Trianions

Paradoxically, although they are electron-rich, S-N compounds are good electron acceptors because the lowest unoccupied molecular orbitals (LUMOs) are low-lying relative to those in the analogous carbon systems. For example, the ten r-electron [SsNs] anion undergoes a two-electron electrochemical reduction to form the trianion [SsNs] whereas benzene, the aromatic hydrocarbon analogue of [SsNs], forms the monoanion radical [CeHg] upon reduction. ... 

The lithium enolate of AUV-dimethylacetamide underwent addition to 2-aryl-1-nitroethenes to give /faryl-y-nitroamides. The lithium dianions and the trianions of /l-oxo esters and /i,y-dioxo esters undergo addition to 2-aryl-1-nitroethenes to give bicyclic compounds as a single dia-stereomer8. 

Fig. 12-1. Correlation between azo coupling rates of substituted benzenediazonium ions with the 2-naph-thoxide-3,6-disulfonate trianion and the chemical shifts of protons at the position of the diazonio group in NMR spectra of the corresponding monosubstituted benzene parent compounds (Diener and Zollinger, 1986).

Cox et al. (1981) found, as expected, that the trianion of 2,3-dihydroxynaph-thalene-6-sulfonic acid has a higher reactivity than the dianion. They observed a specific catalytic effect of borate buffers, but unfortunately they did not investigate it further. 

The secondary a-deuterium isotope effects on azo coupling reactions are small, i.e., km/kiv is very close to unity. For the reaction of the 4-nitrobenzenediazonium ion with the trianion of l-D-2-naphthol-6,8-disulfonic acid catalyzed by pyridine, km/kiv = 1.06 0.04 (Hanna et al., 1974). 

Zollinger (1971) calculated the actual rate constant referring to the monomeric diazo component from the (overall) measured rates and the dimerization equilibrium constant. The ratio of rates of the first to the second azo coupling reaction of the biphenyl-4,4 -bis-diazonium ion with the trianion of 2-naphthol-3,6-disulfonic acid at 15 °C, k /k2 9 is 80. 

When methyltriflone 248 was treated with two equivalents of n-butyllithium at — 50 °C in THF, a, a-dianion 249 is formed. After methylation of this dianion, further treatment with two equivalents of n-butyllithium gives the a, a -dianion 250. This dianion can be alkylated at the terminal carbon atom, like the dianions from ketosulfones. On reaction with three equivalents of n-butyllithium, 248 gives a, a, a -trianion 251 which, upon methylation with methyl iodide, afforded methylated product 252. Hendrickson and Palumbo328 prepared cyclopentenone derivatives using 248 as the starting material. 

Oxidaton of heme goes through the biliverdin species. Octaethylbiliverdin can exist in coordinated form as the fully reduced trianion (OEB)3-, as the two-electron-oxidized monoanion (OEBox), or as the one-electron-oxidized radical (OEB-)2-. Nickel forms complexes with all three moieties, [Nin(OEB)]ra with n I 1, 0, and -1 (689).1787 The most highly oxidized species [Ni(OEBox)]I3 could be crystallized. The structure shows a helical coordination of the linear tetrapyrrole ligand around nickel with Ni—N distances of 1.867 A and 1.879 A. 

A trianionic zinc porphyrin anchored to a membrane by an imidazole link has been used to bind cytochrome c at the membrane surface. UV spectra confirmed the insertion of the zinc porphyrin into the phospholipid vesicle and was used to study surface association of cytochrome c. 

In the aprotic solvent acetonitrile, the trianion of cyclic trimetaphosphoric acid 115 is formed via the phosphorane 112 and the pyrophosphate dianion 113 protic solvents differ by reacting via the phosphorane 114 to give the phosphates 104 or H2PO . 

Fragmentation of 143 is not limited to aqueous media. Reaction of threo-745 with cyclohexylamine, triethylamine, or 2,6-lutidine in acetonitrile also leads to (Z)-144 while the phosphorus appears in various polyphosphates, in the trimetaphosphate trianion (after 110 °C/5 h, before work-up), and in phosphoramidates 95). 

Dianions or trianions derived from 1,3-dicarbonyl compounds react with nitroalkenes at low temperature to give the adduct, which undergoes a nitro-aldol type cyclization (Eq. 4.50).640... 

Figure 4 depicts the esr spectra recorded for both a dianion and a trianion of [21a] in solid solution. From the zero-field splitting D, which is proportional to the inverse distance of the unpaired electrons, one can roughly... 

A boron-containing analog of cyclooctatetraenide dianion (CgHg2-), the C7H7BMe3 trianion, has been obtained via acetylene insertion into the boratabenzene ring, affording complex 126 and other products, e.g., 127.1... 

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