Sulfur transfer reactions

The ion-molecule reaction between thiirane and its radical cation to form a thiirane sulfide radical cation and ethylene has been studied by Qin, Meng and WiUiams [134]. ESR studies using a low-temperature sohd-state Freon radiolysis technique provided compeUing evidence that the hemibonded dimer radical cation of thiirane is an intermediate in this so-called sulfur-transfer reaction see Scheme 2. 

An analogous sulfur transfer reaction has been proposed for the thermal decomposition of neutral thiirane to give ethylene and elemental sulfur, on the basis of ah initio calculations at the G3(MP2) level of theory [135]. 

Cp = Ti -CgHs R = 4-CIC6H4 dppe = (Ph2PCH2)2 TTP = meso-tetra-p-tolylporphyrinato Scheme 47 Sulfur transfer reactions by the use of TiCp2Ss... 

Scheme 49 Sulfur transfer reactions by the use of TiCp2(S6C6Hio) and TiCp2Sg...

It has been reported that the zinc hexasulfido complex, Zn(S6)(TMEDA) (TMEDA=] r,] T,N, N -tetramethylethylenediamine) acts as a sulfur transfer reagent in an analogous manner as the above-mentioned titanium polysulfido complexes. The sulfur transfer reaction between Zn(S6)(TMEDA) and TiCp2Cl2 cleanly proceeds at room temperature to afford ZnCl2(TMEDA) and TiCp2S5 together with Ss (Scheme 51) [132]. This result suggests that... 

From X-ray crystal structures of the products, the reactions of these stereoisomeric disilenes with episulfides, and with sulfur, were shown to proceed with retention of configuration at silicon. These findings suggest that the reaction proceeds in a concerted fashion, through intermediates or transition states involving tetracoordination for the sulfur atom being transferred (Scheme 13). Similar intermediates are believed to occur in other sulfur-transfer reactions.86... 

The chemistry of dithiazole derivatives has received a new impetus due to their sulfur-transfer applications in the solid-phase synthesis of oligodeoxyribonucleotide phosphorothioates via the phosphoroamidite method they are advantageous alternatives to the previously used Beaucage reagent. The general mechanism of the sulfur-transfer reaction is presented in Scheme 32 . 

Three major topics have dominated research activity on thiophenes since 1996 the design and synthesis of dithienylethene molecules for application as photochromic systems (Section 3.10.2.1.3) reactions brought about under transition metal catalysis (Section 3.10.2.11) and the synthesis, characterization, and reactivity of a plethora of transition metal complexes of thiophenes (Section 3.10.6). All three had received brief mention in CHEC-11(1996) (Sections 2.10.2.2.3, 2.10.4.7.3, and 2.10.6, respectively), but together account for almost one-third of the chapter now. In addition, shorter sections have been introduced to cover the following topics one-electron oxidation of thiophenes (Section 3.10.2.2) electrochemical reactions at cathodes (Section 3.10.2.7.5) sulfur-extrusion and sulfur-transfer reactions (Section 3.10.2.10) and reactivity of silicon-linked substituents (Section 3.10.4.5). 

The DCPD polysulfanes with between four and eight sulfur atoms have been independently synthesized from titanocene polysulfides and DCPD sulfenyl chlorides by sulfur transfer reactions. ... 

Reactions of Alkenes with Sulfur Compounds Sulfur Transfer Reactions... 

Of the many reactions known for polysulfanes, only the following types will be dealt with since they are of general importance for inorganic and organic polysulfur compounds interconversion and sulfur transfer reactions, nucleophilic displacement reactions, and oxidation reactions with conservation of chain length. 

For other thermally induced sulfur transfer reactions, see Section 2.2.6. 

Apeloig and Sklenak used high-level ab initio computation (QCISD/6-31G ) to determine the mechanism of a sulfur-transfer reaction between silylene (H2Si ) and thiirane <2000CJC1496>. A complex 41, formed in the first step over a barrier of 7.4kcalmol , was predicted to be observable in a matrix because the barrier to subsequent abstraction of S in a single step is higher at 14.9 kcal moP (Scheme 7). Other studies of abstraction of sulfur from thiirane by carbenes are discussed under Section 1.05.6.3.2. 

Another interesting synthesis of fused-ring thiiranes was reported by Weinkotz and co-workers in a sulfur-transfer reaction from 3,3,7,8-tetramethyl-9,10-dioxa-ll-thiatricyclo[6.2.1.0 ]undec-6-en-5-one (a derivative of thiophene endoperoxide) 37 to cyclic olefins under thermolysis conditions, or at low temperature using tetraphenylporphine cobalt(ll) complex as a catalyst (Scheme 56) <1996CC177>. The endoperoxide was prepared by photo-oxygenation... 

By using C NMR spectroscopy and single crystal X-ray analysis, the previous claims for the isolation of thiaziridines <1896CB59> (see Beilstein database) were shown to be erroneous <2005JSF111>. However, although the intermediacy of thiaziridines cannot be excluded in these and similar sulfur-transfer reactions, the addition of sulfur to aldimines results in the formation of isolable thioamides as products, not thiaziridines <2005JSF111>. 

Several diatomic ligands similar to CO are worth brief mention. Two of these, CS (thio-carbonyl) and CSe (selenocarbonyl), are of interest in part for purposes of comparison with CO. In most cases, synthesis of CS and CSe complexes is somewhat more difficult than for analogous CO complexes, because CS and CSe do not exist as stable, free molecules and do not, therefore, provide a ready ligand source.Therefore, the comparatively small number of such complexes should not be viewed as an indication of their stability. Thiocarbonyl complexes are also of interest as possible intermediates in certain sulfur transfer reactions in the removal of sulfur from natural fuels. In recent years, the chemistry of complexes containing these ligands has developed more rapidly as avenues for their synthesis have been devised. 

The sulfur transfer reaction using titanocene pentasulfide and dichloropoly-sulfanes S Cl2 is very versatile and has made it possible to prepare Sn after the necessary S6CI2 became accessible in sufficient purity ... 

The reaction mechanism for the formation of sulfur sols can be understood on the basis of the following sulfur-transfer reactions. While thiosulfate ions are stable in water at 20 °C, the protonated anion will be attacked by the more nucleophilic dianion resulting in a growth of the sulfur chain [27] ... 

Likewise, the steady-state sulfur activity in Ag2S used as catalyst for sulfur transfer reactions, e.g., COS - - H2 = CO - - H2S may... 

Isomerization of an unbranched sulfur chain to form a branched structure is one possibility (equation 122) to start a sulfur transfer reaction. 

The ion chemistry of thiothionylfluoride 18S) jg characterized by sulfur transfer reactions. 

Rapid desulfurization of thiiranes hy heterodinuclear complexes is achieved by using an early-late dinuclear transition-metal complex. Cp2Zr(/r-N Bu)IrCp reacts with thiiranes in almost diffusion controlled rates to give /r-sulfido complex and corresponding olefin with retention of configuration at the alkenyl carbon center (Scheme 3.68) [132]. Two mechaiusms such as completely concerted sulfur transfer reaction and insertion of the C-S bond into the Zr-Ir bond followed by concerted four-center ehmination are proposed. 

The oxygen of azole A-oxides produces a nucleophihc attack to C=S C-atom of a cycloalkanethione forming a zwitterion, which cyclizes and spontaneously decomposes, yielding the product of this sulfur transfer reaction (Scheme 16). 

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