Rhodium cationic complexes using macrocyclic diphosphines as chiral ligands: Application in asymmetric hydroformylation

Article abstract of DOI:10.1016/S0022-328X(99)00316-2

The mononuclear complexes [Rh(COD)(OC_nP)]BF₄ were prepared by adding 1,1′-binaphthyl-based diphosphine macrocyclic ligands (OC_nP, n=4-6) to a dichloromethane solution of [Rh(COD)₂]BF₄ (COD=1,5-cyclooctadiene). Hydroformylation of styrene was carried out using solutions of rhodium-diphosphine catalyst prepared from [Rh(acac)(CO)₂] and chiral macrocyclic diphosphines OC_nP, n=2, 4-6. At 30 bar of CO/H₂ (1:1) and 65°C regioselectivities in 2-phenylpropanal were >92% when all the chiral diphosphine was added in a P-P/Rh ratio of 2. The solution structure of the dominant species formed during the reaction of [Rh(acac)(CO)₂] with (rac)-OC₆P under hydroformylation conditions has been determined.

Full text of DOI:10.1016/S0022-328X(99)00316-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 587 (1999) 136–143
Rhodium cationic complexes using macrocyclic diphosphines as
chiral ligands:
Application in asymmetric hydroformylation
Oscar Pa`mies, Gemma Net a, Michael Widhalm b, Aurora Ruiz a,*, Carmen Claver a
a Departament de Qu´ımica F´ısica i Inorga`nica, Uni6ersitat Ro6ira i Virgili, Pl. Imperial Ta`rraco 1, ES-43005 Tarragona, Spain
b Institut fu¨r Organische Chemie, Uni6ersita¨t Wien, Wa¨hringerstraße 38, A-1090 Wien, Austria
Received 8 April 1999; received in revised form 19 May 1999
Abstract
The mononuclear complexes [Rh(COD)(OCnP)]BF4 were prepared by adding 1,1%-binaphthyl-based diphosphine macrocyclic
ligands (OCnP, n=4–6) to a dichloromethane solution of [Rh(COD)2]BF4 (COD=1,5-cyclooctadiene). Hydroformylation of
styrene was carried out using solutions of rhodium-diphosphine catalyst prepared from [Rh(acac)(CO)2] and chiral macrocyclic
diphosphines OCnP, n=2, 4–6. At 30 bar of CO/H2 (1:1) and 65°C regioselectivities in 2-phenylpropanal were \92% when all
the chiral diphosphine was added in a PꢀP/Rh ratio of 2. The solution structure of the dominant species formed during the
reaction of [Rh(acac)(CO)2] with (rac)-OC6P under hydroformylation conditions has been determined. © 1999 Elsevier Science
S.A. All rights reserved.
Keywords: Asymmetric hydroformylation; Chiral macrocyclic diphosphine; Rhodium
geometry, is a crucial feature and a necessary condi-
tion for chiral macrocycles if they are to be of use in
asymmetric catalysis [2].
The conformational changes when the ligand is
complexed with transition metals are expected to be
dramatic and should significantly influence the reactiv-
ity and stereoselectivity in a transition metal-catalyzed
reaction.
1. Introduction
One interesting use of chiral macrocycles is as chiral
auxiliaries in asymmetric catalysis [1]. Moderate con-
formational stability, allowing only tuned changes in
For a more detailed understanding of how and to
what extent the intramolecular distances of complexing
sites and asymmetric units affect asymmetric induc-
tion, a group of 1,1%-binaphthyl-based diphosphine
macrocyclic ligands (OCnP, n=2–6) was synthesized
by Widhalm and Klintschar [3] (Fig. 1). Their coordi-
nation to Ni and Pd and their use in asymmetric
carbon–carbon coupling reactions were also studied
[4].
This paper studies the coordination of some of these
macrocyclic diphosphine ligands to rhodium com-
plexes with a view to applying these systems as cata-
lyst precursors in the asymmetric hydroformylation of
styrene.
Fig. 1. 1,1%-Binaphthyl-based diphosphine macrocyclic ligands.
Rhodiumphosphine-catalyzed hydroformylation of
alkenes is one of the most important applications of
* Corresponding author. Fax: +34-977559563.
