Metal-nitrogen-carbon

The objective of most research in the area of pyrolyzed metal/N/C materials has centered around understanding the nature of the active site for the ORR. Similar to heat-treated macrocycles, there has been a parallel controversy over the nature of the active sites and the role of Fe or Co in these metal-nitrogen-carbon catalysts. Based on the activity attainable from a wide-range of precursors, it seems safe to assume that above a certain temperature, the active site formed is the same regardless of the metal-nitrogen-carbon starting material (macrocycle or otherwise). Initially, some researchers believed that the metal clusters protected by a layer of carbon (which prevented leaching of the metal in the acidic electrolyte) were the source of catalytic... 

A third alternative simply uses ferrocenes as walls in cyclophane-like structures.The ferrocenyl units typically are linked via flexible hydrocarbon chains appended to cyclopentadiene ligands. In other words, covalent carbon-carbon bonds rather than coordinate-covalent metal-nitrogen, - carbon, -oxygen, or -phosphorous bonds are used. 

As a solution to provide a long-term solution to Pt cost and scarcity, a variety of non-noble metal-based catalysts has been explored as promising cathode catalysts for fuel cells. These ORR catalysts include heat-treated metal-nitrogen-carbon complexes (M-Nx/C, M = Fe or Co), carbon-supported chalcogen-ides, and carbon-supported metal oxides. These catalysts have been synthesized and showed considerable ORR activity and stability when compared to those of Pt/C catalyst. In the exploration, RDE/RRDE techniques are the most commonly employed tools in evaluating the catalysts activity and stability toward ORR and its associated mechanism. 

Chlorine reacts with most elements, both metals and non-metals except carbon, oxygen and nitrogen, forming chlorides. Sometimes the reaction is catalysed by a trace of water (such as in the case of copper and zinc). If the element attacked exhibits several oxidation states, chlorine, like fluorine, forms compounds of high oxidation state, for example iron forms iron(III) chloride and tin forms tin(IV) chloride. Phosphorus, however, forms first the trichloride, PCI3, and (if excess chlorine is present) the pentachloride PCI5. 

It is easy to reduce anhydrous rare-earth hatides to the metal by reaction of mote electropositive metals such as calcium, lithium, sodium, potassium, and aluminum. Electrolytic reduction is an alternative in the production of the light lanthanide metals, including didymium, a Nd—Pt mixture. The rare-earth metals have a great affinity for oxygen, sulfur, nitrogen, carbon, silicon, boron, phosphoms, and hydrogen at elevated temperature and remove these elements from most other metals. 

The elements of primary importance in this context are oxygen, nitrogen, carbon and hydrogen. In the technology of the liquid alkali metals they play a predominant rdle. Their origin is associated with leakages in the circuit, impurities remaining after construction or residual impurities in the liquid metal. It is convenient to discuss these four elements separately. 

Nickel is required by plants when urea is the source of nitrogen (Price and Morel, 1991). Bicarbonate uptake by cells may be limited by Zn as HCOT transport involves the zinc metal-loenzyme carbonic anhydrase (Morel et al., 1994). Cadmium is not known to be required by organisms but because it can substitute for Zn in some metalloenzymes it can promote the growth of Zn-limited phytoplankton (Price and Morel, 1990). Cobalt can also substitute for Zn but less efficiently than Cd. 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

While metal-nitrogen and metal-oxygen bonded compounds dominate nucleobase coordination chemistry, examples in which metal-carbon bonds are formed have been identified. Early studies on the synthesis of metal-labeled DNA demonstrated that nucleotide-triphosphates, UTP, CTP, dUTP, and dCTP, can undergo mercury modification at C5 (82,83). The UTP derivative was also shown to act as a substrate for RNA polymerase in the presence of mercaptans (83). Later, guano-sine was shown to undergo mercury modification at C8 though, in this case, the purine was multiply substituted, 21 (84). 

The insertion of unsaturated molecules into metal-carbon bonds is a critically important step in many transition-metal catalyzed organic transformations. The difference in insertion propensity of carbon-carbon and carbon-nitrogen multiple bonds can be attributed to the coordination characteristics of the respective molecules. The difficulty in achieving a to it isomerization may be the reason for the paucity of imine insertions. The synthesis of amides by the insertion of imines into palladium(II)-acyl bonds is the first direct observation of the insertion of imines into bonds between transition metals and carbon (see Scheme 7). The alternating copolymerization of imines with carbon monoxide (in which the insertion of the imine into palladium-acyl bonds would be the key step in the chain growth sequence), if successful, should constitute a new procedure for the synthesis of polypeptides (see Scheme 7).348... 

Carbon dioxide, Nitrogen See Carbon dioxide Metals, Nitrogen... 

H-NMR studies of oligocarbene Ru(II) complexes indicate a substantial barrier to rotation about the metal-carbene carbon and nitrogen-R bonds. This restricted rotation is thought to arise as a consequence of intramolecular non-bonding cis interactions of the carbene nitrogen-R substituents, and not because of any significant double bond character in ruthenium-carbene carbon (76). 

Insertion into metal nitrogen bonds is illustrated by the formation of the anion [(C6F5)2Pd(S2CNIIPh)] in the reaction of [Pd2(C6F5)4(p-NHPh)2]2-with carbon disulfide.362... 

An important variant for transition metal-catalyzed carbon-nitrogen bond formation is allylic substitution (for reviews, see1,la lh). Nucleophilic attack by an amine on an 7r-allyl intermediate, generated from either an allylic alcohol derivative,2 16,16a 16f an alkenyloxirane,17-19,19a-19d an alkenylaziridine19,19a 19d, or a propargyl alcohol derivative,21,21a 21d gives an allylic amine derivative. 

There are many metal alloys that contain interstitial atoms embedded in the metal structure. Traditionally, the interstitial alloys most studied are those of the transition metals with carbon and nitrogen, as the addition of these atoms to the crystal structure increases the hardness of the metal considerably. Steel remains the most important traditional interstitial alloy from a world perspective. It consists of carbon atoms distributed at random in interstitial sites within the face-centered cubic structure of iron to form the phase austenite, which exists over the composition range from pure iron to approximately 7 at % carbon. 

Natural gas exploration and transition are accompanied by emission to the atmosphere of various pollutants and first of all, species of nitrogen, carbon, sulfur and some heavy metals. This is connected with different impacts on the surrounding ecosystems in local, regional and continental scale depending upon the areas of exploration and pipeline nets. The extent of impacts is a matter of probability since many uncertainties in both ecosystems properties and impact characteristics are still exist. Accordingly the ERA process is of importance for such activities. 

The M-X or metal-adsorbate region (around 200-450 cm"1), where the metal-carbon, metal- oxygen and metal-nitrogen stretch frequencies in the spectra of adsorbed species are observed. 

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