Hydroformylation of styrene and 1-octene catalyzed by binuclear and oligomer rhodium(I) complexes containing the bis-p-phosphinito ligands [(p- Ph2POC6 H4)2 X] (X = O, CMe2, S)

Article abstract of DOI:10.1016/S1381-1169(99)00118-1

The reactions of rhodium(I) substrates with the ligands [(p- Ph₂POC₆H₄)₂X] (X = O, 1; X = CMe₂, 2; X = S, 3) have been studied with the aim to obtain rhodium(I) complexes to utilize as precatalysts in hydroformylation of olefins. The reactions of [Rh(CO)₂Cl]₂ with ligands 1- 3, in a Rh to ligand 1:1 molar ratio, in toluene, at room temperature afford the products [Rh(CO)(Cl)(μ-L)]₂ (L = 1-3). The reactions of [Rh(acac)(CO)₂] with 2 are strongly dependent on the ligand nature and experimental conditions. The product formed in a 1:0.5 Rh to ligand molar ratio is dimer with the metal centers held together by the ligand, while the product formed in a 1:1 molar ratio is oligomer. The in situ catalytic systems formed either by [Rh(CO)₂Cl]₂ and ligands 1-3 or by [Rh(acac)(CO)₂] and 2, at variable ligand-to-metal molar ratio, have been employed in the hydroformylation of styrene and 1-octene. Almost quantitative conversion of styrene was achieved with the catalytic system formed by [Rh(acac)(CO)₂] and 2, in a 1:0.5 molar ratio, operating at 60°C and 40 atm. The chemoselectivity of the reaction was very high being the linear (L) and the branched (B) aldehydes about 99.9% of the reaction products. The terminal aliphatic olefin 1-octene was hydroformylated with lower conversion in the aldehydes with respect to styrene and isomerization and hydrogenation of the double bond occurred in great extent. Lowering the temperature, the conversion of 1-octene increases but the chemoselectivity drastically decreases owing to the formation of more isomerization products. The results have been explained considering both the flexibility and the number of phosphorus atoms (considering each of them as a monodentate ligand) coordinated to each metal center in the trigonal bipyramidal hydridorhodium intermediates formed, namely {[Rh(H)(CO)₃]₂(μ-2)} (1:0.5 [Rh(acac)(CO)₂] to 2 molar ratio) and the oligomer [Rh(H)(CO)₂(μ-2)]n (1:1 [Rh(acac)(CO)₂] to 2 molar ratio). In the presence of an excess of ligand 2 the conversion in the aldehydes drastically decreases owing to the rigidity of the intermediate hydridorhodium oligomer species formed.

Full text of DOI:10.1016/S1381-1169(99)00118-1

Ž
.
Journal of Molecular Catalysis A: Chemical 144 1999 379–388
www.elsevier.comrlocatermolcata
Hydroformylation of styrene and 1-octene catalyzed by
ž /
binuclear and oligomer rhodium I complexes containing the
wž / x
bis-p-phosphinito ligands p-Ph2 POC6 H4 2 X
ž
/
XsO, CMe2, S
)
Carmela G. Arena, Daniela Drago, Felice Faraone
Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica dell’UniÕersita, Salita Sperone 31, Villaggio S. Agata, I-98166
`
Messina, Italy
Received 20 April 1998; received in revised form 26 October 1998; accepted 26 October 1998
Abstract
Ž .
wŽ
.
x Ž
.
The reactions of rhodium I substrates with the ligands p-Ph2POC6H4 2 X XsO, 1; XsCMe2, 2; XsS, 3 have
Ž .
been studied with the aim to obtain rhodium I complexes to utilize as precatalysts in hydroformylation of olefins. The
w
Ž
.
x
reactions of Rh CO Cl with ligands 1–3, in a Rh to ligand 1:1 molar ratio, in toluene, at room temperature afford the
2
w
Ž
.Ž .Ž 2 .x
Ž
.
w
Ž
.Ž . x
products Rh CO Cl m-L
Ls1–3 . The reactions of Rh acac CO
with 2 are strongly dependent on the ligand
2
2
nature and experimental conditions. The product formed in a 1:0.5 Rh to ligand molar ratio is dimer with the metal centers
held together by the ligand, while the product formed in a 1:1 molar ratio is oligomer. The in situ catalytic systems formed
w
Ž
.
x
w
Ž
.Ž . x
either by Rh CO Cl and ligands 1–3 or by Rh acac CO
and 2, at variable ligand-to-metal molar ratio, have been
2
2
2
employed in the hydroformylation of styrene and 1-octene. Almost quantitative conversion of styrene was achieved with the
.Ž . x
w
Ž
catalytic system formed by Rh acac CO
and 2, in a 1:0.5 molar ratio, operating at 608C and 40 atm. The
2
Ž .
Ž .
chemoselectivity of the reaction was very high being the linear L and the branched B aldehydes about 99.9% of the
reaction products. The terminal aliphatic olefin 1-octene was hydroformylated with lower conversion in the aldehydes with
respect to styrene and isomerization and hydrogenation of the double bond occurred in great extent. Lowering the
temperature, the conversion of 1-octene increases but the chemoselectivity drastically decreases owing to the formation of
more isomerization products. The results have been explained considering both the flexibility and the number of phosphorus
Ž
.
atoms considering each of them as a monodentate ligand coordinated to each metal center in the trigonal bipyramidal
Äw Ž .Ž . x Ž .4 Ž .Ž . x
w
Ž
.
hydridorhodium intermediates formed, namely Rh H CO m-2 1:0.5 Rh acac CO
oligomer Rh H CO m-2 n 1:1 Rh acac CO
conversion in the aldehydes drastically decreases owing to the rigidity of the intermediate hydridorhodium oligomer species
to 2 molar ratio and the
3 2
2
w
Ž .Ž . Ž .x
Ž
w
Ž
.Ž . x
.
to 2 molar ratio . In the presence of an excess of ligand 2 the
2
2
formed. q 1999 Published by Elsevier Science B.V. All rights reserved.
