, J = 4.2 Hz), 17.4
(d, JCP = 47.6 Hz), 13.8 (s). 31P NMR (81.0 MHz, (CD3)2SO) δ
34.9 (s), −16.3 (s). ESI/MS(+) m/z calc. for [C47H83P2]+
709.5965, found 709.5989.
Tributyl(undec-10-enyl)phosphonium bis(trifluoromethylsulfonyl)-
imide. The reaction provided a yellow liquid (92%). H NMR
(300 MHz, CDCl3) δ 5.76 (ddt, J = 16.9, 10.2, 6.7 Hz, 1H),
5.04–4.76 (m, 2H), 2.19–1.86 (m, 12H), 1.58–1.18 (m, 24H),
0.92 (t, J = 6.9 Hz, 9H). 13C NMR (75.5 MHz, CDCl3) δ 139.1
1
(s), 119.9 (q, JCF = 321.6 Hz), 114.1 (s), 33.7 (s), 30.5 (d, JCP
=
14.7 Hz), 29.4–28.6 (m, 5C), 23.7 (d, JCP = 15.1 Hz), 23.4 (d,
JCP = 4.5 Hz), 21.4 (d, JCP = 4.5 Hz), 18.5 (d, JCP = 47.6 Hz),
18.3 (d, JCP = 47.6 Hz), 13.2 (s). 31P NMR (81.0 MHz, CDCl3)
δ 34.2 (s). ESI/MS(+) m/z calc. for [C23H48P]+ 355.3488, found
355.3492.
Trioctyl(undec-10-enyl)phosphonium bis(trifluoromethylsulfonyl)-
imide. The reaction was performed as outlined above expect
CH3CN : H2O (1 : 1) was employed as the solvent to yield a
yellow liquid (91%). 1H NMR (300 MHz, CDCl3) δ 5.76 (ddt, J
= 16.9, 10.2, 6.7 Hz, 1H), 5.01–4.81 (m, 2H), 2.16–1.90 (m,
10H), 1.54–1.18 (m, 50H), 0.84 (t, J = 7.5 Hz, 9H). 13C NMR
(75.5 MHz, CDCl3) δ 139.3 (s), 120.0 (q, JCF = 321.6 Hz),
114.3 (s), 33.9 (s), 31.8 (s), 30.6 (d, JCP = 14.7 Hz), 29.5–28.8
(m, 10H), 22.7 (s), 21.6 (d, JCP = 4.7 Hz), 18.7 (d, JCP = 46.8
Hz), 14.2 (s). 31P NMR (81 MHz, CDCl3) δ 34.1 (s). ESI/MS(+)
m/z calc. for [C35H72P]+ 523.5366, found 523.5361.
(c) Synthesis of phosphonium ionic liquids
Synthesis of [P4,4,4,14]NTf2 was previously reported by Del
Sesto et al. and involved the quaternization of tributylphosphine
with 1-chlorotetradecane, followed by a salt metathesis with
LiNTf2.74 To avoid possible halide contamination,75 [P4,4,4,14]-
NTf2 was synthesized from the quaternization of tetradecyl-
methanesulfonate with tributylphosphine to form tetradecyl-
tributylphosphonium methanesulfonate, [P4,4,4,14]OMs. The
intermediate [P4,4,4,14]OMs salt was subjected to an anion
exchange with LiNTf2 to yield tetradecyltributylphosphonium
bis(trifluoromethylsulfonyl)imide, [P4,4,4,14]NTf2. The exper-
imental procedure for the synthesis of [P4,4,4,14]NTf2 has been
previously reported by our group.65
Synthesis of (11-(diphenylphosphino)undecyl)trialkyl-phos-
phonium bis(trifluoromethylsulfonyl)imide (PFIL 1–3). Trialkyl-
(undec-10-enyl)phosphonium bis(trifluoromethyl-sulfonyl)imide
(3.20 mmol), diphenylphosphine (6.40 mmol) and 1,1′-azobis-
(cyclohexane-carbonitrile) (ABCN) (0.06 mmol) were combined
in a Schlenk flask. The mixture was stirred at 80 °C for 72 h,
during which time ABCN (0.30 mmol) was recharged twice.
