Abstract
Poly(ethylene glycol) (PEG)-armed Ru(II)-bearing microgel-core star polymer catalysts were used for the transfer hydrogenation of ketones. The star catalysts (Ru(II)-PEG Star) were one-pot synthesized by ruthenium-catalyzed living radical polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and a sequential linking reaction with ethylene glycol dimethacrylate (1) and diphenylphosphinostyrene (2). The polymers efficiently and homogeneously reduced acetophenone into 1-phenylethanol in 2-propanol coupled with K2CO3 at a high yield, despite a low catalyst feed ratio to the substrate (Ru(II)/substrate=1/1000). Importantly, the catalytic activity was higher than that of the original RuCl2(PPh3)3, as well as that of similar polymer-supported Ru(II) catalysts, such as poly(methyl methacrylate)-armed star-, polystyrene gel- and random polymer-supported catalysts. Ru(II)-PEG Star is applicable to various substrates, including para-substituted aromatic, aliphatic and bulky ketones, where the activity of Ru(II)-PEG Star is is generally higher than that of RuCl2(PPh3)3. For example, the turnover frequency for 4-chloroacetophenone and cyclohexanone reached ∼1000 h−1, and the reduction rate of cyclopentanone and 3-methyl-5-heptanone was twice as high as that of RuCl2(PPh3)3. The star catalyst also showed high catalyst recyclability, independent of the substrate species. These features most likely arise from its unique reaction space, which consists of a ruthenium-embedded, hydrophobic microgel core surrounded by amphiphilic and polar PEGMA arms.
Similar content being viewed by others
Log in or create a free account to read this content
Gain free access to this article, as well as selected content from this journal and more on nature.com
or
References
Leadbeater, N. E. & Marco, M. Preparation of polymer-supported ligands and metal complexes for use in catalysis. Chem. Rev. 102, 3217–3274 (2002).
Yoshida, J. & Itami, K. Tag strategy for separation and recovery. Chem. Rev. 102, 3693–3716 (2002).
Bergbreiter, D. E., Tian, J. & Hongfa, C. Using soluble polymer supports to facilitate homogeneous catalysis. Chem. Rev. 109, 530–582 (2009).
Akiyama, R. & Kobayashi, S. ‘Microencapsulated’ and related catalysts for organic chemistry and organic synthesis. Chem. Rev. 109, 594–642 (2009).
Helms, B. & Fréchet, J. M. J. The dendrimer effect in homogeneous catalysis. Adv. Synth. Catal. 348, 1125–1148 (2006).
Li, W.- S. & Aida, T. Dendrimer porphyrins and phthalocyanines. Chem. Rev. 109, 6047–6076 (2009).
Piotti, M. E., Rivera, F. Jr., Bond, R., Hawker, C. J. & Fréchet, J. M. J. Synthesis and catalytic activity of unimolecular dendritic reverse micelles with ‘internal’ functional groups. J. Am. Chem. Soc. 121, 9471–9472 (1999).
Dwars, T., Paetzold, E. & Oehme, G. Reactions in micellar systems. Angew. Chem. Int. Ed. 44, 7174–7199 (2005).
Zarka, M. T., Bortenschlager, M., Wurst, K., Nuyken, O. & Weberskirch, R. Immobilization of a rhodium carbene complex to an amphiphilic block copolymer for hydroformylation of 1-octene under aqueous two-phase conditions. Organometallics 23, 4817–4820 (2004).
van Dongen, S. F., de Hoog, H. P., Peters, R. J., Nallani, M., Nolte, R. J. & van Hest, J. C. Biohybrid polymer capsules. Chem. Rev. 109, 6212–6274 (2009).
Vriezema, D. M., Garcia, P. M. L., Oltra, N. S., Hatzakis, N. S., Kuiper, S. M., Nolte, R. J. M., Rowan, A. E. & van Hest, J. C. M. Positional assembly of enzymes in polymersome nanoreactors for cascade reactions. Angew. Chem. Int. Ed. 46, 7378–7382 (2007).
Gao, H. & Matyjaszewski, K. Synthesis of functional polymers with controlled architecture by CRP of monomers in the presence of cross-linkers: From stars to gels. Prog. Polym. Sci. 34, 317–350 (2009).
