Metal-carbon bond energy

Table 2.3 Metal-carbon bond energies for some methyls...

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... 

Interestingly as we have seen this may have a maximum as a function of the metal-carbon bond energy. 

Tec and rn decrease when the carbon adsorption energy increases. Volcano-type behavior of the selectivity to coke formation is found when the activation energy of C-C bond formation decreases faster with increasing metal-carbon bond energy than with the rate of methane formation. Equation (1.16b) indicates that the rate of the nonselective C-C bond forming reaction is slow when Oc is high and when the metal-carbon bond is so strong that methane formation exceeds the carbon-carbon bond formation. The other extreme is the case of very slow CO dissociation, where 0c is so small that the rate of C-C bond formation is minimized. 

Carbon in the form of diamond is an electrical insulator because of its huge band gap. hi fact, its band gap of 580 kJ/mol substantially exceeds the C—C bond energy of 345 kJ/mol. In other words, it requires more energy to promote an electron from band to band in diamond than to break a covalent bond. Lead, in contrast, is a metallic conductor because it has... 

When the rr-interaction between metal and carbene fragments is increased, the metal-carbon 2p. 77 orbital is pushed up higher in energy and is no longer significantly localized on Ca. In complexes of this type, the LUMO is an orbital not associated with the metal-carbon bond (10). 

Examples of silver(l) alkyl and alkenyl (including aryl) complexes have been known from as early as 1941 6-9 however, the number of examples is fairly limited with respect to that of the heavier congeners, copper(l) and gold(l). Such a phenomenon can readily be attributed to the relatively low stability of this class of complexes, both photochemically and thermally. Simple homoleptic alkyl and alkenyl complexes of silver(i) are known to be very unstable under ambient temperature and light, and successful isolation of this class is fairly limited and mainly confined to those involving perfluoroorganics.10 The structures and the metal-carbon bond-dissociation energies for... 

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