E-mail address: aruiz@quimica.urv.es (A. Ruiz)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00316-2

O. Pa`mies et al. / Journal of Organometallic Chemistry 587 (1999) 136–143
137
homogeneous catalysis in industry [5]. The regioselec-
tivity depends on the stereochemistry of the trigonal
bipyramidal complex [RhH(CO)2L2] (L=monophos-
phine, L2=diphosphine) formed under hydroformyla-
tion conditions; high regioselectivities in the
hydroformylation of 1-alkenes have been obtained for
both diphosphite- and diphosphine-modified catalysts
[6]. Asymmetric hydroformylation is a potentially pow-
erful process for synthesising a number of pharmaco-
logically important compounds and different chiral
building blocks [7]. Results for the enantioselective
hydroformylation of a variety of olefins are best when
the rhodium catalyst is used with the phosphine-phos-
phito ligand (R,S)-binaphos [8]. To the best of our
knowledge macrocyclic diphosphine ligands have not
been explored.
It is known that the stereo-electronic properties of
phosphorus ligands have a dramatic influence on the
reactivity of hydroformylation catalysts. Leitner and
co-workers [9] recently investigated how structural
changes in chelating ligands affect the coordination
geometry of the [(P2)Rh] (P2=R2Pꢀ(X)ꢀPR2) fragment
and attempted to correlate the results with catalytic
activity. This influence varied according to the nature
and length or, more precisely, the rigidity of the back-
bone (X). From these results, Leitner et al. introduced
the accessible molecular surface (AMS) model as a
unique approach for describing steric ligand effects in
homogeneous catalysis. This concept may serve as a
general approach for understanding ligand effects on
activity, and especially selectivity, in processes that are
mainly governed by steric interactions. The fact that
not only the size but also the shape of the cavity of the
active fragment can be analysed opens up a whole
range of possible applications. With a better insight
into steric requirements at the substrate complexation
sites, the attempts to optimize the ligand structure and
so obtain high enantioselection will be made on a more
rational basis.
(1)
Elemental analysis of C and H matches the stoi-
chiometry [{Rh(COD)(OCnP)}]x[BF4]x for all com-
plexes. The FAB mass spectra show the heaviest ions at
m/z=899 for complex 1, 927 for complex 2 and 955 for
complex 3. This is indicative of the mononuclear
cations [Rh(COD)(OCnP)].+ The IR spectra show a
strong band between 1090–1050 cm−1 and a medium
band around 450 cm−1 for all complexes. This is
characteristic of the noncoordinated BF4− anion in
cationic complexes [10].
The H- and 13C-NMR data for complexes 1, 2 and
1
3 were assigned using HETCOR, H-, 13C- and COSY
1
1H-1H.
As expected, for a C1-symmetrical ligand, the 1H-
NMR spectrum for complex 1 shows the olefinic ꢀCHꢁ
protons of the coordinated COD ligand as four multi-
plet signals at 4.82, 4.89, 5.16 and 5.24 ppm. For
complex 2, three multiplet signals were observed and
for complex 3 only two. For the endo- and exo-
methylenic protons of cyclooctadiene, two signals were
observed in all complexes. Also as expected, four reso-
nances were observed around 100 ppm in the 13C-NMR
for the olefinic carbons of coordinated COD of com-
plex 1 and 2. For complex 3 only three resonances were
observed. The rest of the 13C-NMR signals were in
accordance with the coordination of the cyclooctadiene
and diphosphine ligand (Table 1)
2. Results and discussion
2.1. Preparation of [Rh(COD)(OCnP)]BF4 (n=4–6)
complexes
The [Rh(COD)(OCnP)]BF4 complexes (COD=1,5-
cyclooctadiene, n=4 (1), 5 (2), 6 (3)) were prepared by
adding the corresponding racemic (S*)a(S*,R*)p
macrocyclic diphosphine ligand OCnP (C1 symmetry) to
a dichloromethane solution of [Rh(COD)2]BF4 (Eq.
(1)). After stirring, the brown solution turned yellow.
By addition of diethyl ether the complexes were isolated
as moderately air-stable powders.
The 31P{1H}-NMR spectra of 1–3 at room tempera-
ture in trichloromethane-d1 show two doublets of dou-
blets between 54 and 57 ppm (1JRhꢀP around 150 Hz,
2JPꢀP around 27 Hz) corresponding to the two
nonequivalent phosphorus atoms of the diphosphine
ligand, as expected for a C1-symmetrical ligand.

