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The photoinduced reactions on mass-selected complexes of Mg(super .+) with tri- and tetrasubstituted benzene by F and/or CH3 are examined. The subsequent decomposition of the benzyne radical cations is discussed.

Density functional theory has been used to probe the mechanism of gas-phase methanol decomposition by bare Fe(+) and ligated Fe(C(2)H(4))(+) in both quartet and sextet states. For the Fe(+)/methanol system, Fe(+) could directly attach to the O and methyl-H atoms of methanol, respectively, forming two encounter isomers. The methanol reaction with Fe(+) prefers initial C-O bond activation to yield methyl with slight endothermicity, whereas CH(4) elimination is hindered by the strong endothermicity and high-energy barrier of hydroxyl-H shift. For the Fe(C(2)H(4))(+)/methanol system, the major product of H(2)O is formed through six elementary steps: encounter complexation, C-O bond activation, C-C coupling, β-H shift, hydride H shift, and nonreactive dissociation. Both ligand exchange and initial C-O bond activation mechanisms could account for ethylene elimination with the ion products Fe(CH(3)OH)(+) and (CH(3))Fe(OH)(+), respectively. With the assistance of a π-type C(2)H(4) ligand, the metal center in the Fe(C(2)H(4))(+)/CH(3)OH system avoids formation of unfavorable multi-σ-type bonding and thus greatly enhances the reactivity compared to that of bare Fe(+).

The activation of ethanol and methanol by VO2(+) in gas phase has been theoretically investigated by using density functional theory (DFT). For the VO2(+)/ethanol system, the activation energy (ΔE) is found to follow the order of ΔE(C(β)-H) < ΔE(C(α)-H) ≈ ΔE(O-H). Loss of methyl and glycol occurs respectively via O-H and C(β)-H activation, while acetaldehyde elimination proceeds through two comparable O-H and C(α)-H activations yielding both VO(H2O)(+) and V(OH)2(+). Loss of water not only gives rise to VO(CH3CHO)(+) via both O-H and C(α)-H activation but also forms VO2(C2H4)(+) via C(β)-H activation. The major product of ethylene is formed via both O-H and C(β)-H activation for yielding VO(OH)2(+) and VO2(H2O)(+). In the methanol reaction, both initial O-H and C(α)-H activation accounts for formaldehyde and water elimination, but the former pathway is preferred.

The potential energy surface (PES) corresponding to the Co(+)-mediated oxidation of ethane by N(2)O has been investigated by using density functional theory (DFT). After initial N(2)O reduction by Co(+) to CoO(+), ethane oxidation by the nascent oxide involves C-H activation followed by two possible pathways, i.e., C-O coupling accounting for ethanol, Co(+)-mediated β-H shift giving the energetically favorable product of CoC(2)H(4)(+) + H(2)O, with minor CoOH(2)(+) + C(2)H(4). CoC(2)H(4)(+) could react with another N(2)O to yield (C(2)H(4))Co(+)O, which could subsequently undergo a cyclization mechanism accounting for acetaldehyde and oxirane and/or a direct H-abstraction mechansim for ethenol. Loss of oxirane and ethenol is hampered by respective endothermicity and high kinetics barrier, whereas acetaldehyde elimination is much energetically favorable. CoOH(2)(+) could facilely react with N(2)O to form OCoOH(2)(+), rather than Co(OH)(2)(+) or CoO(+).

The potential energy surfaces of Mn(+) reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO(+), MnO, MnCH(2)(+), MnCH(3), and MnH(+) are described in detail. Two types of encounter complexes of Mn(+) with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn(+) would insert into a C-O bond or the C-C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO(+)/MnO and MnH(+) are formed in the C-O activation mechanism, while both C-O and C-C activations account for the MnCH(2)(+)/MnCH(3) formation. Products MnO(+), MnCH(2)(+), and MnH(+) could be formed adiabatically on the quintet surface, while formation of MnO and MnCH(3) is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a(5)D is calculated to be more reactive than the ground state a(7)S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations.

