Porous Organic Polymer Supported Rhodium as a Reusable

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Letter Cite This: Org. Lett. XXXX, XXX, XXX−XXX

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Porous Organic Polymer Supported Rhodium as a Reusable Heterogeneous Catalyst for Hydroformylation of Olefins Xiaofei Jia,*,†,§ Zuyu Liang,†,§ Jianbin Chen,‡ Jinhe Lv,† Kai Zhang,† Mingjie Gao,† Lingbo Zong,*,† and Congxia Xie*,† †

Org. Lett. Downloaded from pubs.acs.org by EAST CAROLINA UNIV on 03/11/19. For personal use only.

Key Laboratory of Optic-electric Sensing and Analytical Chemistry for Life Science, MOE, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China ‡ Shandong Provincial Key Laboratory of Molecular Engineering, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, P. R. China S Supporting Information *

ABSTRACT: A new porous organic polymer has been prepared via copolymerization of divinyl-functionalized phosphoramidite ligand and tris(4-vinylphenyl)phosphine. The porous polymer was loaded with Rh(acac)CO2 to yield a supported Rh catalyst, which demonstrated good regioselectivity (l/b = 6.7−52.8) and high catalytic activity (TON up to 45.3 × 104) in hydroformylation of terminal and internal olefins. Remarkably, the heterogeneous catalyst can be reused at least 10 cycles without losing activity and selectivity in hydroformylation of 1-hexene.

H

loading the metals. In 2015, Xiao reported a Rh-dppe-POP catalyst, which provided excellent yields and selectivities for linear aldehydes in hydroformylation of olefins.9 Phossphite/ PPh3 copolymer developed by Yan and Ding was successfully used for hydroformylation of terminal and internal olefins.10 However, the development of novel heterogeneous hydroformylation catalyst with high catalytic activity and good reusability still remains a challenge. It is well-known that PPh3 and bisphosphoramidite ligands11 were widely used in hydroformylation of olefins. Using PPh3 constructed a stable porous organic polymer, while more efficient bisphosphoramidite ligand was added by copolymerization. The porous organic polymer not only has the advantages of PPh3 and bisphosphoramidite ligands but also reduces the loss of metal due to high concentration of ligands. Herein, we report a new Rh-loaded porous organic ligand (Rh/POL-BPa&PPh3), bearing both pyrrolyl-based bisphosphoramidite (BPa) and triphenylphosphane ligand moieties, as a heterogeneous catalyst for hydroformylation of terminal and internal olefins. Because of high π-acidity of the N-pyrrolylphosphorus unit,11 stable PPh3 moieties, and high ligand density, the heterogeneous catalyst exhibited excellent activity, regioselectivity, and recyclability in the hydroformylation of olefins. Our initial effort was focused on the synthesis of the comonomers 6 and 7. The divinyl-functionalized bisphosphoramidite 6 (vBPa) were readily synthesized by using a five-step reaction sequence. As shown in Scheme 1, 2,2′-biphenol 1 was reacted with Br2 to produce dibrominated product 2, which was diacetylated to 3 on treatment with acetyl chloride. Pd-catalyzed

