Jacobsen's catalyst is the common name for N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane­diaminomanganese(III) chloride, a coordination compound of manganese and a salen-type ligand.

[6] The synthesis has been adapted for undergraduate level chemistry courses in order to stress the importance of enantiomerically pure compounds.

However, more recent studies have indicated a radical intermediate is possible, challenging the assumption that non-conjugated alkenes undergo concerted mechanisms.

[8] In the original catalytic reaction, iodosylarenes (PhIO) were used as the stoichiometric oxidant, but soon after it was found that chlorine bleach (NaClO), a cheaper alternative, works as well.

The substrate is thought to approach the metal-oxo bond from the side at a perpendicular orientation in relation to the catalyst in order to allow favorable orbital overlap.

This mechanism, which was originally proposed by John Groves to explain porphyrin-catalyzed epoxidation reactions,[9] is commonly referred to as a "side-on perpendicular approach".

[8] For example, derivatives of Jacobsen's catalyst with small structural changes to the salen backbone have been used in conjunction with low temperatures and the oxidant m-chloroperbenzoic acid (m-CPBA) to epoxidize the terminal alkene styrene.