Metal-carbon reactions

Carbonates. Iron(II) carbonate [563-71-3] FeCO, precipitates as a white soHd when air-free solutions of alkah metal carbonates and iron(II) salts are mixed. The limited tendency of [Fe(H20)g] to hydroly2e is illustrated by the lack of carbon dioxide evolution in this reaction. The soHd rapidly... 

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. 

Niobium Pent chloride. Niobium pentachloride can be prepared in a variety of ways but most easily by direct chlorination of niobium metal. The reaction takes place at 300—350°C. Chlorination of a niobium pentoxide—carbon mixture also yields the pentachloride however, generally the latter is contaminated with niobium oxide trichloride. The pentachloride is a lemon-yeUow crystalline soHd that melts to a red-orange Hquid and hydrolyzes readily to hydrochloric acid and niobic acid. It is soluble in concentrated hydrochloric and sulfuric acids, sulfur monochloride, and many organic solvents. 

The bonding between carbon monoxide and transition-metal atoms is particularly important because transition metals, whether deposited on soHd supports or present as discrete complexes, are required as catalysts for the reaction between carbon monoxide and most organic molecules. A metal—carbon ( -bond forms by overlapping of metal orbitals with orbitals on carbon. Multiple-bond character between the metal and carbon occurs through formation of a metal-to-CO TT-bond by overlap of metal-i -TT orbitals with empty antibonding orbitals of carbon monoxide (Fig. 1). 

Carbon monoxide also reacts with olefins such as ethylene to produce high molecular weight polymers. The reaction of CO with ethylene can be initiated by an x-ray irradiator (62) or transition-metal cataly2ed reactions (63). The copolymeri2ation of ethylene with carbon monoxide is cataly2ed by cationic Pd (II) complexes such as Pd[P(CgH )2] (CH CN) (BF 2 where n = 1-3. With this catalyst, copolymeri2ation can be carried out at 25°C and pressures as low as 2.1 MPa. 

Easily decomposed, volatile metal carbonyls have been used in metal deposition reactions where heating forms the metal and carbon monoxide. Other products such as metal carbides and carbon may also form, depending on the conditions. The commercially important Mond process depends on the thermal decomposition of Ni(CO)4 to form high purity nickel. In a typical vapor deposition process, a purified inert carrier gas is passed over a metal carbonyl containing the metal to be deposited. The carbonyl is volatilized, with or without heat, and carried over a heated substrate. The carbonyl is decomposed and the metal deposited on the substrate. A number of papers have appeared concerning vapor deposition techniques and uses (170—179). 

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

Many anthraquinone reactive and acid dyes are derived from bromamine acid. The bromine atom is replaced with appropriate amines in the presence of copper catalyst in water or water—alcohol mixtures in the presence of acid binding agents such as alkaU metal carbonate, bicarbonate, hydroxide, or acetate (Ullmaim condensation reaction). 

The preparation of semiconductors by thermal decomposition would appear to be impossible because of the high amount of energy required to break all of the metal-carbon bonds before the atomic species could be formed. However, the thermal method is successful because the reaction to form free methyl radicals, which combine to form ethane, lowers the energetic requirements for the formahon of gallium, for example, according to the equation... 

Reaction of NbC F with an alkali metal carbonate, M2CO3, yields carbon dioxide, C02, in an amount equivalent to that of a chemical compound forming at the first stage of the reaction. The general form of the reaction between niobium dioxyfluoride and an alkali metal carbonate, M2C03, is ... 

When the reaction is performed at relatively low temperatures that prevent strong thermal decomposition of the alkali metal carbonate, the formation of C02 will be related only to the reaction and will indicate the stoichiometry of the process. Fig 8 presents mass loss isotherms of Nb02F - M2CO3 mixtures (in which M - Li, Na, K, Rb, Cs) that were subjected to thermal treatment in air at 850°C [84, 85]. It is important to mention that parallel experiments performed without the addition of Nb02F, resulted in alkali metal carbonate mass losses that were in the same order of magnitude as the measurement errors at temperatures below 850°C. 

The compound formed in the first step of the reaction between the solid components and the molten alkali metal carbonate can passivate the surface and prevent subsequent development of the interaction. This special property of M4Me04F, the compound formed in the first step, leads, in effect, to a single-stage interaction. 

It can be concluded from the study of Grubbs and Brunck that indeed a metal-carbon cr-complex might be the key intermediate in the metathesis reaction. For the conversion of I into II several reaction pathways can be... 

The formation of the active metal-carbon bond as a result of the interaction of low-valent ions of the transition metal with olefin is the most intriguing step of the polymerization process by one-component catalysts. The possibility of the formation of the transition metal-carbon bond resulting from the reaction of titanium low-valent ions with ethylene is shown in Dzsabiev et al. (182) ... 

However, these reactions remain hypothetical, and the mechanism of alkylation of low-valent coordinatively insufficient ions during their interaction with hydrocarbons calls for a detailed study. When the activation by some additives is performed the formation of the active transition metal-carbon bond by oxidative addition is also possible, e.g. in the case of such additives as alkylhalogenides or diazocompounds according to the schemes ... 

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