Transannular interactions in mixed superphanes with one thiophene and one CpCo-stabilized cyclobutadiene ring: Syntheses, structures, and electrochemistry

Superphanes consisting of one thiophene ring and various substituted RCo-stabilized cyclobutadiene (CBD) rings (R = Cp, C5H4(CH3), C-5(CH3)(5), C5H4(Si(CH3)(3)), C5H4(COCH3), 8-12) and one superphane with one thiophene ring and one CpCo-stabilized cyclopentadienone ring (13) were synthesized. The starting point was a tricyclic diyne with a central thiophene ring and two condensed 4-cyclodecynes, 19. Heating of 19 with RCo(COD) yielded 8-12, whereas the heating of 19 with CpCo(CO)(2) gave 13. X-ray structural investigation of 8-13 afforded the geometrical parameters in the solid state. Cyclic voltammetry showed a strong interaction between the thiophene ring and the CpCo-stabilized cyclobutadiene part. This interaction was substantiated by comparison between the CV data of 8-12 and model systems containing only the CpCo(CBD) part.