Hydroformylation of 1-hexene and propene with in situ formed rhodium phosphine catalysts

Article abstract of DOI:10.1016/S1381-1169(01)00038-3

A series of triphenylphosphines modified with different heteroatom groups (-SCH₃, -N(CH₃)₂, -OCH₃, -CF₃) in ortho or para position of the phenyl ring was synthesized, and their catalytic behavior in the rhodium catalyzed hydroformylation of 1-hexene (80°C, 15 bar) and propylene (100°C, 10 bar) were studied. The effect of in situ introduced ligands varied with reacting alkene. In the case of 1-hexene, the differences in activity and in chemo- and regioselectivity obtained with various ligands were minor. With propylene, the heterodonor bidentate ligands suppressed the hydroformylation reaction. A similarity between 1-hexene and propylene was observed with CF₃ modified ligands. Isomerization was the main reaction in 1-hexene hydroformylation. The strong σ-donor ligands yielded higher hydroformylation activity than the less basic ligands. In the case of propylene, 1,4-bis(diphenylphosphino)butane and (o-thiomethylphenyl)bis(1-naphthyl)phosphine favored the formation of n-butanal.

Full text of DOI:10.1016/S1381-1169(01)00038-3

Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
Hydroformylation of 1-hexene and propene with in
situ formed rhodium phosphine catalysts
Pekka Suomalainena, Heidi K. Reiniusb, Helena Riihimäkic, Riitta H. Laitinenc,
Sirpa Jääskeläinena, Matti Haukkaa, Jouni T. Pursiainenc,
Tapani A. Pakkanena,∗, A.O.I. Krauseb
a
Department of Chemistry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland
b
Department of Chemical Technology, Helsinki University of Technology, P.O. Box 6100, FIN-02015 HUT, Finland
c
Department of Chemistry, University of Oulu, P.O. Box 3000, FIN-90401 Oulu, Finland
Received 4 September 2000; received in revised form 7 December 2000; accepted 7 December 2000
Abstract
A series of triphenylphosphines modified with different heteroatom groups (–SCH3, –N(CH3)2, –OCH3, –CF3) in ortho
or para position of the phenyl ring(s) were synthesised and tested for their catalytic behaviour in the rhodium catalysed
hydroformylation of 1-hexene (80◦C, 15 bar) and propene (100◦C, 10 bar). Hydroformylation results for 1-hexene and propene
differed markedly. With 1-hexene, the differences in activity and in chemo- and regioselectivity obtained with the various
ligands were minor. Among the heterodonor ligands, the strong ␴-donor ligands yielded higher hydroformylation activity
than the less basic ligands. In the case of propene, heterodonor bidentate ligands suppressed the hydroformylation reaction.
In addition, 1,4-bis(diphenylphosphino)butane and (o-thiomethylphenyl)bis(1-naphthyl)phosphine favoured the formation
of n-butanal. Only the –CF3 modified ligands behaved similarly with the two alkenes. The influence of the structure of
the ligand in hydroformylation was studied by using molecular modelling methods. The steric size of the ab initio energy
minimised free ligand structures was evaluated by Tolman’s cone angle method. Co-ordination properties of –CF3 group
modified phosphines were studied in reaction with Rh2(CO)4Cl2, and the structure of Rh(CO)Cl(P(o-CF3C6H4)Ph2)2 (1) was
determined crystallographically. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Hydroformylation; Rhodium; Phosphine ligands; Propene; 1-Hexene
1. Introduction
the influence of different phosphorus ligands on hy-
droformylation reaction has been studied for decades,
a satisfactory explanation for the consistent correla-
tion between catalytic activity and the geometry of
the ligands has yet to be provided [1]. Aldehydic
regioselectivity is more predictable, and clear trends
are obtained at least within a small set of structurally
similar ligands. Perhaps as the best example, the size
of the natural biting angle of the diphosphine lig-
and, i.e. the P–M–P angle, can be used as a tool to
steer the product distribution of the hydroformylation
Geometrical arrangement of ligands around the
metal centre plays an important role in homogeneous
organometallic catalysis. The selectivity of catalytic
reactions can be modified through tailoring of the cat-
alyst sphere by sophisticated ligand design. Although
∗ Corresponding author. Tel.: +358-13-2513345;
fax: +358-13-2513344.
E-mail address: tapani.pakkanen@joensuu.fi (T.A. Pakkanen).
1381-1169/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(01)00038-3