Keywords: Hydroformylation; Styrene; 1-Octene
1. Introduction
)
Recent homogeneous catalysis studies indi-
cate that structural characteristics of coordinated
Corresponding author. Tel.: q39-90-391961; E-mail:
faraone@chem.unime.it
1381-1169r99r$ - see front matter q 1999 Published by Elsevier Science B.V. All rights reserved.
Ž
.
PII: S1381-1169 99 00118-1

(
)
380
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
diphosphine ligands produce relevant effects on
the activity and selectivity induced by the cata-
indicating that the changes in the X-group have
only a minor influence on the electronic proper-
ties of the phosphorus donor. This result was
w
x
lyst. Casey et al. 1,2 introduced recently the
concepts of ‘natural bite angle’ and ‘flexibility’
as steric parameters of diphosphine ligands. The
modulation of the ‘natural bite angle’ and of the
‘flexibility’ can give rise to metal complexes
having a variety of structures. This possibility
results of particular relevance in homogeneous
catalysis. In the rhodium catalyzed hydroformy-
lation of olefins, the natural bite angle of the
chelating diphosphine used for the synthesis of
the catalytic system influences the regioselectiv-
31
1
Ä
4
confirmed by the P H NMR chemical shift
values found for the ligands. Interestingly the
˚
P . . . P separation ranges from 9.848 A for 2 to
˚
11.506 A for 1 indicating that cis or trans
chelation to one metal atom is hindered using
these ligands. The C–X–C angles range from
100.38 for XsS to 115.98 for XsO; the C–
X–C values are not directly related to the P . . . P
separation. This work deals with the synthesis
Ž .
of binuclear rhodium I complexes containing
w
x
ity of the catalytic process. Casey et al. 1,2
the ligands 1–3 and their use, as precatalysts, in
the hydroformylation of styrene and 1-octene.
X
w
Ž
showed that using the 2,2 -bis diphenylphos-
X
.
x
Ž
.
phino methyl -1,1-biphenyl ligand BISBI ,
which coordinates to rhodium in the trigonal
bipyramidal intermediate species as bis-equa-
2. Results and discussion
Ž
.
torial ligand P–Rh–P angle ca. 1208 , the re-
gioselectivity in the linear aldehyde is 66:1,
Ž
.
while using 1,2-bis diphenylphosphino ethane,
which coordinates as equatorial–axial ligand
2.1. Synthesis
Ž
.
P–Rh–P angle ca. 908 the regioselectivity re-
Ž .
The reactions of rhodium I substrates with
sults lowered to 2.1:1.
wŽ .
x Ž
Recently we have synthesized large valence
the ligands p-Ph2 POC6H4 2 X XsO, 1; X
Ž
.
angle bis-p-phosphinito ligands p-Ph2 POC6-
sCMe2, 2; XsS, 3 have been studied with
.
Ž
.
Ž .
H4 2 X XsO, 1; XsCMe2, 2; XsS; 3
the aim to obtain rhodium I complexes to uti-
Ž
.
Fig. 1 and studied their applications in reac-
lize as precatalysts in hydroformylation of
olefins. The geometry of ligands induce forma-
w
Ž
.
x
w
Ž
.
tions with Ru p-cymene Cl2 2, Rh C5Me5 -
Cl2 2 and Rh C5H5 CO
Ligands 1–3 have been designed to induce a
bridging coordination in transition metal com-
plexes. Their geometry have been most accu-
rately predicted by AMPAC MOPAC calcula-
tions 4 . It has showed that the P–O bond
distances are nearly the same for all the ligands
x
w
Ž
.Ž
.
x w x
Ž .
3 .
tion of rhodium I binuclear or oligomer com-
2
plexes which have the potential of catalyzing
hydroformylation reactions more efficiently. The
w
Ž
.
x
reactions of Rh CO Cl with ligands 1–3 in a
2
2
Ž
.
1:1 rhodium to ligand molar ratio, in toluene at
w x
w Ž .
room temperature, afford the products Rh CO -
Ž
.Ž
.
x
Ž .
Ls1–3 , as yellow-orange moder-
Cl m-L
2
ate air-stable solids. The compounds have been
characterized by analytical data. Their formula-
tion as dimers was supported by the presence of
the corresponding molecular peak in the elec-
tron impact mass spectra. Spectroscopic data
also support the proposed structures. The IR
Ž
.
spectra, in nujol mull, show only one n CO
1
band in the range 1985–1990 cmy as expected
Ž .
for a centrosymmetric binuclear rhodium I
complex in which two square planar units, con-
Fig. 1.

(
)
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
381
taining the CO ligand in trans position to Cl, are
held together by two bridging bidentate ligands
L. A similar structure was reported for the
analogous complexes containing bridging dppm
results of the reaction with ligand 2 because, in
this case, the nature of the products was well
established. However, the reactions with 1 and 3
proceed similarly. Following the reaction of
31
1
w
Ž
.
Ž
.
x
Ž
w Ž .Ž . x Ä 4
Rh acac CO with 2 by IR and P H NMR
2
ligands Rh CO Cl m-dppm
dppm s bis
31
1
Ž
.
.
w2 x
Ä
4
diphenylphosphino methane 5 . The P H
spectra we observed that the addition of 2 to
2 x
in a 1:0.5 Rh to ligand molar
w
Ž
.Ž
.
