Montero-Campillo MM, Rodríguez-Otero J, Cabaleiro-Lago EM. An alternative mechanism to explain the ruthenium(II)-catalyzed [2 + 2 + 2] cycloaddition of 1,6-diynes and tricarbonyl compounds. J Phys Chem A. 2009 Aug 13;113(32):9180–4. doi: 10.1021/jp900962d. PMID: 19610598.