Thioethers oxidative addition

Example The oxidative addition of dimethyl disulfide (DMDS) transforms the double bond to its 1,2-bis-thiomethyl derivative (a). Induced by charge localization at either sulfur atom, the molecular ions of DMDS adducts are prone to a-cleavage at the former double bond position (b). This gives rise to sulfonium ions that are readily identified from the mass spectrum (Chap. 6.2.5). The method can be extended to dienes, trienes, and alkynes. [70,71] (For the mass spectral fragmentation of thioethers cf. Chap. 6.12.4). 

The fluxional bimetallic complex 5 has been prepared by route (a) or altemativley by route (b). Both strategies combine the ability of the functionalized silanes la/b to coordinate metal centers by oxidative addition (reactivity of the Si-H function) or to form dative bonds using the donor properties of the thioether groups. 

The mechanism was postulated to involve a Cu(l)-carboxylate as the active species, which promotes oxidative addition of the thioimide. Subsequent transme-talation and C-S reductive elimination generates the thioether product. An excess of boronic acid is often required, as copper catalysts may competitively oxidize aryl substituted boronic acids to the corresponding phenol in the presence of adventitious water [21]. The rate of acceleration observed with amino acids and carboxylate-based ligands, such as 3-methylsalicylate, is attributed to stabilization of a 7i-Cu intermediate generated through a nucleophilic aromatic substitution type mechanism (Scheme 1) [72]. The amino acid or carboxylate ligand may also simply stabilize putative Cu(lll) intermediates. 

Reactions of [Ru3(CD)i2] towards a variety of reagents are reported. These include the formation of simple adducts from the addition of tris(dimethylphosphino)methane, hexaphosphaferrocenes, l,2-0-isopropylidene-a-D-glucofuian, Ph2PCH2C(0)Ph, and cyclic thioethers. A large number of publications document the oxidative-addition of carbon-... 

When the C-H activation process is inefficient or difficult to carry out, one can often resort to alternative methods such as transmetallation reactions, as in the synthesis of the interesting cycloruthenated complex 13. The corresponding C-H activation process for 2 gives only a 38% yield." A similar method was employed for the synthetically useful cyclopalladated ketone derivative 15 and for the organomolybdenum complex 17.Oxidative additions of suitably substituted iodo derivatives on Pd(0) were employed to synthesize the primary 8-napthylamine complex 19 and the complexes 21 with a variety of substitution patterns on the thioether group. 

Alvinox P is utilized to protect polymers from thermal oxidation particularly during processing. It acts essentially as a decomposer of hydroperoxides. Optimum performance is obtained when the product is used in combination with antioxidants (hindered phenols and/or thioethers) which additionally protect the polymer against long-term heat degradation. 

The importance of steric effects in determining the oxidation state of the product can be illustrated by a thioether linkage, eg (57). If a methyl group is forced to be adjacent to the sulfur bond, the planarity required for efficient electron donation by unshared electrons is prevented and oxidation is not observed (48). Similar chemistry is observed in the addition of organic nitrogen and oxygen nucleophiles as well as inorganic anions. 

---