Ring-opening metathesis polymerization based pore-size-selective functionalization of glycidyl methacrylate based monolithic media: access to size-stable nanoparticles for ligand-free metal catalysis.
Monolithic polymeric supports have been prepared by electron-beam-triggered free-radical polymerization using a mixture of glycidyl methacrylate and trimethylolpropane triacrylate in 2-propanol, 1-dodecanol, and toluene. Under appropriate conditions, phase separation occurred, which resulted in the formation of a porous monolithic matrix that was characterized by large (convective) pores in the 30 μm range as well as pores of <600 nm. The epoxy groups in pores of >7 nm were hydrolyzed by using poly(styrenesulfonic acid) (Mw = 69,400 g mol(-1), PDI=2.4). The remaining epoxy groups inside pores of <7 nm were subjected to aminolysis with norborn-5-en-2-ylmethylamine (2) and provided covalently bound norborn-2-ene (NBE) groups inside these pores. These NBE groups were then treated with the first-generation Grubbs initiator [RuCl2 (PCy3 )2 (CHPh)]. These immobilized Ru-alkylidenes were further used for the surface modification of the small pores by a grafting approach. A series of monomers, that is, 7-oxanorborn-5-ene-2,3-dicarboxylic anhydride (3), norborn-5-ene-2,3-dicarboxylic anhydride (4), N,N-di-2-pyridyl-7-oxanorborn-5-ene-2-carboxylic amide (5), N,N-di-2-pyridylnorborn-5-ene-2-carboxamide (6), N-[2-(dimethylamino)ethyl]bicyclo[2.2.1]hept-5-ene-2-carboxamide (7), and dimethyl bicyclo[2.2.1]hept-5-en-2-ylphosphonate (8), were used for this purpose. Finally, monoliths functionalized with poly-5 graft polymers were used to permanently immobilize Pd(2+) and Pt(4+), respectively, inside the pores. After reduction, metal nanoparticles 2 nm in diameter were formed. The palladium-nanoparticle-loaded monoliths were used in both Heck- and Suzuki-type coupling reactions achieving turnover numbers of up to 167,000 and 63,000, respectively.
Lehrstuhl für Makromolekulare Stoffe und Faserchemie, Institut für Polymerchemie, Universität Stuttgart, Pfaffenwaldring 55, 7 Stuttgart (Germany).
Rajendar
R
Bandari
Thomas
T
Höche
Andrea
A
Prager
Klaus
K
Dirnberger
Michael R
MR
Buchmeiser
D019840:2-Propanol / Q000737:chemistry; D002384:Catalysis; D007851:Dodecanol / Q000737:chemistry; D004852:Epoxy Compounds / Q000737:chemistry*; D008024:Ligands; D008689:Methacrylates / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D058105:Polymerization; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D016062:Porosity
D004852:Epoxy Compounds; D008024:Ligands; D008689:Methacrylates; D011108:Polymers; D007851:Dodecanol; D019840:2-Propanol; C007870:glycidyl methacrylate
metathesis; monoliths; nanoparticles; ring-opening polymerization; supported catalysts