NMR spectra, in CDCl3 solution, show for
Rh acac CO
ratio, in toluene, produces two doublets of dif-
w
Ž
.Ž .Ž
.
x
Ž
.
complexes Rh CO Cl m-L
L s 1–3 a
2
31
1
Ä 4
doublet centered respectively at d 125.8 ppm
ferent intensity in the P H NMR spectrum,
the major product at d 139.6 ppm J RhP s
199.5 Hz and the minor product at d 139.84
ppm J RhP s199.5 Hz . A third signal of
very low intensity was observed at d 140.09
Ž1
Ž1
Ž1
Ž
.
. Ž
.
Ž1
Ž
.
J RhP s145.8 Hz for Ls1 , d 125.5 ppm
Ž
.
. Ž
.
.
J RhP s143.5 Hz for Ls2 , d 124.6 ppm
1
Ž
.
. Ž
.
Ž1
Ž
.
.
J RhP s145.2 Hz for Ls3 . The H NMR
spectra in CDCl3 exhibit the resonances associ-
ated with ligands 1–3 in the correct integration
ratio.
Ž1
.
Ž
.
.
ppm J RhP s199.3 . In the IR spectrum the
Ž
w
Ž
.Ž
.
x
n CO bands of Rh acac CO have been re-
2
The dimeric structure of Rh CO Cl m-L
placed by a n CO band at 1993 cm 1. Further
y
w
Ž
.Ž .Ž
.
x
Ž
.
2
Ž
Ä
.
Ls1–3 is surprising; in fact, starting from
addition of 2, until to reach a 1:1 Rh to ligand
1
Ru p-cymene Cl CH 3CN m-1–3 PF6 2
molar ratio, produces in the 31P H NMR spec-
trum disappearance of the signal centered at d
139.6 ppm and increase of the signal at d
w
Ž
.Ž .Ž
.
x
Ž
.
4
w
x
Ä
4
5
Ä
w
Ž .Ž .Ž
.xŽ
and
Rh h -C 5 Me5 Cl CH 3CN m-1–
.
4
w
x
w x
3 PF6 2 were not able 3 to obtain the corre-
sponding compounds in which the metal centers
are held together by two bridging phosphinito
ligands. Very likely the presence of two bridg-
ing ligands induces strong repulsive interactions
between the phenyl groups of the phosphinito
ligands and the isopropyl moiety of the p-cy-
mene or the methyls of the h5-pentamethyl-
cyclopentadienyl ligand and prevents the forma-
tion of these species. It is very likely that the
presence of small ligands, as CO and Cl, coordi-
Ž
.
139.84 ppm; the n CO in the IR spectrum
remains nearly unchanged. In a separate experi-
ment, the product formed in the reaction be-
w
Ž
.Ž
.
x
tween Rh acac CO and 2, in a 1:0.5 Rh to
2
ligand molar ratio was isolated as a red-orange
solid, soluble in benzene and chlorinated sol-
vents. Analytical and spectroscopic data support
Ä
w
Ž
.Ž
.x
its formulation as the dimer Rh acac CO -
2
Ž
.4
m-2 , with the metal centers hold together by
Ž
.
the ligand 2 Fig. 2 .
Ž .
nated to rhodium I center and in cis position to
In accordance the IR spectrum, nujol mull,
y
1
Ž .
the phosphorus atoms allows the formation of
showed a n CO band at 1992 cm and in the
31
1
w
Ž
.Ž .Ž
.
x
Ž
Ä
4
binuclear complexes as Rh CO Cl m-L
L
P H NMR spectrum, in C6D6 solution, a
2
.
w x
s1–3 . For example 6 , it is well-known that
Ž
bridging coordination of 2- diphenylphos-
.
Ž
.
phino pyridine Ph2 PPy , because of its rigidity
and small bite angle, requires small ligands cis
to the phosphorus atom; consequently bimetallic
complexes in which two d8 metal centers are
surrounded by two ‘head to tail’ Ph2 PPy have
been synthesized only when CO, halogenides or
CNMe are the coordinated ligands cis to phos-
phorus.
w
Ž
.Ž
.2 x
The reactions of Rh acac CO with 1–3
are strongly dependent on the ligand nature and
experimental conditions. We report in detail the
Fig. 2.

(
)
382
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
Ž1
Ž
.
w
Ž
.
x
w
Ž
.
12 x
w
Ž
.16x
doublet centered at d 139.63 ppm J RhP s
HRh CO
,
Rh4 CO
and Rh6 CO
4
.
199.2 Hz appeared.
species were not formed.
Experimental data indicated that the product
The results obtained in the hydroformylation
of styrene are reported in Table 1. The reactions
have been carried out at temperatures of 40 and
w
Ž
.Ž
.
x
formed in the reaction of Rh acac CO with
2
2 in a 1:1 Rh to ligand molar ratio, was the
w
Ž
.Ž
.Ž
.
x
Ž
.
oligomer Rh acac CO m-2 n. Considering the
608C under 20 and 40 atm of CO and H2 1:1 .
acac ligand as chelate, a structure in which the
It is evident that the catalytic system formed by
Ž .
w
Ž .Ž
. x
rhodium I is five-coordinate and the trigonal
Rh acac CO and 2, in a 1:0.5 or 1:1 Rh to
2
bipyramidal units are held together by bridging
ligands 2 seems very likely. The presence of a
ligand molar ratio, displays a catalytic activity,
in the hydroformylation of styrene, more than
31
1
Ä
4
w
Ž
.
x x
single resonance in the P H NMR spectrum
in C6D6, supports a structure with the phospho-
rus atoms of 2 both coordinate to different
rhodium centers either in the equatorial plane or
in the axial position. The unchanged value of
that formed by Rh CO Cl and 2. Almost
quantitative conversion of styrene has been
achieved operating at 608C and 40 atm conver-
sion 99.9% entry 8 or at 608C and 20 atm
2
2
Ž
. Ž
.
