Mechanistic Studies on Gold(I) and Gold(III) Catalytic Transformations

The potential of gold as a catalyst was largely dismissed until the late 20^th century due to its assumed inertness. This situation has significantly shifted in both gold(I) and gold(I)/(III) catalysis. The ability of gold(I) to selectively activate alkynes has led to the construction of molecular complexity, generally under mild conditions. Moreover, gold(I) linear complexes have been recently shown to promote oxidative addition by rational ligand design, giving access to planar gold(III) complexes. In this Doctoral Thesis, both modes of gold catalysis have been explored in different systems.

Our group had devised a folding strategy through the development of a novel ligand design, achieving outstanding results in gold(I)-catalyzed enantioselective enyne cyclizations. This approach relies on the capability of a series of JohnPhos gold(I) complexes with C₂-symmetric 2,5-diarylpyrrolidines. The structure of the ligands was further modified in this work, as well as their performance in asymmetric cyclizations when complexed with gold(I), silver(I), and copper(I). Kinetic investigations have been carried out, contributing to a deeper understanding of the mode of action in the formal [4+2] cycloaddition of 1,6-enynes using this type of chiral complexes.

We studied a new gold(I)/(III) catalytic system involving simple alkyl phosphines as ligands. The use of allyl bromides and organostannanes in the catalytic setting allows a cross-coupling reaction catalyzed by gold, as demonstrated by several control experiments. Furthermore, the stereochemistry of the oxidative addition was evaluated, revealing overall retention at the reaction center. A comprehensive computational mechanistic study indicated an unexpectedly complex behavior of this type of systems.

We developed an alternative synthesis of gold(I) carbenoids bearing phosphines as ligands via transmetalation with zinc carbenoids, avoiding the use of previously required diazo compounds. Additionally, their carbene-like reactivity was tested and confirmed in the formal C–H insertion of benzene. DFT calculations were pursued with the aim of understanding the observed reactivity.

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