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Graphical abstract Highlights • Dihydroxy magnesium carboxylate anions, first discovered in meteorites, have been prepared in the gas-phase. • Sequential CID and IMR are used to synthesise [(RCO 2)Mg(OH) 2 ]– from [(RCO 2)Mg(O 2 CCH 3) 2 ]– precursor ions generated via ESI. • DFT calculations provide structures and energetics associated with these CID and IMR reactions. • The CID fragmentation reactions of [(RCO 2)Mg(OH) 2 ]– are described. Abstract Dihydroxy magnesium carboxylates, [(RCO 2)Mg(OH) 2 ]–, a previously unknown class of compounds, have recently been discovered in meteorites using electrospray ionisation (ESI) ultra high-resolution mass spectrometry (HRMS) and collision-induced dissociation (CID) experiments (A. Ruf et al., Proc. Natl. Acad. Sci. U.S.A. 114 (2017) 2819). Here we present two general strategies for the gas-phase synthesis of [(RCO 2)Mg(OH) 2 ]– (where R = CH 3 and CH 3 (CH 2) 14) in a linear quadrupole ion trap mass spectrometer using combinations of CID and ion-molecule reactions (IMR) with water. Both involve the same first step (Step 1), where [(RCO 2)Mg(O 2 CCH 3) 2 ]– precursor ions generated via ESI are mass selected and subjected to decarboxylation. In Route I the resultant organomagnesate [(RCO 2)Mg(CH 3)(O 2 CCH 3)]– is subjected to the following reactions: Step 2a involves decarboxylation via CID to give [(RCO 2)Mg(CH 3) 2 ]– which undergoes an IMR in Step 3a to give [(RCO 2)Mg(CH 3)(OH)]–. For Route II [(RCO 2)Mg(CH 3)(O 2 CCH 3)]– undergoes an IMR to give in Step 2b, [(RCO 2)Mg(OH)(O 2 CCH 3)]–, which in Step 3b fragments under CID to give [(RCO 2)Mg(CH 3)(OH)]–. Both routes converge in the final Step 4, where the organometallic ion [(RCO 2)Mg(CH 3)(OH)]– reacts with water to give the desired dihydroxy magnesium carboxylate, [(RCO 2)Mg(OH) 2 ]–. All ion molecule reactions proceed rapidly and cleanly to produce the hydroxides. In contrast, the decarboxylation reactions are in competition with other pathways including loss of the carboxylate anion and loss of a neutral ligand to give a magnesium coordinated enolate of acetate. DFT calculations were used to examine the structures and energies of species involved in the competing reactions associated with each of the steps. [ABSTRACT FROM AUTHOR]

The extent of internal energy deposition using three different plasma-based ionization mass spectrometry (MS) methods, atmospheric pressure chemical ionization (APCI), direct analysis in real time (DART), and active capillary dielectric barrier discharge ionization (DBDI), was investigated using benzylammonium 'thermometer' ions. Ions formed by DBDI were activated significantly less than those that were formed by DART and APCI under these conditions. Thermal ion activation by DART can be reduced slightly by positioning the DART source further from the capillary entrance to the MS and reducing the heat that is applied tometastable atoms exiting theDART source. For example, the average ion internal energy distribution decreased by less than 10%(166.9±0.3 to 152.2±1.0 kJ mol-1) when the distance between the DART source and the MS was increased by 250% (10 to 25mm). By lowering the DART temperature from 350 to 150°C, the internal energy distributions of the thermometer ions decreased by ~15% (169.93±0.83 to 150.21±0.52 kJ mol-1). Positioning the DART source nozzle more than 25mm from the entrance to the MS and decreasing the DART temperature further resulted in a significant decrease in ion signal. Thus, varying themajorDART ion source parameters had minimal impact on the 'softness' of the DART ion source under these conditions. Overall, these data indicate that DBDI can be a significantly 'softer' ion source than two of the most widely used plasma-based ion sources that are commercially available. [ABSTRACT FROM AUTHOR]

Electrospray ionization of 2,6-naphthalenedicarboxylic acid readily affords its doubly deprotonated dicarboxylate dianion ( 1 2− ). This species clusters with background water and added alcohols in an ion trap at ∼10 −3 Torr. Sequential solvation is observed to afford mono and dicoordinated ions. Surprisingly, the latter cluster ( 1 2− • 2TFE ) is protonated by 2,2,2-trifluoroethanol (TFE) whereas 1 2− and 1 2− • TFE are not even though Δ H ° acid (TFE) = 361.7 ± 2.5 kcal mol −1 (as given in the NIST website at http://webbook.nist.gov ) and the B3LYP/6-31+G(d,p) proton affinities are 384.7 ( 1 2− ), 377.6 ( 1 2− • TFE ), and 362.7 ( 1 2− • 2TFE ) kcal mol −1 . That is, only the weakest base in this series, and the dianion with an equal number of solvent molecules and charged sites, undergoes proton transfer. In a FTMS instrument at lower pressures (∼10 −8 Torr) inefficient proton abstraction is observed with the monosolvated dianion. This difference, and the observed reactivities of 1 2− , 1 2− • TFE and 1 2− • 2TFE are rationalized with the aid of computed potential energy surfaces. The chemical structures of these cluster ions were also probed via collision-induced dissociations, infrared photodissociation from 2700 to 3200 cm −1 , and extensive calculations. All of the TFE species are found to be solvated dianions, but incipient proton transfer to afford electrostatically defying anion-anion clusters is noted in two cases. In proton transfer reactions, formation of the conjugate acid as a solvated ion lowers the energy of the system and reduces the Coulomb repulsion barrier facilitating the overall process. [ABSTRACT FROM AUTHOR]