138
O. Pa`mies et al. / Journal of Organometallic Chemistry 587 (1999) 136–143
Table 1
13C-NMR data for the rhodium complexes 1–3 a
l CH2
l CHꢁ
l Car
1
2
21.43, 21.94, 26.54, 26.88, 27.25, 27.61, 27.85, 98.61 (dd, a=6.2, a=8.5), 100.67 (t, a= 115.07, 116.42, 119.29 (C), 120.31 (C),
29.43, 29.83, 30.31, 31.49, 31.69, 67.62, 68.81
6.3), 102.94 (t, a=6.9), 103.41 (t, a=7.4) 123.46, 123.56, 125.29, 125.45 (C), 126.12,
126.34, 126.42 (C), 127.80, 129.39, 130.94,
131.21, 131.43, 131.55 (C), 132.23, 133.21,
133.90 (C), 155.32 (C), 155.41 (C)
25.50 (d, J=3.5), 26.18 (d, J=6.3), 26.30 (d, 99.75 (t, a=8.3), 100.12 (t, a=6.7),
J=7.5), 26.49 (d, J=8.3), 26.79, 27.15, 27.34, 103.22 (t, a=7.5), 103.71 (t, a=8.0)
27.71, 29.08 (cod), 29.64 (cod), 30.15 (cod),
114.73, 114.95, 120.11 (C), 120.59 (C),
123.33, 125.39, 126.19, 126.23, 127.39 (C),
127.80, 127.86, 129.13, 129.19 (C), 129.29,
129.51 (C), 129.64, 129.77, 130.89, 131.06,
131.20, 131.24, 131.51, 131.63 (C), 132.42
(C), 133.37, 133.47, 134.24 (C), 153.81 (C),
153.95 (C)
67.69, 67.78.
3
25.38, 25.51 (m), 25.57 (m), 26.91 (m), 27.28
(m), 27.62 (m), 27.82, 28.84, 29.16, 29.57
(cod), 29.66 (cod), 30.10 (m, cod), 30.15,
30.73, 30.94, 68.93, 69.39
99.73 (m), 102.92 (t, a=7.5), 103.38 (t,
a=8.2)
115.63, 116.49, 120.36 (C), 120.95(C),
123.42, 123.54, 125.28, 125.36, 126.13,
127.74, 129.03, 129.10, 129.18 (C), 129.37
(C), 129.60, 129.72, 130.85 (C), 130.90 (C),
131.02, 131.13, 131.27, 133.29, 134.21 (C),
134.32 (C), 154.44 (C), 154.52 (C)
a J refers to PC coupling constants in Hz, a refers to CꢀX (where X= P or Rh) coupling constants in Hz. In spectral areas with extensive signal
overlapping, multiplets could not be assigned; those signals of unclear relationship are underlined, ignoring probable multiplet structures.
Table 2
Styrene hydroformylation with [Rh(acac)(CO)2]/diphosphine catalytic systems a
b
Entry
Diphosphine
PꢀP/Rh
P (atm)
t (h)
%Cald
% 2-PP c
ee% d
1
2
3
4
5
6
7
(S)-OC2P
(S)-OC4P
(S)-OC5P
(S)-OC6P
–
(S)-OC2P
(S)-OC4P
rac-OC5P
rac-OC6P
(S)-OC2P
(S)-OC4P
(S)-OC5P
(S)-OC6P
1
1
1
1
-
2
2
2
2
1
1
1
1
30
30
30
30
30
30
30
30
30
75
75
75
75
20
20
20
20
2
20
20
20
20
12
12
18
18
33
26
72
43
78
77
25
75
81
54
95
99
100
87
82
75
77
63
97
92
94
97
92
82
91
85
12 (S)
5 (S)
0
0
–
10 (S)
0
nd
8 e
9
10
11
12
13
nd
5 (S)
4 (S)
0
0
a Reaction conditions: T=338 K, styrene (10.2 mmol), [Rh(acac)(CO)2] (0.015 mmol), toluene (7.5 ml), CO/H2=1.
b Aldehyde conversion measured by GC.
c 2-PP=2-phenylpropanal.
d %ee was measured by CG with chiral column on the 2-phenylpropanoic acids obtained by oxidating the aldehydes with KMnO4.
e 18% of ethylbenzene was also obtained.
2.2. Styrene hydroformylation
cally pure ligands were used at 30 and 75 bar of syn
gas at 338 K (Table 2).
