Crystal structures of 2-(N,N-dimethylaminoalkyl)ferroceneboronic acids and their diol derivatives. The quest for a B-N intramolecular bond in the solid state

The crystal structures of (S,S)-2-(N,N-dimethyl-1-aminoethyl)ferroceneboronic acid (2), (S,S)-1-(N,N-dimethyl-1-aminoethyl)-2-(4,4,5,5-tetraphenyl-1,3,2-dioxaborolan-2-yl)ferrocene (3), rac-2-(N,N-dimethylaminomethyl)-ferroceneboronic acid (rac-4), (S)-[(1S,2S,3R,5S)-pinane-1,2-diyl] 2-(N,N-dimethylaminomethyl)ferroceneboronate (5) are presented. In connection with our studies of boronic acid-based carbohydrate sensors, we aimed at verifying the existence of an intramolecular B-N bond in these compounds; however, such a bond was not found. This fact, and other structural elements and similarities of the four compounds, are discussed.