Aerobic Alcohol Oxidation in Water by Pd(II)/Pd(0)-based Catalysts bearing Pyridine-modified Poly(ethylene glycol) Werner Oberhauser1, *, Guido Giachi2, Marco Frediani2, Laura Capozzoli3, Elisa Passaglia4 1 Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Area di Ricerca CNR di Firenze, via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy. 2 Dipartimento di Chimica , Università di Firenze, via della Lastruccia 13, 50019 Sesto Fiorentino, Firenze, Italy. 3 Centro di Microscopie Elettroniche (CEME), Area di Ricerca CNR di Firenze, via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy. 4 ICCOM-CNR, UOS Pisa, Area della Ricerca, via Moruzzi 1, 56124 Pisa, Italy. *: Werner Oberhauser, email: werner.oberhauser@iccom.cnr.it Due to the increasing demand for environmentally compatible oxidation protocols, which avoid the generation of amounts of heavy-metal waste or organic solvents as reaction medium, a great deal of research is been focusing on alternative "greener" synthetic protocols using supercritical carbon dioxide1 or water2 as reaction medium and oxygen or air as the final hydrogen acceptor.2 Efficient heterogeneous catalytic systems for aerobic oxidation reactions are based on metal nanoparticles (NPs) which are either incarcerated in organic cross linked polymers3,4 anchored onto carbon5, alumina6, hydroxyapatite7 or stabilized by end-functionalized poly(ethylene glycol) (PEG).8,9 The latter polymer, which is cheap, biocompatible and miscible with water, decreases the polarity of the latter solvent by reducing hydrogen bond interactions between water and the polymer backbone.10 PEG can hence be considered a co-solvent in water which increases the solubility of organic substrates. Moreover, the easy end-functionalization of PEG brings about the formation of water-soluble macroligands which stabilize well-defined molecular metal complexes or metal NPs.11,12 In addition, the polyether structure of PEG is suitable for metal cation coordination.10 We will present the synthesis of well-defined water-soluble Pd(II) compounds and Pd-NPs stabilized by 4-pyridinemethylene-modified MeO-PEG (L). The obtained Pd(II)/Pd(0) precatalysts were successfully applied in the aerobic oxidation reaction of ?,?-unsaturated alcohols carried out in water. Pd-NPs stabilized by L and obtained upon reduction of a well-defined molecular Pd(II) precursor showed high catalytic activity which was maintained in several consecutive recycling experiments, without leaching of Pd in the organic phase. References 1) Leitner W. Acc. Chem. Res. 2002; 35: 746-756. 2) Stahl S.S. Angew. Chem. Int. Ed. 2004; 43: 3400-3420. 3) Biffis A., Minati L. J. Catal. 2005; 236: 405-409. 4) Miyamura H., Matsubara R., Kobayashi S. Chem. Commun. 2008: 2031-2033. 5) Ng Y.H., Ikeda S., Harada T., Morita Y. Matsumura M. Chem. Commun. 2008: 3181-3183. 6) Mallat T., Bodnar Z., Hug P., Baiker A. J. Catal. 1995; 153: 131-143. 7) Jamwal N., Gupta M., Paul S. Green Chem. 2008; 10: 999-1003. 8) Uozumi Y., Nakao R. Angew. Chem. Int. Ed. 2003; 42: 194-197. 9) Feng B., Hou Z., Yang H., Wang X., Hu Y., Li H., Qiao Y., Zhao X., Huang Q. Langmuir 2010; 26: 2505-2513. 10) Chen J., Spear S.K., Huddleston J.G., Rogers R.D. Green Chem. 2005; 7: 64-82. 11) Bergbreiter DE., Tian J., Hongfa C. Chem. Rev. 2009; 109: 530-582. 12) Lu J., Toy H. Chem. Rev. 2009; 109: 815-838.