The gas-phase reaction mechanisms of methylamine (MA) with the ground-state Co(+)((3)F) and Ni(+)((2)D) are theoretically investigated using density functional theory at both the B3LYP/6-311++G(d,p) and B3LYP/6-311++G(3df,2p) levels. The reactions for hydride abstraction and dehydrogenation are analyzed in terms of the topology of potential energy surfaces (PESs). Co(+) and Ni(+) perform similar roles along the isomerization processes to the final products. Hydride abstraction takes place via the key species of metal cation-methyl-H intermediate, followed by a charge transfer process before the direct dissociation of CH(2)NH(2)(+)···MH (M = Co, Ni). The enthalpies of reaction, stability of metal cation-methyl-H species, and competition between different channels account for the sequence of the hydride abstraction products: CoH < NiH < CuH. The most competitive dehydrogenation route occurs through a stepwise reaction, consisting of initial C-H activation, amino-H shift, and direct dissociation of the precursor CH(2)NHM(+)···H(2). This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanisms of amine prototype with late first-row transition metal cations.

We report herein a comprehensive theoretical study of the oxidation of propane by FeO(+) on both the sextet and quartet potential energy surfaces (PESs) using density functional theory. The geometries and energies of all the stationary points involved are located. Interaction of FeO(+) with propane could account for four types of encounters (i.e., alpha,beta,gamma-, 2alpha,beta-, 3alpha-eta(3), and 2alpha,2gamma-eta(4)) complexes. Various mechanisms leading to the loss of CH(3), H(2)O, C(3)H(7)OH (H(2)O + C(3)H(6)), and C(3)H(6) are analyzed in terms of the topology of the PES. The reaction of FeO(+) with propane involves initial C-H activation, while initial C-C activation is indeed unlikely to be important. The loss of CH(3) takes place adiabatically on the sextet PES via the simple C(alpha)-to-O H shift from eta(4)-OFe(+)(C(3)H(8)) followed by CH(3) shift. The C(3)H(7)OH elimination proceeds via direct C(alpha)-to-O H shift followed by C-O coupling, while the loss of H(2)O, C(3)H(6), and (H(2)O + C(3)H(6)) proceeds via the alpha,beta-H and beta,alpha-H abstraction mechanisms from all the eta(3) complexes. The most favorable channel is the alpha,beta-H abstraction mechanism for the H(2)O loss because it not only is energetically and dynamically favorable but also has a high crossing probability between the sextet and quartet PESs. The computational results are in concert with the available experimental information and add new insight into the details of the individual elementary steps.

Molecular geometries, electronic structures, and optical absorption spectra were investigated using density functional theory (DFT) at the B3LYP/6-31G(d) and B3LYP/DZVP levels for [CuL(2)](+) and [CuL(2)][PF(6)] (L = 6,6'-dimethyl-2,2'-bipyridine-4,4'-dimethylformate), both in the gas phase and in methyl cyanide (MeCN) solution. The vertical excitation energies were calculated within the framework of the time-dependent DFT (TD-DFT) approach, whereas the solvent effects were taken into account using the polarizable continuum model (C-PCM). Our results show that the five highest occupied molecular orbitals (HOMOs) are composed of a set of distorted degenerate Cu 3d orbitals, whereas the four lowest unoccupied molecular orbitals (LUMOs) are the bipyridine ligand pi*(C horizontal lineN) orbitals. The spectra in the range of 400-600 nm were found to originate from metal-to-ligand charge-transfer (MLCT) transitions, whereas the spectra in the range of 350-400 nm are excitations mainly from the metal Cu 3d orbitals to the carboxyl pi* orbitals. The solvent effects lead to changes in both the geometries and the absorption spectra. The results of this work suggest that copper-based complexes might be effective sensitizers for next-generation dye-sensitized solar cells.

