Aryl-based ferrocenyl phosphine ligands in the rhodium(I)-catalyzed hydroformylation of olefins

Article abstract of DOI:10.1016/j.molcata.2013.11.027

Ferrocenyl-based phosphine ligands [Fe{1-PPh₂(spacer)-2-NMe ₂CH₂C₅H₃}(C₅H ₅)] (spacer = 1,4-phenylene (rac-1), 1,3-phenylene (rac-2), 4,4′-biphenylene (rac-3), 2,5-thienylene (rac-4)) were applied in the rhodium(I)-catalyzed hydroformylation of various olefins (styrene, allylbenzene and 1-hexene) with higher chemo- and regioselectivity than a rhodium(I) catalyst precursor alone. The different σ-donor properties of rac-1-4 were elucidated by ³¹P{¹H} NMR spectroscopy of the corresponding selenides.

Full text of DOI:10.1016/j.molcata.2013.11.027

Journal of Molecular Catalysis A: Chemical 383–384 (2014) 137–142
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Aryl-based ferrocenyl phosphine ligands in the rhodium(I)-catalyzed
hydroformylation of olefins
Martyna Madalska, Peter Lönnecke, Evamarie Hey-Hawkins∗
Faculty of Chemistry and Mineralogy, Institute of Inorganic Chemistry, Universität Leipzig, Johannisallee 29, 04103 Leipzig, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Ferrocenyl-based phosphine ligands [Fe{1-PPh2(spacer)-2-NMe2CH2C5H3}(C5H5)] (spacer = 1,4-
phenylene (rac-1), 1,3-phenylene (rac-2), 4,4ꢀ-biphenylene (rac-3), 2,5-thienylene (rac-4)) were applied
in the rhodium(I)-catalyzed hydroformylation of various olefins (styrene, allylbenzene and 1-hexene)
with higher chemo- and regioselectivity than a rhodium(I) catalyst precursor alone. The different
Received 10 August 2013
Received in revised form
12 November 2013
Accepted 24 November 2013
Available online 2 December 2013
1
␴-donor properties of rac-1–4 were elucidated by 31P{ H} NMR spectroscopy of the corresponding
selenides.
© 2013 Elsevier B.V. All rights reserved.
Keywords:
Ferrocene
Phosphines
Hydroformylation
Catalysis
Rhodium
1. Introduction
their application in the rhodium(I)-catalyzed hydroformylation of
styrene, allylbenzene and 1-hexene. The studies presented here
Hydroformylation of olefins is one of the most important homo-
geneously catalyzed industrial processes and is currently the main
synthetic route for the production of linear C3–C18 aldehydes [1].
Consequently, hydroformylation is extensively studied and the
design of new ligands for improved rates and selectivity receives
much attention. Since Wilkinson reported the Rh-based catalyst
[RhCl(PPh3)3] [2], the development of new aryl phosphines became
a major focus of interest in synthetic chemistry.
illustrate the influence of the substituents on the phosphorus atom
on the activity and the selectivity.
2. Experimental
2.1. General considerations
Ferrocene plays a significant role as a backbone or substituent in
ancillary ligands [3]. A number of phosphorus-based substituents
can be introduced into ferrocene, and this allows the design of
ligands with various electronic and steric properties in order to
increase their efficiency in catalysis.
All manipulations were carried out by standard Schlenk tech-
niques under an atmosphere of dry, high-purity nitrogen. Toluene
and dichloromethane were dried with an MB SPS-800 Solvent
˚
Purification System and stored over activated 4 A molecular sieves.
Deuterated solvents for NMR spectroscopy were purchased from
Euriso-Top and Chemotrade GmbH. CDCl3 was distilled from P2O5
We have recently described the synthesis of ferrocenylaryl
(or
heteroaryl)
phosphines
[Fe{1-PPh2(spacer)-2-
˚
and stored over activated 4 A molecular sieves. C6D6 was dried with
NMe2CH2C5H3}(C5H5)]
(spacer = 1,4-phenylene
(rac-1),
sodium, filtered, and stored over potassium mirror. Compounds
rac-1 to rac-4 [4] and the rhodium complexes [{Rh(␮-Cl)(cod)}2]
[5], [Rh(acac)(CO)2] [6] and [Rh(cod)2]BF4 [7] were prepared
according to literature procedures. Selenium (␣-allotrope) and
PPh3 are commercially available and were used without further
purification. Styrene, allylbenzene, 1-hexene are commercially
available and were distilled before use.
