Hydroformylation of alkenes catalyzed by new dinuclear aryloxide- and carboxylate-bridged rhodium complexes

Article abstract of DOI:10.1016/j.ica.2004.05.014

The new dinuclear aryloxide- and carboxylate-bridged rhodium complexes bis[μ-(2-methylphenolato)]bis[(η²:η²-cycloocta- 1,5-diene)rhodium], di(μ-docosanoato)bis[(η²: η²-norborna-2,5-diene)rhodium] and bis[(μ-(adamant-1-yl) carboxylato]bis[(η²:η²-norborna-2,5-diene)rhodium] have been prepared. The complexes were tested as catalysts in the hydroformylation of styrene with a total pressure of CO/H₂ (1:1) of 1000 psi, at 25 and 60°C, and displayed a regioselectivity towards the branched aldehyde of up to 97%. The same complexes as catalysts in the hydroformylation of 1-octene displayed a regioselectivity for the linear aldehyde of up to 55%.

Full text of DOI:10.1016/j.ica.2004.05.014

Inorganica Chimica Acta 357 (2004) 3084–3088
www.elsevier.com/locate/ica
Hydroformylation of alkenes catalyzed by new dinuclear
aryloxide- and carboxylate-bridged rhodium complexes
a,
a
b,
c
*
Ioannis D. Kostas *, Kalliopi A. Vallianatou , Panayotis Kyritsis , Jirı Zednık ,
ꢀꢁ
ꢁ
c,
*
ꢀꢁ
Jirı Vohlıdal
ꢁ
a
National Hellenic Research Foundation, Institute of Organic and Pharmaceutical Chemistry, Vas. Constantinou 48, 11635 Athens, Greece
b
Inorganic Chemistry Laboratory, Department of Chemistry, National and Kapodistrian University of Athens, Panepistimiopolis,
Zografou, 15771 Athens, Greece
c
Laboratory of Specialty Polymers, Department of Physical and Macromolecular Chemistry, Charles University, Albertov 2030, CZ-128 40, Prague 2,
Czech Republic
Received 7 April 2004; accepted 1 May 2004
Available online 24 June 2004
Abstract
The new dinuclear aryloxide- and carboxylate-bridged rhodium complexes bis[l-(2-methylphenolato)]bis[(g2:g2-cycloocta-1,5-di-
ene)rhodium], di(l-docosanoato)bis[(g2:g2-norborna-2,5-diene)rhodium] and bis[(l-(adamant-1-yl)carboxylato]bis[(g2:g2-norborna-
2,5-diene)rhodium] have been prepared. The complexes were tested as catalysts in the hydroformylation of styrene with a total pressure
of CO/H2 (1:1) of 1000 psi, at 25 and 60 °C, and displayed a regioselectivity towards the branched aldehyde of up to 97%. The same
complexes as catalysts in the hydroformylation of 1-octene displayed a regioselectivity for the linear aldehyde of up to 55%.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Rhodium complex; Dinuclear complex; Aryloxo complex; Carboxylato complex; Hydroformylation; Homogeneous catalysis
1. Introduction
formylation of vinyl substrates [2]. For instance,
hydroformylation of styrene, catalyzed by [Rh(cod)
(OAc)]2, proceeds with a regioselectivity for the branched
aldehyde of up to 96% [6]. Much attention has also been
focused on the chemistry of late transition-metal com-
plexes containing metal-alkoxide and metal-aryloxide
bonds that are suggested to be intermediates in various
catalytic reactions [7–11]. For these reagents, it is also
known that the thermodynamic stability of the M–OR
bond is comparable to that of M–C (sp3) bonds [12,13].
We have previously reported the synthesis of several
modified transition-metal complexes based on phospho-
rus ligands with additional potential donors like N, S, O
as well as phosphine-free ligands, that were successfully
used as catalysts in homogeneous catalytic reactions, such
as hydroformylation, hydroaminomethylation, hydro-
genation, and the Heck reaction [14–21]. It is among our
research interests to extend our activities to catalysis by
unmodified catalysts. In the last decade, new Rh(diene)
complexes have been prepared and successfully used
as catalysts in controlled polymerization reactions of
Rhodium-catalyzed hydroformylation retains an ex-
tremely active area of research with enormous academic
and industrial interest, and represents one of the most
important homogeneously catalyzed reactions world-
wide [1–4]. Since the regioselectivity of the reaction is
strongly influenced by the use of phosphines, phosphorus-
modified rhodium catalysts have been used much more
extensively than the corresponding unmodified ones [1,2].
