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A combination of gas-phase ion trap multistage mass spectrometry (MS(n)) experiments and density functional theory (DFT) calculations have been used to examine the mechanisms of the sequential decomposition reactions of copper cyanoacetate anions, [(NCCH2CO2)2Cu](-), introduced into the gas-phase via electrospray ionization. Gas phase IR spectroscopy, used to probe the coordination mode of the cyanoacetate ligands, revealed that the initial precursor ions are bound to the Cu via the carboxylate, [NCCH2CO2CuO2CCH2CN], 1. Multistage collision-induced dissociation (CID) of 1 gave sequential losses of CO2 and ethene. DFT calculations suggest that the lowest energy pathways for sequential decarboxylation involve Lewis acid mechanisms in which the binding of the cyanoacetate ligand sequentially rearranges from O to N: [NCCH2CO2CuO2CCH2CN](-) → [NCCH2CO2CuNCCH2CO2](-) → [NCCH2CO2CuNCCH2](-) + CO2 and [NCCH2CO2CuNCCH2](-) → [O2CCH2CNCuNCCH2](-) → [CH2CNCuNCCH2](-) + CO2. Loss of ethene involves sequential rearrangement of the binding of the cyanomethyl carbanion ligands from N to C: [CH2CNCuNCCH2](-) → [NCCH2CuNCCH2](-) → [NCCH2CuCH2CN](-). CH2=CH2 loss then proceeds via a 1,2-dyotropic rearrangement to form [NCCuCH2CH2CN](-) followed by β-cyanide transfer. This study highlights the rich mechanistic possibilities for metal mediated decarboxylation reactions involving ambidentate carboxylate ligands.

Alkynylsilver cations, RC≡CAg2(+) (where R = Me and Ph) have been prepared in the gas phase using multistage mass spectrometry experiments in a quadrupole ion trap mass spectrometer. Two methods were used: (i) electrospray ionisation (ESI) of a mixture of AgNO3 (in MeOH/H2O/acetic acid) and the alkyne carboxylic acid to yield the appropriate silver acetylide cations RC≡CAg2(+), via a facile decarboxylation of the RC≡CCO2Ag2(+) precursor; (ii) ESI of silver acetylides, RC≡CAg, which yields a cluster of the type, [(RC≡CAg)12Ag2Cl](+). Regardless of the method of preparation, these alkynylsilver cations, RC≡CAg2(+), undergo ion-molecule reactions with allyliodide to yield the ionic products Ag2I(+) and [(RC≡CCH2CH=CH2)Ag](+). The CID spectrum of [(PhC≡CCH2CH=CH2)Ag](+) was compared to that of an authentic sample of the silver adduct of 5-phenyl-1-penten-4-yne. Both ions fragment to yield Ag(+) and the radical cation, PhC≡CCH2CH=CH2(+)˙, confirming that C-C bond coupling has taken place in the gas phase. DFT calculations were carried out on these C-C bond coupling reactions for the system R = Me. The reaction is highly exothermic and involves the initial coordination of the allyliodide to both silver atoms, with the iodine coordinating to one atom and the alkene moiety coordinating to the other. The overall mechanism of C-C bond coupling involves oxidative addition of the allyliodide followed by reductive elimination of RC≡CCH2CH=CH2, to ultimately yield two sets of reaction products: (i) Ag2I(+) and RC≡CCH2CH=CH2; and (ii) [(RC≡CCH2CH=CH2)Ag](+) and AgI.

