Thiahelicene Phosphane Derivatives: Chiroptical Properties and Electrochemistry

Tetrathia[7]helicenes (7-TH) are polyconjugated π-systems in which four thiophene rings are orthofused to alternating arene rings to generate a non planar, chiral, stable helix which allows the existence of M and P enantiomers. In the course of our studies on the synthesis of 7-TH phosphorus derivatives as potential innovative chiral ligands in asymmetric organometallic catalysis and organocatalysis, novel 7-TH mono- and diphosphane borane adducts 1 have been synthesized and fully characterized (Figure 1). Enantiopure compounds 1 were obtained by chiral HPLC, and their chiroptical properties were studied by their CD spectra. The structure of some enantiopure boranes 1 was elucidated by X-ray analysis, from which it was possible to assign their absolute configuration. Figure 1 Borane-adducts 1 could be easily converted in the corresponding free phosphanes 2 by treatment with alcohols or amines at 80 °C. The electrochemical properties of this new class of phosphine ligands have been investigated by cyclic voltammetry studies.