The macrocyclic ligands OCnP (n=2, 4–6) were
used to prepare precursor systems in the hydroformy-
lation of styrene by adding one or two equivalents of
diphosphine to [Rh(acac)(CO)2] [11] solution in
toluene. These ligands with different chain lengths
could provide different steric effects and arrangements
around the metal center. Racemic and enantiomeri-
Adding the macrocyclic diphosphine ligands in a
PꢀP/Rh ratio of one at 30 bar produces conversions
in aldehydes between 26 and 72% with complete
chemioselectivity, as expected for Rh/P systems in the
hydroformylation of styrene (entries 1–4). Although
macrocyclic ligands with different chain lengths were
used, catalytic activity did not depend systematically

O. Pa`mies et al. / Journal of Organometallic Chemistry 587 (1999) 136–143
139
on the chain length of the ligand; the best conversion
was for the (S)-OC5P (72%).
For comparison purposes, an experiment using
[Rh(acac)(CO)2] without diphosphine ligand was car-
ried out to give higher activity and lower regioselectiv-
ity (entry 5). As expected, for [Rh(acac)(CO)2]/OCnP
Table 3
31P{1H}- and 1H-NMR data of the species formed in the reaction of [Rh(acac)(CO)2]/rac-OC6P with CO/H2.
Compound
31P{1H}-NMR
1H-NMR
P (atm)
l(ppm)
1JRhꢀP(Hz)
l(ppm)
1JHꢀRh(Hz)
2JHꢀP(Hz)
H2
CO
5 a
6
65.27
66.82
117.8
119.7
42.29 c
42.37 c
142.2
140.1
15
15
7
56.11 c
119.0
15
15
8 b
52.94
53.34
117.2
115.4
−8.52
8.4
56.4
15
15
9
50.73
144.0
−10.51c
15
a JPꢀP=51.3.
b JPꢀP=50.1.
c Broad.
Scheme 1. Intermediate species formed in the reaction of [Rh(acac)(CO)2] with rac-OC6P under hydroformylation conditions.

140
O. Pa`mies et al. / Journal of Organometallic Chemistry 587 (1999) 136–143
Fig. 2. 31P{1H}-HPNMR spectrum of reaction of [Rh(acac)(CO)2]/rac-OC6P with CO and H2: (a) PꢀP/Rh=1; (b) PꢀP/Rh=2.
systems, the intermediate species are modified by the
diphosphine ligand, as HPNMR studies under hydro-
formylation conditions showed (see below).
hydroformylation process, we made a spectroscopic
study of the solution that resulted from adding: (a) 15
bar of CO; and (b) 15 bar of H2 (30 bar of CO/H2) to
solutions of Rh(acac)(CO)2]/rac-OC6P (PꢀP/Rh=1 and
PꢀP/Rh=2) in toluene-d8.
We studied the effect of increasing the PꢀP/Rh ratio
to two and the CO/H2 pressure to 75 bar. Interestingly,
the excess of the diphosphine ligand (entries 6–9) pro-
duces higher conversions in all cases except for the
(S)-OC4P ligand, where conversion is similar (entries 2
and 7). For the rac-OC5P, 18% of hydrogenation to
ethylbenzene was observed (entry 8). As far as regioselec-
tivity is concerned, an excess of ligand, PꢀP/Rh=2,
produces higher regioselectivity in 2-phenylpropanal, as
previously seen for other rhodium diphosphine systems
(diphosphine=dppe, dppp, chiraphos, bdpp) [12].
With respect to the effect of the CO/H2 pressure, both
conversions to aldehydes and regioslectivity in 2-phenyl-
propanal increased at higher pressure (75 bar) (entries
10–13). This is well known for rhodium sys-
tems in the hydroformylation of styrene [12b,13]. Only
for (S)-OC4P diphosphine is the regioselectivity the same
at 30 and 75 bar (entries 2 and 11)
The 31P{1H}-NMR spectrum of solutions of
[Rh(acac)(CO)2]/rac-OC6P (PꢀP/Rh=1 and PꢀP/Rh=
2) showed two doublets of doublets at 65.27 and 66.82
ppm (Table 3) (AB part of an ABX spectrum) attributed
to the mononuclear rhodium complex 5 (Scheme 1).
