Metal-carbon-oxygen system

The Pourbaix-Ellingham diagram of the tantalum-carbon-oxygen (Ta-C-O) system indicates fewer sequential steps between the oxide and the metal as compared to the niobium-carbon-oxygen system ... 

The surface chemistry of carbon is rather complex. At a single adsorption site several chemically inequivalent types of heteroatom bonds may form. Strong interactions between surface functional groups further complicate the list of surface chemical structures as derived for the most relevant carbon-oxygen system An additional dimension of complexity is presented by the large variety of substrate structures of carbon which arise from anisotropic covalent bonding rather than by a isotropic metallic interaction. 

In this chapter and in Chapters 10-12, we will review and validate some methods for asymmetric (transfer) hydrogenation of carbon-oxygen and carbon-carbon double bonds catalysed by non-metallic systems, homogeneous transition metal catalysts and biocatalysts. Reduction of carbon-nitrogen double bond systems will be reported in another volume of this series. 

Dr. William W. Jacques further explored the carbon approach in 1896. His fuel cells had a carbon rod central anode in the electrolyte of molten potassium hydroxide. He made a fuel cell system of 100 cylindrical cells, which produced as much as 1500 W. Francis T. Bacon worked on fuel cells to produce alkaline systems that did not use noble metal catalysts in the 1930s. He developed and built a 6 kW alkaline hydrogen-oxygen system in 1959. In the same year, Dr. Harry Ihrig introduced... 

In the investigation of hydrocarbon partial oxidation reactions the study of the factors that determine selectivity has been of paramount importance. In the past thirty years considerable work relevant to this topic has been carried out. However, there is yet no unified hypothesis to address this problem. In this paper we suggest that the primary reaction pathway in redox type reactions on oxides is determined by the structure of the adsorbed intermediate. When the hydrocarbon intermediate (R) is bonded through a metal oxygen bond (M-O-R) partial oxidation products are likely, but when the intermediate is bonded through a direct metal-carbon bond (M-R) total oxidation products are favored. Results on two redox systems are presented ethane oxidation on vanadium oxide and propylene oxidation on molybdenum oxide. 

Carbon monoxide has 14 electrons, which pair to give a net spin of zero. Carbon monoxide complexes of transition metals, like oxygen complexes, cannot convert an even electron system to an odd electron system. In the case of iron, CO usually binds only to ferrous ions, which have six 3d electrons. As a consequence, CO complexes and O2 complexes with iron-containing proteins are generally not detectable by EPR. 

Tracer studies with 13C showed that the carbon of methoxy species formed in CO hydrogenation appeared as the central C atom of isobutylene.531 Methoxy was shown to be reduced to surface methyl species that was transformed to surface acetyl group via insertion of CO into the methyl-metal bond. Aldol condensation of C2 oxygenates with formaldehyde affords iso-C4 products.532 Earlier results of a different approach for isosynthesis using metal-zeolite catalyst systems are summarized in a 1998 review.533... 

The first point may be intimately connected with the notion that CO activation is achieved in this system by maximal reduction of the carbon-oxygen triple bond via interaction with more than one metal center, while the second is suggestive of the type of Lewis acid binding to carbonyl oxygens as seen by Shriver, Burlitch, and others (47-54). It is noteworthy that molten NaAlCl4, which lacks acidic character, is a relatively ineffective medium under the reaction conditions. 

J. J. Scheer, A. E. van Arkel, and R. D. Heyding, Oxide complexes formed in the systems platinum metals, alkali carbonates, oxygen, Canad. J. Chem. 33, 683-686 (1955). 

Figure 4-26. Unconstrained MD simulations for methyl acrylate bound to the palladium/nickel diimine complex through the oxygen (top-right/bottom-right) and the C=C (top-left/bottom-left) functionalities. The three panels in each of the four graphs represent variations in the metal-carbon (top two panels) and metal-oxygen (bottom panel) distances. The simulations were carried out at 300 K for all the systems, and 700 K for the local minima, as indicated...

---