Novel spiroketal-based diphosphite ligands for hydroformylation of terminal and internal olefins

Article abstract of DOI:10.1039/c3cy00187c

Spiroketal-based diphosphite ligands have been developed for the rhodium-catalyzed hydroformylation reaction. Under the optimized reaction conditions, a turnover number (TON) of up to 2.4 × 10⁴ and a linear to branched ratio (l/b) of up to 93 were obtained in the hydroformylation of terminal olefins. The catalysts were also found to be effective in the isomerization-hydroformylation of some internal olefins.

Full text of DOI:10.1039/c3cy00187c

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Novel spiroketal-based diphosphite ligands for
hydroformylation of terminal and internal olefins†
Xiaofei Jia,ab Zheng Wang,b Chungu Xia*a and Kuiling Ding*b
Cite this: Catal. Sci. Technol., 2013,
3, 1901
Received 20th March 2013,
Accepted 10th April 2013
DOI: 10.1039/c3cy00187c
www.rsc.org/catalysis
Spiroketal-based diphosphite ligands have been developed for the interest in the development of phosphite ligands for hydro-
rhodium-catalyzed hydroformylation reaction. Under the optimized formylation of various olefins.1d Recently, we have reported a
reaction conditions, a turnover number (TON) of up to 2.4 Â 104 and new class of bidentate spiroketal-based bis(dipyrrolyl)phos-
a linear to branched ratio (l/b) of up to 93 were obtained in the phoramidite ligands, which demonstrated high activity and
hydroformylation of terminal olefins. The catalysts were also excellent regioselectivity for the linear aldehydes in the rhodium-
found to be effective in the isomerization–hydroformylation of catalyzed hydroformylation of both terminal and internal olefins.9
some internal olefins.
Encouraged by these results, we sought to extend our studies to
other spiroketal-based diphosphine ligands for hydroformyla-
Hydroformylation of alkenes is one of the most important homo- tion reactions. Herein, we wish to report the synthesis of a new
geneous catalytic reactions in industry. The products containing class of spiroketal-based diphosphite ligands, and their applica-
an aldehyde group are versatile intermediates and building blocks tion in the Rh-catalyzed hydroformylation of linear olefins. It is
for various pharmaceuticals, agrochemicals, commodities and noteworthy that since the introduction of the SPANphos by
fine chemicals.1 One of the key issues in hydroformylation van Leeuwen in 2003,10 a handful of spiroketal-based ligands
research is the development of new ligands to obtain highly active have been successfully developed and used in several catalytic
and selective catalysts. Over the past several decades, a variety of reactions.11 Despite these efforts, however, P-ligands with a spiro
P-ligands have been successfully developed for Rh-catalyzed backbone have only rarely been explored in hydroformylation
hydroformylation of olefins. Some elegant examples include reactions.12
Bisbi,2 Xantphos,3 Biphephos,4 Naphos,5 calix[4]arene-based
The spiroketal bisphosphite ligands 3a–h were easily prepared
bisphosphites,6 pyrrole-based bisphos-phoramidites,7 and self- via a four-step reaction sequence (Scheme 1). Aldol condensation of
assembled bisphosphanes.8 Compared with phosphines, the 2,3-dimethoxyarylaldehyde with acetone, cyclopentanone, or cyclo-
phosphite ligands are generally weak s-donors but strong hexone afforded the corresponding penta-1,4-dien-3-ones 1, which
p-acceptors, which can facilitate the CO dissociation from the upon RANEYs-Ni catalyzed hydrogenation followed by deprotec-
metal centers in the catalytic species. Therefore, the replacement tion with BBr3, led to the formation of the key spiroketal-based
of phosphines by phosphites in the Rh-catalyzed hydroformyla- intermediate diphenols 2.9 Condensation of diphenols 2 with
tion often leads to a substantial enhancement in the reactivity. In the preformed phosphorochloridites with triethylamine as a
addition, the regioselectivity of the phosphate/Rh catalysts can HCl scavenger gave the corresponding bisphosphites 3a–h in
also be modulated by judicious incorporation of appropriate good to excellent yields. These ligands are stable in the air, and
substituents into a ligand backbone. thus were purified under an ambient atmosphere by column
These salient features, coupled with their ready synthesis chromatography on silica gel without special precautions.
