Metals/metalloids free radicals

That the carbon—metal or carbon—metalloid bonds are preserved at all in these reactions is quite surprising. With tetramethylgermanes, for example, this free radical reaction must be a 24 step process. The success in preserving carbon-germanium bonds must arise from very rapid molecular vibrational, rotational, and translational relaxation processes occurring on the cryogenically cooled surfaces such that the energy from the extremely exothermic reaction is smoothly dissipated. 

A variety of in vitro and in vivo toxicological studies have examined the potential health effects of CFA. Most of these studies have concluded that iron release from CFA can generate free radicals, and therefore can trigger DNA damage and toxicity (Smith et al, 1998, 2000 Veranth et al., 2000 van Maanen et al, 1999 Chen et al, 1990). Hence, the deleterious effects from inhalation exposure to CFA may be linked to its content of leachable iron, its alkali content, and the amounts of soluble salts that can dissolve to generate acid and thereby enhance iron release. However, the chemical reactions between CFA and lung and macrophage fluids, and the potential health effects of leachable metals and metalloids other than iron must be studied further. 

Organometallic compounds of less active metals and metalloids (e.g., silicon," antimony, and bismuth, are quite inert to water. Organomercury compounds (RHgX or R2Hg) can be reduced to RH by H2, NaBITj, or other reducing agents." The reduction with NaBH4 takes place by a free-radical mechanism." Alkyl-Si... 

Of the other metals or metalloid hydrides that could be conceivably participate in radical processes, by far the most important from the synthetic point of view are organomercury hydrides. Interest in the free radical chemistry of organomercurials blossomed when it was established that the classical demer-curation reaction with sodium borohydride was in fact a radical chain reaction (Scheme 4.1).2... 

The addition of metal and metalloid hydrides to carbon-carbon double bonds is not a new reaction, having been observed from time to time with silanes of the type R3SiH under free-radical conditions (4%, 85) and with boron hydrides (68). The versatility of such hydride-olefin interactions, nevertheless, first became evident with the recent researches of Ziegler with lithium and aluminum alkyls (139). The observation that attempted distillation of ethyllithium led to decomposition into lithium hydride, ethylene, and higher olefins prompted the following formulation of the reaction course (see 18) ... 

In our studies, the transfer of CH3 or CH3" has been found to be the most predominant reaction mechanism for a number of metals and metalloids. Methylcobalamin has been found to be very stable to nucleophilic attack, but very susceptible to electrophilic attack and free radical attack. 

The homolytic thermal dissociation of R—M, previously used by Paneth in generating and studying free alkyl radicals, occurs with the more electronegative alkyls, such as those of mercury, lead, and the metalloids. Currently there is much interest in evaluating carbon-metal bond dissociation energies from such pyrolyscs (Section III.B). 

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