Studies on Gold(I) Complexes: from Chiral Catalysts to Elusive Intermediates

Identifier:  TDX:4015

Handle: https://hdl.handle.net/20.500.11797/TDX4015

Authors:  Pérez Jimeno, Alba Helena

Abstract:
The special ability of gold(I) to activate unsaturated bonds compared to other transition metals caused an exponential growth in the use of gold(I) complexes as catalysts in organic reactions. This has promoted the study of the asymmetric versions of these reactions together with the analysis of their mechanism. Our group developed a folding strategy via ligand design, which provides excellent results in the gold(I) catalyzed enantioselective cyclization of enynes. The strategy is based on the ability of a family of JohnPhos gold(I) complexes containing C2-symmetric trans-2,5-diaryl pyrrolidines to encapsulate the substrates, directing the nucleophilic attack. To increase the applicability of these complexes, we have designed and synthesized two new members of this family of chiral gold(I) complexes by expanding the central ring of their structure. The new complexes were tested in five different reactions comparing their performance to the one provided by the first generation of these pyrrolidinyl-biaryl phosphine gold(I) complexes. In the context of the mechanistic studies on gold(I) catalyzed transformations, gold(I) carbenes can be considered as the main characters and several groups have invested their efforts in the extensive study of these species. Among gold(I) carbenes, gold(I) vinylidenes are a specially intriguing type. Gold(I) vinylidenes have been proposed as intermediates of different gold(I) catalyzed reactions. However, their high reactivity and lack of stability has limited evidence proving their existence. Based on the studies on gold(I) carbenes performed in our group, we have developed a methodology to access gold(I) vinylidenes from gold(I) vinylidenoids. Thus, we have synthesized a family of gold(I) vinylidenoids, which has shown vinylidene type reactivity. This reactivity has been studied experimentally via NMR spectroscopy and by DFT, disclosing the influence of the gold(I) vinylidene intermediates in the outcome of the reaction. Additionally, the structural features of these computed gold(I) vinylidenes have been analyzed, revealing a major stabilization from the organic fragment over the one provided by the gold(I) unit.