biarylstructuren

Biaryl structures, known in German as Biarylstrukturen, are chemical compounds featuring two aromatic rings linked by a single carbon–carbon bond. This aryl–aryl bond allows varying degrees of rotation, which can influence the overall conformation, conjugation, and properties of the molecule. When the rings adopt a nearly coplanar arrangement, the π-systems are strongly conjugated; steric hindrance from substituents, particularly in the ortho positions, can twist the rings and reduce conjugation.

A key aspect of biaryl structures is atropisomerism. If rotation around the aryl–aryl bond is sufficiently hindered, the two faces of the molecule become non-superimposable mirror images, yielding stable enantiomers or diastereomers. Atropisomerism is especially important in chiral biaryl ligands used in asymmetric catalysis, such as BINOL (2,2'-dihydroxy-1,1'-binaphthyl) and BINAP derivatives, where axial chirality drives selectivity in chemical transformations.

Synthesis of biaryls is typically accomplished through cross-coupling and related methods. Common routes include Suzuki–Miyaura couplings, Ullmann-type and related copper or nickel-catalyzed couplings, and Buchwald–Hartwig amination. Direct C–H activation strategies and photochemical coupling can also form biaryl bonds. The chosen method depends on substrate scope, substituent patterns, and whether the target molecule should display axial chirality.

Applications of biaryl structures span chemistry and materials science. Their extended conjugation affects electronic properties, influencing UV–visible absorption and fluorescence in organic electronics and photonics. Biaryls serve as ligands in transition-metal catalysis and as building blocks in liquid crystals, OLED materials, natural products, and pharmaceutical agents, where axial chirality can influence activity and metabolism.