Planar compounds radicals

Consider now a series of compounds A, that react with two reagents, Bi and B2. A good example is the reactions of alkyl radicals (the A, s are R") with BrCCl3 (B ) and CCI4 (B2). The radicals considered are planar, tt radicals that are primary, secondary, and tertiary, but not bridgehead.21 The scheme is... 

Finally, Gobbi and Frenking analyzed the allyl cation, radical, and anion. They stated that their results show that jr-electron delocalization is a stabilizing factor operative in the symmetric (C2O and bond alternating (Cs) forms of the planar compounds. Delocalization resists the rotation of the methylene groups but not necessarily bond alternation. Subsequently. they analyzed the distortion energy for the three allyl systems. They partitioned the total energy in three parts... 

The persistent radical anion II was obtained by chemical or electrochemical reduction of the parent neutral compound. The EPR spectrum of II is composed of a triplet of triplet (ap(2P)=3.50 mT and ap(2P)=0.89 mT) characteristic of a planar conjugated structure (Fig. 9) [87]. Amazingly, the dianion III was found to be paramagnetic exhibiting an EPR spectrum composed of a distorted dou-... 

Most of the salts based on decamethylmetallocenium radical cations and on planar metal bisdichalcogenate radical anions reported so far present crystal structures with mixed linear chain basic motives. The only known exception is [Fe(Cp )2][Ni (mnt)2], which exhibits another type of crystal structure based on a D+ [A2]2 D+ repeat unit [28]. In the case of this compound the magnetic behavior is dominated by the intradimer antiferromagnetic interactions. 

As most of the work with this type of salts was essentially motivated by the results obtained with the salts based on decamethylmetalocenium cations and polynitrile planar radical anions, the use of different metallocenium derivatives was limited to a small number of compounds. Among these only [Fe (C5Me4SCMe3)2][M(mnt)2], M = Ni and Pt, present crystal structures based on mixed linear chain motives. 

The synthesis of the trismethylenemethane iron tricarbonyl complex [(CH2)3C]-Fe(CO)3 was reported by Emerson et al. in 1966 (27). The geometry of this compound in the gas phase was investigated by Almenningen et al. (28) using electron diffraction methods. These authors pointed out some structural peculiarities which were not amenable to a simple explanation, in particular, why the hypothetical planar (CH2)3C radical is distorted when bound to the Fe(CO)3 conical fragment in such a way that the carbon atoms of the CH2 groups are displaced toward — the iron atom (Fig. 9). 

The second example depicted in Scheme 3.64 is the trioxotriphenylamine cation-radical. Kuratsu et al. (2005) compared structures of the cation-radical and its neutral counterpart. The neutral compound has a shallow bowl structure, whereas the cation-radical has a planar structure. In the latter, spin delocalization embraces a whole molecular contour, involving the oxygen atoms. This contribntes to the cation-radical stability. (The solid species is easily formed after oxidation of the neutral parent compound with tris(p-bromophenyl)aminiumyl hexafluorophosphate in methylene... 

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