Rhodium-catalyzed hydroformylation of styrene at low temperature using potentially hemilabile phosphite-phosphonate ligands

Article abstract of DOI:10.1016/S0040-4039(00)02028-1

The synthesis and the effect of phosphite-phosphonate ligands in rhodium-catalyzed hydroformylation of styrene are described. Activity and selectivity of the catalyst are improved, at low temperature, by increasing bulkiness of both phosphite and phosphonate moieties.

Full text of DOI:10.1016/S0040-4039(00)02028-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 643–645
Rhodium-catalyzed hydroformylation of styrene at low
temperature using potentially hemilabile phosphite–phosphonate
ligands
Caroline Roch-Neirey, Nathalie Le Bris, Pascale Laurent, Jean-Claude Cle´ment and
Herve´ des Abbayes*
Laboratoire de Chimie, Electrochimie Mole´culaires et Chimie Analytique, UMR CNRS 6521,
Universite´ de Bretagne Occidentale, UFR Sciences et Techniques, 6 avenue Le Gorgeu, BP 809, 29285 Brest Cedex, France
Received 10 October 2000; accepted 10 November 2000
Abstract—The synthesis and the effect of phosphite–phosphonate ligands in rhodium-catalyzed hydroformylation of styrene are
described. Activity and selectivity of the catalyst are improved, at low temperature, by increasing bulkiness of both phosphite and
phosphonate moieties. © 2001 Elsevier Science Ltd. All rights reserved.
Since the studies on RhH(CO)(PPh3)3 and hydroformy-
lation of alkenes by Wilkinson and co-workers thirty
years ago,1–6 extensive studies have been devoted to the
search for more active and selective catalysts by ligand
modification. Thus, high selectivities in hydroformyla-
tion of alkenes have been reported for bulky diphos-
phine7,8 and diphosphite9–14 modified Rh-catalysts.
complexes have a great potential in homogeneous cataly-
sis since the chelate structure should readily open to
liberate a vacant site on the metal. For instance, rhodium
complexes with hemilabile phosphine–phosphonate lig-
ands have been shown to have promising catalytic
properties which were ascribed to the easy ring opening
of the chelate structure by phosphonate moiety decoor-
dination.16–20
On the other hand, there has been an increasing interest
in hemilabile chelating ligands:15 their transition-metal
To our knowledge, no potential hemilabile ligand bear-
(1)
(2)
Keywords: hydroformylation; styrene; rhodium; hemilabile ligand; phosphite; phosphonate; catalysis.
* Corresponding author. Tel.: +33 298016153; fax: +33 298017001; e-mail: herve.desabbayes@univ-brest.fr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)02028-1

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C. Roch-Neirey et al. / Tetrahedron Letters 42 (2001) 643–645
Table 1. Rh-catalyzed hydroformylation of styrene25
Entry
Ligand
60°C, 1 h
25°C, 18 h
Conversion (%)a
Conversion (%)a
Iso/n
Iso/n
1
2
3
4
5
6
7
8
9
PPh3
41
42
50
27
92
56
90
93
96
85/15
84/16
86/14
85/15
92/8
87/13
82/18
80/20
73/27
1
15
30
0
71
26
63
69
91
–
Ph2PCH2P(O)(OEt)2
Ph2PCH2P(O)(OiPr)2
P(OEt)3
P(OPh)3
3a
3b
3c
3d
99/1
99/1
–
93/7
93/7
95/5
97/3
97/3
a Converted styrene as percentage of the initial amount. Percentage of aldehydes relative to the converted styrene is >99.
ing both phosphite and phosphonate groups has been
studied in catalysis. We now report the syntheses of
such ligands and the results obtained in the hydro-
formylation of styrene with their rhodium complexes as
catalyst precursors.
the activity of the mixed ligands is clearly superior at
25°C.
For the phosphites bearing ethyl groups (entries 4 and
6), it is noteworthy that the presence of a phosphonate
moiety leads to better results either at 60 or 25°C.
Comparing the results obtained at 60°C with
triphenylphosphite (entry 5) and biphenylphosphites
(entries 7–9), introduction of a phosphonate group
leads to a loss of selectivity, whereas activity is
improved by increasing phosphonate bulkiness. On the
contrary, at 25°C, increasing the size of phosphonate
moiety leads to better conversions and selectivities and
ligand 3d proves to be excellent.
In order to study the influence of each coordinating
group (either phosphite or phosphonate) on the cata-
lytic reaction, the four phosphite–phosphonate ligands
3a–d were prepared by reaction of chlorophosphites 121
with hydroxymethylphosphonates 222 in the presence of
diisopropylethylamine (Eqs. (1) and (2)).23†
The catalytic activities of rhodium complexes of ligands
3a–d on hydroformylation of styrene were compared to
those obtained with hemilabile phosphine–phosphonate
ligands Ph2PCH2P(O)(OR)2 (R=Et, iPr)20 and with
PPh3, P(OEt)3 and P(OPh)3. Standard addition of
[Rh(Cl)(cod)]2 with two parts of bifunctional ligands or
four parts of monofunctional ligands was used for the
catalytic experiments (Eq. (3)). Results are summarized
in Table 1.
In conclusion, examination of catalytic activity of
mixed phosphite–phosphonate ligands on the hydro-
formylation of styrene has shown promising results,
particularly at low temperature. The increased bulki-
ness of both phosphite and phosphonate moieties leads
to improved catalytic activities and selectivities. Synthe-
Table 1 shows the great superiority of the bulky phos-
phites (entries 5–9), P(OPh)3 giving better results at
60°C and ligand 3d (entry 9) leading to better activity
and selectivity at 25°C.
ses of chiral bulkier mixed phosphite–phosphonate lig-
ands and screening of their potential in asymmetric
catalysis are now under investigation.
References
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† To our knowledge, only ligand 3a was previously synthetized by
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