Ž
. Ž
.
conversion 92% entry 4 for 6 h, at a styrene-
Ž
.
Ä
w
Ž
.Ž
.x Ž
the n CO with respect to Rh acac CO m-
to-catalyst ratio of 500. The chemoselectivity of
2
.
4
Ž .
the reaction was very high being the linear L
and the branched B aldehydes about 99.9% of
the reaction products. The molar ratio between
2
supports the trans arrangement of the CO to
Ž .
carbon atom of the acac. Moreover, in the trigo-
nal bipyramidal structures, the preferred config-
uration seems that with bulky ligands in the
w
Ž
.Ž
. x
Rh acac CO and 2 drastically influences the
conversion of styrene; operating at 408C and 20
2
w x
equatorial position 7 . However a structure in
w
Ž
.
which square planar units, formed by coordina-
tion of the acac as monodentate anionic ligand,
are held together by bridging ligands 2 does not
ruled out.
atm and using 1:0.5, 1:1, and 1:2 Rh acac -
2 x
Ž
.
CO
to ligand molar ratios the conversion
Ž
values are 56.2, 46.7 and 2.9, respectively en-
tries 1–3 . The CO–H2 pressure influences the
.
rate of the reaction; operating at 408C the con-
Ž
version raises from 56.2 to 76.8% entries 1 and
.
2.2. Catalytic runs
6 increasing the pressure from 20 to 40 atm. As
expected for the rhodium-catalyzed hydroformy-
lation of styrene, the branched aldehyde was
w
Ž
.
The catalytic systems based on Rh acac -
2 x
Ž
.
w
Ž
.
x
wŽ
w x
CO
or Rh CO Cl and the ligand p-
formed in more extent than the linear one 8 .
2
x
2
.
Ph2 POC6H4 2CMe2 , 2, have been used in the
hydroformylation reactions. However more im-
portant results have been compared with those
The regioselectivity, expressed as the ratio BrL,
is high and in all experiments at 408C, indepen-
dently from the pressure, its value reaches about
26.
w
Ž
.
obtained using the catalytic systems Rh acac -
2 x
Ž
.
CO
and 1 or 3. Styrene and 1-octene have
A comparison of the data obtained with
w
Ž
.Ž
.2 x
been chosen as reference substrates to test the
activity of these new catalytic systems. The
hydroformylation reactions were carried out in
toluene solution under a hydrogen–carbon
monoxide 1:1 pressure. Either the preformed
precatalyst or the in situ systems formed by
Rh acac CO and 2, in a 1:0.5 molar ratio,
with the corresponding ones using ligands 1 and
3 do not evidence significant changes in the
conversion, chemoselectivity and regioselectiv-
Ž
.
ity values entries 8, 9, 10 .
x
The catalytic system based on Rh CO Cl
w
Ž
.
2
2
w
Ž
.Ž
.
2 x
w
Ž
.
x
w Ž .
and 2 resulted less efficient than Rh acac -
CO and 2. In fact, operating at 608C and 20
atm the conversion of styrene was of 30.1% and
Rh acac CO
or Rh CO Cl and ligands
2
2
Ž
. x
1–3, at variable ligand-to-metal molar ratio,
have been employed as catalysts. Preliminary
was ascertained that in catalytic conditions the
2
Ž
.
at 408C only of 5.4% entries 12, 11 . Also the

(
)
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
383
Table 1
Hydroformylation of styrenea
Hydr.b
Aldehydes
Branchedc
LrBd
TOFe
w x w
x
Ž
.
Ž
.
Ž
.
Entry
L r Rh
P atm
T
8C
Conversion %
Linearc
1
2
3
4
5
6
7
8
0.5
1
2
0.5
1
0.5
1
0.5
0.5
0.5
1
20
20
20
20
20
40
40
40
40
40
20
20
40
40
40
60
60
40
40
60
60
60
40
60
56.2
46.7
2.9
92.0
95.1
76.8
65.1
99.9
99
2.7
4.5
6.9
–
3.3
2.5
4.7
–
–
–
29.6
25.0
92.3
91.9
31
5
3.6
–
5r95
4r96
47
39
2.4
0r100
16r84
12r88
4r96
84
16
76.7
79.2
64
54.2
83.2
82.5
82.6
4.5
85.6
93.7
91.8
82
82
82
11.1
3.8
3.5
18
18
18
4r96
18r82
18r82
18r82
19r81
19r81
9f
10g
11h
12h
99.1
5.4
30.1
57.4
61.1
13.0
13.9
1
25.1
aReaction conditions: solvent toluene 10 ml ; COrH2 s1; catalysts Rh acac CO
r
p-Ph2 POC6 H4 2CMe2 ; catalyst:styrenes
Ž
.
w
Ž
.Ž . x wŽ
.
x
2
1:500.
b Ethylbenzene.
c Branched aldehyde 2-phenylpropionaldehyde, linear aldehyde 3-phenylpropionaldehyde.
d LrBslinearrbranched.
e
w
x
TOFs moles of productrmoles of catalyst=reaction time .
f
wŽ
.
.
x
x
Ls p-Ph2 POC6 H4 2O .
g
h
wŽ
Ls p-Ph2 POC6 H4 2 S .
w
Ž
.
x
wŽ x
Catalysts Rh CO 2Cl r p-Ph2 POC6 H4 2CMe2 .
.
2
chemo- and regioselectivity result lower than
presence of the catalytic systems formed by
w
w Ž .Ž . x w Ž . x
Rh acac CO or Rh CO Cl and 2 the ter-
2 2 2
those observed with the catalytic system Rh
Ž
.Ž
.
x
acac CO and 2.
minal aliphatic olefin 1-octene was hydroformy-
lated with lower conversion in the aldehydes
with respect to styrene. With 1-octene, isomer-
2
The results obtained in the hydroformylation
of 1-octene are reported in Table 2. In the
Table 2
Hydroformylation of 1-octenea
Hydr.b
Aldehydes
Branchedc
LrBd
TOFe
w x w
x
Ž
.
