New tetraphosphite ligands for regioselective linear hydroformylation of terminal and internal olefins

Article abstract of DOI:10.1039/c5ra23683e

We successfully developed new tetraphosphite ligands L1-L5 and applied them to the rhodium-catalyzed hydroformylation of terminal and internal olefins. High catalytic reactivities and excellent regioselectivities for linear aldehydes were obtained in the rhodium-catalyzed hydroformylation of simple olefins (l/b ratio up to 90, 98.9% linear selectivity, 99.2% conversion) using the tetraphosphite ligand L2. And the tetraphosphite ligand L2 also displayed moderate to good linear regioselectivities for challenging substrates styrene and internal olefin 2-octene.

Full text of DOI:10.1039/c5ra23683e

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New tetraphosphite ligands for regioselective linear
hydroformylation of terminal and internal olefins†
Cite this: RSC Adv., 2016, 6, 14559
*
Zongpeng Zhang,‡ Caiyou Chen,‡ Qian Wang, Zhengyu Han, Xiu-Qin Dong
*
and Xumu Zhang
Received 10th November 2015
Accepted 21st January 2016
DOI: 10.1039/c5ra23683e
www.rsc.org/advances
We successfully developed new tetraphosphite ligands L1–L5 and tetraphosphorus ligands were developed in our lab.13 These
applied them to the rhodium-catalyzed hydroformylation of terminal ligands owned outstanding catalytic properties for their unique
and internal olefins. High catalytic reactivities and excellent regiose- four identical coordination modes.13a,b Importantly, due to much
lectivities for linear aldehydes were obtained in the rhodium- higher local phosphine concentration around the metal center,
catalyzed hydroformylation of simple olefins (l/b ratio up to 90, the tetraphosphorus ligands afforded better chelating ability and
98.9% linear selectivity, 99.2% conversion) using the tetraphosphite thus exhibited much better regioselectivities compared with the
ligand L2. And the tetraphosphite ligand L2 also displayed moderate to corresponding bisphosphorus ligands. Latter we also success-
good linear regioselectivities for challenging substrates styrene and fully developed new triphosphorus ligands.14 Similar to the tet-
internal olefin 2-octene.
raphosphorus ligands, the triphosphorus ligands also have better
chelating ability with two identical coordination modes with
rhodium and exhibited better regioselectivities compared with
the corresponding bisphosphorus ligands. Although great efforts
have been made to develop new ligands for linear hydro-
formylation, new ligands are still highly desirable to further
resolve the problems of catalytic efficiency and selectivity.
Based on our long standing interest of tetraphosphorus
ligands in hydroformylation,13 our efforts were devoted to
further developing new phosphorus ligands with excellent
performance. Extensive research shown that the phosphines
were typical-donors ligands and phosphites were strong-
acceptors ligands. The phosphite ligands can facilitate the CO
dissociation from the metal centers in the catalytic species.
Therefore, it is helpful to greatly improve the reactivity by using
the phosphite ligands in Rh-catalyzed hydroformylation reac-
tion. We believe that the new tetraphosphite ligands L1–L5 with
four identical coordination modes with rhodium will show good
reactivities and regioselectivities in the linear hydroformylation
(Fig. 1). Importantly, ligands L1–L5 are very concise and can be
facilely synthesized. Herein, we present the synthetic route of
new tetraphosphite ligands L1–L5, and the application in Rh-
catalyzed hydroformylation reaction of simple and unfunc-
tionalized olens, providing the desired products in high
conversions with moderate to excellent regioselectivities.
Introduction
Since its discovery by Otto Roelen in 1938,1 the hydroformylation
reaction is one of the most efficient routes for the functionali-
zation of olens to approach aldehydes now.2 It has been devel-
oped into one of the most important homogeneous catalytic
processes with rhodium-based catalysts in the eld of industrial
chemistry.3 The corresponding aldehyde products are very
important compounds and valuable intermediates for the
synthesis of various chemicals, such as alcohols, amines and
esters etc.4 They are widely applied to construct blocks for phar-
maceuticals, agrochemicals, commodities and ne chemicals.5
Ligand is one of the most signicant factors to access high
activity and selectivity of hydroformylation reaction catalyzed by
the rhodium-based catalysts. Therefore, much attention has been
paid to designing efficient and privileged ligands for the forma-
tion of industrially important aldehydes. A variety of excellent
bisphosphorous ligands have been successfully developed for Rh-
catalyzed hydroformylation reactions in the past decades, such
as bisbi,6 biphephos,7 naphos,8 xantphos,9 calix4 arene-based
bisphosphites,10 pyrrole-based bisphos-phoramidites,11 and self-
assembled bisphosphanes.12 In addition, some new
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei,
430072, P. R. China. E-mail: xumu@whu.edu.cn; xiuqindong@whu.edu.cn
† Electronic supplementary information (ESI) available: Experimental procedures,
NMR spectra of compounds. See DOI: 10.1039/c5ra23683e
Results and discussion
The new tetraphosphite ligands L1–L5 were efficiently synthe-
sized from readily available starting materials (Scheme 1).15 The
‡ Zongpeng Zhang and Caiyou Chen contributed equally to this work.
