binaphthyl

Binaphthyl is a hydrocarbon consisting of two naphthalene rings linked at the 1-position of each ring by a single biaryl bond, giving 1,1'-binaphthyl (C20H14). The axis of the biaryl bond is hindered in many substituted forms, imparting axial chirality and giving enantiomers that are often labeled M and P.

Because rotation around the biaryl axis can be slow, 1,1'-binaphthyl and its derivatives serve as chiral scaffolds. Most notable derivatives arise when the rings are further substituted to lock the axis; one of the best known is BINAP, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, used as a chiral ligand in asymmetric catalysis. Other important relatives include BINOL (1,1'-bi-2-naphthol) and their phosphine analogues.

Binaphthyls are primarily synthetic; the compound can be prepared by oxidative coupling of naphthyl units or by coupling of 1-naphthyl derivatives, and racemic forms can be resolved to obtain enantiopure binaphthyls.

Applications of binaphthyl derivatives center on their use as scaffolds in asymmetric catalysis. BINAP-type ligands coordinate to metals, such as rhodium, ruthenium, or iridium, to catalyze enantioselective hydrogenations, allylic substitutions, and related transformations. This axial chirality provides a versatile platform for designing highly selective catalysts and other chiral reagents in modern organic synthesis. See also BINOL and BINAP.