Role of the Metal, Ligand, and Alkyl/Aryl Group in the Hydrolysis Reactions of Group 10 Organometallic Cations [(L)M(R)]+

The Magnesium Dication and Water Synergistically Promote the Protonolysis of Two of the B-C Bonds in the Tetraphenylborate Anion

Analytes are sampled from both solution phase and gas-phase environments during the ESI process, and thus, the mass spectrum that is measured can reflect both solution and gas-phase conditions. In the gas-phase regime, ion-molecule reactions can influence the types of ions that are observed. Herein, the synergistic effects of a Lewis acid (Mg2+) and background water are shown to lead to protonolysis of two of the B-C bonds of the tetraphenylborate ion in the gas phase, giving rise to different ions at different reaction times in ESI-MS/MS experiments in a linear ion trap mass spectrometer. At short reaction times (1 ms), the expected adduct [Mg(BPh4)]+ is observed. At 10 ms, [(HO)Mg(BPh3)]+ and [(HO)2Mg(BPh2)]+ are observed. At 100 ms, the water adducts [(HO)2Mg(BPh2)(H2O)]+ and [(HO)2Mg(BPh2)(H2O)2]+ appear, and these become the dominant ions at longer reaction times. DFT calculations provide a plausible explanation as to why only [(HO)Mg(BPh3)]+ and [(HO)2Mg(BPh2)]+ but not [(HO)3Mg(BPh)]+ are observed.

Organolanthanide Complexes Containing Ln-CH3 σ-bonds: Unexpectedly Similar Hydrolysis Rates for Trivalent and Tetravalent Organocerium

We report the gas-phase preparation, isolation, and reactivity of a series of organolanthanides featuring the Ln-CH3 bond. The complexes are formed by decarboxylating anionic lanthanide acetates to form trivalent [LnIII(CH3)(CH3CO2)3]- (Ln = La, Ce, Pr, Nd, Sm, Tb, Tm, Yb, Lu), divalent [EuII(CH3)(CH3CO2)2]-, and the first examples of tetravalent organocerium complexes featuring CeIV-Calkyl σ-bonds: [CeIV(O)(CH3)(CH3CO2)2]- and [CeIV(O)(CH3)(NO3)2]-. Attempts to isolate PrIV-CH3 and TbIV-CH3 were unsuccessful; however, fragmentation patterns reveal that the oxidation of LnIII to a LnIV-oxo-acetate complex is more favorable for Ln = Pr than for Ln = Tb. The rate of Ln-CH3 hydrolysis is a measure of bond stability, and it decreases from LaIII-CH3 to LuIII-CH3, with increasing steric crowding for smaller Ln stabilizing the harder Ln-CH3 bond against hydrolysis. [EuII(CH3)(CH3CO2)2]- engages in a much faster hydrolysis versus LnIII-CH3. The surprising observation of similar hydrolysis rates for CeIV-CH3 and CeIII-CH3 is discussed with respect to sterics, the oxo ligand, and bond covalency in σ-bonded organolanthanides.

Gas Phase Protolysis of Trisarylzincate Anions

We have applied a combination of tandem-mass spectrometry, quantum-chemical calculations, and statistical rate theory computations to examine the gas phase reactions between the trisarylzincate anions Ar^XZnPh₂^- (Ar^X = p-X-C₆H₄, X = NMe₂, OMe, Me, H, F, and Cl) and 2,2,2-trifluoroethanol at T = 310 ± 20 K. The observed reactions bring about the protonation of one of the aryl anions, which is then released as the corresponding arene, while the formed alkoxide binds to the zinc center. The protonation is faster for the more electron-rich aryl groups and shows a linear Hammett plot if the rate constant for X = NMe₂ is discarded from the analysis. Although the reactions are highly exothermic, they proceed only with relatively low efficiencies (0.1% ≤ φ ≤ 1.3%). According to the quantum-chemical calculations, this behavior can be ascribed to the reactions proceeding through a double-well potential with a tight transition structure located at the central barrier. Based on these potential energy surfaces, the statistical rate theory computations can reproduce the measured rate constants within factors of 2 to 8. A comparison of the protolysis of the trisarylzincates with that of the corresponding free aryl anions demonstrates how the coordination to the metal center not only stabilizes the carbanions energetically but also moderates their reactivity. Thus, our gas phase study contributes to a better understanding of the fundamentals of organometallic reactivity.