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P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
reaction [2,3]. Regioselective control to branched
product has been reported in the hydroformylation
of 3,3,3-trifluoropropene [4] and some functional
alkenes [5,6], but in these approaches, tailoring was
assisted by substituting one end of the alkene with a
fluoro, phosphine or silyl group.
also strongly dependent on the nature of the substrate.
Trzeciak and Ziolkowski [10] showed that the gen-
eral tendencies observed for the hydroformylation of
1-hexene with a phosphite modified rhodium catalyst
also apply to propene, but that there were essential
differences in the n:i ratios.
We have recently shown [7] that in the hydro-
formylation of methyl methacrylate (MMA) regiose-
lective control to branched product can be obtained
through chelation control with an in situ formed
Here we report the effects of phosphine ligands
differing in stereoelectronic properties on the hydro-
formylation of propene and 1-hexene. Although, dif-
ferent precursors and reaction conditions were applied
for the two alkenes their mutual comparison is reason-
able as the effects of different ligands were examined
relative to PPh3 modified reaction. Furthermore, the
use of different Rh-species were sought to be justified,
as the formation of actual catalyst species, trigonal
bipyramidal rhodium carbonyl hydride, can be formed
from various rhodium precursors.
The phosphine ligands were triphenylphosphine-
type ligands modified in ortho or para position with
different heterodonor groups (–SCH3, –N(CH3)2,
–OCH3 or –CF3). In addition, the phenyl ring was
replaced with a naphthyl or anthracene group to in-
crease the steric stress. Geometries of the free ligands
were calculated by ab initio Hartree–Fock method
and the sizes of the geometry optimised free ligand
structures were measured with Tolman’s cone angle
method [11]. Complexation studies with rhodium
and the ligands containing (–CF3) groups were also
carried out.
(o-thiomethylphenyl)diphenylphosphine
rhodium
complex. We also showed [8] that the complex for-
mation of various heterodonor phosphine ligands with
rhodium differed depending on the ␴-donor group. It
has further been argued that the alkene itself — espe-
cially if polar like MMA or if able to isomerise simul-
taneously — might affect the regioselective control.
In the case of 1-hexene hydroformylation (Fig. 1),
isomerisation is dominant, yielding less reactive 2-
and 3-hexenes [9]. Regardless of the preference for
either normal product (1-heptanal) or the branched
products (2-methylhexanal or 2-ethylpentanal), the
isomerising capability of the catalyst needs to be
clarified. If the normal product is desired the catalyst
should not exhibit isomerising tendency, whereas if
branched products are desired the catalyst should first
isomerise the alkene and thereafter be able to effec-
tively hydroformylate the isomers. Regioselectivity is
2. Experimental
2.1. Ligands
2.1.1. General comments
The commercial ligands used in the experiments
were triphenylphosphine (PPh3, Fluka, ∼99%) and
1,2-bis(diphenylphosphino)ethane (DPPE, Fluka,
98%) and 1,4-bis(diphenylphosphino)butane (DPPB,
Fluka, >97%). The other ligands were prepared
by literature methods (Table 1), except for the
CF3-substituted ligands (o-trifluoromethylphenyl)
diphenylphosphine (oCF3P), (p-trifluoromethylphenyl)
diphenylphosphine (pCF3P), tris(o-trifluoromethyl-
phenyl)phosphine (o(CF3)3P) and tris(p-trifluorome-
thylphenyl)phosphine (p(CF3)3P), which were
prepared by modified literature methods [12,13].
Commercially available reagents were used without
Fig. 1. Hydroformylation of 1-hexene.

P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
69
Table 1
Ligands used in the hydroformylation experiments
Abbreviation
Name
Reference
[30]
oSP
pSP
oNP
(o-Thiomethylphenyl)diphenylphosphine
(p-Thiomethylphenyl)diphenylphosphine
[30]
[31]
(o-N,N-dimethylaminophenyl)diphenylphosphine
oSeP
oOP
(o-Methylselenophenyl)diphenylphosphine
(o-Methoxyphenyl)diphenylphosphine
[32]
[30]
oSP(naf)2
(o-Thiomethylphenyl)bis(1-naphthyl)phosphine
[33]
oOP(naf)2
oCF3P
(o-Methoxyphenyl)bis(1-naphthyl)phosphine
(o-Trifluoromethylphenyl)diphenylphosphine
[33]
[12]
pCF3P
(p-Trifluoromethylphenyl)diphenylphosphine
Tris(o-trifluoromethylphenyl)phosphine
[12]
[12]
o(CF3)3P