The gas-phase reaction of Ti(+) ((4)F and (2)F) with methanol is investigated using density functional theory. Geometries and energies of the reactants, intermediates, and products involved are calculated. The approach of Ti(+) toward methanol could form either a "classical" O- or a "nonclassical" eta(3)-methyl H-attached complex. The reaction products observed in the experiment (Guo, Kerns, Castleman J. Phys. Chem. 1992, 96, 4879) are produced via the classical association rather than the nonclassical complex. All possible pathways starting with C-O, C-H, and O-H activation are searched. Methane and methyl loss products (TiO(+) and TiOH(+)) are produced via the C-O activation; the O-H activation accounts for the H(2) and H elimination (producing TiOCH(2)(+) and TiOCH(3)(+)); and the C-H activation is unlikely to be important. Through the bond insertion (H shift) reductive elimination mechanism, the products of a closed-shell molecule (H(2) or methane) elimination could take place on both the quartet and doublet PESs owing to a spin inversion occurring in the course of initial bond insertion, whereas only the quartet products are produced adiabatically via the simple bond insertion-reductive elimination mechanism for the loss of a radical-type species (H or CH(3)). The computational results are in concert with the available experimental information and add new insight into the details of the individual elementary steps.

The gas-phase Fe(+)-mediated oxidation of acetylene by N2O on both sextet and quartet potential energy surfaces (PESs) is theoretically investigated using density functional theory. Geometries and energies of all the stationary points involved in the catalytic reaction are located. For the catalytic cycles, the crucial step is the initial N2O reduction by Fe(+) to form FeO(+), in which a direct O-abstraction mechanism is located on the sextet PES, whereas the quartet pathway favors a N-O insertion mechanism. Spin inversion moves the energy barrier for this process downward to a position below the ground-state entrance channel. The second step of the catalytic cycles involves two mechanisms corresponding to direct hydrogen abstraction and cyclization. The former mechanism accounts for the ethynol formation with the upmost activation barrier below the entrance channel by about 5 kcal/mol. The other mechanism involves a "metallaoxacyclobutene" structure, followed by four possible pathways, i.e., direct dissociation, C-C insertion, C-to-O hydrogen shift, and/or C-to-C hydrogen shift. Among these pathways, strong exothermicities as well as energetically low location of the intermediates suggest oxidation to ketene and carbon monoxide along the C-to-C hydrogen shift pathway is the most favorable. Reduction of the CO loss partner FeCH2(+) by another N2O molecule constitutes the third step of the catalytic cycles, which contains direct abstraction of O from N2O giving OFeCH2(+), intramolecular rearrangement to form Fe(+)-OCH2, and nonreactive dissociation. This reaction is also energetically favored considering the energy acquired from the initial reactants.

We report herein a comprehensive study of gas-phase reactions of Co(+) with ethylamine using density functional theory. Geometries and energies for all the stationary points involved in the reactions are investigated at the B3LYP/6-311++G(2df,2pd) level. Six different "classical" N and "nonclassical" ethyl-H attached isomers are found for the Co(+)-ethylamine complexes. The classical complexes are much more stable than the nonclassical ones, which have the complexation energies close to Co(+) complexes with small alkanes. Extensive conversions could occur readily between these encounter complexes. All conceivable reaction pathways from each encounter complex to the experimentally observed products are carefully surveyed, and the most likely reaction mechanisms are derived. Activation of the C(alpha)-H bond of ethylamine by Co(+) through both the classical and nonclassical complexes leads to not only the H2 loss but also the hydride abstraction. The loss of ethylene arises from Co(+) insertion into the polar C-N bond in the classical complexes as well as from C(beta)-H activation through the nonclassical methyl-H attached complex of Co(+)- gauche-ethylamine. CH4 only forms via C-C activation from the nonclassical complex with the metal bound to two Hs from the different carbons. Initial N-H insertion is unlikely to be important. It is the reactions of the nonclassical complexes that closely parallel with the Co(+) + alkane reactions. The theoretical work sheds new light on the title reactions and can serve as a theoretical approach to the reaction mechanisms of transition metal ions with primary amines.

The gas-phase reaction of methyl nitrite with Cu+ has been investigated using density functional theory. The geometries and energies of all the stationary points involved in the reaction have been investigated at the B3LYP/6-311+G(2df,2pd) level. Seven different structures of the encounter complexes could be formed when Cu+ attacking at different electronegative heteroatoms of trans and cis conformational isomers of methyl nitrite, in which the inner oxygen attacks account for the most stable complexes. Extensive conversions could take place for these complexes converting into each other. Various mechanisms leading to the loss of NO and HNO are analyzed in terms of the topology of the potential energy surface. The reaction proceeds exclusively from the inner oxygen attachments, followed by four different mechanisms, i.e., direct dissociation, direct H abstraction, N-O activation, and C-H activation, where the former two provide direct channels for the respective losses of NO and HNO, the third one accounts for both of the losses, and C-H activation is unlikely to be important due to the energetics.

