Abstract A series of acetylene-alcohol dicobalt hexacarbonyls was prepared from acetylene-alcohols and dicobalt octacarbonyl. The reactivity towards aqueous sulfuric acid in boiling methanol was investigated. From the ethynyl carbinol complexes, R1R2C(OH)C≡CH·Co2(CO)6, trinuclear cobalt complexes, R1R2CHCH2CCo3(CO)9, were obtained accompanying the reduction of C-OH to a C-H moiety. On the other hand, from the butynediol complexes, R1R2C(OH)C≡CC(OH)R1R2·Co2(CO)6, binuclear cobalt complexes, R1R2CHC≡CCHR1R2·Co2(CO)6, or 1,1,4,4-tetraphenyl-1,3-butadiene were obtained. The structures of all these compounds have been confirmed by analytical measurements and by a study of their absorption spectra.