Short-step syntheses and complexation properties of Z,Z-tribenzodidehydro- and all-Z-tribenzo[12]annulenes

Syntheses of all-Z-tribenzo[12]annulenes (1a–c) and Z,Z-tribenzodidehydro[12]annulenes (2a–c) by the reduction of the corresponding tribenzohexadehydro[12]annulenes 3a–c were carried out using a low valent titanium complex generated from Ti(O-i-Pr)4 and i-PrMgCl. The unique structure of the first reduction products 2a–c as well as 1a–c was fully characterized. Complexation of these annulenes with silver(I) ions produces the corresponding silver complexes. Among them, the silver complexes of 2a–c exhibit interesting monomer–dimer equilibrium.