Density functional theory calculations have been carried out to survey the gas-phase reactions of allylamine with Co+. The geometries and bonding characteristics of all the stationary points involved in the reactions have been investigated at the B3LYP/6-311++G(d,p) level. Final energies are obtained by means of the B3LYP/6-311+G(2df,2pd) single-point calculations. The performance of these theoretical methods is valuated with respect to the available thermochemical data. Co+ strongly binds allylamine by forming a chelated structure in which the metal cation binds concomitantly to the two functional groups of the neutral molecule. Various mechanisms leading to the loss of NH3, NH2, C2H2, and H2 are analyzed in terms of the topology of the potential energy surface. The most favorable mechanism corresponds to the loss of NH3, through a process of C-N activation followed by a concerted beta-H shift. The accompanying NH2 elimination is also discussed. The loss of C2H2 is also favorable, through C-C activation and stepwise beta-H shift, giving Co+(NH2CH3) and Co+H(NH2CH2) as the product ions. Various possible channels for the loss of H2 are considered. The most favorable mechanism of the H2 loss corresponds to a pathway through which the metal acts as a carrier, connecting a hydrogen atom from the methylidyne group of allylamine with a hydrogen atom of the terminal methylene group. The product ion of this pathway has a tricoordinated structure in which Co+ binds to the terminal two Cs and N atoms of the NH2CH2CCH moiety.

We report herein a theoretical study of the reaction of acetaldehyde with Ni+ as an extension of our two recent papers on the decarbonylation of acetaldehyde by late first-row transition metal ions [Zhao, Zhang, Guo, Wu, Lu Chem. Phys. Lett. 2005, 414, 28; Zhao, Guo, Zhang, Wu, Lu ChemPhysChem 2006, 7, 1345]. Geometries of all the stationary points involved in the reaction have been fully optimized at the B3LYP/6-311+G(2df,2pd) level and the decarbonylation mechanism is analyzed in terms of the topology of potential energy surface. Combining with the previous studies, it is found that for the Cr+, Co+, and 4Fe+ mediated systems decarbonylation of CH3CHO only takes place via C-C activation, and aldehyde C-H activation is unlikely to be important, whereas both C-C and aldehyde C-H activations by Ni+ and 6Fe+ could result in the decarbonylation of CH3CHO, where hydride-containing species M+(H)(CO)(CH3) is found to be a common minimum along the reaction pathways.

Photoreactions in the gas-phase complexes Mg(*+)(1,4-dioxane) (1) and Mg(*+)(1,3-dioxane) (1M) have been examined in the wavelength region of 230-440 nm. Photoproduct assignments are facilitated with the help of deuterium substitution experiments. The main energy relaxation channel for both photoexcited complexes is the evaporation of Mg(*+). Also observed from 1 are rich photoproducts with m/z 28, 41, 54-58, 67, 69, and 88; the most abundant one at m/z 54 is designated to Mg(*+)(O=CH(2)). In marked contrast, the photolysis of 1M yields only Mg(*+)(O=CH(2)) other than Mg(*+). Density functional calculations are performed to obtain optimized geometries and potential energy surfaces of 1 and 1M. Although Mg(*+)(chair-1,4-C(4)H(8)O(2)) (1a) and Mg(*+)(boat-1,4-C(4)H(8)O(2)) (1b) are comparable in energy, the much better agreement of the experimental action spectrum of Mg(*+)(1,4-C(4)H(8)O(2)) with the calculated absorption spectrum of 1a than with that of 1b indicates the predominance of 1a in the source due to the stability of the chair-1,4-dioxane. For photoreactions, the C-O bond is found to be much more prone to rupture than the C-C bond due to the coordination of O to Mg(+) in the parent complexes. Photoreaction mechanisms are discussed in terms of two key insertion complexes, which rationalize all of the observed photoproducts.