The volatiles were removed in vacuo and the resulting oil was
washed with pentane (3 × 20 mL). The product was dried
in vacuo overnight at 60 °C.
(d) 31P NMR study
[Rh(COD)2][OTf] (0.05 mmol), PFIL (1, 2, 3 or 4 eq.) and
CD3CN (1.0 g) were combined and stirred at room temperature
for 30 min. 10 mg of OPOct3 was used as internal standard.
31P NMR and 1H NMR were recorded.
13538 | Dalton Trans., 2012, 41, 13533–13540
This journal is © The Royal Society of Chemistry 2012

View Article Online
16 B. Fell and G. Papadogianakis, J. Mol. Catal., 1991, 66, 143–154.
17 H. Ding, B. E. Hanson, T. Bartik and B. Bartik, Organometallics, 1994,
13, 3761–3763.
18 B. E. Hanson, H. Ding and C. W. Kohlpaintner, Catal. Today, 1998, 42,
421–429.
19 R. T. Smith, R. K. Ungar, L. J. Sanderson and M. C. Baird, Organometal-
lics, 1983, 2, 1138–1144.
20 H. Y. Fu, M. Li, J. Chen, R. M. Zhang, W. D. Jiang, M. L. Yuan,
H. Chen and X. J. Li, J. Mol. Catal. A: Chem., 2008, 292, 21–27.
21 E. Monflier, G. Fremy, Y. Castanet and A. Mortreux, Angew. Chem., Int.
Ed. Engl., 1995, 34, 2269–2271.
22 M. T. Reetz, J. Heterocycl. Chem., 1998, 35, 1065–1073.
23 M. T. Reetz, Catal. Today, 1998, 42, 399–411.
24 J. R. Anderson, E. M. Campi and W. R. Jackson, Catal. Lett., 1991, 9,
55–58.
25 E. Monflier, S. Tilloy, G. Fremy, Y. Castanet and A. Mortreux, Tetra-
hedron Lett., 1995, 36, 9481–9484.
26 S. Tilloy, F. Bertoux, A. Mortreux and E. Monflier, Catal. Today, 1999,
48, 245–253.
(e) Procedure for hydroformylation
[Rh(acac)(CO)2] (0.05 mmol), PFIL, alkene, and [P4,4,4,14]NTf2
(1.0 g) were combined and stirred at 50 °C for 15 min. After
evacuating and backfilling the vessel, the mixture was stirred at
100 °C for 3 h under a constant pressure of CO/H2 (1/1). The
mixture was cooled to rt and extracted with pentane (3 × 7 mL).
The organic phase was analyzed by gas chromatography employ-
ing dodecane as an internal standard for 1-octene and 1-decene,
while decane was employed as an internal standard for 1-do-
decene. Recycling experiments were performed once the IL
phase was dried in vacuo for at least 1 h under the reaction
conditions outline above. The IL phase was stored under an inert
atmosphere between catalytic cycles.
27 M. T. Reetz and S. R. Waldvogel, Angew. Chem., Int. Ed. Engl., 1997,
36, 865–867.
(f) Transmission electron microscopy
28 J. W. Rathke, R. J. Klingler and T. R. Krause, Organometallics, 1991, 10,
1350–1355.
29 S. Kainz, D. Koch, W. Baumann and W. Leitner, Angew. Chem., Int. Ed.
Engl., 1997, 36, 1628–1630.
30 G. Francio and W. Leitner, Chem. Commun., 1999, 1663–1664.
31 D. Koch and W. Leitner, J. Am. Chem. Soc., 1998, 120, 13398–13404.
32 S. Kainz and W. Leitner, Catal. Lett., 1998, 55, 223–225.
33 T. E. Kunene, P. B. Webb and D. J. Cole-Hamilton, Green Chem., 2011,
13, 1476–1481.
TEM of the IL phase was obtained on a Phillips CM 200 micro-
scope operating at an accelerating voltage of 200 kV with a
point resolution of 0.24 nm. Sample preparation included
dilution of 2 drops of the IL phase in ∼1.5 mL of MeCN, fol-
lowed by deposition on a carbon-coated copper grid (400 mesh)
at rt.
34 P. B. Webb, T. E. Kunene and D. J. Cole-Hamilton, Green Chem., 2005,
7, 373–379.
