Phenylene- and Biphenylene-Bridged Bis-Imidazolylidenes of Palladium. Influence of the Presence of Pyrene Tags on the Catalytic Activity of the Complexes

Synthesis of Half-Titanocene Complexes Containing π,π-Stacked Aryloxide Ligands, and Their Use as Catalysts for Ethylene (Co)polymerizations

A family of half-titanocene complexes bearing π,π-stacked aryloxide ligands and their catalytic performances towards ethylene homo-/co- polymerizations were disclosed herein. All the complexes were well characterized, and the intermolecular π,π-stacking interactions could be clearly identified from single crystal X-ray analysis, in which a stronger interaction could be reflected for aryloxides bearing bigger π-systems, e.g., pyrenoxide. Due to the formation of such interactions, these complexes were able to highly catalyze the ethylene homopolymerizations and copolymerization with 1-hexene comonomer, even without any additiveson the aryloxide group, which showed striking contrast to other half-titanocene analogues, implying the positive influence of π,π-stacking interaction in enhancing the catalytic performances of the corresponding catalysts. Moreover, it was found that addition of external pyrene molecules was capable of boosting the catalytic efficiency significantly, due to the formation of a stronger π,π-stacking interaction between the complexes and pyrene molecules.

N-Heterocyclic carbene-palladium-PEPPSI complexes and their catalytic activity in the direct C–H bond activation of heteroarene derivatives with aryl bromides: synthesis, and antimicrobial and antioxidant activities

The Pd–NHC–PEPPSI complexes were used as catalysts in the direct C5-arylation of 2-acetyl furan, 2-acetylthiophene, and 2n-propylthiazole with different aryl bromides and were evaluated for their potential antibacterial and antioxidant properties.

In situ XAS study of the local structure and oxidation state evolution of palladium in a reduced graphene oxide supported Pd(ii) carbene complex during an undirected C–H acetoxylation reaction

In situ XAS is used to reveal the evolution of palladium species during an undirected C–H acetoxylation reaction.

Palladium(II)/N-Heterocyclic Carbene-Catalyzed Direct C-H Acylation of Heteroarenes with N-Acylsaccharins

N-Acylsaccharin represents a facile acyl group transfer agent to heteroarenes in the presence of Pd(II)/NHC complexes appended with a pyrene unit. Catalytic acylation of heteroarenes was enhanced by the noncovalent interaction between the pyrene unit and substrates. High functional group tolerance, broad substrate scope, and moderate to good yields of 2-acylated azoles are added features of this method.

Smart N-Heterocyclic Carbene Ligands in Catalysis

It is well-recognized that N-heterocyclic carbene (NHC) ligands have provided a new dimension to the design of homogeneous catalysts. Part of the success of this type of ligands resides in the limitless access to a variety of topologies with tuned electronic properties, but also in the ability of a family of NHCs that are able to adapt their properties to the specific requirements of individual catalytic transformations. The term "smart" is used here to refer to switchable, multifunctional, adaptable, or tunable ligands and, in general, to all those ligands that are able to modify their steric or electronic properties to fulfill the requirements of a defined catalytic reaction. The purpose of this review is to comprehensively describe all types of smart NHC ligands by focusing attention on the catalytically relevant ligand-based reactivity.

Trinuclear complexes of palladium(ii) with chalcogenated N-heterocyclic carbenes: catalysis of selective nitrile–primary amide interconversion and Sonogashira coupling

The interconversion of nitriles to amides and Sonogashira coupling were catalyzed with Pd(ii) complexes (0.5–2 mol%).

Polyaromatic N-heterocyclic carbene ligands and π-stacking. Catalytic consequences

This article highlights how π-stacking interactions have an important influence on the catalytic properties of transition metal complexes decorated with rigid polyaromatic ligands.

Redox-active multinuclear Pd(ii) complexes with bis- and tris-mesoionic carbenes

Synthesis of a ligand platform to generate di- and tri-mesoionic carbenes is reported together with their multinuclear Pd(ii) complexes.

Experimental and theoretical approaches to the influence of the addition of pyrene to a series of Pd and Ni NHC-based complexes: catalytic consequences

A series of Ni and Pd complexes with three different N-heterocyclic carbene (NHC)-based ligands (imidazolylidene, benzimidazolylidene and pyrene-imidazolylidene) has been prepared and fully characterized. The influence of the addition of pyrene to solutions containing these complexes is studied by means of NMR and UV/Vis spectroscopies and by cyclic voltammetry. The addition of pyrene to the pyrene-NHC-containing Pd and Ni complexes gives rise to the formation of adducts by π-π stacking interactions between pyrene and the pyrene group of the NHC ligand. This interaction causes a modification of the electronic properties of the metal, as demonstrated by cyclic voltammetric studies of the Ni-NHC complexes. Theoretical calculations support this type of π-interactions, and justify the higher interactions observed with the pyrene-NHC containing complexes. The catalytic activities of the complexes were tested in the Suzuki-Miyaura C-C coupling and in the α-arylation of ketones. The addition of pyrene as an external π-stacking additive does not affect the activities of the complexes in the Suzuki-Miyaura coupling, but this observation may be justified due to the fact that the process is heterogeneously catalyzed, as indicated by the mercury-drop test. The addition of pyrene to the catalytic α-arylation of ketones results in a decrease in the activity of the reactions catalyzed by the pyrene-imidazolylidene palladium complex, whereas the other two catalysts do not modify their activity in the presence of this π-stacking additive.