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P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
Table 1 (Continued)
Abbreviation
Name
Reference
[12]
p(CF3)3P
Tris(p-trifluoromethylphenyl)phosphine
Bis(9-anthracenyl)phenylphosphine
(9-Anthracenyl)diphenylphosphine
PPh(anthr)2
PPh2(anthr)
[34]
[34]
further purification. Diethyl ether (Lab Scan) was
distilled from sodium/benzophenone ketyl under ni-
trogen before use. All ligand syntheses were carried
out with standard Schlenk techniques under nitrogen
or an argon atmosphere.
at −10 to 0◦C for 1.5 h. After slowly warming to
room temperature, the layers were separated and the
solvent was removed in vacuo.
2.1.4. (o-Trifluoromethylphenyl)diphenylphosphine
(oCF3P)
2.1.2. Spectroscopy
When a solution of n-butyllithium (10 ml, 25 mmol)
in diethyl ether was added to a solution of 2-bromoben-
zotrifluoride (5.63 g, 25 mmol) in diethyl ether, the
reaction mixture turned to red. Addition of a solu-
tion of diphenylchlorophosphine (5.52 g, 25 mmol)
in diethyl ether coloured the reaction mixture
brown. The yield of the brown solid product was
96.9% (8.00 g, 24.2 mmol). 1H NMR (200 MHz,
CDCl3): δ 7.19–7.29 (m, 7H, H6, H8 and H10),
7.30–7.37 (m, 4H, H9), 7.41–7.47 (m, 2H, H4
and H5), 7.72–7.80 (m, 1H, H3). 13C–{1H} NMR
Characterisation of the ligands was based mainly
1
on H, 13C–{1H} and 31P–{1H} NMR spectroscopy.
NMR spectra were recorded on Bruker AM200
and DPX400 spectrometers at room temperature
in CDCl3. 1H NMR: reference SiMe4. 13C–{1H}
NMR: CDCl3 set to 77.0 ppm. 31P–{1H} NMR:
external standard 85% H3PO4. Two-dimensional
HSQC NMR spectra were also measured. Exact
mass peaks were determined on a Micromass LCT,
ESI+.
1
(100 MHz, CDCl3): 124.34 (q, JC–F = 275.7 Hz,
3
2.1.3. Synthetic procedure for CF3-modified ligands
To 2-bromobenzotrifluoride (Aldrich, 99%) or
4-bromobenzotrifluoride (Aldrich, 99%) in 30 ml
diethyl ether was added n-butyllithium (Aldrich,
2.5 M solution in hexane) in 20 ml diethyl ether
at −10 to 0◦C (ice bath). The mixture was stirred
for 1.5 h at −10 to 0◦C, after which a solution of
diphenylchlorophosphane (Aldrich, 95%) or phos-
phorus trichloride (Merck, 99%) in 30 ml of diethyl
ether was added drop-wise. The mixture was stirred
1C, C11), 126.40 (s, 1C, C3), 128.56 (d, JC–P
=
6.3 Hz, 4C, C9), 128.83 (s, 2C, C10), 128.94 (s,
2
1C, C5), 131.58 (s, 1C, C4), 133.68 (d, JC–P
=
19.1 Hz, 4C, C8), 134.94 (d, JC–P = 29.9 Hz,
1
1C, C1), 136.08 (s, 1C, C6), 134.00–137.00 (m,
2C, C1 and C2), 136.44 (d, JC–P = 11.3 Hz, 2C,
1
C7). 31P–{1H} NMR (161 MHz, CDCl3): −9.35
4
(q, JP–F = 53.3 Hz, 1P). TOF MS ES+ calc.
for (M + Na)+ (C19H14F3NaP) 353.0683, found
353.0717.