However, hydroformylation reaction catalyzed by un-
modified rhodium complexes is a subject of intense in-
vestigations for reasons that have been extensively
reviewed [5]. Dinuclear carboxylate-bridged complexes of
rhodium(I) are amongst the unmodified catalyst precur-
sors that are most frequently employed in the hydro-
* Corresponding authors. Tel.: +30-210-7273878; fax: +30-210-
7273831 (I.D. Kostas), +30-210-7274268 (P. Kyritsis), +420-221-
ꢁ
951310 (J. Vohlıdal).
E-mail addresses: ikostas@eie.gr (I.D. Kostas), kyritsis@chem.
ꢁ
uoa.gr (P. Kyritsis), vohlidal@natur.cuni.cz (J. Vohlıdal).
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.05.014

I.D. Kostas et al. / Inorganica Chimica Acta 357 (2004) 3084–3088
3085
various monomers [22]. In this paper, we report the syn-
thesis of new dinuclear aryloxide- and carboxylate-
bridged complexes of rhodium(I) with cod and nbd as
diene ligands, and the activity of these unmodified cata-
lysts in the hydroformylation of styrene and 1-octene.
a representative vinyl aryl substrate. Catalysis was per-
formed under the same reaction conditions previously
reported for the hydroformylation of styrene by the
rhodium carboxylate complex [Rh(cod)(OAc)]2 [6] (0.1
mole% catalyst; 0.1 mM solution of the catalyst in
CH2Cl2; 1000 psi CO/H2, 1:1) (Scheme 3, Table 1). In all
experiments, the chemoselectivity towards aldehydes
was almost quantitative, and side-products were present
only in traces. At 25 °C, the regioselectivity towards the
branched aldehyde 10 was found to be 97% (b=l ¼ 32),
which is higher compared to that observed when
[Rh(cod)(OAc)]2 was used as catalyst (96%, b=l ¼ 24)
[6]. However, the reaction rate is considerably lower. At
25 °C, complex 3 proceeds to 75% conversion of styrene
after 48 h, and complexes 7 and 8 to conversions of only
17% and 12%, respectively. Probably, the low activity of
complexes 7 and 8 is due to the steric hindrance induced
by their bulky carboxylate ligands. As expected for the
hydroformylation of styrene using rhodium complexes
as catalysts, an elevated temperature (60 °C) dramati-
cally increases the reaction rate but, at the same time,
results in a lower regioselectivity.
2. Results and discussion
2.1. Synthesis of the rhodium complexes
The dinuclear aryloxide-bridged complex [Rh(cod)
(OC6H4CH3)]2 (3) was prepared with a yield of 85% by
the reaction of [{Rh(cod)}2(l-Cl)2] (1) with the sodium
alkoxide of o-cresol 2 (Scheme 1), following a modified
known procedure concerning the reaction of 1 with so-
dium phenoxide [23]. In our approach, the use of soni-
cation increased the reaction rate, and at the same time
afforded highly pure product.
The synthesis of the dinuclear carboxylate-bridged
complexes 7 and 8 was achieved with yields of about 70%
by the ultrasound-assisted reaction of [{Rh(nbd)}2
(l-Cl)2] (4) with the silver salts 5 and 6, respectively
(Scheme 2). This approach represents a modification of a
procedure previously employed by us for the synthesis
of di(l-docosanoato)bis[(g2:g2-cycloocta-1,5-diene)rho-
dium], and it is clear that the type of diene ligand (cod or
nbd) has no influence on the bridged-ligand exchange
reaction [24].
The catalytic activity of the complexes was also
studied for the hydroformylation of 1-octene (12),
which is a representative linear 1-alkene, under the
conditions described above (Scheme 4, Table 2). Of
course, with respect to hydroformylation, 1-octene
CHO
CO/H2
Rh cat.
CHO
+
2.2. Hydroformylation
9
10
Scheme 3.
11
The rhodium complexes 3, 7 and 8 were first tested as
catalysts in the hydroformylation of styrene (9), which is
o-CH3C6H4ONa (2)
Cl
Cl
O
Rh
Rh
Rh
Rh
O
))))))
THF,
85%
1
3
Scheme 1.
