Abstract The hexamethylbenzene ruthenium (II) dimer [{RuCl (μ-Cl)(η 6-C 6 Me 6)}] 2 (5 mol%), tested among a series of ruthenium (II) and ruthenium (IV) complexes, represents an efficient precatalyst source for the dimerization of terminal arylalkynes ArC [TRIPLE BOND] CH [Ar= C 6 H 5, 3, 4, 5-(OMe) 3 C 6 H 2, 4-MeOC 6 H 4, 2-MeOC 6 H 4, 4-MeC 6 H 4, 2, 4, 5- Me 3 C 6 H 2, 4-BrC 6 H 4, 4-ClC 6 H 4, 4-FC 6 H 4, 4-HC ([DOUBLE BOND] O) C 6 H 4, 4 ...