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Table 1 Screening ligands for hydroformylation of 1-octenea
Entry
L
Conv.b (%) l/bc Lineard (%) Iso.e (%) TONf
1
2
3
4
5
L1 98.5
L2 88.2
L3 98.4
L4 98.9
L5 99.7
19
31
13
9
95.0
96.9
92.9
90.0
90.0
9.5
9.1
9.7
5.3
7.2
1.97 ꢁ 103
1.76 ꢁ 103
1.97 ꢁ 103
1.97 ꢁ 103
1.97 ꢁ 103
9
Fig. 1 Tetraphosphite ligands L1–L5 and four identical coordination
modes with rhodium.
a
S/C ¼ 2000, [Rh] ¼ 0.2 mM, toluene as solvent, 1-octene as the
substrate, decane as internal standard, L1–L5 as the ligand.
b
Conversion of 1-octene was determined on the basis of GC analysis.
Linear/branched ratio was determined on the basis of GC analysis.
Percentage of linear aldehyde. Percentage of the isomerized
c
ligand backbone 2,6,20,60-tetramethoxybenzene 1 was smoothly
deprotected with BBr3,15a formed the key intermediate [1,10-
biphenyl]-2,20,6,60-tetraol 2. The condensation of compound 2
with the preformed phosphorochloridite in the presence of the
triethylamine as hydrogen chloride scavenger provided the
desired tetraphosphite ligands L1–L5 in good yields.15c
With the tetraphosphite ligands L1–L5 in hand, we began
our studies by evaluating them in the linear hydroformylation of
1-octene as the model substrate with the catalyst generated in
situ by mixing Rh(acac)(CO)2 and ligands L1–L5 in toluene. As
shown in Table 1, ligands L1–L5 displayed high reactivities and
excellent regioselectivities (Table 1, entries 1–5). Almost all of
the reactions nished within 2 h. To our delight, the ligand L2
was revealed as the best ligand in terms of regioselectivity (ratio
of l/b up to 31, Table 1, entry 2). Ligands screening results
demonstrated that the substituents on the biphenyl ring played
a key role in determining the regioselectivity.
Subsequently, we investigated the effects of ligand L2/metal
molar ratios, reaction temperature, and the pressure of CO/H2
on the catalytic activity and regioselectivity. As expected, the
ratio of ligand L2/Rh(acac)(CO)2 has a great inuence on the
reaction, increasing the ratio from 1 : 1 to 3 : 1 (Table 2, entries
1–3) led to the dramatic improvement on the regioselectivity
and the ratio of l/b was improved from 31 to 46. The conversion
d
e
f
alkene. Turn over number (TON) was determined on the basis of the
alkene conversion by GC analysis.
became lower when the ligand/metal ratio was increased to
4 : 1, although a little higher regioselectivity was obtained
(Table 2, entry 4). The further increment of the ligand/metal
ratio to 8 : 1 resulted in nearly no reactivity (Table 2, entry 5).
The reaction temperature also displayed dramatic effect on the
reaction. Decreasing the temperature from 80 C to 60 C gave
lower reactivity (Table 2, entry 3 vs. entry 6). In addition, we
found that the catalytic system is also sensitive to the pressures
of CO/H2. Excellent regioselectivity and reactivity were obtained
when the pressures of CO/H2 was maintained at 5 : 5 bar (up to
93.4% conversion and l/b ratio up to 65, Table 2, entry 7).
