Engineering and Sizing Nanoreactors To Confine Metal Complexes for Enhanced Catalytic Performance

Abstract

Homogeneous metal complexes often display superior activity and selectivity in catalysis of chemical transformations. Heterogenization of these complexes by immobilization on solid supports has been used to facilitate recovery, but this is often associated with a decrease in catalytic performance. We here describe a novel approach of sizing and engineering the cavity structure of nanoporous materials as “nanoreactors” to assemble metal complexes by the “ship-in-the-bottle” synthesis to combine the best of homogeneous and heterogeneous catalysts. Catalysis occurred by free metal complexes in confined liquid in these nanoreactors, while the catalysts were recyclable as being heterogeneous at the macroscopic scale. Subnanometer tailoring of window sizes (0.5–3.7 nm) of the cavities (16–22 nm) allowed control over loading (6–70 mg-metal complex/g-support) and a high turnover frequency (40–600 h–1) for the hydrolytic kinetic resolution of 1,2-epoxyhexane. Most importantly, the ‘heterogeneous homogeneous catalysts’ showed enhanced thermal stability and were stable upon reuse approaching excellent turnover numbers of 100,000. We showed that engineering and sizing of nanoreactors is a powerful approach to control performance of confined catalysts, and this method is generally applicable in host–guest catalysis.

An Overview of the Challenges and Progress of Synthesis, Characterization and Applications of Plugged SBA-15 Materials for Heterogeneous Catalysis

“…The desorption isotherm of m-MCFs shows capillary evaporation at the relative pressure of about 0.49. This is similar to plugged SBA-15, which is an indication for "inkbottle"-type pores consisting of large cavities connected by small windows (≈≤5 nm) (Figure 3) [29]. Consequently, tailoring the morphology and cavity dimensions over a wide range of sizes was achieved by tailoring the synthesis conditions and by the use of additives.…”

“…In addition to the morphology of the particles, changes in the size and shape of the mesochannel were investigated [28]. Addition of the swelling agent 1,3,5-trimethylbenzene into the synthesis mixture of plugged SBA-15 led to the transformation of 2D plugged mesochannels to 3D large cavities (12-20 nm), where each cavity is connected to the neighbors by twelve small windows (2-5 nm) [29]. The obtained material was named modified mesocellular foam "m-MCF".…”

Obtaining 3D Chemical Maps by Energy Filtered Transmission Electron Microscopy Tomography

“…The obtained tilt series is used to reconstruct the volume of the sample by using mathematical algorithms based on the Radon transform 4,5 . Selecting grey levels in the volume helps to model the sample in 3D and quantify 3D parameters like particle localization 6 and size distribution 7 , pore position and size distribution 8 , etc.…”

Encapsulation of chiral Fe(salen) in mesoporous silica structures for use as catalysts to produce optically active sulfoxides

“…Recently, our group reported the synthesis of a new silica material called modified mesocellular foam (m-MCF), which combines large cage sizes (15-22 nm) and narrow entrance sizes (1.8-3.7 nm), showing properties that are very interesting for application in the "ship in the bottle" approach. 15 In this contribution, we encapsulated an Fe(salen) complex in modified m-MCF and SBA-16 materials with different entrance and cage sizes. m-MCF and SBA-16 surfaces were functionalized with n-propyl groups which allowed us to tune their entrance and cage sizes.…”