Selectivity in Adduct Formation of a Bidentate Boron Lewis Acid

Abstract

A bidentate boron Lewis acid based on 1,8‐diethynylan­thracene has been studied in detail with respect to its adduct formation with diamines and diphosphanes of different linker lengths between the donor functions. A clear correlation between the linker length of the bifunctional base and the formation of 1:1 adducts, 1:2 adducts or oligomers was found. The adducts were characterized in solution by NMR titration experiments and structurally by X‐ray diffraction. In addition, adduct formation and competition experiments of the host system with ZR3 (Z = N, P; R = H, Me) demonstrated the generally higher stability of alkylphosphane adducts compared to alkylamine adducts with boron functions. The results provide a gene­ral insight into the adduct formation of bidentate Lewis acids with guests of different sizes as well as the differences in stability between borane‐amine and borane‐phosphane adducts.