Crystal Structures of Spiroborates Derived from [1,1′-Binaphthalene]-2,2′-diol (BINOL)

Ammonium salts of bis[[1,1′-binaphthalene]-2,2′-diolato-O,O’] borate (4) were prepared by the reaction of boric acid with both racemic and enantiomerically pure [1,1′-binaphthalene]-2,2′-diol (BINOL). Four salts were crystallized, and their structures were solved by X-ray diffraction. In all cases examined, spiroborate 4 was found to adopt a flattened D2 conformation similar to the one favored by analogous spiroborates derived from 2,2′-dihydroxybiphenyl. Spiroborate 4 has an essentially invariant molecular geometry, can be synthesized and derivatized by straightforward methods, and is readily available in both racemic and enantiomerically pure forms of high configurational stability. For these reasons, it is an attractive starting point for creating crystals and other ordered materials with predetermined structures and properties.