Aerobic Alcohol Oxidation in Water by Pd(II)/Pd(0)-based Catalysts bearing Pyridine-modified Poly(ethylene glycol)
Oberhauser Werner;Passaglia Elisa
2013
Abstract
Aerobic Alcohol Oxidation in Water by Pd(II)/Pd(0)-based Catalysts bearing Pyridine-modified Poly(ethylene glycol) Werner Oberhauser1, *, Guido Giachi2, Marco Frediani2, Laura Capozzoli3, Elisa Passaglia4 1 Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Area di Ricerca CNR di Firenze, via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy. 2 Dipartimento di Chimica , Università di Firenze, via della Lastruccia 13, 50019 Sesto Fiorentino, Firenze, Italy. 3 Centro di Microscopie Elettroniche (CEME), Area di Ricerca CNR di Firenze, via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy. 4 ICCOM-CNR, UOS Pisa, Area della Ricerca, via Moruzzi 1, 56124 Pisa, Italy. *: Werner Oberhauser, email: werner.oberhauser@iccom.cnr.it Due to the increasing demand for environmentally compatible oxidation protocols, which avoid the generation of amounts of heavy-metal waste or organic solvents as reaction medium, a great deal of research is been focusing on alternative "greener" synthetic protocols using supercritical carbon dioxide1 or water2 as reaction medium and oxygen or air as the final hydrogen acceptor.2 Efficient heterogeneous catalytic systems for aerobic oxidation reactions are based on metal nanoparticles (NPs) which are either incarcerated in organic cross linked polymers3,4 anchored onto carbon5, alumina6, hydroxyapatite7 or stabilized by end-functionalized poly(ethylene glycol) (PEG).8,9 The latter polymer, which is cheap, biocompatible and miscible with water, decreases the polarity of the latter solvent by reducing hydrogen bond interactions between water and the polymer backbone.10 PEG can hence be considered a co-solvent in water which increases the solubility of organic substrates. Moreover, the easy end-functionalization of PEG brings about the formation of water-soluble macroligands which stabilize well-defined molecular metal complexes or metal NPs.11,12 In addition, the polyether structure of PEG is suitable for metal cation coordination.10 We will present the synthesis of well-defined water-soluble Pd(II) compounds and Pd-NPs stabilized by 4-pyridinemethylene-modified MeO-PEG (L). The obtained Pd(II)/Pd(0) precatalysts were successfully applied in the aerobic oxidation reaction of ?,?-unsaturated alcohols carried out in water. Pd-NPs stabilized by L and obtained upon reduction of a well-defined molecular Pd(II) precursor showed high catalytic activity which was maintained in several consecutive recycling experiments, without leaching of Pd in the organic phase. References 1) Leitner W. Acc. Chem. Res. 2002; 35: 746-756. 2) Stahl S.S. Angew. Chem. Int. Ed. 2004; 43: 3400-3420. 3) Biffis A., Minati L. J. Catal. 2005; 236: 405-409. 4) Miyamura H., Matsubara R., Kobayashi S. Chem. Commun. 2008: 2031-2033. 5) Ng Y.H., Ikeda S., Harada T., Morita Y. Matsumura M. Chem. Commun. 2008: 3181-3183. 6) Mallat T., Bodnar Z., Hug P., Baiker A. J. Catal. 1995; 153: 131-143. 7) Jamwal N., Gupta M., Paul S. Green Chem. 2008; 10: 999-1003. 8) Uozumi Y., Nakao R. Angew. Chem. Int. Ed. 2003; 42: 194-197. 9) Feng B., Hou Z., Yang H., Wang X., Hu Y., Li H., Qiao Y., Zhao X., Huang Q. Langmuir 2010; 26: 2505-2513. 10) Chen J., Spear S.K., Huddleston J.G., Rogers R.D. Green Chem. 2005; 7: 64-82. 11) Bergbreiter DE., Tian J., Hongfa C. Chem. Rev. 2009; 109: 530-582. 12) Lu J., Toy H. Chem. Rev. 2009; 109: 815-838.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
