Gase-Phase Organometallic Catalysis: Kinetics and Mechanism of the Hydrogenation of Ethylene by Fe(CO)3(C2H4)2

Article abstract of DOI:10.1021/ja00260a004

Inert homogeneous gas-phase mixtures of ethylene and hydrogen plus a catalytic amount of Fe(CO)5 are transformed into active ethylene hydrogenation systems upon irradiation by near-UV light from a pulsed nitrogen laser.Organometallic species present in the active catalytic mixture are identified and monitored by Fourier transform infrared spectroscopy.The catalyzed reaction is followed by gas chromatography, which provides a measure of ethylene and hydrogenated product concentrations.The catalytic process is efficient in its use of light, with typical room temperature quantum yields (product ethane molecules formed per photon absorbed) of 20 or more.The absorbed laser light generates a reservoir of Fe(CO)3(C2H4)2, which thermally dissociates by losing one highly labile ethylene to yield the active catalyst, Fe(CO)3(C2H4).When the photolysis light is removed, catalytic activity is observed to decline as the catalyst combines with free CO to form stable Fe(CO)4(C2H4).The rate of organic product formation is directly proportional to the catalyst reservoir concentration.Quantum efficiency of ethane production and the rate of Fe(CO)3(C2H4)2 decay are studied as functions of ethylene, hydrogen, CO, and Fe(CO)5 pressures.The results provide information on the mechanism of catalysis, as well as elementary rate parameters for many of the organometallic reactions.