and oxidation stability, contributed to a substantial research
Hydroformylation of terminal olefins was first investigated
with the catalyst generated in situ by mixing Rh(acac)(CO)2 and
ligand 3a in toluene, using 1-hexene as the model substrate at a
substrate/catalyst (S/C) molar ratio of 10 000, with decane as the
internal standard. The effects of ligand to metal molar ratios,
reaction temperature, and the ratio of the partial pressures of
CO/H2 on the regioselectivity and the catalytic activity were
evaluated, and the results are summarized in Table 1. As expected,
the Rh(I)–3a ratio has a significant effect on the reaction, as
a State Key Laboratory of Oxo Synthesis and Selective Oxidation, Lanzhou Institute
of Chemical Physics, Chinese Academy of Sciences, 18 Tianshui Middle Road,
Lanzhou 730000, P. R. China. E-mail: cgxia@lzb.ac.cn; Fax: +86 931 827 7088
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032,
P. R. China. E-mail: kding@mail.sioc.ac.cn; Fax: +86 21 6416 6128
† Electronic supplementary information (ESI) available: Ligand synthesis and
characterization, and hydroformylation procedure. See DOI: 10.1039/c3cy00187c
c
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Table 2 Ligand screening for hydroformylation of 1-hexenea
Entry
L
l/bb
Linearc (%)
Isomerizationd (%)
TONe
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
93
69
66
79
64
36
66
11
98.9
98.6
98.5
98.8
98.5
97.3
98.5
91.9
13
3
13
2
5
13
2
7.5 Â 103
3.3 Â 103
8.4 Â 103
3.3 Â 103
4.8 Â 103
8.7 Â 103
2.7 Â 103
1.7 Â 103
3g
3h
2
a
S/C = 10 000, Rh(acac)(CO)2 (0.001 mmol), ligand/Rh ratio = 3 : 1,
temperature = 90 1C, CO/H2 = 5/10 bar, 3 h, toluene (1.0 mL) as solvent,
b
c
d
decane as the internal standard. See Table 1. See Table 1. See
Table 1. See Table 1.
e
deteriorated activity and linear aldehyde regioselectivity
(entry 6 vs. 3). Raising the H2 partial pressure from 5 to
20 bar led to a comparable regioselectivity and activity
(entry 7 vs. 3). Finally, the reaction temperature also displayed
a significant effect on the hydroformylation. Decreasing the
temperature from 90 to 80 1C resulted in a slight enhancement
in the linear aldehyde selectivity, but the catalytic activity was
compromised in this case (entry 8). In contrast, elevation of the
reaction temperature to 100 1C resulted in an increase of
isomerization and a degraded regioselectivity for linear alde-
hyde (entries 9). Overall, the optimal conditions (toluene, 90 1C,
H2/CO = 10/5 bar, substrate/L/Rh = 10 000/3/1) were chosen for
the subsequent ligand screenings.
Scheme 1 Synthesis of spiroketal bisphosphite ligands 3a–h.
Table 1 Optimization of conditions for hydroformylation of 1-hexene catalyzed
by Rh(acac)(CO)2/3aa
Subsequently, ligands 3b–h were examined as ligands in
combination with Rh(acac)(CO)2 for the catalysis of hydro-
formylation of 1-hexene. The reactions were conducted under
the reaction conditions optimized as above, and the results are
Entry Rh/L T (1C) H2/CO (bar) l/bb Linearc (%) Iso.d (%) TONe
1
2
3
4
5
6
7
8
9
1 : 1
1 : 2
1 : 3
1 : 4
1 : 3
1 : 3
1 : 3
1 : 3
90
90
90
90
90
90
90
80
10/5
10/5
10/5
10/5
10/10
5/5
20/5
10/5
10/5
5
84.1
24
18
13
7
5
7
11
7
15
7.5 Â 103
60 98.4
93 98.9
72 98.6
27 96.5
56 98.3
72 98.6
94 99.0
70 98.6
8.1 Â 103
7.5 Â 103 shown in Table 2. In comparison with the prototype ligand 3a,
6.0 Â 103
ligands with electron-withdrawing substituents on either the
spiroketal phenyl backbone (3b) or the biphenol moieties (3d)
led to a substantially declined reaction rate (entries 2 and 4 vs. 1).
Intriguingly, while the use of 3c with weak electron-donating
5.7 Â 103
6.6 Â 103
8.1 Â 103
4.8 Â 103
1 : 3 100
8.4 Â 103
t-Bu groups on the ligand backbone improved the TON value
a
from 7.5 Â 103 to 8.4 Â 103 (entry 3 vs. 1), ligand 3e with methoxy
groups on the diphenyl moiety exhibited lower catalytic activity
(entry 5 vs. 1). Finally, ligands 3f, 3g and 3h with a tethered
spiroketal backbone are somewhat less favorable in controlling
the regioselectivity as compared with their conformationally more
S/C = 10 000, Rh(acac)(CO)2 (0.001 mmol), toluene (1.0 mL) as the
b
solvent, decane as the internal standard, reaction time = 3 h. Linear/
branched ratio, determined by GC analysis. Percentage of linear
c
d
e
aldehyde in all aldehydes. Isomerization to 2-hexenes. Determined
by GC analysis.
increasing the value from 1 : 1 to 1 : 3 (entries 1–3) resulted in flexible analogue 3a (entries 6–8 vs. 1). In addition, the cis-
alleviated isomerization (24–13%) and a dramatic enhance- configured ligands 3g and 3h consistently delivered lower catalytic
ment in the regioselectivity for the linear aldehyde (l/b ratio activities (entries 7 and 8). These results suggested that the subtle
from 5 to 93). Further increment of the metal–ligand ratio to influences of the ligand backbones and their electronic features
1 : 4, however, led to a decline in catalytic activity (entries 1–3 vs. 4). are important for Rh/3-catalyzed hydroformylation.
