REACTIVITY TUNING BY LIGAND EFFECTS - GAS-PHASE REACTIONS OF FE(C6H6)O+ VERSUS BARE FEO+

The presence of a benzene ligand in Fe(C6H6O+ (1) has a profound effect on the gas-phase reactivity of FeO+. While the latter oxide is known to act as an efficient C-H/C-C bond-activation reagent, the ligated species 1 is entirely unreactive in that respect. However, 1 serves as an excellent reagent for transferring oxygen to various olefins. In addition, it is demonstrated that the ligand substitution Fe(C6H6O+ + X --> Fe(XO+ + C6H6 follows two principally different pathways. For X = C6D6 and C5H5N the traditional direct substitution process with attack at the metal centre is operative. However, for X = olefins it is argued that the olefin will not initially attack the metal center; rather, the reaction commences by coordinating the olefin X to the oxygen atom of Fe(C6H6)(+)/OX, thus bringing about an epoxidation of the olefin rather than ketone formation.