Structure–reactivity landscape of N -hydroxyphthalimides with ionic-pair substituents as organocatalysts in aerobic oxidation

Theoretical study on the catalytic reactivity of N-hydroxyphthalimide tuned by different heterocyclic substitutions on its phenyl ring for aerobic oxidation

“…Full geometry optimization and vibrational frequency calculations were performed employing hybrid functional and B3LYP method combined with 6-311+G(d) basis set, which has been widely used in the theoretical studies on the catalytic reactions promoted by hydroxyimide catalysts [12][13][14][15][16][17][18][19][20][21]. The frequency calculations were undertaken to ensure the nature of all transition states with a pure imaginary frequency and all stationary points with none imaginary frequencies.…”

“…1) is the most representative hydroxyimide catalyst, which serves as an efficient carbonradical-producing catalyst (CRPC). The general mechanistic profiles of their catalytic oxidations have been disclosed extensively [2][3][4][5][6][7][12][13][14][15][16][17][18][19][20][21], where the hydrogen-abstraction reactivity from the substrates by their in situ generated reactive intermediate namely nitroxy radicals, typically phthalimide-N-oxyl radical (PINO Å , Fig. 1), and their thermal decompositions into phthalimide (NH), phthalic anhydride (O) and others [4,22], can crucially influence their catalytic enhancements.…”

“…Besides, the defects like large amount of polar cosolvents required for their solubility in substrates [23], their large amounts needed for good performances [2][3][4][5][6], their difficult recovery from product mixtures [2][3][4][5][6]24] remain technical obstacles for their industrial applications. These backgrounds stimulate both experimental and theoretical chemists to design more reactive [19][20][21], soluble [23], recoverable [21], or thermally stable [25] hydroxyimide catalysts, and investigate their idiosyncratic catalytic behaviors.…”

“…Furthermore, the experimentally observed higher catalytic efficiencies of multi-nitroxyl catalysts than that of NHPI have been rationalized as the stronger electron-withdrawing effects involving in their special nitroxy radicals [19,20]. The rational design strategies on both multi-nitroxyl catalysts [20] and the NHPIs with ionic-pair substituents [21] have been proposed to design possibly recoverable and/or highly reactive hydroxyimide catalysts in series, which could overcome some drawbacks of present catalysts, and may be suitable for the future industrial applications. The thermochemical data of catalysts like their NOAH bond dissociation energies (BDEs) have also been calculated to model their intrinsic catalytic processes [15,16,[18][19][20][21].…”

“…The rational design strategies on both multi-nitroxyl catalysts [20] and the NHPIs with ionic-pair substituents [21] have been proposed to design possibly recoverable and/or highly reactive hydroxyimide catalysts in series, which could overcome some drawbacks of present catalysts, and may be suitable for the future industrial applications. The thermochemical data of catalysts like their NOAH bond dissociation energies (BDEs) have also been calculated to model their intrinsic catalytic processes [15,16,[18][19][20][21]. Despite ongoing extensive studies on their catalytic improvements, a large gap still remains from achieving their state-of-the-art efficiency.…”