Lithium arenethiolates

The latter mixed aggregate is so thermodynamically stable that even in the presence of excess of lithium arenethiolate, which is used during the synthesis, one does not obtain a pure copper(I) arenethiolate [Cu(SAr)] (60). 

An alternative synthetic procedure to lithium arenethiolates is the insertion reaction of elemental sulfur (S8) into the lithium-carbon bond of a suitable or-ganolithium reagent in THF at low temperature (Eq. 12). 

The insertion of sulfur into a reactive metal-carbon bond has been known in organic chemistry for some time, but was mainly used to prepare arenethiols (150). However, this method has only recently found its use in the synthesis of pure lithium arenethiolate complexes, which contain potentially intramolecu-larly coordinating heteroatom donor functions (50, 151). It has since then been reported that this method is also applicable for the preparation of lithium areneselenolates and arenetellurolates (152). This route has also been used for the synthesis of bis(arenethiolato)magnesium complexes with intramolecular coordination (153). 

Figure 20. Hexameric lithium arenethiolates. (n) Planar Li Sh 12-membered ring structure, (b) Li,S cage structure.

Use of this technique results in an equivalent of lithium halide being present in the reaction mixture, unlike when the isolated copper arenethiolates are employed. Lithium salts can have very profound effects on copper-mediated reactions, but in this case a similar ee (40%) and complete y selectivity were still obtained for the reaction between 21 and n-BuMgl when the catalyst was prepared from Cut. Nei-... 

The commonly used bases in this reaction are commercially available solutions of n-BuLi (in hexane) (140-146), or n-Bu2Mg (in heptane) (144) freshly prepared lithium amide LiNH2 has also been used for the synthesis of lithium methylthiolate (147). Similarly, several bulky arenethiols (e.g., HSC6H2Ph3-2,4,6) have been successfully deprotonated with either a 1 1 mixture of n-Bu,Mg and s< c-Bu2Mg in heptane or Mg N(SiMe3)2 2 in toluene (148). A major shortcoming of this procedure is that thiols that are not commercially available have to be prepared via metal thiolate species—clearly a roundabout approach. 

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