ORGANOMETALLIC GAS-PHASE ION CHEMISTRY AND CATALYSIS: INSIGHTS INTO THE USE OF METAL CATALYSTS TO PROMOTE SELECTIVITY IN THE REACTIONS OF CARBOXYLIC ACIDS AND THEIR DERIVATIVES

Carboxylic acids are valuable organic substrates as they are widely available, easy to handle, and exhibit structural and functional variety. While they are used in many standard synthetic protocols, over the past two decades numerous studies have explored new modes of metal-mediated reactivity of carboxylic acids and their derivatives. Mass spectrometry-based studies can provide fundamental mechanistic insights into these new modes of reactivity. Here gas-phase models for the following catalytic transformations of carboxylic acids and their derivatives are reviewed: protodecarboxylation; dehydration; decarbonylation; reaction as coordinated bases in C-H bond activation; remote functionalization and decarboxylative C-C bond coupling. In each case the catalytic problem is defined, insights from gas-phase studies are highlighted, comparisons with condensed-phase systems are made and perspectives are reached. Finally, the potential role for mechanistic studies that integrate both gas- and condensed-phase studies is highlighted by recent studies on the discovery of new catalysts for the selective decomposition of formic acid and the invention of the new extrusion-insertion class of reactions for the synthesis of amides, thioamides, and amidines. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

A noncovalent hybrid of [Pd(phen)(OAc)2] and st-DNA for the enantioselective hydroamination of β-nitrostyrene with methoxyamine

We developed a novel Pd-catalysed enantioselective synthesis of C-N bonds using the chiral scaffold of DNA. The non-covalently linked [Pd(phen)(OAc)2] with st-DNA catalysed the Markonicov hydroamination of β-nitrostyrene with methoxyamine for the first time with >75% enantiomeric excess (ee) in an aqueous buffer (pH 7.4) at room temperature.

Gas-phase studies of copper(I)-mediated CO2 extrusion followed by insertion of the heterocumulenes CS2 or phenylisocyanate

The gas-phase extrusion-insertion reactions of the copper complex [bathophenanthroline (Bphen)CuI (O2 CC6 H5 )]2- , generated via electrospray ionization, was studied in a linear ion trap mass spectrometer with the combination of collision-induced dissociation (CID) and ion-molecule reaction (IMR) events. Multistage mass spectrometry (MSn ) experiments and density functional theory (DFT) demonstrated that extrusion of carbon dioxide from [(Bphen)Cu(O2 CC6 H5 )]2- (CID) gives the organometallic intermediate [(Bphen)Cu(C6 H5 )]2- , which subsequently reacts with carbon disulfide (IMR) via insertion to yield [(Bphen)Cu (SC(S)C6 H5 )]2- . The fragmentation of the product ion resulted in the formation of [Bphen]2- , [(Bphen)Cu]- and C6 H5 CS2 - under CID conditions. The formation of the latter two charge separation products thus provides evidence of C-C bond formation in the IMR step. Although analogous studies with isocyanate, which is isoelectronic with CS2 , showed a poor reactivity in the gas phase, the mechanistic understanding obtained from these model studies encourages future development of a solution phase protocol for the synthesis of amides from carboxylic acids and isocyanates mediated by copper(I) complexes.

Gas-Phase Synthesis and Reactivity of Ligated Group 10 Ions in the Formal +1 Oxidation State

