Pseudopeptidic macrocycles as cooperative minimalistic synzyme systems for the remarkable activation and conversion of CO₂ in the presence of the chloride anion

Abstract

<p>A series of pseudopeptidic compounds have been assayed as organocatalyts for the conversion of CO₂ into organic carbonates through a cooperative multifunctional mechanism.</p>

Immobilized Supramolecular Systems as Efficient Synzymes for CO2 Activation and Conversion

“…We have recently reported organocatalytic synzymatic systems based on pseudopeptidic macrocycles bearing in their structure hydrogen bond donor (HBD) and Lewis‐basic groups. [ 36 ] This bioinspired approach was highly active in the cycloaddition of CO 2 to epoxides, as the pseudopeptides were able to optimally pre‐organize the reaction components in a confined space, favoring their reaction. Nonetheless, large amounts of co‐catalysts acting as nucleophilic source are generally needed for such supramolecular systems, resulting in separation hurdles and increased waste.…”

“…This poor catalytic activity in the presence of iodide anion was assigned to its lower basicity, preventing the formation of hydrogen bonds with the pseudopeptides. [ 36 ] The most active catalytic system (Bu 4 NCl + 3b ), promoted an ≈2.3‐fold increase in yields at lower catalytic loadings, although the yields for the desired organic carbonates were low for the reaction times studied (Entries 7 and 8 in Table 1). Slightly higher TON values were reported for macrocycles related to 3a but lacking the pendant arm.…”

“…Slightly higher TON values were reported for macrocycles related to 3a but lacking the pendant arm. [ 36 ] However, it must be noted that catalytic activity was sensitive to the macrocycle size, with best results obtained for the smallest cavities (TON = 930 for the macrocycle having three methylene groups in the spacer linking the two amino acid moieties). The introduction of the pendant arm requires the use of a larger diethylene amino spacer, comparable in length with the macrocycle containing five methylene groups in the spacer.…”

Synthesis of carbonates from CO2 and epoxides catalyzed by the system of N‐heterocyclic carbene, hydrogen bond donor, CrCl2, and tetrabutylammonium bromide

“…To prove whether the hydrogen bond interaction between the carboxyl group bearing 1a and bromide anion of TBAB occurs, [ 24 ] three control experiments were performed by NMR method (Figure 2). When TBAB was added to 1a , the absorption peak of the carboxyl group bearing 1a had not changed (Figure 2b); however, the addition of 1,2‐hexylene oxide led to the disappearance (Figure 2c).…”

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction

“…Following our previous contributions in the field of synzymes [ 36 , 37 ], and to better understand the phenomena taking place at the molecular and supramolecular levels in enantioselective aldol processes, as well as to advance in the rationalization of the design vectors for this kind of organocatalyst, here, we present the preparation of a series of chiral imidazolium cations containing prolinate as the counteranion and their study as organocatalysts for the aldol reaction. The resulting CILs contain chiral elements in both the anion and the cation, and the results show that both components are relevant for the enhancement in chirality transfer, with the observation of interesting match/mismatch arrangements for the configuration being present in both components.…”