Recent advancements and challenges of palladiumII-catalyzed oxidation reactions with molecular oxygen as the sole oxidant

Abstract

During the past 10 years there have been significant advances in PdII-catalyzed oxidation reactions where the use of ligands has led to the development of catalytic systems capable of achieving high turnover numbers, which employ molecular oxygen as the sole stoichiometric oxidant. This Feature article will highlight some of the recent developments in direct molecular oxygen-coupled PdII-catalyzed oxidation reactions with an emphasis on enhanced catalytic systems and new reactions. Additionally, limitations of current catalytic systems, such as ligand oxidation, are presented and their implications for the development of new reactions are discussed.

Solvent-free aerobic oxidation of hydrocarbons and alcohols with Pd@N-doped carbon from glucose

“…In the past decades, the discovery of versatile and efficient Pd/ligand systems largely promoted the Pd-induced oxidations 8,15,30,32 . In our subsequent investigations, various N-or O-type ligands were added into the indane oxidations, testing the effect of different organic ligands on Pd nanoparticles.…”

“…In particular, the TOF can be enhanced from 452 h À 1 to 863 h À 1 by adding a small amount of 2-acetylpyridine (20 mg) in the catalytic system (Entry 13, Table 2), suggesting that suitable ligands could also accelerate the heterogeneous Pd-catalysed processes. These organic ligands are expected to destabilize the substrate-Pd intermediate and increase the Pd II /Pd 0 reduction potential, thereby largely promoting the redox process 30,32 .…”

“…During the past decade, great progress has also been made in heterogeneous Pd catalysts for oxidation processes, for example, Pd/hydroxyapatite 17 , Pd/mesoporous silicas 18,19 polymer-supported Pd 20,21 , carbon nanotubesupported Pd 22,23 , Pd supported on metal oxide 24 , Pdcontaining metal-organic frameworks 25 etc. In the field of oxidation, the current Pd-based catalysis was focusing mainly on the oxidations associating with dehydrogenation processes (alcohol oxidation 26,27 , Wacker oxidation 28,29 , oxidative couplings 30 , etc.). The aerobic oxidation of hydrocarbons to more functional compounds (aldehydes, ketones, acids or esters), one of the most important processes in petrochemical transformation, has been seldom reported by Pd catalysts 31,32 .…”

“…Meanwhile, in homogeneous Pd-catalysed oxidation reactions, nitrogen-based ligands are frequently used with significant promotion effect on the redox process ( Supplementary Fig. S2) 30 . Here, similar chemical environments of the nitrogen in the homogeneous nitrogen-based ligands and nitrogen-doped carbon materials make us ask if nitrogen-doped carbon materials can function as 'heterogeneous N-type ligands' for Pd-catalysed oxidations, affording some other attractive characters (high stability, recyclability, controllable porous network, etc.)…”

Challenges in modelling homogeneous catalysis: new answers from ab initio molecular dynamics to the controversy over the Wacker process

“…In this sense, recent progress is achieved moving toward using molecular 50 oxygen as oxidant in synthetic reactions. 6 The rate expression for the Wacker process was established by Henry's group in a seminal work, exhibiting a first order in ethene and the catalyst (taking [PdCl 4 ] 2-as the resting state) and inhibition by [H + ] and [Cl -] to the second order (eq. 4).…”