Blencowe, A., Tan, J. F., Goh, T. K. & Qiao, G. G. Core cross-linked star polymers via controlled radical polymerization. Polymer 50, 5–32 (2009).
Terashima, T., Motokawa, R., Koizumi, S., Sawamoto, M., Kamigaito, M., Ando, T. & Hashimoto, T. In situ and time-resolved small-angle neutron scattering observation of star polymer formation via arm-linking reaction in ruthenium-catalyzed living radical polymerization. Macromolecules 43, 8218–8232 (2010).
Terashima, T., Kamigaito, M., Baek, K.- Y., Ando, T. & Sawamoto, M. Polymer catalysts from polymerization catalysts: direct encapsulation of metal catalyst into star polymer core during metal-catalyzed living radical polymerization. J. Am. Chem. Soc. 125, 5288–5289 (2003).
Terashima, T., Ouchi, M., Ando, T., Sawamoto, M. & Kamigaito, M. Metal-complex-bearing star polymers by metal-catalyzed living radical polymerization: Synthesis and characterization of poly(methyl methacrylate) star polymers with Ru(II)-embedded microgel cores. J. Polym. Sci., Part A: Polym. Chem. 44, 4966–4980 (2006).
Terashima, T., Ouchi, M., Ando, T., Kamigaito, M. & Sawamoto, M. Amphiphilic, thermosensitive ruthenium(II)-bearing star polymer catalysts: one-pot synthesis of PEG armed star polymers with ruthenium(II)-enclosed microgel cores via metal-catalyzed living radical polymerization. Macromolecules 40, 3581–3588 (2007).
Terashima, T., Ouchi, M., Ando, T. & Sawamoto, M. Thermoregulated phase-transfer catalysis via PEG-armed Ru(II)-bearing microgel core star polymers: Efficient and reusable Ru(II) catalysts for aqueous transfer hydrogenation of ketones. J. Polym. Sci., Part A: Polym. Chem. 48, 373–379 (2010).
Terashima, T., Ouchi, M., Ando, T. & Sawamoto, M. Oxidation of sec-alcohols with Ru(II)-bearing microgel star polymer catalysts via hydrogen transfer reaction: Unique microgel-core catalysis. J. Polym. Sci., Part A: Polym. Chem. 49, 1061–1069 (2011).
Bosman, A. W., Vestberg, R., Heumann, A., Fréchet, J. M. J. & Hawker, C. J. A. Modular approach toward functionalized three-dimensional macromolecules: from synthetic concepts to practical applications. J. Am. Chem. Soc. 125, 715–728 (2003).
Helms, B., Guillaudeu, S. J., Xie, Y., McMurdo, M., Hawker, C. J. & Fréchet, J. M. J. One-pot reaction cascades using star polymers with core-confined catalysts. Angew. Chem. Int. Ed. 44, 6384–6387 (2005).
Chi, Y., Scroggins, S. T. & Fréchet, J. M. J. One-pot multi-component asymmetric cascade reactions catalyzed by soluble star polymers with highly branched non-interpenetrating catalytic cores. J. Am. Chem. Soc. 130, 6322–6323 (2008).
Kanaoka, S., Yagi, N., Fukuyama, Y., Aoshima, S., Tsunoyama, H., Tsukuda, T. & Sakurai, H. Thermosensitive gold nanoclusters stabilized by well-defined vinyl ether star polymers: reusable and durable catalysts for aerobic alcohol oxidation. J. Am. Chem. Soc. 129, 12060–12061 (2007).
Ouchi, M., Terashima, T. & Sawamoto, M. Precision control of radical polymerization via transition metal catalysis: from dormant species to designed catalysts for precision functional polymers. Acc. Chem. Res. 41, 1120–1132 (2008).
Ouchi, M., Terashima, T. & Sawamoto, M. Transition metal-catalyzed living radical polymerization: toward perfection in catalysis and precision polymer synthesis. Chem. Rev. 109, 4963–5050 (2009).
Matyjaszewski, K. & Tsarevsky, N. V. Nanostructured functional materials prepared by atom transfer radical polymerization. Nature Chem. 1, 276–288 (2009).
Rosen, B. M. & Percec, V. Single-electron transfer and single-electron transfer degenerative chain transfer living radical polymerization. Chem. Rev. 109, 5069–5119 (2009).
