Organogold Reactivity with Palladium, Nickel, and Rhodium: Transmetalation, Cross-Coupling, and Dual Catalysis

Abstract

Using two transition metals to simultaneously catalyze a reaction can offer distinct opportunities for reactivity and selectivity when compared to using single-metal catalyst systems. Creating dual transition metal catalytic systems is complicated, however, by challenges in predicting compatible reactivities and designing turnover pathways for both metals. In this Account, we describe our development of dual-metal catalysis reactions involving gold and a second transition metal. The unique rearrangement intermediates accessible through gold-only catalysis, which exploits the soft Lewis acidity of Au(I), make gold an attractive partner for dual-metal catalysis reactions. Because of the complexity of achieving simultaneous turnover of two catalysts and predicting compatibilities, our approach has been to first gain a fundamental understanding of the reactivity of the two metals with each other, both in stoichiometric and monocatalyzed reactions. To this end, we have investigated the combined reactivity of organogold compounds with palladium, nickel, and rhodium. We narrate the intricacies of turning over two catalysts simultaneously and thereby illuminate the valuable role of fundamental studies in identifying the optimal conditions to promote desirable two-metal reactivity and compatibility. Transmetalation, redox reactivity, and new mechanisms for dual-metal catalytic turnover were probed from this standpoint. We have applied the knowledge gained through these studies to the development of reactions that are dual-catalyzed by gold and palladium, as well as nickel- and rhodium-catalyzed reactions of organogold compounds. More broadly, these new reactions expand the reactivity available to catalytic organogold intermediates via trapping and functionalization reactions with other transition metals. Our investigations reveal strategies useful for designing dual-metal reactions with gold. First, the versatility of gold as a transmetalation partner suggests that many potential methods may exist to intercept catalytic organogold intermediates with a second transition metal. Second, ligands on both metals should be selected carefully in order to prevent catalyst deactivation. Finally, reactions must be designed such that any oxidative steps involving the second metal outcompete undesired reactions with redox-active organogold compounds. We believe that the application of these principles will allow for the design of a diverse set of dual-catalyzed functionalizations befitting the wide variety of gold-catalyzed transformations already established.

Mechanistic Studies of Azaphilic versus Carbophilic Activation by Gold(I) in the Gold/Palladium Dual-Catalyzed Rearrangement of Alkenyl Vinyl Aziridines

“…This first study of the retentive stereochemistry of transmetalation of chiral organogold(I) complexes to palladium and a successful strategy for avoiding competing redox quenching of gold(I) by palladium provide insight into this subset of dual-metal catalysis. 8b,18 …”

Bimetallic Catalysis using Transition and Group 11 Metals: An Emerging Tool for CC Coupling and Other Reactions

“…Whereas the classic transition-metal-catalyzed C À C coupling processes are reviewed quite frequently, [4] and there are a few reviews focused on other types of systems combining metals for synthesis (e.g., tandem catalysis), [5][6][7] only very recently has a review discussing some specific cases of bimetallic systems appeared. [8] A comprehensive review focused on bimetallic systems connected by transmetalation is not available.…”

Formal Gold‐to‐Gold Transmetalation of an Alkynyl Group Mediated by Palladium: A Bisalkynyl Gold Complex as a Ligand to Palladium

“…Recently, the use of two transition metal complexes in catalytic reactions, the so called bimetallic catalysis, is opening new avenues for the synthesis of molecules. [1][2][3][4] These processes rely on the efficient exchange of organic fragments between metal co-catalysts along with a fast and efficient final coupling step that drives the reaction to completion. Among the first examples, the coupling of alkynyl groups has used the cooperative role of two metals, generally a group 11 metal and palladium as, for example, in the Sonogashira reaction.…”