Ionic diamine rhodium(I) complexes - Highly active catalysts for the hydroformylation of olefins

Article abstract of DOI:10.1039/b502435h

Rhodium(I) complexes composed of an anionic rhodium centre containing chloride ligands, and a cationic rhodium centre coordinated by a diamine ligand, were synthesized and characterized. These complexes are able to catalyze the hydroformylation reaction under mild reaction conditions in excellent activity and regioselectivity, and in the absence of a phosphorus ligand. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b502435h

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Ionic diamine rhodium(I) complexes—highly active catalysts for the
hydroformylation of olefins{
Jai Jun Kim and Howard Alper*
Received (in Berkeley, CA, USA) 16th February 2005, Accepted 14th April 2005
First published as an Advance Article on the web 9th May 2005
DOI: 10.1039/b502435h
(Scheme 1).7 Fig. 1 shows the crystal structure of complex 2.{
Rhodium(I) complexes composed of an anionic rhodium centre
The chlorine ligands of 2 reside in the anion, and the cationic
rhodium center is coordinated by both the olefin and diamine
ligands. The bond angles of N–Rh–N9 and Cl–Rh–Cl9 are 83.11u
and 89.63u, respectively. This indicates that the core structure has a
distorted square planar configuration.
containing chloride ligands, and a cationic rhodium centre
coordinated by a diamine ligand, were synthesized and
characterized. These complexes are able to catalyze the
hydroformylation reaction under mild reaction conditions in
excellent activity and regioselectivity, and in the absence of a
phosphorus ligand.
In contrast, no reaction occurred when 1 was treated with
N,N,N9N9-tetraethylethylenediamine (TEEDA) or N,N,N9N9-
tetrabenzylethylenediamine (TBzEDA) even under reflux
conditions.
The metal-catalyzed hydroformylation reaction is one of the most
useful chemical processes for the production of linear or branched
aldehydes by the reaction of alkenes, carbon monoxide, and
hydrogen. Commercially, more than seven million tons of
aldehydes and alcohols are produced by homogeneous hydro-
formylation per year.1
The ionic rhodium carbonyl complexes, 3a and 3b were formed
by the reaction of 1 with TEEDA or TBzEDA respectively, under
CO pressure at room temperature (See ESI{). These complexes
have structures similar to those of complex 2 with the chlorine
atoms localized in the anion, and diamine coordinated cationic
rhodium centers.
The most frequently used catalyst system for hydroformylation
is a rhodium complex with phosphorus compounds as added
ligands.2 Many kinds of phosphorus ligands have been synthe-
sized, and applied as auxiliary ligands for rhodium-catalyzed
hydroformylation reactions to improve activity, regioselectivity,
and stereoselectivity.3 The drawbacks of using most phosphorus
ligands are that larger than stoichiometric amounts are often
required to achieve good selectivity, and reaction conditions can be
harsh in some cases. These problems tend to limit the application
of hydroformylation for the preparation of functionalized organic
molecules. However, relatively few results have been published
concerning cooperative effects involving several metal centers for
the rhodium catalyzed hydroformylation,4 as well as the use of
rhodium without ancillary ligands.5
We now describe the first application of ionic rhodium(I)
diamine complexes for the hydroformylation reaction. These
rhodium complexes are composed of an anionic rhodium center
containing chloride ligands, and a cationic rhodium center
coordinated by a diamine ligand. These complexes are able to
catalyze the hydroformylation reaction under mild reaction
conditions in excellent activity and regioselectivity, and in the
absence of a phosphorus ligand. It should be noted that ruthenium
carbonyl carboxylates with nitrogen containing ligands have been
used for hydroformylation but the yields are rather modest.6
The reaction of the rhodium complex [Rh(COD)Cl]2, 1 (COD:
1,5-cyclooctadiene) with the bidentate N-donor ligand,
N,N,N9N9-tetramethylethylenediamine (TMEDA) in toluene at
25 uC for 16 hours, afforded the ionic complex
Scheme 1 Synthesis of diamine–rhodium complexes.
[Rh(TMEDA)(COD)]+[Rh(COD)Cl2]2,
2
in 90% yield
{ Electronic Supplementary Information (ESI) available: Experimental
details—general procedure for the hydroformylation reaction and
synthesis of catalysts. See http://www.rsc.org/suppdata/cc/b5/b502435h/
*howard.alper@uottawa.ca
Fig. 1 Thermal ellipsoid representation of [(TMEDA)Rh(COD)]
[(COD)RhCl2], 2. Selected bond angles [u]; N(12)–Rh(1)–N(12_2) 5
83.11(18), Cl(3)–Rh(2)–Cl(3_2) 5 89.63(6).
