Promoting a non-heme manganese complex catalyzed oxygen transfer reaction by both lewis acid and Brønsted acid: Similarities and distinctions

Abstract

This work demonstrates that certain Lewis and Brønsted acids can sharply improve the oxygen transfer efficiency of a manganese(II) catalyst bearing non-heme ligand. In the absence of Lewis and Brønsted acids, oxidation of manganese(II) complex will generate di-μ-oxo-bridged dinuclear Mn2(III,IV) core which is very sluggish for olefin epoxidation. Adding non-redox metal ions as Lewis acid or Brønsted acid will both improve the catalytic epoxidation of olefin, and this improvement is dependent on the pKa of Brønsted acid, or the net charge of non-redox metals of Lewis acid. Mechanism study revealed that similar promotional effect by either Lewis or Brønsted acids was originated from a similar reaction pathway by dissociating aforementioned sluggish di-μ-oxo core. However, distinctions of reactive intermediate were also demonstrated for Lewis or Brønsted acids.