1,3-phenylene (rac-2), 4,4ꢀ-biphenylene (rac-3), 2,5-thienylene
(rac-4); Scheme 1) which were prepared in a facile, straightfor-
ward, two-step sequence starting with a Negishi cross-coupling
between N,N-dimethylaminomethylferrocene and aryl halide
phosphine oxides, Br-spacer-P(O)Ph2, followed by reduction of
the phosphine oxide with trichlorosilane [4]. We now report
Spectra were recorded on a Bruker AVANCE DRX 400 NMR spec-
trometer at 400.13 (1H NMR), 161.98 (31P NMR). TMS was used as
internal standard for the 1H NMR spectra and spectra of other nuclei
were referenced to TMS on the ı scale [8].
∗
Corresponding author. Tel.: +49 341 9736151; fax: +49 341 9739319.
E-mail address: hey@uni-leipzig.de (E. Hey-Hawkins).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.11.027

138
M. Madalska et al. / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 137–142
Scheme 1. Reaction of rac-1–4 with [{Rh(␮-Cl)(cod)}2].
2.2. Synthesis
of storing at −30 ◦C, a few crystals suitable for single-crystal X-ray
diffraction appeared.
2.2.1. General synthesis of selenium derivatives rac-1(Se)–4(Se)
0.5 mmol (39.5 mg) of selenium (␣-allotrope) was added to
a solution of 0.5 mmol of compounds rac-1–4 (rac-1: 251.7 mg,
rac-2: 251.7 mg, rac-3: 289.6 mg, rac-4: 254.7 mg) in 10 mL of
dichloromethane. The mixture was refluxed for 4 h, cooled to r.t.
and filtered through filter paper. The solvent was removed and
rac-1(Se)–4(Se) were obtained as orange solids and characterized
2.3. Catalytic tests
Catalytic reactions were performed in an AMTEC SPR16 genera-
tion 2 parallel reactor, allowing for simultaneous screening of up to
sixteen reactions. Stock solutions of all reagents were prepared by
using Schlenk technique under an atmosphere of dry, high-purity
nitrogen. Reactors were purged with dry argon to remove traces
of air. Solutions (10 mL) of Rh catalyst precursor and ligand were
stirred for 30 min and then the reactors were pressurized with
CO/H2.
GC–MS analyses were performed with a GC–MS spectrometer
GCMS-QP2010 designed by Shimadzu. The chromatograms were
obtained in their graphical versions by using GCMS solution version
2.53SU1 with integrated NIST substance databank.
1
1
1
by 31P{ H} NMR spectroscopy only. 31P{ H} NMR data and JPSe
coupling constants are given in Table 1.
2.2.2. In situ synthesis of rhodium complexes rac-1(Rh)–4(Rh)
0.25 mmol of a toluene solution of [{Rh(␮-Cl)(cod)}2] (69.2 mg
in 2 mL toluene) was added to 0.5 mmol of rac-1–4 (rac-1: 251.7 mg,
rac-2: 251.7 mg, rac-3: 289.6 mg, rac-4: 254.7 mg) dissolved in dry
toluene (2 mL). The mixture was stirred for 30 min and the com-
1
pletion of the reaction was monitored by 31P{ H} NMR. After
filtration through filter paper and evaporation of the solvent the
2.4. X-ray structure determination
1
products were characterized by 31P{ H} NMR spectroscopy only.
Chemical shifts and 1JPRh coupling constants of the complexes rac-
1(Rh)–4(Rh) are listed in Table 2.
A
suitable crystal of rac-1(Rh) was mounted on a glass
needle with perfluoropolyalkyl ether and cooled in a nitrogen
stream. Crystallographic measurement was carried out with
In case of rac-1(Rh), the solid was dissolved in toluene (concen-
trated solution) and the solution layered with Et2O. After a few days
a
Gemini diffractometer (Agilent Technologies). Data were
Table 1
Table 2
Chemical shifts and 1JPSe coupling constants of rac-1(Se)–4(Se) and P(Se)Ph3.
31P{ H} NMR chemical shifts and coupling constants of the obtained rhodium
1
complexes.