R
RCOOAg
5: R = heneicosan-1-yl
6: R = adamant-1-yl
O
O
Cl
Rh
Rh
Rh
Rh
Cl
))))))
H2O,
O
O
R
4
7: R = heneicosan-1-yl (72%)
8: R = adamant-1-yl (68%)
Scheme 2.

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I.D. Kostas et al. / Inorganica Chimica Acta 357 (2004) 3084–3088
Table 1
Hydroformylation of styrene catalyzed by aryloxide and carboxylate rhodium complexesa
Entry
Complex
T (°C)
Time (h)
Conversion (%)
Rbrb(%)
TONc
1
2
3
4
5
6
3
3
7
7
8
8
25
60
25
60
25
60
48
16
48
16
48
16
75
98
17
40
12
38
97
92
97
94
97
93
750
980
170
400
120
380
a Reaction conditions: Catalysis was performed by a 0.1 mM solution of the corresponding rhodium complex in CH2Cl2; Styrene:catalyst ¼ 1000:1;
initial total pressure of CO/H2 (1:1) ¼ 1000 psi.
b Rbr ¼ regioselectivity towards branched aldehyde.
c Turnover no. (TON) ¼ aldehydes fraction ꢀ substrate:catalyst ratio.
CHO
14
CHO
CO/H2
CHO
+
Rh cat.
15
12
13
CHO
16
Scheme 4.
Table 2
Hydroformylation of 1-octene catalyzed by aryloxide and carboxylate rhodium complexesa
TONb
T (°C)
Time (h)
Conversion (%)
Selectivity
Entry
Complex
13:14:15:16
1
2
3
4
5
6
3
3
7
7
8
8
25
60
25
60
25
60
48
16
48
16
48
16
94
100
76
55:45:–:–
54:40:5:1
54:46:–:–
52:37:8:3
55:45:–:–
52:41:6:1
940
1000
760
100
63
1000
630
100
1000
a Reaction conditions: Catalysis was performed by a 0.1 mM solution of the corresponding rhodium complex in CH2Cl2; 1-octene:cata-
lyst ¼ 1000:1; initial total pressure of CO/H2 (1:1) ¼ 1000 psi.
b Turnover no. (TON) ¼ aldehydes fraction ꢀ substrate:catalyst ratio.
behaves in a different way compared to styrene. The
latter has a distinct preference for the branched alde-
hyde due to the formation of a stable g3-complex
during the course of the catalytic cycle [25]. At 25 °C,
the complexes 3, 7 and 8 display a 54–55% regiose-
lectivity towards the linear aldehyde 13, slightly higher
to that observed when [Rh(cod)(OAc)]2 was used as
catalyst (52%) [6]. However, the reaction rate was
found to be lower. At room temperature, isomerization
side-products were negligible. On the other hand, at 60
°C, the conversion of 1-octene was quantitative after 16
h. However, more than two regioisomers were observed
as a result of the alkene’s isomerization, due to the
migration of the double bond into internal positions,
and the subsequent hydroformylation of the resulting
internal alkenes [26,27].
2.3. Summary
In summary, we have synthesized a new dinuclear
aryloxide rhodium complex with cod as diene ligand and
an o-methylphenolate bridge, as well as two dinuclear
carboxylate rhodium complexes with nbd as diene li-
gands and docosanoate or (adamant-1-yl)carboxylate
bridges. When these complexes were used as catalysts in
the hydroformylation of styrene and 1-octene, they
displayed regioselectivities comparable or even higher
than those observed when other unmodified catalyst
precursors, most frequently employed in hydroformy-
lation reactions, were used. However, the reaction rates
by the carboxylate complexes reported herein are low,
and this may be due to steric effects exerted by their
bulky carboxylate ligands.