Solvent effects were also investigated and the results were
summarized in Table 3. The reactions were performed well in
ꢀ
ꢀ
Table 2 Optimization conditions for hydroformylation of 1-octene
catalyzed by Rh(acac)(CO)2/L2a
Entry L/Rh Tb (ꢀC) Conv.c (%) l/bd Lineare (%) Iso.f (%) TONg
1
2
3
4
1 : 1 80
2 : 1 80
3 : 1 80
4 : 1 80
8 : 1 80
3 : 1 60
3 : 1 80
88.2
86.9
81.8
70.7
NA
31 96.9
35 97.2
46 97.9
47 97.9
NA NA
9.1
8.5
5.9
5.6
NA
3.5
6.3
1.76 ꢁ 103
1.72 ꢁ 103
1.64 ꢁ 103
1.41 ꢁ 103
NA
5
6
50.9
93.4
43 97.8
65 98.5
1.02 ꢁ 103
7h
1.87 ꢁ 103
a
S/C ¼ 2000, [Rh] ¼ 0.2 mM, toluene as solvent, 1-octene as the
b
substrate, decane as internal standard, L2 as the ligand. Oil bath
temperature. Conversion of 1-octene was determined on the basis of
GC analysis. Linear/branched ratio was determined on the basis of
GC analysis. Percentage of linear aldehyde. Percentage of the
c
d
e
f
g
isomerized alkene. Turn over number (TON) was determined on the
h
basis of the alkene conversion by GC analysis. H2/CO ¼ 5 : 5 bar. NA
¼ not available.
Scheme 1 Synthesis of the tetraphosphite ligands L1–L5.
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Table 3 Screening solvents for hydroformylation of 1-octene cata-
lyzed by Rh(acac)(CO)2/L2a
transformations. Conversion was up to 99.2% and the ratio of
l/b was up to 90 (Table 4, entries 1–2). In addition, we also
applied them into the hydroformylation of styrene, which is
a well-known olenic substrate preferring the branched alde-
hyde in most Rh-catalyzed hydroformylation transformations.
We found that the tetraphosphite ligand L2 displayed moderate
reactivity and regioselectivity (Table 4, entry 3). To our delight,
the challenging substrate internal olen 2-octene (trans/cis
molar ratio ¼ 1 : 1) also proceeded well and obtained good
regioselectivity (Table 4, entry 4).
Entry Solvent Conv.b (%) l/bc Lineard (%) Iso.e (%) TONf
1
2
3
4
5
6
7
8
Toluene 93.4
CH2Cl2 96.9
65 98.5
86 98.8
65 98.5
84 98.8
68 98.6
67 98.6
89 98.9
59 98.3
6.3
6.8
6.7
5.8
5.3
6.6
7.6
7.3
1.87 ꢁ 103
1.94 ꢁ 103
1.85 ꢁ 103
1.77 ꢁ 103
1.50 ꢁ 103
1.95 ꢁ 103
1.83 ꢁ 103
1.94 ꢁ 103
EA
CHCl3
iPrOH
92.6
88.6
74.9
Conclusions
Dioxane 97.5
CH3CN 91.4
In conclusion, new tetraphosphite ligands L1–L5 were
successfully developed and applied in the Rh-catalyzed hydro-
formylation of terminal and internal olens. High catalytic
reactivity and excellent regioselectivity for the linear aldehydes
were obtained in the Rh-catalyzed hydroformylation of simple
and unfunctionalized olens (l/b ratio up to 90, 98.9% linear
selectivity, 99.2% conversion) using the tetraphosphite ligand
L2. In addition, the tetraphosphite ligand L2 displayed
moderate linear regioselectivity for styrene affording 3-phenyl-
propanal. And the challenging substrate internal olen 2-octene
also proceeded well and obtained good regioselectivity. Further
application of the ligands for related catalytic reactions is
underway in our laboratory.
THF
96.9
a
S/C ¼ 2000, [Rh] ¼ 0.2 mM, 1-octene as the substrate, decane as
b
internal standard, L2 as the ligand. Conversion of 1-octene was
determined on the basis of GC analysis. Linear/branched ratio was
determined on the basis of GC analysis. Percentage of linear
aldehyde. Percentage of the isomerized alkene. Turn over number
(TON) was determined on the basis of the alkene conversion by GC
analysis. EA ¼ ethyl acetate.
c
d
e
f
toluene, ethyl acetate and 1,4-dioxane with similar results
(Table 3, entries 1, 3, 6). CH2Cl2 as the solvent afforded high l/b
ratio (up to 86) and excellent conversion (96.9% conversion,
Table 3, entry 2). Moderate conversion was achieved in iso-
propanol (74.9% conversion, Table 3, entry 5). Compared with
CH2Cl2, chloroform and acetonitrile gave similar regioselecti-
vies but with a little lower reactivities (Table 3, entries 4 and 7).
As a result, CH2Cl2 was the best choice as the solvent.
