Geometrical isomerization of penta-1,3-diene catalyzed by cobalt

Cobalt powder and alumina-supported cobalt catalyze the reaction: cis-penta-1,3-diene⇌trans-penta-1,3-diene. Molecular hydrogen is not required as a reactant. Isomerization takes place at temperatures above 75°C, no other isomers of pentadiene have been detected, and self-hydrogenation is negligible. The isomerization of isotopically labelled cis-penta-1,3-diene at 160°C is described in detail. The results are consistent with a mechanism in which the first step is the dissociation of the diolefin by loss of hydrogen from the methyl group, and the overall process is the 1 : 5-transfer of hydrogen.