Tetrahedral molecules radicals

Diphosphinoamines (X2P-NR-PX2) are examples of a more unusual potentially chelating diphosphine. The dimer Co2(F2PN(CH3)PF2)3(CO)2 has three of these ligands bridging symmetrically between the two tetrahedral Co centers, which also carry a terminal CO group this molecule can undergo reduction with LiEt3BH in THF to form a stable mixed valence (d9—d10) radical anion.163... 

From the reaction of the radical anion of l,2-bis[(2,6-diisopropylphenyl)imino]acen-aphthene (dpp-bian) with i -PrMgCl, the persistent radical complex isopropylmagnesium dpp-bian (253) was isolated in yields up to 60% (equation 20). An X-ray crystal-structure determination of 253 showed that the magnesium atom has distorted tetrahedral coordination geometry as the result of the cr-bonded isopropyl group, one coordinate-bonded diethyl ether molecule and A, A -chelate bonding of the dpp-bian radical anion. The radical anionic character of the dpp-bian moiety is indicated by the relatively long Mg—N bond distances [Mg-N 2.120(2) and 2.103(2) A]. 

S04 A distorted tetrahedral radical of AB4-type molecule with 31 electrons as a hole-type centre stabilized by alkali ions substituted at Ca2+ sites. 

The intrinsic stability of the aromatic n system has two major consequences for the course of reactions involving it directly. First, the aromatic ring is less susceptible to electrophilic, nucleophilic, and free-radical attack compared to molecules containing acyclic conjugated n systems. Thus, reaction conditions are usually more severe than would normally be required for parallel reactions of simple olefins. Second, there is a propensity to eject a substituent from the tetrahedral center of the intermediate in such a way as to reestablish the neutral (An + 2)-electron system. Thus, the reaction is two step, an endothermic first step resulting in a four-coordinate carbon atom and an exothermic second step, mechanistically the reverse of the first, in which a group is ejected. The dominant course is therefore a substitution reaction rather than an addition. 

In the polymeric structures of the first members of the homologous series of trivalent chromium derivatives, the metal atoms possess octahedral coordination [1366], while the derivatives of branched radicals are often monomeric [Cr(OR)2L2] molecules with square planar coordination [1571] or dimeric [Cr(OR)2]2 with triangular cordination of the metal atoms [795, 1185]. The monomeric [Cr(OR)3L2] are trigonal bipyramids [1571], while the derivatives of chromium (IV) and (VI) are tetrahedral [167, 1573, 1527]. 

The very reactive Rieke cadmium metal was allowed to react under vacuum with benzoquinone in THF. This resulted in the formation of several different paramagnetic species, [Cd(C6H402 )(THF)3]+,C6H402 or [Cd(C6H402 )(THF)3]+ + C6H402 [215]. The tetrahedral coordination sphere for each species consists of three THF molecules and an anion radical that is asymmetrically or symmetrically coordinated to the metal dication. The original apparatus for the generation of the benzoquinone anion radical via electron transfer from cadmium metal was reported... 

Now the end carbon has a single unpaired electron. What do we do with it Before the bond broke, the end carbon was tetrahedral (sp3 hybridized). We might think that the single electron would still be in an sp3 orbital. However, since an sp3 orbital cannot overlap efficiently with a Jt bond, the single electron would then have to be localized on the end carbon atom. If the end carbon atom becomes trigonal (sp2 hybridized), the single electron could be in a p orbital and this could overlap and combine with the 7t bond. This would mean that the radical could be spread over the molecule in the same orbital that contained tire cation. 

In the hexaphcnylethane molecule the valence bonds of the two ethane carbon atoms are tetrahedral, but during the dissociation this configuration is replaced by the planar configuration which is present in the free radical. The planar structure may, however, be slightly distorted owing to the repulsion of the ortho hydrogen atoms of the benzene rings. 

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