Ž
.
Ž
.
Entry
L r Rh
P atm
T
8C
Conversion %
Isomeriz
Linearc
13
14
15
16
17
18
19
20f
21g
0.5
1
10
0.5
1
0.5
1
1
20
20
20
20
20
40
40
20
20
40
40
40
60
60
40
40
40
60
71.2
88.2
78.8
62.5
60.9
91.6
81.2
72.5
73.8
35.3
12.1
95.7
13.6
11
2.8
17.9
4.3
6.1
5.7
1.5
1.9
–
25.4
28.7
–
33.4
34.8
42.7
37.0
4.7
36.5
41.3
–
46.9
48.5
50.7
48.0
3.7
59r41
59r41
–
58r42
58r42
54r46
56r44
56r44
70r30
37
73.5
5.5
52
50.7
76.3
67.7
60.4
61.5
5.1
13.1
91.6
42.0
1
13.3
13.2
31.5
aReaction conditions: solvent toluene 10 ml ; COrH2 s1; catalysts Rh acac CO
r
p-Ph2 POC6 H4 2CMe2 ; catalyst:styrenes
Ž
.
w
Ž
.Ž . x wŽ
.
x
2
1:500.
bOctane.
c Branched aldehyde 2-methyloctanal, linear aldehyde n-nonal.
d LrBslinearrbranched.
e
w
x
TOFs moles of productrmoles of catalyst=reaction time .
f,g
w
Ž
.
x
wŽ x
.
Catalysts Rh CO 2Cl r p-Ph2 POC6 H4 2CMe2 .
2

(
)
384
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
ization and hydrogenation of the double bond
occurred in great extent during the reaction and
the aldehydes 1-nonanal and 2-methyloctanal
have been obtained together with octane and
isomerization products. Surprisingly, lowering
the temperature, the conversion of 1-octene in-
creases but the chemoselectivity drastically de-
creases owing to the formation of more isomer-
ization products. In the rhodium-catalyzed hy-
droformylation the reduction of the pressure
induces decrease in the aldehydes because the
s-acyl derivative is formed in minor yield. This
was observed also in the hydroformylation of
studied 1-hexene hydroformylation in the pres-
w
Ž
.
ence of catalytic systems formed by Rh acac -
2 x
Ž
.
w Ž .Ž
. x Ž
CO
or Rh acac CO L Lstertiary phos-
.
phine or phosphite and PR3 or clelating biden-
tate modifying ligands; using as catalyst Rh
acac CO PPh3 at 1 MPa and 353 K , the
w
Ž
.Ž
.Ž
.
x
Ž
.
presence of an excess of free PPh3 increases the
yield of aldehydes from 20 to 80% while the
isomerization product 2-hexene drastically de-
w
x
creases 14 . The authors assumed that the for-
mation of non-substituted rhodium carbonyls,
w
Ž
.
x
w Ž
. x
namely Rh4 CO
and Rh6 CO , were re-
12
16
sponsible of the isomerization of 1-hexene to
w
Ž
.Ž
.
2 x
w
Ž
.Ž
.Ž
.x
1-octene with Rh acac CO
and 2 and is
2-hexene. Using Rh acac CO PPh3 as pre-
catalyst, the species active in the hydroformyla-
evident when we consider the amount of alde-
hydes formed. The trend of the conversion is
pointing in opposite direction with respect to the
aldehydes formed and indicates that lowering
the pressure increases the isomerization prod-
ucts. It is noteworthy that the isomerization
products are more than the hydrogenation one.
w
Ž .Ž
.
tion process was assumed to be Rh H CO -
Ž
. x
PPh3 3 ; high selectivity to aldehydes was
achieved in the presence of excess of free ligand
because it is necessary to maintain in solution
rhodium complexes with two or more PPh3
ligands.
It is generally assumed that tertiary phos-
phine and diphosphine ligands form trigonal
bipyramidal hydridorhodium complexes, which
are the active catalysts in the hydroformylation
3. Conclusion
w
x
In the rhodium catalyzed hydroformylation of
terminal aliphatic alkene, as 1-octene, isomer-
ization normally occurs together the hydro-
formylation process and the amount of isomer-
ized product is high. Moasser and Gladfelter,
operating under mass transfer limiting condi-
tions, reported high isomerization rates in the
reaction 1,2,19 . It appeared that structures ei-
ther with the diphosphine ligand in equatorial–
equatorial or in equatorial–axial position are
stabilized depending on the distance between
the phosphorus atoms and the flexibility of the
bridge. In the case of two monodentate phos-
phine ligands, they might occupy two equato-
rial, two axial, or one equatorial and one axial
sites in the trigonal bipyramidal intermediate.
w x
hydroformylation of 1-octene 9 . Recently, von
Rooy et al. have found that the rhodium cat-
alyzed hydroformylation of 1-octene using bulky
diphosphites, occurs with very high selectivity
for the linear aldehyde although the isomeriza-
tion products reach a 26.5% value; interestingly,
hydrogenation of 1-octene was not observed
w x
For LsPPh3, Brown and Kent 7 showed by
NMR studies that a 85:15 of equatorial–equa-
torial:equatorial–axial mixture of isomers of
w
Ž
. Ž
. x
RhH CO PPh3 2 is present in solution, in
2
rapid equilibrium at room temperature. It is
noteworthy that the isomer with the phosphine
ligands both in axial position was not detected.