A combination of multistage mass spectrometry experiments and density functional theory (DFT) calculations were used to examine the decarboxylation reactions of a series of metal carboxylate complexes bearing a fixed-charge phosphine ligand, [(O3SC6H4)(C6H5)2PM(I)O2CR](-) (M = Cu, Ag, Au; R = Me, Et, benzyl, Ph). Collision-induced dissociation (CID) of these complexes using an LTQ linear ion mass spectrometer results in three main classes of reactions being observed: (1) decarboxylation; (2) loss of the phosphine ligand; (3) loss of carboxylic acid. The gas-phase unimolecular chemistry of the resultant decarboxylated organometallic ions, [(O3SC6H4)(C6H5)2PM(I)R](-), were also explored using CID experiments, and fragment primarily via loss of the phosphine ligand. Energy-resolved CID experiments on [(O3SC6H4)(C6H5)2PM(I)O2CR](-) (M = Cu, Ag, Au; R = Me, Et, benzyl, Ph) using a Q-TOF mass spectrometer were performed to gain a more detailed understanding of the factors influencing coinage metal-catalyzed decarboxylation and DFT calculations on the major fragmentation pathways aided in interpretation of the experimental results. Key findings are that: (1) the energy required for loss of the phosphine ligand follows the order Ag < Cu < Au; (2) the ease of decarboxylation of the coordinated RCO2 groups follows the order of R: Ph < PhCH2 < Me < Et; (3) in general, copper is best at facilitating decarboxylation, followed by gold then silver. The one exception to this trend is when R = Ph and M = Au which has the highest overall propensity for decarboxylation. The influence of the phosphine ligand on decarboxylation is also considered in comparison with previous studies on metal carboxylates that do not contain a phosphine ligand.

The gas phase fragmentation reactions of eta2 coordinated aldehydes in [VO2(eta2-OCHR)]-, which have previously been shown to play a role in the catalytic oxidation of alcohols to aldehydes, were examined using a combination of isotope labelling experiments and collision induced dissociation in a quadrupole ion trap mass spectrometer. The experimental data were interpreted with the aid of density functional theory calculations (DFT). The types of fragmentation reactions observed depend on the nature of the R group. When R = H, the dominant fragmentation channel involves formation of [VO2H2]-via loss of CO. Minor losses of H2 and CH2O are also observed. When R = Me, loss of H2 is observed to give rise to an ion at m/z 125 corresponding to the formula [V, O3, C2, H2]-. DFT calculations on the [VO2(eta2-OCHR)]- and their CID reaction products have identified minimum energy structures for all reactants and products involved. DFT calculations also provided insights into key intermediates on the potential energy surface associated with these fragmentation reactions, including: [(H2)VO2(CO)]- in the case of R = H; and [HVO2(eta1-OCHCH2)]- in the case of R = Me. The results presented provide insights into potential side reactions occurring during catalysis of alcohols over vanadium oxides, for instance, the over-oxidation of methanol to carbon monoxide.

Aerial pingpong: The lithium acetate enolate anion, the prototypical lithium salt of an alpha-deprotonated carboxylate, was prepared in the gas phase by electrospray ionization (ESI) and collision-induced ionization (CID). Its structure, reactivity, and energetics are presented along with the results of high-level computations.

The homocuprates [MeCuMe]- and [EtCuEt]- were generated in the gas phase by double decarboxylation of the copper carboxylate centers [MeCO2CuO2CMe]- and [EtCO2CuO2CEt]-, respectively. The same strategy was explored for generating the heterocuprates [MeCuR]- from [MeCO2CuO2CR]- (R = Et, Pr, iPr, tBu, allyl, benzyl, Ph). The formation of these organocuprates was examined by multistage mass spectrometry experiments, including collision-induced dissociation and ion-molecule reactions, and theoretically by density functional theory. A number of side reactions were observed to be in competition with the second stage of decarboxylation, including loss of the anionic carboxylate ligand and loss of neutral alkene via beta-hydride transfer elimination. Interpretation of decarboxylation of the heterocarboxylates [MeCO2CuO2CR]- was more complex because of the possibility of decarboxylation occurring at either of the two different carboxylate ligands and giving rise to the possible isomers [MeCuO2CR]- or [MeCO2CuR]-. Ion-molecule reactions of the products of initial decarboxylation with allyl iodide resulted in C-C coupling to produce the ionic products [ICuO2CR]- or [MeCO2CuI]-, which provided insights into the relative population of the isomers, and indicated that the site of decarboxylation was dependent on R. For example, [MeCO2CuO2CtBu]- underwent decarboxylation at MeCO2- to give [MeCuO2CtBu]-, while [MeCO2CuO2CCH2Ph]- underwent decarboxylation at PhCH2CO2- to give [MeCO2CuCH2Ph]-. Each of the heterocuprates [MeCuR]- (R = Et, Pr, iPr, allyl, benzyl, Ph) could be generated by the double decarboxylation strategy. However, when R = tBu, intermediate [MeCuO2CtBu]- only underwent loss of tBuCO2-, a consequence of the steric bulk of tBu disfavoring decarboxylation and stabilizing the competing channel of carboxylate anion loss. Detailed DFT calculations were carried out on the potential energy surfaces for the first and second decarboxylation reactions of all homo- and heterocuprates, as well as possible competing reactions. These reveal that in all cases the first decarboxylation reaction is favored over loss of the carboxylate ligand. In contrast, other reactions such as carboxylate ligand loss and beta-hydride transfer become more competitive with the second decarboxylation reaction.

