Under H-2 pressure, CoII(dmgBF(2))(2)L-2 (L = H2O, THF) generates a low concentration of an H center dot donor. Transfer of the H center dot onto an olefin gives a radical that can either (1) transfer an H center dot back to the metal, generating an isomerized olefin, or (2) add intramolecularly to a double bond, generating a cyclized radical. Transfer of an H center dot back to the metal from the cyclized radical results in a cycloisomerization. Both outcomes are favored by the low concentration of the cobalt H center dot donor, whereas hydrogenation and cyclohydrogenation are more likely with other catalysts (when the concentration of the H center dot donor is high).