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Table 1 Hydroformylation of styrene and vinyl acetate catalyzed by diamine–rhodium complexesa
Entry
Catalyst
Olefins
Olefin/cat. ratio
Temp./uC
Conv.b (%)
B/L ratioc
1
2
1
1
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Styrene
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
Vinyl acetate
500
1000
500
25
45
25
25
25
25
25
45
45
45
45
45
25
70
25
45
70
25
70
25
25
70
,5
14
30
99.
60
55
42
99.
99.
85
99.
99.
,5
45
73
91
99.
49
—
21
30
39
28
30
28
14
14
16
13
13
—
16
21
18
19
24
18
41
40
23
3d
4
1 + Et3N
2
2
3a
3b
2
2
2
3a
3b
1
1
2
500
5
6
7
8
1000
1000
1000
1000
2000
3000
1000
1000
500
1000
500
1000
1000
500
9
10
11
12
13
14
15e
16
17
18e
19
20e
21f
22
a
2
2
3a
3a
3b
3b
3b
1000
500
500
60
21
37
99.
1000
b
Reaction conditions: catalyst (10 mg), toluene (10 mL), CO/H2 (500/500 psi g), 16 h. See ESI for the general procedure. Determined by GC
and 1H NMR. Branched/linear ratio; determined by 1H NMR. 0.02 mmol of 1 and 0.02 mmol of Et3N were used for reaction. 22 h
reaction time. 48 h reaction time.
c
d
e
f
The catalytic activity of these rhodium complexes was evaluated
for the hydroformylation of various olefins. Table 1 shows the
hydroformylation results for styrene and vinyl acetate. Rhodium
complexes 2, 3a, and 3b exhibit excellent catalytic activity and
selectivity for the hydroformylation of styrene even at room
temperature (entries 4–7), while complex 1 shows poor activity
(entries 1, 2). The high activity and selectivity showed by the ionic
rhodium complexes under mild reaction conditions is a competitive
advantage of the ionic complexes as hydroformylation catalysts.
to 70 uC, the activity increased with a slight loss of selectivity (more
than 95% branched aldehyde) and there is no activity difference
between complexes 2, 3a, and 3b (entries 17, 19, 22). These results
suggest that the reaction pathways may be different depending on
the reaction temperature.
In order to determine the scope of the hydroformylation
reaction catalyzed by ionic rhodium complexes, a variety of olefins
were reacted at room temperature for 22 h, and the results are
summarized in Table 2.
For all substrates, less than 1% of hydrogenated product is
formed. All aryl olefins (styrenes and naphthalenes) are efficiently
hydroformylated, with high selectivity for the branched aldehyde.
The regioselectivity is similar for all styrenes irrespective of whether
they contain electron withdrawing or donating groups.
4-Isobutylstyrene and 2-vinyl-6-methoxynaphthalene are also
converted to branched aldehydes in high yield, both of which
are important precursors to the nonsteroidal anti-inflammatory
agents, ibuprofen and naproxen, respectively (entries 5, 7).9
L3RhCl + H2 + CO + R3N = L3Rh(CO)H + (R3NH)+Cl2 (1)
The addition of a base such as a tertiary amine has been known
to induce a strong promotion effect on the formation of rhodium
hydride species (eqn. 1).8
The activity of the catalyst system with 1 and Et3N was tested to
elucidate the role of the diamine ligand, but it showed poor activity
(30% conversion) compared to the use of ionic rhodium complexes
reacted under the same conditions (entry 3). This result supports
the observation that the diamine ligand does not act as a Lewis
base and the catalytic function of the ionic complex is different
from that of the 1 and Et3N catalyst system.
Table 2 Hydroformylation of various olefins catalyzed by 2aa
Conversionb Selectivityc
When the reaction temperature was increased to 45 uC, the
activity increased with moderate loss of selectivity (more than 90%
branched aldehyde, entries 8–12). When the substrate/catalyst ratio
was increased to 3000, the catalytic activity and selectivity were
retained (e.g. conversion is 85% and selectivity for the branched
aldehyde is 94%, entry 10).
Entry Substrate
(%)
B/L ratio
1
2
3
1-Octene
99.
99.
99.
99.
99.
99.
99.
