heterobiaryl

A heterobiaryl is a biaryl compound in which at least one of the two aromatic rings is heteroaromatic, meaning the ring contains one or more heteroatoms such as nitrogen, oxygen, or sulfur. The defining feature is a single aryl–aryl bond linking two rings, with one or both rings bearing heteroatoms that influence the electronic and steric properties of the molecule. Common motifs include heteroaryl–heteroaryl biaryls (for example bipyridines, bipyrimidines, and related structures) as well as heteroaryl–aryl biaryls (such as a pyridine ring connected to a phenyl ring).

Typical examples and relevance include 2,2'-bipyridine and 4,4'-bipyridine, which are widely used as ligands in coordination chemistry, and various heteroaryl–aryl biaryls that appear in pharmaceuticals and materials science. The presence of heteroatoms often enhances hydrogen-bonding capacity, alters acidity, and modulates the π-system, affecting reactivity, photophysical properties, and metal binding.

Synthesis of heterobiaryls commonly relies on cross-coupling strategies to forge the biaryl C–C bond. Suzuki–Miyaura, Negishi, Kumada, and related cross-couplings using heteroaryl halides or heteroaryl boron reagents are standard approaches. Direct C–H activation methods and nickel- or palladium-catalyzed couplings are increasingly used, especially for challenging or densely substituted substrates. Challenges include catalyst deactivation by coordinating heteroatoms and regioselectivity when multiple reactive sites are available.

Applications span catalysis, where heterobiaryl ligands such as bipyridines coordinate metals, to organic electronics and medicinal chemistry, where the planarity and electronic characteristics of heterobiaryls influence performance and biological interactions.