1
Compound
ı
31P{ H} [ppm]
1JPSe [Hz]
1
Complex
ı
31P{ H} [ppm]
1JPRh [Hz]
rac-1(Se)
rac-2(Se)
rac-3(Se)
rac-4(Se)
P(Se)Ph3
34.8
35.4
34.7
21.7
35.2
724.4
728.7
726.0
731.6
731.5
rac-1(Rh)
rac-2(Rh)
rac-3(Rh)
rac-4(Rh)
30.2
30.8
30.1
20.2
151.3
150.8
151.1
152.7

M. Madalska et al. / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 137–142
139
collected by using monochromatic MoK␣ radiation (ꢀ = 71.073
pm) and ␻-scan rotation. Data reduction with CrysAlis Pro [9].
Structure solution with direct methods (SIR-92) [10]. Structure
refinement with SHELXL-97 [11]. H atoms were calculated on
idealized positions by using the riding model. Structure figures
were generated with ORTEP [12]. Crystal data and details of
data collection and refinement of rac-1(Rh): C39H42ClFeNPRh
0.5 toluene, M = 795.98, T = 130(2) K, monoclinic, space group
P21/c, a = 1019.01(5) pm, b = 3633.5(2) pm, c = 1100.93(6) pm,
ˇ = 116.573(7)◦, V = 3.6457(3) nm3, Z = 4, ꢁcalcd = 1.450 g/cm3,
ꢂ = 0.999 mm−1
,
F(0 0 0) = 1644,
ꢃrange = 2.80–26.37◦,
refl.
coll. = 28,662, ind. refl. = 7434, Goof = 1.052, R1(all data) = 0.0691,
wR2(all data) = 0.1057. CCDC 945286 (rac-1(Rh)) contains the sup-
plementary crystallographic data for this paper. This data can be
obtained free of charge from The Cambridge Crystallographic Data
Center via www.ccdc.cam.ac.uk/data request/cif.
Fig. 1. Molecular structure of rac-1(Rh) with thermal ellipsoids at 30% proba-
bility. Hydrogen atoms and toluene are omitted for clarity. Characteristic bond
lengths (pm) and bond angles (◦): Rh1–C32 210.6(4), Rh1–C33 210.9(4), Rh1–C37
221.1(4), Rh1–C36 221.4(4), Rh1–P1 230.3(1), Rh1–C11 236.2(1), P1–C17 182.1(4),
P1–C20 183.2(4), P1–C26 183.2(4), C33–Rh1–C37 92.9(2), C32–Rh1–C36 92.0(2),
C33–Rh1–C36 80.8(2), C37–Rh1–C36 35.5(2), C32–Rh1–P1 93.6(1), C33–Rh1–P1
94.6(1), C37–Rh1–P1 160.0(1), C36–Rh1–P1 164.43(1), C32–Rh1–C11 159.3(2),
C33–Rh1–C11 161.4(2), C37–Rh1–C11 89.9(1), C36–Rh1–C11 91.2(1), P1–Rh1–C11
88.8(4).
3. Results and discussion
3.1. Electronic properties of compounds rac-1–4
A convenient experimental method that evaluates the elec-
3.3. Catalytical tests
1
tronic properties of phosphine ligands is measuring the JPSe
1
coupling constants in the 31P{ H} NMR spectra of the correspond-
The rhodium(I) complexes rac-1(Rh)–4(Rh), formed in situ,
were employed in the hydroformylation of various olefins. A slight
excess of rac-1–4 was used to avoid reactions catalyzed by the
unmodified rhodium(I) species, which behaves as an unselective
catalyst [15]. The catalytic studies were performed with an AMTEC
SPR16 parallel reactor allowing simultaneous screening of up to
sixteen reactions. In all cases the product mixtures were analyzed
by GC–MS.
1
ing selenides [13]. The magnitude of JPSe is related to the degree
of s character of the lone pair of electrons on the phosphorus atom.
Lower s character indicates a stronger ꢄ donor. The stronger the
1
␴-donor character of the phosphorus atom, the smaller the JPSe
coupling constant [14].
Complexes rac-1–4 were treated with selenium (␣-allotrope)
in dry and degassed chloroform to give the selenium derivatives
[Fe{1-P(Se)Ph2(spacer)-2-NMe2CH2C5H3}(C5H5)]
(spacer = 1,4-
phenylene (rac-1(Se)), 1,3-phenylene (rac-2(Se)), 4,4ꢀ-biphenylene
(rac-3(Se)), 2,5-thienylene (rac-4(Se)), in quantitative yields
3.3.1. Hydroformylation of styrene
1
1
(according to 31P{ H} NMR spectroscopy). The JPSe coupling
constants (and the value for triphenylphosphine selenide obtained
in an analogous experiment and measured under the same
conditions) are summarized in Table 1.
