Rajendar Bandari

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.

Polymeric monolith supported Pt-nanoparticles as ligand-free catalysts for olefin hydrosilylation under batch and continuous conditions

Pt-nanoparticles were generated within the mesopores of polymeric monolithic supports. These monoliths were prepared viaring-opening metathesis polymerization (ROMP) from (Z)-9-oxabicyclo[6.1.0]non-4-ene (OBN) and tris(cyclooct-4-en-1-yloxy)methylsilane (CL) using the 3rd-generation Grubbs-initiator RuCl2(pyridine)2(IMesH2)(CHPh) (1) in the presence of a macro- and microporogen. To generate the Pt nanoparticles inside the porous system, the epoxy-groups of the monolithic supports were hydrolyzed into the corresponding vic-diol with the aid of 0.1 N sulfuric acid. Loading with Pt4+ and reduction with NaBH4 resulted in the formation of Pt nanoparticles <7 nm in diameter that were exclusively located within the mesopores of the support as demonstrated by transmission electron microscopy/EDX spectrometry. The nanoparticles were stabilized by both the vic-diols and the polymeric double bonds as evidenced by control experiments with poly(glycidylmethacrylate)-based monoliths that lack the double bonds. Typical metal loadings of around 1.7 mg g−1 (8.7 μmol g−1) were obtained. Pt(0)-loaded monoliths were used in the hydrosilylation of terminal alkenes, norborn-2-ene and norbornadiene applying both batch and continuous flow conditions. Hydrosilylation of olefins under continuous flow conditions resulted in constant product formation in 98% yield at T = 45 °C applying a linear flow of 12.0 mm min−1. Metal leaching was very low, resulting in Pt-contamination in the addition products of less than 4 ppm throughout.

Ring‐opening metathesis polymerization‐derived, lectin‐functionalized monolithic supports for affinity separation of glycoproteins

Lectin-functionalized monolithic columns were prepared within polyether ether ketone (PEEK) columns (150 × 4.6 mm id) via transition metal-catalyzed ring-opening metathesis polymerization of norborn-2-ene (NBE) and trimethylolpropane-tris(5-norbornene-2-carboxylate) (CL) using the first-generation Grubbs initiator RuCl2 (PCy3 )2 (CHPh) (1, Cy = cyclohexyl) in the presence of a macro- and microporogen, i.e. of 2-propanol and toluene. Postsynthesis functionalization was accomplished via in situ grafting of 2,5-dioxopyrrolidin-1-yl-bicyclo[2.2.1]hept-5-ene-2-carboxylate to the surface of the monoliths followed by reaction with α,ω-diamino-poly(ethyleneglycol). The pore structure of the poly(ethyleneglycol)- derivatized monoliths was investigated by electron microscopy and inverse-size exclusion chromatography, respectively. The amino-poly(ethyleneglycol) functionalized monolithic columns were then successfully used for the immobilization of lectin from Lens culinaris hemagglutinin. The thus prepared lectin-functionalized monoliths were applied to the affinity chromatography-based purification of glucose oxidase. The binding capacity of Lens culinaris hemagglutinin-immobilized monolithic column for glucose oxidase was found to be 2.2 mg/column.

Electron beam triggered, free radical polymerization-derived monolithic capillary columns for high-performance liquid chromatography

Monolithic capillary columns were prepared via electron beam triggered free radical polymerization within the confines of 0.2 and 0.1mm I.D. capillary columns using ethyl methacrylate and trimethylolpropane triacrylate as monomers as well as 2-propanol, 1-dodecanol and toluene as porogenic system. The influence of column diameter on reproducibility and separation performance was investigated. For evaluation, a protein standard consisting of five proteins in the range of 5800-66,000 g mol(-1) was used. Reproducibility was checked by determining the relative standard deviations in retention times, peak widths at half height, asymmetry and resolution. Excellent run-to-run reproducibility was found for both 0.2 and 0.1mm I.D. columns; batch-to-batch reproducibility was good for both column types. In order to enhance the non-polar character of the monolithic columns, lauryl methacrylate-based capillary columns were prepared. These were successfully used for the separation of proteins and a cytochrome c digest.

Selective Reduction of CO2 with Silanes over Platinum Nanoparticles Immobilised on a Polymeric Monolithic Support under Ambient Conditions

Here, we demonstrate the use of Pt(0) nanoparticles immobilised on a polymeric monolithic support as a ligand-free heterogeneous catalytic system for the reduction of (13) CO2 at room temperature and atmospheric pressure. The described system effectively reduces (13) CO2 with dihydrosilanes as the hydrogen source to yield a mixture of silylformates, silylacetals and methoxysilanes, which upon further hydrolysis with D2 O, produces their respective C1-type products, that is H(13) COOD, (13) CH2 (OD)2 and (13) CH3 OD. If a monohydrosilane was used as the hydrogen source, a selective reduction of (13) CO2 to a product mixture of only silylformates was observed. Addition of diethylamine to this reaction mixture results in the formation of H(13) COOH and Et2 N(13) CHO. This robust catalytic system is not only maintenance-free and simple to handle, as compared with organometallic and organocatalyst systems, but also shows 3- to 11-fold better catalytic activity and exhibits higher turnover numbers (TONs) up to 21 900 (activity=6.22 kg CO 2 gPt (-1)  bar(-1) ).

Functional monolithic materials for boronate-affinity chromatography via Schrock catalyst-triggered ring-opening metathesis polymerization.

Monolithic polymeric materials are prepared via ring-opening metathesis copolymerization of norborn-2-ene with 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene in the presence of macro- and microporogens, that is, of n-hexane and 1,2-dichloroethane, using the Schrock catalyst Mo(N-2,6-(2-Pr)(2) -C(6) H(3) )(CHCMe(2) Ph)(OCMe(3) )(2) . Functionalization of the monolithic materials is accomplished by either terminating the living metal alkylidenes with various functional aldehydes or by post-synthesis grafting with norborn-5-en-2-ylmethyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzoate. Finally, boronate-grafted monolithic columns (100 × 3 mm i.d.) are successfully applied to the affinity chromatographic separation of cis-diol-based biomolecules.