Palladium Oxidase Catalysis: Selective Oxidation of Organic Chemicals by Direct Dioxygen‐Coupled Turnover

Abstract

Selective aerobic oxidation of organic molecules is a fundamental and practical challenge in modern chemistry. Effective solutions to this problem must overcome the intrinsic reactivity and selectivity challenges posed by the chemistry of molecular oxygen, and they must find application in diverse classes of oxidation reactions. Palladium oxidase catalysis combines the versatility of Pd(II)-mediated oxidation of organic substrates with dioxygen-coupled oxidation of the reduced palladium catalyst to enable a broad range of selective aerobic oxidation reactions. Recent developments revealed that cocatalysts (e.g. Cu(II), polyoxometalates, and benzoquinone) are not essential for efficient oxidation of Pd(0) by molecular oxygen. Oxidatively stable ligands play an important role in these reactions by minimizing catalyst decomposition, promoting the direct reaction between palladium and dioxygen, modulating organic substrate reactivity and permitting asymmetric catalysis.

Formation and growth of palladium nanoparticles inside porous poly(4-vinyl-pyridine) monitored by operando techniques: The role of different reducing agents

“…As discussed in the introduction, alcohols are often used as solvents in reactions catalyzed by Pdbased catalysts [33], or they may be used even as reactants [34][35][36][37][38][39][40][41]. Therefore, it is important to clarify if they are innocent toward the catalyst, or if they may react with it and eventually lead to its final deactivation.…”

“…In other cases, alcohols are used as reactants. For example, alcohol hydrogenation, oxidation and cross-coupling reactions are also catalyzed by palladium-based catalysts, either homogeneous or heterogeneous [34][35][36][37][38][39][40][41]. In this respect, the homogeneous Pd(OAc)2/pyridine system is by far one of the most efficient and selective catalyst for oxidation of alcohols to aldehydes.…”

“…In this respect, the homogeneous Pd(OAc)2/pyridine system is by far one of the most efficient and selective catalyst for oxidation of alcohols to aldehydes. The reaction mechanism has been proposed by Stahl and coworkers [38][39][40] as an oxidase-style mechanism in which palladium(II)-mediated substrate oxidation (Stage I in Scheme 1) and aerobic oxidation of the catalyst (Stage II in Scheme 1) occur in two independent, sequential stages. Formally, in Stage I Pd(II) species transform into Pd 0 ones, while in the Stage II oxidation by oxygen restores the Pd(II) original complex.…”

“…Scheme 1. Catalytic cycle for alcohol aerobic oxidation catalyzed by homogeneous Pd(OAc)2/Pyridine catalyst as proposed by Stahl et al [38][39][40]. Stage I (black arrows) involves alcohol oxidation into aldehyde/ketone by eliminating acetate ions as acetic acid; Stage II (grey arrows) involves the active species regeneration, by converting acetic acid and O2 into acetate ions and water.…”

Palladium Complex Bearing 3,5-Bis(benzotriazol-1-Ylmethyl)toluene Ligand Catalyzes Oxidative Amination of Allyl Butyl Ether

“…24 On the other hand, a variety of palladium(II) complexes have been successfully studied as catalysts for the aerobic oxidative amination of unactivated alkenes to yield amine derivatives. [25][26][27][28][29][30][31][32][33][34][35][36][37][38] This catalytic reaction leads to the formation of imines or enamines, via b-hydride elimination, through a mechanism analogous to the well-known Wacker process. 25 In this communication we report the synthesis and characterization of the new ligand 3,5-bis(benzotriazol-1-ylmethyl)toluene (1) …”