From Spirocyclic Germanium Alkoxides to their Fluorido Germanates

Abstract

The synthesis of 4,4′-di-tert-butyl-4H,4′H-2,2′-spirobi[benzo[d][1,3,2]dioxagermine] (1) and 4,4′,8,8′-tetra-tert-butyl-4H,4′H-2,2′-spirobi[benzo[d][1,3,2]dioxagermine] (2) being the first representatives of spirocyclic germanium salicyl alcoholates is reported. The reaction of these compounds with potassium fluoride in the presence of 18-crown-6 gives the alkoxido fluorido germanates [K(CH₂CH₂O-)₆][GeF{OC₆H₄(CH^tBuO)-2}₂] (3) and [K(CH₂CH₂O–)₆][GeF{OC₆H₃(CH^tBuO)-2-^tBu-6}₂] (4). All compounds are characterized including single crystal X-ray diffraction analysis, nuclear magnetic resonance spectroscopy [¹H, ¹³C{¹H}, ¹H–¹³C{¹H} heteronuclear single quantum coherence, and ¹⁹F (3 and 4)], infrared spectroscopy, and thermal analyzes. Single crystal X-ray diffraction analyzes unveil a change of chirality in the salicyl alcoholate moieties of 3 with respect to the dominant (≈66%) stereoisomer of 1 upon crystallization as a result of fluoride-induced ligand exchange equilibria. Reactivity studies of the compounds 1 and 2 are discussed in comparison with structurally related silicon-based twin monomers.