P.Moran

Golden times: Recent breakthroughs in gold-catalyzed transformations using nanosized homogeneous gold catalysts are highlighted. These catalysts have activities and stabilities comparable to (or even surpassing) heterogeneous catalysts. Well-defined, ligand-supported gold clusters turned out to be active in homogeneous catalysis, a catalyst concept which holds potential for future studies.

Diastereodivergent is cool: The development of catalytic systems able to generate each and every one of the possible product diastereoisomers from the same starting materials (i.e., that are “diastereodivergent”) is an emerging field in asymmetric catalysis. The possibility of designing such systems in a rational manner based on dual catalysis has now become reality.

Let's coordinate: Copper(I)-catalyzed cross-coupling of alkenyl- and arylsilanes with primary alkyl iodides as well as allylic and benzylic halides as C(sp³)X electrophilic coupling partners has been realized by intramolecular activation through alkoxide coordination. This alkylation tolerates a range of functional groups including a free hydroxy group. IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene.

The mechanism of the gold-catalyzed intermolecular cycloaddition between allenamides and 1,3-dienes has been explored by means of a combined experimental and computational approach. The formation of the major [4+2] cycloaddition products can be explained by invoking different pathways, the preferred ones being determined by the nature of the diene (electron neutral vs. electron rich) and the type of the gold catalyst (AuCl vs. [IPrAu]⁺, IPr=1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). Therefore, in reactions catalyzed by AuCl, electron-neutral dienes favor a concerted [4+3] cycloaddition followed by a ring contraction event, whereas electron-rich dienes prefer a stepwise cationic pathway to give the same type of formal [4+2] products. On the other hand, the theoretical data suggest that by using a cationic gold catalyst, such as [IPrAuCl]/AgSbF₆, the mechanism involves a direct [4+2] cycloaddition between the diene and the gold-activated allenamide. The theoretical data are also consistent with the observed regioselectivity as well as with the high selectivity towards the formation of the enamide products with a Z configuration. Finally, our data also explain the formation of the minor [2+2] products that are obtained in certain cases.

The mechanism of the gold-catalyzed intermolecular cycloaddition between allenamides and 1,3-dienes has been explored by a combined experimental and computational approach. The formation of the major [4+2] cycloaddition products can be explained by invoking different pathways, the preferred ones being determined by the nature of the diene (electron neutral vs. electron rich) and the type of gold catalyst (AuCl vs. [IPrAu]⁺, IPr=1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene, see scheme).

Cationic, two-coordinate gold π complexes that contain a phosphine or N-heterocyclic supporting ligand have attracted considerable attention recently owing to the potential relevance of these species as intermediates in the gold-catalyzed functionalization of CC multiple bonds. Although neutral two-coordinate gold π complexes have been known for over 40 years, examples of the cationic two-coordinate gold(I) π complexes germane to catalysis remained undocumented prior to 2006. This situation has changed dramatically in recent years and well-defined examples of two-coordinate, cationic gold π complexes containing alkene, alkyne, diene, allene, and enol ether ligands have been documented. This Minireview highlights this recent work with a focus on the structure, bonding, and ligand exchange behavior of these complexes.

Unraveling gold: The title complexes have been widely invoked as intermediates in the gold-catalyzed functionalization of CC multiple bonds and yet remained unknown until recently. This Minireview summarizes the recent efforts directed toward the synthesis and such intermediates, which have provided insight into the nature, bonding, and ligand exchange behavior of these complexes.

Two for one gold: Factors governing the formation of isolable digold(I) σ,π-acetylide complexes are given (see scheme), indicating the general tendency of phosphine–Au^I precatalysts to form this type of complexes, which are involved as reaction intermediates in gold(I)-catalyzed reactions. Mechanistic insights into the intermolecular hydroamination of aniline and terminal alkynes catalyzed by gold(I) have shown the role of a fluxional, cationic σ,π-digold alkynide complex as one of the intermediates in the formation of imines.

Why not both? Both β- and α-hydrogen atoms of gold alkyl complexes are hydridic enough to be abstracted, opening a new route to gold–alkene and gold–carbene complexes, respectively.