Macrocyclization of the semiclathrochelate o-carboranylboronate and n-butylboronate iron(II) oximehydrazonates: synthesis and structure of clathrochelate products and unexpected allosteric effect of the apical substituent

The template condensation of diacetylmonooxime hydrazone (HDXO) with n-butylboronic acid and dimethyl ester of o-carboranyldiboronic acid on the iron(II) ion matrix afforded the [Fe(DXO)3(BBu)](BF4) and [Fe(DXO)3(Bo-carb)](BF4) semiclathrochelates. The H+-ion-catalyzed macrocyclization of these precursors with an excess of formaldehyde and triethyl orthoformate (TOF) resulted in the corresponding macrobicyclic complexes. In the case of o-carboranylboronate semiclathrochelate, the macrocyclization with TOF gave the clathrochelate with the previously unknown syn,syn,anti-orientation of the ethoxy substituents relative to the 1,3,5-triazacyclohexane capping fragment. The complexes obtained were characterized using elemental analysis, IR, UV-Vis, MALDI-TOF mass, 1H, 11B, and 13C NMR, and 57Fe Mossbauer spectroscopies and X-ray crystallography.