Bulky ligands show preferential equatorial–
equatorial coordination because of less steric
congestion in the equatorial plane of trigonal
w
x
10 . The results of van Leeuwen study are
consistent with a kinetic scheme in which the
addition of alkene is the rate-determining step
w
x
of the process 10 ; however by other studies
emerges that experimental conditions determi-
nate the rate-determining step of the process
w x
bipyramidal rhodium complexes 7 . The behav-
Ž
ior of a bridging diphosphine or bridging bis-
w
x
w
x
11–13 . Ziolkowski and coworkers 14–18
`

(
)
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
385
.
Ž
phosphinito ligands as 1–3 can be assimilated
ligand molar ratio more than 1:1 entries 3 and
.
to that of a monodentate tertiary phosphine. An
important question arising from this study is the
influence of the nature of the trigonal bipyrami-
dal hydridorhodium on the catalytic process,
being the ligands 1–3 able to induce only bridg-
ing coordination in transition metal complexes.
Very likely, the rigidity of the backbone of
ligands 1–3 makes the formation of the trigonal
bipyramidal rhodium I complexes intermediate
very difficult, particularly when the metal cen-
ters are held together by two bridging ligands,
as well as for the precatalysts Rh CO Cl m-
Ls1–3 Rh CO Cl q1–3 in Rh to
ligand molar ratio 1:2 . Sanger 20 showed that
A-frame complexes, in which the two rhodium
atoms are bridged by two bis diphenylphos-
phino methane ligands, present a low catalytic
activity probably owing to the rigidity of the
15 drastically reduces the aldehydes formed.
These results can be explained considering both
the flexibility and the number of phosphorus
atoms considering each of them as a monoden-
tate ligand coordinated to metal center in the
trigonal bipyramidal hydridorhodium I inter-
mediate. Kalck 21 successfully explored dirh-
odium complexes bridged by two thiolato lig-
ands in the hydroformylation of 1-hexene; the
high catalytic activity has been ascribed to the
good flexibility around the two sulphur atoms
which maintains the binuclear framework and
allows synergistic effects between the hydride–
metal centers. In our study cooperative effects
can be excluded being the metal centers at a
distance more than 9.0 A 3 . Still acceptable
results in the hydroformylation of styrene and
1-octene have been obtained when the trigonal
bipyramidal hydridorhodium intermediates
Ž
.
Ž .
w
x
Ž .
w
Ž
.Ž .Ž
.
L
x
Ž
. Ž
w
Ž
.
x
2
2
.
2 w
x
˚
Ž
w x
.
catalytic system.
Ä
w
Ž .Ž
.
x
2
Ž
.
4
Ž
.
From data of Tables 1 and 2 emerges that the
formed, namely Rh H CO
w
Ž
.Ž
.
x
w
Ž .Ž
.3Ž2
catalytic system formed by Rh acac CO and
and the oligomer Rh H CO m-2 n Fig. 3b ,
show some flexibility; the presence in the inter-
mediate Rh H CO m-2 of two coordinated
P-atoms for each rhodium center increases its
2
2 in the rhodium to ligand molar ratio 1:0.5
exhibits a capability to convert the styrene in
the corresponding aldehydes comparable to that
w
Ž .Ž
. Ž
.x
2
n
w
Ž
.
Ä
w
Ž .
of the catalytic system formed by Rh acac -
catalytic activity with respect to Rh H -
3x2
Ž
.
2 x
Ž
.
Ž
.4
CO
and 2 in the rhodium to ligand molar
CO
m-2 in the aldehydes formation.
Very likely the presence of an excess of
ratio 1:1; in the hydroformylation of 1-octene,
at 20 atm, the aldehydes formed with the cat-
ligand 2 affords, as intermediate, a very rigid
hydridorhodium oligomer species containing
three phosphorus ligands in the equatorial plane
of the trigonal bipyramid, bridged each to a
different rhodium atom. Unfortunately, all the
attempts to characterize the hydridorhodium in-
termediates failed owing to the instability of
w
Ž
.Ž
.
x
alytic system formed by Rh acac CO and 2
2
in the rhodium to ligand molar ratio 1:1 results
significantly more than that obtained with the
w
Ž
.Ž
.
x
catalytic system formed by Rh acac CO and
2
2 in the rhodium to ligand molar ratio 1:0.5. It
is noteworthy that in the hydroformylation ei-
ther of styrene or of 1-octene an rhodium to
Ž
.
these species at 1 atm of CO–H2 1:1 .
Fig. 3.

(
)
386
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
Isomerization, hydrogenation and hydro-
the reactor. The autoclave was closed and de-
gassed through three vacuum-nitrogen cycles. A
formylation catalytic processes require an s-al-
kyl intermediate; thus the ratio of the octene-
isomerization products is dependent on the rela-
tive rate of subsequent steps, reductive elimina-
tion, CO migration and b-hydrogen elimination.
Under our reaction conditions, for high tempera-
tures and CO pressure a faster CO addition, and
subsequent migration with formation of s-acyl
derivative, compared to b-hydrogen elimination
occurs. Low CO pressures and high tempera-
tures facilitate b-hydrogen elimination; in these
conditions the formation of isomerized products
dominates the hydroformylation of 1-octene.
Ž
solution of starting catalyst and of the olefin in
a typical experiment 5 mmol of substrate and
.
Ž
0.01 mmol of rhodium catalyst , in toluene 10
ml, was introduced under nitrogen, and gases
Ž
.
H2rCO 1:1 were admitted up to the desired
pressure. At the end of each catalytic run, the
autoclave was cooled in a cold water bath and
slowly vented. The conversion and the composi-
tion of the reaction products were determined
by GLC with a Carlo Erba HRGC 5160 Mega
Ž
Series apparatus splitrsplitless injector, MEGA
OV1 25 m column, film thickness 2 mm, carrier
.
gas He, FID detector .
