Dimethylcuprate-Mediated Transformation of Acetate to Dithioacetate

Dithiocarboxylic acids, RCS₂H, and their esters, RCS₂R′, are useful reagents that can be synthesized by the reaction of carbon disulfide with organometallic reagents. Here the coinage-metal-mediated transformation of acetate to dithioacetate is explored in the gas phase using multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with density functional theory (DFT) calculations. The ion–molecule reactions between coinage-metal dimethylmetalate anions [CH₃MCH₃]⁻ (M = Au, Ag, Cu), formed via double decarboxylation of the metal acetate anions, [CH₃CO₂MO₂CCH₃]⁻, and carbon disulfide, were examined. Only [CH₃CuCH₃]⁻ reacts with CS₂ with a reaction efficiency of 0.8% of the collision rate 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 major product, with a small amount of [CuS₂CCH₂]⁻ being formed via loss of methane. DFT calculations reveal the following. (i) [CH₃CuCH₃]⁻ reacts via oxidative addition to form a Cu­(III) intermediate, followed by reductive elimination of CH₃CS₂^–, which is captured by Cu to form [CH₃CuS₂CCH₃]⁻. This energetic adduct can fragment via loss of CH₃CS₂^– or can be collisionally cooled by the helium bath gas used in the experiments. (ii) Loss of CH₄ from [CH₃CuS₂CCH₃]⁻ also involves a Cu­(III) intermediate and results in formation of the metalladithiolactone [Cu­(CH₂CS₂)]⁻

Dimethylcuprate-Mediated Transformation of Acetate to Dithioacetate

Dithiocarboxylic acids, RCS₂H, and their esters, RCS₂R′, are useful reagents that can be synthesized by the reaction of carbon disulfide with organometallic reagents. Here the coinage-metal-mediated transformation of acetate to dithioacetate is explored in the gas phase using multistage mass spectrometry experiments in a linear ion trap mass spectrometer in conjunction with density functional theory (DFT) calculations. The ion–molecule reactions between coinage-metal dimethylmetalate anions [CH₃MCH₃]⁻ (M = Au, Ag, Cu), formed via double decarboxylation of the metal acetate anions, [CH₃CO₂MO₂CCH₃]⁻, and carbon disulfide, were examined. Only [CH₃CuCH₃]⁻ reacts with CS₂ with a reaction efficiency of 0.8% of the collision rate 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 major product, with a small amount of [CuS₂CCH₂]⁻ being formed via loss of methane. DFT calculations reveal the following. (i) [CH₃CuCH₃]⁻ reacts via oxidative addition to form a Cu­(III) intermediate, followed by reductive elimination of CH₃CS₂^–, which is captured by Cu to form [CH₃CuS₂CCH₃]⁻. This energetic adduct can fragment via loss of CH₃CS₂^– or can be collisionally cooled by the helium bath gas used in the experiments. (ii) Loss of CH₄ from [CH₃CuS₂CCH₃]⁻ also involves a Cu­(III) intermediate and results in formation of the metalladithiolactone [Cu­(CH₂CS₂)]⁻

Gas-Phase Unimolecular Reactions of Pallada- and Nickelalactone Anions

Electrospray ionization in combination with multistage mass spectrometry experiments in a linear ion trap mass spectrometer was used to generate and study the gas-phase ion chemistry of the metallalactones [(CH₃CO₂)­Ni­(CH₂CO₂)]⁻ (<i>m</i>/<i>z</i> 175, <b>5a</b>) and [(CH₃CO₂)­Pd­(CH₂CO₂)]⁻ (<i>m</i>/<i>z</i> 223, <b>5b</b>). Low-energy collision-induced dissociation (CID) resulted in decarboxylation to produce novel organometallic ions at <i>m</i>/<i>z</i> 131 (Ni) and <i>m</i>/<i>z</i> 179 (Pd). Isotope labeling experiments, bimolecular gas-phase reactions with allyl iodide, and DFT calculations reveal that decarboxylation primarily occurs from the acetato ligand to yield ions of the form [(CH₃)­M­(CH₂CO₂)]⁻ (M = Pd, Ni). Further CID experiments on [(CH₃)­M­(CH₂CO₂)]⁻ together with DFT calculations highlight the following. (1) Both palladium and nickel can facilitate C–C bond formation, with elimination of ethylene being observed. (2) The mechanism for formation of ethylene from [(CH₃)­M­(CH₂CO₂)]⁻ is inherently different for M = Pd versus M = Ni. Elimination of ethylene is competitive with further decarboxylation in the case of nickel, and nickel remains in the 2+ oxidation state throughout. In contrast, the palladium complex is reduced to palladium(0) upon C–C bond formation and undergoes a second decarboxylation before ethylene is released. Finally, the products of the ion–molecule reactions of [(CH₃)­Pd­(CH₂CO₂)]⁻ (<b>7b</b>) with allyl iodide provide evidence for the formation of the Pd­(IV) intermediate [(CH₃)­(I)­(CH₂CHCH₂)­Pd­(CH₂CO₂)]⁻, which decomposes via a range of processes, including losses of iodide, propionate, allyl, and methyl radicals and reductive elimination of butane and methyl iodide

