[9]Cycloparaphenylene: Nickel-mediated Synthesis and Crystal Structure

Nickel-mediated synthesis of [9]cycloparaphenylene ([9]CPP) is described. L-shaped diphenylcyclohexane monomers underwent cyclotrimerization under the influence of [Ni(cod)2]/bipy. X-ray crystal-structure analysis and VT NMR analysis of the thus-formed cyclic trimer confirmed its triangle structure and interesting cyclohexane-flipping behavior in solution. Cyclic trimer was converted to [9]CPP by acid-mediated aromatization. The first X-ray crystal structure of [9]CPP is also described.