Dynamic Au-C sigma-Bonds Leading to an Efficient Synthesis of [n]Cycloparaphenylenes (n = 9-15) by Self-Assembly

The transmetalation of the digold(I) complex [Au2Cl2(dcpm)] (1) (dcpm = bis(dicydohexylphosphino)-methane) with oligophenylene diboronic acids gave the triangular macrocydic complexes [Au-2(C6H4)(x)(dcpm)](3) (x = 3, 4, 5) with yields of over 70%. On the other hand, when the other digold(I) complex [Au2Cl2(dppm)] (1') (dppm = bis(diphenylphosphino)-methane) was used, only a negligible amount of the triangular complex was obtained. The control experiments revealed that the dcpm ligand accelerated an intermolecular Au(I)-C sigma-bond-exchange reaction and that this high reversibility is the origin of the selective formation of the triangular complexes. Structural analyses and theoretical calculations indicate that the dcpm ligand increases the electrophilicity of the Au atom in the complex, thus facilitating the exchange reaction, although the cyclohexyl group is an electron-donating group. Furthermore, the oxidative chlorination of the macrocydic gold complexes afforded a series of [n]cycloparaphenylenes (n = 9, 12, 15) in 78-88% isolated yields. The reorganization of two different macrocydic Au complexes gave a mixture of macrocyclic complexes incorporating different oligophenylene linkers, from which a mixture of [n]cycloparaphenylenes with various numbers of phenylene units was obtained in good yields.