2.3.1. 15 bar of CO
When PꢀP/Rh=1, the 31P{1H}-NMR spectrum of the
solution showed two broad doublets at 42.29 and 42.37
ppm assigned to complex 6 (Scheme 1, Table 3). This type
of signal was previously assigned to carbonyl diphos-
phine dimers [Rh(CO)2(diphosphine)]2 (diphosphine=
dppe, dppp, diop, bdpp) [14] and [Rh2(CO)8−xLx]
(x=0–2, L=phosphite) [15] which have a RhꢀRh bond
and two CO groups bridging the metal atoms. The fact
that there were only two broad doublets for this
AA%A%%A%%%XX% spin system proves either the fast equili-
bration of several isomers or, possibly, the predominance
of a highly symmetrical species. There was also a set of
signals centered at 30 and −27 ppm, which could be
attributed to 10, formed by partial oxidation of the free
diphosphine, and a group of signals at 31 ppm which
were attributed to rhodium complexes 11 derived from
10.
At 30 bar, the percentage enantiomeric excess (ee%)
was low (about 10%) for the precursor containing the
most rigid (S)-OC2P diphosphine and there was practi-
cally no enantioselectivity for the other diphosphines.
2.3. Solution structure of the species formed during the
reaction of [Rh(acac)(CO)2] with rac-OC6P under hydro-
formylation conditions
With PꢀP/Rh=2, a broad doublet at 56.11 ppm
To find out the intermediate species formed during the
(1JPꢀRh=119 Hz) appears. This is attributed to a square

O. Pa`mies et al. / Journal of Organometallic Chemistry 587 (1999) 136–143
141
planar cationic rhodium complex 7 (Scheme 1) with two
diphosphines coordinated to the metal center. Related
compounds have previously been reported, [Rh(LꢀL)2]+
(LꢀL=dppe, dppp, bdpp), which show similar
rhodium–phosphorus coupling constants [14b,16].
1H-NMR of this solution revealed a doubletted pseudo
triplet in the hydride region (Table 3, Fig. 4), indicative
of the coupling of a hydride with the rhodium and two
almost equivalent phosphorus nuclei. Phosphorus–hy-
dride coupling constants observed (2JHꢀP=56.4Hz) are
in agreement with a time-averaged cis, trans relationship
between the phosphorus and hydride nuclei [14b]. A fast
equatorial–axial exchange of the phosphorus atoms
results in averaged rhodium–phosphorus coupling con-
stants of 117.2 and 115.4 Hz (Scheme 2).
2.3.2. 15 bar of CO and 15 bar of H2
When the solution was pressurized at r.t. with 15 bar
of H2 (30 bar of CO/H2), after a few minutes, the
31P{1H}-NMR spectrum, at 65°C, showed two new
doublets of doublets at 52.94 and 53.34 ppm (AB part
of and ABX system), attributed to mononuclear hydride-
rhodium complex 8 (Scheme 1, Figs. 2 and 3). The
After 90 min, with PꢀP/Rh=2, there was a new broad
doublet in the 31P{1H}-NMR spectrum at 50.73 ppm
1
(1JRhꢀP=144 Hz) (Fig. 2(b)). The H-NMR spectrum
also revealed a new broad signal in the hydride region
at −10.5 ppm (Fig. 4(b)). This new phosphorus–hy-
dride–rhodium complex could be attributed to the
mononuclear rhodium complex 9 (Scheme 1) since the
sprectroscopic data agree well with those previously
reported for compounds [HRh(LꢀL)2], where LꢀL=
dppe (1JRhꢀP=142.5 Hz), dppp (1JRhꢀP=141.8 Hz), diop
(1JRhꢀP=146 Hz) and bdpp (1JRhꢀP=141 Hz) [14b,16c].
It is important to note that the amount of species 8
increased with respect to the others in solution when an
excess of diphosphine was used (estimated proportion of
species 8/11=1.3 and 8/6=0.7 for PꢀP/Rh=1; 8/11=
2.2 and 8/6=1.7 for PꢀP/Rh=2) (Fig. 2).
In summary, this study reveals several species under
hydroformylation conditions (Scheme 1). Several papers
have described type 8 species as being responsible for the
catalytic activity [8a,14b]. The partial oxidation of the
diphosphine ligand causes the formation of species 11,
where the PꢀP ligand is bound in monodentate fashion.