ydroformylation, developed by Roelen in the 1930s, is the most cost-effective industrial processes for synthesis of aldehydes.1 As versatile chemical intermediates, more than 10 million metric tons of aldehydes are produced every year.2 Because of the good catalytic activity and selectivity, homogeneous ligand-modified Rh catalysts were successfully used in industrial hydroformylation. However, the heterogeneous catalysts often present significant advantages over homogeneous catalysts in terms of recyclability and catalyst separation.3 In the past decades, many types of solids were used as supporting materials for immobilizing homogeneous hydroformylation catalysts, including various inorganic porous materials (such as SiO2, zeolites and activated carbons)4 and organic polymers (such as polystyrene, chitosan, and cyclodextrin).5 Despite notable achievements, these traditional supported catalysts are often plagued by leaching of metals, decrease of catalytic activity, and/or loss of selectivity, presumably owing to the low concentration of ligands coordinated to the metals. In recent years, porous organic polymers (POPs) have attracted great attention, not only due to their high surface areas but also to the incorporation of various functionalities within their porous structures.6 As POPs constructed from organic ligand-containing monomers, porous organic ligands (POLs) feature a high density of ligand sites, which would improve loading capability and stability of the active metals and thus to enhance the catalytic activity and selectivity and to reduce the loss of metals in a catalytic process.7 In recent years, Xiao, Ding, et al. developed Rh/POL-PPh3 and Rh/phosphite-POP catalysts, which demonstrated high activity and excellent recyclability in hydroformylation of olefins.8 As the monomers, bisphosphorus ligands were also used to construct polymers for © XXXX American Chemical Society

Received: February 3, 2019

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DOI: 10.1021/acs.orglett.9b00459 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters Scheme 1. Synthesis of POL-BPa&PPh3 and BPa

Figure 1. (a) 13C MAS NMR spectrum, (b) 31P MAS NMR spectrum, (c) TGA curve, (d) N2 sorption isotherms, (e) SEM image, (f) TEM image of Rh/POL-BPa&PPh3.

Suzuki coupling reaction of 3 with potassium ethenyltrifluoroborate yielded 4, which underwent a base-mediated hydrolysis to give the key intermediate divinyl-functionalized biphenol 5. The divinyl-functionalized ligand monomer 6 was prepared by treatment of diphenols 5 with chlorodipyrolyphosphine in the presence of Et3N. On the other hand, (4-vinylphenyl)magnesium bromide was reacted with PCl3 to produce trivinyl-functionalized ligand monomer 7 (3vPPh3). AIBN initiated copolymerization of vinyl-functionalized bisphosphoramidite 6 and tris(4-vinylphenyl)phosphine 7 (3vPPh3) in THF afforded the copolymer POL-BPa&PPh3 as a light-yellow solid. Subsequent treatment of the copolymer with Rh(acac)(CO)2 in THF solvent readily furnished Rh-loaded copolymer Rh/POLBPa&PPh3 as a yellow solid (for details, see the Supporting Information (SI)). For comparison purposes, bisphosphoramidite ligand 8 (BPa) and 9 (POL-PPh3) were also prepared. The obtained Rh/POL-BPa&PPh3 was characterized by inductively coupled plasma mass spectrometry (ICP-MS), solid NMR, thermogravimeric analysis (TGA), N2 adsorption−desorption analysis, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). ICP-MS indicated a rhodium loading of 0.71 wt % (Rh:vBPa:3vPPh3 = 1:3:27) in the material. In the 13C MAS NMR spectrum of Rh/ POL-BPa&PPh3, two groups of peaks centered at 127.0 and 40.6 ppm can be assigned to the aromatic carbons and polymerized vinyl groups, respectively (Figure 1a). The 31P MAS NMR spectrum exhibited two peaks at −7.4 and 64.9 ppm, corresponding to the phosphorus signals of polymerized vPPh3 and vBPa moieties, respectively. Remarkably, the peak at 26.1 ppm was attributed to the P atoms of polymerized vPPh3 coordinated to Rh, while two peaks at 107.4 and 97.4 ppm in low-field can be assigned to phosphorus of polymerized vBPa coordinated to Rh (Figure 1b). The polymeric material Rh/ POL-BPa&PPh3 showed good thermal stability according to thermogravimetric analysis (TGA), giving only 5% weight loss upon heating to 200 °C and significant decomposition started