Thegas-phase protodecarboxylation of acetic acid catalyzed bygroup 10 metal complexes was examined using a combination of multistagemass spectrometry experiments in an ion trap mass spectrometer, DFTcalculations, and theoretical kinetic modeling. Two related catalyticcycles sharing two common intermediates were examined. The entry pointsto both cycles are the metal acetate complexes [(phen)M(O2CCH3)](where phen = 1,10-phenanthroline),which were formed via direct electrospray ionization of solutionsof the complexes [(phen)M(O2CCH3)2] in water. Step 1 of both cycles involves decarboxylation of [(phen)M(O2CCH3)]멷 collision-induced dissociation(CID) conditions to form the organometallic species [(phen)M(CH3)]. The ease of decarboxylation follows the orderPd > Pt > Ni as determined via energy-resolved CID experiments,whichis in agreement with the activation energies for decarboxylation estimatedfrom DFT calculations. Step 2 of cycle 1 involves an ion–moleculereaction between [(phen)M(CH3)]橷 aceticacid to close the cycle by regenerating the metal acetate complex[(phen)M(O2CCH3)]. DFT calculationsreveal that an acid–base acetolysis mechanism is favored overan oxidative addition/reductive elimination mechanism proceeding viathe M(IV) intermediate [(phen)M(CH3)(H)(O2CCH3)]. In contrast, step 2 of cycle 2 involves [(phen)M(CH3)]귦鲶⧠ with water to form the hydroxide [(phen)M(OH)], which subsequently reacts with acetic acid in step 3 tore-form [(phen)M(O2CCH3)]橷 water,thereby completing the catalytic cycle. Experiment and theory revealthat cycle 2 operates only for M = Ni. [ABSTRACT FROM AUTHOR]

A combination of gas-phase ion-molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC−CLiCl]− reacts with water more rapidly than [HC−CMgCl2]−, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC−CLiCl]− or [HC−CMgCl2]− enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC−CMgCl2]− enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics. [ABSTRACT FROM AUTHOR]

A combination of gas‐phase ion–molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC≡CLiCl]− reacts with water more rapidly than [HC≡CMgCl2]−, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC≡CLiCl]− or [HC≡CMgCl2]− enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC≡CMgCl2]− enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics. [ABSTRACT FROM AUTHOR]

A combination of gas‐phase ion–molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC≡CLiCl]− reacts with water more rapidly than [HC≡CMgCl2]−, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC≡CLiCl]− or [HC≡CMgCl2]− enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC≡CMgCl2]− enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics. [ABSTRACT FROM AUTHOR]

A combination of gas-phase ion-molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC−CLiCl]− reacts with water more rapidly than [HC−CMgCl2]−, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC−CLiCl]− or [HC−CMgCl2]− enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC−CMgCl2]− enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics. [ABSTRACT FROM AUTHOR]