This species could evolve into monodentate species
[14b,17], which are known to be active and less regiose-
lective than the corresponding chelate species in the
hydroformylation of styrene. On the other hand the
dinuclear inactive species 6, which has been described to
be in equilibrium with the pentacoordinated species 8
[14b], is also present. Species with two diphosphines
coordinated to the rhodium center 7 and 9, have been
observed when PꢀP/Rh=2. As far as we know, these
species are inactive under hydroformylation conditions.
How a change in the PꢀP/Rh ratio from one to two
affects conversion and regioselectivity in the hydro-
formylation experiments may now be explained by the
increased concentration of species 8 when excess diphos-
phine is added.
Fig. 3. 31P{1H}-HPNMR spectrum of compound 8.
Fig. 4. 1H-HPNMR spectrum of reaction of [Rh(acac)(CO)2]/rac-
OC6P with CO and H2 in the high-field region: (a) PꢀP/Rh=1; (b)
PꢀP/Rh=2.
3. Experimental
3.1. General comments
All the rhodium complexes were synthesized using
standard Schlenk techniques under argon atmosphere.
The complexes [Rh(cod)2]BF4 [18], [Rh(acac)(CO)2] [11]
Scheme 2. Equatorial–axial phosphorus exchange.

142
O. Pa`mies et al. / Journal of Organometallic Chemistry 587 (1999) 136–143
and the diphosphine ligands [3] were prepared by previ-
ously described methods. Solvents were purified by
standard procedures. All other reagents were used as
commercially available. Elemental analyses were per-
formed on a Carlo–Erba EA-1108 instrument. 1H-,
13C{1H}- and 31P{1H}-NMR spectra were recorded on
a Varian Gemini 300 MHz spectrometer. Chemical
shifts are relative to SiMe4 (1H and 13C) as internal
standard or H3PO4 (31P) as external standard. All as-
signments in NMR spectra were determined by COSY
and HETCOR spectra. A VG-Autospect equipment was
used for fast atom bombardment (FAB) mass spectral
analyses. The matrix was m-nitrobenzylalcohol. Gas
chromatographic analyses were run on a Hewlett–Pack-
ard HP 5890A instrument (split/splitless injector, J&W
Scientific, Ultra-2 25 m column, internal diameter 0.2
mm, film thickness 0.33 mm, carrier gas: 150 kPa He,
F.I.D. detector) equipped with a Hewlett–Packard HP
3396 series II integrator. Enantiomeric excesses were
measured after oxidation of the aldehydes to the corre-
sponding carboxylic acids on a Hewlett–Packard HP
5890A gas chromatograph (split/splitless injector, J&W
Scientific, FS-Cyclodex b-I/P 50 m column, internal
diameter 0.2 mm, film thickness 0.33 mm, carrier gas:
100 kPa He, F.I.D. detector). Absolute configuration
was determined by comparing the retention times with
optically pure (S)-(+)-2-phenylpropionic and (R)-(−)-
2-phenylpropionic acids. Hydroformylation reactions
were carried out in a home-made 100 ml stainless steel
autoclave.
J
PꢀP=27.02 Hz, JPꢀRh=149.99 Hz). 1H-NMR (CDCl3),
l(ppm): 1.10–1.70 (m, 8H, CH2), 1.80–2.10 (m, 4H,
CH2 cod), 2.10–2.80 (m, 12H, CH2, CH2 cod), 3.80–
4.00 (m, 4H, CH2ꢀO), 4.91 (m, 2H, CHꢁ), 5.23 (m, 1H,
CHꢁ), 5.42 (m, 1H, CHꢁ), 7.05–8.00 (m, 26H, Ar).
3.2.3. [Rh(COD)(OC6P)]BF4 (3)
Yield 85 mg (81%, yellow solid). Elemental analysis.
Found (%): C, 66.59; H, 6.18. Anal. Calc. (%) for
RhC58H62O2P2BF4: C, 66.80; H, 5.99. FAB-MS: m/z:
955 [M+]. 31P-NMR (CDCl3), l(ppm): 55.14 (dd, 1P,
J
J
PꢀP=27.02 Hz, JPꢀRh=149.26 Hz), 55.39 (dd, 1P,
PꢀP=27.02 Hz, JPꢀRh=150.58 Hz). 1H-NMR (CDCl3),
l(ppm): 1.10–1.20 (m, 4H, CH2), 1.20–1.70 (m, 10H,
CH2), 1.80–2.10 (m, 4H, CH2 cod), 2.20–2.70 (m, 10H,
CH2, CH2 cod), 3.70–4.10 (m, 4H, CH2ꢀO), 4.82 (m,
2H, CHꢁ), 5.43 (m, 2H, CHꢁ), 7.00–8.00 (m, 26H, Ar).