35 P. B. Webb, M. F. Sellin, T. E. Kunene, S. Williamson, A. M. Z. Slawin
and D. J. Cole-Hamilton, J. Am. Chem. Soc., 2003, 125, 15577–15588.
36 Y. Chauvin, L. Mussmann and H. Olivier, Angew. Chem., Int. Ed. Engl.,
1995, 34, 2698–2700.
37 F. Favre, H. Olivier-Bourbigou, D. Commereuc and L. Saussine, Chem.
Commun., 2001, 1360–1361.
38 N. Karodia, S. Guise, C. Newlands and J. A. Andersen, Chem. Commun.,
1998, 2341–2342.
39 J. F. Knifton, J. Mol. Catal., 1987, 43, 65–78.
40 M. Haumann and A. Riisager, Chem. Rev., 2008, 108, 1474–1497.
41 M. T. Reetz, G. Lohmer and R. Schwickardi, Angew. Chem., Int. Ed.,
1998, 37, 481–483.
42 R. P. J. Bronger, S. M. Silva, P. C. J. Kamer and P. W. N. M. van
Leeuwen, Chem. Commun., 2002, 3044–3045.
Acknowledgements
We thank Natural Science and Engineering Research Council of
Canada (NSERC), the Canada Foundation for Innovation (CFI),
the Canada Research Chairs (CRC), the Fonds de Recherche sur
la Nature et les Technologies (FQRNT), the Centre for Green
Chemistry and Catalysis (CGCC) and McGill University for
financial support. We also thank Nadim Saade (McGill Univer-
sity) for HRMS analysis as well as Monika Rak and Tomislav
Friscic (McGill University) for fruitful comments on the
manuscript.
43 T. J. Geldbach and P. J. Dyson, J. Am. Chem. Soc., 2004, 126, 8114–
8115.
44 J. J. Tindale and P. J. Ragogna, Can. J. Chem., 2010, 88, 27–34.
45 P. Wasserscheid, H. Waffenschmidt, P. Machnitzki, K. W. Kottsieper and
O. Stelzer, Chem. Commun., 2001, 451–452.
Notes and references
1 R. V. Chaudhari, B. M. Bhanage, R. M. Deshpande and H. Delmas,
Nature, 1995, 373, 501–503.
46 C. C. Brasse, U. Englert, A. Salzer, H. Waffenschmidt and
P. Wasserscheid, Organometallics, 2000, 19, 3818–3823.
47 M. F. Sellin, P. B. Webb and D. J. Cole-Hamilton, Chem. Commun.,
2001, 781–782.
48 J. Dupont, S. M. Silva and R. F. de Souza, Catal. Lett., 2001, 77,
131–133.
2 P. W. N. M. van Leeuwen, Rhodium Catalyzed Hydroformylation, Kluwer
Academic Publishers, New York, USA, 2000.
3 K. H. Shaughnessy, Chem. Rev., 2009, 109, 643–710.
4 I. Hablot, J. Jenck, G. Casamatta and H. Delmas, Chem. Eng. Sci., 1992,
47, 2689–2694.
5 P. Purwanto and H. Delmas, Catal. Today, 1995, 24, 135–140.
6 F. Monteil, R. Queau and P. Kalck, J. Organomet. Chem., 1994, 480,
177–184.
49 P. Wasserscheid, R. van Hal and A. Bosmann, Green Chem., 2002, 4,
400–404.
50 D. J. Brauer, K. W. Kottsieper, C. Liek, O. Stelzer, H. Waffenschmidt and
P. Wasserscheid, J. Organomet. Chem., 2001, 630, 177–184.
51 Q. R. Peng, C. X. Deng, Y. Yang, M. H. Dai and Y. Z. Yuan, React.
Kinet. Catal. Lett., 2007, 90, 53–60.
52 K. W. Kottsieper, O. Stelzer and P. Wasserscheid, J. Mol. Catal. A:
Chem., 2001, 175, 285–288.
7 H. Chen, Y. Z. Li, J. R. Chen, P. M. Cheng, Y. E. He and X. J. Li, J. Mol.
Catal. A: Chem., 1999, 149, 1–6.
