Halogen bonding is a noncovalent interaction similar to hydrogen bonding, which is based on electrophilic halogen substituents. Hydrogen-bonding-based organocatalysis is a well-established strategy which has found numerous applications in recent years. In light of this, halogen bonding has recently been introduced as a key interaction for the design of activators or organocatalysts that is complementary to hydrogen bonding. This Concept features a discussion on the history and electronic origin of halogen bonding, summarizes all relevant examples of its application in organocatalysis, and provides an overview on the use of cationic or polyfluorinated halogen-bond donors in halide abstraction reactions or in the activation of neutral organic substrates.
A well-defined three-point interaction based solely on halogen bonding is presented. X-ray structural analyses of tridentate halogen bond donors (halogen-based Lewis acids) with a carefully chosen triamine illustrate the ideal geometric fit of the Lewis acidic axes of the former with the Lewis basic centers of the latter. Titration experiments reveal that the corresponding binding constant is about 3 orders of magnitude higher than that with a comparable monodentate amine. Other, less perfectly fitting multidentate amines also bind markedly weaker. Multipoint interactions like the one presented herein are the basis of molecular recognition, and we expect this principle to further establish halogen bonding as a reliable tool for solution-phase applications.
Polyfluorinated biphenyls
are interesting and promising substrates
for many different applications. Unfortunately, all current methods
for the syntheses of these compounds only work for a hand full of
molecules or only in very special cases. Thus, many of these compounds
are still inaccessible to date. Here we report a general strategy
for the synthesis of a wide range of highly fluorinated biphenyls.
In our studies we investigated crucial parameters, such as different
phosphine ligands and the influence of various nucleophiles and electrophiles
with different degrees of fluorination. These results extend the scope
of the already very versatile Suzuki–Miyaura reaction toward
the synthesis of very electron-poor products, making these more readily
accessible. The presented methodology is scalable and versatile without
the need for elaborate phosphine ligands or Pd-precatalysts.
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