Promoted by these excellent results, we turned our attention
to investigate the catalytic system Rh(acac)(CO)2/L2 for the
hydroformylation of representative substrates. As shown in
Table 4, 1-octene and 1-hexene provided excellent results in the
Acknowledgements
We thank the grant from Wuhan University (203273463,
203410100064), and “111” Project of the Ministry of Education
of China for nancial support and the National Natural Science
Foundation of China (Grant No. 21372179, 21432007,
21502145).
Notes and references
Table
4 Scope study for the hydroformylation under optimized
reaction conditionsa
1 O. Roelen, (to Chemische Verwertungsgesellscha
Oberhausen m. b. H.) German Pat. DE 849548, 1938/1952,
U.S. Pat. 2.327066, 1943; Chemical Abstracts, 1944, 38, 3631.
2 P. W. N. M. van Leeuwen, Homogeneous Catalysis:
Understanding the Art, 2004, p. 424.
3 (a) C. A. Tolman and J. W. Faller, in Homogeneous
Catalysiswith Metal Phosphine Complexes, 81, ed. L. H.
Pignolet, Plenum, New York, 1983; (b) C. W. Kohlpaintner
and C. D. Frohning in Applied Homogeneous Catalysis with
Organometallic Compounds 1, ed. B. Cornils and W. A.
Herrmann, VCH, Weinheim, 1996, vol. 1; (c) R. Franke,
Entry Substrate Conv.b (%) l/bc Lineard (%) Iso.e (%) TONf
1
2
1-Octene 96.9
1-Hexene 99.2
86 98.8
90 98.9
0.6 37.5
16 94.1
6.8
6.9
ND
ND
1.94 ꢁ 103
1.98 ꢁ 103
1.28 ꢁ 103
1.20 ꢁ 103
3
Styrene
63.4
4g
2-Octene 60.6
¨
D. Selent and A. Borner, Chem. Rev., 2012, 112, 5675.
a
S/C ¼ 2000, [Rh] ¼ 0.2 mM, CH2Cl2 as solvent, decane as internal
4 A. Neves, M. Calvete, T. Pinhoe Melo and M. Pereira, Eur. J.
Org. Chem., 2012, 32, 6309.
b
standard, L2 as the ligand. Conversion was determined on the basis
of GC analysis. Linear/branched ratio was determined on the basis
of GC analysis. Percentage of linear aldehyde. Percentage of the
isomerized alkene. Turn over number (TON) was determined on the
c
d
e
5 For reviews, see: (a) B. Breit and W. Seiche, Synthesis, 2001, 1,
1; (b) C. Claver and P. W. N. M. van Leeuwen, Rhodium
Catalyzed Hydroformylation, Kluwer Academic Publishers,
Dordrecht, The Netherlands, 2002; (c) F. Ungvary, Coord.
Chem. Rev., 2005, 249, 2946.
f
g
basis of the alkene conversion by GC analysis. The reaction
temperature is 100 ꢀC, and the reaction time is 10 h. ND ¼ not
determined.
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6 (a) T. J. Devon, G. W. Phillips, T. A. Puckette, J. L. Stavinoha
and J. J. Vanderbilt, US Pat.4694109, 1987; (b)
Leeuwen, Organometallics, 2002, 21, 3873; (c) Y. Yan,
X. Zhang and X. Zhang, J. Am. Chem. Soc., 2006, 128, 16058.
W. A. Herrmann, C. W. Kohlpaintner, E. Herdtweck and 12 (a) V. F. Slagt, J. N. H. Reek, P. C. J. Kamer and
P. Kiprof, Inorg. Chem., 1991, 30, 4271; (c) C. P. Casey,
G. T. Whiteker, M. G. Melville, L. M. Petrovich, J. A. Gavney
Jr and D. R. Powell, J. Am. Chem. Soc., 1992, 114, 5535; (d)
C. P. Casey, E. L. Paulsen, E. W. Beuttenmueller,
B. R. Pro, L. M. Petrovich, B. A. Matter and D. R. Powell,
J. Am. Chem. Soc., 1997, 119, 11817.
7 (a) E. Billig, A. G. Abatjoglou and D. R. Bryant, European Pat.
EP 213639, 1987; (b) G. D. Cunny and S. L. Buchwald, J. Am.
Chem. Soc., 1993, 115, 2066.
8 (a) W. A. Herrmann, R. Schmid, C. W. Kohlpaintner and
T. Priermeier, Organometallics, 1995, 14, 1961; (b) H. Klein,
R. Jackstell, K.-D. Wiese, C. Borgmann and M. Beller,
Angew. Chem., Int. Ed., 2001, 40, 3408.
