Gas-phase reactivity of ionic iron complexes: comparison with solution chemistry

Unimolecular Double Photoionization-Induced Processes in Iron Pentacarbonyl

The dissociations of nascent Fe(CO)₅⁺⁺ ions created by 40.81 eV photoionization of iron pentacarbonyl have been examined using threefold and fourfold electron–ion coincidence measurements. The energies and forms of the ions have been explored by high-level calculations, revealing several new structures. The most stable form of Fe(CO)₅⁺⁺ has a quite different geometry from that of the neutral molecule. The dissociation pattern can be modeled as a sequence of CO evaporations followed by two-body charge separations. Each Fe(CO)_n⁺⁺ (n = 1–4) dication is stable in a restricted energy range; as its internal energy increases, it first ejects a neutral CO, then loses CO⁺ by charge separation at higher energy. In the initial stages, charge-retaining CO evaporations dominate over charge separation, but the latter become more competitive as the number of residual CO ligands decreases. At energies where ionization is mainly from the CO ligands, new Fe–C and C–C bonds are created by a mechanism which might be relevant to catalysis by Fe.

Dissociations of nascent Fe(CO)₅⁺⁺ ions by sequential CO evaporations, leading (in restricted energy ranges) to stable Fe(CO)_n⁺⁺ (n = 1−4) dicationic species. At energies where ionization is mainly from the CO ligands, new Fe−C and C−C bonds are created by a mechanism which might be relevant to catalysis by Fe.

Reactivity from excited state (4)FeO(+) + CO sampled through reaction of ground state (4)FeCO(+) + N2O

The kinetics of the FeCO(+) + N2O reaction have been studied at thermal energies (300-600 K) using a variable temperature selected ion flow tube apparatus. Rate constants and product branching fractions are reported. The reaction is modestly inefficient, proceeding with a rate constant of 6.2 × 10(-11) cm(3) s(-1) at 300 K, with a small negative temperature dependence, declining to 4.4 × 10(-11) cm(3) s(-1) at 600 K. Both Fe(+) and FeO(+) products are observed, with a constant branching ratio of approximately 40:60 at all temperatures. Calculation of the stationary points along the reaction coordinate shows that only the ground state quartet surface is initially sampled resulting in N2 elimination; a submerged barrier along this portion of the surface dictates the magnitude and temperature dependence of the total rate constant. The product branching fractions are determined by the behavior of the remaining (4)OFeCO(+) fragment, and this behavior is compared to that found in the reaction of FeO(+) + CO, which initially forms (6)OFeCO(+). Thermodynamic and kinetic arguments are used to show that the spin-forbidden surface crossing in this region is efficient, proceeding with an average rate constant of greater than 10(12) s(-1).

Reactions of metal cluster anions with inorganic and organic molecules in the gas phase

Progress on the activation and transformation of important inorganic and organic molecules by negatively charged bare metal clusters as well as ligated systems with oxygen, carbon, and nitrogen, among others.

Iron-Promoted C-C Bond Formation in the Gas Phase

An unusual iron transfer and carbon-carbon coupling take place in gas-phase ionized mixtures containing ferrocene and dichloromethane. Ferrous chloride and the protonated benzenium ion are eventually formed by a thermal and efficient reaction, through stable intermediates that undergo a remarkable reorganization. The mechanism of the concerted iron extrusion, carbon-chlorine bond activation and carbon-carbon bond formation is elucidated by electronic structure calculations that show the crucial role of iron.

The dehydrogenation of alcohols and hydrocarbons by atomic metal anions

The reactivity of anionic metal-carbonyl systems toward hydrocarbons, alcohols and a variety of other classes of molecules is well established in the literature. In this study we explored the reactions of atomic metal anions M(-), notably K(-), Cs(-), Co(-), Fe(-), Cu(-) and Ag(-), with alcohols, alkanes, alkenes and alkynes. All of the metal anions deprotonated the alcohols and alkynes. Also observed were the subsequent reactions of the resulting organic anions. Fe(-) and Cu(-) consistently displayed mono- and bis-dehydrogenation of primary and secondary alcohols, and alkanes, alkenes and alkynes to form MH(-) and MH(2)(-). Mechanisms for the dehydrogenation reactions are proposed and substantiated with isotopically-labelled reagents and thermochemical arguments.

Astrochemistry of transition metals? The selected cases of [FeN]+, [FeNH]+ and [(CO)2FeN]+: pathways toward CH3NH2 and HNCO

Transition metals are proposed to play an active role in the synthesis of organic compounds containing heteroatoms in astrochemistry.

Gas-phase ion thermochemistry in organometallic systems

This review represents a general overview on the determination of bond energies in gas-phase organometallic systems. The paper focuses on articles published in the last 7 years, whose main scope was to experimentally measure metal ion-ligand binding energies. Therefore, studies of reactivity and characterization of ion complexes are not included, even if some of them display bond energies among the data measured. Bond energies are presented according to the metal ion complexed, in increasing order of atomic number. Periodic trends of binding energies and correlations among the various ligand are discussed. A brief summary of the most used techniques specifically devoted to gather bond energies is also provided.

Tandem time-of-flight experiment for low energy collision studies

We present an experiment adapted to collisional studies of cluster ions based on a laser vaporization setup coupled to a supersonic expansion. The ions are selected in a first time-of-flight, slowed down to the desired energy, and collided in an octopolar guide. The parent and fragment ions are then reaccelerated in order to be mass analyzed in a reflectron time-of-flight. An original method for the extraction of the ion that uses a double voltage pulse, is proposed. The experiment has been applied to collisions of hydrated cobalt ions. An absolute cross section of 17 A2 for the loss of one water molecule by Co(H2O)2+ in collision with neon at a center-of-mass energy of 10 eV, has been determined, with an accuracy of 10%. The threshold for this reaction has been measured at 1.5 eV and is in good agreement with the existing literature (Dalleska et al. J. Am. Chem. Soc. 1994, 116, 3519). Ions that cannot be formed by conventional ligand exchange methods, can also be studied. As an example, the threshold for dehydration of the Co2(H2O)+ ion has been measured at 1.5 +/- 0.2 eV.