I.D. Kostas et al. / Inorganica Chimica Acta 357 (2004) 3084–3088
3087
3. Experimental
1594 (m), 1572 (w), 1480 (vs), 1460 (w), 1434 (m), 1378
(w), 1328 (w), 1302 (vw), 1248 (vs), 1211 (vw), 1187 (w),
1174 (vw), 1111 (m), 1037 (w), 999 (m) (cod), 964 (m)
(cod), 895 (w), 870 (m), 857 (m), 833 (vw), 816 (vw), 771
3.1. General
Di(l-chloro)bis[(g2:g2-cycloocta-1,5-diene)rhodium]
(1) and di(l-chloro)bis[(g2:g2-norborna-2,5-diene)rho-
dium] (4) were prepared from rhodium trichloride hy-
drate according to a known procedure [28]. All chemical
reagents used are commercially available, unless other-
wise stated. The synthesis of the complexes and the
catalytic reactions were carried out under argon by us-
ing dry and degassed reagents and solvents. Hydro-
formylation was performed in a stainless steel autoclave
(300 ml) with magnetic stirring. Syngas: CO/H2 (1/1).
NMR spectra were recorded on a Varian UNITYINOVA
400 instrument. COSY experiments were recorded in
absolute value mode using a standard two-pulse se-
quence. HSQC and HMBC were performed as gradient
experiments. All 2D experiments were recorded with
spectral windows 5000 Hz for proton and 25 000 Hz for
carbon. Infrared and Raman spectra were recorded on a
Nicolet Magna 760 IR instrument with Inspector IR
Microscope and using both non-diluted and Nicolet
Nexus FT-Raman module in KBr-diluted samples using
diffuse reflectance technique (128 or more scans at res-
olution 4 cmꢁ1) for IR. GC: Varian Star 3400 CX with a
30 m ꢀ 0.53 mm DB5 column. GC–MS (EI): Varian
Saturn 2000 with a 30 m ꢀ 0.25 mm DB5-MS column.
Melting points were measured on Kofler block Boetius.
(s), 760 (w), 724 (m), 601 (m), 489 (m), 444 (m) cmꢁ1
.
Raman: m 3064 (m), 3036 (s), 2992 (vs), 2976 (m), 2914
(vs), 2896 (s), 2884 (vs), 2835 (s), 1593 (m), 1571 (w),
1470 (m), 1448 (w), 1433 (m), 1378 (w), 1250 (s), 1037
(m), 890 (w), 783 (m), 759 (m), 549 (w), 518 (m), 484 (s),
399 (vs), 264 (m), 177 (s), 119 (m) cmꢁ1. Anal. Calc. for
C30H38O2Rh2 (636.44): C, 56.62; H, 6.02. Found: C,
55.98; H, 6.05%.
3.3. Silver docosanoate (5)
A hot (50 °C) solution of docosanoic acid (0.82 g,
2.41 mmol) in ethanol (50 ml) was added slowly to a hot
solution of silver nitrate (0.51 g, 3.00 mmol) in aqueous
ammonium hydroxide (50 ml, 15%) at 50 °C, in the
dark. The precipitated silver salt was washed with water
to remove non-reacted silver nitrate, then extracted in a
Soxhlet extractor with ethanol to remove traces of non-
reacted carboxylic acid, and dried in vacuum for 12 h,
yielding 5 almost quantitatively.
3.4. Silver adamantane-1-carboxylate (6)
Sodium adamantane-1-carboxylate (0.48 g, 2.38
mmol) and a solution of silver nitrate (0.51 g, 3.00
mmol) in water (10 ml) were mixed at room tempera-
ture, in the dark. The precipitated silver salt 6 was pu-
rified as described above for 5.
3.2.
1,5-diene)rhodium] (3)
Bis[l-(2-methylphenolato)]bis[(g2:g2-cycloocta-
A solution of o-cresol (0.50 g, 4.62 mmol) in THF (15
ml) was added to sodium metal (0.11 g, 4.78 mmol) and
the mixture was allowed to react under sonication for 45
min. The traces of unreacted sodium were removed
mechanically. Subsequently, [{Rh(cod)}2(l-Cl)2] (1)
(0.10 g, 0.20 mmol) was added, and the mixture was
sonicated for 45 min. THF was evaporated by vacuum
and the crude product was washed with water (5 ꢀ 10
ml) in order to remove NaCl and residual sodium o-
methylphenolate. The product was dried in vacuum and
recrystallized from dichloromethane/hexane, yielding 3
3.5.
