The reactivity of a co(I)-H-2 complex was extended toward the semihydrogenation of internal alkynes. Under ambient temperatures and moderate pressures of H-2, a broad scope of alkynes were semihydrogenated using a Co-I-N-2 precatalyst, resulting in the formation of trans-alkene products. Furthermore, mechanistic studies using H-1, H-2, and parahydrogen induced polarization (PHIP) transfer NMR spectroscopy revealed cis -hydrogenation of the alkyne occurs first. The Co-mediated alkene isomerization afforded the E-selective products from a broad group of alkynes with good yields and E/Z selectivity.