Kamigaito, M. Recent developments in metal-catalyzed living radical polymerization. Polym. J. 43, 105–120 (2011).
Sasson, Y. & Blum, J. Homogeneous catalytic transfer-hydrogenation of α,β-unsaturated carbonyl compounds by dichlorotris(triphenylphosphine)ruthenium (II). Tetrahedron Lett. 24, 2167–2170 (1971).
Sasson, Y. & Blum, J. Dichlorotris(triphenylphosphine)ruthenium-catalyzed hydrogen transfer from alcohols to saturated and alpha, beta-unsaturated ketones. J. Org. Chem. 40, 1887–1896 (1975).
Chowdhury, R. L. & Bäckvall, J.- E. Efficient ruthenium-catalysed transfer hydrogenation of ketones by propan-2-ol. J. Chem. Soc., Chem. Commun. 1063–1064 (1991).
Noyori, R. Asymmetric catalysis: science and opportunities (nobel lecture). Angew. Chem. Int. Ed. 41, 2008–2022 (2002).
Everaere, K., Mortreux, A. & Carpentier, J.- F. Ruthenium(II)-catalyzed asymmetric transfer hydrogenation of carbonyl compounds with 2-propanol and ephedrine-type ligands. Adv. Synth. Catal. 345, 67–77 (2003).
Saluzzo, C. & Lemaire, M. Homogeneous-supported catalysts for enantioselective hydrogenation and hydrogen transfer reduction. Adv. Synth. Catal. 344, 915–928 (2002).
Haraguchi, N., Nishiyama, A. & Itsuno, S. Synthesis of polymer microspheres functionalized with chiral ligand by precipitation polymerization and their application to asymmetric transfer hydrogenation. J. Polym. Sci., Part A: Polym. Chem. 48, 3340–3349 (2010).
Ando, T., Kamigaito, M. & Sawamoto, M. Silyl enol ethers: end-capping agents for living radical polymerization of methyl methacrylate with ruthenium complex. Macromolecules 31, 6708–6711 (1998).
Gao, J.- K., Yi, X. D., Tang, C.- L., Xu, P.- P. & Wan, H.- L. Preparation and use of polymer-supported chiral ruthenium complex catalyst. Polym. Adv. Technol. 12, 716–719 (2001).
Cadierno, V., Crochet, P., DÃez, J., GarcÃa-Garrido, S. E. & Gimeno, J. Efficient transfer hydrogenation of ketones catalyzed by the bis(isocyanide)-ruthenium(II) complexes trans,cis,cis-[RuX2(CNR)2(dppf)] (X=Cl, Br; dppf=1,1′-bis(diphenylphosphino)ferrocene): isolation of active mono- and dihydride intermediates. Organometallics 23, 4836–4845 (2004).
Faller, J. W. & Lavoie, A. R. Catalysts for the asymmetric transfer hydrogenation of ketones derived from L-prolinamide and (p-cymeneRuCl2)2 or (Cp*RhCl2)2 . Organometallics 20, 5245–5247 (2001).
Yamada, I. & Noyori, R. Asymmetric transfer hydrogenation of benzaldehydes. Org. Lett. 2, 3425–3427 (2000).
Acknowledgements
This research was supported by a Grant-in-Aid for the Japan Society for the Promotion of Sciences Fellows (No. 16-1205), for which TT is grateful. We thank Hokko Chemical for the kind supply of a phosphine ligand monomer (diphenylphosphinostyrene: 2). We also thank Dr Takeshi Niitani and his colleagues (Nippon Soda, Tokyo, Japan) for ICP-AES analysis.
Author information
Authors and Affiliations
Corresponding authors
Additional information
Supplementary Information accompanies the paper on Polymer Journal website
Supplementary information
Rights and permissions
About this article
Cite this article
Terashima, T., Ouchi, M., Ando, T. et al. Transfer hydrogenation of ketones catalyzed by PEG-armed ruthenium-microgel star polymers: microgel-core reaction space for active, versatile and recyclable catalysis. Polym J 43, 770–777 (2011). https://doi.org/10.1038/pj.2011.52
Received:
Accepted:
Published:
Issue date:
DOI: https://doi.org/10.1038/pj.2011.52
