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

Abstract

Metal-catalyzed decarboxylative coupling reactions of esters offer new opportunities for formation of C-C bonds with CO 2 as 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 twostep catalytic cycle. In Step 1, an organometallic ion, [CH 3 ML] +/-(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, [CH 3 CO 2 ML] +/-. 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 [CH 3 CuCH 3 ] -, [CH 3 Cu 2 ] + , [CH 3 AgCu] + and [CH 3 M(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, [CH 3 Ag 2 ] + 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 S N 2-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 [CH 3 CuCH 3 ] -, [CH 3 Cu 2 ] + , [CH 3 AgCu] + and [CH 3 M(phen)] + (where M = Ni, Pd and Pt). Of the catalysts studied to date, [CH 3 Cu 2 ] + and [CH 3 Pd(phen)] + are best at promoting C-C bond formation (Step 1) as well as being regenerated (Step 2). Preliminary results on the reactions of [C 6 H 5 M(phen)] + (M = Ni and Pd) with C 6 H 5 CO 2 CH 2 CH = CH 2 and C 6 H 5 CO 2 CH 2 C 6 H 5 are described.

Ligand-induced substrate steering and reshaping of [Ag2(H)]+ scaffold for selective CO2 extrusion from formic acid

“…The value of gas-phase studies employing mass spectrometry (MS)-based methods 37 38 is that they allow a systematic exploration of the factors that control reactivity for all steps in a catalytic cycle 39 40 . When used in conjunction with DFT calculations, where mechanistic pathways can be explored, different types of catalysts that vary in the metal, ligand and/or nuclearity that catalyse the same transformation 41 or which transform the same substrate in different ways 42 can be directly compared 43 .…”

Isotope labeling and infrared multiple-photon photodissociation investigation of product ions generated by dissociation of [ZnNO3(CH3OH)2]+: Conversion of methanol to formaldehyde

“…A similar approach was taken with potential intermediates along reaction pathways. Minima identified after the initial calculations were then subjected to full optimization using the same functional and the 6 Our focus in this study was the gas-phase behavior of the methanol-coordinated [ZnNO 3 ] þ ions. Ions that contain Zn are easily identified by a characteristic triplet of peaks that signal the inclusion of the 64 Zn (48.63%), 66 Zn (27.92%), and 68 Zn (18.84%) isotopes.…”

“…The use of electrospray ionization (ESI) to produce a wide array of gas-phase metal ion complexes, and the multidimensional tandem mass spectrometry capability of commercially available quadrupole ion trap mass spectrometers has allowed unprecedented access to the gas-phase behavior of metal ions and metal ion complexes, whether through collision-induced dissociation (CID) experiments or ion molecule reaction (IMR) studies. [1][2][3][4][5][6][7][8][9][10] The former uses energetic collisions to activate ions to probe the pathways and thermochemistry of reactions mediated by metal ions. [10][11][12] In the latter experiment, reactions between ions and neutrals provide complementary information about reactivity and insight into reaction rates.…”

Metal-mediated catalysis in the gas phase: A review

“…Many such gas-phase studies have examined the key steps in industrially and biologically important catalytic cycles, focusing on electronic structures, vital intermediates and the oxidation states of metal centers. Several excellent reviews have summarized gas-phase catalytic cycles [7,23], cooperative effects in clusters [24] and important elementary reactions, such as CO oxidation [15], CO2 transformation [25], CH4 functionalization [26] and decarboxylation reactions [27,28]. The focus of the present article is a review of the latest advances in gas-phase catalytic reactions, with an emphasis on cluster-confined single-atom catalysts.…”