Gas-phase studies utilizing ion-molecule reactions, supported by computational chemistry, demonstrate that the reaction of the enolate complexes [(CH2CO2--C,O)M(CH3)]- (M = Ni (5a), Pd (5b)) with allyl acetate proceed via oxidative addition to give MIV species [(CH2CO2--C,O)M(CH3)(η¹-CH2--CH-CH2)(O2CCH3--O,O')]- (6) that reductively eliminate 1-butene, to form [(CH2CO2--C,O)M(O2CCH3--O,O')]- (4). The mechanism contrasts with the MII-mediated pathway for the analogous reaction of [(phen)M(CH3)]+ (1a,b) (phen = 1,10-phenanthroline). The different pathways demonstrate the marked effect of electron-rich metal centers in enabling higher oxidation state pathways. Due to the presence of two alkyl groups, the metal-occupied d orbitals (particularly dz²) in 5 are considerably destabilized, resulting in more facile oxidative addition; the electron transfer from dz² to the C-C π* orbital is the key interaction leading to oxidative addition of allyl acetate to MII. Upon collision-induced dissociation, 4 undergoes decarboxylation to form 5. These results provide support for the current exploration of roles for NiIV and PdIV in organic synthesis. [ABSTRACT FROM AUTHOR]

Although the deleterious effects of ozone on the human respiratory system are well-known, many of the precise chemical mechanisms that both cause damage and afford protection in the pulmonary epithelial lining fluid are poorly understood. As a key first step to elucidating the intrinsic reactivity of ozone with proteins, its reactions with deprotonated cysteine [Cys−H]− are examined in the gas phase. Reaction proceeds at near the collision limit to give a rich set of products including 1) sequential oxygen atom abstraction reactions to yield cysteine sulfenate, sulfinate and sulfonate anions, and significantly 2) sulfenate radical anions formed by ejection of a hydroperoxy radical. The free-radical pathway occurs only when both thiol and carboxylate moieties are available, implicating electron-transfer as a key step in this reaction. This novel and facile reaction is also observed in small cys-containing peptides indicating a possible role for this chemistry in protein ozonolysis. [ABSTRACT FROM AUTHOR]

Although the deleterious effects of ozone on the human respiratory system are well-known, many of the precise chemical mechanisms that both cause damage and afford protection in the pulmonary epithelial lining fluid are poorly understood. As a key first step to elucidating the intrinsic reactivity of ozone with proteins, its reactions with deprotonated cysteine [Cys−H]− are examined in the gas phase. Reaction proceeds at near the collision limit to give a rich set of products including 1) sequential oxygen atom abstraction reactions to yield cysteine sulfenate, sulfinate and sulfonate anions, and significantly 2) sulfenate radical anions formed by ejection of a hydroperoxy radical. The free-radical pathway occurs only when both thiol and carboxylate moieties are available, implicating electron-transfer as a key step in this reaction. This novel and facile reaction is also observed in small cys-containing peptides indicating a possible role for this chemistry in protein ozonolysis. [ABSTRACT FROM AUTHOR]

RATIONALE: Non-covalent amino acid clusters are the subject of intense research in diverse areas including peptide bond formation studies or the determination of proton affinities or methylating abilities of amino acids. However, most of the research has focused on positive ions and little is known about anionic clusters. METHODS: Fragmentation reactions of deprotonated tryptophan (Trp), [Trp-H]- and Trp singly deprotonated noncovalently bound clusters [Trpn-H]-, n = 2, 3, 4, were investigated using low-energy collision-induced dissociation (CID) with He atoms, high-energy CID with Na atoms, and electron-induced dissociation (EID) with 20-35 eV electrons. Fragmentation of the monomeric Trp anion, where all labile hydrogens were exchanged for deuterium [d4-Trp-D]-, was investigated using low-energy CID and EID, in order to shed light on the dissociation mechanisms. RESULTS: The main fragmentation channel for Trp cluster anions, [Trpn-H]-, n >1, is the loss of the neutral monomer. The fragmentation of the deprotonated Trp monomer induced by electrons resembles the fragmentation induced by high-energy collisions through electronic excitation of the parent. However, the excitation must precede in a different way, shown through only monomer loss from larger clusters, n >1, in case of EID, but intracluster chemistry in the case of high-energy CID. CONCLUSIONS: The anion of the indole ring C8H6N- has been identified in the product ion spectra of [Trpn-H]- using all activation methods, thus providing a diagnostic marker ion. No evidence was found for formation of peptide bonds as a route to prebiotic peptides in the fragmentation reactions of these singly deprotonated Trp cluster ions. [ABSTRACT FROM AUTHOR]

A combination of gas-phase ion trap multistage mass spectrometry (MSn) 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. [ABSTRACT FROM AUTHOR]

Dithiocarboxylicacids, RCS2H, and their esters, RCS2R′,are useful reagents that can be synthesized bythe reaction of carbon disulfide with organometallic reagents. Herethe coinage-metal-mediated transformation of acetate to dithioacetateis explored in the gas phase using multistage mass spectrometry experimentsin a linear ion trap mass spectrometer in conjunction with densityfunctional theory (DFT) calculations. The ion–molecule reactionsbetween coinage-metal dimethylmetalate anions [CH3MCH3]−(M = Au, Ag, Cu), formed via double decarboxylationof the metal acetate anions, [CH3CO2MO2CCH3]−, and carbon disulfide, were examined.Only [CH3CuCH3]−reacts withCS2with a reaction efficiency of 0.8% of the collisionrate to yield the adduct [CH3CuS2CCH3]−(77.5%) as well as CH3CS2–(22.5%). Collision-induced dissociation (CID)of the adduct [CH3CuS2CCH3]−gives CH3CS2–as the majorproduct, with a small amount of [CuS2CCH2]−being formed via loss of methane. DFT calculationsreveal the following. (i) [CH3CuCH3]−reacts via oxidative addition to form a Cu(III) intermediate, followedby reductive elimination of CH3CS2–, which is captured by Cu to form [CH3CuS2CCH3]−. This energetic adduct can fragment vialoss of CH3CS2–or can becollisionally cooled by the helium bath gas used in the experiments.(ii) Loss of CH4from [CH3CuS2CCH3]−also involves a Cu(III) intermediateand results in formation of the metalladithiolactone [Cu(CH2CS2)]−. [ABSTRACT FROM AUTHOR]