around 370 °C (Figure 1c). Furthermore, the nitrogen sorption isotherm (Figure 1d) demonstrated that Rh/POL-BPa&PPh3 has a hierarchical porosity, which is further confirmed by scanning electron microscopy (Figure 1e) and transmission electron microscopy (Figure 1f). The pore sizes of Rh/POLBPa&PPh3 are mainly distributed around 1.2−2.0 and 2.3−25 nm, which is based on the calculations of nonlocal density functional theory (NLDFT), indicating that Rh/POLBPa&PPh3 mainly consists of micro- and mesopores (for details, see the SI). The Brunauer−Emmett−Teller (BET) surface area and pore volume of Rh/POL-BPa&PPh3 are as high as 423.6 and 0.41 m3/g, respectively, which should be beneficial for its application as a catalyst because diffusion of reactants and products would be facilitated in the reaction processes. The catalytic performance of Rh/POL-BPa&PPh3 was evaluated in the hydroformylation of olefins, initially using 1hexene as model substrate. Several reaction parameters, e.g., temperature, pressure of syngas, and reaction time, were investigated. As shown in Table 1, although the conversion of 1-hexene increased with the temperature increment 80−100 °C, a higher temperature (100 °C) resulted in lower regioselectivity toward the linear aldehyde and an enhancement of hydrogenation product (Table 1, entries 1−3). As expected, the pressure of syngas displayed a significant effect on hydroformylation. Either increasing the H2/CO pressure from 10/10 to 20/20 bar, or decreasing H2/CO pressure to 5/5 bar, led to a decline in catalytic activity (Table 1, entries 4, 5 vs 2). Reaction time was also found to be crucial for hydroformylation of 1hexene. In the initial stage of the reaction (1 h), the TON value was determined to be quite high (2.3 × 104, Table 1, entry 6). The conversion of 1-hexene improved with the increasing reaction time, and similar hydrogenation and isomerization reaction results were observed (Table 1, entries 2 and 6−9). The efficiency of different homogeneous ligands in Rh-catalyzed hydroformylation of 1-hexene was also investigated. In B

DOI: 10.1021/acs.orglett.9b00459 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters Table 1. Catalytic Hydroformylation of Olefinsa

entry

catalysts

substrate

H2/CO (bar)

temp (°C)

t (h)

conv (%)

l/bb

linearc

[H]d (%)

isoe (%)

TON

1 2 3 4 5 6 7 8 9 10f 11g 12h 13i 14j 15k

Rh/POL-BPa&PPh3 Rh/POL-BPa&PPh3 Rh/POL-BPa&PPh3 Rh/POL-BPa&PPh3 Rh/POL-BPa&PPh3 Rh/POL-BPa&PPh3 Rh/POL-BPa&PPh3 Rh/POL-BP&PPh3 Rh/POL-BPa&PPh3 Rh/BPa Rh/PPh3 Rh/BPa/PPh3 Rh/POL−PPh3 Rh/POL-BPa&PPh3 Rh/POL-BPa&PPh3

1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-hexene 1-octene 2-octene

10/10 10/10 10/10 5/5 20/20 10/10 10/10 10/10 10/10 10/10 10/10 10/10 10/10 10/10 10/5

80 90 100 90 90 90 90 90 90 90 90 90 90 90 110

5 5 5 5 5 1 2 3 4 5 5 5 5 5 15

83.3 90.3 92.0 82.8 73.8 75.7 80.2 81.9 85.4 99.0 68.9 83.5 61.9 80.0 62.2

34.1 50.1 25.4 54.7 43.5 46.3 51.6 45.0 49.1 15.7 2.9 75.5 3.3 41.0 6.7

97.2 98.0 96.2 98.2 97.7 97.9 98.1 97.8 98.0 94.0 74.5 98.7 76.5 97.6 87.0

5.3 6.2 9.2 5.1 2.9 4.3 5.0 4.7 4.2 0.9 0.8 2.9 1.4 0.7 4.5

5.9 6.0 7.3 4.9 2.6 4.3 5.2 5.2 5.1 3.0 0.4 3.3 2.1 8.0 0.0

2.5 × 104 2.7 × 104 2.8 × 104 2.5 × 104 2.2 × 104 2.3 × 104 2.4 × 104 2.5 × 104 2.6 × 104 3.0 × 104 2.1 × 104 2.5 × 104 1.9 × 104 1.6 × 104 0.6 × 104