Electrospray ionization of the group 10 complexes [(phen)M(O₂CCH₃)₂] (phen=1,10-phenanthroline, M = Ni, Pd, Pt) generates the cations [(phen)M(O₂CCH₃)]⁺, whose gas-phase chemistry was studied using multistage mass spectrometry experiments in an ion trap mass spectrometer with the combination of collision-induced dissociation (CID) and ion-molecule reactions (IMR). Decarboxylation of [(phen)M(O₂CCH₃)]⁺ under CID conditions generates the organometallic cations [(phen)M(CH₃)]⁺, which undergo bond homolysis upon a further stage of CID to generate the cations [(phen)M]^+· in which the metal center is formally in the +1 oxidation state. In the case of [(phen)Pt(CH₃)]⁺, the major product ion [(phen)H]⁺ was formed via loss of the metal carbene Pt=CH₂. DFT calculated energetics for the competition between bond homolysis and M=CH₂ loss are consistent with their experimentally observed branching ratios of 2% and 98% respectively. The IMR of [(phen)M]^+· with O₂, N₂, H₂O, acetone, and allyl iodide were examined. Adduct formation occurs for O₂, N₂, H₂O, and acetone. Upon CID, all adducts fragment to regenerate [(phen)M]^+·, except for [(phen)Pt(OC(CH₃)₂)]^+·, which loses a methyl radical to form [(phen)Pt(OCCH₃)]⁺ which upon a further stage of CID regenerates [(phen)Pt(CH₃)]⁺ via CO loss. This closes a formal catalytic cycle for the decomposition of acetone into CO and two methyl radicals with [(phen)Pt]^+· as catalyst. In the IMR of [(phen)M]^+· with allyl iodide, formation of [(phen)M(CH₂CHCH₂)]⁺ was observed for all three metals, whereas for M = Pt also [(phen)Pt(I)]⁺ and [(phen)Pt(I)₂(CH₂CHCH₂)]⁺ were observed. Finally, DFT calculated reaction energetics for all IMR reaction channels are consistent with the experimental observations.

Formation and hydrolysis of gas-phase [UO2 (R)]+ : R═CH3 , CH2 CH3 , CH═CH2 , and C6 H5

The goals of the present study were (a) to create positively charged organo-uranyl complexes with general formula [UO₂ (R)]⁺ (eg, R═CH₃ and CH₂ CH₃ ) by decarboxylation of [UO₂ (O₂ C─R)]⁺ precursors and (b) to identify the pathways by which the complexes, if formed, dissociate by collisional activation or otherwise react when exposed to gas-phase H₂ O. Collision-induced dissociation (CID) of both [UO₂ (O₂ C─CH₃ )]⁺ and [UO₂ (O₂ C─CH₂ CH₃ )]⁺ causes H⁺ transfer and elimination of a ketene to leave [UO₂ (OH)]⁺ . However, CID of the alkoxides [UO₂ (OCH₂ CH₃ )]⁺ and [UO₂ (OCH₂ CH₂ CH₃ )]⁺ produced [UO₂ (CH₃ )]⁺ and [UO₂ (CH₂ CH₃ )]⁺ , respectively. Isolation of [UO₂ (CH₃ )]⁺ and [UO₂ (CH₂ CH₃ )]⁺ for reaction with H₂ O caused formation of [UO₂ (H₂ O)]⁺ by elimination of ·CH₃ and ·CH₂ CH₃ : Hydrolysis was not observed. CID of the acrylate and benzoate versions of the complexes, [UO₂ (O₂ C─CH═CH₂ )]⁺ and [UO₂ (O₂ C─C₆ H₅ )]⁺ , caused decarboxylation to leave [UO₂ (CH═CH₂ )]⁺ and [UO₂ (C₆ H₅ )]⁺ , respectively. These organometallic species do react with H₂ O to produce [UO₂ (OH)]⁺ , and loss of the respective radicals to leave [UO₂ (H₂ O)]⁺ was not detected. Density functional theory calculations suggest that formation of [UO₂ (OH)]⁺ , rather than the hydrated U^V O₂ ⁺ , cation is energetically favored regardless of the precursor ion. However, for the [UO₂ (CH₃ )]⁺ and [UO₂ (CH₂ CH₃ )]⁺ precursors, the transition state energy for proton transfer to generate [UO₂ (OH)]⁺ and the associated neutral alkanes is higher than the path involving direct elimination of the organic neutral to form [UO₂ (H₂ O)]⁺ . The situation is reversed for the [UO₂ (CH═CH₂ )]⁺ and [UO₂ (C₆ H₅ )]⁺ precursors: The transition state for proton transfer is lower than the energy required for creation of [UO₂ (H₂ O)]⁺ by elimination of CH═CH₂ or C₆ H₅ radical.

