Complexes of Carbon

Organometallic Compounds. Osmium forms numerous mononuclear and polynuclear organometaUic complexes, primarily iu lower oxidation states. There are many complexes of carbon monoxide, such as [Os(CO)3] [16406-49-8], [Os(CO) H2] [22372-70-9], [Os3(CO)2 H2] [56398-24-4],... 

Gosorb Process. Like the copper—Hquor scmbbing method, the Cosorb process also reHes on the formation of a cuprous complex of carbon monoxide but uses a nonaqueous organic solvent. The preferred system uses a cuprous tetrachloroalurninate toluene complex in a toluene solvent (90). Many other organometaUic complex variants have been proposed (91—93) but have not been commercialized. 

The reversible complexing of carbon dioxide by bis[bis(l,2-diphe-nylphosphino)ethane]iridium(I) chloride, [Ir(dpe)2]Cl, in acetonitrile [Eq. (36)] (48) appears not to involve carboxylation of a cyanomethylir-idium(III) complex or its formation by decarboxylation of the cyanoacetate... 

Macromolecules are found in nature. Cellulose, wool, starch, and DNA are but a few of the macromolecules that occur naturally. Carbons ability to form these large, complex molecules is necessary to provide the diversity of compounds needed to make up a tree or a human being. But many of the useful macromolecules that we use every day are created in the lab and industrial complex by chemists. Nylon, rayon, polyethylene, and polyvinyl chloride are all synthetic macromolecules. They differ by which repeating units (monomers) are joined together in the polymerization process. Our society has grown to depend on these plastics, these synthetic fabrics. The complexity of carbon compounds is reflected in the complexity of our modern society. 

TABLE 6.14. Structural and Energy Parameters Calculated at Various Theoretical Levels for XH4- "HE Complexes of Carbon, Silicon, Germanium, and Tin... 

Figure 8.10 Soluble supramolecular complexes of carbon nanotubes, 0.01 M Na2S04, aqueous solution. Scan rate = 0.1 V/s T— 25°C working electrode is Pt disc (r — 0.05 cm). Potentials measured versus silver quasi-reference electrode (approximately —0.05 V versus SCE). Ref. 121, Reproduced by permission of the Royal Society of Chemistry.

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

Metal Complexes of Carbon-Based. Tetrapyrroles Other Than Metal Porphyrins... 

We note that, with the lone participation of a carboxyl group in the coordination, the coordination modes examined earlier for the complexes of carbonic acids (Sec. 2.2.5.4, formulae 276 283) are possible. Additionally, a mixed binding amongst ligands is observed in many complexes of aminoacids, for example chelates 277, 414, and 0,0 -bridge 279 [714],... 

A paper dating from 1976 investigated the reaction of olefins or alcohols with cationic copper and silver complexes of carbon monoxide 49 The remarkable outcome of these kinetic measurements is that there is no difference between the catalytic behavior of Cu(CO) + and Ag(CO)2 +. 

The reason for this poor definition of materials is found in the process of their formation, namely difficult to control polymerization reactions. Such reactions also occur in catalytic reactions with small organic molecules. The nature of carbon deposits therefore reflect all the complexity of the bulk carbon materials One aim of this article is to describe the structural anc chemical complexity of carbon or soot in order tc provide an understanding of the frequently observec complexity of the chemical reactivity (e.g. in reac tivation processes aiming at an oxidative removal o deposits). 

The complexity of carbon materials together with the surface chemical anisotropy and the modifying effects of defects creates a highly complex situation for surface chemistry even when only one heteroelement is considered to be actively bonded. It is a characteristic of this branch of chemistry to describe surfaces in terms of distributions of properties rather than in sharp numbers. 

H. Werner, Complexes of Carbon Monoxide and its Relatives An Organometallic Family Celebrates Its Birthday, Angew. Chem. Int. Ed. Engl. 29, 1077-1089 (1990). 

The first stable actinide complex of carbon monoxide was prepared by reaction of (Me3SiC5H4)3U (Cp sU) with CO in solution or in the solid state to produce Cp 3U(CO), which reversibly dissociates CO. Cp 3U(CO) exhibits a carbonyl stretch in the IR spectrum at 1976 cm, or approximately 170 cm lower than the uco for free carbon monoxide. This is taken as an indication of uranium-to-carbonyl jr-back bonding see Back Bonding). Electronic stracture calculations on the model complex CpsUCO indicated a significant U 5f-CO 2n... 

Van Geen A., Robertson A. P., and Leckie J. O. (1994) Complexation of carbonate species at the goethite surface implications for adsorption of metal ions in natural waters. Geochim. Cosmochem. Acta 58, 2073 -2086. 

Activated carbon, in keeping with the enhanced complexity of carbon-based chemistry, possesses an extensive array of surface moieties, including hydroxyl groups, carboxylic acid groups, aldehyde groups, keto groups, cyclic ethers, and lactone groups. 

The relation between electronic conductivity and chemical reactivity is well established, particularly for graphites.However the suggestion that the detailed chemistry of surface complexes depends on the immediate pretreatment of the surface, makes consideration of surface complexes of carbons very difficult. To quote Papirer et al Major progress in the knowledge of the surface groups on carbons must be expected only if entirely new analytical tools become available. Although this statement seems too... 

The formation, nature, and reactions of surface complexes of carbon are obviously open to considerable question, largely because of the difficulty in determining accurately what is happening on a carbonaceous surface. The problem is that, at least in some cases, the nature of the surface complexes may well affect the reactions (catalytic or non-catalytic) of carbons. Keeping the difficulties of analysis of surface complexes in mind, it is convenient to discuss the catalytic activity and reactivity of carbons in the expectation that this can lead to a closer definition of the information that is needed in the context of the surface complexes. 

---