The hydroformylation of styrene is one of the best-studied
processes and was therefore chosen for screening reactions with
[{Rh(␮-Cl)(cod)}2]/rac-1 as catalyst at various temperatures and
pressures and with various catalyst loadings (Table 3).
Full conversion of styrene was achieved under mild reaction
conditions (50 ◦C, 20 bar, entry 2); higher pressure (50 bar at 50 ◦C,
entry 3) led to higher regioselectivity. A change in catalyst loading
from 0.2 to 0.1 mol% resulted in lower conversion and a decrease in
regioselectivity (entry 5).
The hydroformylation of styrene in the presence of rhodium
catalysts leads mainly to the corresponding branched aldehyde, 2-
phenylpropanal [16]. However, catalysts are known which lead to
pure linear products (cationic palladium hydride species) [17].
A significant change in branched-to-linear aldehyde ratio was
also observed when the syngas pressure was decreased to 20 bar
and the temperature increased to 75 ◦C (entry 4). Under these
conditions, the rhodium(I) ꢅ3-allyl complex which leads to the
branched aldehyde is apparently unfavored [1].
Further studies were conducted under the optimal conditions
(50 ◦C, 50 bar, 0.1 mol% [Rh]), which led not only to the full conver-
sion but also to the highest regioselectivity. The regioselectivity of
ligands rac-1–4 (and PPh3 for comparison) in the hydroformylation
of styrene was tested in the presence of three rhodium com-
plexes as catalyst precursors: [{Rh(␮-Cl)(cod)}2], [Rh(acac)(CO)2]
and [Rh(cod)2]BF4. The ratios of branched-to-linear aldehyde are
given in Table 4.
1
According to the JPSe coupling constants the basic character
of the parent phosphine decreases in the order rac-1 > rac-
3 > rac-2 > PPh3 ≈ rac-4. A decrease in 1JPSe for compounds rac-1–3
compared to P(Se)Ph3 is noticeable and is the result of the electron-
rich ferrocenylaryl substituent. The lowest basicity is found for
rac-4, which has an electron-withdrawing 2,5-thienylene sub-
stituent on the phosphorus atom.
3.2. Coordination chemistry of compounds rac-1–4
Compounds rac-1–4 were treated with [{Rh(␮-Cl)(cod)}2] at
room temperature in toluene (ratio 2:1) to get insight into the
rhodium(I) complexes formed in situ and employed in hydroformy-
lation (vide infra; Scheme 1).
1
Analysis of the reaction mixture by 31P{ H} NMR spectroscopy
indicated quantitative formation of the rhodium monophosphine
1
complexes after 30 min. Chemical shifts and JPRh coupling con-
stants of the complexes rac-1(Rh)–4(Rh) are listed in Table 2.
The molecular structure of rac-1(Rh) was determined by
single-crystal X-ray diffraction. It crystallizes in the monoclinic
space group P21/c with four molecules in the unit cell. In
the unit cell, two equivalent disordered toluene molecules are
located on centers of inversion (0.5 0.5 0.5 and 0.5 0 0). The mon-
odentate phosphine ligand rac-1 cleaved the chloro bridges in
[{Rh(␮-Cl)(cod)}2] to give the heterobimetallic complex rac-1(Rh)
(Fig. 1).
Phosphine ligands that are good ␴ donors lower the positive par-
tial charge on rhodium(I) and thus disfavor ␤-hydride elimination
leading to linear aldehyde formation and increase the regioselec-
tivity [18]. Our experiments are well supported by these theoretical
considerations. With phosphine ligands rac-1–3 a higher b:l ratio

140
M. Madalska et al. / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 137–142
Table 3
Hydroformylation of styrene with [{Rh(␮-Cl)(cod)}2]/rac-1 as catalyst under various conditions.
O
[Rh]/L
CO/H2
+
Toluene
O
l
b
Entry
[Rh]/rac-1 [mol%]
T [◦C]
p (CO/H2) [bar]
b:la
Conversion [%]
1
2
3
4
5
0.1:0.22
0.1:0.22
0.1:0.22
0.1:0.22
0.05:0.11
50
50
50
75
50
10
20
50
20
20
5.6
18.6
24.0
1.7
65.2
100
100
100
86.2
6.1
Catalyst ([Rh]): [Rh(␮-Cl)(cod)]2; Styrene: 0.5 mmol; solvent: toluene; time: 17 h.
a
Branched-to-linear aldehyde ratio.
was obtained. The regioselectivity decreased with rac-4 and PPh3
as ligands.
