Dinuclear gold-silver resting states may explain silver effects in gold(I)-catalysis

A Au(I)-Precatalyst with a Cyclopropenium Counterion: An Unusual Ion Pair

The synthesis and X-ray crystal structure of a novel Au(I)-precatalyst applied to intermolecular alkyne hydroamination is reported. Density functional theory (DFT) calculations revealed the cyclopropenium counterion of this Au(I)-precatalyst imparts stability through H-bonding and other noncovalent interactions.

Gold and diazo reagents: a fruitful tool for developing molecular complexity

After a decade since its discovery and being yet at its sunrise, the use of gold catalysis for the transfer of carbene groups from diazo compounds is becoming a powerful synthetic tool. The main advances in the area and future directions are provided in this Feature Article.

Anatomy of gold catalysts: facts and myths

This review article covers the main types of gold(i) complexes used as precatalysts under homogeneous conditions in organic synthesis and discusses the different ways of catalyst activation as well as ligand, silver, and anion effects.

Gold(I)-catalyzed asymmetric desymmetrization of meso-alkynyl diols and kinetic resolution of the corresponding DL-diols: effects of celite filtration and silver salts

The asymmetric desymmetrization of meso-2-alkynylbenzenediols through the use of a combination of axially chiral diphosphine(AuCl)2 precatalysts and silver salt co-catalysts gave optically active isochromene compounds with high enantioselectivities in good yields. The corresponding DL-diol isomers underwent efficient kinetic resolution to give the cyclized isochromenes and recovered diols with high enantioselectivities under similar conditions. The high reactivity and selectivity in the desymmetrization of the meso-diols is independent of the combination of axially chiral diphosphine(AuCl)2 precatalyst and silver salt co-catalyst, whereas the corresponding tricarbonylchromium complexes of alkynylbenzenediols were affected by the combination of the diphosphine(AuCl)2 and silver salt. The reactivity was largely dependent on the nature of the gold(I) species.

Gel-assisted crystallization of [Ir4(IMe)7(CO)H10]2+ and [Ir4(IMe)8H9]3+ clusters derived from catalytic glycerol dehydrogenation

Two unique Ir₄ clusters isolated during catalytic glycerol dehydrogenation, crystallized using aqueous and organic gel matrices and displaying remarkable structural features are described.

Efficient generation and increased reactivity in cationic gold via Brønsted acid or Lewis acid assisted activation of an imidogold precatalyst

Brønsted or Lewis acid assisted activation of an imidogold precatalyst (L-Au-Pht, Pht = phthalimide) offers a superior way to generate cationic gold compared with the commonly used silver-based system. It is also broadly applicable for most common gold-catalyzed reactions. For reactions that require milder conditions, milder acids can be used for optimized efficiency.

Ambient intermolecular [2 + 2] cycloaddition: an example of carbophilicity and oxophilicity competition in Au/Ag catalysis

The gold-catalyzed intermolecular [2 + 2] cycloaddition of propargyl esters was achieved with good stereoselectivity. The "silver-free" condition was critical for this transformation, while only a trace amount of [2 + 2] products were formed in the presence of silver under otherwise identical conditions.

Silver-free two-component approach in gold catalysis: activation of [LAuCl] complexes with derivatives of copper, zinc, indium, bismuth, and other Lewis acids

Complexes of type [LAuCl] (L = phosphine, phosphite, NHC and others) are widely employed in homogeneous catalysis, however, they are usually inactive as such and must be used jointly with a halide scavenger. To date, this role has mostly been entrusted to silver salts (AgSbF6 , AgPF6, AgBF4, AgOTf, etc.). However, silver salts can be the source of deactivation processes or side reactions, so it is sometimes advisable to use silver-free cationic gold complexes, which can be difficult to synthesize and to handle compared with the more robust chloride. We show in this study that various Lewis acids of the transition and main group metal families are expedient substitutes to silver salts. We have tested Cu(I), Cu(II), Zn(II), In(III), Si(IV), Bi(III), and other salts in a variety of typical Au(I)-catalyzed transformations, and the results have revealed that [LAuCl] can form active species in their presence.

An organic cation as a silver(i) analogue for the arylation of sp2 and sp3 C–H bonds with iodoarenes

A general, cost-effective and sustainable replacement for silver in palladium catalysed direct arylations of C(sp²)–H and C(sp³)–H bonds.

Quantitative kinetic investigation of triazole–gold(i) complex catalyzed [3,3]-rearrangement of propargyl ester

The kinetic study of triazole–Au catalyzed propargylic ester rearrangement was performed, which offered new mechanistic insight into gold catalysis.

Gold(i)- and platinum(iv)-catalyzed intramolecular annulations of allenes towards furans

Intramolecular annulations of allenes towards furans to give six-membered ring fused furans with gold and platinum catalysts have been developed.

Gold catalyzed enantioselective intermolecular [3+2] dipolar cycloaddition of N-allenyl amides with nitrones

A gold catalyzed enantioselective [3+2] dipolar cycloaddition of N-allenyl amides with nitrones was developed to give chiral 4-alkylidenyl isoxazolidine derivatives in high yields and excellent enantioselectivities by using BINOL derived chiral phosphoramidate Au(I) catalysts.

On the silver effect and the formation of chloride-bridged digold complexes

Abstraction of chloride anion from Au(I) complexes such as JohnPhosAuCl in noncoordinating solvents with 1 equiv of a silver salt, or even larger amounts, leads to the formation of chloride-bridged dinuclear gold(I) complexes, irrespective of the counteranion, which are substantially less reactive as catalysts. This incomplete removal of chloride ligand could lead to false negative results when using the in situ generation of the gold(I) active species by silver-promoted chloride abstraction.

σ-π-Diauration as an alternative binding mode for digold intermediates in gold(i) catalysis

While investigating the gold(i)-catalyzed intramolecular hydroarylation of allenes, the structure of a digoldvinyl intermediate was verified. Instead of the previously proposed geminally diaurated binding mode for the digold when L = PPh3, an alternative σ-π-diauration mode was observed with the bulkier ligand L = P(o-Tol)3. Reactivity studies indicate the σ-π-mode has a disproportionate effect on protonolysis reactivity.

Synthesis and study of cationic, two-coordinate triphenylphosphine-gold-π complexes

Cationic, two-coordinate triphenylphosphine-gold(I)-π complexes of the form [(PPh₃)Au(π ligand)]⁺SbF₆⁻ (π ligand=4-methylstyrene, 1∙SbF₆), 2-methyl-2-butene (3∙SbF₆), 3-hexyne (6∙SbF₆), 1,3-cyclohexadiene (7∙SbF₆), 3-methyl-1,2-butadiene (8∙SbF₆), and 1,7-diphenyl-3,4-heptadiene (10∙SbF₆) were generated in situ from reaction of [(PPh₃)AuCl], AgSbF₆, and π ligand at -78 °C and were characterized by low-temperature, multinuclear NMR spectroscopy without isolation. The π ligands of these complexes were both weakly bound and kinetically labile and underwent facile intermolecular exchange with free ligand (ΔG(≠) ≈9 kcal mol(-1) in the case of 6∙SbF₆) and competitive displacement by weak σ donors, such as trifluoromethane sulfonate. Triphenylphosphine-gold(I)-π complexes were thermally unstable and decomposed above -20 °C to form the bis(triphenylphosphine) gold cation [(PPh₃)₂Au]⁺SbF₆⁻ (2∙SbF₆).