Organometallic radicals structure

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. 

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. 

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... 

Within the last few years there has been considerable activity directed towards the synthesis of organic and organometallic derivatives of heteropolyanions. Reactions of lacunary polyanions with RMC13, where R is an organic or organometallic radical, provide a simple route to such derivatives.97 Some examples of these reactions are presented in Scheme 5. For the most part the reactions proceed smoothly and the products are remarkably stable towards hydrolysis. Apart from their structural characterization via crystallography and NMR spectroscopy the chemistry of these complexes has not been completely described. 

Generally, ESR spectra of organometallic radicals are unexceptional and are similar to those of organic radicals with g 2. For example, rm 5-[Mo(CO)2(dmpe)2] has a g = 2.053 and a coupling of ap = 25 G is resolved.A value of g = 2.085 and poorly resolved fine structures are found for HFe(diphos) The relative sharpness of the resonances is important, particularly with iron compounds, because inadvertent oxidation could give rise to a low spin complex. Since these complexes have... 

Organic and organometallic free radicals structure, kinetics and mechanism... 

Cerrada, E., Laguna, M., Bartolome, J., Campo, J., Orera, V. and Jones, P.G. (1998) Cation-radical salts with organometallic gold anions. X-ray structure of TTFPh]2[Au(C6F5)2]. Synthetic Metals, 92(3), 245—251. 

The site of reaction on an unsaturated organometallic molecule is not restricted to the most probable position of the metallic atom or cation or to a position corresponding to any one resonance structure of the anion. This has been discussed in a previous section with reference to the special case of reaction with a proton. Although the multiple reactivity is particularly noticeable in the case of derivatives of carbonyl compounds, it is not entirely lacking even in the case of the derivatives of unsaturated hydrocarbons. Triphenylmethyl sodium reacts with triphenylsilyl chloride to give not only the substance related to hexaphenylethane but also a substance related to Chichi-babin s hydrocarbon.401 It will be recalled that both the triphenyl-carbonium ion and triphenylmethyl radical did the same sort of thing. 

Electrochemistry, organic, structure and mechanism in, 12, 1 Electrode processes, physical parameters for the control of, 10, 155 Electron donor-acceptor complexes, electron transfer in the thermal and photochemical activation of, in organic and organometallic reactions. 29, 185 Electron spin resonance, identification of organic free radicals, 1, 284 Electron spin resonance, studies of short-lived organic radicals, 5, 23 Electron storage and transfer in organic redox systems with multiple electrophores, 28, 1 Electron transfer, 35, 117... 

Alike metallocomplex anion-radicals, cation-radicals of odd-electron structure exhibit enforced reactivity. Thus, the 17-electron cyclopentadienyl dicarbonyl cobalt cation-radical [CoCp(CO)2] undergoes an unusual organometallic chemical reaction with the neutral parent complex. The reaction leads to [Co2Cp2(CO)4]. This dimeric cation-radical contains a metal-metal bond unsupported by bridging ligands. The Co—Co bond happens to be robust and persists in all further transformations of the binuclear cation-radical (Nafady et al. 2006). 

Since the properties of a polymer can be noticeably influenced by small variations in the molecular structure, and these in turn depend on the preparation conditions, it is necessary when reporting data to indicate not only the type of measurement (e.g., molecular weight by end group analysis crystallinity by infrared measurement or by X-ray diffraction etc.), but also the type of preparation (e.g., radical polymerization in bulk at 80 °C polymerization with a particular organometallic catalyst at 20 °C). 

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