P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
71
2.1.5. Tris(o-trifluoromethylphenyl)phosphine
(o(CF3)3P)
ands was estimated by Tolman’s cone angle method.
Metal(dummy atom)-phosphorus distance 2.28 Å and
the van der Waals radii of hydrogen 1.2 Å were used
in cone angle determinations.
When a solution of n-butyllithium (10 ml, 25 mmol)
in diethyl ether was added to a solution of 2-bromoben-
zotrifluoride (5.63 g, 25 mmol) in diethyl ether, the
reaction mixture turned orange. Addition of a solution
of phosphorus trichloride (1.14 g, 8.3 mmol) in diethyl
ether coloured the reaction mixture to brown. The
yield of the brown solid product was 92.3% (3.59 g,
7.69 mmol). 1H NMR (400 MHz, CDCl3): δ 6.93 (dd,
2.2. Complex synthesis
Synthetic reactions were carried out using standard
Schlenk techniques in nitrogen atmosphere. The sol-
vents, methanol and toluene (p.a. grade), were deoxy-
genated with nitrogen before use. Rh2(CO)4Cl2 was
prepared according to a literature method [16]. NMR
spectra were recorded on a Bruker AM250 spectrome-
ter. 31P NMR spectra were referenced to 85% H3PO4.
Elemental analyses were recorded on a Perkin-Elmer
2400 Series II CHNS/O analyser.
3
3JH–H = 7.4 Hz, JH–P = 3.4 Hz, 3H, H6), 7.43 (t,
3
3JH–H = 7.4 Hz, 3H, H4), 7.49 (t, JH–H = 7.4 Hz,
3H, H5), 7.75–7.80 (m, 3H, H3). 13C–{1H} NMR
1
(100 MHz, CDCl3): 124.06 (q, JC–F = 275.3 Hz,
3C, C11), 127.03 (s, 3C, C3), 129.32 (s, 3C, C5),
2
131.63 (s, 3C, C4), 134.27 (q, JC–F = 29.8 Hz, 3C,
1
C2), 134.84 (d, JC–P = 29.8 Hz, 3C, C1), 136.02
(s, 3C, C6). 31P–{1H} NMR (161 MHz, CDCl3):
−15.60 (q, 4JP–F = 55.3 Hz, 1P). TOF MS ES+ calc.
for (M + Na)+ (C21H12F9NaP) 489.0431, found
489.0445.
2.2.1. Preparation of Rh(CO)Cl(oCF3P)2 (1)
Rh2(CO)4Cl2 (25 mg, 0.064 mol) and oCF3P
(42 mg, 0.127 mol) were dissolved in methanol in sep-
arate flasks. The ligand solution was added drop-wise
to the solution of the rhodium compound. The yellow
precipitate was filtered, washed with methanol and
dried quickly under vacuum. Yellow crystals for X-ray
studies were grown from CH2Cl2. Elemental analysis
for 1 C39H28P2F6OClRh: calc. % C, 56.65; H, 3.41;
2.1.6. Tris(p-trifluoromethylphenyl)phosphine
(p(CF3)3P)
When
a solution of n-butyllithium (9.4 ml,
23.3 mmol) in diethyl ether was added to a solution
of 4-bromobenzotrifluoride (5.25 g, 23.3 mmol) in
diethyl ether, the reaction mixture turned red. Addi-
tion of a solution of phosphorus trichloride (1.07 g,
7.8 mmol) in diethyl ether caused the reaction mixture
to turn orange. When the orange oily product was
washed with hexane and cooled (−20◦C) an orange
solid product precipitated. The yield of the product
found % C, 56.40; H, 3.40. IR: υ(CO) = 1977 cm−1
.
31P NMR: δ = 37.5 ppm, J(Rh–P) = 136 Hz.
2.2.2. Preparation of [Rh(CO)Cl(p(CF3)3P)]2 (2)
A similar procedure as for 1 was used for 2.
Starting form Rh2(CO)4Cl2 (25 mg, 0.064 mol) and
p(CF3)3P (60 mg, 0.129 mol). Elemental analysis for
2 C44H24P2F18O2Cl2Rh2: calc. % C, 41.77; H, 1.91;
1
was 67.6% (2.45 g, 5.25 mmol). H NMR (400 MHz,
found % C, 41.70; H, 1.79. IR: υ(CO) = 1999 cm−1
.
3
CDCl3): δ 7.41 (t, JH–H = 7.8 Hz, 6H, H2), 7.63
31P NMR: δ = 46.9 ppm, J(Rh–P) = 170 Hz.
3
(d, JH–H = 8.0 Hz, 6H, H3). 13C–{1H} NMR
(100 MHz, CDCl3): 123.82 (q, 1JC–F = 272.4 Hz, 3C,
2
C9), 125.64 (s, 6C, C3), 131.55 (q, JC–F = 32.7 Hz,
2.3. X-ray crystallography
3C, C4), 134.96 (d, 3JC–P = 30.8 Hz, 6C, C2), 140.26
1
(d, JC–P = 14.1 Hz, 3C, C1). 31P–{1H} NMR
X-ray diffraction data were collected with a Non-
ius KappaCCD diffractometer using Mo K␣ radiation
(λ = 0.71073 Å). Denzo and Scalepack [17] programs
were used for cell refinements and data reduction.
The structure was solved by direct methods using the
SIR97 [18] program with the WinGX [19] graphical
user interface. The structure refinement was carried
out with SHELXL97 [20]. A multi-scan absorption
correction, based on equivalent reflections (XPERP in
(161 MHz, CDCl3): −4.29 (s). TOF MS ES+ calc. for
(M + H)+ (C21H13F9P) 467.0611, found 467.0639.
2.1.7. Computational details
Gaussian 94 [14] and Sybyl [15] programs were
used in modelling. Geometric optimisations at the
Hartree–Fock level were done using the 3-21G∗ basis
set. The steric size of the prepared phosphine lig-

