Strong Closed-Shell Interactions in Inorganic Chemistry.

The need to reduce the accumulation of CO2 into the atmosphere requires new technologies able to reduce the CO2 emission. The utilization of CO2 as a building block may represent an interesting approach to synthetic methodologies less intensive in carbon and energy. In this paper the general properties of carbon dioxide and its interaction with metal centres is first considered. The potential of carbon dioxide as a raw material in the synthesis of chemicals such as carboxylates, carbonates, carbamates is then discussed. The utilization of CO2 as source of carbon for the synthesis of fuels or other C1 molecules such as formic acid and methanol is also described and the conditions for its implementation are outlined. A comparison of chemical and biotechnological conversion routes of CO2 is made and the barriers to their exploitation are highlighted.

Utilisation of CO2 as a chemical feedstock: opportunities and challenges

Starting with coal, followed by petroleum oil and natural gas, the utilization of fossil fuels has allowed the fast and unprecedented development of human society. However, the burning of these resources in ever increasing pace is accompanied by large amounts of anthropogenic CO2 emissions, which are outpacing the natural carbon cycle, causing adverse global environmental changes, the full extent of which is still unclear. Even through fossil fuels are still abundant, they are nevertheless limited and will, in time, be depleted. Chemical recycling of CO2 to renewable fuels and materials, primarily methanol, offers a powerful alternative to tackle both issues, that is, global climate change and fossil fuel depletion. The energy needed for the reduction of CO2 can come from any renewable energy source such as solar and wind. Methanol, the simplest C1 liquid product that can be easily obtained from any carbon source, including biomass and CO2, has been proposed as a key component of such an anthropogenic carbon cycle in the framework of a “Methanol Economy”. Methanol itself is an excellent fuel for internal combustion engines, fuel cells, stoves, etc. It's dehydration product, dimethyl ether, is a diesel fuel and liquefied petroleum gas (LPG) substitute. Furthermore, methanol can be transformed to ethylene, propylene and most of the petrochemical products currently obtained from fossil fuels. The conversion of CO2 to methanol is discussed in detail in this review.

Recycling of carbon dioxide to methanol and derived products – closing the loop

Green oxidation with aqueous hydrogen peroxide

There is now compelling experimental evidence for the existence of specific intra- and intermolecular bonding between seemingly closed-shell gold(I) centers (5d10) which manifests itself in all areas of gold chemistry. This “aurophilic interaction”, which had not been predicted by conventional valence theory, was found to be associated with binding energies in some cases exceeding even those of strong hydrogen bonds and therefore to be highly significant in co-determining molecular structure and dynamics. In high-level theoretical treatments the attraction is rationalized as a “super van der Waals bonding” based on particularly strong relativistic, dispersion and correlation effects (critical review, 265 references).

A briefing on aurophilicity.

Polynuclear aryl derivatives of Group 11 metals. Synthesis, solid state-solution structural relationship, and reactivity with phosphines

Carbon dioxide activation. Deoxygenation and disproportionation of carbon dioxide promoted by bis(cyclopentadienyl)titanium and -zirconium derivatives. A novel bonding mode of the carbonato and a trimer of the zirconyl unit

Carbon dioxide and formaldehyde coordination on molybdenocene to metal and hydrogen bonds of the C1 molecule in the solid state

Mise en evidence de 2 etapes, la premiere conduisant au formaldehyde et a [cp 2 Zr(Cl)] 2 O et l'autre mettant en jeu la reduction du formaldehyde en un coordinat methoxy dans [cp 2 Z(OCH 3 )(Cl)] par [cp 2 Z(Cl)(H)]

Stepwise reduction of carbon dioxide to formaldehyde and methanol: reactions of carbon dioxide and carbon dioxide like molecules with hydridochlorobis(cyclopentadienyl)zirconium(IV)

All chemists interested in carbon monoxide activation are familiar with Bercaw's modeling studies based on zirconium hydrides, which detail the promotion of the stoichiometric reduction of CO to methanol and to C/sub 2/-unit precursors. Many of the Bercaw's observations have been interpreted in a sequence involving, as a key intermediate, the oxymethylene ligand bridging two zirconium atoms (Zr-O-CH/sub 2/Zr), whose reactivity with carbon monoxide was viewed as the reaction leading to C/sub 2/ units. The intermediacy of such a unit is partially supported by the isolation of a complex coming from the reaction of CO with ((cp)/sub 2/Zr(H)Cl)/sub n/ by the authors. The choice of ((cp)/sub 2/Zr(H)Cl)/sub n/ was mainly dictated by the fact that it contains only one potential migrating ligand rather than two as in ((n/sup 5/-C/sub 5/Me/sub 5/)/sub 2/ZrH/sub 2/). Further the solid-state structure of this species, some unexpected peculiarities, and its reaction with CO are described.

Carlo Guastini

Papers

Polynuclear aryl derivatives of Group 11 metals. Synthesis, solid state-solution structural relationship, and reactivity with phosphines

Carbon dioxide activation. Deoxygenation and disproportionation of carbon dioxide promoted by bis(cyclopentadienyl)titanium and -zirconium derivatives. A novel bonding mode of the carbonato and a trimer of the zirconyl unit

Carbon dioxide and formaldehyde coordination on molybdenocene to metal and hydrogen bonds of the C1 molecule in the solid state

Stepwise reduction of carbon dioxide to formaldehyde and methanol: reactions of carbon dioxide and carbon dioxide like molecules with hydridochlorobis(cyclopentadienyl)zirconium(IV)

Genesis, bonding mode and reaction with carbon monoxide of an oxymethylene unit bridging two metal atoms