Gas-Phase Reactions of [VO₂(OH)₂]⁻ and [V₂O₅(OH)]⁻ with Methanol: Experiment and Theory

The gas-phase reactivity of the vanadium hydroxides [VO₂(OH)₂]⁻ and [V₂O₅(OH)]⁻ toward methanol was examined using a combination of ion–molecule reactions (IMRs) and collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer. Isotope-labeling experiments with CD₃OH, ¹³CH₃OH, and CH₃¹⁸OH were used to confirm the stoichiometry of ions and the observed sequence of reactions. The experimental data were 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 metathesis reaction to yield [V₂O₅(OCH₃)]⁻. The DFT calculations reveal that the metathesis reaction of 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 reactions with both transition states being below the energy of the separated reactants. CID of [V₂O₅(OCH₃)]⁻ (<i>m</i>/<i>z</i> 213) yields three ions arising from activation of the methoxo ligand: [V₂, O₆, C, H]⁻ (<i>m</i>/<i>z</i> 211); [V₂, O₅, H]⁻ (<i>m</i>/<i>z</i> 183); and [V₂, O₄, H]⁻ (<i>m</i>/<i>z</i> 167). Additional experiments and DFT calculations suggest that these ions arise from losses of H₂, formaldehyde and the sequential losses of H₂ and CO₂, respectively. The use of an ¹⁸O-labeled methoxo ligand in [V₂O₅(¹⁸OCH₃)]⁻ (<i>m</i>/<i>z</i> 215) showed the competing losses of H₂C¹⁶O and H₂C¹⁸O and [H₂ and C¹⁶O¹⁸O] and [H₂ and C¹⁶O₂], highlighting that ¹⁶O/¹⁸O exchange between the methoxo ligand and the vanadium oxide occurs prior to the subsequent fragmentation of the ligand. DFT calculations reveal that a key step involves hydrogen atom transfer from the methoxo ligand to the oxo ligand of the same vanadium center, producing the intermediate [V₂O₄(OH)­(OCH₂)]⁻ containing a ketyl radical ligand and a hydroxo ligand. This intermediate can either undergo CH₂O loss, or the ketyl radical can couple with an oxo ligand of the adjacent vanadium center, producing [V₂O₃(μ₂-O₂CH₂)]⁻, which is a key intermediate in the ¹⁶O/¹⁸O scrambling and in the H₂ loss channel

Catalytic Decarboxylative Coupling of Allyl Acetate: Role of the Metal Centers in the Organometallic Cluster Cations [CH₃Cu₂]⁺, [CH₃AgCu]⁺, and [CH₃Ag₂]⁺

Metal-catalyzed decarboxylative coupling reactions offer new opportunities for formation of C–C bonds. Here, multistage ion trap mass spectrometry experiments together with DFT calculations are used to examine the role of the metal centers in coinage metal cluster catalyzed decarboxylative coupling of allyl acetate in the gas phase via a simple two-step catalytic cycle. In step 1, the metal acetate cluster cation [CH₃CO₂Cu₂]⁺, [CH₃CO₂AgCu]⁺, or [CH₃CO₂Ag₂]⁺ is subjected to collision-induced dissociation to yield the organometallic cluster cation [CH₃Cu₂]⁺, [CH₃AgCu]⁺, or [CH₃Ag₂]⁺, respectively. Step 2 involves subjecting these organometallic cluster cations to ion–molecule reactions with allyl acetate with the aim of generating 1-butene and re-forming the metal acetate cluster cations to close the catalytic cycle. Experiment and theory reveal the role of the two metal centers in both steps of the gas-phase catalytic reaction. All three metal acetates undergo decarboxylation (step 1), although when competing reactions are taken into account, the yield of [CH₃Cu₂]⁺ is highest (83.3%). Ion–molecule reactions of the organometallic cations with allyl acetate all proceed at the collision rate; however, the types of products formed and their yields vary considerably. For example, only [CH₃Cu₂]⁺ and [CH₃AgCu]⁺ undergo the C–C bond-coupling reaction (step 2) in yields of 52.7% and 1.2%, respectively. Overall the dicopper clusters are the superior decarboxylative coupling catalysts, since they give the highest yields of the desired products for both steps 1 and 2. These results highlight that the reactivity of organometallic coinage metal clusters can be “tuned” by varying the composition of the metal core

