Pyrolysis transition-metal complexes

Carbon dioxide, 0=C=6 , mp —57°C (5.2 atm), bp —79 °C (sublimes), is obtained from the combustion of carbon and hydrocarbons in excess air or oxygen or by the pyrolysis ( calcination ) of CaCOs (limestone). The photosynthesis in plants reduces CO2 to organic matter, but the similar reduction of CO2 in a nonliving system ( in vitro ) appears to be very difficult. However, CO2 can be reduced electrochemically to methanol, formate, oxalate, methane, and/or CO depending upon the conditions. Numerous transition metal complexes of CO2 are known,which exhibit the modes of metal-C02 bonding depicted in Figure 2. 

Summary The stepwise synthesis of the polycarbosilanes (Cl2SiCH2CH2) (5) and (H2SiCH2CH2)n (6) are described. On addition of catalytical amounts of transition metal complexes to polymer 6 dehydrogenation occurs and a further crosslinked carbosilane (8) is obtained by formation of new silicon-silicon bonds. Pyrolysis of carbosilane 8 produces a black ceramic material, containing P-SiC together with carbon. The ceramic yield after pyrolysis of 8 is approximately four times the yield obtained when 6 is employed as the starting material. From polymeric 8 preceramic fibers are accessible subsequent pyrolysis yields ceramic fibers. Moreover, the carbosilane 8 can be utilized as a binder for ceramic powders. 

Pyrolysis of dihalocyclopropanes was studied along with the effects of electrophilic reagents, and confirms the foregoing results (33-37). In many cases, those authors observed that polymeric residues, in addition to ally lie and diene-type products, were present at the end of pyrolysis. The formation of these polymers confirms the hypothesis that the dihalocyclopropanes are monomers that can be polymerized either by cationic processes or by the action of transition-metal complex catalysts. 

Electrochemistry of pyropolymers obtained on pyrolysis of charge-transfer complexes of transition metals with porphyrins and phthalo-cyanins 90MI17. 

The formation of carbido-atoms in transition metal clusters is quite often achieved by pyrolysis or thermolysis of low-nuclearity carbonyl complexes. For example, the vacuum pyrolysis of [Ru3(CO)i2] produces octahedral [Ru6C(CO)i7] in 65% yield, and the thermolysis of a solution containing [H2Re(CO)4] yields salts of [H2Re6C(CO)i8] , [Re7C(CO)2i] , and [Re8C(CO)24] -, all of which are based on octahedral or capped-octahedral frameworks with a carbide atom occupying their central cavities. 

Non-precious metal catalyst research covers a broad range of materials. The most promising catalysts investigated thus far are carbon-supported M-N /C materials (M = Co, Fe, Ni, Mn, etc.) formed by pyrolysis of a variety of metal, nitrogen, and carbon precursor materials [106]. Other non-precious metal electrocatalyst materials investigated include non-pyrolyzed transition metal macrocycles [107-122], coti-ductive polymer-based complexes (pyrolyzed and non-pyrolyzed) [123-140], transition metal chalcogenides [141-148], metal oxide/carbide/nitride materials [149-166], as well as carbon-based materials [167-179]. The advances of these types of materials can be found in Chaps. 7-10 and 12-15 of this book. 

Very recently a critical review of the work on heat-treated macrocylic complexes on carbon was published It showed that the results for gas diffusion electrodes obtained can hardly be compared with each other. The activity and pyrolysis behaviour of carbon-supported transition metal chelates is determined by various factors such as the chelate, the texture of the carbon, the dispersion of the catalyst on the support, the kinetics of the pyrolysis reactions, etc. The processes which occur during the metal loading on the carbon and the pyrolysis were discussed. The authors developed a new carbon modified rotating ring disc electrode which can be used for quick comparisons of both the activity and selectivity of carbon-supported catalysts... 

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