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Miniaturized catalysis: monolithic, highly porous, large surface area capillary flow reactors constructed in situ from polyhedral oligomeric silsesquioxanes (POSS).

Scholder P, Nischang I - Catal Sci Technol (2015)

Bottom Line: A single-step molding process utilizing free-radical cross-linking reaction of vinyl POSS in microliter-sized dimensions leads to hierarchically-structured, mechanically robust, porous hybrid structures.Functional variants show excellent performance in Suzuki-type coupling reactions.Due to their small volume, long-term operational robustness, and potential chemical diversity, these materials are promising candidates for catalyst screening applications.

View Article: PubMed Central - PubMed

Affiliation: Institute of Polymer Chemistry , Johannes Kepler University Linz , A-4060 , Leonding , Austria . Email: ivo.nischang@jku.at.

ABSTRACT

A single-step molding process utilizing free-radical cross-linking reaction of vinyl POSS in microliter-sized dimensions leads to hierarchically-structured, mechanically robust, porous hybrid structures. Functional variants show excellent performance in Suzuki-type coupling reactions. Due to their small volume, long-term operational robustness, and potential chemical diversity, these materials are promising candidates for catalyst screening applications.

No MeSH data available.


(a) Impact of fluid contact time in the reactors on yield obtained for the reaction of 0.1 mol L–1 iodobenzene with 0.125 mol L–1p-tolylboronic acid (entry 1, Table 1). (b) Long term stability of the reactors in steady-state at a fluid contact time of 49 min. (c) Yield achieved from flow-through catalysis of the reaction of iodobenzene with p-tolylboronic acid keeping a stoichiometric ratio of 1 : 1.25 but varying concentration at a fluid contact time of 32.6 min. The reactors had the same length of 30 cm. Other conditions: fluid phase of 75/25 acetonitrile/water (%, v/v) and 2 equiv. triethylamine (to that of the iodobenzene) as the base. Reactions were performed at a constant reactor temperature of T = 80 °C.
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fig3: (a) Impact of fluid contact time in the reactors on yield obtained for the reaction of 0.1 mol L–1 iodobenzene with 0.125 mol L–1p-tolylboronic acid (entry 1, Table 1). (b) Long term stability of the reactors in steady-state at a fluid contact time of 49 min. (c) Yield achieved from flow-through catalysis of the reaction of iodobenzene with p-tolylboronic acid keeping a stoichiometric ratio of 1 : 1.25 but varying concentration at a fluid contact time of 32.6 min. The reactors had the same length of 30 cm. Other conditions: fluid phase of 75/25 acetonitrile/water (%, v/v) and 2 equiv. triethylamine (to that of the iodobenzene) as the base. Reactions were performed at a constant reactor temperature of T = 80 °C.

Mentions: The reaction of iodobenzene with p-tolylboronic acid in 75/25 acetonitrile/water (%, v/v) was used as a model to judge the reactor performance under typical conditions, i.e. at a temperature of T = 80 °C and continuous flow. Fig. 3a compares the respective yields of the flow reactor systems originating from the same pristine material. The materials with chelated palladium functionality (catalysts 1 and 2, Scheme 1) approach greater than 85% quantitative yield after a mere 30 min fluid contact time (Fig. 3a). The shape of the yield–fluid contact time curves of catalysts 1 and 2 is similar. The performance of both reactors with chelated palladium is better than the homogeneous “control” variants in batch experiments and an open tube implementation both with 1 mol% pristine palladium complex Pd(MeCN)2Cl2 as a catalyst (with respect to the iodobenzene) in the same fluid phase (Fig. S4†). Yet, we calculated overall catalyst concentrations of 10 mmol L–1 (catalyst 1) and 4 mmol L–1 (catalyst 2) in the monolithic reactors (see the ESI†). This qualitatively indicates that at a reactant concentration of 0.1 mol L–1 in the fluid phase of one reactor volume, a 10 mol% of the palladium sites is present for catalyst 1. Eventually, not all of the palladium sites in the material are catalytically active, which may originate from the limited accessibility of the very small pores providing diffusional resistance and significantly contributing to the large dry-state surface areas (Fig. S1†).


