Dedicated, with admiration, to K. Peter C. Vollhardt
Abstract
Cationic gold(I) complexes are soft Lewis acids that are able to trigger numerous types of nucleophilic attack onto alkenes, allenes, and alkynes (π-acid catalysis). In this account, we initially summarize the novel methods that we have developed to generate such catalysts by silver-free activation of ligated gold(I) chlorides. The advantages of this approach are the use of lower quantities of gold and the ability to scale-up transformations during which the standard gold/silver catalytic system is rapidly decomposed. In the second part, the synthesis and catalytic activity of original organogallium compounds is described. We have shown that (NHC)GaCl2
+-type complexes display a high affinity for alkenes and alkynes, and trigger tandem C–C/C–C or C–C/C–H bond formation processes. Thus, they also behave as π-acids. Practical applications of these different gold- and gallium-based catalytic systems for the synthesis of cyclic compounds are presented.
1 Introduction
2 Silver-Free Two-Component Approaches in Gold Catalysis
2.1 The Gold/Copper Catalytic System
2.2 Other Applications with Gold/Lewis Acid Systems
3 Gallium Catalysis
3.1 Cationic Gallium Complexes Supported by N-Heterocyclic Carbene Ligands
3.2 Catalytic Applications
4 Conclusions
Key words
gold - gallium - copper - homogeneous catalysis - N-heterocyclic carbenes
