EXPERIMENTAL AND THEORETICAL-STUDIES OF FEC7H7- FE+-C7H7 BOND-ENERGIES AND ISOMERIC DIFFERENTIATION( ISOMERS )

Three isomeric structures of Fe(C7H7)(+) presumably, Fe(tropylium)(+), Fe(benzyl)(+), and Fe(tolyl)(+), are studied with Fourier transform i on cyclotron resonance (FTICR) mass spectrometry and by theoretical ca lculations. Of particular interest is the role of the metal in stabili zing the tolyl ligand, given that the unmetallated tolyl ion, C6H4CH3, rearranges to benzyl ion on the time scale of the FTICR experiment. Ions with the empirical formula Fe(C7H7)(+) were generated by three sy nthetic routes: (1) reaction of bare metal Fe+ with cycloheptatriene, (2) reaction of Fe(phenyl)(+) with toluene, and (3) reaction of Fe(ben zyne)(+) with methyl iodide. The hypothesis is that these three reacti ons result in the formation of Fe(tropylium)(+), Fe(benzyl)(+) and Fe( tolyl)(+), respectively. Energy resolved collision-induced dissociatio n, photodissociation, and selected ion/molecule reactions readily dist inguish Fe(tropylium)(+) from the other two structures. Fe(benzyl)(+) and Fe(tolyl)(+), however, are indistinguishable by collision-induced dissociation and photodissociation, but exhibit differences in reactiv ity with selected reagents. These results indicate that while Fe stabi lizes the tolyl ion structure, upon activation the ion can rearrange t o the benzyl structure. From photodissociation experiments we infer D degrees(Fe+-benzyl) = 63 +/- 5 kcal mol(-1), D degrees(Fe+-tolyl) = 83 +/- 10 kcal mol(-1), and an upper limit of D degrees(Fe+-cycloheptatr ienyl) less than or equal to 129 +/- 5 kcal mol(-1), while ion-molecul e reactions yield the lower limits D degrees(Fe+-benzyl) > 55 +/- 5 kc al mol(-1), D degrees(Fe+-tolyl) > 60 +/- 5 kcal mol(-1) and D degrees (Fe+-cycloheptatrienyl) > 73 kcal mol(-1). These results are self-cons istent and in general agreement with ab initio calculations which yiel d D degrees(Fe+-cycloheptatrienyl) = 86.8 kcal mol(-1), D degrees(Fe+- tolyl) = 84.4 kcal mol(-1), and D degrees(Fe+-benzyl) = 69.4 kcal mol( -1).