Silver-free Gold(I) Catalysts for Organic Transformations

The majority of gold(I) catalysts employed in organic transformations in homogeneous systems are presently generated in situ by reactions of gold halides AuX or their 1 : 1 complexes [(L)AuX] with silver salts AgY (X = Cl, Br; L = R3P, NHC, tht etc.; Y = BF4, PF6, SbF6, OSO2CF3, OC(O)CF3 etc.). This usage of silver salts is not only economically unfavorable, but also has several practical disadvantages regarding inter alia the thermal and photochemical stability of the reaction mixtures, problems of inexact stoichiometries, difficulties in separation and recycling, and cooperative effects due to Au-Ag metallophilic interactions which can induce a different course of the reactions. There is therefore a move towards syntheses of silver-free homogeneous gold(I) catalysts. The past and current approaches and opportunities are summarized in this review.