72
P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
Table 2
Table 3
Crystallographic data for 1
Interatomic bond distances and angles for 1
Empirical formula
Molecular weight
Crystal size (mm)
Crystal system
Space group
λ (Å)
C39H28ClF6OP2Rh
826.91
0.30 × 0.20 × 0.10
Monoclinic
P21/n
Atoms
Bond distances (Å)
Rh(1)–C(21)
Rh(1)–P(1)
Rh(1)–Cl(1)
O(21)–C(21)
P(1)–C(13)
P(1)–C(7)
P(1)–C(1)
C(2)–C(19)
F(1)–C(19)
1.722(8)
2.332(6)
2.408(3)
1.148(9)
1.821(3)
1.826(3)
1.851(3)
1.505(4)
1.334(3)
0.71073
a (Å)
b (Å)
11.4595(4)
11.1631(5)
13.8105(5)
100.965(2)
1734.43(12)
2
1.583
0.726
120
2.36–26.03
3278
2672
226
0.0327
c (Å)
β (◦)
V (Å3)
Z
C(21)–Rh(1)–P(1)
P(1)–Rh(1)–Cl(1)
Cl(1)–C(21)–Rh(1)
O(21)–C(21)–Rh(1)
C(13)–P(1)–Rh(1)
C(7)–P(1)–Rh(1)
C(1)–P(1)–Rh(1)
C(21)–Cl(1)–Rh(1)
C(13)–P(1)–C(7)
C(13)–P(1)–C(1)
C(7)–P(1)–C(1)
87.6(2)
86.97(5)
176.2(8)
176.3(6)
109.10(9)
123.23(9)
112.82(8)
2.7(6)
102.21(1)
103.76(1)
103.67(1)
112.5(2)
106.3(2)
Dcalc (g/cm3)
µ (mm−1
T (◦C)
)
θ range (◦)
No. of unique reflections
No. of observed dataa
No. of parameters
R1
wR2
0.0662
0.698 and −0.451
Largest different peak and hole (e/Å3)
F(1)–C(19)–C(2)
F(1)–C(19)–F(3)
a I > 2σ.
SHELXTL, version 5.1) [21], was applied to the data
(T min/T max = 0.2271/0.2764). CO and Cl ligands
were disordered in two-positions with equal popula-
tion parameter 0.5. This type of disorder is typical for
trans-triphenylphosphines (PPh)–Rh(CO)Cl–(PPh).
Because of disorder, C(21), O(21) and Cl(1) were
refined only isotropically. All hydrogens were con-
strained to ride on their parent atom. Crystallographic
data are summarised in Table 2 and selected bond
lengths and angles are given in Table 3. Crystallo-
graphic data (excluding structure factors) for the struc-
ture reported in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supple-
mentary publication no. CCDC 145349. Copies of the
data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK. 1
The experiments were done in semi-batch mode. The
rhodium precursor was Rh(NO3)3·2H2O (Fluka). In a
typical experiment, the autoclave was charged with the
rhodium precursor (0.02 mmol calculated as rhodium),
acetone (310 mmol, Merck, 99.5%), internal standards
decane (7 mmol, Fluka, >98%) and hexane (12 mmol,
Riedel de Häen, >99%), and the phosphine. If not oth-
erwise stated, the ligand to rhodium ratio was 10:1 on
molar basis. The system was first flushed with nitro-
gen, pressurised with propene (2 bar, Aga, >99.8%),
heated to the reaction temperature (100◦C) with con-
tinuous stirring, and then pressurised to the reaction
pressure (10 bar) with a 1:1 molar ratio of H2 and CO
(MG, 99.997%). At least nine samples were taken for
analysis in each experiment: one of the fresh reaction
mixture, one immediately after pressurising with H2
and CO, which was considered as the starting point of
the reaction, six during the experiment and one after
the reaction.
2.4. Hydroformylation of propene
Propene hydroformylation experiments were car-
ried out in a 250 ml autoclave (Berghof) equipped
with a sampling system and a 230 ml Teflon liner.
2.5. Hydroformylation of 1-hexene
1 Fax: +44-1223-336-033; e-mail address: deposit@ccdc.
1-Hexene hydroformylation reactions were con-
ducted in a 100 ml autoclave (Berghof) with 60 ml
camac.uk.

P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
73
Teflon liner. The experiments were carried out in
3. Results
batch mode with rhodium precursor Rh4(CO)12. The
reactor was charged under a nitrogen purge with sub-
strate, rhodium precursor, ligand, internal standard,
cyclohexane and solvent (toluene). The autoclave was
then sealed and pressurised using a 1:1 mixture of
H2 and CO (MG, 99.997%) to 15 bar and heated to
80◦C. After 6 h the autoclave was cooled and brought
to atmospheric pressure.
The reproducibility of the system was confirmed
by accomplishing the tests twice. A disposable inner
Teflon liner was used to avoid the accumulation of
rhodium on the reactor walls. Furthermore, the pu-
rity of the system was checked with blank runs be-
fore each experiment. The products were analysed
with a Hewlett-Packard 5890 GC equipped with a
capillary column (HP-1, 1.0 ␮m × 0.32 mm × 60 m)
and a flame-ionisation detector. Products were quan-
tified by the internal standard method. In addition,
the aldehydes that formed were identified by GC–MS
analysis.
In the case of 1-hexene hydroformylation, the var-
ious catalysts were compared at equal conversion
levels. With propene, conversion dependence was
more straightforward: the isomerisation reforms the
substrate and no hydrogenation products were de-
tected. As Fig. 2 shows, in the hydroformylation of
propene, the selectivity of the reaction did not de-
pend on the conversion level and thus the comparison
of the catalysts is valid even at different conversion
levels.
3.1. Properties of the ligands
The calculated and measured properties of the lig-
ands are shown in Tables 4 and 5. The cone angles for
the ligands varied from 149 to 221◦. Cone angles of
all the ortho-substituted ligands were larger than that
of PPh3 (149◦), whereas cone angles of the analogous
para-substituted ligands were similar in size to that of
PPh3 evidently because para-substituents did not di-
rectly affect the angle. However, since ligands exhibit
a large flexibility range, cone angle calculations based
on optimised free ligand structures may be insuffi-
cient for the estimation of steric requirements of the
co-ordinated ligands. The values should nevertheless
give a qualitative idea of the steric size of the ligand.
The electronegative effect of the substituents on
phosphorus and the angles between the substituents are
the two most important variables determining the 31P
NMR-shifts, and hence the shift reflects the stereoelec-
tronic state of the phosphorus atom [11]. As Tables 4
and 5 show, the 31P NMR-shift of the ligands varied
markedly, from −3.3 to −31.9 ppm. Small, ␲-acceptor
ligands were observed at high field while fairly large
ligands with aromatic rings occupied lower field.
3.2. Hydroformylation tests
Tables 4 and 5 show the effect of different lig-
ands on the 1-hexene and propene hydroformylation.
Fig. 2. Regioselectivity of propene hydroformylation as a function of propene conversion.