Thereactions of water with the coordinatively unsaturated group 10 organometalliccations [(L)M(R)]+(4; where L = 1,10-phenanthroline(phen), neocuproine (neo); M = nickel, palladium, platinum; R = CH3, C6H5, CH2C6H5), formed via decarboxylation of the carboxylate complexes[(L)M(O2CR)]+, were examined in the gas phaseusing a combination of multistage mass spectrometry experiments andDFT calculations at the M06/SDD6-31+G(d) level of theory. Two maintypes of primary product ions were observed: the aqua adduct [(L)M(R)(H2O)]+(5) and the hydroxide [(L)M(OH)]+(7), formed via a hydrolysis reaction. A secondaryproduct ion, arising from formation of the adduct [(L)M(OH)(H2O)]+, was also observed when L = phen, R = CH3, and M = Pt. The rates of reaction of 4andthe product branching ratios for 5and 7were dependent upon the nature of M, L, and R. When L = phenand R = CH3, the hydroxide 7dominates forNi, with the adduct 5as the major product for both Pdand Pt. For R = C6H5the rate of the reactionis slower, while for R = CH2C6H5noreaction occurs. Replacing the phen auxiliary ligand with neo dramaticallyslows down the rate of reaction with water. DFT calculations revealthat an acid–base hydrolysis mechanism is favored over an oxidativeaddition/reductive elimination mechanism proceeding via the M(IV)intermediate [(L)M(CH3)(H)(OH)]+. Furthermore,the relative energies calculated for the barriers of these hydrolysisreactions are consistent with the experimentally observed reactivitytrends. This mechanism is also supported by RRKM theory/master equationsimulations, which demonstrate that formation of the aqua adduct andhydroxide can be explained by competition between unimolecular dissociationand collisional deactivation of the chemically activated reactionadduct within the ion trap. The lack of reactivity of the benzyl systemsappears to arise from η3bindingof the benzyl group, which blocks access to the incoming water. Finally,links are made to group 10 three-coordinate organometallic complexesin the condensed phase. [ABSTRACT FROM AUTHOR]

A combination of multistage mass spectrometry experiments and DFT calculations were used to examine the synthesis and reactivity of dimethylaurate. Collision induced dissociation (CID) of [(CH3CO2)4Au]−proceeded viareductive elimination of acetylperoxide to yield the diacetate [CH3CO2AuO2CCH3]−, which in turn underwent sequential CID decarboxylation reactions to yield the organoaurates [CH3CO2AuCH3]−and [CH3AuCH3]−. The unimolecular chemistry of the dimethylaurate proceeds viaa combination of bond homolysis to yield the methyl aurate radical anion [CH3Au]−as well as formation of the gold dihydride [HAuH]−. DFT calculations reveal that the latter anion is formed viaa 1,2-dyotropic rearrangement to yield the isomer [CH3CH2AuH]−, followed by a β-hydride elimination reaction. Ion-molecule reactions of [CH3AuCH3]−with methyl iodide did not yield any products even at relatively high concentrations of the neutral substrate and longer reaction times, indicating a reaction efficiency of less than 1 in 20 000 collisions. DFT calculations were carried out on two different potential energy surfaces (PES) for the reaction of [CH3AuCH3]−with CH3I: (i) an SN2 mechanism proceeding viaa side-on transition state; and (ii) a stepwise mechanism proceeding viaoxidative addition followed by reductive elimination. Both pathways have significant endothermic barriers, consistent with the lack of C–C bond coupling products being formed in the experiments. Finally, the reactivity of [CH3AuCH3]−is compared to the previously studied [CH3AgCH3]−and [CH3CuCH3]−, as well as condensed phase studies on dimethylaurate salts. [ABSTRACT FROM AUTHOR]

