Precious Metal-Free LaMnO₃ Perovskite Catalyst with an Optimized Nanostructure for Aerobic C–H Bond Activation Reactions: Alkylarene Oxidation and Naphthol Dimerization

Abstract

In this article, we describe the development of a new aerobic C−H oxidation methodology catalyzed by a precious metal-free LaMnO 3 perovskite catalyst. Molecular oxygen is used as the sole oxidant in this approach, obviating the need for other expensive and/or environmentally hazardous stoichiometric oxidants. The electronic and structural properties of the LaMnO 3 catalysts were systematically optimized, and a reductive pretreatment protocol was proved to be essential for acquiring the observed high catalytic activities. It is demonstrated that this newly developed method was extremely effective for the oxidation of alkylarenes to ketones as well as for the oxidative dimerization of 2-naphthol to 1,1-binaphthyl-2,2-diol (BINOL), a particularly important scaffold for asymmetric catalysis. Detailed spectroscopic and mechanistic studies provided valuable insights into the structural aspects of the active catalyst and the reaction mechanism.

Organic building blocks at inorganic nanomaterial interfaces

“…3.2.3 Photocatalysis. QDs, [265][266][267] perovskites, [268][269][270] metal oxides, 271,272 and metal NCs 273,274 have been widely explored as sensitizers and catalysts for photoredox reactions in recent years. There have been numerous strategies employed to improve catalytic performance, such as utilizing engineered defects 275 and heterostructured architectures.…”

Base-Assisted Aerobic C–H Oxidation of Alkylarenes with a Murdochite-Type Oxide Mg6MnO8 Nanoparticle Catalyst

“…are required to afford a high yield of 2a in S1). [7][8][9][10][11][12][13][14][15][16]25 To confirm whether the observed catalysis is due to solid Mg 6 MnO 8 -MA or leached Mn or Mg species, the oxidation of 1a was carried out under the conditions described in Figure 4a.…”

Two-Dimensional Bimetallic Hydroxide Nanostructures for Catalyzing Low-Temperature Aerobic C–H Bond Activation in Alkylarene and Alcohol Partial Oxidation

“…It should also be emphasized that the formation of the dimer 7 was not seen in any of the previous experiments involving molecular oxygen as the sole oxidant, in agreement with one of our recent studies where we utilized LaMnO 3 (i.e., perovskite-type) catalysts for the aerobic oxidation reactions. 34 Note that additional control experiments were also carried out in the absence of a catalyst by using xanthene (1a), fluorene (2a), and diphenylmethane (3a) as substrates and NaOH or KOH as Brønsted basic catalysts (Table S5). As expected, these control experiments lacking any bimetallic hydroxide catalysts also did not reveal any significant extent of products.…”

“…As a part of our ongoing efforts toward the development of effective heterogeneous catalysts for alcohol and C−H bond oxidation reactions that work under aerobic conditions, we recently reported the utilization of LaMnO 3 as a perovskite-based catalyst for alkylarene oxidation and oxidative dimerization of 2-naphthol. 34 It should be noted that several other perovskite-and metal-oxide-based materials have been shown to be effective catalysts for C−H oxidation reactions. 35−38 In our quest to develop heterogeneous oxidation catalysts with higher activity and selectivity, we next turned our focus to nonprecious metal hydroxide-containing catalytic systems, which can be exploited in low-temperature catalytic processes as promising alternatives to the existing conventional PGMbased oxidation catalysts.…”