Boron(II) Cations: Interplay between Lewis‐Pair‐Acceptor and Electron‐Donor Properties

Boron(III) cations are widely used as highly Lewis acidic reagents in synthetic chemistry. In contrast, boron(II) cations are extremely rare and their chemistry almost completely unknown. They are both Lewis acids and electron donors, properties that are commonly associated with catalytically active late‐transition‐metal complexes. This double reactivity pattern ensures a rich and diverse chemistry. Herein we report the facile synthesis of several new boron(II) cations starting with a special diborane with two easily exchangeable triflate substituents. By increasing the π‐acceptor character of the neutral σ‐donor reaction partners, first reactions were developed in which the combined Lewis acidity and electron‐donor properties of boron(II) cations are applied for the reduction of organic molecules. The results of our study pave the way for applications of these unusual compounds in synthetic chemistry.     

Evolved Gas Analysis‐Mass Spectrometry to Identify the Earliest Organic Binder in Aegean Style Wall Paintings

An organic binder was identified in the painted fragments from the Canaanite palace of Tel Kabri, Israel. Recently dated to the late 18th century B.C.E. by ¹⁴C, Tel Kabri is the most ancient of the Eastern Mediterranean sites in which Aegean style paintings have been found. The application of pigments was suspected to be using an organic binding medium, particularly for the Egyptian Blue pigment. Samples of blue paint were examined using evolved gas analysis‐mass spectrometry (EGA‐MS) in order to overcome the analytical challenges imposed by highly degraded aged proteinaceous materials. Egg was identified as the binder based on the presence of hexadecanonitrile and octadecanonitrile, confirming the use of a secco painting technique. Lysozyme C from Gallus gallus was detected by proteomics analysis, confirming the presence of egg. To our knowledge, this is the earliest use of egg as a binder in Aegean style wall paintings.     

Manipulation of Molecular Aggregation States to Realize Polymorphism,AIE, MCL,and TADF in a Single Molecule

Multifunctional emitting materials are scarce and need to be further explored. Now, a newly anthraquinone derivative, 2‐(phenothiazine‐10‐yl)‐anthraquinone (PTZ‐AQ) was designed and synthesized and found to demonstrate polymorphism, multi‐color emission, aggregation‐induced emission (AIE), mechanochromic luminescence (MCL), and thermally activated delayed fluorescence (TADF) in its different solid forms. It is shown for the first time that TADF properties of a compound can be systematically tuned via its aggregation state. The optimized PTZ‐AQ crystal shows a small singlet–triplet energy splitting of 0.01 eV and exhibits red TADF with a photoluminescence quantum yield as high as 0.848. This study shows that the unique multiple functions can be integrated into one single compound through controlling the aggregation states, which provides a new strategy for the investigation and application of multifunctional organic materials.     

Giant Hysteretic Single‐Molecule Electric Polarisation Switching above Room Temperature

Continual progress has been achieved in information technology through unrelenting miniaturisation of the single memory bit in integrated ferromagnetic, ferroelectric, optical, and related circuits. However, as miniaturisation approaches its theoretical limit, new memory materials are being sought. Herein, we report a unique material exhibiting single‐molecule electric polarisation switching that can operate above room temperature. The phenomenon occurs in a Preyssler‐type polyoxometalate (POM) cluster we call a single‐molecule electret (SME). It exhibits all the characteristics of ferroelectricity but without long‐range dipole ordering. The SME affords bi‐stability as a result of the two potential positions of localisation of a Tb³⁺ ion trapped in the POM, resulting in extremely slow relaxation of the polarisation and electric hysteresis with high spontaneous polarisation and coercive electric fields. Our findings suggest that SMEs can potentially be applied to ultrahigh‐density memory 1 and other molecular‐level electronic devices operating above room temperature. 2     

Applications of Selenonium Cations as Lewis Acids in Organocatalytic Reactions

The use of trisubstituted selenonium salts as organic Lewis acids in electrophilic halogenation and aldol‐type reactions has been developed. The substrate scope is broad. The reaction conditions are mild and compatible with various functionalities. This study opens a new avenue for the development of nonmetallic Lewis acid catalysis.     

Enantioselective Construction of Silicon‐Stereogenic Silanes by Scandium‐Catalyzed Intermolecular Alkene Hydrosilylation

The catalytic asymmetric construction of silicon‐stereogenic silanes is of great interest and significance, but has met with only limited success to date. We herein report the enantioselective hydrosilylation of alkenes with dihydrosilanes by a chiral half‐sandwich scandium catalyst, which constitutes an efficient and general route for the synthesis of a wide range of enantioenriched silicon‐stereogenic silanes from easily accessible starting materials. This reaction features a broad substrate scope, high yields, and high enantioselectivity. Some of the chiral tertiary silane products were also converted into valuable derivatives, such as chiral silanol, quaternary silane, and benzosilole compounds.     

Palladium‐Catalyzed Reductive [5+1] Cycloaddition of 3‐Acetoxy‐1,4‐enynes with CO: Access to Phenols Enabled by Hydrosilanes

A new palladium‐catalyzed reductive [5+1] cycloaddition of 3‐acetoxy‐1,4‐enynes with CO, enabled by hydrosilanes, has been developed for delivering valuable functionalized phenols. This methodology employs hydrosilanes as the external reagent to facilitate the [5+1] carbonylative benzannulation. The reaction is a conceptually and mechanistically novel carbonylative cycloaddition route for the construction of substituted phenols, through the formation of four new chemical bonds, with excellent functional‐group tolerance.