Catalysis with Gold Complexes Immobilised on Carbon Nanotubes by π-π Stacking Interactions: Heterogeneous Catalysis versus the Boomerang Effect

Chiral Chromium Salen@rGO as Multipurpose and Recyclable Heterogeneous Catalyst

The first immobilization of a pyrene-tagged chromium salen complex through π-π noncovalent interactions on reduced graphene oxide (rGO) is described. A very robust supported catalytic system is obtained to promote asymmetric catalysis in repeated cycles, without loss of activity or enantioselectivity. This specific behavior was demonstrated in two different catalytic reactions (up to ten reuses) promoted by chromium salen complexes, the cyclohexene oxide ring-opening reaction and the hetero-Diels-Alder cycloaddition between various aldehydes and Danishefsky's diene. Furthermore, the chiral chromium salen@rGO has been found to be compatible with a multi-substrate type use, in which the structure of the substrate involved is modified each time the catalyst is reused.

Silica-Supported Phosphine-Gold Complexes as an Efficient Catalytic System for a Dearomative Spirocyclization

The combination of metal catalyst and inorganic silica frameworks provides a greener approach to recyclable catalysis. In this study, three phosphine-gold chloride complexes have been successfully covalently grafted onto chiral silica nanohelices. The resulting 3D ensembles showed chiroptical properties that allowed the monitoring of the supported ligands. The heterogeneous gold chloride catalysts in cooperation with silver triflate exhibited high reactivity in various reactions, especially in the spirocyclization of aryl alkynoate esters, for which a catalytic loading of 0.05 mol % could be employed. The heterogeneous catalysts could be easily recovered and recycled seven or eight times without any loss of efficiency. By adding more silver triflate, 25 cycles with full conversion were achieved owing to a complex catalytic system based on silica and metallic species.

Enantiopure isothiourea@carbon-based support: stacking interactions for recycling a lewis base in asymmetric catalysis

An enantiopure isothiourea (hyperBTM) was functionalized by a pyrene moiety via click chemistry; immobilized on reduced Graphene Oxide, this recyclable chiral organocatalyst promotes formal [3+2] cycloaddition of ammonium enolates with oxaziridines.

Highly para-selective C‒H alkylation of unactivated arenes with α-aryl-α-diazoesters catalyzed by gold(I) immobilized on MCM-41

The heterogeneous gold(I)-catalyzed highly para-selective C(sp2)–H bond alkylation of benzene derivatives with α-aryl-α-diazoesters possessing electron-withdrawing substituents on the aryl rings are achieved. The reactions proceed under mild conditions in good to excellent yields by using an MCM-41-anchored diphenylphosphine gold(I) complex [MCM-41-PPh2-AuOTf] as a recyclable catalyst.

Pyrene-tagged carbohydrate-based mixed P/S ligand: spacer effect on the Rh(i)-catalyzed hydrogenation of methyl α-acetamidocinnamate

The chain length between the pyrene group and the rhodium atom in mixed P/S catalysts is crucial in the enantioselective hydrogenation of enamides, and the most active catalyst can be used in catch and release process.

Ruthenium molecular complexes immobilized on graphene as active catalysts for the synthesis of carboxylic acids from alcohol dehydrogenation

Green efficient synthesis of carboxylic acids catalyzed by molecular ruthenium complexes supported on graphene using water as solvent and with the formation of molecular hydrogen as a by-product.

pH controlled adsorption of water-soluble ruthenium clusters onto carbon nanotubes and nanofiber surfaces

Nanocarbon supported catalysts were prepared from water-soluble molecular clusters by pH controlled impregnations in order to probe the clusters/surface interactions and to maximize them.

Enzymatic Catalysis Combining the Breath Figures and Layer-by-Layer Techniques: Toward the Design of Microreactors

Herein, we report the fabrication of microstructured porous surfaces with controlled enzymatic activity by combining the breath figures and the layer-by-layer techniques. Two different types of porous surfaces were designed based on fluorinated and carboxylated copolymers in combination with PS, using poly(2,3,4,5,6-pentafluorostyrene)-b-polystyrene (PS5F31-b-PS21) and polystyrene-b-poly(acrylic acid) (PS19-b-PAA10) block copolymers, respectively. For comparative purposes, flat surfaces having similar chemistry were obtained by spin-coating. Poly(sodium 4-styrenesulfonate)/poly(allylamine hydrochloride) (PSS/PAH) multilayers incorporating alkaline phosphatase (ALP) were built on these porous surfaces to localize the enzyme both inside and outside of the pores using PS/PS5F31-b-PS21 surfaces and only inside the pores on PS/PS19-b-PAA10 surfaces. A higher catalytic activity of ALP (about three times) was obtained with porous surfaces compared to the flat ones. The catalysis happens specifically inside the holes of PS/PS19-b-PAA10surfaces, where ALP is located. This opens the route for applications in microreactors.

The advantages of covalently attaching organometallic catalysts to a carbon black support: recyclable Rh(i) complexes that deliver enhanced conversion and product selectivity

A bidentate Rh(i) coordination complex was covalently anchored to a carbon black support. The resultant hybrid catalyst was found to be active for both hydroamination and dihydroalkoxylation reactions and was readily recycled.

Metal–organic frameworks catalyzed C–C and C–heteroatom coupling reactions

This critical review aims to illustrate the recent developments in the field of C–C and C–X (X = O, N) coupling reactions promoted by metal–organic frameworks.

Evaluating the effects of carbon nanoreactor diameter and internal structure on the pathways of the catalytic hydrosilylation reaction

Three different types of carbon nanoreactors, double-walled nanotubes (DWNT), multi-walled nanotubes (MWNT) and graphitised carbon nanofibers (GNF) have been appraised for the first time as containers for the reactions of phenylacetylene hydrosilylation catalysed by a confined molecular catalyst [Rh₄(CO)₁₂]. Interactions of [Rh₄(CO)₁₂] with carbon nanoreactors determining the ratio of β-addition products are unchanged for all nanoreactors and are virtually unaffected by the confinement of [Rh₄(CO)₁₂] inside carbon nanostructures. Conversely, the relative concentrations of reactants affecting the ratio of addition and dehydrogenative silylation products is very sensitive to nanoscale confinement, with all nanoreactors demonstrating significant effects on the distribution of reaction products as compared to control experiments with the catalyst in bulk solution or adsorbed on the outer surface of nanoreactors. Surprisingly, the widest nanoreactors (GNF) change the reaction pathway most significantly, which is attributed to the graphitic step-edges inside GNF providing effective anchoring points for the catalyst and creating local environments with greatly altered concentrations of reactants as compared to bulk solution. Possessing diameters significantly wider than molecules, GNF impose no restrictions on the transfer of reactants while providing the strongest confinement effects for the reaction. Furthermore, GNF facilitate the effective recyclability of the catalyst and thus represents a superior nanoreactor system to carbon nanotubes.