rhodium] (7)
Di(l-docosanoato)bis[(g2:g2-norborna-2,5-diene)
[{Rh(nbd)}2(l-Cl)2] (0.10 g, 0.22 mmol) was added to
a suspension of silver docosanoate (5) (0.98 g, 2.20
mmol) in water (10 ml) and the resulting suspension was
sonicated for 15 min. At that stage, the formation of
AgCl was observed. Water was removed by vacuum, the
residue was suspended in THF (100 ml), and AgCl was
removed by filtration. The filtrate was concentrated to
ca. 5 ml and cooled to 4 °C, yielding crystals of the
1
1
(0.11 g, 85%), m.p. (dec.) >90 °C. H NMR (CDCl3): d
rhodium complex 7 (0.17 g, 72%), m.p. 56–59 °C. H
7.09 (d, J ¼ 7:2 Hz, 2H, Ar), 6.89 (br t, J ¼ 7:5 Hz, 2H,
Ar), 6.67 (dt, J ¼ 7:3 Hz, J ¼ 1:2 Hz, 2H, Ar), 6.59 (d,
J ¼ 7:6 Hz, 2H, Ar), 3.29 (br s, 4H, ¼ CH, cod), 3.10 (s,
6H, CH3), 2.54 (br s, 4H, ¼ CH, cod), 2.40 (m, 4H,
CH2, cod), 2.18 (m, 4H, CH2, cod), 1.37 (m, 4H, CH2,
cod), 1.30 (m, 4H, CH2, cod). 13C NMR (CDCl3): d
159.05 (C–(O), Ar), 130.33 (Ar), 129.54 (C–CH3, Ar),
125.93, 121.53 and 119.89 (Ar), 74.76 (d, J ¼ 15:9 Hz,
¼ CH, cod), 74.41 (d, J ¼ 15:9 Hz, ¼ CH, cod), 30.15
(CH2, cod), 18.58 (CH3). FT-IR (KBr): m 3060 (w), 2995
(w), 2975 (w), 2936 (w), 2918 (w), 2879 (m), 2832 (m),
NMR (CDCl3): d 4.01 (s, 8H, @CH, nbd), 1.23 (s, 4H,
CH2, nbd), 4.07 (br s, 4H, CH, nbd), 1.89 (4H, s, CH2),
1.29 (4H, s, CH2), 1.26 (72H, m, CH2), 0.81 (t, J ¼ 7 Hz,
6H, CH3). 13C NMR (CDCl3): d 184.5 (C@O), 60.1
(CH2, nbd), 50.6 (@CH, nbd), 50.2 (CH, nbd), 37.1,
30.9, 29.7, 29.1, 26.2 and 22.7 (CH2), 14.1 (CH3). FT-IR
(KBr): m 2916 (vs), 2849 (s), 1562 (s), 1471 (w), 1420 (w),
1396 (w), 1303 (w), 1168 (vw), 1112 (vw), 1032 (vw), 995
(vw), 881 (vw), 719 (w) cmꢁ1. Raman: m 3064 (w), 2999
(w), 2929 (m), 2881 (vs), 2846 (s), 1458 (w), 1439 (w),
1396 (w), 1294 (w), 1072 (w), 933 (w), 619 (w), 568 (w),

3088
I.D. Kostas et al. / Inorganica Chimica Acta 357 (2004) 3084–3088
310 (w) cmꢁ1. Anal. Calc. for C58H102O4Rh2 (1069.30):
C, 65.15; H, 9.62. Found: C, 64.79; H, 9.86%.
Specific Account of the University of Athens (P.K.,
Grant 70/4/5728), the Ministry of Education of the
Czech Republic, project MSM 113100001, and the
Czech Science Foundation (203/03/0281).
3.6. Bis[(l-(adamant-1-yl)carboxylato]bis[(g2:g2-norb-
orna-2,5-diene)rhodium] (8)
Following the procedure described above for the
synthesis of 7, rhodium complex 8 was prepared from
[{Rh(nbd)}2(l-Cl)2] (0.10 g, 0.22 mmol) and silver ad-
amantane-1-carboxylate (6) (0.63 g, 2.20 mmol) with a
References
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1
yield of 68% (0.112 g), m.p. (dec.) >190 °C. H NMR
(CDCl3): d 4.20 (br s, 4H, CH, nbd), 4.02 (s, 8H, @CH,
nbd), 1.84 (s, 6H, CH, adam), 1.60–1.53 (m, 24H, CH2,
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Acknowledgements
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The investigation was supported by the General
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