Aprotic Amine‐modified Manganese Dioxide Catalysts for Selectivity‐tunable Oxidation of Amines

Abstract

Organic modifiers have shown promising potential for regulating the activity and selectivity of heterogeneous catalysts via tuning their surface properties. Despite the increasing application of organic modification technique in regulating the redox-acid catalysis of metal oxides, control of the acidity of metal oxide catalysts for enhanced reaction selectivity without sacrificing their redox activity remains a substantial challenge. Herein, we show the successful control of redox-acid catalysis of metal oxides with aprotic tertiary amine modifiers. Robust modification of manganese dioxide catalysts with N,N-dialkylcyclohexylamine selectively blocks the Lewis acid sites, with their redox activity mostly unaffected. This enables efficient synthesis of imines in high to excellent selectivity via aerobic oxidation of structurally diverse aryl amines.

Manganese oxide-based catalysts for the sustainable synthesis of value-added chemicals through oxidation processes: a critical review and perspectives for the future

“…Many efforts have been made to study facet engineering of MnO x catalysts (Table 1). He et al 61 developed a novel phase transition strategy to enable the facet-controlled synthesis of Mn 3 O 4 with predominantly exposed ( 103), (101), and ( 112) facets (Fig. 5).…”

Visible‐Light‐Driven One‐Pot Synthesis of Benzimidazoles, Benzothiazoles, and Quinazolinones Catalyzed by Scalable and Reusable Ba‐Doped CoMoO4 Nanoparticles Under Air Atmosphere

“…[24] However, they have their own disadvantages such as expensive nature of the ligands and transition metals, stringent reaction conditions, use of excess metal catalysts, extended reaction times, lower yields and lack of substrate scope. Notably, various heterogeneous catalysts such as (Co 3 O 4 @Al 2 O 3 /SiO 2 ), [25] elemental Sulfur, [26] carbon dots (CD) embedded Bi 2 MoO 6 nanoplates, [27] graphene oxide, [28] graphene oxide-Al 2 O 3 , [29] MnO 2 with N, Ndialkylcyclohexylamine, [30] Mo-Co 3 O 4 , [31] Cu/magnetic chitosan [32] and WÀ ZnO@NH 2 [33] were used for its versatile recyclable ability. These catalysts were employed under conventional heating reaction conditions.…”

Efficient Synthesis of Imines by Oxidative Coupling Catalyzed by Ce‐Mn Oxide Microspheres

“…α‐MnO 2 was demonstrated as a good catalyst for tert ‐butyl hydroperoxide‐mediated oxidative self‐coupling of amines to imines [7] . Aprotic amine‐modified MnO 2 catalysts provided enhanced imine selectivity in the synthesis [8] . Recently, MnO x /CeO 2 materials with morphology such as nanoparticles, [9] nanorods [10] and sheet‐like [11] were described as high performance catalysts for the oxidation of various amines.…”

“…[7] Aprotic amine-modified MnO 2 catalysts provided enhanced imine selectivity in the synthesis. [8] Recently, MnO x /CeO 2 materials with morphology such as nanoparticles, [9] nanorods [10] and sheet-like [11] were described as high performance catalysts for the oxidation of various amines. The presence of Ce could induce the formation of oxygen vacancies, leading to increased oxygen storage ability and active surface oxygen.…”