Spectroscopic Identification of a Bidentate Binding Motif in the Anionic Magnesium–CO₂ Complex ([ClMgCO₂]⁻)

Abstract

A magnesium complex incorporating a novel metal–CO2 binding motif is spectroscopically identified. Here we show with the help of infrared photodissociation spectroscopy that the complex exists solely in the [ClMg(η2‐O2C)]− form. This bidentate double oxygen metal–CO2 coordination has previously not been observed in neutral nor in charged unimetallic complexes. The antisymmetric CO2 stretching mode in [ClMg(η2‐O2C)]− is found at 1128 cm−1, which is considerably redshifted from the corresponding mode in bare CO2 at 2349 cm−1, suggesting that the CO2 moiety has a considerable negative charge (∼1.8 e−). We also employed electronic structure calculations and kinetic analysis to support the interpretation of the experimental results.

C−C Bond Formation of Mg‐ and Zn‐Activated Carbon Dioxide

“…Starting with M=Mg (the upper panel), we first note that the thermodynamically preferred geometric structure of [ClMg,CO 2 ] − is [ClMg(κ 2 ‐O 2 C)] − ( 3 A ). Indeed, upon CID of the oxalate complex 1 A , it is the 3 A isomer that is formed, as confirmed by the IR action spectroscopy already mentioned in the Introduction . However, in the gas‐phase reaction between [ClMg] − and CO 2 , the calculations suggest that instead 4 A is formed, owing to the considerable barrier due to TS12A at 138 kJ mol −1 preventing the formation of the 3 A isomer.…”

“…This idea was propelled by the discovery of an activated Mg–CO 2 complex with a bidentate structure, [ClMg(κ 2 ‐O 2 C)] − , in which the CO 2 moiety is strongly bent with a bond angle of 114° . This molecular structure has been confirmed by IR action spectroscopy and supported by the results of very accurate quantum chemical calculations . Its nucleophilic character, inferred from the electronic structure calculations, has been experimentally demonstrated by the observation of its ability to displace chloride and bromide in gas‐phase S N 2 reactions with CH 3 Cl and CH 3 Br, thereby giving rise to C−C bonds .…”

“…Reaction (3 b), using both 12 CO 2 and 13 CO 2 reactants, was investigated in separate experiments where [ClM, 12 CO 2 ] − was formed by in‐source dissociation of [ClMC 2 O 4 ] − . Fragmentation of [ClMgC 2 O 4 ] − results in the bidentate [ClMg(κ 2 ‐O 2 C)] − complex as described in the Introduction, whereas [ClZnC 2 O 4 ] − gives [ClZn,CO 2 ] − of unknown structure.…”

Dimethylberyllium + CO2 → Fire! A DFT and ab Initio Study into the Photon Emission Observed in a Gas Phase Carbon Dioxide Activation Reaction

“…We note that four-membered ring carbenes similar to 24, containing a magnesium instead of a beryllium ring atom, have been observed in mass spectrometry experiments, [28][29][30] and that there is also evidence for formation of magnesium-CO2 adducts similar to 25. 29 Figure 7 shows a graphical representation of some of the thermochemical data, and Figure 8 calculated geometries. As far as the data in Figure 7 as well as in Table S3 are concerned, we note that the energy of the reference point (atomic beryllium + CO2) cannot reliably be calculated at the DFT level of theory employed.…”

Infrared Multiple Photon Dissociation Spectroscopy of Hydrated Cobalt Anions Doped with Carbon Dioxide CoCO2(H2O)n−, n=1–10, in the C−O Stretch Region

“…The same is true in a salt environment where the interaction with positive charge centers is responsible for the stabilization . In the interaction of CO 2 with metal ions, electron transfer from the metal to the electrophilic carbon atom can occur spontaneously, leading to complexes of the metal center with CO 2 − . When a single bond is formed between the metal and the carbon atom, as observed for example, with the nickel group, coinage metal, or bismuth anions, the excess charge in this metalloformate η 1 ‐(C) complex, MCO 2 − , is delocalized over the whole molecular ion …”