Chiral Phosphotungstate Functionalized with (S)-1-Phenylethylamine: Synthesis, Characterization, and Asymmetric Epoxidation of Styrene

Abstract

In the present work, an attempt has been made to induce chirality in coppersubstituted phosphotungstate (PW 11 Cu) by functionalization with (S)-(+)-1-phenylethylamine (S-PEA) via a ligand substitution approach. The formation of a N→Cu dative bond was confirmed by 13 C NMR, while 1 H NMR, circular dichroism spectroscopy and optical rotation studies confirmed the introduction of chirality to the Keggin structure. The synthesized material was used as the heterogeneous catalyst for the asymmetric epoxidation of styrene using various green oxidants to obtain high enantiomeric excess (ee), and the reaction with molecular oxygen was found to give the best ee. Regeneration studies were carried out, and the catalyst was found to be suitable for the same. A probable mechanism is also proposed. A comparison with other copper-based polyoxometalate catalysts clearly demonstrate the superiority and novelty of the present catalyst in terms of the reaction conditions as well as the obtained ee.

Immobilization of a [CoIIICoII(H2O)W11O39]7– Polyoxoanion for the Photocatalytic Oxygen Evolution Reaction

“…Once the TiO 2 surface was functionalized by APTES linkers, we proceeded with {Co III Co II W 11 } immobilization (refer to the Experimental Section). In the [Co III Co II (H 2 O)­W 11 O 39 ] 7– cluster, due to the weak coordination bond between peripheral Co­(II) ions and the H 2 O ligand, the aqua ligand can be replaced by a stronger NH 2 from APTES, resulting in a H 2 N: → Co­(II) dative bond, − which we confirmed preliminarily by reacting {Co III Co II W 11 } with a model n -butylamine (Figure S3). With this choice of the components and attachment procedure, the formation of the {Co III Co II W 11 }-APTES-TiO 2 composite is driven by self-assembly (Figure a).…”

Polyoxometalate‐based Inorganic‐Organic Hybrids as Heterogeneous Catalysts for Asymmetric and Tandem Reactions

“…With molecular O 2 as the oxidant, the enantioselectivity was improved due to the interactions of the oxidant with the chiral catalyst. [70] The encapsulation of POMs into the pores of chiral MOFs can endow the catalysts with interesting structures and high catalytic activity. The advantages of chiral MOFs as catalysts are 1) tunable pores which allow shape-and size-selectivity of the catalytic products, and 2) high enantioselectivity owing to regularly arrayed chiral groups in their frameworks.…”

“…The results showed that most of TBHP molecules underwent self‐disproportionation and small interactions between the oxidant and the catalyst resulted in the ee of 6 % for the products. With molecular O 2 as the oxidant, the enantioselectivity was improved due to the interactions of the oxidant with the chiral catalyst [70] …”

Flowing scalable production of sulfenamides by active site-tuned lacunary polyoxometalate foams

“…1(d) and S8 †). 31,32 The four TM-LPOMs were formed by replacing one W atom in the saturated Keggin-type [PW 12 O 40 ] 3− polyanion with the transition metal and formulated as [TM-PW 11 O 39 ] n− (TM = Cu 2+ , Co 2+ , Ni 2+ , and Mn 2+ ) (denoted as TM-LPOMs). 33 Aer that, TM-LPOMs (TM = Cu, Co, Ni, and Mn) were added into carboxymethylcellulose sodium salt (CMC) aqueous solution followed by high-speed mechanical stirring and freeze-drying to obtain a series of TM-LPOMs@CMC (TM = Cu, Co, Ni, and Mn) foams (Fig.…”

“…Synthesis of TM-LPOMs@CMC (TM = Cu, Mn, Co, and Ni; loading = 17, 29, 38, 44 wt%) TMO 39 ] (TM = Cu, Co, Ni, and Mn) were successively prepared according to the literature methods. 31,32 Briey, 3.0 g CMC was dissolved in 50 mL distilled water and mechanically stirred for 30 min. A solution of Cu-LPOMs in 5 mL acetonitrile was added dropwise to the CMC solution and continued to stir for another 10 min.…”