4. Experimental
{
(
)
[
(
4.3. Syntheses Rh CO Cl m- p-Ph2 POC6-
)
]}
O
H4 2
2
4.1. Materials
Ž
Ž
.
Ž
Styrene and 1-octene were purchased Al-
A toluene solution 5 ml of 1 0.234 g, 0.41
.
mmol was added to a stirring solution of
.
drich and distilled before use. All other reagents
w
Ž . x Ž .
Rh CO Cl 0.08 g, 0.205 mmol in the same
2 2
Ž .
solvent 15 ml . After about 1 h, the reaction
mixture was reduced to ca. 3 ml and hexane 20
ml was added. The yellow-orange solid ob-
tained was filtered, washed with hexane 3=10
ml and dried. Yield: 80% Anal. Calcd. for
C74H56Cl2O8P4Rh2: C, 60.31;H 3.83; Cl, 4.81.
Found: C, 60.43; H 4.11, Cl, 5.02. IR KBr,
Nujol n CO 1985 cm . H NMR CDCl3
Ž . Ž .
6.7–6.9 m, CH, 16H 7.29–7.50 m, CH, 24H ,
7.73–7.9 m, CH, 16H . P H NMR CDCl3
d 125.8 d, J RhP s145.8 Hz .
were used as supplied.
Solvents were dried by standard procedures.
All experiments were performed under an atmo-
sphere of purified nitrogen. IR spectra were
obtained as Nujol mulls on KBr plates using a
Perkin-Elmer FTIR 1720 spectrophotometer. 1H
and P H NMR spectra were recorded on a
Bruker AMX R300. 1H NMR spectra were
referenced to internal standard tetramethylsilane
and P H spectra to external 85% H3PO4;
positive chemical shifts are for all nuclei to
higher frequency. Elemental analyses were per-
formed by Redox s.n.c., Cologno Monzese, Mi-
lano, Italy.
Ž
.
Ž
.
31
1
Ä
4
Ž
1
y
1
.
Ž
.
Ž
.
31
1
Ä
4
31
1
Ž
.
Ä
4
Ž
.
1
Ž
Ž
.
.
{
(
) [ ]}
4.4. Rh CO Cl m- p-Ph2 POC6 H4 2CMe2
2
(
)
4.2. Hydroformylation procedure
This compound was obtained similarly to 4,
Ž
All high pressure experiments were per-
formed in a 100 ml Berghoff stainless-steel
autoclave equipped with gas and liquid inlets, a
heating device, and magnetic stirring. The reac-
tions were carried out in a Teflon vessel fitted
to the internal wall of the autoclave, thus pre-
venting undesirable effects due to the metal of
as yellow-orange solid, by starting from 2 0.230
.
w
Ž
.
x Ž
2
g, 0.386 mmol and Rh CO Cl 0.75 g, 0.193
mmol . Yield: 87%. Anal. Calcd for C80H68-
Cl2O6P4Rh2: C, 62.97; H 4.49; Cl, 4.65. Found:
C, 63.17; H 4.66, Cl, 4.44. IR KBr, Nujol
n CO 1990 cm . H NMR CDCl3 d 1.60
s, CH3, 12H 6.5–6.8 m, CH, 16H 7.25–7.48
2
.
Ž
.
1
y
1
Ž
.
Ž
.
Ž
.
Ž
.

(
)
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
387
31
1
Ž
.
Ž
.
Ä
4
m, CH, 24H , 7.70–7.88 m, CH, 16H . P H
tion mixture was reduced to ca. 3 ml and hex-
1
Ž
.
Ž
Ž
.
Ž
.
NMR CDCl3 d 125.5 d, J RhP s143.5
ane 20 ml was added. The orange solid ob-
tained was filtered, washed with diethyl ether
.
Hz .
Ž
.
3=10 ml and dried in vacuo. Yield: 75%.
Calcd for C44H41O5P2Rh: C, 64.87; H 5.07.
{
(
) [ ) ]}
4.5. Rh CO Cl m- p-Ph2 POC6 H4 2 S
2
(
Ž
.
Ž
.
Found: C, 64.61; H 4.75 IR KBr, Nujol n CO
1
1
1995 cmy . H NMR C6D6 d 1.3 s, CH3,
Ž
.
Ž
This compound was obtained similarly to 4,
Ž
.
Ž
.
Ž
.
.
as yellow-orange solid, by starting from 3 0.256
12H , 1.59 s, CH3, 6H , 5.08 s, CH, 2H ,
.
w
Ž
.
x Ž
Ž
.
Ž
g, 0.437 mmol and Rh CO Cl 0.85 g, 0.218
mmol . Yield: 81%. Anal. Calcd. for C74H56-
6.7–6.9 m, CH, 8H , 7.28–7.51 m, CH, 12H ,
2
2
31
1
.
Ž
.
Ä
4
.
Ž
.
7.74–7.8 m, CH, 8H . P H NMR C6D6 d
1
Ž
Ž
.
Cl2O6P2S2Rh2: C, 59.02; H 3.75; Cl, 4.71.
139.2 d, J RhP s199.4 Hz .
Ž
Found: C, 59.27; H 4.05, Cl, 4.94. IR KBr,
1
y
1
.
Ž
.
Ž
Ž
.
Nujol n CO 1990 cm . H NMR CDCl3
6.66–6.85 m, CH, 8H 7.18–7.45 m, CH,
12H , 7.69–7.88 m, CH, 8H . P H NMR
Ž
.
31
1
Acknowledgements
.
Ž
Ž
.
Ä
4
1
Ž
.
Ž
.
.
CDCl3 d 124.6 d, J RhP s145.2 Hz .
Financial support from MURST and the Ital-
ian CNR is gratefully acknowledged.
