Organometallic radical

Acyclic Tricoordinate Radicals As one can easily note, the above examples of the cyclic radicals of Si and Ge atoms have rather particular structures featuring the cyclic delocalization of the odd electrons. The simple tricoordinate acyclic radicals of the type RsE (E = Si, Ge, Sn, Pb), lacking the stabilization effects of the cyclic Jt-delocalization, constitute another, more general and even more challenging, class of stable organometallic radicals. " Consequently, the search for such highly symmetrical species appeared to be of primary importance for synthetic chemists. 

Structural applications range from organic, inorganic and organometallic radicals to coordination complexes and biological macromolecules containing a paramagnetic center. 

Most of the information content from ESR spectra of organometallic radicals and coordination complexes comes from dilute single-crystal spectra or frozen solution spectra. Nonetheless, there are some bits of information and applications that come uniquely from isotropic spectra, and we discuss those aspects in this chapter. 

ESR spectral lines in a frozen solution or powder spectrum are sometimes peculiarly broad. The phenomenon is sometimes called g-strain . In most cases, the matter is dropped at that point and no attempt to explain further is made. A successful interpretation of the effect has, however, been made for some organometallic radicals.48... 

We consider, primarily, events in solids since most e.s.r. studies have been carried out on radicals trapped in solids. Only relatively persistent organometallic radicals have been studied by liquid-phase e.s.r. with in situ radiolysis, because of the technical difficulties involved. In most solid systems at low temperature radical centres are physically trapped in the rigid matrix and hence can be studied by e.s.r. without difficulty. However, although radicals as such may be immobile, this does not necessarily apply to electron-gain or -loss centres, particularly if these are charged, since electron-transfer may be facile. 

Organometallic radicals are important intermediates in biological and catalytic reactions. The structure and formation mechanism of radicals trapped in y-irradiated molecular sieves exposed to methanol and ethylene have been studied by EPR spectroscopy. It was found that Ag CH2OH+ radical with one-electron bond between Ag and C is formed by the attack of -CH2OH hydroxymethyl radical on Ag+ cation. 

Organometallic Nitrogen Compounds of Germanium, Tin, and Lead, 3, 397 Organometallic Pseudohalides, 5, 169 Organometallic Radical Anions, 15, 273 Organometallic Reaction Mechanisms, 4, 267... 

Tyler, David R., Mechanic Aspects of Organometallic Radical Reactions. .. 36 125... 

The formation of the RZn(f-BuDAB) radicals is notable and it appeared that these radicals are examples of persistent organometallic radicals in equilibrium with their C—C coupled dimer. These dimers could be independently synthesized in high yield from the reaction of (f-BuDAB)K and the corresponding RZnCl compound. The rate constant of the equilibrium between the persistent radical and its C—C coupled dimer is sufficiently small to study the dimers by NMR spectroscopy and the radicals by ESR spectroscopy . The obtained ESR data are in agreement with a structure for the radical in which the zinc atom adopts a trigonal planar geometry. In this respect it should be noted that the in situ... 

A further complication in the reduction of aryl Group IV derivatives is the formation of biphenyl radical anion (135, 100, 97, 20) or its derivatives (32). However, this reaction is not peculiar to organometallic radical anions but appears to be quite general for alkali metal reduction of phenylated compounds (135). 

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