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 M?ssbauer spectroscopies and X-ray crystallography. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1724–1731, September, 2007.