Catalytic Decarboxylative Coupling of Allyl Acetate: Role of the Metal Centers in the Organometallic Cluster Cations [CH₃Cu₂]⁺, [CH₃AgCu]⁺, and [CH₃Ag₂]⁺

Metal-catalyzed decarboxylative coupling reactions offer new opportunities for formation of C–C bonds. Here, multistage ion trap mass spectrometry experiments together with DFT calculations are used to examine the role of the metal centers in coinage metal cluster catalyzed decarboxylative coupling of allyl acetate in the gas phase via a simple two-step catalytic cycle. In step 1, the metal acetate cluster cation [CH₃CO₂Cu₂]⁺, [CH₃CO₂AgCu]⁺, or [CH₃CO₂Ag₂]⁺ is subjected to collision-induced dissociation to yield the organometallic cluster cation [CH₃Cu₂]⁺, [CH₃AgCu]⁺, or [CH₃Ag₂]⁺, respectively. Step 2 involves subjecting these organometallic cluster cations to ion–molecule reactions with allyl acetate with the aim of generating 1-butene and re-forming the metal acetate cluster cations to close the catalytic cycle. Experiment and theory reveal the role of the two metal centers in both steps of the gas-phase catalytic reaction. All three metal acetates undergo decarboxylation (step 1), although when competing reactions are taken into account, the yield of [CH₃Cu₂]⁺ is highest (83.3%). Ion–molecule reactions of the organometallic cations with allyl acetate all proceed at the collision rate; however, the types of products formed and their yields vary considerably. For example, only [CH₃Cu₂]⁺ and [CH₃AgCu]⁺ undergo the C–C bond-coupling reaction (step 2) in yields of 52.7% and 1.2%, respectively. Overall the dicopper clusters are the superior decarboxylative coupling catalysts, since they give the highest yields of the desired products for both steps 1 and 2. These results highlight that the reactivity of organometallic coinage metal clusters can be “tuned” by varying the composition of the metal core

Catalytic Decarboxylative Coupling of Allyl Acetate: Role of the Metal Centers in the Organometallic Cluster Cations [CH₃Cu₂]⁺, [CH₃AgCu]⁺, and [CH₃Ag₂]⁺

Metal-catalyzed decarboxylative coupling reactions offer new opportunities for formation of C–C bonds. Here, multistage ion trap mass spectrometry experiments together with DFT calculations are used to examine the role of the metal centers in coinage metal cluster catalyzed decarboxylative coupling of allyl acetate in the gas phase via a simple two-step catalytic cycle. In step 1, the metal acetate cluster cation [CH₃CO₂Cu₂]⁺, [CH₃CO₂AgCu]⁺, or [CH₃CO₂Ag₂]⁺ is subjected to collision-induced dissociation to yield the organometallic cluster cation [CH₃Cu₂]⁺, [CH₃AgCu]⁺, or [CH₃Ag₂]⁺, respectively. Step 2 involves subjecting these organometallic cluster cations to ion–molecule reactions with allyl acetate with the aim of generating 1-butene and re-forming the metal acetate cluster cations to close the catalytic cycle. Experiment and theory reveal the role of the two metal centers in both steps of the gas-phase catalytic reaction. All three metal acetates undergo decarboxylation (step 1), although when competing reactions are taken into account, the yield of [CH₃Cu₂]⁺ is highest (83.3%). Ion–molecule reactions of the organometallic cations with allyl acetate all proceed at the collision rate; however, the types of products formed and their yields vary considerably. For example, only [CH₃Cu₂]⁺ and [CH₃AgCu]⁺ undergo the C–C bond-coupling reaction (step 2) in yields of 52.7% and 1.2%, respectively. Overall the dicopper clusters are the superior decarboxylative coupling catalysts, since they give the highest yields of the desired products for both steps 1 and 2. These results highlight that the reactivity of organometallic coinage metal clusters can be “tuned” by varying the composition of the metal core

Who Wins: Pesci, Peters, or Deacon? Intrinsic Reactivity Orders for Organocuprate Formation via Ligand Decomposition