3.3. Hydroformylation of styrene
The autoclave was purged three times with CO. The
solution was formed from [Rh(acac)(CO)2] (0.015
mmol), diphosphine and substrate (10.2 mmol) in
toluene (7.5 ml). After pressurizing to the desired pres-
sure with syn gas and heating the autoclave to the
reaction temperature, the reaction mixture was stirred.
During the reaction several samples were taken from the
autoclave. After the desired reaction time, the autoclave
was cooled to r.t. and depressurized. The reaction
mixture was analysed by gas chromatography.
The aldehydes obtained from the hydroformylation
were oxidized to carboxylic acids to determine the
enantioselective excess. A small portion of the hydro-
formylation reaction mixture (2 ml) was added to the
solution prepared from 10 ml of a potassium perman-
ganate 1 M solution and 10 ml of a potassium dihydro-
genphosphate 1.25 M solution. After 1 h of agitation, 5
ml of a saturated solution of sodium sulfite was added.
Diluted hydrochloric acid was then added until the
brown precipitate of manganese(IV) oxide disappeared.
The acids formed were extracted with diethyl ether
(3×10 ml) and the organic phase was concentrated to
dryness. A 2 M solution of sodium hydroxide (10 ml)
was then added. After washing the solution with diethyl
ether, 10 ml of concentrated hydrochloric acid was
added and the product was extracted with diethyl ether
(3×10 ml). The carboxylic acids were obtained after
washing the etheric phase with water, drying it with
magnesium sulfate and evaporating it to dryness.
3.2. Preparation of rhodium complexes
Diphosphine ligand (0.1 mmol) was added to a solu-
tion of [Rh(cod)2]BF4 (40.5 mg, 0.1 mmol) in 2 ml of
dichloromethane. After 10 min, the desired products
were obtained by precipitation with diethyl ether.
3.2.1. [Rh(COD)(OC4P)]BF4 (1)
Yield: 79 mg (80%, yellow solid). Elemental analysis.
Found (%): C, 65.53; H, 5.43. Anal. Calc. (%) for
RhC54H54O2P2BF4: C, 65.74; H, 5.52. FAB-MS: m/z:
899 [M+]. 31P-NMR (CDCl3), l(ppm): 54.32 (dd, 1P,
J
J
PꢀP=26.72 Hz, JPꢀRh=150.55 Hz), 55.40 (dd, 1P,
PꢀP=26.72 Hz, JPꢀRh=148.57 Hz). 1H-NMR (CDCl3),
l(ppm): 1.10–1.90 (m, 10H, CH2, CH2 cod), 2.00–2.90
(m, 10H, CH2, CH2 cod), 3.60–4.10 (m, 4H, CH2ꢀO),
4.82 (m, H, CHꢁ), 4.89 (m, H, CHꢁ), 5.16 (m, 1H, CHꢁ),
5.24 (m, 1H, CHꢁ), 7.05–8.00 (m, 26H, Ar).
3.2.2. [Rh(COD)(OC5P)]BF4 (2)
Yield: 87 mg (86%, yellow solid). Elemental analysis.
Found (%): C, 67.01; H, 5.61. Anal. Calc. (%) for
RhC56H58O2P2BF4: C, 66.29; H, 5.76. FAB-MS: m/z:
927 [M+]. 31P-NMR (CDCl3), l(ppm): 54.92 (dd, 1P,
3.4. In situ HPNMR experiments
In a typical experiment a sapphire tube (¥=10 mm)
was filled under argon with
a
solution of
J
PꢀP=27.02 Hz, JPꢀRh=149.37 Hz), 56.20 (dd, 1P,
[Rh(acac)(CO)2] (0.030 mmol) and diphosphine ligand

O. Pa`mies et al. / Journal of Organometallic Chemistry 587 (1999) 136–143
143
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Acknowledgements
We thank the Ministerio de Educacio´n y Ciencia for
financial support (PB97-0407-C05-01) and the Generali-
tat de Catalunya (CIRIT) for awarding a research grant
(to O.P.). We are also very much indebted to Professor
Piet W.N.M. van Leeuwen for his very useful com-
ments and suggestions.
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