a

5.0 mg catalyst, 1-hexene (1.5 mL), S/C = 30000, decane as the internal standard. bLinear/branched aldehyde ratio. cPercentage of linear aldehyde in all aldehydes. dHydrogenation to alkane. eIsomerization to 2-alkene. fRh(acac)(CO)2:Bpa = 1:3, S/C = 30000. gRh(acac)(CO)2:PPh3 = 1:27, S/C = 30000. hRh(acac)(CO)2:Bpa:PPh3 = 1:3:27, S/C = 30000. i3.0 mg catalyst, 1-hexene (1.5 mL), S/C = 30000. j5.0 mg catalyst, S/C = 20000. k5.0 mg catalyst, S/C = 10000.

comparison with Rh/POL-BPa&PPh3 , Rh/PPh 3 gave a substantially lower regioselectivity and catalytic activity, whereas Rh/BPa afforded higher TON value and slightly lower l/b ratio (Table 1, entries 2 vs 10, 11). Adding excess free PPh3 to Rh/ BPa catalyst resulted in higher regioselectivity (Table 1, entries 12 vs 10). We assumed that high concentration of PPh3 ligands coordinated with Rh-Bpa complexes, affording high steric hindrance catalytic intermediate, leading to superior regioselectivity in the hydroformylation process. Rh/POL-PPh3 was also tested in this reaction, affording a lower regioselectivity (Table 1, entries 13 vs 2). On the basis of the above results, we concluded that the heregeneous Rh/POL-BPa&PPh3 catalyst could afford similar regioselectivity and catalytic activity compared with its homogeneous counterpart (Table 1, entries 2 vs 12). BPa ligand moieties were more favorable for improving catalytic activity and regioselectivity than PPh3 moieties, and the synergetic effect of PPh3 and BPa moieties with Rh species probably contributed to high regioselectivity.10b Under optimized reaction conditions, longer chain 1-octene was readily amenable to the Rh/POL-BPa&PPh3 catalyzed hydroformylation procedure, affording excellent linear/branched ratios (l/b = 41.0). Furthermore, a modest TON value and l/b ratio were achieved in the isomerization-hydroformylation of 2octene (Z/E = 3.6/1), owing to PPh3 moieties in the catalyst reducing the isomerization rate of 2-octene to 1-octene. To evaluate the activity of a catalyst, the substrate/catalyst (S/ C) ratios were surveyed in Rh/POL-BPa&PPh3 catalyzed hydroformylation of 1-hexene under optimized reaction conditions (CO/H2 = 10/10 bar, T = 90 °C, 5 h) (Table 2). Increasing the S/C ratio from 3 × 104 to 50 × 104 resulted in a considerable enhancement of TON value (from 2.7 × 104 to 18.4 × 104) in 5 h reaction time, while the chemo- and regioselectivites were well retained. Under substrate/catalyst ratio of 50 × 104, conversion of 1-hexene in 24 h was increased to 90.5%, albeit at a cost of slightly lower regioselectivity. It is noteworthy that such a high activity is rare for a heterogeneous hydroformylation catalyst and hence might be a valuable attribute for further practical development.

Table 2. Substrate/Catalyst (S/C) Ratios Screening for Hydroformylation of 1-Hexenea

entry

S/C

conv. (%)

l/bb

linearc

[H]d (%)

iso.e (%)

