Dehydrogenation of Ethane by CpM+ (M = Fe, Co, Ni) in the Gas Phase. An FT-ICR-MS Study

Dehydrogenation and demethanation of 2-methylpropane and propane in the gas-phase by the 16-electron complex [Ru(bipy)2(CO)]2+* chemically activated by the association of [Ru(bipy)2]2+ and CO

The reactions of [Ru(bipy)(2)](2+) with 2-methylpropane, propane, and propene have been investigated in the ICR cell of a mass spectrometer. In these reactions, the association of one molecule of each hydrocarbon was observed. When [Ru(bipy)(2)](2+) was ligated with CO, and the newly formed [Ru(bipy)(2)(CO)](2+) was allowed to react with 2-methylpropane and propane both dehydrogenation and demethanation were observed among association and substitution products. Density functional calculations were used to help elucidate the mechanism and the energy requirement for the dehydrogenation and demethanation reactions of 2-methylpropane mediated by [Ru(bipy)(2)(CO)](2+)*. These very interesting elimination reactions of [Ru(bipy)(2)(CO)](2+) are attributed to a hot 16-electron intermediate, [Ru(bipy)(2)(CO)](2+)*, formed upon ligation of [Ru(bipy)(2)](2+) with CO which has no efficient means of dissipating its internal energy in the low-pressure confines of the ICR cell. The reactions were concluded to occur via a concerted elimination mechanism rather than by oxidative addition/reductive elimination following the dissociation of one Ru-N bond.

Methane activation by MH+ (M = Os, Ir, and Pt) and comparisons to the congeners of MH+ (M = Fe, Co, Ni and Ru, Rh, Pd)

The mechanism of ligated-transition-metal- [MH(+) (M = Os, Ir, and Pt)] catalyzed methane activation has been computed at the B3LYP level of density functional theory. The B3LYP energies of important species on the potential energy surfaces were compared to CCSD(T) single-point energy calculations. Newer kinetic and dispersion-corrected methods such as M05-2X provide significantly better descriptions of the bonding interactions. The reactions take place more easily along the low-spin potential energy surface. The minimum-energy pathway proceeds as MH(+) + CH(4) → M(H)(2)(CH(3))(+) → TS → MH(CH(2))(H(2))(+) → MH(CH(2))(+) + H(2). The ground states are (5)Π, (4)Σ(-), and (1)Σ(+) for OsH(+), IrH(+), and PtH(+), respectively. The energy level differences of the reactants between the high- and low-spin states gradually become smaller from OsH(+) to PtH(+), being 30.66, 9.17, and 0.09 kcal/mol, respectively. The C-H bond can be readily activated by MH(+) (M = Os, Ir, and Pt) with a negligible barrier in the low-spin state; thus, OsH(+), IrH(+), and PtH(+) are likely to be excellent mediators for the activition of the C-H bond of methane. H(2) elimination is quite facile without barriers in the presence of excess reactants. The products of the reactions of MH(+) (M = Os, Ir, and Pt) + methane are all carbene complexes MH(CH(2))(+). The exothermicities of the reactions are 3.99, 15.66, and 12.14 kcal/mol, respectively. The results for MH(+) (M = Os, Ir, and Pt) are compared with those for the first- and second-row congeners, and the differences in behavior and mechanism are discussed.

Reactive MALDI mass spectrometry: application to high mass alkanes and polyethylene

A molecular solid of fullerene (C(60)) intercalated with cobalt cyclopentadienyl dicarbonyl (CoCp(CO)(2)) was shown to be an effective matrix for matrix-assisted laser desorption/ionization mass spectrometry (MALDI) of large alkanes (demonstrated up to C(94)H(190)) and polyethylenes that otherwise cannot be produced as intact ions in the gas phase.

Thermochemistry, bonding, and reactivity of Ni+ and Ni2+ in the gas phase

In this review, we present a general overview on the studies carried out on Ni(+-)- and Ni(2+)-containing systems in the gas phase since 1996. We have focused our attention in the determination of binding energies in parallel with an analysis of the structure and bonding of the complexes formed by the interaction of Ni(+) with one ligand, or in clusters where this metal ion binds several identical or different ligands. Solvation of Ni(2+) by different ligands is also discussed, together with the theoretical information available of doubly charged Ni-containing species. The final section of this review is devoted to an analysis of the gas-phase uni- and bimolecular reactivity of Ni(+) and Ni(2+) complexes.

Gas-phase ion chemistry in organometallic systems

This review essentially deals with positive ion/molecule reactions occurring in gas-phase organometallic systems, and encompasses a period of time of approximately 7 years, going from 1997 to early 2004. Following the example of the excellent review by Eller & Schwarz (1991; Chem Rev 91:1121-1177), in the first part, results of reaction of naked ions are presented by grouping them according to the neutral substrate, while in the second part, ligated ions are grouped according to the different ligands. Whenever possible, comparison among similar studies is attempted, and general trends of reactivities are evidenced.

