The increase in atmospheric carbon dioxide is linked to climate changes; hence there is an urgent need to reduce the accumulation of CO2 in the atmosphere. The utilization of CO2 as a raw material in the synthesis of chemicals and liquid energy carriers offers a way to mitigate the increasing CO2 buildup. This review covers six important CO2 transformations namely: chemical transformations, photochemical reductions, chemical and electrochemical reductions, biological conversions, reforming and inorganic transformations. Furthermore, the vast research area of carbon capture and storage is reviewed briefly. This review is intended as an introduction to CO2, its synthetic reactions and their possible role in future CO2 mitigation schemes that has to match the scale of man-made CO2 in the atmosphere, which rapidly approaches 1 teraton.

The teraton challenge. A review of fixation and transformation of carbon dioxide

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

Infrared spectroscopic identification of species arising from reactive adsorption of carbon oxides on metal oxide surfaces

The possibility of recycling CO{sub 2} from industrial emissions and of removing some of this greenhouse gas, an environmental pollutant, is receiving increased attention. Also, the possibility of using CO{sub 2} as the starting material for the synthesis of fine chemicals provides an attractive alternative to compounds presently derived from petroleum. Efforts to convert CO{sub 2} to useful chemicals will inevitably center on transition metal catalysts. Furthermore, efforts to enhance the yield of hydrogen in water gas shift reactions are also centered on carbon dioxide interactions with transition metal catalysts. For all these reasons, a broader understanding of the organometallic chemistry of CO{sub 2} is being sought. In this article, only those compounds that can be clearly identified as having carbon dioxide bound to metal centers through carbon will be considered. Thus the discussions will not include metal formate complexes whose chemistry has been reviewed recently. Also, the discussions will not include metallocarboxylic acids or metallocarboxylate esters except where these compounds have been used as reagents for the synthesis of CO{sub 2} complexes or result from reactions of these compounds. 111 refs.

The Organometallic Chemistry of Carbon Dioxide.

Reactivities of carbonyl sulfide (COS), carbon disulfide (CS2) and carbon dioxide(CO2)with transition metal complexes

An improved synthesis of the hexaruthenium carbido cluster Ru6C(CO)17; X-ray structure of the salt [Ph4As]2[Ru6C(CO)16]

Dodecacarbonyltriosmium reacts with H2 under pressure to produce [Os4(CO)12H4] almost quantitatively. Methanolic K[OH] converts this into [Os4(CO)12H3]– which gives the title compound [Os4(CO)12H3l] with l2. Crystals of [Os4(CO)12H3l] are monoclinic, with a= 17.307(8), b= 8.040(3), c= 17.760(9)A, β= 119.80(2)°, space group C2/c, and Z= 4. The final residuals for 2 724 unique observed reflections are R 0.036 and R′ 0.039. The four Os atoms are in a ‘butterfly’ configuration: one edge has been extended and a bridging iodine inserted [Os-l 2.749(4)A]. A crystallographic two-fold axis passes through the iodine atom and bisects the opposite Os–Os bond. The Os–Os distances are 2.876(1)(two), 2.927(3), and 3.052(1)A(two): the crystallographic symmetry, 1H n.m.r. spectrum, and geometrical arrangements of the carbonyls indicate that the three longest Os–Os bonds are hydride-bridged. Methanolic Na(OMe) converts [Os4(CO)12H4] into [Os4(CO)11(CO2Me)H4]–, isolated as the [N(PPh3)2]+ salt.

The chemistry of polynuclear compounds. Part 30. Some reactions of dodecacarbonyltetrahydridotetraosmium: the molecular and crystal structure of trihydrido-µ2-iodo-cyclo-tetrakis(tricarbonylosmium)-(4Os–Os)

The synthesis of clusters containing a μ2-CO2 linkage

The complexes [Os4(CO)11(cyclo-olefin – H)H3](cyclo-olefin = cyclo-octatetraene, cyclo-octa-1,5-diene, cyclo-hexene, or norbornene) have been identified as the products of reaction of [Os4(CO)12H4] with the appropriate cyclic olefin. The structures of these complexes are discussed in terms of available spectroscopic data and in the case of the title complex [Os4(CO)11(C6H9)H3] on the basis of a single-crystal X-ray analysis. This molecule crystallises in space group P21/n with a= 9.266(4), b= 14.850(8), c= 16.847(9)A, β= 93.39(3)°, and Z= 4. The osmium atoms define a tetrahedron, with the cyclohexene ring σ-bonded to one metal and π-bonded to another. The complex [Os4(CO)12H4] also reacts with the acyclic olefins CH2CH2, CH2CHPh, CH2CHCMe3, CH2CMeCMe3, and cis-CHPhCHPh to give the related complexes [Os4(CO)11(olefin – H)H3]. On heating, apart from the complex where the olefin is CH2CMeCMe3, dehydrogenation occurs to produce the dihydrido-complexes [Os4(CO)11(R1CCR2)H2](R1= H, R2= H, Ph, or CMe3; R1= R2= Ph). These complexes have been shown to contain a R1CCR2 fragment bound via two σ and one π bond to one tetrahedral face of the Os4 cluster unit.

Some reactions of dodecacarbonyltetrahydridotetraosmium with olefins; the molecular structure of 1,1,1,2,2,3,3,3,4,4,4-undecacarbonyl-1,2-µ-(1′-σ,1′–2′-η-cyclohexenyl)-tri-µ-hydrido-tetrahedro-tetraosmium

Reactions of the hexaruthenium carbide cluster Ru6C(CO)17 with some π-acid ligands; direct location of the μ-hydride ligand in HRu6C(CO)15(SEt)3 by x-ray analysis

Kenneth Wong

Papers

An improved synthesis of the hexaruthenium carbido cluster Ru6C(CO)17; X-ray structure of the salt [Ph4As]2[Ru6C(CO)16]

The chemistry of polynuclear compounds. Part 30. Some reactions of dodecacarbonyltetrahydridotetraosmium: the molecular and crystal structure of trihydrido-µ2-iodo-cyclo-tetrakis(tricarbonylosmium)-(4Os–Os)

The synthesis of clusters containing a μ2-CO2 linkage

Some reactions of dodecacarbonyltetrahydridotetraosmium with olefins; the molecular structure of 1,1,1,2,2,3,3,3,4,4,4-undecacarbonyl-1,2-µ-(1′-σ,1′–2′-η-cyclohexenyl)-tri-µ-hydrido-tetrahedro-tetraosmium

Reactions of the hexaruthenium carbide cluster Ru6C(CO)17 with some π-acid ligands; direct location of the μ-hydride ligand in HRu6C(CO)15(SEt)3 by x-ray analysis