Carbon-sulfur bond formation by reductive elimination of gold(III) thiolates

Whereas the reaction of the gold(iii) pincer complex (CANAC)AuCl with 1-adamantyl thiol (AdSH) in the presence of base affords (CANAC)AuSAd, the same reaction in the absence of base leads to formation of aryl thioethers as the products of reductive elimination of the Au-C and Au-S ligands (CANAC = dianion of 2-6-diphenylpyridine or 2-6-diphenylpyrazine). Although high chemical stability is usually taken as a characteristic of pincer complexes, results show that thiols are capable of cleaving one of the pincer Au-C bonds. This reaction is not simply a function of S-H acidity, since no cleavage takes place with other more acidic X----H compounds, such as carbazole, amides, phenols and malonates. The reductive C-S elimination follows a second-order rate law,-dflaUdt- ktlallAdSHI. Reductive elimination is enabled by displacement of the N-donor by thiol; this provides the conformational flexibility necessary for C----S bond formation to occur. Alternatively, reductive C----S bond formation can be induced by reaction of pre-formed thiolates (CANAC)AuSR with a strong Bransted acid, followed by addition of SMe2 as base. On the other hand, treatment of (CANAC)AuR (R- Me, aryl, alkynyl) with thiols under similar conditions leads to selective C C rather than C S bond formation. The reaction of (CANAC)AuSAd with Fr' in the absence of a donor ligand affords the thiolato-bridged complex [{(CAN-CH)Au(IA-SAd))212 which was crystallographically characterised.