Miniaturized catalysis: monolithic, highly porous, large surface area capillary flow reactors constructed in situ from polyhedral oligomeric silsesquioxanes (POSS).

Scholder P, Nischang I - Catal Sci Technol (2015)

(a) Impact of fluid contact time in the reactors on yield obtained for the reaction of 0.1 mol L–1 iodobenzene with 0.125 mol L–1p-tolylboronic acid (entry 1, Table 1). (b) Long term stability of the reactors in steady-state at a fluid contact time of 49 min. (c) Yield achieved from flow-through catalysis of the reaction of iodobenzene with p-tolylboronic acid keeping a stoichiometric ratio of 1 : 1.25 but varying concentration at a fluid contact time of 32.6 min. The reactors had the same length of 30 cm. Other conditions: fluid phase of 75/25 acetonitrile/water (%, v/v) and 2 equiv. triethylamine (to that of the iodobenzene) as the base. Reactions were performed at a constant reactor temperature of T = 80 °C.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4530614&req=5

fig3: (a) Impact of fluid contact time in the reactors on yield obtained for the reaction of 0.1 mol L–1 iodobenzene with 0.125 mol L–1p-tolylboronic acid (entry 1, Table 1). (b) Long term stability of the reactors in steady-state at a fluid contact time of 49 min. (c) Yield achieved from flow-through catalysis of the reaction of iodobenzene with p-tolylboronic acid keeping a stoichiometric ratio of 1 : 1.25 but varying concentration at a fluid contact time of 32.6 min. The reactors had the same length of 30 cm. Other conditions: fluid phase of 75/25 acetonitrile/water (%, v/v) and 2 equiv. triethylamine (to that of the iodobenzene) as the base. Reactions were performed at a constant reactor temperature of T = 80 °C.
Mentions: The reaction of iodobenzene with p-tolylboronic acid in 75/25 acetonitrile/water (%, v/v) was used as a model to judge the reactor performance under typical conditions, i.e. at a temperature of T = 80 °C and continuous flow. Fig. 3a compares the respective yields of the flow reactor systems originating from the same pristine material. The materials with chelated palladium functionality (catalysts 1 and 2, Scheme 1) approach greater than 85% quantitative yield after a mere 30 min fluid contact time (Fig. 3a). The shape of the yield–fluid contact time curves of catalysts 1 and 2 is similar. The performance of both reactors with chelated palladium is better than the homogeneous “control” variants in batch experiments and an open tube implementation both with 1 mol% pristine palladium complex Pd(MeCN)2Cl2 as a catalyst (with respect to the iodobenzene) in the same fluid phase (Fig. S4†). Yet, we calculated overall catalyst concentrations of 10 mmol L–1 (catalyst 1) and 4 mmol L–1 (catalyst 2) in the monolithic reactors (see the ESI†). This qualitatively indicates that at a reactant concentration of 0.1 mol L–1 in the fluid phase of one reactor volume, a 10 mol% of the palladium sites is present for catalyst 1. Eventually, not all of the palladium sites in the material are catalytically active, which may originate from the limited accessibility of the very small pores providing diffusional resistance and significantly contributing to the large dry-state surface areas (Fig. S1†).

Bottom Line: A single-step molding process utilizing free-radical cross-linking reaction of vinyl POSS in microliter-sized dimensions leads to hierarchically-structured, mechanically robust, porous hybrid structures.Functional variants show excellent performance in Suzuki-type coupling reactions.Due to their small volume, long-term operational robustness, and potential chemical diversity, these materials are promising candidates for catalyst screening applications.

View Article: PubMed Central - PubMed

Affiliation: Institute of Polymer Chemistry , Johannes Kepler University Linz , A-4060 , Leonding , Austria . Email: ivo.nischang@jku.at.

ABSTRACT

A single-step molding process utilizing free-radical cross-linking reaction of vinyl POSS in microliter-sized dimensions leads to hierarchically-structured, mechanically robust, porous hybrid structures. Functional variants show excellent performance in Suzuki-type coupling reactions. Due to their small volume, long-term operational robustness, and potential chemical diversity, these materials are promising candidates for catalyst screening applications.

No MeSH data available.