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 bis(diphenylphosphino)methane-ligated trinuclear silver hydride nanocluster, [Ag3((Ph2P)2CH2)3(μ3-H)](BF4)2, featuring three silver(I) ions coordinated to a μ3-hydride, and its deuteride analogue, [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2, have been isolated and structurally characterized using electrospray ionization mass spectrometry (ESI-MS), X-ray crystallography, NMR and IR spectroscopy. The position of the deuteride in [Ag3((Ph2P)2CH2)3(μ3-D)](BF4)2 was determined by neutron diffraction. ESI-MS of [Ag3L3(μ3-H/D)](BF4)2 [L = ((Ph2P)2CH2)2] produces [Ag3L3(μ3-H/D)]2+ and [Ag3L3(μ3-H/D)(BF4)]+. A rich gas-phase ion chemistry of [Ag3L3(μ3-H/D)]2+ is observed under conditions of collision-induced dissociation (CID) and electron-capture dissociation (ECD). CID gives rise to the following complementary ion pairs: [Ag3L2]+ and [L+(H/D)]+; [Ag2(H/D)L2]+ and [AgL]+; [Ag2(H/D)L]+ and [AgL2]+. ECD gives rise to a number of dissociation channels including loss of the bis(phosphine) ligand, fragmentation of a coordinated bis(phosphine) ligand via C-P bond activation, and loss of a hydrogen (deuterium) atom with concomitant formation of [Ag3L3]+. Under CID conditions, [Ag3L3(μ3-H/D)(BF4)]+ fragments via ligand loss, the combined loss of a ligand and [H,B,F4], and cluster fragmentation to give [Ag2(BF4)L2]+ and [Ag2(L-H)L]+ [where (L-H) =(Ph2P)2CH-]. [ABSTRACT FROM AUTHOR]

Productand mechanistic studies were performed for the reactionof aromatic distonic peroxyl radical cations 4-PyrOO•+and 3-PyrOO•+with phenylacetylene (7) in the gas phase using mass spectrometric and computational techniques.PyrOO•+was generated through reaction of the respectivedistonic aryl radical cation Pyr•+with O2in the ion source of the mass spectrometer. For the reaction involvingthe more electrophilic 4-PyrOO•+, a rate coefficientof k1= (2.2 ± 0.6) × 10–10cm3molecule–1s–1was determined at 298 K, while a value of k2= (8.2 ± 2.1) × 10–11cm3molecule–1s–1was obtained for the reaction involving the less electrophilic 3-PyrOO•+. This highlights the role of polar effects in thesereactions, which are likely of high relevance for processes in combustionsand atmospheric transformations. The mechanism was studied by computationalmethods, which showed that radical addition occurs exclusively atthe less substituted alkyne site to give the distonic vinyl radicalcation 8. The latter undergoes a series of subsequentrearrangements/fragmentations that are similar for both isomeric PyrOO•+. γ-Fragmentation in 8leads tothe distonic aryloxyl radical cation PyrO•+anda singlet carbene 10. The product association complex[PyrO•+– 10] is the startingpoint for two important subsequent reactions, e.g., (i) rapid hydrogentransfer to form ketenyl radical 11and the closed-shellspecies PyrOH+, and (ii) oxygen transfer from PyrO•+to 10that leads to α-keto aldehyde 13and Pyr•+, followed by hydrogen abstractionto give acyl radical 14and PyrH+. Additionalmajor products are the closed-shell aromatic carbonyl compounds 20and 30that result from multistep rearrangementsin vinyl radical 8, which are terminated by homolyticbond scission and release of neutral acyl radicals. [ABSTRACT FROM AUTHOR]

Cobalt-mediated decarboxylative Glaser-like C-C bond coupling of carboxylates has been studied in the gas phase using collision-induced dissociation (CID) multistage mass spectrometry (MS[sup n]) experiments. Both the identity of the carboxylate RCO[sup -][sub 2] (R= Me, HC≡C, MeC≡C, and PhC≡C) and the nuclearity of the complex ([CoCl(O[sub 2]CR)[sub 2]][sup -] versus [Co[sub 2]Cl[sub 3](O[sub 2]CR)[sub 2]][sup -]) play a role in the types of reactions observed and their relative activation energies. In the first stage of CID, the mononuclear complex [CoCl(O[sub 2]CMe)[sub 2]][sup -] undergoes decarboxylation, while the dinuclear [Co[sub 2]Cl[sub 3](O[sub 2]CMe)[sub 2]][sup -] undergoes cluster fission to yield [CoCl[sub 3]][sup -]; all acetylenic carboxylate complexes [CoCl(O[sub 2]CR)[sub 2]][sup -] and [Co[sub 2]Cl[sub 3](O[sub 2]CR)[sub 2]][sup -] undergo decarboxylation. Isolation of the decarboxylated products followed by a second stage of CID results in a second decarboxylation event for all systems except for [CoCl(Me)(O[sub 2]CMe)][sup -], which undergoes bond homolysis. In the final stage of CID, all acetylenic complexes undergo Glaser coupling, forming reduced Co anions. Overall dinuclear cobalt clusters are superior to mononuclear complexes at promoting decarboxylation and reductive coupling. The order of reactivity among the acetylide ligands is PhC≡C > MeC≡C > HC≡C. [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]

Highlights: [•] Bis(diphenylphosphino)methane (dppm) protected Au cluster cations, [Au x L1 y ] z+, were formed via condensed phase synthesis. [•] These and organometallic clusters [Au x L1 y (CH(PPh2)2)] n+ (x =5, y =3, n =2; x =14, y=6, n =3) were observed via ESI/MS. [•] Their unimolecular chemistry was examined via CID and ECD. [•] A range of pathways appear for CID including dppm loss, cluster fragmentation and C P bond activation of dppm. [•] The main ECD reaction was charge reduction which was sometimes followed by ligand loss or C P bond activation of dppm. [Copyright &y& Elsevier]

Highlights: [•] Silver alkynyl cations RC CAg2 + (R=H, Me, Et, Pr, Bu, tBu and Ph) were “synthesized” in the gas phase. [•] These cations fragment via a range of pathways including C H and C C bond activation. [•] H/D scrambling is not involved in the C C bond activation pathway of CD3CH2CH2C CAg2 + and CD3CD2CH2C CAg2 +. [•] Formation of Ag2H+ involves regiospecific C H bond activation of the CH2 adjacent to the CH3 group in CH3CH2CH2C CAg2 +. [Copyright &y& Elsevier]

Eine massenspektrometrische Analyse zeigt, dass die Umsetzung von Silbersalzen mit Natriumborhydrid in Gegenwart eines Diphosphanliganden nicht zu reinen Silber ‐ Nanoclusterkationen führt, sondern zu neuartigen Silberhydrid ‐ Nanoclusterkationen. Diese Entdeckung beflügelte die Flüssigphasensynthese, Isolierung und Charakterisierung von [Ag3{(Ph2P)2CH2}3(μ3 ‐ H)(μ3 ‐ Cl)]BF4 ⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

