Poly(imidazolium) Carbosilane Dendrimers: Synthesis, Catalytic Activity in Redox Esterification of α,β-Unsaturated Aldehydes and Recycling via Organic Solvent Nanofiltration

Abstract

Three series of poly(ionic) carbosilane dendrimers peripherally functionalized with imidazolium groups substituted on N-3 with methyl, isopropyl and 2,6-diisopropylphenyl (Dipp) were prepared up to the 3rd generation together with model monovalent imidazolium iodides and used as N-heterocyclic carbene (NHC) precursors. Catalytic activity of model and dendritic NHCs generated in situ by deprotonation with DBU was tested in redox esterification of α,β-unsaturated aldehydes and the influence of substitution, dendrimer generation, temperature and substrate structure on the reaction outcome was evaluated. Dipp substituted NHCs showed high activity and selectivity in the reaction with primary alcohols. Effectiveness of organic solvent nanofiltration for the recycling of dendritic NHCs was demonstrated on the 1st generation Dipp substituted catalyst in model redox esterification of cinnamaldehyde with benzyl alcohol. A marked increase in both activity and selectivity in the first four reaction runs was observed and this improved performance was preserved in the following catalytic cycles.

Organic Solvent Nanofiltration in Pharmaceutical Applications

“…Besides the Pd, Rh and Ru catalysts, some other homogeneous catalysts such as gold-based, − platinum-based, tungsten-based, − magnesium triflate, , Co-Jacobsen catalyst, and quinidine-based organocatalyst − have been explored for recovery/recycling. For example, gold N-heterocyclic carbene complexes in the hydration of diphenylacetylene (Scheme ) were first recovered by Bayrakdar et al The Borsig oNF-1 membrane was selected due to its high rejection toward the catalyst (98.5%) and moderate rejection toward the product (53%) in the mixture of THF/water.…”

Adaptive Synthesis of Functional Amphiphilic Dendrons as a Novel Approach to Artificial Supramolecular Objects

“…In most cases, the excess reagent is readily separable by using extraction or evaporation. Only in the case of compound-L1-9-bearing dimethylammonium groups, the separation requires organic solvent nanofiltration (OSN) [35][36][37]-an effective method which we previously exploited for the purification of CS-dendrimers [27,28,38,39]. The key feature of synthetic amphiphiles, essential for their investigation in biological environments, is their water-solubility.…”

“…Our long-term interest has been focused on CS dendrimers with a well-defined structure that express multivalent presentation of functional moieties at their periphery [27][28][29][30][31] and, due to the incompatibility of their hydrophobic interior with polar periphery, can be considered as unimolecular micelles [32]. Here we turn our attention to a development of new versatile synthetic protocols for amphiphilic building blocks capable of self-assembly to regular micelles and other supramolecular objects.…”