Addition of selenium to the nickel(l) complex, [Ni(Me-4[12]aneN(4))(CO)]PF6, effects a redox reaction leading to the diselenido dinickel(II) complex, {[(Ni(Me-4[12]aneN(4))](2)(Se-2)}(PF6)(2), in 70% crystalline yield. The product's structure features a mu-eta(2):eta(2)-Se-2 ligand with Se-Se bond length of 2.379(13) angstrom. Upon mild heating, {[(Ni(Me-4[12]aneN(4))](2)(mu-eta(2):eta(2)-Se-2)}(PF6)(2) oxidizes 9,10-dihydroanthracene or 1,4-cyclohexadiene forming the terminal hydroselenide, [Ni(Me-4[12]aneN(4))(SeH)PF6, and anthracene or benzene, respectively. [Ni(Me-4[12]aneN(4))(SeH)]PF6 cleanly converts back to the diselenido dinickel(II) adduct upon addition of a phenoxy radical.