Mass spectrometry shows the way! MS analysis of silver salts treated with sodium borohydride in the presence of a bis(phosphino) ligand revealed the formation of novel silver hydride nanocluster cations instead of all silver nanocluster cations. This serendipitous discovery prompted the condensed‐phase synthesis, isolation, and characterization of [Ag3{(Ph2P)2CH2}3(μ3‐H)(μ3‐Cl)]BF4⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

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+Ṗ, 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. [ABSTRACT FROM AUTHOR]

The reaction of the aromatic distonic peroxyl radical cations N-methyl pyridinium-4-peroxyl (PyrOO.+) and 4-( N, N, N-trimethyl ammonium)-phenyl peroxyl (AnOO.+), with symmetrical dialkyl alkynes 10 a- c was studied in the gas phase by mass spectrometry. PyrOO.+ and AnOO.+ were produced through reaction of the respective distonic aryl radical cations Pyr.+ and An.+ with oxygen, O2. For the reaction of Pyr.+ with O2 an absolute rate coefficient of k1=7.1×10−12 cm3 molecule−1 s−1 and a collision efficiency of 1.2 % was determined at 298 K. The strongly electrophilic PyrOO.+ reacts with 3-hexyne and 4-octyne with absolute rate coefficients of khexyne=1.5×10−10 cm3 molecule−1 s−1 and koctyne=2.8×10−10 cm3 molecule−1 s−1, respectively, at 298 K. The reaction of both PyrOO.+ and AnOO.+ proceeds by radical addition to the alkyne, whereas propargylic hydrogen abstraction was observed as a very minor pathway only in the reactions involving PyrOO.+. A major reaction pathway of the vinyl radicals 11 formed upon PyrOO.+ addition to the alkynes involves γ-fragmentation of the peroxy OO bond and formation of PyrO.+. The PyrO.+ is rapidly trapped by intermolecular hydrogen abstraction, presumably from a propargylic methylene group in the alkyne. The reaction of the less electrophilic AnOO.+ with alkynes is considerably slower and resulted in formation of AnO.+ as the only charged product. These findings suggest that electrophilic aromatic peroxyl radicals act as oxygen atom donors, which can be used to generate α-oxo carbenes 13 (or isomeric species) from alkynes in a single step. Besides γ-fragmentation, a number of competing unimolecular dissociative reactions also occur in vinyl radicals 11. The potential energy diagrams of these reactions were explored with density functional theory and ab initio methods, which enabled identification of the chemical structures of the most important products. [ABSTRACT FROM AUTHOR]

Electrospray ionization in combination with multistagemass spectrometry experiments in a linear ion trap mass spectrometerwas used to generate and study the gas-phase ion chemistry of themetallalactones [(CH3CO2)Ni(CH2CO2)]−(m/z175, 5a) and [(CH3CO2)Pd(CH2CO2)]−(m/z223, 5b). Low-energy collision-induced dissociation(CID) resulted in decarboxylation to produce novel organometallicions at m/z131 (Ni) and m/z179 (Pd). Isotope labeling experiments,bimolecular gas-phase reactions with allyl iodide, and DFT calculationsreveal that decarboxylation primarily occurs from the acetato ligandto yield ions of the form [(CH3)M(CH2CO2)]−(M = Pd, Ni). Further CID experimentson [(CH3)M(CH2CO2)]−together with DFT calculations highlight the following. (1) Bothpalladium and nickel can facilitate C–C bond formation, withelimination of ethylene being observed. (2) The mechanism for formationof ethylene from [(CH3)M(CH2CO2)]−is inherently different for M = Pd versus M = Ni.Elimination of ethylene is competitive with further decarboxylationin the case of nickel, and nickel remains in the 2+ oxidation statethroughout. In contrast, the palladium complex is reduced to palladium(0)upon C–C bond formation and undergoes a second decarboxylationbefore ethylene is released. Finally, the products of the ion–moleculereactions of [(CH3)Pd(CH2CO2)]−(7b) with allyl iodide provide evidencefor the formation of the Pd(IV) intermediate [(CH3)(I)(CH2CHCH2)Pd(CH2CO2)]−, which decomposes via a range of processes, including losses ofiodide, propionate, allyl, and methyl radicals and reductive eliminationof butane and methyl iodide. [ABSTRACT FROM AUTHOR]

There are three metal-mediated ligand decomposition reactionsthatgive rise to organometallics: (i) decarboxylation of a metal carboxylate,“the Pesci reaction”; (ii) desulfination of a metalsulfinate, “the Peters reaction”; (iii) desulfonationof a metal sulfonate, “the Deacon reaction”. Despitegrowing interest in their use in applications in organic synthesis,little is known about the relative ease of thermal extrusion of CO2versus SO2versus SO3in metal complexes.Here the intrinsic reactivity orders for organocuprate formation vialigand decomposition have been studied in the gas phase for the firsttime. A combination of low-energy collision-induced dissociation experimentsin an ion trap mass spectrometer and DFT calculations was used. Simpleligand competition experiments in the heterocopper complexes [MeXOCuOYMe]−(where X = CO or SO and Y = SO or SO2),formed via electrospray ionization, show that desulfination occursmore easily than decarboxylation, which in turn is more facile thandesulfonation. This is consistent with DFT calculations at the M06/SDD/cc-pVTZ//M06/cc-pVDZlevel of theory, which show that the barriers associated with thetransition states follow the order SO2< CO2< SO3. [ABSTRACT FROM AUTHOR]

Abstract: High-resolution multistage mass spectrometric studies of isotope-labelled derivatives of a fixed-charge labelled sugar triazole assisted the identification of 5-hydroxy-1,2,3-triazoles as byproducts of the copper(I)-catalyzed cycloaddition of azides and terminal alkynes. Reaction optimization with inclusion of the auxiliary ligand, tris(benzyltriazolylmethyl)amine furnished an improved ligation protocol in which formation of the 5-hydroxytriazole is mitigated. [Copyright &y& Elsevier]