Regio- and chemoselectivity depend on the used rhodium pre-
cursor. The best results were obtained when [Rh(cod)2]BF4 in a
metal:ligand ratio of 1:4.2 was employed.
It is well established that electron-withdrawing groups on phos-
phorus increase the activity of the derived rhodium complexes in
hydroformylation [19], as they lead to decreased back-bonding,
resulting in a weaker metal CO bond and thus in higher reaction
rates. This explains the higher turnover frequencies (TOF) calcu-
lated for [Rh(cod)2]BF4/rac-4 and [Rh(cod)2]BF4/PPh3 as catalysts
(Table 5).
In the case of allylbenzene, chemoselectivity is determined by
the relative reactivity of the branched alkyl–[Rh] species toward
carbonylation versus ␤- and ␣-hydride elimination [13c]. Under
the applied conditions, ␤-hydride elimination did not take place.
It is noteworthy that ligands rac-1–4 gave, in most cases (except
for [Rh(acac)(CO)2]/PPh3), slightly better chemoselectivity com-
pared to the unmodified rhodium complexes or the [Rh]/PPh3
system (Table 6).
Since the phosphine ligand is a good ␴ donor, its presence should
disfavor hydride transfer from the ␣-carbon atom to the rhodium
atom resulting in olefin isomerization. Thus, in most cases com-
pounds rac-1–3 exhibit slightly higher chemoselectivity than rac-4
and PPh3.
Furthermore, good ␴ donors increase the electron density on the
metal center and thus modify its nucleophilic properties. Rhodium
donates some of the partial charge to the coordinated hydride
and in this case, the hydride transfer to the ␥-carbon atom occurs
more easily. Thus, the regioselectivity of the reaction decreases.
Moreover, higher nucleophilicity of the hydride in the intermediate
trigonal-bipyramidal rhodium complex seems to favor equatorial
coordination of allylbenzene to the metal in a way favoring H− addi-
tion to the ␥-carbon atom (since the substituent on the C C bond
is orientated to the opposite side of the hydride ligand site) [21d].
This could be seen in the reaction performed in the presence of
the ionic rhodium precursor [Rh(cod)2]+ with four equivalents of
phosphine, in which the regioselectivity was lower with rac-1–3
compared to rac-4.
3.3.2. Hydroformylation of allylbenzene
Even though the hydroformylation of aromatic vinyl com-
pounds has been widely studied [20], fewer studies were conducted
on the hydroformylation of allylbenzenes and propenylbenzenes
[21]. This is surprising, since aldehydes derived from substituted
allylbenzenes and propenylbenzenes show biological and phy-
tosanitary activities and are useful in the flavor, perfume and
pharmaceutical industry [22].
Hydroformylation of allylbenzene led mainly to two isomeric
aldehydes, namely 2-methyl-3-phenylpropanal and 4-phenyl-
butanal, although in every case a small amount of the isomerization
product (1-phenylpropene) was detected [23].
The results are summarized in Table 6. In all cases, full conver-
sion of allylbenzene was observed and no other products besides
the three stated above were detected.
Table 4
Hydroformylation of styrene under optimal conditions with various rhodium(I)
complexes as catalyst precursors.
The turnover frequency for [Rh(cod)2]BF4/rac-4 is also highest
here, as was observed for the hydroformylation of styrene (Table 5).
Complex
b:l
rac-1
rac-2
rac-3
rac-4
PPh3
[{Rh(␮-Cl)(cod)}2]
[Rh(acac)(CO)2]
[Rh(cod)2]BF4
24.0
31.2
26.3
29.8
28.0
27.5
25.9
36.7
29.2
19.7
25.0
25.5
6.6
25.9
12.8
3.3.3. Hydroformylation of 1-hexene
Even though all types of alkenes can be hydroformylated, they
undergo the process with different efficiency. The most reactive
are linear olefins (with various chain lengths) with terminal dou-
ble bonds [13c]. Similar to the case of allylbenzene, both isomeric
aldehydes are obtained in very similar amounts (Table 7) [1].
