Graphene Film-Supported Oriented 1.1.1 Gold(0) Versus 2.0.0 Copper(I) Nanoplatelets as Very Efficient Catalysts for Coupling Reactions

Abstract

Few-layered graphene-supported 1.1.1 and 2.0.0 oriented Au and Cu2O nanoplatelets were prepared by one-step pyrolysis of the corresponding metal salts embedded in chitosan at 900 C under inert atmosphere. These nanometric films containing oriented nanoplatelets were investigated in a series of reactions as Ullmann-type homocoupling, C-N cross-coupling and Michael addition. The catalysts exhibited turnover numbers (TONs) three to six orders of magnitude higher than those of analogous graphene-supported unoriented metal nanoparticles. In addition it has been found that oriented Cu2O and Au nanoplatelets grafted on defective graphene also exhibit activity to promote the Michael addition of compounds with active methylene and methine hydrogens to conjugated ketone. An exhaustive characterization of these materials using spectroscopic and electron microscopy analyses has been carried out. CO2 thermoprogrammed desorption measurements show that films of these two graphene supported catalysts exhibit some basicity that can explain their activity to promote Michael addition.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

“…Candu et al considered these materials for Ullmann homocoupling of iodobenzene, where good turnover numbers (TON) and selectivity to diphenyls were observed. 343 Primo et al made a comparison with 5 nm Au NPs on graphene, and a 5-fold improvement in TON was observed with 83% selectivity, although this was observed only at low conversion (0.3%). 344 Graphene oxide was used to support Au NPs of 3.5 nm by Mondal et al 338 Again, a strong support−nanoparticle interaction was formed between the cationic Au and the anionic oxygen of graphene oxide.…”

“…In both cases, the NPs were 3 nm deep and had surface areas of ∼20 nm. Candu et al considered these materials for Ullmann homocoupling of iodobenzene, where good turnover numbers (TON) and selectivity to diphenyls were observed . Primo et al made a comparison with 5 nm Au NPs on graphene, and a 5-fold improvement in TON was observed with 83% selectivity, although this was observed only at low conversion (0.3%) .…”

Copper nanocatalysts applied in coupling reactions: a mechanistic insight

“…Parvulescu, Garcia and co-workers have recently prepared graphene-film supported Cu2O nanoplatelets (8 nm in size) by one-step pyrolysis of Cu(NO3)2 embedded in chitosan at 900 °C under inert atmosphere that were active towards the homocoupling of iodobenzene in the absence of base. 35 Studies on the catalytic regimes of Cu2O-nanoparticle-catalysed C-C couplings carried out by Andiappan and co-workers 36 indicate that Cu2O systems can catalyze homocoupling reactions precluding the need of ligands or base via surface reactivity, enabling their implementation in flow applications.…”

UV Cross-Linked Polymer Stabilized Gold Nanoparticles as a Reusable Dip-Catalyst for Aerobic Oxidation of Alcohols and Cross-Aldol Reactions

“…Among the precious metal nanoparticles, gold nanoparticle (AuNP)-based catalysts have become a hot research topic in recent years due to their variety of reactions like oxidation, − reduction, − dye degradation, coupling reactions, , etc. To prevent their aggregation, AuNPs have been immobilized on suitable supports like alumina, TiO 2 , silica spheres, zeolites, SBA-15, graphenes, different polymers, − etc.…”