TON

1 2 3 4f 5f 6g

3 × 104 5 × 104 10 × 104 20 × 104 50 × 104 50 × 104

90.3 78.5 50.0 43.0 36.7 90.5

50.1 50.2 52.8 25.1 43.9 12.1

98.0 98.0 98.1 96.2 97.8 92.4

6.2 6.9 9.6 7.7 3.3 11.0

6.0 7.2 6.6 5.5 4.1 16.4

2.7 × 104 3.9 × 104 5.0 × 104 8.6 × 104 18.4 × 104 45.3 × 104

a

Reaction conditions: 5.0 mg Rh/POL-BPa&PPh3, CO/H2 = 10/10 bar, T = 90 °C, 5 h. bLinear/branched aldehyde ratio. cPercentage of linear aldehyde in all aldehydes. dHydrogenation to alkane. e Isomerization to 2-alkene. f3.0 mg Rh/POL-BPa&PPh3. g3.0 mg Rh/POL-BPa&PPh3, 24 h.

Reusability of Rh/POL-BPa&PPh3 was evaluated in hydroformylation of 1-hexene. Under optimized conditions, Rh/POLBPa&PPh3 catalyst preserved high activities and excellent chemo- and regioselectivites during its 10 reruns, highlighting its excellent reusability (SI). As shown in Figure 2, similar results demonstrated that the catalyst has excellent stability and reusability. After each run, the catalyst was recovered via centrifugal separation. The supernatant liquid showed no activity in hydroformylation of 1-hexene, thus confirming the heterogeneous nature of the catalysis. Meanwhile, Rh leaching in the residual liquids was determined to be ∼0.1 ppm by ICP-MS analysis. The results indicated that the Rh leaching from the Rh/ POL-BPa&PPh3 is negligible, probably owing to the high density of ligands in the catalyst. In conclusion, a new porous organic polymer (POLBPa&PPh3) was synthesized through copolymerization of divinyl-functionalized phosphoramidite ligand and trivinylfunctionalized triphenylphosphane. The rhodium-loaded polymeric material, Rh/POL-BPa&PPh3, was successfully used as a C

