Periphery-functionalized organometallic dendrimers for homogeneous catalysis

Synthesis and Reactivity of the Rare-Earth Metal Complexes Bearing the Indol-2-yl-Based NCN Pincer Ligand

The pincer rare-earth dialkyl complexes [κ3-LRE(CH2SiMe3)2 (RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e))] with the indol-2-yl-based NCN pincer ligand were synthesized by the reactions of the proligand HL (L = 1-Me2NCH2CH2-3-(2-iPrC6H5N═CH)C8H4N) with RE(CH2SiMe3)3(THF)2. These complexes exhibited a variety of reactivities toward organic compounds such as amines, triphenylphosphine ylide, N-phenylimidazole, pyridine derivatives, and o-carborane leading to σ-bond metathesis, migration insertion, and redox reaction products. The reactions of the dialkyl rare-earth metal complexes with o-carborane afforded the novel NCN pincer-ligated carboryne-based metallacyclopropanes which reacted with diphenyl ketone to give insertion products of the RE-C2-ind and one of the RE-Ccage bonds, while the reaction of the carboryne-based metallacyclopropanes with diphenyldiazomethane produced the di-aza-metallacyclopentanes via the insertions of the N═N bond of the diphenyldiazomethane into two RE-Ccage bonds and the RE-C2-ind bond. The reactions of the dialkyl complexes with 2 equiv of 2,2'-bipyridine afforded the pincer-ligated bis(2,2'-bipyridyl monoanionic radical) complexes via the homolytic redox reaction.

Carbosilane dendritic nanostructures, highly versatile platforms for pharmaceutical applications

Dendrimers are multifunctional molecules with well-defined size and structure due to the step-by-step synthetic procedures required in their preparation. Dendritic constructs based on carbosilane scaffolds present carbon-carbon and carbon-silicon bonds, which results in stable, lipophilic, inert, and flexible structures. These properties are highly appreciated in different areas, including the pharmaceutical field, as they can increase the interaction with cell membranes and improve the therapeutic action. This article summarizes the most recent advances in the pharmaceutical applications of carbosilane dendritic molecules, from therapeutics to diagnostics and prevention tools. Dendrimers decorated with cationic, anionic, or other moieties, including metallodendrimers; supramolecular assemblies; dendronized nanoparticles and surfaces; as well as dendritic networks like hydrogels are described. The collected examples confirm the potential of carbosilane dendrimers and dendritic materials as antiviral or antibacterial agents; in therapy against cancer, neurodegenerative disease, or oxidative stress; or many other biomedical applications. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Structural Mimics of Phenyl Pyridine (ppy) - Substituted, Phosphorescent Cyclometalated Homo and Heteroleptic Iridium(III) Complexes for Organic Light Emitting Diodes - An Overview

Today organic light emitting diodes are a topic of significant academic and industrial research interest. OLED technology is used in commercially available displays, and efforts have been directed to improve this technology. Design and synthesis of phosphorescent based transition metals are capable of harvesting both singlet and triplet excitons and achieve 100 % internal quantum efficiency is an active area of research. Among all the transition metals, iridium is considered a prime candidate for OLEDs due to its prominent photophysical characteristics. In the present review, we have concentrated on the Iridium based homo and heteroleptic complexes that have dissimilar substitutions on phenylpyridine ligands, different ancillary ligands and the effect of substitution on HOMO/LUMO energies and a brief discussion and correlation on the photophysical, electrochemical and device performances of the different complexes have been reviewed for organic light emitting diodes.

Synthesis and Properties of Dumbbell-Shaped Dendrimers Containing 9-Phenylcarbazole Dendrons

We report the synthesis and structural characterization of two dumbbell-shaped dendrimers incorporating 9-phenylcarbazole units as dendrons, as well as their thermal, morphological, photophysical, and electrochemical properties.

