Synthesis and a Catalytic Study of Diastereomeric Cationic Chiral-at-Cobalt Complexes Based on (R,R)-1,2-Diphenylethylenediamine

Abstract

Here we report the first synthesis of two diastereomeric cationic octahedral Co­(III) complexes based on commercially available (R,R)-1,2-diphenylethylenediamine and salicylaldehyde. Both diastereoisomers with opposite chiralities at the metal center (Λ and Δ configurations) were prepared. The new Co­(III) complexes possessed both acidic hydrogen-bond donating (HBD) NH moieties and nucleophilic counteranions and operate as bifunctional chiral catalysts for the challenging kinetic resolution of terminal and disubstituted epoxides by the reaction with CO2 under mild conditions. The highest selectivity factor (s) of 2.8 for the trans-chalcone epoxide was achieved at low catalyst loading (2 mol %) in chlorobenzene, which is the best achieved result currently for this type of substrate.

Cobalt(III) Complexes as Bifunctional Hydrogen‐Bond Donor Catalysts Featuring Halide Anions for Cyclic Carbonate Synthesis at Ambient Temperature and Pressure: A Mechanistic Insight

“…In this paper, continuing our ongoing interest to this important field, [21,25] we demonstrate that a simple modification of the cobalt(III) complex structure increases their HBD ability and, as a result, the complex obtained from chiral 1,2‐diphenylethylenediamine and salicylaldehyde Λ( R , R )‐ 2 [21b] efficiently catalyzes the cycloaddition reaction at ambient temperature and pressure in contrast to the previously developed catalyst Δ( S , S )‐ 1 a [21a] (Scheme 1). We also present a detailed mechanistic study of the reaction using a combination of experimental analysis of kinetics, and DFT calculations.…”

“…The best yield of the cyclic carbonate 4 a (99%) was achieved at 10 bars pressure of CO 2 and 40 °C in case of using Λ( R , R )‐ 2 (Table 1, entry 11). Surprisingly, the second diastereomer (Δ‐form) of the complex 2 [21b] didn't show any catalytic activity in the reaction at ambient conditions (Table 1, entry 12). However, the increasing of CO 2 pressure to 10 bars and temperature to 60 °C allowed to obtain the desirable product 4 a with 97% yield (Table 1, entry 13).…”

Cobalt complexes with α-amino acid ligands catalyze the incorporation of CO2into cyclic carbonates

“…The cases of SO and PGE (Table 4, entries 2 and 3) are particularly interesting where SO exhibits a lower conversion in comparison with PGE, presumably because the electron withdrawing effect in PGE is higher due to the phenoxy methyl substituent, thus increasing methine carbon's electrophilicity, favoring the backbiting reaction. 59 Overall, the conversion of SO and PGE was much slower than the reactivity of ECH and PO. In addition, CHO showed a decreased cyclic carbonate conversion due to the steric profile; more detailed substrate scoping studies for internal oxiranes will be necessary in the future.…”

“…Initially, the amine moieties form a hydrogen bond with the oxygen atom of PO ( 1b ). 59 Subsequently, the epoxide is activated, and the less hindered carbon undergoes nucleophilic attack by Cl − (provided by PPNCl or the complex itself), leading to the ring-opened intermediate 2b . The CO 2 activation can be promoted either by the presence of PPNCl or by forming a carbamate salt as shown in cycle A ( 1a ) in the outer coordination sphere.…”

CO2 Cycloaddition under Ambient Conditions over Cu–Fe Bimetallic Metal–Organic Frameworks

“…In the past few decades, numerous pioneered homogeneous catalytic systems, such as ionic liquids and organic molecules, with satisfactory conversion and selectivity have made extensive contributions to CO 2 cycloaddition. ,− Nevertheless, homogeneous catalysts usually suffer from poor stability and separation feasibility, which has dramatically raised their costs and inevitably hindered practical applications. − To overcome these shortcomings and obtain stable and efficient catalysts, efforts converge toward heterogeneous platforms. ,− Metal–organic frameworks (MOFs) constructed from organic linkers and secondary building units (SBUs) support ideal platforms to incorporate homogeneous molecular and metal catalysts into heterogeneous systems. ,− With the merits of well-exposed active sites, tunable pore size, and well-defined structures, MOFs provide a tunable platform for CO 2 cycloaddition. − In this field, the Cr-MIL-101 MOF was constructed to encapsulate imidazolium-based poly­(ionic liquid)­s as polyILs@MIL-101 for CO 2 cycloaddition reaction with over 90% conversion at 70 °C . To further improve the performance, PCN-224 and Hf-NU-1000 MOFs were used as photocatalysts for activating epoxides and facilitating the quantitative chemical fixation of CO 2 into cyclic carbonates under ambient conditions and visible irradiation .…”