DOI: 10.1021/acs.orglett.9b00459 Org. Lett. XXXX, XXX, XXX−XXX

Letter

Organic Letters

(3) (a) De Vos, D. E.; Dams, M.; Sels, B. F.; Jacobs, P. Chem. Rev. 2002, 102, 3615. (b) Wang, Z.; Chen, G.; Ding, K. Chem. Rev. 2009, 109, 322. (c) Thomas, J. M.; Raja, R.; Lewis, D. W. Angew. Chem., Int. Ed. 2005, 44, 6456. (d) Coperet, C.; Chabanas, M.; Petroff SaintArroman, R.; Basset, J.-M. Angew. Chem., Int. Ed. 2003, 42, 156. (e) Li, C.; Wang, W.; Yan, L.; Ding, Y. Front. Chem. Sci. Eng. 2018, 12, 113. (4) (a) Han, D.; Li, X.; Zhang, H.; Liu, Z.; Li, J.; Li, C. J. Catal. 2006, 243, 318. (b) Shylesh, S.; Hanna, D.; Mlinar, A.; Kǒng, X.-Q.; Reimer, J. A.; Bell, A. T. ACS Catal. 2013, 3, 348. (c) Han, D.; Li, X.; Zhang, H.; Liu, Z.; Li, J.; Li, C. J. Catal. 2006, 243, 318. (d) Shylesh, S.; Hanna, D.; Mlinar, A.; Kǒng, X.-Q.; Reimer, J. A.; Bell, A. T. ACS Catal. 2013, 3, 348. (e) Andersen, J.-A. M.; Currie, A. W. S. Chem. Commun. 1996, 1543. (f) Li, X.; Zhang, Y.; Meng, F.; San, X.; Yang, G.; Meng, M.; Takahashi, M.; Tsubaki, N. Top. Catal. 2010, 53, 608. (g) Tan, M.; Wang, D.; Ai, P.; Liu, G.; Wu, M.; Zheng, J.; Yang, G.; Yoneyama, Y.; Tsubaki, N. Appl. Catal., A 2016, 527, 53. (h) Ganga, V. S. R.; Dabbawala, A. A.; Munusamy, K.; Abdi, S. H.R.; Kureshy, R. I.; Khan, N. H.; Bajaj, H. C. Catal. Commun. 2016, 84, 21. (5) (a) Shibahara, F.; Nozaki, K.; Hiyama, T. J. Am. Chem. Soc. 2003, 125, 8555. (b) Cardozo, A. F.; Manoury, E.; Julcour, C.; Blanco, J.-F.; Delmas, H.; Gayet, F.; Poli, R. Dalton Trans 2013, 42, 9148. (c) Potier, J.; Menuel, S.; Fournier, D.; Fourmentin, S.; Woisel, P.; Monflier, E.; Hapiot, F. ACS Catal. 2012, 2, 1417. (d) Parrinello, G.; Stille, J. K. J. Am. Chem. Soc. 1987, 109, 7122. (e) Makhubela, B. C. E.; Jardine, A.; Smith, G. S. Green Chem. 2012, 14, 338. (f) Paganelli, S.; Piccolo, O.; Baldi, F.; Gallo, M.; Tassini, R.; Rancan, M.; Armelao, L. Catal. Commun. 2015, 17, 32. (g) Zeelie, T. A.; Root, A.; Krause, A. O. I. Appl. Catal., A 2005, 285, 96. (h) Shibahara, F.; Nozaki, K.; Matsuo, T.; Hiyama, T. Bioorg. Med. Chem. Lett. 2002, 12, 1825. (i) Zarka, M. T.; Bortenschlager, M.; Wurst, K.; Nuyken, O.; Weberskirch, R. Organometallics 2004, 23, 4817. (j) Altava, B.; Burguete, M. I.; García-Verdugo, E.; Luis, S. V. Chem. Soc. Rev. 2018, 47, 2722. (k) Jana, R.; Tunge, J. A. J. Org. Chem. 2011, 76, 8376. (6) (a) Kramer, S.; Bennedsen, N. R.; Kegnæs, S. ACS Catal. 2018, 8, 6961. (b) Sun, Q.; Dai, Z.; Meng, X.; Xiao, F.-S. Chem. Soc. Rev. 2015, 44, 6018. (c) Kaur, P.; Hupp, J. T.; Nguyen, S. T. ACS Catal. 2011, 1, 819. (7) (a) Li, R.-H.; An, X.-M.; Yang, Y.; Li, D.-C.; Hu, Z.-L.; Zhan, Z.-P. Org. Lett. 2018, 20, 5023. (b) Li, W.-H.; Li, C.-Y.; Li, Y.; Tang, H.-T.; Wang, H.-S.; Pan, Y.-M.; Ding, Y.-J. Chem. Commun. 2018, 54, 8446. (c) Kann, A.; Hartmann, H.; Besmehn, A.; Hausoul, P. J. C.; Palkovits, R. ChemSusChem 2018, 11, 1857. (d) Chen, X.; Wang, W.; Zhu, H.; Yang, W.; Ding, Y. Mol. Catal. 2018, 456, 49. (e) Wang, W.; Li, C.; Jin, J.; Yan, L.; Ding, Y. Dalton Trans 2018, 47, 13135. (8) (a) Sun, Q.; Jiang, M.; Shen, Z.; Jin, Y.; Pan, S.; Wang, L.; Meng, X.; Chen, W.; Ding, Y.; Li, J.; Xiao, F.-S. Chem. Commun. 2014, 50, 11844. (b) Sun, Q.; Aguila, B.; Verma, G.; Liu, X.; Dai, Z.; Deng, F.; Meng, X.; Xiao, F.-S.; Ma, S. Chem. 2016, 1, 628. (9) Sun, Q.; Dai, Z.; Liu, X.; Sheng, N.; Deng, F.; Meng, X.; Xiao, F. S. J. Am. Chem. Soc. 2015, 137, 5204. (10) (a) Li, C.; Xiong, K.; Yan, L.; Jiang, M.; Song, X.; Wang, T.; Chen, X.; Zhan, Z.; Ding, Y. Catal. Sci. Technol. 2016, 6, 2143. (b) Wang, Y.; Yan, L.; Li, C.; Jiang, M.; Wang, W.; Ding, Y. Appl. Catal., A 2018, 551, 98. (c) Li, C.; Yan, L.; Lu, L.; Xiong, K.; Wang, W.; Jiang, M.; Liu, J.; Song, X.; Zhan, Z.; Jiang, Z.; Ding, Y. Green Chem. 2016, 18, 2995. (d) Wang, Y.; Yan, L.; Li, C.; Jiang, M.; Zhao, Z.; Hou, G.; Ding, Y. J. Catal. 2018, 368, 197. (11) (a) van der Slot, S. C.; Duran, J.; Luten, J.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Organometallics 2002, 21, 3873. (b) Jia, X.; Wang, Z.; Xia, C.; Ding, K. Chem. - Eur. J. 2012, 18, 15288. (c) Ren, X.; Zheng, Z.; Zhang, L.; Wang, Z.; Xia, C.; Ding, K. Angew. Chem., Int. Ed. 2017, 56, 310. (d) Yu, S.; Chie, Y.; Guan, Z.; Zhang, X. Org. Lett. 2008, 10, 3469. (e) Zhang, Z.; Wang, Q.; Chen, C.; Han, Z.; Dong, X.-Q.; Zhang, X. Org. Lett. 2016, 18, 3290. (f) Yan, Y.; Zhang, X.; Zhang, X. J. Am. Chem. Soc. 2006, 128, 16058.

