Dramatic ligand effects on gas-phase transition-metal reactivity and selectivity: Studies of Fe+, Fe+(H2O), and Fe+(CO) with propane

The kinetic energy dependent reactions of ligated iron ions (FeL+) with propane are examined using a guided ion beam mass spectrometer. In analogy with previous observations for atomic iron ions, propane reacts with both Fe+(H2O) and Fe+(CO) by dehydrogenation to form LFe+(C3H6) and by demethanation to form. LFe+(C2H4) in exothermic processes. These processes are barrierless in all cases except demethanation by Fe+(CO). Dramatic changes in the overall reactivity anal selectivity are observed upon ligation. Fe+(H2O) has a reactivity at thermal energies comparable to that of Fe+(D-6) and about two orders of magnitude larger than that of Fe+(CO). Atomic iron ions form Fe+(C2H4) three times more efficiently than Fe+(C3H6), while demethanation is favored by a factor of about 25 for reaction of Fe+(H2O), and for Fe+(CO) dehydrogenation is preferred by over an order of magnitude. Although a definitive explanation of these interesting results is not yet available, several factors that play influential roles are discussed.