Revisiting the early days of conjugated polyyne synthesis. Syntheses and structures of Bis(triethylsilyl) Polyynediyl Adducts Et3Si(CC)nSiEt3 previously regarded as Unisolable (n = 6, 8, 12)

Abstract

An overview of bis(trialkylsilyl) polyynediyl adducts R₃Si(CC)_nSiR₃ with n ≥ 5 is followed by syntheses of TESC_xTES where x = 8, 12, 16, and 24 (TES = SiEt₃; x = 2n). In a seminal 1972 study, the last three were presented as too unstable to isolate and thus only characterized by UV-visible spectroscopy. Although not a rational route, TESC₂₄TES is consistently obtained from the reaction of trans-(C₆F₅)(p-tol₃P)₂Pt(CC)₅SiEt₃ and crude HC₈TES under Hay oxidative cross coupling conditions. The latter contains some HC₈H and TESC₈TES. Hay oxidative homocouplings of HC₄TES and crude HC₈TES afford TESC₈TES (83%) and TESC₁₆TES (5%). A Cadiot-Chodkiewicz reaction of BrC₄Br and HC₄TES (2 equiv) yields TESC₁₂TES (11%). All of these compounds are crystalline, and the crystal structures of TESC₈TES and TESC₁₆TES are determined. The ¹³C{¹H} NMR and UV-visible properties are also compared.