CO2 Activation and Hydrogenation by PtHn (-) Cluster Anions

Designer Metallic Acceptor-Containing Halogen Bonds: General Strategies

Being electrostatic interactions in nature, hydrogen bonding (HB) and halogen bonding (XB) are considered to be two parallel worlds. In principle, all the applications that HB have could also be applied to XB. However, there has been no report on an anionic, metallic XB acceptor, but metal anions have been observed to be good HB acceptors. This missing mosaic piece of XB theory is because common metal anions are reactive for XB donors. In view of this, two strategies are proposed for designing metallic acceptor-containing XB using ab initio calculations. The first one is to utilize a metal cluster anion with a high electron detachment energy, such as the superatom, Al₁₃^- as the XB acceptor. The second strategy is to design a ligand-passivated/protected metal core that can maintain the negative charge; several exotic clusters, such as PtH₅^- , PtZnH₅^- , and PtMgH₅^- , are used as examples. Based on these two strategies, it is anticipated that more metallic acceptor-containing XBs will be discovered.

Sequential Gas-Phase Activation of Carbon Dioxide and Methane by [Re(CO)2]+: The Sequence of Events Matters!

The potential of carbonyl rhenium complexes in activating and coupling carbon dioxide and methane has been explored by using a combination of gas-phase experiments (FT-ICR mass spectrometry) and high-level quantum chemical calculations. While the complexes [Re(CO)_x]⁺ (x = 0, 1, 3) are thermally unreactive toward CO₂, [Re(CO)₂]⁺ abstracts one oxygen atom from this substrate spontaneously at ambient conditions. Based on ¹³C and ¹⁸O labeling experiments, the newly generated CO ligand is preferentially eliminated, and two mechanistic scenarios are considered to account for this unexpected finding. The oxo complex [ORe(CO)₂]⁺ reacts further with CH₄ to produce the dihydridomethylene complex [ORe(CO)(CH₂)(H)₂]⁺. However, coupling of the CO and CH₂ ligands to form CH₂═C═O does not take place. Further, the complexes [Re(CO)_x(CH₂)]⁺ (x = 1, 2), generated in the thermal reaction of [Re(CO)_x]⁺ (x = 1, 2) with CH₄, are inert toward CO₂. Mechanistic insight on the origin of this remarkable reactivity pattern has been derived from detailed quantum chemical calculations.

Rational design of super-alkalis and their role in CO2 activation

Super-alkalis are clusters of atoms. With ionization potentials smaller than those of the alkali atoms, they are playing an increasing role in chemistry as highlighted by recent applications in solar cells as well as in Li-ion batteries. For the past 40 years superalkalis were designed using inorganic elements with the sp orbital character. Here, we show that a large class of superalkalis composed of only simple metal atoms, transition metal complexes as well as organic molecules can be designed by making use of electron counting rules beyond the octet rule. Examples include Al₃⁺, Mn(B₃N₃H₆)₂⁺, B₉C₃H₁₂⁺, and C₅NH₆⁺ which obey the jellium shell closure rule, the 18-electron rule, the Wade-Mingos rule, and Hückel's aromatic rule, respectively. We further show that the ability of superalkalis to transfer an electron easily can be used to activate a CO₂ molecule by transforming it from a linear to a bent structure. These results, based on density functional theory with generalized gradient approximation for exchange-correlation potential, open the door to a new class of catalysts for CO₂ activation.

Formation of Gas-Phase Formate in Thermal Reactions of Carbon Dioxide with Diatomic Iron Hydride Anions

The hydrogenation of carbon dioxide involves the activation of the thermodynamically very stable molecule CO₂ and formation of a C-H bond. Herein, we report that HCO₂^- and CO can be formed in the thermal reaction of CO₂ with a diatomic metal hydride species, FeH^- . The FeH^- anions were produced by laser ablation, and the reaction with CO₂ was analyzed by mass spectrometry and quantum-chemical calculations. Gas-phase HCO₂^- was observed directly as a product, and its formation was predicted to proceed by facile hydride transfer. The mechanism of CO₂ hydrogenation in this gas-phase study parallels similar behavior of a condensed-phase iron catalyst.

Oxidizing CO2 with superhalogens

The Sb₃F₁₆ species was found to be capable of ionizing the CO₂ molecule.