Radicals ligand-centred

The key feature of these reactions is the interplay between metal-centred and ligand-centred radical species, as discussed in Chapter 5. To summarise, the process involves generation of a nitrogen-centred radical, which is stabilised by charge transfer from the... 

Tn other studies, reaction of [MnX(TPP)] (X = Nf or OCN ) with iodosylbenzene in hydrocarbon or halocarbon solvents yielded products formulated as yi-oxo dimers, [MnlvX(TPP)]20.678 [Mn,vN3(TPP)]20 has been characterized by X-ray diffraction (see Section 41.5.7.1). Infrared evidence supports678,679 the formulation of the dimers as being metal-centred oxidized products rather than containing porphyrin cation radicals the possibility of ligand-centred versus metal-centred oxidation in higher-valent metallo porphyrins has been discussed by several authors.680-682... 

Figure 5. Illustrative example of an EPR spectrum of a ligand-centred radical species in isotropic solution at room temperature. The spectrum reveals hyperfine couplings with all nitrogen and hydrogen atoms of the le-reduced pyridine-2,6-diimine ligand.

D for [V(22)] was consistent with a system best described as rather than as an organic (ligand centred) di-radical, expected to produce zero-field splittings much... 

Dicarbonyl compounds also act as excellent spin traps for neutral RsM radicals, forming adducts of structure 5, 6 or 7 depending upon the dicarbonyl compound and the nature of the ligand bound to the metal centre. Of course, for cyclic dicarbonyl compounds such as ortho quinones the trans structure 7 is not accessible because of geometric constraints. Data for these radicals are contained in Table 4. 

The tin hyperfine coupling constants for the hexaphenylditin radical anion enable values for the occupancy of the unpaired electron in the tin 5s and 5p orbitals of 0.10 and 0.34, respectively, to be calculated. This would imply that the electron occupies a tin sp3 hybrid orbital. Since the radical contains two tin atoms, the total spin density residing with the tin centres is ca 0.9. There is very little spin density residing with the ligands, and the... 

These reactions provide an efficient route to the formation of tin-centred radicals carrying a variety of ligands. Their reactions with a variety of ligands such as alkyl halides, alkenes and 1,2-diones have been investigated55, and are summarized in Scheme 13. 

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