8 B. Fell, C. Schobben and G. Papadogianakis, J. Mol. Catal. A: Chem.,
1995, 101, 179–186.
9 F. Van Vyve and A. Renken, Catal. Today, 1999, 48, 237–243.
10 Y. Q. Zhang, Z. S. Mao and T. Y. Chen, Catal. Today, 2002, 74, 23–35.
11 H. Chen, Y. Z. Li, J. R. Chen, P. M. Cheng and X. J. Li, Catal. Today,
2002, 74, 131–135.
53 Q. Lin, W. D. Jiang, H. Y. Fu, H. Chen and X. J. Li, Appl. Catal., A,
2007, 328, 83–87.
54 P. B. Webb and D. J. Cole-Hamilton, Chem. Commun., 2004, 612–613.
55 J. Dupont and J. D. Scholten, Chem. Soc. Rev., 2010, 39, 1780–1804.
56 N. Yan, C. X. Xiao and Y. Kou, Coord. Chem. Rev., 2010, 254, 1179–
1218.
57 K. L. Luska and A. Moores, ChemCatChem, 2012, DOI: 10.1002/
cctc.201100366.
12 A. Riisager and B. E. Hanson, J. Mol. Catal. A: Chem., 2002, 189, 195–
202.
13 S. L. Desset, D. J. Cole-Hamilton and D. F. Foster, Chem. Commun.,
2007, 1933–1935.
14 H. Y. Fu, M. Li, H. Chen and X. J. Li, J. Mol. Catal. A: Chem., 2006,
259, 156–160.
15 S. L. Desset, S. W. Reader and D. J. Cole-Hamilton, Green Chem., 2009,
11, 630–637.
58 H. Olivier-Bourbigou, L. Magna and D. Morvan, Appl. Catal., A, 2010,
373, 1–56.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 13533–13540 | 13539

View Article Online
59 Z. F. Fei, T. J. Geldbach, D. B. Zhao and P. J. Dyson, Chem.–Eur. J.,
2006, 12, 2123–2130.
69 C. J. Bradaric, A. Downard, C. Kennedy, A. J. Robertson and Y.
H. Zhou, Green Chem., 2003, 5, 143–152.
60 A. Banerjee, R. Theron and R. W. J. Scott, ChemSusChem, 2012, 5, 109–
116.
70 K. J. Fraser and D. R. MacFarlane, Aust. J. Chem., 2009, 62, 309–
321.
61 P. Dash, S. M. Miller and R. W. J. Scott, J. Mol. Catal. A: Chem., 2010,
329, 86–95.
71 D. J. M. Snelders, K. Kunna, C. Muller, D. Vogt, G. van Koten
and R. J. M. K. Gebbink, Tetrahedron: Asymmetry, 2010, 21,
1411–1420.
72 A. J. Bruss, M. A. Gelesky, G. Machado and J. Dupont, J. Mol. Catal. A:
Chem., 2006, 252, 212–218.
73 D. Pijper, E. Bulten, J. Smisterova, A. Wagenaar, D. Hoekstra,
J. B. F. N. Engberts and R. Hulst, Eur. J. Org. Chem., 2003, 4406–4412.
74 R. E. Del Sesto, C. Corley, A. Robertson and J. S. Wilkes, J. Organomet.
Chem., 2005, 690, 2536–2542.
62 P. Dash and R. W. J. Scott, Chem. Commun., 2009, 812–814.
63 P. Dash and R. W. J. Scott, Mater. Lett., 2011, 65, 7–9.
64 H. A. Kalviri and F. M. Kerton, Green Chem., 2011, 13, 681–686.
65 K. L. Luska and A. Moores, Green Chem., 2012, 14, 1736–1742.
66 K. L. Luska and A. Moores, Adv. Synth. Catal., 2011, 353, 3167–3177.
67 S. A. Stratton, K. L. Luska and A. Moores, Catal. Today, 2012, 183,
96–100.
68 R. R. Dykeman, N. Yan, R. Scopelliti and P. J. Dyson, Inorg. Chem.,
2011, 50, 717–719.
75 C. C. Cassol, G. Ebeling, B. Ferrera and J. Dupont, Adv. Synth. Catal.,
2006, 348, 243–248.
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