An illusive chiral aminoalkylferroceneboronic acid. Structural assignment of a strong 1∶1 sorbitol complex and new insight into boronate–polyol interactions

The structure of a strong complex between D-sorbitol and (S,S)-2-(N,N-dimethyl-1-aminoethyl)ferroceneboronic acid (1) has been determined by NMR spectroscopy. On the basis of 1H, 13C and 11B NMR spectral data, including information from COSY, NOESY and HSQC two-dimensional experiments, a 2,3,5-bound sorbitol complex is deduced. On the basis of coalescence phenomena observed when varying the temperature and pH, an equilibrium between a complex with a covalent and a coordinative B–O5 bond, respectively, is elucidated, and a possible stabilisation of the latter by hydrogen bonding to the amino group is discussed. The existence of intramolecular B–N bonds in 1 and its complexes has been evaluated but no evidence of such bonds was obtained.