Bioinspired Manganese Catalyzed Direct Deamination of Primary Amines With Water Forming Carboxylic Acids and Ketones

Abstract

Herein, we are demonstrating an earth-abundant manganese-catalyzed oxidative deamination of linear and branched primary amines to selectively form carboxylic acids and ketones using water as the oxygen atom source. A series of pincer and non-pincer Mn complexes were assessed for these deaminative transformations. A bio-inspired DAFO (4,5-diazafluoren-9-one) ligand-based [(DAFO)Mn(CO)3Br] complex (Mn-1) was found to be effective for the reaction proceeding under mildly basic aqueous medium, generating NH3 and H2 as sole by-products without the requirement of any oxidant. An optimized condition of 5 mol% Mn-1, Na2CO3 (1 equiv) at 150°C for 48 h in water/1,4-dioxane mixture furnished 92% of the corresponding benzoic acid from benzylamine. A wide variety of electron-donating and withdrawing para-, meta-, and ortho-substituted benzylamines, including promising hetero and aliphatic linear primary amines, afforded moderate to excellent yield of the desired carboxylate product. We have also examined a few branched primary amines using 5 mol% Mn-1 and catalytic sodium carbonate at 150°C for 48 h, affording good yield of ketones. The reaction was found to be chemo-selective for primary amine moieties over alcohol functionalities. Further, stoichiometric mechanistic investigation and preliminary computational data provide insights into the possible mechanistic steps.