Decarboxylation of the ligands in the magnesium cations [CH3CO2MgO2CCH2X(CH3)2]+ (where X = NCH3, 1a; and S, 1b) can give rise to either an organometallic cation [CH3MgO2CCH2X(CH3)2]+, 2, or a coordinated ylide [CH3CO2MgCH2X(CH3)2]+, 3. Collision-induced dissociation of a precursor complex in which the acetate ligand was 13C labeled allowed the direct determination of the relative ratio of formation of 2 and 3 via a comparison of the losses of 13CO2 and CO2. For the nitrogen betaine, 1a, both 2a and 3a are formed, in a ratio of ca 1:3, respectively. In contrast, for the sulfur betaine, 1b, the coordinated ylide, 3b, is almost exclusively formed. These striking differences are confirmed by DFT calculations at the B3LYP/6-31+G(d) level of theory, which show that the activation energies associated with the formation of 2a and 3a are close (2.33 eV versus 2.28 eV), but that formation of 3b (Ea = 1.97 eV) is favored over formation of 2b (Ea = 2.33 eV). Use of the 13C-labeled acetate ligand also allowed the bimolecular hydrolysis reactions of isomerically pure populations of mass-selected 2 and 3 to be examined. Ion−molecule reactions with water proceeded via addition/elimination reactions, but the nature of the magnesium hydroxide is different for each isomer. Thus 2a reacted to yield the charged magnesium hydroxide [HOMgO2CCH2N(CH3)3]+, plus methane, while 3a and 3b reacted to yield the neutral magnesium hydroxide [CH3CO2MgOH] plus the charged onium ions (CH3)3X+. Kinetic measurements reveal a reactivity order of 2a > 3a ≈ 3b, consistent with DFT calculations on the potential energy surfaces associated with these hydrolysis reactions. The preferred site of decarboxylation of [MeCO2MgO2CCH2XMe2]+ (where X = NMe (m/z 201) and S (m/z 204)), investigated using 13C labeling experiments, depends on the nature of the betaine. For X = NMe, decarboxylation occurs at both ligands, but when X = S, decarboxylation occurs almost exclusively at the betaine. [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]

Electrospray ionization (ESI) of solutions containing deoxyguanosine (dG) and tridentate platinum chloride complexes yields clusters of general formula [PtII(L)(dG)n]2+, where L = 2,2':6',2'' terpyridine (terpy), or diethyltriamine (dien). When these clusters were mass selected and subjected to collision induced dissociation (CID), the primary fragmentation channels arise from loss of dG and protonated dG to yield the fragment ions [PtII(L)(dG)n-x]2+ and [PtII(L)(dG)n-x-H]+ respectively. The relative abundances of the [PtII(L)(dG)n-x]2+ fragments depend on the nature of the ligand, L. The most abundant peaks observed were: n-x = 5 for terpy and n-x = 4 for dien. In order to further understand these gas phase reactions, molecular dynamics calculations were carried out. These simulated collision calculations not only predict with fidelity the experimental profiles for the relative abundances for the [PtII(L)(dG)n-x]2+ fragments, for both terpy and dien ligand systems, but they also provide structural insights into the complex interplay of hydrogen bonding and stacking interactions within these clusters. [ABSTRACT FROM AUTHOR]

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 β-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 producethe 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]- underwentdecarboxylation 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 β-hydride transfer become more competitive with the second decarboxylation reaction. [ABSTRACT FROM AUTHOR]

Abstract: A two step gas-phase catalytic cycle for the dehydrogenation of formic acid was established using a combination of experiments carried out on a quadrupole ion trap mass spectrometer and DFT calculations. The catalysts are the magnesium hydride anions HMgL2 − (L=Cl and HCO2), which are formed from the formate complexes, HCO2MgL2 −, via elimination of carbon dioxide under conditions of collision induced dissociation. This is followed by an ion–molecule reaction between HMgL2 − and formic acid, which yields hydrogen and also reforms the formate complex, HCO2MgL2 −. A kinetic isotope effect in the range 2.3–2.9 was estimated for the rate determining decarboxylation step by carrying out CID on the (HCO2)(DCO2)MgCl2 − and subjecting the resultant mixture of (H)(DCO2)MgCl2 − and (HCO2)(D)MgCl2 − ions at m/z 106 to ion–molecule reactions. DFT calculations (at the B3LYP/6−31+G* level of theory) were carried out on the HMgCl2 − system and revealed that: (i) the decarboxylation of HCO2MgCl2 − is endothermic by 47.8kcalmol−1, consistent with the need to carry out CID to form the HMgCl2 −; (ii) HMgCl2 − can react with formic acid via either a four centred transition state or a six centred transition state. The former reaction is favoured by 7.8kcal mol−1. [Copyright &y& Elsevier]

Oxidative damage to DNA yields guanine radical cations. Their gas-phase IR spectroscopic signature and acidity have been modelled by the radical cation of 9-methylguanine. Comparisons with quantum chemistry calculations suggest that radical cation formation produces the ground-state keto tautomer, which has an N–H acidity enhanced by ∼470 kJ mol−1. [ABSTRACT FROM AUTHOR]

The chaperone protein CopC from Pseudomonas syringae features high-affinity binding sites ( K D ~ 10−13 M) for both CuI (Met-rich) and CuII (His-rich). When presented with these sites in the apoprotein, electrospray ionisation mass spectrometry confirmed that cis-Pt(NH3)2Cl2 (cisplatin) and the fragments [PtIIL]2+ (L is 1,2-diaminoethane, 2,2′-bipyridine) occupied the CuI site specifically in the 1:1 Pt–CopC adducts (purified by cation-exchange chromatography). The cis-Pt(NH3)2 fragment was not present in these adducts (the dominant product for cisplatin was Pt–CopC in which all original ligands were displaced), while bidentate ligands L were retained in LPt–CopC adducts. In the context of the Met-rich CuI pump Ctr1 as a significant entry point for cisplatin into mammalian cells, the present work confirms the ability of Met-rich sites in proteins to remove all ligands from cisplatin. It focuses attention on the potential of proteins that are part of the natural copper transport pathways to sequester the drug. These pathways are worthy of further study at the molecular level. [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. Salzeffekte: Wie beeinflussen bestimmte Salze die kinetische Basizität von mit Wasser reagierenden Organometallaten? Die Zugabe von LiCl zu [HCCLiCl]− oder [HCCMgCl2]− beschleunigt die Reaktion mit Wasser ungefähr um den Faktor zwei, und die Zugabe von MgCl2 zu [HCCMgCl2]− um den Faktor vier (siehe Bild). Der Mechanismus der Hydratisierung wird theoretisch untersucht. [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]