74
P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
Table 4
Measured and calculated properties of the ligands and 1-hexene hydroformylation resultsa
Ligand
θ
31P NMR-shift
Conversion S2-hexenes
S3-hexenes
S2-EP
S2-MH
S1-heptanal
Stotal aldehydes
n:i
(%)
(%)
(%)
(%)
(%)
(%)
(%)
ratio
oSP
oNP
oOP
oSP(naf)2
oOP(naf)2
oCF3P
158
180
166
166
204
174
149
149
207
176
149
–
−12.9
−12.5
−15.6
−29.7
−31.9
−9.4
−4.1
−4.3
−27.7
−22.9
−3.3
–
88
84
86
87
84
0
62
65
67
63
68
0
19
20
19
20
19
0
1
1
1
1
0
0
0
2
1
1
2
2
7
5
5
6
5
0
0
9
7
6
7
8
11
9
9
10
9
0
19
15
14
17
14
0
1.4
1.5
1.7
1.4
2.0
0.0
0.0
1.1
1.2
1.3
1.2
1.1
pCF3P
0
0
0
0
0
p(CF3)3P
PPh(anthr)2
PPh2(anthr)
PPh3
88
87
79
88
86
58
62
64
61
60
18
20
20
20
19
12
10
9
10
11
23
18
16
19
20
No ligand
a Condition: 80◦C, 15 bar, 1-hexene:Rh = 10,000, L:Rh = 10, 6 h.
In general, in 1-hexene hydroformylation, fairly high
isomerisation activity was associated with all ligands,
and no hydrogenation was detected. Furthermore, the
product distribution differed little from that of the un-
modified and PPh3 modified reactions. In every case,
the major isomerisation product was 2-hexene. More-
over, with most of the ligands, the molar ratio of 2-
to 3-hexenes was 3.1–3.2, which is close to that of
the thermodynamic equilibrium (3.1) at 80◦C [22,23].
Only for oOP and oOP(naf)2 was the distribution of
isomers further from the equilibrium: 3.5 and 3.6, re-
spectively. In propene hydroformylation, the activity
was highly dependent on the modifying ligand and the
n:i ratio was always higher than that of the unmodified
reaction.
3.2.1. σ-Donor ligands
The heterodonor ligand had a notable effect on the
propene hydroformylation (Table 5). In some cases,
small changes in the ligand structure resulted in total
suppression of the reaction. Among the heterodonor
ligands, only oNP, pSP and oSP(naf)2 showed catalytic
Table 5
Measured and calculated properties of the ligands and propene hydroformylation resultsa
Ligand
θ
31P-shift
L:Rh ratio
Conversion (%)
Sisobutanal (%)
Sbutanal (%)
n:i ratio
oSP
158
−12.9
10
2
0
1
49
0
0
98
0
20
0
2
0
0
74
15
9
100
5
0
0
39
0
0
40
0
27
0
0
0
0
38
29
36
36
50
0
0
61
0
0
60
0
73
0
0
0
0
62
71
64
64
50
0.0
0.0
1.7
0.0
0.0
1.5
0.0
2.7
0.0
0.0
0.0
0.0
1.6
2.4
1.8
1.8
1.0
pSP
oOP
152
166
–
180
n.a.
n.a.
174
−4.7
−15.6
−10.4
−12.5
–
10
10
10
10
10
10
10
4
10
10
10
10
10
10
–
oSeP
oNP
DPPE
DPPB
oCF3P
–
−9.4
pCF3P
149
221
149
166
207
149
–
−4.1
−15.6
−4.3
−29.7
−27.7
−3.3
–
o(CF3)3P
p(CF3)3P
oSP(naf)2
PPh(anthr)2
PPh3
No ligand
a Condition: 100◦C, 10 bar, propene:Rh = 3200, 4 h.