Gas-Phase Deconstruction of UO22+: Mass Spectrometry Evidence for Generation of [OUVICH]+ by Collision-Induced Dissociation of [UVIO2(C≡CH)]. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019;30:796-805. [PMID: 30911904 DOI: 10.1007/s13361-019-02179-6]

Because of the high stability and inertness of the U=O bonds, activation and/or functionalization of UO₂²⁺ and UO₂⁺ remain challenging tasks. We show here that collision-induced dissociation (CID) of the uranyl-propiolate cation, [U^VIO₂(O₂C-C≡CH)]⁺, can be used to prepare [U^VIO₂(C≡CH)]⁺ in the gas phase by decarboxylation. Remarkably, CID of [U^VIO₂(C≡CH)]⁺ caused elimination of CO to create [OU^VICH]⁺, thus providing a new example of a well-defined substitution of an "yl" oxo ligand of U^VIO₂²⁺ in a unimolecular reaction. Relative energies for candidate structures based on density functional theory calculations suggest that the [OU^VICH]⁺ ion is a uranium-methylidyne product, with a U≡C triple bond composed of one σ-bond with contributions from the U df and C sp hybrid orbitals, and two π-bonds with contributions from the U df and C p orbitals. Upon isolation, without imposed collisional activation, [OU^VICH]⁺ appears to react spontaneously with O₂ to produce [U^VO₂]⁺. Graphical Abstract .

Gas-Phase Reactions of the Group 10 Organometallic Cations, [(phen)M(CH3)]+ with Acetone: Only Platinum Promotes a Catalytic Cycle via the Enolate [(phen)Pt(OC(CH2)CH3)]+

Electrospray ionisation of the ligated group 10 metal complexes [(phen)M(O2CCH3)2] (M = Ni, Pd, Pt) generates the cations [(phen)M(O2CCH3)]+, whose gas-phase chemistry was studied using multistage mass spectrometry experiments in an ion trap mass spectrometer with the combination of collision-induced dissociation (CID) and ion-molecule reactions (IMR). A new catalytic cycle has been discovered. In step 1, decarboxylation of [(phen)M(O2CCH3)]+ under CID conditions generates the organometallic cations [(phen)M(CH3)]+, which react with acetone to generate the [(phen)M(CH3)(OC(CH3)2)]+ adducts in competition with formation of the coordinated enolate for M = Pt (step 2). For M = Ni and Pd, the adducts regenerate [(phen)M(CH3)]+ upon CID. In the case of M = Pt, loss of methane is favored over loss of acetone and results in the formation of the enolate complex, [(phen)Pt(OC(CH2)CH3)]+. Upon further CID, both methane and CO loss can be observed resulting in the formation of the ketenyl and ethyl complexes [(phen)Pt(OCCH)]+ and [(phen)Pt(CH2CH3)]+ (step 3), respectively. In step 4, CID of [(phen)Pt(CH2CH3)]+ results in a beta-hydride elimination reaction to yield the hydride complex, [(phen)Pt(H)]+, which reacts with acetic acid to regenerate the acetate complex [(phen)Pt(O2CCH3)]+ and H2 in step 5. Thus, the catalytic cycle is formally closed, which corresponds to the decomposition of acetone and acetic acid into methane, CO, CO2, ethene and H2. All except the last step of the catalytic cycle are modelled using DFT calculations with optimizations of structures at the M06/SDD 6-31G(d) level of theory.

Mild and selective Pd-Ar protonolysis and C-H activation promoted by a ligand aryloxide group

A bidentate nitrogen-donor ligand with an appended phenol group, C₅H₄NCH[double bond, length as m-dash]N-2-C₆H₄OH, H(L1) was treated with a palladium cycloneophyl complex [Pd(CH₂CMe₂C₆H₄)(COD)], with both Pd-aryl and Pd-alkyl bonds, to give a Pd-alkyl complex, [Pd(CH₂CMe₂C₆H₅)(κ³-N,N',O-OC₆H₄N[double bond, length as m-dash]CH(2-C₅H₄N))], 1. The cleavage of the Pd-aryl bond and the deprotonation of the ligand phenol to afford a bound aryloxide, indicates facile Pd-aryl bond protonolysis. Deuterium labelling experiments confirmed that the ligand phenol promotes protonolysis and that the reverse, aryl C-H activation, occurs under very mild reaction conditions (within 10 min at room temperature). An unusual isomerization of the Pd-alkyl complex 1 to a Pd-aryl complex, [Pd(C₆H₄(2-t-Bu))(κ³-N,N',O-OC₆H₄N[double bond, length as m-dash]CH(2-C₅H₄N))], 2, was observed to give an equilibrium with [2]/[1] = 9 after 5 days in methanol. The isomerization requires that both aryl C-H activation and Pd-alkyl protonolysis steps occur. The very large KIE value (k_H/k_D = ca. 40) for isomerization of 1 to 2, suggests a concerted S_E2-type mechanism for the Pd-alkyl protonolysis step.

