The Use of Ultra- and Nanofiltration Techniques in Homogeneous Catalyst Recycling

Abstract

In recent years, the application of membrane technology in homogeneous catalyst recycling has received widespread attention. This technology offers a solution for the major drawback of homogeneous catalysis, that is, recycling of the catalyst. From both an environmental and an industrial point of view, this technology is very interesting, since it allows the future application of homogeneous catalysts in the synthesis of commercial products, leading to faster, cleaner and highly selective green industrial processes. In this Account, an overview is given of the promising results obtained in the field of homogeneous catalyst recycling using nanofiltration membrane technology.

Ionic Core−Shell Dendrimers with an Octacationic Core as Noncovalent Supports for Homogeneous Catalysts

“…We do not find contacts from H1 to the cationic protons H14, but we do observe clear cross-peaks from H1-H5 to H15 of the cation, suggesting that the anionic group does not penetrate quite as far in [3][5] 8 as in the previous assemblies. , were studied by pulse gradient spin-echo (PGSE) NMR diffusion measurements in dichloromethane solution.…”

“…This spectrum shows characteristic fragment ion peaks for [2] [2][5] 8 upon loss of three halide ions, two anions 5 plus a halide ion, three anions 5, and three anions 5 plus a halide ion, respectively. Unfortunately, we were not able to obtain a mass spectrum of the third-generation metallodendritic assemblies [3][5] 8 and [3][6] 8 due to precipitation of the assemblies during ESI-MS analysis.…”

“…In addition, at higher generations strong shifts to lower frequencies were observed for the SiMe 2 group and the NCN moiety. In case of the third-generation metallodendritic assemblies [3][5] 8 shifts to lower frequencies in the range of 0.12-0.24 ppm were found for the protons of the NCN moiety.…”

“…The Overhauser results for [3][5] 8 are a bit more ambiguous, due to the increased signal overlap associated with the higher molecular weight ( Figure S2b in the Supporting Information). We do not find contacts from H1 to the cationic protons H14, but we do observe clear cross-peaks from H1-H5 to H15 of the cation, suggesting that the anionic group does not penetrate quite as far in [3][5] 8 as in the previous assemblies.…”

“…1,2 The nanoscopic size of the dendrimer support facilitates recovery of the catalyst, for example, by means of nanofiltration. 3 Furthermore, the high solubility and monodisperse structure of the dendritic support allow for the formation of well-defined supported homogeneous catalysts, which can be characterized and studied in situ by various standard analysis techniques. In the reported systems, the homogeneous catalyst, which is often a transition metal complex, is attached to a dendritic support either via a covalent or a dative bond.…”