P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
75
activity, with conversions of 98, 49 and 15%, respec-
3.2.3. Steric effects
tively. Relative to the regioselectivity of PPh3 (n:i =
1.8) oNP and pSP slightly enhanced the formation
of isobutanal (n:i = 1.5 and 1.7), whereas oSP(naf)2
favoured the formation of n-butanal (n:i = 2.4). Of
the diphosphine ligands, DPPB favoured the forma-
tion of n-butanal (n:i = 2.7), whereas the analogue
DPPE gave no conversion.
Increasing the steric stress of the ligand by replacing
some of the phenyl rings with anthracyl rings had var-
ied effects. Relative to PPh3, in 1-hexene hydroformy-
lation conversion drop was lower for PPh2(anthr)
ligand and, surprisingly, at the same level for the more
bulky PPh(anthr)2. The regioselectivity obtained with
both anthracyl modified ligands resembled that of the
PPh3 modified reaction. Again relative to PPh3, in
propene hydroformylation. The replacement of two
phenyl rings with anthracyl rings did not affect the
regioselectivity but decreased the conversion.
3.2.2. π-Acceptor ligands
Number and position of the CF3 groups markedly
affected the activity of the reaction with 1-hexene
and propene (Tables 4 and 5). The addition of oCF3P
or pCF3P blocked the reactions entirely, whereas
p(CF3)3P showed good hydroformylation activity
with both substrates. With 1-hexene, p(CF3)3P gave
the best selectivity to aldehydes (23.4%), and the
regioselectivity to the branched products (n:i = 1.1)
was slightly better than that of the unmodified re-
action. In propene hydroformylation, p(CF3)3P gave
a fairly rapid reaction with similar regioselectivity
to that of PPh3 (n:i = 1.6 and 1.8, respectively).
The catalyst modified with o(CF3)3P ligand gave no
reaction in propene hydroformylation.
3.3. Rh–P complexes
In view of unexpected behaviour of the –CF3 lig-
and modified reactions, we proceeded to study their
rhodium complexes. Ortho-substituted o(CF3)P ligand
reacted with Rh2(CO)4Cl2 through the bridge split-
ting route to yield monometallic tetra-co-ordinated
rhodium chlorocarbonyl complex having two phos-
phorus ligands in mutual trans position bonded
in monodentate fashion, [Rh(CO)Cl(oCF3P)2] (1)
(Fig. 3). Selected interatomic bond distances and
Fig. 3. Ortep drawing of compound 1 with thermal ellipsoids at 50% level.

76
P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
angles are given in Table 3. The structure shows a
planar geometry around the rhodium atom with a
slight deviation from ideal. As is characteristic of
Rh(CO)Cl(PX3)2 species, the compound shows dis-
order along the carbonyl/chloro axis. It gives a strong
CO stretching vibration (IR) at 1977 cm−1, and the
31P NMR spectrum shows a doublet at 37.5 ppm with
Rh–P coupling constant of 136 Hz.
The triply para-substituted p(CF3)3P ligand af-
forded dinuclear chloro-bridged complex [Rh(CO)2
Cl(p(CF3)3P)2]2 (2). The carbonyl stretching fre-
quency (IR) was shifted to higher field 1999 cm−1
relative to 1 due to the more electron-withdrawing
ligand. Similarly, the 31P NMR-shift was found at
higher field (46.9 ppm) with higher 1JRh–P of 170 Hz.
However, the steric factors do not explain the
behaviour of the corresponding para-substituted
CF3-modified ligands. Both the pCF3P and the
p(CF3)3P ligand have a cone angle of 149◦ (the
same as PPh3) but pCF3P gave zero conversion while
p(CF3)3P worked well with both substrates. The rea-
son for this kind of behaviour is not clear. Possibly,
the polarity of p(CF3)3P resembles that of with PPh3,
leading to similar catalytic behaviour. In the case of
pCF3P, the lack of rhodium hydride formation could
explain the inactivity.
The vast majority of published literature reports
describe the isomerisation of 1-hexene to 2-hexenes
[24,25] and even to 3-hexenes [9] concurrently with
hydroformylation, whereafter hydroformylation of the
isomers occurs (Fig. 1). With all tested ligands, the iso-
merisation activity was in line with the hydroformyla-
tion activity of the catalyst. Those catalysts (oOP and
oOP(naf)2 modified) that did not produce an equilib-
rium between 2- and 3-hexenes were also in general
less reactive, yielding lower selectivity to aldehydes.
Strong ␴-donor ligands oSP and oSP(naf)2 yielded
slightly higher hydroformylation activity with
1-hexene than did the less basic oOP and oOP(naf)2
ligands. This is in contrast to the general belief that
strongly basic phosphines are less active in hydro-
formylation [26,27]. It was shown in our previous
paper [8] that both oSP and oNP bind bidentately to
the rhodium, whereas oOP ligand co-ordinated mon-
odentately (Fig. 4). Planar substructures formed as a
result of bidentate co-ordination make the rhodium
centre more accessible and may explain the enhanced
hydroformylation activity. However, the oNP chelate
complex with rhodium is considered to be weaker
than that of oSP. Since nitrogen lacks ␲-orbitals
and thus does not exhibit ␲-acceptor capability, the
co-ordination might be more labile. This kind of
hemilabile character, earlier proposed by Horner and
Simons [28], allows oNP ligand to act — at least
partly — monodentately during the catalytic cycle.
4. Discussion
4.1. Activity
The ligands induced different effects on the hydro-
formylation activity of 1-hexene and propene. Only
the CF3-modified ligands behaved alike with the two
alkenes. Apparently, the changes in the stereoelec-
tronic properties of the CF3-modified ligands, and so
also the properties of the respective rhodium com-
plexes were significant enough to outstrip the individ-
ual properties of the two alkenes.
Even though the main purpose of the CF3 sub-
stituents was to modify the electronic state of the
phosphorus atom, the substitution also affected the
cone angles of the ortho-substituted oCF3P and
o(CF3)3P ligands. With both alkenes the oCF3P mod-
ified catalyst system showed no activity most likely
due to steric reasons. Co-ordination of the oCF3P
ligand (Fig. 3) shows that CF3 groups are nearby the
rhodium centre preventing the approach of alkenes.
Similarly, sterically more-crowded o(CF3)3P blocked
the hydroformylation of propene.
Fig. 4. Illustration of bidentate vs. monodentate binding.

