Characterization of the alkali metal oxalates (MC2O4-) and their formation by CO2 reduction via the alkali metal carbonites (MCO2-)

Infrared Spectroscopy of [M(CO2)n]+ (M = Ca, Sr, and Ba; n = 1-4) in the Gas Phase: Solvation-Induced Electron Transfer and Activation of CO2

Cationic complexes of heavy alkaline earth metal and carbon dioxide [M(CO2)n]+ (M = Ca, Sr, and Ba) are produced by a laser vaporization-supersonic expansion ion source in the gas phase and are studied by infrared photodissociation spectroscopy in conjunction with quantum chemistry calculations. For the n = 1 complexes, the metal-ligand binding arises primarily from the electrostatic interaction with the CO2 ligand bound to the metal (+I) center in an end-on η1-O fashion. The more highly coordinated complexes [M(CO2)n]+ with n ≥ 2 are characterized to involve a [M2+(CO2-)] core ion with the CO2- ligand bound to the metal (+II) center in a bidentate η2-O, O manner. The activation of CO2 in forming a bent CO2- moiety occurs via solvation-induced metal cation-ligand electron transfer reactions. Bonding analyses reveal that the attractive forces between M2+ and CO2- in the core cation come mainly from electrostatic attraction, but the contribution of covalent orbital interactions should not be underestimated. The atomic orbitals of metal dications that are engaged in the orbital interactions are ns and (n - 1)d orbitals.

Carbon Dioxide Activation by Alkaline-Earth Metals: Formation and Spectroscopic Characterization of OCMCO3 and MC2O4 (M = Ca, Sr, Ba) in Solid Neon

The reactions of alkaline-earth metal atoms (Ca, Sr, and Ba) with carbon dioxide are investigated using matrix isolation infrared spectroscopy in solid neon. The ground-state metal atoms react with two carbon dioxide molecules to produce the oxalate complexes MC₂O₄ and the carbonate-carbonyl complexes OCMCO₃ (M = Ca, Sr, Ba) spontaneously on annealing. The species are identified by the effects of isotopic substitution on their infrared spectra as well as density functional calculations. Bonding analyses reveal that the attractive forces between M²⁺ and (CO₃)^2- or (C₂O₄)₂^- in the OCMCO₃ and MC₂O₄ complexes come mainly from electrostatic attraction, but covalent orbital interactions also play an important role, which are dominated by the ligand-to-metal donation bonding. The calcium, strontium, and barium metal centers in these complexes use their ns and predominately (n - 1)d atomic orbitals for covalent bonding that mimic transition metals.

Infrared spectroscopy of Be(CO2)4+ in the gas phase: electron transfer and C-C coupling of CO2

Beryllium-carbon dioxide cation complexes Be(CO₂)_n⁺ are produced by a laser vaporization-supersonic expansion ion source in the gas phase. Mass-selected infrared photodissociation spectroscopy supplemented by theoretical calculations confirms that Be(CO₂)₄⁺ is a coordination saturated complex that can be assigned to a mixture of two isomers. The first structure involves a bent CO₂^- ligand that is bound in a monodentate η¹-O coordination mode. Another isomer has a metal oxalate-type C₂O₄^- moiety with a C-C hemibond.

Interactions of CO2 Anion Radicals with Electrolyte Environments from First-Principles Simulations

Successful transformation of carbon dioxide (CO₂) into value-added products is of great interest, as it contributes in part to the circular carbon economy. Understanding chemical interactions that stabilize crucial reaction intermediates of CO₂ is important, and in this contribution, we employ atom centered density matrix propagation (ADMP) molecular dynamics simulations to investigate interactions between CO₂ ^- anion radicals with surrounding solvent molecules and electrolyte cations in both aqueous and nonaqueous environments. We show how different cations and solvents affect the stability of the CO₂ ^- anion radical by examining its angle and distance to a coordinating cation in molecular dynamics simulations. We identify that the strength of CO₂ ^- interactions can be tailored through choosing an appropriate cation and solvent combination. We anticipate that this fundamental understanding of cation/solvent interactions can facilitate the optimization of a chemical pathway that results from selective stabilization of a crucial reaction intermediate.

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.

Spectroscopic Identification of Transition-Metal M[η2-(O,O)C] Species for Highly-Efficient CO2 Activation

The CO₂ activation by transition metals is important in CO₂ utilization but has proven to be challenging for experimental targets. Here we report first synthesis and spectroscopic characterization of transition-metal M[η²-(O,O)C] species with bidentate double oxygen metal-CO₂ coordination in the [ZrO(CO₂)_n≥4]⁺ complexes. The Zr[η²-(O,O)C] species yields a CO₂^- radical ligand, showing a high efficiency in CO₂ activation. We find that two important prerequisites are demanded for certain metals to form this intriguing M[η²-(O,O)C] species. One is that the metal center has high reduction capability, and the other is that the oxidation state of the metal center is lower than its highest one by 1. This study highlights the pivotal roles played by the M[η²-(O,O)C] species in CO₂ activation and also open new avenues toward the development of related single-atom catalysts with isolated transition-metal atoms dispersed on supports.