Sulfur abstraction

Abstraction of a sulfur atom from a thiirane by a sulfur radical cation has been reported [352]. EPR spectroscopic studies provide insight into this process. Irradiation of thiirane with y-rays in CF3C1 at 77 K generates the corresponding radical cation. In more mobile Freons the dimeric radical cation is produced. On warming this species fragments and it was proposed that 173a and ethene form. 

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Lee, M. K. Prince, R. C. Pickering, I. J., et al., Microbial Desulfurization of Crude Oil Distillate Fractions Analysis of the Extent of Sulfur Removal and the Effect on Remaining Sulfur. Abstracts of Papers of the American Chemical Society, 1997. 213 p. 11-FUEL. 

Some preparations of polysulfido complexes with sulfur-abstracting reagents have been reported. For example, [Pt(Ss)3] (15), reacts with CN to yield [Pt(S5)2] 168,192). During the course of this reaction, an interesting two-electron transfer occurs, reducing Pt(IV) to Pt(II). The same substrate reacts with PhjP in the following way 42, 81) ... 

The latter case has been demonstrated with the reaction of [ReCl3(PPh3)2(CH3CN)] with a large excess of sodium diethyldithiocarbamate which results in sulfur abstraction and in the formation of a mixed phosphine/diethyldithiocarbamato/r/ -thiocarbamoyl complex. For the molecular structure of this compound see formula (225) which represents that of the corresponding rhe-nium(IV) cation which is formed by oxidation of the primarily formed Re complex and contains one rhenium-carbon bond. The formation of thiocarbamoyl compounds seems to be an essential... 

Reactions other than Lewis acid-base associations/dissociations are frequently observed wit donor molecules, leading notably to solvolysis, oxygen or sulfur abstraction, insertion reaction and carbon-carbon coupling reactions. The tendency to form metal-element multiple bonds i remarkable in this respect the activation of dinitrogen by tantalum or niobium is unique. Th formation and chemistry of constrained reactive metallacycles open another promisin fast-developing area, on the frontier with organometallic chemistry. 

The question of whether sulfur insertion occurs at the C-S or the M- S bond was raised following the first isolation of the perthio-l,l-dithiolate complexes (156). Early studies of the sulfur-addition and sulfur-abstraction reactions using 33S were reported for Ni(CS3)2" (Eq. 54). It was concluded that the added sulfur was inserted into the C -S bond (156). 

Kinetic studies on the reaction of NiL S with Ph3P established that the rate of sulfur abstraction depends on the concentration of both the complex and the phosphine (233). 

The complexes are reactive towards nucleophilic as well as electrophilic attack. Attack by alkyl halides yields thioalkylated compounds. Mostly an alkylation at one sulfur atom takes place, but examples of alkylation at both sulfur atoms are known (reactions 1 and 2). The facile sulfur abstraction with PPh3 yielding a thiocarbonyl complex is a nucleophilic reaction (reaction 3). 

Complexation of COS with metals is an exception rather than a rule.3 To stabilize the M—COS bond formation, a basic metal centre is needed. This, however, weakens the C—S bond, promoting disproportionation reactions or sulfur abstraction.27 Complexes of Ni,28 Pd, Pt,29 Ru,30 Ir and Rh31 were prepared. COS is CS bonded in these complexes. Decomposition reactions, in which the M—COS complexes play a role, give either dithiocarbonates30 or carbonyls (reactions 6 and 7). 

The model was designed to study the ability of sulfur-oxidizing bacteria to use the organically bound sulfur as substrate. The symmetry of the sulfides provided an insight into the sulfur abstracting prowess of T. thiooxidans. 

For example, the distonic anion radical of cyclopentadienylidene trimethylen-emethane reacts under mass spectrometer gaseous-phase conditions with carbon disulfide by sulfur abstraction and with nitric oxide by NO-radical addition. The first reaction characterizes the distonic anion radical mentioned as a nucleophile bearing a negative charged moiety. The second reaction describes the same anion radical as a species having a group with radical unsaturation (Zhao et al. 1996). 

Preparative routes involve sulfur abstraction by osmium(VI) nitrido complexes from S2C12 or SCN , though the mechanisms of these reactions are not clear reaction of halides with (NSC1)3 has also been used. 

Another example of sulfur abstraction by an osmium nitrido complex occurs in the reaction of [OsNC14]- with (PPh4)NCS to give (Ph4P)2[Os(NS)(NCS)3], in which the thiocyanate groups are thought to be bonded to the metal via nitrogen.265 For reactions of the complex see Scheme 10, p. 563. 

Mo is the element of choice for clean and direct sulfur abstractions. A comparison with appropriate C atom reactions, where the ratio cyclopropane/propene was 10 1, indicates an Insertion mechanism, in which Mo atoms attack the C H bond to form an allyl intermediate (see Mechanisms of Reaction of Organometallic Complexes). 

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]. 

Haake, M. Jiirgler, W. XIIIth International Symposium on the Organic Chemistry of Sulfur, Abstracts of Papers, Odense, 1988. 

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