P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
77
Indeed, the chemoselectivity to aldehydes decreases
in the order oSP, oNP and oOP, as does the bidentate
character.
neither of these properties can really explain the ob-
tained regioselectivity.
The binding mode discussed in the previous section
(Fig. 4) also explains the differences in regioselectivity
between oSP, oOP (n:i = 1.4 and 1.7) and oSP(naf)2,
oOP(naf)2 (n:i = 1.4 and 2.0) in 1-hexene hydro-
formylation. According to complex studies, oSP and
oSP(naf)2 are bound bidentately yielding a planar sub-
structure and a smaller and more accessible complex
also capable of hydroformylating 2- and 3-hexenes,
whereas oOP and oOP(naf)2 are bounded monoden-
tately resulting in a more hindered complex mainly
hydroformylating 1-hexene [8].
The steric stress of the ligand does not totally ex-
plain the regioselectivity of the reaction in 1-hexene
hydroformylation. Replacement of the phenyl rings
with bulkier rings (PPh2(anthr) and PPh(anthr)2)
caused the n:i ratio to increase slightly, but introduc-
tion of heterodonor groups to ortho position of the
phenyl ring caused greater increase.
In propene hydroformylation with catalysts contain-
ing ligand with heterodonor group in ortho position,
only the oNP modified catalyst led to reaction resem-
bling that of the PPh3 modified catalyst. We believe,
for the reasons already stated above for 1-hexene, that
the oNP ligand could possess hemilabile character and
act as a monodentate ligand during the catalytic cycle.
We have previously shown [7] that in the hydro-
formylation of MMA with the oSP modified catalyst,
the chelation control plays an essential role in deter-
mining the activity and regioselectivity of the reac-
tion. Evidently, the chelation control is at work here:
when the thiomethyl group is moved from ortho po-
sition (oSP) to the para position (pSP) or when the
ligand contains bulky groups (oSP(naf)2) that weaken
the chelation, the catalytic activity is restored. Indeed,
the plain steric stress of the oSP, pSP and oSP(naf)2
ligands (the cone angles 158, 152 and 166◦, respec-
tively) is too similar to alone explain differences in
the reactivity. At high ligand to rhodium ratios (L:Rh
at least 5) the DPPB ligand acts as a monodentate lig-
and, whereas the DPPE ligand acts as a bidentate one
[29]. This further reinforces our conclusion that under
tested conditions, this type of small chelating biden-
tate ligands hindered hydroformylation of propene.
5. Conclusions
The effect of in situ introduced ligands was
found to vary with reacting alkene. However, anal-
ogy between 1-hexene and propene was found
with CF3 modified ligands. In 1-hexene hydro-
formylation, isomerisation was the main reaction
and the differences in the activity as well as the
chemo- and regioselectivity were minor, whereas in
propene hydroformylation even a small change in
the ligand structure affected markedly the activity
and regioselectivity of the catalyst system. In the
case of propene, 1,4-bis(diphenylphosphino)butane
and (o-thiomethylphenyl)bis(1-naphthyl)phosphine
favoured the formation of n-butanal.
4.2. Regioselectivity
The effect of the modifying ligand on the regio-
selectivity of the reaction was individual for 1-hexene
and propene. No analogy between the two substrates
was found. In 1-hexene hydroformylation, the iso-
merisation had a dominant effect on the regioselecti-
vity, whereas in propene hydroformylation the n:i ratio
seemed mostly to depend on the direct stereoelectronic
effect of the ligand in the hydroformylation transition
state.
Acknowledgements
In propene hydroformylation, DPPB and oSP(naf)2
modified the regioselectivity of the reaction relative
to PPh3. DPPB and oSP(naf)2 favoured the forma-
tion of n-butanal most likely for steric reasons. Steri-
cally, the PPh2(anthr) ligand is more demanding than
PPh3, and the 31P-shift differs markedly from that of
PPh3; however, comparison with the properties and
catalytic behaviour of the other ligands, suggests that
We gratefully acknowledge the financial support
from Neste Chemicals. We wish to thank Ms. Päivi
Joensuu and Ms. Sari Ek for the mass spectra and Ms.
Johanna Suutari for performing part of the propene
hydroformylation tests. The assistance of Ms. Liisa
Saharinen in 1-hexene hydroformylation and prepara-
tion of rhodium complexes was most helpful.

78
P. Suomalainen et al. / Journal of Molecular Catalysis A: Chemical 169 (2001) 67–78
[16] J.A. Cleverty, G. Wilkinson, Inorganic Syntheses, Vol. 8,
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