Thiolates arylthiolates

The hydrothiolation of terminal alkyl alkynes with 96 (Fig. 2.17) proceeds with good degree of regio- and chemo-selectivity, especially with thiophenol and p-methoxy-thiophenol as substrates. Isomerisation to the internal alkenyl thiolates accounts for less than 9% of the thiolated products under the reaction conditions. In addition, further hydrothiolation of the vinyl thioether product is not observed. Typical conversions of 70-85% at 1 mol% loading at 80°C within 5 h are observed. Arylthiols substituted with electron-withdrawing groups afford lower conversions. 

Mononuclear tetrahedral complexes of Co", Zn" and Cd" are also formed with high molar ratios of arylthiolate whereas at lower thiolate concentrations polynuclear species can be obtained. The equilibria existing in acetonitrile solution containing Co", PhS and halide have been postulated as shown in Scheme l,114... 

Ham and coworkers85 have developed a one-pot synthetic method for the formation of aryl-alkyl sulfides, 94, from various alkyl halides and lithium aryl thiolates 93, which are prepared in situ from 92 formed by lithium—halogen exchange of 91, employing n-butyllithium (Scheme 31). The method avoids the use of unstable arylthiols and a catalyst is not required. Several aryl bromides were successfully employed in the reaction, and the corresponding sulfides were obtained in 71 to 96% yields. 

HIPIP). The rates of initial thiolate substitution in reactions of (11) (R = Et or Bu ) with arylthiols in acetonitrile solution have been reported/ and the mechanism shown in Scheme 3 is proposed for the ligand-exchange process (S represents a sulphide S in the Fe4Si core). 

Kinetic studies of thiolate substitution in alkyl (R = ethyl or tert-butyl) tetrameres dianions with arylthiols (R = XC6H4SH with X = P-NH2, P-CH3, P-NO2, 0-NO2) indicate that the rates are overall second order, first order in each tetramere and thiol. The most interesting feature of these kinetic studies is the dependence of rate constants on thiol acidity. This has led to the postulation of the mechanism illustrated in the scheme on Fig. 5.8. Here the slow protonation step should be followed by fast separation of the alkylthiol from and subsequent capturing of the generated arylthiolate anion by the metal center. 

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