Manganese Asymmetric Catalysis: From Mn-Salen Epoxidation to Base-Metal Pincer Catalysts

May 18, 2026 Metal Catalysis, Science manganese, Mn-salen, Jacobsen, base metal, epoxidation, pincer, chiral

Manganese occupies a unique position in asymmetric catalysis: it is both the metal of the classic Jacobsen epoxidation catalyst (since 1990) and a leading base-metal candidate in the current drive to replace Ru, Rh, and Ir. The combination of earth abundance, low toxicity, and rich redox chemistry (Mn(II)/Mn(III)/Mn(V)) makes manganese attractive for sustainable asymmetric synthesis.

Mn-Salen Asymmetric Epoxidation

The Jacobsen (Mn(III)-salen) catalyst remains the benchmark for enantioselective epoxidation of unfunctionalized cis-disubstituted and trisubstituted olefins. The Mn(III) center activates NaOCl (bleach) to a high-valent Mn(V)=O species that transfers oxygen to the olefin through a chiral salen pocket. The (1R,2R)-diaminocyclohexane backbone of the salen controls facial selectivity.

Key features:

  • Inexpensive oxidant — aqueous NaOCl.
  • No allylic alcohol required — unlike Sharpless epoxidation.
  • Both enantiomers available — (R,R) and (S,S) catalysts.
  • Documented scale-up — deployed in indinavir and warfarin synthesis.

Emerging Mn-Pincer Asymmetric Catalysis

Recent work (2015–present) has developed Mn(I) pincer complexes — particularly chiral bis(imino)pyridine and PNP pincer ligands — that catalyze:

  • Asymmetric hydrogenation of ketones — Mn(I)-PNP with chiral diamines; replaces Ru.
  • Asymmetric transfer hydrogenation — formate/water as H donor.
  • Enantioselective hydrosilylation — of ketones and imines.

These catalysts achieve >90% ee on several substrate classes and represent the leading edge of base-metal asymmetric hydrogenation.

Why Manganese Matters Now

  • Cost: Manganese is ~10⁵× cheaper than rhodium.
  • Sustainability: ICH Q3D classifies Mn as a Class 2 metal with higher permitted daily exposure than Pd, Ru, Rh.
  • Supply security: No geopolitical concentration of supply.
  • Functional group tolerance: Mn-salen tolerates heterocycles, halogens, and sulfur.

Frontier and Outlook

The Jacobsen Mn-salen system remains the default for asymmetric epoxidation of cis- and trisubstituted olefins, while chiral Mn-pincer catalysts are rapidly closing the performance gap with Ru and Rh in asymmetric hydrogenation. Heterogenized Mn-salen on silica and polymer supports enables catalyst recycling in flow, and chiral Mn(III)-salen derivatives continue to find new applications in kinetic resolution of epoxides and racemic alcohols. Manganese is positioned to capture significant share of the base-metal asymmetric catalysis market over the next decade.

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