Solvent-dependent regiochemical cyclotrimerisation of phenylacetylene with cobalt catalysts containing disulfide ligands: A case study

The intermolecular cobalt-catalysed cyclotrimerisation of phenylacetylene as a benchmark alkyne with [1,2-bis(4-methoxyphenylthio)ethane]cobalt dibromide gave the symmetrical 1,3,5-triphenylbenzene as the major product when dichloromethane was used as the solvent, whereas the unsymmetrical 1,2,4-trisubstituted product was obtained in acetonitrile in quantitative yield. Optimisation of the aromatic and aliphatic disulfide ligands in different solvents is discussed. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).