Synthesis, structure, and reactivity of fluorous phosphorus/carbon/phosphorus pincer ligands and metal complexes

Reactions of the diphosphine 1,3-C6H4(CH2PH2)2 and fluorous alkenes H2C=CHR(fn)(R(fn)=(CF2)(n-1)CF3; n = 6, 8) at 75 degrees C in the presence of AIBN give the title ligands 1,3-C6H4(CH2P(CH2CH2R(fn))2)2(3-R(fn)) and byproducts 1,3-C6H4(CH3)(CH2P(CH2CH2R(fn))2)(4-R(fn)) in 1 : 3 to 1 : 5 ratios. Workups give -R(fn) in 4--17% yields. Similar results are obtained photochemically. Reaction of 1,3-C6H4(CH2Br)2 and HP(CH2CH2R(f8))2 (5) at 80 degrees C (neat, 1 : 2 mol ratio) gives instead of simple substitution the metacyclophane [1,3-C6H4(CH2P(CH2CH2R(f8))2 CH2-1,3-C(6)H(4)CH(2)P[lower bond 1 end](CH2CH2R(f8))2C[upper bond 1 end]H2](2+)2Br-, which upon treatment with LiAlH(4) yields 3-R(f8)(20%), 4-R(f8), and other products. Efforts to better access 3-R(f8), either by altering stoichiometry or using various combinations of the phosphine borane (H3B)PH(CH2CH2R(f8))2 and base, are unsuccessful. Reactions of 3-R(fn) with Pd(O2CCF3)2 and [IrCl(COE)2]2(COE=cyclooctene) give the palladium and iridium pincer complexes (2,6,1-C6H3(CH2 P(CH2CH2R(fn))(2)(2)Pd(O2CCF3)(10-R(fn); 80-90%) and (2,6,1-C6H3(CH2P(CH2CH2R(f8))2)2)Ir(Cl)(H)(11-R(f8); 29%), which exhibit CF3C6F(11)/toluene partition coefficients of >96 : <4. The crystal structure of 10-R(f8) shows CH2CH2R(f8) groups with all-anti conformations that extend in parallel above and below the palladium square plane to create fluorous lattice domains. NMR monitoring shows a precursor to 11-R(f8) that is believed to be a COE adduct.

Quantitative Evaluation of the Catalytic Activity of Dendrimers with Only One Active Center at the Core: Application to the Nitroaldol (Henry) Reaction

One reference tertiary amine and three families of structurally related trialkylamines and dendrimers have been synthesized, characterized, and studied by molecular dynamics simulations. The catalytic activity of these amines in the nitroaldol (Henry) reaction between 2-nitroethanol and benzaldehyde has been measured by FT-IR spectroscopy. It is found that, in this kind of molecule with only one catalytic center at the core, the efficiency of the catalytic process decreases with the size and/or the degree of ramification of the dendrimer. According to these results, there is a linear departure from the behavior predicted by the hard sphere collision theory (HSCT) as the size of the dendrimer increases. Therefore, the behavior of structurally related dendrimers can be quantified in terms of their molecular weight and reagent accessible surfaces.

Platinum Group Organometallics Based on "Pincer" Complexes: Sensors, Switches, and Catalysts

Since the first reports in the late 1970s on transition metal complexes containing pincer-type ligands-named after the particular coordination mode of these ligands-these systems have attracted increasing interest owing to the unusual properties of the metal centers imparted by the pincer ligand. Typically, such a ligand comprises an anionic aryl ring which is ortho,ortho-disubstituted with heteroatom substituents, for example, CH₂ NR₂ , CH₂ PR₂ or CH₂ SR, which generally coordinate to the metal center, and therefore support the M-C σ bond. This commonly results in a terdentate and meridional coordination mode consisting of two metallacycles which share the M-C bond. Detailed studies of the formation and the properties of a large variety of pincers containing platinum group metal complexes have provided direct access to both a fundamental understanding of a variety of reactions in organometallic chemistry and to a range of new applications of these complexes. The discovery of alkane dehydrogenation catalysts, the mechanistic elucidation of fundamental transformations (for example, C-C bond activation), the construction of the first metallodendrimers for sustainable homogeneous catalysis, and the engineering of crystalline switches for materials processing represent only a few of the many highlights which have emanated from these numerous investigations. This review discusses the synthetic methodologies that are currently available for the preparation of platinum group metal complexes containing pincer ligands and especially emphasizes different applications that have been realized in materials science such as the development and engineering of sensors, switches, and catalysts.