Square‐Planar Ruthenium(II) Complexes: Control of Spin State by Pincer Ligand Functionalization

Functionalization of the PNP pincer ligand backbone allows for a comparison of the dialkyl amido, vinyl alkyl amido, and divinyl amido ruthenium(II) pincer complex series [RuCl{N(CH₂CH₂PtBu₂)₂}], [RuCl{N(CHCHPtBu₂)(CH₂CH₂PtBu₂)}], and [RuCl{N(CHCHPtBu₂)₂}], in which the ruthenium(II) ions are in the extremely rare square‐planar coordination geometry. Whereas the dialkylamido complex adopts an electronic singlet (S=0) ground state and energetically low‐lying triplet (S=1) state, the vinyl alkyl amido and the divinyl amido complexes exhibit unusual triplet (S=1) ground states as confirmed by experimental and computational examination. However, essentially non‐magnetic ground states arise for the two intermediate‐spin complexes owing to unusually large zero‐field splitting (D>+200 cm^?1). The change in ground state electronic configuration is attributed to tailored pincer ligand‐to‐metal π‐donation within the PNP ligand series.     

Autonomously Propelled Motors for Value‐Added Product Synthesis and Purification

A proof‐of‐concept design for autonomous, self‐propelling motors towards value‐added product synthesis and separation is presented. The hybrid motor design consists of two distinct functional blocks. The first, a sodium borohydride (NaBH₄) granule, serves both as a reaction prerequisite for the reduction of vanillin and also as a localized solid‐state fuel in the reaction mixture. The second capping functional block consisting of a graphene–polymer composite serves as a hydrophobic matrix to attract the reaction product vanillyl alcohol (VA), resulting in facile separation of this edible value‐added product. These autonomously propelled motors were fabricated at a length scale down to 400 μm, and once introduced in the reaction environment showed rapid bubble‐propulsion followed by high‐purity separation of the reaction product (VA) by the virtue of the graphene–polymer cap acting as a mesoporous sponge. The concept has excellent potential towards the synthesis/isolation of industrially important compounds, affinity‐based product separation, pollutant remediation (such as heavy metal chelation/adsorption), as well as localized fuel‐gradients as an alternative to external fuel dependency.     

Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5‐tert‐butyl‐2‐phenylbenzoxazole ( IrO ) or 5‐tert‐butyl‐2‐phenylbenzothiazole ( IrS ) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5–5.0 mol % catalyst loading) for a variety of reactions with α,β‐unsaturated carbonyl compounds, namely Friedel–Crafts alkylations (94–99 % ee), Michael additions with CH‐acidic compounds (81–97 % ee), and a variety of cycloadditions (92–99 % ee with high d.r.). Mechanistic investigations and crystal structures of an iridium‐coordinated substrates and iridium‐coordinated products are consistent with a mechanistic picture in which the α,β‐unsaturated carbonyl compounds are activated by two‐point binding (bidentate coordination) to the chiral Lewis acid.     

Monitoring of the shrinkage during the photopolymerization of acrylates using hyphenated photorheometry/near‐infrared spectroscopy

This article describes a new method for the quantitative determination and time‐resolved monitoring of the polymerization shrinkage during ultraviolet (UV) photopolymerization. It is based on rheometry using a modified oscillating rheometer. Shrinkage is determined from the decrease of the gap between the rheometer plates. Moreover, near‐infrared (NIR) spectra can be recorded directly in the rheometer, which allows continuous determination of the conversion at any time of a shrinkage measurement. As both shrinkage and conversion data come from the same experiment, shrinkage can be analyzed in dependence on the current conversion achieved during UV irradiation, which enables direct investigation of correlations between both parameters. Hyphenated photorheometry/FT‐NIR spectroscopy was used for the determination of the polymerization shrinkage of pure acrylate monomers and oligomers as well as acrylate‐based formulations. Quantitative shrinkage values were found to be in excellent correlation with data that were determined by an independent method (via buoyancy measurements) and data from literature. Furthermore, the effect of ambient and irradiation conditions or the content of nanoparticles on the degree of shrinkage was studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 729–739     

A Rhodium Catalyst Superior to Iridium Congeners for Enantioselective Radical Amination Activated by Visible Light

A bis‐cyclometalated rhodium(III) complex catalyzes a visible‐light‐activated enantioselective α‐amination of 2‐acyl imidazoles with up to 99 % yield and 98 % ee. The rhodium catalyst is ascribed a dual function as a chiral Lewis acid and, simultaneously, as a light‐activated smart initiator of a radical‐chain process through intermediate aminyl radicals. Notably, related iridium‐based photoredox catalysts reported before were unsuccessful in this enantioselective radical C?N bond formation. The surprising preference for rhodium over iridium is attributed to much faster ligand‐exchange kinetics of the rhodium complexes involved in the catalytic cycle, which is crucial to keep pace with the highly reactive and thus short‐lived nitrogen‐centered radical intermediate.     

Solvent‐free Liquid Crystals and Liquids from DNA

As DNA exhibits persistent structures with dimensions that exceed the range of their intermolecular forces, solid‐state DNA undergoes thermal degradation at elevated temperatures. Therefore, the realization of solvent‐free DNA fluids, including liquid crystals and liquids, still remains a significant challenge. To address this intriguing issue, we demonstrate that combining DNA with suitable cationic surfactants, followed by dehydration, can be a simple generic scheme for producing these solvent‐free DNA fluid systems. In the anhydrous smectic liquid crystalline phase, DNA sublayers are intercalated between aliphatic hydrocarbon sublayers. The lengths of the DNA and surfactant are found to be extremely important in tuning the physical properties of the fluids. Stable liquid‐crystalline and liquid phases are obtained in the ?20 °C to 200 °C temperature range without thermal degradation of the DNA. Thus, a new type of DNA‐based soft biomaterial has been achieved, which will promote the study and application of DNA in a much broader context.