The ratio of the CO/H2 partial pressures was also found to have
Under the optimized reaction conditions, a variety of olefins were
a profound effect on the reaction (entries 5–7). While increasing investigated as substrates for the Rh-catalyzed hydroformylation
the partial pressure of CO resulted in a marked depression of using 3a or 3c as the ligand. As shown in Table 3, the industrially
alkene isomerization, the TON (turnover number) value and important short-chain feedstocks propylene and 1-butylene are
especially the l/b ratio decreased to a considerable extent readily amenable to the hydroformylation procedure, affording the
(entry 5 vs. 3). On the other hand, lowering the H2 partial corresponding aldehydes with high l/b ratios (12–55, entries 1–4)
pressure from 10 to 5 bar also resulted in a somewhat and good TON values (1.6 Â 104–2.4 Â 104, entries 1–4) at a S/C ratio
c
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Table 3 Rh/3 catalyzed hydroformylation of terminal olefinsa
In conclusion, a new series of spiroketal-based diphosphite
ligands have been synthesized and applied in the Rh-catalyzed
hydroformylation of unfunctionalized olefins. High catalytic
activity and good to excellent regioselectivity for the linear
aldehydes were obtained in the Rh-catalyzed hydroformylation
of terminal olefins. In the case of the isomerizing hydroformyl-
ation of internal olefins, the linear aldehydes were obtained
with a moderate linear regioselectivity. Further application of
the ligands for related catalytic reactions is underway.
We thank the financial support for this work from the
National Natural Science Foundation of China (grant no.
21172237, 21121062, 21032009), the Major Basic Research
Development Program of China (grant no. 2010CB833300),
the Chinese Academy of Sciences, and the Science and Tech-
nology Commission of Shanghai Municipality.
Entry Substrate
L
T (1C) l/bb Linearc (%) Iso.d (%) TONe
1 f
2 f
3g
4g
5
Propylene 3a 90
Propylene 3c 90
1-Butylene 3a 90
1-Butylene 3c 90
1-Hexene 3a 90
1-Hexene 3c 90
15
12
55
37
93
66
43
36
93.9
92.8
98.2
97.4
98.9
98.5
97.7
97.4
—
—
—
—
13
13
16
12
—
—
1.8 Â 104
1.6 Â 104
2.4 Â 104
2.3 Â 104
7.5 Â 103
8.4 Â 103
6.4 Â 103
7.8 Â 103
7.2 Â 103
6.0 Â 103
6
7
1-Octene
1-Octene
Styrene
Styrene
3a 90
3c 90
3a 100
3c 100
8
9h
10h
2.1 68.0
3.6 78.1
a
S/C = 10 000, Rh(acac)(CO)2 (0.001 mmol), Rh/ligand ratio = 1 : 3,
temperature = 90 1C, CO/H2 = 5/10 bar, 3 h, toluene (1.0 mL) as solvent,
b
c
decane as the internal standard. See Table 1. See Table 1.
d
g
e
f
See Table 1. See Table 1. S/C = 50 000, toluene (2.0 mL) as solvent.
S/C = 50 000. Rh/ligand ratio = 1 : 2, CO/H2 = 5/5 bar.
h
Notes and references
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Table 4 Rh/3 catalyzed hydroformylation of internal olefinsa
Entry
Substrate
L
l/bb
Linearc (%)
TONd
¨
A. Borner, Chem. Rev., 2012, 112, 5675; (e) J. Pospech,
1
2
3
(Z)-2-Butylene
(Z)-2-Butylene
(E)-2-Butylene
(E)-2-Butylene
2-Octene
3a
3c
3a
3c
3a
3c
3.8
3.2
3.5
3.2
3.8
3.2
79.3
76.1
77.9
75.9
79.3
76.0
6.0 Â 103
5.5 Â 103
5.2 Â 103
4.7 Â 103
2.7 Â 103
2.9 Â 103
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was also investigated using 3a/Rh or 3c/Rh as the catalyst. At a
S/C ratio of 50 000, the industrially important olefins (Z)- and
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c
1904 Catal. Sci. Technol., 2013, 3, 1901--1904
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