There are three metal-mediated ligand decomposition reactions that give rise to organometallics: (i) decarboxylation of a metal carboxylate, “the Pesci reaction”; (ii) desulfination of a metal sulfinate, “the Peters reaction”; (iii) desulfonation of a metal sulfonate, “the Deacon reaction”. Despite growing interest in their use in applications in organic synthesis, little is known about the relative ease of thermal extrusion of CO₂ versus SO₂ versus SO₃ in metal complexes. Here the intrinsic reactivity orders for organocuprate formation via ligand decomposition have been studied in the gas phase for the first time. A combination of low-energy collision-induced dissociation experiments in an ion trap mass spectrometer and DFT calculations was used. Simple ligand competition experiments in the heterocopper complexes [MeXOCuOYMe]⁻ (where X = CO or SO and Y = SO or SO₂), formed via electrospray ionization, show that desulfination occurs more easily than decarboxylation, which in turn is more facile than desulfonation. This is consistent with DFT calculations at the M06/SDD/cc-pVTZ//M06/cc-pVDZ level of theory, which show that the barriers associated with the transition states follow the order SO₂ < CO₂ < SO₃

Gas-Phase and Computational Study of Identical Nickel- and Palladium-Mediated Organic Transformations Where Mechanisms Proceeding via M^II or M^IV Oxidation States Are Determined by Ancillary Ligands

Gas-phase studies utilizing ion–molecule reactions, supported by computational chemistry, demonstrate that the reaction of the enolate complexes [(CH₂CO₂<i>C</i>,<i>O</i>)­M­(CH₃)]⁻ (M = Ni (<b>5a</b>), Pd (<b>5b</b>)) with allyl acetate proceed via oxidative addition to give M^IV species [(CH₂CO₂<i>C</i>,<i>O</i>)­M­(CH₃)­(η¹-CH₂CHCH₂)­(O₂CCH₃<i>O</i>,<i>O</i>′)]⁻ (<b>6</b>) that reductively eliminate 1-butene, to form [(CH₂CO₂<i>C</i>,<i>O</i>)­M­(O₂CCH₃<i>O</i>,<i>O</i>′)]⁻ (<b>4</b>). The mechanism contrasts with the M^II-mediated pathway for the analogous reaction of [(phen)­M­(CH₃)]⁺ (<b>1a,b</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 d_<i>z</i>²) in <b>5</b> are considerably destabilized, resulting in more facile oxidative addition; the electron transfer from d_<i>z</i>² to the CC π* orbital is the key interaction leading to oxidative addition of allyl acetate to M^II. Upon collision-induced dissociation, <b>4</b> undergoes decarboxylation to form <b>5</b>. These results provide support for the current exploration of roles for Ni^IV and Pd^IV in organic synthesis

Direct versus Water-Mediated Protodecarboxylation of Acetic Acid Catalyzed by Group 10 Carboxylates, [(phen)M(O₂CCH₃)]⁺

The gas-phase protodecarboxylation of acetic acid catalyzed by group 10 metal complexes was examined using a combination of multistage mass spectrometry experiments in an ion trap mass spectrometer, DFT calculations, and theoretical kinetic modeling. Two related catalytic cycles sharing two common intermediates were examined. The entry points to both cycles are the metal acetate complexes [(phen)­M­(O₂CCH₃)]⁺ (where phen = 1,10-phenanthroline), which were formed via direct electrospray ionization of solutions of the complexes [(phen)­M­(O₂CCH₃)₂] in water. Step 1 of both cycles involves decarboxylation of [(phen)­M­(O₂CCH₃)]⁺ under collision-induced dissociation (CID) conditions to form the organometallic species [(phen)­M­(CH₃)]⁺. The ease of decarboxylation follows the order Pd > Pt > Ni as determined via energy-resolved CID experiments, which is in agreement with the activation energies for decarboxylation estimated from DFT calculations. Step 2 of cycle 1 involves an ion–molecule reaction between [(phen)­M­(CH₃)]⁺ and acetic acid to close the cycle by regenerating the metal acetate complex [(phen)­M­(O₂CCH₃)]⁺. DFT calculations reveal that an acid–base acetolysis mechanism is favored over an oxidative addition/reductive elimination mechanism proceeding via the M­(IV) intermediate [(phen)­M­(CH₃)­(H)­(O₂CCH₃)]⁺. In contrast, step 2 of cycle 2 involves [(phen)­M­(CH₃)]⁺ reacting with water to form the hydroxide [(phen)­M­(OH)]⁺, which subsequently reacts with acetic acid in step 3 to re-form [(phen)­M­(O₂CCH₃)]⁺ and water, thereby completing the catalytic cycle. Experiment and theory reveal that cycle 2 operates only for M = Ni