C,C cross-coupling reactions for the synthesis of nonsymmetrical biaryls represent one of the most significant transformations in contemporary organic chemistry. A variety of useful synthetic methods have been developed in recent decades, since nonsymmetrical biaryls play an evident role in natural product synthesis, as ligand systems in homogeneous catalysis and materials science. Transformation of simple arenes by direct C,H activation belongs to the cutting-edge strategies for creating biaryls; in particular the 2-fold C,H activation is of significant interest. However, in most examples very costly noble metal catalysts, ligand systems, and significant amount of waste-producing oxidants are required. Electrochemical procedures are considered as inherently "green" methods, because only electrons are required and therefore, no reagent waste is produced. Here, we report a metal-free electrochemical method for cross-coupling between phenols and arenes using boron-doped diamond (BDD) anodes in fluorinated media. Our sustainable approach requires no leaving functionalities. Employing water or methanol as mediator represents the key improvement for achieving nonsymmetrical biaryls with superb selectivity and synthetic attractive yields.
SiO in a complex: The first silanone that is stable at room temperature (3) is reported. The two-step synthesis involves carbonylation of the silylidyne complex 1 to give the chromiosilylene 2, followed by oxidation of 2 with N2 O. Silanone 3 features a polar, short SiO bond (1.526(3) Å) to a trigonal-planar-coordinated silicon center and reacts with water to give the dihydroxysilyl complex.
Silylene with a carbene carabiner: The synthesis, structure, and some reactions of a stable carbene adduct of dibromosilylene, SiBr2(Idipp) (see picture; Idipp=1,3‐bis(2,6‐diisopropylphenyl)‐ imidazol‐2‐ylidene), are described. SiBr2(Idipp) was characterized by X‐ray crystallography, NMR spectroscopy, and theoretical methods.
Particularly sustainable: The anodic cross‐coupling reaction between phenols and arenes can be performed on boron‐doped diamond electrodes. The arylated products are formed directly and obtained, in some cases, with high selectivity. Since only hydrogen atoms are sacrificed in the course of reaction this methodology opens the door to a novel concept for biaryl formation.
Structural
diffraction analysis of an anilino squaraine with branched isobutyl side chains shows crystallization into
two polymorphic structures in the bulk and in spin-casted thin films.
We observe multipeaked and pleochroic absorption spectra being blue-(red)-shifted
for the monoclinic (orthorhombic) polymorph. We understand the packing
as Coulombic molecular H-(J)-aggregates supporting Davydov splitting.
Pictures of projected Davydov components in oriented thin films fit
well to polarization resolved spectro-microscopy and crossed-polarized
light microscopy investigations. By comparison with literature on
anilino squaraines with linear alkyl side chains,
we point out a general trend for steering the thin film excitonic
properties by simple side chain and/or processing condition variation.
Combined with the ability to locally probe the direction of transition
dipole moments, this adds value to the rational design of functional
thin films for optoelectronic applications, especially envisioning
ultrastrong light–matter interactions.
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