Ligand-induced decarbonylation in diphosphine-ligated palladium acetates [CH3CO2Pd((PR2)2CH2)]+ (R = Me and Ph)

Isotope labelling, IR spectroscopy and DFT calculations reveal a novel ligand-induced decarbonylation reaction.

Sulphur dioxide cooperation in hydrolysis reactions of vanadium oxide and hydroxide cluster dianions

Gas-phase hydrolysis takes place due to the synergistic action of SO₂ and vanadium-containing dianions that succeeds in tightening hydrogen bonds.

Anionic Palladium(0) and Palladium(II) Ate Complexes

Palladium ate complexes are frequently invoked as important intermediates in Heck and cross-coupling reactions, but so far have largely eluded characterization at the molecular level. Here, we use electrospray-ionization mass spectrometry, electrical conductivity measurements, and NMR spectroscopy to show that the electron-poor catalyst [L₃ Pd] (L=tris[3,5-bis(trifluoromethyl)phenyl]phosphine) readily reacts with Br^- ions to afford the anionic, zero-valent ate complex [L₃ PdBr]^- . In contrast, more-electron-rich Pd catalysts display lower tendencies toward the formation of ate complexes. Combining [L₃ Pd] with LiI and an aryl iodide substrate (ArI) results in the observation of the Pd^II ate complex [L₂ Pd(Ar)I₂ ]^- .

Gas-phase studies of metal catalyzed decarboxylative cross-coupling reactions of esters

Metal-catalyzed decarboxylative coupling reactions of esters offer new opportunities for formation of C–C bonds with CO2as the only coproduct. Here I provide an overview of: key solution phase literature; thermochemical considerations for decarboxylation of esters and thermolysis of esters in the absence of a metal catalyst. Results from my laboratory on the use of multistage ion trap mass spectrometry experiments and DFT calculations to probe the gas-phase metal catalyzed decarboxylative cross-coupling reactions of allyl acetate and related esters are then reviewed. These studies have explored the role of the metal carboxylate complex in the gas phase decarboxylative coupling of allyl acetate proceeding via a simple two-step catalytic cycle. In Step 1, an organometallic ion, [CH3ML]+/–(where M is a group 10 or 11 metal and L is an auxillary ligand), is allowed to undergo ion-molecule reactions with allyl acetate to generate 1-butene and the metal acetate ion, [CH3CO2ML]+/–. In Step 2, the metal acetate ion is subjected to collision-induced dissociation to reform the organometallic ion and thereby close the catalytic cycle. DFT calculations have been used to explore the mechanisms of these reactions. The organometallic ions [CH3CuCH3]–, [CH3Cu2]+, [CH3AgCu]+and [CH3M(phen)]+(where M = Ni, Pd and Pt) all undergo C–C bond coupling reactions with allyl acetate (Step 1), although the reaction efficiencies and product branching ratios are highly dependant on the nature of the metal complex. For example, [CH3Ag2]+does not undergo C–C bond coupling. Using DFT calculations, a diverse range of mechanisms have been explored for these C–C bond-coupling reactions including: oxidative-addition, followed by reductive elimination; insertion reactions and SN2-like reactions. Which of these mechanisms operate is dependant on the nature of the metal complex. A wide range of organometallic ions can be formed via decarboxylation (Step 2) although these reactions can be in competition with other fragmentation channels. DFT calculations have located different types of transition states for the formation of [CH3CuCH3]–, [CH3Cu2]+, [CH3AgCu]+and [CH3M(phen)]+(where M = Ni, Pd and Pt). Of the catalysts studied to date, [CH3Cu2]+and [CH3Pd(phen)]+are best at promoting C–C bond formation (Step 1) as well as being regenerated (Step 2). Preliminary results on the reactions of [C6H5M(phen)]+(M = Ni and Pd) with C6H5CO2CH2CH=CH2and C6H5CO2CH2C6H5are described.