Laser-Induced Acoustic Desorption/Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Petroleum Distillate Analysis

Laser-induced acoustic desorption (LIAD) coupled with a 3-T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR) allows the simultaneous analysis of both the nonpolar and polar components in petroleum distillates. The LIAD/FT-ICR method was validated by examining model compounds representative of the various classes of polar and nonpolar hydrocarbons commonly found in petroleum. LIAD successfully desorbs all the compounds as intact neutral molecules into the FT-ICR. Electron ionization (EI) at low energies (10 eV) and chemical ionization using cyclopentadienyl cobalt radical cation (CpCo*+) were employed to ionize the desorbed molecules. The EI experiments lead to extensive fragmentation of many of the hydrocarbon compounds studied. However, the CpCo*+ ion ionizes all the hydrocarbon compounds by producing only pseudomolecular ions without other fragmentation, with the exception of one compound (*CH3 loss occurs). Examination of two different petroleum distillate samples revealed hundreds of compounds. The most abundant components have an even molecular weight; i.e., they are likely to contain no (or possibly an even number of) nitrogen atoms.

Analysis of saturated hydrocarbons by using chemical ionization combined with laser-induced acoustic desorption/Fourier transform ion cyclotron resonance mass spectrometry

Laser-induced acoustic desorption (LIAD), combined with chemical ionization by the cyclopentadienyl cobalt radical cation (CpCo.+), is demonstrated to facilitate the analysis of saturated hydrocarbons by Fourier transform ion cyclotron resonance mass spectrometry. The LIAD/CpCo.+ method produces unique pseudomolecular ions for alkanes from C(24)H(50) to C(50)H(102). These alkanes were tested individually and in artificial mixtures of up to seven components. Only one product ion, [R + CpCo - 2H(2)].+, was detected for each alkane (R). The product ions' relative abundances correspond to the relative molar concentration of each alkane in mixtures. These findings provide a solid groundwork for the future application of this method for hydrocarbon polymer analyses.

Molecular mass determination of saturated hydrocarbons: reactivity of eta5-cyclopentadienylcobalt ion (CpCo*+) and linear alkanes up to C-30

The present study demonstrates the feasibility of the eta5-cyclopentadienylcobalt ion (CpCo*+) as a suitable cationization reagent for saturated hydrocarbon analysis by mass spectrometry. Ion/molecule reactions of CpCo*+ and three medium chain-length n-alkanes were examined using Fourier-transform ion cyclotron resonance mass spectrometry. Second-order rate constants and reaction efficiencies were determined for the reactions studied. Loss of two hydrogen molecules from the CpCo-alkane ion complex was found to dominate all reactions ( > or = 80%). Furthermore, this dehydrogenation reaction efficiency increases with increasing chain length. These preliminary results suggest that the CpCo*+ ion may be a promising cationization reagent of longer chain saturated hydrocarbons and polyolefins.

Density functional study of the retrocyclization of norbornadiene and norbornene catalyzed by Fe(+)

In the presence of Fe(+) catalyst, the retro Diels-Alder reaction of norbornadiene (NBD) is predicted to be stepwise with an activation barrier of 18.8 kcal/mol, which is 3.1 kcal/mol lower than the concerted retro reaction. For norbornene (NBN), the Fe(+)-catalyzed retro reaction is also calculated to be stepwise with an activation barrier of 24.9 kcal/mol, which is 8.5 kcal/mol lower than the uncatalyzed stepwise reaction but 3.8 kcal/mol higher than the concerted reaction. The intermediates from the NBD and NBN retro Diels-Alder reactions, C(5)H(6)FeC(2)H(2)(+) and C(5)H(6)FeC(2)H(4)(+), are predicted to have low activation barriers for ligand-to-ligand hydrogen transfers (through an iron-hydrido intermediate) to form CpFeC(2)H(3)(+) and CpFeC(2)H(5)(+) and, ultimately, vinyl- and ethyl-substituted cyclopentadiene-iron complexes, respectively. In contrast to FeC(2)H(2)(+) and FeC(2)H(4)(+), the lowest-energy pathways on the C(5)H(6)FeC(2)H(2)(+) and C(5)H(6)FeC(2)H(4)(+) potential energy surfaces involve only one multiplicity (quartet). The C(2)H(2) and C(2)H(4) complexes of CpFe(+) and C(5)H(6)Fe(+) are compared.

Reactions of first-row transition metal ions with propargyl alcohol in the gas phase

The gas-phase reactions with propargyl alcohol (PPA) of all the singly charged ions of the first-row transition metals, generated by laser ablation in an external ion source, were studied by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS.). The reactivities of the metal ions change irregularly across the periodic table, and the reactivity of each ion is a function of its electronic configuration and corresponding metal-oxygen (M-O) bond energies. The 10 metal ions were classified into three categories according to their reactivities: Sc(+), Ti(+) and V(+) are the most reactive ions which react with PPA to give many kinds of oxygen-rich products due to stronger M-O bonds; Fe(+), Co(+) and Ni(+) are less reactive; Cr(+), Mn(+), Cu(+) and Zn(+) are the most unreactive ions, due to the half and completely occupied valence electronic configurations. The order of reactivity is Ti(+) > V(+) > Sc(+) >> Co(+) > Fe(+) approximately Ni(+) > Zn(+) > Cr(+) approximately Mn(+) approximately Cu(+).

Self-chemical ionization of diethylzinc

The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd.