Mechanistic Study on Allylic Arylation in Water with Linear Polystyrene-Stabilized Pd and PdO Nanoparticles

Abstract

The catalytic cycle of allylic arylation in water catalyzed by linear polystyrene-stabilized Pd or PdO nanoparticles (PS-PdNPs or PS-PdONPs) was investigated. Stoichiometric stepwise reactions indicated that the reaction did not proceed stepwise on the surface of the catalyst. In the case of the reaction with PS-PdNPs, the leached Pd species is the catalytically active species and the reaction takes place through a similar reaction pathway accepted in the case of a complex catalyst. In contrast, allylic arylation using PS-PdONPs as a catalyst occurs via a Pd(II) catalytic cycle.

Palladium nanoparticles immobilized on a nano-silica triazine dendritic polymer: a recyclable and sustainable nanoreactor for C–S cross-coupling

“…Aer the corresponding product forms via reductive elimination, the leached Pd species are restabilized on the surface of the dendritic polymer. [56][57][58] Based on these ndings, the C-S cross-coupling mechanism is shown in Scheme 2. First, the aryl halide (ArX) is added to palladium nanoparticles via an oxidative-addition pathway to form the organopalladium species 1.…”

Heterogeneous Dendrimer-Based Catalysts

“…Heck coupling proceeded with quantitative yields within 1 h only for para -substituted iodoarenes and styrene. The replacement of iodoarene by bromoarene and, moreover, for chloroarene resulted in the noticeable decrease in the catalyst activity, making the reaction strongly sensitive to substrate structure and electronic properties [ 344 ]. The yields of 60–89% within 2–5 h appeared to be achievable for bromo- and chloroarenes only with acceptor para -substituents (NO 2 , C(=O)OCH 3 ), while the use of donor- or meta-substituted bromoarenes (bromobenzene, 4-bromotoluene, and anisole, 3-bromonitrobenzene) led to the sharp downfall in conversion to 0–25%.…”

“…The hybrid dendritic Pd- n STDP catalyst appeared highly stable at recycling, and no decrease in the reaction rate and product yield, nanoparticle agglomeration, or noticeable Pd leaching were observed after seven runs in both C–C and C–S coupling reactions under both thermal and MW conditions [ 342 , 345 ]. A reaction mechanism was proposed, and accordingly, dendron moieties functioned as micro/nanoreactors for Pd nanoparticles, strongly retaining them and, therefore, prevented their leaching ( Scheme 21 ) [ 344 , 345 , 346 , 347 , 348 ]. Herein, at the first stage, an oxidative addition of arylhalide (ArX) to the surface of Pd nanoparticle took place, followed by diaryldisulfide addition and halide release in the presence of base.…”

Recent Progress of Metal Nanoparticle Catalysts for C–C Bond Forming Reactions

“…These heterogeneous gel-phase catalysts were successfully applied for several C-C coupling reactions (Scheme 29) [306][307][308]. Simple hydrophobic polymers without a coordination site such as polystyrene and poly(tetrafluoroethylene) have been confirmed to stabilize metal NPs and polymer-supported metal NPs were applicable to the recyclable catalyst for several reactions in water [309][310][311][312][313].…”