Knölker’s iron complex is a “green” catalyst that exhibits low toxicity and is abundant in nature. Density functional theory (DFT) was used to explore the highly chemoselective nature of the catalytic hydrogenation of CH2═CHCH2CHO. An outer-sphere concerted hydrogen transfer was found to be the most reasonable kinetic route for the hydrogenation of the olefin. However, the C═C hydrogenation reaction has a high free energy barrier of 28.1 kcal/mol, requiring a high temperature to overcome. By comparison, the CH═O bond concerted hydrogen-transfer reaction catalyzed using Knölker’s iron catalyst has an energy barrier of only 14.0 kcal/mol. Therefore, only the CH═O of CH2═CHCH2CHO can be hydrogenated in the presence of Knölker’s catalyst at room temperature, due to kinetic domination. All computational results were in good agreement with experimental results.