C-C Coupling Enabled by Mn Complexes with Diacyl Peroxides: Alkylation versus Oxygenation

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Manganese complexes are known catalysts, often involved in oxidation reactions.
• Peroxides are common oxidants, typically leading to substrate oxidation.
• The reactivity of manganese complexes with peroxides is not fully understood, particularly concerning C-H functionalization.

Purpose of the Study:

• To explore a novel reactivity pathway of manganese complexes with diacyl peroxides.
• To investigate the C-H functionalization of imidazole N-oxides using an alkyl fragment.
• To elucidate the mechanism of this unexpected transformation.

Main Methods:

• Reaction of manganese(II) acetate (Mn(OAc)2) with diacyl peroxides and imidazole N-oxides.
• Spectroscopic analysis to identify catalytic species (Mn(IV)/Mn(III)).
• Mechanistic studies involving radical intermediates and C-H oxidation.

Main Results:

• Demonstrated C-H functionalization of imidazole N-oxides by an alkyl fragment, deviating from expected oxidation.
• Proposed a catalytic cycle involving Mn(IV)/Mn(III) species and a noninnocent carboxylate ligand.
• Identified alkyl radicals as key intermediates, leading to product formation in 23-89% yields.

Conclusions:

• Manganese complexes with diacyl peroxides enable a unique C-H functionalization pathway.
• The reaction proceeds via a multistep process involving radical intermediates and catalytic manganese species.
• This study expands the known reactivity of Mn complexes and offers a new synthetic route.