Other Organometallic Radicals

Distinction between PL and ET mechanisms is not straightforward. Various experimental methods have been used so far to demonstrate the ET process, including spectroscopic detection of radical intermediates detection of products indicative of radical intermediates " and measurement of secondary deuterium " and carbonyl carbon kinetic isotope effects (KlEs) "" . The combination of several experimental methods, including KIE, substituent effect and probe experiments, was shown to be useful in distinguishing the ET process from the PL process for the addition reactions of the Grignard and other organometallic reagents . 

The behaviour of phosphonodithioformates has been extensively examined by Masson and recently reviewed [36, 155]. Among the nucleophiles used, phosphites have been shown to provide new phosphonium ylides. Other reagents (organometallics, radicals, amines, thiols) have been employed for carbon-carbon bond formation and synthesis of new functionalised phosphonates, of potential biological interest. 

The radical polymerization of various other organometallic vinyl monomers has been well studied. For example, in 1978, it was shown that vinylcymantrene 43 undergoes radical homopolymerization in the presence of AIBN as initiator at 50-80 °C in organic solvents such as benzene to yield poly(vinylcymantrene) 44 (Equation (15)). Molecular weights varied from = S x 10 to 3.6 x 10 with broad PDI values in the range 3.2-8.9. 

The "radical anion" or S/ l mode offers a coherent explanation for so-called "direct" nucleophilic substitutions in the absence of activating electron-acceptors. It accounts also for other organometallic condensation reactions that neither obey an Sat2 nor an addition/elimination mechanism. In this category falls the condensation of haloarenes with second and higher row elements. As typical examples may be quoted the... 

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