Der Massenspektrometrie ‐ Mann rettet den Tag! Bei der Reise von seinem Heimatplaneten Gasphase nutzte er seine ESI ‐ MS ‐ Kräfte, um G. N. Khairallah, P. S. Donnelly, R. A. J. O'Hair et al. mit essenziellen Informationen für die Zuschrift auf S. 8549 ff. zu versorgen. Die Kräfte des MS ‐ Manns enthüllten die Bildung eines neuartigen Silberhydrid ‐ Nanoclusterkations in Silbersalzen, die mit Natriumborhydrid in Gegenwart eines Bis(phosphanyl) ‐ Liganden reduziert wurden, und wiesen den Weg zu der Synthese von [Ag3{(Ph2P)2CH2}3(μ3 ‐ H)(μ3 ‐ Cl)]BF4⋅0.5 CHCl3 in kondensierter Phase, seiner Isolierung und Charakterisierung. [ABSTRACT FROM AUTHOR]

Mass Spectrometry Man saves the day! Traveling from his home on planet Gas Phase, he used his ESI‐MS powers to provide G. N. Khairallah, P. S. Donnelly, R. A. J. O'Hair, and co‐workers with vital information for their Communication on page 8391 ff. MS Man's powers revealed the formation of novel silver hydride nanocluster cations in silver salts reduced by sodium borohydride in the presence of a bis(phosphino) ligand, and led the way to the condensed‐phase synthesis, isolation, and characterization of [Ag3{(Ph2P)2CH2}3(μ3‐H)(μ3‐Cl)]BF4⋅0.5 CHCl3. [ABSTRACT FROM AUTHOR]

Collision-induced dissociation mass spectrometry of the ammonium ions 4a and 4b results in the formation of the seleniranium ion 5, the structure and purity of which were verified using gas-phase infrared spectroscopy coupled to mass spectrometry and gas-phase ion-mobility measurements. Ion-molecule reactions between the ion 5 (m/z = 261) and cyclopentene, cyclohexene, cycloheptene, and cyclooctene resulted in the formation of the seleniranium ions 7 (m/z = 225), 6 (m/z = 239), 8 (m/z = 253), and 9 (m/z = 267), respectively. Further reaction of seleniranium 6 with cyclopentene resulted in further π-ligand exchange giving seleniranium ion 7, confirming that direct π-ligand exchange between seleniranium ion 5 and cycloalkenes occurs in the gas phase. Pseudo-first-order kinetics established relative reaction efficiencies for π-ligand exchange for cyclopentene, cyclohexene, cycloheptene. and cyclooctene as 0.20, 0.07, 0.43, and 4.32. respectively. DFT calculations at the M06/6-31+G(d) level of theory provide the following insights into the mechanism of the π-ligand exchange reactions; the cycloalkene forms a complex with the seleniranium ion 5 with binding energies of 57 and 62 kJ/mol for cyclopentene and cyclohexene, respectively, with transition states for π-ligand exchange having barriers of 17.8 and 19.3 kJ/mol for cyclopentene and cyclohexene, respectively. [ABSTRACT FROM AUTHOR]

A new palladium mediated “one pot” synthesis of thioamides from aromatic carboxylic acids (ArCO2H + RNCS → ArC(S)NHR + CO2) was discovered by gas-phase experiments and theoretical studies. Palladium-mediated decarboxylation of aromatic carboxylic acids followed by addition of substituted isothiocyanates leads to the corresponding thioamide derivatives. [ABSTRACT FROM AUTHOR]

When the bis(diphenylphosphino)methane (dppm) ligated silver hydride nanocluster salt [Ag 3 (L) 3 ( μ 3 -H)](BF 4 ) 2 is allowed to react with NaBH 4 in a methanol/chloroform solution for 5 mins., and then diluted with acetonitrile and subjected to electrospray ionization mass spectrometry (ESI/MS), a range of silver hydride nanocluster dications are observed including: [Ag 8 H 6 L 5 ] 2+ and [Ag x H x−2 L 6 ] 2+ , where x = 9–15 and L = dppm. All of these clusters are no longer present in the ESI mass spectrum at 40 mins after mixing. Multistage mass spectrometry (MS n ) experiments were carried out to determine the fragmentation chemistry of [Ag 10 H 8 L 6 ] 2+ under conditions of collision-induced dissociation (CID). The initial CID reactions involve sequential loss of two ligands (L) to produce [Ag 10 H 8 L 4 ] 2+ . Further isolation and CID of [Ag 10 H 8 L 4 ] 2+ resulted in a rich series of product ions which arise from three classes of fragmentation reactions: (i) cluster fission to yield complementary ion pairs [Ag 10−x H 8-(x−1) L 4−y ] + and [Ag x H x−1 L y ] + (x = 1, 2 and 4); (ii) ligand loss associated with cluster fission to yield pairs of singly charged clusters [Ag 10−x H 8-(x−1) L 4−y ] + and [Ag x H x−1 L y−1 ] + (x = 1–4); (iii) ligand loss with concomitant loss of all the hydrides, presumably as four molecules of hydrogen to give the ligated silver cluster, [Ag 10 L 3 ] 2+ . The subsequent fragmentation reactions of the product ions were also examined. Most of the singly charged ligated silver hydride clusters fragment to form [Ag x H x−1 L y ] + . The exceptions are [Ag 9 H 8 L 2 ] + and [Ag 7 H 6 L 2 ] + which, upon ligand loss also release all of the hydrides to form the ligated silver clusters, [Ag 9 L] + and [Ag 7 L] + respectively. DFT calculations were carried out to examine how the cluster geometry changes for the following processes: [Ag 10 H 8 L 6 ] 2+ → [Ag 10 H 8 L 4 ] 2+ + 2L → [Ag 10 H 8 L 3 ] 2+ + L → [Ag 10 L 3 ] 2+ + 4H 2 . Losses of 2 L from [Ag 10 H 8 L 6 ] 2+ and L from [Ag 10 H 8 L 4 ] 2+ were calculated to be endothermic by 2.9 and 1.9 eV respectively, but the subsequent loss of 4H 2 from [Ag 10 H 8 L 3 ] 2+ is exothermic by 0.2 eV. [ABSTRACT FROM AUTHOR]

