Axially Chiral Spiro Compounds with Heavier Group 14 Elements as Spiro-Centers

Homo- and heteroditopic 4-tert-butyl-1,2-benzene-bischalcogenol ligands, namely t-BuC₆H₃(SH)₂ and t-BuC₆H₃(SH)(SeH) (t-Bu = C(CH₃)₃), have been prepared through the functionalization of the ortho position of the t-BuC₆H₄(SH) precursor with thiol (-SH) or selenol (-SeH) groups. The lithiated derivatives of these compounds have been isolated and structurally characterized. With these versatile precursors at hand, we explored the preparation of axially chiral compounds ((t-BuC₆H₃S₂)₂E; (t-BuC₆H₃(S)(Se))₂E; E = Sn; Ge; Pb) with a group 14 element in the center. All complexes have been characterized by multinuclear NMR spectroscopy, EA, HR-MS spectrometry, and SCXRD in the case of the germanium compound. In the case of lead, we observed reduction of Pb(IV) to Pb(II) with oxidation of the ligand. The resulting Pb(II) products were isolated and characterized. Their tendency for aggregation is pronounced, and reaction with donor molecules such as pyridine or 1,3,4,5-tetramethylimidazol-2-ylidene yields adducts, albeit without deaggregation of the polymeric plumbylene in the solid state. For the stable germanes (t-BuC₆H₃(S)(Ch))₂Ge with (Ch = S, Se), additional attempts to achieve chiral resolution were explored using high-performance liquid chromatography (HPLC).