Structure–performance landscape of N-alkoxyphthalimides as organocatalysts in aerobic oxidation

• Published in: Journal of catalysis 2016-12, Vol.344, p.229-235
• Main Authors: Chen, Kexian, Xie, Haiying, Mao, Jianyong, Jiang, Kezhi
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Homolysis; Hydroxyimide; Organocatalysis; Oxidation; Photochemistry; Radicals; Structure; Thermochemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2016.09.015

[Display omitted] •Structural and thermochemical properties of N-alkoxyphthalimides were studied.•Their thermal homolysis over 100°C favors their industrial catalytic oxidation.•N-alkoxy groups are powerful in adjusting both >NO–C bond strengths and HOMO-LUMO gaps.•The potential photochemical homolytic orders of N-alkoxyphthalimides are proposed.•Unlike N-acetyloxy cases, hydrolysis of N-alkoxyphthalimides would be very difficult. N-Alkoxyphthalimides were studied to design new-type organocatalysts for aerobic oxidation that are capable of metal/initiator-freely forming both phthalimide N-oxyl radicals and alkyl radicals in situ via their light/heat-induced homolysis. Our results show that their >NO–C bond strengths and HOMO-LUMO gaps change greatly upon altering N-alkoxy groups, which greatly decrease when their N-alkoxy groups include steric fluorenyl, xanthenyloxy, or triphenylmethyl groups. The conventional substituents on the bilateral phenyl rings of N-benzyloxyphthalimide have negligible effects on their >NO–C bond strengths, but significantly tune their HOMO-LUMO gaps. The photochemical activity of N-benzyloxy-4-aminophthalimide and N-4-amino-benzyloxyphthalimide may be similar to that of known N-triphenylmethyloxyphthalimide and N-diphenylmethyloxyphthalimide. Both the thermal and photochemical stability of N-acetyloxyphthalimides are higher than those of N-alkoxyphthalimides, but their hydrolysis to form N-hydroxyphthalimide is more favorable. The present work allows a reasonable prediction of the catalytic performance of N-alkoxyphthalimides and provides a new perspective for the rational design of organocatalysts for industrial applications.