Reactions with 1-hexene occur in agreement with theoretical
considerations [1]. From the performed studies it can be concluded
that the ␴-donor properties and the number of phosphine ligands
coordinated to the catalytically active rhodium species play the
main role in the regioselectivity of the reaction. Increasing the con-
centration of phosphine with respect to [Rh(cod)2]BF4 ([Rh]:L ratio
1:4.2) gave better regioselectivity, and the less basic ligands (rac-4
and PPh3) led to a higher percentage of linear product. Hydrogena-
tion products were below 2.5%.
[Rh]:ligand = 1:2.2; catalyst loading: 0.1 mol%; styrene: 0.5 mmol; p = 50 bar;
T = 50 ◦C; solvent: toluene; time: 17 h.
Table 5
Turnover frequencies (TOF) in the hydroformylation of styrene, allylbenzene and
1-hexene with [Rh(cod)2]BF4 as rhodium source.
rac-1
rac-2
rac-3
rac-4
PPh3
Styrene
Allylbenzene
1-Hexene
302.7
135.6
221.7
313.0
124.5
202.6
285.4
152.3
230.5
391.9
376.2
604.0
328.7
211.3
471.2
TOF = (mol of converted substrate) × (mol of catalyst)−1 h−1
.
[Rh]:ligand ratio = 1:2.2; catalyst loading: 0.1 mol%; solvent: toluene; p = 50 bar;
T = 50 ◦C; time:17 h. Styrene, allylbenzene or 1-hexene: 0.5 mmol.

M. Madalska et al. / Journal of Molecular Catalysis A: Chemical 383–384 (2014) 137–142
141
Table 6
Hydroformylation of allylbenzene with various rhodium(I) complexes and rac-1 to rac-4 and PPh3 as catalyst.
[Rh]/L
O
CO/H2
+
+
Toluene
O
l
b
Precursor
[Rh]/L ratio
Ligand
Product distribution [%]
b
l
Isomeric olefin
[{Rh(␮-Cl)(cod)}2]
1:2.2
1:2.2
1:4.2
rac-1
rac-2
rac-3
rac-4
PPh3
none
46.2
46.1
45.3
45.1
43.1
46.5
51.1
51.5
52.7
51.8
49.2
47.6
2.7
2.4
2.0
3.1
7.7
5.9
[Rh(acac)(CO)2]
[Rh(cod)2]BF4
rac-1
rac-2
rac-3
rac-4
PPh3
none
45.6
44.9
43.8
43.5
33.5
49.7
50.6
50.7
52.5
52.1
53.2
42.4
3.8
4.4
3.7
4.4
13.3
7.9
rac-1
rac-2
rac-3
rac-4
PPh3
none
46.7
45.8
43.5
40.2
45.5
43.4
51.3
51.3
53.7
59.0
53.9
49.4
2.0
2.9
2.8
0.8
0.6
7.2
Catalyst loading: 0.1 mol%; allylbenzene: 0.5 mmol; solvent: toluene; p = 50 bar; T = 50 ◦C; time: 17 h.
Table 7
Rhodium-catalyzed hydroformylation of 1-hexene.
[Rh]/L
CO/H2
O
+
Toluene
O
l
b
Complex
l:ba
rac-1
rac-2
rac-3
rac-4
PPh3
none
[{Rh(␮-Cl)(cod)}2]
[Rh(acac)(CO)2]
[Rh(cod)2]BF4
1.2
1.2
1.1
1.4
1.1
1.1
1.1
1.6
1.1
1.3
1.3
1.7
1.2
1.3
1.4
1.8
1.2
1.3
1.6
1.8
1.1
1.3
1.1
1.1
b
[Rh(cod)2]BF4
a Linear-to-branched aldehyde ratio. [Rh]:ligand ratio = 1:2.2 (except in b [Rh]/ligand ratio 1:4.2); catalyst loading: 0.1 mol%; 1-hexene: 0.5 mmol; solvent: toluene; p = 50 bar;
T = 50 ◦C; time: 17 h.
Turnover frequencies (TOF) follow the same trend as observed
for styrene and allylbenzene (Table 5).
080937615). Support from the Graduate School BuildMoNa (funded
by the Deutsche Forschungsgemeinschaft) and the EU COST Action
CM0802 PhoSciNet is gratefully acknowledged. We thank Cheme-
tall GmbH and BASF SE for generous donations of chemicals.
4. Conclusion
Compounds rac-1–4 influence the rhodium(I)-catalyzed hydro-
formylation reaction of various olefins (styrene, allylbenzene and
1-hexene), leading to higher chemo- and regioselectivity com-
pared with a rhodium(I) catalyst precursor alone. The different
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