P. W. N. M. van Leeuwen, Angew. Chem., Int. Ed., 2001, 40,
4271; (b) V. F. Slagt, P. W. N. M. van Leeuwen and
J. N. H. Reek, Angew. Chem., Int. Ed., 2003, 42, 5619; (c)
V. F. Slagt, P. C. J. Kamer, P. W. N. M. van Leeuwen and
J. N. H. Reek, J. Am. Chem. Soc., 2004, 126, 1526; (d)
B. Breit and W. Seiche, J. Am. Chem. Soc., 2003, 125, 6608;
(e) B. Breit and W. Seiche, Angew. Chem., Int. Ed., 2005, 44,
1640; (f) W. Seiche, A. Schuschkowski and B. Breit, Adv.
Synth. Catal., 2005, 347, 1488; (g) M. Kuil, T. Soltner,
P. W. N. M. van Leeuwen and J. N. H. Reek, J. Am. Chem.
Soc., 2006, 128, 11344; (h) P. Dydio, W. I. Dzik and M. Lu,
Angew. Chem., Int. Ed., 2011, 50, 396; (i) U. Gellrich,
W. Seiche, M. Keller and B. Breit, Angew. Chem., Int. Ed.,
2012, 51, 11033.
9 (a) M. Kranenburg, Y. E. M. van der Burgt, P. C. J. Kamer,
P. W. N. M. van Leeuwen, K. Goubitz and J. Fraanje, 13 (a) Y. Yan, X. Zhang and X. Zhang, J. Am. Chem. Soc., 2006,
Organometallics, 1995, 14, 3081; (b) L. A. Van der Veen,
M. D. K. Boele, F. R. Bregman, P. C. J. Kamer,
P. W. N. M. van Leeuwen, K. Goubitz, J. Fraanje, H. Schenk
and C. Bo, J. Am. Chem. Soc., 1998, 120, 11616; (c) L. A. van
der Veen, P. C. J. Kamer and P. W. N. M. van Leeuwen,
Angew. Chem., Int. Ed., 1999, 38, 336; (d) L. A. van der Veen,
P. C. J. Kamer and P. W. N. M. van Leeuwen,
128, 16058; (b) Y. Yan, X. Zhang and X. Zhang, Adv. Synth.
Catal., 2007, 349, 1582; (c) S. Yu, Y. Chie and X. Zhang,
Adv. Synth. Catal., 2009, 351, 537; (d) S. Yu, X. Zhang,
Y. Yan, C. Cai, L. Dai and X. Zhang, Chem.–Eur. J., 2010,
16, 4938; (e) S. Yu, Y. Chie, Z. Guan and X. Zhang, Org.
Lett., 2008, 10, 3469; (f) S. Yu, Y. Chie, Z. Guan, Y. Zou,
W. Li and X. Zhang, Org. Lett., 2009, 11, 241.
´
Organometallics, 1999, 18, 4765; (e) J. J. Carbo, F. Maseras, 14 (a) C. Chen, Y. Qiao, H. Geng and X. Zhang, Org. Lett., 2013,
C. Bo and P. W. N. M. van Leeuwen, J. Am. Chem. Soc.,
2001, 123, 7630; (f) P. C. J. Kamer, P. W. N. M. van
Leeuwen and J. N. H. Reek, Acc. Chem. Res., 2001, 34, 895.
15, 1048; (b) C. Chen, P. Li, Z. Hu, H. Wang, H. Zhu, X. Hu,
Y. Wang, H. Lv and X. Zhang, Org. Chem. Front., 2014, 1, 947.
15 (a) H. Kakei, R. Tsuji, T. Ohshima, H. Morimoto,
S. Matsunaga and M. Shibasaki, Chem.–Asian J., 2007, 2,
257; (b) F. Fang, F. Xie, H. Yu, H. Zhang, B. Yang and
W. Zhang, Tetrahedron Lett., 2009, 50, 6672; (c) J. Ruchti
and E. M. Carreira, J. Am. Chem. Soc., 2014, 136, 16756.
¨
10 R. Paciello, L. Siggel and M. Roer, Angew. Chem., Int. Ed.,
1999, 38, 1920.
11 (a) R. Jackstell, H. Klein, M. Beller, K.-D. Wiese and
D. Rottger, Eur. J. Org. Chem., 2001, 3871; (b) S. C. van der
Slot, J. Duran, J. Luten, P. C. J. Kamer and P. W. N. M. van
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