Gas-phase experiments using collision-induced dissociation in an ion trap mass spectrometer have been used in combination with density functional theory (DFT) calculations (at the B3LYP/SDD6-31+G(d) level of theory) to examine the competition between decarboxylation and loss of a coordinated acetonitrile in the unimolecular fragmentation reactions of the silver acetate and silver propiolate complexes, [RCO2Ag2 (CH3CN) n]+ (where R = CH3 and CH3C=C; n = 1 and 2), introduced into the gas-phase via electrospray ionisation. When R = CH[sub 3], loss of acetonitrile is the sole reaction channel observed for both complexes (n = 1 and 2), consistent with DFT calculations, which highlight that the barriers for decarboxylation 2.18 eV (n = 2) and 1.96 eV (n = 1) are greater than the binding energies of the coordinated acetonitriles (1.60 eV for n = 2; 1.64 eV for n = 1). In contrast, when R = CH3C=C, decarboxylation is the main fragmentation pathway observed for both complexes (n = 1 and 2), with loss of acetonitrile only being a minor product channel. This is consistent with DFT calculations, which reveal that the barriers for decarboxylation are 1.17 eV (n = 2) and 1.16 eV (n = 1), which are both below the binding energies of the coordinated acetonitriles (1.55 eV for n = 2; 1.56 eV for n = 1). The barrier for decarboxylation of [CH3C=CCO2Ag2]+ is 1.22 eV, which is less than the 2.06 eV reported for decarboxylation of [CH3CO2Ag2]+ (Al Sharif et al. Organometallics, 2013, 32, 5416). The observed ease of decarboxylation of silver propiolate complexes in the gas-phase is consistent with the recently reported use of silver salts in metal catalysed decarboxylative C-C and C-X bond forming reactions of propiolic acids. Fragmentation of the complexes [RCO2Ag2 (CH3CN)n]+ (n = 1 and 2) is dictated by the R group. Decarboxylation is preferred over loss of a coordinated acetonitrile for R = CH[sub 3]C=C, but ligand loss is the sole pathway when R = CH3. [ABSTRACT FROM AUTHOR]

Electrospray ionization mass spectrometry (ESI/MS) of mixtures of AgNO 3 or AgBF 4 with the capping ligand Me 2 P (CH 2 ) PMe 2 (dmpm, L) in a solution of 1:1 methanol:chloroform or acetonitrile revealed the formation of: dinuclear clusters [Ag 2 L 2 ] 2+ , [Ag 2 (L H)L] + , and [Ag 2 ClL 2 ] + ; trinuclear clusters primarily as [Ag 3 Cl 2 L 3 ] + ; and the tetranuclear cluster [Ag 4 Cl 3 L 3 ] + . Addition of NaBH 4 to these solutions of dmpm-protected clusters results in the formation of the silver hydride cluster cations [Ag 2 HL 2 ] + , [Ag 3 HL 3 ] 2+ , [Ag 3 HL 4 ] 2+ , [Ag 3 H(CN)L 3 ] + and [Ag 3 HClL 3 ] + as determined by ESI/MS. Use of NaBD 4 confirmed that the borohydride is the source of the hydride in these clusters. The gas-phase unimolecular chemistry of selected clusters was examined in a LTQ-FT hybrid linear ion trap (LIT) mass spectrometer. Low-energy collision-induced dissociation (CID) was performed on the clusters [Ag 3 Cl 2 L 3 ] + , [Ag 3 HClL 3 ] + , [Ag 3 H(CN)L 3 ] + , [Ag 3 HL 3 ] 2+ , [Ag 3 HL 4 ] 2+ and their nascent fragments. Neutral ligand loss, core fission and ligand activation were observed to depend on the cluster stoichiometry. Thus, [Ag 3 XYL 3 ] + (X, Y = Cl; X = H; Y = Cl or CN) mainly fragment via ligand loss, [Ag 3 XYL 2 ] + undergoes both ligand loss and core fission, [Ag 3 XYL] + undergoes core fission and [Ag 2 YL] + undergoes ligand activation. Small yields of reductive elimination of HY are observed for [Ag 3 HYL 2 ] + (Y = Cl and CN). Density functional theory (DFT) calculations were used to calculate the energetics of the optimised structures for all parent, fragment ions and neutrals and to estimate the reaction endothermicities. Generally there is a reasonable agreement between the most abundant product ion formed and the predicted endothermicity, except for the reductive elimination reactions. Finally, electron-induced dissociation (EID) of [Ag 3 HL 3 ] 2+ and [Ag 3 HL 4 ] 2+ gave similar fragmentation channels to CID. [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]

Metal-catalyzed decarboxylative couplingreactions offer new opportunitiesfor formation of C–C bonds. Here, multistage ion trap massspectrometry experiments together with DFT calculations are used toexamine the role of the metal centers in coinage metal cluster catalyzeddecarboxylative coupling of allyl acetate in the gas phase via a simpletwo-step catalytic cycle. In step 1, the metal acetate cluster cation[CH3CO2Cu2]+, [CH3CO2AgCu]+, or [CH3CO2Ag2]+is subjected to collision-induceddissociation to yield the organometallic cluster cation [CH3Cu2]+, [CH3AgCu]+, or[CH3Ag2]+, respectively. Step 2 involvessubjecting these organometallic cluster cations to ion–moleculereactions with allyl acetate with the aim of generating 1-butene andre-forming the metal acetate cluster cations to close the catalyticcycle. Experiment and theory reveal the role of the two metal centersin both steps of the gas-phase catalytic reaction. All three metalacetates undergo decarboxylation (step 1), although when competingreactions are taken into account, the yield of [CH3Cu2]+is highest (83.3%). Ion–molecule reactionsof the organometallic cations with allyl acetate all proceed at thecollision rate; however, the types of products formed and their yieldsvary considerably. For example, only [CH3Cu2]+and [CH3AgCu]+undergo the C–Cbond-coupling reaction (step 2) in yields of 52.7% and 1.2%, respectively.Overall the dicopper clusters are the superior decarboxylative couplingcatalysts, since they give the highest yields of the desired productsfor both steps 1 and 2. These results highlight that the reactivityof organometallic coinage metal clusters can be “tuned”by varying the composition of the metal core. [ABSTRACT FROM AUTHOR]