75
1
27
21
21
26
28
26
29
3.5
2.5
2,4-Dimethylstyrene
4-Chlorostyrene
4-Bromostyrene
4
5
6
4-Isobutylstyrene
2-Vinylstyrene
In the case of vinyl acetate, complex 2 and 3a show good
activity and selectivity. However complex 3b, containing the
sterically hindered rhodium cation, is much less active as a catalyst
but the selectivity is excellent at 25 uC (entries 20, 21). This result
indicates that the diamine ligand is retained in the original
coordination position, and this affects the access of the substrate to
the rhodium center. When the reaction temperature was increased
7
8
9
2-Vinyl-6-methoxynaphthalene
Vinyl benzoate
Isopropyl vinyl ether
37
10
a
2,2-Dimethyl-4-vinyl-1,3-dioxolane 46
Reaction conditions: substrate (8.2 mmol), catalyst (0.016 mmol),
toluene (10 mL), CO/H2 (1000 psi g), temperature (25 uC), 22 h.
b
c
Determined by GC and 1H NMR. Determined by 1H NMR.
3060 | Chem. Commun., 2005, 3059–3061
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absorption coefficient 5 1.635 mm21, reflections collected 5 7324,
independent reflections 5 2804 [ R(int) 5 0.0435], The final wR2 was
0.0849 (all data). CCDC 264125. See http://www.rsc.org/suppdata/cc/b5/
b502435h/ for crystallographic data in CIF or other electronic format.
While vinyl acetate and vinyl benzoate also show good
conversions and selectivities, 1-octene reacts well but with no
selectivity. Several functionalized olefins did not react under
these conditions (for example phenyl vinyl sulfone,
N-methylvinylacetamide), while isopropyl vinyl ether and 2,2-
dimethyl-4- vinyl-1,3-dioxolane gave aldehydes in moderate yield
but in quite low selectivity.
1 I. Ojima, C.-Y. Tsai, M. Tzamarioudaki and D. Bonafoux, The
Hydroformylation Reaction, Org. React., 2000, 56, 1–354.
2 D. Evans, J. A. Osborn and G. Wilkinson, J. Chem. Soc. A, 1968, 3133;
P. W. N. M. van Leeuwen and C. Claver, Rhodium Catalyzed
Hydroformylation, Kluwer Academic, Dordrecht, 2000; F. Ungvary,
Coord. Chem. Rev., 2003, 241, 295; V. V. Grushin, Chem. Rev., 2004, 104,
1629.
3 G. D. Cuny and S. L. Buchwald, J. Am. Chem. Soc., 1993, 115, 2066;
K. Nozaki, N. Sakai, T. Nanno, T. Higashijima, S. Mano, T. Horiuchi
and H. Takaya, J. Am. Chem. Soc., 1997, 119, 4413; D. Selent,
K. D. Wiese, D. Ro¨ttger and A. Bo¨rner, Angew. Chem., Int. Ed., 2000, 39,
1639.
4 D. A. Aubry, N. N. Bridges, K. Ezell and G. G. Stanley, J. Am. Chem.
Soc., 2003, 125, 11180; C. Li, E. Widjaja and M. Garland, J. Am. Chem.
Soc., 2003, 125, 5540.
5 I. Amer and H. Alper, J. Am. Chem. Soc., 1990, 112, 3674.
6 P. Frediani, M. Bianchi, A. Salvini, L. C. Carluccio and L. Rosi,
J. Organomet. Chem., 1997, 547, 35.
In conclusion, ionic diamine–rhodium complexes, which have a
chloride localized anionic rhodium and a chlorine free cationic
rhodium center, were synthesized and used as catalysts for the
hydroformylation reaction. These complexes show excellent
activity and regioselectivity without any phosphorus ligand, under
very mild reaction conditions.
We are indebted to Sasol Technology Ltd. for support of this
research.
Jai Jun Kim and Howard Alper*
Centre for Catalysis Research and Innovation, Department of
Chemistry, University of Ottawa, 10 Marie Curie, Ottawa, Canada
264125. E-mail: howard.alper@uottawa.ca; Fax: +1 613 562 5871;
Tel: +1 613 562 5189
7 M. A. Garralda and L. Ibarlucea, J. Organomet. Chem., 1986, 311,
225.
8 J. A. Moulijn, P. W. N. M. van Leeuwen and R. A. van Santen,
Catalysis: An Integrated Approach to Homogeneous, Heterogeneous and
Industrial Catalysis, Elsevier, Amsterdam, 1993.
Notes and references
9 B. G. Reuben and H. A. Wittcoff, Pharmaceutical Chemicals in
Perspective, John Wiley, New York, 1989; D. P. Riley, D. P. Getman,
G. R. Beck and R. M. Heintz, J. Org. Chem., 1987, 52, 287.
{ Crystal data. For complex 2: C11H20ClNRh, M 5 304.6, monoclinic,
3
a 5 10.9386(18), b 5 9.6760(16), c 5 11.3108(19), A, U 5 1181.0(3) A ,
˚
˚
T 5 205(2) K, space group P2/n, Z 5 4, b cell angle 5 99.428(3)u,
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 3059–3061 | 3061