Thiols protonated, cleavage

The protonated sulfides are less susceptible to cleavage than the corresponding protonated ethers and also more stable than the protonated thiols.149 Protonated tert-butyl methyl ether is completely cleaved to tot-butyl cation and protonated methanol even at 70°C. On the other hand, protonated tert-butyl methyl sulfide 60 is stable even at —60°C. When the temperature is increased to — 15°C, protonated fert-butyl methyl sulfide very slowly cleaves to tert- butyl cation and protonated methyl thiol149 [Eq. (4.39)]. 

The protonation of a thiolate donor, formation of a nonclassical r 2-H2 complex, release of H2 and addition of D2, and the heterolytic cleavage of this D2 by the concerted attack of the Lewis acidic metal center and the Brpnsted basic thiolate donor are essential steps. The acidic thiol deuteron can exchange with EtOH protons. The resulting free protons and the deuteride complex yield HD and the coordinatively unsaturated species that is the actual catalyst. The detailed mechanism comprises a considerably larger number of steps (and equilibria) (143). For example, the occurrence of r 2-D2 and [M(D)(SD)] intermediates that exchange with H+ should give rise to [M(D)(SH)]... 

For other Co(ll)complexes, spontaneous oxidative addition of water (protons) or of thiols (cleavage of the H-SR bond) - and of dioxygen - is also known. Mixed-ligand hydridocobaltates(lll) can then release molecular hydrogen by either photolysis (Hennig and Ritter 1995) or acid attack... 

Similar to alcohols, aliphatic ethers [54], thiols [55], and sulfides are also protonated on oxygen or sulfur, respectively, at -60 °C in magic acid carbocations are subsequently formed upon raising the temperature. Promoted sulfides, excluding tertiary alkyl, are resistant to cleavage up to -i-70 °C [56]. 

In analogy to the preparation of iminium salts, thiocarbenium ions (115) can be created by treatment of carbonyl compounds (1) with thiols," by alkylating (or Lewis acid catalyzed) cleavage of dithioace-tals U14) or by protonation of vinyl sulfides (thio enol ethers) (116 Scheme 55)." ... 

LC/MS analysis of the N-acetylcysteine conjugate is shown in Figure 9. The base peak molecular ion was observed at m/z 334. Very little fragmentation occurred with the exception of a small amount of S-C cleavage to produce a protonated thiol at m/z 202. 

The model in the first theoretical study used SH groups to mimic the S-Cys used by the enzyme. A mechanism proposed by Pavlov et u/. involved H2 binding to the Fe atom, with subsequent heterolytic cleavage to yield a protonated thiol group and a hydride that was transferred from the Fe to the Ni atom. A similar mechanism was suggested by Pavlov et al. 

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