Intrinsic coordination properties of iron: Gas-phase ligation of ground-state Fe+ with alkanes, alkenes, and alkynes and intramolecular interligand interactions mediated by Fe+

The kinetics and mode of coordination of the electronic ground state Fe+(D-6) have been investigated in the gas phase with the organic molecules methane, ethane, propane, butane, ethylene, allene, propene, 1,3-butadiene, isobutene, acetylene, propyne, and diacetylene. Reaction rate coefficients and product distributions for sequential ligation were measured with the selected-ion flow tube (SIFT) technique operating at 294 +/- 3 K and a helium buffer-gas pressure of 0.35 +/- 0.01 Torr. Also, bond connectivities in the ligated species were probed with multicollision-induced dissociation (CID) experiments. Rates of ligation with a single ligand were found to increase with an increasing number of degrees of freedom, or size, of the ligand and to follow the reactivity order alkynes > alkenes > alkanes. Ligation with at least two, at least three, and at least five molecules was observed with alkanes, alkenes and alkynes, respectively. Possible modes of bonding in the multiply-ligated Fe+ cations are briefly described. The CID results provide evidence for the occurrence of intramolecular interactions between ligands mediated by Fe+, resulting in C-C bond formation in the ligated ions Fe(1,3-C4H6)(4)(+), Fe(C2H2)(3)(+) and Fe(C2H2)(5)(+), Fe(CH3C2H)(2)(+) and Fe(CH3C2H)(4)(+), and Fe(C4H2)(2)(+) and Fe(C4H2)(4)(+). The postulated interligand interactions are attributed to cyclization or oligomerization reactions leading to the formation of benzene, dimethylcyclobutadiene, and diethynylcyclobutadiene in Fe(C2H2)(3)(+),Fe(CH3C2H)(2)(+), and Fe(C4H2)(2)(+), respectively, and the formation of a dimer of 1,3-butadiene in Fe(1,3-C4H6)(4)(+).