The gas-phase reactivity of the vanadium hydroxides [VO2(OH)2]−and [V2O5(OH)]−toward methanol was examined usinga combinationof ion–molecule reactions (IMRs) and collision-induced dissociation(CID) in a quadrupole ion trap mass spectrometer. Isotope-labelingexperiments with CD3OH, 13CH3OH,and CH318OH were used to confirm the stoichiometryof ions and the observed sequence of reactions. The experimental datawere interpreted with the aid of density functional theory calculations,carried out at the B3LYP/SDD6-311++G** level of theory. While [VO2(OH)2]−is unreactive, [V2O5(OH)]−undergoes a metathesisreaction to yield [V2O5(OCH3)]−. The DFT calculations reveal that the metathesis reactionof methanol with [VO2(OH)2]−suffers from a barrier of +0.52 eV (relative to separated reactants)but that the reaction of [V2O5(OH)]−with methanol readily proceeds via addition/elimination reactionswith both transition states being below the energy of the separatedreactants. CID of [V2O5(OCH3)]−(m/z213) yieldsthree ions arising from activation of the methoxo ligand: [V2, O6, C, H]−(m/z211); [V2, O5, H]−(m/z183); and [V2,O4, H]−(m/z167). Additional experiments and DFT calculations suggest that theseions arise from losses of H2, formaldehyde and the sequentiallosses of H2and CO2, respectively. The useof an 18O-labeled methoxo ligand in [V2O5(18OCH3)]−(m/z215) showed the competing losses ofH2C16O and H2C18O and[H2and C16O18O] and [H2and C16O2], highlighting that 16O/18O exchange between the methoxo ligand and the vanadiumoxide occurs prior to the subsequent fragmentation of the ligand.DFT calculations reveal that a key step involves hydrogen atom transferfrom the methoxo ligand to the oxo ligand of the same vanadium center,producing the intermediate [V2O4(OH)(OCH2)]−containing a ketyl radical ligand anda hydroxo ligand. This intermediate can either undergo CH2O loss, or the ketyl radical can couple with an oxo ligand of theadjacent vanadium center, producing [V2O3(μ2-O2CH2)]−, which isa key intermediate in the 16O/18O scramblingand in the H2loss channel. [ABSTRACT FROM AUTHOR]

Electrospray ionization and tandem mass spectrometry experiments have been used to study the fragmentation and electron-ion interactions of doubly charged zwitterionic clusters, [M15 + 2H]2+ (where M = Glycine Betaine (GB), (CH15)15N+CH2CO2-, and Di-methylsulfonioacetate (DMSA),(CH3)2S+CH2CO2 which are close to the stability limit, i.e., the Coulomb repulsion of the charge within the cluster competes with attractive forces. The intercluster chemistry was studied using collision-induced dissociation (CID) and electron-induced dissociation (ELD) in which the energy of the electrons has been varied from >0 to 30 eV. Experimental results suggest that the zwitterionic binding energy in the clusters follow the order GB > DMSA, which is consistent with theoretical calculations that highlight that the lower dipole moment of DMSA leads to a binding energy of DMSA that is 0.86 times smaller than that for GB. Multiply protonated dusters of both GB and DMSA dissociate through Coulomb explosion, which is in competition with neutral evaporation for DMSA. Electronic excitation of the cluster under EID conditions at higher electron energies >12 eV can lead to new intercluster reactions associated with bond cleavages where differences between the sulfur and nitrogen betaines are minor. [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: Translating a homogenous catalyst into a heterogeneous catalyst requires a fundamental understanding of how the catalyst “fits” into the zeolite and how the reaction is influenced. Previous studies of bimetallic catalyst design identified a potent copper homobinuclear catalyst, [(L)Cu2(H)]+ for the selective decomposition of formic acid. Here, a close interplay between theory and experiment shows how to preserve this selective reactivity within zeolites. Gas‐phase experiments and DFT calculations showed that switching from 1,1‐bis(diphenylphosphino)‐methane ligand to the 1,8‐naphthyridine ligand produced an equally potent catalyst. DFT calculations show that this new catalyst neatly fits into a zeolite which does not perturb reactivity, thus providing a unique example on how “heterogenization” of a homogenous catalyst for the selective catalysed extrusion of carbon dioxide from formic acid can be achieved, with important application in hydrogen storage and in situ generation of H2. [ABSTRACT FROM AUTHOR]

The hydroxyl radical is a well known reactive oxygen species important for interstellar, atmospheric, and combustion chemistry in addition to multiple biochemical processes. Although there are many methods to generate the hydroxyl radical, most of these are inorganic based, with only a few originating from organic precursor molecules. Reported herein is the observation that trimethylammonium benzyl alcohols and their corresponding deuterated isotopologues act as a good source of hydroxyl and deuteroxyl radicals in the gas-phase under collision-induced dissociation (CID) conditions. Attempts to replicate this chemistry in the condensed phase are described. [ABSTRACT FROM AUTHOR]

Multistage mass spectrometry and density functional theory (DFT) were used to characterise the small silver hydride nanocluster, [Ag3H2L]+ (where L=(Ph2P)2CH2) and its gas-phase unimolecular chemistry. Collision-induced dissociation (CID) yields [Ag2HL]+ as the major product while laser-induced dissociation (LID) proceeds via H2 formation and subsequent release from [Ag3H2L]+, giving rise to [Ag3L]+ as the major product. Deuterium labelling studies on [Ag3D2L]+ prove that the source of H2 is from the hydrides and not from the ligand. Comparison of TD-DFT absorption patterns obtained for the optimised structures with action spectroscopy results, allows assignment of the measured features to structures of precursors and products. Molecular dynamics 'on the fly' reveal that AgH loss is favoured in the ground state, but H2 formation and loss is preferred in the first excited state S1, in agreement with CID and LID experimental findings. This indicates favourable photo-induced formation of H2 and subsequent release from [Ag3H2L]+, an important finding in context of metal hydrides as a hydrogen storage medium, which can subsequently be released by heating or irradiation with light. [ABSTRACT FROM AUTHOR]