Mechanistic insights from mass spectrometry: examination of the elementary steps of catalytic reactions in the gas phase

Real-time mass spectrometric monitoring of speciation in a catalytic reaction while it is occurring provides powerful insights into mechanistic aspects of the reaction, but cannot be expected to elucidate all details. However, mass spectrometers are not limited just to analysis: they can serve as reaction vessels in their own right, and given their powers of separation and activation in the gas phase, they are also capable of generating and isolating reactive intermediates. We can use these capabilities to help fill in our overall understanding of the catalytic cycle by examining the elementary steps that make it up. This article provides examples of how these simple reactions have been examined in the gas phase.

Gas phase studies of the Pesci decarboxylation reaction: synthesis, structure, and unimolecular and bimolecular reactivity of organometallic ions

CONSPECTUS: Decarboxylation chemistry has a rich history, and in more recent times, it has been recruited in the quest to develop cheaper, cleaner, and more efficient bond-coupling reactions. Thus, over the past two decades, there has been intense investigation into new metal-catalyzed reactions of carboxylic substrates. Understanding the elementary steps of metal-mediated transformations is at the heart of inventing new reactions and improving the performance of existing ones. Fortunately, during the same time period, there has been a convergence in mass spectrometry (MS) techniques, which allows these catalytic processes to be examined efficiently in the gas phase. Thus, electrospray ionization (ESI) sources have been combined with ion-trap mass spectrometers, which in turn have been modified to either accept radiation from tunable OPO lasers for spectroscopy based structural assignment of ions or to allow the study of ion-molecule reactions (IMR). The resultant "complete" gas-phase chemical laboratories provide a platform to study the elementary steps of metal-catalyzed decarboxylation reactions in exquisite detail. In this Account, we illustrate how the powerful combination of ion trap mass spectrometry experiments and DFT calculations can be systematically used to examine the formation of organometallic ions and their chemical transformations. Specifically, ESI-MS allows the transfer of inorganic carboxylate complexes, [RCO2M(L)n](x), (x = charge) from the condensed to the gas phase. These mass selected ions serve as precursors to organometallic ions [RM(L)n](x) via neutral extrusion of CO2, accessible by slow heating in the ion trap using collision induced dissociation (CID). This approach provides access to an array of organometallic ions with well-defined stoichiometry. In terms of understanding the decarboxylation process, we highlight the role of the metal center (M), the organic group (R), and the auxiliary ligand (L), along with cluster nuclearity, in promoting the formation of the organometallic ion. Where isomeric organometallic ions are generated and normal MS approaches cannot distinguish them, we describe approaches to elucidate the decarboxylation mechanism via determination of their structure. These "unmasked" organometallic ions, [RM(L)n](x), can also be structurally interrogated spectroscopically or via CID. We have thus compared the gas-phase structures and decomposition of several highly reactive and synthetically important organometallic ions for the first time. Perhaps the most significant aspect of this work is the study of bimolecular reactions, which provides experimental information on mechanistically obscure bond-formation and cross-coupling steps and the intrinsic reactivity of ions. We have sought to understand transformations of substrates including acid-base and hydrolysis reactions, along with reactions resulting in C-C bond formation. Our studies also allow a direct comparison of the performance of different metal catalysts in the individual elementary steps associated with protodecarboxylation and decarboxylative alkylation cycles. Electronic structure (DFT and ab initio) and dynamics (RRKM) calculations provide further mechanistic insights into these reactions. The broad implications of this research are that new reactions can be discovered and that the performance of metal catalysts can be evaluated in terms of each of their elementary steps. This has been particularly useful for the study of metal-mediated decarboxylation reactions.

Copper mediated decyano decarboxylative coupling of cyanoacetate ligands: Pesci versus Lewis acid mechanism

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]⁻.

Gas phase chemistry of N-benzylbenzamides with silver(i) cations: characterization of benzylsilver cation

Benzylsilver cations are synthesized in the gas phase from the collisional dissociation of argentinated N-benzylbenzamides, when the carbonyl oxygen nucleophilically attacks an α-hydrogen.

Decarboxylative-coupling of allyl acetate catalyzed by group 10 organometallics, [(phen)M(CH3)]+

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.

Molecular salt effects in the gas phase: tuning the kinetic basicity of [HCCLiCl]⁻ and [HCCMgCl₂]⁻ by LiCl and MgCl₂

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.