Abstract: Previous studies have demonstrated that the silver hydride cluster cation Ag4H+ promotes Cupling of allylbromide [G.N. Khairallah, R.A.J. O’Hair, Angewandte Chemie International Edition 44 (2005) 728]. Here the influence of both the nature and the size of the silver cluster cation and the substrate on Cupling are examined. Thus each of the cations Ag2H+, Ag4H+, Ag3 +, and Ag5 + were allowed to react with three different halides: allyl chloride, allyl bromide and allyl iodide. No Cupling is observed in the reactions of the cluster cations with allyl chloride. There are four main reaction sequences that result in Cupling for allyl bromide and allyl iodide mediated by Ag n + and Ag n−1H+ clusters: [(i)] A sequence involving the reactions of silver cluster cations with two molecules of C3H5X: Ag n + →Ag n (C3H5X)+ →Ag n X2 +. This only occurs in the cases of: n =3 and X=I; n =5 and X=Br. [(ii)] A sequence involving the reactions of silver cluster cations with two molecules of C3H5X via an organometallic intermediate: Ag n + →Ag n−1(C3H5)+ →Ag n−1X+. This only occurs in the cases of: n =5 and X=Br and I. [(iii)] A sequence involving the reactions of silver hydride cluster cations with three molecules of C3H5X: Ag n−1H+ →Ag n−1X+ →Ag n−1X(C3H5X)+ →Ag(C3H5)2 + and Ag n−1X3 +. This only occurs in the cases of: n =5 and X=Br and I. [(iv)] A sequence involving the reactions of silver hydride cluster cations with three molecules of C3H5X via an organometallic intermediate: Ag n−1H+ →Ag n−1X+ →Ag n−3(C3H5)+ →Ag(C3H5)2 + and Ag n−3X+. This only occurs in the cases of: n =5 and X=I. [Copyright &y& Elsevier]

Electrospray ionisation on a mixture of AgNO3 (in MeOH/H2O/acetic acid), (CH3CO2)2Cu (in MeOH) and acetic acid (in MeOH) yields the metal carboxylate cations CH3CO2Ag2 +, CH3CO2AgCu+ and CH3CO2Cu2+. Collision induced dissociation of these carboxylate cations yields the organometallic cations CH3Ag2+, CH3AgCu+ and CH3Cu2+. The ion-molecule reactions of these organometallic cations with allyliodide were studied in a quadrupole ion trap mass spectrometer. C-C bond coupling occurred to yield the ionic products Ag2I+, AgCuI+ and Cu2I+. DFT calculations were carried out on these C-C bond coupling reactions. In all cases, the reactions are highly exothermic and involve initial coordination of the allyliodide to both metal atoms, with the iodine coordinating to one atom and the alkene moiety coordinating to the other. The overall mechanism of C-C bond coupling involves oxidative addition of the allyliodide followed by reductive elimination of 1-butene. [ABSTRACT FROM AUTHOR]

The mystery of why water and salt contaminants destroy organometallic reagents has been solved by G. N. Khairallah, G. da Silva, and R. A. J. O'Hair in their Communication on page 10979 ff. The addition of an individual salt molecule to an organometallic reagent dramatically enhances its reactivity towards water. This second metal center plays an active role in altering the fundamental chemical transformations that take place when water attacks the organometallic compound. [ABSTRACT FROM AUTHOR]

Gas-phase carbon-carbon bond forming reactions, catalyzed by group 10 metal acetate cations [(phen)M(O2CCH3)]+ (where M = Ni, Pd or Pt) formed via electrospray ionization of metal acetate complexes [(phen)M(O2CCH3)2], were examined using an ion trap mass spectrometer and density functional theory (DFT) calculations. In step 1 of the catalytic cycle, collision induced dissociation (CID) of [(phen)M(O2CCH3)]+ yields the organometallic complex, [(phen)M(CH3)]+, via decarboxylation. [(phen)M(CH3)]+ reacts with allyl acetate via three competing reactions, with reactivity orders (% reaction efficiencies) established via kinetic modeling. In step 2a, allylic alkylation occurs to give 1-butene and reform metal acetate, [(phen)M(O2CCH3)]+, with Ni (36%) > Pd (28%) > Pt (2%). Adduct formation, [(phen)M(C6H11O2)]+, occurs with Pt (24%) > Pd (21%) > Ni(11%). The major losses upon CID on the adduct, [(phen)M(C6H11O2)]+, are 1-butene for M = Ni and Pd and methane for Pt. Loss of methane only occurs for Pt (10%) to give [(phen)Pt(C5H7O2)]+. The sequences of steps 1 and 2a close a catalytic cycle for decarboxylative carbon-carbon bond coupling. DFT calculations suggest that carbon-carbon bond formation occurs via alkene insertion as the initial step for all three metals, without involving higher oxidation states for the metal centers. [ABSTRACT FROM AUTHOR]