{
[
(
)( )] [
(
)
m- p-Ph2 POC6 H4 -
2
4.6.
Rh acac CO
2
]}
CMe2
2
Ž
.
Ž
A toluene solution 5 ml of 2 0.095 g, 0.16
References
.
mmol was added to a stirring solution of
w
Ž
.Ž
.
Ž
.
Rh acac CO
0.082 g, 0.32 mmol in the
Ž2
.
w x
1
C.P. Casey, G.T. Whiteker, M.G. Melville, L.M. Petrovich,
J.A. Gavney Jr., D.R. Powell, J. Am. Chem. Soc. 114 1992
same solvent 15 ml . Immediately the solution
color turned from yellow to red-orange. Then
reaction mixture was reduced to ca. 3 ml and
hexane 20 ml was added. The yellow-orange
solid obtained was filtered, washed with diethyl
Ž
.
5535.
w x
Ž .
2
w x
3
C.P. Casey, G.T. Whiteker, Isr. J. Chem. 30 1990 299.
C.G. Arena, D. Drago, M. Panzalorto, G. Bruno, F. Faraone,
Inorg. Chim. Acta, submitted.
Ž
.
w x
Ž .
4
w x
5
AMPAC 5.0 1994 Semichem, 7128, Shawnee, K966216.
M. Cowie, S.K. Dwight, Inorg. Chem. 19 1980 2500.
C.G. Arena, E. Rotondo, F. Faraone, M. Lanfranchi, A.
Ž
.
ether 3=10 ml and dried in vacuo. Yield:
78%. Anal. Calcd. for C51H48O8P2Rh2: C,
Ž
.
w x
6
Ž
.
Tiripicchio, Organometallics 10 1991 3877, and references
therein.
57.97; H 4.58. Found: C, 57.78; H 4.31. IR
KBr, Nujol n CO 1992 cmy
.
1H NMR
1
Ž
Ž
.
Ž
.
w x
7
J.M. Brown, A.G. Kent, J. Chem. Soc., Perkin Trans. II
Ž
.
.
Ž
.
Ž
Ž
.
1987 1597.
C6D6 d 1.2 s, CH3, 12H , 1.6 s, CH3, 6H ,
5.06 s, CH, 2H , 6.7–6.9 m, CH, 8H , 7.28–
7.51 m, CH, 12H , 7.74–7.8 m, CH, 8H .
w x
8
Ž
.
.
T. Hayashi, M. Tanaka, I. Ogata, J. Mol. Catal. 13 1981
323, and references therein.
Ž
.
.
Ž
.
Ž
Ž
.
w x
9
Ž
B. Moasser, W.L. Gladfelter, Organometallics 14 1995
3832.
31
1
1
Ä
4
Ž
.
Ž
.
P H NMR C6D6 d 139.63 d, J RhP s
w
x
10 A. von Rooy, P.C.J. Kamer, P.W.N.M. van Leeuwen, K.
.
199.2 Hz .
Goubitz, J. Fraanje, N. Veldman, A.L. Spek, Organometallics
Ž
.
15 1996 835, and references therein.
{
(
)(
)[
(
)
Rh acac CO m- p-Ph2 POC6 H4 -
2
}
4.7.
CMe2
w
w
x
Ž
.
11 R.F. Heck, D.S. Breslow, J. Am. Chem. Soc. 83 1961
4023.
]
n
x
12 J.P. Collman, L.S. Hegedus, J.R. Norton, R.G. Finke, Princi-
ples and Applications of Organotransition Metal Chemistry,
2nd edn., University Science Books, Mill Valley, 1987.
Ž
.
Ž
A toluene solution 5 ml of 2 0.190 g, 0.16
mmol was added to a stirring solution of
Rh acac CO
same solvent 15 ml . Immediately the solution
w
x
.
13 P.W.N.M. van Leeuwen, G. van Koten, Catalysis, in: J.A.
Ž
.
Moulijn, P.W.N.M. van Leeuwen, R.A. van Santen Eds. ,
An Integrated Approach to Homogeneous, Heterogeneous
and Industrial Catalysis, 2nd edn., Elsevier, Amsterdam,
1995, p. 199 and references therein.
w
Ž
.Ž
.
Ž
.
0.082 g, 0.32 mmol in the
Ž2
.
color turned from yellow to red. Then the reac-

(
)
388
C.G. Arena et al.rJournal of Molecular Catalysis A: Chemical 144 1999 379–388
w
w
w
w
x
w
w
w
x
18 H. Janecko, A.M. Trzeciak, J.J. Ziolkowski, J. Mol. Catal. 26
`
14 E. Mieczynska, A.M. Trzeciak, J.J. Ziolkowski, J. Mol.
`
Ž
.
Ž
.
Catal. 73 1992 1.
1984 355.
x
x
15 A.M. Trzeciak, J.J. Ziolkowski, R. Choukroun, J.
19 G.J.H. Buisman, L.A. van der Veen, P.C.J. Kamer, P.W.N.M.
`
Ž
.
Ž .
van Leeuwen, Organometallics 16 1997 5681.
Organometal. Chem. 420 1991 353.
x
x
Ž
.
16 A.M. Trzeciak, T. Glowiak, R. Grzybek, J.J. Ziolkowski, J.
20 A.R. Sanger, in: L.H. Pignolet Ed. , Homogeneous Catalysis
with Metal–Phosphine Complexes, Plenum, New York, 1983,
p. 228.
`
Ž
.
Chem. Soc., Dalton Trans. 1997 1831.
x
17 A.M. Trzeciak, J.J. Ziolkowski, J. Organometal. Chem. 429
`
Ž
.
w
x Ž .
1992 239.
21 P. Kalck, Polyhedron 7 1988 2441.