Figure 2. Recycling tests of the Rh/POL-BPa&PPh3 in 1-hexene hydroformylation. Reaction conditions: 50.0 mg Rh/POL-BPa&PPh3, 1-hexene (5.7 mL), S/C = 10000, CO/H2 = 10/10 bar, 90 °C for 5 h. After each run, the catalyst was recovered via centrifugal separation.

heterogeneous catalyst in hydroformylation of terminal and internal olefins, affording high l/b ratios (6.7−52.8) and excellent TON values (up to 45.3 × 104). Remarkably, the heterogeneous catalyst was also reused for 10 cycles in hydroformylation of 1-hexene without losing activity and selectivity.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.9b00459. Experimental procedures, analytical data, and NMR spectra (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*X.J.: E-mail, [email protected]. *L.Z.: E-mail, [email protected]. *C.X.: E-mail, [email protected]. ORCID

Xiaofei Jia: 0000-0002-5306-0395 Author Contributions §

Xiaofei Jia and Zuyu Liang contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge financial support from the Natural Science Foundation of Shandong Province (no. ZR2016BQ24) and Natural Science Foundation of China (no. 21703116, 51702180).

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REFERENCES

(1) (a) Roelen, O. German Patent DE 849548, 1938/1952; U.S. Patent 2327066, 1943. Chem. Abstr. 1944, 38, 363. (b) van Leeuwen, P. W. N. M.; Claver, C. Rhodium Catalyzed Hydroformylation; Kluwer Academic Publishers: Dordrecht, 2000. (c) Haumann, M.; Riisager, A. Chem. Rev. 2008, 108, 1474. (d) Hebrard, F.; Kalck, P. Chem. Rev. 2009, 109, 4272. (e) Franke, R.; Selent, D.; Borner, A. Chem. Rev. 2012, 112, 5675. (f) Pospech, J.; Fleischer, I.; Franke, R.; Buchholz, S.; Beller, M. Angew. Chem., Int. Ed. 2013, 52, 2852. (2) Börner, A.; Franke, R. Hydroformylation: Fundamentals, Processes, and Applications in Organic Synthesis; Wiley-VCH: Weinheim, 2016. D

DOI: 10.1021/acs.orglett.9b00459 Org. Lett. XXXX, XXX, XXX−XXX