Sulfur atom abstraction reactions structures

Abstract Inorganic polysulfide anions and the related radical anions S play an important role in the redox reactions of elemental sulfur and therefore also in the geobio chemical sulfur cycle. This chapter describes the preparation of the solid polysulfides with up to eight sulfur atoms and univalent cations, as well as their solid state structures, vibrational spectra and their behavior in aqueous and non-aqueous solutions. In addition, the highly colored and reactive radical anions S with n = 2, 3, and 6 are discussed, some of which exist in equilibrium with the corresponding diamagnetic dianions. 

Due to the high rate of reaction observed by Meissner and coworkers it is unlikely that the reaction of OH with DMSO is a direct abstraction of a hydrogen atom. Gilbert and colleagues proposed a sequence of four reactions (equations 20-23) to explain the formation of both CH3 and CH3S02 radicals in the reaction of OH radicals with aqueous DMSO. The reaction mechanism started with addition of OH radical to the sulfur atom [they revised the rate constant of Meissner and coworkers to 7 X 10 M s according to a revision in the hexacyanoferrate(II) standard]. The S atom in sulfoxides is known to be at the center of a pyramidal structure with the free electron pair pointing toward one of the corners which provides an easy access for the electrophilic OH radical. 

The methylene carbon atom in a condensed 4-thiazolidinone flanked by a sulfur atom and a carbonyl group possesses enhanced nucleophilic activity and attacks an electrophilic center with ease. If the structure permits, the reaction product loses a molecule of water, and an unsaturated derivative is formed. The reaction is carried out in the presence of a base which abstracts a methylene proton. It is the anion thus formed that attacks the electrophilic center. Generally, the anion condenses with aromatic aldehydes, nitroso compounds, aryidiazonium salts, and ethyl orthoformate, as well as undergoing Vilsmeier-Haack and Mannich reactions. 

Inspection of the citrate structure shows a total of four chemically equivalent hydrogens, but only one of these—the pro-/J H atom of the pro-i arm of citrate—is abstracted by aeonitase, which is quite stereospecific. Formation of the double bond of aconitate following proton abstraction requires departure of hydroxide ion from the C-3 position. Hydroxide is a relatively poor leaving group, and its departure is facilitated in the aeonitase reaction by coordination with an iron atom in an iron-sulfur cluster. 

In the reaction with thiophene 32, the disilathiirane 38 was unexpectedly formed in about 50 % yield by way of sulfur extraction. The X-ray structure analysis of the disilathiirane 38 revealed a very short Si-Si bond length of 230.5 pm and an almost planar environment at the silicon atoms (angular sum C-Si-C + C-Si-Si + Si-Si-C = 358 7°) [10]. These features are typical for related three-membered rings of this type and were also observed for other disilathiiranes [13]. As illustrated by the isolation of the 1,2-disilacyclohexadiene 39, sulfur abstraction from 32 seems to be initiated by [2+4]-cycloaddition of disilene 3. The bicyclic compound 40 is most likely formed by photoisomerization of 39 [14]. 

Reported rhenium complexes possess one [70-74], two [75], and three [75] dithiocarboxylato ligands coordinated to the one rhenium atom to form a high coordination state, as in the case of the technetium complex [76]. One of these complexes 29 is synthesized from Re(VII)S4 and (PhCSS)2 (Fig. 10) [72]. An internal redox reaction occurs and Re( VII) is reduced to Re(III) in the synthetic process. Addition of sulfur-abstracting reagents, Ph3P or Et4NCN, produces the heptacoordinate complex 30 with the neutral capped octahedron structure or... 

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